Frank C. Mendel

Morphometry of the lumbar spine: anatomical perspectives related to transpedicular fixation.

The pedicles of lumbar vertebrae were measured both directly and radiographically to determine the differences between the sexes and the accuracy of radiographic measurement. The lumbar pedicles of cadavera of forty-nine patients--twenty-four men and twenty-five women--who died between the ages of sixty and ninety-eight years were measured directly and on radiographs. The pedicles of lumbar vertebrae from fifty-one patients--twenty-three men and twenty-eight women--between the ages of twenty and fifty years who had low-back problems were measured on radiographs and computerized tomographic scans. Comparison revealed that the average transverse and sagittal diameters of the pedicles and the distance from the posterior aspect of the laminar cortex to the anterior aspect of the cortex of the vertebral body along the central axis of the pedicles were 5 to 20 per cent greater in men, but the transverse and sagittal angles of the pedicle did not differ significantly between the sexes. Measurements on radiographs and computerized tomographic scans of the transverse angles of the pedicles and of the distances from the posterior aspect of the laminar cortex to the anterior aspect of the cortex of the vertebral body from the second to the fifth lumbar vertebra were greater than direct measurements, even without magnification. Direct measurements of the diameters of the transverse and sagittal diameters of the pedicle of the fifth lumbar vertebra, however, were greater than the radiographic measurements.

Evidence from Cadavers Suggestive of Entrapment of Fifth Lumbar Spinal Nerves by Lumbosacral Ligaments

Lumbosacral spines from 51 geriatric-age cadavers (25 men and 26 women) were examined both grossly and under the dissecting microscope for evidence of compression of fifth lumbar spinal nerves by their respective lumbosacral ligaments. These ligaments were found to extend from the transverse process and body of L5 to the ala of the sacrum in 97% of the specimens, and from the transverse process and body of L5 to the promontory of the sacrum in 3% of the specimens. Anterior primary rami of the fifth lumbar spinal nerve were observed to be compressed in 11% (11 of 102) of the specimens examined grossly and under the dissecting microscope. Histologic evidence of chronic compression, as suggested by perineurial and endoneurial fibrosis, peripheral thinning of myelin sheaths, or subjective evidence of a shift in fiber diameter to a population of smaller size fibers was found, deep to the lumbosacral ligament, in three of the 11 nerves judged to be compressed. The information derived is of interest to the clinician whose patient presents with L5 root signs and a myelogram, discogram, and computed tomographic scan which do not show any abnormality. The possibility of extraforaminal compression must be considered as a possible source of the clinical signs.

Use of Hands and Feet of Three-Toed Sloths (Bradypus variegatus) during Climbing and Terrestrial Locomotion

Bradypus does not drag itself along the ground, as has been often reported, except when on a smooth, hard surface. Limb-movement patterns are similar throughout terrestrial and climbing activities, but gaits vary from lateral-sequence, diagonal-couplet modes during terrestrial walking, to trots and diagonal-sequence, diagonal-couplet gaits during climbing of supports of small diameter. Bradypus and Choloepus move similarly when on the ground, and while climbing small caliber supports, but differ in their means of climbing larger supports and descending.

The hand of two -toed sloths (Choloepus): Its anatomy and potential uses relative to size of support

Hands of two‐toed sloths (Choloepus) are long, narrow, hook‐like apparatuses with only two functional digits (II and III); rays I and IV are represented only by metacarpals. The proximal phalanges of digits II and III are shortened to essentially proximal and distal articulating surfaces, and all but distal interphalangeal joints of these digits are restricted by interlocking surfaces to minimal ranges of flexion and extension. Several intercarpal joints and the wrist joint, however, allow wide ranges of movement in several axes. Wide excursion at the wrist is permitted by an extremely lax joint capsule, the manner of insertion of several prime movers of the carpus, and the reduced participation of the ulna in the wrist joint. Several extrinsic digital muscles, particularly extensors, are absent and others have unusual actions. Intrinsic musculature consists primarily of mm. interossei and m. extensor digitorum brevis, although other, inconstant muscles do occur. Hands of Choloepus are used as flexible hooks on supports less than 52 mm in diameter and as fixed grapnels on larger supports. In both cases, distal phalanges (and covering claws) form the “hook” element. Whereas bare volar pads seem to be adjunctive on supports smaller than 52 mm in diameter, they are essential on those larger than 65 mm. Two‐toed sloths may prefer supports 50 mm in diameter or smaller. The potential importance of vines as supports is discussed.

Foot of two‐toed sloths: Its anatomy and potential uses relative to size of support

Feet of two‐toed sloths (Choloepus) are long, narrow, hook‐like appendages with only three functional digits, numbers II, III, and IV; Rays I and V are represented by metatarsals. Proximal phalanges of complete digits are little more than proximal and distal articulating surfaces. All interphalangeal joints are restricted, by interlocking surfaces, to flexion and extension. Ankle and transverse tarsal joints, however, allow extreme flexion and inversion of foot. Powerful digital flexion is augmented by several muscles from extensor compartment of leg. Intrinsic foot musculature is reduced to flexors and extensors but these, with the exception of lumbricals, are large and well developed. Choloepus uses its feet much like hooks with distal phalanges and covering claws forming the “hook” element. These hook‐like appendages are seemingly best suited for supports less than 50 mm in diameter suggesting that two‐toed sloths may prefer supports of this size in their natural habitat.

High-Voltage Pulsed Current: Its Influence on Diameters of Histamine-Dilated Arterioles in Hamster Cheek Pouches

Results from five independent studies from our laboratory indicate that cathodal high-voltage pulsed current (HVPC) significantly curbs posttraumatic edema formation in several animal models. Conversely, anodal HVPC did not curb edema formation. The mechanism by which HVPC reduces edema formation is unknown. We hypothesize that HVPC causes a decrease in local blood flow by active vasoconstriction of arterioles. Because we had previously observed positive effects with cathodal HVPC but not anodal HVPC, we further hypothesized that cathodal but not anodal HVPC would reduce diameters of histamine-dilated arterioles. Changes in diameters of resistance arterioles (5 to 30 microns internal diameter) were measured directly in cheek pouches of anesthetized hamsters, using in vivo video microscopy. Three minutes after superfusion with the inflammatory mediator (histamine) was begun, sensory-level HVPC at 120pps was applied concurrently for 30 minutes. Five animals received cathodal HVPC and five received anodal HVPC. Four other animals received 30-minute treatments of both cathodal and anodal HVPC in random order. Three control animals received histamine without HVPC for 30 minutes. Diameter changes of one arteriole from each cheek pouch was measured every 20 seconds throughout the treatment period. One-way analysis of variance (ANOVA) with repeated measures showed that diameters of histamine-dilated controls varied little over 30 minutes, and that adding cathodal HVPC did not significantly alter diameters of arterioles superfused with histamine. However, applying anodal HVPC to histamine-dilated arterioles significantly reduced arteriolar diameters. These results do not support the hypothesis that cathodal HVPC curbs edema formation by increasing arteriolar tone in the injured area.

Simulation-Based Design of Exoskeletons Using Musculoskeletal Analysis

Exoskeletons are a new class of articulated mechanical systems whose performance is realized while in intimate contact with the human user. The overall performance depends on many factors including selection of architecture, device, parameters and the nature of the coupling to the human, offering numerous challenges to design-evaluation and refinement. In this paper, we discuss merger of techniques from the musculoskeletal analysis and simulation-based design to study and analyze the performance of such exoskeletons. A representative example of a simplified exoskeleton interacting with and assisting the human arm is used to illustrate principal ideas. Overall, four different case-scenarios are developed and examined with quantitative performance measures to evaluate the effectiveness of the design and allow for design refinement. The results show that augmentation by way of the exoskeleton can lead to a significant reduction in muscle loading.© 2010 ASME

Kinematics analysis of in-parallel 5 DOF haptic device

Parallel-architecture haptic devices offer significant advantages over serial-architecture counterparts in applications requiring high stiffness and high accuracy. To this end, many haptic devices have been created and deployed by modularly piecing together several serial-chain arms to form an in-parallel system. However, the overall system performance depends both on the nature of the individual arms as well as their interactions. We build on the rich theoretical background of constrained articulated mechanical systems to provide a systematic framework for formulation of system-level kinematic performance from individual-arm characteristics. Specifically, we develop the system-level kinematic model in a symbolic (yet algorithmic) fashion that facilitates: (i) computational development of pertinent symbolic equations; (ii) generalization to arbitrary architectures; and (iii) combined symbolic/numeric analyses of performance (workspace, singularities, design sensitivities). These various aspects are illustrated using the example of the Quanser High Definition Haptic Device (HD)2 — an in-parallel haptic device formed by coupling two 3-link Phantom 1.5 type serial chain manipulators with appropriate passive joints. We also briefly discuss aspects of ongoing work for design-prototyping and validation, taking advantage of tools from Virtual Prototyping and Hardware-in-the-Loop testing.

Virtual musculoskeletal scenario-testing case-studies

Doctors, dentists, nurses, athletic trainers, occupational therapists and allied health-care professionals are expected to learn the linkage between anatomy, physiology and ultimately functional-performance of muscles i.e. how muscles affect movement or which sets of muscles carry various loads. However the extent of understanding of functional-performance that can be imparted in a didactic-lecture or cadaver-lab setting of a ldquoGross Anatomyrdquo class is limited. Hence we seek to create the architecture and algorithms for scaffolded interaction with human musculoskeletal simulation models (virtual prototypes) that can make varied ldquowhat-ifrdquo type analyses and hypothesis-testing possible. This is very pertinent in the context of the target audience of healthcare professionals who may lack prior exposure to such virtual computational scenario testing tools. Providing such access is vital to training of the next generation of health care professionals to leverage ubiquitous computing and the quantitative-paradigm.

Virtual prototyping and hardware-in-the-loop testing for musculoskeletal system analysis

In this paper, we present some ongoing research in the development of tools for biological hypothesis testing, leveraging research methodologies that have revolutionized the mechatronics domain. In particular, this work emphasizes: (a) development of suitable low-resolution computational models, (b) simulation, testing and iterative what-if studies performed using virtual prototyping; and (c) development of a test-bed suitable for hardware-in-the-loop testing. We anticipate that such a coupling of computational analysis with development of hardware-in-the-loop simulations plays a significant role in rapid and systematic validation of biological hypotheses. Specifically in the context of musculoskeletal system analysis, we focus on presenting two aspects in greater detail: (i) development of a low-resolution screw-theoretic computational model; and (ii) development of an integrated framework for rapid virtual prototyping and hardware-in-the-loop testing. A case study of bite force estimation in members of the felid (cat) family helps unify the presentation of many of these aspects.