A 32 male presents to the ED following a hefty collision with another player during a football game. During the altercation he sustained a direct blow to the medial aspect of his left knee.
On examination the patient is lying on a trolley in considerable pain, you look at the left kneecap and noticed it’s displaced laterally. The nurse starts administering Nitrous Oxide to the patient which helps the pain considerably.
- Majority of patella dislocations occur in females, especially targeting teenage girls.
- Literature shows, depending on the study that 30-72% of patellar dislocations are sports related and 28-39% will involve osteochrondral fractures
- The most common location of patella dislocations is lateral dislocation.
- Patients complain of the knee suddenly giving way, and inability to weight-bear or extend the knee and are often in considerable pain.
- The Patellar is the largest sesamoid bone in the body, and it resides within the complex of the quadriceps and patellar tendons.
- It functions as both a lever and a pulley.
- As a lever, the patella magnifies the force exerted by the quadriceps or knee extension.
- As a pulley, the patella redirects the quadriceps force as it undergoes normal lateral tracking during flexion.
Mechanism of Injury:
- Generally there is two types of mechanisms that result in patella dislocations.
- Type 1: results when there is a powerful contraction of the quadriceps in combination with sudden flexion and external rotation of the tibia on the femur. This is the most common reason for the patellar to dislocate.
- Type 2: results from direct trauma to the patella with the knee in flexion, can cause dislocation, however this is seen uncommonly.
Patellar Dislocations are common in patients with the following:
- Genu valgum
- Genu recurvatum
- Excessive femoral neck anteversion or internal femoral torsion
- External tibial torsion
- Lateral insertion of patella ligament on the tibia
- Contracture of the lateral patellar retinaculum
- Relaxation of attenuation of medial patellar retinaculum
- Hypoplasia or dysplasia of the patellar
- Hypoplasia or flattening of the trochlear grove
- Patellar alta or high riding patellar
- Atrophy of the vastus medialis muscle
- Pes planus
- Generalised joint laxity
Assessment of Patellar Dislocation:
- Assess neurovascular status distal to the patellar
- The apprehension test can be used to assess for patellar dislocation and subluxation. Apprehension sign occurs when the knee is placed at 30° flexion, and lateral pressure is applied. Medial instability results in apprehension by the patient.
- Examine for anterior defect, the laterally deviated patellar, and swelling and medial joint line tenderness of the partially flexed knee.
- Order X-rays of the knee AP and lateral generally provide adequate views.
- If the patellar is already relocated, still order X-rays to rule out fracture
Management of Patellar Dislocation
- Provide analgesia, Nitrous Oxide with oxygen is generally effective and can also be used during reduction of the dislocation
- Reduction is achieved by pushing the patellar medially with firm pressure, whilst extending the knee.
- First time dislocations should be splinted in above knee plaster cast and referred to the next available fracture/orthopaedic clinic
- Patients presenting with recurrent dislocations post reduction, can be splinted in a pressure bandage or Richards splint, until follow up can be arranged.
- Patients should be discharge home on crutches with simple analgesia for pain control.
- Generally conservative management is all that is required for patellar dislocations, surgical intervention is considered when recurrent dislocations occur, and those with anatomical abnormality.
- Fiebel, R. Dehghan, N. Cwinn, A. (2007). Irreducable lateral pattelar dislocation: The importance of impaction fracture recognition. The Journal of Emergency Medicine. 33(1), 11-15. [Reference]
- Patellar Dislocations. (2007). In Buttaravoli, P (Ed), Minor Injuries Splinter to Fractures (p.509-512). Philadelphia: Mosby Elsevier.
- Lu, D. Wang, E. Self, W. & Kharasch, M. (2010). Patellar Dislocation Reduction. Academic Emergency Medicine. 226.
- Malanga, G. White, B. Lee, W. & Angeson, T. (2009). Patellar Injury and Dislocation. Accessed 30/04/2010 @ http://emedicine.medscape.com/article/90068-overview
- Simon, R. Sherman, S. Koenigsknecht, S. (2007). Patellar Dislocations: Emergency Orthopaedics The Extremities. pp.430-432. New York: McGraw Hill