Introduction

Wear and survival of total joint replacements do not depend on the duration of the implant in situ, but rather on the amount of its use, i.e. the patient's activity level [1]. With this in mind, the present study was driven by two questions: (1) How does total knee replacement (TKR) respond to the simulation of daily highly demanding activities? (2) How does implant size affect wear response of total knee replacement (TKR)?

Introduction

Total knee arthroplasty (TKA) is a consolidated orthopaedic procedure and success of such operation depends on the prosthetic design [1]. Unfortunately, as there is a good survival rate of primary TKA, failures occur for factors concerning the polyethylene composition of the implants, secondary osteolysis, and ultimately loosening of the implants are the usual causes of failure after normal use [2]. Dynamic in vitro testing of the human knee continues to be an area of interest to the orthopaedic biomechanics community. The scope of this work was to assess pre-clinically the wear behaviour of polyethylene knee insert under a realistic stair climbing activity using a displacement knee simulator.

Introduction: Preliminary data suggest that immobilization in external rotation may be effective in lowering the incidence of recurrence after first traumatic shoulder dislocation, with a zero reoccurrence rate reported at 15 months follow-up. The purpose of the present study was to ascertain whether this method could lower the incidence of recurrent dislocation in a young, very physically active population.

Methods: In an IRB approved prospective study, young males who sustained first traumatic shoulder dislocation were randomized to be treated for four weeks either using a traditional internal rotation brace or a new device which immobilizes the shoulder at 15 to 20 degrees of external rotation. Subjects were then treated according to a standard physical therapy protocol. Follow-up was done at five time points in the first year post dislocation. Subjects with clinically stable shoulders resumed full activity after three months. Differences in outcome were assessed by the chi square test.

Results: Thirty nine subjects participated in the study. Thirty of them were soldiers. Twenty four subjects were treated with external rotation braces. At follow-up of between 4 to 28 months, a new dislocation was documented in 8 of the 24 subjects immobilized in external rotation (33%) and in 5 of the 15 subjects immobilized in internal rotation (33 %). No statistical difference (p=1.0) was found between the instability rates of the two treatment groups.

Discussion: The present study indicates that even in a short-term follow-up the technique of immobilizing a first dislocation in external rotation was not effective in lowering the incidence of recurrent shoulder dislocations in a young, physically active population.

Introduction The accuracy of ultrasonography has been reported to be high in diagnosing full thickness rotator cuff tears if measurements are made in both in the coronal and sagital planes. The purpose of this study is to determine how well pre-operative shoulder ultrasound rotator tear measurements when performed only in the coronal plane, the common practice in Israel, predicts the intra-operative surgical findings.

Materials and Methods Fifty consecutive patients who underwent open rotator cuff repairs were included in the study. All patients underwent a pre-operative ultrasound by the same experienced musculoskeletal ultrasoundist. Rotator cuff tears were measured in the coronal plane only. This was compared with the tear size measured intra-operatively. Regression analysis was done between the two variables.

Results The mean size of rotator cuff tears as determined by ultrasonography was 15.56±8.07mm and the measure size of the tears intraoperatively was 27.94±9.8 mm. The result of the regression analysis of the two variables was R2= 0.268405 for the first 25 patients and R2= 0.310309 for the second 25 patients.

Discussion Using ultrasound it is easy to visualize the extent of rotator tears in the coronal plane, but more time consuming to measure the extent in the sagital plane, where the tear may have its greatest extension. Ultrasound measurements tear measurements in this study, made only in the coronal plane correlated poorly with intraoperative findings and only minimally improved over the time course of the study.

Conclusion Proper assessment of a possible candidate for a rotator cuff repair should include an ultrasound with the tear size measured specifically in both the coronal and sagital planes.