Purpose of the study: Compter-assisted surgery enables improved precision of prosthetic implantations, but the basis of data acquisition remains variable. The purpose of this study was to assess the radiological quality of a total knee arthroplasty (TKA) implanted with a computer-assisted surgical technique with or without pre-operative imaging.

Material and methods: This was a case-control study of a group of 40 patients who underwent TKA implanted with a navigation systm (N+) which was compared with a control group of patients who underwent the same procedure with a conventional technique (N-). The two groups were comparable for: age, gender, BMI, preoperative HKA. The same surgeon operated all patients using the same cemented posterior stabilized TKA. Outcome was analyzed by an independent operator. The same navigation system was used for all knees, with, for the first 20 knees, acquisition based on preoperative computed tomography and for the next 20 knee, intra-operative acquisition. Postoperatively, six radiographic parameters were studied for each knee on the ap and lateral views. An optimal interval was determined for each parameter and the number of optimal criteria was noted for each knee.

Results: The mean HKA was 177.5° in the N- group and 179.2° in the N+ group. The angle of implantation of the femoral piece was 90.3° in the N- group and 90° in the n+ group. The mean posterior tibial slope was 3.5° in the N+ group and 3.1° in the N- group. There was a significant difference for the tibial prosthetic angle in favor of the N+ group, i.e. 89° compared with 87.3° for the N- group. The overall quality of the implantation was considered optimal for 54.5% of knees in the N+ group and for 29.8% in the N- group. There was no significant difference between computed tomographic acquisition and intraoperative acquisition.

Discussion and conclusion: This study demonstrates that the results exhibit a distribution closer to the ideal values for the navigation group but that the difference is solely significant for the tibial implantation. This improvement requires a longer operative time of 18 minutes. The lack of any difference between the computed tomographic acquisition and the intraoperative acquisition suggests that intraoperative acquisition should be favored for reasons of cost and simplicity. Computed tomography imaging can still be useful for a precision of the biepicondylar line in certain complex situations such as revision arthroplasty.

Purpose: Most revisions of total knee arthroplasty (TKA) occur before the fifth year. The leading cause is prosthesis malalignment. Computer-assisted surgery is presented as a technique which improves implantation precision. The purpose of this study was to evaluate the radiographic quality of computer-assisted TKA implantation in comparison with conventional implantation.

Material and methods: A prospective randomised study was conducted with a total of 82 patients assigned randomly to conventional instrumentation (group 1) or computer-assisted implantation (group 2). The two groups were comparable for age, gender, body mass index, side, and preoperative femorotibial angle (HKA). The same surgeon operated all patients using the same cemented posterostabilised prosthesis. Radiographically, the HKA, the theta angle between the mechanical and anatomic femoral axis, the angle of the femoral and tibial implantations, and the posterior tibial slope were noted. All measures were taken by an independent operator who was unaware of the operative technique.

Results: There was no statistical difference in the HKA 177.5° in group 1 and 179.2° in group 2 (p=0.13); the theta angle was 6° in group 1 and 5.9° in group 2 (p=0.78); the femoral implantation angle was 90.3° in group 1 and 90° in group 2 (p=0.74); the posterior tibial slope was 3.5° in group 1 and 3.15° in group 2 (p=0.65). There was a statistical difference in the tibial angle, 87.3° in group 1 and 89° in group 2 (p=0.012).

Discussion: This study demonstrates a significant improvement in the navigation group for the position of the tibial implant and no difference for the femoral implant. This might be related to the cut guide which allowed more intra-operative adjustment for the tibia. Blood loss was equivalent in the two groups (503 mg) and operative time was longer in the navigation group (18 minutes).

Conclusion: It appears important to have specifically adapted cut guides for computer-assisted surgery and to reduce operative time.

Purpose: The Oxford unicompartmental prosthesis has congruent joint surfaces due to use of a mobile meniscus whose upper part matches the sphere constituted by the femoral component. The purpose of this work was to report results in a series of 75 prostheses studied with mean follow-up of 12.4 years (range 10–14 years).

Material and methods: Mean age of patients was 65 years (38–84), with 67% women and mean body mass index of 28.7 (21.2–40.6). Patients gave their subjective assessment of the arthroplasty and the IKS scores were determined. Radiographically, the mechanical alignment of the lower limb was evaluated pre- and postoperatively on the full stance images. The Kennedy classification (4 grades) was used to assess passage of the mechanical axis through the knee.

Results: At last follow-up, three patients were lost and eight had died. According to their subjective assessment, 84% of the patients were enthusiastic or satisfied. The overall IKS score showed that 52% of the patients were above 180 points, 25% above 150 points. Mean varus was 11° (2–24°) preoperatively and 5.7° (5° valgus to 14° varus) at last follow-up. The mechanical axis passed in the sufficient correction zone (c or 2) in 77% of the knees, undercorrection zone in 17% and in the overcorrection zone in 6%.Seven prostheses were revised for mechanical failure: four for loosening, two for extensive degeneration, and one for pain giving a survival curve of 90% at 12 years. It must be added that two meniscal dislocations occurred, one early due to wound dehiscence and infection and one late, both after a fall.

Discussion: Most loosenings occurred early and at the tibial level. Defective alignment could be incriminated in one case. The other knees exhibited a reactive line under the tibial plateau. The rate of dislocation should probably decline with the use of progressive reamers, not available at the time of this series. Finally none of the prostheses were revised for wear, confirming the proper prosthesis design.