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 therefore utilizing absolute values is erroneous.
Key Wordshallux rigidus, MTP, metatarsophalangeal, interphalangeal, great toe, arthrodesis
Arthrodesis of the Hallux Metatarsophalangeal Joint
Approach to Arthrodesis
Arthrodesis of the hallux metatarsophalangeal (MTP) joint is indicated for correction of deformity, to treat arthritis, and to address neuromuscular imbalance of the MTP 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 MTP 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 therefore using absolute values is erroneous. In some patients, a very careful discussion must be held with respect to their footwear needs following arthrodesis. For those who really want to have more flexibility, an arthroplasty of the joint with a soft tissue interposition or hemisynthetic cartilage implant is preferable. This may be a requirement particularly if the patient is engaged in activities that require a lot of dorsiflexion such as dance or yoga. Presented here is a patient who developed avascular necrosis following bunion surgery, with marked stiffness who wanted to undergo a predictable procedure such as an arthrodesis despite her intermittent interest in dance. The consequences of the decision to perform an arthrodesis were significant because she did not like the position of the hallux and wanted more dorsiflexion, which was provided in a subsequent surgery. However, as the hallux dorsiflexes, particularly with an arthrodesis, there is increased load on the sesamoid, which became very painful for her, requiring additional surgery ( Fig. 27.1 ). Given the complications with normal footwear, increased stress to the sesamoid complex, and excessive flexion of the IP joint, our preference is to perform arthroplasty as described earlier, as opposed to a dorsiflexed position of the arthrodesis. The use of metallic or silicone arthroplasty should be avoided given the significant bony loss that occurs with these techniques that require complex revision. With arthrodesis performed for correction of severe hallux valgus, concomitant correction of the intermetatarsal (IM) angle occurs with correction of the hallux valgus angle. The correction is very predictable, and concomitant proximal correction is only required in rare cases of extreme rigidity and severity ( Figs. 27.2 and 27.3 ).
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 MTP 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 MTP 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 MTP joint will lead to excessive pressure under the IP joint, which is intolerably uncomfortable for the patient. Plantar flexion of the MTP 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 MTP joint ( Fig. 27.4 ).
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 footwear needs ( Fig. 27.5 ). Fusion of the hallux MTP 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 plantarflexed first metatarsal, however, arthrodesis of the hallux MTP joint will result in pain under the first metatarsal head and sesamoiditis. If MTP joint fusion is the only possible treatment option in the setting of a fixed forefoot equinus or plantarflexed 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 MTP joint in patients with metatarsus primus elevatus ( Fig. 27.6 ). There are certain situations where a malunion of the MTP joint arthrodesis is present with such severe dorsal extension to the joint that one has to plan the approach very carefully. For example, in the case presented in Fig. 27.7 , there was severe scarring medially, and one could not use a medial approach for correction, and the extensor hallucis longus (EHL) had to be lengthened. This required a straight dorsal approach through which the EHL was lengthened, the osteotomy made and the fixation performed. This approach is not ideal, however, because of the possibility of wound dehiscence and then exposure of the EHL and hardware.
The position of the hallux in the transverse plane can be difficult in the presence of a marked increase in the first to second IM space (angle). After correction of hallux valgus with an arthrodesis of the MTP joint, the decrease in the IM 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 IM angle will occur postoperatively, the hallux is ultimately going to abut the second toe. With moderate deformity, manual reduction of the IM angle with correction of the hallux valgus angle is sufficient (see Fig. 27.2 ). For this reason, if we are dealing with severe deformity, we place a temporary lag screw between the first and second metatarsals to close down the IM space. The deformity is thereby reduced, allowing more accurate prediction of the location for correction of the hallux with the arthrodesis.
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 ( Fig. 27.8 ). Pronation of the hallux MTP 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 MTP 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 along with flexion of the IP joint as this will unmask subtle rotational deformity.
Occasionally patients experience sesamoiditis after arthrodesis of the hallux MTP joint. If present, this condition is usually the result of soft tissue atrophy under a plantarflexed 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, and we have noted that it is far more common in patients with rheumatoid arthritis. 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 MTP joint. It is possible to resect the sesamoid(s) through the dorsal incision ( Fig. 27.9 ). If such resection is anticipated, a medial approach to the MTP arthrodesis can be used, making the sesamoidectomy easier to perform. However, it is our preferred method to approach the sesamoidectomy through a standard dorsal incision using a pin distractor to gain access to the deeper recess of the joint ( Fig. 27.10 ). It is necessary to strip with a curved periosteal elevator under the metatarsal head to free up the sesamoid and then the dissection is performed under direct vision. The flexor hallucis longus (FHL) lies lateral to the tibial sesamoid, and while it may be seen during dissection, it rarely is in the way. 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 MTP joint. The success of the fusion is unaltered following simultaneous sesamoid resection ( Fig. 27.11 ).
Bone graft is not used for the standard MTP 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 ( Figs. 27.12 and 27.13 ). 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 MTP joint, as well as the use of orthobiologic agents, our preference is usually to lengthen the MTP joint with a structural bone graft ( Fig. 27.14 ).
Approach and Joint Preparation
The technique for arthrodesis of the MTP joint with standard exposure and crossed cannulated screw fixation is demonstrated in Fig. 27.15 ( ). The incision is made medial to the 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 plantarflexing 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.
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 . We start with the metatarsal using the largest concave reamer that matches the size of the metatarsal head. Care is taken to protect the soft tissues and to use only light pressure to avoid excessive shortening of the metatarsal. The phalanx is subsequently performed using the smallest convex reamer to ream out the central cartilage and subchondral bone. Sequentially larger convex reamers are used until the same size as that used for the metatarsal is reached. This method will result in two surfaces with near-symmetrical radii of curvature maximizing bony contact and positioning. Given the sclerotic nature of the phalanx, the reamers can be used to remove the remaining cartilage and a portion of the subchondral bone with final preparation completed with a 2.0-mm drill to minimize the risk of further shortening . If the reamers are not available, then we use a burr, beginning with the phalanx, and preserve as much of the medial cortex of the base of the proximal phalanx for later screw fixation. We 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.
We are now fortunate to have available a system for arthrodesis of the hallux MTP joint to use, which is extremely reliable and predictable (Paragon28 hallux MTP joint fusion system, Englewood, United States). The main advantage of the system is the use of the precision guide intraoperatively, which helps determine the exact position in valgus and dorsiflexion of the hallux, but also permits cross compression screw fixation followed by application of the dorsal plate where none of the plate screws will interfere with the initially inserted crossed screw ( Fig. 27.16 ).
The hallux is reduced, and the alignment of the hallux is determined with the use of an intraoperative flat plate. 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. Given the difficulty of intraoperative measurements, a useful tool is to ensure that the proximal phalanx should be parallel to the flat plate. Temporary fixation with a 0.062 Kirschner wire (K-wire) allows confirmation of position with the flat plate and fluoroscopy. 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 MTP joint.
These aforementioned principles do not apply in the presence of severe deformity, whether associated with hallux valgus or hallux varus. For example, in patients with gross deformity, the primary concern has to be correction in the absence of ischemia, and the only way that this can be accomplished is by shortening of the proximal phalanx and first metatarsal. It goes without stating that a tourniquet cannot be used in these cases, since one has to be able to monitor the changes in skin perfusion with changes in alignment of the hallux. In these cases, following routine dorsal exposure and release with joint debridement, the hallux is realigned and the extent of ischemia noted. In the first example presented, this young man had severe spasticity associated with cerebral palsy with the hallux underneath the foot and sitting at a 90-degree angle with respect to the metatarsal ( Fig. 27.17 ). The same concept applies to severe hallux varus as it does to hallux valgus, but in particular the elderly patient is at far more risk for ischemia and shortening is absolutely necessary ( Fig. 27.18 ). In these cases of severe deformity, the use of flat cuts minimizes the stretching of the soft tissue while allowing for excellent bony contact, deformity correction, and shortening.
For a straightforward arthrodesis with good bone support, the use of cannulated 4.0-mm screws for fixation is a cost-effective technique. 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. 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. A very effective method and our most used—if isolated screws fixation is not chosen—is cross screw placed in a lag fashion from distal to proximal followed by stabilization with a precontoured dorsal plate. Although a 1/4 tubular or 1/3 tubular plate may be used, they provide minimal rigidity and have significant hardware prominence of the screw heads that may compromise patient satisfaction. Given the ability to achieve bone-on-bone apposition with manual compression, dorsal plating may be performed first followed by placement of a fully threaded cross screw to improve rigidity. Compression must be applied manually with the hallux stabilized with one or two K-wires with this technique. The use of a precontoured anatomic plate in isolation has been associated with increased nonunion rates and therefore a cross screw is advocated in all cases if possible ( ).
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 MTP joint has to be anchored with the distal phalanx for support.
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, we 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 Fig. 27.19 . In the case illustrated, the patient underwent multiple unsuccessful surgical attempts at an MTP 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.
Joint Exposure and Preparation for Distraction Bone Block Arthrodesis
The exposure for the arthrodesis is similar to that described previously, but the EHL tendon may need lengthening. There is no standard way to prepare the bone, because irregular bone defects are frequent. In addition to flat bone cuts, the head and phalanx can be prepared in exactly the same way as discussed previously with a burr, and then a reciprocal shape can be created with a slight contour and indentation in the bone graft ( Fig. 27.20 ).
Considerable sclerosis of the bone margins is often present, and once the sclerosis is debrided down to bleeding bone margins, the defect can be quite considerable. After the cuts at the bone ends have been fashioned, a lamina spreader is inserted into the joint space with maximum distraction, and the gap is measured using fluoroscopic imaging. While the laminar spreader is in place, it is important to check the perfusion to the soft tissues and the hallux, because ischemia may be present. We do not use a tourniquet for this procedure because the lengthening may have to be adjusted according to the perfusion of the hallux. Slight adjustment to the bone cuts may need to be made with a saw or burr, and the final position of the MTP joint may again need to be checked fluoroscopically. We use a structural allograft, to fill the void in the MTP joint. We try to preserve as much length of the metatarsal as possible, meaning that the phalanx and the metatarsal are not cut transversely. The shape of the graft is cut according to the shape of the metatarsal and phalanx so as to maximize bone length. It is only when the edge of the bone is very abnormal, causing instability of the graft, that we use a straight cut. Once the graft has been contoured, it is cut repeatedly until it can easily be recessed into the prepared slot of the MTP joint. Note that the allograft is cut from the femoral head at the neck, thereby incorporating slight dorsiflexion into the arthrodesis.
A lengthening bone block arthrodesis of the hallux MTP joint is easy and is facilitated with plantar flexion of the hallux and insertion of the graft under distraction. One can also use a pin distractor to sufficiently distract the joint, but do not rely on the pin distractor to stretch the joint from the beginning since it will cut through the bone. We prefer to use a laminar spreader to recreate the gap with more tension for insertion of the graft. No tension should be on the skin, which must close easily. The graft must be intrinsically stable at this point, with minimal motion present on passive manipulation of the joint. Fixation must be stable, and a plate is invariably used. There are now custom graft and plating systems in use for a lengthening arthrodesis of the hallux MTP joint. The main advantage of the graft is that there are precontoured in multiple sizes, so that following debridement of the joint with spherical reamers, the graft contours perfectly to the defect. The bone graft (Paragon28 preserve graft, Englewood, United States) is not bleached or irradiated, and is harvested from either the patella or the distal femoral condyle and is very hard and will accept a screw without fear of fracture, provided that the graft is well hydrated. It is not recommended to insert a screw from the plate into the graft directly; however, an oblique compression screw may be used and penetrate the graft easily ( Fig. 27.21 ). In these revision cases where block structural grafts are used, addition of a biologic adjuvant is helpful, and in the case presented, V92 a proprietary cellular bone matrix to which living stem cells are added is used (Paragon28, Englewood, United States) ( ).
Arthrodesis of the hallux metatarsophalangeal (MTP) joint must be performed carefully if the interphalangeal (IP) joint is already hyperextended. Even if the hallux MTP joint is correctly positioned in slight dorsiflexion, overload of the hallux IP joint may still occur. If the hallux MTP joint is fused in too much dorsiflexion, the tip of the hallux is subjected to pressure on the shoe, with consequent discomfort, as a result of the preexisting hyperextension of the IP joint.
The hyperextension of the IP joint may require correction, which can be done simultaneously or subsequently if the condition is symptomatic. In Fig. 27.22 , although the hyperextension was not severe, it was not tolerated by the patient because it resulted in pressure on the tip of the hallux, so correction was indicated. A malunion of an arthrodesis in excessive dorsiflexion or plantar flexion is easiest to approach from a medial incision, with use of a dome saw blade to contour and reposition the joint. If a dome saw blade is not available, a closing wedge osteotomy of the appropriate direction is superior to attempting an opening wedge.
Arthrodesis of the MTP joint in the setting of a short hallux must be done carefully because the hallux will always shorten further simply from preparation of the joint surface. Careful decision making is required to determine if a lengthening of the hallux is appropriate or if it is superior to shorten the lesser metatarsals to recreate a more normal cascade. In older, lower-demand patients, we err on the side of shortening the lesser metatarsal given the superior union rate of a primary arthrodesis.
Nonunion after hallux MTP arthrodesis is unusual and results from inadequate joint preparation, inappropriate fixation technique, or lack of patient compliance with mobilization postoperatively. The approach to revision can be identical to that for the primary procedure, provided that stable fixation is obtained and bone graft or bone graft substitutes are used to fill any defects or bone deficits. In these cases, a rigid dorsal plate combined with cross screw fixation is used.
If an arthrodesis of the MTP joint is performed for correction of severe hallux valgus deformity associated with arthritis, the lesser toe deformities must be corrected simultaneously. If they are not, a large, uncomfortable gap between the hallux and the second toe will occur. Release of the lesser toe MTP joints does not provide sufficient correction, and relaxation of the intrinsic tendons can only be accompanied with shortening osteotomies of the metatarsal head.
With severe deformity of both the first metatarsal and the hallux associated with arthritis, positioning the hallux and the arthrodesis correctly is difficult. In such cases, intraoperatively realigning the first metatarsal with a compression screw inserted from the first across to the second metatarsal is helpful. This is a temporary stabilizing screw that can be removed at 3 months postoperatively. Use of a stabilizing screw is advantageous in that it realigns the metatarsal and facilitates correct positioning of the arthrodesis. Otherwise, as the position of the first metatarsal changes after surgery, the position of the hallux may change as well, potentially leading to an abutment between the hallux and the second toe.
If bone is avascular or the success of the arthrodesis is questionable, orthobiologic agents are used to enhance the rate of fusion.
The alignment of arthrodesis of the MTP joint in the presence of hallux valgus interphalangeus is difficult, and even if positioned in slight varus, arthritis of the IP joint may ultimately occur ( Fig. 27.23 ; see also Fig. 27.22 ). An additional osteotomy of the phalanx (a distal Akin osteotomy) should be performed to correct deformity. The alternative is to force the MTP fusion into a neutral position to accommodate the valgus interphalangeus. This maneuver will work only for very mild interphalangeus deformity.