Delbet–Colonna Classification — Paediatric Femoral Neck Fractures

Overview & Why Paediatric Femoral Neck Fractures Are Different

Fractures of the femoral neck in children are rare but serious injuries, accounting for fewer than 1% of all paediatric fractures. Despite their rarity, they carry the highest rate of serious complications of any paediatric fracture — avascular necrosis (AVN) of the femoral head, coxa vara, premature physeal closure, and non-union. These complications profoundly affect long-term function and may necessitate complex reconstructive procedures or even total hip arthroplasty in young adulthood. The Delbet-Colonna classification, based on the anatomical level of the fracture, is the universal system for describing these injuries and directly guides prognosis, surgical approach, and the risk of AVN.

Epidemiology: peak incidence 5–10 years; male-to-female ratio approximately 1.5:1; most are high-energy injuries in older children (road traffic accidents, falls from height); in children under 5, a femoral neck fracture must raise the suspicion of non-accidental injury (NAI) or pathological fracture through underlying bone disease (metabolic bone disease, fibrous dysplasia, unicameral bone cyst); stress fractures of the femoral neck occur in young athletes
Vascular anatomy — the key to understanding AVN risk: in children, the femoral head blood supply is derived from: (1) the retinacular vessels (medial and lateral femoral circumflex arteries — MFCA and LFCA — running along the femoral neck beneath the capsule and periosteum); these are the dominant supply to the femoral head after infancy; (2) the artery of the ligamentum teres (obturator artery — the sole supply in infancy, progressively less important after age 8 years as the retinacular vessels develop); (3) the metaphyseal vessels (crossing the growth plate — important in infancy but limited after 4 years as the growth plate acts as a barrier); the more proximal the femoral neck fracture (Delbet Type I vs Type IV), the higher the disruption of retinacular vessels and the higher the AVN risk; intracapsular location = higher AVN risk (the fracture haematoma raises intracapsular pressure, compromising the retinacular vessels)

Delbet-Colonna Classification

Type	Anatomical Level	Description	AVN Risk	Frequency
Type I — Transphyseal	Through the proximal femoral physis (the growth plate between the femoral head and neck); the fracture passes through or just adjacent to the physis; the femoral head epiphysis is separated from the femoral neck	The most proximal fracture type; equivalent to a Salter-Harris Type I physeal fracture; the fracture line traverses the epiphysis-metaphysis junction; in children under 2 years, a transphyseal separation may not be visible on X-ray (the epiphysis is not yet ossified) — the hip appears dislocated; in infants, this injury is associated with birth trauma (difficult deliveries)	HIGHEST — ~100% in displaced Type I; the extreme proximity of the fracture to the femoral head epiphysis means that ALL retinacular vessels are disrupted at the time of fracture; even with perfect reduction, the already devascularised femoral head has a very high rate of AVN; some series report near-universal AVN in displaced Type I injuries	~8–10% of paediatric femoral neck fractures; the rarest type; associated with hip dislocation (Type IA) or without dislocation (Type IB); Type IA has even higher AVN risk
Type II — Transcervical	Through the MID-femoral neck (transcervical); the fracture passes through the middle of the femoral neck at right angles to the neck axis; entirely intracapsular; the most common type	The fracture line passes through the waist of the femoral neck; both displaced and undisplaced variants occur; the retinacular vessels are at high risk from the fracture haematoma (intracapsular haematoma raises pressure and kinks or compresses the vessels); urgency of treatment directly impacts AVN risk	HIGH — ~28–50% AVN in displaced fractures; ~10–20% in undisplaced; AVN risk is reduced by: (1) urgent aspiration of the intracapsular haematoma (reducing intracapsular pressure); (2) anatomical reduction within 24 hours; (3) internal fixation avoiding placement of screws through the proximal femoral physis	~45–50% of paediatric femoral neck fractures — the most common type
Type III — Cervicotrochanteric (Basiocervical)	At the base of the femoral neck — where the neck meets the trochanter; a fracture at the cervico-trochanteric junction; partially intracapsular, partially extracapsular depending on exact fracture position; the proximal femoral capsule inserts just above the intertrochanteric line anteriorly and at the posterior base of the neck posteriorly	The fracture is at the base of the femoral neck; lower risk than Types I and II because the retinacular vessels are less likely to be completely disrupted; the lateral circumflex femoral artery blood supply to the trochanteric region is preserved; the femoral head blood supply via the retinacular system may still be compromised depending on the direction of displacement	MODERATE — ~20–25% AVN in displaced fractures; substantially lower than Types I and II; the extracapsular/partially extracapsular location means the intracapsular haematoma pressure is lower and the retinacular vessels are less uniformly disrupted	~30–35% of paediatric femoral neck fractures
Type IV — Intertrochanteric	Between the greater and lesser trochanters — the intertrochanteric region; entirely extracapsular; the fracture is below the capsular insertion; equivalent to an adult intertrochanteric fracture in terms of anatomical location	Entirely extracapsular fracture; the femoral head blood supply via the retinacular vessels is NOT compromised by the fracture (the retinacular vessels run along the femoral neck — below the fracture line — and are not disrupted); no intracapsular haematoma; the periosteal blood supply to the trochanteric region is not disrupted	LOWEST — ~5–10% AVN; the extracapsular location means AVN risk is minimal; the main concerns for Type IV are: coxa vara (varus malunion from deforming forces — iliopsoas + abductors pull the proximal fragment into varus); non-union (less common than Types I–III); leg length discrepancy	~10–15% of paediatric femoral neck fractures; the rarest of the common types

Management Principles

Delbet Type	Treatment Principle	Fixation	Special Considerations
Type I	Urgent closed or open reduction + aspiration of hip haematoma + fixation; even with perfect management, AVN is frequent; the family must be counselled about the very high probability of AVN; in infants (transphyseal separation) — spica cast may be sufficient (the periosteum is intact; remodelling potential is high)	Smooth K-wires (crossing the physis in infants/young children) or cannulated screws NOT crossing the physis in older children; avoid screw purchase in the physis to reduce growth arrest risk	Type IA (with hip dislocation): urgent reduction of dislocation within 6 hours; AVN risk highest of any hip fracture type; counsel family regarding likely need for future THA in adulthood
Type II	URGENT surgical management within 24 hours (ideally within 6–8 hours of presentation); (1) Aspiration of the intracapsular haematoma — reduces intracapsular pressure and decompresses the retinacular vessels; (2) Anatomical closed or open reduction; (3) Internal fixation with cannulated cancellous screws	2–3 cannulated screws (placed parallel, below the proximal femoral physis — screws should NOT penetrate the physis as growth arrest would result); in older adolescents approaching skeletal maturity, screws may cross the physis; a sliding hip screw may be used for Type III and IV	The importance of urgency — delay beyond 24 hours dramatically increases AVN risk; haematoma aspiration should be performed before or at the time of fixation; the needle is inserted anteriorly along the femoral neck under fluoroscopic guidance
Type III	Surgical fixation (internal fixation); less urgent than Types I and II but still within 24 hours; reduction and fixation reduces AVN, coxa vara, and non-union risk; undisplaced Type III in young children may be managed with a spica cast with close radiological surveillance	Cannulated screws (not crossing the physis in growing children) or a paediatric sliding hip screw; valgus reduction to protect against coxa vara; fixation in slight valgus (corrects any tendency toward varus)	Coxa vara is the principal late complication; valgus fixation and stable internal fixation reduce this risk; if coxa vara develops → valgus intertrochanteric osteotomy
Type IV	Internal fixation (sliding hip screw or fixed-angle device) for displaced fractures; undisplaced Type IV in young children can be managed with a hip spica cast with careful radiological monitoring; displaced Type IV must be reduced and fixed to prevent coxa vara and varus malunion	Sliding hip screw or paediatric nail with anti-rotation screw; or spica cast in young children with undisplaced fractures; the intertrochanteric region heals reliably in children	Coxa vara: the deforming forces (iliopsoas, gluteus medius) tend to produce varus at the fracture — the neck-shaft angle decreases; the `deforming force` of the abductors pulls the greater trochanter proximally; varus malunion produces Trendelenburg gait, limb shortening, and poor hip abductor function

Complications

Avascular necrosis (AVN): the most feared and most common complication; overall AVN rate across all types approximately 30%; highest in Type I (up to 100% displaced) and Type II (28–50% displaced); the clinical presentation of AVN is variable — it may be apparent within 6–12 months (early collapse) or may not manifest for 2–3 years; radiological signs: sclerosis of the femoral head, subchondral fracture (crescent sign), flattening; MRI is the most sensitive investigation (T1 dark + STIR bright); treatment options: for mild AVN in young growing children — core decompression + bone grafting; for severe AVN with femoral head collapse — vascularised bone grafting (fibular graft); for end-stage AVN with secondary OA — THA (usually deferred until adulthood); the outcome is directly related to the extent of femoral head involvement
Coxa vara: varus deformity of the femoral neck (neck-shaft angle <120°); develops from malunion, non-union, or AVN with femoral head collapse; produces Trendelenburg gait, limb shortening, and hip abductor dysfunction; Hilgenreiner-epiphyseal (HE) angle >45° = at risk for progressive coxa vara; managed with valgus-extension intertrochanteric osteotomy when progressive or symptomatic
Premature physeal closure: the proximal femoral physis may close prematurely following injury or if internal fixation crosses the physis; resulting leg length discrepancy depends on the age at closure and the amount of remaining growth; monitor with serial scanograms; contralateral epiphysiodesis may be required for significant LLD
Non-union: less common than in adults (~5–10% overall in paediatric series); higher in displaced fractures and in those managed with inadequate fixation; treatment: revision fixation with bone graft (autologous iliac crest graft or vascularised bone graft for avascular segments); valgus osteotomy to convert shear forces to compression at the non-union site

Exam Pearls

Delbet classification: Type I = transphyseal (through the physis — highest AVN ~100% displaced); Type II = transcervical (through femoral neck waist — most common, AVN ~30–50%); Type III = cervicotrochanteric (base of neck — AVN ~20–25%); Type IV = intertrochanteric (extracapsular — lowest AVN ~5–10%)
AVN rule: the more proximal the fracture → the more intracapsular → the more retinacular vessels disrupted → the higher the AVN risk; Type I > II > III > IV for AVN risk; Type IV is extracapsular = minimal AVN risk
Haematoma aspiration: reducing intracapsular pressure by aspiring the haematoma before or at the time of fixation for Types I–III reduces AVN risk; must be done urgently (within 6–8 hours for Type I; within 24 hours for Types II–III)
Cannulated screws NOT crossing the physis: placing screws across the proximal femoral physis causes growth arrest → leg length discrepancy; in growing children, fixation must be below the physis; in adolescents approaching skeletal maturity, crossing the physis is acceptable
Type II (transcervical) = most common; most serious if displaced; urgency of reduction and fixation is critical; delay beyond 24 hours dramatically increases AVN risk; haematoma aspiration + anatomical reduction + cannulated screws
Coxa vara: neck-shaft angle <120°; HE angle >45° = progressive coxa vara risk; deforming forces = iliopsoas + abductors pull into varus; treat with valgus-extension intertrochanteric osteotomy
Type I in infants: transphyseal separation may not be visible on X-ray (epiphysis not yet ossified → appears as `hip dislocation`); birth trauma cause; arthrogram under GA confirms; smooth K-wires ± spica cast; high AVN risk even with perfect treatment
NAI consideration: femoral neck fracture in a child under 5 years + no adequate history of high-energy mechanism = must consider non-accidental injury (NAI) and pathological fracture; full safeguarding assessment and skeletal survey required

Delbet–Colonna Classification — Paediatric Femoral Neck Fractures

References

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