Luxation of the knee cap

Anatomy: The large anterior thigh muscle (musculus quadriceps femoris) consists of four muscles (m vastus lateralis, m vastus medialis, m vastus intermedius & m rectus femoris). All the muscles fasten on the upper edge of the knee cap. The knee cap ligament (ligamentum patellae) connects the lower edge of the knee cap with the front part of the shin bone (tuberositas tibiae). The knee cap is held in place by the structures that fasten on the knee cap, especially the anterior thigh muscle, joint capsule and several ligaments (retiaculum patellae mediale & retiaculum patellae laterale) as well as the knee cap ligament.

Symptoms: Sudden insetting severe pain that renders continued sports activity impossible. The knee cap can become completely displaced to the external side of the knee in some cases, and the knee will consequently be locked in a flexed position (total luxation) until the knee cap suddenly slips into place again allowing the knee to be stretched once more. In other cases, the knee cap will only be partially displaced to the external side of the knee (subluxatio patellae).

Acute treatment: Click here.

Examination: The diagnosis can be difficult if the knee cap is in its correct position, and anyone with suspicions of displacement of the knee cap should always seek medical attention to ensure the diagnosis and correct treatment. The examination will typically provoke severe pain when the knee cap is pressed outwards (lateral) whilst the knee is flexed (Apprehension test). The knee cap will often be able to be pressed further out on an injured knee than a healthy one. An MR scan will be able to reveal more information regarding the cartilage condition in the knee after a partial or total luxation of the knee cap (article).

Treatment: Partial luxation should primarily be treated with relief and rehabilitation. There is no general consensus of opinion regarding treatment of total luxation of the knee cap, some recommend surgery whilst others advocate relief and rehabilitation (article 1) (article 2). Surgery should however be considered with repeated (total or partial) luxation.

Rehabilitation of non-operated, partial luxation of the knee cap (subluxatio patellae).

Bandage: Tape and bandaging has no documented preventive effect subsequent to previous total or partial luxation of the knee cap (article), however experience has shown that this is utilised to a large degree (tape-instruction).

Complications: In case of lack of progress it should be considered whether the diagnosis is correct. Special consideration should be given to:

• Cartilage damage (osteochondral lesions)
• Cartilage damage on the knee cap (chondromalacia patellae)
• Bone fracture
• Meniscus lesion
• Anterior cruciate ligament rupture
• Posterior cruciate ligament rupture
• Bone membrane tear (periosteal avulsion)
• Fluid accumulation in the joint (traumatic arthritis/synovitis))
• Inflamed mucous fold (plica synovialis)
• Knee cap ligament rupture

Special: Since there is a risk that the injury can cause permanent disability, the injury should be reported to your insurance company. A running style analysis can be considered to evaluate whether a correction to the running style can be recommended.