Purpose of the study: Leg length discrepancy (LLD) can be a common reason for patient dissatisfaction after implantation of a total hip arthroplasty (THA). The failure rate is non negligible for conventional implantation techniques. Navigation systems might be able to improve precision.

Material and method: We used an imageless navigation system (Orthopilot™, Aesculap, FRG) for routine first-intention THA. LLD was determined on the AP view of the pelvis in the upright position to determine the desired correction. Captors were screwed onto the homolateral iliac crest and femur. The system analysed their respective positions at the beginning of the procedure thus defining the reference length. During implantation, the size and the height of the femoral implant and the length of the prosthetic neck were programmed virtually by the navigation system in order to obtain the desired correction which was then reproduced on the definitive implants. At the end of the operation, the final length of the limb was measured the same way as initially. The result of the correction was measured on the AP view of the pelvis in the upright position under the same conditions as initially. We compared 30 navigated THA with 30 THA implanted with the conventional technique. We analysed the residual length discrepancy and the percentage of the cases where the desired correction was achieved. Student’s t test and the chi-square test were used for the statistical analysis taking p< 0.05 as significant.

Results: Residual length discrepancy was 5 mm for the navigated THA and 9 mm for the conventional THA. The mean difference between the desired correction and the final correction was 2 mm for the navigated THA and 6 mm for the conventional THA. The desired length was obtained in 26 hips with navigated THA and in 17 with conventional THA. Residual LLD > 10mm was observed in 2 navigated THA and 9 conventional THA. All differences were significant.

Discussion: The navigation system used in this study enabled improved quality correction of lower limb length after implantation of a THA. Patient satisfaction should be globally improved.

Purpose of the study: Navigation systems have proven efficacy for the implantation of unicompartmental knee prostheses. Minimally invasive methods, which limit access to non-operated compartments, might compromise system accuracy.

Material and methods: A standard navigation software was used for kinematic acquisition of the lower limb and to acquire anatomic landmarks for both femorotibial compartments. A modified version of the navigation software designed for minimally invasive surgery replaed palpation of the anatomic landmarks of the non-operated compartment by a computation method based on other data. Three groups of patients were analyzed. Group 1 included 64 patients who underwent minimally invasive surgery for implantation of a medial unicompartmental prosthesis. Group B included 60 patients selected randomly among 140 cases of medial unicompartmental prosthesis patients treated with the standard navigation technique. Group C included 30 patients selected randomly among 180 patients who underwent total knee arthroplasty with the standard navigation system. The quality of the implantation was assessed on the postoperative ap and lateral views by comparing five criteria describing the desired prosthetic alignment. The number of criteria describing correct alignment was noted for each patient, thus yielding a quality score from 0 to 5. ANOVA was used to compare the mean scores of the three groups using Boneffini-Dunn correction at the 5% risk level.

Results: The mean quality score was 3.5±1.2 for group A, 4.5±0.8 for group B and 4.2±1.0 for grup C (p< 0.001). Ther was no significant difference between groups B and C (p=0.24). The quality score was significantly lower in group A (A versus B: p=0.015; A versus C: p< 0.001).

Discussion: The minimally invasive approach is proposed to enable more rapid functional recovery after implantation of a unicompartmental knee prosthesis. The long-term outcome however depends on the quality of the implantation. The quality of the implantation with a minimally invasive method should thus be equivalent to that achieved with the standard method. Conventional minimally invasive methods are more difficult. Navigation could be expected to overcome this difficulty without sacrificing implantation quality. However, the version used here did no enable an implantation equal to the quality achieved with the standard navigation system.

Conclusion: The standard navigation system for the conventional access remains the gold standard for implantation quality. Changes resulting from a less invasive approach should be validated before routine use.

Purpose of the study: Navigation systems have proven their capacity to improve the quuality of total knee arthroplasty (TKA) implantation. The navigation system coud also be used to record knee kinematics intraoperatively.

Material and methods: Twenty TKA implantations were studied. The series included six males and 14 females, mean age 71 years (range 63–78 years). All underwent surgery for overall osteoarthritis. A TKA with a mobile plateau was implanted with preservation of the posterior cruciate ligament. The OrthoPilot® imageless navigation system (Aesculap, Tuttlingen, German) was used. The software was modified to enable recording the relative movement of the femur in relation to the tibia during flexion-extension movements. Infrared locators were fixed on the lower part of the femur and the proximal part of the tibia. After kinematic and anatomic acquisition of conventional navigation data, the kinematic recordings were made during passive flexion-extension before performing any procedures on the bones. The system recorded femur rotation in relation to the tibia in the frontal plane (varus-valgus), in the sagittal plane (flexion-extension), and in the horizontal plane (internal-external rotation) as well as anteroposterior translation of the femur on the tibia. The prosthesis was implanted using the conventional navigation technique. After implantation, the same kinematic recordings were repeated. Each measurement was taken in duplicate to study reproducibility in the same patient. Pre- and postoperative kinematic recordings in the same patient were compared to obtain objective evidence of changes induced by prosthesis implantation. The pre- and postoperative results were compared with those reported to date in the literature.

Results: The recorded kinematic curves, both before and after TKA implantation, were coherent with generally accepted values, particularly for rotation and antero-posterior translation. Paradoxical kinematic recordings were noted after implantation. There was no significant difference between the two recordings in the same patient.

Discussion: The software enables a reliable study of knee kinematics before and after TKA implantation. This could be useful to test new prosthetic solutions, but also to choose for a given patient, the best kinematic compromise. It would be interesting to compare these results with data on in vivo kinematic recordings made in the same patients.

Conclusion: Intraoperative kinematic analysis is a research tool at the present time, but could be useful to improve the quality of TKA implantations.

Purpose: Implantation quality is an important prognostic factor for long-term outcome of unicompartmental knee prostheses. Minimally invasive techniques allow more rapid rehabilitation but at the price of potentially diminished implantation quality. Navigation systems have been developed to overcome this problem.

Material and methods: We analysed a preliminary series of 20 patients (group A) whose unicompartmental medial femorotibial prosthesis (Search(r), Aesculap, Tuttlingen, Germany) was implanted with the CT-free Orthopilot(r) system (Aesculap, Tuttlingen, Germany). This system uses intra-operative kinematic and anatomic analysis to define the mechanical axes of the femur and tibia in space. The femoral and tibial cut lines are aligned on these axes. This series was compared with a retrospective historical series (group B) of 60 knees with the same prostheses implanted with the same navigation system but with a conventional approach requiring patellofemoral subluxation. Implantation quality was measured using the following angles: AP mechanical femorotibial angle, orientation of the tibial and femoral prostheses (AP and lateral), vertical level of the prosthetic joint space in relation to the preserved joint space.

Results: The AP mechanical femorotibial angle was in the desired range in 16 knees in group A (80%) and in 48 in group B (80%). The femoral component exhibited optimal position in 18 knees in group A (90%) and in 54 in group B (90%). The tibial component exhibited optimal position in 17 knees in group A (85%) and in 53 in group B (88%). Thirteen prostheses in group A (65%) and 37 in group B (62%) were implanted optimally using the studied criteria. The length of the incision varied from 7 to 10 cm in group A. There was no significant difference.

Discussion: This navigation system allows very precise implantation of the medial unicompartmental knee prosthesis, both with the conventional technique and the minimally invasive technique. Use of the minimally invasive technique does not decrease the radiographic quality of the implantation in comparison with the conventional navigation technique. This technique could become the gold standard for implantation of unicompartmental knee prostheses.

Purpose: The design of the contact surfaces of total knee prostheses is a recognised factor affecting polyethylene wear and thus prosthesis survival. Flat-on-flat prostheses have a limited surface area of contact and are thought to favour polyethylene wear. They are not currently recommended for implantation. Nevertheless, several series have reported similar survival with other more congruent prostheses. We studied a series followed for eight years.

Material and methods: We implanted 223 flat-on-flat design total knee prostheses between 1992 and 1996 (Search®, Aesculap, Chaumont). All patients were followed prospectively and seen at regular intervals for physical examination and x-rays. We noted any intervention for implant revision and recorded time to any such procedures as well as the underlying cause. Kaplan-Meier survival curves were plotted taking revision for any cause other than infection as the endpoint.

Results: Ninety-four percent of the patients were reexamined or questioned by phone for this study conducted during 2001. Six percent of the patients were lost to follow-up after a mean 24 months. Seventy-four percent of the prostheses were still in situ at the time of this study at a mean 78 months follow-up. Ten percent of the patients died with their initial implant in place at a mean 50 months. Ten percent of the patients underwent revision surgery at a mean 37 months, half of them for infection and one quarter for a mechanical cause. The overall rate of revision at eight years was 11%; The rate of revision, infection excluded, at eight years was 6%.

Discussion: Survival of this prosthesis in non-infected patients is similar to that of other more congruent implants. This study confirms earlier clinical findings.The undesirable effect of the linear contact surfaces is proven in the laboratory but must not be considered to be automatically transferable to the clinical level. Polyethylene wear is a multifactorial phenomenon which cannot be reduced to a simple question of prosthesis design.