Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Patella Dislocation

SYMPTOMS

The knee gives way (often with a loud popping sound) followed by immediate haemarthrosis and pain in the anterior part of the knee, preventing further activity.

AETIOLOGY

The medial patella retinaculum ruptures, allowing the kneecap to migrate laterally. The kneecap can lock the knee in the flexed position by getting stuck outside the lateral femur condyle. The patella dislocates during a valgus hyper-extension sprain or from direct side trauma. The first time this happens the diagnosis is clear unless there is a
spontaneous reduction. In many cases it is however a non-contact injury where the player loses their balance and twists the knee. This injury is often associated with other injuries to cartilage, menisci, capsule or ligaments.

CLINICAL FINDINGS

There is intra-articular bleeding (haemarthrosis) in most cases. In first dislocations, if there is a retinaculum rupture, blood can penetrate from the joint and cause bruising around the medial anterior part of the knee. There
is distinct tenderness on palpation around the patella. Since there are often associated injuries, examination must also include tests for cruciate ligaments, menisci and cartilage.

INVESTIGATIONS

Clinical examination is the most important tool for diagnosis and should include tests for all ligaments and other structures in the knee. X-ray is valuable to rule out fractures, in particular in growing or elderly athletes. MRI or
arthroscopy is important for evaluating associated injuries. Note! There is a high risk that the cartilage on the kneecap as well as on the femur condyle will have been damaged. The combination of ACL rupture and patella dislocation is also not uncommon.

TREATMENT

A dislocated kneecap can be repositioned by gently extending the knee with the foot externally rotated to allow the kneecap to slide back into position. An athlete with haemarthrosis and suspected patella dislocation should be seen by an orthopaedic surgeon to consider early arthroscopy. This procedure can verify the diagnosis and deal with
associated injuries that are often missed. Surgical repair of the medial retinaculum is only indicated in severe cases. If the injury reoccurs despite thorough physiotherapy other surgical options are available. These cases should be handled by a knee specialist.

REFERRALS

Refer to an Dr Kevin Yip (+65 9724 1219), consultant senior orthopaedic surgeon for further investigations to verify the extent of the injury. Physiotherapists will be involved in close collaboration with the surgeon.

EXERCISE PRESCRIPTION

Cycling and swimming are good alternatives to keep up general fitness. Valgus stress to the knee should be
avoided so breast stroke is not recommended.

EVALUATION OF TREATMENT OUTCOMES

Monitor clinical symptoms and signs. Different functional knee scores for different sports are available to measure when the knee allows a return to full sport.

DIFFERENTIAL DIAGNOSES

This is a straight – forward diagnosis but associated injuries to the menisci, cartilage or cruciate ligaments should
always be borne in mind.

PROGNOSIS

Good-Fair. Appropriate treatment will allow a return to professional sports within three (non-operative) to six months (after surgery).

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