What Are the Causes of Hip Impingement?

If you’ve been told you have hip impingement syndrome, one of the first questions is usually “why me?” It’s a fair question. Hip impingement, or femoroacetabular impingement (FAI), isn’t caused by a single injury or bad habit. It comes down to the shape of the hip joint itself, and how that shape develops over childhood and adolescence. Understanding the cause matters, because it explains why the condition is so common in active young people, and why it tends to run in families.

This guide explains what actually causes hip impingement, the different types, and the main risk factors to be aware of.

It Starts With the Shape of the Joint

The hip is a ball-and-socket joint: the femoral head (the “ball” at the top of the thigh bone) sits inside the acetabulum (the “socket” in the pelvis). In a healthy hip, the two surfaces glide against each other smoothly through a full range of movement. In hip impingement, subtle differences in the shape of the ball, the socket, or both mean the bones make contact too early, pinching the soft tissue at the rim of the joint. Over time, this repeated contact irritates the labrum (the cartilage rim of the socket) and the joint surfaces themselves.

There are two main structural patterns behind this, and most patients have some degree of both.

Cam Impingement

In cam impingement, the femoral head isn’t perfectly round. Instead, there’s extra bone at the junction where the head meets the neck of the femur, giving it a slightly bullet-shaped or aspherical appearance. When the hip bends and rotates, this irregular shape doesn’t rotate cleanly inside the socket, and the extra bone catches against the labrum and cartilage. Cam impingement is more common in men, particularly those who were highly active in sport during their teenage years.

Pincer Impingement

In pincer impingement, the problem sits on the socket side. The acetabulum covers more of the femoral head than it should, either across the whole socket or focally at one part of the rim. This means the rim of the socket meets the femoral neck earlier than normal during hip movement, again pinching the labrum. Pincer impingement is more common in women.

Combined Impingement

Many patients have a mix of both cam and pincer features, which is generally described as combined or mixed impingement. This is actually the most frequently seen pattern in clinic.

Why Does the Bone Develop This Way?

This is where it gets interesting, because hip impingement isn’t something people are typically born with fully formed. In most cases, the bony changes develop during childhood and adolescence, while the growth plates around the hip are still open and the bone is still maturing.

Growth Plate Changes During Adolescence

The growth plate at the top of the femur (the proximal femoral physis) stays open until around age 13 to 15 in girls and 15 to 17 in boys. During this window, the bone is more responsive, and also more vulnerable, to mechanical stress. Research suggests that repetitive loading and shearing forces on the growth plate during this period, particularly from high-intensity training, can influence how the femoral head and neck develop, contributing to the cam-type bone changes seen later in life.

This is consistent with what’s often seen in clinic: many adult patients with cam impingement describe having played competitive sport intensively from a young age.

Sport and Activity Levels

Certain sports appear to carry a higher risk, particularly those involving repetitive hip flexion, pivoting, and high-impact loading during the teenage years, such as football, ice hockey, basketball, and dance. Studies have found a dose-response relationship: the more frequently someone trained during their growth years, the higher the likelihood of developing cam-type changes later on. This doesn’t mean sport should be avoided. It simply helps explain why so many patients presenting with FAI in their 20s, 30s, and 40s have a background of competitive sport in adolescence.

Genetic and Family Factors

There also appears to be a familial pattern to hip impingement. Studies looking at siblings of patients with FAI have found a significantly higher rate of the same cam and pincer bone changes compared with the general population, suggesting an inherited tendency toward the shape of the hip joint, even though no single gene has been identified as responsible. If a close family member has been diagnosed with hip impingement, it’s worth mentioning this when you’re assessed.

Previous Hip Injury

Less commonly, a previous hip injury, such as a fracture around the growth plate or significant trauma in childhood, can alter the alignment or shape of the joint and contribute to impingement developing later.

Who Is Most at Risk?

Putting these factors together, the people most likely to develop hip impingement tend to be:

• Younger, active adults, particularly those under 50
• People who played competitive or high-intensity sport regularly during adolescence
• Those with a close family member diagnosed with hip impingement or early hip arthritis
• People with a previous hip injury or abnormal hip development in childhood

It’s worth stressing that having one or more of these risk factors doesn’t mean impingement is inevitable, and plenty of people with cam or pincer-shaped hips on imaging never develop symptoms at all. What matters clinically is whether the shape of the joint is actually causing pain, stiffness, or damage, not the shape alone.

Why Understanding the Cause Matters

Knowing what’s driving your hip impingement helps shape the right treatment plan. Someone with mild cam morphology and early symptoms may do well with activity modification and physiotherapy focused on hip control and mechanics. Someone with more significant bony changes and labral damage may need surgical reshaping of the joint via hip arthroscopy to address the underlying structural cause, not just the symptoms. An accurate diagnosis, built on a proper history, examination, and imaging, is the starting point for working out which category you fall into.

Speak to a Specialist

If you have hip or groin pain and want to understand what’s behind it, the cause matters just as much as the symptoms. Mr Mark Webb is a fellowship-trained consultant orthopaedic surgeon specialising in knee and hip surgery, including hip arthroscopy for femoroacetabular impingement, seeing patients at clinics in London and Surrey. Get in touch to arrange a consultation.