Medial knee osteoarthritis precedes medial meniscal posterior root tear with an event of painful popping.

Background: An event of painful popping is a highly predictive clinical sign of medial meniscal posterior root tears (MMPRTs) in middle-aged to older patients. There are lacks of studies about the prevalence of a painful popping event and the condition of the medial compartment at the time of popping event in MMPRTs.

Hypothesis: We hypothesized that most of MMPRTs with a single painful popping event would show pre-existed pathologic medial meniscal extrusion (MME) and articular cartilage degeneration, and larger contact area of medial femoral condyle to medial tibial plateau could affect the MME. In addition, MME would be correlated with knee osteoarthritis.

Patients And Methods: Thirty-eight patients (mean age 58.5±10.5) who had painful popping within 3 weeks were included. On MRIs, absolute MME, relative percentage of extrusion (RPE), MME-medial femoral condyle (MFC)/medial tibial condyle (MTC) at 0° ratio, and medial compartments' Modified Outerbridge Scale (MOS) were evaluated. Kellgren-Lawrence (K-L) grade was also assessed.

Results: The MME parameters including absolute MME, RPE, and the ratio between MME and MFC/MTC at 0° were 2.9±1.2mm, 22.0±10.3%, and 3.2±1.3. Patients who with MOS and K-L grade≥2 were 33 (86.8%) and 32 (84.2%). Patients were divided into MME≥3mm (group G, n=20) and MME<3mm (groupL, n=18). The MME parameters were significantly greater in group G than group L (all, p<0.001). The group G had worse osteoarthritis progression in terms of MOS and K-L grade than the group L (p=0.035 and 0.077, respectively) MME≥3mm showed significantly association with MOS≥3 (p=0.045).

Discussion: More than 80% of MMPRT patients with an event of painful popping within 3 weeks showed that medial compartment degeneration preceded the event of popping. Therefore, identification of MME and articular cartilage degeneration at the time of painful popping in MMPRTs could be helpful when the surgeon determines the most appropriate treatment.

Level Of Evidence: IV, Case-series.