Trochleoplasty for Patellar Instability

Indication. Symptomatic recurrent lateral patellar instability with severe high-grade trochlear dysplasia (Dejour type B or D) — a prominent supratrochlear spur with a crossing sign — in a skeletally mature patient, where an isolated soft-tissue reconstruction (MPFL) is predicted to fail because the bony deformity will overload the graft. Trochleoplasty is a salvage of anatomy, not a first-line stabiliser: routine instability with normal or mild dysplasia is managed by MPFL reconstruction alone. Absolute indications

• Recurrent lateral patellar instability with failed prior soft-tissue stabilisation (for example a failed MPFL reconstruction) in the presence of severe trochlear dysplasia.
• Severe high-grade trochlear dysplasia (Dejour B or D) with a massive supratrochlear spur that prevents the patella from engaging in early flexion. Relative indications
• Primary surgical intervention for recurrent instability in Dejour B/D dysplasia where the bony deformity is so severe that isolated MPFL reconstruction is deemed guaranteed to fail.
• A J-sign in early flexion driven by the prominent trochlear bump forcing the patella laterally. Contraindications.
• Absolute: an 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 with normal trochlear morphology.
• Relative: mild to moderate dysplasia (Dejour A or C without a prominent bump) where MPFL reconstruction alone usually suffices; a stiff knee or inability to comply with postoperative rehabilitation. The one decision that matters. A trochleoplasty creates a groove, but it does not pull the patella into it. In Dejour B or D the supratrochlear bump acts as a bony cam, levering the patella out in terminal extension; soft-tissue reconstruction alone cannot overcome this and the graft stretches and fails. The choice is therefore between an isolated MPFL (wrong in severe dysplasia) and a combined bony plus soft-tissue reconstruction:

Consent specifically for the learning-curve risks: chondral flap necrosis and rapid patellofemoral arthritis, arthrofibrosis and the possible need for manipulation, recurrent instability, hardware irritation, and the prolonged rehabilitation with delayed return to sport (6 to 9 months). Setup. Supine on a standard operating table with a lateral post or leg holder allowing full flexion and stability; a thigh tourniquet is applied but used only if necessary. General or spinal anaesthesia with an adductor canal or femoral nerve block for postoperative analgesia. Equipment: high-speed burr, sharp straight and curved osteotomes, absorbable anchors or transosseous sutures, and fluoroscopy.

The goal is to expose the entire trochlea, elevate a thin osteochondral flap, remove the prominent supratrochlear spur and deepen the central groove into a physiological V-shaped sulcus of about 138 degrees, then re-fix the flap recessed beneath the cartilage surface — almost always combined with an MPFL reconstruction, and a tibial tubercle osteotomy when alignment demands it. The exposure is laid out as the first step below (and in depth on the lateral parapatellar approach to the knee and medial parapatellar approach to the knee pages).

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Rehabilitation — cautious early range of motion protects the cartilage flap and prevents arthrofibrosis; weight bearing and brace weaning depend on any concurrent TTO. | Phase | Timing | Weight bearing & bracing | Motion & therapy | |-------|--------|--------------------------|------------------| | Early | 0 to 2 weeks | Weight bearing as tolerated in a hinged brace locked in extension (restricted if TTO performed) | Continuous passive motion or active-assisted ROM, usually 0 to 90 degrees; multimodal analgesia and cryotherapy | | Intermediate | 2 to 6 weeks | Progress to full weight bearing without brace as quad control returns | Progress to full ROM; isometric quads, straight-leg raises, closed-chain mini-squats; avoid open-chain extension against resistance | | Late | 6 to 12 weeks and beyond | — | Advance closed-chain strengthening and proprioception | | Return to sport | 6 to 9 months | — | Requires full ROM, no effusion, and isokinetic quad strength greater than 85 percent of the contralateral side |

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, producing a severe J-sign (lateral deviation of the patella in terminal extension). Soft-tissue reconstruction alone cannot overcome this bony lever; trochleoplasty removes the bump and eliminates the mechanical cam. Concomitant procedures are the rule. A trochleoplasty makes a groove but does not pull the patella into it. The MPFL is the primary soft-tissue checkrein against lateral subluxation in early flexion (0 to 30 degrees) and is stretched or ruptured in chronic dislocators, so a trochleoplasty is almost universally combined with an MPFL reconstruction.

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, providing a bony buttress against lateral patellar translation. The normal sulcus angle is approximately 138 degrees, and the patella engages the trochlea at about 20 to 30 degrees of knee flexion. Pathological anatomy in dysplasia. Trochlear dysplasia is characterised by loss of the normal concavity and by proximal prominence. The Dejour classification grades the deformity and the associated radiographic signs, and it is the classification that drives the decision to trochleoplasty — types B and D, with a supratrochlear spur, are the operative targets.

Radiographic signs (true lateral radiograph).

• Crossing sign: the deepest line of the trochlear groove crosses the anterior border of the femoral condyles, indicating the groove is flush with the condyles at that level.
• Supratrochlear spur (bump): a bony prominence at the proximal trochlea that physically pushes the patella out of the joint in full extension.
• Double contour sign: the anterior border of the medial condyle lies posterior to the anterior border of the lateral condyle, indicating a hypoplastic medial facet. Goal of trochleoplasty. A sulcus-deepening trochleoplasty removes the supratrochlear spur, deepens the central groove, and elevates the relative height of the lateral facet, allowing the patella to engage smoothly without being levered out by a proximal bump. The two techniques.
• Bereiter technique: elevates a thin osteochondral flap (3 to 5 mm) leaving the cartilage attached proximally, creates a new V-shaped cancellous bed, and depresses the flap into the bed, secured with transosseous sutures or anchors. This is the dominant contemporary technique.
• Dejour technique: elevates a thicker osteochondral block, removes the underlying bone, and fixes the block back with screws. Less commonly performed today owing to higher morbidity than the Bereiter flap technique. Key evidence. The largest reported series — Metcalfe and colleagues' 11-year experience of 214 Bereiter trochleoplasties — showed a very low redislocation rate (0.5 percent) and good long-term clinical outcomes, validating the thin osteochondral flap technique. Dejour's Lyon sulcus-deepening trochleoplasty, reported in patients with failed prior surgery, achieved excellent prevention of recurrent dislocation but carried a long-term risk of progressive patellofemoral osteoarthritis. Banke and colleagues' prospective minimum 2-year study of combined trochleoplasty and MPFL reconstruction reported 0 percent redislocation, confirming that isolated MPFL reconstruction in severe dysplasia leads to graft failure. Longo and colleagues' systematic review concluded the procedure is technically demanding with a steep learning curve but provides good clinical outcomes when reserved for severe dysplasia, with arthrofibrosis, chondral necrosis and progressive osteoarthritis the most significant complications — hence the strict indications.