Does high knee flexion cause separation of meniscal repairs?

Background: Previous clinical studies comparing nonrestrictive and restrictive protocols after meniscal repair have shown no difference in outcomes; however, some surgeons still limit range of motion out of concern that it will place undue stress on the repair.

Hypothesis: Large acute medial meniscal tears will gap during simulated open chain exercises at high flexion angles, and a repaired construct with vertical mattress sutures will not gap.

Study design: Controlled laboratory study.

Methods: Tantalum beads were implanted in the medial menisci of 6 fresh-frozen cadaveric knees via an open posteromedial approach. Each knee underwent 10 simulated open chain flexion cycles with loading of the quadriceps and hamstrings. Testing was performed on 3 different states of the meniscus: intact, torn, and repaired. Biplanar radiographs were taken of the loaded knee in 90°, 110°, and 135° of flexion for each state. A 2.5-cm tear was created in the posteromedial meniscus and repaired with inside-out vertical mattress sutures. Displacement of pairs of beads spanning the tear was measured in all planes by use of radiostereometric analysis (RSA) with an accuracy of better than 80 μm.

Results: With a longitudinal tear, compression rather than gapping occurred in all 3 regions of the posterior horn of the meniscus (mean ± standard deviation for medial collateral ligament [MCL], -321 ± 320 μm; midposterior, -487 ± 256 μm; root, -318 ± 150 μm) with knee flexion. After repair, meniscal displacement returned part way to intact values in both the MCL (+55 ± 250 μm) and root region (-170 ± 123 μm) but not the midposterior region, where further compression was seen (-661 ± 278 μm).

Conclusions: Acute posteromedial meniscal tears and repairs with vertical mattress sutures do not gap, but rather compress in the transverse plane at higher flexion angles when subjected to physiologic loads consistent with active, open kinetic chain range of motion rehabilitation exercises. The kinematics of the repaired meniscus more closely resemble that of the intact meniscus than that of the torn meniscus in regions adjacent to the MCL and the root but not in the midposterior region, where meniscal repair led to increased compression across the tear plane.

Clinical relevance: This study supports the idea that nonrestrictive unresisted open chain range of motion protocols do not place undue stress on meniscal repairs.