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Hallux extensus is a medical condition in which the big toe, also known as the hallux, is in a permanently extended or upward-lifted position. Also referred to as a cockup deformity, this condition occurs most often at the metatarsophalangeal joint, the joint at the base of the big toe where it meets with the foot, but it may also involve the interphalangeal joint, the joint in the middle of the toe. Hallux extensus can be brought about by multiple conditions ranging from surgical complications to the inflammation or shortening of the extensor tendons on the top side of the foot. It almost always requires foot surgery to correct.
A range of deformities can afflict the metatarsophalangeal joint and cause the big toe to permanently angle into an abnormal position. In addition to hallux extensus, there is hallux valgus, also known as a bunion, in which the toe angles too far inward toward the second toe; hallux varus, in which the toe flares outward; and hallux rigidus, in which the joint suffers an inflammation that leaves the toe stiff and immovable. These conditions may require surgery to correct. Hallux extensus deformity can actually be a complication of hallux valgus and hallux rigidus surgeries.
During a Keller bunionectomy procedure, for instance, the bony projection along the inside of the base of the big toe that distinguishes a bunion is shaved down, a portion of the proximal or near bone in the big toe is removed, and a pin is placed lengthwise across the joint. At the same time, the attachments of soft tissue at the site, such as the tendon of the flexor hallucis brevis, the muscle that curls the big toe, are to be preserved. Along with that of the flexor hallucis longus, this tendon pulls downward on the toe from the plantar surface or sole of the foot, just as the tendon of the extensor hallucis muscles pull upward on the toe from the dorsal or top surface of the foot. If any of the flexor tendons is damaged or reattached improperly, the hallux extensus deformity may occur as the toe heals in an extended position. The deformity may then require a follow-up surgery to correct.
Other causes of hallux extensus include a shortening or inflammation of the tendons attaching to the top side of the big toe, collectively known as the extensor tendons. When these become stiffened or shortened, as can occur due to improper healing of an injury or tendinitis, they pull the top surface of the toe toward the shin. Corrective surgery may involve lengthening or moving these tendons to return the toe to its normal position.