Summary

Medial MAT results in more pronounced meniscal extrusion than lateral MAT as measured by ultrasound in a long-term follow-up and is also associated with inferior patient reported outcomes.

Abstract

Introduction

Meniscal extrusion is common after meniscal allograft transplantation (MAT). However, there is no consensus regarding normal extent of extrusion and how it correlates with clinical outcome. Few studies have assessed meniscal extrusion in different weight-bearing states using ultrasound. This study aimed to compare meniscal extrusion after medial and lateral MAT on ultrasound and evaluate its correlation with clinical outcome measures. It was hypothesized that patients who underwent medial MAT will have greater meniscal extrusion than patients who underwent lateral MAT and that they have inferior patient reported outcomes (PROs).

Methods

Patients who underwent MAT with minimum 1-year follow-up were included. Exclusion criteria included untreated cartilage injury grade IV at the time of MAT, subsequent complete MAT resection, and subsequent total knee arthroplasty. All ultrasound measurements were taken in supine position, bipodal, and unipodal stance. Ultrasound was used to measure cross-sectional area (CSA) and distance of extrusion of the transplanted meniscus and compared to the equivalent contralateral meniscus to assess side-to-side (STS) differences. Measurements were assessed anterior to the lateral collateral ligament for the lateral meniscus and parallel to the medial collateral ligament for the medial meniscus. Extrusion distance was measured from a line connecting femur and tibia to the most extruded edge of the meniscus, while extrusion CSA was defined as the meniscus area outside this line. Additionally, International Knee Documentation Committee Subjective Knee Form (IKDC SKF) was assessed at the latest follow-up. Statistical analyses included Chi square and Fisher’s exact tests for categorical variables, or Mann Whitney U tests and independent sample t-tests for nonparametric and parametric variables, respectively.

Results

Thirty-three patients (average age at MAT 29.8 ± 10.5 years; 33 % females; 33 % lateral MAT) were assessed via ultrasound at a mean follow-up of 10.0 ± 5.4 years after MAT. Mean IKDC SKF was 64.1 ± 18.9. In the overall cohort, ultrasound revealed greater extrusion CSA of the transplanted meniscus compared to the contralateral meniscus in all positions (supine/bipodal/unipodal, 39.3 vs. 19.0 / 43.4 vs. 21.1 / 44.5 vs. 23.0 mm2, respectively, p<0.05). Regarding medial and lateral MAT group, there were no significant differences of baseline demographics between the groups. Extrusion CSA STS difference was greater in the medial MAT group than the lateral MAT group in all positions (bipodal/unipodal/supine, 27.6 vs. 11.8 / 27.4 vs. 9.7 / 25.8 vs. 9.2 mm2, respectively, p<0.05). Similarly, the STS difference in extrusion distance was greater in the medial MAT group than in the lateral MAT group in two positions (supine/unipodal, 3.3 vs. 1.5/3.2 vs. 1.5 mm, respectively, p<0.05) (Table 2). The IKDC SKF was significantly inferior in the medial MAT group compared to the lateral MAT group (57.2 vs. 78.1, respectively, p<0.05).

Conclusion

The findings of this study indicate that medial MAT results in more pronounced meniscal extrusion than lateral MAT as measured by ultrasound in a long-term follow-up and is also associated with inferior PROs. Further research is required to evaluate long-term effects of meniscal extrusion on radiological outcomes.