Meniscal extrusion and spontaneous osteonecrosis with root tear of medial meniscus: comparison with horizontal tear.

PURPOSE: The incidence of root tears in patients with spontaneous osteonecrosis of the knee has been studied, but the incidence of spontaneous osteonecrosis of the knee in patients with medial meniscus root tears has not. We assessed the latter incidence and evaluated the characteristics of medial meniscus root tears by comparing clinical status, the degree of osteonecrosis, and meniscal extrusion in patients with horizontal tears.

METHODS

Sixty-three patients who were diagnosed with medial meniscus posterior horn tear and treated by arthroscopic surgery between March 2005 and March 2009 were evaluated retrospectively. Patients were divided into 2 groups, the root tear group (R group) and the horizontal tear group (H group). Functional scores and radiography, simple radiography, and magnetic resonance imaging were investigated.

RESULTS

No significant differences in age, body mass index, and symptom duration were observed between the 2 groups. The incidence of osteonecrosis was 12 of 36 knees (33.3%) in the R group and 4 of 27 (14.8%) in the H group. The mean absolute extrusion was 4.1 ± 0.7 mm and 3.5 ± 1.4 mm in the R and H groups, respectively (P = not significant). The mean relative percentage of extrusion in the R group (46.1% ± 9.0%) was greater than that in the H group (35.3% ± 13.2%) (P = .01). The degree of osteonecrosis (ellipsoidal volume) was also greater in the R group (423.1 ± 236.7 mm(3)) than that in the H group (175.8 ± 43.6 mm(3)) (P = .03). Though not significant, the visual analog pain score had a tendency to be more severe and knee scores had a tendency to be lower in the R group than in the H group.

CONCLUSIONS

Medial meniscus root tears had a greater degree of meniscal extrusion and wider osteonecrosis than horizontal tears of the posterior horn related to loss of the main function of the meniscus.

LEVEL OF EVIDENCE: Level III, retrospective comparative study.