Variation in Scapulohumeral Rhythm on Dynamic Radiography in Pathologic Shoulders: A Novel Diagnostic Tool.

Abstract

Alterations in scapulohumeral joint kinematics occur in various shoulder pathologies. Conventional imaging provides a static assessment of soft tissue and morphologic changes. Quantifying the scapulohumeral rhythm (SHR), using Dynamic Digital Radiography (DDR) can offer clinicians a greater understanding of the pattern and extent of motion impairment as well as reliably monitor changes throughout the treatment course. The purpose of this study was to analyze the SHR of patients diagnosed with small (SRCT) and massive rotator cuff tears (MRCT), adhesive capsulitis (AC), and glenohumeral osteoarthritis (GH-OA) and compare their measurements to those of patient controls with healthy shoulders using DDR. 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 0-30°, 30-60°, 60-90°, 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. 121 shoulders were analyzed. 40 normal controls were compared to 13 SRCT, 29 MRCT, 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 30o intervals of abduction, there was a significantly lower SHR found at 0-30°, 30-60° and 60-90° in MRCT, AC, and GH-OA across each motion range compared to controls. Control patients had an arc of abduction of 103° ± 32° which was significantly larger than all other pathologies (MRCT: 76° ± 23°, SRCT: 81° ± 21°, AC: 65° ± 27°, GH-OA: 71° ± 35°) and an average scapular abduction of 33° ± 14°, which was significantly less than patients with a MRCT (46° ± 10°) and AC (65° ± 27°). SHR remained significantly lower throughout shoulder abduction in MRCT (43.65%), AC (-54.29%), and GH-OA (32.01%) compared to controls. When isolating for humeral and scapular motion, all 4 pathologies had decreased GH abduction, while 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.