Dorsal Exostosis, refers to an osteoarthritic change that occurs in the first metatarsal joint on the top side of the joint. It manifests as osteophytic lipping, which is viewed easily by x-ray, and shows as a bump on the top of the joint.
This condition is similar to bunions although there is no deviation of the big toe. The bony enlargement occurs on the dorsum or top of the first metatarsal phalangeal joint.
What is exostosis?
It can be painful, but also benign. The toe can have limitations in its range of movement (dorsiflexion) or extension of the big toe due to the osteoarthritic changes in the joint.
This is often referred to as hallux limitus or in more severe cases hallus rigidus.
The cause of dorsal exostosis is biomechanical factors that alter the alignment of the foot. This leads to excess pronation and an inability of the first toe to flex correctly during toe-off.
This inability to flex leads to joint space narrowing and osteoarthritic changes in the joint.
There may have been some trauma to the joint on the past.
Tight calf muscles play a role by forcing the arch to sag, as a way of compensating, leading to a limitation in first toe function and joint space narrowing.
Treatment for dorsal exostosis
Treatment involves correcting the biomechanics, stretching and orthotics to improve foot function and reduce pronation.
This will ease the stress on the joint. Some joints though may already be too rigid from arthritic changes. In some cases stretching and foot mobilisation will suffice to relief pain.
Painful joints that do not respond to conservative care, may need surgery to clean the joint up.