Does Decreased Meniscal Thickness Affect Surgical Outcomes After Medial Meniscectomy? Sung-Jae Kim,* MD, PhD, Su-Keon Lee,y MD, Sung-Hwan Kim,* MD, Jae-Hoon Jeong,z MD, Hak-Soo Kim,* MD, Se-Won Lee,* MD, Jae-Hoo Lee,* MD, and Min Jung,*§ MD Investigation performed at the Arthroscopy and Joint Research Institute, Department of Orthopaedic Surgery, Yonsei University College of Medicine, Seoul, Korea Background: There have been no clinical studies regarding the effect of decreased meniscal thickness on outcomes after meniscectomy. Purpose: To examine the postoperative outcomes of partial meniscectomy with or without horizontal resection compared with the outcomes of subtotal meniscectomy and to evaluate the influence of decreased thickness of the medial meniscus on outcomes after partial meniscectomy. Study Design: Cohort study; Level of evidence, 3. Methods: A total of 312 patients who underwent medial meniscectomy were retrospectively reviewed. Patients were divided into 3 groups: group A (n = 84) included patients with partial meniscectomy with vertical resection, group B (n = 140) consisted of those with partial meniscectomy with horizontal resection, and group C (n = 88) included those with subtotal meniscectomy. Clinical function was evaluated by use of the Lysholm knee scoring scale, International Knee Documentation Committee (IKDC) subjective knee evaluation form, and Tapper and Hoover grading system. Radiologic evaluation was performed with the IKDC radiographic assessment scale as well as with measurements of the medial compartment height at the tibiofemoral joint. Preoperative values and postoperative values measured 5 years after operation were assessed. Results: Functional outcomes in group C were inferior to those in groups A and B according to the Lysholm knee score (mean 6 SD for group A = 96.1 6 4.7, group B = 94.9 6 5.2, group C = 84.8 6 11.4; P \ .001), IKDC subjective score (group A = 92.1 6 6.5, group B = 91.3 6 8.8, group C = 81 6 11.4; P \ .001), and Tapper and Hoover grading system (P = .003). There was no significant difference in scores between groups A and B. With regard to radiologic evaluation, the IKDC radiographic grade for group C was worse than the grades for groups A and B (P \ .001); there was no significant difference between groups A and B. However, the postoperative joint space on the affected side was higher for group A (4.7 6 0.6 mm) than for groups B (4.3 6 0.5 mm; P \ .001) and C (3.7 6 0.8 mm; P \ .001). The joint space was higher in group B than in group C (P \ .001). Conclusion: Despite joint space narrowing, decreases in meniscal thickness after partial meniscectomy for horizontal tear had no additional adverse effect on 5-year functional and radiographic outcomes compared with conventional partial meniscectomy preserving whole meniscal thickness. In treating horizontal tears of the meniscus, partial meniscectomy with complete resection of the unstable leaf was an effective method in a 5-year follow-up study. Keywords: arthroscopy; meniscus; meniscectomy; horizontal tear
§ Address correspondence to Min Jung, MD, Department of Orthopaedic Surgery, Arthroscopy and Joint Research Institute, Yonsei University College of Medicine, C.P.O. Box 8044, 134, Shinchon-dong, Seodaemungu, Seoul 120-752, South Korea (e-mail: [email protected]). *Arthroscopy and Joint Research Institute, Department of Orthopaedic Surgery, Yonsei University College of Medicine, Seoul, Korea. y Department of Orthopaedic Surgery, Gwangmyung Sungae Hospital, Gyeonggi, Korea. z Department of Orthopaedic Surgery, Seoul Wooridul Hospital, Seoul, Korea. The authors declared that they have no conflicts of interest in the authorship and publication of this contribution. There was no external funding source related to the study.
Meniscal tears are the most common knee injury, leading to an annual incidence in Denmark of 60 to 70 meniscectomies per 100,000 people.8,21 In the past, the meniscus was considered the vestigial remnant of muscle within the knee,28 and total meniscectomy was the prevailing treatment for meniscal tears.19 However, since Fairbank4 noted radiographic changes after meniscectomy, many reports regarding long-term results after total meniscectomy have shown a high risk of osteoarthritic change and serious deterioration of function.1,13 In addition, various important roles of the meniscus in load bearing,25 shock absorption,30 joint stability,15 joint lubrication,17 nutrition of the articular cartilage,24 and proprioception31 have been
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recognized. Consequently, to decrease the progression of osteoarthritis, the recommended procedure entails partial meniscectomy with minimal resection of the torn unstable meniscus and preservation of as much of the stable meniscus component as possible.24 In long-term studies, partial meniscectomy has shown results superior to those of total meniscectomy in terms of radiologic change and functional outcomes.2,9,10 However, in previous studies, partial meniscectomy has focused on a surface area based on width viewed in the axial plane. According to an experimental study,7 a decrease of meniscal thickness by single-leaf resection of a horizontal tear compromised biomechanical function of the meniscus and led to decreased contact area and increased mean pressure. As far as we know, no clinical study has dealt with the effect of decreased thickness of the meniscus on surgical outcomes. Accordingly, the purpose of the present study is to compare postoperative outcomes between partial meniscectomy with or without horizontal resection and subtotal meniscectomy and to evaluate the influence of decreased thickness of the medial meniscus on outcomes after partial meniscectomy. We hypothesized that decreased thickness of the meniscus would have an adverse effect on postoperative results in terms of radiologic findings and functional outcomes.
MATERIALS AND METHODS Patients A total of 1274 patients who underwent meniscectomy between January 2002 and August 2008 at the Severance Hospital of Yonsei University College of Medicine were retrospectively reviewed after the study was approved by the institutional review board. Patients who met the following criteria were included in the study: (1) isolated medial meniscal tear treated with arthroscopic meniscectomy, (2) width of the peripheral meniscus remaining after meniscectomy of less than 3 mm (subtotal meniscectomy) or more than 5 mm (partial meniscectomy), (3) no arthritic change on preoperative radiographs (International Knee Documentation Committee [IKDC] radiologic grade11 of normal), and (4) a minimum follow-up duration of 5 years. The exclusion criteria were as follows: (1) repair of torn meniscus; (2) concomitant chondral lesion (grade I or higher according to the Outerbridge grading system22 at arthroscopy), cystic lesion, or ligament injury; (3) malalignment of the lower extremity (.5 mm of mechanical axis deviation as measured on standing hip-knee-ankle radiographs23); (4) previous surgery of the affected knee; (5) previous injury of the contralateral knee; and (6) arthritic change in the contralateral unaffected knee 5 years after operation (to rule out the effect of natural degeneration according to age). After excluding 68 patients (20 patients in group A, 33 patients in group B, and 15 patients in group C) who were lost to follow-up, 409 patients were selected according to the inclusion criteria. From these 409 patients, 90 patients, including 22 with arthritic changes in the contralateral knee at 5 years, were
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Figure 1. Preoperative and postoperative meniscus in group A. The preoperative meniscal tear in this group did not include a horizontally torn component. The remaining meniscus after meniscectomy was more than 5 mm wide and preserved full thickness. Thus, menisci of patients included in group A had only decreased width without decreased thickness. (A) Preoperative axial view. (B) Postoperative axial view. excluded. Additionally, 7 patients were excluded: 1 due to anterior cruciate ligament rupture caused by new trauma during follow-up and 6 with postoperative complications (1 complex regional pain syndrome, 1 superficial skin infection at the suture site, and 4 with iatrogenic chondral damage resulting from a tight medial compartment). Therefore, 312 patients were included in the current study. The patients were divided into 3 groups according to the state of the meniscus remnant after meniscectomy. The width of the peripheral meniscus remaining was intraoperatively measured with a graduated probe. On the basis of previous studies,14,27 the meniscectomy was considered subtotal if less than 3 mm in width of the peripheral meniscus remained, and meniscectomy was considered partial if more than 5 mm in width of the peripheral meniscus remained. For a clear separation between partial meniscectomy and subtotal meniscectomy, procedures that left 3 to 5 mm in width of the peripheral meniscus remaining were not included in this study. Group A included 84 patients without horizontal tearing who underwent partial meniscectomy including vertical resection. The remaining meniscus was greater than 5 mm wide, with full thickness preserved. The menisci of these patients had decreased width without decreased thickness (Figure 1). Group B consisted of 140 patients who underwent partial meniscectomy including horizontal resection for a horizontally torn component of the meniscus. As with group A, the remaining meniscus was greater than 5 mm wide, but the thickness of the remaining meniscus in group B was less than that of group A. There was a practical limitation in intraoperatively measuring the exact thickness of the remaining meniscus. However, to prevent retear in a meniscus with a horizontal tear, the more unstable leaf of the superior and inferior leaves was excised close to the peripheral rim for a smooth margin. Therefore, in most patients in group B, the remaining meniscus had decreased thickness from the inner portion almost to the peripheral margin. Although
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Figure 3. Preoperative and postoperative meniscus in group C. Subtotal meniscectomy was performed, after which the remaining meniscus was less than 3 mm wide. (A) Preoperative axial view. (B) Postoperative axial view.
Figure 2. Preoperative and postoperative meniscus in group B. The preoperative meniscal tear in this group included a horizontally torn component. To prevent retear, the more unstable leaf of the superior and inferior leaves was excised close to the peripheral rim for a smooth margin. The meniscus that remained after meniscectomy was more than 5 mm wide, but its thickness was reduced due to horizontal resection. The postoperative meniscus had decreased thickness near the peripheral rim. (A) Preoperative axial view. (B) Postoperative axial view. (C) Preoperative coronal section. (D) Postoperative coronal section. full thickness was preserved in the peripheral portion of the remaining meniscus, its width was less than 5 mm (Figure 2). The major difference between groups A and B was that the remaining meniscus of patients in group A was full thickness (.5 mm wide), while for patients in group B the thickness of the remaining meniscus had decreased near the peripheral rim. Group C consisted of 88 patients who underwent subtotal meniscectomy. The remaining meniscus was less than 3 mm wide (Figure 3). Preoperative magnetic resonance imaging (MRI) was performed in all patients. All surgeries were performed by a single surgeon, the senior author (S.-J.K.). The unstable portion of the torn meniscus was removed. The edges of the meniscus remaining after resection were smoothed by shaver.
Clinical Assessment Postoperative follow-up examinations were performed at 3 months, 6 months, and then annually during a patient’s regular annual visit. The preoperative values were compared with postoperative values measured at 5 years after surgery. If a patient did not attend a scheduled
appointment at the outpatient clinic, we called and asked the patient to visit the clinic for the follow-up evaluation. This evaluation consisted of an interview, a physical examination, a questionnaire, and radiographic inspection, which were used to assess clinical function and radiologic findings. Those patients lost to follow-up were not included in the present study. Clinical function was evaluated with the Lysholm knee scoring scale,16 the IKDC subjective knee evaluation form,12 and the Tapper and Hoover grading system,29 and patients received 1 of 4 grades based on each of these evaluations. The Lysholm score falls into the following 4 grades according to Mitsou et al20: excellent = 95-100; good = 84-94; fair = 65-83; poor = \65. The IKDC score is classified into the following 4 grades by Haas et al6: excellent = 90-100; good = 80-89; fair = 70-79; poor = \70. The Tapper and Hoover system29 also has 4 grades: Excellent indicates that the patient has no symptoms and no disability related to the knee. Good means that the patient has minimal symptoms, such as aching or weakness after heavy use or effusion after heavy exertion, but essentially no disability. Fair indicates that the patient has symptoms such as trouble kneeling or climbing stairs and enough weakness, pain, or discomfort to interfere somewhat with everyday activities; the patient thinks he or she has some disability and cannot participate in vigorous sports (eg, skiing, tennis, football). Poor denotes that the patient has severe symptoms, including all of those listed under fair as well as pain at rest, limitation of motion, and locking; the patient is clearly disabled, and activities, including walking, are definitely limited. The radiologic evaluation was performed by independent experienced clinical fellows who were blinded to the method of treatment applied to the patients. Bilateral, double-leg weightbearing radiographs of anteroposterior, lateral, and posteroanterior views at 45° of flexion and Merchant views were obtained. The radiologic evaluation of the tibiofemoral joint was carried out according to the IKDC radiographic assessment scale11 and categorized as follows: A = normal; B = nearly normal, .4 mm joint space, but early osteophyte; C = abnormal, joint space 2 to 4 mm, or .50%; D = severely abnormal, joint space \2 mm, or
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meniscus remnant after meniscectomy, demographic characteristics (age, sex, body mass index [BMI], affected side, duration of symptoms, and trauma history), and preoperative values (Lysholm knee score, IKDC subjective score, height of joint space on the affected side, and location of tear). The same analytic method as described above was used to assess whether differences in the patterns of meniscal tear affected postoperative outcomes within the respective group. Interobserver reliability in measurement of the height of the joint space was evaluated by use of the intraclass correlation set at a 95% CI. The level of significance was set at P \ .05. Statistical analysis was performed with IBM SPSS Statistics for Windows (v 19.0; IBM Inc).
RESULTS Figure 4. Preoperative radiograph of 46-year-old female patient in group B: bilateral, 45° flexion, weightbearing, posteroanterior. The height of the medial compartment at the tibiofemoral joint was measured from the center of the medial femoral condyle to the center of the medial tibial plateau on the radiograph. The left knee was the affected side. For both knees, the height of the medial compartment was 4.7 mm. \50%. The heights of medial compartments at the tibiofemoral joints of both knees were measured on the 45° flexion weightbearing posteroanterior radiograph, according to the method described by Shelbourne et al.26 The height was measured from the center of the medial femoral condyle to the center of the medial tibial plateau by use of a picture archiving and communication system (Centricity PACS; GE Medical System Information Technologies) (Figure 4). To increase reliability, measurements of the height of the joint space were made twice by 2 different investigators on the bilateral digital radiographs. The mean of 2 numerical values was used.
Statistical Analysis An analysis of variance (ANOVA) for continuous variables and the chi-square or Fisher exact test for categorical variables were used to compare the 3 groups with regard to demographic characteristics and preoperative and postoperative values. A post hoc analysis with Bonferroni correction was performed to make pairwise comparisons between the 3 groups. Comparisons between pre- and postoperative values in the same group were performed with a paired t test for continuous numerical data. Multivariate analysis using a generalized linear model for continuous data and multinomial logistic regression for categorical data according to the characteristics of postoperative variables was used to identify factors that significantly influenced the changes in postoperative outcomes (Lysholm knee score, IKDC subjective score, Tapper and Hoover grade, IKDC radiographic scale, and height of joint space on the affected side) among variables: These variables included differences between groups in the postoperative state of the
There were 59 male and 25 female patients in group A, 84 male and 56 female patients in group B, and 49 male and 39 female patients in group C. The average age at the time of surgery was 39.6 years (range, 16-58 years) in group A, 41.6 years (range, 13-62 years) in group B, and 40.8 years (range, 16-57 years) in group C. The mean duration of symptom was 23.1 months (range, 1-168 months) in group A, 23.9 months (range, 1-252 months) in group B, and 18.8 months (range, 1-172 months) in group C. There was no statistically significant difference between groups in regard to sex, age, mean BMI, proportion of patients with history of trauma, or mean duration of symptoms before operative treatment (see Appendix 1, available online at http://ajsm.sagepub.com/supplemental). There was no statistically significant difference in location of tear between the 3 groups (P = .938). In group B, the remaining meniscus leaf portion after meniscectomy was superior in 114 patients (81.4%) and inferior in 26 patients (18.6%). No significant differences were found between the 3 groups in regard to the mean of the preoperative Lysholm score (P = .276) and IKDC subjective score (P = .167). There was no statistically significant difference in preoperative height on the affected side (P = .188) or the unaffected side (P = .364) between the 3 groups (Table 1). No patient included in the current study underwent a second operation for retear of the meniscus. The preoperative values were compared with the postoperative values measured at 5 years after operation within each group. All 3 groups had statistically significant differences between preoperative and postoperative values for the Lysholm knee score (P \ .001), the IKDC subjective score (P \ .001), and height of the joint space of the affected side (P \ .001). However, comparison of the height of the joint space of the unaffected side did not show a statistically significant difference (Appendix 2, available online). We compared postoperative functional outcomes and radiologic findings between the 3 groups. The mean postoperative Lysholm score was 96.1 in group A, 94.9 in group B, and 84.8 in group C, and the mean postoperative IKDC subjective score was 92.1 in group A, 91.3 in group B, and 81.0 in group C. Both of these functional scores showed
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TABLE 1 Comparison of Preoperative Variables Between the 3 Groupsa Variable Location of tear Posterior horn Body .1 portion Lysholm knee score IKDC subjective score Height of joint space, mm Affected side Unaffected side
Group A (n = 84)
Group B (n = 140)
Group C (n = 88)
P Value .938
52 5 27 65.8 60.5
(61.9) (6.0) (32.1) 6 6.6 6 6.0
4.9 6 0.5 4.9 6 0.5
86 9 45 65.1 59.6
(61.4) (6.4) (32.1) 6 6.1 6 8.9
5.0 6 0.5 5.0 6 0.5
53 8 27 66.5 61.8
(60.2) (9.1) (30.7) 6 7.5 6 10.1
4.9 6 0.4 5.0 6 0.4
.276 .167 .188 .364
a
Values are expressed as n (%) or mean 6 SD. IKDC, International Knee Documentation Committee.
statistically significant differences between the 3 groups (P \ .001). The grades assigned according to the Lysholm score and the IKDC subjective score also showed statistically significant differences between the 3 groups (P \ .001). Postoperative function according to the Tapper and Hoover grading system was as follows: group A, excellent = 49 (58.3%), good = 27 (32.1%), fair = 8 (9.5%), poor = 0 (0%); group B, excellent = 78 (55.7%), good = 46 (32.9%), fair = 15 (10.7%), poor = 1 (0.7%); group C, excellent = 35 (39.8%), good = 26 (29.6%), fair = 24 (27.3%), poor = 3 (3.4%). There were statistically significant differences between the 3 groups (P = .003) for postoperative functional grades. Comparison of postoperative IKDC radiographic scales showed statistically significant differences between the groups (P \ .001). The IKDC radiographic scale results were as follows: for group A, A = 57 (67.9%), B = 19 (22.6%), C = 8 (9.5%), D = 0 (0.0%); for group B, A = 90 (64.3%), B = 34 (24.3%), C = 16 (11.4%), D = 0 (0.0%); for group C, A = 27 (30.7%), B = 37 (42.1%), C = 18 (20.5%), D = 6 (6.8%) (Table 2). In terms of functional scores, grades, and radiographic scales, the post hoc test showed that group C had significantly poorer outcomes than did groups A and B (P \ .05) but that there was no statistically significant difference between groups A and B (P . .05) (Appendix 3, available online). The mean 6 SD postoperative heights of joint spaces on the affected side were 4.7 6 0.6 mm in group A, 4.3 6 0.5 mm in group B, and 3.7 6 0.8 mm in group C. The mean 6 SD percentages of the postoperative heights of joint spaces in relation to the preoperative heights of joint spaces on the affected side were 95.9% 6 9.8% in group A, 86.1% 6 10.3% in group B, and 76.5% 6 18.6% in group C. Comparison of the heights of joint spaces on the affected side between the 3 groups showed statistically significant differences (P \ .001) (Table 2). According to the post hoc test, the joint space of group A was significantly higher than the joint space of groups B and C (P \ .001). The joint space of group B was significantly higher than that of group C (P \ .001) (Appendix 3). Comparison of the postoperative heights of the joint space between the affected side and the unaffected side showed a statistically significant difference in each group: P .002 in group A, P \ .001
in group B, P \ .001 in group C (Appendix 4, available online). The intraclass correlation coefficient (ICC) for preoperative joint space height was 0.709 for the affected knee and 0.675 for the unaffected knee, and the ICC for postoperative joint space height was 0.892 for the affected knee and 0.654 for the unaffected knee. Univariate analysis with a generalized linear model and multinomial logistic regression was conducted to determine the factors that significantly influenced the changes in postoperative outcomes. This analysis showed that differences in groups divided according to the postoperative state of the meniscus remnant after meniscectomy had a significant effect on all postoperative variables, including Lysholm knee score (P \ .001) (Appendix 5), IKDC subjective score (P \ .001) (Appendix 6), Tapper and Hoover grade (P = .010) (Appendix 7), IKDC radiographic scale (P \ .001) (Appendix 8), and height of the joint space on the affected side (P \ .001) (Appendix 9). The BMI correlated with the postoperative Lysholm knee score (P = .013) (Appendix 5), the IKDC radiographic scale (P \ .001) (Appendix 8), and the postoperative height of the joint space on the affected side (P = .030) (Appendix 9). There was a positive correlation between preoperative height of the joint space on the affected side and postoperative height of the joint space on the affected side (P \ .001) (Appendix 9). The multivariate analysis, which was performed according to the results of the univariate analysis, showed that difference between group and BMI still had an effect on postoperative Lysholm knee score (P \ .001 and P \ .009, respectively) (Appendix 5) and IKDC radiographic scale (P \ .001 for both) (Appendix 10). According to the multivariate analysis of the postoperative height of the joint space on the affected side, differences between groups (P \ .001), BMI (P = .003), and preoperative height of the joint space on the affected side (P \ .001) still had a positive correlation (Appendix 9). To sum up, the difference between postoperative states of the meniscus remnant after meniscectomy had a significant influence on the postoperative variables even when the effects of other factors such as BMI and preoperative height of the joint space were excluded. In addition, because there was no statistically significant difference in BMI and preoperative height
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TABLE 2 Comparison of Postoperative Variables Between the 3 Groupsa Variable Lysholm knee score Lysholm knee score grade Excellent Good Fair Poor IKDC subjective score IKDC subjective score grade Excellent Good Fair Poor Tapper and Hoover grade Excellent Good Fair Poor IKDC radiographic scale A B C D Height of joint space, mm Affected side Unaffected side Height of joint space, %b Affected side Unaffected side
Group A (n = 84)
Group B (n = 140)
Group C (n = 88)
P Value
96.1 6 4.7
94.9 6 5.2
84.8 6 11.4
\.001 \.001
54 (64.3) 23 (27.4) 7 (8.3) 0 (0.0) 92.1 6 6.5
87 (62.1) 44 (31.4) 8 (5.7) 1 (0.7) 91.3 6 8.8
38 (43.2) 22 (25.0) 26 (29.6) 2 (2.3) 81 6 11.4
58 18 8 0
(69.1) (21.4) (9.5) (0.0)
92 31 15 2
(65.7) (22.1) (10.7) (1.4)
26 25 29 8
(29.6) (28.4) (33.0) (9.1)
49 27 8 0
(58.3) (32.1) (9.5) (0.0)
78 46 15 1
(55.7) (32.9) (10.7) (0.7)
35 26 24 3
(39.8) (29.6) (27.3) (3.4)
57 19 8 0
(67.9) (22.6) (9.5) (0.0)
90 34 16 0
(64.3) (24.3) (11.4) (0.0)
27 37 18 6
(30.7) (42.1) (20.5) (6.8)
\.001 \.001
.003
\.001
4.7 6 0.6 4.9 6 0.4
4.3 6 0.5 4.9 6 0.5
3.7 6 0.8 5.0 6 0.3
\.001 .261
95.9 6 9.8 99.6 6 5.9
86.1 6 10.3 99.0 6 7.9
76.5 6 18.6 99.9 6 5.3
\.001 .568
a
Values are expressed as mean 6 SD or n (%). IKDC, International Knee Documentation Committee. Percentage of the postoperative heights of joint spaces in relation to the preoperative heights of joint spaces.
b
of the joint space on the affected side between the 3 groups, there was no significant effect of BMI and preoperative height of the joint space on the affected side. Differences of patterns of meniscal tear had no statistically significant effect on postoperative outcomes within each group (Appendices 11-13).
DISCUSSION The present study found that surgical outcomes, including functional and radiologic results, of partial meniscectomy for horizontal tear resulting in decreased meniscal thickness were comparable to postoperative outcomes of conventional partial meniscectomy preserving whole meniscal thickness. Previous long-term studies have shown superior clinical results of partial meniscectomy over total meniscectomy.1,13 Preserving as much meniscus tissue as possible has become a principle of surgical treatment of meniscal tear given the important functions of the meniscus in the knee.15,17,24,25,30,31 To preserve the meniscus tissue, meniscal repair should be a top priority in treatment of meniscal tear. However, in the case of meniscal tear with severe meniscal degeneration, complex tear, large flap tear, and meniscal tear involving the inner one-third
region, resection of the meniscus is inevitable. The main objective of operative treatment is to remove the unstable meniscus fragment and preserve a stable peripheral rim. However, in horizontal cleavage tear, which was reported to be the most common type of tear,5 conventional resection of both superior and inferior leaves leads to a decrease of remnant meniscus tissue. Therefore, resection of only a single unstable leaf is preferred. Preservation of one leaf should be balanced against the risk of retear and consequent reoperation, and so the more unstable leaf is completely excised.3 However, when the resection of meniscus tissue extends close to the peripheral rim, loss of height of meniscus tissue can be a concern, as it is another cause of deterioration in meniscal function. The present study compared 3 groups divided according to the state of remnant meniscus tissue. The results showed that group C had inferior functional outcomes, compared with groups A and B, according to the Lysholm knee score, IKDC subjective score, and Tapper and Hoover grade. On the IKDC radiographic scale, the outcome of group C was worse than outcomes of groups A and B; however, there was no statistically significant difference between groups A and B. In the present study, outcomes of subtotal meniscectomy were worse than those of partial meniscectomy. These results are consistent with the
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findings of previous studies,2,10 which noted that the amount of excised meniscal tissue was inversely related to the function of the knee and that preservation of the peripheral rim of the meniscus in partial meniscectomy provided better outcomes. The important point of the present study is that partial meniscectomy for horizontal tear of the medial meniscus that completely excises the unstable leaf had no additional adverse effect on 5-year surgical outcomes compared with partial meniscectomy that preserves the whole height of the medial meniscus. These results are not in accord with the results of a biomechanical study7 that noted resection of a single meniscus leaf in horizontal tear of the lateral meniscus decreased contact area by 40% to 59% and increased mean pressure by 24% to 55% compared with the intact lateral meniscus. Inconsistency between these 2 studies is thought to come from the difference in location of the targeted meniscus. While the lateral meniscus carries 70% of the load acting on the lateral tibiofemoral joint, the medial meniscus carries 50% of the load acting on the medial tibiofemoral joint.25 In addition, because of the concavity of the medial tibial plateau compared with the convexity of the lateral tibial plateau, a more congruent characteristic of the medial compartment has less tendency toward a decrease in contact area and an increase in mean pressure.18 In the present study, a postoperative decrease of medial meniscal thickness resulting from partial meniscectomy for horizontal tear that completely excised the unstable leaf had no clinically detectable deleterious effect on functional scores or on radiologic outcome according to the IKDC radiographic scale. Height of the joint space in the medial compartment of the tibiofemoral joint was measured and compared between 3 groups. The mean 6 SD postoperative heights of joint spaces on the affected side were 4.7 6 0.6 mm in group A, 4.3 6 0.5 mm in group B, and 3.7 6 0.8 mm in group C (P \ .001). The mean 6 SD percentages of the postoperative heights of the joint spaces in relation to the preoperative heights of joint spaces on the affected side were 95.9% 6 9.8% in group A, 86.1% 6 10.3% in group B, and 76.5% 6 18.6% in group C (P \ .001). Post hoc analysis showed that the joint space of group A was significantly wider than the joint spaces of groups B and C (P \ .001). The joint space of group B was significantly wider than that of group C (P \ .001). In comparisons between groups A and B, although there was no significant difference in functional scores and IKDC radiographic scale, the remnant meniscus was thinner in group B than in group A, and the joint space on radiograph was lower in group B than in group A. Decreased thickness of the remnant meniscus leads to an increase in mean contact pressure and peak contact pressure in the tibiofemoral joint,7 which can contribute to arthritic change. Although evaluation with the IKDC radiographic scale showed no significant difference between groups A and B in the present study with regard to 5-year outcomes, long-term study is needed to determine the possible negative outcomes in radiologic evaluation and consequent functional loss. Several limitations prevented us from reaching a firm conclusion in the present study. First, the study was based
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on retrospective review. Second, no previous study has noted average values of the postoperative variables used in the present study in partial meniscectomy for horizontal tear of the meniscus. Therefore, the sample size calculated from statistical power analysis could not be obtained. The numbers of patients in each group may not be sufficient to show lack of difference between groups A and B with substantial statistical power. Third, in the present study, subtotal meniscectomy was defined as meniscectomy with less than 3 mm in width of the peripheral meniscus remaining, in accordance with previous studies.14,27 Partial meniscectomy was defined as meniscectomy with more than 5 mm in width of the peripheral meniscus remaining. However, no biomechanical study has supported a clear reference point dividing partial and subtotal meniscectomy depending on resistance to hoop stress. Fourth, thickness of the remnant meniscus after meniscectomy for horizontal tear can affect surgical outcomes. However, there is a practical limitation in intraoperatively measuring thickness of the remaining meniscus. Fifth, radiologic evaluation is inevitably subjective in assessing arthritic change. Even though the height of the joint space was measured twice by 2 different investigators to increase reliability, the intraclass correlation coefficient (0.6540.892) was not high enough to present greater reliability.
CONCLUSION A decrease of meniscal thickness after partial meniscectomy for horizontal tear had no additional adverse effect on 5-year functional outcomes and radiographic scale compared with conventional partial meniscectomy preserving whole meniscal thickness despite joint space narrowing. In treating horizontal tear of the meniscus, partial meniscectomy with complete resection of the unstable leaf was an effective method in a 5-year follow-up study.
ACKNOWLEDGMENT The authors thank Dong-Su Jang (medical illustrator, Medical Research Support Section, Yonsei University College of Medicine, Seoul, Korea) for his support with the medical figures. REFERENCES 1. Allen PR, Denham RA, Swan AV. Late degenerative changes after meniscectomy: factors affecting the knee after operation. J Bone Joint Surg Br. 1984;66(5):666-671. 2. Andersson-Molina H, Karlsson H, Rockborn P. Arthroscopic partial and total meniscectomy: a long-term follow-up study with matched controls. Arthroscopy. 2002;18(2):183-189. 3. Bin SI, Jeong SI, Kim JM, Shon HC. Arthroscopic partial meniscectomy for horizontal tear of discoid lateral meniscus. Knee Surg Sports Traumatol Arthrosc. 2002;10(1):20-24. 4. Fairbank TJ. Knee joint changes after meniscectomy. J Bone Joint Surg Br. 1948;30(4):664-670. 5. Ferrer-Roca O, Vilalta C. Lesions of the meniscus, part II: horizontal cleavages and lateral cysts. Clin Orthop Relat Res. 1980;146:301307.
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6. Haas AL, Schepsis AA, Hornstein J, Edgar CM. Meniscal repair using the FasT-Fix all-inside meniscal repair device. Arthroscopy. 2005; 21(2):167-175. 7. Haemer JM, Wang MJ, Carter DR, Giori NJ. Benefit of single-leaf resection for horizontal meniscus tear. Clin Orthop Relat Res. 2007; 457:194-202. 8. Hede A, Jensen DB, Blyme P, Sonneholm S. Epidemiology of meniscal lesions in the knee: 1,215 open operations in Copenhagen 198284. Acta Orthop Scand. 1990;61:435-437. 9. Hede A, Larsen E, Sandberg H. Partial versus total meniscectomy: a prospective, randomised study with long-term follow-up. J Bone Joint Surg Br. 1992;74(1):118-121. 10. Hede A, Larsen E, Sandberg H. The long-term outcome of open total and partial meniscectomy related to the quantity and site of the meniscus removed. Int Orthop. 1992;16(2):122-125. 11. Hefti F, Mu¨ller W, Jakob RP, Sta¨ubli HU. Evaluation of knee ligament injuries with the IKDC form. Knee Surg Sports Traumatol Arthrosc. 1993;1(3-4):226-234. 12. Irrgang JJ, Anderson AF, Boland AL, et al. Development and validation of the International Knee Documentation Committee subjective knee form. Am J Sports Med. 2001;29(5):600-613. 13. Johnsson RJ, Kettelkamp DB, Clark W, Leaverton P. Factors affecting late results after meniscectomy. J Bone Joint Surg Am. 1974;56(4):719-729. 14. Lee DH, Kim TH, Kim JM, Bin SI. Results of subtotal/total or partial meniscectomy for discoid lateral meniscus in children. Arthroscopy. 2009;25(5):496-503. 15. Levy IM, Torzilli PA, Warren RF. The effect of medial meniscectomy on anterior-posterior motion of the knee. J Bone Joint Surg Am. 1982;64(6):883-888. 16. Lysholm J, Gillquist J. Evaluation of knee ligament surgery results with special emphasis on use of a scoring scale. Am J Sports Med. 1982;10(3):150-154. 17. MacConaill MA. The movements of bones and joints: the synovial fluid and its assistants. J Bone Joint Surg Br. 1950;32(2):244-252.
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18. McDermott ID, Amis AA. The consequences of meniscectomy. J Bone Joint Surg Br. 2006;88(12):1549-1556. 19. McMurray TP. The semilunar cartilages. Br J Surg. 1942;29:407414. 20. Mitsou A, Vallianatos P, Piskopakis N, Maheras S. Anterior cruciate ligament reconstruction by over-the-top repair combined with popliteus tendon plasty. J Bone Joint Surg Br. 1990;72(3):398404. 21. Neilson AB, Yde J. Epidemiology of acute knee injuries: a prospective hospital investigation. J Trauma. 1991;31(12):1644-1648. 22. Outerbridge RE. The etiology of chondromalacia patellae. J Bone Joint Surg Br. 1961;43:752-757. 23. Paley D, Herzenberg JE, Tetsworth K, McKie J, Bhave A. Deformity planning for frontal and sagittal plane corrective osteotomies. Orthop Clin North Am. 1994;25(3):425-465. 24. Renstrom P, Johnson RJ. Anatomy and biomechanics of the menisci. Clin Sports Med. 1990;9(3):523-538. 25. Seedholm BB, Dowson D, Wright V. Functions of the menisci: a preliminary study. J Bone Joint Surg Br. 1974;56:381-382. 26. Shelbourne KD, Dickens JF. Digital radiographic evaluation of medial joint space narrowing after partial meniscectomy of bucket-handle medial meniscus tears in anterior cruciate ligament-intact knees. Am J Sports Med. 2006;34(10):1648-1655. 27. Sugawara O, Miyatsu M, Yamashita I, Takemitsu Y, Onozawa T. Problems with repeated arthroscopic surgery in the discoid meniscus. Arthroscopy. 1991;7(1):68-71. 28. Sutton JB. Ligaments: Their Nature and Morphology. 2nd ed. London, UK: HK Lewis & Co; 1897:67-73. 29. Tapper EM, Hoover NW. Late results after meniscectomy. J Bone Joint Surg Am. 1969;51(3):517-526. 30. Voloshin AS, Wosk J. Shock absorption of meniscectomized and painful knees: a comparative in vivo study. J Biomed Eng. 1983;5(2): 157-161. 31. Zimmy ML, Albright DJ, Dabezies E. Mechanoreceptors in the human medial meniscus. Acta Anat (Basel). 1988;133(1):35-40.
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§ Address correspondence to Min Jung, MD, Department of Orthopaedic Surgery, Arthroscopy and Joint Research Institute, Yonsei University College of Medicine, C.P.O. Box 8044, 134, Shinchon-dong, Seodaemungu, Seoul 120-752, South Korea (e-mail: [email protected]). *Arthroscopy and Joint Research Institute, Department of Orthopaedic Surgery, Yonsei University College of Medicine, Seoul, Korea. y Department of Orthopaedic Surgery, Gwangmyung Sungae Hospital, Gyeonggi, Korea. z Department of Orthopaedic Surgery, Seoul Wooridul Hospital, Seoul, Korea. The authors declared that they have no conflicts of interest in the authorship and publication of this contribution. There was no external funding source related to the study.
Meniscal tears are the most common knee injury, leading to an annual incidence in Denmark of 60 to 70 meniscectomies per 100,000 people.8,21 In the past, the meniscus was considered the vestigial remnant of muscle within the knee,28 and total meniscectomy was the prevailing treatment for meniscal tears.19 However, since Fairbank4 noted radiographic changes after meniscectomy, many reports regarding long-term results after total meniscectomy have shown a high risk of osteoarthritic change and serious deterioration of function.1,13 In addition, various important roles of the meniscus in load bearing,25 shock absorption,30 joint stability,15 joint lubrication,17 nutrition of the articular cartilage,24 and proprioception31 have been
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recognized. Consequently, to decrease the progression of osteoarthritis, the recommended procedure entails partial meniscectomy with minimal resection of the torn unstable meniscus and preservation of as much of the stable meniscus component as possible.24 In long-term studies, partial meniscectomy has shown results superior to those of total meniscectomy in terms of radiologic change and functional outcomes.2,9,10 However, in previous studies, partial meniscectomy has focused on a surface area based on width viewed in the axial plane. According to an experimental study,7 a decrease of meniscal thickness by single-leaf resection of a horizontal tear compromised biomechanical function of the meniscus and led to decreased contact area and increased mean pressure. As far as we know, no clinical study has dealt with the effect of decreased thickness of the meniscus on surgical outcomes. Accordingly, the purpose of the present study is to compare postoperative outcomes between partial meniscectomy with or without horizontal resection and subtotal meniscectomy and to evaluate the influence of decreased thickness of the medial meniscus on outcomes after partial meniscectomy. We hypothesized that decreased thickness of the meniscus would have an adverse effect on postoperative results in terms of radiologic findings and functional outcomes.
MATERIALS AND METHODS Patients A total of 1274 patients who underwent meniscectomy between January 2002 and August 2008 at the Severance Hospital of Yonsei University College of Medicine were retrospectively reviewed after the study was approved by the institutional review board. Patients who met the following criteria were included in the study: (1) isolated medial meniscal tear treated with arthroscopic meniscectomy, (2) width of the peripheral meniscus remaining after meniscectomy of less than 3 mm (subtotal meniscectomy) or more than 5 mm (partial meniscectomy), (3) no arthritic change on preoperative radiographs (International Knee Documentation Committee [IKDC] radiologic grade11 of normal), and (4) a minimum follow-up duration of 5 years. The exclusion criteria were as follows: (1) repair of torn meniscus; (2) concomitant chondral lesion (grade I or higher according to the Outerbridge grading system22 at arthroscopy), cystic lesion, or ligament injury; (3) malalignment of the lower extremity (.5 mm of mechanical axis deviation as measured on standing hip-knee-ankle radiographs23); (4) previous surgery of the affected knee; (5) previous injury of the contralateral knee; and (6) arthritic change in the contralateral unaffected knee 5 years after operation (to rule out the effect of natural degeneration according to age). After excluding 68 patients (20 patients in group A, 33 patients in group B, and 15 patients in group C) who were lost to follow-up, 409 patients were selected according to the inclusion criteria. From these 409 patients, 90 patients, including 22 with arthritic changes in the contralateral knee at 5 years, were
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Figure 1. Preoperative and postoperative meniscus in group A. The preoperative meniscal tear in this group did not include a horizontally torn component. The remaining meniscus after meniscectomy was more than 5 mm wide and preserved full thickness. Thus, menisci of patients included in group A had only decreased width without decreased thickness. (A) Preoperative axial view. (B) Postoperative axial view. excluded. Additionally, 7 patients were excluded: 1 due to anterior cruciate ligament rupture caused by new trauma during follow-up and 6 with postoperative complications (1 complex regional pain syndrome, 1 superficial skin infection at the suture site, and 4 with iatrogenic chondral damage resulting from a tight medial compartment). Therefore, 312 patients were included in the current study. The patients were divided into 3 groups according to the state of the meniscus remnant after meniscectomy. The width of the peripheral meniscus remaining was intraoperatively measured with a graduated probe. On the basis of previous studies,14,27 the meniscectomy was considered subtotal if less than 3 mm in width of the peripheral meniscus remained, and meniscectomy was considered partial if more than 5 mm in width of the peripheral meniscus remained. For a clear separation between partial meniscectomy and subtotal meniscectomy, procedures that left 3 to 5 mm in width of the peripheral meniscus remaining were not included in this study. Group A included 84 patients without horizontal tearing who underwent partial meniscectomy including vertical resection. The remaining meniscus was greater than 5 mm wide, with full thickness preserved. The menisci of these patients had decreased width without decreased thickness (Figure 1). Group B consisted of 140 patients who underwent partial meniscectomy including horizontal resection for a horizontally torn component of the meniscus. As with group A, the remaining meniscus was greater than 5 mm wide, but the thickness of the remaining meniscus in group B was less than that of group A. There was a practical limitation in intraoperatively measuring the exact thickness of the remaining meniscus. However, to prevent retear in a meniscus with a horizontal tear, the more unstable leaf of the superior and inferior leaves was excised close to the peripheral rim for a smooth margin. Therefore, in most patients in group B, the remaining meniscus had decreased thickness from the inner portion almost to the peripheral margin. Although
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Figure 3. Preoperative and postoperative meniscus in group C. Subtotal meniscectomy was performed, after which the remaining meniscus was less than 3 mm wide. (A) Preoperative axial view. (B) Postoperative axial view.
Figure 2. Preoperative and postoperative meniscus in group B. The preoperative meniscal tear in this group included a horizontally torn component. To prevent retear, the more unstable leaf of the superior and inferior leaves was excised close to the peripheral rim for a smooth margin. The meniscus that remained after meniscectomy was more than 5 mm wide, but its thickness was reduced due to horizontal resection. The postoperative meniscus had decreased thickness near the peripheral rim. (A) Preoperative axial view. (B) Postoperative axial view. (C) Preoperative coronal section. (D) Postoperative coronal section. full thickness was preserved in the peripheral portion of the remaining meniscus, its width was less than 5 mm (Figure 2). The major difference between groups A and B was that the remaining meniscus of patients in group A was full thickness (.5 mm wide), while for patients in group B the thickness of the remaining meniscus had decreased near the peripheral rim. Group C consisted of 88 patients who underwent subtotal meniscectomy. The remaining meniscus was less than 3 mm wide (Figure 3). Preoperative magnetic resonance imaging (MRI) was performed in all patients. All surgeries were performed by a single surgeon, the senior author (S.-J.K.). The unstable portion of the torn meniscus was removed. The edges of the meniscus remaining after resection were smoothed by shaver.
Clinical Assessment Postoperative follow-up examinations were performed at 3 months, 6 months, and then annually during a patient’s regular annual visit. The preoperative values were compared with postoperative values measured at 5 years after surgery. If a patient did not attend a scheduled
appointment at the outpatient clinic, we called and asked the patient to visit the clinic for the follow-up evaluation. This evaluation consisted of an interview, a physical examination, a questionnaire, and radiographic inspection, which were used to assess clinical function and radiologic findings. Those patients lost to follow-up were not included in the present study. Clinical function was evaluated with the Lysholm knee scoring scale,16 the IKDC subjective knee evaluation form,12 and the Tapper and Hoover grading system,29 and patients received 1 of 4 grades based on each of these evaluations. The Lysholm score falls into the following 4 grades according to Mitsou et al20: excellent = 95-100; good = 84-94; fair = 65-83; poor = \65. The IKDC score is classified into the following 4 grades by Haas et al6: excellent = 90-100; good = 80-89; fair = 70-79; poor = \70. The Tapper and Hoover system29 also has 4 grades: Excellent indicates that the patient has no symptoms and no disability related to the knee. Good means that the patient has minimal symptoms, such as aching or weakness after heavy use or effusion after heavy exertion, but essentially no disability. Fair indicates that the patient has symptoms such as trouble kneeling or climbing stairs and enough weakness, pain, or discomfort to interfere somewhat with everyday activities; the patient thinks he or she has some disability and cannot participate in vigorous sports (eg, skiing, tennis, football). Poor denotes that the patient has severe symptoms, including all of those listed under fair as well as pain at rest, limitation of motion, and locking; the patient is clearly disabled, and activities, including walking, are definitely limited. The radiologic evaluation was performed by independent experienced clinical fellows who were blinded to the method of treatment applied to the patients. Bilateral, double-leg weightbearing radiographs of anteroposterior, lateral, and posteroanterior views at 45° of flexion and Merchant views were obtained. The radiologic evaluation of the tibiofemoral joint was carried out according to the IKDC radiographic assessment scale11 and categorized as follows: A = normal; B = nearly normal, .4 mm joint space, but early osteophyte; C = abnormal, joint space 2 to 4 mm, or .50%; D = severely abnormal, joint space \2 mm, or
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meniscus remnant after meniscectomy, demographic characteristics (age, sex, body mass index [BMI], affected side, duration of symptoms, and trauma history), and preoperative values (Lysholm knee score, IKDC subjective score, height of joint space on the affected side, and location of tear). The same analytic method as described above was used to assess whether differences in the patterns of meniscal tear affected postoperative outcomes within the respective group. Interobserver reliability in measurement of the height of the joint space was evaluated by use of the intraclass correlation set at a 95% CI. The level of significance was set at P \ .05. Statistical analysis was performed with IBM SPSS Statistics for Windows (v 19.0; IBM Inc).
RESULTS Figure 4. Preoperative radiograph of 46-year-old female patient in group B: bilateral, 45° flexion, weightbearing, posteroanterior. The height of the medial compartment at the tibiofemoral joint was measured from the center of the medial femoral condyle to the center of the medial tibial plateau on the radiograph. The left knee was the affected side. For both knees, the height of the medial compartment was 4.7 mm. \50%. The heights of medial compartments at the tibiofemoral joints of both knees were measured on the 45° flexion weightbearing posteroanterior radiograph, according to the method described by Shelbourne et al.26 The height was measured from the center of the medial femoral condyle to the center of the medial tibial plateau by use of a picture archiving and communication system (Centricity PACS; GE Medical System Information Technologies) (Figure 4). To increase reliability, measurements of the height of the joint space were made twice by 2 different investigators on the bilateral digital radiographs. The mean of 2 numerical values was used.
Statistical Analysis An analysis of variance (ANOVA) for continuous variables and the chi-square or Fisher exact test for categorical variables were used to compare the 3 groups with regard to demographic characteristics and preoperative and postoperative values. A post hoc analysis with Bonferroni correction was performed to make pairwise comparisons between the 3 groups. Comparisons between pre- and postoperative values in the same group were performed with a paired t test for continuous numerical data. Multivariate analysis using a generalized linear model for continuous data and multinomial logistic regression for categorical data according to the characteristics of postoperative variables was used to identify factors that significantly influenced the changes in postoperative outcomes (Lysholm knee score, IKDC subjective score, Tapper and Hoover grade, IKDC radiographic scale, and height of joint space on the affected side) among variables: These variables included differences between groups in the postoperative state of the
There were 59 male and 25 female patients in group A, 84 male and 56 female patients in group B, and 49 male and 39 female patients in group C. The average age at the time of surgery was 39.6 years (range, 16-58 years) in group A, 41.6 years (range, 13-62 years) in group B, and 40.8 years (range, 16-57 years) in group C. The mean duration of symptom was 23.1 months (range, 1-168 months) in group A, 23.9 months (range, 1-252 months) in group B, and 18.8 months (range, 1-172 months) in group C. There was no statistically significant difference between groups in regard to sex, age, mean BMI, proportion of patients with history of trauma, or mean duration of symptoms before operative treatment (see Appendix 1, available online at http://ajsm.sagepub.com/supplemental). There was no statistically significant difference in location of tear between the 3 groups (P = .938). In group B, the remaining meniscus leaf portion after meniscectomy was superior in 114 patients (81.4%) and inferior in 26 patients (18.6%). No significant differences were found between the 3 groups in regard to the mean of the preoperative Lysholm score (P = .276) and IKDC subjective score (P = .167). There was no statistically significant difference in preoperative height on the affected side (P = .188) or the unaffected side (P = .364) between the 3 groups (Table 1). No patient included in the current study underwent a second operation for retear of the meniscus. The preoperative values were compared with the postoperative values measured at 5 years after operation within each group. All 3 groups had statistically significant differences between preoperative and postoperative values for the Lysholm knee score (P \ .001), the IKDC subjective score (P \ .001), and height of the joint space of the affected side (P \ .001). However, comparison of the height of the joint space of the unaffected side did not show a statistically significant difference (Appendix 2, available online). We compared postoperative functional outcomes and radiologic findings between the 3 groups. The mean postoperative Lysholm score was 96.1 in group A, 94.9 in group B, and 84.8 in group C, and the mean postoperative IKDC subjective score was 92.1 in group A, 91.3 in group B, and 81.0 in group C. Both of these functional scores showed
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TABLE 1 Comparison of Preoperative Variables Between the 3 Groupsa Variable Location of tear Posterior horn Body .1 portion Lysholm knee score IKDC subjective score Height of joint space, mm Affected side Unaffected side
Group A (n = 84)
Group B (n = 140)
Group C (n = 88)
P Value .938
52 5 27 65.8 60.5
(61.9) (6.0) (32.1) 6 6.6 6 6.0
4.9 6 0.5 4.9 6 0.5
86 9 45 65.1 59.6
(61.4) (6.4) (32.1) 6 6.1 6 8.9
5.0 6 0.5 5.0 6 0.5
53 8 27 66.5 61.8
(60.2) (9.1) (30.7) 6 7.5 6 10.1
4.9 6 0.4 5.0 6 0.4
.276 .167 .188 .364
a
Values are expressed as n (%) or mean 6 SD. IKDC, International Knee Documentation Committee.
statistically significant differences between the 3 groups (P \ .001). The grades assigned according to the Lysholm score and the IKDC subjective score also showed statistically significant differences between the 3 groups (P \ .001). Postoperative function according to the Tapper and Hoover grading system was as follows: group A, excellent = 49 (58.3%), good = 27 (32.1%), fair = 8 (9.5%), poor = 0 (0%); group B, excellent = 78 (55.7%), good = 46 (32.9%), fair = 15 (10.7%), poor = 1 (0.7%); group C, excellent = 35 (39.8%), good = 26 (29.6%), fair = 24 (27.3%), poor = 3 (3.4%). There were statistically significant differences between the 3 groups (P = .003) for postoperative functional grades. Comparison of postoperative IKDC radiographic scales showed statistically significant differences between the groups (P \ .001). The IKDC radiographic scale results were as follows: for group A, A = 57 (67.9%), B = 19 (22.6%), C = 8 (9.5%), D = 0 (0.0%); for group B, A = 90 (64.3%), B = 34 (24.3%), C = 16 (11.4%), D = 0 (0.0%); for group C, A = 27 (30.7%), B = 37 (42.1%), C = 18 (20.5%), D = 6 (6.8%) (Table 2). In terms of functional scores, grades, and radiographic scales, the post hoc test showed that group C had significantly poorer outcomes than did groups A and B (P \ .05) but that there was no statistically significant difference between groups A and B (P . .05) (Appendix 3, available online). The mean 6 SD postoperative heights of joint spaces on the affected side were 4.7 6 0.6 mm in group A, 4.3 6 0.5 mm in group B, and 3.7 6 0.8 mm in group C. The mean 6 SD percentages of the postoperative heights of joint spaces in relation to the preoperative heights of joint spaces on the affected side were 95.9% 6 9.8% in group A, 86.1% 6 10.3% in group B, and 76.5% 6 18.6% in group C. Comparison of the heights of joint spaces on the affected side between the 3 groups showed statistically significant differences (P \ .001) (Table 2). According to the post hoc test, the joint space of group A was significantly higher than the joint space of groups B and C (P \ .001). The joint space of group B was significantly higher than that of group C (P \ .001) (Appendix 3). Comparison of the postoperative heights of the joint space between the affected side and the unaffected side showed a statistically significant difference in each group: P .002 in group A, P \ .001
in group B, P \ .001 in group C (Appendix 4, available online). The intraclass correlation coefficient (ICC) for preoperative joint space height was 0.709 for the affected knee and 0.675 for the unaffected knee, and the ICC for postoperative joint space height was 0.892 for the affected knee and 0.654 for the unaffected knee. Univariate analysis with a generalized linear model and multinomial logistic regression was conducted to determine the factors that significantly influenced the changes in postoperative outcomes. This analysis showed that differences in groups divided according to the postoperative state of the meniscus remnant after meniscectomy had a significant effect on all postoperative variables, including Lysholm knee score (P \ .001) (Appendix 5), IKDC subjective score (P \ .001) (Appendix 6), Tapper and Hoover grade (P = .010) (Appendix 7), IKDC radiographic scale (P \ .001) (Appendix 8), and height of the joint space on the affected side (P \ .001) (Appendix 9). The BMI correlated with the postoperative Lysholm knee score (P = .013) (Appendix 5), the IKDC radiographic scale (P \ .001) (Appendix 8), and the postoperative height of the joint space on the affected side (P = .030) (Appendix 9). There was a positive correlation between preoperative height of the joint space on the affected side and postoperative height of the joint space on the affected side (P \ .001) (Appendix 9). The multivariate analysis, which was performed according to the results of the univariate analysis, showed that difference between group and BMI still had an effect on postoperative Lysholm knee score (P \ .001 and P \ .009, respectively) (Appendix 5) and IKDC radiographic scale (P \ .001 for both) (Appendix 10). According to the multivariate analysis of the postoperative height of the joint space on the affected side, differences between groups (P \ .001), BMI (P = .003), and preoperative height of the joint space on the affected side (P \ .001) still had a positive correlation (Appendix 9). To sum up, the difference between postoperative states of the meniscus remnant after meniscectomy had a significant influence on the postoperative variables even when the effects of other factors such as BMI and preoperative height of the joint space were excluded. In addition, because there was no statistically significant difference in BMI and preoperative height
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TABLE 2 Comparison of Postoperative Variables Between the 3 Groupsa Variable Lysholm knee score Lysholm knee score grade Excellent Good Fair Poor IKDC subjective score IKDC subjective score grade Excellent Good Fair Poor Tapper and Hoover grade Excellent Good Fair Poor IKDC radiographic scale A B C D Height of joint space, mm Affected side Unaffected side Height of joint space, %b Affected side Unaffected side
Group A (n = 84)
Group B (n = 140)
Group C (n = 88)
P Value
96.1 6 4.7
94.9 6 5.2
84.8 6 11.4
\.001 \.001
54 (64.3) 23 (27.4) 7 (8.3) 0 (0.0) 92.1 6 6.5
87 (62.1) 44 (31.4) 8 (5.7) 1 (0.7) 91.3 6 8.8
38 (43.2) 22 (25.0) 26 (29.6) 2 (2.3) 81 6 11.4
58 18 8 0
(69.1) (21.4) (9.5) (0.0)
92 31 15 2
(65.7) (22.1) (10.7) (1.4)
26 25 29 8
(29.6) (28.4) (33.0) (9.1)
49 27 8 0
(58.3) (32.1) (9.5) (0.0)
78 46 15 1
(55.7) (32.9) (10.7) (0.7)
35 26 24 3
(39.8) (29.6) (27.3) (3.4)
57 19 8 0
(67.9) (22.6) (9.5) (0.0)
90 34 16 0
(64.3) (24.3) (11.4) (0.0)
27 37 18 6
(30.7) (42.1) (20.5) (6.8)
\.001 \.001
.003
\.001
4.7 6 0.6 4.9 6 0.4
4.3 6 0.5 4.9 6 0.5
3.7 6 0.8 5.0 6 0.3
\.001 .261
95.9 6 9.8 99.6 6 5.9
86.1 6 10.3 99.0 6 7.9
76.5 6 18.6 99.9 6 5.3
\.001 .568
a
Values are expressed as mean 6 SD or n (%). IKDC, International Knee Documentation Committee. Percentage of the postoperative heights of joint spaces in relation to the preoperative heights of joint spaces.
b
of the joint space on the affected side between the 3 groups, there was no significant effect of BMI and preoperative height of the joint space on the affected side. Differences of patterns of meniscal tear had no statistically significant effect on postoperative outcomes within each group (Appendices 11-13).
DISCUSSION The present study found that surgical outcomes, including functional and radiologic results, of partial meniscectomy for horizontal tear resulting in decreased meniscal thickness were comparable to postoperative outcomes of conventional partial meniscectomy preserving whole meniscal thickness. Previous long-term studies have shown superior clinical results of partial meniscectomy over total meniscectomy.1,13 Preserving as much meniscus tissue as possible has become a principle of surgical treatment of meniscal tear given the important functions of the meniscus in the knee.15,17,24,25,30,31 To preserve the meniscus tissue, meniscal repair should be a top priority in treatment of meniscal tear. However, in the case of meniscal tear with severe meniscal degeneration, complex tear, large flap tear, and meniscal tear involving the inner one-third
region, resection of the meniscus is inevitable. The main objective of operative treatment is to remove the unstable meniscus fragment and preserve a stable peripheral rim. However, in horizontal cleavage tear, which was reported to be the most common type of tear,5 conventional resection of both superior and inferior leaves leads to a decrease of remnant meniscus tissue. Therefore, resection of only a single unstable leaf is preferred. Preservation of one leaf should be balanced against the risk of retear and consequent reoperation, and so the more unstable leaf is completely excised.3 However, when the resection of meniscus tissue extends close to the peripheral rim, loss of height of meniscus tissue can be a concern, as it is another cause of deterioration in meniscal function. The present study compared 3 groups divided according to the state of remnant meniscus tissue. The results showed that group C had inferior functional outcomes, compared with groups A and B, according to the Lysholm knee score, IKDC subjective score, and Tapper and Hoover grade. On the IKDC radiographic scale, the outcome of group C was worse than outcomes of groups A and B; however, there was no statistically significant difference between groups A and B. In the present study, outcomes of subtotal meniscectomy were worse than those of partial meniscectomy. These results are consistent with the
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findings of previous studies,2,10 which noted that the amount of excised meniscal tissue was inversely related to the function of the knee and that preservation of the peripheral rim of the meniscus in partial meniscectomy provided better outcomes. The important point of the present study is that partial meniscectomy for horizontal tear of the medial meniscus that completely excises the unstable leaf had no additional adverse effect on 5-year surgical outcomes compared with partial meniscectomy that preserves the whole height of the medial meniscus. These results are not in accord with the results of a biomechanical study7 that noted resection of a single meniscus leaf in horizontal tear of the lateral meniscus decreased contact area by 40% to 59% and increased mean pressure by 24% to 55% compared with the intact lateral meniscus. Inconsistency between these 2 studies is thought to come from the difference in location of the targeted meniscus. While the lateral meniscus carries 70% of the load acting on the lateral tibiofemoral joint, the medial meniscus carries 50% of the load acting on the medial tibiofemoral joint.25 In addition, because of the concavity of the medial tibial plateau compared with the convexity of the lateral tibial plateau, a more congruent characteristic of the medial compartment has less tendency toward a decrease in contact area and an increase in mean pressure.18 In the present study, a postoperative decrease of medial meniscal thickness resulting from partial meniscectomy for horizontal tear that completely excised the unstable leaf had no clinically detectable deleterious effect on functional scores or on radiologic outcome according to the IKDC radiographic scale. Height of the joint space in the medial compartment of the tibiofemoral joint was measured and compared between 3 groups. The mean 6 SD postoperative heights of joint spaces on the affected side were 4.7 6 0.6 mm in group A, 4.3 6 0.5 mm in group B, and 3.7 6 0.8 mm in group C (P \ .001). The mean 6 SD percentages of the postoperative heights of the joint spaces in relation to the preoperative heights of joint spaces on the affected side were 95.9% 6 9.8% in group A, 86.1% 6 10.3% in group B, and 76.5% 6 18.6% in group C (P \ .001). Post hoc analysis showed that the joint space of group A was significantly wider than the joint spaces of groups B and C (P \ .001). The joint space of group B was significantly wider than that of group C (P \ .001). In comparisons between groups A and B, although there was no significant difference in functional scores and IKDC radiographic scale, the remnant meniscus was thinner in group B than in group A, and the joint space on radiograph was lower in group B than in group A. Decreased thickness of the remnant meniscus leads to an increase in mean contact pressure and peak contact pressure in the tibiofemoral joint,7 which can contribute to arthritic change. Although evaluation with the IKDC radiographic scale showed no significant difference between groups A and B in the present study with regard to 5-year outcomes, long-term study is needed to determine the possible negative outcomes in radiologic evaluation and consequent functional loss. Several limitations prevented us from reaching a firm conclusion in the present study. First, the study was based
Effect of Meniscal Thickness on Outcome After Meniscectomy
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on retrospective review. Second, no previous study has noted average values of the postoperative variables used in the present study in partial meniscectomy for horizontal tear of the meniscus. Therefore, the sample size calculated from statistical power analysis could not be obtained. The numbers of patients in each group may not be sufficient to show lack of difference between groups A and B with substantial statistical power. Third, in the present study, subtotal meniscectomy was defined as meniscectomy with less than 3 mm in width of the peripheral meniscus remaining, in accordance with previous studies.14,27 Partial meniscectomy was defined as meniscectomy with more than 5 mm in width of the peripheral meniscus remaining. However, no biomechanical study has supported a clear reference point dividing partial and subtotal meniscectomy depending on resistance to hoop stress. Fourth, thickness of the remnant meniscus after meniscectomy for horizontal tear can affect surgical outcomes. However, there is a practical limitation in intraoperatively measuring thickness of the remaining meniscus. Fifth, radiologic evaluation is inevitably subjective in assessing arthritic change. Even though the height of the joint space was measured twice by 2 different investigators to increase reliability, the intraclass correlation coefficient (0.6540.892) was not high enough to present greater reliability.
CONCLUSION A decrease of meniscal thickness after partial meniscectomy for horizontal tear had no additional adverse effect on 5-year functional outcomes and radiographic scale compared with conventional partial meniscectomy preserving whole meniscal thickness despite joint space narrowing. In treating horizontal tear of the meniscus, partial meniscectomy with complete resection of the unstable leaf was an effective method in a 5-year follow-up study.
ACKNOWLEDGMENT The authors thank Dong-Su Jang (medical illustrator, Medical Research Support Section, Yonsei University College of Medicine, Seoul, Korea) for his support with the medical figures. REFERENCES 1. Allen PR, Denham RA, Swan AV. Late degenerative changes after meniscectomy: factors affecting the knee after operation. J Bone Joint Surg Br. 1984;66(5):666-671. 2. Andersson-Molina H, Karlsson H, Rockborn P. Arthroscopic partial and total meniscectomy: a long-term follow-up study with matched controls. Arthroscopy. 2002;18(2):183-189. 3. Bin SI, Jeong SI, Kim JM, Shon HC. Arthroscopic partial meniscectomy for horizontal tear of discoid lateral meniscus. Knee Surg Sports Traumatol Arthrosc. 2002;10(1):20-24. 4. Fairbank TJ. Knee joint changes after meniscectomy. J Bone Joint Surg Br. 1948;30(4):664-670. 5. Ferrer-Roca O, Vilalta C. Lesions of the meniscus, part II: horizontal cleavages and lateral cysts. Clin Orthop Relat Res. 1980;146:301307.
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