NAVIGATION IN TOTAL KNEE REPLACEMENT :-

Limb alignment and soft tissue balancing are important for the success of TKA. Malalignment may negatively affect implant function and lead to decreased survival rate in TKA1. The decreased survival due to malalignemnt is likely due to off -axis loading, polyethylene wear, and subsequent implant loosening2. Therefore, components must be placed as precisely as possible and ligaments must be carefully balanced. Despite the use of manual intramedullary or extramedullary guides, significant errors in postoperative mechanical axis of greater than 3° are estimated to occur in at least 10% of TKAs, including those performed by experienced surgeons3.

HISTORY:-

Navigation was first introduced experimentally in the 1980s and clinically in the 1990s, but has only entered mainstream orthopaedics in the last 15 years. Computer assisted navigation was first applied in orthopedic surgery for the insertion of pedicle screws. Intraoperative navigation in total joint replacement began in 1992, when W. Barger, in Sacramento (California) performed the first computer assisted surgery in orthopaedics for total hip replacement, while the first total knee replacement began in France, in January 1997, by F. Picard4.

Classification:-

Navigation system can be classified as
A. Open or closed
Open- navigation system can be applied to any prosthesis of different manufacturer.
Closed- in this navigation can apply to a particular prosthesis or manufacturer only.
B. Active or passive
Computer-assisted systems are active (surgical robots) or passive i.e. systems that do not perform any part of the surgery, but assist in the positioning of the surgical instruments.

  1. Computer navigation systems can be grouped into three different types according to the referencing methods: CT-based, fluoroscopy based, and imageless systems.
    (a) In CT-based systems, CT scans of the femoral head, knee, and the distal tibia are performed before TKA and images are used to make a three-dimensional model. Th e main advantages of the CT-based system are that it is specific to the patient’s anatomy and it can be used in cases of extreme deformities. The main disadvantage is that it is mandatory to obtain a CT scan which may be seen an additional expense, waste of time, or an unreasonable source of radiation for the patient.

(b)The fluoro-based system uses an instrumented image intensifier and permits the collection of a limited number of fluoro images. While taking the fluoro images, specific markers are captured in the images allowing the computer to relate the image position to the marker position. Aft er imaging is complete, the instrument is identified by the tracking system.

(c) The imageless or non-image system functions without CT or fluoroscopy. The manufacturer of the navigation system obtains CT scans from a large number of patients and stores them in a database. During TKA, multiple landmarks are obtained from surface points, such as femoral epicondyles and tibial plateaus, or from kinematic algorithms to determine joint centers. The database morphs a model of the femur and tibia that best fits the registered surface points. The main advantages of the imageless system are the avoidance of a CT scan and its irradiation. However, information concerning the rotational positioning of the implants is questionable and this method relies on the surgeon’s ability to indicate bony landmarks using a pointer. This system is the simplest and most widely used computer assisted tools for TKA.

COMPONENTS OF COMPUTER ASSISTED NAVIGATION

Navigation consists of three elements: computer platform, tracking system, and rigid body marker. The tracking system visualizes the rigid body markers and tracks their motion with the help of computer processing within the three dimensional space. The marker or tracker should be attached to the patient’s bones or surgical instruments to track the target objects. It corresponds to the dynamic reference base (DRB) when the target objects are the patient’s bones, and it corresponds to the cutting block adaptor when the target objects are the surgical instruments or implants.

Computer Platform-

The computer platform controls the coordination of inputs from the surgical field, interprets the data mathematically, and displays the resultant information on a monitor. The computer is programmed to know the shape and position of the instrument, pointer probe, and cutting block adaptor. The computer platform calculates the three-dimensional position of the trackers.

Tracking System –

The tracking system can be of two type-
1. Optical tracking system
2. Electromagnetic tracking system
The tracking system consists of an optical camera, electromagnetic coil, or an ultrasonic probe to pick up infrared light, electromagnetic pulses, or ultrasonic waves, respectively, that originate from the trackers. Optic tracking systems require two or three charged coupled device cameras to pick up infrared light from the trackers, which are recognized by three to five active emitters or passive reflective balls. Measurement error increases with increasing distance from the camera. The disadvantages of optical tracking systems include the volume of the infrared camera, wear of reflecting balls, and the adaptation of the surgical technique to maintain the line of sight. Electromagnetic (EM) tracking systems require a transmitter and trackers (dynamic reference frames, a pointer probe, and a paddle probe). EM tracking systems do not require reference arrays, cameras, or line of sight. The disadvantage of EM tracking systems is the distortion of the field created by metals and some non-metals. In addition, trackers are linked to the computer by wires which can be troublesome during the surgical procedure. Validation studies have shown that occasional outliers may be off by several degrees which makes this method less reliable.

Tracker or Marker (Pointer Probe, DRB, Cutting Block Adaptor)-

Active markers emit light from a bulb and have a battery or wire as a power source. Passive markers reflect infrared light. The tracking system and its associated computer perform a triangulation process to determine the position of each marker. The computer does not detect bone. Any movement of a DRB represents movement of the bone itself. In addition to DRBs, a variety of equipment has associated markers to track the instruments. The software particular to the navigation system has been programmed with the geometry of the instrument. For example, the system can determine the location of the pointer tip and the longitudinal axis of the pointer probe.

PREOPERATIVE PREPARATION :-

The preparation for navigated TKR should include the setup of computer and camera unit in operating room in such a manner that this does not interfere with usual procedure. The camera unit needs to be placed in such a manner that both femoral and tibial arrays are in range and easily tracked throughout the entire procedure. The computer monitor unit needs to be in full view so that the surgeon can visualize and control the navigation process.

SURGICAL METHODS –

Image-free navigation is the most commonly used navigation technique. The author have used the image free Ci navigation system with its software (Brainlab, Munich, Germany). The use of navigation system involve the following basic steps-
Fixation of arrays – after initial exposure femoral and tibial arrays are attach to distal third of femur and proximal third of tibia. These arrays with three reflactive spheres are fixed to the bone using two schanz screws placed unicortically. Two pins of 3 mm diameter is preferred to single 5 mm pins with bicortical fixation to avoid incidental fracture. The arrays may be fixed within the surgical wound or outside of it using stab incision. when these placed within the surgical wound, care should be taken so that these pins do not impede the cutting blocks or components.
Registration – registration is done in the standard fashion as described by the particular navigation workflow. Registration starts with kinematic referencing of center of femoral head, mapping of distal femur and proximal tibia and bony landmarks of ankle. the centre of femoral head is computed by pivoting the femur and moving the entire limb in circular motion while the pelvis is steadied. The computer calculates the centre of femoral head as the apex of a cone described in space by the arrays as the leg is pivoted. This is followed by registration of bony landmarks, lines and surfaces of distal femur and proximal tibia. After registration of all computer shows overall coronal and saggital plane deformity.
Navigation cutting blocks- conventional cutting blocks for tibial, distal femoral and AP femoral cuts can be navigated in position to match the default recommendations of the computer in order to obtain the desired cuts. The surgeon can choose to alter the thickness and orientation of cuts if desired. Navigation enables surgeon to check alignment in all 3 planes (saggital, coronal, axial). We can titrate femoral cut in terms of thickness, flexion & extension, rotation. While in the tibia, cut can be titrated in thickness and posterior slope.
Verification of bone cuts – after initial registration different cuts of TKA can be verified using flat verification arrays with computer navigation.
Gap Balancing :- In extension, navigation allows quantification of medial and lateral gaps and the limb alignment for a given spacer or trial component. It also allows visualising the degree of medio-lateral laxity present for a given spacer. In flexion, medio-lateral gap balance can be assessed with respect to the position of distal femoral bony landmarks such as the transepicondylar line, Whiteside’s line and the posterior condylar axis. The optimized version of the Ci navigation software allows the surgeon to simulate the effect of change in rotation, flexion or extension, upsizing or downsizing of the femoral component on the flexion gap vis-à-vis the extension gap without actually performing the cuts.
Final Alignment :- The final alignment of the limb and gaps can be confirmed with trial components and again after implantation of the prosthesis especially when the cement is setting. Holding the limb in the appropriate position while the cement is setting is crucial to avoid malalignment of tibial and femoral components due to an uneven cement mantle or incomplete seating of the components. Navigation allows for real-time continuous visuali-sation of the limb position in both the coronal and sagittal plane while the cement is setting.

Indication for navigation in total knee arthroplasty :-

Computer-assisted navigation decrease the number of outliers and extend the longevity of the implant. navigation seems to be helpful in those difficult situations where accurate alignment remains crucial but traditional instrumentation is not applicable. conventional cutting guides during knee arthroplasty use intramedullary (IM) femoral instruments and either intramedullary or extramedullary (EM) tibial instruments to obtain proper axial alignment. Intramedullary instruments cannot be used in patients with:
• Retained hardware that would be difficult or inadvisable to remove
• Long stemmed hip implants that could obstruct introduction of long IM instruments;
• Severe posttraumatic extra-articular femoral deformity when one is unable to pass an IM guide to accurately make a distal femoral cut;
• IM guides may increase the infection risk in patients with history of focal diaphyseal osteomyelitis around the knee joint5
• Patients with severe cardiopulmonary disease or a history of foramen ovale who may be at risk for embolic dissemination because of femoral IM instrumentation6.
In these cases navigation helps to accurately estimate the center of the femoral head and the overall limb and component alignment, otherwise difficult to be clinically judged with conventional technique.

Advantages of navigation :-

Computer-assisted surgery in TKA offers several advantages against traditional surgery, that can be resumed as follow:
• Better accuracy in bone cutting and positioning of prosthetic components7,8 . In a study of Martin et al7, they found that the mechanical axis of the limb was within 3° varus/valgus in 92% of the patients who had navigated procedures versus 76% of patients who had conventional surgery. The tibial slope showed a rate of inaccuracy of 3° or less for 98 % of the patients in the navigated TKA group versus 80% of the patients in the conventional group
• possibility to do a three-dimensional planning and alignment of the prosthesis9
• Dynamic assessment of deformity at any angle as opposed to conventional technique where tensioning devices can be used in 0° extension and 90° flexion
• Titration of soft tissue release. In computer assisted navigation technique after all registration process navigation software shows deformity at every angle of flexion. In majority of patients with varus deformity in extension, the overall alignment goes into valgus in flexion so in these type of patients no soft tissue release is neccesory to obtain good alignment.
• At the completion of total knee replacement surgery balancing the ligaments surrounding the knee has always been the most difficult and “subjective” part of knee arthroplasty. In conventional surgery the knee ligaments are balanced chiefly by the surgeons “feel” to determine if the ligaments are appropriately taut. Though experienced surgeons can achieve excellent ligament balance in most cases, reproducibility is difficult and results are subjective. With computer navigation, ligament balancing can potentially be quantified to the nearest millimeter of ligament laxity or tautness. As computer navigation software improves, the surgeon will be able to more precisely
balance the ligaments of the knee. This, in the end, may prove to be computer navigation’s greatest advantage over conventional surgery
• In TKR surgery if there is significant deformity in the femur above the knee or in the tibia below the knee conventional alignment systems can be difficult or impossible to use. This is due to the fact that intramedullary systems require an unobstructed femoral and tibial canal. Similarly if as a result of previous surgery any hardware is present such as plates, screws or rods in the bone blocking the femoral or tibial canal, conventional alignment systems often cannot be utilized. With computer navigation systems deformity and /or the presence of hardware provides no obstacle since access to the intramedullary canal is not a requirement. Thus, patients with bony deformity or hardware above or below the knee are ideal candidates for utilizing computer navigation guidance systems.
• Assessment of soft tissue and collateral tension when gap balancing technique applied10
• Intra-operative range of motion analysis to achieve maximum function, as confirmed by some reports like that of Austin et al11, who observed as navigation could be a reliable tool for performing in vivo assessment of range of motion
• Decreased incidence of pulmonary embolism in knee surgery, due to using of only extra-medullary guidance12
• Minimally invasive surgery, which allows lesser blood loss during and after operation, reduces risks at transfusion and decreased hospital admission duration, those gives financial saving12
• Early rehabilitation and shorter hospital stay, due to improved accuracy in limb alignment and soft tissue balance obtained with computer-assisted TKA13

Disadvantages of navigation

Nevertheless, there are some disadvantages by using navigation:
• The surgical time was longer for navigated TKA than for the conventional procedure.7 but after experience surgical time decreases and remains same as conventional procedure.
• Certain learning curves
• Additional incisions for reference pins;
• Increased incidence of fractures or infections related to the pins sites (less than 1% reported complication rate). According to literature, larger pins diameter (5 mm), eccentric or repeated drilling and diaphyseal placement may be at greater risk of such complication14,15
• Significant cost implication for purchase and maintenance of the system. Solver et al16 applying Moarkov decision model to evaluate the impact of hospital volume on the cost-effectiveness of CAS arthroplasty, have revealed that CAS is less likely to be cost-effective investment in health care improvement in centers with low volume of joint replacements, where its benefit is most likely to be realized; anyway it may be effective in centers with high volume of joint replacements

REFERENCES-

1. Ritter MA, Faris PM, Keating EM, Meding JB. Postoperative alignment of total knee replacement: its eff ect on survival. Clin Orthop Relat Res. 1994;(299):153-6.
2. Mason JB, Fehring TK, Estok R, Banel D, Fahrbach K. Metaanalysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty. 2007;22(8):1097- 106.
3. Stulberg SD, Loan P, Sarin V. Computer-assisted navigation in total knee replacement: results of an initial experience in thirty-fi ve patients. J Bone Joint Surg Am. 2002;84 Suppl 2:90-8.
4. Delp SL, Stulberg SD, Davies B, Picard F, Leitner F. Computer assisted knee replacement. Clin Orthop Relat Res. 1998;354:49– 56.
5. Fehring TK, Mason JB, Moskal J, Pollock DC, Mann J, Williams VJ. (2006). When computerassisted knee replacement is the best alternative. Clin Orthop Relat Res. Vol.452, (November 2006), pp.132-6, ISSN 1528-1132
6. Berman AT, Parmet JL, Harding SP, Israelite CL, Chandrasekaran K. (1998). Emboli observed with use of transesophageal echocardiography immediately after tourniquet release during total knee arthroplasty with cement. J Bone Joint Surg Am, Vol.80, No.3, (March 1998), pp.389–94, ISSN 1535-1386
7. Martin A, Wohlgenannt O, Prenn M, Prenn M, Oelsch C, von Strempel A. (2007). Imageless navigation for TKA increased implant accuracy. Clin Orthop Relat Res, Vol.460, (July 2007), pp.178–84, ISSN 1528-1132
8. Bäthis H, Perlick L, Tingart M, Lüring C, Zurakowski D, Grifka J. (2004). Alignment in total knee arthroplasty. A comparison of computer-assisted surgery with the conventional technique. J Bone Joint Surg Br, Vol.86, No.5, (July 2004), pp.682-7, ISSN:0301-620X
9. Stöckl B, Nogler M, Rosiek R, Fischer M, Krismer M, Kessler O. (2004). Navigation improved accuracy of rotational alignment in total knee arthroplasty. Clin Orthop Relat Res, Vol.426, (September 2004), pp.180–6, ISSN 1528-1132
10. Chauhan SK, Clark GW, Lioyd S, Scott RG, Breidahl W, Sikorski JM. (2004). Computer assisted total knee replacement. A controlled cadaver study using multi-parametrer quantitative CT assessment of alignment (the Perth CT protocol). J Bone Joint Surgery Br, Vol.86, No.6, (August 2004), pp.818-23, ISSN:0301-620X
11. Austin, MD Elie Ghanem, MD Ashish Joshi, MD Rachel Trappler, BS Javad Parvizi, MD, FRCS William J. Hozack, MD. (2008). The Assessment of Intraoperative Prosthetic Knee Range of Motion Using Two Methods. J Arthroplasty. Vol.23, No.4, (June 2008), pp.515-21, ISSN:0883-5403
12. Kalairajah Y, Simpson D, Cossey AJ, Verrall GM, Spriggins AJ. (2006). Are systemic emboli reduced in computer-assisted knee surgery? A prospective, randomized, clinical trial. J Bone Joint Surg Br,Vol.88, No.2, (February 2006), pp.198-202, ISSN:0301-620X
13. Choong PF, Dowsey MM, Stoney JD. (2009). Does accurate anatomical alignment result in better function and quality of life? Comparing conventional and computer-assisted total knee arthroplasty. J Arthroplasty, Vol.24, No.4, (June 2009), pp.560-569, ISSN:0883-5403
14. Wysocki WR, Sheinkop B, Virkus WW, Della Valle CJ. (2008). Femoral fracture through a previous pin site after computer-assisted total knee arthroplasty. J Arthroplasty, Vol.23, No.3, (April 2008), pp.462-5, ISSN:0883-5403
15. Chi-Huan L, Tain-Hsiung C, Yu-Ping S, Po-Chou S, Kung-Sheng L, Wei-Ming C. (2008). Periprosthetic femoral supracondylar fracture after total knee arthroplasty with navigation system. J Arthroplasty, Vol.23, No.2, (February 2008), pp.304-7, ISSN:0883-5403
16. Solver JM, Anna N, Tosteson A, Bozic KJ, Rubash HE, Malchau H. (2008). Impact of the hospital valume on economic value of the computer navigation for total knee replacement. J Bone Joint Surg Am, Vol.90, No.7, (July 2008), pp.1492-500, ISSN 1535- 1386

Fig 1. Computer monitor with navigation software and camera unit

Fig 2. Fixation of femoral and tibial arrays with three reflactive spheres each with help of two 3 mm schanz screw within the surgical wound

Fig 3. Kinematic referencing of center of femoral head

Fig 4. Dynamic assessment of deformity

Fig 5. Navigation of distal femur cutting block

Fig 6. Verification of distal femoral cut

Fig7. Extramedullary tibial cutting guide can be set with navigation and also can be checked clinically.

Fig8. Verification of tibial cut.

Fig9. Checking final alignment with trials.