Patellar Injuries, Emergency Medicine

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Patellar Injuries, Emergency Medicine

Basics

Description

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

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 mechanismDirect blow or fall on patellaUsually 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 tendonUsually 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

Most common mechanism
Direct blow or fall on patella
Usually results in comminuted or minimally displaced fracture, or open injury

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)

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 athletesMicrotrauma from repetitive activity

Microtrauma from repetitive activity

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

Etiology

Risk factors for patellar dislocation:Genu valgum (knock-knee)Genu recurvatum (hyperextension of knee)Shallow lateral femoral condyleDeficient vastus medialisLateral insertion of patellar tendonShallow patellar groovePatella alta (high-riding patella)Deformed patellaPes 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

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)

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 tendinitisHistory of diabetes mellitus, previous steroid injections, rheumatoid arthritis, gout, systemic lupus erythematosusPrevious major knee surgery

Often in athletes

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

Signs and Symptoms

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 apprehensionAttempts to push patella medially do not

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

Essential Workup

Diagnosis Tests & Interpretation

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

Comparison view may help differentiate

Differential Diagnosis

Patellar subluxation
Femoral or tibial fracture
Traumatic bursitis
Quadriceps tendon rupture

Treatment

Pre-Hospital

Initial Stabilization/Therapy

Ed Treatment/Procedures

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

Occasionally, simultaneous pressure may have to be applied over the lateral aspect of patella in a medial direction

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

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

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 mmUnable to raise extended leg off bedArticular step-off >3 mm
All open fractures require debridement and irrigation; such patients should be admitted.
For patellar tendon rupture, discuss case with orthopedics.

Fragments displaced >4 mm
Unable to raise extended leg off bed
Articular step-off >3 mm

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

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)