Medial Displacement Calcaneal Osteotomy (MDCO)

Surgical Indications

Primary Indications

• Flexible hindfoot valgus deformity in stage II posterior tibial tendon dysfunction (PTTD) with preserved subtalar motion
• Symptomatic flexible flatfoot with hindfoot valgus greater than 5-7 degrees on weight-bearing radiographs
• Cavovarus foot correction using the lateralising variant of the osteotomy (reverse MDCO)
• Combined reconstruction when medial column insufficiency and Achilles valgus vector require realignment

Concomitant Procedures (Almost Always Required)

• Flexor digitorum longus (FDL) transfer to the navicular or medial cuneiform
• Spring ligament repair or reconstruction (direct repair, graft augmentation or internal brace)
• Lateral column lengthening (Evans or Hintermann osteotomy) when forefoot abduction or lateral column shortening is present
• Gastrocnemius or Achilles lengthening when equinus contracture contributes to the deformity

Contraindications

Absolute:

• Rigid hindfoot valgus (stage III or IV PTTD) with subtalar arthritis or fixed deformity — requires arthrodesis
• Active infection or ulceration over the lateral heel
• Severe peripheral vascular disease precluding safe wound healing

Relative:

• Poor bone quality (severe osteoporosis) increasing nonunion risk
• Smokers who cannot cease nicotine use peri-operatively
• Isolated hindfoot valgus without medial column pathology (rare — MDCO alone is seldom sufficient)

Evidence for MDCO in PTTD Reconstruction

Biomechanical Rationale

Medial translation of the calcaneal tuberosity shifts the Achilles insertion medially, reducing the valgus moment arm and converting the Achilles from a deforming force into a corrective one. Cadaveric studies demonstrate that 8-10 mm of medial displacement corrects hindfoot valgus alignment and reduces medial column overload without significantly altering subtalar kinematics when combined with appropriate soft-tissue procedures.

Clinical Outcomes

Combined MDCO with FDL transfer and spring ligament reconstruction achieves good to excellent results in 75-85% of stage II PTTD patients at 5-10 year follow-up, with significant improvement in AOFAS scores, hindfoot alignment and patient-reported function. Isolated MDCO without addressing the posterior tibial tendon and spring ligament has higher failure rates and is not recommended.

Nonunion and Complication Rates

Nonunion rates range from 2-8% in modern series with stable screw fixation; risk factors include smoking, diabetes and inadequate screw purchase. Sural nerve injury occurs in 5-15% when the nerve is not specifically protected. Hardware prominence requiring removal occurs in 10-20% of cases.

Key Evidence

Calcaneal Anatomy Relevant to MDCO

Osteotomy Landmarks

The calcaneus is a rectangular bone with distinct surfaces that guide safe osteotomy placement.

• Posterior facet: superior articular surface of the subtalar joint; the osteotomy must remain at least 8-10 mm inferior and posterior to its posterior margin
• Sustentaculum tali: medial projection that supports the talar head; the osteotomy trajectory aims just anterior to the sustentaculum to allow medial translation without entering the subtalar joint
• Calcaneal tuberosity: posterior process that receives the Achilles insertion; the osteotomy begins 1-2 cm anterior to its most posterior border
• Lateral wall: thin cortical bone posterior to the peroneal tubercle; the incision and osteotomy are performed directly on this surface after retracting the peroneal tendons

Neurovascular Structures

• Sural nerve: runs in the subcutaneous fat along the lateral border of the Achilles tendon, crossing the incision line obliquely; it must be identified and protected in every case
• Lateral calcaneal nerve: terminal branch supplying sensation to the lateral heel skin; division causes chronic dysaesthesia
• Medial neurovascular bundle: posterior tibial artery, tibial nerve and calcaneal branches lie immediately medial to the osteotomy plane; protected by the medial cortex until the final osteotome cut
• Medial plantar nerve: crosses the medial tuberosity and can be stretched with excessive medial translation

Tendon Anatomy

• Peroneus longus and brevis: run in a common sheath immediately anterior to the incision; must be retracted anteriorly with a protective retractor
• Achilles tendon: inserts on the posterior tuberosity; its vector is medialised by the osteotomy, converting a valgus deforming force into a corrective one
• Posterior tibial tendon: inserts on the navicular and medial cuneiform; diseased in PTTD but not directly addressed by the osteotomy itself

Biomechanical Effect of Translation

Medial displacement of 8-10 mm shifts the ground reaction force vector medially relative to the subtalar joint axis. This reduces the valgus moment arm of the Achilles by approximately 25-35% and decreases medial column overload. Translation beyond 12 mm risks medial soft-tissue impingement and wound complications without additional corrective benefit.

Positioning and Preparation

Patient position: Supine with a bump under the ipsilateral hip to internally rotate the leg, or lateral decubitus with the operative side up. The foot is placed at the end of the table to allow full ankle and subtalar motion. A thigh tourniquet is applied but rarely inflated for this procedure.

Anaesthesia: General or spinal anaesthesia with a popliteal or ankle block for post-operative analgesia. WALANT is not suitable for this bony procedure.

Fluoroscopy: Mini C-arm or standard image intensifier positioned to obtain lateral, axial and Harris heel views intra-operatively. Confirm the ability to visualise the entire calcaneus and subtalar joint before prepping.

Consent: Discuss risk of sural nerve injury (5-15%), nonunion (3-8%), hardware prominence requiring removal (10-20%), under- or over-correction, wound complications, and the frequent need for concomitant procedures (FDL transfer, lateral column lengthening).

Lateral Oblique Approach — Step-by-Step

Step 1: Incision and Superficial Dissection

With the foot in slight plantarflexion and inversion, mark the sural nerve course using a skin marker. Make a 5-7 cm oblique incision starting 2 cm posterior to the tip of the lateral malleolus and directed toward the plantar-medial calcaneus, ending 1-2 cm anterior to the posterior border of the calcaneal tuberosity. The incision lies posterior to the peroneal tendons and crosses the sural nerve in most patients.

Identify and protect the sural nerve in the subcutaneous fat. Mobilise it with a vessel loop and retract it posteriorly or anteriorly depending on its position. Preserve visible lateral calcaneal nerve branches.

Step 2: Exposure of the Calcaneal Lateral Wall

Retract the peroneal tendons anteriorly using a blunt Hohmann or Langenbeck retractor protected with a rubber dam. Expose the lateral wall of the calcaneus from the posterior facet margin to the tuberosity. Identify the peroneal tubercle as an anterior landmark.

Elevate periosteum sharply from the lateral wall in a single layer. Place two Hohmann retractors — one superiorly under the posterior facet and one inferiorly at the plantar border — to protect the soft tissues during the osteotomy.

Step 3: Osteotomy Planning and Execution

Confirm the osteotomy level with fluoroscopy or direct palpation. The cut starts approximately 1 cm posterior and inferior to the posterior facet and is oriented 45 degrees to the plantar surface, directed toward the plantar-medial calcaneus just anterior to the sustentaculum.

Use an oscillating saw with a narrow blade to make the lateral cut under direct vision, stopping 2-3 mm short of the medial cortex. Complete the osteotomy with a broad osteotome, feeling the give as the medial cortex fractures in a controlled manner. Protect the medial neurovascular bundle by keeping the osteotome trajectory anterior to the sustentaculum.

Step 4: Medial Translation and Temporary Fixation

Translate the tuberosity fragment medially 8-10 mm using a lamina spreader or bone hook. Confirm the amount of correction with an axial (Harris) heel view — the tuberosity should sit directly under the talus with neutral or slight valgus alignment.

Place a 1.6 mm or 2.0 mm K-wire from the tuberosity into the anterior calcaneus as temporary fixation. Obtain lateral and axial fluoroscopic views to confirm position and translation before definitive fixation.

Step 5: Definitive Fixation

Insert one or two 6.5-7.0 mm cannulated partially threaded screws (typically 50-60 mm length) over the K-wires. The screws must engage the anterior process or sustentaculum for stable purchase. Confirm compression across the osteotomy and absence of screw penetration into the subtalar joint or calcaneocuboid joint on fluoroscopy.

If two screws are used, place them in a divergent or parallel configuration. Countersink the screw heads to reduce hardware prominence.

Step 6: Wound Closure

Irrigate the wound and confirm haemostasis. Close the subcutaneous layer with 3-0 absorbable suture, taking care not to catch the sural nerve. Close skin with 3-0 nylon or staples. Apply a bulky compressive dressing and a below-knee posterior splint with the ankle in neutral.

Post-operative Protocol

Immediate Post-operative (Day 0-14)

• Non-weight-bearing in below-knee splint or cast for 2 weeks
• Strict elevation for 48-72 hours to minimise swelling
• Wound review at 10-14 days; sutures removed if healed
• Transition to removable boot at 2 weeks once wound stable

Protected Weight-Bearing Phase (2-8 Weeks)

• Touch weight-bearing in boot from 2-6 weeks
• Active ankle and subtalar range-of-motion exercises begin at 2 weeks
• Formal physiotherapy for oedema control and gentle mobilisation
• Radiographs at 6 weeks to assess maintenance of correction and early healing

Progressive Loading (8-12 Weeks)

• Gradual progression to full weight-bearing in supportive orthotics by 10-12 weeks
• Strengthening exercises for intrinsic foot muscles and peroneals
• Custom medial arch orthotics prescribed for long-term support

Return to Activity (3-6 Months)

• Low-impact activities (swimming, cycling) from 3 months
• Running and sports from 4-6 months once strength and proprioception restored
• Full recovery of function expected by 6-9 months in uncomplicated cases

Rehabilitation Milestones and Red Flags

• 2 weeks: wound healed, transition to boot, begin gentle ROM
• 6 weeks: radiographic evidence of early union, progress weight-bearing
• 3 months: full weight-bearing without support, near-normal gait
• Red flags: increasing pain at osteotomy site, wound breakdown, new neurological symptoms — investigate promptly with imaging and clinical review