Search

Soft materials, such as soft biological tissue and soft silicone rubber, are non-linear materials which require the classical uniaxial and biaxial tensile testing methods for characterisation. Unfortunately, in special cases, such as for soft biological tissue, the samples are smaller than 10 mm × 10 mm in size and these classical tensile testing methods produce unwanted stress and strain gradients due to the fastening techniques associated with these methods. Micro-indentation is proposed as an alternative method for characterising soft materials. Using inverse Finite Element (FE) analysis and a known Mooney-Rivlin three parameter material model, six different micro-indentation tests were proposed. A theoretical approach was used to determine which indentation test best characterised a silicone sample, by using two FE models. The results showed that microindentation is capable of characterising a soft material in ideal conditions with a cylindrical indenter applied in a diagonal orientation over the sample, as the best indentation method. Finally, it was observed that the material model can either match the displacements with the smallest objective function or the stress vs. stretch curve can be matched to 99 % over the whole stretch range but not both simultaneously. [ABSTRACT FROM AUTHOR]

The incorporation of perforated cortical bone allografts was compared with non-perforated allografts. A 5-cm circumferential defect in the middiaphysis at the tibia was created in adult sheep. A frozen tibial allograft was implanted and fixed with a locked nail for 6 months. There was no postoperative immobilization. Group I consisted of eight sheep with non-perforated allografts, whereas Group II was comprised of 10 sheep with perforated allografts. Union was evaluated radiographically, whereas the central part of the allograft had a densitometric evaluation. Creeping substitution was assessed on microradiographs from cross-sections of the central 3 cm of graft by measurement of porosity and percentage of new and old bone area within the confines of the graft. The width of periosteal and endosteal callus also was determined. There was no statistical difference between both groups for the union score and bone density. However, the cortical bone graft porosity and the amount of new bone within the cortical bone differed significantly between the perforated allografts and the non-perforated ones. Periosteal callus was similar in both groups, whereas endosteal callus was significantly more wide and extended in the perforated allografts. Perforation of a cortical bone substantially improved the amount of newly formed bone by the host when compared with a non-perforated bone. The creation of channels seemed to increase the interface between living soft tissues of the host and the allografted bone with a resulting enhanced incorporation.

We compared the reliability of computer-assisted radiographic analysis (CARA) and visual evaluation of radiographs to assess host-graft junctions. 68 host bone/allograft junctions were obtained from an ongoing study on bone allografting in sheep. At 6 months, the grafted tibias were explanted and healing of the host-graft junctions were macroscopically determined. 49 junctions were macroscopically healed, whereas 19 had not united. 51 (0.8) of the junctions were correctly classified by radiographs, while 63 (0.9) of the junctions were correctly classified by CARA (p = 0.03). These findings warrant further evaluation in a clinical setting.

Since 1974, we have more than 20 years experience with cementless rehabitable total hip arthroplasty.The purpose of this work is a long term study of development of this type of fixation about a personal series of 83 hips which benefitted from this type of arthroplasty before 50 years old between 1974 and 1980., Material and Methods: The implants used are among the oldest. On the acetabular side, we used the BG spiked acetabular component (Fig. 1), containing 4 teeth for primary fixation, 3 equatorial armatures and a surface treatment. This metal back in two sizes 50 and 54 mm, initially permitted the insertion of a polyethylen insert of an interior diameter of 32 mm with a peripheric thickness of 5.5 mm; since 1979, the insert had a 22.2 mm diameter, assuring 10 mm minimal thickness of. The femoral implant (Fig. 2) for 62 hips was the Huchet prothesis, then in 16 cases, the minimadreporic prothesis composed of a morse cone and a head of 22.2, the Huchet prothesis was one-piece femoral implant.The dominant etiology was coxarthrosis (56 cases) of which 50 % had major dysplasis. The average age at the time of the intervention was 41 years old (18-50 years), the follow-up of this series is 17 years, and 8 months (15-21 years). Resumption of former activities was the rule.Results of the rehabitable pro thesis up to 12.31.1995: Of the 83 cases, the outcome of 55 of them (66.3%) is known : 49 (59%) were examined for this study; the evolution has been documented; 28 (33.7%) were uncontactable, 6 patients (7.3%) were deceased between 8 and 9 years following the operation, without having had the hip revised.Among the 49 protheses which were evaluated, 22 (44.9%) have not been revised to date. Clinically, the function is normal and there are no radiological signs of attrition of the insert or mobilisation of implants. There are 10 Huchet Protheses and 12 minimadreporic protheses in this group. The average age at the time of the intervention was 42 years old (30-50 years old), the follow-up was 16 years and 7 months (15-19 years) (Fig. 3a-d).27 hips (51%) needed to be revised, but the causes of reoperationn include different reasons tied to the failure of biological fixation but particularly to errors in the initial concept of the Huchet prothesis.Reoperation linked to the failure of the biological fixation: Out of 7 acetabular implant reoperations, one was carried out systematically on a cup which was perfectly bone-integrated during the changing of a femoral component, 3 were necessary due to perforation (attrition of the insert). Only 3 acetabular implants (6.1%) required reoperation for symptomatic loosening.Four femoral implants (8.6%) have been taken out because of failure of biological fixation between 2 and 11 years follow-up. Finally, for one patient the persistance of the incapacitating crural pain which lasted for more than one year led to the removal of the femoral stem, nevertheless perfectly integrated.Reoperation linked to the concept of the Huchet prothesis: These were undertaken in two sets of circumstances.Changing only the polyethylene insert was only called for in the Huchet prosthesis and concerned 18 hips (36.7%); the delay to reoperation varied from 11 to 18 years with an average of 14 years delay. Changing of the insert had a simple short post-operative outcome and functional recuperation was between 6 and 8 weeks (Fig. 4a-c).Removal for perforative attrition of polyethylene insert causing metal-to-metal wear between head and metal back. Five Huchet prostheses are included in this group, with an average delay to reoperation of 16 years and 3 months (14-19 years)., Comments: This retrospective study with a 66.3 % rate of re-examination permits three types of comments.The principal cause of revision (23 cases), is linked to polyethylene attrition and is only found in the group with Huchet prosthesis. More than the quality of the polyethylene used at this time, it is its thickness in contact with a 32 mm head which led to the complete removal of the prosthesis in 10.2% of the cases.The second comment argues for the modularisation of the femoral implant. The presence of a stem with a cone and a removable head would have avoided the removal of 5 perfectly bone-integrated femoral implants. Certainly, the literature demonstrates the risk of corrosion generated by the morse cone but it is up to the manufacturers to improve their procedures.Finally, the third comment concerns the current state of the long term of the biological fixation by rehabilitation with surface treatment. With 17 years 8 months follow-up (15-21 years), 81.6% of components are still fixed, the real failure of the bony ingrowth of 10.2% is comparable to the rate of failure in long term follow-up of totally cemented prothesis found in young subjects., Conclusion: With more than 20 years follow-up for the older cases, the concept of the biological fixation of an implant by bony ingrowth using surface treatment seems to be very reliable.The experience of this long term study argues for the thickness of polyethylene to be at least 10 mm for all metal back acetabular component and the future of this kind of implant seems to lie in modularisation made possible by the morse cone which would allow the replacement of the bearing surfaces.

We reviewed 47 type 3 femoral fractures (below the femoral stem according to the Johansson classification). There were 36 women and 11 men. The average age was 73,4 years, at the time of the fracture.These patients had had a total arthroplasty in 32 cases, a hemi arthroplasty in 10 cases and a bipolar arthroplasty in 5 cases.Of these 47 patients:- 6 underwent an orthopedic treatment (2 trans-tibial traction, and 4 plaster of Paris immobilisations) for a period averaging 60 days. Two (33%) developed pseudoarthritis and 2 (33%) developed bed-sores and decubitus complications.- The remaining, 41 patients underwent a surgical procedure:- 34 osteosynthesis using plates or screw plates brought about : - 4 fractures under the plate; - 4 pseudo-arthrosis; - 4 infections; - 4 plate breakages; - 1 femoral stem loose-ring;- 6 femoral stems were replaced with longer stems going through and extending past the fractures, without any material breakage or local complications (one patient died however, following other complications).- One patient had an Olerud procedure and unfortunately died after 3 months.At last follow up : - 4 patients had died; - consolidation occured in 41 cases over an average period of 130 days (45 to 590); - fractures treated by using osteosynthesis plates, showed a 50% incidence of complication; - on the other hand, when using stem replacement, no mechanical or local complications occured.

Radiologists are often confronted to the choice of the most appropriate statistic tool for evaluating diagnostic imaging methods. Using a radiological literature example, the Kappa agreement test is herein described and its applications are determined. Although widely performed to determine the inter-rater agreement, this test is also suited for the confrontation of two or more diagnostic imaging methods applied on the same subjects and providing categorical data. It procures the degree of agreement between the different methods.

Purpose of the Study: The authors describe an arthroscopic technique of tibio-talar arthrodesis. They discuss the advantages, indications and results of this technique., Material: Seven arthroscopic tibio-talar arthrodeses (A.T.T.A.) were performed between may 1992 and september 1993 for post traumatic arthritis (five following bimalleolar fractures, two following talar fractures)., Method: Traction by means of a transcalcaneus pin was applied to obtain articular distraction. Arthroscopic debridement was performed using two standard anterolateral and anteromedial portals. The arthrodesis was secured in neutral position by two percutaneous tibio talar cannulated cancellous screws., Results: Fusion was obtained in all cases over an average period of 12 weeks. No infections or cutaneous complications were noted. In one case, however, screw positioning caused an injury to a branch of the superficial peroneal nerve. At last follow-up, according to the Duquennoy grading system, the results were good or very good., Discussion: In this study, we noticed a particularly low rate of complications, a significantly lesser recovery time and a higher fusion rate compared to open ankle arthrodesis techniques. This is probably due to the careful handling of the periarticular soft tissues, possible with the arthroscopic procedure. The best indication for this procedure seems to be "centered" ankle arthritis. However, a significant deviation in one plane, or a tibial or talar bone loss needing an autogenous graft is considered to be a contra-indication for the procedure., Conclusion: A.T.T.A. seems to be a simple and reliable technique for centered ankle arthritis.

We have followed up 227 total hip replacements using a cementless minimadreporic prosthesis for an average of 9 1/2 years. Special attention was paid to the acetabular component, of which 2 types were used; 77 incorporated screw rings and 134 were stabilised by spikes. The screw prostheses were evaluated at an average of 8 1/2 years from operation; one third showed radiological evidence of migration, and revision because of this was required in 12.6% of cases. The spiked cups were followed up for an average of 10 years; 14.8% showed radiological evidence of migration and 2.3% needed revision. We observed no radiological features to explain this difference. The quality of the bone and the mechanical characteristics of the bone/implant contrast may influence the result. We feel that an uncemented spiked acetabular implants is a worthwhile concept.

Unlabelled: A functional assessment of fifty patients after ankle arthrodesis for post traumatic arthritis was carried out by means of an extensive clinical evaluation after an average follow-up of nine years. The data on position of ankle arthrodesis and gait analysis were examined to determine the effect of arthrodesis of the ankle on the subtalar and small joints of the foot. The Duquennoy point system was used to grade the ankle clinically and a new radiological method to determine the sagittal position of the ankle arthrodesis was developed. Equinus position was related with clinical damage on sub talar joint, and anterior cavus foot (92.8 per cent). This position was related with metatarsalgia in 26.9 per cent. Calcaneus position was related with posterior cavus foot (verticalization of the calcaneus). This position was related with the best functional results on walking, jumping and running., Clinical Relevance: this study has showed that the ideal position of fusion of the ankle was neutral or slight flexion, slight valgus angulation of the hind part of the foot and 10 degrees of external rotation.