1.1.2 Macro-traumatic Posterior Instability
- In maco-traumatic posterior shoulder instability (PSI), the history is usually one with arm
in a position of flexion, horizontal flexion (adduction) and internal rotation usually at or above
90° of GHJ flexion, where the force of the mechanism subluxes or dislocates the HH posteriorly.
Examples are a fall onto an outstretched arm in a forwards (flexed) position or tackle or
fall with the arm coming across the body (shoulder in adducted position). A fall in a workplace
scenario can also result in a similar injury. - Damage typically occurs to the posterior capsuloligamentous and labral complex,
plus or minus the posterior glenoid rim (reverse bony bankart lesion) and/or anterior
humeral head (reverse Hill Sachs) - Spontaneous relocation of posterior dislocations is much more common in posterior
instability as only 23 % of traumatic posterior instabilities require reduction. (Goubier,
Iserin, Duranthon, Vandenbussche, & Augereau, 2003; L. F. McIntyre, Caspari, & Savoie,
1997; Williams, Strickland, Cohen, Altchek, & Warren, 2003; Xu et al., 2015). This may
be due to the posterior aspect of the shoulder having more anatomical variations
(e.g. glenoid retroversion, glenoid dysplasia, variations in labral shape and attatchments)
(Ogul, Taydas, Sakci, Altinsoy, & Kantarci, 2021) and a thinner capsulolabral complex
compared to the anteriorly(Dashottar & Borstad, 2012); allowing for less restraint
to spontaneous relocation of the HH when the patient moves. - After a maco-traumatic PSI incident, the patient will often report that they experienced
a specific incident where their arm was injured but have no awareness that a dislocation
or subluxation occurred. The next day, the patient may report difficulty using their arm
and significant pain that lasts for weeks. This is often from the bleeding that has occurred
overnight from damage to the capsuloligamentous, labral and/or bony structures that results
in joint effusion (swelling), limiting range and creating pain. - The spontaneous relocation of many posterior dislocations,(Goubier et al., 2003;
L. Watson et al., 2023; Williams et al., 2003) reduced awareness of posterior dislocations
by the patient, and a low level of clinical suspicion of the condition,(Valencia Mora et al.,
2017; L. Watson et al., 2023) often leads to PSI being missed or misdiagnosed when the
patient presents to the health practitioner.(Schubert & Duralde, 2021) - Patients with macro-traumatic posterior instability may report pain rather than apprehension
(ref) (though apprehension and avoidance may still be reported) in combined positions
of flexion, HF and IR (see more in aggravating factors and symptomology section).