全髋关节置换前后股骨应力变化的有限元分析

目的:研究Chamley Elite骨水泥型和Summit近端多孔非骨水泥型股骨假体置换后股骨总体应力以及假体周围骨质区应力分布的变化。方法:根据Charnley Elite骨水泥柄和Summit非骨水泥柄假体形态建立三维有限元模型，并加载关节合力以及相关肌肉的肌力负荷，分析假体植入前后股骨总体应力模式并对股骨近端假体周围区域骨质应力分布进行分区量化研究。结果:两种假体植入后没有改变股骨总体的应力模式，应力峰值区域均位于全长股骨的中下段，但股骨应力峰值有所下降。股骨近端假体周围骨质等效应力水平出现了显著下降，下降最严重的区域为近段内侧象限即股骨距区，应力遮挡率分别达90．8％和95．3％；向假体远端应力水平逐渐增大，直至假体远段和末段水平应力值逐渐恢复并接近生理水平。就该两种不同固定方式的假体比较而言，引起的应力遮挡区域分布基本一致，应力下降程度Summit近端多孔非骨水泥型假体要高于Charnley Elite骨水泥型假体。结论:两种假体植入后均在股骨近端形成显著的应力遮挡，假体周围骨质应力大小和分布的改变是引起术后骨量丢失和假体松动的原因之一，也是术后股骨骨折发生的类型以术后肢体疼痛发生的力学基础。两种固定方式的假体均需通过进一步改进以减少应力遮挡。     

The effect of proximally and fully porous-coated canine hip stem design on bone modeling

Porous coated canine femoral hip replacement implants were evaluated for biological fixation by bone ingrowth and the effect of the extent of porous coating on bone modeling. The Co-Cr alloy implants were either fully porous coated or coated only on the proximal 40% of the stem. Two implants of each type were studied 9, 16, and 36 months after surgery. Implant fixation and bone modeling were assessed radiographically throughout the implant periods and histologically after the test animals were killed. All 12 implants appeared stably fixed within the femur and were bone-ingrown in the porous region. Radiographic features such as proximal medial and anterior cortical thinning, proximal cancellous bone hypertrophy, and new endosteal bone formation near the stem tip were noted within the first postoperative year, with no appreciable change thereafter. The extent of proximal cortical thinning varied from virtually none to as much as 40%, being more prominent with the proximally coated implants at 16 months and with the fully coated implants at 36 months. Of consistent note was cancellous hypertrophy at the junction of porous and smooth implant surfaces with proximally coated implants and new endosteal bone formation and ingrowth at the stem tip of fully coated implants. These results indicate that the proximally porous-coated implant design causes increased proximal stress transfer, but this does not necessarily preclude proximal cortical resorption.     

Influence of porous coating level on proximal femoral remodeling. A postmortem analysis

This study used femurs retrieved at autopsy to compare the extent and location of bone remodeling between four patients implanted with proximally porous coated femoral prostheses and a matched group of four patients implanted with extensively porous coated femoral prostheses. The femoral components studied were large, cementless, straight, cobalt chrome stems and were identical except for the amount of porous coating. The contralateral normal femur of each patient also was retrieved, implanted with an identical prosthesis, and used as a control for bone mineral content. Dual energy x-ray absorptiometric analysis showed marked loss of bone mineral content in both groups of patients. The extensively coated group had less bone loss on average (18.4%) than did the proximally coated group (38.6%). There was no relationship between the extent of coating and the location of bone mineral loss; specifically, proximal coating did not protect against loss of bone mineral content proximally or distally in the femur. Videodensitometric analysis of cross sections of periprosthetic bone also showed that the extensively coated group tended to have less decrease in bone density than did the proximally coated group (14.3% versus 28.4%). Although one cannot presume that all proximally fixed stem designs would produce results similar to those presented here, these findings show that decreasing the extent of porous coating alone does not necessarily reduce proximal femoral bone loss.     

Extensometry and primary anchorage of femur implants. Study of the upper metaphyseal intracortical support of the B.P.R cement-less implant

This study uses extensometry to compare the distribution of strain on a fresh femur before and after implantation of various titanium prostheses: one is a cementless implant with metaphyseal endosteal support; the second is a cemented prosthesis with and without calcar collar contact; the last is a titanium implant with fixation by screens. The precision of the measurements have been improved particularly in the proximal metaphyseal area using bidirectional gauges. The system of loading permits comparison of the different implants and the results obtained with the B.P.R. prosthesis compared with the cemented implant without calcar contact are very close. The effect of the collar appears very limited despite the optimal conditions of the in vivo implantation that improve the calcar-collar contact. The screw implant increases the stress shielding of the proximal area of the femur. The different steps of the experiment illustrate the strain distribution in relation to the implantation of the devices and the contact bone prosthesis. The significant endosteal fixation of the B.P.R. prosthesis in the proximal metaphyseal area allows a better primary anchorage which increases distribution of the stress and therefore results in better secondary fixation by bony ingrowth.     

髋表面置换股骨侧假体外翻位植入后股骨近端应力变化的有限元分析

目的 探讨髋表面置换股骨侧假体外翻位植入后股骨近端的应力变化,并寻求最佳外翻植入角度.方法 建立正常股骨近端髋表面置换股骨侧假体(Wright假体)三维模型,其中股骨假体按解剖颈干角(本文选用股骨模型的生理解剖颈干角为135°)、外翻5°、10°、15°植入,加载关节合力及相关肌肉的肌力负荷,分析假体植入前后股骨近端的应力分布变化,并对股骨近端假体周围区域骨质应力分布进行分区量化研究.结果 股骨假体轻度外翻植入降低了股骨头颈交界处上方(2、8区)的应力,5°外翻植入股骨头上方假体杯下缘(1、7区)应力遮挡最小,股骨颈下方(4、10区)应力分布更接近正常股骨.结论 外翻5°植入假体股骨近端应力更接近正常股骨,降低了股骨颈骨折和假体松动的危险.     

Stress analyses of joint arthroplasty in the proximal humerus

Finite element stress analyses were performed on the proximal humerus before and after the simulated implantation of stemmed, metallic prosthetic components with porous sintered surfaces for direct bony attachment. Design geometries with surfaces at the prosthetic head/bone interface that were (a) convex, (b) flat, and (c) concave were studied. Analyses for each of the three geometries were conducted to reflect (a) bone ingrowth on all the prosthesis/bone surfaces and (b) bone ingrowth only along the underside of the prosthetic humeral head (assuming the stem was not coated with a porous material). Three loading conditions were used to model various degrees of abduction of the arm. Results indicated that in the normal humerus the compressive joint forces are transmitted from the articular surface through cancellous bone to the inferior cortical shell. Contraction of the rotator cuff muscles created tensile stresses in the superolateral cancellous bone and the superior cortical shell of the humerus. Results of the implanted humeral component models indicated that the use of a prosthesis with bone ingrowth along the stem would cause marked stress shielding proximally whereas the use of implants with porous ingrowth only on the underside of the humeral head replacement produced stress fields more similar to the normal humerus. The convex, flat, and concave surfaces provided similar load transfer from the component to the underlying bone in all loading cases. Other prosthetic head designs that may offer better initial stability produced stress fields similar to those of existing prostheses.     

Quantification of implant micromotion, strain shielding, and bone resorption with porous-coated anatomic medullary locking femoral prostheses.

Fourteen femora containing porous-coated anatomic medullary locking (AML) femoral prostheses were retrieved from 12 patients at autopsy. Clinical roentgenograms in 13 femora showed bone remodeling changes, indicating that the implants were fixed by osseointegration. Under simulated physiologic loading, micromotion between the implant and the bone was measured using electrical displacement transducers connected to the implant and to the adjacent cortex. The micromotion between the implants at the areas of porous coating and the adjacent cortex in the one case of failed bone ingrowth measured 150 microns. Maximum relative motion between the cortex and the implant in the areas of porous coating for the 13 cases showing signs of bone ingrowth was 40 microns, and this was completely elastic relative displacement. With all implants, the micromotion between the cortex and the stem was always greatest over the uncoated portion of the stem. Four of the implants were proximally porous coated. With these, the micromotion was greater over the uncoated areas than with more extensively coated stems and was always greatest at the uncoated tip of the prosthesis. The amount of micromotion was directly related to the extent of porous coating on the implant. Maximum tip motion for the proximally coated implants was 210 micra, whereas for the fully porous-coated implants, it was 40 microns. In nine of the autopsies, the contralateral normal femur was obtained in addition to the femur containing the AML (the in vivo remodeled femur). These were used for comparative studies of strain shielding and femoral remodeling. Cortical strains were measured in the in vivo remodeled femora and were compared with measurements made in the contralateral normal femora before and following implantation of a stem identical to that present on the clinically treated side. The data showed major strain reductions in all the postmortem implanted normal femora. Comparison of the strain data from the postmortem implanted normal femora with those from the in vivo remodeled femora clearly indicated that extensive bone remodeling did not result in restoration of cortical strain levels anywhere near normal. Strain shielding continued to exist in all of the remodeled specimens, even up to 7.5 years after surgery. This strain shielding was associated with bone remodeling changes that resulted in regional reductions in bone mineral content that ranged from 7% to 78%. These observations are unique, important, and valuable in defining the in vivo function and clinical behavior of this type of porous-coated femoral component.     

Photoelastic stress analysis of human femurs before and after implantation of different models of femur neck prostheses

AIM: The aim of this study was the detection of areas at risk at the proximal femur after implantation of different femur neck prostheses using the photoelastic stress analysis. METHODS: Twelve pairs of human femurs were used as examination material. The analysis of the stress pattern was done with a stepwise increasing load up to the quadruple of body weight before and after implantation of three models of femur neck prostheses which were implanted cementless. The "CUT" and "Cigar" models are coated with a tripod structure. The "Cigar" model has a lateral thrust plate. The lateral end of the "CUT" model is curved and this end is attached to the lateral corticalis. The third model, the "rip prosthesis" has two layers for rotational stability. Subsequently, the micromotions of the implanted prosthesis in the femural neck were examined with alternating weight loads (1000 +/- 700 N). RESULTS: The Cigar prosthesis showed the most changes of stress distribution because of the lateral thrust plate with concentration of isochromatic lines to the lateral boring. In the region of the oseotomy an increase of strain up 1440 microm/m could be detected for the Cigar and up to 1000 microm/m for the rib prosthesis. The stress pattern after implantation of the CUT prosthesis remained very similar apart from a slight increase of stress values (720 microm/m). Only for the Cigar prostheses were the measured micromotions below the critical value for a possible osteointegration with a mean value of 134 microm/m. CONCLUSION: The stress pattern after implantation of the CUT prosthesis remained most similar to the preinterventional stress distribution. Because of this, it is to be expected that the osseous modification would stay at a low level. The question of osteointegration can only be answered in long-term in-vivo studies.     

Stress analysis of an anatomically-adapted femur shaft prosthesis (Lubinus SPII)]

OBJECTIVE: Very good clinical long-term results of the Lubinus SP II hip prosthesis stem were reported in the literature. We therefore asked whether there is a relationship between these findings with biomechanical data of strain gauge measurements. METHOD: 14 strain gauges were applied at a femur being measured at 10 different load cases before and after implantation of the stem. RESULTS: After stem implantation a similar patterns of principal stress distributions was observed, however, the magnitude was markedly reduced. A striking reduction of the hoop stresses at the femoral calcar was seen in the case of a missing collar contact. Even in the case of a perfect collar contact the hoop stresses were diminished after strem implantation. The S-shaped physiological stem did not correspond with a specific stress pattern measured at the femoral surface. CONCLUSION: These results suggest that the stresses at the femoral calcar may be lower than the limits of bone growth while the other parts of the femur are more physiologically stressed. However, the prosthesis may tolerate a missing collar contact during a long follow-up period. The large experimental data file presented here could be used to validate future finite element analyses which could evaluate the stress distribution within internal parts of the bone and the cement layer.     

Proximal strain distribution in the loaded femur. An in vitro comparison of the distributions in the intact femur and after insertion of different hip-replacement femoral components

The distribution of strain in the proximal part of loaded cadaver femora was measured in vitro using strain gauges applied to the cortex. The loading conditions simulated single-limb stance and the strains were recorded first with the femora intact and then with the femoral components of six different designs inserted. Each femur served as its own control. After insertion of a femoral component, the pattern of strain in the proximal part of the femur was reversed compared with that in the intact femur, in that the maximum strain occurred around the tip of the prosthesis rather than at the calcar femorale. A massive decrease in stress in the region of the calcar femorale was found when the implants were in place, and it was concluded that this decrease could contribute substantially to the calcar femorale resorption sometimes observed in patients after total hip replacement. Transfer of load directly to the calcar femorale through a larger collar in direct contact with the cortical bone restored 30 to 40 per cent of the normal strain to the calcar femorale and shifted the strain pattern toward normal. Compared with the less stiff stems tested, the larger, stiffer stems, which provide more protection against fatigue failure, did not affect the strain pattern adversely.     

Computerized templating in uncemented total hip arthroplasty to assess component fit and fill.

The aim of the uncemented femoral component in total hip arthroplasty is to achieve a stable bone-prosthesis interface without the use of polymethyl methacrylate (PMMA). Maximal fill of the femoral canal by the prosthesis promotes initial stability and long-term optimal stress transfer to the bone. The percentage "fit and fill" of the proximal femur by three prostheses, the porous coated anatomic, anatomic medullary locking, and the Harris-Galante, was compared by use of a computerized templating model to assess preoperative radiographs of 20 patients. Results showed that overall percentage fit and fill was similar and satisfactory (greater than 60%) in 17 of 20 patients. If a satisfactory fill was not achieved with one prosthesis, another prosthesis did not significantly improve fill. Lack of bony contact in the proximomedial femur was the most common deficiency noted.     

The effect of femoral stem geometry on interface motion in uncemented porous-coated total hip prostheses. Comparison of straight-stem and curved-stem designs.

We compared the magnitudes of motion between the prosthesis and bone during axial and torsional loading in seven matched pairs of fresh-frozen femora of cadavera in which an uncemented, collarless, isthmus-filling, straight-stem (Harris-Galante) prosthesis had been placed in one femur and an uncemented, collarless, proximal-filling, curved-stem (anatomic) prosthesis had been placed in the other femur. The comparison was performed in order to determine the effect of the geometry of the stem on the magnitude of motion. Single-limb-stance loads and combined axial and torsional loads were applied to the implanted femoral prostheses with the use of a jig that simulated acetabular and trochanteric loading. Extensometers were used to measure motion at the prosthesis-bone interface. The prostheses were then removed and were reinserted, with cement applied to the proximal porous coating to simulate ingrowth of bone. The single-limb-stance and combined axial and torsional loads were reapplied and the magnitude of motion was recorded again. No significant differences in the magnitudes of the motion were found between the femora in which the straight stem had been implanted and the femora in which the curved stem had been implanted, during either simulated single-limb-stance or low-intensity torsional loading. When large torsional moments (twenty-two newton-meters) were applied, significantly less motion occurred at the bone-prosthesis interface, both proximally (p = 0.019) and distally (p = 0.0013), in the femora with the curved-stem implant than in the femora with the straight-stem implant. When cement had been applied proximally, proximal and distal motion between the prosthesis and the femur was decreased during simulated single-limb-stance and during torsional loading in the femora with the straight stem and the femora with the curved stem.     

Bone stress. A hitherto neglected factor in hip endoprosthesis design

Growing interest in hip endoprostheses is giving rise to new ideas on form and materials, although it is not precisely known what forces the proximal femur is subject to. To find out more about these forces, we made computerized analyses of the stresses on some different types of prostheses in an artificial standardized femur. The E-module amounts to about 14,000 N/mm. Following measurements in tension-optic trials, we inserted Student gages (EA-13-060LZ-120) at 16 points around the proximal femur; these transmitted the pressure, tensile and torsion stresses to a multipoint measuring instrument (UPM 60) and on-line to a computer. The quality of implantation was monitored by X-ray. With loads varying from 0 to 1.5 kN in 250-N steps we made five readings to reproduce the measurements, without having any material failure. To ensure an absolutely reproducible outcome we used an artificial standardized femur (KNF by Mecron), which without prostheses shows the typical and well-known (Pauwels, Perren) pressure tensions medially and tensile stresses laterally, without crossing the zero line. A distinctly reduced stress profile was seen for pressure and tensile stresses with the ribbed system prosthesis, which might be due to the anchor and collar. Nevertheless, the torsion tensions should be noted. As expected, the shaft systems without anchor and collar show a lesser degree of stiffness. The Mecroblock MR system produces preponderantly pressure stresses, while the CLS (Spotorno) prosthesis sets up more torsion tensions in different directions.(ABSTRACT TRUNCATED AT 250 WORDS)     

A proximal fixed anatomic femoral stem reduces stress shielding

In 24 patients with total hip replacement using a short anatomic femoral stem, bone mineral density (BMD) was measured after a 7-year follow-up using dual-energy X-ray absorptiometry. The contralateral side was used as a control. The BMD on the side of the prosthesis was lower by a mean of 7% than that on the control side. The difference was greatest in the area of the calcar and laterally and proximally around the stem. BMD at the metaphyseal and diaphyseal areas were the same as on the contralateral side. The bone loss around the proximal aspect of the stem may be related to the proximal porous coating. It is concluded that stress shielding can be diminished by appropriate design of the femoral component.     

Clinical results and radiologic findings after cementless implantation of PCA stems in total hip replacement

Summary The results of radiologic and clinical follow-up of 81 PCA (porous coated anatomic) hip joint prostheses implanted in our clinic between 1986 and 1988 are presented. One of the prostheses had to be explanted because of aseptic loosening after 2.5 years' implantation. Contrary to the fixation concept of the prosthesis, which requires both proximal osseointegration and free axial shifting of the distal part of the prosthesis, our follow-up radiographs showed proximal lysis of 2 mm and more as well as distal hypersclerosis of 3 mm and more in the form of endosteal bone formation in 70% of cases 3 years after implantation. On the basis of our data, the question whether these bone reactions will finally lead to aseptic loosening of the implant cannot be answered yet.     

Effect of porous coating and loading conditions on total hip femoral stem stability

An examination of femoral bone—prosthesis interface behavior under different load types is undertaken using finite-element analysis. Three-dimensional finite-element models are made of two designs of hip prostheses after implantation in a femur. Femoral geometry was determined by computed tomography scans. The models were loaded in one-legged stance and stairclimbing configurations. The implants were modeled as both smooth surfaced and porous coated. The amount of contact and the relative motion between bone and implant were calculated. It is shown that torsional loads such as occur during stairclimbing contribute to larger amounts of implant micromotion than does stance loading. Contact at the bone—prosthesis interface is more dependent on load type than on implant geometry or surface coating type.     

Fixation of proximal humeral prostheses and rotational micromotion

Twenty pairs of cadaveric humeri were used to compare the rotational stability of proximal humeral prostheses fixed by proximal cementation with the stability offered by press fit or full cementation. For each proximally cemented specimen, only the upper portion of the prosthesis was coated with cement. For the fully cemented specimens, a cement restrictor was used just distal to the prosthesis, and a finger-packing technique was used to fill the proximal humeral medullary canal. Torque was applied to the Morse taper of the prostheses, and rotational micromotion was measured at the level of the osteotomy. In each of 11 pairs of cadaveric humeri, one side was press fit and the contralateral side was proximally cemented; in each of 9 pairs, proximal cementation was compared with full cementation. Proximally cemented prostheses' micromotion was significantly less than that of press-fit prostheses (P = .0016). There was no difference in micromotion between proximal cementation and full cementation (P = .82). Proximal cementation increased initial fixation over press fit. Full cementation did not increase rotational stability.     

Distally locked, fully hydroxyapatite coated modular long stems in salvage revision hip arthroplasty: a report of early experience

Introduction

Revision hip arthroplasty can sometimes be very challenging due to poor proximal bonestock following multiple revisions, bone resorption, infection or peri-prosthetic fracture. The challenge for the surgeon is to achieve fixation of the implant distally in healthy bone, yet allow bone in-growth proximally to encourage regeneration of the deficient femur. We present our early experiences with a fully hydroxyapatite coated modular long stems with distal screw locking (REEF, Depuy) in difficult revision scenarios.

Methods

A total of 21 patients with a mean age of 68 (range 37–86) were followed up for a mean period of 19 months (9–36 months). Revision was performed for aseptic loosening with severe proximal bone loss in 14 cases (67%), peri-prosthetic fractures in 6 cases (28%) and 1 case with infection (5%). Oxford hip score was determined for each patient. Radiographs were assessed for the formation of spot welds, cortical hypertrophy, radiolucent lines, subsidence of implants, calcar resorption and heterotopic ossification.

Results

One patient underwent re-revision due to initial undersizing of the stem. Radiological review of all the femoral components, including the one re-revision showed stable bony in-growth and no radiolucent lines in any zone. The incidence of spot weld formation and cortical hypertrophy was highest in zone 6. One patient had persistent thigh pain and subsidence of 2 cm occurred in one case (5%). There were no dislocations, infections or calcar resorption. Three patients developed Grade 1 and three patients developed Grade 2 heterotopic ossification.

Conclusion

Improvement in stem design, surface coating, distal locking and modularity allow independent fitting of the diaphysis and metaphysis, adjustment of length, offset and version to facilitate more biological reconstruction of proximal femur. Early results with this stem in salvage revisions appear promising.     

聚醚醚酮髋股骨头假体置换术后股骨近段的力学分析

[目的]探讨复合材料住全髋股骨头假体中的应用前景，旨在寻找能与股骨紧密结合、增加股骨近端应力传递的新型假体，期望进一步提高全髋关节置换术的远期疗效。[方法]5对人体新鲜尸体股骨平均分成左右2组，1组行钴铬钼合金（CoCrMo）股骨头假体置换术，另1组行碳纤维增强聚醚醚酮（CF／PEEK）假体置换术。在假体和近端股骨表面粘贴应变片，模拟单肢站立施加载荷。首先记录正常股骨产生的应变分布，然后行2种假体的股骨头置换术，再记录2组标本所产生的应变分布。[结果]股骨应变在假体植入后，从近端到远端逐渐增加，变化形式与完整股骨的应变形式相似，并且在假体远端最大。2种假体植入后，股骨内外侧表面的应变皆减少；但CF／PEEK假体组产生的应变形式和大小比CoCrMo合金假体组更接近正常股骨。[结论]CF／PEEK复合材料股骨头假体能提供术后即刻稳定性和良好的近端载荷传递，因此能进一步减少应力遮挡、骨吸收、骨萎缩，最终避免假体松动失败。     

Mechanical changes in the femur induced by a joint prosthesis. Comparative extensometric studies]

This study using electrical extensometry is aimed at comparing the relative deformations of the same fresh femur before and after the successive implantation of the following titanium prostheses: a cement-free prosthesis with metaphyseal endocortical support, a cemented prosthesis with, then without collar, and finally a screwed titanium prosthesis. The 56 deformation measurement paths produce an overall exploration of the behavior of the femur. The results applied to the same straight section of the femur are different from those of earlier works. The density of the measurement areas has particularly been increased in the upper metaphysis by the use of bidirectional gages. The loading device ensures the absence of variations of the external stress torsion transmitted to the femur between the individual prostheses. The results recorded with the cement-free prosthesis with metaphyseal endocortical support and with the collar-free cemented prosthesis are very similar. The incidence of the "collar effect" is very low in spite of optimal in vitro implantation conditions ensuring good contact between the collar and the neck of the femur. The screwed prosthesis is the implant that most stiffens the upper end of the femur. The testing procedure chosen has allowed recording the deformations caused by the mere insertion of the implants and the bone. The importance of the upper metaphysea endocortical support of the cement-free, screwless implant contributes in ensuring a better primary anchorage, producing stresses that will then foster the secondary anchorage through endosteal osteogenesis.