High Yield Overview
BONE TRANSPORT TECHNIQUES
Segmental Defects | Distraction Osteogenesis | Docking Site
1mm/dayStandard transport rate
4-8cmTypical defect size treatable
DockingCritical site requiring bone graft
2-3cm/monthTransport rate achievable
BONE TRANSPORT METHODS
Monofocal Transport
PatternSingle osteotomy, transport in one direction
TreatmentSimple defects
Bifocal Transport
PatternTwo osteotomies, transport from both ends
TreatmentLarge defects, faster treatment
Trifocal Transport
PatternThree osteotomies, three segments
TreatmentVery large defects
Bone Transport over Nail
PatternExternal fixator + IM nail
TreatmentReduces frame time
Critical Must-Knows
- Transport rate: 1mm/day standard, same as lengthening
- Docking site: Where transported segment meets target - often requires bone graft
- Regenerate: New bone forming at osteotomy site during transport
- Bifocal: Two osteotomies halve the transport distance each segment travels
- Shortening-lengthening: Alternative for infected defects - acute shortening then gradual lengthening
Examiner's Pearls
- "Defects greater than 4cm generally require transport rather than bone graft alone
- "Docking site union is the Achilles heel - expect 25-50% need bone grafting
- "Infected nonunion: Debride, external fixation, transport through healthy bone
- "Consider prophylactic fibular osteotomy for tibial transport
Clinical Imaging
Imaging Gallery
Click to expand
Clinical Imaging
Imaging Gallery
Critical Bone Transport Exam Points
Docking Site Management
The docking site is where the transported bone meets the target bone. Union here is unpredictable. Plan for bone grafting in 25-50% of cases. Options: Autograft, refresh ends, compression across site, combined approach.
Indications
Segmental bone loss greater than 4cm - transport preferred over bone grafting alone. Also for: post-traumatic defects, tumor resection gaps, infected nonunion with bone loss. Consider patient factors and compliance.
Regenerate vs Docking
Regenerate (at osteotomy site) - usually heals well if biology preserved. Docking site - often problematic, avascular bone ends meeting. Different management: Regenerate = distraction principles; Docking = bone graft principles.
Frame Time Calculation
Total time = Transport time + Consolidation time. Transport = defect size / 1mm per day. Consolidation = 1 month per cm of transport (regenerate). Docking site adds time. May be 6-18 months total.
Mnemonic
DRIFTTransport Principles
D
Defect size determines method
Monofocal, bifocal, or trifocal
R
Rate 1mm/day
Same as distraction osteogenesis
I
Infection must be controlled first
Debride before transport
F
Fibula osteotomy if tibia transport
Allows transport without tether
T
Terminate at docking site
May need bone graft for union
Memory Hook:Let the bone DRIFT across the defect!
Mnemonic
DOCKDocking Site Management
D
Debride ends
Freshen sclerotic bone surfaces
O
Open bone graft if needed
Autograft from iliac crest
C
Compress across site
Maintain compression with fixator
K
Keep stable until union
Protect docking site fixation
Memory Hook:DOCK the transported bone properly for union!
Mnemonic
HALFBifocal vs Monofocal
H
Halve the transport distance
Each segment moves half the defect size
A
Add complexity
Two osteotomies, two regenerates
L
Less soft tissue stretch
Better tolerated over large distances
F
Faster overall treatment
Parallel transport reduces time
Memory Hook:Bifocal cuts the time in HALF!
Overview and Epidemiology
Bone transport is a technique using distraction osteogenesis to move a bone segment across a defect, generating new bone in its wake. Developed from Ilizarov's principles, it is the definitive treatment for segmental bone defects not amenable to conventional bone grafting.
Indications:
- Segmental bone loss greater than 4cm
- Post-traumatic bone defects
- Post-tumor resection reconstruction
- Infected nonunion with bone loss
- Congenital pseudarthrosis
Advantages over massive bone grafting:
- Uses patient's own regenerative capacity
- No donor site morbidity for large grafts
- Can address defects larger than available graft
- Simultaneous soft tissue regeneration
- Can be combined with infection treatment
Disadvantages:
- Prolonged treatment time (months)
- Pin site complications
- Technical complexity
- Patient compliance required
Click to expand
Pathophysiology
Biology of Bone Transport
Regenerate formation:
- New bone forms at the corticotomy site during transport
- Same principles as limb lengthening
- Rate 1mm/day preserves biology
- Regenerate consolidates after transport complete
Docking site biology:
- Two bone ends meeting - often avascular
- Variable healing potential
- May have fibrous interposition
- Frequently requires augmentation
Transport Methods
Monofocal:
- Single osteotomy proximal or distal to defect
- Transport segment moves across defect
- Simple technique, longer transport distance
- Docking site at one end
Bifocal:
- Two osteotomies, one at each end of defect
- Two segments transport toward middle
- Each segment moves half the distance
- Docking site in middle of defect
Trifocal:
- Three osteotomies
- Central segment transported, end segments moved in
- For very large defects
- Complex but faster
Shortening-Lengthening
An alternative to transport for infected defects: Acutely shorten the limb to achieve bony contact and compression, then gradually re-lengthen through a distant osteotomy. Avoids transport through infected zone and provides compression at nonunion site.
Clinical Presentation
Patient Assessment
History:
- Mechanism of bone loss
- Infection history (critical for planning)
- Previous surgery and implants
- Comorbidities affecting healing
Physical examination:
- Soft tissue envelope quality
- Limb alignment
- Neurovascular status
- Signs of active infection
Preoperative Planning
Imaging:
- Full-length bone radiographs
- CT for defect measurement and bone quality
- MRI if infection suspected
Defect characterization:
- Size in centimeters
- Location (metaphyseal vs diaphyseal)
- Bone quality at proposed osteotomy sites
- Soft tissue condition
Investigations
Imaging
Plain radiographs:
- Full-length views of affected bone
- Assess defect size and location
- Bone quality evaluation
CT scan:
- Accurate defect measurement
- Plan osteotomy site
- Assess sequestra in infection
MRI:
- Soft tissue evaluation
- Infection extent
- Marrow involvement
Imaging Gallery
Infection Workup
For infected cases:
- ESR and CRP (baseline and monitoring)
- White cell count
- Intraoperative cultures (at least 5 samples)
- Histopathology
Management
Bone Transport Technique
Frame application:
- Ilizarov or hexapod frame (TSF)
- Minimum 2 rings per segment
- Transport ring connected to segment to be moved
Osteotomy:
- Low-energy corticotomy
- Metaphyseal if possible
- Preserve periosteum and blood supply
- Same technique as for lengthening
Latency:
- 5-7 days before beginning transport
- Allows initial callus formation
Transport phase:
- 1mm/day in 4 divided doses
- Monitor regenerate weekly
- Adjust rate based on regenerate quality
Docking:
- When transported segment reaches target
- Freshen bone ends
- Compress across site
- Bone graft if needed
Consolidation:
- Continue frame until regenerate solid
- Approximately 1 month per cm of transport
- Frame removal when 3 cortices visible
This section covers the bone transport technique.
Surgical Management
Method Selection
Monofocal Transport
Indications:
- Defects less than 6cm
- Single segment adequate
- Simpler technique preferred
Technique:
- Single osteotomy at one end of bone
- Transport segment across defect
- Docking at opposite end
Advantages:
- Simpler construct
- Single regenerate to monitor
Disadvantages:
- Longer transport distance
- More soft tissue stretch
- Longer treatment time
This section covers monofocal transport.
Complications
Transport Complications
- Poor regenerate: Slow rate, bone graft if persistent
- Premature consolidation: Speed up rate or accordion
- Axial deviation: Adjust frame during transport
- Soft tissue tethering: May limit transport
Docking Site Complications
- Nonunion: 25-50% need bone grafting
- Malalignment: Correct before union
- Infection persistence: Further debridement
General Complications
- Pin site infection: Standard external fixator issue
- Joint contracture: Aggressive physiotherapy
- Refracture: Protect after frame removal
Evidence Base
Bone Transport for Tibial Defects
Paley D et al. • Clin Orthop Relat Res (1989)
Key Findings:
- 85% ultimate union rate
- Docking site often requires bone grafting
- External fixation index 1.5 months/cm
Docking Site Management
Rozbruch SR et al. • J Bone Joint Surg Am (2003)
Key Findings:
- 50% of docking sites required bone grafting
- Refresh and compress improves union
- Plan for secondary procedure
Bone Transport over Nail
Kocaoglu M et al. • J Orthop Trauma (2006)
Key Findings:
- Reduced external fixation time
- IM nail protects regenerate during consolidation
- Acceptable complication rates
Shortening-Lengthening for Infected Nonunion
Marsh DR et al. • J Bone Joint Surg Br (1997)
Key Findings:
- Avoids transport through infected zone
- Compression promotes healing
- High union rates with infection control
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
Scenario 1: Tibial Segmental Defect
EXAMINER
"A 35-year-old man has a 6cm segmental tibial bone defect following debridement of infected nonunion. The soft tissues are healthy after flap coverage. How do you plan management?"
EXCEPTIONAL ANSWER
Thank you. This is a significant segmental defect requiring bone transport as the preferred method of reconstruction. For a 6cm defect, I would consider bifocal transport to reduce treatment time - two osteotomies at each end of the defect with segments transporting toward the middle. Before transport, I must ensure infection is controlled with normalized inflammatory markers. I would apply an Ilizarov frame with adequate rings above and below. I would perform a fibular osteotomy to allow tibial transport without tether. After a 7-day latency period, I would transport at 1mm/day. The total transport phase would be approximately 3cm per segment, taking about 30 days each. I would plan for docking site management - likely bone grafting when the segments meet. Consolidation would take an additional 3-4 months. Total frame time approximately 6-9 months.
KEY POINTS TO SCORE
6cm defect - bifocal transport preferred
Ensure infection controlled before transport
Fibular osteotomy for tibial transport
Plan for docking site bone grafting
COMMON TRAPS
✗Choosing bone graft alone for 6cm defect
✗Transporting through infected bone
✗Not planning for docking site problems
LIKELY FOLLOW-UPS
"What if only monofocal transport is used?"
"How do you manage docking site nonunion?"
"What is the role of induced membrane technique?"
VIVA SCENARIOStandard
Scenario 2: Docking Site Nonunion
EXAMINER
"A patient has completed tibial bone transport for a 5cm defect. The regenerate looks excellent, but at 4 months there is no union at the docking site. What is your management?"
EXCEPTIONAL ANSWER
Thank you. Docking site nonunion is a common problem after bone transport - occurring in 25-50% of cases. The regenerate healing well confirms good biology for distraction osteogenesis, but the docking site is different - two avascular bone ends meeting. My management would be surgical. I would open the docking site, debride any fibrous tissue, and refresh the bone ends by decorticating or removing sclerotic bone. I would then pack autologous bone graft from the iliac crest into the docking site. Using the external fixator, I would apply compression across the site. I would maintain stability and allow time for union - typically 3-4 months. If the regenerate is fully consolidated, I could consider converting to internal fixation or cast. Serial X-rays would monitor healing.
KEY POINTS TO SCORE
Docking site nonunion common (25-50%)
Open, debride fibrous tissue, refresh bone ends
Autologous bone graft
Compress and stabilize
COMMON TRAPS
✗Waiting too long for spontaneous healing
✗Not grafting the docking site
✗Removing frame before docking site healed
LIKELY FOLLOW-UPS
"What is the accordion maneuver?"
"Could you use BMP at the docking site?"
"When would you use internal fixation?"
VIVA SCENARIOAdvanced
Scenario 3: Shortening-Lengthening
EXAMINER
"Describe the shortening-lengthening technique as an alternative to bone transport for infected tibial nonunion."
EXCEPTIONAL ANSWER
Thank you. Shortening-lengthening, also known as acute shortening and gradual distraction, is an alternative to bone transport particularly useful for infected nonunions. The principle is to acutely shorten the limb to achieve bony contact and compression at the nonunion site, then restore length through distraction osteogenesis at a distant healthy site. The technique involves: First, radical debridement of infected bone. Second, acute shortening of the tibia to bring healthy bone ends into contact - typically limited to 3-4cm to avoid vascular and nerve problems. Third, application of external fixator with compression at the nonunion site. Fourth, once the nonunion shows healing (usually 4-6 weeks), performing a corticotomy at a distant healthy location and gradually lengthening to restore limb length. The advantages are avoiding transport through potentially infected bone and providing compression to promote healing. The disadvantage is the limit on acute shortening tolerable.
KEY POINTS TO SCORE
Acute shortening brings healthy bone ends together
Compression promotes healing at nonunion
Lengthening at distant healthy site
Avoids transport through infected zone
COMMON TRAPS
✗Shortening more than 3-4cm acutely
✗Not debriding adequately
✗Starting lengthening before nonunion healed
LIKELY FOLLOW-UPS
"What is the maximum safe acute shortening?"
"When would you choose transport over shortening-lengthening?"
"How do you monitor for neurovascular compromise?"
Australian Context
In Australia, bone transport is performed at specialized limb reconstruction units within major trauma and orthopaedic centers. The technique requires subspecialty training and significant institutional experience.
Technical considerations:
- Ilizarov and Taylor Spatial Frame systems available
- Bone transport over nail increasing in popularity
- Multidisciplinary involvement (plastics for soft tissue, ID for infection)
The induced membrane technique (Masquelet) is an alternative approach used in some Australian centers, involving a two-stage procedure with cement spacer followed by bone grafting within the induced membrane. Choice between transport and induced membrane depends on defect size, soft tissue condition, and surgeon experience.
BONE TRANSPORT TECHNIQUES
High-Yield Exam Summary
Transport Parameters
- •Rate: 1mm/day (same as lengthening)
- •Latency: 5-7 days before transport
- •Rhythm: 0.25mm QID
- •Frame time: 1.5 months per cm typical
Method Selection
- •Monofocal: Defects less than 6cm, simpler
- •Bifocal: Defects greater than 6cm, faster
- •Trifocal: Very large defects
- •Over nail: Reduces external fixation time
Docking Site Management
- •25-50% require bone grafting
- •Refresh sclerotic bone ends
- •Autograft from iliac crest
- •Compress and stabilize
Special Considerations - Tibia
- •Fibular osteotomy allows transport
- •Anteromedial surface accessible
- •Soft tissue often compromised
- •Consider induced membrane as alternative
Infected Nonunion Principles
- •Debride all infected/necrotic bone first
- •Transport through healthy bone only
- •Alternative: Shortening-lengthening
- •Monitor infection markers throughout
Complications
- •Docking site nonunion: Most problematic
- •Poor regenerate: Adjust rate
- •Pin site infection: Standard management
- •Joint contracture: Physiotherapy essential