Biomechanics
5/7/99

Bone
•	Support
•	Used as the lever system
•	Protection
•	Mineral storage—calcium
•	Small % of calcium is found in the blood
•	Bone is weak under tension and strong under compression
•	Collagen is found in the bone which is strong under tension
•	This makes the bone stronger overall
•	Muscles help the bones from bending
•	Ex:  in the foot the plantar aponerosis always prevents bending
•	Get stress fractures in the metatarsals, shin splints (tibia), hip in elderly
•	Periosteum of the bone is the most sensitive to pain
•	3 things needed for bone to heal
1.	blood supply
2.	immobilization
3.	proximation of the ends
4.	time
•	should take a normal person about 2 months to heal
•	abnormal bones include
•	vertebrae—has good blood supply, can immobilize w/body cast, can never get them back together b/c it was a compression fracture and pressure is always present
•	scaphoid of the wrist—most common tarsal broken, takes most of the pressure b/w the forearm and the hand—has a lack of blood supply—surgically need to wire for it to heal
•	ribs—good blood supply, ends are together, can't immobilize b/c we have to breathe
•	clavicle—hard to immobilize and does not have a great blood supply—predisposes to thoracic outlet syndrome
•	femur neck—blood supply (obturator a) 20% do not have the artery, no muscle directly around it, can immobilize, ends are there
•	lose about 1% a week of bone mass, lose 2% of bone strength
•	takes 2 to 3 x's as long w/ rehab to get back to normal