{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,23]],"date-time":"2026-05-23T08:05:56Z","timestamp":1779523556529,"version":"3.53.1"},"reference-count":7,"publisher":"Springer Science and Business Media LLC","issue":"7","license":[{"start":{"date-parts":[[2026,4,25]],"date-time":"2026-04-25T00:00:00Z","timestamp":1777075200000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0"},{"start":{"date-parts":[[2026,4,25]],"date-time":"2026-04-25T00:00:00Z","timestamp":1777075200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0"}],"content-domain":{"domain":["link.springer.com"],"crossmark-restriction":false},"short-container-title":["Skeletal Radiol"],"published-print":{"date-parts":[[2026,7]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>Bipolar hemiarthroplasty dislocation is an uncommon but clinically significant complication of closed reduction that often necessitates revision, causing prolonged recovery, increased morbidity, and higher costs. A recently described radiographic marker, the \u201cO sign\u201d\u2014a concentric circle appearance of the prosthesis on radiographs\u2014has been proposed as an indicator that closed reduction may be safely attempted. While potentially useful for pre-reduction assessment, its predictive value remains uncertain. We report a case evaluating the diagnostic value of the O sign in bipolar hemiarthroplasty dislocation. A patient underwent both radiography and computed tomography (CT) prior to closed reduction. Radiographic features, including concentricity of the external shell and central positioning of the inner femoral head, were assessed for alignment and eccentricity. On anteroposterior radiographs, the external shell displayed a concentric \u201cO\u201d appearance. However, closer inspection revealed unequal circumferential shell thickness suggesting anterior rotation. CT imaging confirmed eccentric positioning of the femoral head within the outer shell, consistent with early bipolar head dissociation. This case demonstrates that while a concentric O sign on radiographs may suggest closed reduction is feasible, subtle misalignments such as asymmetric shell thickness or eccentric head positioning can be missed without CT. The predictive value of the O sign therefore depends not only on external shell symmetry but also on internal head alignment. Failure to meet either criterion may indicate early dissociation and warrants caution before attempting closed reduction. By integrating CT into assessment, the O sign may evolve from a binary marker to a more refined tool for guiding management of bipolar hemiarthroplasty dislocations.<\/jats:p>","DOI":"10.1007\/s00256-026-05233-z","type":"journal-article","created":{"date-parts":[[2026,4,25]],"date-time":"2026-04-25T04:30:22Z","timestamp":1777091422000},"page":"1695-1698","update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Bipolar head dissociation: radiographic assessment of bipolar hemiarthroplasty dislocation and the role of the \u201cO\u201d sign"],"prefix":"10.1007","volume":"55","author":[{"ORCID":"https:\/\/orcid.org\/0009-0008-9569-3255","authenticated-orcid":false,"given":"Elliot F.","family":"Forst","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sami","family":"Alaraj","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"William M.","family":"Weiss","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,4,25]]},"reference":[{"issue":"5","key":"5233_CR1","doi-asserted-by":"publisher","first-page":"260","DOI":"10.1097\/BOT.0000000000000814","volume":"31","author":"Z Wang","year":"2017","unstructured":"Wang Z, Bhattacharyya T. Outcomes of hemiarthroplasty and total hip arthroplasty for femoral neck fracture. J Orthop Trauma. 2017;31(5):260\u20133.","journal-title":"J Orthop Trauma"},{"key":"5233_CR2","doi-asserted-by":"publisher","first-page":"101","DOI":"10.2147\/TCRM.S350213","volume":"18","author":"Y Yang","year":"2022","unstructured":"Yang Y, Fu G, Li Q, Zhang R, Liao W, Ma Y, et al. Multivariable analysis of risk factors affecting dislocation after bipolar hemiarthroplasty in patients with femoral neck fracture. Ther Clin Risk Manag. 2022;18:101\u201311.","journal-title":"Ther Clin Risk Manag"},{"key":"5233_CR3","doi-asserted-by":"publisher","unstructured":"Saini MK, Reddy NR, Reddy PJ. Disassembly of components of a monoblock bipolar hip prosthesis following dislocation: a case report and review on \u201cbottle opener effect.\u201d J Orthop Case Rep. 2020;10(9):90\u201393.\u00a0https:\/\/doi.org\/10.13107\/jocr.2020.v10.i09.1916.","DOI":"10.13107\/jocr.2020.v10.i09.1916"},{"issue":"37","key":"5233_CR4","doi-asserted-by":"publisher","first-page":"e35234","DOI":"10.1097\/MD.0000000000035234","volume":"102","author":"SB Sim","year":"2023","unstructured":"Sim SB, Son SW, Shim BJ. Be aware of the \u201cO\u201d sign in the bipolar cup dissociation during closed reduction of bipolar dislocation: a case report. Medicine. 2023Sep 15;102(37):e35234\u201344.","journal-title":"Medicine"},{"key":"5233_CR5","doi-asserted-by":"crossref","unstructured":"Lee YK, Park CH, Ha YC, Koo KH. What is the frequency of early dissociation of bipolar cups and what factors are associated with dissociation? Clinical orthopaedics and related research [Internet]. 2018 [cited 2025 Sep 15];476(8):1585\u201390. Available from:\u00a0https:\/\/www.ncbi.nlm.nih.gov\/pubmed\/29781911.","DOI":"10.1097\/CORR.0000000000000350"},{"key":"5233_CR6","doi-asserted-by":"crossref","unstructured":"Sierra RJ, Schleck CD, Cabanela ME. Dislocation of bipolar hemiarthroplasty. Clin Orthop Relat Res. 2006;442(&NA;):230\u20138.","DOI":"10.1097\/01.blo.0000183741.96610.c3"},{"issue":"2","key":"5233_CR7","doi-asserted-by":"publisher","first-page":"162","DOI":"10.1016\/j.injury.2005.09.014","volume":"37","author":"G Georgiou","year":"2006","unstructured":"Georgiou G, Siapkara A, Dimitrakopoulou A, Provelengios S, Dounis E. Dissociation of bipolar hemiarthroplasty of the hip after dislocation. Injury. 2006;37(2):162\u20138.","journal-title":"Injury"}],"container-title":["Skeletal Radiology"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/link.springer.com\/content\/pdf\/10.1007\/s00256-026-05233-z.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/link.springer.com\/article\/10.1007\/s00256-026-05233-z","content-type":"text\/html","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/link.springer.com\/content\/pdf\/10.1007\/s00256-026-05233-z.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,5,23]],"date-time":"2026-05-23T07:46:15Z","timestamp":1779522375000},"score":1,"resource":{"primary":{"URL":"https:\/\/link.springer.com\/10.1007\/s00256-026-05233-z"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,4,25]]},"references-count":7,"journal-issue":{"issue":"7","published-print":{"date-parts":[[2026,7]]}},"alternative-id":["5233"],"URL":"https:\/\/doi.org\/10.1007\/s00256-026-05233-z","relation":{},"ISSN":["0364-2348","1432-2161"],"issn-type":[{"value":"0364-2348","type":"print"},{"value":"1432-2161","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,4,25]]},"assertion":[{"value":"10 October 2025","order":1,"name":"received","label":"Received","group":{"name":"ArticleHistory","label":"Article History"}},{"value":"14 April 2026","order":2,"name":"revised","label":"Revised","group":{"name":"ArticleHistory","label":"Article History"}},{"value":"20 April 2026","order":3,"name":"accepted","label":"Accepted","group":{"name":"ArticleHistory","label":"Article History"}},{"value":"25 April 2026","order":4,"name":"first_online","label":"First Online","group":{"name":"ArticleHistory","label":"Article History"}},{"order":1,"name":"Ethics","group":{"name":"EthicsHeading","label":"Declarations"}},{"value":"Written informed consent was obtained from the subject described in this report.","order":2,"name":"Ethics","group":{"name":"EthicsHeading","label":"Ethics approval and consent to participate"}},{"value":"The authors declare no competing interests.","order":3,"name":"Ethics","group":{"name":"EthicsHeading","label":"Conflict of interest"}}]}}