The ROBODOC® Surgical System consists of two components: ORTHODOC®, a three dimensional (3-D) workstation for preoperative surgical planning, and the ROBODOC® Surgical Assistant, a computer-controlled surgical robot utilized for precise bone cavity and joint surface preparation for total hip and total knee replacement surgeries. Preoperative planning with ORTHODOC® begins with a CT scan of the patient’s affected joint that is converted into a 3-D virtual bone model that can be manipulated and viewed in any plane. The surgeon then selects and positions a 3-D model of the new artificial joint (prosthesis / implant) within the reconstructed CT bone model that best fits the patient’s anatomy. Using this surgeon-formulated plan, the ROBODOC® Surgical Assistant precisely mills (cuts) the bone / joint to accept the prosthetic implant. The ROBODOC® Surgical System is the only active robotic system cleared by the Food and Drug Administration (FDA) for use in orthopedic surgery in the U.S. Worldwide, the system has been used in over 28,000 total hip and total knee* surgical procedures. [*ROBODOC® is not cleared for total knee replacement surgery in the U.S.]. ROBODOC® and ORTHODOC® are registered trademarks of Curexo Technology Corporation (CTC).
Please note that a Glossary of Terms at the end of this section provides definitions of the various medical terms used in this and other sections of the website.
Misconceptions about robotic / robot-assisted surgery
The robot performs the surgery.
Yes and no. The ROBODOC® Surgical Assistant performs only a portion of the procedure. Your surgeon is responsible for planning and performing the majority of the procedure including selection of implant type, size and the final implant positioning. He/she is also performs the initial surgical incision and frees up muscle and other soft tissues clear from the joint site. The ROBODOC® Surgical Assistant is then securely positioned to remove bone and joint surfaces to precisely fit the desired implant.
Your surgeon is present in the operating room and monitors the progress of the ROBODOC® Surgical Assistant at all times, observing a real-time display of the position of the robotic cutter in relation to the bone on a computer screen. By means of a hand-held device, he/she can immediately interrupt ROBODOC® at any time if something unexpected should occur. Additionally, the ROBODOC® Surgical Assistant continually monitors its own progress and will immediately stop if it senses any deviation from your surgeon’s prescribed plan.
When the milling is complete, the ROBODOC® Surgical Assistant is moved away from the operating table. Your surgeon then places the implant into the precisely milled bone and checks for the fit, alignment, and function. Muscle and other tissues are reattached, and the incision is closed in the standard manner.
The robot might stray from the described surgical plan and remove too much bone or bone from the wrong area.
Multiple safety sensors constantly track the position of the robotic cutting device. As reviewed above, any deviation from the ORTHODOC® programmed plan will immediately halt the robotic arm. During surgery, a bone motion monitor detects any motion between the operative site and ROBODOC®. Any motion that changes the relative position of the bone with respect to ROBODOC® immediately halts all further robotic action. In addition to monitoring bone motion, a force sensor stops milling if excessive resistance is encountered during any part of the procedure.
ROBODOC® is designed so that no single point of failure can cause uncontrolled arm movement. The system uses multiple independently operating computers and microprocessors that if not in agreement deactivate power to the robot and the cutter. In over 900 total hip replacement cases monitored in Germany, no unpredicted or dangerous robot movements were observed (Bargar et al., 1998). Additionally, in no case did a surgeon find it necessary to stop a procedure. If for any reason ROBODOC® is not able to complete the milling of the bone / joint, the surgeon can use manual instruments to finish the procedure.
Figure 1. A. View of half of the pelvic area showing the hip joint and the femur (thigh bone). The femoral head fits inside a cup-like depression (the acetabulum) in the hip bone to form the “ball and socket” hip joint. B. The head, neck and shaft of the upper femur. The shaft has been cut in half to reveal the outer dense hard cortical bone that surrounds the inner (intramedullary) space filled with a meshwork of soft trabecular bone. The stem portion of a hip implant (Figure 3) will be positioned within a cavity created within the intramedullary space (Figure 5).
Figure 2. Side views of the anatomy of the knee and movement of the knee joint from full extension to full flexion.
Figure 3. A. Three views of a typical hip implant, demonstrating the head, neck and stem components. Here they are shown as a single unit, but some implants have interchangeable components. B. A close up view of a hip implant showing the head partially covered and fitting inside a prosthetic acetabular cup. The inner surface of this metal acetabular cup is polished to allow it to glide smoothly over the prosthetic head, whereas the outer surface has a rough, porous (open mesh) coating for placement against the hip bone (see Figure 5). Most implants now have separate inner cup liners made of hard plastic, as shown in Figure 5, to avoid metal-on-metal contact.
Figure 4. A. The individual components used in total knee replacement. B. The implants and joint liner assembled in place, minus the patellar implant.
Figure 5. Overview of hip replacement surgery. A. The original femoral head and acetabulum have been removed and a new depression made in the pelvic bones for the acetabular prosthesis and the plastic liner cup. B. The new acetabular cup and liner have been placed in the pelvic bones and prosthetic femoral stem and head positioned within a new cavity in the upper femur. C. The hip prosthesis components in their final positions in the pelvis.
Figure 6. Following removal of portions of the lower femur, upper tibia and the inner aspect of the knee cap, prosthetic implants are placed to create a new functional knee joint. Proper alignment of the femoral and tibial implants is critical for a good outcome. (Adapted from indiahospitaltour.com).
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Q: Why should I consider using ROBODOC® for total hip or total knee replacement surgery in place of traditional manual surgery?
Total hip replacement (primary total hip surgery / total hip arthroplasty (THA) )
A: The ORTHODOC® Preoperative Planning Workstation permits your surgeon to manipulate three-dimensional (3-D) models of hip implants within a 3-D model of your upper thigh (femur) and hip bones. Your surgeon will use his/her judgment and experience to select the type, size and final placement of a femoral stem implant that best fits your individual anatomy. As shown in Figure 7, the ORTHODOC® computer workstation provides for detailed preoperative 3-D spatial views of the implant and bone anatomy. This enables selection and placement of an implant with much greater accuracy than can be accomplished with plain 2-D x-rays used in planning traditional manual procedures. Using information specific for your surgery, the ROBODOC® Surgical Assistant then prepares the inner cavity of the femur to accept the hip implant selected by your surgeon as specified pre-operatively in ORTHODOC® with sub-millimeter precision (cutting accuracy of less than 0.4 mm) not possible even by the most skilled surgeon due to the limitations of traditional hand-held surgical instruments (Figures 8 and 9).
Total knee replacement (primary total knee surgery / total knee arthroplasty (TKA) )
A: Using information specific to your anatomy based on a CT scan, your surgeon can use the ORTHODOC® Preoperative Planning Workstation to align the femoral and tibial implant components in 3-D to restore your natural knee alignment. The ROBODOC® Surgical Assistant will then prepare the bones of the knee joint (the lower femur and upper tibia) to accept prosthetic knee implants with accuracy that cannot be achieved by traditional manual surgery.
Figure 7. ORTHODOC® Workstation screen showing an example of three planar views of a hip implant (displayed in brown and yellow) positioned within the femoral cavity. The red circle represents the position of the new prosthetic head. The image in the right lower panel shows an implant (silver; without prosthetic head) positioned within a portion of the upper femur.
Q: Precisely what does the ROBODOC® do?
Based on the pre-operative plan created by your surgeon on ORTHODOC®, ROBODOC® cuts away (mills) through the femoral head and then the less dense, trabecular / intramedullary bone in the inner femoral cavity to the precise shape of the surgeon-selected implant. In traditional manual surgery, removal of bone is done using saws and hand/mallet-driven reamers and broaches (Figure 8). The marked increased in precision of implant cavity preparation provided by ROBODOC® is shown in Figure 9.
Figure 8. Examples of surgical instruments used in traditional manual hip replacement surgery. A) hand-torqued reamers and B) mallet-driven femoral cavity broaches. Reamers remove bone with a twisting motion whereas broaches cut bone with abrading (rasping) teeth. These instruments limit the precision of a surgeon to prepare bone cavities and joint surfaces to accept prosthetic implants.
Figure 9. Cross sections of femurs prepared manually (A) or by ROBODOC® (B) showing the inner cavity (central black areas) where a femoral implant would be placed. The manually broached femur has irregular gaps created when trabecular bone was torn away by the teeth of a broach. The femur milled by ROBODOC® has a smooth inner cavity contour (Adapted from Paul et al., 1992). The smooth cavity contour allows for a much closer fit of a femoral stem implant.
Q: How do the outcomes of total hip and total knee replacement surgeries performed with ROBODOC® system compare to results from traditional manual total hip or total knee surgery?
Total hip replacement
A: Clinical studies conducted in the U.S., Europe and Japan have compared short-term post-operative complications and long-term functional outcomes of total hip replacement surgery done by ROBODOC® and by traditional manual surgery. Fewer short-term complications were observed with ROBODOC® procedures. These included no intra-operative fractures of the femur caused by implant insertion (Borner et al., 1997, Bargar et al., 1998, Nishihara et al., 2006), decreased incidence of blood clots / pulmonary embolism (blood clots in the lungs) (Hagio et al., 2003), and decreased time after surgery to full weight bearing and ability to walk unaided without a cane (Bargar et al., 1998, Nishihara et al., 2006). Length of hospital stay, and various other potential post-operations complications, such as infection, were found to occur at rates similar to traditional manual surgery (Bargar et al., 1998).
Regarding long-term outcomes, the more precise fit of the femoral stem implant in ROBODOC® procedures provides for better ingrowth of bone necessary to firmly secure the hip implant in the femur (Nishihara et al., 2006, Hananouchi et al., 2007), better transfer of body weight through the upper femur leading to less loss of bone density / bone strength that may be observed after traditional hip replacement surgery (Hananouch et al., 2007, Nakamura et al., 2010) and decreased incidence of leg length discrepancies (ROBODOC IDE Trial G000071, Nakamura et al., 2010), a frequent complaint after total hip replacement surgery and the most common reason for malpractice suits for this type of surgery (Clark et al., 2006). In addition, when evaluated 3-5 years after surgery, no differences were detected in general overall assessments of health and ease of daily activities between hip replacement procedures performed manually or by ROBODOC® (ROBODOC IDE Trial G000071).
Total knee replacement
A: For total knee replacement surgery, no post-operative errors in leg alignment were observed with ROBODOC® compared to 24% for conventional surgery (Song et al., 2012). Additional improved outcomes with ROBODOC® included better flexion-extension gap balance. No differences were detected between ROBODOC® and conventional total knee replacement procedures in post-operative measures of joint function (Western Ontario and McMaster Universities (WOMAC) osteoarthritic index and Hospital for Special Surgery (HSS) hip scores) (Song et al., 2012).
Q: Hip and knee implants made from different materials (metal, ceramic, hard plastic) are available from various manufactures. What type of implant can my surgeon use with the ROBODOC® Surgical System?
A: ROBODOC® has a “library” of the 3-D shape and size of many of the commonly used hip and knee implants, and this library is continually being expanded and updated. Ultimately, the ROBODOC® Surgical System can incorporate any manufacturer’s implant.
Q: What is the difference in cemented and cement-free implants?
Hip (and other) joint implants may be secured in place with the use of bone cement; polymethylmethacrylate (PMMA). For a cemented implant, the bone cavity created by the surgeon could have a rough, irregular surface, as any gaps between the implant and the inner bone surface could be filled in with bone cement. However, bone cement does not physically adhere the implant to bone, but instead fills in gaps between the implant and the surrounding bone. Over time, bone cement may loosen, resulting in a shift in the position of the implant, causing misalignment of the joint, resulting in alterations in gait and/or pain due to maldistribution of body weight through the leg.
Cement-free implants rely on ingrowth of bone cells into the implant to hold it securely in position. For bony ingrowth to occur, the gap between the implant and the bone must be very small, generally less than 1 mm (0.04 inch)(Dalton et al., 1995). Implants intended for cement-free placement have special porous (open mesh) surface coatings to promote the ingrowth of bone cells. Once bony ingrowth has occurred, an extremely strong bone-implant bond is created and the likelihood an implant loosening and/or shifting position is greatly minimized. Studies with ROBODOC® have demonstrated a 95% bone-to-implant contact vs. an average of 21% direct bone-to-implant contact observed with manual surgery (Paul et al., 1992).
Q: Why is a more precise implant fit important in cement-free implant surgery?
A: In the case of total hip replacement, a more precise implant fit in the femoral cavity ensures minimal gaps at the implant-bone interface, thereby promoting the ingrowth of bones cells into the porous surface coating of the implant. X-ray studies confirm that hip implants performed with ROBODOC® have more secure bone-implant bonding sites (“spot welds”) compared to implants placed by traditional surgery (Nishihara et al., 2006, Hananouchi et al., 2007). For total knee replacement, a poorly prepared bone surface can reduce the likelihood of the success of a cemented implant (cement-free knee implants generally are not used).
Q: Under what circumstances are cemented and cement-free hip implants used?
A: Generally, a cement-free implant is considered for individuals with good bone structure / good bone health. Older individuals or those with poor / weakened bone structure (thin / decreased bone density due to osteoporosis or other conditions affecting bone health) often are candidates for placement of a cemented implant. In the U.S., over 88% of all total hip replacement surgical procedures involve cement-free femoral stem (and cement-free acetabular cup) implants (Dunbar MJ., 2009)
Q: What criteria and/or medical conditions determine whether an individual is a suitable candidate for ROBODOC® hip or knee replacement surgery?
A: In general, there is no upper age limit that would preclude robotic surgery. Rather, issues relating to good bone strength and overall general health are the factors that are considered.
Bargar WL, Bauer A, Börner M. Primary and revision total hip replacement using the Robodoc system. Clin Orthop Relat Res. 1998 Sep;(354):82-91.
Börner M, Bauer A, Lahmer A. [Computer-guided robot-assisted hip endoprosthesis]. Orthopade. 1997 Mar;26(3):251-7. German.
Clark CR, Huddleston HD, Schoch EP, Thomas BJ. Leg-length discrepancy after total hip arthroplasty. J Am Acad Orthop Surg. 2006 Jan;14:38-45.
Dalton JE, Cook SD, Thomas KA, Kay JF. The effect of operative fit and hydroxyapatite coating on the mechanical and biological response of porous implants. J Bone Joint Surg Am. 1995 Jan;77(1):97-110.
Dunbar MJ. Cemented femoral fixation: the North Atlantic divide. Orthopedics. 2009 Sept;32(9):662-665.
Hagio K, Sugano N, Takashina M, et al. Effectiveness of the ROBODOC system in preventing intraoperative pulmonary embolism. Acta Orthop Scand. 2003 Jun;74(3):264-9.
Hananouchi T, Sugano N, Nishii T, et al. Effect of robotic milling on periprosthetic bone remodeling. J Orthop Res. 2007 Aug;25(8):1062-9.
Nakamura N, Sugano N, Nishii T, et al. A comparison between robotic-assisted and manual implantation of cementless total hip arthroplasty. Clin Orthop Relat Res. 2010 Apr;468(4):1072-81. Epub 2009 Nov 5
Nishihara S, Sugano N, Nishii T, et al. Comparison between hand rasping and robotic milling for stem implantation in cementless total hip arthroplasty. J Arthroplasty. 2006 Oct;21(7):957-66.
Paul HA, Bargar WL, Mittlestadt B, et al. Development of a surgical robot for cementless total hip arthroplasty. Clin Orthop Relat Res. 1992 Dec;(285):57-66.
ROBODOC® IDE Trial G000071 (Data on file).
Song EK, Seon JK, Yim JH, et al. Robotic-assisted TKA Reduces Postoperative Alignment Outliers and Improves Gap Balance Compared to Conventional TKA. Clin Orthop Relat Res. Epub 2012 Jun 6.
acetabulum The cup-like depression in the hip bone into which the femoral head fits and rotates, forming the “ball and socket” hip joint
acetabular cup Component of a hip implant placed in the hip bone to replace the patient’s worn / diseased acetabulum
acetabular liner Component of a hip implant that fit inside
arthroplasty Surgical removal or reformation of a joint
broach A surgical tool with rasp-like metal teeth driven by a mallet into the intramedullary space to create a cavity for a prosthetic implant
centimeter A metric system measure of length; one centimeter equals about 0.4 inch
cortical bone Dense, hard bone that comprises the outer rim of bones, providing bone strength
CT scan Computed Tomography scan; a technique that uses a series of individual X-rays that can be assembled to provide images of the body
embolism Reduced blood flow due to a blood clot, fat or particulate matter
extension Straightening of a joint, as compared to bending (flextion)
femur Thigh bone
fibula The smaller of the two bones in the lower leg
flextion Bending of a joint, as compared to straightening (extension)
HSS Hospital for Special Surgery (HSS) knee score; a survey to assess pain, stiffness and physical function in patients with knee arthritis, also used to assess post-operative pain, stiffness and function after knee surgery
implant A term to describe an artificial (prosthetic) joint
intramedullary The space inside the outer rim of hard cortical bone filled with a meshwork of less dense “spongy” trabecular bone.
lateral Referring to the side of a body part, farthest from the center plane of the body
medial Referring to the inner aspect of a body part, closer to the center plane of the body
mill Cut / shape bone
millimeter A metric system of measure of length, equal to 0.04 inch
osteoporosis Decreased bone mass / density resulting in decreased bone strength
polymethylmethacrylate (PMMA) Bone cement used to secure cemented implants
porous The rough, mesh-like coating on the surface of an implant to promote the ingrowth of bone cells to create firm bone-implant bond
prosthesis An artificial organ or body part; a joint implant
pulmonary embolism Interrupted blood flow to a portion of the lungs due to a blood clot, fat or particulate matter in a pulmonary artery
reamer A surgical instrument that removes trabecular bone with a twisting motion
sagittal Referring to a cross sectional view of a body part
spot welds Sites where bone cells have grown into the porous surface coating of a cement-free implant, creating a very secure bone-implant bond
stem The slender, tapering portion of a hip implant that is placed within the intramedullary space
THA Total Hip Arthroplasty; total hip replacement surgery
TKA Total Knee Arthroplasty; total knee replacement surgery
tibia The larger of the two bone sin the lower leg; the shin bone. The head of the tibia forms the lower portion of the knee joint
trabecular Less dense, mesh-like intramedullary bone.
WOMAC Western Ontario and McMaster (WOMAC) Universities osteoarthritis index; a survey to assess pain, stiffness and physical function in patients with hip or knee arthritis, also used to assess post-operative pain, stiffness and function after hip or knee surgery