FDL surgery, which stands for Flexor Digitorum Longus surgery, is a common orthopedic procedure most often performed on the foot and ankle. The operation typically involves repairing or repositioning the FDL tendon to correct painful deformities and restore proper function to the foot. Its primary application is treating conditions that lead to the collapse of the foot’s arch, but it is also used for certain toe deformities.
Anatomy and Function of the FDL Tendon
The Flexor Digitorum Longus (FDL) is a muscle located deep within the back compartment of the lower leg, and its tendon extends down into the foot. This long, slender tendon travels behind the inner ankle bone, or medial malleolus, before entering the sole of the foot. It eventually splits into four separate slips, which attach to the undersurface of the second through fifth toes.
The primary role of the FDL muscle is to flex the four smaller toes downward at their joints, which is important for gripping the ground. The FDL tendon also contributes significantly to the structural integrity of the foot. It assists with plantarflexion, the motion of pointing the foot downward, and helps to stabilize the medial longitudinal arch.
The FDL tendon is often used as a “donor” in reconstructive procedures. Because other smaller muscles within the foot also contribute to toe flexion, the FDL can be repurposed to take over the function of a damaged or non-functional tendon without causing significant loss of toe movement.
Common Conditions Treated by FDL Surgery
The most frequent reason for FDL surgery is to treat Posterior Tibial Tendon Dysfunction (PTTD), which is the leading cause of adult-acquired flatfoot deformity. The posterior tibial tendon is the main structure supporting the arch of the foot, and when it becomes inflamed, torn, or stretched out, the arch gradually collapses. The FDL tendon transfer replaces the failed or weakened posterior tibial tendon.
The FDL tendon is rerouted and fixed to the navicular bone, which is the attachment site of the original posterior tibial tendon. This transfer provides a necessary dynamic force to support the arch. This tendon transfer procedure is almost always performed in conjunction with other operations, such as a calcaneal osteotomy, where the heel bone is cut and repositioned to realign the foot.
A different application of FDL surgery addresses hammertoe deformities, where one or more of the smaller toes bend abnormally at the middle joint. In these cases, the FDL tendon can be released or partially cut, a procedure known as a tenotomy, to relieve the excessive pull that causes the toe to buckle. Releasing the tight tendon allows the toe to straighten and lie flat, correcting the painful deformity.
Details of the Surgical Procedure
FDL surgery is typically performed under general anesthesia or a regional nerve block. The patient may be admitted for one or two days for monitoring and initial pain management. The primary surgical technique involves making an incision along the inner side of the ankle and foot to access the tendons. The surgeon first identifies the FDL tendon and traces it to the sole of the foot.
The tendon is then cut and separated from its connections to the toes, leaving the remaining toe flexors to maintain some function. The detached end of the FDL is rerouted and prepared for its new function. A bone tunnel is drilled into the navicular bone, the target insertion point for the transferred tendon.
The FDL tendon is then passed through this tunnel and secured with a specialized device, such as a bio-absorbable screw or a suture anchor. This fixation anchors the tendon, ensuring it can exert the necessary force to lift and support the arch. This primary transfer procedure is often followed immediately by a medializing calcaneal osteotomy, which involves shifting the heel bone to improve the foot’s mechanical alignment.
The combined procedures are necessary because the flatfoot deformity is a complex structural issue, not just a tendon problem. The surgeon closes the incisions with sutures and a splint or cast is applied to immobilize the foot in a corrected position.
Recovery and Rehabilitation Timeline
Recovery from FDL tendon transfer surgery follows a structured, multi-phase timeline. Immediately after the operation, the foot is immobilized in a cast or splint, and the patient must remain strictly non-weight-bearing for the first six weeks. During this time, the focus is on elevating the foot to control swelling and managing post-operative pain.
The intermediate phase begins around six weeks post-surgery, when the patient transitions from a cast to a removable walking boot. Progressive weight-bearing is permitted, gradually increasing the pressure placed on the foot over several weeks. Physical therapy begins during this phase, concentrating on gentle range-of-motion exercises to activate the transferred tendon and prevent stiffness.
From three to six months, the rehabilitation intensifies to rebuild strength and endurance. The patient works to transition out of the boot and into supportive shoes, focusing on gait training and strengthening exercises. Full recovery, including the ability to perform a single heel raise, often takes nine to twelve months, but the patient can typically return to most daily activities by six months.