muscle atrophy ( reduced muscle bulk ) is a nonspecific sign , and it may occur as a consequence of muscle disuse , tendon tear , or denervation .
fatty infiltration ( replacement of muscle fibers by fat ) is mostly seen in association of chronic , massive rotator cuff tear .
however , supraspinatus muscle fatty infiltration can occur in the absence of any intrinsic tendon rupture as a result of suprascapular neuropathy .
suprascapular nerve ( ssn ) injury associated with traumatic shoulder dislocation is most likely due to a traction injury to the nerve.[13 ] the location of ssn injury can be predicted by the pattern of the muscles involvement .
while the infraspinatus muscle is always affected , the supraspinatus muscle will be spared when the injury is at spinoglenoid notch level or distal , whereas both supra - and infraspinatus muscle denervation will occur when the injury is at the level of suprascapular notch or proximal , making the distribution of muscle involvement helpful in localizing the site of injury .
only one other case reported of isolated supraspinatus muscle paralysis following an anterior shoulder dislocation .
diagnosis is based on clinical history , physical examination , appropriate imaging , and electrodiagnostic studies .
traction injuries typically respond well to the non - operative management , whereas mass compression usually responds best to surgical decompression , and the causes of nerve dysfunction should be determined .
she sustained her first dislocation eight years ago , which was a traumatic anterior shoulder dislocation and has had an increasing frequency of shoulder dislocation since .
, she has experienced multiple painful subluxation episodes that have occurred with abduction and external rotation of the shoulder .
she had a full range of motion of her shoulder and had positive apprehension and positive relocation tests .
rotator cuff muscles strength were within normal except for the supraspinatus muscle , which showed a significant weakness .
neurological examination of all peripheral nerves was normal , and there was no evidence of generalized ligamentous laxity .
magnetic resonance imaging ( mri ) revealed significant atrophy and diffuse fatty infiltration of the supraspinatus muscle associated with supraspinatus tendinopathy and a shallow hill - sachs defect . because of associated history of instability
, an mri arthrogram was performed , which showed a bankart lesion that could not be appreciated in the previous plain mri .
the infraspinatus muscle appeared unremarkable , and no structural lesion was apparent in the suprascapular or spinoglenoid notch or along the course of the suprascapular nerve .
magnetic resonance imaging coronal view showing significant atrophy and fatty infiltration of the supraspinatus muscle magnetic resonance imaging oblique view showing significant fatty infiltration of the supraspinatus muscle ; note the normal appearance of the infraspinatus muscle electromyographic study showed an injury to ssn branch affecting only the supraspinatus muscle .
non - operative treatment failed to alleviate the patient 's shoulder instability ; therefore , she underwent arthroscopic bankart repair . arthroscopic evaluation of the shoulder joint revealed evidence of a detached anterior labrum with a flap tear of superior labrum [ figure 3 ] and a small hill - sachs lesion . the biceps anchor , supraspinatus tendon and the rest of the rotator cuff appeared normal [ figure 4 ] .
arthroscopy of the shoulder showing bankart lesion of the glenoid ( posterior portal view ) .
hh : humeral head , g : glenoid arthroscopy of the shoulder showing the normal appearance of the supraspinatus tendon ( posterior portal view ) .
hh : humeral head , sm : supraspinatus muscle , lhbt : long head of biceps tendon postoperatively , the patient followed a post - bankart rehabilitation program . at two - year follow - up , she reported no more instability in her left shoulder . on physical examination ,
non - operative treatment failed to alleviate the patient 's shoulder instability ; therefore , she underwent arthroscopic bankart repair . arthroscopic evaluation of the shoulder joint revealed evidence of a detached anterior labrum with a flap tear of superior labrum [ figure 3 ] and a small hill - sachs lesion . the biceps anchor , supraspinatus tendon and the rest of the rotator cuff appeared normal [ figure 4 ] .
arthroscopy of the shoulder showing bankart lesion of the glenoid ( posterior portal view ) .
hh : humeral head , g : glenoid arthroscopy of the shoulder showing the normal appearance of the supraspinatus tendon ( posterior portal view ) .
hh : humeral head , sm : supraspinatus muscle , lhbt : long head of biceps tendon
postoperatively , the patient followed a post - bankart rehabilitation program . at two - year follow - up , she reported no more instability in her left shoulder . on physical examination ,
the natural history of the rotator cuff fatty infiltration associated with cuff tear is well described and reported in the literature .
however , the incidence and the nature history of rotator cuff atrophy and fatty infiltration resulted from traumatic muscle denervation is still unknown and not clear in the literature .
the reported incidence rate of ssn injury in association with anterior shoulder dislocation vary from 14% to 29% .
however , because the infraspinatus muscle is used as a reference for ssn injury in emg study , the true incidence of the isolated supraspinatus muscle denervation and fatty degeneration in the absence of tendon tear remains unknown , and none of these reported cases had described an isolated ssn injury to the supraspinatus muscle only . in the literature , there is only one other case which reported of isolated nerve injury to the motor branch of ssn following an anterior shoulder dislocation .
reported a 42-year - old female , who sustained isolated supraspinatus muscle denervation after a traumatic shoulder dislocation . in this reported case
, we think the cause of supraspinatus muscle atrophy and fatty infiltration is a traction injury to the terminal motor branches of ssn to the supraspinatus muscle resulting from traumatic anterior shoulder dislocation .
the complete sparing of the infraspinatus muscle seen in this patient is an unusual and extremely rare presentation of ssn injury associated with shoulder dislocation .
we propose three potential explanations for this rare phenomenon ; first , the short tether motor branches to the supraspinatus muscle are more prone to injury as compared to the motor branches to the infraspinatus muscle , which are longer and larger .
second , the infraspinatus muscle had three or four motor branches , where the supraspinatus had only tow motor branches as being shown by a suprascapular nerve anatomy study done by warner et al . finally , lee et al . and bergman et al . have proposed that the axillary nerve can contribute to the innervation of the infraspinatus muscle .
indicates that the axillary nerve may give a branch to the long head of triceps and ( or ) the infraspinatus muscles .
the cadaver dissection of the left side of a 65-year - old female korean showed that the infraspinatus muscle entirely received its innervation from a branch of the axillary nerve , and ssn supply only the supraspinatus muscle .
associated rotator cuff tear and fatty infiltration had a negative influence on the outcome of ssn injury after shoulder dislocation .
the progression of the fatty infiltration associated with cuff tear can be minimized after a successful repair ; however , improvement or reversal of muscle fatty degeneration will be unlikely .
while the fatty degeneration associated with traumatic peripheral nerve injury is likely to be irreversible , the time of onset and progression of the fatty infiltration after traumatic muscle denervation is still unclear yet .
when there is no rotator cuff tear or fatty infiltration , the outcome after ssn injury is favorable and full recovery can be expected . in this reported case , the patient persists to exhibit some weakness and atrophy of the supraspinatus muscle even after a supervised and considerable preoperative physiotherapy and surgical treatment of her shoulder instability .
probably , this can be explained by the presence of a significant and irreversible fatty infiltration after long standing ( eight years ) muscle denervation .
the favorable overall shoulder 's function outcome which had seen with this patient is most likely due to complete preservation of the infraspinatus muscle and surgical stabilization of her shoulder . despite significant
atrophy and fatty infiltration of the supraspinatus muscle on mri , no visible changes were apparent arthroscopically .
further preoperative investigations like computed tomography ( ct ) scan , mri , or ultra sound of the rotator cuff will be more helpful to address the presence and the extent of fatty infiltration when supraspinatus muscle atrophy and paralysis persist .
persistent supraspinatus muscle atrophy and weakness after traumatic anterior shoulder dislocation should be worked up to rule out associated ssn injury .
further investigations , like mri , should be done to assess the presence and extent of fatty infiltration , which might affect the overall outcome of the treatment .
it is still largely unknown if the early recognition and surgical treatment of this condition have any role in delaying the progression of atrophy and fatty infiltration of the supraspinatus muscle .
 supraspinatus muscle atrophy and fatty infiltration are two distinct muscle abnormalities which can be seen after a chronic massive tear or suprascapular neuropathy . 
 isolated supraspinatus muscle denervation due to suprascapular nerve injury after shoulder dislocation is extremely rare . 
 we report on a patient who developed isolated supraspinatus muscle atrophy and fatty infiltration after traumatic anterior shoulder instability . 
 possible explanations and etiologies of this rare condition are discussed in this report . 
INTRODUCTION
CASE REPORT
Operative treatment
Postoperative follow up
DISCUSSION
CONCLUSION