When The Step Isn't The Only Thing Missed: A Case Of Undiagnosed Posterior Malleolar Fracture

HISTORY: Isolated posterior malleolar fracture are uncommon with low energy trauma. Identification is typically part of more complex injuries. In this case we discuss a 15yo female who missed a step on the front porch at home and twisted her ankle leading to an undiagnosed posterior malleolar fracture. PHYSICAL EXAMINATION: Examination in the office showed mild edema and ecchymosis over the lateral ankle. Tender to palpation at the distal posterior medial tibia and the fifth metatarsal. Non-tender to palpation at the anterior ankle joint or syndesmosis, posterior calf, deltoid ligament, and across the first and second tarsal-metatarsal joints. Negative squeeze test DIFFERENTIAL DIAGNOSIS: Ankle sprain Posterior malleolar fracture Bimalleolar or trimalleolar fracture Maisonneuve fracture Pilon fracture TESTS AND RESULTS: 10/5/24 XR Right ankle: Lateral ankle soft tissue swelling, intact ankle mortise, and no evidence of acute fracture. 10/9/24 XR Right Ankle/Tibia/Fibula: Joint spaces and mortise well maintained. Nondisplaced posterior malleolus fracture. No other evidence of fracture or dislocation. Upon review, posterior malleolus fracture was evident on X-ray from 10/5/24 but was not indicated in the radiology impression. 10/9/24 CT Right Ankle: Acute nondisplaced posterior malleolus fracture. Minimal soft tissue swelling over the lateral malleolus. No evidence of tibiotalar widening or other fractures. 10/15/24 XR Right Ankle Weightbearing: Again, demonstrates posterior malleolus fracture with no medial clear space widening. 11/7/24 XR Right Ankle Non-Weightbearing: Redemonstration of nondisplaced posterior malleolus fracture with some interval healing compared to previous imaging. Ankle mortise intact and no medial clear space widening. FINAL WORKING DIAGNOSIS: Right posterior malleolus fracture Right lateral ankle ligament sprain TREATMENT AND OUTCOMES: Initial non-weight bearing for 4 weeks in short leg cast Transitioned to weight bearing as tolerated in walking boot Self-paced home exercise program and begin physical therapy Plan for continued follow up with pending weight bearing radiographs