• Skip to main content
  • Skip to primary sidebar
  • Skip to footer
  • General Ortho
  • Procedures
  • Spine
  • Upper Limb
  • Lower Limb
  • Pain
  • Trauma
  • Tumors
  • Newsletter/Updates
  • About Us
  • Contact Us

Bone and Spine

Orthopedic health, conditions and treatment

Hip Biomechanics and Its Clinical Uses

By Dr Arun Pal Singh

In this article
    • Few Definitions
    • Forces Acting on the Hip
    • Trendelenburg Sign
    • Factors Affecting Hip Biomechanics

Hip biomechanics are quite complex due to pelvic motion associated with it and range of movements it produces. Biomechanics is the science that studies forces acting on a living body.

Hip is a mobile and stable joint that because of its anatomy and strong attachments of muscles and ligaments.

The neck of femur and its orientation plays an important role in the mobility of the hip. The neck is angulated in relation to the femur in the sagittal and coronal plane.

Neck-shaft angle is about 140 degrees at birth and reduces to 120-135 degrees in adults.

The anteversion is about 40 degrees at birth but reduces to 13-16 degrees in adults.

The orientation of acetabulum is also important for hip stability and transfer of the forces.

It is directed forwards 15-20 degrees and 45 degrees downwards.

Mechanical axis of the lower limb passes between the center of the hip joint and center of the ankle joint.

Anatomical axis line is between the tip of the greater trochanter to the center of the knee joint.

There is about 7 degrees of angle between the two axes.

Few Definitions

Joint reaction force

Force generated within a joint in response to forces acting on the joint
in the hip. The joint reaction force is the result of the need to balance the arms of the body weight and abductor tension that maintains the pelvis at level.

Joint congruence

This refers to how well the two joints surfaces conform to each other. A higher congruence increases the joint contact area.

Instant center of rotation

It is the point about which a joint rotates. It may remain same or may change depending on translation of the joint surfaces [as in knee]

Center of gravity

The center of gravity is the average location of the weight of an object. In humans, it is just anterior to S2.

Forces Acting on the Hip

The hip joint is the first class lever. In a first class lever, the fulcrum is placed between the effort and load.

The fulcrum here is hip and the load is body weight. Abductor tension is the effort.

To maintain a stable hip, the torques that are produced by the body weight are opposed by the pull of the abductor muscles. [see the diagram below]

Abductor force x lever arm A = weight x lever arm

Thus the forces acting across hip joint are

  • Body weight
  • Abductor muscles force
  • Joint reaction force

As we noted before, the joint reaction force is the force that is generated within a joint in response to forces that act on the joint.

In the hip, it is generated to balance the moment arms of the body weight and abductor tension to maintain a level pelvis.

The joint reaction force is measured in terms of body weight.

In two leg stance, the weight of the upper body is equally divided on both hips and there is little need for muscular force.

Each hip supports about one-third of body weight in two leg stance.

During single leg stance, this force is 3 times body weight. The limb on which weight is supported would have to bear the upper body weight and contralateral, non supporting, limb.

In single leg stance, the effective centre of gravity shifts to the non-supportive leg and   a downward force attempts to tilt pelvis on unsupported side.

the abductors on the hip which supports the body, must exert a downward counter balancing force with right hip joint acting as a fulcrum.

The use of the cane may relieve upto 60% of the load on hip in stance phase because cane transmits weight to the ground and results inlesser force required.

During walking it is 5 times in and during running it is 10 times.

Roughly, the joint reaction force would be equal to the sum of body weight and abductor force.

Weight on each femoral head is half of the body weight above hips.

joint reaction forces during supine straight leg raising is  more than 3 times body weight.

Similarly, getting on & off bed pan puts a load equal to four times body weight.

The factors that affect the joint reaction force are

  • Body weight and its moment arm
  • Abductor force and its moment arm

hip biomechanics

The body weight can be taken as the load applied to a lever arm extending from the body’s center of gravity to the center of the femoral head.

The abductor mechanism acts on the lever arm extending from the lateral aspect of the greater trochanter to the center of the femoral head.

This force by abductors must be equal to the load applied by weight to hold the pelvis level when in a one-legged stance and a greater moment to tilt the pelvis to the same side when walking.

The ratio of the length of the lever arm of the body weight to that of the abductor musculature is about 2.5: 1. Therefore the force needed by abductor muscles must approximate 2.5 times the body weight to become equal to the force applied by body weight.

The estimated load on the femoral head in the stance phase of gait is equal to the sum of the forces created by the abductors and the body weight and is at least three times the body weight.

Changes During Gait

During normal gait, on heel-strike, the hip moves into 30 degrees of flexion and at toe-off [when the foot is finally off the ground] about 10° of extension. The range of abduction to adduction is about 11°, and for internal-external rotation, the range is about 8°.

During different phases of the gait cycle, different forces act on the femoral head. Approximately two-thirds of the hip force is produced by the abductors.

The directions of the resultant force on the joint are important to the function of total hips.

It is useful to consider the forces relative to axes based on the long axis of the femur.

In the coronal plane, the forces acting make an angle of 15° to 27° to the long axis of the femur during the stance phase of gait which results in axial compression, varus, and mediolateral forces. In the sagittal plane, anteroposterior forces on the femoral head, resulting in torsion.

Trendelenburg Sign

This is done to check abductor function.

The patient stands on a single limb. As described before, the body weight center of gravity shifts to the lifted limb and lowers the pelvis.

The abductor muscles on the side the patient is standing on exert the force to lift the pelvis up on the contralateral side.

A failure to do so results in dropping of the pelvis on single leg stance and indicates abductor malfunction.

It is called a positive Trendelenburg sign.

Factors Affecting Hip Biomechanics

Shortening of abductor lever arm

Shortening of Abductor lever arm would result in increase in abductor workout.

The abductor lever arm may be shortened in

  • Arthritis
  • Supratrochanteric shortening
  • Femoral anteversion
  • External rotational deformities
  • Developmental dysplasia of the hip.

If the muscles are not able to generate the rquisite force to counterbalance body weight, it would result in a lurch during the gait or pelvic tilt.

Weight Gain

We have seen that forces acting on the hip are measured as multiple of body weight. Therefore, the increase in weight leads to increase in forces acting on the joint.

Femoral Offset
Image Credit: http://www.traumazamora.org/articulos/offset/offset.html

Biomechnics in Hip Prosthesis Design

Hip biomechanics are used in designing of the hip prostheses. The idea of the design is to decrease the the joint force by

  • Centralization of femoral head by deepening of Acetabulum – decreases body wt lever arm
  • Increase in neck length and Lateral reattachment of trochanter – lengthens abductor lever arm

This aims at decreasing  abductor force, joint reaction force, & so the wear of the implants.

Femoral offset is the distance between the center of the head to the center of axis of the stem

An inadequate medial offset shortens the moment arm  leading to increased abductor work. It could lead to limp and increase bony impingement

If the offset is increased, there is increased stress on the stem and leads to implant loosening as an  increase in offset would reduce the force but  causes an increase in the bending moment on the stem.

In the saggital plane, the forces act to bend the stem posteriorly and become more pronounced when the hip is flexed. It has been found that the joint reaction force was lower when the hip center was placed in the anatomical location compared with a superior and lateral or posterior position.

Spread the Knowledge
  • 32
    Shares
  •  
    32
    Shares
  •  
  • 32
  •  
  •  
  •  

Filed Under: General Ortho

About Dr Arun Pal Singh

Arun Pal Singh is an orthopedic and trauma surgeon, founder and chief editor of this website. He works in Kanwar Bone and Spine Clinic, Dasuya, Hoshiarpur, Punjab.

This website is an effort to educate and support people and medical personnel on orthopedic issues and musculoskeletal health.

You can follow him on Facebook, Linkedin and Twitter

Reader Interactions

Comments

  1. Chandrika says

    March 10, 2016 at 6:33 am

    I am PT in hx AZ USA. I really like the way you are explaining the hip, thr and mechanics. Thx.

  2. Dr Arun Pal Singh says

    March 12, 2016 at 4:58 pm

    Thanks Chandrika. I am glad you liked it.

  3. costa says

    April 7, 2016 at 1:05 am

    Thats really good. i enjoyed it. PT from ZIM

  4. Ankit Saxena says

    May 1, 2016 at 7:12 pm

    Thank you Sir, Your explanation is wonderful and beneficial. I am a research scholar in IIT Roorkee and my area of interest is bio mechanics. This article would help me a lot.

  5. Dr Arun Pal Singh says

    May 8, 2016 at 8:16 pm

    Hi Ankit,
    I am glad you found the article useful.

  6. sujika says

    February 24, 2017 at 7:03 pm

    I am a orthopedic tranee. This is very helpful. hank you sir sujika from sri lanka

  7. Dr Arun Pal Singh says

    February 26, 2017 at 3:56 pm

    Sujika,

    I am glad that it was of help. All the best.

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Primary Sidebar

SAUVE-KAPANDJI procedure on distal ulna

Sauve Kapandji Procedure

Sauve Kapandji procedure is a procedure which  involves removal of about 10 mm of ulna proximal to distal radio ulnar joint and fixing the distal fragment of ulna to radius by means of screw. Sauve Kapandji procedure aims at creating a new joint at the level where ulna is cut and serves two purposes. First […]

Rolando Fracture

Rolando Fracture – Presentation and Treatment

Rolando fracture is a three-part intraarticular fracture-dislocation of the base of the thumb. This is an unstable injury that requires surgical reduction and fixation. It is named after Silvio Rolando, an Italian surgeon who described it first. Relevant Anatomy, Mechanism of Injury and Pathophysiology The carpometacarpal joint is between the base of thumb and trapezium […]

What is Melorheostosis?

Melorheostosis (also known as Leri disease) is a rare dysplasia manifesting as regions of sclerosing bone with a characteristic dripping wax appearance or flowing candle wax appearance The disease, described by Leri and Joanny in 1922, is a rare, non-hereditary lesion. Patients with melorheostosis may have associated Vascular malformations Neurofibromatosis Hemangioma Arterial aneurysms Linear scleroderma […]

anatomical snuffbox image and surface anatomy

Anatomical Snuffbox Anatomy and Significance

The anatomical snuffbox is a triangular deepening on the dorsoradial aspect of the hand at the level of the carpal bones. It is visible with ulnar deviation of the wrist and extension and abduction of the thumb. The name snuffbox is derived because this depression was used as a means of placement for the inhalation […]

mosaicplasty

Mosaicplasty or Osteochondral Graft Transfer System

Mosaicplasty or autologous osteochondral autograft/allograft transfer system or OATS is a single stage resurfacing procedure for focal defects of the femoral condyles, trochlea, patella, proximal and distal tibia, and talus. It may be used for both focal chondral defects as well as cases of osteochondritis dissecans. Indications of Mosaicplasty Ideal lesions are small, focal, full-thickness […]

tarsal bones

Tarsal Bones Anatomy

There are seven tarsal bones. The proximal row is formed by the talus above, and the calcaneus below. The distal row contains, from medial to lateral side, medial cuneiform, the intermediate cuneiform, the lateral cuneiform and the cuboid. Navicular is interposed between the talus and the three cuneiform bones. In other words, it is interposed […]

Severe scoliosis

Neuromuscular Scoliosis Causes and Treatment

Neuromuscular scoliosis is a coronal and sagittal plane deformity of the spine in patients with abnormalities of the nervous system or muscles. myoneural pathways of the body. The progression more severe in case of neuromuscular scoliosis and continues into adulthood. The long-term effects of the spinal deformity in patients with neuromuscular conditions can be disabling. […]

Browse Articles

Footer

Pages

  • About
    • Policies
    • Contact Us

Featured Article

Congenital Kyphosis

Congenital kyphosis is the presence of ky[hotic deformity or hump in the spine due to congenital vertebral anomalies.Kyphosis is exaggerated forward … [Read More...] about Congenital Kyphosis

Search Articles

© Copyright: BoneAndSpine.com