Microfracture and Bone-Marrow Stimulation for Osteochondral Lesions of the Talus

Surgical Indications

Absolute Indications

• Symptomatic OLT less than 1.0-1.5 cm squared with failed non-operative treatment for greater than 3-6 months
• Lesions with unstable cartilage flaps causing mechanical symptoms (locking, catching)
• Contained lesions with intact subchondral shoulders allowing clot containment

Relative Indications

• Smaller lesions in low-demand patients where quick recovery is prioritised over hyaline cartilage restoration
• Lesions in the anterior two-thirds of the talar dome accessible by standard anterior arthroscopy
• Patients who understand the fibrocartilage nature of the repair and accept potential later revision

Contraindications

Absolute:

• Lesion size greater than 1.5 cm squared or cystic depth greater than 5-7 mm — these require OATS, allograft or scaffold
• Uncontained lesions with loss of the medial or lateral shoulder — the marrow clot will not be contained
• Active ankle infection or systemic inflammatory disease flare

Relative:

• High-demand athletes with lesions greater than 1 cm squared — consider OATS from the outset for better long-term durability
• Extensive subchondral oedema (greater than 50% of talar dome on MRI) — higher failure rate with microfracture alone
• Posterior lesions requiring osteotomy in patients with poor bone quality or medical comorbidities

Evidence for Marrow Stimulation

Short-Term Outcomes

• Microfracture produces fibrocartilage fill in 60-80% of cases at second-look arthroscopy
• Clinical success (good to excellent AOFAS scores) reported in 70-85% at 2 years across multiple series
• Lesions less than 1 cm squared have significantly better outcomes than lesions 1-1.5 cm squared

Long-Term Durability Concerns

• Outcomes decline after 5 years, with 30-50% of patients showing deterioration in pain and function by 10 years
• Larger lesions (greater than 1 cm squared), cystic lesions, and athletes have higher failure rates
• Subchondral cyst formation and persistent bone marrow oedema are common radiographic findings at mid-term follow-up

Comparison with Alternative Techniques

• OATS provides hyaline cartilage restoration with better long-term durability for lesions greater than 1.5 cm squared but requires donor-site morbidity and open arthrotomy or osteotomy
• Allograft and scaffold techniques (e.g., BioCartilage, AMIC) are emerging options for larger lesions without donor-site morbidity, though long-term data are still maturing
• A systematic review of 52 studies (Hannon 2020) found no significant difference in clinical scores between microfracture and OATS at 2 years, but OATS showed superior outcomes at 5+ years for larger lesions

Classification Systems

Berndt-Harty Radiographic Classification (1959)

• Stage I: subchondral compression fracture, no displacement
• Stage II: partial osteochondral fragment detachment
• Stage III: complete detachment, non-displaced
• Stage IV: displaced osteochondral fragment
• Stage V: subchondral cyst formation (added later)

Hepple MRI Classification (1999)

• Stage I: cartilage injury only, intact subchondral plate
• Stage II: cartilage injury with subchondral fracture and oedema
• Stage III: detached osteochondral fragment, non-displaced
• Stage IV: displaced osteochondral fragment
• Stage V: subchondral cyst formation

Clinical utility: Hepple staging guides treatment. Stage I-II lesions with intact shoulders are ideal for microfracture. Stage V cystic lesions and stage IV displaced lesions often require grafting.

Preoperative Imaging Workup

Weight-Bearing Radiographs

• AP, lateral and mortise views to assess joint alignment, loose bodies and gross bony architecture
• May miss small or posterior lesions — sensitivity approximately 50-60% for OLT

CT Scan

• Essential for surgical planning: defines lesion size in three planes, subchondral plate integrity, cystic extent and shoulder containment
• Coronal and sagittal reformats critical for deciding anterior arthroscopy versus medial malleolar osteotomy
• Measure lesion area: length times width on the largest coronal and sagittal slices

MRI

• Gold standard for cartilage status, subchondral oedema volume and associated soft-tissue pathology
• Assess lesion containment: a stable cartilage rim greater than 2-3 mm around the defect is required for clot containment
• Quantify subchondral oedema: extensive oedema (greater than 50% of talar body) predicts poorer microfracture outcomes

Decision Threshold

Lesions less than 1.0-1.5 cm squared with contained shoulders and minimal cystic change proceed to microfracture. Lesions greater than 1.5 cm squared, cystic depth greater than 5 mm, or uncontained shoulders are referred for OATS, allograft or scaffold discussion.

Talar Dome Anatomy Relevant to Microfracture

Osteochondral Unit

• Hyaline cartilage (2-3 mm thick) rests on calcified cartilage layer (tidemark)
• Subchondral plate (0.5-1 mm) separates cartilage from cancellous bone
• Microfracture penetrates the subchondral plate to allow marrow elements (mesenchymal stem cells, growth factors) to fill the defect and form fibrocartilage

Vascular Supply

• Talar dome blood supply from posterior tibial, peroneal and anterior tibial arteries via intraosseous anastomoses
• Subchondral plate disruption during microfracture recruits these vessels — excessive disruption risks osteonecrosis or cyst formation

Safe Intervals for Anterior Arthroscopy

• Anteromedial portal: medial to tibialis anterior tendon, lateral to saphenous vein and nerve
• Anterolateral portal: lateral to peroneus tertius, medial to superficial peroneal nerve (identify with ankle plantarflexion and inversion)
• The superficial peroneal nerve is the most commonly injured structure in anterior ankle arthroscopy — transillumination and careful portal placement reduce risk to less than 1%

Approach Selection

Standard Anterior Arthroscopy (Most Lesions)

• Anteromedial and anterolateral portals
• 2.7 mm or 4.0 mm 30-degree and 70-degree arthroscopes
• Ankle distraction (non-invasive or invasive) improves access to the talar dome
• Plantarflexion brings anterior talar dome lesions into view; dorsiflexion improves posterior access

Medial Malleolar Osteotomy (Posteromedial Lesions)

• Indicated when the lesion lies in the posterior one-third of the medial talar dome and cannot be reached perpendicularly through anterior portals
• Oblique osteotomy starting 1 cm above the joint line, directed toward the intercollicular groove of the medial malleolus
• Protects the posterior tibial tendon (retracted posteriorly) and the deltoid ligament origin
• After lesion treatment, the osteotomy is reduced anatomically and fixed with two 4.0 mm partially threaded cancellous screws (or tension band wiring in poor bone)

Posteromedial Portal (Alternative)

• Useful for posterior lesions without osteotomy
• Requires 70-degree scope and careful portal placement between flexor hallucis longus and the neurovascular bundle
• Higher technical demand and risk to the tibial nerve

Positioning and Preparation

Patient position: Supine on radiolucent table. Knee flexed 90 degrees over a bump or leg holder. Ankle in neutral to slight plantarflexion. Non-invasive ankle distractor applied.

Anaesthesia: General or spinal with regional block (popliteal + saphenous). Tourniquet applied to thigh (250-300 mmHg) or calf (200-250 mmHg). Prophylactic antibiotics administered.

Consent: Discuss lesion size and expected fibrocartilage repair, risk of incomplete fill or cyst formation (10-20%), persistent pain (15-25%), need for later revision (OATS or fusion in 5-15% at 5-10 years), and rehabilitation timeline (NWB 2-6 weeks, sport 4-6 months).

Anterior Arthroscopic Microfracture — Step-by-Step

Step 1: Portal Establishment and Diagnostic Arthroscopy

Establish anteromedial portal under direct vision with 18-gauge needle localisation. Introduce 2.7 mm or 4.0 mm 30-degree arthroscope. Establish anterolateral portal under direct vision, avoiding the superficial peroneal nerve (transilluminate with ankle plantarflexed and inverted).

Perform systematic diagnostic arthroscopy: inspect the entire talar dome, tibial plafond, gutters, and syndesmosis. Document lesion location, size, cartilage status, and any loose bodies. Probe the lesion to assess stability of the cartilage rim and subchondral plate.

Step 2: Lesion Debridement to Stable Rim

Using a combination of curettes, shavers and radiofrequency ablation, debride all unstable cartilage and fibrous tissue from the lesion bed. Create a stable, perpendicular cartilage rim around the entire defect — this contains the marrow clot.

Remove the calcified cartilage layer completely down to the subchondral plate. The bed should appear white and avascular until the calcified layer is removed; once removed, punctate bleeding from cancellous bone is visible. This step is critical — residual calcified cartilage prevents clot adhesion and fibrocartilage formation.

Step 3: Microfracture / Microdrilling

Select an appropriate awl (2.5-3.5 mm diameter) or low-speed drill with a 2-3 mm Kirschner wire. Create holes perpendicular to the lesion surface, 3-4 mm apart, 2-4 mm deep. The goal is to penetrate the subchondral plate without excessive depth that would weaken it or cause collapse.

Work from the periphery toward the centre. After each hole, confirm bleeding by releasing the tourniquet briefly or observing marrow elements extruding. If the subchondral plate feels soft or the lesion is borderline in size, consider adding a scaffold (BioCartilage, AMIC) to augment the repair.

Avoid thermal necrosis from high-speed drilling. Power microdrilling should be performed at low RPM with continuous irrigation. Manual awl tapping is often preferred for precise depth control.

Step 4: Verification and Closure

Release the tourniquet and confirm active bleeding from each microfracture hole. The lesion bed should fill with a stable marrow clot within 5-10 minutes. If the clot is unstable or the lesion is large, consider scaffold augmentation.

Remove all instruments. Close portals with absorbable suture or Steri-Strips. Apply a well-padded posterior splint or controlled ankle motion (CAM) boot with the ankle in neutral.

Postoperative Rehabilitation Protocol

Phase 1: Protection (0-2 or 0-6 weeks)

• Non-weight-bearing in CAM boot or splint for 2 weeks (small contained lesions) to 6 weeks (larger lesions or osteotomy)
• Ankle range of motion exercises begin at 1-2 weeks (dorsiflexion/plantarflexion only, no inversion/eversion)
• Oedema control: elevation, compression, cryotherapy
• If medial malleolar osteotomy performed: NWB for 6 weeks, then progressive weight-bearing with radiographic confirmation of osteotomy healing

Phase 2: Progressive Loading (3-8 weeks)

• Begin partial weight-bearing at 25% body weight, advancing 25% weekly as tolerated
• Transition to full weight-bearing by 6-8 weeks in supportive brace
• Introduce stationary cycling and pool therapy (once incisions healed)
• Proprioception training begins once full weight-bearing achieved

Phase 3: Functional Recovery (2-6 months)

• Progressive strengthening and balance exercises
• Sport-specific drills begin at 3-4 months
• Return to running at 4 months if pain-free with full ROM and strength
• Return to competitive sport at 5-6 months after functional testing clearance

Complications

Early Complications (less than 6 weeks)

• Portal site infection or wound dehiscence (less than 1%)
• Iatrogenic chondral injury to tibial plafond (rare with careful technique)
• Deep vein thrombosis (prophylaxis considered in high-risk patients)
• Medial malleolar osteotomy non-union or malunion (2-5% — prevented by anatomic reduction and rigid fixation)

Intermediate Complications (6 weeks to 1 year)

• Subchondral cyst formation (10-20% on MRI at 1 year) — associated with larger lesions and excessive microfracture depth
• Persistent bone marrow oedema (30-50% at 1 year) — correlates with ongoing pain
• Incomplete fibrocartilage fill (20-40% at second-look arthroscopy)
• Stiffness and reduced dorsiflexion (common after prolonged immobilisation)

Late Complications (greater than 1 year)

• Deterioration of clinical outcome after 5 years (30-50% of patients) — fibrocartilage wear
• Progression to ankle osteoarthritis (higher in lesions greater than 1 cm squared or athletes)
• Need for revision surgery (OATS, allograft, or ankle fusion/arthroplasty in 5-15% at 10 years)

Outcomes and Comparison with Alternatives

Microfracture remains the first-line marrow stimulation technique for small contained OLT because of its technical simplicity, low morbidity and good short-term results. However, the fibrocartilage repair tissue is mechanically inferior to native hyaline cartilage and deteriorates over time. For lesions greater than 1.5 cm squared or in high-demand athletes, OATS or scaffold techniques offer superior long-term durability at the cost of increased surgical complexity and donor-site morbidity.