Introduction (Instability: 1:60 at birth; 1:240 at 1 wk: Dislocation untreated; 1:700).
(a) There is originally a congenital instability of the hip which later dislocates by muscle pulls or gravity if untreated.
(b) There is familial predisposition for this problem and female predominance.
(c) Growth of the femoral head, acetabulum and innominate bone are delayed until the femoral head fits firmly into the acetabulum.
Mechanisms of Production
(a) There is familial displasia of the hip.
(b) There is a relationship between placental transmission of material joint softening hormones (e.g. Relaxin) which are inhibited by androgens in the male foetus. When a and b are present there is instability of the hip.
(c) Dislocation is produced by the small head slipping out of the shallow acetabulum in the extended position of the hip and is inhibited by the abducted position of the hip.
Treatment
Treatment must be instituted early to avoid a growth deformity of the hip. To ensure there is no instability, infants are tested at birth for hip stability and unstable hip children are nursed in the Frog Position (abducted hip posture).
Delay in treatment leads to frank dislocation of the hip (the femoral head comes out of joint), and there is a shallow acetabulum and a small femoral head. See Photo CDH3. If this condition is allowed to occur an operation may be necessary to produce a more horizontal roof to the acetabulum and produce hip stability. See Photo CDH4.
Posterior dislocation of the hip produces flexion deformities of the hip with compensatory Lordosis - exaggerated lumbar curvature. See Photo CDH5 (both female).
Questions:
1. In CDH5 the smaller child on the right shows Trendelenberg's Sign - as she raises her right foot the right side of the pelvis lowers instead of raising. In the normal patient the hip rises when the ipsilateral foot is raised from the ground. What muscle is chiefly responsible for the normal tilting of the hip?
2. What conditions may give rise to Trendelenberg's Sign?
Scoliosis
This is involved with assymetric growth impairment of the vertebral bodies.
There is lateral deviation of the spine with a 3-fold deformity:
Lateral flexion
Forward flexion
Rotation of the vertebral column on the long axis
The deformity is compensated by movement of the vertebral column above and below the affected region producing a primary and two secondary curves. This deformity progresses rapidly in adolescence and becomes fixed once bone growth is completed
Muscular Dystrophies
There are several different types of Muscular Dystrophies (wasting) including: Duchenne Muscular Dystrophy, Autosomal Recessive Muscular Dystrophy, Congenital Muscular Dystrophy and Myotonic Dystrophy.
Duchenne Muscular Dystrophy
The most common occuring in Boys and in Duchenne Muscular Dystrophy (DMD). This cause of the disease was discovered in 1988 as a mutation in dystrophin, a protein that lies under the muscle fiber membrane and maintains the cell's integrity. As skeletal muscles have little prenatal load or use it is not until postnatally that muscle wasting occurs, usually in the anti-gravity muscles first. This is a progressive disease usually detected between 3-5 years old.
There is a milder adult (30-40 years old) onset form of the disease Becker's Muscular Dystrophy (BMD) that involves mutations in the same gene
Congenital Muscular Dystrophy
Mutations in the laminin alpha-2 chain (LAMA2, merosin) gene lead to a deficiency of this protein.
Laminin is an extracellular matrix glycoprotein expressed in basement membranes. The laminin alpha-2 chain is specifically found in basement membranes of striated muscle and Schwann cells.
Autosomal Recessive Muscular Dystrophy
Dystroglycan, a protein that associates with both dystrophin and membrane molecules, is a candidate gene for the site of the mutation in autosomal recessive muscular dystrophies. A knockout mouse has been generated that has early developmental abnormalities.
Myotonic Dystrophy
An inherited disorder in which the muscles contract but have decreasing power to relax. With this condition, the muscles also become weak and waste away. The myotonic dystrophy gene, found on chromosome 19, codes for a protein kinase that is found in skeletal muscle, where it likely plays a regulatory role. The disease is "amplified" through generations probably by a similar GC expansion associated with Huntington disease.
Arthrogryposis
(Multiplex Congenita)
A rare disease. Severe cases are characterised by multiple deformities at birth with gross stiffening of joints and hypotonia or wasting of muscles.
Such a stiff fetus frequently sustains fractures before or during delivery, this newborn has had a fractured right humerus.
Photo AG2 shows deformities originally thought to be joints, then joints and muscles then finally innervation was also implicated.
Photo AG3 shows normal and abnormal muscles in close proximity. Variations in the degree of severity of joint deformity are expressions of varying degrees of muscular and neurological abnormality.
Limb Abnormalities
Congenital Limb Reduction
Thalilomide was the most celebrated limb reducing insult (teratogen) in humans which also produced a range of other deformities depending on developmental time and concentration of the drug exposure.
Agents - Many substances have been found capable of producing limb reduction defects in experimental animals but few have been related to humans.
Mechanisms - Limb reduction defects may also be indirect, for example with loss of blood supply to part of the limb or to defects in innervation at the spinal or cerebral level. Also there are a number of as yet undefined mechanisms involved.
Limb reduction defects may be apical (congenital amputation) or pre- or post-axial (absence of radius and lateral digits; ulnar and medial digits).
Finger and Toe Defects
Fusion of fingers or toes which may be single or multiple and may affect: skin only, skin and soft tissues or skin, soft tissues and bone.
The condition is unimportant in toes but disabling in fingers and requires operative separation and is frequently inherited as an autosomal dominant.
The presence of this additional "webbing" reflects preservation of the developmental tissues that in normal development are removed by programmed cell death (apotosis).
Presence of additional toes or fingers also called polydactylia or polydactylism. The condition is often treated surgically in the infant.
Ernest Hemingway in the 1930's had a six-toed cat (Snowball) showing a form of polydactyly and cats with a similar condition are now called "Hemingway cats".
Polysyndactyly
Developmental abnormality where there is a combination of polydactyly with syndactyly is known as polysyndactyly.
Triphalangeal Thumb (TPT)
Developmental abnormality with three phalanges instead of two, forming a long, finger-like thumb. Usually inherited as an autosomal dominant trait, gene locus chromosome region 7q36.