Antirotation Pins Improve Stability of the Compress Limb Salvage Implant: A Biomechanical Study

Background Limb salvage implants that rely on compliant compression osseointegration to achieve bone fixation may achieve longer survivorship rates compared with traditional cemented or press-fit stemmed implants; however, failures resulting from rotational instability have been reported. The effect of using antirotation pins on the rotational stability of the fixation has not been well studied. Questions/purposes Weasked the following question: When tested in a cadaver model, does the use of antirotation pins increase the torque required to cause implant failure or rotation? Methods Thirty-two cadaver femurs were divided into four groups of eight femurs. We compared the torque to failure among groups containing zero, one, two, three, and four pins using a servohydraulic testing device. Results Adding antirotation pins increased the torque required to cause failure (R-2 = 0.77; p < 0.001). This increase was most notable in groups comparing zero pins with one pin (14 N-m, [95% CI, 10.9-17.1] versus 23 N-m, [95% CI 22.5-23.48]; p = 0.01) and two compared with three pins (29 N-m, [95% CI, 21.7-36.3] versus 42 N-m, [95% CI, 37.8-46.2]; p = 0.35). Conclusions It appears that the use of antirotation pins improves rotational stability of the compliant compression endoprosthesis. Although these findings need to be verified in a clinical study, the addition of antirotation pins may improve osteointegration and we have changed our practice to use a minimumof three antirotation pins when implanting this device.