Adult acquired flatfoot

Last evidence check April 2011

The Johnson and Strom classification

Johnson and Strom (1989) proposed a staging system which is in general use in the orthopaedic foot and ankle community. They recognised three basic stages:

Myerson added a stage 4, where there is fixed foot deformity and tilting of the talus in the ankle mortise. Dereymaeker also proposed a stage 0, where there is biomechanical abnormality but no symptoms – this acknowledges the more importance of pre-existing biomechanics but implies that stage 0 feet are likely to progress.

Hattrup and Johnson’s classification was based on clinical examination, with treatment recommendations as follows:

1 2 3
Tendon condition
peritendonitis/degeneration elongation elongation
mobile, normal mobile, valgus fixed, valgus
medial, focal medial, along tendon medial + sinus tarsi/lat ankle
Single heel rise
mild weakness marked weakness marked weakness
"Too many toes" sign
normal positive positive
synovitis/degeneration degeneration degeneration
conservative/debridement FDL => tib post transfer subtalar arthrodesis

Unfortunately, there are a number of problems with the Hattrup and Johnson staging system:

For all these reasons, it is probably time to re-evaluate the classification and staging of adult acquired flatfoot, acknowledging both the seminal work of Hattrup and Johnson and subsequent work. A revised classification should probably incorporate:

The Truro classification

A development of the Johnson and Strom classification was described by Parsons (the Truro classification). It principally divides stage 2 into three stages, depending on the severity and reducibility of the classification, and also recognises that stage 1 patients may have a pre-existing flatfoot deformity:

Preliminary studies show the Truro classification is usable by different professional groups and is fairly reproducible. The greatest discrepancies occur between stages 2a and 2b.

Truro stage



Truro staging in Jackson (2009)

Jackson (2009) reported the clinical characteristics of the complete consecutive Blackburn series. Half their patients were in stage 2. Stage 2c (whose existence was denied by Johnson) accounted for 13%.

Jackson drew attention to an additional group of patients previously alluded to by the Seattle group (Greisberg 2003). Eighty percent of Jackson's series persented with symptoms related primarily to the tibialis posterior tendon, spring ligament and deltoid ligament. However, the remaining 20% had mainly arthritic symptoms, especially in the 1st TMT joint, were slightly older and much more likely to require surgery.

Myerson(2005) has proposed that there should be radiological criteria of the severity of deformity and is evaluating such criteria. It seems likely that there will be a revised classification within the next five years.

The natural history is believed to be a progression from tendonopathy without deformity, through a mobile deformity to a foxed deformity. However, few patients have been followed to demonstrate progression of the condition. In the Blackburn series (Jackson 2009) the median age of Truro stage 1 patients was 15 years less than that of the rest. Patients in stages 2C-4 (stiffer deformities) were slightly older than in stages 2A/B (flexible deformities) but the difference was not significant. About 25% of Blackburn patients had progressed under observation, although follow-up was incomplete.