Hip Anatomy

The hip joint is the largest weight-bearing joint in the human body. It is also referred to as a ball and socket joint and is surrounded by muscles, ligaments and tendons. The thighbone or femur and the pelvis join to form the hip joint.

Any injury or disease of the hip will adversely affect the joint’s range of motion and ability to bear weight.

The Hip Joint is made up of the following:

• Bones and joints
• Ligaments of the joint capsule
• Muscles and tendons
• Nerves and blood vessels that supply the bones and muscles of the hip

Bones and Joints of the Hip

The hip joint is the junction where the hip joins the leg to the trunk of the body. It is comprised of two bones: the thighbone or femur, and the pelvis, which is made up of three bones called ilium, ischium and pubis.

The ball of the hip joint is made by the femoral head while the socket is formed by the acetabulum. The acetabulum is a deep, circular socket formed on the outer edge of the pelvis by the union of three bones: ilium, ischium and pubis. The lower part of the ilium is attached by the pubis while the ischium is considerably behind the pubis. The stability of the hip is provided by the joint capsule or acetabulum and the muscles and ligaments that surround and support the hip joint.

The head of the femur rotates and glides within the acetabulum. A fibrocartilaginous lining called the labrum is attached to the acetabulum and further increases the depth of the socket.

The femur is one of the longest bones in the human body. The upper part of the thighbone consists of the femoral head, femoral neck, and greater and lesser trochanters. The head of the femur joins the pelvis (acetabulum) to form the hip joint. Next to the femoral neck, there are two protrusions known as greater and lesser trochanters which serve as sites of muscle attachment.

Articular cartilage is the thin, tough, flexible and slippery surface lubricated by synovial fluid that covers the weight-bearing bones of the body. It enables smooth movements of the bones and reduces friction.

Ligaments of the Hip Joint

Ligaments are fibrous structures that connect bones to other bones. The hip joint is encircled with ligaments to provide stability to the hip by forming a dense and fibrous structure around the joint capsule. The ligaments adjoining the hip joint include:

• Iliofemoral ligament: This is a Y-shaped ligament that connects the pelvis to the femoral head at the front of the joint. It helps in limiting over-extension of the hip.
• Pubofemoral ligament: This is a triangular shaped ligament that extends between the upper portion of the pubis and the iliofemoral ligament. It attaches the pubis to the femoral head.
• Ischiofemoral ligament: This is a group of strong fibres that arise from the ischium behind the acetabulum and merge with the fibres of the joint capsule.
• Ligamentum teres: This is a small ligament that extends from the tip of the femoral head to the acetabulum. Although it has no role in hip movement, it does have a small artery within that supplies blood to a part of the femoral head.
• Acetabular labrum: The labrum is a fibrous cartilage ring which lines the acetabular socket. It deepens the cavity increasing the stability and strength of the hip joint.

Muscles and Tendons of the Hip Joint

A long tendon called the iliotibial band runs along the femur from the hip to the knee and serves as an attachment site for several hip muscles including the following:

• Gluteals: These are the muscles that form the buttocks. There are three muscles (gluteus minimus, gluteus maximus, and gluteus medius) that attach to the back of the pelvis and insert into the greater trochanter of the femur.
• Adductors: These muscles are in the thighs which help in adduction, the action of pulling the leg back towards the midline.
• Iliopsoas: This muscle is in front of the hip joint and provides flexion. It is a deep muscle that originates from the lower back and pelvis, and extends up to the inside surface of the upper part of the femur.
• Rectus femoris: This is the largest band of muscles located in front of the thigh. They are also called hip flexors.
• Hamstring muscles: These begin at the bottom of the pelvis and run down the back of the thigh. Because they cross the back of the hip joint, they help in extension of the hip by pulling it backwards.

Nerves and Arteries of the Hip Joint

Nerves of the hip transfer signals from the brain to the muscles to aid in hip movement. They also carry the sensory signals such as touch, pain, and temperature back to the brain.

The main nerves in the hip region include the femoral nerve in the front of the femur and the sciatic nerve at the back. The hip is also supplied by a smaller nerve known as the obturator nerve.

In addition to these nerves, there are blood vessels that supply blood to the lower limbs. The femoral artery, one of the largest arteries in the body, arises deep in the pelvis and can be felt in front of the upper thigh.

Hip Movements

All the anatomical parts of the hip work together to enable various movements. Hip movements include flexion, extension, abduction, adduction, circumduction, and hip rotation.

Hip Fracture

The hip joint is a “ball and socket” joint. The “ball” is the head of the femur, or thighbone, and the “socket” is the cup shaped acetabulum. The joint surface is covered by a smooth articular surface that allows pain free movement in the joint.

Hip fracture is a break that occurs near the hip in the upper part of the femur or thighbone. The thighbone has two bony processes on the upper part – the greater and lesser trochanters. There are two main types of hip fractures. The type of fracture you have determines what the treatment will be and how well you are likely to do. 

We know that fractures just below the head of the femur do poorly when fixed and often require further operations and ultimately a hip replacement. The reason for this is that there is poor blood supply to that area and therefore the fractures tend not to grow and the hip bone can die due to poor blood supply. As most of these patients are reasonably frail, it is best not to expose them to multiple procedures and rather to “do the last operation first” and do a hip replacement as treatment.

Fractures lower down the femur tend to heal better as they have better blood supply and they are usually fixed using a nail and screw fixation system.

Osteoarthritis of the Hip

Osteoarthritis, also called degenerative joint disease is the most common form of arthritis. It occurs most often in older people. This disease affects the tissue covering the ends of bones in a joint (cartilage). In a person with osteoarthritis, the cartilage becomes damaged and worn out causing pain, swelling, stiffness and restricted movement in the affected joint.

Although osteoarthritis may affect various joints including hips, knees, hands, and spine, hip joint is most commonly affected. Rarely, the disease may affect the shoulders, wrists and feet.

Rheumatoid Arthritis

Rheumatoid arthritis is an inflammatory disease of the joint; it is caused by your own body’s defense system attacking the joint lining. This is what is known as an Auto-Immune disease. This disease can have a huge variety of presentations, but typically involves many joints and usually starts in the hands.

Rheumatoid arthritis can result in the destruction of the hip joint at a very early age and due to the lower demands placed on the joints, hip replacement can be considered earlier.

Treating Hip Fractures

Some hip fractures are best treated with a hip replacement and that decision is based on the type of fracture. Obviously, this category of hip replacement is not really for you to decide when or whereas it is invariably an emergency.

There are 3 main options of hip surgery in this scenario:

1. Hemi-Arthroplasty:

This is the replacement of the ball part of the femur and is usually only for people with very limited mobility. Its advantages are cost and time in theatre, but they can remain symptomatic and are not suitable for people who are reasonably mobile. I would not consider this option on anyone who still goes out of the house and walks around – even if they need support with a stick or walker.

2. Total Hip Arthroplasty or Total Hip Replacement:

This is the replacement of both the ball and socket of the hip joint. This can be done by either cementing the stem into the femur or making use of the structure of the bone to press-fit the stem in place. This is dependant on the quality of bone of the patient and the decision is usually made based on the X-rays.

3. Resurfacing procedures:

This is a procedure that allows a minimal amount of bone to be removed and placing a metal bearing surface as the new joint surface. The worldwide results of this operation are poor when compared to those of Total Hip Arthroplasty and therefore I do not do this operation at all.

Hip Replacements

There are various reasons that a hip replacement may be necessary. The most common reasons for a hip replacement are hip fractures and Arthritis, including Osteoarthritis and Rheumatoid Arthritis.

Hip Surgery

I use a frontal approach to the hip. This technique is the only hip replacement which does not require any muscles to be cut during the surgery. This generally results in less pain and faster mobility. Furthermore, patients really appreciate the absence of dislocation precautions, which means they can sleep in any position they choose and are not required to use elevated toilet seats. Many patients are cane free and driving within 1 – 3 weeks.

A total hip replacement usually takes between 1 and 2 hours. I always have an experienced assistant to help speed thing up and make the operation go smoothly. We have many different sizes and types of hips available in theatre and usually only make a final decision in theatre as to what hip will be used. The hip is custom fitted for you.

There are 4 main layers of stitches to close the wound and we apply a dry, waterproof dressing. We do not use wound drains.

Your Hospital Stay

Usually after a hip replacement you will stay in hospital between 5 and 7 days. Patients usually need to see a physician before the procedure and are admitted the day before the surgery or the morning of the surgery. The physician checks all the medical systems to make sure that the patient is as strong as possible for the procedure.

After the operation you will go to the High Care Unit as a routine way of monitoring your progress. The physician is the doctor who is in charge in the HCU, but there is input from the anaethetist and the orthopaedic surgeon.

Your pain will be controlled using a local anaesthetic infusion into the groin area and this stays in for 3 days.

After 1 night in the HCU we usually transfer you to the orthopaedic ward – C ward. Here the physiotherapists will see you and begin doing your exercises. Usually you will do exercises in bed until day 2 and then they will start getting you up and walking with the walking frame. You will have elasticized stockings which need to be worn for 6 weeks and calf pumps to reduce the chance of getting a Deep Vein Thrombosis (DVT). You will also receive injections to thin your blood.

Usually you will be walking reasonably pain free by the 4th day after surgery but will still need support. You will be ready for discharge between day 5 and day 7 after the operation. Depending on your personal circumstances and progress you could either go straight home to your family, get nursing help or go to a Step Down facility for further training in walking etc. Please speak to Sr. Val to help you with arrangements for discharge.

Recovering From Hip Surgery

The recovery following a Total Hip Replacement is initially very quick and one rapidly achieves milestones.

Once you have achieved mobility time seems to stop and the progress slows drastically. Your hip will continue improving for up to 18 months after the operation. There are always good and bad days and you may find that the weather becomes very predictable for a while after the operation.

You will need to visit the physiotherapist weekly and when the wound has healed at 2 – 3 weeks you should consider joining the rehab classes run by Marcelle Piennaar and her team.

Due to the type of surgery, you will have weak muscles for a couple of months and tend to limp a bit. This will improve as your muscle strength improves.

Hip Complications

The most common complications are infection and dislocation. I am not too concerned about dislocation and although the physios have a generic rehab for all surgeons, I am not as strict when it comes to sitting, raised toilet seats or bending over. Your body will usually let you know when it is uncomfortable and you will need to listen to it and not get yourself into positions where it is uncomfortable.

Infection is a rare complication and we have a far lower rate at Constantiaberg than what is regarded as an acceptable rate. Infection is an extremely difficult condition to treat. Usually by analyzing the bacteria causing the infection we can tell where the infection came from. It almost always happens at the time of the operation and can be either from your own normal bacteria on your skin or from resistant hospital bacteria.

Every attempt is made to avoid the chance of getting an infection by giving antibiotics and cleaning the skin properly, but it is not a risk that can be completely eliminated.

Medical complications

The most common medical complications following THA are electrolyte disturbances, cardiovascular complications and DVT with or without pulmonary embolus and chest or bladder infections. The physician looking after you will treat all these conditions if they arise.