Comparison of biomechanical properties associated with the diameter and insertion depth of bone anchors in the femoral condyle of toy breed cadaver dogs

Abstract

The objective of the present study was to compare the biomechanical properties of implanted bone anchors based on diameter and insertion depth to yield selection criteria for bone anchor size in toy breed dogs. Twenty toy breed dog cadavers weighing < 5 kg underwent placement of five types of veterinary bone anchors (short diameter, short length [SDSL]; short diameter, medium length [SDML]; medium diameter, medium length [MDML]; medium diameter, long length [MDLL]; and long diameter, medium length [LDML]) at a predetermined femoral attachment site. Anchor screw depth/femoral condyle width (FCW) and anchor screw diameter/femoral condyle length (FCL) were measured using radiography. The yield load, Young’s modulus and failure load were measured and the causes of failure for each construct were recorded. The anchor screw depth/FCW was < 50%, 50%–75%, ~50%, and 75%–100% in the SDSL, SDML, MDML, and MDLL groups, respectively. The yield load, Young’s modulus and failure load were higher in the SDML and MDLL groups than in the SDSL and MDML groups. The anchor screw diameter/FCL was 12%–15% and 24%–30% in the SDML and LDML groups, respectively. No differences in biomechanical parameters were found between the SDML and LDML groups. The cause of failure in all constructs was pull-out of the bone anchor, except for distal femur fracture in five LDML constructs. In conclusion, when implanting bone anchors in toy breed dogs, the insertion depth should be > 50% of the FCW, regardless of diameter. Moreover, distal femur fracture can occur if the bone anchor diameter/FCL ratio exceeds 24%.