Interphalangeal Joint Arthritis (Foot)

Interphalangeal joint arthritis of the foot is less common than first MTP arthritis, and no source cited on this page quantifies its share of forefoot arthritis. When it is symptomatic, especially at the hallux, it significantly affects gait and footwear.

Where. The hallux IPJ accounts for over 80% of cases and the lesser toe PIPJ for under 20%. The hallux IPJ matters more because it contributes push-off power in gait; the lesser toe IPJs have a minimal functional role, so their arthritis can often be managed conservatively.

Who. Post-traumatic arthritis presents at 20-50 years and affects men and women equally; it is the most common cause under 50. Degenerative arthritis presents over 50, with a female predominance, and predominates in older adults. Bilateral disease is uncommon unless the cause is inflammatory.

Why fusion works here. Finger IPJs need their motion; toe IPJs have little normal motion to lose. That is why arthrodesis is an excellent treatment for the symptomatic toe IPJ, reliably relieving pain with minimal functional deficit.

The joints. The interphalangeal joints of the foot are hinge joints with minimal normal motion compared with the fingers. The collateral ligaments provide mediolateral stability. The plantar plate belongs to the MTP joint and does not extend to IPJ level.

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From injury to arthritis. The initiating event in post-traumatic disease is an intra-articular fracture, a dislocation or a severe hyperextension (turf toe) injury that damages the articular cartilage; even if the joint is anatomically reduced, the cartilage is permanently injured. Over months to years the damaged cartilage degenerates progressively: its proteoglycan and collagen structure is lost, chondrocytes undergo apoptosis, and subchondral bone becomes exposed in places.

Established disease. Once the cartilage is lost completely, exposed subchondral bone produces mechanical pain with motion and weight-bearing, osteophytes form at the joint margins, and the joint space narrows on X-ray. At end stage the joint may collapse, chronic pain produces an antalgic gait, dorsal osteophytes cause shoe pressure, and surgery is required for symptom relief.

Post-traumatic arthritis. The history is of a specific injury, with unilateral, progressive pain and stiffness. Symptoms develop 6 months to 5 years after the injury, earlier after a more severe one, and X-ray changes may precede symptoms. The causes:

• Intra-articular fracture, even if well reduced, and the missed undisplaced intra-articular fracture
• IPJ dislocation, which reduces but leaves a cartilage shear injury
• Severe turf toe, a hyperextension injury that contuses the hallux IPJ cartilage
• Repeated microtrauma in athletes (soccer, ballet)
• Chronic mallet or hammer toe deformity, which leads to secondary arthritis

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Degenerative arthritis. Age-related cartilage wear, chronic mechanical overload and genetic predisposition produce an insidious onset over years, typically after 60, with slow progression and no specific injury. These patients may have arthritis elsewhere (hands, knees), and the condition is associated with hallux rigidus (MTP arthritis). Risk factors:

• Age over 60 years
• Obesity, through increased forefoot load
• High-impact activities (running, jumping)

Inflammatory arthritis. Rheumatoid arthritis is the most common inflammatory cause; psoriatic arthritis is another, and gout is rare at the IPJ. The signature is multiple IPJ involvement, bilateral and symmetric, with morning stiffness, swelling and synovitis, and systemic disease markers (RF, anti-CCP). Always screen for inflammatory arthritis if multiple IPJs are affected. Medical management (DMARDs, biologics) comes first, fusion follows if it fails, and these patients often require multiple joint fusions.

History. Pain localises to a specific IPJ, hallux or lesser toe, and is aggravated by walking, push-off (at the hallux) and shoe pressure. Onset is months to years after an injury in post-traumatic disease and insidious in degenerative disease. Morning stiffness suggests an inflammatory cause, end-of-day stiffness a degenerative one. Patients have often already tried NSAIDs or shoe modifications, and the functional impact falls on walking distance and athletic activities.

Examination. Look for swelling, a dorsal prominence from osteophytes and malalignment: hyperextension or flexion contracture at the hallux IPJ, hammer or mallet toe in the lesser toes. The affected IPJ is tender, and warm if inflamed; motion is reduced and painful at end range, with crepitus. The gait is antalgic with reduced push-off in hallux IPJ arthritis. Check shoe wear pattern and pressure areas.

Differential diagnosis. Nail dystrophy with oedema and erythema centred on the hallux IPJ should raise suspicion of psoriatic onycho-pachydermo periostitis rather than isolated mechanical osteoarthritis. Chronic tophaceous gout produces asymmetric nodular swelling and yellow-white deposits around the great toe and other interphalangeal joints.

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Because radiographic nonunion is common and only some of those toes are symptomatic, the decisive clinical skill after hallux IPJ arthrodesis is telling a benign fibrous union, left alone, from a symptomatic mobile nonunion, revised. The radiograph still counts: in Braswell's cohort it was the patients labelled radiographic nonunion who carried the higher reoperation risk, but reoperation was driven by symptoms and mobility, not the radiograph alone. The judgement is made on the patient in front of you.

How to assess it in clinic. Take weightbearing radiographs (CT only if union is genuinely equivocal or revision is being planned), stress the toe manually at the IPJ to detect micromotion, and correlate strictly with the patient's pain.

Confirm the pain generator. A diagnostic local-anaesthetic infiltration of the IPJ that abolishes the pain confirms the joint as the source before committing to revision. This matters because adjacent first-MTP arthritis (hallux rigidus) or a neighbouring nail or soft-tissue problem can mimic IPJ pain, and radiographic nonunion at a nearby fused MTP can coexist.

The target. At the hallux IPJ the target is roughly 10-15° plantar flexion, slight physiological valgus to match the contralateral great toe, neutral rotation, and alignment with the first metatarsal axis. It must be set and confirmed on the table, not eyeballed.

Why it matters. Malposition, rather than nonunion, is the most avoidable cause of a disappointed patient.

• Excessive dorsiflexion - the nail catches the ground at toe-off, painfully
• Excessive plantar flexion - the toe tip and dorsal joint are driven into the shoe, with dorsal toe pressure and the nail driven dorsally
• Varus or valgus - medial or lateral shoe pressure and an unstable gait

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Setting and checking it. This is the model answer to the viva follow-up "how would you verify correct position intra-operatively?", and doing it on the table is what prevents the excessive-dorsiflexion malunion that produces nail ground-strike.

1. Reference the contralateral hallux - keep the opposite foot in the field, or note its cascade pre-operatively, and reproduce its resting angle and valgus
2. Simulate stance - press a flat rigid plate (an instrument tray lid, or the surgeon's flat hand) against the whole plantar forefoot as though the foot were flat on the floor. The pulp should just contact the plate with the nail facing forwards, not skywards; too much plantar flexion and the pulp digs in hard, too much dorsiflexion and the toe lifts off the plate and will catch the ground in gait
3. Check rotation - the nail plate should lie in the same plane as the lesser-toe nails, with no pronation or supination
4. Provisional K-wire, then mini-fluoroscopy (AP and lateral) to confirm alignment, surface coaptation and hardware placement before definitive fixation
5. Re-assess clearance once definitive fixation is applied, before closure

Combined first-ray fusions. Set the first MTP position first, then tailor the IPJ to it and re-check whole-ray pulp-to-floor clearance. Immobilising the MTP shifts load and geometry onto the IPJ.

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Radiographs. X-rays are sufficient for diagnosis in most cases. The standard foot series:

• AP - IPJ alignment and joint space
• Lateral - osteophytes and the dorsal prominence
• Oblique - additional detail of the IPJs

A subtle IPJ dislocation can be missed without a true lateral radiograph, so obtain a dedicated lateral when alignment is uncertain.

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The findings are joint space narrowing (bone-on-bone in severe cases), osteophytes (especially dorsal), subchondral sclerosis, subchondral cysts, and malalignment into flexion or extension. Severity is graded on the same features:

• Mild - joint space narrowing, small osteophytes
• Moderate - significant narrowing, larger osteophytes, sclerosis
• Severe - bone-on-bone contact, collapse, deformity

MRI is rarely needed; clinical examination and X-ray are usually sufficient. It shows cartilage thinning and full-thickness defects, subchondral bone marrow oedema, synovitis (fluid, thickened synovium), osteophytes and loose bodies. Order it when:

• The diagnosis is uncertain and other pathology must be ruled out
• Cartilage status needs assessing for pre-operative planning
• An osteochondral defect is suspected
• Inflammatory arthritis is suspected and synovitis needs assessing

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Laboratory tests help differentiate inflammatory from degenerative arthritis. They are indicated when inflammatory arthritis (multiple IPJs involved), septic arthritis (acute, systemically ill) or gout is suspected:

• ESR and CRP - elevated in RA and infection
• Rheumatoid factor and anti-CCP - RA screening
• Serum uric acid - gout screening
• Joint aspiration - cell count, culture and crystal analysis if sepsis or gout is suspected

The goal is pain relief and restoration of function. Conservative treatment is first-line for mild symptoms. For symptomatic hallux IPJ arthritis that has failed it, arthrodesis is the gold standard. Lesser toe IPJ arthritis can often be managed conservatively, or with resection arthroplasty if surgery is needed.

Non-operative management suits mild to moderate symptoms, the patient medically unfit for surgery and the patient who refuses it. It is palliative rather than curative: 40-50% achieve acceptable symptom control, and most eventually progress to surgery.

• Footwear - a stiff sole reduces IPJ motion; a rocker-bottom sole offloads the forefoot and reduces push-off stress; an extra-depth toe box accommodates dorsal osteophytes
• Orthotics - a carbon fibre plate insole stiffens the forefoot; a Morton extension limits hallux motion
• Medication - NSAIDs; intra-articular corticosteroid injection gives temporary relief for 3-6 months
• Activity - avoid high-impact activity; low-impact exercise such as swimming or cycling

Hallux IPJ arthrodesis. The indications are symptomatic hallux IPJ arthritis that has failed conservative treatment, pain limiting daily activities, and arthritis confirmed on X-ray. The technique:

1. Exposure - dorsal longitudinal incision over the IPJ, protecting the neurovascular bundles (medial and lateral digital nerves)
2. Joint preparation - excise all articular cartilage from the proximal and distal phalanx and curette the opposing surfaces to bleeding subchondral bone; a power burr may be used for precise preparation
3. Position - set and confirmed on the table (see the fusion position section below)
4. Fixation - plate and screw, two or three crossed K-wires (less expensive), or a single lag screw for compression
5. Closure - layered, with a subcuticular skin suture

Choosing the fixation. Plate and screw fixation is preferred at the hallux for its rigidity, and K-wires suffice for the lesser toes. The comparative data, however, do not show any single construct (single screw, multiple screws, screw plus plate, non-screw) reliably eliminating nonunion at this joint, and in the largest series implant type made no significant difference. Meticulous joint preparation to bleeding bone matters more than the specific implant.

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Lesser toe surgery has good outcomes with simple techniques.

• PIPJ arthrodesis - for severe arthritis or rigid deformity; technique as for the hallux but with simpler fixation, K-wires usually sufficing; fused in slight flexion (neutral or 10° flexion)
• PIPJ resection arthroplasty - excision of the proximal phalanx head creates a pseudoarthrosis that preserves some motion; less stable than fusion but acceptable in a lesser toe; used for a flexible hammer toe with PIPJ arthritis
• DIPJ arthrodesis - rarely needed as DIPJ arthritis is uncommon; K-wire fixation, fused in neutral

Rehabilitation. Union is expected at 8-12 weeks with rigid fixation.

• Weeks 0-2 - post-operative shoe with a rigid sole, weight-bearing as tolerated through the heel only, elevation, ice and dressing changes
• Weeks 2-6 - continue the post-operative shoe and progress to full forefoot weight-bearing; remove K-wires at 3-4 weeks if used; X-ray at 6 weeks to assess healing
• Weeks 6-12 - stiff-soled athletic shoe, full weight-bearing, low-impact activities
• Months 3-6 - regular shoes (most patients by 3-4 months) and most activities; high-impact sport at 4-6 months

IPJ stiffness after fusion is expected, since ankylosis is the goal of the operation. Malunion and its consequences are covered with the fusion position below.

Hallux IPJ fusion. Pain relief and patient satisfaction are generally high despite imperfect radiographic union, and the functional deficit is minimal because the IPJ has limited normal motion. Older texts quote over 90% union. The largest contemporary series (Braswell 2023, 227 fusions) reports ~25% radiographic nonunion and ~21% reoperation, and in that series radiographic nonunion strongly predicted reoperation (p less than 0.0001). When the IPJ is fused alongside a first MTP fusion, nonunion reaches up to 40% (Brodsky 2021).

How far fibrous union reassures. A stable, painless fibrous union (fibrous ankylosis) is an accepted clinical endpoint that behaves like a solid fusion. The evidence that it is tolerable comes from Brodsky's 20 feet, where IP nonunion did not predict AOFAS score or satisfaction. Braswell defines clinical fibrous union but does not report how many of its 58 nonunions were painless. So a fibrous union can be an acceptable outcome, and a quarter of these fusions will not unite radiographically, but "most nonunions are painless" is not something either paper establishes.

Prognostic factors. Favourable factors are rigid fixation (plate preferred over K-wires), good bone quality, non-smoking, normal body weight, compliance with the post-operative protocol and correct fusion position. Unfavourable ones are smoking (it impairs bone healing), poor bone quality (osteoporosis, RA), inadequate fixation, infection, non-compliance with weight-bearing restrictions and inflammatory arthritis (higher nonunion risk). The largest series tested several of these against nonunion: smoking status, inflammatory arthritis and implant type made no significant difference to nonunion, whereas diabetes was a significant risk factor.

Lesser toe surgery. Fusion and resection arthroplasty are both used; resection is less predictable but acceptable because motion is non-critical. Correcting a hammer or mallet toe improves appearance and footwear.

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.