From an anatomical point of view the joints are junctional devices between bone heads interconnected by connective tissues . Depending on their different mobility, may be of the mobile type (eg. knee joint or shoulder), semi-mobile (between the vertebrae) or immobile (skull bones) . More precisely are divided into:
They are junctional devices generally rigid or semirigid between two bone heads contiguous and can be further subdivided into more subcategories depending on the connective tissue that is interposed between the same heads in:
They are junctional devices between two contiguous bone heads that allow a certain degree of mobility to the bones addressed allowing to carry out different movements. In Diarthrosis the bone heads are covered with hyaline cartilage which has a motor function of compressibility and elasticity. Diarthrosis can also be harmonious, with corresponding bone heads, and disharmonious, in which case the discrepancies are eliminated through the fibrous cartilaginous discus, which allow exchange of nutrients and greater mechanical stress. Diarthrosis can be classified as:
The two bone heads have a cylindrical shape, one with a concave surface (trochlea) that fits into the convex face of the other. It allows an angular movement (flexion, extension). Eg. elbow joint between the humerus and ulna and knee joint.
It is an uniaxial joint in which the two bone heads have a cylindrical shape, one cable and the other full. It allows a rotary motion (pronation, supination). Eg. proximal and distal joints between radius and ulna.
The two bone bodies are biaxial, convex and concave recessed mutual (have a shape of a saddle horse). It allows an axial rotation and flexion, extension, adduction, abduction and circling (eg. wrist and metacarpus; sternum and clavicle).
The two bone heads are ellipsoidal, one concave (condyle) and the other one convex (condylar cavity). It allows an angular motion on two floors (flexion, extension, adduction, abduction and circling). Eg humeral-radial (elbow) joint, tempo-mandibular joint .
The two bone heads have a spherical shape, one concave and the other one convex (head) and it allows movements in all planes (flexion, extension, adduction, abduction, intra-and extra rotation and circling). They are in fact the most mobile joints in the body (eg. hip joint ).
The two joint surfaces are flat or nearly with the interposition of a cartilaginous discus (eg. vertebrae). It only allows sliding but not angular movements.
In healthy articulation, bones slide in a regular and correct each other. The ends of the bones are covered with cartilage, a slippery tissue that provides a point of contact with low friction and shock absorbing properties. The joint is made up of many structures that interact to form a functional unit. The basic and vital components are: the underlying bone supporting the joint, the muscles that convey movement, and the nerves that control, analyze, and provide a response in relation to these movements. The joint is also surrounded by a hard capsule, often further stabilized by the ligaments. The inner lining of the capsule, the synovial membrane, rich in blood vessels, plays an important role in the joint. Then the structures of the joint are:
Bone is a dynamic tissue constantly undergoing decomposition and reconstruction. Osteoblasts (involved in bone formation) and osteoclasts (involved in bone erosion) are active cells that remodel the mineralized bone matrix whose mineral content consists of crystals of hydroxyapatite and calcium phosphate, arranged close to the collagen fibers. This dynamic and highly organized mixture of organic and inorganic components provide maximum strength with minimal mass as possible.
The articular cartilage is a highly specialized tissue which covers the surface of the joint and is characterized by the absence of nerve endings and blood vessels.
It contains only a few cells, chondrocytes, which synthesize and secrete various substances that make up cartilage. These cells are arranged in a highly organized three-dimensional network, formed by the structural fibers of collagen that secure the cartilage to the underlying bone and enclose a matrix consisting mainly of water (75%) and macromolecules of hyaluronic acid and proteoglycans which, by binding to water, swell providing cartilage its elastic properties and resistance to stress. The chondrocytes are also able to degrade the cartilage, so they are in a constant and dynamic balance between anabolism and catabolism.
The cartilage is able to adapt to variable stress of the joints themselves, but this balance can be stopped either by an overload that from a low utilization of the joint. Although the thickness of the cartilage is a few mm, its characteristic in terms of strength to the stresses allows it to withstand considerable pressure generated in the weight-bearing joints. In fact it allows the joint to withstand the stresses, helping to distribute the stress generated in the joint during movement through the bone. The three-dimensional network of collagen holds in place the highly absorbent molecules, similar to a sponge soaked in an elastic gel water binding. When a pressure is exerted on the joint, the water is squeezed out and the cartilage compresses. The cartilage tends to reabsorb the water lost as soon as the pressure is released, regaining its original shape.
The inner surface of the joint capsule is lined by synovium, a thin membrane pleated and very vascularized by capillaries which exudes a liquid in which soluble components, from the bloodstream. Synovial cells, the synoviocytes, secrete hyaluronic acid that makes the resulting liquid viscous. A thin layer of this synovial fluid lubricates the joint and provides the underlying cartilage of essential nutrients, given that the cartilage lacks a blood supply.
The joint capsule is formed by bundles of collagen fibers arranged in irregular spirals around the joint. Then the capsule is always under tension, independently of the position of the joint and this tension is recorded from the nerve endings in the capsule and ligaments. These proprioceptive nerve endings send signals to the brain about the position and tension of the joint. The capsule also contains ligaments, large bundles of fibrous tissue that connect the adjacent bones. The muscles are attached to the capsule through the tendons and the capsule is firmly anchored to the bone by the periosteum, a connective tissue that covering the bone.
In cartilage there are no nerve endings, while the synovial membrane has only a few nerve endings and is therefore relatively insensitive to pain. Instead the joint capsule, ligaments and periosteum are highly innervated. In these tissues the nerve endings are involved in proprioception, the detection of the position, and are also responsible for the sensation of pain felt in joint diseases.
The physiological joints disorders are generically called rheumatism or arthritis and include a number of diseases with very different causes and symptoms, and may be inflammatory or degenerative. In fact, according to the Arthritis Foundation, the term “arthritis” refers to more than 100 different disorders that cause pain, swelling and limited movement of the joints, so that arthritis in the Western world is in second place, after cardiovascular diseases as a cause of disability.
The most common forms of arthritis are:
Rheumatoid arthritis is a chronic (long-lasting) inflammatory disease that affects the whole body, including the synovial membranes that surround the synovial fluid in the joints. It is an auto-imnnune disease, in which the immune system attacks its own tissues. Rheumatoid arthritis involves several joints and not only causes swelling, rigidity, pain, and partial dislocation of the joints, but also anemia, fatigue, weight loss, fever and disability. The causes of inflammation include genetic predisposition, lifestyle, nutrition, allergies to foods and microorganisms (viruses and bacteria). Rheumatoid arthritis is manifested by:
– Morning stiffness lasting at least 1 hour
– Arthritis of 3 or more joints
– Arthritis of hand joints
– Symmetrical arthritis
– Cutaneous rheumatoid nodules
– Positive test for Rheumatoid Factor (FR)
– Radiological changes
It mainly affects men and electively the spinal column that undergoes total stiffness and fusion of the vertebrae. The involvement of the rib joints, often leads to respiratory problems. Is also frequent the involvement of the joints of the pelvis.
It is often a hereditary disease caused by the increased uric acid in the blood. In the chronic form kidney is often compromised so that stones are formed frequently.
It is a serious disease because it affects the joints and cause injury to the heart. It mainly affects children and young people after an episode of acute tonsillitis caused by streptococcus. Today it is almost disappeared after the introduction of penicillin.
To this group belong some conditions , infrequent, all serious and evolutionary preferably affecting some organs and systems. The most common inflammation of connective tissue is Systemic Lupus Erythematosus (SLE) that affects the musculoskeletal system, kidney, lung, CNS and heart.
It is a typical disease of old age, infrequent, characterized by a strong pain symptoms predominantly localized to the limb muscles (hip and shoulder) with anemia and elevated ESR.
Fibromyalgia is a condition of unknown origin, characterized by chronic and generalized pain in the muscles (especially neck, back and lumbar), joint pain, stiffness, weakness, paresthesia, insomnia, anxiety, headaches, and irritable colon syndrome. It affects most commonly women aged between 20 and 50 years.
It is an inflammation that affects the structures close to shoulder joint, and is frequent common among subjects who undergo repeated microtrauma to the shoulder. It is characterized by severe pain and functional limitation of the joint.
It is a condition caused by inflammation and compression of the median nerve causing pain in the wrist. It is characterized by loss of sensitivity or tingling in the fingers of the hands.
The Osteoarthritis (OA) is a degenerative disease of the joints , mono-or polyarticular -onset characterized by alterations in articular cartilage with subchondral bone involvement also , of the other constituents of the joint and the components of the extracellular matrix and manifests itself with a considerable reduction of the functionality of the joint. Osteoarthritis can be classified into:
– primary osteoarthritis when it is linked to a metabolic primitive articular cartilage . The primary osteoarthritis can in turn be localized or generalized , and is further subdivided according to the anatomical localization of the affected joint . In the generalized form you have the involvement of at least three districts joints.
– secondary osteoarthritis when an event or a known disease are related to the disease and the degenerative process is related to factors extrinsic to the cartilage. The secondary osteoarthritis is then subdivided according to the etiological factors or diseases associated with it.
However, a more accurate classification can be achieved when they are fully elucidated the pathogenetic mechanisms that underlie this disease.