Pain limited but intact extension suggests continuity
Active knee extension against gravity
Passive range limits from effusion
Effusion and hemarthrosis
Large tense effusion
Patellar ballotment
Associated injuries
Ligament and joint line screening when tolerated
Medial joint line tenderness
Lateral joint line tenderness
Varus and valgus laxity in extension suspicion
ACL and PCL concern with high energy mechanism
Hip and ankle screen
Ipsilateral hip pain
Ipsilateral ankle pain
Neurovascular and compartments
Distal status
Pulses and capillary refill
Motor and sensory screening
Compartment syndrome screen
Leg compartment firmness
Pain with passive toe stretch
Progressive paresthesia
Differential Diagnosis
Traumatic knee conditions
Differential set
Patellar dislocation with osteochondral fracture
Lateral tenderness and apprehension
Medial patellofemoral ligament tenderness
Quadriceps tendon rupture
Suprapatellar gap
Low riding patella possible
Patellar tendon rupture
High riding patella
Inability to extend knee
Tibial plateau fracture
Joint line tenderness
Inability to bear weight
Distal femur fracture
Supracondylar tenderness
Deformity or shortening
Knee hemarthrosis from intra articular injury
ACL tear
Osteochondral fracture
Mimics and chronic variants
Mimics
Bipartite patella
Smooth corticated fragment
Superolateral location
Patellofemoral arthritis flare with effusion
Prepatellar bursitis after trauma
Medical coding anchors
Coding concepts
ICD-10 patella fracture category S82.0
SNOMED CT concept patellar fracture
Laboratory Tests
Routine labs and selective use
Minimal lab strategy
No routine labs for isolated closed stable fracture
Labs driven by operative pathway or systemic risk
Preoperative or significant injury labs
Complete blood count for anemia or open fracture
Hemoglobin trend if major bleeding concern
Leukocytosis nonspecific for trauma stress
Basic metabolic panel for sedation or comorbidity
Creatinine for medication selection
Electrolytes for peri sedation risk
Coagulation studies for anticoagulant use or planned OR
INR interpretation for warfarin
Anti Xa only if protocolized for LMWH
Rhabdomyolysis or crush context
Creatine kinase for prolonged entrapment
Renal injury risk linkage
IV fluid trigger by protocol
Open fracture and infection context
Open injury adjuncts
Type and screen if operative likely
Lactate only for systemic shock evaluation
Cultures not recommended pre antibiotics in ED for uncomplicated open fracture
Diagnostic Tests
Scoring Systems
Classification and implications
AO OTA patella fracture framework
Extra articular versus partial articular versus complete articular grouping concept
Comminution as operative planning modifier
Gustilo Anderson open fracture classification
Grade I small clean wound low energy
Grade II wound size greater soft tissue injury
Grade III high energy extensive soft tissue damage
Antibiotics and urgent orthopedics tied to grade
Radiographs
X-ray strategy
Standard knee views
AP
Lateral
Sunrise or Merchant view
Vertical fracture detection
Sunrise view improves sensitivity versus AP alone
CT if persistent suspicion
Alignment and displacement documentation
Fracture gap measurement
Articular step off measurement
Patella height assessment for tendon disruption
Nonoperative candidacy radiographic thresholds
Minimally displaced definition
Fracture gap less than 3 mm reported in narrative review
Articular step off less than 2 to 3 mm reported in narrative review
Post immobilization imaging
Repeat radiographs after significant swelling change or new symptoms
MRI
MRI indications
Suspected extensor tendon rupture with equivocal exam
Suspected osteochondral injury after patellar dislocation
Persistent pain with negative radiographs and CT when occult injury suspected
MRI limitations
Availability and time constraints in ED
Acute pain limits positioning
Metal artifact if prior hardware
CT
CT indications
Complex comminution requiring operative planning
Suspected vertical fracture not seen on X-ray
Suspected intra articular impaction or loose body
CT interpretation pearls
Articular congruity assessment
Fragment count and size for fixation feasibility
Associated trochlear or femoral condyle injury
Disposition
ED disposition pathways
Discharge criteria
Closed injury
Neurovascularly intact
Pain controlled on oral regimen
Extensor mechanism intact
Minimal displacement on imaging
Safe ambulation with aids
Admission criteria
Open fracture
Extensor mechanism disruption
Displacement likely requiring fixation
Uncontrolled pain
Inability to mobilize safely
Polytrauma or unsafe social situation
Transfer criteria
Open fracture requiring orthoplastic capability
Urgent fixation need without local coverage
Vascular injury concern
Compartment syndrome concern
Follow up and timing
Follow up targets
Orthopedics within 3 to 7 days for closed stable fractures
Same day or next day orthopedics for suspected operative fractures
Earlier review for worsening swelling or skin compromise
Mobility instructions
Weight bearing status per stability and immobilization plan
Crutches or walker fitting and training
Treatment
Immediate life-saving interventions
Life threats and escalation
Trauma resuscitation pathway for high energy injury
If open fracture suspected then antibiotics and tetanus pathway without delay
If threatened skin then urgent orthopedics escalation
If neurovascular deficit then immediate ortho and vascular escalation
Immobilization and Splinting
Immobilization choice
Knee immobilizer in extension
Preferred for most stable patellar fractures
Allows skin checks and swelling accommodation
Hinged knee brace locked in extension
Option when early supervised ROM planned
Posterior long leg splint
Option for severe pain or noncompliance concern
Principles
Knee extension position to reduce extensor mechanism tension
Swelling phase avoidance of circumferential casting
Post application neurovascular recheck
Two finger tightness check at straps
Skin protection
Padding at malleoli and heel
Padding at popliteal fossa strap edges
Pressure point reassessment after ambulation trial
Reduction
Reduction considerations
No routine reduction for isolated patellar fracture fragments
If patellar dislocation present then reduction pathway
Analgesia and sedation options
Non opioid base
Acetaminophen PO 1000 mg once then 650 to 1000 mg every 6 to 8 hours
Ibuprofen PO 400 to 600 mg every 6 to 8 hours if no contraindication
Opioid titration
Morphine IV 0.05 to 0.1 mg per kg incremental dosing
Hydromorphone IV 0.2 to 0.5 mg incremental dosing
Regional anesthesia options
Femoral nerve block or adductor canal block
Ultrasound guidance preferred
Local anesthetic selection per institutional protocol
LAST monitoring readiness
Procedural sedation if needed
Airway and monitoring readiness
Continuous pulse oximetry
Cardiac monitor
End tidal CO2 monitoring
Suction and BVM at bedside
Ketamine IV 1 mg per kg initial
Supplemental 0.25 to 0.5 mg per kg as needed
Propofol IV 0.5 to 1 mg per kg initial
Supplemental 10 to 20 mg aliquots as needed
Post reduction requirements
Post reduction radiographs
Neurovascular recheck
Brace in extension
Early ortho follow up due to osteochondral risk
Open fracture medications and timing
Antibiotics and tetanus
IV antibiotics as soon as possible
Ideally within 1 hour of injury per BOAST open fracture guidance
Local protocol selection for agent and duration
Gustilo based approach
Grade I and II typical coverage first generation cephalosporin pathway
Grade III expanded gram negative coverage per protocol
Farm or soil contamination high risk clostridial coverage per protocol
Tetanus prophylaxis
Vaccine status based dosing
Tetanus immune globulin when indicated
Wound handling
Saline soaked sterile dressing
Gross contamination removal only
No deep probing in ED
Urgent orthopedics involvement
DVT prophylaxis when relevant
VTE risk approach
Lower limb immobilization risk stratification
Prior VTE history
Active cancer
Major trauma or surgery planned
Pharmacologic prophylaxis
Align with local ortho protocol
Contraindications documentation
Special Populations
Pregnancy
Pregnancy considerations
Maternal stabilization priority
Trauma pathway alignment
Left lateral tilt if hypotension concern
Imaging safety
Knee radiographs low fetal dose with shielding
CT only if clinically required for maternal care
Analgesia selection
Acetaminophen preferred
NSAID avoidance in later gestation per obstetric guidance
VTE risk increased in pregnancy
Lower threshold for prophylaxis discussion if immobilized
Geriatric
Older adult considerations
Fragility mechanism common
Fall from standing height
Osteoporosis evaluation trigger
Higher functional risk from immobilization
Deconditioning and falls risk
Home supports assessment
Medication risks
Opioid delirium risk
NSAID renal and GI risk
Admission threshold lower
Unsafe mobility
Inadequate pain control
Pediatrics
Pediatric considerations
Sleeve fracture risk
Patellar cartilage avulsion pattern
High suspicion with large hemarthrosis and minimal X-ray changes
MRI consideration for occult sleeve fracture
Growth and remodeling
Articular congruity still critical
Early orthopedics input for suspected sleeve injuries
Weight based analgesia
Acetaminophen 15 mg per kg per dose
Ibuprofen 10 mg per kg per dose if appropriate
Nonaccidental trauma consideration when story inconsistent
Social work pathway when indicated
Background
Epidemiology
Epidemiology facts
Patellar fractures uncommon compared with other lower limb fractures
Approximately 20 to 30 percent reported operative treatment rates in cohort data
Surgical treatment proportion 26 percent in a large cohort cited by AO Foundation solution page
Mechanisms
Direct trauma common
Indirect eccentric contraction less common
Pathophysiology
Pathophysiology essentials
Patella as sesamoid bone in quadriceps tendon
Extensor mechanism continuity as primary functional determinant
Intra articular fracture with hemarthrosis common
Force vector to pattern mapping
Transverse fracture from tensile failure during quadriceps contraction
Comminuted fracture from direct blow with articular cartilage injury risk
Vertical fracture from compressive or direct force often stable if extensor intact
Complication mechanisms
Post traumatic patellofemoral arthritis from articular incongruity
Stiffness from prolonged immobilization
Symptomatic hardware after fixation
Therapeutic Considerations
Treatment rationale
Primary goal restoration of extensor mechanism and articular congruity
Nonoperative success predictors
Intact straight leg raise
Minimal displacement thresholds
Fracture gap less than 3 mm
Articular step off less than 2 to 3 mm
Operative indications commonly cited
Extensor mechanism disruption
Articular step off at least 2 mm
Displacement greater than 2 to 4 mm depending on source
Open fracture
Early motion tradeoff
Earlier supervised ROM reduces stiffness risk
Fixation stability required for early ROM
Evidence framing
Operative indication thresholds supported in narrative reviews and guideline style summaries
Procedural sedation safety guided by ACEP clinical policy for ED sedation when used
Patient Discharge Instructions
copy discharge instructions
Discharge instructions bundle
Brace or splint
Keep knee straight in immobilizer unless orthopedics instructed otherwise
Keep splint clean and dry
Do not adjust tight straps without reassessment if numbness occurs
Swelling control
Elevation above heart as much as possible first 48 hours
Ice 15 to 20 minutes at a time several times daily
Pain plan
Acetaminophen as directed on label or prescription
NSAID only if safe for kidneys stomach and bleeding risk
Opioid only if prescribed and avoid driving
Activity
Weight bearing only as instructed
Crutches or walker use until safe gait
No sports running or jumping until cleared
Return to ED now if
New numbness or weakness in foot
Foot becomes cold pale or blue
Rapidly worsening pain despite medication
Increasing tightness or severe swelling in leg
Brace feels too tight and symptoms do not improve after loosening straps
Fever or wound drainage
Any concern for open wound worsening
Follow up
Orthopedics appointment timing as provided
Earlier review for worsening swelling or skin changes
References
Clinical guidelines and key sources
Patellar fracture displacement thresholds and nonoperative criteria
Narrative review defining minimally displaced gap less than 3 mm and step off less than 2 to 3 mm
StatPearls summary of nonoperative criteria and extensor mechanism priority
Practical guidelines paper citing operative indications step off greater than 2 mm and displacement thresholds
Open fracture initial management timing
BOAST open fracture guidance antibiotics ideally within 1 hour
General ED orthopedic reference
Orthobullets patella fracture summary for immobilization and indications
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.