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Biomedical subjects

S M Howell

Publications and source records attributed to S M Howell.

At least 37 records · Page 2Linked to original sources
PubMed1999

Comparison of endoscopic and two-incision techniques for reconstructing a torn anterior cruciate ligament using hamstring tendons.

This study compared the differences in clinical outcome between an endoscopic (67 of 70) and two-incision (41 of 49) technique used to reconstruct tom anterior cruciate ligaments (ACL) using a double-looped semitendinosus and gracilis (DLSTG) graft. In both techniques, the graft was placed without roof impingement, the looped end of the graft was fixed around a post with bone compaction, and the free ends were fixed with either double staples or a soft tissue washer(s). No graft required suture fixation. The postoperative treatment featured an aggressive rehabilitation protocol without a brace, and allowed unrestricted sports participation 4 months after reconstruction. Age, sex distribution, duration from injury to surgery, and preoperative laxity were not significantly different between treatment groups. The operative time for the endoscopic technique averaged 48 minutes less than the two-incision technique. There were no significant differences in thigh circumference, knee extension, stability, and the single leg hop test between the two treatment groups at 4 and 24 months. Ninety-one percent of the knees in the endoscopic group and 90% in the two-incision group had less than a 3 mm increase in anterior translation compared with the normal knee using the manual maximum test (KT-1000) and had either a normal or near normal knee (IKDC score) at 2 years. A second surgery for removal of painful, prominent hardware was required in 21% of the subjects in the endoscopic group and 12% of the subjects in the two-incision treatment group. Patients preferred the endoscopic technique because the result was more cosmetic and aggressive rehabilitation could be accomplished without the assistance of a physical therapist. Unfortunately, objective stability could not be restored in about 10% of knees with either technique. Reoperation for removal of prominent staples and washers continues to be the primary source of postoperative morbidity.

Adolescent↗
PubMed1998

Can an isometer predict the tensile behavior of a double-looped hamstring graft during anterior cruciate ligament reconstruction?

An isometer, a highly compliant spring-scale device for measuring suture displacement, has been used intraoperatively by surgeons to select the optimal placement of the femoral tunnel for an anterior cruciate ligament graft. The isometer measures the displacement of a suture centered in a tibial tunnel and attached to an intraarticular location on the femur before the femoral tunnel is drilled. Because the placement of the femoral tunnel strongly impacts the tensile behavior of an anterior cruciate ligament graft and because surgeons have used the amount of suture displacement to guide the placement of the femoral tunnel, the objective of this study was to determine the ability of an isometer to predict graft tension. In 14 patients undergoing reconstructive surgery of the anterior cruciate ligament, an isometer was used to measure suture displacement during passive knee motion for a provisional femoral tunnel location. An electrogoniometer recorded the flexion angle of the knee. The femoral tunnel was drilled. A double-looped semitendinosus and gracilis autograft was inserted around a post in the femoral tunnel, and the tension in the four limbs of the graft exiting the tibial tunnel was measured during passive knee motion. Graft-tension versus knee-flexion-angle curves revealed that each knee exhibited one of two distinct curve shapes: L-shaped, characterized by the maximum tension occurring at full extension and a nearly flat profile from 35 to 90 degrees of flexion, or U-shaped, with elevated tensions at 80-90 degrees of flexion (p < 0.001) reaching at least half of the tension in full extension. Because the shapes of the suture-displacement versus flexion-angle curves were more consistently L-shaped, the intraoperative measurement of suture displacement was not a useful predictor of either the increase in tension in the graft with flexion or the maximum tension in the graft.

Adolescent↗
PubMed1998

Quadriceps load aggravates and roofplasty mitigates active impingement of anterior cruciate ligament grafts against the intercondylar roof.

Because of the complications of impingement of anterior cruciate ligament grafts on the intercondylar roof and because current surgical procedures locate the tibial tunnel such that impingement is avoided during passive but not active extension, the objectives of this study were to determine if (a) active extension precipitates and aggravates roof impingement, and (b) a roofplasty mitigates the effects of impingement. The tibial translation, flexion angle defining the onset of roof impingement, graft-roof contact pressure, and graft tension were measured for six cadaveric specimens. In each specimen, two tibial tunnel positions were studied: one customized for the slope of the intercondylar roof, and the other translated 6 mm anteriorly from the customized position. For a quadriceps load of 1,500 N, the flexion angle defining the onset of impingement, the peak contact pressure, and the graft tension increased significantly for both tunnel positions. The increases occurred because of the anterior tibial translation caused by the active load. Although a roofplasty decreased the onset of the angle of impingement, the graft tension remained unaffected. Thus, to mitigate the effect of impingement during active rehabilitative knee extension exercises, the position of the tibial tunnel must be customized to the angle of the intercondylar roof and a roofplasty must be performed. The extent of bone removed must be customized as well and can be determined by removing bone from the intercondylar roof in excess of that required to freely pass a rod, the same diameter of the graft, through the tibial tunnel into the intercondylar notch with the knee in full passive extension.

Adult↗
PubMed1998

Telemetry system for monitoring anterior cruciate ligament graft forces in vivo.

Quantifying changes in the tension of an anterior cruciate ligament (ACL) graft in vivo during rehabilitative exercises is useful for developing the optimum rehabilitation for patients who have had reconstructive surgery. The purpose of the work reported is to design, build and test a telemetry system that can measure the in vivo ACL graft tension post-operatively. A commercially available fixation device is modified to sense the graft tension, house electronic components, transmit an output signal and pass the power generating signal. A transcutaneous inductive link is used to power the implanted telemetry electronics. The current difference technique is used to measure changes in two resistance strain gauges that monitor shear strain developed on the femoral fixation device by the ACL graft. This current regulates a frequency-modulated output signal that is transmitted using a new technique. Harnessing the ionic and volume conduction properties of the body fluids, the new technique involves injecting current subcutaneously into the tissue and then sensing the potential developed on the skin by surface electrodes. The waveform shape, amount of charge injected, charge density and current density are regulated to avoid tissue damage, pain and unwanted muscular stimulation. A signal conditioning board detects and converts the output to an analogue voltage for collection by a computer data-acquisition system. A performance evaluation demonstrates that the telemetry system either meets or exceeds all of the criteria necessary for the application.

Anterior Cruciate Ligament↗
PubMed1998

Principles for placing the tibial tunnel and avoiding roof impingement during reconstruction of a torn anterior cruciate ligament.

Reconstruction of a form anterior cruciate ligament (ACL) cannot be successful without a properly placed tibial tunnel. Preventable complications such as anterior knee pain, effusions, extension loss, and recurrent instability can occur when the tibial tunnel is improperly placed and the roof and notchplasty are insufficient. This article reviews the principles for anatomic placement of the tibial tunnel so that complications associated with impingement of the ACL graft on the intercondylar roof can be prevented. Five factors that contribute to roof impingement are discussed, including differences in the size and shape of the ACL and the graft, variability in knee extension and roof angle between patients, inability to view the contact between the intercondylar roof and the graft, accentuation of roof impingement from anterior tibial translation caused by quadriceps contraction, and the use of tibial guides that rely on soft-tissue landmarks. A surgical technique is presented which consistently places the tibial tunnel in the pathway of the normal ACL (i.e., anatomic placement) and avoids roof impingement. The indications and need for roof- and wallplasty are discussed.

Anterior Cruciate Ligament↗
PubMed1998

A high-accuracy three-dimensional coordinate digitizing system for reconstructing the geometry of diarthrodial joints.

This paper describes the design and performance evaluation of a three-dimensional (3-D) coordinate digitizing system (3-DCDS) for measuring both soft and hard biological tissue. The system incorporates a visible semiconducting laser beam and an X-Y positioning table to directly measure 3-D coordinates that define surface points. Experiments conducted to evaluate the performance of the system showed that it delivers an accuracy of 0.1 microm in the Z-direction and 1.4 microm in the X-Y plane, and an overall system root-mean-squared error (RMSE) of 8 microm on surfaces with slopes of less than 45 degrees . This error is lower than that of previously reported measurement techniques. The 3-DCDS measures 3-D coordinates of surface points uniformly separated by 500 microm in the X-Y plane. Because the 3-DCDS is automated, the coordinates are measured efficiently and the accuracy is independent of operator skill. These highly accurate coordinates can be easily incorporated into nodal values for 3-D finite element models (FEM) of diarthrodial joints. To show the use of the 3-DCDS, the 3-D surface coordinates of human menisci were measured from a cadaver specimen.

Cadaver↗
PubMed1998

The effect of intersegmental knee moments on patellofemoral contact mechanics in cycling.

The aim of this study was to evaluate the effect of bicycle pedal design on the mechanics of the patellofemoral joint. Previous research determined that for certain riders the non-driving varus and internal knee moments could be reduced by switching from fixed to free floating pedals (Ruby and Hull, 1993). It was postulated that the presence of varus and internal knee moments during fixed pedal cycling may adversely affect patellofemoral joint contact mechanics which could lead to the development of anterior knee pain. To investigate the effect of pedal design the hypothesis that varus and internal intersegmental knee moments significantly increase patellofemoral contact pressure, contact area and contact force was tested. To test this hypothesis cycling loads were simulated in vitro using a six-degree-of-freedom load application system (LAS). Using the LAS, varus moments ranging from 0-20 Nm and internal knee moments ranging from 0-10 Nm were applied simultaneously with quadriceps force at knee flexion angles of 60 and 90 degrees. Patellofemoral contact patterns were measured using pressure sensitive film. An applied 10 Nm internal moment significantly increased both contact area by 16% and contact force by 22% at 90 of flexion. The application of a 20 Nm varus moment modestly yet significantly increased contact area by 6% and contact force by 5%. When applied in combination, varus and internal knee moments increased contact area and force by as much as 29% and 28% respectively. The mean contact pressure was not significantly increased by either of the two moments. The results suggest that non-driving intersegmental knee moments subject the patellofemoral joint to loads and contact patterns which may accelerate the development of chondromalacia.

Aged↗
PubMed1998

A new technique for transmission of signals from implantable transducers.

To reduce space requirements for implant electronics in in vivo telemetry applications, the purpose of this project was to develop and test a new data transmission method that utilizes the ionic properties of bodily fluids as the transmission medium. Motivated by an interest in using the new method to transmit information from a sensor which measures tension in anterior cruciate ligament (ACL) grafts, a sine wave was injected into a cadaver leg using platinum electrodes implanted into the lateral femoral epicondyle. The signal was detected by electromyogram (EMG) surface electrodes. The effect of transmission frequency, the current injected, interelectrode separation, distance of the electrodes from the joint line, and the surface of electrode placement on the signal attenuation was studied. The logarithmic relation between attenuation and frequency was constant from 2 kHz until 10 kHz. For frequencies above 10 kHz, the attenuation increased linearly at the rate of 1 dB/octave. Attenuation was inversely sensitive to both current and interelectrode separation with larger separations and currents giving less attenuation. Attenuation was significantly less for the lateral thigh surface than for the anterior surface and increased with increasing distance from the joint line for both surfaces. For the application of interest here, suitable values of transmission variables to avoid the possible negative consequences of injecting current into living tissue are a current of 3 mA injected at a frequency of 37 kHz. The values of reception variables for minimum attenuation are wide interelectrode separation (5 cm) with the electrodes placed 5 cm proximal of the joint line on the lateral surface of the thigh. With the exception of the surface which is application dependent, these values of the reception variables should also be appropriate for other applications.

Anterior Cruciate Ligament↗
PubMed1998

An implantable transducer for measuring tension in an anterior cruciate ligament graft.

The goal of this study was to develop a new implantable transducer for measuring anterior cruciate ligament (ACL) graft tension postoperatively in patients who have undergone ACL reconstructive surgery. A unique approach was taken of integrating the transducer into a femoral fixation device. To devise a practical in vivo calibration protocol for the fixation device transducer (FDT), several hypotheses were investigated: (1) The use of a cable versus the actual graft as the means for applying load to the FDT during calibration has no significant effect on the accuracy of the FDT tension measurements; (2) the number of flexion angles at which the device is calibrated has no significant effect on the accuracy of the FDT measurements; (3) the friction between the graft and femoral tunnel has no significant effect on measurement accuracy. To provide data for testing these hypotheses, the FDT was first calibrated with both a cable and a graft over the full range of flexion. Then graft tension was measured simultaneously with both the FDT on the femoral side and load cells, which were connected to the graft on the tibial side, as five cadaver knees were loaded externally. Measurements were made with both standard and overdrilled tunnels. The error in the FDT tension measurements was the difference between the graft tension measured by the FDT and the load cells. Results of the statistical analyses showed that neither the means of applying the calibration load, the number of flexion angles used for calibration, nor the tunnel size had a significant effect on the accuracy of the FDT. Thus a cable may be used instead of the graft to transmit loads to the FDT during calibration, thus simplifying the procedure. Accurate calibration requires data from just three flexion angles of 0, 45, and 90 deg and a curve fit to obtain a calibration curve over a continuous range of flexion within the limits of this angle group. Since friction did not adversely affect the measurement accuracy of the FDT, the femoral tunnel can be drilled to match the diameter of the graft and does not need to be overdrilled. Following these procedures, the error in measuring graft tension with the FDT averages less than 10 percent relative to a full-scale load of 257 N.

Aged↗
PubMed1997

Contact pressure and tension in anterior cruciate ligament grafts subjected to roof impingement during passive extension.

Contact between an anterior cruciate ligament graft and the intercondylar roof has been termed roof impingement. Grafts with impingement sustain permanent damage, and if the injury is extensive enough, then the graft may fail, causing recurrent instability. This study evaluated two mechanical factors that could be responsible for the graft injury associated with roof impingement: an increase in graft tension or elevated pressures between the graft and the roof, or both. An anterior cruciate ligament reconstruction was performed using an Achilles tendon graft in five fresh-frozen cadaveric knees. Using a six-degree-of-freedom load application system, the anterior displacement of the knee with the native anterior cruciate ligament was restored in the reconstructed knee at a flexion angle of 30 degrees and with an anterior force of 200 N applied. Pressure between the graft and intercondylar roof, graft tension, and flexion angle were measured during passive knee extension for three tibial tunnel placements (anterior, center, and posterior). Intercondylar roof impingement increased the contact pressure between the graft and the roof but had no significant effect on graft tension. Therefore, during passive knee extension, the contact pressure between the anterior cruciate ligament graft and the intercondylar roof is a more likely cause of graft damage than increased graft tension.

Achilles Tendon↗
PubMed1997

In vivo tensile behavior of a four-bundle hamstring graft as a replacement for the anterior cruciate ligament.

The purpose of this study was to measure the in vivo tensile behavior of a double-looped semitendinosus and gracilis graft used to reconstruct a torn anterior cruciate ligament in the human knee. In 14 subjects, intraoperative tension was measured for each of the four graft bundles during passive motion from 0 to 90 degrees of flexion. Two hypotheses were tested: (a) the peak tension carried by each of the four bundles was equal during passive motion, and (b) the mechanics of the bundles mimicked the functional bands of the native anterior cruciate ligament. The total tension was also calculated and used to determine strength requirements for fixation devices. The peak tensions of the four bundles during passive motion were not equal; however, enough tension was present in each bundle that load-sharing occurred between bundles. The pattern of tension between the anterior and posterior bundles mimicked the reciprocating load-sharing behavior of the functional bands of the native anterior cruciate ligament. Reciprocal tensile behavior was consistently achieved with the use of a single femoral tunnel centered on the most isometric line without the need for two separate femoral sockets. The maximum total tension was 296 N; this was nearly equal to the strength of one commonly used fixation device.

Adolescent↗
PubMed1997

An in vitro osteotomy method to expose the medial compartment of the human knee.

This study was conducted to validate a new in vitro method to expose the medial compartment of the knee to be used in subsequent studies aimed at examining the load bearing capabilities of medial meniscal allografts. The new method involves an osteotomy and reattachment of the medial femoral condyle. The primary hypothesis was that the new method does not alter tibio-femoral contact pressure and area. To validate this method, the baseline contact pressure of the intact medial compartment was measured using a new nondestructive procedure for inserting pressure measurement film into the intact medial hemijoint. A secondary and related hypothesis was that incising the coronary ligament, a destructive method used by previous investigators to position pressure measurement film, alters the normal tibio-femoral contact pressure. To test these hypotheses, Fuji Prescale pressure-sensitive film was used to measure both tibio-femoral contact pressure and area within the medial compartment of the (1) intact knee, (2) the knee after osteotomizing and reattaching the medial femoral condyle, and (3) the osteotomized knee with an incised coronary ligament, using seven cadaver specimens. Measurements were taken at a compressive load of approximately two times body weight with the knee in 0, 15, 30, 45 deg of flexion. No significant differences between the intact and osteotomized knee were detected. Likewise, no significant differences were observed between the osteotomized knee and the osteotomized knee with an incised coronary ligament. These results confirm the utility of the new method in exposing the medial compartment for manipulation and placement of medial meniscal allografts in future studies examining the load-bearing characteristics of meniscal allografts.

Cadaver↗
PubMed1996

Brace-free rehabilitation, with early return to activity, for knees reconstructed with a double-looped semitendinosus and gracilis graft.

Forty-one patients in whom operative reconstruction of a torn anterior cruciate ligament had been performed by one surgeon with use of a double-looped semitendinosus and gracilis hamstring graft were studied to determine (1) if a brace-free rehabilitation program compromised the early stability of the knee; (2) if the stability of the knee deteriorated between four months, when the patient returned to unrestricted activities, and two years; and (3) if the function of the treated knee was completely restored by four months after the operation. The graft was placed arthroscopically, without impingement by the intercondylar roof, and was fixed within the tibial tunnel to conserve the length of the graft. The stability and function of thirty-seven of the knees were assessed at four months as part of a larger prospective study. Four patients chose not to return for the four-month evaluation. The patients returned to unrestricted sports and work activities after the four-month evaluation. At two years, all forty-one patients were evaluated. At four months, after completion of the brace-free rehabilitation program, thirty-three (82 per cent) of the thirty-seven patients had an absent pivot shift and a normal Lachman test. Twenty-eight (88 per cent) of thirty-four knees had less than three millimeters of difference in laxity compared with the contralateral knee, as determined by testing at the maximum manual force with use of a KT-1000 arthrometer. Stability remained unchanged at two years, justifying the early return to vigorous activities at four months. The girth of the thigh, the extension of the knee, and the Lysholm and Gillquist score were the same at four months as at two years, verifying the success of the brace-free intensive rehabilitation program in the restoration of early function to the treated knee. However, some continued improvement was observed in the performance of the one-leg-hop for distance test between four months and two years.

Activities of Daily Living↗
PubMed1993

Localization of the CYP2D gene locus to human chromosome 22q13.1 by polymerase chain reaction, in situ hybridization, and linkage analysis.

Using a combination of somatic cell hybrids, in situ hybridization, and linkage mapping, we have been able to localize the cytochrome P450 CYP2D6 gene to chromosome 22 in the region q13.1. Linkage analysis, using locus-specific primers, showed a maximum sex-average lod score of 8.12 (theta = 0.00) between the marker pH130 (D22S64) and CYP2D6, of 6.92 (theta = 0.00) between the marker KI839 (D22S95) and CYP2D6, and of 4.80 (theta = 0.036) between the platelet-derived growth factor beta subunit gene (PDGFB) and CYP2D6.

Chromosome Mapping↗
PubMed1993

Failure of reconstruction of the anterior cruciate ligament due to impingement by the intercondylar roof.

The relationship between impingement of the roof of the intercondylar notch on a reconstructed anterior cruciate ligament, and the subsequent stability and range of extension of the joint, was analyzed in forty-seven knees. The extent of the impingement was determined by analysis of the relationship of the tibial tunnel to the intersection of the line of slope of the intercondylar roof with the plane of the subchondral bone of the articular surface of the tibial plateau. These lines were drawn on a lateral roentgenogram that was made with the knee in maximum extension, two years after the operation. In all four knees in which the entire articular opening of the tibial tunnel was anterior to the slope of the intercondylar roof, there was severe impingement on the graft, and all four grafts failed. In the fourteen knees in which a portion of the articular opening of the tibial tunnel was anterior to the slope of the intercondylar roof, there was moderate impingement on the graft, and four grafts failed (an unacceptable rate of failure). There was no impingement in the knees in which the entire articular opening of the tibial tunnel was posterior to the slope of the intercondylar roof, and these knees were associated with the lowest rate of failure of the grafts (three of twenty-nine). Knees that had an impinged graft and regained a complete range of extension became unstable.

Adult↗
PubMed1992

The accuracy of signal intensity measurements in magnetic resonance imaging as evaluated within the knee.

Quantitative signal intensity measurements are being utilized in both clinical and research magnetic resonance imaging protocols. This paper addresses three questions in quantitative MRI measurements as evaluated within the knee: 1) the accuracy of quantitative measurements; 2) improvement of accuracy by phantom normalization; and 3) the amount of signal change that is clinically significant. Seven normal subjects were imaged on three different days within a 1-wk period. Test-tube phantoms of manganous chloride (MnCl2) were imaged posterior to the knee and were used to normalize each image. The variation in signal intensity within the same subject averaged 20% for both the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). The phantom variation was approximately 18%. Signal intensity normalization by background subtraction, background division, phantom division, or a combination of subtraction and division did not significantly improve either the phantom variation or the ligament variation. Given that an individual ligament intensity will be measured with standard errors of +/- 20% of its value, we calculated the minimum increase in signal intensity to be considered abnormal relative to a normal ligament. A relative signal increase of 46% can be considered pathologic with 95% confidence. These findings emphasize that quantitative measurements must be carefully assessed when being applied in clinical settings.

Evaluation Studies as Topic↗
PubMed1992

Serial magnetic resonance study assessing the effects of impingement on the MR image of the patellar tendon graft.

This study was designed to serially analyze the magnetic resonance (MR) appearance of patella tendon grafts during the first year of implantation, and to determine if the sagittal location of the tibial tunnel affects the MR appearance of the graft. An additional goal was to analyze the effect of the sagittal placement of the tibial tunnel placement on knee extension and stability. Two groups were defined by comparing the sagittal relationship of the tibial tunnel to the slope of the intercondylar roof from a lateral roentgenogram of the knee in full extension. The roof impinged group consisted of nine patients who had the tibial tunnel placed anterior to the tibial intersection of the slope of the intercondylar roof. The unimpinged group was composed of eleven patients who had the tibial tunnel placed posterior and parallel to the slope of the intercondylar roof. MR scans were obtained at 0-2, 12, 24, 36, and greater than 48 weeks postoperatively. The signal intensities of grafts in both groups were identical at 1 week, but increased in the impinged group by 3 months and remained increased at 12 months postoperatively (p less than 0.01). In contrast, the MR signal of grafts in the unimpinged group remained unchanged during the first year. Knees with impinged grafts had extension deficits but remained stable. Roof impingement was impossible to view directly with the knee in full extension.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗