Introduction

Architectural changes occurring in the proximal femur after THA continues to be a problem. Stress shielding occurs regardless of fixation method. The resultant bone loss can lead to implant loosening and breakage of the implant. A new novel tissue sparing neck-stabilised stem has been designed to address these concerns.

Background: Dual-energy X-ray absorptiometry has been validated as an accurate method for assessing periprosthetic bone loss around the femoral stem after uncemented total hip arthroplasty. A prospective longitudinal study was conducted to evaluate bone mineral density (BMD) changes around a series of double-threaded cone-shaped modular femoral stems.

Materials: 64 hips with implanted double-threaded cone-shaped femoral stem were scanned in the anteroposterior femoral plane using a Lunar DPXL densitometer with special software. The initial MBD scan was performed 2–4 weeks after the surgery and thereafter yearly for up to three years.

Results: Significant changes occurred during the first year after surgery. In the proximal femur the mean BMD decreased to 73%±17% (p< 0.001) in the calcar area and to 91%±13% (p< 0.001) in the greater trochanter region. In the middle part of the stem the mean BMD decreased to 86%±17% (p< 0.001) on the medial side and to 84%±12% (p< 0.001) on the lateral side. No significant changes occurred around the distal part of the stem. During the second and third postoperative years, small progressive changes in BMD were noticed in all Gruen zones, in keeping with age-related bone loss.

Conclusion: Significant decreases in BMD around the femoral stem prosthesis in the proximal parts of the femur were recorded during the first postoperative year. These changes may be explained by the metaphyseal-diaphyseal gripping prosthesis design. No significant distal changes were found.

Background: Dual-energy x-ray absorptiometry has been validated as an accurate method for assessing periprosthetic bone loss around the femoral stem after uncemented total hip arthroplasty. A prospective longitudinal study was conducted to evaluate bone mineral density (BMD) changes around a series of double-threaded cone-shaped modular femoral stems.

Methods: Sixty-two hips with implanted double-threaded cone-shaped femoral stems were scanned in the antero-posterior femoral plane using a Lunar DPXL densitometer with special software. The initial BMD scan was performed between two and four weeks after the surgery and thereafter yearly for up to three years.

Results: Significant changes occurred during the first year after surgery. In the proximal femur the mean BMD decreased to 73%, by17% in the calcar area and to 91%, by13% in the greater trochanter region. In the middle part of the stem the mean BMD decreased to 86%, by 17% on the medial side and to 84%, 12% on the lateral side. No significant changes occurred around the distal part of the stem. During the second and third postoperative years, small progressive changes in BMD were noticed in all Gruen zones, in keeping with age-related bone loss.

Conclusions: Significant decreases in BMD around the prosthetic femoral stem in the proximal parts of the femur were recorded during the first postoperative year. These changes may be explained by the metaphyseal-diaphyseal gripping prosthesis design. No significant distal changes were found.