posterior instability after total shoulder arthroplasty ( tsa ) is a reported complication and can occur for a variety of reasons .
factors related to the development of this condition include glenoid and humeral retroversion , glenoid component loosening , soft tissue imbalance , and rotator cuff tears . in a cohort of
tsa 's performed at the mayo clinic , posterior instability was described in 1.8% of cases . because of the low reported incidence after anatomic tsa , the methods of treatment are likewise not well studied .
treatment options for posterior instability are dependent on the causes of the instability , and the outcomes for revision surgery demonstrate a moderately high rate of failure .
a thorough evaluation is required to determine the potential etiology of the instability before any revision surgical procedure is contemplated .
we present guidelines to aid in the diagnosis , cause , severity , and treatment options of posterior instability .
in addition , we present a novel treatment method for a case of posterior instability with glenoid retroversion and a well - fixed glenoid component treated with an arthroscopic posterior bone block procedure .
a 50-year - old male house painter with longstanding shoulder pain and glenohumeral arthritis refractory to conservative management underwent a tsa with press - fit humeral stem ( global unite , depuy , warsaw , in , usa ) and uncemented glenoid component ( anchor peg glenoid , depuy , warsaw , in , usa ) in his nondominant extremity .
his preoperative imaging revealed a biconcave glenoid with 20 of glenoid retroversion and posterior subluxation of the humeral head [ figure 1a ] .
intraoperatively , the anterior glenoid was reamed preferentially in an attempt to correct the posterior retroversion of the biconcave glenoid prior to placement of the glenoid component .
postoperative imaging revealed a well - fixed glenoid component with persistent 20 of retroversion [ figure 1b ] .
intra - operative examination following component implantation revealed a stable glenohumeral joint and no additional corrections or modifications were performed .
postoperatively , the patient had a sense of instability coupled with pain and weakness . while he did not experience frank dislocation episodes , the pain and dysfunction prevented him from returning to work .
his examination revealed posterior apprehension , but normal strength of both the deltoid and rotator cuff musculature .
given the clinical history , imaging and exam findings , the patient was diagnosed with posterior instability as a result of glenoid retroversion .
preoperative axillary x - ray postoperative axillary x - ray with posterior subluxation and glenoid component retroversion potential options for treatment in this situation included revision of the glenoid component with bone grafting or placement of a posterior bone block with retention of the glenoid component .
given the amount of morbidity involved in a revision surgery , a less invasive and alternative method of treatment was chosen .
a 25 mm  10 mm  10 mm tri - cortical bone graft was harvested and prepared .
verification of glenoid fixation was confirmed , and a horizontal slit in the posterior rotator cuff muscles was performed .
in addition , the bone on the posterior glenoid was prepared to a flat surface with an arthroscopic burr [ figure 2a ] . utilizing a custom double cannula instrument ( depuy - mitek , raynham , ma , usa ) , the graft was advanced through the widened posterior portal [ figure 2b ] .
graft was then precisely placed on the posterior glenoid with the surface of the bone block placed parallel and flush with the surface of the glenoid prosthesis [ figure 3a ] .
fixation of the bone block was performed with two parallel , cannulated , titanium , 3.5 mm screws .
given the existing anchor peg glenoid component ( dupuy , raynham , ma , usa ) relies heavily on the central peg , care was taken to ensure that both screws lie below the equator of the glenoid prosthesis [ figure 3b ] .
this was critical as damage to the central peg risks compromising the fixation of the glenoid component . by placing the 10 mm wide graft flush with the size 48 mm glenoid , the anterior to posterior articular surface area
pre- and post - arthroscopic preparation of the posterior glenoid bone surface iliac crest bone graft in custom double cannula instrument ( depuy - mitek , raynham , ma , usa ) for insertion through the posterior portal intra - articular placement of bone block flush with the surface of glenoid component axial computed tomography scan showing orientation of screws relative to intact central peg of glenoid component at 14-month postoperatively from the bone block procedure , the patient regained near full motion and strength .
he has no sense of pain or instability with resisted forward flexion with his arm in an adducted and internally rotated position [ figure 4a ] .
the patient 's subjective shoulder value is 80 , with a 2 out of 10 pain score .
imaging obtained at 14-month revealed osseous integration of the bone block to the posterior glenoid , no evidence of glenoid prosthesis loosening and an intact central peg [ figure 4b ] .
postoperative examination without instability postoperative x - ray and computed tomography scan demonstrating osseous integration and intact central peg
instability in the setting of tsa is well described in the literature . in a large review ,
instability was noted in 5.2% of the cases and was the most common complication of the procedure , however , isolated posterior instability is felt to be relatively rare .
the type of instability is classified by the direction ( superior , inferior , anterior , and posterior ) , and the etiology is often multifactorial . in cases of posterior instability ,
causative factors are reported to be excessive glenoid component retroversion , humeral component retroversion , glenoid component loosening , continued static posterior subluxation , a smaller glenoid component , and soft tissue imbalances or insufficiency including rotator cuff tear .
preoperative factors include posterior glenoid wear , bone loss , a biconcave glenoid , and static posterior subluxation .
a detailed understanding of the underlying etiology is essential to determine the appropriate treatment . at the time of the arthroplasty ,
methods to prevent postoperative instability include eccentric reaming , posterior bone grafting , using an augmented glenoid component , and addressing posterior capsular laxity or rotator cuff pathology .
a study has demonstrated that increasing the humeral component anteversion does not provide improved stability in the setting of persistent glenoid retroversion .
patients with postoperative instability of the prosthesis despite the use of the aforementioned methods present a difficult clinical challenge .
nonoperative measures may not be successful in alleviating the symptoms . in evaluating a patient with instability , the etiology must be determined through a clinical exam and appropriate imaging .
the position of the components , loosening , static posterior subluxation and soft tissue stabilizers are all assessed . based on the underlying cause of the instability ,
operative options include revision of one or both of the components , soft tissue plication or repair , bone grafting procedures with or without component revision , and bone block type procedures .
understanding the reasons for posterior instability is critical to determining the treatment options [ figure 5 ] . in many cases ,
causes and treatment options for posterior instability in the case presented here , the patient was found to have clinically symptomatic posterior instability after a primary tsa with persistent subluxation and glenoid retroversion .
an open revision surgery was considered , but secondary to the reported mixed results of these procedures a novel , less invasive surgery was undertaken .
this included an arthroscopic posterior bone block augmentation of the glenoid with iliac crest autograft . while this procedure has recently been published for posterior instability , there are no reports to our knowledge of this technique in the setting of a tsa .
endres and warner described two patients with anterior instability after tsa successfully treated with an open latarjet procedure .
it can be performed through a minimally invasive approach , and excellent visualization is achieved to allow proper positioning of the graft .
the graft helps to re - center the humeral head by increasing the surface area of the glenoid , thus making a dislocation more difficult .
in addition , the graft is placed flush against the glenoid component , which may help stabilize this and prevent loosening from edge loading .
this case report describes the management of symptomatic posterior shoulder instability following tsa and also reports a novel technique . to our knowledge
, this is the first description of a posterior , arthroscopic iliac crest bone block grafting procedure in this setting .
the procedure represents a treatment option for posterior instability in the setting of a stable glenoid prosthesis following tsa .
 we report a case of posterior shoulder instability following anatomic total shoulder arthroplasty ( tsa ) . 
 in addition , we present guidelines to aid in the management of posterior instability after tsa . 
 a 50-year - old male underwent anatomic tsa for glenohumeral osteoarthritis . 
 postoperatively , the patient developed posterior instability secondary to glenoid retroversion . 
 he did not improve despite conservative treatment . 
 he underwent an arthroscopic posterior bone block procedure , 4-month after his index arthroplasty . at 14-month follow - up 
 , the patient had regained near full motion and strength , and radiographs demonstrated osseous integration with no evidence of component loosening . 
 posterior instability following tsa is a relatively rare complication and challenging to manage . 
 the posterior , arthroscopic iliac crest bone block grafting procedure represents a treatment option for posterior instability in the setting of a stable glenoid prosthesis following tsa . 
INTRODUCTION
CASE REPORT
DISCUSSION
CONCLUSION