Wednesday, March 17, 2010

Forfoot Deformity

A bunion is essentially a shift of the toe bones into the improper position causing pain and loss of function. The deformity involves the big toe and the long bone behind the big toe, the 1st metatarsal. Over time, the 1st metatarsal will begin to move towards the other foot (medial) while the big toe will move out of joint towards the 2nd toe (lateral). As the end of the 1st metatarsal bone begins to stick out, it will be under pressure from shoes and the ground. This constant pressure and friction will cause extra bone formation, leading to the bump that is seen on the side of the foot. The big toe will continue to shift towards the second toe causing an unbalanced big toe joint. Over time arthritis can develop in the joint due to the mal-positioned joint. A bunion deformity is always progressive. It will always get worse over time.



Severe bunion deformity with shift of the great toe under the second toe and hammertoe of the second toe.


Symptoms:
A bunion deformity does not always have to be associated with pain. Some patients have a very severe deformity and no pain, while others with a mild deformity have severe pain. Patients usually will have pain right over the bump with continued irritation and bruising to the bone from shoe gear and the ground forces. As the deformity progresses, pain will then be noticed in the joint itself when the big toe is moving. The big toe is very important during the gait cycle for pushing off the ground. With this imbalance of the joint there is a loss of the proper range of motion of the big toe joint leading to an inefficient gait. Over time arthritis will develop in the joint as the cartilage is scraped away each time the joint moves. The pain can be of different degrees depending on the degree of deformity, shoe gear, and activity level.

Causes:
Bunions are usually a genetic deformity. There is an imbalance of the muscles and the ligaments that are holding the 1st metatarsal in place. As this joint becomes weaker over time, the long metatarsal bone will begin to shift medially. The big toe is then under stress and begins to shift laterally under the pressure of the joint and shoes. Shoes with a tight and narrow toe box can help to create and make a bunion worse over time. High heeled shoes can also worsen and cause a bunion. Patients will a flat foot type (pronation) have a higher chance of having a bunion in the future.

Symptoms:
A bunion deformity does not always have to be associated with pain. Some patients have a very severe deformity and no pain, while others with a mild deformity have severe pain. Patients usually will have pain right over the bump with continued irritation and bruising to the bone from shoe gear and the ground forces. As the deformity progresses, pain will then be noticed in the joint itself when the big toe is moving. The big toe is very important during the gait cycle for pushing off the ground. With this imbalance of the joint there is a loss of the proper range of motion of the big toe joint leading to an inefficient gait. Over time arthritis will develop in the joint as the cartilage is scraped away each time the joint moves. The pain can be of different degrees depending on the degree of deformity, shoe gear, and activity level.

Diagnosis:

A clinical examination of the foot is done first. It is very important that the structure and biomechanics of the patient’s entire foot is examined. In order to identify the severity of the deformity, the stability of the joints around the bones involved is essential. The doctor will analyze the gait pattern of the patient. The doctor will identify if there is pain with joint movement and if the big toe can easily be re-located back into the joint. X-ray evaluation is essential in order to determine the degree of the bone shift and specific angles and the relationships between the bones.

Treatment Options:
Conservative treatments for bunions are limited. Wider shoe gear and accommodation for the deformity can be used to take the pressure off the area. Bracing and spacers are often used to brace the big toe back into position and can take some of the pressure of the big toe. However, this does not address the deformity and shift in the metatarsal bone. Furthermore, the bracing techniques are only work when used, once the brace is removed, the big toe will immediately go back into its deformed position. Custom molded Orthotics can take some pressure off the big toe and redistribute the forces of the ground through the rest of the foot. Orthotics can slow the progression of the deformity. There is no way to stop the progression or reverse the deformity without literally moving the bones back into the correct position and realigning the joint. This can only be accomplished through surgery.

We know that in order to realign the joint, the first metatarsal must be repositioned and fixated in the proper position. This can be accomplished by three basic types of procedures. First MPJ fusion, Offset Austin and Lapidus bunionectomy are the ideal procedures as they limit the chance of the bunion deformity from returning.

The choice of the procedure to be performed will be dictated by the severity of the deformity.


Mild Bunion Deformity
In mild and moderate bunion cases, we try to allow patients to have a more rapid recovery and limit the amount of time they need to spend off their feet. The Tightrope and Offset Austin bunion procedures allow immediate weight on the foot in a boot and also allow for rapid return to shoes. The choice of procedure best for each patient depends on the deformity size, the stiffness of the 1st metatarsal and the ease of realignment of the 1st metatarsal during the clinical exam.



Drawing of a bunoin prior surgery. Note poor alignment of the great toe and the 1st metatarsal. Grey shaded are will be removed during surgery and dotted line shows the region of bone cut.



Drawing of bunion after surgery. Note the shift of the 1st metarsal towards the second meatarsal for realignment of the column and fixation of the bones together with the two screws from top to bottom.





Clinical representations of pre and post surgery of mild bunion corrections.


Severe Bunion Deformity
In severe bunion cases, the 1st metatarsal is dramatically shifted away from the second metatarsal and there is looseness of the 1st metatarsal at the base of the bone. This is a difficult problem to correct unless the entire 1st metatarsal is realigned and held stable so it does not shift again. The Lapidus procedure allows for the 1st metatarsal to be repositioned with ideal correction and limited to no chance of bunion return. Recovery is slightly more difficult due to the need for crutches but the result is well worth it in difficult and severe cases. Some patients even require fusion of the first metatarsophalangeal joint secondary to this variation of deformity.

Hypermobility

The underlying cause of severe bunions is thought to be at the medial cuneiform joint and not at the great toe joint. If there is looseness of the medial cuneiform joint, there is motion of the metatarsal allowing the metatarsal to move out of position resulting in a bunion. The metatarsal may also move up resulting in poor position on the ground and collapse of the arch.

Clinical Pictures