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Pseudarthrosis

Pseudarthrosis

Tibia

Between 40% and 80% are associated with neurofibromatosis

Incidence

Estimated to be 1 per 190,000 live births

Aetiology

  • Exact cellular mechanism is not known and despite a definite clinical relationship with neurofibromatosis, a cellular cause and effect has not been proven
  • Proposed theories include :
    • Neurofibromatosis
    • Fibrous dysplasia "Hamartomatous" tissue
    • Abnormal blood supply
    • Abnormal growth and maturation of bone
    • Proliferative constricting fibrous tissue ring about the lesion 

Classification

  • Crawford
    • Type I : Anterior bowing with increased cortical density
    • Type II : Anterior bowing with a failure of tubulation and narrowed, sclerotic medullary canal
    • Type III : Anterior bowing with a cystic lesion or pre fracture
    • Type IV : Anterior bowing with a frank fracture and pseudarthrosis, usually involving the tibia and fibula
  • Boyd
    • Type I : Anterior bowing and defect in the tibia at birth, associated with other congenital abnormalities
    • Type II : Anterior bowing and hour glass constriction of the tibia, spontaneous fracture by 2 years is the most frequent variety and is associated with neurofibromatosis. Recurrence is common
    • Type III : Pseudarthrosis develops through a congenital cyst
    • Type IV : Pseudarthrosis develops in a sclerotic segment of bone without narrowing, stress fracture
    • Type V : Pseudarthrosis of the tibia occurs with a dysplastic fibula, pseudarthrosis of one or both bones (prognosis similar to Type II)
    • Type VI : Pseudarthrosis occurs in association with an intra-osseous neurofibroma or schwannoma (rare)

Clinically

  • About half are evident at birth, the remainder usually become evident by the age of 2 years
  • Present with anterior bowing of the tibia shortly after birth or acute fracture
  • Bowing is usually antero-lateral, but may be antero-medial
  • Characterised by de ossification of a weight bearing long bone, bending, pathologic fracture and inability to form normal callus in healing
  • At least half the cases are associated with neurofibromatosis, cafe au lait spots being common
  • The tibia in the lower 2/3 is the most commonly affected bone and the left slightly more frequently than the right
  • The fibula is also frequently involved and other long bones are not excluded (clavicle and radius particularly, but having more than one bone involved in any one patient is extremely rare)
  • The limb and foot are often shorter than normal

Pathology

  • Inability to replace bone that is lost
  • Histologically, the area of the pseudarthrosis or the area immediately surrounding the lesion, has the appearance of dense cellular, fibrous connective tissue with variable cartilaginous areas and sclerosis of bone ends
  • In some cases, the tissue has the characteristics of fibrous dysplasis
  • Sometimes there is sufficient fibro-osseous metaplasia to stimulate normal repair, but when weight-bearing is resumed, the bone that has been formed melts away and re fracture occurs
  • Formation of a false joint (pseudarthrosis)
  • Microscopically, there is monotonous pattern of purposeless fibrocytes, the spindle cells are rather small and there is little evidence of organisation into a pattern of trabeculation, collagen formation is usually ample, but there is little attempt to form osteoid
  • There appears to be no defect in mineralisation, if normal osteoid can be produced
  • Cartilage formation is entirely lacking or very scant

Treatment

  • Bowing of the tibia pre-fracture or a pre-pseudarthrosis lesion is best treated initially with a total contact orthosis, which may delay or prevent a fracture and frank pseudarthrosis from developing
  • Operation
    • Paterson (1984) technique : rod & bone graft with electrical stimulation, 75% union, average time to union 7.2 months
    • Boyd : Double onlay bone graft
    • Free vascularised fibular graft
    • Bone transportation (Ilizarov technique)
  • May require amputation if unable to achieve a stable functional limb without deformity (about 50% of the patients with neurofibromatosis need amputation)
  • Leg length inequality is common and there may be a need for contralateral epiphyseodesis or rarely ipsilateral lengthening

Prognosis

  • 50% of fractures will heal with firm internal fixation (IM nail prefered) and autogenous bone graft
  • The use of electrical stimulation after the first surgical procedure is controversial, but the younger the child, the less likely the fracture is to heal
  • If re-grafting is considered essential, then electrical stimulation should be used
  • If failure of union ensues, despite at least two of the above surgical efforts, then microvascular transplantation is justified
  • Tendency for the condition to improve on skeletal maturity

Clavicle

  • Postulated to be related to the location and effect of the subclavian artery, but is also related to neurofibromatosis
  • Failure of ossification of medial and lateral ossification centres of the clavicle (medial centre for inner 2/3, lateral for the outer 1/3)
  • All reported cases have been on the right side
  • Not related to birth trauma 
  • Associated with little functional disability

Clinically

  • Painless lump
  • May have a shoulder droop
  • There is often asymmetry of axillary folds

X-Rays

  • No callus
  • Rounded bone ends

Treatment

  • Usually not indicated
  • If  treatment is justified for functional or cosmetic reasons, use bone graft and internal fixation

Proximal Femoral Focal Deficiency

  • Spectrum of abnormalities ranging from minimal hypoplasia of the femur to near total absence of the femur
  • Deficiencies may include LLD, malrotation of the proximal femur, instability of the hip joint and inadequacy of the proximal hip and thigh musculature

Classification

  • Class A 
    • Represents the fullest expression of development
    • Femoral head is present with an adequate acetabulum and a very short femoral segment
    • Pseudarthrosis present at the sub-trochanteric level
    • At maturity a bony connection is present between the shaft and head of femur, but in some cases pseudarthrosis is present in the femoral neck, which does not heal
  • Class B
    • Femoral head is present in an adequate acetabulum
    • Femur is short, usually a bone tuft on the proximal femur
    • At maturity there is no connection between the head and proximal end of the femur
  • Class C
    • Characterised by a severely dysplastic acetabulum and there is no femoral head
    • Femur is short
  • Class D
    • Absence of the femoral head and acetabulum 
    • Markedly deformed and shortened femoral shaft is not associated with a proximal tuft 

Clinically

  • Characteristically shortened bulky thigh held flexed and abducted
  • Hip rotated externally
  • The incidence of associated anomalies in these children is high (68.9% in Aitkens' series) 
  • Longitudinal deficiency of the ipsilateral fibula is the most common concurrent anomaly

Investigation

MRI may demonstrate the presence of tissue not visualized on plain radiographs

Treatment

  • Reconstruct or amputate
  • No attempt at reconstruction should be made in patients with class C or D involvement
  • Early operation is recommended to prevent displacement of a pseudarthrosis and to encourage healing
  • 1950 Van Nes described a procedure of osteotomising the tibia and rotating the distal tibial segment 180 degrees to change the arc of ankle joint motion, in a manner that would simulate the knee action in a below the knee stump. Must have a stable hip and a femur that places the ipsilateral ankle at the level of the contralateral knee
  • Children with bilateral PFFD generally walk quite well without any form of prosthetic restoration and surgical procedures almost always detract from their ambulatory independence rather than benefit them, unless they have severe foot deformities
  • The treatment of these patients must be individualized on the basis of the limb length discrepancy, adequacy of the proximal musculature, degree of malrotation of the femur and stability of the proximal joint
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