Objective To investigate the postoperative analgesic efficacy of ultrasound-guided infraspinatus-teres minor interfascial block （ITMIB） in patients who undergo arthroscopic shoulder surgery and to evaluate its impact on diaphragmatic function， motor recovery， and adverse effects. Methods Eighty patients who underwent arthroscopic rotator cuff repair at Zhongshan Hospital of Traditional Chinese Medicine between May 2024 and February 2025 were randomly allocated into the infraspinatus-teres minor interfuscial block group （Group A， n = 40） and the interscalene brachial plexus block group （Group B， n = 40）. Both groups received ultrasound-guided nerve block using 20 mL of 0.375% ropivacaine in combination with general anesthesia. A comparison was made between the two groups regarding resting VAS scores at various postoperative time points， the incidence of diaphragmatic paralysis， the recovery of sensory and motor function in the affected limb， and adverse reactions. Results Four cases in Group A were excluded from the analysis because of insufficient block efficacy， resulting in 36 cases in Group A and 40 cases in Group B available for analysis. There were no significant differences in static Visual Analog Scale （VAS） scores at 6 h， 12 h， and 24 h post-operatively （P > 0.05）. Nevertheless， Group A exhibited higher VAS scores in the Post-Anesthesia Care Unit （PACU） and at 2 h post-operatively compared with Group B （P < 0.05）. Moreover， Group A required a greater amount of flurbiprofen axetil within the first 2 h （P < 0.05）. At T1 （post-block assessment）， the incidence of hemidiaphragmatic paralysis was significantly lower in Group A （0%） than in Group B （90%） （P < 0.05）， and the degree of limb numbness was milder in Group A （P < 0.05）. Additionally， the forearm muscle strength was higher in Group A at T5 and T7 （P < 0.05）. The incidence of paresthesia during block placement was lower in Group A （P < 0.05）. Conclusions For patients undergoing arthroscopic shoulder surgery， ITMIB offers marginally less effective analgesia during the early postoperative period； however， it attains comparable pain relief thereafter. Moreover， it prevents diaphragmatic paralysis， promotes the early restoration of motor function in the affected limb， and does not elevate the risk of adverse reactions. These characteristics render it especially appropriate for patients with respiratory comorbidities.