In the late 1960s papers began to appear describing the development of a flatfoot deformity in association with a tear of the tibialis posterior tendon. Most of the early cases were traumatic, but in 1969 Kettlekamp and Alexander described several cases with no traumatic history. In 1989 Johnson and Strom classified the condition of "tibialis posterior tendon dysfunction" and proposed a system of treatment. Tibialis posterior tendon dysfunction came to be seen as " the commonest cause of the adult acquired flatfoot". Physical signs, as discussed later, were viewed as evidence of tibialis posterior insufficiency. Johnson and Strom discussed staging as though there were an established progression from tenosynovitis without foot deformity, through partial to complete rupture of the tendon with increasing but flexible deformity to fixed deformity without tendon function. Johnson and Strom’s treatment recommendations for most patients concentrated on replacing the function of the absent tendon.
However, further research over the last 10 years has shown that the situation is much more complex than previously thought
- Dyal et al showed that 70% of patients with unilateral tibialis posterior insufficiency had a contralateral flat foot, implying that the symptomatic foot was probably flat to start with.
- Division of the tibialis posterior tendon in a normal foot cadaver model does not in itself necessarily produce a flatfoot deformity – division of the plantar fascia, long and short plantar ligaments and deltoid/spring ligament complex are required.
- The spring ligament appears to play an important part in arch integrity in live patients
- MRI of flatfeet shows abnormality in the spring ligament as well as the tibialis posterior tendon in neary all feet, and in the superficial deltoid and interosseous talocalcaneal ligaments in most
- The tibialis posterior is inactive in quiet standing although it is active during mid-stance phase of walking. In standing the main support of the arch is the plantar fascia.
- Singh et al showed that patients without tibialis posterior function due to neurological deficit or tibialis posterior tendon transfer do not necessarily develop a flat foot, even in the presence of peroneus brevis function.
- The cardinal physical sign of tibialis posterior insufficiency is generally considered to be inability to perform a single foot tiptoe test, but Tansey (2001) showed that over 50% of heel supination on tiptoe in the normal foot is due to the plantar fascia windlass effect. Results in flat feet are awaited.
- Some patients have an obviously functional tibialis posterior tendon yet have progressive foot deformity with the apex at their degenerate 1st TMT joints. This was noted in 1982 by Henceroth and Deyerle, and was described by Menz (2010).
It is notable that a symposium in Clinical Orthopaedics and Related Research in 1999 was entitled "Adult Acquired Flatfoot". Probably adult flatfoot and tibialis posterior tendonopathy should be thought of as inter-related conditions rather than as a single disease entity. It seems likely that, in most patients, a pre-existing flatfoot may predispose to tendonopathy which permits the progression of deformity, and so on as a vicious cycle. This view of the syndrome would have the important corollary that attention to the tendon will be of little value unless the deformity is addressed to improve the biomechanics of the foot.