Assessment of Extra-Cortical Bone Bridge Interface in Cemented Mega Endoprosthesis for Limb Salvage Surgery

Mega endoprosthesis replacement for resection of primary malignant bone tumour requires immediate and long-term stability, particularly in the young and active patient. Extracortical bone bridge interface (EBBI) is a technique whereby autograft is wrapped around the interface junction of bone and porous-coated implant to induce and enhance bone formation for biological incorporation. This procedure increases the mean torsional stiffness and the mean maximum torque, which eventually improves the implant's long-term survival.

The extracortical bone bridge interface's radiological parameter was evaluated at the prosthesis bone junction two years after surgery utilising a picture archiving and communication system (PACS). The radiograph's anteroposterior and lateral view was analysed for both thickness and length in all four cortices. The analysis was done in SPSS Version 24 using One-Way ANOVA and independent T-Test. Results were presented as mean and standard deviation and considered significant when the p-value was < 0.05.

The mean average thickness was 2.2293mm (SD 1.829), and the mean average length was 31.95% (SD 24.55). We observed that the thickness and length of EBBI were superior in the young patient or patients with giant cell tumour that did not receive chemotherapy, compared to patients treated for osteosarcoma. The distal femur also had better EBBI compared to the proximal tibia. However, the final multivariable statistical analysis showed no significant difference in all variables. EBBI thickness was significantly and positively correlated with EBBI Length (p<0.001). We conclude that, for each 1mm increase in EBBI thickness, the length will increase by 0.06% on average. About 17.2% of patients out of the 29 showed no radiological evidence of EBBI.

From our study, there were no factors that significantly contributed to the formation and incorporation of EBBI.