Comparison of proximal humeral bone stresses between stemless, short stem, and standard stem length: a finite element analysis

doi:10.1016/j.jse.2015.11.011

Journal of Shoulder and Elbow Surgery

Volume 25, Issue 7, July 2016, Pages 1076-1083

https://doi.org/10.1016/j.jse.2015.11.011 Get rights and content

Background

The stem lengths of humeral components used in shoulder arthroplasty vary; however, the literature on these devices is limited. This finite element study investigates the effect of humeral component length on stresses in the proximal humerus.

Methods

Intact and 3 reconstructed (standard length, short, and stemless implants) finite element models were created from shoulder computed tomography scan data (N = 5). Loading was simulated at varying abduction angles (15°, 45°, and 75°). The average bone stress (represented as a percentage of intact values) was reported at 8 transverse slices. In addition, the overall average change in cortical and trabecular bone stresses was quantified.

Results

Cortical bone stresses in the most proximal slice for the standard (58% ± 12%) and short (78% ± 10%) stem models were significantly reduced compared with the intact (100%) and stemless (101% ± 6%) models (P = .005). These reductions persisted in the second cortical slice for the standard stem compared with the intact, stemless, and short models (P = .025). Interestingly, stresses in the trabecular bone within these proximal slices were significantly elevated when stemless implants were used compared with all other implants (P < .001), regardless of abduction angle.

Conclusion

Reducing stem length produced humeral stresses that more closely matched the intact stress distribution in proximal cortical bone. Opposing trends presented in the proximal trabecular bone, probably because of differences in load transfer when shorter stems are used. Accordingly, the results suggest that implant stem length is 1 variable that can be modified in an attempt to better mimic intact bone stresses during humeral component insertion, provided stem fixation is adequate.

Section snippets

Methods

Preoperative computed tomography (CT) scans were acquired from 5 subjects (3 women and 2 men, 70 ± 6 years) who later underwent TSA. CT images, in DICOM format, were processed using Mimics (Materialise, Leuven, Belgium) to form a 3-dimensional solid model of the proximal humerus. Separate 3-dimensional models of the cortical and trabecular bones were created using a combination of automatic threshold-based segmentation and manual identification of trabecular/cortical bone boundaries. Under the

Results

Considering the average stress in cortical bone slices, it was found that only the 2 most proximal slices (slices I and II) presented with significant differences (Fig. 4). Within slice I, the stemless implant caused significantly higher cortical bone stresses than both the short (22% ± 11% change; P = .005) and standard stem designs (43% ± 13% change; P = .005), although all were still typically less than the bone stresses produced in the intact model. In addition, significant reductions in

Discussion

Significant differences in bone stresses were identified in the proximal humerus in comparing the standard length, short stem, and stemless implants. These differences are thoughtto arise because of changes in the load transfer patterns between the implants and bone. In the intact humerus, the load is directly borne by the subchondral bone and is transferred distally through and around the trabecular bone by a hard peripheral cortical shell. However, in the reconstructed humerus, the load is

Conclusion

This work quantifies stress changes in the proximal humerus after reconstruction with stemless, short, and standard length humeral implants using identical mesh multiple-specimen finite element modeling techniques. Variations in stem length were quantified for 3 abduction angles, and the overall average change in stress in the total cortical and trabecular bone regions was determined. As hypothesized, reductions in stem length resulted in cortical stresses that better mimicked the intact

Disclaimer

George S. Athwal is a consultant for DePuy-Synthes and Tornier Inc. In addition, he has received research support from Tornier, DePuy-Synthes, and Exactech for research related to the subject of this article. No company had any input into the study design, protocol, testing, data analysis, or manuscript preparation. All the other authors, their immediate families, and any research foundation with which they are affiliated have not received any financial payments or other benefits from any

Acknowledgment

The authors thank Jakub Szmit for his dedication in data analysis.

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Medium-term clinical and radiographic outcomes of a cementless prosthesis with a 140° neck–shaft angle in reverse total shoulder arthroplasty
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The design of humeral implants has evolved from the initial Grammont design, notably regarding the neck–shaft angle (NSA) and through the use of cementless prostheses. Stress shielding was frequently reported with cementless implants, the 2 main risk factors being humeral stem misalignment and high filling ratios. Our hypothesis was that standard length cementless stems with an NSA of 140° would facilitate good alignment with moderate filling ratios, thereby limiting stress shielding and ensuring good clinical outcomes.
A single-center retrospective study was conducted of patients who underwent reverse total shoulder arthroplasty between January 2015 and August 2017, with at least 2 years' follow-up. Clinical evaluations included range of motion measurements and Constant and subjective shoulder values scores. Frontal alignment was assessed in terms of the angle (α) between axes of the stem and of the humerus. Filling ratios were measured in the metaphysis of the humerus, in the diaphysis, and at the distal end of the stem and considered excessive above 0.7. Stress shielding was evidenced radiographically by the observation of medial cortical narrowing, medial metaphysis thinning, lateral metaphysis thinning or under-the-baseplate osteolysis.
Eighty-two shoulders were included and 70 had radiographic follow-up data available. The mean patient age was 78 years and 63/81 patients (78%) were female. The mean follow-up time was 39 ± 7 months. The mean α angle was 1.4° ± 0.9° and was less than 5° in all cases. The mean metaphyseal, diaphyseal, and distal filling ratios were 0.61 ± 0.06, 0.70 ± 0.08, and 0.64 ± 0.09, respectively. The mean Constant score improved from 28 ± 11 preoperatively to 64 ± 14 at last follow-up. The mean subjective shoulder values score at last follow-up was 81 ± 12. Seventy-nine percent of patients (55/70) had at least 1 form of stress-shielding related, which were not associated with clinical outcomes, apart from lateral metaphysis thinning, which was associated with lower active anterior elevation (mean, 106° ± 30° vs. 126° ± 28°; P = .01) and lower Constant scores (mean, 56 ± 17 vs. 65 ± 14; P = .06).
The use of cementless reverse shoulder prostheses with a NSA of 140° was associated with good clinical outcomes at 2 years' follow-up. The prosthesis stem was correctly aligned with the humeral axis and the filling ratios were <0.7 in all cases. Stress-shielding was common but, apart from lateral metaphysis thinning, this had no impact on clinical outcomes.
Factors affecting stress shielding and osteolysis after reverse shoulder arthroplasty: A multicenter study in a Japanese population
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Stress shielding and osteolysis around the humeral stem after reverse shoulder arthroplasty causes loosening and periprosthetic fractures and reduces bone stock during revision surgery. In Japanese patients, who have relatively small bodies, different characteristics may exist regarding the occurrence of these changes compared with the characteristics of Westerners, who have relatively larger frames. The purpose of this multicenter study was to investigate the incidence and clarify the predictors of stress shielding and osteolysis in Japanese individuals who underwent reverse shoulder arthroplasty.
The occurrence of stress shielding and osteolysis was investigated in 135 shoulders that had undergone reverse shoulder arthroplasty at least 2 years prior in five Japanese hospitals. During post-surgical follow-up, which was conducted every 3 months, the locations of the stress shielding occurrences, such as cortical thinning and osteopenia (which primarily occurred in zones 1, 2, and 7, where 1 is the greater tuberosity and 7 is the calcar part), spot weld, and condensation lines, were recorded. Cases without any abnormal findings on radiographs obtained up to ≥2 years after surgery were regarded as having no abnormalities. Finally, the predictors of cortical thinning and proximal humeral osteolysis were assessed using univariate and multivariate regression analyses.
Cortical thinning and osteopenia occurred in 68 shoulders, a condensation line occurred in 37 shoulders, and spot weld occurred in 23 shoulders. In particular, greater tuberosity and calcar osteolysis occurred in 40 and 47 shoulders, respectively. Long stem, cementless stem, and a larger proximal filling ratio were independent predictors of cortical thinning and osteopenia, whereas a cementless stem, larger metaphysis diameter, and a larger proximal filling ratio were associated with proximal humeral osteolysis.
The predictors of stress shielding and osteolysis included the use of long stems, cementless stems, larger proximal filling ratios, and larger metaphysis diameters.
retrospective comparative study (Level III).
The effect of humeral diaphyseal stem filling ratio on clinical and radiological outcome
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The stem of the reverse shoulder arthroplasty (RSA) used in this study population relies on diaphyseal anchorage. The surgical strategy was to insert the largest possible stem size to achieve an adequate press-fit fixation resulting in a high diaphyseal filling ratio (FR). However, for different reasons, a high FR was sometimes not achievable. The aim of this study was to analyze the effect of different FR (high/medium/low) on clinical and radiographic outcome (ie, subsidence and humeral peri-implant bone resorption), complications, and revision surgeries after RSA.
One hundred ninety nine patients were included and analyzed for clinical and radiologic outcome at a mean follow-up of 31.8 months after RSA. Diaphyseal humeral stem FR were measured directly postoperative and patients were divided into a low (N = 67), medium (N = 66), or high (N = 66) FR group. Humeral component complications and revision surgeries were measured as primary end points. Constant-Murley Score, range of motion, and the Subjective Shoulder Value were analyzed for clinical outcome. Periprosthetic bone resorption, radiolucent lines, shaft subsidence, and change in shaft alignment were measured for radiologic outcome.
Two intraoperative fractures were seen in the high FR group (3%) and none in the other groups. There was no clinical humeral component loosening and no correlation could be found between FR and revision surgery. No differences were found between the low, medium, or high FR groups regarding range of motion, Subjective Shoulder Value, and absolute and relative Constant-Murley Scores (P > .05). Bone resorption was significantly more present in the high FR group, compared to the low FR ratio group, 4.5 (standard deviation ± 2.2) vs. 6.4 (standard deviation ± 1.8), respectively (P < .001). However, no difference could be observed regarding radiolucent lines, shaft subsidence, or shaft alignment changes between the 3 groups.
High humeral diaphyseal stem FR in RSA is associated with more humeral bone resorption and might increase the risk for intraoperative stem fractures, compared to medium and low humeral diaphyseal stem FR. However, the FR does not have an effect on functional outcome or radiographic loosening signs after a mid-term follow-up of 31.8 months.
Two-year minimum survivorship and radiographic analysis of a pressfit short humeral stem for total shoulder arthroplasty
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Newer generation humeral stem designs in total shoulder arthroplasty (TSA) are trending towards shorter lengths and uncemented fixation. The goal of this study is to report a 2-yr minimum clinical and radiographic outcomes of an uncemented short-stem press-fit humeral stem in anatomic total shoulder arthroplasty (ATSA) and reverse total shoulder arthroplasty (RTSA).
A retrospective multicenter database review was performed of all patients who received an uncemented short-length press-fit humeral stem (Equinoxe Preserve humeral stem, Exactech, Inc., Gainesville, FL, USA) in ATSA and RTSA with a minimum two-year follow-up. The primary outcome was the prevalence of humeral stems at risk of radiographic loosening. Secondary outcomes included evaluation of functional outcome scores and prevalence of revision TSA for humeral stem loosening. Two blinded observers performed radiographic analyses, which included humeral stem alignment, canal filling ratio, radiolucent lines, stress shielding (calcar and greater tuberosity), and changes in component position (subsidence and stem shift). At risk stems were defined by the presence of one or more of the following: humeral stem with shifting or subsidence, scalloping of the humeral cortex, or radiolucent lines measuring 2 mm or greater in 3 or more zones.
287 patients (97 ATSA and 190 RTSA) were included in this study. The mean follow-up was 35.9 (±6.1) months. There were significant improvements for all functional outcome scores (P < .05), range of motion (P < .05), and visual analogue pain scale pain (P < .05). The prevalence of humeral stem at risk of radiographic loosening was 1% in the ATSA group (1/97) and 18.4% in the RTSA group (35/190). Calcar resorption was seen in 34% of ATSA and 19% of RTSA, with severe resorption in 12.4% of ATSA and only 3.2% of RTSA. Greater tuberosity resorption was present in 3.1% of ATSA and 7.9% of RTSA. The mean canal filling ratio was 50.2% (standard deviation 11.2%). Using logistic regression, a significant positive correlation between canal filling ratio and stress shielding (P < .01) was seen for both calcar and tuberosity stress shielding. The revision surgery rate was 0% in ATSA compared to 1.6% in RTSA.
This retrospective study demonstrates a low revision rate and low prevalence of humeral stems at risk of radiographic loosening at two years with a press-fit short-stem humeral design in ATSA. Physiologic subsidence of humeral stems can account for higher prevalence of humeral stems at radiographic risk of loosening in RTSA compared to ATSA
Stemless total shoulder arthroplasty for multiple epiphyseal dysplasia in a 52-year-old patient: a case report
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There are numerous reports of bone adaptation observed on plain radiography studies after the use of cementless short stems in reverse shoulder arthroplasty. However, reports on changes in bone mineral density (BMD) around the stem using dual-energy X-ray absorptiometry (DEXA) are prominently absent. In the present study, we measured BMD around the stem using DEXA and investigated changes over time from postoperative year 1 to year 2. Additionally, the relationship between BMD changes, filling ratio, and stem alignment was examined.
Forty-seven patients with short cementless stems who could be assessed via DEXA at 1-2 years postoperatively were included. After dividing the zones around the stem into 5, the BMD in each zone was measured, in addition to BMD changes and amount of change from postoperative year 1 to year 2. The relationship between filling ratio and stem alignment on postoperative plain radiography was assessed.
A significant decrease in BMD in zone 3 was observed between postoperative year 1 and year 2 (P = .02). Regarding filling ratio and stem alignment, a negative correlation between valgus stem alignment and BMD change observed in zone 1 (r = −0.470, P < .01). In addition, stem valgus greater than 6° correlated with a significant decrease in BMD in zone 1. (P = .01). No significant differences were found in the other zones. Furthermore, there was no correlation between filling ratio and BMD change.
In reverse shoulder arthroplasty cementless short stems, changes that that occurred between postoperative year 1 to year 2 demonstrated a decrease in BMD in zone 3. In addition, a decrease in BMD in zone 1 was observed with a stem alignment of valgus 6° or higher, suggesting that stem alignment within valgus 6° is required to prevent a decrease in BMD.

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: Institutional Review Board approval was granted by Lawson Health Research Institute (Health Sciences REB No. 105912, Approval No. R-15-057).

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Comparison of proximal humeral bone stresses between stemless, short stem, and standard stem length: a finite element analysis

Background

Methods

Results

Conclusion

Section snippets

Methods

Results

Discussion

Conclusion

Disclaimer

Acknowledgment

Clin Biomech

J Arthroplasty

J Biomech

J Biomech

Clin Biomech

J Biomech

J Shoulder Elbow Surg

J Biomech

J Biomech

J Arthroplasty

J Shoulder Elbow Surg

J Biomech

J Biomed Eng

J Biomech

J Arthroplasty

J Biomech

Med Eng Phys

J Shoulder Elbow Surg

Options and limits of stemless shoulder prostheses

Orthopade

Bone stresses before and after insertion of two commercially available distal ulnar implants using finite element analysis

J Orthop Res