University of Bath, Claverton Down Rd, Bath, North East Somerset BA2 7AY, UK.
Southmead Hospital, Department of Trauma and Orthopaedics, North Bristol NHS Trust, Southmead Way, Bristol, BS10 5NB, UK.
Bone Joint Res. 2016 Aug;5(8):338-46. doi: 10.1302/2046-3758.58.BJR-2016-0044.R1.
Modular junctions are ubiquitous in contemporary hip arthroplasty. The head-trunnion junction is implicated in the failure of large diameter metal-on-metal (MoM) hips which are the currently the topic of one the largest legal actions in the history of orthopaedics (estimated costs are stated to exceed $4 billion). Several factors are known to influence the strength of these press-fit modular connections. However, the influence of different head sizes has not previously been investigated. The aim of the study was to establish whether the choice of head size influences the initial strength of the trunnion-head connection.
Ti-6Al-4V trunnions (n = 60) and two different sizes of cobalt-chromium (Co-Cr) heads (28 mm and 36 mm; 30 of each size) were used in the study. Three different levels of assembly force were considered: 4 kN; 5 kN; and 6 kN (n = 10 each). The strength of the press-fit connection was subsequently evaluated by measuring the pull-off force required to break the connection. The statistical differences in pull-off force were examined using a Kruskal-Wallis test and two-sample Mann-Whitney U test. Finite element and analytical models were developed to understand the reasons for the experimentally observed differences.
36 mm diameter heads had significantly lower pull-off forces than 28 mm heads when impacted at 4 kN and 5 kN (p < 0.001; p < 0.001), but not at 6 kN (p = 0.21). Mean pull-off forces at 4 kN and 5 kN impaction forces were approximately 20% larger for 28 mm heads compared with 36 mm heads. Finite element and analytical models demonstrate that the differences in pull-off strength can be explained by differences in structural rigidity and the resulting interface pressures.
This is the first study to show that 36 mm Co-Cr heads have up to 20% lower pull-off connection strength compared with 28 mm heads for equivalent assembly forces. This effect is likely to play a role in the high failure rates of large diameter MoM hips.Cite this article: A. R. MacLeod, N. P. T. Sullivan, M. R. Whitehouse, H. S. Gill. Large-diameter total hip arthroplasty modular heads require greater assembly forces for initial stability. Bone Joint Res 2016;5:338-346. DOI: 10.1302/2046-3758.58.BJR-2016-0044.R1.
模块化连接在当代髋关节置换术中无处不在。头臼连接与大直径金属对金属（MoM）髋关节的失效有关，而这些髋关节目前是矫形外科史上最大的法律诉讼之一（估计成本超过 40 亿美元）。有几个已知的因素会影响这些压配合式模块化连接的强度。然而，不同头大小的影响尚未被研究。本研究的目的是确定头大小的选择是否会影响臼-头连接的初始强度。
使用 Ti-6Al-4V 臼（n = 60）和两种不同大小的钴铬（Co-Cr）头（28mm 和 36mm；每种大小各 30 个）进行研究。考虑了三种不同的装配力水平：4 kN；5 kN；和 6 kN（n = 10 每个）。随后通过测量断开连接所需的拔出力来评估压配合连接的强度。使用 Kruskal-Wallis 检验和两样本曼-惠特尼 U 检验检查拔出力的统计差异。开发了有限元和分析模型来理解实验观察到的差异的原因。
在 4 kN 和 5 kN 冲击时，36mm 直径的头的拔出力明显低于 28mm 直径的头（p < 0.001；p < 0.001），但在 6 kN 时则没有（p = 0.21）。在 4 kN 和 5 kN 冲击力下，28mm 头的平均拔出力比 36mm 头大约大 20%。有限元和分析模型表明，拔出强度的差异可以用结构刚性的差异和由此产生的界面压力来解释。
这是第一项表明，对于等效的装配力，36mm Co-Cr 头的拔出连接强度比 28mm 头低 20%的研究。这种效应可能在大直径 MoM 髋关节的高失败率中发挥作用。
A. R. MacLeod、N. P. T. Sullivan、M. R. Whitehouse、H. S. Gill. 大直径全髋关节置换模块化头需要更大的装配力以获得初始稳定性。骨与关节研究 2016;5:338-346. DOI: 10.1302/2046-3758.58.BJR-2016-0044.R1.
Zotero 插件
