Patella

Sinding-Larsson Johansson syndrome

This is tenderness of the apex (lower pole) of the patella after repetitive pulling by the patellar ligament. It is one of the juvenile osteochondroses, and causes anterior knee pain. It is commonest in children aged twelve to fourteen years of age, and among those children that play a lot of sports. The same kind of symptoms have been reported where the quadriceps inserts onto the base of the patella. A similar disease process occurs at the tibial tuberosity, and is known as Osgood-Schlatter disease.

Patellar reflex

Patellar reflex also known as knee jerk is the contraction of quadriceps femoris muscle resulting in the extension of knee joint. The myotome that causes knee extension is L2-4 i.e. the femoral the lower two divisions of the femoral nerve. The patient is asked to relax their knee, and the patella ligament (below the tibial tuberosity, and above the tibial shaft) is struck.

In normal patients the knee should extend slightly. The patellar reflex may be more pronounced or diminished in some individuals and is not always a sign of neurological disease. If the knee fails to react (absent reflex), it may be a sign of a lower motor neuron lesion. If the knee extends too much and rapidly or forcefully extends (brisk/exaggerated reflex), it can be a sign of an upper motor neuron lesion.

Patellar dislocation

These dislocations are relatively common among athletes, particularly young female athletes. The patella most often dislocates laterally, as the medial femoral condyle projects further anteriorly than the lateral femoral condyle. The apprehension test is utilised to determine if the patient has previously had a patellar dislocation. The clinician will apply pressure to the medial surface of the patella, and if the patient has previously had a dislocation they will express concern. If they have not had a dislocation previously i.e. not experienced the pain of the dislocation, they are less likely to be concerned.

Patellar dislocation is also common in patients who have had prolonged bed rest. The patella is pulled medially by the vastus medialis, and laterally by the vastus lateralis and the vastus intermedius. When the patient is in bed for a prolonged period, the vastus medialis wastes more than the lateral pulling muscles, and hence the patella can be dislocated laterally, due to the pull of two muscles (vastus lateralis and vastus intermedius) against one medially pulling muscle (vastus medialis).

Patellar fracture

The patella sits on the anterior surface of the femoral condyles, and is hence relatively vulnerable. Direct trauma to the knee is the commonest cause of patellar fracture. Symptoms include swelling of the knee and pain in the region. Surgery is the most usual treatment.