Hindfoot and Pantalar Arthritis

History, Physical Examination, and Imaging

A thorough history should be obtained focused on the location, quality and severity of pain and disability, duration of symptoms, potential etiology, treatment successes and failures, and associated medical conditions. A past history of diabetes, vascular insufficiency, skin ulcers, infection, and prior trauma and surgeries should be obtained to optimize preoperative health. Open wounds or prior infection necessitate ruling out deep infection prior to placing internal fixation so as to avoid recurrence of infection. Finally, understanding each patient’s social support and living conditions helps gauge their ability to maintain the limited weight bearing necessary after hindfoot arthrodesis.

Standard radiographs include weight-bearing views of the ankle and foot, as well as hindfoot alignment view and possibly a lower limb alignment view. Computed tomography (CT) scans provided a more detailed view of the irregular joint surfaces and bony relationships in the hindfoot, and with special equipment can be taken with the patient bearing weight. MRI scans are sensitive for early arthritis and osteochondral damage that may not appear on radiographs. Nuclear imaging including SPECT-CT scans highlight physiological evidence of areas of high bone turnover frequently seen with arthritis as well as fractures.

Nonoperative Management

Although this chapter primarily discusses arthrodesis of the joints of the hindfoot, arthrodesis should be avoided when possible, particularly in younger patients. This is more important in the hindfoot than the forefoot as there is little evidence that midfoot fusion results in accelerated surrounding joint arthritis. In supple hindfoot deformities, an osteotomy or a tendon transfer may frequently be used to create a plantigrade foot without resorting to an arthrodesis. If the patient can receive 5 to 10 years of improved quality of life from a reconstructive procedure without an arthrodesis, this is the desired approach.

Alignment

Arthrodeses may be in situ when the foot is already plantigrade, or they may be used to correct an existing deformity. In contrast to an in situ fusion, a deformity-correcting fusion requires careful consideration of the methods to achieve the precise alignment required to produce a plantigrade foot. Deformities are often multiplanar and involve both angulation and rotation. A particular arthrodesis is not always placed into a standard alignment; rather, it must be individualized for each patient.

To determine the appropriate alignment for fusion, first evaluate the normal extremity. With the patient in a supine position, the patella is aligned to the ceiling, providing a common reference point from which all measurements are made and making alignment at surgery much more precise. The degrees of internal or external rotation, varus or valgus, and abduction or adduction are noted.

In order to establish the proper alignment of the fusion site, also consider the lower extremity above the fusion and the foot distal to the fusion. The position of the knee or the bow of the tibia, which can occur either naturally or as a result of prior trauma, must be carefully examined when planning the arthrodesis. Consider correcting severe lower limb malalignment prior to fusing the hindfoot. For example, a well-aligned subtalar fusion in a patient with a severe genu varum or valgum will be malaligned when the proximal deformity is corrected with a knee replacement. The alignment of the extremity distal to the fusion site is also important to be sure a plantigrade foot is created. One common hazard is fixed forefoot varus that is revealed after the subtalar joint is reduced and fused in a patient with long-standing posterior tibial tendon dysfunction. In this case, a double or triple arthrodesis may be more appropriate to derotate the midfoot and create a plantigrade final alignment.

The biomechanics of the foot dictates its optimal alignment. When the subtalar joint is placed into an everted (valgus) position , it creates flexibility of the transverse tarsal joint and results in a supple forefoot. When the subtalar joint is in an inverted (varus) position , it locks the transverse tarsal joint. This creates a rigid forefoot and increased stress under the lateral aspect of the foot. It is therefore important to align the subtalar joint in 5 to 7 degrees of valgus when a fusion is carried out, to maintain flexibility of the forefoot. When a talonavicular arthrodesis is performed, the surgeon must remember that motion in the subtalar joint will no longer occur. Therefore the subtalar joint should be aligned into 5 degrees of valgus first, after which the talonavicular joint is aligned while taking into account abduction or adduction of the transverse tarsal joint as well as forefoot rotation (varus) that might be present. While this complex realignment is technically challenging, if the joints surrounding the talonavicular joint are not properly aligned, a plantigrade foot will not be restored.

Surrounding Joint Arthritis

When evaluating the patient for an arthrodesis, examine the surrounding joints for preexisting arthrosis. A hindfoot arthrodesis places more stress on the surrounding joints and leads to modest increase in ankle arthritis grades over time ( Fig. 25-1 ). In 50 ankles followed over 7.5 years from triple arthrodesis, 58% of ankles showed no change in Kellgren-Lawrence arthritis grade, 31% increased one grade, and only 2% increased more than one grade. Subgroup analysis showed only the group with the greatest varus alignment trended toward significant increase in ankle arthritis grade ( P = 0.063) with the numbers available. Another group of 40 patients followed 15 years after triple arthrodesis found 25% increased ankle Kellgren-Lawrence arthritis grade one level and 15% increased two levels, but no association between alignment and progression of ankle arthritis was found.

Other factors may affect the progression of adjacent joint arthrosis such as the overall stiffness or laxity of the surrounding joints and the degree of preexisting posttraumatic cartilage damage. The stiffer the surrounding joints, the less the limb is able to dissipate the increased stress created by a hindfoot fusion compared with a patient who has more joint laxity. Because an arthrodesis is often performed on a traumatized extremity, the adjacent joints, although not demonstrating arthrosis, might have sustained cartilage damage at the time of the initial injury that makes them more vulnerable to develop arthrosis when subjected to increased stress.

The recognition of potential adjacent joint issues during the evaluation of a hindfoot prior to fusion may help direct clinical decision making. The hindfoot fusion patient should be informed preoperatively that the surgery might exacerbate arthritic pain elsewhere in the foot because of increased stress. When faced with preexisting asymmetric ankle arthritis, for instance, slight overcorrection of the hindfoot fusion may unload the compromised side of the ankle joint. When multiple joints are involved, differential injections can help determine the most painful joints. If arthritis is too widespread for all to be addressed surgically, it may be best to treat the patient conservatively with an AFO rather than carry out an arthrodesis that leaves the patient in pain.

Soft Tissue Considerations

Careful management of the soft tissues at the time of surgery is important to minimize the risk of delayed wound healing and infection. The soft tissue envelope of the foot and ankle often contains little fatty tissue, and at times, the soft tissue has been further compromised by previous surgery or trauma, resulting in adherence to the underlying bone. Other times, systemic illness such as diabetes or peripheral vascular disease creates a physiologic environment detrimental to healing. The surgical approach should be as precise as possible to avoid placing undue tension on the skin edges. Skin flaps should be made as close to full thickness as possible, avoiding undermining the skin, to diminish the possibility of a skin slough. Creating an incision down to the bone or joint, then placing retractors on the deep structures rather than the skin edge, helps avoid skin necrosis. Planning incisions around large realignments should be made to avoid excess skin tension at closure. For example, this can occur when attempting to correct a valgus deformity of the heel using an opening lateral-wedge osteotomy. The surgeon should be adept at multiple approaches so the safest incision can be chosen for a given circumstance.

When making an incision, be cognizant of the location of the cutaneous nerves about the foot and ankle. Although cutaneous nerves tend to lie in certain anatomic areas, great variation exists. Therefore as the incision is carried down through the subcutaneous tissues, it is important always to look for an aberrant cutaneous nerve. The cutaneous nerves can be quite superficial and easily transected but sometimes become adherent within scar tissue. If this occurs, a painful scar or dysesthesias distal to the injury can result in a dissatisfied patient despite a satisfactory fusion. If an inadvertent nerve transection is identified during a surgical approach, it should be carefully dissected to a more proximal level and the cut end buried beneath some fatty tissue or muscle to reduce the chance it will become symptomatic. Sometimes, although a nerve is not cut, it can be stretched as a result of retraction, which can result in a transient loss of function. Patients should be made aware of the potential for nerve injury and the areas where they may experience numbness.

Joint-Preserving Surgery

Debridement of arthritic hindfoot joints is of negligible benefit but may be considered in select circumstances. Focal areas of arthrosis in an otherwise intact joint are at times painful due to flaps of cartilage or entrapped loose bodies. In these cases, arthroscopic debridement may provide relief, but the patient should understand that the joint will likely continue to degrade over time. Osteophyte excision can be considered when specific symptomatic bone spurs or bridging osteophytes around a maintained joint have been identified. It may improve comfort in shoes, but it is questionable whether it will provide long-term pain relief. A small series of four patients were followed 2.8 ± 0.9 years after lateral wall debridement and subtalar arthroscopic debridement for postcalcaneal fracture subtalar arthrosis. Three (75%) were satisfied with results including final numerical pain score of 2.3 (range 1–5) and Japanese Society for Surgery of the Foot Score improving from 65 ± 14 to 83 ± 7 ( P <0.05).

Interposition arthroplasty offers the potential to retain joint motion in select circumstances. Three cases of talonavicular joint resection and interposition arthroplasty using an Achilles tendon autograft were reported in low-demand patients undergoing ankle fusion with associated talonavicular joint arthritis with the goal of maintaining motion and minimizing adjacent joint arthritis. At 1 year, patients maintained motion, reported pain relief, and did not show radiographic collapse.

Surgical Principles

When carrying out an arthrodesis of the foot and ankle, a number of surgical principles should be observed ( Box 25-1 ). The overall goal is to create broad bleeding surfaces of cancellous bone, brought together to create a plantigrade foot, and rigidly compressed and fixed to allow bone to bone healing. Multiple fixation options are available, including screws, staples, locking and nonlocking plates, intramedullary nails, and external fixation.

Popliteal and saphenous nerve blocks are used for most fusions, which generally provides 18 to 36 hours of pain relief. The popliteal block may be repeated after 18 to 24 hours if the patient has too much breakthrough pain. Alternatively, an indwelling nerve catheter may be placed for prolonged analgesia. If there are reasons not to do a popliteal block, an ankle block could give similar pain relief, as long as all the nerves are included (deep and superficial peroneal, tibial, sural, and saphenous).

Careful mobilization of soft tissue around the joints undergoing fusion allows for the exposure required to prepare the joint surfaces as well as placement of the joints into proper alignment and apposition. After exposure of the fusion site, the joint capsule and soft tissues surrounding the joints are elevated while maintaining as much blood supply to the bones as possible. Surrounding bone spurs may need to be removed with a rongeur, which can be saved for bone graft. At times, dense scar tissue overgrowth will need to be carefully excised to expose the joints. A small smooth lamina spreader or pin distractor may be used to further stretch the soft tissue around the joint.

At times, because of previous trauma or severe malalignment, mobilization of the joints is not possible, and bone resection needs to be carried out. Flat cuts on either side of the joint to be fused may allow the joint to come together in proper alignment through slight shortening. Angling the cut based on the direction of deformity can help achieve correction. In the most contracted cases, complete bone resection, such as talectomy or navicular excision, may be required to achieve a plantigrade foot. Alternatively, multiplanar external fixation may be used prior to arthrodesis to bring severe deformities into a better position for fusion, though these techniques should only be used by surgeons with considerable experience.

The articular surfaces of the joints to be fused are meticulously debrided of their articular cartilage and any fibrous tissue until subchondral bone is exposed. This is frequently achieved with a curette or a small, sharp osteotome. A lamina spreader or pin distractor can facilitate exposure, making the debridement easier, but this can damage the bone if it is osteoporotic. The exposed bone surfaces may be scaled using a small sharp osteotome or drilled to penetrate the subchondral bone allowing marrow bleeding into the fusion site and creating greater surface area contact. Minimally invasive techniques rely on arthroscopic visualization to achieve debridement and joint surface preparation. Fluoroscopically guided techniques have also been described using a handheld burr.

Once the subchondral bone is exposed, the foot is once again manipulated, placing it into the desired alignment. The reduction can be stabilized with provisional fixation such as 1.6 mm Kirschner wires (K-wires). It is also advisable to confirm reduction in all planes with fluoroscopy before definitive hardware placement. Interfragmentary compression can be achieved using appropriate definitive fixation. In some joints, applying compression prior to fixation using pin-based clamps may be useful as well.

Bone graft is rarely necessary when carrying out an in situ hindfoot arthrodesis. Sometimes, however, bone has been lost, making a bone graft necessary, such as in a distraction subtalar arthrodesis after calcaneal fracture malunion or tibiotalocalcaneal (TTC) fusion after total ankle replacement. Other times, the surgeon wishes to augment healing potential in patients with risk factors for delayed bone healing. If a small amount of bone is needed, it can be harvested from the calcaneus, medial malleolus, or proximal medial tibia, or from the iliac crest using percutaneous techniques. Larger autografts may be taken from the iliac crest, femoral reaming, or locally, depending on the underlying pathology. Allograft bone has been used successfully as bulk graft in the hindfoot. Bone graft substitutes, including demineralized bone matrix, recombinant bone growth–stimulating hormones, and synthetic tri-calcium phosphate crystals, have all been studied with similar but not superior results to autograft. Porous ingrowth metal implants are also available for a variety of distraction arthrodesis applications. Care should be given when using new products without proven success since they are not always as good as traditional options and may hold unexpected risks.

Internal fixation options include interfragmentary compression screws, compression plates and screws, compression staples, hybrid staple-plate or interlocked screws, and intramedullary nails. Although an external fixator can provide excellent fixation, if possible, a closed system without an external fixator may be preferred because of possible pin-tract problems with prolonged immobilization requirements. Because of soft bone or soft tissue problems, however, it may become necessary to use an external fixator either primarily or to augment internal fixation. Fortunately, external fixators provide excellent rigid fixation.

The skin closure after a fusion is critical. If possible, obtain soft tissue coverage underneath the skin flaps. This is important because if a superficial wound slough occurs, it will be over an underlying bed of soft tissue rather than bone or hardware. This is not always possible, particularly on the dorsum of the foot, where bone lies directly beneath the skin. If any tension is noticeable on the skin edge, some type of a relaxing skin suture or relaxing incision should be used.

The initial postoperative dressing should support the soft tissues as well as the arthrodesis site. A well-padded cotton compression wrap and plaster splints is placed in neutral ankle flexion to provide uniform tissue pressure while allowing for postoperative swelling and avoiding gastroc-soleus contracture. The splint should be applied with the foot and ankle in a neutral position, and the ankle should be kept in that position while the plaster hardens. Dorsiflexing or plantarflexing the ankle or foot after application and before hardening will change the pressure on the soft tissues and could result in pressure sores. A circumferential cast should be avoided during the immediate postoperative period because it can result in undue pressure against the expanding extremity, increasing pain, jeopardizing healing of the wound edges, and potentially leading to compartment syndrome. The postoperative dressing is left on for approximately 12 to 15 days, at which time sutures are removed and a fiberglass cast is placed.

Complications

The main complications after an attempted arthrodesis include infection, skin slough, nerve disruption or entrapment, nonunion, and malalignment. During surgery, debridement of nonvital tissue, irrigation, parenteral antibiotics, careful handling of tissues, and prevention of hematoma formation play an important role in minimizing the risk of infection. If an infection occurs, it is important to recognize and treat it promptly with debridement, deep cultures, and appropriate antibiotics. Fusion is possible if the infection is adequately suppressed, though hardware may need to be removed once the fusion had occurred. A vacuum-assisted dressing may help if the skin cannot be closed after debridement. If infection cannot be controlled, all hardware should be removed and the limb supported with either a splint or external fixation.

Wound healing issues such as skin slough around the foot and ankle are difficult because of the lack of adequate subcutaneous tissue. The potential for a skin slough can be minimized by creating full-thickness skin flaps, making incisions of adequate length to minimize tension on the skin edges during retraction, using postoperative drainage when hematoma is expected, and applying a uniform compression dressing postoperatively. When a skin slough occurs, treat it with local debridement and application of wet-to-dry dressings to promote granulation tissue, potentially followed by coverage with a split-thickness skin graft. Vacuum-assisted closure is also useful to manage a wound slough. If the slough is too large, a plastic surgeon should be consulted as soft tissue coverage may be critical to achieving a successful outcome.

Nerve disruption or entrapment around the foot and ankle creates numbness and can cause chronic pain from footwear rubbing against the neuroma. Prevention using a carefully planned surgical approach is the best treatment. If a symptomatic neuroma occurs, it should be identified and resected proximally into an area not subject to pressure and then buried either beneath muscle or into bone.

A nonunion of an attempted fusion cannot always be avoided despite a surgeon’s best efforts. Cigarette smoking should be ceased or reduced when possible before surgery as there is a two to three times higher risk of nonunion in smokers. As a general rule, of the joints around the foot and ankle, the talonavicular has the highest incidence of nonunion. Its curved surfaces make adequate exposure difficult, preparation of the joint surfaces may be inadequate, and the considerable forces placed on the joint may overwhelm the stability of hardware. Achieving union of a hindfoot fusion is more difficult under a prior ankle fusion due to the added stresses on the fusion site ( Fig. 25-2 ). In cases where nonunion is a particular concern, use more hardware, or augment with external fixation, to achieve greater stability.

The vascularity of the bone plays an important role in the development of a nonunion. Avascular necrosis from any cause creates a situation that is difficult to manage. The most common areas of avascular necrosis in the hindfoot are the talus and navicular. The talus is prone to avascular necrosis either spontaneously, such as after systemic steroid or chronic alcohol use, or after traumatic disruption to its blood supply ( Fig. 25-3 ). The navicular can develop evidence of avascular changes either spontaneously (Kohler or Mueller-Weiss syndrome) or secondary to previous injury. When avascular bone is present, an attempt is made either to debride or bypass the avascular area and to determine the portions of the joint that still have adequate vascularity for fusion. For example, when the lateral half of the navicular is avascular, the medial healthy bone should be included in the fusion, while bone graft is placed laterally between the talus and cuneiforms.

An asymptomatic nonunion frequently can be treated with observation. After a triple arthrodesis, the talonavicular joint occasionally does not fuse, but because of a successful fusion of the subtalar and calcaneocuboid joints, it may not be a source of pain. If a nonunion is symptomatic, a revision of the fusion should be considered. If the overall alignment of the nonunion is satisfactory, bone grafting or inlaying bone across the nonunion site often results in a fusion if internal fixation is adequate. Alternatively, if the nonunion has resulted in loss of alignment, the area needs to be revised. This is done by removing the internal fixation and the fibrous tissue between the bone ends, realigning the surfaces, performing a bone graft if necessary, and re-inserting rigid fixation.

Malunion after a hindfoot fusion can be related to improper positioning of the joints that go on to a successful fusion or to loss of reduction during the healing process. Malalignment after a triple arthrodesis most often consists of varus of the heel and adduction or supination of the forefoot. The patient walks on the lateral aspect of the foot, causing pain and dissatisfaction. Malunion is a problem best avoided by adequate joint mobilization, meticulous bone preparation, and attention to alignment during application of rigid internal fixation. Scrutiny of hindfoot and forefoot alignment in relation to the entire lower limb after placing the fusion in the desired position, and possibly provisionally fixing the fusion site prior to definitive fixation, may help avoid malunion during surgery. The opposite limb often can be used as a guide. Adequate immobilization and protecting against weight bearing in the postoperative period helps prevent postoperative loss of correction.

Subtalar Arthrodesis

An isolated subtalar joint arthrodesis provides powerful deformity correction and pain relief, and it enables the patient to regain the ability to perform most activities. Subtalar fusion allows the patient to achieve a level of function closer to normal, with less stress on the ankle joint, than more extensive arthrodeses.

The position of the subtalar joint determines the flexibility of the transverse tarsal (talonavicular and calcaneocuboid) joints. After subtalar fusion, the talonavicular joint retains over 25% of its motion and the calcaneocuboid joint over 50% of its motion ( Table 25-1 ). If it is placed in varus, the transverse tarsal joint is locked, the foot is stiff, and the patient tends to walk on the lateral side of the foot. Therefore it is imperative that a subtalar arthrodesis be positioned in about 5 degrees of valgus to permit transverse tarsal joint mobility.

The posture of the forefoot also needs to be considered, because if there is more than 10 to 12 degrees of fixed forefoot varus after a subtalar arthrodesis, the patient’s foot cannot compensate. They will walk on the lateral side of the foot, resulting in discomfort beneath the fifth metatarsal head or base, or both, and in severe stress on the lateral ankle ligaments. If there is a fixed forefoot varus with the hindfoot well aligned, it can be corrected by carrying out a simultaneous medial cuneiform opening wedge (Cotton) osteotomy, naviculocuneiform and/or cuneiform-first metatarsal fusion, or transition to a triple arthrodesis.

Posttraumatic subtalar arthritis secondary to a joint depression calcaneal fracture frequently results in arthritis associated with dorsiflexion of the talus into the calcaneal defect. This can result in anterior ankle impingement if left uncorrected during subtalar fusion. Subtalar distraction arthrodesis adds a contoured structural graft between the fusion surfaces to achieve the desired hindfoot alignment and talar inclination.

Indications

The most common indication for a subtalar arthrodesis is arthrosis secondary to trauma, rheumatoid arthritis, primary arthrosis, chronic talocalcaneal coalition, and arthrosis related to chronic hindfoot deformity ( Fig. 25-4 ). The most common deformity leading to subtalar fusion is posterior tibial tendon dysfunction with an unstable subtalar joint but normal transverse tarsal joint motion and a fixed forefoot varus deformity of less than 12 degrees. It is also indicated for a muscle imbalance (e.g., loss of peroneal muscle function) and neuromuscular disorders, such as Charcot-Marie-Tooth disease, poliomyelitis, or nerve injury. Patients with instability of the subtalar joint refractory to stabilization procedures may also benefit from subtalar fusion.

Although a subtalar fusion can have an excellent result, if the deformity can be corrected with a calcaneal osteotomy instead of a fusion, or muscle imbalance can be corrected with tendon transfers, this should be strongly considered.

Deformity correction

• 11.

  Once all the articular cartilage has been removed, the lamina spreader is removed and the alignment of the subtalar joint observed. An initial attempt at placing the hindfoot into the desired position in situ is attempted.

• 12.

  If a varus deformity needs to be corrected, bone is removed from the lateral aspect of the posterior facet to correct the deformity. It is unusual to remove more than 3 to 5 mm of bone when correcting a deformity, although occasionally more bone needs to be removed.

• 13.

  A valgus deformity is common in posterior tibial tendon dysfunction. It is seldom necessary to remove bone from the medial side of the joint because this is primarily a rotational deformity. A multiplanar maneuver reducing the navicular on the talar head while the subtalar joint rotates out of valgus typically achieves the desired hindfoot position. A lamina spreader in the sinus tarsi between the lateral process of the talus and the anterior process of the calcaneus can facilitate this maneuver. Do not overdistract, because this will place the hindfoot into varus.

• 14.

  If a previous calcaneal fracture is present in which a lateral wall decompression is required, the peroneal tendons are elevated from the lateral aspect of the calcaneus as far posteriorly and plantarward as possible. The impinging lateral wall is removed so that it is approximately in line with the lateral aspect of the talus and saved for bone graft. Sometimes, up to 7 to 10 mm of bone needs to be resected.

Joint preparation

• 15.

  The posterior and middle facets, along with the bone in the base of the sinus tarsi, are heavily scaled using a sharp osteotome, K-wire, or drill ( Fig. 25-5D ).

• 16.

  Loose fragments created during scaling may be saved for bone grafting. An osteotome is also used to remove some bone from the anterior process of the calcaneus, away from the calcaneocuboid joint. This is preserved for later bone grafting. When a lateral decompression has been carried out, even more bone is available. Rarely is bone harvested from the iliac crest or proximal tibia.

• 17.

  After the bone surfaces have been scaled, the subtalar joint is manipulated and placed into the desired position of 5 degrees of hindfoot valgus.

• 18.

  If the calcaneus is severely collapsed, height can be restored through subtalar distraction arthrodesis , which uses a contoured block of autograft or allograft bone, or with metallic wedges with bony ingrowth surfaces, to restore calcaneal height and valgus alignment. The block should be wedged in two planes to allow correction of calcaneal pitch as well as varus malalignment. That is, the larger sides of the block should always go medially and posteriorly. Be careful not to put too large a block in the subtalar joint or to force the hindfoot into varus. To avoid wound problems, a posterior incision along the Achilles tendon can be used considered when using this technique.

Internal fixation

• 19.

  Internal fixation is carried out with large-diameter (6.5–7.5 mm) cannulated or noncannulated screws to obtain maximum interfragmentary compression. Either partially threaded screws or fully threaded screws with an overdrilling technique may be used. We typically use a headed 7.3 mm fully threaded cannulated screw with a washer for maximal compression, though headless variable pitch compression screws can also be used successfully.

• 20.

  A variety of screw patterns may be used for fixation of the subtalar joint. Our most common pattern is one or two screws from the posterior inferior calcaneus, one directed slightly medial to the dorsal talar neck and the optional second into the talar body across the posterior facet. If there is an anterior incision for another reason, such as when fusing the subtalar joint under a total ankle replacement, the screw may be placed from the neck of the talus into the calcaneus. Two screws are most commonly used under a prior ankle fusion, when fusion is performed primarily for instability, for smokers or other high risk categories, and for large, noncompliant patients where there is concern for premature weight bearing.

• 21.

  When placing the screw, the ankle is dorsiflexed with the hindfoot held in the desired position. This typically locks the reduction avoiding the need for provisional fixation.

• 22.

  Screw placement starts by percutaneously placing a guidewire on the posterior inferior calcaneus a centimeter from the interior surface ( Fig. 25-5E ). If two screws are to be used, the first guidewire is slightly medial to the midline, otherwise it can be on the midline of the calcaneus.

• 23.

  The guidewire is passed across the calcaneus, heading slightly medial so as to center on the talar neck. It typically passes just along the anterior aspect of the posterior facet ( Fig. 25-6A ). Placement can either be freehand or it is facilitated by placing an ACL aiming guide with the sharp tine on the anterior aspect of the posterior facet of the subtalar joint and the other end of the guide is placed on the heel pad just above the weight-bearing area. This alignment permits the screw to pass through the anterior aspect of the posterior facet and into the neck of the talus but does not penetrate the sinus tarsi area. It provides maximum purchase in the talar neck.

  

• 24.

  The subtalar joint alignment is checked to verify 5 degrees of hindfoot valgus while also correcting any peritalar rotation/subluxation, and the guidewire is drilled into the talus until it just penetrates the dorsal aspect of the neck of the talus. The pin placement is confirmed by fluoroscopy. A lateral view shows the path from calcaneus into talar neck, anteroposterior (AP) view of the ankle confirms the pin is centered in the talar neck, and a heel alignment view verifies position within the calcaneus ( Fig. 25-5F and G ).

• 25.

  A 2- to 3-cm transverse incision is made over the entrance of the guidewire into the heel pad. This incision must be made wide enough to accommodate the screw(s) and, if used, the washer(s) to prevent compressing the skin and fat of the heel pad. The incision is carried directly to bone and slight stripping is done on each side of the guidewire to accommodate the washer. A depth gauge is used to determine the length of the screw. It is usually a few millimeters shorter than what is measured owing to compression of the joint as the screw is tightened.

• 26.

  If one screw is used, the guidewire is tapped beyond the talar neck until it appears on the dorsal aspect of the ankle and it is secured with a clamp outside the skin. This prevents the guidewire from coming out during drilling, which can result in loss of alignment.

• 27.

  If two screws are to be used, a second guidewire is placed starting lateral to the first and aiming across the posterior facet into the talar body, creating divergence with the first screw to improve stability. Fluoroscopy is valuable to confirm placement and also to prevent violating the ankle joint with the pin, drill, or screw ( Fig. 25-5H ). We do not find placing two guidewires at this point prevents compression of the subtalar joint.

• 28.

  The initial hole is drilled with an appropriately sized drill to match the screw’s core diameter (e.g., 4.5 mm), just penetrating the neck of the talus. When using a fully threaded screw , a second drill bit matching the thread diameter (e.g., 7.3 mm) is used to over-drill only the calcaneus, preventing the screw threads from engaging the calcaneus and allowing maximum thread engagement in the talus ( Fig. 25-5I ). By over-drilling the calcaneus, interfragmentary compression at the arthrodesis site is achieved. Bone fragments in the flutes of the two drills are added to the previously saved bone graft.

• 29.

  A partially or fully threaded screw of appropriate length with a washer is inserted. In placing the screw, the surgeon should not have more than 2 to 3 mm of screw exposed beyond the neck of the talus ( Fig. 25-6B ). The position of the screw is verified with fluoroscopy.

• 30.

  When using two screws, the second screw depth is measured and the smaller core diameter drill is used to carefully drill into the talar body, using fluoroscopy to be sure not to drill into the ankle joint ( Fig. 25-5J ). Finally, a partially threaded screw without a washer is placed. The greatest compression comes from the first screw, while the second screw provides primarily resistance to rotation. Final hardware position is checked by fluoroscopy in multiple planes ( Fig. 25-5K and L ).

• 31.

  The guidewire(s) is (are) removed. The previously collected bone graft is packed into the tarsal canal and the sinus tarsi area, packing it medially at first as the tarsal canal expands from medial to lateral (see Fig. 25-6B ). It is not necessary to fill up the sinus tarsi completely. If more bone is needed, it can be obtained from the calcaneus or proximal tibia using a trephine.

Closure

• 32.

  After irrigation, the extensor digitorum brevis muscle and fat pad are placed back over the sinus tarsi area. The extensor digitorum brevis fascia and joint capsule are closed. The subcutaneous tissue and skin are closed in a routine manner. The heel incision is closed with a nonabsorbable horizontal-mattress skin suture.

• 33.

  The patient is placed into a well-padded plaster splint and side stirrups.

Postoperative Care

The patient’s splint is changed approximately 10 to 14 days after surgery, and the sutures are removed if the incisions are healed. The patient is placed into a short-leg cast and is kept non–weight bearing for 4 more weeks. At 6 weeks, if the radiographs demonstrate adequate bony healing, the patient is permitted to bear weight as tolerated in a removable boot. Approximately 12 weeks after surgery, radiographs are obtained, and if satisfactory union has occurred, the patient is permitted to ambulate with an elastic compression stocking ( Fig. 25-7 ). Neuropathic patients should be protected longer to avoid nonunion.

Results

Clinical outcomes

Subtalar fusion has a high fusion rate and excellent clinical outcomes. A large series of 129 open and arthroscopic subtalar fusion with 2 (0.5–11) year follow-up found 92% fusion rate in 13.5 weeks. Patients returned to activities of daily living in 13 weeks, returned to work in 16 weeks, and returned to recreational activity in 27 weeks. Visual analog scale for pain decreased 5 out of 10 points, and both SF-36 and Foot Function Index (FFI) scores improved significantly. Imaging showed postoperative hindfoot alignment was varus malaligned in 5 (4%) ankles and valgus in 13 (10%) ankles. The varus malaligned subtalar fusions had worse VAS, FFI, and SF-36 scores. The overall complication rate was 36%, including nonunion, painful hardware, neuropraxia, scar sensitivity, complex regional pain syndrome, and superficial wound infection. Another series reviewed 77 subtalar arthrodesis using a minimal incision followed an average of 4.2 years, finding 92% achieved radiographic and clinical fusion with no deep infection or wound dehiscence. AOFAS hindfoot score improved 26.9 ± 8.6 to 74.5 ± 13.3. Clinically, abduction–adduction range of motion is reduced 60% at the transverse tarsal joint, while sagittal plane motion decreased 14% after subtalar fusion.

Return to sport after subtalar fusion is more likely for low-impact activities. A series of 33 in situ subtalar fusions for posttraumatic arthritis was evaluated at 4 (1–6) years after surgery. The mean time from initial fracture to subtalar fusion was 2 years. There was no measurable change in number of patients participating in sports from before (67%) to after (73%) fusion. The most common sports were swimming, cycling, skiing, hiking, and walking, while higher impact sports such as soccer and jogging decrease in participation after subtalar fusion. Mann et al ¹¹⁰ found half of patients observed problems walking on uneven ground and climbing steps and inclines after subtalar fusion. Seventy percent participated in recreational sports (e.g., walking for pleasure, biking, skiing, swimming), and 14% were able to play sports that required running and pivoting (e.g., basketball, racquet sports).

The severity of trauma, complications, and patient factors all predict worse outcomes after subtalar fusion for postcalcaneal fracture osteoarthritis. In a series of 84 patients that underwent subtalar fusion for posttraumatic subtalar arthritis, patient-reported outcomes were lower than population norms (EQ-5D 0.78, PROMIS PF 45, FAAM 79) and were significantly reduced in smokers, patients with nonunion or infection, or those with high-energy trauma or multiple limb injuries. Another series of 30 patients after subtalar fusion for posttraumatic arthrosis found 94% fusion rate; 90% would recommend the procedure again, pain improved in 76%, and walking ability improved in 69%, but EuroQol quality of life scores were lower compared to a reference population, likely related to the effects of multi-trauma.

In the long term, subtalar or triple arthrodesis is associated with development of radiographic arthrosis in the surrounding joints. A series of 72 hindfoot fusions were followed for 15 ± 5 years. Pain at final follow-up was greater than at the 1 year postsurgery evaluation, and arthrosis in the ankle, hindfoot, and midfoot joints was present in 54% to 73% of cases, though the presence of arthrosis did not correlate with the degree of pain.

Subtalar fusion can be successful in the setting of talar avascular necrosis. Twelve patients that underwent isolated subtalar fusion for idiopathic or posttraumatic talar avascular necrosis successfully fused in 100% of cases. Five (83%) of six posttraumatic patients required additional procedures while only one (17%) of six with idiopathic AVN needed additional surgery.

Surgical factors

Bone grafting may not be required for in situ subtalar joint fusion. A retrospective review of 133 subtalar fusions was stratified by use of bone grafting (iliac crest autograft, allograft chips, ß-tricalcium phosphate plus bone marrow aspirate, demineralized bone matrix plus bone marrow aspirate) but found no effect of fusion rate based on use of bone graft (78 of 93, 83%) versus no graft (37 of 42, 88%). Another series of 121 open and arthroscopic subtalar fusions similarly found the type of bone graft did not affect fusion rates.

Adequately sized screws, though not number or direction, may affect rate of fusion. A retrospective comparison of number and size of plantar to dorsal screws used during 65 arthroscopic subtalar fusion found a single 6.5 mm screw had lower nonunion rate (25%) compared with a single 7.3 mm screw (0%) or two 7.3 mm screws (0%). On the other hand, the size of screws did not affect fusion rates in a series of 121 open and arthroscopic fusions. Multiple screws should be considered when fusing the subtalar joint beneath a prior ankle fusion, since time to fusion and nonunion rate are both higher in this circumstance.

The number and direction of screws used affects biomechanical stability. A highly divergent screw pattern increased torsional stiffness and maximum torque compared with traditional divergent and single screw patterns using headed or headless screws in a cadaver model. The use of a third headless compression screw increased internal rotation stiffness, but not external rotation or torsional stiffness, and improves compression to levels seen with traditional headed screws. Directing a screw from dorsal to plantar or plantar to dorsal provided similar stiffness in a biomechanical cadaveric study.

Compression staples offer an alternative to screw fixation of subtalar fusion. In a retrospective comparison of fixation technique for subtalar fusion, compression screws successfully fused in 15 (88%) of 17, while in the compression stable group 14 (88%) of 16 fused.

Screw removal for hardware related pain is common. Seven (9.7%) of seventy-seven screws required removal for painful hardware, with no relation between number of screws and need for removal found.

Distraction subtalar arthrodesis

Distraction arthrodesis for malunited calcaneus fractures improves clinical outcomes as well as hindfoot alignment ( Fig. 25-8 ). A systematic review of 25 level-3 and level-4 studies found a variety of techniques produced similar improvements in radiographic parameters and clinical outcomes, including pooled 33 point improvement in AOFAS ankle-hindfoot score. Common complications included nonunion, hardware prominence, wound complications, and sural neuralgia. Distraction arthrodesis combined with peroneal tenotomy resulted in improved hindfoot alignment (10.0 ± 2.1° valgus to 3.2 ± 1.6° valgus, P <0.05), talocalcaneal height, VAS (7.6 ± 1.1 to 1.3 ± 1.2, P <0.05), and AOFAS score (46.6 ± 16.6 to 84.9 ± 10.3 , P <0.05) in 20 patients with 2.5 ± 0.4 year follow-up.

The choice of bone graft material affects outcome when using the distraction arthrodesis technique. A series comparing subtalar distraction arthrodesis for calcaneal malunion using iliac crest autograft in 40 ankle and freeze-dried iliac crest allograft in 17 ankles found visual analog scale for pain was better in the autograft group at 3 months (4.5 ± 1.2 vs. 5.5 ± 1.4, P <0.05), 6 months (2.4 ± 1.3 vs. 3.5 ± 2.2, P <0.05), and 1 year (2.0 ± 1.4 vs. 3.1 ± 2.3, P <0.05). Comparing local calcaneal autograft (28) with iliac crest autograft (10) for distraction subtalar arthrodesis found similar fusion rates (96% and 100%, respectively), radiographic, and clinical outcomes, with the only difference being donor site pain in 40% of the iliac crest donor sites. A series of 12 distraction subtalar fusion using femoral neck allograft found 100% fusion rate at 7.7 months with improved radiographic parameters and 16% complication rate.

Metallic implants with porous coated surfaces have also been used for distraction subtalar arthrodesis with promising results in small series with short follow-up. A series of 18 distraction subtalar joint fusion using a Tantalum metal insert found 100% fused at 1.5 years with no infection, and all cases achieved acceptable alignment. A subset of the fusions was verified by CT scan, which showed osseus integration and no bone-metal interface lucency. AOFAS score increased from 41.3 to 71.5 ( P <0.05) and VAS decreased from 8.6 to 2.4 ( P <0.05). Radiographic measures improved (talocalcaneal angle 21.6 to 29.2 degrees, talar declination angle 5.8 to 24.1 degrees, talocalcaneal height 63.7 to 71.8 degrees). Another small series of 4 patients followed for 1 year after fusion using a titanium wedge found fusion in all cases at average 13 weeks and improved radiographic and patient reported outcomes.

A technique of distraction subtalar arthrodesis using external fixator applied distraction osteogenesis has been described. Eight posttraumatic cases were followed at 1.2 years after external fixator applied distraction of the subtalar joint. Fusion occurred within 4 to 6 months, and partial calcaneal height was restored in all cases. AOFAS hindfoot score improved from 25.3 to 76.3.

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