Proximal Femoral Focal Deficiency or PFFD

Proximal femoral focal deficiency  is a congenital disorder  where the proximal femur is partially absent, and the entire limb is shortened. It is a rare disorder and affects 1-4 person per 50,000. It is also known as congenital femoral deficiency.

Cause and Pathophysiology

The exact cause of proximal femoral deficiency is not known but injury to the neural crest cells that form the precursors to the peripheral sensory nerves of L4 and L5 results in PFFD has been suggested as a factor.

A a defect in proliferation and maturation of chondrocytes in the proximal growth plate has also been suggested. A drug like thalidomide, when taken between the fourth and sixth weeks of gestation, has been shown to cause of proximal femoral focal deficiency.

Patients with proximal femoral focal deficiency also have limb-length inequalities, malrotation, joint instability, and deficient proximal musculature.

Vessels and ligaments are also known to be hypoplastic.

Spectrum of disease includes

• absent hip
• femoral neck pseudoarthrosis
• absent femur
• shortened femur

Proximal femoral focal deficiency is bilateral in about 15% cases.

A rare autosomal dominant form associated with sonic hedge-hog gene but the condition mostly is sporadic.

Associated conditions

• Fibular hemimelia (50%)
• ACL deficiency
• Coxa vara
• Knee contractures
• Dysmorphic facies in rare autosomal dominant type
• Cleft palate
• Clubfoot
• Congenital heart defects
• Spinal anomalies

Clinical Presentation

There is  severe shortening of one or both legs. The proportion of the shortening remains constant with growth. The thigh appears short and bulky  [bulbous] which tapers into knee. The limb is  flexed, abducted, and externally rotated.

Feet is usually normal.

The knee is unstable on examination due to absent cruciate ligaments. Hypoplastic knee has been reported.

Classification of Proximal Femoral Focal Deficiency

Aitken classification

Class A

• Shortened proximal, ending at or slightly above the level of the acetabulum
• Femoral head is often absent but later ossifies; femoral head presence is indicated by a well-developed acetabulum
• A subtrochanteric defect is present , which eventually ossifies and thereby establishes bony continuity but leaves a residual subtrochanteric varus deformity

Class B

• More severe defect or absence of the proximal femur that does not heal spontaneously
• End of the proximal femur is above the acetabulum
• Femoral head is present but may have delayed ossification is mildly dysplastic
• A bony tuft on the proximal end of the shaft is present

Class C

• Absent femoral head that does not ossify
• Severley dysplastic acetabulum
• Femoral shaft is shorter than in a person with class B

Class D

• Most severe form
• Severely shortened shaft
• Often has only an irregularly ossified tuft of bone proximal to the distal femoral epiphysis
• Acetabulum is absent

Gillespie’s functional classification

Group A

• Possible candidates for limb-lengthening
• Congenitally short femurs but clinically stable hips
• No significant knee flexion contractures
• Ipsilateral foot at or below the level of the middle of the contralateral tibia

Group B

• Aitken as classes A, B, and C who require prosthetic treatment.
• Surgical procedure is designed to maximize prosthetic function

Group C

• Aitken class D. These patients do not require knee fusions before prosthetic fitting

Imaging

X-ray is the basic investigation and  Aitken classification is based on radiographic appearance.

It is held that radiographic evaluation tends to overestimate the degree of deficiency and that MRI is the better modality.

Treatment  of Proximal Femoral Focal Deficiency

Treatment of proximal femoral focal deficiency must be individualized from patient to patient.

The following factors help in devising the treatment plan

• Ultimate leg length discrepancy at skeletal maturity
• Presence  and severity of foot deformities
• Adequacy of musculature of lower limbs
• Joint instability of proximal joints

Most of the patients with unilateral deficiency require surgical treatment. Observation is indicated often in children with bilateral deficiency

Some selected patients with unilateral disease may be offered prosthesis but prosthesis acceptance is less because of cumbersomeness and large size of prosthesis.

Surgical treatment

Goal – Ambulation without prosthesis

Procedure – limb lengthening with or without contralateral epiphysiodesis

This option is indicated if there is

• Predicted limb length discrepancy of <20 cm  at maturity
• stable hip and functional foot
• Affected femur has femoral length >50% of opposite side
• Femoral head present (Aiken classifications A & B)

The procedure is contraindicated in uncorrected coxa vara, proximal femoral neck pseudoarthrosis, or acetabular dysplasia

Goal – Ambulation with a prosthesis

Knee Arthrodesis with Foot Amputation

This procedure is done in cases where ipsilateral foot is proximal to the level of contralateral knee so that prosthetic knee will not be below the level of the contralateral knee at maturity

Femoral Pelvic Fusion

It is also called Brown’s procedure and is indicated in patients in whom femoral head is absent (Aitken classifications C & D)

Van Ness rotationplasty 

This procedure is done in cases where ipsilateral foot is at level of opposite knee and ankle as more than two thirds of its motion and femoral head is absent [Aitken classifications C & D]

The procedure involves rotating the limb through femur through 180 degrees, so that ankle which is at position of knee serves the function of knee. The ankle dorsiflexion becomes knee flexion.

This   allows the use of below-knee prosthesis to improve gait and efficiency

Amputation

Limb amputation is indicated  when femoral length <50% of opposite side. As much as possible length should be preserved.

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