The purpose of this study was to investigate whether the femoral
head–neck contour, characterised by the alpha angle, varies with
the stage of physeal maturation using MRI evaluation of an asymptomatic
paediatric population. Paediatric volunteers with asymptomatic hips were recruited to
undergo MRI of both hips. Femoral head physes were graded from 1
(completely open) to 6 (completely fused). The femoral head–neck
contour was evaluated using the alpha angle, measured at the 3:00
(anterior) and 1:30 (anterosuperior) positions and correlated with
physeal grade, with gender sub-analysis performed.Objectives
Methods
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.Objectives
Materials and Methods
