Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

Featured on Channel NewsAsia

Fibrous Dysplasia

Basics
Description
  • Fibrous dysplasia is a benign bone process in which there is a failure to produce mature lamellar bone.
  • The condition:
    • Causes focal defects in bone quality
    • Is characterized by multiple, gradual bone deformities; a risk of endocrinopathy (in the polyostotic variety); and a tendency toward pain in the lesions
  • Cafe-au-lait spots are common signs in multifocal disease.
  • Physical findings require some time to develop.
  • Precocious puberty may occur as early as the 1st year of life.
  • Classification:
    • Monostotic: Involves only 1 bone
    • Polyostotic: Involves multiple bones, usually more on 1 side of the body
  • Synonym: Osteitis fibrosa cystica
Epidemiology
Incidence
  • Rare
  • Occurs equally in males and females
Risk Factors
McCune-Albright syndrome (the triad of polyostotic fibrous dysplasia, cafe-au-lait spots, and precocious puberty) is an age-related risk factor.
 
Genetics
(See Etiology)
 
Etiology
  • A defect in the gene occurs for a subunit of a certain G-protein, a type of protein that couples cell-surface receptors to extracellular signals and activates intracellular synthesis of cyclic adenosine monophosphate.
  • The extent and severity of the disease are related to the period in embryonic life when the mutation occurred.
Associated Conditions
  • Endocrinopathy
  • Osteosarcoma
  • Fibrosarcoma
Diagnosis
The diagnosis is made from the characteristic plain radiograph.
 
Signs and Symptoms
  • Signs:
    • Progressive distortion of bone, as in the proximal femur, pelvis, and cranium
    • Possible neurologic compromise, caused by cranial or spinal deformity
    • Cafe-au-lait spots in the polyostotic form (spots have irregular margins likened to the coast of Maine)
    • Pain and a waddling gait
    • Scoliosis
  • Symptoms: Constant aches from bones affected by dysplasia under loading
Physical Exam
  • Measure the patient’s height.
  • Check for scoliosis, because sometimes it may develop in this condition.
  • Measure limb-length and angular deformities.
  • Check all 4 extremities for bowing.
  • Document the ROM, especially about the hip.
  • Palpate tender areas of bone.
  • Observe the patient’s gait.
Tests
Lab
  • Specific tests for any of the described endocrinopathies should be performed if clinically indicated.
    • May include measurement of growth hormone, thyroid function, and adrenal function
Imaging
  • Radiography:
    • The internal appearance of bone with fibrous dysplasia on radiographs is so homogeneous that it is called ground glass.
      • This finding is not surprising, given the histologic findings of multiple small disorganized trabeculae.
    • Fibrous dysplasia usually is seen occupying a large segment of the diaphysis, and sometimes the entire diaphysis, of a bone.
    • The classic teaching is that fibrous dysplasia is a long lesion in a long bone.
    • A characteristic deformity is the shepherd’s crook appearance of the proximal femur:
      • A diffuse, severe bowing of the entire proximal end, secondary to bone weakening
  • Technetium bone scans may be used to locate other lesions of fibrous dysplasia, if needed.
    • The lesions are usually hot on bone scans, although not universally so.
  • CT is useful for imaging cranial or spinal disorders.
Pathological Findings
  • Bone lesions show multiple small, disorganized bony trabeculae, not organized to provide normal mechanical support.
    • Likened to alphabet soup in their disorganized appearance
  • The marrow is filled with fibrous tissue.
  • Osteoblastic rimming of the trabeculae is absent; the bone forms from fibro-osseous metaplasia.
Differential Diagnosis
  • Unicameral bone cyst
  • Fibrous cortical defect
  • Ollier disease
Treatment
General Measures
  • Correct progressive skeletal deformity when painful.
  • Treat endocrinopathy appropriately.
  • Perform craniofacial reconstruction in patients with severe deformity.
  • Manage pain with analgesics, or consult a pain management specialist.
    • Early trials of diphosphonate agents are promising.
Special Therapy
Physical Therapy
  • Therapy is useful for postoperative rehabilitation.
  • The involvement of multiple limbs often poses special challenges to the therapist.
Medication
  • Pain should be managed with analgesics, or a pain management specialist should be consulted.
    • Early trials of diphosphonates are promising.
  • No evidence suggests that increasing a patient’s activity level will strengthen the dysplastic bone.
    • Generally, pain should be the patient’s guide to what is allowed.
    • High-impact or endurance activities pose an increased risk of fracture.
Surgery
  • Orthopaedic principles:
    • A marked bowing deformity should be straightened to minimize additional bending forces.
    • In the proximal femur, this procedure involves a valgus osteotomy or a medial displacement osteotomy.
    • Diseased bone should be supported with a stronger material, such as cortical bone or a metal implant.
    • An intramedullary device usually is better than a plate because it can protect the length of the bone and is more centrally located and therefore more effective (less subject to fatigue fracture).
    • Lesions of fibrous dysplasia often recur after simple bone grafting.
  • Lesions often bleed copiously during surgery.
  • Autogenous cancellous grafts are not used because this graft material is remodeled quickly into fibrous dysplasia.
Follow-up
Prognosis
  • Progression of dysplasia and new lesions may occur in adulthood.
  • About 1/3 of patients have chronic pain.
  • Life expectancy is shortened in patients with the polyostotic form because of pneumonia, thrombosis, and malignant transformation.
Complications
  • Fracture
  • Chronic pain
  • Depression
  • Malignant transformation, most commonly to osteosarcoma (~1%)
Patient Monitoring
  • Patients should be seen periodically by the same physician or set of specialists to detect progressive deformity.
  • In particular, this regimen should include yearly visits to the orthopaedic surgeon to track femoral bowing and scoliosis.
  • Patients also should be told about the risk and warning signs of malignant transformation to sarcoma:
    • Increase in pain, size, or warmth of the lesion
Miscellaneous
Codes
ICD9-CM
  • 733.29 Monostotic fibrous dysplasia
  • 756.54 Polyostotic fibrous dysplasia
Patient Teaching
  • Patients should be supported because of the chronic nature of the disease.
  • Sports restrictions, specific to the patient’s individual lesions, should be discussed.
  • Career counseling should be given.
Prevention
Avoid irradiation of the lesions because of the risk of malignant transformation.
 
FAQ
Q: Is the solitary form of fibrous dysplasia painful?
A: In general, no pain is present, but some patients do have unexplained pain.
 
Q: Is it necessary to perform curettage and bone grafting in patients with no symptoms?
A: Patients who have no symptoms should be treated with observation.
 
Q: Will the bone heal in fibrous dysplasia after a fracture?
A: Yes, it will heal in ~6-12 weeks. If a marked deformity is present, the risk of repeat fracture is high.

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