Patella Fractures

Descriptors

Open vs closed
Nondisplaced vs displaced
Displaced: step-off >2-3 mm or fracture gap >1-4 mm

Pattern: Transverse
Pole or sleeve (upper or lower)
Vertical
Marginal
Osteochondral
Comminuted (stellate)
Note: bipartite patella may be mistaken for a patella fracture. It is generally found in the superolateral position, has well-corticated/smooth edges, and may have intervening fibrocartilage

Exam Pearls

Always document a good neurovascular exam.

May feel palpable defect

Can perform saline load test to rule out open fracture, however a CT scan looking for IA air may be more comfortable for patient and more accurate

Assess extensor mechanism by having patient perform a straight leg raise (SLR) Patients should be able to maintain SLR without an extensor lag

How to differentiate extensor mechanism disruption from quadriceps inhibition (usually 2/2 hemarthrosis):
Displaced transverse fractures and those associated with eccentric contraction mechanism are more likely to have a disrupted extensor mechanism In a patient who is unable to SLR AND you would expect them to be able to based on fracture pattern or they have a large hemarthrosis, you can perform arthrocentesis to drain hemarthrosis +/- inject 1% lidocaine. This should relieve their quadriceps inhibition. You can also place your hand under the patient’s extended knee and ask them to push their knee down into bed. If they are able to do this, they are able to activate their quadriceps and do not have quadriceps inhibition.

Workup

Radiographs: AP, lateral and tangential of affected knee Patellar alta and baja (Insall-Salvati index) may indicate patellar or quadriceps tendon disruption respectively

Other imaging: Not usually required. If dashboard injury, can get ipsilateral hip XR to assess for femoral neck or posterior acetabular fracture. Can get CT to assess for intra-articular air indicative of open injury. In child who is unable to SLR, can get MRI if high suspicion but negative XRs.

Labs: Preop CBC/BMP/Coags/T&S/COVID if operative (see below)

Other: CXR, EKG pre-op if indicated if operative (see below)

Management

Need for acute intervention: Yes, immobilization without reduction

Weight-bearing and range of motion: WBAT with knee immobilized in extension

Type of immobilization: Knee immobilizer

Admission or discharge status: If operative injury (see surgical indications), admit. Otherwise, discharge home with 1-2 week follow-up

Anticoagulation: per HOTI protocol

Antibiotics: None needed unless open fracture

Surgical Indications

Absolute: Extensor mechanism disruption, open fracture, articular displacement >2 mm, displacement >3 mm, patella sleeve fracture in child

Relative: n/a

Not an indication: n/a

Operative Options: ORIF: tension band, cerclage wire, plate and screws Partial patellectomy: not ideal, want to preserve patella whenever possible but may be necessary if significant comminution