Failure of the polyethylene glenoid component is the most common complication of Total Shoulder Arthroplasty (TSA) and accounts for a majority of the unsatisfactory results after this procedure. Nowadays, most of the shoulder prostheses consist of metal on polyethylene bearing components. Repetitive contact between the metal ball and the polyethylene socket produces progressive abrasion of the implant if the moving part is made of polyethylene. Its debris may then lead to an active osteolysis and implant loosening. Failure of the glenoid component is often manifested clinically by pain, loss of function, and the presence of a clunking noise and leads to revision surgery. The use of ceramic balls aims at the reduction of this phenomenon. In many studies regarding knee and hip replacement it has been shown that the use of ceramic on polyethylene (CoP) is more beneficial in terms of polyethylene wear and failure, when compared to metal on polyethylene (MoP). Since a human shoulder is very different from a hip and a knee, it is not a self-centering, neither congruent joint. And its stability is provided by healthy muscles of the rotator cuff. We decided to compare CoP against MoP in semi- force controlled test setup. Where, for a given governing angular motion the translational motion was a function of contact (frictional) forces between the tested couple (humeral head and PE). This is to our knowledge the first study to address in direct comparison wear in TSA in semi force controlled test setup. Up today, there is no test standard for wear testing of TSA. A customised joint simulator was used to create worst-case scenario motion allowing for simulation of the muscles in two perpendicular axes: inferior – superior (I-S) and anterior – posterior (A-P). Were a governing angular motion (GAM) was the abduction – adduction (±30°) in I-S. A system of springs was created so that the I-S translation and the A-P rotation were a result of the GAM. The stiffens of the springs was tuned based on the MoP pair initial kinematic (1000 cycles) to result in: about 2mm I-S translation, and about ±10° A-P rotation. All samples were tested at the same test station in order to obtain maximal repeatability. Axial load was in range of 100N to 750 N. Three articulating couples for each material were tested for total of 2M cycles. Standard midterm gravimetric measurements were conducted at each 0.5 M cycles.Introduction
Materials and methods
A secure taper connection in shoulder arthroplasty is mandatory to avoid loosening and fretting. This study's objective was to determine the amount of Impaction data was collected from experienced shoulder surgeons (n=5) during a cadaver lab. Testing groups (n=5 each) were: 1) The Statistics and data analysis were performed in MATLAB (2014b, Mathworks, Natick, MA, α=0.05). Two-tailed, pearson's linear correlation coefficients are reported. Group differences were determined using Kruskal Wallis test. Pair-wise comparisons were performed using a Tukey correction. Extremely high and variable impaction forces were measured (Table 1, Figure 2). The maximum force was nearly 27 kN; however, that value reduced to ∼18kN when the data from an outlier surgeon was removed. Maximum impaction forces were 12.45±4.36 kN, and the average was 10.47±3.63 kN. The pulloff force ranged from 0.94 kN to 5.54 kN with an average of 2.76±1.19 kN. Higher impaction forces required higher pulloff forces to disengage the taper connection (p<0.001, R>−0.608). Ceramic humeral heads showed a 24% higher fixation strength (p=0.004) under similar engagement conditions (p=0.18) in comparison to metal components. Head size does not appear to influence either the magnitude of the impaction force surgeons use (p>0.20) nor the force needed to disengage the taper (p=0.25). The surgeon performing the insertion had a significant influence on the impaction strike timing (p<0.001), number of strikes (p<0.001), and the impaction forces (p<0.03) and the pulloff force (p<0.001).Methods
Results
