Clinical improvement despite structural degeneration after nonoperative treatment of medial meniscus posterior root tear: A prospective longitudinal study.

PURPOSE: To longitudinally evaluate clinical, radiographic and magnetic resonance imaging (MRI) changes in patients with medial meniscus posterior root tear (MMPRT) managed nonoperatively and to identify factors associated with patient-driven conversion to surgery. METHODS: A prospective longitudinal study was conducted in patients with acute MMPRT (≤3 months from symptom onset) who opted for nonoperative treatment during 2017-2024. Patients with <2 years of follow-up, chronic tears (>3 months) or Kellgren-Lawrence (K-L) grade ≥3 were excluded. Clinical outcomes (Numerical Rating Scale [NRS] and Knee injury and Osteoarthritis Outcome Score [KOOS]), radiographic parameters (K-L grade, hip-knee-ankle angle [HKA] and medial joint space width) and MRI findings (medial meniscus extrusion and full-thickness cartilage defect length on coronal images) were assessed. Baseline factors were compared between patients who continued nonoperative treatment and those who elected to undergo surgery. RESULTS: Sixty-four patients (mean age at onset, 65.6 years) were included. Nonoperative treatment was continued in 49 patients (76.6%); 15 (23.4%) converted to surgery after a median of 6 months (interquartile range, 3-8 months). Clinical outcomes improved significantly within 6 months (NRS, 7.6 ± 2.4 to 1.3 ± 1.2; KOOS symptom, 64.0 ± 13.0 to 79.1 ± 10.8; p < 0.05) and remained stable. Conversely, structural degeneration progressed early: The K-L grade worsened (Grade 0, 28-11 cases), joint space narrowed (3.5 ± 0.8 to 2.9 ± 0.7 mm) and meniscal extrusion progressed (3.1 ± 1.0 to 4.3 ± 1.3 mm) within 6 months (p < 0.05). Femoral and tibial cartilage loss also progressed within 1 year (femoral, 3.2 ± 3.5 to 6.9 ± 3.8 mm; tibial, 0.6 ± 1.9 to 2.6 ± 3.6 mm; p < 0.05). Baseline varus alignment was greater in patients who underwent surgery than in those who continued nonoperative treatment (HKA, 6.0° vs. 3.7°, p < 0.01). Receiver operating characteristic analysis identified an HKA threshold of 5.5° for predicting conversion to surgery (area under the curve, 0.742). CONCLUSION: Most patients with MMPRT managed nonoperatively showed clinical improvement despite early structural deterioration. Varus alignment was associated with patient-initiated conversion to surgery, and an HKA threshold of 5.5° may help identify patients at increased risk of conversion to surgery. These findings highlight a critical clinical paradox and support alignment-based decision-making in MMPRT management. LEVEL OF EVIDENCE: Level II, study design: prospective cohort.