Weekly alterations in bone mineral density in the gruen zonesafter total hip arthroplasty (clinical case and brief literature review)

Introduction Dual-energy X-ray absorptiometry (DEXA) provides a quantitative estimation of the projectional bone mineral density (PBMD) with minor radiation exposure and in a cost-effective way. It is one of the ways for a dynamic control of stem integration into the host bone after total hip arthroplasty (THA). Osteocytes are considered to play the key role in the regulation of implant integration process. Hence, DEXA could be used for estimation of functional activity and directions for regulation of osteocytes activities in the periprosthetic area. Purpose Current study presents the results of chronologic and biological PBMD in the periprosthetic zone after THA in two patients with a perspective for a future use of such an approach to reveal a local response of tissue to the implant. Material and methods PBMD was studied daily for 10 days with PRODIGY densitometer after THA in a 54-year old patient with posttraumatic right hip osteoarthrosis and a 59-year old patient with right femoral neck fracture nonunion. Cementless ZIMMER implants were used. Results In the first patient, oscillatory BMD alterations in the Gruen zones ranged from 2.4 to 11.6 % with an average wavelength of 4.6 days. In the second patient, the alterations were within the range of 2.3-8.7 % with an average wavelength of 4.5 days. PBMD changes in the adjacent Gruen zones occurred asymmetrically with some oscillational phase lagging relative to each other. After approximation of the results by linear trend, PBMD increased by 1.7 % on average in all Gruen zones in the first patient, except zones 2 and 3, and its mean growth was 1.7 %. On the contrary, PBMD decreased in all the zones in the second patient, except zones 4 and 7. Mean decrease was 1.7 %. Conclusion Chronobiological approach opens up possibilities for evaluation of structural and functional skeleton reorganization in the periprosthetic zone after THA. Further research is needed for a deeper insight into this complex issue.