Os acromiale is a rare anatomical variant that is caused by failure of fusion of the acromial apophysis and is usually asymptomatic. We report a case of impingement syndrome of the left shoulder secondary to unstable os acromiale, which was initially overlooked and confirmed only during arthroscopic examination. Arthroscopic excision of the unstable fragment was successful without residual dysfunction of the deltoid muscle

Fukuta, Shoji

Goto, Tomohiro

Hamada, Daisuke

Kawaguchi, Shinji

Kita, Kenichiro

Matsumura, Toshihiko

Matsuura, Tetsuya

Miyagi, Ryo

Nagamachi, Akihiro

Sairyo, Koichi

Suzue, Naoto

Tamaki, Shunsuke

Tsutsui, Takahiko

Wada, Keizo

Tokushima University Institutional Repository

INTRODUCTIONThe acromial apophysis develops from four separate centers ofossification : pre-acromion, meso-acromion, meta-acromion, andbasi -acromion (1). Complete union of all centers may occur by theage of 25 years (2). Os acromiale is a failure of union of the acromialapophysis of the scapula, with a reported incidence ranging from1% to 18.2% (1, 3, 4). Bilateral involvement is found in 33.3-62% ofcases. It is thought to be an anatomical variant of the scapula andrarely causes shoulder pain.Although os acromiale is usually identified incidentally on plainaxillary radiograph of the shoulders, shoulder pain has been re-ported in the literature (5-10). Conservative treatment with mus-cle strengthening, stretching, anti - inflammatory medications, andsteroid injections is the first option for symptomatic os acromiale.However, surgical treatment may be required if conservative treat-ment fails. Several surgical treatments, including excision by openor arthroscopic procedure, arthroscopic acromioplasty, and inter-nal fixation with or without bone graft, have been described withmixed clinical outcomes (5-10). The optimal surgical option is there-fore controversial.We present a case of unstable os acromiale in an elderly patientwho was diagnosed with an impingement syndrome with intact ro-tator cuff. Unstable os acromiale was identified during arthroscopicexamination. Retrospective review of the preoperative magneticresonance imaging (MRI) and computed tomography (CT) ar-throgram showed os acromiale between the meso-acromion andmeta-acromion. Arthroscopic excision resolved the pain and im-proved the shoulder functions. Based on this case report, we rec-ommend that clinicians include this pathology in the differentialdiagnosis of impingement syndrome of the shoulder.CASE REPORTA 73-year-old, right-hand dominant woman presented with a 2-month history of pain in the left shoulder with no history of trauma.The pain was described to be moderate in severity and was asso-ciated with active flexion and abduction, but not at rest. Physicalexamination showed that she had no limited range of motion, withactive forward flexion to 170, abduction to 170, external rotationto 70, and internal rotation up to the eighth thoracic spine with thearm on the side. Passive range of motion findings was the same asthose during active range of motion. Neer’s impingement sign waspositive. Plain radiographs at that time were interpreted by theorthopedic surgeon as mild arthritic change in the glenohumeraljoint (Fig. 1).The patient underwent physical therapy for 6 months, which failedto relieve the shoulder pain. Arthroscopic subacromial decompres-sion was then planned. Moderate-grade chondrosis was noted inboth the humeral head and glenoid surface of the glenohumeraljoint. The long head of the biceps and the articular surface of therotator cuff were normal. During examination of the subacromialbursa, abnormal mobility of the anterolateral acromion was seen.Retrospective review of the CT scan and MRI revealed the pres-ence of os acromiale (Figs. 2 and 3) between the meso-acromionand the meta-acromion (meso-acromiale). Hypertrophy and degen-erative changes at the junction of the os meso-acromiale and theacromion were also seen. Arthroscopically, the os meso-acromialewas carefully excised with a motorized shaver, leaving the pe-riosteal sleeve and deltoid fascial insertion intact (Fig. 4). Rotatorcuff tear was not identified from the bursal side.Post-operatively, the left shoulder was placed in a sling for 2weeks, followed by mild range of motion exercises. Three monthspost-operatively, CT scan showed complete excision of the meso-acromiale (Fig. 5). The patient regained full shoulder range of mo-tion 3 months after arthroscopic excision. At the final follow-up 27months post-operatively, she had no functional deficits and theUCLA shoulder score (11) improved from 14 to 35.DISCUSSIONOs acromiale results from a failure of osseous fusion betweenCASE REPORTArthroscopic excision of unstable os acromiale associatedwith impingement syndrome : a case reportShinji Kawaguchi, Shoji Fukuta, Takahiko Tsutsui, Tetsuya Matsuura, Naoto Suzue, Daisuke Hamada,Tomohiro Goto, Ryo Miyagi, Keizo Wada, Kenichiro Kita, Shunsuke Tamaki, Toshihiko Matsumura,Akihiro Nagamachi, and Koichi Sairyo*Department of Orthopedics, Tokushima University, 3-18-15 Kuramoto-cho, Tokushima, JapanAbstract :Os acromiale is a rare anatomical variant that is caused by failure of fusion of the acromial apophysisand is usually asymptomatic. We report a case of impingement syndrome of the left shoulder secondary to un-stable os acromiale, which was initially overlooked and confirmed only during arthroscopic examination. Ar-throscopic excision of the unstable fragment was successful without residual dysfunction of the deltoid muscle.J. Med. Invest. 63 : 131-134, February, 2016Keywords : os acromiale, impingement, arthroscopic excision, shoulderReceived for publication October 5, 2015 ; accepted October 28, 2015.Address correspondence and reprint requests to Shoji Fukuta, MD,PhD, Associate Professor, Department of Orthopedics, Tokushima Uni-versity 3 -18 -15 Kuramoto, Tokushima 770-8503, Japan and Fax : +81-88 -633-0178.The Journal of Medical Investigation Vol. 63 2016131any two apophyses, most commonly between the meso-acromionand the meta-acromion. It is usually asymptomatic and discoveredby chance on radiographs, CT, or MRI of the shoulder. Although osacromiale is often associated with rotator cuff tear and impingementsyndrome (5), no clinical study has revealed that the presence of osacromiale results in a predisposition to rotator cuff disease (12).Nevertheless, successful outcomes of surgical treatment for symp-tomatic os acromiale suggest that this pathology may still be clini-cally relevant. Bone marrow edema on MRI and increased uptakeon bone scan strongly suggest that inflammation secondary to ab-normal motion of the fragment at the non-union site may causeshoulder pain (12, 13). The pain may be due to inflammation orcaused by abnormal motion at the site of non-union. Inferior tilt-ing of the os fragment during contraction of the deltoid musclemay be another possible mechanism for subacromial impingementassociated with this condition (6).A BFig. 1 Plain radiographs of the left shoulder of an elderly patient with os acromiale.Mild degenerative arthritis is demonstrated on the anteroposterior view (A). Non-union between the meso-acromion and the meta-acromion(arrow) is noted on the scapular outlet view (B).Fig. 2 Computed tomography scan of an elderly patient with os acromi-ale of the left shoulder. Sclerotic and cystic changes around the pseudoar-throsis are seen.A BFig. 3 Magnetic resonance imaging in an elderly patient with os acromiale of the left shoulder. T2-weighted axial image (A) and T2-weightedoblique coronal image (B) clearly demonstrate the os acromiale with irregular margins. There was no fluid - like signal within the interface. The rotatorcuff is not torn.132 S. Kawaguchi, et al. Os acromialewith impingement syndromeConservative therapies with non-steroidal anti - inflammatorydrugs, physical therapy, and subacromial corticosteroid injectionhave been recommended for initial treatment of symptomatic osacromiale. If conservative management over a few months fails,surgical intervention may be warranted. Various surgical optionshave been reported with mixed clinical outcomes.Open excision for unstable os acromiale is recommended onlyfor pre-acromiale with a small fragment because in this case, theattachment of the deltoid muscle is not disrupted. Excision of alarge fragment may lead to dysfunction of the deltoid muscle. Neerand Marberry described that radical acromionectomy weakenedthe deltoid by removing its lever arm and by encouraging retrac-tion (7). Mudge et al. reported excellent clinical results of patientswho underwent fragment excision and rotator cuff repair ; how-ever, two of six patients had unsatisfactory results (5). They con-cluded that large fragments should be retained and fixed.Arthroscopic subacromial decompression is another option forsymptomatic stable os acromiale associated with the impingementsyndrome (8). Hutchinson and Veenstra described recurrence ofpain after a period of symptom relief from arthroscopic decompres-sion (9). Wright and associates described a modified subacromialdecompression procedure with more aggressive boney resectionthan the typical arthroscopic acromioplasty (10). This procedureretained the superficial cortical shell of the os acromiale and itsdeltoid attachment and led to satisfactory results in 12 of 13 pa-tients. However, residual instability of the fragment may result inshoulder pain after subacromial decompression.Open reduction and internal fixation with concomitant bone graft-ing may be the most ideal procedure because it allows preservationof both the large fragment and anterior deltoid function. The rangeof reported rates for successful union after surgical repair of osacromiale is wide. Peckett et al. reported a 96% union rate aftertension band wiring and bone grafting in 26 patients (9), whereasWarner et al. observed a 58% rate of complete union in 12 patients(6). Furthermore, most of the patients required a second proce-dure of hardware removal, secondary to hardware-related discom-fort or pain, even after the non-union healed.In our case, arthroscopic excision of meso-acromiale was selectedbecause of the patient’s old age and low activity. By this method,the periosteal sleeve and deltoid attachment could be preservedto avoid dysfunction of the deltoid, which is the most commondisadvantage of open excision. In addition, the minimally invasivearthroscopic procedure allowed the patient to move her shoul-der earlier, which led to rapid post-operative functional recovery.Pangani et al. have reported satisfactory results of arthroscopicexcision in 9 young athletes, with no deficits in abduction or rota-tion strength (10).Although we initially misdiagnosed the condition as impinge-ment syndrome, the pre-operative images clearly demonstratedthe presence of os acromiale. The symptoms of a painful os acromi-ale may strongly resemble those seen in impingement syndrome ;therefore, this anatomical variation should be considered in thedifferential diagnosis in patients with suspected impingement syn-drome.CONCLUSIONWe report a case of impingement syndrome of the shoulder sec-ondary to unstable os acromiale. Os acromiale is rare but cliniciansshould be aware of this pathology.REFERENCES1. Liberson F : Os acromiale - contested anatomy. J Bone JointSurg 19 : 683-689, 19372. McClure JG, Raney RB : Anomalies of the scapula. Clin Orthop110 : 22-31, 19753. Case DT, Burnett SE, Nielsen T : Os acromiale : populationdifferences and their etiological significance. Homo 57 : 1-18,2006A BFig. 4 Arthroscopy findings in an elderly patient with os acromiale of the left shoulder.Failure of union of the meso-acromion (MESO) and the meta-acromion (META) is demonstrated (A). The meso-acromiale was easily pushed downwhen the fragment was pressed over the skin (B) (black arrows)Fig. 5 Computed tomography scan of an elderly patient with os acromi-ale of the left shoulder after excision. Post -operative CT scan shows thatos acromiale was completely excised.The Journal of Medical Investigation Vol. 63 February 2016 1334. Sammarco VJ : Os acromiale : frequency, anatomy, and clini-cal implications. J Bone Joint Surg Am 82 : 394-400, 20005. Mudge MK, Wood VE, Frykman GK : Rotator cuff tears asso-ciated with os acromiale. J Bone Joint Surg Am 66 : 427-429,19846. Warner JJ, Beim GM, Higgins L : The treatment of sympto-matic os acromiale. J Bone Joint Surg Am 80 : 1320-6, 19987. Neer CS II, Marberry TA : On the disadvantages of radical ac-romionectomy. J Bone Joint Surg Am 63 : 416-9, 19818. Boehm TD, Matzer M, Brazda D, Gohlke FE : Os acromialeassociated with tear of the rotator cuff treated operatively.Review of 33 patients. J Bone Joint Surg Br 85 : 545-9, 20039. Peckett WR, Gunther SB, Harper GD, Hughes JS, SonnabendDH : Internal fixation of symptomatic os acromiale : a seriesof twenty-six cases. J Shoulder Elbow Surg 13 : 381-5, 200410. Pagnani MJ, Mathis CE, Solman CG : Painful os acromiale(or unfused acromial apophysis) in athletes. J Shoulder ElbowSurg 15 : 432-5, 200611. Amstutz HC, Sew Hoy AL, Clarke IC : UCLA anatomic totalshoulder arthroplasty. Clin Orthop 155 : 7-20, 198112. Ouellette H, Thomas BJ, Kassarjian A, Fritz B, Tétreault P,Palmer WE, Torriani M : Re-examining the association of osacromiale with supraspinatus and infraspinatus tears. SkeletalRadiol 36 : 835-9, 200713. Winfeld M, Rosenberg ZS, Wang A, Bencardino J : Differen-tiating os acromiale from normally developing acromial ossi-fication centers using magnetic resonance imaging. SkeletalRadiol 44 : 667-72, 2015134 S. Kawaguchi, et al. Os acromialewith impingement syndrome

Arthroscopic excision of unstable os acromiale associated with impingement syndrome : a case report

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Arthroscopic excision of unstable os acromiale associated with impingement syndrome : a case report

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