High Yield Overview

LIMB LENGTHENING PRINCIPLES

Distraction Osteogenesis | Ilizarov Technique | Regenerate Formation

1mm/dayStandard distraction rate

0.25mmQID rhythm (4 times daily)

5-7 daysLatency period before distraction

1 month/cmConsolidation time rule

PHASES OF DISTRACTION OSTEOGENESIS

Latency Phase

Pattern5-7 days post-corticotomy

TreatmentAllow callus initiation

Distraction Phase

PatternActive lengthening 1mm/day

TreatmentMonitor regenerate, ROM

Consolidation Phase

PatternRegenerate mineralization

TreatmentPartial weight-bearing

Remodeling Phase

PatternCortical remodeling

TreatmentFull weight-bearing, frame removal

Critical Must-Knows

Distraction rate: 1mm/day in 4 divided doses (0.25mm QID)
Latency period: 5-7 days (longer in adults, smokers)
Consolidation: Approximately 1 month per cm of lengthening
Maximum safe lengthening: Generally 20% of original bone length
Corticotomy vs osteotomy: Corticotomy preserves periosteum and medullary blood supply

Examiner's Pearls

"
Ilizarov discovered distraction osteogenesis principles in Kurgan, Russia
"
Faster distraction causes fibrous tissue; slower causes premature consolidation
"
Healing index = days in frame / cm lengthened (normal 30-45 days/cm)
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Regenerate problems: Too fast = cyst/fibrous; Too slow = premature consolidation

Clinical Imaging

Imaging Gallery

A 52-year-old man with bone lengthening following the Ilizarov procedure.A. The anterior-posterior radiograph shows multiple bone defects with the Ilizarov external fixator. B. Sonogram shows an anech — A 52-year-old man with bone lengthening following the Ilizarov procedure.A. The anterior-posterior radiograph shows multiple bone defects with the IliCredit: Chun KA et al. via Ultrasonography via Open-i (NIH) (Open Access (CC BY))

A variety of external fixators are used for fracture fixation, most often for tibia fractures as demonstrated here. (A) Clinical image of an Ilizarov external fixator applied to a fractured leg, with — A variety of external fixators are used for fracture fixation, most often for tibia fractures as demonstrated here. (A) Clinical image of an Ilizarov Credit: Open-i / NIH via Open-i (NIH) (Open Access (CC BY))

(a) Preoperative AP and lateral X-rays of left thigh including hip and knee. (b) Lengthening performed over a modified Humerus nail 7.5 cm length achieved. External fixator was removed in 13 weeks. (c — (a) Preoperative AP and lateral X-rays of left thigh including hip and knee. (b) Lengthening performed over a modified Humerus nail 7.5 cm length achiCredit: Chaudhary M et al. via Indian J Orthop via Open-i (NIH) (Open Access (CC BY))

25 year old lady had 12 cm shortening of her femur due to growth arrest. (a) AP and lateral X-rays of thigh including hip and knee. (b) LON method with rapid bone formation lead to premature consolida — 25 year old lady had 12 cm shortening of her femur due to growth arrest. (a) AP and lateral X-rays of thigh including hip and knee. (b) LON method witCredit: Chaudhary M et al. via Indian J Orthop via Open-i (NIH) (Open Access (CC BY))

Critical Limb Lengthening Exam Points

Distraction Rate

1mm per day is the standard rate, divided into 4 increments of 0.25mm (QID rhythm). Faster distraction causes fibrous regenerate or cyst formation. Slower distraction causes premature consolidation. Adjust based on regenerate quality on X-ray.

Latency Period

5-7 days in children, 7-14 days in adults. This allows initial callus formation before distraction begins. Shorter latency risks poor regenerate; longer risks premature consolidation. Smokers and diabetics need longer latency.

Corticotomy Technique

Corticotomy (not osteotomy) preserves periosteum, medullary blood supply, and marrow contents. Low-energy technique with multiple drill holes and osteotome completion. Minimally invasive approach preferred to preserve biology.

Soft Tissue Management

Soft tissues limit lengthening - muscles, nerves, vessels all resist distraction. Physiotherapy essential throughout. Monitor for joint contractures, nerve symptoms. Maximum safe lengthening is 20% of original length per session.

External Fixation vs Internal Lengthening Nail

Feature	External Fixator (Ilizarov/TSF)	Internal Lengthening Nail (PRECICE)
Pin site care	Required daily	None
Patient comfort	Lower - frame cumbersome	Higher - no external device
Simultaneous deformity correction	Excellent (6 axes)	Limited
Infection risk	Pin site infections common	Lower
Cost	Lower	Higher (implant cost)
Ideal indication	Complex deformity + lengthening	Isolated lengthening

Mnemonic

LDCRDistraction Osteogenesis Phases

Latency

5-7 days - initial callus formation

Distraction

1mm/day in 4 divided doses

Consolidation

1 month per cm - regenerate mineralizes

Remodeling

Cortical remodeling after frame removal

Memory Hook:Latency-Distraction-Consolidation-Remodeling: The 4 phases of regenerate formation!

Mnemonic

BLOODFactors Affecting Regenerate Quality

Blood supply preserved

Periosteum, endosteum intact

Low-energy corticotomy

Minimal thermal necrosis

Optimal rate (1mm/day)

Not too fast, not too slow

Osteogenic cells preserved

Marrow elements retained

Distraction rhythm (QID)

Small frequent increments

Memory Hook:Good BLOOD supply and technique = good regenerate!

Mnemonic

PAIN JCComplications of Lengthening

Pin site infection

Most common complication

Axial deviation

Angulation during lengthening

Inadequate regenerate

Cyst, fibrous tissue

Nerve injury/neuropraxia

Stretch neuropathy

Joint contracture/subluxation

Soft tissue tethering

Consolidation problems

Delayed/premature

Memory Hook:Lengthening causes PAIN JC - but manageable with good technique!

Overview and Epidemiology

Limb lengthening utilizes the biological principle of distraction osteogenesis to generate new bone within a gradually widening gap created by controlled separation of bone ends. First described by Codivilla in 1905 and refined by Ilizarov in the 1950s, it has revolutionized treatment of limb length discrepancy and short stature conditions.

Indications:

Congenital: Fibular hemimelia, congenital femoral deficiency, hemihypertrophy
Developmental: Achondroplasia, hypochondroplasia, other skeletal dysplasias
Acquired: Post-traumatic, post-infection, post-tumour resection
Limb length discrepancy: Greater than 2.5cm predicted at maturity

Contraindications:

Active infection
Poor soft tissue envelope
Inadequate bone stock
Poor patient compliance
Uncontrolled vascular disease
Severe psychological issues

Radiographs showing congenital limb length discrepancy requiring distraction osteogenesis — Indications for limb lengthening - congenital limb deficiency: (A) Anteroposterior radiograph of 1-day-old infant showing congenital short femur with significant limb length discrepancy compared to contralateral side. (B) Same patient at 7 months with external fixator in place, demonstrating early initiation of lengthening treatment. Congenital conditions including fibular hemimelia and congenital femoral deficiency are primary indications for distraction osteogenesis.Credit: Alzahrani MM et al., Front Endocrinol - PMC4261813 (CC-BY)

Historical Context

Gavriil Ilizarov developed the principles of distraction osteogenesis while treating World War II veterans in Kurgan, Siberia. His work remained unknown in the West until the 1980s when Italian surgeons visited his institute. The "tension-stress effect" describes how gradual traction stimulates tissue regeneration.

Pathophysiology

Understanding the biology of distraction osteogenesis is fundamental to successful limb lengthening.

The Tension-Stress Effect

Ilizarov's principle:

Gradual traction on living tissues creates stress that stimulates regeneration
Applies to bone, soft tissues, blood vessels, nerves, skin
Optimal tension maintains cellular viability while stimulating proliferation
Too much tension = ischemia and tissue death
Too little tension = insufficient stimulation

Biology of Bone Regeneration

Histological zones in regenerate:

Fibrous interzone: Central region of collagen fibers aligned parallel to distraction
Primary mineralization front: Active osteoid formation at bone ends
Microcolumn formation: Longitudinal columns of bone forming
Remodeling zone: Mature lamellar bone formation

Cellular response:

Periosteal and endosteal osteoprogenitor cells activated
Angiogenesis critical for regenerate formation
Mechanical strain drives mesenchymal stem cell differentiation
Growth factors (BMP, VEGF, TGF-beta) upregulated

Optimal Conditions for Regenerate

Corticotomy technique:

Low-energy technique preserving periosteum
Multiple drill holes followed by osteotome completion
Minimally invasive approach preferred
Avoid saw (thermal necrosis) or Gigli wire (periosteal stripping)

Rate and rhythm:

1mm/day is optimal for most situations
Divided into 4 increments (0.25mm QID) better than single daily adjustment
Continuous distraction (motorized devices) may be superior
Adjust based on regenerate appearance

Rate Adjustment

Regenerate quality guides rate adjustment. Cystic/poor regenerate = slow down to 0.5-0.75mm/day. Premature consolidation = speed up to 1.5mm/day or perform regenerate "accordioning" (compress then re-distract). Always assess regenerate on orthogonal X-rays.

Clinical Presentation

Patient Assessment

History:

Aetiology of limb length discrepancy
Functional limitations and goals
Previous surgery
Medical comorbidities (diabetes, smoking - affect healing)
Psychological readiness for prolonged treatment

Physical examination:

Accurate limb length measurement (blocks, CT scanogram)
Joint range of motion
Muscle strength and soft tissue quality
Neurovascular status
Skin condition and previous scars

Limb Length Discrepancy Measurement

Clinical methods:

Block method with standing
Tape measure (ASIS to medial malleolus)
Galeazzi test for femoral vs tibial discrepancy

Imaging methods:

CT scanogram: Gold standard, accurate to 1mm
Standing long-leg radiograph: Also shows alignment
EOS imaging: Low radiation, full-length imaging

Prediction of Discrepancy at Maturity

Methods:

Moseley straight-line graph
Multiplier method (Paley)
Anderson-Green growth remaining charts

Decision thresholds:

Less than 2cm: Shoe lift, observe
2-5cm: Epiphysiodesis or lengthening
Greater than 5cm: Lengthening (possibly staged)

Investigations

Preoperative Imaging

CT scanogram:

Accurate measurement of bone lengths
Assessment of bone quality
Deformity analysis

Long-leg standing radiographs:

Mechanical axis assessment
Joint orientation angles
Planning for concurrent deformity correction

MRI:

Soft tissue assessment
Physeal mapping if epiphysiodesis considered
Intramedullary canal assessment for nail

Vascular Assessment

Indications for angiography:

Previous vascular injury
Absent pulses
Congenital limb deficiency (vessel anomalies common)
Large lengthening planned (greater than 5cm)

Psychological Assessment

Important in:

Cosmetic lengthening (achondroplasia)
Adolescent patients
Multiple previous surgeries
Complex family dynamics

AP and lateral radiographs of proximal tibia during distraction osteogenesis showing regenerate — Radiographic monitoring during distraction osteogenesis: (a) Anteroposterior and (b) lateral radiographs of the proximal tibia 4 months into lengthening. The circular external fixator is visible with regenerate bone forming in the distraction gap. Note the 'asymmetric scalloping' of the posterolateral aspect of the regenerate - this radiological sign can indicate pseudoaneurysm complication and requires vigilant monitoring. Orthogonal radiographs are essential for assessing regenerate quality and guiding rate adjustments.Credit: Fagg J et al., Strategies Trauma Limb Reconstr - PMC3225571 (CC-BY)

Management

Corticotomy Technique

Principles:

Low-energy technique to preserve biology
Metaphyseal location preferred (better blood supply)
Minimally invasive approach

Technique:

Small incision at planned osteotomy site
Apply external fixator or prepare for nail
Multiple drill holes circumferentially through cortex
Complete osteotomy with osteotome
Confirm mobility of bone ends
Wound closure

Frame application:

Ilizarov: Rings with tensioned wires and half-pins
TSF: Hexapod system with struts for multiplanar correction
Monolateral: Rail fixator, simpler but less versatile

For internal lengthening nail:

Corticotomy as above
Ream canal
Insert lengthening nail (PRECICE or similar)
Lock proximally and distally
Confirm device activation

This section covers surgical technique.

Surgical Management

Device Selection

External Fixation Devices

Ilizarov circular fixator:

Classic ring fixator with tensioned wires
Excellent stability
Allows weight-bearing
Complex application, steep learning curve

Taylor Spatial Frame (TSF):

Hexapod based on Stewart platform
Computer-assisted deformity correction
Six-axis control simultaneously
Web-based planning software

Monolateral fixators:

Rail-based systems
Simpler application
Less versatile for deformity correction
May have higher complication rates

Advantages:

Can correct deformity simultaneously
Lower implant cost
Can adjust postoperatively
Suitable for complex cases

Disadvantages:

Pin site care burden
Pin site infections common
Patient discomfort
Cosmetically unacceptable to some

This section covers external fixation options.

Complications

Bone Complications

Premature consolidation: Rate too slow, requires re-osteotomy
Delayed consolidation: Rate too fast, bone grafting may be needed
Regenerate fracture: After frame removal, protect with cast/brace
Axial deviation: Angulation during lengthening, adjust fixator

Soft Tissue Complications

Joint contracture: Most common, aggressive physiotherapy essential
Joint subluxation/dislocation: Over-lengthening, reduce length
Nerve injury: Stretch neuropathy, slow or stop distraction
Vascular compromise: Rare, urgent assessment needed

Pin Site Complications

Pin site infection: Most common overall (30-100% incidence)
Pin tract osteomyelitis: Rare but serious
Pin loosening: May require replacement

Device Complications

Frame instability: Construct failure, revision
Nail mechanical failure: Device malfunction, exchange

Complication Prevention

Joint contractures are the most significant functional complication. Aggressive physiotherapy from day one is essential. Consider prophylactic soft tissue releases (Achilles lengthening, knee capsulotomy) for large lengthenings. Monitor joint ROM at every visit.

Evidence Base

Distraction Rate Optimization

Ilizarov GA • Clin Orthop Relat Res (1989)

Key Findings:

1mm/day optimal rate for regenerate formation
Divided doses (4x/day) superior to single daily increment
Rate adjusted based on regenerate quality

PRECICE Nail Outcomes

III

Kirane YM et al. • J Bone Joint Surg Am (2014)

Key Findings:

Fewer pin-related complications
Good regenerate formation
Mechanical failures in early series addressed in newer designs

Lengthening Over Nail vs External Fixation

III

Rozbruch SR et al. • Clin Orthop Relat Res (2008)

Key Findings:

Reduced external fixation time
Acceptable infection rates
Good regenerate healing

Consolidation Index

Paley D • J Pediatr Orthop (1990)

Key Findings:

Healing index 30-45 days/cm is normal
Higher index indicates delayed healing
Useful for comparing techniques and outcomes

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

Scenario 1: Limb Length Discrepancy Planning

EXAMINER

"A 10-year-old boy with left fibular hemimelia has a predicted limb length discrepancy of 6cm at maturity. His parents ask about treatment options."

EXCEPTIONAL ANSWER

Thank you. A predicted 6cm limb length discrepancy at maturity is significant and warrants active intervention. Options include epiphysiodesis of the contralateral limb (if discrepancy allows), limb lengthening, or a combination. For 6cm, lengthening is typically required as epiphysiodesis alone would create unacceptable short stature. I would plan staged lengthening if needed, typically limiting each session to 4-5cm or 20% of bone length. Given his age, we have time to complete lengthening before skeletal maturity. I would obtain accurate measurements with CT scanogram, use the multiplier method for prediction, and plan the procedure. Options include external fixation (Ilizarov or TSF) or internal lengthening nail when the canal is mature enough. I would discuss the prolonged treatment time, complications, and physiotherapy requirements with the family.

KEY POINTS TO SCORE

6cm discrepancy requires lengthening

Maximum 4-5cm or 20% per session

CT scanogram for accurate measurement

Consider staged procedures if needed

COMMON TRAPS

✗Recommending only epiphysiodesis for large discrepancy

✗Planning excessive lengthening in single session

✗Not discussing complications and treatment duration

LIKELY FOLLOW-UPS

"How do you predict discrepancy at maturity?"

"What are the complications of lengthening?"

"When would you use external vs internal device?"

VIVA SCENARIOStandard

Scenario 2: Poor Regenerate

EXAMINER

"You are 3 weeks into tibial lengthening on a 14-year-old with an Ilizarov frame. X-rays show a cystic regenerate with poor bone formation. The distraction rate has been 1mm/day."

EXCEPTIONAL ANSWER

Thank you. A cystic or poor regenerate at 3 weeks indicates the distraction rate is too fast for this patient's biology. My immediate management would be to slow the distraction rate to 0.5-0.75mm/day. I would also review patient factors: Is he a smoker, is nutrition adequate, does he have any metabolic bone disease? I would check vitamin D levels. If the regenerate does not improve over the next 2-3 weeks with reduced rate, I would consider accordion maneuver - compressing the regenerate slightly then resuming distraction to stimulate osteogenesis. In refractory cases, bone grafting of the regenerate site may be needed. I would continue monitoring with weekly X-rays and ensure physiotherapy is maintained to prevent joint stiffness.

KEY POINTS TO SCORE

Cystic regenerate = distraction too fast

Slow rate to 0.5-0.75mm/day

Check patient factors: smoking, nutrition, vitamin D

Accordion maneuver or bone grafting if refractory

COMMON TRAPS

✗Continuing at same rate

✗Stopping distraction completely

✗Not investigating patient factors

LIKELY FOLLOW-UPS

"What is the accordion maneuver?"

"When would you bone graft a regenerate?"

"How do you know when to remove the frame?"

VIVA SCENARIOStandard

Scenario 3: Joint Contracture

EXAMINER

"A 16-year-old undergoing femoral lengthening for post-traumatic shortening develops a 30-degree knee flexion contracture at 4cm of lengthening. Target is 5cm."

EXCEPTIONAL ANSWER

Thank you. A 30-degree knee flexion contracture during femoral lengthening is a common and concerning complication. The rectus femoris and other knee extensors are under tension from the lengthening. My management would first be to intensify physiotherapy with aggressive stretching and splinting. I would consider serial casting or dynamic splinting. If the contracture is not improving, I should reduce the distraction rate or temporarily pause distraction. If we are close to target (4 of 5cm), I may accept slightly less lengthening to preserve function. For severe or refractory contractures, surgical release may be needed - quadriceps lengthening or distal femoral extension osteotomy. Prevention is key - physiotherapy from day one, and considering prophylactic releases for large lengthenings.

KEY POINTS TO SCORE

Knee flexion contracture common in femoral lengthening

Intensify physiotherapy, splinting

May need to slow or stop distraction

Consider surgical release if refractory

COMMON TRAPS

✗Ignoring the contracture and continuing lengthening

✗Not involving physiotherapy

✗Pushing to achieve full target length despite complications

LIKELY FOLLOW-UPS

"What is the maximum safe lengthening per session?"

"How would you prevent this complication?"

"What surgical releases are available?"

Australian Context

In Australia, limb lengthening is performed at specialized limb reconstruction units within major paediatric and adult hospitals. The procedure requires multidisciplinary input including orthopaedic surgeons with limb reconstruction training, specialized physiotherapists, and often psychological support.

Device availability:

External fixation systems (Ilizarov, TSF): Widely available
PRECICE internal lengthening nail: Available but expensive (approximately $15,000-20,000 implant cost)
Both approaches available in major centres

Management requires significant patient commitment to the prolonged treatment course, daily pin site care (for external fixation), and intensive physiotherapy. Australian centres typically follow international protocols with 1mm/day distraction and careful monitoring of regenerate quality. Patient selection is critical, with psychological assessment recommended for cosmetic lengthening cases such as achondroplasia.