Objectives. In total hip arthroplasty (THA), the cementless, tapered-wedge stem design contributes to achieving initial stability and providing optimal load transfer in the proximal femur. However, loading conditions on the femur following THA are also influenced by femoral structure. Therefore, we determined the effects of tapered-wedge stems on the load distribution of the femur using subject-specific finite element models of femurs with various canal shapes. Patients and Methods. We studied 20 femurs, including seven champagne flute-type femurs, five stovepipe-type femurs, and eight intermediate-type femurs, in patients who had undergone cementless THA using the Accolade TMZF stem at our institution. Subject–specific finite element (FE) models of pre- and post-operative femurs with stems were constructed and used to perform FE analyses (FEAs) to simulate single-leg stance. FEA predictions were compared with changes in bone mineral density (BMD) measured for each patient during the first post-operative year. Results. Stovepipe models implanted with large-size stems had significantly lower equivalent stress on the proximal-medial area of the femur compared with champagne-flute and intermediate models, with a significant loss of BMD in the corresponding area at one year post-operatively. Conclusions. The stovepipe femurs required a large-size stem to obtain an optimal fit of the stem. The FEA result and post-operative BMD change of the femur suggest that the combination of a large-size Accolade TMZF stem and stovepipe femur may be associated with proximal stress shielding. Cite this article: M. Oba, Y. Inaba, N. Kobayashi, H. Ike, T. Tezuka, T. Saito. Effect of femoral canal shape on mechanical stress distribution and adaptive bone remodelling around a cementless tapered-wedge stem. Bone Joint Res 2016;5:362–369. DOI: 10.1302/2046-3758.59.2000525

Background. Short stem has potential advantages of bone and muscle preservation. Current papers demonstrate that direct anterior approach (DAA) is a significant minimally invasive muscle-sparing approach to total hip arthroplasty. Theoretically, a short length stem with a reduced lateral shoulder is the most appropriate design for DAA. Objectives. To clarify the necessity of the standard length stem in tapered-wedge stem. Patients and methods. We prepared two kinds of tapered-wedge stem, Taperloc (standard length stem) and Microplasty (short stem) (Biomet, warsaw, Indiana) at the surgery. If the rasp for the short stem had not been fixed rigidly intra-operatively, it would have been changed to the standard length stem. Between May in 2010 and April in 2011, 94 patients (107 hips, 13 bilateral) were included in this study. All THAs were performed by direct anterior approach (DAA) on a standard surgical table. We analyzed the early clinical and radiographic results of 107 THAs in 94 patients (60 women, 34 men). The mean age was 61 (33∼84) years. The mean height was 161 (142∼182) cm and the mean weight was 63 (40∼92) kg. Results. All hips were implanted with the short stem. There was no need of the standard length stem. The mean operative time was 54 (28–140) minutes and the mean operative blood loss was 422 (60∼2400) ml. There was a significant improvement in functional outcome of these patients as measured by Japanese Orthopedic association hip scores. There were three complications intra-operatively or post-operatively. These were one intraoperative femoral fracture which was salvaged with circular wiring, one femoral fatigue fracture which occurred 6 weeks and cured conservatively, and one pulmonary embolism. There were no stem subsidence, dislocations and infections. Conclusion. This study confirms that there is no need of a standard length stem in THA using tapered-wedge stem. The short stem and DAA would be a winning combination for THA

Introduction. Micro-arc oxidation (MAO) is an electrochemical method used to treat metal surfaces. It provides nanoporous pits, and thick oxide layers, and incorporates calcium and phosphorus into the coating layer of titanium alloy. This modification on the surface of titanium alloy by MAO coating would improve the ability of cementless stems to osseointegrate. In spite of these structural and chemical advantages, clinical study of total hip arthroplasty (THA) using MAO coated stem has not yet been reported. In this study, we evaluated the clinical and radiographic results associated with cementless grit-blasted tapered-wedge stems that were identical in geometry but differed with regard to surface treatment with or without MAO coating. Materials & Methods. We performed a retrospective review of 141 THAs using MAO coated stem for a minimum of 5 years and compared them to 219 THAs using the same geometry stem without MAO coating. A cementless Bencox femoral component (Corentec, Seoul, Korea) was used in all hips. It is made of titanium alloy with a straight, double wedged, tapered stem with a rectangular cross-section. Surface treatment was performed using grit blasting with a roughness of 5.5ųm that was available either with or without MAO coating. Clinical and radiographic evaluations were performed preoperatively and at 6 weeks, 3 months, 6 months, and 1 year postoperatively, and then annually. Results. In the MAO coating group, the mean Harris hip score improved from 43.7 points preoperatively to 93.9 points postoperatively. The mean WOMAC score and UCLA activity score at the final follow-up was 17 points (range, 6–34 points) and 6.9 points (range, 5–10 points), respectively. Thigh pain at final follow-up was reported in 2 hips (1.4%), but neither of these hips showed signs of implant loosening or limited daily activities. Complications included one squeaking, one iliopsoas tendonitis, and one deep vein thrombosis. Postoperative Harris hip scores, WOMAC scores, UCLA activity scores, and complication rates did not differ between the two groups. In both groups, no femoral or acetabular component showed radiographic evidence of mechanical loosening, and no components had been revised at the final follow-up. Conclusions. Primary THA using a cementless grit-blasted tapered-wedge stem with MAO coating showed encouraging medium-term outcomes. Further prospective controlled study is required to investigate the long-term implant survival, possible complications, and cost-effectiveness of utilizing MAO coating in THA

Purpose. The purpose of this study was to evaluate periprosthetic bone mineral density (BMD) changes around a cementless short tapered-wedge stem and determine correlations between BMD changes and various clinical factors, including daily activity, after total hip arthroplasty (THA) with a short tapered-wedge stem. Methods. The study included 65 patients (65 joints) who underwent THA with a TriLock stem. At baseline, and 6, 12, and 24 months postoperatively, BMDs of the seven Gruen zones were evaluated using dual-energy X-ray absorptiometry. Correlations were determined between BMD changes and clinical factors, including the Harris hip score, body mass index, University of California at Los Angeles (UCLA) activity rating score, age at surgery, and initial lumbar BMD. Results. Minimal BMD changes were noted in the distal femur (Gruen zones 3, 4, and 5). However, significant BMD loss was noted in zone 7 at each time point. BMD loss was also noted in zone 1 at 6 and 12 months postoperatively, but BMD recovered after 18 months. Significant positive correlations were noted between BMD changes and the UCLA activity rating score in zones 1, 6, and 7. Additionally, negative correlations were noted between BMD changes and initial spine BMD in zones 2 and 3. Table legends. Table 1 Background of the patients. Table 2 Bone mineral density changes (%) at 6, 12, and 24 months postoperatively in the seven Gruen zones. Columns represent mean ± standard deviation. ※indicates P < 0.05 compared with baseline bone mineral density. Table 3 Correlations between periprosthetic bone mineral density changes and clinical factors (the Harris hip score, body mass index, University of California at Los Angeles activity rating score, age at surgery, and initial lumbar bone mineral density) in the seven Gruen zones at 24 months postoperatively. Correlation coefficients and P-values are presented. Boldface indicates P < 0.05. Conclusion. Periprosthetic BMD was maintained in the proximal femur, especially Gruen zone 1, with a short tapered stem. Daily activity may reflect improvements in periprosthetic bone quality after THA with a short tapered stem; however, this stem is not recommended in patients with low bone quality. To view tables, please contact authors directly

Introduction. Resorptive bone remodeling secondary to stress shielding has been a concern associated with cementless total hip arthroplasty (THA). At present, various types of cementless implants are commercially available. The difference in femoral stem design may affect the degree of postoperative stress shielding. In the present study, we aimed to compare the difference in bone mineral density (BMD) change postoperatively in femurs after the use of 1 of the 3 types of cementless stems. Methods. Ninety hips of 90 patients who underwent primary cementless THA for the treatment of osteoarthritis were included in this study. A fit-and-fill type stem was used for 28 hips, a tapered-rectangular Zweymüller type stem was used for 32 hips, and a tapered-wedge type stem was used for 30 hips. The male/female ratio of the patients was 7/21 in the fit-and-fill type stem group, 6/26 in the tapered-rectangular Zweymüller type stem group, and 6/24 in the tapered-wedge type stem group. The mean age at surgery was 59.9 (39–80) in the fit-and-fill type stem group, 61.7 (48–84) in the tapered-rectangular Zweymüller type stem group and 59.6 (33–89) in the tapered-wedge type stem group. To assess BMD change after THA, we obtained dual-energy X-ray absorptiometry scans preoperatively and at 6, 12, 24, and 36 months postoperatively. Results. There were no differences in demographic data, such as gender, age at surgery, and body mass index, among the 3 groups (Table1). In terms of BMD change after THA, no differences were observed in Gruen zones 1–5 among the 3 groups during the 3-year follow-up. The BMD in Gruen zone 6 was maintained in the tapered-wedge type stem group, but decreased by 5% in the fit-and-fill type stem group and by 20% in the tapered-rectangular Zweymüller type stem group (p < 0.01). The BMD loss in Gruen zone 7 was observed in all stem types; however, the BMD loss at 36 months in the tapered-wedge type stem group (−15%) was significantly less than that of the other 2 groups (the fit-and-fill type stem group: −29%; the tapered-rectangular Zweymüller type stem group: −30%; p < 0.001 for both groups) (Figure). Discussion and Conclusion. A difference in postoperative BMD loss was observed among the 3 stem designs. This may be a result of the different fixation concept associated with each stem design. In the present study, we compared the postoperative BMD change after THA among a fit-and-fill type stem, a tapered-rectangular Zweymüller type stem, and a tapered-wedge type stem. BMD in the medial-proximal femur was maintained 3 years after THA in the group with the tapered-wedge type stem, which is fixed in a more proximal part of the femur compared to the other stems

Short stems have been developed to conserve bone stock, especially in younger populations undergoing a total hip arthroplasty (THA), and showed similar functional outcomes compared to conventional stems. Recent literature suggested that stem length might be an independent risk factor for acute periprosthetic femoral fracture in direct anterior THA (1) or with different short stem designs (2). The purpose of the present study was to compare the incidence of acute periprosthetic femoral fractures, between stems of the same manufacture (Taperloc microplasty vs Taperloc complete), which have the same stem characteristics, except for the stem length which is 35 mm shorter in Taperloc microplasty during posterior and lateral THA. Our institution's arthroplasty database was searched for all primary total hip arthroplasties utilizing short femoral stems performed between August 2016 and August 2023. Pre-operative X-rays for each case were analysed to characterize the proximal femoral geometry, specifically the canal bone ratio (CBR) and canal flare index (CFI). Data analysis was performed to identify risk factors for periprosthetic fractures. For the time period assessed, 2107 femoral stems (Taperloc Microplasty:1727, Taperloc complete: 380) were implanted. Females constituted 53% of the cohort. The average patient age was 70±11 years. The periprosthetic fracture rate was 0.94%, with 20 periprosthetic fractures (Taperloc Microplasty:17, Taperloc complete: 3) excluding 2 greater trochanteric fractures (1 at each group), identified at follow-up of three months. There was no significant difference between the periprosthetic fracture rates between the two stems (0.98% vs 0.79%, p>0.72) The multivariate regression analysis demonstrated that the stem length, CBR, CFI, age, and gender were not risk factors for periprosthetic fracture. The present study demonstrated that both Taperloc Microplasty and Taperloc complete stems had similar rates of periprosthetic fractures, and the stem length was not a risk factor for a periprosthetic fracture during uncemented THA. 1. Tamaki T, Cementless Tapered-Wedge Stem Length Affects the Risk of Periprosthetic Femoral Fractures in Direct Anterior Total Hip Arthroplasty. J Arthroplasty. 2018 Mar;33(3):805-809. 2. Staunton P. Acute Periprosthetic Hip Fracture with Short Uncemented Femoral Stems. J Arthroplasty 2024 accepted

Introduction. Cementless grit-blasted tapered-wedge titanium femoral stems are being used with increasing frequency in hip arthroplasty because of excellent long-term outcomes. However, periprosthetic femur fracture is a potentially worrisome phenomenon in these types of femoral stems. The aim of this study is to report the incidence of stem loosening in association with periprosthetic femur fractures following hip arthroplasty using cementless grit-blasted tapered-wedge stems. Materials & Methods. A total of 36 Vancouver Type B1 and B2 periprosthetic femur fractures following either hemiarthroplasty or total hip arthroplasty using cementless grit-blasted tapered-wedge titanium femoral stems (GB group) were identified from a retrospective review of the medical records at three participating academic institutions. The control group consisted of 21 Vancouver Type B1 and B2 periprosthetic femur fractures following either hemiarthroplasty or total hip arthroplasty using cementless proximal porous-coated femoral stems (PC group) at the same institutions during the same period of the study. All femoral stems included in this study had been a well-fixed state before the occurrence of periprosthetic femur fractures. All patients in both groups were treated surgically with either open reduction and internal fixation or femoral stem revision. Femoral stem stability was assessed by preoperative radiographs and was confirmed by intraoperative scrutinization. The incidence of stem loosening was compared between the groups. Results. There was no significant difference between the groups with respect to demographic data including age, gender, body mass index, primary diagnosis, Dorr types of proximal femur, and time to fracture. All fractures occurred from low-energy mechanisms. Mean age at the time of hip arthroplasty was 54.5 years in the GB group and 57.0 years in the PC group. Mean time interval between hip arthroplasty and periprosthetic fracture was 49.6 months in the GB group and 44.4 months in the PC group. At the time of the last follow-up, 29 (80.6%) of 36 fractures was Vancouver B2 in the GB group, whereas only 3 (14.3%) of 21 fractures was Vancouver B2 in the PC group (P <0.001). Conclusions. High incidence of stem loosening was developed in association with periprosthetic femur fractures in previously well-fixed cementless grit-blasted tapered-wedge femoral stems in our population. We believe that this is an underreported phenomenon of these types of stem design

Background. In total hip arthroplasty (THA), the importance of preserving muscles is widely recognized; therefore, muscle-sparing approaches are widely used. Recently, we reported that there are bony impressions, that we called the obturator attachment (OA), on the greater trochanter that indicate the insertions of the short external rotator tendons. In this study, we used a three-dimensional (3-D) template to evaluate damage to the insertions of the short external rotator muscles during a femoral procedure. Methods. We investigated 12 hips in 10 patients who underwent THA. Preoperative CT imaging of the hip was performed, and 3-D reconstruction of the greater trochanter was used to visualize the bony impressions that indicate the insertions of the obturator internus and externus muscles (Fig 1A). We performed preoperative 3-D templating of two different femoral prosthesis (flat tapered-wedge stem: J-Taper, cylindrical straight stem: PerFix910) and then evaluated the extent of damage to the OA during the stem placement (Fig 1B, 1C). The extent of damage to the OA was classified using the following scale: grade 0, no damage of the insertion area; grade 1, less than 1/3; grade 2, equal to or more than 1/3–2/3; grade 3, equal to or more than 2/3; grade 4, complete. Results. The attachment area of the obturator internus tendon was damaged in 9 hips (7 hips: grade 1, 2 hips: grade 2) using J-Taper and all hips (8 hips: grade 2, 4 hip: grade 3) using PerFix910. The attachment area of the obturator externus tendon was not damaged in any hip using J-Taper but was damaged in 5 hips (5 hips: grade 1) using PerFix910. Conclusions. The tendon insertion site for the obturator internus was more likely to be damaged by rasping or reaming. The tapered-wedge type stem was considered to be superior to the straight, cylindrical stem for preserving the tendon insertions on the greater trochanter. Fig.1 Three-dimensional reconstructed images of the left greater trochanter, after removal of the femoral head. A: The deep depression in the anterior part of the trochanteric fossa (blue area) indicates the insertion of the obturator internus, and the posterior depression in the trochanteric fossa (red area) indicates the insertion of the obturator externus. B: Preoperative 3-D templating of the J-taper (Kyocera, Kyoto, Japan) was performed. The insertion area of the obturator internus was damaged (Grade 1), while the insertion area of the obturator externus was not damaged. C: Preoperative 3-D templating of the PerFix910 (Kyocera, Kyoto, Japan) was performed. The most of the insertion area of the obturator internus was damaged (Grade 3), while the insertion area of the obturator externus was not damaged. Oi = obturator internus, Oe = obturator externus, Lt = lessor trochanter, Sup = superior, and Ant = anterior

Aims

There are concerns regarding initial stability and early periprosthetic fractures in cementless hip arthroplasty using short stems. This study aimed to investigate stress on the cortical bone around the stem and micromotions between the stem and cortical bone according to femoral stem length and positioning.