Paper 13: Weightbearing After Medial Meniscus Root Repair: A Cadaveric Study Analyzing the Integrity of Meniscal Root Repairs Subjected to Physiologic Cyclic Loading.

Objectives: The purpose of this study was to evaluate the integrity of medial meniscus root repairs performed using an inlay transosseus single-tunnel repair technique. Methods: Fifteen cadaveric fresh frozen whole knee specimens (7 left, 8 right, ages 40-62) with intact collaterals, cruciates and meniscocapsular attachments were utilized for the study. All specimens underwent diagnostic knee arthroscopy to confirm that the medial menisci (MM) were intact. Of the 15 knees, only 11 (6 left, 7 right) cadaveric specimens had intact MM and underwent further testing. One metallic tracer (Arthrex Mini Corkscrew 2.5 mm x 7 mm fully threaded anchors) were placed into the medial tibial spines and another into the midsubstance of the posterior horns of the MM in all tested specimens. The intact MM roots were then detached using arthroscopic scissors, and root repair was performed using a transosseus single-tunnel repair technique (Arthrex 6 mm FlipCutter, two 0 FiberLink luggage tag sutures, one 4.75 mm PEEK SwiveLock anchor). The knee specimens were then attached to a proprietary jig and loaded in full extension using an Instron. Mini C-arm fluoroscopic anterior posterior views were obtained to document the posterior horn/medial tibial spine metallic tracer spatial relationships. The knee specimens underwent the following loading conditions: 1. Intact MM loaded statically with 1700 N (roughly 2.5 x body weight for a 75 kg patient). 2. Cut MM loaded statically with 1700 N. 3. Repaired MM loaded statically with 1700 N 4. Repaired MM root after cyclic loading with 1700 N x 250 cycles and then loaded statically with 1700 N in full extension. The knee specimens underwent repeat knee arthroscopy after cycling to assess the clinical integrity of the MM root repairs. Post hoc measurements were performed between the medial tibial spine/posterior horn metallic tracers to calculate meniscal displacement in the different loading scenarios. Results: All 11 tested specimens demonstrated intact MM root repairs after cyclic loading upon direct arthroscopic inspection. We compared the relationship of the medial tibial spine/posterior horn MM metallic markers to the entire medial tibial plateau for each knee specimen. When comparing the different testing scenarios, we found that there was statistically significant meniscal displacement between the intact and cut MM loading states (p = 0.011). Additionally, when loading the MM root repair, we noted statistically significant meniscal displacement between the intact and repaired MM loading states (p = 0.004) and the intact versus repaired and cycled MM states (p = 0.012). There was no difference in meniscal displacement noted between the repaired and cut MM loading states (p = 0.6), and no difference in meniscal displacement between the repaired and the repaired and cycled MM states as well (p = 0.5). Conclusions: MM root repairs performed using a transosseus single-tunnel repair technique do not withstand simulated physiologic cyclic weightbearing in full extension. Although the repair construct does not catastrophically fail, the repair construct allows for high amounts of creep/strain and resulting meniscal displacement that rivals the cut state. The lack of statistical significance between all repaired and cut states indicates that there is unacceptable meniscal displacement with this repair technique. This research highlights the clinical importance that creep/strain within a construct can pose, and correlates positively with recent publications regarding this method of fixation. Direct aperture fixation at the tibial plateau articular surface would theoretically perform better for MM root tears because it would allow for diminished working length of the construct, ultimately decreasing strain. [ABSTRACT FROM AUTHOR]