The Knee-Part 2
Posted: Thursday, November 12, 2009
by Jonathan Blood Smyth
As the knee approaches the position where it is going to lock the femur rotates inwards, a movement which is only small but vital to the normal function of the knee, indicating its great complexity beyond a simple hinge. The minor movements which occur internally in the joint are restricted in the knee and it cannot manage to lose any of these small motions without functional loss as a consequence. Accessory movements are the name given to these limited gliding and sliding movements which normally occur during activity but which can't be done on their own.
The knee is controlled by very powerful musculature and can perform fine coordinated actions as well as power movements. We can do a full knee bend and then get right up again without any delay in the movement. The amplitude of the accessory knee movements is not large but may be useful in managing uneven surfaces. The medial side of the knee gaps more significantly under stress as the medial ligament is looser than the lateral and the slight natural knock knee alignment tends to stress the knee that way.
As reviewed in the article which precedes this one, the knee functions typically only in one plane, that of forwards and backwards. If a sideways stress is introduced so movement occurs in another plane also, as with knock-knee or bow leg, the patello-femoral joint and the knee compartments can suffers degenerative consequences. The compartments of the knee are the division into the outside half and the inside half of the joint, with each consisting of a tibial and femoral condyle, a meniscus and the ligament. The amount of sideways angulation alters the way that stresses pass across the knee compartments.
If a degree of bow leg develops in the knee the pull of the quadriceps on the kneecap tends to bowstring it inwards to some extent, making the kneecap grate against the inner side of the femoral groove, potentially causing pain. This also forces increased stresses onto the lateral compartment of the knee, increasing the degenerative processes on that side of the joint. Slight knock knee is more common, and this predisposes the person to lateral kneecap pain and degenerative changes in the medial compartment of the knee.
If the knee is not capable of full extension then the kneecap can develop problems due to the persistent flexion which makes the quadriceps overactive to hold the knee in place, increasing patellar compression. This increased compression can cause a very common condition known as anterior knee pain or patellofemoral pain. To correct the lateral misalignment a small wedge can be placed under the outer edge of the heel to correct alignment of the shin and so influence the stresses which are passing through the knee joint above.
The patella can also suffer as a consequence of changes which occur in other joints nearby. The arches of the feet can weaken from bearing our weight for many years, losing strength and collapsing to some degree towards flat foot. When the foot bears weight the arch collapses inwards and takes the ankle and the lower leg with it, increasing the degree of knock knee. This can predispose towards anterior knee pain as the patella is forced medially against the femur. Corrective orthotics to be worn in the shoes can be a useful treatment, allowing heel correction as well as support for the arches in weight bearing.
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapists, physiotherapy, physiotherapists in Leeds, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
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