P2.ch3

2. Hip 
1. Functional anatomy and characteristics of the deformities
	Hip joint has a developed specific mechanism for achieving 
stable upright posture.

Muscle Functions
Antigravity muscles
   Flexors:
	-Iliacus
	 This muscle flexes the thigh upwards against the gravity, and 
helps the lower extremity to clear from ground during walking 
(Fig. 51). 
	-Pectineus
	 This muscle flexes and externally rotates the thigh against 
gravity.
   
  Abductors:
	-Gluteus medius 
	-Gluteus minimus 
	 These muscles abduct the thigh, against gravity, and support 
the pelvis on the lower extremity while walking, preventing lateral 
tilt of the pelvis to the opposite side (Fig. 54).
 
   Extensor:
	-Gluteus maximus
      This muscle extends and externally rotates the hip, and 
supports all the weight of the body against gravity, while standing 
and in gait (Fig. 55).

   Adductors:
	-Adductor brevis
	-Adductor longus 
	 These muscles adduct and externally rotate the hip, against 
gravity, and help the lower extremity to clear ground while 
walking. They also stabilize the hip, by covering antero-medial 
side of the hip, while in standing and in gait. They also support the 
pelvis on the lower extremity while crawling and walking, by 
preventing hyperabduction of the hip (Fig. 49, 54).

   External Rotators:
	-Piriformis
	-Obturator internus 
	-Superior and inferior gemelli
	-Quadratus femoris
	 These muscles externally rotate the thigh cover the posterior 
aspect of the hip, and prevent posterior dislocation of the hip. They 
also are stabilizers of the hip, in various phases of hip movement.

Non-antigravity muscles 
(See the clause of "Turnover") 

Musculo-skeletal characteristics
Shallow Acetabulum
	Shallow acetabulum is the most characteristic structure that 
has developed in the human body, during the process of evolution 
to bipedal locomotion. 
	Mammals with quadrupedal locomotion have a deep 
acetabulum allowing flexion and extension movements with a very 
limited range of motion in other directions. It is reasonable to say 
that deep acetabulum is stable, but at the same time, it presents 
limitation in the range of motion.
	On the other hand, humans with bipedal locomotion needed 
full extension at the hip. Wide range of motions in abduction, 
adduction, external rotation and internal rotation was also needed. 
So a shallow acetabulum was a necessity to provide wide range of 
motion in the hips. Thus, the human body developed a shallow 
acetabulum, providing a possibility to stand in extended postures.  
	However, shallowness of the acetabulum makes the hip 
unstable and easily dislocatable in some special conditions, 
presenting serious problems such as developmental dislocations in 
the human body. Dislocation of the hips in cerebral palsy can also 
be caused by hypertonicity in the muscles and skeletal 
characteristics of a shallow acetabulum.  

Muscular Stability
	Hip joint in the normal human body is shallow and therefore, 
originally an unstable skeletal structure. However, in the human 
body, short monoarticular muscles are well developed, and cover 
the hip joint, keeping it firmly in a concentric position. As 
mentioned previously, human body developed the short 
monoarticular muscles, such as the iliacus, adductor brevis, 
gluteus medius, minimus, and pericapsular short rotators, in the 
developmental process, from quadrupedal locomotion to bipedal 
locomotion. Although these muscles participate in supporting the 
body in upright posture, they also cover the hip joint, and act as 
muscular stabilizers, and keep it in a concentric position. Thus, the 
hip in humans is firmly fixed, by muscular activities, in spite of a 
shallow bony acetabulum. However, if muscular coverage is 
inadequate, dislocation of the hip can also be easily induced. 
Developmental dislocation of the hip can be induced in the foetus, 
where the muscles which cover the hip joint are not still well 
activated.  Similarly, dislocation of the hip in cerebral palsy is 
caused by shallow acetabulum, and weakness of the short 
monoarticular muscles.

Derotation of the Femur
	Ontogenically, proximal portion of the femur is in a 
condition of excessive anteversion, in the human baby. In the 
normal development, the femoral head is fixed in a concentric 
position with the proximal part of the femur in an internally rotated 
position in a well shaped acetabulum, by joint capsule, iliofemoral 
and pubofemoral ligaments, and well developed iliacus, gluteus 
medius and minimus, and pericapsular muscles. On the other hand, 
the gluteus maximum acts as a strong external rotator of the distal 
part of the femur through the iliotibial tract, twisting the lower part 
externally against the upper part. This twisting movement seems to 
result in decrease of excessive anteversion of the femur, so as to 
attain the normal femoral torsion. With this rotational change of 
the femur, the lower part of the femur can now be kept in neutral 
rotation while the upper part is kept internally rotated with the head 
fixed in concentric position.
	However, in developmental dislocation of the hip, 
periarticular muscles cannot hold the femoral head in the 
acetabulum and the proximal part cannot be fixed in a centered 
position, resulting in a dislocated hip. The torsion force of external 
rotation of the gluteus maximus cannot act on the lower part of the 
femur and hence, anteversion of the femur remains uncorrected. 
Thus, in developmental dislocation of the hip, this excessive 
anteversion becomes a serious problem, preventing relocation of 
the femoral head.
	In cerebral palsy, because of weakness of gluteus maximus, 
force of external rotation does not work on the distal part of the 
femur. So, it is obvious that derotation of the proximal femur does 
not occur. As a result, anteversion remains unchanged. Excessive 
anteversion presents serious problems, such as difficulty in 
reduction of the dislocated hip, and intoeing gait.

Characteristics of Hip Deformity 
	One of the most characteristic feature of the hip in cerebral 
palsy is paralysis or weakness of the antigravity muscles, such as 
gluteus maximus, medius and periarticular short rotators which 
cover the hip joint and keep it stable. 
	Another characteristic feature is the hypertonicity caused by 
hyperactivity of the multiarticular muscles. Various kinds of 
deformities such as flexion deformity, adduction and internal 
rotation deformity and extension deformity are caused by 
combined muscular factors of paralysis and hypertonicity. 
Excessive anteversion of the proximal femur remains uncorrected 
due to decreased activity of external rotation of gluteus maximus. 
Loss of activities of the antigravity muscles and excessive 
hypertonicity of the multiarticular muscles easily induces 
dislocation and subluxation of the hip, and acetabulum dysplasia is 
exaggerated by lateralization of the femoral head. Dislocation, 
subluxation and acetabular dysplasia result in osteoarthritis of the 
hips when the patients are middle aged and they will suffer from 
immense hip pain. Following deformities are mostly seen in 
combined forms.
1) Adduction deformity
2) Flexion deformity
3) Internal rotation deformity
4) Extension deformity
5) Dislocation and subluxation with anteversion of the femur 
   and dysplastic shallow acetabulum

Fig. 100A: Before OSSCS


Fig. 100B: After OSSCS

Fig. 100AB: Effect of OSSCS for scissors posture 
              with flexed hips and extended knees
Spastic and ataxic diplegia

To Contents
Back
Next