Congenital Disorders of Bone and Joint Development

9 Congenital Disorders of Bone and Joint Development

9.1 Bone Age Assessment in Growth Disorders

Skeletal maturity is closely associated with physical maturation, especially growth rate and sexual maturity. Disturbances of physical maturation may occur secondary to a genetic, hormonal, nutritional, or other cause. Clinical monitoring of growth is done with age-related percentile graphs. If longitudinal growth or somatic maturity demonstrates progressive deviation from the norm or if the patient’s height falls below the 3rd percentile or above the 97th percentile, then skeletal age should be determined. Assessment of skeletal development provides prognostic information with regard to further development.

Radiography.

• Neonates/infants: In newborns, the presence and form of ossification centers are analyzed using a radiograph of the lateral lower leg (including knee and ankle joints) according to the method of Sénécal and a special points system. The skeletal age is then expressed in percentiles. This can assess the severity of, for example, congenital hypothyroidism. A possible alternative is the determination of skeletal maturation of the newborn by ultrasound of the distal femur and proximal tibial epiphysis.

• Two years of age and older: A dorsopalmar radiograph of the left hand, including the distal portions of the radius and ulna, is needed for assessing skeletal age. Skeletal age is determined using the method of Greulich and Pyle or that of Tanner and Whitehouse.

The Greulich and Pyle method for bone age assessment evaluates the extent of ossification of the carpal bones and is the more practical method for daily clinical practice. The development of the ossification centers within the initially cartilaginous carpal bones is tracked and their maturation is assessed according to form and size. The growth plates of the first to fifth digits and radius and ulna as well as the maturation of the epiphyses are employed in a similar way. The skeletal age of the child can be determined by comparison with standard radiographs provided in the Greulich and Pyle atlas. The more elaborate method proposed by Tanner and Whitehouse is more suitable when skeletal development of the bones of the hand is asynchronous. This method assigns an individual score to each ossification center of the carpus and the epiphyses based on their current stage of development. A total maturity score is calculated by summing all these scores. This score is correlated with the bone age separately for males and females. The Tanner and Whitehouse method is the more complex and requires more time but it is more accurate and more reproducible than the Greulich and Pyle method.

Deviations of skeletal age from the norm by more than a year either way are rated as “retarded” or “accelerated.” The corresponding tables by Bayley and Pinneau (in the appendix of the Greulich and Pyle atlas) list what percentage a child has reached of their final height. The child’s expected final height (ultimate height) may be determined using this information. The standard deviation (SD) of the predicted values from the actual height reached was only ±2.5 cm in children up to the age of 14 years, and only ±1 cm in older children in the series reported by Bayley and Pinneau.

Additionally, digital applications using the method of Tanner and Whitehouse can calculate both bone age and future adult height with considerable time-saving by evaluating a digital radiograph and entering the child’s chronological age and current height.

By the age of 18 years, bone age cannot be computed from hand and wrist radiographs, therefore the medial end of the clavicle is used for bone age calculation in individuals aged 18 to 22 years. Radiographs or CT are used for visualization of the clavicle. MRI-based methods are being developed but require more research.

9.2 Congenital Dysplasia of the Hip

Congenital dysplasia of the hip involves abnormal development of the acetabular roof and the acetabular rim. The result is an unstable joint with subluxation or even dislocation of the femoral head.

Pathology. This is a multifactorial disorder that may be secondary to a mechanical cause such as breech presentation or oligohydramnios, an endogenous cause, or familial disposition. Congenital dysplasia of the hip results from a disturbance of growth and ossification of the acetabular roof, especially of its cranial margin so that it no longer supports the femoral head. This leads to instability of the hip joint, subluxation, and a shift of the hip’s center of rotation ( Fig. 9.1). Complete dislocation can occur and result in the formation of a secondary pseudoacetabulum. With subluxation or dislocation, an elongated ligamentum teres and/or entrapped joint capsule and adipose tissue may impede adequate reduction of the joint.

Clinical presentation. Girls are six times more commonly affected. Although the left hip is most commonly involved, bilateral involvement is seen in 25% of cases. The Ortolani and Barlow maneuvers are important functional tests to assess stability.

Treatment. Treatment depends on the age of the patient and stage of the disorder. The aims of treatment are to retain the femoral head within the acetabulum, resulting in remodeling of the acetabulum and prevention of subluxation. Reduction is required in the presence of subluxation or dislocation.

US. Ultrasound provides a direct demonstration of the cartilaginous femoral head, the hyaline cartilage of the acetabular rim and fibrocartilaginous labrum, and the bony and cartilaginous acetabular roof. Coronal slices produce images comparable to a radiograph with better detail and the option of dynamic testing of mobility and stability of the femoral head.

Ultrasound or radiography?

• Ultrasound:

In newborns with risk factors (familial disposition, breech presentation, unusual clinical presentation).

Obligatory in the 4th to 6th weeks of life.

Still useful to the age of approximately 1 year.

• Radiograph: from the 9th month onward or when ultrasound assessment is limited.

Ultrasound classification of developmental dysplasia of the hip is generally performed using the Graf technique; it is divided into four basic types. After definition of the standard plane, the joint is assessed using the acetabular roof line (through the bony acetabular roof) and the acetabular inclination line (from the osseous acetabular rim through the acetabular labrum). These two reference lines each form an angle with a baseline parallel to the contour of the iliac wing. These angles are used to classify dysplasia of the hip ( Fig. 9.2a). The ultrasound assessment of hip maturity therefore takes into consideration both the bony architecture of the acetabulum and acetabular rim and the extent of coverage of the femoral head by the cartilaginous acetabular roof. With a displaced femoral head, the labrum is moved cranially ( Fig. 9.2b).

Ultrasound assessment requires an experienced examiner since even a minimally suboptimal imaging plane (tilt, shift) will produce an aberrant measurement result and the potential for misdiagnosis.

Fig. 9.1 Configuration of the acetabular cup and the labrum.

Fig. 9.2 Ultrasound of the infant hip. (a) Normal finding. (b) Dysplasia with reduced alpha angle (Graf Type II). 1, baseline; 2, acetabular roof line; 3, inclination line.

Radiography/CT. Given the availability of ultrasound, radiographs are only indicated in exceptional cases in the first nine months of life, e.g., in clinical courses with an unclear differential diagnosis or on completion of treatment for developmental dysplasia of the hip.

Between 3 and 6 months, ossification of the hip progresses to the extent that dysplasia of the hip can be confidently identified. A diagnosis is reached by measuring the geometry of the acetabular cup and the centering of the ossification of the femoral head within the acetabulum ( Fig. 9.3). The acetabular roof angle decreases with increasing ossification of the acetabular cup. Depending on the severity of the hip dysplasia, the bony roof of the femoral head deteriorates, the acetabular inclination angle becomes steeper, and ultimately the femoral head becomes displaced and subluxated ( Figs. 9.4 and 9.5). With chronic dislocation a secondary, “pseudoacetabular cup” develops where the femoral head abuts the lateral margin of the acetabulum and/or ilium.

MRI. Indications for MRI include failure of conservative treatment and preoperative planning. Causes of a failure to be able to reduce the hip such as displacement of the margin of the acetabular roof into the joint (inverted limbus), entrapped parts of the capsule or fatty tissue, are more readily identified with MRI than with ultrasound ( Fig. 9.6). Another indication is suspected osteonecrosis of the femoral head, which can develop after forced attempts at reduction.

9.3 Congenital Deformities of the Foot

The foot of the neonate and the infant has a characteristic pattern of development: until early childhood, the arch of the foot is flat because it is filled with a fat pad. A mild talipes calcaneus position of the hindfoot and a supination position of the forefoot are also temporary. Weight bearing during the standing phase results in an apparent pes planovalgus (flat valgus foot), which corrects itself by the age of 7 to 8 years.

Congenital foot deformities must be distinguished from these physiological and age-related changes within the child’s foot. From an etiological standpoint, congenital deformities occur with higher familial frequency or may be associated with underlying neurogenic or myogenic conditions (e.g., meningomyelocele, cerebral palsy, arthrogryposis).

Early initiation of treatment is crucial for providing optimal therapy because the mobility of the infant foot is still great but ossification and fixation of the foot skeleton progresses rapidly in the first 2 years.

Club foot (pes equinovarus). This is a complex deformity of the foot which cannot be corrected passively and comprises four components:

• Pes equinus (horse foot) with a vertical calcaneus and shortened Achilles tendon.

• Pes varus (varus position of the heel).

• Metatarsus adductus (sickle foot) with inward turning of the midfoot.

• Pes cavus (hollow foot) with a high arch of the foot.

Club foot is the second most common congenital skeletal deformity after congenital dysplasia of the hip, affecting 0.1% of all newborns. It may be unilateral or bilateral and is commonly associated with other malformations, especially congenital dysplasia of the hip.

Metatarsus adductus (sickle foot). Metatarsus adductus is a foot deformity with adduction or varus position of the forefoot relative to the hindfoot.

Flat foot (vertical talus). This malformation involves an increased vertical position of the talus and dislocation of the navicular on the talus (not to be confused with a flexible flat foot deformity and physiologic pes planovalgus [flat valgus foot]).

Hollow foot (pes cavus). Pes cavus refers to a foot deformity with a deepened (high) longitudinal arch and increased vertical position of the metatarsals, especially the first ray.

Talipes calcaneus. This term refers to a malalignment with the dorsum of the foot fully dorsiflexed toward the lower leg. Congenital talipes calcaneus should be distinguished from the often encountered, harmless and transient talipes calcaneus of the neonate.

Pes equinus. A foot fixed in plantar flexion due to tightness of the Achilles tendon is referred to as pes equinus.

Radiography. Radiography serves to assess the axes of the tarsal bones in the dorsoplantar and lateral projections ( Figs. 9.7 and 9.8).

CT/MRI. The tarsal bones are largely preformed in cartilage at birth and in early infancy—at a time when important decisions should be made regarding therapy. The calcaneus, talus, and cuboid initially have small ossification centers. At this time MRI provides an exact demonstration of malalignment in three planes.

As ossification of the bones of the foot progresses, CT with 3D-reconstructed images provides a good spatial overview of the foot deformity.

Fig. 9.3 Measurement of the acetabular roof angle. 1, Hilgenreiner line; 2, acetabular roof line; 3, Ombredanne’s vertical line; α = acetabular angle.

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