Keller Resection Arthroplasty

What it is. The Keller procedure is a resection arthroplasty of the first metatarsophalangeal joint: the base, the proximal third, of the proximal phalanx of the hallux is excised to decompress an arthritic or deformed joint. It relieves pain and improves the alignment of a bunion, and radiographs show a reduced intermetatarsal and first-MTP angle in many cases.

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Who it is for. Historically the Keller was used widely for both hallux valgus and hallux rigidus, but its indications have narrowed. It is now reserved largely for the low-demand, elderly patient with a painful arthritic and/or deformed first MTP joint, sometimes for ulcerated or at-risk first MTP joints, and as a salvage option. It is generally avoided in young, active or high-demand patients, who tolerate the loss of push-off poorly and in whom it predictably causes transfer metatarsalgia and a weak, cock-up toe.

The trade-off. Resecting the phalangeal base detaches the plantar plate and the intrinsic flexor hallucis brevis/sesamoid mechanism and disrupts the windlass. The hallux loses its push-off and weight-bearing role, and load transfers to the lesser metatarsals. Every complication below follows from that.

What replaced it. For hallux valgus the Keller has been largely superseded by corrective bunion osteotomies. For hallux rigidus it has given way to cheilectomy in early grades and first MTP arthrodesis in advanced disease, especially in active patients.

The complications. Each is a consequence of the lost push-off, and together they are common:

• Transfer metatarsalgia - pain under the lesser metatarsal heads as load passes from the hallux, and the commonest functional complaint
• Cock-up deformity - dorsiflexion or hyperextension of the hallux
• Flail, floppy or excessively short toe - from detachment of the intrinsics and plantar plate, and from over-resection
• Recurrent valgus deformity
• Cosmetic shortening

Satisfaction despite them. In elderly low-demand patients, pain relief and footwear tolerance are often still satisfactory despite the complications.

Salvage. The two errors to avoid are using the Keller in the wrong patient and mismanaging its failures. A failed Keller typically presents with recurrent valgus, a cock-up deformity, a flail toe or transfer metatarsalgia. The recommended salvage is first MTP arthrodesis, which gives higher satisfaction and better clinical results than a repeat Keller or an isolated soft-tissue release. It is technically demanding because of the bone loss, and often needs bone graft to restore length.

Beyond the low-demand elderly bunion, the Keller has a second and arguably more active modern role. Here the very feature that limits it elsewhere becomes the point of the operation.

The problem. A neuropathic plantar ulcer under the hallux or the first metatarsal head is driven by peak pressure at push-off in a foot with a stiff, arthritic or clawed first MTP. Offloading devices work, but require the patient to comply indefinitely.

Surgical offloading. Resecting the base of the proximal phalanx decompresses the joint, restores dorsiflexion and drops the peak plantar pressure under the first ray. This is permanent, structural offloading that does not depend on the patient wearing anything. It is often called surgical offloading, and the Keller sits alongside flexor tenotomy and metatarsal osteotomy in that group.

Vascular status first. A neuropathic ulcer in an ischaemic foot needs revascularisation before, or instead of, any elective bone resection. The wound will not heal on a poorly perfused ray whatever is done to the joint.

Then infection. An ulcer probing to bone means osteomyelitis until proven otherwise. That changes the operation from an elective offloading procedure to a debridement with bone resection and culture-directed antibiotics.

Push-off matters less here. These patients are typically low-demand and already have an insensate foot and a disturbed gait, so the trade of push-off for a healed ulcer is usually the right one.

Transfer is still the risk. Offloading the first ray predictably shifts load laterally. Warn about, and monitor for, a transfer ulcer under the lesser metatarsal heads, the ulcer equivalent of transfer metatarsalgia.

The broader ulcer pathway, including non-surgical offloading, belongs to Diabetic Foot Ulcers and Foot & Ankle Orthotics.

The push-off lever. The first ray is the main push-off lever. The hallux and first MTP transmit a large share of forefoot load at terminal stance and toe-off, and a competent first ray is needed to drive push-off.

The windlass. In terminal stance, dorsiflexion of the hallux winds the plantar aponeurosis around the metatarsal head, shortening it. That raises the medial arch and locks the midfoot into a rigid lever for push-off: the windlass (Hicks) mechanism.

The sesamoid-FHB sling. The two sesamoids sit within the medial and lateral heads of flexor hallucis brevis, with abductor and adductor hallucis, and glide under the metatarsal head. They bear load, cushion the head and increase the FHB plantarflexion moment arm.

What resection does. Removing the base detaches the whole sling. Active hallux plantarflexion and the windlass are abolished, the hallux no longer purchases the ground or stiffens the foot, and load transfers to the lesser metatarsal heads as transfer metatarsalgia. With the intrinsic flexor anchor gone, the unopposed long extensor pulls the toe into the cock-up deformity, and the shortened, destabilised toe becomes flail.

Sesamoid and plantar-plate pathology in their own right are covered in Sesamoid Disorders and Plantar Plate Insufficiency.

Several operative principles are taught to limit the complications, each following from the biomechanics above.

Approach. A dorsomedial or medial longitudinal incision over the first MTP, protecting the dorsomedial cutaneous nerve. The medial eminence is excised if there is a bunion.

Resect a third. Removing about a third of the proximal phalanx decompresses the joint while preserving length. Over-resection gives a flail, short or floppy toe; under-resection leaves inadequate decompression, stiffness and recurrence.

Reattach the soft tissues. Where possible, reattach the plantar plate/flexor hallucis brevis to the residual phalangeal base or capsule, and interpose capsule or soft tissue over the cut surface. This retains some active plantarflexion and resists the cock-up deformity.

Hold length on a wire. A temporary longitudinal K-wire across the MTP keeps the toe out to length, in slight plantarflexion and correct rotation, while the soft tissues scar in. It reduces cock-up and excessive shortening, and is removed after a few weeks.

Aftercare. A stiff-soled or heel-weight-bearing shoe and early mobilisation. The salvage fusion technique is developed in First MTP Arthrodesis.

How much of this is proven. These principles are mechanically coherent and they are what is taught, but the clinical evidence is thinner than the reasoning, so be careful about asserting them as established fact. In the 49-foot series cited below, the amount of proximal phalanx resected showed no association with either metatarsalgia or the final outcome. More surprisingly, the occurrence of complications showed no association with the final result or the patient's functional grade either.

What to conclude. The biomechanical case for conservative resection stands: detaching the flexor sling is what produces the cock-up toe, and taking less bone leaves more to reattach to, so resect a third rather than a half. The claim that outcome tracks resection length is unsupported, and in a low-demand elderly patient a radiographically imperfect result with a documented complication frequently still gives a satisfied patient in comfortable shoes.

Why the operation persists. That mismatch between anatomical result and reported satisfaction is precisely why the Keller survives in this narrow group. It is also why it should not be judged by the standards applied to a fusion in an active patient.