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STUDY DESIGN: In the field of numerical simulation, the finite element method provides a virtual tool to study human tolerance and postulate on potential trauma under crash situations, particularly in case of whiplash trauma. OBJECTIVES: To show how medical and biomechanical interpretations of numerical simulation can be used to postulate on human injuries during crash situations. This methodology was applied to whiplash trauma analysis. A detailed analysis of kinematics of joints, stress level in hard tissues, and strain level in soft tissues was used to postulate on chronology and patterns of injury. Data were compared with published biomechanical and clinical studies of whiplash. SUMMARY OF BACKGROUND DATA: Although many in vitro and in vivo studies have been conducted to investigate whiplash cervical injury, and despite the number of finite element models developed to simulate the biomechanical behavior of the cervical spine, to date, there are only limited finite element models reported in the literature on the biomechanical response of the whole cervical spine in these respects. METHODS: A complete finite element model of the human body (HUMOS) build in a sitting position in a car environment was created to investigate injury mechanisms and to provide data for automotive safety improvements. It includes approximately 50,000 elements, including descriptions of all bones, ligaments, tendons, skin, muscles, and internal organs. A 15-g whiplash injury was simulated with the HUMOS model. The model predicted cervical motion segment kinematics, deformations of disks and ligaments, and stresses in bone. Model output was then compared with experimental and clinical whiplash literature. RESULTS: In term of kinematics during the chronology of whiplash, two injury phases were identified: the first was hyperextension of the lower cervical spine (C6-C7 and C5-C6) and mild flexion of the upper cervical spine(C0-C4). The amount of upper cervical flexion was 15 degrees from C0 to C4. The second phase was hyperextension of the entire cervical spine. Potential patterns of ligamentous injuries were observed; the anterior longitudinal ligament experienced the most strain (30%) at the lower cervical spine at the time of lower cervical extension and the interspinous ligament experienced the most strain (60%) at the time of upper cervical flexion. Von Mises stresses in bone do not exceed 15 Mpa, which is largely under injury levels reported in the literature. CONCLUSIONS.: This study reports a methodology to describe and postulate on human injuries based on finite element model analysis. The output of the HUMOS model in the context of whiplash shows a strong correlation with clinical and experimental reported data. HUMOS shows promise for the modeling of other types of trauma as well.

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This study investigated cytotoxicity of cement fragments harvested from two prosthesis revisions by the MTT test using L929 fibroblasts and human osteoblasts. The results did not show any toxicity of the extracts prepared after 48 and 78 months implantation. We consider that no MMA monomer has been released from the cement fragments. Histological studies on undecalcified samples harvested around revising prosthesis from 11 patients were used to evaluate tissue reactions at the bone-cement interface after 2-168 months implantation. Cement and prosthesis particles (5-35 microm) either dispersed or forming a layer were observed. A fibrous tissue layer, osteolysis, and osteonecrosis areas were observed at the interface. Besides, fibroblasts, macrophages, and multinucleated giant cells were also observed. New bone formation with osteoid, osteoblasts, and endochondral ossification with fibrocartilaginous tissue has been observed. The tissue reactions seemed to decrease with time. However, osseous trabeculae fractures were observed in the samples after 19 months. Although we consider that monomer toxicity, exothermic reaction, and particles formation may cause short-term prosthesis loosening; the trabeculae fractures may be due to prosthesis and bone cement micromovements. This fractures and particles formation may cause long-term prosthesis loosening.

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PURPOSE OF THE STUDY: Based on our experience with plate fixation of humeral shaft fractures and an analysis of the international literature, we attempted to answer the following questions. What functional outcome and what complications can be expected after surgery? Are the classical complications of open fracture surgery (screw fixation, wiring, plate fixation without compression.) as frequent after plate fixation using the Müller technique? MATERIAL AND METHODS: We reviewed our series of 156 humeral shaft fractures (61 p. 100 men, mean age 45 years) including 21 cases of multiple trauma and 24 multiple fractures. A floating elbow was present in 8 cases and skin opening in 16. Initial radial deficiency was observed in 28 cases. Plate fixation was the only method used for the humeral shaft fractures. We used the modified Stewart and Hundley classification. RESULTS: Postoperative paralysis occurred in 8 cases (5.1 p. 100, 5 complete paralysis); only one patient suffered persistent severe sequelae. There were also 8 malunions and 3 late consolidations. Consolidation rate was 94.2 p. 100, sepsis rate was 1.5 p. 100. Good or very good outcome was achieved in 86.6 p. 100 of the cases. DISCUSSION: In the literature, (71 series, 5 000 patients), plate fixation of humeral shaft fractures has given very good functional results with few initial failures, malunions or cases of sepsis. Radial paralysis is cited as a complication in 6.5 p. 100 of all plate fixations but is reversible in 90 p. 100 of cases. Classical orthopedic methods and centromedullar techniques produce more stiffness. The Sarmiento cuff can give good results after rigorous patient selection. CONCLUSION: Plate fixation according to the Müller technique is a reliable osteosynthesis method with few initial failures or malunions as evidenced by data in the literature. Infection is also rare. Although the radial nerve risk makes this technique rather difficult, excellent functional results can be achieved.

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UNLABELLED: A Plasmapore-coated titanium alloy block was implanted in ewes for the purpose of providing interbody fusion. Four blocks were implanted in each ewe: one uncoated block (without Plasmapore) serving as a reference specimen and three blocks coated with Plasmapore. Mechanical testing and histological study were performed on five ewes. OBJECTIVES: Determination of the quality of the mechanical and histological anchorage of the Plasmapore implanted in the interbody space in the same animal living under conditions of physical strain exerted on the spine. METHODS: Four months after surgical implantation of the block, the ewes were sacrificed: the removed spines were frozen for subsequent mechanical analysis and preserved in a solution of 40 degrees alcohol for subsequent histological analysis. X-rays were taken to evaluate the positioning of the implant. The mechanical analysis included extraction tests, measuring the maximum extraction force and evaluating the stiffness of the system, being indicative of the mechanical fixation quality. The histological study included both qualitative and quantitative analysis, together with an evaluation of the osteointegration of the blocks coated with Plasmapore. RESULTS: After 4 months of implantation, a mean extraction force of 990 N was necessary for the blocks coated with Plasmapore, and of 1.338 N for the blocks coated with Plasmapore with additional osteosynthesis, whereas a mean extraction force of 332 N was necessary for the uncoated blocks. Anchorage and resistance against uprooting of the blocks coated with Plasmapore were significantly more efficient. The histological study revealed the presence of bone neoformation adhering to the implant. Quantification of this bone formation covering nearly 45% of the implant perimeter, confirmed both osteointegration of the implant perimeter, confirmed both osteointegration of the implant surfaces being in contact with the vertebral endplates and osteoconduction along the lateral surfaces. CONCLUSION: The titanium Plasmapore block enables interbody fusion due to an osteointegration of the vertebral endplates by Plasmapore coating, which was proved by the results of extraction testing and histological study. It should be taken into account that no additional bone grafts have been used and that the implant had not been forced into the spongiosa.

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UNLABELLED: The hip revision surgery like oncology surgery may need massive allografts to rebuilt the acetabulum or an hemi pelvis. Since 1982 we have chosen to use deep frozen massive allografts instead of massive metallic prosthesis, resection, or osteosynthesis of the femur to the iliac bone or the sacrum. These last proposal seems for our patients too heavy, the functional results being always bad. PATIENTS AND METHODS: --37 Acetabulum reconstruction has been performed. (18 hemi-pelvis). --The follow-up is from 1 to 12 years with a medical of 5 years and 2 months. --The tumoral pathology (14 cases) was for 50% chondrosarcomas [7]. 6 infections (1 massive echinococcosis and 5 osteomyelitis) --17 hip reconstruction for revision surgery. We use deep frozen allografts cryopreserved with Dimethylsulfoxide 10%. No secondary irradiation. The allografts were used after securisation (after the 6th month after the procurement). Most for the time we used 2 platres, one posterior outside the pelvis, one anterior inside the pelvis. Screwed on the contralateral pubis bone and the sacrum. A hip prosthesis was used in almost all the cases. In tumoral cases, the results were excellent with chondrosarcomas but in the other cases metastasis and death were usually seen in the 2 or 3 years following the surgery. --3 instability of the prosthesis. --2 fractures of the allograft. In the non tumoral cases, the integration of the graft was excellent. --1 instability of the prosthesis needed a antiluxent crescent. --1 fracture of the graft needed adjonction of autografts and new osteosynthesis. --1 superficial infection. Good functional results has been obtained with the use of massive allografts. The fracture of the allografts can heal without a new operation. In some cases we have had some liquid surrounding the grafts which can be a immunological response.

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Currently cryopreservation offers the best means of preserving bone tissue for allografts. At -196 degrees C all enzyme activity is halted and tissue preservation is unlimited. Perfect sterilization, adapted cryoprotection and controlled freezing and thawing are now part of the well-controlled process of bone preservation in bone banks. At implantation, the mechanical properties of cryopreserved bone is as good as or better than fresh bone, although the diaphyseal cortical bone is more fragile. Anatomic and physiologic reconstruction of the graft area is a major factor in graft resistance. It takes approximately three weeks for vessels to penetrate cancellous allografts and at least one month for total revascularization. The delay may reach several years for cortical bone. The immune response of the host is determined by the antigenic properties of the leukocytes in the bone marrow as well as the blood vessels and nerves. The protein-mineral complex itself has little antigenic effect. A certain number of non-specific immune reactions result from transfusions almost always performed with bone grafting. At the present time, there is no artificial material capable of providing a mechanically acceptable substitute for allograft bone in limb reconstruction. Allograft bone currently stocked in bone banks provides a biologically and clinically acceptable means of reconstruction after major bone loss. Other factors such as public acceptance and administrative authorizations will also play an important role in the future of massive reconstruction with bone allografts.

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PURPOSE: The purpose of our study is to analyse the indications, results and limits of secondary internal fixation after external fixation for open fracture of the lower limb. MATERIAL: Our series covered 21 patients treated between 1991 and 1994. There were 17 men and 4 women. Tibia was affected 17 times and femur 5 times (one bifocal fracture). In Gustilo's classification, we had 1 case of type 1, 12 of type II and 8 of type III. METHODS: We used 15 times the FESSA External Fixator and 6 times a monotube external fixator in emergency. We have done secondary 11 intra medullary nailing and 11 patients were treated by plating (one patient had both) 13 patients had a bone graft (cortico-cancellous graft). In the first group of patients (10 cases), the initial treatment gave us good results for both skin and bone healing. The external fixation was replaced by an internal one in order to accelerate bone consolidation and to allow an early weight-bearing. Removal of the external fixation was made at an average of 4 months postoperative. In the Second group (11 cases) the internal fixation was proposed because of an insufficiency of the external fixation leading to complications as: non union, mal union and bone defects. External fixation was removed in a mean time of 8 months. Internal fixation was completed by local bone autograft. RESULTS: 17 patients have been reviewed. Consolidation occurred with an average of 6 months after internal fixation 1 to 24 months. We had no deep infection but only 2 superficial ones. DISCUSSION: We chose 2 types of indication, and we called them programmed and for necessity. The first group of 10 patients whose stain was moderate and whose initial setting up had permitted a perfect anatomic reduction with a rapid wound healing. Internal fixation was performed after a short duration of external fixator. An early weight bearing was allowed so that the functional recovery could be obtained quickly. The second group is represented by patients whose internal fixation was done for non union, malunion or bone defect. In such a case autogenous cancellous graft was used to fill the defect.

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In revision hip surgery, allografts are useful for restoring the bone stock and allow the muscle fixation avoiding the use of massive metallic prothesis. MATERIAL AND METHODS: We have reviewed 51 hip reconstructions with a follow up of 4 years and half (1982 - 1991). Indications were: - revision arthroplasties with destroyed acetabulum, - bone tumors (mainly chondrosarcoma). RESULTS: The results are good for pain, articular movement and the consolidation of the allograft host bone junction. Some complications were encountered: - Post-operative death (early or late for tumoral extension) in case of major surgery for tumor (4 cases). - Deep infections (2 cases). - Weakness of the gluteus medius with hip dislocation needing anti-dislocation device. - Aseptic serous fluid leak meaning immunobiologic reaction of bone grafts (3 cases). DISCUSSION: This surgery has to be compared to massive reconstruction prostheses, arthrodesis with limb shortening, femoral head and neck resection and in some cases inter ilio-abdominal amputation which gives also major post-operative complication.

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The use of deep frozen allografts is not a recent technic. The evolution of the conservative technics authorize a sufficient preservation of osseous and cartilaginous structure. The clinical results are considered as good in most of the cases. The intra medullary cells are most involved in immunological responses but clinically speaking only 10% to 20% of the case treated has a reject. The becoming of the grafted tissue is best if the recipient is young, the graft well fixed and the muscular surrounding well vascularized. 454 grafts and 64 massive osteochondral allografts have been archived between 1979 and 1993 for traumatic, tumoral, and surgical diseases. The results have been considered as good or excellent in 85% of the cases. The actual problems are the biomechanical behaviour of the ligamentary revascularization and fixation which gives in numerous cases a high percentage of loosening.

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There has been much progress in the cytogenesis, and molecular biology of bone tumours such as Ewing sarcoma and osteosarcomas, greatly improving diagnostic possibilities and prognosis. Ewing's sarcoma is an indifferentiated sarcoma with round cells which usually occurs in children or adolescents. Ewing's sarcoma corresponds to 6% of all bone tumours. Histologically Ewing's sarcoma belongs to a group of small round cell tumours including neuroblastoma, embryon and alveolar rhabdomyosarcoma and non-Hodgkin's lymphoma. Differential diagnosis is difficult. Cytogenetic examinations can now differentiate Ewing's sarcoma from other small round cell tumours. There is a specific 11:12 translocation (q24; q12) which can be used as a marker.

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PATIENTS AND METHODS: We have performed 34 massive bone-cartilage grafts with a follow-up of 2 to 7 years (1988-1993) including 5 complete joint grafts of the knee. Between 1988 and 1993, 8 massive diaphyso-metaphyseal bone grafts were performed. Joint reconstructions using massive bone-cartilage allografts are increasingly used in routine oncology surgery. Long-term rehabilitation and possibilities of immediate anatomic reconstruction of the articular surface, together with mid-term results suggest that the functional results are promising compared with major reconstruction prostheses. Indications for operations are being increasingly widened to younger subjects who have undergone partial or total joint exeresis for tumour. Sleeved prostheses were used for 12 reconstructions (1988-1993) for sarcoma of the knee. RESULTS The risk of sepsis are comparable for the different groups and are mainly related to the quality of the skin repair during chemotherapy. Fractures of the graft occur when the fixation is insufficient or when rehabilitation exercises were too aggressive. Non-consolidation was exceptional when the junction between the allograft and the receiver bone is not surrounded with autologous spongious autografts. Joint instability and arthrosis depend on the stability of the ligament reconstruction. To this day, no Charcot type joint disease has been demonstrated, periarticular innervation has maintained joint trophism. DISCUSSION: There are still some incompletely resolved problems concerning the revascularization of the graft, its integration into the skeleton, the outcome of the grafted cartilage and that of the ligament formations attached to the graft or used as allografts. These massive grafts must be studied over a longer period of time but the early results are encouraging. Sleeved grafts using bone-bank specimens could be an intermediary solution which appears to be indicated in cases where the tumoural resection was particularly large removing bone, cartilage, ligaments and muscles. With these sleeved prostheses, the muscles can be refixed onto the graft thus reducing the risk of shank fracture and loosening. The use of a tibial graft with the patellar tendon is helpful in reconstructing the extensor apparatus. However, if rehabilitation is not undertaken rapidly and followed regularly for several months, the graft favours the development of muscular adherances which can be a major limitation to joint mobility.

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Bone allografts are used in situations of repeated hip surgery to repair bone loss and allow muscle fixation without excessive use of massive metallic prostheses. We examined 51 cases of hip reconstruction after a mean follow-up of 3 and a half years. Indications were: reoperations on arthroplasties, usually after the weight carrying areas of the acetabulum had been destroyed; repeated operations on the upper extremity pellucid femurs; bone tumours (especially chondrosarcomas). Results have been good based on patient satisfaction, mobility and consolidation of the allograft-bone junction. Complications included: post-operative death after major surgery for invasive tumours (n = 4); sepsis (n = 2); hip luxation requiring an anti-luxation crescent (n = 3); and aseptic serous effusion suggestive of possible immunologic reactions against the bone grafts (n = 3). These operations were compared with massive reconstruction prostheses, with arthrodeses with limb shortening and with hanging limbs, and in certain cases with interilioabdominal amputations.

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The increase in the number of the studies of the stress around the anatomic prosthesis by the finite element method incited the authors' work. Our purpose was to study the methodology of a technic with simple cases. The finite element method is a method of calculation which allow the calculation of the displacement under the stresses of each element that we created in the structure. Before this calculation, we needed to define the exact geometry of the structure, the elementary properties of the material and the conditions of the experimentation, particularly the strains that exist in the structure. Three simple examples are given: an osteosynthesis plate with an hole, a knee model that Maquet studied with the photoelasticimetry method and a bidimensional knee model. The results are traduced by different colours or by coloured ligns. The conclusion is to warn the orthopaedic surgeons to look carefully what model is behind the pretty coloured results.

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