Cup inclination is a major factor in the success of a total hip replacement. An open cup position can lead to dislocation or increased wear from rim loading and a closed cup position lead to impingement against the femoral neck or psoas. Although the ideal inclination for cup position is recommended as between 40 and 45 degrees, accurate positioning of the implant might be influenced by pelvic flexion and movement of the patient's pelvis during the procedure. We wanted to examine if the transvers acetabular ligament (TAL) could be used to determine cup inclination intra-operatively. 16 hips from 9 cadaveric specimens were used for the study. A computer navigation system (Brain lab) was used to measure and document the exact inclination and version of the acetabular trial component in three positions: flush with the transvers acetabular ligament (TAL), with the rim of the cup 5 mm from the TAL in a cranial direction and with the rim of the cup 5 mm caudally displaced. Statistical analysis of the results was performed by the Department of Biostatistics.Background
Methods
Using digital X-rays to plan a hip replacement can cause problems with sizing and templating the prosthesis. Using an AP view of both hips is desirable as this allows the use of the sometimes unaffected contralateral hip for templating. We devised a method of using a 20mm ball bearing as a marker positioned at the same depth as the greater trochanter, but between the patient's legs. Placing the marker between the patient's legs avoids the problem of the marker disappearing off the side of the X-ray, as is seen when placing the marker at the side of the obese patient. The marker is then used to calibrate the size of the digital X-ray. We used a hundred consecutive post-operative X-rays, comparing the size of the head of the femoral prosthesis used at surgery with the size measured pre-operatively using the marker.Background
Method
A variety of cerclage systems are available for the fixation of periprosthetic fractures. The aim of this study was to compare the forces applied by these systems. We designed and manufactured a device to measure the forces applied to a cylindrical structure by a cerclage cable. Five different commonly used systems were evaluated. The forces exerted were measured at four different locations on the cylinder and this was compared to the force indicated by the tensioning device.Background
Methods
