An os acromiale (OA) originates from failure of fusion of the anterior acromial apophysis (Kurtz et al., 2006). The acromial apophysis derives from four separate sites of ossification: the basiacromion, meta- acromion, mesoacromion, and preacromion (Figure 1). Complete union of all centres may occur as late as age 25 years. The great majority of OAs are of the mesoacromial type (Edelson et al., 1993; McClure and Raney, 1975; Nicholson et al., 1996; Sammarco, 2000). The frequency of os acromiale ranges from 1 to 15% of cases in different anatomical studies (Edelson et al., 1993, Nicholson et al., 1996) and radiographic (Grasso, 1992; Liberson, 1937), and bilateral involvement is reported in 41 to 62% of cases (Sammarco, 2000). Several ossification nuclei give origin to the three anterior acromial ossification centers, and, between 15 and 18 year of age, they unify into the meta-acromion, mesoacromion, and preacromion (Kurtz et al., 2006). Many young athletes engaged in overhead sports reach elite level at this age, and can result useful to diagnose the presence of os acromiale to plan a correct therapeutic path. The presence of an OA is typically ascertained with plain radiographs (Andrews et al., 1991; Edelson et al., 1993; Liberson, 1937), computed tomography (CT) (i2), Magnetic Resonance (MR) (Park et al., 1994), and at surgery (Mudge et al., 1984; Neer, 1972). We identified an OA with ultrasonography (Smith et al., 2008) in a young overhead athlete affected by impingement-like pain.

This case report presents the results of successful management of a painful os acromiale associated with rotator cuff impingement in a competitive swimmer, based on ultrasonography diagnosis, a low cost and dynamic exam, and a specific conservative treatment.

A competitive, right-hand-dominant swimmer, aged 22, was referred with persistent shoulder impingement-like pain of several years' duration. He reported worsening of pain after back stroke and front crawl training, typically associated with overhead movement of the shoulders. Moreover, he did never report pain at night. He continued swimming tolerating his antero-superior shoulder pain for some years. He felt very limited in his competitive sport activity even if he had always performed self-treatment with long rest periods, general rotator cuff muscles exercises associated to oral anti-inflammatory drugs with poor results.

Clinical and physical examination showed symmetric shoulders and absence of muscular hypotrophy or scapular dyskinesia. We found full range of motion in all directions, but associated to pain in overhead position in the right shoulder only, and absence of neurological compromise. Specific impingement tests as Neer, Hawkins, Whipple and Yocum were positive, digital compression of the OA site was painful, Jobe test for supraspinatus muscle was positive as were the palm-up test for long head of biceps, all only in the right shoulder.

Preliminary standard plain radiographs (antero-posterior and lateral) (Figure 2) were interpreted as “negative for fracture; normal sub-acromial space”. Considering his pain, we thought to continue imaging examination with diagnostic ultrasonography interpreted by the SG author who had more than 20 years of experience performing musculoskeletal sonography (Siemens Sonoline Antares, with probe 5-13 Mhz.). Ultrasonographic examination showed thickening of the supraspinatus tendon and of the subacromial bursa (Mudge et al., 1984). The right acromioclavicular joint was normal, but adjacent to it was “another pseudo-joint” (os acromiale) surrounded by hypertrophic changes of the tissues and little oedema. Digital pressure over the os acromiale site was painful. The acromial fragment and synchondrosis were easily identified, and the borders of the synchondrosis were hypertrophic.

The panoramic field of view (Siescape) allowed to visualise better the two OA fragments (Figure 3), and to identify the “real” acromioclavicular joint from the more narrow and without synovial membrane “pseudo” acromioclavicular joint. The tendon of the long head of the biceps showed presence of fluid around it (Figures 4). Power Doppler examination did not show visible signs in the subacromial bursa, rotator cuff, and in the synchondrosis. To exclude bilateral involvement, ultrasonographic examination was performed also in the left shoulder with negative result. To validate our findings, we performed an MRI of the right shoulder (axial and oblique coronal T1- and T2 and oblique sagittal T2-weighted images). This showed and unfused acromial apophysis with oedema around the synchondrosis site (Figure 5). Our patient underwent a targeted physical and rehabilitation programme to reduce pain, strengthen the rotator cuff muscles and lower the humeral head muscles. The athlete agreed to start a rehabilitation program consisting of (Figure 6):

At the end of these two months of conservative treatment, the patient was pain free, and all clinical tests for impingement syndrome (Neer, Hawkins, Whipple and Yocum tests) were negative. Jobe and palm up tests were negative. Ultrasonographic examination showed normal subacromial-deltoid bursa and no oedema around the acromial unfused site. Digital pressure on the OA site was still painful.

The patient returned to his sport activity, and we suggested that he continued the above exercises three times a week, avoiding overhead exercises out of the swimming-pool. At one year follow-up, the patient reported full compliance to the exercise programme and complete absence of pain. All the clinical tests continued to be negative.

Reports of unstable OA as a possible origin of impingement are copious. Sammarco, 2000 found no studies providing evidence that the frequency of OA is higher in patients with shoulder pain than in the general population. However, trauma or repetitive microtrauma to the acromial joint, as in competitive swimmers, may reveal this condition. Ultrasound (US) imaging is a validated instrument for immediate and dynamic evaluation of shoulder disorders, especially rotator cuff impingement (Al-Shawi, 2008; Bureau, 2006; Iannotti et al., 2005). Barbiera et al., 2002 and Boehm et al., 2003 first introduced the use of ultrasonography in the evaluation of OA. They described the downward motion of the acromial fragment during active shoulder elevation, linking the os acromiale hypermobility to the pathogenesis of the rotator cuff tear. Smith at al. (2008) demonstrated that ultrasonography, given its dynamic capabilities, is useful in the evaluation of fragment hypermobility associated to pain reproduction guiding injection treatment. According to the previous authors and based on the presented clinical experience we suggest that, when an OA is not clearly evidenced by plain radiographs, or even as first choice exam, ultrasonography is a reliable means for early diagnosis. The satisfactory experience of Itoi and Tabata, 1992 on conservative treatment in patients with rotator cuff tear, when administered in presence of preserved range of motion and muscles strength, encouraged us to subject our patient to a conservative treatment regimen aiming to reduce pain, strengthen the rotator cuff and lower the humeral head. The conservative program allowed fully recovery from pain even after one year of follow-up, and the return to sport after 2 months.

It is possible to formulate a diagnosis of unstable and symptomatic OA quickly and with low cost using ultrasonography. Rehabilitation using a conservative management regimen may represent, in responder patients, a valid alternative to surgery in athletic patients.