VOL. 92-B, No. 5, MAY 2010 743 Classification of the morphology of the acromioclavicular joint using cadaveric and radiological analysis T. Colegate-Stone, R. Allom, R. Singh, D. A. Elias, S. Standring, J. Sinha From King’s College Hospital, London, England  T. Colegate-Stone, MA, MBBS, MRCS(Eng), SpR in Trauma & Orthopaedics  R. Allom, BSc, MBBS, MRCS, SpR in Trauma & Orthopaedics  J. Sinha, BSc(Hons), MBChB, FRCS, FRCS(Orth), Consultant Orthopaedic Surgeon Upper Limb Unit  D. A. Elias, MBBS, MRCP, FRCR, Consultant Radiologist Department of Radiology King’s College Hospital, Denmark Hill, London SE5 9RS, UK.  R. Singh, FRCS(Trauma & Orth), DNB(Orth), MS(Orth), Consultant Orthopaedic Surgeon Wrexham Maelor Hospital, Croesnewydd Road, Wrexham LL13 7TD, UK.  S. Standring, PhD, DSc, Emeritus Professor Department of Anatomy King’s College London, Strand, London WC2R 2LS, UK. Correspondence should be sent to Mr J. Sinha; e-mail: joydeep.sinha@btinternet.com ©2010 British Editorial Society of Bone and Joint Surgery doi:10.1302/0301-620X.92B5. 22876 $2.00 J Bone Joint Surg [Br] 2010;92-B:743-6. Received 27 May 2009; Accepted after revision 22 January 2010 The aim of this study was to establish a classification system for the acromioclavicular joint using cadaveric dissection and radiological analyses of both reformatted computed tomographic scans and conventional radiographs centred on the joint. This classification should be useful for planning arthroscopic procedures or introducing a needle and in prospective studies of biomechanical stresses across the joint which may be associated with the development of joint pathology. We have demonstrated three main three-dimensional morphological groups namely flat, oblique and curved, on both cadaveric examination and radiological assessment. These groups were recognised in both the coronal and axial planes and were independent of age. Injection and minimally invasive surgical exci- sion of the acromioclavicular joint are com- monly performed procedures. In order to improve clinical efficiency and reduce poten- tial complications, both require a detailed appreciation of the morphology of the joint. The acromioclavicular joint is a plane diathroidal joint formed from the outer sur- faces of the lateral end of the clavicle and the anterior aspect of the acromion, and contains a fibrocartilaginous disc. 1 It is stabilised by the shape of the articulating surfaces, by the joint capsule, which is reinforced superiorly by the superior acromioclavicular ligament and infe- riorly by the inferior acromioclavicular liga- ment, the superior being the stronger of the two, and by the coracoclavicular ligament, which is composed of trapezoid (lateral) and conoid (medial) parts. 2 Varying inclinations have been described at the articulating ends of the clavicle and acro- mion, 3 but the shape of the joint has been examined only with respect to its inclination in the coronal plane. 4 The aim of this study was to use cadaveric dissection and radiological analysis to classify the morphology of the acromioclavicular joint in a way that might be of practical use both anatomically and clinically. Materials and Methods Cadaveric assessment. A total of 79 joints were analysed in 41 cadavers, 17 male and 24 female, with a mean age of 81.2 years (54 to 96). The specimens were systematically prepared and standardised with respect to the plane of dissection and the degree of exposure. The acromioclavicular joint was stripped down to its capsule, and an oscillating saw was used to make transverse and coronal cuts through the joint and the articulating ends of the acromion and clavicle. Assessment of acromioclavicular joint morphology was made with respect to the true axis of the acromioclavicular joint and not to the cadaveric axis as the acromioclavicular joint axis has a variation with respect to cadav- eric axis. The shapes of the articulating sur- faces of each side of the acromioclavicular joint were assessed visually in both transverse and coronal planes and recorded. Radiological assessment. The morphology of the acromioclavicular joint was assessed radio- logically on both the reformatted CT scans and on conventional radiographs centred on the joint. A total of 78 acromioclavicular joints were assessed using CT in 39 patients of which there were 62 males and 16 females, with a mean age of 58.6 years (31 to 91). All were examined on a GE Lightspeed 16-slice system (GE Healthcare, General Electric Company, Chalfont St Giles, United Kingdom). Patients who had previously undergone CT angiogra- phy of the head and neck were identified because these scans are performed with the arms by the patient’s side. For scanning, the patient lay supine on a head rest. The set parameters for imaging were slice thickness 0.625 mm; interval 0.625 mm; pitch 0.938:1; limit 440 mAs; field of view 40 cm; and