Distraction Osteogenesis is based on the law of distraction neohistogenesis which is ” when tissue is fixed with a stable device subjected to planar distraction forces after an atraumatic corticotomy, new tissue formation occurs in the presence of intact vascularity and maintained function.
New tissue formation: Not only new bone between osteotomized bony cut ends but also a new muscle, tendon, connective tissue, blood vessels, nerves, skin, and integuments
The principle of Distraction osteogenesis is given by Gavriil Abramovich Ilizarov (15 June 1921 – 24 July 1992)
So Ilizarov’s technique works in the above-mentioned principles
7-Rules of Distraction Osteogenesis (Ilizarov techniques)
Principles of Distraction Osteogenesis are summarized as:
Rule 1: Stability of fixation
- Painfree mobilization and weight-bearing are essential
- Stability can be increased by more fixation pins, more connection of pins to circular rings having small diameter rings
- If reduced stability, regenerate formation will be poor, patchy, and nonhomogenous or absent
Rule 2: Atraumatic corticotomy
- Corticotomy:- Formation of physics anywhere in bone after skeletal maturity
- Performed after minimal invasive procedure (5 mm) incision
- Cut only the hard part of the bone and preserve the periosteum
- In the end: Bony fragment shouldn’t be displaced and must remain in contact with no separation of bony ends
Rule 3: Latency Period
- 5-7 days of latency is required before starting distraction at corticotomy site
- The younger patient requires less time: 4-5 days
- The older patient requires more time: 10-15 days
- Soft tissue good: Decrease latency
- Percutaneous corticotomy ( By drill holes): Decrease latency
Rule 4: Rate of distraction
- In well-vascularized tissue, a rate of 1mm/day can produce good regenerate bones
- In bone with poor blood supply: Rate can be halves
- Poliomyelitis
- Thromboangitis obliterans
- Younger children in the femur, Achrondoplasia: rate can be doubled
Rule 5: Rhythm of distraction
- Rate 1mm/day-> distraction into 4 distraction turns each 0.25mm/day
- Higher rhythm: better bone formation
- Lower rhythm ( 0.5 mm twice daily, 1 mm daily): slow down bone formation
Rule 6: Intact Vascularity
- Essential for good bone formation
- Limb has undergone radiation-> Less likely to form bone
Rule 7: Preserved function
- New bone formation occurs best when the patient is able to walk and retain its function
- An exercise regime of 4-6 hr/day gives the best result, regenerate formation in homogenous and bone hardens quickly
Phases of Limb Lengthening in Ilizarov
Latency
During this period the construct is kept still with no lengthening.
5-15 days
Lengthening
- 1 mm/day
- For 6 days/week
- 1 inch/month
- Should be monitored radiologically
If regenerate bone formation is patchy, non-homogenous or defective==> better to slow down distraction
Sometimes it is better to stop distractions together for a few days
Hardening
After lengthening ends, can last for 2-3 times as long as the lengthening phase
Adequate Stability+ Resumption of function + Good nutrition ensure hardening
Formation of at least 5 cortical walls (out of 8) as seen in AP, lateral and 2 oblique views is necessary for removal of Ilizarov apparatus and prevention of refracture or bending of bone.
See also: External Fixator Principles
