Osteoarthritis (OA) of the 1st metatarsophalangeal joint (MTPJ) is a common and disabling condition. The aims of this study were to determine if differences exist in the foot structure of people with and without radiographically defined 1st MTPJ OA, and whether structural differences are associated with radiographic severity of 1st MTPJ OA.
Weight-bearing dorso-plantar and lateral radiographs were obtained for the symptomatic foot of 137 participants (60 men, 77 women, aged 22 to 85, mean 58.1 +/- 11.4 years) with clinically diagnosed 1st MTPJ OA. Radiographic 1st MTPJ OA cases were identified and participants were graded into four severity categories using a validated atlas. The following radiographic measurements were performed: hallux abductus angle, hallux abductus interphalangeus angle, intermetatarsal angle, metatarsal protrusion distance, metatarsus adductus angle, first metatarsal declination angle, lateral intermetatarsal angle, calcaneal inclination angle, 1st metatarsal length and width, hallux proximal phalanx length and width and hallux distal phalanx length. Structural differences were compared using univariate general linear models, adjusting for age, sex and body mass index.
One hundred and four participants were categorised as having radiographic 1st MTPJ OA. The OA case group displayed a greater hallux abductus interphalageus angle compared to the no OA case group. Participants were further categorised into no OA (n=6), mild OA (n=27), moderate OA (n=49) or severe OA (n=55) categories. Participants of the mild, moderate and severe OA categories displayed a longer 1st metatarsal compared to the no OA category. The moderate and severe OA categories displayed a greater hallux interphalangeus angle compared to the mild category OA.
Discussion and clinical relevance
Overall, there were few structural differences between OA cases and non-OA cases and between OA severity categories, although there was some evidence to suggest greater 1st metatarsal length in more severe cases of 1st MTPJ OA. The greater abduction of the hallux distal phalanx in OA cases and greater severity OA categories suggest a structural adaptation secondary to biomechanical factors. Further research is required to determine whether measures of dynamic foot function are associated with the presence and/or severity of 1st MTPJ OA.