Capsular Interpositional Arthroplasty

Hallux rigidus refers to degenerative arthritis of the first metatarsophalangeal (MTP) joint that is characterized by pain, decreased range of motion (ROM), and proliferative osteophyte formation.

ANATOMY

The first MTP joint is composed of the dorsal joint capsule, the medial and lateral collateral ligaments, the plantar plate–sesamoid–flexor hallucis brevis (FHB) tendon complex, the first metatarsal head, and the proximal articulating end of the proximal phalanx.

Pathology is limited primarily to the first MTP joint, with prominent dorsal osteophyte on the metatarsal head.

PATHOGENESIS

The origin of progressive first MTP joint cartilage degeneration is uncertain. Most attribute hallux rigidus to biomechanical disturbance or local pathology that leads to repetitive stress on articular cartilage and subsequent deterioration of the cartilage surface.

Trauma

Inflammatory arthritides (eg, rheumatoid arthritis, gout)

Primary osteoarthritis

Associated factors such as long first metatarsal, flat metatarsal head, metatarsus primus elevatus, pronated feet, or hallux valgus interphalangeus are often found in patients with arthritis of the first MTP joint.

Long first metatarsal may be correlated with development of hallux rigidus.

NATURAL HISTORY

Initially, pain is localized to the dorsal aspect of the great toe MTP joint. Loss of motion is minimal but can be seen with activities that require maximum dorsiflexion. Over time, generally several years, the degree of involvement and loss of motion increase. Eventually, in the end stage of the process, the first MTP joint will lose nearly all motion. A varus or valgus deformity is usually not associated with this process.

Pain may or may not progress as osteophytes form to stabilize the joint.

Progression of osteophytes and joint space narrowing on radiographs may or may not correlate with symptoms.

PATIENT HISTORY AND PHYSICAL FINDINGS

Typical history is swelling around the first MTP joint. Patients will complain frequently of a progressive increase in the size of the MTP joint and attribute this to a bunion-type deformity.

Occasionally, avoidance gait can result and cause an increased weight-bearing load on the lateral aspect of the foot.

Initially, a tender dorsal osteophyte will be noted with MTP joint flexion retrograde elevation and uncovering of the dorsal portion of the articulation. Pain may be associated with local dorsal cutaneous nerve irritation caused by the osteophyte.

Limited dorsiflexion with abutment of articular surfaces of the phalanx onto the metatarsal head can be seen. Periarticular osteophytes can be noted, particularly laterally.

Compensatory hyperextension of the hallucal interphalangeal joint can be seen with long-standing disease.

Axial compression of the MTP joint with pain can often differentiate the level of involvement of the degenerative process.

Pain is felt with dorsiflexion activities (wearing high-heeled shoes, running, yoga).

Progressive proliferation of osteophytes about the joint occurs and pain is felt with small toe box shoes.

Decreased dorsiflexion and plantarflexion motion of the joint is seen and pain is elicited with attempting these motions.

Physical examination includes the following:

Visualize the dorsal osteophyte to check for swelling.

For lesser toe evaluation, examine for hammer toe formation or evidence of a more systemic process: Presence of multiple hammer toe formation with hallux rigidus suggests rheumatoid arthritis.

Evaluate ROM for dorsal-based blocking of dorsiflexion.

Check axial compression by stabilizing the first metatarsal while compressing the proximal phalanx against the metatarsal head. Increasing levels of pain are associated with more complete joint involvement.

Tomassen sign: With the ankle held in neutral, dorsiflexion of the MTP joint is measured. A positive result is suggestive of a stenosing flexor hallucis longus (FHL) tenosynovitis and not a static dorsal osteophyte.

Pain at the midrange of the motion arc implies a global first MTP joint arthritis that may not be amenable to dorsal cheilectomy alone but instead is better treated with interpositional arthroplasty or arthrodesis.

IMAGING AND OTHER DIAGNOSTIC STUDIES

Standard weight-bearing anteroposterior (AP), oblique, and lateral radiographs of the foot

Grade I: small lateral spurs with joint space preservation

Grade II: metatarsal and phalangeal osteophytes with dorsal joint space narrowing and subchondral sclerosis

Grade III: marked osteophyte formation with loss of joint space and subchondral cyst formation (FIG 1).

Laboratory studies if serologic etiology suspected

DIFFERENTIAL DIAGNOSIS

Trauma

Primary osteoarthritis

Degenerative arthritis

Rheumatoid arthritis

Seronegative arthropathy

Gout

Stenosing FHL tendon⁸

NONOPERATIVE MANAGEMENT

Low-heeled shoes

Steel shanks

Stiff Morton extension orthoses

Nonsteroidal anti-inflammatory drugs

Cortisone injection

Rocker sole shoe or over-the-counter rocker shoe

SURGICAL MANAGEMENT

Grade I: cheilectomy to address mild osteophyte formation, joint space intact, minimal dorsal spur formation

Grade II: cheilectomy with Moberg dorsal phalangeal osteotomy to address moderate osteophyte formation, joint space narrowing, subchondral sclerosis, bony proliferation on metatarsal head and phalanx on radiograph or significant intraoperative joint involvement

Grade III: interposition arthroplasty or fusion to address marked osteophyte formation, loss of visible joint space, extensive bony proliferation^3,4

Preoperative Planning

Standing AP and lateral foot radiographs to anticipate level of intervention

Consider consent for cheilectomy, Moberg dorsal osteotomy, and interposition arthroplasty. Although arthrodesis could be considered as well, the goal of interpositional arthroplasty is to preserve motion in end-stage first MTP joint arthritis.

Patients who do well with interpositional arthroplasty typically are moderately but not extremely active athletes who wish for retention of dorsiflexion of the toe for activities of daily living such as sports or use of certain shoe wear.

Relative contraindications to interpositional arthroplasty include cases in which first MTP joint arthrodesis may be favored.

Long second metatarsal (potential risk for development of transfer metatarsalgia) (see FIG 1A)

Hallux valgus

Sesamoid arthritis

First tarsometatarsal instability: inflammatory arthritides

High-demand patients (athletes, dancers) present a challenge as we believe that they should be discouraged from this procedure yet are also not ideal candidates for first MTP joint arthrodesis.⁵

Poor vascular status, neuropathy, and infection are absolute contraindications to this procedure.

Positioning

The patient is placed supine with a bump under the contralateral lumbar region if needed to evert the foot for better exposure.

The foot is placed at the bottom corner of the bed.

A bolster is placed under the greater trochanter of the ipsilateral hip to avoid external rotation of the operated extremity.

A mini C-arm is placed on the ipsilateral side of the bed, about 6 feet past the corner of the operating room table and at a 45-degree angle. In our experience, this positioning affords the best access to the foot and simplifies intraoperative imaging. Blankets or sheets are used to elevate the operated extremity to facilitate lateral fluoroscopic imaging unobstructed by the contralateral lower extremity.

Approach

Two approaches are commonly used: dorsal and medial.

The dorsal approach allows for easier access to the lateral osteophyte. This approach makes suturing the interposition tissue to plantar surface of the joint difficult, however.

In contrast, the medial incision allows for easier access to the plantar surface and is the approach used by the senior author (W.G.H.). The capsule is carefully protected, with particular attention given to protecting the plantar nerve (Joplin nerve) as well as the dorsal cutaneous branch.

Protect the extensor hallucis longus (EHL) tendon and the dorsal and plantar digital nerves. Identify the extensor hallucis brevis (EHB) and the joint capsule.

Ankle block anesthesia is used, plus an Esmarch ankle tourniquet with three wraps approximating 300 mm Hg, incorporating a full roll of Webril wrapped around the ankle to protect the skin overlying the Achilles tendon.