Magnetic Resonance Imaging Findings in Symptomatic Patients After Arthroscopic Partial Meniscectomy for Torn Discoid Lateral Meniscus.

PURPOSE: To evaluate the change in the thickness and width of the residual meniscus using magnetic resonance imaging (MRI) in patients who underwent arthroscopic partial meniscectomy for discoid lateral meniscus (DLM), to assess whether the degeneration of the articular cartilage in the lateral compartment of the knee progressed, and to evaluate clinical results.

METHODS: Among the patients who underwent arthroscopic partial meniscectomy for DLM between January 1997 and December 2011, those who were aged 40 or below at surgery were followed up for at least 3 years, and received at least 2 follow-up MRIs that were retrospectively reviewed. MRIs were done in symptomatic knees. Using MRI, the relative thickness and width were measured in the anterior horn, midportion, and posterior horn. To determine whether the degeneration of the lateral compartment would progress, the articular cartilage was graded based on the Outerbridge classification in MRIs. The clinical results were evaluated using the Lysholm score.

RESULTS: A total of 20 patients (21 knees) were included. The average follow-up period was 6.8 years. In residual meniscus, the relative thickness of the midportion decreased from 9.0% ± 2.4% to 7.3% ± 2.3% (P < .001), the relative thickness of the anterior horn decreased from 15.6% ± 4.3% to 14.3% ± 6.7% (P = .030), and the relative thickness of the posterior horn decreased from 20.0% ± 4.4% to 16.7% ± 6.7% (P = .019). A decrease in the relative width was observed in the midportion (12.4% ± 4.8% to 10.9% ± 4.9%, P = .003). No significant changes in size were observed in the medial meniscus. A progression of degeneration in the lateral compartment was observed. However, the clinical results did not present significant changes.

CONCLUSIONS: In symptomatic patients after arthroscopic partial meniscectomy for DLM, the thickness and width of the residual meniscus decreases over time. The arthritic change of the lateral compartment of the knee progressed. However, the change in the size of the residual meniscus was of unknown clinical significance.

LEVEL OF EVIDENCE: Level IV, therapeutic case series.