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Updated: 5/6/2022

Patella Fracture

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Images alta with avulsion fx.jpg
  • summary
    • Patella Fractures are traumatic knee injuries caused by direct trauma or rapid contracture of the quadriceps with a flexed knee that can lead to loss of the extensor mechanism.
    • Diagnosis can be made clinically with the inability to perform a straight leg raise and confirmed with radiographs of the knee. 
    • Treatment is either immobilization or surgical fixation depending on fracture displacement and integrity of the extensor mechanism.
  • Epidemiology
    • Incidence
      • account for 1% of all skeletal injuries
      • 6-9% are open fractures
    • Demographics
      • male to female 2:1
      • most fractures occur in 20-50 year olds
  • Etiology
    • Pathophysiology
      • mechanism of injury
        • direct impact
          • due to fall, dashboard injury or other high energy mechanism
            • often causes comminuted fracture pattern with chondral damage
            • retinaculum may remain intact
        • indirect eccentric contraction
          • occurs from rapid knee flexion against contracted quadriceps muscle
            • causes failure in tension
            • often results in transverse fracture or inferior pole avulsion
            • retinacular injury is typical
          • patella sleeve fracture
            • seen in the pediatric population (8-10-year-olds)
            • high index of suspicion required
    • Associated conditions
      • orthopaedic conditions
        • femoral neck fracture
        • posterior wall acetabular fracture
        • knee dislocation
  • Anatomy
    • Osteology
      • patella is the largest sesamoid bone in the body
      • superior 3/4 of posterior surface covered by articular cartilage
        • articular cartilage thickest in body (up to 1cm)
        • inferior 1/4 devoid of cartilage
      • posterior articular surface comprised of two large facets (medial and lateral)
        • lateral facet is larger
        • each facet separated into smaller facets and divided by vertical ridge
      • bipartite patella (variably present)
        • usually superolateral
        • occurs in approximately 2-3% of population
    • Ligaments
      • medial patellofemoral ligament (MPFL)
        • origin between medial epicondyle and adductor tubercle on femur
        • attaches approximately to upper 2/3 of medial patella
        • acts as primary ligamentous restraint to lateral patellar translation
          • most effective from 0-30º of flexion before patella engages trochlear groove
    • Tendons
      • quadriceps tendon
        • quadriceps tendon and fascia lata attach to anterosuperior margin of patella
        • 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 pole of patella
      • retinaculum
        • formed by fascia lata, vastus medialis and vastus lateralis
        • contributes to strength of extensor mechanism
        • should be repaired at time of patellar fixation
    • Blood Supply
      • derives from anastomotic ring originating from geniculate arteries
        • lies anterior to quadriceps tendon and posterior to patellar tendon
      • most important blood supply to the patella is located at the inferior pole
    • Biomechanics 
      • patella increases power and mechanical advantage of extensor mechanism by 30-50% by displacing it anteriorly away from the center of rotation
      • during knee flexion, patella experiences tension from quadriceps and patellar tendon and compressive loads across posterior patella
  • Classification
    • Descriptive based on fracture pattern
      • Fracture pattern classification
      • Nondisplaced
      • Displaced (step-off >2-3mm or fracture gap >1-4mm)
      • Transverse
      • Pole or sleeve (upper or lower)
      • Vertical
      • Marginal
      • Osteochondral
      • Comminuted (stellate)
    • AO/OTA classification
      • 34-A: extra articular
      • 34-B: partial articular
      • 34-C: complete articular
    • History
      • direct blow to knee or extensor mechanism injury
    • Physical exam
      • inspection
        • palpable patellar defect
        • significant hemarthrosis
        • lacerations, abrasions in setting of open fracture
      • motion
        • inability to perform straight leg raise
          • extensor mechanism and retinaculum disrupted
          • can aspirate hemarthrosis and inject local anesthetic if patient unable to perform due to pain
      • provocative tests
        • saline load test can be performed to rule out concomitant knee joint involvement
  • Imaging
    • Radiographs
      • recommended views
        • AP
        • lateral
          • best view to see transverse fx
          • obtained with knee in 30º of flexion if possible
          • helps evaluate articular step-off
        • axial (sunrise/merchant views)
          • best view to see vertical fx
      • findings
        • fracture displacement
          • degree of fracture displacement correlates with degree of retinacular disruption
        • patella alta
          • Insall-Salvati ratio > 1.0
          • indicates disruption of patellar tendon
        • patella baja
          • Insall-Salvati ratio < 1.0
          • indicates disruption of quadriceps tendon
      • criteria dictating treatment
        • articular step-off > 2-3 mm and displaced fracture gap > 3 mm dictate operative management
    • CT
      • indications
        • suspected distal pole comminution
        • patellar stress fracture
        • nonunion
        • malunion
      • views
        • sagittal views particularly useful for visualizing distal pole comminution
      • findings
        • change in operative plan in 50% of cases with CT
        • improved understanding of fracture patterns
          • particularly true in distal pole fracture patterns that are unappreciated on plain radiographs
    • MRI
      • not typically indicated
  • Differential
    • Bipartite patella
      • may be mistaken for patella fracture
        • smooth, regular borders seen on radiographs
      • affects 2-3% of population
      • caused by failure to unite secondary ossific nucleus
      • characteristic superolateral position
      • bilateral in 50% of cases
  • Treatment
    • Nonoperative
      • knee immobilized in extension (knee immobilizer, hinged knee brace or cast) with full weight bearing
        • indications
          • intact extensor mechanism (patient able to perform straight leg raise)
          • nondisplaced or minimally displaced fractures
          • vertical fracture patterns
          • significant medical comorbidities
        • modalities
          • early active ROM with hinged knee brace
            • early WBAT in full extension
            • active & active assist ROM at 1-2 weeks with resistance exercises beginning at 6 weeks
        • outcomes
          • good or excellent results in >95% of patients with proper indications
    • Operative
      • open reduction and internal fixation (ORIF) 
        • indications
          • preserve patella whenever possible
          • extensor mechanism failure (unable to perform straight leg raise)
          • open fractures
          • fracture articular step-off > 2-3 mm 
          • displaced articular patella gap > 3 mm
          • loose bodies
          • osteochondral fractures
          • patella sleeve fractures in children
        • techniques
          • multiple techniques exist:
            • tension band construct
              • k-wires + wire
              • k-wires + suture
              • cannulated screws  + wire
              • cannulated screws + suture
            • plate/screws
              • mini-fragment plate
              • mesh plate
              • may be preferred over tension band in cases of significant articular sided comminution
            • cerclage wiring
              • used alone or as supplement to primary fixation
        • outcomes
          • high rates of union (>95%) despite technique 
            • rates of nonunion higher with open fracture
          • symptomatic hardware requiring removal is common
          • recommended postoperative protocol
            • WBAT in hinged knee brace with flexion limited to 30º for 4 weeks and progressed incrementally thereafter
      • partial patellectomy +/- tendon advancement 
        • indications
          • comminuted extra-articular inferior pole fracture measuring <40% patellar height
            • only if ORIF is not possible
        • techniques
          • remove least bone possible
          • patellar tendon should be advanced into defect on anterior surface of patella
        • outcomes
          • decreases strength of extensor mechanism to increasing degree based on size of fragment removed
      • total patellectomy +/- tendon advancement 
        • indications (rare)
          • severe and extensive comminution not amenable to salvage
          • infection
          • tumor
        • techniques
          • removal of patella
          • imbrication of quadriceps/patellar tendons
          • advancement of vastus and retinaculum
        • outcomes
          • poor outcomes noted
          • decrease in extensor mechanism strength >50%
  • Techniques
    • Open reduction and internal fixation (ORIF) 
      • approach
        • midline longitudinal incision centered over patella
        • expose articular surface either through fracture site or retinacular rents
        • can alternatively perform lateral parapatellar arthrotomy and invert patella if retinaculum is not damaged or if better visualization of articular surface is desired
      • technique
        • avoid extensive soft tissue dissection to preserve blood supply and viability of skin flaps
        • retain as much of patella as possible
        • remove devitalized fragments and loose bodies
        • tension band construct
          • converts tensile forces generated by quadriceps complex at anterior surface into compressive forces at articular surface
          • tension band using 0.062 K-wires 
            • k-wires + 18-gauge stainless steel wire
              • difficult to manipulate and high re-operation rates due to painful hardware or wire migration
            • k-wires + suture
              • has 75% tensile strength of 18-gauge stainless steel wire but performs similarly clinically
              • lower rates of hardware removal when suture used
          • tension band using longitudinal 4.0 mm cannulated screws
            • biomechanically stronger than K-wires
        • plate/screws construct
          • biomechanically superior to tension band construct 
          • multiple plate options available
            • mini-fragment plates
              • useful in simple/comminuted fractures
              • helpful in osteoporotic bone
            • mesh plates
              • versatile with multiplanar screw options available
              • effective in stabilizing distal pole fractures with comminution
              • less fracture gapping compared to tension band wiring
        • cerclage wiring
          • used alone or to augment additional fixation such as interfragmentary lag screws or tension band construct
          • useful in comminuted fractures
      • complications
        • painful hardware/anterior knee pain
          • important to place tension wire at superior aspect of construct where more soft tissue coverage is available
          • consider using braided suture as opposed to 18-gauge stainless steel wire
          • plates may have lower rates of hardware irritation compared to tension banding
        • hardware failure
          • to prevent hardware failure in tension band construct:
            • 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
    • Partial patellectomy +/- tendon advancement
      • approach
        • same as ORIF (see above)
      • technique
        • retain as much patella as possible
          • must remove devitalized fragments and loose bodies
        • reattach quadriceps 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
        • perform retinacular repair
        • if necessary, reinforce with cerclage suture or wire from quadriceps tendon to tibial tubercle 
      • complications
        • weakness
        • extensor lag
    • Total patellectomy +/- tendon advancement
      • approach
        • same as ORIF (see above)
      • technique
        • remove all bony patellar fragments and loose bodies
        • restore integrity of extensor mechanism via imbrication of quadriceps and patellar tendons
        • medial and lateral retinacular repair remain essential
        • consider advancing VMO
          • found to have better strength and outcomes
      • complications
        • weakness
        • extensor lag
          • may avoid by performing sufficient imbrication
  • Complications
    • Anterior knee pain
      • risk factors
        • more common with ORIF
      • treatment
        • hardware removal after union
    • Symptomatic hardware
      • incidence
        • most common complication, up to 50%
      • risk factors
        • thin body habitus
        • open fractures
          • thought to be due to compromised soft-tissue envelope
        • tension band construct using K-wires 
      • treatment
        • hardware removal after union
    • Weakness
      • risk factors
        • partial or total patellectomy
        • insufficient retinacular repair
      • treatment
        • physical therapy
        • improvement may be limited based on procedure performed
    • Loss of reduction
      • incidence
        • 0-22% of cases although catastrophic hardware failure is rare
      • risk factors
        • increasing age
        • osteoporotic bone
      • treatment
        • may require revision ORIF, but if degree of reduction loss is small, may not affect union
    • Nonunion
      • incidence
        • <1-5%
      • risk factors
        • open fracture
      • treatment
        • typically well-tolerated
        • revision ORIF with bone grafting
        • can consider partial patellectomy
    • Osteonecrosis 
      • incidence
        • up to 25%, usually asymptomatic 
      • risk factors
        • proximal pole fracture
          • thought to be due to excessive initial fracture displacement
      • treatment
        • can observe these, as most spontaneously revascularize by 2 years
    • Infection
      • incidence 
        • 0-5%
      • risk factors
        • open fracture
          • rates 10-11%
      • treatment
        • may require I&D, possible hardware removal
    • Stiffness
      • risk factors
        • longer period of immobilization
        • open fracture or soft tissue injury
        • concomitant lower extremity injuries
      • treatment
        • usually resolves with aggressive physical therapy after fracture union 
    • Post-traumatic patellofemoral osteoarthritis
      •  incidence
        • up to 50%
      • risk factors
        • degree of traumatic mechanism
        • articular malreduction
      • treatment
        • symptomatic management
        • total knee arthroplasty (TKA)
  • Prognosis
    • Most patella fractures heal uneventfully 
      • osteonecrosis reported to occur in up to 25% but not found to affect clinical outcome
    • Poor prognostic variables
      • significant comminution
        • treated with partial or total patellectomy
      • open fracture
      • history of smoking

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(OBQ13.186) A 42-year-old female sustains the injury shown in Figure A as the result of a fall from a ladder. Which of the following is the most common complication after the procedure shown in Figure B?

QID: 4821

Knee arthrofibrosis



Symptomatic implant



Implant failure



Patella alta



Patella baja



L 2 B

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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?

QID: 4403

Long leg cast



Hinged knee brace use with functional rehabilitation protocol



Open treatment with internal fixation or excision with patellar tendon advancement



Distal patellar resection and allograft reconstruction



Placement of a cerclage wire from patella to proximal tibia



L 4 B

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(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?

QID: 4589

Symptomatic treatment of his patellofemoral arthritis



Manipulation under anesthesia



Operative treatment of his non-union



Knee intrarticular corticosteroid injection



Removal of symptomatic hardware



L 1 B

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(OBQ07.207) Partial patellectomy is the recommended treatment for which of the following injuries?

QID: 868

Vertical patella fractures



Bipartite patella



Severely comminuted inferior pole fracture



Stellate patella fracture



Chronic quadriceps tendon rupture



L 1 C

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