髋臼方位与全髋置换术后脱位的关系

目的研究人工全髋置换术后髋臼方位对髋关节脱位的影响,并为临床提供评价标准。方法测量318例(326髋)X线片的髋臼外展角、前倾角及股骨头旋转中心垂直位置,通过平均2.7年随访来确定上述3因素与术后髋脱位的关系,并进行统计学处理。结果在最近随访时,326髋有10髋发生脱位。外展角≥55°,较<55°脱位发生率有显著性差异;股骨头旋转中心垂直位置≥30mm,较<30mm脱位发生率也有显著性差异;前倾角≥15°和<15°相比,脱位发生率没有显著性差异;前倾角与外展角没有交互作用。结论髋臼方位不当与全髋置换术后的脱位明显相关;外展角<55°,股骨头旋转中心垂直位置<30mm及合适的前倾角可以提供较稳定的髋关节,明显降低术后髋脱位的发生率。     

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。     

全髋关节表面置换术治疗成人髋关节发育不良25例中期随访

目的探讨全髋关节表面置换术（total hip resurfacing arthroplasty,THRA）治疗成人髋关节发育不良（developmental dysplasia of the hip,DDH）继发骨关节炎的中期疗效。方法2005年3月至2006年6月,采用THRA治疗DDH患者25例,女18例,男7例;30～59岁,平均48岁;双髋1例,共26髋。根据Hartofilakidis分型,半脱位22髋,低位脱位4髋。采用Conserve-plus金属对金属全髋关节表面置换假体,髋臼假体为非骨水泥固定,股骨头假体采用低黏骨水泥固定。临床随访采用Harris评分,测量髋臼外展角、垂直距离、水平距离、股骨柄干角、髋臼假体覆盖率;记录髋臼和股骨假体周围透亮线及骨溶解;以各种原因所致翻修或影像学松动为随访终点。结果所有患者均随访3年以上,平均随访3.5年。截至随访终点无翻修或影像学松动。患者的Harris评分由术前平均46分提高至术后平均92.1分,26髋均为优。术后轻度跛行2例,所有患者均无迟发感染、术后股骨颈骨折、术后残余股骨头坏死、术后假体松动、脱位、术后异位骨化。髋关节活动度：屈曲由97.5°增加至127.5°,外展由19.3°增加至40°,外旋由23.2°增加至42.5°,内旋由4.2°增加至28.5°。X线片显示：关节假体位置正常,髋臼假体平均外展角为41.6°,髋关节旋转中心位置平均下移6.2 mm、内移15 mm,股骨柄干角平均146.4°。宿主骨对臼杯的平均覆盖率为94.4%,1例宿主骨与臼杯界面在2区出现透亮线,宿主骨与股骨假体柄界面无一例出现透亮线。结论THRA治疗成人半脱位型及低位脱位型DDH继发骨关节炎具有良好的中期疗效,熟练的手术技术和正确的适应证选择是降低中远期并发症的关键。     

髋关节表面置换术治疗先天性髋关节发育不良

目的 探讨髋关节表面置换术治疗先天性髋关节发育不良的临床疗效.方法 2005年3月至2006年12月对34例(37髋)先天性髋关节发育不良患者行髋关节表面置换术,其中Crowe Ⅰ型28例(31髋)、Crowe Ⅱ型6例(6髋).其中女性29例(32髋),男性5例(5髋),患者平均年龄45岁(26～57岁).患者在术后6周、3个月、1年,及此后每年1次进行随访,接受放射学及临床评价.术前患者Harris评分平均35分,髋关节屈曲101°,外展24°,内收15°,术前12例患者双下肢等长.结果 34例患者中,3例(3髋)患者术中改行全髋关节置换术.31例(34髋)行表面置换.31例表面置换患者平均随访时间21.4个月(12～33个月).患者术后最后一次随访平均为94分(82～100分),与术前比较差异具有统计学意义(P＜0.01).术后髋关节屈曲改善至133°,外展48°,内收26°.术后23例患者双下肢等长.患者股骨及髋臼假体周围均未见透亮线,髋臼假体的平均外展角为43°(40°～53°),股骨假体柄干角平均为139°(130°～145°).结论 本组患者短期随访结果令人满意,良好的手术技术和手术适应证的严格掌握是先天性髋关节发育不良患者手术成功的关键.     

全髋关节置换术中骨盆旋转对髋臼假体角度的影响

目的研究骨盆旋转对髋臼假体实际角度的影响,探讨髋臼安全区范围内可以接受的骨盆旋转角度。方法建立骨盆三维模型,确定冠状面、矢状面及髋臼轴,假设髋臼假体外展45°,前倾15°,简化成坐标图,运用解析几何原理,推导出骨盆旋转角度与实际髋臼外展角、前倾角关系的函数公式,运用函数公式计算骨盆旋转角度与实际外展角、前倾角变化趋势,在保持安全区范围内的可以接受的骨盆旋转角度。结果在假设髋臼假体外展角45°、前倾角15°不变的情况下,骨盆每前旋转5°,髋臼外展角增加0.24°~1.64°,前倾角减少3.70°~3.69°,骨盆每后旋转5°,髋臼外展角减少2.00°~3.47°,前倾角增加2.61°~3.62°。随着骨盆的前旋转,其实际外展角呈增大趋势,实际前倾角呈减小趋势;随着骨盆的后旋转,其实际外展角呈减小趋势,实际前倾角呈增大趋势,两者之间呈函数关系。如果骨盆旋转在+13.43°~-14.05°范围内,髋臼假体角度理论上保持在"安全区"范围内。结论全髋关节置换术中骨盆旋转对髋臼假体外展角、前倾角均有影响,其中对前倾角的影响更显著。骨盆在旋转+13.43°~-14.05°时,髋臼假体角度理论上仍在"安全区"范围内。     

全髋关节置换术中髋臼假体位相的安全范围及杯颈前倾角的优化组合

目的 探讨全髋关节置换术(THA)中髋臼杯的安全范围及杯颈前倾角的优化组合方法. 方法 建立THA三维可视化模型,定义两种髋关节活动度标准:一般标准(髋关节屈曲≥110°、屈曲90°时内旋≥30°、后伸≥30°和中立位外旋≥40°而没有假体撞击)和严格标准(髋关节屈曲≥120°、屈曲90°时内旋≥45°、后伸≥30°和中立位外旋≥40°而没有假体撞击).头颈比变化范围为2.00 ～2.92,股骨假体前倾角变化范围为0～30°,髋臼假体外展角变化范围为10°～60°,髋臼前倾角变化范围为0 ～ 70°,计算满足髋关节两组活动标准、臼杯外展角每变化5°相应的髋臼假体前倾角的安装参数.结果 严格标准下的安全范围较一般标准小,两种标准下的髋臼杯安全范围面积随着头颈比增大而增大.当颈干角为130°时,一般标准和严格标准下髋臼杯前倾角(Y)与股骨假体前倾角(X)的关系分别为Y1=-0.840X1+38.41,Y2=- 1.007 X2 +47.46;允许的最小髋臼外展角(OImin)和头颈比(GR)的关系分别为OImin'1=168.13 GR1-2.504,OImin'2=213.79 GR2-2.272.当颈干角从135°移向130°时,杯安全范围移向杯前倾角较小的区域,面积也有所减小.结论 THA中可以通过增大头颈比来扩大臼杯安放的安全范围.允许的最小髋臼外展角随着头颈比增大而变小,杯前倾角与股骨颈前倾角呈负相关.股骨颈前倾角的增大和颈干角的变小均使得杯安全范围移向杯前倾角较小的区域.     

结构性植骨全髋关节置换在成人高位先天性髋关节脱位中的应用

[目的]探讨结构性植骨全髋关节置换治疗成人高位先天性髋关节脱位的临床疗效。[方法]2003年8月～2006年10月,采用结构性植骨全髋置换治疗成人高位先髋脱位22例,29髋。男10例,女12例。左13例,右16例,年龄平均34.6岁(23～42岁)。临床症状主要为患髋疼痛、不稳定和跛行。术前Harris评分平均为46.8分,双下肢长度差异平均为3.8cm,股骨头脱位高度平均为3.9cm,髋关节平均活动度:屈曲66.5°,外展23.8°,外旋20.4°,内旋5.3°。术中臼杯均安装于真臼处,自体股骨头结构性植骨使臼杯完全覆盖,充分软组织松解后髋关节复位。髋臼侧选用骨水泥假体18髋、小髋臼生物型假体5髋和普通生物型髋臼6髋;股骨侧选用生物型假体10髋、普通骨水泥假体13髋、窄直柄水泥假体柄4髋和长柄骨水泥假体柄2髋。观察手术时间、出血量、关节活动度、双下肢长度差异、并发症等并进行Harris关节功能评分。[结果]本组平均手术时间95min(70～135min),出血400ml(300～650ml);伤口均一期愈合,无1例感染;术后1周X线片示假体位置良好,人工髋臼外展角平均为48.6°,前倾角平均13.2°。本组22例均获随访,随访时间平均17.6个月(10～47个月),Harris评分平均89.2分(72～93分);髋关节平均活动度:屈曲115.3°,外展44.6°,外旋49.5°,内旋26.8°。双下肢长度差异平均1.2cm,2例术后股神经麻痹,术后4个月内恢复。随访期间未见明显植骨块吸收、假体松动和脱位。[结论]结构性植骨全髋关节置换是治疗成人高位先天性髋关节脱位的一种有效方法,很大程度地改善了患者的症状、功能和外形。结构性植骨可提供良好的髋臼覆盖,恢复髋关节旋转中心高度并可保留骨盆骨量。脱位高度小于4cm经软组织充分松解后能下拉复位,不会造成股神经及坐骨神经永久性麻痹。     

不同手术入路髋臼假体放置角度差异对疗效的影响

目的 探讨前外侧入路和后外侧入路行全髋关节置换术时髋臼假体放置角度差异对疗效的影响.方法 对2006年1月至2011年12月67例行初次单侧全髋关节置换术患者的临床资料进行回顾性研究,根据手术入路不同分为前外侧入路组(31例)和后外侧入路组(36例),两组患者术前一般资料比较差异均无统计学意义(P＞0.05),具有可比性.术中测量髋臼假体安放时的前倾角、外展角,比较两组患者术中髋关节中立位的最大髋关节屈曲角和后伸角,以及术后髋关节Harris评分和脱位发生率.结果 前外侧入路组术中髋臼假体放置的前倾角为8°～ 20°,外展角为30°～40°;后外侧入路组中髋臼假体放置的前倾角为15°～30°,外展角为35°～45°.两组患者的髋关节平均最大屈曲角(110°±11°比100°±10°)和最大后伸角(15°±4°比25°±6°)差异均有统计学意义(P＜0.05).所有患者术后获12～18个月(平均15.6个月)随访,两组患者的术后Harris评分[(89±11)分比(88±12)分]和髋关节脱位发生率[3.2％(1/31)比5.5％(2/36)]差异均无统计学意义(P＞0.05). 结论 不同手术入路行全髋关节置换术时对髋臼假体前倾角的放置有不同要求,前外侧入路中髋臼假体的前倾角应当比后外侧入路中髋臼假体的前倾角小;髋臼假体放置角度差异对疗效无显著影响.     

小切口人工全髋置换假体位置的准确性分析

[目的]评价小切口人工全髋关节置换术假体安放位置的准确性.[方法]自2005年9月～2006年3月行后外侧单切口入路小切口人工全髋关节置换术26例30髋和常规切口人工全髋关节置换术34例35髋.小切口组男15例,女11例,平均52±14.4岁,常规切口组男17例,女17例,平均48±11.7岁.比较两组手术时间、术中出血量、术后引流量、输血量、切口长度和并发症,分析术后影像学资料,测量髋臼杯外展角,髋臼杯前倾角,髋关节旋转中心,肢体长度,股骨假体内外翻比例.比较两组患者的临床疗效和假体安放位置的准确性.[结果]两组在年龄、性别、术后引流量、手术时间、体重质量指数无统计学差别.小切口组25例(29髋),常规切口组32例(33髋)随访18～24月(平均20.1个月).小切口组术中出血量(497±64.9 ml)比常规切口组(675±181.4 ml)少(P<0.05).常规切口组术后需要输血量明显增多(P<0.05).两组患者无严重并发症发生.术后测量髋臼杯外展角小切口组37.7°±6.8°,常规切口组40.3°±5.8°;髋臼杯前倾角小切口组10.8°±7.2°, 常规切口组13.2°±8.9°; 髋关节旋转中心平均上移小切口组-1.4±2.5 mm, 常规切口组-1.5±3.8 mm;术后肢体延长小切口组1.1±7.1 mm, 常规切口组1.5±8.4 mm;股骨假体小切口组内翻1例,中置27例,外翻2例; 常规切口组内翻2例,中置30例,外翻3例.两组假体位置相关参数测量数值差别无统计意义.[结论]在合理选择病例,术者具有丰富经验的情况下,小切口人工全髋关节置换术创伤小、出血少,与常规切口手术相比并不影响假体位置的安放.     

Loci of movement of selected points on the femoral head during normal gait: Three-dimensional computer simulation

Wear of ultrahigh-molecular-weight polyethylene and the subsequent lytic response to the particulate wear debris are the dominant problems in total joint arthroplasty surgery. Wear testing apparatus can play a vital role in the in vitro evaluation of the many factors involved in wear, such as head size, surface roughness, materials for the head, and new materials for the socket. Wear of ultrahigh-molecular-weight polyethylene may be influenced by the wear path. For the related polymer, high-density polyethylene, the wear path is critical to wear magnitude. What is the actual path taken by a single point (or by multiple representative points) on the femoral head of a total hip arthroplasty as it passes through the gait cycle? The goal of this computer simulation study was to trace the paths of specific points on the femoral head as they moved against the polyethylene cup during a single cycle of normal gait to illustrate the motions occurring at the intraarticular surface of the hip joint. This study also yielded unusual data on the “distance traversed” by these points during a single gait cycle. It was found that there was not one path, but rather there were many, and the paths varied widely in both shape and length depending on the location on the femoral head. Moreover, the differences in excursion and direction at different sites during the loaded phase were great. In addition, distances traveled by different points on the femoral head of any given size varied by a factor greater than 2. Most of the points traced quasielliptical paths. This automatically means that the paths of neighboring points cross each other, creating multidirectional shear forces on the acetabular cup surface which may be important in the localization and extent of wear. The plots of traces of the points derived from this study can serve as benchmarks for the ability of hip simulators to reproduce the actual distances and paths of travel of individual points on the femoral head.     

Relation between vertical orientation and stability of acetabular component in the dysplastic hip simulated by nonlinear three-dimensional finite element method

In acetabular dysplasia, more vertical orientation of the acetabular component is often used to minimize the superolateral bone grafting. This study was designed to determine the effects of vertical orientation of the cup on the stability and polyethylene wear of the acetabular component in uncemented total hip arthroplasty (THA). Three-dimensional finite element models of the hemipelvis with dysplastic acetabulum were developed. Metal-backed hemispherical cups were placed in the true acetabulum with abduction angles of 35, 45, 55, and 65 degrees. It was found that more vertical orientation of the cup was associated with larger relative motion of the metal shell between the acetabulum and metal shell. Furthermore, tilting and torsional shear stresses in the model of the cup abduction angle of 65 degrees were found to be 1.7 times larger than that in the model with 35 degrees at the bone-metal shell interface. More vertically oriented cups caused larger contact stresses at the articulating surfaces of the polyethylene liners. The results suggest that the abduction angle of the acetabular component significantly influences cup loosening and polyethylene wear in THA.     

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.     

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.     

Ten- to Sixteen-Year Follow-Up of Highly Cross-Linked Polyethylene in Total Hip Arthroplasty: What Factors Affect Wear?

BackgroundIncrease in acetabular cup abduction in total hip arthroplasty (THA) using conventional polyethylene is associated with greater linear wear. Whether this relationship holds true for highly crosslinked liners, particularly with long-term follow-up, is still controversial. The effect of liner thickness on wear of highly cross-linked liners also remains to be clarified.This study sought to determine (1) the long-term clinical and radiological performance of highly cross-linked polyethylene in THA and (2) the effect of acetabular component positioning, polyethylene thickness, and patient demographics on wear.MethodsNinety-three THAs using a 28-mm hip ball, single brand of highly cross-linked polyethylene liner, and cementless cup were performed in 87 patients. Clinical outcomes were evaluated using the Harris Hip Score and need for revision surgery. Linear and volumetric wear, presence of osteolysis, and cup abduction angle were assessed.ResultsThe mean age at operation was 51.4 years. The mean duration of follow-up was 12.7 years (10-16 years). Patients aged >50 years had higher rates of linear wear than those aged <50 years (P = .015). Positive correlation was found between cup abduction angle (P = .014) and cup version (P = .035) with a linear wear rate. Thinner liners (≤7 mm) had similar rates of linear and volumetric wear as thicker liners (≥8 mm) (P = .447).ConclusionThis is the only study to demonstrate a positive significant relationship between cup abduction angle and version with linear wear rate in THA with at least 10 years of follow-up. Liner thickness was not found to affect wear rates.     

The 22-mm vs the 32-mm femoral head in cemented primary hip arthroplasty long-term clinical and radiological follow-up study

A retrospective clinical and radiological analysis was performed on 117 patients (138 hips) with a mean age of 75 years and a mean follow-up of 11 years. The prostheses used were 2 similar monoblock femoral components with 22- and 32-mm head sizes; their effects on the wear of the high-density polyethylene cup were studied. Wear of component was determined by evaluating the standardized initial and follow-up radiographs. The mean rate of linear wear was higher in the 22-mm femoral head, whereas the volumetric wear was higher in the 32-mm femoral head. In both groups, volumetric wear was significantly correlated with cup lysis. Increasing body weight in both groups was associated with more volumetric wear. The radiological evidence of prosthetic loosening did not correlate well with clinical evaluation of the hip.     

The effect of abduction differences between cup and contralateral acetabular angle on polyethylene component wear.

One hundred forty-two patients who underwent cemented or uncemented hip replacement were studied radiographically to determine acetabular component wear. Mean duration of follow-up was 58 months (range: 35-92 months). Average linear wear was 0.78 mm (range: 0-1.9 mm), and average wear rate was 0.16 mm/year (range: 0-0.45 mm/year). An increased wear rate per year correlated with a discrepancy >18.3 degrees between contralateral acetabular angle and acetabular cup inclination (P<.005). Statistical analysis revealed no significant correlation between cup inclination and polyethylene wear, which was studied without considering the contralateral hip (P>.3). There was no relationship between polyethylene wear and cup design, weight, and initial polyethylene thickness.     

Movement loci of selected points on the femoral head for individual total hip arthroplasty patients using three-dimensional computer simulation

Wear of ultra-high-molecular-weight polyethylene (UHMWPE) and the subsequent adverse tissue reaction to the wear particles has been cited as the predominant problem affecting total joint arthroplasties. Wear of the UHMWPE acetabular cup in total hip arthroplasties (THAs) is influenced by the sliding distance and direction of individual points on the femoral head, which has as yet been ascertained only for normal subjects. This study seeks to determine the trajectory of specified points on the femoral head for individual THA patients and the distances traversed by these points. A computer program was designed to use gait data from THA patients to simulate the motion of these points. Gait analysis was performed on 19 THA patients at a period of 5 years after operation. The orientation of the acetabular cup was ascertained from radiographs to determine the position of the points on the head most involved in the wear process. The loci of the points differed widely in size, shape, and direction between subjects. The largest average distance traversed was 140% greater than the smallest average distance traversed. Shorter longitudinal paths would tend to cause less wear than larger, wider paths, which cross a greater number of adjacent paths.     

Alarming wear of the first-generation polyethylene liner of the cementless porous-coated Biomet Universal cup: 107 hips followed for mean 6 years

Wear of the socket liner and resulting osteolysis are the major causes of failure in cementless hip arthroplasties. We report alarming wear of the first-generation polyethylene liner of the cementless porous-coated Biomet Universal cup. Radiographs of 107 primary hip arthroplasties were analyzed retrospectively. The mean follow-up time was 74 (47-91) months. The linear wear of the polyethylene liners was assessed using a modification of the Livermore method. The median linear wear was 1.0 (0-6.2) and the median linear wear rate was 0.17 mm/year. There was a statistically significant difference between the 28 mm and 32 mm femoral head groups both in the volumetric wear and in the volumetric wear rate. The median linear wear was 0.28 mm/year and 0.14 mm/year for the 32 mm and 28 mm heads, respectively. So far, 14 revisions have been performed or have been scheduled because of excessive wear of the polyethylene liner. In regression analysis, the factors related to the wear rate were the 32 mm size of the femoral head and screw fixation of acetabular shell. We found that the cases with calcar rounding were associated with significantly greater wear. Possible reasons for increased wear of the Hexloc liner may be the cylindrical design, thin polyethylene, and poor quality of the polyethylene. Regular clinical and radiographic follow-ups are recommended especially for hips with 32 mm femoral heads or with screw fixation. If progressive wear of the liner is observed, revision must be considered.