IMPINGEMENT

An impingement is a compression of soft tissues through a narrow space, leading to irritation and inflammation. Impingements can lead to tendinitis, tendon tears and bursitis as the structures struggle to fit in the confined space and rub against each other.

The most common type of impingement is found in the shoulder due to its complex structure, however, it can also be found in the hip, ankle, knee and elbow.

Shoulder

Impingement in the shoulder is due to the narrowing of the space between the acromion (bony structure in the front of shoulder) and the humerus (bone of the upper arm), where the rotator cuff tendons pass through. The rotator cuff muscles are responsible for raising your arm above your head, repetitive overhead movements can lead to shoulder impingement as these tendons can swell when irritated or injured, constricting the space, and leading to pain and reduced range of motion. 

You also have a bursa (fluid filled sac) at that location in your shoulder, and if this is irritated and inflamed it can restrict the space and lead to impingement of the shoulder. 

It is important to note that some people may have an 'impingement' in this area but not experience any pain and so it is starting to be called Sub Acromial Pain Syndrome as of recent. 

Hip

Also known as femoroacetabular impingement.  This type of impingement is caused by the head of the femur (thigh bone) pinching in the acetabulum (the hip socket) and it is due to repetitive hip flexion. 

There are 3 types of hip impingement: - 

1. Pincer - An extended piece of bone lays over the edge of your acetabulum/ hip socket, causing the femur to rub against a layer of cartilage which lines the outside of the socket, called the labrum, and leading to degeneration of the joint. 

2. Cam - When the head of the femur (or the ball of the hip's ball and socket joint) is not perfectly round it will not move smoothly. This can lead to a bump forming on the femur head which would grind down the cartilage of the socket, the labrum. 

3. Combined - As implied this would be a combination of both hip impingement types mentioned about.

Hip impingement can lead to osteoarthritis in the hip.

Ankle

Ankle impingement can occur either anteriorly (front of ankle) or posteriorly (back of ankle). It usually develops due to ankle instability, when an individual has weak ankles and 'loose' ligaments and tendons, as this makes them more likely to get trapped/ impinged during movements.

 Anterior - is the most common type of ankle impingement, and it is caused by repetitive ankle sprains. It is seen when ligaments are pinched between the bottom of the tibia (shin bone) and the bones of the foot. Sometimes the healing process can produce too much scar tissue and osteophytes (bony growths) which lead to further ankle impingement. 

Posterior - is also known as ' Dancers heel' and is caused by repetitive compression of the bones at the back of the ankle leading to swollen soft tissue in that area and osteophytes which can further pinch the soft tissues. The soft tissues can thicken over time which would permanently reduce the space between the ankle and the foot and lead to repetitive impingements. 

Knee

Behind and just below the patella (kneecap) there is a fat pad called the Infrapatellar fat pad. Fat pads are fatty soft tissue that act like protective cushioning between bones.  Impingement to this fat pad can be caused by a direct blow to the knee or by repetitive over-extension (straightening on the leg). People who are hyper-mobile may be more prone to this type of impingement.

Elbow

Fully straightening the elbow leads to a compression of soft tissue at the back of the joint. Posterior elbow impingement is caused by repetitive straightening of the elbow, and it can also be coupled with a valgus force (sideways movement from the outer side of the elbow to the inside). Osteocytes can form due to the excesses compression forces at the back of the elbow and that further contribute to the impingement.