Microdamage at the pin-bone interface of external skeletal fixation pins after short-term cyclical loading ex-vivo

Abstract

SummaryThis study determined microdamage associated with external fixation pin insertion and short-term cyclical loading, using an ex vivo ovine tibial model. Orthofix tapered blunt-tipped 3.5/4.5 mm fixation pins and Apex® self-drilling self-tapping fixation pins, 4 mm in diameter, were used. After insertion, the constructs were either loaded in cantilever bending or not loaded. Constructs were then bulk-stained in basic fuchsin, and calcified sections were made. The sections were reviewed qualitatively and the microcrack surface density (Cr.S.Dn, μm/mm2) was quantified at the pin-bone interface. The pattern and quantity of microdamage induced was significantly influenced by fixation pin design and cortical region within the cisor transcortex, but not short-term cyclical loading. Overall, Cr.S.Dn was significantly increased with use of the Orthofix fixation pin (P < 0.01). Cr.S.Dn was also increased in the medial cis-cortex, compared with the lateral transcortex (P < 0.05). Diffuse damage within the medial cis-cortex was higher with the Orthofix pin. In contrast, the Howmedica Apex® fixation pin caused fracture of the periosteal region of the lateral transcortex, but relatively little microdamage within the medial cis-cortex. In this model as a consequence of pin insertion, fixation pin design had significant specific damage effects on both the medial cis-cortex and the lateral trans-cortex

Generation of microdamage around endosseous implants

“…Microcracks have been found to be associated with the insertion of endosseous implants into long bone (Huja et al 1999a) and with external skeletal fixation pins (Cohen et al 2003). The number of microcracks was seen to decrease during a 4‐week healing period following implant placement in long bones due to bone remodelling (Hoshaw et al 1994a, 1994b).…”

“…This should be considered as a limitation of this study. Cohen et al (2003) reported a similarly intensely stained area that occured in vitro in the bone adjacent to external skeletal fixation pins used in orthopaedic surgical treatment and extended beyond a 1.5 mm zone next to the pin–bone interface as a result of pin insertion (Cohen et al 2003). Diffuse staining areas were also observed by Lee (1997) on the machined bone surface as a result of the cutting procedure.…”