The interactions between surgery type and obesity status on several mid-term shoulder-specific general outcomes were tested. The novel findings are (a) morbidly obese patients made significant improvements in functional and QOL outcomes over the mid-term; (b) there were no significant main effects for surgery type on ASES, SPADI, UCLA, and Constant scores; and (c) shoulder replacement adverse events and radiological outcomes were not different among the BMI groups. These findings demonstrate sustained benefit of both surgery types on clinically meaningful outcomes even in patients with high BMIs. The magnitude of improvement in QOL was less in the morbidly obese patients compared with the remaining groups by follow-up.
General health QOL and ROM/strength assessments were compared among non-obese, obese, and morbidly obese patients. Surgery benefits on outcomes were maintained past 2 years, suggesting that shoulder arthroplasty effectively relieves symptoms and improves function in patients across the BMI spectrum. Because morbidly obese patients had worse function and QOL before the surgery, they did not achieve the same absolute level of improvement as the other BMI groups on the ASES, SPADI, and UCLA scores. Improvements in these outcomes ranged from 48 to 65% in the morbidly obese group, and from 60 to 115% in the other groups. Despite the lesser gain in perceived function, morbidly obese groups achieved similar relative improvements in the SF-12 physical component score and over twice the improvement in the SF-12 mental component score than the other BMI groups. Few directly comparable data are available in obese patients. However, patient-reported QOL after RSA has been shown to reach comparable levels to that of healthy age-matched norms using the SF-36. Also, SF-36 domains have been shown to be higher than those reported by a normalized age-matched cohort after TSA (Gruson et al. 2010).
Recent studies measured shoulder replacement outcomes in obese patients. First, a case control study of obese and non-obese patients (N = 84) with RSA similarly found that obese patients did not achieve the same ASES improvement as non-obese controls after surgery (86 vs. 105%) (Pappou et al. 2014). Pain subscores improved similarly in the two patients groups (78–80%), but the greatest change occurred in the ASES function subscores in the non-obese and obese patients (142 vs. 89%). Second, a prospective study of patients enrolled in a shoulder registry (N = 76) collected preoperative and 2-year ASES and SF-36 scores, and visual analogue scales of pain and fatigue (Li et al. 2013). Patients were stratified into ‘‘normal’’ weight, overweight, and obese groups based on BMI. The ASES scores improved by 108 and 123% in the normal weight and obese patients, respectively. Improvements on the SF-36 physical and mental subscores were less in the obese patients than the normal weight patients, however. The obese patients experienced 2.1–12% improvements in the physical SF-36 subscores compared to the normal weight patients, who experienced improvements ranging from 11.3 to 40.2%. Third, a study of morbidly obese patients with TSA (N = 45 shoulders) found a 53.5% reduction in pain out to an average of 4.6 years of follow up (Linberg et al. 2009). These studies and ours suggest that obese patients may report improvements in shoulder-related function, but potentially less improvement in reported QOL.
Individuals with low and high BMI values can improve active elevation, external rotation, and internal rotation abduction and forward flexion after TSA and RSA (Constant et al. 2008; Gupta et al. 2014). We observed improvements in active (external rotation, active elevation) and passive (external rotation, elevation) ROM between morbidly obese, obese, and non-obese patients. Shoulder raise strength gains were made across all groups, with continued strength gain in the morbidly obese group. Obesity reduces upper body muscle strength and endurance (Cavuoto and Nussbaum 2014), compromises shoulder ROM as much as 38.9% for actions like shoulder abduction (Park et al. 2010), and increases upward scapular rotation during movement (Gupta et al. 2013). The combination of low muscle strength and shoulder ROM negatively impacts the ability to perform daily activities. Thus, improvements in ROM and strength in obese patients after surgery might translate to sustained performance of activities of daily living over time (Maier et al. 2014).
Case–control data comparing outcomes between TSA and RSA revealed that ASES scores, pain severity, elevation, abduction, and internal rotation improved similarly after the two procedures (Kiet et al. 2015). After RSA and TSA, a significant proportion of patients continue to participate in medium or high-demand activities (84 and 89%, respectively), but there are specific activities that people with RSA are unable to do well (Ware et al. 1996). Morbidly obese patients may experience unique difficulties with shoulder movements that are not captured with current instruments. Development of task inventories that may be relevant to an obese person may provide researchers and clinicians with better insight into the impact of the surgery on shoulder function. Surgeons and patients would benefit from discussing functional and QOL goals to determine which procedure would yield the best results (Schwarzkopf et al. 2013). Here, the morbidly obese group’s pain may be more related to degenerative disease and less to rotator cuff issues, whereas the non-obese group’s pain may be more linked with rotator cuff arthropathy and acute fracture. The fact that there were no differences in adverse events and radiological outcomes in the three patient groups indicates that obesity does not compromise the success of shoulder replacement. Surgical possibilities are open to both procedures, even in morbidly obese patients.
To our knowledge, this is the first study to examine the mid-term changes in function and patient-reported QOL after two shoulder replacement surgery types. Some limitations and strengths deserve comment. First, the patient subgroup sizes are different, with the morbidly obese subgroup being the smallest size. Based on clinical tracking of patient population demographics, we believe that this distribution represents the actual proportions of patients seen in this tertiary care institution. This study collected a battery of standardized assessments, most of which were self-report surveys. These surveys were joint-specific and general, providing a more comprehensive assessment of the patient experience. The same investigators administered the surveys and performed functional testing in all patients, minimizing interrater error.