Multistage Additive Manufacturing for Complex Limb Bone Deformity Reconstruction

Complex limb bone deformities may arise from post-traumatic malunion or nonunion, infection-related sequelae, tumour-related bone resection, congenital or developmental abnormalities, iatrogenic deformity or failure of previous reconstruction. Affected patients may have shortening, coronal or sagittal angulation, axial rotational deformity and structural bone deficiency, frequently accompanied by compromised soft tissue and multiple previous operations. Successful reconstruction therefore requires restoration of bone length, alignment and rotation, together with reconstruction of a stable skeletal column.

This is a multicentre, prospective observational cohort study involving 30 adult participants. The study will observe patients who receive a multistage additive manufacturing pathway as part of their clinical care. Eligibility for treatment and all clinical decisions, including the timing and type of surgery, will be determined by the treating multidisciplinary team independently of study participation. The study will not randomise participants, assign treatment or mandate a comparator procedure.

The clinical pathway may comprise three principal stages. The first stage consists of aetiology-specific preparation and definition of the reconstructive defect. Infection-related cases may require radical debridement, deep-tissue microbiological sampling, temporary stabilisation and antimicrobial treatment. Tumour-related cases may undergo oncologically appropriate resection. Patients with aseptic malunion, nonunion, developmental deformity or failed previous reconstruction may undergo corrective osteotomy, implant removal, nonunion-site preparation, soft-tissue release or other clinically indicated procedures.

The second stage consists of three-dimensional deformity analysis and restoration of bone length, alignment and rotation. Thin-slice computed tomography and calibrated radiographs will be used to construct a patient-specific anatomical model and quantify shortening, coronal and sagittal angulation, axial rotation and the anticipated bone defect after correction. Angular and rotational deformities may be corrected acutely when permitted by neurovascular and soft-tissue conditions. Patients with substantial shortening, multiplanar deformity or soft-tissue contracture may undergo gradual distraction and correction using circular or monolateral external fixation.

The third stage consists of definitive patient-specific reconstruction. After the planned correction has been achieved and the treating team confirms that the patient is ready for reconstruction, a porous Ti6Al4V implant will be designed for the corrected anatomy and manufactured using additive manufacturing. Patient-specific guides may be used to transfer the virtual plan to surgery. The implant will be stabilised using an intramedullary nail, locking plate, screws, integrated fixation structures or a combination selected according to the anatomical and mechanical requirements.

Postoperative rehabilitation will be individualised according to soft-tissue healing, bone quality, fixation stability and radiographic findings. Lower-limb participants will progress from protected or partial weight-bearing to full weight-bearing, whereas upper-limb participants will progress from protected motion to unrestricted functional loading.

Clinical and imaging assessments will be performed at baseline, during treatment and approximately 1, 3, 6 and 12 months after definitive reconstruction. The study will evaluate the clinical success and safety of the complete pathway, including correction accuracy, implant stability, radiographic bone-implant integration, limb-specific function, pain, health status, functional loading, reoperations and adverse events.

Inclusion criteria

• Age 18 years or older. Complex deformity involving a major upper- or lower-limb bone, including the humerus, radius, ulna, femur or tibia.

Angular deformity, shortening, rotational deformity or any combination of these.

Structural bone deficiency present before treatment or anticipated after corrective osteotomy, debridement or bone resection.

The treating multidisciplinary team determines that a patient-specific additively manufactured implant is clinically indicated to restore skeletal continuity, length, alignment, rotation or mechanical load transfer.

Ability to undergo CT-based three-dimensional planning and the planned multistage reconstructive treatment.

Ability to provide written informed consent and willingness to complete 12 months of follow-up after definitive reconstruction.

Exclusion criteria

• Isolated osteoarthritis-related deformity without a reconstructive limb bone defect.

Acute fracture without an established deformity or structural bone deficiency requiring patient-specific reconstruction.

Uncontrolled systemic infection. Severe vascular insufficiency or a soft-tissue condition that precludes definitive reconstruction.

Anticipated inability to achieve adequate debridement when required, viable soft-tissue coverage or stable fixation.

Known allergy or contraindication to the implant material. Pregnancy when the required imaging or surgery would be inappropriate. Inability to comply with rehabilitation or outcome assessments. Participation in another clinical study that could materially affect the study outcomes.