Articles
Focus on The Knee and Hip Joints in Osteoarthritis
These articles are independently commissioned and the author may express opinions which are not necessarily those of Smith & Nephew limited.
First of all, let's focus on the types of joints that we have in our bodies then we can begin to see how conditions affect them. We will be focusing on the joints in respect of the condition of osteoarthritis (OA) but there many conditions other than OA that can cause problems.
- Fibrous - like the joints that make up the skull
- Cartilaginous - the area where the ribs are joined to the manubrium (chest bone).
- Synovial - joints capsular joints which facilitate voluntary movement throughout the body.
We will concentrate now on synovial joints because it is synovial joints that are affected by osteoarthritis.
Synovial joints are those that allow us to move. A synovial joint occurs where two bones meet and are moved by muscles. The knee and the hip joint are both synovial joints and the elbow, shoulder, spine, hands and feet are all composed of synovial joints. Essentially anywhere where a muscle moves a part of your body which is under your control you will find a synovial joint.
All synovial joints have several things in common.
- The ends of the bones which meet have a covering of a very specialised cartilage which protects the joint and allows for smooth movement.
- The joint is enclosed by a capsule called the synovium.
- The joints all contain a fluid called synovial fluid.
- They can be affected by osteoarthritis.
The Knee Joint
As one of the main weight bearing joints of the body, the knee is exposed to a lot of stress during normal use. You use your knee joint over one million times per year and as a result it is the joint that is most susceptible to injury.
The knee is composed of three bones, the femur (thigh bone), the patella (kneecap) and the Tibia (shin bone).
The knee joint is one the main joints affected by osteoarthritis and there are over 35,000 knee replacements performed in the UK each year.
Knee ligaments
The knee is inherently unstable due its mobility and range of flexion so there are many powerful ligaments both inside and outside the joint which stabilise the joint whilst allowing flexibility.
Injuries to one of the main ligaments inside the knee joint, the anterior cruciate ligament or ACL, is one of the main problems affecting professional and amateur sportspeople.
The ACL connects the tibia to the femur at the centre of the knee. Its function is to limit rotation and forward motion of the tibia. A damaged ACL is replaced in a procedure known as an ACL reconstruction. And an injured knee which is also unstable can have a tendency to develop osteoarthritis over time.
There is another ligament which helps to stabilise the knee which is actually outside the joint. This ligament has a close relationship with the ACL and is called the posterior cruciate ligament or PCL.
The ACL and PCL ligaments cross over each other in the centre of the knee joint. It is rarer the injure the PCL because of the anatomy but when injuries do occur to the PCL they tend to be serious as the PCL is not as easy to reconstruct.
The other main ligaments which stabilise the knee are called the collateral ligaments and these run down the lateral (outside) and medial (nearside) aspects of the knee joint. These ligaments are also susceptible to injury and can be a source of pain in advanced osteoarthritis due to stretching stress caused by joint deformation.
The actual joint is formed by the two main weight bearing bones (the femur and the Tibia) The patella forms the frontal part of the knee joint and help smooth the path of the quadriceps muscle at the front of the thigh, the function of which is to extend the leg.
Articular Cartilage
Hyaline or articular cartilage is the tissue that covers the ends of the bones of synovial joints. It is normally 2-4mm thick in the main weight bearing joints. It is white and shiny with a rubbery consistency. Articular cartilage allows the surfaces of the bones to slide over one another facilitating almost frictionless movement. Without articular cartilage this movement would damage the surface of the joint which is essentially what happens in osteoarthritis.
We have articular cartilage where ever two bony surfaces move against one another, or articulate. In the knee, articular cartilage covers the ends of the femur, the top of the tibia, and the back of the patella.
Cartilage performs the very important function of protection for the joints and when this cartilage becomes damaged as result of the osteoarthritis it can cause significant pain and loss of function.
The Hip
The hip joint is a synovial joint situated deep within the pelvis and is one of the main weight bearing joints of the lower skeleton. Whilst traumatic injury to the hip joint is far less common than the knee, the hip is susceptible to osteoarthritis and fractures in the elderly. The upper end of the femur (thighbone) has large bony bumps (trochanters) where powerful muscles attach, then a short neck, and finally a spherical head that forms the outer half of the hip joint.
The hip joint itself is formed from where the head of the femur articulates with the hip bone or pelvic girdle. The rounded head of the femur sits inside a cup called the acetabulum. The acetabulum is the point where the three components of the hip bone (ilium, ischium, and pubis) meet.
Whilst the knee is more like a hinge joint the hip is a ball and socket joint surrounded by soft tissue and muscle which means that it is inherently more stable than the knee although dislocation of the hip is quite common in the elderly and infants.
Osteoarthritis of the hip affects more than 3% of the overall population and there are approximately 45,000 hip replacements carried out in the UK each year. Osteoarthritis of the hip can rapidly deteriorate leaving patients in considerable and constant pain. There are few treatments for osteoarthritis of the hip other than pain medication & surgery so there is significant interest when new treatments offer hope to those with the condition.
Because of the anatomy of the hip joint certain treatments like Durolane which are injected into the joint are made a little more complicated and accessing the hip joint accurately generally requires imaging equipment (such as X-ray or ultrasound) to allow the doctor to know that the injection is in the joint space.