The Journal of Arthroplasty 29 (2014) 530–534
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The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Clinical Outcomes in High Flexion Total Knee Arthroplasty Were Not Superior to Standard Posterior Stabilized Total Knee Arthroplasty. A Multicenter, Prospective, Randomized Study George N. Guild III, MD a, Sameh A. Labib, MD b a b
Insall Scott Kelly Institute for Orthopaedics and Sports Medicine, Lenox Hill Hospital, New York, New York Emory Sports Medicine Center, Emory University, Atlanta, Georgia
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Article history: Received 6 March 2013 Accepted 24 July 2013 Keywords: total knee arthroplasty high flexion range of motion
a b s t r a c t High flexion prostheses have been introduced to achieve high flexion and improve clinical outcomes. Controversy exists in the literature regarding outcomes of high flexion vs. standard implants. This multicenter study compares outcomes in patients receiving a high flexion prosthesis vs. standard prosthesis. 278 high flexion and standard knee prostheses were used. Patients were followed for two years and evaluated prospectively. The mean HSS was 87.3 for the standard group and 88.9 for the flexion group. At two-year follow up the standard prosthesis group had mean flexion of 121° and the high flexion group had mean flexion 120°. No knee had aseptic loosening, infection, or osteolysis. At two-year follow up, there were no significant differences in range of motion, clinical outcome, or radiographic evaluation. Pre-operative motion and functional status have greater impact on clinical outcome than implant alone. © 2014 Elsevier Inc. All rights reserved.
Range of motion in total knee arthroplasty is a key determining factor in a patient’s overall functional outcome [1]. The fact that most knees do not flex more than 120° after surgery has been studied extensively, but no one theory sufficiently explains this phenomenon [2–5]. To improve deep flexion after total knee arthroplasty high flexion designs have been developed in the last decade. The NexGen LPS Flex total knee system (Zimmer, Warsaw IN) was designed to achieve high knee flexion, increase surface area articulation, and improve patient outcomes. Compared to the standard, the NexGen LPS Flex has 3 principle design modifications: extension of the posterior femoral condyles and posterior condylar radii to increase contact area, an increased cam height, and cut out in the polyethylene insert to prevent patellar tendon impingement. Theoretically these design modifications may lead to better postoperative range of motion, increase longevity, and provide improved clinical outcomes. However, there are conflicting reports in the literature on the early results of high flexion prosthesis. A previous meta-analysis including six studies did show a significant difference in favor of the high flexion design but, only two of those studies were randomized controlled trials [6]. In another systematic review no difference was found between the prostheses but, data synthesis and quantitative analysis were not performed [7]. Several authors have also reported on early increased loosening at high The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2013.07.035. Reprint requests: George N. Guild III, MD, 1007 Lexington Ave Apt. 2R, New York, NY 10021. 0883-5403/2903-0017$36.00/0 – see front matter © 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2013.07.035
flexion angles in the high-flexion prosthesis [8,9]. Because of this conflicting data regarding motion, loosening, and outcomes from individual centers, we performed a pooled data multicenter prospective randomized trial to assess differences in pain, functioning, aseptic loosening, and range of motion in the NexGen LPS and NexGen LPSFlex total knee systems. Materials and Methods Demographics Between 2002 and 2007, 278 total knee arthroplasties were performed at nine clinical centers associated with a university. The study was approved by the institutional review board and informed consent was obtained. Randomization of the total knee prosthesis, NexGen LPS standard or LPS-High Flexion (Zimmer, Warsaw IN), was determined on a sequential pool on the basis of a table of random numbers. The patient demographics are summarized in Table 1. The mean age of the patients at the time of operation was 65 years (range 43–80). 140 patients were men and 138 were women. 124 patients had previous knee surgery (25 open meniscectomies, 68 arthroscopic meniscectomies, 24 arthroscopies, 2 arthroscopic loose body removal, 2 prepatella bursa removals, 1 popliteal cyst excision, 1 MCL reconstruction, 1 PCL reconstruction) The preoperative diagnosis for 267 patients was osteoarthritis, 3 had post-traumatic arthritis, 2 inflammatory arthritis, 1 avascular necrosis, and 5 had rheumatoid arthritis. The mean patient height and standard deviation were 66.8 ± 4 inches and the mean weight
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Table 1 Comparisons Between LPS and LPS-Flex. Characteristic Gender Patient Age Weight Patient Height (Inch) Preoperative Diagnosis
Female Male
OSTEOARTHRITIS RHEUMATOID ARTHRITIS POST-TRAUMATIC ARTHRITIS INFLAMMATORY ARTHRITIS AVASCULAR NECROSIS OTHER
Overall (n = 278)
LPS-FLEX (n = 138)
138/278 (49.6%) 140/278 (50.4%) 64.4 ± 8.3 (278)
71/138 67/138 64.8 ± 8.5 190.2 ± 32.9 66.3 ± 4.1 131/137 3/137 2/137 0/137 0/137 1/137
66.8 ± 4.0 (278) 265/277 (95.7%) 5/277 (1.8%) 3/277 (1.1%) 2/277 (0.7%) 1/277 (0.4%) 1/277 (0.4%)
and standard deviation were 190.2 ± 32.9 lb for the flex group and 192.3 ± 41.2 for the standard group. Surgical Technique The operative procedures were performed at nine separate centers with some surgical technique differences with regard to implantation of the total knee arthroplasties however; they did share the following general characteristics. All procedures were performed via a midline skin incision approximately ten centimeters with a medial parapatellar arthrotomy. The cruciate ligaments were sacrificed in all patients. The magnitude and angles of the bony resections were standardized across treatment groups. The distal femoral resection was made with an intramedullary guide to resect 10 mm of bone from the most prominent femoral condyle at an angle of 5° of valgus. The tibial resection was made using an extramedullary guide with the goal of producing a neutral cut in the coronal plane and 7° of posterior slope in the sagittal plane. The anterior, posterior, and Chamfer cuts were made with a posterior femoral condylar referencing guide in 3° of external rotation. In the NexGen LPS-Flex group, 2 additional mm of posterior femoral condylar bone was resected compared to the NexGen LPS group. Posterior condylar osteophytes were resected in all patients. Ligament balancing was aided with the use of spacer blocks with the goal of creating symmetrical gaps of equal magnitude in flexion and extension. Superficial MCL release was required in 7 patients including four in the high flexion group and three in standard group. The amount of bone removed during patellar resection was equal to or slightly greater than the thickness of the patellar component. All implants were cemented. The capsule was closed in 30° of flexion in all patients. Rehabilitation Starting on the second post-operative day, the patients used a continuous passive motion machine applied for at least 6 h per day. Also on post-operative day two, active and passive range of motion was initiated, as well as ambulation with crutches or a walker once a day with physical therapy supervision. The patients used crutches or a walker with full weight bearing for six weeks and used a cane as needed subsequently. Clinical Evaluation Clinical and radiographic evaluations were made pre-operatively, 6 weeks post-operatively, 6 months, one year, and two years. Each knee was rated pre-operatively and post-operatively by the systems of the Knee Society and the Hospital for Special Surgery. Patients also completed the Short Form 36 (SF-36) questionnaire. Active range of motion was determined preoperatively and postoperatively with a 12-in goniometer at 6 weeks, 6 months, 1 year,
(51.4%) (48.6%) (138) (138) (138) (95.6%) (2.2%) (1.5%) (0.0%) (0.0%) (0.7%)
STD (n = 140) 67/140 (47.9%) 73/140 (52.1%) 64.0 ± 8.1 (140) 192.3 ± 41.2 (140) 67.3 ± 3.8 (140) 134/140 (95.7%) 2/140 (1.4%) 1/140 (0.7%) 2/140 (1.4%) 1/140 (0.7%) 0/140 (0.0%)
P Value 0.631 0.348 0.801 0.052* 0.633
and two years. Clinicians were blinded with regard to which total knee prosthesis was implanted. Radiographic evaluations were made pre-operatively and postoperatively by obtaining AP, Lateral, and skyline views. Evaluations were made at 6 weeks, 6 months, 1 year, and 2 years. Assessments were made based on limb alignment and component position. Radiolucencies and bone loss were also noted on AP, Lateral, and sunrise views. Skyline views were also examined for patellar tilt, subluxation, and dislocation. Results Clinical Outcomes Knee Score The pre-operative and post-operative knee scores are summarized in Table 2. The Hospital for Special Surgery (HSS) and Knee Society Scores (KSS) did not differ significantly between the two groups pre-operatively (P = 0.790 and P = 0.490, respectively) or postoperatively (P = 0.9177 and P = 0.2313, respectively). The mean pre-operative HSS score for the standard knee prosthesis group was 62.3 (mean ± SD 10.3) and 62.8 (mean ± SD 10.5) in the highflexion group. In the NexGen LPS group, the mean postoperative HSS score was 87.3 (mean ± SD 12.7) and 87.7 (mean ± SD 12.7) for the Knee Society Score. In the NexGen LPS Flex Group, the mean postoperative HSS score was 88.9 (mean ± SD 7.6) and 89.8. (mean ± SD 9.9) for the Knee Society Score. Range of Motion The mean pre-operative and post-operative range of motion is summarized in Table 2. Preoperatively, the mean flexion contracture was 4.5° (mean ± SD 4.6°) for the NexGen LPS Group and 4.7° (mean ± SD 5.2°) in the NexGen LPS-Flex Group. At two years the mean flexion contracture in the NexGen LPS-Flex group was 0.3° (mean ± SD 2.9°), and 0.4° (mean ± SD 2.3°) in the NexGen LPS Group. The flexion preoperatively in the NexGen LPS Group was 114.7° (mean ± SD 11.0°) and 113° (mean ± SD 11.2°) in the NexGen LPS Flex Group. At two-year follow up, the mean postoperative flexion in the standard group was 121.0° (mean ± SD 9.7) and 120.9° (mean ± SD 10.4°) in the high flexion group. There was no significant difference between the two groups with regard to flexion contracture preoperatively (P = 1.000) or at the two-year follow up (P = 0.713). There was also no significant difference with regard to flexion between the two groups preoperatively (P = 0.248) and at two-year follow up (P = 0.797). Quality of Life Outcomes The NexGen LPS Group had SF-36 Physical Scores of 32.5 (mean ± SD 8.3) preoperatively and 48.1 (mean ± SD 8.8) at the two-year follow up. The NexGen LPS Flex Group had SF-36 Physical Scores of 33.8 (mean ± SD 9.3) preoperatively and 49.7 (mean ± SD 8.1) at
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Table 2 Comparisons Between LPS and LPS-Flex by CPE.
CPE Name PREOP
6 Weeks
6 Months
1 Year
2 Years
Characteristic SF36 (Mental) SF36 (Physical) Range Of Motion–Flexion Range Of Motion–Extension Weight Records calculated HSS Score Records calculated KSS Score for function Records calculated KSS Assessment score SF36 (Mental) SF36 (Physical) Range Of Motion–Flexion Range Of Motion–Extension Weight Records calculated HSS Score Records calculated KSS Score for function Records calculated KSS Assessment score SF36 (Mental) SF36 (Physical) Range Of Motion–Flexion Range Of Motion–Extension Weight Records calculated HSS Score Records calculated KSS Score for function Records calculated KSS Assessment score SF36 (Mental) SF36 (Physical) Range Of Motion–Flexion Range Of Motion–Extension Weight Records calculated HSS Score Records calculated KSS Score for function Records calculated KSS Assessment score SF36 (Mental) SF36 (Physical) Range Of Motion–Flexion Range Of Motion–Extension Weight Records calculated HSS Score Records calculated KSS Score for function Records calculated KSS Assessment score
the two-year follow up. There was no significant difference in SF-36 Physical Scores between the two groups preoperatively (P = 0.433) or at the two-year follow up (P = 0.126). In the NexGen LPS Group the SF-36 Mental Score was 54.7 (mean ± SD 10.2) preoperatively and 55.5 (mean ± SD 8.3) at the two-year follow up. In the NexGen LPS Flex group the SF-36 Mental Score was 55.2 (mean ± SD 10.5) preoperatively and 56.1 (mean ± SD 7.4) at the two-year follow up visit. There was no significant difference in SF-36 Mental Scores between the two groups preoperatively (P = 0.693) or at two-year follow up (P = 0.734). Radiographic Evaluation There were no significant differences between groups with regard to the position of the femoral and tibial components in the coronal and sagittal planes or varus and valgus alignment of the knee. There were also no significant differences between the patellar angle (the angle between a line along the patellar cut surface and a line joining the most proximal margins of the femoral condyle of the component on the skyline radiographs), the amount of tibial surface area covered by the implants, or the mean level of the joint line. In the high flexion group, two patients had a radiolucency in the patella, four patients had a femoral radiolucency, and four patients had a tibial radiolucency at two-year follow-up. These radiographic findings were considered normal and were not progressive radiolucencies. In the standard group, one patient had a radiolucency in the patella, five patients had a femoral radiolucency, and four patients had a tibial radiolucency at
LPS-FLEX (n = 138) 55.2 ± 10.5 33.8 ± 9.3 113.0 ± 11.2 4.7 ± 5.2 190.2 ± 32.9 62.8 ± 10.5 57.3 ± 18.8 39.7 ± 15.5 52.1 ± 10.1 37.6 ± 8.9 106.9 ± 15.9 3.9 ± 5.0 186.2 ± 34.1 70.8 ± 11.9 57.6 ± 21.2 74.4 ± 18.2 55.9 ± 8.4 46.6 ± 10.0 119.3 ± 10.4 1.8 ± 4.1 187.9 ± 35.0 83.0 ± 11.4 81.1 ± 18.9 83.2 ± 15.8 54.4 ± 9.3 48.4 ± 9.2 120.6 ± 10.6 0.6 ± 3.0 190.4 ± 35.1 86.3 ± 10.4 83.0 ± 21.4 86.3 ± 14.6 56.1 ± 7.4 49.7 ± 8.1 120.9 ± 10.4 0.3 ± 2.9 192.2 ± 32.7 88.9 ± 7.6 85.6 ± 17.7 89.8 ± 9.9
(134) (134) (138) (138) (138) (138) (138) (138) (132) (127) (138) (138) (138) (135) (138) (135) (131) (126) (132) (132) (131) (132) (132) (132) (127) (122) (134) (134) (133) (131) (131) (132) (118) (118) (119) (119) (120) (117) (120) (118)
STD (n = 140) 54.7 ± 10.2 32.5 ± 8.3 114.7 ± 11.0 4.5 ± 4.6 192.3 ± 41.2 62.3 ± 10.3 55.7 ± 18.4 39.2 ± 16.0 53.8 ± 9.9 37.5 ± 9.1 110.7 ± 11.3 4.0 ± 5.0 189.0 ± 39.1 72.6 ± 11.5 59.6 ± 19.4 74.8 ± 18.0 54.8 ± 8.1 46.7 ± 9.4 120.2 ± 9.4 1.8 ± 3.9 192.3 ± 38.7 84.3 ± 9.8 81.1 ± 19.3 85.7 ± 14.4 54.6 ± 8.2 48.0 ± 9.1 122.2 ± 9.4 0.9 ± 3.0 193.5 ± 40.5 86.8 ± 9.5 83.1 ± 18.5 87.9 ± 13.5 55.5 ± 8.3 48.1 ± 8.8 121.0 ± 9.7 0.4 ± 2.3 195.1 ± 39.8 87.3 ± 8.8 83.0 ± 19.1 87.7 ± 12.7
(138) (136) (140) (140) (140) (140) (140) (140) (132) (126) (137) (137) (137) (136) (136) (136) (133) (129) (137) (137) (137) (137) (137) (137) (130) (126) (134) (134) (134) (133) (134) (133) (116) (113) (123) (123) (123) (122) (122) (122)
P Value 0.693 0.433 0.248 1.000 0.801 0.709 0.490 0.976 0.093* 0.972 0.068* 0.856 0.790 0.247 0.684 0.895 0.132 0.772 0.302 0.916 0.467 0.554 0.912 0.309 0.889 0.495 0.240 0.687 0.550 0.990 0.521 0.278 0.734 0.126 0.797 0.713 0.847 0.235 0.280 0.349
two-year follow-up. These findings were also considered normal and were not progressive radiolucencies. There were no statistically significant differences regarding incidence of radiolucency between the groups at two years. Complications The complication rate was low in both groups. Five patients in the NexGen LPS Flex Group and one patient in the standard group developed arthrofibrosis requiring manipulation under anesthesia approximately ten weeks after the index procedure. Afterwards with aggressive physiotherapy all patients achieved a functional range of motion. One patient in the high flexion group sustained a postoperative patellar fracture without extensor mechanism disruption treated conservatively. There were one superficial infection and one deep vein thrombosis in the high flexion group. Discussion The NexGen LPS-Flex Total Knee system (Zimmer, Warsaw IN) was introduced to improve flexion, increase contact area, and improve clinical outcomes. This prosthesis has three principle design modifications compared to the LPS standard system. Firstly, to address potential point loading of the posterior femoral condyle on the polyethylene liner at flexion angles of up to 155°, the posterior femoral condyles were extended by 1 mm and the condylar radii extended to provide larger tibio-femoral contact area in high flexion
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Fig. 1. Diagram of a cruciate retaining standard total knee arthroplasty compared to high flexion total knee arthroplasty design at 155° of flexion. This figure is reproduced with permission from Zimmer (Warsaw, Indiana).
(Fig. 1). The outside A/P dimension of the component is increased by 1 mm as a result of these modifications. Secondly, an increase in cam height was made. This greater jump height is to prevent tibio-femoral disassociation during flexion from 120° to 155° (Fig. 2). In some posterior stabilized knees, as the knee goes into deeper flexion, the cam on the femoral component begins to move superiorly on the spine of the tibial articular surface. To address this, the shape of the cam on the LPS-Flex femoral component has been modified to contact the spine more inferiorly and thereby provide a greater jump height at flexion angles greater than 130°. The third modification is a recess in the anterior polyethylene to minimize extensor mechanism impingement in high flexion.
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Multiple investigations with outcome measures evaluating the effectiveness of high flexion total knee arthroplasty designs have not shown significant difference to its standard flexion counterparts. Kim et al [10] published a prospective randomized trial on bilateral total knee arthroplasty in which high flexion designs were compared to standard posterior stabilized designs. 250 patients with bilateral total knee arthroplasty one being high flexion and one being standard were compared using questionnaires, knee scoring systems, clinical, and radiographic examinations. The authors found no significant clinical differences between groups. Seon et al [11] provided a study of 50 knees randomized to high flexion or standard design. These cruciate retaining high flexion implants had femoral alterations with 2 mm of extended femoral condyle as well as polyethylene modifications. The patients were followed prospectively for two years and had similar range of motion, function, and knee ratings. They suggested that high flexion design alone did not improve clinical outcome after total knee arthroplasty. McCalden et al [12] compared high flexion total knee arthroplasty design to standard design in a study of 100 patients. 50 patients received a high flexion polyethylene design and the group received standard polyethylene insert. After 2.7 years there was no difference of range of motion between implant designs. Conversely, Gupta et al [13] performed a matched pair study comparing 50 high flexion mobile bearing knees to 50 standard mobile bearing knees. The high flexion group achieved a statistically significant greater mean increase in active range of motion (17° vs. 6°) than the standard group. Also, patients who had decreased preoperative range of motion (b120°) had a greater increase in post operative range of motion when using the high flexion prosthesis. They concluded that greater range of motion could be achieved with implant design alone, irrespective of preoperative motion. Bin et al [14] compared 180 total knee arthroplasties prospectively with 12month follow up. They showed significantly greater average knee range of motion at one year in patients receiving high flexion prostheses vs. standard prostheses. Furthermore, patients with preoperative flexion less than 90° had greater benefit from the high flexion prosthesis with regard to post-operative motion. Minoda et al [15] prospectively randomized 171 patients with 181 cruciate retaining total knee arthroplasties. The high flexion group and standard group were followed prospectively for one year. There were no differences in knee outcome scores or radiographic data, but the high flexion group had an increased final range of motion compared to the standard group. Early aseptic loosening as a consequence of high flexion designs has also been reported in the literature. Han et al [8], in a series of 47 high flexion knees had a 38% incidence of aseptic loosening at
Fig. 2. Diagram of difference in cam height and theoretical increased jump distance in standard total knee prosthesis vs. high flexion prosthesis. This figure is reproduced from Zimmer (Warsaw, Indiana).
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32 months of follow up. 15 patients required revision total knee arthroplasty at a mean of 23 months. They found that patients with aseptic loosening had statistically significant greater range of motion and ability to squat, kneel, and sit cross-legged. They concluded that the aseptic loosening was a consequence of deep flexion where the femoral component remained on the posterior edge of the polyethylene liner and caused asymmetrical loading in the medial and lateral compartments. Zelle et al [9] examined this conclusion by developing a 3D finite knee model to examine stresses on the femoral component cement–implant interface at varying degrees of flexion. They reported critical stresses on femoral component fixation at increased flexion angles from 120° to 145°, and concluded there is an increased risk of fixation failure at higher flexion angles. In contrast to the work by Han et al [8], there were no patients in this study with clinical or radiographic evidence of aseptic loosening at two-year follow-up. The femoral and tibial radiolucent lines that were discovered in both the high flexion and standard groups did not show progression, and were not considered significant. Furthermore, there was no statistical difference between groups with regard to the incidence of radiolucent findings. The fact that no patient had aseptic loosening in our study is consistent with current literature [10–16]. This reinforces the notion that the high incidence of aseptic loosening reported by Han et al is an outlier, and may be related to surgical technique rather than prosthetic design. This study attempts to standardize pre-operative and postoperative factors between standard and high flexion groups to determine whether modifications to the NexGen LPS alone would influence post-operative range of motion and outcome measures. In this study there was no difference between the two groups with regard to range of motion, knee scores, clinical or radiographic data. These findings support other previous literature that high flexion total knee arthroplasty, as an independent variable, does not correlate with improved clinical outcomes or improved postoperative range of motion [10–12]. Therefore we believe that other characteristics, such as preoperative motion, flexion space balancing, limb girth and length, and patient’s motivation to participate with physical therapy are the determinants of postoperative knee motion. These findings are consistent with previous publications on post-operative range of motion [17]. There are several strengths to the study. First, by evaluating patients treated by multiple surgeons and centers, it provides clinically relevant information that can be readily applied to a broader range of knee arthroplasty patients regardless of characteristics unique to the center they are treated in. Second, the patients were randomized and data collected prospectively eliminating bias associated with retrospective analysis. Third, the pooled multicenter data allow for increased power decreasing the chances of beta error. The present study had some limitations. The data collected reports outcomes at two years which represent early outcomes for total knee arthroplasty. Long term conclusions cannot be made based on this early data. Also, we did not assess interobserver variability in the radiographic measurements. However, we did determine intraobserver agreement of radiographic measurements [18]. At a minimum of two years, high-flexion implant designs alone do not provide a significant improvement over conventional total knee
arthroplasty in this multicenter trial. Further investigation is required in the future to determine long term consequences of high flexion design changes with regard to loosening, osteolysis, and function. Furthermore, continued study of revision of these implants is imperative as it may affect bone stock and gap balancing in revision situations [19–25]. References 1. Ritter MA, Campbell ED. Effect of range of motion on the success of a total knee arthroplasty. J Arthroplasty 1987;2:95. 2. Bellemans J, Banks S, Victor J, et al. Fluoroscopic analysis of the kinematics of deep flexion in total knee arthroplasty. Influence of posterior condylar offset. J Bone Joint Surg Br 2002;84:50. 3. Anouchi YS, McShane M, Kelly Jr F, et al. Range of motion in total knee replacement. Clin Orthop Relat Res 1996;331:87. 4. Hartford JM, Banit D, Hall K, et al. Radiographic analysis of low contact stress meniscal bearing total knee replacements. J Bone Joint Surg Am 2001;83:229. 5. Li G, Schule SL, Zyontz SJ, et al. In: Callaghan JJ, Rosenberg AG, Rubash HE, Simonian PT, Wickiowicz TL, editors. The adult knee. Philadelphia: Lippincott Williams and Wilkins; 2003. p. 1233. 6. Gandhi R, Tso P, Davey JR, et al. High flexion implants in primary total knee arthroplasty: a meta-analysis. Knee 2009;16:14. 7. Luo S, Su W, Zhao J, et al. High-flexion vs conventional prostheses total knee arthroplasty: a meta-analysis. J Arthroplasty 2010;09:008. 8. Han HS, Kang SB, Yoon KS. High incidence of loosening of the femoral component in legacy posterior stabilised-flex total knee replacement. J Bone Joint Surg Br 2007;89(11):1457. 9. Zelle J, Janssen D, Van Eijden J, et al. Does high-flexion total knee arthroplasty promote early loosening of the femoral component?J Orthop Res 2011;29(7):976. http://dx.doi.org/10.1002/jor.21363 [Epub 2011 Feb 9]. 10. Kim YH, Choi Y, Kwon OR, et al. Functional outcome and range of motion of highflexion posterior cruciate-retaining and high-flexion posterior cruciate-substituting total knee prostheses. A prospective, randomized study. J Bone Joint Surg Am 2009;91:753. 11. Seon JK, Park SJ, Lee KB, et al. Range of motion in total knee arthroplasty: a prospective comparison of high-flexion and standard cruciate-retaining designs. J Bone Joint Surg Am 2009;91:672. 12. McCalden RW, MacDonald SJ, Bourne RB, et al. A randomized controlled trial comparing "high-flex" vs "standard" posterior cruciate substituting polyethylene tibial inserts in total knee arthroplasty. J Arthroplasty 2009;24(6 Suppl):33. 13. Gupta SK, Ranawat AS, Shah V, et al. The P.F.C.Sigma RP-F TKA designed for improved performance: a matched-pair study. Orthopedics 2006;29(9 Suppl):S49. 14. Bin SI, Nam TS. Early results of high-flex total knee arthroplasty: comparison study at 1 year after surgery. Knee Surg Sports Traumatol Arthrosc 2007;15:350. 15. Minoda Y, Aihara M, Sakawa A, et al. Range of motion of standard and high-flexion cruciate retaining total knee prostheses. J Arthroplasty 2009;24:674. 16. Lee BS, Chung JW, Kim JM, et al. High-flexion prosthesis improves function of TKA in Asian patients without decreasing early survivorship. Clin Orthop Relat Res 2013;471(5):1504. http://dx.doi.org/10.1007/s11999-012-2661-4. 17. Ritter MA, Harty LD, Davis KE, et al. Predicting range of motion after total knee arthroplasty: clustering, log-linear regression, and regression tree analysis. J Bone Joint Surg Am 2003;85:1278. 18. Bach CM, Biedermann R, Goebel G, et al. Reproducible assessment of radiolucent lines in total knee arthroplasty. Clin Orthop Relat Res 2005;434:183. 19. Scranton Jr PE. Management of knee pain and stiffness after total knee arthroplasty. J Arthroplasty 2001;16:428. 20. Shoji H, Yoshino S, Komagamine M. Improved range of motion with the Y/S total knee arthroplasty system. Clin Orthop 1987;218:150. 21. Daluga D, Jr LombardiAV, Mallory TH, et al. Knee manipulation following total knee arthroplasty: analysis of prognostic variables. J Arthroplasty 1991;6:119. 22. Mauerhan DR, Mokris JG, Ly A, et al. Relationship between length of stay and manipulation rate after total knee arthroplasty. J Arthroplasty 1998;13:896. 23. Kettelkamp D. Gait characteristics of the knee: normal, abnormal, and post reconstruction. American Academy of Orthopaedic Surgeons Symposium on Reconstructive Surgery of the Knee. St. Louis, MO: CV Mosby; 1978. p. 47. 24. Laubenthal KN, Smidt GL, Kettelkamp DB. A quantitative analysis of knee motion during activities of daily living. Phys Ther 1972;52:34. 25. Ritter MA, Stringer EA. Predictive range of motion after total knee replacement. Clin Orthop 1979;143:115.
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The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Clinical Outcomes in High Flexion Total Knee Arthroplasty Were Not Superior to Standard Posterior Stabilized Total Knee Arthroplasty. A Multicenter, Prospective, Randomized Study George N. Guild III, MD a, Sameh A. Labib, MD b a b
Insall Scott Kelly Institute for Orthopaedics and Sports Medicine, Lenox Hill Hospital, New York, New York Emory Sports Medicine Center, Emory University, Atlanta, Georgia
a r t i c l e
i n f o
Article history: Received 6 March 2013 Accepted 24 July 2013 Keywords: total knee arthroplasty high flexion range of motion
a b s t r a c t High flexion prostheses have been introduced to achieve high flexion and improve clinical outcomes. Controversy exists in the literature regarding outcomes of high flexion vs. standard implants. This multicenter study compares outcomes in patients receiving a high flexion prosthesis vs. standard prosthesis. 278 high flexion and standard knee prostheses were used. Patients were followed for two years and evaluated prospectively. The mean HSS was 87.3 for the standard group and 88.9 for the flexion group. At two-year follow up the standard prosthesis group had mean flexion of 121° and the high flexion group had mean flexion 120°. No knee had aseptic loosening, infection, or osteolysis. At two-year follow up, there were no significant differences in range of motion, clinical outcome, or radiographic evaluation. Pre-operative motion and functional status have greater impact on clinical outcome than implant alone. © 2014 Elsevier Inc. All rights reserved.
Range of motion in total knee arthroplasty is a key determining factor in a patient’s overall functional outcome [1]. The fact that most knees do not flex more than 120° after surgery has been studied extensively, but no one theory sufficiently explains this phenomenon [2–5]. To improve deep flexion after total knee arthroplasty high flexion designs have been developed in the last decade. The NexGen LPS Flex total knee system (Zimmer, Warsaw IN) was designed to achieve high knee flexion, increase surface area articulation, and improve patient outcomes. Compared to the standard, the NexGen LPS Flex has 3 principle design modifications: extension of the posterior femoral condyles and posterior condylar radii to increase contact area, an increased cam height, and cut out in the polyethylene insert to prevent patellar tendon impingement. Theoretically these design modifications may lead to better postoperative range of motion, increase longevity, and provide improved clinical outcomes. However, there are conflicting reports in the literature on the early results of high flexion prosthesis. A previous meta-analysis including six studies did show a significant difference in favor of the high flexion design but, only two of those studies were randomized controlled trials [6]. In another systematic review no difference was found between the prostheses but, data synthesis and quantitative analysis were not performed [7]. Several authors have also reported on early increased loosening at high The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2013.07.035. Reprint requests: George N. Guild III, MD, 1007 Lexington Ave Apt. 2R, New York, NY 10021. 0883-5403/2903-0017$36.00/0 – see front matter © 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2013.07.035
flexion angles in the high-flexion prosthesis [8,9]. Because of this conflicting data regarding motion, loosening, and outcomes from individual centers, we performed a pooled data multicenter prospective randomized trial to assess differences in pain, functioning, aseptic loosening, and range of motion in the NexGen LPS and NexGen LPSFlex total knee systems. Materials and Methods Demographics Between 2002 and 2007, 278 total knee arthroplasties were performed at nine clinical centers associated with a university. The study was approved by the institutional review board and informed consent was obtained. Randomization of the total knee prosthesis, NexGen LPS standard or LPS-High Flexion (Zimmer, Warsaw IN), was determined on a sequential pool on the basis of a table of random numbers. The patient demographics are summarized in Table 1. The mean age of the patients at the time of operation was 65 years (range 43–80). 140 patients were men and 138 were women. 124 patients had previous knee surgery (25 open meniscectomies, 68 arthroscopic meniscectomies, 24 arthroscopies, 2 arthroscopic loose body removal, 2 prepatella bursa removals, 1 popliteal cyst excision, 1 MCL reconstruction, 1 PCL reconstruction) The preoperative diagnosis for 267 patients was osteoarthritis, 3 had post-traumatic arthritis, 2 inflammatory arthritis, 1 avascular necrosis, and 5 had rheumatoid arthritis. The mean patient height and standard deviation were 66.8 ± 4 inches and the mean weight
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Table 1 Comparisons Between LPS and LPS-Flex. Characteristic Gender Patient Age Weight Patient Height (Inch) Preoperative Diagnosis
Female Male
OSTEOARTHRITIS RHEUMATOID ARTHRITIS POST-TRAUMATIC ARTHRITIS INFLAMMATORY ARTHRITIS AVASCULAR NECROSIS OTHER
Overall (n = 278)
LPS-FLEX (n = 138)
138/278 (49.6%) 140/278 (50.4%) 64.4 ± 8.3 (278)
71/138 67/138 64.8 ± 8.5 190.2 ± 32.9 66.3 ± 4.1 131/137 3/137 2/137 0/137 0/137 1/137
66.8 ± 4.0 (278) 265/277 (95.7%) 5/277 (1.8%) 3/277 (1.1%) 2/277 (0.7%) 1/277 (0.4%) 1/277 (0.4%)
and standard deviation were 190.2 ± 32.9 lb for the flex group and 192.3 ± 41.2 for the standard group. Surgical Technique The operative procedures were performed at nine separate centers with some surgical technique differences with regard to implantation of the total knee arthroplasties however; they did share the following general characteristics. All procedures were performed via a midline skin incision approximately ten centimeters with a medial parapatellar arthrotomy. The cruciate ligaments were sacrificed in all patients. The magnitude and angles of the bony resections were standardized across treatment groups. The distal femoral resection was made with an intramedullary guide to resect 10 mm of bone from the most prominent femoral condyle at an angle of 5° of valgus. The tibial resection was made using an extramedullary guide with the goal of producing a neutral cut in the coronal plane and 7° of posterior slope in the sagittal plane. The anterior, posterior, and Chamfer cuts were made with a posterior femoral condylar referencing guide in 3° of external rotation. In the NexGen LPS-Flex group, 2 additional mm of posterior femoral condylar bone was resected compared to the NexGen LPS group. Posterior condylar osteophytes were resected in all patients. Ligament balancing was aided with the use of spacer blocks with the goal of creating symmetrical gaps of equal magnitude in flexion and extension. Superficial MCL release was required in 7 patients including four in the high flexion group and three in standard group. The amount of bone removed during patellar resection was equal to or slightly greater than the thickness of the patellar component. All implants were cemented. The capsule was closed in 30° of flexion in all patients. Rehabilitation Starting on the second post-operative day, the patients used a continuous passive motion machine applied for at least 6 h per day. Also on post-operative day two, active and passive range of motion was initiated, as well as ambulation with crutches or a walker once a day with physical therapy supervision. The patients used crutches or a walker with full weight bearing for six weeks and used a cane as needed subsequently. Clinical Evaluation Clinical and radiographic evaluations were made pre-operatively, 6 weeks post-operatively, 6 months, one year, and two years. Each knee was rated pre-operatively and post-operatively by the systems of the Knee Society and the Hospital for Special Surgery. Patients also completed the Short Form 36 (SF-36) questionnaire. Active range of motion was determined preoperatively and postoperatively with a 12-in goniometer at 6 weeks, 6 months, 1 year,
(51.4%) (48.6%) (138) (138) (138) (95.6%) (2.2%) (1.5%) (0.0%) (0.0%) (0.7%)
STD (n = 140) 67/140 (47.9%) 73/140 (52.1%) 64.0 ± 8.1 (140) 192.3 ± 41.2 (140) 67.3 ± 3.8 (140) 134/140 (95.7%) 2/140 (1.4%) 1/140 (0.7%) 2/140 (1.4%) 1/140 (0.7%) 0/140 (0.0%)
P Value 0.631 0.348 0.801 0.052* 0.633
and two years. Clinicians were blinded with regard to which total knee prosthesis was implanted. Radiographic evaluations were made pre-operatively and postoperatively by obtaining AP, Lateral, and skyline views. Evaluations were made at 6 weeks, 6 months, 1 year, and 2 years. Assessments were made based on limb alignment and component position. Radiolucencies and bone loss were also noted on AP, Lateral, and sunrise views. Skyline views were also examined for patellar tilt, subluxation, and dislocation. Results Clinical Outcomes Knee Score The pre-operative and post-operative knee scores are summarized in Table 2. The Hospital for Special Surgery (HSS) and Knee Society Scores (KSS) did not differ significantly between the two groups pre-operatively (P = 0.790 and P = 0.490, respectively) or postoperatively (P = 0.9177 and P = 0.2313, respectively). The mean pre-operative HSS score for the standard knee prosthesis group was 62.3 (mean ± SD 10.3) and 62.8 (mean ± SD 10.5) in the highflexion group. In the NexGen LPS group, the mean postoperative HSS score was 87.3 (mean ± SD 12.7) and 87.7 (mean ± SD 12.7) for the Knee Society Score. In the NexGen LPS Flex Group, the mean postoperative HSS score was 88.9 (mean ± SD 7.6) and 89.8. (mean ± SD 9.9) for the Knee Society Score. Range of Motion The mean pre-operative and post-operative range of motion is summarized in Table 2. Preoperatively, the mean flexion contracture was 4.5° (mean ± SD 4.6°) for the NexGen LPS Group and 4.7° (mean ± SD 5.2°) in the NexGen LPS-Flex Group. At two years the mean flexion contracture in the NexGen LPS-Flex group was 0.3° (mean ± SD 2.9°), and 0.4° (mean ± SD 2.3°) in the NexGen LPS Group. The flexion preoperatively in the NexGen LPS Group was 114.7° (mean ± SD 11.0°) and 113° (mean ± SD 11.2°) in the NexGen LPS Flex Group. At two-year follow up, the mean postoperative flexion in the standard group was 121.0° (mean ± SD 9.7) and 120.9° (mean ± SD 10.4°) in the high flexion group. There was no significant difference between the two groups with regard to flexion contracture preoperatively (P = 1.000) or at the two-year follow up (P = 0.713). There was also no significant difference with regard to flexion between the two groups preoperatively (P = 0.248) and at two-year follow up (P = 0.797). Quality of Life Outcomes The NexGen LPS Group had SF-36 Physical Scores of 32.5 (mean ± SD 8.3) preoperatively and 48.1 (mean ± SD 8.8) at the two-year follow up. The NexGen LPS Flex Group had SF-36 Physical Scores of 33.8 (mean ± SD 9.3) preoperatively and 49.7 (mean ± SD 8.1) at
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Table 2 Comparisons Between LPS and LPS-Flex by CPE.
CPE Name PREOP
6 Weeks
6 Months
1 Year
2 Years
Characteristic SF36 (Mental) SF36 (Physical) Range Of Motion–Flexion Range Of Motion–Extension Weight Records calculated HSS Score Records calculated KSS Score for function Records calculated KSS Assessment score SF36 (Mental) SF36 (Physical) Range Of Motion–Flexion Range Of Motion–Extension Weight Records calculated HSS Score Records calculated KSS Score for function Records calculated KSS Assessment score SF36 (Mental) SF36 (Physical) Range Of Motion–Flexion Range Of Motion–Extension Weight Records calculated HSS Score Records calculated KSS Score for function Records calculated KSS Assessment score SF36 (Mental) SF36 (Physical) Range Of Motion–Flexion Range Of Motion–Extension Weight Records calculated HSS Score Records calculated KSS Score for function Records calculated KSS Assessment score SF36 (Mental) SF36 (Physical) Range Of Motion–Flexion Range Of Motion–Extension Weight Records calculated HSS Score Records calculated KSS Score for function Records calculated KSS Assessment score
the two-year follow up. There was no significant difference in SF-36 Physical Scores between the two groups preoperatively (P = 0.433) or at the two-year follow up (P = 0.126). In the NexGen LPS Group the SF-36 Mental Score was 54.7 (mean ± SD 10.2) preoperatively and 55.5 (mean ± SD 8.3) at the two-year follow up. In the NexGen LPS Flex group the SF-36 Mental Score was 55.2 (mean ± SD 10.5) preoperatively and 56.1 (mean ± SD 7.4) at the two-year follow up visit. There was no significant difference in SF-36 Mental Scores between the two groups preoperatively (P = 0.693) or at two-year follow up (P = 0.734). Radiographic Evaluation There were no significant differences between groups with regard to the position of the femoral and tibial components in the coronal and sagittal planes or varus and valgus alignment of the knee. There were also no significant differences between the patellar angle (the angle between a line along the patellar cut surface and a line joining the most proximal margins of the femoral condyle of the component on the skyline radiographs), the amount of tibial surface area covered by the implants, or the mean level of the joint line. In the high flexion group, two patients had a radiolucency in the patella, four patients had a femoral radiolucency, and four patients had a tibial radiolucency at two-year follow-up. These radiographic findings were considered normal and were not progressive radiolucencies. In the standard group, one patient had a radiolucency in the patella, five patients had a femoral radiolucency, and four patients had a tibial radiolucency at
LPS-FLEX (n = 138) 55.2 ± 10.5 33.8 ± 9.3 113.0 ± 11.2 4.7 ± 5.2 190.2 ± 32.9 62.8 ± 10.5 57.3 ± 18.8 39.7 ± 15.5 52.1 ± 10.1 37.6 ± 8.9 106.9 ± 15.9 3.9 ± 5.0 186.2 ± 34.1 70.8 ± 11.9 57.6 ± 21.2 74.4 ± 18.2 55.9 ± 8.4 46.6 ± 10.0 119.3 ± 10.4 1.8 ± 4.1 187.9 ± 35.0 83.0 ± 11.4 81.1 ± 18.9 83.2 ± 15.8 54.4 ± 9.3 48.4 ± 9.2 120.6 ± 10.6 0.6 ± 3.0 190.4 ± 35.1 86.3 ± 10.4 83.0 ± 21.4 86.3 ± 14.6 56.1 ± 7.4 49.7 ± 8.1 120.9 ± 10.4 0.3 ± 2.9 192.2 ± 32.7 88.9 ± 7.6 85.6 ± 17.7 89.8 ± 9.9
(134) (134) (138) (138) (138) (138) (138) (138) (132) (127) (138) (138) (138) (135) (138) (135) (131) (126) (132) (132) (131) (132) (132) (132) (127) (122) (134) (134) (133) (131) (131) (132) (118) (118) (119) (119) (120) (117) (120) (118)
STD (n = 140) 54.7 ± 10.2 32.5 ± 8.3 114.7 ± 11.0 4.5 ± 4.6 192.3 ± 41.2 62.3 ± 10.3 55.7 ± 18.4 39.2 ± 16.0 53.8 ± 9.9 37.5 ± 9.1 110.7 ± 11.3 4.0 ± 5.0 189.0 ± 39.1 72.6 ± 11.5 59.6 ± 19.4 74.8 ± 18.0 54.8 ± 8.1 46.7 ± 9.4 120.2 ± 9.4 1.8 ± 3.9 192.3 ± 38.7 84.3 ± 9.8 81.1 ± 19.3 85.7 ± 14.4 54.6 ± 8.2 48.0 ± 9.1 122.2 ± 9.4 0.9 ± 3.0 193.5 ± 40.5 86.8 ± 9.5 83.1 ± 18.5 87.9 ± 13.5 55.5 ± 8.3 48.1 ± 8.8 121.0 ± 9.7 0.4 ± 2.3 195.1 ± 39.8 87.3 ± 8.8 83.0 ± 19.1 87.7 ± 12.7
(138) (136) (140) (140) (140) (140) (140) (140) (132) (126) (137) (137) (137) (136) (136) (136) (133) (129) (137) (137) (137) (137) (137) (137) (130) (126) (134) (134) (134) (133) (134) (133) (116) (113) (123) (123) (123) (122) (122) (122)
P Value 0.693 0.433 0.248 1.000 0.801 0.709 0.490 0.976 0.093* 0.972 0.068* 0.856 0.790 0.247 0.684 0.895 0.132 0.772 0.302 0.916 0.467 0.554 0.912 0.309 0.889 0.495 0.240 0.687 0.550 0.990 0.521 0.278 0.734 0.126 0.797 0.713 0.847 0.235 0.280 0.349
two-year follow-up. These findings were also considered normal and were not progressive radiolucencies. There were no statistically significant differences regarding incidence of radiolucency between the groups at two years. Complications The complication rate was low in both groups. Five patients in the NexGen LPS Flex Group and one patient in the standard group developed arthrofibrosis requiring manipulation under anesthesia approximately ten weeks after the index procedure. Afterwards with aggressive physiotherapy all patients achieved a functional range of motion. One patient in the high flexion group sustained a postoperative patellar fracture without extensor mechanism disruption treated conservatively. There were one superficial infection and one deep vein thrombosis in the high flexion group. Discussion The NexGen LPS-Flex Total Knee system (Zimmer, Warsaw IN) was introduced to improve flexion, increase contact area, and improve clinical outcomes. This prosthesis has three principle design modifications compared to the LPS standard system. Firstly, to address potential point loading of the posterior femoral condyle on the polyethylene liner at flexion angles of up to 155°, the posterior femoral condyles were extended by 1 mm and the condylar radii extended to provide larger tibio-femoral contact area in high flexion
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Fig. 1. Diagram of a cruciate retaining standard total knee arthroplasty compared to high flexion total knee arthroplasty design at 155° of flexion. This figure is reproduced with permission from Zimmer (Warsaw, Indiana).
(Fig. 1). The outside A/P dimension of the component is increased by 1 mm as a result of these modifications. Secondly, an increase in cam height was made. This greater jump height is to prevent tibio-femoral disassociation during flexion from 120° to 155° (Fig. 2). In some posterior stabilized knees, as the knee goes into deeper flexion, the cam on the femoral component begins to move superiorly on the spine of the tibial articular surface. To address this, the shape of the cam on the LPS-Flex femoral component has been modified to contact the spine more inferiorly and thereby provide a greater jump height at flexion angles greater than 130°. The third modification is a recess in the anterior polyethylene to minimize extensor mechanism impingement in high flexion.
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Multiple investigations with outcome measures evaluating the effectiveness of high flexion total knee arthroplasty designs have not shown significant difference to its standard flexion counterparts. Kim et al [10] published a prospective randomized trial on bilateral total knee arthroplasty in which high flexion designs were compared to standard posterior stabilized designs. 250 patients with bilateral total knee arthroplasty one being high flexion and one being standard were compared using questionnaires, knee scoring systems, clinical, and radiographic examinations. The authors found no significant clinical differences between groups. Seon et al [11] provided a study of 50 knees randomized to high flexion or standard design. These cruciate retaining high flexion implants had femoral alterations with 2 mm of extended femoral condyle as well as polyethylene modifications. The patients were followed prospectively for two years and had similar range of motion, function, and knee ratings. They suggested that high flexion design alone did not improve clinical outcome after total knee arthroplasty. McCalden et al [12] compared high flexion total knee arthroplasty design to standard design in a study of 100 patients. 50 patients received a high flexion polyethylene design and the group received standard polyethylene insert. After 2.7 years there was no difference of range of motion between implant designs. Conversely, Gupta et al [13] performed a matched pair study comparing 50 high flexion mobile bearing knees to 50 standard mobile bearing knees. The high flexion group achieved a statistically significant greater mean increase in active range of motion (17° vs. 6°) than the standard group. Also, patients who had decreased preoperative range of motion (b120°) had a greater increase in post operative range of motion when using the high flexion prosthesis. They concluded that greater range of motion could be achieved with implant design alone, irrespective of preoperative motion. Bin et al [14] compared 180 total knee arthroplasties prospectively with 12month follow up. They showed significantly greater average knee range of motion at one year in patients receiving high flexion prostheses vs. standard prostheses. Furthermore, patients with preoperative flexion less than 90° had greater benefit from the high flexion prosthesis with regard to post-operative motion. Minoda et al [15] prospectively randomized 171 patients with 181 cruciate retaining total knee arthroplasties. The high flexion group and standard group were followed prospectively for one year. There were no differences in knee outcome scores or radiographic data, but the high flexion group had an increased final range of motion compared to the standard group. Early aseptic loosening as a consequence of high flexion designs has also been reported in the literature. Han et al [8], in a series of 47 high flexion knees had a 38% incidence of aseptic loosening at
Fig. 2. Diagram of difference in cam height and theoretical increased jump distance in standard total knee prosthesis vs. high flexion prosthesis. This figure is reproduced from Zimmer (Warsaw, Indiana).
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32 months of follow up. 15 patients required revision total knee arthroplasty at a mean of 23 months. They found that patients with aseptic loosening had statistically significant greater range of motion and ability to squat, kneel, and sit cross-legged. They concluded that the aseptic loosening was a consequence of deep flexion where the femoral component remained on the posterior edge of the polyethylene liner and caused asymmetrical loading in the medial and lateral compartments. Zelle et al [9] examined this conclusion by developing a 3D finite knee model to examine stresses on the femoral component cement–implant interface at varying degrees of flexion. They reported critical stresses on femoral component fixation at increased flexion angles from 120° to 145°, and concluded there is an increased risk of fixation failure at higher flexion angles. In contrast to the work by Han et al [8], there were no patients in this study with clinical or radiographic evidence of aseptic loosening at two-year follow-up. The femoral and tibial radiolucent lines that were discovered in both the high flexion and standard groups did not show progression, and were not considered significant. Furthermore, there was no statistical difference between groups with regard to the incidence of radiolucent findings. The fact that no patient had aseptic loosening in our study is consistent with current literature [10–16]. This reinforces the notion that the high incidence of aseptic loosening reported by Han et al is an outlier, and may be related to surgical technique rather than prosthetic design. This study attempts to standardize pre-operative and postoperative factors between standard and high flexion groups to determine whether modifications to the NexGen LPS alone would influence post-operative range of motion and outcome measures. In this study there was no difference between the two groups with regard to range of motion, knee scores, clinical or radiographic data. These findings support other previous literature that high flexion total knee arthroplasty, as an independent variable, does not correlate with improved clinical outcomes or improved postoperative range of motion [10–12]. Therefore we believe that other characteristics, such as preoperative motion, flexion space balancing, limb girth and length, and patient’s motivation to participate with physical therapy are the determinants of postoperative knee motion. These findings are consistent with previous publications on post-operative range of motion [17]. There are several strengths to the study. First, by evaluating patients treated by multiple surgeons and centers, it provides clinically relevant information that can be readily applied to a broader range of knee arthroplasty patients regardless of characteristics unique to the center they are treated in. Second, the patients were randomized and data collected prospectively eliminating bias associated with retrospective analysis. Third, the pooled multicenter data allow for increased power decreasing the chances of beta error. The present study had some limitations. The data collected reports outcomes at two years which represent early outcomes for total knee arthroplasty. Long term conclusions cannot be made based on this early data. Also, we did not assess interobserver variability in the radiographic measurements. However, we did determine intraobserver agreement of radiographic measurements [18]. At a minimum of two years, high-flexion implant designs alone do not provide a significant improvement over conventional total knee
arthroplasty in this multicenter trial. Further investigation is required in the future to determine long term consequences of high flexion design changes with regard to loosening, osteolysis, and function. Furthermore, continued study of revision of these implants is imperative as it may affect bone stock and gap balancing in revision situations [19–25]. References 1. Ritter MA, Campbell ED. Effect of range of motion on the success of a total knee arthroplasty. J Arthroplasty 1987;2:95. 2. Bellemans J, Banks S, Victor J, et al. Fluoroscopic analysis of the kinematics of deep flexion in total knee arthroplasty. Influence of posterior condylar offset. J Bone Joint Surg Br 2002;84:50. 3. Anouchi YS, McShane M, Kelly Jr F, et al. Range of motion in total knee replacement. Clin Orthop Relat Res 1996;331:87. 4. Hartford JM, Banit D, Hall K, et al. Radiographic analysis of low contact stress meniscal bearing total knee replacements. J Bone Joint Surg Am 2001;83:229. 5. Li G, Schule SL, Zyontz SJ, et al. In: Callaghan JJ, Rosenberg AG, Rubash HE, Simonian PT, Wickiowicz TL, editors. The adult knee. Philadelphia: Lippincott Williams and Wilkins; 2003. p. 1233. 6. Gandhi R, Tso P, Davey JR, et al. High flexion implants in primary total knee arthroplasty: a meta-analysis. Knee 2009;16:14. 7. Luo S, Su W, Zhao J, et al. High-flexion vs conventional prostheses total knee arthroplasty: a meta-analysis. J Arthroplasty 2010;09:008. 8. Han HS, Kang SB, Yoon KS. High incidence of loosening of the femoral component in legacy posterior stabilised-flex total knee replacement. J Bone Joint Surg Br 2007;89(11):1457. 9. Zelle J, Janssen D, Van Eijden J, et al. Does high-flexion total knee arthroplasty promote early loosening of the femoral component?J Orthop Res 2011;29(7):976. http://dx.doi.org/10.1002/jor.21363 [Epub 2011 Feb 9]. 10. Kim YH, Choi Y, Kwon OR, et al. Functional outcome and range of motion of highflexion posterior cruciate-retaining and high-flexion posterior cruciate-substituting total knee prostheses. A prospective, randomized study. J Bone Joint Surg Am 2009;91:753. 11. Seon JK, Park SJ, Lee KB, et al. Range of motion in total knee arthroplasty: a prospective comparison of high-flexion and standard cruciate-retaining designs. J Bone Joint Surg Am 2009;91:672. 12. McCalden RW, MacDonald SJ, Bourne RB, et al. A randomized controlled trial comparing "high-flex" vs "standard" posterior cruciate substituting polyethylene tibial inserts in total knee arthroplasty. J Arthroplasty 2009;24(6 Suppl):33. 13. Gupta SK, Ranawat AS, Shah V, et al. The P.F.C.Sigma RP-F TKA designed for improved performance: a matched-pair study. Orthopedics 2006;29(9 Suppl):S49. 14. Bin SI, Nam TS. Early results of high-flex total knee arthroplasty: comparison study at 1 year after surgery. Knee Surg Sports Traumatol Arthrosc 2007;15:350. 15. Minoda Y, Aihara M, Sakawa A, et al. Range of motion of standard and high-flexion cruciate retaining total knee prostheses. J Arthroplasty 2009;24:674. 16. Lee BS, Chung JW, Kim JM, et al. High-flexion prosthesis improves function of TKA in Asian patients without decreasing early survivorship. Clin Orthop Relat Res 2013;471(5):1504. http://dx.doi.org/10.1007/s11999-012-2661-4. 17. Ritter MA, Harty LD, Davis KE, et al. Predicting range of motion after total knee arthroplasty: clustering, log-linear regression, and regression tree analysis. J Bone Joint Surg Am 2003;85:1278. 18. Bach CM, Biedermann R, Goebel G, et al. Reproducible assessment of radiolucent lines in total knee arthroplasty. Clin Orthop Relat Res 2005;434:183. 19. Scranton Jr PE. Management of knee pain and stiffness after total knee arthroplasty. J Arthroplasty 2001;16:428. 20. Shoji H, Yoshino S, Komagamine M. Improved range of motion with the Y/S total knee arthroplasty system. Clin Orthop 1987;218:150. 21. Daluga D, Jr LombardiAV, Mallory TH, et al. Knee manipulation following total knee arthroplasty: analysis of prognostic variables. J Arthroplasty 1991;6:119. 22. Mauerhan DR, Mokris JG, Ly A, et al. Relationship between length of stay and manipulation rate after total knee arthroplasty. J Arthroplasty 1998;13:896. 23. Kettelkamp D. Gait characteristics of the knee: normal, abnormal, and post reconstruction. American Academy of Orthopaedic Surgeons Symposium on Reconstructive Surgery of the Knee. St. Louis, MO: CV Mosby; 1978. p. 47. 24. Laubenthal KN, Smidt GL, Kettelkamp DB. A quantitative analysis of knee motion during activities of daily living. Phys Ther 1972;52:34. 25. Ritter MA, Stringer EA. Predictive range of motion after total knee replacement. Clin Orthop 1979;143:115.
