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Biomedical subjects

K L Markolf

Publications and source records attributed to K L Markolf.

At least 55 records · Page 3Linked to original sources
PubMed1982

In vivo rotatory knee stability. Ligamentous and muscular contributions.

Active and passive components of torsional stability of the knee were measured with an instrumented clinical knee-testing apparatus. Torque-versus-rotation response curves were recorded in the non-weight-bearing condition with muscles relaxed for twenty normal subjects who were tested at 20 and 90 degrees of knee flexion with the hips flexed and extended. At applied torque levels as high as +/-10 newton-meters, tibial rotation averaged approximately one-half the foot rotation. The mean algebraic right-left rotation difference for the group was nearly zero; however, sizable standard deviations for this difference indicated considerable right-left variations between individuals in the test group. Maximum isometrically generated tibial torques were measured by asking the subjects to twist with an explosive effort against a locked torque-cell. No significant differences in generated torque were measured between preferred and non-preferred lower limbs, with only one minor exception. Subjects generally were able to generate greater internal torque than external torque. When the foot was locked in a position of internal or external rotation, an individual was able to generate increased tibial torque in the direction that would tend to return the foot to the neutral position. Flexion of the knee from 20 to 90 degrees increased externally generated torque, while internal torque was affected to a lesser degree. Flexion of the hip had little effect on generated torque. Six cadaver knees without menisci that were tested to failure in external rotation showed torque levels for ligament failure to be similar in magnitude to the maximum generated isometric torque that acts to protect the knee ligaments.

Adolescent↗
PubMed1981

Twelfth thoracic-first lumbar vertebral mechanical stability of fractures after Harrington-rod instrumentation.

UNLABELLED: Thirteen fresh cadaver spinal segments (fifth thoracic to fifth lumbar vertebra) with a posterior ligamentous defect at the twelfth thoracic-first lumbar level were tested to failure in flexion, creating an unstable fracture at the twelfth thoracic and first lumbar vertebrae. The fractured spines were then instrumented with Harrington distraction rods and retested. Spines instrumented at the eleventh thoracic to second lumbar vertebrae were not significantly stronger than uninstrumented specimens (with a posterior ligamentous defect). Repositioning the upper hook from the eleventh to the tenth thoracic vertebra increased the failure moment by an average of 36 per cent. Instrumentation of the spine at either level protected the spinal column against distraction at the fracture site until a threshold movement was reached. Moving the upper hook from the eleventh up to the tenth thoracic vertebra increased the threshold moment by an average of 65 per cent. Our recommended hook placement at the tenth thoracic and second lumbar vertebrae tends to reduce tilting of the upper vertebra, changing the mode of failure from slip-out of the upper hook (with partial laminar fracture) to total laminar fracture. CLINICAL RELEVANCE: The presence of internal fixation rods in itself does not make the unstable fractured spine stronger in a flexion mode. The level of hook placement above and below the fracture is important in determining with bending strength of the instrumented spine. When the use of Harrington distraction rods is contemplated for internally stabilizing a fractured spine, a specific level of hook placement, three laminae above and two laminae below the point of instability, is recommended. This configuration allows the instrumentation to maintain increased spinal stability in a flexion mode by reducing the tendency for the upper hooks to "back out" and lose their hold secondary to vertebral tilting.

Aged↗
PubMed1980

The effect of calcar contact on femoral component micromovement. A mechanical study.

Extra-long-neck, large-stem Trapezoidal-28 femoral components with standard and modified large flanges were cemented into fresh cadaver femora and measurements were made of the movement of the prostheses relative to the bone as load was applied to the head of the prosthesis. In the presence of collar-calcar femoral contact, the prosthesis subsided very little under load; displacements for a load of 2000 newtons were less than 0.1 millimeter. Removal of bone and acrylic support beneath the undersurface of the flange by sawing a thin gap caused no increase in the displacement of the stem tip in most specimens, but the displacements of the collar relative to bone for the standard flange design increased by an average of 0.014 millimeter (8 to 28 per cent) under a 2000-newton force when contact was removed, while the displacements for the prostheses with a modified large flange that extended to the cortical rim of the resected neck increased 0.047 to 0.060 millimeter (56 to 432 per cent), indicating greater support from the collar due to the increased area of contact. An increase of the stem-flange angle of 22 degrees (from 30 to 52 degrees), making the flange more horizontal, had no significant effect on the results for large-flanged units. Prostheses with a standard flange and a one to two-millimeter Silastic liner between cement and bone subsided as much as twenty times more than rigidly cemented units. In the presence of the liner, removal of collar-calcar contact increased the collar displacement by 29 to 75 per cent, indicating a possibly important function of the flange for components cemented in soft bone or components that may become loose or be surrounded by a fibrous membrane. Repacking of the gap between the collar and bone with acrylic after removal of part of the calcar femoral reduced subsidence in one specimen, while the acrylic in a second specimen cracked out during reloading. Based on our laboratory experience with sixteen specimens, we believe that it would be extremely difficult to achieve an effective degree of uniform calcar femorale-collar contact at operation and that one or two localized contact areas would be the more common situation after total hip replacement.

Acrylates↗
PubMed1979

Mechanical stability of the greater trochanter following osteotomy and reattachment by wiring.

Greater trochanters of fresh and formalin-perserved cadaver femora were osteotomized, rewired using techniques described by Amstutz, Charnley, Coventry and Harris, and then mechanically tested. Force simulating abductor muscle pull was applied to the trochanter in the plane of section while its displacement was measured continuously with an extensometer. Although many trochanters appeared rigidly fixed when stressed manually, all displaced visibly when 27 kg load was first applied. When released, permanent sets averaging 0.1 mm (Charnley and Harris) to 3--4 mm (Coventry) were measured. Subsequent repeated loadings (0--27 kg) from this new "rest" position produced recoverable cyclic "functional" displacements averaging 0.7 mm (Charnley and Harris) to 2.3 mm (Coventry). With the exception of the specimens wired by the Coventry technique, results for a simulated 45 degrees anterior pull were generally comparable to those for a neutral pull. Ultimate failure loads of the trochanteric fixation were on the order of 110 kg for selected fresh specimens.

Cadaver↗
PubMed1978

Wear characteristics of UHMW polyethylene: a method for accurately measuring extremely low wear rates.

The wear of UHMW polyethylene bearing against 316 stainless steel or cobalt chrome alloy was measured using a 12-channel wear tester especially developed for the evaluation of candidate materials for prosthetic joints. The coefficient of friction and wear rate was determined as a function of lubricant, contact stress, and metallic surface roughness in tests lasting two to three million cycles, the equivalent of several years' use of a prosthesis. Wear was determined from the weight loss of the polyethylene specimens corrected for the effect of fluid absorption. The friction and wear processes in blood serum differed markedly from those in saline solution or distilled water. Only serum lubrication produced wear surfaces resembling those observed on removed prostheses. The experimental method provided a very accurate reproducible measurement of polyethylene wear. The long-term wear rates were proportional to load and sliding distance and were much lower than expected from previously published data. Although the polyethylene wear rate increased with increasing surface roughness, wear was not severe except with very coarse metal surfaces. The data obtained in these studies forms a basis for the subsequent comparative evaluation of potentially superior materials for prosthetic joints.

Absorption↗
PubMed1978

In vivo knee stability. A quantitative assessment using an instrumented clinical testing apparatus.

Twenty-eight male and twenty-one female subjects with no history of previous injury to their knees were examined using a newly developed clinical testing apparatus designed to record anterior-posterior tibial force versus displacement and varus-valgus moment versus angulation during manual manipulation of the knee. Joint stiffness and laxity were measured from test tracings made with the knee muscles relaxed and tensed. Agreement between these measurements and those made previously on thirty-five fresh cadaver knee specimens was very good. Anterior-posterior laxity averaged 3.7 millimeters in full extension, 5.5 in 20 degrees of flexion, and 4.8 millimeters in 90 degrees of flexion, while the mean varus-valgus laxity was 6.7 degrees in full extension. The common clinical assumption that normal right-left differences are negligible was found to be invalid. Individual right-left differences averaged 26 to 35 per cent for laxity and 19 to 24 per cent for stiffness. There was no discernible tendency for one knee to be more stable than the other; random interchanges of relative stability between the right and left knees were observed for each individual at different knee positions. When requested to tense the knee muscles, these subjects were able to increase their knee stiffness an average of two to four times while knee laxity was reduced to 25 to 50 per cent of the normal value.

Adolescent↗
PubMed1976

Experimental stabilization of segmental defects in the human femur. A torsional study.

One of each of thirty-five pairs of fresh intact femora were tested to failure in torsion, recording the dynamic torque, the absorbed energy, and the angle of rotation. These results were compared with the results obtained with the contralateral femur, reconstituted after removal of a segment. Intramedullary nails with polymethylmethacrylate cement, strips of titanium mesh with cement, bone plates with and without cement, and multiple Steinmann pins with cement were the reconstituting configurations. Bone plates were the strongest configuration; the failure torques in all cases were limited by the stress concentration effects of the holes in the bone used for screw fixation. The use of cement as an adjunct to single-plate fixation provided some additional strength. The torsional strength of femora fixed with Küntscher and Schneider nails was limited by failure of the cement and bone. The use of titanium mesh with polymethylmethacrylate was less effective, because this composite has a low torsional rigidity. The use of multiple Steinmann pins packed with polymethylmethacrylate in the medullary cavity should be discouraged because severe twisting and fragmentation of the surrounding acrylic will occur at low levels of torque.

Bone Cements↗
PubMed1976

Stiffness and laxity of the knee--the contributions of the supporting structures. A quantitative in vitro study.

Thirty-five normal cadaver knees were tested manually in six positions of the knee using apparatus designed to measure the moment-rotation responses for both varus-valgus angulation and torsion of the tibia, as well as the force-displacement responses for anterior-posterior movement of the tibia. The responses of all knees to all modes of loading were non-linear, reflecting increasing stiffness. With the knee at full extension, stiffness was maximum and laxity was minimum. Hence, it was in this position that changes in stability (laxity and stiffness) were best demonstrated when ligament structures were sectioned. Differences in laxity were observed between right and left knees of intact paired specimens. Torsional laxity and internal rotation stiffness were most affected by sectioning the medial collateral ligament, while external rotation stiffness was only affected by division of both the lateral collateral ligament and the posterior capsule. Varus-valgus laxity was relatively unaffected by removal of the menisci or section of the cruciate ligaments but increased greatly when either collateral ligament was cut. The medial collateral ligament was the main contributor to valgus stiffness, whereas the lateral collateral ligament had no measurable effect on varus stiffness. Anterior-posterior stability was affected to some extent by virtually every sectioning procedure. Isolated section of the anterior cruciate ligament produced the greatest increase in anterior-posterior laxity at full extension and section of the posterior cruciate, the greatest increase at 90 degrees of flexion. Large increases in anterior-posterior laxity were also observed when the medial collateral ligament and posterior capsule were sectioned in combination.

Aged↗
PubMed1976

Effects of laminations and blood entrapment on the strength of acrylic bone cement.

The tensile and shear strengths of surgically mixed acrylic bone cement were measured for intact specimens and for special two-part cylindrical specimens containing single laminations perpendicular to their longitudinal axes. Laminations were formed at times ranging from 3 1/2 to 6 1/2 minutes after initial mixing of the powder and liquid for dry interfaces and for interfaces containing fresh blood at the time of lamination formation. In additon, special tests were conducted to measure the bond strength between freshly mixed and pre-polymerized acrylic. The tensile and shear strengths at the lamination interface decreased significantly when the laminations were formed late in the working life of the acrylic. The presence of blood at the interface further weakened the bond to approximately 25 per cent (tension) and 36 per cent (shear) of the virgin strengths of the material. These results support early acrylic placement with dry surgical fields. The bonding of fresh acrylic to pre-polymerized material was most effective when the material was poured into the mold before dough stage. This technique would have practical application in special cases for re-cementing revision prostheses without removing the old acrylic from within the bone.

Blood↗
PubMedDate not supplied

Mechanical strength of the femur following resurfacing and conventional total hip replacement procedures.

A series of static and fatigue loading tests was performed on fresh frozen cadaver femora which had undergone THARIES surface replacement and conventional T-28 stem-type replacement. The strength, stiffness, and energy absorbed during static loading tests were comparable for femora containing the 2 designs. Superior notching of the femoral neck during valgus reaming reduced the ultimate static fracture load in 2 specimens. The large scatter in fatigue life observed was most likely due to variations in bone quality and geometry, techniques of reaming and positioning of the prosthetic components, and the initial selection of the cyclic load for each individual specimen. Significant differences in cycles to failure were observed between paired specimens tested under similar conditions. Based upon tests performed upon surface replacement specimens that did not fail in fatigue, and which were subsequently tested to static failure, it appears that a cyclic load roughly one-fourth of ultimate can be tolerated without fatigue fracture.

Adult↗
PubMedDate not supplied

In vivo stability testing of post-meniscectomy knees.

Post-meniscectomy knees examined with an instrumented clinical testing device reveal that meniscectomy alone does not cause a measurable degree of instability. If meniscectomy causes a minor degree of instability, the degree is within the right-left variation for a normal population. Medical meniscectomy in combination with a torn anterior cruciate results in an increased anterior-posterior instability at 20 degrees knee flexion. The device used in this study was more reliable in diagnosing increased anterior-posterior instability secondary to anterior-cruciate tear than was a clinical examiner.

Adolescent↗
PubMedDate not supplied

In vitro measurement of bone-acrylic interface pressure during femoral component insertion.

Bone-acrylic interface pressure measurements were recorded at the medial interior rasped surfaces of fresh cadaver femurs during digital packing of acrylic bone cement and during insertion and seating of a Trapezoidal-28 femoral total hip component. Plugging of the femoral canal below the tip of the prosthesis stem was an effective means for increasing pressure in the distal femoral canal when the stem was inserted in the early stages of acrylic polymerization (i.e. immediately after dough time). At surgery, this can be accomplished by inserting a small bolus of acrylic down the canal to a depth below the tip of the seated stem and allowing it to polymerize in place. This forms an effective seal which prevents distal extrusion of the acrylic when the cavity is then packed prior to prosthesis insertion. Elimination of cement in the distal canal also avoids any future difficulty of acrylic removal should revision become necessary due to loosening or infection. No significant pressure differences were observed between one and two millimeter thicknesses of acrylic between the metal and bone. Interface pressures developed during finger packing were of the same order of magnitude as those achieved during seating of the femoral component. Use of a rubber diaphragm stretched tightly over the margins of the rasped femoral cavity helped to contain the acrylic and prevent extrusion during finger packing but was ineffective in increasing interface pressure. When this method is used, the acrylic can be poured or injected into the canal and packed before dough stage and thus facilitate increased cancellous penetration when the acrylic is in a state of low viscosity.

Arthroplasty↗