Introduction

Complete healing following posterior meniscal root (PMR) repair has been observed in only 50–60%. One reason for these low healing rates might be excess loading during the early postoperative phase. Thus, the purpose of this study was to determine the distraction forces on the PMR in the native knee and following transosseous PMR repair in various tibiofemoral loading conditions throughout the range of motion. It was hypothesized, that with increasing axial load and flexion angle, the distraction forces on the PMR will increase continuously.

Methods

8 fresh-frozen human cadaveric knees (mean age 76.7) were mounted in a custom-made kinematics rig. The tibia and femur of the knee were extended with a 12mm steel nail to a length of 37cm and 46cm, respectively, in order to simulate the average length of the lower extremity in Caucasians. The distal end of the tibial nail, representing the ankle joint, was either not loaded or loaded with 200N and 400N to simulate passive mobilization, toe touch and partial weightbearing. A transosseous PMR repair was performed with a No.2 FiberWire (Arthrex Inc., Naples). The sutures were shuttled through a 2.4mm tibial bone tunnel and tied over a force sensor mounted on the anterior tibia with a pretension of 2N. After measuring the native distraction forces throughout a flexion–extension cycle, the PMR and the ACL were detached sequentially. For the posterior lateral meniscal root (PLMR) an additional non–anatomic repair close to the insertion of the ACL was performed as some studies suggested a transtibial repair through the ACL tunnel. A repeated-measures ANOVA was used for data analysis (p<0.05).

Results

For both menisci a significant overall effect of the state of the knee (native, ACL deficient, root repair) as well as the flexion angle was observed (p<0.01). Furthermore, axial loading of 200N and 400N resulted in a significant increase of distraction forces on both menisci throughout the range of motion (p<0.01). Interestingly, distraction forces following posterior lateral as well as medial meniscal root (PMMR) repair were not significantly affected by flexion angle when no axial load was applied (NS).
With axial loading of 200N and 400N, the distraction forces on the PLMR were significantly higher at flexion angles between 15° and 90° compared to full extension (up to 15.9N; p<0.01). Similar results have been observed in ACL deficient knees. Furthermore, no significant differences were observed when comparing anatomic and non-anatomic PLMR repairs (NS).
On the medial side, distraction forces were highest (up to 7.0N; 0° - 30°) and decreased significantly towards 90° of flexion with 200N and 400N axial load (p<0.01).

Conclusion

Data of the study suggests, that following PMR repair, axial load should be avoided in order to reduce distraction forces on the repair. Furthermore, it is shown, that passive flexion–extension exercises can be performed without significantly affecting the forces on the repair. With axial loading, the forces on the PLMR increased continuously with higher knee flexion, while on the PMMR the distraction forces were highest at full extension.