At what mechanical angle is an osteotomy (bone cutting procedure) justified?

Osteotomy Justification Based on Mechanical Angle

An osteotomy is justified at a mechanical angle above or below 85-90 degrees. 1

Understanding Mechanical Axis Deviation

The mechanical axis refers to the load-bearing axis of the limb. Deviation from normal alignment can lead to:

• Abnormal joint loading and progressive deformity 1
• Increased risk of joint degeneration and pain 2
• Functional limitations in mobility and activities 1

Clinical Guidelines for Osteotomy Decision-Making

Radiographic Indications

• Deviation of the mechanical axis into zones 3 or 4 requires surgical intervention 1
• Progressive deviation through zone 2 despite optimized medical care may merit treatment, especially in growing children 1
• The normal mechanical axis should be neutral (85-90 degrees) for optimal joint loading 1

Timing Considerations

• In children who are still growing, earlier intervention may be beneficial when the mechanical axis deviates significantly 1
• For guided growth techniques, intervention should occur at least 2-3 years before skeletal maturity (age 14 in girls, age 16 in boys) 1
• Complications associated with osteotomy reduce when performed later in childhood or after skeletal maturity 1

Surgical Approaches Based on Mechanical Axis Deviation

For Growing Children

• Guided growth techniques are preferred when the mechanical axis deviation is in zone 2 or greater 1
• This approach corrects deformity at the physis before significant diaphyseal deformity develops 1
• Both varus and valgus deformities can be corrected, though genu varum might respond less in adolescents 1

For Adolescents and Adults

• Osteotomies at the site of major deformity with correction in all three planes may be required 1
• Correction can be achieved through:
  • Acute correction with internal fixation 1
  • Gradual correction using external fixation techniques 1

Potential Complications and Considerations

• Surgery is associated with notable rates of recurrence and complications (57% of patients experienced at least one complication in one study) 1
• Recurrent deformity occurs in approximately 29% of patients 1
• Poor metabolic control increases complication risk, particularly in young children 1
• Single-plane rotational osteotomies generally do not cause clinically relevant changes in frontal or sagittal leg alignment when correction is ≤20° 3

Post-Surgical Monitoring

• Regular clinical and functional assessments should be performed 1
• Radiographic follow-up at 12 months post-surgery, or earlier if bone deformity worsens 1
• Further assessments should continue intermittently until skeletal maturity 1

Clinical Pearls

• Elective surgical treatment should only be performed after medical treatment has been maximized for at least 12 months 1
• Surgery should be performed by a surgeon with expertise in metabolic bone diseases 1
• The aim of surgical treatment is to achieve equal limb length, neutral lower limb mechanical axes, and horizontal knee and ankle joints 1
• Substantial deformity may exist in multiple planes, increasing surgical complexity 1