The effect of augmentation with resorbable or conventional bone cement on the holding strength for femoral neck fracture devices.

Abstract

To compare maximum extraction torque and pull-out load for femoral neck fracture implants inserted with standard technique or after augmentation with polymethylmethacrylate (PMMA) or calcium phosphate cement (Norian SRS). Biomechanical study using synthetic bone. Implants were inserted in foam blocks with three different densities for simulation of normal bone or slight or severe osteoporosis. Tested implants included three screws (AO, Olmed, Hansson), one screw with both threads and a barb (Hybrid), and one pin with a hook (LIH hook-pin). Implants were inserted by standard technique and after augmentation with PMMA or Norian SRS. The effect of (a) density of the synthetic bone (low, medium, high), (b) augmentation (none, PMMA, SRS), and (c) type of implant (AO, Olmed, Hansson, Hybrid, LIH) on the maximum extraction torque and pull-out load was determined using a material testing machine. Analysis of variance with Fisher's PLSD post hoc test was used to determine statistical differences. PMMA significantly increased maximum torque and pull-out load for all implants and block densities when compared without cement (p < 0.0001), whereas enhancement with SRS was far less pronounced and most obvious in low density blocks. For screws normally inserted without predrilling (Olmed and Hansson) the use of SRS in high density blocks caused a significant reduction in maximum torque (p < 0.0001) and pull-out load (p < 0.0001). SRS-augmented specimens failed through the cement at the periphery of the threads, whereas PMMA-augmented specimens failed between the cement and the synthetic bone. This study suggests that augmentation with PMMA around femoral neck fracture implants will increase the holding power significantly when compared with standard insertion technique as well as augmentation with calcium phosphate cement. Augmentation with calcium phosphate cement like SRS will increase the holding characteristics mainly in low density bone, whereas in high density bone it might even reduce the maximum torque because of the need for predrilling when using the cement for augmentation.