Week 1 Required Reading Flashcards
Gluteus Medius
The direction of the muscle fibres of each part determines the line of pull of that individual segment.
The fibres of the more horizontal or posterior part run almost (parallel/perpendicular) to the neck of the femur.
The anterior part has fibres running almost (horizontally/vertically) from the anterior iliac crest to the top of the trochanter.
The fibres of the middle part also tend to be more (horizontally/vertically) orientated.
parallel; vertically; vertically
The electromyographic studies showed a phasic action of the three parts of the gluteus medius from posterior to anterior with the tensor fasciae latae being most active during full (stance/swing). In isolated abduction, gluteus medius did not show strong electromyographic activity and in some subjects no activity was seen, while tensor
fasciae latae showed (weak/intense) activity.
stance; intense
We propose a new model of the anatomy and function of the glutei, whereby the gluteus medius is a segmented muscle with each part separately innervated and with a phasic action in different directions. In addition, we define the functions of gluteus medius and minimus primarily as hip (stabilisers/abductors) and pelvic (abductors/rotators) and regard their role in the initiation and assistance in abduction as a (primary/secondary) function. This would explain the waddling gait with congenitally dislocated hips and the swinging of the buttocks during normal walking. The primary function of hip abduction would then be via the
(gluteus medius/TFL).
This anatomical configuration suggests a different function for each of the three parts rather than a total single muscle action. The EMG study showed that the functions of the three parts are phasic and related to different gait determinants.
stabilisers; rotators; secondary; TFL
They examined electromyographically the three segments and showed that the gluteus medius is active in the (stance/swing) phase and that the three parts of the muscle fire sequentially. The posterior part fires first at the beginning of (stance/swing) phase (heel strike) and continues until the point of toe-off. The anterior part showed the maximum activity during (stance/swing) and (single/double) support phase.
stance; stance; stance; single
Because of the anatomical configuration of the glutei and as a result of our electromyographic study, we believe that the primary function of the posterior part of the gluteus medius and the whole of gluteus minimus is to (abduct/stabilise) the femoral head in the acetabulum in different positions of rotation of the femoral head and during different parts of the gait cycle. The force generated by these muscles applied along their line of action will pull the head of the femur into the acetabulum, resulting in a stable ball and socket joint. The posterior part also helps in the initiation of load transfer from one leg to the other.
The anterior and middle parts of the gluteus medius have a more (horizontal/vertical) pull and help initiate (adduction/abduction) which is then completed by the tensor fasciae latae. The
increase in activity of the anterior part from the midstance which is coincident with the initiation of pelvic rotation, when combined with the geometrical configuration and the line of action of this part, suggests the anterior part of the gluteus medius as the (primary/secondary) pelvic rotator.
stabilise; vertical; abduction; primary
The tensor fasciae latae is the major (adductor/abductor) and holds the pelvis horizontal during the (stance/swing) phase of gait.
abductor; stance
In a typical gait cycle the abduction function starts immediately after the end of the initial double support phase of the weight-bearing foot. Due to the geometrical position of the femur and the hip, abduction is initiated by the middle part of the gluteus (maximus/medius). As the transition to midstance takes place, the (TFL/Gluteus maximus) is situated in an advantageous position to effect and continue the abduction process and it is at this point that it shows the most intense EMG activity. In this position, the
(anterior/posterior) part of the gluteus medius will apply a force that has a rotational component that will effect the pelvic rotation. During the weight-transfer phase of gait, the hip joint is stabilised by the force of the (anterior/posterior) part of the gluteus medius from heel strike to full stance and the force of the gluteus minimus during the full stance and terminal double support.
medius; TFL; anterior; posterior
Mechanically, the gluteus medius and minimus are at a major disadvantage to act as the primary hip (adductors/abductors), whereas the tensor fasciae latae is at a major (advantage/disadvantage) to exert the necessary force to counterbalance the force of weight during the full stance
phase of the gait cycle. The iliotibial tract helps the gluteal abductors prevent the Trendelenburg gait and quotes a case of release of the iliotibial tract for trochanteric bursitis, which resulted in a positive Trendelenburg gait and sign. Furthermore, results obtained with the long-tried Ober test for an abduction contracture of the fasciae latae are additional proof
that the major hip abductor is the tensor fasciae latae.
abductors; advantage; advantage;
The gluteus medius and minimus (abduct/stabilise) the hip during the weight-bearing phase of the gait cycle and act as pelvic (abductors/rotators) to rotate the opposite side of the pelvis forward and to be energy efficient for the swing through phase of gait. The Trendelenburg test relies on weakness of the glutei and the sagging of the pelvis on the sound side occurs because the femoral head cannot be held stable in the acetabulum. The geometry and positioning of the tensor fasciae latae does not allow it to hold the pelvis and stop it from tilting when it is still able to rotate on the unstable femoral head.
stabilise; rotators;
