Patellar fractures account for approximately 1% of all fractures, predominantly affect elderly women (median age 67, 64% female), and are most commonly caused by low-energy falls from standing height (70%) or direct blows to the knee. [1-2] The patella is the largest sesamoid bone and is critical for the extensor mechanism, increasing the mechanical advantage of the quadriceps. [3-4]
1. History
- Mechanism: Direct blow (fall onto flexed knee, dashboard injury, assault) vs. indirect (sudden eccentric quadriceps contraction, e.g., stumbling/missing a step) [1][5]
- Symptom characterization: Acute anterior knee pain, immediate swelling, inability to walk or bear weight
- Timing: Acute onset at time of injury; delayed presentations may indicate stress fracture or pathologic fracture
- Severity/progression: Inability to perform a straight leg raise (SLR) suggests extensor mechanism disruption — a critical distinction [6]
- Associated symptoms: Knee locking, giving way, sensation of a "pop" or "crack"
- Important negatives: Prior knee surgery, prosthetic hardware, anticoagulant use, history of patellar dislocation, prior contralateral injury
2. Alarm Features
- Loss of active knee extension / inability to perform SLR → disrupted extensor mechanism requiring surgical consultation [4-5]
- Open fracture (2–7% of patellar fractures) → emergent irrigation, debridement, and fixation [1][5]
- Palpable gap in the patella with significant displacement
- Lipohemarthrosis on cross-table lateral radiograph → intra-articular fracture [7]
- Tense effusion with neurovascular compromise → consider compartment syndrome (rare but reported with periarticular knee fractures) [8]
- High-energy mechanism (MVC, fall from height) → evaluate for polytrauma, ipsilateral femur/tibia fractures
3. Medications
- First-line analgesia: Topical NSAIDs have the greatest net benefit for acute musculoskeletal injuries; oral NSAIDs (ibuprofen 400–600 mg q6–8h, naproxen 500 mg q12h) are recommended as secondary agents [9-10]
- Acetaminophen (1 g q6–8h, max 3–4 g/day) is effective and can be combined with NSAIDs [11]
- Opioids should be avoided when possible; no opioid achieves benefit greater than NSAIDs, and opioids cause more harms. Short-course opioids may be considered for severe pain refractory to multimodal therapy [10][12]
- NSAIDs and fracture healing: The Orthopaedic Trauma Association states there is no conclusive clinical evidence to prohibit NSAID use in fracture care and recommends routine use as part of multimodal analgesia [13-14]
- Contraindicated: Avoid NSAIDs in patients with renal insufficiency, active GI bleeding, or significant cardiovascular disease
- DVT prophylaxis: Routine pharmacologic thromboprophylaxis is not clearly indicated for isolated patellar fractures managed with immobilization, as symptomatic VTE rates are low (~0.6%); however, risk-stratify patients individually (age >52, open injuries, polytrauma, delayed surgery increase DVT risk) [15-17]
4. Diet
- Calcium and vitamin D supplementation for bone healing, particularly in elderly patients and those with suspected osteoporosis
- Adequate protein intake to support fracture healing and soft tissue recovery
- Hydration: Maintain adequate hydration, especially if immobilized
- Avoid excessive alcohol: Impairs bone healing and increases fall risk
5. Review of Systems
- Musculoskeletal: Pain with weight-bearing, knee stiffness, inability to extend knee
- Vascular: Assess for calf pain/swelling (DVT), especially with immobilization
- Neurologic: Numbness/tingling distal to injury (peroneal nerve)
- Skin/integumentary: Open wounds, abrasions over the patella (open fracture risk)
- Constitutional: Fever (if delayed presentation — concern for septic joint or infection)
- Endocrine: History of osteoporosis, metabolic bone disease (fragility fracture in elderly)
6. Collateral History and Family History
- Witnesses to mechanism: Was it a fall, direct blow, or twisting injury?
- Pre-injury functional status: Ambulatory baseline, use of assistive devices
- Anticoagulation status: Increases hemarthrosis risk
- Family history: Osteoporosis, connective tissue disorders (e.g., osteogenesis imperfecta)
- Social context: Fall risk assessment in elderly, occupational demands, living situation (stairs, support at home)
7. Risk Factors
- Age >60 years, particularly postmenopausal women [1-2]
- Osteoporosis / low bone mineral density — low-energy falls can cause fragility fractures [1]
- Prior patellar dislocation or surgery
- High-energy activities: Contact sports, motor vehicle collisions
- Diabetes mellitus: Increases risk of reoperation and complications post-fixation (OR 8.69) [18]
- Cerebrovascular accident history: Significantly increases infection (OR 6.18) and nonunion risk [18]
- Obesity: Increased load on extensor mechanism
8. Differential Diagnosis
- Quadriceps tendon rupture: Suprapatellar gap, patella baja, intact patella on X-ray; more common in patients >40 years
- Patellar tendon rupture: Infrapatellar gap, patella alta on lateral radiograph
- Patellar dislocation/subluxation: Lateral displacement, apprehension test positive; may have associated osteochondral fracture
- Tibial plateau fracture: Tenderness at joint line, valgus/varus stress pain
- Bipartite patella: Incidental finding, typically superolateral, smooth rounded edges (vs. sharp fracture lines); present bilaterally in ~50% of cases
- Prepatellar bursitis: Anterior swelling without bony tenderness or extensor mechanism disruption
- Osteochondral fracture: May be occult on plain films; consider with effusion and locking
- Patellar sleeve fracture (pediatric): Skeletally immature patients, cartilaginous avulsion from inferior pole, easily missed on X-ray [6]
9. Past Medical History
- Prior knee injuries, surgeries, or arthroscopy
- Osteoporosis or fragility fractures
- Total knee arthroplasty (periprosthetic fracture consideration)
- Diabetes, peripheral vascular disease, immunosuppression (affect healing and infection risk) [18]
- Chronic steroid use (weakens bone and tendon)
- Prior DVT/PE or coagulopathy
10. Physical Exam
- Inspection: Anterior knee swelling, ecchymosis, deformity, skin integrity (open vs. closed), palpable gap over patella [1]
- Palpation: Point tenderness over the patella; palpable defect between fracture fragments
- Effusion: Tense hemarthrosis is common; ballottement or fluid wave test
- Extensor mechanism testing: Straight leg raise (SLR) is the critical test — inability to perform SLR or actively extend the knee indicates extensor mechanism disruption and likely need for surgery [5-6]
- Range of motion: Inability to flex knee to 90° (Ottawa knee rule criterion) [7]
- Neurovascular exam: Palpate dorsalis pedis and posterior tibial pulses; assess peroneal nerve function (dorsiflexion, sensation at first web space)
- Skin: Carefully inspect for lacerations communicating with the fracture (open fracture)
11. Lab Studies
- Routine labs are generally not required for isolated closed patellar fractures
- If surgical candidate: CBC, BMP, coagulation studies, type and screen
- D-dimer: Elevated D-dimer (>0.5 µg/mL) is an independent risk factor for preoperative DVT (OR 2.47) [17]
- If open fracture or concern for infection: CBC with differential, ESR, CRP, blood cultures
- Elderly patients: Consider vitamin D level, calcium, bone density screening for fragility fracture workup
12. Imaging
- First-line: AP and lateral knee radiographs; add a sunrise/Merchant (patellofemoral) view for suspected patellar fractures [7]
- Lateral view: Best for identifying transverse fractures, displacement, patella alta/baja, and lipohemarthrosis (cross-table lateral with horizontal beam) [7]
- CT scan: Indicated preoperatively for comminuted fractures or when plain films underestimate fracture complexity — CT changes both classification and treatment plan [3][19]
- MRI: Reserved for suspected occult fractures, osteochondral injuries, or soft tissue/ligamentous injuries not visible on X-ray [1]
- When imaging is unnecessary: The Ottawa Knee Rule (sensitivity 98.5–100%) can safely exclude fracture if all criteria are negative — no patellar tenderness, no fibular head tenderness, can flex to 90°, can bear weight for 4 steps, age <55 [7][20-21]
13. Special Tests
- Ottawa Knee Rule: Age ≥55, isolated patellar tenderness, fibular head tenderness, inability to flex to 90°, inability to bear weight for 4 steps → if any positive, obtain radiographs. Pooled sensitivity 98.5%, specificity 48.6%. Meta-analysis confirms it can safely rule out fracture [7][20-21]
- Straight leg raise test: The single most important bedside test — inability to perform SLR indicates extensor mechanism disruption [6]
- Joint aspiration: If tense effusion, aspiration provides pain relief; fat globules (lipohemarthrosis) confirm intra-articular fracture
- AO/OTA Classification: Used to classify fracture pattern (Type A: extra-articular; Type B: partial articular; Type C: complete articular/transverse/comminuted) [2][19]
14. ECG
- Not routinely indicated for isolated patellar fracture
- Obtain ECG in elderly patients or those with cardiac comorbidities being evaluated for surgical clearance
- Consider if high-energy mechanism (MVC) with concern for myocardial contusion
15. Assessment
Patellar fractures are classified by pattern: transverse (most common, 56%), vertical (26%), comminuted, marginal, and osteochondral. [2] The critical clinical determination is whether the extensor mechanism is intact (patient can perform SLR) and whether there is significant articular displacement.
- Non-displaced, intact extensor mechanism → conservative management [1][3]
- Displaced (>2–3 mm step-off, >1–4 mm separation), disrupted extensor mechanism, or open fracture → surgical fixation [4-5][22]
- Complications are common after surgical treatment: symptomatic hardware requiring removal (29.6%), fixation failure (5.2%), infection (3.1%), nonunion (1.7%) [23]
- Long-term sequelae include knee stiffness, extension lag, and patellofemoral osteoarthritis [3]
16. Treatment Plan
Non-operative (67% of all patellar fractures): [2]
- Indications: Non-displaced fracture, intact extensor mechanism, <2 mm articular step-off [1][3][24]
- Immobilization in near-full extension (knee immobilizer or hinged brace locked in extension) for 5–6 weeks [1]
- Weight-bearing as tolerated with crutches
- Serial radiographs at 2, 4, and 6 weeks to monitor for displacement
- Begin gentle ROM exercises after fracture consolidation confirmed
Operative: [4-5][22]
- Indications: Articular step-off >2 mm, fragment separation >3 mm, open fracture, disrupted extensor mechanism
- Tension band wiring (TBW): Most commonly used technique (24% of all cases); converts tensile forces to compressive forces across the fracture [2]
- Cannulated screw fixation: Alternative for simple transverse fractures
- Plate fixation: Increasingly popular; low-profile, fewer symptomatic hardware issues [25]
- Partial/total patellectomy: Reserved for severely comminuted fractures not amenable to reconstruction [1]
- Open fractures: Emergent irrigation, debridement, and internal fixation [5]
Pain management: Multimodal approach — topical NSAIDs first-line, oral NSAIDs + acetaminophen, ice, elevation; avoid opioid monotherapy [9-10][13]
17. Disposition
- Discharge criteria: Non-displaced closed fracture, intact extensor mechanism, adequate pain control, able to ambulate with crutches, reliable follow-up
- Admission criteria: Open fracture, polytrauma, high-energy mechanism requiring observation, significant comorbidities, inability to safely ambulate
- Observation: Borderline displacement (2–3 mm) — immobilize and obtain orthopedic follow-up within 3–5 days with repeat imaging
- Orthopedic consultation triggers: Any displaced fracture, disrupted extensor mechanism, open fracture, comminuted fracture, intra-articular loose bodies
18. Follow Up / Return Precautions
- Follow-up timing: Orthopedic follow-up within 5–7 days for non-operative management; repeat X-ray at 1–2 weeks to ensure no interval displacement
- Return precautions (instruct patient to return immediately for):
- Increasing pain despite medications
- Inability to move toes or new numbness/tingling (neurovascular compromise)
- Calf swelling, redness, or pain (DVT)
- Fever, wound drainage, or increasing redness (infection, especially post-operative)
- Feeling of the knee "giving way" or sudden loss of ability to straighten the leg (secondary displacement/extensor mechanism failure)
- Expected recovery: Non-operative fractures typically heal in 6–8 weeks; full functional recovery may take 3–6 months. Post-surgical patients should expect hardware-related discomfort in up to 29.6% of cases, often requiring removal [23]
- Physical therapy: Initiate after fracture consolidation; focus on quadriceps strengthening, ROM restoration, and gait training
References
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