Background

Although 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 a complex one. In the past, PFFD was commonly grouped with other disorders, such as coxa vara and short bowed femurs, which led to confusion and misunderstanding.^[2] Current understanding is more complete, and various classification systems have been developed.

The 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.

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Pathophysiology

In general, in individuals with PFFD, the proximal femur is partially absent, and the entire limb is overall shortened. 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 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.^[3]

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.^[3]

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.^[4]

Etiology

The etiology of PFFD is not known exactly, but certain theories have been proposed and 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.^[5]

A second 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.^[6] Agents implicated in causing such injuries include anoxia, ischemia, irradiation, bacterial and viral infections and toxins, hormones, mechanical energy, and thermal injury.^{[5, 7]} 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.^[7] Currently, no evidence indicates a genetic etiology.^{[1, 8]}

Clinical Presentation