Authors

 Dr Keran Sundaraj MBBS MSc (Trauma) FRACS FAOA

In normal motion, the patella (kneecap) sits within the trochlear (groove at the end of the thigh bone). Patella dislocation occurs when the patella 'pops' out of this groove. Patella instability can be a troublesome condition, with recurrent episodes of dislocation or symptoms that mimic the patella popping out of its usual groove.

Cause

Patella dislocation most commonly occurs due to a non-contact twisting injury. Less commonly, it may be due to a forceful blow, such as in a collision during sport. There are general patient factors and local knee factors that make this more likely.

General patient factors;

• Ligamentous laxity (hypermobility, "double jointed")

• Previous patellar dislocations

• Valgus alignment (knock-kneed)

Local knee factors;

• Patella alta (high knee caps)

• Trochlear dysplasia (flat groove)

• Patella tilt (kneecap tilts to the outside)

• Weak Vastus Medialis Oblique (VMO) muscle (part of the inner quadriceps)

• Tight lateral structures - iliotibial band (ITB)

Symptoms

Patients sometimes experience ongoing issues with their knee after the first episode of dislocation. Such symptoms can include;

• Pain in the front of the knee with activity

• Knee buckling

• Catching during movement

• Stiffness

• Crepitus (crackling)

• Swelling

Imaging Tests

X-rays

• They are used in acute episodes of dislocation to assess whether the patella is reduced (back in its usual place).

• Floating or fractured bone may be seen - this is usually an indication for surgery.

• These may also demonstrate local knee factors that place a patient at risk of repeat dislocation.

MRI

• MRI is performed for all first-time dislocations. Plain x-rays can miss fragments of cartilage that can be sheared off when the patella dislocates/relocates.

• This should be obtained within the first two weeks after injury.

Treatment

The initial step for a dislocated patella is to replace it to its normal position. Relocation may have already occurred spontaneously or may need to be undertaken with the help of pain-relieving medications. For those whose patella has been out for some time (usually more than an hour), sedating medications may be necessary to relax the muscles. Once relocated, a brace is generally not required except in the most extreme examples.

In the days following the injury, patients need a period of rest, ice, compression and elevation (RICE). It is vital to commence some activity as soon as possible, as the quadriceps will atrophy (shrink). This risks the patella becoming more unstable. Appropriate exercise includes the use of an exercise bike.

In the weeks following the injury, patients undertake a rehabilitation program tailored to their specific needs. Most commonly, this includes;

• VMO strengthening (terminal extension exercises)

• ITB stretches

• Hip abductor strengthening

• Core strengthening

Patella taping (McConnell taping) is sometimes used to help activate the VMO. A cycling program is a valuable way of maintaining strength and mobility in the knee joint.

Surgery may be necessary if the imaging tests show cartilage or bone that is free-floating. Surgery is otherwise reserved for patients who experience ongoing dislocation or instability symptoms despite conservative measures. Options for surgery vary depending on the previously mentioned factors that contribute to instability. These include, but are not limited to;

• Arthroscopy - to remove loose bodies and assess the joint

• Ligament reconstruction - medial patellofemoral ligament (MPFL) is a 'checkrein' to guide the patella into the groove.

• Iliotibial band release - a structure on the outside of the knee that can become tight and pull the patella outwards

• Tibial tubercle osteotomy - a realignment of the patella tendon if in an abnormal position.

More information on the rehabilitation process following MPFL reconstruction can be found here. 

What to Discuss with Dr Sundaraj

• What combinations of surgical procedures might I require?

• When can I return to work?

• When can I start driving?

• Will I be in a splint?

• When can I start physiotherapy?

• What is the likely outcome from this treatment?

• When do I need to come back?