Extensor Mechanism Problems

Patella Dislocation

• 1st time dislocations: Equal in men and women
• Recurrent dislocations: More common in women

Risk Factors

• Patella Alta – Patella does not engage trochlea till late in flexion
• Trochlea Dysplasia – Shallow trochlea does not contain patella well
• Increased Q angle
• Lateralised tibial tubercle
• Patella tilt
• Connective tissue disorders
• Hypermobility syndromes

Mechanism

• Non-contact pivot with knee near extension

Examination

• Swelling: If gross, consider OC fracture
  • Lack of hint tissues so lax, patella dislocates without MPFL damage
• Medial patella border pain: Torn MPFL
• Quads inhibition: Weak straight leg raise
• Apprehension when patella moved laterally
• Patella translation: How far across does patella move?
  • Medial patella border should not translate further than lateral trochlea groove
• Lateral patella tilt:
  • Lateral border patella should not be able to tilt horizontally
  • Ability to do so indicates lateral retinacular tightness
• Q Angle Assessment
  • ASIS to centre of patella to tibial tubercle
  • Normal = Females 15 degrees; Men 10 degrees (+/- 5)
• Tubercle Sulcus Angle:
  • Angle between centre of trochlea sulcus and tubercle at 90 deg flexion
  • Should be zero (i.e., tubercle should lie directly under sulcus)
  • This is a clinical way of assessing if tubercle is lateralised
• Limb Version:
  • Anteversion or femoral internal torsion can cause maltracking
  • Assess in prone position
  • Increased internal rotation indicates torsion or anteversion
• J Sign:
  • When the patella lies laterally in extension and flexion causes it to ‘pop back’ into sulcus visibly
  • Indicative of patella alta

Imaging

• XRays:
  • AP and lateral should be full weight bearing views – relaxes Quads
  • Patella height calculated on true lateral
    • 3 common methods:
      • Insall-Salvetti Ratio (1.0): Patella tendon length: Length of patella
      • Blackburn-Peel Ratio (0.8): Distance from a line perpendicular to the joint line to inferior pole patella: Length patella articular surface
      • Blummensat’s line: Inferior pole lies at Blummensat’s in 30 deg flexion
• Trochlea Shape:
  • Plain XR perfect lateral view allows assessment
  • Three lines – MFC, LFC, and Trochlea groove are visible
  • Trochlea should be below – if crosses either, is a positive crossover sign
  • Visible as anterior continuation of Blummensat’s
• Axial Imaging:
  • CT scan is best – cuts at prox & distal femur and tubercle & distal tibia
  • Look for femoral version, trochlea dysplasia, TTG, and Patella tilt angle
    • 15 deg anteversion normal
  • TTG – distance between longitudinal lines through the sulcus and tubercle
    • 15-20mm is borderline; >20mm is abnormal
  • Patella tilt:
    • Angle between a line through patella body and another along the posterior condyles
    • Should be about parallel – >20 degrees abnormal

Management of Patella Dislocation

Acute First-Time Dislocations

• Aspirate if tense – comfort and to check for fat
• OC fracture occurs on the medial facet typically as the patella relocates
• Non-Operative:
  • No evidence supports primary MPFL reconstruction, therefore non-operative is first line for almost all
  • Splinting for comfort in extension
  • ROM and Quads rehab, especially VMO
  • Limb control under pelvis is actually more important – core therapy, gluteals, etc.
  • Proprioception and sport-specific training
  • McConnell Taping can help with this
  • Orthotics for very pronated feet
• Operative:
  • For fixable OC fragments or those that need removal
  • Primary MPFL recon – consider in elite athletes, etc.

Recurrent Dislocation

• Operative Treatment is warranted if problematic
  • Address risk factors:
    • Patella Alta – distalising tibial tubercle osteotomy
    • Lateralised tubercle – medialising osteotomy
    • Dysplastic trochlea – trochleaplasty
    • Isolated patella tilt (rare) – lateral release
    • Excessive femoral version or torsion – corrective osteotomy
    • MPFL reconstruction:
      • Can be done alone if no other risk factors or to supplement another operation
      • Allograft or autograft
      • Hamstrings; Achilles most common

Patella and Quads Tendon Ruptures

Mechanism

• Eccentric loading of the flexed knee
• Landing from a jump; missing a step
• Rarely a direct blow

Risk Factors

• Prior Steroid injection or anabolic steroids for both
• For Quads:
  • Gout; Renal failure; Diabetes; SLE; Rheumatoid, etc.
• Patella tendon: Younger people, Quads: Older (over 40 years)

Pathoanatomy

• Angiofibroblastic tendinosis
• Mucoid Degeneration
• Pseudocyst formation at bone insertion
• Rupture usually at bony attachment for both
• Quads tendon is made of 4 layers, therefore more partial ruptures

Diagnosis

• Typical history of mechanism or risk factors
• Examination: Gap, swelling, unable to SLR
• Imaging: XR (baja or alta), US, MRI

Management

• Non-Operative:
  • For partial ruptures that can SLR
  • 6 weeks in knee brace followed by ROM and strengthening program
• Operative:
  • Drill holes and locking sutures or suture anchors
  • Protective wire or heavy suture
  • Knee should bend to 90 degrees intra-operatively

Chronic Ruptures

• Patella:
  • Mobilise Quads to free up proximally migrated patella
  • Reinforce with hamstrings or fascia lata autograft or allograft
  • Harvest contralateral BTB graft
• Quadriceps:
  • VY plasty
  • Hamstrings, fascia lata, allograft for augmentation

Patella and Quadriceps Tendinopathy

Pathoanatomy

• Angiofibroblastic mucoid degeneration
• Deep surface and medial fibres most commonly affected
• Due to poor blood supply

Mechanism/Risk Factors

• Repetitive sports, especially jumping, is typical (Jumper’s knee)
• Patella tendinopathy: Young people, quads: Older people
• Same metabolic risk factors in quads as for rupture

Diagnosis

• Typical history – during or after activity
• Examination:
  • Focal tenderness and reproducibility with stressing
  • Tendon thickening
• Imaging:
  • Associated bone spurs on XR
  • Main MRI finding is tendon thickening but high signal may be present

Management

• Non-Operative:
  • Activity modification
  • Eccentric exercises
  • Proprioceptive therapy
  • Autologous Platelet injections – some studies support this
• Operative:
  • Tendon debridement and excision of degenerate tissue
  • Stimulation of healing by decorticating adjacent bone surfaces