Human Gross Anatomy Lecture 9
Human Gross Anatomy Lecture 9 BISC 2581
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This 14 page Class Notes was uploaded by Anais Ioschpe on Saturday February 13, 2016. The Class Notes belongs to BISC 2581 at George Washington University taught by Jeffrey Rosenstein; Raymond Walsh; in Spring 2016. Since its upload, it has received 40 views. For similar materials see Human Gross Anatomy in Anatomy at George Washington University.
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Date Created: 02/13/16
Introduction to the Lower Limb— Synovial Joint Learning Objectives: 1) Name the four structural components of all synovial joints and their function. 2) Name the optional features present at some synovial joints and their functions. 3) For the hip, knee, and ankle joints you should be able to: a) Name the parts of the bones that participate in the articulation. b) Name its major ligaments and their function. c) Describe the stability of the joint and factors that contribute to it. d) List any articular discs or signiﬁcant bursa associated with the joint. e) Discuss the clinical injuries or tests described for the joint. - Synovial joints: Synovial joints are typically designed to permit signiﬁcant movement between the articulating bones. All but one of the joints in the lower limbs are synovial joints. The one exception is the inferior tibioﬁbular joint, which is a ﬁbrous joint where the two opposing bones are attached to each other by bands of ﬁbrous connective tissue. - Structural features • Articular cartilage • Synovial membrane • Fibrous capsule - Articular cartilage • a smooth layer of hyaline cartilage that covers the opposing surfaces of the articulating bones. • aids in reducing the friction between the opposing bones and, due to the resiliency of cartilage, it acts like a shock absorber. • is avascular (no blood vessels) and lacks sensory innervation • joint space – the term used in radiology to denote the gap seen in plain ﬁlm x-ray between the articulating bones; reﬂects the radiolucent nature of articular cartilage. - Synovial membrane • a thin, highly vascular layer of specialized connective tissue; attached to the margins of the articular cartilages and extends from the articular cartilage of one bone to that of the opposing bone(s). The synovial membrane does not overlie the articular cartilages. • Synovial cavity: the region deep to the synovial membrane. Cells of the synovial membrane secrete a viscous ﬂuid called synovial ﬂuid (syn. synovia; often described as resembling egg white) into the synovial cavity where it serves to nourish and lubricate the surfaces of the articular cartilages. - Can be the site for infection - Fibrous capsule • Every joint has a ﬁbrous capsule around it • a strong yet ﬂexible layer of dense ﬁbrous connective tissue that ﬁts like a sleeve around the joint; continuous with the outer connective tissue covering (periosteum) of the articulating bones - Can be compared to neoprene sleeves that support the knee joint - Can be subject to tearing and inﬂammation Functions • - protects the underlying structures - helps to maintain the position of the opposing bones - limits the range of movements permitted at the joint • Joint cavity: the region of the joint deep to the ﬁbrous capsule, which includes but is not limited to the synovial cavity. - Optional structural features of synovial joints • Articular discs - Some people have a contoured pieces of ﬁbrocartilage that articulate with the hyaline articular cartilage of the bones. The synovial membrane attaches to the margins of articular discs just as it does to the margins of articular cartilage. - serve to improve the congruity between the articulating surfaces of the joint and assist in the spread of synovial ﬂuid; serves as the inner platform for the two bones to contact one another - They can tear or break - Lubricated by synovial ﬂuid • Ligaments - a ligament is a dense bundle of collagen ﬁbers that connects the articulating bones, being continuous with the periosteum of the bones. - spatially arranged so as to resist stresses on the joint that are brought about by particular movements, thereby limiting excessive movement in those directions. - may reside superﬁcial to, deep to, or within the ﬁbrous capsule of the joint. • extracapsular ligaments: outside the ﬁbrous capsule or sometimes embedded in the capsule • intracapsular ligaments: deep to the ﬁbrous capsule, within the joint cavity but outside of the synovial cavity. • capsular ligaments: regional thickenings of the ﬁbrous capsule itself. Bursae (sing. bursa) • - ﬂuid-ﬁlled sacs comprised histologically of the same cell types and structural arrangement as occurs in a synovial membrane; acts like a “pillow” - function as lubricating devices between structures that slide upon each other during movement at a joint, such as between a tendon of a muscle and the ﬁbrous capsule of the joint that the tendon crosses. - may be continuous with the synovial membrane of a joint through an opening in the ﬁbrous capsule; thus the cavity of the bursa is continuous with the synovial cavity of the joint. • constitutes a path for the spread of infection between the outside and the inside of a joint. • excess ﬂuid accumulation in the synovial cavity may be visible and palpable on the surface of the body by its ﬂow into a bursa close to the skin. - can become aggravated, and when aggravated they secrete ﬂuid outside the sacs and cause a ﬂuid build up. Very painful due to the pain ﬁbers at the joints. • Fat pads - serves to buffer any type of tendon movement on the bone and can also provide a bit of nourishment. In reality not as important as the bursae - accumulations of adipose tissue that serve to cushion the pressure between opposing structures of a joint, such as between a bone and a tendon. - frequently reside within the joint cavity, deep to the ﬁbrous capsule but outside the synovial membrane and thus outside of the synovial cavity. - The neurovascular supply to joints • Articular nerves - sensory nerves to a joint. - Articular cartilage lacks sensory innervation and thus no pain results from compression of the cartilage during weight bearing. - The ﬁbrous capsule and ligaments have rich nerve supplies that consist primarily of pain and proprioceptive ﬁbers. - Articular nerves are usually branches of the nerves that innervate the muscles that act at the joint and/or are branches of the sensory nerves that supply the skin around the joint. • Articular arteries and articular veins – the blood supply to a joint. - Derived from neighboring blood vessels that pass to and from the muscle groups that surround the joint. - The major blood vessels that cross a synovial joint often form an extensive series of anastomoses around the joint that serves to ensure adequate blood ﬂow pass the joint during potential constriction of the major blood vessels during certain movements of the joint; this is referred to as a collateral circulation. - Hip joint • A synovial ball-and-socket type of joint. • Acetabulum: the cup-shaped depression on the lateral surface of a hip bone. - Lunate surface: the horseshoe-shaped articular surface of the acetabulum - Acetabular notch: between the two ends of the lunate surface - Acetabular fossa: a central depression (bottom of the “cup”) surrounded by the lunate surface and acetabular notch. • The head of the femur is extremely important since it is where movement takes place. Several times more articular surface on the head of the femur and the acetabular fossa that any other joint. Articular surfaces • - Lunate surface of the acetabulum with the hemi-spherical head of the femur; the weight of the body is transmitted through the hip bones to the femoral heads. - Acetabular labrum - a circular band of ﬁbrocartilage that encircles the acetabulum. The acetabular labrum encircles the head of the femur distal to its widest diameter, which secures the head of the femur in the acetabulum. Ligament of the head of the femur: an intracapsular ligament that extends from the • acetabular notch to the fovea capitis of the femur (a “pit” on the head of the femur that lacks articular cartilage); not considered signiﬁcant in strengthening the hip joint. - Structurally it does almost nothing, but if you look closely there is an artery in the middle which is called the artery of the ligament of the head of the femur. It serves as the only blood supply to much of the head of the femur. The femur is the most vascular bone. Fibrous capsule Synovial cavity • Fat pad: ﬁlls the acetabular fossa. • Fibrous capsule: attached to the rim of the acetabulum. Its femoral attachment is more extensive, extending down the neck of the femur. Keeps the head of the femur in place. • Synovial membrane and cavity: extends down the neck of the femur. • The capsule of the hip joint exhibits three regional thickenings (capsular ligaments) which play an important role in strengthening the hip joint. - The ligaments are attached at one end to the hip bone and at the other end to the femur. They are named according to the region of the hip bone to which they attach, i.e. the iliofemoral syn. Y ligament), pubofemoral, and ischiofemoral ligaments. - The important point is that all three ligaments become most taut during full extension of the hip joint, thus resisting hyperextension of the joint. • The hip joint is a very stable joint due to: - well-ﬁtting articular surfaces (the deep acetabulum accommodating the large hemi- spherical head of the femur) the presence of multiple strong ligaments. - numerous large, powerful muscles surrounding the joint (the hip joint is not directly palpable due to the masses of surrounding muscles). • Movements: the hip joint is capable of abduction and adduction, ﬂexion and extension, internal (medial) and external (lateral) rotation, and circumduction. • Injuries - Traumatic dislocation of the hip joint requires major force, typiﬁed by automobile accidents in which the dashboard of the car is driven into the distal end of the ﬂexed (sitting position) thigh, posteriorly displacing the femur from the acetabulum (posterior hip dislocation). - “Broken hip” – a common misnomer for a fractured neck of the femur, which is most common in elderly woman with osteoporosis, a disease that weakens bone and renders it more susceptible to fracture. Fractures of the femoral neck occur within the capsule of the hip joint and often involve damage to the arteries that supply blood to the head and neck of the femur. - A broken femur can make someone actually bleed out since it is highly vascular. If you have a cast for a broken femur, your quadriceps muscle will start to waste away as it not being used— disuse atrophy - Knee Joint • The largest and anatomically most complex synovial joint in the body. • Consists of two articulations, i.e. the patella with the femur and the femoral condyles with the articular facets on the tibial plateau. - tibiofemoral articulation is a hinge type of joint, permitting ﬂexion and extension but also some gliding movement. A very limited degree of medial and lateral rotation is also possible, most prominent when the joint is ﬂexed to 90 degrees. - patellofemoral articulation is a plane-type of joint in which the patella glides up-and-down on the femur during ﬂexion and extension of the tibiofemoral articulation. • Stability of the knee joint depends primarily on ligaments and the strength of the muscles that surround the joint. The poorly ﬁtting articular surfaces offer little assistance to the stability of the knee joint. • The patella can move up and down the femur as the knee ﬂexes • Articular discs - medial and lateral menisci: (menisci is Greek for crescents; syn. semilunar cartilages) two C-shaped articular discs of ﬁbrocartilage that help to deepen the articular surfaces of the articular facets of the tibial plateau. • medial meniscus is also attached to the deep surface of the medial collateral ligament on the medial side of the joint, rendering the medial meniscus less mobile than the lateral meniscus that is not attached to the lateral collateral ligament. Not the same shape as one another • Synovial membrane: the largest in the body and creates a complicated synovial cavity. • The synovial membrane extends above the patella, between the tendon of the quadriceps femoris muscle and the distal anterior surface of the shaft of the femur, as the large suprapatellar bursa. The continuity between the suprapatellar bursa and the synovial cavity is so large that the bursa is actually considered a part of the synovial cavity. • Bursae (Don’t need to know the names, just overall understanding of it) - The knee joint has numerous bursae, some of which communicate with the synovial cavity of the joint and some of which do not. - Bursae on the posterior aspect of the knee joint are associated with muscles that pass or insert around the knee joint, e.g. gastrocnemius, popliteus, semimembranosus, biceps femoris, etc. These bursae often communicate with the synovial cavity. - Four bursae on the anterior aspect of the knee joint are associated with the patella and patellar ligament. Except for the suprapatellar bursae described above, they usually do not communicate with the synovial cavity. • prepatellar bursa - lies between the skin and the anterior surface of the patella. • superﬁcial infrapatellar bursa and deep infrapatellar bursa – lie superﬁcial and deep respectively to the patellar ligament. - Bursitis – inﬂammation of a bursa typically accompanied by an effusion (L. effusio, “a pouring out”), which is an abnormal accumulation of ﬂuid in a tissue or cavity. May result from excessive friction, overuse and compressive forces, e.g. prepatellar bursitis (a.k.a. “plumber’s knee” or “housemaid’s knee”) is common in workers who kneel a lot doing their work and who do not wear protective knee pads. • Ligaments: contribute signiﬁcantly to the stability of the knee joint. - Capsular ligaments • Lateral collateral ligament (syn. ﬁbular collateral ligament) - extends from the lateral epicondyle of the femur to the lateral side of the head of the ﬁbula. Its upper end is part of the true ﬁbrous capsule (thus capsular) while its lower end is cord-like and distinct from capsular ﬁbers (thus extracapsular). Noteworthy is that the lateral collateral ligament is not attached to the lateral meniscus. - Common ﬁbular nerve sits on top of it • Medial collateral ligament (syn. tibial collateral ligament) - a thickening of the true ﬁbrous capsule. It is a broad ﬂat ligament that extends from the medial epicondyle of the femur to the upper medial surface of the shaft of the tibia. The deep ﬁbers of the medial collateral ligament are ﬁrmly attached to the peripheral margin of the medial meniscus. - The center of gravity of the body lies anterior to the axis of movement of the knee joint, giving the body a tendency to fall forward (hyperextend) at the knee joint. Both collateral ligaments become taut during extension of the knee joint and thus resist hyperextension of the joint. The collateral ligaments also provide side-to-side stability to the joint, where muscles are absent, and resist unwanted movements such as abduction and adduction. • Intracapsular ligaments - Called the cruciate ligaments, so named because they cross each other like the lines of a cross. They are named according to their tibial attachment. - Anterior cruciate ligament (ACL) - attaches to the anterior region of the intercondylar area of the tibia and ascends posteriorly in the intercondylar fossa of the femur to attach to the posteromedial side of the lateral femoral condyle; becomes taut when the knee joint is extended and thus serves to limit hyperextension of the joint. It also prevents the femur from sliding posteriorly on the tibial plateau. - Posterior cruciate ligament (PCL) - attached to the posterior region of the intercondylar area of the tibia and ascends anteriorly in the intercondylar fossa to attach to the anterolateral side of the medial femoral condyle; becomes taut when the knee joint is ﬂexed and thus assists in preventing hyperﬂexion. It also prevents the femur from sliding anteriorly on the tibia. • Injuries and clinical tests - The rupture of the medial and lateral collateral ligaments and the tearing of the medial and lateral menisci are common injuries, often induced by an external force applied to the limb. Frequently one gets a concomitant tearing or straining of multiple ligaments, e.g. a tear or strain of the medial (tibial) collateral ligament will often result in a tear of the medial meniscus to which it is ﬁrmly attached. - Drawer sign: (*Know this*) a clinical test for rupture of the ACL or PCL that demonstrates excessive movement of the leg either anteriorly or posteriorly when the knee is ﬂexed to 90 degrees. The patient sits on the examining table with their legs hanging freely over the edge of the table. The leg is pulled anterior and pushed posteriorly on the stationary femur, like the opening and closing of a drawer on a bureau. Rupture of the ACL results in excessive movement of the leg anteriorly; rupture of the PCL results in excessive movement of the leg posteriorly • If the tibia can be moved anteriorly, it means the ACL is broken, because you are hyperextending the knee - Unhappy Triad • Very common in sports • Occurs with lateral collision to the knee - Torn ACL, torn or stretched LCL, and a displaces medial meniscus - Ankle Joint • A hinge-type of joint • Articulating surfaces include the distal inferior surface of the tibia, the deep surface of the medial malleolus of the tibia, the deep surface of the lateral malleolus of the ﬁbula, and the upper body of the talus. • Fibrous capsule: thin but is reinforced medially and laterally by two strong collateral ligaments, the deltoid ligament and the lateral ligament. • Ligaments - Deltoid ligament (syn. medial ligament) • Shaped like a fan or delta and strengthens the medial side of the ankle joint • Extends from the medial malleolus of the tibia to a broad base that attaches across the talus, calcaneus, and navicular tarsal bones of the foot. • Strongest ligament in the body - Lateral ligament • Not as strong as the medial ligament. • Comprised of three distinct bands that attach the lateral malleolus of the ﬁbula to the talus and calcaneus. • Movements - Capable of dorsiﬂexion and plantarﬂexion. When the joint is fully plantarﬂexed, a small amount of rotation, abduction, and adduction is possible. Remember that inversion and eversion do not occur at the ankle joint but rather at intertarsal joints. • Injuries - Sprained ankle: a tearing or excessive stretching of the ligaments; typically occurs during excessive inversion of the foot, which stretches or tears one or more components of the lateral ligament. Anterior taloﬁbular ligament component of the lateral ligament is the most commonly injured ligament in the body. - Pott’s fracture: (*Know this*) forceful, excessive eversion of the foot that results in a fracture-dislocation of the ankle. The term is applied to a variety of bimalleolar injuries. Among the more common, the talus is driven into the distal end of the ﬁbula, fracturing the ﬁbula superior to the lateral malleolus. This is often combined with avulsion (ripping or tearing away) of the medial malleolus rather than rupture of the strong deltoid (medial) ligament. Finally, if the tibia should move anteriorly on the talus then the posterior margin of the distal tibia could get sheered off during its forward displacement over the talus. • A very common serious fracture due to the strong deltoid ligament
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