Ultrasound Evaluation of Pediatric Orthopaedic Patients

Jody Litrenta, MD; Karim Masrouha, MD; Amy Wasterlain, MD; Pablo Castaneda, MD

Disclosures

J Am Acad Orthop Surg. 2020;28(16):e696-e705. 

In This Article

Congenital Bony Abnormalities

Patients with congenital conditions often have a cartilaginous component of their bony morphology that can be readily evaluated by ultrasonography. In many cases, identifying these cartilaginous components has diagnostic and prognostic implications. Some examples include congenital longitudinal deficiency, achondroplasia, and congenital dislocations of the knee.

Congenital Longitudinal Deficiencies

Two examples of congenital longitudinal deficiencies in which ultrasonography can play a role are proximal focal femoral deficiency (PFFD) and congenital tibial deficiency. PFFD ranges from mild shortening of the femur to complete absence, with associated abnormalities of the acetabulum and femoral head. It is most commonly classified according to Aitken,[35] with four types ranging in severity from A to D. Congenital tibial deficiency, most commonly classified according to Jones et al,[36] describing varying absence of the tibia with associated deformities of the knee, fibula, and foot. In both conditions, ultrasonography can be used for structural information and to provide prognostic values.

PFFD is difficult to classify in infants because the components of the proximal femur may be present, but not ossified. The femoral head and its connection to the femoral shaft may exist as fibrocartilaginous components that are not initially visible on plain radiographs. Monitoring with serial radiographs often demonstrates ossification over time, and images taken between 12 and 15 months will have better prognostic values.[37]

However, ultrasonography can be used early to identify cartilaginous structures predictive of ossification. This information is valuable for discussing treatment options with the family as early as possible. In some cases, particularly in neonates, ultrasonography can serve as a diagnostic tool. Suspected DDH, in rare cases, can be PFFD. Characteristic hip ultrasonography findings in PFFD include an inability to achieve a standard coronal image composed of the ilium, acetabular roof, labrum, and femoral head.[37,38] In addition, as in DDH, ultrasonography can identify a hip dislocation and provide dynamic information about the stability of the hip. When screening for infants with dysplasia, PFFD should be considered an unusual but possible diagnosis.[38]

Similar to PFFD, limbs with congenital tibial deficiency can contain cartilaginous precursors. The most widely used classification for congenital tibial deficiency is the Jones classification, which describes four different morphologic types.[36] Type 1 is divided into 1a and 1b and differ based on the presence of a cartilaginous anlage in the proximal tibia. Sonographic imaging is probably most useful in distinguishing Jones type 1a from type 1b because it allows for visualization of the cartilaginous anlage. This distinction is important because it has significance for determining amputation versus surgical reconstruction. Patients with a cartilaginous anlage will develop a functional knee mechanism, whereas patients without (Jones type 1a) have typically been treated with an amputation.

Besides defining a cartilaginous anlage, ultrasonography can visualize other components of the knee extensor mechanism. Static and dynamic techniques can be used to identify the quadriceps, patella, and patellar tendon.[39] A thorough understanding of the knee structure and its functionality can help the surgeon plan for surgical intervention. Although MRI is also a useful tool that depicts morphology in great detail, there is a concurrent role for ultrasonography in both PFFD and congenital tibial deficiency. Ultrasonography is a readily accessible tool, requires no patient sedation, and can provide dynamic information about the stability and function.

Achondroplasia

Achondroplasia is the most common form of skeletal dysplasia. Although inheritance is autosomal dominant, about 80% of cases are sporadic. In many instances, the diagnosis may not be expected at birth. Children with achondroplasia can be clinically identified by common features including bowed, rhizomelic extremities, an enlarged head with frontal bossing, and midface hypoplasia. Although the appearance is characteristic, the diagnosis is not clinically apparent in the newborn. Radiographic evaluation can demonstrate classic skeletal features, such as a squared "champagne glass" pelvis, and anomalies of the spine and ribs.

Ultrasonography is an additional tool that can confirm the diagnosis by characteristic hip findings. A study conducted by De Pellegrin et al[40] assessed 22 patients with achondroplasia between the ages of 7 days and 29 months with ultrasonography. They reported that hips affected by achondroplasia had a sharp, well-developed edge of the iliac wing, deep coverage, and low beta angle. The average coverage was 86.7%, with an average beta angle of 20°. The ossific nucleus appears later than the normal and was seen, on average, at around 2 years of age. In addition to achondroplasia, the same authors have also used ultrasonography to characterize other osteochondrodysplasias.[40]

Congenital Knee Dislocation

Congenital knee dislocations are rare occurrences among neonates, easily diagnosed by clinical examination. Ultrasonography is a useful adjunct to evaluate the abnormal morphology of the knee. A previous study of infants with this condition revealed thinning and fibrosis of the quadriceps tendon and abnormal development of the suprapatellar bursa and anterior cruciate ligament.[41] In addition, ultrasonography has proven to be a valuable tool to monitor the dynamic stability of congenital knee dislocations throughout treatment with serial castings.[41] Although many congenital knee dislocations easily reduce with casting, some cases may be particularly stiff and refractory to treatment. This scenario is more likely to be found in association with a syndrome, such as Larsen. Bedside ultrasonography performed in conjunction with serial casting would be most useful to evaluate the progress of treatment in these patients (Figure 13).

Figure 13.

Figure demonstrating congenital knee dislocation and reduction with serial casting in flexion.

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