Abstract
Most of the controversy surrounding management of the adult acquired flatfoot deformity revolves around the correction of Stage 2 deformity. Stage 1 deformity, uncommonly corrected surgically, involves tenosynovitis with preservation of tendon length and absence of structural deformity. Attempts at tenosynovectomy in light of structural deformity leads to operative failure, found in 10% of Teasdall and Johnson's 1992 patient population. Thus, with tenosynovectomy rarely becoming an operative situation, Stage 2 deformity becomes the mainstay of operative treatment of the adult flatfoot. Stage 2 deformity patients present with swelling medially, the inability to do a single heel raise, with a passively correctable subtalar joint. The tendon is functionally torn. In recent years, authors have subdivided Stage 2 deformity even further into A and B subcategories, where A involves less than 50% uncovering of the talonavicular joint, and B patients more than 50%. Recently, Anderson has added a C subtype, which may be applied to either A and B patients, in patients who have forefoot varus. Thus, Stage 2 patients suffer from pain that begins medially and progresses to the subfibular region over time. Most important, recognition of the continued sub classification in Stage 2 disease echoes the fact that this disorder is on a continuum, challenging the surgeon to recognize subtleties that, if unrecognized, lead to a poor patient outcome. The mainstay of treatment in Stage 2 disease is the medial slide calcaneal osteotomy, which realigns the hindfoot axis reducing valgus, improves the medial arch, protects the FDL tendon transfer, and allows the Achilles tendon to become a strong inverter. Over shift of the calcaneus can compromise the outcome, as will a lack of recognition of the congenital subtleties such that a valgus hindfoot can have a varus orientation to the calcaneus, both leading to lateral overload. A pure medial slide of a calcaneus that has a varus orientation does not correct deformity, rather, it creates it. Thus, an axial calcaneal view must be studied carefully, for a varus orientation may be corrected via a closing wedge osteotomy commensurate with the medial shift of the tuberosity. As noted above, the flexor digitorum longus tendon transfer is the staple procedure to replace the damaged posterior tibial tendon. This transfer balances the eversion power of the peroneal tendons, works in phase with the former posterior tibial tendon in the stance phase of gait, and replaces a painful diseased posterior tibial tendon. However, over tensioning the transfer results in a tenodesis rather than a functional tendon transfer, the relative weakness of the FDL tendon (30% as strong as the PTT) creates difficulty with heel raise, and inappropriate transfer to distal tarsal bones may compromise the result by limiting torque from the transferred tendon. Preservation of the posterior tibial tendon in combination with the transferred FDL tendon remains a consideration without answer, though Rosenfeld (2005) suggests a substantial improvement in strength through PTT preservation. Failure of the above protocol for treating Stage 2 disease most often revolves around the insufficient corrective power of the tandem procedures in longstanding ruptures. According to Guyton (2001), only 50% of patients report a perception in deformity improvement following FDL/calcaneal osteotomy procedures, and only 4% report a significant improvement in pre-existing deformity. Sangeorzan (2001) found such patients could not achieve a painless plantigrade foot due to acquired ligament laxity (primarily the Spring Ligament). Sangeorzan applied Evans' pediatric procedure to adults without confirming the pathomechanics of correction. Some speculate the windlass effect on the plantar fascia creates correction (refuted by Horton, 1998, finding the plantar fascia is loosened by a lateral column lengthening), others believe tightening the peroneus longus through lateral column lengthening increases first ray plantarflexion, restoring the medial arch. Controversy also remains in answering Cooper's (1997) claim that lengthening through the calcaneus creates static increase in pressure about the calcaneocuboid joint (1.4mPa total) that may lead to an arthritic joint long term. Painful lateral overload following lateral column lengthening remains difficult problem to both prevent and correct. This last point leads to some focusing their efforts on restoration of the medial column. This group focuses on the “C” type deformity noted by Anderson, those with forefoot varus. It is known that the medial column is supported by the navicular, the cuneiforms, and the first, second, and third metatarsals. While a Cotton (opening wedge medial cuneiform) osteotomy, a first tarsometatarsal joint arthrodesis, or a metatarsal osteotomy has value, the surgeon must note that this only corrects the first ray. Complete correction of the medial column is best achieved through naviculocuneiform joint arthrodesis. Standing radiographs commonly reveal collapse at that level; however, surgeons are reticent to perform such fusions in light of the higher nonunion rate.
