Approach to Arthrodesis

Arthrodesis of the hallux metatarsophalangeal (MP) joint is indicated for correction of deformity, to treat arthritis, and to address neuromuscular imbalance of the MP joint (with or without deformity). As a generalization, this is an operation that is technically easy to perform, with a predictable outcome, provided that the hallux is well positioned. Although the focus of the procedure is on the MP joint, the presence of interphalangeal (IP) joint instability, hyperextension, or arthritis may preclude a successful outcome of the arthrodesis. The key to this operation is in the correct positioning of the arthrodesis: The hallux must be slightly supinated into a neutral position, in slight dorsiflexion with respect to the correct position of the floor, and in slight valgus. Some of these parameters will need to be modified depending on patient characteristics and preferences (e.g., the running athlete, the patient who desires to wear slightly higher-heeled shoes) (Figures 33-1 and 33-2). With arthrodesis performed for correction of severe hallux valgus, a straight toe is not tolerated, and the hallux should be fused in 5 to 10 degrees of valgus (Figure 33-3).

Figure 33-1 A, The patient was a recreational dancer who desired marked dorsiflexion in the hallux to enable her activities. She had undergone two previous failed surgeries and preferred the stability of arthrodesis to an arthroplasty. B-D, Note the position of the hallux at rest (B and C) and in a 7-cm high-heeled shoe (D).

Figure 33-2 The patient was a short-distance runner who desired more dorsiflexion to permit rapid toe-off. Note the clearance of the hallux off the ground.

Figure 33-3 A and B, Correction of hallux valgus and metatarsus adductus was obtained with an arthrodesis, placing the metatarsophalangeal joint in slightly more valgus than that used for management of arthritis.

Alignment of Arthrodesis

The dilemma always arises of how much dorsiflexion the hallux will tolerate in the fusion. Clearly, the greater the angle of dorsiflexion, the easier it will be to wear a high-heeled shoe, to perform toe-off, and to avoid any pressure on the IP joint. With a steeper MP joint angle, however, the tendency to incur rubbing on the dorsal surface of the IP joint and the nail with the underside of the shoe increases. In some patients, the tip of the hallux and the nail become painfully thickened. Furthermore, over time, if the hallux MP joint is excessively dorsiflexed, a reciprocal flexion contracture will occur at the IP joint that ultimately will become fixed and may be associated with arthritis. Conversely, too much plantar flexion of the MP joint will lead to excessive pressure under the IP joint, which is intolerably uncomfortable for the patient. Plantar flexion of the MP fusion will always lead to loosening and ultimately hyperextension of the IP joint with arthritis. The hyperextension of the hallux IP joint is a problem regardless of the status of the MP joint.

Therefore the decision regarding how much dorsiflexion to incorporate into the fusion has to be made after consideration of various factors including the presence of any preexisting hyperextension and instability of the IP joint and the patient’s types and level of activity, sports interests, and shoe wear needs (Figure 33-4). Fusion of the hallux MP joint at an angle is preferable to the position of the floor rather than the metatarsal. The metatarsal declination varies considerably, and the more predictable position would be with reference to the floor. In the setting of a cavus foot or a steep plantar flexed first metatarsal, however, arthrodesis of the hallux MP joint will result in pain under the first metatarsal head and sesamoiditis. If MP joint fusion is the only possible treatment option in the setting of a fixed forefoot equinus or plantar flexed first ray, a dorsal wedge osteotomy of the first metatarsal may have to be performed before proceeding with the arthrodesis. The converse applies in a patient with severe elevatus of the first metatarsal. Here, position of the fusion relative to the metatarsal may be in neutral alignment, but the hallux remains elevated relative to the floor. Not much, if any, dorsiflexion can be incorporated in the hallux MP joint in patients with metatarsus primus elevatus.

Figure 33-4 A-C, The ideal position for an arthrodesis is demonstrated with the hallux slightly elevated off the floor, correctly positioned in the coronal plane, and in very slight valgus.

The position of the hallux in the transverse plane can be difficult in the presence of a marked increase in the first to second intermetatarsal space (angle). After correction of hallux valgus with an arthrodesis of the MP joint, the decrease in the intermetatarsal angle will be almost proportionate to the magnitude of the deformity preoperatively. Therefore, in view of the expected decrease of this deformity, where is the hallux placed in the fusion intraoperatively? For example, if the hallux is placed in slight valgus, with the anticipation that a decrease in the intermetatarsal angle will occur postoperatively, the hallux is ultimately going to abut the second toe. For this reason, if I am dealing with severe deformity, I place a temporary lag screw between the first and second metatarsals to close down the intermetatarsal space. The deformity is thereby reduced, allowing more accurate prediction of the location for correction of the hallux with the arthrodesis. The other option is to undercorrect the hallux and leave it in a slightly more neutral position than usual, with the anticipation of the change in position of the first ray after the operation.

The alignment of the hallux in the coronal plane must be accurate. If the hallux is overpronated, pain will be present at both the medial aspect of the IP joint and the medial margin of the nail, with consequent ingrowth of the toenail (Figure 33-5). Pronation of the hallux MP joint fusion will lead to marked fixed deformity of the IP joint in flexion and valgus, which is very difficult to correct. If indeed this deformity develops, the MP fusion should be revised to prevent fixed changes with arthritis in the IP joint. Oversupination leads to pain on the medial or lateral nail fold, and an ingrown toenail can result as well. The best way to check alignment of the hallux is to look at the way the hallux nail lines up with the adjacent toenails.

Figure 33-5 A and B, The hallux has been fused in too much pronation in these two patients. The nail of the hallux does not line up with the nails of the lesser toes, and development of an ingrown toenail is likely.

Sesamoid Issues

Occasionally patients experience sesamoiditis after arthrodesis of the hallux MP joint. If present, this condition usually is the result of soft tissue atrophy under a plantar flexed first metatarsal, rather than painful arthritis between the sesamoid and the first metatarsal head. If the latter occurs, it can be secondary to a hypertrophy of the sesamoid. It cannot always be anticipated, and a sesamoidectomy may need to be performed at a later date after the arthrodesis. If the patient has sesamoid pain (from pressure) preoperatively, however, the sesamoid can be resected in conjunction with the arthrodesis of the hallux MP joint. It is possible to resect the sesamoid(s) through the dorsal incision. If such resection is anticipated, a medial approach to the MP arthrodesis can be used, making the sesamoidectomy easier to perform. If symptoms of pain under the metatarsal head occur after arthrodesis, removal of the sesamoid is very easy from a direct medial approach to the MP joint.

Bone Grafting

Bone graft is not used for the standard MP fusion and is necessary only when either shortening of the hallux, osteolysis, or cystic defects are present. To correct a very short hallux or one for which graft is clearly required, the decision is between fusing the hallux in situ with cancellous bone graft and using a bone block graft to lengthen the hallux. Clearly, if severe shortening of the hallux is present with transfer metatarsalgia, then an arthrodesis with a bone block graft would be ideal. Even with minor bone loss, although an arthrodesis is technically feasible, some further shortening of the hallux always occurs as a result of preparation of the joint surfaces; from a functional as well as a cosmetic standpoint, even minimal shortening is undesirable (Figures 33-6 and 33-7). If an in situ arthrodesis is performed when metatarsalgia is present, then either shortening osteotomies of the lesser metatarsals or metatarsal head resection should be considered. With the current custom plates designed specifically for use with a lengthening arthrodesis of the MP joint, as well as the use of orthobiologic agents, my preference usually is to lengthen the MP joint with a structural bone graft (Figure 33-8).

Figure 33-6 A, The patient presented with persistent pain and deformity after an unsuccessful resection arthroplasty. B, Despite shortening of the hallux, an in situ arthrodesis was performed.

Figure 33-7 A, Avascular necrosis with shortening after bunionectomy. B and C, Treatment was with an in situ arthrodesis with plate fixation, supplemented by bone morphogenetic protein stimulation.

Figure 33-8 A, Avascular necrosis associated with second and third metatarsalgia and a crossover toe deformity. B and C, Treatment consisted of a bone block lengthening arthrodesis for the hallux and tendon transfers to correct the crossover toe deformity of the second toe.

Approach and Joint Preparation

The technique for arthrodesis of the MP joint with standard exposure and crossed cannulated screw fixation is demonstrated in Figure 33-9. The incision is made medial to the extensor hallucis longus (EHL) tendon, over a length of 4 cm, with a small cuff of extensor retinaculum left for later closure. The extensor tendon is retracted laterally, and using subperiosteal dissection, the entire articulation is exposed. Forcibly plantar flexing the proximal phalanx is helpful; plantar flexion facilitates dissection of the periosteum off both sides of the joint. With further plantar flexion of the hallux, the undersurface of the proximal phalanx, including the attachment of the volar plate, is easily dissected. Stripping the attachment of the sesamoids is unnecessary because they retract once the volar plate is released.

Figure 33-9 The steps for metatarsophalangeal arthrodesis. A, A dorsal longitudinal incision is made medial to the extensor hallucis longus. B, The joint is plantar flexed, and a cup and cone debridement is performed using a burr. C, The position of the hallux is moved from neutral to a corrected position of slight supination so that the nails line up correctly. D, The first guide pin is introduced from the plantar-medial hallux. E, The countersink is prepared with a burr on the metatarsal neck. F and G, Placement of a cannulated 4.0-mm screw, followed by insertion of the second screw. H, The final position of the hallux is verified by pushing upward from the plantar surface; note the slight elevation of the toe.

The maximum length of the hallux should be preserved when the bone cuts are planned. If a saw is used to create flat cuts, apposition of the bone surfaces is not difficult, but more bone will be removed, and the hallux is shortened. Planning the ultimate position of the hallux is not as easy with flat saw cuts, and repeated shaving of either side of the joint may need to be done until the hallux is in the correct position. Alternatively, a cup and cone shape can be created to contour the joint surfaces, with use of either custom conical reamers or a 5-mm burr to denude the articular surface. I start with the hallux, burr into the phalanx, and preserve as much of the medial cortex of the base of the proximal phalanx for later screw fixation. I try to maintain as much of the rim of the joint as possible, but it is important to burr down to healthy, bleeding cancellous bone. A reciprocal cone shape is created with the burr on the metatarsal head, and the proximal phalanx is used as a guide for the shaping of the metatarsal head. With this technique, a cock-up position of the hallux resulting from excessive dorsal bone resection should be avoided.

The hallux is reduced, and the alignment of the hallux is determined on the basis of decision making with the patient regarding shoe wear, type and level of activity, and the shape of the forefoot. The hallux is placed in 10 degrees of dorsiflexion relative to the weight-bearing surface of the floor and supinated so that the hallux nail is now parallel with the nails of the lesser toes, and slight valgus is incorporated into the position of the arthrodesis. Before reduction and fixation of the joint are performed, it is important to ensure that the head or phalanx has no bone defect. Even when good bone apposition can be achieved, if minimal bone contact is present circumferentially, a small cancellous bone graft is required; either cancellous autograft or an orthobiologic substitute can be used. Graft can be obtained from the calcaneus through a 1-cm incision on the posterior inferior heel, posterior to the sural nerve and anterior to the Achilles tendon. A small trephine can be used to harvest a 1-cm-long cylindrical tube of cancellous bone, which can be contoured and placed in the defect in the MP joint.

Fixation

For a straightforward arthrodesis with good bone support, I typically use cannulated 4.0-mm screws for fixation. Of note, use of partially threaded screws is not necessary, because broad cancellous bone surfaces are present, and the fusion requires rigidity and stability as much as compression. Nonetheless, if the bone quality is good, I currently use partially threaded screws. With the hallux in the reduced position, guide pins are introduced to cross the articular surface. The first guide pin is introduced from the plantar medial aspect of the undersurface of the metatarsal neck just proximal to the metatarsal head. This pin is aimed distally and passed out of the metatarsal head and into the lateral base of the proximal phalanx. It is useful to make a small pilot burr hole as a countersink maneuver before inserting the guide pin. The second guide pin is introduced from distal to proximal from the medial aspect of the base of the proximal phalanx across the metatarsal head and exits slightly dorsally and laterally. If the bone on the base of the phalanx or medial head is inadequate (as, for example, after bunionectomy), one of the screws is introduced from the dorsal neck of the metatarsal head distally into the phalanx.

Before insertion of the screws, the neck must be prepared with either a countersink maneuver or by creating a larger hole with a burr, to prevent fracture and to facilitate the correct angulation of the screw across the joint. The first screw is introduced from the metatarsal head going distally. During the introduction of the first screw, the hallux is compressed manually across the articular surface to provide maximum contact and compression during the screw fixation. The second screw is introduced from distal to proximal, but before insertion the medial cortex of the base of the proximal phalanx must be prepared to prevent fracture with a cannulated drill.

Sometimes the standard screw fixation is not sufficient because of the plane of the metatarsal head or the proximal phalanx. This problem may arise, for example, after failed bunionectomy, when a medial eminence is not present and less of an anchor point is available for the head of the screw. If bone loss is a factor or if the contour of the metatarsal head does not facilitate internal fixation, other means of fixation must be used instead of screws. Alternatives include a dorsal plate, multiple threaded small K-wires, and large threaded Steinmann pins (Figure 33-10). Clearly, crossing the hallux IP joint is not desirable but is necessary with use of the larger threaded pins. Sometimes, however, the bone loss is so severe that the MP joint has to be anchored with the distal phalanx for support. An anchoring method that I have found to be very stable is to use one crossed oblique 4.0-mm partially threaded screw supplemented by a custom dorsal MP fusion plate (Orthohelix, Akron, Ohio).

Figure 33-10 A, Severe erosive dislocation of the hallux, with no bone of substance remaining in the proximal phalanx. B, The arthrodesis was performed with threaded Steinmann pins inserted in antegrade and then retrograde fashion. Two transverse pins were inserted between the first and second metatarsals. There was significant diastasis between the metatarsals, and the alignment of the hallux could not be based on the relationship between the hallux and the first metatarsal. C, The first and second metatarsals were squeezed together, the transverse pins were introduced, and then the Steinmann pins were inserted retrograde across the metatarsophalangeal joint.

Correction of Deformity Associated With Bone Loss

In cases with severe bone resorption or bone loss, an in situ arthrodesis is not sufficient, and structural support with an interposition graft must be considered. With the use of custom-designed plates and added orthobiologic agents, structural grafting has now become a relatively easy procedure to perform. For selected patients, such as those with severe bone loss and erosive synovitis associated with failed implant arthroplasty, the surgery can be staged. For these patients, I remove the implant, resect the fibrinous debris, lengthen the EHL tendon, and fill the defect in the phalanx and metatarsal head with cancellous bone graft. After 6 months, once the graft has incorporated, the second-stage structural graft–fusion procedure is performed. Some patients, however, are reasonably comfortable after the first stage of the surgery, so the second stage with arthrodesis is not performed. Although the hallux remains short and weak, the pain from the inflammatory synovitis dissipates, and function is acceptable. Another alternative is to stage surgery by removing all debris, hardware, and necrotic bone, in particular when the possibility of infection is a concern. A good example is presented in Figure 33-11. In the case illustrated, the patient underwent multiple unsuccessful surgical attempts at an MP arthrodesis, resulting in a nonunion, as well as a questionable nonunion of the tarsometatarsal joint and possible chronic infection. The hardware was removed, and after culture samples were obtained, antibiotic-impregnated cement was inserted as a spacer to maintain bone length; the second-stage surgery was performed 6 weeks later with a bone block lengthening arthrodesis.

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