Bone Transport Techniques

Transport is one answer to a segmental defect, and the page is only useful beside the alternatives. The biology it exploits is distraction osteogenesis - the same principle applied to a shortened rather than a defective bone in limb lengthening - and the hardware is Ilizarov external fixation. Its main rival for the same defect is the induced-membrane (Masquelet) technique, and the decision between them belongs with the defect's cause: nonunion, chronic osteomyelitis after debridement, or an open fracture that has lost bone - most often of the tibial shaft. When neither reconstruction is realistic, the question becomes salvage versus amputation, which is on mangled extremity.

What it is. Bone transport uses 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.

When it is chosen. Segmental bone loss greater than 4cm is the threshold at which transport is generally preferred to bone grafting alone. The defects that reach that size come from a short list:

• Post-traumatic bone defects
• Post-tumour resection reconstruction
• Infected nonunion with bone loss
• Congenital pseudarthrosis

What it buys. Transport uses the patient's own regenerative capacity, so there is no donor-site morbidity for a large graft and no ceiling set by the volume of graft available - a defect larger than any graft can still be filled. Soft tissue regenerates alongside the bone, and the reconstruction can be combined with treatment of infection.

What it costs. Treatment runs for months, the frame brings pin-site complications, the technique is complex, and none of it works without a compliant patient.

Two junctions, two biologies. Transport asks bone to unite in two places, and they behave differently. The regenerate at the corticotomy follows distraction principles and usually heals well if the biology is preserved; the docking site is two bone ends meeting and follows bone-graft principles. Most of what goes wrong in this operation goes wrong at the second one.

The regenerate. New bone forms at the corticotomy site during transport, by the same principles as limb lengthening, and a rate of 1mm/day preserves that biology. Once transport is complete the regenerate consolidates.

The docking site. The two ends that meet are often avascular, their healing potential is variable, and fibrous tissue may interpose between them. Augmentation is needed often enough that it is planned for rather than discovered.

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Frame time. Total time is transport time plus consolidation time. Transport time is the defect divided by 1mm per day; consolidation is indexed at roughly 1 month per cm transported, and the docking site adds time of its own. In practice the whole treatment may run 6 to 18 months.

Bone transport itself is described by the number of osteotomies (focal level), but the defect and host are classified by widely used trauma and reconstruction systems that drive decision-making.

When bone transport follows an infected nonunion, the Cierny-Mader classification named above determines how much bone must be resected and whether the host can heal a reconstruction at all. It combines an anatomic type with a physiological host class.

History. How the bone was lost governs the plan: the mechanism, the infection history, previous surgery and the implants left behind, and any comorbidity that impairs healing. The infection history is the part that changes the operation.

Examination. Assess the quality of the soft-tissue envelope, limb alignment, neurovascular status, and any signs of active infection.

Characterising the defect. Before the frame is planned the defect is described by its size in centimetres, its location (metaphyseal or diaphyseal), the bone quality at the proposed osteotomy sites, and the condition of the soft tissues over it.

Radiographs. Full-length views of the affected bone, read for the size and location of the defect and for bone quality.

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CT measures the defect accurately, plans the osteotomy site, and identifies sequestra in infection.

MRI evaluates the soft tissues, the extent of infection, and marrow involvement.

Infection workup. Where infection is suspected or established, take ESR and CRP at baseline and to monitor, a white cell count, at least 5 intraoperative culture samples, and histopathology.

The number of corticotomies is chosen from the size of the defect: more levels means less distance for each segment to travel, at the cost of another regenerate to look after.

MonofocalBifocalTrifocalOver a nail

One osteotomy, one moving segment. A single osteotomy proximal or distal to the defect, and the transport segment crosses the whole defect to dock at the far end. Suited to defects less than 6cm, where one segment is adequate and the simpler construct is preferred.

The trade-off. One regenerate to monitor and a simpler frame, against the longest transport distance, the most soft-tissue stretch, and the longest treatment time.

Two osteotomies, two moving segments. One osteotomy at each end of the defect, with both segments transported towards the middle, so each travels half the distance and the docking site lies in the centre of the defect. Used for large defects greater than 6cm, to cut treatment time and soft-tissue stretch.

The trade-off. A more complex construct, two regenerates to monitor, and a docking site that may end up in an awkward location.

Three osteotomies, three segments. The central segment is transported and the end segments are moved in, for very large defects. Complex, but faster than asking one segment to cross the whole gap.

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Frame plus intramedullary nail. The transport segment is carried along a nail that controls alignment and, once docking and regenerate consolidation are secure, allows the frame to come off early. What it improves is time in a frame: the external fixation index falls from roughly 1.5 months/cm with a frame alone to as low as 0.4 months/cm. The biology of the regenerate is unchanged.

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During transport. These are the problems the fortnightly films are read for.

• Poor regenerate: slow the rate; bone graft if it persists
• Premature consolidation: speed the rate up, or perform an accordion manoeuvre
• Axial deviation: adjust the frame during transport
• Soft-tissue tethering: may limit how far the segment will travel

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At the docking site. Nonunion is the predictable complication, and bone grafting is what resolves it. Malalignment is corrected before union, and persistent infection means further debridement.

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Of the frame and of the limb. Pin-site infection is the standard external fixator problem, joint contracture is prevented by physiotherapy rather than treated late, and the limb may refracture once the frame is off.

The decision that carries the marks is which technique suits this defect, this host and these soft tissues. The four mainstream options are compared below.

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The induced-membrane technique is the principal alternative to transport for a segmental defect, and the examiner expects you to know its two stages and why the membrane matters.

Why the induced membrane works. The foreign-body reaction to the cement creates a vascularised pseudosynovial membrane that secretes growth factors (VEGF, BMP-2, TGF-beta), prevents graft resorption, and provides a contained, well-vascularised bed.

When to graft. Bioactivity peaks at around one month, and grafting is usually performed at 4 to 8 weeks, commonly at 6 to 8. The window is not a cliff, though: reviews report that the membrane retains bioactivity even beyond 8 weeks.

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The transport phase. The patient or carer performs the adjustments, 0.25mm four times daily, once the latency period is over. Pin sites are cleaned daily; pin-site infection is expected and treated early with oral antibiotics, escalating only if it becomes deep. Weight-bearing is encouraged within tolerance, because loading the regenerate improves its quality.

Monitoring. Radiographs review the regenerate approximately every 2 weeks, and the rate is set by what they show. Physiotherapy for the adjacent joints runs throughout and is aggressive, to prevent equinus in the tibia and knee or hip contractures.

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Consolidation and frame removal. The frame stays on through consolidation. Before it comes off, confirm union of both the regenerate and the docking site, with 3 of 4 cortices visible on orthogonal views. After removal the limb is protected in a cast or brace to reduce the risk of refracture, particularly where the defect exceeded 8cm.

Pooled data come from systematic reviews and case series rather than registries. Reported figures (verified in the Evidence Base) include:

• Union: achievable in the high 80s to mid 90s percent with appropriate docking-site management; nonunion rates are comparable between transport and free fibula.
• Infection eradication: transport markedly reduces deep infection in infected lesions (risk ratio 0.14 in meta-analysis).
• Docking-site grafting: required in 25 to 50% of cases - the principal predictable hurdle.
• Refracture: about 5% overall, rising roughly 3.7-fold for tibial defects over 8cm.
• Amputation: around 2.9%, including a voluntary amputation rate of about 1.6% reflecting treatment burden.

Functional outcomes (ASAMI) are good to excellent in most series, but treatment is long and demanding; patient selection and counselling are decisive prognostic factors.

Global Epidemiology

Segmental long-bone defects most often follow high-energy open tibial fractures (Gustilo IIIB/IIIC), infected nonunion/osteomyelitis, and tumour resection. Worldwide the tibia is the commonest site because of its subcutaneous position and tenuous blood supply. There is no dedicated international registry for bone transport; the evidence base is dominated by single-centre case series and a small number of systematic reviews, so reported figures vary widely with defect size, infection and host status.

Side-by-Side Guidance

The common thread across all bodies: control infection and achieve healthy soft-tissue cover first, then reconstruct bone with the method best matched to defect length, host biology and local expertise. None mandates a single technique.

Registry and Outcome Notes

No arthroplasty-style registry tracks bone transport. The best pooled outcome data come from systematic reviews (e.g. Papakostidis 2013, Paul 2024) rather than national registries, so quoted union, refracture and amputation rates derive from aggregated case series and carry meaningful heterogeneity.

High- vs Limited-Resource Practice Variation

The induced-membrane (Masquelet) technique is the principal global alternative to transport: a two-stage approach with a PMMA cement spacer to induce a vascular membrane, followed by autologous cancellous grafting (usually at 4 to 8 weeks). Transport better tolerates very large defects and active infection; induced membrane is technically simpler and avoids prolonged external fixation but is graft-volume limited. Vascularised free fibula is favoured for large defects with a good recipient vessel bed.

Transport, induced membrane or free fibula. No high-quality randomised data establishes superiority. Systematic review evidence shows equivalent bony and functional outcomes between transport and free fibula, with free fibula achieving faster union and fewer complications but requiring microsurgery (Paul 2024). The choice remains expertise- and biology-driven.

Prophylactic docking-site grafting. Whether to graft the docking site at the time of contact, or wait to see whether it unites spontaneously, is unresolved. Acute grafting, as in the nail-assisted series, may pre-empt the 25 to 50% nonunion rate but commits every patient to an extra procedure.

Rate and rhythm. 1mm/day in four increments is conventional, but slower rates may be needed for a poor regenerate and faster increments are tolerated in children. The ideal rhythm for transport, as opposed to lengthening, is extrapolated rather than proven.

Biologics. BMP, PRP and bone-graft substitutes are used adjunctively at problem docking sites and to augment the regenerate, but the evidence is largely off-label and low-level; routine use is not established.

Salvage versus amputation. For very large defects with severe soft-tissue and neurovascular injury, prolonged reconstruction may not outperform early amputation and prosthetic rehabilitation in function or cost. This is a shared decision, not a technical default.