Stress shielding following stemless anatomic total shoulder arthroplasty

Background

Finite element analysis has suggested that stemless implants may theoretically decrease stress shielding. The purpose of this study was to assess the radiographic proximal humeral bone adaptations seen following stemless anatomic total shoulder arthroplasty.

Methods

A retrospective review of 152 prospectively followed stemless total shoulder arthroplasty utilizing a single implant design was performed. Anteroposterior and lateral radiographs were reviewed at standard time points. Stress shielding was graded as mild, moderate, and severe. The effect of stress shielding on clinical and functional outcomes was assessed. Also, the influence of subscapularis management on the occurrence of stress shielding was determined.

Results

At 2 years postoperatively, stress shielding was noted in 61 (41%) shoulders. A total of 11 (7%) shoulders demonstrated severe stress shielding with 6 occurring along the medial calcar. There was one instance of greater tuberosity resorption. At the final follow-up, no humeral implants were radiographically loose or migrated. There was no statistically significant difference in clinical and functional outcomes between shoulders with and without stress shielding. Patients undergoing a lesser tuberosity osteotomy had lower rates of stress shielding, which was statistically significant (p = 0.021).

Discussion

Stress shielding does occur at higher rates than anticipated following stemless total shoulder arthroplasty, but was not associated with implant migration or failure at 2 years follow-up.

Level of evidence

IV, Case series.

Fixed- vs. variable-angle humeral neck cut in anatomic total shoulder arthroplasty: a randomized controlled trial

BACKGROUND

Variable neck-shaft angle (NSA) stemmed humeral components have been incorporated into certain implant designs to better re-create normal anatomy in total shoulder arthroplasty (TSA). The purpose of this study was to determine if premorbid glenohumeral joint anatomy is better restored with a fixed- vs. variable-NSA prosthesis.

METHODS

A randomized controlled trial was performed including 50 patients with osteoarthritis indicated for primary anatomic TSA. Patients were randomized preoperatively to receive either a variable- (n = 26) or fixed-NSA (n = 24) prosthesis. Humeral neck cut in the variable-NSA group matched the patient's anatomic neck, with prosthetic NSA of 127.5°, 132.5°, and 137.5° available. Fixed-NSA cuts were made with an intramedullary guide of 132.5°. Preoperative and postoperative radiographs were evaluated for specific radiographic anatomic variables: NSA, head thickness, tuberosity-to-head height, head offset, articular arc, greater tuberosity offset, and center of rotation (COR). Postoperative radiographic criteria were compared between groups.

RESULTS

No differences were found between groups in demographics or preoperative radiographic measures. When comparing average difference in preoperative and postoperative measurements in the fixed-NSA group, the humeral head offset from the humeral shaft axis significantly decreased by 1.4 mm (P = .046), and the COR moved superiorly (3.0 mm, P = .002) without significant medialization or lateralization. In the variable angle group, humeral head offset decreased but did not reach significance (1.2 mm, P = .091), and the COR also moved superiorly (2.9 mm, P < .001) without significant medialization or lateralization. All remaining radiographic parameters did not significantly change from pre- to postoperative imaging. In comparing the fixed- and variable-NSA groups' net change from the premorbid measurements, no significant differences were found in tuberosity-to-head height, head offset, or COR position in both the horizontal and vertical planes.

CONCLUSIONS

Both fixed- and variable-NSA anatomic TSA humeral components demonstrate adequate restoration of premorbid anatomy radiographically.

Total shoulder arthroplasty using a subscapularis-sparing approach: a radiographic analysis

BACKGROUND

Traditional total shoulder arthroplasty (TSA) involves releasing the subscapularis tendon for exposure. This can potentially lead to subscapularis insufficiency, compromised function, and dissatisfaction. A novel TSA technique preserves the subscapularis tendon by performing the procedure entirely through the rotator interval, allowing accelerated rehabilitation. However, early reports on this approach have noted malpositioning of the humeral component and residual osteophytes. In a randomized trial, we examined the incidence of humeral head malpositioning, incorrect sizing, and residual osteophytes on postoperative radiographs after subscapularis-sparing TSA compared with the traditional approach.

METHODS

Patients were prospectively randomized to undergo TSA performed through the traditional or subscapularis-sparing approach. The operating surgeon was blinded to the randomization until the day of surgery. Anatomic reconstruction measurements included humeral head height, humeral head centering, humeral head medial offset, humeral head diameter (HHD), and head-neck angle. Two independent reviewers analyzed the postoperative radiographs to determine anatomic restoration of the humeral head and the presence of residual osteophytes.

RESULTS

We randomized 96 patients to undergo either the standard approach (n = 50) or the subscapularis-sparing approach (n = 46). There were no significant differences in humeral head height, humeral head centering, humeral head medial offset, HHD, head-neck angle, and anatomic reconstruction index between the 2 groups. However, significantly more postoperative osteophytes (P = .0001) were noted in the subscapularis-sparing TSA group. Although the overall mean was not statistically different, further analysis of HHD showed that more patients in the subscapularis-sparing TSA group were outliers (mismatch >4 mm) than in the traditional TSA group.

CONCLUSIONS

Although anatomic restoration of the shoulder can be accomplished using subscapularis-sparing TSA, retained osteophytes and significant mismatch of the HHD raise concerns regarding long-term outcomes.