Double-threaded Screws Research Articles

Reduction of lumbar spondylolisthesis using a CDI pedicle screw system.

To evaluate reduction methods using two of the several types of Cotrel-Dubousset instrumentation (CDI), 39 patients with low-grade (Meyerding grades I and II [12]) lumbar spondylolisthesis were followed clinically and radiologically for a minimum of 6 months. Our surgical methods were classified into three types as follow: reduction by 2-level assembly using double-threaded screws (type I); reduction by single-level assembly using the double-threaded screws (type II); and reduction by single-level assembly using tulip screws (type III). We found that satisfactory reduction could be achieved by single-level assembly using either the double-threaded or tulip screw without resection of disc material or the posterior leverage method. We found that the tulip screw was superior in obtaining stable reduction. We discuss the mechanism of reducing spondylolisthesis in comparison with that of previously reported methods.

Transartikuläre Verschraubung von Atlas und Axis bei chronischer Polyarthritis

In 45 patients (34 female, 11 male) suffering from rheumatoid arthritis, a transarticular screw fixation was performed to establish stability between atlas and axis. Mean age was 57 (ranging from 31-79 years). Mean history of rheumatoid arthritis was 17 years (3-42 years) before surgery was indicated. The ventral atlantoaxial interval was 11 mm on average. In all patients the joints between atlas and axis were affected only, there being no single case of destruction of the occipito-atlantal joints. There was no invagination of the dens into the posterior cranial fossa. In 17 cases neurological deficits were detected (Ranawat classes II and III). Surgical technique has been thoroughly described. For the first 16 operations, 2.2 mm double-threaded screws were used, where after 3.5 mm cortical I screws were inserted. Autologous bone was placed on the laminae of the atlas and the axis in 37 patients, 21 of which received additional fixation of the bone by means of a cable-cerclage. In 2 operations methylmethacrylate was applied as a spacer between the dorsal arch of the atlas and the spinous process of the axis. Screws alone were inserted in 6 cases. No intraoperative complications were observed. Injuries to the vertebral artery or the dura mater did not occur. Mean follow up in 43 of 45 patients was 28 months (6-62 months). Two pseudarthrosis were observed in patients without additional bone graft. In patients with bone grafting, one pseudarthrosis only occurred as a result of a misplacement of one screw. As long as exact placement of the screws (described in detail) was achieved and bone grafting was applied no pseudarthrosis was observed in 35 cases. There were two cases of screw breakage with 2.2 mm screws, but none with 3.5 mm screws. Revision surgery was not necessary in any of the cases. A preoperative CT-scan is mandatory to establish any abnormal courses of the vertebral arteries (described in the literature), which is a contraindication for this technique, whereas age need not be considered. In contrast to previous techniques, transarticular screw fixation is possible in cases with a split or a missing dorsal arch of the atlas. This technique should be considered, because of its low complication rate, even in cases with increasing instability without neurological deficits, to ease the burden of the patient knowing that a transverse syndrome may result in cases of untreated instability.

Internal fixation of dens fractures by double-threaded screws

Surgical Principles After closed reduction of the displaced dens of the axis, the position is maintained pre- and intraoperatively by extension. By diagonal insertion of two screws the odontoid process is solidly fixed in an anatomical position and the axis of rotation of the head is restored. (The procedure of internal fixation of the odontoid process with screws was elaborated and published in 1981 [2, 3] by J. Bohler following a suggestion by F. Magerl.) The use of double-threaded screws eliminates the irritation which normal screw heads nearly always cause at the C2/3 segment [8, 9].

Osteosynthesis of injuries and rheumatic or congenital instabilities of the upper cervical spine using double-threaded screws.

The surgical treatment of instabilities of the upper cervical spine, independent of their cause, requires the use of differentiated procedures if functional anatomy is to be largely restored. Successful procedures have been the diagonal screw fixation of the axis from the anterolateral aspect in case of acute fractures of the odontoid process, transpedicular screw osteosynthesis of C2 in hangman's fractures with bony instability, and the transarticular screw fixation of C 1/2 with interarcual fusion for atlantoaxial instabilities. Compared with conventional screws, the use of double-threaded screws which are almost totally imbedded in the vertebral body has the advantage of eliminating local irritation, reducing the risk of surgery, and simplifying the operative procedure itself.

Two modifications for insertion of the Herbert screw in the fractured scaphoid

Since its introduction in 1984, the Herbert screw system has been used increasingly for fracture fixation and reconstruction of the scaphoid. The differential pitch of the double-threaded screw is designed to fix and compress the fracture fragments such that external immobilization is not necessary. The thread design al­ lows the trailing threads to be countersunk so that the screw does not impinge on articular surfaces and thus does not have to be removed. As experience with the fixation system has devel­ oped, several technical difficulties have become appar­ ent. A common difficulty involves excessive palmar placement of the screw with resultant inadequate frac ­ ture fixation (Fig. 1). A second common difficulty is accurately determining the prospective course of the screw after jig placement. Two modifications of the insertion technique are pre­ sented to help eliminate these difficulties. The first in­ volves creation of a trough in the palmar aspect of the trapezium to allow adequate dorsal jig placement. The second is a Kirschner (K) wire insert sleeve designed for the jig, which simplifies wire placement, allowing accurate radiologic determination of the eventual course of the screw. Technique

Metatarsal osteotomy using a double-threaded compression screw: an adjunct to revision forefoot surgery.

A double-threaded compression screw (Herbert) was used as internal fixation of metatarsal neck osteotomy and nonunion repair in 16 patients (18 feet). Fifteen patients had associated symptomatic conditions of the foot. Twelve patients had one or more previous surgical procedures on the involved foot. Fourteen patients (15 feet) underwent 20 primary or revision lesser metatarsal osteotomies. Four of these patients had undergone previous lesser metatarsal osteotomies and had developed recurrent pain beneath six metatarsals and transfer metatarsalgia in one case. The remaining two patients (three feet), with six nonunions from previous metatarsal osteotomies, had repair with screw fixation and bone grafting. Follow-up for the series averaged 14 months.

Reduction and stabilisation of severe spondylolisthesis. A report of three cases.

A modification of a previously reported one-stage technique for reduction and stabilisation of severe spondylolisthesis using a posterior route is described. Reduction is obtained by inserting Harrington rods to lift L5 vertically out of the pelvis and two double-threaded screws to pull it backwards. After reduction the rods are taken away and stabilisation achieved by means of screws and a sacral bar. With this modified technique lumbar vertebrae above L5 are never immobilised, compared with the previous method where the retention of the Harrington rods resulted in more lumbar vertebrae being immobilised than was necessary for fusion. Bone is resected from the sacrum and the fifth lumbar vertebra to avoid too much tension on the nerve roots. Bone grafts are not needed and lumbosacral fusion is achieved within six months due to close contact between the raw bone of the vertebral bodies. Three patients have been treated with this modified technique; there was no reslip, neither during the period when the metallic fixation was in situ nor after its removal.

Centenary of Practical Marine Screw Propulsion

To mark the centenary of practical marine screw propulsion, a special exhibit was opened at the Science Museum, South Kensington, on February 11. In accordance with the usual practice of the Museum, this shows both the history of the pioneer experimental work, as well as the subsequent developments and current practice in marine screw propellers. In February 1837, Francis Pettit Smith successfully tried his first screw-propelled steam launch (a model of which is shown) on the Paddington Canal. The screw had two complete turns; on one of the trips it struck an obstacle, and about one-half of it was broken off. To the inventor's astonishment, this accident materially increased the speed of the boat. The S.S. Archimedes (1838) was fitted with a double-threaded screw of half a turn, in accordance with Smith's amended patent. Other historical exhibits include models of Ericsson's experimental screw of 1837, and those of the S.S. James Lowe (1838), the S.S. Novelty (1839-40), and the first French screw steamer Napoleon (1843). Screws were at first used as an auxiliary means of propulsion, and in order that they should not impede the vessel when under sail only, lifting screws (an example by Maudslay, 1846, is shown) were introduced, which could be disconnected from the shaft and raised clear of the water. Other developments represented are the ‘common screw’, which was the most successful form of propeller up to about 1860, Hirsch's propeller (1860-66), and the adjustable pitch propeller patented by Griffiths in 1868. Various examples of modern practice are also included, notably a model of the four-bladed bronze propellers of the Cunard White Star liner R.M.S. Queen Mary, which are 20 ft. in diameter, each weighing 35 tons. These are the largest screw propellers which have ever been cast in one piece.