let’s take stock of … the lower limb !

Hello everybody! Since the number of daily readers (and followers) of my blog is (surprisingly) increasing day after day (Thank you everybody!), I thought it could be useful to take stock of some important posts I wrote about the lower limb. Let’s start from the top -the hip- and go down to the bottom -the ankle-, with 9 posts that got many views and some funny comments ūüôā

Obviously, since my PhD project is about a knee prosthesis, most of the posts (5 out of 9) are about the knee joint.¬†But in general I tried to give an overall view of some interesting topics related to the biomechanics of the lower limb. Enjoy! ūüôā

leg skeletal anatomythe Hip Joint: some hints

hammers, screws and Intramedullary nails

the Knee Bursae: some hints

the Meniscus: some hints

the Patella: some hints

Knee Alignment Conditions

Patellar Reflex

How many limbs do you actually perceive?

the Ankle Joint: some hints

the Hip Joint: some hints

The¬†femur head¬†(Latin:¬†caput femoris)¬†hip joint bonesis the highest part¬†of the thigh bone (femur).¬†It has a roughly semispherical shape, with a short ‚Äúneck of the femur‚ÄĚ angling the head anteriorly, medially and superiorly to fit into the acetabulum of the pelvis bone.

The acetabulum, also called socket, is the cavity in the pelvis which “hosts” the femur head. It is¬†formed by three innominate bones: the ilium, the ischium and the pubis.

The femur head’s surface is smooth and normally coated with¬†cartilage. It¬†is supported by the neck of the femur and¬†gives attachment to one single intracapsular ligament,¬†the “ligament of head of femur” (ligamentum teres, on the top of the femur head in the figure on the left). head of femur and its ligamentIt may be not¬†that important as a ligament (it is only stretched when the hip is dislocated, and may then prevent further displacement) but can often be vitally important as a conduit of a small artery to the head of the femur. This small artery¬†is not present in everyone but can become the only blood supply to the bone in the head of the femur when the neck of the femur is fractured or disrupted by injury in childhood.

The femur head together with the acetabulum form the hip flexion-extensionHip Joint. The hip joint has three degrees of freedom, since it can move in three different planes:

  1. sagittal plane: flexion/extension of the leg.
    With just this movement, approximately 3 to 3¬Ĺ times the body weight acts on the hip joint. An example of this motion is shown by the figure on the right.
  2. hip adduction-abductionfrontal plane: abduction/adduction of the leg. Regardless of the direction, the respective supporting leg is then subject to approximately 3 times the body weight. This kind of motion is represented by the figure on the left.
  3. transverse plane: external/internal femur rotationrotation of the femur with respect to the pelvis bone. This motion, typical when crossing  legs, makes the femur head rotate in several directions. An example is shown by the figure on the right.

The head of the femur is attached to the femur shaft by a thin neck region that is often prone to fracture in the elderly, which is mainly due to the degenerative effects of osteoporosis. If there is a fracture of the neck of the femur, the blood supply through the ligament becomes crucial. In orthopedic surgery, the Total Hip Arthroplasty surgery consists in removing the femur head and the acetabulum and replacing them with a total prosthesis.

Normally, the two involved prosthetical components are:

  1. the Acetabular Cup, a shell that fits the pelvistotal hip prosthesis components bone to replace the acetabulum. It is usually attached to the bone by using friction or cement. Additional fixation can be achieved by means of screws.
  2. the Femoral Component, that is a stem with attached prosthetic femoral neck and head (a ball that fits the Acetabular Cup). Femoral bone is removed and the femur is shaped to accept the femoral stem.

The figure below shows the difference between a healthy hip (on the left) and a prosthetic hip (on the right).

hip before and after

sources: Wikipedia, this website and this other website