Evaluation of surgical impaction technique and how it affects locking strength of the head–stem taper junction

Abstract

Cases of fretting and corrosion at the taper junction have been reported in large metal-on-metal bearing combinations, and more recently, this concern has included metal-on-polyethylene bearing combinations. Many of these patients have been revised due to adverse local tissue reaction secondary to taper corrosion. This taper corrosion-related adverse local tissue reaction seems to be a multifactorial issue and difficult to assess. The aim of this study was to look at one potential variable, the impaction behavior (impaction force, number of blows, etc.) of orthopedic surgeons, and understand how this can affect the locking strength of tapers. A group of experienced orthopedic surgeons were asked to use their typical surgical approach to impact a femoral head onto a hip femoral stem using an Operating Room (OR)-simulated test setup. Impaction parameters such as impaction force, velocity, and energy, as well as the number of impacts, were characterized and applied in a bench-top study used to evaluate the effect of these parameters on the initial stability of the taper junction. High variation was found in the surgical impaction parameters, but overall it was determined that increased impaction force correlated to superior stability of the taper junction.

What the Surgeon Can Do to Reduce the Risk of Trunnionosis in Hip Arthroplasty: Recommendations from the Literature

“…When all other parameters are equal, MacLeod's model estimates a higher fixation force than Fessler's model by about a third ( Figure 2). However, when considering the technical aspects of the different experimental setups, nearly all fixation force values described in the literature correspond to the values estimated by Fessler's formula, ranging 40% to 55% of the impaction force [6,21,44,[47][48][49][50][51][52]. Surprisingly, the values measured by MacLeod et al do not correspond to those estimated by their own model [43].…”

“…In both models, the fixation force correlates linearly with the force applied to impact the taper. The fixation force, therefore, has a major effect on the stability of the taper connection [6,[44][45][46][47][48][49][50][51][52]. Because the taper angle α is determined by the chosen prosthesis design (typically between 5 • 30 and 6 • [36]), this parameter has to be considered as fixed.…”

“…As the rate of impaction has no relevant effect on the fixation force [49,78], impaction with a hammer might be considered equivalent, even if minor mechanical differences might be identified [55]. While force sensors at the tip of the impactor might approximate the assembly force applied to the taper, the energy dissipated by the impactor must be subtracted from the values measured by the sensing hammers [10,43,50,78,79]. Some studies do not even adequately describe the impaction force used or the fixation force measured [45,74].…”

“…Impaction with at least 4000 N is recommended. An adequate impaction force can be reached with a strong blow from a 500 g hammer [46,50]. Surgeons should become familiar and proficient with force-measuring instruments, especially those surgeons with low levels of experience in arthroplasty, to avoid the application of insufficient or off-axis impaction force [46].…”

Investigation of Assembly Forces During Creation of Head-Neck Taper Junction Following Total Hip Arthroplasty: A Biomechanical Study

“…Reproducing physiological damping behaviour of human soft tissues in vitro not only enables the comparison of the assembly forces of different surgeons, but can also be used to determine the forces actually acting on the patient. For example, Scholl et al [21] have carried out a similar investigation on a very rigid structure and have measured assembly forces up to approximately 25 kN. They explained the very high forces in comparison to other studies [14] by the point where the force was measured (striking pad of the hammer).…”