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

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. A prospective longitudinal study was conducted in patients with acute MMPRT (&#x2264;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 &#x2265;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. 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&#x2009;&#xb1;&#x2009;2.4 to 1.3&#x2009;&#xb1;&#x2009;1.2; KOOS symptom, 64.0&#x2009;&#xb1;&#x2009;13.0 to 79.1&#x2009;&#xb1;&#x2009;10.8; p&#x2009;<&#x2009;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&#x2009;&#xb1;&#x2009;0.8 to 2.9&#x2009;&#xb1;&#x2009;0.7&#x2009;mm) and meniscal extrusion progressed (3.1&#x2009;&#xb1;&#x2009;1.0 to 4.3&#x2009;&#xb1;&#x2009;1.3&#x2009;mm) within 6 months (p&#x2009;<&#x2009;0.05). Femoral and tibial cartilage loss also progressed within 1 year (femoral, 3.2&#x2009;&#xb1;&#x2009;3.5 to 6.9&#x2009;&#xb1;&#x2009;3.8&#x2009;mm; tibial, 0.6&#x2009;&#xb1;&#x2009;1.9 to 2.6&#x2009;&#xb1;&#x2009;3.6&#x2009;mm; p&#x2009;<&#x2009;0.05). Baseline varus alignment was greater in patients who underwent surgery than in those who continued nonoperative treatment (HKA, 6.0&#xb0; vs. 3.7&#xb0;, p&#x2009;<&#x2009;0.01). Receiver operating characteristic analysis identified an HKA threshold of 5.5&#xb0; for predicting conversion to surgery (area under the curve, 0.742). 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&#xb0; 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 II, study design: prospective cohort.