Fundamental engineering considerations indicate that micro-movement of the components of any hip arthroplasty is inevitable: stress cannot exist without strain and vice versa. Micromovement can be classified either as inducible recoverable movement that takes place between the weight-bearing and non-weight-bearing phases of each stride, or as non-recoverable displacement between successive loading cycles. Radiostereometric analysis is now sufficiently advanced to clarify migration and its significance, and is beginning to throw light on the extent and significance of recoverable cyclical micromovement. We discuss the value of radiostereometric analysis in identifying, early in their in-service life, implants that are likely to loosen

To measure any observed migration and rotation of humeral and ulnar components using radiostereometric analysis. From 2002–2004 in a prospective ongoing study, twelve elbows in patients treated with either a linked or unlinked Acclaim total elbow prosthesis were included in a radiostereometry study. Six tantalum markers were introduced into the humerus another three markers were located on a humeral component. Four markers were placed in to ulna and three markers located on the ulnar component. RSA radiographs were taken postoperatively, six, twelve and twenty-four months. The radiographs were digitised and analysed using UmRSA software. The relative movement of the humeral and ulnar implants with respect to the bone was measured. At twelve months, the largest segment translation of the humeral component was in the anterior/posterior direction with a mean of 0.44mm followed by medial/lateral translation of 0.39 mm; there was minimal proximal/ distal translation or with a mean of 0.16mm. Paired t-tests between twelve and 24 months segment translation data showed the mean differences to be no more than 0.056mm. The largest rotation at twelve months was anteversion/retroversion with a mean of 2.40deg, anterior tilt had a mean of 1.20deg and varus/valgus tilt was minimal mean 0.60deg. Mean difference between twelve and 24 months segment rotation was no more than 0.30deg. In contrast, humeral tip motion produced a mean of 1.1mm at 12 months dominated by movement in the plane horizontal plane with a mean difference at 24 months of 0.06mm. No patients could be measured for segment micromotion of the ulnar component due to technical difficulty in visualising tantalum markers in the ulna. Early micromotion of the Acclaim humeral implant occurs mostly by rotation about the vertical axis accompanied by anterior tilt. This motion reaches a plateau at 12 months after operation.

To measure any observed differences in migration and rotation between keeled and pegged glenoid components using roentgen stereo-photogrammetric analysis.

Between 2000–2001 in a prospective randomised study, 20 patients with osteoarthritis had a TSR with roentgen stereo-photogrammetric analysis. Five tantalum markers were introduced into the scapula and acromion, spaced widely apart. Another 4 markers were placed in either a pegged or keeled glenoid component.

RSA radiographs were taken postoperatively, three, six, twelve and eighteen months. The radiographs were digitised and analysed using dedicated software (UmRSA). The relative movement of the glenoid with respect to the scapula was measured.

The largest translation for the keeled components was in the proximal/distal direction with a mean of 1.3mm, the pegged group mean was 0.27mm. This difference was significant, P = 0.001. Both other translation axes showed no significant difference between the two component types. Medial/lateral migration gave means of 0.38mm(keel) and 0.52mm(peg) and the anterior/ posterior translation with means of 0.54mm(keel) and 0.41mm(peg). Maximal total point motion mean values at 18 months were 2.6mm for keeled and 1.1mm for pegged glenoid components. This difference was also significant P=0.001

The largest rotation was anterior/posterior tilt with means of 3.5°(keel) and 1.1°(peg) this difference was significant p=0.005; varus/valgus tilt with a mean of 3.2°(keel) compared to 20(peg) was again, significant P = 0.002. and finally anteversion/retroversion means were 3.3°(keel) and 2.7°(peg). Multivariate analysis identified 2 principal components from the keeled data each accounting for 35% of the variation in the data. The first included transverse and saggital translation together with rotation about the longitudinal axis; the second component consisted of translation on the longitudinal axis with rotation about the transverse axis.

Purpose: The causes of glenoid loosening are multifactorial (implant design, surgical technique, bone properties, soft tissue properties). This biomechanical study was conducted to evaluate the consequences of two clinical problems often encountered in shoulder arthroplasty: subscapular tension and glenoid retroversion. Material and methods: We developed a 3D model of the shoulder including the rotator cuff. A total prosthesis was implanted by digital modellisation. The humeral prosthesis imitated the adaptable third-generation implants, with a stem and a portion of a metal sphere, were used to achieve anatomic reconstruction of the proximal humerus. The polyethylene glenoid, cemented to bone, had a central stem and a flat base. Two subscapular tension (normal and twice normal) and two glenoid positions (0° and 20° retroversion) were tested. External rotation (0–40°) and internal rotation (0–60°) were simulated. We calculated displacement of the glenohumeral contact point, joint forces and contact pressures, interosseous glenoid stress, and micromovement of the bone-cement-implant interfaces. Results: Subscapular tension produced increased forces and joint pressures, associated with moderate posterior translation of the glenohumeral contact point. Retroversion induced more marked posterior displacement of the contact point, leading to significantly higher intraosseous glenoid stress and micromovements at the interfaces. The association of subscapular tension and glenoid retroversion produced important concentration of stress forces in the posterior part of the glenoid and increased all the micromovements. Discussion: Subscapular tension and retroversion of the glenoid implant have significant biomechanical effects which can favour glenoid loosening. Correction of these two parameters must be carefully controlled during shoulder arthroplasty

Purpose: We performed mechanical trials to quantify the contribution of locking to the stability of revision femoral implants. The implant tested was a revision prosthesis with anatomic metaphyseal contact locked with three distal bolts measuring 4.5 mm. Material and methods: Twelve implants were impacted into composite saw bones with constant and known dimensions and mechanical properties. Three displacement sensors were used to measure micromovements between the prosthesis and the bone: three specially designed force sensors were inserted into the bolt holes to measure the force distributions for each hole. Measurements were made with an Instron. Compression cycles (780 1-Hz cycles, 100daN applied to the femoral head) and torsion cycles (780 1-Hz cycles, 4.5 Nm applied to the femoral head) were used to simulate loading and weight-bearing and to estimate the evolution of the system. Trials were conducted in two different configurations: stable metaphyseal prosthesis, unstable metaphyseal prosthesis (simulating surgical resection). These two configurations were tested with a locked and with a non-locked implant. Results: Loading distribution between the bolts was variable and depended on the insertion conditions, implant/bolt tolerance, and the quality of the supporting bone. In the “stable” metaphyseal configuration, the bolts carried a large percentage of the compression force (up to 30%) despite the support provided by the metaphysis; when exposed to torsion stress, the metaphyseal form of the prosthesis carried the charge and avoided this phenomenon. Locking had only minimal effect on micromovements, the impaction and the form of the prosthesis maintaining its stability. For the “unstable” configuration, locking created a stable situation: micromovements were limited to those observed in the stable prosthesis (< 150 μm), compatible with bone regrowth. The bolts carried most of the charge (74.8 ±20%; 56.0±41.7%) during the compression and torsion tests. Loading created major stress within the bolts whose properties (strict diameter 4.5 mm, lateral threading) should be taken into consideration to avoid risk of rupture beyond the elastic limit of the material. Discussion: These results can be reasonably extrapolated to surgical situations leading to the following conclusions: locking is useful and reliable after surgical resection, all the holes available should be used for locking, “rational” unlocking can be useful if “physiological” metaphyseal stress is desired

Aims

This study aimed to demonstrate the promoting effect of elastic fixation on fracture, and further explore its mechanism at the gene and protein expression levels.

Aims

The main objective of this study is to analyze the penetration of bone cement in four different full cementation techniques of the tibial tray.

Purpose: Finite element analysis can be used to assess the behaviour of loaded structures. We used this method to evaluate the influence of glenoid implant design on the behaviour of an osteoarthritic scapula. Material and methods: A 76-year-old female patient scheduled for a shoulder prosthesis underwent preoperative computed tomography of the osteoarthritic shoulder. Two polyethylene implants were evaluated: one with a triangular stem and the same prosthesis with three studs. 3D reconstruction of the glenoid cavity with the implants was then obtained and processed with the finite elements method. Three loadings were applied to the model: centred loading to reproduce the case of an ideally stable prosthesis with a normal tendinomuscular environment and excentred loading to simulate a deficient rotator cuff or prosthesis instability. Results: With centred loading, stress remained low, to the order of 7 MPa, at the stem-glenoid cavity interface. Excentered loading produced peak stress on the borders of the glenoid implants, directly under the loading zone and at the tip of the stem, at the bone-cement interface, reaching 20 MPa. The implant tended to bend in the anteroposterior direction producing strong shear forces on the posterior part of the glenoid cavity. These forces caused micromovement at the cement-bone interface. There was no significant difference between the stem and stud implants. Discussion: Eccentric loading of the glenoid implant appears to have a negative effect on long-term survival, the stress reaching levels greater than the values of cement fatigue fracture. Peak stress was situated on the posterior border of the cement layer due to the small space available between the implant the cortical bone in the posterior part of the osteoarthritic scapula. In this situation, the tip of the stem or the studs tend to come into contact with the posterior cortical of the scapula. When inserting a total shoulder prosthesis, it appears to be more important to keep in mind the geometry and the mechanical properties of the scapula than the implant design

Aims: The holding power of new designed implants, need to be improved by osseointegration, in particular in osteoporotic bone. The osseo-integration depends on the interface mechanical conditions during fracture healing or fusion leading either to bony incorporation or to micro-movement and encapsulation. The aim of the current study was to evaluate the load sharing conditions after the fusion process between implant and bone with respect to the fusion status of the stabilized segment. Methods: The hollow cylinder based implant was used to stabilize a corpectomy of L4 in 17 sheep (9 osteoporotic and 8 control). After a survival time of 4 month the spine specimens were tested in a six-degree-of-freedom (6DOF) device in the three principal directions (flex/ex, lat. bending, torsion). Hysteresis curves were recorded before and after removal of the stabilizing longitudinal bar. The changes in ROM and stiffness in the different planes were compared statistically (α < 0.05). The results were validated histologically. Results: The increase in range of motion in all planes was significantly higher after implant removal in animals that were classified as non-fused spines (+35±15% in non-fused vs. +12±8% in fused spines). At the same time stiffness decreased significantly more (stiffness ex/flex −31±14% in non-fused vs −7±7% in fused spines) without differnces between normal and osteoporotic spines. Histology revealed 3 capsules in the fused spines. Conclusions: If fusion takes place in the presence of a relatively stiff implant the load flow through the implant is interrupted by connective tissue on one of the implant/bone interfaces. The changes in ROM and stiffness indicate the remaining contribution of the implant to the load sharing of the implant/ bone complex in case of non-fusion and are highly sensitive therefore to predict micromovement

Implant positioning is a critical factor in assuring the primary stability of cementless Total Hip Replacements (THRs). Although it is under the direct control of surgeons, finding the optimal implant position and achieving a perfect fit remain a challenge even with the advent of computer navigation. Placement of the femoral stem in an excessive ante/retroversion or varus/valgus orientation can be detrimental to the performance of THR. To determine the effect of such malalignment, finite element (FE) computer modelling is often used. However, this can be time consuming since FE meshes must be repeatedly generated and solved each time for a range of defined implant positions. In the present study, a mesh morphing technique is developed for the automatic generation of FE models of the implanted femur; in this way, many implant orientations can be investigated in a single analysis. An average femur geometry generated from a CT scan population of 13 male and 8 female patients aged between 43 and 84 years was considered. The femur was virtually implanted with the Furlong HAC titanium alloy stem (JRI Ltd, Sheffield, UK) and placed in the medullary canal in a baseline neutral nominal position. The head of the femur was then removed and both femur and implant volumes were joined together to form a single piece that was exported into ANSYS11 ICEM CFD (ANSYS Inc., 2008) for meshing. To adequately replicate implant ante/retroversion, varus/valgus or anterior/posterior orientations, the rigid body displacement of the implant was controlled by three rotations with respect to a local coordinate system. One hundred different implant positions were analysed and the quality of the morphed meshes analysed for consistency. To check the morphed meshes, corresponding models were generated individually by re-positioning the implant in the femur. Selected models were solved to predict the strain distribution in the bone and the boneimplant relative micromovements under joint and muscle loading. A good agreement was found for bone strains and implant micromotions between the morphed models and their individually run counterparts. In the postprocessing stage further metrics were analysed to corroborate the findings of the morphed and individually run models. These included: average and maximum strains in bone interface area and its entire volume, percentage of bone interface area and its volume strained up to and beyond 0.7%; implant average and maximum micromotions and finally percentages of implant area undergoing reported critical micromotions of 50 μm, 100 μm and 150 μm for bone in growth. Excellent correlation was observed in all cases. In conclusion, the proposed technique allowed an automatic generation of FE meshes of the implanted femur as the implant position varies; the required computational resources were considerably reduced and the biomechanical response was evaluated. This model forms a good basis for the development of a tool for multiple statistical analyses of the effects of implant orientation in pre-clinical studies

Purpose of Study: Current knowledge links the biological cascade of fracture healing to the fracture muscle envelope and to the preservation of stable, perpetual axial micromovements. The active biological compounds in the initiation of osteoneogenesis are cytokines. The current study correlates the latter by their molecular weight to their osteoneogenetic activity. Materials and Methods: Under GA and strict aseptic conditions, experimental fractures were produced in the mid-diaphysis of the left tibia in 60 adults Wistar rats. They were stabilized by an intramedullary no 20 needle. They were split into for equal groups:. Group A: Fractures were left to heal spontaneously. This was the control group. Groups B,C,D: Using meticulous dissection, a sterile nitrocellulose membrane was wrapped around the fracture between the periosteum and muscle envelope. The membranes pore sizes were: 3.5 kDa in group G; 12–14 kDa in group C; and 50 kDa in group D. The rats were euthanized at weeks 2, 5, 10 by an overdose of pentobarbital. Fracture healing was assessed by radiographies, histologic examinations and immunohistochemical localization of bone specific genes [IGF-1, IGF-1 receptor, cartilage proteoglycans, type II collagen, osteocalcin]. Results: In group A, callus formation was present at 2 weeks and progressed to full fracture healing by 5 weeks. In group B, no callus was detectable even at 10 weeks. In group C, most rats did not develop any callus, while a few started to develop calluses at 10 weeks. In group D, callus development was comparable to group A. A good correlation was found between the radiological and morphological results. Immunohistochemical localization of gene expression revealed a high level of PCNA [proliferating cellular nuclear antigen] with high local levels of IGF-1, and high levels of type II collagen as well as osteocalcin. In group B, this level of activity was very mild and did not reach bone healing level. In groups A and D, the results were comparable. They developed both medullary and periosteal callus, the former being persistently absent in groups B and C. Conclusions: Extensive direct contact between fractured bone and it’s muscle envelope is essential for the biological sequence of new bone formation, i.e. fracture healing. Preventing the diffusion of cytokines with a molecular weight higher than 14 kDa from muscle to fractured bone effectively interrupts the biological cascade of osteoneogenesis

We tested the hypothesis that it is possible to accelerate fracture healing by changing the mechanical environment used in current methods i.e., from initial rigidity or micromovement followed by dynamisation to initial macromovement followed by rigidity (micro-movement). It is accepted that callus formation requires movement at the fracture site and this callus response is limited to the first few weeks after fracture. Logically, early macromovement at the fracture site would be beneficial for callus formation. Additional callus is not produced by further movement. Indeed, it may be counter-productive, just as continuing movement around two ends of a wooden stick bonded with glue will retard and even prevent “union”. We postulate that continuing movement at the fracture site after the callus response has ceased will also delay union. As a result, rigidity rather than dynamisation is required in the later stage of fracture healing. After testing an animal model, we built an external fixator which allowed 5 mm of axial movement without “self-locking” and could be compressed at a later date in order to prevent further movement. A trial containing 15 patients with unilateral tibial shaft fractures (closed or grade 1 open) was undertaken after permission was obtained from the Helsinki Ethical Committee. So far, 13 patients have been entered into the trial. They have completed therapy and are at least one year post-fracture (12 months to 22 months). Age range is from 20 to 49. The group is composed of nine males and one female. Under general anaesthetic, an external fixator was applied and the fracture reduced. The patients started ankle exercises (active and passive) the following day, with as much weight-bearing on the fractured leg as possible on the day after. The patients were seen every two weeks and AP and lateral radiographs were taken. The fracture was compressed two to six weeks later. The percentage of body weight that the patient was able to tolerate through the fractured limb was measured by using the scales of Meggit’s step test. The fixators were removed when there was radiographic union and the patient could take at least 80% of body weight through the fractured limb. Mean time duration up to removal of the fixator was 10.8 weeks (range 7 to 15.4 weeks). We conclude that it is possible to increase the speed of bone healing by changing the mechanical environment to initial macromovement followed by elimination of movement

Aims

This study aims to enhance understanding of clinical and radiological consequences and involved mechanisms that led to corrosion of the Precice Stryde (Stryde) intramedullary lengthening nail in the post market surveillance era of the device. Between 2018 and 2021 more than 2,000 Stryde nails have been implanted worldwide. However, the outcome of treatment with the Stryde system is insufficiently reported.

The outcomes of any procedure in our clinical practice have to be looked upon in several ways:. a.The benefit the individual obtains from the procedure, in respect to the quality of life or well being. b.All these gains, if they are produced, must have a cost inferior to the ones that had occurred if the operation had not been done: (medical and social costs). c.The changes observed in pain, mobility and stability of the joint before and after the operation. d.The changes in the individual functional state: what the patient can do in his normal life activities (walk, stairs, fasten shoes, personal wash-up, etc) and any needed help for a normal daily living. e.Length of time the procedure will be holding the results, and the necessity of revision (survivorship), depending on the clinical state and the radiographic studies (migration, inclination, subsidence, lucent lines in the surfaces, etc). The aspects on well-being and cost-benefit after the total knee replacement have changed for better in a parallel way to the improvement on the function of the knee joint and the function of the body as a whole. We have recently studied the first two (a and b) outcome measures with positive results, that compare well to the published ones. In considering others aspects or measures of the outcomes, we agree with M. A. R. Freeman that the year 1980 could be the milestone for looking back and forth in the history of total knee replacement. Before 1980 the number of early failures was high, mainly due to sinkage and inclination of the tibial component, wear of the components, instability of the joint, and patelo-femoral pain. We did work on the design of a new method of fixation for the tibial plateau from 1980 to 1988, because of the many publications on bad results due to tibial loosening; our method of fixation was based in an intramedullary elastic, press-fit, stem, trying to avoid the fixation on the tibial surface, mainly because the trabecular bone was weak to stand the weight pressures, and because it was very difficult to cover all the surface of the tibia cut (the tibial not only differs in size but also in shape). Following the introduction of the ligament tensor by Freeman and the use of the “gaps” technique by Insall, in order obtain hte proper ligament tension and equal flexion and extension spaces and proper joint alignment, the short-term results published made us think that the tibial plateau problems were due more to bad surgical technique, that to other causes; we, therefore left aside our work. The functional results since then have shown little changes; we have not obtained more flexion or stability, and the patello femoral problems have not improved much. The different new designs have more to do with early wear of the polyethylene and consequent osteolysis and instability, than with function. The challenges of the future, in order to get better outcomes are:. To obtain better flexion. To obtain a better patelar tracking. To reduce the lucent lines around the prosthetic components. 1 and 2 should be addressed with a better geometry of the components. Practically every design and every technique change the geometric arrangement, specially, of the distal femur. We change the troncoconical (medial bigger than lateral) shape of the condyles into a cylindrical one; we change the oblique hinge into a normal one; we do not allow space for the lateral condyle to run backwards and forwards on the lateral tibial plateau in flexion and extension. This last problem is made even worse by the tension of the lateral ligament in flexion of the knee. If we had all this into consideration we could get more flexion and better patellar tracking. Actually, we are working on this subject. The issue 3 on the radiolucent lines: the coating of Hydroxiapatite might finally give a better fixation than cement. Hydroxiapatite resists the micromovements better and its interface membrane dissapears in favour of bone

Bone is one of the most highly adaptive tissues in the body, possessing the capability to alter its morphology and function in response to stimuli in its surrounding environment. The ability of bone to sense and convert external mechanical stimuli into a biochemical response, which ultimately alters the phenotype and function of the cell, is described as mechanotransduction. This review aims to describe the fundamental physiology and biomechanisms that occur to induce osteogenic adaptation of a cell following application of a physical stimulus. Considerable developments have been made in recent years in our understanding of how cells orchestrate this complex interplay of processes, and have become the focus of research in osteogenesis. We will discuss current areas of preclinical and clinical research exploring the harnessing of mechanotransductive properties of cells and applying them therapeutically, both in the context of fracture healing and de novo bone formation in situations such as nonunion.

Cite this article: Bone Joint Res 2019;9(1):1–14.

Aims

Loosening is a well-known complication in the fixation of fractures using devices such as locking plates or unilateral fixators. It is believed that high strains in the bone at the bone-screw interface can initiate loosening, which can result in infection, and further loosening. Here, we present a new theory of loosening of implants. The time-dependent response of bone subjected to loads results in interfacial deformations in the bone which accumulate with cyclical loading and thus accentuates loosening.

Objectives

In order to address acetabular defects, porous metal revision acetabular components and augments have been developed, which require fixation to each other. The fixation technique that results in the smallest relative movement between the components, as well as its influence on the primary stability with the host bone, have not previously been determined.

Objectives

Studies reporting specifically on squeaking in total hip arthroplasty have focused on cementless, and not on hybrid, fixation. We hypothesised that the cement mantle of the femur might have a damping effect on the sound transmitted through the metal stem. The objective of this study was to test the effect of cement on sound propagation along different stem designs and under different fixation conditions.

Objectives

A successful outcome following treatment of nonunion requires the correct identification of all of the underlying cause(s) and addressing them appropriately. The aim of this study was to assess the distribution and frequency of causative factors in a consecutive cohort of nonunion patients in order to optimise the management strategy for individual patients presenting with nonunion.

Objectives

This study aimed to characterise and qualitatively grade the severity of the corrosion particles released into the hip joint following taper corrosion.