The Knee-Part 3
Posted: Thursday, November 12, 2009
by Jonathan Blood Smyth
The knee can be catapulted into a painful condition by a traumatic event or injury, often minor, which sets off the process. It does not take a large injury to start up swelling within the joint and the knee is sensitive to the presence of any amounts of fluid within it. The lining of the joint capsule is made up of synovial membrane, the tissue which secretes the lubricating fluid vital to a joint. However, this swelling is maintained within the capsule and irritates the capsule as the joint is repetitively moved. Thirty degrees is the usual angle injures knees are held at.
Chondromalacia patellae is a commonly diagnosed problem with the cartilage on the underside of the kneecap. Normally the kneecap sits lightly against the groove on the front of the femur and is only strongly pressed against it in loaded movements such as getting up from a chair or descending stairs. If the knee tightens and loses some of its accessory movements then the patella can become more tightly compressed against the femur. This can set up a frictional process between the two bony areas, particularly if there is bow leg or knock knee, where the tibia is rotated abnormally or where one leg is longer than the other.
The articular surface of the patella can become more inflamed and reduce the wish to keep the kneecap against the femur such as when the knee is kept bent, with regular extension to relieve the pain. The surface of the cartilage on the back of the kneecap suffers from gradual degenerative changes as increased forces are applied to it. As the surface becomes softened and lined, the amount of swelling increases as the condition worsens. The patella can sublux, where it moves off the edge of its femoral surface to some amount, in response to unplanned vigorous movements such as turning and twisting.
A patellar subluxation is of sudden onset and often exceptionally painful for the short time it occurs, damaging the joint surfaces and bringing on swelling and pain in the knee. Dislocation or subluxation of the patella mostly occurs towards the outside of the knee and subjects the inner knee tissues to a stretch. This slackness permits the pathological movements to recur more easily. Recurrent dislocation of the patella is common and can cause significant disability, with several orthopaedic procedures typically employed, such as medial reefing, where the inside tissues of the knee are tightened up to draw the kneecap more firmly in towards the middle.
After an attempt at minor interventions has not been successful then the surgeon can progress to tibial tubercle transposition, the moving of the bony prominence on the upper shin bone towards the inner side of the knee. This brings the line of pull of the quadriceps muscles into a more inwards line and draws the kneecap in away from the side where the pressure is greatest. Investigation by arthroscopy can show an appearance of fissures and softened cartilage in worse cases of damage. Wasting of the quadriceps muscle can occur in response to the inflammation and pain of this process.
The knee become gradually less supported as the main thigh muscle weakens and wastes, with going down slopes and stairs more difficult as these activities involve the imposition of greater forces across the patello-femoral joints. When we go downhill the quadriceps has to lengthen as it controls the body weight and this is a more stressful process than activities which involve muscle shortening.
Arthroscopic debridement of the patella, the surgical cleaning of the under surface of the kneecap, can be performed but the results are not clearly positive. Physiotherapists can use manual pressure techniques to approximate the joint surfaces and attempt to smooth out the irregularities of the joint but whether this actually occurs anatomically is not clear.
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapy, back pain, orthopaedic conditions, neck pain, injury management and physiotherapists in Gloucester. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
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