The hindfoot is essentially defined as the talus and calcaneus.1 There is, however, a significant contribution from the Chopart complex that articulates with the hindfoot. Functionally, the talonavicular and calcaneocuboid joint are part of the peritalar complex, and as such, the navicular and to a lesser degree the cuboid form part of hindfoot function and may be included in any discussion of the hindfoot.
The subtalar joint is described as the most indispensable joint in the hindfoot in the first chapter of Prof Sigvard T. Hansen's2 book. It enables the hindfoot to perform inversion and eversion and conform to changes in surface inclination. Three planes of subtalar movement may be observed.3 Inversion and eversion occurs in the coronal plane, abduction and adduction in the transverse plane, and sagittal dorsiflexion and plantarflexion is observed. In association with the talonavicular joint, the complex shape of the joint allows the foot to invert with anterior translation and evert while moving posterolaterally. This supports the foot at heel strike cushioning ground reaction forces. It locks to form a rigid medial column for propulsion during gait. This complex relationship may also contribute to surgeons' lack of understanding and impair efforts to realign it after trauma. Restored gait may be achieved without significant contribution from tarsometatarsal and calcaneocuboid joint. Getting the position of the hindfoot correct at heel strike is a large part of hindfoot salvage.
The concept of “essential” joints in the hindfoot is described by Hansen2 in the chapter on functional anatomy of his book. It identifies the subtalar and talonavicular joints as prerequisite for normal hindfoot mobility, gait, and stability along with the ankle joint. Nonessential joints (calcaneocuboid) are not a prerequisite for normal foot function.
THE ANATOMY OF THE SUBTALAR JOINT
The subtalar joint consists of 4 bones forming 3 separate parts forming 2 functional joint complexes.4 These are the talocalcaneal (TC) and talocalcaneonavicular (TCN) joints that form a foot plate and the Chopart joint formed by the talonavicular (TN) and calcaneocuboid joints (CC). Therefore, a 4 bone osseous structure constrained by ligaments that attach to either the talus or calcaneus is formed.
BIOMECHANICS OF THE SUBTALAR JOINT
The subtalar joint may be considered as 2 functional units enclosed by separate synovial sheaths.3 These are formed by the posterior and medial talocalcaneal facets in one unit and the anterior talocalcaneal facet, talonavicular articulation, and the articular cartilage of the spring ligament from the second unit. A peritalar joint complex exists as the talus is the central structure around which these joints contribute to the overall triplanar movement.
Motion at the peritalar joint complex is therefore constrained by a highly congruent articulation and forming an axis described by Inman and Isman5 as 42 deg upward in the sagittal plane of a plantigrade foot, 23 degrees internally rotated in the transverse plane. Work conducted in Basel has attempted to describe subtalar alignment in the frontal plane. A large variation in the varus/valgus angle has been described between individuals based on the method of measurement.6 The close-packed or locked position of the subtalar joint, with a narrow talocalcaneal angle, allows for forward propulsion on a rigid foot. This would occur in inversion, adduction, and plantarflexion at the end of the stance phase. The lever arm of the gastrocnemius–soleus complex depends on the shape of the calcaneus with implications for the management of fractures and subtalar arthritis.
A change in the contact area may occur with altered congruency, joint surface irregularities, and alignment of the subtalar joint. Sangeorzan et al7 described a point loading of the posterior facet and unloading of the anteromedial facet in talar neck fractures displaced greater than 2 mm. Considering calcaneal fractures, Sangeorzan8 described a similar finding of point contact pressures in the posterior calcaneal facet where the joint irregularity was greater than 2 mm.
PATHOLOGY OF THE SUBTALAR JOINT
The clinical and radiographical presentation of hindfoot valgus is contributed to by the bony and ligamentous structures of the medial column. In the adult, posterior tibial tendon insufficiency is associated with adult onset pes planovalgus,9 although whether this is the cause or effect is unknown. The advent of weightbearing computed tomography scanning allowed Apostle et al10 to conclude that subtalar valgus formed a significant etiological factor for the development of the adult planovalgus foot. A large force vector created by the coronal plane valgus alone may be calculated as a valgus torque of increasing magnitude as the deformity increases, leading to attenuation of medial soft tissue structures, as described by Sangeorzan.4
The cavovarus foot may be driven by a pronounced medial longitudinal arch and rigid hindfoot with a net varus talocalcaneal axis. The torque moments at the subtalar joint would prevent the joint from returning to neutral or valgus alignment, causing impingement between the lateral margin of the navicular and the anterior process of cuboid.4 The extreme form of this deformity is called plantar medial peritalar subluxation, resulting in depression of the first metatarsal and accentuation of the medial longitudinal arch. Radiologically, the dorsal talocalcaneal angle is significantly narrowed functionally forming a locked subtalar joint and a rigid cavus foot. Hansen2 places great emphasis on the rotational deformity of the talus.
TRAUMA AFFECTING THE SUBTALAR JOINT
Talar fractures involve the peritalar complex by dislocations or fracture dislocations of the peritalar complex. Partial collapse of the talus can also contribute to hindfoot deformity. Individual tarsal bones, such as talar body and neck fractures, and calcaneal fractures can involve the subtalar joint and may be displaced sufficiently to significantly raise the risk of post-traumatic arthrosis. The incidence of subtalar fusion after calcaneal fractures varies between 3% and 32% as quoted by Rammelt11 and is indicated in highly comminuted calcaneal fractures.12 Articular fractures of the talus and calcaneus are associated with up to 100% occurrence of subtalar arthritis. Drawing from anatomical and biomechanical understanding of the natural history of articular fractures, an anatomical reduction means no step or a step of less than 2 mm.8,9 To achieve this, a closed reduction may only be effective in pure subtalar dislocations that are anatomically reduced. Despite this, a 39% rate of subtalar arthritis with subtalar dislocations is a high figure to consider.
The anatomical reduction of displaced articular calcaneal fractures reduces the sequela of subtalar arthritis.3 In 2004, Bernischke et al13 retrospectively reviewed 10 years of calcaneal operative reduction and fixation. This allowed the understanding of the natural history of articular calcaneal fractures to be understood along with likely complications, which were described later.14 Certain articles15–18 described variable benefit attributed to the operative fixation of calcaneal fractures. Analysis of data on the accuracy of reduction before internal fixation suggested that articular incongruence of greater than 2 mm was present and acceptable in the studies analysed.19,20 Primary anatomical reduction and stable fixation with an effective postoperative management regime are essential factors that determine the outcome. Primary arthrodesis for severely comminuted calcaneal fractures is an accepted intervention. This has advantages in that malunion results in calcaneal deformities that add surgical complexity to obtaining a well-aligned subtalar arthrodesis as salvage. The issues relate to loss of heel height, widening of the heel, and coronal plane malalignment, which will affect peritalar articulations leading to early arthrosis. The goals of salvage are to treat subtalar arthritis with an arthrodesis, correct heel alignment such that the weightbearing axis and the calcaneal tuberosity alignment are restored, and return normal plantar alignment of the talus.21 A subtalar bone block may be used to correct height and alignment22 and a sliding osteotomy of the calcaneus to correct varus or valgus. Ostectomy of a prominent calcaneal lateral wall extrusion would narrow the heel. Salvage may be achieved through a subtalar arthrodesis with bone graft. Thus, recommendations made by Hansen (2000) remain current and are echoed by other authorities in foot and ankle trauma.
Navicular fractures may be due to acute trauma or due to repetitive loading (stress fractures). Inclusion of navicular fractures while essentially a midfoot bone is due to the talonavicular articulation forming part of the peritalar complex. Sangeorzan (1989)23 described 3 types of fracture with increasing severity based on the fracture pattern and displacement of the forefoot.
Regardless of the fracture type, anatomical reduction and fixation is paramount. The likely alteration in talonavicular alignment would adversely affect hindfoot alignment and mobility, thus resulting in progressive arthritis from shortening of the medial column and progression to a rigid cavus foot.
The subtalar and talonavicular joints are Hansen's essential joints of the foot which allow normal foot inversion/eversion, abduction/adduction, and dorsiflexion/plantar flexion.4 The talonavicular joint provides 60%–80% of constraint to the subtalar joint and the subtalar joint between 40% and 88% constraint to hindfoot motion. The calcaneocuboid joint and the nonessential joints are smaller contributors of hindfoot motion.24 A vertical talus produces hindfoot valgus with lengthening of the medial column resulting in a pronated foot flat. The opposite of this would be, a horizontal talus with loss of medial column length varising the hindfoot and presents with a cavovarus deformity.
Post-traumatic arthritis affecting the subtalar joint is associated with talar alignment in displaced intra-articular calcaneal fractures. As joint degeneration progresses, the talus rotates medially and plantarflexes. The calcaneus rotates laterally (increasing the dorsal talocalcaneal angle) while plantarflexing relative to the talus causing the cuboid to move under the navicular. The resultant planovalgus foot and decreased lateral talocalcaneal angle are apparent clinically and radiologically. Salvage of calcaneal fractures that have developed post-traumatic arthritis requires derotation of the talus laterally, restitution of Meary's angle, and relative lengthening of the lateral column. This may be achieved with a triple arthrodesis with a cortico-cancellous graft at the calcaneocuboid joint.
Fractures of the talar neck and navicular shorten the medial column resulting in a varus hindfoot with a supinated midfoot. The resultant post-traumatic arthritis of the talonavicular and/or the subtalar joint aim requires restoration of medial column length and physiological hindfoot valgus. This may be achieved by correcting the talocalcaneal angle in both planes at the subtalar and talonavicular joints and performing arthrodesis for stability.
Two radiologic grading systems exist for the assessment of subtalar osteoarthritis.25 Both have been found to be reliable methods of describing subtalar arthritis in this study. However, they may not be the best guide to treatment. Clinical assessment and its correlation with osteoarthritis and malalignment may be more effective guides to treatment.
Hindfoot arthrodesis is indicated for pain and deformity affecting the hindfoot joints and should be used judiciously for pain relief and the correction of deformity.26 Arthrodesis is appropriate when the deformity is fixed or associated with degenerative post-traumatic arthritis requiring sacrifice of an essential joint to achieve correct alignment with a stable foot.
The natural history of deformity and degeneration of the hindfoot and midfoot was described by Greisberg et al.27 A third of adult-acquired flatfoot patients had arthritis affecting the subtalar, calcaneocuboid, and talonavicular joints. In addition, the first tarsometatarsal joint and the naviculocuneiform joint subluxed inferiorly exclusive to the hindfoot joints but did not correlate with the degree of deformity. The operative management of the subtalar joint and the peritalar complex aims to achieve a pain-free, functional foot that fits in a shoe. This has guided approaches to fracture fixation, which aims to preserve the joint surfaces and the intricate function of the peritalar complex.
Multiple factors influence the outcomes of subtalar arthritis after calcaneal fracture. It is however clear that subtalar arthrodesis provides acceptable functional outcomes and quality of life.28 Much of the adverse outcomes were attributed to smoking and severity of injury preoperatively and postoperative complications such as nonunion. Advocates for osteotomies in the management of hindfoot arthritis aim to correct deformity and unload the symptomatic side of the joint.29 Arthrodesis can achieve both deformity correction and a stable joint in advanced osteoarthritis as a single procedure.
APPROACHES TO THE SUBTALAR JOINT
Sinus Tarsi Approach
The landmarks for this approach are the tip of the lateral malleolus and base of fourth metatarsal (Fig. 1). It is important to palpate, mark, and protect the superficial peroneal nerve with this approach. It allows access to both subtalar facets and the calcaneocuboid joint.
This approach has been identified as more accommodating for soft tissue without losing vision of the posterior calcaneal facet. The subtalar approach over the sinus tarsi provides sufficient exposure to view the articular surfaces of the subtalar joint and may be combined with arthroscopy to aid vision.
Hansen2 describes the medial utility approach (Fig. 2) which is midway between the tibialis posterior and tibialis anterior tendons. This approach is helpful when the sustentaculum fragment is displaced or access is required to the medial facet and tibialis posterior sheath. The main difficulty with this approach is identifying the medial joint line. Various techniques have been used to identify the medial joint line. A useful approach is one where a blunt guide wire is passed through the sinus tarsi and into the medial facet to exit subcutaneously. This provides a central point for the skin incision to be made medially. Access to the talonavicular joint is then possible by extending the incision distally.
Visualization of the articular surface may be achieved by arthroscopic inspection of the joint surfaces. In trauma where the capsule is torn, dry arthroscopy is sufficient to visualize small steps in the articular surface with a small arthroscope. In a degenerative joint, the use of arthroscopy may allow meticulous preparation of the joint surfaces by direct visualization and use of a burr. However, use of arthroscopy may not necessarily improve soft-tissue preservation compared with a mini-open approach.
THE TRIPLE ARTHRODESIS
Hansen2 described the goals of a triple arthrodesis as pain relief, deformity correction, and to obtain a stable foot with normal appearance. This is performed through a 2-incision approach (medial utility, lateral longitudinal). Fixation may be obtained through staples, compression screws, or plates. This approach has been shown to effectively achieve Hansen's goals in the valgus hindfoot.30 This has clear implications for valgus deformity with osteoarthritic hindfoot joints (Fig. 3). The principles of arthrodesis are strictly adhered to and patient compliance is clearly a limiting factor. However, despite its complexity, it provides powerful correction to hindfoot deformity (Fig. 4).
THE DOUBLE ARTHRODESIS
Sammarco31 described good radiological and clinical outcomes with a double arthrodesis involving the subtalar and talonavicular joints. This may be approached entirely from the medial side.32 The resultant double arthrodesis avoids arthrodesis and nonunion of the calcaneocuboid joint. However, its use needs to be based on adequate clinical and radiological assessment of the degenerative changes of the hindfoot. An arthritic calcaneocuboid joint may preclude the use of a double arthrodesis.
Subtalar distraction arthrodesis is indicated where a loss of heel height of greater than 8 mm, with the resultant anterior ankle impingement from superior tilting of the talus and the resultant planovalgus medial longitudinal arch.33 (Fig. 5). Espinosa and Vacas34 describe a posterior approach to the subtalar joint with an associated z-lengthening of the achilles tendon in the prone position. Sangeorzan35 advocates the use of tricortical iliac crest graft and a posterolateral approach which spares the achilles tendon and may be performed in a lateral decubitus position. A laminar spreader or femoral distractor is used to separate the joint surfaces adequately for debridement (Fig. 6). This approach corrects for deformity and achieves a stable arthrodesis (Fig. 7).
ISOLATED TALONAVICULAR ARTHRODESIS
Chen et al36 described a single surgeon series for isolated talonavicular arthritis. Good results on the AOFAS hindfoot score were obtained using a protocol of compression fixation. Intraoperative grafting was used and non-weightbearing was observed for 9 weeks.
Steiner et al37 describes a combined subtalar and naviculocuneiform arthrodesis for subtalar arthritis arising from pes planovalgus. The main benefits are preservation of the Chopart articulation and avoidance of an overly rigid hindfoot.
The term ‘Pantalar arthrodesis' is most accurately defined as fusion of all joints involving the talus. Thus a pantalar arthrodesis involves fusion of the ankle, subtalar and talonavicular joints. Often the term is used to define a tibiotalocalcaneal (TTC) arthrodesis although the talonavicular joint is spared.
The principles of fusion would require meticulous debridement to bleeding bone of opposing articular surfaces, preparation of the subchondral bone with drill fenestration, and compression and absolute stability of the construct with or without bone graft. Rammelt et al29 achieved an 84% fusion rate with a hindfoot nail technique for tibiotalocalcaneal arthrodesis (Fig. 8) with a significant improvement in function and return to work. This intervention will produce a stiff but well-aligned and pain-free hindfoot. However, adjacent joint arthritis in the midfoot is expected to develop as a consequence although it may already be present preoperatively.
Because Prof Sigvard T. Hansen published his book in 2000, the principles driving treatment were founded on the restoration of alignment and preservation of motion. The principles and observations laid out in his book provide a pathway to implementing them. The peritalar complex is now being better understood through anatomy, biomechanics, techniques, and tools at the surgeon's disposal. Studies have mainly concurred with the principles of the body of knowledge that is a legacy of his experience.
Prof Bruce J. Sangeorzan for assistance and comments.
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