Biomechanical Assessment of Bicortical Suspension Device Fixation for Proximal Tibiofibular Joint Instability: Single Versus Double Device

Abstract

Background: Bicortical suspension device (BCSD) fixation treats proximal tibiofibular joint (PTFJ) instability in both the anterolateral and posteromedial directions. However, biomechanical data are lacking as to whether this technique restores the native stability and strength of the joint. Purpose: To test (1) if BCSD fixation restores the native stability and strength and (2) if using 2 devices is needed. Study Design: Controlled laboratory study. Methods: Sixteen pairs of fresh-frozen cadaveric specimens were obtained. Six pairs were assigned to the control group and 10 matched pairs assigned for transection to model PTFJ and subsequent BCSD fixation (one specimen with 1-device repair and the other with 2-device repair). Joint stability and strength were assessed by translating the fibular head relative to the fixed tibia either anterolaterally or posteromedially. Control specimens received 20 cycles of 0- to 2.5-mm joint displacement tests (subfailure) and then proceeded to load to failure (5 mm). For the experimental group, cyclic tests were repeated after ligament resection and after fixation. Forces and stiffness at 2.5- and 5-mm displacement were recorded for comparisons of joint strength and stability at subfailure and failure loads, respectively. Results: After repair of anterolateral instability, both the single- and double-device fixations successfully restored near-native states, with no significant differences as compared with the intact group for forces at subfailure load ( P = .410) or failure load ( P = .397). Regarding posteromedial instability, single-device repair did not restore forces to the near-native state at subfailure load (intact: 92.9 N vs single: 37.4 N; P = .001) or failure load (intact: 170.7 N vs single: 70.4 N; P = .024). However, the double-device repair successfully restored near-native posteromedial forces at both subfailure load ( P = .066) and failure load ( P = .723). Conclusion: For treatment of the most common form of PTFJ instability (anterolateral), this cadaveric study suggests that 1 BCSD is sufficient to restore stability and strength. The current biomechanical results also suggest that 2 devices are needed for restoring PTFJ posteromedial stability and strength. Using 2 devices addresses both types of instability and provides more PTFJ posteromedial stability. Clinical Relevance: The results suggest that 1 device should be used for treating anterolateral instability and 2 devices used for posteromedial instability based on the biomechanical study.