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 login to view 3 more bullets indirect eccentric contraction login to view 7 more bullets 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 login to view 1 more bullet Tendons quadriceps tendon quadriceps tendon and fascia lata attach to anterosuperior margin of patella quadriceps tendon comprised of 3 layers login to view 3 more bullets 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 login to view 2 more bullets provocative tests saline load test can be performed to rule out concomitant knee joint involvement Imaging Radiographs recommended views AP lateral login to view 3 more bullets axial (sunrise/merchant views) login to view 1 more bullet findings fracture displacement login to view 1 more bullet patella alta login to view 2 more bullets patella baja login to view 2 more bullets 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 login to view 1 more bullet 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 login to view 4 more bullets modalities login to view 3 more bullets outcomes login to view 1 more bullet Operative open reduction and internal fixation (ORIF) indications login to view 8 more bullets techniques login to view 12 more bullets outcomes login to view 5 more bullets partial patellectomy +/- tendon advancement indications login to view 2 more bullets techniques login to view 2 more bullets outcomes login to view 1 more bullet total patellectomy +/- tendon advancement indications (rare) login to view 3 more bullets techniques login to view 3 more bullets outcomes login to view 2 more bullets 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 login to view 9 more bullets plate/screws construct login to view 9 more bullets cerclage wiring login to view 2 more bullets complications painful hardware/anterior knee pain login to view 3 more bullets hardware failure login to view 4 more bullets Partial patellectomy +/- tendon advancement approach same as ORIF (see above) technique retain as much patella as possible login to view 1 more bullet reattach quadriceps or patellar tendon login to view 3 more bullets perform retinacular repair if necessary, reinforce with cerclage suture or wire from quadriceps tendon to tibial tubercle complications weakness extensor lag patella baja 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 login to view 1 more bullet complications weakness extensor lag login to view 1 more bullet 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 login to view 1 more bullet 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 login to view 1 more bullet treatment can observe these, as most spontaneously revascularize by 2 years Infection incidence 0-5% risk factors open fracture login to view 1 more bullet 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