The design of hip replacements is based on the morphology of the proximal femur. Populations living in hard water regions have higher levels of serum calcium and magnesium which promote bone mineralization. A case control study was performed comparing proximal femoral morphology in patients living in soft and hard water regions to determine whether the effect of water hardness had an implication in the future design of hip-prostheses.

The proximal femoral morphology of 2 groups of 70 aged and sex matched patients living in hard and soft water regions at mean age 72.24 (range, 50 to 87 years) were measured using an antero-posterior radiograph of the non-operated hip with magnification adjusted.

The medullary canal diameter at the level of the lesser trochanter was significantly wider in patients living in the hard water region (mean width 1.9 mm wider; p=0.003). No difference was found at the isthmus, Dorr index, or cortical bone ratio.

In conclusion proximal femoral morphology does differ: a wider medullary canal at the level of the lesser trochanter in hard water regions. This size difference is relatively small and is unlikely therefore to affect the mechanics of the current femoral stem prostheses components.