Validity of rotational laxity coupled with anterior translation of the knee: A cadaveric study comparing radiostereometry and the Rotab®.

BACKGROUND: In current practice, anterior cruciate ligament (ACL) tears can be diagnosed using several devices to measure anterior tibial translation and rotational knee laxity, but these measures are never collected together. The Rotab®, which yields simultaneous measurements of anterior tibial translation and passive lower limb rotation under stress, would therefore be advantageous in current practice, but its reliability has never been tested. AIM OF STUDY: To evaluate the accuracy and reliability of the Rotab® compared to the reference system, radiostereometric analysis (RSA). METHODS: This anatomical study was conducted on 14 lower limbs collected from fresh cadavers. Simultaneous measurements of anterior tibial translation and rotation were obtained with both systems, with antero-posterior (AP) forces of 134N and 250N using the Rotab®. Measurements were made on intact ACL and then repeated after ACL section. Variables were analyzed in univariate analysis by ANOVA, and the intraclass correlation coefficient (ICC) between the systems was determined by the Bland and Altman method. RESULTS: The difference between the two methods for evaluating anterior tibial translation was 0.05±0.98mm at 134N and 0.29±1.04mm at 250N. The correlation between the tests was high (r134=r250=0.97, p=0.8). The difference between the two methods for rotational laxity was 0.69±2.7° at 134N and 0.5±0.6° at 250N. The Rotab® showed a significant difference only at 250N for rotational laxity after the ACL tear. CONCLUSION: The Rotab® is a reliable device to measure rotational laxity coupled with anterior translation of the knee.

Is determination of the hip rotation center during computer-assisted surgery influenced by the pinless femoral sensor attachment method? An in vitro preliminary study comparing osseous pin fixation.

INTRODUCTION: Computer-assisted surgery improves the positioning of hip prostheses but requires use of transosseous pins requiring a complementary approach exposing the patient to rare but at times serious complications. The use of sensor arrays attached to the skin could advantageously replace pins provided that comparable results are obtained, but their validity has not yet been assessed. We conducted a prospective in vitro study to: measure the possible error of a cutaneous versus transosseous fixation to determine the hip rotation center (HRC) position and determine the inter- and intraobserver reproducibility of the cutaneous versus the transosseous fixation. HYPOTHESIS: Use of cutaneous sensor arrays while recording the HRC is sufficiently reliable for its calculation algorithm to provide measurement accuracy within 5mm. MATERIALS AND METHODS: A rigid array attached with either a silicone strap or an adhesive were compared to a transosseous array. Four series of 96 HRC measurements were collected by four operators on two cadavers, half with an array attached with a strap and half with an adhesive. The results were compared to those obtained by a sensor attached with transosseous pins. RESULTS: On condition that the hip-knee is mobilized in extension, a sensor array attached with an adhesive gives results with comparable accuracy (standard deviation [SD]: 2.89mm [1.9-4.8]) to the results obtained with a transosseous fixation (SD: 1.2mm [0.9-1.6]), with no significant inter- or intraobserver variation (0.97

Validation of the in vivo volumetric wear measurement for total knee prostheses in model-based RSA.

Implant failure related to polyethylene wear remains an important issue in total knee arthroplasty. Polyethylene wear is usually assessed in vivo by measuring the remaining insert thickness on X-ray images of the knee. To reflect the amount of wear debris more accurately, a 3-dimensional overlap measurement has been suggested, which is based on implant component models which are matched on calibrated stereo X-ray images using model-based roentgen stereophotogrammatic analysis. The goal of this study was to determine the influence of pose estimation, insert thickness deviation and variation in the femoral-tibial contact location on the accuracy and precision of the measurement using simulations and a phantom experiment. We found that the pose estimation was the largest source of variation. The 95% prediction interval varied between 111 and 283 mm(3), which is approximately 100-200% of the detected volumetric wear. Insert thickness variation resulted in prediction intervals of 74-174 mm(3). Variation of the femoral-tibial contact location in the phantom experiment gave a prediction interval of 40 mm(3). Large differences in the detected wear volume were found for different flexion angles. At most 56% of the true wear volume was detected (129 of 230 mm(3), 30° of flexion). In summary, both the accuracy and precision of the volumetric wear measurement were low. The prediction interval of the volumetric wear measurement is at least as large as the measurement outcome itself. This is an important limitation to the applicability of the volumetric wear measurement in clinical practice and further clinical validation is required.

Oral thromboprophylaxis following total hip replacement: the issue of compliance.

INTRODUCTION: Thirty-five to 40 days' thromboprophylaxis is recommended following total hip replacement (THR). Low molecular weight heparin (LMWH) injected by a health professional ensures good compliance. Compliance with recent oral anticoagulants has not been precisely assessed. Oral self-administration, without coagulation monitoring tests, may be a worrying issue in the management of what is a potentially catastrophic adverse event, without prodromal symptoms alerting the patient to the need for regular intake throughout the prescription period. HYPOTHESIS: It was hypothesized that compliance with these new oral anticoagulants is good over the entire treatment period. PATIENTS AND METHOD: The present cohort study prospectively assessed compliance with oral medication (two capsules of dabigatran etexilate [Pradaxa(®)] per day in a single dose at a set time) following THR. An electronic device continuously monitored the day and time of extraction of capsules from the package. All included patients underwent clinical and echo-Doppler examination at day 30±5 after the start of the study. RESULTS: Fifty-six patients were included at their discharge home. Overall compliance was 98.1% (3,188/3246 capsules correctly taken), falling off slightly over time but never below 97.1%. One patient was diagnosed with symptomatic thrombophlebitis 34 days postoperatively, associated with non-compliance at day 11. End of follow-up echo-Doppler found four cases of asymptomatic distal venous thrombosis. There were no hemorrhagic complications. DISCUSSION: The risk of thromboembolic complications diminishes over time, while oral anticoagulants have a wide therapeutic window and relatively long half-life (15-17 hrs). Efficacy was demonstrated, with improved patient comfort and cost-saving. Compliance in the present series was satisfactory. This, however, should not mean that patients not be appropriately informed, as in the present study, so as to improve compliance. LEVEL OF EVIDENCE: Level III, prospective diagnostic.

Total knee arthroplasty three-dimensional kinematic estimation prevision. From a two-dimensional fluoroscopy acquired dynamic model.

INTRODUCTION: To determine six-degree of freedom of total knee arthroplasty kinematics (TKA), optimized matching algorithms for single fluoroscopic image system may be used. Theoretical accuracy of these systems was reported. Nevertheless, all reports were done under idealized laboratory experimental conditions. The aim of this study was to evaluate the "true" accuracy of a flat panel single plane video-fluoroscopy system based on computed-assisted design (CAD) model matching and compare it to TKA kinematics obtained from optoelectronic measurements as gold standard. HYPOTHESIS: The estimation of the error produced by 2D/3D fluoroscopic registration in daily practice is misjudged in most available laboratory reports. MATERIAL AND METHODS: The experimental set-up used a TKA implanted into femoral and tibial cadaver bones. Thirty flexions were simultaneously registered using single plane fluoroscopy and an active optical tracking system. Kinematics registered were compared using the root mean square error (RMS), the concordance correlation coefficient and Bland & Altman plot analysis. RESULTS: The mean range of motion of flexion during the experiment was 106°. The respective RMS for flexion, varus-valgus and internal-external rotation were 0.68, 0.67 and 1.02°. The respective RMS for antero-posterior, medio-lateral and proximo-distal displacement were 1.3, 2.4 and 1.06 mm. Extreme values of the measured error concerning medio-lateral displacement were -5.4 and 22,1mm. DISCUSSIONS: Analysis found some outliners in all degree of freedom with a systematic error and larger standard deviation than already published data. One should make sure that during the experiment the motion of interest is in the in-plane direction. Moreover, this study brings out the true threshold detection of this type of analysis.

Dual mobility hip arthroplasty wear measurement: Experimental accuracy assessment using radiostereometric analysis (RSA).

INTRODUCTION: The use of dual mobility cups is an effective method to prevent dislocations. However, the specific design of these implants can raise the suspicion of increased wear and subsequent periprosthetic osteolysis. HYPOTHESIS: Using radiostereometric analysis (RSA), migration of the femoral head inside the cup of a dual mobility implant can be defined to apprehend polyethylene wear rate. STUDY OBJECTIVES: The study aimed to establish the precision of RSA measurement of femoral head migration in the cup of a dual mobility implant, and its intra- and interobserver variability. MATERIAL AND METHODS: A total hip prosthesis phantom was implanted and placed under weight loading conditions in a simulator. Model-based RSA measurement of implant penetration involved specially machined polyethylene liners with increasing concentric wear (no wear, then 0.25, 0.5 and 0.75mm). Three examiners, blinded to the level of wear, analyzed (10 times) the radiostereometric films of the four liners. There was one experienced, one trained, and one inexperienced examiner. Statistical analysis measured the accuracy, precision, and intra- and interobserver variability by calculating Root Mean Square Error (RMSE), Concordance Correlation Coefficient (CCC), Intra Class correlation Coefficient (ICC), and Bland-Altman plots. RESULTS: Our protocol, that used a simple geometric model rather than the manufacturer's CAD files, showed precision of 0.072mm and accuracy of 0.034mm, comparable with machining tolerances with low variability. Correlation between wear measurement and true value was excellent with a CCC of 0.9772. Intraobserver reproducibility was very good with an ICC of 0.9856, 0.9883 and 0.9842, respectively for examiners 1, 2 and 3. Interobserver reproducibility was excellent with a CCC of 0.9818 between examiners 2 and 1, and 0.9713 between examiners 3 and 1. DISCUSSION: Quantification of wear is indispensable for the surveillance of dual mobility implants. This in vitro study validates our measurement method. Our results, and comparison with other studies using different measurement technologies (RSA, standard radiographs, Martell method) make model-based RSA the reference method for measuring the wear of total hip prostheses in vivo. LEVEL OF EVIDENCE: Level 3. Prospective diagnostic study.