GE 345: Week 8
Joint Stability and Movement
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[ Stability & Movement ]
Joint stability refers to its resistance to displacement. Joints provide the axis around which movement occurs. However, movement comes at the price of stability, so they must provide stability without interfering with the desired motions.
Stability
Several factors contribute to joint stability:
- Joint Ligaments: these strong, flexible, fibrous tissues help maintain two articulating bones' relationship to one another and check movement when it reaches its normal limits. However, violent motions can tear them, and prolonged stress can stretch them. Ligaments are not very elastic and take a long time to recover from a stretch -- sometimes they never regain normal length.
- Muscle Tension: muscles and tendons spanning a joint not only contribute to motion around the joint, but also its stability. For example, the rotator cuff (subscapularis, supraspinatus, infraspinatus, teres minor) around the shoulder joint act to prevent displacement of the humeral head.
- Fascia: fibrous connective tissue forming sheaths for individual muscles, partitions between muscles and smaller partitions separating muscle fibers within a muscle. Similar to ligaments in that they are susceptible to permanent stretch. The iliotibial tract of the fascia lata helps stabilize the hip.
- Atmospheric Pressure: a femoral head remained intact in a hip joint where supporting tissues were removed. In a joint with supporting tissues intact, a hole was drilled through the acetabulum, whereupon the femoral head separated from the acetabulum. ex: a scuba mask with a good seal.
- Shape of Bony Structures: characteristics of the articulating surfaces. Shoulder & hip joints are both ball-and-socket, but the acetabulum is much deeper than the glenoid fossa.
Range of Motion
All joints in an individual or the same joint in different individuals may have differing range of motion (ROM). Range of motion is influenced by:
- Shape of Articular Surfaces
- Ligaments
- Muscles: extensibility
- Bulk: well-developed muscles or excessive fatty tissue can provide obstacles to motion.
- Sex: hormones influencing extensibility.
- Body Type: ectomorphs tend to be more flexible than endomorphs.
- Heredity
- Habits/Physical State
Muscles and tendons probably influence both stability and ROM the most. Therefore, flexibility should not exceed the muscles' ability to maintain joint integrity. Developing antagonistic muscle groups contributes to both flexibility and strength.
[ Bone ]
[ Skeleton ]
[ Terms ]
[ Articulations ]
[ Stability & Movement ]