Figure 9.1 All joints are trade-off between mobility and stability
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
Spine: A series of 24 individual vertebrae + sacrum (5 fused vertebrae) + coccyx (~4 fused vertebrae). Functionally: bears and transmits upper body weight onto the pelvis while permitting movement. –Accomplished by being made of many individual bones stacked on one another –Small movement between each vert considerable mobility with decent stability protects the spinal cord
Regions Cervical — secondary curve—created and maintained by muscle use associated with upright posture Thoracic—primary curve—present at birth and maintained by associated bones Lumbar — secondary curve—created and maintained by muscle use associated with upright posture Sacrococcygeal—primary curve—present at birth and maintained by associated bones Presence of Curves places body weight in the correct place for upright posture. Primary curvatures are less mobile, but more stable and less prone to injury.
Vertebral Anatomy Body is the weight bearing portion Processes are sites of muscle and ligament attachment the pedicle and lamina help create the vertebral foramen through which passes the spinal cord (also protects the cord) Articulating processes help define movements that are possible between adjacent vertebrae
Intervertebral Joints There are two joints between individual vertebrae 1.Joints between bodies: symphysis—intervertebral discs –disc both absorbs shock and acts as a flexible spacer that allows intervertebral movement. 2.Joint between superior and inferior articulating processes (facets): synovial joint –direction/orientation and shape of the articulating processes defines/determines what kind of movements are possible between vertebra—especially the degree of rotation possible nucleus pulposus annulus fibrosus
intervertebral disk--symphisis synovial joint – plane-- between articulating processes Joints of the spine
Refer to lecture notes for details on the structure and function of intervertebral discs
Herniation of disc (rupturing and protrusion of nucleus pulposus) can pinch nerves between the expanded disc and nearby bone structures which creates pressure on the nerve and thus pain and dysfunction.
Joint Mobility Mobility (types and range of motion) at a joint can be influenced by: 1.shape of articulating bone surfaces and boney structures interfering with joint movement (bone-bone interference) 2.ligaments becoming tight and braking/stopping further movement in a particular direction 3.the compression of soft tissue (e.g., muscle, adipose) preventing further joint movement.
anterior ligaments Posterior ligaments lateral ligaments Ligaments of the Spine: Simplified Scheme
Bones are held in place and supported in much the same way that a pole is supported/held in place by guy-lines/ropes anchoring them into the ground. Bone—which structurally bears/transmits compressive force is supported (i.e., held in place) by fibrous tissue and muscle—tensile structures (the tensegrity model)
SPINAL EXTENSION In extension/hyperextension: spinous processes move toward one another and can limit movement on the side being moved to Anterior ligaments become tight and limit/brake movement Note: nucleus pulposus is being pushed anteriorly
SPINAL FLEXION In Flexion: There are no boney structures of the vertebrae to limit flexion Posterior ligaments become tight and act as a brake to flexion Note: the disc is stressed toward the posterior.
LATERAL FLEXION (I.E., SIDE BENDING) Lateral flexion The transverse processes on the side being flexed toward (ipsilateral) move toward one another and will limit movement the lateral ligament on the opposite side (contralateral) will become tight to limit movement Note: disc being stressed toward the side being bent away from (contralateral).
ROTATION Largely influenced by orientation of articulating processes and presence/absence of ribs