Biomedical subjects

K N An

Publications and source records attributed to K N An.

At least 145 records · Page 8Linked to original sources

PubMed1997

Effect of plantar fasciotomy on stability of arch of foot.

Five anatomic specimen feet were studied at three different loading levels to determine the three-dimensional position of the individual bones constituting the arch. Bone displacements were compared before and after plantar fasciotomy. Bone displacements changed to a greater extent with higher loads. With a 222-N load the greatest difference in position in dorsiflexion after fasciotomy occurred at the talar to tibial joint, followed by the metatarsal relative to navicular and navicular to talar joints. The greatest difference in displacement in eversion was at the metatarsal relative to navicular, followed by the navicular to talar and calcaneal to talar joints. The greatest difference in displacement in abduction was at the navicular to talar and then the calcaneal to talar joints. The observed displacement of all joints, with changes about all three axes, was consistent with the finding of flattening of the arch in previous reports on plantar fasciotomy. Thus, these data suggest that sectioning of the fascia, which sometimes is performed for fasciitis, may have an effect on the mechanical behavior of the arch.

Aged↗

PubMed1997

Differences in patellar tracking and knee kinematics among three different total knee designs.

Patellar complications are the primary reason for reoperation of the current condylar type designs. The aim of this study was to compare patellar tracking of various knee implant designs: Genesis II NexGen, and the P.F.C. Sigma Modular Knee System regarding trochlear groove center curvature. Nine unembalmed whole cadaveric lower extremities were used. The quadriceps and hamstrings were dissected into their individual muscles and loads were applied onto the muscles proximally based on the cross sectional area of the muscles. The three-dimensional kinematics of the patellofemoral and tibiofemoral joint of the intact knee were measured using a 3Space tracking system. Three implants (one from each company) were implanted onto the same cadaveric knee in random order consecutively. This was done to ensure consistency of the soft tissue constraints in influencing the amount of patellar tracking. Patellar rotation, patellar tilting, patellar lateral shift and patellar displacement in relation to groove center were measured. There was no significant difference between the intact knee and the various implants regarding patellar rotation and lateral shift. However, all three prosthetic designs showed a significant degree of lateral tilting when compared with the intact knee. At 60 degrees knee flexion, the normal patella was tilted laterally to 0.44 degree +/- 2.15 degrees as compared with the Genesis II patella at 4.75 degrees +/- 4.81 degrees, the NexGen patella at 4.85 degrees +/- 4.81 degrees, and the P.F.C. Sigma patella at 4.89 degrees +/- 3.79 degrees lateral tilt. There was no difference between the intact knee compared with the resurfaced patella in patellar displacement in relation to the groove center. This study suggests the relatively similar kinematic behavior between the implant designs as compared with the intact knees. However, additional modification of implant geometry may be required to help decrease the amount of patellar tilt.

Arthroplasty, Replacement, Knee↗

PubMed1996

A method for determination of the anisotropic properties of biomembranes.

A methodology was developed for potential determination of the anisotropic properties of biomembranes. This method is based on the theoretical discretization of a continuous membrane used for finite element analysis and the simultaneous measurement of the displacement of nodes on the surface of a membrane. From the given loads and measured nodal displacements, one can assemble the resulting stiffness matrix and approximate the material properties associated with the membrane. Mathematical estimations and computer simulations were performed to determine the perturbation of load and displacement errors on the resulting material properties. The results indicated that the material properties are particularly sensitive to displacement errors. The displacement measurements may require an accuracy of 20 microns for a 4 x 4 cm2 specimen. Significant inaccuracies occur close to the points of load application.

Anisotropy↗

PubMed1996

Cement viscosity affects the bone-cement interface in total hip arthroplasty.

Quantitative information regarding the interface strength and degree of cement penetration associated with cement viscosity during total hip arthroplasty is limited. The aim of the present study was to determine the effect of the viscosity of bone cement at the time of implantation on the mechanical integrity of total hip arthroplasty. Cement that was injected at an early less viscous stage produced greater failure strength in a push-out test than its more viscous counterpart.

Analysis of Variance↗

PubMed1996

Determination of the proximity tolerance for measurement of surface contact areas using a magnetic tracking device.

Undisrupted joint contact areas can be determined based on surface proximity from combined surface geometry and bony kinematics measured with a magnetic tracking device. This technique is useful for evaluating the apparent region of contact in the normal joint. After disruption of the supporting structures or other simulated pathology, the locations and size of the contact region can be compared with the normal condition. However, the contact results may be highly sensitive to measurement errors. In this study, the accuracy of this method was evaluated for three simple geometric objects: (1) a flat plate, (2) a cylinder, and (3) a sphere, all in contact with a flat surface. The results indicated the contact can be determined within an average proximity of 0.16 +/- 0.01 mm (mean +/- standard error) with the flat plate, 0.07 +/- 0.02 mm with the cylinder, and 0.06 +/- 0.08 mm with the sphere. The proximity values are nearly the same as the translational accuracy of the equipment, and might be used as thresholds for in vitro studies.

Acrylic Resins↗

PubMed1996

Accuracy of a video strain measurement system.

The purpose of this study was to determine the accuracy of a video system which our laboratory has been using to measure soft tissue strain. Both static and dynamic error analyses were performed to assess the accuracy of our video system. Static error was defined as the amount of movement reported by the video system for markers that were stationary. Dynamic error was defined as the difference between the motion of the markers as reported by the video system and their actual motion. Two sets of fluorescent markers were attached to a servo-hydraulic materials test machine. One marker set was attached to the hydraulic actuator (moving markers) and the other set was attached to the base of the machine (stationary markers). Five different marker sizes, five camera distances, and seven different loading rates were studied. Results indicated that the static error was independent of marker size, and that the dynamic error was independent of the loading rate and marker size for loading rates of 50% of the camera field of view (CFV) per second or slower. For loading rates greater than 50 percent of CFV per second, the marker size did have an affect on the dynamic error. The mean static error was found to be 0.026 percent of CFV and the mean dynamic error was found to be 0.062 percent of CFV.

Computer Systems↗

PubMed1996

The capitohamate ligaments. A comparison of biomechanical properties.

The physical attributes of the three capitohamate interosseous ligaments were tested in a computer-controlled multi-axis testing machine using 12 human cadaver specimens. After an intact test run, selected ligaments were cut in random sequence and the test repeated. The remaining ligaments were tested to failure with servohydrolic stress at 5 mm/second. In the intact joint complex, the average dorsopalmar rotational displacement was approximately 9 degrees in each direction. Under the load limit, the dorsopalmar translational displacement averaged 0.9 mm and 0.5 mm respectively, proximal-distal translational displacement averaged 0.8 mm and 0.4 mm respectively, and distractional displacement averaged 0.3 mm. Based on the sequential sectioning it was found that the dorsal ligament provided 76% (SD 14) of the rotational resistance with palmar rotation of the capitate and 44% (SD 19) of translational constraint with palmar translation of the capitate. The deep ligament provided 51% (SD 15) of the rotational resistance with dorsal rotation of the capitate and 63% (SD 24) of translational resistance with dorsal translation of the capitate. With proximal-distal translation, the dorsal ligament was the most important constraint in each direction. In resisting distraction, each of the three ligaments was equally effective. Failure testing showed the deep ligament was strongest at 289 N, followed by the palmar at 171 N and the dorsal at 133 N.

Adult↗

PubMed1996

Kinematics of the trapeziometacarpal joint: a biomechanical analysis comparing tendon interposition arthroplasty and total-joint arthroplasty.

The kinematics of the trapeziometacarpal joint were studied in 15 cadaver hands; normal joints were compared with simulated arthroplasties-either a total-joint arthroplasty of the ball-and-socket variety or a fibrous suspension arthroplasty of ligament reconstruction with tendon interposition. The motion of the thumb metacarpal was analyzed based on a trapezial coordinate system, using a magnetic tracking system. The pivot point (instantaneous center of rotation) for the thumb metacarpal changed during active and passive circumduction. Compared with normal trapeziometacarpal joint motion, the pivot point after ligament reconstruction with tendon interposition shifted significantly in palmar and ulnar directions in reference to the trapezial coordinate system, whereas after total-joint arthroplasty, the pivot point shifted slightly palmarly and radially. The axes of rotation were also compared for ligament reconstruction with tendon interposition and total-joint arthroplasty during thumb flexion-extension and abduction-adduction motions. After ligament reconstruction with tendon interposition, the center of flexion-extension shifted palmarly and the center of abduction-adduction shifted ulnarly. After total-joint arthroplasty, the center of rotation for flexion-extension shifted distally and palmarly and that for abduction-adduction shifted palmarly and proximally. In comparison with the normal joint, passive circumduction increased after tendon interposition arthroplasty but was less with total-joint arthroplasty. Changes in kinematics suggest a suspensory ligament function of ligament reconstruction with tendon interposition arthroplasty, whereas total-joint arthroplasty results in axes of rotation that reflect the joint replacement rather those of the normal joint.

Arthroplasty↗

PubMed1996

Influence of patellar thickness on patellar tracking and patellofemoral contact characteristics after total knee arthroplasty.

Although total knee arthroplasty (TKA) has become a very common procedure, patellar problems remain a major cause of disability. Patellar thickness is one of the most challenging factors. The influence of patellar thickness on patellofemoral kinematics and contact characteristics following TKA was investigated. Seven unembalmed whole-lower-extremity cadaveric specimens were used. The kinematics was measured with a magnetic tracking device (3Space Tracker System, Polhemus Navigation Sciences Division, Colchester, VT). Contact area was calculated from the kinematic data and the digitized joint surface geometrics based on a theoretical method. The patellofemoral joint contact force was measured directly using a uniaxial force transducer. Kinematically, the influence of patellar thickness on patellar flexion, rotation, and proximodistal shift was not significant. Orthopaedic surgeons are often challenged by derangement of the patellofemoral joint, especially following TKA. It is commonly assumed that restoration of overall patellar thickness is most desirable. A thin patella can reduce the contact force, but it also poses the potential risks of stress fracture and anteroposterior instability. Increasing patellar thickness might be expected to increase the effective quadriceps moment arm at low flexion angles of the knee, but potentially reduces the range of motion of the knee and predisposes to patellar subluxation. Either a thicker or a thinner patella had a smaller contact area than intact and normal-thickness patella. Therefore, the surgical technique of patellar resurfacing during TKA should attempt to reproduce the original patellar thickness.

Aged↗

PubMed1996

Aetiology of work-related carpal tunnel syndrome: the role of lumbrical muscles and tool size on carpal tunnel pressures.

A cadaveric study was undertaken to investigate the effect of tool size and lumbrical muscle incursion on carpal tunnel pressure during active grip. Active grip was simulated by securing the specimens on an apparatus and loading each of the eight finger flexor tendons with 1 kg each. Carpal tunnel pressures were measured with and without 1- and 2-in. tubing in the hand and before and after removing the lumbrical muscles. Both variables, tool size and lumbrical muscles, were found to have a statistically significant effect on carpal tunnel pressure. Higher pressure changes were found for the 2-in. tubing, compared with 1-in. tubing, but this difference was not statistically significant.

Biomechanical Phenomena↗

PubMed1996

Intercalary spacers in the treatment of segmentally destructive diaphyseal humeral lesions in disseminated malignancies.

During a 10-year period, 17 patients with segmentally destructive bone lesions of the humeral diaphysis in disseminated malignancies resulting in impending fracture (8 patients), pathologic fracture (6 patients), or failure of attempted internal fixation techniques (3 patients) were treated with resection of the involved diaphyseal segment and reconstruction with a cemented modular intercalary humeral spacer. Fourteen patients had metastatic cancer, 2 had multiple myeloma, and 1 had lymphoma. Breast and renal carcinoma were the most common pathologic diagnoses. The involved site was within the middle 1/3 in 8 patients, in the proximal-middle junction in 5, in the middle-distal junction in 2, and within the proximal and distal 1/3 in 1 patient each. Early pain relief was successful in 88% of patients. Early in the postoperative hospital course, patients generally were able to use the ipsilateral hand to assist feeding. Radiographic analysis revealed that the limited selection of stem lengths led to 76% of the distal stems and 47% of the proximal stems being shorter than the ideal length. The complication rate independent of disease progression was 29%. The most common complication was temporary radial nerve injury (3 patients). There were 3 implant failures, most commonly due to disengagement of the male-female junction. Two periprosthetic fractures occurred, 1 proximally (due to tumor progression) and 1 distally. Suggestions are given for modification of the implants to improve the major problems of limited versatility in intramedullary stem length and inadequate mating at the junction.

Adult↗

PubMed1996

Contact features of the talonavicular joint of the foot.

Seven cadaveric feet were studied to determine the distribution of the contact area of the talonavicular joint. Feet were loaded axially with soft tissue structures intact and after sectioning of static elements that support the arch. Bony displacement was monitored with a magnetic tracking device, and joint contact was determined from proximity calculations of digitized joint surfaces. With physiologic loading of the intact foot, the number of regions in contact increased. In the unstable foot, there was a shift in contact distribution toward more dorsal and central regions of the navicular bone. This is consistent with the clinical observation that fatigue fractures, acute fractures, and nonunion of navicular fractures occur often in the central navicular body. The alteration in contact characteristics in unstable feet is also consistent with the observation that osteoarthrosis of the hindfoot joints occurs commonly with long-standing arch instability or pes planus deformity.

Aged↗

PubMed1996

Force analysis of rotator cuff muscles.

A 3-dimensional static biomechanical model of the glenohumeral joint was used to investigate rotator cuff muscle forces during maximal isometric exertions (abduction, adduction, internal rotation, and external rotation) and static arm elevation. Muscle moment arms and cross sectional areas were determined from studies of cadaveric specimens, and maximal isometric strength data were collected using a Cybex II dynamometer. Predicted posterior deltoid forces were very low during abduction in the scapular plane. The model predicted the highest rotator cuff muscle forces during maximal internal rotation (subscapularis) and external rotation (infraspinatus, teres minor, and supraspinatus) exertions. The results indicate that abduction exertions may not produce the greatest loads on the supraspinatus tendon, and that analyses of arm elevation may underestimate the potential loads on the rotator cuff. The strong effect of external rotation exertions on supraspinatus and infraspinatus forces suggest that ergonomic efforts to prevent rotator cuff disease should include reduction of internal rotation loading on the arm. Moreover, it may be important to include warnings about external rotation exertions, in addition to arm elevation, in patient education.

Adult↗

PubMed1996

EMG analysis of shoulder positioning in testing and strengthening the supraspinatus.

We examined the electromyographic (EMG) activity of the supraspinatus and other rotator cuff muscles, the three portions of the deltoid muscle, and the pectoralis major muscle in two previously suggested positions for isolating the supraspinatus. The position suggested by Jobe and colleagues is with the elbow extended, the shoulder in full internal rotation, and the arm in the scapular plane. Blackburn and colleagues recommended the prone position, with the elbow extended and the arm abducted to 100 degrees and externally rotated. Fine-wire EMG activity was obtained from the rotator cuff muscles and surface EMG from the other muscles in 17 subjects tested in these two positions. Both positions resulted in significant activity of the supraspinatus, but the difference between these two positions was not statistically significant. The Jobe position produced greater activation of the anterior deltoid and pectoralis major, whereas the Blackburn position caused greater activation of the posterior deltoid. Both positions produced significant activation of the middle deltoid. We conclude that either position can be used to strengthen the supraspinatus; however, neither position selectively isolates the supraspinatus during manual muscle testing.

Adult↗

PubMed1996

Importance of soft tissue integrity on biomechanical studies of the patella after TKA.

This study evaluated the effects of soft tissue integrity on patellar tracking and patellofemoral joint force after total knee arthroplasty. The results indicate that partial dissection of the soft tissue integrity in the in vitro biomechanical studies of the patellofemoral joint can alter patellar tracking and joint force significantly, leading to improper conclusions.

Adipose Tissue↗

PubMed1996

An apparatus for spine biomechanical testing.

A testing system that applies a pure bending moment will uniformly load a spinal construct and be capable of identifying its weakest point. This study describes an apparatus for use with a material testing machine that is simple, inexpensive, and reliably creates a pure bending moment along the whole spine. We tested the system using two strain gauges attached to an aluminum alloy beam. First we verified the reliability and accuracy of the strain gauges system by comparing experimental measurement strain to theoretical prediction of strain in a cantilever beam model. The second experiment assessed the moment and strain created at two locations on a beam which was fixed at one end. The mean strain recorded from the two gauges demonstrated that moment is not uniformly distributed along the length of beam that is fixed at one end. The third experiment was similar to the second except that the beam was attached to an X-Y table instead of being fixed. Results demonstrated that a pure bending moment status is achieved when the end of the beam is fixed to an X-Y table.

Biomechanical Phenomena↗

PubMed1996

The use of a direct current electromagnetic tracking device in a metallic environment.

The use of a relatively new direct current (DC) electromagnetic tracking device in conjunction with a hostile metal environment of Material Testing Machine was studied. In this research, we first evaluated the reliability and performance of the DC tracking system operating in an ideal metal-free environment for both the translational and rotational error in static and dynamic conditions. When the tracking system with the same factory default configuration was moved into a heavy metal environment, serious translational and rotational distortion were observed. Through a series of evaluation of the physical environment and modification of the settings, the tracking system could perform satisfactorily and both the translational and angular error could be reduced in manufacturer's specifications. The safe working region for the DC tracking systems operating in a material testing machine environment was successfully mapped out. This study provides information for using the DC electromagnetic tracing device in the heavy metal environment exists in the material testing machine.

Biomechanical Phenomena↗

PubMed1996

In vitro study of patellar position during sitting, standing from squatting, and the stance phase of walking.

Muscle balance in quadricep muscles is an important factor for patellar instability. However, in vivo, the activity of the quadriceps varies during knee motion. To simulate this clinical condition, different loading conditions of the rectus femoris, vastus lateralis, and vastus medialis oblique at different knee flexion angles were studied, and patellar motion during knee extension was determined. Seven fresh-frozen adult cadaver knees were use. Patellar motion in terms of patellar shift, patellar tilt, and rotation were measured using a magnetic tracker system. The loads applied to each quadriceps muscle were calculated using clinical electromyographical data for three activities: 1) knee extension while sitting, 2) standing from squatting, and 3) stance phase of walking. The patellar tracking in these three loading patterns was compared with that under constant loading of each quadriceps muscle. Each activity demonstrated a neutral patellar shift and tilt, as did the traditional constant loading. However, the patella in walking showed internal rotation when the rectus femoris was much weaker than the other vasti.

Adult↗