Muscles extending the hip joint

Gluteus maximus

Semitendinosus	HAMSTRINGS
Semimbranosus
Biceps femoris

Gluteus maximus

As its name implies, this is the largest of the gluteal muscles. It is very powerful and is situated on the posterior aspect of the hip joint, being responsible for the very pleasant shape of this region in humans. In lower primates gluteus maximus in an adductor of the hip; this was also the case in early, primitive humans. However, with the changes that have occurred in the human pelvis to enable the erect posture to be adopted, the muscle has become mainly an extensor of the hip. It is the muscle mainly responsible for the erect position, thereby freeing the forelimbs from a weight-bearing role, and enabling them to become the precision implements that they are today.

Gluteus maximus is quadrilateral in shape consisting of bundles of muscle fibers laid down in the line of pull of the muscle, giving the surface of the muscle a coarse appearance. The muscle is thick and forms two layers as it passes down to its lower attachment. Above, it attaches to the gluteal surface of the ilium behind the posterior gluteal line, the posterior border of the ilium and from the adjacent part of the iliac crest. It also arises from the side of the coccyx and the posterior aspect of the sacrum, including the upper part of the sacrotuberous ligament. Its upper fibres attach to the aponeurosis of the sacrospinalis while its deep anterior fibres come from the fascia which covers gluteus medius. Although this appears to be a vast area, it must be remembered that most of these structures can be covered with one hand if it were slipped into the back pocket of a pair of trousers.

The fibres pass downwards and forwards towards the upper end of the femur. The most superficial, about three-quarters, of the fibres form a separate lamina, which narrows down and attaches between the two layers of the fascia lata helping to form the iliotibial tract. The deeper remaining one-quarter of the muscle fibres form a broad aponeurosis which attaches to the gluteal tuberosity of the femur. 

Nerve supply

Gluteus maximus is supplied by the inferior gluteal nerve, root value L5, S1, 2. The skin covering the muscle, however, is mainly supplied by branches from L2 and S3.

Action

When acting from above, the muscle pulls the shaft of the femur backwards producing extension of the flexed hip joint. As its lower attachment is nearer to the lateral side of the thigh, the muscle will tend to rotate the thigh laterally during extension. The lower fibres can adduct the thigh, while the upper fibres may help in abduction.

The fibres which attach to the iliotibial tract can produce extension of the knee joint because the lower end of the tract attaches to the lateral tibial condyle anterior to the axis of movement. Through the iliotibial tract, gluteus maximus provides powerful support on the lateral side of the knee. If the femur is fixed, contraction of gluteus maximus will pull the ilium and pelvis backwards around the hip joint, but this time the pelvis and trunk are the moving parts, and a lifting of the trunk from a flexed position occurs.

Functional activity

Being a powerful extensor of the thigh, especially when the hip has been flexed, means that this muscle is ideally suited for fulfilling its role in such powerful movements as stepping up onto a stool, climbing and running. However, it is not used greatly as an extensor in ordinary walking.

With the hamstrings, it will take part in raising the trunk from a flexed position, as in standing upright from a bent forward position. Indeed, gluteus maximus and the hamstrings provide the main control in forward bending of the body, as the movement primarily occurs at the hip joint.

It plays an important role in balancing the pelvis on the femoral heads thus helping to maintain the upright posture; its ability to aid lateral rotation of the femur when standing assists in raising the medial longitudinal arch of the foot.

The role of gluteus maximus during sitting should not be dismissed. Although the ischial tuberosities support the majority of the weight of the trunk when sitting, pressure is regularly relieved from these bony points by a static or sometimes dynamic contraction of the muscle which raises the tuberosities of the ischium from the supporting surfaces. The muscle is then relaxed and the weight is then lowered. Sometimes the weight is shifted from side to side with the alternate use of gluteus maximus of each side.

Paralysis of the muscle will lead to a flattening of the buttock with a loss of the beautiful contour, and an inability to climb stairs and run. However, it must be kept in mind that there are other muscles which can be brought into action to produce extension of the hip, although it is much weaker movement. Gluteus maximus can be developed to produce a functional extension of the knee in patients where quadriceps femoris is either very weak or paralysed. This is not a powerful movement, but may be sufficient to enable the patient to extend the knee and enable the lower limb to become weight-bearing during walking or standing.

Palpation

On a model or on yourself, first find some bony prominences which will give useful landmarks of the muscle. The iliac crest is easily palpated approximately at the belt level; moving the hand backwards along the crest a small bony process can be felt: this is the posterior superior iliac spine. With the fingers running inferiorly and medially let this be the centre of the palm. The hand will now just about cover the upper attachment of gluteus maximus; the palm is over the posterior part of the ilium, the sacrum and the back of the sacroiliac joint, while the tips of the fingers are on the edge of the coccyx and the upper end of the sacrotuberous ligament. The bulk of the muscle is now under the palm, follow this path to the greater trochanter of the femur. Now try the following:

1. Extend the lower limb whilst in the standing position, keeping the hand on the muscle; it goes hard and produces a much clearer shape.
2. Place the foot onto a stool and put the hand in the same position as before and step up. Again the muscle will be felt coming into action very strongly.
3. Take up the standing position and place the hands on each gluteus maximus as if they were in the back pocket. Raise the medial borders of the feet as if to shorten the medial longitudinal arch of the foot. As the arch is raised gluteus maximus will be felt working quite strongly, with the femur tending to rotate laterally.
4. Finally, take up the sitting position but this time place a hand under each buttock so that the ischial tuberosity now rests on the hand. Now move the weight from side to side as if getting tired of sitting. Gluteus maximus now contacts alternately, taking the weight off the tuberosity and then lowering it down again.

Semitendinosus

The upper attachment of this muscle is from the lower medial facet of the lateral section of the ischial tuberosity. Its tendon of attachment is combined with that of the biceps femoris and the two muscles run together for a short distance. It then forms a fusiform muscle belly which quickly gives way to a long tendon, thus accounting for its name. This tendon passes downwards and medially behind the medial condyle of the femur, being separated from the medial collateral ligament by a small bursa, to attach to a vertical line on the medial surface of the medial condyle of the tibia just behind the insertion of the sartorius and behind and below the attachment of the gracilis. Near its insertion it is separated from gracilis is separated from sartorius by another bursa. 

Nerve supply. Semitendinosus is supplied by the tibial division of the sciatic nerve, root value L5, S1, 2. The skin covering the muscle is supplied mainly by S2.

Action. Semitendinosus will, when working from below, help to extend the hip joint when the trunk is bent forward. When working from above it will aid in flexion of the knee joint; if the knee is semiflexed it will produce medial rotation of the knee. If the foot is fixed, semitendinosus will act as a lateral rotator of the femur and pelvis on the tibia.

Semimembranosus

This muscle is situated on the posteromedial side of the thigh in its lower part, deep to semitendinosus. It attaches by a strong membranous tendon to the upper lateral facet on the rough part of the ischial tuberosity and passes downwards and medially. The muscle becomes fleshy on the medial side of the tendon, being deep to semitendinosus and biceps femoris. From the lower part of the muscle a second aponeurotic tendon arises narrowing down towards its lower attachment, which is a horizontal groove on the posteromedial surface of the medial tibial condyle. From here its fibres spread in all directions, but particularly upwards and laterally forming the oblique popliteal ligament. Bursae separate the muscle from the medial head of gastrocnemius and from the tibia near its attachment.

Nerve supply. Semimembranosus is supplied from the tibial division of the sciatic nerve, root value L5, S1, 2. The nerve supply to the skin covering the muscle is the same as that for the semitendinosus, that is mainly from S2.

Action. As for semitendinosus.

Biceps femoris

 Biceps femoris is situated on the posterolateral aspect of the thigh, arising by two heads as the name implies, these being separated by a considerable distance.

The long head attaches to the lower medial facet on the ischial tuberosity with the tendon of the semitendinosus, spreading on to the sacrotuberous ligament. These two tendons descend together for a short distance then separate into the two individual muscles, the long head of biceps forming a fusiform muscle running downwards and laterally across the posterior aspect of the thigh superficial to the sciatic nerve. In the lower third of the thigh the long head begins to narrow and is joined on its deep aspect by the short head of biceps.

The short head has its upper attachment from the lower half of the lateral lip of the linea aspera reaching almost as far up as the attachment of gluteus maximus and running down onto the upper half of the lateral supracondylar line of the femur; some fibres arise from the lateral intermuscular septum. The fibres of this short head gradually blend with the narrowing tendon of the long head which lies superficial to it.

On approaching the knee, the tendon can be felt crossing its posterolateral aspect running towards the head of the fibula. 

Prior to its attachment to the head of the fibula the tendon of biceps femoris is split in two by the fibular collateral ligament. Some fibres of the tendon join the ligament, while a few others attach to the lateral tibial condyle and some to the posterior aspect of the lateral intermuscular septum which lies just in front of it. A bursa separates the tendon from the fibular collateral ligament.

Nerve supply. The long head of biceps femoris is supplied by the tibial portion of the sciatic nerve, while the short head is supplied by the common peroneal portion; the root value of both is L5, S1, 2. The skin covering the muscle is supplied mainly by S2.

Action. Biceps femoris helps the previous three muscles to extend the hip joint, particularly when the trunk is bent forwards and is to be raised to the erect position. All three hamstrings will, of course, control the lowering forward of the trunk; however in this case they are working eccentrically, that is working, but its two ends moving apart. Biceps femoris aids the semimembranosus and semitendinosus muscles in flexing the knee joint. With the knee in a semiflexed position biceps femoris will rotate the leg laterally on the thigh or if the foot is fixed, medially rotate the thigh and pelvis on the leg.

The hamstrings

Semitendinosus, semimbranosus and biceps femoris are collectively known as the hamstrings.

They make up the large mass of muscle which can be palpated on the posterior aspect of the thigh, and are involved with extension of the hip, flexion of the knee and rotation of the flexed knee. When working from above they can either flex the knee as a group, or they can work individually in rotating the flexed knee. If they are working with the lower attachment fixed, they will act as a group extending the hip joint.

Functional activity of the hamstrings

All three muscles cross the posterior aspect of both the hip and the knee joints. Flexion of the knee and their stabilizing effect is no doubt a very important function of these muscles, although for this action a much smaller muscle bulk would have been sufficient. Extension of the hip joint when the thigh is the moving part would also require a far smaller group of muscles, especially when it is remembered that gluteus maximus is far better situated to do the job. Raising the trunk from a flexed position on the other hand requires a great deal more power as the muscles are working with a very short lever arm: the ischium and its ramus. The weight of the trunk acting on the other side of the hip joint is considerable.

The mode of action of this group of muscles may well be the reason it is injured so frequently during sports activities. The most common cause of sports injury appears to be in the running section of athletics, being more common in the first 10-20m of a sprint. This is often blamed on inadequate preparation and warm-up before the start, and to some extent this may be true. It must, however, be remembered that at this stage in a race the hamstrings are contracting strongly and are acting over two joints.

At the start of a race the athlete is in a forward-lean position in order to gain as much forward motion as possible. Starting blocks serve to increase the degree of forward leaning. The hamstrings are therefore working to their maximum, either to raise the trunk to an upright position, or to hold the trunk in such a position that forward collapse of the body as a whole is imminent. At the same time the lower limb is being thrust forward to gain as much ground as possible, with flexion of the knee to prevent the foot touching the ground. The hamstrings must be under immense strain in this position and it is not surprising that the muscle may tear.

The hamstrings play an important part in the fine balancing of the pelvis in the standing position, particularly when the upper trunk is being moved off the vertical axis. Working in conjunction with the abdominal muscles anterosuperiorly and gluteus maximus posteroinferiorly, the anteroposterior tilt of the pelvis can be altered. This will have an effect on the lumbar lordosis.

Finally, the hamstrings  have a role in decelerating the forward motion of the tibia when the free swinging leg is extended during walking, and so prevents the knee snapping into extension.