Article

Osteosynthesis implants, which remain in the patient after fracture
union to save additional surgery, may affect the strain distribution within the
bone. A reduction of strain within the bone is known to result in localized bone
loss ("stress shielding") and increased fracture risk.
The purpose of this study
was to examine whether extramedullary fixations for femoral neck fractures have
to be removed after fracture union to prevent reductions in cortex strains.
METHODS: In a biomechanical experiment, six pairs of human cadaver femora (mean
age 56 years, range 48 to 64) were supplied with five strain gauges per bone. The
bones were equally supplied with a compression hip screw or a femoral neck plate.
Before surgery, after surgery and after removal of the implants, axial
compression tests were conducted to measure surface strains during loading.
FINDINGS: The compression hip screw reduced the amount of strain at the superior
neck by 88% (P=0.015) and at the lesser trochanter by 51% (P=0.038). The femoral
neck plate reduced the amount of strain at the superior neck by 89% (P=0.001),
and increased the amount of strain at the inferior neck by 58% (P=0.02) and at
the lesser trochanter by 63% (P=0.005). After implant removal, there was no
significant difference in strain compared to pre-fracture levels, except for the
compression hip screw with 21% less strain (P=0.047) at the superior neck.
INTERPRETATION: Removal of osteosynthesis implants after bone union reverts bone
strains to pre-fracture levels, and might prevent further bone loss induced by
stress shielding.
CI - Copyright (c) 2010 Elsevier Ltd. All rights reserved.

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