Biomechanical comparisons of knee stability after anterior cruciate ligament reconstruction between 2 clinically available transtibial procedures anatomic double bundle versus single bundle

Background: Several trials have compared the clinical results between anatomic double-bundle and single-bundle anterior cruciate ligament reconstruction procedures. However, it remains controversial whether the anatomic double-bundle procedure is superior to the single-bundle procedure. Hypothesis: The anatomic double-bundle procedure will be better than the single-bundle procedure at resisting anterior laxity, internal rotation laxity, and pivot-shift instability. Study Design: Controlled laboratory study. Methods: Eight cadaveric knees were tested in a 6 degrees of freedom rig using the following loading conditions: 90-N anterior tibial force, 5-N.m internal and external tibial torques, and a simulated pivot-shift test. Tibiofemoral kinematics during the flexion-extension cycle were recorded with an optical tracking system for (1) intact, (2) anterior cruciate ligament deficient knee, (3) anatomic double-bundle reconstruction, and (4) single-bundle reconstruction placed at 11 o'clock in the intercondylar notch. Results: There were significant reductions of anterior laxity of 3.5 mm at 20 degrees of flexion, internal rotational laxity of 2.5 degrees at 20 degrees of flexion, and anterior translations (2 mm) and internal rotations (5 degrees) in the simulated pivot-shift test in the double-bundle reconstruction compared with the single-bundle reconstruction. There were no significant differences between the 2 procedures for external rotation laxity. Conclusion: The postoperative anterior translation and internal rotation stability after anatomic double-bundle anterior cruciate ligament reconstruction were significantly better than after single-bundle reconstruction, in both static tests and the pivot shift. \textbackslashClinical Relevance: Unlike previous laboratory studies, this work used clinical arthroscopic methods for anterior cruciate ligament reconstruction, and found that the anatomic reconstruction was superior to a single graft placed at 11 o'clock

A technique of staged lateral release to correct patellar tracking in total knee arthroplasty

Optimal patellar tracking and component alignment are important in achieving a well-functioning total knee arthroplasty (TKA). The patella is constrained partly by design of the prosthetic trochlear groove, and patellar tracking is governed by a combination of static and dynamic factors. Maltracking may result from excessive or unbalanced tension in the surrounding soft tissues. This article describes a staged progressive lateral release of the patellar retinaculum in TKA, which is classified into 6 stages. Stage 1 transects the deep lateral patellofemoral ligament; stages 2 to 6 extend the lateral patellar incision distally from vastus lateralis to the tibial tubercle. This technique was used in a series of 96 primary TKAs. We report the rates of the various stages of lateral release and the variables that might affect the decision to perform such a release

Patellofemoral joint kinematics: The circular path of the patella around the trochlear axis

Differing descriptions of patellar motion relative to the femur have resulted from previous studies. We hypothesized that patellar kinematics would correlate to the trochlear geometry and that differing descriptions could be reconciled by accounting for differing alignments of measurement axes. Seven normal fresh-frozen knees were CT scanned, and their kinematics with quadriceps loading was measured by an optical tracker system. Kinematics was calculated in relation to the femoral epicondylar, anatomic, and mechanical axes. A novel trochlear axis was defined, between the centers of spheres best fitted to the medial and lateral trochlear articular surfaces. The path of the center of the patella was circular and uniplanar (root-mean-square error 0.3 mm) above 16 +/- 3 degrees (mean +/- SD) knee flexion. In the coronal plane, this circle was aligned 6 +/- 2 degrees from the femoral anatomical axis, close to the mechanical axis alignment. It was 91 +/- 3 degrees from the epicondylar axis, and 88 +/- 3 degrees from the trochlear axis. In the transverse plane it was 91 +/- 3 degrees and 88 +/- 3 degrees from the epicondylar and trochlear axes, respectively. Manipulation of the data to different axis alignments showed that differing previously published data could be reconciled. The circular path of patellar motion around the trochlea, aligned with the mechanical axis of the leg, is easily visualized and understood. (C) 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:589-594, 201

The influence of tibial component fixation techniques on resorption of supporting bone stock after total knee replacement

Item does not contain fulltextPeriprosthetic bone resorption after tibial prosthesis implantation remains a concern for long-term fixation performance. The fixation techniques may inherently aggravate the "stress-shielding" effect of the implant, leading to weakened bone foundation. In this study, two cemented tibial fixation cases (fully cemented and hybrid cementing with cement applied under the tibial tray leaving the stem uncemented) and three cementless cases relying on bony ingrowth (no, partial and fully ingrown) were modelled using the finite element method with a strain-adaptive remodelling theory incorporated to predict the change in the bone apparent density after prosthesis implantation. When the models were loaded with physiological knee joint loads, the predicted patterns of bone resorption correlated well with reported densitometry results. The modelling results showed that the firm anchorage fixation formed between the prosthesis and the bone for the fully cemented and fully ingrown cases greatly increased the amount of proximal bone resorption. Bone resorption in tibial fixations with a less secure anchorage (hybrid cementing, partial and no ingrowth) occurred at almost half the rate of the changes around the fixations with a firm anchorage. The results suggested that the hybrid cementing fixation or the cementless fixation with partial bony ingrowth (into the porous-coated prosthesis surface) is preferred for preserving proximal tibial bone stock, which should help to maintain post-operative fixation stability. Specifically, the hybrid cementing fixation induced the least amount of bone resorption

Finite element modelling of glenohumeral kinematics following total shoulder arthroplasty

Due to the shallowness of the glenohumeral joint, a challenging but essential requirement of a glenohumeral prosthesis is theprevention of joint dislocation. Weak glenoid bone stock and frequent dysfunction of the rotator cuff, both of which are common with rheumatoid arthritis, make it particularly difficult to achieve this design goal. Although a variety of prosthetic designs are commercially available only a few experimental studies have investigated the kinematics and dislocation characteristics of design variations. Analytical or numerical methods, which are predictive and more cost-effective, are, apart from simple rigid-body analyses, non-existent. The current investigation presents the results of a finite element analysis of the kinematics of a total shoulder joint validated using recently published experimental data for the same prostheses. The finite element model determined the loading required to dislocate the humeral head, and the corresponding translations, to within 4% of the experimental data. The finite element method compared dramatically better to the experimental data (mean difference = 2.9%) than did rigid-body predictions (mean difference = 37%).The goal of this study was to develop an accurate method that in future studies can be used for further investigations of the effect of design parameters on dislocation, particularly in the case of a dysfunctional rotator cuff. Inherently, the method also evaluates the glenoid fixation stresses in the relatively weak glenoid bone stock. Hence, design characteristics can be simultaneously optimised against dislocation as well as glenoid loosening