Orthopaedic Manifestations of NF

The Shriners Hospital for Children, Montreal

The Shriners Hospital for Children, located in Montreal, has been operating since 1925 and is one of 22 Shriners hospitals across North America. It is an orthopaedic hospital offering special care to children from around the world under the age of 18. The Shriners Hospital is equipped and staffed with skilled specialists to provide comprehensive treatment for children with congenital bone diseases such as osteogenesis imperfecta (OI) and a wide range of orthopaedic problems including; scoliosis, cerebral palsy, limb length discrepancy, fractures and dislocations. In addition, the Shriners Hospital is also involved in basic and clinical orthopaedic research.

Regular orthopaedic clinics offered by the hospital include scoliosis, spinal deformities, OI, metabolic, hip, neuromuscular disorders (cerebral palsy, spina bifida), rheumatology, plastics and prosthetics. The Shriners Hospital works in conjunction with the Montreal Children’s Hospital in order to continue providing the best care for its patients.

Neurofibromatosis: Orthopaedic Manifestations

Neurofibromatosis type I (NF1) is an autosomal dominant disorder. It is one of the most frequent genetic disorder in man. The disease can also occur sporadically and may affect the skin, nervous tissues, bones and soft tissues. Often, its full manifestations are not present until after puberty. However, in approximately 50% of cases, significant musculoskeletal disorders may occur during early childhood.

Orthopedic Manifestations of Neurofibromatosis:

The orthopaedic manifestations of NF1 can be categorized into basically 4 components including:

Spinal deformities
Pseudoarthrosis
Overgrowth
Bone erosion
Rare complications

Spinal Deformities:

Approximately 60 % of neurofibromatosis patients have some form of spinal disorder including one of the following:

a) Scoliosis

Scoliosis is a lateral deviation of the vertebral column and rib cage resulting in an “S” shaped spine and rotated vertebrae. This may cause uneven shoulders, hip deformities, and back pain. As a result of the rotated spine, a hump in the back is possible and long term cardiac and respiratory problems are a threat.

Scoliosis due to neurofibromatosis generally results in a short and sharply angulated curve either on the left or right side. The scoliosis is usually progressive and can be accompanied by other spinal deformities. It is often a result of intraspinal lesions such as tumors.

There are basically two patterns of scoliosis which are observed in neurofibromatosis. These include:

Dystrophic scoliosis which usually involves 1-6 vertebrae and is characterized by short segmented, sharp angled curves accompanied by strong rotation of the vertebrae. Pedicle erosion, foraminal enlargement, spinal canal widening, development of vertebral soft tissue mass, and twisting of the ribs, referred to as penciling, can also occur. These features are most likely due to primary bone dysplasia as well as intraspinal lesions or neurofibromas (dumbbell tumors). Dystrophic scoliosis may lead to a vertebral body dislocation, destabilization of the spine and eventual severe deformity. For curvatures exceeding 20-40o, surgical treatment is usually recommended during childhood. Treatments include bone grafts or a posterior\anterior fusion with or without internal fixation. Brace treatment is generally not sufficient for treating dystrophic curves.

Nondystrophic scoliosis is the type of spinal deformity most commonly affecting NF1 patients. It resembles idiopathic scoliosis (common abnormal spinal curvatures with unknown cause) and usually affects 8-12 vertebrae. Depending on the severity of the deformation, it can be treated using a brace for curves less than 35o. These curves, however, may progress into dystrophic scoliosis.

b) Kyphoscoliosis

Kyphoscoliosis is a posterior deviation of the vertebral column (commonly referred to as “hunchback”) resulting in perturbation of the thoracic region of the spine and back. Approximately, 10 % of patients with NF1 have kyphoscoliosis. The development of paraplegia (paralysis of the lower part of the body) can be observed as a result of excessive tension on the spinal cord. Surgical treatment of kyphoscoliosis is often complicated by the presence of spinal neurofibromas and dural ectasia (swelling of the ‘dura’ which is the outer membrane of the spinal cord). Anterior and posterior spinal fusions are often necessary.

c) Other spinal deformities

Spinal deformities observed less frequently in patients with NF1 include cervical spine disorders, lordoscoliosis (An abnormal forward curvature of the lumbar region which is the lower area of the spine) and spondylolisthesis (slippage of one vertebra onto another resulting in stiffness in the back).

2) Pseudoarthrosis:

Pseudoarthrosis is a form of abnormal union or non union between two bone segments resulting in a false joint formation. This can occur following a fracture or bending but can also be present at birth. Most commonly, this involves the tibia but the ulna, femur, clavicle, radius and humerus may also be affected.

Congenital pseudoarthrosis of the tibia causes abnormal bone development, bone weakening, and anterolateral bowing. It can occur in 1-2 % of patients with NF1. Limb length discrepancy due to growth deficiencies is often associated with this condition. Symptoms can become apparent within the age of 1 and fractures resulting from tibial bowing can manifest within 2-2.5 years. There are two types of pseudoarthrosis of the tibia:

Type I (nondysplastic): characterized by anterolateral bowing with increased bone density and thickening of the bone. This type rarely causes fractures.

Type II (dysplastic): Characterized by anterolateral bowing and usually leads to fracture as well as pseudoarthrosis of both tibia and fibula. The development of cystic lesions adding on to bone fragility is often observed.

Treatments for pseudoarthrosis usually consist of using braces to prevent fractures. Surgical interventions include rod insertion (telescoping or not) which may be combined with bone graft. Several surgeries are often necessary to get a solid bone. The use of external fixators (Ilizarov) helps improving clinical results. Bone graft (vascularized fibula) also remains an option. Amputation may be recommended after several failures.

3) Bone Overgrowth:

Patients with NF1 often have zones of bone and soft tissue overgrowth in the lower extremities, head or neck. This results in the abnormal enlargement of a particular limb or body part often causing the skin to become rough and have an elephant-like appearance. Limb length inequality which results from the asymmetrical overgrowth can be treated with epiphysiodesis (growth arrest) of the long leg around the age of puberty.

4) Erosive defects of bone

Bone lesions appearing as pits may occur either due to cystic lesions from neurofibromatosis or from a contiguous tumor.

5) Rare Complications:

Some rare complication from NF1 inlcude hip dislocations, subperiosteal bleeding and malignant tumors (neurfibrosarcomas)

Conclusion:

Symptoms of NF1 vary highly in severity and can develop starting from birth through adulthood. The diagnosis and treatment of the common orthopaedic manifestation including scoliosis, pseudoarthrosis, neurofibromas and overgrowth is a challenging process. All current existing treatments are aimed at restoring function and improving the quality of life of the patient.

F Fassier, MD. FRCSC

Department of Surgery, Division of Orthopedic Surgery, McGill University, Montreal, Quebec
Chief of Staff, Shriners Hospital for Children
1529, Cedar Avenue, Montreal, Quebec, Canada H3G 1A6
Tel: (514) 842-4464
E-mail: (JavaScript must be enabled to view this email address)