Health: OSTEOARTHRITIS OF THE KNEE

Definition

The word “OSTEOARTHRITIS” can be broken into its root words – ‘Osteum (bone) + Artho (joint) + Itis (inflammation)’. Hence, Osteoarthritis (OA) is defined as an inflammatory disease of characterised by progressive loss of joint articular cartilage that results in pain and deformity. The disease is also known as degenerative arthritis or degenerative join disease.

OA is the most common form of joint disease and the knee is one of the most commonly affected joints.

The Knee

The knee joint is the largest and most superficial joint in the human body. It is formed by the thigh bone (femur) and the shin bone (tibia); the condyles (lateral and medial) of both bones covered by cartilage provide the articular surfaces for the knee joint. It is the articular cartilage that makes the articular surface of the joint smooth and slippery, hence, allowing the movement of the joint without friction. Between the femur and tibia lies additional rings of cartilage known as the menisci (singular: meniscus) – they act a bit like shock absorbers. The Knee joint is covered and held in place by a joint capsule, thereby forming a cavity containing the articular components of the joint and within this cavity is contained in the cavity is the synovial fluid, which lubricates and nourish the articular surface of the joint. The synovial fluid is secreted by the internal surface of the knee capsule referred to as the synovial membrane.

The knee capsule is strengthened by 5 ligaments (extracapsular ligaments) –Anterior cruciate ligament, Posterior cruciate ligament, Lateral collateral ligament, Popliteofibular ligament and Medial collateral ligament. Alongside the capsule, and ligaments, the thigh muscles (especially the quadriceps femoris) play the role of stabilising the knee joint. Another important component of the knee joint is the patellar (knee cap) – a sesamoid bone, which attaches to some muscles (Quadriceps femoris and vastusmedialis) at the knee joint and functions to aid the extension of the knee.

Osteoarthritis of the Knee

OA of the knee is a common knee joint disease that occurs when the cartilage of the joint wears down. When a joint develops OA, some of the cartilages covering the ends of the bone gradually roughens and become thin - this wear happen over the main surface of the main surface of the knee joint and in the cartilage underneath the kneecap. When this happens, the bone underneath the cartilage reacts by growing thicker and becoming broader. As the wear of the cartilages continues, all the tissues within the joint become more active than normal – as if the body is trying to repair the damage. Following this, the following occur:

a.                 The bone at the edge of the joint gains outwards bony spurs called osteophytes and this can affect the thigh bone, shin bone and/ or knee cap.

b.                 The synovial membrane may swell and produce extra fluid, which then cause the joint to swell. This is called an “effusion” or sometimes “water on the knee”.

c.                 The capsule and ligaments slowly thicken and contract as if they were trying to stabilize the knee.

These changes occurring in and around the joint are partly as a result of inflammatory process and partly the body’s attempt to repair the damage. In some cases, the repairs are quite successful and the changes inside the joint do not cause much pain or if there is pain, its mild and may be seasonal. However in many other cases, the repair does not work as well and the knee becomes damaged. This leads to instability and more weight being put onto other parts of the joint, which can cause symptoms to become gradually worse and more persistent over time.

Symptoms

The main symptoms in patients with osteoarthritis are pains; especially when moving the knee. The pains are as a result of the wear of the cartilages on the articular surface which may expose the bones to rub against each other and the inflammatory activities within the knee joint.

Other profound symptoms may include;

a.                 Stiffness of Knee

b.                 Limited movement of knee

c.                 Bent knee

d.                 Swollen knee

e.                 Thinning down of muscles around the knee

f.                    Crepitus – a creaking, crunching sensation when moving the joint

Causes

a.                 Age: the chances of OA increase with advancement in age. People stand the chances of having OA from their late 40s. this might be because the muscles is becoming weaker, the body is less able to heal itself or because the joints have gradually worn out over time.

b.                 Occupation: athletes and workers whose job involves bearing of heavy loads (e.g. farmers, miners, etc) are more prone to OA.

c.                 Gender: OA is more common and more severe in women of ages 55 years and above than it is in men of same age. Reasons have been point towards the female anatomy – women have wider hips, which experts believe affects the alignment of the knee, hence, causing uneven stress on the knee.

d.                 Overweight: this adds more weight on the knee, thereby increasing the chances of developing OA and of it becoming worse.

e.                 Genetics: an individual whose parents suffered from OA is likely to have it if their parents OA were not due to some other external factors. This is because they have the gene that is responsible for this.

f.                    Injury on the knee: knee injuries increase the chances of OA. This is because the injury might affect the articular cartilages directly, or affect the stabilizing components of the knee, e.g. the ligaments, muscle, etc.

g.                 Surgery: a surgical operation on the knee (e.g. meniscectomy – removal of damaged cartilage) or repairs to the ligaments can add a bit of disability on the knee, hence, leading to OA.

Treatment/Management

The primary goals of treating OA of the knee are to relieve pains and return mobility. The treatment plan will typically include a combination of the following;

a.                 Weight loss: when weight is a contributing factor, loosing even a small amount of weight can significantly decrease pain from OA.

b.                 Exercise: strengthening the muscles around the knee makes the joint more stable and decrease pain. Stretching exercise help keep joint mobile and flexible.

c.                 Pain relievers and anti-inflammatory drugs: e.g. ibuprofen, have analgesic effect, hence reducing pain .

d.                 Injections of Corticosteroids: corticosteroids are powerful anti-inflammatory drugs and hence its injection into the knee reduces its inflammation.

e.                 Use of devices: devices such as braces are used to provide support to the knee.

f.                    Alternative therapies: therapies such as, topical creams with capsaicin, acupuncture or SAMe may be effective.

g.            Surgery: when other treatments did not work, surgery becomes an option to explore. Types of surgery includes – Arthroscopy, Osteotomy, Joint replacement, etc. 

Author: Orji, Emmanuel
Physiologist