Week 112 – Muscles of the hip joint

In week 112 we talked about the movements of the hip joints and the muscles that cause and control those movements, trying to link them to our upright, bipedal locomotion. We started off by looking at the joint itself: the acetabulum (socket) of the pelvis and the head of the femur (ball). It’s helpful to be aware that each half of the pelvis was originally three, separate bones: the ilium, the ischium and the pubis. In the adult those bones have fused together, but when we talk about the muscles of the hip we can talk about the ilium, ischium and pubis as the bones to which they attach. You are probably already aware of some of the surface anatomy of these bones.
The femur also has some notable lumpy bits. You must be able to recognise the greater trochanter, the lesser trochanter, the intertrochanteric crest linking them, and the linea aspera. Look also for the pectineal line and maybe the gluteal tuberosity. These ridges and lumps are formed by the attachments of muscle to bone, and the greater trochanter is so large because many muscles attach here. So if you are comfortable with where these bony bits are, and if you know which muscles attach to them it is then clear for you to work out the actions of those muscles.
Helpfully, the muscles of the hip and thigh are well grouped together. They are physically grouped by fascia bounding them (great for remembering which nerve and artery supplies a compartment and thus all the muscles therein) and also grouped by function. Around the hip there are groups of muscles that will flex the hip, extend it, abduct the lower limb and adduct it. There are also muscles that will specifically laterally rotate the hip, and many of the other muscles will medially rotate it.
In the anterior thigh we have the quadriceps femoris muscle. The term “quadriceps” suggests it has four heads, and only one of those heads crosses the hip joint from the ilium: rectus femoris. The other three heads (vastus lateralis, vastus medialis and vastus intermedius) pass from the femur, and all parts of the muscle come together to form the patellar tendon and insert into the tibial tuberosity. The functions of the “quads” are to flex the hip and extend the knee.
However, when we looked at the posterior abdominal wall we saw the iliopsoas group. Iliacus passes from the iliac bone and the psoas muscles pass from vertebrae T12-LV. They insert into the lesser trochanter, and these muscles are the powerful hip flexors. Also take a look as the sartorius muscle (the tailor’s muscle, think of moving your leg to a position for sitting cross-legged).
The muscles in the posterior thigh cross both the hip and knee joints, and as such are usually limited to acting on one or the other at a time. The hamstrings are made up of the biceps femoris, semitendinosus and semimembranosus, and can extend the hip and flex the knee. They all pass from the ischial tuberosity (the bony bits you’re sitting on) to either the tibia or the fibula. The semimembranosus and semitendinosus muscles are both medial (passing to the tibia) and biceps femoris is lateral (passing to the fibula). These muscles are very important in walking and running.
The gluteus maximus muscle is a large, powerful hip extensor. It is important in keeping the trunk erect, and also when climbing stairs or straightening up after bending over. It is attached to the ilium and most of its fibres insert into the iliotibial band (a lateral thickening of the fasica lata). Other fibres insert into the gluteal tuberosity. It’s association with the iliotibial band suggests that it has a role in stabilising the knee when standing.
Deep to the gluteus maximus muscle we have the gluteus medius and gluteus minimus muscles. Again, they arise from the ilium but pass to the greater trochanter. These muscles abduct the thigh, which is a vital function of efficient bipedal locomotion, keeping the pelvis level when the opposite foot is lifted off the ground. Mine are rather weak on one side and cause me problems when I run for 80-90 minutes or longer. My pelvis starts to dip to the other side and the hamstrings and calf muscles on that side get very tired having to raise my dipped weight with each stride.
Deep to those muscles are a group of smaller muscles that pretty much all work together to laterally rotate the femur at the hip. Investigate these muscles (piriformis, superior gemellus, inferior gemellus, obturator internus, etc) yourselves. They pass from parts of the pelvis to the greater trochanter. The movement of lateral rotation here is probably one that you’ve not really thought about before. Think of this: look down as you walk and notice how your pelvis twists forward as you walk. The hip joint on the side of your leading leg is moved anteriorly, and your pelvis is now “open” to the left (assuming you’ve stepped forward with your right foot). But your foot points forward. Why doesn’t it point to the left, like your pelvis? Because of the lateral rotation of the femur at the hip joint. And what about the other foot? Why is that still pointing forward?
The final group of muscles is the adductor group. These muscles are in the medial compartment of the thigh and pass from the pubis to the femur, inserting into the linea aspera. Their action is clear, and their site of origin should remind you of an athlete’s groin strain – these are the muscles involved in those strains. Also look at the gracilis muscle.
OK, as you can see this is an area of the body with some serious musculoskeletal anatomy. The rest of the leg is just as good. It’s an area that you have to spend time with yourselves and get to know in layers and compartments. My teaching session was just an introduction and I’d be happy to think about it in more detail with you in tutorials if you’d need them.
How Stuff Works: Why do humans walk on two legs? – an article exploring some of the thoughts of why we walk on two legs.
BBC Science & Nature: Mother of man – 3.2 million years ago – part of a series of human evolution articles, this one about the discovery of “Lucy” and the importance of “bipedalism” in differentiating between apes and man.
Running Planet: Leg blasting circuit – strengthen, tone and sculpt your leg muscles with this cross training workout. There’s some good anatomy in there too.