Does discoid lateral meniscus have inborn peripheral rim instability? Comparison between intact discoid lateral meniscus and normal lateral meniscus.

INTRODUCTION: Little is known about peripheral rim instability (PRI) of adult discoid lateral meniscus (DLM). We compared PRI of the intact DLM (iDLM) to those of intact normal lateral meniscus (LM) in adult patients and also investigated whether there was any association between PRI and DLM tears.

MATERIALS AND METHODS: We investigated PRI in 17 DLMs and 60 normal LMs without tears during arthroscopic surgery for medial compartmental pathologies between June 2012 and October 2015. We also investigate PRI of torn DLM (tDLM) excluding peripheral tear to compare the PRI between intact and torn DLM. Stability parameters were measured using a probing hook and arthroscopic ruler at the anterior, middle, and posterior parts of the peripheral rim of the menisci: translating the anterior horn (AH) and mid-body (MB) and lifting the posterior horn (PH).

RESULTS: AH and PH instabilities were greater in the iDLM group than in the iLM group (2.2 ± 1.4 vs. 0.9 ± 1.4 mm, p = 0.006 and 3.4 ± 1.7 vs. 1.7 ± 1.2 mm, p = 0.004, respectively). However, there was no significant difference in MB instability between two groups. In addition, no significant difference was observed in all the parameters between the iDLM and tDLM groups.

CONCLUSION: Both iDLM and tDLM had greater PRI of the AH and PH than the iLM in adult patients. Thus, the DLM is prone to tear and careful inspection is needed not to overlook PRI of a DLM even if the peripheral attachment is intact.

LEVEL OF EVIDENCE: Level 3, comparative study of anatomical instability of living subjects.