Viscosupplementation involves using hyaluronic acid in a dedicated joint formulation, administered as an ultrasound-guided injection by the orthopaedist. Delivered from the articular fluid, hyaluronic acid is the main component of articular (joint) cartilage matrix. Owing to its oily formulation, hyaluronic acid administered to the joint in an injection improves joint function and range of motion, by making the joint movements “smoother”. Physiologically, hyaluronate is synthesized in a human body and released to the articular fluid by bursal cells.
Its main task in a healthy joint is to surround and protect the synovial membrane and the collagen surface of articular cartilage against mechanical damage, as the joint carries the weight of the entire body. Hyaluronic acid is a proper joint lubricant both due to its molecular properties and their ability to be dispersed throughout the joint surface. Synovial fluid protects and lubricates the joint. Constant motion of joints facilitates hyaluronic acid dispersion to the superficial, acellular layer of articular cartilage, where it is found at the concentration five times higher than in the deeper, cellular cartilage layers. Hyaluronic acid permeates into the intercellular matrix of the synovial tissue and capsule, filling the collagen matrix of the intercellular space, where it provides structural support.
Hyaluronic acid fills the intercellular spaces of the collagen fibre network surrounding all cells, blood and lymphatic vessels as well as nerve endings of the joints, acting as the lubricant.
Owing to viscoelastic properties of hyaluronate-based network, the joint can adjust to mechanical stress. During low-stress motion (when performing slower movements), linear particles of the hyaluronic acid have enough time to face the flow direction. They have all properties of a thick, viscous fluid and disperse mechanical energy as heat.
However, when the joint is subjected to rapid stress, such as when running, hyaluronic acid particles do not have enough time to change direction and use their elastic properties. In such case, the energy is stored in a particle network, and the shock wave is absorbed until the energy can be dispersed in a flow of the viscous fluid.
Hyaluronic acid shows elastic properties for high-stress movements (e.g. when running) and ensures proper viscosity of the synovial fluid for lower-stress movements (e.g. when walking). Therefore, owing to the presence of hyaluronic acid, the synovial fluid can effectively protect the joint when performing quick movements with a significant stress to the joint, and ensure proper viscosity when performing slower movements. Significant long-term joint overload with the lack of proper regeneration may disturb synovial fluid production, which is unable to effectively lubricate and protect joints absorbing the shock, e.g. during heavy training and supramaximal exercise in professional runners. As a result, any shock caused by joint motion may cause cartilage to shred into a mass of fibres, by disrupting the collagen network on the surface of cartilage and synovial tissue. The nerve endings in a healthy joint are protected owing to the elasticity of the synovial fluid. This elasticity is significantly impaired in degenerated joints. Further joint movements may damage the hyaluronic acid producing cells of the synovial membrane, thus causing further polymer production dysfunction. When the cartilage matrix disappears completely, bones and other tissues are left exposed to potential damage leading to injury and chronic conditions.
Viscoelastic properties of synovial fluid change with ageing. The most affected property is the synovial fluid’s ability to effectively store energy while performing activities significantly loading (i.e. putting pressure on) the joint. The synovial fluid in the joints of the elderly is not elastic enough to effectively protect the joint during such activities. With age, it also loses its viscosity, but not to the extent seen in elasticity. As a result, the elderly experience joint pain and impaired joint function. With their physical activity reduced due to pain, the muscles get weaker and the ligaments loosen, which further impairs joint stability and makes it susceptible to injuries. At the same time, the cells lose their once excellent sensitivity to growth factors, which stimulate joint repair mechanisms. Additional changes to the location of calcified and non-calcified tissues increase the cartilage’s susceptibility to shock impulses.
Clinical research involving intraarticular administration of hyaluronic acid confirmed its analgesic and anti-inflammatory effect. It also showed that hyaluronic acid protects articular cartilage. As a result of treatment, the synovial fluid gets more elastic, and articular cartilage gets nourished, smoother, thus improving its “gliding” properties and biochemical condition of the joint. Viscosupplementation delays joint ageing and destruction, improves its function and protects synovial membrane as a good alternative to oral painkillers and glucocorticosteroids.
After administration to e.g. the knee, hyaluronic acid surrounds and permeates the surface of the femoral condyles (i.e. projections of the thigh bone), tibia (i.e. shinbone) and the adjacent structures, forming a shock-absorbing and lubricating layer to ensure smooth gliding movements of femoral condyles.
The unique chemical structure of intraarticular formulations enables active compound to reside longer within the joint, which ensures a long-term therapeutic effect, that is, stimulating its proper function and improving extracellular cartilage matrix.
Patient eligibility assessment for hyaluronic acid treatment involves a consultation with an orthopaedist and is based on patient medical history, clinical examination findings as well as an additional ultrasound scan.
In chondromalacia and degenerative joint disease, the effect can be sustained for at least 6 months, depending on disease severity.
As prevention in athletes and physically active individuals, hyaluronic acid treatment should be repeated every 1-2 years, depending on their lifestyle and activity levels.
Avoid sports-related activity for a week following an injection.
Reduce your activity throughout the entire therapy duration (be it 3 injections to the knee at weekly intervals or 3 injections to the hip at 2-4-weekly intervals).
An intraarticular injection (i.e. injection administered to the joint) may cause transient pain, oedema and/or exudate (fluid accumulation in tissues). The symptoms usually resolve within a few days.
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