Laser engravings as reason for mechanical failure of titanium-alloyed total hip stems

Electrocautery Damage Can Reduce Implant Fatigue Strength: Cases and in Vitro Investigation

BACKGROUND

The risk of femoral stem fracture after total hip replacement is low and can often be associated with a specific implant system or other factors that may reduce the fatigue strength. Additionally, damage to a metal component during revision surgery by an electrocautery device may further affect the fatigue behavior.

METHODS

Two clinical cases of stem failure after revision of fractured ceramic components are presented; the retrieved components were analyzed for the cause of failure. In vitro cyclic load-to-failure testing of titanium alloy femoral stems after electrocautery application at 2 different locations (at the base and about midway on the femoral neck) was performed using a stepwise increase in load until implant fracture occurred. In addition, a detailed characterization of the local material structure around the electrocautery marks was performed.

RESULTS

Superficial discoloration and melting marks were found on the retrieved components, including at the location of crack initiation in the anterolateral region, which may have reduced the fatigue strength of the material. In addition, elemental analysis indicated material transfer from the electrocautery tip. Damage to the surface by the electrocautery device significantly reduced the in vitro load to failure by up to 47% compared with that of undamaged femoral neck specimens. Material analysis revealed a relevant modification in microstructure, with an extension of approximately 2.7 mm and a depth of 550 µm, which could be divided in 3 structural zones.

CONCLUSIONS

Intraoperative electrocautery device contact with the implant during surgical revision of a total hip replacement cannot always be avoided. However, on the basis of our findings, the risk of implant failure is increased due to a change in microstructure and a potential reduction of the implant's fatigue strength. Surgeons and manufacturers of electrocautery devices should be aware of this concern.

CLINICAL RELEVANCE

During revision surgery, contact between an electrocautery device and the femoral component should be avoided to reduce the chance of subsequent femoral neck fracture.

A Method for Prediction of Femoral Component of Hip Prosthesis Durability due to Aseptic Loosening by Using Coffin/Manson Fatigue Model

The purpose of this work is to develop a new model estimate of the fatigue life of a hip prosthesis due to aseptic loosening as a multifactorial phenomenon. The formula developed here is a three-parameter model based on Basquin's law for fatigue, eccentric compression formula for the compressive stress and torsion in the prosthesis due to the horizontal components of the contact force. With our model, we can accurately predict the durability of a hip prosthesis due to the following four parameters: body weight, femoral offset, duration, and intensity of daily physical activities of a patient. The agreement of the prediction with the real life of the prosthesis, observed on 15 patients, is found to be adequate. Based on the formula derived for a particular implant, there was a high degree of concurrence between the model-predicted and actual values of aseptic loosening (durability) proved by the Mann–Whitney U test. By virtue of the validated model, it is possible to predict, quantitatively, the influence of various factors on the hip life. For example, we can conclude that a 10% decrease of a patient's body mass, with all other conditions being the same, causes 5% increase of the hip fatigue life.

[Handling of retrieved implants in orthopedic surgery : Results of a survey within the framework of the EndoCert initiative]

BACKGROUND

Although investigations of retrieved medical implants can provide valuable information about the cause of the revision, there is a lack of information, which could be avoided by consequent failure analyses. In the framework of the EndoCert certification system it is obligatory to record and report incidents.

OBJECTIVES

The present work examines how the willingness to report has developed in certified arthroplasty centers and which method of handling retrievals is preferred and actually used.

MATERIALS AND METHODS

On the basis of a questionnaire for handling retrievals, all 508 arthroplasty centers that were certified till June 1, 2016, were included (return rate = 97.2%).

RESULTS

A total of 93.3% of the centers have established an algorithm for handling of retrievals and 83.0% of the centers prefer to hand out the retrieval to the patient, while only 25.7% wish to store it in the center for research purposes. In the case of a potential incident as the cause of revision, centers prefer to forward the retrieval to damage analysis, whereby the centers act in different ways, depending on the case. An implant fracture is, e.g., considered a reportable event in most cases without temporal limitation. On the other hand, breakage or failure of surgical instruments is considered not to be reported in the case of more than half of the centers. In 2014 and 2015, approximately 71% of EPZs reported no incidents.

CONCLUSIONS

According to our survey, many certified arthroplasty centers are sensitized to careful handling of retrievals. The treatment of the explanted components is conducted in different ways. The assessment of whether an incident is to be reported shows large differences. In view of the relatively high number of revision surgeries, the number of reports to the authorities appears to be low.