Absolute Meniscal Extrusion After Lateral Meniscal Allograft Transplantation Does Not Progress During Long-term Follow-up: Average of 10.3 Years’ Follow-up Longitudinal Magnetic Resonance Imaging Study

Abstract

Background: Long-term outcomes after lateral meniscal allograft transplantation (MAT) are not completely understood. Purpose/Hypothesis: We investigated changes in meniscal extrusion in the coronal and sagittal planes using magnetic resonance imaging (MRI) after lateral MAT through long-term follow-up. We hypothesized that meniscal extrusion would progress during follow-up. Study Design: Case series; Level of evidence, 4. Methods: Patients subjected to lateral MAT were followed up by MRI evaluation in both planes at 1, 4 to 6, and >8 years after MAT. Meniscal extrusion and entire meniscal widths in the coronal plane and anterior (ACMD) and posterior (PCMD) cartilage meniscal distances in the sagittal plane were measured, and values were compared at each time point. Clinical outcomes were evaluated using the Lysholm score. Results: A total of 27 lateral MATs were included with a mean MRI follow-up period of 10.3 years (range, 8.1-15.3 years). The mean absolute meniscal extrusion (coronal plane) was not significantly different at each time point. However, the relative value differed (0.27 ± 0.04 at 1 year; 0.33 ± 0.06 at >8 years after MAT) owing to entire meniscal width reduction. There was no difference in the mean absolute value of the ACMD in the sagittal plane. However, relative values differed (0.21 ± 0.01 at 1 year; 0.27 ± 0.06 at >8 years) owing to entire meniscal width reduction. Absolute and relative values of the PCMD remained unaffected at each time point. The Lysholm score increased after surgery but did not differ postoperatively. Conclusion: During the long-term follow-up of extrusion after lateral MAT using MRI, absolute extrusion remained unchanged across all planes. Relative extrusion in the coronal plane and of the ACMD in the sagittal plane significantly increased, with no differences in the PCMD on follow-up. Clinical outcomes after surgery improved compared with those before surgery and were maintained throughout the long-term follow-up period.