CASE REPORT Spontaneous reduction of dissociated components of modular bipolar hip prosthesis—a case report Received: 11 November 2002 / Accepted: 25 November 2002 / Published online: 1 April 2003 Ó Springer-Verlag 2003 Abstract Three years after modular bipolar hemiar- throplasty for avascular necrosis of the femoral head, a patient’s modular head and neck components became dissociated following a minor twist of the lower limb. Spontaneous reduction of the components took place subsequently while the patient was asleep. The mechanism of dissociation is discussed. This un- usual late traumatic head and neck dissociation followed by spontaneous reduction has not been reported previously. Keywords Spontaneous reduction Æ Modular bipolar prosthesis Luxation intraprothe´ tique spontane´ e d’une prothe` se de hanche interme´diaire Re´ sume´ Trois ans apre` s la pose d’une prothe` se de hanche modulaire interme´diaire pour oste´one´crose aseptique de la teˆ te fe´ morale, une se´ paration entre col et teˆ te prothe´tique se produisit lors d’un mouvement de rota- tion minime du membre infe´rieur. Une re´duction spon- tane´e eut lieu alors que le patient e´tait endormi. Le me´canisme de cette luxation intra-prothe´tique est di- scute´. Un tel tableau avec re´duction spontane´e n’a pas encore e´te´ de´crit jusqu’a` pre´sent. Mots cle´s Re´ duction spontane´ e Æ Prothe` se modulaire bipolaire Introduction Dislocation after hip replacement occurs at an overall incidence of 2–3% and has significant cost and morbidity implications [5]. The usual reported zone of dislocation is at the cup-head interface [3]. Modular hip arthroplasty, currently widely used, offers the advantage of increased intra-operative flexibility in component selection with reduced inventory. There are a few case reports about dissociation of head-neck components of a modular femoral system during reduction of a dislocated hip from the acetabulum [1, 6]. We present a case in which minor trauma caused head-neck dissociation without disloca- tion of the head out of the polyethylene cup of the mod- ular bipolar hip prosthesis. The dissociation reduced spontaneously while the patient was sleeping. Case report A 39-year-old man had a modular bipolar hip replacement hem- iarthroplasty for idiopathic avascular necrosis of the femoral head about 3 years prior to presentation at our institute. This replace- ment had been done at another referral centre. The patient had been asymptomatic in this 3-year period. He presented to us with history of a minor slip after which he had a fall and was unable to bear weight on the affected limb. He had a painful, shortened, flexed, adducted, and internally rotated limb at presentation. Roentgenograms revealed dissociation of the prosthetic head from the neck of the femoral component, but the head was in place in the acetabulum (Fig. 1). There was no associated neuro-vascular in- volvement. The patient was planned for open reduction and was put on skin traction pending investigations for fitness for anaesthesia. Two days following admission, the patient woke up at night after he accidentally twisted the affected limb during sleep and felt a clunk in his hip resulting in complete pain relief. Fresh roentgenograms were obtained the next morning, and they revealed a complete re- duction of the components (Fig. 2). The patient was advised revi- sion surgery for ensuring press fitting of the components, but he did not give consent for surgery. Manual longitudinal thumping of the extended limb on the sole was done to try locking the components. He was kept on skin traction for 3 weeks and was discharged with the advice of partial weight bearing. The components have not dissociated 2 years since the episode. Eur J Orthop Surg Traumatol (2003) 13: 50–51 DOI 10.1007/s00590-002-0056-z S. C. Sharma Æ A. Devgan Æ K. M. Marya Æ V. Yadav S. C. Sharma Æ A. Devgan Æ K. M. Marya (&) Æ V. Yadav Department of Orthopaedics Paraplegia and Rehabilitation, Postgraduate Institute of Medical Sciences, Rohtak, Haryana, India K. M. Marya 1166, Sector 1, Rohtak 124 001, India E-mail: dr_marya@hotmail.com Tel.: +91-1262-272043 Fax: +91-1262-243791