Knee Osteoarthritis (OA)

The knee joint is made up of two joints. The patellofemoral joint and the tibiofemoral joint. The patellofemoral joint is formed between the patella (knee cap) and the femur (long bone of the upper thigh).  The larger of the two knee joints is the tibiofemoral joint, which is the focus of this blog. The tibiofemoral joint is formed by the femoral condyles (the large bony expansions of the distal aspect of the femur) and the tibia (the largest of the two shin bones). The femoral condyles and top of the tibia are covered in a protective coating called articular cartilage. This articular cartilage is designed to create a friction free surface during movement. Sitting on the top of the tibia are 2 semi-circular structures called the menisci (commonly known as knee cartilage). The role of the menisci is to add congruency to the knee joint as well as provide a shock absorbing, friction reducing surface for the femoral condyles to glide on during knee movement.

Osteoarthritis is the most common musculoskeletal pathology worldwide, affecting up to 15% of all people (Hubbert et al., 2018). Osteoarthritis is more prevalent in the load bearing joints of the lower limb (hip, knee, ankle, and big toe).  The most common joint to be affected by this degenerative and progressive condition is the knee. Osteoarthritis of the knee occurs when the articular cartilage is placed under repeated periods of increased stress. Over time increased stress can lead to thinning of the articular cartilage. Eventually the cartilage can be worn away to the point where the bones of the femur and tibia come to contact. This bone-on-bone contact can be very painful. Furthermore, the knee joint is surrounded by a capsule. The inner surface of this capsule is called the synovial membrane. This synovial membrane can become irritated and inflamed due to osteoarthritic change. When the synovial membrane becomes inflamed it is called synovitis. Synovitis is the main cause of flare-ups in pain associated with osteoarthritis of the knee.

Risk factors, described by Katz et al. (2021), commonly associated with osteoarthritis of the knee include:

• Age. There is a positive correlation between age and the development of osteoarthritis of the knee. It is estimated that 30% of all people over the age of 45 will have some evidence of osteoarthritis of the knee on x-ray.
• Sex. Women are more likely to develop osteoarthritis of the knee. One large study suggested 19% of women suffer, compared to 13.5% of men.
• Obesity. Increasing body mass has been shown to increase the risk of osteoarthritis of the knee. People with a body mass index of over 30 have been reported to have twice the risk of developing osteoarthritis of the knee compared to individuals who are not obese.
• Previous trauma to the knee increases the risk of developing osteoarthritis of the knee. Historical trauma has been reported to account for 12% of all cases of osteoarthritis of the knee.
• Weakness in the muscles of the hip and thigh result in poor control of the knee. Over time this can lead to degenerative changes of the knee.
• Prolonged periods of inappropriate pressure through the knee can also lead to osteoarthritis.
• Repetitive periods of excessive, high intensity exercise without adequate leg strength can lead to an osteoarthritic change in the knee.

Risk Factors

Risk factors, described by Katz et al. (2021), commonly associated with osteoarthritis of the knee include:

• Age. There is a positive correlation between age and the development of osteoarthritis of the knee. It is estimated that 30% of all people over the age of 45 will have some evidence of osteoarthritis of the knee on x-ray.
• Sex. Women are more likely to develop osteoarthritis of the knee. One large study suggested 19% of women suffer, compared to 13.5% of men.
• Obesity. Increasing body mass has been shown to increase the risk of osteoarthritis of the knee. People with a body mass index of over 30 have been reported to have twice the risk of developing osteoarthritis of the knee compared to individuals who are not obese.
• Previous trauma to the knee increases the risk of developing osteoarthritis of the knee. Historical trauma has been reported to account for 12% of all cases of osteoarthritis of the knee.
• Weakness in the muscles of the hip and thigh result in poor control of the knee. Over time this can lead to degenerative changes of the knee.
• Prolonged periods of inappropriate pressure through the knee can also lead to osteoarthritis.
• Repetitive periods of excessive, high intensity exercise without adequate leg strength can lead to an osteoarthritic change in the knee.

How do you know if you have osteoarthritis of the knee?

Osteoarthritis of the knee is a progressive, degenerative condition. This means it slowly gets worse over time. Initially you may notice only the occasional episode of knee pain and stiffness. Typically, pain and stiffness associated with osteoarthritis of the knee is worse first thing in the morning and feels better once you get up and moving.

Over time these intermittent episodes of pain and stiffness may become more regular or start to affect activities of daily living including walking, exercise or kneeling. You may also notice a change in shape of your knee (this is called bony deformity). This is a common symptom of well-established osteoarthritis of the knee.

The pain associated with osteoarthritis of the knee can be hard to locate. Patients usually report a dull, diffuse ache deep in the knee.

How is osteoarthritis of the knee diagnosed?

The key to successful treatment is getting the right diagnosis.

A formal diagnosis of osteoarthritis of the knee requires an x-ray. An x-ray can assess the severity of degenerative change in the knee and can be requested quickly and easily by your GP. This is usually a very quick process as waiting times for x-rays are often short. Occasionally your GP may also request a series of blood tests. This is to rule out other causes of knee pain such as rheumatoid arthritis.

Interestingly, x-ray evidence of osteoarthritis does not always correlate with symptoms. As previously discussed, many symptoms associated with osteoarthritis are caused by synovitis. Synovitis does not show on x-ray however, synovitis can be well assessed using diagnostic ultrasound imaging.

At complete we have a team of expert physiotherapists who are also qualified musculoskeletal sonographers. An assessment by one of our clinical specialists includes a series of clinical tests and a formal diagnostic ultrasound.

Although diagnostic ultrasound cannot see deep inside your knee it reveals valuable information about the condition of the outer margins of your knee joint and any swelling or synovitis that may be present within your knee joint (Wakefield et al., 2000; Kaeley et al., 2020).

How do we treat osteoarthritis of the knee?

Although it is not possible to reverse osteoarthritic change in the knee it is possible to manage the symptoms, increase the flexibility and strength of the knee, and maintain function.

Most people suffering from osteoarthritis of the knee respond positively to physiotherapy. Physiotherapy plays an important role in the management of osteoarthritis of the knee. Evidence has shown that maintaining strength and flexibility helps reduce the progression of osteoarthritis (Hunter et al., 2009).

Physiotherapy treats osteoarthritis by increasing the strength of the surrounding muscles of the knee and hip, increasing flexibility of the knee joint and increasing the balance and stability of the leg. This is achieved by using a combination of exercises and manual techniques including soft tissue massage, joint mobilisations and acupuncture.

Here are a few top tips you may like to try yourself:

• Rest or change activities that cause your knee pain.
• Embark on a gentle strengthening and stretching exercise program.
• Try a short course of over-the-counter pain killers (talk to your pharmacist first).
• Try applying an anti-inflammatory cream or gel, such as Voltarol.
• Try to lose weight. This will help to take pressure off your knee.