Three-dimensional bone kinematics in an anterior laxity test of the ankle joint

Questions addressed in this in-vitro study are (1) what are the actual three-dimensional kinematics of talus and calcaneus during an anterior drawer test as performed with the quasi-static anterior ankle tester (QAAT) (2) does laxity measurement with the QAAT represent the true anterior translation of talus relative to the tibia?. Simultaneous measurements were made with the QAAT and a three-dimensional kinematics analysis system in five specimens. The three-dimensional translations and rotations on three axes were analysed at 25, 50 and 100 N of applied anterior load, with increased ligament damage. For four out of five remaining specimens, anterior translation values of talus and calcaneus and values as measured with the QAAT show a significant increase with growing ligament damage and with higher loads. Skeletal motions of talus and calcaneus show great similarity in three different motion axes, with increased ligament damage and at any given load. Skeletal translations and rotations of talus and calcaneus show great similarity during an anterior drawer movement of the ankle joint. Anterior skeletal translation of the talus and calcaneus show fair correlation with the anterior displacements measurements of the QAAT. These QAAT measurements show an overestimation of the laxity value by more than 200% irrespective of the load applied. © Springer-Verlag 2007

The efficacy of autologous platelet gel in pain control and blood loss in total knee arthroplasty: An analysis of the haemoglobin, narcotic requirement and range of motion

Biological materials used to assist in haemostasis following total knee arthroplasty have been the subject of much recent research. Autologous platelet gel is a substance that is derived from platelet-rich plasma extracted from the patient's blood and centrifuged perioperatively, and is applied to exposed tissues, synovium and the lining of the wound at closure. Concentrating and applying these factors directly to the wound at the end of a total knee arthroplasty procedure may lead to more complete haemostasis, a reduction in perioperative blood loss, accelerated tissue repair and decreased postoperative pain. In this study, 98 unilateral total knee arthroplasties were evaluated retrospectively, 61 of which involved the intaroperative use of platelet gel, and 37 of which served as control subjects. Outcomes analysed were postoperative haemoglobin changes, intravenous and oral narcotic requirements, range of motion on discharge and total days in hospital. Patients receiving platelet gel during surgery had less postoperative blood loss as measured by differences in the preoperative and postoperative haemoglobin on day 3 (2.7 vs. 3.2 g/dl; P=0.026). The narcotic requirement was less in the platelet gel group for both intravenous (17.0 vs. 36.3 mg/day; P=0.024) and oral (1.84 vs. 2.75 tabs/day; P=0.063) medication. This group also achieved a higher range of motion prior to discharge (78.2 vs. 71.9; P=0.052) and were discharged an average of 1 day earlier than their control counterparts. Though further prospective trials are necessary, this study indicates that the application of autologous platelet gel may lead to improved haemostasis, better pain control and a shortened hospital stay

Accuracy of Model-based RSA Contour Reduction in a Typical Clinical Application

Marker-based roentgen stereophotogrammetric analysis (RSA) is an accurate method for measuring in vivo implant migration, which requires attachment of tantalum markers to the implant. Model-based RSA allows migration measurement without implant markers; digital pose estimation, which can be thought of as casting a shadow of a surface model of the implant into the stereoradiographs, is used instead. The number of surface models required in a given clinical study depends on the number of implanted sizes and design variations of prostheses. Contour selection can be used to limit pose estimation to areas of the prosthesis that do not vary with design, reducing the number of surface models required. The effect of contour reduction on the accuracy of the model-based method was investigated using three different contour selection schemes on tibial components in 24 patients at 3 and 6 month followup. The agreement interval (mean ± 2 standard deviations), which bounds the differences between the marker-based and model-based methods with contour reduction was smaller than −0.028 ± 0.254 mm. The data suggest that contour reduction does not result in unacceptable loss of model-based RSA accuracy, and that the model-based method can be used interchangeably with the marker-based method for measuring tibial component migration