Imageless computer navigation systems in total hip arthroplasty (THA) improve acetabular cup position, thereby reducing the risk of revision surgery for all causes as well as dislocation. We aimed to evaluate the registration accuracy of 3 alternate registration planes. A prospective, observational study was conducted with 45 THA in the supine position using two imageless navigation systems and 3 registration planes. Patient position was registered sequentially using an optical system (Stryker OrthoMap) and an inertial sensor-based system (Navbit Sprint) with 3 planes of reference: (Plane 1) an anatomical plane using the anterior superior iliac spines (ASISs) and the pubic symphysis; (Plane 2) a functional plane parallel to the line between the ASISs and the table plane; and, (Plane 3) a functional plane that was perpendicular to the gravity vector and aligned with the longitudinal axis of the patient. The 3 measurements of acetabular cup inclination and anteversion were compared with the measurements from postoperative computed tomography (CT) scans. For inclination, the mean absolute error was significantly lower for Plane 3 (1.80°) than for Plane 2 (2.74°), p = .038 and was lower for both functional planes than for the anatomical plane (3.75°), p < .001. For anteversion, the mean absolute error was significantly lower for Plane 3 (2.00°) than for Plane 2 (3.69°), p = .004 and was lower for both functional planes than for the anatomical plane (8.58°), p < .001. Patient registration using functional planes more accurately measured the acetabular cup position than registration using anatomic planes.
1. Twenty-eight patients with pyogenic infection of the spine are reported. 2. Diagnosis was by clinical, radiological and bacteriological means. Investigations of the spinal lesions by needle aspiration or open operation was needed in four patients. 3. Treatment consisted primarily of antibiotics and rest. 4. Twenty-five patients were fit and well after follow-up of one to fifteen years. Three deaths occurred, but only one was directly connected with the infection ; urinary infection with paraplegia and haemophilia were the cause in two others. 5. The relatively benign course is stressed, as are some of the diagnostic pitfalls in the early stages, particularly with thoracic lesions.
1. The spinal branches of the vertebral artery were injected with a suspension of barium sulphate and the blood supply of the vertebral bodies of the lower four or five cervical vertebrae investigated radiologically. 2. Beneath the posterior longitudinal ligament there is a free dorsal arterial plexus from which a large branch arises to enter the back of the vertebral body. This vessel terminates abruptly at the centre of the body where numerous, much smaller, branches radiate towards the upper and lower surfaces. 3. The possible significance of the form of the intravertebral arteries is considered in relation to embolic lesion in vertebral bodies.
