Posterior Tibial Slope and Risk of Posterior Cruciate Ligament Injury.

BACKGROUND: Recent biomechanical studies have identified sagittal plane posterior tibial slope as a potential risk factor for posterior cruciate ligament (PCL) injury because of its effects on the kinematics of the native and surgically treated knee. However, the literature lacks clinical correlation between primary PCL injuries and decreased posterior tibial slope. PURPOSE/HYPOTHESIS: The purpose of this study was to retrospectively compare the amount of posterior tibial slope between patients with PCL injuries and age/sex-matched controls with intact PCLs. It was hypothesized that patients with PCL injuries would have a significantly decreased amount of posterior tibial slope when compared with patients without PCL injuries. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Patients who underwent primary PCL reconstruction without anterior cruciate ligament injury between 2010 and 2017 by a single surgeon were retrospectively analyzed. Measurements of posterior tibial slope were performed with lateral radiographs of PCL-injured knees and matched controls without clinical or magnetic resonance imaging evidence of ligamentous injury. Mean values of posterior tibial slope were compared between the groups. Inter- and intrarater agreement was assessed for the tibial slope measurement technique via a 2-way random effects model to calculate the intraclass correlation coefficient (ICC). RESULTS: In sum, 104 patients with PCL tears met the inclusion criteria, and 104 controls were matched according to age and sex. There were no significant differences in age ( P = .166), sex ( P = .345), or body mass index ( P = .424) between the PCL-injured and control groups. Of the PCL tear cohort, 91 patients (87.5%) sustained a contact mechanism of injury, while 13 (12.5%) reported a noncontact mechanism of injury. The mean ± SD posterior tibial slopes were 5.7°± 2.1° (95% CI, 5.3°-6.1°) and 8.6°± 2.2° (95% CI, 8.1°-9.0°) for the PCL-injured and matched control groups, respectively ( P < .0001). Subgroup analysis of the PCL-injured knees according to mechanism of injury demonstrated significant differences in posterior tibial slope between noncontact (4.6°± 1.8°) and contact (6.2°± 2.2°) injuries for all patients with PCL tears ( P = .013) and among patients with isolated PCL tears ( P = .003). The tibial slope measurement technique was highly reliable, with an ICC of 0.852 for interrater reliability and an ICC of 0.872 for intrarater reliability. CONCLUSION: A decreased posterior tibial slope was associated with patients with PCL tears as compared with age- and sex-matched controls with intact PCLs. Decreased tibial slope appears to be a risk factor for primary PCL injury. However, further clinical research is needed to assess if decreased posterior tibial slope affects posterior knee stability and outcomes after PCL reconstruction.

Decreased Posterior Tibial Slope Does Not Affect Postoperative Posterior Knee Laxity After Double-Bundle Posterior Cruciate Ligament Reconstruction.

BACKGROUND: Recent clinical studies identified sagittal plane posterior tibial slope as a risk factor for increased postoperative laxity after single-bundle posterior cruciate ligament reconstruction (PCLR). PURPOSE/HYPOTHESIS: To retrospectively compare the degree of posterior tibial slope and its effect on posterior tibial translation (PTT) after double-bundle (DB) PCLR. Our null hypothesis was that preoperative tibial slope would not be associated with graft laxity. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Patients who underwent DB PCLR between 2010 and 2017 by a single surgeon were retrospectively analyzed. Measurements of posterior tibial slope were performed on lateral radiographs, and PTT was measured with pre- and postoperative kneeling stress radiographs. Simple and multiple linear regression was performed to estimate the unadjusted and adjusted effect of tibial slope on postoperative graft laxity, respectively. RESULTS: A total of 103 patients with posterior cruciate ligament tears and subsequent reconstructions were included. There was a significant reduction of the mean ± SD side-to-side difference in PTT between stress radiographs (preoperative, 10.6 ± 2.7 mm; postoperative, 1.5 ± 2.6 mm; mean difference, 9.1 mm; 95% CI, 8.4-9.8; P < .001). Linear regression analysis revealed no significant correlation between preoperative posterior tibial slope and the amount of side-to-side difference in PTT on postoperative stress radiographs obtained at a mean 18.5 months ( R = -0.115, P = .249). Combined ligament injury (beta = -1.01; 95% CI, -2.00 to -0.01; P = .047) was a significant independent predictor of decreased postoperative side-to-side difference in PTT. CONCLUSION: Graft laxity, determined by PTT in posterior kneeling stress radiographs, was not influenced by decreased posterior tibial slope after DB PCLRs. The observed results in the current study support the use of DB PCLR. Future studies should be conducted to compare the effect of tibial slope after SB PCLR and DB PCLR at long-term follow-up.

Posterior Tibial Translation Measurements on Magnetic Resonance Imaging Improve Diagnostic Sensitivity for Chronic Posterior Cruciate Ligament Injuries and Graft Tears.

BACKGROUND: Magnetic resonance imaging (MRI) of the knee is a highly sensitive and specific method for diagnosing acute posterior cruciate ligament (PCL) tears, with a reported accuracy of 96% to 100%. In chronic and revision settings, these injuries may be missed on MRI because of the apparent continuity of nonfunctional PCL fibers. Posterior tibial translation (PTT) of the medial compartment has been identified as a potential secondary finding of PCL tear on routine MRI. Purpose/Hypothesis: The purpose of this study was to evaluate the sensitivity of PTT on MRI associated with PCL injuries and compare it with the sensitivity of a radiologist's MRI interpretation with preoperative posterior knee stress radiographs as the gold standard. Our hypothesis was that the MRI measurement of PTT of the medial compartment would improve diagnostic sensitivity as compared with the diagnosis made by the interpreting radiologist's evaluation of the continuity of the PCL fibers for chronic and postrecostruction graft injuries. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 2. METHODS: Cases of patients who underwent a primary or revision PCL reconstruction, without anterior cruciate ligament injury, by a single surgeon between 2010 and 2016 were retrospectively analyzed. Measurements of medial and lateral compartment PTT were performed with the MRI of PCL-injured cases and controls without clinical or MRI evidence of ligamentous injury. The sensitivity of this technique was compared with the preoperative MRI diagnosis determined by review of the musculoskeletal radiologist's report and confirmed by the gold standard of posterior knee stress radiographs. The sensitivity of medial compartment PTT was determined by receiver operator characteristic (ROC) analysis and compared with the MRI sensitivity for chronic PCL and PCL graft tears. RESULTS: One hundred patients (80 males and 20 females) with a mean age of 31.1 years (range, 15-66 years) met the inclusion criteria: 57 acute primary tears, 32 chronic primary, and 11 PCL graft tears. MRI sensitivity was 100% for acute primary PCL tears, 62.5% for chronic primary PCL tears, and 18.1% for PCL graft tears. There were significant differences in medial compartment PTT on MRI for acute versus chronic injuries ( P = .025) and acute versus graft injuries ( P = .007). ROC curve analysis indicated that the most accurate cutoff point for the detection of chronic PCL tears was 2.0 mm of medial compartment PTT on MRI, with a sensitivity and specificity of 0.80 and 0.89, respectively. For PCL graft injuries, the ROC curve indicated that the most accurate medial compartment PTT cutoff for the detection of PCL graft failure was 3.6 mm (sensitivity, 0.92; specificity, 0.72). CONCLUSION: MRI evaluation of the PCL fibers had poor sensitivity for chronic PCL tears and PCL reconstruction graft tears. The sensitivity for diagnosing chronic PCL tears and PCL reconstruction graft failures was improved by measuring posteromedial tibial translation.