easy way to learn "Hip joint forces and muscle function in stance".

1. HIP JOINT FORCES AND MUSCLE
FUNCTION IN STANCE

2. HIP JOINT FORCES AND MUSCLE
FUNCTION IN STANCE
IN THIS TOPIC WE WILL LEARN ABOUT HOW THE HIP
JOINT HANDLES THE FORCES APPLIED ON IT BY THE
HATLL (head , arms , trunk , lower limbs) IN THE FOLLOWING
CONDITIONS:-
1) BILATERAL STANCE
2) UNILATERAL STANCE
i. COMPENSATORY LATERAL LEAN OF THE TRUNK
ii. USE OF THE CANE IPSILATERALLY
iii. USE OF THE CANE CONTRALATERALLY.

3. BASIC THINGS TO REMEMBER DURING
THIS TOPIC
1. TORQUE.
2. MOMENT ARM.
3. CENTRE OF GRAVITY.
4. LINE OF GRAVITY.
5. HIP ADDUCTOR MUSCLES.
6. HIP ABDUCTOR MUSCLES.

4. BILATERAL STANCE
• BOTH THE HIPS ARE IN NEUTRAL OR SLIGHT
HYPEREXTENSION , AND WEIGHT IS EVENLY
DISTRIBUTED BETWEEN BOTH THE LEGS.
• THE POSTERIOR LOCATION OF THE LINE OF
GRAVITY (LoG) CREATES AN EXTENSION MOMENT OF
FORCE AROUND THE HIP THAT TILT THE PELVIS
POSTERIORLY ON THE FEMORAL HEADS.
• IN THE FRONTAL PLANE , THE SUPERINCUMBENT
BODY WEIGHT IS TRANSMITTED THROUGH THE
SACROILIAC JOINTS AND PELVIS TO THE RIGHT AND
LEFT FEMORAL HEADS EVENLY ; THAT IS , WR = WL.

5. • JOINT AXIS OF EACH HIP JOINT LIES AT AN EQUAL DISTANCE
FROM THE LINE OF GRAVITY OF HAT ; THAT IS , THE
GRAVITATIONAL MOMENT ARM FOR THE RIGHT HIP (DR) AND
LEFT HIP (DL) ARE EQUAL.
• MAGNITUDE OF GRAVITATIONAL TORQUE ON EACH HIP MUST
BE IDENTICAL ACCORDING TO THE UPPER HYPOTHESIS :-
• WR X DR = WL X DL.
• THE GRAVITATIONAL TORQUES ON THE RIGHT AND LEFT HIP
OCCURS IN OPPOSITE DIRECTIONS KNOWN AS RIGHT
ADDUCTION MOMENT AND LEFT ADDUCTION MOMENT.
• THESE TWO OPPOSING 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.
• ASSUMING THAT MUSCULAR FORCES ARE NOT REQUIRED TO
MAINTAIN EITHER SAGITTAL OR FRONTAL PLANE STABILITY AT
THE HIP JOINT IN BILATERAL STANCE, THE COMPRESSION
ACROSS EACH HIP SHOULD SIMPLY BE THE HALF OF
SUPERINCUMBENT BODY WEIGHT.

6. • HOWEVER , BERGMANN AND COLLEAGUES SHOWED IN SEVERAL SUBJECTS WITH AN
INSTRUMENTED PRESSURE SENSITIVE HIP PROSTHESES THAT THE JOINT COMPRESSION
ACROSS EACH HIP IN BILATERAL STANCE WAS 80% TO 100% OF BODY WEIGHT.
• THIS MORE JOINT COMPRESSION MIGHT BE DUE TO :-
i. ACTIVITY OF ILIOPSOAS MUSCLE,
ii. CAPSULOLIGAMENTOUS TENSION.
• IN BILATERAL STANCE WHEN BOTH LOWER LIMBS BEAR ATLEAT SOME OF THE
SUPERIMPOSED WEIGHT , THE CONTRALATERAL ADDUCTORS AND ABDUCTORS MAY
ACT SYNERGISTICALLY TO CONTROL THE FRONTAL PLANE MOTION OF THE PELVIS
WHICH IS NOT SEEN IN UNILATERAL STANCE.

7. UNILATERAL STANCE
• A LEG IS LIFTED UP FROM THE GROUND AND THE FULL
SUPERIMPOSED BODY WEIGHT (HAT) ALONG WITH THE
WEIGHT OF LIFTED LEG IS SUPPORTED BY THE ANOTHER
LEG.
• TOTAL HIP COMPRESSION HAPPENS TO BE :-
[ 2/3 × W ] + [ 1/6 × W ] = 5/6 W
• THE FORCE OF GRAVITY ACTING ON HAT AND THE NON-
WEIGHTBEARING LOWER LIMB (HATLL) WILL CREATE AN
ADDUCTION TORQUE AROUND THE WEIGHT BEARING HIP
JOINT.
• THE ABDUCTION COUNTERTORQUE WILL BE SUPPLIED BY
THE HIP ABDUCTION MUSCULATURE .

8. • THE HYPOTHETICAL FIGURES USED IN THE
EXAMPLE OVERSIMPLIFY AND UNDERESTIMATE
THE FORCE INVOLVED IN THE HIP JOINT AS
ALREADY NOTED IN BILATERAL STANCE.
• THE TOTAL HIP JOINT COMPRESSION IS FOUND
TO BE 2 TO 3 TIMES MORE THEN THE BODY
WEIGHT IN THE UNILATERAL STANCE.
• TO REDUCE THE JOINT COMPRESSIONS IN THE
UNILATERAL STANCE SEVERAL STRATEGIES ARE
APPLIED LIKE :-
i. COMPENSATORY LEAN OF TRUNK .
ii. USE OF CANE IPSILATERALLY.
iii. USE OF CANE CONTRALATERALLY.

9. COMPENSATORY LATERAL LEAN OF
TRUNK
• THE COMPENSATORY LATERAL LEAN OF THE TRUNK
TOWARDS THE PAINFUL STANCE LIMB WILL DECREASE THE
GRAVITATIONAL MOMENT ARM , THEREFORE DECREASES
THE GRAVITATIONAL TORQUE.
• THIS REDUCTION IN THE GRAVITATIONAL ADDUCTION
TORQUE WILL ALSO REDUCE THE NEED OF ABDUCTOR
COUNTERTORQUE.
• THE LATERAL LEAN MIGHT LEAD TO THE WEAR AND TEAR
IN THE LUMBAR SPINE AND CAN ALSO LEAD TO THE
PATHOLOGICAL GAITS.

10. USE OF CANE IPSILATERALLY
• CANE IS HELD IN THE HAND ON THE SIDE OF PAIN OR
WEAKNESS .
• REALISTICALLY AROUND 15% OF BODY WEIGHT CAN BE
TRANSFERRED THROUGH CANE AND THAT DOESN’T CREATE
THE ADDUCTION TORQUE.
• WHEN CANE IS USED IPSILATERALLY , SOME RELIEF CAN BE
SEEN AS COMPARED TO THE TOTAL HIP COMPRESSION
EXPERIENCED IN ORDINARY UNILATERAL STANCE.
• TOTAL HIP COMPRESSION WITH CANE = 1691.35N
• TOTAL HIP COMPRESSION IN ORDINARY UNILATERAL
STANCE = 2062.5 N.

11. USE OF CANE CONTRALATERALLY
• CANE IS HELD IN THE HAND OPPOSITE TO THE SIDE OF PAIN OR
WEAKNESS.
• THE FORCES ARE SAME AS OF THE CANE USED IPSILATERALLY BUT
THE CANE NOW IS IN POSITION TO ASSIST THE ABDUCTOR MUSCLES
IN PROVIDING THE COUNTERTORQUE TO THE TORQUE OF GRAVITY.
• THE DOWNWARD FORCE ON THE CANE ACTS THROUGH THE FULL
DISTANCE BETWEEN THE HAND AND THE WEIGHT BEARING
(IMPAIRED) HIP JOINT.
• THE LATISSIMUS DORSI ON THE SIDE OF CANE COULD ACCOUNT FOR
THE DIFFERENCE IN COMPRESSIVE FORCES BETWEEN CLASSIC
CALCULATIONS WITH THE CANE USED ON THE CONTRALATERAL
SIDE AND ACTUAL FORCE MEASURED IN VIVO.

14. THANK
YOU