Why is female gender associated with poorer clinical outcome after reverse total shoulder arthroplasty?

Abstract

INTRODUCTION: There is a lack of gender-specific research after reverse total shoulder arthroplasty (RTSA). While previous studies have documented worse outcome in women - a more thorough understanding of why outcome may differ is needed. We therefore asked: (1) Are there gender-specific differences in pre- and postoperative clinical scores, complications, surgery-related parameters and demographics? (2) Is female gender an independent risk factor for poorer clinical outcome after RTSA? (3) If so, why is female gender associated with poorer outcome after RTSA?
MATERIALS AND METHODS: Between 2005 and 2019, 987 primary RTSAs were performed in our institution. After exclusion criteria were applied, data of 422 female and 271 male patients were analyzed. Clinical outcome (absolute/relative Constant Score (a/rCS) and Subjective Shoulder Value (SSV)), complications (intra- and/or postoperative fracture, loosening), surgery-related parameters (indication, implant related characteristics) and demographics (age, gender, body mass index (BMI) and number of previous surgeries) were evaluated. Pre- and postoperative radiographs were analyzed (Critical Shoulder Angle (CSA), Deltoid-Tuberosity Index (DTI), Reverse Shoulder Angle (RSA), Lateralization (LSA) and Distalization Shoulder Angle (DSA)).
RESULTS: Preoperative clinical scores (aCS, rCS, SSV and pain level) as well as postoperative clinical outcome (aCS, rCS) were significantly worse in women. However, the improvement between pre- and postoperative outcome was significantly higher in female patients for rCS (p=0.037), internal rotation (p<0.001) and regarding pain (p<0.001). Female patients had a significantly higher number of intraoperative as well as postoperative fractures (24.9% vs. 11.4%, p<0.001). The proportion of female patients with a DTI<1.4 was significantly higher than in males (p=0.01). Female gender was an independent negative predictor for postoperative rCS (p=0.047, Coefficient -0.084) and pain (p=0.017, Coefficient -0.574). In addition to female sex per se being a predictive factor of worse outcome, females were significantly more likely to meet two of the three most significant predictive factors: (1) significantly worse preoperative clinical scores and (2) higher rate of intra- and/or postoperative fractures.
CONCLUSIONS: Female sex is a very weak, but isolated, negative predictive factor that negatively affects objective clinical outcome (rCS) after RTSA. However, differences did not reach the minimal clinically important difference (MCID) and it is not a predictor for subjective outcome (SSV). The main reason for worse outcome in female patients seems to be a combination of higher preoperative disability and higher incidence of fractures. To improve the outcome of women, all measures that contribute to the reduction of perioperative fracture risk should be utilized.