Dorsal Metatarsal Cuneiform Exostosis

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A dorsal first metatarsocuneiform exostosis is an enlargement of the bone on the dorsum of the foot at the base of the first metatarsal and the medial cuneiform due to osteoproliferation. The enlarged exostosis can become painful from shoe pressure and a bursitis may develop or the neve impinged. It is reasonably common problem and most people do have a ‘hump’ in that area on the dorsum of the foot, but it is not large enough to cause any problems. This sometimes gets called a saddle bone deformity.

Aetiology
Dorsal ‘humping’ of midfoot is common in those with a pes cavus (especially if it is the anterior type of pes cavus).
Proliferation of bone from dorsal hypermobility or movement of the first ray (the exostosis develops from that dorsal ‘jamming’ at the metatarsocuneiform joint).
Trauma may also be involved.

Clinical features:
There is a prominence of base of first metatarsal and medial cuneiform that may be all osseous or may have a soft tissue bursitis in addition to the exostosis.
The pain is most often described as dull or sharp in its nature.
The main cause of the symptoms are pressure from footwear over the prominence resulting in discomfort and erythema from that shoe pressure. This can be a particular problem in activities that require rigid footwear (eg ice skates or ski boots).
There may be parathesias, tingling and numbness due to a compression of medial dorsal cutaneous nerve over the area. The medial dorsal cutaneous nerve almost always crosses the metatarsocuneiform joint.
Sensory testing, especially in the dorsal first web space may indicate any involvement of the nerve.
On a lateral x-ray, the dorsal prominence will be visible; there may be plantar gap in metatarsocuneiform joint due to the dorsal hypermobility of the first ray.
There may be some osteoarthritis in the joint contributing to the symptoms.

Classification of a Dorsal Metatarsal Cuneiform Exostosis:
Type 1: Local dorsal exostosis
Type 2: Dorsal exostosis with osteoarthritis of joint
Type 3: Dorsal exostosis with angular deformity
Type 4: Exostosis extends across other metatarsocuneiform joints
Type 5: Pseudoexostosis of dorsal humping of anterior pes cavus

Differential Diagnosis:
Ganglion cyst; bursitis; extensor tendonopathy

Management:
Initially, avoid closed in footwear as much as possible to settle it down.
Sometimes, removing the laces from the eyelets over the area of the exostosis will be enough to help.
Padding on the underside of tongue of the shoe to accommodate the prominence – either U-shaped or donut shaped to accommodate the deformity; can be made from silicone, adhesive felt or fashioned from other materials such as EVA or Poron.
Foot orthotics with design features to plantarflex the first ray may be useful, but can also elevate the arch area and cause more pressure from the shoe on the exostosis.
Steroid injections and nonsteroidal anti-inflammatory drugs may give relief from the symptoms.
Surgical options include excision or arthrodesis of the joint if conservative measures fail. Care needs to be taken not to damage the nerve during the procedure.

Related Topics:
Saddle Bone Deformity

Page last updated: Jul 18, 2022 @ 5:14 am

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