2017 ISAKOS Biennial Congress ePoster #1251
Component Design Has an Effect on Midflexion Varus-Valgus Laxity in Total Knee Arthroplasty
Kazunori Hino, MD, PhD, Toon, Ehime JAPAN
Tatsuhiko Kutsuna, MD, PhD, Toon, Ehime JAPAN
Kunihiko Watamori, MD, Toon, Ehime JAPAN
Hiroshi Kiyomatsu, MD, PhD, Toon-City, Ehime JAPAN
Yasutake Iseki, MD, Toon, Ehime JAPAN
Yasumitsu Ishimaru, Toon City, Ehime JAPAN
Seiji Watanabe, MD, Toon, Ehime JAPAN
Hiromasa Miura, MD, PhD, Prof., Toon, Ehime JAPAN
Department of Orthopaedic Surgery / Ehime University Graduate School of Medicine, Toon, Ehime, JAPAN
FDA Status Cleared
The TKA design might play a role in midflexion stability, therefore, the purpose of this study was to compare the varus-valgus stability throughout flexion in knees treated with either conventional symmetrical design PS-TKA or anatomical asymmetrical design BCS-TKA, using an intra-operative navigation technique, BCS knees had less varus-valgus laxity than PS knees at 0 to 70° flexion.
Proper soft tissue balance is crucial for a successful clinical outcome after total knee arthroplasty (TKA). Midflexion stability is considered as a candidate factor for improving the outcome of TKA. TKA design might play a role in midflexion stability. Therefore, we hypothesized that post-operative midflexion varus-valgus laxity is different according to TKA design. The purpose of this study was to compare the varus-valgus stability throughout flexion in knees treated with either conventional symmetrical design PS-TKA or anatomical asymmetrical design BCS-TKA, using an intra-operative navigation system.
This study was prospective cohort study. To fairly assess and minimize the influences of clinical variables, patients with a valgus deformity, preoperative severe flexion (<90°), and extension (>20°) restriction were excluded. We analyzed a total of 70 osteoarthritic knees in 70 Japanese patients for this study: 26 knees with the BCS prosthesis (BCS : Journey II BCS; Smith & Nephew, Memphis, Tenn), and the other 44 knees with a popular high-flexion PS prosthesis as a control group (PS : NexGen LPS-Flex, Zimmer, Warsaw, IN). Patients in BCS group underwent TKA from 2015 to 2016 and patients in PS group underwent TKA from 2012 to 2014 at our university hospital.
Manual mild passive varus-valgus stress was applied to the knees, and the maximum varus and valgus laxity at each 10° flexion angle was measured automatically by a navigation system before and after TKA. (precisioN Knee Navigation Software, version 4.0; Stryker, Kalamazoo, MI, USA).
The test-retest reliability of these varus and valgus stress angle indicated that interclass and intraclass correlation coefficients (ICCs) were sufficiently high, with values >0.8 at each flexion angle. The differences in varus-valgus laxity between the BCS and PS groups were compared using the non-parametric Wilcoxon signed-rank test due to the small sample size, although an arithmetically sufficient normal distribution was found. Analyses were performed with JMP version 11.0 (SAS Institute, Tokyo, Japan). P = 0.05 was considered to indicate statistical significance.
No significant differences were noted in the age, preoperative ROM and HKA distribution between the BCS and PS groups. Pre-operative assessment revealed that no statistically significant difference were seen at each flexion angle between the groups. However, BCS knees had less varus laxity than PS knees at 10 to 40° flexion angles, And BCS knees had less valgus laxity than PS knees at 10 to 30° flexion angles. As a result, postoperative assessment revealed that BCS knees had less varus-valgus laxity than PS knees at 0 to 100° flexion angles, and the differences were statistically significant at 0 to 70° flexion angles.
Discussion And Conclusion
We successfully evaluated pre- and post-TKA varus-valgus laxity according to difference of component design using a navigation system. The results showed that BCS knees had less varus-valgus laxity than PS knees throughout the ROM, and the differences were statistically significant for the flexion range of 0 to 70°. Component design has an effect on midflexion varus-valgus laxity.