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Suspected fifth metatarsal base fracture after inversion injury — MSRA MCQ

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HardSoft Tissue InjurySuspected fifth metatarsal base fracture after inversion injuryMSRA

A 34-year-old recreational runner attends general practice 3 days after an inversion injury to her right foot when stepping off a kerb. At an urgent treatment centre on the day of injury, ankle radiographs (anteroposterior, mortise and lateral views; no foot series) were reported as normal and she was diagnosed with a lateral ankle sprain. She has used paracetamol, elevation and an ankle support, but lateral foot pain is worsening and she cannot complete four weight-bearing steps. There is bruising over the lateral midfoot and marked focal bony tenderness at the base of the fifth metatarsal. There is no tenderness over either malleolus, the navicular or proximal fibula. The Achilles tendon is intact and distal neurovascular examination is normal. What is the most appropriate management today?

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Correct answer: C — Arrange same-day assessment for a foot radiograph series, with protected weight-bearing pending imaging

Explanation lettering: E = shown as A · C = shown as B · A = shown as C · B = shown as E

This presentation requires a foot radiograph series today. The important change is localisation of pain and tenderness to the base of the fifth metatarsal after an inversion mechanism, with inability to take four steps. This is not adequately explained away by previously normal ankle radiographs, because no dedicated foot series was obtained. A fifth-metatarsal base fracture, including an inversion-related avulsion fracture, must be excluded. NICE recommends use of the Ottawa ankle and foot rules to determine the need for radiography in suspected ankle-region fractures. Under the Ottawa foot rules, midfoot pain with bony tenderness at the base of the fifth metatarsal is an indication for foot radiography; inability to bear weight further increases concern. Protected weight-bearing is appropriate while fracture is being excluded. B is incorrect because the discriminating tenderness is in the midfoot/base of the fifth metatarsal rather than the malleolar zone; repeating ankle views may again fail to provide the appropriate foot assessment. C would be appropriate for an uncomplicated ligament sprain after fracture has been reasonably excluded, but not with focal fifth-metatarsal bony tenderness. D is not first-line imaging for an acute suspected fracture. E may be relevant for suspected peroneal tendon pathology, but it does not address the immediate need to exclude a bony injury.

Reference: NICE Guideline NG38: Fractures (non-complex): assessment and management, recommendation 1.2.2 (2016) — https://www.nice.org.uk/guidance/ng38/chapter/recommendations Peroneal tendon subluxation: the other lateral ankle injury (2010) — https://bjsm.bmj.com/content/44/14/1047 Diagnostic accuracy of the Ottawa Ankle and Midfoot Rules: a systematic review with meta-analysis (2017) — https://pubmed.ncbi.nlm.nih.gov/27884861/