Revisional Arthrodesis of the Subtalar Joint

Thomas Mittlmeier

Introduction

Subtalar joint arthrodesis (STA) may be indicated for a variety of reasons including primary osteoarthritis, degenerative changes as in advanced flatfoot deformity, or instability to posttraumatic osteoarthritis following calcaneal, talar ,or ankle fractures, which generally makes up a majority of cases.¹ ^–⁵ STA comprises different technical modifications including an in situ arthrodesis, a distraction bone-block arthrodesis, as well as open and arthroscopic approach variants employing different implant types and implant arrangements, for example, regarding numbers and preferred directions of screws to fix the arthrodesis.²^,⁴^,⁶^,⁷ Furthermore, STA may represent an isolated procedure or be part of a hindfoot or triple arthrodesis or ankle joint replacement or follow a previous adjacent joint arthrodesis, for example, an arthrodesis of the ankle joint.⁸^,⁹

There are quite a few clinical studies on the success and functional outcome following STA comprising 50 cases or more. Although some authors reported rather high union rates after STA ranging between 90 and 100%,¹⁰^,¹¹ other reports demonstrate less successful STA fusion rates ranging between 55 and 90%.⁸^,¹² ^–¹⁴ The main reason for this discrepancy may be that conventional plain film radiographs cannot definitively demonstrate complete osseous union of STA. Therefore, computed tomography (CT) is the gold standard for documenting the degree of osseous fusion, where between 33% and 66% of the subtalar joint cross section was taken as the minimum amount of proven successful osseous fusion.¹³^,¹⁵ Apart from radiographic STA nonunion, there is a wide range of reported incidence of complications from <10% to almost 50%.⁸^,¹¹ Consecutively, the functional outcome following STA assessed by the American Orthopaedic Foot and Ankle Society Hindfoot-Ankle Scoring Scale ranges from 47 to 76 points.³ Although the choice of the approach, the implant selection, and the technical variants of in situ versus distraction bone block STA play a minor role for the outcome and for definite osseous healing according to the opinion of most authors,¹^,²^,⁵^,⁸ concomitant diseases (eg, diabetes mellitus, obesity, peripheral arterial occlusive disease) of the patients and other risk factors, for example, previous ipsilateral ankle joint arthrodesis, nicotine, drugs, or alcohol abuse, were identified as relevant confounders.⁹^,¹⁴ Although there are sporadic reports where the relevance of those confounders was questioned,⁷ most authors consent to the importance of negatively interfering factors, in particular, if they combine in the same patient.⁵^,⁸^,¹⁴

The number of original studies on revisional STA (RSTA) involving 10 or more cases is even more scarce than reports about outcome after primary STA (see Table 12.1). The interpretation of the data is even made more difficult as some authors focused on the assessment of the value of stand-alone measures or adjunct measures to surgery such as low-intensity ultrasound or extracorporeal shock wave treatment.¹⁶ ^–¹⁸

Table 12.1

Outcome After Primary Subtalar Joint Arthrodesis

Author	Cases	Bone Graft	Nonunion (%)	Complications Other Than Nonunion (%)	Infection	AOFAS Score	Return-to-Work (%)
Easley et al⁸	28	+	29	n.s.	n.s.	58	n.s.
Jones et al¹⁵	10	+ +LIPUS	10	n.s.	n.s.	72.3	n.s.
Hungerer et al¹⁴	33	+	31	30	n.s.	46	8
Ziegler et al⁵	86	+	23.6	n.s.	n.s.	46	n.s.
Everding et al¹⁶	12	− +ESWT	75	0	0	n.s.	n.s.

ESWT, extracorporeal shock wave treatment; LIPUS, low-intensity ultrasound stimulation; n.s., not stated.

Summarizing, although the functional outcome appears to be comparable with the results reported on primary STA, greater than two-thirds of RSTA are successful regarding osseous healing with a considerable rate of further complications and an astonishingly low rate of return-to-work status. Correspondingly, any approach to RSTA should take into account why these redo procedures might eventually fail, again.

Indications

For RSTA indications resemble those chosen for primary STA:

Painful nonunion after an attempt for STA
Hardware complications in conjunction with failed previous STA, for example, protruding screw heads, loosened or broken implants
Infected nonunion following previous and failed STA
Painful malunion, for example, varus deformity of the hindfoot
Failed nonsurgical treatment of nonunion, for example, following low-intensity ultrasound or extracorporeal shock wave treatment application

Contraindications

Relative contraindications comprise metabolically deranged patients where an optimization of the underlying problem, for example, the reduction of excessive blood glucose levels or a balancing of preterminal renal failure, might indirectly aid in achievement of STA via restoration of at least near-normal metabolism. The same applies to any regional peripheral arterial occlusive disease where nonsurgical or surgical interventions might enhance the local macrocirculation in the hindfoot in support of uneventful osseous healing of RSTA. The detection of deep infection, in particular of low-grade infection, might not be trivial. But the latter does represent an essential risk factor for impending recurrent failure of the procedure. Absolute contraindications refer to a local status nonamenable to any improvement such as in recalcitrant deep infections of the hindfoot with advanced soft tissue and osseous defects that might only qualify for below-the-knee amputation, for example, in Charcot neuroarthropathy.

Preoperative Considerations

A scrutiny of the potential reasons of the previous failed STA represents an essential step to prevent a failure of RSTA, again. A thorough clinical examination is the key for indicating further laboratory studies or imaging techniques. A detailed view at the long-term medication of the patient appears to be essential for a predictable success of the planned revision procedure, in particular in patients where immunosuppressives or biologics are administered, as in rheumatoid arthritis or psoriasis. In this specific situation a temporary discontinuity of these long-term medications should be discussed with the rheumatologist to improve local healing. In view of the overwhelming relevance of metabolic disorders or addiction to alcohol, drugs, and/or nicotine a screening for latent diabetes or advanced renal failure appears to be essential. Even in supposedly simple and clear cases weight-bearing plain film radiographs should be supplemented by CT imaging of the hindfoot with multiplanar 2-D reformatting to display the spatial characteristics of the STA nonunion that might be beneficial for selecting the tactics during the revision. If low-grade infection is suspected, a contrast-enhanced magnetic resonance imaging (MRI) or positron emission tomography–CT might be helpful to identify this relevant problem before undertaking the revision. In contrast to the conventional indications for bone block distraction, STA bone grafting is obligatory in RSTA to support definitive osseous healing.² Therefore, the draping of the surgical field should respect the potential autologous bone graft harvesting from the ipsilateral posterior iliac crest among other sites.

Detailed Surgical Technique

The previous failed procedure and approach and any implants in situ frequently dictate the approach in the revisional situation. In case of excessive or unstable scarring an alternative approach for RSTA may be desirable. If there are only antegrade or retrograde screws to be removed via stab incisions a lateral or sinus tarsi approach may be alternated by a posterolateral or a medial approach and vice versa.¹⁹ Furthermore, it can be decided before revision if the hardware in place should be retrieved or could be left if an interference with the implants or grafts planned for revision is unlikely.² In the case of plates that require removal it is generally necessary to exploit the previous surgical approach (Figures 12.1A and 12.2A and B). The chosen approach also determines the positioning of the patient on the surgical table. Posterior approaches are preferably performed in prone positioning, which allows for a good view to the entire posterior subtalar joint. The proximal extension of the previous posterolateral approach allows for a safe identification of the sural nerve and its protection during distal preparation in scarred tissue. During deeper dissection the typical preparation of the Kager fat triangle in the intermediate layer is often impossible owing to scarring and adhesions between the corresponding layers. Before it is possible to identify the former subtalar joint level, identification of the flexor hallucis longus (FHL) muscle and tendon, which can be distorted to the lateral side, allows a safe corridor to the subtalar joint avoiding the neurovascular bundle (Figure 12.1 B and C). In case of ectopic ossifications, for example, due to the remnants of a former bone graft, direct visualization of the subtalar joint level is impaired and the use of intraoperative imaging intensification can be beneficial (compare Figure 12.5B). Using a 10- to 15-mm straight or curved osteotome can be beneficial to enter the subtalar nonunion level under image intensification control as well as to mobilize the nonunion. The feedback received from prying the joint with the osteotome is superior to the image intensification views. A slightly curved osteotome is commonly employed since the subtalar joint line is physiologically curved, as well.² Once the osteotome reaches the region of the anterior border of the subtalar joint, a Hintermann-type distractor can be employed to keep the former articular surfaces of the subtalar joint open that facilitates the sequential debridement of the nonunion (Figures 12.1B, C and 12.2C). Any extraarticular distraction device is superior to the use of a laminar spreader, which partially blocks the bone surfaces undergoing debridement. When correcting a subtalar joint malunion, which mostly corresponds to excessive calcaneal varus, eccentric placement of the distractor to the medial half of the subtalar joint space aids correction of the hindfoot realignment (Figure 12.3A). The osseous debridement should encompass all fibrous scar tissue within the former subtalar joint space as well as the focal hypovascular sclerotic bone regions impeding osseous healing. However, excessive resection of the former subchondral bone layer leaving only the soft cancellous bone for RSTA bears the risk that a structural bone graft will collapse into the soft cancellous bone substrate. The author prefers to set multiplex drill holes with a 1.8-mm or 2-mm Kirschner wire into the inferior surface of the talus and the corresponding surface of the calcaneus to enhance osseous ingrowth. The ratchet of the distractor allows for a targeted adjustment of the talar inclination under lateral image intensification view and a determination of the geometry of the autologous tricortical posterior iliac crest bone graft (Figure 12.2 C).

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