Diagnosis of Medial Shoulder Instability
13 November 2019 (online)
Medial shoulder instability is typically attributed to injury of the medial glenohumeral ligament, subscapularis tendon and/or medial joint capsule resulting in laxity or instability of the shoulder joint. The gold standard for assessing the aforementioned anatomic structures and making a clinical diagnosis of medial shoulder instability is arthroscopy. However, arthroscopy is relatively invasive and expensive when used solely as a diagnostic tool and so there is a need to establish a less involved method for diagnosing medial shoulder instability. To this end, a series of seminal studies suggested that measurement of shoulder abduction angles with physical examination can be repeatable and clinically useful.    Conversely, another study failed to demonstrate that increased shoulder abduction angles are specific to damage to the medial glenohumeral ligament or subscapularis tendon. Accordingly, it has remained a little unclear how repeatable and accurate this physical examination manoeuvre is among a larger group of practitioners, and whether additional diagnostic techniques could help diagnose medial shoulder instability.
Two studies  in this this issue of VCOT had observers measure shoulder abduction angles on cadaveric specimens that were normal and following transection of either the medial glenohumeral ligament alone or the medial glenohumeral ligament plus the subscapularis tendon. Both studies compared the goniometrically measured abduction angles to those obtained using stress radiography or stress fluoroscopy. The studies failed to demonstrate that goniometry consistently provided the same values as those obtained using stress radiography or fluoroscopy. Furthermore, one study showed poor inter-observer repeatability of goniometric measurement of shoulder abduction angles. The other study also showed good inter- and intra-observer repeatability of their stress radiographic technique. Accordingly, both studies question whether palpation with goniometry provides sufficient accuracy, and one study suggests that the described radiographic technique could potentially be developed into a clinically relevant alternative. However, it should also be mentioned that both studies provided data that could be interpreted as supporting goniometry as being useful. In one study, goniometry was significantly different between shoulders that did and did not have the medial glenohumeral ligament transected and correlation between the goniometric and radiographic measures was very good. In the other study, the one board-certified surgeon produced repeatable values and such values were, on average, only 2.9° different than those obtained fluoroscopically.
These studies are particularly valuable in highlighting that we should question whether published results in the hands of other veterinarians are representative of those we would obtain ourselves in clinical practice. It would be ideal if we all perform some self-assessment, preferably that is quantitative in nature, when it comes to how we assess increased shoulder abduction and make a diagnosis of medial shoulder instability. The stress radiographic technique that is described by Livet and colleagues may provide another technique to help meet these objectives.
- 1 Cogar SM, Cook CR, Curry SL, Grandis A, Cook JL. Prospective evaluation of techniques for differentiating shoulder pathology as a source of forelimb lameness in medium and large breed dogs. Vet Surg 2008; 37 (02) 132-141
- 2 Cook JL, Cook CR. Bilateral shoulder and elbow arthroscopy in dogs with forelimb lameness: diagnostic findings and treatment outcomes. Vet Surg 2009; 38 (02) 224-232
- 3 Cook JL, Renfro DC, Tomlinson JL, Sorensen JE. Measurement of angles of abduction for diagnosis of shoulder instability in dogs using goniometry and digital image analysis. Vet Surg 2005; 34 (05) 463-468
- 4 Cook JL, Tomlinson JL, Fox DB, Kenter K, Cook CR. Treatment of dogs diagnosed with medial shoulder instability using radiofrequency-induced thermal capsulorrhaphy. Vet Surg 2005; 34 (05) 469-475
- 5 Devitt CM, Neely MR, Vanvechten BJ. Relationship of physical examination test of shoulder instability to arthroscopic findings in dogs. Vet Surg 2007; 36 (07) 661-668
- 6 Jones SC, Howard J, Bertran J. , et al. 2019 Measurement of shoulder abduction angles in dogs: an ex vivo study of accuracy and repeatability. Veterinary and Comparative Orthopaedics and Traumatology: VCOT
- 7 Livet V, Harel M, Taroni M. , et al. 2019 Stress radiography for the diagnosis of medial glenohumeral ligament rupture in canine shoulders. Veterinary and Comparative Orthopaedics and Traumatology: VCOT