Dislocated patella

 Findings

a)      The patella dislocates to the lateral side of the knee but may reduce spontaneously with pressure on the lateral side of the patella or require sedation to achieve reduction.

b)      An athlete may present after the incident because of pain but with a history of immediate swelling. However, this may in fact be a description of the displaced patella or a haemarthrosis, and, because the knee capsule ruptures, the swelling may be generalized around the knee rather than confined to the joint. Bruising may occur later.

c)      Pain on quadriceps loading.

d)     Clarke’s test remain positive for some time after the patella is reduced.

e)      A positive ballottement or bulge test may persist for some time.

f)       Apprehension test is positive for some time after.

g)      The patellar facets, usually medial, remain tender to palpation for some time after.

h)      The lateral femoral condylar articular surface remains tender to palpation for some time after.

Cause

a)      A traumatic, extrinsic impact dislocates the patella.

b)      Recurrent dislocation ( Many normal knees that suffer patellar dislocation will develop chondral or osteochondral damage on the deep surface of the patella or lateral femoral condyle.  In contrast, the abnormally lax patella may suffer recurrent dislocation without any damage being caused to the underlying bone; this is because the patella and femoral condyle do not grind across one another during the dislocation.)

Treatment

a)      Reduction of the dislocation and aspiration of any haemarthrosis, if present.

b)      Possible open repair of the ruptured lateral capsule.

c)      Electrical and physiotherapeutic modalities to relieve pain, settle soft tissue swelling and maintain muscle strength.

d)     Low load, high repetition exercise. Increase the loads as improvement in pain tolerance permits.

e)      Correct any pronation at the foot, functional valgus at the knee and weakness of the external rotators of the hip as these will hinder healing by promoting lateral tracking of the patella.

f)       Control patella maltracking with a patella brace or McConnell strapping techniques, as the lateral capsule is usually either ruptured or lax.

g)      Cross-train by rowing, cycling, backstroke or freestyle swimming.

h)      Closed chain leg exercises.

i)        Progress to the knee ladders.

Sports

Osteochondral damage will take much longer to heal, and may prevent deep knee bends or much quadriceps power beind applied to the knee until it has healed. Cross-training and low load, high repetition weights may have to be maintained for a considerate time.

Acute dislocation in a normal knee is a severe injury and only 60% may return to their previous sporting activity with no or minor limitations.

"Concise guide to sports injuries, 2^nd edition",Churchill Livingstone, Malcolm T.F. Read,  foreword by Bryan English