Biomechanics of the Hip

Pelvic GirdleThe two hip bones plus the sacrum Can be rotated forward, backward, and laterally to optimize positioning of the hip joint

Obturator foramenischiumiliumpubissacrumacetabulumPelvic girdle

Pelvic Bone

Pelvic Bone

Anterior TiltForward tilting and downward movement of the pelvisOccurs when the hip extends

Posterior TiltTilting of the pelvis posteriorlyOccurs when the hip flexes

Lateral TiltTilting of the pelvis from neutral position to the right or leftLateral tilt tends to occur naturally when you support your weight on your leg This allows you raise your opposite leg enough to swing through during gait

Pelvic RotationRotation of the pelvis defined by the direction in which the anterior aspect of the pelvis movesOccurs naturally during unilateral leg movements (walking)As the right leg swings forward during gait the pelvis rotates left

Hip JointConsists of Pelvic boneAcetabulumFemur

Acetabulum

Acetabulum

Femur

Femur

Femur

Structure of the HipA ball and socket joint in which the head of the femur articulates with the concave acetabulumThe hip is more stable than the shoulder Bone structure The number and strength of the muscles and ligaments crossing the joint

Acetabular LabrumAcetabulum is not a complete circle, open inferiorlyThis opening is closed by the transverse ligament

Head LigamentHead of femur attached to inside of acetabulum by ligamentum teres

Capsule

LigamentsIliofemoral ligament or the Y ligament of BigeloTriangular in shapeSupports hip anteriorly, resists extension, internal rotation and some external rotationPubofemoralRuns from the superior pubic ramus and the acetabular rim, to just above lesser trochanterResists abduction with some resistance to external rotation

LigamentsIschiofemoral ligamentFrom the ischium to the posterior neck of the femur is directed upwards and laterallyResists adduction and internal rotationAll three loose during flexion

LigamentsAnterior viewPosterior view

Vascular

Vascular

Lumbar Division

Hip GoniometryFlexion/Extension125-140 (with knees flexed)/0/10-2090 (with knees extended)/0/10-20Abduction/Adduction45/0/20-30Internal Rotation/External Rotation35-45/0/40-50

Hip MovementsHip Flexion

FlexionPsoas majorIliacusAssisted by:PectineusRectus femorisSartoriusTensor fascia lataeHip Movements

Psoas majorIliacus

Pectineus

Rectus femoris

SartoriousTensor fascia lataeIliotibial band

Hip ExtensionHip Movements

ExtensionGluteus Maximus HamstringsBiceps FemorisSemimembranosusSemitendinosusHip Movements

Gluteus maximus

Hip AbductionHip Movements

AbductionGluteus MediusAssisted By: Gulteus MinimusHip Movements

Gluteus medius

Gluteus minimus

Hip AdductionHip Movements

AdductionAdductor MagnusAdductor LongusAdductor BrevisAssisted By:GracilisHip Movements

Gracilis

Internal/Medial RotationGulteus MinimusTensor fascia lataeHip Movements

External/Lateral RotationObturator ExternusObturator InternusQuadratus femorisPiriformisHip Movements

Obturator Externus

Obturator InternusPiriformisQuadratus femoris

Angle of Inclination

Coxa VaraThe angle of inclination is less than 125 degrees This shortens the limbIncreases the effectiveness of the abductorsReduces the load on the femoral head Increases the load on the femoral neck

Coxa ValgaThe angle of inclination is greater than 125 degrees This lengthens the limbReduces the effectiveness of the abductors Increases the load on the femoral head Reduces the load on the femoral neck

Hip Angles14-15 degrees Moves CM more directly over base of support

AnteversionThe angle of the femoral neck in the transverse planeNormally the femoral neck is rotated anteriorly 12 to 14 degrees with respect to the femur

Excessive AnteversionExcessive anteversion beyond 14 degrees causes the head of the femur become uncoveredIn order to keep the head of the femur within the acetabulum a person must internally rotate the femur

RetroversionThe angle of anteversion is reversed so that it moves posteriorlyThis condition causes the person to externally rotate the femur

Loads on the HipDuring swing phase of walking:Compression on hip approx. same as body weight (due to muscle tension)Increases with hard-soled shoesIncreases with gait increases (both support and swing phase)Body weight, impact forces translated upward thru skeleton from feet and muscle tension contribute to compressive load on hip

600 N250 N

Using A Walking Stick

Using a walking stick how it reduces JRF

Using a walking stick how it reduces JRFIn equilibrium sum of moments = 0Without stick M x A = W x BM = (W x B)/A

Using a walking stick how it reduces JRF

Using a walking stick how it reduces JRFWith sitck(M x A)+(Ws x C) = W x BM = [(W x B)-(Ws x C)]/ASo the force required by the abductors M is smaller if a stick is used The bigger C is, the smaller M is therefore a walking stick in the hand furthest away from the hip is most effective

Using a walking stick how it reduces JRFIn equilibrium, the sum of the forces in the Y plane = 0 Without stick JRF sin = M + WWith stickJRF sin + Ws = M +WJRF sin = M + W - Ws

Using a walking stick how it reduces JRFTherefore JRF is less when a walking stick is used. Not only is M force smaller, but the upward force exerted by the stick reduces the JRF further