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Knee biomechanics dr.bhuvanesh

This document discusses knee biomechanics and provides definitions of key concepts. It summarizes the biomechanics of the knee joint, including range of motion, meniscus function, ligament function, and alignment. Key points are that the knee is a hinge joint with rolling and sliding motion. The menisci absorb shock, distribute load, and aid lubrication. The ACL and PCL prevent unwanted translation of the tibia. Proper lower extremity alignment and the Q-angle are important for knee function.

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KNEE BIOMECHANICS DR. BHUVANESH GOPAL
Definition  Biomechanics is the science of the action of forces, internal or external on the living body.  Statics is the study of forces on bodies at rest  Dynamics is the study of the motion of bodies and the forces that produce the motion
JOINT BIOMECHANICS  Degree of freedom  Joint reaction force  Coupled forces  Joint congruence  Instant center of rotation  Friction and lubrication
KINEMATICS  Kinematics is the study of motion in terms of displacement, velocity, and acceleration with reference to the cause of the motion  Kinesiology is the the study of human movement and motion
KINEMATICS - Knee Joint  Hinge type  ROM • Ext 10-15 degrees • Flex 130-150
JOINT MOTION  J -shaped curve  Both rolling and sliding motion
J-Curve
ROTATION  Axis lies close to medial condyle  At 90 degree flexion • 45 degree ER • 30 degree IR
Adduction and abduction • 0 degree at full extension • Around 10 degrees at 30 degrees of knee flexion
Adduction and abduction • 0 degree at full extension • Around 10 degrees at 30 degrees of knee flexion
MENISCI
MENISCI
MENISCI  Fibrocartilagenous crescent; triangular in cross-section  Lateral meniscus is more circular; medial meniscus more c-shaped  Lateral meniscus has twice the excursion of the medial meniscus during knee motion.  Anterior horn of LM & post horns of both menisci attach to the intercondylar eminence
MENISCI
MENISCI Contd…  Anterior horns attached to each other by the intermeniscal ligament  Popliteus muscle is attached to lateral meniscus (not the tendon)  Semimembranosis is attached to medial meniscus
MENISCI
MENISCI Contd…  Provision of stability  Shock absorption  Provision of increased congruity  Aids lubrication  Prevents synovial impingement  Limits extremes of flexion & extension  Transmits loads across the joint – 50- 100% of load is transmitted through menisci  Reduces contact stresses
MENISCI Contd…  The compression of the menisci by the tibia and the femur generates outward forces that push the meniscus out from between the bones.  The circumferential tension in the menisci counteracts this radial force.
HOOP STRESS  Hoop stress is the stress in a direction perpendicular to the axis of an item  As the thickness of the item decreases the hoop stress increases
MENISCI Contd…  These hoop forces are transmitted to the tibia through the strong anterior and posterior attachments of the menisci.  This hoop tension is lost when a single radial cut or tear extends to the capsular margin and that in terms of load-bearing, a single radial cut through the meniscus is equivalent to meniscectomy.
MENISCECTOMY  Decrease in TF contact area and increase in contact stress.  Partial Meniscetomy  65% increase in contact stress.  Total Meniscetomy  235%
SCREW HOME MECHANISM • Locking • Femur internally rotates( external tibial torsion) during last 10-20 degrees of extension
FEMORAL ROLL BACK  Posterior roll back of femur on tibia increases during knee flexion  PCL  0.5cm of excursion of the medial meniscus and 1.1cm of excursion of lateral meniscus during a 0- 120 degree arc of knee motion
KINETICS  Extension – quadriceps mech via patellar apparatus  Flexion – hamstrings  Knee stablizers
ACL
ACL  Intraarticular extrasynovial  Anteromedial fibers - tight in flexion - limits anterior translation of tibia on femur  Posterolateral fibers - tight in extension - limits anterior translation plus external rotation  Bl.supply - middle genicular a. (post) & synovial vv (ant)  Mechanoceptors with a proprioceptive role  Acl strength = 50% pcl strength  Load to failure = 1700n
ACL
ACL
PCL
PCL  2 bundles: posteromedial and anterolateral  Function: • Limits hyperextension • Prevents post translation of tibia on femur especially during flexion
AXIS OF LOWER EXTREMITY
MECHANICAL AXES OF LOWER EXTREMITY Hip joint Centre Mechanical Axis Ankle Joint Centre Knee Joint
VERTICAL AXIS Vertical Axis Femoral Shaft Axis Mechanical Axis Transverse Knee Axis Transverse Ankle Axis 6◦ 9◦3◦ 3◦ 3◦ 90◦
ANATOMICAL AXIS Anatomic Axis Tibiofemoral Angle Mechanical Axis 6◦
MECHANICAL AXIS OF TIBIA from the centre of tibial plateau to the centre of tibial plafond
MECHANICAL VALGUS/ VARUS ALIGNMENT AXfm AXfm AXtm AXtm AXIIm Femur Tibia Ankle Knee Femur Head
 Tibial articular surface is normally 3 degree varus with respect to mechanical axis  Femoral articular surface is normally 9 degree valgus
 The mechanical axis of the lower extremity is in 3 degree of valgus from the vertical axis  The anatomic axis of the femur is in 6 degrees of valgus, the mechanical axis(9 degree valgus with the vertical axis)  The anatomic axis of the tibia is in 2-3 degrees of varus from the mechanical axis
Arthrodesis • The position for knee arthrodesis should be 0-7 degrees of valgus and 10-15 degreees of flexion
Neutral Femoral Rotational Axis Whiteside’s Line TEA PCA
PATELLOFEMORAL JOINT  Patella • Pulley / changes the direction of pull • Enhances the moment arm of quadriceps • Varies from 6cm at full extension to about 4cm at 120 degree flexion  Forces at the patellofemoral jt. tend to increase with quadriceps muscle force except during the last 15-20 degrees of ext.
Q - ANGLE  Brattstrom • Q angle formed by the line of pull of the quadriceps mechanism and that of the patellar tendon as they intersect at the centre of the patella  Males: 8-10 degrees  Females: 15 degrees ± 5 degrees
Q - Angle Q-Angle Line 1 ASIS to midpoint Of patella Line 2 Tibial tubercle to midpoint of patella Midpoint of patella Tibial tubercle Anterior Superior Iliac Spine (ASIS) Line 1 Line 2
FACTORS INCREASING Q ANGLE  Genu valgum  Increased femoral anteversion  External tibial torsion  Laterally positioned tibial tuberosity  Tight lateral retinaculum
GOALS OF KNEE REPLACEMENT  Restoring mechanical alignment  Restoring the joint line  Balancing ligaments  Maintaining a normal Q-angle
Knee biomechanics dr.bhuvanesh