Approach Considerations
Establishing an early antenatal diagnosis of proximal femoral focal deficiency (PFFD) facilitates the choice of the optimal management strategy. Three-dimensional (3D) and four-dimensional (4D) ultrasonographic options are helpful in explaining the nature of the syndrome to parents as early as the first trimester. They are also useful in planning future rehabilitation and determining appropriate use of a prosthesis. [11]
Imaging Studies
Plain radiographs of patients with PFFD show an apparent loss of continuity between the femoral shaft and the head/neck. [19] The fibrous or fibrocartilaginous tissue is responsible for this defect, which can ossify later on. Ultrasonography (US) and magnetic resonance imaging (MRI) are particularly useful for assessing the exact nature of the tissue at the loss of continuity. MRI is also useful for evaluating unossified structures, the hip joint, adjacent soft tissue, the knee, and other malformations of the limb. [20]
The Aitken classification divides PFFD into four categories on the basis of radiographic appearance (see Classification below). [17] It is important to remember that late ossification may occur, whereby the bone may be present but not visualized radiographically. Occasionally, push-pull comparison radiographs, as well as abduction-adduction views, are necessary to distinguish between Aitken class A and class B. Arthrography also can be helpful. [7, 9, 20, 21]
A study by Maldjian et al of the efficacy of magnetic resonance imaging (MRI) in classifying PFFD also compared MRI findings with radiographic classification. [20] The study, which used the Amstutz classification system, found that radiographic evaluation tended to overestimate the degree of deficiency and suggested that MRI was therefore the better modality.
There is a paucity of radiographic images of PFFD in mature skeletons; the appearance of PFFD evolves as the child grows and is different in an adult patient. [22]
US has been employed for antenatal diagnosis of PFFD. [23, 24]
Classification
Several classification systems have described congenital anomalies of the femur, but most have been based on radiographic appearances alone. The Amstutz and Pappas classifications provided detailed radiologic descriptions of the various forms of PFFD that these researchers encountered. [25, 26] Hamanishi described a progressive reduction of the femur, ranging from simple shortening to total absence. [27] Fixsen and Lloyd-Roberts divided their patients into stable and unstable categories. [28]
Gillespie and Torode reviewed their patients from both a radiographic and, more important, a clinical viewpoint and found that most could be divided into the following two groups:
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Group 1 - Persons with congenital short femurs
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Group 2 - Individuals with true PFFD
These two groups not only differed with respect to clinical and radiographic appearances but also were functionally unique and had different surgical and prosthetic requirements. [3]
The Aitken classification, which has been the most widely used system, divided PFFD into the following four classes on the basis of radiographic appearance [17] :
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Class A - A shortened femur is present proximally, ending at or slightly above the level of the acetabulum; the femoral head is often absent but later ossifies; femoral head presence is indicated by a well-developed acetabulum; additionally, there is a subtrochanteric defect, which eventually ossifies and thereby establishes bony continuity; after ossification, there is usually a residual subtrochanteric varus deformity
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Class B - There is a more severe defect or absence of the proximal femur, and the defect does not heal spontaneously; at skeletal maturity, there is no connection between the femoral head and proximal femur; the end of the proximal femur is above the acetabulum; the femoral head, though present, may have delayed ossification, and there is often a bony tuft on the proximal end of the shaft
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Class C - There is an absent femoral head that does not ossify and a markedly dysplastic acetabulum; the femoral shaft is shorter than in a person with class B, in whom the entire proximal femur, including the trochanters, does not develop
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Class D (the most severe form) - There is a severely shortened shaft, which often has only an irregularly ossified tuft of bone proximal to the distal femoral epiphysis; no acetabulum is present, because the lateral pelvic wall is flat
In a symposium, Gillespie proposed a more functional classification system, in which patients were divided into three treatment groups from a surgical and prosthetic viewpoint. [15] The groups in this system were as follows:
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Group A - Possible candidates for limb-lengthening; this group included individuals who had congenitally short femurs but clinically stable hips, had no significant knee flexion contractures, and had the ipsilateral foot at or below the level of the middle of the contralateral tibia
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Group B - Patients classified by Aitken as classes A, B, and C and who required prosthetic treatment. Therefore, any surgical procedure is designed to maximize prosthetic function
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Group C - The same patients as Aitken class D, in that they had subtotal absence of the femur; Gillespie also recommended prosthetic treatment for his group C patients, but these patients did not require knee fusions before prosthetic fitting
