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Shoulder crane: a concept of suspension, stability, control and motion

2019; Elsevier BV; Volume: 4; Issue: 2 Linguagem: Inglês

10.1136/jisakos-2017-000187

2059-7762

Gregory I. Bain, Joideep Phadnis, Eiji Itoi, Giovanni Di Giacomo, Hiroyuki Sugaya, David H. Sonnabend, James M. McLean,

Nerve Injury and Rehabilitation

Framework and suspensory cascadeThis novel model uses the structure and workings of the industrial crane as a simile to explain the function of the human shoulder. As a crane consists of a base, axial tower, boom and suspensory cascade that move and position loads in space, the base consists of the pelvic platform, with outriggers (legs) that provide stability in human body. The axial tower consists of an articulated spinal column and thoracic platform, which are stabilised by the core muscles. The clavicular boom articulates with the anterior thoracic platform and is elevated by the trapezius from the posterior tower. The 'suspensory cascade' extends from the skull and cervical spine to the trapezius and on to the clavicle, coracoclavicular ligaments, coracoid process, coracohumeral ligament and humeral head.MotionThe rotator cuff muscles take origin from the scapula and coalesce with each other to form a multilayered rotator cuff tendon and cable, which cups to closely contain the humeral head. The four muscles insert into the common tendon and together share the load to stabilise and mobilise the arm in space. The coracoid is a pulley that allows the scapula to swivel on the coracoclavicular ligaments to enable adjustment of the angle of force transmission delivered by the rotator cuff to the humeral head.Stability and controlThe inferior glenoid and labrum are a fixed organ of compression, which coalesces with the hammock formed by the static inferior glenohumeral ligaments. The rotator cuff and deltoid compress the humeral head onto this static structure.The biceps tendon passes adjacent to the condensations of the coracohumeral ligament to insert into the mobile superior labrum and glenoid. Contraction of the biceps pulls the mobile superior labrum onto the humeral head and tightens the glenohumeral ligaments that wrap around the humeral head at the extremes of motion. The coracohumeral ligament is a sensory organ that interfaces with these structures and is well positioned to work as a servomechanism to redirect the rotator cuff in providing stability, control and motion.Level of evidenceLevel V. This novel model uses the structure and workings of the industrial crane as a simile to explain the function of the human shoulder. As a crane consists of a base, axial tower, boom and suspensory cascade that move and position loads in space, the base consists of the pelvic platform, with outriggers (legs) that provide stability in human body. The axial tower consists of an articulated spinal column and thoracic platform, which are stabilised by the core muscles. The clavicular boom articulates with the anterior thoracic platform and is elevated by the trapezius from the posterior tower. The 'suspensory cascade' extends from the skull and cervical spine to the trapezius and on to the clavicle, coracoclavicular ligaments, coracoid process, coracohumeral ligament and humeral head. The rotator cuff muscles take origin from the scapula and coalesce with each other to form a multilayered rotator cuff tendon and cable, which cups to closely contain the humeral head. The four muscles insert into the common tendon and together share the load to stabilise and mobilise the arm in space. The coracoid is a pulley that allows the scapula to swivel on the coracoclavicular ligaments to enable adjustment of the angle of force transmission delivered by the rotator cuff to the humeral head. The inferior glenoid and labrum are a fixed organ of compression, which coalesces with the hammock formed by the static inferior glenohumeral ligaments. The rotator cuff and deltoid compress the humeral head onto this static structure. The biceps tendon passes adjacent to the condensations of the coracohumeral ligament to insert into the mobile superior labrum and glenoid. Contraction of the biceps pulls the mobile superior labrum onto the humeral head and tightens the glenohumeral ligaments that wrap around the humeral head at the extremes of motion. The coracohumeral ligament is a sensory organ that interfaces with these structures and is well positioned to work as a servomechanism to redirect the rotator cuff in providing stability, control and motion. Level V. What are the new findings•The shoulder crane consists of the primary parts: the base, axial tower, clavicular boom, suspensory cascade, pulley, and motor.•The core stabilises the tower, the periscapular muscles stabilise the scapular and the rotator cuff stabilises the glenohumeral joint.•The suspensory cascade extends from the skull to the trapezius muscle, clavicle, coracoclavicular ligaments (CCLs), coracoid, coracohumeral ligament (CHL) and finally humeral head. The coracoid is a pulley that swivels below the clavicle to allow the rotator cuff to be realigned.•The CHL is a sensory organ that interfaces with the rotator cuff and interval, biceps tendon, labrum and glenohumeral ligaments.•The dynamic biceps tendon inserts into the mobile superior labrum, which is confluent with the static superior and middle glenohumeral ligamentous restraints that wrap around humeral head at the extremes of rotation.•The shoulder crane is a biomechanical model, which explains shoulder suspension, stability, control and motion. •The shoulder crane consists of the primary parts: the base, axial tower, clavicular boom, suspensory cascade, pulley, and motor.•The core stabilises the tower, the periscapular muscles stabilise the scapular and the rotator cuff stabilises the glenohumeral joint.•The suspensory cascade extends from the skull to the trapezius muscle, clavicle, coracoclavicular ligaments (CCLs), coracoid, coracohumeral ligament (CHL) and finally humeral head. The coracoid is a pulley that swivels below the clavicle to allow the rotator cuff to be realigned.•The CHL is a sensory organ that interfaces with the rotator cuff and interval, biceps tendon, labrum and glenohumeral ligaments.•The dynamic biceps tendon inserts into the mobile superior labrum, which is confluent with the static superior and middle glenohumeral ligamentous restraints that wrap around humeral head at the extremes of rotation.•The shoulder crane is a biomechanical model, which explains shoulder suspension, stability, control and motion. PrefaceIn 2015, the members of the Shoulder and Upper Limb Committee of ISAKOS published a text book titled 'Normal and Pathological Anatomy of the Shoulder'. The editors were Gregory Bain, Eiji Itoi, Giovanni Di Giacomo and Hiro Sugaya.31Bain GI Itoi E Di Giacomo G Sugaya H Normal and Pathological Anatomy of the Shoulder. Springer-Verlag, Berlin Heidelberg2015Crossref Scopus (0) Google Scholar This book is a comprehensive state-of-the-art text on clinical anatomy of the shoulder and how it is affected by dysplasia, trauma, disease and degeneration. The concluding chapter titled 'The Functional Shoulder', brings together the many concepts presented by the authors throughout the book and presents a new model of normal shoulder anatomy.32Bain GI Phadnis J Sonnabend DH The functional shoulder.in: Bain GJ Itoi E Di Giacomo G Sugaya H Normal and Pathological Anatomy of the Shoulder. Springer-Verlag, Berlin Heidelberg2015Crossref Google ScholarThis article is based on the chapter 'The Functional Shoulder' and includes many of the concepts and images from this original chapter.32Bain GI Phadnis J Sonnabend DH The functional shoulder.in: Bain GJ Itoi E Di Giacomo G Sugaya H Normal and Pathological Anatomy of the Shoulder. Springer-Verlag, Berlin Heidelberg2015Crossref Google Scholar The original publication has been modified for publication with the support of the editorial board of JISAKOS, on the basis that it offers an important academic and educational contribution to the readers and the literature. In 2015, the members of the Shoulder and Upper Limb Committee of ISAKOS published a text book titled 'Normal and Pathological Anatomy of the Shoulder'. The editors were Gregory Bain, Eiji Itoi, Giovanni Di Giacomo and Hiro Sugaya.31Bain GI Itoi E Di Giacomo G Sugaya H Normal and Pathological Anatomy of the Shoulder. Springer-Verlag, Berlin Heidelberg2015Crossref Scopus (0) Google Scholar This book is a comprehensive state-of-the-art text on clinical anatomy of the shoulder and how it is affected by dysplasia, trauma, disease and degeneration. The concluding chapter titled 'The Functional Shoulder', brings together the many concepts presented by the authors throughout the book and presents a new model of normal shoulder anatomy.32Bain GI Phadnis J Sonnabend DH The functional shoulder.in: Bain GJ Itoi E Di Giacomo G Sugaya H Normal and Pathological Anatomy of the Shoulder. Springer-Verlag, Berlin Heidelberg2015Crossref Google Scholar This article is based on the chapter 'The Functional Shoulder' and includes many of the concepts and images from this original chapter.32Bain GI Phadnis J Sonnabend DH The functional shoulder.in: Bain GJ Itoi E Di Giacomo G Sugaya H Normal and Pathological Anatomy of the Shoulder. Springer-Verlag, Berlin Heidelberg2015Crossref Google Scholar The original publication has been modified for publication with the support of the editorial board of JISAKOS, on the basis that it offers an important academic and educational contribution to the readers and the literature.