[Changes of periprosthetic bone mineral density in cementless bicontact stem implantation; influence of different parameters--a prospective 4-year follow-up].

AIM

This prospective study describes the periprosthetic BMD (bone mineral density) after implantation of the cementless Bicontact stem over a period of 4 years. Additionally, the influence of several relevant parameters like age, sex, BMI (body mass index) and the influence of the stem-size on the periprosthetic BMD course were investigated.

METHOD

Measurement of the periprosthetic BMD in 36 patients (15 female, 21 male) in a prospective longitudinal study over 4 years with DEXA (dual energy X Ray absorptiometry) of the proximal Gruen zones 1 and 7.

RESULTS

We found a good precision of the method in vivo with a CV (coefficient of variation) of 1.04 %. There was a decline of the periprosthetic BMD at the whole proximal stem (ROI 0) of 20 % in the first 6 months. Afterwards there was a significant increase at the lateral stem (ROI 1) of 3.46 %, in contrast no significant change could be found medially, maybe as a result of a more lateral induction of power. The investigated parameters BMI, age and sex had no influence on the relative course of mineralisation. At stem sizes bigger than 15 the decline of BMD was significantly larger than at the stem sizes smaller than 15.

CONCLUSION

DEXA is a sufficiently precise method to investigate periprosthetic BMD. The postoperative periprosthetic course of mineralisation and the extent of BMD loss in the first 6 months after the Bicontact stem is similar to other periprosthetic BMD courses of prosthesis with a similar design. The course of mineralisation in "smaller" stems is obviously more auspicious than the course of "bigger" stems.