Introduction         and         History                  

Robotic surgery is a semiautonomous procedure performed by a robotic arm under the direct or indirect control of the surgeon.1 The classification for Computer Assisted Orthopedic Surgery (CAOS) is divided into active systems, passive systems and semiactive systems.1,2

1. Active systems are those capable of performing individual tasks or entire procedure autonomously, although under the watchful eye of the surgeon (e.g. ROBODOC, CASPAR).

1. Passive systems are those that don’t perform action independently, but provide the surgeon with additional information before and during a procedure, augmenting the information provided by the real world (e.g. Navigation).

2. Semiactive or templating systems are a system in which the surgical action is physically constrained by the surgeon to follow a predefined strategy. The action is guided, which means the intervention is performed with respect to previously defined strategy, but the final control and action still depends on the surgeon (e.g. Computer-aided saw guides).

The first robotic surgery was performed in 1992 in California using the ROBODOC system (Integrated Surgical Systems, Sacramento, CA). It is computed tomography (CT) based, computer aided robotic milling device that allows accurate preparation of the femoral bone and anatomic placement of femoral component in cementless THA. The failures of early cementless femoral implants gave the idea for developing the ROBODOC. The reasons for failure were lack of bone ingrowth, activity-limiting thigh pain, or both. These problems were attributed to poor fit and stability of the implants.3 The early results of ROBODOC showed good results when compared with manual THA.4

Another recent innovation in robotic surgery is RIO (Robotic Arm Interactive Orthopedic system) from MAKO surgical corp (Fig. 35.1). The RIO is intended to assist the surgeon in providing software defined spatial boundaries for orientation and reference information to anatomical structures during the surgery.

The RIO is indicated for use in surgical knee and hip procedures which are Unicondylar knee replacement and/or patellofemoral knee replacement and Total Hip Arthroplasty (THA). The use of stereotactic surgery may be appropriate in these types of surgeries, and where reference to the rigid anatomical bony structures can be identified relative to a CT based model of the anatomy. For the hip, using the patient specific information gathered from a preoperative CT scan, the surgeon has the flexibility to adjust his plan to achieve proper biomechanical reconstruction of the hip with correct acetabular component placement, leg length and offset.

35

 

 

 

 

 

Total Hip Arthroplasty

 

Figure 35.1: Robot is seen in the middle with computer screen and camera on sides

 

Rationale     for     Robot     in     THA                 

A robot is more accurate than the human hand in certain tasks and the results are reproducible.3 A robot has ability to execute the preoperative plan accurately. It provides information in appropriate sizing and fit of implant which is ultimately required for longterm success of THA.3 Nakamura et al found that the robotic-assisted group (ROBODOC) had slightly better clinical scores than the hand rasping group at 2 and 3 year follow up, but found no significant difference at 5 year follow up. The leg length variance and stress shielding of the proximal femur was less in the robotic-assisted group as compared to hand-rasping group and it may be because of more precise implant positioning.5 Honl et al found higher dislocation rate and revision rate in robotic group (ROBODOC) as compared to control group and found at revision surgery that abductor muscle were detached from trochanter. They implied that in those cases the robot damaged the abductor muscles, causing rupture.6 But this may be more because of human error. The limitation with ROBODOC and the data from its use, is that this robot surgery prepares and implants the femur only. The cup is prepared and implanted free hand, so the data such as dislocation are meaningless.

The robotic guided total hip replacement we use is that MAKO surgical program. It was developed by surgeons Lawrence Dorr, Richard Jones, Mark Pagnano and Robert Trousdale from Rochester Mayo clinic, Douglas Padgett and Amar Ranawat from Hospital for special surgery. The robot (RIO) provides the acetabular cup inclination and anteversion within 5 degrees of the preoperative plan and the acetabular COR (center of rotation) within 2 mm. The RIO consistently and reproducibly places the acetabular cup during total hip arthroplasty (Cadaveric study and in a study in forty patients). The robotic arm will stop reaming if the reaming depth is beyond the plan or anteversion and inclination angles are not according to preoperative plan.

We are going to describe the technique of total hip arthroplasty performed with robotic guided bone preparation and implantation using RIO (Robotic Arm Interactive Orthopedic system) from MAKO surgical corp.

 

Technical                  Consideration                  

A preoperative CT scan is required for each patient undergoing THA with RIO (Makoplasty Hip Procedure). The patient specific virtual 3-D bone model of the pelvis and femur is created by the software and specific points are defined on the anatomy to help the software determine

35

 

 

 

 

 

Robotics in Total Hip Arthroplasty

 

Figure 35.2A: Preoperative planning shows cup size, cup position and cup COR. The new planned cup COR (green) is 3 mm medial to the native acetabular COR (magenta)

 

 

 

 

Figure 35.2B: The position of cup can also be decided by X-ray view of the software. The cup is positioned according to ilioischial line (Kohler’s line) and tear drop

 

the patient’s position intraoperatively. The software accounts for the pelvic tilt by using the patient’s anterior/posterior pelvic tilt when lying supine on the CT table. All inclination and version numbers include this tilt, and so are on the radiographic plane of Murray.7 This implants the cup on the coronal (functional) plane of the body which is more correct than the anatomic plane.

 

PREOPERATIVE PLANNING

The objective of the preoperative planning is to determine the correct position of the cup and stem and the correct size. The cup is positioned for depth of reaming in the acetabulum and stem by the correct neck cut of femoral bony neck. Of most importance, the center of rotation of the cup, and of the femoral stem is determined (Figs 35.2A and B).

 

REGISTRATION OF TOOLS

The registration of tools is done by a scrub nurse while patient is prepared for anesthesia. Our patient receives a combination of epidural anesthesia and sedation with continuous infusion of propofol while the airway is secured with oral airway or laryngeal mask.

35

 

 

 

 

 

 

Total Hip Arthroplasty

 

Figure 35.3: The pelvic array is attached to the pelvis and operative area covered with betadine drape

 

PELVIC ARRAY PLACEMENT

If the operation is to be done in the lateral position, the patient is turned lateral, and secured with anterior and posterior supports for both pelvis and chest. With aseptic precaution, three threaded pins are inserted in the thickest portion of iliac crest (where bone grafts are taken) after making stab wounds with #15 blade. After the pins have been inserted, the acetabular attachment device is attached to pelvis. The operative area, including the device, is covered with a betadine drape (e.g. Ioban 3M). This base is used for attachment of the pelvic array (Fig. 35.3).

 

FEMORAL REGISTRATION

We use the posterior mini-incision approach for exposure. We are focusing in this chapter on the robotic surgery and not the approach. The femoral head is dislocated out of the acetabulum. Femoral registration requires insertion of two screws; one large screw for holding the femoral array and a smaller screw to be used to verify accuracy of registration (check point). The position for screw and check point is different for the posterior and the anterolateral approaches. For the posterior approach, the large screw is inserted in the cortical bone at the junction of the intertrochanteric ridge and the lesser trochanter. The femoral check point (smaller screw) is placed just anterior to this in the greater trochanter (Figs 35.4A and B). If the array screw becomes loose, the accuracy verification by the check point screw will show this. If this happens, the registration is no longer valid and final leg length and offset can be inaccurate. The check point is verified by touching the probe to it. Femoral registration is accomplished by touching the probe to thirty two required points on the proximal femur as identified on the software and displayed on the computer screen (Fig. 35.5). These points verify the anatomic geometry defined preoperatively by the CT scan. Ideally the femoral registration error should be less than 0.5 mm. Verification of the registration is done by touching the probe to the surface of the bone on 6-8 points of proximal femur (Fig. 35.6). If the registration error is more than 1 mm the verification fails and the surgeon must re-register the femur.

 

FEMORAL PREPARATION

After registration, the level of femoral bony neck cut is marked intraoperatively by touching the probe to the bone and the computer displays the probe in relation to the cut line on the screen (Figs 35.7A and B). The cut level is marked with the bovie (cautery) tip and can be confirmed with a ruler according to the preoperative plan. The femur is prepared first, to measure the anteversion of the femoral stem so that, the cup anteversion can be adjusted to

35

 

 

 

 

 

Robotics in Total Hip Arthroplasty

 

Figure 35.4A: The two screws are inserted into the femur. The bigger one is for holding the femoral array and the small one is femoral check point

 

 

 

Figure 35.4B: The bigger screw is inserted in the cortical bone at the junction of the intertrochanteric ridge and the lesser trochanter. The smaller screw (femoral check point) is placed just anterior to this in the greater trochanter

 

 

 

 

Figure 35.5: Thirty-two points are touched with probe on the proximal femur which is required for the registration process. Thirty-two points on proximal femur are shown as blue color target dots and these turn green when touched by the probe

35

 

 

 

 

 

 

 

Total Hip Arthroplasty

 

Figure 35.6: The verification is done by touching the probe to points on the proximal femur (shown as blue sphere). Blue spheres turn white if registration error is less than 1 mm otherwise it turns red. The probe is seen as a blue colored pencil like thing

 

Figure 35.7A: Femoral neck cut level is seen in preoperative planning and it is 11.3 mm above the lesser trochanter level

 

 

 

Figure 35.7B: Femoral cut level is confirmed and marked intraoperatively by touching the probe to the bone and marked with bovie tip. The green line represents the mark level and blue long pencil like thing is probe

35

 

 

 

 

 

 

 

Robotics in Total Hip Arthroplasty

 

Figure 35.8: With final femur broach in, surgeon can know the anteversion and change in leg length and offset

 

Figure 35.9: The position of acetabular check point is superior to posterior-superior acetabular rim and needs to be away from reaming direction

 

the stem anteversion (correct combined anteversion).8-11 The femur is prepared with broaches and with the final broach in place the anteversion is measured. The broach position in the femur allows the software to provide the millimeters of change in leg length and offset that will be obtained with a neutral head (Fig. 35.8). This is accurate because the cup COR is known and will not change (the reaming accuracy is controlled by the robot). With the final broach, the stem (and thus femoral) COR is known and is matched to the acetabular COR to give leg length and offset.

 

ACETABULAR REGISTRATION

The acetabulum is exposed. The pelvic check point (screw) is inserted outside the acetabular cavity in the bone just superior to the posterior-superior acetabulum rim (Fig. 35.9). The screw is directed away from acetabular surface. The probe is touched to the pelvic check point to verify the registration. Thirty two points on the acetabulum are identified by the software for the registration process and are touched using the probe to the bone surface. As with registration of the femur, verification is done by touching the probe to 8-10 points defined on the surface of the acetabulum (Fig. 35.10). As with the femur, if the software displays a registration error of more than 1 mm the registration must be repeated.

35

 

 

 

 

 

 

Total Hip Arthroplasty

 

Figure 35.10: The verification of acetabular registration is done by touching 8-10 software defined points with probe on acetabular surface

 

ACETABULAR REAMING

The preoperative cup plan may need to have the desired anteversion of the cup changed after stem anteversion is known. The surgeon can ream traditionally by using multiple reamers to achieve the final socket size. However, the RIO Robotic Arm will also allow the surgeon to ream only once with the final planned size (Figs 35.11A and B). If the surgeon starts reaming 3 mm or more below the planned cup size, he has the ability to orient the reamer in any direction; however, the reamer itself remains constrained to the plan so it can not go “out of bounds” superior, medial or anterior-posterior. When reaming is started within 2 mm of the planned cup size, the surgeon must ream within +/– 5 degree of the planned cup position (constrained by virtual haptic tunnel). The reaming is line-to-line because of the precision of the reaming process (e.g. for 50 mm cup ream to 50 mm). For patients with hard bone or a sclerotic acetabulum, the rim is reamed 1mm greater than the cup size (e.g. ream to 51 mm for 50 mm cup). The reaming is complete when the COR numbers for superior/ inferior, medial/lateral, anterior/posterior are 0 and the box (containing the numbers) turns green. The 3D model of the bone will also illustrate the planned bone resection has been achieved when the green color of the acetabulum has been removed, showing white

 

 

 

Figure 35.11A: The reamer is attached to the robotic arm and reaming is being done

35

 

 

 

 

 

 

 

Robotics in Total Hip Arthroplasty

 

Figure 35.11B: The computer screen is showing the reamer position, inclination and anteversion. The green area means it needs to be reamed away. The reamer path is constrained. It does not allow going beyond the preoperative plan. As seen in the figure, the inclination of the reamer is good but the anteversion is not within 5 degree of the plan and so the robot will not start reaming until it is within 5 degree

 

Figure 35.11C: The completion of reaming is also confirmed when the computer screen displaying the green area on the acetabulum is reamed away and showing the white bone. White area means complete reaming has been done. Red area means reaming is past the plan

 

 

bone (Fig. 35.11C). Both methods confirm the surgeon has reached the new acetabular center of rotation. The bone model will turn red when the surgeon has reamed more than

0.5 mm past the plan. When the surgeon has reamed 1 mm past the plan in any direction the power drill will turn off.

 

FINAL CUP PLACEMENT

The precision of Robotic arm assistance allows the reamer to replace the traditional use of a trial cup. The porous shell is loaded onto the robotic arm and inserted in the acetabulum through a haptic tunnel which keeps the cup inclination and anteversion within 3 degree of the plan as the cup is implanted (Figs 35.12 and 35.13). Then liner is inserted inside the shell. A standard liner should be used because the correct combined anteversion has been reconstructed so stability is insured and a hooded liner will cause impingement. After the liner is inserted the fit plane measurement can be done to confirm the cup position by touching the liner with the probe at five points. If the inclination and/or anteversion change by 4 degree or more the cup is likely loose, and screws should be inserted.

35

 

 

 

 

 

 

 

Total Hip Arthroplasty

 

Figure 35.12: The porous coated acetabular cup (shell) is loaded on the robot

 

Figure 35.13: Implantation of final cup with the robotic arm. Cup position with actual and planned numbers of inclination and anteversion are displayed on screen. This cup needs to be impacted 7 more mm to be seated against bone

 

 

FINAL REDUCTION AND NUMBERS

The final stem is implanted and the trial head placed on the taper. The hip is reduced and the femoral array is inserted into the femoral screw. The computer screen displays the leg length and offset change and the planned change (Fig. 35.14). The adjustment to a shorter or longer head length is done as needed. The preoperative and postoperative X-rays of a 70-year-old male with left hip arthritis who had a THA with robotic guided navigation is shown in Figures 35.15A and B. The postoperative X-ray shows that the robot can position the cup very accurately and restore the COR (center of rotation), leg length and offset.

 

Results                         

MAKO robotic guided hip replacement is in the final development. Forty surgeries are completed at Mayo clinic (Rochester), Hospital for Special Surgery (New York) and Good Samaritan hospital (Los Angles) in from October 2010 to January 2011. The operative achievement of planned reconstruction has been accomplished proving the technology is predictable and reproducible. The surgical result is better for patients than a manual operation

35

 

 

 

 

 

Robotics in Total Hip Arthroplasty

 

Figure 35.14: After the reduction is done and femoral array is attached, the screen will display the final reduction results. Inclination and anteversion of cup are according to plan. Hip offset and leg length are restored as well

 

 

 

Figure 35.15A: Preoperative X-ray of a 70-year- old male with left hip arthritis and superior migration of COR

 

 

 

Figure 35.15B: Postoperative X-ray shows accurate position of the cup with restoration of COR, leg length and offset

35

 

 

 

because it is personalized for that patient based on their femoral and acetabular anatomy. The robot allows reconstruction of the correct COR of the hip which essentially eliminates impingement and insures correct leg length and offset. The combined anteversion is determined on the functional plane (tilt of pelvis known) which maximizes the stability. We use no dislocation precautions in these patients. This robotic guided operation provides precision of both the femoral and acetabular side of the hip joint not just half the hip (femur with ROBODOC and acetabular with navigation systems). For the surgeon, this robotic guided operation reduces the stress in the operating room because there is quantitative knowledge that confirms the surgeon’s intuition and instinct that the reconstruction is correct. For the patient, the operation is personalized with the correct functional combined anteversion rather than an operation where the cup is placed in a “safe zone” of 40 degree inclination and 20 degree anteversion, etc. no matter the anteversion of the stem (one size fits all technique).

 

Total Hip Arthroplasty

 

References

 

1. DiGioia AM 3rd, Jaramaz B, Colgan BD. Computer assisted orthopaedic surgery. Image guided and robotic assistive technologies. Clin Orthop Relat Res 1998;354:8-16.

2. Breisch S. Future is here does ity work? American Academy of orthopaedic Surgeons website. 1998; available at: http//www2.aaos.org/aaos/archives/bulletin/aug98/future.htm. accessed May 16, 2007(August Bulletin).

3. Bargar WL. Robots in orthopaedic surgery: past, present, and future. Clin Orthop Relat Res 2007;463:31-6.

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

5. Nakamura N, Sugano N, Nishii T, Kakimoto A, Miki H. A comparison between robotic-assisted and manual implantation of cementless total hip arthroplasty. Clin Orthop Relat Res 2010;468(4):1072-81.

6. Honl M, Dierk O, Gauck C, Carrero V, Lampe F, Dries S, et al. Comparison of robotic-assisted and manual implantation of a primary total hip replacement. A prospective study. J Bone Joint Surg Am 2003;85-A(8):1470-8.

7. Murray DW. The definition and measurement of acetabular orientation. J Bone Joint Surg Br 1993;75(2):228-32.

8. Widmer KH, Zurfluh B. Compliant positioning of total hip components for optimal range of motion. J Orthop Res 2004;22(4):815-21.

9. Ranawat C. Modern techniues of cemented total hip arthroplasty. . Tech Orthopedics 1991;6:17-25.

10. Dorr LD, Malik A, Dastane M, Wan Z. Combined anteversion technique for total hip arthroplasty. Clin Orthop Relat Res 2009;467(1):119-27.

11. Amuwa C, Dorr LD. The combined anteversion technique for acetabular component anteversion. J Arthroplasty 2008;23(7):10