Summary
Preoperative knee laxity in ACL injury was quantitatively evaluated using an electromagnetic measurement system, and the results suggest that ramp lesions of the medial meniscus are associated with greater anterior tibial translation in Lachman test in ACL-injured knee.
Abstract
Background
Ramp lesions of the medial meniscus associated with anterior cruciate ligament (ACL) injuries have received considerable attention in recent years, but there is still a lack of consensus regarding the influence of ramp lesions on knee laxity. Thus, the purpose of this study was to quantitatively evaluate the relationship between ramp lesions and preoperative anterior knee laxity and anterolateral rotatory instability (ALRI) using three-dimensional electromagnetic measurement system (EMS). It was hypothesized that preoperative anterior tibial translation would be greater in patients with ramp lesions than in patients without ramp lesions.
Method
Two hundred and six patients with primary ACL rupture (average age: 26.9 years, 107 males/99 females) were included in the present study. At the time of surgery, a definitive diagnosis was made regarding the presence of concomitant meniscal injuries. Ramp group consisted of cases in which only the ramp lesions were injured and no other meniscal injuries was involved. Control group was defined as those without medial/lateral meniscus injury. Prior to the surgery under general anesthesia, the side-to-side difference (SSD) in anterior tibial translation (ATT) during the Lachman test, and tibial acceleration during the pivot-shift test were measured using the EMS as previously reported. The SSD in ATT using KT-2000 arthrometer was also measured. These data were compared between the two groups by using unpaired t-test (P < 0.05).
Results
Ramp lesions were observed in 30 patients (14.7%), and 13 of whom had also lateral meniscal injury. Finally, there were 17 patients in the ramp group (age: 26.5 years, M/F: 10/7) and 77 patients in the control group (age: 27.2 years, M/F: 39/38), and no significant differences were observed between the two groups in terms of patients’ demographic data. The SSD in ATT during Lachman test was significantly greater in the ramp group (9.1 ± 6.6 mm) than the control group (6.2 ± 4.4 mm, P = 0.037), while no significant difference was observed in terms of SSD in ATT using KT-2000 between ramp group (5.5 ± 2.5 mm) and control group (5.1 ± 2.2 mm, P = 0.55), as well as in the tibial acceleration between the two groups (1.3 ± 0.9 m/s2 vs. 1.5 ± 0.9 m/s2, P = 0.65).
Discussion
The main finding of the present study was that quantitative measurement using the EMS has shown the ramp lesions of the medial meniscus are associated with greater preoperative ATT during the Lachman test in ACL injury. On the other hand, no significant difference was observed in ATT using an arthrometer and tibial acceleration during the pivot-shift test. This discrepancy in the results between Lachman test and KT-2000 measurement could be partially attributable to the difference in the maneuver and precision between two examinations. The present findings suggest the ramp lesions are contributed to increased anterior knee laxity in ACL injury, and the posterior horn of the medial meniscus acts as a secondary restraint to anterior tibial translation in ACL-deficient knee.