MRI Protocol and Likely Structures Involved
Order an MRI of the ankle without IV contrast, and consider extending the field of view to include the midfoot given your pain distribution extending to the bases of the 2nd and 3rd metatarsals. At 6 weeks post-injury with persistent lateral ankle and midfoot pain, you need to evaluate for occult fractures, ligamentous injuries, and tendon pathology that may have been missed initially 1.
Imaging Recommendation
MRI ankle without contrast is the appropriate study for your clinical scenario of persistent pain 6 weeks after ankle sprain 1. The ACR Appropriateness Criteria specifically identify MRI as the reference standard for:
- Occult fractures with bone marrow edema patterns
- Persistent lateral ankle pain after inversion injury
- Soft-tissue injuries including ligaments and tendons
- Osteochondral lesions 1
Given your pain extends across the midfoot to the 2nd and 3rd metatarsal bases, request that the radiologist include the midfoot in the imaging protocol to evaluate for Lisfranc complex injuries or midfoot ligamentous pathology 2.
Why MRI at This Point?
At 6 weeks post-injury with ongoing symptoms, you've exceeded the typical recovery timeline. MRI has 93-96% sensitivity and 100% specificity for visualizing ligament injuries, occult fractures, and osteochondral defects 3. The guidelines note that if an ankle sprain doesn't follow the expected recovery course, MRI should be performed to evaluate for other causes of acute lateral ankle injuries 4.
Likely Structures Involved
Primary Lateral Ligaments
Anterior talofibular ligament (ATFL) is the most commonly injured structure in lateral ankle sprains, followed by the calcaneofibular ligament (CFL) 5. These comprise the lateral ligamentous complex along with the posterior talofibular ligament. Your pain under the lateral malleolus strongly suggests involvement of these structures.
Peroneal Tendons
Peroneal tendon pathology is a critical consideration given your lateral malleolar pain. The peroneal tendons (peroneus longus and brevis) run posterior to the lateral malleolus and can sustain:
- Tendinopathy
- Partial or complete tears
- Subluxation/dislocation
- Superior peroneal retinaculum injury 1
The peroneus longus tendon courses under the foot and inserts at the base of the 1st metatarsal, but peroneal pathology can cause referred pain patterns across the lateral midfoot.
Midfoot Structures
Your pain extending to the 2nd and 3rd metatarsal bases raises concern for:
- Lisfranc ligament complex injury - connecting the medial cuneiform to the 2nd metatarsal base
- Midfoot ligamentous sprains affecting the tarsometatarsal joints
- Occult fractures of the cuboid, cuneiforms, or metatarsal bases 2
Other Considerations
Lateral talar process fracture ("snowboarder's fracture") - This is frequently missed on initial radiographs (40-50% of the time) and presents with swelling inferior to the lateral malleolus, often misdiagnosed as a lateral ankle sprain 1. This should be specifically evaluated on MRI.
Osteochondral lesions of the talus - Can occur with inversion injuries and cause persistent pain 1.
Sinus tarsi syndrome - Injury to the ligaments and soft tissues in the sinus tarsi (between talus and calcaneus) can cause lateral ankle and midfoot pain.
Clinical Pitfalls to Avoid
Don't assume simple ligament sprain at 6 weeks - Persistent symptoms warrant advanced imaging 4
Don't overlook the peroneal tendons - These are commonly injured but can be missed on physical exam alone 1
Don't ignore the midfoot pain distribution - Your pain pattern extending to metatarsal bases is atypical for isolated lateral ankle sprain and suggests more extensive injury 2
Don't delay imaging further - At 6 weeks, you're already beyond typical recovery timelines for uncomplicated ankle sprains, which generally improve within 4-6 weeks with appropriate treatment 6
What to Tell the Radiologist
Request: "MRI ankle and midfoot without contrast for evaluation of persistent pain 6 weeks post-ankle sprain. Please evaluate for lateral ligament complex injury, peroneal tendon pathology, lateral talar process fracture, osteochondral lesions, and midfoot ligamentous injury including Lisfranc complex."
This ensures comprehensive evaluation of all structures potentially contributing to your symptom pattern.