MANAGEMENT OF DEFORMITIES SECONDARY TO BONE DYSPLASIA Stuart L. Weinstein, M.D. Professor Department of Orthopaedic Surgery University of Iowa Iowa City, Iowa 52242 In evaluating a patient with skeletal dysplasia the ortho- atlas. The spine shows characteristic decrease in the inter- paedic surgeon must keep several general concepts in pedicular distances on the AP view proceeding cephalad mind. Children with a skeletal dysplasia have dispropor- to caudal. On the lateral view, the pedicles are broad and tionate growth of various portions of the skeleton. These thick. The vertebrae are often bullet shaped. The AP disproportions may change during growth, i.g. in spon- diameter of the body is small with scalloping of the pos- dyloepiphyseal dysplasia congenita the trunk grows at a terior body margins (secondary to dural compression). relatively slower rate than the limbs during the first decade23. The pelvis has short square ilia, the sciatic notches are The portion of the skeleton primarily affected tends to narrow and deep and the acetabulum is horizontal. The have the greatest number of problems. Thus short trunked long bones are short and broad with wide flaring of the dwarfs tend to have more problems with spinal deformity metaphyses. The growth plate is like an inverted V and and atlantoaxial instability while short limbed dwarfs tend the fibula is longer than the tibia. The radial head may be to have more problems with joint malalignment, joint con- dislocated. tractures, etc. The more severely involved the individual Most achondroplasts will develop a thoracolumbar is, the greater the likelihood of having associated prob- kyphosis in the T10 to L4 region (Fig. 1). These curves lems. In addition, once the patient becomes ambulatory have been reported to reach 70 degrees23 40. These curves secondary deformities may be superimposed as the effects are usually supple and 90 percent will regress when inde- of weight bearing are exerted on the dysplastic bones and pendent gait is achieved23. However, some achondroplasts joints. will have anterior vertebral body wedging or body reces- It would be a monumental task to discuss the manage- sion leading to kyphosis. These kyphotic curves may prog- ment of all of the musculoskeletal dysplasias. Therefore ress and lead to anterior spinal cord compression requiring we will attempt to discuss the management of the mus- anterior decompression in addition to anterior and poste- culoskeletal problems of the most common skeletal rior fusion. If the deformity is less than 60 degrees and if dysplasias23. The basic principles used in the management the patient has no neurologic deficit, the kyphosis should of these conditions can then be applied to other skeletal be treated with a Milwaukee brace with kyphosis pads. dysplasias. Should the deformity reach greater than 60 degrees, con- sideration should be given to anterior and posterior spine Achondroplasia fusion5"4'23 Achondroplasia is the most common form of dwarfism2 16,20,23,34,36,40,43 and is the prototype of the short limbed dwarf. It is an autosomal dominant disorder but 80 percent of the cases represent spontaneous mutations40. These children are easily recognizable at birth. Their char- acteristic features include an enlarged head with frontal bossing, mild hypoplasia of the mid face, prominent man- dible, broad short hands with a space between the third and fourth digits (trident hand), rhizomelic shortening of the extremities with ligamentous laxity and slight hypotonia23'40. These patients commonly have delays in reaching milestones secondary to their disporportionate enlarged head and trunk relative to their extremities and relative hypotonia. Roentgenographic features of the cranium include over- all cranial enlargement with shortening of the base of the Fig. 1 skull while the foramen magnum is small and the frontal Achondroplasia. (A) Newborn with thoracolumbar kyphosis. (B) area is prominent. There may be occipitalization of the By age twenty-three months the kyphosis is resolving. 46 The Iowa Orthopaedic Journal Management of Deformities Secondary to Bone Dysplasia Scoliosis is uncommon in achondroplasts and if present is usually insignificant5'23. Odontoid hypoplasia is also not a problem in these patients. Genu varum is a common problem in achondroplasia23. Ponseti feels that the genu varum is secondary to fibular overgrowth36. The bowing primarily affects the proximal leg but occasionally may be evident distally. Patients may complain of pain where the fibula comes in contact with the calcaneus if there is heel valgus to accommodate the genu varum. If the deformity is distal, this should be Fig. 3 treated by a supramalleolar osteotomy. Ligamentous laxity Achondroplasia. CAT scan of a twenty-three year old with contributes to the deformity although this tends to decrease symptoms of spinal stenosis. Note the narrowed canal in both with age. Bracing will not correct this deformity and is not AP and transverse planes. recommnended. These patients' extremities are extremely difficult to fit with an orthosis and the closeness of the Lumbar myelography may be difficult to perform and joints make them cumbersome. In addition, the brace acts even hazardous because of the small canal. Typically it will through lax ligaments rather than bone4'23. We have treated show pooling of dye at the body levels and filling defects the genu varum deformity by proximal fibular epiphyseo- at the disc levels and possibly a block at L3. desis in the preadolescent patients with mild deformity. In The treatment is adequate laminectomy. This usually older children with knee discomfort, resection of the encompasses five to ten levels and may require partial prominent fibular head and, in the more severe deformi- pediculectomy, facetectomy and formaninotomy. An inad- ties, opening wedge spike osteotomies have been done to equate decompression will often lead to increasing symp- correct the malalignment (Fig. 2)36. The deformities tend toms necessitating extension of the laminectomy in length not to recur. Flexion contractures are present about the and width. The facet joints are very close to midline in hip and elbow and are usually well tolerated. achondroplasts and thus postlaminectomy instability is usu- ally not a problem. Therefore fusion is usually only needed if the facet joint congruity is disrupted5'23'28. Pseudoachondroplasia Dysplasia Pseudoachondroplasia dysplasia was first described by Maroteaux and Lamy in 195929. Subsequently four forms have been delineated5'17 with both autosomal dominant and recessive inheritance and varying severity of musculo- skeletal problems. It represents the second most common type of short limbed dwarf after achondroplasia. The dis- order can be differentiated from achondroplasia because Fig. 2 the patients have a normal sized and shaped head, a greater Achondroplasia. Left, preoperative roentgenogram demonstrat- degree of ligamentous laxity, particularly about the wrists, ing genu varum and fibular overgrowth. Center, roentgenogram immediate postoperative opening wedge spike osteotomies and ankles, and knees, and severe lower extremity deformities proximal fibular head resections. Right, roentgenogram one year (Fig. 4). The disorder is not detectable at birth, the rhi- postoperatively. zomelic shortening becoming evident at age two to three. The most significant problem facing the achondroplast They have a waddling gait and excessive lumbar lordosis. is spinal stenosis. Approxinately 40 percent of adult patients Roentgenographically there is generalized involvement are affected; however, the number is significantly greater of both the epiphyses and metaphyses of the tubular bones. if one takes into account those with mnild symptoms5. The The epiphyses are delayed in their appearance and are etiology is the narrowed canal in the frontal and sagittal small and fragmented when they do appear8. The central planes (Fig. 3). Other contributing factors may include portions appear normal but the periphery is markedly increasing lumbar lordosis, herniated nucleus pulposis, deformed, especially at the sites of ligament insertions9. bulging annulae, hypertrophied facet joints and The metaphyses are splayed and frayed. The vertebrae osteophytes"15'23'28. The average age of symptom onset is show varying degrees of platyspondylia, being biconvex thirty-eight years' 28. The patients may present with either with anterior tonguing. The severity of these changes signs or symptoms of nerve root compression, cauda equina decreases with age. The pelvis demonstrates large ilia and syndrome, paralysis or claudication28. short ischia and pubi. Volume 8 47 S. L. Weinstein cation of the epiphyses may require the surgeon to use arthrography at surgery to insure proper joint alignment. These deformities have a tendency to recur; therefore slight overcorrection with the opening wedge osteotomies should be obtained at surgery to prevent recurrence (Fig. 5)2. Patients with pseudoachondroplasia dysplasia have a tendency to develop degenerative joint disease2'9'43 which may require joint replacements. Fig. 5 Pseudoachondroplasia Dysplasia. Left, preoperative roentgen- ogram demonstrating genu varum. Note also the splaying and fraying of the metaphyseal regions. Right, roentgenogram one year postoperative bilateral opening wedge tibial and fibular osteotomies. Scoliosis may develop but it is usually not severe and if progressive should be treated by standard Milwaukee brace Fig. 4 causes Pseudoachondroplasia Dysplasia. Seven year old male.