Clinical Assessment of Suspected Patellar Fracture Without X-ray Access
When X-ray is unavailable, you should strongly suspect a patellar fracture based on specific clinical findings: inability to perform straight leg raise against gravity, palpable defect in the patella, severe focal patellar tenderness, large knee effusion, and inability to bear weight—and immediately immobilize the knee in full extension pending definitive imaging. 1
Key Clinical Indicators of Patellar Fracture
High-Probability Physical Examination Findings
Loss of extensor mechanism function is the most critical finding—inability to extend the knee against resistance or perform a straight leg raise strongly suggests patellar fracture with retinacular disruption 2
Palpable defect or gap over the anterior patella indicates displaced fracture, which you can feel as a horizontal step-off or separation in the bone 3, 4
Focal bony tenderness directly over the patella (not just soft tissue tenderness) meets Ottawa Knee Rule criteria and indicates need for imaging 1, 5
Large hemarthrosis/effusion develops rapidly after patellar fracture, causing visible swelling and a tense, ballotable patella 1
Functional Assessment Criteria
Inability to bear weight for 4 steps immediately after injury is an Ottawa Knee Rule criterion that mandates imaging 1, 5
Inability to flex the knee to 90 degrees due to pain (not just apprehension) suggests significant bony or soft tissue injury 1
Age >55 years combined with any of the above findings increases fracture probability per Ottawa rules 5
Point-of-Care Ultrasound as Alternative Imaging
If available, bedside ultrasound can identify patellar fractures with 95% sensitivity and 86% positive predictive value, making it a reasonable alternative when X-ray is inaccessible. 3
Ultrasound Technique and Findings
Place the linear high-frequency probe transversely across the patella to identify horizontal fracture lines appearing as cortical disruptions 3
Scan longitudinally to assess the quadriceps and patellar tendons—ultrasound has 87% sensitivity for patellar tendon rupture and 100% for quadriceps tendon rupture 3
Look for fluid collection (hemarthrosis) and loss of normal smooth cortical contour of the patella 3
Immediate Management Without Imaging Confirmation
Immobilization Protocol
Apply knee immobilizer in full extension for any suspected patellar fracture based on clinical findings—this is the standard initial treatment regardless of fracture type 6, 7
Full extension immobilization prevents further displacement and protects the extensor mechanism from additional injury 6
Avoid allowing knee flexion until fracture is ruled out or definitively treated, as flexion can displace fractures and worsen retinacular tears 2
Weight-Bearing Restrictions
Non-weight-bearing status should be maintained until fracture is excluded or surgical consultation obtained 1, 5
Provide crutches and explicit instructions against bearing weight on the affected limb 5
Critical Pitfalls to Avoid
Do not rely on ability to extend the knee as evidence against fracture—many patellar fractures, especially non-displaced ones, maintain some extensor function if the retinaculum remains intact 2, 4
Anteroposterior X-rays alone miss many patellar fractures—lateral views are essential, which is why clinical diagnosis must be thorough when imaging is unavailable 4
Transverse fractures from indirect trauma (eccentric quadriceps contraction) may have deceptively benign initial appearance compared to stellate fractures from direct trauma 2
Mandatory Referral Criteria
Any suspected patellar fracture requires orthopedic evaluation within 24-48 hours, as displaced fractures (>2-3mm separation or articular step-off) typically require surgical fixation 7
Arrange urgent transport for definitive imaging (standard radiographs with AP, lateral, and patellofemoral views) as soon as feasible 1, 5
Document your clinical findings thoroughly, including specific Ottawa Knee Rule criteria present, to justify imaging when the patient reaches appropriate facility 1, 5