High-yield overview

Lateral sinus tarsi incision with posterior facet and anterior-middle facet preparation | intermediate

Surgical Imaging

Imaging Gallery

Lateral foot with portal markings drawn on skin for arthroscopic subtalar arthrodesis — Portal site marking for arthroscopic subtalar arthrodesis: lateral view of the foot with skin markings indicating the anterolateral and posterolateral sinus tarsi portals. Arrowhead and cursor markers delineate the sinus tarsi entry zone, with the three-portal approach allowing access to the posterior facet for cartilage removal and bone surface preparation.Credit: Open-i NIH (PMC2701499) (CC BY PMC Open Access)

Intraoperative arthroscopic subtalar arthrodesis setup with foot draped — Arthroscopic subtalar arthrodesis — intraoperative setup: the foot is draped in surgical green with arthroscope portals established. The lateral decubitus positioning is demonstrated with the arthroscope and working instruments inserted into the sinus tarsi, providing access to the posterior subtalar facet for joint preparation.Credit: Open-i NIH (PMC3200126) (CC BY PMC Open Access)

Open subtalar arthrodesis intraoperative view with probe showing posterior facet — Open subtalar arthrodesis — posterior facet exposure: intraoperative view through a lateral sinus tarsi approach showing the posterior facet of the subtalar joint fully exposed. Cartilage has been denuded from the calcaneal and talar surfaces, with a probe/instrument demonstrating the prepared bone bed ready for cancellous bone graft and screw fixation.Credit: Open-i NIH (PMC4855898) (CC BY PMC Open Access)

Critical Danger Structures

Danger 1: Sural Nerve

Sural nerve. Location: crosses the lateral hindfoot 1–2 cm posterior to the lateral malleolus, running superficially over the peroneal tendons and sinus tarsi toward the fifth metatarsal base. Protection: identify and retract with a vessel loop during the sinus tarsi incision; avoid excessive traction and unprotected retraction. Injury causes painful neuroma on the lateral foot and is the most common neurological complication.

Danger 2: Posterior Tibial Artery / Medial Neurovascular Bundle

Posterior tibial artery and tibial nerve. Location: medial to the sustentaculum tali, passing through the tarsal tunnel. Protection: stay lateral to the posterior facet during bone preparation; avoid placing retractors or Kirschner wires medially under the sustentaculum. Violation causes catastrophic medial neurovascular injury and compartment syndrome.

Danger 3: Heel Malposition

Malposition of the os calcis in varus or excessive valgus. Target is 0–5° valgus relative to the tibial axis. Varus position creates a rigid supinated hindfoot causing lateral border overload, stress fractures, and peroneal tendon pathology. Excessive valgus beyond 5° overloads the medial midfoot, accelerates talonavicular arthrosis, and causes abnormal valgus loading of the ipsilateral knee. Intra-operative fluoroscopy and clinical heel alignment check are mandatory before screw insertion.

Danger 4: Adjacent Joint Damage (TN and CC)

Talonavicular and calcaneocuboid joints. Location: immediately anterior to the subtalar joints; the talonavicular is particularly vulnerable to inadvertent curettage when preparing the anterior-middle facets. Protection: use direct visualisation, avoid aggressive instrumentation beyond the anterior margin of the posterior facet, and confirm joint boundaries on fluoroscopy. Chondral damage accelerates adjacent joint arthrosis and may convert an isolated fusion to a triple fusion requirement.

Danger 5: Wound Dehiscence / Peroneal Tendon Injury

Lateral wound closure and peroneal tendons. Location: the sinus tarsi incision passes directly over the peroneal tendons at the lateral calcaneal wall. Protection: identify the peroneal tendon sheath and retract it inferiorly; use layered wound closure and ensure skin is not closed under tension. Wound dehiscence exposes hardware and risks deep infection; peroneal tendon disruption causes lateral instability and requires separate repair.

Mnemonic

SAFESAFE Fusion — Four Steps to Solid Union

Mnemonic

VALGUSVALGUS — Consequences of Heel Malposition

Primary Indications

Post-Traumatic Subtalar Osteoarthritis (Calcaneal Fracture Sequelae)

Most common indication worldwide
Displaced intra-articular calcaneal fractures cause irreversible posterior facet cartilage destruction in a substantial proportion of patients
Indication: end-stage subtalar OA with pain, stiffness, and functional limitation refractory to 3–6 months of conservative management (insoles, activity modification, corticosteroid injection)
Sanders Type III and IV fractures carry the highest risk of symptomatic subtalar OA
Subtalar arthrodesis at the time of calcaneal fracture malunion correction (lateral wall exostectomy, calcaneal osteotomy) may be performed simultaneously

Primary Subtalar Osteoarthritis

Less common than post-traumatic; presents in older patients with insidious hindfoot pain
Confirm with weight-bearing radiographs (Harris-Heath axial view, lateral view) and CT scan
Indication: refractory to conservative management, preserved talonavicular and calcaneocuboid joints

Talocalcaneal Coalition (Failed Conservative Management)

Resection is preferred in younger patients (before secondary OA) but subtalar arthrodesis is appropriate for:
- Coalition involving more than 50% of the posterior facet (fibrous or bony)
- Severe secondary subtalar OA after failed resection
- Adult patients with established OA at presentation

Adult Acquired Flatfoot Deformity — Stage II PTT Dysfunction with Subtalar OA

Stage IIB/C with fixed subtalar valgus deformity and secondary arthrosis
Isolated subtalar fusion combined with medial column procedures if talonavicular joint is preserved
Distinguished from Stage III/IV where triple arthrodesis is indicated

Inflammatory Arthritis

Rheumatoid arthritis, seronegative spondyloarthropathy with isolated subtalar joint involvement
Indication: refractory subtalar pain and deformity not controlled by systemic disease management
Wound healing must be optimised; immunosuppressant dose reduction discussed with rheumatologist peri-operatively

Avascular Necrosis of the Talus (Stage III–IV)

Hawkins Stage III–IV talar AVN with secondary subtalar arthrosis
Subtalar fusion provides pain relief and stability; extent of AVN and tibiotalar joint involvement determines whether total ankle replacement or tibiotalocalcaneal fusion is preferred

Contraindications

Active infection (absolute)
Preserved subtalar cartilage — pain not attributable to subtalar OA
Significant talonavicular and calcaneocuboid OA — triple arthrodesis preferred
Peripheral arterial disease with critical ischaemia (relative; vascular surgery opinion first)
Severe osteoporosis (relative; augmented fixation strategies)

Evidence Base

Union Rates and Outcomes — Key Figures to Quote

Primary isolated fusion union rate: roughly 84–95% depending on patient selection. Easley's large series reported an overall union rate of 84% (154 of 184 feet), rising to 96% only after excluding smokers, revisions, structural grafts, and fusions adjacent to a prior ankle fusion — examiners reward candidates who quote the real overall figure rather than the best-case subgroup.
Smoking is the dominant modifiable risk factor: union fell from 92% in non-smokers to 73% in smokers (Easley 2000).
Avascular bone matters: in Easley's series, every non-union occurred in feet with greater than 2 mm of avascular bone at the subtalar joint.
For calcaneal-fracture sequelae specifically, Flemister (2000) reported a 96% union rate across 86 fusions with a mean AOFAS hindfoot score of 75.
CT is the gold standard for assessing union — plain radiographs substantially overestimate the percentage of joint fused (Coughlin 2006).

Harris-Heath Footprint

The Harris-Heath axial (ski-jump) weight-bearing view is the key intra-operative and post-operative view for assessing calcaneal alignment. A valgus heel position of 0–5° is confirmed when the calcaneal tuberosity subtends the appropriate angle relative to the tibial axis on axial and lateral fluoroscopy.

Screw Configuration

One or two large cancellous/cannulated lag screws (6.5–7.3 mm) directed from the posterior-inferior calcaneus into the talar body remain the standard construct. Mann (1998) achieved union in all 48 feet using one or two screws; two-screw constructs are generally preferred for rotational control, while a single 7.3 mm screw can suffice in good-quality bone with well-apposed surfaces.

Verified Evidence

Isolated subtalar arthrodesis

Level IV

Easley ME, Trnka HJ, Schon LC, Myerson MS • J Bone Joint Surg Am

Clinical Implication: The single largest isolated subtalar fusion series. Quote the realistic 84% overall union rate, the smoking effect, and the role of avascular bone — these are the figures examiners expect.

Verify on PubMed (PMID 10819272)

Subtalar arthrodesis for complications of intra-articular calcaneal fractures

Level IV

Flemister AS, Infante AF, Sanders RW, Walling AK • Foot Ankle Int

Clinical Implication: Supports subtalar fusion for post-traumatic calcaneal sequelae with a high union rate, and supports using local lateral-wall bone graft to avoid iliac-crest donor-site morbidity.

Verify on PubMed (PMID 10830657)

Isolated subtalar arthrodesis

Level IV

Mann RA, Beaman DN, Horton GA • Foot Ankle Int

Clinical Implication: Demonstrates excellent union with one or two screws and documents the degree of compensatory motion lost — useful when counselling patients that the midtarsal joints stiffen but are not abolished.

Verify on PubMed (PMID 9728697)

Foot function after subtalar distraction bone-block arthrodesis: a prospective study

Level IV

Rammelt S, Grass R, Zawadski T, Biewener A, Zwipp H • J Bone Joint Surg Br

Clinical Implication: Where a calcaneal malunion has lost height and produced anterior ankle impingement, an interpositional distraction bone block restores talocalcaneal height rather than a simple in-situ fusion.

Verify on PubMed (PMID 15274260)

Comparison of radiographs and CT scans in the prospective evaluation of the fusion of hindfoot arthrodesis

Level II

Coughlin MJ, Grimes JS, Traughber PD, Jones CP • Foot Ankle Int

Clinical Implication: When non-union is suspected after subtalar fusion, obtain CT rather than relying on plain films, which systematically overestimate union.

Verify on PubMed (PMID 17054877)

Clinical Decision Scenarios

Use these scenarios to practise clinical reasoning and management decisions

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"A 42-year-old builder sustained a displaced intra-articular calcaneal fracture 3 years ago, treated non-operatively. He now presents with severe lateral hindfoot pain, inability to work, and stiffness. Weight-bearing CT confirms subtalar OA with preserved talonavicular and calcaneocuboid joints. What is your surgical plan, and what is the most critical technical decision?"

PRACTICAL APPROACH

This patient has post-traumatic subtalar OA following a calcaneal fracture — the most common indication for isolated subtalar arthrodesis. I would confirm he has completed an adequate conservative trial of 3–6 months including orthotics, activity modification, and at least one corticosteroid injection to the subtalar joint under ultrasound guidance. My surgical plan is isolated subtalar arthrodesis via a sinus tarsi approach. Since the talonavicular and calcaneocuboid joints are preserved on CT, isolated subtalar fusion is appropriate — this preserves useful transverse tarsal motion (reduced by about 40% rather than abolished — Mann 1998) and is preferable to triple arthrodesis. The most critical technical decision is heel position at fusion. I must position the calcaneus in 0–5° valgus relative to the tibial axis with the foot plantigrade. Varus malposition — the most common technical error — creates a rigid supinated hindfoot with lateral border overload, stress fractures, and peroneal tendon pathology. Excessive valgus beyond 5° causes medial midfoot strain and accelerates talonavicular arthrosis. I confirm alignment clinically (simulate weight-bearing with the foot held in position) and fluoroscopically using lateral and Harris-Heath axial views before inserting definitive fixation. My technique: sinus tarsi incision identifying and protecting the sural nerve, excision of the interosseous talocalcaneal ligament to expose posterior and anterior-middle facets, complete cartilage removal to bleeding cancellous bone, provisional K-wire fixation in confirmed alignment, then two cannulated large cancellous screws from posterior calcaneus to talar body providing compression and rotational stability. Union rates for primary isolated fusion are around 84–96% (overall 84% in Easley's 184-foot series, 96% in optimised non-smokers; Easley 2000); union is markedly reduced by smoking (73% vs 92% in Easley's data). I would counsel him to stop smoking and would discuss the realistic long-term risk of symptomatic adjacent joint arthrosis that may require conversion to triple arthrodesis.

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"What are the consequences of malposition at subtalar arthrodesis and how do you prevent them? A patient returns 18 months post-operatively with lateral border foot pain and difficulty walking on uneven terrain. Their subtalar fusion is confirmed solid on CT. What is your assessment?"

PRACTICAL APPROACH

Malposition is the most common technical complication of subtalar arthrodesis and the most functionally significant. Varus malposition is more disabling than mild valgus. In varus, the heel is inverted, creating a rigid supinated hindfoot. This results in: lateral border overload causing fifth metatarsal and cuboid stress fractures; peroneal tendon pathology from altered vector and tension; inability to evert the foot for normal gait; and cosmetically obvious deformity. Ipsilateral knee varus stress may also develop over time. Excessive valgus beyond 5° causes different problems: the flattened hindfoot overloads the medial midfoot and spring ligament, accelerating talonavicular arthrosis; ipsilateral knee valgus stress; and medial arch pain. I prevent malposition by: confirming target alignment as 0–5° valgus clinically and fluoroscopically before definitive fixation; using provisional K-wires to hold position while reassessing; ensuring the forefoot is not supinated; and comparing to the contralateral foot. For the 18-month post-op patient with solid fusion and lateral border pain, the likely diagnosis is fusion malposition in varus. I would take weight-bearing radiographs (AP and lateral foot, Harris-Heath axial) and clinical alignment examination. With a solid fusion, options are: conservative management with lateral-posting orthotics if mild; revision osteotomy through the fusion mass to correct varus if functionally significant and conservative measures fail. I would distinguish this from adjacent joint problems (TN/CC — medial and dorsal symptoms, not lateral), hardware pain, stress fracture, and peroneal tendon pathology. Each requires a different management pathway and should be assessed with targeted imaging.

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"You are asked to consent a 55-year-old woman with rheumatoid arthritis for isolated subtalar arthrodesis. Her subtalar OA is severe, talonavicular and calcaneocuboid joints have mild OA changes on CT. What additional considerations apply and how does this affect your consent discussion and surgical planning?"

PRACTICAL APPROACH

Rheumatoid arthritis introduces several important modifications to standard subtalar arthrodesis planning and consent. My assessment must first address whether isolated subtalar fusion is appropriate or whether triple arthrodesis is preferable given the mild TN and CC changes. In rheumatoid patients, mild radiographic adjacent joint changes often progress more rapidly than in post-traumatic OA, and reoperation for triple arthrodesis carries greater surgical risk in this population. I would discuss with the patient the risk that an isolated fusion may need to be converted to triple arthrodesis within 5–10 years if TN and CC disease progresses symptomatically. Specific considerations: First, wound healing. Rheumatoid arthritis, methotrexate, and biological therapies all impair wound healing. I would involve her rheumatologist to plan drug management peri-operatively: methotrexate is generally continued, but biological agents (anti-TNF, anti-IL6) are typically stopped 2–4 weeks before surgery and restarted once the wound is healed. This must be agreed with the rheumatologist. Second, bone quality. Rheumatoid disease and long-term corticosteroids cause osteoporosis. I would check DEXA, optimise with bisphosphonates or denosumab if indicated, and plan larger-diameter screws or supplementary bone graft. Third, anaesthetic risk. Cervical spine involvement must be assessed (flexion-extension neck radiographs) before any general anaesthetic for atlantoaxial instability. Fourth, skin fragility. Rheumatoid skin is often thin and fragile; I plan a generous subcutaneous layer closure, avoid wound tension, and have low threshold for prolonged dressing. I would consent her specifically for: wound complications (higher base rate in RA), non-union (higher in RA and on immunosuppression), hardware failure, adjacent joint progression, and the possibility of conversion to triple arthrodesis.