Background
In vitro biomechanical research demonstrated the detrimental impact of lateral meniscus posterior root (LMPR) tears on rotatory laxity in the anterior cruciate ligament (ACL)-injured knee. However, the impact of LMPR tears on the pivot shift (PS) in ACL-injured patients remains unclear. The purpose of this study was to evaluate the effect of LMPR tears on rotatory knee laxity using a clinically validated quantitative pivot shift (QPS) analysis system.
Methods
Patients with ACL injury enrolled in a prospective ACL registry from 2012 to 2020 were retrospectively screened for eligibility. To limit confounders, patients were included if they had primary ACL tears, no concurrent ligamentous or bony injuries requiring operative treatment, and no previous surgeries to either knee. Data pertinent to patient demographics, and manual and instrumented clinical exams were extracted through chart review. Intraoperative data with regards to the presence of a LMPR tear, tear depth, position, and relation to the popliteal hiatus were collected by a single fellowship-trained orthopedic sports medicine surgeon.
Patients were assigned to two cohorts based on the presence (LMPR+) or absence (LMPR-) of an LMPR tear concomitant with ACL injury. Each patient underwent examination under anesthesia, performed by the operating surgeon. Examination included a standardized PS test, measurement of anterior tibial translation (mm) using the Rolimeter, and QPS assessment (mm) with a tablet-based image analysis system (PIVOT App). Descriptive statistics included frequency, proportion (%), median, and interquartile rage (IQR). Between-group comparisons of categorical variables were performed using the Fisher exact and Chi-square tests. Non-normally distributed continuous variables were compared between groups with the Mann-Whitney U test. Level of significance was set at p<0.05.
Results
A total of 111 patients were included in the study, of which 25(23%) were assigned to the LMPR+, and 86(77%) to the LMPR- group. The majority of LMPR tears were localized to zone 1 (n=9,36%) or zone 2 (n=9,36%). Tear depth was considered partial in 15(60%) patients and full in 10 (40%) patients. Of the LMPR tears, 7(28%) were central to the popliteal hiatus. There was no significant difference in age, gender, body mass index and time from injury to surgery between the LMPR+ and LMPR- groups. No difference was observed in anterior tibial translation measured using the Rolimeter between patients with (5.0mm;IQR=3.0) and without (5.0mm;IQR=3.0) LMPR tears (p=0.85). The majority of patients in both LMPR+ (n=37,43%) and LMPR- (n=16,64%) groups had a grade 2 preoperative manual pivot shift. The side-to-side difference in QPS was significantly greater in the LMPR+ (2.4mm;IQR=2.5) compared with the LMPR- (1.9mm;IQR=2.1) group (p=0.033). The prevalence of medial meniscus tears was greater in the LMPR+ (n=17, 68%) compared with the LMPR- (n=34,40%) group(p=0.021).
Conclusion
Preoperative quantitative rotatory knee laxity is significantly greater in patients with concurrent ACL and LMPR tears compared to patients with ACL but no LMPR tears. Consequently, high-grade PS should raise the index of suspicion for concomitant soft tissue injury, including LMPR tears, which should be repaired to avoid persistent rotatory knee laxity and further intraarticular injury in patients with ACL tears.