Coxa Vara

• Localised bony dysplasia of the femoral neck
• Characterised by a decreased neck shaft angle and the presence of a triangular ossification defect (Fairbanks Triangle) of the inferior femoral neck 
• Results in decreased length of the involved limb
• The normal neck shaft angle in a child is ~ 160^o, which decreases to about 120^o in the adult

Classification

• Congenital
  • Assumed to be a limb bud abnormality occurring in the developing embryo
  • May be difficult to differentiate from DDH
  • Significant varus present at birth, but usually minimal progression during growth
  • Associations
    • PFFD
    • Congenital short femur
    • Congenital bowed femur
• Developmental
  • Normal at birth
  • Develops coxa vara in early childhood
  • Progressive with growth
• Acquired : Due to neck bending due to bone softening or due to fracture
  • Softening
    • Children
      • Rickets
      • Bone dystrophies
      • Perthes
      • Fibrous dysplasia
      • SUFE
    • Adults
      • Osteomalacia
    • Elderly
      • Osteoporosis
      • Paget
    • Any age
      • Infection : TB or pyogenic
  • Fracture
    • Children
      • Bone cyst
    • Adult
      • Malunion of fracture
      • NOF

Incidence

• Rare, 1/ 25000 live births
• M = F
• R = L, Bilateral in 30%
• Autosomal dominant inheritance pattern
• May be more common in black race

Aetiology

• Histological abnormalities have been found in biopsy of the femoral necks
  • Width of the growth plate
  • Absence of normal orderly progression of cartilage columns, similar to appearance of Blounts disease
• Current theory : deformity due to a primary ossification defect in the inferior femoral neck
• Physiologic shearing stresses in weight bearing fatigues the abnormal bone, leading to progressive deformity

Clinically

• Most present with a progressive gait deformity between walking age and  6 y/o
• Pain is rare
• Unilateral disease presents with gait abnormality 2^o to abductor weakness and LLD
• Bilateral disease presents with waddling gait similar to that of DDH

Examination

• Prominent and elevated greater trochanter
• Positive Trendelenberg
• LLD usually mild, average 2.5 cm
• FFD with ROM, esp. abduction and internal rotation

X-Ray

• Neck- shaft angle changed
• More vertical position of the physeal plate
  • Defined by the angle between Hilgenreiners line and the line through the epiphyseal plate
  • Normally 25^o or less
• Fairbanks triangle 
  • A triangular metaphyseal fragment in the inferior femoral neck surrounded by an inverted radiolucent Y 
  • Represents a zone of abnormal ossification with an interposed triangular segment of dystrophic bone
• Coxa breva
• Rarely mild acetabular dysplasia

Natural History

( Weinstein etal, J Paediatr Orthop 1984; 470)

• The determining factor for progression is the epiphyseal angle
• If remains less than 45°, femoral neck defect usually heals spontaneously and do not progress
• If more than 45°, will progress, ultimately resulting in the development of a stress fracture related nonunion of the femoral neck, as well as premature degenerate changes in the hip joint by late teens

Treatment

Conservative treatment has no value

Aim to

• Correct neck-shaft angle to a more physiologic range
• Change load from shear to compression at physis
• Correct LLD
• Restore proper length-tension relation for the abductors

Surgery

• Valgus proximal femoral osteotomy either inter-trochanteric or sub-trochanteric
• Internally fixed to maintain correction
• Combine with adductor release to allow easier correction of the deformity at the osteotomy
• Indications
  • Epiphyseal angle 45° - 60°
    • Observe
    • If progresses proceed to operation
  • >60° : Operation
  • Shaft- neck angle less than 90°
  • Development of Trendelenberg gait
• Aim is to over correct to a neck- shaft angle of more than 160°, an epiphyseal angle of 30° or less
• Operate when child is younger, remodelling is better in young patient

Prognosis

• Spontaneous healing of metaphyseal defect within 3 - 6 months, if adequate valgus achieved
• 50- 89% of operated hips develop premature closure of the proximal femoral physis
  • Usually within 2 years of surgery
  • If it occurs, need to monitor for recurrence of deformity or LLD
• To prevent recurrence of deformity, due to premature closure of physis, greater trochanteric apophyseodesis or advancement can be performed
• If recurrent deformity occurred, repeat osteotomy

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