The prevalence of adult acquired flatfoot or tibialis posterior tendonopathy has not been established. It is quite likely that there are many more or less asymptomatic persons in the community which makes it difficult to measure the numerator. In Blackburn we see about 20 new patients a year in a catchment area of 260,000.
Tibialis posterior tendonopathy is commonest in middle-aged females. The only series to report the characteristics of an entire patient population is that of Suneja (2006). The median age was 59 years and the female:male ratio 3:1.
Myerson et al (1989) also identified a group of younger male patients with seronegative arthropathies and synovitis. Suneja et al found that patients without progressive flatfoot had a median age of 45 years and the female:male ratio was 2:1; however, they excluded patients with known inflammatory arthropathy. Suneja et al also identified a group who presented with predominantly arthritic symptoms, mainly in the 1st TMT joint, and had less tibialis posterior tendon abnormalities.
Some workers have examined the relationship between tibialis posterior tendonopathy and rheumatoid hindfoot deformity. Keenan et al (1991) found increased tibialis posterior EMG activity in rheumatoid flatfeet – although this would not exclude the possibility that the increased activity was ineffectual because of tendonopathy. Coakley et al (1994) found no clinical evidence of insufficiency in 18 rheumatoid valgus feet. Michelson et al(1995) found clinical evidence of tibialis posterior insufficiency in 11% of rheumatoid feet. Jernberg et al (1999)found tibialis posterior tendonopathy in 12/19 rheumatoid patients with flatfoot, but only 7/21 in non-flat feet. However, there were only 2 complete ruptures on MR scan and MR and clinical findings correlated poorly. Tibialis posterior tendonopathy probably contributes to the development of rheumatoid planovalgus deformity, but joint instability due to synovitis and abnormal biomechanics due to other deformities is probably more important. This may also be relevant to the "typical" adult acquired flatfoot.
Some patients give a clear history of a forced valgus injury which precipitates their problem. 48% of Myerson’s series had such a history. Traditionally this has been viewed as a missed tibialis posterior tear, and such injuries have been described. However, it may be that these injuries are more complex and involve, in particular, the deltoid and spring ligament complex.
Holmes and Mann (1992) reviewed the general medical conditions in 67 patients with tibialis posterior tendonopathy and found that half had hypertension, diabetes mellitus or obesity – obesity had the greatest association followed by hypertension. While it is intuitive that obesity may promote deformity of an unstable foot, the other conditions may simply be markers for middle-aged relatively unfit patients.