Signal intensity of lateral meniscal allografts deteriorates over time: a longitudinal MRI analysis during a minimum follow-up of 8 years

Abstract

Purpose: To evaluate the serial change of magnetic resonance imaging (MRI) signal intensity (SI) of lateral meniscal allografts in a long-term period of > 8 years and to determine whether the SI change adversely affected clinical outcomes.

Methods: Thirty-three lateral meniscal allograft transplantation (LMAT) patients with MRI taken > 8 years after surgery were included. The allograft was assessed using MRI at five serial time points (1, 2-4, 4-6, 6-8, and > 8 years after surgery), based on the following grading system: grade 1, globular increased SI not adjacent to the articular surface; grade 2, linear SI within the meniscus; and grade 3, increased SI extended to the articular surface. MRI evaluation was performed for three locations of the allograft (anterior horn, mid-body, and posterior horn), and the serial changes of allograft SI at each location were analyzed using the generalized estimating equation (GEE) with cumulative logit link function. The patients were classified according to SI change at each location (stationary group and deterioration group), and the two groups were compared in terms of clinical outcomes using the Lysholm score.

Results: The mean follow-up duration was 9.2 ± 1.2 years. During that period, SI of the allograft deteriorated over time, regardless of the location (anterior horn, p = 0.034; mid-body, p = 0.002; posterior horn, p < 0.001). The amount of SI deterioration at each location of the graft differed with a borderline significance (p = 0.050, GEE), and the proportion of grade 3 SI was higher at the posterior horn (36.4%) than at the other locations at the last follow-up (p < 0.001, chi-square test). However, no significant differences in the Lysholm scores were found between the stationary group and the deterioration group at all locations.

Conclusion: SI of the meniscal allograft deteriorated over time at all locations during the long-term follow-up. Deterioration of the graft was more prominent at the posterior horn than at the other locations. SI deterioration did not adversely affect the clinical outcomes, which should be interpreted with caution, considering the small sample size of this study. In the prognosis of lateral MAT, SI deterioration at the posterior horn is a more determining factor than that at the other part of the allograft. Therefore, SI at the posterior horn needs to be examined with special concern.