Resection of the Lateral Prominence of the Calcaneus: The Modified Kashiwagi Procedure

INTRODUCTION TO CALCANEAL MALUNION AND SUBFIBULAR IMPINGEMENT

Fractures of the calcaneus, particularly displaced intra-articular variants, are notoriously challenging to manage. When treated nonoperatively or following failure of surgical fixation, these injuries frequently progress to a symptomatic malunion. The classic pathoanatomy of a calcaneal malunion is characterized by loss of calcaneal height, varus deformity of the tuberosity, and a severe "blowout" of the lateral calcaneal wall.

Historically, chronic pain following a calcaneal fracture was almost exclusively attributed to post-traumatic subtalar arthrosis. However, as pioneered by Kashiwagi, it is now widely recognized in orthopedic surgery that a significant proportion of lateral hindfoot pain stems from extra-articular sources—specifically, the changes occurring around the peroneal tendons due to the expanded lateral calcaneal wall.

The modified Kashiwagi procedure (lateral calcaneal exostectomy with peroneal tendon decompression, with or without subtalar arthrodesis) remains a cornerstone technique for addressing this complex pathology. This masterclass details the biomechanical rationale, preoperative evaluation, and precise surgical execution required to achieve optimal outcomes in the management of lateral calcaneal prominence.

PATHOANATOMY AND BIOMECHANICS

Understanding the three-dimensional deformity of a calcaneal malunion is critical for successful surgical reconstruction. The primary fracture line in axial load injuries typically splits the posterior facet, driving the lateral articular fragment inferiorly and laterally.

The Subfibular Space and Peroneal Pathology

As the lateral wall of the calcaneus expands, it encroaches upon the subfibular space—the narrow anatomical corridor bordered by the lateral malleolus medially and the lateral calcaneal wall laterally. The peroneus longus and brevis tendons traverse this space.

When the lateral wall blows out, several pathological changes occur:
* Direct Impingement: The bony prominence physically compresses the peroneal tendons against the distal fibula (fibular abutment).
* Tendon Entrapment: Tendons may become buried in exuberant fracture callus or caught by displaced bony fragments.
* Adhesive Tenosynovitis: Chronic friction leads to severe inflammation, scarring, and adhesions within the peroneal tendon sheaths.
* Superior Displacement and Subluxation: The expanding lateral wall can displace the tendons superiorly, stretching or rupturing the superior peroneal retinaculum, leading to chronic tendon subluxation.
* Tendon Attrition: Chronic impingement frequently results in longitudinal split tears, particularly of the peroneus brevis.

💡 Clinical Pearl: The "Double Crush" of Calcaneal Malunion

Patients with calcaneal malunions often suffer from a "double crush" phenomenon: intra-articular pain from subtalar arthritis combined with extra-articular pain from subfibular peroneal impingement. Surgical intervention must address both components to achieve a satisfactory clinical outcome.

PREOPERATIVE EVALUATION

Clinical Examination

Patients typically present with chronic, debilitating lateral hindfoot pain exacerbated by weight-bearing and uneven surfaces.
* Inspection: Look for a widened heel, loss of the longitudinal arch, and a varus alignment of the hindfoot.
* Palpation: Point tenderness is usually localized to the subfibular region, directly over the peroneal tendons, rather than isolated to the sinus tarsi.
* Range of Motion: Subtalar motion is typically severely restricted or entirely absent. Pain with passive inversion and eversion is common.
* Peroneal Provocation: Resisted eversion often elicits sharp pain, indicating peroneal tendinopathy or tearing. Assess for peroneal tendon subluxation by having the patient actively dorsiflex and evert the foot.

Diagnostic Imaging

While Kashiwagi originally recommended "peroneal tomography" to visualize changes around the tendons and their sheaths, modern imaging relies on advanced cross-sectional modalities.

• Weight-Bearing Radiographs: AP, lateral, and Harris axial views of the heel. The Harris axial view is critical for demonstrating the lateral wall blowout and subfibular impingement.
• Computed Tomography (CT): The gold standard for evaluating calcaneal malunions. Coronal cuts accurately quantify the degree of lateral wall expansion, fibular abutment, and the status of the subtalar and calcaneocuboid joints.
• Magnetic Resonance Imaging (MRI): Indicated if severe peroneal tendon pathology (e.g., high-grade partial tears or complete ruptures) is suspected, though CT is usually sufficient for bony planning.

INDICATIONS AND CONTRAINDICATIONS

Indications

• Symptomatic lateral calcaneal prominence causing subfibular impingement and peroneal tendon entrapment.
• Post-traumatic subtalar arthrosis secondary to calcaneal fracture (when combined with subtalar arthrodesis).
• Failure of conservative management (e.g., custom orthotics, NSAIDs, targeted corticosteroid injections, physical therapy).

Contraindications

• Active local or systemic infection.
• Severe peripheral vascular disease (PVD) or inadequate soft tissue envelope.
• Severe varus malalignment of the calcaneal tuberosity (requires a corrective calcaneal osteotomy, such as a Dwyer or sliding osteotomy, rather than simple exostectomy).

⚠️ Surgical Warning: Assessing Hindfoot Alignment

The Kashiwagi procedure is an in situ decompression. It does not correct severe varus or valgus malalignment of the hindfoot. If the calcaneal tuberosity is in significant varus, an isolated lateral wall resection will fail to restore normal biomechanics, and a corrective osteotomy is mandatory.

SURGICAL TECHNIQUE: THE MODIFIED KASHIWAGI PROCEDURE

The goal of this procedure is to decompress the subfibular space by resecting the lateral bony prominence, freeing the peroneal tendons, and, if indicated, fusing the subtalar joint.

1. Patient Positioning and Preparation

• Place the patient in the lateral decubitus position on a beanbag, with the operative leg facing upward.
• Ensure all bony prominences are heavily padded.
• Apply a well-padded thigh tourniquet.
• Administer prophylactic intravenous antibiotics prior to tourniquet inflation.
• Prepare and drape the limb in a standard sterile fashion, allowing access for intraoperative fluoroscopy.

2. The Surgical Incision

The approach utilizes a modified Kocher incision to provide expansive access to the lateral calcaneus while protecting vital neurovascular structures.

• Begin the incision posterior to the fibula, following the course of the peroneal tendons.
• Curve the incision distally and anteriorly.
• Crucial Modification: Extend the distal half of the incision one fingerbreadth superior to the plantar aspect (sole) of the foot, terminating at the base of the fifth metatarsal.
• This inferior extension ensures the incision avoids crossing directly over the lateral prominence, reducing the risk of wound dehiscence and painful scar formation over bony prominences.

3. Superficial Dissection and Nerve Protection

• Deepen the incision through the subcutaneous tissue.
• Identify and protect the sural nerve. The nerve typically crosses the surgical field in the distal portion of the incision. Mobilize it gently and retract it out of harm's way. Injury to the sural nerve can result in a debilitating postoperative neuroma, which may be more painful than the original pathology.

4. Peroneal Tendon Mobilization

• Identify the peroneus longus and brevis tendons.
• Without opening their primary sheaths prematurely, deepen the incision to the lateral surface of the calcaneus, approximately 0.6 cm inferior to the peroneus longus tendon.
• Extend the dissection superiorly, staying strictly extraperiosteal next to the bone and deep to the tendons.
• Carefully separate the peroneal retinaculum from the underlying bone as a continuous, robust flap. This tissue will be essential for closure to prevent postoperative tendon subluxation.
• Retract the peroneal tendons superiorly over the tip of the lateral malleolus.
• Inspect the tendons. If longitudinal split tears are present (most commonly in the peroneus brevis), perform a primary tubularization repair using 4-0 non-absorbable suture.

5. Exposure of the Lateral Calcaneus

• Identify the origin of the extensor digiti brevis (EDB) muscle belly on the lateral calcaneus.
• Sharply free the EDB origin and retract it superiorly and anteriorly.
• The entire lateral surface of the calcaneus is now exposed, providing clear visualization of the lateral aspect of the subtalar joint and the calcaneocuboid joint.

6. The Sagittal Osteotomy (Lateral Wall Resection)

This is the critical step of the Kashiwagi procedure. The objective is to create a flat, vertical lateral wall, completely eliminating the subfibular impingement.

• Utilize a wide, sharp osteotome or a sagittal saw.
• Begin the osteotomy at the calcaneocuboid joint anteriorly and extend it to the calcaneal tuberosity posteriorly.
• The cut must extend from the subtalar joint superiorly down to the plantar surface inferiorly.
• Trajectory: The osteotomy must be strictly in the sagittal plane.
• Discard the resected bone.
• Palpate the newly created lateral wall. It should consist of a sheer vertical surface. Ensure that all excessive bone lateral to the subtalar joint and inferior to the lateral malleolus has been completely removed.
• Pass an instrument between the fibula and the new lateral calcaneal wall to confirm adequate decompression of the subfibular space.

🔪 Surgical Pitfall: Under-Resection

The most common error during this step is under-resection of the plantar-lateral aspect of the calcaneus. If a bony ledge is left inferiorly, the peroneal tendons will continue to impinge against it when they are relocated. Ensure the osteotomy exits cleanly at the plantar margin.

7. Subtalar Arthrodesis (If Indicated)

If the patient has concurrent subtalar arthrosis (which is highly common in malunions), an in situ subtalar arthrodesis is performed at this stage.

• The lateral aspect of the subtalar joint is already widely exposed following the exostectomy.
• Use a lamina spreader in the sinus tarsi to distract the subtalar joint.
• Using curettes, osteotomes, and a high-speed burr, meticulously denude all remaining articular cartilage from the posterior, middle, and anterior facets of the subtalar joint.
• Feather the subchondral bone to expose bleeding, cancellous bone (the "paprika sign").
• If necessary, use the bone previously resected from the lateral wall as local autograft to pack any defects within the subtalar joint.
• Fix the joint rigidly using two large-fragment (6.5 mm or 7.3 mm) cannulated partially threaded screws, typically passed from the calcaneal tuberosity into the body of the talus.

8. Closure and Retinaculum Repair

• Thoroughly irrigate the wound to remove all bone debris.
• Release the tourniquet and achieve meticulous hemostasis. Hematoma formation in this dead space can lead to severe wound complications.
• Relocate the peroneal tendons and their sheaths inferior to the lateral malleolus into their newly decompressed anatomical position.
• Critical Step: Suture the previously elevated peroneal retinaculum securely to the plantar fascia or the periosteum of the inferior calcaneus. This prevents postoperative anterior and superior subluxation of the peroneal tendons.
• Close the subcutaneous tissue with absorbable sutures and the skin with non-absorbable nylon or staples, utilizing a tension-free technique (e.g., Allgöwer-Donati stitches).

POSTOPERATIVE CARE AND REHABILITATION

The postoperative protocol depends entirely on whether an isolated exostectomy was performed or if it was combined with a subtalar arthrodesis.

Protocol for Isolated Lateral Wall Resection

• Immediate Post-op: Apply a bulky, well-padded posterior splint or a long-leg cast with the knee flexed at 30 degrees and the ankle in neutral. The flexed knee relaxes the gastrocnemius, reducing tension on the Achilles and the posterior hindfoot.
• 10 to 14 Days: The patient is seen in the clinic. The cast and skin sutures are removed.
• 2 to 6 Weeks: The patient is transitioned to a controlled ankle motion (CAM) boot. Progressive weight-bearing is initiated as tolerated. Early active range of motion of the ankle and subtalar joint is highly encouraged to prevent stiffness and tendon adhesions.
• Physical Therapy: Focuses on peroneal tendon strengthening, proprioception, and gait retraining.

Protocol for Resection Combined with Subtalar Arthrodesis

If the operation includes an arthrodesis, the rehabilitation timeline is significantly extended to allow for bony union, mirroring the protocol for a triple arthrodesis.

• Immediate Post-op: Bulky posterior splint, strictly non-weight-bearing.
• 10 to 14 Days: Suture removal. Apply a short-leg cast. The patient remains strictly non-weight-bearing.
• 6 Weeks: Radiographic evaluation. If early consolidation is visible, the patient may be transitioned to a short-leg walking cast or a CAM boot with progressive partial weight-bearing.
• 10 to 12 Weeks: Clinical and radiographic assessment of fusion. If solid union is achieved, the patient is transitioned to regular footwear, often utilizing a supportive orthotic, and formal physical therapy begins.

COMPLICATIONS AND MANAGEMENT

While highly effective, the modified Kashiwagi procedure carries specific risks inherent to lateral hindfoot surgery:

1. Wound Dehiscence and Infection: The lateral soft tissue envelope of the heel is tenuous. Meticulous handling of the skin flaps, avoiding excessive retraction, and ensuring a tension-free closure are paramount.
2. Sural Nerve Injury: Can result in a painful neuroma or lateral foot numbness. Careful superficial dissection and gentle retraction are required.
3. Peroneal Tendon Subluxation: Failure to adequately repair the peroneal retinaculum to the plantar fascia will result in the tendons snapping over the lateral malleolus.
4. Nonunion (If Arthrodesis Performed): Risk factors include smoking, diabetes, and inadequate joint preparation. Rigid internal fixation and strict adherence to non-weight-bearing protocols mitigate this risk.
5. Persistent Pain: Usually due to under-resection of the lateral wall (leaving a plantar ledge) or failure to recognize and address concurrent varus malalignment of the calcaneal tuberosity.

CONCLUSION

The resection of the lateral prominence of the calcaneus, as modified from Kashiwagi's original description, is a highly reliable procedure for salvaging the painful malunited calcaneus. By thoroughly understanding the pathoanatomy of subfibular impingement, meticulously decompressing the peroneal tendons, creating a vertical lateral calcaneal wall, and addressing concurrent subtalar arthrosis, the orthopedic surgeon can predictably restore function and alleviate chronic lateral hindfoot pain. Strict adherence to the anatomical landmarks and postoperative protocols outlined in this guide is essential for achieving excellence in patient outcomes.