Progression of Allograft Extrusion in Both the Coronal and Sagittal Planes at Midterm Follow-up After Medial Meniscal Allograft Transplant

BACKGROUND: Although many studies have examined allograft extrusion after medial meniscal allograft transplant (MMAT), it is unclear whether allograft extrusion progresses at midterm follow-up. HYPOTHESIS: After MMAT, allograft extrusion would not progress during the midterm follow-up period. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: A total of 30 patients who underwent MMAT between December 1996 and March 2016 were enrolled. Allograft extrusion was measured on magnetic resonance imaging scans obtained at 6 weeks, 1 year, and 3 to 7 years postoperatively. In the coronal plane, the absolute allograft extrusion and relative percentage of extrusion were measured. In the sagittal plane, the absolute and relative anterior cartilage meniscal distance and posterior cartilage meniscal distance were measured. The joint-space width (JSW) on radiographic Rosenberg view was measured at 3 time points. The axial alignment was measured preoperatively and at the midterm follow-up. RESULTS: In the coronal plane, there were no significant differences in absolute and relative coronal extrusions between 6 weeks and 1 year postoperatively; however, the values were significantly increased at midterm follow-up compared with both of the earlier follow-up periods. Similarly, in the sagittal plane, the mean absolute and relative anterior and posterior cartilage meniscal distances were not significantly different between 6 weeks and 1 year postoperatively but showed significant increases at midterm follow-up compared with both of the earlier follow-up periods. The mean preoperative axial alignment showed a positive correlation with the delta value of relative percentage of extrusion in the coronal plane (r = 0.378; P = .036). The mean JSW was 4.42 ± 0.88 mm preoperatively, 4.30 ± 0.83 mm at 1-year follow-up, and 3.96 ± 1.06 mm at the midterm follow-up. No significant difference was found between the preoperative and postoperative 1-year values, but the mean JSW was significantly decreased at midterm follow-up compared with both of the other time points (P = .001 for both). CONCLUSION: Allograft extrusion did not progress until 1 year after MMAT; however, by midterm follow-up, extrusion had progressed in both the coronal and the sagittal planes. Preoperative axial alignment showed a positive correlation with allograft extrusion in the coronal plane.