VOL. 81-B, NO. 5, SEPTEMBER 1999 881 M. S. Dhillon, MS, MNAMS, Associate Professor O. N. Nagi, MS, FAMS, MSc Oxon, Professor and Head Department of Orthopaedic Surgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India. Correspondence should be sent to Dr M. S. Dhillon at 1090/2 Sector 39-B, Chandigarh 160036, India. ©1999 British Editorial Society of Bone and Joint Surgery 0301-620X/99/59873 $2.00 Total dislocations of the navicular: are they ever isolated injuries? M. S. Dhillon, O. N. Nagi From the Postgraduate Institute of Medical Education and Research, Chandigarh, India I solated dislocations of the navicular are rare injuries; we present our experience of six cases in which the navicular was dislocated without fracture. All patients had complex injuries, with considerable disruption of the midfoot. Five patients had open reduction and stabilisation with Kirschner wires. One developed subluxation and deformity of the midfoot because of inadequate stabilisation of the lateral column, and there was one patient with ischaemic necrosis. We believe that the navicular cannot dislocate in isolation because of the rigid bony supports around it; there has to be significant disruption of both longitudinal columns of the foot. Most commonly, an abduction/pronation injury causes a midtarsal dislocation, and on spontaneous reduction the navicular may dislocate medially. This mechanism is similar to a perilunate dislocation. Stabilisation of both medial and lateral columns of the foot may sometimes be essential for isolated dislocations. In spite of our low incidence of ischaemic necrosis, there is always a likelihood of this complication. J Bone Joint Surg [Br] 1999;81-B:881-5. Received 1 February 1999; Accepted after revision 5 March 1999 Midtarsal injuries are the result of complex multidirectional forces. 1 The bones of the midfoot fit snugly to one another and are shaped to form transverse and longitudinal arches. The navicular, the keystone of the medial longitudinal arch, is rigidly stabilised by an extensive network of dorsal and plantar ligaments. 2 Because of the strong ligamentous attachments and the recessed position of the navicular, fractures are much more common than dislocations. The usual mechanism is a plantar flexion/compressive injury, which crushes the bone and may sometimes displace a part of the fractured bone from the naviculocuneiform and the talonavicular joints. 3 This usually occurs when an element of longitudinally directed force compresses the navicular, in addition to an abduction/plantar flexion injury. 4 Isolated dislocations without fractures of the body are extremely rare, and it has been claimed that dislocation without fracture is an anatomical impossibility 5 since the foot is composed of two longitudinal columns, the lateral and the medial, each adding to the stability of the other. Conse- quently, for the navicular to dislocate completely without fracture, there must be a break in both columns, with marked instability. We have reviewed all patients seen at our institute in whom the navicular was found to be dislocated without a fracture of the body, in order to analyse the mechanism and forces involved. A review of the literature from 1920 onwards revealed only six cases of either total or isolated dislocations of the navicular. 5-11 Patients and Methods Between 1990 and 1997, we encountered six patients in whom the navicular had dislocated from the talonavicular as well as the naviculocuneiform joints without a fracture of the body. These injuries were six of 35 complex mid- tarsal fractures/dislocations seen during this period. The records of the mechanism of trauma, the nature of the injury, the clinical details and radiographs taken when first seen (Fig. 1) and at the last follow-up, were reviewed. All patients were seen primarily at our centre and four were reviewed in the period between September 1997 and Sep- tember 1998. The details of these six patients are given in Table I. There were five men and one woman with a mean age of 35.8 years (24 to 60). One patient (case 5) has been reported elsewhere. 11 Results Five patients were injured in road-traffic accidents. One had an injury from a buffalo’s hoof. One (case 6) had multiple injuries, and management of the foot was given low priority. The dislocated navicular was observed to lie inferomedially to the head of the talus in three patients (Fig. 2). One (case 3) had a complete naviculocuneiform dislocation, but partial dislocation of the talonavicular joint