Why is hip mobility so important? Is there a gold standard for hip mobility? After an osteotomy, why is there a narrow relationship with the mobility of the hip joint?
The hip joint, commonly known as the hip shaft, is composed of the acetabulum and the femoral head. The hip joint has the largest “head” and the deepest “socket” in the human body, commonly known as “a head” and “a socket”. It is composed of the femoral head and the acetabulum, which is both strong and flexible, and is the most typical and perfect mortar and pestle joint. On the surface of this “head” and this “fossa”, i.e., the femoral head and the acetabulum, there is a layer of smooth articular cartilage. At the edge of this “head” and “socket”, a strong capsule seals the entire hip joint. Under normal conditions, this “head” and this “socket” can rotate freely in six directions with the restriction of the joint capsule and the driving of the surrounding muscles.
The gold standard of hip joint movement is determined by the degree of free rotation in these six directions. Therefore, we can also say that these are the 6 golden directions of hip mobility: flexion, extension, internal rotation, external rotation, internal retraction and abduction. These 6 golden directions are interlinked and mutually constrained, and one cannot be missing without the other, and the free rotation in all 6 directions must reach the golden standard. Only when the mobility of our hip joint is considered qualified.
Before the osteotomy, the mobility of our hip joint was mostly greater than normal people. Why is this?
This is because our acetabulum does not wrap around the head of the femur properly, which means that our cap cannot be fastened and our “head” cannot be fastened, so our hip joint is flabby and dinged up.
We do osteotomy for patients, which is to correct the hat that was originally worn crooked in the acetabulum through osteotomy.
After osteotomy, there are 4 major factors that can affect the mobility of our hip joint.
One factor: after osteotomy, the position of the acetabulum is corrected, and there are new bones wrapped around the femoral head where there was no bone wrapped, and these new bones are likely to restrict the movement of the femoral head.
Factor two: the joint is in the post-operative restricted activity stage for 6-8 weeks after osteotomy, and cannot move as normal, the muscles around the joint will become shorter and harder, not as elastic as before, and the muscles cannot be stretched well, so the movement of the joint is restricted.
Factor No. 3: After osteotomy, scar will be formed in the deep incision tissues, such as muscles and joint capsule, and scar tissues are not elastic and cannot be stretched easily, which will also restrict the movement of the joint.
Factor No. 4: Osteotomy is a rescue for the hip joint, but this rescue cannot be guaranteed for life. After a decade or two of osteotomy, as the joint wears down, the osteoarthritis will get worse and the joint mobility will be limited as a result.
So, what is limited joint mobility?
Restricted joint motion is when the range of motion of the hip joint does not reach the normal number of degrees in six directions.
Strictly speaking, as long as the range of motion in one direction is not normal, it is considered to be “limited joint motion”.
Therefore, when we say the “gold standard” of joint mobility, we are repeatedly emphasizing that we should do our best to pursue the maximum freedom and health of any joint in the human body, including the hip joint.
So how do you know the mobility of your joints in all directions?
Hip flexion mobility refers to the angle formed between the thigh and the body when the thigh is bent close to the chest, and we usually perform this check while lying down. In normal people this angle should be greater than 120°. To measure the posterior extension mobility of the hip joint, you generally need to lie on your back with your thighs extended towards the back of your body, and the angle between your thighs and your body is the posterior extension mobility of the hip joint, usually about 20°.
The internal and external rotation of the hip joint, that is, the hip joint rotates on the axis of the thigh, making inward or outward rotation. The angle of rotation relative to the neutral position is the degree of internal or external rotation of the hip joint. These angles can be measured while sitting (with the chest up and stomach in) or while lying on the back. Generally the internal rotation mobility is around 30° and the external rotation mobility is around 40°.
Hip inversion is the angle at which our thighs skew toward the inside of the body, while abduction is the angle at which the thighs skew toward the outside of the body. These two angles are usually measured while lying down, but be careful that the pelvis does not swing with the swing of the thighs during the measurement. In normal people, the adduction is around 30° and the abduction is around 45°. Knowing the mobility makes it clear why we should pursue the gold standard of joint mobility.
When joint mobility does not reach the normal standard, our daily life will be affected, such as walking, squatting, wearing socks, and physical exercise.