- Proximal focal femoral deficiency (PFFD) is part of a spectrum of congenital deformities affecting the femur, more comprehensively named congenital femoral deficiency (CFD).
- CFD may range from simple shortening of a normal-appearing femur to the complete absence of the proximal two-thirds of the bone. Deficiencies of the hip and knee joint often coexist and are determinants for treatment.
- Treatment is complex and should be undertaken in specialized centers with experience in congenital deformities. Nearly all patients with CFD will require some combination of surgical and orthotic treatment.
- Complex reconstruction and limb-lengthening up to 25-30 cm is possible for patients with reconstructable hip and knee joints.
- In patients with very severe deformity, limb modification may be an option. This aims to level the ankle on the involved side with the knee of the uninvolved side at maturity, and may include different techniques of foot ablation, knee and/or hip arthrodesis, or rotationplasty.
Description:Congenital deformities involving the femur consist of a spectrum of disorders and considerable variation regarding terminology exists. Congenital deficiency of the femur (CFD) is a spectrum of disorders which includes proximal focal femoral deficiency (PFFD), coxa vara, hypoplastic and congenital short femur. (Morrissy, 2006; Gillespie, 1983; Aitken, 1969; Epps, 1983; Paley, 2006; Lee, 2104) This text will focus on the PFFD component of CFD.
Epidemiology:CFD is considered to be a failure of formation and is grouped with transverse limb deficiencies. The exact etiology of CFD remains a mystery. The sclerotome subtraction theory posits that early damage to the neural crest cells which will eventually give rise to the L4 and L5 sensory roots may play a role in the development of CFD. Another theory holds that CFD may be the result of a defect in chondrocyte proliferation and maturation in the proximal femoral growth plate. Such injuries may be caused by ischemia, hypoxia, irradiation, microbiological agents, toxins, hormones, mechanical and thermal injury. Thalidomide has been demonstrated to be a definite cause of femoral deformity in humans.
PFFD is a distinct subset of CFD where the deficiency is mainly proximal. The bone is globally shortened and often smaller than the opposite side. The femoral head may or may not be present. Although a lucency may be apparent in the subtrochanteric region, there is usually bony continuity with delayed ossification rather than a segmental defect. There may or may not be continuity in the femoral neck. Contractures of the hip and knee exist often and are variable in severity. PFFD may coexist with congenital knee instability, fibular hemimelia, and foot deformities.
Clinical Findings:The degree of the shortening of the femur is variable, but generally gives rise to a thick, bulky thigh. The classic deformity in patients with moderate to severe PFFD is a contracture of the hip joint in flexion, external rotation, and abduction. This brings the lower limb anterior to the weight-bearing axis of the body and causes a decrease in the efficiency of the lower extremity lever arm. Both the hip and knee joints may be dysplastic and unstable. There is often a concurrent deficiency of the cruciate ligaments in the knee and a flexion deformity in this joint as well. PFFD is bilateral in about 15% of cases.
Imaging Studies:On radiographic examination, the femur is shortened. The femoral head may or may not be present, depending on the degree of deficiency. There may be a radiolucency in the proximal femur, usually in the subtrochanteric region. This generally represents delayed ossification. Coxa vara may be present. The distal femoral condyles may be hypoplastic as well.
Treatment:CFD is a complex problem where treatment options will vary for every case. While severity of the deformity is a big factor to be considered, it is safe to say that each of these children is unique and will benefit from a tailored, multidisciplinary approach that combines non-operative, orthotic, and surgical treatment to maximize function. The first step in establishing a treatment plan should be to determine whether the patient is a candidate for limb-lengthening or limb-modification. In order to be suitable for limb-lengthening, the expected limb-length discrepancy at maturity should be acceptable and the hip and knee joints should be either stable or reconstructable. Limb-modification includes partial amputations, arthrodeses and rotationplasty. Almost all children with PFFD will utilize some form of orthotic at some point of their lives.
Non-operative: observation, bracing and prosthetic fitting should be employed while waiting for the child to reach appropriate age for surgery or between episodes of surgical treatment. The principal goal of bracing is to establish a stable weight-bearing extremity and may require ‘non-standard’ or unconventional braces produced to accommodate the shortened and deformed thigh, compensate for hip and knee instability, and provide a stable base for weight-bearing. These require an experienced and skilled orthotist that is willing to work with the individual child and family to produce the best possible orthosis.
Operative: The Paley classification broadly addresses treatment and suggests that Type 1 and 2a femurs can be successfully treated with complex reconstruction, 2b femurs can be treated with lengthening and pelvic support osteotomy, whereas a Syme’s amputation or rotationplasty can be considered for the extensively shortened Type 3 femurs with incompetent knee and/or hip joints. Anticipated growth of both extremities should be calculated and a clear idea of the final limb-length discrepancy be established before either treatment is selected. By utilizing modern limb-lengthening techniques, successful total lengthening of up to 20-30cm has been previously reported in these children. This requires multiple episodes of lengthening and often is accompanied by contralateral epiphysiodesis. Again, treatment should be highly individualized to the patient and family, and in general, should be undertaken in specialized centers with sufficient experience in congenital limb deficiencies and complex limb lengthening.
Limb lengthening: Limb salvage in these children includes correction of the limb-length discrepancy, which can be significant. Hip and knee stability must be properly addressed to avoid devastating complications during lengthening. Undercoverage of the acetabulum can be treated with acetabuloplasty prior to lengthening. Knee instability can be treated with soft tissue reconstruction or bridging the fixator across the knee during lengthening. Contractures about the hip and knee are common, and should be recognized and addressed during surgical reconstruction. Coxa vara can be treated with valgus osteotomy. If a pseudarthrosis in the proximal femur exists, it must be treated and stable union achieved. Once these prerequisites have been met, limb-lengthening procedures may be scheduled. The profound shortness of the femur may dictate that multiple sessions of limb-lengthening be performed throughout childhood to achieve similar length in both limbs. Children from 4 ½ to 6 years of age are at high risk of rejecting caretakers and parents during the arduous lengthening process, and initiation of lengthening during this age range is not recommended.
Limb-modification: If the deficiencies of the femur and adjacent joints are too severe to allow successful lengthening, or if the family does not want to pursue a complex reconstructive process, surgical treatment should focus on achieving a stable lever arm for the bearing of weight. This may require arthrodesis of the hip and/or knee, or pelvic support osteotomy. The main goal for limb modification is to ensure that the ankle is at the level of the normal knee at maturity to allow for more advantageous prosthetic fitting and lesser energy expenditure with ambulation.
Amputation in children with PFFD usually consists of ablation of the foot in a Boyd or Syme amputation. As growth occurs, growth of the foot adds length that is not advantageous to weight-bearing and which interferes with prosthetic fitting.
In rotationplasty, the lower extremity is rotated 180 degrees through the remaining femur and/or arthrodesed tibia in order to allow the ankle joint to function like the knee. The foot after a rotationplasty functions as would the residual tibia in a below-knee amputation, therefore providing the patient with more advantageous mobility. While it can be considered an unconventional approach, rotationplasty has held its place as a viable alternative in PFFD as well as for children with tumors of the proximal lower extremity requiring wide resections. Several recent reports have underlined the fact that children who underwent this procedure have favorable functional and quality of life outcomes and are usually accepting of the cosmetic result. Studies have found that rotationplasty patients measure more favorably than above knee amputees functionally, both in regard to oxygen consumption and that their gait is faster and more symmetric. (Gupta, 2012; Lee, 2014)
The prerequisites of a successful rotationplasty include a mobile and sensate foot, ankle mobility within the functional range, and adequate plantarflexion strength. If there is inadequate pelvic stability the femur can be fused proximally.
Children with bilateral PFFD make up a unique subset for this deformity and require a different approach to treatment, as they will most likely choose not to make use of prostheses during their lives. Limb-length inequality and foot problems make up the bulk of their problems and should be addressed with proper surgical treatment according to the patient’s needs and wishes.
PFFD, and CFD, are members of a family of complex deformities and should be considered to involve not just the femur but the entire lower extremity. Today’s treatment options may allow these children to achieve a level of function that was unimaginable in the past decades. However, treatment remains lengthy and complex and requires full participation of the patient and family, along with an experienced and competent multidisciplinary team to address all aspects of this complex deformity.
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