Despite improved precision of component placement and consistent and accurate restoration of neutral limb alignment, controversy persists regarding the clinical benefits of computer-assisted total knee arthroplasty (TKA). Computer-assisted TKA provides excellent information regarding gap equality and symmetry throughout the knee range of motion and allows precise, quantitative soft tissue release for deformities, especially in knees with severe flexion contractures and severe rigid valgus deformities. Hence accurate restoration of gap balance, joint line, and posterior femoral offset consequently improves functional results. Knee arthritis with complex extra-articular deformities and in situ hardware can be tackled appropriately using computer navigation where conventional techniques may be inadequate. It also allows intra-articular correction for extra-articular deformities due to malunions and facilitates extra-articular correction in cases with severe extra-articular tibial deformities. In obese patients, where the alignment of the limb is difficult to assess, computer navigation improves accuracy and reduces the number of outliers. The ability to quantify the precise amount of bone cuts and soft tissue releases needed to equalize gaps and restore alignment, reduced blood loss, and incidence of systemic emboli improves the safety of the procedure and hastens functional recovery of the patient. Hence, computer-assisted TKA not only provides greater precision, but also greater clinical benefit.
Computer-assisted total knee arthroplasty (TKA) systems were developed to improve the accuracy of limb alignment and component position. Numerous studies have reported improved precision of component placement, consistent and accurate restoration of neutral limb alignment, and decrease in the number of outliers with computer-assisted TKAs when compared to conventional TKAs.1-3 However, many have argued that although computer navigation may improve accuracy, it does not translate to better clinical outcomes.
A recent study by Choong et al1 reported improved function and better quality of life after computer-assisted TKA when compared to conventional TKA. Apart from accurate restoration of alignment, computer navigation also helps to precisely restore the joint line and posterior femoral offset and to accurately balance flexion and extension gaps, all of which have a direct effect on the overall function of the knee postoperatively.
Accurate Gap Balancing
Accurate restoration of limb alignment and adequate soft tissue and gap balancing during TKA have been well documented to be of great importance to obtain a symptom-free, stable, and fully mobile joint postoperatively.4-6 Gap asymmetry may occur following inadequate or improper soft tissue release, inaccurate bone cuts, incorrect femoral rotation or sizing, and incorrect tibial slope.6 This may consequently result in knee instability, poor joint range of motion (ROM), and abnormal patellofemoral tracking.6 Hence, gap symmetry in both flexion and extension, joint line position, and posterior femoral offset needs to be fairly accurate for the joint to function optimally postoperatively. All of these parameters are interrelated, and the surgeon must ensure accuracy and precision while performing each stage of the procedure.
In our experience, computer-assisted TKA provides excellent information regarding gap equality and symmetry throughout the knee ROM and regarding how to titrate the soft tissue releases. We have quantified the release and the effect it has on flexion/extension gaps, and this allows precise release for deformities.7 In our prospective study of 118 TKAs, the joint line was seen to be restored accurately following computer-assisted TKA (preoperative joint line=15.2±3.4 mm; postoperative joint line=15.2±2.8 mm; P<.0001; r=0.5). The posterior femoral offset was also found to be accurately restored postoperatively (preoperative offset=30.7±4.1 mm; postoperative offset=30.2±3.5 mm; P<.001; r=0.32). Similarly, during lateral epicondylar osteotomy for severe, rigid valgus knees, computer navigation allowed us to accurately measure the lateral-medial gap asymmetry and measure the exact amount of distance the lateral epicondyle needs to be displaced distally to create equal, symmetrical rectangular gaps (Figure 1).
Complex Deformity Correction
The use of conventional intramedullary instrumentation is difficult in the presence of hardware, a deformed femoral or tibial canal, and canal sclerosis.8 Computer navigation overcomes these shortcomings by aligning the component based on the mechanical axis derived from the femoral head center, knee center, and center of the ankle and bypassing the deformity or hardware (Figure 2). It allows intra-articular correction of extra-articular deformities and perfect restoration of alignment by precisely quantifying the amount of soft tissue release required. In cases with severe extra-articular deformities, such as a 20° varus angulation in the upper tibia, computer-assisted TKA facilitates extra-articular correction and helps avoid massive intra-articular soft tissue releases (Figure 3). Following a minimal release, a tibial cut is performed in 10° of varus accurately and a wedge of 10° is removed extra-articularly, resulting in perfect correction of the deformity. In cases with complex bilateral deformities, accurate restoration of alignment can be achieved with decreased patient morbidity.
Obese patients are another challenging subgroup undergoing TKA. Berend et al9 reported a high incidence of revision when body mass index (BMI) was >33, the tibial component had been placed in >3° of varus, and the final limb alignment was in varus. Computer navigation helps to accurately estimate the center of the femoral head and the overall limb and component alignment (Figure 4). Choong et al,1 in their prospective study of patients with BMI >30, reported that compared to 93% in the navigated group, only 56% of knees had a final mechanical axis aligned within 3° of neutral in the conventional group. In our series of 236 computer-assisted TKAs in patients with BMIs >30, 94.1% of the knees had a final mechanical axis aligned within 3° of neutral (5.9% outliers).
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Figure 4: Typical example of an obese patient in whom it is difficult to clinically judge the overall alignment of the limb (A). Postoperative standing hip-to-ankle full-length radiograph of the same patient showing complete restoration of limb alignment (B).
The safety of TKA with regard to the incidence of embolism and postoperative morbidity and mortality has been a major concern, especially when simultaneous bilateral TKA needs to performed. Studies have shown that the incidence of systemic emboli detected intraoperatively by transesophageal and transcranial Doppler is significantly less during computer-assisted TKA compared to conventional TKA.10,11 Similarly, the amount of blood loss has also been reported to be significantly less with computer-assisted TKA compared to conventional TKA.12,13 This could be due to the avoidance of entering the femoral canal and limiting the amount of bone resection and soft tissue release during computer-assisted TKA. Dutton et al,14 in their series of 108 minimally invasive computer-assisted TKAs, reported no complications.
Early Functional Recovery
With an increasing number of TKAs done each year, the current stress is on early functional recovery and reducing the length of the hospital stay to reduce the overall cost of the procedure. Choong et al1 reported that knees with alignment within 3° of neutral have better functional outcomes compared to the outliers. The improved accuracy in limb alignment and soft tissue balance obtained with computer-assisted TKA helps in early rehabilitation and better functional outcome. Choong et al (written communication) also observed a shorter length of hospital stay (by approximately 2 days) in TKAs with alignment within 3° of neutral compared to those >3°. Dutton et al,14 in a prospective randomized study comparing minimally invasive computer-assisted TKA with standard conventional TKA, reported significantly shorter inpatient stays and better functional outcomes with minimally invasive computer-assisted TKA. In our experience, this has been observed even in patients undergoing bilateral simultaneous TKAs. Early functional milestones and pain scores at the time of discharge (mean, 5.1 days) were comparable to unilateral TKAs (mean, 4.4 days).
The benefits of computer-assisted TKA are precise alignment and good soft tissue balancing throughout the knee ROM, consequently improving functional results. Knee arthritis with complex extra-articular deformities, hardware, and obesity can be tackled appropriately. The ability to quantify the precise amount of bone cuts and soft tissue releases needed to equalize gaps and restore alignment, reduced blood loss, and incidence of systemic emboli improves the safety of the procedure and hastens functional recovery of the patient. Therefore, computer-assisted TKA not only provides greater precision, but also greater clinical benefit.
- Choong PF, Dowsey MM, Stoney JD. Does accurate anatomical alignment result in better function and quality of life? Comparing conventional and computer-assisted total knee arthroplasty. J Arthroplasty. 2009; 24(4):560-569.
- Mullaji A, Kanna R, Marawar S, Kohli A, Sharma A. Comparison of limb and component alignment using computer-assisted navigation versus image intensifier-guided conventional total knee arthroplasty: a prospective, randomized, single-surgeon study of 467 knees. J Arthroplasty. 2007; 22(7):953-959.
- Rosenberger RE, Hoser C, Quirbach S, Attal R, Hennerbichler A, Fink C. Improved accuracy of component alignment with the implementation of image-free navigation in total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc. 2008; 16(3):249-257.
- Fehring TK. Rotational malalignment of the femoral component in total knee arthroplasty. Clin Orthop Relat Res. 2000; (380):72-79.
- Griffin FM, Insall JN, Scuderi GR. Accuracy of soft tissue balancing in total knee arthroplasty. J Arthroplasty. 2000; 15(8):970-973.
- Gorab RS, Barnett SL. Ligamentous balancing in primary total knee replacement. Curr Opin Orthop. 2002; 13(1):14-22.
- Mullaji A, Sharma A, Marawar S, Kanna R. Quantification of effect of sequential posteromedial release on flexion and extension gaps: a computer-assisted study in cadaveric knees using 2 different types of distractors. J Arthroplasty. In press.
- Fehring TK, Mason JB, Moskal J, Pollock DC, Mann J, Williams VJ. When computer-assisted knee replacement is the best alternative. Clin Orthop Relat Res. 2006; (452):132-136.
- Berend ME, Ritter MA, Meding JB, et al. Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res. 2004; (428):26-34.
- Kalairajah Y, Cossey AJ, Verrall GM, Ludbrook G, Spriggins AJ. Are systemic emboli reduced in computer-assisted knee surgery?: A prospective, randomised, clinical trial. J Bone Joint Surg Br. 2006; 88(2):198-202.
- Church JS, Scadden JE, Gupta RR, Cokis C, Williams KA, Janes GC. Embolic phenomena during computer-assisted and conventional total knee replacement. J Bone Joint Surg Br. 2007; 89(4):481-485.
- Kalairajah Y, Simpson D, Cossey AJ, Verrall GM, Spriggins AJ. Blood loss after total knee replacement: effects of computer-assisted surgery. J Bone Joint Surg Br. 2005; 87(11):1480-1482.
- Chauhan SK, Scott RG, Breidahl W, Beaver RJ. Computer-assisted knee arthroplasty versus a conventional jig-based technique. A randomised, prospective trial. J Bone Joint Surg Br. 2004; 86(3):372-377.
- Dutton AQ, Yeo SJ, Yang KY, Lo NN, Chia KU, Chong HC. Computer-assisted minimally invasive total knee arthroplasty compared with standard total knee arthroplasty. A prospective, randomized study. J Bone Joint Surg Am. 2008; 90(1):2-9.
Drs Mullaji and Shetty are from the Department of Orthopedic Surgery, Breach Candy Hospital, Mumbai, India.
Drs Mullaji and Shetty have no relevant financial relationships to disclose.
Presented at Current Concepts in Joint Replacement 2008 Winter Meeting; December 10-13, 2008; Orlando, Florida.
Orthopaedic Crossfire is a registered trademark of A. Seth Greenwald, DPhil(Oxon).
Correspondence should be addressed to: Arun Mullaji, FRCS(Ed), MCh(Orth), MS(Orth), The Arthritis Clinic, 101, Cornelian, Kemps Corner, Cumballa Hill, Mumbai 400036, India.