The diagnostic accuracy of MRI for evaluating the posterolateral corner in acute knee dislocation.

OBJECTIVE

To investigate the diagnostic performance of preoperative MRI in evaluating posterolateral corner (PLC) structures after acute knee dislocation (KD) and determine the correlation of MRI with operative findings for grading structure integrity.

METHODS

Acute knee (femorotibial) dislocations between 2005 and 2020 with preoperative MRI and surgical posterolateral corner repair were identified from a single academic institution. From MRI, integrity was evaluated for PLC structures: lateral collateral ligament (LCL), popliteus tendon (PT), biceps femoris tendon (BFT), and ligamento-capsular complex (LCC). Frequency of injury to each structure and number of PLC structures torn in each case were tabulated. Diagnostic performance of MRI was determined using surgery as the reference standard. Correlation between MRI and surgery for each PLC structure was determined using kappa.

RESULTS

Thirty-nine KD cases (19 right) in 39 patients (28 male) were included, with mean age of 33 years. Mechanism of injury was as follows: high energy 52%, low energy 38%, ultra-low energy 10%. LCL was most frequently torn, in 95% (37/39) of cases. Most commonly, three of four PLC structures were torn in 54% (21/39) of cases. Diagnostic accuracy of MRI was high for LCL 95%, BFT 87%, PT 82%, and LCC 92%. Correlation between MRI and surgical findings was variable: substantial for BFT, moderate for LCL and PT, and fair for LCC.

CONCLUSION

MRI has high accuracy for detecting tears of posterolateral corner stabilizers in the setting of acute KD. However, for grading structure integrity, the correlation of MRI with surgical findings is variable, ranging from fair to substantial.

KEY POINTS

• In acute knee dislocation, MRI has high diagnostic accuracy for detecting tears of posterolateral corner (PLC) structures. • Preoperative MRI should be considered by orthopedic surgeons when there is clinical concern for posterolateral corner instability following acute knee dislocation. • Although MRI is valuable in the preoperative investigation of knee dislocation, clinical assessment and intraoperative exploration may still be required for definitive diagnosis.