The use of intramedullary column screws in the treatment of acetabular fractures is becoming more widely utilized. The development of percutaneous methods to insert these screws under image intensifier guidance is one of the main reasons for their increased use. Few groups are navigating insertion of these screws. The available screws are cannulated 6.5–8 mm screws. Most surgeons prefer using 3.2 mm guide wires to reduce deflection. With a shank diameter of 4.5 mm, 3.2 mm cannulation significantly weakens the screws. We postulated that both columns, specially the posterior column can accommodate larger screw diameters which will increase the stability of fixation allowing earlier full weight bearing. The currently used screws were designed for fixation of femoral neck fractures. As percutaneous fixation of acetabular fractures is a growing area of interest, this warrants designing suitable screws with larger diameters. Eight CT scans of the adult pelvis –performed for non fracture related indications-, were studied (7 females, 1 male). We found that the anatomical cross-section of the columns is irregular but approximately triangular. The method we used to determine the largest diameter of a screw to fit each column was fitting cylinders in the columns. Robin’s 3D software was used to segment acetabula and convert the CT data into polygon mesh (stereolithography STL format) bone surfaces at an appropriate Hounsfield value. The resulting STL files were imported in Robin’s Cloud software, where polygon mesh cylinders of 10 mm diameter were fitted in each column. These cylinders were then manipulated to achieve best fit and their diameters were gradually increased to the biggest diameter which still fitted in the column. The mean diameters of the fitted cylinders were 10.8 mm (range: 10–13mm) and 15.2 mm (range 14–16.5mm) for the anterior and posterior columns respectively. To our knowledge, this is the first investigation to study the cross sectional dimensions of the anterior and posterior columns of the acetabulum. Our small sample shows that both columns can safely accommodate larger screws than those currently used. We plan to investigate this further using cadavers.
Acetabular and pelvic fractures are amongst the most challenging to treat, still requiring major open surgery. The operations to reduce and fix them entail lengthy operative time, significant blood loss and use of ionising radiation. We report on the initial stages of developement of a minimally invasive method for navigated reduction and percutaneous fixation of acetabular fractures (NRFA). A commercial navigation platform (Acrobot Ltd.) will be adapted for use with this technique. CT based planning will be used to identify the correct realignment of the the bone fragments, which will then be reduced percutaneously with the aid of two tracked arms attached to the navigation system. Schanz pins, which are inserted in pre-operatively planned sites in each fragment using safe trajectories, are handled as joysticks to manipulate the fracture under computer assistance. Registration of the fragments after insertion of the joysticks will be carried out by means of fluoroscopic images of the AP and Judet views of the fractured acetabulum. Once reduction is achieved by following on-screen instructions, the joysticks are held in place by a custom clamping system connected to one of the arms, while the other is used for percutaneous insertion of column screws. This technique is potentially suitable for a number of acetabular fractures which include transverse, anterior column, posterior column, T-fractures and some associated both columns fractures. These constitute over 50% of Letournel’s and 60% of Matta’s original series of acetabular fractures. Furthermore, this percutaneous technique could reduce bleeding, wound complications, hospital stay and cost of treatment. Intra operative ionising radiation would be greatly reduced for both patients and the surgeons. Adequate training with the use of this software may provide a greater number of surgeons the capability to surgically treat these complex fractures.
We performed a prospective, randomised controlled trial of unicompartmental knee arthroplasty comparing the performance of the Acrobot system with conventional surgery. A total of 27 patients (28 knees) awaiting unicompartmental knee arthroplasty were randomly allocated to have the operation performed conventionally or with the assistance of the Acrobot. The primary outcome measurement was the angle of tibiofemoral alignment in the coronal plane, measured by CT. Other secondary parameters were evaluated and are reported. All of the Acrobot group had tibiofemoral alignment in the coronal plane within 2° of the planned position, while only 40% of the conventional group achieved this level of accuracy. While the operations took longer, no adverse effects were noted, and there was a trend towards improvement in performance with increasing accuracy based on the Western Ontario and McMaster Universities Osteoarthritis Index and American Knee Society scores at six weeks and three months. The Acrobot device allows the surgeon to reproduce a pre-operative plan more reliably than is possible using conventional techniques which may have clinical advantages.
