Practice Essentials
Proximal femoral focal deficiency (PFFD) is an uncommon problem, with an incidence ranging from 1 case per 50,000 population to 1 case per 200,000 population. [1] It is commonly grouped with fibular hemimelia and tarsal coalition in the general category of postaxial limb hypoplasia (PALH). [2]
In the past, PFFD was commonly grouped with other disorders, such as coxa vara and short bowed femurs, which led to confusion and misunderstanding. [3] Subsequently, a more complete understanding was achieved, and various classification systems have been developed. At present, Aitken’s classification is the one that is most widely used.
Clinically, the thigh is shortened, with flexion of hip and knee joints associated with a stable or unstable hip joint. PFFD may be associated with other malformations of the affected limb, such as fibular hemimelia and cruciate-ligament agenesis. [4]
Management of PFFD requires a multidisciplinary team, which includes the pediatric orthopedic surgeon, prosthetists, and physical therapists. The goals of treatment are to compensate for the functional deficits. No single treatment approach applies to all cases. Each person with PFFD must be assessed individually.
The primary goal of treatment for children with PFFD is to compensate for the various functional deficits that may be present—more specifically, to enable patients to have as much function and walking ability as possible with the lowest possible consumption of oxygen per meter traveled. Cosmesis is much less of an issue.
Treatment is planned on the basis of limb-length discrepancy, the presence of foot and other deformities, the adequacy and power of the musculature, and proximal joint stability.
Pathophysiology
Generally, in individuals with PFFD, the proximal femur is partially absent, and the entire limb is shortened overall. A few main biomechanical abnormalities are present in children with PFFD, as well as in adults with limb deficiencies. These include limb-length discrepancies, malrotation, proximal joint instability, and inadequacy of the proximal musculature.
Vascular changes occur. Chomiak et al, using computed tomography (CT) angiography (CTA) in 21 patients to identify vascular changes associated with PFFD, found that in patients with Pappas type I-IV PFFD, the external iliac, femoral, and deep femoral arteries were substantially reduced in length and diameter, and the deep femoral artery arose more proximally than that in the contralateral extremity. [5]
In addition, two patients with type III disease in this study had an atypical anatomy of the vessels: the anterior part of the thigh and the pseudarthrosis were supplied through the femoral artery (the external iliac artery) as a terminal branch, whereas the remainder of the extremity was supplied from the internal iliac artery. [5]
Ligamentous changes also occur. In a study that used knee arthroscopy to identify changes in cruciate ligaments and their relation to the different types of PFFD in patients with Pappas type III, IV, VII, VIII, or IX deficiency, Chomiak et al found variable changes of the cruciate ligaments in all but one patient. Although these changes were not clinically relevant in most of the patients and were not related to the Pappas classification, the authors recommended imaging of cruciate ligaments before lengthening of the extremity in order to avoid knee dislocation. [6]
Etiology
The etiology of PFFD is not known exactly, but certain theories have been proposed and certain agents implicated. Sclerotome subtraction is one such theory that has been offered to explain several different limb deficiencies. Specifically, this theory states that injury to the neural crest cells that form the precursors to the peripheral sensory nerves of L4 and L5 results in PFFD. [7]
Another theory, advanced by Boden et al, is that PFFD may result from a defect in proliferation and maturation of chondrocytes in the proximal growth plate. [8] Agents implicated in causing such injuries include anoxia, ischemia, irradiation, bacterial and viral infections and toxins, hormones, mechanical energy, and thermal injury. [7, 9] Thalidomide, when taken by the mother between the fourth and sixth weeks of gestation, has been shown to be a definite cause of PFFD in humans. [9] Evidence indicative of a genetic etiology has not been reported. [1, 10]
Epidemiology
The incidence of PFFD is on the order of 0.5-2 per 100,000 live births. PFFD is the third most common longitudinal deficiency of the lower limb. [11] It is predominantly (85-90%) unilateral, [12] with bilateral involvement noted in only 10-15% of cases.
Patient Education
Parents should receive a detailed explanation of the disease process. Individual parents will have differing ideas regarding the most appropriate goal of and approach to treatment. Some will prefer a one-time surgical procedure at a young age, whereas others will be more inclined to attempt to preserve the natural limb no matter what. Treatment must be individualized on the basis of the following factors [13] :
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Limb-length discrepancy
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Presence of associated malformations
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Adequacy of musculature
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Proximal joint stability
