A12 Biomechanics Flashcards
Understand why the skeleton must withstand static & dynamic, tensile & compressive forces
Skeleton must withstand static & dynamic forces imposed by bodymass & by locomotion
Bones in the skeleton can be thought of acting like beams & columns withstanding forces of gravity & locomotion, loading of columns can produce compressive or tensile stresses with the nature of the stress depending on now the column’s loaded
Explain why eccentric (asymmetric) loading of long bones must be taken into account when repairing fractures using bone plates
Eccentric loading of a long bone means that one side will be subject to distracting forces & the opposite side will be subject to compressive forces
The tension side is usually the convex surface of a bowed bone
If a bone plate is placed on the tension side of the bone, it’II hold the fragments together neutralising the distracting forces & stabilising the fracture
If a bone plate is placed on the compression side it won’t neutralise the distracting forces at the tension aspect & is more likely to bend/fail
Recognise how the composition & microscopic structure of bone help it to withstand forces & resist failure
Bone is a composite material with stiff but brittle mineral aspect (without it bone would bend) as well as tough but compliant collagen aspects (without it bone would shatter)
Microscopic structure of Haversian bone imparts toughness
Has crack-stopping ability, as crack can’t propagate far before it intersects with an osteon impending its progress, this increases toughness & resistance to fracture
Explain why a tubular structure is biomechanically suitable for the shaft of a long bone
When beams are loaded in bending, stresses are concentrated at the edges and minimal at the core.
Neutral axis experiences little stress so can reduce the amount of material without losing strength, the material can be concentrated where needed.
Discuss the biomechanical significance of the flared epiphyses of the long bones
Flaring of the epiphysis expands the articular surface reducing the stress experienced by the particular cartilage.
The epiphysis comprise cancellous bone, less material is required to form the expansion & it’s less dense than compact bone
Appreciate the dynamic nature of bone & its capacity for functional adaptation
Bone is not a static structure, alterations can be made in osteoblast recruitment & osteoclast activity as well changes in bone density.
The adaptation to loading/exercise is site-dependent, e.g. Increased density of bone due to training.
Disuse osteopenia can also occur from immobilisation/not weight-bearing, as well as from zero gravity
Understand the significance of body size to the appendicular skeleton
Larger animals require relatively more robust bones
The strength of limb bones relates to their cross-sectional area, if similar objects increase in linear dimensions by a given factor then the areas increase proportionally to the factor squared & the volumes to that factor cubed.
Discuss now the general pattern of the limbs differs between cursorial & graviportal mammals
Curatorial mammals are adapted to running so have long bones connected with moderately- angled joints. Movement around each joint is additive so the limb moves with greater velocity. Adding/lengthening limb segments produces greater total extension, speed is more important than strength.
Graviportal mammals are adapted to move large mass at a walking pace so have long bones that are orientated vertically with little angulation. They act as columns for supporting weight & have the ability to withstand larger forces of locomotion that result from increased body mass. Strength more important than speed.
Define mechanical advantage & explain its significance when considering the function of skeletal muscle & the site of tendon insertion
Muscles of the locomotor system pull against bones, acting around joints, creating a system of levers.
Mechanical advantage: the ratio of the moment arm of the effort to that of the load
Mechanical advantage for most skeletal muscles is <1, thus forces generated by the skeletal muscles must be greater than those exerted on their loads. Disadvantageous in terms of strength but allowed for greater range of movement & speed.
Tendon insertion further from joint gives stronger output force but slower movement with less range of motion. Insertion closer to the joint gives weaker output but faster movement with greater range of motion.
Understand the basic biomechanics of the vertebral column, & the roles of the spinal & abdominal musculature in flexion & extension of the spine
Thoracolumbar vertebral column acts as a bridge spanning the pectoral & pelvic girdles
The bow & string theory likens the column to a bow with the abdominal muscles/ linea alba forming the string. Tension on the string causes abdominal muscles to contract & the spine to flex. Relaxing the string causes epaxial muscles to contract & extend the spine
