Reverse total shoulder replacement (RTSR) depends
on adequate deltoid function for a successful outcome. However, the
anterior deltoid and/or axillary nerve may be damaged due to prior
procedures or injury. The purpose of this study was to determine
the compensatory muscle forces required for scapular plane elevation
following RTSR when the anterior deltoid is deficient. The soft
tissues were removed from six cadaver shoulders, except for tendon
attachments. After implantation of the RTSR, the shoulders were
mounted on a custom-made shoulder simulator to determine the mean
force in each muscle required to achieve 30° and 60° of scapular
plane elevation. Two conditions were tested: 1) Control with an
absent supraspinatus and infraspinatus; and 2) Control with anterior
deltoid deficiency. Anterior deltoid deficiency resulted in a mean
increase of 195% in subscapularis force at 30° when compared with
the control (p = 0.02). At 60°, the subscapularis force increased
a mean of 82% (p <
0.001) and the middle deltoid force increased
a mean of 26% (p = 0.04). Scapular plane elevation may still be possible following an RTSR
in the setting of anterior deltoid deficiency. When the anterior
deltoid is deficient, there is a compensatory increase in the force
required by the subscapularis and middle deltoid. Attempts to preserve
the subscapularis, if present, might maximise post-operative function.
The sternoclavicular joint (SCJ) is a pivotal
articulation in the linked system of the upper limb girdle, providing
load-bearing in compression while resisting displacement in tension
or distraction at the manubrium sterni. The SCJ and acromioclavicular
joint (ACJ) both have a small surface area of contact protected
by an intra-articular fibrocartilaginous disc and are supported
by strong extrinsic and intrinsic capsular ligaments. The function
of load-sharing in the upper limb by bulky periscapular and thoracobrachial
muscles is extremely important to the longevity of both joints.
Ligamentous and capsular laxity changes with age, exposing both
joints to greater strain, which may explain the rising incidence
of arthritis in both with age. The incidence of arthritis in the
SCJ is less than that in the ACJ, suggesting that the extrinsic
ligaments of the SCJ provide greater stability than the coracoclavicular
ligaments of the ACJ. Instability of the SCJ is rare and can be difficult to distinguish
from medial clavicular physeal or metaphyseal fracture-separation:
cross-sectional imaging is often required. The distinction is important
because the treatment options and outcomes of treatment are dissimilar,
whereas the treatment and outcomes of ACJ separation and fracture
of the lateral clavicle can be similar. Proper recognition and treatment
of traumatic instability is vital as these injuries may be life-threatening.
Instability of the SCJ does not always require surgical intervention.
An accurate diagnosis is required before surgery can be considered,
and we recommend the use of the Stanmore instability triangle. Most
poor outcomes result from a failure to recognise the underlying
pathology. There is a natural reluctance for orthopaedic surgeons to operate
in this area owing to unfamiliarity with, and the close proximity
of, the related vascular structures, but the interposed sternohyoid
and sternothyroid muscles are rarely injured and provide a clear
boundary to the medial retroclavicular space, as well as an anatomical
barrier to unsafe intervention. This review presents current concepts of instability of the SCJ,
describes the relevant surgical anatomy, provides a framework for
diagnosis and management, including physiotherapy, and discusses
the technical challenges of operative intervention. Cite this article:
