Variation in scapulohumeral rhythm on dynamic radiography in pathologic shoulders: a novel diagnostic tool

Hypothesis: The purpose of this study was to analyze the SHR of patients diagnosed with small (SRCTs) and massive rotator cuff tears (MRCTs), adhesive capsulitis (AC), and glenohumeral osteoarthritis (GH-OA) and compare their measurements to those of patient controls with healthy shoulders using DDR. We hypothesize that various diagnoses will vary with regards to SHR. Methods: The sequences of pulsed radiographs collated in DDR to create a moving image were prospectively analyzed during humeral abduction in normal controls and in 4 distinct shoulder pathology groups: SRCT, MRCT, AC, and GH-OA. GH and ST joint angles were measured at 0 degrees -30 degrees, 30 degrees -60 degrees, 60 degrees -90 degrees, and maximal coronal plane humeral abduction. SHR was defined as the ratio of the change in humeral abduction over the change in scapula upward rotation during humeral abduction and was calculated within the above angle intervals. Results: A total of 121 shoulders were analyzed. Forty normal controls were compared to 13 SRCTs, 29 MRCTs, 16 AC, and 23 GH-OA. SHR during humeral abduction differed significantly in patients with MRCT (1.91 +/- 0.72), AC (1.55 +/- 0.37), and GH-OA (2.31 +/- 1.01) compared to controls (3.39 +/- 0.79). When analyzed across 30 degrees intervals of abduction, there was a significantly lower SHR found at 0 degrees -30 degrees, 30 degrees -60 degrees, and 60 degrees -90 degrees in MRCT, AC, and GH-OA across each motion range compared to controls. Control patients had an arc of abduction of 103 degrees +/- 32 degrees, which was significantly larger than all other pathologies (MRCT: 76 degrees +/- 23 degrees, SRCT: 81 degrees +/- 21 degrees, AC: 65 degrees +/- 27 degrees, GH-OA: 71 degrees +/- 35 degrees) and an average scapular abduction of 33 degrees +/- 14 degrees, which was significantly less than patients with an MRCT (46 degrees +/- 10 degrees) and AC (65 degrees +/- 27 degrees). Conclusion: SHR remained significantly lower throughout shoulder abduction in MRCT (43.65%), AC (similar to 54.29%), and GH-OA (32.01%) compared to controls. When isolating for humeral and scapular motion, all 4 pathologies had decreased GH abduction, whereas AC and MRCT had an increased scapular compensatory motion compared to controls. Quantifying kinematic patterns like SHR using DDR can be implemented as a novel, safe, and cost-effective method to diagnose shoulder pathology and to monitor response to treatment. Level of evidence: Basic Science Study; Kinesiology (C) 2023 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.