This procedure is performed if the muscles and tendons that normally pass in front of the ankle and lift the foot up are weak or non-functioning (Drop Foot). Often this condition can be treated with bracing, but in patients who desire increased function or who cannot tolerate bracing, this procedure may be of significant benefit. A common cause of a drop foot is the loss of muscle function in the front of the lower leg due to compartment syndrome or peroneal nerve injury. In addition, conditions that cause selective or generalized nerve or muscle weakness, such as Charcot-Marie-Tooth disease, muscular dystrophy, or stroke, may develop dysfunction of the anterior compartment muscles and benefit from this procedure.
In this procedure, the surgeon releases the posterior tibial tendon from its insertion into the navicular. The incision is made on the inside (medial) aspect of the foot, and the tendon is released.
A second incision, which is about an inch long, is made on the inside of the lower leg, just above the bony lump (medial malleolus) on the inside of the ankle. To identify this spot for yourself, find the bony prominence on the inside of the ankle then go back about an inch and a half, and then up about three inches. This is where the cut tendon of the posterior tibialis is pulled out and then passed behind the tibia, right along the bone.
The third incision is made in front of the lower leg, three or four inches above the ankle. The rest of the procedure involves pulling the tendon out through the front of the lower leg, in between the tibia and fibula and through a hole in the strong tissue that holds these two bones together (the interosseous membrane). From there the surgeon has a number of options, depending on the deformity and whether the transferred tendon needs to pull straight up, up and to the inside, or up and to the outside.
The surgeon can hook the tendon into bone at the top of the midfoot and use a screw to anchor it there. However, one problem with this is that the harvested tendon often isn’t long enough to easily reach the top of the foot.
Another option is to attach the tendon to other tendons, like the tibialis anterior, located at the top inside of the foot, or one of the extensor tendons, which can then be transferred to the top of the foot.
Overview of surgery
The posterior tibial muscle and tendon remains attached at the proximal point, runs through the interosseous membrane and is then anchored into the midfoot (ex. The lateral cuneiform).
The tendons have to be rerouted under the band of tissue that keeps the tendons passing across the front of the ankle in place (the extensor retinaculum). This presents an issue, because the procedure requires forcing a tendon through an already packed space.
Re-routing the tendon
The tendon can be routed in various ways: it either can be split and then re-routed into two tendons, or it can be routed singularly into the tibialis anterior. The re-routing can be done in a number of ways. The two tendons in question are often woven together. This is done by creating a slit in the tendon you are transferring through which to pull the tendon being transferred, and then suture it into position with non-absorbable sutures. Another slit is then made perpendicular to the other slit, and the process is repeated.
To allow the tendon transfer to heal, the patient will need six weeks in a cast boot without weight bearing. They will then require another four to six weeks of physical therapy and retraining. Patients will achieve approximately 75% of their recovery in the first six months, as they work to regain the lost muscle strength. It is often longer than a year after surgery before the patient achieves their maximal improvement.
The usual potential risks of surgery are present with this operation, including the risk of:
Potential complications that are specific to this procedure include:
- Failure of the tendon transfer: The transferred tendon could fail by pulling apart after it is loaded.
- Loss of muscle strength: Weakness of the tendon transfer will occur because transferred tendons automatically lose some strength. Muscle strength is graded on a scale of 0 to 5 (0/5 = No function, 5/5 = normal strength). Transferred muscle-tendon units will tend to lose one grade of strength, leading to 4 out of 5 strength when the results are good.
- Out of phase muscles: Another problem is that the muscles-tendon unit that was transferred is now “out of phase”. The muscle isn’t supposed to be activated during that phase of gait, but it does in this case. The tibialis anterior usually lowers the foot to the ground and doesn’t function much during midstance, but posterior tibialis does.
- Persistent gait asymmetry: This procedure is designed to improve a patient’s gait, and hopefully allow patients to go without a brace. However, it will not produce a symmetrical gait and this can lead to symptoms elsewhere (ex. low back)
Edited April 17, 2015