Morphologic Variants of Posterolateral Tibial Plateau Impaction Fractures in the Setting of Primary Anterior Cruciate Ligament Tear

Abstract

Background: Impaction fractures of the posterolateral tibial plateau commonly occur in the setting of anterior cruciate ligament (ACL) tears, with considerable variability found in fracture size and morphologic features. Purpose: The primary objective was to characterize different morphologic variants of posterolateral tibial plateau impaction fractures. The secondary objective was to investigate the association between these impaction fracture variants and concomitant meniscal and ligamentous injuries. Study Design: Cross-sectional study; Level of evidence 3. Methods: Patients treated for primary ACL tears and having magnetic resonance imaging available were included in this study, and magnetic resonance images were reviewed with denotation of displaced posterolateral tibial impaction fractures. A classification system was created based on morphologic variants of impaction fractures; associations were evaluated through use of independent chi-square testing. Results: There were 825 knees meeting the inclusion criteria, with displaced posterolateral tibial plateau impaction fractures present in 407 knees (49.3%). We observed 3 distinct morphologic variants of lateral tibial plateau impaction fractures: (I) posterior cortical buckle not involving the articular surface; (II) posterior impaction fracture involving the articular surface, with subtypes based on (A) tibial plateau depth bone loss <10% and (B) bone loss >10%; and (III) displaced osteochondral fragment, with subtypes for (A) shear or (B) depressed fragment. Type IIIA impaction fractures were associated with an increased incidence of lateral meniscus posterior root tears (33.3% vs 12.4%; P = .009) and an increased incidence of lateral meniscal tears (83.3% vs 56.7%; P = .024) compared with all knees without type IIIA impaction fracture. An increased incidence of medial collateral ligament (MCL) tears was noted in patients with type IIIA impaction fractures compared with those who had no fracture or had another fracture type (61.1% vs 20.1%; P < .001). Type IIIB impaction fractures were associated with an increased incidence of lateral meniscal tears (80.0% vs 56.2%; P = .005). Conclusion: A high prevalence of displaced posterolateral tibial plateau impaction fractures occur in the setting of ACL tears, and they can be classified into distinct morphologic subtypes. Posterolateral tibial plateau impaction fractures with displaced depressed or shear fragments were both associated with an increased incidence of lateral meniscal tears, whereas impaction fractures with a shear fragment were associated with an increased incidence of lateral meniscus posterior root tears and MCL tears.

High-Grade Posterolateral Tibial Plateau Impaction Fractures in the Setting of a Primary Anterior Cruciate Ligament Tear Are Correlated With an Increased Preoperative Pivot Shift and Inferior Postoperative Outcomes After Anterior Cruciate Ligament Reconstruction

“…Given that we observed tibial plateau bone loss depth of greater than 10% in 8.6% of the patients in our primary ACL tear cohort, we found that altered lateral tibial plateau geometry was not that uncommon after a primary ACL tear. It has been previously reported that higher grade posterolateral tibial plateau impaction fractures were associated with concomitant meniscal and ligamentous abnormalities, 4 which could also affect postoperative outcomes after ACLR; however, our statistical analysis did control for concomitant meniscal or ligamentous abnormalities. It is unclear whether the association with decreased postoperative Lysholm scores that we identified was caused by tibial plateau bone loss or if it was merely the effect of increased concomitant abnormalities associated with a higher energy injury.…”

“…The classification system for posterolateral tibial plateau impaction fractures in the setting of an ACL tear utilized in this study was recently introduced, 4 and in this study, we have validated it to be clinically relevant because patients with higher grade impaction fractures had lower Lysholm scores at 2 years postoperatively. Previous studies have assessed the effect of milder impaction injuries (eg, bone bruising) on clinical outcomes after ACLR but have failed to show any difference in outcomes.…”

“…Part 1 of our evaluation detailed the incidence of posterolateral tibial plateau impaction fractures and associated injuries, and part 2 detailed morphological subtypes of these impaction fractures with a proposed classification system. 3,4 The inclusion criteria were shared with the 2 previous studies, consisting of patients with primary ACL tears and available preoperative MRI scans treated by a single board-certified orthopaedic surgeon (R.F.L.) between April 2010 and March 2019.…”

“…Preoperative MRI scans were reviewed for all patients per the protocol outlined in study parts 1 and 2 3,4 to determine (1) whether posterolateral tibial plateau impaction fractures were present and (2) to classify these impaction fractures according to a classification system based on fracture morphology. A review of MRI scans was performed by a single board-certified orthopaedic surgeon (D.L.B.).…”

“…A standardized technique for measurements of the impaction fracture has been previously developed and reported. 4 The tibial plateau anteroposterior bone loss depth and the height of the impaction fracture lesions were measured from a sagittal slice at the 50th percentile of the lateral tibial plateau's width ( Figure 1).…”