PT 720 Week 3 Joint Structure and Function PDF

STRUCTURE AND FUNCTION OF JOINTS PT 720 Applied Biomechanics West Coast University DPT James E. Taylor PT, DPT, OCS, COMT September 18, 2024:  I. Joint Classification By Movement Potential LECTURE OUTLINE By Mechanical Analog...

STRUCTURE AND FUNCTION OF JOINTS PT 720 Applied Biomechanics West Coast University DPT James E. Taylor PT, DPT, OCS, COMT September 18, 2024:  I. Joint Classification By Movement Potential LECTURE OUTLINE By Mechanical Analogy?? II. Peri-Articular Joint Tissue Histology Elementary Components Tissue Classifications PT School III. Bony Structure IV. Joint Pathology Immobilization Trauma Arthritis A. MOVEMENT POTENTIAL 1. SYNARTHROSES 2. DIARTHROSES B. MECHANICAL ANALOGY 1. HINGE 2. PIVOT 3. ELLIPSOID 4. BALL-AND-SOCKET 5. PLANE 6. SADDLE 7. CONDYLOID JOINT CLASSIFICATION  Junction between joints that provides essentially no movement SYNARTHROSES  Further subdivided into fibrous or cartilaginous  Fibrous joints are dense with a high collagen concentration  typically immovable and lack a joint cavity (Juneja, 2024)  Cartilaginous joints use flexible fibro- or hyaline cartilage that is mixed with collagen  Cartilaginous can be further divided into either primary or secondary groups DIARTHROSES  Are always characterized by the following seven characteristics: - Articular cartilage - Joint capsule - Synovial membrane - Synovial fluid - Ligaments - Blood vessels - Sensory nerves JOINTS CLASSIFIED ACCORDING TO MECHANICAL ANALOGY  HINGE JOINTS Similar in structure to a central pan or bar surrounded by a hollow cylinder Rotational motion occurs in a plane at right angle to the axis of rotation  PIVOT JOINT Central pin surrounded by a larger cylinder What does this sound like? Key difference is that the moving component of the joint is parallel to the axis of rotation Key movement: Spin  ELLIPSOID JOINT One surface  elongated convex surface paired with an elongated concave surface on opposite surface The shape of the ellipses significantly limits any potential for spin More accommodating to two planes of movement  BALL AND SOCKET JOINT Spherical convex surface paired with a concave socket Provides mobility in all three planes Greater symmetry between the X and Y axes of the joint allows for spin  PLANE JOINT Congruence of two (relatively) flat surfaces Primary available movements include sliding and rotation (to some degree) Stability in these joints created by tension in muscles / ligaments surrounding the joint  SADDLE JOINT Each surface that comprises the joint has a convex surface and a concave joint at approximately 90 degrees to it Analogous to a horse’s saddle  CONDYLOID JOINTS Very similar in concept to a ball-and-socket joint, however the concave surface is very shallow As a result, these only provide two DOF Exact kinematics may vary joint-to-joint depending on specific joint structure A. E L E M E N TA R Y C O M P O N E N T S 1. FIBROUS PROTEINS - TYPE 1 COLLAGEN - TYPE 2 COLLAGEN - ELASTIN 2. G R O U N D S U B S TA N C E 3. CELLS - FIBROBLASTS - CHONDROCYTES B. T I S S U E C L A S S I F I C AT I O N S 1. DENSE CONNECTIVE TISSUE 2. ARTICULAR CARTILAGE 3. FIBROCARTILAGE HISTOLOGY OF PERIARTICULAR TISSUE PERIARTICULAR CONNECTIVE TISSUE  Composed of three fundamental materials: fibrous proteins, ground substance, and formative cells  Fibrous Proteins - Collagen – most common protein in the body, primarily composed of amino acid chains wound together in a triple helix - Elastin – protein fibers that appear as small fibers interwoven that resist stretch but are more “elastic” in that they increase in greater length FIBROUS PROTEINS  Collagen – most common protein in the body, primarily composed of amino acid chains wound together in a triple helix - Type I: strong, stiff fibers that demonstrate little elongation when stretched, ideal for structures needed to maintain stability in an articulation or in force transmission - Type II: thin fibers with less tensile strength though ideal for maintaining shape and consistency in complex structures  Elastin – protein fibers that appear as small fibers interwoven that resist stretch but are more “elastic” in that they increase in greater length GROUND SUBSTANCE Acts as the “cement” that the collagen and elastin fibers sit within Comprised primarily glycosaminoglycans (GAGs), water, and solutes Typically bound to a core protein, forming a proteoglycan unit  creates a “bottle brush” appearance A number of these proteoglycan units are bonded to hyaluronic acid, forming a larger proteoglycan unit These GAGs are highly negatively charged which accomplishes two things – it repels other GAGs which increases the volume of the complex and also attracts immense amounts of water FORMATIVE CELLS Both fibroblasts and chondrocytes are the primary cells contained in their respective structures Fibroblasts  ligaments, tendons, joint capsules Chondrocytes  hyaline cartilage and fibrocartilage These cells help to synthesize ground substance specific to that structure type – also involved in maintenance and repair This process stimulated by mechanotransduction – mechanical stimuli lead to changes in biochemical reaction rates and expression of genes specific to the repair process THREE TYPES OF PERIARTICULAR CONNECTIVE TISSUE  DENSE CONNECTIVE TISSUE LOCATION HISTOLOGIC FUNCTION CLINICAL CONSISTENCY EXAMPLES Ligaments High Type I Collagen Resistant to Incidence of Joint Capsules Low Elastin tension chronic (fibrous layer) Limited fibroblasts Protect / bind instability Tendons Low-mod joints proteoglycan Force transduction  ARTICULAR CARTILAGE LOCATION HISTOLOGIC FUNCTION CLINICAL CONSISTENCY EXAMPLES Hyaline Cartilage High Type II Collagen Distributes and Loss of Low – mod absorbs joint forces proteoglycan chondrocyte density Minimizes joint content in early OA High Proteoglycan friction  cartilage loses ability to absorb “shock”  goes to subchondral bone FIBROCARTILAGE LOCATION HISTOLOGIC FUNCTION CLINICAL CONSISTENCY EXAMPLES Menisci High Type I Collagen Provides support Tears in menisci Labral Tissue Low to Mod and stability to lead to increased Discs Fibroblasts AND joints stress on the femur chondrocytes Helps with load leading to increase Mod Proteoglycans dissipation in incidence of OA Guides arthrokinematics A. COMPACT BONE B. CANCELLOUS BONE BONY STRUCTURE BONY STRUCTURE  Similar to periarticular connective tissue, bone is comprised of type I collagen, formative cells, and ground substance  The proteoglycans contain proteins that bind strongly to calcium, particularly calcium hydroxyapatite  Outer cortex of bone is comprised of thick compact bone, though this is most pronounced at the mid-point of long bones and thinner at the end  Inner cortex is comprised of a scaffold-like structure known as trabeculae – a complex structure of struts and plates A. IMMOBILIZATION B. TRAUMA C. ARTHRITIS JOINT / BONY PATHOLOGY EFFECTS OF IMMOBILIZATION  Rate of decline in joint tissue (bones, ligaments, etc.) will vary depending on specific tissue metabolism  Ligaments will demonstrate decreased tensile strength and bones will demonstrate decreased mass, volume, and strength  Research is attempting to observe whether or not removable braces are superior to traditional casting, however no results that definitively show that braces are superior (Li, 2023) EFFECTS OF TRAUMA ON JOINT TISSUE  Acute trauma creates a cascade of inflammation and thus pain  Cytokines are released as a response to injury and promote inflammation, contributing to joint pain by acting on free nerve endings in the periarticular tissue  In acute trauma, this process is perfectly normal, however an issue arises when this persists  Cytokines can either be pro-inflammatory or anti- inflammatory  exercise helps facilitate production and circulation of anti-inflammatory cytokines OSTEO-/RHEUMATOID ARTHRITIS  Factors predisposing to OA  altered loading patterns 2/2 trauma, chronic overuse, atypical joint morphology, and obesity, specific areas may be more specific to gender  Rheumatoid arthritis  significantly different, instead of being mechanically related, this reflects a systemic, autoimmune disorder that involves inflammatory cycles  In RA, multiple joints are typically involved, females > males  Reactions in RA typically involve significant inflammation of joint capsule, synovium, and synovial fluid  articular cartilage becomes rapidly eroded  WORKS CITED 1. Juneja P, Munjal A, Hubbard JB. Anatomy, Joints. [Updated 2024 Apr 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507893/ 2. Li, B., Xie, J., Zhang, Z., Liu, Q., Xu, J., & Yang, C. (2023). Braces versus casts for post- operational immobilization of ankle fractures: A meta-analysis. Frontiers in surgery, 9, 1055008. https://doi.org/10.3389/fsurg.2022.1055008 3. Neumann, D. A. ([Insert Year of Publication]). Neumann's Kinesiology of the Musculoskeletal System (4th ed.). Elsevier Health Sciences (US). https://pageburstls.elsevier.com/books/9780323831499