With knee breakdown on the rise - increasingly with fit people - the question of what causes knee arthritis has never been more immediate. Truth is, over-exercising is strongly implicated. And with high-impact exercise at the forefront, knee alignment problems are invariably the backdrop on which early knee arthritis is played out.
Watch Sarah on video taking you through the A to Z on knees: the anatomy, the joint cartilage, the cushion of fluid in the joint capsule preventing bone-to-bone contact. Sarah also takes you through the causes of knee arthritis through faulty alignment of knees, ankles and feet - and yes, even diet. Most importantly of all, the video shows you the 5 important exercises to prevent knee arthritis. You can download this video now.
The knee is a huge weight-bearing synovial joint. And, like all such joints it is made up of a thin, shiny, super-slippery buffer of hyaline cartilage covering the surfaces of the thigh (femur) and shin bone (tibia). Hyaline cartilage covering the opposing bones has the yielding compliance of dense plastic.
The knee joint is held together by a super-strong joint capsule and reinforced either side by the medial and lateral ligaments of the knee. The synovial membrane lining the inside of the capsule secretes synovial fluid to lubricate and cool the joint - and many other things besides. Synovial fluid is magic stuff!
The knee joint endures massive forces of wear and tear. Two additional 'C' shaped fibro-elastic cartilage rings on the top surface of the tibia - called the medial and lateral menisci - help to mitigate bone-to-bone contact and defray the crushing forces of jarring and grinding through the knee. The knee meniscii have a resilient rubbery texture, like the cartilage of your ear or nose, specifically designed to absorb shock. This dual menisci set-up also locks the knee.
Because of their workload, knee cartilages look tatty with bits and pieces of fibrous cartilage hanging off, even at the best of times. So even if your scans look alarming, there may be no cause for concern. Having said that, knee breakdown is common . . . . and knee arthritis usually starts on the inner side (medial compartment) of the knee joint, with the medial meniscus the first to break down.
Depending whether you are bow-legged (genu varus) or knock-kneed (genu valgus) you will load up either the inner or outer compartment more and cause it to breakdown earlier. Sometimes knee arthritis will limit itself to one compartment only, with the inside of the knee 90% more common that the outer.
You can be born with a congenital pre-disposition to bows legs, but you can also develop bow legs with complicated diseases like rickets. The angulation at the knee greatly adds to the inner loading of the medial compartment and leads to early breakdown. You will read below that ankle posture also effects load-bearing through the knee.
An inverted or varus heel in another of the common causes of knee arthritis. It adds a potent varus (bow-legged) strain to the knee. You will read below that this can be corrected to a degree with wedge-shaped inserts worn in the shoe. However, errant foot posture can sometimes be more complicated - particularly when a varus heel co-exists with fallen inner arches of the foot. Pronation (or rolling in of the forefoot) occurs as a compensatory measure, twisting the mid-foot and potentiating the falling medial arch of the foot. The podiatrist may need to provide orthotics that correct both anomalies - to literally 'untwist' the foot - and this will help the knee.
Walking with the toes turned out like Charlie Chaplin is another of the potent causes of knee arthritis - bringing about early breakdown of the medial compartment. The action during walking involves striking the ground with the outside of the heel (which wears the heel rubber down as shown above) and rolling diagonally inwards over the foot as you roll your weight forward to push off. Push off then happens through the inside of the big toe, rather than the toe tip, causing calluses or thickened skin there.
Outer heel strike also adds unwanted twisting forces to the 2D-hingeing-motion of the knee bending and straightening. Although it may take decades to manifest, walking with the toes turned out stresses the medial knee compartment through both excessive loading and twisting of the joint. It also tends to flatten the medial arches of the feet, thus causing developmental foot problems.
The surgical procedure of wedge osteotomy is rarely performed these days, even though it was a highly successful orthopaedic operation. It involved realigning the bow-leg by cutting out a wedge of bone and screwing the bones of the leg back straight.
More commonly today, surgeons go straight to knee medial compartment joint replacement. Be warned however, this operation is not always successful and has a high revision rate. Total knee replacement is more successful than single compartment replacement, although residual poor knee alignment post-op is the downfall of these procedures.
You may like to listen to a Part 1 ABC Radio National 'Health Report' on knees and Part 2 for more information here.
Wearing 4-5mm cork heel wedges can dramatically slow the progression of medial compartment knee arthritis. Lifting the outer heel moves the line of gravity outwards (laterally) and causes more weight to be taken through the outside of the knee. In other words, it loads the outer knee more and off-loads the inner knee. You can ask your boot maker to makes these for you! Or we can send you some.
The leg mal alignment of knock knees causes excessive loading of the outer knee compartment. The inside of the knee joint is much looser than the outside, with medial ligamant sprain by far the most common soft tissue injury of the knee. This natural weakness and laxity of the inside of the knee joint can also predispose to developmental knock knees with advancing years.
Knee arthritis of the lateral compartment progresses more slowly and is less common than medial medial compartment. The outer knee is more sturdy and it is harder to strain the lateral ligament of the knee as a result of soft tissue injury. Thus, this part of the knee is more likely to suffer compression strain only.
Apart from the inherent weakness of the inner knee, poor foot and ankle alignment can also stress the outer knee compartment. The most common of the causes of knee arthritis of the lateral compartment is fallen medial arches of the foot and a valgus or 'splay' alignment of the heel. It is common for both anomalies of the feet to occur together.
The line of gravity falling outside the knee creates a lateral buckling effect on the knee which takes advantage of the natural weakness of the inner knee. The medial ligament is passively stretched as the outer compartment is compressed. The pain of genu valgus knee arthritis is often a complex cocktail of chronic medial ligament sprain and lateral compartment cartilage erosion.
The surgical solutions of knee arthritis of the lateral compartment are similar to the medial, with knee replacement increasingly common.
Watch a fascinating video of Sarah explaining all about the knee joint, hyaline cartilage - even diet. Best of all, watch her simple exercises to start you on the road to recovery. Download here.