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Biomedical subjects

D Kohn

Publications and source records attributed to D Kohn.

At least 73 records · Page 4Linked to original sources
PubMed1999

A comparative study of two cerclage systems.

Intraoperative femoral fracture is a well recognized technical complication of cementless total hip arthroplasty (THA). The aim of this study was to establish an in vitro model for initiation of fractures of the femur in cementless THA and to assess the effect of fracture fixation by cerclage wiring. An in vitro comparison of two methods of cerclage fixation was performed using steel wire (Protasul) versus multifilament Vitallium alloy cable. Ten fresh human femur specimens were studied. Longitudinal fractures were created on a material testing machine. The force to create a longitudinal fracture in the femur was 1915 N to 9288 N (median 6531 N). This force corresponds 3 to 15 times (median 11 times) the body weight. The femoral cortex was fractured in 5 cases ventrally, in 6 cases medially and in 1 case laterally. After monofile cerclage wire application, the force required to press the prosthesis 5 mm deeper into the medullary canal was 0.3-2.7 times body weight. After Vitallium alloy cable application in other specimens, the force was 1.3-2.7 times body weight. The difference was not statistically significant. After monofile cerclage wire application, a force of 1.8-8.1 times body weight was necessary to press the prosthesis 30 mm deeper into the medullary canal. After polyfile Vitallium alloy cable application in other specimens, the force was 7.7-12 times body weight. The difference was statistically significant (U-test, alpha < 0.025).

Adult↗
PubMed1999

Prevalence of popliteal cysts in children. A sonographic study and review of the literature.

Popliteal cysts in children differ from those in adults. They are considered to be less frequent and usually appear in the absence of intra-articular lesions. However, their prevalence in asymptomatic children is unknown. We present a prospective epidemiological study of 168 asymptomatic children under 15 years of age hospitalised for various pathologies. Children with knee problems and rheumatic diseases were excluded from the study. The children were examined ultrasonographically with a 7.5 MHz linear scanner. A popliteal cyst could be identified in 4 patients. The prevalence of asymptomatic popliteal cysts was thus 2.4%. For 2 of these patients, we obtained magnetic resonance image of the knee which showed no concommitant intra-articular pathology.

Adolescent↗
PubMed1999

Immune response to green fluorescent protein: implications for gene therapy.

Green fluorescent protein (GFP) is a widely used intracellular reporter molecule to assess gene transfer and expression. A potential use for GFP is as a co-expressed marker, to select and enrich gene-modified cells by flow cytometry. Processed peptides derived from GFP and presented by the major histocompatibility complex on the cell surface could potentially induce T cell immune responses against GFP+ cells. Thus, clinical application of GFP is premature, since in vivo studies on its immunogenicity are lacking. Therefore, we investigated immune responses against EGFP (enhanced-GFP) in two transplantable murine models: the BALB/c (H-2d) BM185 pre-B leukemia and the C57BL/6 (H-2b) EL-4 T cell lymphoma. BM185 and EL-4 cell lines modified to express high levels of EGFP showed drastic reduction of disease development when transplanted into immunocompetent mice. BM185/ EGFP did lead to rapid development of disease in immunodeficient Nu/Nu mice. Mice surviving BM185/EGFP leukemia challenge developed high cytotoxic T lymphocyte (CTL) responses against EGFP-expressing cells. Furthermore, immune stimulation against BM185/EGFP cells could also be induced by immunization with EGFP+ transduced dendritic cells. The effects of the co-expression of EGFP and immunomodulators (CD80 plus GM-CSF) were also investigated as an irradiated leukemia vaccine. EGFP co-expression by the vaccine did not interfere with the development of CTLs against the parental leukemia or with the anti-leukemia response in vivo. These results indicate that the immune response against EGFP may interfere with its applicability in gene insertion/replacement strategies but could potentially be employed for leukemia cell vaccines.

Animals↗
PubMed1999

Meniscal substitutes--animal experience.

Animal studies have shown that meniscus allografts and tendon autografts generally heal to the capsule, are revascularized and repopulated with host cells. In animals, neither meniscal allografts nor tendon or fat autografts gain the properties of a normal meniscus. Meniscus allografts and tendon autografts are promising as both seem to offer some protection to the cartilage of the tibial plateau. There is no evidence that meniscal transplantation can prevent cartilage degenerative changes, and the long-term effect of meniscal transplantation on articular cartilage remains unknown. Whether cellular repopulation of the meniscal allograft is sufficient to restore its biomechanical properties is unknown. Collagen scaffolds and tissue engineered grafts are still under investigation, showing promising results especially for the former. Viable meniscal allografts should be implanted within 1 to 2 weeks after harvesting, as the production of proteoglycans decreases after 2 weeks.

Animals↗
PubMed1999

Meniscal substitutes--human experience.

A number of clinical series have described the effect of meniscus allograft replacement in humans. The general indication has been disabling pain following loss of a meniscus in a skeletally mature individual. Overall, healing of the graft to the capsule occurs in up to 80% of all transplants. Revascularization and cell repopulation is found in all grafts but is highly variable. The risk for graft failure seems to be greater with irradiated grafts and in patients with grade III or IV osteoarthritic changes. In most series, patients experienced a decrease in pain and an increase in activity level postoperatively. In many series, concominant surgery (cruciate ligament reconstruction or osteotomy) had been performed. Meniscus replacement with frozen or cryopreserved allografts seems to give the most promising short-term results in patients with post-meniscectomy pain. Controlled, randomized prospective studies are needed to confirm a long-term benefit and better define transplantation indications. Viable meniscus allografts seem to survive transplantation, as donor cells were found in the graft after 2 years. Clinically, pain was reduced and activity increased following transplantation, but after 4 years some of these gains were lost. There was no correlation between postoperative findings on MRI and clinical outcome. Meniscal replacement with a quadriceps tendon autograft in humans resulted in pain reduction, but at second-look arthroscopy, only 2 of 9 tendon autografts looked like a meniscus. Six were in position but still looked like tendons. Total medial meniscus replacement by quadriceps tendon autrograft is still an experimental procedure. There is no proof at present that meniscal substitutes (meniscus allografts or tendon autografts) in humans can protect the hyaline cartilage of the knee from the degeneration, following loss of a meniscus. There is some evidence in animal experiments that under circumstances not yet exactly known, a meniscus substitute can have a protective effect on articular cartilage. Three factors have been identified that prevent proper meniscal function: poor fixation of the meniscal horns, no contact of the graft with the articulating surfaces under load and incorrect positioning of the horns. Meniscal allograft transplantation sensitizes humoral and cell mediated immune systems. Bone plugs attached to meniscal allograft tissue may increase cell surface antigenicity. Deep freezing and especially freeze drying of meniscal tissue decreases host immunogenicity. Cryopreservation maintains the content of donor HLA encoded antigens and is likely more sensitizing to the host. The clinical importance of immune responses to meniscal allografts is not known, but it has not been shown to result in graft failure or rejection. Prospective studies are needed.

Antibody Formation↗
PubMed1999

Harvest and conservation of meniscal allografts.

Meniscal allografts can be harvested and preserved in different ways. A technique for harvesting and conserving viable allografts is described. The meniscus should be harvested within 12 h after the start of ischaemia. The ideal time for implantation of the viable graft is 10 to 14 days after harvest, in which time a recipient should be identified. Frozen grafts are avital. Cryopreserved grafts are not avital, as 10-30% of the fibrochondrocytes are preserved. Frozen and cryopreserved grafts can be stored for a long time and if a graft bank is established, grafts are always readily available. There is no proven advantage of one graft type over others.

Cryopreservation↗
PubMed1999

Meniscus transplantation: preoperative planning.

Precise preoperative planning is mandatory to obtain good results of meniscus transplantation. Any pathology in addition to the missing meniscus should be detected, including malalignment, and ligament instability. A full status of the changes in the cartilage should be made. It is unknown how precisely the donor meniscus needs to fit the size of the original meniscus to allow healing and regeneration. The effect of incongruency and wrong insertion of the meniscal horns has been investigated in an animal experiment. The incongruous grafts did not entirely avoid chondromalacia after meniscectomy, but provided some chondroprotective effect. A wrong bony insertion of the meniscal horns leads to even more serious chondral damage than meniscectomy.

Animals↗
PubMed1999

Arthroscopic and open surgical techniques for meniscus replacement--meniscal allograft transplantation and tendon autograft transplantation.

Open, arthroscopically assisted and arthroscopic methods for lateral and medial meniscus allograft transplantation with bone plug fixation are described. An open technique for medial and lateral meniscus transplantation without bone plug fixation, as well as an open technique for autograft quadriceps tendon replacement of the medial meniscus are described.

Arthroscopy↗
PubMed1999

Postoperative follow-up and rehabilitation after meniscus replacement.

Even though basic scientific knowledge about the meniscal loading pattern may advocate restrictive rehabilitation after meniscus repair, experience and one controlled study favour accelerated rehabilitation. The current protocols for rehabilitation after meniscal substitution follow personal experience with parameters such as pain, effusion, locking, and gait pattern used as clinical guidance. Controlled clinical studies on rehabilitation should be encouraged. An example of a rehabilitation protocol is given. As meniscus replacement is a new treatment option, it is essential to document details about the graft, the knee status at operation and the surgical procedure. The goal of a postoperative follow-up is to control quality, to measure patient satisfaction and to show whether meniscus replacement is beneficial in relation to the natural history of meniscectomy cases. There is a need for a standard follow-up evaluation of patients after meniscus replacement, and the development of a meniscus transplantation score including subjective and objective data is suggested.

Humans↗
PubMed1999

Future research in meniscal replacement.

To study the remodelling process after meniscus replacement and to learn how to control it will be a key topic for future research. Not enough is known about the importance of precision in meniscal fixation and how to make the insertions as strong as in the normal meniscus. Methods to measure load-distribution, mechanical properties of the graft and status of the cartilage should be developed. A number of different auto- and allografts have been shown to heal and revascularize, but whether the grafts are functioning is not known. Meniscal scaffolds, which can be used for replacement of partial meniscal loss, need to be tested. Scaffolds and tissue engineering will be the subject of intensive research in the future.

Cryopreservation↗
PubMed1998

Drill hole position in endoscopic anterior cruciate ligament reconstruction. Results of an advanced arthroscopy course.

In 24 cadaver knees the anterior cruciate ligament (ACL) was replaced by a bone-tendon-bone patellar tendon autograft in an endoscopic technique. This was carried out during an advanced arthroscopy course after intensive instruction and practice on a plastic model. When the knees were opened and evaluated according to the recent orthopaedic literature, only four good results with correct tunnels and a non-impinging graft were found. In 12 knees the femoral tunnel was too far anterior (10) or had broken through the posterior femoral cortex (2). In 6 knees the tibial tunnel was too far anterior (2) or too far posterior (4). The notchplasty was insufficient in 6 knees. We conclude that endoscopic ACL reconstruction cannot be mastered after attending a course alone. Expert help is necessary during the first clinical cases.

Adolescent↗