The hip joint is a bolt and socket joint that is formed between the acetabulum of the pelvic and the head of femur. And between the acetabulum and the head of femur, there's acetabulum labrum that serves as a shock absorber and also it increases the joint's stability by increasing the depth of the acetabulum. And the hip joint allow three degrees of freedom that the hip can move in a sagittal plan for a flexion extension and for frontal plan to perform abduction and adduction and in horizontal plan or transverse plan to do internal and external rotation.
The hip joint itself is secured by three major ligaments and the labrum. We talked about the labrum earlier that increased the joint stability and for the three major ligaments from the anterior side we can see there's a ligament that connect the ilium and the femur bone called iliofemoral ligaments and from the posterior side we can see there's an ischial of femoral ligament and then from the anterior side we can see there's a pupil of femoral ligaments all three major ligaments limit hip extension so it's not too hard to understand that the closed pack position for the hip is actually when the hip is in full extension and the opposite way for the open pack position of the hip is when the hip is in flexion. From the surface, we can identify muscle groups using the boning landmark. So in the back, we can identify the PSIS and from the side, we can identify the greater trochanter. If you go back to the picture of the hip joint right here, This is the head of the femur.
This is the neck of the femur and then you can see There's a greater trochanter right here and then the lesser trochanter right here. So you can Understand that we from the outside we can palpate the greater trochanter so on the surface we first identify the PSIS and the greater trochanter right here and then we can draw a line in this line we we can divide gluteus maximus and the gluteus medius. And also when we turn our focus to the front, we can identify the ASIS. Combined with the greater trochanter, if we draw a line right there, you can see on the anterior side, we can locate the tensor fascia lata. And then on the other side, we can see the IT band or ilio.
a tibial band right here. And also at the ASIS connected to the middle side of the knee, there is a muscle called sartorius. This sartorius happens to be able to separate the quadriceps and the hip adductors. So this is something from the surface anatomy that we can identify the muscle group.
So let's look deeper on the muscles. The muscles acting on the hip have several compartments. So the anterior compartments are major hip flexors. Here you can see there's iliacus and the psoas major.
And when they pass the increnal ligament, the two muscles join as one and we name it iliopsoas. So please remember that iliopsoas is actually two muscles, one from iliacus and one from psoas major. And this is a big hip flexor. And another muscle that originated from the ASIS and the medial side of the knee is sartorius. And the muscle acting...
sorry the muscle of the quadriceps that's actually acting on the hip is only rectus femoris because you can see there's attachment to the hip sorry to the pelvic um the posterior compartments are hip extensors the major hip extensors is gluteus maximus right here and the hamstrings so so at the hamstrings the most superficial layer is on the middle side is semi-tendinosis when we take this muscle out you can see the another muscle line beneath that is semimembranosus on the lateral side there are biceps femoris long long head and then beneath this bicep femoris short head so these muscles acting as the hip extensors on the middle side of the hip it is hip adductors or adductors they are pectineous and adductor longus and beneath the longus you can see the brevis sorry adductor brevis right there and when we take all these out you can see a huge piece of adductors that's named as adductor magnus on the far medial border that's a grassless So these muscles form the medial compartment of the hip and they function as hip adductors. On the lateral side, they are hip abductor or abductors. They are gluteus medius. When we take the gluteus medius out, you can see the gluteus minimus.
And also our tensor fascia lata is another hip abductors. these three muscles acting as the hip stabilizer because their function is to align the hip. And also by the tensor fascia lata there's IT band. The IT band is separate from the tensor fascia lata so they're not the same. IT band is actually a band of fascia.
and it kind of connects to the tensile fascia lata to the knee right here there's another deep layer in the back of the hip there's actually six muscles and they are external rotators it's hard to remember so I'm going to try my best to help you review these muscles. So right beneath the gluteus minimus, there's a piriformis right here. I also use a piriformis to identify the sciatic nerve because sciatic nerve kind of came through, came under the piriformis muscle.
And then the border of these six muscles, the far end is that you know this rectangle shape. it's quadratus femoris. in between piriformis and quadratus femoris there are three muscles. in the middle it is obturator internus. above it that's gemellus superior and below it of course is the inferior.
and it's from the posterior side that we cannot see the obturator externus. So in the pin tests, this muscle will not be tested. When we look at osteokinematics, we also need to consider the arthrokinematics that's happening within the joint space.
When the person is doing hip flexion extension, the arthrokinematics is primarily spinning. When the person is doing abduction, adduction or external rotation internal rotation the arthrokinematics is doing rolling and gliding so now let's look at the movement itself when a person is performing open chin hip flexion we're actually recruiting the hip flexor to do concentric contraction they are iliopsoas and rectus femoris and sartorius to do a hip flexion When we are doing closed chain hip flexion, because the distal part is fixed and what we see is this person is bending the trunk. So the situation when we do this is when we are doing weight bearing, right? And the typical activity for us to do closed chain hip flexion is when we are trying to sit upright from a supine position. To do that, when we bring our trunk up, the hip flexors are contracting concentrically to do that.
And then to maintain balance, the gravity continues to pull us downward. If the gravity is pulling us anteriorly and to prevent us from falling forward, the hip extensors are contracting eccentrically. On the other hand, when the gravity is pulling us posteriorly, and the hip flexors will be recruited, to contract eccentrically to prevent us from falling backward.
And the hip flexors and extensors also have a role in control of trunk movement. The idiosaurus or hip flexors, they can reinforce the lumbar curve and they have a part of anterior pelvic tilt. The hamstring or the hip extensors, they have a whirl in posterior pelvic tilt. You can anticipate when a person who has tight hamstrings and very likely this person will develop a flat curve of the lumbar spine and that will limit the forward movement like when they're trying to touch their toe.
And this is also commonly contributing to the back pain issue. For the hip abduction and adduction in closed chain, open chain movement, the two muscle groups are acting to maintain the lateral stability of the pelvis and the trunk. We can see this as when a person is standing. in one leg and the gravity pulls the pelvic down. The opposite side of the hip abductor is recruited to pull the pelvic up to maintain the balance.
For external internal rotation it's kind of tricky in some situations, but overall in open chin movement of external rotation the gluteus maximus is actually a powerful lateral rotators and there are in the deep layers there are six small rotator muscles they contributing to external rotation when it's open chain movement when it's closed chain movement that that doing walk that kind of closed chain movement they are acting to balance the pelvic and the trunk over the lower extremity. When a person is doing open chain internal rotation like when we are doing ski we are trying to stop we perform this internal rotation it is the role of hip abductors specifically they are gluteus minimus, tensor fascia lata and anterior fiber of the gluteus medius.