Background: Primary tarsometatarsal arthrosis is relatively
uncommon. The etiology of osteoarthritis in the foot is poorly understood, and
it is possible that mechanical or anatomic factors play a role.
Methods: We compared the relative length of the metatarsals in
patients with idiopathic arthrosis of the midfoot with that in a group of
controls without arthrosis. We analyzed the radiographs of all patients who
had had an arthrodesis of the first, second, and third tarsometatarsal joints
to treat arthrosis during a three-year period at a tertiary teaching hospital.
We excluded patients with a history of inflammatory arthritis, trauma, or
Charcot arthropathy. Nine patients (fifteen feet), seven women and two men
with an average age of 64.2 years, met the inclusion criteria. We compared
them with a control group consisting of the uninjured feet of patients with an
acute traumatic injury to the hindfoot and the feet of volunteers with no foot
problems. We measured the first, second, and fourth metatarsal lengths and the
intermetatarsal angles on weight-bearing anteroposterior radiographs. We also
measured the length of the first metatarsal relative to the long axis of the
second metatarsal to define the functional first metatarsal length. The ratios
of metatarsal lengths and the ratios of functional lengths were used for
analysis to minimize differences in foot size and differences caused by
radiographic magnification. Statistical comparisons between groups were then
carried out.
Results: In the study group, the length of the first metatarsal was,
on the average, 77.0% of the length of the second metatarsal, whereas, in the
control group, the first metatarsal length was an average of 82.0% of the
second metatarsal length. The functional length of the second metatarsal was,
on the average, 18.6% greater than that of the first metatarsal in the study
group and only an average of 4.1% greater than that of the first metatarsal in
the control group. Both differences were significant (p < 0.0004 and p <
0.0001, respectively).
Conclusions: Patients with midfoot arthrosis had a different ratio
of the first to the second metatarsal length than did a similarly aged cohort
without midfoot arthrosis. The patients had a relatively short first
metatarsal or a relatively long second metatarsal, or both. Midfoot arthrosis
may have a mechanical etiology. Recognition of risk factors is the first step
in developing prevention strategies.
Level of Evidence: Prognostic Level III. See Instructions
to Authors for a complete description of levels of evidence.