A new spiral linking technique for tendon repair in which one end of the tendon is spiralled around the other end has been developed. Using pig trotter extensor tendons, the Pulvertaft weave technique was compared with this new technique. Twenty-five repairs using each technique were tested by tensile loading with an Instron testing machine. The spiral linking technique matched the strength of Pulvertaft method: the mean peak loads were 102 and 105 N, respectively. The Pulvertaft weave was stiffer than the spiral linking technique: mean stiffness of 11.1 and 6.7 N/mm, respectively. The spiral linking technique also absorbed considerably more energy: energy absorbed prior to failure to 90% of peak load, 1.75 and 1.13 kN mm, respectively. In conclusion, the spiral linking technique appears as strong as the Pulvertaft weave and we believe it is easier to perform.

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Percutanous vertebroplasty (PVP) is gaining popularity for the treatment of vertebral compression fractures. The need of obtaining low viscosity materials for injection through small bore needles and the necessity of visualising the fluid flow during injection have led users to the formulation of a number of ad-hoc recipes aimed at adapting PMMA cements for this use. Industry, on its part, has addressed these requirements by developing specific products for this application. This study aimed at providing a direct comparison of a wide range of mechanical properties between three commercially available biomaterials developed for PVP: two PMMA based materials, Osteopal V (Merck Biomaterial GMBH, Dermstedt, D) and Verterbroplastic (DePuy Acromed, Inc, MA, USA), and a Bis-GMA composite, Cortoss (Orthovita, PA, USA). Cortoss consistently exhibited higher values for compressive strength, bending modulus and shear strength to both Osteopal V and Vertebroplastic. The creep behaviour of Cortoss was also different from that of the two PMMA cements.PVP can take advantage from the development of new injectable biomaterials in response to the problems associated with the use of PMMA in a highly vascularised area such as the vertebral body. In addition careful modulation of the mechanical properties of the material has the potential to further improve the outcome of PVP, possibly reducing the risk of adjacent level fractures associated with the procedure.

Immediate postoperative stability of femoral stems is one of the key factors for the long-term success of total hip replacement. The need to develop a reliable technique to assess in vitro implant stability under physiological loading conditions is widely recognized. A critical review of the in vitro techniques developed for the assessment of implant stability is presented. In vitro predictions of subsidence are compared to in vivo clinical data available from Roentgen stereophotogrammetric analysis (RSA) studies. Limited correlation between in vitro predictions of stability and clinical measurements of subsidence obtained through RSA data was found even though similar migration patterns could be distinguished.

We studied the mechanical characteristics of cement-antibiotic combinations in vitro. Palacos R was tested without antibiotics, with gentamicin alone and with gentamicin plus vancomycin or flucloxacillin. Palacos LV was studied only with gentamicin added. CMW 1 was studied with gentamicin added, with gentamicin plus vancomycin, and with gentamicin plus flucloxacillin. We performed four-point bending tests on beams of cement to establish bending strength and modulus, and compared the values to ISO standards. Density was also assessed. Palacos R was the strongest of the cements (bending strength 80 MPa). Palacos formulations (apart from Palacos LV) had a higher density and bending modulus than CMW 1. Statistical comparison of various cements with plain Palacos R showed lower density in 4 of the mixtures, and lower bending strength and modulus in 6 of the mixtures. Palacos R/gentamicin plus vancomycin and CMW 1/gentamicin plus vancomycin had bending strength slightly above minimum ISO standards, suggesting that the addition of vancomycin during cement mixing may compromise the outcome in revision surgery for sepsis.

The assumption of stiffness matrix symmetry used in many previous studies is not valid. The biomechanical testing of spinal specimens should be completed in 6 df, at physiologic loading rates, and incorporate the application of an axial preload. The present study has provided new data on the mechanical properties of spinal specimens and demonstrates that the dynamic stiffness matrix method provides a means to more fully understand the natural spine and quantitatively assess spinal instrumentation.

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