Recent studies, including the Swedish Hip Register, have confirmed that modern cementing techniques are important to achieve long-term implant survival. Their ultimate goal is to obtain an increased strength of cement and its interfaces with bone, thereby maintaining secure fixation and effective load transmission. The objective of this study was to measure the medullary pressures generated during bone cement injection, pressurisation and femoral prosthesis insertion for total hip arthroplasty. The measurements were recorded throughout the length of an in vitro femoral model while implanting a series of prosthetic hip stems using different pressurisation techniques. The prostheses used were the Charnley 40 flanged stem, an Exeter No. 3 stem, and a custom primary femoral component used in Belfast (Johnson &
Johnson, DePuy International Ltd.). The following parameters were derived from the pressure data recorded; peak pressure, decay pressure and duration above 76 kPa, the pressure regarded as the threshold to obtain adequate bone penetration. The range of peak distal stem pressures expected for all stems was 200–500kPa. The custom and Exeter stems generated proximal cement pressures in the range 100–300kPa. These pressures were attained through cement containment by stem design or auxiliary pressurising devices, respectively. It was observed that the Charnley femoral component did not perform as well with regard to proximal pressurisation, irrespective of which pressurisation technique was implemented. The durations of pressure maintenance above 76kPa are also important, 5 seconds being accepted as a minimum for an effective interface. These results reflect the pressure measurements, with adequate durations being maintained by those stems and pressurisers that were characterised by higher peak pressures. It is concluded that stem design and the complementary cement management techniques are essential to realise the pressure/time characteristics that are regarded as necessary to form an optimum bone/cement interface.
