MPFL (Medial Patellofemoral Ligament) Repair/Reconstruction

MS Orthopaedics | 20 Marks Answer

1. Introduction

2. Anatomy

• Origin: Superomedial border of the patella (upper two-thirds)
• Insertion: Femoral attachment between the medial epicondyle and adductor tubercle ("saddle point" - Nomura point)
• Layer: Deep to the medial retinaculum, within the second anatomical layer
• Blood supply: Superior medial geniculate artery
• Length: Average 55 mm; width 30 mm
• Function: Primary checkrein to lateral patellar translation from 0-30° flexion. Role diminishes as trochlear engagement increases beyond 30°.

3. Mechanism of Injury

• Knee flexion + external rotation + valgus stress (non-contact mechanism)
• Direct blow to the medial patella
• The patella dislocates laterally, tearing the MPFL (most commonly at the femoral origin - 50%; midsubstance - 10%; patellar origin - 10%; multiple sites - 22%)

4. Risk Factors for Recurrent Instability (Predisposing Factors)

5. Clinical Assessment

• Acute episode: sudden knee giving way, pop, swelling, unable to bear weight
• Recurrent episode: repeated instability with less force

• Patellar apprehension test - positive (with lateral displacement at 30° flexion)
• Patellar glide test - excess lateral glide (>2 quadrants = abnormal)
• Patellar tilt test
• J sign - visible lateral jump of patella during terminal extension
• Medial patellar tenderness (MPFL insertion)
• Hemarthrosis (acute)

• X-ray: AP, lateral, and Merchant/sunrise views - assess patellar height, tilt, trochlear morphology
• MRI (gold standard): Identifies MPFL tear location, osteochondral injuries, trochlear dysplasia; articular cartilage injury seen in 94% of cases
• CT scan: TT-TG distance measurement (>20 mm = surgical correction needed)

6. Indications for Surgery

• Acute first dislocation with a discrete, localized avulsion (patellar or femoral end) with good tissue quality
• Osteochondral fragment requiring fixation
• Associated ligamentous injury

• Recurrent lateral patellar instability (after two or more dislocations) - primary indication
• Failed conservative management after first dislocation
• High-demand athletes after first dislocation
• Poor tissue quality precluding primary repair
• Combined tear (midsubstance + end avulsion)
• In adolescents with trochlear dysplasia and a 31% failure rate with nonoperative treatment

• Medial instability or overtightening risk
• Significant patellofemoral arthritis
• TT-TG >20 mm (add tibial tubercle osteotomy)
• Severe trochlear dysplasia (may need trochleoplasty)

Note: Routine repair of torn medial stabilizing soft tissues in acute patellar dislocation is NOT recommended as a standard - it has not been shown to improve long-term outcome (Campbell's, 15th Ed).

7. Surgical Techniques

A. MPFL Primary Repair (Technique 65.1 - Campbell's)

1. Medial parapatellar incision
2. Explore the tear in the medial patellar retinaculum
3. Irrigate and explore the knee joint - remove/fix any loose osteochondral fragments
4. Repair disruption in the vastus medialis muscle belly or medial patellar retinaculum
5. Pay careful attention to VMO origin at femoral adductor tubercle - if retracted proximally, fibers are critical for preventing recurrent dislocation
6. Lateral release may be performed if indicated
7. Close in layers + knee immobilizer

B. MPFL Reconstruction (Preferred Procedure)

• Autograft (preferred):
  • Gracilis tendon (most common - 14-16 cm length available)
  • Semitendinosus tendon
  • Quadriceps tendon
  • Bone-patellar tendon-bone
• Allograft: Tibialis anterior, gracilis - used when autograft not available

• Supine, tourniquet, knee hanging free; C-arm fluoroscopy available

• 3-4 cm incision over pes anserinus (anteromedial tibia)
• Identify gracilis/semitendinosus at their insertion
• Harvest with open tendon stripper
• Prepare graft: clean of muscle, whip-stitch both ends (No. 0 or No. 2 FiberWire), double the graft if needed (folded gracilis = 4-5 mm diameter ideal)

• 1-2 cm medial border of patella - superomedial aspect
• Two diverging tunnels drilled in patella (2.5-3.5 mm drill, Beath pin) - superolateral and inferomedial convergence - ensuring no cortical breach (risk of patellar fracture)
• Alternative: suture anchors in patellar cortex
• Pass both limbs of graft through patellar tunnels (or anchor them)

• Identify femoral MPFL footprint - between the medial epicondyle and adductor tubercle (Nomura/saddle point)
• Confirmed with fluoroscopy: on lateral view, insertion is at the posterior cortex line, proximal to Blumensaat's line (Schöttle point)
• Drill a 7-8 mm femoral tunnel over a guidewire
• Femoral fixation achieved with:
  • Interference screw (bioabsorbable/metal)
  • Suture anchor
  • Endobutton

• Set tension with knee at 30° of flexion - this is critical
• With the knee at 30°, patella should be centrally located and 2 quadrants of lateral displacement allowed - do not overtighten (risk: medial cartilage overload and patellofemoral arthritis)
• Confirm with fluoroscopy that patellar tracking is correct
• Fix femoral end while maintaining tension

• Close retinaculum, subcutaneous tissue, skin in layers
• Drain optional

C. Combined Procedures (when needed)

8. Postoperative Rehabilitation

• Immobilizer for 10-14 days post-repair
• Palumbo-type brace at 2 weeks
• Stiff-legged resistance followed by short-arc knee extensions for quadriceps strengthening (3-4 months)
• Return to full sports when quadriceps strength reaches 90% of uninvolved side

9. Complications

10. Results / Outcomes

• Good to excellent results in 85-95% of patients after MPFL reconstruction
• Recurrence rate with reconstruction: <5-10% (vs. 49% recurrence after second dislocation with conservative treatment)
• Repair vs. reconstruction: reconstruction generally preferred for recurrent instability; direct repair for acute, discrete femoral/patellar avulsions shows comparable early results but higher long-term failure
• MPFL repair alone without addressing bony abnormalities (TT-TG >20 mm, trochlear dysplasia) has significantly higher failure rates
• Return to sport rates: ~85-90% in athletes

11. Summary Algorithm

Patellar Dislocation
        |
   ─────────────
   |            |
First time    Recurrent
   |            |
  No risk     ─────────────────────
  factors     |          |         |
   |          TT-TG     Normal    Trochlear
Conservative  >20mm     anatomy   dysplasia
treatment     |          |         |
          TTO +      MPFL recon  Trochleoplasty
          MPFL recon              + MPFL recon

1. MPFL is torn in 98% of lateral patellar dislocations - most commonly at femoral origin (50%)
2. MPFL is the primary static restraint (50-60%) to lateral patellar translation from 0-30°
3. Femoral tunnel: between medial epicondyle and adductor tubercle (Schöttle point on lateral X-ray)
4. Graft tensioned at 30° flexion - never overtighten
5. TT-TG >20 mm mandates tibial tubercle osteotomy
6. Reconstruction is superior to plication/repair for recurrent instability
7. Patellar fracture and medial cartilage overload are the two most feared complications