Endurance testing of hip prostheses: a comparison between the load fixed in ISO 7206 standard and the physiological loads.
BACKGROUND
Pre-clinical endurance validation of innovative hip prostheses femoral components are carried out following the ISO 7206 standard. The in vitro fatigue test must simulate accurately the physiological load to correctly define the section of the stem.


OBJECTIVE
This study investigates if the loads defined in the ISO 7206 standard simulate correctly the physiological load that occur in vivo.


METHODS
Simulation of the damage induced by in vitro test and in vivo loads is performed. Different designs of the stem are examined. Materials with different fatigue limit are considered. For the in vivo loads, different body weights are modelled.


METHODS
The minimal stem dimensions required to stand 20years of patient use and to pass the fatigue test are calculated based on linear damage accumulation.


RESULTS
The results show that the ISO load simulates reasonably well the physiological load that is likely to occur in active patients with a low or normal body weight. Conversely, the ISO test underestimates the physiological load that heavy and active patients are likely to apply to the implant.


CONCLUSIONS
Different minimum requirements for endurance strength should be fixed for hip prostheses designed for patients of different weight. This solution would reduce the risk of undersizing or oversizing the stem.


CONCLUSIONS
The introduction of a classification of the hip prostheses, fixing different minimum requirements for endurance strength, will lead to correctly size stems made of new materials or coated using new surface treatments, reducing the risk of implant failure of innovative prostheses.
Baleani
M
M
Laboratory for Biomaterials Technology, Rizzoli Orthopaedic Institute, Bologna, Italy. baleani@tecno.ior.it
Cristofolini
L
L
Viceconti
M
M
D006622:Hip Prosthesis; D006801:Humans; D008422:Materials Testing; D011474:Prosthesis Design; D013314:Stress, Mechanical