Bone remodelling in humeral arthroplasty: follow-up using CT imaging and finite element modeling--an in vivo case study

The Applications of Finite Element Analysis in Proximal Humeral Fractures

Proximal humeral fractures are common and most challenging, due to the complexity of the glenohumeral joint, especially in the geriatric population with impacted fractures, that the development of implants continues because currently the problems with their fixation are not solved. Pre-, intra-, and postoperative assessments are crucial in management of those patients. Finite element analysis, as one of the valuable tools, has been implemented as an effective and noninvasive method to analyze proximal humeral fractures, providing solid evidence for management of troublesome patients. However, no review article about the applications and effects of finite element analysis in assessing proximal humeral fractures has been reported yet. This review article summarized the applications, contribution, and clinical significance of finite element analysis in assessing proximal humeral fractures. Furthermore, the limitations of finite element analysis, the difficulties of more realistic simulation, and the validation and also the creation of validated FE models were discussed. We concluded that although some advancements in proximal humeral fractures researches have been made by using finite element analysis, utility of this powerful tool for routine clinical management and adequate simulation requires more state-of-the-art studies to provide evidence and bases.

SPECT/CT demonstrates the osseointegrative response of a stemless shoulder prosthesis

BACKGROUND

This study evaluates bone remodeling processes in the proximal humerus induced by the implantation of a stemless shoulder prosthesis with regard to time of response and type and extent of bone turnover.

METHODS

Twenty-eight patients with primary osteoarthritis of the shoulder undergoing a stemless shoulder arthroplasty were prospectively evaluated. The local metabolic bone activity in 5 regions of interest (ROIs 1-5) around the implant and in 1 reference region (ROI ref.) in the humeral diaphysis was analyzed after the application of technetium Tc 99m DPD using single-photon emission computed tomography integrated with multidetector computed tomography (SPECT/CT). The study cohort was divided into 4 groups according to the timing of the most recent follow-up appointment to evaluate the primary osseointegrative response after surgery. The bone uptake values were expressed in target (ROIs 1-5) to nontarget (ROI ref.) ratios.

RESULTS

No difference within the 4 subgroups with respect to the time of local metabolic bone activity in the ROIs was found at 90 days after surgery. The highest initial metabolic activity and most temporal modifications were found in ROI 1, which was localized in the superior segment of the stem.

CONCLUSIONS

SPECT/CT data suggest that the primary osseointegration of a stemless shoulder prosthesis is almost completed 3 months after implantation. Variations in metabolic activity pattern in the ROIs during follow-up may be caused by different loading conditions of the bone.

Patterns of proximal humeral bone resorption after total shoulder arthroplasty with an uncemented rectangular stem

BACKGROUND

The aim of this study was to assess the timing and location of cortical bone resorption after total shoulder arthroplasty with an uncemented rectangular stem and investigate its effect on shoulder function up to 5 years after implantation.

METHODS

Between June 2003 and September 2006, 183 consecutive total shoulder arthroplasties were performed, 133 of which received a cementless rectangular stem as indicated by primary or post-traumatic osteoarthritis (OA). The 5-year postoperative follow-up rate was 80%. Standardized radiographic controls and clinical assessments were performed at 6 weeks, 6 months, and 1, 2, and 5 years.

RESULTS

Twenty-two patients (17%) showed full-thickness cortical bone resorption, 21 of whom were diagnosed with Sperling zone 2 resorption. The maximum craniocaudal distance of full resorption averaged 19.1 mm (range, 5.6-46.7 mm). The median distance progressed significantly from 9.6 mm to 13.8 mm between 6 and 12 months (P = .005). The risk of bone resorption was 3.1 times higher for post-traumatic OA patients than for those with primary OA. The occurrence of bone resorption increased significantly with increasing stem diameters relative to the humeral diameter. There was no significant effect of bone resorption on functional outcome.

CONCLUSION

Full-thickness cortical bone resorption in the proximal posterolateral humerus after receipt of a cementless rectangular stem has a prevalence of 17%, mostly occurring within the first year after surgery. Risk factors include age, post-traumatic conditions, and larger stem sizes relative to the humerus. This is a radiographic phenomenon without significant impairment of function or need for revision within 5 years after surgery.