Impaction fractures of the posterolateral tibial plateau have been well described in association with injury to the anterior cruciate ligament (ACL). No consensus has been reached on the role these injuries play in rotatory knee stability, with some studies suggesting that increasing severity of the fracture leads to increased rotatory knee instability. The purpose of this study was to evaluate these injuries and how they contribute to rotatory knee stability via the use of quantitative data.
Two hundred eighty-four consecutive patients with complete ACL tears had data prospectively collected. All patients underwent ACL reconstruction by a single, fellowship-trained orthopaedic sports medicine surgeon. Basic demographic information was obtained via chart review. The magnetic resonance imaging (MRI) of each patient was reviewed to identify posterolateral tibial plateau impaction fractures. Patients were placed into two cohorts: fractures or no fractures. The cohort with fractures were further categorized based on fracture morphology: extra-articular, articular-impaction, or displaced-articular fragment. All data were collected during the exam under anesthesia (EUA). This included a standard, subjectively graded, pivot shift test graded by the examiner and quantitative data including the Rolimeter measure of anterior tibial translation, quantitative pivot shift (QPS) exam, and acceleration during the pivot shift. The PIVOT application, a previously verified application for a computer tablet, was used for the QPS. An accelerometer was used to obtain the knee’s acceleration during the pivot shift exam. These quantitative exams were compared to the contralateral knee. The quantitative pivot, Rolimeter, and accelerometer were used to remove any subjective bias of the physical exam. Significance was met if p<0.05.
The prevalence of posterolateral impaction fractures was 39.44%. Of the fractures, 63.4% were extra-articular, 25.0% were articular-impaction, and 11.6% were displaced-articular. There were no differences in patient demographics or time from injury to surgery. There was no difference in the average of subjectively graded pivot shift in those with fractures vs those without (1.8±0.3 vs1.7±0.4, respectively, p=0.81). Similarly, the QPS revealed no statistically significant difference regardless of presence or not of a fracture (2.4±1.6mm vs 2.7±2.2mm, respectively, p=0.26). Anterior tibial translation measurements were not statistically significant different whether or not a fracture was present (5.5±2.7mm vs 5.4±2.6mm, respectively, p=0.74). The acceleration of the knee during the pivot did not reveal a statistically significant difference with or without a fracture (1.7±2.3m/s2 vs 1.8±3.2m/s2, respectively, p=0.86). When the fractures were further subdivided, there were no statistically significant differences noted in any of the measured exams between the variants.
The results of this study demonstrate posterolateral tibial plateau impaction fractures in the setting of ACL tears do not significantly impact rotatory knee instability. Therefore, surgeons may consider in-situ fixation of these injuries in patients with ACL tears.