Non-adherence to pain medication increases risk of postoperative frozen shoulder

Background: Postoperative frozen shoulder (FS) or adhesive capsulitis is a relatively frequent complication (5-20%), even after simple arthroscopic shoulder surgeries. The pathophysiology is still unclear, but psychological factors may play a pivotal role. From clinical experience, we hypothesized that patients, who are reluctant to take medications, particularly "pain-killers," have an increased incidence of postoperative FS. Methods: We identified twenty patients who underwent limited arthroscopic operations of the shoulder and developed postoperative FS. Twenty patients with matching type of surgery, age, and gender served as control group (n = 20). All patients were at least one year postoperative and asymptomatic at the time of examination. Demographic data, the patient's adherence to self-medication (including self-medicating scale, SMS), development the Quality of life (QoL), and depression scale (PHQ-4-questionnaire) were assessed. Results: Patients with FS had a 2-fold longer rehabilitation and 3-fold longer work inability compared to the patients without FS (P < 0.009 and P < 0.003, respectively). Subjective shoulder value SSV (P = 0.075) and post-operative improvement of QoL (P = 0.292) did not differ among the groups. There was a trend-but not significant-toward less coherence to self-medication in the FS-group (26.50 vs. 29.50; P = 0.094). Patients with postoperative FS significantly more often stated not to have "taken pain-killers as prescribed" (P = 0.003). Conclusions: Patients reporting unwillingness to take the prescribed pain medications had a significantly higher incidence of postoperative FS. It remains unclear whether the increased risk of developing FS is due to reduced postoperative analgesia or a critical attitude toward taking medication. However, patients who are reluctant to take painkillers should strongly be encouraged to take medications as prescribed.