The Story of Shoulder Balance in AIS

Abstract

The saga of shoulder balance in scoliosis starts with the very definition of shoulder balance itself. Dzulkarnian has described defining, measuring, and indeed correcting shoulder balance as challenging for a lack of consensus in every domain [1]. Since the original description of scoliosis by Hippocrates in 450 BC, the cosmetic relevance of the shoulder in spinal deformity has been recognized. Mark Asher reported the significant contribution the shoulder levels may have on the ultimate outcomes of scoliosis surgery [2]. The definition of shoulder balance can range from the simplistic radiological level of the acromion processes (Fig. 1a, b) to the 3-D spatial orientation of the head and neck on the torso depending on the level of understanding and the requirements of the deformity correction strategies planned [3]. Since the SRS recognized it as a major cosmetic concern, several authors have tried to refine what superficially appeared to be a radiological measure. Over ten such measures are practiced today—most based on images of the standing X-ray measuring discrete points on the scapula, lateral clavicle, rib cage, etc. but others have added soft tissue shadows and medial markers like rib-clavicle angle and inter-clavicular angle [4]. Over time it became obvious that the skeletal levels alone had lesser importance and the soft tissue envelope needed to be factored in and that the medial torso consisting of the base of the neck and trapezius slope were of equal cosmetic concern [5]. Several authors reported their results on clinical photographs of the upper trunk and head-neck region of AIS patients and sought to define shoulder symmetry in more absolute terms [6]. Yong Qui et al. first described axial plane deformity of the shoulder while others have defined the spatial position of the neck and shoulder in three dimensions [7]. Though from a surgical planning perspective many surgeons (particularly North Americans) still use radiological levels to define shoulder levels, others have moved on to consider shoulder balance as an essential element of trunk cosmesis in AIS and determine the upper torso region on clinical photographs taken from multiple directions [8]. The present author has divided the torso into four regions—the base of the neck, the epaulette region, the axillary folds, and the scapular impression based on multidirectional clinical photography of AIS patients [9] (Fig. 2). Kwon and the team have redefined medial and lateral shoulder balance based on the residual neck tilt and neck mobility [10]. Additionally, axial plane rotation of the torso is also seen in these patients through the therapeutic import of these findings were hitherto unknown [11] (Fig. 3). Therefore, to summarize, shoulder balance refers to the spatial orientation of the shoulders about one another (each side comprising the neck base, upper trunk, scapular, and deltoid regions) and about the body alignment, about the X, Y, and Z axes in a given case of spinal deformity and not just the radiographic height of the acromion processes.