An in vivo evaluation of surface polishing of TAN intermedullary nails for ease of removal

Abstract

Fractures of the tibia and femoral diaphysis are commonly repaired by intra-medullary (IM) nailing. Currently IM nails are available in either electropolished stainless steel (SS) or in Titanium-Aluminium-Niobium (TAN). After healing, removal of the nails still is common but removal of TAN IM nails often has complications whereas SS IM nails of the same design are less often associated with problems. We believe the differences in removal are due to the ability of TAN to promote strong bone on-growth. We have previously shown in vivo that polishing cortical screws reduces removal torque and the percentage of bone-implant contact. Therefore, we postulate that bony on-growth onto IM nails can be reduced by means of surface polishing, for ease of removal. Here we aim to compare the pull-out forces for removal of standard TAN (TAN-S) compared to experimental paste polished TAN (TAN-PP) IM nails from a bilateral non-fracture sheep tibia model after 12 months implantation. Histological analysis was also performed to assess tissue on-growth to the nails. We show that polishing significantly reduces (p=0.05) the extraction force required for TAN IM nail removal. This effect in part is attributable to the distinct tissue-material reaction produced. For TAN-S nails direct bone contact was observed while for TAN-PP nails a fibrous tissue interface was noted. Since TAN is preferred over SS for IM nailing due to superior biocompatibility and mechanical properties, we believe these findings could be used to recommend changes to current surface technologies of intramedullary nails to reduce complications seen with nail removal especially in rapidly growing bone in children.

Titanium and steel fracture fixation plates with different surface topographies: Influence on infection rate in a rabbit fracture model

“…It was necessary to modify the screw entry procedure for polished screws, which would be an easily overcome manufacturing issue should such screws become clinically available. Overall, these findings support earlier results that surface polishing titanium implants offer eased implant removal, without compromising stability, or infection risk [15,26,32,34].…”

“…Polishing of titanium and its alloys has been investigated as a potential approach for easing implant removal in fracture care [26,32,33]. It has already been clinically implemented.…”

Surface polishing positively influences ease of plate and screw removal

“…More recently, we have also shown that polishing of TAN intramedullary nails can significantly reduce the pullout force required for removal after 18 months implantation within sheep. This result was associated with the formation of a fibro-osseous interface, compared to direct bone bonding observed for standard microrough TAN nails (Hayes et al, 2009a). Nevertheless, no incidences of nail instability were observed.…”

“…Indeed extensive studies have focused on enhancing osseointegration through surface microtopography manipulation, which is a major determining factor for osseointegration (Albreksston and Hansson, 1986;Pearce et al, 2008;Hayes et al, 2009a). However, we postulate that direct, strong osseointegration provided by 'standard' microrough IF is not necessary for fracture fixation implant Fig.…”

“…Currently commercially pure titanium (cpTi) locking compression plates and titanium-6%aluminium-7%niobium (TAN) screws (as well as all other IFs with the exception of hand polished hand plates) are provided for clinics with a 'standard' micro-rough surface. However, the ability of 'standard' cpTi and TAN to promote direct bone on-growth has been implicated as the cause of removal difficulties (Qu et al, 1996;Ferris et al, 1999;Boyan et al, 2002;Pearce et al, 2008;Hayes et al, 2009a). Therefore, in this in vivo sheep non-fracture model study we hypothesize that a smooth surface created by polishing of standard micro-rough cpTi LCPs and TAN screws will help to eliminate the removal problems associated with excessive direct bone-on-growth.…”