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Dislocation of both ends of the clavicle is a rare traumatic lesion and the mechanism of the lesion is usually related to major trauma. The first case was described in 1831.
We present the oldest referenced case of this alteration. The skeleton studied belonged to an old woman buried inside the Sant Pere de Madrona Church in Berga (Barcelona/Spain) and its dating indicated it corresponded to the end of the 17th century. There was a pseudarthrosis between the clavicle and coracoid ligament; when the bones were reconstructed by pseudarthrosis both ends of the clavicle appeared dislocated.
Bipolar dislocation of both ends of the clavicle, or “floating-clavicle”, is a rare injury. Since 1831 when this type of injury was first reported, approximately 40 cases have been published. No archaeological case has been published.
Despite experiencing bipolar dislocation of both ends of the clavicle, or floating-clavicle, it is possible to have acceptable function of the arm as suggested by the anthropologic parameters analyzed here. The head of the humerus of the affected shoulder shows no abnormalities and the contralateral glenoid cavity shows severe osteochondritis of the anteroinferior side.
Bipolar dislocation of both ends of the clavicle, or floating-clavicle, is a rare injury. It was first described by Porral in 1831 . Almost a century later, Beckman  reported 15 cases and carefully reviewed the prior cases. One hundred fifty years later in 1982, a new case was published . Although road-traffic and sports injuries have increased the frequency of this injury, most reports have been based on single cases [1, 2, 5, 7, 8, 11, 12, 17, 27]. Only five studies presented multiple cases (four cases published by Rockwood  in 1984, six cases by Sanders et al.  in 1990, two cases by Le Huec et al.  in 1998, three cases by Dieme et al.  in 2007, and two cases by Schemitsch et al. in 2011 ).
Before the study by Porral , there were no references of this kind of lesion. There are no archaeological cases of this lesion described in paleopathologic literature, perhaps owing to the complexity of producing simultaneous dislocation of both acromioclavicular and sternoclavicular joints and the difficulty of finding evidence of dislocation in skeletal remains. We present a case in which the most probable diagnosis is a floating-clavicle injury. The skeleton of this individual was recovered from inside the Romanesque Church of Sant Pere de Madrona, near Berga, Spain. In the same place, anthropologists recovered skeletal remains from a total of 63 individuals. Historical and parish registers indicate they were buried at the end of 17th century [13, 14].
The analyzed skeleton (Fig. 1) is that of an approximately 60-year-old woman (SPM’07 UE 78) buried beneath the church . There was a new joint of the right coracoid process (Fig. 2) that articulated with the posterior side of the clavicle (Fig. 3); the dimensions of the pseudarthrosis were 3.2 cm in length × 2.6 cm in width × 1.1 cm in height. There were osteophytes and narrowing of the diaphysis from the anteroinferior side of the middle third of the right clavicle (Fig. 4). Eburnation was produced in the area of the new joint at the inferior side of the clavicle and the uppermost side of the coracoid process (Fig. 5) where apposition of the cortical bone shows a smooth and shiny aspect. After assembling the clavicle and scapula on the basis of the new coracoclavicular joint (pseudarthrosis), macroscopic or radiographic evaluation showed the external end of the clavicle was located in front of the acromion. The ends of the right clavicle (sternal and acromial) were smaller and had more rounded morphologic changes than the left clavicle. These patterns in the acromial end were presumed attributable to a chronic acromioclavicular disruption. Radiographic analysis from the dry bone shows loose cancellous bone and the appearance of sclerotic bone (Figs. 6A–B).
In addition, the individual had an os acromiale in the left scapula (Fig. 7) and severe degenerative disease in the cervical spine, specifically in the posterior joints of C4 and C5, affecting only the right side (Fig. 8).
The features observed in the right clavicle and scapula are compatible with a bipolar dislocation of the clavicle. The clavicle normally has little inherent stability owing to the lack of congruence of its joint surfaces and stability is provided by the joint capsules, muscle attachments, and intrinsic ligaments . The lesion we describe was produced long before the woman’s death, since it formed a neoarticulation between the lower margin of the clavicle and the upper margin of the coracoid process, forming a synchondrosis. The acromion ossification centers appear between the 15th and 16th years and fusion usually is complete by the 25th year . The incidence of os acromiale ranges from 1.4% to 8%  and is bilateral in as much as 62% of cases . Overuse reportedly retards or prevents fusion of this apophysis . Because our subject was older than 60 years, the presence of a contralateral acromiale (MSA/MTA type)  bone suggests to us the injury occurred during the period of growth, the patient compensated for the injury with use of the left arm, and overuse of the left arm did not permit fusion to the rest of the acromion. Furthermore, unilateral osteoarthritis of the right facet of the cervical vertebrae might be attributable to a postural change or an antalgic posture secondary to the clavicular dislocation.
Although in a few cases the floating clavicles were atraumatic , dislocation of both ends of the clavicle is usually a result of major trauma acting through an indirect mechanism like a violent blow on the lateral face of the shoulder or heavy compression (squeezing) with some kind of torsion of the trunk [9, 15]. The mechanism of the lesion presumably is based on an initial anterior subluxation of the sternoclavicular joint followed by subsequent posterior subluxation of the acromioclavicular joint . The conoid and trapezoid ligaments may be preserved . This lesion is more easily produced if it is associated with congenital joint laxity, although in some cases the dislocation is attributable to minor trauma [4, 7, 12, 17].
Although the function of the right upper limb for our subject would be speculative, according to Rockwood , who studied four patients who had clavicle dislocation, all patients functioned well after nonsurgical treatment.
One or more of the authors (AM, AI) has received funding from the Spanish Ministerio de Educación y Ciencia and from the Generalitat of Catalunya.
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The work was performed at the Unitat d’Antropologia Biològica. Dept. Biologia Animal, Biologia Vegetal i Ecologia. Universitat Autònoma de Barcelona, Spain.
Assumpció Malgosa, Email: firstname.lastname@example.org.
Albert Isidro, Email: email@example.comA.