Diseases of the peroneal tendons and superior peroneal retinaculum (SPR) are frequently underdiagnosed causes of lateral ankle pain and instability. Common diseases include tenosynovitis, rupture, and dislocation of the peroneal tendons as well as injuries to the SPR. Many anatomic variants, such as a flat or convex retromalleolar fibular groove, hypertrophy of the peroneal tubercle, an accessory peroneus quartus muscle, a low-lying peroneus brevis muscle belly, or an os peroneum, may be associated with or predispose to lateral ankle disease. Magnetic resonance (MR) imaging is excellent for detecting soft-tissue and bone variants and abnormalities related to the lateral ankle. Knowledge of the MR imaging appearances of these entities aids radiologists in making the precise diagnosis of disorders of the peroneal tendons and SPR. Pitfalls and normal variants of the peroneal tendons, including magic angle phenomenon, pseudosubluxation of the peroneus brevis tendon, a bifurcated or mildly crescentic peroneus brevis tendon, insertion of the peroneus quartus tendon into the peroneus brevis tendon, and the presence of an os peroneum are important to recognize. It is also useful to be familiar with the MR imaging appearances of SPR injuries, which can be an overlooked but treatable cause of lateral ankle pain and instability.
Purpose
To evaluate the performance of diffusion tensor imaging (DTI) in the evaluation of chronic exertional compartment syndrome (CECS) as compared to T2-weighted imaging.
Materials and Methods
Using an IRB-approved HIPAA-compliant protocol, spectral adiabatic inversion recovery (SPAIR) T2-weighted imaging (T2w) and stimulated echo DTI were applied to 8 healthy volunteers and 14 suspected CECS patients before and after exertion. Longitudinal and transverse diffusion eigenvalues, mean diffusivity (MD), and fractional anisotropy (FA) were measured in 7 calf muscle compartments, which in patients were classified by their response on T2w: normal (<20% change), and CECS (>20% change). Mixed model analysis of variance compared subject groups and compartments in terms of response factors (post-/pre-exercise ratios) of DTI parameters.
Results
All diffusivities significantly increased (p<0.0001) and FA decreased (p=.0014) with exercise. Longitudinal diffusion responses were significantly smaller than transversal diffusion responses (p<0.0001). 19 of 98 patient compartments were classified as CECS on T2w. MD increased by 3.8±3.4% (volunteer), 7.4±4.2 % (normal), and 9.1±7.0% (CECS) with exercise.
Conclusion
DTI shows promise as an ancillary imaging method in the diagnosis and understanding of the pathophysiology in CECS. Future studies may explore its utility in predicting response to treatment.
Based on 4.7% of cases requiring a change in the operative plan as a result of preoperative MRI, the authors recommend considering performing screening MRI in operative SK patients.
Most repeated radiographs (chest more so than musculoskeletal radiographs) did not add significant clinical information or alter diagnosis, although they did increase radiation exposure. The decision to repeat images should be made after viewing the questionable image in context with all images in a study and might best be made by a radiologist rather than the performing technologist.
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