#2 Case of the week: non-union of fifth metatarsal stress fracture and symptomatic os peroneum
Non-union of fifth metatarsal stress fracture, symptomatic os peroneum and peroneus longus tendinopathy in a mild cavovarus foot.
Today we discuss a 65 year old lady with lateral column foot pathology on a background of cavovarus foot deformity.
Mrs M is a 65 year old retiree who was prescribed orthotics three years ago for lateral column foot pain. Two years later, she had one episode of tripping over a power cord at home, and sprained her right ankle. She was then reviewed by another podiatrist who was concerned about point tenderness over the base of fifth metatarsal and very appropriately ordered an x-ray. This demonstrated a chronic non-union at the metaphyseal/diaphyseal junction of the right fifth metatarsal. It is likely the non-union was a chronic stress response and possible cause of her pre-existing foot pain.
The podiatrist trialled a period of offloading in a CAM boot, but as the pain persisted Mrs M was subsequently referred to a sports physician where an ultrasound was done demonstrating peroneus longus tenosynovitis. This pain resolved with a combination of an ultrasound guided steroid injection into the peroneus longus tendon sheath and change in orthotics to accommodate the supinated midfoot and cavus foot type. Mrs M's ankle was taped into hindfoot valgus and orthotics were adjusted to add a lateral eversion wedge, but the lateral column pain persisted (albeit much better with taping and orthotic adjustment). Mrs M then went on an extended overseas holiday with substantial amounts of walking, and returned in severe pain and difficulty mobilising short distances.
Mrs M was then sent to her general practitioner for further management by her podiatrist, and a referral was made to me for a surgical opinion. On examination, she had a mild cavovarus foot type bilaterally with no evidence of spinal dysraphism or neurolgical dysfunction. Coleman block testing demonstrated the deformity was forefoot driven. Her fifth metatarsal was very tender to palpation and her peroneal tendons were irritable to palpation and eversion stress testing. Plain weight bearing radiographs demonstrated a non-union of a fracture at the metaphyseal/diaphyseal junction of the fifth metatarsal as well as an os peroneum (see below).
An MRI scan was ordered which confirmed an inflamed os peroneum, severe peroneus longus tendinopathy as well as confirmation of fifth metatarsral non-union. As she had exhausted non-operative management options, surgery was discussed.
The decision was made to proceed with open reduction, internal fixation and bone grafting of the fifth metatarsal fracture, excision of the os peroneum, debridement of the peroneus longus tendon and peroneus longus to brevis transfer. I was concerned about her cavovarus foot type and we discussed the option of deformity correction as well, but Mrs M was very reluctant to undergo any bony procedures given she only developed severe foot pain after an ankle sprain. We proceeded with surgery, on the proviso that should she have ongoing non-union or recalcitrant tendinopathy we would need to consider deformity correction with osteotomies to the first metatarsal and calcaneum in the future.
The procedure was uneventful and Mrs M had an uncomplicated post-operative course. She was non-weight bearing for two weeks, then partial weight bearing in a CAM boot for a further four weeks, then weight bearing as tolerated with a gradual transition to a normal shoe. She returned to golf and walking three months post-operatively. Her six-week post-operative x-ray demonstrated complete union of the fifth metatarsal fracture and successful removal of the os peroneum.
Six months post-operatively, she returned to see me with irritation underneath the fifth metatarsal screw, which I had inadvertently left a little proud, so this was removed in theatre and Mrs M was back playing golf two weeks later. One year later, she is enjoying walking 10,000 steps a day and playing golf three times a week. She has some mild ankle instability when walking on soft sand but otherwise her activities are unlimited.
Patients with a cavovarus foot type are prone to non-union of fifth metatarsal fractures due to lateral column overload.
An os peroneum can be associated with tears in the peroneus longus tendon (see Brodsky 2014, below)
An MRI scan is a reliable investigation if concerned about peroneal tendon tears, stress fracture or symptomatic os peroneum.