BIOMECHANICS OF HIP JOINT BY Dr. VIKRAM

BIOMECHANICS OF HIP JOINT BY Dr. VIKRAM

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  BIOMECHANICS OF HIP JOINT Seminarby Dr. T. Vikram M.S ORTHO Prathima institute of medical sciences karimnagar
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  INTRODUCTION • The hipjoint, or coxofemoral joint, is the articulation of the acetabulum of the pelvis and the head of the femur • diarthrodial ball-and-socket joint • three degrees of freedom: 1. flexion/extension in the sagittal plane 2. abduction/adduction in the frontal plane 3. medial/lateral rotation in the transverse plane
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  • The primaryfunction of the hip joint is to support the weight of the head, arms, and trunk (HAT) both in static erect posture and in dynamic postures such as ambulation, running, and stair climbing.
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  STRUCTURE OF THEHIP JOINT Proximal Articular Surface Acetabulum • The opening of the acetabulum is approximately laterally inclined 50°; anteriorly rotated (anteversion) 20°; and anteriorly tilted 20° in the frontal, transverse, and sagittal planes, respectively
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  • Acetabular depthcan be measured as the center edge angle of Wiberg
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  • Center edgeangles are classified as follows: • definite dysplasia less than 16° • possible dysplasia 16° to 25° and • normal greater than 25° • In addition, abnormalities in acetabular depth, inclination, and version (abnormal positioning in the transverse plane) can also affect femoral head coverage
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  • Anteversion ofthe acetabulum exists when the acetabulum is positioned too far anteriorly in the transverse plane • Retroversion exists when the acetabulum is positioned too far posteriorly in the transverse plane
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  Acetabular labrum • Theentire periphery of the acetabulum is rimmed by a ring of wedge-shaped fibrocartilage called the acetabular labrum • Deepens the socket, increases the concavity of the acetabulum, grasping the head of the femur to maintain contact with the acetabulum • It enhances joint stability by acting as a seal to maintain negative intra-articular pressure • Also provide proprioceptive feedback
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  Distal articular surface •The head of the femur ofovea or fovea capitis oligament of the head of the femur (ligamentum teres)
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  ANGULATION OF THEFEMUR • There are two angulations made by the head and neck of the femur in relation to the shaft Angle of inclination occurs in the frontal plane between an axis through the femoral head and neck and the longitudinal axis of the femoral shaft Angle of torsion occurs in the transverse plane between an axis through the femoral head and neck and an axis through the distal femoral condyles
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  1.ANGLE IF INCLINATIONOF FEMUR • The angle of inclination of the femur approximates 125° • Normal range from 110° to 144° in the unimpaired adult • With a normal angle of inclination, the greater trochanter lies at the level of the center of the femoral head • A pathological increase in the medial angulation between the neck and shaft is called coxa valga • A pathological decrease is called coxa vara
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  • Both coxavara and coxa valga can lead to abnormal lower extremity biomechanics altered muscle function,and gait abnormalities
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  2.ANGLE OF TORSIONOF THE FEMUR • The angle of torsion of the femur can best be viewed by looking down the length of the femur from top to bottom • An axis through the femoral head and neck in the transverse plane will lie at an angle to an axis through the femoral condyles, with the head and neck torsioned anteriorly (laterally) with regard to an angle through the femoral condyles
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  • In theadult, the normal angle of torsion is considered to be 10° to 20°, 15° for males and 18° for females • Femoral anteversion is considered to exist when angle of anterior torsion is greater than 15° to 20° • A reversal of anterior torsion, known as femoral retroversion, occurs when angles are less than 15° to 20°
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  • Femoral anteversionis associated with increased medial rotation ROM and concurrent decreased lateral rotation so that the total excursion of hip rotation motion remains the same • Anteversion of the femoral head reduces hip joint stability because the femoral articular surface is more exposed anteriorly • The line of the hip abductors may fall more posterior to the joint, reducing the moment arm for abduction
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  • When thefemoral head is anteverted, pressure from the anterior capsuloligamentous structures and the anterior musculature may push the femoral head back into the acetabulum, causing the entire femur to rotate medially • The knee joint axis through the femoral condyles is now turned medially • Medial rotation of the femoral condyles alters the plane of knee flexion/extension and results, at least initially,in a toe-in gait and a compensatory lateral tibial torsion develop
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  • An antevertedfemur will also affect the biomechanics of the patellofemoral joint at the knee and of the subtalar joint in the foot • The effect of femoral anteversion may also be seen at the knee joint
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  COXA VARA • Inadolescence, growth of the bone results in a more oblique orientation of the epiphyseal plate • The epiphyseal obliquity makes the plate more vulnerable to shear forces at a time when the plate is already weakened by the rapid growth that occurs during this period of life
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  • Weight-bearing forcesmay slide the femoral head inferiorly, resulting in a slipped capital femoral epiphysis in case of coxa vara • Disadvantage of increasing the bending moment along the femoral head and neck • The increased shear force along the femoral neck will increase the predisposition toward femoral neck fracture
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  COXA VALGA • Coxavalga also decreases the amount of femoral articular surface in contact with the dome of the acetabulum. • As the femoral head points more superiorly, there is a decreasing amount of coverage from the acetabulum superiorly. • Consequently, decreases the stability of the hip and predisposes the hip to dislocation • The resulting need for additional abductor muscle force may predispose the joint to arthrosis or may functionally weaken the joint, producing energy-consuming and wearing gait deviations
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  ARTICULAR CONGRUENCE • Inthe neutral or standing position, the articular surface of the femoral head remains exposed anteriorly and somewhat superiorly • Articular contact between the femur and the acetabulum can be increased in the normal non-weight-bearing hip joint by a combination of flexion, abduction, and slight lateral rotation
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  HIP JOINT CAPSULE •Both joint capsule and ligamentum teres provide stability of the hip joint during distractive forces
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  HIP JOINT LIGAMENTS •Iliofemoral ligament(Y ligament of Bigelow) • Pubofemoral ligament • Ischiofemoral ligament
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  STRUCTURALADAPTATIONS TO WEIGHT BEARING •In standing or upright weightbearing activities, at least half the weight of the HAT (the gravitational force) passes down through the pelvis to the femoral head, whereas the ground reaction force (GRF) travels up the shaft.
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  • These twoforces, nearly parallel and in opposite directions, create a force couple with a moment arm • (MA) equal to the distance between the superimposed body weight on the femoral head and the GRF up the shaft. • These forces create a bending moment (or set of shear forces) across the femoral neck
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  Trabecular system • Themedial (or principal compressive) trabecular system • The lateral (or principal tensile) trabecular system • Accessory (or secondary) trabecular systems • zone of weakness
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  • The forcesof HAT and the ground reaction force that act on the articular surfaces of the hip joint and on the femoral head and neck also act on the femoral shaft
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  • Ranges ofpassive joint motion typical of the hip joint :- Flexion 90° with the knee extended and 120° when the knee is flexed Hip extension 10° to 20° Abducted 45° to 50° Adducted 20° to 30° Medial and lateral rotations of the hip the typical range is 42° to 50°
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  Hip Joint Musculature Movements Flexion: chiefly by psoas major, iliacus assisted by rectus femoris and sartorius  Adductor longus assists in early flexion following full extension Extension : gluteus maximus and the hamstrings. Abduction : gluteus medius and minimus assisted by sartorius,tensor fasciae latae and piriformis  Action is limited by adductor longus,pubofemoral ligament and medial band of ilio femoral ligament
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  Adduction : byadductor longus, adductor brevis and adductor fibers of adductor magnus Lateral rotation : piriformis, obturator internus and externus, superior and inferior gemelli and quadratus femoris  assisted by the gluteus maximus Medial rotation : the anterior fibers of the gluteus medius and gluteus minimus, tensor fasciae latae Piriformis muscle was a lateral rotator at 0° of hip flexion but a medial rotator at 90° of hip flexion
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  MOTION OF PELVISON THE FEMUR • Whenever the hip joint is weight-bearing, the femur is relatively fixed, and motion of the hip joint is produced by movement of the pelvis on the femur
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  Anterior and PosteriorPelvic Tilt  Anterior and posterior pelvic tilts are motions of the entire pelvic ring in the sagittal plane around a coronal axis  In the normally aligned pelvis, the anterior superior iliac spines (ASISs) of the pelvis lie on a horizontal line with the posterior superior iliac spines and on a vertical line with the symphysis pubis  Anterior and posterior tilting of the pelvis on the fixed femur produce hip flexion and extension
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   Hip jointextension through posterior tilting of the pelvis  Hip flexion through anterior tilting of the pelvis
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  Lateral Pelvic Tilt Lateral pelvic tilt is a frontal plane motion of the entire pelvis around an anteroposterior axis  In the normally aligned pelvis, a line through the anterior superior iliac spines is horizontal  In lateral tilt of the pelvis in unilateral stance, one hip joint (e.g., the left hip joint) is the pivot point or axis for motion of the opposite side of the pelvis (e.g., the right side) as that side of the pelvis elevates (pelvic hike) or drops (pelvic drop).
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  • If aperson stands on the left limb and hikes the pelvis, the left hip joint is being abducted because the medial angle between the femur and a line through the anterior superior iliac spines increases. • If a person stands on the left leg and drops the pelvis, the left hip joint will adduct because the medial angle formed by the femur and a line through the anterior superior iliac spines will decrease
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  Lateral Shift ofthe Pelvis • With pelvic shift, the pelvis cannot hike; it can only drop. • Because there is a closed chain between the two weight-bearing feet and the pelvis, both hip joints will move in the frontal plane in a predictable way as the pelvic tilt (or pelvic shift) occurs
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  Forward and BackwardPelvic Rotation • Pelvic rotation is motion of the entire pelvic ring in the transverse plane around a vertical axis.
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  • Forward (anterior)rotation of the pelvis occurs in unilateral stance when the side of the pelvis opposite to the weight-bearing hip joint moves anteriorly from the neutral position • Forward rotation of the pelvis produces medial rotation of the weight-bearing hip joint
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  • Backward (posterior)rotation of the pelvis occurs when the side of the pelvis opposite the weight-bearing hip moves posteriorly • Backward rotation of the pelvis produces lateral rotation of the supporting hip joint
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  Pelvic Rotation inGait  In normal gait, the pelvis forwardly rotates around the weight-bearing hip while the other limb prepares for or is in swing  Because this happens first on one leg and then on the other, it appears to the eye as if the pelvis is forwardly rotating and then backwardly rotating
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  Coordinated Motions ofthe Femur,Pelvis, and Lumbar Spine Pelvifemoral Motion  When the femur, pelvis, and spine move in a coordinated manner to produce a larger ROM than is available to one segment alone, the hip joint is participating in what will predominantly be an open-chain motion termed pelvifemoral motion.  Also been referred to as pelvifemoral rhythm
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   2 typesof response • The open-chain response (the ability of each joint in the chain to move independently) the head and trunk will follow the motion of the pelvis (moving the head through space) • Closed-Chain response the head will continue to remain relatively upright and vertical despite the pelvic motions
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  Moving the headand arms through space If the goal is to bend forward to bring the hands (and head) toward the floor, isolated flexion at the hip joints (anteriorly tilting the pelvis on the femurs) is generally insufficient to reach the ground
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  Moving the footthrough space When a person is lying on the right side, the left foot may be moved through an arc of motion approaching 90° The abducting limb is in an open chain
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  • A trueopen-chain response to isolated hip flexion would displace the head and trunk forward, with the line of gravity falling in front of the supporting feet • In a functional closed chain, motion at the hip (one link in the chain) is accompanied by an essentially mandatory lumbar extension to maintain the head over the sacrum
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  • Compensatory motionsof the lumbar spine that accompany given motions of the pelvis and hip joint in a functional closed chain
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  HIP JOINT FORCESAND MUSCLE FUNCTION IN STANCE Bilateral Stance • The line of gravity falls just posterior to the axis for flexion/extension of the hip joint • In the frontal plane during bilateral stance, the superincumbent body weight is transmitted through the sacroiliac joints and pelvis to the right and left femoral heads • joint axis of each hip lies at an equal distance from the line of gravity of HAT • The gravitational moment arms for the right hip(DR) and the left hip (DL) are equal
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  • Because thebody weight (W) on each femoral head is the same (WR = WL), the magnitude of the gravitational torques around each hip must be identical • WR X DR =WL X DL • The gravitational torques on the right and left hips occur in opposite directions. • The weight of the body acting around the right hip tends to drop the pelvis down on the left (right adduction moment), whereas the weight acting around the left hip tends to drop the pelvis down on the right (left adduction moment)
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  • These twoopposing gravitational moments of equal magnitude balance each other, and the pelvis is maintained in equilibrium in the frontal plane without the assistance of active muscles
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  • Assuming thatmuscular forces are not required to maintain either sagittal or frontal plane stability at the hip joint in bilateral stance, the compression across each hip joint in bilateral stance should simply be half the superimposed body weight (or one third of HAT to each hip) • In bilateral stance when both lower limbs bear at least some of the superimposed weight, the contralateral abductors and adductors may function as synergists to control the frontal plane motion of the pelvis.
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  Unilateral stance • Theleft leg has been lifted from the ground and the full superimposed body weight (HAT) is being supported by the right hip joint. • The weight of the non-weightbearing left limb that is hanging on the left side of the pelvis must be supported along with the weight of HAT by right hip joint. • Of the one-third of the portion of body weight found in the lower extremities, the non-weightbearing limb must account for half of that, or one sixth of the full body weight
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  • The magnitudeof body weight (W) compressing the right hip joint in right unilateral stance, therefore, is • Right hip joint compressionbody weight =[2/3 x W] + [1/6 x W]= 5/6 x W
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  • The forceof gravity acting on HAT and the nonweightbearing left lower limb (HATLL) will create an adduction torque around the weight-bearing hip joint • Gravity will attempt to drop the pelvis around the right weight-bearing hip joint axis. • The abduction countertorque will have to be supplied by the hip abductor musculature • The result will be joint compression or a joint reaction force that is a combination of both body weight and abductor muscular compression.
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  Compensatory Lateral Leanof the Trunk • the compensatory lateral lean of the trunk toward the painful stance limb will swing the line of gravity closer to the hip joint, thereby reducing the gravitational moment arm • It does reduce the gravitational torque
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  Use of aCane Ipsilaterally  Body wt passes mainly through cane Use of a Cane Contralaterally  Cane assists the abductor muscles in providing counter torque
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  Pathological Gaits • Whena lateral trunk lean is seen during gait and is due to hip abductor muscle weakness, it is known as a gluteus medius gait • If the same compensation is due to hip joint pain, it is known as an antalgic gait • If lateral lean and pelvic drop occur during walking, the gait deviation is commonly referred to as a Trendelenburg gait
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  Femoroacetabular Impingement Cam impingement  Pistolgripdeformity of the femoral neck
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  Pincer impingement  causedby aberrations of the acetabulum
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  Reducing joint reactionforce Reduced by Reducing the body weight- generated momentum  By reducing body weight or reducing the body weight lever arm  Seen in Trelendenburg gait(leaning towards the diseased hip)
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  Reducing the requiredhip abductor force Altering the neck-shaft angle through varus osteotomy/varus placement of the femoral stem Increasing offset or medialization of the socket Use of cane in contralateral hand
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  Biomechanics of totalhip arthroplasty Stability and range of motion depends on : 1. Head size 2. Head-neck ratio and 3. Implant design
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  Increasing the head diameterincreases the jumping distance(i.e., the radius of the femoral head) Reduction of rates of revision for dislocation with increasing head size Primary arc of the joint
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  Increase in head-neckratio increases this arc, improving the range of motion Head-neck ratio < 2:1 increase the risk of impingment leading to fixation failure, limited function and dislocation
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  Acetabular design featuresthat can help increase the primary arc Semicaptive sockets that are greater than hemisphere reduce the primary arc and may have paradoxically adverse effect on stability
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  Acetabular hemispherical component 1. Ifrelatively small , stress transferred to the center 2. If relatively large , stress transferred to the periphery  Peripheral strains acting on a force vector perpendicular to the tangent at the rim stabilize the cup
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  Optimizing fixation andthe low frictional torque arthroplasty  CHARNLEY concept Shorten lever arm of the body weight by deepening the acetabulum and To lengthen the lever arm of the abductor mechanism by reattaching the osteotomized greater trochanter laterally Leading to decrease in moment produced by body weight there by reducing counterbalance force that the abductor mechanism must exert
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  Estimated load ofemoral head in stance phase of gait is 3 times body weight When standing on 1 leg abductor muscles work done is 2.5 times body weight Load on femoral head during straight leg raising is 3 times body weight While lifting, running, jumping 10 times body weight
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  Abductor lever armshortened in arthritis and also where head is lost or neck is shortened During the gait cycle, forces are directed against the prosthetic femoral head from a polar angle between 15-25 degrees anterior to the saggital plane of the prosthesis
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  Body’s center ofgravity is posterior to the axis of the joint making the stem to deflect medially in coronal plane and posteriorly in saggital plane producing torsion of the stem As seen in arising from chair, ascending and descending stairs, lifting
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  Reducing the jointreaction force in total hip arthroplasty Lateralizing the femoral component by increasing the horizontal femoral offset Inadequate restoration of offset results in hip abductor insufficiency and soft tissue laxity Excessive femoral offset can also predispose to failure by overtightening of the hip, increasing the stress placed on the femoral fixation interface