大直径股骨头金属对金属全髋关节置换术的近期临床疗效

目的 评价大直径股骨头(大头)金属对金属全髋关节置换术治疗晚期髋关节疾病的近期疗效,回顾性分析影响该类全髋关节置换术临床疗效的因素.方法 对2007年10月至12月,采用大头金属对金属全髋关节置换术治疗晚期髋关节疾病患者41例(49髋)进行术后随访.临床评估以Harris评分为标准,记录患髋的活动范围及并发症发生情况.影像学评估根据随访骨盆X线片及患髋正、侧位X线片,测量髋臼外展角、前倾角,记录髋臼和股骨假体周围透亮线和骨溶解情况.结果 截至随访终点,共39例(47髋)获得2年以上随访,平均随访25个月,随访率为95.1%.Harris评分由术前的(43.8±13.1)分提高到末次随访时的(92.0±5.4)分.患髋活动度较术前明显改善,术后3个月屈髋由79.8°增加至110.2°,外展由20.9°增加至38.3°,外旋由12.0°增加至26.0°;术后2年屈髋平均可达113.2°,外展可达40.2°,外旋可达30.8°.术后患者轻度跛行3例,大腿不适2例,所有患者均无感染、假体周围骨折、术后假体松动或脱位、术后异位骨化发生.X线片显示:关节假体位置正常,髋臼假体外展角为39.5°±4.9°,前倾角为14.5°±2.1°,髋臼未见松动、移位.术后均未发现透亮线和假体周围骨溶解.结论 大头金属对金属全髋关节置换术治疗髋关节疾病具有良好的近期疗效,特别适用于活动量大、预期寿命较长的年轻患者.

Abstract：

Objective To evaluate clinical and radiographic outcomes associated with total hip arthroplasty (THA) using metal-on-metal prosthesis with large diameter femoral head.Methods From October 2007 to December 2007,41 patients (49 hips) underwent large diameter femoral head metal-on-metal THA in our hospital were involved in this study.Clinical outcomes measures were Harris score,hip range of motion and incidence of complications.Abduction angle and anteversion angle of cup were measured on radiological films.The radiolucent line and osteolysis around the prosthesis were also recorded.Results Thirty-nine patients (47 hips) were followed up at least 2 years.The average Harris hip score had improved from (43.8±13.1) points preoperatively to (92.0±5.4) points at final follow-up.All the patients had attained satisfactory results.No late complication happened.For the rang of motion at final follow-up:flexion of the hip had improved from 79.8° to 113.2°,abduction had improved from 20.9° to 40.2°,external rotation had improved from 12.0° to 30.8°.Radiological measurement showed the mean abduction angle of cup was 39.5°±4.9°,the mean anteversion angle of cup was 14.5°±2.1°.No radiolucent line and osteolysis were found after THA.Conclusion The short-term effects of THA using metal-on-metal prosthesis with large diameter femoral head is encouraging,especially for young patients.     

全髋关节置换术后聚乙烯内衬磨损的测量及其临床意义

目的以计算机数字化方法计测人工全髋假体二维线性磨损,并探讨磨损程度与长期随访结果的临床相关性。方法利用计算机软件测量股骨头中心相对于髋臼中心的矢量位移,来决定关节面磨损的大小和方向。对 104髋非骨水泥型人工假体进行磨损计测、临床和放射学检查,平均随访时间为 8.4年。结果 14髋股骨或髋臼假体松动,假体松动率为 13.5％。平均线性磨损值为 1.14 mm,磨损率为 0.15 mm/年。聚乙烯磨损与髋臼侧骨溶解及假体松动相关 (P< 0.05)。多因素回归分析未发现磨损和患者年龄、体重、髋杯大小和外展角、活动量水平以及 Harris髋关节评分的相关关系。结论此方法可应用于各种不同设计的人工假体内衬的二维磨损测量。磨损与骨溶解显著相关,并与假体松动互为因果。因此,在进行临床随访、放射学观察的同时,磨损情况也是全面评价全髋置换术临床结果的一个重要指标。     

3D打印髋关节旋转中心定位器在全髋关节置换术中的辅助作用

目的探讨3D打印髋关节旋转中心定位器在全髋关节置换术中的辅助作用。方法回顾性分析2015年8月至2017年12月期间郑州市骨科医院关节Ⅰ科采用单侧人工全髋关节置换术治疗的14例股骨头缺血性坏死或股骨颈骨折患者资料。男8例,女6例;年龄为37~65岁,平均51.8岁。运用3D打印髋关节旋转中心定位器辅助进行全髋关节置换术。术后测量臼杯的外展角、前倾角及髋关节旋转中心,记录患者手术后髋关节旋转中心O2(患侧)与解剖旋转中心O1(健侧)的符合情况、末次随访时髋关节功能及并发症发生情况。结果14例患者术后获6~24个月(平均18个月)随访。髋关节旋转中心O2与解剖旋转中心O1的纵坐标分别为(19.36±3.61)、(18.33±3.41)mm,横坐标分别为(39.93±2.97)、(39.99±3.16)mm,差异均无统计学意义(P>0.05),旋转中心符合。术后患侧外展角与髋臼前倾角均在正常范围内:外展39.3°±3.2°,前倾14.6°±1.2°。末次随访时14例患者的髋关节Harris评分由术前(42.3±3.2)分提高至(94.3±4.7)分,差异有统计学意义(t=2.873,P=0.002);优13例,良1例。随访期间X线片示假体位置良好,无髋臼及股骨假体松动,未见异位骨化形成。结论3D打印髋关节旋转中心定位器应用于人工全髋关节置换术,可有效协助髋关节旋转中心的重建,精准植入髋臼假体。     

Guidelines for Implant Placement to Minimize Impingement During Activities of Daily Living After Total Hip Arthroplasty

Impingement, both prosthetic and bony, precedes the vast majority of dislocations after total hip arthroplasty and may adversely impact component wear. Reconstructed computer hip models of 8 subjects were used to evaluate hip range of motion for activities of daily living (ADLs) associated with posterior instability and anterior instability. Variables examined included acetabular position, femoral offset, and head size. The majority of flexion ADLs (associated with posterior instability) encountered prosthetic impingement, whereas extension ADLs demonstrated bony impingement with the 45/20 cup placement position. Cup placement in natural anteversion and adduction allowed normal joint motion in anterior and posterior impinging activities. Insufficient femoral offset and smaller head size negatively impacted range of motion. Any anterior cup and posterior cup protrusions greater than 5 mm should be avoided.     

Poor eight-year survival of cemented zirconia-polyethylene total hip replacements.

Between January 1988 and January 1991 we performed 100 consecutive cemented total hip replacements using a zirconia head, a titanium alloy stem and a polyethylene cup. We reviewed 78 of these hips in 61 patients in detail at a mean of 5.8 years (1 to 9). Aseptic loosening was seen in 11 hips (14%). Eight needed revision. In total, 37 cups (47.5%) showed radiolucent lines, all at the cement-bone interface, with 18 (23%) involving all the interface. Of the 78 femoral implants, 17 (21.7%) showed radiolucent lines, and two, which had a complete line of more than 1 mm thick, definite endocortical osteolyses. There was also an abnormally high incidence of osteolysis of more than 2 mm at the calcar. Survivorship analysis showed that only 63% were in situ at eight years. These worrying results led us to abandon the use of zirconia heads, since at the same hospital, using the same femoral stem, cement and polyethylene cup, but with alumina femoral heads, the survival rate was 93% at nine years. We discuss the possible reasons for the poor performance of zirconia ceramic.     

全髋关节置换术中的髋臼外展角和磨损的关系

目的研究人工全髋关节置换术中的髋臼外展角与磨损的关系,及其对人工全髋关节稳定性的影响。方法对30例32髋进行平均4.2年的随访。测量髋臼杯的外展角,并通过测量在随访期间股骨头中心相对于髋臼中心的矢量位移,来确定关节面磨损的大小和方向,并进行统计学分析。结果最近随访时,30例患者的32个髋关节假体均未发现临床松动和失败征象,假体柄轴线与股骨纵轴成角均在3°以内。聚乙烯平均线性磨损量为0.81mm,磨损速度为0.18mm/年,髋臼外展角平均54.5°。磨损方向平均为?6.93°,指向上方稍偏外侧。线性回归分析显示磨损方向与髋臼假体外展角度存在负相关关系。随着外展角度的增加,磨损方向由内上方转为外上方,外展角55°以上的假体磨损方向基本指向外上方。未发现线性磨损速度与外展角及磨损方向之间的相关关系。结论过大的外展角使股骨头中心向外上方迁移,可能会造成应力分布不均和假体磨损增加,因此临床上应该避免髋臼假体植入的外展角超过55°,以维持髋关节的活动度和稳定性。     

Effect of acetabular cup position and orientation in cemented total hip arthroplasty.

Long-term clinical results of total hip arthroplasty for patients with developmental acetabular dysplasia of the hip have been reported, but placement of the femoral head center or cup orientation remains controversial, especially with a severe anterolateral shallow acetabulum or dislocated femoral head. Results of 41 Müller and 34 Harris Design 2 cemented total hip arthroplasties were evaluated for developmental dysplasia of the hip. The femoral head center and acetabular cup inclination angle were measured from the interteardrop line. Linear wear and wear direction were measured using the Livermore technique. The best position of the femoral head center was less than 35 mm vertically from the interteardrop line and 25 mm laterally from the teardrop. Femoral head center analysis showed that hips with the cup in a lateral and superior cup position all were revised, but a superior and medial position combined with a cup inclination angle less than 40 degrees did not require revision. Hips with a cup inclination angle more than 45 degrees had superior and lateral penetration patterns of the polyethylene. However, hips with an inclination angle less than 35 degrees and medial placement had medial head penetration patterns. With these all-polyethylene monolithic cemented cups, regardless of the femoral head diameter or cup thickness, better long-term results occurred with a cup inclination angle of 40 degrees or less and medial position of the cup.     

Hip abduction can prevent posterior edge loading of hip replacements

Edge loading causes clinical problems for hard‐on‐hard hip replacements, and edge loading wear scars are present on the majority of retrieved components. We asked the question: are the lines of action of hip joint muscles such that edge loading can occur in a well‐designed, well‐positioned acetabular cup? A musculoskeletal model, based on cadaveric lower limb geometry, was used to calculate for each muscle, in every position within the complete range of motion, whether its contraction would safely pull the femoral head into the cup or contribute to edge loading. The results show that all the muscles that insert into the distal femur, patella, or tibia could cause edge loading of a well‐positioned cup when the hip is in deep flexion. Patients frequently use distally inserting muscles for movements requiring deep hip flexion, such as sit‐to‐stand. Importantly, the results, which are supported by in vivo data and clinical findings, also show that risk of edge loading is dramatically reduced by combining deep hip flexion with hip abduction. Patients, including those with sub‐optimally positioned cups, may be able to reduce the prevalence of edge loading by rising from chairs or stooping with the hip abducted. © 2013 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 31:1172–1179, 2013

     

Specific inferior dislocation of the hip： one case report

Hip joint dislocations are generally classified as anterior, posterior, and central dislocations. In 1970s, the anterior dislocation was divided into pubic type and obturator type.1 It is generally recognized that for anterior dislocation of the hip joint, the femoral head is located at anteriorinferior part of the acetabulum, characterized clinically as abduction, extorsion, slight flexion deformity, and longer limb than the opposite side. When posterior dislocation is present, the femoral head is located at posteriorsuperior part of the acetabulum and manifested clinically as flexion, adduction, intorsion, and shortening deformity.     

Alternative bearing surfaces in total hip arthroplasty: zirconia-alumina pairing. Contribution or caveat?

The aim of the present study was to evaluate the zirconia and alumina articulation in total hip arthroplasty in regard to clinical and radiological outcome. This is the first report concerning the clinical application of a hybrid ceramic articulation. Owing to ethical reasons, a limited number of patients was enrolled in the study. Ten consecutive patients with degenerative arthritis were randomly allocated after informed consent to hybrid total hip arthroplasty treatment using an alumina femoral head and an alumina acetabular liner (5 hips), or using a zirconia femoral head and an alumina acetabular liner (5 hips). The median age of patients at index operation was 57.8 years. Current criteria were used for clinical and radiological assessment. The mean follow-up was 5.1 years (5 to 5.3 years). No hip required revision, and no clinical and radiological differences were observed between the two groups of hips. The median preoperative Harris hip score was rated 55.3 points in the control group of hips with alumina head, and 55.6 in the group of hips with zirconia head. The median Harris hip score increased to 94.9 points at the time of follow-up in the control group, and 96 points in the zirconia group. No radiological signs of cup loosening or focal acetabular osteolysis were detected at follow-up. All stems showed stable fixation without radiolucent lines or focal osteolysis. Zirconia femoral heads and alumina acetabular liners have been successfully used in the present series of 5 total hip arthroplasties with a mean follow-up of 5.1 years. Nevertheless, the use of femoral heads made of zirconia in total hip arthroplasties remains an important clinical concern due to the potential genesis of wear microparticles which can lead to progressive osteolysis. Further in-vitro and in-vivo investigations are required to define the value of this alternative bearing surface.     

The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different head-neck ratios

BACKGROUND: Prosthetic impingement due to poor positioning can limit the range of motion of the hip after total hip arthroplasty. In this study, a computer model was used to determine the effects of the positions of the acetabular and femoral components and of varying head-neck ratios on impingement and range of motion. METHODS: A three-dimensional generic hip prosthesis with a hemispherical cup, a neck diameter of 12.25 millimeters, and a head size ranging from twenty-two to thirty-two millimeters was simulated on a computer. The maximum range of motion of the hip was measured, before the neck impinged on the liner of the cup, for acetabular abduction angles ranging from 35 to 55 degrees and acetabular and femoral anteversion ranging from 0 to 30 degrees. Stability of the hip was estimated as the maximum possible flexion coupled with 10 degrees of adduction and 10 degrees of internal rotation and also as the maximum possible extension coupled with 10 degrees of external rotation. The effects of prosthetic orientation on activities of daily living were analyzed as well. RESULTS: Acetabular abduction angles of less than 45 degrees decreased flexion and abduction of the hip, whereas higher angles decreased adduction and rotation. Femoral and acetabular anteversion increased flexion but decreased extension. Acetabular abduction angles of between 45 and 55 degrees permitted a better overall range of motion and stability when combined with appropriate acetabular and femoral anteversion. Lower head-neck ratios decreased the range of motion that was possible without prosthetic impingement. The addition of a modular sleeve that increased the diameter of the femoral neck by two millimeters decreased the range of motion by 1.5 to 8.5 degrees, depending on the direction of motion that was studied. CONCLUSIONS: There is a complex interplay between the angles of orientation of the femoral and acetabular components. Acetabular abduction angles between 45 and 55 degrees, when combined with appropriate acetabular and femoral anteversion, resulted in a maximum overall range of motion and stability with respect to prosthetic impingement. CLINICAL RELEVANCE: During total hip arthroplasty, acetabular abduction is often constrained by available bone coverage, while femoral anteversion may be dictated by the geometry of the femoral shaft. For each combination of acetabular abduction and femoral anteversion, there is an optimum range of acetabular anteversion that allows the potential for a maximum range of motion without prosthetic impingement after total hip arthroplasty. These data can be used intraoperatively to determine optimum position.     

Mathematical evaluation of jumping distance in total hip arthroplasty: Influence of abduction angle, femoral head offset, and head diameter

Background and purpose The jumping distance (JD) is the degree of lateral translation of the femoral head center required before dislocation occurs. The smaller the distance, the higher the theoretical risk of dislocation. The aim of our study was to evaluate this jumping distance and its variation according to the characteristics of the implant, and also the theoretical gain in using large head diameters of above 38 mm.Methods The JD was calculated as a function of the cup ante-version and abduction angles, the head diameter, and the head offset (defined as the distance between the center of the femoral head and the cup opening plane). Head diameters of 28, 32, 36, 40, 44 and 48 mm were analyzed. The abduction angle was increased from 0° to 80° with a 10° increment. The anteversion angle was increased from 0° to 40° with a 5° increment.Results The jumping distance was found to decrease as the cup abduction angle increased (0.25 mm each 1° for 32-mm head diameter). It increased by 0.05 mm for a 1° increase in the ante-version angle. The jumping distance increased as the head diameter increased (0.4 mm each mm diameter for a 45° abduction angle). The net gain obtained by increasing the diameter, however, decreased when abduction angle increased (0.25 each mm diameter for 60° abduction). The JD decreased by 0.92 mm for each 1-mm increase in head offset, showing that head offset was the most important parameter influencing the JD.Interpretation The theoretical gain in stability obtained by using a large femoral head (above 36 mm) is negligible in cases where there is a high cup abduction angle. An increase in offset of the femoral head substantially reduces the jumping distance and it should therefore be avoided.     

A forty millimetre head significantly improves range of motion compared with a twenty eight millimetre head in total hip arthroplasty using a computed tomography-based navigation system

Purpose

Larger-diameter (≥40 mm) femoral heads decrease the incidence of post-operative dislocation in total hip arthroplasty (THA). This study was conducted to discover whether larger-diameter femoral heads result in greater range of motion of the hip with the use of a computed tomography (CT)-based navigation system.

Methods

Thirty-nine primary THAs were performed via a posterolateral approach using a CT-based navigation system. The stem was inserted in the femur in line with the original femoral neck anteversion. Considering the range of motion during various daily activities which could occur without impingement, the cup anteversion was decided at 10 ° increments according to the stem anteversion. While the cup inclination was set at 40 ° in order to avoid a high inclination angle to prevent the edge roading between the HXLPE liner and ceramic head. After implantation, trial liners and femoral heads were used with either 28 or 40 mm diameter. Maximal hip flexion, extension, abduction, external rotation in extension at 0° and internal rotation angles in flexion at 90 ° were measured. The differences between the ranges of motion with the 40-mm and 28-mm heads were tested. The results were assessed with paired Student t-tests.

Results

The ranges of motion in flexion, extension, abduction and internal rotation angles improved significantly with the 40-mm heads compared with the 28-mm heads. The ranges of motion of cases where maximal flexion angle was 90° or less were excluded, improved significantly with the 40 mm heads.

Conclusions

We concluded that the larger-diameter 40-mm femoral prosthetic heads result in greater ranges of motion in flexion, extension, abduction and internal rotation.

     

How does anteroposterior cup placement affect bone coverage and range of motion in primary total hip arthroplasty for hip dysplasia?

Background

Due to anterior bone defects, high and/or posterior placement of an acetabular cup is often required to achieve sufficient coverage in patients with hip dysplasia. We examined whether posterior cup placement affected the postoperative range of motion (ROM) in primary total hip arthroplasty (THA).

Femoral shortening and cementless arthroplasty in high congenital dislocation of the hip.

We performed cementless total hip arthroplasty with femoral shortening in 28 hips of 23 patients with high-riding congenital dislocation of the hip. All the acetabular cups were placed in their original anatomic location. If needed, the acetabulum was reconstructed using the femoral head. The proximal diaphyseal step-cut shortening osteotomy was performed and stabilized by cerclage or cable grips. The follow-up results at average 48 months postoperatively were scored clinically by the Merle D'Aubigné and Harris hip scores and were good and excellent in 89.2%. One acetabular cup showed progressive radiolucent lines suggesting aseptic loosening. Two superficial wound infections, 1 femoral nerve palsy, 1 sciatic nerve palsy, 2 nonunions, and 1 acetabular fracture were observed during the follow-up.     

H/G非骨水泥人工全髋关节置换术后聚乙烯内杯磨损临床研究

目的 对H/G非骨水泥人工全髋关节置换术后聚乙烯内杯的磨损及髋臼周围骨溶解的情况进行总结.方法 我院1991至1995年共进行58例(65髋)H/G非骨水泥人工全髋关节置换,其中35例(40髋)获得10年以上随访.对这35例(40髋)患者获得随访的病例,采用计算机数字化方法测量髋臼聚乙烯内杯的二维线性磨损.结果 35例40髋均有不同程度的磨损,磨损范围2～8 mm,平均磨损为(0.32±0.31)mm/年.10髋聚乙烯磨损超过6 mm,髋臼假体周围的骨溶解严重,并伴有金属假体的移位,其中5髋聚乙烯内杯完伞磨透,金属股骨头与金属髋臼相接触;5髋聚乙烯内杯磨损严重伴明显骨溶解,内杯松动.2髋聚乙烯内杯脱位.共实施翻修手术12例,包括更换聚乙烯内杯和金属股骨头2例、金属闩杯翻修2例、全髋翻修8例.28髋在髋臼侧发现骨溶解,其中14髋股骨侧亦有骨溶解发生.结论 本组病例所观测到的H/G髋臼聚乙烯内杯的磨损程度超过文献所报道,而且由于磨损产生的大量磨屑,导致假体周围出现明显骨溶解,直接影响到假体的稳定.关节置换术后应定期随访,避免出现严重骨溶解后增加翻修手术的困难.     

Comparison of preoperative radiographs and intraoperative findings of fixation of hemispheric porous-coated sockets.

BACKGROUND: The radiographic criteria for identification of loose cementless acetabular components have not been well established. The purpose of this study was to compare the radiographic appearance of a hemispheric porous-coated cementless cup fixed with screws with the intraoperative findings with regard to the fixation status. METHODS: The quality of the cup fixation was evaluated at fifty-two hip revisions that were performed, for reasons other than infection, at an average of 89.9 months (range, 33.8 to 150.1 months) after the primary operations. The fixation status at the revision surgery was compared with the findings on sequential anteroposterior and lateral radiographs of these sockets. Sequential radiographs of an additional 100 total hip replacements that had not required a reoperation and that had been followed for an average of 121 months were also measured. RESULTS: Loosening of the socket was radiographically identified by (1) radiolucent lines that initially appeared after two years, (2) progression of radiolucent lines after two years, (3) radiolucent lines in all three zones, (4) radiolucent lines 2 mm or wider in any zone, or (5) migration. The sensitivity of these criteria was 94%, and the specificity was 100%. The criteria had a positive predictive value of 100% and a negative predictive value of 97%. CONCLUSIONS: The most predictive radiographic findings for early diagnosis of loosening of a hemispheric porous-coated cup were progression of radiolucent lines more than two years after the operation and any new radiolucent line of 1 mm or wider that appeared more than two years postoperatively. Sequential anteroposterior and lateral radiographs are necessary to assess the time of onset and progression of radiolucent lines in order to identify loose hemispheric porous-coated cups accurately.     

Migration of the acetabular component: effect of cement pressurization and significance of early radiolucency: a randomized 5-year study using radiostereometry

BACKGROUND: Cementing technique is a crucial factor in prosthesis fixation. No randomized studies have been published, however, comparing the outcome of conventional fingerpacking with the outcome of pressurization of the cement prior to cup insertion. PATIENTS AND METHODS: We randomized 50 THAs to either fingerpacking or sequential pressurization (including individual pressurization of each anchorage hole) and followed the patients with RSA for 5 years. The penetration of cement into the anchorage holes was measured on digital radiographs. Postoperative radiolucent lines around the cup were correlated to later RSA results. For clinical evaluation, we used SF-36 and HHS. RESULTS: The pressurized group of THAs was more stable regarding changes in inclination. We found no other difference in the migratory behavior. The cement penetration into the anchorage holes was deeper with the pressurization technique than with fingerpacking. For the whole group taken together, there was a strong relation between the presence of radiolucent lines as measured on the postoperative radiograph and later migration observed by RSA at 2 and 5 years. INTERPRETATION: Pressurization of the cement produced better cement penetration and increased the cup stability in terms of changes in inclination. Early findings of radiolucent lines can predict later unfavorable cup migration.     

No increased stem subsidence after arthroplasty in young patients with femoral head osteonecrosis: 41 patients followed for 1-9 years

BACKGROUND: Poor bone stock in patients with osteonecrosis of the femoral head may be a reason for poor outcome after hip replacement. One way of studying bone quality is to measure implant migration. We thus investigated the clinical and radiographic results of cementless THR in younger patients with femoral head osteonecrosis. PATIENTS AND METHODS: We studied hips in 41 patients (mean age 48 (25-63) years) with a cementless hip arthroplasty after late stage osteonecrosis. Clinical evaluation was by the Harris hip score, the WOMAC score and the SF-36 score. Stem subsidence was measured with the Ein Bild Roentgen Analyse femoral component analysis (EBRA-FCA) at 3, 12, 24, 60, and 72 months after operation. The average duration of follow-up was 7(1-9) years, with less than 2 years for 2 patients. RESULTS: There was no revision of any hip. No radiographic or clinical stem loosening was seen. After 60 months, the cementless stems showed a median subsidence of -0.7 mm (95% CI: -0.9 to -0.2). No femoral osteolysis occurred. Femoral radiolucent lines, all < 1 mm, were seen in 10 hips. At the latest follow-up the Harris hip score was 83 (23-100) points. INTERPRETATION: Our findings for porous-coated stems in patients with femoral osteonecrosis indicate no greater risk of stem subsidence and rate of osteolysis after an average of 7 years follow-up. Thus, we continue to use uncemented stems in younger patients with femoral osteonecrosis. However, continued follow-up will be necessary to evaluate the long-term outcome.     

Accuracy of migration analysis in hip arthroplasty Digitized and conventional radiography,compared to radiostereometry in 51 patients

We assessed the accuracy of migration measurements on conventional and digitized radiographs of total hip arthroplasties by comparing the results with radiostereometry (RSA). 4 stem and 3 acetabular designs were studied. 2 of the stem designs and 1 cup design were uncemented. 180 manual and 202 digitized measurements were done on 120 conventional radiographic examinations.

The readings on digitized radiographs did not differ from the manual measurements on the same radiographs. A comparison of the measurements from plain radiographs and with RSA of the femoral stems revealed an accuracy (absolute mean + 2 SD) of between 3.9 and 12.3 mm, depending on the choice of landmarks. The greatest accuracy was obtained by using tantalum markers inserted into the greater or the lesser trochanter and the shoulder of the stem. The most medial point of the lesser trochanter proved to be the best bony landmark. Measurements, including both the center of the femoral head and the greater trochanter, were associated with poor accuracy. The accuracy as regards horizontal cup migration varied from 4.4 to 6.5 mm and the accuracy as regards vertical migration varied between 4.4 and 6.3 mm.

The intraobserver error (2 SD) ranged from 1.6 mm to 5.6 mm, The corresponding figures for the inter-observer error were 2.6 mm and 6.6 mm, respectively. One of the cemented cup designs was associated with inferior accuracy. Stem design did not affect the accuracy.