Evaluation of a child with skeletal dysplasia is best performed by a multidisciplinary team (including orthopedic surgery, genetics, physical and occupational therapists, and other necessary specialists such as otorhinolaryngology, neurosurgery, ophthalmology, and dentistry) familiar with these conditions [5, 11]. A thorough history, including questions regarding pain, endurance, gait abnormalities, activities of daily living, and recreation, provides clues to functional limitations. A detailed systemic evaluation is also indicated and may identify major, sometimes life-threatening, issues (see Table 19.2). The extremities should be examined for range of motion, ligamentous laxity, joint contractures, and malalignment (in all planes). Examination of the spine for sagittal and coronal plane deformities and a thorough neurological examination are needed because of the frequent incidence of spinal deformities, instability, and neurological compromise in certain dysplasias. Cervical spine instability is common in mucopolysaccharidoses like Morquio syndrome, spondyloepiphyseal dysplasia (SED), diastrophic dysplasia, pseudoachondroplasia, and chondrodysplasia punctata. Flexion-extension radiographs are useful in evaluating such patients who may be at risk for cervical instability, especially if they have symptoms of neck pain and long track signs. We use flexion-extension radiographs in most dysplasias, except for achondroplasia, at presentation and also intermittently thereafter, especially in dysplasias such as SED or Morquio syndrome, where instability may develop over time. These, however, may be somewhat difficult to interpret in this population given the delayed ossification, odontoid hypoplasia, limited neck motion, and abnormal anatomy seen in many of these patients. Additionally, sometimes the bony landmarks used for measurement may be obscured by overlapping shadows cast by the mandible, occiput, and foramen magnum. Any patient with back or radicular pain, neurogenic claudication, incontinence, or objective neurologic findings (such as hypertonia, brisk reflexes, clonus, motor weakness) should be evaluated with an MRI [12]. The child’s gait is assessed by observing the child walk, run, and play [13]. Gait analysis can be helpful in these patients. Discussion with the family is critical to establish the goals of treatment as well as to manage expectations appropriately.

A skeletal survey is often performed at the initial visit to identify the skeletal features that aid in diagnosis. At our institution, skeletal survey for skeletal dysplasia typically includes anteroposterior (AP) and lateral radiographs of the cervical, thoracic, and lumbar spine and AP view of the long bones of the upper and lower extremities as well as of the pelvis, hands, and feet. Cervical flexion-extension views are obtained in most dysplasias (except for achondroplasia). We add further radiographs as clinically indicated. AP and lateral full-length radiographs of the lower extremities (preferably weight-bearing views) are mandatory prior to surgical intervention. These allow for an evaluation of the overall alignment and location of deformities. It is also imperative to obtain dedicated weight-bearing radiographs of the specific joints to allow for appropriate deformity analysis (please refer to Chap. 2). The full-length radiographs alone will not always allow for an accurate quantitative determination of the magnitude of deformity. For example, the magnitude of ankle deformity can be misjudged based on full-length radiographs centered at the knee because of the parallax of the X-ray beam. Additional three-dimensional studies such as computed tomography and/or magnetic resonance imaging may be performed for detailed evaluation of bone and cartilage anatomy, measurement of torsional abnormalities, assessment of joint condition, etc. However, these are static studies and may not always reflect the alignment of the limb in conditions of dynamic loading (gait). We often perform a three-dimensional gait analysis in these patients as an adjunct to X-rays to aid in preoperative decision making. Such dynamic evaluation helps to quantify the forces across the various joints and also helps us compare pre- and postoperative function.

Preparation of the patient for the surgical procedure is at least as important as the surgical procedure itself (Box 19.2). Given the fact that many of these patients have small and “difficult” airways, preoperative anesthesia consults and discussion of the various issues specific to that patient are very useful. There may be minor surgical procedures but there is no “minor anesthesia” for these patients. Anesthesia should be performed by an anesthesiologist familiar with various medical comorbidities associated with this patient population. Our institution has described a “difficult” airway management in these patients as one which requires two anesthesia providers when ventilating with a facemask. One provider applies the face mask while maintaining anterior mandibular displacement and cervical stabilization while the other ventilates with positive pressure [14]. Care must be taken to protect the neck in patients with cervical instability by using in-line cervical traction [15]. In addition, specialized tools such as video laryngoscope and fiberoptic intubation should be readily available in these situations. Given the fact that each anesthetic session poses a certain risk to the patient, we prefer to combine as many procedures as feasible under the same anesthetic.

Regional anesthesia is often used for pain control and to reduce the amount of narcotic needed during and after surgery. Caudal epidural analgesia is preferred over lumbar epidurals in patients with known vertebral anomalies, prior fusions, and thoracolumbar kyphosis that can co-exist with these conditions. Typically, caudal epidural may be administered to those patients 10 years of age and younger who undergo lower extremity osteotomies. Careful dosing of the epidural medications and regular neurovascular checks are essential to avoid missing the diagnosis of an early compartment syndrome.

Positioning these patients is also critical as patients with severe kyphosis are at risk for developing paraparesis/paraplegia with prolonged supine position. The pathogenesis of this phenomenon is poorly understood at this time. Neuromonitoring should be considered in long procedures in such high-risk patients undergoing lower extremity surgery.

Implant size and design needs to be considered in preoperative planning. Some of these patients are extremely small (primordial dwarfism) and appropriately sized implants are critical to the successful execution of the preoperative plan. The popular commercially available precontoured implants will rarely accommodate the morphology of bones in patients with skeletal dysplasias. Given the poor bone quality in some of the patients, locking plate and screw constructs may be useful when performing acute corrections. Even while planning deformity correction with external fixators, implant selection should be kept in mind. For example, the appropriate fit of a Taylor Spatial Frame (Smith & Nephew; Memphis, TN, USA) may necessitate use of extra-extra short struts (which may need to be ordered preoperatively). Frequently, given the multifocal nature of the deformities, more than one osteotomy and therefore fixation options may be needed in the same bone. Having an appropriate inventory of instruments and implants saves the surgeon from frustration and improves patient outcome.

Achondroplasia is the most frequently encountered form of skeletal dysplasia with an incidence of approximately 1 in 10,000 live births [36]. This results from a mutation in the FGFR3 gene. This over-activity of FGFR3 results in abnormalities in endochondral ossification, whereas intramembranous ossification is not affected. This therefore results in involvement of the base of the skull (resulting in foramen magnum stenosis) and the extremities. There are predictable patterns of deformity in this population. In the upper extremity elbow flexion deformities are common and often associated with distal humeral recurvatum. The severe rhizomelia seen in these individuals can result in marked limitation in reach and humeral lengthening can improve function in these patients. In the lower extremity, hip flexion and knee deformity are often noted. The most commonly addressed deformity is genu varum, which is often associated with internal tibial torsion and occasionally genu recurvatum. A common misconception is that uncorrected genu varum in children with achondroplasia results in knee osteoarthritis later in life. In fact, osteoarthritis is rare and the knee joint is usually not a source of functional limitation in these patients. Spine problems such as central stenosis of the lumbar segments often result in limited function. The etiology of genu varum is unclear. Several mechanisms have been proposed, including ligamentous laxity, obesity, asymmetric growth of the proximal tibial physis, and asymmetric growth of the fibula relative to the tibia [37–39]. As previously mentioned the varus deformity can exist in the distal femur, the knee joint, and the proximal and distal tibia. Indications for surgical correction of genu varum and internal tibial torsion in these children include knee pain, progressive deformity, lateral thrust during gait, and rarely, cosmesis. Genu valgum, though uncommon, may also be seen in some patients. However, the valgus deformity is rarely severe enough to warrant surgical correction.

Several techniques for correction of genu varum in achondroplastic patients have been described previously. Fibular epiphysiodesis or shortening may be useful in young patients (5–8 years old) with mild deformity [18, 40]. However, long-term data on this technique is lacking. Acute correction in young children with an oblique proximal tibial osteotomy (Fig. 19.1a–k), simultaneously correcting the tibial varus and internal rotation, has achieved reliable results with a low recurrence rate as long as the joint line and mechanical axis are brought to a neutral position [41, 42].