Biomechanics of posterior shoulder instability - current knowledge and literature review

Table 1 The role of computed tomography scans, magnetic resonance imaging arthrograms and diagnostic rigor

	CT arthrography	MRI arthrography
Sensitivity	82%-100%[75]	48%-89%[76,77]
Specificity	96%-100%[75]	93%[77]
Advantage Disadvantage	Identifying bony lesions, severity of fractures, assessing humeral and glenoid version[78] lower inter-examiner reliability[79]	Identifying the soft tissue from labrum to the rotator cuff[80], good for preoperative classification of labroligamentous injuries[81] Limited in elderly patients[80]
	Radiation
Pathologies	Small soft tissue lesions[82]
	Bony lesions/ fractures (Bankart fragments, Hill-Sachs Lesion)[82,83]	Avulsion of posterior periosteum[82]
	Accurate in labroligamentous, cartilaginous lesions[75]	Medial displacement of the labrum (posterior labro-scapular sleeve avulsion)[84]
		Kim lesion - incomplete and concealed superficial tear in the posterior glenoid labrum
		Glenoid rim articular divot lesion[7]
		Chondral loose bodies[85]

CT: Computed tomography scans; MRI: Magnetic resonance imaging.

Table 2 Different therapeutic options and considerations of posterior shoulder instability

Procedure	Consideration	Success rate
Conservative	Leads to loss of rotation and deformity of the shoulder, mainly performed in elderly patients	68%-77%, however only in isolated posterior shoulder instability; recurrence rate up to 96%[38,86]
Capsular-labral repair (i.e., post. - inf. capsular shift) or reverse Bankart repair	In isolated unidirectional posterior instability	96% in post. - inf. capsular shift[73] 91% in posterior capsulorrhaphy in isolated post. instability[5] Posterior Bankart repair – 93%[87]
Other procedures not/or rarely performed:
Thermal capsulorrhaphy	High recurrence rate	57%, capsular insufficiency 33%[88,89]
Posterior bone block or posterior wedge osteotomy	After failed capsular plication, or congenital formations	Posterior glenoid transfer: 53%; 41% complication rate[22,90] Posterior bone block: 45%; 36% osteoarthritis[36]
McLaughlin’s procedure	In patients with locked posterior shoulder dislocation from reverse Hill-Sachs lesions	improvement in average constant scoring system from 16 preoperatively to 72 postoperatively[91]
Humeral head allograft	Alternative option to McLauglin’s procedure	Complication rate between 25%-50%[92,93]