reverse shoulder prosthesis is an excellent surgical option for patients with certain shoulder pathologies , of which rotator cuff arthropathy is one .
one area where we are gaining a greater understanding is that of managing acromial pathology .
recent studies are showing that not all acromial pathology is a contraindication to reverse shoulder arthroplasty ; in both pre- and post - operative patients , small lateral fractures of the acromion can be treated non - operatively or fixed surgically with a tension band technique .
overall , results comparable to that of reverse arthroplasty can be achieved with either of these treatment options .
however , fractures at the base of the acromion or of the scapular spine present a different problem . in these types of fractures , a larger length of deltoid muscle is detached , and therefore defunctioned . in reverse shoulder arthroplasty , in order to achieve a stable shoulder , the deltoid must be tensioned a great deal .
this in turn causes a deforming force and distraction at the fracture site , making for a poor healing potential . also , as the reverse shoulder prosthesis relies on the deltoid muscle to move the arm , if the deltoid is detensioned or improperly tensioned , this will lead to poor functional capacity .
we present a case of treatment of a fracture at the base of the acromion using a 90/90 plating construct that healed in a good position .
a 71-year - old right - handed woman presented with a 2-year history of right shoulder pain and dysfunction , which began abruptly when lifting a heavy load . at the initial evaluation ,
her range of motion was limited , particularly in active abduction as she achieved only 45 degrees in this plane . a cuff arthropathy ( hamada grade 3 )
was diagnosed and the decision was taken to proceed with reverse shoulder arthroplasty . to complete the pre - operative assessment ,
a ct scan was performed which confirmed there was no acromial pathology involved . a reverse shoulder prosthesis and a biceps tenodesis
was carried out ( delta xtend , depuy , warsaw , in , usa ) through a deltopecoral approach [ figure 1 ] .
the patient 's right arm was immobilized in a sling and the range of motion exercises were started 6 weeks after arthroplasty [ figure 1a ] .
five months after surgery , she sustained a blow to the right shoulder but sought medical attention 1 month later , at her scheduled follow - up visit .
radiographs showed a displaced fracture at the base of the acromion [ figure 1 ] .
this showed that both the humeral and glenoid components were well fixed and the only pathology was the fracture .
antero - posterior radiographs showing the patient 's right shoulder immediately after reverse shoulder arthroplasty ( a ) and after fracture , 5 months later ( b ) .
the post - operative image shows no pre - existing acromial pathology she was taken to the operating room and her previous incision was extended into a  sabre  incision to better expose the acromion .
two small fragment ( 3.5 mm ) locking plates ( synthes , west chester , pa , usa ) were used in a 90/90 configuration ; one was a fragment specific clavicular plate and the other a reconstruction plate .
the fragment specific clavicular plate was applied on the superior edge of the scapular spine in a compression mode .
a second reconsrtuction plate was applied from the posterior acromion to the posterior cortex of the scapular spine , in the infraspinatus fossa .
fixation was solid , but in order to protect the construct , the patient was placed in an abduction brace for 6 weeks .
eighteen months after fracture fixation , the patient was satisfied with the clinical result [ figure 2 ] .
she was capable of 125 degrees of abduction , 160 degrees of forward flexion , 85 degrees of external rotation in adduction , and 60 degrees of internal rotation .
her quickdash score was 29.5 ( compared to 82.5 pre - op ) and constant score was 69 on the affected side compared to 85 on the left side , for a  good  functional outcome .
a medline search using the key words [ acromion fracture ] , [ scapula fracture ] , [ reverse arthroplasty ] was performed .
we then sought to classify and separate the cases by location ; there were 30 cases of fractures at the base of the acromion , and scapular spine . when our case is added , we have a total of 31 cases .
results are summarized in table 1 . in brief , of the 30 more proximal cases , 21 were treated non - operatively in a sling , 7 were treated with open reduction and open fixation and one with revision of the prosthesis . of those treated non - operatively , and for whom results are published , fourteen had a non - union , four had a malunion and in two cases , it was unclear whether union was achieved . for patients receiving fixation of the fracture , there was one non - union , two repeat fixations , and one patient required removal of the fixation .
the patient who had a revision of the prosthesis had a malunion of the acromion .
results of the literature review . in the fracture location column , the fracture description provided by the authors is presented .
although recent studies have shown that good outcomes may be achieved with non - surgical management of lateral acromial fractures , the same does not hold true for basal acromial fractures .
the likely reason for this is that with fractures at the base of the acromion , a large length of the deltoid is defunctioned and the deltoid muscle is essential to the functioning of the reverse shoulder prosthesis .
previously described techniques , such as tension band fixation achieved poor functional results for fractures at the base of the acromion .
we postulate that this is because the fixation method is insufficient to withstand the forces generated by the deltoid muscle  a tension band can neutralize forces parallel to the axis of the band but in the case of the deltoid , force vectors are generated in different directions .
it also allows for compression along the fracture site and resists motion in all directions .
good screw purchase can be achieved by angling the screws either toward the scapular spine or the coracoid .
the locking option enables good fixation and improves cut - out strength in osteopenic or osteoporotic bone .
in addition to the stable fixation achieved with this technique , we further recommend immobilization of the affected shoulder using a sling and an abduction pillow to detension the deltoid , thus at least partially removing the distractive forces at the fracture site . also essential to achieving a good functional result
we thus also recommend a program of range of motion exercises followed by strengthening exercises to maximize functional capabilities . based on results from previous studies ,
fractures of the tip were those of the most lateral or anterior portion of the acromion .
fractures of the body of the acromion are those medial to the tip of the acromion and lateral to the beginning of the scapular base .
the scapular base is the lateral border of the scapular spine , which is smooth and round . in our nomenclature ,
fractures at the scapular base are termed fractures at the base of the acromion as functionally , this zone connects the acromion to the rest of the scapula and this term avoids confusion with any more medially occurring fractures .
coronal ( a ) and axial ( b ) representations of the proposed classification scheme for acromial fractures associated with revere arthroplasty we propose the above mentioned classification system as it provides a nomenclature for acromial fractures that is descriptive and is based on the anatomy and functionality of the scapula . as the results from the review of the literature indicate , the more medial the fracture , the worse the prognosis with non - operative treatment .
thus , this classification system may be used to predict outcomes and determine treatment offered .
it differs from other classification systems ( crosby ) in that it further subclassifies more medial fractures , which are the more ominous fractures . as more research is carried out in this field
 fractures of the acromion and scapula are known to occur after reverse shoulder arthroplasty . 
 we present a case of a fracture at the base of the acromion 5 months after arthroplasty treated successfully with dual plating of the acromion . 
 eighteen months after fracture fixation , the patient had 160 degrees of active forward flexion , a quickdash of 29.5 , a constant score of 69 and she was satisfied with the result . a concomitant review of the literature produced , in addition to our patient , 56 cases . 
 these were used to produce a classification system , based on bony and functional anatomy as follows . 
 tip fractures are of the most lateral or anterior portion of the acromion , those of the body of the acromion are medial to the tip but lateral to the beginning of the scapular base 
 . fractures at the scapular base are termed fractures of the base of the acromion and those more medial to that , fractures of the scapular spine . 
 the functional results of these case series demonstrated poorer functional outcomes for more medial fractures . 
 as future research in this domain increases , clarity on the nomenclature of these fractures will allow for prognostication and treatment based on fracture location as well as comparison between studies . 