Innovative Design Methodology for Patient-Specific Short Femoral Stems

The biomechanical performance of hip prostheses is often suboptimal, which leads to problems such as strain shielding, bone resorption and implant loosening, affecting the long-term viability of these implants for articular repair. Different studies have highlighted the interest of short stems for preserving bone stock and minimizing shielding, hence providing an alternative to conventional hip prostheses with long stems. Such short stems are especially valuable for younger patients, as they may require additional surgical interventions and replacements in the future, for which the preservation of bone stock is fundamental. Arguably, enhanced results may be achieved by combining the benefits of short stems with the possibilities of personalization, which are now empowered by a wise combination of medical images, computer-aided design and engineering resources and automated manufacturing tools. In this study, an innovative design methodology for custom-made short femoral stems is presented. The design process is enhanced through a novel app employing elliptical adjustment for the quasi-automated CAD modeling of personalized short femoral stems. The proposed methodology is validated by completely developing two personalized short femoral stems, which are evaluated by combining in silico studies (finite element method (FEM) simulations), for quantifying their biomechanical performance, and rapid prototyping, for evaluating implantability.

More than a feeling?—Overruling the preoperatively templated offset option leads to a minor offset increase in short stem total hip arthroplasty

Purpose Short stems are increasingly used in total hip arthroplasty (THA) because of advantages in bone and soft tissue preservation and reconstruction of hip geometry. Digital templating is essential in determining the correct offset option and stem size in THA. However, the preoperative template sizes might be intraoperatively overruled. Patients and methods We evaluated the effect of intraoperative overruling of the preoperatively templated offset option of a short curved stem on hip offset, leg length, implant positioning, and femoral canal fill index. The overruling was performed in case of intraoperative instability, telescoping, or both. A series of 1052 consecutive THAs with a cementless short curved stem and press-fit cup was retrospectively screened. One hundred patients with unilateral THA and a contralateral native and morphologically healthy hip as a reference met the inclusion criteria. Measurements were carried out on preoperative and 3 months anterior–posterior postoperative radiographs. Patients were divided according to the overruling by offset option or stem size. Results Hip offset was increased in all groups, but only with significant increase if an offset option + 1 was used intraoperatively (p = 0.025). LLD was restored without significance in all groups (p = 0.323; p = 0.157). Conclusion Intraoperative overruling of the preoperative digital template in cementless short stem total hip arthroplasty results in an increase of hip offset compared to a contralateral healthy hip. However, the increase is marginal and clearly under 5 mm compared to the contralateral healthy hip.

Preserved periprosthetic bone stock at 5 years post-operatively with uncemented short hip stem in both collared and collarless version

Introduction Previous bone density studies have generally shown bone resorption around both cemented and uncemented total hip arthroplasty (THA) stems. This is presumed to be due to stress shielding. Short stems have been introduced partly to preserve bone in the proximal femur by a more physiological loading of the bone. The purpose of this study was to evaluate bone remodeling around a short, fully hydroxyapatite-coated titanium stem that comes in a collared and collarless version. Patients and methods A prospective cohort of 50 patients included in a study evaluating the Furlong Evolution stem has been followed for 5 years. Examination was done with dual energy X-ray absorptiometry (DXA) postoperatively, at 1, 2 and 5 years. Clinical outcome was followed with radiography and both general and hip specific outcome measures. Results The two versions of the stem behaved similarly regarding bone remodeling. After an initial decrease up to 1 year, bone mineral density (BMD) increased in all Gruen zones up to 2 years and at 5 years bone stock was still preserved compared with postoperatively (net BMD + 1.2% (95% CI − 0.4 to 2.8)). Increase in BMD occurred mainly in the greater trochanter and distally around the stem with a decrease in the calcar area. Both versions showed excellent clinical outcome up to 5 years. Conclusion This short stem seems to preserve proximal bone stock up to 5 years, exhibiting similar behaviour both with and without a collar. Trial registration number and date of registration ClinicalTrials.gov, (identifier: NCT01894854). July 10, 2013.

Problems, complications, and reinterventions in 4893 onlay humeral lateralized reverse shoulder arthroplasties, a systematic review: part II—problems and reinterventions

Background Several modifications to the original Grammont reverse shoulder arthroplasty (RSA) design have been proposed to prevent distinctive issues, such as both glenoid and humeral lateralization. The aim of this systematic review was to determine rates of problems, complications, reoperations, and revisions after onlay lateralized humeral stem RSA, hypothesizing that these are design related. Methods This systematic review was performed in accordance with the PRISMA statement guidelines. A literature search was conducted (1 January 2000 to 14 April 2020) using PubMed, Cochrane Reviews, Scopus, and Google Scholar, employing several combinations of keywords: “reverse shoulder arthroplasty,” “reverse shoulder prosthesis,” “inverse shoulder arthroplasty,” “inverse shoulder prosthesis,” “problems,” “complications,” “results,” “outcomes,” “reoperation,” and “revision.” Results Thirty-one studies with 4893 RSA met inclusion criteria. The 892 postoperative problems and 296 postoperative complications represented overall problem and complication rates of 22.7% and 7.5%, respectively. Forty-one reoperations and 63 revisions resulted, with overall reoperation and revision rates of 1.7% and 2.6%, respectively. Conclusions Problem, complication, and reintervention rates proved acceptable when implanting a high humeral lateralization stem RSA. The most frequent problem was scapular notching (12.6%), and the most common postoperative complication was scapular stress fracture (1.8%). An overall humeral complication rate of 1.9% was identified, whereas no humeral fractures or stem loosening were reported with short stems. Infections (1.3%) were the most common reason for component revision, followed by instability (0.8%). Level of evidence Systematic review IV.

Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty

The history of humeral component design has evolved from prostheses with relatively long stems and limited anatomic head options to a contemporary platform with short stems and stemless implants with shared instrumentation and the ability to provide optimal shoulder reconstruction for both anatomic and reverse configurations. Contemporary humeral components aim to preserve the bone, but they are potentially subject to malalignment. Modern components are expected to favorably load the humerus and minimize adverse bone reactions. Although there will likely continue to be further refinements in humeral component design, the next frontiers in primary shoulder arthroplasty will revolve around designing an optimal plan, including adequate soft tissue tension and providing computer-assisted tools for the accurate execution of the preoperative plan in the operating room.

Short-term success of proximal bone stock preservation in short hip stems: a systematic review of the literature

Total hip arthroplasty is performed more frequently in younger patients nowadays, making long-term bone stock preservation an important topic. A mechanism for late implant failure is periprosthetic bone loss, caused by stress shielding around the hip stem due to different load distribution. Short stems are designed to keep the physical loading in the proximal part of the femur to reduce stress shielding. The aim of this review is to give more insight into how short and anatomic stems behave and whether they succeed in preservation of proximal bone stock. A systematic literature search was performed to find all published studies on bone mineral density in short and anatomic hip stems. Results on periprosthetic femoral bone mineral density, measured with dual-energy X-ray absorptiometry (DEXA), were compiled and analysed per Gruen zone in percentual change. A total of 29 studies were included. In short stems, Gruen 1 showed bone loss of 5% after one year (n = 855) and 5% after two years (n = 266). Gruen 7 showed bone loss of 10% after one year and –11% after two years. In anatomic stems, Gruen 1 showed bone loss of 8% after one year (n = 731) and 11% after two years (n = 227). Gruen 7 showed bone loss of 14% after one year and 15% after two years. Short stems are capable of preserving proximal bone stock and have slightly less proximal bone loss in the first years, compared to anatomic stems. Cite this article: EFORT Open Rev 2021;6:1040-1051. DOI: 10.1302/2058-5241.6.210030

Downsizing in total hip arthroplasty. A short stem as a revision implant

Background Short stems have constantly gained popularity in primary total hip arthroplasty (THA) over the last decade. Although cementless short stems are not primarily designed to be used as revision implants, there may be certain indications for which downsizing the femoral component in failed conventional THA is potentially advantageous. Methods In this single center retrospective case series, six patients who underwent revision using a calcar-guided short stem after failed THA are presented. The mean follow-up was 3.32 years (SD 0.63 years). The health status was evaluated by the EQ-5D-5L score. Patient reported outcome measurements (PROM) were recorded using the Harris hip score (HHS) and The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Pain and satisfaction were assessed using a visual analogue scale (VAS). Radiographic analysis was performed by evaluating osteolysis, stress shielding, alignment and signs of aseptic loosening. Complications were documented. Results At last follow-up the mean EQ-5D-5L index was 0.851 (SD 0.098). Clinical outcome was excellent (HHS ≥ 90) in 4 patients and moderate (HHS 71 and 79) in 2 patients. The mean WOMAC score was 9.20% (SD 12.61%). Pain and satisfaction on VAS were 1.00 (SD 1.15) and 9.17 (SD 0.37), respectively. No major complications occurred. To date, no further revision surgery was needed. Radiologically, no signs of subsidence, aseptic loosening, stress shielding and fractures were obvious. Conclusion The present case series indicates that in failed conventional THA downsizing may be considered a treatment option, using short stem THA in selected cases.

High varus stem alignment in short-stem total hip arthroplasty: a risk for reconstruction of femoro-acetabular offset, leg length discrepancy and stem undersizing?

Purpose Short stems are increasingly used in in total hip arthroplasty (THA) because of advantages in bone and soft tissue preservation and reconstruction of hip geometry. Short stems can be inserted in a more varus position compared to conventional straight stems. This poses the risk of final varus misplacement of the femoral component, which is not intended in all femoral short stems. Methods We wanted to evaluate the effect of a high varus stem positioning in MIS THA on hip offset, leg length and femoral canal fill index. A series of 1052 consecutive THAs with a singular cementless femoral short stem and press-fit cup was retrospectively screened for inclusion. One hundred six patients with unilateral THA and a contralateral healthy hip met the inclusion criteria. Measurements were carried out on preoperative and 3 months anterior–posterior postoperative radiographs. Patients were divided into Group A (varus stem alignment ≤ 3°) and Group B (varus stem alignment > 3°). Results Hip offset (HO) increased significantly in Group B by 4 mm (p = 0.013). No influence on leg length difference was detected in both groups. Preoperative CCD angle was significantly lower in Group B (p < 0.001). Canal Fill Indices (CFI) were significantly lower in Group B (CFI I: p < 0.001; CFI II p = 0.003; CF III p = 0.002). Conclusion High varus stem alignment > 3° leads to a statistically significant but minor increase in HO and poses the risk of stem undersizing. A preoperatively low genuine CCD angle pose a risk for varus stem positioning.