CHAPTER 20 Great Toe Arthroscopy
Arthroscopy of the first metatarsophalangeal joint (MTP-1) was originally described by Watanabe in 1972.1 Because of the small size of the joint, the applicability of arthroscopy has been limited by the small number of clinical results reported in the literature. Advances in technology for visualization and instrumentation and the recent clinical experience of the surgeons have propelled small joint arthroscopy into a new era. Although arthroscopy in the MTP-1 has not been as widely used as arthroscopy in the knee or the shoulder, its value has been demonstrated, and its use continues to grow for the treatment of traumatic and degenerative conditions and for reconstructive procedures. With proper patient selection and familiarity with the technique, MTP-1 arthroscopy can be a useful addition to the surgeon’s armamentarium.
NORMAL AND PATHOLOGIC ANATOMY
The MTP-1 is composed of the first metatarsal head and neck, proximal phalangeal base, and medial and lateral sesamoids. The first metatarsal articular surface is composed of two fields in continuity, the superior phalangeal and inferior sesamoidal fields. The former is smaller and convex, whereas the latter is larger and separated into two sloped surfaces by a small bony ridge or crista (Fig. 20-1). The proximal phalanx articular surface is oval, concave, and smaller than the corresponding articular surface of the metatarsal head. The base of the proximal phalanx serves as insertions of the extensor hallucis brevis and longus dorsally and the intrinsic muscles of the big toe and plantar plate plantarly.
FIGURE 20-1 The anatomy of the first metatarsophalangeal joint is illustrated with the dorsal capsule and extensor tendons removed and the joint hyperflexed: superior phalangeal part of the first metatarsal articular surface (A); inferior sesamoidal part of the first metatarsal articular surface and the crista (B); metatarsophalangeal part of the lateral collateral ligament (C); lateral sesamoid (D); medial sesamoid (E); metatarsophalangeal part of the medial collateral ligament (F).
The two sesamoids embedded in the thick plantar plate have two surfaces: the inferior, convex, nonarticular, insertional surface and the superior articular surface. The medial sesamoid is usually larger, ovoid, and elongated, whereas the lateral sesamoid is smaller and more circular. The articular surface of each sesamoid is convex in the coronal plane and concave in the sagittal plane and fits well with the corresponding trochlear surface.
The dorsomedial aspect of the joint contains a sizable synovial fold, with the average width of 7 mm and covering 29% of the joint.2 It has abundant blood supply, but the nerve supply is found only in the periphery.
The stability of the joint is provided mainly by the capsuloligamentous complex. The medial and lateral collateral ligaments have two components, the metatarsophalangeal and the metatarsosesamoid suspensory ligaments. The latter components insert directly on the medial and lateral borders of the plantar plate. Balance of the joint is also affected by the function of the musculotendinous structures, including short and long flexors and extensors, abductor hallucis, and adductor hallucis.
At the level of the MTP-1, the distribution of the cutaneous nerve varies, but the dorsomedial and dorsolateral cutaneous branches usually originate from the medial dorsal cutaneous branch of the superficial peroneal nerve and the deep peroneal nerve, respectively (Fig. 20-2). The plantar medial and plantar lateral branches originate from the medial plantar nerve. The dorsomedial cutaneous nerve lies close to the dorsomedial portal and is on average 13.1 mm medial to the extensor hallucis longus tendon,3 but it has been reported to be 2 to 5 mm from it.4 The plantar medial hallucal nerve is on average 10.6 mm plantar to the midline, which is the location for the medial portal. Because of the variations of the nerves in the foot, all the arthroscopic portals should be handled as if a nerve was located directly underneath. The pathologic anatomy of various conditions of the MTP-1 that can be addressed arthroscopically or endoscopically are listed in Table 20-1.
FIGURE 20-2 In the dissected specimen, the dorsomedial and dorsolateral portals are on the medial and lateral aspects of the extensor hallucis longus tendon. The dorsomedial and dorsolateral hallucal nerves are adjacent to the portals.
History and Physical Examination
Patients with MTP-1 problems usually present with forefoot pain. Obtaining a problem-focused history should include the characteristics of pain, swelling, deformities, associated injuries, preexisting diseases, shoewear, prior treatments, and a family history. Athletic activities and expectation are also important factors. Systemic diseases can be associated with increased uric acid and urate crystal arthropathy, which is a common cause of MTP-1 pain.5
Physical examination is the cornerstone of all clinical judgments. We always perform a systematic and thorough examination of all patients with foot and ankle problems, starting with gait, skin, motor, motion, palpation, and special tests. Patients with considerable pain in the MTP-1 may walk on the lateral border of the foot. The forefoot should be observed for deformities, swelling, and discoloration. Active and passive motion of the MTP-1 should be evaluated and compared with the contralateral side. The average passive motion of the MTP-1 in men older than 45 years is 87 degrees, with 67 degrees of dorsiflexion and 20 degrees of plantar flexion.6 Patients with decreased range of motion of the MTP-1 should be differentiated by the characteristics of stiffness. Arthrofibrosis or osteoarthrosis may result in global loss of motion, whereas an early hallux rigidus may produce primarily limited dorsiflexion. Pseudo-hallux rigidus can mimic or be associated with a hallux rigidus, but the tightness from the flexor hallucis longus tendon contracture can usually be decreased by ankle plantar flexion.7 Occasionally, crepitus can be differentiated from arthritis, osteochondral injury, or loose bodies. Pain can be provoked with forced dorsiflexion in patients with hallux rigidus or soft tissue impingement. Bony landmarks, such as the head of the first metatarsal and the base of the proximal phalanx, are superficial and easily palpable. Pain in daily activities often can be reproduced by direct palpation over the osteophytes or the sesamoids.
Soft tissue landmarks should be palpated, including the dorsomedial hallucal nerve at the dorsomedial edge of the medial eminence and the plantar medial hallucal nerve just medial and dorsal to the medial sesamoid. The sensory branches of the deep peroneal nerve supplying the first web space are small and usually not palpable.
In hallux valgus, the first metatarsal adduction can be evaluated if it can be manually corrected, which is a requirement for an endoscopic correction of hallux valgus deformity.8 Sometimes, complete correction may not be achieved because of obstruction by the dislocated fibular sesamoid bone in the web space. This is not a contraindication for the procedure, because the sesamoid bone can be reduced after lateral release, and the intermetatarsal space can then be closed. Specific physical examinations for various pathologies of the MTP-1 that are amendable to arthroscopic treatment are listed in Table 20-1.
We use standard weight-bearing anteroposterior, lateral, and axial sesamoid views for initial evaluation of all patients with forefoot problems (Fig. 20-3). Osteophytes, joint space narrowing, and loose bodies usually can be demonstrated.
FIGURE 20-3 The standard forefoot radiographs include a weight-bearing anteroposterior view (A), a weight-bearing lateral view (B), and a weight-bearing sesamoid view (C).
Elevation of the first metatarsal in relation to the lesser metatarsals can be associated with hallux rigidus.9 Inflammatory arthropathy can develop juxta-articular osteopenia or joint destruction in the late stages, whereas gouty tophi often have juxta-articular punch-out lesions and soft tissue thickening. Hallux valgus requires measurements of the hallux valgus angle, intermetatarsal angle, distal metatarsal articular angle, and proximal phalanx articular angle. Oblique views may be helpful in visualizing dorsal MTP-1 osteophytes, the joint space, and the profile of an individual sesamoid.
Computed tomography (CT) is rarely indicated, but it can better visualize the osteochondral lesions or loose bodies with an osseous component. Magnetic resonance imaging (MRI) can demonstrate a bone bruise, cartilage defects, and synovial hyperplasia, especially with pigmented villonodular synovitis (PVNS), which has low signal intensity on T1-weighted and T2-weighted images.10 MR images of a symptomatic, bipartite medial sesamoid are shown in Figure 20-4. Ultrasound imaging is advantageous in the forefoot because of its magnification power and real-time visualization.11 It can identify loose bodies and small bone spurs. The probe can also be used to reproduce pain with direct pressure over the suspected location.
Indications and Contraindications
Arthroscopic treatment of MTP-1 generally has the same indications as open operations, including failure of nonoperative treatment for 3 to 6 months. Indications are as follows:
Contraindications to arthroscopic treatment are as follows:
Immobilization is beneficial for most MTP-1 pathologies, including degenerative, traumatic, and inflammatory processes. In the acute setting, a walking cast or boot can be helpful. Taping can be applied before athletic activities. A cortisone injection may provide at least a temporary relief for the patient with pain from an inflammatory component, such as synovitis and osteoarthritis.
Shoes should have a low heel and a stable sole to decrease MTP joint motion and loading. A carbon-reinforced insert can be used to increase the rigidity of the sole. Unloading is the mainstay treatment for the sesamoid problems. A silicone gel pad can be placed to support the painful sesamoid and to produce medial posting to shift the load laterally. Shoes with a wide toe box are necessary for patients with MTP-1 osteoarthritis or tophi and hallux valgus.
We prefer to do the arthroscopy of the MTP-1 with the patient in a supine position and with both hips in abduction (Fig. 20-5). The surgeon has 360-degree access to the forefoot, but most of the procedures can be done with the surgeon at the end of the bed. Plantar portals, if needed, can be approached with the surgeon sitting between the patient’s legs.
Manual traction is usually sufficient for visualization of the metatarsal head and the base of the proximal phalanx. We do not routinely use Chinese finger trap traction. Joint distraction, although opening up the distance between articular facets, obliterates the intra-articular gutters and decreases the maneuverability of the arthroscope and instruments. However, it can be useful for access to some osteochondral lesions and in arthroscopy-assisted arthrodesis, which requires passing instruments between the joint facets. The Chinese finger trap traction can be attached to 3- to 5-kg weights, or the limb can be suspended from a pole so that it is just off the operating table.
A 1.9- or 2.7-mm, 30-degree, small joint arthroscope is used for most arthroscopic visualization of the MTP-1. The 1.9-mm arthroscope is used in tight joints, especially when no traction is applied, but it should be handled with care because of its fragility. A 4-mm, 30-degree arthroscope, which provides a wider field of view and easier orientation, is helpful in periarticular endoscopy, such as in a first web space release and gouty tophi excision. The gravity-driven inflow usually is adequate, and the arthroscopic pump is rarely required. An alternative is to use a 50-mL syringe with continuous irrigation controlled by an assistant. Small bone-cutting shavers allow soft tissue and bone débridement, which can minimize instrument switching. Equipment is listed Box 20-1 and Figure 20-6.