The musculoskeletal system is the decisive framework of the body and assumes the essential function for mobility and stability. It is therefore directly connected to the vitality and zest for life of our four-legged friends. Diseases of the musculoskeletal system can be very painful and thus significantly limit the joy of life. Since the interaction in the skeletal system is so important for unrestricted mobility, keeping it healthy is also the basis for a long, healthy dog's life.
Elementary building blocks of the musculoskeletal system
The individual building blocks that our dog needs for the structure and function of the musculoskeletal system can be taken in through food. This also applies to all other tissues of the body. These ingredients from the food are first broken down by the metabolism and converted into bones, tendons, ligaments or muscles or needed for these processes.
Puppies in particular achieve remarkable feats in the first months of life when they are born as light, tiny little things and within a few months grow into stately dogs with a body weight of up to 80 kg. Thin bones and small vertebral bodies quickly grow into a strong skeleton with stable joints. Especially during the growth phase, most development takes place in the joints.
However, muscles, cartilage and tissues can wear out over the course of a lifetime and should be maintained and supported in their function to counteract damage and allow the dog to move painlessly and smoothly.
Joint structure of the dog
Dogs - like humans - have different joints that differ in terms of their structure as well as their mobility. Nevertheless, the individual joint components are largely the same.
Most dog joints are made of:
- Synovial fluid (synovia)
- Articular carnlage
- Joint capsule
The synovial fluid (also called synovial fluid) is located inside the joint and fills the cavities of the joint cavity. Its function is to nourish the joint cartilage and act as a lubricant to reduce friction in the joint. A lack of synovia would lead to wear and tear of the cartilage and eventually to changes in the bones involved.
It consists mainly of water, hyaluronic acid, proteins and lipids. The components it contains give the synovia its gel-like consistency and form a lubricating film on the joint surfaces. The cartilage is supplied exclusively by this synovial fluid, which is transported into the cartilage when the joints move.
Articular cartilage lines the ends of the bones that meet at the joint. They are elastic and thus prevent excessive friction in the joints and act like cushioning "shock absorbers". In this way, they are responsible for damping the pressure of every movement and protect against wear and tear.
Articular cartilage consists of cartilage cells called chondrocytes and of an intermediate cell substance, the extracellular cartilage matrix. This matrix is mainly composed of water, collagen fibres, hyaluronic acid and proteoglycans.
Proteoglycans are large molecules in which proteins combine with glycosaminoglycans (GAG). The GAG forms found in articular cartilage are predominantly chondroitin sulphate, keratan sulphate and hyaluronic acid. These proteoglycans have hydrophilic properties and thus the ability to bind large amounts of water in the cartilage. This ensures the strength and at the same time the elasticity of the cartilage. Healthy cartilage tissue contains up to 70 % water. This matrix functions in a similar way to a sponge: under stress, it is compressed and thus the water is pressed out - when it relaxes, water is sucked back in from the synovia to optimally nourish the cartilage.
The joint capsule surrounds the entire joint and has a protective and supply function. On the outside, it consists of a tight connective tissue that gives the capsule its strength. In the joint area, this outer fibrous layer (= fibrosa) merges into the periosteum (= periosteum), which surrounds the bone. The synovial membrane (= synovium) lines the inside of the joint capsule. This membrane is traversed by many nerves and blood vessels and contains covering cells that secrete the synovial fluid. At the same time, they also ensure the removal of unhealthy metabolic products from the joint.
Furthermore, depending on the type of joint, ligaments outside the joint capsule ensure that the intended range of motion is guided and maintained and, together with the muscles, give the joint the necessary stability.
In the course of life, cartilage structures are continuously broken down through wear and tear, but they also have to be rebuilt accordingly. In a healthy joint, this build-up and breakdown is usually in balance under normal load, so that natural wear and tear can be compensated for.
Joint types of the dog
The types of joints are often differentiated according to their shape. In principle, they are divided into simple and compound joints, whereby the difference lies in the number of bones connected to each other. Simple joints connect two bones (.g. toe joint), whereas compound joints connect more than two bones (e.g. elbow joint).
The joints are further differentiated according to the shape of the joint surfaces, for example into ball joint, ellipsoid joint, roller joint and saddle joint.
Ball and socket joints are located in the shoulder and hip of the dog. A spherical joint head is enclosed by a cup-shaped socket. This allows movements in all irections. Spherical joints are therefore also called triaxial or multiaxial joints. However, this full movement is often restricted by ligaments and tendons.
An ellipsoid joint is an upper cervical joint located between the skull and the first cervical vertebra. An ellipsoidal joint head lies in a corresponding socket. It is biaxial, therefore movements are only given in two main directions.
Roller joints are found in the elbow or also in the knee of our dogs. One often also speaks of the sub-forms, namely the hinge joint, the sledge joint and the pivot or wheel joint. These correspond to uniaxial joints with a cylindrical joint head. These roller joints allow movements in two directions. In the case of the hinge joint, this involves bending and stretching, and in the case of the wheel joint, turning around the longitudinal axis.
Saddle joints are visible in dogs, for example, when the tarsal bone is connected to the metatarsal bone. It is a joint elevation that appears like a saddle and allows flexing and extending, even slight lateral movements, to better compensate for unevenness in the ground if necessary.
In addition, a distinction can be made between tight and incongruent joints. In tight joints, the possible movements are limited by very tight ligaments. An example is the sacroiliac joint in the posterior section of the spine. In incongruent joints, separate cartilage discs are needed because the joint surfaces do not fit together exactly. These cartilage discs counteract the inequality, e.g this affects the meniscus in the knee joint.
As you can see, the topic of joints and the musculoskeletal system has many facets and is of great importance for your animal.