Proximal femoral defect classifications in revision total hip arthroplasty from X-rays imaging to advanced 3D imaging: a narrative review.

Background and Objective: Femoral bone defect in hip arthroplasty revision surgery represents a complex problem, and the treatment is a challenge for orthopedic surgeons called to assess the residual bone stock in an altered anatomy and obtain stability for the new implant. Classification systems available are mostly based on X-rays two-dimensional images and lack of accuracy and reproducibility and comprehensive therapeutic algorithms. However, there is no record of any classification based on computed tomography (CT)-scan images or three-dimensional (3D) modeling modern techniques. We aimed to review the current literature around femoral defect classifications (FDCs) analyzing their different rationale basis, reliability and accuracy, and their benefit in clinical practice. Moreover, we highlighted the role of CT scan-based 3D modeling techniques in the setting of femoral bone defects and revision hip arthroplasty. Methods: A narrative review was conducted. The articles were selected from the PubMed and Scopus medical database updated to March 2023. All Level-I to IV studies in the English language were considered for inclusion. The research was performed using relevant search term items: "femoral defects", "classification", "radiographic", "revision hip arthroplasty", "CT scan" and "3D" and we included only articles that evaluated the accuracy or reliability (or both) of the different femoral bone defects classification system. Key Content and Findings: Our search yielded 408 results, of which 17 were deemed highly relevant. We found seven X-ray-based classification systems which have been attempted to quantify the degree of bone loss with low to good reproducibility. The most used classification system for femoral bone defects were the AAOS and Paprosky classification, which also offers a clinical therapeutic algorithm. In 2021, the FDC interestingly showed a new simple classification system with sub-optimal reproducibility and a practical therapeutic algorithm. Despite the numerous classification system of femoral defects, none of them comprehends the use of CT scan and 3D imaging technologies. Conclusions: Traditional X-rays-based classification system are still widely used event if their intra-observer and inter-observer reliability is sub-optimal. 3D modeling techniques represent an important diagnostic tool that could improve the understanding of bone defects and residual bone supportive structures, allowing to elaborate new, more precise, classification systems.

Periprosthetic joint infections in patients with rheumatoid arthritis are associated with higher complication and mortality rates.

INTRODUCTION: Periprosthetic joint infection (PJI) remains the most devasting complication after total joint arthroplasty (TJA). There has been a significant focus on this topic in recently-published medical literature. However, relatively little has been published about PJI in patients with rheumatoid arthritis (RA), which are often physiologically frail and immunocompromised. A better understanding of PJI in this patient population is therefore crucial. The main aims of this paper are to (1) report complication and mortality rates in a cohort of PJI-RA patients; and (2) clinically characterize them. METHODS: Medical and surgical records of all RA PJI patients treated surgically from 2003 to 2020 were retrospectively reviewed. Medical history, physical examination, reactive protein (CRP) level, procalcitonin, white blood cell (WBC) count, joint aspiration results, and cultures were used to determine PJI. RESULTS: 54PJIs, 49 of them chronic, were treated in 53RA patients. Mean patient age was 65 yrs. (range = 32-88); 33females and 20 males (one bilateral hip). The overall mortality rate was 18.9%(n = 10), with five deaths directly attributed to PJI. Staphylococci accounted for 34 infections (63%), while 11(20.4%) had multiorganism infections and six culture-negative PJI. At the end of treatment 79.6%(n = 43) still had an implanted TJR, 7.4% (n = 4) had spacers, 5.6%(n = 3) had undergone resection arthroplasty, 3.7%(n = 2) arthrodesis, and one each amputation and exarticulation. CONCLUSIONS: Mortality and specially complication rates were (are) high in this RA patients group presenting PJI. Delays to diagnosis and treatment may explain some of these poor outcomes. LEVEL OF EVIDENCE: A cohort level III retrospective study.

Fluoroscopy-based robotics in total hip arthroplasty mitigates laterality-based differences in acetabular cup placement when compared to the manual, fluoroscopic- assisted technique.

BACKGROUND: Robotic assistance in total hip arthroplasty (RA-THA) has been shown to minimize laterality-based differences in acetabular cup positioning. OBJECTIVE: To determine if the use of a novel, fluoroscopy-based RA-THA system mitigates differences in acetabular cup placement between left (L) and right (R) side hip procedures, when compared to manual, fluoroscopic-assisted technique. METHODS: We conducted a retrospective review of 106 consecutive mTHA (40 L/66 R) and 102 RA-THA (48 L/54 R) primary direct anterior approach procedures. All cases were performed by a single right-hand-dominant surgeon, for a pre-operative diagnosis of osteoarthritis, avascular necrosis, or rheumatoid arthritis. Outcomes included acetabular cup inclination and anteversion, and the proportion of cups within the Lewinnek safe-zone. RESULTS: The average inclination of mTHA L cases was smaller than that of mTHA R cases (41.10∘± 7.38 vs. 43.97∘± 6.27; p= 0.04). For RA-THA, L and R cup angles were similar. There were fewer overall mTHA hips within the Lewinnek safe-zone compared to RA-THA (0.59 vs. 0.78; p= 0.003), as well as fewer mTHA R cases than RA-THA R cases (0.59 vs. 0.80; p= 0.03) within safe zone. CONCLUSION: Use of a novel, fluoroscopy-based robotic system mitigates laterality-based differences in acetabular cup placement that were observed in a manual, fluoroscopic-assisted cohort.

Fluoroscopy-based robotic assistance for total hip arthroplasty improves acetabular cup placement accuracy for obese patients compared to the manual, fluoroscopic- assisted technique.

BACKGROUND: Patient obesity is a risk factor for poor acetabular cup positioning in total hip arthroplasty (THA). OBJECTIVE: To assess the impact of using a novel, fluoroscopy-based robotic THA system on acetabular cup placement in obese versus non-obese patients. METHODS: A review of 105 consecutive manual unassisted (mTHA) (47 Obese/58 Non-obese) and 102 robotic-assisted (RA-THA) (50 Obese/52 Non-obese) primary, direct anterior approach THA procedures was conducted. All cases were performed by a single surgeon, for a pre-operative diagnosis of osteoarthritis, avascular necrosis, or rheumatoid arthritis. Obesity was defined as a Body Mass Index (BMI) ⩾ 30 kg/m2. Outcomes included acetabular cup inclination and anteversion, and the proportion of cups within the Lewinnek safe-zone. RESULTS: Obese patients in the mTHA cohort had larger cup inclination angles on average compared to non-obese patients (44.82∘± 6.51 vs. 41.39∘± 6.75; p= 0.009). Obese mTHA patients were less likely to have cup placement within the Lewinnek zone compared to non-obese mTHA patients (0.48 vs. 0.67; p= 0.027). Obesity had no effect on the accuracy of RA-THA. CONCLUSION: Obesity affects the placement of the acetabular component in manual THA. The novel, fluoroscopy-based robotic THA system in this study demonstrated accurate cup placement regardless of obesity status.

Improved accuracy of a novel fluoroscopy-based robotically assisted THA system compared to manual THA.

Accurate acetabular cup position remains a persistent challenge in total hip arthroplasty (THA). Studies investigating the early outcomes of robotic-assisted THA (RA-THA) systems have shown improved cup placement compared to manual THA (mTHA) approaches, however, contemporary robotic platforms are reliant on pre-operative CT imaging. The goal of this study was to analyze the accuracy of a novel, fluoroscopy-based RA-THA system compared to an unassisted mTHA approach and determine the effect of the robotic system on operative time. We performed a retrospective cohort analysis on a consecutive series of 198 patients who received mTHA and RA-THA between March 2021 and July 2022. The primary outcome of interest was the accuracy of acetabular component placement, defined by average cup inclination and anteversion. Secondary outcomes included the proportion of acetabular cups positioned within the Lewinnek safe zone, operative time, and overall room time. The RA-THA group demonstrated significantly higher accuracy of acetabular anteversion to target compared to the manual group (18.5 vs. 21.7˚; p < 0.001), and had a significantly greater proportion of acetabular cups placed within the Lewinnek safe zone (81.6 vs. 59.0%; p < 0.001). The RA-THA cohort had longer operative times compared to mTHA group (39.0 vs. 35.3 min; p = 0.003), but no difference was seen in total operating room time (101.2 vs. 101.2 min; p = 0.982). This study demonstrates that the use of a novel, fluoroscopy-based, pin-less THA robotic platform increased the accuracy of acetabular cup placement, including a 22.6% improvement in safe zone placement, compared to mTHA approach, with no increase in overall case time.

High early failure rate for a new unicondylar knee system.

Background: This single-center retrospective study evaluated early failure rates for an unicompartmental knee arthroplasty (UKA) system with an anti-allergic surface. Methods: We studied 87 consecutive joints received an UKA at a single center between 2017 and 2020. All patients received a fully cemented anti-allergic Univation-Aesculap partial knee replacement implant with a corundum blasting surface. All joints had precise indication of unicompartmental arthroplasty according to the current criteria of this procedure. The current series was restricted to patients undergoing medial cemented UKA. Medial compartment osteoarthritis was the main indication. Results: We found early failure (aseptic loosening) was documented in 20 of the 87 joints (23%). The time to failure ranged from 7 weeks to 3 years, for an estimated 33% (15-46%) cumulative hazard rate for implant loosening over three years. No cases of periprosthetic joint infection were found. On average, the patients began complaining about first symptoms during the third month after surgery. In most cases (66.66%), the cement remained fixed to the bone. Conclusions: Based on these early results, the manufacturer of this implant stopped all further distribution. Continued efforts should be made to understand the clinical and radiographic outcomes of alternative and anti-allergic surface coatings in knee arthroplasty.

A comparison of joint line height after revision total knee replacement using a rotating hinge versus a condylar revision knee system.

Purpose: This retrospective study aimed to assess the effects of two differing revision total knee implants designs (condylar and rotating hinge) on joint line height. Method: The use of distal augmentation and pre and post revision radiographic joint line heights were compared in 19 condylar type knee replacements (Zimmer NexGen Legacy Constrained Condylar Knee - LCCK) and 40 LINK-Endo-rotating hinge knee replacements. Joint line and patellar heights were determined for each implant using four validated methods. For comparison within a group a two tailed paired Student's t-test was used, for comparison between the groups an unpaired, two tailed Student's t-test was used. A p value of less than 0.05 was deemed statistically significant. Results: In 15 of 19 NexGen revision knee replacements distal augments were used. No distal augments were used in the LINK-Endo RHK group. In both systems there was no tendency to elevate the joint line relative to the tibia. The joint line was distalised relative to the femur in the NexGen group and proximalised in the rotating hinge knee group. Measurements using antero-posterior radiographs were found to be the most reliable method of assessing joint line height when compared to lateral radiographs. Conclusion: Both revision knee implant systems adequately restored joint line height. In condylar type knee revision implants elevation of the joint line height may be avoided through the use of distal augmentation. We found AP radiographs to be the most reliable method of accurately assessing joint line height.

Activated polymorphonuclear derived extracellular vesicles are potential biomarkers of periprosthetic joint infection.

BACKGROUND: Extracellular vesicles (EVs) are considered as crucial players in a wide variety of biological processes. Although their importance in joint diseases or infections has been shown by numerous studies, much less is known about their function in periprosthetic joint infection (PJI). Our aim was to investigate activated polymorphonuclear (PMN)-derived synovial EVs in patients with PJI. QUESTIONS/PURPOSES: (1) Is there a difference in the number and size of extracellular vesicles between periprosthetic joint aspirates of patients with PJI and aseptic loosening? (2) Are these vesicles morphologically different in the two groups? (3) Are there activated PMN-derived EVs in septic samples evaluated by flow cytometry after CD177 labelling? (4) Is there a difference in the protein composition carried by septic and aseptic vesicles? METHODS: Thirty-four patients (n = 34) were enrolled into our investigation, 17 with PJI and 17 with aseptic prosthesis loosening. Periprosthetic joint fluid was aspirated and EVs were separated. Samples were analysed by nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM) and flow cytometry (after Annexin V and CD177 labelling). The protein content of the EVs was studied by mass spectrometry (MS). RESULTS: NTA showed particle size distribution in both groups between 150 nm and 450 nm. The concentration of EVs was significantly higher in the septic samples (p = 0.0105) and showed a different size pattern as compared to the aseptic ones. The vesicular nature of the particles was confirmed by TEM and differential detergent lysis. In the septic group, FC analysis showed a significantly increased event number both after single and double labelling with fluorochrome conjugated Annexin V (p = 0.046) and Annexin V and anti-CD177 (p = 0.0105), respectively. MS detected a significant difference in the abundance of lactotransferrin (p = 0.00646), myeloperoxidase (p = 0.01061), lysozyme C (p = 0.04687), annexin A6 (p = 0.03921) and alpha-2-HS-glycoprotein (p = 0.03146) between the studied groups. CONCLUSIONS: An increased number of activated PMN derived EVs were detected in the synovial fluid of PJI patients with a characteristic size distribution and a specific protein composition. The activated PMNs-derived extracellular vesicles can be potential biomarkers of PJI.

The Paradox of Prosthetic Joint Infection and the Microbiome: Are Some Bacteria Actually Helpful?

Periprosthetic joint infection (PJI) is a potentially catastrophic complication of total joint arthroplasty of the lower extremity. PJI is associated with significant burden of illness and economic cost. There are a number of well-established modifiable risk factors for PJI. Myriad perioperative protocols are used with the intent of reducing the incidence of PJI. However, it remains unclear why infections occur despite correction of modifiable risk factors and/or adherence to prophylactic protocols. There is emerging evidence that the microbiome-the diverse population of commensal microorganisms that inhabit the human body-may play a role in the pathogenesis of musculoskeletal infections. The impact of the microbiome on PJI warrants further investigation and may change how we conceptualize, prevent, and treat PJI.

Silver Coatings in Reconstructive Orthopaedics: Basic Science and Clinical Rationale.

Prosthetic joint infection (PJI) is one of the most devastating complications that can occur following total hip and total knee arthroplasty. Despite the remarkable advances that have been made in surgical techniques and implant technology, the incidence of PJI has remained largely unchanged over the past two decades. One approach that has been described in the literature to minimize the risk of PJI has been the use of silver-coated prostheses. Silver has been reported to have antimicrobial properties when added to a variety of orthopaedic materials including bone cement, hydroxyapatite coatings and wound dressings. Silver is also being increasingly used as a surface coating for endoprostheses used for reconstruction around the hip and the knee with the specific aim of reducing the incidence of prosthetic joint infection. Despite the increasing adoption of this technology, the use of silver coatings remains controversial. The optimal method for preparation and the thickness of the coating, as well as the mechanism(s) of action in reducing the incidence of PJI, are unclear. The issue of silver toxicity is also an important consideration. This paper provides an overview of the use of silver coatings in reconstructive orthopaedics, as well as the types available and techniques used to coat endoprostheses. We also review the basic science as well as the clinical applications of silver coatings in the prevention of PJIs.

A Novel Method Facilitating the Simple and Low-Cost Preparation of Human Osteochondral Slice Explants for Large-Scale Native Tissue Analysis.

For in vitro modeling of human joints, osteochondral explants represent an acceptable compromise between conventional cell culture and animal models. However, the scarcity of native human joint tissue poses a challenge for experiments requiring high numbers of samples and makes the method rather unsuitable for toxicity analyses and dosing studies. To scale their application, we developed a novel method that allows the preparation of up to 100 explant cultures from a single human sample with a simple setup. Explants were cultured for 21 days, stimulated with TNF-α or TGF-ß3, and analyzed for cell viability, gene expression and histological changes. Tissue cell viability remained stable at >90% for three weeks. Proteoglycan levels and gene expression of COL2A1, ACAN and COMP were maintained for 14 days before decreasing. TNF-α and TGF-ß3 caused dose-dependent changes in cartilage marker gene expression as early as 7 days. Histologically, cultures under TNF-α stimulation showed a 32% reduction in proteoglycans, detachment of collagen fibers and cell swelling after 7 days. In conclusion, thin osteochondral slice cultures behaved analogously to conventional punch explants despite cell stress exerted during fabrication. In pharmacological testing, both the shorter diffusion distance and the lack of need for serum in the culture suggest a positive effect on sensitivity. The ease of fabrication and the scalability of the sample number make this manufacturing method a promising platform for large-scale preclinical testing in joint research.

International Organism Profile of Periprosthetic Total Hip and Knee Infections.

BACKGROUND: There is scarce literature describing pathogens responsible for periprosthetic joint infections (PJIs) around the world. Therefore, we sought to describe periprosthetic joint infection causative organisms, rates of resistant organisms, and polymicrobial infections at 7 large institutions located in North/South America and Europe. METHODS: We performed a retrospective study of 654 periprosthetic hip (n = 361) and knee (n = 293) infections (January 2006 to October 2019) identified at Cleveland Clinic Ohio/Florida in the United States (US) (n = 159), Hospital Italiano de Buenos Aires in Argentina (n = 99), Hospital Asociación Española in Uruguay (n = 130), Guy's and St Thomas' Hospital in the United Kingdom (UK) (n = 103), HELIOS Klinikum in Germany (n = 59), and Vreden Institute for Orthopedics in St. Petersburg, Russia (n = 104). Analyses were performed for the entire cohort, knees, and hips. Alpha was set at 0.05. RESULTS: Overall, the most frequent organisms identified were Staphylococcus aureus (24.8%) and Staphylococcus epidermidis (21.7%). The incidence of organisms resistant to at least one antibiotic was 58% and there was a significant difference between hips (62.3%) and knees (52.6%) (P = .014). Rates of resistant organisms among countries were 37.7% (US), 66.7% (Argentina), 71.5% (Uruguay), 40.8% (UK), 62.7% (Germany), and 77.9% (Russia) (P < .001). The overall incidence of polymicrobial infections was 9.3% and the rates across nations were 9.4% in the US, 11.1% in Argentina, 4.6% in Uruguay, 4.9% in UK, 11.9% in Germany, and 16.3% in Russia (P = .026). CONCLUSION: In the evaluated institutions, S aureus and S epidermidis accounted for almost 50% of all infections. The US and the UK had the lowest incidence of resistant organisms while Germany and Russia had the highest. The UK and Uruguay had the lowest rates of polymicrobial infections.

What is the optimal duration of intravenous antibiotics following single-stage revision total hip arthroplasty for prosthetic joint infection? A systematic review.

Prosthetic joint infection (PJI) is 1 of the most challenging potential complications following total joint arthroplasty. Several surgical treatment strategies have been proposed for management of this diagnosis. The single-stage approach has been gaining popularity in contemporary literature. 1 fundamental aspect in the management of hip PJI is the administration of antibiotics, usually intravenously immediately after surgery, followed by a period of oral antibiotics. The optimal duration of the period of antibiotic therapy is undecided. The aim of this paper is to examine the trend in intravenous antibiotic use over the last 18 years and examine the influence this has had on the results of single-stage revision over that time period.

Serum C-reactive protein and WBC count in conservatively and operatively managed bacterial spondylodiscitis.

PURPOSE: C-reactive protein (CRP) and white blood cell (WBC) count are routine blood chemistry parameters in monitoring infection. Little is known about the natural history of their serum levels in conservative and operative spondylodiscitis treatment. METHODS: Pre- and postoperative serum levels of CRP and WBC count in 145 patients with spondylodiscitis were retrospectively assessed. One hundred and four patients were treated by debridement, spondylodesis, and an antibiotic regime, 41 only with a brace and antibiotics. The results of the surgical group were compared to 156 patients fused for degenerative disc disease (DDD). RESULTS: Surgery had a significant effect on peak postoperative CRP levels. In surgically managed patients, CRP peaked at 2-3 days after surgery (spondylodiscitis: pre-OP: 90 mg/dl vs. post-OP days 2-3: 146 mg/dl; DDD: 9 mg/dl vs. 141 mg/dl; p < 0.001), followed by a sharp decline. Although values were higher for spondylodiscitis patients, dynamics of CRP values were similar in both groups. Nonoperative treatment showed a slower decline. Surgically managed spondylodiscitis showed a higher success rate in identifying bacteria. Specific antibiotic treatment led to a more predictable decline of CRP values. WBC did not show an interpretable profile. CONCLUSION: CRP is a predictable serum parameter in patients with spondylodiscitis. WBC count is unspecific. Initial CRP increase after surgery is of little value in monitoring infection. A preoperative CRP value, and control once during the first 3 days after surgery is sufficient. Closer monitoring should then be continued. Should a decline not be observed, therapy needs to be scrutinized, antibiotic treatment reassessed, and concomitant infection contemplated.

Management of Gonarthrosis with a Rotating Hinge Prosthesis: Minimum 10-Year Follow-up.

BACKGROUND: The use of hinged designs is usually reserved for severe deformities or instability in contemporary total knee arthroplasty (TKA). Results have been mixed with some authors reporting relatively high incidences of complications. The aim of this study is to present the results of primary TKA performed with a hinged prosthesis with a minimum 10-year follow-up. We also examined the factors that influence survivorship of this prosthesis. METHODS: A total of 238 primary TKA procedures were performed using hinged prostheses. Indications included osteoarthritis, rheumatoid arthritis, posttraumatic deformity, and arthritis. Clinical outcomes were assessed using the Hospital for Special Surgery score. Radiologic assessment was performed at each follow-up. Survivorship was calculated based on the Kaplan-Meier method. All complications were documented. RESULTS: Mean follow-up was 13.5 years (standard deviation [SD], 3.4). Mean flexion at final review was 118° (SD, 20°). Fifty-four percent and 20% reported excellent and good functional scores, respectively. Survivorship was 94% at 13.5 years in patients over 60 years of age and 77% in patients less than 60 years of age. Survivorship in patients with preoperative varus deformity was 96% and that in valgus knees was 79%. CONCLUSIONS: The results of this study suggest that when rotating hinges are used for primary TKA, the best results are achieved in patients over 60 years old. The indications for this design in the setting of primary TKA include significant deformities, severe bone loss, and ligamentous laxity.

Defensive antibacterial coating in revision total hip arthroplasty: new concept and early experience.

BACKGROUND: Infections remains the most feared complication in total hip arthroplasty (THA). New strategies of PJI prevention includes coating of conventional implants. Defensive Antibacterial Coating (DAC), an antibacterial hydrogel coating made of hyaluronan, poly-D and L-lactide can protect biomaterials as an effective barrier at the time of implantation. In addition, it can be used with topical antibiotics to prevent early colonisation of the implant. SCOPE: This manuscript describes the detailed function of the DAC in general as well as an analysis of its use in revision THA in a series of 28 patients in a short-term follow-up.Its use in patients undergoing cementless re-implantation after 2-staged procedures in THA is described in detail within the manuscript. CONCLUSION: DAC found to be effective in terms of infection control and safety in our patient cohort and has been expanded for cementless 1-staged revisions in PJI of the hip in our institution.

Survey of AAHKS International Members on the Impact of COVID-19 on Hip and Knee Arthroplasty Practices.

BACKGROUND: Coronavirus disease 2019 (COVID-19) pandemic poses an important risk to global health. METHODS: This study surveyed 370 international orthopedic surgeons affiliated with the American Association of Hip and Knee Surgeons to help identify the global impact of the COVID-19 pandemic on patient care. RESULTS: A total of 99 surgeons (27% of those surveyed) completed the questionnaire representing 32 different countries. Except for surgeons in Japan, all respondents noted that their practice had been affected to some degree and 70% of the surgeons have canceled elective procedures. More than a third of the surgeons have had to close their practices altogether and the remaining open practices were estimated to be sustainable for 7 weeks on average given their current situation. CONCLUSION: The COVID-19 pandemic has resulted in marked changes to the majority of international arthroplasty practices.

Noise levels during total hip arthroplasty: the silent health hazard.

BACKGROUND: While there is an enormous amount of data on various surgical aspects of total hip arthroplasty (THA), there is only limited literature on the health hazards incurred by the surgical team. Since THA surgery produces noise, exposure over a long period of time may lead to gradual hearing loss which is known as noise-induced hearing loss. METHODS: We investigated the noise levels during THA and compared it with the maximum allowed limits at the workplace in the United Kingdom. In collaboration with specialised audio engineers, we analysed the noise levels during various steps of performing 7 uncemented THA. RESULTS: The results showed that the noise levels were close to the allowed limits for a workplace in the UK. CONCLUSION: Hospitals and staff who work in orthopaedic operating theatres should be aware of this risk and precautions should be put in place.

Anatomic grooved stem mitigates strain shielding compared to established total hip arthroplasty stem designs in finite-element models.

Aseptic loosening remains a major problem for uncemented femoral components in primary total hip arthroplasty (THA). Ideally, bone adaptation after THA manifests minimally and local bone density reduction is widely avoided. Different design features may help to approximate initial, post-THA bone strain to levels pre-THA. Strain-shielding effects of different SP-CL stem design features are systematically analyzed and compared to CLS Spotorno and CORAIL using finite element models and physiological musculoskeletal loading conditions. All designs show substantial proximal strain-shielding: 50% reduced medial surface strain, 40-50% reduction at lateral surface, >120 µm/m root mean square error (RMSE) compared to intact bone in Gruen zone 1 and >60 µm/m RMSE in Gruen zones 2, 6, and 7. Geometrical changes (ribs, grooves, cross sections, stem length, anatomic curvature) have a considerable effect on strain-shielding; up to 20%. Combinations of reduced stem stiffness with larger proximal contact area (anatomically curved, grooves) lead to less strain-shielding compared to clinically established implant designs. We found that only the combination of a structurally flexible stem with anatomical curvature and grooves improves strain-shielding compared to other designs. The clinical implications in vivo of this initial strain-shielding difference are currently under evaluation in an ongoing clinical analysis.