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Biomedical subjects

S M Perren

Publications and source records attributed to S M Perren.

At least 73 records · Page 4Linked to original sources
PubMed1994

[Histologic studies of replacement of the anterior cruciate ligament with PDS-augmented patellar tendon transplants].

The bone-patellar tendon-bone graft is currently the best substitute for the anterior cruciate ligament (ACL). To improve the results we compared a modified Jones procedure with an additional PDS augmentation. In 25 sheep the ACL was reconstructed in the left knee after total resection. The only resection of the ACL was done in all right knees. One year postoperative 21 sheep remained in the experiment and came to evaluation. There were 10 modified Jones procedures and 11 PDS augmentations. In both groups, the central one-third of the patellar tendon was implanted through a femoral and tibial drill hole for reconstruction of the anterior cruciate ligament. The transplants were fixed on both ends with a 1-mm cord of polydioxanon (PDS), a soft preload of 50 N was given with a spring balance and the ends of the cords were fixed with a screw and a washer. In the second group we did an additional augmentation with a doubled cord of 2 mm PDS. Early mobilization and weight-bearing was allowed. Throughout the observation period all animals were labelled for fluorescence microscopy. One year after resection of the ACL without reconstruction there were totally destroyed joints. Histology showed damaged menisci and joint surfaces without any cartilage as a sign of severe arthrosis. The macroscopic aspect of the transplants showed strong ligaments coated totally by a synovial membrane with good vascularization. Only little signs of degeneration were to be seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Tissue response and in vivo degradation of selected polyhydroxyacids: polylactides (PLA), poly(3-hydroxybutyrate) (PHB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/VA).

The tissue response and in vivo molecular stability of injection-molded polyhydroxyacids--polylactides (PLA), poly(3-hydroxybutyrate) (PHB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/VA, 5-22% VA content)--were studied. Polymers were implanted subcutaneously in mice and extirpated at 1, 3, and 6 months in order to study tissue response and polymer degradation. All polymers were well tolerated by the tissue. No acute inflammation, abscess formation, or tissue necrosis was observed in tissues adjacent to the implanted materials. Furthermore, no tissue reactivity or cellular mobilization was evident remote from the implant site. Mononuclear macrophages, proliferating fibroblasts, and mature vascularized fibrous capsules were typical of the tissue response. Degradation of the polymers was accompanied by an increase in collagen deposition. For the polylactide series, the inflammatory response after 1 month of implantation was less for materials containing the D-unit in the polymer chain, whereas in the case of the polyhydroxybutyrate/valerates, the number of inflammatory cells increased with increasing content of the valerate unit in the polymer chain. Between 1-3 months, there was slightly more tissue response to the PHB and PHB/VA polymers than to PLA. This response is attributed to the presence of leachable impurities and a low molecular weight soluble component in the polyhydroxybutyrate/valerates. At 6 months, the extent of tissue reaction was similar for both types of polymers. All polylactides degraded significantly (56-99%) by 6 months. For a poly(L-lactide) series, degradation rate in vivo decreased with increasing initial molecular weight of the injection-molded polymer. Several samples showed pronounced bimodal molecular weight distributions (MWD), which may be due to differences in degradation rate, resulting from variability in distribution of crystalline and amorphous regions within the samples. This may also be the result of two different mechanisms, i.e., nonenzymatic and enzymatic, which are involved in the degradation process, the latter being more extensive at the later stage of partially hydrolyzed polymer. The PHB and PHB/VA polymers degraded less (15-43%) than the polylactides following 6 months of implantation. Generally, the polymer with higher valerate content (19%, 22%) degraded most. The decrease in molecular weight was accompanied by a narrowing of the MWD for PHB and copolymers; there was no evidence of a bimodal MWD, possibly indicating that the critical molecular weight that would permit enzyme/polymer interaction had not been reached. Weight loss during implantation ranged from 0-50% for the polylactides, whereas for the PHB polymers weight loss ranged from 0-1.6%.

Absorption↗
PubMed1993

Influence of the compression force on the intramedullary pressure development in reaming of the femoral medullary cavity.

The reaming process is considered the main damage factor in intramedullary nailing, as there are repeated increases in intramedullary pressure and cortical temperature, which can lead to aseptic cortex necroses and fat embolisms. In this study, the influence of the compression force on the increase in pressure is to be examined. The intramedullary pressure was measured in the middle of the diaphysis and in the metaphysis of human femora reamed under various compression forces. The compression force exerted by the surgeon was measured on polyurethane femora. It was observed that an increase in the compression force of 1.8 times led to an increase in the diaphyseal pressure of 4.7 times and of the metaphyseal pressure of 3.1 times. As surgeons exert high compression forces, peak pressures of 970 mmHg diaphyseally and 1150 mmHg metaphyseally must be expected in the hospital. If reaming is carried out with less compression force, the intramedullary pressure can easily be reduced by 79% in the area of the diaphysis and by 68% in the metaphysis.

Femoral Fractures↗
PubMed1993

Intramedullary pressure in reamed and unreamed nailing of the femur and tibia--an in vitro study in intact, human bones.

The generation of intramedullary pressure during nailing of the femur and the tibia using reamed and unreamed nailing techniques was investigated and compared in an in vitro study in intact, cadaveric human bones. The pressure was assessed by distal supracondylar measurements via a small hole in the metaphyseal cortex. No significant difference in the intramedullary pressure increase was seen in the femur whether a reamed or unreamed nailing technique was used in contrast to the tibia (p = 0.01). A distal venting hole in the femur did not lower the increase in pressure during insertion of an unreamed nail. Using the cannulated cutter to open the medullary canal showed a significant increase in pressure compared to the use of the awl in the femur (p = 0.01), but not in the tibia.

Bone Nails↗
PubMed1993

The role of corticotomy and osteotomy in the treatment of bone defects using the Ilizarov technique.

Posttraumatic bone defects are usually bridged using autogenous or exogenous cancellous bone grafts. These grafts consolidate to form a solid bone structure that is mechanically stiffer than natural bone. Likewise, the procedure of corticotomy and distraction is appropriate for treatment of bone defects. In our experiment, a 2-cm bone defect was created in 25 sheep tibiae. We performed corticotomy or osteotomy of the intact bone, thus creating a bone segment that was drawn across the defect using a specially designed traction device. The limb was stabilized using an external fixator. Four groups were formed for comparison: corticotomy and osteotomy with distraction at a rate of 1 mm/day; corticotomy and osteotomy with immediate transportation of the segment to the docking site. The animals were killed after 4, 8, 12, 16 and 52 weeks. Evaluation of the results was based on standard radiographs. In the two groups involving gradual transportation, spontaneous bone regeneration occurred in all cases whereby after corticotomy the new bone was tubular (around the medulla). Following osteotomy, bone regeneration occurred initially on the dorsal and lateral sides of the tibia leaving a defect on the ventral and medial sides. This defect subsequently closed. At the end of segment transportation, healing was observed at the docking site. In Groups 3 and 4, the bone did not regenerate at all. Therefore, this procedure, immediate transportation, was not investigated further because no clinical success could be expected from its application.

Animals↗
PubMed1993

Extra-articular augmentation for residual hip dysplasia. Radiological assessment after Chiari osteotomies and shelf procedures.

The Chiari osteotomy and various shelf procedures are used to augment the weight-bearing area in dysplastic acetabula. The new articular surface derives by metaplasia from the acetabular rim and joint capsule, and is therefore of poorer quality than congruous hyaline cartilage. We reviewed 32 patients after augmentation procedures, using conventional radiographs and three-dimensional reconstruction from CT scans. We showed that Chiari osteotomy and shelf procedures generally achieve less than complete cover, especially over the posterolateral quadrant of the femoral head. Our results suggest that alternative methods which reorientate the whole of the acetabulum are the treatment of choice. Augmentation procedures remain as a salvage option when reorientation is inappropriate or the original hyaline cartilage surface is absent, as in subluxed joints with a secondary acetabulum. Computerised assessment is recommended before operation to assess existing cover and the possible extent of provision of new cover.

Adolescent↗
PubMed1993

The effect of fracture on femoral head blood flow. Osteonecrosis and revascularization studied in miniature swine.

Miniature swine were used to study the effect of cervical fracture on femoral head blood flow. Laser Doppler flowmetry was used to evaluate femoral head blood flow before and after the fracture, after internal fixation with or without compression, and 8 weeks post-fracture. Fluorescent bone-labeling was performed at 2, 4 and 6 weeks post-fracture. Femoral head blood flow decreased to 40 percent of baseline following fracture, partly from the disruption of venous drainage. Histologically, all femoral heads showed some degree of trabecular thinning, microfracture, and neovascularization when compared with controls. Analyses of the laser Doppler flowmetry data, fluorescent label histology, microradiography and bone densitometry indicated that late (4-6 weeks) revascularization produces severe trabecular mechanical weakening and resultant femoral head collapse. Femoral head ischemia following fracture probably falls along a continuum, with only the more severe cases proceeding to mechanical collapse. Femoral neck fractures in the minipig produce femoral head necrosis of a severity and incidence which closely parallels that of the human population; thus, the minipig is a useful model for further study of complications following femoral neck fracture in humans.

Animals↗
PubMed1993

The effects of antibiotic-impregnated autogeneic cancellous bone graft on bone healing.

Autogeneic cancellous bone graft has been recommended as a vehicle for local antibiotic delivery. Its effect on graft incorporation, however, is unknown. The healing of defects grafted with tobramycin-impregnated cancellous bone were compared with those grafted with cancellous bone alone. Plane roentgenographs, microradiographs, bone density analyses, histologic examination, and biomechanical testing were performed on specimens throughout the course of healing. The presence of large concentrations of local tobramycin does not appear to affect the normal healing characteristics of cancellous bone graft.

Animals↗
PubMed1992

Effect of bone size, not density, on the stiffness of the proximal part of normal and osteoporotic human femora.

Proximal femur fractures in the elderly lead to a high rate of hospitalization. In studying the operative treatment of such fractures, it is first necessary to understand the relationship between the morphologic properties of this part of the femur (related to both geometry and density) and its mechanical properties. Numerous investigations showed that femoral strength correlates with bone mass; however, the dimension of the bones was not taken into account. We measured the relationship between the stiffness of the proximal femur under physiologic load and its geometry and density. Conventional x-rays and quantitative computed tomography (QCT) were carried out on pairs of human cadaver femora. Eight pairs were instrumented with strain gauges. Bones were subjected to an eccentric load that simulates moderate weight bearing (single-leg stance), and the strain parallel to the bone axis was plotted as a function of the load applied. An apparent bone stiffness was calculated as the ratio between the strain gradient within the section and the load applied. Strong correlation was found between x-ray densitometry and QCT. The bone stiffness also correlates strongly with the geometry (area) and slightly with bone mass; however, an unexpectedly low correlation was found between stiffness and density. We chose stiffness as a mechanical parameter (not strength) because it describes the "normal" bone behavior under load. Our results clearly demonstrate that the cross-sectional size of the bones must be taken into account when establishing the relationship between the mechanical characteristics of the bone and its morphology. In accordance with previous predictions, our results support that bone loss due to osteoporosis is compensated for by an increase in bone diameter.

Absorptiometry, Photon↗
PubMed1992

Effect of animal species and age on plate-induced vascular damage in cortical bone.

Plates used for fracture fixation produce vascular injury to the underlying cortical bone. During the recovery of the blood supply, temporary osteoporosis is observed as a result of Haversian remodeling of the necrotic bone. This process temporarily reduces the strength of the bone. We tackled the postulate that quantitative differences exist between animal species, and in different bones within the same species, due to variations in the relative importance of the endosteal and periosteal blood supplies. Using implants scaled to the size of the bone, we found comparable cortical vascular damage in the sheep and in the dog, and in the tibia and femur of each animal. We observed a significant reduction in cortical vascular damage using plates that had a smaller contact area with the underlying bone. No significant difference in cortical vascular damage was noted in animals of different ages.

Age Factors↗
PubMed1992

Drill bit failure without implant involvement--an intraoperative complication in orthopaedic surgery.

The aetiology, frequency and consequences of drill bit failure during surgical intervention in human and animal bone tissue are investigated and discussed to provide the surgeon confronted with this problem with a scientifically based procedure. The literature on this subject is rather inadequate, i.e. only one publication in the last decade could be found dealing with this topic and this was a veterinary case. The Laboratory for Experimental Surgery in Davos has received several enquiries from the medical profession worldwide as to correct procedure in the case of drill bit failure. Three sources of information were investigated in order to furbish a reply to these enquiries, these were the AO/ASIF documentation centre in Berne, a survey of 280 surgeons and orthopedic doctors in Switzerland and a survey of 83 AO/ASIF foundation members. One broken tap (tool steel) was removed two years after the operation and metallographic investigations carried out. A frequency of 3 drill bit failure per 1000 internal fixations (0.3%) is apparent in nearly all data. The reasons for drill bit failure were investigated. Drill bit failure occurs more frequently in the proximal femur and when using angled plates. On the basis of this enquiry the following guidelines can be offered to the surgeon. A broken drill bit which is not in contact with an implant can be left in the body without any risk of delayed recovery. However, if the drill fragment is situated near a joint or if it can be easily removed without further trauma to the bone, then it should be removed. Once the fracture has healed the broken drill bit should be removed along with the implant provided no exceptional difficulties are involved.

Adult↗
PubMed1992

Drill bit failure with implant involvement--an intraoperative complication in orthopaedic surgery.

This paper aims to investigate whether drill bit fragments which are in contact with an implant behave differently to those without contact to the implant and if so in what way. There is particular emphasis on whether two metals in contact are subject to corrosion and whether the products of such a corrosion lead to undesirable tissue reactions. The orthopaedic surgeon must know whether a drill bit fragment should be removed if it is in contact with an implant, in particular, whether there will be negative consequences for the tissue if it is left in the body. It is necessary to establish how much additional trauma is justified in removing a broken fragment and how the surgeon can determine intraoperatively whether there is contact between the fragment and the implant. Finally, this investigation aims to establish whether the fragment can be left in the body until implant removal or whether it can be left permanently in situ.

Animals↗
PubMed1992

[Limited Contact Dynamic Compression Plate (LC-DCP)--biomechanical research as basis to new plate design].

Our continuously evolving understanding of bone biology has led to a new approach to plate fixation. In comminuted fractures, anatomical reduction of all fragments is no longer a goal in itself. Preservation of the viability of the bone fragments seems to be the key to unimpaired fracture healing in internal fixation. The rapid integration of unreduced but vital fragments into the fracture callus functions as a bio-buttress system and prevents fatigue fracture of the implant. To realize the new concept of biological internal fixation, the limited contact dynamic compression plate, which minimizes vascular damage to the plated bone segment, has been developed.

Animals↗