Changes of the bone mineral density in proximal femur following total hip resurfacing arthroplasty in osteonecrosis of femoral head

Total hip resurfacing arthroplasty (THRA) is being performed with increasing frequency for osteonecrosis of femoral head (ONFH). To evaluate femoral bone remodeling in ONFH after THRA and determine the impact of stem‐neck angle (SNA) of inserted femoral component on bone remodeling, we monitored the changes in BMD in proximal femur in 23 patients with ONFH after surgery. Patients were divided into group A (SNA ≥ 5°) and group B (SNA < 5°). The BMD was measured in seven Gruen zones and two neck zones using dual‐energy X‐ray absorptiometry preoperatively, then at 3, 6, 12, and 24 months after surgery. At all ROIs, the BMD decreased significantly by 3 months postoperatively. The BMD ceased to decrease and reversed by 6 months. The BMD in neck increased significantly in group A, compared with group B at 24 months. The BMD increased 2% at ROI1 at 24 months in both groups, and at ROI7, the BMD in group A reversed to baseline value by 6 months and increased 5.81% at 24 months. These findings implied that the bone stock of proximal femur in ONFH can be well reserved after total hip resurfacing arthroplasty with valgus positioning of the femoral component. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:453–459, 2008     

Sequential changes in periprosthetic bone mineral density following total hip arthroplasty: a 3-year follow-up

 We sequentially measured the periprosthetic bone mineral density (BMD) of the femur after cementless total hip arthroplasty, using dual-energy X-ray absorptiometry, over a 3-year period. The periprosthetic bone was divided into three regions (proximo-medial, middle, and distal to the prosthetic stem). After the insertion of a fully porous coated stem in 21 patients, the BMD was measured within 3 weeks, and 6, 12, 24, and 36 months after surgery. At 6 months, all zones showed a decrease in BMD relative to the BMD within 3 weeks, but subsequently the BMD was unchanged. The lower the BMD within 3 weeks of surgery, or the lower the body weight, the higher the percent loss of BMD at 6 months. Received: September 9, 2002 / Accepted: December 12, 2002 RID="*" ID="*" Offprint requests to: H. Ohta     

Determination of bone mineral density by dual x-ray absorptiometry in patients with uncemented total hip arthroplasty.

Bone remodeling is an expected sequela with total hip arthroplasty (THA). Although there are several methods of estimating bone response in THA patients from radiographs, there are no accurate and generally accepted methods for quantitative determinations in vivo. In this study, we describe an application of dual x-ray absorptiometry (DXA) for measuring bone mineral content and bone mineral density in the proximal femur following THA. DXA is a noninvasive technique with minimal radiation exposure (< 5 mrem). Various aspects of measurement error (accuracy and reliability) of this application of DXA were determined in a series of studies reported here. Accuracy error (how similar are the measured and actual values) was < 1% determined in bone phantoms of four densities. Precision error (how reproducible are the measurements) was also < 1% at all four densities in the phantoms and was only slightly elevated (0.9-1.5%) in repeated measurements of implanted cadaver femora. Precision error in vivo, determined both from multiple replicates on five patients and from duplicate scans on 30 patients, was further elevated but remained < 5%. Contributions to precision error, rotation of the leg, and interoperator variability were assessed; none was found to elevate precision error appreciably. We suggest that DXA is a feasible method for quantifying bone response following THA, and will allow discrimination of small changes (> 5%) not previously measurable.     

股骨假体周围骨密度定量测定

目的 通过双能X线骨密度仪测定不同情况下股骨假体周围的骨密度变化情况,了解骨丢失与股骨假体松动的关系。方法 分为骨水泥固定的股骨假体组、非骨水泥固定的股骨假体组、股骨假体松动组共3个组,采用LUNAR DPXL-L型双能X线骨密度仅(Lunar Corp Wisconsin,USA)及Orthopaedies软件,分析时用Gruen’s 7区法。结果 骨水泥固定的股骨假体组骨丢失为15．1%～29．3%,非骨水泥固定的股骨假体组骨丢失为13．2％～27．9%,股骨假体松动组骨丢失为25．4％～43．4%,3组均是股骨近端骨丢失明显．骨丢失主要发生在术后8年以内。结论 骨水泥固定的股骨假体和非骨水泥固定的股骨假体周周骨密度降低一样,假体松动者假体周围骨丢失明显增加。股骨近端2个以上区域骨丢失大于35％或术后8年以后突然出现明显的骨丢失,考虑有股骨假体松动存在的可能性。     

Measurement of periprosthetic bone mineral density after cementless hip arthroplasty by dual energy X-ray absorptiometry: Longitudinal and cross-sectional evaluation

To clarify changes in bone mass around a femoral prosthesis, periprosthetic bone mineral density (BMD) was measured by dual energy X-ray absorptiometry (DXA) in 60 patients after unilateral cementless hip arthroplasty. Changes in BMD were evaluated by cross-sectional analysis in all patients and by longitudinal analysis in 26 patients who were available for measurement from 1 month to 2 years after surgery. The mean reproducibility of BMD measurements was within 1.74% in vivo. Periprosthetic BMD began to decrease early after surgery, and although it recovered temporarily within 1 year, it did not return to the level of the 1st month even after 2 years. BMD was reduced by 30.4% in the whole periprosthetic region compared with the contralateral untreated femora 4–7 years after surgery. The reduction in BMD was remarkable around the proximal part of the stem, especially in zone 7 (44.7% reduction 4–7 years after surgery). Significant positive correlations were observed between the low level of the preoperative cortical remodelling index and the reduction in BMD and between the preoperative femoral BMD and the reduction in BMD, indicating that the postoperative bone loss was greater in patients who preoperatively showed quantitative and qualitative deterioration of the femur. Abstracts of this paper were presented at the 66th and 67th Annual Meeting of the Japanese Orthopaedic Association, the 19th Conference of Société Internationale de Chirurgie Orthopédique et de Traumatologie (SICOT), and the 20th Conference of the Japanese Hip Society     

Larger femoral periprosthetic bone mineral density decrease following total hip arthroplasty for femoral neck fracture than for osteoarthritis: A prospective,observational cohort study

Studies on patients with degenerative joint disease of the hip show that femoral periprosthetic bone mineral decreases following total hip arthroplasty. Scarcely any osteodensitometric data exist on femoral neck fracture (FNF) patients and periprosthetic bone remodelling. In two parallel cohorts we enrolled 87 patients (mean age, 72 ± 12 years; male:female ratio, 30:57) undergoing total hip arthroplasty for either primary osteoarthritis (OA) of the hip (n = 37) or for an acute FNF (n = 50) and followed them for a mean of 5.4 years. Outcomes were bone mineral density (BMD) changes in the periprosthetic Gruen zones 1–7, the incidence of periprosthetic fractures and clinical outcome. The bone mineral loss in the fracture group was more than twice that of the osteoarthritis group, ?16.9% versus ?6.8% (p = 0.004). The incidence of periprosthetic fractures was 12% (6/50) in the fracture cohort compared with none (0%) in the OA cohort (p = 0.03). Periprosthetic bone mineral loss following total hip arthroplasty is significantly greater in patients who are treated for acute FNF than in OA patients. This decrease of BMD follows a different pattern with the FNF patients losing larger proportions of bone in Gruen zones 1, 2, 6, and 7 while the OA patients tend to have larger losses only in zones 1 and 7. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:504–512, 2015.

     

Gait analysis of patients with resurfacing hip arthroplasty compared with hip osteoarthritis and standard total hip arthroplasty

Patients with standard total hip arthroplasties may have reduced hip abduction and extension moments when compared with normal nonosteoarthritic hips. In comparison, patients after resurfacing total hip arthroplasty appear to have a near-normal gait. The authors evaluated temporal-spatial parameters, hip kinematics, and kinetics in hip resurfacing patients compared with patients with unilateral osteoarthritic hips and unilateral standard total hip arthroplasties. Patients with resurfacing walked faster (average 1.26 m/s) and were comparable with normals. There were no significant differences in hip abductor and extensor moments of patients with resurfacing compared with patients in the standard hip arthroplasty group. This study showed more normal hip kinematics and functionality in resurfacing hip arthroplasty, which may be due to the large femoral head.     

Risedronate reduces postoperative bone resorption after cementless total hip arthroplasty

Summary Forty-three patients who had undergone cementless THA were randomly assigned to receive no osteoactive drug or oral risedronate for 6 months. Postoperative decrease of BMD in the risedronate group was significantly lower than that seen in the control group in zones 1, 2, 3, 6, and 7. Introduction Proximal bone resorption around the femoral stem often has been observed after total hip arthroplasty (THA), could lead to late stem loosening. We previously reported the efficacy of etidronate on periprosthetic bone resorption after cementless THA. Recently risedronate is suggested to be effective for the prevention and treatment of for osteoporosis. The purpose of the present study was to evaluate the effects of risedronate on periprosthetic bone loss after cementless THA. Methods Forty-three patients who had undergone cementless THA were randomly assigned to receive no osteoactive drug (21 patients) or oral risedronate 2.5 mg/day (22 patients) for 6 months. Three patients were eliminated from the risedronate group because of dyspepsia. Periprosthetic bone mineral density (BMD) in seven regions of interest based on the zones of Gruen et al. was measured with dual energy X-ray absorptiometry at 3 weeks and 6 months postoperatively. Results At 6 months after surgery, postoperative decrease of BMD in the risedronate group was significantly lower than that seen in the control group in zones 1, 2, 3, 6, and 7 (p < 0.05, p < 0.01, p < 0.01, p < 0.05, and p < 0.05, respectively). Conclusion These outcomes suggested that risedronate might reduce the periprosthetic bone resorption after cementless THA.     

利塞膦酸钠对非骨水泥型全髓关节置换术后早期股骨假体周围骨密度的影响

目的 探讨利塞膦酸钠对非骨水泥型全髋关节置换术后早期股骨假体周围骨密度的影响及治疗作用,以其为临床提供防止假体周围骨丢失和松动的预防措施和处理方法.方法 2011年3月～2012年5月于本院行非骨水泥型人工全髋关节置换术中符合纳入标准的患者共26例随机分成利塞膦酸钠组与对照组;试验组术后每日口服利塞膦酸钠5 mg+钙剂600 mg,而对照组仅服用钙剂600 mg;分别于术后1周、3、6个月测定股骨近端各感兴趣区(ROI)的骨密度.结果 获得完整病例24例,术后3、6个月各区骨密度均呈持续下降趋势,和对照组相比,术后3个月利塞膦酸钠组股骨假体(ROI1、ROI7)的差异有统计学意义(P＜0.01),其余各测量区骨密度2组相比差异无统计学意义(P＞0.05).与对照组相比,术后6个月利塞膦酸钠组股骨假体(ROI1、ROI7)的差异有统计学意义(P＜0.01),其余各测量区骨密度2组相比差异无统计学意义(P＞0.05).结论 利塞膦酸钠能够有效的减少非骨水泥型全髋关节置换术后假体周围的骨丢失,从而减缓假体松动,延长假体使用寿命.     

Comparison of bone mineral density changes around short, metaphyseal-fitting, and conventional cementless anatomical femoral components

We investigated the incidence and degree of stress shielding and clinical and radiographic results in 2 groups of patients. Fifty patients (60 hips) in each group were enrolled for a randomized study. One group received a short, metaphyseal-fitting femoral component and another group received a conventional metaphyseal- and diaphyseal-filling femoral component. The mean follow-up was 3.35 years in both groups. Bone mineral density was significantly increased in femoral zone 1 but slightly decreased in zone 7 in the short, metaphyseal-fitting stem group. In the conventional metaphyseal- and diaphyseal-fitting stem group, bone mineral density was markedly decreased in both zones 1 and 7. Clinical and radiographic results were similar between the 2 groups. No hip in either group required revision of the component.     

全髋关节表面置换术后股骨近端骨密度的变化

目的评价全髋关节表面置换术对股骨近端骨量变化的影响。方法2002年7月至2005年6月,对行全髋关节表面置换术（表面置换组）和人工全髋关节置换术（全髋置换组）各26例患者作为研究对象,均在术前、术后3、6、12和24个月时对股骨近端按Gruen分区设为7个测量感兴趣区,表面置换组加股骨颈外上和内下区,应用双能X线吸收测定仪测定骨密度,比较两组术前和术后股骨近端骨密度变化。结果术后3、6、12和24个月时,表面置换组股骨近端骨密度分别降低5．8％、4．9％、2．6％和0．4％;测量感兴趣区1的骨密度术后6个月时降至89．7％,至24个月时增至103．8％;测量感兴趣区7的骨密度术后6个月时降至95．1％,24个月时增至103．7％;股骨颈部骨密度在术后6个月时即可恢复至术前水平,股骨颈外上区的骨密度术后3个月时降至97．1％,术后24个月时增至107．4％（P〈0．05）;股骨颈内下区的骨密度术后24个月时增至117．9％（P〈0．05）。全髋置换组股骨近端骨密度分别降低7．0％、10．6％、1．0％和4．1％。测量感兴趣区1的骨密度术后6个月降至90．8％,术后24个月时为94．4％;测量感兴趣区7术后3个月降至94．2％,术后24个月时为96．7％。结论全髋关节表面置换术后股骨近端骨量可以得到有效保存和恢复。     

Influence of bone density on the cement fixation of femoral hip resurfacing components

In clinical outcome studies, small component sizes, female gender, femoral shape, focal bone defects, bad bone quality, and biomechanics have been associated with failures of resurfacing arthroplasties. We used a well‐established experimental setup and human bone specimens to analyze the effects of bone density on cement fixation of femoral hip resurfacing components. Thirty‐one fresh frozen femora were prepared for resurfacing using the original instruments. ASR? resurfacing prostheses were implanted after dual‐energy X‐ray densitometer scans. Real‐time measurements of pressure and temperature during implantation, analyses of cement penetration, and measurements of micro motions under torque application were performed. The associations of bone density and measurement data were examined calculating regression lines and multiple correlation coefficients; acceptability was tested with ANOVA. We found significant relations between bone density and micro motion, cement penetration, cement mantle thickness, cement pressure, and interface temperature. Mean bone density of the femora was 0.82 ± 0.13 g/cm², t‐score was ?0.7 ± 1.0, and mean micro motion between bone and femoral resurfacing component was 17.5 ± 9.1 µm/Nm. The regression line between bone density and micro motion was equal to ?56.7 × bone density + 63.8, R = 0.815 (p < 0.001). Bone density scans are most helpful for patient selection in hip resurfacing, and a better bone quality leads to higher initial component stability. A sophisticated cementing technique is recommended to avoid vigorous impaction and incomplete seating, since increasing bone density also results in higher cement pressures, lower cement penetration, lower interface temperatures, and thicker cement mantles. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:986–991, 2010     

Bone mineral density and biochemical markers of bone turnover in aseptic loosening after total hip arthroplasty.

The aims of this study were to determine whether subjects with aseptic loosening after total hip arthroplasty (THA) have regional differences in periprosthetic bone mineral density (BMD) and systemic biochemical markers of bone turnover compared to subjects with successful implants.Proximal femoral and pelvic BMD were measured by dual energy X-ray absorptiometry and bone turnover markers were assayed in 49 subjects 12.6+/-4.3 (mean+/-SD) years after cemented THA. Femoral BMD was lower in Gruen zones 2, 5, 6, and 7 in subjects with a loose femoral implant (n=17) compared to those (n=32) with fixed femoral implants (P<0.05 all comparisons). This BMD difference was greatest (-31%, P=0.02) in the proximal and medial region of the femur. Subjects with femoral loosening had higher levels of the bone resorption marker N-telopeptides of type-I collagen (P=0.02) than those with a fixed femoral implant. No differences in pelvic BMD or bone turnover markers were found between subjects with loose (n=18) versus fixed (n=31) pelvic implants.This study suggests that failure of femoral components after cemented THA is associated with region-specific decreases in BMD and an increase in urinary excretion of N-telopeptide cross-links of type-I collagen. These surrogate outcome markers may be of value in monitoring response to antiresorptive therapies used to treat periprosthetic osteolysis, although the diagnosis of aseptic loosening remains clinical and radiological.     

Dual X-ray absorptiometry for the evaluation of bone density from the proximal femur after total hip arthroplasty: Analysis protocols and reproducibility

Summary Dual X-ray absorptiometry (DXA) instruments are now able to evaluate bone mineral density (BMD) of bone surrounding metal implants. The assessment of BMD around prosthetic components could provide additional information for the follow-up of total hip arthroplasty (THA). In this study, we evaluated the potential application of DXA in the field of THA. BMD was measured in the proximal femur of both THA and THA-free sides in 14 postmenopausal women 6–18 months after THA. The explored segment was divided into seven zones as proposed by Gruen et al. [18]. The precision error of BMD measurements ranged from 1.8 to 6.8% on the THA side and from 1.1 to 2% to the THA-free side. The reduction of BMD of the THA versus the THA-free side was significant in all seven zones (P < 0.01, t-test for paired data). These results showed significant differences in BMD around femoral components of THA with respect to contralateral healthy side, and demonstrate the sensitivity of DXA for detecting these changes.     

Changes of femoral periprosthetic bone mineral density 6 years after treatment with alendronate following total hip arthroplasty

Earlier osteodensitometric results of femoral periprosthetic bone showed that postoperative antiresorptive treatment with alendronate following total hip arthroplasty (THA) reduces the periprosthetic bone loss that commonly occurs in the first months after surgery. However, whether alendronate can prevent periprosthetic bone loss over the long term, or if bone loss occurs after discontinuing alendronate is unknown. Femoral periprosthetic bone mineral density (BMD) was assessed in 49 patients 6 years after cementless total hip arthroplasty using dual energy X‐ray absorptiometry. Twenty‐nine patients were treated postoperatively with alendronate and 20 control patients received no treatment. All patients were followed up at 12 months after surgery in a prospective randomized study. The bone mineral density was evaluated in 7 regions of interest according to the Gruen protocol. Six years after total hip arthroplasty, no significant changes were detected in femoral periprosthetic BMD when compared with results at 1 year, and the bone loss in patients with postoperative alendronate treatment was still significantly less than those without treatment. These results suggest that the prevention of femoral periprosthetic bone loss following THA achieved by postoperative antiresorptive treatment with alendronate is of long‐standing effect, and further bone loss does not occur after the first postoperative year. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:183–188, 2009     

髋关节骨性关节炎及髋臼发育不良对髋关节表面置换术中髋臼安装角度的影响

[目的]研究全髋关节表面置换术中,单纯骨性关节炎及髋关节发育不良对髋臼安装角度的影响及两组病例疗效比较。[方法]自2006～2009年,本科共实施全髋表面关节置换术20例23髋,病因包括单纯骨性关节炎10髋及髋关节发育不良13髋。手术假体均采用金属对金属大直径表面置换假体,股骨侧骨水泥固定,髋臼侧生物型固定。[结果]所有患者均获得近期随访(6个月～3年),随访包括临床评估和放射学评估。两组患者术前术后Harris评分均无明显统计学差异。无一发生术后脱位、股骨颈骨折等并发症。其中单纯骨性关节炎患者术后臼杯外展角25.6°～56.0°(平均43.9°±9.9°),平均髋臼覆盖率达95.8%。髋臼发育不良患者术后臼杯外展角22.4°～69.3°(平均46.8°±12.9°),髋臼覆盖率达84.3%。[结论]金属对金属大直径表面置换假体在治疗单纯骨性关节炎及髋关节发育不良早期临床疗效并无明显统计学差异。但是髋关节发育不良患者行髋关节表面置换术中,髋臼假体外展角离散度要明显高于单纯骨性关节炎组,其髋臼杯假体外展角度控制要难于单纯骨性关节炎。     

Co and Cr accumulation in hair after metal-on-metal hip resurfacing arthroplasty

Background: Currently, it is unclear whether Co and Cr levels are persistently elevated in the body after hip resurfacing arthroplasty (HRA). This study aimed to evaluate Co and Cr levels in the body after HRA using hair as samples. Methods: Among 22 patients who had metal‐on‐metal HRA (m‐o‐m group) using the DePuy ASR system, scalp hair of 1.5 cm in length and 2 g in weight was collected before and at 6 and 12 months after surgery. Inductively coupled plasma‐mass spectrometry (ICP‐MS) was used to detect Co and Cr levels in the scalp hair. Another 22 patients with total hip replacements were randomly selected from a similar age range as controls (m‐o‐p group). Metal levels in hair were detected with multiple measurements and analysed by repeated measures analysis of variance. Results: Both Co and Cr levels were significantly increased in the m‐o‐m group after surgery compared with those in the m‐o‐p group (P < 0.01). Co levels at 6 months post‐operatively were 12‐fold those before surgery, and Co levels 12 months post‐operatively were lower than those at 6 months, but this difference was not significant (P= 0.0805) between the two time points in the m‐o‐m group. Cr levels were persistently elevated after surgery and were increased by 10‐fold compared with those at baseline in the m‐o‐m group. Conclusions: Co and Cr levels in scalp hair are ideal indicators for metal levels in the body after HRA. Co and Cr levels in the body were greatly increased after metal‐on‐metal HRA. Long‐term accumulation of these metals needs to be further investigated.     

Gait symmetry: a comparison of hip resurfacing and jumbo head total hip arthroplasty patients

Proponents of large femoral head total hip arthroplasty (THA) and hip resurfacing arthroplasty (HRA) have touted the potential for restoration of more normal hip kinematics. This study examined 20 patients (10 THA and 10 HRA patients) approximately 18 months after surgery. Subjects were evaluated at a self-selected pace, while bilateral spatial-temporal gait variables, hip flexion/extension kinematics, and ground reaction forces were collected. For both groups, swing time was increased on the surgical side, whereas peak hip flexion, peak extension, and flexion at heel strike were decreased. Peak hip extension and peak vertical ground reaction forces were decreased in THA subjects compared with HRA subjects. After a large-diameter THA or HRA, subjects do not display symmetric gait approximately 18 months postoperatively. Total hip arthroplasty subjects demonstrated restricted hip extension and reduced limb loading when compared with HRA subjects.     

全髋表面置换术后发生股骨颈狭窄非手术相关危险因素分析

[目的]探讨全髋表面置换术(resurfacing arthroplasty of the hip,RSAH)术后发生股骨颈狭窄的非手术相关危险因素.[方法]回顾性分析行全髋表面置换术的患者53例(61髋),男31例,女22例;年龄26 ～ 54岁,平均45.3岁;体重指数(RMI)为20.4～37.8,平均为27.4.按病因学分类:股骨头坏死22例(26髋),先天性髋关节发育不良13例(15髋),骨性关节炎10例(12髋)和创伤性关节炎8例(8髋).观察术后股骨颈狭窄发生情况并分组,股骨颈狭窄率≥5％纳入研究组,＜5％列入对照组.对可能导致股骨颈狭窄的17个变量进行单因素分析,对差异有统计学意义的变量进行多因素非条件logistic回归分析.[结果]将37例(43髋)狭窄率＞0％且＜5％和未狭窄的病例纳入对照组;将16例(18髋)狭窄率≥5％的病例,纳入研究组.在研究组中,2例在术后1年于股骨头杯柄周围1、3区出现透光线;1例于术后2年出现假体松动、移位.单因素分析显示,体重指数、患髋疾病、颈干角、头颈比、股骨头囊肿大小及股骨假体柄固定方式6个变量差异有统计学意义(P值均＜0.05);多因素分析显示,患髋疾病、颈干角、头颈比为独立危险因素(P值均＜0.05).[结论]髋关节原发病的诊断、头颈比、颈干角是全髋表面置换术术后股骨颈狭窄发生的非手术独立危险因素.     

Changes in Bone Mineral Density of the Acetabulum and Proximal Femur After Total Hip Resurfacing Arthroplasty

Our aim was to investigate the changes in bone mineral density (BMD) of acetabulum and proximal femur after total hip resurfacing arthroplasty. A comparative study was carried out on 51 hips in 48 patients. Group A consisted of 25 patients (26 hips) who had undergone total hip resurfacing and group B consisted of 23 patients (25 hips) who had had large-diameter metal-on-metal total hip arthroplasty (THA). BMDs around the acetabulum and proximal femur were measured using dual-energy x-ray absorptiometry (DEXA) at 2 weeks, 6 months, 1 year and annually thereafter during the 3 years after surgery. At final follow-up, the acetabular net mean BMD decreased by 11% in group A and 10% in group B with no differences between two groups (P = .35). For the femoral side, in Gruen zone 1, the mean BMD increased by 4% in group A, whereas it decreased by 11% in group B (P = .029). In Gruen zone 7, the mean BMD increased by 8% at the final follow-up in group A, whereas it decreased by 13% in group B (P = .02). In both groups the mean BMD increased by 3% in Gruen zones 3, 4, 5, and 6. Stress-related bone loss of the acetabulum was comparable for MOM THA and resurfacing devices, but proximal femoral bone density increased in the resurfacing group and decreased in the THA group.