Treatment of Hindfoot and Midfoot Arthritis

Chapter 20


Treatment of Hindfoot and Midfoot Arthritis




Midfoot and hindfoot arthritis and deformity can cause debilitating pain and limitation in function. Unlike some other lower extremity joints, there are limited surgical options short of arthrodesis of the affected joints. Initial treatment could include shoe and activity modifications as well as the addition of orthotics. It is seldom, if ever, that these measures will halt the progression of the disease, but a fair number of patients could get by without surgery for an extended period of time.


“Conservative” surgery consists of removal of bone spurs and osteophytes from the midfoot joints. It will improve comfort in shoes, but it is questionable whether it gives good long-term pain relief. Temporary relief can be fairly reliably obtained with intermittent fluoroscopic- or ultrasound-guided cortisone injections. Intermittent injections could be a valuable alternative to surgery, especially in cases where surgery is contraindicated because of medical issues.


Arthrodesis is still the most valuable treatment option in reconstructive surgery of the foot, enabling the surgeon to create a foot that is stable, plantigrade, and relatively painfree. It is used most often to correct a painful joint secondary to arthrosis, whether it is posttraumatic, primary, or rheumatoid-related arthritis. Chronic instability of the foot and ankle from muscle dysfunction (e.g., posterior tibial tendon, poliomyelitis), or a deformity that has resulted in a nonplantigrade foot, can also be improved with selective fusions.


Arthrodesis can greatly enhance a patient’s functional capacity, and there is no evidence in the literature that midfoot fusions will cause adjacent joint stress and subsequent arthrosis.


Hindfoot fusions place increased stress on the joints proximal and distal to the fusion site. After an ankle or triple arthrodesis, approximately 30% of patients demonstrate arthroses distal or proximal to the fusion site within 5 years. Although most of these findings are radiographic, their presence at 5 years raise concerns about what will happen at these joints 20 to 30 years in the future.


Many factors probably affect the onset of this arthrosis besides the increased stress. One factor is probably related to the overall stiffness or laxity of the surrounding joints. The stiffer the surrounding joints, the less the patient is able to dissipate the increased stress created by the 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 tissue damage at the time of the initial injury that makes them more vulnerable to develop arthrosis when subjected to increased stress.


Although this chapter discusses arthrodesis of the joints of the foot and ankle, the clinician should always remember that, if possible, arthrodesis should be avoided, particularly in patients younger than 50 years. This is more important in the hindfoot than the forefoot. There is little evidence that midfoot fusion results in accelerated surrounding joint arthritis. In the hindfoot, especially for posterior tibial tendon disorders, an osteotomy or a tendon transfer can be used to create a plantigrade foot without resorting to an arthrodesis. If the surgeon can offer the patient 5 to 10 years of improved quality of life from a reconstructive procedure without using an arthrodesis, this is the desired approach.



Technical Considerations


The two basic types of arthrodeses are an in situ fusion and one that corrects a deformity. In an in situ fusion, positioning the foot or ankle is usually not difficult because no deformity is present. In a deformity-correcting fusion, however, the surgeon must decide the precise alignment that must be obtained to produce a plantigrade foot. To determine the alignment, the surgeon first must evaluate the normal extremity. With the patient in a supine position, the patella is aligned to the ceiling, giving the surgeon a reference point from which all measurements are made. The degree of internal or external rotation, varus or valgus, and abduction or adduction is carefully noted. A particular arthrodesis is not always placed into a standard alignment; rather, it must be individualized for each patient. Using the patella as a reference point makes alignment at surgery much easier and more precise.


When evaluating the patient for an arthrodesis, the surgeon should also examine the surrounding joints as well as the limb alignment. A hindfoot arthrodesis places more stress on the surrounding joints and could accelerate degenerative changes of these joints. The most common example is acceleration of ankle arthritis after a subtalar or triple arthrodesis. This is especially true if there is valgus or varus tilt of the talus in the ankle mortise before fusion. The surgeon should consider the options and might even slightly overcorrect the fusion to unload the compromised side of the ankle joint. It is important to inform the patient who is about to undergo an arthrodesis that the surgery should render the specific joint painfree, but it might result in arthritis and pain elsewhere in the foot because of increased stress. In some cases, when multiple joints are involved, it may be more desirable to treat the patient conservatively with an orthotic device, such as an ankle–foot orthosis (AFO), rather than carry out an arthrodesis.


The surgeon should also consider correcting severe limb alignment before a hindfoot fusion. 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. It is therefore critical to establish the proper alignment of the fusion site. To do this, the surgeon must consider the entire lower extremity and not just the foot. 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. The alignment of the extremity distal to the fusion site is also important to be sure a plantigrade foot is created.


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 must be aligned into 5 degrees of valgus, after which the talonavicular joint is aligned while taking into account abduction or adduction of the transverse tarsal joint as well as correcting any forefoot varus that might be present. This complex alignment creates a technically challenging situation for the surgeon. If the joints surrounding the talonavicular joint are not properly aligned, a plantigrade foot will not be created.


When arthrodesing the midtarsal or tarsometatarsal joints, the surgeon should always try to match the abnormal foot to the normal foot by carefully evaluating the weight-bearing posture of both feet preoperatively. The most common deformity is abduction with varying degrees of dorsiflexion. Any malalignment needs to be corrected. Once the first metatarsocuneiform joint is stabilized, the other joints need to be aligned, both in the transverse and in the dorsoplantar direction. This will align the metatarsal heads and prevent one head from being too prominent, which can result in an intractable plantar keratosis.



Soft Tissue Considerations


The soft tissue envelope of the foot and ankle often contains little or no fatty tissue. At times, this lack of soft tissue padding has been further compromised by previous surgery or trauma to the soft tissues, resulting in adherence of the soft tissue to the underlying bone. The surgical approach should be as precise as possible to avoid placing undue tension on the skin edges. If significant realignment is to be achieved, it must not be at the expense of proper wound approximation. This occasionally occurs when attempting to correct a valgus deformity of the heel in which an opening lateral-wedge osteotomy results in increased tension on the lateral skin edges, which makes closure difficult. Skin flaps should be made as full thickness as possible to diminish the possibility of a skin slough. Creating an incision down to the bone, then retracting on the deep structures and not the skin edge, is probably the best way to avoid a skin problem.


When making an incision, the surgeon must always 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 to always 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.


Another unique problem after foot surgery is the impact of footwear, which can rub against a subcutaneous neuroma, further aggravating the problem.


If a nerve is inadvertently transected 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 so that it will not 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 must be made aware of the potential for nerve injury and the area where they can experience numbness.



Surgical Principles


When carrying out an arthrodesis of the foot and ankle, the following surgical principles should be carefully observed:



After exposure of the fusion site, the soft tissues surrounding the joints are removed. This mobilizes the joints, allowing the surgeon to realign the foot. It is most often difficult to initially visualize the joints because of dense scar tissue overgrowth and/or dorsal osteophyte formation. It is helpful to use a ronguer or osteotomes to remove the tissue and bone covering the joints.


At times, because of previous trauma or severe malalignment, mobilization of the joints is not possible, and bone resection needs to be carried out. However, alignment is possible in the majority of cases, even when a significant deformity is present, by complete mobilization of the involved joints, followed by manipulation to create a plantigrade foot.


Once the joints have been mobilized and it is determined that bone does not need to be removed, the articular surfaces are meticulously debrided of their articular cartilage and any fibrous tissue to subchondral bone. This is achieved with a curette or a small, sharp osteotome. A lamina spreader or a towel clip can facilitate distraction of the articular surfaces, making the debridement easier, but this can damage the bone if it is soft.


Once the subchondral bone is exposed, the foot is once again manipulated, placing it into the desired alignment. If this is achievable, internal fixation can be inserted. If large amounts of bone need to be removed to create a plantigrade foot, this should be done before removing the articular cartilage. The subchondral surfaces are heavily feathered or scaled with a 4- or 6-mm osteotome, which creates a broader, bleeding cancellous surface required for successful fusion. The articular surfaces to be arthrodesed are brought together and stabilized with provisional fixation. Several 0.62-mm Kirschner wires (K-wires) will help keep the reduction before fixation. It is also advisable to confirm reduction in all planes with fluoroscopy before definitive hardware placement. Then interfragmentary compression is achieved using appropriate definitive fixation.


By carrying out a fusion in this manner, broad bleeding surfaces of cancellous bone are brought together, which provides the best possible chance for a successful arthrodesis.


Bone graft from the iliac crest is rarely necessary when carrying out a foot or ankle arthrodesis. Sometimes bone has been lost, making a bone graft necessary, but in an in situ fusion, grafting is not usually required. If a small amount of bone is needed, it can be harvested from the calcaneus, medial malleolus, or proximal medial tibia without violating the iliac crest and causing its attendant morbidity. Likewise, bone substitutes or other materials are rarely required if the bone preparation is carried out correctly.


For internal fixation, the author prefers an interfragmentary screw that compresses the joint surfaces. With good bone quality and well-apposed bone surfaces screws or compression, staples will suffice. However, in a situation with poor bone quality or correction of severe deformities, there are several excellent midfoot plating systems available.


Although an external fixator can provide excellent fixation, if possible, a closed system without an external fixator is safer because of possible pin-tract problems with prolonged immobilization. Because of soft bone or soft tissue problems, however, it may become necessary to use an external fixator. Under these circumstances, this device provides excellent rigid fixation.


The skin closure after a fusion is very critical. The surgeon should always attempt, if possible, to obtain a soft tissue cover underneath the skin flaps, such as fat or muscle. This is important because if a superficial wound slough occurs, it will be over an underlying bed of soft tissue rather than bone. 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 should be used. A drain is useful if profuse bleeding is anticipated.


The initial postoperative dressing is very important and should support the soft tissues as well as the arthrodesis site. A heavy cotton gauze roll provides uniform compression about the extremity, supported by plaster splints. A circumferential cast should be avoided during the immediate postoperative period because it can result in undue pressure against the expanding extremity, increasing pain and possibly jeopardizing healing of the wound edges. The postoperative dressing is used for approximately 10 to 14 days before removing the sutures. The cast splint should be applied with the foot and ankle in a neutral position, and the ankle should be kept in that position while the cast 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 wound issues.


A popliteal block is 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. It is much easier to prevent postoperative pain than play catch-up after the pain cycle has been established. If there are reasons not to do a popliteal block, an ankle block could give fairly similar pain relief, as long as all the nerves are included (deep and superficial peroneal, tibialis, sural, and saphaneous).



Complications


The main complications after an attempted arthrodesis include infection, skin slough, nerve disruption or entrapment, nonunion, and malalignment.


The possibility of infection is always a postsurgical concern. During surgery, antibiotic irrigation as well as parenteral antibiotics can help minimize this complication. Good surgical technique with careful handling of the tissues, removal of devitalized tissue, and prevention of hematoma formation also play an important role in minimizing the possibility of infection. If an infection occurs, it is important to recognize and treat it promptly with appropriate antibiotics.


A skin slough around the foot and ankle can present a difficult management problem 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, using postoperative drainage when appropriate, and applying a firm compression dressing postoperatively. Placing a patient into a cast without adequate padding is not advisable. When a skin slough occurs, it is important to treat it vigorously with local debridement and application of wet-to-dry dressings to promote granulation tissue, followed by coverage with a split-thickness skin graft. Vacuum-assisted closure (wound-VAC) can be extremely useful to manage a wound slough. If the slough is too large, a plastic surgeon should be consulted (Fig. 20-1).



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


A nonunion of an attempted fusion site is always an unfortunate event. As a general rule, of the joints around the foot and ankle, the talonavicular probably has the highest incidence of nonunion. Its curved surfaces make adequate exposure difficult, and preparation of the joint surfaces may be inadequate. Even when the bone surfaces have been adequately prepared, nonunion can occur if internal fixation is inadequate. In the author’s experience, more hardware is better, and thus a combination of screws, staples, and plates is recommended for the talonavicular joint.


The vascularity of the bone plays an important role in the development of a nonunion. Avascular necrosis of the talus from any cause creates a situation that is very difficult to manage. When avascular bone is present, it is often not possible to obtain a fusion to the dysvascular bone, and an attempt must be made either to bypass the avascular area or to determine the portions of the talus that still have adequate vascularity and attempt a fusion using these areas. The most common area of avascular necrosis in the midfoot is the navicular. The navicular can develop evidence of avascular changes either spontaneously (Kohlers or Mueller-Weiss syndrome) or secondary to previous injury. When this problem is encountered, the involved area needs to be resected and bone grafted. When dealing with dysvascular bone preoperatively, it is important to identify the areas of potential problems and create a surgical plan that will help solve the problem. Recognizing a dysvascular problem also helps to predict the outcome for the patient. Most often, the lateral half of the navicular is avascular, whereas the medial half still has good healthy bone. The medial healthy bone should be included in the fusion while bone graft is placed lateral between the talus and cuneiforms.


Occasionally, an asymptomatic nonunion occurs and 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 site needs to be considered. If the overall alignment of the nonunion is satisfactory, bone grafting by inlaying bone across the nonunion site often results in a fusion if internal fixation is adequate. At other times, if the nonunion site 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 inserting rigid fixation, usually with a plate-and-screw construct.


Malalignment after a fusion is a problem that usually can be avoided by meticulous bone preparation and rigid internal fixation. Malalignment after a triple arthrodesis is seen most often. The usual malalignment after a triple arthrodesis is varus of the heel and adduction or supination (or both) of the forefoot. This requires the patient to walk on the lateral aspect of the foot, causing patient dissatisfaction. When a fusion of the hindfoot is performed, it is important to evaluate the entire lower extremity preoperatively and intraoperatively to reduce the risk of malalignment. After carefully observing the normal extremity, the surgeon should always relate the foot alignment to the patella. Once the joint surfaces have been prepared and provisionally stabilized, the alignment should again be checked to be sure it is correct. Malalignment can only be prevented by careful observation of the extremity at surgery.



Specific Arthrodeses


Much has been written about arthrodesis of the foot and ankle. Many surgical approaches, site preparations, and types of internal and external fixation have been proposed. This section presents the techniques and principles the author’s group uses and believes can achieve satisfactory outcomes with careful adherence to technique. Other techniques may be equally effective, but reproducibly good results have been achieved with subtalar arthrodesis, talonavicular arthrodesis, double arthrodesis, triple arthrodesis, naviculocuneiform arthrodesis, and tarsometatarsal arthrodesis.





Subtalar Arthrodesis (Fig. 20-2A and Video Clips 26 and 27image)

An isolated subtalar joint arthrodesis is the workhorse procedure of the hindfoot and results in satisfactory correction of deformity and relief of pain that enables the patient to regain the ability to perform most activities. Of the hindfoot fusions, the patient’s ability to achieve a high level of function is greatest after a subtalar arthrodesis. It was previously believed that an isolated subtalar arthrodesis should not be carried out and that a triple arthrodesis would be the procedure of choice when a hindfoot fusion was indicated. The literature has demonstrated, however, that an isolated subtalar arthrodesis produces a superior result with less stress on the ankle joint than a triple arthrodesis.



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Figure 20-2 Subtalar joint fusion. A, Site of fusion. B, The universal lateral incision is made from the tip of the fibula and extends toward the base of the fourth metatarsal so as to place it in the interval between a branch of the superficial peroneal nerve dorsally and the sural nerve plantarly. This gives exposure to the subtalar (ST) and calcaneocuboid (C-C) joints. The alternative is a smaller curved sinus tarsi incision for exposure of the subtalar joint only. C, Exposure of subtalar joint with Weitlaner retractor. All the soft tissue is removed from the sinus tarsi and a Freer is placed in the middle facet. D, Also easy exposure of the posterior facet. E, Distraction with a lamina spreader gives excellent exposure of the subtalar joint. F, The opposing surfaces are deeply feathered. G, A lamina spreader is placed between the neck of the calcaneus and the lateral process of the talus. When distraction is applied, the talus is forced back on top of the calcaneus. H, The anterior cruciate guide is placed into the subtalar joint with the tine in posterior facet, as marked on the model. The guide is then set on the heel, after which a guide pin is placed across the subtalar joint. I, An instrument tray under the calf to allow easy access to the posterior aspect of the heel for screw placement. It also facilitates simple fluoroscopy access for a lateral view. J, Postoperative anteroposterior (AP) and mortise radiographs demonstrate subtalar fusion using two 6.5-mm screws. One screw goes through the anterior and medial aspect of the posterior facet into the neck of the talus. The second goes more posterior and lateral to increase two-point fixation and stability. The screw begins off the weight-bearing area of the heel. K-M, Preoperative, intraoperative, and postoperative radiographs demonstrate subtalar arthrodesis after calcaneal fracture. Interpositional bone graft is used to reestablish the talocalcaneal relationship. N, Wound complications are not uncommon with distraction bone blocks. The incision should be straight. The usual curved incision for a calcaneal exposure have a much higher wound complication rate because of tension on the distal limb after distraction. O, When lateral subluxation of the subtalar joint is present, the joint must be reduced and not fused in situ. Note the calcaneus is dislocated with subfibular impingement. P and Q, Lateral and AP radiographs showing correction of the calcaneal dislocation with a combination of a subtalar bone block fusion and calcaneocuboid fusion. R, Preoperative radiograph demonstrating subtalar and talonavicular arthrosis in a patient with prior ankle fusion. Screw placement for the subtalar fusion is relatively simple because it can extend across the ankle joint.


The position of the subtalar joint determines the flexibility of the transverse tarsal (talonavicular–calcaneocuboid) joint, and therefore it is imperative that a subtalar arthrodesis be positioned in about 5 degrees of valgus to permit mobility of the transverse tarsal joint. If it is placed in varus, the transverse tarsal joint is locked, and the patient tends to walk on the lateral side of the foot. 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 cannot compensate for this deformity and walks 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 naviculocuneiform and/or cuneiform–first metatarsal fusion.



Indications

The most common indication for a subtalar arthrodesis is arthrosis secondary to trauma, usually a calcaneal fracture, rheumatoid arthritis, primary arthrosis, or talocalcaneal coalition that cannot be resected. It is also indicated for a muscle imbalance (e.g., loss of peroneal muscle function) or 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. A subtalar arthrodesis is indicated in patients with a neuromuscular disorder, such as Charcot-Marie-Tooth disease, poliomyelitis, or nerve injury with instability of the subtalar joint.


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




Surgical Technique



1. The patient is placed in the supine position with a support under the ipsilateral hip to facilitate exposure of the subtalar joint.


2. A thigh tourniquet is applied.


3. The skin incision begins at the tip of the fibula and is carried distally toward the base of the fourth metatarsal. When an isolated subtalar arthrodesis is carried out, the incision usually stops at about the level of the calcaneocuboid joint (Fig. 20-2B).


4. While deepening the incision, the surgeon should be cautious, because the anterior branch of the sural nerve may be crossing the operative site plantarly and the superficial peroneal nerve dorsally.


5. The incision passes along the dorsal aspect of the peroneal tendon sheath and distally along the floor of the sinus tarsi.


6. The extensor digitorum brevis muscle origin is detached and the muscle belly reflected distally, exposing the underlying sinus tarsi, subtalar joint, and calcaneocuboid joint (Fig. 20-2C). The fat pad is dissected out of the sinus tarsi and reflected dorsally. The only way to visualize the middle and anterior facets of the subtalar joint is to remove all the soft tissue from the sinus tarsi. Using a curet will facilitate that.


7. A small elevator is passed along the lateral side of the posterior facet of the subtalar joint. It is not necessary to strip the peroneal tendons off the lateral side of the calcaneus unless a lateral impingement from a previous calcaneal fracture requires decompressing.


8. A lamina spreader is inserted into the sinus tarsi to visualize the posterior facet of the subtalar joint (Fig. 20-2D and E). When looking across the sinus tarsi, the surgeon can see the middle facet of the subtalar joint. If the surgery is being carried out for severe arthrosis or a talocalcaneal coalition, it is often not possible to open the subtalar joint very far. Under these circumstances, a small curet is used to remove the cartilage from the posterior facet. A thin, wide elevator then can be inserted into the joint to pry it open, after which a lamina spreader is inserted.


9. Power osteotomes are ideal to start the preparation of the posterior facet. Articular cartilage can be removed in large strips and subcondral bone exposed. Regular sharp image– or image-inch osteotomes could do the same.


10. For safety, a curet of appropriate size is used to remove the cartilage posterior and posteromedial and from the middle and anterior facets. This reduces the possibility of damaging the flexor hallucis longus tendon in the posterior aspect of the joint or the neurovascular bundle along the posteromedial aspect of the joint. When removing the articular cartilage from the middle facet, it is important not to inadvertently go too far distally and damage the cartilage on the plantar aspect of the head of the talus, which lies just in front of it.


11. Once all the articular cartilage has been removed, the lamina spreader is removed and the alignment of the subtalar joint observed. If no deformity is present, the surgeon may proceed with feathering or scaling the articular surfaces (Fig 20-2F). 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.


12. 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 by and large a rotational deformity. There is peritalar subluxation with the navicular subluxing lateral and dorsal, while the calcaneus rotates lateral and posterior, creating a hindfoot valgus. This is corrected by placing a lamina spreader in the sinus tarsi between the lateral process of the talus and the anterior process of the calcaneus. Spreading this space open facilitates reduction around the peritalar joint. There should be caution not to overdistract because this will force the hindfoot in varus (Fig. 20-2G).


13. If a previous calcaneal fracture is present in which the lateral wall needs to be decompressed, 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. Sometimes, up to 7 to 10 mm of bone needs to be resected in severe cases. This bone could be morcelized and packed into the sinus tarsi.


14. The posterior and middle facets, along with the bone in the base of the sinus tarsi, are heavily scaled. The dense bone in the floor of the sinus tarsi is deeply scaled and is mobilized so that it can be packed into the tarsal canal after the internal fixation has been inserted. The bone along the lateral aspect of the calcaneus that forms the anterior process may be mobilized to within about 0.5 cm of the calcaneocuboid joint and used for bone graft. When a lateral decompression has been carried out, even more bone is available to the surgeon. Rarely is bone harvested from the iliac crest.


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


16. If the calcaneus is severely collapsed, height can be restored with a bone block inserted from posterior (Fig. 20-2K-M). In this case, the incision runs along the Achilles tendon and does not curve around the plantar aspect of the foot to avoid wound problems (Fig. 20-2N).


17. The surgeon should be careful not to put too large a block in the subtalar joint. Also be careful not to force the hindfoot into varus. The larger side of the block should always go medial to create a valgus alignment.



Internal Fixation

Internal fixation is carried out with large-diameter (6.5, 7.0, or 7.3 mm) cannulated or noncannulated screws to obtain maximum interfragmentary compression. A washer is used if the bone is soft and the head is sucked into the calcaneus.


Screw patterns used for fixation of the subtalar joint include placing the screw from the neck of the talus into the calcaneus, placing a screw from the calcaneus into the talus, and placing two screws between the calcaneus and the talus. The author prefers two screws, starting off the weight-bearing surface posterior on the calcaneus, one screw aiming a bit medial into the neck of the talus while the second screw goes across the posterior facet more lateral. This results in a rigid internal fixation with maximum purchase and interfragmentary compression across the joint. In some cases, a single screw will suffice.



18. The preferred method for stabilization is to place the screw from the heel across the subtalar joint and into the neck of the talus. Screw placement is carried out by placing an aiming guide with the sharp tine in the anterior aspect of the posterior facet of the subtalar joint (Fig. 20-2H).2 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 the screw does not penetrate the sinus tarsi area. This placement provides maximum purchase in the talar neck from the screw. If a fully threaded screw is used, the calcaneus should be overdrilled to create a gliding hole. A guide pin is drilled into the calcaneus until it is visible in the posterior facet of the subtalar joint. If placement is satisfactory, the guide is removed; if not, another attempt is made to place the guide pin correctly (Fig. 20-2I).


19. The subtalar joint is placed into 5 degrees of valgus while also correcting any peritalar rotation/subluxation, and the guide pin 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.


20. With the pin properly placed, a 2- to 3-cm transverse incision is made over the entrance of the guide pin 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 pin to accommodate the washer. A depth gauge is used to determine the length of the screw.


21. The guide pin is advanced through the talar neck, appears on the dorsal aspect of the ankle, and is secured with a clamp. This is important so that when the holes are drilled, the guide pin cannot come out, which can result in loss of alignment. If 7.0-mm cannulated screws are used, the initial hole is drilled with a 4.5-mm bit, just penetrating the neck of the talus. A 7.0-mm drill bit is used to overdrill only the calcaneus, creating the glide hole. The hole in the talar neck is tapped, and a fully threaded, 7.0-mm cannulated screw of appropriate length is inserted. By overdrilling the calcaneus, intrafragmentary compression at the arthrodesis site is achieved. Every screw system will have a smaller and larger drill to achieve the gliding and compression holes. With a fully threaded screw, the maximum number of threads is placed in the neck of the talus, maximizing the compression. In placing the screw, the surgeon should not have more than 2 to 3 mm of screw exposed on the neck of the talus. The position of the screw is verified with fluoroscopy.


22. If a second screw is placed, a parallel guide could be used to place the screw more lateral and posterior to the first. Fluoroscopic guidance is valuable to confirm placement and also to prevent violating the ankle joint with the drill or screw (Fig. 20-2J).


23. The guide pin is removed, and the small bone fragments that have been mobilized are packed into the tarsal canal and the sinus tarsi area. It is not necessary to fill up the sinus tarsi completely when carrying out an isolated subtalar joint fusion. If more bone is needed, it can be obtained from the calcaneus or medial malleolus by using a trephine.




Arthroscopic Subtalar Fusion

There is significant interest lately in doing the subtalar fusion arthroscopically. Several recent papers with further information on the topic are listed.5,8 The theoretic advantages of an arthroscopic fusion are a more cosmetic approach and fewer wound complications.1,7 In experienced hands, the results appear to be comparable to open fusions, but there are several pitfalls as well. There is a higher risk of nerve a vascular injury, and there is a very steep learning curve. There are few surgeons at present who are well enough versed in complex hindfoot arthroscopy to make this a viable mainstream alternative. That situation could theoretically change in future but is unlikely.




Complications

The two most common complications are nonunions and varus malalignment. Nonunion of the subtalar joint occurs in 15% of cases, with a range of 1% to 45% in the reported literature. The rates of nonunion have been reported to be higher for patients with risk factors such as smoking, after high-energy injury, avascular necrosis, and diabetes. A nonunion should be repaired with bone grafting and further internal fixation.


Malalignment of the subtalar joint in too much varus results in locking of the transverse tarsal joint and increased weight bearing on the lateral side of the foot. To accommodate this, the patient often walks with the extremity in external rotation.


If the subtalar joint is placed into excessive valgus, it can impinge against the fibula, causing pain over the peroneal tendons. It can also place increased stress along the medial aspect of the ankle joint and pronation of the foot. Orthotics do not work well because the transverse tarsal joint stays locked. These are difficult to revise, and a takedown and redo of the fusion is necessary.


Sural nerve entrapment or laceration can occur and may be bothersome to the patient. Unfortunately, the anterior branch of the sural nerve can pass next to the incision, making this complication almost unavoidable, but an attempt should be made to identify it and retract it if possible. If the neuroma is too bothersome, it requires resection to a more proximal level.



Author’s Experience

There are ongoing issues in getting subtalar fusions to heal. The reported nonunion rate varies from 5% to 45%. In the largest study in the literature, by Myerson and coworkers, the union rate was 84% (154 of 184) overall, 86% (134 of 156) after primary arthrodesis, and 71% (20 of 28) after revision arthrodesis.4


Coughlin et al3 did a study comparing standard radiographs to computed tomography (CT) scan in evaluating subtalar fusions. The mean observed fusion of the posterior facet of the subtalar joint ranged from 41% at 6 weeks to 61% at 12 weeks and to 86% at 6 months on the radiographs; the mean fusion of the posterior facet on the CT scans ranged from 23% to 48% to 64% at the same time intervals. The agreement between the two methods was poor. The clinical results based on the American Orthopaedic Foot and Ankle Society (AOFAS) score, visual analog score (VAS), and Short Form-12 (SF-12) score were compared with the percentage of joints fused on the CT scans. Coughlin et al3 believe the progress of the fusion cannot be determined accurately from standard radiographs. CT scanning appears to be significantly more reliable. The concept of what constitutes an adequate fusion deserves more extensive study, but it appears that fusion of more than 40% of the surface is adequate.


Mann et al6 showed that, functionally, the patients did well, although half observed problems walking on uneven ground and climbing steps and inclines. 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). This is a much higher level of activity compared with patients who have undergone a triple arthrodesis.


The physical examination demonstrated that the alignment averaged 5.7 degrees of valgus, and the one patient with fusion in varus was dissatisfied. The range of motion demonstrated an average of 9.8 degrees of dorsiflexion compared with 14.2 degrees on the uninvolved side, for a 30% loss of motion, and plantar flexion averaged 47.2 degrees compared with 52.4 degrees, for a 9.2% loss of motion. This resulted in a 14% loss of sagittal plane motion. The transverse tarsal joint motion demonstrated 60% loss of abduction and adduction compared with the uninvolved side.6


Patients undergoing a subtalar arthrodesis for talocalcaneal coalition generally do very well. Talonavicular arthrosis is a rare occurrence. A triple arthrodesis is not necessary to obtain a satisfactory result, even in the presence of beaking of the talonavicular joint.



Special Considerations

Occasionally, in the patient with rheumatoid arthritis, severe subluxation occurs at the subtalar joint. It is imperative that the clinician recognizes this problem so that when a subtalar arthrodesis is carried out, the calcaneus is repositioned under the talus, restoring the normal weight-bearing alignment. Similar severe deformity is seen with a small subset of calcaneal fractures, where the tuberosity dislocates laterally and sits under the fibula. In chronic malunion/nonunion situations, the reduction could be difficult. If the surgeon fails to recognize this malalignment and places a bone block into the lateral side of the subtalar joint, wedging it open will not reposition the calcaneus into correct anatomic alignment (Fig. 20-2O-Q).


Infrequently, a subtalar fusion is required after a previous ankle fusion. It is most common after a previous talus fracture, but it could also be due to excess stress after an ankle arthrodesis. In this situation, the author’s group carries out its standard type of fusion. The screw placement is a little simpler because there is no concern about penetrating the ankle joint with the screw (Fig. 20-2R). Two screws are routinely used. The subtalar joint takes longer to heal, and there is a higher nonunion rate.

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Aug 26, 2016 | Posted by in ORTHOPEDIC | Comments Off on Treatment of Hindfoot and Midfoot Arthritis

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