Point-Counterpoint: Is The Flexor Digitorum Longus Tendon Transfer Effective For Stage 2 Adult-Acquired Flatfoot?

William T. DeCarbo, DPM, AACFAS; Lawrence A. DiDomenico, DPM, FACFAS, Ramy Fahim, DPM, AACFAS, and Zachary Thomas, DPM

   In our previous case series of 34 patients, we accomplished considerable radiographic correction in pursuing extra-articular hindfoot osteotomies (medializing calcaneal osteotomy and/or Evans lateral column lengthening) as well as medial column fusions.18 Patients demonstrated successful postoperative outcomes over an average follow-up period of 14 months.

Other Pertinent Points

Addressing the structural corrections at the apex of the deformity significantly relieves the stress on the posterior tibial tendon. Cadaveric studies have proven that realigning the hindfoot can decrease the elongating strain on the posterior tibial tendon by 51 percent.19 This redirects the transverse plane deformity and the loading of forces on the foot as the medial longitudinal arch stabilizes while preserving essential motion at the hindfoot. Positioning the heel in rectus alignment with the leg eliminates the abnormal pull of the tendo-Achilles and mechanical advantage of the peroneus brevis.

   Another important advantage of avoiding the flexor digitorum longus tendon transfer is decreasing the operative morbidity. This decision is both patient- and surgeon-friendly for the following reasons:

• less operating time (including tourniquet time) as well as anesthesia time;
• fewer incision sites;
• better cosmesis;
• reduced postoperative edema; and
• quicker postoperative rehabilitation as there is less morbidity.

   Ultimately, the use of flexor digitorum longus tendon transfers for posterior tibial augmentation in flatfoot deformity correction has been well documented in the foot and ankle literature. However, the exact role of those transfers in the overall deformity correction still remains an area of debate. There is no proof that one can predictably reproduce the structural support with those tendon transfers alone.

   Paradoxically, Murray and colleagues have demonstrated a significantly smaller cross-sectional area of the flexor digitorum longus tendon by 50 percent in comparison to the posterior tibial tendon counterpart.20 In addition, by applying various levels of plantar load, the authors showed the posterior tibial tendon to tolerate twice the amount of plantar load than that of the flexor digitorum longus tendon.

Final Words

In essence, in relying on the flexor digitorum longus tendon transfer, we would be replacing the function of a weakened tendon with an inherently weak tendon for structural support. We offer a different perspective and advocate for structural reconstruction of the deformity to establish a mechanically stable and functional foot.

   Rather than performing the flexor digitorum longus tendon, we choose to offload the posterior tibial tendon by creating a mechanical advantage. With the time the patient is in a non-weightbearing, below-the-knee cast postoperatively, the tendon has sufficient time to heal. When the patient returns to weightbearing, the foot is mechanically balanced and the stress that caused the initial symptoms is neutralized.

   In conclusion, we do not believe that a smaller tendon (flexor digitorum longus tendon) can predictably provide the mechanical advantage to stabilize the midfoot in the long term in cases in which patients suffer from stage 2 PTTD. Additionally, our experience demonstrates that the diseased posterior tibial tendon does respond to non-operative care by being immobilized in the postoperative period of the surgical reconstruction. The reconstructive foot surgery provides a mechanical advantage and offloads the stress from the posterior tibial tendon. We suggest this process is similar to other successful immobilization techniques for other tendonopathies.

   In our experience, we reserve the flexor digitorum longus tendon transfer for those few select cases in which one has identified a significant tear of the posterior tibial tendon.

   Dr. DiDomenico is affiliated with the Forum Health/Western Reserve Care System in Youngstown, Ohio. He is the Section Chief of Podiatry at St. Elizabeth’s Hospital in Youngstown, Ohio. He is the Director of the Reconstructive Rearfoot and Ankle Surgical Fellowship within the Ankle and Foot Care Centers in Ohio, and the Kent State University College of Podiatric Medicine. Dr. DiDomenico is a Fellow of the American College of Foot and Ankle Surgeons.

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