Point-Counterpoint: Is The Flexor Digitorum Longus Tendon Transfer Effective For Stage 2 Adult-Acquired Flatfoot?
Citing multiple advantages, this author emphasizes that combining a flexor digitorum longus tendon transfer with a gastrocnemius recession and medial displacement calcaneal osteotomy can provide pain relief to patients with stage 2 posterior tibial tendon dysfunction.
By William T. DeCarbo, DPM, AACFAS
Posterior tibial tendon dysfunction (PTTD) is a common pathology that foot and ankle specialists encounter. Posterior tibial tendon dysfunction is characterized by a valgus hindfoot, flattening of the longitudinal arch of the foot and abduction of the forefoot. This is a progressive deformity that begins with the foot being flexible but it can become rigid over time. Johnson and Strom classified Stage 1 PTTD as a foot with an intact arch, Stage 2 as a flexible flatfoot deformity and Stage 3 as a fixed flatfoot deformity.1 Myerson later introduced Stage 4 as an underlying Stage 2 or Stage 3 deformity with the addition of deltoid ligament laxity leading to a valgus tilt of the ankle joint.2
Initial treatment is based on the degree of deformity and flexibility at the initial presentation. Conservative treatment includes orthotics or ankle foot orthoses to support the posterior tibial tendon and the longitudinal arch, anti-inflammatories, activity modification and physical therapy. If conservative treatment fails, consider offering surgical intervention. For a Stage 1 deformity, a posterior tibial tendon tenosynovectomy or primary repair may be indicated. For Stage 2, a combination of Achilles lengthening with calcaneal osteotomies and tendon transfers is common.3 In Stage 3 or 4 PTTD, isolated fusions may be indicated.4
The normal biomechanics of the posterior tibial tendon are to invert the subtalar joint (STJ), plantarflex the ankle and adduct the forefoot.5 The posterior tibial tendon also stabilizes the hindfoot in conjunction with the gastrocnemius-soleus complex by inverting the heel during gait, which locks the transverse tarsal joints, converting the foot into a rigid lever for push-off.6 This initial inversion of the hindfoot by the posterior tibial tendon is crucial in the gait cycle for normal ambulation. Any pathology that attenuates or damages the posterior tibial tendon may have an adverse effect on this function.7
With pathology of the posterior tibial tendon, its antagonist, the peroneus brevis tendon, acts as a deforming force in the development of hindfoot valgus and forefoot abduction.5,8 This leads to the hindfoot not being supinated during heel strike, resulting in the midfoot remaining flexible with no rigid lever for push-off. Over time, the longitudinal arch decreases due to the secondary static ligaments (spring ligament) stretching, resulting in abduction of the forefoot.9
A Closer Look At Tendon Transfers And Adjunctive Procedures For Stage 2 PTTD
In Stage 2 flexible PTTD, tendon transfers to help restore the longitudinal arch and the posterior tibial tendon are common. Which tendon to transfer depends on multiple issues including the axes of motion around the ankle and hindfoot, the muscle strength of the individual tendons and the phase the muscle fires in the gait cycle.10
Silver and colleagues calculated the strength of the posterior tibial tendon to be 6.4, the anterior tibial tendon to be 5.6, the peroneus longus 5.5, the flexor hallucis longus 3.6, the peroneus brevis 2.6 and the flexor digitorum longus tendon to be 1.8, with muscle strength relative to the proportional cross-sectional area.11 The posterior tibial tendon, flexor hallucis longus tendon and the flexor digitorum longus tendon all fire in the same phase of the gait cycle.5 Due to the relative strength of the flexor digitorum longus tendon, surgeons often combine its transfer to augment the posterior tibial tendon with adjunctive procedures to decrease the biomechanical stress on the transferred tendon.5