Foot Drop: A Posterior Tibial Tendon Transfer Approach

A casual glance at the photograph may not reveal the clinical abnormality in one of the lower extremities in a seated patient. The abnormality is unilateral weakness of dorsiflexion at the ankle.

Question: Which side of the patient has this weakness?

NOTE: Unless otherwise stated, all images courtesy of V. K. Panchbhavi MD, FACS.

Answer: The patient's right lower extremity

Foot drop is associated with a wide variety of conditions that result in loss of dorsiflexion at the ankle and lead to the development of a high-steppage gait.^[1-3] The muscles that cause dorsiflexion motion at the ankle joint, the ankle dorsiflexors, are overpowered by muscles that cause plantar flexion motion at the ankle joint, the ankle plantar flexors. This imbalance leads to the subtle difference in the plantar flexion that a trained eye can observe. In the photograph, the right foot is slightly more plantar flexed at the ankle joint (arrow) than the other foot, and the right toes are closer to the floor.

Images courtesy of Sam Shlomo Spaeth (left) and V. K. Panchbhavi MD, FACS (right).

Relevant Anatomy and Function
The muscles in the anterolateral compartment of the leg (shown) are responsible for dorsiflexion of the foot at the ankle joint. These muscles—the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and peroneus tertius muscles—are supplied by branches of the deep peroneal nerve.^[2] The deep peroneal nerve is a branch of the common peroneal nerve which, in turn, is a branch of the sciatic nerve, derived from the dorsal branches of the fourth and fifth lumbar nerves and the first and second sacral nerves.

Normal function of the anterolateral compartment muscles allow the foot to be lifted off the ground during normal walking, thus clearing the foot and toes from the ground during the swing phase and controlling plantar flexion of the foot on heel strike to prevent the foot from slapping on the floor during the stance phase.^[2]

Image courtesy of Science Photo Library/Springer Medizin.

Etiology
Foot drop results from the loss of function in the muscles in the anterolateral compartment of the leg. The loss of muscle function can be due to variety of causes, including traumatic, anatomic, neurologic, and muscular (shown) or a combination of these factors.^[2,3]

Clinical Features
The classic clinical finding of high-steppage gait can be observed when patients with foot drop walk barefoot or in regular shoes without any orthotic support around the ankle. The patient in the photographs has a foot drop on the right side and can be seen lifting the right foot higher (right image) than the left foot (left image) to clear the toes from the floor.

Management
Foot drop is a feature of an underlying condition.^[1-3] As discussed in slide 4, causes for this condition vary, therefore, management of a patient with foot drop requires investigation and treatment of the underlying cause as well as management of the foot drop itself.^[2,3] There are various therapeutic interventions to manage the difficulty with gait that is related to the foot drop itself.

Conservative approaches in established cases of foot drop often involve the use of an ankle-foot orthosis—a foot drop splint (shown).^[2,3] These polypropylene splints fit at the back of the leg, are molded around the ankle to continue as a foot plate, and have straps to hold them at the legs. Foot drop splints are worn inside shoes and prevent the affected feet from dropping at the ankle joints, thereby eliminating the need to lift the involved feet higher to clear the ground.

Images courtesy of Sam Shlomo Spaeth (left) and V. K. Panchbhavi MD, FACS (right).

Surgical Intervention
Patients in whom the foot drop is unlikely to improve or resolve with time and/or conservative measures and therefore is permanent, may consider surgical interventions as an alternative to wearing a foot drop splint. A commonly performed procedure to restore the lost muscle function is a tendon transfer that involves part of the posterior tibial tendon.^[4]

This image and the subsequent ones show intraoperative steps in a posterior tibial tendon transfer procedure. The skin markings with hatch marks indicate the incision sites for harvesting and inserting part of the posterior tibial tendon. In this image, the blue arrow points to the location of the posterior tibial tendon insertion, the yellow arrow points to the medial malleolus, and the red arrow points to the proximal incision site overlying the proximal part of the posterior tibial tendon.

The posterior tibial tendon is exposed at its insertion over the navicular tuberosity.

The posterior tibial tendon is withdrawn from the proximal incision. The muscle belly is clearly seen.

A hemostat (arrow) is used to make a wide opening and a generous window in the interosseous membrane as well as to create a route for the harvested tendon to be transferred to the anterolateral compartment in the leg.

The lateral aspect of the leg is shown with skin markings that indicate the distal fibula and outlines of the calcaneus, the cuboid, and the base of the fifth metatarsal. The arrow points to the incision through which the hemostat is brought out through a generous opening made in the interosseous membrane.

The end of the posterior tibial tendon is prepared for transfer by suturing it and passing the suture across the interosseous membrane opening.

The posterior tibial tendon is brought out through the anterolateral exposure in the leg.

A subcutaneous tunnel is created with a blunt rod that is inserted from the proximal exposure in the leg and exits at another exposure site that is made over the cuboid bone.

The posterior tibial tendon is routed through the previously made tunnel, with the end visible through the exposure over the cuboid bone. The arrow points to the end of the transferred posterior tibial tendon.

A bone tunnel (shown) is drilled into the cuboid bone to accept the end of the posterior tibial tendon.

The end of the posterior tibial tendon is fixed in the tunnel (arrow) with the use of an interference screw that also attaches the tendon to the periosteum and the adjacent peroneus tertius muscle for additional stability.