Purpose: Minimally invasive surgery (MIS) total knee arthroplasty (TKA) makes faster rehabilitation in many cases, but it was sometimes difficult to performed the precise osteotomy and place the implants correctly due to loss of view or orientation for its small exposure. The computer-assisted navigation TKA system (CAS) was reported to achieve the optimal alignment and placement. However, it had disadvantages of longer operation time and wider exposure to acquire the reference points than these of the conventional method. Now MIS technique needs the accuracy of implant placement, on the other hand, CAS needs less-invasive methods. Among CAS methods, CT-based navigation system would have the potential for MIS because it would be referred to preoperative CT images. This study examined the accuracy of the registration with CT-based navigation system and the possibility of its application for MIS.

Material and Methods: CT data were obtained from the femur and tibia of “Sawbone” (synthetic bone, Pacific Research Laboratories, Vashon, WA, USA) with a slice thickness of 1 mm. These data were transferred to Vector Vision Knee 1.5 (BrainLab Inc, Heimstettenm, Germany) and reconstructed to three-dimensional model. Two registrations were performed by a surface-matching algorithm. One is the conventional method as Vector Vision protocol; another is MIS approach which was allowed the limited area around the femoral notch and joint surface of tibia for registration. The accuracy of registration with these two methods was evaluated by Vector Vision Knee. And these registration points of these different methods were measured using a coordinate measuring machine, 3D surface scanner (Mitsutoyo, JAPAN) and were analyzed and calculated the distribution of points.

Results and Discussion: There was a high degree of reproducibility of the MIS approach compared with the conventional method in the femur. However, the reference points in the distal tibia were deviated 1.5 cm to medial and thus 2.39 degree in varus would be happened at the proximal tibia in both methods. Now this software should be improving to be more accurate.

Arthrogryposis multiplex congenita (AMC) is a rare disease with multiple joint contractures. It is widely believed that bilaterally dislocated hips should not be reduced since movement is satisfactory and open reduction has had poor results. Since 1977 we have performed a new method of open reduction using an extensive anterolateral approach on ten hips in five children with AMC. The mean age at surgery was 31.5 months (17 to 64) and the mean follow-up was 11.8 years (3.8 to 19.5).

At the final follow-up all children walked without crutches or canes. Two managed independently, one required a long leg brace and two had short leg braces because of knee and/or foot problems. The clinical results were good in eight hips and fair in two and on the Severin classification seven hips were rated as good (group I or group II).

We recommend the extensive anterolateral approach for unilateral or bilateral dislocation of the hip in children with arthrogryposis or developmental dislocation of the hip.