Impact magnitudes applied by surgeons and their importance when applying the femoral head onto the Morse taper for total hip arthroplasty

Abstract

We recommend at least two firm, axially aligned blows to impact the femoral head onto the trunnion intra-operatively.

A computational approach to fretting wear prediction at the head–stem taper junction of total hip replacements

“…4 with the maximum force set at 4000 N [1] (a value in the range typically applied by surgeons). During this impaction the base of the stem trunnion is fixed in all degrees-of-freedom.…”

“…The prosthetic femoral head in THR is assembled to the stem using a conical taper fixation. The head is impacted onto the stem trunnion intraoperatively with long-term and safe fixation of the assembly dependent on the taper junction design and the impaction load applied [1].…”

The effect of different assembly loads on taper junction fretting wear in total hip replacements

“…All of these studies involved (at least) the simulation of the assembly and disassembly of cobalt chrome alloy heads with titanium alloy stem trunnions. The magnitude of the impaction forces used in the studies were determined initially using tests in [9], [10], and [12] where surgeons were required to apply an impact typical of that used intra-operatively to assemble the head to the stem. The average of the measured forces from the three studies were approximately 5000N (1 surgeon × 11 impacts) [10]; 1633N, Standard Deviation 422N (8 surgeons × 5 impacts each) [12]; and 4409N (10 surgeons × 1 impact each) [9].…”

“…It is known that the magnitude of this impaction force affects the initial taper strength (taper lock) and it has been postulated that attaining maximum fixation is crucial in minimizing problems associated with these tapers such as corrosion, fretting and micromotion. A number of experimental studies have investigated parameters that affect taper fixation [9][10][11][12] with the axial taper 'pull-off' force being used as the measure to assess taper strength. All of these studies involved (at least) the simulation of the assembly and disassembly of cobalt chrome alloy heads with titanium alloy stem trunnions.…”

CORR Insights®: High Risk of Failure With Bimodular Femoral Components in THA

“…From what we know now, I believe surgeons should take particular care to clean and dry the mating surfaces of the taper prior to impacting [2], and then impact the assembled junction in a direction that is in line with the taper junction. Impaction should be done with as large a force as is safe when considering the risk for femoral fracture [1].…”