PubMed Health⌕ Search

Biomedical subjects

K L Markolf

Publications and source records attributed to K L Markolf.

At least 37 records · Page 2Linked to original sources
PubMed1990

Arthrodesis of the ankle with cancellous-bone screws and fibular strut graft. Biomechanical analysis.

The stability of an arthrodesis with two cancellous-bone screws across the ankle joint was evaluated in eighteen ankles from fresh-frozen cadavera. Tibiotalar motion was recorded in response to the following loading modes: medial-lateral moment, plantar flexion-dorsiflexion moment, and internal-external tibial torque. The series of loading tests was performed with two cancellous-bone screws through the tibia into the talus and a lateral fibular strut graft fixed with a proximal and a distal screw. The tests were repeated after the strut graft was removed, and again after it had been reapplied. The amount of motion at the site of the arthrodesis was greatest with tibial torque and was least with medial-lateral bending; this was true for specimens with or without a fibular strut graft. Removal of the strut graft allowed increased tibiotalar motion for all modes of loading; increases in motion were far greater for specimens of poor bone quality.

Aged↗
PubMed1990

Direct measurement of resultant forces in the anterior cruciate ligament. An in vitro study performed with a new experimental technique.

A new technique was used to measure the resultant forces in the anterior cruciate ligament during a series of loading experiments on seventeen fresh-frozen cadaver specimens. The base of the ligament's tibial attachment was mechanically isolated with a coring cutter, and a specially designed load-transducer was fixed to the bone-plug that contained the ligament's tibial insertion so that the resultant forces were directly measured by the load-cell. Although the magnitudes of values for forces varied considerably between specimens for a given test condition, the patterns of loading with respect to direction of loading and the angle of flexion of the knee were remarkably consistent. Passive extension of the knee generated forces in the ligament only during the last 10 degrees of extension; at 5 degrees of hyperextension, the forces ranged from fifty to 240 newtons (mean, 118 newtons). When a 200-newton pull of the quadriceps tendon was applied to extend a knee slowly against tibial resistance, however, the force in the ligament increased at all angles of flexion of the knee. Internal tibial torque always generated greater forces in the ligament than did external tibial torque; higher forces were recorded as the knee was extended. The greatest forces (133 to 370 newtons) were generated when ten newton-meters of internal tibial torque was applied to a hyperextended knee. Fifteen newton-meters of applied varus moment generated forces of ninety-four to 177 newtons at full extension; fifteen newton-meters of applied valgus moment generated a mean force of fifty-six newtons, which remained unchanged with flexion of the knee. The force during straight anterior translation of the tibia was approximately equal to the anterior force applied to the tibia. The application of 925 newtons of tibiofemoral contact force reduced the mean force in the ligament that was generated by 200 newtons of anterior pull on the tibia by 36 per cent at full extension and 46 per cent at 20 degrees of flexion.

Aged↗
PubMed1990

Strength of initial mechanical fixation of screw ring acetabular components.

This study was conducted to determine the effects of design on the initial fixation of several types of screw-ring acetabular components. The components were tested in polyurethane foam to assess relative screw fixation strengths with a consistent material. Embalmed pelves from anatomic specimens were used to conduct paired tests between designs that showed large differences in insertional torque to failure in foam. The quality of the initial fixation in foam was found to be dependent on the design features of the components. Components with widely spaced, deep threads, and minimal thread interruptions offered the strongest initial fixation in foam. Tests in bone revealed a wide range of fixation strengths reflecting the variability in bone quality. No differences in fixation strength attributable to component design were observed in bone. When the insertional failure torque was greater than 60 N.m, one-half of the pelves fractured, and these fractures occurred with all designs. At failure torques less than 60 N.m, failure was predominantly due to thread strippage of the screw, with only two of 20 specimens experiencing pelvic fracture.

Acetabulum↗
PubMed1989

Torsional strength of the ankle in vitro. The supination-external-rotation injury.

Nineteen fresh-frozen anatomic specimens of the ankle were mounted in an experimental test device with the foot in supination. Torque versus rotation curves were recorded as each foot was rotated externally to failure. The mean failure torque was 45.3 Nm, the mean rotation to failure was 41.4 degrees, and the mean energy absorbed to failure was 10.6 Nm. Twelve specimens failed by fracture of the fibula, five by failure of lateral ligaments with no fibular fracture, one by a subtalar dislocation, and one by fracture of the calcaneous through a fixation screw hole. There were no statistically significant differences in torque or energy to failure between those specimens that failed by fibular fracture and those with ligamentous failure alone. Rotation to failure was 6 degrees greater in the ligamentous failure group. Ankles with less initial rotatory laxity tended to fail at higher torque levels. The mean ankle fracture torque measured in this study is similar to previously reported mean ligamentous failure torque for the knee flexed to 20 degrees and rotated externally to failure. In a prior in vivo study, approximately 10 Nm of external foot torque and 20 degrees of foot rotation could be tolerated prior to the initiation of pain. The present study indicates that these in vivo pain threshold levels represent approximately 50% of the rotation to failure and 25% of the torque to failure.

Ankle Injuries↗
PubMed1989

Instrumented measurements of laxity in patients who have a Gore-Tex anterior cruciate-ligament substitute.

Twenty patients who had substitution of the anterior cruciate ligament with a Gore-Tex synthetic ligament were evaluated preoperatively and postoperatively with the University of California at Los Angeles instrumented clinical-testing apparatus, which records anterior-posterior force versus displacement-response curves of the tibia with respect to the femur at 20 degrees of flexion of the knee. The mean age of the patients was thirty-three years (range, nineteen to fifty-four years). The duration of follow-up ranged from twenty-four to forty-four months (mean, thirty-one months). The mean preoperative difference in anterior laxity between the injured knee and the normal knee (4.5 millimeters with neutral rotation of the foot) was unchanged two years after the operation; at that time, all patients had an anterior laxity of the injured knee of more than eight millimeters, and 90 per cent had a difference in anterior laxity of more than two millimeters between sides. The mean values for anterior stiffness at fifty and 100 newtons of anterior force were unchanged after the operation, remaining at 40 to 50 per cent of normal levels. At 200 newtons, or 20.4 kilograms (forty-five pounds) of anterior force, the mean stiffness of the involved knee was 11 to 17 per cent greater than that of the normal knee. Clinically, there were improvements in both subjective and objective knee-rating scores. All but four patients had a reduction of at least one grade in the pivot-shift score; in thirteen, the pivot-shift sign was eliminated.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Tibial torque generation in a flexed weight-bearing stance.

Internal and external torque generated about the long axis of the lower extremity was measured in 18 male subjects who were instructed to twist with maximal effort against a fixed footplate containing an instrumented torque cell. Mean torque values ranged from 30 to 71 newton meters (Nm) depending upon the test conditions. Torques recorded during the flexed single-leg stance were 19% to 49% higher than those measured while seated. Values at 45 degrees of knee flexion were 11% to 16% greater than those at 20 degrees. Torques generated while wearing a ski boot were 8% to 11% greater than those recorded in an athletic shoe. When movement of the pelvis and upper torso was allowed, torque values were 17% to 49% higher than those recorded when the hips and shoulders were restrained which allowed only lower leg musculature to act in an isolated fashion. There were no differences between internal versus external generated torques when the hips and torso were restrained. When the hips and shoulders were unrestrained, internal torque was 12% greater than external torque. There were no strong correlations between generated torque and body weight or height. These generated torque values suggest that if ski bindings are set to American Society for Testing and Materials (ASTM) standards for twist-release torque, then upper torso and pelvic movement in conjunction with tensed knee musculature (i.e., a "locked knee") may be necessary to accomplish binding release. Use of the lower leg musculature alone (i.e., ankle twist) may not generate sufficient torque for release.

Adult↗
PubMed1988

Measurement of stability of the knee and ligament force after implantation of a synthetic anterior cruciate ligament. In vitro measurement.

A Gore-Tex prosthetic ligament was inserted, with an over-the-top femoral placement, into thirteen fresh-frozen cadaver knees as a substitute for the anterior cruciate ligament. The femoral eyelet was screwed into bone and the tibial eyelet was attached to a force-transducer, which was positioned and locked on a tibial slider track to record forces in the ligament as the tibia was externally loaded. A reference position was established for the tibial eyelet so that, after the Gore-Tex ligament was implanted, the total anterior-posterior laxity of the knee (at 200 newtons of applied tibial force) matched that of the intact knee (that is, before the anterior cruciate ligament had been cut) at 20 degrees of flexion. With both ends of the ligament secured in the knee, repeated 200-newton anterior-posterior load cycles produced an increase of five to seven millimeters in the total laxity. This apparent stretch-out of the ligament could be worked out of the knee by manually flexing and extending the knee thirty times between zero and 90 degrees of flexion while a constant 200-newton force was applied to the tibial eyelet. After implantation of the Gore-Tex ligament, the laxity of the knee matched that of the intact specimen at 20 degrees of flexion and matched it within one millimeter at zero, 5, and 10 degrees of flexion. For each millimeter that the tibial eyelet was moved distally, the total anterior-posterior laxity decreased by the same amount. The anterior stiffness of the knee after implantation of the Gore-Tex ligament was always less than that of the intact specimen. With an applied extension moment of ten newton-meters, section of the anterior cruciate ligament increased hyperextension of the knee by 2.3 degrees; implantation of the Gore-Tex ligament did not restore full extension, even when the ligament was over-tightened by using a distal location for the tibial eyelet. When the eyelet was in the reference position, the ligament forces ranged from three to 319 newtons when the knee was in full extension, they rose dramatically as the knee was hyperextended, and they decreased to zero in most specimens as the knee was flexed more than 15 degrees. The pull of the quadriceps tendon against fixed resistance always increased the ligament forces. The application of tibiofemoral contact force reduced the ligament forces that were generated during a straight anterior tibial pull.(ABSTRACT TRUNCATED AT 400 WORDS)

Calibration↗
PubMed1987

The clinical relevance of instrumented testing for ACL insufficiency. Experience with the UCLA clinical knee testing apparatus.

An instrumented clinical testing device developed at UCLA records a continuous anteroposterior force versus displacement curve of the tibia with respect to the femur at 20 degrees of flexion. Laxity and stiffness are calculated from the response curve. With this device, 95% of normal knees have an anterior laxity less than 7.5 mm and a side-to-side difference less than 2 mm. In contrast, an anterior cruciate ligament (ACL) absent knee has a mean anterior laxity of 10 mm and a mean side-to-side difference of 5 mm. In a small group of patients with an intraarticular ACL substitution using the medial or lateral one-third of the patellar tendon, laxity and stiffness of the injured knees were returned to within the normal range and remained constant three years after surgery. In a group of 76 patients treated with ACL substitution using the torn meniscus, 51% of the patients still had an anterior laxity outside the normal range 3.5 years after surgery. In a preliminary study of 19 patients receiving a Gore-Tex synthetic ACL substitution, 55% of the patients still had a side-to-side difference greater than 2 mm two years after the procedure. These studies illustrate the advantages of impartial, objective measurements of knee stability. Laxity and stiffness values can supplement, but never replace, a thorough patient examination and patient history. As sports medicine matures as a scientific discipline, improved instrumented test devices may ultimately provide a standardized means for reporting knee stability parameters.

Humans↗
PubMed1987

Measurements of anterior laxity in normal and anterior cruciate absent knees with two instrumented test devices.

A new portable model of the University of California at Los Angeles (UCLA) instrumented clinical knee testing apparatus and the KT-1000 knee arthrometer were used to measure anterior laxity in normal and anterior cruciate absent knees. Normal ranges for both devices were established for a control group of 48 normal subjects. With the UCLA device at 200 N of applied tibial force, 95% of normal knees have an anterior laxity less than 8.0 mm and a side to side difference less than 2.0 mm; corresponding values for the KT-1000 at 89 N are 9.0 mm and 2.0 mm. Both devices showed that anterior laxity of 19 anterior cruciate absent knees was approximately double that for normal knees. Measurements taken with these two testing instruments do not have a one-to-one correlation, as the method of femoral constraint and the amount of applied tibial force will influence the magnitude of the recorded laxities. Proper interpretation of laxities measured with each device requires consideration of right-left scatter in a normal population tested with that particular device. Both devices were 90%-95% accurate in correctly classifying an anterior cruciate absent knee outside the normal range.

Adult↗
PubMed1986

The role of the meniscus in the anterior-posterior stability of the loaded anterior cruciate-deficient knee. Effects of partial versus total excision.

The effects of progressive removal of the menisci on the anterior-posterior force-versus-displacement response of the anterior cruciate-deficient knee were studied in fresh cadaver specimens at 20 degrees of flexion without and with tibial-femoral contact force (joint load). In the absence of joint load, removal of the medial meniscus increased total anterior-posterior laxity measured at 200 newtons of applied tibial force by 10 per cent, and subsequent lateral meniscectomy produced an additional 10 per cent increase. When a bucket-handle tear of the medial meniscus was removed, the application of joint load caused the tibia to displace (subluxate) forward on the femur, thereby changing the balance condition of the knee. Subsequent removal of the remainder of the medial meniscus and complete lateral meniscectomy both produced additional smaller anterior tibial subluxations. Changes in total anterior-posterior laxity due to progressive meniscectomy in the loaded knee were dependent on both the amount of applied anterior-posterior force and the level of compressive force. At 200 newtons of anterior-posterior tibial force, increases in laxity in the loaded knee due to progressive meniscal removal were not significantly different than those recorded in the unloaded condition. At applied forces of fifty newtons or less, the laxities for loaded specimens were always significantly less than those for unloaded specimens at comparable stages of meniscal removal. Bilateral meniscectomy had no significant effect on the posterior response curve, as posterior tibial translation was effectively checked by the intact posterior cruciate ligament.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1985

Effects of joint load on the stiffness and laxity of ligament-deficient knees. An in vitro study of the anterior cruciate and medial collateral ligaments.

We measured the effects of serial section of the medial collateral ligament and anterior cruciate ligament and of the anterior cruciate ligament and medial collateral ligament on anterior-posterior force-versus-displacement and tibial torque-versus-rotation response curves for seven fresh frozen cadaver knees at zero and 20 degrees of flexion before and after application of as much as 925 newtons of compressive load on the tibiofemoral joint. Section of the anterior cruciate ligament always increased anterior laxity in an unloaded specimen; joint load reduced this increase by a greater amount at zero degrees than at 20 degrees of flexion. Joint load was more effective in limiting anterior laxity in anterior cruciate-deficient specimens at low levels of applied anterior force; at higher levels of applied force, the effects of joint congruency were overcome and ligament restraints came into play. Section of the medial collateral ligament increased anterior laxity in an unloaded knee only for specimens in which the anterior cruciate ligament had been previously sectioned; joint load eliminated this increase at full extension but did not do so at 20 degrees of flexion. The medial collateral ligament was the more important of the two ligaments in controlling torsional laxity. Secondary section of either ligament (the other ligament having been sectioned first) produced a greater increase in laxity than did primary section of that ligament in an intact knee. Increases in torsional laxity due to primary section of either ligament were unaffected by the application of joint load. Joint load reduced increases in laxity that were due to secondary section of the medial collateral ligament.

Aged↗
PubMed1984

Anterior-posterior stiffness and laxity of the knee after major ligament reconstruction.

We recorded anterior-posterior force-versus-displacement curves at 20 and 90 degrees of flexion preoperatively and three years after major ligament reconstruction in patients with documented absence of the anterior cruciate ligament. Patients who had an extracapsular stabilization procedure alone showed no significant changes in laxity or stiffness of the injured knee in either position of flexion. Those who underwent reconstruction of the absent anterior cruciate ligament utilizing the middle or medial one-third of the patellar ligament in addition to the extracapsular procedure showed a significant decrease in anterior laxity and increase in anterior stiffness of the injured knee at 20 degrees of flexion. These changes in stability were not observed at 90 degrees of flexion. Six patients with a cruciate substitution had improved laxity and stiffness values at one year postoperatively which were unchanged at three years. At three-year follow-up the increases in activity scores, decreased feelings of giving-way and pain, and elimination of the pivot shift were comparable in both groups of patients.

Adolescent↗
PubMed1984

Measurement of knee stiffness and laxity in patients with documented absence of the anterior cruciate ligament.

Thirty-five patients with documented absence of the anterior cruciate ligament were tested on the University of California, Los Angeles, instrumented clinical knee-testing apparatus and we measured the response curves for the following testing modes: anterior-posterior force versus displacement at full extension and at 20 and 90 degrees of flexion; varus-valgus moment versus angulation at full extension and 20 degrees of flexion; and tibial torque versus rotation at 20 degrees of flexion. Absolute values of stiffness and laxity and right-left differences for these injured knees were compared with identical quantities measured previously for a control population of forty-nine normal subjects with no history of treatment for injury to the knee. For both the uninjured knees and the knees without an anterior cruciate ligament, at 20 and 90 degrees of flexion the anterior-posterior laxity was greatest at approximately 15 degrees of external rotation of the foot. The injured knees demonstrated significantly increased total anterior-posterior laxity and decreased anterior stiffness when compared with the uninjured knees in all tested positions of the foot and knee. The mean increase in paired anterior-posterior laxity for the injured knees in this group of patients at +/- 200 newtons of applied anterior-posterior force was 3.1 millimeters (+39 per cent) at full extension, 5.5 millimeters (+57 per cent) at 20 degrees of flexion, and 2.5 millimeters (+34 per cent) at 90 degrees of flexion. The mean reduction in anterior stiffness for injured knees was also greatest (-54 per cent) at 20 degrees of knee flexion. Only slight reduction in posterior stiffness (-16 per cent) was measured at 20 degrees of flexion, and this probably reflected the presence of associated capsular and meniscal injuries. In the group of anterior cruciate-deficient knees, the patients with an absent medial meniscus showed greater total anterior-posterior laxity in all three positions of knee flexion than did the patients with an intact or torn meniscus. Varus-valgus laxity at full extension increased an average of 1.7 degrees (+36 per cent) for the injured knees, while varus and valgus stiffness decreased 21 per cent and 24 per cent. Absence of the medial meniscus (in a knee with absence of the anterior cruciate ligament) increased varus-valgus laxity at zero and 20 degrees of flexion.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1984

Flow characteristics of acrylic bone cements.

Flow properties of Simplex, Zimmer Regular, Zimmer LVC, and Sulfix bone cements were measured as functions of time between two and five minutes after mixing. The mass flowrates measured for Zimmer Regular and Simplex were quite similar in the temperature range of 20.0 degrees -23.3 degrees. At 18.3 degrees Simplex had approximately double the flowrate of Zimmer Regular two minutes after mixing. The flowrate for LVC was approximately four times that measured for Zimmer Regular at 20.0 degrees. Sulfix displayed the greatest sensitivity of flowrate with temperature; at 18.3 degrees its flow characteristics were similar to those of LVC, and at 23.3 degrees it behaved more like Simplex and Zimmer Regular. All cements demonstrated substantial relative increases in flowrates with only slight increases in pressure; Sulfix was the most pressure sensitive. Set times for Zimmer, LVC, and Sulfix were virtually identical, ranging from a mean of 11 minutes (at 18.3 degrees) to 7.5 minutes (at 23.3 degrees). Simplex had considerably longer set times, averaging 15.8 minutes (at 18.3 degrees) and 9.4 minutes (at 23.3 degrees). Although Simplex demonstrated the greatest sensitivity of set time with temperature (almost double that measured for the other 3 cements), it did not show the greatest sensitivity of flowrate with temperature.

Bone Cements↗
PubMed1983

The effect of tibia-foot rotatory position on the anterior drawer test.

The effect of the position of the foot and tibia on the anteroposterior drawer test was quantified using a clinical testing device. Maximum laxity occurred at 15 degrees of external rotation of the foot. Extreme rotation of the foot and tibia resulted in reductions of anteroposterior laxity of 63% for internal rotation and 50% for external rotation. The ratio of foot rotation to tibia rotation was approximately 2:1. Medial meniscectomy alone did not result in increased anteroposterior laxities when compared with normal knees. Medial meniscectomy with an unrepaired anterior cruciate ligament tear resulted in increased anteroposterior laxities at 15 degrees, 30 degrees, and maximum external rotation of the foot.

Adult↗
PubMed1983

The effects of exercise, ice, and ultrasonography on torsional laxity of the knee.

Changes in torsional knee laxity, after subjects ran 3.5 miles during a 30-minute period, were studied in 13 subjects. The effects of ice and ultrasonographic treatments on these laxity changes were then investigated. Knee laxity was determined by measuring torque versus rotation responses of the tibia at 90 degrees of knee flexion. Total rotational laxity of the tibia was tabulated at +/- 10 newton-meters of applied torque. There were significant increases in postexercise laxities over preexercise levels for internal and external tibial rotation. Postexercise laxity changes followed a uniform time course of recovery. The maximum postexercise laxity represented a mean increase of 14% over pre-exercise levels, with a mean recovery time of 52.4 minutes and a standard deviation of 17.8 minutes. The application of ten-minute treatments of either ice or ultrasonography significantly reduced postexercise recovery times, to 20.0 +/- 4.6 SD and 20.9 +/- 6.4 SD, respectively. A common clinical assumption, that cold and heat have opposite effects on knee laxity, was found invalid. In the authors' study, ice and ultrasonography had equivalent effects in accelerating the return to pre-exercise laxities. No laxity changes were observed in unexercised subjects, with either ice or ultrasonographic treatments. The time course of laxity recovery and the subsequent effects of heat and ice are important clinically. Immediately after injury, both knees are more lax than normal, and after approximately one hour, recovery to pre-exercise laxity levels will be complete for the uninjured leg. Ice (or ultrasonography) will shorten this time to 20 minutes. If these recovery time courses are recognized and taken into account, a more accurate diagnosis can be made during this "golden opportunity" period before pain and swelling ensue. The fact that ice and ultrasonography have identical effects on the time course of recovery in the exercised knee raises new questions and suggests additional areas for future work in the recently developing field of sports medicine biomechanics.

Adult↗
PubMed1983

The contribution of the anterior talofibular ligament to ankle laxity.

The motion responses of thirty fresh-frozen cadaver tibiotalar joints were measured for applied anterior-posterior force, inversion-eversion moment, and internal-external rotary torque. The load-motion response curves obtained after sectioning the anterior talofibular ligament were compared with those for intact specimens in three positions of flexion of the ankle. Laxity of the intact ankle was shown to be dependent on flexion position; dorsiflexion was consistently the position of least laxity, reflecting the effects of talar geometry and its articulation with the tibiotalar syndesmosis. Section of the anterior talofibular ligament produced significant increases in laxity for all modes tested. Total anterior-posterior laxity increased by 4.3 millimeters in dorsiflexion, which was the position of maximum change. In contrast, the greatest increases in total inversion-eversion laxity (5.2 degrees) and total internal-external rotation laxity (10.8 degrees) were recorded in plantar flexion.

Adult↗