Introduction Considerable advances have been made in improving cementing techniques in total hip replacement. Recently, the increasing need to minimize healthcare costs has led to the development of methods to reduce surgical time. It has been proposed that the curing time for bone cement can be markedly reduced by preheating the femoral component before insertion. A reduction of the period between insertion of the implant and ultimate curing decreases operative time, bleeding into the bone-cement interface and the likelihood of accidental loss of position. In a previous in-vitro study, preheating the femoral component to a temperature of about 50° resulted in a reduction in the bone cement curing time of approximately 50%. No adverse changes of the mechanical properties of cement were found. E-modulus, fracture toughness and fatigue strength were unaffected by increased temperature. A uniform trend of decreasing porosity of bone cement with increased temperature of the implant was also observed. To-date, there have been no reports on the in-vivo outcome of the preheating cementing technique. The aim of this prospective study was to assess the clinical and radiological five year follow-up results of the preheating cementing technique used for the fixation of the femoral stem (Lubinus, Link, Germany).

Methods One hundred consecutive patients (100 hips) with osteoarthritis and an average age of 72 years (range 65 to 85) have been operated on by one surgeon in a single institution. In a cohort of 50 hips a conventional cementing technique was used. The cement used was Cemex (Tecres, Italy). The anterior-posterior and lateral radiographs have been evaluated with a computer-aided system. The quality of cement mantle was assessed on the radiographs according to the A-B-C1-C2-D classification.

Results The curing time of the bone cement was markedly reduced (average five minutes, range four to seven minutes) by preheating the femoral component (40° to 50°). The estimated reduction of intra-operative blood loss was 75 ml (range 45 to 130). The mean Harris Hip Score was 94.8 points at follow-up (range 79 to 100). The clinical status of 92% of hips was rated good or excellent, eight percent was rated fair. A satisfactory cementing technique was obtained in 96% of hips. Small voids in the cement mantle (grade C1) were present in four percent of hips. Non-progressive radiolucent lines at the bone-cement interface were observed at Gruen zone one in four hips, at zone eight in three hips and at zone 14 in three hips. No signs of osteolysis were observed at follow-up, all stems were rated radiologically stable.

Conclusion A reduction in curing time of bone cement provides a significant time saving without compromising implant performance. We recommend preheating of femoral components to surgeons experienced in joint replacement and have a skilled surgical team, because of the potential risk of premature polymerization before complete seating of the implant.

In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.

This is a biomechanical study measuring the maximum pull-out strength of implants inserted into vertebral bodies of the calf spine. The objective is to investigate the influence of different anchoring systems.

The following implants were used: Zielke USIS (Ulrich, Ulm), Kaneda KASS (DePuy, Sulzbach). Universal Spine System (USS, Synthes, Umkirch) and Hollow Modular Anchorage (HMA) system (Aesculap, Tuttlingen). We selected nine groups with seven vertebrae equal in mean sizes and Bone Mineral Density (BMD) for each system. Vertebral body and implant were connected to both ends of a servohydraulic testing machine. Distraction was applied until failure and the maximum axial pullout force was recorded.

No significant correlation of BMD and pullout strength appeared. The student t-test showed significant higher stability for USS with pullout resistant nut (4.0 kN) and KASS (two-screws, 4.2 kN) compared to all other systems (p < 0.025). The mode of failure was a burst fracture in these vertebrae and shearing in all other systems. Bicortical screws of USS (3.2 kN) showed stronger hold than single bicortical KASS (2.5 kN) and HMA 12 mm (2.6 kN). Zielke (2.1 kN) was equal to monocortical KASS (one screw 2.1 kN) and superior to monocortical USS (1.6 kN). All those provided less stability than HMA 14 mm (2.4 kN).

For in-vitro testing with calf spines the influence of BMD seems to be less important than that of implant design. Maximum strength of Kaneda KASS depends on angulation of screws. Stability of USS implants can be increased by use of pullout resistant nuts. Of all monocortical implants only HMA presents pullout resistant strength comparable to bicortical screws. In-vivo use of monocortical anchorage bears the lowest risk of vascular injury, because the far cortex remains intact.