Bone Function and Composition

Bone Function

• Bone gives a rigid skeletal frame for support and protection.
• Bone forms a lever system moved by attached muscles.

Material Constituents of Bone

• Major building blocks include calcium carbonate and calcium phosphate which give bone its stiffness.
• Calcium carbonate and calcium phosphate are primary determinants of compressive strength.
• Collagen provides bone flexibility and contributes to tensile strength.
• Water contributes to bone strength and carries nutrients to and waste away from bone cells.

Structural Organization of Bone

• The relative percentage of bone mineralization changes with age and the specific bone in the body.
• The proportion of calcium phosphate and calcium carbonate is smaller in more porous bone.
• The proportion of nonmineralized tissue is greater in more porous bone.
• Cortical bone has low porosity, with 5-30% of the bone volume occupied by nonmineralized tissue.
• Spongy, cancellous, or trabecular bone has high porosity, with 30-90% of the bone volume occupied by nonmineralized tissue.

Biomechanical Properties

• Trabecular bone has a honeycomb structure with mineralized vertical and horizontal bars, called trabeculae.
• Trabeculae form cells filled with marrow and fat.
• Cortical bone is stiffer and can withstand greater stress because of its high mineral content.
• Cortical bone is subject to less strain or relative deformation than trabecular bone.
• Trabecular bone is spongier than cortical bone, so it can undergo more strain before fracturing.

Structure - Function

• A bone's function dictates its structure.
• Long bone shafts are composed of strong cortical bone.
• The high trabecular bone content of vertebrae contributes to their shock absorption.
• Cortical and trabecular bone are anisotropic, exhibiting different strength and stiffness based on the direction of forces.
• Bone is strongest when resisting compressive stress and most vulnerable to shear stress.

Types of Bones

• The skeletal system includes central/axial and peripheral/appendicular skeletons.
• Axial skeleton bones are the skull, vertebrae, sternum, and ribs.
• Appendicular skeleton refers to the bones that form limbs and appendages .
• Short bones are approximately cubical and are carpals and tarsals.
• Flat bones protect organs/soft tissues and provide muscle and ligament attachment areas such as scapulae, sternum, ribs, patellae, and some bones of the skull.
• Irregular bones have unique shapes for special bodily functions.
• Vertebrae can be considered irregular bones that provide a bony protective tunnel for the spinal cord.
• Long bones form the appendicular skeleton framework, consisting of a long, roughly cylindrical shaft of cortical bone.
• Long bones contain bulbous ends such as condyles, tubercles, or tuberosities.
• Articular cartilage protects the ends of long bones from wear at points of contact with other bones
• Long bones also contain a central hollow area known as the medullary cavity or canal.
• Examples of long bones are the tibia, femur, radius, and ulna.

Bone Growth and Development

• Bone growth begins early in fetal development and continues changing in composition/structure during life.
• Longitudinal bone growth occurs at epiphyses or epiphyseal plates.
• Epiphyses are cartilaginous discs near long bone ends.
• The diaphysis side constantly produces new bone cells.
• The plate disappears and the bone fuses terminating longitudinal growth during or shortly after adolescence.
• Long bones can grow in diameter throughout life, with the most rapid growth before adulthood.
• The periosteum's internal layer builds concentric layers of new bone tissue on top of existing tissue.
• At the same time, bone around the circumference of the medullary cavity is resorbed or eliminated to enlarge the cavity diameter.

Upper Extremities: Structure of the Shoulder

• The shoulder is the most complex joint due to its five articulations.
• The shoulder's five articulations are: glenohumeral, sternoclavicular, acromioclavicular, coracoclavicular, and scapulothoracic joints.
• The glenohumeral joint links the head of the humerus and the glenoid fossa of the scapula.
• The Glenohumeral is a type of ball-and-socket joint.
• Sternoclavicular and acromioclavicular joints enable movement for the clavicle and scapula that are the shoulder girdle bones.
• The head of the humerus articulates with the glenoid fossa of the scapula in the glenohumeral joint, which enables a ball-and-socket motion.
• The surrounding capsule in the glenohumeral joint contributes to joint stability, allowing for extreme mobility.
• The sternoclavicular joints drive much of the shoulder girdle motion.
• The Sternoclavicular joint is a type of saddle joint

Upper Extremities: Muscles of Rotator Cuff

• Rotator cuff muscles enable humerus rotation.
• Rotator cuff tendons create a collagenous cuff around the glenohumeral joint.
• The rotator cuff contains the supraspinatus, infraspinatus, teres minor, and subscapularis (SITS).
• The supraspinatus, infraspinatus, and teres minor facilitate lateral rotation.
• The subscapularis contributes to medial rotation.

Upper Extremities: Muscles of Scapula

• Scapular muscles are responsible for two functions.
• Scapular muscles stabilize the scapula when the shoulder complex is loaded.
• The scapular muscles aid in movement when positioning the scapula to assist motion at the glenohumeral joint.

Lower Extremities: Structure of the Hip

• The hip is a ball-and-socket joint.
• The ball is the head of the femur, which forms approximately two-thirds of a sphere.
• The socket is the concave acetabulum angled obliquely anteriorly, laterally, and inferiorly.
• The joint cartilage covers articulating surfaces of the hip.
• The hip is more stable than the shoulder from bone structure and the amount/strength of muscles and ligaments crossing the joint.
• The hip's pubofemoral and iliofemoral ligaments strengthen the joint capsule anteriorly.
• The hip's ischiofemoral ligament strengthens the joint capsule posteriorly.

Lower Extremities: Loads on the Hip

• The hip is a primary weight-bearing joint.
• Half the weight above the hip (1/3 of total body weight) is supported at each side.
• Compression force is 3-4 times body weight during walking.

Lower Extremities: Structure of the Knee

• The knee is a large synovial joint with three articulations within the joint capsule.
• The tibiofemoral joint, the two condylar articulations, form the weight-bearing joints, and is a hinge joint.
• The patellofemoral joint is the third articulation and is a saddle joint.

Lower Extremities: Function Of Menisci of the Knee

• The menisci are cartilaginous discs between tibial and femoral condyles.
• The menisci deepen the articulating depressions of the tibia and help with load transmission and shock absorption.

Lower Extremities: Movement of the Knee

• The medial and lateral collateral ligaments prevent lateral motion at the knee.
• Moving forward/backward of the femur is controlled by anterior and posterior cruciate ligaments.
• Knee flexion/extension are also controlled by anterior/posterior cruciate ligaments.
• These ligaments limit knee hyperextension.

Lower Extremities: Hip Movement

• Hip movements include medial rotation, lateral rotation, extension, flexion, abduction, and adduction.

Reminders

• A lab report is due on Friday, March 28th at 11:59 PM.
• Quiz #3 is on Wednesday, March 26th, at the start of Class.
• Quiz #3 covers the material from Week 8 and 9 lectures.