MPFL Reconstruction

Indication. Recurrent lateral patellar instability - two or more dislocations with a torn or incompetent MPFL on MRI, objective instability (a positive apprehension sign and a J-sign), that has failed structured non-operative management (a brace, physiotherapy focused on the vastus medialis obliquus and hip abductors, and activity modification). MPFL reconstruction restores the primary soft-tissue checkrein that is torn in the great majority of first-time lateral dislocations. Assess the whole patient, not just the ligament. Before committing, characterise the bony morphology, because MPFL reconstruction does not change the bone: - Absolute indications - recurrent lateral patellar dislocation (two or more episodes) with a torn or incompetent MPFL; objective instability with positive apprehension and a J-sign confirmed on MRI; failed structured non-operative management; recurrent instability after a first dislocation associated with an osteochondral fragment or significant risk factors.

• Relative indications - first-time dislocation with a displaced osteochondral fracture requiring fixation, where the MPFL is addressed at the same sitting; a high-demand athlete with persistent functional instability despite rehabilitation; instability with correctable bony risk factors (combined a la carte); persistent instability after prior lateral release or distal realignment without medial reconstruction.
• Contraindications - active infection overlying or within the knee; established patellofemoral osteoarthritis where reconstruction may worsen medial overload (relative); an uncorrected major bony abnormality (high-grade trochlear dysplasia, grossly elevated TT-TG, marked patella alta) where MPFL reconstruction alone will predictably fail unless the bone is addressed; a skeletally immature patient with an open physis, where femoral fixation must avoid the distal femoral physis (use a physeal-sparing technique); and painful maltracking without true instability (a wrong diagnosis - reconstruction will not help patellofemoral pain alone). Measure the bony risk factors before you operate. MPFL reconstruction restores the soft-tissue checkrein but does not change the bone, so the classic risk factors (Dejour) must be quantified pre-operatively: - TT-TG distance (tibial tubercle to trochlear groove) - measured on superimposed CT or MRI axial slices. Normal is roughly less than 15 mm; greater than 20 mm is abnormal and an indication to consider a medialising (and/or distalising) tibial tubercle osteotomy. Values of 15-20 mm are a grey zone judged alongside other factors.
• Trochlear dysplasia (Dejour A-D) - high-grade dysplasia (types B-D), particularly with a prominent supratrochlear spur, is the indication to consider a sulcus-deepening trochleoplasty (full morphology in Background & Evidence).
• Patellar height - Caton-Deschamps index greater than 1.2 or Insall-Salvati ratio greater than 1.2 defines patella alta, which may warrant a distalising tubercle osteotomy. The one decision that matters - the a la carte approach (Dejour). Individualise the operation to the measured anatomy rather than applying one operation to every patient:

Consent specifically for recurrent instability (the commonest mode of failure when the bone is not addressed), stiffness or loss of flexion from over-tensioning, medial patellofemoral pain, a small risk of patellar fracture through fixation tunnels, and anteromedial numbness or a painful neuroma from saphenous nerve injury. Setup. Supine on a radiolucent table with a side support and a foot bump so the knee can be flexed and the leg externally rotated for medial access. The image intensifier must be available and able to obtain a true lateral of the knee. Tourniquet optional; if used, deflate before closure to secure haemostasis. General or regional anaesthesia, with examination under anaesthesia as a routine and informative first step.

The goal: confirm the instability under anaesthesia, harvest a gracilis graft, recreate the broad patellar footprint, identify the femoral insertion at Schottle's point on a true lateral, confirm favourable length-change before drilling, and tension the graft as a checkrein at 30-60 degrees of flexion - restoring stability without tethering the patella. The exposure and femoral landmark are laid out in full in the steps below.

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Rehabilitation | Phase | Timing | Immobilisation / loading | Therapy | |-------|--------|---------------------------|---------| | 1 | 0-2 weeks | Hinged brace, weight-bearing as tolerated, often locked in extension for ambulation | Immediate quadriceps sets, straight-leg raises, patellar mobilisation (no forced lateral glide); controlled flexion progressed to roughly 90 degrees by week 2 | | 2 | 2-6 weeks | Wean the brace as quadriceps control and gait normalise | Advance flexion towards full; closed-chain quadriceps and hip (gluteal/abductor) strengthening; avoid aggressive open-chain resisted extension and early patellofemoral loading | | 3 | 6 weeks to 6-9 months | Brace discarded | Progressive resistance, proprioception and neuromuscular re-education; restore symmetrical quadriceps strength and dynamic patellar control | | 4 | Return to sport | - | Running and agility commonly around 3-4 months; pivoting and contact sport typically around 4-6 months, only after passing functional and strength criteria | Multimodal analgesia, elevation and ice or compression control the effusion; monitor for a tense haemarthrosis. If a concomitant tibial tubercle osteotomy or trochleoplasty was added, follow the more protective osteotomy weight-bearing and range-of-motion protocol and delay return to sport until bony union is secure. Anatomic reconstruction restores stability in the great majority when technique is correct and the bony factors are addressed. Follow-up & warning signs - Wound and range-of-motion check at 2 weeks; progress review at 6 weeks and 3 months; a functional and return-to-sport assessment around 4-6 months; longer-term surveillance for patellofemoral pain or degeneration, especially if cartilage damage was present.

• Recurrent dislocation or apprehension suggests failure; persistent loss of flexion suggests over-tension or arthrofibrosis; acute patellar pain with loss of extension suggests a patellar fracture; and medial-sided pain with crepitus suggests medial overload from over-tensioning or malposition. Complications

The failed reconstruction. When instability recurs, ask the two questions that matter: was the femoral tunnel anatomic, and were the bony risk factors addressed? Re-image with CT and MRI to remeasure the TT-TG, patellar height and trochlear morphology and to assess the tunnel position. Revision almost always involves correcting the tunnel position and adding the bony procedure that was originally omitted - a tubercle osteotomy and/or a trochleoplasty.

Epidemiology & natural history. Acute lateral patellar dislocation is one of the most common acute knee injuries in adolescents and young adults, particularly in females and in athletes involved in pivoting and cutting sports. The medial patellofemoral ligament is torn in the great majority of first-time lateral dislocations, and without reconstruction a substantial proportion of patients experience recurrent instability - the risk rising sharply when the classic anatomic risk factors (trochlear dysplasia, patella alta, an elevated TT-TG and increased tilt) are present. The natural history and recurrence risk are defined by Fithian's cohort (see References). Pathoanatomy - the medial knee in three layers. The medial side is described in three layers (Warren and Marshall). The MPFL lies in layer 2, between the deep crural fascia (layer 1) and the joint capsule and deep medial collateral complex (layer 3); it is a discrete condensation of the medial retinaculum running transversely from the medial patella to the femur. Reconstruction recreates this layer 2 plane, which both restores anatomy and protects the saphenous nerve and the capsule during graft passage. - Patellar footprint - a broad attachment to the proximal half to two-thirds of the medial patellar border (the superomedial corner); wide and fan-shaped, which is why reconstruction usually recreates it with two limbs to the proximal medial patella. Fixation must stay in the proximal half to respect the bone and reduce fracture risk.

• Femoral footprint - the saddle between the adductor tubercle and the medial epicondyle, deep to the adductor magnus tendon and the superficial MCL origin. This footprint is the key to length-change behaviour: the native ligament is near-isometric, tightest in extension and early flexion and relaxing as the patella engages the trochlea. Schottle's point is the validated radiographic surrogate on a true lateral - approximately 1 mm anterior to the posterior femoral cortical line, 2.5 mm distal to the posterior origin of the medial femoral condyle, and proximal to the level of the posterior point of Blumensaat's line.
• Function and biomechanics - the primary passive restraint to lateral patellar translation in the first 0-30 degrees of flexion before bony engagement of the trochlea takes over, providing roughly 50-60 percent of the medial restraining force (Conlan et al.). It acts as a checkrein, not a primary stabiliser through full flexion - which is why tensioning technique and femoral position are critical.
• The trochlea - the bony groove that captures the patella from roughly 20-30 degrees of flexion onwards; dysplasia (a shallow, flat or convex groove with a supratrochlear spur) removes this bony containment and shifts the entire instability burden onto the MPFL.
• The extensor mechanism vector and TT-TG - the quadriceps-patella-patellar tendon line of pull has a lateral vector (the Q-angle); the TT-TG distance quantifies lateralisation of the tubercle relative to the groove, so a high value increases the lateralising force the MPFL must resist.
• Neurovascular structures at risk - the saphenous nerve and its infrapatellar branch cross the medial knee superficially and are at risk during medial incisions and subcutaneous graft passage (causing numbness and painful neuroma); the medial superior genicular vessels lie near the femoral footprint; and the distal femoral physis in adolescents lies just proximal to the femoral footprint, so femoral fixation must be placed distal to the physis or a physeal-sparing technique used. Patellar height indices. Two ratios define patella alta: the Caton-Deschamps index (patellar articular surface length related to the articular surface-to-tibial plateau distance), where a value greater than 1.2 defines alta; and the Insall-Salvati ratio (patellar tendon length divided by patellar bone length), where a ratio greater than 1.2 suggests alta (less than 0.8 suggests baja). Alta delays engagement of the patella in the trochlea, prolonging the unstable arc, and may warrant a distalising tubercle osteotomy. Trochlear dysplasia - the Dejour classification.

Key evidence. The technique and its pitfalls rest on a small, well-defined evidence base. Schottle defined and validated the radiographic femoral insertion centre that bears his name, making reproducible femoral tunnel placement possible. Stephen showed that the femoral attachment - not the patellar attachment - governs graft length-change, and that a proximal or anterior tunnel over-tensions the graft in flexion; this is the basis for the on-table length-change check. Conlan established the MPFL as the principal medial restraint (roughly 50-60 percent of the restraining force). Dejour's anatomic-radiographic study defined trochlear dysplasia, an elevated TT-TG and patella alta as the measurable bony risk factors and gave the numeric thresholds (TT-TG 20 mm, Caton-Deschamps 1.2) that drive the a la carte approach. Shah's systematic review quantified the complication burden (around 26 percent) and identified femoral malposition and patellar fracture as key avoidable failure modes. Nelitz supported adding a trochleoplasty to MPFL reconstruction in high-grade dysplasia.