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.

The association of patellar tendinosis with patellar maltracking and Hoffa's fat pad impingement: A case-control MRI study.

OBJECTIVES: To assess whether proximal or distal patellar tendinosis is associated with patellar maltracking parameters and superolateral Hoffa's fat pad impingement. METHODS: Institutional radiology database was reviewed for knee MRI scans performed over a 7-year period identifying cases of unequivocal patellar tendinosis, which were separated into 2 groups: proximal and distal tendinosis. For each group of proximal and distal patellar tendinosis, a control group of age and gender matched subjects was assigned. The scans were evaluated for patellar maltracking parameters including patellar alta, tibial tuberosity lateralization, trochlear dysplasia and lateral patellar tilt and for presence of superolateral Hoffa's fat pad edema. These parameters were compared between the case and control groups. RESULTS: Out of 9852 MRI scans, 94 patellar tendinosis cases were included (65 proximal and 29 distal tendinosis) and matched with equal numbers of controls. In the proximal patellar tendinosis group, more subjects had patella alta (22 versus 6, p = 0.0006), lateralization of tibial tuberosity (16 versus 7, p = 0.0495) and superolateral Hoffa's fat pad edema (16 versus 4, p = 0.0073) compared to the control group. In the distal patellar tendinosis group, there was no significant difference in the prevalence of any maltracking indicator or superolateral Hoffa's fat pad edema compared to the control group. CONCLUSION: Proximal patellar tendinosis was associated with patellar maltracking parameters including patella alta, lateralized tibial tuberosity and superolateral Hoffa's fat pad impingement. No association was demonstrated between distal patellar tendinosis and patellar maltracking indicators or superolateral Hoffa's fat pad impingement.

Subperiosteal chondromyxoid fibroma: a rare case involving the humeral diaphysis.

Initially described, in 1948, as a tumor that could be mistaken with chondrosarcoma at histopathology, chondromyxoid fibroma is now a well-recognized entity. Surface-type chondromyxoid fibroma, however, remains an extremely rare occurrence. We present a case of a 55-year-old woman, who experienced right arm pain for 5 years. After unsuccessful treatment for presumed thoracic outlet syndrome, MRI revealed a large mass abutting the anteromedial cortex of the distal humeral diaphysis in a subperiosteal location. Further characterization was made with radiography, CT, and bone scan, which were followed by ultrasound-guided biopsy. Although histopathologic features were suggestive of chondromyxoid fibroma, the diagnosis remained somewhat uncertain initially due to the very unusual location involving the diaphysis of the humerus. Surgical resection was performed, and subsequent histopathologic analysis confirmed the diagnosis of chondromyxoid fibroma. Despite being a rare entity, surface-type chondromyxoid fibroma would need to be considered in the differential when dealing with expansile surface diaphyseal lesions.