RUPERT: a Device for Robotic Upper Extremity Repetitive Therapy.

We report the development and initial evaluation of a device for robotic assisted upper extremity repetitive therapy (RUPERT). Intense repetitive physical therapies provided by individualized interaction between the patient and a rehabilitation specialist to overcome upper extremity impairment after stroke are beneficial, however, they are expensive and difficult to evaluate quantitatively and objectively. The need is urgent and growing for a low cost, safe and easy to use robotic device to assist the patient and the therapist to fully achieve the potential benefit of task-based repetitive physical therapies. We designed a pneumatic muscle (PM) driven therapeutic device, the RUPERT, that is wearable and provides assistive forces required to move the arm during performance of several critical tasks of daily living. The robot has four degrees of freedom at shoulder, elbow and wrist. The sensors feedback position and force information for quantitative evaluation of task performance. It has the potential of providing a take-home method of supplementing therapy. The device can also provide real-time, objective assessment of functional improvement of therapy.

A pneumatic muscle hand therapy device.

Intensive repetitive therapy improves function and quality of life for stroke patients. Intense therapies to overcome upper extremity impairment are beneficial, however, they are expensive because, in part, they rely on individualized interaction between the patient and rehabilitation specialist. The development of a pneumatic muscle driven hand therapy device, the Mentortrade mark, reinforces the need for volitional activation of joint movement while concurrently offering knowledge of results about range of motion, muscle activity or resistance to movement. The device is well tolerated and has received favorable comments from stroke survivors, their caregivers, and therapists.

A biomechanical comparison of Gardner-Wells tongs and halo device used for cervical spine traction.

SUMMARY OF BACKGROUND DATA: Unstable cervical spine fractures and dislocations are often reduced by the application of axial traction using a halo or Gardner-Wells tongs. Failure of tong or halo attachment can cause substantial morbidity and usually occurs at the pin-bone interface. Institutions commonly clean and reuse tongs. The effect of tong wear on pullout strength and the strength of the halo used as a traction device have not been documented. METHODS: A skull model biomechanically similar to human calvarium was used to compare the axial pullout strengths of four sets of new tongs, three sets of rarely used tongs, and one set of heavily used tongs, as well as a standard four-pin halo. RESULTS: The pullout strength of tongs tightened to the manufacturer's recommended level appeared to decrease with increased use. Measurement of the pin force generated by each set of tongs and of the spring constant of each spring, as well as inspection of the tongs after testing, suggested that the decrease in pull-out strength may be partly attributable to spring and/or pin wear. The pullout strength of the halo or of the new or slightly used tongs but not the heavily used tongs exceeded the maximum weight used clinically in cervical spine traction. CONCLUSION: The data suggest that consideration be given to replacement or recalibration of heavily used tongs.

The effects of pedicle screw fit. An in vitro study.

STUDY DESIGN: The effects of pedicle screw size (major diameter and length) on fixation stiffness in osteoporotic and nonosteoporotic vertebrae were evaluated in vitro. METHODS: Lumbar vertebrae were obtained from two fresh frozen human spines. Bone mineral densities were determined using dual energy radiograph absorptiometry, followed by nondestructive mechanical testing of the specimens instrumented with pedicle screws. A loading technique was used that more closely mimics loading of pedicle screws in vivo. RESULTS: Testing revealed that for good quality bone, screw size had a significant effect on fixation stiffness, but the effect of penetration depth depended on pedicle fill, and vice versa. In nonosteoporotic bone, the use of a longer screw increased fixation stiffness if the screw filled up the pedicle by 70% or more. The use of wider screws increased the fixation stiffness if the penetration depth was 80% or more. CONCLUSION: Screw size had little or no effect on fixation stiffness in osteoporotic bone.

Bone remodeling and in vivo strain analysis of intact and implanted greyhound proximal femora.

Pre- and poststudy motion and gait analyses of eight size-matched male greyhounds confirmed uniform loading of their femora. Subminiature strain gages implanted on the intact inferior and anterior aspects of the femoral neck in six greyhounds indicated in vivo strain variations among test animals. Motion and gait analyses confirmed uniform loading of femora following unilateral hemiarthroplasty with cobalt-chromium hip implants. In vivo strain measurements adjacent to the implants indicated large variations among test animals. A consistent direction of strain change relative to the intact femur was noted, even though strain changes varied in magnitude. Image analysis of microradiographs indicated insignificant differences in the cortical areas of implanted and intact femora. Extensive new trabecular bone formation was noted along the implant in the endosteal cavity and correlated with a combination of implant placement and exercise level. Most of the bone was formed with centrally placed implants in exercised dogs, and the least with stems on the medial neck surface in rested dogs. Iliac crest biopsies indicated that bone formation rates slowed in rested animals and remained constant throughout the study in exercised animals. All implanted femora had a thin (< 1 mm thick) aligned fibrous tissue layer separating the implant from bone. It varied in thickness as a function of the aspect of the implant. Exercised dogs had a larger proportion of fibrous tissue on the anterior and posterior aspects, while rested dogs had a larger proportion of fibrous tissue on the medial and lateral aspects.

Measurements of long-term periprosthetic bone changes around a unique composite implant.

Periprosthetic bone changes around a non-bonded composite implant were measured after 6.5 years of implantation. The implanted and unimplanted femora of three canines were cut simultaneously at 3-mm increments. Cortical bone changes at all levels were determined from contact radiographs of the sections using an image analysis system. Alternating sections were cut into 3-mm cubes. The elastic properties of the cancellous bone cubes were determined using ultrasonic techniques. The method of directed secants was used to determine the cancellous bone orientation. The proximal cortical wall thickness on the implanted side increases by an average of 30%. The cancellous bone directly adjacent to the implant was an almost continuous shell encircling the prosthesis. The periprosthetic orientation was circumferential around the implant. The elastic and shear moduli of the cancellous bone increased on the implanted side. The bone changes are currently being correlated with results from finite element calculations.

A hydrogel pericardial patch.

Patients undergoing repeat cardiac operations are higher operative risks than those undergoing an initial cardiac procedure because adhesion formation can occur if the native pericardium is not closed. A unique composite patch that may be used to augment the pericardial tissue when primary closure is not possible has been developed. The patch is made of a hydrogel, poly (2-hydroxyethyl methacrylate), reinforced with an ethylene tetrafluoroethylene (ETFE) mesh. The mesh provides the needed mechanical properties, whereas the patch's surface properties are comparable to the hydrogel. Two types of patches were fabricated: one with the mesh weave at a perpendicular orientation and one at 45 degrees to the principle loading direction. The patches were mechanically tested and compared with canine pericardium. Ultimate tensile strength of the patches is not significantly different from canine pericardium (p less than 0.05), are the patch suture strength is nearly twice that of canine pericardium. The perpendicular patch is stiffer than canine pericardium, whereas the 45 degree patch is not (p less than 0.05). The 45 degree patch shows considerable promise as a pericardial substitute because it closely matches the properties native canine pericardium.

Alteration of retrieved implants in vitro by processing and infiltrating fluids.

Undecalcified histology has proved of immense value in the examination of the interface membrane between the prosthesis and bone. However, to provide such histological sections, dehydrating and clearing fluids as well as plastic infiltrating fluids must be used. This study investigates the possibility that some of these commonly used fluids may alter the biomaterial after removal from the body and be misinterpreted as an in vivo product. Ten different routinely used fluids were tested on 11 different biomaterials that are commonly used in prosthetic devices. The nonmetal biomaterials were placed in glass tubes containing the different fluids at room temperature for 5 days. The biomaterials were assessed for changes each day. After 5 days the biomaterial was examined and discarded and the glass tube was centrifuged. The pellet was examined using polarized light microscopy. Polysulfone and bone cement was found to be considerably altered in vitro by most of these fluids. While the components (plasticizer and catalyst) of the plastic fluids caused some changes to the biomaterial. Spurr's and GMA did not cause any alterations to any of the biomaterials that were examined.

A canine composite femoral stem. An in vivo study.

To evaluate a carbon fiber/polysulfone composite femoral stem, a press-fit unilateral hemiarthroplasty was performed in 17 greyhounds. The implant was designed to have strength and elastic properties commensurate with the proximal canine femur. The implant geometry was such that the naturally occurring internal cancellous structures of the proximal femur would be preserved and participate in load transfer from the implant to the bone. Animals were killed at one, five, ten, 16, and 24 months. At necropsy all the femoral stems were well fixed and functioning. All implants maintained their structural integrity. Radiographs and computed tomography scans showed a constructive bone remodeling response. Histologic analysis revealed a benign host tissue response, with few inflammatory cells observed. Both bone and fibrous tissue were observed at the implant-host tissue interface. Implants fabricated from carbon/polysulfone composites have the potential for use in load-bearing applications. An implant with appropriate elastic properties provides the opportunity for the natural bone remodeling response to enhance implant stability. Naturally occurring internal cancellous structures can be utilized for load transfer by femoral components. Press-fit devices with no physical or chemical bone-bonding mechanisms can attain long-term successful functional performance.