MPFL Reconstruction - 10 Marks PG Answer

Definition

Anatomy

Axial MRI of the patellofemoral joint demonstrating the medial soft tissue structures and MPFL attachment zone

Patellofemoral Instability - Predisposing Factors (TAMP mnemonic)

• Trochlear dysplasia (most important bony risk factor)
• Alta - Patella alta (Caton-Deschamps index >1.2)
• Malalignment - Increased TT-TG distance (>20 mm = abnormal)
• Positional - Hyperlaxity, Q angle >20°, female sex, age <15 years

Indications for MPFL Reconstruction

Absolute Indications

• Recurrent patellar dislocation (≥2 episodes) with failure of conservative treatment
• First-time dislocation with associated osteochondral fracture requiring fixation
• Ongoing symptoms of patellar instability after appropriate non-operative management

Relative Indications

• First-time dislocation in elite athletes
• Mild bony malalignment (TT-TG 15-20 mm) - combined with bony procedure
• Symptomatic patellar subluxation refractory to physiotherapy

Contraindications

• Significant trochlear dysplasia (Dejour C/D) - needs trochleoplasty first or combined
• TT-TG >20 mm - tibial tubercle transfer (TTT) required concomitantly
• Patella alta (Caton-Deschamps >1.4) - anteromedial TTT or distalization needed
• Uncorrected bony malalignment as isolated MPFL reconstruction will fail

Pre-operative Assessment

Clinical

• Apprehension test (positive at 0-30° flexion)
• J-sign (patella jumps laterally at terminal extension)
• Q-angle measurement (>20° abnormal)
• Hyperlaxity assessment (Beighton score)

Investigations

• X-ray (AP, lateral, skyline/axial): Patella alta (Caton-Deschamps, Insall-Salvati ratio), trochlear dysplasia, crossing sign, supratrochlear spur
• CT scan: TT-TG distance (normal <15 mm, borderline 15-20 mm, abnormal >20 mm), torsional alignment
• MRI: MPFL tear location, chondral injury, trochlear morphology, bone edema ("kissing contusion" at lateral trochlea and medial patella)

Surgical Technique

Graft Options

Step-by-Step Technique

• Supine with tourniquet; knee over bolster; fluoroscopy available
• Arthroscopy first to assess chondral surfaces and confirm diagnosis

• Gracilis or semitendinosus via 2-3 cm incision posteromedial to tibial tuberosity
• Prepare to ~180-200 mm length, tubularize with whip stitch
• Double the graft for adequate strength

• 3 cm incision over medial border of patella
• Identify the superomedial patella - attachment is at the junction of the proximal 1/3 and middle 1/3
• Suture anchors (most common): Two 1.8-3.5 mm anchors placed in the medial patella
• OR Bone tunnels: Two converging tunnels in the patella (risk of iatrogenic fracture if <25 mm bone width)
• The graft is split into two limbs for double-bundle attachment

Schottle's point is located on lateral fluoroscopy: anterior to the posterior femoral cortex line, at the level of the posterior edge of Blumensaat's line, 1 mm proximal to a line drawn along the posterior cortex of the medial femoral condyle.

• 3 cm incision over medial femoral condyle
• Dissect between the superficial MCL and the vastus medialis
• Under fluoroscopic guidance, place a guide wire at Schottle's point
• Confirm isometry: anchor a suture at the femoral point, tie to patella, and check tension is equal from 0-90° flexion
• Drill a 7-8 mm tunnel; dock the graft with an interference screw at 30-60° knee flexion
• Fixation tension: patella should allow <1/4 width lateral translation; tracking must be smooth

• Fix the graft with knee at 30-60° flexion (patella fully engaged in trochlea at 60°)
• Graft should be non-isometric: slightly tighter in extension, looser in deeper flexion - avoid over-constraint
• Final check: patella tracks centrally with no excessive medial or lateral tilt

• Deep fascia repair, subcutaneous and skin closure
• Drain optional

Flowchart

Complications

Intraoperative

• Patellar fracture (bone tunnel technique; incidence 0.9-3.6%)
• Femoral guide-wire misplacement - nonanatomic graft leads to over-constraint

Early Postoperative

• Infection, haematoma
• Deep vein thrombosis
• Wound complications

Late Complications

Rehabilitation Protocol

Outcomes

• Success rates: 83-93% across all techniques
• Return to prior activity: ~90% of patients
• Re-dislocation rate with anatomic technique: <2-4%
• Key predictor of failure: nonanatomic femoral placement (accounts for 50% of graft failures)

Special Considerations

Skeletally Immature Patients

• Avoid drilling through the distal femoral physis
• Femoral fixation around the adductor magnus tendon (physeal-sparing technique) instead of a bone tunnel
• Tibial tubercle transfer deferred until skeletal maturity

Concomitant Procedures

• TT-TG >20 mm: Anteromedial tibial tubercle transfer (Fulkerson osteotomy) + MPFL
• Trochlear dysplasia (Dejour B/C/D): Trochleoplasty + MPFL
• Patella alta: Tubercle distalization or Caton-Deschamps correction + MPFL
• Osteochondral fragment: MPFL + fragment fixation or microfracture

Key Points to Remember for Exam

1. MPFL provides 50-60% of medial restraint to lateral patellar translation
2. Schottle's point is the femoral isometric attachment - the most critical step
3. Graft fixed at 30-60° flexion to ensure correct length-tension relationship
4. Over-tensioning → medial patellofemoral arthritis (most common pitfall)
5. TT-TG >20 mm mandates bony realignment in addition to MPFL reconstruction
6. Patellar fracture risk with bone tunnels - use suture anchors if patella width <25 mm
7. Overall outcomes are excellent: >90% return to sport, <4% re-dislocation with anatomic technique