Collier Matthew B, Engh C Anderson, McAuley James P, Engh Gerard A
Anderson Orthopaedic Research Institute, P.O. Box 7088, Alexandria, VA 22307, USA.
J Bone Joint Surg Am. 2007 Jun;89(6):1306-14. doi: 10.2106/JBJS.F.00667.
Wear of the polyethylene tibial bearing is a leading cause of failure of knee replacements done prior to the current decade. The objective of this study was to determine how patient-related factors, implant-related factors, and limb or tibial component alignment influenced the amount of thickness loss in polyethylene tibial bearings that were retrieved at the time of revision surgery or after the death of the patient.
We retrieved polyethylene tibial bearings from eighty-one unicondylar and eighty-nine total knee replacements that had been performed because of osteoarthritis with varus deformity from 1984 to 1998. All of the polyethylene bearings had been sterilized with gamma radiation in air. Polyethylene loss was quantified as the change in the minimum bearing thickness per years in vivo (the mean time in vivo [and standard deviation] was 8 +/- 4 years). Multiple linear regression was used to assess whether polyethylene loss was associated with age, weight, gender, varus angle of the tibial component, postoperative hip-knee-ankle angle, initial thickness of the polyethylene, shelf age of the polyethylene, and either the type of polyethylene (for total knee replacements, which were of one posterior cruciate ligament-retaining design) or the manufacturer (for unicondylar knee replacements), and to determine the magnitude by which polyethylene loss would change if any of the significant risk factors were changed.
The mean loss (and standard deviation) of polyethylene thickness in the medial compartment of total knee replacements (0.33 +/- 0.28 mm/yr) and that in medial unicompartmental knee replacements (0.49 +/- 0.40 mm/yr) were significantly (p < 0.05) associated with the same three variables: patient age, postoperative hip-knee-ankle angle, and shelf age of the polyethylene. A total knee bearing with a one-year increase in shelf age, a unicondylar knee bearing with a six-month increase in shelf age, a patient who was ten years younger at the time of operation, or a limb that was aligned in 5 degrees more varus (less valgus) had similar effects on the loss of polyethylene thickness in the medial compartment; the coefficients of the linear regression equations indicated that any one of these changes would increase polyethylene loss by 0.11 to 0.14 mm/yr.
The wear-related loss of thickness in gamma-irradiated-in-air polyethylene bearings from unicondylar and total knee replacements implanted in osteoarthritic knees with varus deformity is influenced mainly by the shelf age of the polyethylene, the age of the patient, and the postoperative angulation of the knee in the coronal plane.
Although polyethylene bearings have not been sterilized with gamma radiation in air since the end of the last decade, many arthroplasty patients have polyethylene bearings that were sterilized with use of this method. An understanding of the findings of this study may be of value as these patients return for follow-up care. Whether the study findings have relevance to bearings sterilized with other methods is unclear and will remain so for many years.
Prognostic Level II.
聚乙烯胫骨平台磨损是本世纪前十年膝关节置换失败的主要原因。本研究的目的是确定患者相关因素、植入物相关因素以及肢体或胫骨部件对线如何影响翻修手术时或患者死亡后取出的聚乙烯胫骨平台的厚度损失量。
我们从1984年至1998年因骨关节炎伴内翻畸形而进行的81例单髁膝关节置换和89例全膝关节置换中取出聚乙烯胫骨平台。所有聚乙烯平台均在空气中进行伽马射线灭菌。聚乙烯损失量通过体内每年最小平台厚度的变化来量化（体内平均时间[及标准差]为8±4年）。采用多元线性回归评估聚乙烯损失是否与年龄、体重、性别、胫骨部件的内翻角度、术后髋-膝-踝角度、聚乙烯的初始厚度、聚乙烯的储存年限、聚乙烯类型（对于全膝关节置换，为一种保留后交叉韧带的设计）或制造商（对于单髁膝关节置换）相关，并确定如果任何一个显著风险因素发生变化，聚乙烯损失量将改变的幅度。
全膝关节置换内侧间室聚乙烯厚度的平均损失（及标准差）（0.33±0.28mm/年）和内侧单髁膝关节置换的平均损失（0.49±0.40mm/年）与相同的三个变量显著相关（p<0.05）：患者年龄、术后髋-膝-踝角度和聚乙烯的储存年限。储存年限增加1年的全膝关节平台、储存年限增加6个月的单髁膝关节平台、手术时年轻10岁的患者或内翻角度增加5度（外翻角度减小）的肢体对内侧间室聚乙烯厚度损失有类似影响；线性回归方程的系数表明，这些变化中的任何一个都会使聚乙烯损失量增加0.11至0.14mm/年。
植入有内翻畸形的骨关节炎膝关节的单髁和全膝关节置换中，在空气中进行伽马射线灭菌的聚乙烯平台与磨损相关的厚度损失主要受聚乙烯的储存年限、患者年龄以及膝关节在冠状面的术后角度影响。
尽管自上世纪末以来聚乙烯平台未再在空气中进行伽马射线灭菌，但许多关节置换患者的聚乙烯平台是采用这种方法灭菌的。了解本研究结果对于这些患者复诊接受后续治疗可能有价值。本研究结果是否与采用其他方法灭菌的平台相关尚不清楚，且在未来许多年仍将如此。证据水平：预后II级。
