Positioning, biomechanical

The ability of cleansers to positively affect the moisturization of skin can further be measured by evaluating biomechanical properties that are intrinsically linked to hydration state. For example, changes in skin softness are directly related to hydration state, and Figure 31.16 shows how biomechanical... 

Ovariectomized athymic mice under premenopausal-simulated conditions and estrogen receptor-positive human breast cancer cells (MCF-7) were fed a diet containing 10% sesame seed and implanted with tamoxifen pellets (5 mg 60-day release). Results indicated that sesame did not inhibit tumor growth and tended to negate the tumor inhibitory effect of tamoxifen. Sesame alone and combined with tamoxifen enhanced femur biomechanical strength but caused no differences in bone mineral content or bone mineral density in either the femur or lumbar vertebrae (Sacco et al. 2007). 

Studies of the normal biomechanics of the proximal wrist joint have determined that the scaphoid and lunate bones have separate, distinct areas of contact on the distal radius/triangular fibrocartil-age complex surface [Viegas et al., 1987] so that the contact areas were localized and accounted for a relatively small fraction of the joint surface, regardless of wrist position (average of 20.6%). The contact areas shift from a more volar location to a more dorsal location as the wrist moves from flexion to extension. Overall, the scaphoid contact area is 1.47 times greater than that of the lunate. The... 

FIGURE 76.1 Planes and axes are illustrated in anatomical position. The central coordinate system with its origin between the cornua of the sacrum is shown. (From White III A.A. and Panjabi M.M. 1990. Clinical Biomechanics of the Spine, 2nd ed., p. 87. Philadelphia, JB Lippincott Company. With permission.)... 

Cappozzo, A., Catani, F., Della Croce, U., and Leardini, A. (1995). Position and orientation in space of bones during movement anatomical frame definition and determination. Clinical Biomechanics, 10(4), 171-178. 

The primary sources of control for body-powered devices are biomechanical in nature. Movement, or force, from a body joint or multiple joints is used to change position, or develop a force/ pressure that can be transduced by a harness and Bowden cable and/or mechanical switches. Typically, inputs such as chin and head force/movement, glenohumeral flexion/extension or abduction/ adduction, biscapular and scapular abduction, shoulder elevation and depression, chest expansion, and elbow or wrist movements are used. However, direct force/motion from muscle(s) has also been used by way of surgical procedures such as muscle tunnel cinepiasty (Sauerbruch, 1916) and the Krukenberg cinepiasty (Krukenberg, 1917). 

Previously, anatomical studies have been performed to know the position of the anatomical anterior cruciate ligament (ACL) insertion [1-18], and the ACL can be divided into two parts the anteromedial (AM) and posterolateral (PL) bundles [1], These bundles have different functimis with different lengths and force-change patterns [19-21], and some biomechanical studies described that anatomical double-bundle (DB) ACL reconstruction achieved equal knee kinematics to those of the intact knee with stability of tibial anterior translation and rotation [22-24]. As a result, anatomical DB ACL reconstruction is a widely used procedure. Femoral... 

The second aim of this chapter is to answer the following question Can the clinically available transtibial procedure for anatomic DB reconstruction really obtain significantly better knee stability in comparison with the conventional SB reconstruction procedure This question must be asked because the previous biomechanical studies, which reported that the former procedure can obtain significantly better knee stability than the latter procedure [11-13], widely exposed the knee joint and directly identify the anatomic attachments. Clinically, however, the authors have used an arthroscopic transtibial procedure for femoral tuimel creation. Therefore, there is a possibility that the femoral tunnel positions in the clinical are not identical to the ideal tuimel locations created in the previous biomechanical studies. To answer the following question, the authors performed the arthroscopic transtibial procedure of anatomic DB reconstruction, which had been performed in the authors clinical practice, in cadaver specimens, and compared the results with those of the conventional SB reconstruction procedure [11]. 

The second study question was whether the clinically available transtibial procedure for anatomic DB reconstruction can really obtain significantly better knee stability in comparison with the conventional SB reconstruction procedure. The anterior translation laxity in response to a 90-N anterior drawer force was significantly less after the anatomic DB reconstmction than after the SB reconstruction from 0 to 75° of knee flexion. Previous biomechanical studies have shown that the PL bundle of the intact ACL carries one-half to two-thirds of the total force in the ACL near full extension of the knee, when the knee is subjected to an anterior tibial load [8, 26, 27]. As the conventional SB reconstmction reproduces only the AM bundle, loss of the function of the natural PL bundle is considered to result in the insufficient function in the conventional SB reconstmction in the range between 0 and 75° of knee flexion. On the other hand, Yamamoto et al. [22] and Yasuda et al. [28] reported that the reconstmcted PL bundle cannot restrain anterior tibial translation at flexion angles of the knee. This fact explains the similarity concerning the knee laxity between the two reconstmctions namely, only the reconstmcted AM bundle stabilizes the knee near flexion position in response to anterior tibial load. 

It is critical to understand functional anatomy and biomechanics of the AM and PL bundles of the ACL in order to understand the theory of the anatomic double-bimdle ACL reconstruction. It has been well known that the mid-substance fibers of the AM and PL bundles have different functions The AM bundle mid-substance is stretched in the full extension position, relaxed at 20-60 ° of knee flexion, and again stretched in a flexion position of more than 90° [9]. The PL bundle mid-substance is stretched in the full extension position, whereas it becomes slack in a flexion position [9]. In response to an anterior tibial load, the magnitude of the in situ force in the PL bundle mid-substance was larger than that in the AM bundle mid-substance at knee flexion angles between 0 ° and 45 ° [10]. Under a combined rotatory load, the PL bundle mid-substance is as important as the AM bundle mid-substance, especially when the knee is in the near extension position [11]. 

A key factor for successful ACLR is the initial graft tension. There is a close correlation between the initial tension required to control abnormal anterior laxity and the tunnel position [17-20]. Thus, the biomechanical study on human cadaveric knees was conducted to determine the desirable graft tension in the rectangular tunnel ACLR in which the femoral tuimel creation is independent of the tibial tunnel or the round tunnel ACLR in which the femoral tunnel is created via the transtibial tunnel [16] (Fig. 31.4). We found that at 15° of flexion, the mean laxity match pretension for the rectangular tuimel ACL-reconstructed knees was 8.6 4.8 N, whereas that for the round tunnel ACL-reconstructed knees was 34.8 9.3 N. Thus, initial graft tension required to restore normal anteroposterior... 

Transport the plumb line on the IV pole with its hand position marked, the force plate paper with force plate center and foot positions marked and the subject to the X-ray facilities at the Spine Institute of the Orthopaedic Department at Doctors Hospital (about 2 blocks away from the Biomechanics Laboratory) with all of the LEDs in place. Have the subject stand in the second position, with arms out of the path of the X-ray in the sagittal plane view. Align the subject as closely to the true sagittal plane as possible by viewing along the sight of the X-ray beam and noting the position of the shoulders and patellas as in the plane of the... 

Kinematics of the Lumbosacral Junction. The second major biomechanical fundamental of the spine is to allow movement. The study of rigid body movement is kinematics. It is important to realize that as a vertebra moves from one position to the next, this motion can be described in a variety of ways. By assuming the vertebra is a rigid body, we may describe its motion in terms of rotation and translation. Note that translation is dependent upon which point on the vertebra is selected. In two dimensions, the... 

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