ASFYT Part I: The Skeletal System Module S3 (Joints)

Transcription

1 Mdule S3 (Jints) (1) Overview f Jints Classificatin f Jints Fibrus Jints Cartilaginus Jints Synvial Jints Factrs Determining the Stability f Synvial Jints Menisci and Articulating Discs Classificatin f Synvial Jints (Uniaxial, Biaxial & Triaxial) Fcus n Ball & Scket Jint Mvement Nn-Axial Synvial Jints (2) Classificatin f Jints Jints, r articulatins, are sites where tw r mre bnes meet They can be classified structurally r functinally The structural classificatin fcuses n the material binding the bnes tgether and whether r nt a jint cavity is present The structural classificatins are: 1. Fibrus 2. Cartilaginus 3. Synvial The functinal classificatin is based n the amunt f mvement allwed at the jint The functinal classificatins are: 1. Immvable (synarthrtic) 1 f 9

2 Mdule S3 (Jints) 2. Slightly mvable (amphiarthrtic) 3. Freely mvable (diarthrtic) Freely mvable jints dminate in the limbs, whereas immvable and slightly mvable jints dminate in the axial skeletn (3) Fibrus Jints In fibrus jints, the bnes are jined by fibrus tissue, and n jint cavity is present The amunt f mvement available in a fibrus jint depends n the length f the cnnective tissue fibers uniting the bnes, but mst are immvable r nly slightly mveable Three types f fibrus jints are: 1. Suture Jints ccur nly between bnes f the skull the wavy articulating bne edges interlck and the junctin is cmpletely filled by a minimal amunt f very shrt cnnective tissue fibers that are cntinuus with the peristeum during middle age, this fibrus tissue ssifies and the skull bnes fuse int a single unit (nt mvable) 2. Ligamentus (Syndesmses): Syndesms means ligament ; in this type f jint the bnes are cnnected by a ligament The amunt f mvement available in a ligamentus jint depends upn the length f the ligament -- slight t cnsiderable mvement is pssible The ligament cnnecting the distal ends f the tibia and fibula is very shrt, allwing nly slightly mre mvement than a suture 2 f 9

3 Mdule S3 (Jints) The fibers f the ligament-like intersseus membrane cnnecting the radius and ulna are lng enugh t permit rtatin f the radius arund the ulna 3. Peg-in-Scket (Gmphses) The nly example is the articulatin f a tth in its bny alvelar scket Gmph means nail, r blt, and refers t the way that teeth are embedded in their sckets (as if hammered in) immvable (4) Cartilaginus Jints In cartilaginus jints, the articulating bnes are united by cartilage, and n jint cavity is present There are tw type f cartilaginus jints: 1. Synchndrsis a bar r plate f hyaline cartilage unites the bnes Mst are immvable, but sme allw a little mvement Example: Cstal cartilage, which unites a rib with the sternum 2. Symphysis the articular surfaces f the bnes are cvered with hyaline cartilage, which in turn is fused t an intervening pad f fibrcartilage the fibrcartilage acts as a shck absrber and permits a limited amunt f mvement at the jint Symphysis jints are designed fr strength with flexibility Examples include the pubic symphysis f the pelvis, and the intervertebral disc jints f the spinal clumn 3 f 9

4 Mdule S3 (Jints) (5) Synvial Jints Synvial jints are thse in which the articulating bnes are separated by a fluid-cntaining jint cavity This arrangement permits substantial freedm f mvement All jints f the limbs (which cnstitute mst jints f the bdy), fall int this categry (6) Synvial jints have the fllwing distinguishing features: Articular Cartilage A Jint Cavity (aka, synvial cavity) An Articular Capsule (aka jint capsule) Synvial Fluid Reinfrcing Ligaments (7) Articular Cartilage Glassy-smth articular cartilage (aka hyaline cartilage) cvers the ppsing bne surfaces These spngy cushins absrb cmpressin that is placed n the jint and thereby keep the bne ends frm being crushed Recall that cartilage is fr the mst part avascular, and therefre unable t heal when trn r wrn away (8) Jint Cavity (synvial cavity) A feature unique t synvial jints, the jint cavity is really just a ptential space that cntains a small amunt f synvial fluid The jint cavity is enclsed by a tw-layered articular capsule (aka the jint capsule) 4 f 9

5 Mdule S3 (Jints) (9) Articular Capsule The external layer is a tugh fibrus capsule, cmpsed f dense cnnective tissue that is cntinuus with the peristea f the articulating bnes The inner layer is a synvial membrane cmpsed f lse cnnective tissue that lines the fibrus capsule as well as all the internal jint surfaces (ther than thse cvered in hyaline cartilage) (10) Synvial Fluid A small amunt f slippery synvial fluid ccupies all the free spaces within the jint capsule This fluid is derived largely by filtratin frm bld flwing thrugh the capillaries in the synvial membrane Synvial fluid has a viscus, egg-white cnsistency, but thins and becmes less viscus as it warms during jint activity It is als fund within the articular cartilage, where it acts as a slippery film that reduces frictin between the cartilages - it is frced frm the cartilage during cmpressin, then as pressure is relieved it seeps back in (like a spnge) This mechanism is called weeping lubricatin, and lubricates the free surfaces f the cartilage and nurishes their cells Synvial fluid als cntains phagcytic cells that rid the jint cavity f micrbes and cellular debris (11) Reinfrcing Ligaments Synvial jints are reinfrced by a number f bandlike ligaments Mst ften, these ligaments are intrinsic(capsular); that is, they are thickened parts f the fibrus capsule itself In ther cases, ligaments evlved t becme distinct frm the fibrus capsule, and can be fund utside the capsule (extracapsular) r deep t the capsule (intracapsular) -- nte that intracapsular ligaments are 5 f 9

6 Mdule S3 (Jints) cvered with synvial membrane, and d nt actually lie within the jint cavity itself The articular capsule and ligaments are richly supplied with sensry nerve endings that mnitr the psitin f the jints and help t maintain muscle tne Stretching f these structures sends nerve impulses t the CNS, resulting in reflexive cntractin f muscles surrunding the jint (12) Factrs Influencing the Stability f Synvial Jints Because jints are cnstantly stretched and cmpressed, they must be stabilized s that they d nt dislcate The stability f a synvial jint depends n three factrs: 1. Articular Surfaces: the shape f the articular surfaces determine what mvements are pssible at a jint, and can als influence jint stability (cmpare the shallw scket f the shulder jint with the deep scket f the hip jint) 2. Ligaments: the capsule and ligaments f synvial jints unite the bnes and prevent excessive r undesirable mtin; as a rule, the mre ligaments a jint has the mre stable it is; hwever, when ther stabilizing factrs are inadequate, undue tensin is placed n the ligaments and they stretch; stretched ligaments stay stretched, like taffy, and a ligament can nly stretch abut 6% f its length befre it snaps 3. Muscle Tnicity: muscle tnicity is defined as lw levels f cntractile activity in relaxed muscles that keep the muscles healthy and ready t react t stimulatin; adequate tnicity in muscles will cause the tendns t becme mre taught, which will lend stability t the jint(s) that they crss. Cnversely, inadequate tnicity (hyptnicity) culd lead t instability in a jint. Fr example, if there is hyptnicity in the muscles whse tendns crss the arches f the feet, the arches might drp resulting in functinally flat feet. Muscle tne is especially imprtant in reinfrcing the shulder, knee jints and arches f the ft 6 f 9

7 Mdule S3 (Jints) [NOTE: This is the nly aspect f jint stability that we actually have any cntrl ver!] (13) Articular Discs & Menisci When the articulating surfaces f tw bnes are nt well matched (they are nt cngruent), additinal intra-articular structures may be present t help imprve the fit These intra-articular structures are made f dense fibrcartilage and help t d tw things: 1. Imprve fit in rder t maintain nrmal jint mvements 2. Cushin the jint by absrbing and transmitting frces Articular Discs are discs f fibr-cartilage; examples include the ringshaped articular discs fund between adjacent vertebrae within the spinal clumn (the intervertebral discs), within the temprmandibular jint (the TMJ), and within the pubic symphysis jint Menisci are crescent-shaped articular discs and are fund between the femur and tibia within the knee jint (14) Classificatin f Synvial Jints Synvial jints can be divided int fur categries, based n the number f axes f mvement that exist at the jint 1. (15) Uniaxial jints allw mtin t ccur arund ne axis, within ne plane Tw types f uniaxial jints exist Hinge jint: the surface f ne bne is spl-like, and the ther is cncave (the spl-like surface mves within the cncave surface); an example is the elbw 7 f 9

8 Mdule S3 (Jints) Pivt jint: ne surface is shaped like a ring, and the ther is shaped s that it can rtate within the ring; an example is the atlantaxial jint between the ring-shaped atlas (C1) and the dntid prcess f the axis (C2) 2. (16) Biaxial jints allw mtin t ccur arund tw axes, within tw planes Tw types f biaxial jints exist: Cndylid jints: the surface f ne bne is cncave in shape, and the ther is cnvex; an example is the metacarpphalangeal (MCP jint) Saddle jints: a mdified cndylid jint, but instead a cnvexshaped bne that fits int a cncave-shaped bne, bth bnes f a saddle jint are shaped such that each has a cnvexity and a cncavity t its surface (think f a rider n a hrse); examples include the carpmetacarpal (CMC) jint f the thumb, and the sternclavicular jint Mvements available are flexin/extensin, and abductin/ adductin 3. (17) Triaxial jints allw mtin t ccur arund three axes, within three planes In ball-and-scket jints, ne bne has a ball-like cnvex surface that fits int the cncave-shaped scket f the ther bne The tw ball-and-scket jints in the bdy are the hip jint and the shulder jint (18) Mvements include flexin/extensin, abductin/adductin and medial/lateral rtatin 4. (19) Nnaxial jints allw mtin t ccur within ne plane, but this mtin des nt ccur arund an axis The mtin that ccurs is a gliding mvement in which the surface f ne bne merely glides (r translates) alng the surface f the ther bne 8 f 9

9 Mdule S3 (Jints) Examples include the jints fund between adjacent carpal bnes (intercarpal jints), and the facet jints f the spine (20) What Factrs Affect Range f Mtin at a Jint? (21) Factrs That Affect Range f Mtin at a Jint include: The shape f the articulating bnes (sex, race and bdy type all play a rle) The cnditin f the ligaments (lax r taut, lng r shrt) The resting tne f the muscles whse tendns crss the jint The prximatin f sft-tissue (a thick calf/thigh will result in less knee flexin than a thin calf/thigh) The ptential jint pathlgy that may be present (i.e., stearthritis, injury, swelling, muscle splinting, lss f innervatin, etc.) 9 f 9