Here I have tried to explain the basic hip joint anatomy for runners. I personally think that this is enough information for most amateur runners, to give you a basic understanding of the joint and its structures.
Hip Joint Anatomy: The Bones
The hip joint is a ball and socket joint formed by the head of the Femur (thigh bone) which is the ball part and the socket – known as the Acetabulum – on the lateral, lower pelvis. Ball and socket joints typically allow a good range of motion in all directions, but can sometimes sacrifice stability for this mobility. Think Shoulder dislocations. But luckily the hip joint is far more stable due to a deeper socket and strong supporting muscles and ligaments. Hip dislocations, although possible, are pretty rare!
Fractures of the hip joint do occasionally occur but generally in the older population as a result of falls. Stress fractures of the Femoral neck do occasionally occur in runners, as do stress fractures of the main shaft of the Femur, lower down the thigh.
Hip Joint Anatomy: The Joint
As with most other joints, the ends of the bones are covered in a layer of articular cartilage which helps with smooth movement and shock absorption.
Surrounding the edge of the socket of the hip is a ring of cartilage known as the labrum. There is also a labrum in the shoulder joint. The function of this ring is to help with stability.
Also surrounding the joint, but in this case the entire joint including the femoral head and acetabulum is the joint capsule. Every synovial (freely moving) joint in the body has a capsule, which serves to stabilise and lubricate the joint. This capsule is made stronger by three ligaments which wrap around the joint and are often seen as an extension, or thickening of the capsule. These ligaments are the:
- Iliofemoral ligament
- Pubofemoral ligament
- Ischiofemoral ligament
They are all named due to their attachment points – for example, the iliofemoral ligament passes from the Ilium to the Femur. This is a Y shaped ligament which is thought to be the strongest ligament in the body.
Most ‘hip injuries’ in runners aren’t actually injuries of the hip joint itself. In fact, hip joint injuries are not overly common in any sport. Things such as labral tears do occur occasionally, and osteoarthritis is always something to consider in older athletes, but for most runners these are never a problem.
Hip Joint Anatomy: The Muscles
Instead, injuries around the hip area tend to be muscular or tendinous in nature. Even the ligaments are rarely injured due to being strong, thick and very close to the joint – more part of the capsule than separate ligaments.
There are lots of muscles in the vicinity of the hip joint which can be grouped together as follows:
- The hip flexors – which raise the leg in front – including Iliopsoas, Rectus Femoris and Sartorius. These muscles are found at the front of the hip joint, passing from the pelvis down on to the Femur, or even the Tibia below the knee.
- The adductors – also known as the groin muscles which move the leg inwards and across the body – including three ‘adductor’ muscles, Pectineus and Gracilis. The adductors attach to the inner pelvis and either to the inner Femur, or the Tibia just below the inner knee.
- The glutes – or Gluteals – basically, the bum muscles. These perform movements such as abduction (moving the leg out to the side, away from the body); extension (moving the leg backwards) and both medial and lateral rotation. I tend to group the glutes into one big group rather than trying to separate them as many of the muscles perform two or even three movements so it gets pretty complicated!
They all attach superiorly to the iliac crest and / or sacrum and pass laterally and downwards, across the buttock to the two trochanters (bony lumps) at the top of the Femur.
Injuries to the muscles and tendons of the hip joint are the most frequent type of injury in runners due to the massive demands on these muscles, not only to move the joint forwards, but also to stabilise the pelvis and control frontal plane (sideways) and rotational forces.
Common hip muscle injuries in runners include Piriformis Syndrome; Myofascial pain; groin strains and tendinopathies to name just a few.
Hip Joint Anatomy: The Bursae
A Bursa is a sack of fluid which reduces friction between tendons or other soft tissues and underlying bone. There are several bursae in the hip region, but by far the most famous in runners is the Greater Trochanteric Bursa. This bursa sits on the outside of the hip joint, between the Greater Trochanter of the Femur and the gluteal tendons which attach to it. The next most common, although a long way behind trochanteric bursitis are Iliopectineal bursitis (at the front of the hip, between the Ilium and the Pectineus) and Ischial bursitis, which cushions the sitting bones at the back of the pelvis.