Peri-acetabular bone remodelling after uncemented total hip arthroplasty with monoblock press-fit cups: an observational study

Mechanobiochemical bone remodelling around an uncemented acetabular component: influence of bone orthotropy

Mechanical loosening of an implant is often caused by bone resorption, owing to stress/strain shielding. Adaptive bone remodelling elucidates the response of bone tissue to alterations in mechanical and biochemical environments. This study aims to propose a novel framework of bone remodelling based on the combined effects of bone orthotropy and mechanobiochemical stimulus. The proposed remodelling framework was employed in the finite element model of an implanted hemipelvis to predict evolutionary changes in bone density and associated orthotropic bone material properties. In order to account for variations in load transfer during common daily activities, several musculoskeletal loading conditions of hip joint corresponding to sitting down/up, stairs ascend/descend and normal walking were considered. The bone remodelling predictions were compared with those of isotropic strain energy density (SED)-based, isotropic mechanobiochemical and orthotropic strain-based bone remodelling formulations. Although similar trends of bone resorption were predicted by orthotropic mechanobiochemical (MBC) and orthotropic strain-based models across implanted acetabulum, more volume (10-20%) of bone elements was subjected to bone resorption for the orthotropic MBC model. Higher bone resorption (75-85%) was predicted by the orthotropic strain-based and orthotropic MBC models compared to the isotropic MBC and SED-based models. Higher bone apposition (35-160%) across the implanted acetabulum was predicted by the isotropic MBC model, compared to the SED-based model. The remodelling predictions indicated that a reduction in estrogen level might lead to an increase in bone resorption. The study highlighted the importance of including mechanobiochemical stimulus and bone anisotropy to predict bone remodelling adequately.

The role of bone remodeling in measuring migration of custom implants for large acetabular defects

In revision total hip arthroplasty, achieving robust fixation is difficult and implant movement may occur over time. Bone may also rearrange around the implant as a result of mechanical loading, making the measurement of migration challenging. The study aimed to quantify changes in bone shape and implant position 1 year following acetabular reconstruction using custom three-dimensional-printed cups. This observational retrospective cohort study involved 23 patients with Paprosky type IIIB defects. Postop computed tomography scans taken within 1 week of surgery and at 1-year postsurgery were co-registered and analyzed. Three co-registration strategies were implemented including bone-to-bone and implant-to-implant. (1) Co-registration of the ipsilateral innominate bone (diseased anatomy) was used to measure changes in implant position. (2) Co-registration of the implant was carried out to quantify changes in the ipsilateral innominate bone shape. (3) Co-registration of the contralateral innominate bone (nondiseased anatomy) was performed to measure changes in the ipsilateral innominate bone shape and implant position. The median centroid distances (interquartile range [IQR]) were 2.3 mm (IQR: 3.7-1.7 mm) for changes in implant position, 2.4 mm (IQR: 3.6-1.6 mm) for changes in ipsilateral innominate bone shape, and 3.7 mm (IQR: 4.6-3.5 mm) for changes in ipsilateral innominate bone shape and implant position. Following acetabular reconstruction, implant movements and periprosthetic bone remodeling are physiological and of a similar extent. Surgeons and engineers should consider this when performing implant monitoring in these patients.

Comparison study of periprosthetic bone remodeling between simultaneous bilateral total hip arthroplasty and unilateral total hip arthroplasty: a matched cohort study

PURPOSE

The load-bearing pattern of periprosthetic bone may differ between patients who underwent simultaneous bilateral and unilateral total hip arthroplasty (THA). We investigated the differences in periprosthetic bone remodeling after simultaneous bilateral total hip arthroplasty and unilateral total hip arthroplasty.

METHODS

This retrospective cohort study enrolled 154 consecutive patients undergoing THA using full hydroxyapatite (HA) compaction short stems. Patient characteristics including age, body mass index, University of California Los Angeles (UCLA) activity score, and bone shape of the proximal femur were adjusted by propensity score matching. Subsequently, periprosthetic bone mineral density changes were compared between simultaneous bilateral and unilateral THA.

RESULTS

We found that bone mineral density loss in the simultaneous bilateral THA group was significantly higher in zones 6 and 7 at 24 months after THA (zone 6, p = 0.019; zone 7, p = 0.041). Periprosthetic bone mineral density loss was not associated with clinical factors, including age, body mass index, and daily activity. Additionally, we demonstrated that periprosthetic bone mineral density loss was higher in zones 1, 4, 6, and 7 of patients with a normal hip on the contralateral side after unilateral THA (zone 1, p = 0.041; zone 4, p = 0.041; zone 6, p = 0.037; zone7, p = 0.019).

CONCLUSIONS

The postoperative periprosthetic bone remodeling was lower in patients who underwent simultaneous bilateral THA than in those who underwent unilateral THA, even though patient characteristics were adjusted by propensity matching. Further observation of periprosthetic bone mineral density loss is needed to clarify the differences between the groups.

Bone Preservation in Total Hip Arthroplasty

BACKGROUND

Preserving bone stock in younger and more active patients after total hip arthroplasty (THA) is important for future revision. Newer prosthesis designs, including short femoral stems and isoelastic acetabular cups, are likely to preserve more bone stock. However, long-term follow-up studies on bone remodeling after short-stem THA with an isoelastic monoblock acetabular cup are few. Therefore, we evaluated bone preservation after THA using these prostheses at a 5-year follow-up.

METHODS

This prospective observational study is a 5-year follow-up of our previously reported 2-year observational study on the same cohort of patients. We included 45 patients with primary osteoarthritis treated with a calcar-guided femoral short-stem prosthesis and a monoblock press-fit acetabular cup. We evaluated bone mineral density (BMD) around the prostheses using dual-energy X-ray absorptiometry and reported functional outcomes preoperatively and at 3, 12, 24, and 60 months postoperatively. All complications were recorded.

RESULTS

At the final follow-up, the BMD was comparable with that at 24 months in Gruen zones 3, 4, 5, 6, and 7, whereas it significantly differed in Gruen zones 1 (P < .0001) and 2 (P < .004). On the acetabular side, the BMD leveled off similarly in all DeLee and Charnley zones between 24 and 60 months (P > .05). Moreover, all measured clinical outcomes significantly improved (P < .001). One perioperative dislocation was reported.

CONCLUSION

Patients undergoing THA with a calcar-guided femoral short-stem prosthesis and a monoblock acetabular cup can expect preservation of bone stock over a longer follow-up with excellent clinical outcomes and few complications.