Retention of Distal Femoral Osteotomy Fixed with a AO Condylar Plate and Grosse-Kempf Locked Nail in Relation to Bone Mineral in Cadavers

On the basis of previous studies showing good correlations between the structural strength of the femur and bone mass as assessed by single energy quantitative computed tomography, this study was scheduled to analyze the mode of failure of an oblique osteotomy in the distal femur in geriatric cadavers stabilized by an AO condylar plate and Grosse-Kempf locked intramedullary nail in axial eccentric loads and to relate the mode of failure to bone mineral content. A pilot study of two pairs of osteotomized, internally fixed femora were loaded axially and the loads correlated with bone mineral content. These correlations were used to calculate estimated failure load in 12 pairs of osteotomized femora (12 plated and 12 nailed specimens) which then were sustained to a cyclic eccentric axial load of 50% of the estimated failure load. The failure patterns in the two groups were different. Fixation failure occurred in all specimens in the plated group at the site of the osteotomy, while in the nailed group the fixation failures in 50% of the specimens were unrelated to the site of the osteotomy. The study suggests that locked intramedullary nailing of a distal femoral fracture in osteoporotic bone gives more secure fracture retention than fixation with a 95 degrees AO/ASIF condylar plate. Furthermore, it shows that bone mineral assessment by densitometric methods can be used to predict the mechanical strength of a bone/implant construct.