Comparison of Range of Motion of High-Flexion Prosthesis and Mobile-Bearing Prosthesis in Total Knee Arthroplasty

ByJong Keun Seon, MD; Eun Kyoo Song, MD; Jun Yub Lee, MD
ORTHOPEDICS 2005; 28:1247


October 2005

Abstract

The purpose of this study was to compare the range of motion (ROM) of conventional total knee arthroplasty (TKA) using high-flexion, posterior cruciate ligament (PCL) stabilized prostheses and the ROM of conventional knee arthroplasty using navigation-assisted TKA, with mobile-bearing, cruciate ligament-retaining knees. Fifty conventional TKAs with high-flexion knees and 50 navigation-assisted TKAs with mobile-bearing knees were included in this study. The ROM and number of knees that allowed comfortable kneeling and cross-legged sitting 2 years postoperatively were evaluated and compared. Functional outcomes of the two groups were assessed with the Hospital for Special Surgery (HSS) scores. The authors found no difference between the ROM and functional outcomes of conventional TKA with high-flexion knees and navigation-assisted TKA with mobile-bearing knees.

Range of motion (ROM) after total knee arthroplasty (TKA) is an important variable in determining clinical outcomes. This is especially true for patients in Asia because high ROM is required for social and religious activities and for working.1 Normally, the clinical results achieved by the majority of modern TKA designs are satisfactory in terms of pain relief and walking ability. However, patients do not achieve satisfactorily high degrees of flexion after TKA. Range of motion after TKA has reportedly been influenced by preoperative, intraoperative, and postoperative factors. However, clinical studies have rarely described knee flexion of 120°. More importantly, even patients who had good preoperative ROM often lose deep flexion (defined as flexion >120°) after TKA.2-8

Therefore, high-flexion, posterior cruciate ligament (PCL) stabilized total knee prostheses enhance knee flexion by restoring posterior femoral translation. The use of these prostheses has attracted attention in recent years. However, the question, “Does high-flexion TKA result in good ROM in vivo?”, has not been clearly answered.

This study was conducted to compare ROM changes 2 years after primary TKA in patients who had conventional TKA with high-flexion fixed-bearing posterior stabilized (PS) knee prosthesis and in patients who had navigation-assisted TKA with standard mobile-bearing cruciate retaining (CR) knee prosthesis. The authors' hypothesis was that high-flexion PS knees would have better postoperative ROM than mobile-bearing CR knees.

Materials and Methods

The study included 50 patients who underwent primary TKA without a navigation system using high-flexion fixed-bearing PS knees (Figure 1, NexGen LPS-Flex, Zimmer, Warsaw, Ind) with a minimum 2-year follow-up, and 50 patients who underwent primary TKA with the OrthoPilot navigation system (B. Braun-Aesculap, Tuttlingen, Germany) using mobile-bearing CR knees (Figure 2, e-motion, B. Braun-Aesculap), with a minimum 2-year follow-up. In both groups, all patients had primary osteoarthritis. Patients with a diagnosis other than osteoarthritis or had revision surgery or missing data were not included.

Figure 1: An 81-year-old woman had TKA with a high-flexion PS knee. The patient with high-flexion PS knees sitting cross-legged (A) and full flexion lateral of the same patient.(B).

All TKAs were performed using a medial parapatellar arthrotomy extending several centimeters into the quadriceps tendon with patella eversion. All prostheses were fixed with cement, and no patellas were resurfaced in either group. In the high-flexion group, intramedullary instrumentation was used for femoral alignment, with 6° of valgus cut for all knees, and a tibial cut performed with extramedullary instrumentation. All TKAs were performed by the senior author (EKS).

The intraoperative and postoperative protocols were identical for each group. A tourniquet was used for all procedures and was not deflated until after wound closure. All knees were fitted with a drain that was removed on the second postoperative day. Postoperatively, none of the patients had continuous passive motion, but all patients received standardized physical therapy that began with full weight bearing on the first postoperative day.

Available preoperative demographic information included patient age at the time of the procedure, gender, and body mass index (BMI). Also, the preoperative femorotibial angle was assessed.

The following variables were reviewed for clinical ROM comparisons: maximum flexion, minimum flexion contracture, and arc of motion. The number of knees that allowed comfortable kneeling and cross-legged sitting was also determined. These values were compared in the two groups preoperatively and at the 2-year follow-up. All flexion and extension measurements were made by physical therapists using a goniometer.

Figure 2: A 72-year-old woman had bilateral navigation-assisted TKA. Patient with mobile-bearing CR knees sitting cross-legged (A). Full flexion lateral left knee (B) and full flexion lateral right knee (C).

Functional outcomes based on the Hospital for Special Surgery (HSS) scores of the two groups at the 2-year follow-up were also assessed and compared.

Statistical analyses were performed using SPSS for Windows Release 11.0 (SPSS Inc, Chicago, Ill). The student’s t-test was used to analyze numeric data, and the Chi square analysis was used to analyze non-numeric data, using a confidence interval of 95%.

Results

No significant difference was observed between the high-flexion group and the navigation group in age, BMI, gender, or femorotibial angle. Preoperatively, the groups were similar in terms of average knee flexion, flexion contracture, and arc of motion, and no differences were observed in HSS scores (Table 1).

At the 2-year follow-up, average flexion for the high-flexion group was 130.7° (range: 95°-155°), and average flexion for the navigation group was 128.5° (range: 95°-160°), showing no statistical significance (P=.527). No significant difference was observed between the two groups in flexion contracture (high-flexion=1.0°, range: 0°-15°; navigation=1.4°, range: 0°-10°) (P=.414), and arc of motion (high-flexion=129.7°, navigation=127.1°) (P=.354) at the 2-year follow-up. No significant changes in flexion, flexion contracture, or arc of motion between the two groups postoperatively were observed (Table 2). Twenty (40%) knees in the high-flexion group and 18 (36%) knees in the navigation group allowed comfortable kneeling postoperatively. Forty (80%) knees in the high-flexion group and 37 (74%) knees in the navigation group allowed sitting in a cross-legged position. However, no significant difference in comfortable kneeling or cross-legged sitting was evident between the two groups (P=.418, P=.318) (Table 2). Also, average HSS knee scores (high flexion=92.8 points, navigation=90.7 points, P=.127) showed no significant difference 2 years postoperatively (Table 2).

Discussion

In certain ethnic and religious groups (ie, Koreans, Indians, Chinese, Japanese, and Muslims), a high ROM is necessary to perform daily activities, which include prolonged kneeling and cross-legged sitting.1,9 To squat and sit cross-legged for certain religious activities, a person needs >120° of knee flexion. Kneeling during prayer may demand knee flexion of >135°, whereas stair climbing and sitting on a chair require only 90° to 120° of knee flexion.9-11 However, the majority of total knee systems have been designed to accommodate flexion up to only 130°, which does not satisfy many patients. Moreover, few clinical studies have described knee flexion of >120°.2-8

Therefore, several implant companies, such as Zimmer (Warsaw, Ind), have been developing high-flexion knee prostheses. The Zimmer high-flexion NexGen LPS-Flex PS design is a posterior cruciate stabilized prosthesis designed to accommodate a knee flexion of 155° with a cam-spine mechanism to facilitate posterior femoral translation, which improves knee flexion. In an in vitro experimental study, the NexGen LPS-Flex PS design was found to restore intact, native knee kinematics at flexion angles up to 150°.12,13 However, it remains unclear if high-flexion TKA results in improved ROM in vivo.

Initially, the authors hypothesized that high-flexion PS knees would provide better postoperative ROM than mobile-bearing CR knees. However, this study showed no significant difference between the high-flexion group and the navigation-assisted mobile-bearing group. Although high-flexion PS knees had 2° more flexion than navigation-assisted knees, this difference was not significant. In addition, no significant postoperative differences were found in flexion contracture, arc of motion, or the number of knees capable of kneeling or cross-legged sitting (cross-legged sitting: 80% in high-flexion, 74% in navigation; kneeling: 40% in high-flexion, 36% in navigation). The results of the high-flexion group are similar to those of Cho et al,14 who found 84% for cross-legged sitting and 30% for kneeling in high-flexion knee. Moreover, no differences in functional outcomes determined by HSS scores were observed between the two groups after a 2-year follow-up.

This comparative study has three limitations. The first limitation is that ROM after TKA is influenced by preoperative, intraoperative, and postoperative factors in addition to implant design. However, in the authors’ study, these factors were minimized by including only patients with osteoarthritis. Moreover, preoperative factors such as primary diagnosis, ROM, degree of deformity, and function were similar in the two groups. The second limitation is that the one prosthesis included in the study was of a PS design, whereas the other prosthesis was of a CR design. The third limitation is the difference in the surgical techniques. One group had conventional TKA, and the other group had navigation-assisted TKA. The ROM results were due to the better alignment of navigated TKA and the additional possibilities of navigated soft tissue management.15,16 To evaluate the influence of a navigation system on ROM and flexion, a second study in which the same prosthesis is used in both groups is necessary.

The authors conclude that although high-flexion prostheses have been shown to have more flexion in ROM and functional results than navigation prostheses, it is unclear if high-flexion prostheses allow more flexion than navigation prostheses in vivo.

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Authors

From the Center for Joint Disease at ChonnamNationalUniversityHwasunHospital, Jeonnam, Korea