Background

Arthroscopic reshaping surgery for discoid lateral meniscus (DLM) showed good clinical result but could not completely prevent degenerative change. The degree of DLM extrusion and the association for degenerative change was unclear.

Hypothesis

The meniscal extrusion existed before surgery, proceeded in postoperative course, and related to knee joint degeneration.
Study Design: Case seriese

Methods

We retrospectively reviewed the medical records of patients who underwent meniscal reshaping for symptomatic DLM and who had undergone follow-up for =2 years. Magnetic resonance imaging (MRI) examinations were performed preoperatively and 24 months postoperatively, and the extrusion of the residual meniscal midbody was measured. Radiographic early OA was detected when whole-organ magnetic resonance imaging score (WORMS) of the lateral compartment was grade 3 or higher at 2 years after surgery. The associated factors for radiographic early OA was evaluated.
Result: We included 62 knees in 53 patients in this study. Patients’ mean age at operation was 15.9 years. The extrusion of the midbody proceeded significantly from preoperative to 24 months after surgery (0.91 mm to 1.6 mm, P<.001). According to the WORMS cartilage score, 23 knees were categorized as early OA. Multivariate logistic analyses showed that preoperative Lysholm score (OR = 0.90, P = .018) and the postoperative extrusion (OR = 6.52, P = .002) significantly increased the risk of radiographic early OA. The receiver operating characteristic curve showed that a 1.9 mm residual meniscal extrusion was the cutoff value leading to evidence of degeneration.

Conclusion

The DLM extrusion was 0.9mm before surgery and significantly proceeded by 1.6mm at 2 years after surgery. The postoperative extrusion and preoperative Lysholm score was the factor related to radiographic early OA. Postoperative extrusion of 1.9mm was the cut off value for radiographic early OA.