Orthopedics - Oleksa A.P. 2006

Examination of the Orthopedic Patient
Structural Elements of the Joint
Joint Capsule

The joint capsule is a Connective Tissue sheath that encloses and hermetically seals the articular ends of bones, thereby forming the joint cavity. The capsule consists of an outer fibrous layer and an inner lining, the synovial membrane.

The fibrous capsule is formed by Collagen and elastic fibers; the superficial layer is oriented longitudinally and along the axis of movement within the joint, while the deep subsynovial layer runs circularly. Both the capsule and the synovial membrane feature two arterial networks: a deep and a superficial one.

Ligaments, and occasionally tendon fibers at their insertion points, interweave into the fibrous capsule from various sides. The capsule attaches to the bones by merging with the adjacent periosteum, whereas in certain joints it abuts the margins of the articular Cartilage.

The synovial membrane features a loose connective tissue and adipose sublining that ensures its limited mobility and The formation of numerous folds. These folds cushion shocks and impacts within the joint and allow the membrane surface to expand during joint movements in cases of synovitis and hemarthrosis. In places, the membrane evaginates through the fibrous capsule to form synovial bursae.

The synovial membrane is rich in connective tissue elements, Blood and Lymphatic vessels, and nerves, including sympathetic ones. Synovial folds and their villi are particularly rich in capillaries, varying in size depending on the functional load on the joint and the person's age.

Electron Cell/15.html">Microscopy of the membrane has revealed two cell types: A and B. Type A Cells are predominantly absorptive and capable of phagocytosis, while Type B cells mainly produce hyaluronic acid complexes and Proteins.

Normal synovial fluid residing within the joint cavity is typically transparent, viscous, and pale yellow. It is a Blood Plasma dialysate that penetrates through the synovial membrane, becomes enriched with hyaluronic acid and synovioblastic elements, and enters the joint cavity.

Analysis of normal synovial fluid reveals a specific gravity of 1010, a mildly alkaline reaction (pH — 8.8), and a leukocyte count ranging from 200 to 600 cells per 1 mm³ (Hollander J.L. et al., 1961).

Mononuclear cells predominate in the cellular composition, with lymphocytes and polynuclears accounting for nearly 25%. The sediment contains cells from the synovial membrane and superficial cartilage layers, as well as fragments of villi.

The Biochemical Composition of normal synovial fluid differs slightly from that of blood plasma. It contains a lower amount of proteins (18-22 g/L), yet an increased proportion of albumins (50-75%). Normally, synovial fluid lacks proteins with a molecular weight exceeding 160,000, specifically fibrinogen, blood clotting factors, and a₂- and ß₂-macroglobulins. Other globulins (a1, ß, and y) are present in lower quantities than in blood plasma. This is because the synovial membrane acts as a hyaluronic acid filter that blocks high-molecular-weight substances. The hyaluronic acid concentration in synovial fluid is (3 ± 0.6) g/L; it imparts viscosity to the fluid and provides lubricating properties. Regarding electrolytes, the content of chlorides and bicarbonates in synovial fluid is higher than in blood plasma, whereas glucose levels remain nearly identical (4.5 mmol/L in synovial fluid). We omit a detailed Structure/133.html">Discussion of synovial fluid Enzymes, as their quantitative and qualitative parameters fluctuate depending on the condition of the joint.

Physiologically, synovial fluid acts to a certain extent as an additional Shock absorber between articular surfaces, reduces their mutual friction, provides Nutrition to the cartilage, and enhances the co-adaptation of joint surfaces.

Within the joint cavity, menisci and discs attach to the capsule; they are composed of Cytology/practical/45.html">Dense connective tissue containing elastic fibers and covered by a thin layer of cartilage. These discs and menisci compartmentalize the joint, improve the congruency of articular surfaces, and function as shock absorbers during movement and weight-bearing.

The Hip and knee joints contain intra-articular ligaments covered by the synovial membrane. Along with other periarticular fibrous ligaments, these structures represent the primary functional factor ensuring the static and dynamic Stability of the joint.

Mucous bursae lie in close apposition to the joint as isolated structures situated beneath tendons, where they cushion tendon gliding. Some periarticular bursae communicate with the joint cavity via a narrow channel and can enlarge during excessive exudation in synovitis (for example, Baker's cysts in the popliteal region).

Joints are also reinforced by adjacent Muscles that secure their physiological function. Intermuscular spaces filled with loose connective tissue house numerous nerves, blood and Lymphatic vessels. Joints receive their blood supply from a surrounding arterial network formed by three to eight Arteries.

As an organ, a joint performs the locomotor function in The Human Body; consequently, alterations in its condition can modify static and dynamic living conditions.