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The Hip

Understanding the Hip

The hip is the body’s second largest weight-bearing joint (after the knee). The hip joint is a ball-and-socket type of joint that is encapsulated synovial fluid. The ball is the femoral head, and the socket is the acetabulum. The hip joint is the articulates the pelvis and connects the skeleton (iliac crescent) to the lower body as pictured on the right. The hip joint is normally very sturdy because of the fit between the femoral head and acetabulum as well as strong ligaments and muscles at the joint.

 

Muscles

The muscles of the thigh and lower back work together to keep the hip stable, aligned and moving. The hip also shares similar muscle groups with the knee, these muscles work in conjunction for us perform ‘bulk’ movements in our lower body.

The quadriceps are a group of 4 muscles that are located at the front of the femur. All four attaches to the top of the tibia.

Hamstrings are the three muscles at the back of the thigh. All three attaches to the lowest part of the pelvis leading to the buttocks.

The buttock muscles, formerly known as gluteal muscles, these are the three muscles attached to back of the pelvis and insert into the femur.

The muscles that help you perform flexor movements are called the Iliopsoas These muscles attach the lower part of the spine and pelvis, then cross the joint and insert into the femur.

Groin muscles including the adductors are something many of us are familiar with, these muscles run down in the inside of your thighs.

The iliopsoas as previously mentioned is an important muscle to keep an eye out for. Throughout the day it is often called into play with forward motions like walking, running and lifting your legs. It also picks up the slack when weaker muscles can’t perform their movements effectively, which can overwork this muscle.

If your glutes are weak, the side-to-side movements can irritate the hip flexor. The glutes are a strong muscle, the hip flexor is not. It can easily be overworked if it is performing duties it is not supposed to.

Tendons

Tendons are elastic tissues that connect muscles to bones. The tendons main role is to stabilize the hip joint. There is a very prominent bump on the femur known as the greater trochanter, it is easy to feel on the outside of your thigh. This is particularly important since it is where the tendons of several muscles attach. The lesser trochanter serves as the attachment for the iliopsoas and iliacus muscle tendons.

Notice the colour of the tendons, they are white. Whereas muscles are red. The reason is due to blood flow, muscles are strong and repair quickly due to good blood flow. If tendons take damage, they take a very long time to repair. Since muscles are strong, they can pull on the weak tendons and cause them to flair up. This is very common, and it is known as tendonitis. Especially in the hip joint, this can create a significantly sharp pain in a single location since many of the tendons attach in a similar location.

Ligaments

Ligaments are designed to connect one bone to another. They are soft tissue structures that are strong, but not particularly flexible. Once stretched, they tend to stay stretched, if they stretch too far, they can snap.

Ligaments connect the ball to the socket and usually provide tremendous stability to the joint. There are 3 main ligaments.

1. Iliofemoral ligament
2. Pubofemoral ligament
3. Ischiofemoral ligament

These ligaments completely encompass the hip joint and form the joint capsule. The iliofemoral ligament is the strongest ligament in the body.

Cartilage

A smooth cushion of shiny white articular cartilage covers the femoral head and the acetabulum. These bones are naturally kept slippery, so the bones move against each other easily. Cartilage also acts a shock absorber however, cartilage wears out and cannot repair itself.

Majority of the force from our daily activities such as walking and running is placed at the back of the hip joint socket. Naturally this is the thickest point of cartilage in the hip socket. When standing, the body’s center of gravity passes through the center of this point. If you have sustained injury, this may lead to uneven weight distribution, therefore uneven wear and tear.

Joint Capsule (lubrication membrane)

The capsule is a thick, fibrous structure that wraps around the hip socket. Inside the capsule is the synovial membrane which is lined by the synovium, a soft tissue that secretes synovial fluid and provides lubrication for the hip. The synovial fluid is both viscous and sticky lubricant. Synovial fluid is what allows us to flex our joints under great pressure without wear.

Joint Sacs

Joint sacs, known as bursae are fluid filled sacs which are lined with a synovial membrane. The bursae sacks are often found near joints, they are filled with synovial fluid and their function is to lessen the friction between soft and hard tissue interaction. There are as many as 20 bursae around the hip.

The greater trochanteric bursa is located between the greater trochanter and the muscles and tendons that cross over the greater trochanter. This bursa can be prone to irritation, it is more common for people who have tight iliotibial bands.

There are two other common bursae sacks that can get inflamed, these are the iliopsoas bursa, located under the iliopsoas muscle and easily noticed is the bursae sack you sit on, this is located over the ischial tuberosity.

Pathological Conditions of the Hip

Hip osteoarthritis:

Osteoarthritis is the most common form of arthritis, and often affects the hips. Caused by aging and wear and tear of cartilage, osteoarthritis symptoms may include hip pain, stiffness, and swelling. Osteoarthritis is not simple to understand, there are many links with the wear and tear of cartilage that also affects every other part of your joint. We discuss this in our treatment information pack.

Avascular necrosis:

This is a condition that occurs due to loss of blood to the bone. The interruption to the blood supply causes bone to slowly die. In many cases AVN is not easy to diagnose until a fair amount of damage has already occurred.

Septic arthritis:

An infection caused by bacteria, a virus, or fungus inside the hip can cause inflammation, pain, swelling, and difficulty moving the hip. Although uncommon, septic arthritis is a serious condition that usually gets worse quickly without treatment.

Acetabular dysplasia:

Also known as hip dysplasia, is a disorder that occurs when the acetabulum (hip socket) is too shallow and it doesnot provide sufficient coverage of the femoral head (ball). This leads to consistent instability of the hip joint.

Gout & pseudogout:

A form of arthritis caused by buildup of uric acid crystals in a joint. Though this is more common in the knee and feet, it can rarely occur in the hip joint.

Issues that often occur with Osteoarthritis

Tendonitis:

Inflammation of the tendons that are connecting muscle to bone. As previously discussed tendonitis is very common. It can occur due to simple overuse, overstrain or even underuse. Tendons can become weak very quickly and they take a very long time to repair due to lack of blood flow.

Cartilage tear:

The labrum of your hip is the most common tear to occur. This is the ring of cartilage that follows the outside rim of the socket of your hip joint. The labrum also acts like a rubber seal or gasket to help hold the ball at the top of your thighbone securely. Some of the symptoms noticed may be locking or catching sensation in your hip joint.

Ligament strain or tear:

The ligaments of your hip can strain when one of the muscles supporting the hip joint is stretched beyond its limit. In severe cases this can lead to a tear, not just a strain.  If the ligaments are degenerate due to low activity, this will be more likely to tear.

Bursitis:

When the bursa sacks become inflamed, this will lead to pain, swelling, and warmth in any of the bursae of the hip. Bursitis often occurs from overuse or injury. It is very common since there are over 20 bursa sacks around the hip joint.

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