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All joints are trade-off between mobility and stability. Figure 9.1 . Factors that influence mobility and stability of a joint. Articulating surface and surrounding bones Joint capsule and ligaments Muscles that cross joint or are near joint.
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All joints are trade-off between mobility and stability Figure 9.1
Factors that influence mobility and stability of a joint • Articulating surface and surrounding bones • Joint capsule and ligaments • Muscles that cross joint or are near joint
Factors that influence mobility and stability of a joint • Articulating surface and surrounding bones • Determines types of movements possible • Bone-hitting-bone can limit movements • Joint capsule and ligaments • Can restrict or permit movements • Muscle that crosses joint or is near joint • Can stabilize joints • Can limit movement • E.g., hip and knee flex more passively than actively
Shoulder (glenohumoral) joint • shallow ball and socket • Very mobile with poor stability • Loose joint capsule (particularly anteriorly) and lacks well developed ligaments • Promotes mobility, lacks stability • Stabilized largely by muscles (rotator cuff) • Small rotator cuff muscles • Small muscles + big forces = easy injury • Other muscles crossing joint • E.g., Tendon of long head of biceps also stabilizes
Hip/coxal Joint (acetabulofemoral) • Deep ball and socket • Very stable with decent mobility (but significantly less than shoulder) • Thick joint capsule with well developed ligaments • Creates stability • Large muscles stabilize joint • Stabilizes, but may mildly limits mobility
Deep socket • Acetabular labrum (fibrocartilage), enhances depth • increases stability, but reduces mobility • Movement stops when “bone hits bone” labrum
Thick, complete joint capsule • 3 well developed ligaments • Stabilize the joint, limit movement
Knee joint • “modified hinge joint” • Little stability from articulating surfaces • Joint capsule & Complex set of ligaments • Large muscles cross joint Primary stabilizers Limit mobility
Hinge joint • Primarily flexion and extension • Articulating surfaces do not support one another
Menisci • Improve fit • Stabilizes joint • Distributes weight/force
Joint capsule • Loose, slack anteriorly • Permits flexion • Thick and tight posteriorly • Prevents, “brake to” extension
Collateral (tibial & fibular) ligaments • On medial and lateral joint surfaces • Prevent side-to-side (medial-lateral) displacement
Cruciate Ligaments • Allow flexion and extension • Prevents anterior and posterior displacement of tibia
Cruciate ligaments prevents prevents Posterior cruciate Why not located on anterior and posterior surfaces? Anterior cruciate
Muscles vm vl • Quadriceps femoris group • Petallapetallar ligament • Hamstrings • Gastrocnemius • popliteus