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Improved Clinical Outcomes After High-Flexion Total Knee Arthroplasty
The Journal of Arthroplasty Vol. 26 No. 7 2011
Improved Clinical Outcomes After High-Flexion Total Knee Arthroplasty A 5-Year Follow-Up Study Chusheng Seng, MBBS, MRCS (Edin),* Seng Jin Yeo, MBBS, FRCS (Edin), FAMS,* James L.Wee,MBBS,MRCS(Edin),* S.Subanesh,MBBS(India),MSOrth(UKM),AM(Mal),y Hwee Chi Chong, BASc (Physiotherapy),* and Ngai Nung Lo, MBBS, FRCS (Edin), FAMS*
Abstract: The purpose of this study was to determine if high-flexion total knee arthroplasty resulted in improved outcomes compared with conventional total knee arthroplasty. This was a prospective, double-blind, randomized controlled trial involving 76 patients over 5 years. We compared the postoperative flexion range, Knee Society scores, Oxford knee scores, and SF-36 scores between 2 groups. The high-flexion group was able to achieve a significant sustainable increase in postoperative knee flexion angle; and this correlated to a significant improvement in the General Health, Vitality, and Physical Functioning scales of SF-36 at 5 years postoperatively. Our results signify that high-flexion total knee arthroplasty has additional benefits to the quality of life in patients who require higher degrees of knee flexion in their activities of daily living. Keywords: improved outcomes, total knee arthroplasty, high-flexion, conventional, quality of life. © 2011 Elsevier Inc. All rights reserved.
Primary total knee arthroplasty (TKA) is one of the fastest-growing elective orthopedic procedures in the past decade. The principal aim of TKA is to create a stable and painless knee with a range of motion adequate to perform the activities of daily living. With current conventional prosthetic designs and surgical techniques, gaining a range of motion of the knee from 0° to 110° and 120° after TKA is readily achievable [1-4]. Studies have shown that 83° of flexion is required for stair climbing, 93° for rising from a seated position, and 106° for shoelace tying [5]. In most Western cultures, achieving a range of motion beyond this may have limited clinical value. However, in some countries, squatting and sitting cross-legged are an essential part of their daily lives. These activities require up to 165° of flexion, and deep flexion of the knee after TKA may be required [6-9]. Furthermore, some sporting activities
From the *Department of Orthopaedic Surgery, Singapore General Hospital, Singapore, Singapore; and yDepartment of Orthopaedic and Traumatology, Faculty of Medicine, Universiti Kebangsaan Malaysia, Malaysia. Submitted May 11, 2010; accepted September 17, 2010. No benefits or funds were received in support of the study. Reprint requests: Chusheng Seng, MBBS, MRCS(Edin), Department of Orthopaedic Surgery, Singapore General Hospital, Outram Rd., Singapore 169608, Singapore. © 2011 Elsevier Inc. All rights reserved. 0883-5403/2607-0009$36.00/0 doi:10.1016/j.arth.2010.09.006
and workplace demands may also require, or benefit from, higher degrees of flexion. High flexion is traditionally defined as greater than 125° of flexion after TKA [10]. However, achieving a deep flexion angle and maintaining the stability of the knee are competing goals and require refinements in design, as well as careful surgical technique [11]. The Zimmer (Warsaw, Ind) NexGen LPS-Flex implant is designed to achieve up to 150° of flexion after TKA, with design modifications to improve the kinematics at high-flexion angles [12]. Firstly, the implant is designed with an increased posterior condylar offset with an additional cut of 2mm bone from the posterior femoral condyle to extend the surface of the femoral component posteriorly to increase the articular contact area between the femur and the tibia at high flexion angles and thereby increase posterior femoral translation and the range of flexion. Secondly, to ensure that the patella is not caught in the intercondylar box as the patellar contact region moves distally during high flexion, a longer trochlear groove is incorporated into the design. Furthermore, an anterior cutout of the tibial polyethylene insert reduces patellar tendon impingement during deep flexion. Lastly, in the NexGen LPS-Flex posterior-stabilized designs, modifications to the campost mechanism increase the jump distance, ensure continued contact, and prevent dislocation over the post at deep flexion angles [13-15].
1025
1026 The Journal of Arthroplasty Vol. 26 No. 7 October 2011 Table 1. Patient Demographics No. of patients Age (mean) Sex BMI (mean)
Conventional
High-Flexion
35 68 Female: 24 Male: 11 28
41 67 Female: 34 Male: 7 27
BMI indicates body mass index.
Thus far, biomechanical studies have shown that these high-flexion TKA implant design modifications do not cause compromises to stability, contact mechanics, patellar kinematics, and durability [16-18]. Han et al [19] reported that 38% of their patients had aseptic loosening of the femoral component at a mean of 32 months and 21% required revision at a mean of 23 months in his series of 72 Zimmer NexGen LPS-Flex fixed TKAs in 47 patients. However, this study is a single-surgeon series and may not be a true reflection of the actual incidence of aseptic loosening of this highflexion implant. Moreover, the relatively small sample size may have skewed the final outcomes of the TKAs. Kim et al [20]reported in a large series of 278 knees that the NexGen LPS-Flex prosthesis provided satisfactory results at 3 to 4.8 years of follow-up with an extremely low incidence of adverse radiological findings. There were in total 2 cases of radiolucency at the femoral component that did not require revision because there was no evidence of prosthesis migration or loosening. The purpose of our study is to determine whether the high-flexion TKA implant design modifications significantly improve the range of motion in vivo and, if so, whether the quality of life and functional outcome are enhanced as a result.
Material and Methods In total, there were 76 patients enrolled into our prospective, double-blinded, and randomized clinical
trial from the period November 2001 to September 2003. Institutional review board approval was obtained from our hospital ethics committee. Patients who had degenerative joint disease with a minimum preoperative range of motion of 90° were included into our study. Exclusion criteria included patients with inflammatory arthritis, history of septic arthritis, and previous ipsilateral knee surgery. However, patients who had prior contralateral TKA were eligible for our study. The conventional implant used in this study was the J&J DePuy (Warsaw, Ind) PFC Modular Knee System, whereas the Zimmer NexGen LPS-Flex system was selected for the high-flexion group. Both systems were nonmobile, fixed-bearing systems. The conventional implant was used in 24 female and 11 male patients; 34 female and 7 male patients received the highflexion implant. This was a randomized double-blinded study. The patients were blinded to the type of prosthesis being implanted; sealed envelopes were randomly issued to every patient and only opened by the surgeon just before surgery to reveal which study group the patient had been assigned to. Preoperative functional assessments were performed by physiotherapists from the Orthopaedic Diagnostic Center, who were likewise blinded to the study group allocation. The physiotherapists assessed all patients 2 weeks before surgery. The range of motion was measured passively with a standard goniometer by the physiotherapists from the Orthopaedic Diagnostic Center. The SF-36 Quality of Life questionnaire was administered to every patient 2 weeks before surgery, and the Knee Society scoring and the Oxford knee scoring were performed at the same time. Postoperatively, all patients were assessed again by the physiotherapists at 6 months, 2 years, and 5 years postoperatively. All study patients were operated on by 2 senior consultants from the Adult Reconstruction Service of
Table 2. Preoperative Comparison
Range of motion Knee Society scores Oxford knee score SF-36 scores
Extension Flexion Function score Knee score Physical Function Role Physical Bodily Pain General Health Vitality Social Functioning Role Emotional Mental Health Physical Component score Mental Component score
Conventional
High-Flexion
Preop Mean
Preop Mean
3± 122 ± 48 ± 42 ± 36 ± 37 ± 53 ± 44 ± 77 ± 63 ± 71 ± 83 ± 75 ± 38 ± 51 ±
6 12 19 18 8 20 41 20 14 19 34 38 17 12 10
3± 123 ± 48 ± 42 ± 36 ± 37 ± 51 ± 41 ± 69 ± 62 ± 63 ± 83 ± 70 ± 39 ± 48 ±
6 23 17 17 7 17 41 17 22 18 32 38 19 11 10
P Value .918 .888 .978 .960 .742 .888 .831 .567 .064 .876 .290 .994 .159 .992 .123
Improved Clinical Outcomes After High-Flexion TKA Seng et al
Fig. 1. Graph comparing the flexion range of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
our institution during the period from November 2001 to September 2003. The operative procedure was standardized—the medial parapatellar approach with patella eversion and soft tissue balancing was used by both surgeons, and all implants were cemented. All the patellae were resurfaced. Postoperatively, all study patients were managed on our institution's standardized TKA pathway and underwent the same physiotherapy regimen. The mean range of motion and mean functional scores were evaluated and the level of statistical significance was taken to be P b .05. All calculations were performed using SPSS (Chicago, IL) version 12.
Results There were a total of 76 patients enrolled in this study, with 35 patients assigned to the group using the conventional J&J implant and 41 patients in the group using the Zimmer Hi-flex implant. Computer-generated random numbers were used for patient randomization. The patients in the conventional group and the highflexion group were similar in terms of mean age (68 and 67 years), mean body mass index (28 and 27), and mean preoperative range of knee flexion (122° and 123°). The patients' demographics are shown in Table 1. Preoperatively, the patients in the conventional and highflexion groups were also similar in terms of range of motion, Knee Society scores, Oxford knee scores, and SF-36 scores (Table 2).
Fig. 2. Graph comparing the Knee score component of the Knee Society score of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
1027
Fig. 3. Graph comparing the Function score component of the Knee Society score of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
A total of 13 patients were lost to follow-up, with 8 patients from the conventional group and 5 patients from the high-flexion group. Four of these patients died during the study period, one refused further follow-up, and the remainder were not contactable for various reasons. Our study found that the group with the Zimmer Hiflex implant managed to achieve a significantly higher angle of flexion postoperatively(128°) when compared with group using the conventional J&J implant (117°); and more significantly, this benefit was consistently achieved throughout the 5-year period of follow-up (P b .001). Preoperatively, the mean flexion angle was 122° for the conventional group and 123° for the highflexion group (Fig. 1). Our patients in the high-flexion group showed an increase in flexion angle postoperatively from 123° to 128° at 2 years, and this was sustained until the 5-year mark (128°). Our patients in the conventional group showed a decrease in flexion angle postoperatively, and the mean flexion angle at the end of 5 years (117°) was lower than that preoperatively (122°). We reported the Knee Society score as 2 separate scores, the Knee score and Function score. The Knee scoring for our patients showed a significant improvement from preoperative values in both our high-flexion and conventional groups; however, there was no statistical difference between the 2 groups at 6 months to 5 years postoperatively (Fig. 2).
Fig. 4. Graph comparing the Physical Function score component of SF-36 of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
1028 The Journal of Arthroplasty Vol. 26 No. 7 October 2011
Fig. 5. Graph comparing the General Health score component of SF-36 of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
There was an improvement in the function scores for both our high-flexion and conventional groups postoperatively; and at the end of the 5-year follow-up, the final function score for the high-flexion group (69) was higher than the standard group (62), although this was not statistically significant (Fig. 3). We reported the SF-36 scores individually as 8 measures: Physical Function, Role Physical, Bodily Pain, General Health, Vitality, Social Functioning, Role Emotional, and Mental Health. These 8 measures were further aggregated into 2 summary scales: the Physical Component score and Mental Component score [21]. There was a statistically significant difference (P = .03) between the mean physical function score at a longterm follow-up period of 5 years when comparing the high-flexion group (63) to the conventional group (53) (Fig. 4). Furthermore, the mean General Health score at 5 years for patients in the high-flexion group (79) was significantly better (P b .001) than the conventional group (62) (Fig. 5). The mean Vitality score was also significantly better (P = .03) at the 5-year mark for the high-flexion group (74) compared with the conventional group(62) (Fig. 6). In contrast, the overall Physical and Mental Component scores of SF-36 revealed no statistical difference between both groups throughout the 5-year follow up (Fig. 7).
There was an improvement in the Oxford knee scores postoperatively for both the high-flexion and conventional groups all the way to the 5-year follow-up, with no statistical difference between the scores in both groups (Fig. 8). There was one case of deep infection that required a 2stage revision. The survival rate of the TKA for this study is 98.7% (1 case of revision TKA). There were no cases of femoral or tibia implant aseptic loosening on radiological imaging at the 5-year follow-up.
Fig. 6. Graph comparing the Vitality score component of SF36 of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
Fig. 8. Graph comparing the Oxford knee score of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
Fig. 7. Graph comparing the Physical Component score and Mental Component score of SF-36 between the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
Discussion There are several studies that have concluded that there are no significant differences in clinical outcome between conventional and high-flexion TKA [22-24]. However, the mean postoperative flexion angles achieved by the high-flexion groups in these studies were usually less than 125°. Notably, Ritter et al [25]
Improved Clinical Outcomes After High-Flexion TKA Seng et al
have reported that the best overall functional outcome results post-TKA were achieved with postoperative flexion angles of between 128° and 132°. In our study, we managed to achieve a mean flexion angle of 128° in our high-flexion group. Moreover, the studies we found to date only had postoperative follow-up periods of approximately 2 years, compared with our study in which we followed up both patient groups for a period of 5 years. This has allowed us to compare the midterm results of highflexion TKA and its correlation with functional outcomes. Indeed, our study has found that the greater angle of flexion achieved post-TKA when using the high-flexion implant is correlated with better long-term functional outcomes at 5 years. This is evidenced by the significantly better Physical Function, General Health, and Vitality component scores of SF-36 in our high-flexion group at the 5-year mark. Interestingly, these scores did not significantly differ between both study groups at 6 months and 2 years postoperatively, which is consistent with the findings of the aforementioned studies. These results have led us to conclude that significant clinical changes do continue to occur beyond 2 years post-TKA, and are in contrast with earlier study reports that clinical outcomes post-TKA tend to plateau around 1 year after surgery [24,26,27]. This is despite the fact that there was no noted increase in mean flexion angle for the highflexion group at both the 2- and 5-year follow-up at 128°. We believe that a possible reason could be that the higher flexion angles postoperatively allow the patients to better maintain their activities of daily living even as they continue to age and hence lead to an increase in quality of life due to continued or increased satisfaction. The Physical Function, General Health, and Vitality scores are the most precise among the 8 scales comprising the SF-36 [28] and also define the widest range of health states (hence usually producing the least skewed score distributions). As such, our results indicate that there are tangible quality of life benefits after achieving higher angle of knee flexion postoperatively in the midterm period of 5 years. However, it should be noted that there were no significant differences between the 2 study groups when comparing the SF-36 summary scales (overall Physical and Mental Component scores) and also when comparing the Oxford knee scores. This has led us to conclude that the high-flexion implant would likely yield the best outcomes only when used with careful patient selection, that is, in patients who would benefit most from the gains in physical function that the high-flexion implant is capable of delivering. There are several limitations to our study. We acknowledged that the patients in both the conventional and high-flexion groups were predominantly female, with 24 women and 11 men in the conventional group and 34 women and 7 men in the high-flexion group. This unequal sex distribution could lead to a potential
1029
bias in our study. However, this sex distribution mirrors the usual demographic of TKA patients in our country, who are usually female. Furthermore, the subjects in our study were predominantly Asian; hence, the results of our study may not be well extrapolated to a Western population. This is particularly true with respect to comparing functional outcomes because of cultural requirements for higher degrees of knee flexion among Asian patients whose daily activities often comprise squatting and kneeling, which require a higher degree of flexion [29]. In particular, squatting and sitting cross-legged are integral parts of the lives of Asians; and these require 111° to 165° of knee flexion. In the Western world, 110° of flexion generally allows for normal function in most activities [30]. We used the Zimmer NexGen LPS-Flex system for our high-flexion TKA group of patients, whereas the J&J DePuy PFC Modular Knee System was used for the conventional TKA group. As the purpose of the study was primarily to assess if higher knee flexion in a particular group of patients would result in better quality of life scores and secondarily to compare knee flexion outcomes between high-flexion and conventional implants, we felt that it was not mandatory to use the standard Zimmer implant for our conventional TKA group. The reason for choosing the Zimmer NexGen LPSFlex implant for our high-flexion group was due to the fact that it has been well documented in the literature that this system is consistently capable of delivering higher degrees of knee flexion postoperatively [31,32]. Lastly, our study had 13 patients in total who were lost to follow-up; and this could potentially lead to bias in the postoperative TKA results. In conclusion, we have found that high-flexion implants are capable of producing a sustainable and consistently higher angle of knee flexion post-TKA when compared with conventional implants. This has resulted in better outcomes in the Physical Function, General Health, and Vitality components of the SF-36, which we feel would be beneficial to a select group of patients who require higher degrees of knee flexion in their daily activities and would thus appreciate the gains in physical function that the high-flexion implant delivers. Therefore, we propose that careful history-taking and patient selection should be performed preoperatively to identify patients who would benefit the most from high-flexion implants, and this would be crucial in optimizing the long-term functional outcomes post-TKA.
References 1. Wright J, Ewald FC, Walker PS, et al. Total knee arthroplasty with the kinematic prosthesis. Results after five to nine years: a follow-up note. J Bone Joint Surg Am 1990;72:1003. 2. Insall JN, Lachiewicz PF, Burstein AH. The posterior stabilized condylar prosthesis: a modification of the total
1030 The Journal of Arthroplasty Vol. 26 No. 7 October 2011
3.
4.
5. 6.
7.
8. 9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
condylar design. Two- to four-year clinical experience. J Bone Joint Surg Am 1982;64:1317. Banks S, Bellemans J, Nozaki H, et al. Knee motions during maximum flexion in fixed and mobile bearing arthroplasties. Clin Orthop 2003;410:131. Kurosaka M, Yoshiya S, Mizuno K, et al. Maximizing flexion after total knee arthroplasty: the need and pitfalls. J Arthroplasty 2001;17(Supp 1):59. Laubenthal KN. A quantitative analysis of knee motion during activities of daily living. Phys Ther 1972;52:34. Mulholland SJ, Wyss UP. Activities of daily living in nonWestern cultures: range of motion requirements for hip and knee joint implants. Int J Rehabil Res 2001;24:191. Park KK, Chang CB, Kang YG, et al. Correlation of maximum flexion with clinical outcome after total knee replacement in Asian patients. J Bone Jt Surg Br 2007;89:604. Kim JM, Moon MS. Squatting following total knee arthroplasty. Clin Orthop 1995;313:177. Kurosaka M, Yoshiya S, Mizuno K, et al. Maximizing flexion after total knee arthroplasty: the need and the pitfalls. J Arthroplast 2002;17(Suppl 1):59. Jones RE. High-flexion rotating-platform knees: rationale, design, and patient selection. Orthopedics 2006;29 (9 Suppl):S76. Delp SL, Kocmond JH, Stern SH. Tradeoffs between motion and stability in posterior substituting knee arthroplasty design. J Biomech 1995;28:1155. Argenson JN, Scuderi GR, Komistek RD, et al. In vivo kinematic evaluation and design considerations related to high flexion in total knee arthroplasty. J Biomech 2005;38:277. Li G, Most E, Sultan PG, et al. Knee kinematics with a high-flexion posterior stabilized total knee prosthesis: an in vitro robotic experimental investigation. J Bone Joint Surg Am 2004;86-A:1721. Goldstein WM, Raab DJ, Gleason TF, et al. Why posterior cruciate-retaining and substituting total knee replacements have similar ranges of motion. The importance of posterior condylar offset and clean out of posterior condylar space. J Bone Joint Surg Am 2006;88(Suppl 4):182. Massin P, Gournay A. Optimization of the posterior condylar offset, tibial slope, and condylar roll-back in total knee arthroplasty. J Arthroplasty 2006;21:889. Most E, Sultan PG, Park SE, et al. Tibiofemoral contact behavior is improved in high-flexion cruciate retaining TKA. Clin Orthop Relat Res 2006;452:59. Sharma A, Leszko F, Komistek RD, et al. In vivo patellofemoral forces in high flexion total knee arthroplasty. J Biomech 2008;41:642. Sharma A, Komistek RD, Scuderi GR, et al. High flexion TKA designs: what are their in vivo contact mechanics. Clin Orthop Relat Res 2007;464:117.
19. Han HS, Kang SB, Yoon KS. High incidence of loosening of the femoral component in legacy posterior stabilisedflex total knee replacement. J Bone Joint Surg Br 2007; 89:1457. 20. Kim TH, Lee DH, Bin SI. The NexGen LPS-flex to the knee prosthesis at a minimum of three years. J Bone Joint Surg Br 2008;90-B:1304. 21. Ware JE, Kosinski M, Keller SD. SF-36 physical and mental health summary scales: a user's manual. Boston, MA: The Health Institute; 1994. 22. Nutton RW, van der Linden ML, Rowe PJ, et al. A prospective randomized double-blind study of functional outcome and range of flexion following total knee replacement with the NexGen standard and high flexion components. J Bone Joint Surg[Br] 2008;90-B:37. 23. Huang HT, Su JY, Wang GJ. The early results of high-flex total knee arthroplasty: a minimum 2 yrs follow-up. J Arthroplasty 2005;20:674. 24. Kim YH, Sohn KS, Kim JS. Range of motion of standard and high-flexion posterior stabilized total knee prosthesis: a prospective, randomized study. J Bone Joint Surg[Am] 2005;87-A:1460. 25. Ritter MA, Lutgring JD, Davis KE, et al. The effect of postoperative range of motion on functional activities after posterior cruciate retaining total knee arthroplasty. J Bone Joint Surg[Am] 2008;90-A:777. 26. Banks S, Bellemans J, Nozaki H, et al. Knee motions during maximum flexion in fixed and mobile-bearing arthroplasties. Clin Orthop 2003;410:131. 27. Aglietti P, Baldini A, Buzzi R, et al. Comparison of mobile bearing and fixed-bearing total knee arthroplasty: a prospective randomized study. J Arthroplasty 2005;20:145. 28. McHorney CA, Ware JE, Rogers W, et al. The validity and relative precision of MOS short- and long-form health status scales and Dartmouth COOP charts: results from the Medical Outcomes Study. Med Care 1992;30 (Suppl 5):MS253. 29. Mulholland SJ, Wyss UP. Activities of daily living in non Western cultures: range of motion requirements for hip and knee joint implants. Int J Rehabil Res 2001; 24:1918. 30. Rowe PJ, Myles CM, Walker C, et al. Knee joint kinematics in gait and other functional activities measured using flexible electrogoniometry: how much knee motion is sufficient for normal daily life? Gait posture 2000;12:143. 31. Seong II B, Tae SN. Early results of high-flex total knee arthroplasty: comparison study at 1 year after surgery. Knee Surg Sports Traumatol Arthrosc 2006;15:350. 32. Huang HT, Su JY, Wang GJ. The early results of high-flex total knee arthroplasty: a minimum of 2 years of followup. J Arthroplasty 2005;20:674.
Improved Clinical Outcomes After High-Flexion Total Knee Arthroplasty A 5-Year Follow-Up Study Chusheng Seng, MBBS, MRCS (Edin),* Seng Jin Yeo, MBBS, FRCS (Edin), FAMS,* James L.Wee,MBBS,MRCS(Edin),* S.Subanesh,MBBS(India),MSOrth(UKM),AM(Mal),y Hwee Chi Chong, BASc (Physiotherapy),* and Ngai Nung Lo, MBBS, FRCS (Edin), FAMS*
Abstract: The purpose of this study was to determine if high-flexion total knee arthroplasty resulted in improved outcomes compared with conventional total knee arthroplasty. This was a prospective, double-blind, randomized controlled trial involving 76 patients over 5 years. We compared the postoperative flexion range, Knee Society scores, Oxford knee scores, and SF-36 scores between 2 groups. The high-flexion group was able to achieve a significant sustainable increase in postoperative knee flexion angle; and this correlated to a significant improvement in the General Health, Vitality, and Physical Functioning scales of SF-36 at 5 years postoperatively. Our results signify that high-flexion total knee arthroplasty has additional benefits to the quality of life in patients who require higher degrees of knee flexion in their activities of daily living. Keywords: improved outcomes, total knee arthroplasty, high-flexion, conventional, quality of life. © 2011 Elsevier Inc. All rights reserved.
Primary total knee arthroplasty (TKA) is one of the fastest-growing elective orthopedic procedures in the past decade. The principal aim of TKA is to create a stable and painless knee with a range of motion adequate to perform the activities of daily living. With current conventional prosthetic designs and surgical techniques, gaining a range of motion of the knee from 0° to 110° and 120° after TKA is readily achievable [1-4]. Studies have shown that 83° of flexion is required for stair climbing, 93° for rising from a seated position, and 106° for shoelace tying [5]. In most Western cultures, achieving a range of motion beyond this may have limited clinical value. However, in some countries, squatting and sitting cross-legged are an essential part of their daily lives. These activities require up to 165° of flexion, and deep flexion of the knee after TKA may be required [6-9]. Furthermore, some sporting activities
From the *Department of Orthopaedic Surgery, Singapore General Hospital, Singapore, Singapore; and yDepartment of Orthopaedic and Traumatology, Faculty of Medicine, Universiti Kebangsaan Malaysia, Malaysia. Submitted May 11, 2010; accepted September 17, 2010. No benefits or funds were received in support of the study. Reprint requests: Chusheng Seng, MBBS, MRCS(Edin), Department of Orthopaedic Surgery, Singapore General Hospital, Outram Rd., Singapore 169608, Singapore. © 2011 Elsevier Inc. All rights reserved. 0883-5403/2607-0009$36.00/0 doi:10.1016/j.arth.2010.09.006
and workplace demands may also require, or benefit from, higher degrees of flexion. High flexion is traditionally defined as greater than 125° of flexion after TKA [10]. However, achieving a deep flexion angle and maintaining the stability of the knee are competing goals and require refinements in design, as well as careful surgical technique [11]. The Zimmer (Warsaw, Ind) NexGen LPS-Flex implant is designed to achieve up to 150° of flexion after TKA, with design modifications to improve the kinematics at high-flexion angles [12]. Firstly, the implant is designed with an increased posterior condylar offset with an additional cut of 2mm bone from the posterior femoral condyle to extend the surface of the femoral component posteriorly to increase the articular contact area between the femur and the tibia at high flexion angles and thereby increase posterior femoral translation and the range of flexion. Secondly, to ensure that the patella is not caught in the intercondylar box as the patellar contact region moves distally during high flexion, a longer trochlear groove is incorporated into the design. Furthermore, an anterior cutout of the tibial polyethylene insert reduces patellar tendon impingement during deep flexion. Lastly, in the NexGen LPS-Flex posterior-stabilized designs, modifications to the campost mechanism increase the jump distance, ensure continued contact, and prevent dislocation over the post at deep flexion angles [13-15].
1025
1026 The Journal of Arthroplasty Vol. 26 No. 7 October 2011 Table 1. Patient Demographics No. of patients Age (mean) Sex BMI (mean)
Conventional
High-Flexion
35 68 Female: 24 Male: 11 28
41 67 Female: 34 Male: 7 27
BMI indicates body mass index.
Thus far, biomechanical studies have shown that these high-flexion TKA implant design modifications do not cause compromises to stability, contact mechanics, patellar kinematics, and durability [16-18]. Han et al [19] reported that 38% of their patients had aseptic loosening of the femoral component at a mean of 32 months and 21% required revision at a mean of 23 months in his series of 72 Zimmer NexGen LPS-Flex fixed TKAs in 47 patients. However, this study is a single-surgeon series and may not be a true reflection of the actual incidence of aseptic loosening of this highflexion implant. Moreover, the relatively small sample size may have skewed the final outcomes of the TKAs. Kim et al [20]reported in a large series of 278 knees that the NexGen LPS-Flex prosthesis provided satisfactory results at 3 to 4.8 years of follow-up with an extremely low incidence of adverse radiological findings. There were in total 2 cases of radiolucency at the femoral component that did not require revision because there was no evidence of prosthesis migration or loosening. The purpose of our study is to determine whether the high-flexion TKA implant design modifications significantly improve the range of motion in vivo and, if so, whether the quality of life and functional outcome are enhanced as a result.
Material and Methods In total, there were 76 patients enrolled into our prospective, double-blinded, and randomized clinical
trial from the period November 2001 to September 2003. Institutional review board approval was obtained from our hospital ethics committee. Patients who had degenerative joint disease with a minimum preoperative range of motion of 90° were included into our study. Exclusion criteria included patients with inflammatory arthritis, history of septic arthritis, and previous ipsilateral knee surgery. However, patients who had prior contralateral TKA were eligible for our study. The conventional implant used in this study was the J&J DePuy (Warsaw, Ind) PFC Modular Knee System, whereas the Zimmer NexGen LPS-Flex system was selected for the high-flexion group. Both systems were nonmobile, fixed-bearing systems. The conventional implant was used in 24 female and 11 male patients; 34 female and 7 male patients received the highflexion implant. This was a randomized double-blinded study. The patients were blinded to the type of prosthesis being implanted; sealed envelopes were randomly issued to every patient and only opened by the surgeon just before surgery to reveal which study group the patient had been assigned to. Preoperative functional assessments were performed by physiotherapists from the Orthopaedic Diagnostic Center, who were likewise blinded to the study group allocation. The physiotherapists assessed all patients 2 weeks before surgery. The range of motion was measured passively with a standard goniometer by the physiotherapists from the Orthopaedic Diagnostic Center. The SF-36 Quality of Life questionnaire was administered to every patient 2 weeks before surgery, and the Knee Society scoring and the Oxford knee scoring were performed at the same time. Postoperatively, all patients were assessed again by the physiotherapists at 6 months, 2 years, and 5 years postoperatively. All study patients were operated on by 2 senior consultants from the Adult Reconstruction Service of
Table 2. Preoperative Comparison
Range of motion Knee Society scores Oxford knee score SF-36 scores
Extension Flexion Function score Knee score Physical Function Role Physical Bodily Pain General Health Vitality Social Functioning Role Emotional Mental Health Physical Component score Mental Component score
Conventional
High-Flexion
Preop Mean
Preop Mean
3± 122 ± 48 ± 42 ± 36 ± 37 ± 53 ± 44 ± 77 ± 63 ± 71 ± 83 ± 75 ± 38 ± 51 ±
6 12 19 18 8 20 41 20 14 19 34 38 17 12 10
3± 123 ± 48 ± 42 ± 36 ± 37 ± 51 ± 41 ± 69 ± 62 ± 63 ± 83 ± 70 ± 39 ± 48 ±
6 23 17 17 7 17 41 17 22 18 32 38 19 11 10
P Value .918 .888 .978 .960 .742 .888 .831 .567 .064 .876 .290 .994 .159 .992 .123
Improved Clinical Outcomes After High-Flexion TKA Seng et al
Fig. 1. Graph comparing the flexion range of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
our institution during the period from November 2001 to September 2003. The operative procedure was standardized—the medial parapatellar approach with patella eversion and soft tissue balancing was used by both surgeons, and all implants were cemented. All the patellae were resurfaced. Postoperatively, all study patients were managed on our institution's standardized TKA pathway and underwent the same physiotherapy regimen. The mean range of motion and mean functional scores were evaluated and the level of statistical significance was taken to be P b .05. All calculations were performed using SPSS (Chicago, IL) version 12.
Results There were a total of 76 patients enrolled in this study, with 35 patients assigned to the group using the conventional J&J implant and 41 patients in the group using the Zimmer Hi-flex implant. Computer-generated random numbers were used for patient randomization. The patients in the conventional group and the highflexion group were similar in terms of mean age (68 and 67 years), mean body mass index (28 and 27), and mean preoperative range of knee flexion (122° and 123°). The patients' demographics are shown in Table 1. Preoperatively, the patients in the conventional and highflexion groups were also similar in terms of range of motion, Knee Society scores, Oxford knee scores, and SF-36 scores (Table 2).
Fig. 2. Graph comparing the Knee score component of the Knee Society score of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
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Fig. 3. Graph comparing the Function score component of the Knee Society score of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
A total of 13 patients were lost to follow-up, with 8 patients from the conventional group and 5 patients from the high-flexion group. Four of these patients died during the study period, one refused further follow-up, and the remainder were not contactable for various reasons. Our study found that the group with the Zimmer Hiflex implant managed to achieve a significantly higher angle of flexion postoperatively(128°) when compared with group using the conventional J&J implant (117°); and more significantly, this benefit was consistently achieved throughout the 5-year period of follow-up (P b .001). Preoperatively, the mean flexion angle was 122° for the conventional group and 123° for the highflexion group (Fig. 1). Our patients in the high-flexion group showed an increase in flexion angle postoperatively from 123° to 128° at 2 years, and this was sustained until the 5-year mark (128°). Our patients in the conventional group showed a decrease in flexion angle postoperatively, and the mean flexion angle at the end of 5 years (117°) was lower than that preoperatively (122°). We reported the Knee Society score as 2 separate scores, the Knee score and Function score. The Knee scoring for our patients showed a significant improvement from preoperative values in both our high-flexion and conventional groups; however, there was no statistical difference between the 2 groups at 6 months to 5 years postoperatively (Fig. 2).
Fig. 4. Graph comparing the Physical Function score component of SF-36 of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
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Fig. 5. Graph comparing the General Health score component of SF-36 of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
There was an improvement in the function scores for both our high-flexion and conventional groups postoperatively; and at the end of the 5-year follow-up, the final function score for the high-flexion group (69) was higher than the standard group (62), although this was not statistically significant (Fig. 3). We reported the SF-36 scores individually as 8 measures: Physical Function, Role Physical, Bodily Pain, General Health, Vitality, Social Functioning, Role Emotional, and Mental Health. These 8 measures were further aggregated into 2 summary scales: the Physical Component score and Mental Component score [21]. There was a statistically significant difference (P = .03) between the mean physical function score at a longterm follow-up period of 5 years when comparing the high-flexion group (63) to the conventional group (53) (Fig. 4). Furthermore, the mean General Health score at 5 years for patients in the high-flexion group (79) was significantly better (P b .001) than the conventional group (62) (Fig. 5). The mean Vitality score was also significantly better (P = .03) at the 5-year mark for the high-flexion group (74) compared with the conventional group(62) (Fig. 6). In contrast, the overall Physical and Mental Component scores of SF-36 revealed no statistical difference between both groups throughout the 5-year follow up (Fig. 7).
There was an improvement in the Oxford knee scores postoperatively for both the high-flexion and conventional groups all the way to the 5-year follow-up, with no statistical difference between the scores in both groups (Fig. 8). There was one case of deep infection that required a 2stage revision. The survival rate of the TKA for this study is 98.7% (1 case of revision TKA). There were no cases of femoral or tibia implant aseptic loosening on radiological imaging at the 5-year follow-up.
Fig. 6. Graph comparing the Vitality score component of SF36 of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
Fig. 8. Graph comparing the Oxford knee score of the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
Fig. 7. Graph comparing the Physical Component score and Mental Component score of SF-36 between the conventional and high-flexion groups preoperatively and at 6 months, 2 years, and 5 years.
Discussion There are several studies that have concluded that there are no significant differences in clinical outcome between conventional and high-flexion TKA [22-24]. However, the mean postoperative flexion angles achieved by the high-flexion groups in these studies were usually less than 125°. Notably, Ritter et al [25]
Improved Clinical Outcomes After High-Flexion TKA Seng et al
have reported that the best overall functional outcome results post-TKA were achieved with postoperative flexion angles of between 128° and 132°. In our study, we managed to achieve a mean flexion angle of 128° in our high-flexion group. Moreover, the studies we found to date only had postoperative follow-up periods of approximately 2 years, compared with our study in which we followed up both patient groups for a period of 5 years. This has allowed us to compare the midterm results of highflexion TKA and its correlation with functional outcomes. Indeed, our study has found that the greater angle of flexion achieved post-TKA when using the high-flexion implant is correlated with better long-term functional outcomes at 5 years. This is evidenced by the significantly better Physical Function, General Health, and Vitality component scores of SF-36 in our high-flexion group at the 5-year mark. Interestingly, these scores did not significantly differ between both study groups at 6 months and 2 years postoperatively, which is consistent with the findings of the aforementioned studies. These results have led us to conclude that significant clinical changes do continue to occur beyond 2 years post-TKA, and are in contrast with earlier study reports that clinical outcomes post-TKA tend to plateau around 1 year after surgery [24,26,27]. This is despite the fact that there was no noted increase in mean flexion angle for the highflexion group at both the 2- and 5-year follow-up at 128°. We believe that a possible reason could be that the higher flexion angles postoperatively allow the patients to better maintain their activities of daily living even as they continue to age and hence lead to an increase in quality of life due to continued or increased satisfaction. The Physical Function, General Health, and Vitality scores are the most precise among the 8 scales comprising the SF-36 [28] and also define the widest range of health states (hence usually producing the least skewed score distributions). As such, our results indicate that there are tangible quality of life benefits after achieving higher angle of knee flexion postoperatively in the midterm period of 5 years. However, it should be noted that there were no significant differences between the 2 study groups when comparing the SF-36 summary scales (overall Physical and Mental Component scores) and also when comparing the Oxford knee scores. This has led us to conclude that the high-flexion implant would likely yield the best outcomes only when used with careful patient selection, that is, in patients who would benefit most from the gains in physical function that the high-flexion implant is capable of delivering. There are several limitations to our study. We acknowledged that the patients in both the conventional and high-flexion groups were predominantly female, with 24 women and 11 men in the conventional group and 34 women and 7 men in the high-flexion group. This unequal sex distribution could lead to a potential
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bias in our study. However, this sex distribution mirrors the usual demographic of TKA patients in our country, who are usually female. Furthermore, the subjects in our study were predominantly Asian; hence, the results of our study may not be well extrapolated to a Western population. This is particularly true with respect to comparing functional outcomes because of cultural requirements for higher degrees of knee flexion among Asian patients whose daily activities often comprise squatting and kneeling, which require a higher degree of flexion [29]. In particular, squatting and sitting cross-legged are integral parts of the lives of Asians; and these require 111° to 165° of knee flexion. In the Western world, 110° of flexion generally allows for normal function in most activities [30]. We used the Zimmer NexGen LPS-Flex system for our high-flexion TKA group of patients, whereas the J&J DePuy PFC Modular Knee System was used for the conventional TKA group. As the purpose of the study was primarily to assess if higher knee flexion in a particular group of patients would result in better quality of life scores and secondarily to compare knee flexion outcomes between high-flexion and conventional implants, we felt that it was not mandatory to use the standard Zimmer implant for our conventional TKA group. The reason for choosing the Zimmer NexGen LPSFlex implant for our high-flexion group was due to the fact that it has been well documented in the literature that this system is consistently capable of delivering higher degrees of knee flexion postoperatively [31,32]. Lastly, our study had 13 patients in total who were lost to follow-up; and this could potentially lead to bias in the postoperative TKA results. In conclusion, we have found that high-flexion implants are capable of producing a sustainable and consistently higher angle of knee flexion post-TKA when compared with conventional implants. This has resulted in better outcomes in the Physical Function, General Health, and Vitality components of the SF-36, which we feel would be beneficial to a select group of patients who require higher degrees of knee flexion in their daily activities and would thus appreciate the gains in physical function that the high-flexion implant delivers. Therefore, we propose that careful history-taking and patient selection should be performed preoperatively to identify patients who would benefit the most from high-flexion implants, and this would be crucial in optimizing the long-term functional outcomes post-TKA.
References 1. Wright J, Ewald FC, Walker PS, et al. Total knee arthroplasty with the kinematic prosthesis. Results after five to nine years: a follow-up note. J Bone Joint Surg Am 1990;72:1003. 2. Insall JN, Lachiewicz PF, Burstein AH. The posterior stabilized condylar prosthesis: a modification of the total
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3.
4.
5. 6.
7.
8. 9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
condylar design. Two- to four-year clinical experience. J Bone Joint Surg Am 1982;64:1317. Banks S, Bellemans J, Nozaki H, et al. Knee motions during maximum flexion in fixed and mobile bearing arthroplasties. Clin Orthop 2003;410:131. Kurosaka M, Yoshiya S, Mizuno K, et al. Maximizing flexion after total knee arthroplasty: the need and pitfalls. J Arthroplasty 2001;17(Supp 1):59. Laubenthal KN. A quantitative analysis of knee motion during activities of daily living. Phys Ther 1972;52:34. Mulholland SJ, Wyss UP. Activities of daily living in nonWestern cultures: range of motion requirements for hip and knee joint implants. Int J Rehabil Res 2001;24:191. Park KK, Chang CB, Kang YG, et al. Correlation of maximum flexion with clinical outcome after total knee replacement in Asian patients. J Bone Jt Surg Br 2007;89:604. Kim JM, Moon MS. Squatting following total knee arthroplasty. Clin Orthop 1995;313:177. Kurosaka M, Yoshiya S, Mizuno K, et al. Maximizing flexion after total knee arthroplasty: the need and the pitfalls. J Arthroplast 2002;17(Suppl 1):59. Jones RE. High-flexion rotating-platform knees: rationale, design, and patient selection. Orthopedics 2006;29 (9 Suppl):S76. Delp SL, Kocmond JH, Stern SH. Tradeoffs between motion and stability in posterior substituting knee arthroplasty design. J Biomech 1995;28:1155. Argenson JN, Scuderi GR, Komistek RD, et al. In vivo kinematic evaluation and design considerations related to high flexion in total knee arthroplasty. J Biomech 2005;38:277. Li G, Most E, Sultan PG, et al. Knee kinematics with a high-flexion posterior stabilized total knee prosthesis: an in vitro robotic experimental investigation. J Bone Joint Surg Am 2004;86-A:1721. Goldstein WM, Raab DJ, Gleason TF, et al. Why posterior cruciate-retaining and substituting total knee replacements have similar ranges of motion. The importance of posterior condylar offset and clean out of posterior condylar space. J Bone Joint Surg Am 2006;88(Suppl 4):182. Massin P, Gournay A. Optimization of the posterior condylar offset, tibial slope, and condylar roll-back in total knee arthroplasty. J Arthroplasty 2006;21:889. Most E, Sultan PG, Park SE, et al. Tibiofemoral contact behavior is improved in high-flexion cruciate retaining TKA. Clin Orthop Relat Res 2006;452:59. Sharma A, Leszko F, Komistek RD, et al. In vivo patellofemoral forces in high flexion total knee arthroplasty. J Biomech 2008;41:642. Sharma A, Komistek RD, Scuderi GR, et al. High flexion TKA designs: what are their in vivo contact mechanics. Clin Orthop Relat Res 2007;464:117.
19. Han HS, Kang SB, Yoon KS. High incidence of loosening of the femoral component in legacy posterior stabilisedflex total knee replacement. J Bone Joint Surg Br 2007; 89:1457. 20. Kim TH, Lee DH, Bin SI. The NexGen LPS-flex to the knee prosthesis at a minimum of three years. J Bone Joint Surg Br 2008;90-B:1304. 21. Ware JE, Kosinski M, Keller SD. SF-36 physical and mental health summary scales: a user's manual. Boston, MA: The Health Institute; 1994. 22. Nutton RW, van der Linden ML, Rowe PJ, et al. A prospective randomized double-blind study of functional outcome and range of flexion following total knee replacement with the NexGen standard and high flexion components. J Bone Joint Surg[Br] 2008;90-B:37. 23. Huang HT, Su JY, Wang GJ. The early results of high-flex total knee arthroplasty: a minimum 2 yrs follow-up. J Arthroplasty 2005;20:674. 24. Kim YH, Sohn KS, Kim JS. Range of motion of standard and high-flexion posterior stabilized total knee prosthesis: a prospective, randomized study. J Bone Joint Surg[Am] 2005;87-A:1460. 25. Ritter MA, Lutgring JD, Davis KE, et al. The effect of postoperative range of motion on functional activities after posterior cruciate retaining total knee arthroplasty. J Bone Joint Surg[Am] 2008;90-A:777. 26. Banks S, Bellemans J, Nozaki H, et al. Knee motions during maximum flexion in fixed and mobile-bearing arthroplasties. Clin Orthop 2003;410:131. 27. Aglietti P, Baldini A, Buzzi R, et al. Comparison of mobile bearing and fixed-bearing total knee arthroplasty: a prospective randomized study. J Arthroplasty 2005;20:145. 28. McHorney CA, Ware JE, Rogers W, et al. The validity and relative precision of MOS short- and long-form health status scales and Dartmouth COOP charts: results from the Medical Outcomes Study. Med Care 1992;30 (Suppl 5):MS253. 29. Mulholland SJ, Wyss UP. Activities of daily living in non Western cultures: range of motion requirements for hip and knee joint implants. Int J Rehabil Res 2001; 24:1918. 30. Rowe PJ, Myles CM, Walker C, et al. Knee joint kinematics in gait and other functional activities measured using flexible electrogoniometry: how much knee motion is sufficient for normal daily life? Gait posture 2000;12:143. 31. Seong II B, Tae SN. Early results of high-flex total knee arthroplasty: comparison study at 1 year after surgery. Knee Surg Sports Traumatol Arthrosc 2006;15:350. 32. Huang HT, Su JY, Wang GJ. The early results of high-flex total knee arthroplasty: a minimum of 2 years of followup. J Arthroplasty 2005;20:674.