THEKNE-01893; No of Pages 4 The Knee xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
The Knee
No effect of obesity on limb and component alignment after computer-assisted total knee arthroplasty☆ Gautam M. Shetty ⁎, Arun B. Mullaji, Sagar Bhayde, A.P. Lingaraju Department of Orthopaedic Surgery, Breach Candy Hospital, Mumbai, India
a r t i c l e
i n f o
Article history: Received 14 September 2013 Received in revised form 2 April 2014 Accepted 5 April 2014 Available online xxxx Keywords: Total knee arthroplasty Obesity Alignment Computer-assisted surgery Knee
a b s t r a c t Purpose: This retrospective study aimed to determine if computer navigation provides consistent accuracy for limb and component alignment during TKA irrespective of body mass index (BMI) by comparing limb and component alignment and the outlier rates in obese versus non-obese individuals undergoing computer-assisted TKA. Methods: Six hundred and thirty-five computer assisted total knee arthroplasties (TKAs) performed in nonobese individuals (BMI b 30 kg/m2) were compared with 520 computer-assisted TKAs in obese individuals (BMI ≥ 30 kg/m2) for postoperative limb and component alignment using full length standing hip-to-ankle radiographs. Results: No significant difference in postoperative limb alignment (179.7° ± 1.7° vs 179.6° ± 1.8°), coronal femoral (90.2° ± 1.6° vs 89.8° ± 1.9°) and tibial component (90.2° ± 1.6° vs 90.3° ± 1.7°) alignment and outlier rates (6.2% vs 7.5%) was found between non-obese and obese individuals. Similarly, alignment and the outlier rates were similar when non-obese individuals and a subgroup of morbidly obese individuals (BMI N 40 kg/m2) were compared. Conclusions: Computer navigation can achieve excellent limb and component alignment irrespective of a patient's BMI. Although obesity may not be an indication per se for using computer navigation during TKA, it will help achieve consistently accurate limb and component alignment in obese patients. Level of Evidence: Level II © 2014 Elsevier B.V. All rights reserved.
1. Introduction Risk of revision after total knee arthroplasty (TKA) is significantly higher when obesity is combined with malalignment of tibial component or the limb [1]. Reports have suggested that implant survival is significantly lower in obese patients (60–92%) in the long-term when compared to non-obese individuals (89–98.5%) [2–6] with loosening of tibial components and polyethylene wear being the major causes of revision [4,5]. Hence it is all the more important to ensure symmetric loading of implant and bone in the obese by accurate implant positioning and restoration of mechanical axis. Conventional techniques have shown lower consistency in achieving accurate limb and component alignment when compared to navigation techniques during TKA [7–14]. Furthermore, recent studies have reported greater risk for limb malalignment with conventional TKAs when performed in the obese [15,16]. Computer navigation using the ☆ No benefits or funds were received in support of this study by any of the authors. This article is original and has not been published before or currently submitted to any other journal. ⁎ Corresponding author at: The Arthritis Clinic, 101, Cornelian, Kemp's Corner, Cumballa Hill, Mumbai 400036, India. Tel.: +91 22 23856161; fax: +91 22 23876110. E-mail address: [email protected] (G.M. Shetty).
optical tracking system locates the centre of the femoral head, centre of the knee joint and the centre of the ankle to calculate the mechanical axis of the limb. However, during navigated TKA, obese patients may be prone to errors due to difficulty in exposing, palpating and registering important bony landmarks such as the malleoli and the femoral epicondyles. Although several studies have validated the accuracy and consistency of computer-assisted navigation and have reported significant improvement in component orientation and limb alignment in TKA with computer navigation [7–14], literature is lacking for limb and component alignment in computer-assisted TKA in the obese. Accuracy of computer navigation during TKA in the obese has not been studied and whether computer navigation achieves the same degree of accurate limb and component alignment in the obese individuals vis-a-vis non-obese patients is not known. Hence, the purpose of the present study was to determine if computer navigation provides consistent accuracy for limb and component alignment during TKA irrespective of body mass index (BMI) by comparing limb and component alignment and the outlier rates in obese versus non-obese individuals undergoing computer-assisted TKA. Our hypothesis was that limb and component alignment will not be significantly different when obese and non-obese individuals were compared after computer-assisted TKA.
http://dx.doi.org/10.1016/j.knee.2014.04.004 0968-0160/© 2014 Elsevier B.V. All rights reserved.
Please cite this article as: Shetty GM, et al, No effect of obesity on limb and component alignment after computer-assisted total knee arthroplasty, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.04.004
2
G.M. Shetty et al. / The Knee xxx (2014) xxx–xxx
2. Patients and methods We retrospectively reviewed the clinical and radiographic records of 1500 computer-assisted TKAs (in 1250 patients) performed between 2005 and 2009. Non-obese individuals were defined as those having a BMI of b30 kg/m2 (calculated by dividing the subject's weight in kilogrammes by their height in metres squared), obese individuals were defined as those having a BMI of ≥30 kg/m2 and morbidly obese individuals were defined as those having BMI N40 kg/m2. The inclusion criteria were primary computer-assisted total knee arthroplasties (TKAs) performed for knee arthritis in patients with a body mass index (BMI) of ≥ 30 for the obese group and b 30 for the non-obese group at the time of surgery. The exclusion criteria was incomplete clinical or radiographic records where the height and weight data of a patient was unavailable to calculate BMI or full length hip-to-ankle or knee radiographs were incomplete or not available to determine limb and component alignment. Based on the above criteria, complete data of 635 computer-assisted TKAs performed in 484 non-obese patients and 520 computer-assisted TKAs performed in 390 obese patients was available for analysis. Amongst the 390 obese patients, a subgroup of 56 TKAs was performed in 43 morbidly obese patients. Standing full length (hip to ankle) weight-bearing radiographs, weight-bearing anteroposterior knee radiographs and knee lateral radiographs were obtained in all patients pre- and postoperatively. The degree of knee deformity or hip–knee–ankle (HKA) angle was determined on the standing full-length radiographs as the angle between the mechanical axis of the femur (centre of the femoral head to the centre of the knee joint) and the mechanical axis of the tibia (centre of the knee joint to the centre of the ankle) [17]. Postoperatively, coronal alignment of femoral and tibial components was measured using their respective mechanical axes on full-length radiographs [17]. On lateral radiographs, the sagittal alignment of femoral component and tibial slope was measured using the distal femoral medullary axis and proximal tibial medullary axis [18]. Limbs with postoperative HKA angle outside the acceptable ±3° range from a neutral alignment of 180° were considered outliers for limb alignment [19]. Similarly, components outside the acceptable ±3° range from a neutral alignment of 90° in the coronal and sagittal plane were considered outliers for component alignment [19]. All radiographs were analysed by two surgeons blinded to the BMI of the patient. Radiographs taken preoperatively and at last follow-up (mean follow-up 4 years; range 2–6 years) were used to measure various parameters. Both height and weight were recorded by a ward nurse preoperatively on admission of the patient to the hospital. The height was measured using a wall mounted measuring scale and the weight was measured using a weighing scale. Height (m) and weight (kg) were then used to derive BMI (kg/m2) in each patient. All TKAs were performed by a single surgeon using the computerassisted technique. All procedures in the non-obese group were performed with the tourniquet inflated, which was deflated after the cement had hardened. However, in the obese group, tourniquet was inflated only for the duration of cementing and was deflated once the cement had set. An anterior longitudinal incision and a medial parapatellar arthrotomy were used in all cases. All patients underwent TKA using a cemented, posterior cruciate substituting design and all patients had resurfacing of the patella. The P.F.C. Sigma implant (DePuy Orthopaedics, Warsaw, Indiana) was used in all patients. The surgical aim in all patients of both groups was to align both femoral and tibial components perpendicular to the respective mechanical axes, femoral rotation aligned to the epicondylar axis, and to achieve a neutral lower limb mechanical axis. We used the Ci navigation system with its software (Version 2.1, Brainlab, Munich, Germany). Using 2 infra-red arrays affixed to the tibia and femur each, the centre of femoral head was computed by pivoting the femur without hindrance within the free range of motion of the hip joint and was accepted if the accuracy was within 3 mm. To minimise errors during registration of the femoral head centre, care was taken to ensure that the pelvis was properly stabilised at the anterior superior iliac spine by an
assistant and the hip joint moved through a smooth, gradual circulatory movement mimicking the base of a cone. Following standard registration process, the mechanical axis of the limb was determined by the navigation software. Conventional cutting blocks were navigated into position to perform the appropriate bone cuts. The degree of soft tissue release was governed by the amount of soft tissue tightness assessed using a tensioning device and medial and lateral gap imbalance as quantified by the computer. The tensioning device used was a modified laminar spreader containing a fixed tibial base plate and two mobile, medial and lateral femoral plates which can be individually moved using a screw mechanism to assess gap tension (Protek, Bettlach, Switzerland). Medial release for varus knees and lateral release for valgus knees were performed to achieve rectangular balanced gaps and a fully restored mechanical axis. Radiographic parameters in terms of limb (HKA angle) and component alignment (tibial and femoral sagittal and coronal alignment) of the non-obese TKA group were compared to those in the obese TKA group and of the non-obese and the morbidly obese groups using the t test. The percentage of outliers for limb and component alignment was compared between the groups using the Fisher's exact test. A p value of b 0.05 was taken to be statistically significant. 3. Results Demographic and radiographic parameters in the non-obese, obese and morbidly obese groups are summarised in Table 1. Postoperatively, the limb alignment (mean HKA angle) was not significantly different when the non-obese group was compared with the obese group (p = 0.33) and when the non-obese group was compared with the morbidly obese group (p = 0.20). Although the postoperative coronal alignment of the femoral component was not significantly different when the non-obese group was compared to the morbidly obese group (p = 0.66), the difference was statistically significant when non-obese and obese groups were compared (p = 0.0001). However this mean difference (0.4°) although statistically significant was very small to be of any clinical significance. Similarly, the postoperative coronal alignment of the tibial component was not significantly different when the non-obese group was compared with the obese group (p = 0.30) and when the non-obese group was compared with the morbidly obese group (p = 0.37). In the sagittal plane, the alignment of the femoral component was not significantly different when the non-obese group was compared to the obese group (p = 0.42). However, the mean difference (1.7°) was statistically significant when non-obese and morbidly obese groups were compared (p = 0.002). The sagittal alignment of the tibial component was not significantly different when the non-obese group was compared with the obese group (p = 0.42) and when the non-obese group was compared with the morbidly obese group (p = 0.32). Outlier rates for the postoperative limb and component alignment in non-obese, obese and morbidly obese groups is illustrated in Fig. 1. The outlier rates for postoperative HKA angle between the obese and non-obese groups were not significant (p = 0.48) and between the non-obese and morbidly obese groups, the rates were also not significant (p = 1.00). Similarly the outlier rates for coronal alignment of the femoral component were not significantly different when the non-obese group was compared to the obese group (p = 0.15) and when the non-obese group was compared to the morbidly obese group (p = 0.50). The outlier rates for coronal alignment of the tibial component were not significantly different when the non-obese group was compared to the obese group (p = 0.54) and when the non-obese group was compared to the morbidly obese group (p = 0.24).
4. Discussion Despite showing superior and consistent results in the restoration of limb and component alignment, the technical challenges during computer-assisted TKA in obese individuals remain. Obese patients may be prone to errors due to difficulty in registering the femoral head centre because of substantial weight of the leg and difficulty in registering the ankle centre due to difficulty in palpating the malleoli. Furthermore, excessive fat makes effective exposure difficult in the obese and excessive pressure due to the subluxated or everted patella or due to the thick medial flap may cause difficulty in palpating and registering the femoral epicondyles. Also, in the surgeon's experience, the weight of the limb may adversely impact the computer software's algorithms to equalise flexion and extension gaps and thereby component size and position. Most studies of TKAs in the obese have focussed on functional outcome and survival of implant vis-a-vis these rates in the non-obese
Please cite this article as: Shetty GM, et al, No effect of obesity on limb and component alignment after computer-assisted total knee arthroplasty, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.04.004
G.M. Shetty et al. / The Knee xxx (2014) xxx–xxx
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Table 1 Demographic and radiographic parameters in the non-obese, obese and morbidly obese patients. Parameters
Non-obese group (BMI b 30)
Obese group (BMI ≥ 30)
Morbidly obese subgroup (BMI N 40)
Number of limbs (patients) Age (years) BMI (kg/m2) Preoperative HKA angle (degrees) Postoperative HKA angle (degrees) Coronal alignment of femoral component (degrees) Coronal alignment of tibial component (degrees) Sagittal alignment of femoral component (degrees) Sagittal alignment of tibial component (degrees)
635 (484) 67.3 ± 7.8 (42–86) 26.4 ± 2.5 (15.2–29.9) 167.9 ± 7.8 (130.6–206.2) 179.7 ± 1.7 (172–185.5) 90.2 ± 1.6 (86–95.1) 90.2 ± 1.6 (84.8–96.2) 95.5 ± 4 (82–106.6) 87.6 ± 2.2 (81.7–97)
520 (390) 65.5 ± 7.7 (46–94) 34.9 ± 4.4 (30–54.1) 169.1 ± 8 (144.3–210) 179.6 ± 1.8 (173.1–185) 89.8 ± 1.9 (82–101.2) 90.3 ± 1.7 (86–95.2) 95.7 ± 4.5 (80–104.8) 87.5 ± 2.0 (82.1–99.4)
56 (43) 65.4 ± 7.5 (50–78) 44.7 ± 4 (40.3–54.1) 169.4 ± 9.2 (151.2–203) 179.4 ± 1.7 (175–182.6) 90.3 ± 2.1 (87–101.2) 90 ± 1.8 (86–95) 97.2 ± 4.3 (82.8–104.5) 87.3 ± 2.2 (83.8–95.6)
All values given as Mean ± Standard deviation (range). BMI — Body mass index; HKA angle — Hip–knee–ankle angle.
population [2–5,11,20]. Literature is lacking on the results of component and limb alignment in obese patients when compared to non-obese individuals. To the best of our knowledge, this study is the first of its kind which aimed to compare limb and component alignment in non-obese versus obese patients after computer-assisted TKA. The results of the current study showed that computer-assisted TKA resulted in excellent limb and component alignment in obese patients similar to what was seen in the non-obese group. This was true even when the morbidly obese subgroup was compared to the non-obese group. The outlier rate for postoperative limb mechanical axis (HKA angle) was 7.5% in the obese group which was not significantly different from the outlier rate in the non-obese group (6.2%). Choong et al. [10] in a comparative study between conventional and navigated TKA performed a subgroup analysis of 56 TKAs done in obese patients. The outlier rate of 7% for HKA angle in the obese subgroup as reported by Choong et al. [10] was similar to the outlier rate of 7.5% in the current study. Few studies have reported limb and component alignment after conventional TKA in the obese individual versus the non-obese individual. Amin et al. [21] in a prospective, controlled study of 41 conventional TKAs performed in non-obese and morbidly obese individuals reported no significant difference in the limb and component alignment between the two groups based on short film measurements. Similarly, Foran et al. [3] in a retrospective, matched study of 30 conventional TKAs performed in non-obese and obese individuals found no difference in limb and component alignment based on short film measurements. Despite these findings, both studies reported a significantly lower functional outcome and higher revision rate in the obese group (a majority of revisions due to aseptic loosening) when compared to the non-
obese group. Besides having a smaller number of patients in their study, the radiographic measurements of limb alignment and component position were based on short knee radiographs. Although this may be a reliable method to routinely assess the knee alignment and implant position, a full length hip-to-ankle is required to provide accurate information on limb alignment and component alignment with respect to the weight-bearing mechanical axis. A recent study by Estes et al. [15] analysing the effect of BMI on postoperative limb alignment (on full length hip-to-ankle radiographs) in 196 conventional TKAs reported that BMI along with preoperative deformity had a significant effect on postoperative limb alignment. Similarly, a recent study by Kamat et al. [16] comparing conventional and navigated TKAs in the obese reported greater malalignment of the tibial component with conventional TKA. Hence, conventional techniques in TKA may not help in consistently achieving accurate limb and component alignment during TKA in the obese and may put the patient at greater risk for malalignment. In summary, this study clearly demonstrates that computer navigation can achieve excellent limb and component alignment irrespective of a patient's BMI. Although obesity may not be an indication per se for using computer navigation during TKA, it will help achieve consistently accurate limb and component alignment in obese patients. Conflict of interest statement The authors wish to state that no funds or benefits were received by any of the authors in support of this study/article from any source. References
Fig. 1. Outlier rates for the postoperative limb and component alignment in non-obese, obese and morbidly obese groups. HKA — hip–knee–ankle angle; MFCA — medial femoral condylar angle; MTCA — medial tibial condylar angle.
[1] Berend ME, Ritter MA, Meding JB, Faris PM, Keating EM, Redelman R, et al. Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res 2004;428:26–34. [2] Vazquez-Vela Johnson G, Worland RL, Keenan J, Norambuena N. Patient demographics as a predictor of the ten-year survival rate in primary total knee replacement. J Bone Joint Surg Br 2003;85:52–6. [3] Foran JR, Mont MA, Rajadhyaksha AD, Jones LC, Etienne G, Hungerford DS. Total knee arthroplasty in obese patients: a comparison with a matched control group. J Arthroplasty 2004;19:817–24. [4] Foran JR, Mont MA, Etienne G, Jones LC, Hungerford DS. The outcome of total knee arthroplasty in obese patients. J Bone Joint Surg Am 2004;86:1609–15. [5] Mulhall KJ, Ghomrawi HM, Mihalko W, Cui Q, Saleh KJ. Adverse effects of increased body mass index and weight on survivorship of total knee arthroplasty and subsequent outcomes of revision TKA. J Knee Surg 2007;20:199–204. [6] Gillespie GN, Porteous AJ. Obesity and knee arthroplasty. Knee 2007;14:81–6. [7] Mullaji A, Kanna R, Marawar S, Kohli A, Sharma A. Comparison of limb and component alignment using computer-assisted navigation versus image intensifier-guided conventional total knee arthroplasty: a prospective, randomized, single-surgeon study of 467 knees. J Arthroplasty 2007;22:953–9. [8] Kim SJ, MacDonald M, Hernandez J, Wixson RL. Computer assisted navigation in total knee arthroplasty: improved coronal alignment. J Arthroplasty 2005;20(7 Suppl. 3):123–31. [9] Mason JB, Fehring TK, Estok R, Banel D, Fahrbach K. Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty 2007;22:1097–106.
Please cite this article as: Shetty GM, et al, No effect of obesity on limb and component alignment after computer-assisted total knee arthroplasty, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.04.004
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G.M. Shetty et al. / The Knee xxx (2014) xxx–xxx
[10] Choong PF, Dowsey MM, Stoney JD. Does accurate anatomical alignment result in better function and quality of life? A prospective randomized controlled trial comparing conventional and computer-assisted total knee arthroplasty. J Arthroplasty 2009;24:560–9. [11] Bäthis H, Perlick L, Tingart M, Lüring C, Zurakowski D, Grifka J. Alignment in total knee arthroplasty. A comparison of computer-assisted surgery with the conventional technique. J Bone Joint Surg Br 2004;86:682–7. [12] Siston RA, Cromie MJ, Gold GE, Goodman SB, Delp SL, Maloney WJ, et al. Averaging different alignment axes improves femoral rotational alignment in computernavigated total knee arthroplasty. J Bone Joint Surg Am 2008;90:2098–104. [13] Bauwens K, Matthes G, Wich M, Gebhard F, Hanson B, Ekkernkamp A, et al. Navigated total knee replacement. A meta-analysis. J Bone Joint Surg Am 2007;89:261–9. [14] Quack VM, Kathrein S, Rath B, Tingart M, Lüring C. Computer-assisted navigation in total knee arthroplasty: a review of literature. Biomed Tech (Berl) 2012;57:269–75. [15] Estes CS, Schmidt KJ, McLemore R, Spangehl MJ, Clarke HD. Effect of body mass index on limb alignment after total knee arthroplasty. J Arthroplasty 2013;28(8 Suppl.):101–5.
[16] Kamat YD, Aurakzai KM, Adhikari AR. Total knee replacement in the obese patient: comparing computer assisted and conventional technique. Scientific World Journal Jan 9 2014;2014:272838. [17] Mullaji AB, Shetty GM, Kanna R, Vadapalli RC. The influence of preoperative deformity on valgus correction angle: an analysis of 503 total knee arthroplasties. J Arthroplasty 2013;28:20–7. [18] Ewald FC. The Knee Society total knee arthroplasty roentgenographic evaluation and scoring system. Clin Orthop Relat Res 1989;248:9–12. [19] Mullaji AB, Shetty GM, Lingaraju AP, Bhayde S. Which factors increase risk of malalignment of the hip–knee–ankle axis in TKA? Clin Orthop Relat Res 2013;471:134–41. [20] Bordini B, Stea S, Cremonini S, Viceconti M, De Palma R, Toni A. Relationship between obesity and early failure of total knee prostheses. BMC Musculoskelet Disord 2009;10:29–36. [21] Amin AK, Clayton RA, Patton JT, Gaston M, Cook RE, Brenkel IJ. Total knee replacement in morbidly obese patients. Results of a prospective, matched study. J Bone Joint Surg Br 2006;88:1321–6.
Please cite this article as: Shetty GM, et al, No effect of obesity on limb and component alignment after computer-assisted total knee arthroplasty, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.04.004
Contents lists available at ScienceDirect
The Knee
No effect of obesity on limb and component alignment after computer-assisted total knee arthroplasty☆ Gautam M. Shetty ⁎, Arun B. Mullaji, Sagar Bhayde, A.P. Lingaraju Department of Orthopaedic Surgery, Breach Candy Hospital, Mumbai, India
a r t i c l e
i n f o
Article history: Received 14 September 2013 Received in revised form 2 April 2014 Accepted 5 April 2014 Available online xxxx Keywords: Total knee arthroplasty Obesity Alignment Computer-assisted surgery Knee
a b s t r a c t Purpose: This retrospective study aimed to determine if computer navigation provides consistent accuracy for limb and component alignment during TKA irrespective of body mass index (BMI) by comparing limb and component alignment and the outlier rates in obese versus non-obese individuals undergoing computer-assisted TKA. Methods: Six hundred and thirty-five computer assisted total knee arthroplasties (TKAs) performed in nonobese individuals (BMI b 30 kg/m2) were compared with 520 computer-assisted TKAs in obese individuals (BMI ≥ 30 kg/m2) for postoperative limb and component alignment using full length standing hip-to-ankle radiographs. Results: No significant difference in postoperative limb alignment (179.7° ± 1.7° vs 179.6° ± 1.8°), coronal femoral (90.2° ± 1.6° vs 89.8° ± 1.9°) and tibial component (90.2° ± 1.6° vs 90.3° ± 1.7°) alignment and outlier rates (6.2% vs 7.5%) was found between non-obese and obese individuals. Similarly, alignment and the outlier rates were similar when non-obese individuals and a subgroup of morbidly obese individuals (BMI N 40 kg/m2) were compared. Conclusions: Computer navigation can achieve excellent limb and component alignment irrespective of a patient's BMI. Although obesity may not be an indication per se for using computer navigation during TKA, it will help achieve consistently accurate limb and component alignment in obese patients. Level of Evidence: Level II © 2014 Elsevier B.V. All rights reserved.
1. Introduction Risk of revision after total knee arthroplasty (TKA) is significantly higher when obesity is combined with malalignment of tibial component or the limb [1]. Reports have suggested that implant survival is significantly lower in obese patients (60–92%) in the long-term when compared to non-obese individuals (89–98.5%) [2–6] with loosening of tibial components and polyethylene wear being the major causes of revision [4,5]. Hence it is all the more important to ensure symmetric loading of implant and bone in the obese by accurate implant positioning and restoration of mechanical axis. Conventional techniques have shown lower consistency in achieving accurate limb and component alignment when compared to navigation techniques during TKA [7–14]. Furthermore, recent studies have reported greater risk for limb malalignment with conventional TKAs when performed in the obese [15,16]. Computer navigation using the ☆ No benefits or funds were received in support of this study by any of the authors. This article is original and has not been published before or currently submitted to any other journal. ⁎ Corresponding author at: The Arthritis Clinic, 101, Cornelian, Kemp's Corner, Cumballa Hill, Mumbai 400036, India. Tel.: +91 22 23856161; fax: +91 22 23876110. E-mail address: [email protected] (G.M. Shetty).
optical tracking system locates the centre of the femoral head, centre of the knee joint and the centre of the ankle to calculate the mechanical axis of the limb. However, during navigated TKA, obese patients may be prone to errors due to difficulty in exposing, palpating and registering important bony landmarks such as the malleoli and the femoral epicondyles. Although several studies have validated the accuracy and consistency of computer-assisted navigation and have reported significant improvement in component orientation and limb alignment in TKA with computer navigation [7–14], literature is lacking for limb and component alignment in computer-assisted TKA in the obese. Accuracy of computer navigation during TKA in the obese has not been studied and whether computer navigation achieves the same degree of accurate limb and component alignment in the obese individuals vis-a-vis non-obese patients is not known. Hence, the purpose of the present study was to determine if computer navigation provides consistent accuracy for limb and component alignment during TKA irrespective of body mass index (BMI) by comparing limb and component alignment and the outlier rates in obese versus non-obese individuals undergoing computer-assisted TKA. Our hypothesis was that limb and component alignment will not be significantly different when obese and non-obese individuals were compared after computer-assisted TKA.
http://dx.doi.org/10.1016/j.knee.2014.04.004 0968-0160/© 2014 Elsevier B.V. All rights reserved.
Please cite this article as: Shetty GM, et al, No effect of obesity on limb and component alignment after computer-assisted total knee arthroplasty, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.04.004
2
G.M. Shetty et al. / The Knee xxx (2014) xxx–xxx
2. Patients and methods We retrospectively reviewed the clinical and radiographic records of 1500 computer-assisted TKAs (in 1250 patients) performed between 2005 and 2009. Non-obese individuals were defined as those having a BMI of b30 kg/m2 (calculated by dividing the subject's weight in kilogrammes by their height in metres squared), obese individuals were defined as those having a BMI of ≥30 kg/m2 and morbidly obese individuals were defined as those having BMI N40 kg/m2. The inclusion criteria were primary computer-assisted total knee arthroplasties (TKAs) performed for knee arthritis in patients with a body mass index (BMI) of ≥ 30 for the obese group and b 30 for the non-obese group at the time of surgery. The exclusion criteria was incomplete clinical or radiographic records where the height and weight data of a patient was unavailable to calculate BMI or full length hip-to-ankle or knee radiographs were incomplete or not available to determine limb and component alignment. Based on the above criteria, complete data of 635 computer-assisted TKAs performed in 484 non-obese patients and 520 computer-assisted TKAs performed in 390 obese patients was available for analysis. Amongst the 390 obese patients, a subgroup of 56 TKAs was performed in 43 morbidly obese patients. Standing full length (hip to ankle) weight-bearing radiographs, weight-bearing anteroposterior knee radiographs and knee lateral radiographs were obtained in all patients pre- and postoperatively. The degree of knee deformity or hip–knee–ankle (HKA) angle was determined on the standing full-length radiographs as the angle between the mechanical axis of the femur (centre of the femoral head to the centre of the knee joint) and the mechanical axis of the tibia (centre of the knee joint to the centre of the ankle) [17]. Postoperatively, coronal alignment of femoral and tibial components was measured using their respective mechanical axes on full-length radiographs [17]. On lateral radiographs, the sagittal alignment of femoral component and tibial slope was measured using the distal femoral medullary axis and proximal tibial medullary axis [18]. Limbs with postoperative HKA angle outside the acceptable ±3° range from a neutral alignment of 180° were considered outliers for limb alignment [19]. Similarly, components outside the acceptable ±3° range from a neutral alignment of 90° in the coronal and sagittal plane were considered outliers for component alignment [19]. All radiographs were analysed by two surgeons blinded to the BMI of the patient. Radiographs taken preoperatively and at last follow-up (mean follow-up 4 years; range 2–6 years) were used to measure various parameters. Both height and weight were recorded by a ward nurse preoperatively on admission of the patient to the hospital. The height was measured using a wall mounted measuring scale and the weight was measured using a weighing scale. Height (m) and weight (kg) were then used to derive BMI (kg/m2) in each patient. All TKAs were performed by a single surgeon using the computerassisted technique. All procedures in the non-obese group were performed with the tourniquet inflated, which was deflated after the cement had hardened. However, in the obese group, tourniquet was inflated only for the duration of cementing and was deflated once the cement had set. An anterior longitudinal incision and a medial parapatellar arthrotomy were used in all cases. All patients underwent TKA using a cemented, posterior cruciate substituting design and all patients had resurfacing of the patella. The P.F.C. Sigma implant (DePuy Orthopaedics, Warsaw, Indiana) was used in all patients. The surgical aim in all patients of both groups was to align both femoral and tibial components perpendicular to the respective mechanical axes, femoral rotation aligned to the epicondylar axis, and to achieve a neutral lower limb mechanical axis. We used the Ci navigation system with its software (Version 2.1, Brainlab, Munich, Germany). Using 2 infra-red arrays affixed to the tibia and femur each, the centre of femoral head was computed by pivoting the femur without hindrance within the free range of motion of the hip joint and was accepted if the accuracy was within 3 mm. To minimise errors during registration of the femoral head centre, care was taken to ensure that the pelvis was properly stabilised at the anterior superior iliac spine by an
assistant and the hip joint moved through a smooth, gradual circulatory movement mimicking the base of a cone. Following standard registration process, the mechanical axis of the limb was determined by the navigation software. Conventional cutting blocks were navigated into position to perform the appropriate bone cuts. The degree of soft tissue release was governed by the amount of soft tissue tightness assessed using a tensioning device and medial and lateral gap imbalance as quantified by the computer. The tensioning device used was a modified laminar spreader containing a fixed tibial base plate and two mobile, medial and lateral femoral plates which can be individually moved using a screw mechanism to assess gap tension (Protek, Bettlach, Switzerland). Medial release for varus knees and lateral release for valgus knees were performed to achieve rectangular balanced gaps and a fully restored mechanical axis. Radiographic parameters in terms of limb (HKA angle) and component alignment (tibial and femoral sagittal and coronal alignment) of the non-obese TKA group were compared to those in the obese TKA group and of the non-obese and the morbidly obese groups using the t test. The percentage of outliers for limb and component alignment was compared between the groups using the Fisher's exact test. A p value of b 0.05 was taken to be statistically significant. 3. Results Demographic and radiographic parameters in the non-obese, obese and morbidly obese groups are summarised in Table 1. Postoperatively, the limb alignment (mean HKA angle) was not significantly different when the non-obese group was compared with the obese group (p = 0.33) and when the non-obese group was compared with the morbidly obese group (p = 0.20). Although the postoperative coronal alignment of the femoral component was not significantly different when the non-obese group was compared to the morbidly obese group (p = 0.66), the difference was statistically significant when non-obese and obese groups were compared (p = 0.0001). However this mean difference (0.4°) although statistically significant was very small to be of any clinical significance. Similarly, the postoperative coronal alignment of the tibial component was not significantly different when the non-obese group was compared with the obese group (p = 0.30) and when the non-obese group was compared with the morbidly obese group (p = 0.37). In the sagittal plane, the alignment of the femoral component was not significantly different when the non-obese group was compared to the obese group (p = 0.42). However, the mean difference (1.7°) was statistically significant when non-obese and morbidly obese groups were compared (p = 0.002). The sagittal alignment of the tibial component was not significantly different when the non-obese group was compared with the obese group (p = 0.42) and when the non-obese group was compared with the morbidly obese group (p = 0.32). Outlier rates for the postoperative limb and component alignment in non-obese, obese and morbidly obese groups is illustrated in Fig. 1. The outlier rates for postoperative HKA angle between the obese and non-obese groups were not significant (p = 0.48) and between the non-obese and morbidly obese groups, the rates were also not significant (p = 1.00). Similarly the outlier rates for coronal alignment of the femoral component were not significantly different when the non-obese group was compared to the obese group (p = 0.15) and when the non-obese group was compared to the morbidly obese group (p = 0.50). The outlier rates for coronal alignment of the tibial component were not significantly different when the non-obese group was compared to the obese group (p = 0.54) and when the non-obese group was compared to the morbidly obese group (p = 0.24).
4. Discussion Despite showing superior and consistent results in the restoration of limb and component alignment, the technical challenges during computer-assisted TKA in obese individuals remain. Obese patients may be prone to errors due to difficulty in registering the femoral head centre because of substantial weight of the leg and difficulty in registering the ankle centre due to difficulty in palpating the malleoli. Furthermore, excessive fat makes effective exposure difficult in the obese and excessive pressure due to the subluxated or everted patella or due to the thick medial flap may cause difficulty in palpating and registering the femoral epicondyles. Also, in the surgeon's experience, the weight of the limb may adversely impact the computer software's algorithms to equalise flexion and extension gaps and thereby component size and position. Most studies of TKAs in the obese have focussed on functional outcome and survival of implant vis-a-vis these rates in the non-obese
Please cite this article as: Shetty GM, et al, No effect of obesity on limb and component alignment after computer-assisted total knee arthroplasty, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.04.004
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Table 1 Demographic and radiographic parameters in the non-obese, obese and morbidly obese patients. Parameters
Non-obese group (BMI b 30)
Obese group (BMI ≥ 30)
Morbidly obese subgroup (BMI N 40)
Number of limbs (patients) Age (years) BMI (kg/m2) Preoperative HKA angle (degrees) Postoperative HKA angle (degrees) Coronal alignment of femoral component (degrees) Coronal alignment of tibial component (degrees) Sagittal alignment of femoral component (degrees) Sagittal alignment of tibial component (degrees)
635 (484) 67.3 ± 7.8 (42–86) 26.4 ± 2.5 (15.2–29.9) 167.9 ± 7.8 (130.6–206.2) 179.7 ± 1.7 (172–185.5) 90.2 ± 1.6 (86–95.1) 90.2 ± 1.6 (84.8–96.2) 95.5 ± 4 (82–106.6) 87.6 ± 2.2 (81.7–97)
520 (390) 65.5 ± 7.7 (46–94) 34.9 ± 4.4 (30–54.1) 169.1 ± 8 (144.3–210) 179.6 ± 1.8 (173.1–185) 89.8 ± 1.9 (82–101.2) 90.3 ± 1.7 (86–95.2) 95.7 ± 4.5 (80–104.8) 87.5 ± 2.0 (82.1–99.4)
56 (43) 65.4 ± 7.5 (50–78) 44.7 ± 4 (40.3–54.1) 169.4 ± 9.2 (151.2–203) 179.4 ± 1.7 (175–182.6) 90.3 ± 2.1 (87–101.2) 90 ± 1.8 (86–95) 97.2 ± 4.3 (82.8–104.5) 87.3 ± 2.2 (83.8–95.6)
All values given as Mean ± Standard deviation (range). BMI — Body mass index; HKA angle — Hip–knee–ankle angle.
population [2–5,11,20]. Literature is lacking on the results of component and limb alignment in obese patients when compared to non-obese individuals. To the best of our knowledge, this study is the first of its kind which aimed to compare limb and component alignment in non-obese versus obese patients after computer-assisted TKA. The results of the current study showed that computer-assisted TKA resulted in excellent limb and component alignment in obese patients similar to what was seen in the non-obese group. This was true even when the morbidly obese subgroup was compared to the non-obese group. The outlier rate for postoperative limb mechanical axis (HKA angle) was 7.5% in the obese group which was not significantly different from the outlier rate in the non-obese group (6.2%). Choong et al. [10] in a comparative study between conventional and navigated TKA performed a subgroup analysis of 56 TKAs done in obese patients. The outlier rate of 7% for HKA angle in the obese subgroup as reported by Choong et al. [10] was similar to the outlier rate of 7.5% in the current study. Few studies have reported limb and component alignment after conventional TKA in the obese individual versus the non-obese individual. Amin et al. [21] in a prospective, controlled study of 41 conventional TKAs performed in non-obese and morbidly obese individuals reported no significant difference in the limb and component alignment between the two groups based on short film measurements. Similarly, Foran et al. [3] in a retrospective, matched study of 30 conventional TKAs performed in non-obese and obese individuals found no difference in limb and component alignment based on short film measurements. Despite these findings, both studies reported a significantly lower functional outcome and higher revision rate in the obese group (a majority of revisions due to aseptic loosening) when compared to the non-
obese group. Besides having a smaller number of patients in their study, the radiographic measurements of limb alignment and component position were based on short knee radiographs. Although this may be a reliable method to routinely assess the knee alignment and implant position, a full length hip-to-ankle is required to provide accurate information on limb alignment and component alignment with respect to the weight-bearing mechanical axis. A recent study by Estes et al. [15] analysing the effect of BMI on postoperative limb alignment (on full length hip-to-ankle radiographs) in 196 conventional TKAs reported that BMI along with preoperative deformity had a significant effect on postoperative limb alignment. Similarly, a recent study by Kamat et al. [16] comparing conventional and navigated TKAs in the obese reported greater malalignment of the tibial component with conventional TKA. Hence, conventional techniques in TKA may not help in consistently achieving accurate limb and component alignment during TKA in the obese and may put the patient at greater risk for malalignment. In summary, this study clearly demonstrates that computer navigation can achieve excellent limb and component alignment irrespective of a patient's BMI. Although obesity may not be an indication per se for using computer navigation during TKA, it will help achieve consistently accurate limb and component alignment in obese patients. Conflict of interest statement The authors wish to state that no funds or benefits were received by any of the authors in support of this study/article from any source. References
Fig. 1. Outlier rates for the postoperative limb and component alignment in non-obese, obese and morbidly obese groups. HKA — hip–knee–ankle angle; MFCA — medial femoral condylar angle; MTCA — medial tibial condylar angle.
[1] Berend ME, Ritter MA, Meding JB, Faris PM, Keating EM, Redelman R, et al. Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res 2004;428:26–34. [2] Vazquez-Vela Johnson G, Worland RL, Keenan J, Norambuena N. Patient demographics as a predictor of the ten-year survival rate in primary total knee replacement. J Bone Joint Surg Br 2003;85:52–6. [3] Foran JR, Mont MA, Rajadhyaksha AD, Jones LC, Etienne G, Hungerford DS. Total knee arthroplasty in obese patients: a comparison with a matched control group. J Arthroplasty 2004;19:817–24. [4] Foran JR, Mont MA, Etienne G, Jones LC, Hungerford DS. The outcome of total knee arthroplasty in obese patients. J Bone Joint Surg Am 2004;86:1609–15. [5] Mulhall KJ, Ghomrawi HM, Mihalko W, Cui Q, Saleh KJ. Adverse effects of increased body mass index and weight on survivorship of total knee arthroplasty and subsequent outcomes of revision TKA. J Knee Surg 2007;20:199–204. [6] Gillespie GN, Porteous AJ. Obesity and knee arthroplasty. Knee 2007;14:81–6. [7] Mullaji A, Kanna R, Marawar S, Kohli A, Sharma A. Comparison of limb and component alignment using computer-assisted navigation versus image intensifier-guided conventional total knee arthroplasty: a prospective, randomized, single-surgeon study of 467 knees. J Arthroplasty 2007;22:953–9. [8] Kim SJ, MacDonald M, Hernandez J, Wixson RL. Computer assisted navigation in total knee arthroplasty: improved coronal alignment. J Arthroplasty 2005;20(7 Suppl. 3):123–31. [9] Mason JB, Fehring TK, Estok R, Banel D, Fahrbach K. Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty 2007;22:1097–106.
Please cite this article as: Shetty GM, et al, No effect of obesity on limb and component alignment after computer-assisted total knee arthroplasty, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.04.004
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[10] Choong PF, Dowsey MM, Stoney JD. Does accurate anatomical alignment result in better function and quality of life? A prospective randomized controlled trial comparing conventional and computer-assisted total knee arthroplasty. J Arthroplasty 2009;24:560–9. [11] Bäthis H, Perlick L, Tingart M, Lüring C, Zurakowski D, Grifka J. Alignment in total knee arthroplasty. A comparison of computer-assisted surgery with the conventional technique. J Bone Joint Surg Br 2004;86:682–7. [12] Siston RA, Cromie MJ, Gold GE, Goodman SB, Delp SL, Maloney WJ, et al. Averaging different alignment axes improves femoral rotational alignment in computernavigated total knee arthroplasty. J Bone Joint Surg Am 2008;90:2098–104. [13] Bauwens K, Matthes G, Wich M, Gebhard F, Hanson B, Ekkernkamp A, et al. Navigated total knee replacement. A meta-analysis. J Bone Joint Surg Am 2007;89:261–9. [14] Quack VM, Kathrein S, Rath B, Tingart M, Lüring C. Computer-assisted navigation in total knee arthroplasty: a review of literature. Biomed Tech (Berl) 2012;57:269–75. [15] Estes CS, Schmidt KJ, McLemore R, Spangehl MJ, Clarke HD. Effect of body mass index on limb alignment after total knee arthroplasty. J Arthroplasty 2013;28(8 Suppl.):101–5.
[16] Kamat YD, Aurakzai KM, Adhikari AR. Total knee replacement in the obese patient: comparing computer assisted and conventional technique. Scientific World Journal Jan 9 2014;2014:272838. [17] Mullaji AB, Shetty GM, Kanna R, Vadapalli RC. The influence of preoperative deformity on valgus correction angle: an analysis of 503 total knee arthroplasties. J Arthroplasty 2013;28:20–7. [18] Ewald FC. The Knee Society total knee arthroplasty roentgenographic evaluation and scoring system. Clin Orthop Relat Res 1989;248:9–12. [19] Mullaji AB, Shetty GM, Lingaraju AP, Bhayde S. Which factors increase risk of malalignment of the hip–knee–ankle axis in TKA? Clin Orthop Relat Res 2013;471:134–41. [20] Bordini B, Stea S, Cremonini S, Viceconti M, De Palma R, Toni A. Relationship between obesity and early failure of total knee prostheses. BMC Musculoskelet Disord 2009;10:29–36. [21] Amin AK, Clayton RA, Patton JT, Gaston M, Cook RE, Brenkel IJ. Total knee replacement in morbidly obese patients. Results of a prospective, matched study. J Bone Joint Surg Br 2006;88:1321–6.
Please cite this article as: Shetty GM, et al, No effect of obesity on limb and component alignment after computer-assisted total knee arthroplasty, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.04.004
