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Biomedical subjects

A B Weiss

Publications and source records attributed to A B Weiss.

At least 19 recordsLinked to original sources
PubMed1989

An evaluation of purified reconstituted type 1 collagen fibers.

Collagen fibers composed of type I collagen molecules were studied for biocompatibility and mechanical properties. These fibers were crosslinked using two different processes: 1) glutaraldehyde, 2) dehydration followed by exposure to cyanamide (DHT/C); the latter method produces only urea as a by-product of the crosslinking process and is postulated to be more biocompatible. An in vitro model using rat tendon fibroblasts growing on individual fibers was used to evaluate outgrowth rates, cell/fiber interactions, and cell morphology. These studies showed an advantage with DHT/C crosslinking, relative to glutaraldehyde crosslinking, in promoting fibroblast growth. In vivo intramuscular implantation in rats showed excellent biocompatibility for both kinds of collagen implants. In addition, aligned ingrowth into the implant from the medial collateral ligament when applied in that location was demonstrated. Mechanical testing demonstrated the higher strength of dry fibers; however, upon hydration, there was a marked decrease in stress to failure. This reduction in strength was due principally to an increase in cross section due to swelling. These collagen fibers appear to be very biocompatible even in the presence of low concentrations of glutaraldehyde. They promote fibrous aligned ingrowth in a setting of ligament healing. Thus, they represent a strong candidate as a scaffold ligament or tendon prosthesis if crosslink density can be increased.

Animals↗
PubMed1989

Long-term follow-up of achilles tendon repair with an absorbable polymer carbon fiber composite.

In this cooperative multicenter study for surgical repair of Achilles tendon rupture using a composite implant, 48 patients underwent 52 procedures. This implant is composed of filamentous uniaxially aligned carbon fibers coated with an absorbable polymer. This highly biocompatible implant acts as a scaffold for regrowth of collagenous tissue. The early strength of this repair is provided by the composite implant and by the rapid ingrowth and attachment of new tissue, which allows for an earlier and more vigorous rehabilitation program. Patients with a minimum follow-up of 1 year form the basis of this article. The overall average follow-up is 2.1 years. Three cohort groups were observed on a temporal basis and quantitatively evaluated at 1 year (N = 29), 18 months (N = 22), and 2 years (N = 20), respectively. These three groups demonstrated continuous improvement during the first postoperative year. A high level of function was maintained throughout the second year. Repair of chronic injuries (N = 15) was compared with repair of acute injuries (N = 12) at 1 year following surgery. Both groups greatly improved. However, the acute group had more serious preoperative deficits but improved to a slightly better overall level. Of the patients having at least 1 year follow-up, 86% had a good or excellent result. There was no increased morbidity associated with the use of the carbon implant.

Achilles Tendon↗
PubMed1986

Ligament and tendon repair with an absorbable polymer-coated carbon fiber stent.

Ribbon-like composite structures of filamentous carbon fiber and absorbable polymers have been used in the repair and replacement of both tendons and ligaments. The composite acts as a scaffold upon which new collagenous tissue can grow and has proved successful in a variety of animal models. The results of the first three years of human clinical trials have revealed ingrowth potential similar to that seen in the animal studies. Most patients have shown significant improvement, with many demonstrating good to excellent stability and function.

Animals↗
PubMed1985

Carbon fiber debris within the synovial joint. A time-dependent mechanical and histologic study.

The consequences of release of carbon debris within the synovial joint are of interest to surgeons contemplating the intra-articular repair of cruciate-deficient knees with a carbon fiber-based material. Coverage of carbon fiber implants with absorbable polymer as well as autogeneic graft material has resulted in surgical procedures that minimize potential fiber release. However, finite risk of release of fiber debris certainly exists. With this in mind, a controlled animal experiment to model debris release in the synovial joint was performed. As a positive control, magnesium tetrasilicate (talc) in suspension was injected into the knees of rabbits. Talc produced a transient synovitis severe enough to alter the mechanical properties of the joint cartilage. Carbon fiber debris, when similarly injected, also produced a synovitis. However, the synovitis induced by carbon particulate was not of sufficient severity or duration to alter the mechanical properties of the cartilage. Neither talc nor carbon fiber debris appeared to physically abrade cartilage.

Animals↗
PubMed1985

Ligament replacement with an absorbable copolymer carbon fiber scaffold--early clinical experience.

Eighty-two patients, average age 29 years, were surgically treated (during the period from April 1981 to July 1983) for both acute (8%) and chronic (92%) knee ligament instabilities. An absorbable copolymer-carbon fiber ligament prosthesis was used as a tissue scaffold. Seventy-five percent had anterior cruciate ligament reconstructions, 6% had anterior cruciate and posterior cruciate ligament reconstructions, 6% had just posterior cruciate ligament reconstructions, and 9% had other combinations of anterior cruciate ligament, medical collateral ligament, and lateral collateral ligament reconstructions. Preoperative and postoperative evaluation, consisting of questionnaires, physical examinations, and isoskinetic testing, revealed significant improvements in categories of stability, pain, function, and strength persisting to the end of the study at 24 months. Arthroscopic examination and histologic studies of retrieved specimens demonstrated well-vascularized reconstructions with collagenous tissue ingrowth into the carbon-copolymer implants.

Adolescent↗
PubMed1984

The electrical stimulation of bone using a filamentous carbon cathode.

Filamentous carbon fiber is an extremely compatible biomaterial. It does not corrode and elicits almost no foreign body response. In addition, this material is an efficient electrical conductor in vivo. These desirable characteristics suggest that carbon fiber may be of use as an electrode material for the stimulation of bone and/or soft tissue growth. This possibility has been investigated in a well established laboratory animal model. When used as a cathode material in conjunction with an implantable constant direct current device, carbon fiber was shown to be an effective electrode material for the stimulation of bone and fibrous tissue within the medullary canal of the tibia of the rabbit. Further, adjustment of current levels appear to allow some selectivity in terms of the amount and type of tissue produced. Currents in the 1 microA range produced a maximum amount of bone, whereas a 20 microA current produced a maximum amount of fibrous tissue. Intermediate current levels produced a proportional mix of bone and soft tissue.

Animals↗
PubMed1983

Absorbable polymer-filamentous carbon composites--a new class of tissue scaffolding materials.

The utility of filamentous carbon in tendon and ligament repair is limited by its premature mechanical degradation. When filamentous carbon is coated with an absorbable polymer, polylactic acid (PLA), a composite material results which serves as a tissue scaffold, maintaining its integrity long enough for new tissue to grow in and around it before it gradually degrades. Biocompatibility studies showed excellent tissue response to the PLA-carbon composite. Dog patellar tendons and medial collateral ligaments and rabbit Achilles tendons fashioned from the composite were then implanted. The implants allowed almost immediate resumption of activity and encouraged the growth of new structures histologically and mechanically similar to the natural structures. Its high initial strength, rapid ingrowth and benign tissue reaction suggest that this new composite material may be useful in the treatment of tendon and ligament injuries in humans. Consequently, the material was entered into limited clinical trials. To date, thirty patients have had implant surgery for the repair of extensor mechanisms, knee ligaments, Achilles tendons, and rotator cuffs. At this writing, seven month follow-up is available. Early results are encouraging.

Absorption↗
PubMed1983

Treatment of unstable intertrochanteric fractures with anatomic reduction and compression hip screw fixation.

One hundred sixty-two cases of unstable intertrochanteric fractures treated by anatomic reduction and compression hip screw fixation were reviewed. One hundred twenty-four of these patients were followed up for an average of 19.2 months. Loss of fixation, with varus angulation of the fracture, occurred in five patients, a 4% incidence of failure. One hundred ten patients were bearing full weight an average of three weeks after operation. Fracture healing occurred an average of 18 weeks after operation. After compression was applied, 90% of the fractures moved into medial displacement position. Eight percent of the fractures laterally displaced; 2% of the fractures maintained their anatomic alignment. Nonanatomic reduction, e.g., stable reduction accomplished by displacement osteotomy (after Dimon and Hughston), has no advantage over anatomic reduction and fixation by a compression hip screw. The advantages of the latter technique are that weight-bearing can be started early, the device can be used for stable and unstable intertrochanteric fractures with identical technique, and fixation is rigid and allows for compression of the fracture site, while maintaining alignment.

Adult↗
PubMed1981

Soft tissue attachment of a filamentous carbon-absorbable polymer tendon and ligament replacement.

Soft tissue structures can be replaced by a filamentous carbon-polylactic acid polymer tissue scaffold. A successful replacement requires a secure bond between the synthetic material and living soft tissue. This attachment has been investigated in a rabbit model. In 23 male, white New Zealand rabbits, the proximal third of the Achilles tendon of the hind leg was resected. Seventeen of these rabbits received composite tendon implants; six received no implants and served as shams. In all cases, the contralateral limb served as a unoperated control. Biological fixation of the synthetic material to the tendinous and myotendinous tissues of the rabbit gastrocnemius system was achieved. This occurred by ingrowth of soft tissue into the 7 mu carbon fiber network. This bond developed rapidly and was mechanically secure under physiologic loading conditions. The anastomoses' strengths were tested in tension over a 12-week period and compared to the breaking strengths of their contralateral, unoperated gastrocnemius systems and the sham systems. After four weeks, the systems with implants had strengths equivalent to those of the unoperated systems. Sham systems were significantly weaker throughout the test period. Histologically, the ingrowth process was associated with little inflammatory response. The ingrown tissue was found to be highly cellular with collagen oriented longitudinally to the tendon. After 12 weeks, the volume of collagenous tissue making up the regrown tendon section appeared nearly normal. Secure biological fixation of the carbon-polylactic acid scaffold to soft tissues may allow it application in repair or replacement of tendon or ligament deficits.

Achilles Tendon↗
PubMed1980

The role of bioengineering in orthopedics.

Orthopedic bioengineering is an example of professionals in distinct disciplines applying their skills to problems that require an interdisciplinary approach. Two current research projects, the development of replacement ligaments and tendons and of an absorbable fracture fixation device, illustrate this integrated approach.

Biocompatible Materials↗
PubMed1980

Surgical treatment of the difficult humeral neck fracture: acromial shortening anterolateral approach.

A surgical approach to the shoulder joint for the difficult humeral neck fracture is described with illustration of a case. Resection of a middle portion of the acromial process in addition to the detachment of the anterior origin of the deltoid using an anterolateral approach is presented. This provides an unrestricted exposure to the shoulder joint and eliminates the possible complications arising from acromionectomy.

Acromion↗
PubMed1980

The "silent hip" of idiopathic ischemic necrosis of the femoral head in adults.

Of thirty-three patients with the asymptomatic (so-called silent) stage of idiopathic ischemic necrosis of the femoral head, eleven had serial roentgenograms available to review the progression of the disease during this stage. Pathological specimens obtained during bone-grafting of eleven femoral heads were available for histological study in another eleven patients. It was found that the duration of the asymptomatic period averaged 5.5 years (range, three to eight years). No evidence of spontaneous regression of the avascular change was found. Typical histological findings were: (1) early clogging of the marrow spaces by amorphous material in the necrotic zone, and (2) limited evidence of so-called crreping substitution (seams of new bone laid on old, dead bone trabeculae) during the early stages of idiopathic ischemic necrosis.

Adult↗