Basics
Description
Dislocation
- 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
Fracture
- 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
Patellar Tendon Rupture
- 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
Patellar Tendinitis
- Overuse syndrome from repeated acceleration and deceleration (jumping, landing)
Etiology
Dislocation
- 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
Fracture
- Male:female ratio 2:1
- Highest incidence in those 20 " 50 yr old
Patellar Tendon Rupture
- Peak incidence in 3rd and 4th decades:
- Risk factors:
- History of patellar tendinitis
- History of diabetes mellitus, previous steroid injections, rheumatoid arthritis, gout, systemic lupus erythematosus
- Previous major knee surgery
Patellar Tendinitis
- Microtears of tendon matrix from overuse
- Seen in high jumpers, volleyball and basketball players, runners
Diagnosis
Signs and Symptoms
Dislocation
- 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
Fracture
- 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
Patellar Tendon Rupture
- 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
Patellar Tendinitis
- 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
Essential Workup
Radiographs essential
Diagnosis Tests & Interpretation
Imaging
- 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
Differential Diagnosis
- Patellar subluxation
- Femoral or tibial fracture
- Traumatic bursitis
- Quadriceps tendon rupture
Treatment
Pre-Hospital
Patient should be transported in supine position with knee flexed and supported.
Initial Stabilization/Therapy
Appropriate history and physical exam to identify any associated injuries (e.g., femoral fracture, hip fracture, posterior hip dislocation) and assess extensor mechanism
Ed Treatment/Procedures
Dislocation
- 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
Fracture
- 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
Patellar Tendon Rupture
- Orthopedic consultation, with surgical repair within 2 " 6 wk
Patellar Tendinitis
- Rest, avoidance of inciting activity, heat, and NSAIDs
Medication
- Fentanyl citrate: 0.5 " 1.5 ¼g/kg (peds: 0.5 " 1.0 ¼g/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
Disposition
Admission Criteria
- Patients with superior, medial, or intra-articular dislocation or in whom a lateral dislocation cannot be reduced require orthopedic consultation in the ED and possible admission
- Patellar dislocation associated with a fracture (osteochondral or lateral femoral condyle) requires orthopedic consultation in the ED
- Indications for operative intervention:
- Fragments displaced >4 mm
- Unable to raise extended leg off bed
- Articular step-off >3 mm
- All open fractures require debridement and irrigation; such patients should be admitted.
- For patellar tendon rupture, discuss case with orthopedics.
Discharge Criteria
- Dislocation: Patients with successful reduction of lateral patellar dislocation and normal postreduction radiographs may be discharged with knee immobilization, crutches, and orthopedic follow-up.
- Fracture: If displaced <3 mm and patient has full active knee extension:
- Knee immobilizer, or bulky long-leg splint, partial to full weight bearing as tolerated with crutches and orthopedic follow-up within a few days
Pearls and Pitfalls
- Lateral patella dislocations often reduce spontaneously prior to arrival in ED; do not dismiss patients history of dislocation.
- In patella tendon ruptures, tendon defect may not be palpable if sufficient time has elapsed and swelling has occurred
Additional Reading
- Ahmad CS, McCarthy M, Gomez JA, et al. The moving patellar apprehension test for lateral patellar instability. Am J Sports Med. 2009;37(4):791 " 796.
- Fithian DC, Paxton EW, Stone ML, et al. Epidemiology and natural history of acute patellar dislocation. Am J Sports Med. 2004;32(5):1114 " 1121.
- Hing CB, Smith TO, Donell S, et al. Surgical versus non-surgical interventions for treating patellar dislocation. Cochrane Database Syst Rev. 2011;(11):CD008106.
- Melvin JS, Mehta S. Patellar fractures in adults. J Am Acad Orthop Surg. 2011;19(4):198 " 207.
- Rees JD, Maffulli N, Cook J. Management of tendinopathy. Am J Sports Med. 2009;37(9):1855 " 1867.
- Scolaro J, Bernstein J, Ahn J. Patellar fractures. Clin Orthop Relat Res. 2011;469(4):1213 " 1215.
- Stefancin JJ, Parker RD. First-time traumatic patellar dislocation: A systematic review. Clin Orthop Relat Res. 2007;455:93 " 101.
Codes
ICD9
- 726.64 Patellar tendinitis
- 836.3 Dislocation of patella, closed
- 836.59 Other dislocation of knee, closed
- 822.1 Open fracture of patella
ICD10
- M76.50 Patellar tendinitis, unspecified knee
- S83.006A Unspecified dislocation of unspecified patella, init encntr
- S83.016A Lateral dislocation of unspecified patella, init encntr
- S82.033C Displ transverse fx unsp patella, 7thC
- S82.009B Unsp fracture of unsp patella, init for opn fx type I/2
- S82.023A Displaced longitudinal fracture of unsp patella, init
- S82.026A Nondisplaced longitudinal fracture of unsp patella, init
- S82.036A Nondisplaced transverse fracture of unsp patella, init
- S82.043A Displaced comminuted fracture of unsp patella, init
- S82.046A Nondisplaced comminuted fracture of unsp patella, init
SNOMED
- 263029007 dislocation of patellofemoral joint (disorder)
- 281504005 Lateral patellofemoral dislocation (disorder)
- 37785001 Patellar tendonitis (disorder)
- 208596007 Closed fracture patella, transverse (disorder)
- 111643005 Open fracture of patella (disorder)
- 208601003 Closed fracture patella, comminuted (stellate) (disorder)
- 282773000 Injury of patella (disorder)
- 51037009 Fracture of patella (disorder)
- 80756009 Closed fracture of patella (disorder)