Updated: 9/9/2018

Patella Fracture

Topic
Review Topic
0
0
Questions
7
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0
Evidence
11
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0
Cases
4
Techniques
1
https://upload.orthobullets.com/topic/1042/images/patella alta with avulsion fx.jpg
https://upload.orthobullets.com/topic/1042/images/bipartite_patella.jpg
https://upload.orthobullets.com/topic/1042/images/kwires.jpg
https://upload.orthobullets.com/topic/1042/images/cann.jpg
https://upload.orthobullets.com/topic/1042/images/cannulated.jpg
Introduction
  • Epidemiology
    • incidence
      • patella fractures account for 1% of all skeletal injuries
    • demographics
      • male to female 2:1
      • most fractures occur in 20-50 year olds
  • Mechanism of injury
    • direct impact injury
      • occurs from fall or dashboard injury
        • causes failure in compression
    • indirect eccentric contraction
      • occurs from rapid knee flexion against contracted quads muscle
        • causes failure in tension
      • patella sleeve fracture
        • seen in pediatric population (8-10 year olds)
        • high index of suspicion required
  • Associated injuries
    • high-energy dashboard injuries are associated with femoral neck fracture, posterior wall acetabular fracture, or knee dislocation
  • Prognosis
    • osteonecrosis reported to occur in up to 25% but not found to affect clinical outcome
Anatomy
  • Osteology
    • patella is largest sesamoid bone in body
    • superior 3/4 of posterior surface covered by articular cartilage
      • articular cartilage thickest in body (up to 1cm)
    • posterior articular surface comprised of medial and lateral facets
      • lateral facet is larger
      • facets separated by vertical ridge
  • Soft tissue attachments
    • quadriceps tendon and fascia lata attach to anterosuperior margin
      • quadriceps tendon comprised of 3 layers
        • superficial layer formed from rectus femoris tendon
        • middle layer formed by vastus medialis and vastus lateralis tendons
        • deep layer formed by vastus intermedius tendon
    • patellar tendon attaches to inferior margin
  • Blood Supply
    • derives from anastomotic ring originating from geniculate arteries
    • most important blood supply to the patella is located at the inferior pol
Classification
  • Can be described based on fracture pattern 
    • nondisplaced
    • displaced
      • step-off >2-3mm or fracture gap >1-4mm
    • transverse
    • pole or sleeve (upper or lower)
    • vertical
    • marginal
    • osteochondral
    • comminuted (stellate)
Presentation
  • History
    • direct blow to knee or extensor mechanism injury
  • Physical exam
    • inspection
      • palpable patellar defect 
      • significant hemarthrosis
    • motion
      • unable to perform straight leg raise indicates failure of extensor mechanism 
        • retinaculum disrupted
        • can aspirate hemarthrosis and inject local anesthetic if patient unable to perform due to pain
    • provocative tests
      • perform saline load test to rule out open fracture
Imaging
  • Radiographs
    • recommended views
      • AP
      • lateral
        • best view to see transverse fx 
      • tangential
        • best view to see vertical fx 
    • findings
      • fracture displacement
        • degree of fracture displacement correlates with degree of retinacular disruption
      • patella alta
        • Insall-Salvati ratio <1
        • indicates disruption of patellar tendon
      • patella baja
        • Insall-Salvati ratio >1
        • indicates disruption of quads tendon
  • CT
    • obtain if suspicion for patellar stress fracture, nonunion, or malunion
  • MRI 
    • obtain MRI if child has normal xrays but is unable to straight leg raise
Differential
  • Bipartite patella 
    • may be mistaken for patella fracture 
    • affects 8% of population
    • characteristic superolateral position
    • bilateral in 50% of cases
Treatment
  • Nonoperative
    • knee immobilized in extension (brace or cylinder cast) and full weight bearing
      • indications
        • intact extensor mechanism (patient able to perform straight leg raise)
        • nondisplaced or minimally displaced fractures
        • vertical fracture patterns
      • early active ROM with hinged knee brace
        • early WBAT in full extension 
        • progress in flexion after 2-3 weeks
  • Operative
    • ORIF with tension band construct
      • indications
        • preserve patella whenever possible
        • extensor mechanism failure (unable to perform straight leg raise)
        • open fractures
        • fracture articular displacement >2mm
        • displaced patella fracture >3mm
        • patella sleeve fractures in children
    • partial patellectomy
      • indications
        • comminuted superior or inferior pole fracture measuring <50% patellar height ONLY if ORIF is not possible 
    • total patellectomy 
      • indications
        • reserved for severe and extensive comminution not amenable to salvage
Techniques
  • ORIF with tension band construct
    • approach
      • midline longitudinal incision centered over patella
      • expose articular surface either through fracture site or retinacular rents
      • can alternatively perform lateral parapellar arthrotomy and invertt patella if retinaculum is not damaged or if better visualization of articular surface is desired
    • soft tissue
      • avoid extensive soft tissue dissection to preserve blood supply and viability of skin flaps
    • bone work
      • remove devitalized fragments and loose bodies
      • retain as much of patella as possible
    • instrumentation
      • minifrag lag screw fixation for independent fragments
      • tension band using 0.062 K wires with figure of 8 wire
        • converts tensile forces generated by quads complex at anterior surface into compressive forces at articular surface
        • figure-of-8 typically constructed using 18-gauge stainless steel wire
          • difficult to manipulate and high reoperation rates due to painful hardware or wire migration
        • can alternatively use braided polyester suture
          • found to have 75% tensile strength of 18-gauge stainless steel wire
      • longitudinal cannulated screws combined with tension band wires shown to be biomechanically superior
      • circumferential cerclage wiring
        • good for comminuted fractures
      • interfragmentary screw compression supplemented by cerclage wiring
        • good for comminuted fractures
    • complications
      • painful hardware/anterior knee pain
        • important to tension wire at superior aspect of construct where more soft tissue coverage is available
        • consider using braided polyester suture as opposed to 18-gauge stainless steel wire
      • hardware failure
        • important to tension wire in 2 places to apply equivalent tension in both sides of construct
        • avoid overtensioning wire to prevent articular gapping or wire failure
        • avoid prominent cannulated screw tips that can cause wire failure
    • outcomes
      • modified anterior tension band wiring shown to produce best results
  • Partial patellectomy
    • approach
      • same as ORIF (see above)
    • soft tissue
      • reattach quads or patellar tendon
        • perform with transosseous tunnels or suture anchors with knee in hyperextension 
        • reattach as close to articular surface as possible
          • prevents patellar tilt and minimizes contact stresses
      • medial and lateral retinacular repair essential
    • bone work
      • remove devitalized fragments and loose bodies
      • retain as much of patella as possible
    • instrumentation
      • transosseous tunnels or suture anchors to rettach quads or patellar tendon
      • if necessary, reinforce with cerclage suture or wire from quads tendon to tibial tubercle
    • complications
      • weakness
    • outcomes
      • poor outcomes with removal of >40% patella
  • Total patellectomy 
    • approach
      • same as ORIF (see above)
    • soft tissue
      • restore integrity of extensor mechanism via imbrication
      • medial and lateral retinacular repair essential
      • consider advancing VMO
        • found to have better strength and outcomes
    • bone work
      • remove all bony fragments
    • complications
      • weakness
      • extensor lag
        • avoid by performing sufficient imbrication
    • outcomes
      • quadriceps torque reduced by 50%
Complications
  • Anterior knee pain
    • more common with ORIF
  • Symptomatic hardware (up to 50%) 
    • most common  
    • more common in open fractures, thought to be due to compromised soft-tissue envelope
  • Hardware Migration
    • has been associated with tension band wiring with K-wires 
  • Weakness
    • more common with partial or total patellectomy
  • Loss of reduction (22%)
    • increased in osteoporotic bone
  • Nonunion (<5%)
    • can consider partial patellectomy
  • Osteonecrosis (proximal fragment)
    • thought to be due to excessive initial fracture displacement
    • can observe these, as most spontaneously revascularize by 2 years
  • Infection
    • more common in open fractures
  • Stiffness
  • Hardware failure
    • rare
 
 

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Technique Guides (1)
Questions (7)
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(OBQ12.43) A 36-year-old female sustains a knee injury after falling from a ladder onto her flexed knee; she cannot do a straight leg raise after a lidocaine injection into her knee. A radiograph is shown in Figure A. Which of the following treatment options has been shown to have the best outcomes with this injury? Review Topic

QID: 4403
FIGURES:
1

Long leg cast

2%

(56/3392)

2

Hinged knee brace use with functional rehabilitation protocol

46%

(1574/3392)

3

Open treatment with internal fixation or excision with patellar tendon advancement

47%

(1603/3392)

4

Distal patellar resection and allograft reconstruction

1%

(31/3392)

5

Placement of a cerclage wire from patella to proximal tibia

3%

(112/3392)

ML 4

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PREFERRED RESPONSE 3
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(OBQ07.207) Partial patellectomy is the recommended treatment for which of the following injuries? Review Topic

QID: 868
1

Vertical patella fractures

1%

(7/917)

2

Bipartite patella

2%

(16/917)

3

Severely comminuted inferior pole fracture

93%

(853/917)

4

Stellate patella fracture

3%

(28/917)

5

Chronic quadriceps tendon rupture

1%

(8/917)

ML 1

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PREFERRED RESPONSE 3

(OBQ12.229) A 43-year-old male suffers a knee injury and undergoes the operation seen in Figures A and B. At his one-year follow-up appointment, the patient notes pain in the peri-patellar region that is aggravated by palpation and kneeling. Range-of-motion is from -5 degrees to 130 degrees. A merchant view is performed which shows no significant degenerative changes of the patellofemoral joint. Which of the following treatments would most likely alleviate his pain? Review Topic

QID: 4589
FIGURES:
1

Symptomatic treatment of his patellofemoral arthritis

1%

(37/4447)

2

Manipulation under anesthesia

0%

(15/4447)

3

Operative treatment of his non-union

1%

(26/4447)

4

Knee intrarticular corticosteroid injection

0%

(21/4447)

5

Removal of symptomatic hardware

97%

(4332/4447)

ML 1

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PREFERRED RESPONSE 5
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