Background: Joint replacements are being performed on ever younger patients at a time when average expectancy of life is continuing to rise. Any reduction in the strength and mass of periprosthetic bone could threaten the longevity of implant by predisposing to loosening and migration of prosthesis, periprosthetic fracture and problems in revision arthroplasty. Aims & Objectives: This study aims to analyse and compare prospectively the femoral periprosthetic stress-shielding around 4/5th and 1/3rd porous coated cementless femoral stems in patients undergoing unilateral cementless total hip replacement done using DEXA scan by quantifying the changes in bone mineral density around femoral component. Material & Method: Femoral periprosthetic bone mineral density was measured in the seven Gruen Zones with DEXA scan at 2 weeks, 1 years and 2 years after surgery in 60 patients who had undergone unilateral cementless total hip replacement, of which 30 patients had been implanted with 4/5th porous coated stems and other 30 patients with 1/3rd porous coated stems. Results: At both one and two years postoperatively, bone loss due to stress-shielding was seen in both stems with maximum loss in zone VII and minimum in zone III, IV, V. The maximum mean percentage bone mineral density loss in 4/5th porous coated stems in zone VII was 16.03% at one year and 22.42% at 2 years as compared to loss of 10.07% and 16.01% in 1/3rd porous coated stems. Increased bone loss was seen in patients who had larger diameter stem (> 13.0 mm) and in patients with low bone mineral density in the unoperated hip. Conclusion: Bone loss as a result of stress-shielding is more pronounced in 4/5th porous coated stems as compared to 1/3rd porous coated stems

Background: Joint replacements are being performed on ever younger patients at a time when average expectancy of life is continuing to rise. Any reduction in the strength and mass of periprosthetic bone could threaten the longevity of implant by predisposing to loosening and migration of prosthesis, periprosthetic fracture and problems in revision arthroplasty. Aims & Objectives: This study aims to analyse the femoral periprosthetic stress-shielding following unilateral cementless total hip replacement using DEXA scan by quantifying the changes in bone mineral density around femoral component over a period of one year and identify the factors influencing the bone loss. Material & Method: Femoral periprosthetic bone mineral density was measured in the seven Gruen Zones with DEXA scan at 2 weeks, 3 months and 1 year after surgery in 20 patients who had undergone unilateral cementless total hip replacement, of which 10 patients had been implanted with 4/5. th. porous coated CoCr stems and other 10 patients with 1/3. rd. porous coated titanium alloy stems. Results: At both 3 months and one year postoperatively, bone loss due to stress-shielding was seen in both stems with maximum loss in zone VII and minimum in zone III, IV, V. The maximum mean percentage bone mineral density loss in 4/5. th. porous coated CoCr stems in zone VII was 16.03% at 3 month and 22.42% at 1 year as compared to loss of 10.07% and 16.01% in 1/3. rd. porous coated Ti alloy stems. Increased bone loss was seen in patients who had larger diameter stem (> 13.0 mm) and in patients with low bone mineral density in the unoperated hip. Conclusion: Bone loss as a result of stress-shielding is more pronounced in 4/5. th. porous coated CoCr stems as compared to 1/3. rd. porous coated titanium alloy stems

Background: Joint replacements are being performed on ever younger patients at a time when average expectancy of life is continuing to rise. Any reduction in the strength and mass of periprosthetic bone could threaten the longevity of implant by predisposing to loosening and migration of prosthesis, periprosthetic fracture and problems in revision arthroplasty. Aims & Objectives: This study aims to analyse and compare prospectively the femoral periprosthetic stress-shielding around 4/5th and 1/3rd porous coated cementless femoral stems in patients undergoing unilateral cementless total hip replacement done using DEXA scan by quantifying the changes in bone mineral density around femoral component. Material & Method: Femoral periprosthetic bone mineral density was measured in the seven Gruen Zones with DEXA scan at 2 weeks, 1 years and 2 years after surgery in 60 patients who had undergone unilateral cementless total hip replacement, of which 30 patients had been implanted with 4/5th porous coated stems and other 30 patients with 1/3rd porous coated stems. Results: At both one and two years postoperatively, bone loss due to stress-shielding was seen in both stems with maximum loss in zone VII and minimum in zone III, IV, V. The maximum mean percentage bone mineral density loss in 4/5th porous coated stems in zone VII was 16.03% at one year and 22.42% at 2 years as compared to loss of 10.07% and 16.01% in 1/3rd porous coated stems. Increased bone loss was seen in patients who had larger diameter stem (> 13.0 mm) and in patients with low bone mineral density in the unoperated hip. Conclusion: Bone loss as a result of stress-shielding is more pronounced in 4/5. th. porous coated stems as compared to 1/3. rd. porous coated stems

Background: Joint replacements are being performed on ever younger patients at a time when average expectancy of life is continuing to rise. Any reduction in the strength and mass of periprosthetic bone could threaten the longevity of implant by predisposing to loosening and migration of prosthesis, periprosthetic fracture and problems in revision arthroplasty. Aims and Objectives: This study aims to analyse and compare prospectively the femoral periprosthetic stress-shielding around 4/5th and 1/3rd porous coated cementless femoral stems in patients undergoing unilateral cementless total hip replacement done using DEXA scan by quantifying the changes in bone mineral density around femoral component. Material and Method: Femoral periprosthetic bone mineral density was measured in the seven Gruen Zones with DEXA scan at 2 weeks, 1 years and 2 years after surgery in 60 patients who had undergone unilateral cementless total hip replacement, of which 30 patients had been implanted with 4/5th porous coated stems and other 30 patients with 1/3rd porous coated stems. Results: At both one and two years postoperatively, bone loss due to stress-shielding was seen in both stems with maximum loss in zone VII and minimum in zone III, IV, V. The maximum mean percentage bone mineral density loss in 4/5th porous coated stems in zone VII was 16.03% at one year and 22.42% at 2 years as compared to loss of 10.07% and 16.01% in 1/3rd porous coated stems. Increased bone loss was seen in patients who had larger diameter stem (> 13.0 mm) and in patients with low bone mineral density in the unoperated hip. Conclusion: Bone loss as a result of stress-shielding is more pronounced in 4/5th porous coated stems as compared to 1/3rd porous coated stems

Background: Joint replacements are being performed on ever younger patients at a time when average expectancy of life is continuing to rise. Any reduction in the strength and mass of periprosthetic bone could threaten the longevity of implant by predisposing to loosening and migration of prosthesis, periprosthetic fracture and problems in revision arthroplasty. Aims & Objectives: This study aims to analyse the femoral periprosthetic stress-shielding following unilateral cementless total hip replacement using DEXA scan by quantifying the changes in bone mineral density around femoral component. Materials and Methods: Femoral periprosthetic bone mineral density was measured in the seven Gruen Zones with DEXA scan at 2 weeks, 1 year and 2 year after surgery in 60 patients who had undergone unilateral cementless total hip replacement, of which 30 patients had been implanted with 4/5th porous coated CoCr stems and other 30 patients with 1/3rd porous coated titanium alloy stems. Results: At both one and two years postoperatively, bone loss due to stress-shielding was seen in both stems with maximum loss in zone VII and minimum in zone III, IV, V. The maximum mean percentage bone mineral density loss in 4/5th porous coated CoCr stems in zone VII was 16.03% at one year and 22.42% at 2 years as compared to loss of 10.07% and 16.01% in 1/3rd porous coated Ti alloy stems. Increased bone loss was seen in patients who had larger diameter stem (> 13.0 mm) and in patients with low bone mineral density in the unoperated hip. Conclusion: Bone loss as a result of stress-shielding is more pronounced in 4/5th porous coated CoCr stems as compared to 1/3rd porous coated titanium alloy stems

Introduction. Osteloysis following metal-on-UHMW polyethylene Total Hip Arthroplasty (THA) is well reported, as is lack of osteolysis following Ceramic-on-Ceramic (CoC)THA. Early ceramic failures did report some osteolysis, but in flawed implants. As 3rd and now 4th generation ceramic THAs come into mid- and long-term use, the orthopaedic community has begun to see reports of high survival rates and very low incidence of osteolysis in these bearings. Osteolysis reported after 3rd generation CoC THA often included metallosis due to neck rim impingement. In our department we have revised only 2 hips in over 6000 CoC THAs for osteolysis. Both had evidence of metallosis as well as ceramic wear. The technique used by Radiologists for identifying the nature of lesions on CT is the Hounsfield score which will identify the density of the tissue within the lucent area. It is common for radiologist to have no access to previous imaging, especially pre-operative imaging if a long time has elapsed. With such a low incidence of osteolysis in this patient group, what, then, should a surgeon do on receiving a CT report on a ceramic-on-ceramic THA which states there is osteolysis? Revision of such implants in elderly patients has a high risk of morbidity and mortality. Objectives. This retrospective review aims to determine the accuracy of CT in identifying true osteolysis in a cohort of long-term third generation ceramic-on-ceramic uncemented hip arthroplasties in our department. Methods. Pelvic CT scans were performed on the first 27 patients from a cohort of 301 patients undergoing 15 year review with 3rd generation alumina-alumina cementless THAs. The average follow-up was 15 years (15–17). The CT scans were reviewed against pre-operative and post-operative radiographs and reviewed by a second musculoskeletal specialist radiologist. Results. Eleven of the CTscans were reported to show acetabular osteolysis, two reported osteolysis or possible pre-existing cyst and one reported a definitive pre-existing cyst. After review of previous imaging including pre-operative radiographs, eleven of the thirteen patients initially reported to have osteolysis were found to have pre-existing cysts or geodes in the same size and position as the reported osteolysis, and a further patient had spot-welds with stress-shielding. One patient with evidence of true osteolysis awaits aspiration or biopsy to determine if he has evidence of ceramic wear or metallosis. Conclusions. Reports of osteolysis on CT should be interpreted with care in modern ceramic-on-ceramic THA to prevent unnecessary revision. Further imaging and investigations may be necessary to exclude other conditions such as geodes, or stress shielding which are frequently confused with osteolysis on CT scans

Aim: Stress-shielding is a common problem after uncemented THA that may lead to proximal femoral atrophy and consecutive aseptic loosening. Methods: In 143 patients with 154 uncemented CLS-stems periprosthetic bone mineral density (BMD) was measured using DXA after a mean of 12 years (10–15) postoperatively (T1). Five years later the same group of patients was examined at a mean of 17 years (range: 15–20) (T2) using the identical protocol. Results: We obtained a complete prospective set of data of two consecutive DXA measurements in 76 cases (32 men, 44 women). In all cases regular bone ongrowth did occur and there were no signs of radiographic loosening (T1 and T2). On radiographic evaluation there was no significant change in periprosthetic bone formation in all Gruen zones between T1 and T2. There was no significant change in activity and BMD. In male patients we found no significant changes in periprosthetic BMD (netavg T1–T2: −1,19%, p< 0,01), in female patients there was no significant difference either (netavg T1–T2: −1,32%,p< 0,01). We analyzed the differences in BMD in all Gruen zones (zone 1–7) comparing T1 and T2 and found no significant differences in any zone (p< 0,01). Conclusion: This study showed that there is no significant change in periprosthetic bone mineral density in the long term using the uncemented CLS stem. There was not a single case of stress shielding in the long term. Once osseous integration has occurred the periprostethic BMD changes remain minimal in the long term

Introduction and Aims: Little is known about peri-acetabular bone remodelling after insertion of the acetabular cup in total hip arthroplasty. This study was designed to analyse retroacetabular bone changes using quantitative CT-assisted osteodensitometry. This is a new method for a detailed measurement of bone density (BD) changes around the implants.

Method: Prospective cohort study. Operations were performed on 26 consecutive hips (26 patients) using an uncemented prosthesis with alumina-alumina pairing (Cerafit, Ceraver Osteal, France). The average age of patients was 58.4 years. There were 15 men and 11 women. CT investigations were performed within two weeks of surgery and then one year and three years post-operatively. Cancellous, cortical and total bone density (mgCaHA/ml) were assessed using specific software (Impact-Hip, VAMP, Moehrendorf, Germany).

Results: All 26 hips were available for follow-up at one year, seven patients were available at three years. At three-year follow-up we found an 18.4% decrease of cancellous BD proximal to the upper rim of the cup. Cortical BD increased by + 5.2% in this region. Cortical BD decreased ventral to the cup by −5.0% and by −2.3% dorsal to the cup. Of more interest, cancellous BD was observed to decrease by −40.9% in the ventral region and −32.2% in the dorsal region.

Conclusion: We have observed a progressive decrease of cancellous BD after insertion of an uncemented ace-tabular component. These phenomenon could explain the onset of late migration and implant failure of pressfit cups. Only minor changes have been observed in cortical BD. Further investigations are required to define the role of implant design and material in periprosthetic bone remodelling of the acetabulum.

Aims. This study aimed to identify the effect of anatomical tibial component (ATC) design on load distribution in the periprosthetic tibial bone of Koreans using finite element analysis (FEA). Methods. 3D finite element models of 30 tibiae in Korean women were created. A symmetric tibial component (STC, NexGen LPS-Flex) and an ATC (Persona) were used in surgical simulation. We compared the FEA measurements (von Mises stress and principal strains) around the stem tip and in the medial half of the proximal tibial bone, as well as the distance from the distal stem tip to the shortest anteromedial cortical bone. Correlations between this distance and FEA measurements were then analyzed. Results. The distance from the distal stem tip to the shortest cortical bone showed no statistically significant difference between implants. However, the peak von Mises stress around the distal stem tip was higher with STC than with ATC. In the medial half of the proximal tibial bone: 1) the mean von Mises stress, maximum principal strain, and minimum principal strain were higher with ATC; 2) ATC showed a positive correlation between the distance and mean von Mises stress; 3) ATC showed a negative correlation between the distance and mean minimum principal strain; and 4) STC showed no correlation between the distance and mean measurements. Conclusion. Implant design affects the load distribution on the periprosthetic tibial bone, and ATC can be more advantageous in preventing stress-shielding than STC. However, under certain circumstances with short distances, the advantage of ATC may be offset. Cite this article: Bone Joint Res 2022;11(5):252–259

According to the latest report from the German Arthroplasty Registry, aseptic loosening is the primary cause of implant failure following primary hip arthroplasty. Osteolysis of the proximal femur due to the stress-shielding of the bone by the implant causes loss of fixation of the proximal femoral stem, while the distal stem remains fixed. Removing a fixed stem is a challenging process. Current removal methods rely on manual tools such as chisels, burrs, osteotomes, drills and mills, which pose the risk of bone fracture and cortical perforation. Others such as ultrasound and laser, generate temperatures that could cause thermal injury to the surrounding tissues and bone. It is crucial to develop techniques that preserve the host bone, as its quality after implant removal affects the outcome of a revision surgery. A gentler removal method based on the transcutaneous heating of the implant by induction is proposed. By reaching the glass transition temperature (T. G. ) of the periprosthetic cement, the cement is expected to soften, enabling the implant to be gently pulled out. The in-vivo environment comprises body fluids and elevated temperatures, which deteriorate the inherent mechanical properties of bone cement, including its T. G. We aimed to investigate the effect of fluid absorption on the T. G. (ASTM E2716-09) and Vicat softening temperature (VST) (ISO 306) of Palacos R cement (Heraeus Medical GmbH) when dry and after storage in Ringer's solution for up to 8 weeks. Samples stored in Ringer's solution exhibited lower T. G. and VST than those stored in air. After 8 weeks, the T. G. decreased from 95.2°C to 81.5°C in the Ringer's group, while the VST decreased from 104.4°C to 91.9°C. These findings will be useful in the ultimate goal of this project which is to design an induction-based system for implant removal. Acknowledgements: Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – SFB/TRR-298-SIIRI – Project-ID 426335750

Revision surgeries for orthopaedic infections are done in two stages – one surgery to implant an antibiotic spacer to clear the infection and another to install a permanent implant. A permanent porous implant, that can be loaded with antibiotics and allow for single-stage revision surgery, will benefit patients and save healthcare resources. Gyroid structures can be constructed with high porosity, without stress concentrations that can develop in other period porous structures [1] [2]. The purpose of this research is to compare the resulting bone and prosthesis stress distributions when porous versus solid stems are implanted into three proximal humeri with varying bone densities, using finite element models (FEM). Porous humeral stems were constructed in a gyroid structure at porosities of 60%, 70%, and 80% using computer-aided design (CAD) software. These CAD models were analyzed using FEM (Abaqus) to look at the stress distributions within the proximal humerus and the stem components with loads and boundary conditions representing the arm actively maintained at 120˚ of flexion. The stem was assumed to be made of titanium (Ti6Al4V). Three different bone densities were investigated, representing a healthy, an osteopenic, and an osteoporotic humerus, with an average bone shape created using a statistical shape and density model (SSDM) based on 75 cadaveric shoulders (57 males and 18 females, 73 12 years) [3]. The Young's moduli (E) of the cortical and trabecular bones were defined on an element-by-element basis, with a minimum allowable E of 15 MPa. The Von Mises stress distributions in the bone and the stems were compared between different stem scenarios for each bone density model. A preliminary analysis shows an increase in stress values at the proximal-lateral region of the humerus when using the porous stems compared to the solid stem, which becomes more prominent as bone density decreases. With the exception of a few mesh dependent singularities, all three porous stems show stress distributions below the fatigue strength of Ti-6Al-4V (410 MPa) for this loading scenario when employed in the osteopenic and osteoporotic humeri [4]. The 80% porosity stem had a single strut exceeding the fatigue strength when employed in the healthy bone. The results of this study indicate that the more compliant nature of the porous stem geometries may allow for better load transmission through the proximal humeral bone, better matching the stress distributions of the intact bone and possibly mitigating stress-shielding effects. Importantly, this study also indicates that these porous stems have adequate strength for long-term use, as none were predicted to have catastrophic failure under the physiologically-relevant loads. Although these results are limited to a single boney geometry, it is based on the average shape of 75 shoulders and different bone densities are considered. Future work could leverage the shape model for probabilistic models that could explore the effect of stem porosity across a broader population. The development of these models are instrumental in determining if these structures are a viable solution to combatting orthopaedic implant infections

Shoulder arthroplasty is effective at restoring function and relieving pain in patients suffering from glenohumeral arthritis; however, cortex thinning has been significantly associated with larger press-fit stems (fill ratio = 0.57 vs 0.48; P = 0.013)1. Additionally, excessively stiff implant-bone constructs are considered undesirable, as high initial stiffness of rigid fracture fixation implants has been related to premature loosening and an ultimate failure of the implant-bone interface2. Consequently, one objective which has driven the evolution of humeral stem design has been the reduction of stress-shielding induced bone resorption; this in-part has led to the introduction of short stems, which rely on metaphyseal fixation. However, the selection of short stem diametral (i.e., thickness) sizing remains subjective, and its impact on the resulting stem-bone construct stiffness has yet to be quantified. Eight paired cadaveric humeri (age = 75±15 years) were reconstructed with surgeon selected ‘standard’ sized and 2mm ‘oversized’ short-stemmed implants. Standard stem sizing was based on a haptic assessment of stem and broach stability per typical surgical practice. Anteroposterior radiographs were taken, and the metaphyseal and diaphyseal fill ratios were quantified. Each humerus was then potted in polymethyl methacrylate bone cement and subjected to 2000 cycles of compressive loading representing 90º forward flexion to simulate postoperative seating. Following this, a custom 3D printed metal implant adapter was affixed to the stem, which allowed for compressive loading in-line with the stem axis (Fig.1). Each stem was then forced to subside by 5mm at a rate of 1mm/min, from which the compressive stiffness of the stem-bone construct was assessed. The bone-implant construct stiffness was quantified as the slope of the linear portion of the resulting force-displacement curves. The metaphyseal and diaphyseal fill ratios were 0.50±0.10 and 0.45±0.07 for the standard sized stems and 0.50±0.06 and 0.52±0.06 for the oversized stems, respectively. Neither was found to correlate significantly with the stem-bone construct stiffness measure (metaphysis: P = 0.259, diaphysis: P = 0.529); however, the diaphyseal fill ratio was significantly different between standard and oversized stems (P < 0.001, Power = 1.0). Increasing the stem size by 2mm had a significant impact on the stiffness of the stem-bone construct (P = 0.003, Power = 0.971; Fig.2). Stem oversizing yielded a construct stiffness of −741±243N/mm; more than double that of the standard stems, which was −334±120N/mm. The fill ratios reported in the present investigation match well with those of a finite element assessment of oversizing short humeral stems3. This work complements that investigation's conclusion, that small reductions in diaphyseal fill ratio may reduce the likelihood of stress shielding, by also demonstrating that oversizing stems by 2mm dramatically increases the stiffness of the resulting implant-bone construct, as stiffer implants have been associated with decreased bone stimulus4 and premature loosening2. The present findings suggest that even a small, 2mm, variation in the thickness of short stem humeral components can have a marked influence on the resulting stiffness of the implant-bone construct. This highlights the need for more objective intraoperative methods for selecting stem size to provide guidelines for appropriate diametral sizing. For any figures or tables, please contact the authors directly

Introduction. In total hip arthroplasty, press-fit anchorage is one of the most common fixation methods for acetabular cups and mostly ensures sufficient primary stability. Nevertheless, implants may fail due to aseptic loosening over time, especially when the surrounding bone is affected by stress-shielding. The use of acetabular cups made of isoelastic materials might help to avoid stress-shielding and osteolysis. The aim of the present numerical study was to determine whether a modular acetabular cup with a shell made of polyetheretherketone (PEEK) may be an alternative to conventional titanium shells (Ti6Al4V). For this purpose, a 3D finite element analysis was performed, in which the implantation of modular acetabular cups into an artificial bone stock using shells made of either PEEK or Ti6Al4V, was simulated with respect to stresses and deformations within the implants. Methods. The implantation of a modular cup, consisting of a shell made of PEEK or Ti6Al4V and an insert made of either ceramic or polyethylene (PE), into a bone cavity made of polyurethane foam (20 pcf), was analysed by 3D finite element simulation. A two-point clamping cavity was chosen to represent a worst-case situation in terms of shell deformation. Five materials were considered; with Ti6Al4V and ceramic being defined as linear elastic and PE and PEEK as plastic materials. The artificial bone stock was simulated as a crushable foam. Contacts were generated between the cavity and shell (μ = 0.5) and between the shell and insert (μ = 0.16). In total, the FE models consisted of 45,282 linear hexahedron elements and the implantation process was simulated in four steps: 1. Displacement driven insertion of the cup; 2. Relief of the cup; 3. Displacement driven placement of the insert; 4. Load driven insertion of the insert (maximum push-in force of 500 N). The FE model was evaluated with respect to the radial deformations of the shell and insert as well as the principal stresses in case of the ceramic inserts. The model was experimentally validated via comparison of nominal strains of the titanium shells. Results. The maximum radial deformation of the shell made of PEEK was 581 μm (insertion) and 470 μm (relief) and therefore multiple times higher compared to the Ti6Al4V shell (42 μm and 21 μm). As a result, larger deformations occurred at the PE and ceramic inserts in combination with the PEEK shell. Partially, the deformations were above an usual clearance of 100 μm. When the ceramic insert was combined with the shell made of PEEK, maximum principal stresses in the ceramic insert amounted to 30 MPa and were clearly lower than approved bending strength of the ceramic material (948 MPa). Conclusion. The examined acetabular shell made of PEEK was intensively deformed during insertion compared to the geometrically identical Ti6Al4V shell and is therefore not suitable for modular acetabular cups. In future studies it should be clarified to what extent acetabular cups with shells made of carbon fiber reinforced PEEK materials with higher stiffness lead to reduced deformations during the insertion procedure

The skeletal system exhibits functional adaptation. For bone the mechanotransduction mechanisms have been well elucidated; in contrast, the response of tendon to its mechanical environment is much more poorly understood despite tendon disorders being commonly encountered in clinical practice. This study presents a novel approach to developing an isolated tendon system in vivo. This model is used to test the hypothesis that stress-shielding, and subsequent restressing, causes significant biomechanical changes. We propose a control mechanism that governs this process. A custom-built external fixator was used to functionally isolate the ovine patellar tendon(PT). In group 1 animals(n=5) the right PT was stress-shielded for 6 weeks. This was achieved by drawing the patella towards the tibial tubercle, thus slackening the PT. In group 2 (n=5) the PT was stress-shielded for 6 weeks. The external fixator was then removed and the PT physiologically loaded for a further 6 weeks. In each case, the PT subsequently underwent tensile testing and measurement of length(L) and cross-sectional area(CSA). The untreated left PTs acted as controls (n=10). 6 weeks of stress-shielding significantly decreased material and structural properties of tendon compared to controls (elastic modulus(E) 76.2%, ultimate tensile strength(UTS) 69.3%, stiffness(S) 79.2%, ultimate load(UL) 68.5%, strain energy(SE) 60.7%; p< 0.05). Ultimate strain(US), L and CSA were not significantly changed. 6 weeks of subsequent functional loading (Group 2) caused some improvement in material properties, but greater recovery in structural properties (E 79.8%, UTS 91.8%, S 96.7%, UL 92.7%, SE 96.5%). CSA was significantly greater than Group 1 tendons at 114% of control value. Previous models of tendon remodelling have relied on either joint immobilization or direct surgical procedures. This model allows close control of the tendon’s mechanical environment whilst allowing normal joint movement and avoiding surgical insult to the tendon itself. The hypothesis that stress-shielding, and subsequent restressing, causes significant biomechanical changes has been upheld. We propose that the biomechanical changes observed are governed by a strain homeostasis feedback mechanism

Background: Poor results were observed at medium term follow-up (FU) after first and second generation cementless stems implantation in total hip arthroplasty (THA). Revision rate up to 24% is reported with anatomic stems; stress-shielding rate up to 50%, thigh pain rate up to 21%, loosening rate up to 20% and osteolysis rate up to 29% were reported with cylindrical stems. A third generation tapered stem, the Synergy stem, was introduced in 1996 to rise such weakness points. Material and methods: A retrospective, cohort study was carried out in two academic centers (London, Toronto, Canada & Rome, Italy) on 232 primary THA in 215 patients with a 10 to 12 yrs FU. Mean age at surgery was 60 yrs (18–82), 95 patients were males and 120 females. Thirty-six patients were lost at FU (13 died before the 10 yrs mark, 22 changed residency, 1 not willing to be seen) with no problems related to the replaced hip. Remained at FU 196 THA. Patients selection: Dorr type A and B femurs suitable for receive a Synergy stem. Its characteristics are the following: Ti-6Al-4V, straight, tapered, 3D wedge cross-section, proximal antirotational fins, low-profile neck, neck angle 131°, metaphyseal part porous or HA coated, diaphyseal part grit blasted, polished tip, surgeon-friendly ancillary instruments. Clinical results of the 196 THA with more than 10 yrs of FU were assessed preoperatively and postoperatively at 5 and 10 or 11 or 12 yrs by means of standard evaluation tools: SF12, WOMAC and Harris Hip Score. Thigh pain frequency and intensity were also scored. Radiographic analysis was focused on stem alignment, bone ingrowth, radiolucent lines presence, width and progression, stress-shielding, heterotophic ossification (HTO). Student paired test and Kaplan-Meier survival analysis were used for statistical analysis. Results: All clinical evaluation tools showed both at 5 years FU and at latest FU (10–12 years) a statistically significant (p=0,001) improvement compared to the preoperative scores. We observed a not constant thigh pain in 7 patients (5,5%). Nineteen patients (10%) underwent evision due to polyethylene wear (6 cases), late periprosthetic fracture (5 cases), subsidence (2 cases), instability (3 cases), infection (3 cases). Cumulative survival rate was 97% at 2 and 5 years, 90% at 10 years. Stem related revisions were the 2 cases of subsidence, both related to occult intraoperative calcar crack and early revised (within 1 year); cumulative stem-related survival rate at 10 years was 99%. Alignment was varus in 9 cases and valgus in 3. Bone in-growth was observed in 194 patients (98%). Radiolucent lines were uncommon, non progressive, less than 2 mm, in Gruen zones 2 and 6. Stress-shielding was present as cortical reaction in 5 femurs in Gruen zones 3 and 5. Thirty-four cases of HTO (grade I and II in 27 case and grade III in 7 cases) were observed. Conclusions: The Synergy stem demonstrates excellent clinical and radiographic results at 10–12 yerars FU in 196 patients. Survivorship (with stem revision as end point) is 99% at 10 years. Thigh pain is uncommon and the level of activity and autonomy is excellent. Radiographically bone ingrowth is evident in all stems and radiolucent lines are “benign” with no aseptic loosening. Attention must be paid at the moment of stem press fit insertion to avoid occult proximal femoral fractures that may require revision surgery

Background. Tapered cementless femoral components have been used in total hip arthroplasty (THA) constructs for more than 20 years. The Synergy femoral component was introduced in 1996 as a second generation titanium proximally porous-coated tapered stem with dual offsets to better restore femoral offset at THA (Figure 1). The purpose of this study was to evaluate the outcome of the authors' experience using the Synergy stem at minimum 15 years of follow-up. Material and methods. We retrospectively reviewed a consecutive series of 102 patients (112 hips) who underwent surgery between November 1996 and October 1998 for primary THA using cementless Synergy stem with a minimum 15-years follow-up. The mean age at the time of surgery was 61 years, and the mean duration of follow-up was 16.3 years. Seventeen patients were lost at FU (8 died before the 15 years mark, 8 changed residency, 1 not willing to be seen) with no problems related to the replaced hip. Ninety-four hips in 85 patients were available for clinical and radiologic analysis. Clinical results of the 94 THAs with more than 15 years of follow-up were assessed preoperatively and postoperatively at 5, 10 and 15 years by means of standard evaluation tools: SF12, WOMAC and Harris Hip Score. Thigh pain frequency and intensity were also recorded. Radiographic analysis (Figure 2) was focused on stem alignment, bone ingrowth, radiolucent lines presence, width and progression, stress-shielding and heterotopic ossification (HTO). Student paired test and Kaplan-Meier survival analysis were used for statistical analysis. Results. All clinical evaluation tools showed at 5-year FU, 10-year FU and at latest FU (15–17 years) a statistically significant improvement compared to the preoperative scores. We observed a not constant thigh pain in 5 hips (4.75%). Nine stems were revised due to polyethylene wear (3 cases), late periprosthetic fracture (2 cases), infection (2 cases), subsidence (1 case) and instability (1 case). Stem related revision was a case of subsidence, related to occult intraoperative calcar crack and early revised (within 1 year); cumulative stem-related survival rate at 15 years was 99%. Alignment was varus in 5 cases and valgus in 1. Bone in-growth was observed in 93 hips (98%). Radiolucent lines were uncommon, non progressive, less than 2 mm, in Gruen zones 2 and 6. Stress-shielding was present as cortical reaction in 5 femurs in Gruen zones 3 and 5. Fifteen cases of HTO (grade I and II in 12 case and grade III in 3 cases) were observed. Conclusions. The Synergy stem demonstrated excellent clinical and radiographic results at 15–17 years FU in 85 patients. Survivorship (with stem revision as end point) was 99% at 15 years. Thigh pain was uncommon and the level of activity and autonomy is excellent. Radiographically bone ingrowth is evident in all stems and radiolucent lines are “benign” with no aseptic loosening

Distal radius fractures are the most common osteoporotic fractures among women. The treatment of these fractures has been shifting from a traditional non-operative approach to surgery, using volar locking plate (VLP) technology. Surgery, however, is not without risk, complications including failure to restore an anatomic reduction, fracture re-displacement, and tendon rupture. The VLP implant is also marked by bone loss due to stress-shielding related to its high stiffness relative to adjacent bone. Recently, a novel internal, composite-based implant, with a stiffness less than the VLP, was designed to eradicate the shortcomings associated with the VLP implant. It is unclear, however, what effect this less-stiff implant will have upon adjacent bone density distributions long-term. The objective of this study was to evaluate the long-term effects of the two implants (the novel surgical implant and the gold-standard VLP) by using subject-specific finite element (FE) models integrated with an adaptive bone formation/resorption algorithm. Specimen: One fresh-frozen human forearm specimen (female, age = 84 years old) was imaged using CT and was used to create a subject-specific FE model of the radius. Finite element modeling: In order to simulate a clinically relevant (unstable) fracture of the distal radius, a wedge of bone was removed from the model, which was approximately 10 mm wide and centered 20 mm proximal to the tip of the radial styloid. Bone remodeling algorithm: A strain-energy density (SED) based bone remodeling theory was used to account for bone remodeling. With this approach, bone density decreased linearly when SED per bone density was less than 67.5 µJ/g and increased when it was more than 232.5 µJ/g. When it was in the lazy zone (67.5 to 232.5 µJ/g), no changes in density occurred. Boundary conditions: A 180 N quasi-static force representing the scaphoid, and a 120 N quasi-static force representing the lunate was applied to the radius. The midshaft of the radius was constrained. FE outcomes: To examine the effects of stress shielding associated with each implant, the long-term changes of bone density within proximal transverse cross-sections of radius were inspected. The regional density analysis focused on three transverse cross-sections. The transverse cross-sections were positioned proximal to the subchondral plate, and were distanced 50 (cross-section A), 57 (cross-section B), and 64 mm (cross-section C) from the subchondral endplate. For both implants in all three cross-sections, cortical bone was reserved completely at the volar side. On the dorsal side, the cortical bone was completely resorbed in the VLP model. In all cross-sections, the averaged resultant density was higher for the “novel implant”. The difference ranged from 33% (cross-section A) to 36% (cross-section C) in favor of the “novel implant”. On average, the density values of the novel implant were 34% higher in transverse cross-sections (A, B, and C). This study showed that the novel implant offered higher density distributions compared to the VLP, which suggests that the novel implant may be superior to the VLP in terms of avoiding stress shielding

Negative remodelling of the femoral cortex in the form of calcar resorption due to stress-shielding, and femoral cortical hypertrophy at the level of the tip of the implant due to distal load transfer, is frequenly noted following cemented total hip replacement, most commonly with composite beam implants, but also with polished double tapered components. The C-stem polished femoral component was designed with a third taper running from lateral to medial across and along the entire length of the implant, with the aim of achieving more proximal and therefore more natural loading of the femur. The implant is designed to subside within the femoral cement mantle utilising the cement property of creep, generating hoop stresses, which are transferred more proximally to the femoral bone, starting at the level of the medial calcar. The intention is to load the proximal femur minimising stress-shielding and calcar resorption, as well as reducing distal load transfer as signified by the lack of distal femoral cortical hypertrophy. We present the results of a consecutive series of 500 total hip replacements using C-stem femoral components, performed between March 2000 and December 2005 at a single institution. Data was collected prospectively and all patients remain under annual follow-up by a Specialist Arthroplasty Practitioner. The operations were performed using a standard surgical technique with third generation cementing using Palacos-R antibiotic loaded cement. 500 arthroplasties were performed on 455 patients with an average age at the time of surgery of 68.3 years (23-92). There were 282 (62%) female and 173 (38%) male patients with osteoarthritis being the predominant diagnosis. 77 patients have died (73 hips) and the average duration of follow-up for the entire series is 81 months (52-124). Only 2 femoral implants have been revised - one for deep sepsis and the other as part of a revision procedure for a loose acetabulum, although the femoral component itself was not loose. One implant is currently loose following a periprosthetic fracture treated by internal fixation, but none of the remaining implants demonstrates any progressive radiolucencies in any Gruen zones or any features suggestive of current or future loosening. Calcar rounding has been observed, but there have been no cases with obvious loss of calcar height and no cases of distal femoral cortical hypertrophy. The C-stem femoral component has therefore performed well in clinical practice and the objective of eradicating negative bone remodelling has been achieved. The study is ongoing

Introduction. In our institution, we started to perform THA with SuperPATH approach, including preservation of soft tissue around the hip (James Chow et al. Musculoskelet Med 2011) since July 2014, aiming for fast recovery and prevention of hip dislocation. For minimally-invasive approaches, however, there have been a few reports on malalignment of the implants related to shortage of operative field. The purpose of this study is to examine the short-term results of THA using SuperPATH, especially implant alignment. Materials and methods. We performed a study of 45 patients (45 hips) with osteoarthritis of the hip joint who had a THA with SuperPATH approach. There were 8 men and 37 women with an average age of 73 years, which were minimally 24 months followed. Dynasty Bioform cup and Profemur Z stem (Microport Orthopaedics) were used for all cases. Patients were clinically assessed with Merle d'Aubigne score and complications. Implant alignment and stability were radiologically evaluated by annual X-ray and CT acquired two months after surgery. Results. Merle d'Aubigne score was 10.2 (pain:2.8, mobility:4.4 walking ability:3.0) preoperatively and 16.6(pain:5.8, mobility:5.8, walking ability:5.0) at the latest follow-up. There were no dislocation and infection, but intraoperative proximal femoral fracture was found for two cases, which was managed to treat with additional circulating wire intraoperatively. Latest follow-up X-ray image showed 95% of the stem A-P alignment to be within 2 degrees and 5% to be more than 2 degrees and less than 5 degrees, while 44% of the stem lateral alignment to be within 2 degrees, 47% to be more than 2 degrees and less than 5 degrees, and 8% to be more than 5 degrees. From CT images averaged cup position found to be 40±5 degrees for inclination, and 19±5 degrees for anatomic anteversion, averaged stem anteversion to be 33±9 degrees. Annual X-ray evaluation showed no radiolucent line and less than Grade 2 stress-shielding (Engh classification) around the implants for all cases. One case had more than 5mm subsidence of the stem in early postoperative period, but not progressively subsided. No loosening of components was evident. Discussion and Conclusion. Many minimally-invasive approaches have developed, there have been many reports on fast recovery and low incidence of postoperative hip dislocation, however, the risk of complications or malalignment related to shortage of operative field has been pointed out. In this study, intraoperative proximal femoral fracture occurred for two cases. Also, though there were no loosening and the components position seemed excellent but lateral view of the X-ray showed 8% to be more than 5 degrees tilting alignment, resulting from femoral broaching required before femoral neck resection. SuperPATH approach, including pass way from between the Gluteus Medius and the piriformis tendon, can preserve the whole short external rotators and capsule of the hip joint, leading to fast recovery and low incidence of postoperative dislocation. Moreover, this approach may be friendly to the surgeons familiar with the posterior approach because of easily conversion to the conventional posterior approach

Introduction. Dysplastic hip has not only deficiency of acetabulum but also femoral deformity. Therefore, selection of stem is important in cementless THA for dysplasia. Especially using of short stem should be challenge for deformed femur. We studied clinical performance and radiological findings after THA with triple tapered short stem (Optimys hip) for dysplastic hip. Materials and method. From May 2013, we performed cementless THA for osteoarthritis with dysplasia. Seventy-one hips of 67 patients were examined including four males and 63 females. Age at surgery was from 36 to 88 years old (61.7 in average). Surgical approach was used modified Watson-Jones in all hips. Clinical evaluation was used modified Harris hip score (MHSS), incidence of complications and thig pain. Radiological findings were evaluated according Engh's classification and grade of stress shielding. Follow-up period was minimum one year and was 21.3 months in average. Results. MHHS before surgery was 41 points and that at follow-up was 88 points in average and pain score was significantly improved. Calcar fracture during surgery occurred in two hips and circular wiring was performed. Deep infection, DVT and dislocation were not observed. Incidence of thigh pain was 1.4% of one hip. Radiological findings were assessed as bone in-grown in all of the hips and grade of stress-shielding was very low. There were no aseptic loosening and no revision for any reasons. Conclusions. Cementless THA with triple tapered short stem was useful for treatment of dysplastic hips. Radiological findings of all hip were assessed as bone in-grown