The role of meniscal tears and meniscectomy in the mechanical stability of the anterior cruciate ligament deficient knee.

BACKGROUND: The role of an intact meniscus in providing mechanical stability to the knee of anterior cruciate ligament (ACL) deficient and ACL reconstructed patients has not been well studied.

METHODS: This was a prospective cohort study. A total of 205 patients undergoing ACL reconstruction were enrolled, of which 61 had normal menisci, 49 had a tear in the posterior horn of the medial meniscus (PHMM) (tear <40% of width = 19; >40% of width = 30), 35 had a tear in the lateral meniscus (<40% of width = 15; >40% = 20), 13 had a tear in the body and/or anterior horn of the medial meniscus (<40% of width = 6; >40% = 7) and 47 patients had a tear in both menisci. Patients with a tear in both menisci were excluded. The anterior translation of the tibia (ATT) was calculated preoperatively and postoperatively at three months and six months using KT-1000. Partial meniscectomy was performed in all unstable meniscal tears.

RESULTS: The mean age at the time of surgery was 25.2 ± 5.1 years. Patients with a normal meniscus showed side to side difference in KT-1000 of 4.8 ± 2.5 mm whereas those with a <40% tear and >40% tear in PHMM had a difference of 5.36 ± 3.07 mm (P = 0.46) and 7.08 ± 2.78 mm (P = 0.0002), respectively. Patients with a lateral meniscus <40% and >40% tear had a mean difference of 5.68 ± 2.96 mm (P = 0.22) and 5.95 ± 2.39 mm (P = 0.09), respectively. Patients with body and/or anterior horn of medial meniscus <40% and >40% had a difference of 5.41 ± 1.11 mm (P = 0.59) and 5.78 ± 2.38 mm (P = 0.35), respectively. At three months and six months KT-1000 differences of 2.3 ± 1.2 mm and 2.1 ± 1.2 mm were seen in patients with normal meniscus; 2.26 ± 1.51 mm and 2.16 ± 0.9 mm with partial meniscectomy of the PHMM <40%; 2.65 ± 1.53 mm and 2.4 ± 1.35 mm with partial meniscectomy of the PHMM >40%; 2.27 ± 1.19 mm and 2.07 ± 1.52 mm with partial meniscectomy of the lateral meniscus <40%; and 2.27 ± 1.44 mm and 2.07 ± 1.14 mm with partial meniscectomy of the lateral meniscus >40%; 2.55 ± 1.56 mm and 1.91 ± 1.09 mm with partial meniscectomy in body and/or anterior horn of medial meniscus <40% and 2.07 ± 1.81 and 2.14 ± 1.10 mm with partial meniscectomy in body and/or anterior horn of medial meniscus >40% (P > 0.05).

CONCLUSION: PHMM acts as a secondary stabilizer of the knee joint in the absence of functional ACL. There is no effect of partial meniscectomy on mechanical stability of the knee in ACL reconstructed patients. Medial or lateral partial meniscectomy performed at the time of ACL reconstruction does not affect the stability of ACL reconstructed knee. However, the presence of a concomitant tear in PHMM is associated with increased instability in ACL deficient knee.