Temporary internal stabilisation for staged reconstruction of critical long-bone defects: A biomechanical study

Critical long-bone defects remain a major challenge in orthopaedic trauma and reconstructive surgery, particularly following high-energy injury, infection, and extensive segmental bone loss. Their management frequently requires staged reconstruction with temporary skeletal stabilisation between initial debridement and definitive reconstruction. External fixation remains an established strategy during this interval, while temporary internal fixation represents an alternative approach. However, biomechanical evidence regarding purpose-designed modular intramedullary constructs used in conjunction with polymethylmethacrylate (PMMA) spacers remains limited.

To evaluate the axial and bending mechanical characteristics of a modular intramedullary temporary stabilisation system used with a PMMA spacer and to compare its mechanical behaviour with selected plate and external fixation constructs in segmental long-bone defect models.

Five synthetic long-bone models were evaluated, with one specimen assigned to each experimental configuration. Three 50-mm femoral defect models were stabilised using plate osteosynthesis, external fixation, or modular intramedullary temporary stabilisation. Two additional modular intramedullary configurations comprised a 400-mm femoral defect and a 50-mm humeral defect. Each specimen underwent sequential quasi-static axial compression and bending using a TIRATEST-2151 testing machine, with continuous force-displacement recording and complementary optical displacement assessment. Axial and bending stiffness were analysed descriptively; no inferential statistical comparisons were performed.

In the 50-mm femoral defect configurations, measured axial stiffness was approximately 60 N/mm for plate osteosynthesis, 80 N/mm for external fixation, and 90 N/mm for modular intramedullary stabilisation; corresponding bending stiffness values were approximately 1.0, 0.6, and 1.2 N/mm, respectively. The 400-mm femoral modular configuration demonstrated axial and bending stiffness of 155 and 1.2 N/mm, respectively, while the 50-mm humeral modular configuration showed the highest measured values, at 325 and 1.5 N/mm. Given the single-specimen design, these differences were analysed descriptively and no inferential comparisons were performed.

The modular intramedullary temporary stabilisation system demonstrated measurable axial and bending stiffness across the tested segmental defect configurations, including the 400-mm femoral model. These findings provide an initial mechanical characterisation of the concept and support further replicated biomechanical evaluation incorporating standardised spacer preparation, additional comparators, and torsional and cyclic loading.