Background

The CoCrMo large bearings had shown a high failure rate, because of metal ion and particle release. Alumina matrix composite (AMC) ball heads have shown to mitigate such phenomena. The aim of this study was to investigate the leaching properties of AMC clinically as well as experimentally.

Introduction

Metal-on-metal bearings (MoM) have been reported to release metal ions that are potentially leading to adverse tissue reactions. Alternatively, ceramic-on-ceramic bearings (CoC) are an attractive treatment for young and active patients and composite materials like zirconia toughened alumina (ZTA) have been successfully introduced clinically. One of the most common ZTA-material in CoC is the Biolox® delta, manufactured by Ceramtec. Along with alumina and zirconia, this material also contains traces of chromium, strontium and yttrium. The aim of this study was to analyse the ion release for these materials clinically as well as experimentally.

In THA navigation systems mostly the anterior pelvic plane (APP) is used as reference for cup orientation. For the femoral torsion the sagittal plane of the leg in 90° knee flexion is used as reference. The common procedure is associated with a pointer based palpation of anatomical landmarks. But sometimes it shows difficulties especially in obese patients. The purpose of the current prospective study was to evaluate the THA navigation based on palpation of the APP and the femoral sagittal plane using a novel intra-operative ultrasound device in comparison to standard palpation technique.

Methods: In 2006 the data of 50 patients with navigated THA were analyzed. An image free computer-assisted navigation system (OrthoPilot, B. Braun Aesculap, Germany) was used together with an integrated ultrasound device (probe: 80mm, 5–8 MHz, Telemed, Latvia). First, the registration of bony landmarks, i.e. anterior iliac spines and symphysis for APP as well as patella and tibial pylon for the femoral sagittal axis was performed using the conventional pointer method (PO). Then registration was repeated using the ultrasound device (US). The landmarks of the APP and the dorsal condylar line to define the femoral torsion alignment were recorded. The intra-operative cup orientation and the resulting range of motion was monitored. After cup placement in the “safe zone” described by Lewinnek the femoral stem was rasped monitoring the predicted final ROM, leg length and offset. The navigation software provides simultaneously data for for both, pointer and ultrasound palpation. Cup anteversion, inclination, the antetorsion angle of the rasp as well as the predicted amount of impingement free internal (IR) and external rotation (ER) of the leg are shown. At the end of operation ROM was checked clinically. Plain standardized post-operative X-rays were evaluated for inclination and anteversion angles according to Pradhan.

Results: The calculated mean difference between US registration and PO palpation was 2,2° (range -1,7 – 5.9°) for the cup inclination and 8,7° (range 1,5° – 16°) for anteversion. The impingement free total ROM of the femur as predicted by the Orthopilot, i.e. 109° for PO and 103° for US registration matched well with the clinical data. The clinical findings confirmed the US registration based ratio of mean external (ER 62°) to internal rotation (IR 41°). However, the predicted mean IR as calculated for PO palpation, i.e. 31°, was reduced by a mean of 9° in favor of 13° of more ER (76°).

Conclusion: The results show a higher coincidence of US based registration with the clinical findings. The difference is due to a registration at the bone surface with the US method, while PO palpation cannot overcome a undefined thickness of soft tissue layer, especially in front of the symphysis in obese patients.

Objective: Kinematic computer navigation technology has already shown improved alignment results in knee arthroplasty over the past years. But still all items and results are not perfect. The updated Orthopilot 4.0 navigation software is more sophisticated and gives the ability of additional navigation of soft tissue balancing. Together with the use of the new designed ultracongruent E-motion prosthesis, the Orthopilot 4.0 technology is very promising.

Material and Methods: In this combined study equal groups (n=100) of patients were prospectively operated using E-motion prostheses navigated by Orthopilot 4.0 technology including ligament tension balancing (group G1), and Search prostheses navigated by the older Orthopilot 3.0 technique (G3). Conventionally operated patients served as control using LCS prostheses (G2, n=100), and former implanted Search prostheses (G4, n=50). The results of all groups were compared retrospectively. The results were radiologically evaluated by measuring pre-, and postoperative mechanical leg axes, femoral and tibial angles in both the coronal and the sagittal plane. In each cohort all surgeries were consecutively performed. Patients suffered from primary or secondary osteoarthritis.

Results: Time of surgery did not differ significantly between group G1 and G2, but it was prolonged significantly for groups G3 and G4. In all patients of G1 a mechanical axis of 0 ± 5°, having 93% inside the excellent range of ± 3°, could be reached. Showing excellent ligament stability, full extension was possible much earlier than in the other groups. The mechanical axes in the control groups were more often different from optimum, with 63% inside an excellent range (G2), 76% (G3), and 57% (G4), respectively.

For the femoral axis in the coronal plane, excellent results, i.e. ± 2% off optimum, were found in 95% (G1), 91% (G2), 97% (G3), and 77% (G4). The corresponding results for the femoral axes in the sagittal plane were 81% (G1), 79% (G2), 71% (G3), and 67% (G4). For the tibial axes in both planes the results were similar.

All 5 axes in a perfect alignment at the same time were seen in 65% (G1), 40% (G2), 28% (G3), 22% (G4). In G1 femoral notching was inexistent.

Discussion and Conclusion: During surgery, the new Orthopilot 4.0 navigation technique allows precise determination of collateral ligament tension in full extension and in flexion up to 90 degrees. This leads to perfect intraoperative planning of the tibial and femoral cut with respect to the required soft tissue release. In comparison to the control groups, this new technique leads to a significant improvement in postoperative results towards the desired optimal criteria, as there are: straight mechanical leg axes, little deviations from optimum for each single femoral and tibial axis, perfect collateral ligament balancing, and optimal range of movement.

Background: The aim of introduction of navigation in knee arthroplasty was to further contribute to precision of endoprosthetic alignment.

Methods and material: A multicentre comparative study was conducted including 821 patients. The SEARCH knee system was used throughout the series. 555 TKA’s were implanted with the use of a navigation system (OrthoPilot) and 266 cases were operated using manual instrumentation. Alignment was radiographically evaluated at the three months follow-up with respect to mechanical axis and femoral and tibial axes using one-leg stance x-rays and standardized lateral radiographs.

Results: The summarized results of the series are shown in the table below. The chi-square test was applied for the statistical analysis.

Conclusions: Endoprosthetic alignment using the navigation system was superior to manual implantation technique on the average with respect to all parameters. Results were more consistent on the tibial side. The navigation system proved to be reliable. The overall results justify the further use and development of navigation tools in knee arthroplasty.

Aims: Malposition of the acetabular cup after THR leads to dislocations and impingement, reduces ROM and increases pressure and wear inside the cup. The use of the OrthoPilot? kinematic computer navigation technique may reduce the rate of cup malposition. Methods: After the registration of 3 pelvic bone landmarks, stereocameras record the motion of bone and instument- þxed infrared Ç ridgid bodies È. From these data the hip center, the position and direction of reamers and cup insertion instruments are calculated. Since 2001, 155 cementless plasma coated titanium pressþt cups were implanted by using this OrthoPilot¨technique. The intraop measured data of inclination and anteversion angles were compared to the angles from postop X-rays. Results: In 147 evaluated cases no speciþc complications occurred. After the þrst 35 cases minor primary technical problems could be solved. In the following cases the operation time was prolonged by 9 minutes only compared to conventional technique. The mean intra-operative value for inclination was 41¡, (29–48¡), for anteversion 15.9¡, (3–29¡). The evaluated data from the x-rays were 42¡ (34–50¡) for inclination and 10.9¡ (3–22¡) for anteversion. No dislocation occurred due to cup mal-position. Conclusions: By using kinematic navigation technique an improvement of the cup position can be shown clearly. The intended þnal cup position within the Ç safe zone È can be reached reliable. The technique is easy, safe, quick and inexpensive. The rate of postop dislocations might be reduced.

INTRODUCTION

Nowadays, longevity of total knee arthroplasties is very acceptable. Survivorship analyses demonstrate a success in a range of 80% to more than 95% over a period of more than ten years (1–4). However, long-term results largely depend, amongst other factors, on restoration of physiological alignment of the lower limb (5–11). Jeffery et al. (12) reported a three percent loosening rate over eight years when knees were correctly aligned whereas insufficient alignment lead to prosthetic loosening in 24 percent. Rand and Coventry (13) found a 90 percent survivorship rate at ten years when the mechanical axis was aligned in a range from nought to four degrees of valgus. Valgus position of more than four degrees or varus alignment resulted in only 71 percent and 73 percent of survivorship respectively.

Recently, computer aided instrumentation systems (14,15) became available and preliminary results of small series were reported (16–17).

The purpose of this study was to assess the accuracy of computer integrated instrumentation for knee alignment.

MATERIAL AND METHOD

The OrthoPilot^® represents a computer controlled image supported alignment system. A 3-D Optotrak™ camera localizes infra-red diodes fixed to rigid bodies within the surgical field. Thereby a spatial coordinate reference system is provided. The localizer is linked to a UNIX work station which performs the operative protocol using a graphical interface and a foot pedal. The rigid bodies are fixed to the bones by bicortical screws. An intraoperative kinematic analysis and various additional landmarks lead to definition of the centres of hip, ankle and knee joint and sizing of endoprosthetic components. With the use of LED-equipped alignment instruments the femoral and tibial resection planes are determined.

The OrthoPilot^® navigation system is not dependant on CT data and no additional preoperative planning is therefore necessary.

A prospective comparative multicentre study in five institutions, four in Germany and one in France, was carried out. 821 patients with primary tricompartimental knee arthroplasty using the SEARCH LC knee (B|Braun AESCULAP) were included in the study. The OrthoPilot^® Navigation system was used in 555 cases and 266 knees were implanted with the use of conventional instrumentation. At the three months follow-up alignment was assessed using standardized one leg stance radiographs with regard to the mechanical axis and the femoral and tibial angels in the coronal plane. For the lateral femoral and tibial angels standard lateral x-rays were used. Prosthetic alignment was verified by an independent observer.

RESULTS

The radiographically assessed results were subdivided into three groups. An error of ± one degree in the radiographical measurements and small deviations caused by the play of surgical instruments have to be considered. With respect to the femoral and tibial angels in the ap and lateral view the group of very good clinical results was, therefore, defined in the range between ninty degrees and ± two degrees. Deviations of three and four degrees from the optimum were classified as being clinically acceptable. Aberrations of more than four degrees were classified as outliers. When measuring the mechanical axis deviations from fully precise femoral and tibial angels may add up. For this reason zero degrees ± three degrees were rated as a very good result, deviations of four to five degrees were considered to be acceptable and alignment beyond five degrees from the optimum was classified as an unsatisfactory result.

Mechanical axis:

35. 2% of the navigated cases were aligned at exactly zero degrees. This was achieved in only 24. 4% of the manual cases. 88. 6% of cases using navigation and 72. 2% in the manual group showed zero degrees and varus or valgus angles of up to three degrees. 8. 9% and 18. 1% of cases respectively showed deviations of four or five degrees of valgus or varus alignment representing an acceptable clinical result. In only 2. 5% of the navigation group aberrations of more than five degrees occurred. The rate of dissatisfying results was 9. 8% in the manual group.

Femoral axis (coronal plane):

In the navigation group 48. 1% of cases showed an alignment at exactly 90 degrees which was the case in only 33. 5% of the control group. Altogether, in 89. 4% of the navigated cases a very good result was observed. In the conventionally instrumented cases only 77. 1% very good results were found. There were 1. 6% outliers beyond the limits of four degrees in the navigation group in comparison to 4. 9% amongst the control cases.

Femoral axis (sagittal plane):

Very good results with up to two degrees of deviation from a ninety degree position were obtained in 75. 5% of navigated cases and 70. 7% of manual cases. 37. 3% and 34. 6% respectively showed an ideal alignment of exactly ninety degrees. Unsatisfactory results were observed in 9. 5% of the navigated cases and 9. 4% of the manual cases.

Tibial axis (coronal plane):

58. 7% of the computer assisted and 40. 6% of the reference cases were exactly aligned at rectangles. All in all, in 91. 9% navigated and only 83. 5% manual cases a very good result was obtained. Only 1. 1% outliers had to be observed in the navigation group whereas 3. 4% unsatisfactory results were registered with manual technique.

Tibial axis (sagittal plane):

44. 3% of the navigated cases and only 26. 7% of cases in the control group were aligned perpendicular to the dorsal tibial cortex, thus showing no posterior slope. Altogether, 81. 3% could be classified as very good clinical results in the computer assisted group. The corresponding rate of the manual group was 69. 9%. Equivalent values of 8. 6% in the navigation group and 8. 3% in the reference group were registered beyond the limits of four degrees deviation.

The additional operation time for the use of the navigation system is calculated between eight and ten minutes after having passed through the learning curve.

CONCLUSIONS

Knee navigation facilitates proper alignment of endoprosthetic components and with the use of the Ortho-Pilot^® system results are clearly more favourable in comparison to conventional instrumentation technique. In addition, the data obtained from literature demonstrate that the use of this navigation system contributes to reducing outliers in number. With the learning curve the OrthoPilot^® alignment system proved to gain in reliability.

Deviations from perfect alignment are still difficult to be classified into surgical or technical deficiencies.

Many technical and software improvements which were introduced in the meantime will, in addition, contribute to reliability and time saving.

Comparative studies with different navigation systems are not yet available. They might allow an even more profound insight into the possibilities and advantages or disadvantages of computer assisted knee alignment.

LITERATURE

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