Angular Deformity - 15 Marks Structured Answer (KNRUHS)

Definition

• Normal femorotibial angle: The anatomic axes of femur and tibia form a laterally open angle of 174° at the knee (i.e., 6° of physiologic valgus).

Terminology / Types

Physiologic Angular Changes with Age (Normal Development)

Etiology / Causes

A. Congenital

• Congenital bowing of tibia (posteromedial / anterolateral)
• Coxa vara congenita
• Achondroplasia and skeletal dysplasias (disproportionately short extremities → genu varum; short trunk → genu valgum)
• Osteogenesis imperfecta

B. Developmental

• Physiologic - normal variant in children (see above)
• Blount's disease (tibia vara) - abnormal growth of posteromedial tibial physis
  • Infantile (0-4 yrs): bilateral, obese early walkers; internal tibial torsion; Drennan's metaphyseal-diaphyseal angle > 16° is pathologic; Langenskiold classification (Stages I-VI)
  • Adolescent (8-15 yrs): usually unilateral, obesity-related

C. Traumatic

• Malunion after fractures (commonest cause in adults)
• Physeal arrest after growth plate injury (Salter-Harris fractures, especially distal femur - high rate of angular deformity)
• Traction pin through proximal tibial physis → genu recurvatum
• Supracondylar fracture of humerus → cubitus varus (gunstock deformity) - most common angular deformity of elbow in children

D. Metabolic / Nutritional

• Rickets (nutritional, renal osteodystrophy, vitamin D-resistant) → genu varum/valgum
• Paget's disease → bowing of long bones

E. Infective

• Osteomyelitis/septic arthritis damaging growth plates → limb length discrepancy and angular deformity

F. Neoplastic

• Osteochondromas tethering growth → angular deformity (e.g., multiple hereditary exostoses)
• Fibrous dysplasia → "shepherd's crook" deformity of proximal femur

G. Neuromuscular

• Cerebral palsy, poliomyelitis → muscle imbalance → angular deformity

Clinical Assessment

History

• Age of onset, progression, family history, trauma, nutritional status
• Symptoms: pain, cosmetic concern, gait abnormality

Clinical Examination

• Genu varum: Measure intercondylar distance (knees together, feet together; >3 cm = abnormal)
• Genu valgum: Measure intermalleolar distance (knees together; >5 cm = abnormal)
• Cubitus varus/valgus: Measure carrying angle (normal 5-15° valgus in adults)

• Site, direction, degree of angulation
• Rotational deformity (often coexists)
• Leg length discrepancy
• Joint stability (ligamentous laxity vs. bony deformity)
• Neurovascular status

Radiological Assessment

• Full-length standing AP radiograph of lower limbs (scanogram) - from femoral head to ankle
• Measure:
  • Mechanical axis deviation (MAD): Distance of mechanical axis from center of tibial plateau (normal = 0-10 mm medial)
  • Mechanical lateral distal femoral angle (mLDFA): Normal = 88° ± 3°
  • Medial proximal tibial angle (MPTA): Normal = 87° ± 3°
  • CORA (Center of Rotation of Angulation): Point where bisectors of proximal and distal bone segments intersect - the apex of the deformity; guides the level of corrective osteotomy

Pathological Consequences of Untreated Angular Deformity

• Genu varum: Increased medial compartment loading → medial joint OA; lateral collateral ligament and iliotibial band tension; stress on lateral foot border
• Genu valgum: Increased lateral compartment loading → lateral joint OA; medial ligament stretching; patellofemoral maltracking
• Abnormal joint loading leads to premature osteoarthritis
• Limb length inequality if asymmetric
• Compensatory deformities in adjacent joints

Treatment

Conservative (Non-operative)

• Observation: Physiologic deformities in children self-correct with growth; reassure parents
• Bracing / Orthoses:
  • Infantile Blount disease (Langenskiold Stage I-II, age < 3 years): knee-ankle-foot orthosis (KAFO) used until age 3, then consider surgery if no improvement
  • Rickets: treat underlying metabolic cause; deformity may correct with medical management

Operative Treatment - Indications

• Deformity not correcting with growth/conservative measures
• Progressive deformity
• Symptomatic (pain, gait disturbance, limb length discrepancy)
• Angular deformity causing significant joint stress or secondary OA
• In post-fracture malunion: corrective osteotomy delayed at least 1 year unless function impaired

Osteotomy - Principles

• Opening wedge osteotomy: Bone defect filled with graft; opens on concave side; fixation with plate
• Closing wedge osteotomy: Bone removed on convex side; shortens limb slightly but more stable healing
• Dome (barrel vault) osteotomy: Used near physis; no limb length change
• Acute vs. gradual correction: Acute correction (osteotomy + plate/nail) vs. gradual (external fixator, Ilizarov, Taylor Spatial Frame)

Specific Procedures by Location

Epiphysiodesis / Guided Growth

• In skeletally immature patients with sufficient growth remaining
• Hemiepiphysiodesis: Temporary tethering of the growth plate on the convex side using staples or tension band plate (8-plate) to gradually correct the deformity
• Advantages: minimally invasive, gradual, reversible
• Used for Blount disease, rickets, idiopathic valgus/varus in children

Complications of Corrective Osteotomy

• Neurovascular injury (especially anterior tibial artery at HTO - compression with valgus correction, stretching with varus correction)
• Anterior compartment syndrome (post HTO)
• Peroneal nerve palsy
• Over/under-correction
• Delayed union / non-union
• Infection
• Late angular deformity recurrence (up to 46% in some series; revision rates 19-40%)

Summary Table