William L. Bargar

An image-directed robotic system for precise orthopaedic surgery

The authors have developed an image-directed robotic system to augment the performance of human surgeons in precise bone machining procedures in orthopaedic surgery, initially targeted at cementless total hip replacement surgery. The total system consists of an interactive CT-based presurgical planning component and a surgical system consisting of a robot, redundant motion monitoring, and man-machine interface components. In vitro experiments conducted with this system have demonstrated an order-of-magnitude improvement in implant fit and placement accuracy, compared to standard manual preparation techniques. The first generation system described in this paper was used in a successful veterinary clinical trial on 26 dogs needing hip replacement surgery. It was the basis for subsequent development of a second-generation system that is now in human clinical trials. >

Primary and revision total hip replacement using the Robodoc system.

The ROBODOC® system was designed to address potential human errors in performing cementless total hip replacement. The system consists of a preoperative planning computer workstation (called ORTHODOC) and a five-axis robotic arm with a high speed milling device as an end effector. The combined experience of the United States Food and Drug Administration multicenter trial and the German postmarket use of the system are reported. The United States study is controlled and randomized with 136 hip replacements performed at three centers (65 ROBODOC® and 62 control). Followup was 1 year on 127 hip replacements and 2 years on 93 hip replacements. No differences were found in the Harris hip scores or the Short Form Health Survey outcomes questionnaire. Length of stay also was not different, but the surgical time and blood loss were greater in the ROBODOC® group. This was attributed to a learning curve at each center. Radiographs were evaluated by an independent bone radiologist and showed statistically better fit and positioning of the femoral component in the ROBODOC® group. Complications were not different, except for three cases of intraoperative femoral fracture in the control group and none in the ROBODOC® group. The German study reports on 858 patients, 42 with bilateral hip replacements and this includes 30 revision cases for a total of 900 hip replacements. The Harris hip score rose from 43.7 to 91.5. In these cases the surgical time declined quickly from 240 minutes for the first case to 90 minutes. No intraoperative femoral fractures occurred in 900 cases. Other complications were comparable with total hip replacements performed using conventional techniques. The ROBODOC® system is thought to be safe and effective in producing radiographically superior implant fit and positioning while eliminating femoral fractures.

A surgical robot for total hip replacement surgery

The authors describe a robotic surgical system that has been designed to create femoral cavities that are precisely shaped and positioned for implantation of uncemented prostheses. This robotics system creates cavities with a dimensional accuracy more than 50 times greater than broached cavities, exceeds the tolerances to which implants are manufactured, and does not produce gaps that prevent bone ingrowth. A canine study was undertaken to evaluate the prosthesis fit and placement achieved by employing a surgical robot to prepare the femur. This study compared the results achieved on 15 dogs undergoing total hip replacement with manual broaching techniques and 25 dogs undergoing robotically assisted surgery. Among the 25 dogs, which ranged in age from 2/sup 1///sub 2/ to 11 years, there were no deaths, no infections, and no intraoperative complications. Human applications of this technique are also considered.<<ETX>>

Femoral Anteversion in THA and its Lack of Correlation with Native Acetabular Anteversion

Several studies support the concept that, for optimum range of motion in THA, the combined femoral and acetabular anteversion should be some constant or fall within some “safe zone.” When using a cementless femoral component, the surgeon has little control of the anteversion of the component since it is dictated by native femoral anteversion. Given this constraint, we asked whether the surgeon should use the native anteversion of the acetabulum as a target for implant position in THA. Forty-six patients scheduled for primary THA underwent CT scanning and preoperative planning using a computer workstation. The native acetabular anteversion and the native femoral anteversion were measured. Prosthetic femoral anteversion was measured on the workstation by three-dimensional templating of a straight-stemmed tapered implant. The mean of the sum of the native acetabular anteversion and native femoral anteversion was 28.9°; however, 17% varied by 10° to 15° and 11% by more than 15°. The mean of native femoral anteversion and prosthetic femoral anteversion was 13.8° (range, −6.1°–32.7°) and 22.5° (range, 1°–39°), respectively. Based on our data, we believe the surgeon should not use the native acetabular anteversion as a target for positioning the acetabular component.

Management of bone loss in revision total hip arthroplasty using custom cementless femoral components

Forty-seven consecutive revision total hip arthroplasties were performed using porous ingrowth custom-made prostheses designed from plain radiographs and computed tomography scans. At an average follow-up period of 30 months (range, 2-4 years), one revision has been required for loosening. The average Harris pain score was 39 and the average total score was 84 at the last follow-up evaluation. Complications included nine cases (19%) with intraoperatively detected fractures of the proximal femur treated with cerclage wires and seven cases (15%) with subsidence greater than 3 mm. There were no postoperative infections and only two dislocations. At the time of surgery local particulate bone graft was used in all cases. Thirty-four percent required structural graft to restore bone stock; no case required grafting for prosthesis stability. Management of bone loss in total hip arthroplasty using a custom cementless prosthesis appears to provide an attractive alternative to massive bone grafting.

Robotic total hip replacement surgery in dogs

Approximately half of over 120000 total hip replacement operations performed annually in the United States use cementless implants. The standard method for preparing the femoral cavity for such implants improves the use of mallet-driven handheld broach whose shape matches that of the desired implant. In vitro experiments have supported the possibility that more accurate (and efficacious) results can be achieved by using a robot to machine the cavity. The authors are developing a second-generation system suitable for use in an operating room, targeted at clinical trials on dogs needing hip implants. A description is given of the background, objectives, architecture, and surgical procedure for this system. Also provided are brief descriptions of key results from earlier experiments and planned future work.<<ETX>>

Use of acetabular models in planning complex acetabular reconstructions

The number of patients requiring revision total hip arthroplasty continues to increase each year. Accurate preoperative planning is a key factor in obtaining a good result. Radiographs provide little information concerning the actual extent of the acetabular defects. Computed tomography-generated models of the acetabulum can provide the surgeon with accurate information concerning the size and location of the defects. Evaluation of radiographs and models in 24 cases showed that radiographs alone failed to detect all 13 anterior wall defects (P < .001), 8 of 18 posterior wall defects (44.4%, P < .001), and 8 of 19 segmental central defects (42%, P < .001), all of which were easily identified with the models. This study showed that preoperative planning based on the foam models accurately predicted the actual implant used in 22 of 24 cases (92%).

Time to revision of primary THA is shorter for specialists than nonspecialists.

We asked if there was a shorter time to revision, and different indications for revision, for primary total hip arthroplasties performed in the community by general orthopaedic surgeons (nonspecialists) as compared with primary total hip arthroplasties performed by specialists. We retrospectively reviewed 560 revision total hip arthroplasties performed in 486 patients from 1998 to 2006 at our tertiary referral center. One hundred ninety revisions from the community (nonspecialists cohort) and 109 revisions for which the primary arthroplasty was performed by the specialists (specialist cohort) at our center met the criteria for inclusion. These cohorts were analyzed by the time to revision and the indications for revision. Our findings were that the specialists had a shorter mean time to revision (8.3 years versus 10.1 years). This result may reflect a greater concern by specialists over the potential complications of osteolysis as reflected by the finding that the indication for surgery was more often aseptic loosening for the nonspecialists (57.9% versus 12.8%) and osteolysis for the specialists (61.5% versus 15.8%). As a result of possible selection bias in cases referred by the non-specialists, the indications for revision may not represent the modes of failure for arthroplasties performed by nonspecialists.Level of Evidence: Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

The calcar bone graft

A canine model was developed to investigate the use of an autogeneic iliac bone graft to treat the calcar deficiency commonly found at the time of revision surgery for femoral component loosening. Five large male mixed-breed dogs had bilateral total hip arthroplasty staged at three-month intervals, and were sacrificed at six months. Prior to cementing the femoral component, an experimental calcar defect was made, and a bicortical iliac bone graft was fashioned to fill the defect. Serial roentgenograms showed the grafts had united with no resorption. Technetium-99 bone scans showed more uptake at three months than at six months in the graft region. Disulfine blue injection indicated all grafts were perfused at both three and six months. Thin section histology, fluorochromes, and microradiographs confirmed graft viability in all dogs. Semiquantitative grading of the fluorochromes indicated new bone deposition in 20%-50% of each graft at three months and 50%-80% at six months. Although the calcar bone graft was uniformly successful in this canine study, the clinical application of this technique should be evaluated by long-term results in humans.

The use of oblong acetabular components in complex acetabular reconstructions

Superior acetabular defects that are combined cavitary and segmental (American Association of Orthopaedic Surgeons [AAOS] type III) can be reconstructed with oblong acetabular components and have several theoretical advantages to the previously described techniques that use high hip center or bulk allografts. The indications and technique of oblong cup acetabular revisions is presented. The results have been favorable with 67% good to excellent clinical results and a 100% survivorship at a minimum 5-year follow-up.