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Document Title: Ramsey-CB-Jan01.shtml
Article Title: Assessment of functional knee bracing: an in vivo three-dimensional
kinematic analysis of the anterior cruciate deficient knee
Authors: Dan K. Ramsey, Mario Lamontagne, Per F. Wretenberg, Anders Valentin,
Björn Engström, Gunnar Németh
Publication: Clinical Biomechanics (Elsevier Science)
Date: January 2001
Volume 16, pages 61-70
Keywords: Functional knee bracing, brace, Steinmann bone-traction pins, three-dimensional infra-red kinematic analysis, 3D, ACL-deficient knee, biomechanics, anterior drawer, forwards tibial sliding, tibiofemoral kinematics, Three-dimensional kinematics; Anterior cruciate ligament; ACL deficiency, knee instability.
(Reference-denoting numbers appear in the same font and point size as the document text. As with all Knee Library documents, this article is provided in full-text form, complete with all figures and tables.)
Comments: This innovative study, the first knee-bracing study to use bone pins (one implanted into the tibia and another in the femur, and protruding through the skin and tipped with markers designed to be seen by three-dimensional infrared motion-recording cameras) comes to the conclusion that many others have come to: that functional knee bracing cannot be depended on to control forwards sliding of the tibia (also known as anterior tibial translation). Note that this same conclusion can also be arrived at by via a simple biomechanical analysis which takes into account the inherent difficulty in applying forwards forcing to the distal end of the femur. Said difficulty arises largely as a consequence of the hamstring tendons, whose presence makes it nearly impossible for the brace strap (the one located immediately above and behind the knee) to exert the required forwards forcing on the distal end of the femur. Although it is easy for any brace to exert the necessary rearwards forcing on the proximal end of the tibia (i.e. at the tibial tuberosity, hence just below the kneecap), this is of little value unless the brace can exert a force of equal magnitude (but in the opposite direction) above and behind the knee. Once again, this limitation is imposed by simple physical principles, particularly with regards to how the soft tissues of the leg impede any external device's ability to control movement of the leg bones. These same physical principles also explain why used-in-isolation functional braces are well-suited to protecting against sideways forcing and injurious hyperextension, but not against twisting. In other words, what a brace can and cannot do is heavily influenced by the general anatomy of the leg. (This means that a brace's limitations do not constitute a "failure". So, instead of saying that "knee braces fail when high loads are encountered or when load is applied in an unpredictable manner", the authors should be saying something similar to the following: "As would be expected from a simple biomechanical analysis, and as shown by our study and the findings of other researchers, it is inappropriate to expect a functional knee brace to be capable of exerting sufficient anterior-drawer-counteraction forcing to protect an ACL-deficient knee against pathological forwards tibial translation, just as it is inappropriate to expect any externally-worn used-in-isolation knee brace to be able to grip the leg bones well enough to protect against twisting-type injuries. Because braces seek to control the motion of the leg bones, the inherent limitations of functional knee bracing are primarily a consequence of the interference resulting from the presence of various soft-tissue structures.")
Note that in this study, the tension of the brace straps was not standardized, nor were efforts made to correlate strap tension to soft-tissue compression. All that was done was that the same person applied the bracing in each case, and that the bracing was applied in accordance with the manufacturer's recommendations. For any brace to have any hope of applying even a minor amount of anterior-drawer-counteraction forcing, special attention must be paid to the tensioning of the straps immediately above and below the knee; regrettably, this was not done here, and so it seems that all straps were tightened roughly equally and then only by feel. But even if concerted efforts were made to generate a certain amount of tissue compression, particularly just above the rear of the knee, then it is very likely that the conclusion would be that bracing is not able to reliably prevent anterior drawer. However, since this study found a minor amount of anterior-drawer counteraction, it is plausible that, if the brace's knee-region straps had been tightened more firmly, a significant amount of anterior-drawer counteraction might have been obtained. Finally, the reader should keep in mind that the DonJoy brace is not unique, because these same points apply to all other dual-upright, frame-type functional knee braces.
Abstract
Objective. To describe three-dimensional tibial and femoral movements in vivo and examine the effect of a brace on knee kinematics during moderate to intense activity.
Design. Skeletal kinematics of anterior cruciate ligament deficient knees was measured with and without braces during moderate to intense activity.
Background. Invasive markers implanted into the tibia and femur are the most accurate means to directly measure skeletal motion and may provide a more sensitive measure of the differences between brace conditions.
Methods. Steinmann traction pins were implanted into the femur and tibia of four subjects having a partial or complete anterior cruciate ligament rupture. Non-braced and braced conditions were randomly assigned and subjects jumped for maximal horizontal distance to sufficiently stress the anterior cruciate ligament.
Results. Intra-subject peak vertical force and posterior shear force were generally consistent between conditions. Intra-subject kinematics was repeatable but linear displacements between brace conditions were small. differences in angular and linear skeletal motion were observed across subjects. Bracing the anterior cruciate ligament deficient knee resulted in only minor kinematic changes in tibiofemoral joint motion.
Conclusion. In this study, no consistent reductions in anterior tibial translations were observed as a function of the knee brace tested.
Relevance. Investigations have reported that knee braces fail when high loads are encountered or when load is applied in an unpredictable manner. Questions remain regarding tibiofemoral joint motion, in particular linear displacements. The pin technique is a means for direct skeletal measurement and may provide a more sensitive measure of the differences between brace conditions.
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