Elbow Interposition / Distraction Arthroplasty

Who it is for. Total elbow arthroplasty in a young, high-demand patient has a high failure rate and imposes a strict lifelong lifting restriction, often around 2-5 kg, which such patients cannot accept. Interposition arthroplasty is the joint- and bone-preserving alternative for that patient: end-stage elbow arthritis, most often post-traumatic, sometimes inflammatory.

The idea. The arthritic distal humerus is debrided and contoured, then resurfaced with an interposed soft-tissue graft, classically autologous fascia lata or an Achilles tendon or dermal allograft. The graft acts as a biological resurfacing layer between the humerus and the ulna and radius, relieving pain while preserving bone and motion.

Distraction. Distraction interposition arthroplasty adds a hinged distraction external fixator. The distractor separates the articular surfaces to unload and protect the graft and maintain the joint space, while its hinge, aligned to the elbow's flexion-extension axis, allows early protected motion. It is particularly valuable where there is instability or to protect the graft. When ligamentous stability is good, modern practice may allow immediate protected motion in a hinged brace without external distraction.

It does not burn bridges. Because the bone is preserved, a failed interposition can be converted to TEA later, with good results in reported cases. That makes it a reasonable joint-preserving first step for the young arthritic elbow, reserving the motion-and-load-limited but more reliable TEA for older or lower-demand patients, or as the eventual salvage.

Stability decides. Elbow stability is the single most important determinant of success. Instability of the elbow, before or after surgery, is strongly associated with unsatisfactory results, so the operation must restore or rely on competent collateral ligaments and bony columns.

Reconstruction does not rescue it. In the largest series, pre-operative instability was associated with poor scores despite attempted collateral reconstruction, and four of the five patients in whom both collateral ligaments were reconstructed ended with a net decrease in Mayo score. A bi-collateral reconstruction is a marker of an elbow too far gone for a soft-tissue resurfacing, not a step that rescues it. An unstable elbow is a relative contraindication unless the instability can be corrected, and demonstrable pre-operative instability, especially if both collaterals would need reconstructing, is a reason not to do the operation rather than to do a bigger one.

Contraindications. These make interposition the wrong operation.

• Active or recent infection. Post-traumatic elbows often carry a history of prior surgery and infection. Active sepsis is a contraindication, and a prior deep infection demands confidence that the elbow is quiescent before a graft is interposed.
• Gross, uncorrectable instability or deficient columns. A relative contraindication: the graft will not survive a sloppy, poorly contained joint whose collateral ligaments and columns cannot be reconstructed.
• A neuropathic (Charcot) joint. A destroyed, insensate joint is unsuitable for a soft-tissue resurfacing. (Charcot of the elbow is covered in our Neuropathic (Charcot) Elbow topic.)
• An inadequate soft-tissue envelope. Poor skin, or scarred or contracted soft tissues, that cannot support the graft or tolerate a fixator.

Where it sits on the ladder. Interposition is one rung among the alternatives, chosen specifically for the young, high-demand patient who needs pain relief and retained load capacity without burning the bony bridges to a future TEA.

• Debridement ("ulnohumeral") arthroplasty suits impingement-type osteoarthritis with preserved joint space
• TEA remains the reliable choice for the older, lower-demand patient, and the eventual salvage of a failed interposition
• Arthrodesis is a definitive salvage for the very heavy labourer, or the failed or infected elbow that cannot be reconstructed

The osteoarthritis treatment ladder and debridement arthroplasty are developed in our Elbow Arthritis topic.

Exposure. An extensile posterior approach is used, managing the triceps through a triceps-reflecting or triceps-splitting window, or an olecranon-sparing exposure that preserves the extensor mechanism. The ulnar nerve is identified, protected and usually decompressed or transposed at the outset, because ulnar neuropathy is the commonest neurological complication. (The posterior approach is detailed in our Surgical Approaches to the Shoulder & Elbow topic, and ulnar nerve handling in our Ulnar Nerve topics.)

Joint preparation. The arthritic distal humerus is debrided of osteophytes and devitalised cartilage and re-contoured to a smooth, congruent trochlea and capitellum shape, and the olecranon and the coronoid or radial head are addressed as needed. Enough bone is removed to relieve impingement and make space for the graft, while the bony columns that confer stability are preserved.

The graft. Autologous fascia lata is harvested from the thigh, or an Achilles tendon or dermal allograft is used. It is draped over the contoured distal humerus and secured through drill holes in the humerus, sometimes also around the epicondyles, so that it covers the articulating surface.

Stability. The medial and lateral collateral ligaments and the columns must be competent, and deficient ones are repaired or reconstructed, bearing in mind the selection caveat above. (Isolated collateral-ligament reconstruction is covered in our Elbow UCL Injury and Posterolateral Rotatory Instability topics.)

The distractor and its axis. The hinge must lie on the elbow's true flexion-extension axis, a line through the centre of the trochlea and the centre of the capitellum, anterior and inferior to the lateral epicondyle. An axis pin placed along this line guides the hinge; off the axis, the construct fights motion and loads the graft. The joint is then distracted a few millimetres to unload the graft while permitting early protected motion, and the fixator is classically retained for around three to four weeks.

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The early series. The classic 13-patient distraction-interposition series reported about 69% satisfactory pain relief and 62% excellent or good Mayo scores, with similar results in post-traumatic and inflammatory arthritis. It is the source of the "roughly two-thirds satisfactory" figure, and even at that level the operation is less reliable than prosthetic replacement.

The larger series. The largest published experience is more sobering. In 45 elbows at a mean of six years the flexion-extension arc improved from 51 to 97 degrees and the Mayo Elbow Performance Score rose from 41 to 65, which is a fair score; graded, 13 were good or excellent, 14 fair, 11 poor and 7 revised. The authors' conclusion is the one to quote in a viva: interposition neither completely eliminates pain nor restores full function.

Complications to consent for. They are not uncommon, especially in post-traumatic cases.

• Ulnar neuropathy, the commonest neurological problem
• Persistent pain: expect improvement, not abolition, and set this expectation above all others
• Instability, either unmasked by the debridement or progressive afterwards
• Pin-site infection and pin-track problems, including the rare pin-site stress fracture, and deep infection over the graft
• Recurrent stiffness and heterotopic ossification, particularly in the multiply-operated post-traumatic elbow that is the usual candidate
• Graft failure, resorption or progressive bone loss, with recurrence of symptoms
• Triceps insufficiency where the extensor mechanism was taken down for exposure
• Revision to TEA, a real and reasonably common endpoint, planned for from the outset rather than treated as a failure of judgement

Motion starts early. The graft is a passive spacer that survives on an elbow that moves, and a stiff post-operative elbow defeats the whole exercise, so rehabilitation begins within the first few days rather than after the fixator comes off. With a distractor in place, motion is performed through the hinge from the outset, the joint held distracted so the graft is unloaded while it is moved. After the frame is removed, motion continues in a hinged brace.

Pin sites are cleaned daily and reviewed at every visit, since a neglected pin track is the commonest route to an infection sitting directly over a fresh soft-tissue graft.

The therapy programme is the one used for any released stiff elbow:

• Active and active-assisted motion in both flexion-extension and pronation-supination
• Static progressive or turnbuckle splinting to recover the end of the arc
• Extension splinting at night, since it is extension that is lost first and regained last

Heterotopic ossification. Prophylaxis is worth considering in the elbow that has had multiple prior operations or a head injury, though the choice between indomethacin and radiation remains debated.

No lifting limit. Unlike TEA, there is no permanent lifting restriction to impose once healing is complete. That freedom is the entire reason the patient accepted a less predictable operation.