Computer Assisted Orthopaedic Surgery – CAOS

The use of computer navigation in orthopedic surgery allows for real time intraoperative feedback resulting in higher precision of bone cuts, better alignment of implants and extremities, easier fracture reductions, less radiation and better documentation than what is possible in classical orthopaedic procedures. There is no need for direct and repeated visualization of many anatomical landmarks (classical method) in order to have good intraoperative orientation. Navigation technology depicts anatomy and position of "smart tools" on the screen allowing for high surgical precision (smaller number of outliers from desired goal) and with less soft tissue dissection (minimally invasive surgery - MIS). As a result, there are more happy patients with less pain, faster recovery, better functional outcome and well positioned, long lasting implants. In general, navigation cases are longer on the average 10 to 20 minutes, special training is required and equipment is relatively expensive. CAOS applications in knee and hip joint replacement are discussed.


Introduction
It is well documented in the literature that function and longevity of extremities depend on natural or reconstructed bone and joint alignments and stability.A varus knee has a higher risk of developing medial compartment arthritis or early wearing of the poly insert in an artificial knee joint; retroverted or vertical acetabular cup will have a higher dislocation rate; total knee arthroplasty with internally malrotated femoral component will have more problems with patella tracking and so on (, ).Global Positioning System (GPS) is a widespread and very useful tool in many aspects of our daily lives.It presents on monitor the position of still and/or moving objects in space and how they relate to each other (car on the street...).The operating room navigation system works in similar way: on the screen, we are able to see images of bone-anatomy (obtained through a registration process) and mobile "smart tools" (drills or saws with attached trackers communicating with localizer cameras) and their positions during cutting or drilling procedures.There are threes steps necessary for surgical navigation: .Data acquisition of: a. Images: done preoperatively (CT -computer tomograms or MRI -magnetic resonance images) or intraoperatively (fluoroscopy images) or b. "Imageless data": intraoperatively gathered kinematic information such as centers of rotation (mathematically determined by moving the adjacent bones with attached, fixed trackers) and anatomical bone landmarks (such as acetabulum inner wall or femoral epicondyle, using the mobile tracker -pointer)..Tracking -provides feedback during surgery, communicating via infrared rays to localizer camera (Fig. ) the relative position of trackers attached to the bone ("bony anatomy", Figures  and ) or tools (making them "smart" Fig. ).Infrared rays are emitted by LED ("light emitting diodes" that are battery operated multiple light sources placed on different positions on the trackers (more reliable option) or reflected by "differently positioned reflective spheres" (their surface could be masked by blood or fluid affecting the function; they are more bulky)..Registration -process of relating the collected data of the patient's three-dimensional anatomy to the patient's position and anatomy on the surgical field.Surgical tools are also registered by the navigational system (via infrared cameras and computer) which allow us to see on the monitor their position (via attached mobile trackers) in relationship to the patient's anatomy (via trackers attached to the bone,) in real time.Based on data acquired intraoperatively, the system automatically calculates an initial optimal implant position and allows for preparing the bone using the navigated tools and jigs and in some degree evaluates the soft tissues (ligament balancing, via observing different kinematic curves, Figure ).

Knee Arthroplasty
The goal of partial or total joint arthroplasty is to relieve the pain and improve long lasting function of the affected joint when non-operative measures were not able to alleviate the problems any more.In full extension the knee joint line should be perpendicular to the mechanical axis of the lower extremity (connecting centers of the hip, knee and the ankle) and the ground, close to it's original height (no patella baja) and with well matching surfaces and rotations of components (especially femoral -no internal malrotation).The joint has to be balanced (symmetrical gaps in extension and flexion -slightly looser) and stable, allowing painless motion in range from  to  degrees (important for climbing the stairs) or up to  degrees (important for kneeling during prayers or cross-legged sitting) ().Rand and Coventry () found that survival rate of knee arthroplasty in  years was  if knee alignment was within  degrees of neutral, and in cases where deviation was more than  degrees revision was not required only in  varus knees, and  in valgus knees () .Similar findings have been reported by Jeffrey at al (), with loosening rate of  if deviation was more than three degrees and  if deviation was within three degrees ().How often do we encounter malalignment using the classical, manual instrumentation?Peterson and Engh () looked at  randomly chosen cases from their casuistic and found that  of knees had more than  degrees of varus/valgus malpositioning ().Another high volume center found similar problems in  of their  patients ().Barrack () had  of patients (out of ) with anterior knee pain and combined internal rotation of , degrees (ranging from  degrees of internal rotation to  degrees of external rotation), and no pain in patients with a mean external rotation of , degrees ().Chauhan at al () did a prospective randomized controlled study, comparing navigation and manual-jig based techniques in  patients.The Perth CT protocol was used for alignment verification.Significantly better results were found in navigated knees in next parameters: varus/valgus of the knee, femoral component rotation, varus/valgus of tibial component, tibial posterior slope and femur-tibial components mismatch.Also, estimated blood loss was significantly less in the navigated group (no medullar canal opening) but navigated cases took on the average  minutes longer ( minutes) ().These results were confirmed by three other prospective randomized studies looking together at  patients without complication specifically related to navigation alone (, , ).

Technique
After patient is anesthetized (usually with a regional anesthetic), patient knee joint is opened.Navigation minimizes the risk involved with MIS technique, there is no need to physically see or touch all important landmarks (like the lateral epicondyle).The usual MIS incision length is double the height of patella (skin tensions and pressures must be avoided, incision is lengthened as necessary).We need to make sure that the patella is mobile enough (mid-vastus approach) so that we have ENES M. KANLIĆ ET AL.: COMPUTER ASSISTED ORTHOPAEDIC SURGERY -CAOS access to the joint surfaces.Femoral and tibial trackers are attached to corresponding bones, and rotational hip motion will determine the hip center.A pointer instrument is used to register transepicondylar axis, center of the femur, Whiteside anteroposterior (AP) line, femoral condyles and anterior cortex of the femur (Figures  and ).On the tibial side center of tibial plateau (ACL insertion), neutral AP axis, medial and lateral articular surfaces, the medial and lateral malleolus with the ankle center are registered.From acquired data, the software creates images of the knee joint in different views (AP, lateral, cross-sectional) with present mechanical axis.The knee joint is put through the range of motion, and deformities (varus-valgus, maximal flexion and extension, contractures and laxities) are documented.Mobile tracker is attached to cutting blocks (" in " cutting block or J-jig,) and we are able to adjust and fix it in perfect position (femoral rotation, no anterior cortex notching, posterior tibial slope and rotation, and desired level of joint surfaces resection, Figures  and ).Tibial side is resected immediately after the first femoral distal cut (to open the joint space using the guidance displayed on the monitor (Figures  and ).After insertion of trial components, joint is tested for range of motion, stability -need for ligament balancing.Necessary adjustments (different poly thickness, additional cuts) are done with immediate, real time information displayed on the screen.If satisfied, final components are inserted (cemented or non-cemented, patella with or without resurfacing).Tourniquet, if used, is usually released after the implants are in place, and joint drain is not necessary.Minimally invasive technique (smaller incision, no averting patella, preserving the suprapatellar pouch, minimally resected retropatellar Hoffa tissue, lessening or avoiding tibial dislocation) is done with and without navigation.The results are more pleasing to patients; they have less immediate and first three months postoperative pain (comparing it with classical approach) and faster functional recovery.Procedure is less expensive because of shorter hospital stay (same day surgery for unicondylar knee replacement, and a couple of days after bicondylar replacement) (-).Preoperative patient education, specific pain control protocols (regional blocks such as epidural anesthesia and analgesia, regional femoral block, intra-articular pain pump, intra-articular injections of different "cocktails", oral medications -NSAIDs, COX- inhibitors, narcotics ), postoperative modalities (cold) and physical therapy play extremely important role in overall patient recovery, in hospital length of stay and general satisfaction.

Hip Arthroplasty
Malpositioned acetabular cup may cause decreased range of motion with impingement, higher risk of dislocation and increased wear.Total hip dislocation ( to ) is often devastating complication for the patient and his surgeon.It is more common in posterior approach, than in anterior or direct lateral approaches.Reasons for the different dislocation rates are multifactorial.(, ).Component position surely plays there a significant role.Biederman at al () compared the position of acetabular component in  dislocated total hips with control of  patients without dislocation.They found that ideal cup position should have radiological abduction of  degrees and anteversion or flexion of  degrees in order to function well ().There are few other studies confirming that safe cup position as  ±  degrees of abduction, and  ±  degrees of flexion (, ).The true position of the pelvis is hard to estimate due to unknown amounts of patient's lordosis or kyphosis.Also, problem is that pelvic orientation changes (flexes and tilts anteriorly) in typical intraoperative lateral decubitus comparing it with pelvis in supine or standing position, or even comparing it to the position at the beginning of procedure () .In revision situation often is very hard to find usual anatomical landmarks (columns, transverse acetabular ligament, Figure ).Hassan at al () reported that desired cup position can not be reached consistently when using conventional technique even by experienced surgeons in up to .()

Technique
Pelvic entrance plane is defined by anterior superior iliac spines and symphysis.There is a constant relationship of that imaginary plane and acetabulums.Using kinematic registration of plane's landmarks (touching them with pointer), navigation allows for cup implantation in desired position independently on patient's position on the table.Pelvic tracker is securely attached to the ipsilateral iliac crest or supra-acetabular bone and that position should not change at all.MIS approach of choice will expose piriformis fossa which will be registered, as well as center of popliteal fossa and Achilles tendon.Ranging the hip joint computer will register patient anatomy (hip center, leg length, offset).After femoral head and neck resection (for primary THA), "bone morphing"(with pointer) of the acetabulum inner wall, articular surface and rim is done.Attaching the mobile tracker to the reamer handle, it is possible to get positioned within one degree of desired abduction and


BOSNIAN JOURNAL OF BASIC MEDICAL SCIENCES 2006; 6 (1): 7-14 ENES M. KANLIĆ ET AL.: COMPUTER ASSISTED ORTHOPAEDIC SURGERY -CAOS anteversion (Figure ).Also, the computer will warn the surgeon if we are approaching medial wall and there is a risk of penetration (Figure ).The cup is introduced with navigation as well (Figure ).After femoral preparation and implantation of trial components (Figure .), new kinematic registration is performed (ranging the hip).The values of the reconstructed joint will be display on the screen (length, offset, Figure ).Putting the hip through maximal range of motion (flexion, extension, rotations, abduction -adduction), the surgeon is able to see at which positions impingement, lift-off or dislocation occur (Figure ).Needed corrections are done accordingly including periacetabular bone removal, neck length adjustment, offset, femoral rotation, or cup reorientation if necessary, Figure ).Haaker () performed  navigated cases, consuming on average  ±  minutes.Cup position was , ± ,, anteversion  ± ,.They had no outliers, no complications and no dislocations ().Large surgical exposures could improve direct orientation and help in position of components (Figure ), but this can also account for higher number of wound problems.MIS in hip reconstruction is well developed today (Figure ), and there are multiple reports with excellent results.Sculco () had  total hip hybrid arthroplasties done through posterolateral incision with an average length , cm and dislocation rate of only ,.() Di-Gioia at al () compared MIS and classical navigated approaches.They found significantly better function with MIS technique regarding limping, stairs climbing and distance walking after three and six months and no difference in-between groups after one year () .Lazovic at al () compared  hips done with conventional technique to  navigated hips in prospective, randomized study.Navigated joints were significantly better regarding cup position and lack of dislocation.() This is also our experience (Figures  and ).

Conclusion
Computer navigation joint replacement allows for higher precision than what is possible using just classical, manual technique.Implants are aligned better and reconstructions are lasting longer.Minimally invasive approaches are sparing soft tissues facilitating faster recovery and shorter hospital stay.Combined together, CAOS and MIS are making patients and their surgeons happy.Navigation technology has been used in spine surgery (pedicular screws), fractures care (reductions, nailing, percutaneous screws in pelvic and hip surgery with minimal radiation), osteotomies and even ligamentous reconstructions (tunnel positioning for ACL and PCL grafts).New generations of young surgeons could be trained easier on computers even before they get to the operating rooms.Navigation is an excellent research tool.It will gradually become a routine technique used for the most of orthopaedic procedures.