Meniscus extrusion assessed by ultrasound does not correlate with knee function or radiographic signs of joint degeneration after medial and lateral meniscus allograft transplantation at a mean follow-up of 13 years.

PURPOSE: The aim of this study was to assess meniscus extrusion using ultrasound after meniscus allograft transplantation (MAT) and its association with clinical outcomes.

METHODS: Patients who underwent medial or lateral MAT with a minimum 5-year follow-up were included. Exclusion criteria included bilateral MAT. Meniscus extrusion cross-sectional area (CSA) and extrusion distance, for the index and contralateral meniscus, in supine position, bipodal and unipodal stance were measured using ultrasound. Joint space width (JSW) and Kellgren and Lawrence (KL) grade were assessed on radiographs. The International Knee Documentation Committee Subjective Knee Form (IKDC SKF) was collected to assess clinical outcomes. Significance was set at p < 0.05. Friedman and analysis of variance tests were used to compare meniscus extrusion across weight-bearing conditions. Between MAT groups, Mann-Whitney U test and independent-samples t test were performed. Multiple regression assessed associations between meniscus extrusion and (1) standardized IKDC-SKF, (2) JSW and (3) KL grade.

RESULTS: Thirty-five patients (average age at MAT 29 ± 10 years; 46% females) were assessed at a mean follow-up of 13.3 ± 6.7 years. Meniscus extrusion CSA of the MAT meniscus, assessed at the latest follow-up, was significantly greater than that of the opposite meniscus (supine: 43.2 vs. 20.2; bipodal: 46.2 vs. 22.7; unipodal: 46.6 vs. 23.8 mm2, p < 0.05). Meniscus extrusion CSA and meniscus extrusion distance were significantly greater in the medial MAT group compared to the lateral MAT group (p < 0.05). No significant associations were found between meniscus extrusion CSA and standardized IKDC SKF, KL grade and JSW at final follow-up (p > 0.05).

CONCLUSION: Medial MAT resulted in greater meniscus extrusion than lateral MAT in supine position, unipodal and bipodal stance. Meniscus extrusion was not significantly associated with clinical outcomes in this cohort and should not be considered a surrogate marker for clinical outcomes after MAT; rather, it may be better interpreted as a surrogate marker of biomechanical alterations associated with the risk of structural joint degeneration.

LEVEL OF EVIDENCE: Level III.