Objective: To compare the cup and stem position in matched pairs of cadaveric hips performing a minimally invaisve total hip arthroplasty (MIS-THA) either by using manual guidance tools or by the STRYKER Hip-track Navigation System.

Background: Minimally invasive techniques are currently introduced to THA. Our workgroup has developed a direct anterior single incission approach. Special instruments have been designed for retraction and implantation. Instruments are navigable with the STRYKER hiptracksystem. Perfect positioning of the acetabular and femoral component are among the most important factors in THA. Malpositioning may result in significant clinical problems such as dislocation, impingement, limited range of motion or extensive wear.

Design/Methods: In twelve fixated human cadavers hemispherical pressfit cups (TRIDENT, Stryker, Alledale, NJ) and straight femoral components (ACCOLADE, Stryker, Allendale, NJ) were implanted. All implantation were done throught the minimally invasive direct anterior approach. On one side the surgery was performed with spezial MIS instruments. On the oposite side the navigation system was used for placement of the implants. The aim was to achieve an alignment for the cups with 45° of inclination and 15° of anteversion in reference to the frontal pelvic plane. For the stem the goal was to position the stem in 0° of varus/valgus relative to the proximal shaft axes. This plane and the resulting cup positions were measured on CT-scans with a 3D imaging software (Stryker-Leibinger, Freiburg, Germany).

Results: The Innsbruck MIS approach to the hip could be performed in all cases. For both groups cup and stem position where within the range of variation reported in the literature. Yet, variance of the deviation from the goal was higher in the conventional group for both inclination and anteversion with the medians for the navigated group for inclination, anteversion and stem position being closer to the goal then in the conventional group.

Conclusion: The described minimally invasive approach to the hip is feasible and renders results compareable to those reported for conventionally operated THA. By the use of the navigation system tested it is possible to increase placement precission

In navigated total hip arthroplasty, the pelvis and the femur are tracked by means of rigid bodies fixed directly to the bones. Exact tracking throughout the procedure requires that the connection between the marker and bone remains stable in terms of translation and rotation. We carried out a cadaver study to compare the intra-operative stability of markers consisting of an anchoring screw with a rotational stabiliser and of pairs of pins and wires of different diameters connected with clamps. These devices were tested at different locations in the femur. Three human cadavers were placed supine on an operating table, with a reference marker positioned in the area of the greater trochanter. K-wires (3.2 mm), Steinman pins (3 and 4 mm), Apex pins (3 and 4 mm), and a standard screw were used as fixation devices. They were positioned medially in the proximal third of the femur, ventrally in the middle third and laterally in the distal portion. In six different positions of the leg, the spatial positions were recorded with a navigation system.

Compared with the standard single screw, with the exception of the 3 mm Apex pins, the two-pin systems were associated with less movement of the marker and could be inserted less invasively. With the knee flexed to 90° and the dislocated hip rotated externally until the lower leg was parallel to the table (figure-four position), all the anchoring devices showed substantial deflection of 1.5° to 2.5°. The most secure area for anchoring markers was the lateral aspect of the femur.

Introduction Malpositioning of cup and stem in total hip replacement can result in significant clinical problems such as dislocation, impingement, limited range of motion and increased polyethylene wear. The use of mechanical alignment guides for correct cup positioning has been shown to result in large variations of cup inclination and version.

Methods Bilateral total hip replacements were performed in twelve human cadavers. While in each cadaver the operation on one side was performed with the aid of a non image based hip navigation system, the cup positioning at the contralateral hip was controlled by use of a conventional mechanical alignment guide. Post-operative cup position relative to the pelvic reference plane was assessed in both groups by the use of a 3D digitizing arm.

Results By aiming for 45° inclination and 20° anteversion for cup position the median inclination was assessed as 45.5° for the navigated group and 41.8° for the control group. Median anteversion in the navigated group was calculated as 21.9° and 24.6° for the control group. The 90 percentile showed a much wider range for the control group (36.1° to 51.8° inclination, 15° to 33.5° anteversion) than for the navigated group (43.9° to 48.2° inclination, 18.3 ° to 25.4° anteversion).

Conclusions The cadaver study demonstrates that computer assisted cup positioning using a non-image based hip navigation system allowed a more precise placement of the acetabular component in the surgeon’s desired orientation with less variance than in the control group.

In relation to the conduct of this study, one or more the authors have received, or are likely to receive direct material benefits.

Aims: For planning of Total Hip Arthroplasties (THA) plain X-rays of the pelvis in anterior posterior orientation are used. New methods such as CT scans and intraoperative digitization with navigation devices introduce the third dimension into orthopaedic planning. In order to compare measurements derived from three-dimensional data-acquisition with standard pelvic measurements it is important to estimate the underlying variances of those standards. Methods: 120 patients were investigated and subdivided in 4 groups depending of their age or the condition of their hip joints. The patients were positioned in a supine position on a table and in a standing position. Three landmarks at the patientñs pelvis (left and right anterior superior iliac spine (ASIS) and the pubic tubercle (PT)) were percutaneously digitized with a digitizing arm (Micro-Scribe-3DX, Vizion, Glendale, CA). The pelvic positions in space were calculated in relation to the horizontal and the vertical plane. Results: Despite the anatomical deþnition (0¡), we found an inclination of 4-6¡. There is no signiþcant difference between supine and standing position and no signiþcant difference between the groups and no diffenrence between genders. All patients lyed ßat in supine position without special positioning effort Conclusions: The pelvis orientation ist very stable in standing as well in supine position no matter if the patient is old or young, has coxarthrosis ore none or a THA. Therefore it can be concluded that our knowledge derived from measurements of planar a.-p.x-rays is not inßuenced by a massive variance in pelvic positions

Instruments used in surgery which rotate or vibrate at a high frequency can produce potentially contaminated aerosols. Such tools are in use in cemented hip revision arthroplasties. We aimed to measure the extent of the environmental and body contamination caused by an ultrasound device and a high-speed cutter.

On a human cadaver we carried out a complete surgical procedure including draping and simulated blood flow contaminated with Staphylococcus aureus (ATCC 12600). After cemented total hip arthroplasty, we undertook repeated extractions of cement using either an ultrasound device or a high-speed cutter. Surveillance cultures detected any environmental and body contamination of the surgical team.

Environmental contamination was present in an area of 6 x 8 m for both devices. The concentration of contamination was lower for the ultrasound device. Both the ultrasound and the high-speed cutter contaminated all members of the surgical team. The devices tested produced aerosols which covered the whole operating theatre and all personnel present during the procedure. In contaminated and infected patients, infectious agents may be present in these aerosols. We therefore recommend the introduction of effective measures to control infection and thorough disinfection of the operating theatre after such procedures.