Case Study and Failure Analysis of a total hip Stem Fracture

Abstract

A total hip replacement is a procedure that requires removal of the affected joint lesions and replacing it with artificial elements. Nevertheless, like any invasive surgery, it is associated with the risk of complications, including joint infection, fracture of the bone during and after surgery, scarring and limitation of motion of the hip, and loosening of the prosthesis. In this work we present and describe the results of its investigations. In order to determine the mechanism of failure, a broken stem components were analyzed by means of macroscopic and microscopic observations and hardness measurements. The hardness, microstructure and chemical composition of the broken part of the hip stem were analyzed. Microscopic examination revealed numerous defects in material. Among them are pores and emptiness, located on the outskirts of the tested samples and a plurality of micro-cracking, debonding and delamination of the material due to the overloading of a fatigue character. There were no changes caused by intergranular corrosion or pitting, which may indicate for an even distribution of the major alloying components such as chromium and nickel. Observations of the material by using scanning electron microscopy (SEM), clearly proved that the destruction was caused by material fatigue. The investigation showed that the crack had originated due to a high stress concentration on the lateral corner section of the stem. Large surface of the fatigue crack zone area indicated for small stresses and small crack propagation velocities. There was a clear correlation between the grain size of the steel hardness. The results of hardness test revealed a significant increase hardness of stem in relation to the normative values. In addition, the measured average grain size is less than the standard accepted. Using Solid Works simulation and FEM a model of the stem was created and analyzed in terms of strength and rated the distribution of the generated stress. The finite-element analysis confirmed that there is the highest stress concentration in the middle of the stem

The 16-Year Evolution of Proximal Modular Stem Design – Eliminating Failure of Modular Junction

“…The greater the torque a muscle can produce, the greater the movement it will produce on the body's levers. We now know by experience that the hip sees torque values over (128.8 Nm), as demonstrated in our mechanical failures of the Apex Modular hip stems [10,12] (Figure 13). This paper follows on previous publications of this unique modular junction and demonstrates that design and materials can be improved upon once there is clear understanding of the failure mode.…”

“…Historical review and preclinical testing might meet the required standards set by regulatory bodies to achieve market release, but often these standards do not consider the ever-increasing physical activity and loads that these devices are encountering [10].…”

“…Since there are no standards established for modular junctions the overall performance of modular junctions are not equal. Careful review of basic engineering principles is necessary and recognizing design limits will reduce the indication of overuse [2,4,8,9,10].…”

“…So it is important to realize that fatigue cycles are accumulative and this has been the historical failure mode of fractured total hip stems [9,10] (Figure 10). …”

Simulation and experimentation crack analysis of annealed TC4 ELI alloy in the room and body fluid environment

“…Stress concentration plays a vital role in the growth and spread of cracks [18]. The Paris law determined the critical crack size and forecast fatigue life under LEFM assumptions [2,[19][20][21].…”