Trochleoplasty for Patellar Instability

Surgical Indications

Absolute Indications

• Recurrent lateral patellar instability with failed prior soft-tissue stabilisation (e.g., failed MPFL reconstruction) in the presence of severe trochlear dysplasia.
• Severe high-grade trochlear dysplasia (Dejour type B or D) with a massive supratrochlear spur (bump) that prevents the patella from engaging in early flexion.

Relative Indications

• Primary surgical intervention for recurrent instability in a patient with Dejour B/D dysplasia where the bony deformity is so severe that isolated MPFL reconstruction is deemed guaranteed to fail.
• J-sign in early flexion driven by the prominent trochlear bump forcing the patella laterally.

Contraindications

Absolute:

• Open distal femoral physis (wait for skeletal maturity).
• Established patellofemoral osteoarthritis (Outerbridge grade 3 or 4 of the patella or trochlea).
• Isolated soft-tissue deficiency (normal trochlear morphology).

Relative:

• Mild to moderate dysplasia (Dejour type A or C without a prominent bump) where an MPFL reconstruction alone usually suffices.
• Stiff knee or inability to comply with postoperative rehabilitation.

Evidence for Trochleoplasty

Techniques

• Bereiter Technique: Elevates a thin osteochondral flap (3 to 5 mm) leaving the cartilage attached proximally, creating a new V-shaped cancellous bed, and depressing the flap into the bed. Secured with transosseous sutures or anchors.
• Dejour Technique: Elevates a thicker osteochondral block, removes underlying bone, and fixes the block back with screws. Less commonly performed today due to higher morbidity compared to the Bereiter flap technique.

Trochlear Dysplasia Anatomy

Normal Trochlea

The normal trochlea is a concave groove on the anterior distal femur. The lateral facet is higher and more prominent than the medial facet, providing a bony buttress against lateral patellar translation. The normal sulcus angle is approximately 138 degrees. The patella engages the trochlea at about 20 to 30 degrees of knee flexion.

Pathological Anatomy in Dysplasia

Trochlear dysplasia is characterised by a loss of the normal concavity and proximal prominence.

• Dejour Classification:
  • Type A: Shallow trochlea. Sulcus angle greater than 145 degrees. Crossing sign present.
  • Type B: Flat trochlea with a prominent supratrochlear spur (bump). Crossing sign and supratrochlear spur sign present.
  • Type C: Convex lateral facet, medial facet hypoplastic. Crossing sign and double contour sign present.
  • Type D: Convex trochlea with a supratrochlear spur (cliff pattern). Crossing sign, double contour sign, and supratrochlear spur sign present.

Radiographic Signs

• Crossing Sign: On a true lateral radiograph, the deepest line of the trochlear groove crosses the anterior border of the femoral condyles. Indicates the groove is flush with the condyles.
• Supratrochlear Spur (Bump): A bony prominence at the proximal aspect of the trochlea. This bump physically pushes the patella out of the joint in full extension.
• Double Contour Sign: The anterior border of the medial condyle is seen posterior to the anterior border of the lateral condyle, indicating a hypoplastic medial facet.

Goal of Trochleoplasty

The goal of a sulcus-deepening trochleoplasty is to remove the supratrochlear spur, deepen the central groove, and elevate the relative height of the lateral facet, allowing the patella to engage smoothly without being levered out by a proximal bump.

Positioning and Preparation

Patient position: Supine on a standard operating table. A lateral post or leg holder is used to allow full flexion and stability. A thigh tourniquet is applied but used only if necessary. Anaesthesia: General or spinal anaesthesia. Regional blocks (adductor canal or femoral nerve) are excellent for postoperative pain control. Equipment: High-speed burr, sharp straight and curved osteotomes, absorbable anchors or transosseous sutures, fluoroscopy.

Bereiter Sulcus-Deepening Technique — Step-by-Step

Step 1: Approach and Exposure

A midline or lateral parapatellar skin incision is made. A standard lateral parapatellar arthrotomy or medial parapatellar arthrotomy is performed, depending on the need for concurrent procedures. The patella is everted or subluxated to fully expose the entire trochlea from the notch to the proximal synovial reflection.

Step 2: Marking the Flap

Using a sterile marker or electrocautery, mark the borders of the intended osteochondral flap. The margins typically extend from the intercondylar notch distally, along the margins of the medial and lateral facets, and proximal to the supratrochlear spur.

Step 3: Elevating the Osteochondral Flap

Using a sharp, thin, curved osteotome, begin elevating the osteochondral flap from distal (at the notch) to proximal. The flap must be 3 to 5 mm thick. Thinner flaps risk cartilage necrosis; thicker flaps are too stiff to bend into the new sulcus. The flap is elevated but left attached proximally via the intact periosteum and synovium, maintaining its blood supply.

Step 4: Deepening the Subchondral Bed (Burring)

Once the flap is elevated and protected, use a high-speed burr to deepen the exposed cancellous bone bed. Create a V-shaped sulcus with an angle of approximately 138 to 140 degrees. Remove the prominent supratrochlear spur entirely.

Step 5: Shaping and Depressing the Flap

If the elevated flap is too stiff to bend into the new V-shaped groove, it may require carefully controlled longitudinal scoring (cortico-cancellous weakening) on its undersurface, being extremely careful not to breach the cartilage. Depress the flap into the newly prepared bed.

Step 6: Flap Fixation

Secure the flap into the new sulcus. This is typically done using 2 to 4 absorbable suture anchors placed in the depth of the new groove, or via transosseous sutures passed through the lateral and medial condyles. The sutures are passed through the osteochondral flap and tied securely, pulling the flap down into the V-shape. Ensure no suture material or anchor is proud of the cartilage surface.

Step 7: Concurrent Procedures

A trochleoplasty is rarely performed in isolation.

• MPFL Reconstruction: Performed using a hamstring autograft or allograft to restore the medial restraint.
• Tibial Tubercle Osteotomy (TTO): Performed if the TT-TG distance is greater than 20 mm (medialisation) or if there is severe patella alta (distalisation).

Step 8: Assessment and Closure

Run the knee through a full range of motion. The patella should engage smoothly into the newly created trochlea in early flexion (by 20 to 30 degrees) without subluxation or abnormal tilt. The lateral retinaculum may be lengthened if tight, but routine release is avoided. Close the arthrotomy securely in layers.

Post-operative Protocol

Early Phase (Weeks 0-2)

• Weight Bearing: Generally allowed as tolerated in a hinged knee brace locked in extension, depending on concurrent procedures (e.g., TTO requires restricted weight bearing).
• Bracing: Hinged knee brace locked in extension for walking.
• Range of Motion: Early continuous passive motion (CPM) or active-assisted ROM is critical to prevent adhesions and nourish the cartilage flap. Usually limited to 0-90 degrees for the first 2-4 weeks.
• Analgesia: Multimodal pain management, regular cryotherapy.

Intermediate Phase (Weeks 2-6)

• Weight Bearing: Progress to full weight bearing without brace as quad control returns (if no TTO).
• Range of Motion: Progress to full ROM.
• Strengthening: Isometric quadriceps, straight leg raises, closed kinetic chain exercises (e.g., mini-squats). Avoid open kinetic chain extension against resistance.

Late Phase (Weeks 6-12 and beyond)

• Strengthening: Advance closed kinetic chain exercises. Begin proprioceptive training.
• Return to Sport: Return to pivoting or cutting sports is heavily delayed, typically 6 to 9 months post-operatively, requiring full ROM, no effusion, and isokinetic quadriceps strength greater than 85% of the contralateral side.

Special Considerations

The "Bump" and the J-Sign

In Dejour B and D dysplasia, the massive supratrochlear bump actively pushes the patella anteriorly and laterally out of the groove as the knee reaches full extension. This creates a severe "J-sign" (lateral deviation of the patella in terminal extension). Soft tissue reconstruction (MPFL) alone cannot overcome this bony lever; the ligament will inevitably stretch out and fail. Trochleoplasty removes the bump, eliminating the mechanical lever.

Concomitant Procedures are the Rule

A trochleoplasty creates a groove, but it does not pull the patella into it. The MPFL is the primary soft-tissue checkrein against lateral subluxation in early flexion (0-30 degrees). In chronic dislocators, the MPFL is stretched or ruptured. Therefore, a trochleoplasty is almost universally combined with an MPFL reconstruction to ensure stability.