D. Stulberg – Northwestern

He stated that his initial experiences with computer-assisted total hip systems have confirmed their safety and reliability. Cups inserted are more reproducible when navigation is used.

Aaron Hoffman, MD - University of Utah Medical Center, Salt Lake City, UT,
Symposium III: Computer-Assisted Surgery, Feb. '05

He utilized the navigation system in 50 total knee arthroplasties. 98% of all components were placed within +/-3 degrees of the goal. 100% of the tibial components were placed within +/-3 degrees. Standard instrumentation was within 90% for femoral components and 92% for the tibial components based upon the same goal. It provides for improved accuracy compared with the standard technique.

Andrew Cossey, MBBS, FRCS - Journal of Arthroplasty, Vol. 20, No. 1, 2005

This involved 30 primary Unicompartmental knee arthroplasties. Basically it resulted in better mechanical axis alignment of the total knee arthroplasty. Thus it increased the longevity of the unicondylar replacement. This was through a medial parapatellar incision of only 7.5 cm (2 '/2" to 3"). Without computer-assisted, they would have had to use intramedullary rods which would lengthen the incision. The alignment was checked using x-ray analysis. They point out that ultimately the system has the potential to improve long-term survivorship and therefore reduced revision rates because of the better alignment.

Michael Nogler, MD, MA, et. al. - Clinical Orthopaedics and Related Research, Num. 426, pp. 159-163, 2004

They compared acetabular cup alignment using a non-image based hip navigation system versus conventional mechanically guided procedure in 12 human cadavers. Position of the acetabular component has an impact on many of the factors that determine a long-term success in a total hip arthroplasty. Mal-position of the cup can result in clinical problems like dislocation, impingement, range of motion limitations, increased polyethylene wear, length discrepancy and changes in offset and center rotation. Dislocation is a major early post-operative complication in total hip arthroplasty that is associated with acetabular component mal-position. In this study, they found that using computer-assisted cup positioning, based on a percutaneously digitized pelvic reference plane, allowed for a more predictable placement and orientation of the cup with less variance than that found with the use of mechanical instrumentation.

Jan Victor, MD and Davey Hoste, MD - Clinical Orthopedics and Related Research, Num. 428, pp. 131-139, 2004

This was a prospective, randomized controlled study. 50 patients had a conventional total knee and 50 patients had total knee arthroplasty performed with a fluoroscopy based computer navigation system. The variability in the coronal plane was significantly reduced in the computer-assisted surgical group compared with the conventional group. Correlation between full leg standing x-rays and the computer navigation system for determining the mechanical alignment of the lower and coronal plane was high. The groups of patients were compared. The post operative coronal alignment variability in the computer-assisted group showed a mechanical alignment between zero and 2 degrees. In the conventional group 73% were between zero and 2 degrees and 26% were within 3-4 degrees. He did point out several studies. There were 5 studies mentioned in the article. Each one pointed out that outliers beyond 3 degrees were between 50% to 200% greater than with the computer navigated systems. These results were for the OrthoPilot navigation system. However, using the Stryker System the outliers in the conventional system were 10 times as frequent. Victor and Hoste’s current study had no computer-assisted outliers and they had 26% outliers for the conventional instrumentation group.

Bernd Stockl, MD - Clinical Orthopaedics and Related Research, Num. 426, pp. 180-186, 2004

This was a prospective, randomized study. It was designed to test whether optical navigation systems for total knee arthroplasty improved implant positioning relative to non-navigated techniques. It showed that patients having their knees navigated had better rotational alignment of the femoral component than patients who did not. In addition, superior post-operative alignment of the mechanical axis, posterior tibial slope, and rotational alignment was achieved in the computerized group. It points out that rotational problems with the femoral component lead to patellar dislocation and possibly early revision. Furthermore, mal-alignment greater than 4 degrees leads to early wear, poly disintegration, and early revision of the total knee arthroplasty. Both of these factors can be greatly improved with the use of navigation.

Dr. Stulberg - Northwestern Orthopedic Institute
Published International Computer-Assisted Surgical Poster 2004

They did a conventional total knee arthroplasty and then compared the accuracy with the computer. They found that initial position of the femoral and tibial blocks was most accurate and consistent in the frontal plane and least accurate in the sagittal plane. Pinning of blocks was associated with substantial change of an average of 4 degrees. Resection through slots introduced a small average error of 1 degree but a wide range of up to 5 degrees. The final femoral implant position was associated with small error of less than 1 degree. The final tibial position introduced an average error of 2 degrees into hyperextension. The conclusion was that substantial errors occur during the performance of each step of the surgical procedure when using manual instruments.

Holger Bathis and Lars Perlick, et. al. in Orthopaedics May 2004

In 96% of the cases, the leg mechanical axis was within 3 degrees of the computer mechanical axis compared with 76% in the conventional group. In the literature, a maximum varus/valgus deviation of 3 degrees is believed to be associated with improved long-term results. Multiple studies demonstrate 25% of patients using conventional methods are greater than 3 degrees out of alignment while only 12% of patients were greater than 3 degrees out of alignment with the computer. Therefore, computer navigation reduced outliers by at least 50%. They do point out that it takes a lot longer to perform this procedure but that it warrants the effort due to the potential benefits of improved long-term outcomes and function.

W.J. Donnelly - Published in Australian Orthopedic Association 2004

This is a comparison of 24 conventional total knee replacements with 23 computer-assisted Stryker navigated knees. The variances of mechanical axis of the and the coronal alignment of the femoral and tibial components were significantly less in the navigated than in the non-navigated groups. Because there is a significant decrease in alignment variance with navigated knees this may lead to the decrease in mechanical failure of total knee arthroplasties.

M. Sparmann - Published in Berlin, Germany - Emmanuel Hospital 2004

This is a study of 11 revision knees that experienced early loosening. With the use of the navigation system they were able to analyze the mal-positioning of the implants and disturbed soft tissue balancing. The navigation system provided information about the incorrect angle of the implant, and indirectly via kinematics, the implant mal-position. The mal-position of the implants showed extreme polyethylene wear demonstrating that the positioning of the implants does significantly influence the outcome.

R. J. Beaver - Western Australia
Published in International Computer-Assisted Surgery Meeting 2003

They measured the post-operative results using a CT scan. There was a clear improvement in component alignment with the computer navigation system. It measured femoral rotation, tibia varus/valgus, and posterior slope of the tibial component.

Dr. D. Stulberg, MD - Northwestern Orthopaedic Institute, - Clinical Orthopaedics and Related Research, Num. 416, pp. 177-184, 2003

It is approximately +/-3 degrees. It gives the majority of patients a well-aligned mechanical knee but computer-assisted techniques permit measurement of each step of the procedure with a high degree of accuracy, (i.e. - less than 1 degree.) Mechanical instrumentation does not allow measurement. With mechanical instrumentation there is a consistent tendency to internally rotate the femoral component that cannot be measured with mechanical instruments. If pain relief and function are related to the accuracy with which a total knee arthroplasty is done then this study points out that the current mechanical instrumentation does not result in a high incidence of accurate implant placement.

Anthony Digioia III, MD, et. al. - Journal of Arthroplasty Vol. 18 No. 2, pp. 123, 2003

He compared traditional incision versus mini incision. The mini-incision patients did much better; however, the biggest problem with mini-incision is adequate placement of the cup. Cup mal-position is the most significant potential pitfall with the mini-incision technique. They found that the navigation system allowed them to position the mini cup more predictably and allowed for faster recovery in these patients.

Dr. M. Sparmann - University of Berlin, Rheumatologic Research - Berlin, Germany pp. 830-835, 2003

This compared a navigation system in total knee arthroplasty against the hand-guided techniques currently available. 120 were navigated and 120 were hand-guided. For the computer-assisted navigated knees, there were no knees that deviated more than 3 degrees from the mechanical axis. 80% of the hand-guided group had a mechanical axis within the 3 degree range but for 16 patients (the remaining 20%) there were major mal-alignments as high as 6-7 degrees.

Dr. J. Lang, et. al. - University of California, Davis, School of Medicine, Sacramento, California,
Shasta Orthopedics and Sports Medicine, Redding, California
Published International Computer-Assisted Surgical Conference 2003

The important result was the complete elimination of seriously mal-aligned knees. The fact that alignment outliers could be eliminated from total knee arthroplasty procedures is a strong argument in support of computer-assisted total knee arthroplasty. They compared 28 computer-aided patients with 60 conventional total knee arthroplasties. 19% of the conventional total knee arthroplasties had 5 or more degrees of mal-alignment. In the computer-aided group there were no knees with 5 or more degrees of mal-alignment.

S.B. Murphy - University School of Medicine, Harvard Medical School, Boston

Published International Computer-Assisted Surgical Conference 2003. 41 consecutive total knee arthroplasties were performed. 32 were using the image-guided computer-assisted total knee arthroplasty system using a Smith & Nephew Medtronic navigation system. The mechanical axis of the femoral component averaged 0.1 degree and the tibial alignment averaged 0.4 degrees. Intraoperative surgical time was increased by 10 minutes. It eliminated intramedullary alignment guides while improving alignment accuracy of the total knee arthroplasty.

S. David Stulberg, MD - Published Journal of Bone & Joint Surgery, US, pp. 90, 2002

While using the OrthoPilot navigation system they have had no complications associated with its use. They point out that there is a learning curve even for the registration portion of the procedure. It is a useful measurement tool for determination of the accuracy of conventional instrumentation systems.

A case controlled comparative study with classical instrumentation
Jan Yves Jenny M.D., et, al. - Strassburg, France, published 2000 and 2001

The navigation report compared classical technique with the OrthoPilot computer navigation system. It compared 30 cases with navigation and 30 without navigation. The navigation system allowed a significant improvement in the quality of implantation of the total knee prosthesis in comparison to those done using standard mechanical instrumentation. This was published in computeraided surgery journal.

Stephen Murphy, MD - Center for Computer-Assisted Reconstructive Surgery, New England Baptist
Bone and Joint Institute, Tufts University School of Medicine, Harvard Medical School

They studied 58 patients using an image-guided computer-assisted total knee arthroplasty system. They measured alignment on long-leg radiographs in 59 of the 69 limbs. The navigation system allowed for the elimination of small cumulative errors that would ordinarily occur during a total knee arthroplasty. The femoral mechanical axis averaged 0.2 degrees of valgus and the tibial average was 0.5 degrees of valgus. Intra-operative surgical navigation can eliminate the use of intramedullary alignment guides while improving alignment accuracy during total knee arthroplasty.

FW Hajena - Published in Clinics for Orthopedics and Rheumatologic Surgery, Bad Oeynhausen, German

They used a radiographic Medtronic Navigation system. There was a slight improvement in the range of motion for navigated knees post-operatively versus the traditional total knee arthroplasties.

C. Carson - Total Joint Arthroplasty Computer-Assisted Surgery Talks

They did 14 cadaver total knee arthroplasties using image-guided systems and compared them to non-navigated systems. The alignment accuracy was superior using the navigated system versus using traditional knee instrumentation. The average accuracy of alignment in each mode was within the ideal alignment range of +1- 2 degrees. They had 95% competence level. The difference between the navigated results and the post-operative measurements for tibial varus/valgus and tibial flexion/extension were -.8 degrees and 1.81 degrees respectively. The difference for femoral varus/valgus and femoral external rotation were +.03 degrees and -.5 degrees respectively.

Strasburg, France - Boeri

The article points out that you can do a minimally invasive unicompartmental knee with a navigation system. It allows for very precise implantation with a minimally invasive approach.

R. Hart - Published from the Czech Republic

50 patients had navigated knees. 30 patients had conventional knees. The femoral component varus/valgus alignment was greater than 2 degrees in 12.3% of the patients for the navigated group and in the conventional mechanically aligned knees it was 27.8%. Navigation allows for more precise femoral component placement.

S.K. Chauhan and R.G. Scott, et. al. - Perth Hospital, Western Australia

Testing the post-operative CT of varus/valgus alignment showed that the computer-assisted technique versus the standard technique had a statistically significant improvement. Testing the post-op long leg radiographic shows the computer-assisted group was more likely to have a neutral femoral tibial angle or be in slight; valgus also noted was a higher blood loss in the conventional group versus the computerized knees. Surgery took longer in the computerized knees – an average of 13 minutes – with a range 60-120 minutes versus 55-90 minutes for mechanical alignment. The statistically significant improvement in 7 of the 8 radiographic parameters for alignment of the component using computer navigation over conventional surgery is clear from the results. The computer method avoids the need to penetrate the medullary canal which is associated with morbidity. In their matched study, 28% of the conventional patients who had their femur instrumented experienced confusion that was attributed to transient hypoxia. In the conclusion of the article they demonstrated that the computer-assisted total knee arthroplasty is more accurate than the jig based total knee arthroplasty and has a reduced morbidity in the short term.

M. Sparmann - University of Berlin, Germany

There was a significant difference between the group of non-navigated and navigated total knee arthroplasties. The group without navigation had between 3-6% of the implants mal-aligned by more than 3 degrees. In the navigated group there was no case that differed significantly from the ideal mechanical axis. This was a study of 120 patients that were done in a customary fashion using the Stryker Navigation Knee System.

B. Wolke and M. Sparmann - Berlin, Germany

The navigational systems allow for kinematic analysis of the components. It can measure malrotation and mal-alignment of the components so they can be corrected during a revision.

H. Kiefer and I. Frohlich - Bunde, Germany

The OrthoPilot navigation system was used with a pelvic-fixed array. 147 cases were evaluated. The inclination was 41 degrees and for anteversion, 15 degrees. No dislocations occurred due to cup mal-position. Kinematic navigation demonstrated improvement of cup position.

Michael Bolognesi, MD and Aaron Hoffman, MD - University of Utah

It points out that 100% of the computerized total knee arthroplasties were in ideal alignment whereas only about 90% of the conventional knees were ideally aligned (as previously pointed out in his Knee Society talk). He also points out that with a computer-assisted knee replacement the intramedullary canal is not violated.