First Metatarsophalangeal Joint Hemiarthroplasty

Hallux rigidus is arthritis of the first metatarsophalangeal (MTP) joint.

The amount of arthritis can range from focal areas of cartilage injury or osteophyte formation without joint space narrowing to ankylosis with complete loss of the joint space. In one classification system proposed by Hattrup and Johnson, grade I is osteophyte formation without joint space narrowing, grade II is narrowing of the joint space, and grade III is loss of visible joint space.

ANATOMY

The joint consists of the articulation of the first metatarsal head with the hallux proximal phalanx and the medial and lateral sesamoids (FIG 1).

The flexor hallucis brevis contains the two sesamoids within its medial and lateral heads and inserts on the plantar base of the hallux proximal phalanx.

The flexor hallucis longus runs between the medial and lateral sesamoids and inserts on the plantar base of the hallux distal phalanx.

The extensor hallucis longus and the more lateral extensor hallucis brevis insert into the extensor mechanism of the great toe.

The abductor hallucis and adductor hallucis insert on the medial and lateral sesamoids, respectively, along with the plantar base of the hallux proximal phalanx.

PATHOGENESIS

Hallux rigidus may be secondary to primary osteoarthritis, systemic inflammatory arthritis, or less commonly septic arthritis.

It may also be posttraumatic in nature, developing after a previous intra-articular fracture or significant turf toe injury to the ligamentous structures of the first MTP joint.

Biomechanical factors such as a long, hypermobile, or dorsally elevated first metatarsal may lead to dorsal impingement of the proximal phalangeal base on the first metatarsal head with first MTP dorsiflexion.

NATURAL HISTORY

The extent of arthritis often progresses with time, leading to increased osteophyte formation and joint space narrowing. This may occur with or without joint-sparing surgical intervention.

PATIENT HISTORY AND PHYSICAL FINDINGS

Patients often complain of pain and stiffness in their first MTP joint. Symptoms may be exacerbated by shoes with a restrictive toe box and by walking barefoot or in shoes with a flexible forefoot.

On examination, there may be a prominent first metatarsal head, a swollen first MTP joint, and tender osteophytes of the metatarsal head and phalangeal base.

First MTP joint motion may be limited and painful.

Dorsiflexion range of motion should also be assessed with the patient bearing weight or with dorsal translation applied to the first metatarsal head to simulate weight bearing to assess for “functional hallux rigidus.”

• In mild to moderate hallux rigidus (Hattrup and Johnson grade I and II), pain is principally with maximum joint dorsiflexion or plantarflexion secondary to dorsal osteophytes causing bone impingement or soft tissue tenting, respectively.

• With severe arthritis (Hattrup and Johnson grade III), there is usually pain throughout the entire arc of motion and a positive “grind test,” in which midrange of motion with axial compression applied to the first MTP joint is painful.

IMAGING AND OTHER DIAGNOSTIC STUDIES

Anteroposterior (AP), lateral, oblique, and sesamoid views of the foot should be obtained to assess the extent of arthritis in the first MTP and in the adjacent first tarsometatarsal and hallux interphalangeal joints.

An assessment is also made for any concurrent hallux valgus or hallux varus deformity, osteopenia, avascular necrosis, or occult sesamoid fracture.

If needed, magnetic resonance imaging (MRI) and computed tomography (CT) scan can provide more, with respect to detailed information, particularly sesamoid pathology, which is important, as this procedure leaves the metatarsosesamoid joint intact.

DIFFERENTIAL DIAGNOSIS

Osteochondral lesion

Avascular necrosis

Occult fracture

NONOPERATIVE MANAGEMENT

Conservative treatment should always be offered before performing first MTP joint hermiarthroplasty.

The principal goal is to limit painful motion of the first MTP joint and pressure on prominent osteophytes. An accommodative shoe with a soft upper and a rigid forefoot rocker may be worn. A rigid turf toe plate may be placed under a removable soft insole or an orthotic with a Morton’s extension may be worn. Doughnut pads may be placed over tender osteophytes.

Medications such as nonsteroidal anti-inflammatories, glucosamine and chondroitin sulfate, and acetaminophen may be taken.

Corticosteroid and possibly hyaluronic acid injections may be performed.

SURGICAL MANAGEMENT

There are many surgical options for hallux rigidus, including cheilectomy, metatarsal osteotomy, proximal phalangeal osteotomy, distraction arthroplasty, tissue interposition arthroplasty, implant arthroplasty, and arthrodesis.

Of the many implants available, our preference is a cobalt-chrome proximal phalangeal hemiarthroplasty made by BioPro (FIG 2). The material does not break down with associated extensive bone destruction such as the silicone total and hemi implants; there are good long-term results published in the literature, and the amount of bone removed is small, making salvage of a failed prosthesis less challenging. The prosthesis is also available in titanium for patients with metal sensitivity.

Our potential indications for performing a first MTP hemiarthroplasty are symptomatic grade II arthritis with loss of greater than 50% of the metatarsal head articular cartilage and grade III arthritis without severe involvement of the articulation between the metatarsal head and the sesamoids.

Preoperative Planning

History, physical examination, and radiographs are reviewed to confirm the appropriate indications for the procedure and determine if there are any concurrent deformities or biomechanical abnormalities that also need to be addressed.

The patient needs to be told that based on the intraoperative findings, a decision may be made that hemiarthroplasty is not the best option and that a simple cheilectomy, arthrodesis, or tissue interposition arthroplasty may be preferable.

The equipment to perform the hemiarthroplasty and the alternatives mentioned earlier should be readily available in the operating room.

Positioning

The patient is placed in the supine position with a leg or thigh tourniquet.

Approach

A dorsomedial approach is preferable, although a medial longitudinal approach can also be used in the presence of a previous incision there.

Perioperative antibiotics and a regional anesthetic block are given.

TECHNIQUES

Exposure

Make a longitudinal dorsomedial incision over the first MTP joint.

Protecting the dorsomedial sensory nerve, expose the extensor digitorum longus tendon and dorsomedial joint capsule.

Leaving a sufficient cuff of capsular tissue for subsequent repair, make a longitudinal capsulotomy medial to the extensor digitorum longus tendon.

Using subperiosteal dissection and preserving the collateral ligaments, expose the dorsal aspect of the proximal phalanx and the dorsal, medial, and, if prominent, lateral aspect of the metatarsal head (TECH FIG 1).