Updated: 5/6/2022

Patella Fracture

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https://upload.orthobullets.com/topic/1042/images/patella alta with avulsion fx.jpg
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https://upload.orthobullets.com/topic/1042/images/bipartite_patella.jpg
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  • 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
  • PRESENTATION
    • 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
FIGURES:

Knee arthrofibrosis

3%

(119/4633)

Symptomatic implant

93%

(4327/4633)

Implant failure

2%

(97/4633)

Patella alta

1%

(29/4633)

Patella baja

1%

(32/4633)

L 2 B

Select Answer to see Preferred Response

(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
FIGURES:

Long leg cast

1%

(59/4495)

Hinged knee brace use with functional rehabilitation protocol

35%

(1580/4495)

Open treatment with internal fixation or excision with patellar tendon advancement

59%

(2659/4495)

Distal patellar resection and allograft reconstruction

1%

(44/4495)

Placement of a cerclage wire from patella to proximal tibia

3%

(130/4495)

L 4 B

Select Answer to see Preferred Response

(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
FIGURES:

Symptomatic treatment of his patellofemoral arthritis

1%

(47/5066)

Manipulation under anesthesia

0%

(23/5066)

Operative treatment of his non-union

1%

(28/5066)

Knee intrarticular corticosteroid injection

1%

(27/5066)

Removal of symptomatic hardware

97%

(4918/5066)

L 1 B

Select Answer to see Preferred Response

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

QID: 868

Vertical patella fractures

1%

(15/1535)

Bipartite patella

2%

(32/1535)

Severely comminuted inferior pole fracture

93%

(1421/1535)

Stellate patella fracture

3%

(46/1535)

Chronic quadriceps tendon rupture

1%

(14/1535)

L 1 C

Select Answer to see Preferred Response

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