Elsevier

The Journal of Arthroplasty

Volume 32, Issue 2, February 2017, Pages 594-600
The Journal of Arthroplasty

Basic Science
Comparison of Bone Remodeling Between an Anatomic Short Stem and a Straight Stem in 1-Stage Bilateral Total Hip Arthroplasty

https://doi.org/10.1016/j.arth.2016.07.016Get rights and content

Abstract

Background

Femurs of dysplastic hips exhibit specific abnormalities, and use of modular or specially designed components is recommended. An anatomic short stem was previously designed specifically for dysplastic hips using 3-dimensional data acquired from dysplastic patients. To investigate effects of stem geometry on bone remodeling, we undertook a prospective, randomized study of patients who had undergone 1-stage bilateral total hip arthroplasty (THA) with the anatomic short stem on one side and a conventional straight stem on the other.

Methods

The study included 36 patients who underwent the above THA procedure. We assessed bone mineral density as well as the presence of cancellous condensation or bony atrophy due to stress shielding based on the analysis of Gruen's zones and newly defined equal-interval zones, at an average follow-up period of 9.2 years.

Results

All stems were bone ingrown stable. Cancellous condensation was observed more proximally, and areas of bone atrophy were narrower on the anatomic short stem side than on the straight stem side. Bone mineral density values reflected results of cancellous condensation and stress shielding and were higher in more proximal zones on the anatomic short stem side than on the straight stem side.

Conclusion

Although radiographic results indicated good midterm outcomes of THA with both stems, the loading pattern differed. The anatomic short stem achieved its design purpose in terms of proximal fixation and load transfer and led to better preservation of the proximal femur.

Section snippets

Subjects

The study included 41 patients (6 men and 35 women; mean age at surgery, 51.7 years) who underwent 1-stage bilateral THA between 2004 and 2007. Cases with extreme differences in stage or severity of OA were excluded. OA severity was evaluated using radiographic grading of the Japanese Orthopaedic Association (JOA grade) [23] and Crowe group [24], and cases with differences of more than 1 grade based on either system were excluded, as were cases with a difference of more than 1.0 in preoperative

Results

Preoperative morphology of femur was assessed as follows. Bone types were classified according to Dorr et al [31]. Specifically, hip types A, B, and C were 8/10 (straight stem/anatomic stem), 28/26, and 0/0 (P = .868), respectively. Average flare indices for the straight stem and anatomic stem were 4.34 ± 0.70 and 4.37 ± 0.75, respectively (P = .517). Average neck anteversion for the straight stem was 21.6° ± 13.8° and that for the anatomic stem was 25.4° ± 14.2° (P = .069). We observed no

Discussion

Radiographic changes indicative of cancellous condensation, bone atrophy due to stress shielding, or cortical hypertrophy were evaluated by analyzing both Gruen's [33] and equal-interval zones in hips of patients who had undergone 1-stage bilateral THA with the anatomic short stem on one side and a conventional straight stem on the other. Gruen's zone analysis is often used in radiographic evaluation of periprosthetic changes. In it, zones are proportional to stem length, and the corresponding

Acknowledgments

We thank Drs. Yoshinori Asou and Sadao Morita for clinical support of this study. We also acknowledge the excellent contributions of Ms. Rie Kitano and our radiological technologists to the dual-energy X-ray absorptiometry analysis.

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    One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2016.07.016.

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