207 C OPYRIGHT Ó 2014

BY

T HE J OURNAL

OF

B ONE

AND J OINT

S URGERY, I NCORPORATED

Patellar Eversion During Total Knee Replacement A Prospective, Randomized Trial Michael J. Reid, FRCS(Tr&Orth), Grant Booth, FRACS, Riaz J.K. Khan, FRCS(Tr&Orth), and Greg Janes, FRACS Investigation performed at Sir Charles Gairdner Hospital, Nedlands, Western Australia, Australia

Background: Proponents of minimally invasive total knee arthroplasty argue that retracting rather than everting the patella results in quicker postoperative recovery and improved function. We aimed to investigate this in patients undergoing knee arthroplasty through a standard medial parapatellar approach. Methods: In a prospective randomized double-blinded study, sixty-eight patients undergoing total knee arthroplasty through a standard medial parapatellar approach were assigned to either retraction or eversion of the patella. Postoperatively, at three months, and at one year after surgery, an independent observer assessed the primary outcome measure (i.e., knee flexion) and secondary outcome measures (i.e., Oxford knee score, Short Form-12 [SF-12] score, visual analog scale pain score, knee motion, and alignment and patellar height as measured on radiographs with use of the Insall-Salvati ratio). Results: Early (three-month) follow-up showed no significant difference between patellar eversion and subluxation in flexion (mean and 95% confidence interval [CI], 101° ± 5.37° versus 102° ± 4.14°, respectively), Oxford knee scores (25 ± 3 versus 27 ± 2.69, respectively), SF-12, or visual analog scale pain scores (1.9 ± 0.54 versus 1.1 ± 0.44, respectively). A significant improvement in extension was found (23.9° ± 1.12° versus 22.0° ± 0.91°, respectively [p = 0.034]), but this was not clinically significant. There was no significant difference in any of the outcomes at one year. There was a significant difference in implant malpositioning between the eversion group and the subluxation group, with an increased percentage of lateral tibial overhang in the subluxation group (0.45 ± 0.39 versus 1.84 ± 0.82, respectively [p = 0.005]), but this did not correlate with functional outcome. There was no significant difference in alignment between the two groups (178.29° ± 0.84° versus 178.18° ± 0.78°). At one year after surgery, there was no difference between the two groups in Insall-Salvati ratio (1.15 ± 0.06 versus 1.12 ± 0.06) although there was a correlation between the percentage reduction in the ratio and functional outcome. There were two partial divisions of the patella tendon in the subluxation group, but no patella-related complications in the eversion group. Conclusions: The results of this trial showed that retracting rather than everting the patella during total knee arthroplasty resulted in no significant clinical benefit in the early to medium term. We observed no increase in patellar tendon shortening as a result of eversion rather than subluxation. Our findings did suggest that, with subluxation, there may be an increased risk of damage to the patellar tendon and reduced visualization of the lateral compartment, leading to an increase in implant malpositioning with lateral tibial overhang. Level of Evidence: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Peer Review: This article was reviewed by the Editor-in-Chief and one Deputy Editor, and it underwent blinded review by two or more outside experts. It was also reviewed by an expert in methodology and statistics. The Deputy Editor reviewed each revision of the article, and it underwent a final review by the Editor-in-Chief prior to publication. Final corrections and clarifications occurred during one or more exchanges between the author(s) and copyeditors.

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espite the success of conventional total knee arthroplasty for the treatment of arthritis of the knee1-4, there has been a movement toward performing the procedure in a less invasive manner.

The key surgical features of minimally invasive knee surgery include reducing the length of the incision to between 6 and 11 cm, reducing the amount of soft-tissue disruption, avoiding knee joint dislocation, and retracting (subluxing) rather than everting

Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

J Bone Joint Surg Am. 2014;96:207-13

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http://dx.doi.org/10.2106/JBJS.J.00947

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(dislocating) the patella5,6. Proponents of the new techniques state that patient demand, potential health-care savings, and the development of new instrumentation and techniques have led to the advancement of these less invasive surgical approaches5. The reported benefits of less invasive knee arthroplasty have included more rapid functional recovery, decreased postoperative pain, improvements in knee motion, less blood loss, fewer lateral releases, reduced pain scores and analgesia requirements, and reduced hospital stay7-15. Caution has been raised by a recent systematic review of these positive findings, and a call for more prospective randomized controlled trials to isolate the benefits of this surgical technique has been made16. Studies comparing a less invasive technique with a standard medial parapatellar approach often are comparing multiple variations in technique, making it difficult to isolate the alteration that has led to the difference in outcome. Supporters of a less invasive technique have theorized that noted differences in clinical outcome are a result of patella eversion, which leads to increased patellar fibrosis and contraction14,15,17. The aim of our study was to isolate and investigate one aspect of less invasive surgery: whether retraction rather than eversion of the patella would lead to a significant difference in implant positioning, pain, knee motion, function, and patellar fibrosis. Materials and Methods Participants

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ale or female patients of any age who required primary total knee arthroplasty while under the care of the participating surgeons were included. Exclusion criteria were a body mass index >40, a nondislocatable patella (e.g., secondary to patella baja or obesity), a patient whose domicile was outside of Western Australia, a previous femoral fracture, the need for patellar resurfacing, and prior high tibial osteotomy or patellar realignment procedures. The study was approved by the Human Research Ethics Committee of Sir Charles Gairdner Hospital, and patients provided informed consent according to the protocol. This study is registered in the Australian New Zealand Clinical Trials Registry (ACTRN12610000433000).

was measured on standardized weight-bearing anteroposterior long leg radiographs, and patellar height was measured on the lateral radiographs, which were digitally 18 enhanced by the methods described by Sharma et al. . The passive knee motion recorded was measured with use of a goniometer. The visual analog scale pain score was determined by asking patients to mark their pain on a graduated line starting at zero (indicating no pain) and ending at ten (indicating the worst pain imaginable). Additional outcome measures included length of hospital stay and complications related to the approach. Data collection was conducted preoperatively, immediately postoperatively, at three months, and at one year postoperatively.

Sample Size 12

Haas et al. reported a 12° difference in knee flexion at three-months postoperatively as compared with preoperatively. This finding was used to perform a pre-study power analysis. To achieve a power of 90% with an alpha value of 5%, thirty-three patients would be needed in each group.

Randomization A computerized random sequence generator was used to assign the order of randomization. The sequence was concealed until the interventions were assigned via a sealed envelope method in the operating room. Patients were recruited from November 2006 to November 2007 from the waiting lists of the two surgeons (G.J. and R.J.K.K.) at two hospitals in Perth.

Blinding The baseline and subsequent outcome data were collected by independent physical therapists and the radiographic evaluation was performed by an independent observer, all of whom were blinded to the treatment allocation. The baseline data were collected prior to randomization. Patients were blinded as to their allocation.

Statistical Methods Bimodal data were assessed with use of the Fisher exact test. After the initial data verification, the Student t test was used to investigate differences in parametric data and the Mann-Whitney test was used to assess nonparametric data. The relationship between radiographic and functional outcome was estimated with use of the Kendall rank correlation coefficient (the Kendall tau coefficient). The level of significance was set at p < 0.05.

Source of Funding There were no external sources of funding.

Interventions All patients received the same anesthetic for the procedure. A standard total knee replacement procedure was then performed through a midline incision and a medial parapatellar approach, with the quadriceps tendon split longitudinally to allow eversion and lateral retraction of the patella. All procedures were performed by the admitting surgeon (R.J.K.K. or G.J.). A cruciateretaining, cemented GENESIS II (Smith & Nephew, Memphis, Tennessee) prosthesis was implanted without patellar resurfacing. Patellar tracking was checked at the end of the procedure, and no lateral releases were required. Postoperatively, the patients were mobilized according to a standardized physical therapy protocol.

Objectives The null hypothesis was that retracting rather that everting the patella would not lead to a significant improvement in knee flexion or secondary outcome measures.

Outcomes The primary outcome measure was knee flexion, with secondary outcome measures including the Short Form-12 (SF-12) score, the Oxford knee score, knee motion, visual analog scale pain score, and radiographic assessment of alignment and patellar height (with use of the Insall-Salvati [IS] ratio). Alignment

Results Participant Flow eventy participants were assessed for eligibility (Fig. 1). One was excluded for prior fracture of the femur and one for living outside of Australia and not being able to attend regular follow-up. After randomization, thirty-seven received the standard treatment and constituted the eversion group and thirty-one received the less-disruptive treatment and composed the subluxation group. Two patients were lost to follow-up (one patient in the eversion group died of medical causes unrelated to surgery, and one patient in the subluxation group failed to attend the independent assessment), leaving thirtysix patients in the eversion group and thirty patients in the subluxation group.

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Baseline Data The two groups were equally matched with regard to age and sex. There were no significant differences found between the

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TABLE I Baseline Data

Age* Men:women

Eversion Group

Subluxation Group

P Value

68 (48 to 81)

70 (55 to 87)

0.19

16:20

12:18

0.31

Maximum knee flexion†

108° ± 17°

110° ± 13°

0.57

Maximum knee extension†

6.5° ± 6°

4.0° ± 4°

0.09

Oxford knee score†

40 ± 7

37 ± 7

0.31

Short Form-12 Physical component score† Mental component score†

32 ± 8 46 ± 11

33 ± 8 48 ± 11

0.66 0.45

Visual analog scale pain score

5.3 ± 2.5

5.1 ± 2.4

0.61

Alignment† Insall-Salvati ratio†

181.7° ± 6.5°

178.5° ± 5.8°

0.61

1.11 ± 0.15

1.09 ± 0.15

0.64

*The values are given as the mean, with the range in parentheses. †The values are given as the mean and the standard deviation.

two groups with regard to preoperative knee scores, knee motion, or pain. Baseline demographic and clinical data are presented in Table I.

Fig. 1

Patient flowchart.

Outcomes The predischarge postoperative data are presented in Table II. There was an increased but statistically insignificant length of

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TABLE II Postoperative Clinical and Radiographic Outcomes Before Discharge from Hospital Eversion Group Length of stay* Alignment* Posterior tibial slope*

8.62 ± 1.32

Subluxation Group 7.09 ± 0.65

P Value 0.12

178.29° ± 0.84°

178.18° ± 0.78°

0.55

2.38° ± 0.51°

1.97° ± 0.89°

0.45

Percentage of lateral tibial overhang*

0.45 ± 0.39

1.84 ± 0.82

0.005

Insall-Salvati ratio* Percent change*

1.16 ± 0.05 5.09 ± 3.7

1.14 ± 0.06 4.65 ± 3.6

0.626 0.678

*The values are given as the mean and the 95% confidence interval.

hospital stay in the eversion group (p = 0.12). Alignment, Insall-Salvati ratio, and percentage change in the Insall-Salvati ratio were similar between the two groups. There was a statistically significant difference (p = 0.005) in the percentage of lateral tibial overhang, with an increase in the subluxation group; however, there was no significant correlation between this and pain or any of the functional outcome scores at any time point, suggesting that this was not a clinically significant result in the short-term. The three-month data are presented in Table III. Both groups had an improvement in the Oxford knee score, the physical and mental components of the SF-12 score, and the visual analog scale pain score. No between-group differences were found with regard to these results. Compared with preoperative data, mean knee flexion was decreased in both groups by a similar amount. There was a significant difference in the maximum passive extension gained postoperatively, with a mean fixed flexion contracture of 23.9° in the eversion group and 22° in the subluxation group (p = 0.034). There was a trend for lower visual analog scale pain scores in the subluxation group, with a mean of 1.08 compared with 1.93 in the eversion group, but this did not reach significance (p = 0.062). There was a correlation between

the three-month knee extension and pain (p = 0.001) and the three-month knee extension and length of hospital stay (p = 0.027). At three months, the Insall-Salvati ratio decreased from that measured on the postoperative radiographs in both groups but there was no significant difference between the two groups (p = 0.723) The one-year data are presented in Table IV. The Oxford knee scores continued to show improvement, with a mean score of twenty-two in both groups. The SF-12 scores were essentially unchanged from the three-month mark. The visual analog scale pain scores were lower in both groups at one year. The maximum knee flexion that could be attained was similar in both groups, and the difference in knee extension that was seen at the three-month mark was no longer significant. The prevalence of patella baja in our study was 1.5% (one of sixty-six patients), and that patient was part of the subluxation group. There were two additional knees in the eversion group (5.6%) and three in the subluxation group (10%) that had a decrease in the Insall-Salvati ratio of >10%. There was no significant difference or correlation between reduction in Insall-Salvati ratio and the management of the patella. There was,

TABLE III Clinical and Radiographic Outcomes at Three Months After Surgery Eversion Group Maximum passive knee flexion* Maximum passive knee extension* Oxford knee score*

Subluxation Group

P Value

101° ± 5.37°

102° ± 4.14°

0.99

23.9° ± 1.12°

22.0° ± 0.91°

0.034

25 ± 3

27 ± 2.69

0.27

Short Form-12 Physical component score* Mental component score*

42.5 ± 2.89 50.7 ± 3.04

39.8 ± 3.98 50.1 ± 3.63

0.26 0.87

Visual analog scale pain score

1.93 ± 0.54

1.08 ± 0.44

0.062

1.15 ± 0.05 20.52 ± 1.95 4.64 ± 3.48

1.13 ± 0.06 21.07 ± 1.62 3.10 ± 3.72

0.741 0.723 0.624

Insall-Salvati ratio* Percent change* Percent overall change*

*The values are given as the mean and the 95% confidence interval.

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TABLE IV Clinical and Radiographic Outcomes at One Year After Surgery

Maximum knee flexion* Maximum knee extension*

Eversion Group

Subluxation Group

108° ± 3.68°

109° ± 3.992°

23.2° ± 1.18°

21.9° ± 1°

P Value 0.78 0.15

22 ± 2.23

22 ± 2.24

0.76

Short Form-12 Physical component score* Mental component score*

41.7 ± 3.27 51.0 ± 3.68

41.3 ± 3.69 51.3 ± 3.5

0.93 0.93

Visual analog scale pain score

1.1 ± 0.47

0.9 ± 0.38

0.76

1.15 ± 0.06 0.11 ± 2.62 4.58 ± 3.79

1.12 ± 0.06 20.073 ± 3.3 2.09 ± 3.92

Oxford knee score*

Insall-Salvati ratio* Percent change* Percent overall change*

0.520 0.604 0.464

*The values are given as the mean and the 95% confidence interval.

however, a correlation between percentage reduction in the Insall-Salvati ratio and the Oxford knee scores at three and twelve-months (p = 0.016), the maximum knee extension at twelve-months (p = 0.037), and the visual analog scale pain score at twelve-months (p = 0.045). The correlations are >0.01 and thus should be considered with caution; however, they do suggest a correlation between a poor functional outcome and reduction in Insall-Salvati ratio. These outcomes did not correlate with the eversion or subluxation of the patella, however. Surgical complications included two injuries to the patellar tendon in the subluxation group. One was minor, involving

Patellar eversion during total knee replacement: a prospective, randomized trial.

Proponents of minimally invasive total knee arthroplasty argue that retracting rather than everting the patella results in quicker postoperative recov...
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