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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 ~ 160o, which decreases to about 120o 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 2o 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 25o 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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