Sports Medicine
Sports Injury Prevention & Rehabilitation

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Patellar Dislocation

(Also known as Patella Dislocation, Dislocated Patella, Knee Cap Dislocation, Knee Dislocation)
What is patellar dislocation?
Patellar dislocation is a condition where the knee cap completely moves out of its normal position.
The knee comprises of the union of three bones – the long bone of the thigh (femur), the shin bone (tibia) and the knee cap (patella). The patella (knee cap) is situated at the front of the knee and lies within a groove at the front of the thigh bone. The tendon of the quadriceps muscle (the muscle at the front of the thigh) envelops the patella and attaches to the top end of the tibia. Due to this relationship, the knee cap sits in front of the femur forming a joint in which the bones are almost in contact with each other. The surface of each bone, however, is lined with cartilage to allow cushioning between the bones. The patella also has strong bands of connective tissue known as the patella retinaculum attaching the knee cap on either side of the femur. This joint is called the patellofemoral joint.
Normally, the patella is aligned in the middle of the patellofemoral joint and is held firmly in place by the quadriceps muscle and patella retinaculum. Occasionally, the patella may be pushed completely out of its normal position. This normally occurs due to traumatic forces pushing the knee cap out of position beyond what the quadriceps and patella retinaculum can withstand. When this occurs the condition is known as patellar dislocation.
Patellar dislocation usually occurs in a direction towards the outside of the knee (i.e. away from the other leg). During dislocation, tearing and disruption of the patellar retinaculum usually occurs. The joint surfaces may also be damaged and occasionally there may be an associated fracture. In many cases of patellar dislocation, the patella spontaneously moves back into its original position often with knee extension (i.e. straightening of the knee).

Causes of patellar dislocation
Patellar dislocation typically occurs when the forces pushing the knee cap out of its normal position are greater than the quadriceps muscle and patella retinaculum can resist. This typically occurs traumatically due to excessive twisting or jumping forces or due to a direct blow (usually to the inner aspect of the patella). Occasionally however, it may occur in the absence of trauma especially in young girls who are hyper-flexible. Patients with this condition are frequently seen in contact sports or sports requiring rapid changes in direction such as football or rugby.

Signs and symptoms of patellar dislocation
Patients with this condition usually experience sudden, intense pain at the front of the knee during injury. Pain is usually associated with a feeling of the knee 'giving way' or of something 'popping out'. There may be a noticeable visible deformity of the knee owing to the knee cap moving out of position (normally to the outer aspect of the knee) when compared to the unaffected knee. There may also be a rapid onset of knee swelling within the first 1-2 hours following injury. In patients who have experienced recurrent episodes of patellar dislocation, the knee cap may easily move back into its original position with certain knee movements (normally straightening of the knee). In these cases, pain and swelling may also be relatively minimal.
Once the patella has returned to its original position following dislocation, patients usually experience an ache that may increase to a sharper pain with activity. Pain is typically experienced during activities that bend or straighten the knee particularly whilst weight bearing. Activities that frequently aggravate symptoms include going up and down stairs or hills, squatting, running or jumping. There may also be an associated clicking or grinding sound when bending or straightening the knee. Patients may also experience episodes of the knee giving way or collapsing due to pain. In long standing cases, there may be evidence of quadriceps muscle wasting.

Diagnosis of patellar dislocation
A thorough subjective and objective examination from a physician is usually sufficient to diagnose patellar dislocation. Investigations such as X-ray or MRI should usually be performed to assist with diagnosis and rule out other conditions such as fractures or severe cartilage damage.

Treatment for patellar dislocation

For patients who do not have fractures or severe cartilage damage, treatment generally entails an appropriate physical therapy program. The success rate of treatment is largely dictated by patient compliance. Patients are usually required to use crutches in the first few days to weeks following patellar dislocation. A knee brace is often required for a number of weeks following injury and is dependent on the severity of injury and how well the patient is progressing with rehabilitation.
  • One of the key components of treatment is that the patient rests sufficiently from ANY activity that increases their pain until they are symptom free. Activities which place large amounts of stress through the patellofemoral joint should also be minimized, these include: squatting, jumping, running and going up and down stairs. Rest from aggravating activities allows the body to begin the healing process in the absence of further tissue damage.
  • Ignoring symptoms or adopting a 'no pain, no gain' attitude is likely to lead to the problem becoming chronic. Immediate, appropriate treatment in patients with patellar dislocation is essential to ensure a speedy recovery and reduce the likelihood of surgical intervention. Once the condition is chronic, healing slows significantly resulting in markedly increased recovery times and an increased likelihood of future recurrence.
  • Patients with this condition should follow RICE. RICE is beneficial in the initial phase of the injury (first 72 hours) or when inflammatory signs are present (i.e. morning pain or pain with rest). This involves resting from aggravating activities (crutches and a brace are usually required), regular icing, the use of a compression bandage and keeping the leg elevated. Anti-inflammatory medication may also significantly hasten the healing process by reducing the pain and swelling associated with inflammation.
  • Patients with patellar dislocation should perform pain-free flexibility and strengthening exercises as part of their rehabilitation to ensure an optimal outcome. One of the key components of rehabilitation is pain-free strengthening of structures that pull the knee cap away from the side of dislocation (i.e. the vastus medialis obliquus muscle (VMO) and stretching of tight structures that pull the kneecap towards the side of dislocation (particularly the ITB and lateral retinaculum). This is often in combination with core stability, pelvic and gluteal strengthening exercises to improve the control of the patellofemoral joint with weight-bearing activities. The treating physical therapist can advise which exercises are most appropriate for the patient and when they should be commenced. A gradual return to activity program should occur in the final stages of rehabilitation as guided by the treating physical therapist. Knee taping or bracing is usually required upon return to sport.

Surgery for patellar dislocation

Despite appropriate physical therapy management, some patients undergoing conservative treatment fail to improve or experience recurrent episodes of dislocation and subsequently require surgery for an optimal outcome. The majority of patients with severe cartilage damage or fractures also require surgery. Surgery for patellar dislocation is usually arthroscopic and typically involves removal of any loose bodies or torn cartilage and reconstruction of the torn patella retinaculum. The treating physical therapist and doctor will refer to a specialist if surgery may be indicated. Physical therapy and rehabilitation is required following surgery to ensure an optimal outcome and enable a safe return to activity or sport.

Contributing factors to the development of patellar dislocation

There are several factors which can predispose patients to developing this condition. These need to be assessed and, where possible, corrected with direction from a physical therapist. Some of these factors include:
  • muscle weakness (especially the VMO)
  • tight lateral (outer) patella retinaculum
  • loose medial (inner) patella retinaculum
  • general hypermobility
  • shallow femoral groove (i.e. the groove that the knee cap sits within)
  • genu valgum ('knock knees')
  • femoral anteversion (where the thigh bones turn inward)
  • patella alta (abnormally high patella in relation to the thigh bone)
  • poor lower limb biomechanics (flat feet, increase Q angle)

Physical therapy for patellar dislocation
Physical therapy treatment for patellar dislocation is vital to hasten the healing process, reduce the likelihood of recurrence and ensure an optimal outcome. Treatment may comprise:
  • soft tissue massage
  • electrotherapy
  • the use of crutches
  • taping or bracing to correct patella position
  • mobilization
  • dry needling
  • ice or heat treatment
  • progressive exercises to improve flexibility, balance and strength (especially the VMO muscle)
  • activity modification advice
  • biomechanical correction
  • anti-inflammatory advice
  • the use of Ultrasound to assess and retrain the VMO muscle
  • a gradual return to activity program

Other intervention for patellar dislocation
Despite appropriate physical therapy management, some patients with this condition do not improve. When this occurs the treating physical therapist or doctor can advise on the best course of management. This may include pharmaceutical intervention, corticosteroid injection or referral to an orthopaedic specialist who will advise on any procedures that may be appropriate to improve the condition. A review with a podiatrist may also be indicated for the prescription of orthotics to correct any foot posture abnormalities.