The speed of sound correlates with implant insertion torque in rabbit bone: an in vitro experiment

Objectives: This study investigated the correlation of quantitative ultrasound with bone quality as evaluable from implant final insertion torque. Material and methods: Implants were planned at diaphyses (group 1) and epiphyses (group 2) of 16 rabbit femurs where amplitude-dependent speed of sound (Ad-SOS) was measured. The insertion torque from 7-mm-long implants placed at planned sites was recorded. The correlation between cutting torque and Ad-SOS was evaluated using Spearman's coefficient. Results: Statistics were based on data from 15 diaphyses and 13 epiphyses. The mean insertion torque was 8.8 N cm while the mean Ad-SOS was 1710.9 m/s. A negative correlation resulted between insertion torque and Ad-SOS. Conclusions: In the rabbit bone model investigated, quantitative ultrasound correlates inversely with implant insertion torque. Although this correlation remains to be verified in humans because rabbit femur does not convincingly represents different human bone qualities, it seems that ultrasound could convey potentially useful, pre-surgical, site-specific, non-invasive information on bone mechanical characteristics therefore deserving further research efforts.