Rosen & Barkin's 5-Minute Emergency Medicine Consult (512 page)

CODES

• 112.3 Candidiasis of skin and nails
  
• 681.02 Onychia and paronychia of finger
  
• 681.9 Cellulitis and abscess of unspecified digit
  

BASICS

• Usually caused by sudden flexion and external rotation of tibia on femur, with simultaneous contraction of quadriceps muscle
  
• Direct trauma to patella is a less common cause
  
• Lateral dislocation of the patella is most common, with the patella displaced over the lateral femoral condyle
  
• Uncommon dislocations include superior, medial, and rare intra-articular dislocation
  

• Direct trauma:
  
  • Most common mechanism
    
  • Direct blow or fall on patella
    
  • Usually results in comminuted or minimally displaced fracture, or open injury
    
• Indirect forces:
  
  • The result of excessive tension through the extensor mechanism during deceleration from a fall (can also cause patellar tendon rupture)
    
  • Avulsion injury from sudden contraction of the quadriceps tendon
    
  • Usually results in transverse or displaced fracture (often both)
    
• Types of patellar fractures:
  
  • Transverse: 50–80% (usually middle or lower 3rd of patella)
    
  • Comminuted (or stellate): 30–35%
    
  • Longitudinal: 25%
    
  • Osteochondral
    

• Usually caused by forceful eccentric contraction of quadriceps muscle on a flexed knee during deceleration (e.g., jump landing and weight lifting)
  
• Often occurs in older athletes
  
  • Microtrauma from repetitive activity
    

• Overuse syndrome from repeated acceleration and deceleration (jumping, landing)
  

• Risk factors for patellar dislocation:
  
  • Genu valgum (knock-knee)
    
  • Genu recurvatum (hyperextension of knee)
    
  • Shallow lateral femoral condyle
    
  • Deficient vastus medialis
    
  • Lateral insertion of patellar tendon
    
  • Shallow patellar groove
    
  • Patella alta (high-riding patella)
    
  • Deformed patella
    
  • Pes planus (flatfoot)
    
• Common injury in adolescent athletes, especially girls
  
• The younger the patient at the time of initial dislocation, the greater the risk of recurrence
  

• Male:female ratio 2:1
  
• Highest incidence in those 20–50 yr old
  

• Peak incidence in 3rd and 4th decades:
  
  • Often in athletes
    
• Risk factors:
  
  • History of patellar tendinitis
    
  • History of diabetes mellitus, previous steroid injections, rheumatoid arthritis, gout, systemic lupus erythematosus
    
  • Previous major knee surgery
    

• Microtears of tendon matrix from overuse
  
• Seen in high jumpers, volleyball and basketball players, runners
  

DIAGNOSIS

• History of feeling knee “go out”; popping, ripping, or tearing sensation
  
• Pain
  
• Inability to bear weight
  
• Obvious lateral deformity of patella
  
• Mild to moderate swelling
  
• Often reduces spontaneously before ED evaluation
  
• Tenderness along patella
  
• Positive apprehension test or Fairbanks sign:
  
  • Attempts to push the patella laterally elicits patient apprehension
    
  • Attempts to push patella medially do not
    

• Pain over anterior knee
  
• Difficulty ambulating
  
• Increased pain with movement of patella
  
• Tenderness and swelling over patella
  
• Difficulty or inability to extend knee
  
• Palpable defect, crepitus, or joint effusion/hemarthrosis
  

• Abrupt onset of severe pain
  
• Decreased ability to bear weight
  
• Occasionally hemarthrosis
  
• Proximally displaced patella
  
• Incomplete extensor function
  
• Inability to maintain knee extension against force
  

• Pain in area of patellar tendon
  
• Pain worse from sitting to standing or going up stairs
  
• Point tenderness at distal aspect of patella or proximal patellar tendon
  

Radiographs essential

• Anteroposterior (AP), lateral, and sunrise views of the knee should be obtained, pre- and postreduction
  
• Postreduction radiographs help exclude osteochondral fracture (in patellar dislocations)
  
• Bipartite patella (patella with accessory bony fragment connected to main body by cartilage) may be mistaken for fracture:
  
  • Comparison view may help differentiate
    
• For patellar tendon rupture, a high-riding patella (i.e., patella located superior to level of intercondylar notch) is observed
  
• For patellar tendinitis, radiographic findings unlikely with symptom duration of <6 mo
  

• Patellar subluxation
  
• Femoral or tibial fracture
  
• Traumatic bursitis
  
• Quadriceps tendon rupture
  

TREATMENT

Patient should be transported in supine position with knee flexed and supported.

Appropriate history and physical exam to identify any associated injuries (e.g., femoral fracture, hip fracture, posterior hip dislocation) and assess extensor mechanism

• For simple lateral patellar dislocation, reduce dislocation by extending the knee gently to 180°:
  
  • Occasionally, simultaneous pressure may have to be applied over the lateral aspect of patella in a medial direction
    
• For other types of patellar dislocation (superior, medial, intra-articular), do not attempt reduction; consult orthopedics
  
• Aspiration of hemarthrosis with sterile technique is necessary if reduction is difficult
  
• If osteochondral fracture is present (28–50% of cases), obtain orthopedic consultation
  
• Although reduction is typically easy to accomplish, procedural sedation or parenteral analgesia may facilitate it
  
• Conservative (nonoperative) management of dislocations leads to recurrent instability in 60% of patients, but there is no evidence to support operative care in primary dislocations
  

• Orthopedic consultation when patellar fracture is confirmed
  
• Nondisplaced fractures with intact extensor mechanism are managed nonsurgically
  
• Initial treatment often consists of long-leg bulky splint and subsequent operative repair
  

• Orthopedic consultation, with surgical repair within 2–6 wk
  

• Rest, avoidance of inciting activity, heat, and NSAIDs
  

• Fentanyl citrate: 0.5–1.5 μg/kg (peds: 0.5–1.0 μg/kg) IV
  
• Midazolam HCl: 1–2.5 mg (peds: 0.05–0.1 mg/kg, max. dose 6 mg) IV
  
• Morphine sulfate: 2–5 mg per dose (peds: 0.1–0.2 mg/kg per dose) IV
  
• Meperidine: 50–150 mg (peds: 1.1–1.8 mg/kg) IM q3–4h prn
  
• Ketorolac: 60 mg IM; 30 mg IV (peds: 0.5–1 mg/kg IV, max. 15 mg dose if <50 kg; max. 30 mg dose if >50 kg, IV)
  
• Methohexital: 1–1.5 mg/kg (1 mL q5sec) (peds: 0.5–1 mg IV) IV
  
• Propofol: 1–2 mg/kg IV (20 mg bolus q45sec) push slow IV to avoid dec BP (peds: 1 mg/kg not to exceed 40 mg))
  

FOLLOW-UP