Interphalangeal Joint Arthritis (Foot)

Differential Diagnosis

Because radiographic nonunion is common (~25%) yet does NOT predict pain or dissatisfaction, the decisive clinical skill after hallux IPJ arthrodesis is distinguishing a benign fibrous union (leave alone) from a symptomatic mobile nonunion (revise). The topic leans on the "painless fibrous union is acceptable" concept throughout, so the operational criteria must be explicit. The largest series (Braswell 2023) defined these categories precisely:

How to assess it in clinic. Take weightbearing radiographs (CT only if union is genuinely equivocal or revision is being planned), then stress the toe manually at the IPJ to detect micromotion, and correlate strictly with the patient's pain. A diagnostic local-anaesthetic infiltration of the IPJ that abolishes the pain confirms the joint as the true pain generator before committing to revision - important because adjacent first-MTP arthritis (hallux rigidus) or a neighbouring nail/soft-tissue problem can mimic IPJ pain, and radiographic nonunion at a nearby fused MTP can coexist. In Braswell's cohort it was specifically the patients labelled radiographic nonunion who carried the higher reoperation risk, but reoperation was driven by symptoms and mobility, not the radiograph alone.

Malposition - not nonunion - is the most avoidable cause of a disappointed patient: excessive dorsiflexion makes the nail strike the ground at toe-off, while excessive plantarflexion drives the toe tip and dorsal joint into the shoe. The target of roughly 10-15 degrees plantar flexion at the hallux IPJ, slight physiological valgus, and neutral rotation must be set and confirmed on the table, not eyeballed. This is the model answer to the viva follow-up "how would you verify correct position intra-operatively?"

Imaging

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Algorithm

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Functional Outcomes

Global epidemiology. IPJ arthritis of the foot is uncommon relative to first MTP (hallux rigidus) and lesser-toe MTP disease. The hallux IPJ accounts for the large majority of symptomatic cases; isolated lesser-toe IPJ arthritis is usually incidental. Post-traumatic disease (turf toe / hyperextension injury, intra-articular fracture, dislocation) predominates in younger and athletic populations worldwide, while primary degenerative and inflammatory (rheumatoid, psoriatic) disease predominate with age.

Society guidance (side by side). No orthopaedic society publishes an IPJ-arthritis-specific guideline; recommendations are extrapolated from first-ray degenerative-disease and inflammatory-arthritis pathways. Practice converges on a non-operative-first approach with arthrodesis for refractory disease.

Registry note. Toe IPJ arthrodesis is not separately tracked by national joint registries (NJR, AOANJRR, AJRR, SHAR), which capture replacement arthroplasty rather than small-joint fusion - so the best evidence remains institutional case series rather than registry data. This is itself an exam-worthy point about the limits of the evidence base.

High- vs limited-resource practice variation. In well-resourced settings, weightbearing radiographs, occasional MRI/ultrasound, plate or screw fixation, and formal gait/footwear rehabilitation are standard. In limited-resource settings, plain radiographs and K-wire fixation (inexpensive, effective) predominate, and accommodative footwear plus simple analgesia carry much of the non-operative burden. Outcomes hinge on joint preparation and patient selection rather than implant cost.

Interphalangeal joint arthritis of the foot most commonly affects the hallux IPJ, which is functionally more significant than lesser toe IPJs due to its contribution to push-off power during gait. Post-traumatic arthritis (previous fracture, dislocation, turf toe injury) is the primary etiology in younger patients, while degenerative and inflammatory causes predominate in older populations. Arthrodesis (fusion) is the gold standard treatment for symptomatic hallux IPJ arthritis, providing reliable pain relief with minimal functional deficit given the normally limited IPJ motion. Contrary to older teaching, radiographic union is NOT guaranteed: the largest published series reports roughly a 25% nonunion rate, but most nonunions are painless fibrous unions that do not require revision. The critical fusion position is 10-15° plantar flexion with slight valgus matching the contralateral toe—excessive dorsiflexion causes the nail to catch on the ground, while excessive plantar flexion creates dorsal nail pressure in footwear. Lesser toe IPJs can be managed with resection arthroplasty as motion is less critical; K-wire fixation suffices for lesser toes while plate/screw fixation is preferred for the hallux.