bySaifullah Khalid

(Lecturer)School of Physiotherapy,

IPM&R, Dow University of Health Sciences, Karachi 05/03/23 1

Objectives After completion of this lecture the

student should be able;1. To know the basic definition of

biomechanics2. To know the types of biomechanics3. To know the basic terms of biomechanics4. To know that why biomechanics is

important to study?5. To know about the brief clinical

applications of biomechanics

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Human BiomechanicsHuman BiomechanicsBiomechanicsBiomechanics

Mechanics

Structure

Function

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What Is Biomechanics? Biomechanics;

“ The application of mechanical principles in the study of The application of mechanical principles in the study of living organismsliving organisms ”

Involves the principles of anatomy and physics in the descriptions and analysis of movement.

The study of biological structures, processes and functions by applying the methods and principles of mechanics

BioBio = = LivingLivingMechanicsMechanics = = Forces & EffectsForces & Effects

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Why Study Biomechanics? The purpose of studying Biomechanics is; To understand the forces acting on the human

body To manipulate these forces in treatment

procedures so that human performance may be improved and further injury may be prevented.

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Why Study Biomechanics? Better understanding of both joint function and

dysfunction Design improvements in devices e.g. joint

arthroplasty systems and orthotic devices To understand how the musculoskeletal system

functions Useful in patient evaluations and treatments Important for clinicians such as orthopaedic

surgeons and physical and occupational therapists

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Kinematics Kinematics …

Description of motion (e.g. how fast, how high, etc.) without consideration given to its mass or the forces acting on it.

This may include …This may include … The movement of a single point on the body (e.g.

COG) Position of several segments (e.g. the Upper

Extremity) Position of a single joint Motions that occur between adjacent joint surfaces Kinematics examines how, when, and where a body

moves 05/03/23 7

Types of Kinematics Arthrokinematics …… The movements occurring

between joint surfaces in relation to the direction of movement of the distal extremity of the bone

Osteokinematics ……. Concerned with the movements

of the bones

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Kinetics Kinetics ….. The study of forces that lead to produce, stop or modify

motions of the body It examines ……It examines …… The causes of motion The internal and external forces that cause motion or

cause a body to remain at rest The interactions between these forces Forces affecting motion …..Forces affecting motion ….. Gravity Muscle tension External resistance Friction

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Types of Kinetics Statics….. Refers to situations where the body or object remains

at rest, or is moving at a constant speed in a state of equilibrium.

Equilibrium Equilibrium is a balanced state in which there is no acceleration

Dynamics... Deals with the changes in motion (acceleration)

brought on by unbalanced forces

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Arthrokinematics When a joint moves, three types of

motion can occur between the two articulating surfaces

Rolling or Rocking Sliding or Gliding Turning or Spinning

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Arthrokinematics In a pure rolling motionIn a pure rolling motion ………… Each subsequent point on one surface contacts a

new point on the other surface In sliding and spinning ……In sliding and spinning …… the same point on one surface contacts new

points on the mating surface

Most normal joint movementMost normal joint movement has some combination of rolling, sliding and spinning

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The knee jointThe knee joint ………… Shows the combination of

these movements most clearly

If there were only a rolling of the condyles of the femur on the tibial plateau, the femur would roll off the tibia and the knee would dislocate

ArthrokinematicsArthrokinematics

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Arthrokinematics in Sit To Stand

Rising from a Seated to a Rising from a Seated to a Standing Position ……..Standing Position ……..

the femur is extended on the fixed tibia, the femoral condyles roll and slide so that they are always in contact with the tibial condyles

In the last part of knee extension, the femur spins (internally rotates on the tibia)

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Clinical importance of Arthrokinematics

Arthrokinematics (combination of Roll, Slide and (combination of Roll, Slide and Spin) …… Spin) ……

Permits a Large ROM while using a Small Articular Surface

If joints possessed only one of these motions ……..If joints possessed only one of these motions …….. The ROM would be limited The Larger joint surfaces would be needed to

accomplish the same ROM

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Kinematic Chains A kinematic chain refers to a series

of articulated segmented links, such as the connected pelvis, thigh, leg, and foot of the lower extremity (Lower Kinematic Chains )

Open Kinematic Chain the distal segment of the chain moves in

space while the proximal segment is fixed or stable

Closed Kinematic Chain the distal segment is fixed, and

proximal parts move05/03/23 16

A Squat is an example of an close-chain motion

A leg curl from sitting in a chair is an example of an open-chain motion05/03/23 17

Kinematic Chains Activities Reaching or bringing the hand to the mouth …….

Open - Chain Motion Performing a chin-up …….. Closed - Chain Motion Standing to Sit …….. Closed - Chain Motion Sitting down in a Chair …… Closed - Chain Motion The leg moves forward on the fixed foot (dorsiflexion) The thigh approaches the leg (knee flexion) The thigh approaches the pelvis (hip flexion)

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Walking and Stair Climbing ……………. alternation of closed-chain motion and open-chain motion

Standing from a Chair………. When a person uses the uses the armrest of a chair to assist in coming to the standing armrest of a chair to assist in coming to the standing positionposition, the hand is fixed and the forearm moves in relation to the hand, the arm moves away from the forearm, and the arm moves toward the trunk

Crutch-walking ……… the arms are fixed and the

body moves in relation to the arms ( Close – Chain activity )

Kinematic Chains ActivitiesKinematic Chains Activities

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Sitting Down in a chair

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Arthrokinematic Relative to the Osteokinematics

Convex-Concave Relationships ……….. If the bone with the convex joint surface moves on the

bone with the concavity, the convex joint surfaces move in the opposite direction to the bone segment ………….Shoulder Movements

If the bone with the concavity moves on the convex surface, the concave Articular surfaces moves in the same direction as the bone segment ………………………….Knee Movements

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Examples Shoulder Abduction ……. A downward motion of the humeral head on the Glenoid

Cavity occurs when the humerus is moving upward Handstand …….. An upward movement of the glenoid on the humeral head

occurs when the scapula is moving ( Closed Kinematic Chain )

Knee Extension …….. An anterior movement of the concave tibial plateau on

the femur occurs during anterior movement of tibia

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Convex - Concave Principle Example

Normal Interphalangeal Joint Movements

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Close-Packed and Open-Packed Positions

The ovoid surfaces of joint pairs match each other perfectly in only one position of the joint. This point of congruency is called the Close -packed position

This position usually occurs at one extreme in the range of motion e.g. ………..e.g. ………..

Elbow, Wrist, Hip, and Knee JointsElbow, Wrist, Hip, and Knee Joints …….. Full extension Ankle JointAnkle Joint ……………..Dorsiflexion MP JointsMP Joints …………. Flexion at the In all other positions, the ovoid joint surfaces do not fit

perfectly but are incongruent and called Open - packed position or Loose - packed position05/03/23 24

Close-Packed Position VS. Open-Packed PositionClose-Packed Position

The maximum area of surface contact occurs

The attachments of the ligaments are farthest apart and under tension

Capsular structures are taut ( under tension)

The joint is mechanically compressed and difficult to distract

Open-Packed Position The ligamentous and

capsular structures are slack The joint surfaces may be

distracted several millimeters

This position allows the necessary motions of spin, roll, and slide and may decrease joint friction

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Mechanical Advantage of Close-Packed Position Provides Great mechanical stability to the joint Reduces the need for muscle forces to maintain a position

for example;for example; Standing Position Standing Position …………………………During standing, the hips

and knees are in their close-packed positions. This permits erect standing with little or no contraction of the muscles of the hips or knees and results in an economy of energy expenditure

Gripping Action ……………. Gripping Action ……………. At 90 degrees of flexion, the MPJs are in their close-packed positions. This provides Mechanical advantage in gripping action

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Accessory Motions

ln addition to angular motions (flexion or abduction) joint surfaces can be moved passively a few millimeters in translatory motion, called accessory movements or joint play

Examples Examples ………..……….. Distraction of joint Lateral glide Anterior-posterior glide Rotation

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Accessory Motions These are the passive movements applied by an examiner These motions cannot be performed voluntarily by the

subject Require relaxation of muscles Essential for normal pain-free joint function Performed by physical therapists in Performed by physical therapists in ……………………………… Assessment of the integrity of joint structures (e.g. In

Ligament Injury, there is excessive accessory motion ………. hypermobile joint )

Joint mobilization techniques in the treatment of hypomobile or painful joints ( e.g. In limited IP Joint flexion, downward glide should be applied close to the joint and in the line of normal joint surface movements)

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Clinical Consideration

If the necessary distal movement of the head of the humerus on the glenoid fossa were not present, elevation of the arm would be severely restricted …………………………. frozen shoulder

The greater tuberosity may strike the acromion process

instead of sliding beneath it. Striking the acromion process (and adjacent soft tissues) would produce additional injury and pain ….………. impingement syndrome

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End-Feel of Range of Motion When a normal joint is moved passively to the end of its

ROM, resistance to further motion is felt by the examiner. This resistance is called the End-feel or The Physiologic End-feel

This is described as Hard, Firm or Soft End-feels Normal End-feel Normal End-feel …………….……………. Hard or Bony End-feel: when the motion is stopped by

contact of bone on bone, as in elbow extension Firm or Springy End-feel: when the limitation is from

ligamentous, capsular, or muscle structures, as in wrist flexion

Soft End-feel: when the motion is stopped by the contact of adjacent soft tissues, as in full flexion of elbow

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Pathologic end-feel An end-feel that is not characteristic of the normal joint

End-feel and occur at a different place in the ROM of a joint

Empty End-feelEmpty End-feel …….……. Pain on motion but absence of resistance associated with infection, active inflammation and tumors

Hard end-feel …….Hard end-feel ……. bony blocking as in Arthritic joints Springy end-feelSpringy end-feel ………………rebound feel at the inner of ROM

as in torn meniscus blocking knee extension Sudden Hard-feelSudden Hard-feel …...... …...... Spasm of muscles Capsular feelCapsular feel ………………a hardest arrest of movement

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