Late dissociation of an alumina-on-alumina bearing modular acetabular component

Alumina-on-alumina bearings for total hip arthroplasty have been introduced as a promising alternative to reduce wear debris and to increase the life expectancy of the prosthesis. We report a case of a late dissociation of an alumina-on-alumina bearing modular acetabular component, which occurred 2 years, 8 months after surgery. Detailed analysis of the retrieved prosthesis suggested that the cause of the failure may be strong rotational torque developed by a roughening of the bearing's alumina surface caused by edge loading (microseparation). The strong friction torque in articulation may explain the higher reported rate of mechanical loosening of the acetabular component in alumina-on-alumina bearing total hip prostheses.     

Wear in alumina-on-alumina ceramic total hip replacements: a retrieval analysis of edge loading

We analysed 54 alumina ceramic-on-ceramic bearings from total hip replacements retrieved at one centre after a mean duration of 3.5 years (0.2 to 10.6) in situ. These implants were obtained from 54 patients (16 men and 38 women) with a mean age of 67 years (33 to 88) who underwent revision for a variety of reasons. Posterior edge loading was found in the majority of these retrievals (32 out of 54). Anterosuperior edge loading occurred less often but produced a higher rate of wear. Stripe wear on the femoral heads had a median volumetric wear rate of 0.2 mm(3)/year (0 to 7.2). The wear volume on the femoral heads corresponded to the width of edge wear on the matching liner. Anteversion of the acetabular component was found to be a more important determinant than inclination for wear in ceramic bearings. Posterior edge loading may be considered to be a normal occurrence in ceramic-on-ceramic bearings, with minimal clinical consequences. Edge loading should be defined as either anterosuperior or posterior, as each edge loading mechanism may result in different clinical implications.     

Survival analysis of an uncemented ceramic acetabular component in total hip replacement

Follow-up examinations of 67 implants of cement-free ceramic sockets show the need for an exact definition of failure, to warrant comparable evaluations of results. Statistical survival analysis offers the possibility of presenting both the incidence of failures and the dates of their occurrence. If only revision surgery with removal of the socket is considered to be a failure, our material shows the "survival quota" of the ceramic socket after 8 years to be 96.7% +/- 2.2%. If radiological signs of loosening are included in the evaluation of failures, the "survival quota" of the stable implants is reduced to 81.9% +/- 6.9%.     

Survival analysis of an uncemented ceramic acetabular component in total hip replacement

Summary Follow-up examinations of 67 implants of cement-free ceramic sockets show the need for an exact definition of failure, to warrant comparable evaluations of results. Statistical survival analysis offers the possibility of presenting both the incidence of failures and the dates of their occurrence. If only revision surgery with removal of the socket is considered to be a failure, our material shows the survival quota of the ceramic socket after 8 years to be 96.7% ± 2.2%. If radiological signs of loosening are included in the evaluation of failures, the survival quota of the stable implants is reduced to 81.9% ±6.9%.

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Zusammenfassung Anhand der Nachuntersuchung von 67 zementfrei implantierten keramischen Füßchenpfannen wird die Notwendigkeit der genauen Definition des Fehlschlages aufgezeigt, um dadurch eine vergleichbare Beurteilung der Ergebnisse zu gewährleisten. Die statistische Methode der Überlebenszeitanalyse bietet die Möglichkeit, sowohl die Häufigkeit der Fehlschläge als such den Zeitpunkt ihres Auftretens darzustellen. Wird ausschließlich die Reoperation mit Austausch der Pfanne als Fehlschlag bewertet, so ergibt sich im eigenen Material nach 8 Jahren eine Überlebensquote der keramischen Pfanne von 96,7% ± 2,2. Werden zusätzlich radiologische Lockerungszeichen in die Fehlschlagbeurteilung aufgenommen, so reduziert sich die Überlebensquote der stabilen Implantate auf 81,9% ± 6,9.

     

Failure analysis of a ceramic bearing acetabular component

BACKGROUND: Alternative bearings have been explored in an attempt to improve the longevity of total hip prostheses. A Food and Drug Administration (FDA)-approved clinical study of a nonmodular acetabular component consisting of a porous metal shell, compression-molded polyethylene, and a ceramic liner inlay was discontinued following reports of early failures. METHODS: Between October 1999 and January 2003, 429 patients were enrolled in a prospective study to evaluate a cementless ceramic-on-ceramic total hip arthroplasty design (Hedrocel ceramic bearing cup; Implex, Allendale, New Jersey). Two hundred and eighty-two patients (315 hips) were treated with the experimental acetabular implant and 147 patients (157 hips) were treated with an acetabular implant that consisted of the same porous shell but an allpolyethylene liner. Clinical data including a Harris hip score and responses to the Short Form-12 (SF-12) health survey were collected preoperatively and at twelve and twenty-four months postoperatively. Serial radiographs were made preoperatively; at six weeks, three months, six months, and twelve months postoperatively; and annually thereafter. Retrieval analysis was performed on all failed explanted components. Failure was defined as fracture or displacement of the ceramic liner out of the acetabular component. In addition, biomechanical testing was performed on unimplanted acetabular components and mechanically altered cups in an effort to recreate the mechanisms of failure. Finite element analysis was used to estimate stress and strain within the ceramic liner under extreme physiologic loading conditions. RESULTS: The ceramic liner failed in fourteen of the 315 experimental acetabular components; all of the failures were at the ceramic-polyethylene interface. Patients with a body weight of >91 kg had a 4.76 times greater odds of the ceramic liner failing than those who weighed < or =91 kg. Retrieval analysis demonstrated stripe and rim wear with evidence of adhesive wear, indicating a potentially high-friction interaction at the articulation. Finite element analysis demonstrated that the forces on the ceramic liner in cups subjected to extreme loading conditions were insufficient to cause fracture. Biomechanical testing was unable to reproduce an initial ceramic liner displacement in vitro; however, when the ceramic liner was forcibly displaced prior to biomechanical testing, complete displacement and eventual fracture of the ceramic liner resulted. CONCLUSIONS: We hypothesized that the combination of a high patient body weight, an extensive range of motion, and subluxation of the femoral head led to high friction at the articulation between the femoral head and the rim of the liner, which initiated displacement of the ceramic liner. Subsequent normal gait led to further displacement of the liner in all of the fourteen failed components and eventually to ceramic fracture in twelve of the fourteen components.     

Medial placement of the acetabular component in an alumina-on-alumina total hip arthroplasty: a comparative study with propensity score matching

Purpose

In an alumina-on-alumina total hip arthroplasty (THA), recommended with a small inclination angle <45°, the acetabular component (cup) may be positioned more medially to be covered almost completely by host bone. The purpose of this study was to identify the correlating factors and to evaluate the outcomes of medial placement of the cup in patients with alumina-on-alumina THAs.

Methods

Using the propensity score matching with age, gender, body mass index, initial diagnosis, and the length of follow-up as variables, 38 hips with a medialized cup and 38 hips with a non-medialized one were identified from 389 hips in 347 who patients underwent primary alumina-on-alumina THA and followed up for more than 7 years. Clinical and radiological outcomes were compared between the two groups.

Results

Preoperative acetabular medial wall thickness and the cup inclination angle were significantly smaller in the medialization group compared to the non-medialization group. Center edge angle, cup size, and coverage by host bone were not significantly different between the two groups. The hip center of rotation was significantly medialized in the medialization group. The Harris hip scores were not significantly different between the two groups. No component loosening or osteolysis was observed and no revision was required in either groups.

Conclusions

Thin acetabular medial wall and a small inclination angle of the cup were the correlating factors of medial placement of the cup in patients who underwent an alumina-on-alumina THA. Medial placement did not lead to differences in the clinical or radiological outcomes.     

Squeaking in ceramic-on-ceramic hips: the importance of acetabular component orientation

Audible squeaking in total hip replacements with ceramic-on-ceramic bearings is a rare problem. Acetabular component orientation was compared for 17 squeaking hips and 17 matched controls. Ninety-four percent of control hips were in a range of 25 degrees +/- 10 degrees anteversion and 45 degrees +/- 10 degrees inclination, but only 35% of squeaking hips were in this range (P = .0003). Eight hips squeak with bending. Four hips squeak with walking, and 5 hips squeak after prolonged periods of walking. Hips that squeaked with walking had acetabular components that were more anteverted (40 degrees ) than hips that squeaked with bending (19 degrees ) (P = .001) or prolonged walking (18 degrees ) (P = .020). The hips started squeaking after an average of 14 months. Patients with squeaking hips were younger, heavier, and taller than patients with silent hips.     

Edge loading in third generation alumina ceramic-on-ceramic bearings: stripe wear

Alumina ceramic-on-ceramic bearings perform exceptionally well under standard hip simulator conditions, but in vivo some retrieved bearings have shown an unusual stripe pattern of wear. We studied 16 bearings retrieved from a series of 1,588 cementless hip arthroplasties with third generation alumina ceramic-on-ceramic bearings to characterize the mechanism of stripe wear formation. None of these bearings were retrieved for bearing failure. The average wear volume was 0.4 mm(3) per year in the heads and 0.3 mm(3) per year in the liners. Mapping of wear stripes on the heads and liners showed that the majority do not occur with normal walking; instead they probably occur with edge loading when the hip is flexed, such as with rising from a chair or with climbing a high step.     

大直径陶瓷-陶瓷股骨头在保留股骨假体全髋关节翻修术中的应用

目的评价大直径陶瓷-陶瓷股骨头在保留股骨假体全髋关节翻修术中应用的临床疗效。方法回顾性分析自2006-01—2012-12在保留股骨假体全髋关节翻修术中应用直径36 mm陶瓷-陶瓷股骨头假体的32例（32髋）的临床资料。手术前后评估髋关节功能Harris评分,术后6周、6个月、1年及随后每隔半年随访中临床及X线片评价是否出现假体脱位、松动、下沉、骨溶解、陶瓷碎裂。结果 32例均获得随访平均26.2（11.0-38.0）个月。末次随访时髋关节功能Harris评分从术前平均68.9（9.0-87.0）分提高到85.0（39.0-98.0）分,差异有统计学意义（t=17.36,P=0.013）。均未出现假体脱位、松动、下沉、骨溶解、陶瓷破碎。结论大直径陶瓷-陶瓷股骨头在保留股骨假体的全髋关节翻修术中可以显著降低术后假体脱位率,不增加股骨侧假体周围骨溶解,可以获得较好的近、中期疗效。     

计算机辅助置入髋臼假体的可靠性和准确性分析

目的分析计算机辅助置入髋臼假体的可靠性和准确性。方法采用计算机辅助全髋关节置换手术30例。从计算机导航软件中获取术中显示髋臼假体的前倾角和外展角,并于术后骨盆平片上测算髋臼假体角度。结果术后1例假体下骨折,1例大粗隆骨折但无移位。平均切口长度(4.9±0.7)cm,手术时间(78.0±28.4)min,术中失血量(378.5±137.4)ml,术后引流量(551.6±257.1)ml。术中导航系统显示的前倾角与术后影像所测差异无统计学意义(P>0.05),而外展角差异则具有显著的统计学意义(P<0.01)。导航显示的髋臼杯方位全部位于Lewinnek安全区,术后影像所测显示有25例83%位于Lewinnek安全区,其余5例前倾角均位于安全区,而外展角则超出安全区。结论术中导航系统显示的前倾角有着较高的可靠性,而外展角的可靠性则较差。导航辅助置入髋臼假体前倾角的准确性较高,而外展角准确性则稍差。     

The transverse acetabular ligament: an aid to orientation of the acetabular component during primary total hip replacement: a preliminary study of 1000 cases investigating postoperative stability

Ensuring the accuracy of the intra-operative orientation of the acetabular component during a total hip replacement can be difficult. In this paper we introduce a reproducible technique using the transverse acetabular ligament to determine the anteversion of the acetabular component. We have found that this ligament can be identified in virtually every hip undergoing primary surgery. We describe an intra-operative grading system for the appearance of the ligament. This technique has been used in 1000 consecutive cases. During a minimum follow-up of eight months the dislocation rate was 0.6%. This confirms our hypothesis that the transverse acetabular ligament can be used to determine the position of the acetabular component. The method has been used in both conventional and minimally-invasive approaches.     

脊柱矢状面平衡对髋臼假体朝向的影响及其临床意义

全髋关节置换术临床应用广泛,髋臼假体的放置对于全髋关节置换术的效果及并发症的发生至关重要。自髋臼假体放置的“安全区”的概念提出以来,“安全区”一直是关节外科医生遵循的原则,而近年受到了挑战。临床中发现即使是髋臼假体放置在“安全区”,亦可能会发生全髋关节置换术的术后髋臼假体脱位。通过检索PubMed、Web of Science等数据库,根据纳入和排除标准进行筛选,最终纳入40篇文献,并查阅了相关专著。新近的研究表明,矢状面脊柱的平衡以及脊柱-骨盆活动度可以影响髋臼假体的空间位置。脊柱退变、长节段腰椎融合和脊柱强直等因素可导致矢状面脊柱不平衡和/或影响脊柱骨盆活动度,从而影响骨盆的后倾。合适的骨盆后倾是一种代偿方式,有利于髋关节置换术后假体的稳定。因而,有必要重新认识“安全区”,在行髋关节置换术前,有必要理解矢状面脊柱的平衡以及脊柱骨盆的活动度,以期进一步减少全髋关节置换术后脱位风险。本文以近年来国外文献中常见的脊柱-骨盆活动相关参数、髋臼假体空间朝向定义为切入口,介绍了脊柱矢状面平衡的定义、代偿机制,以此为基础并根据不同体位来讨论脊柱矢状面平衡和脊柱活动度在脊柱-骨盆活动下的意义。     

Wear analysis of failed acetabular polyethylene: a comparison of analytical methods

There are many methods for analysing wear volume in failed polyethylene acetabular components. We compared a radiological technique with three recognised ex vivo methods of measurement. We tested 18 ultra-high-molecular-weight polyethylene acetabular components revised for wear and aseptic loosening, of which 13 had pre-revision radiographs, from which the wear volume was calculated based upon the linear wear. We used a shadowgraph technique on silicone casts of all of the retrievals and a coordinate measuring method on the components directly. For these techniques, the wear vector was calculated for each component and the wear volume extrapolated using mathematical equations. The volumetric wear was also measured directly using a fluid-displacement method. The results of each technique were compared. The series had high wear volumes (mean 1385 mm(3); 730 to 1850) and high wear rates (mean 205 mm(3)/year; 92 to 363). There were wide variations in the measurements of wear volume between the radiological and the other techniques. Radiograph-derived wear volume correlated poorly with that of the fluid-displacement method, co-ordinate measuring method and shadowgraph methods, becoming less accurate as the wear increased. The mean overestimation in radiological wear volume was 47.7% of the fluid-displacement method wear volume. Fluid-displacement method, coordinate measuring method and shadowgraph determinations of wear volume were all better than that of the radiograph-derived linear measurements since they took into account the direction of wear. However, only radiological techniques can be used in vivo and remain useful for monitoring linear wear in the clinical setting. Interpretation of radiological measurements of acetabular wear must be done judiciously in the clinical setting. In vitro laboratory techniques, in particular the fluid-displacement method, remain the most accurate and reliable methods of assessing the wear of acetabular polyethylene.     

Effect of pelvic obliquity on the orientation of the acetabular component in total hip arthroplasty

In infrapelvic obliquity, coronal pelvic malrotation entails a change in the spatial location of the bony acetabulum. In the present study, 77 patients presented with infrapelvic obliquity with types 1 and 2 hip pathologies in which the pelvis is lower and higher, respectively, on the short-leg side. The 2 types were classified into 3 subtypes (A, B, and C) according to the severity of the pelvic obliquity (0°-3°, 3°-6°, and >6°). Angles of inclination of pelvic obliquity postoperatively, anteversions, and inclinations (abduction angle) for acetabular components were measured after total hip arthroplasty. Increased inclination (mean, 8.79°) was observed in type 1C, where the angle of inclination to pelvic obliquity postoperatively was minimally corrected. This increase may lead to cup instability. Rebalancing the pelvis in these cases with preoperative skeletal traction and/or sufficient release of hip contractures may be necessary. A correction of the mean inclination of the cup by 8.79° is required.     

侧卧位时头尾侧骨盆倾斜对全髋关节置换髋臼杯外展角的影响及校正

 目的 探讨侧卧位时骨盆向头尾侧倾斜的程度及其对髋关节置换术中髋臼假体外展角的影响及校正方法。方法 将50例62髋拟行全髋关节置换术的患者随机分为校正组及对照组,均采用侧卧位后外侧入路手术。对照组25例28髋以常规方法放置髋臼假体,校正组25例34髋进行水平仪及铅垂法校正后放置髋臼假体。术后测量两组患者髋臼杯外展角,并比较与术中预估的差异。结果 校正组在侧卧位未校正前骨盆整体倾斜-1.647°±4.512°,向头侧倾斜-(4.989°±2.778°),向尾侧倾斜2.587°±1.927°;头侧倾斜偏离大于尾侧,差异有统计学意义。校正组术后髋臼杯外展角为42.685°±3.355°,术中预估与术后测量偏差1.962°±1.515°;对照组术后髋臼杯外展角为44.534°±4.844°,术中预估与术后测量偏差4.244°±3.042°;校正组偏差小于对照组,差异有统计学意义。结论 侧卧位时头尾侧骨盆倾斜影响术者对髋臼外展角的判断,可能造成髋臼假体放置角度不准确。通过水平仪及铅垂法进行校正可提高判定髋臼假体外展角的准确性。     

Fractures of ceramic bearings: history and present status

During a period of 25 years (1977 to 2001), 13 fractures of an alumina component were recorded retrospectively. During the same period, approximately 5500 alumina components were implanted (3300 with all-alumina bearings and 1200 with alumina-on-polyethylene). These events occurred in seven women and six men, with a mean age of 59 years and a mean weight of 71 kg. There were eight fractures of the femoral head and five fractures of the socket component. Three fractures clearly were related to trauma (two fractures of the socket and one fracture of the head) and two were related to an abnormal design (one 22-mm head and one extra-long neck). Five fractures occurred without any rational explanation, but two fractures that occurred in the early phase could have been caused by a weaker alumina material. Finally three recent fractures of the liner were related to a change in the design of the material. This has been corrected and no additional fractures were observed. Although this dramatic event is of concern, it is infrequent and easy to solve by a limited revision procedure if done emergently. This rare complication should be balanced with the other complications of THR, including mechanical failures and osteolysis, often described with metal-on-polyethylene prostheses.     

Reducing the risk of dislocation after total hip arthroplasty: the effect of orientation of the acetabular component

Malposition of the acetabular component is a risk factor for post-operative dislocation after total hip replacement (THR). We have investigated the influence of the orientation of the acetabular component on the probability of dislocation. Radiological anteversion and abduction of the component of 127 hips which dislocated post-operatively were measured by Einzel-Bild-R?entgen-Analysis and compared with those in a control group of 342 patients. In the control group, the mean value of anteversion was 15 degrees and of abduction 44 degrees. Patients with anterior dislocation after primary THR showed significant differences in the mean angle of anteversion (17 degrees), and abduction (48 degrees) as did patients with posterior dislocation (anteversion 11 degrees, abduction 42 degrees). After revision patients with posterior dislocation showed significant differences in anteversion (12 degrees) and abduction (40 degrees). Our results demonstrate the importance of accurate positioning of the acetabular component in order to reduce the frequency of subsequent dislocations. Radiological anteversion of 15 degrees and abduction of 45 degrees are the lowest at-risk values for dislocation.     

Wear of the acetabular socket: Comparison of polyacetat and polyethylene

Frictional characteristics of polyacetal (Delrin®) sockets and of ultra-high molecular weight polyethylene sockets retrieved in revision after aseptic loosening were compared with measurements of friction in new sockets. Friction in retrieved polyacetal sockets was twice as great as in retrieved polyethylene sockets. We also found that frictional characteristics of polyacetal changed as the material aged in vivo. In contrast, friction in polyethylene sockets remained fairly constant, even though most of them contained bone-cement particles. Friction in polyacetal sockets may be important for the relatively high incidence of socket loosening of the Christiansen prosthesis.

Measurements of wear of the polyacetal sockets showed a mean annual dimensional change of 240 mm³, four times greater than that reported for the Charnley polyethylene acetabular prosthesis.