Purpose: Dislocation is a short-term complication frequently encountered after implantation of a total hip arthroplasty (THA). Different strategies can be used to limit the influence of technical, particularly surgical, factors. The position of the acetabular element is a key factor, particularly the anteversion angle and the abduction angle. The purpose of this work was to determine the precision, the reproducibility, and the ease of use of a new mechanical guide for insertion of the acetabular cup.

Material and methods: After calculating the sample size necessary to achieve 90% statistical power for a 5% type I error, we had five surgeons who regularly implanted THA implant 310 press-fit hip cups on a plastic anatomic model of the pelvis. A new mechanical guide was developed using the constant direction of gravity as the reference frame. We determined the precision of acetabular cup implantation, its reproducibility, and ease of use compared with that of the Müller mechanical guide during in vitro implantation of 310 cups via a posterolateral approach that allowed the usual vision of the operative field.

Results: The error of cup anteversion relative to the reference set at 15 was 10.4±5.0 (range 3–21) for the Müller guide and 0.4±0.7 (range 1–3) for the new guide. Cup abduction, relative to the reference set at 45, was −4.7±2.3 (range 7–11) for the Müller guide and 0.3±0.5 (range 0–3) for the new guide. Mean time for positioning the cup was comparable with the two guides (mean 6s for the Müller guide and 5s for the new guide).

Discussion: The precision and reproducibility of cup positioning obtained with the new guide are better than those obtained with mechanical guides currently available on the market (p< 0.00001 with the Müller guide). They are more comparable with values found in in vitro studies using computer-assisted surgery techniques. Use of the new guide was also found to be rapid and simple.

Conclusion: The excellent results obtained with this new mechanical guide, as assessed in terms of cup position for THA, should be confirmed with in vivo trials.

Aims: To determine the precision of conventional versus computer assisted techniques for positioning the acetab-ular component in total hip arthroplasty (THA). Methods: Using a lateral approach, 150 cups were placed by 10 different surgeons in 10 identical plastic pelvis models. Only the immediate operating þeld was visible. Preoperative planning was performed with a computerized tomographic scan. Fifty cups were placed free hand, 50 others with the standard cup ancillary, and the remaining 50 cups using computer-assisted orthopaedic surgery. The accuracy of cup abduction and ante-version was assessed with an electromagnetic system. Results: Using conventional techniques, free hand placement revealed a mean precision of cup anteversion and abduction of 10¡ [range: 5.5–14] and 3.5¡ [2.5–5] respectively. With the cup positioner, these angles measured 8¡ [5–10.5] and 4¡ [3–5.5] respectively, and using the computer assisted method, the mean cup anteversion precision was 1.5¡ [1–2] and mean cup abduction measured 2.5¡ [2–3.5]. Conclusions: Computer assisted cup placement is a very accurate and reproducible technique during THA. It is clearly more precise than either of the two traditional methods of cup positioning, even for well-trained surgeons.

Aims: All health care systems in the developed world are facing everincreasing health care costs and faced with this prospect, governments and other health care payers seek greater beneþts from existing health resources. An inexpensive alternative without excessive technical demands on physicians or operating room personnel, is two-dimensional (2D) computerassisted preoperative planning. The purpose of the study was to clinically validate the SYMBIOS X-Rays Preoperative Planning software for preoperative planning of cementless total hip replacement. Methods: For each of the thirty patients with osteoarthritis who underwent a total hip arthroplasty using an uncemented anatomic stem, the manual preoperative planning of the surgeon, the 2D computer-assisted one and the result after the real implantation were compared by an independent observer. Comparisons were based on stem and neck sizes as well as stem and rotation center position, using the deþnitive implantation as the reference standard. Results: There were no statistical differences between the results of the manual and 2D computer-assisted preoperative plans in terms of stem size and neck length (< 1 size) as well as for rotation center positioning (< 5mm) when compared to the deþnitive implantation. Conclusion: Two-dimensional computer-assisted preoperative planning seems to provide results as good as those of the manual procedure with the great advantage of allowing the surgeon to simulate various stem designs and to take into account biomechanical criteria.

The aim of the study was to determine the precision of conventional versus computer-assisted techniques for positioning the acetabular component in total hip arthroplasty (THA).

Malposition of the acetabular component during THA increases the occurrence of impingement, reduces range of motion, and increases the risk of dislocation and long-term wear. To prevent malpositioned hip implants, an increasing number of computer assisted surgery systems have been described, but their accuracy is not well established.

Using a lateral approach, 150 cups were placed by 10 different surgeons in 10 identical plastic pelvis models. Only the immediate operating field was visible. Pre-operative planning was performed with a computerised tomography scan. Fifty cups were placed free hand, 50 others with the standard cup positioner, and the remaining 50 cups using computer-assisted orthopaedic surgery (Medivision). The accuracy of cup abduction and anteversion was assessed with an electromagnetic system (Fastrak™).

Using conventional techniques, free hand placement revealed a mean precision of cup anteversion and abduction of 10° [range 5.5 to 14] and 3.5° [2.5 to 5] respectively. With the cup positioner, these angles measured 8° [5 to 10.5] and 4° [3 to 5.5] respectively, and using the computer assisted method, the mean cup anteversion precision was 1.5° [1 to 2] and mean cup abduction measured 2.5° [2 to 3.5].

Computer assisted cup placement is a very accurate and reproducible technique during THA. It is clearly more precise than either of the two traditional methods of cup positioning, even for well-trained surgeons.

To determine the precision of conventional versus computer assisted techniques for positioning the acetabular component in total hip arthroplasty (THA).

Malposition of the acetabular component during THA increases the occurrence of impingement, reduces range of motion, and increases the risk of dislocation and long-term wear. To prevent malpositioned hip implants, an increasing number of computer assisted surgery systems have been described, but their accuracy is not well established.

Using a lateral approach, 150 cups were placed by 10 different surgeons in 10 identical plastic pelvis models. Only the immediate operating field was visible. Pre-operative planning was performed with a computerised tomography scan. Fifty cups were placed free hand, 50 others with the standard cup positioner, and the remaining 50 cups using computer-assisted orthopaedic surgery (Medivision). The accuracy of cup abduction and anteversion was assessed with an electromagnetic system (Fastrak™).

Using conventional techniques, free hand placement revealed a mean precision of cup anteversion and abduction of 10° (range 5.5 to 14) and 3.5° (2.5 to 5) respectively. With the cup positioner, these angles measured 8° (5 to 10.5) and 4° (3 to 5.5) respectively, and using the computer assisted method, the mean cup anteversion precision was 1.5° (1 to 2) and mean cup abduction measured 2.5° (2 to 3.5).

Computer assisted cup placement is a very accurate and reproducible technique during THA. It is clearly more precise than either of the two traditional methods of cup positioning, even for well-trained surgeons.