Alterations of Musculoskeletal Function in Children

Chapter 45


Alterations of Musculoskeletal Function in Children


Kristen Lee Carroll and Lynn M. Kerr



Musculoskeletal alterations in children are very common. They may be congenital, such as clubfoot; hereditary, such as muscular dystrophy; or acquired, such as Legg-Calvé-Perthes disease. Some of these disorders are acute, and the child will recover completely; other disorders are chronic or, in some cases, terminal. An understanding of the pathophysiology of these alterations will aid in providing the best care possible for these children.



Musculoskeletal Development in Children


Bone Formation


Bone formation, which begins at about the sixth week of gestation, involves two phases: (1) the delivery of bone cell precursors to sites of bone formation and (2) the aggregation of these cells at primary centers of ossification, where they mature and begin to secrete osteoid (see Chapter 43). Some of the bone cell precursors are present in fetal connective tissues, whereas others migrate in blood to sites of bone formation after blood vessels have grown into the tissue.


Cellular aggregation and maturation occur in two types of fetal tissue, depending on which bones are being formed. The cranium, facial bones, clavicles, and parts of the jawbone (classically called “flatbones”) arise from a fetal membrane termed the mesenchyme. Bones that develop on or within the mesenchyme grow by the process of intramembranous formation of bone. As the mesenchyme becomes vascularized, the immature bone cells aggregate and mature into osteoblasts, which form the centers of ossification and create solid bone or osteoid.


Endochondral formation of bone is the development of new bone from cartilage (Figure 45-1). First, mesenchymal tissue forms a cartilage anlage, which defines the shape of the bone. This is usually found by 6 weeks of gestation. Blood vessel invasion to inside the anlage brings osteoprogenitor cells leading to primary centers of calcification by 8 weeks. Endochondral bone formation begins in the outer layer of the cartilage model, which consists of a layer of dense connective tissue called perichondrium. The perichondrium contains cells that develop into osteoblasts, forming a collar of bone, termed the periosteal collar, around the cartilage model. Cartilage enclosed within the periosteal collar degenerates, and capillaries from outside the perichondrium invade the degenerating cartilage cells, carrying with them osteoblast precursors from the inner layer of the perichondrium and osteoclast precursors from the blood itself.


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FIGURE 45-1 Stages of Endochondral Bone Formation and Centers of Ossification in Long Bone.

Endochondral bone formation progresses at the primary center of ossification in the middle of the cartilage model and extends toward either end of the developing bone. At the same time, the periosteal collar thickens and becomes wider toward the epiphyses. By the end of gestation secondary centers of ossification (i.e., the epiphyseal centers) begin to lay down bone at both ends of the cartilage model. Here, too, cartilage within the periosteal collar degenerates, and blood vessels grow inward, delivering bone cell precursors. Once the osteoblasts begin to secrete osteoid, ossification spreads from the secondary centers in all directions until all the cartilage within the model is replaced by bone.


Two regions of cartilage remain at the ends of long bones: (1) articular cartilage over the free ends of the bone, and (2) the physeal plate, a layer of cartilage between the metaphysis and epiphysis. (These structures are described and illustrated in Chapter 43; see Figure 43-3.) The physeal plate retains the ability to form and calcify new cartilage and deposit bone until the skeleton matures approximately 1 year after sexual maturity (11 to 15 years of age in females, 15 to 18 in males).



Bone Growth


Until adult stature is reached, growth in the length of long bones occurs at the physeal plate through endochondral ossification. Cartilage cells at the epiphyseal side of the physeal plate multiply and enlarge. As rapidly as new cartilage cells form, cartilage cells at the metaphyseal side of the plate are destroyed and replaced by bone.


In the shaft of new bone, where growth is relatively slow, the bone produced by accretion is compact and dense. The compact bone is thickest where it has to withstand the maximal stresses, which generally occur in the middle of the shaft.


The two physes of the long bone often have varying activity rates. For example, the distal physis in the femur contributes 80% of the overall length, whereas the proximal physis at the hip contributes only 20%. The more active of the two has more power to remodel deformity but also can be more sensitive to injury. The architecture of the physis also dictates its sensitivity to injury. The distal femur, for example, has an undulating pattern that increases its resistance to sheer force; when injured, however, growth disturbance is highly likely, whereas the distal radius, which contributes 80% of overall radial length, is a flat, smooth physis that is far more resistant to traumatic injury.


Growth in the diameter of bone occurs by deposition of new bone on an existing bone surface. Bone matrix is laid down by osteoblasts on the periosteal surface and subsequently becomes calcified. At the same time, bone resorption occurs on the endosteal surface. Endosteal resorption increases the diameter of the medullary cavity, which contains marrow and spongy bone.


Many factors affect the development, physiology, and rate of growth of the epiphyseal plate. Growth hormone must be secreted by the pituitary gland at a constant rate to stimulate the growth plate consistently. Other known factors affecting growth include peptide regulatory factors (e.g., fibroblast growth factor [FGF]); changes in cell-to-cell interactions through cell adhesion molecules (CAMs) and cell junctions; and complex interactions or changes in the extracellular matrix (ECM), nutrition, general health, and other hormones (e.g., thyroid hormone, adrenal and gonadal androgens, estrogens). When these factors are poorly controlled, skeletal dysplasias, such as achondroplasia, can occur.


Even after physeal closure at skeletal maturity, bone is constantly being destroyed and re-formed (see Chapter 43). This is a rapid process in young children, allowing them to heal bone injury more quickly than adults. By adulthood, however, bone turnover, or remodeling, occurs at a relatively slow rate. Peak bone mass is achieved by the middle to late twenties and slowly decreases throughout life; therefore, ensuring appropriate levels of calcium and phosphorous intake, performing weightbearing lifting and exercise, and minimizing caffeine intake are especially important for a young female if she is to avoid osteoporosis in later life. Recently, the importance of vitamin D levels also has been emphasized. In one study, nearly 70% of American children had low levels of vitamin D.1



Skeletal Development


The axial skeleton changes shape with growth. (The axial skeleton and appendicular skeleton are described and illustrated in Chapter 43; see Figure 43-5). In a newborn the entire spine is concave anteriorly, or kyphosed. In the first 3 months of life, with the infant’s ability to control the head, the upper (cervical) spine begins to arch, or become lordotic. The normal lordotic curve of the lower (lumbar) spine begins to develop with sitting.


The appendicular skeleton (the extremities) grows faster during childhood than does the axial skeleton (see Figure 43-5). The newborn has a relatively large head and long spine with disproportionately shorter limbs than an adult. By 1 year of age, 50% of the total growth of the spine has occurred and is more than 70% complete by age 8.2 Therefore, failure of the spine to grow (e.g., spinal fusion) does not limit eventual height as much as the premature fusion of the growth plates of the lower extremities. In children with congenital curvature of the spine, growth tends to worsen the deformity rather than to increase the length of the spine.


Besides getting longer, growing bones of the extremities undergo changes in rotation and alignment. In the newborn the proximal femur is rotated forward up to 40 degrees and the tibia is rotated inward. With growth the femur assumes its normal alignment (by 12 years of age) and tibial rotation neutralizes at 8 years of age.3 Bowlegs and knock knees can be normal at certain stages of growth. At birth the newborn’s legs are bowed because of stresses in utero. Genu varum (bowleg) reaches a peak by 30 months of age, whereas genu valgum (knock knee) maximizes by 5 to 6 years of age. If genu varum or genu valgum persists past these ages, a pathologic process rather than a physiologic phase may be present. Pathologic causes of genu varum are Blount disease, rickets, skeletal dysplasias (such as achondroplastic dwarfism), and traumatic injury. Genu valgum may persist also as a result of skeletal dysplasia or genetic predisposition.



Muscle Growth


The composition and size of muscles vary with age. In the fetus, muscle tissue contains a large amount of water and much intercellular matrix. After birth, both are reduced considerably as the muscle fibers (cells) enlarge by accumulating cytoplasm. Little information is available about the numbers of fibers in a given muscle at various ages, but the total mass of muscle in the body can be estimated from the amount of creatinine excreted in the urine, because the conversion of creatine to creatinine takes place only in muscle (see Chapter 43). Between birth and maturity the number of muscle nuclei in the body increases 14 times in boys and 10 times in girls. Muscle fibers reach their maximal size in girls at approximately 10 years of age and in boys by 14 years. Growth in length occurs at the ends of muscles, and the increase in length is accompanied by an increase in number of nuclei in the fibers. Muscle fibers increase in diameter as the fibrils become more numerous. The fibrils themselves do not increase in diameter. Connective tissue components of muscle grow where the tendon and muscle meet.


A potent stimulus to the growth of a muscle is the separation of its attachments as the skeleton grows. The length of a muscle fiber is the direct consequence of its intended range of movement. The stimulus for the formation of a tendon is probably the pull of the muscle rudiment on undifferentiated connective tissue. If the normal opponents of a muscle are paralyzed, the muscle fails to grow properly and can result in contracture of a joint.


Muscle growth during adolescence is a major factor in weight gain. Gender differences in muscle size and weight are minor in childhood but become considerable with the onset of puberty.


In the infant, muscle accounts for approximately 25% of total body weight, compared with 40% in the adult. In the adult, approximately 55% of muscle weight is in the lower limb muscles, whereas in the infant the majority of the weight is axial musculature. The respiratory and facial muscles are well developed at birth so that the infant can perform the vital functions of breathing and sucking. Other muscle groups, such as the pelvic muscles, take several years to develop fully. Throughout life the weight of the skeletal muscles can be increased by exercise.



Musculoskeletal Alterations in Children


Congenital Defects


Syndactyly


The most common congenital defect of the upper extremity is syndactyly, or webbing of the fingers (Figure 45-2). Simple webbing involves the soft tissue envelope alone and is best released surgically when the child is 6 months to 1 year of age. Complex syndactyly involves fusion of the bones and nails as well as the soft tissues; it may be associated with absence or anomaly of bony or neurovascular units. The primary goal in surgical correction of these defects is to achieve maximal function and appearance. Ideally, corrective surgery is deferred until the child is 1 to 2 years old and completed before the child enters school. Vestigial tabs, such as an extra digit, however, are best removed during the immediate neonatal period. Anomalies on the radial aspect of the arm, such as a foreshortened or absent radius, are often associated with abnormalities of blood, heart, or kidneys. Lateral or ulnar-sided defects are less often associated with systemic anomalies and are far more rare.


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FIGURE 45-2 Syndactyly with Polydactyly.


Developmental Dysplasia of the Hip


Developmental dysplasia of the hip (DDH), formerly known as congenital dislocation of the hip, is an abnormality in the development of the proximal femur, acetabulum, or both (Figure 45-3). Although most often present at birth, it may occur at any time in the newborn or infant period.


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FIGURE 45-3 Hip Dysplasia in Children.
Developmental dysplasia of the hip (DDH) with residual acetabular dysplasia. Radiographs at birth, 3, 10, and 19 years (top to bottom) show persisting dysplasia.

The incidence of true dislocation of the hip or a dislocatable hip is 1 in 1000 live births. Some degree of instability of the hip is present in approximately 10 per 1000 live births. The left hip is affected in 60% of cases, whereas the right hip alone is affected only 20% of the time. Bilateral DDH occurs 20% of the time.


Risk factors for DDH include family history, female gender (6:1), metatarsus adductus (20%), torticollis (10%), oligohydramnios, first pregnancy, and breech presentation. First pregnancies and oligohydramnios (deficient volume of amniotic fluid) are thought to limit fetal movement, and breech presentation not only limits movement but also places the hips in a position of flexion and adduction, which creates a more shallow socket, or acetabulum. Although only 2% of births have breech history, as many as 40% of infants with DDH had a breech birth. Maternal hormones that reportedly increase joint laxity also have an effect on DDH, although the exact mechanism is unknown. DDH also is more common in whites and those cultures that swaddle infants with the hips in extension and adduction. It is almost unknown in African cultures where infants are carried, with legs abducted, on the back.



Pathophysiology

The hip can be described as subluxated (partial contact only), dislocated (no contact between femoral head and acetabulum), and acetabular dysplasia (the femoral head is located properly but the acetabulum is shallow) (Figure 45-4). The subluxated hip maintains contact with the acetabulum but is not well seated within the hip joint. The acetabulum is often dysplastic (or shallow) although the femur is often normal. The dislocatable hip is sometimes located but can be dislocated easily. The dislocated hip has no contact between the femoral head and the acetabulum. Some degree of acetabular dysplasia is present in almost all cases. Typically the acetabulum is shallow or sloping rather than cup shaped.


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FIGURE 45-4 Configuration and Relationship of Structures in Developmental Dysplasia of the Hip. (From Hockenberry MJ, Wilson D: Wong’s nursing care of infants and children, ed 9, St Louis, 2011, Mosby.)

By approximately 10 weeks of gestation, the femur, acetabulum, and hip joint capsule are well developed. It appears that most dysplasias occur within the second and third trimesters and are often the result of positioning factors. Experimentally, DDH can be produced in laboratory animals by placing the developing hip in adduction and extension, replicating the breech position. There is, however, a genetic component that is poorly understood. In addition, 2% of DDH cases are teratologic or caused by a systemic syndrome, such as arthrogryposis or spina bifida, in which muscle contracture or imbalance leads to DDH.


If DDH is left untreated in the growing child, secondary changes occur. If the hip remains subluxated or dislocated, the acetabulum becomes increasingly shallow and the soft tissues shorten around the proximal femur. Subluxation leads to early osteoarthritis (OA), and it is now estimated that at least 60% of all OA of the hip is related to DDH. If the hip is dislocated, the bone acetabulum fills with soft tissue and a false acetabulum forms where the femoral head contacts the iliac crest. An apparent limb length inequity and hip muscle weakness occurs, leading to a waddling gait. Back pain and hip pain develop in adulthood. Adult reconstruction of a dislocated hip, even with an artificial hip, is very difficult.4



Clinical Manifestations

The clinical manifestations of DDH vary with the severity of the condition and the age of the child. Signs and symptoms that should be noted include the following:



1. Asymmetry of gluteal or thigh folds


2. Limb length discrepancy (Galeazzi sign)


3. Limitation of hip abduction


4. Positive Barlow maneuver (hip reduced, but dislocatable) (Figure 45-5, A)


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FIGURE 45-5 Congenital Dislocation of the Hip.
A, Barlow maneuver. With one hand pressing the symphysis in front and the sacral spine in back, lateral pressure is applied to the thigh with the thumb of the other hand while pressure is applied with the palm to the knee on the side being examined. The hip that has been flexed to 90 degrees is then adducted. A positive sign is a sensation of abnormal movement, indicating dislocation of the femoral head from the acetabulum. The hands are reversed for examining the other hip. This sign and Ortolani sign may be found only in the first weeks of life. B, Ortolani maneuver. Sign of jerking into correct position. After the Barlow maneuver (A), the hip should be abducted to about 80 degrees while the femur is lifted anteriorly with the fingers along the thigh. A positive sign is a sensation of a jerk or snap with reduction into the joint socket. (Adapted from Specht EE: Am Fam Physician 9:88–96, 1974.)

5. Positive Ortolani sign (hip dislocated, but reducible) (Figure 45-5, B)


6. Positive Trendelenburg gait (waddling)


7. Pain (very late)


The child also should be examined for other anomalies, such as torticollis or metatarsus adductus, which can be associated with DDH.



Evaluation and Treatment

In the newborn period clinical examination is the most important diagnostic tool. Real-time ultrasound, in which the hip is examined while the ultrasound is performed, also is extremely valuable in the newborn period, especially in high-risk infants. The use of ultrasound allows visualization of the cartilaginous structures of the hip (the femoral head and the outer lip of the acetabulum), which are not seen on plain roentgenogram. Radiographs are used after age 6 months when the ossific nucleus of the femoral head appears.5


Treatment depends on the age of the child, severity of dysplasia, and duration of dysplasia. The earlier that treatment is begun, the better the result. In children less than 4 months of age, a Pavlik harness can brace the hip in abduction and flexion, and the acetabulum will remodel as the femoral head rests centered in the socket (Figure 45-6). With this treatment, up to 98% of children will have an excellent result. A “closed” reduction (without opening the joint) followed by spica or body casting for up to 3 months can be done in children up to 12 months of age. After 12 months, surgical intervention—including opening the joint and cutting and realigning the femur and/or acetabulum—may be required. As the child ages, the percentage of good outcomes decreases. Up to 70% of children treated surgically for DDH after age 3 develop early osteoarthritis.6 Early intervention before age 1 is critical for a good outcome; therefore, vigilance for this problem within the first year is essential.


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FIGURE 45-6 Pavlik Harness for Bilateral Hip Dislocation. (From Wheaton Brace Co.)


Deformities of the Foot



Congenital Deformity

Congenital foot deformity is found in approximately 4% of all newborns, and metatarsus adductus accounts for 75% of these deformities (Table 45-1). Metatarsus adductus is a forefoot adduction deformity associated with a normal, plantigrade hindfoot and is believed to be secondary to intrauterine positioning. It is associated with developmental dysplasia of the hip in 20% of cases; consequently, the hips of these infants must be carefully evaluated. Metatarsus adductus is usually classified by two criteria: flexibility (passively correctable or rigid) and degree of deformity. The degree of deformity (mild, moderate, severe) is ascertained by the heel bisection line. A mild deformity is one in which the heel bisection line passes medial to the third toe; moderate, through the third or fourth toes; and severe, lateral to the fourth toe. Serial casts during the first 6 months of life are suggested for moderate to severe deformities and those deformities that appear less flexible. Casts are changed weekly for 6 to 12 weeks. By 6 years of age, 87% of children usually correct spontaneously, and 95% by 15 years of age. Even in those children with some residual deformity, functional symptoms are rare.




Clubfoot: Equinovarus Deformity

Clubfoot describes a range of foot deformities in which the foot turns inward and downward. Technically called equinovarus, the heel is positioned varus (inwardly deviated) and equinus (plantar flexed) (Figures 45-7 and 45-8). The clubfoot deformity can be positional (correctable passively), idiopathic, or teratologic equinovarus (as a result of another syndrome, such as spina bifida). These three types are discussed in the following sections. Overall, the true positional equinovarus lends itself to rapid correction by application of serial casts. The idiopathic variety is treated by attempting cast correction, followed by surgical intervention of resistant deformities. Teratologic equinovarus nearly always requires surgical correction and/or muscle balancing procedures.


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FIGURE 45-7 Bilateral Clubfoot.
A, Infant with bilateral congenital talipes equinovarus. B, Ponseti casting. (A courtesy of Dr. a.E. Chudley, Section of Genetics and Metabolism, Department of Pediatrics and Child Health, Children’s Hospital and University of Manitoba, Winnipeg, Manitoba, Canada. In Moore KL, et al: The developing human, ed 9, Philadelphia, 2013, Saunders.)

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FIGURE 45-8 Idiopathic Clubfoot.
Idiopathic clubfoot displaying forefoot adduction (toward midline of body) and supination (upturning) and hindfoot equinus (pointed downward). Note skin creases along arch and back of heal.



Idiopathic Congenital Equinovarus

The etiology of idiopathic equinovarus (clubfoot) is unknown. In one human fetal study, all clubfeet were associated with identifiable anterior horn cell changes in L5 and S1. Muscle biopsies of both the anterior tibialis long flexors and the peroneus brevis muscles in clubfoot reveal that at least 50% of cases show a decreased number of muscle fibers and/or abnormal fiber histology. The soleus often has an increase in type 1 fibers, whereas the peroneus brevis has a fiber type disproportion. The more abnormal the histopathology, the more severe the deformity, and the greater the chance of recurrent deformity after treatment. The genetic component is unclear and studies are ongoing.


Idiopathic equinovarus occurs in approximately 1 of every 1000 live births, with males being affected twice as often as females. Historically, these deformities were treated by posteromedial release, a surgical procedure that lengthened all tight structures and opened the capsule of all tight joints in the foot. However, since 1998 the casting technique developed by Ignacio Ponseti (see Figure 45-7, B) has been used; the technique involves six to eight above-knee casts, left on for 5 to 7 days each, followed by a percutaneous tendoachilles lengthening procedure performed with local anesthesia. The child then uses special braces at night until 3 years of age. Noncompliance with braces leads to increased recurrence and need for additional casting or surgery. Nearly 30% of children may need an anterior tibialis transfer around age 3.7 Studies comparing operative posteromedial release with Ponseti techniques show better long-term results with less invasive Ponseti method8 (Box 45-1).



Teratologic Equinovarus

The most common causes of teratologic equinovarus are either neuromuscular (such as spina bifida) or syndromic, as in arthrogryposis or osteochondrodysplasia (such as diastrophic dwarfism). The teratologic clubfoot, unlike the idiopathic type, more often fails to be corrected with Ponseti casting and may require operative intervention. The surgery is often more extensive than that for an idiopathic clubfoot, and revision surgery is also more common (Box 45-1).



BOX 45-1   PONSETI CASTING


Ponseti casting implements toe-to-groin casts changed weekly for 6 weeks. Casting begins as early as possible after birth and culminates in a percutaneous tendoachilles lengthening in the clinic, followed by a final cast worn for 3 weeks. In recalcitrant cases, a full surgical posteromedial release (PMR) still may be required. The need for PMR in idiopathic clubfoot has decreased from 90% to less than 20% of infants when this casting technique is used. Long-term results, presumably because of less scarring and more long-term flexibility, are better with Ponseti casting than the PMR method.



Pes Planus (Flatfoot) Deformity

Pes planus (flatfoot) commonly raises parental concern. Despite medical evidence to the contrary, it can be very difficult to convince families that a flexible flatfoot is often as functional as one with a “normal” arch. The majority of babies are born with flat (or “fat”) feet, with the arch becoming more apparent with age. The relatively benign natural history, however, should not overshadow the importance of accurate diagnosis. Significant ankle valgus, vertical talus, tarsal coalition, and skewfoot must be accurately differentiated from flexible pes planus.


Flexible flatfoot deformity appears to be familial, with occasional association of generalized ligamentous laxity. Careful evaluation of possible occult Achilles contracture is done by holding the hindfoot in varus position and dorsiflexing the ankle. Achilles contracture can signify a more severe flatfoot variant. The flexibility of the hindfoot is evaluated by having the child stand on his or her toes facing away from the examiner. In flexible pes planus, the hindfoot swings into a varus position as the planter fascia tightens in toe raise. In rigid pes planus, the hindfoot stays in valgus and the child has more difficulty going up onto tip-toe.


The surgical or orthotic treatment of asymptomatic flexible pes planus is unnecessary. Custom orthotics, Helfet heelcups, and corrective orthopedic shoes have no influence over the natural history (clinically or radiographically) of flat feet. Adult studies on army recruits have shown that soldiers with flat feet perform just as well as their counterparts without “fallen” arches.


There is a small subset of children with painful flexible flat feet. For these children careful attention to the possibility of Achilles contracture or tarsal coalition (congenital union of the hindfoot bones) must be made. This group of children is best treated with inexpensive shoe inserts and then expectantly watched. If pain continues into adolescence, requiring more aggressive treatment, calcaneal lengthening will correct the pes planus without decreasing hindfoot motion. In rigid flat feet, a computed tomographic (CT) scan often will reveal a coalition, a bony or cartilaginous connection between the bones—if painful, this can be resected. Heel cord contractures can be surgically lengthened if stretching alone is inadequate. All surgery carries risk; if a foot is flat but nonpainful, treatment is not required. The painless flatfoot should be viewed as a variation of normal feet.



Abnormal Density or Modeling of the Skeleton


Osteogenesis Imperfecta


Osteogenesis imperfecta (OI) (brittle bone disease) is a spectrum of disease caused by genetic mutation in the gene that codes for type I collagen, the main component of bone and blood vessels. The disorder was first described in 1840 as a syndrome in newborns that consisted of osteoporosis with fractures and skeletal deformities. The Sillence classification is based on both models of inheritance and clinical findings (Table 45-2). In the most severe form of this disorder, the child is usually stillborn or dies soon after birth, although some survive into childhood. OI in its more severe forms is evident at birth because fractures and deformity have occurred in utero. The less severe forms may not become evident until the child begins to walk. Some children with this milder form then experience numerous fractures and can be mistaken for nonaccidental trauma until the diagnosis is made.



TABLE 45-2


SILLENCE CLASSIFICATION OF OSTEOGENESIS IMPERFECTA SYNDROMES







































































TYPE TRANSMISSION MAIN BIOCHEMICAL DEFECT ORTHOPEDIC MISCELLANEOUS
 IA AD Decreased production of type I collagen Mild to moderate bone fragility, osteoporosis, normal stature Blue sclera, hearing loss, easy bruising, dentinogenesis imperfecta absent
 IB AD   Short stature More severe in IA with dentinogenesis imperfecta
II AD, AR, and mosaic Substitutions of glycyl residue in X1 or X2 chains in triple helix Multiple intrauterine fractures, extreme bone fragility Usually lethal in perinatal period, delayed ossification of skull, intrauterine growth restriction
 IIA     Long bones broad, crumpled; ribs broad with continuous beading  
 IIB     Long bones broad, crumpled; ribs discontinuous or beading  
 IIC     Long bones thin, fractured; ribs thin, beaded  
 IID     Severely osteoporotic with generally well-formed skeleton; normal-shaped vertebrae and pelvis  
III AD and AR Abnormal type I collagen Progressive deforming phenotype, severe bone fragility with fractures Hearing loss, short stature, blue sclerae becoming less blue with age, shortened life expectancy, dentinogenesis imperfecta, relative macrocephaly with triangular facies
 IVA AD Shortened pro-α (I)-chains Mild to moderate bone fragility, osteoporosis, bowing of long bones, scoliosis Light sclerae, normal hearing, normal dentition, dentinogenesis imperfecta absent
 IVB AD     Dentinogenesis imperfecta present


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AD, Autosomal dominant; AR, autosomal recessive.


Reproduced with permission from Vaccaro AR, editor: Orthopaedic knowledge update 8, p 248, Rosemont, IL, 2005, American Academy of Orthopaedic Surgeons.


The prevalence rate of the most common form is about 1 in 30,000. Inheritance is usually autosomal dominant but can be autosomal recessive. At least four syndromes have been identified that have various clinical manifestations and prognoses (see Table 45-2).



Pathophysiology

The major errors in OI lie in the synthesis of collagen, a triple helix with two matching alpha chains and one beta chain. Collagen is present in bone, cartilage, eye tissue, skin, and the vascular system. The severity of the OI phenotype and the related anomalies of the eye, dentition, or vascular system are all dependent on the severity of the genetic anomaly and the part of the triple helix that is affected.9 (Genes are discussed in Chapter 4.)


A number of metabolic abnormalities are associated with OI. Some individuals have increased serum thyroxine levels, suggesting hyperthyroidism. This is consistent with the findings of increased sweating, heat intolerance, increased body temperature, a resting tachycardia, and tachypnea. Studies of leukocyte metabolism suggest an uncoupling of oxidative phosphorylation. Reports of alterations of platelet function with defects in adhesion and clot retraction also exist.



Clinical Manifestations

The classic clinical manifestations of OI are osteoporosis and increased rate of fractures, possible bony deformation, triangular facies, possible vascular weakness (i.e., aortic aneurysm), possible blue sclerae, and poor dentition. The Sillence classification designated types I through IV on the basis of severity. The most severe, types II and III, are comparable to osteogenesis imperfecta congenita. These two types are characterized by autosomal recessive inheritance and early onset of manifestations. Both can cause stillbirth or severe neonatal deformity and a short life expectancy. Less severe are types I and IV, which are comparable to osteogenesis imperfecta tarda. Type I is slightly more common than types II and III, and type IV is quite rare. Types I and IV are inherited as autosomal dominant traits and vary in age of onset from birth to adulthood. Type IV, especially when the sclerae are white, is the least deforming type and is often confused with nonaccidental trauma (child abuse).



Evaluation and Treatment

Evaluation of OI is based primarily on clinical manifestations. Serum alkaline phosphatase level is elevated in all forms of the disease. OI can be diagnosed prenatally by ultrasound or chorionic villi sampling. Quantitative analysis of cultured skin fibroblast collagen by electrophoresis shows a decreased quantity of collagen in 95% of individuals.


Type II OI is often terminal in the perinatal period, and therefore little is known about appropriate treatment for the few children who survive. For other types of OI, careful positioning and handling of the newborn help prevent fractures. Beyond the neonatal period, various orthopedic measures are applied, such as prompt splinting of fractures and correction of deformities arising from the progressive bowing or bending of the skeleton by intramedullary rodding of the bones (Figure 45-9). Newer, telescoping rods, which grow with the child, have been shown to reduce the reoperative rate by 30%.10 Scoliosis is present in up to 50% of Sillence III cases and often requires surgery. A multicenter study of a bisphosphonate therapy showed promising results in type III OI, with marked improvements of bone density (up to 30%). Despite these results, there is concern that the healing of fractures and surgical intervention can be more difficult. More study is needed to address the efficacy and safety of these types of drugs. Genetic counseling for affected families should aim at primary prevention.


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FIGURE 45-9 Osteogenesis Imperfecta Treated with Osteotomies and Telescoping Medullary Rods.
A, Severe deformity of both femurs. B, Same individual after multiple osteotomies with telescoping medullary rod fixation. C, Same individual 4 years later demonstrating growth of femurs, no recurrence of deformity, and elongation of rods. (Plaster casts are in place for immobilization of tibial osteotomies.) (From Crenshaw AH, editor: Campbell’s operative orthopaedics, ed 8, vol 3, St Louis, 1992, Mosby.)


Rickets


Rickets is a disorder in which growing bone fails to become mineralized (ossified), resulting in “soft” bones and skeletal deformity (Figure 45-10). Rickets results from either insufficient vitamin D, insensitivity to vitamin D, wasting of vitamin D by the kidney, or inability to absorb vitamin D and calcium in the gut. The most common form is X-linked hypophosphatemic rickets in industrialized nations. In addition to the severe form of metabolic rickets, dietary and lifestyle changes in the United States have led to widespread vitamin D deficiency in children.11 Although unprotected exposure to ultraviolet rays is not suggested, children still need 15 to 20 minutes per week of true sun exposure to activate vitamin D, the mineral necessary for absorption and metabolism of calcium and phosphate. In one recent study up to 90% of normal American children had a low vitamin D level, especially children of color. This can lead to early fracture or slow bone healing after fracture.12


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FIGURE 45-10 Rickets.

Severe metabolic rickets in the immature skeleton leads to short stature and bowing of the limbs with broad, irregular growth plates. The rows of cells in the growth plate that are intended to ossify fail to do so as they reach the metaphysis since calcification is impeded.


Children with rickets are often listless and irritable. They have hypotonia and muscle weakness and may be unable to walk without support. Abnormal parietal flattening and frontal bossing occur in the skull. The calvaria become soft, and the sutures may widen. Cartilaginous attachments of the ribs become prominent, and the long bones of the extremities (tibia, femur, radius, ulna) may be bowed. Growth is restricted, and fractures are common.


Like osteogenesis imperfecta, surgical treatment of bony deformity can be required. However, medical management of calcium, phosphorous, and vitamin D levels must be optimized before surgical intervention. Deformity often improves with normalization of bone metabolism.



Scoliosis


Scoliosis is a rotational curvature of the spine most obvious in the anteroposterior plane (Figure 45-11). It can be classified as nonstructural or structural. Nonstructural scoliosis results from a cause other than the spine itself, such as posture, leg length discrepancy, or pain. Structural scoliosis is curvature of the spine associated with vertebral rotation. Nonstructural scoliosis can become structural if the underlying cause is not found and treated.


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FIGURE 45-11 Scoliosis in Children.
Normal spinal alignment and abnormal spinal curvatures associated with scoliosis. A, Normal. B, Mild. C, Severe. D, Rotation and curvature of scoliosis.

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Sep 9, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Alterations of Musculoskeletal Function in Children

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