Fusion: When and How

CHAPTER PREVIEW

CHAPTER SYNOPSIS:

The goal of this chapter is to discuss the indications, techniques, and outcomes for great toe metatarsophalangeal fusions. The importance of optimal position for fusion is emphasized.

IMPORTANT POINTS:

1

The ideal position for a great toe fusion is 20 degrees valgus and 25 degrees dorsiflexion in relation to the floor.
2

The method of fixation is less important than the preparation of the joint. There are many adequate ways of fixation.
3

Warn patients of potential issues with getting their foot into a downhill ski boot. Other than that there are very few, if any, footwear issues with a great toe fusion.

CLINICAL/SURGICAL PEARLS:

1

Deviation in any direction from the ideal positioning may cause late complications.
2

Too little valgus places the interphalangeal joint at risk of degenerative arthritis, and excessive valgus may cause difficulty in shoe wear and transfer metatarsalgia.
3

Excessive dorsiflexion may lead to clawing of the interphalangeal joint and subsequent impingement of the interphalangeal joint and the distal phalanx against the toe-box of the shoe.
4

Inadequate dorsiflexion may create pressure on the tip of the toe and secondary arthritis of the interphalangeal joint. It also makes it difficult to “walk over” the toe.
5

Nonunion or delayed union of the arthrodesis site may occur when the joint surface is inadequately prepared. In the presence of sclerotic bone, meticulous joint preparation requires reaming to cancellous bone to enable a successful arthrodesis.

CLINICAL/SURGICAL PITFALLS:

1

Be especially careful with osteopenic bone. A plate and screw construct might be the best fixation.
2

Osteopenic bone should also be dealt with extreme caution when using the power reamers.
3

Do not fuse the toe too straight. It is difficult for the foot to compensate for that toe position.
4

Malpositioning is one of the most common complications associated with this surgery. It is critical to achieve neutral rotation, adequate dorsiflexion, and adequate valgus.

VIDEO AVAILABLE:

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MTP fusion.

HISTORY/INTRODUCTION/SCOPE OF THE PROBLEM

Hallux rigidus is a term that describes a localized painful arthritic condition of the first metatarsophalangeal (MTP) joint that can be challenging to treat. The main goals of surgical interventions are to provide relief of pain and improve function. Arthrodesis of the first MTP joint is a satisfactory procedure for moderate to severe hallux rigidus and is a salvage procedure when other surgical methods fail. It is most suitable for patients with an active lifestyle and provides long-term relief of pain and stability to the first ray. The clinical and cosmetic results are excellent, providing that a successful arthrodesis is achieved in good position.

Arthrodesis of the first MTP joint was described by Broca in 1852 but received only little attention until the middle of the 20th century. Since then, numerous methods for achieving a successful joint fusion have been described. Arthrodesis was reported as a treatment for a number of conditions, not limited to hallux rigidus. However, the cumulative reported experience with this procedure has not been without complications, which led to a continuous debate on methods of fixation and preparation of bone surfaces.

In 1894, Clutton advocated fusion of the first MTP joint as a permanent and satisfactory cure for severe painful hallux valgus. In 1940, Thompson and McElvenny were the first to emphasize the need for optimal positioning of arthrodesis for the treatment of hallux rigidus, and in 1952, McKeever reported the first large series on first MTP fusion. He indicated that his experience had been so favorable that he adopted arthrodesis as the standard procedure for hallux valgus and hallux rigidus.

SURGICAL PROBLEM

Site Preparation

In the evolution process of first MTP joint arthrodesis, much attention was given to the different surgical techniques of bone site preparation, the selection of the appropriate fixation method, and the proper alignment of the arthrodesis. Multiple techniques have been described for arthrodesis. They have undergone refinements and variations in an attempt to improve long-term clinical outcomes, reduce complications, and more appropriately address the specific deformities of individual patients.

To achieve a successful fusion, the joint surfaces must be optimally prepared. In 1894, Clutton simply removed the local cartilage and exostoses. In 1940, Thompson and McElvenny went further by “fish scaling” the bone and adding bone chips and an inlay graft to improve surface apposition. McKeever was apparently the first surgeon to prepare the surfaces into a reciprocal relationship by using an osteotome on the metatarsal head to fashion a crude peg. A cup was then created in the proximal phalanx with a Kerrison rongeur, and the peg and cup were then docked. In 1958, Laird Wilson described a simpler method of preparing the joint surface for fusion. He used a small oscillating saw to excise the metatarsal head and the proximal surface of the proximal phalanx and then brought the two cancellous surfaces together. This planar cartilage removing technique does not require special instrumentation, and it is easy to tailor the cuts to provide an ideal fusion angle. Another simple alternative for fusion site preparation involves simply denuding the joint surfaces of all articular cartilage and creating small drill holes in multiple areas of the subchondral bone. This again allows apposition of the two bleeding cancellous surfaces across which fusion may occur. Bone chips from the debrided osteophytes and drill holes may be added to this fusion site as bone graft material. In 1968, Marin developed special instruments to expand upon the McKeever arthrodesis. He initially shaped the metatarsal head into cone using an osteotome and a concave (female) cone reamer. He then used a reciprocal convex (male) reamer on the proximal phalanx. The more precise fit and the larger intimate contact area provide increased stability across the fusion site. The cone reamer instruments have been further refined into power cannulated reamers in different sizes for accurate adaptation to the patient bone.

Mode of Fixation

The first MTP joint is a frequently loaded joint, which can be stressed with up to 90% of body weight during each step in gait. Rigid fixation in a compression mode is desired for arthrodesis to help increase the rate of bony union and maintain the desired position of fusion. Numerous methods of internal fixation have been proposed, including heavy suture, crossed Kirschner wires, Steinman pins, staples, Rush rods, interfragmentary screws, Herbert screws, small fragment plates, external compression clamps, and external fixation. To date, there have been no prospective randomized clinical trials to determine the optimal method.

BIOMECHANICAL STUDIES

Although hallux MTP fusion is successfully achieved in most patients, the optimal form of fixation continues to be explored. The most common postoperative complication of first MTP joint arthrodesis is nonunion. It is likely that the cause of these nonunions is subtle micromotion that occurs during each step in gait. A more stable construct theoretically allows a higher fusion rate and permits earlier weight-bearing. Several biomechanical studies on cadaver feet have reported results comparing first MTP arthrodesis fixation techniques and joint surface preparations. In 1986, Sykes and Hughes compared planar joint excision to cup and cone preparation with different fixation methods. Their results showed that a cancellous screw with planar joint excision was superior and more stable as compared with external fixators, and wire stabilization techniques. In 1993, Curtis et al. published the results of a similar biomechanical study which partially contradicted Sykes and Hughes findings. This study found that cup and cone preparation with an interfragmentary screw had the best fixation. The authors concluded that the cup and cone method of fusion site preparation accounted for the majority of this increased stability, whereas the method of fixation was considered secondarily important. In 1994, Rongstad et al. compared cancellous screw with mini-plate fixation, Herbert screw, and Steinmann pin fixation. The cancellous screw with mini-plate provided the best fixation. In 2002, Neaufeld et al. compared two crossed cancellous screws, dorsal plate with oblique Kirschner wire, and two compression staples with oblique Kirschner wire. Both the plate and screw constructs were statistically stronger than the compression construct. All these biomechanical studies compared matched pairs of cadaver toes with different types of fixation and testing them to failure by loading them in a dorsal direction. In 2003, Politi et al. studied the combination of different fixation technique and joint surface preparation on synthetic bone model in order to ensure greater standardization and reproducibility. The mini-plate and oblique lag screw combination with cup and cone surface preparation provided significantly more stability and resistance to micro-motion and required more than twice the force for displacement compared with lag screw alone, which was the next strongest technique. These findings substantiate Rongstad’s finding and support the clinical studies using this type of fixation.

INDICATION/CONTRAINDICATION

The choice of surgical procedure depends on a number of variables, including patient’s age, activity level, expectations, prior treatment history, and an accurate diagnosis of the disease process and its stage. Arthrodesis of the first MTP joint is indicated for a wide variety of conditions. The primary surgical indication is osteoarthritis of the first MTP joint (hallux rigidus) when nonoperative measures, such as rigid rocker sole, orthotics, anti-inflammatory medications, or more, have failed. Other indications for arthrodesis are inflammatory arthritis, metabolic disorders such as gout with secondary degenerative changes, neuromuscular disorders, failed hemi or total toe implants, failed excisional arthroplasty, failed cheilectomy, severe hallux valgus, and revision hallux valgus surgery. Therefore, this surgical technique can be used either as the primary surgical treatment or as a salvage procedure. In the scope of the large variability in presentation of hallux rigidus, Coughlin and Shurnas advocated the use of a clinical-radiographic grading system that will assist in choosing the correct surgical procedure. By comparing the outcome of two procedures, cheilectomy and first MTP arthrodesis in a subset of patients with first MTP osteoarthritis, he concluded that the system appeared to be reliable as it correctly predicted a successful or poor outcome of cheilectomy. Its advantage was in the distinction between grade III and grade IV hallux rigidus. Cheilectomy uniformly failed in patients with grade IV and in patients with grade III hallux rigidus when the percentage of metatarsal head cartilage coverage, as estimated during surgery, was less than 50%. In these patients, first MTP arthrodesis is indicated.

It is important to counsel the patient that the main goal of the surgical intervention is to provide pain relief, and that arthrodesis will eliminate first MTP joint motion. If this is understood by the patient and the physician, the results of surgical intervention can be rewarding. Arthrodesis is best reserved for patients who have an active lifestyle, and after a successful well-positioned fusion, recreation that includes running can be expected. However, activities that require hallux en pointe position are mechanically impossible, and shoe wear will be restricted to a heel height less than 2 inches. Preoperative consideration should include a thorough physical examination to evaluate neuromuscular status, hallux position, and MTP and interphalangeal (IP) joint ranges of motion, forefoot pronation and supination, previous incisions, foot prints, gait, transfer lesions, gastrocnemius contracture, and other foot deformities. The postoperative course expectations, outcomes, and complications also should be reviewed with the patient preoperatively, including type of anesthesia, assistive ambulatory devices, pain medication, and postoperative follow-up. The deleterious effects of tobacco on wound and osseous healing must also be discussed with the patient.

Relatively few contraindications exist for first MTP joint arthrodesis. Absolute contraindications are recent joint infection, vascular insufficiency that might impair adequate healing, patients in whom the absence of MTP joint motion is unacceptable, and the presence of IP joint arthritis with restricted range of motion or IP joint instability. Relative contraindications include severe osteopenia, which may preclude rigid internal fixation, and a less severe hallux rigidus when more than 50% of the metatarsal head articular surface remains.

SURGICAL TECHNIQUE

Arthrodesis of the first MTP joint is performed with use of regional anesthesia by means of a popliteal block or ankle block. The patient is placed on the operating table in the supine position. An Esmarch bandage is used to exsanguinate the extremity and then is used as an above-the-ankle tourniquet. A longitudinal dorsal incision is centered over the MTP joint. It begins at the middle of the proximal phalanx and extends 4 to 5 cm proximally. The incision is deepened along the medial border of the extensor hallucis longus tendon and is then deepened through the extensor hood and joint capsule. The capsule is preserved for later repair. Marginal osteophytes and loose bodies are removed to expose the joint surface. The base of the proximal phalanx and the metatarsal head are exposed subperiosteally by releasing of the collateral ligaments until the proximal phalanx can be plantarflexed to clear a full access to the metatarsal head. Joint surface preparation is made by conical power reamers. This type of joint surface preparation is easy, precise, and accurate. It involves less metatarsal shortening than planar resection arthrodesis, and more versatility when dialing in the final hallux position. When power reamers are unavailable, hand-crafted shaping of the concave proximal phalanx and the convex metatarsal head can be performed with a high-speed 4-mm to 6-mm round bur.

The proximal phalanx is then plantarflexed, and a 1.6-mm Kirschner wire is centered on the first metatarsal head articular surface and driven in a proximal direction along the longitudinal axis of the metatarsus. A concave cannulated metatarsal reamer is used to create a convex metatarsal head ( Fig. 37-1 ). The head is sized to allow the largest diameter concave reamer. Gentle reaming is carried down to cancellous bleeding bone. The Kirschner wire is then removed, and attention is directed to the proximal phalanx. Another Kirschner wire is centered on the articular surface of the base of the proximal phalanx and driven distally to prepare for the cannulated reaming. A convex cannulated reamer is used to prepare a concave cup-shaped surface in the proximal phalanx. A small-diameter reamer is used first to deepen the center followed by upsizing reaming to widen the joint surface. The Kirschner wire is removed and any joint debris is resected. Typically, the hallux is placed in neutral rotation, 15 to 20 degrees of valgus, and 15 to 25 degrees of dorsiflexion in reference to the axis of the first metatarsal Figs. 37-2 through 37-4 ). The position of the arthrodesis is adjusted according to the alignment of the foot (supinated or pronated) of each patient, to allow the great toe to lie alongside the second toe without impingement. Patients who have associated hallux valgus interphalangeus may need less than 15 to 20 degrees of valgus deviation to avoid impingement on the second toe. Simulated weight-bearing with use of a flat plate (an instrument case lid) intraoperatively helps the surgeon to assess the appropriate position of the arthrodesis. There should be approximately up to 5 mm of space between the plate and the pulp of the hallux.