Biomedical subjects
Publications and source records attributed to K R Kaufman.
A dynamic knee-brace system (DKBS) has been designed which provides stance phase stability and swing phase freedom. A wrap-spring clutch controls knee flexion. Clutch optimization was performed minimizing clutch length. Kinematic tests on a normal subject using the DKBS document nearly normal dynamic knee flexion during swing (38 degrees versus 53 degrees for normal).
A self-contained electronically controlled dynamic knee-brace system (DKBS) has been designed and tested which allows knee flexion during swing phase, but restricts flexion during the stance phase of gait. Cardiovascular energy measurements indicate that DKBS use allowed a more energy efficient gait.
This paper examined the feasibility of using different optimization criteria in inverse dynamic optimization to predict antagonistic muscle forces and joint reaction forces during isokinetic flexion/extension and isometric extension exercises of the knee. Both quadriceps and hamstrings muscle groups were included in this study. The knee joint motion included flexion/extension, varus/valgus, and internal/external rotations. Four linear, nonlinear, and physiological optimization criteria were utilized in the optimization procedure. All optimization criteria adopted in this paper were shown to be able to predict antagonistic muscle contraction during flexion and extension of the knee. The predicted muscle forces were compared in temporal patterns with EMG activities (averaged data measured from five subjects). Joint reaction forces were predicted to be similar using all optimization criteria. In comparison with previous studies, these results suggested that the kinematic information involved in the inverse dynamic optimization plays an important role in prediction of the recruitment of antagonistic muscles rather than the selection of a particular optimization criterion. Therefore, it might be concluded that a properly formulated inverse dynamic optimization procedure should describe the knee joint rotation in three orthogonal planes.
This biomechanical study evaluated the static response of a new opening-wedge osteotomy plate to compression and torsion loads in a human cadaver model. This plate incorporates a metal block that distracts the medial tibial cortices to ensure precise correction and prevent bone collapse. The 15-mm plate was inserted into 23 fresh cadaver specimens using a standard surgical technique. Axial loading of 13 specimens (compression) and external rotation loading of 10 specimens (torsion) was performed using a servohydraulic-testing machine. Compression loading resulted in failure at a mean of 1810 N due to bone collapse, fracture, or translation. Torsional loading resulted in failure at a mean of 10 Nm due to fracture of the lateral tibial cortex in all specimens. The ratio of the experimental failure load to the calculated estimate of the knee joint forces during gait were 1.07 in axial compression and 0.925 in torsion. This opening-wedge osteotomy plate construct appears marginally strong enough to withstand the estimated axial load on the proximal tibia during gait. Estimated torsional load on the knee during level walking slightly exceeds the failure load prior to osteotomy healing. This information can be used to guide further experimental protocols for static and dynamic testing of this device to determine the appropriate rehabilitation guidelines following opening-wedge proximal tibial osteotomy.
Blood level monitoring helps to determine the therapeutic and toxic ranges for anticonvulsants and antidepressants. We investigated initial drug-drug interactions between lamotrigine and sertraline. We report on case histories of two epileptic patients who were initially on lamotrigine and to whom sertraline was added to control psychiatric features. In case 1, a total daily dose of 25 mg sertraline, with nondetectable sertraline and desmethylsertraline blood levels, resulted in a doubling of the lamotrigine blood level with symptoms of toxicity. In case 2, a 25 mg reduction in the total daily dose of sertraline resulted in halving of the lamotrigine blood level even though the lamotrigine dosage was increased by 33%. This shows that sertraline has potent interactions with lamotrigine metabolism. The authors hypothesize that inhibition of glucuronidation is responsible. Clinicians are advised to observe for symptoms of toxicity and to do serial blood levels to monitor this interaction.
Anticonvulsants which effectively treat complex partial seizures are noted to have mood stabilizing effects (carbamazepine, valproate, lamotrigine, gabapentin). Tiagabine, a novel GABA uptake inhibitor anticonvulsant with similar indications, was used as adjunctive therapy to control psychiatric symptoms in three patients--two with bipolar disorder and one with schizoaffective disorder, bipolar type. All three patients improved during adjunctive low dosage tiagabine treatment and no untoward side effects were noted. Clinicians are advised to consider this new anticonvulsant as a potential adjunctive agent in the treatment of bipolar and schizoaffective disorders. Controlled trials are indicated.
The increased use of anticonvulsants in the treatment of bipolar disorders necessitates a greater appreciation of potential complications from these agents. The authors present a bipolar disorder patient with dose-dependent valproic acid thrombocytopenia and suggest treatment strategies.
This study was undertaken to evaluate the medial ligamentous stabilizers of the patella in restraining lateral displacement and to assess their relative contribution after individual repair. Seventeen fresh frozen human anatomic specimen knee joints were studied. The specimens were loaded onto a testing instrument that was designed to measure the compliance of the medial and lateral patellar restraints in the coronal plane. Two different cutting and repair sequences were used to test the individual contributions of the patellar ligaments. The medial patellofemoral ligament was found to be the major medial ligamentous stabilizer of the patella. Isolated release resulted in a 50% increase in lateral displacement, and isolated repair restored balance to the patella. In addition, the patellotibial and patellomeniscal ligament complex played an important secondary role in restraining lateral patellar displacement. Isolated repair of these ligaments restored balance to near normal levels. The medial patellofemoral retinaculum played only a minor role in patellofemoral instability. Proximal realignment or medial ligament repair for patellofemoral instability specifically should address repair of the deep layers that contain the restraints to lateral patellar displacement. Failure to include these structures in repair, especially of the medial patellofemoral ligament, may lead to persistent or recurrent instability.
Experimental measurement of loads occurring in the human knee joint will allow validation of analytical models and provide data for the design of total knee implants. A customized transducer was developed to measure the dynamic tibiofemoral force and center of pressure after total knee arthroplasty. The transducer consists of a standard tibial component to which four uniaxial load cells and an additional tibial tray have been added. The transducer was calibrated using a loading device traceable to the National Institute of Standards and Technology (NIST). The transducer was accurate to within 1% in magnitude, 0.07 mm in medial/lateral location and 0.24 m in anterior/posterior location.
To increase in vivo tendon force and gliding after flexor tendon repair, a variety of modifications to the methods by which protective passive motion is administered have been advocated. To determine the relationship between the prime variables, wrist and digital position, muscle activation, and in vivo tendon force, a clinically relevant canine model was developed. Force was measured in the flexor tendon during several joint manipulation paradigms: single-finger flexion-extension with the wrist flexed (group 1F), single-finger flexion-extension with the wrist extended (group 1E), four-finger flexion-extension with the wrist flexed (group 4F), four-finger flexion-extension with the wrist extended (group 4E), and synergistic wrist and finger motion where wrist extension and finger flexion were performed simultaneously, followed by wrist flexion and finger extension (group SYN). In addition, tendon force was measured during electric stimulation of the proximal flexor muscle mass. Passive tendon force with the wrist extended (groups 1E and 4E) was two to three times greater than that measured with the wrist flexed, independent of the number of digits moved. With the wrist extended, peak tendon force reached 1,997 g +/- 194 g during single-digit manipulation (group 1E), compared to only 853 g +/- 104 g with the wrist flexed during the same maneuver (group 1F). Statistical comparison between means revealed that groups 1E and 4E were significantly different from groups 1F, 4F, and SYN (p < .005). There were no significant differences between groups 1E and 4E or between groups 1F, 4F, and SYN (p > .200). Active muscle force elicited by electrical stimulation and passive force varied dramatically as the wrist was flexed from full extension 3460 g +/- 766 g to full flexion 427 g +/- 239 g (p < .001). Simultaneously, passive tension decreased from 940 g +/- 143 g with wrist extended to 76 g +/- 37 g with the wrist flexed. These data indicate that wrist position has the greatest effect on flexor tendon force during motions that are commonly used to rehabilitate flexor tendon repairs. Thus, if force is to be controlled during passive motion, wrist-joint angle will have the dominant effect, while the number of digits manipulated will have much less of an effect. If the clinical goal is to minimize tendon force, rehabilitation could be carried out with the wrist flexed, whereas if the goal is to increase tendon force, rehabilitation could include exercise programs that use a greater degree of wrist extension.
Psychopathology following epilepsy neurosurgery is a significant risk. Treatment modalities have not been addressed in the literature. As disproportionately elevated suicide rates have been reported, it is critical to treat aggressively any psychiatric illness wherein suicidal ideation is a key component. This case reports the safe utilization of electroconvulsive therapy (ECT) for intractable depression following epilepsy neurosurgery (24 references).
Ten unembalmed cadaveric knees were dissected to the capsule preserving the ligamentous and tendinous structures. A posterior cruciate ligament sparing total condylar knee arthroplasty was implanted routinely. A force transducer that measured compression force and shear was implanted into each patella. For each knee, 3 thicknesses of the patellar composite (osteotomized patella, transducer, polyethylene component) were evaluated: (1) precut patellar thickness, (2) precut plus 2 mm, and (3) precut plus 4 mm. The knees were tested in an Oxford Knee Testing Rig, which allowed dynamic testing with 6 degrees of freedom. Values of patellar forces were obtained throughout a range of motion of 0 degrees to 95 degrees flexion. At higher flexion angles (45 degrees and above), the total patellofemoral shear forces for the precut plus 2 mm and the precut plus 4 mm composites were altered significantly from the precut thickness. Increasing the patellar thickness results in a significant increase in shear forces, potentially leading to early loosening of the component or increased wear or both. Therefore, bone conserving resections that increase the patellar composite thickness above the precut thickness should be avoided.
This study assesses the diagnostic capability of statistically defined prediction regions, developed by a 'bootstrap' method, for assessing the curves of angular rotation of joints in children as they walk. The prediction regions had been previously developed in the authors' laboratory from a study of 309 normal children. The goal of the present study was to determine whether these computer-generated prediction regions could be used as a screen in clinical gait analysis, to determine whether a movement falls outside the normal range of variability. Kinematic analysis of 38 consecutive children referred to the motion analysis laboratory for clinical gait assessment provided 912 curves of lower-extremity joint angle dynamics. An experienced observer first inspected the patients' curves with mean normal curves superimposed and designated the curves as normal or abnormal. The performance of the computer-generated prediction regions was judged by comparison with the experienced observer's designations. The prediction regions were found to have a high sensitivity (81%), indicating that they can be used as an initial screen to identify deficits in lower limb function.
The purpose of this study was to determine the effect of patellar bone and patellar implant thickness on patellofemoral forces after resurfacing in total knee arthroplasty. Seven cadaver knees were tested using an Oxford Knee Testing Rig. This model gave the specimens 6 degrees freedom while dynamic data were collected. Each knee was tested from full extension to 95 degrees knee flexion. Knees were implanted with Press Fit Condylar femoral, tibial, and patellar implants. The effect of varying patellar thickness on patellofemoral forces was determined by using custom modular oval-domed polyethylene patellar components with progressive thickness increments of 2 mm. Patellofemoral forces were measured by a custom-designed uniaxial patellar load cell. Statistically significant increases in patellofemoral compression forces were found from 70 degrees to 95 degrees flexion with increased patellar bone and patellar implant thickness.
This study quantified the errors associated with measurements obtained using an isokinetic dynamometer for knee evaluation at 60 degrees and 180 degrees s-1. Five normal subjects were tested. A triaxial electrogoniometer was used to measure the kinematics. A custom-designed load cell was used to measure the three orthogonal components of the reaction force applied by the isokinetic dynamometer to the leg. The inverse dynamics problem was solved to obtain the intersegmental dynamics at the knee joint. These data were compared to those obtained from the isokinetic dynamometer. The results indicate that the knee motion recorded by the isokinetic dynamometer was in error by 7-9 degrees during flexion and 10-13 degrees during extension. The isokinetic dynamometer recorded knee flexions which were less than actual during the flexion portion of the exercise and greater than actual during extension. The duration of constant velocity was limited based on the speed selected. The knee moment was in error by 5 Nm during flexion and 25-29 Nm during extension. The use of a gravity correction factor reduced the knee moment error during extension, but increased it during flexion.
The rare complication of asystole with beta-adrenergic blockade by labetalol following electroconvulsive therapy (ECT) is described with a literature review of cardiac mechanisms (33 references).
To determine whether variation in suture placement could improve the results of the arytenoid adduction procedure, a model was developed using fresh human cadaver larynges. Three-dimensional (3-D) motion of the arytenoid was determined by utilizing computed tomographic imaging with radiopaque markers on the apex and muscular and vocal processes. By utilizing principles previously applied to the study of rigid body mechanics for the carpal, knee, and tarsal joints, rotation and translation of the arytenoid about the axial, coronal, and sagittal axes were calculated. Subglottic airflow resistance was measured before and after the procedure. Posterior glottic closure was reproducibly achieved, as determined by computed tomographic imaging and airway resistance. Conflicting reports on cricoarytenoid joint mechanics can be attributed to reliance on trigonometric analysis of two-dimensional images, which results in errors in out-of-plane motion. This paper presents a useful model for obtaining detailed anatomic information describing arytenoid 3-D motion.
Biomechanical testing was performed on 5 cadaveric knees to evaluate the effect of patellofemoral design on shear and compressive force at the patellar component-bone interface. Three patellofemoral designs with identical tibiofemoral articular surfaces were tested. The knees were tested under dynamic loading conditions from 0 degree to 100 degrees flexion. A transducer that measured 3 orthogonal force components was mounted between the patellar component and the patella. The combination of an oval dome patella with a 2-mm deeper trochlear groove and associated increased femoral resection was compared with a biconcave patella with standard trochlea and normal femoral resection. Alignment of the trochlear groove in 7 degrees valgus (anatomic) decreased medial-lateral shear by 10% to symmetric trochlear groove alignment.