Proximal Load Transfer Research Articles

Long-term results of short stem total hip arthroplasty in patients with osteonecrosis of the femoral head.

Short stem total hip arthroplasty (THA) is an alternative to conventional stem, designed to facilitate minimal-invasive surgery, physiological loading and preserve bone stock. However, there is insufficient evidence of the long-term outcomes in patients with osteonecrosis of the femoral head (ONFH). This study aims to analyze the clinical and radiographic results with a minimum follow-up of 10 years. Furthermore, the survival rate of the short stem was calculated. There were 81 patients (101 hips) with the mean age of 45 years (range, 21 to 68) in this study. The Harris Hip Scores (HHS) and Forgotten Joint Scores (FJS) were recorded to evaluate the clinical results. The appearance of osteointegration and radiolucent line were reviewed. The mean follow-up period was 129.3 months (range, 120-154). At the latest follow-up, the mean HHS and FJS were 96.9 ± 5.7 (range, 69-100) and 95 ± 7 (range, 75-100) points respectively. The radiographic changes around the stem showed osteointegration mainly in the proximal part, zones 1 (94.1%), 2 (84.2%), 6 (99%) and 7 (92.1%). One stem underwent revision due to periprosthetic fracture, using conventional stem with plate and screws. Survivorship of the stem with the endpoint for any reason was 99.01% (95% confidence interval [CI], 93.18-99.86%) and for aseptic loosening was 100% at 10 years. Short stem showed promising long-term clinical outcomes in patients with ONFH. The radiographic results demonstrated physiological proximal load transfer.

A Finite Element Analysis Study of Influence of Femoral Stem Material in Stress Shielding in a Model of Uncemented Total Hip Arthroplasty: Ti-6Al-4V versus Carbon Fibre-Reinforced PEEK Composite

Total hip arthroplasty is one of the most common and successful orthopaedic operations. Occasionally, periprosthetic osteolysis associated with stress shielding occurs, resulting in a reduction of bone density where the femur is not properly loaded and the formation of denser bone where stresses are confined. To enhance proximal load transfer and reduce stress shielding, approaches, including decreasing the stiffness of femoral stems, such as carbon fibre-reinforced polymer composites (CFRPCs), have been explored through novel modular prostheses. The purpose of the present study was to analyse, by the finite element analysis (FEA) method, the effect that the variation of material for the distal part of the femoral stem has on stress transmission between a modulable prosthesis and the adjacent bone. Methods: Through three-dimensional modelling and the use of commercially available FEA software Ansys R2023, the mechanical behaviour of the distal part of the femoral stem made of CFRPC or Ti-6Al-4V was obtained. A load was applied to the head of the femoral stem that simulates a complete walking cycle. Results: The results showed that the use of a material with mechanical characteristics close to the bone, like CFRPC, allowed for optimisation of the transmitted loads, promoting a better distribution of stress from the proximal to the distal part of the femur. This observation was also found in some clinical studies in literature, which reported not only an improved load transfer with the use of CFRPC but also a higher cell attachment than Ti-6Al-4V. Conclusions: The use of a material that has mechanical properties that are close to bone promotes load transfer from the proximal to the distal area. In particular, the use of CFRPC allows the material to be designed based on the patient’s actual bone characteristics. This provides a customised design with a lower risk of prosthesis loss due to stress shielding.

Does preclinical analysis based on static loading underestimate post-surgery stem micromotion in THA as opposed to dynamic gait loading?

The success of cementless hip stems depends on the primary stability of the implant quantified by the amount of micromotion at the bone-stem interface. Most finite element (FE)-based preclinical studies on post-surgery stem stability rely on static analysis. Hence, the effect of dynamic gait loading on bone-stem relative micromotion remains virtually unexplored. Furthermore, there is a paucity of research on the primary stability of grooved stems as opposed to plain stem design. The primary aim of this FE study was to understand whether transient dynamic gait had any incremental effect on the net micromotion results and to further draw insights into the effects of grooved texture vis-à-vis a plain model on micromotion and proximal load transfer in host bone. Two musculoskeletal loading regimes corresponding to normal walking (NW) and stair climbing (SC) were considered. Although marginally improved load transfer was predicted proximally for the grooved construct under static loading, the micromotion values (max: NW ~ 7μm; SC ~ 10μm) were found to be considerably less in comparison to plain stem (max: NW ~ 50μm; SC ~ 20μm). For both physiological load cases, a significant surge in micromotion values was predicted in dynamic analyses as opposed to static analyses for the grooved stem (~ 390% greater). For the plain model, the increase in these values from static to dynamic loading is relatively moderate yet clinically significant (~ 230% greater). This suggests that the qualitative similarities notwithstanding, there were significant dissimilarities in the quantitative trends of micromotion for different cases under both analyses.

Mid-term results of short versus conventional cementless femoral stems in patients with bilateral osteonecrosis of the femoral head.

This study aimed to compare the clinical and radiographic mid-term results between short and conventional stems. Patients with bilateral osteonecrosis of the femoral head (ONFH) who had undergone bilateral staged THAs using short stem in one hip and conventional stem in the contralateral hip were included. The Harris Hip Score (HHS), thigh pain, patient's joint perception (PJP) and patients' preferred hip were recorded. Using x-ray, osseointegration and stress shielding were analyzed and compared between stems. There were 35 cases (70 hips) with the mean age of 46.3years (25-63), and the mean follow-up was 75.1months (60-108). HHS was significantly improved in both short and conventional groups (p < 0.001). There was mild thigh pain in 2 cases (5.7%) of the short stem group and 6 cases (17.1%) of the conventional group. With regard to the PJP, we found slightly more natural joint feeling in the short stem group. Of the patients' preferred hip, 11 cases (31.4%) preferred short stem hip and 6 cases (17.1%) preferred conventional stem hip. The short stem group showed osseointegration mainly in the proximal part. The conventional stem group showed osseointegration mainly in the distal part. We found stress shielding grade 1 in 31 cases (88.6%) and grade 2 in 3 cases (8.6%) in the conventional stem group, whereas only grade 1 in 34 cases (97.1%) in the short stem group. The clinical results were promising in both short and conventional stems; however, short stem showed less thigh pain, slightly more natural joint feeling (PJP) and more patients' preferred hip. The short stem provided more favorable results for proximal load transfer and slightly less stress shielding.

Mid-term results of short-stem total hip arthroplasty in patients with Crowe type I and II developmental dysplasia of the hip.

This study aimed to evaluate the clinical and radiographic mid-term results of short-stem THA in patients with DDH. We reviewed 32 cases that underwent Metha stem between November 2010 and February 2015. WOMAC scores, Oxford Hip Scores (OHS) and Harris Hip Scores (HHS) were recorded to evaluate the clinical results. The appearance of bone trabeculae development and stress shielding was analyzed. The mean age of patients was 50.3years (33-67) with the mean follow-up of 77months (60-106). According to Crowe classification, 13 cases were graded as Crowe I and 19 cases as Crowe II. According to Dorr classification, 17 cases were graded as Dorr A and 15 cases as Dorr B. The postoperative WOMAC scores decreased, and OHS and HHS increased significantly compared with preoperative (p < 0.001). The caput-column-diaphysis angles decreased significantly (p < 0.001) and limb length discrepancy decreased significantly (p = 0.013) after surgery. The radiographic change around the stem showed bone trabeculae development at zones 1 (93.9%), 2 (93.9%), 3 (25%), 5 (6.3%), 6 (96.9%) and 7 (90.6%). There was grade 1 stress shielding in 30 cases (93.9%). There was no stem subsidence greater than 2mm in all hips, no sciatic nerve injury or no dislocation. Neither acetabulum nor femoral stem was defined as definite loosening, and none of the implants was revised. The short stem showed promising mid-term clinical results in patients with DDH. The radiographic results demonstrated that the short stem provided physiological proximal load transfer with less stress shielding, being a useful alternative for femoral reconstruction.

Up to 10-year follow-up of the Symax stem in THA: a Danish single-centre study.

The design of the cementless Symax-HA femoral stem is based on geometrical analysis of human femoral anatomy to optimise the fit within the femur. The stem combines an anatomical proximal section enabling a metaphyseal anchorage with a straight distal section. This results in an improved proximal load transfer. We aimed to determine the overall survival of total hip arthroplasty (THA) in patients operated at our institution with the Symax stem. Secondly, we investigated the cause of revision for patients having THA including the Symax stem. The study is a registry study with results from a single centre, Vejle Hospital. From the Danish Hip -Arthroplasty Registry, we identified all THAs operated with the Symax stem. The primary outcome was revision. The secondary outcomes were aseptic loosening, periprosthetic fracture, and all other causes for revision. In total, 1,055 THAs were performed in 875 patients. The median 6.5-year survival rate was 97.5% (95% confidence interval [CI]: 96.6%-98.3%). 29 THAs had undergone revision due to the following causes: periprosthetic fracture (n = 11); aseptic loosening of the cup (n = 1); infection (n = 5); dislocation (n = 10); and component failure (n = 2). There was no revision due to aseptic loosening of the stem. From the Danish Hip Arthroplasty Registry, we identified the overall 6.5-year survival rate to be 95% for cementless THAs. In the present study, the Symax stem has a median 6.5-year survival rate at 97.5% (96.6%-98.3%). No revisions were due to aseptic loosening but the stem had a relative high prevalence of periprosthetic fractures.

Mid-term outcome of total hip arthroplasty using a short stem.

To review the outcome of total hip arthroplasty (THA) using a short femoral stem in 33 hips. Records of 33 hips in 20 men and 10 women aged 25 to 40 (mean, 30) years who underwent cementless THA using a short femoral stem by a single senior surgeon were reviewed. The diagnosis included avascular necrosis (n=9), ankylosing spondylitis (n=12), rheumatoid arthritis (n=7), posttraumatic arthritis (n=4), and Hurler syndrome (n=1). Clinical outcome was assessed using the Harris Hip Score. Radiological outcome was assessed according to a modified Gruen zoning system. Stem positioning (neutral, varus, valgus) and bone contact wereevaluated, as were fixation and early host response as well as subsidence and changes in the calcar region (zone 5). Trabecular response (trabecular attachment), spot welds, cortical hypertrophy, and pedestal formation were determined. Heterotopic ossification was graded by the Brooker classification. The mean follow-up period was 6.5 years. The mean Harris Hip Score improved from 40 to 90. All hips achieved immediate postoperative stability. No patient had thigh pain. Four hips had varus placement (5º-7º) of the stem; all were asymptomatic and remained stable without any migration. Evidence of proximal load transfer (endosteal spot welds) between the endosteum and the stem in zones 2 and/or 4 was noted in 12 hips on both sides and in 8 hips on the lateral side only. At one year, all stems showed evidence of osseointegration. None had subsidence or progressive varus migration. There was no radiolucent line or osteolysis around the stem, pedestal formation or buttressing at the prosthesis tip, or cortical hypertrophy. One patient had grade I heterotopic ossification that was not clinically significant. One patient had a 1.5 cm leg lengthening. One patient had a discharging sinus, a loosened acetabular component, and intrapelvic migration at 2 years and underwent implant removal and debridement. One patient developed a crack in the proximal femur even with the smallest stem. The stem was fixed with cerclage wiring and remained stable with no migration. A short femoral stem design that transfers load proximally through a prominent lateral flare achieved good short-term outcome in younger patients. Nonetheless, the ease of removal and preservation of bone at the time of revision should guide the choice of the design of the short stem.

Bone remodelling after femoral short stem implantation in total hip arthroplasty: 1-year results from a randomized DEXA study.

Short stem prostheses have been developed to preserve proximal femoral bone stock. This prospective, randomized study compared periprosthetic bone remodelling following short and straight stem implantation 1 year after surgery. One hundred and forty-four consecutive patients undergoing total hip arthroplasty were randomized to either a Fitmore short or a cementless straight stem (both Zimmer, Winterthur, Switzerland). Periprosthetic bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry performed the day before surgery and at 7 days, 3 months and 1 year postoperatively. Furthermore, the HHS and the WOMAC were obtained. One hundred and thirty-eight patients completed 1-year follow-up. Periprosthetic BMD changes at 1 year were most pronounced in the proximal medial region of interest (ROI) 7 with -17.2% after short stem and -16.7% after straight implantation (p = 0.67). However, there was significantly less BMD reduction in ROI 6 following short (-4.7%) versus straight stem (-10.8%) implantation (p = 0.01). There were no significant differences between the two groups in terms of the HHS and the WOMAC either before or after surgery. One year after surgery, both stems showed an implant-specific periprosthetic bone remodelling. Nevertheless, proximal load transfer was more pronounced after short stem implantation than with a straight stem.

Trade-off between stress shielding and initial stability on an anatomical cementless stem shortening: in-vitro biomechanical study

Shortened cementless femoral stems have become popular with the advent of minimally invasive total hip arthroplasty (THA). Successful THA requires initial stem stability and prevention of stress shielding-mediated bone loss, although the effect of stem shortening is controversial. Here we experimentally examined whether stem shortening affects stress shielding and initial stability. Anatomical stems (length, 120 mm) were cut to an 80 mm or 50 mm length. Ten tri-axial strain gauges measured the cortical strain on each stem-implanted femur to evaluate stress shielding. Two transducers measured axial relative displacement and rotation under single-leg stance loading. The 50 mm stem increased the equivalent strains with respect to the original stem in the proximal calcar region (31.0% relative to intact strain), proximal medial region (63.1%), and proximal lateral region (53.9%). In contrast, axial displacement and rotation increased with a decreasing stem length. However, the axial displacement of the 50 mm stem was below a critical value of 150 µm for bone ingrowth. Our findings indicate that, with regard to a reduction in stem length, there is a tradeoff between stress shielding and initial stability. Shortening the stem up to 50 mm can promote proximal load transfer, but bone loss would be inevitable, even with sufficient initial stability for long-term fixation.

Metal-carbon fiber composite femoral stems in hip replacements: a randomized controlled parallel-group study with mean ten-year follow-up.

Attempts to improve proximal load transfer and minimize stress shielding have included reducing the stiffness of femoral stems and using alternative stem materials, including carbon fiber composites. An uncemented implant (SR71) composed of a carbon-fiber-composite distal section and a porous-coated titanium-alloy proximal section, designed to improve proximal load transfer and provide good fixation, was clinically evaluated in a prospective randomized study. Sixty patients were enrolled and randomized to receive either the SR71 stem or an all-metal stem (Stability). All patients received a cemented all-polyethylene acetabular component and a 28-mm metal femoral head. All uncemented stems were implanted by the same surgeon. Patients were followed for up to ten years with repeated assessments of bone mineral density, radiographs, Harris hip scores (HHS), and visual analog scale (VAS) pain scores. Ten years postoperatively, nineteen patients who had been treated with the SR71 stem and not lost to follow-up showed a significantly greater increase in proximal bone mineral density (Gruen zones 1 [p = 0.003] and 7 [p = 0.0007]) from baseline than did the twenty-two who had been treated with the Stability stem and not lost to follow-up. In contrast, the Stability group showed a significantly greater increase in distal bone mineral density (Gruen zones 2 [p = 0.0004], 3 [p = 0.0001], and 5 [p = 0.0035]) compared with the SR71 group. Radiographs demonstrated one case of progressive migration of an acetabular component used with an SR71 stem and one case of bone resorption in Gruen zones 7 and 14 in a patient treated with a Stability stem. There was no significant difference between the SR71 and Stability stems in terms of changes in the total HHS, HHS for pain, HHS for range of motion, or VAS pain scores ten years postoperatively relative to preoperative levels. There was one reported revision of an SR71 femoral stem at the ten-year review. The investigational SR71 implant provided increased proximal bone density and reduced distal bone density. The implant showed promising results at the time of early follow-up, and the clinical outcomes were similar to those of an all-metal stem at the time of a ten-year follow-up.

A Complication During Femoral Broaching in Total Hip Arthroplasty: A Case Report

Press-fit component fixation is one of the primary goals in uncemented total hip arthroplasty. When aiming at proximal load transfer, the stem size has to be selected with regard to the shape of the proximal femoral canal. This can be challenging in patients with ‘champagne flute’ femurs with a relatively narrow diaphysis, especially when a long stem femoral component is used. The present case report describes a complication during femoral broaching for a primary uncemented femoral component. Because of the narrow diaphysis, the distal portion of the broach got caught in the narrow canal and it became impossible to remove the broach with conventional techniques. Via a second distal incision, the femur was split from the distal tip of the broach to approximately 5 cm distal of the femoral neck cut along the posterior aspects of the femur. This loosened the broach enough to allow for an uncomplicated removal. The longitudinal split was secured with cables before a similar size primary implant was press fitted into the femoral canal.

Versatile application of short stem during total hip arthroplasty

Total hip arthroplasty (THA) is one of the most commonly performed orthopedic surgery worldwide. Current research and development had improved the designs of modern total hip prosthesis. Although long femoral stems are widely used, short stems are thought to preserve more native host bone and optimize proximal load transfer utilized with the advent of less invasive surgery. Modular short femoral stems in THA may have versatile applicability by virtue of their unique geometry, mechanism of fixation, and modularity. In this report, we present two unique case scenarios where the use of short stems has given successful results.

Modified Metaphyseal‐Loading Anterolaterally Flared Anatomic Femoral Stem: Five‐ to Nine‐Year Prospective Follow‐Up Evaluation and Results of Three‐Dimensional Finite Element Analysis

We have designed a proximal-fitting, anterolaterally flared, arc-deposit hydroxyapatite-coated anatomical femoral stem (FMS-anatomic stem; KYOCERA Medical, Osaka, Japan) for cementless total hip arthroplasty (THA) for Japanese patients with dysplastic hip osteoarthritis, using a nonlinear three-dimensional finite element analysis simulating loading conditions. The Anatomic Fit stem was modified in the region of the arc-sprayed surface, to allow more proximal appearance of spot welds. The aim of the present study was to analyze the clinical and radiographic outcomes of patients who underwent THA using this stem. We reviewed 73 consecutive patients (79 hips; 13 men 16 hips; 60 women 63 hips; age at surgery, 57.6 years, range, 35-78) who underwent cementless THA using the Anatomic Fit stem, at a follow-up period of 7.1 years (range, 5.1-9.4). Harris Hip score improved from 40.7 ± 17.1 before surgery to 91.0 ± 5.2 points at follow-up. The 7.1-year stem survival rate was 100%. Radiographs at follow-up confirmed the stability of the femoral stems within the femoral canal in all cases, with sufficient bone ingrowth. None of the patients had subsidence of the stem exceeding 2.0 mm within the femoral canal or changes in varus or valgus position of more than 2.0°. The Anatomic Fit stem provided excellent results. The nonlinear three-dimensional finite element analysis demonstrated that the stem-bone relative motion was 10 µm at the proximal end of the stem and proximal load transfer. Our analysis confirmed reduced radiolucency around the stem, minimal subsidence, appropriate stress shielding, and promising medium-term stability within the femoral canal.

Bone Remodelling around A Cementless Straight Tha Stem: A Prospective Dual-Energy X-Ray Absorptiometry Study

The design of the Bicontact® stem (BBraun, Aesculap, Tuttlingen, Germany) and the implantation technique have undergone no major alterations in the last 20 years leading, and good clinical results have been reported. The aim of our study was to investigate whether the implant encourages beneficial bone remodelling. Twenty-four patients were included in a prospective dual-energy X-ray absorptiometry (DEXA) study of this stem, after appropriate statistical power analysis. Preoperative and postoperative (1 week, 6 months, and 12 months) clinical and DEXA examinations were performed. The Harris Hip Score increased significantly by 39 points. The strongest decreases in BMD were observed in the greater trochanter region (-11%) and the calcar (-12%). In the second half of the study period the bone mineral density recovered slightly and even returned to baseline values in the lesser trochanter region. Therefore, proximal load transfer and physiological bone remodelling around the Bicontact® stem appeared to be achieved.

Bone remodelling around the Metha short stem in total hip arthroplasty: a prospective dual-energy X-ray absorptiometry study

On the basis of positive clinical results with mid- and long-term follow-up using the Mayo short stem, the Metha neck-preserving stem (BBraun, Aesculap, Tuttlingen, Germany) was introduced. The purpose of this study was to validate the implant design by direct acquisition of bone remodelling data from total hip arthroplasty (THA) recipients using dual-energy X-ray absorptiometry (DEXA). After power analysis, 25 patients were included in this prospective study. Patients were examined clinically and underwent DEXA examinations preoperatively and postoperatively at one week, six months and one and two years after THA. Gruen zones were adapted to the short stem design (R1-R7). The Harris Hip Score (HHS) increased significantly by 31 points. No stem had to be revised. Bone mineral density (BMD) in the greater trochanter decreased significantly from 0.78 g/cm(2) postoperatively to 0.72 g/cm(2) two years after surgery. Marginal changes were seen in the lateral distal regions (R4-R5). In the minor trochanter region, BMD increased significantly after two years by 12.9%. In the calcar region, BMD exceeded the baseline value by 6.1% two years after implantation. Stress shielding seems to occur at the greater trochanter due to the vast cross-section of the implant. However, the aim of proximal load transfer of the Metha stem seems to be partially achieved. DEXA analysis revealed a concentrated load distribution on the medial portion of the femur, which is an important region to guarantee long-term implant survival.

Biomechanical evaluation of different offset versions of a cementless hip prosthesis by 3-dimensional measurement of micromotions

BackgroundCementless hip prostheses with different offsets are frequently used to restore the rotation center of the hip. However, a rising offset is theoretically associated with a potential risk for increased interface stresses and early loosening. MethodsTo assess this potential risk for cementless stems, the primary stability of the CLS Spotorno stem was examined with respect to three different femoral neck versions (125°, 135° and 145°) measuring 3-dimensional micromotions. For this purpose 18 stems were implanted in composite femurs and tested dynamically using physiological loading conditions considering the necessary adaptation according to the different offsets. Additionally the deformations at the surface of the composite femur were recorded to draw conclusions about the tendency for stress shielding. FindingsThe micromotions of the different offset versions were not significantly different. The highest values were obtained at the tip of the stems, even exceeding the critical limit for osseous integration of 150μm. Compared to untreated composite femurs the alteration of the deformations at the surface remained relatively low. A significant difference was only observed in the ventral measurement points. InterpretationAccording to the measured micromotions no offset version of the CLS Spotorno can be declared as superior. The assumption that the varus version is characterized by extended interface stresses could not be confirmed. Furthermore, it could be demonstrated that according to the principle of proximal load transfer of the CLS Spotorno stem an osseous integration of the distal part cannot be expected and that the risk for stress shielding appears to be relatively low.

Bleibt der Krafteinfluss der Kurzschaftprothese auf den methaphysären proximalen Femur begrenzt? Osteodensitometrische Analysen der NANOS®-Schaftendoprothese

It has been suggested that the use of a short-stem prosthesis could conserve proximal bone by proximal load transfer. Proximal stress shielding should be reduced, a phenomenon that has been associated with bone resorption around traditional stems. Bone remodelling of a metaphyseal fixed stem (Nanos, Smith & Nephew Int.) was analysed by the dual-energy x-ray absorptiometry. This study included 36 patients undergoing the total hip replacement using the Nanos short stem in comparison to 36 patients operated by a traditional long-stemmed femoral stem (Alloclassic). In all cases a threaded cup was inserted. Both groups were not different in regard to the BMI or in regard to the quality of bone (BMI). The average age of the group of patients with the short-stem prosthesis was slightly younger (average 54.2 years [range: 29 to 75]) than the patient group with the long-stem prosthesis (average 61.1 years [range: 39 to 71]). A prospective clinical analysis was done by the Harris hip score (HHS) and the Sutherland score to evaluate the social quality of life. With a minimum follow-up of 12 months in all cases, radiological changes in regard to stem subsidence, periprosthetic osteolysis or linear radiolucencies were analysed. The changes of periprosthetic bone density were examined with DEXA in all patients 3 and 12 months postoperatively. No patients required reoperation because of loosening or subsidence of the short-stem prosthesis. The HHS improved from a mean of 43.1 (range: 9 to 51) to 96.5 points (range: 79 to 100) in the short-stem group and to 91.3 points (range: 61 to 100) in the group of patients with long-stemmed femoral component. Radiographic follow-up revealed no evidence of component loosening or migration of the short-stem. Along the greater trochanter an osteolysis of the bone structure was found in two cases. A decrease of the proximal periprosthetic bone density (Gruen zone I, -6.4%) and in zone VII (-7.2%) were measured. An increase of the BMD in the lateral inferior region (Gruen zone II, +9.7%) superior to the polished tip of the short stem was observed over a period of one year after implantation. At the polished tip of the prosthesis a significant change of bone density in zone III (+1.03%) and in zone V (+0.7%) could not be observed. The desired proximal load transfer of a short-stemmed implant in the metaphyseal region of the proximal femur could not be reached with this device. On the basis of the excellent clinical results of the patients operated with the Nanos short-stem prosthesis we conclude that the component induces bone ingrowth in the lateral/distal region of the proximal femur.

The DePuy Proxima™ Hip: A Short Stem for Total Hip Arthroplasty. Early Experience and Technical Considerations

The rationale for short stems in cementless total hip arthroplasty (THA) is proximal load transfer and absence of distal fixation resulting in preserved femoral bone stock and avoidance of thigh pain. We report a consecutive series of 65 THAs inserted mainly for osteoarthritis with the DePuy Proxima hip, a short, anatomic implant with a pronounced lateral flare. Patients were assessed preoperatively and postoperatively at 3, 6 and 12 months and annually thereafter, using the Harris Hip Score (HHS), the Oxford Hip Score (OHS) and standard radiographs. No thigh pain was reported. Ata mean follow-up of 1.7 years the HHS improved from a preoperative mean value of 51 to 91 and the OHS decreased from a mean value of 42.5 to 12.4. Complications included 1 intraoperative fracture,1 superficial infection, and 3 deep vein thromboses. The proximal medial edge of the resected femoral neck appeared rounded off in 49 cases whilst in 16 cases a further loss of medial cortical density was observed. Patient selection and surgical technique are crucial factors contributing to a successful outcome. The surgical technique is different from standard THA.

Changes in periprosthetic bone remodelling after redesigning an anatomic cementless stem

The aim of this prospective cohort study was to determine the densitometric relevance of minor design modifications of a cementless stem designed to improve proximal load transfer. We used a prospective cohort study with densitometric analysis over a five-year period of two groups of patients with primary osteoarthritis. The first group, 56 hips, received the first version of the ABG stem (ABG-I); the second group, 54 hips, had the ABG-II stem. The results obtained with the ABG-I stem showed a decrease of bone density in proximal areas that ranged from 13% to 37%. However, the new design had a decrease of the same areas that ranged from 9% to 23%. These differences were noted at the end of the first post-operative year and remained stable, except in zone 7, where they were progressive. There is little evidence that the modified stem reduces femoral bone density loss.

Effect of robotic milling on periprosthetic bone remodeling

The ROBODOC system has provided better fit and fill of the stem and less destruction of the bony architecture than with manual surgery. These benefits might affect femoral periprosthetic bone remodeling. We evaluated the effects of robotic milling in cementless total hip arthroplasty (THA) in a longitudinal 24-month follow-up study using dual energy X-ray absorptiometry (DEXA) and plain radiographs of 29 patients (31 hips) after ROBODOC THA and 24 patients (27 hips) after manual THA with the same stem design. To minimize the influence of other factors on bone remodeling, only female osteoarthritis patients, who had no drugs that might affect bone metabolism were enrolled. Significantly less bone loss occurred at the proximal periprosthetic areas in the ROBODOC group. In zone 1, the decrease was 15.5 versus 29.9% using conventional rasping; in zone 7, the loss was 17.0% with ROBODOC compared to 30.5% with conventional rasping (p < 0.05). On radiographs, endosteal spot welds in the proximal medial portion were more pronounced in the ROBODOC group (48 vs. 11% in the conventional group, p < 0.05). Our results suggest that robotic milling is effective in facilitating proximal load transfer around the femoral component and minimizing bone loss after cementless THA.