2017 ISAKOS Biennial Congress ePoster #1216
Does Extension and Flexion Stability Correlate with Midflexion Stability in Posterior-Stabilized Total Knee Arthroplasty?
Yasutake Iseki, MD, Toon, Ehime JAPAN
Kazunori Hino, MD, PhD, Toon, Ehime JAPAN
Tatsuhiko Kutsuna, MD, PhD, Toon, Ehime JAPAN
Kunihiko Watamori, MD, Toon, Ehime JAPAN
Seiji Watanabe, MD, Toon, Ehime JAPAN
Hiroshi Kiyomatsu, MD, PhD, Toon-City, Ehime JAPAN
Yasumitsu Ishimaru, Toon City, 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 Not Applicable
The aim of this study is to evaluate the correlation between varus-valgus stability at 0° and 90°and that at the midflexion range in PS-TKA, the stability at 90° strongly correlates with the stability at wide midflextion range, the stability of 0°correlated with narrow initial flextion range, initial flexion stability did not strongly correlate with the stability at either 0° or 90°.
Activities of daily living cause mechanical load on the knee joint, both in full extension and in midflexion. Several studies demonstrated that the difficulty of restoring intraoperative proper coronal plane stability, particularly at the midflexion range in total knee arthroplasty (TKA). Midflexion stability is a candidate factor for improving outcomes and patient satisfaction. To avoid instability caused by inappropriate soft tissue balance, a widely recognized goal is to adjust the soft tissue envelope to feel ‘stable’ in 0° of extension and 90° of flexion by using a manual stress test, a gap spacer, or tension meter. This technique can reliably achieve a more stabilized knee in 0° of extension and 90° of flexion. However, whether it can achieve stability at the midflexion range is unclear. The aim of this study is to evaluate the correlation between varus-valgus stability at 0° of extension and 90° of flexion and that at the midflexion range in posterior-stabilized (PS) - TKA.
Forty-three knees that underwent PS-TKA (NexGen LPS-Flex, Zimmer, Warsaw, IN) were evaluated. Manual mild passive varus–valgus stress was applied to the knees, and the postoperative maximum varus-valgus laxity was measured every 10° throughout flexion by a navigation system (precisioN Knee Navigation Software, version 4.0; Stryker, Kalamazoo, MI, USA). Correlations between the stability at 0°, 90° of flexion and that at each midflexion angle were evaluated by using Spearman’s correlation coefficients. Correlations were evaluated using Spearman’s coefficients of correlation. Analyses were performed with JMP, version 11.0 (SAS Institute, Tokyo, Japan). x > 0.7 was considered a strong correlation; 0.4 < x < 0.7 was considered a modest correlation; and 0.2 < x < 0.4 was considered a weak correlation. P < 0.05 was considered statistically significant.
The stability of 0° strongly correlated with that of 10°, modestly correlated with that of 20°, and weakly correlated with that of 30°, but did not significantly correlate with that of 40° to 80°. On the other hand, the stability of 90° strongly correlated with that of 50° to 80°, modestly correlated with that of 20° to 40°, but did not correlate with that of 10°.
The varus-valgus stability at 90° flexion strongly correlates with the stability at wide midflextion range, confirming its importance in acquiring stability at 90° flexion in PS-TKA. On the other hand, initial flexion stability did not strongly correlate with the stability at either 0° or 90° in PS-TKA. Attention would be necessary to prevent varus-valgus instability at the initial flexion range in PS-TKA.