These authors identified 1520 patients having primary anatomic (aTSA) arthroplasty and 2054 patients having primary reverse total shoulder arthroplasty with a minimum follow-up of 2 years (mean 5 years). All patients received the same platform shoulder prosthesis.
Patients were stratified according implant type (anatomic or reverse), and further stratification was based on patient BMI, with obese patients having a BMI ≥ 30 kg/m2 and non-obese patients with a BMI <30 kg/m2.
Obsesity is common among patients having elective arthroplasty: 41% of aTSA and 35% of rTSA were obese.
Obese patients in both groups reported higher preoperative and postoperative visual analog scale (VAS) pain scores (i.e. more pain) and less preoperative and postoperative ROM compared to non-obese patients.
Compared to non-obese patients, obese patients receiving an aTSA reported significantly worse postoperative SST, Constant, ASES, UCLA, and SPADI scores compared to non-obese patients, and those receiving rTSA reported significantly worse ASES and SPADI scores. However, these
22 differences did not exceed the minimal clinical important difference (MCID) or substantial benefit (SCB) criteria.
Statistically significant differences between obese and non-obese groups were not found to be clinically relevant given that the differences between the two groups with regards to VAS pain scores, ROM, and functional outcome scores did not exceed the MCID and SCB criteria in both the aTSA and rTSA groups.
Radiographic analysis 23 showed that in rTSA, obese patients had significantly less postoperative scapular notching and a lower scapular notching grade when compared to non-obese patients (P<0.05).
Obese patients had more comorbidities, greater intraoperative blood loss.
Overall complication rates were similar between obese and non-obese groups for both aTSA (7.6% vs. 8.4%; p = 0.57) and rTSA (3.4% vs. 3.9%), including rotator cuff tears, instability, infection, component loosening or failure, dislocation, liner dissociation, stress fracture, neurological complaints, and pain. Revision rates secondary to these complications were also similar between obese and non-obese groups for both aTSA (5.1% vs 5.9%) and rTSA (2.1% vs. 1.7%).
One of the more interesting findings in this study was that obesity seemed to protect patients against scapular notching and a higher notching grade. It seems possible that obesity limited adduction of the arm, reducing the contact between the medial edge of the humeral cup and the lateral scapular neck.
While obesity is commonly listed as a "modifiable" risk factor for shoulder arthroplasty outcomes, to our knowledge no study has demonstrated improved outcomes in patients who have "modified" their BMI.
It seems that obesity is less of a concern in shoulder arthroplasty than in hip and knee arthroplasty, yet we take extra time to discuss with these patients the need for extra attention to skin care (in the axilla and underneath the breast) and to care to protect the arm after surgery.