Healing Integrity Determines Meniscal Extrusion After Isolated Medial Meniscus Posterior Root Repair in Knees With No Lower Limb Malalignment.

Abstract

Purpose: To investigate changes in meniscal extrusion and meniscal healing status following root repair, and the relationship between meniscal extrusion and healing conditions.

Methods: Patients who underwent isolated root repair between 2019 and 2023 and consented to undergo second-look arthroscopy to evaluate their healing condition (1 year postoperatively) were included. The mean interval between root repair and second-look arthroscopy was 12.2 ± 1.3 months. The healing condition of the repaired meniscus was evaluated based on morphological continuity and meniscal tension at the bony attachment by probing (non-lax healing group, Group 1; lax healing group, Group 2). Meniscal extrusion was assessed in the coronal plane on magnetic resonance imaging preoperatively, immediately postoperatively, and at 1 year postoperatively. We analyzed the serial changes in meniscal extrusion according to the healing status observed during second-look arthroscopy.

Results: A total of 51 patients were enrolled in the study (7 patients refused to undergo second-look arthroscopy, and 5 patients were lost to follow-up), with 30 assigned to Group 1 and 21 to Group 2. The mean age was 59.1 ± 6.2 years with 8 male and 43 female. Regarding postoperative clinical scores, the minimal clinically important difference (MCID) for Group 1 was as follows: Lysholm, 84.0 ± 7.4 (MCID: 3.55); WOMAC, 16.1 ± 8.1 (MCID: 4.67); and KOOS, 23.7 ± 6.6 (MCID: 5.69). Group 1 showed significantly better outcomes than Group 2, which had the following scores: Lysholm: 77.1 ± 7.8 (MCID: 3.78), WOMAC: 24.1 ± 9.2 (MCID: 4.41), and KOOS: 32.1 ± 9.2 (MCID: 6.03). All patients in both groups achieved the MCID for Lysholm, WOMAC, and KOOS (Group 1: 100% [30/30]; Group 2: 100% [21/21]). Immediately after surgery, meniscal extrusion decreased in both Group 1 (3.4 ± 0.8 to 2.0 ± 0.8) and Group 2 (3.2 ± 0.8 to 2.3 ± 0.8), with no significant difference between the groups. However, at the 1-year follow-up, extrusion increased again, with a greater increase observed in the lax healing group (2.8 ± 0.6 vs 4.5 ± 1.2, P < .001). Meniscal extrusion decreased by 0.6 ± 0.9 mm in the non-lax healing group, whereas it increased by 1.2 ± 1.3 mm in the lax healing group, showing a significant difference between the groups.

Conclusions: These findings suggest that non-lax healing is associated with reduced meniscal extrusion postoperatively, whereas lax healing showed no such improvement. Differences in healing quality, as identified using second-look arthroscopy, appear to be closely associated with postoperative meniscal extrusion.

Level of evidence: Level IV, retrospective case series.