Paradoxical cerebral embolism is seen in 50–60% of patients following hip and knee arthroplasty surgery. It is responsible for post-operative symptoms like confusion and cerebral ischemic episodes. Embolism is less common with the use of uncemented implants. No study has looked into incidence of cerebral emboli in hip resurfacing. We undertook a prospective randomised study to look at the incidence of cranial emboli in hip resurfacing. Patients were randomized to receive either uncemented or cemented femoral component. An arm of the study included evaluation of the effects of femoral venting by randomising patients to ‘venting’ or ‘no venting’ of proximal femur intra-operatively. The operations were performed by a single surgeon using a uniform surgical technique. Transcranial Doppler device was used to quantify the occurrence and distribution of cerebral microemboli. Emboli counts were recorded continuously and were correlated any major procedural event. Eight patients (5 vented, 3 unvented) underwent cemented resurfacing and 7 patients (4 vented, 3 unvented) had cementless resurfacing. There was no difference between the two groups for age, gender, weight, or ASA status. Peri-operatively both groups were similar for vital observations (heart rate, temperature, blood pressure), haemoglobin change, mini – mental score at day 1 and 2, and oxygen saturation at day 1 and 3. The mean number of significant emboli in the cemented group was 8.1 and in the cementless group was 1.7 (significant, p=0.009). Venting did not influence rate of emboli however, venting was independently associated with significantly higher drainage (mean 604mls compared to 335mls without venting, p=0.018). There was no significant difference in post-operative haemoglobin or number of units transfused. Cranial emboli occur commonly after hip resurfacing. Their incidence is significantly reduced by the use of uncemented femoral component, however venting of proximal femur doesnot appear to make any difference.
This study investigated the difference in proximal tibial cortical strain distribution using a fixed or mobile bearing design for TKA. Eight fresh frozen human cadaver tibias were used. The strain magnitude and distribution on the anterior cortex of the proximal tibia during axial and rotational loading of the knee were measured with a quantitative full-field strain measurement technique (Electronic Speckle Pattern Interferometry). First, strain distributions of the intact knee were acquired. Subsequently, strain distributions after implantation of conventional and mobile bearing PCL retaining total knee implants (Scorpio®) were measured Under each loading condition, the minimum principal strain was greater in magnitude as compared to the maximum principal strain. Under 1,500 N axial loading, the resulting minimum principal strain magnitude and orientation was nearly identical between the mobile bearing configuration(500 ± 287m;e;), and the fixed bearing configuration (500 ± 286m;e;). In response to 10° internal rotation, this strain increased to 782 ± 371m;e; and 1000± 389m;e; for the mobile and fixed tibial component, respectively. In 10° external rotation, minimal principal strain decreased to 421 ± 233m;e; for the mobile bearing, but increased to 632 ± 293m;e; for the fixed bearing. These differences between mobile and fixed bearing scenarios were highly statistically significant. For this in-vitro study under exact controlled loading conditions the mobile bearing design induced less strain in the proximal tibia than the fixed bearing tibial component. The difference in strain levels may be of importance for bone remodeling and osseointegration.
We sought to identify the tensile properties of the medial patellofemoral ligament (MPFL), and determine whether its repair was sufficient as a means of restoring stability after acute lateral patella dislocation. We also sought to establish whether there was a correlation between the tensile properties of the anterior cruciate ligament (ACL) and the MPFL. 16 hind limbs of Merino Wethers were obtained and stored fresh frozen. The specimens were thawed overnight, dissected out and then placed in a water bath at 37 degrees centigrade for 30 minutes prior to testing. All testing was carried out in the water bath to approximate a more physiological environment. For each specimen the ACL was first tested to failure on an Instron 8511. The MPFL was then tested to failure, then repaired and retested to failure. Finally a reconstruction was carried out, using a flexor tendon, which was again tested to failure. Results: There was no correlation between ACL and MPFL strength (p=0.677). Statistical analysis showed that the intact MPFL was significantly stronger than the repaired MPFL (P=0.001) but no different to the reconstructed MPFL (P=0.224), with no difference between repaired and reconstructed (P=0.174). A Power analysis showed that there was not adequate power to detect a significant difference between the last two pairs, and that we would have needed over 35 specimens to show a difference. This study does not support carrying out a repair of the MPFL following an acute lateral patella dislocation, as it does not restore its tensile properties. It further suggests that a reconstruction may better restore the tensile properties of this ligament.
The majority of the scientific literature is based on data obtained from elderly cadaveric material. Little is known about the biomechanical properties of the soft tissue grafts currently used prior to implantation. The correct preconditioning and intraoperative tensioning of the soft tissue grafts has also not been investigated. The initial graft biomechanical properties are important. Inadequate tension will lead to continuing instability whilst excessive tension may cause accelerated joint arthrosis. The tension in the graft may decrease by 30% if it has not been cyclically pretensioned.
This device will also allow the accurate preconditioning of the graft, providing objective data that can then be compared to the subsequent clinical progress of the patient. All testing will be accomplished during the time it takes to prepare the tunnels for insertion of the graft, and as such will not prolong unnecessarily the operative time.
This set-up will be immersed in a saline water bath maintained at body temperature during testing. The load cell will be hermetically sealed, with clamps and water bath being autoclavable. With the facilities for draping, the test area will remain sterile. The auto graft clamps will be designed to allow fixation of various graft materials (eg semitendinosus, gracilis, bone-patella tendon-bone) and adjustable for graft lengths. The water bath will house a thermocouple, heating mat and controller to maintain the saline temperature to within 1°C. The testing system will be mounted on a stainless steel trolley for mobility in the operating room with an underlying shelf to house the associated electronics and a retractable side draw for storage of the laptop computer. The autograft will be preconditioned between two known loads for 20 cycles recording load and displacement simultaneously on a laptop computer. Once preconditioned, the autograft will then be used for the ACL reconstruction in the standard way.
