INTRODUCTION TO SUBTALAR ARTHRODESIS
Subtalar arthrodesis represents a cornerstone procedure in hindfoot reconstruction, frequently indicated as a primary intervention for highly comminuted intra-articular calcaneal fractures (e.g., Sanders Type IV) or as a secondary salvage procedure for post-traumatic subtalar arthritis. The primary objectives of this procedure are the alleviation of pain, the restoration of hindfoot alignment, the re-establishment of calcaneal height, and the creation of a stable, plantigrade foot.
When addressing severe calcaneal trauma, the integration of Open Reduction and Internal Fixation (ORIF) with immediate or staged subtalar arthrodesis demands a profound understanding of hindfoot biomechanics, meticulous soft tissue handling, and precise surgical execution. The following comprehensive guide delineates the operative protocols, focusing on the combined medial and lateral approaches, structural bone grafting, and rigid internal fixation techniques.
BIOMECHANICS AND PREOPERATIVE CONSIDERATIONS
Hindfoot Kinematics
The subtalar (talocalcaneal) joint is a complex, multi-faceted articulation primarily responsible for hindfoot inversion and eversion. It functions in a highly coupled manner with the transverse tarsal joint (talonavicular and calcaneocuboid joints).
Clinical Pearl: Arthrodesis of the subtalar joint eliminates approximately 70% of the motion at the talonavicular joint and 30% at the calcaneocuboid joint. Therefore, achieving optimal alignment (typically 5 degrees of valgus) is critical to prevent adjacent segment disease and lateral column overload.
Pathoanatomy of the Calcaneal Fracture
In severe calcaneal fractures, the talus often drives into the body of the calcaneus, resulting in:
* Loss of calcaneal height (decreased Böhler’s angle).
* Widening of the heel (lateral wall blowout), leading to subfibular impingement.
* Varus deformity of the tuberosity.
* Severe articular comminution of the posterior facet.
Failure to restore the three-dimensional anatomy—specifically calcaneal height and width—results in anterior ankle impingement, loss of the Achilles tendon lever arm, and chronic peroneal tendon pathology.
Preoperative Imaging
- Radiographs: Weight-bearing anteroposterior (AP), lateral, and Harris axial views of the heel. Broden's views may be utilized to assess the posterior facet.
- Computed Tomography (CT): A fine-cut CT scan (axial, coronal, and sagittal planes) is mandatory for evaluating the degree of articular comminution, the integrity of the sustentaculum tali (the "constant" fragment), and the volume of bone voids requiring structural grafting.
SURGICAL APPROACHES
The Combined Medial and Lateral Approach (Technique 88-2)
Historically championed by the Campbell Clinic, the combined medial and lateral approach offers a robust solution for complex calcaneal fractures requiring ORIF and potential arthrodesis.
Advantages of the Combined Approach
- Direct Sustentacular Visualization: Allows for the accurate, direct reduction of the tuberosity and lateral fragments to the medial sustentacular fragment, which remains tethered to the talus via the deltoid ligament complex.
- Superior Articular Exposure: The lateral window provides excellent visualization of the subtalar joint for joint preparation and reduction.
- Soft Tissue Preservation: By utilizing two smaller, strategically placed incisions rather than a single massive extensile lateral approach, the risk of catastrophic wound breakdown and flap necrosis is significantly mitigated.
Disadvantages and Pitfalls
The primary disadvantage of this dual-incision technique is the increased difficulty in achieving complete lateral wall decompression. Because the lateral exposure is less extensile, mobilizing the lateral wall blowout to decompress the subfibular space requires meticulous, targeted retraction and specialized instrumentation.
Surgical Warning: When utilizing the medial approach, the surgeon must maintain profound respect for the neurovascular bundle (posterior tibial artery and tibial nerve) and the flexor hallucis longus (FHL) tendon. Vigorous retraction in this area can lead to iatrogenic neurapraxia or vascular compromise.
STEP-BY-STEP SURGICAL TECHNIQUE: SUBTALAR ARTHRODESIS
1. Patient Positioning and Anesthesia
- Anesthesia: General anesthesia or regional anesthesia (spinal/epidural) combined with a continuous popliteal sciatic nerve block for postoperative pain control.
- Positioning: The patient is typically placed in the lateral decubitus position to facilitate the lateral approach. If a combined approach is utilized, a "sloppy lateral" or supine position with a large ipsilateral hip bump may be preferred to allow access to both the medial and lateral aspects of the hindfoot.
- Tourniquet: A thigh or calf tourniquet is applied and inflated after exsanguination to ensure a bloodless surgical field.
2. Initial ORIF of the Calcaneus
Before arthrodesis can be achieved, the overall envelope of the calcaneus must be restored.
* Execute the ORIF of the calcaneus (as described in standard protocols, e.g., Technique 88-1).
* Reduce the tuberosity fragment to the sustentaculum tali to correct varus malalignment and restore length.
* Elevate the depressed articular fragments to restore Böhler’s angle.
* Apply provisional fixation using Kirschner wires (K-wires).
3. Management of Major Bone Voids
Elevation of the depressed posterior facet inevitably creates a substantial cancellous bone void within the body of the calcaneus.
* Structural Grafting: Major bone voids in the posterior aspect of the calcaneus require structural support to prevent late collapse.
* Tricortical Iliac Crest Bone Graft (ICBG): Harvest a tricortical block from the anterior or posterior iliac crest. Shape the graft to precisely fit the defect. This structural graft is paramount for restoring the normal orientation, height, and mechanical integrity of the calcaneus.
4. Joint Preparation for Arthrodesis
Once the calcaneal morphology is restored, attention is turned to the subtalar joint.
* Cartilage Removal: Using a high-speed burr, aggressively remove all remaining hyaline cartilage from the posterior facet of the calcaneus and the corresponding posterior facet of the talus.
* Subchondral Bone Resection: Penetrate the subchondral bone to expose healthy, bleeding cancellous bone. This "fish-scaling" or "feathering" technique maximizes the surface area for osteogenesis.
* Defect Filling: Pack the remaining joint space and any residual defects with extensive autogenous cancellous iliac crest bone graft. The osteogenic, osteoinductive, and osteoconductive properties of autograft remain the gold standard for achieving solid fusion.
5. Intra-articular and Extra-articular Arthrodesis
To maximize fusion rates, a combined intra-articular and extra-articular arthrodesis is performed.
* Denuding the Lateral Talus: Use an osteotome or burr to denude the lateral aspect of the talus (the lateral process) and the adjacent lateral wall of the calcaneus.
* Packing this lateral gutter with autogenous bone graft creates an extra-articular fusion mass that bridges the talus and calcaneus, significantly enhancing the biomechanical stability of the construct.
6. Internal Fixation
Rigid internal fixation is the final intraoperative step, ensuring compression and stability across the arthrodesis site.
* Screw Selection: The construct is typically fixed with two fully threaded, 6.5-mm cancellous screws.
* Biomechanical Note on Screw Threading: While partially threaded lag screws are traditionally used to achieve interfragmentary compression, fully threaded screws can be utilized effectively if inserted using a lag technique (overdrilling the near cortex). Alternatively, if a large structural graft has been placed to restore height, fully threaded screws may be used as positional screws to prevent the compression from crushing the graft and subsequently losing the restored calcaneal height.
* Trajectory: Screws are generally introduced from the non-weight-bearing portion of the posterior calcaneal tuberosity, directed anteriorly, medially, and superiorly into the dense bone of the talar body and dome. Care must be taken to avoid penetrating the ankle joint.
* Fluoroscopic Confirmation: Utilize intraoperative fluoroscopy (lateral, Harris axial, and AP ankle views) to confirm hardware placement, joint reduction, and restoration of calcaneal height.
POSTOPERATIVE CARE AND REHABILITATION
The success of a subtalar arthrodesis relies as heavily on strict postoperative protocols as it does on surgical execution.
Immediate Postoperative Phase (Weeks 0-3)
- Wound Management: A closed suction drain is typically placed during surgery to prevent hematoma formation and is removed on the first postoperative day.
- Immobilization: The limb is placed in a bulky, well-padded posterior splint. Elevation is strictly enforced to minimize edema and protect the soft tissue envelope.
- Suture Removal: Sutures or staples are removed at 2 to 3 weeks postoperatively, contingent upon complete wound healing.
Intermediate Phase (Weeks 3-12)
- Casting: Following suture removal, the patient is transitioned into a short-leg cast.
- Weight-Bearing Status: The patient remains strictly non-weight-bearing (NWB) to protect the structural bone graft and the arthrodesis site.
- Clinical and Radiographic Monitoring: Serial radiographs are obtained at 6 and 12 weeks to assess the progression of bony union and the maintenance of hardware position.
Late Phase (Weeks 12 and Beyond)
- Transition to Weight-Bearing: A short-leg cast is worn until definitive evidence of radiographic and clinical union is apparent, which generally occurs between 10 and 12 weeks.
- Bracing: Once union is confirmed, the cast is discontinued, and a prefabricated controlled ankle motion (CAM) walking brace is applied.
- Physical Therapy: The patient is gradually allowed to return to full activities. Physical therapy is initiated to restore ankle dorsiflexion/plantarflexion, strengthen the gastrosoleus complex, and improve proprioception.
COMPLICATIONS AND MANAGEMENT
Despite meticulous technique, subtalar arthrodesis carries inherent risks that the orthopedic surgeon must be prepared to manage.
1. Nonunion
Nonunion occurs in approximately 5% to 10% of subtalar arthrodeses. Risk factors include smoking, diabetes, avascular necrosis of the talus, and inadequate rigid fixation.
* Management: Symptomatic nonunions require revision surgery. This involves removal of hardware, aggressive debridement of the nonunion site, application of fresh autogenous bone graft (or orthobiologics such as BMP-2), and revision internal fixation, potentially utilizing a stiffer construct such as a hindfoot fusion nail or specialized plating systems.
2. Malunion
Fusing the subtalar joint in varus is a catastrophic error that locks the transverse tarsal joint, leading to a rigid, painful foot and lateral column overload.
* Prevention: Intraoperative fluoroscopy and clinical assessment of the heel alignment (aiming for 5 degrees of valgus) are critical.
* Management: Corrective calcaneal osteotomy and revision arthrodesis.
3. Wound Complications
The lateral soft tissue envelope of the calcaneus is notoriously tenuous.
* Prevention: The combined medial and lateral approach significantly reduces this risk. Furthermore, adhering to strict "no-touch" techniques for the skin edges and delaying surgery until the "wrinkle sign" appears post-injury are mandatory principles.
* Management: Superficial necrosis may be managed with local wound care and oral antibiotics. Deep infections involving hardware or bone graft require urgent surgical debridement, hardware removal (if stability is compromised), and potentially negative pressure wound therapy or free tissue transfer.
4. Adjacent Segment Disease
Due to the coupled kinematics of the hindfoot, subtalar fusion places increased stress on the talonavicular, calcaneocuboid, and ankle joints. Over time, patients may develop symptomatic osteoarthritis in these adjacent joints.
* Management: Initial management is conservative, utilizing custom orthotics (rigid Morton's extension or rocker-bottom shoes) and intra-articular corticosteroid injections. Refractory cases may necessitate extension of the fusion to a triple arthrodesis or pantalar arthrodesis.
CONCLUSION
Subtalar arthrodesis, particularly when performed in conjunction with ORIF for severe calcaneal fractures, is a highly demanding yet rewarding procedure. By utilizing a combined medial and lateral approach, the surgeon can achieve precise anatomical reduction of the sustentacular fragment while minimizing the risk of devastating wound complications. The meticulous preparation of the articular surfaces, the strategic use of tricortical iliac crest bone graft to restore calcaneal height, and the application of rigid internal fixation are the non-negotiable pillars of a successful outcome. Strict adherence to these evidence-based surgical techniques and postoperative protocols ensures the highest probability of achieving a stable, painless, and functional plantigrade foot.
