Commentary & Perspective

Commentary & Perspective on
"Comparison of Robotic-Assisted and Manual Implantation of a Primary Total Hip Replacement. A Prospective Study"
by Matthias Honl, MD, et al.

Commentary & Perspective by
William Lamont Bargar, MD*,
School of Medicine, University of California, Davis, Sacramento, California

This is a very well done study by surgeons from a single center who compared primary total hip arthroplasty performed using the Robodoc Surgical Assistant (Integrated Surgical Systems, Davis, California) with a conventional manual technique. The incidence of complications involving the soft tissues found in the Robodoc Group is alarming, and is in contradistinction to what has been observed in the United States Food and Drug Administration (USFDA) trial¹ as well as in post-market surveillance of Robodoc throughout Europe, Asia, and Japan. More than 10,000 cases have been performed worldwide. The question is, what happened at this center and why?

The authors correctly point out that the surgeon must remove all soft tissue at the reamer's starting point prior to initiating robotic reaming. This is very important. Indeed, it is the surgeon's responsibility to provide a clear path for the robot for robotic milling in order to prevent damage to the soft tissues. It is true that the S-ROM prosthesis (DePuy) used in this study, with its longer stem and lateral flare of the sleeve, requires the cutting path for the robot to encroach more laterally on the greater trochanter and the insertion of the abductor muscles than would be required with a more anatomical design. On the other hand, the initial USFDA study used either the AML (DePuy) or the Osteoloc (Howmedica) implants, both of which have straight stems. In addition, the Osteoloc stem has a proximal lateral flare. Yet that same randomized controlled study did not show any increase in dislocations or appreciable abductor weakness for the Robodoc group. It should be noted that the USFDA study utilized the posterior approach, which inflicts less potential damage to the abductor muscles and the superior gluteal nerve than does the direct anterolateral approach used in this report.

The increase in sciatic nerve damage seen in this study was also seen in a few patients at one of the three centers in the USFDA study. The authors are most likely correct in their supposition that application of the fixator device and the positioning of the leg in which it is held during robotic milling may have played a role in the nerve injury. This complication has been avoided, in my experience, by careful attention to the application of the fixator apparatus and positioning of the leg to avoid traction on the nerve.

The procedure had to be aborted and then completed by manual technique in 18% of patients, which is also unusually high. In our experience, this problem occurs less than 5% of the time and usually in the beginning of a user's experience. The authors reported that nearly all occurrences of this problem were due to a "force freeze" when reaming sclerotic bone. The fact that this occurred so frequently in this study may be an indication that the planned fit of the implant, as performed on the Orthodoc Pre-planning Workstation, was too aggressive. The robot was designed to ream the endosteal bone at the junction of the cortical and cancellous bone to permit a tight fit of the implant. It was not intended that substantial amounts of cortical bone be reamed away. The device has a "force freeze" feature to avoid damage to the cortical bone and overheating. If the fit that has been planned is too aggressive, force freezes will be encountered. If that was the case in this study, the feature seems to have functioned properly.

There are many findings in this study that are positive. The radiographs showed that the intended goal of increased accuracy with less variance in the placement of the femoral component was achieved. The learning curve seen in the initial USFDA study was eliminated. The clinical scores were significantly better at six and twelve months for the Robodoc group, but similar to the control group at twenty-four months. It should be noted, however, that the scores at twenty-four months were still greater for the Robodoc group. Although the differences were not statistically significant, the p value was less than 0.06, indicating a strong trend. When the cases of muscle damage requiring revision are excluded, the remaining cases showed no difference in the incidence of limp or Trendelenberg sign between the Robodoc and the manual group. This implies that the problem was limited to specific cases where the abductor muscles were damaged. If these cases can be prevented with attention to protection of the soft tissues or possibly by selecting a different implant or surgical approach, the high rate of complications found in this single-center study can be avoided.

The authors are to be commended for bringing this potential problem to the readers' attention. As we progress into less invasive surgical techniques, we will see an increasing need for computer-aided techniques such as navigation and robotics. It will be articles like this that ensure the safe application of new, increasingly used techniques to joint replacement surgery.

*The author did not receive grants or outside funding in support of his research or preparation of this manuscript. The author received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity (Integrated Surgical Systems). No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author is affiliated or associated.

References

1. Bargar WL, Bauer A, Borner M. Primary and revision total hip replacement using the Robodoc system. Clin Orthop. 1998;354:82-91.