Johnson and Strom (1989) recommended subtalar fusion for correction of the acquired flatfoot when the deformity of the foot was fixed (stage 3). This was based on the concept that the midfoot and forefoot would follow the calcaneum – the "two-piece concept".
Three series of around 20 patients, one from Kitaoka (Johnson’s successor at the Mayo Clinic), report good radiographic correction, with clinical scores similar to those of lateral column lengthening (mean AOFAS scores about 80) and no non-unions. Most patients also had FDL transfers, so the fusion was really an alternative to posterior calcaneal osteotomy. One series used fusion particularly for lateral impingement pain. Interestingly, Kitaoka commented that subtalar fusion is not appropriate in patients with midfoot supination as the forefoot deformity is not corrected – a denial of Johnson’s “two-piece concept”.
Subtalar fusion seems to be a useful procedure, although for indications other than described by Johnson. In particular it may be useful for patients whose main complaint is lateral impingement pain.
As the commonest deformity of adult acquired flatfoot is maximal at the talonavicular joint (Kitaoka et al 1998) it seems logical to consider stabilising this joint to restore the anatomy. Talonavicular fusion produces marked limitation of hindfoot motion in a cadaver model: 70% of pronation/supination and 25% of dorsiflexion/plantarflexion (Gellman et al 1987). Fogel et al (1982) performed gait analysis on patients 9 years after talonavicular fusion and found up to 30% loss of inversion/eversion, particularly on slopes, and reduction in late-stance plantarflexion.
One clinical series reported 26 patients who had talonavicular fusions for "the disorder known as insufficiency of the posterior tibial tendon". There was one non-union and one major wound problem. Over half had some residual pain, usually in the lateral midfoot. OA had developed or progressed in five surrounding joints. It is not clear whether the patients were selected for severe deformities or the procedure was applied “across the board”; there was no record of pre-op or post-op deformity.
In Blackburn we use talonavicular fusion particularly for some patients with severe deformities and fixed hindfoot-forefoot malalignment. Good correction of deformity is usually achieved, but we have also seen patients who develop lateral column pain.
One double fusion technique fuses the talonavicular and calcaneocuboid joints. It aims to increase the stability of the midfoot correction and to avoid lateral column pain after isolated talonavicular fusion. It is particularly indicated where both midtarsal joints are arthritic, and in very obese patients.
One series (Mann and Beaman 1999) reported 16 patients who had double arthrodesis for tibialis posterior insufficiency. Mean AOFAS score was 79. The non-union rate was 25%, none of which had compression fixation. Although radiological correction was good, most feet appeared flat "but symmetrical".
An alternative double fusion is performed on the talonavicular and subtalar joints. Sammarco (2006) performed this in 14 patients with various conditions, mainly flatfoot. Deformity was well corrected, with one talonavicular non-union.
For patients with severe fixed deformities or degenerate changes in all hindfoot joints a triple fusion is generally indicated. This allows correction of all elements of the deformity and stabilisation of the correction, but greatly alters the biomechanics of the foot.
Three series (Graves, Mann and Graves (1993), Fortin and Walling (1999) and Coetzee and Hansen (2001)) report good improvement in pain and AOFAS scores about 75. Patients tended to have problems with slopes, uneven ground and stairs. Radiological correction was good. The non-union rate was about 5%, and there were some overcorrections, wound problems, fibular tip pain and nerve injuries.
Most patients were corrected by minimal resection of the joint surfaces and rotation/translation of the joints to the corrected position. Two modifications of this technique are worth having in the armamentarium:
A few patients have ankle OA or develop it after initial treatment. The surgical options here are:
extended hindfoot fusion with at least a tibiotalocalcaneal fusion and usually fusion of the talonavicular, calcaneocuboid and possibly lesser tarsal joints also. The use of a retrograde nail helps with stabilisation of such procedures
osteotomies and/or arthrodesis to correct the hindfoot deformity and any necessary soft tissue reconstruction such as FDL transfer to the navicular or deltospring ligament repair, plus ankle replacement
There are no useful outcome figures available for these procedures.