Internal fixation of meta- and diaphyseal intercalary bone defects after tumour resection with intramedullary nailing and porous polymethylmetacrylate (PMMA) spacer

Background. Radical resection of bone tumours localized in the meta- or diaphysis of long bones frequently results in segmental defects. Several stabilization techniques with preservation of the adjacent joint have been published, but the failure rate appears to be considerable. The objective of this study is the experimental and clinical testing of a new technique which combines unreamed nailing with support of the defect by a porous polymethylmetacrylate (PMMA) spacer. Methods. For spacer preparation, PMMA spheres were adhered to a cylindrical spacer (0 32 mm) with interconnective porosity. Axial strength was determined, as was the stiffness/strengths of the combination osteosynthesis in human cadaver tibias (defect lengths 6 cm; empty defect served as a control). An experiment was also conducted with sheep. A 3 cm diaphyseal tibia defect was prepared and stabilized by nailing. For the control there was an empty defect. Group A had support of the defect with a PMMA spacer and group B a PMMA spacer coated with osteoconductive RGD-peptide. Evaluation after was made after 6 months including histology and a determination of relative torsional strength. In addition, a clinical study has been under way since October 1998, with 13 patients (defect lengths between 3-15 cm) being operated. Results. Axial stability was 12,750 +/- 300 N (17.56 +/- 0.59 MPa). There was an enhancement of 4-point bending stiffness by 35% (P=0.028), of axial stiffness by 36% (ns) and of axial strength by 553% (P=0.028). Histology showed the formation of a new bone at the spacer/muscle interface. For the sheep, relative torsional strength was enhanced by 95% (P=0.08) in group A and by 91 % (P=0.047) in group B. For the patients studied, the mean follow-up period was 16.1 months, max. 48 months. One mechanical failure occurred after 24 months, which was solved by callus distraction. Conclusions. Combination osteosynthesis is suitable for stabilizing segmental bone defects. The risk of mechanical failure appears to be low. Nevertheless, this technique should only be applied as a definitive solution if callus distraction is unfavourable due to advanced age or a poor lifetime prognosis. The method can also be used for temporary internal stabilization during prolonged postoperative chemotherapy.