Patella Fractures - Orthopaedic Trauma - Lecture Slides, Slides of Orthopedics

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Patella Fractures & Extensor

Mechanism Injuries

Anatomy

• Largest sesamoid bone
• Thick articular cartilage proximally
• Articular surface divided into medial and lateral facets by longitudinal ridge
• Distal pole nonarticular

Anatomy

• Patellar Retinaculum
  • Longitudinal tendinous fibers
  • Patellofemoral ligaments
• Blood Supply
  • Primarily derived from geniculate arteries

Biomechanics

• The patella undergoes approximately 7 cm of

translation from full flexion to extension

• Only 13-38% of the patellar surface is in

contact with the femur throughout its range of

motion

Biomechanics

• The patella increases the moment arm about the knee - Contributes up to 30% increase in force with extension
• Patella withstands compressive forces greater than 7X body weight with squatting

Biomechanics

• Twice as much torque is needed to extend the knee the final 15 degrees than to extend from a fully flexed position to 15 degrees of flexion

History

• Direct blow to the anterior knee (dashboard injury)
• Fall from height
• Rapid knee flexion with quadriceps resistance

Physical Examination

• Pain, swelling, contusions, lacerations and/or

abrasions at the site of injury

• Palpable defect
• Assessment of ability to extend the knee

against gravity or maintain the knee in full

extension against gravity

Radiographic Evaluation

• AP & Lateral
  • Patella alta or baja
  • Note fracture pattern
    • Articular step-off, diastasis
• Special views
  • Axial or sunrise
• CT Scan

-Occult fractures

Radiographic Evaluation

• Bipartite Patella
  • Obtain bilateral views
  • Often involves superolateral corner
  • Accessory ossification center

Etiology

• Allows prediction of outcome
• Direct trauma
  • Dashboard injury
  • Increasing cases withpenetrating trauma
  • Often with comminution andarticular damage
• Indirect trauma
  • Violent flexion directedthrough the extensor mechanism against acontracted quadriceps
  • Results in simple, transversefractures

Classification

• Allows prediction of treatment
• Types
  • Transverse
  • Marginal
  • Vertical
  • Comminuted
  • Osteochondral

Nonoperative Treatment

• Indicated for nondisplaced fractures
  • <2mm of articular stepoff and <3mm of diastasis with an intact extensor mechanism
• May also be considered for minimally

displaced fractures in the elderly

• Patients with a extensive medical

comorbidities

Nonoperative Treatment

• Long leg cylinder cast for 4-6 weeks
  • May consider a knee immobilizer for the elderly
• Immediate weightbearing as tolerated
• Rehabilitation includes range of motion

exercises with gradual quadriceps

strengthening

Operative Treatment

• Goals
  • Preserve extensor function
  • Restore articular congruency
• Preoperative Setup
  • Tourniquet
    • Prior to inflation, gently flex the knee
• Approach
  • Longitudinal midline incision recommended
  • Transverse approach alternative
  • Consider future surgeries!

Operative Techniques

• Modified tension band wiring
• Lag-screw fixation
• Cannulated lag-screw with tension band
• Partial patellectomy
• Patellectomy

Modified Tension Band Wiring

• Transverse, noncomminuted fractures
• After reduction, fracture is fixed with two parallel, 1.6mm Kirschner wires placed perpendicular to the fracture
• 18 gauge wire passed behind proximally and distally

Modified Tension Band Wiring

• Wire converts anterior distractive forces to compressive forces at the articular surface
• Two twists are placed on opposite sides of the wire - Tighten simultaneously to achieve symmetric tension
• Repair any retinacular tears

Lag-Screw Fixation

• Indicated for stabilization of comminuted fragments in conjunction with tension band wiring or cerclage wires
• May also be used as an alternative to tension band wiring for transverse or vertical fractures

Lag-Screw Fixation

• Contraindicated for extensive comminution

and osteopenic bone

• Small secondary fractures may be stabilized

with 2.7mm or 3.5mm cortical screws

• Transverse or vertical fractures require 3.5mm

or 4.5mm cortical screws

• Retrograde insertion of screws may be technically easier

Cannulated Lag-Screw With Tension Band

• Fully threaded screws placed with a lag technique
• Wire through screws and across anterior patella in figure of eight tension band

Cannulated Lag-Screw With Tension Band

• Most stable construct
  • Screws and tension band wire combination eliminates both possible separation seen at the fracture site with modified tension band and screw failure due to excessive three point bending

Suture vs. Wire Tension Band

Gosal et al Injury 2001

• Wire v. #5 Ethibond
• 37 patients
• Reoperation 38% wire group vs. 6%
• Infection 3 pts wire group vs. 0

Patel et al, Injury 2000 McGreal et al, J Med Eng Tech, 1999

• Cadaveric models
• Quality and stability of fixation comparable to wire
• Conclude suture an acceptable alternative

Partial Patellectomy

• Indicated for fractures involving extensive comminution not amenable to fixation
• Larger fragments repaired with screws to preserve maximum cartilage
• Smaller fragments excised
  • Usually involving the distal pole

Partial Patellectomy

• Tendon is attached to fragment with nonabsorbable suture passed through drill holes in the fragment - Drill holes should be near the articular surface to prevent tilting of the tendon and minimize articular step-off
• Watch for patellar tilt!
• Load sharing wire passed through drill holes in the tibial tubercle and patella may be used to protect the repair and facilitate early range of motion