Proximal Femoral Focal Deficiency

Proximal femoral focal deficiency (PFFD) is a rare congenital condition in which part or all of the proximal femur is absent. It is a spectrum, from mild shortening with coxa vara to complete absence of the proximal femur and acetabulum, and it often involves the knee, fibula, ankle and foot as well.

Who. The incidence is 1 in 50,000 live births, and males and females are affected equally. The left side is affected more often than the right, and roughly 10-15% of cases are bilateral.

Cause. PFFD results from failure of normal development of the proximal femur during embryogenesis, at 4-8 weeks' gestation. The exact cause is unknown and there is no clear pattern of inheritance; the condition is sporadic. Mechanisms that may be involved:

• Vascular insult during development
• Teratogenic exposure
• Genetic factors, with rare familial cases reported
• Failure of mesenchymal condensation

Normal development. The proximal femur develops from mesenchymal condensation at 4-6 weeks' gestation. The femoral head, neck and greater trochanter develop from separate ossification centres that fuse during childhood.

What fails. In PFFD that development fails, and the result ranges across the Aitken types (see Classification):

• Shortened or absent proximal femur
• A short neck with coxa vara (Type A)
• Pseudarthrosis at the neck (Type B)
• Absent femoral head (Types C and D)
• A dysplastic acetabulum (Type C) or an absent one (Type D)
• Associated soft-tissue deficiencies of the muscles and ligaments

The rest of the limb. Understanding the whole-limb anatomy helps determine reconstruction feasibility and treatment planning. Associated deficiencies can change what is feasible more than the proximal-femoral label does:

• Fibular hemimelia, in 50% of cases
• Cruciate ligament deficiency, including anterior cruciate deficiency, and cruciate dysplasia; these are common, and the knee instability they bring affects function
• Foot anomalies, which are common: tarsal coalition, equinovarus and ray deficiency, alongside ankle deformity
• Patellar anomalies
• Tibial shortening, less common than fibular deficiency

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Two systems do different jobs. Aitken records femoral-head and acetabular morphology; Paley adds neck and subtrochanteric ossification and joint function. Neither substitutes for whole-limb assessment or shared decision-making.

Aitken ClassificationGillespie ClassificationPaley Classification

Aitken Classification (1969)

Aitken is the most widely used system, based on the radiographic appearance of the femoral head and acetabulum.

Type A

Femoral Head

Present

Femoral Neck/Connection

Short/deficient but connected

Acetabulum

Usually adequate

Interpretation

Potentially reconstructable morphology

What Still Must Be Defined

Continuity, coxa vara, hip stability, whole-limb function

Type B

Femoral Head

Present, often cartilaginous

Femoral Neck/Connection

No osseous continuity

Acetabulum

Present

Interpretation

MRI and mobility determine anatomy

What Still Must Be Defined

Cartilaginous connection, mobility, reconstructability

Type C

Femoral Head

Absent

Femoral Neck/Connection

Absent

Acetabulum

Present but dysplastic

Interpretation

Severe morphology; plan functionally

What Still Must Be Defined

Pelvic-femoral relationship and prosthetic options

Type D

Femoral Head

Absent

Femoral Neck/Connection

Absent

Acetabulum

Absent/severely deficient

Interpretation

Most severe morphology; plan functionally

What Still Must Be Defined

Residual limb, knee/ankle/foot function and goals

Aitken Classification Summary

Type	Femoral Head	Femoral Neck/Connection	Acetabulum	Interpretation	What Still Must Be Defined
Type A	Present	Short/deficient but connected	Usually adequate	Potentially reconstructable morphology	Continuity, coxa vara, hip stability, whole-limb function
Type B	Present, often cartilaginous	No osseous continuity	Present	MRI and mobility determine anatomy	Cartilaginous connection, mobility, reconstructability
Type C	Absent	Absent	Present but dysplastic	Severe morphology; plan functionally	Pelvic-femoral relationship and prosthetic options
Type D	Absent	Absent	Absent/severely deficient	Most severe morphology; plan functionally	Residual limb, knee/ankle/foot function and goals

In infants, radiographs can under-call a cartilaginous head or neck, so ultrasound or MRI may change the apparent class. Aitken does not encode the knee, ankle, foot, soft tissues, expected stature, family priorities or prosthetic access, and must not be used as a stand-alone treatment rule.

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Gillespie Functional Classification

Based on functional capacity rather than anatomy, it helps determine functional outcome and prosthetic needs.

• Group 1: Hip stable, foot at or near level of opposite knee
• Group 2: Hip stable, foot at level of opposite ankle
• Group 3: Hip unstable, foot at level of opposite ankle or lower

Paley Classification (for Lengthening)

Paley's classification of congenital femoral deficiency is used to plan lengthening: it determines the lengthening strategy and the need for hip or knee reconstruction. It maps neck and subtrochanteric ossification, femoral-head mobility, acetabular status and increasingly severe deficiency; the figure below shows each type and subtype. Type 1b hips, with a mobile femoral head, coxa vara/retroversion and delayed proximal ossification, are the pattern the SUPERhip procedure addresses, and in the 1b2 example under Investigations the femoral neck ossifies late and is cartilaginous on MRI.

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History. The short limb is noticed at birth or in early infancy. Walking may be delayed, a unilateral case may walk with a limp, and activities that require equal leg length are difficult. A family history is rare but may be present.

Inspection. The thigh is short, and the hip sits flexed, abducted and externally rotated, the pseudarthrosis position. The knee may be flexed in compensation. Note the position of the foot for associated anomalies, and compare with the other side.

Palpation. The proximal femur may be absent or very short. The greater trochanter may be palpable in Types A and B, or absent in Types C and D. Assess the stability of the hip and of the knee.

Range of motion. Hip flexion and abduction are limited. The knee may hyperextend or have a flexion contracture, and the ankle is checked for equinus or other deformity.

Limb length. Three measurements:

• True leg length - ASIS to medial malleolus
• Apparent leg length - umbilicus to medial malleolus
• Thigh length - greater trochanter to lateral joint line

Neurovascular. Neurovascular status is usually normal, but assess femoral nerve function, which may be affected in severe cases.

Radiographs. The AP pelvis and hip film answers the anatomical questions:

• Is the femoral head present? Its ossification may be delayed in Type A
• Is the acetabulum present, dysplastic or absent?
• The coxa vara angle, in Type A
• A pseudarthrosis, in Type B

Full-length standing radiographs measure the limb-length discrepancy and alignment, and show associated anomalies such as fibular hemimelia and tibial shortening.

MRI and ultrasound. MRI, when indicated, shows an unossified femoral head, the acetabular cartilage and the soft tissues, muscles and ligaments; in Type A a head may appear absent on X-ray yet be present on MRI. In infants, ultrasound may identify an unossified femoral head and assesses hip stability.

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Predicting the discrepancy. Prediction is a range, checked against serial growth, skeletal maturity and prior operations. Two methods:

• Multiplier method - current LLD × the multiplier for age and sex = predicted final LLD
• Paley method - more complex, and accounts for growth remaining

What the number decides. Discrepancy is one variable. It is integrated with hip, knee, ankle and foot function, stature, deformity, surgical burden and prosthetic options, and there is no universal 15-centimetre branch.

Genetic evaluation. Genetic evaluation is usually not indicated, as the condition is sporadic. Consider it if the deficiency is bilateral or there is a family history.

The shortened, abnormally positioned thigh of PFFD overlaps with several other causes of a congenitally short femur or limb-length discrepancy. The discriminator is the state of the proximal femur, hip and the rest of the limb.

The questions that frame rotationplasty counselling, once the options are on the table:

The SUPERhip is one technically demanding reconstructive strategy for selected Paley Type 1b hips with a mobile femoral head, coxa vara/retroversion, delayed proximal ossification and extra-articular contractures. It may prepare a stable hip for later lengthening, but it does not guarantee it, and it is not required for every reconstructable CFD hip.

Core elements are selected from the demonstrated deformity:

• Release flexion-abduction-external-rotation contractures while protecting neurovascular structures and preserving muscle function
• Correct proximal-femoral varus and rotation with stable fixation suited to bone size and ossification
• Restore abductor mechanics, and address acetabular deficiency only when clinically or radiographically indicated
• Confirm containment and preserve a hip able to tolerate the intended future pathway

Risks. Recurrent coxa vara, persistent delayed neck ossification, stiffness, hardware problems and revision are material risks. Candidacy, fixation, acetabular work and biologics are individual decisions.

Fixation and BMP-2. Retrospective developer-centre data associate fixed-angle fixation and BMP-2 use with improved radiographic ossification and maintenance, but the technique evolved alongside experience. Off-label biologic use requires jurisdiction-specific governance and cannot be presented as mandatory.

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An extension or equinus prosthesis is a limb-preserving option: the intact shortened limb and foot fit within a custom socket that restores length and provides a prosthetic knee and foot arrangement. Socket design and foot position are individual, and maximal fixed equinus is not a universal requirement.

Advantages and trade-offs. It is reversible and avoids irreversible bony conversion at that stage. The trade-offs are bulk, limb-length asymmetry while sitting, skin pressure, joint posture and contracture, frequent refitting with growth, and dependence on specialist prosthetic services.

Suitability. Discuss it alongside reconstruction, rotationplasty and ablative prosthetic pathways. Fit, skin, joint position, function, appearance and service access determine suitability.

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Complications follow the selected pathway and the child's baseline anatomy.

Prevention means realistic target selection, protection of hip, knee and ankle motion, neurovascular surveillance, early response to pain or loss of function and coordinated rehabilitation, not simply more aggressive therapy.

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Aftercare is specific to the construct and the pathway:

• Immediate: analgesia, wound, skin and neurovascular monitoring, safe positioning, thrombosis and infection measures where indicated, and family education
• Reconstruction: protect fixation according to bone quality and osteotomy and hip stability; restore motion without jeopardising containment
• Lengthening: review the distraction prescription, regenerate, axis, pin or device sites, pain, nerve function and hip, knee and ankle motion frequently enough to act before fixed contracture or subluxation
• Rotationplasty or ablative surgery: protect union and soft tissues, preserve ankle and foot or residual-limb health, and begin prosthetic planning with the rehabilitation team
• Extension prosthesis: monitor skin, joint posture, socket fit and growth-related refitting

Long-term review tracks growth, discrepancy, alignment, joint stability, muscle power, prosthetic fit, participation and the child's evolving preferences. Calendar intervals follow the rate of change and the treatment window rather than a universal annual schedule.

Outcome evidence is dominated by single-centre retrospective series, developer cohorts and a small gait-laboratory comparison. Radiographic correction is not the same as mature function.

• Reconstruction and lengthening: can create a stable aligned limb in selected anatomy, but may require staged surgery and exposes the hip, knee, regenerate and hardware to repeated risk
• Rotationplasty: can support durable prosthetic ambulation in selected patients; derotation, revision, appearance and lifelong prosthetic care remain relevant
• Ablative prosthetic pathway: may reduce reconstruction burden but is irreversible, and introduces residual-limb, overgrowth or neuroma, socket and prosthetic-knee issues
• Extension prosthesis: preserves anatomy and defers irreversible conversion, but requires ongoing fit, skin and joint-posture management

Measure participation, pain, joint health, operation count, psychosocial outcomes and the child's own priorities, not only limb length or radiographic angles.

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There is no global PFFD guideline and no registry comparing complete lifetime pathways. Evidence comes from single-centre reconstruction series, prosthetic cohorts and small gait studies.

Multidisciplinary care includes paediatric limb reconstruction, rehabilitation, prosthetics/orthotics, psychology/social support and—when appropriate—genetics and vascular/plastic expertise. Consent must cover uncertainty, repeated operations/refitting and the possibility that the preferred pathway changes with growth.

Related pages: Fibular Hemimelia, Tibial Hemimelia, Coxa Vara, Rotationplasty, Limb Lengthening Principles, and Prosthetic Limb Components.

PFFD management is one of the more genuinely contested areas in paediatric limb reconstruction. Examiners reward candidates who can hold the uncertainty rather than reciting dogma.

• Rotationplasty versus amputation. The long-held belief that rotationplasty is functionally superior has been challenged. The JBJS 2021 gait-analysis comparison found no advantage in oxygen cost, gait deviation index or patient-reported outcomes over Syme amputation with a prosthetic knee, despite more operations. The counterpoint is that rotationplasty preserves an active joint with good long-term acceptance (Kowalczyk 2018) and durable, energy-efficient gait at very long follow-up in rotationplasty cohorts overall (Krebbekx 2026). The honest position: individualised, family-centred decision-making.

• Reconstruction/lengthening versus prosthetic management. With modern hip reconstruction and serial lengthening (SUPERhip-type strategies, motorized implants), some severe deficiencies once destined for amputation are now reconstructed. Critics note the burden of multiple operations, complications and uncertain long-term durability. There is no level-1 evidence comparing a full reconstructive pathway against early prosthetic conversion.

• Classification: Aitken versus Paley. Aitken is descriptive and widely known but does not directly guide reconstruction feasibility. The Paley classification is function- and reconstruction-oriented and increasingly used in lengthening centres. Candidates should know both and why the field is shifting.

• Implant choice in the young child. Intramedullary lengthening nails carry a femoral-head AVN risk in skeletally immature children, so external fixation or motorized expandable plates are used instead - but the plate evidence is early (small case series; Georgiadis 2022).

• Terminology. "Fibular hemimelia" is increasingly regarded as inaccurate; some authors prefer "postaxial/fibular longitudinal deficiency" and group PFFD with associated fibular and midline metatarsal deficiencies as a single dysvascular spectrum.