Skip to main content
2024 BMES Annual Meeting Main banner
Icon Legend
This session is not in your schedule.
This session is in your schedule. Click again to remove it.

Orthopedic and Rehabilitation Engineering

Orthopedic and Rehabilitation Engineering - Poster Session D

Poster K10 - Radiographic Comparison of Total Shoulder Arthroplasty Implants with Different Stem Lengths and their Effect on Stress Shielding and Bone Resorption Due to Load Transfer

Friday, October 25, 2024
3:30 PM - 4:30 PM EST
Location: Exhibit Hall E, F & G

Introduction:  Anatomic total shoulder arthroplasty (aTSA) is a popular treatment for various arthritic conditions [1] [2]. Neer’s early TSA designs included a long-stemmed component that showed good performance but had disadvantages regarding bone preservation and difficult revisions [3] [4]. To reduce some complications, shorter and even stemless implants have been introduced to ultimately preserve bone stock and simplify the revision process with generally favorable outcomes [5] [6] [7] [8]. Although newer prostheses have shown to provide good clinical results in short- and long-term studies, stress shielding and osteolysis have become greater concerns due to the change of stress distributions along the humerus [9]. The length of the stem directly influences the location of load transfer along the humerus, leaving the bone above susceptible to stress shielding [10]. A newer implant was developed to potentially address some of these challenges by placing the fixation-resultant load transfer more proximally on the subchondral bone cortex, similar to native bone [11].
It is hypothesized that longer stems would result in higher grades of resorption and increased humeral lucency due to load transfer providing insufficient stimulation for bone tissue which may lead to implant failure or fracture over time. The purposes of the study are to determine if the humeral implant length influences the presence of bone resorptions and radiolucent lines (RLL) and if this newer implant could reduce these factors.

Materials and

Methods:  A retrospective cohort review of patients undergoing total shoulder arthroplasty with three different stem designs was performed. 21 patients were treated with a traditional standard-length implant (Univers™ II; Arthrex, Naples, FL, USA), 22 patients with a short-stem implant (Univers™ Apex; Arthrex, Naples, FL, USA), and 45 patients with a stemless implant (Catalyst CSR™; Catalyst OrthoScience, Naples, FL, USA). The cumulative mean follow-up period was 70.8 +- 26.8 months. Patients were excluded if they underwent revision procedures prior to follow up. A summary of patient demographics is shown in Table 1.
Radiographs were evaluated for the presence of bone resorptions and presence radiolucent lines (RLL) to identify loosening. The presence of calcar and greater tuberosity (GT) bone resorption was evaluated by comparing the initial postoperative anteroposterior/Grashey radiographs to the one received in last follow up. Using the classification proposed by Vegas et al., Grade 0 corresponds to no resorption, Grade 1 to decreased bone density, Grade 2 to cortical thinning of less than 50%, Grade 3 to cortical thinning of more than 50%, and Grade 4 to complete resorption [12].
Fisher’s Exact Test and Cramer’s V statistic were used to analyze all categorical data. Standard descriptive statistics summaries such as mean, standard deviations, and percentages, are reported in Table 1. All data were analyzed using SPSS Statistics Data Editor version 29 (IBM, Armonk, NY, USA).

Results, Conclusions, and Discussions: 

Results: Radiographic assessments are summarized on Table 2 with their respective statistical values. Amongst 88 shoulders studied, patients with a stemless implant showed significantly lower rates and severity of resorptions. The designs showed to have a strong association with calcar resorption (P < .001), and a relatively strong association with GT resorption (P < .001). However, the moderate association between the designs and the presence of RLL was insignificant (P = .068).

Discussions: Our study compared the observance of bone adaptations and/or radiolucent lines on three stem designs commonly used in TSA. The findings show agreement with the hypothesis that bone resorptions increase with longer stems, however, a correlation between the presence of RLL and stem lengths was not observed.
These outcomes suggest that the design of the humeral component plays a crucial role in mitigating stress shielding and bone resorption, which are theorized to be critical factors influencing the long-term survival of TSA implants. The reduction in bone resorption with stemless implants may be attributed to the more physiological, proximal load transfer, which may provide mechanical stimulation to bone, reducing stress shielding and subsequent bone loss. In contrast, longer stems, which rely on diaphyseal fixation, alter load distribution, decreasing mechanical stimulus and increasing bone resorption [13].
The major strength of this study is that it provides a comparison between three stems with a consistent surgical technique. However, there are limitations including sample size and possible selection bias. Although no studies were found where stress shielding directly correlates to functional outcomes, it still is a latent concern regarding long-term implant survival. Therefore, it is recommended that a study be completed with larger sample sizes, longer follow-up periods, and other possible factors such as revision rates and gender correlations.

Conclusions: Patients who received the stemless humeral component with a proximal fixation technique observe significantly lower rates of medial calcar and greater tuberosity resorption when compared to patients who received either the traditional standard-length or the short-stemmed implants.

Acknowledgements (Optional):  The authors would like to acknowledge Steven Goldberg, MD, for his contribution to and mentorship for this study.