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Intraoperative Measurements of Joint Line Changes Using Computer Navigation Do Not Correlate With Postoperative Radiographic Measurements in Total Knee Arthroplasty
The Journal of Arthroplasty xxx (2016) 1e5
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Original Article
Intraoperative Measurements of Joint Line Changes Using Computer Navigation Do Not Correlate With Postoperative Radiographic Measurements in Total Knee Arthroplasty Graham Seow-Hng Goh, MBBS a, Hamid Rahmatullah Bin Abd Razak, MBBS, MRCS (Glasg), DipSpMed (IOC) a, *, Joshua Yuan-Wang Tan, MBBS b, Seng-Jin Yeo, MBBS, FRCS (Edin), FAMS a a b
Department of Orthopaedic Surgery, Singapore General Hospital, Singapore, Singapore Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
a r t i c l e i n f o
a b s t r a c t
Article history: Received 10 February 2016 Received in revised form 8 June 2016 Accepted 9 June 2016 Available online xxx
Background: The adverse effects of joint line (JL) changes on kinematics and outcomes of total knee arthroplasty (TKA) have been studied. Some authors have quantified JL changes using intraoperative data from computer navigation, despite no studies validating these measurements to date. We designed a prospective study to determine whether intraoperative measurements of JL changes using computer navigation correlate with measurements obtained on weight-bearing radiographs postoperatively. Methods: A total of 195 consecutive patients (195 knees) underwent computer-navigated cruciateretaining TKA by the senior author. Twenty-four patients had missing radiographic data and were excluded from the study. The final JL change was calculated intraoperatively from the verified bony cuts and planned JL change as determined by the computer. JL position was also measured on preoperative and postoperative radiographs using an anteroposterior method. Results: One hundred seventy-one knees were evaluated. Using computer-navigated and radiographic measurements, the mean JL change was 1.95 ± 1.5 mm (0-8.0 mm) and 4.05 ± 2.9 mm (0-17.3 mm), respectively. One hundred fourteen (67%) vs 129 (75%) had JL elevation, 44 (26%) vs 30 (18%) had JL depression, and 13 (7%) vs 12 (7%) had no JL change, respectively. Inter-rater and intrarater reliability of radiographic measurements was excellent. We found a poor correlation between computer-navigated and radiographic measurements (r ¼ 0.303). Conclusion: There is a poor correlation between computer-aided and radiographic measurements of JL changes post-TKA. Elevation/depression of the JL needs to be considered in patients who remain symptomatic despite TKA, although the optimal method of assessment remains uncertain. © 2016 Elsevier Inc. All rights reserved.
Keywords: total knee arthroplasty CAS computer navigation joint line elevation radiograph
The success of total knee arthroplasty (TKA) hinges upon the restoration of the mechanical axis, joint line (JL), balanced flexion/ extension gaps, balanced soft tissues, and restoration of patellofemoral alignment [1]. Gap balancing affects the final knee kinematics [2], and suboptimal soft tissue balancing can lead to accelerated polyethylene wear.
No author associated with this paper has disclosed any potential or pertinent conflicts which may be perceived to have impending conflict with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2016.06.018. * Reprint requests: Hamid Rahmatullah Bin Abd Razak, MBBS, MRCS (Glasg), DipSpMed (IOC), Department of Orthopaedic Surgery, Singapore General Hospital, 20 College Road, Academia Level 4, 169865, Singapore. http://dx.doi.org/10.1016/j.arth.2016.06.018 0883-5403/© 2016 Elsevier Inc. All rights reserved.
JL changes with respect to the attachments of the collateral ligaments can result in instability, decreased range of motion, patella maltracking, and an increased incidence of anterior knee pain [3,4]. JL malposition may also result in instability and an increased incidence of anterior knee pain, accounting for a decrease in joint flexion [4]. Martin and Whiteside [5] demonstrated that a proximal displacement of the JL as little as 5 mm could result in midflexion instability. Restoration of the JL is therefore essential. Before the evolution of computer-navigated TKA, there have been no reliable methods to evaluate changes in JL intraoperatively. Moreover, the control of the JL is difficult intraoperatively as the only useful reference point is the transepicondylar axis of the femur [6]. As such, JL measurements have traditionally been taken using
2
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radiographic measurements preoperatively and postoperatively. Numerous studies have evaluated the effect of JL changes in posterior cruciate-retaining mobile-bearing TKA [7] and in revision TKA [8], most of which are based on measurements using preoperative and postoperative anteroposterior (AP) [9-12] or lateral view [4,13] radiographs. At present, computer-assisted surgery (CAS) has been proven as a useful tool to improve accuracy in alignment and implant positioning in TKA [14] and can provide quantitative data to balance the JL both in flexion and in extension [15]. Few authors have quantified JL changes using the intraoperative data collected during CAS [16-19]. However, there are no studies comparing the JL changes measured during computer navigation with those measured on weight-bearing radiographs to date. We therefore designed a prospective study of patients undergoing a computer-navigated TKA to determine whether the intraoperative measurements using computer navigation correlate with preoperative and postoperative measurements obtained on weight-bearing radiographs. With the increased precision offered by computer navigation, we hypothesized that JL measurements acquired from computer navigation are as accurate as radiographic measurements and are therefore a reliable tool to assess JL changes intraoperatively. Materials and Methods Study Design Between October 2007 and May 2010, 195 consecutive patients (195 knees) underwent CAS TKA by a single surgeon. Patients were included in this prospective study after approval was sought for our study protocol from our institutional review board. The inclusion criterion was primary osteoarthritis of the knee requiring primary unilateral TKA after a failed trial of conservative treatment. Exclusion criteria included patients with rheumatoid arthritis, previous knee surgery, infection, and those who could not be treated with unconstrained TKA and a short stem tibial implant. Of the 195 patients, 24 had missing radiographic data and were excluded from the study. Hence, 171 knees were available for this study. Operative Technique All operations were performed by the senior author using the same surgical technique over the duration of this study. A cobalt-chrome cruciate-retaining femoral component and an all-polyethylene fixed-bearing tibial prosthesis (PFC; Depuy Orthopaedic International, Leeds, UK) were used in each patient. All patellae were resurfaced. The software used for the CAS was Ci Mi TKR version 2.0 by BrainLab/Depuy Orthopaedic Inc (Johnson and Johnson, Leeds, UK). Anatomic landmarks were registered through the use of dual 3-mm unicortical pins drilled into the femur and tibia at a distance from the surgical approach, and a pointer with passive infrared reflectors. The tibial cut was made first. This was followed by bone morphing of the femur and ligament balancing. The Tensor Sensor from Depuy was used to deliver a constant pressure of 23 N/cm2 to both medial and lateral compartments simultaneously [20]. Soft tissue releases were made to achieve a rectangular gap at 0 extension and the space between the distal femur and proximal tibia was stored. Subsequently, the knee was brought to 90 flexion and the space between the posterior femoral condyles and proximal tibia recorded. The size and the position of the femoral component were adjusted on a virtual computer model to achieve equal flexion and extension gaps and the planned polyethylene thickness was recorded. The planned femoral component was then rotated to achieve a rectangular flexion space
at 90 flexion. Following this, the navigated anterior and distal femoral bone cuts were made to within 1 mm as planned. The femoral chamfer cuts and tibial preparation were completed, and this was followed by a trial of the tibial and femoral components with a tibial insert. Further soft tissue releases were made if necessary to obtain rectangular and equal flexion and extension gaps. Subsequently, the appropriately sized tibial and femoral components were implanted with cement, and the final flexion and extension gaps were recorded. Measurement of Joint Line Changes Using Computer Navigation After the femoral modeling, the computer automatically generated the amount of bony resection, size of femoral component, and the thickness of the tibial insert, to create rectangular gaps. The amount of JL shift was also demonstrated. The bony resections were performed as planned, and the amount of resection was confirmed by the plane verifier. For the calculation of the JL level at the tibia, the thickness of the polyethylene insert was considered. This was the distance between the deepest point of the polyethylene insert and its base. After prosthesis component implantation, the tibial JL level was assumed as the highest tibial prosthesis compartment between the medial and lateral tibial plateaus. Tibial JL variation was assumed as the difference between after and before prosthesis component implantation. The femoral JL level was also analyzed similarly. The femoral JL level before prosthesis implantation was assumed to be the maximum between the medial and lateral femoral resections. Femoral JL level variation was the difference in the JL between before and after prosthesis component implantation. The total thickness of the resected segments was assumed to be the maximum value between the 2 sums on the medial (medial tibial and femoral resections) and lateral (lateral tibial and femoral resections) compartments. Similarly, the overall thickness of the implanted prosthesis was assumed to be the maximum value between the 2 sums on the medial (medial tibial and femoral prostheses) and lateral (lateral tibial and femoral prostheses) compartments. The change in the JL position was determined by the difference in the 2 thicknesses [19]. All values were calculated by the navigation system using digitized point clouds. Measurement of Joint Line Changes Using Radiographs Standardized coronal hip-to-ankle radiographs were taken with the patient standing and the knee in full extension on a 5-cm riser to visualize the ankle joint. Both lateral malleoli were placed 20 cm apart with the toes pointing forward. The patella was placed in the direction of the X-ray source as a rotation guide, with its anterior surface perpendicular to the X-ray source. We acknowledged the need to reproduce accurate and consistent X-rays for assessment. Radiographs were repeated if malrotation was detected. Malrotation was defined as follows: (1) asymmetry of the distal medial and lateral femoral condyles or (2) unequal medial and lateral joint spaces in the ankle joint. They were done preoperatively and at 6 weeks postoperatively. The JL positions were measured on AP radiographs using a modification of the Kawamura method as described by Lee et al [21]. The JL was defined as the line through the distal aspect of the lateral femoral condyle, whereas the JL position was defined as the distance from the proximal tip of the fibular head to the JL in the weight-bearing AP radiograph (Figs. 1 and 2). The reliability of measurements was assessed by intraobserver and interobserver variability. Measurements were made independently twice with an interval of 1 week by 2 authors on preoperative and postoperative radiographs.
G.S.-H. Goh et al. / The Journal of Arthroplasty xxx (2016) 1e5
3
Fig. 2. Postoperative radiograph showing the measurement of the joint line change. Fig. 1. Preoperative radiograph showing the measurement of the joint line change. A line was first drawn to identify the tibial mechanical axis. The line perpendicular to the tibial mechanical axis and on the tip of the fibula head is line A. The line parallel to the line A on the lateral femoral condyle is joint line B. The amount of the joint line change is the distance between line A and line B.
Statistical Analysis Interobserver and intraobserver reliability for radiographic measurements was measured using 1-way random single-measure intraclass correlation coefficients (ICCs) with associated 95% confidence intervals (CI) to gauge the precision of the ICCs. Recommendations from Landis and Koch [22]stated that an ICC value of more than 0.8 is considered excellent; 0.6-0.8 is good; 0.4-0.6 is moderate, and <0.4 is considered bad correlation. Pearson correlation was used to demonstrate any significant difference between CAS measurements and radiographic measurement methods. We defined statistical significance at the 5% (P .05) level. Statistical analysis was carried out with SPSS software version 20.0 (SPSS Inc, Chicago, IL). A power analysis was conducted prior to the study to determine the sample size needed. Considering the probability of a type I error (a) to be 0.05 and correlation coefficient (r) of 0.5, a sample size of 27 patients was needed to achieve a power of 80%. This confirmed that our study was more than adequately powered to test our hypothesis. Results For analysis, all 171 patients followed through all evaluations of the JL. A single cruciate-retaining implant was performed in all patients. The patient demographics are summarized in Table 1. Using CAS measurements, the mean JL change of all the 171 patients (171 knees) was 1.95 ± 1.5 mm (range, 0-8.0 mm), with 114 cases (67%) having a JL elevation and 44 cases (26%) having a JL
depression. The mean elevation was 2.33 ± 1.5 mm whereas the mean depression was 1.56 ± 1.1 mm. In the cohort, 13 cases (7%) had no change in JL. JL elevation was assigned a positive value and depression a negative value. The mean JL changes were calculated based on absolute values. Using radiographic measurements, the mean JL change was 4.05 ± 2.9 mm (range, 0-17.3 mm), with 129 cases (75%) having a JL elevation and 30 cases (18%) having a JL depression. The mean elevation was 4.81 ± 2.9 mm whereas the mean depression was 2.11 ± 1.9 mm. In the cohort, 12 cases (7%) had no change in JL. The ICC for intraobserver and interobserver reliability was 0.91 (95% CI, 0.91-0.92) and 0.87 (95% CI, 0.86-0.90). Intraobserver and interobserver reliability of radiographic measurements showed excellent correlation with ICC values of more than 0.8. The mean JL change for the first 50 cases measured was 3.80 ± 2.4 mm, and the mean JL change for the last 50 cases measured was 3.44 ± 2.4 mm. There was no significant difference between the measurements for the first 50 cases and the last 50 cases (P ¼ .468), indicating that
Table 1 Patient Demographics (n ¼ 171). Mean age (y; range) Gender (%) Female Male Body mass index (kg/m2 ± SD) Mean preoperative flexion range of motion (degrees ± SD) Mean preoperative flexion contracture (degrees ± SD) Mechanical axis (degrees ± SD) Mean preoperative knee score ± SD Mean preoperative function score ± SD Mean preoperative Oxford knee score ± SD Mean SF-36 physical component score ± SD Mean SF-36 mental component core ± SD SD, standard deviation.
66.4 (50-90) 134 (78) 37 (22) 28.4 ± 3.6 118 ± 19.3 7 ± 7.3 4.7 ± 6.2 varus 36.8 ± 19.8 55.0 ± 18.1 34.4 ± 8.0 33.7 ± 10.9 52.1 ± 10.1
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Fig. 3. Scatterplot of computer-assisted surgery (CAS) measurements against radiographic measurements of joint line changes. Joint line elevation was assigned a positive value and depression a negative value.
there was no “learning curve” effect confounding the results of the radiographic measurements. We analyzed a total of 171 patients (171 knees) and found a significant linear correlation (P < .001) between changes in JL measured using CAS and radiographs, with a correlation coefficient (r) of 0.303 as illustrated in Figure 3. Our results demonstrate a poor correlation between the JL changes measured using radiographs and computer navigation.
Discussion The adverse effects of JL changes on knee kinematics and clinical outcomes of TKA have been extensively studied. JL elevation results in an inferior shift of the contact point between the patella and femur, with patellofemoral contact forces increasing by 3% per millimeter of displacement [23], often with clinical consequences of anterior knee pain and decreased flexion [24]. Similarly, JL depression may increase patella strain, increasing the risk of subluxation and accelerated wear [25]. These abnormalities of the patellofemoral joint may account for up to 50% of all TKA-related complications [26]. CAS has been shown to be beneficial in determining crucial landmarks including component positioning and mechanical axis [27]. In a meta-analysis of 29 studies comparing CAS to conventional techniques, Mason et al [28] demonstrated significantly improved accuracy in mechanical axis and tibial/femoral alignment. The mean JL change in our study was 1.95 mm, and this correlated well with other studies using navigation systems as a measuring tool [16-19]. Ee et al [16] calculated a mean JL shift of 1.63 mm after CAS TKA, whereas other studies by Yang et al [17] and Ensini et al [19] reported a mean JL change of 1.93 mm and 1.9 mm, respectively. Bin Abd Razak et al [18] compared cruciate-retaining with cruciate-substituting implant design and reported mean JL changes of 1.7 and 2.34 mm, respectively, using the same navigation system as was used in our study. Using a modification of the Kawamura method, the radiographic measurements, the mean JL change measured on AP radiographs was 4.05 ± 2.9 mm. The study by Lee et al [21] using the same radiographic technique found the mean JL change to be 2.8 ± 0.9 mm, whereas other studies using the
Kawamura method reported mean JL changes of 4.0 mm [10] and 3.5 mm [11] using cruciate-retaining implants. The accuracy of calibration of anatomic landmarks using CAS as a measuring tool has been reported to be within 0.5 mm [29]; however, systematic error due to inappropriate selection of landmarks intraoperatively cannot be excluded. We acknowledge that JL calculations are based on registration by the surgeon; hence, if these points were placed inaccurately, JL calculation would be affected. This can be a potential problem in inexperienced CAS users. However, the senior surgeon involved in this study has independently performed more than 800 CAS knee arthroplasties, and we believe that any outliers in the data presented were not due to errors in the CAS technique. Additionally, any errors in the CAS technique were minimized through the acquisition of a large number of points during the registration phase. This was achieved through acquiring multiple landmarks across a bony surface as well as single landmarks on the bone. A verification step was performed in all cases, wherein the surgeon checks on the CAS screens if the area shown on the screen correctly corresponds to the actual area on the bone. Secondly, a pointer was also run along the bone to check whether the area shown on the screen correctly corresponds to the actual area on the bone. Another potential source of inaccuracy arises when the knee deformity is addressed with oblique bone resection and soft tissue release to obtain balanced ligaments with equal flexion and extension gaps. These surgical steps can lead to JL changes when the thickness of removed femoral or tibial bone and amount of soft tissue released are not accurately considered and replaced by implants of the same height. Also, the calculation of the 3-dimensional shape of the bone in knee osteoarthritis is based on geometric models implemented within the navigation software, and this remains to be a potential source of error [29]. Although the introduction and development of CAS has allowed quantitative measurement of intraoperative JL changes as opposed to conventional surgery, our study found a poor correlation between CAS measurements and radiographic measurements performed by the same observer preoperatively and postoperatively on well-positioned radiographs using a single measurement method, with a mean difference amounting to 2.10 mm. This mean difference, however, is small and may still lie within a margin of clinical acceptability. We also noted that CAS measurements had a smaller standard deviation and range of values compared to radiographic measurements, therefore suggesting that CAS has greater precision in measuring JL changes. However, greater precision does not equate to greater accuracy, and there remains no consensus on the best method for calculating JL changes, although radiographic evaluation has been extensively used in the literature [4,9-13]. The validity of CT in measuring JL changes has not been described to date, suggesting that a direct comparison of the preoperative and postoperative plain radiographs is sufficient for assessment [30]. Several limitations were acknowledged in our study. Firstly, only 1 navigation system was used in our study. However, given that most available navigation systems used similar concepts to determine alignments and implant size, the results of our present study may be applicable across navigation systems. Secondly, the methods of radiographic measurement in this study may have biases. However, as these methods were applied to both preoperative and postoperative radiographs in a similar fashion, the results of our study are still meaningful as we are essentially evaluating the change in JL position. We also found no significant difference between the radiographic measurements of JL changes for the first 50 cases and the last 50 cases, indicating that there was no “learning curve” effect confounding the results of the radiographic measurements. Although the mean difference between the radiographic and computer navigation measurements was 2.10 mm, our
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study still found a poor correlation that warrants further evaluation. The strengths of our study are that it is a single-surgeon series, thus minimizing confounding factors in surgical technique that could increase the variability of JL position. We also used a single implant in this study, eliminating the confounding effect that different implants of various shapes would have on our analysis. In conclusion, our study shows that while CAS does have its benefits of improved accuracy in mechanical axis and tibial/femoral component positioning, the JL measurements obtained by CAS intraoperatively correlate poorly with radiographic measurements, and the optimal method of assessment remains uncertain. Although there is currently no gold standard for JL measurement postoperatively, JL elevation/depression will need to be considered in patients who remain symptomatic despite TKA. Clinicians will still have to rely on history taking, physical examination, good quality radiographs, and additional imaging to assess any clinical symptoms that may be related to an alteration in the JL in patients after TKA. References 1. Freeman MA, Todd RC, Bamert P, et al. ICLH arthroplasty of the knee: 1968e1977. J Bone Joint Surg Br 1978;60-B(3):339. 2. Insall JN, Easley ME. Surgical techniques and instrumentation in total knee arthroplasty. In: Insall JN, editor. Surgery of the knee. 3rd ed. Philadelphia (PA): Churchill Livingston; 2001. p. 1553e7. 3. Crottet D, Kowal J, Sarfert SA, et al. Ligament balancing in TKA: evaluation of a force-sensing device and the influence of patellar eversion and ligament release. J Biomech 2007;40(8):1709. 4. Figgie III HE, Goldberg VM, Heiple KG, et al. The influence of tibial patellofemoral location on function of the knee in patients with the posterior stabilized knee prosthesis. J Bone Joint Surg Am 1986;68A:1035. 5. Martin JW, Whiteside LA. The influence of joint line position on knee stability after condylar knee arthroplasty. Clin Orthop Relat Res 1990;259:146. 6. Mountney J, Karamfiles R, Breidahl W, et al. The position of the joint line in relation to the trans-epicondylar axis of the knee: complementary radiologic and computer-based studies. J Arthroplasty 2007;22:1201. 7. Selvarajah E, Hooper G. Restoration of the joint line in total knee arthroplasty. J Arthroplasty 2009;24(7):1099. 8. Hofmann AA, Kurtin SM, Lyons S, et al. Clinical and radiographical analysis of accurate restoration of the joint line in revision total knee arthroplasty. J Arthroplasty 2006;21:1154. 9. Ritter MA, Montgomery TJ, Zhou H, et al. The clinical significance of proximal tibial resection level in total knee arthroplasty. Clin Orthop Relat Res 1999;360:174. 10. Snider MG, Macdonald SJ. The influence of the posterior cruciate ligament and component design on joint line position after primary total knee arthroplasty. J Arthroplasty 2009;24:1093.
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11. Kawamura H, Bourne RB. Factors affecting range of flexion after total knee arthroplasty. J Orthop Sci 2001;6:248. 12. Jawhar A, Shah V, Sohoni S, et al. Joint line changes after primary total knee arthroplasty: navigated versus non-navigated. Knee Surg Sports Traumatol Arthrosc 2013;21:2355. 13. Cope MR, O'Brien BS, Nanu AM. The influence of the posterior cruciate ligament in the maintenance of joint line in primary total knee arthroplasty: a radiologic study. J Arthroplasty 2002;17:206. 14. Bauwens K, Matthes G, Wich M, et al. Navigated total knee replacement. A meta-analysis. J Bone Joint Surg Am 2007;89(2):261. 15. Matsumoto T, Muratsu H, Tsumura N, et al. Soft tissue balance measurement in posterior-stabilized total knee arthroplasty with a navigation system. J Arthroplasty 2009;24(3):358. 16. Ee G, Pang HN, Chong HC, et al. Computer navigation is a useful intra-operative tool for joint line measurement in total knee arthroplasty. Knee 2013;20:256. 17. Yang JH, Seo JG, Moon YW, et al. Joint line changes after navigation-assisted mobile-bearing TKA. Orthopedics 2009;32:35. 18. Bin Abd Razak HR, Pang HN, Yeo SJ, et al. Joint line changes in cruciate-retaining versus posterior-stabilized computer-navigated total knee arthroplasty. Arch Orthop Trauma Surg 2013;133:853. 19. Ensini A, Catani F, Biasca N, et al. Joint line is well restored when navigation surgery is performed for total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2012;20:495. 20. Wasielewski RC, Galat DD, Komistek RD. Correlation of compartment pressure data from an intraoperative sensing device with postoperative fluoroscopic kinematic results in TKA patients. J Biomech 2005;38:333. 21. Lee HJ, Lee JS, Jung HJ, et al. Comparison of joint line position changes after primary bilateral total knee arthroplasty performed using the navigationassisted measured gap resection or gap balancing techniques. Knee Surg Sports Traumatol Arthrosc 2011;19(12):2027. 22. Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977;33(1):159. 23. Singerman R, Davy DT, Goldberg VM. Effects of patella alta and patella infera on patellofemoral contact forces. J Biomech 1994;27:1059. 24. Grelsamer R, Moss G, Ee G, et al. The patellofemoral syndrome; the same problem as the Loch Ness Monster? Knee 2009;16(5):301. 25. Wasielewski RC, Galante JO, Leighty RM, et al. Wear patterns on retrieved polyethylene tibial inserts and their relationship to technical considerations during total knee arthroplasty. Clin Orthop Relat Res 1994;299:31. 26. Goldberg VM, Figgie III HE, Figgie MP. Technical considerations in total knee surgery: management of patella problems. Orthop Clin North Am 1989;20:189. 27. Cheng T, Zhang G, Zhang X. Clinical and radiographic outcomes of image-based computer-assisted total knee arthroplasty: an evidence-based evaluation. Surg Innov 2010;18(1):15. 28. Mason JB, Fehring TK, Estok R, et al. Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty 2007;22(8): 1097. 29. Stockl B, Nogler M, Rosiek R, et al. Navigation improves accuracy of rotational alignment in total knee arthroplasty. Clin Orthop Relat Res 2004;426:180. 30. Sarmah SS, Patel S, Hossain FS, et al. The radiological assessment of total and unicompartmental knee replacements. J Bone Joint Surg Br 2012;94(10): 1321.
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Original Article
Intraoperative Measurements of Joint Line Changes Using Computer Navigation Do Not Correlate With Postoperative Radiographic Measurements in Total Knee Arthroplasty Graham Seow-Hng Goh, MBBS a, Hamid Rahmatullah Bin Abd Razak, MBBS, MRCS (Glasg), DipSpMed (IOC) a, *, Joshua Yuan-Wang Tan, MBBS b, Seng-Jin Yeo, MBBS, FRCS (Edin), FAMS a a b
Department of Orthopaedic Surgery, Singapore General Hospital, Singapore, Singapore Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
a r t i c l e i n f o
a b s t r a c t
Article history: Received 10 February 2016 Received in revised form 8 June 2016 Accepted 9 June 2016 Available online xxx
Background: The adverse effects of joint line (JL) changes on kinematics and outcomes of total knee arthroplasty (TKA) have been studied. Some authors have quantified JL changes using intraoperative data from computer navigation, despite no studies validating these measurements to date. We designed a prospective study to determine whether intraoperative measurements of JL changes using computer navigation correlate with measurements obtained on weight-bearing radiographs postoperatively. Methods: A total of 195 consecutive patients (195 knees) underwent computer-navigated cruciateretaining TKA by the senior author. Twenty-four patients had missing radiographic data and were excluded from the study. The final JL change was calculated intraoperatively from the verified bony cuts and planned JL change as determined by the computer. JL position was also measured on preoperative and postoperative radiographs using an anteroposterior method. Results: One hundred seventy-one knees were evaluated. Using computer-navigated and radiographic measurements, the mean JL change was 1.95 ± 1.5 mm (0-8.0 mm) and 4.05 ± 2.9 mm (0-17.3 mm), respectively. One hundred fourteen (67%) vs 129 (75%) had JL elevation, 44 (26%) vs 30 (18%) had JL depression, and 13 (7%) vs 12 (7%) had no JL change, respectively. Inter-rater and intrarater reliability of radiographic measurements was excellent. We found a poor correlation between computer-navigated and radiographic measurements (r ¼ 0.303). Conclusion: There is a poor correlation between computer-aided and radiographic measurements of JL changes post-TKA. Elevation/depression of the JL needs to be considered in patients who remain symptomatic despite TKA, although the optimal method of assessment remains uncertain. © 2016 Elsevier Inc. All rights reserved.
Keywords: total knee arthroplasty CAS computer navigation joint line elevation radiograph
The success of total knee arthroplasty (TKA) hinges upon the restoration of the mechanical axis, joint line (JL), balanced flexion/ extension gaps, balanced soft tissues, and restoration of patellofemoral alignment [1]. Gap balancing affects the final knee kinematics [2], and suboptimal soft tissue balancing can lead to accelerated polyethylene wear.
No author associated with this paper has disclosed any potential or pertinent conflicts which may be perceived to have impending conflict with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2016.06.018. * Reprint requests: Hamid Rahmatullah Bin Abd Razak, MBBS, MRCS (Glasg), DipSpMed (IOC), Department of Orthopaedic Surgery, Singapore General Hospital, 20 College Road, Academia Level 4, 169865, Singapore. http://dx.doi.org/10.1016/j.arth.2016.06.018 0883-5403/© 2016 Elsevier Inc. All rights reserved.
JL changes with respect to the attachments of the collateral ligaments can result in instability, decreased range of motion, patella maltracking, and an increased incidence of anterior knee pain [3,4]. JL malposition may also result in instability and an increased incidence of anterior knee pain, accounting for a decrease in joint flexion [4]. Martin and Whiteside [5] demonstrated that a proximal displacement of the JL as little as 5 mm could result in midflexion instability. Restoration of the JL is therefore essential. Before the evolution of computer-navigated TKA, there have been no reliable methods to evaluate changes in JL intraoperatively. Moreover, the control of the JL is difficult intraoperatively as the only useful reference point is the transepicondylar axis of the femur [6]. As such, JL measurements have traditionally been taken using
2
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radiographic measurements preoperatively and postoperatively. Numerous studies have evaluated the effect of JL changes in posterior cruciate-retaining mobile-bearing TKA [7] and in revision TKA [8], most of which are based on measurements using preoperative and postoperative anteroposterior (AP) [9-12] or lateral view [4,13] radiographs. At present, computer-assisted surgery (CAS) has been proven as a useful tool to improve accuracy in alignment and implant positioning in TKA [14] and can provide quantitative data to balance the JL both in flexion and in extension [15]. Few authors have quantified JL changes using the intraoperative data collected during CAS [16-19]. However, there are no studies comparing the JL changes measured during computer navigation with those measured on weight-bearing radiographs to date. We therefore designed a prospective study of patients undergoing a computer-navigated TKA to determine whether the intraoperative measurements using computer navigation correlate with preoperative and postoperative measurements obtained on weight-bearing radiographs. With the increased precision offered by computer navigation, we hypothesized that JL measurements acquired from computer navigation are as accurate as radiographic measurements and are therefore a reliable tool to assess JL changes intraoperatively. Materials and Methods Study Design Between October 2007 and May 2010, 195 consecutive patients (195 knees) underwent CAS TKA by a single surgeon. Patients were included in this prospective study after approval was sought for our study protocol from our institutional review board. The inclusion criterion was primary osteoarthritis of the knee requiring primary unilateral TKA after a failed trial of conservative treatment. Exclusion criteria included patients with rheumatoid arthritis, previous knee surgery, infection, and those who could not be treated with unconstrained TKA and a short stem tibial implant. Of the 195 patients, 24 had missing radiographic data and were excluded from the study. Hence, 171 knees were available for this study. Operative Technique All operations were performed by the senior author using the same surgical technique over the duration of this study. A cobalt-chrome cruciate-retaining femoral component and an all-polyethylene fixed-bearing tibial prosthesis (PFC; Depuy Orthopaedic International, Leeds, UK) were used in each patient. All patellae were resurfaced. The software used for the CAS was Ci Mi TKR version 2.0 by BrainLab/Depuy Orthopaedic Inc (Johnson and Johnson, Leeds, UK). Anatomic landmarks were registered through the use of dual 3-mm unicortical pins drilled into the femur and tibia at a distance from the surgical approach, and a pointer with passive infrared reflectors. The tibial cut was made first. This was followed by bone morphing of the femur and ligament balancing. The Tensor Sensor from Depuy was used to deliver a constant pressure of 23 N/cm2 to both medial and lateral compartments simultaneously [20]. Soft tissue releases were made to achieve a rectangular gap at 0 extension and the space between the distal femur and proximal tibia was stored. Subsequently, the knee was brought to 90 flexion and the space between the posterior femoral condyles and proximal tibia recorded. The size and the position of the femoral component were adjusted on a virtual computer model to achieve equal flexion and extension gaps and the planned polyethylene thickness was recorded. The planned femoral component was then rotated to achieve a rectangular flexion space
at 90 flexion. Following this, the navigated anterior and distal femoral bone cuts were made to within 1 mm as planned. The femoral chamfer cuts and tibial preparation were completed, and this was followed by a trial of the tibial and femoral components with a tibial insert. Further soft tissue releases were made if necessary to obtain rectangular and equal flexion and extension gaps. Subsequently, the appropriately sized tibial and femoral components were implanted with cement, and the final flexion and extension gaps were recorded. Measurement of Joint Line Changes Using Computer Navigation After the femoral modeling, the computer automatically generated the amount of bony resection, size of femoral component, and the thickness of the tibial insert, to create rectangular gaps. The amount of JL shift was also demonstrated. The bony resections were performed as planned, and the amount of resection was confirmed by the plane verifier. For the calculation of the JL level at the tibia, the thickness of the polyethylene insert was considered. This was the distance between the deepest point of the polyethylene insert and its base. After prosthesis component implantation, the tibial JL level was assumed as the highest tibial prosthesis compartment between the medial and lateral tibial plateaus. Tibial JL variation was assumed as the difference between after and before prosthesis component implantation. The femoral JL level was also analyzed similarly. The femoral JL level before prosthesis implantation was assumed to be the maximum between the medial and lateral femoral resections. Femoral JL level variation was the difference in the JL between before and after prosthesis component implantation. The total thickness of the resected segments was assumed to be the maximum value between the 2 sums on the medial (medial tibial and femoral resections) and lateral (lateral tibial and femoral resections) compartments. Similarly, the overall thickness of the implanted prosthesis was assumed to be the maximum value between the 2 sums on the medial (medial tibial and femoral prostheses) and lateral (lateral tibial and femoral prostheses) compartments. The change in the JL position was determined by the difference in the 2 thicknesses [19]. All values were calculated by the navigation system using digitized point clouds. Measurement of Joint Line Changes Using Radiographs Standardized coronal hip-to-ankle radiographs were taken with the patient standing and the knee in full extension on a 5-cm riser to visualize the ankle joint. Both lateral malleoli were placed 20 cm apart with the toes pointing forward. The patella was placed in the direction of the X-ray source as a rotation guide, with its anterior surface perpendicular to the X-ray source. We acknowledged the need to reproduce accurate and consistent X-rays for assessment. Radiographs were repeated if malrotation was detected. Malrotation was defined as follows: (1) asymmetry of the distal medial and lateral femoral condyles or (2) unequal medial and lateral joint spaces in the ankle joint. They were done preoperatively and at 6 weeks postoperatively. The JL positions were measured on AP radiographs using a modification of the Kawamura method as described by Lee et al [21]. The JL was defined as the line through the distal aspect of the lateral femoral condyle, whereas the JL position was defined as the distance from the proximal tip of the fibular head to the JL in the weight-bearing AP radiograph (Figs. 1 and 2). The reliability of measurements was assessed by intraobserver and interobserver variability. Measurements were made independently twice with an interval of 1 week by 2 authors on preoperative and postoperative radiographs.
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Fig. 2. Postoperative radiograph showing the measurement of the joint line change. Fig. 1. Preoperative radiograph showing the measurement of the joint line change. A line was first drawn to identify the tibial mechanical axis. The line perpendicular to the tibial mechanical axis and on the tip of the fibula head is line A. The line parallel to the line A on the lateral femoral condyle is joint line B. The amount of the joint line change is the distance between line A and line B.
Statistical Analysis Interobserver and intraobserver reliability for radiographic measurements was measured using 1-way random single-measure intraclass correlation coefficients (ICCs) with associated 95% confidence intervals (CI) to gauge the precision of the ICCs. Recommendations from Landis and Koch [22]stated that an ICC value of more than 0.8 is considered excellent; 0.6-0.8 is good; 0.4-0.6 is moderate, and <0.4 is considered bad correlation. Pearson correlation was used to demonstrate any significant difference between CAS measurements and radiographic measurement methods. We defined statistical significance at the 5% (P .05) level. Statistical analysis was carried out with SPSS software version 20.0 (SPSS Inc, Chicago, IL). A power analysis was conducted prior to the study to determine the sample size needed. Considering the probability of a type I error (a) to be 0.05 and correlation coefficient (r) of 0.5, a sample size of 27 patients was needed to achieve a power of 80%. This confirmed that our study was more than adequately powered to test our hypothesis. Results For analysis, all 171 patients followed through all evaluations of the JL. A single cruciate-retaining implant was performed in all patients. The patient demographics are summarized in Table 1. Using CAS measurements, the mean JL change of all the 171 patients (171 knees) was 1.95 ± 1.5 mm (range, 0-8.0 mm), with 114 cases (67%) having a JL elevation and 44 cases (26%) having a JL
depression. The mean elevation was 2.33 ± 1.5 mm whereas the mean depression was 1.56 ± 1.1 mm. In the cohort, 13 cases (7%) had no change in JL. JL elevation was assigned a positive value and depression a negative value. The mean JL changes were calculated based on absolute values. Using radiographic measurements, the mean JL change was 4.05 ± 2.9 mm (range, 0-17.3 mm), with 129 cases (75%) having a JL elevation and 30 cases (18%) having a JL depression. The mean elevation was 4.81 ± 2.9 mm whereas the mean depression was 2.11 ± 1.9 mm. In the cohort, 12 cases (7%) had no change in JL. The ICC for intraobserver and interobserver reliability was 0.91 (95% CI, 0.91-0.92) and 0.87 (95% CI, 0.86-0.90). Intraobserver and interobserver reliability of radiographic measurements showed excellent correlation with ICC values of more than 0.8. The mean JL change for the first 50 cases measured was 3.80 ± 2.4 mm, and the mean JL change for the last 50 cases measured was 3.44 ± 2.4 mm. There was no significant difference between the measurements for the first 50 cases and the last 50 cases (P ¼ .468), indicating that
Table 1 Patient Demographics (n ¼ 171). Mean age (y; range) Gender (%) Female Male Body mass index (kg/m2 ± SD) Mean preoperative flexion range of motion (degrees ± SD) Mean preoperative flexion contracture (degrees ± SD) Mechanical axis (degrees ± SD) Mean preoperative knee score ± SD Mean preoperative function score ± SD Mean preoperative Oxford knee score ± SD Mean SF-36 physical component score ± SD Mean SF-36 mental component core ± SD SD, standard deviation.
66.4 (50-90) 134 (78) 37 (22) 28.4 ± 3.6 118 ± 19.3 7 ± 7.3 4.7 ± 6.2 varus 36.8 ± 19.8 55.0 ± 18.1 34.4 ± 8.0 33.7 ± 10.9 52.1 ± 10.1
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Fig. 3. Scatterplot of computer-assisted surgery (CAS) measurements against radiographic measurements of joint line changes. Joint line elevation was assigned a positive value and depression a negative value.
there was no “learning curve” effect confounding the results of the radiographic measurements. We analyzed a total of 171 patients (171 knees) and found a significant linear correlation (P < .001) between changes in JL measured using CAS and radiographs, with a correlation coefficient (r) of 0.303 as illustrated in Figure 3. Our results demonstrate a poor correlation between the JL changes measured using radiographs and computer navigation.
Discussion The adverse effects of JL changes on knee kinematics and clinical outcomes of TKA have been extensively studied. JL elevation results in an inferior shift of the contact point between the patella and femur, with patellofemoral contact forces increasing by 3% per millimeter of displacement [23], often with clinical consequences of anterior knee pain and decreased flexion [24]. Similarly, JL depression may increase patella strain, increasing the risk of subluxation and accelerated wear [25]. These abnormalities of the patellofemoral joint may account for up to 50% of all TKA-related complications [26]. CAS has been shown to be beneficial in determining crucial landmarks including component positioning and mechanical axis [27]. In a meta-analysis of 29 studies comparing CAS to conventional techniques, Mason et al [28] demonstrated significantly improved accuracy in mechanical axis and tibial/femoral alignment. The mean JL change in our study was 1.95 mm, and this correlated well with other studies using navigation systems as a measuring tool [16-19]. Ee et al [16] calculated a mean JL shift of 1.63 mm after CAS TKA, whereas other studies by Yang et al [17] and Ensini et al [19] reported a mean JL change of 1.93 mm and 1.9 mm, respectively. Bin Abd Razak et al [18] compared cruciate-retaining with cruciate-substituting implant design and reported mean JL changes of 1.7 and 2.34 mm, respectively, using the same navigation system as was used in our study. Using a modification of the Kawamura method, the radiographic measurements, the mean JL change measured on AP radiographs was 4.05 ± 2.9 mm. The study by Lee et al [21] using the same radiographic technique found the mean JL change to be 2.8 ± 0.9 mm, whereas other studies using the
Kawamura method reported mean JL changes of 4.0 mm [10] and 3.5 mm [11] using cruciate-retaining implants. The accuracy of calibration of anatomic landmarks using CAS as a measuring tool has been reported to be within 0.5 mm [29]; however, systematic error due to inappropriate selection of landmarks intraoperatively cannot be excluded. We acknowledge that JL calculations are based on registration by the surgeon; hence, if these points were placed inaccurately, JL calculation would be affected. This can be a potential problem in inexperienced CAS users. However, the senior surgeon involved in this study has independently performed more than 800 CAS knee arthroplasties, and we believe that any outliers in the data presented were not due to errors in the CAS technique. Additionally, any errors in the CAS technique were minimized through the acquisition of a large number of points during the registration phase. This was achieved through acquiring multiple landmarks across a bony surface as well as single landmarks on the bone. A verification step was performed in all cases, wherein the surgeon checks on the CAS screens if the area shown on the screen correctly corresponds to the actual area on the bone. Secondly, a pointer was also run along the bone to check whether the area shown on the screen correctly corresponds to the actual area on the bone. Another potential source of inaccuracy arises when the knee deformity is addressed with oblique bone resection and soft tissue release to obtain balanced ligaments with equal flexion and extension gaps. These surgical steps can lead to JL changes when the thickness of removed femoral or tibial bone and amount of soft tissue released are not accurately considered and replaced by implants of the same height. Also, the calculation of the 3-dimensional shape of the bone in knee osteoarthritis is based on geometric models implemented within the navigation software, and this remains to be a potential source of error [29]. Although the introduction and development of CAS has allowed quantitative measurement of intraoperative JL changes as opposed to conventional surgery, our study found a poor correlation between CAS measurements and radiographic measurements performed by the same observer preoperatively and postoperatively on well-positioned radiographs using a single measurement method, with a mean difference amounting to 2.10 mm. This mean difference, however, is small and may still lie within a margin of clinical acceptability. We also noted that CAS measurements had a smaller standard deviation and range of values compared to radiographic measurements, therefore suggesting that CAS has greater precision in measuring JL changes. However, greater precision does not equate to greater accuracy, and there remains no consensus on the best method for calculating JL changes, although radiographic evaluation has been extensively used in the literature [4,9-13]. The validity of CT in measuring JL changes has not been described to date, suggesting that a direct comparison of the preoperative and postoperative plain radiographs is sufficient for assessment [30]. Several limitations were acknowledged in our study. Firstly, only 1 navigation system was used in our study. However, given that most available navigation systems used similar concepts to determine alignments and implant size, the results of our present study may be applicable across navigation systems. Secondly, the methods of radiographic measurement in this study may have biases. However, as these methods were applied to both preoperative and postoperative radiographs in a similar fashion, the results of our study are still meaningful as we are essentially evaluating the change in JL position. We also found no significant difference between the radiographic measurements of JL changes for the first 50 cases and the last 50 cases, indicating that there was no “learning curve” effect confounding the results of the radiographic measurements. Although the mean difference between the radiographic and computer navigation measurements was 2.10 mm, our
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study still found a poor correlation that warrants further evaluation. The strengths of our study are that it is a single-surgeon series, thus minimizing confounding factors in surgical technique that could increase the variability of JL position. We also used a single implant in this study, eliminating the confounding effect that different implants of various shapes would have on our analysis. In conclusion, our study shows that while CAS does have its benefits of improved accuracy in mechanical axis and tibial/femoral component positioning, the JL measurements obtained by CAS intraoperatively correlate poorly with radiographic measurements, and the optimal method of assessment remains uncertain. Although there is currently no gold standard for JL measurement postoperatively, JL elevation/depression will need to be considered in patients who remain symptomatic despite TKA. Clinicians will still have to rely on history taking, physical examination, good quality radiographs, and additional imaging to assess any clinical symptoms that may be related to an alteration in the JL in patients after TKA. References 1. Freeman MA, Todd RC, Bamert P, et al. ICLH arthroplasty of the knee: 1968e1977. J Bone Joint Surg Br 1978;60-B(3):339. 2. Insall JN, Easley ME. Surgical techniques and instrumentation in total knee arthroplasty. In: Insall JN, editor. Surgery of the knee. 3rd ed. Philadelphia (PA): Churchill Livingston; 2001. p. 1553e7. 3. Crottet D, Kowal J, Sarfert SA, et al. Ligament balancing in TKA: evaluation of a force-sensing device and the influence of patellar eversion and ligament release. J Biomech 2007;40(8):1709. 4. Figgie III HE, Goldberg VM, Heiple KG, et al. The influence of tibial patellofemoral location on function of the knee in patients with the posterior stabilized knee prosthesis. J Bone Joint Surg Am 1986;68A:1035. 5. Martin JW, Whiteside LA. The influence of joint line position on knee stability after condylar knee arthroplasty. Clin Orthop Relat Res 1990;259:146. 6. Mountney J, Karamfiles R, Breidahl W, et al. The position of the joint line in relation to the trans-epicondylar axis of the knee: complementary radiologic and computer-based studies. J Arthroplasty 2007;22:1201. 7. Selvarajah E, Hooper G. Restoration of the joint line in total knee arthroplasty. J Arthroplasty 2009;24(7):1099. 8. Hofmann AA, Kurtin SM, Lyons S, et al. Clinical and radiographical analysis of accurate restoration of the joint line in revision total knee arthroplasty. J Arthroplasty 2006;21:1154. 9. Ritter MA, Montgomery TJ, Zhou H, et al. The clinical significance of proximal tibial resection level in total knee arthroplasty. Clin Orthop Relat Res 1999;360:174. 10. Snider MG, Macdonald SJ. The influence of the posterior cruciate ligament and component design on joint line position after primary total knee arthroplasty. J Arthroplasty 2009;24:1093.
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11. Kawamura H, Bourne RB. Factors affecting range of flexion after total knee arthroplasty. J Orthop Sci 2001;6:248. 12. Jawhar A, Shah V, Sohoni S, et al. Joint line changes after primary total knee arthroplasty: navigated versus non-navigated. Knee Surg Sports Traumatol Arthrosc 2013;21:2355. 13. Cope MR, O'Brien BS, Nanu AM. The influence of the posterior cruciate ligament in the maintenance of joint line in primary total knee arthroplasty: a radiologic study. J Arthroplasty 2002;17:206. 14. Bauwens K, Matthes G, Wich M, et al. Navigated total knee replacement. A meta-analysis. J Bone Joint Surg Am 2007;89(2):261. 15. Matsumoto T, Muratsu H, Tsumura N, et al. Soft tissue balance measurement in posterior-stabilized total knee arthroplasty with a navigation system. J Arthroplasty 2009;24(3):358. 16. Ee G, Pang HN, Chong HC, et al. Computer navigation is a useful intra-operative tool for joint line measurement in total knee arthroplasty. Knee 2013;20:256. 17. Yang JH, Seo JG, Moon YW, et al. Joint line changes after navigation-assisted mobile-bearing TKA. Orthopedics 2009;32:35. 18. Bin Abd Razak HR, Pang HN, Yeo SJ, et al. Joint line changes in cruciate-retaining versus posterior-stabilized computer-navigated total knee arthroplasty. Arch Orthop Trauma Surg 2013;133:853. 19. Ensini A, Catani F, Biasca N, et al. Joint line is well restored when navigation surgery is performed for total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2012;20:495. 20. Wasielewski RC, Galat DD, Komistek RD. Correlation of compartment pressure data from an intraoperative sensing device with postoperative fluoroscopic kinematic results in TKA patients. J Biomech 2005;38:333. 21. Lee HJ, Lee JS, Jung HJ, et al. Comparison of joint line position changes after primary bilateral total knee arthroplasty performed using the navigationassisted measured gap resection or gap balancing techniques. Knee Surg Sports Traumatol Arthrosc 2011;19(12):2027. 22. Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977;33(1):159. 23. Singerman R, Davy DT, Goldberg VM. Effects of patella alta and patella infera on patellofemoral contact forces. J Biomech 1994;27:1059. 24. Grelsamer R, Moss G, Ee G, et al. The patellofemoral syndrome; the same problem as the Loch Ness Monster? Knee 2009;16(5):301. 25. Wasielewski RC, Galante JO, Leighty RM, et al. Wear patterns on retrieved polyethylene tibial inserts and their relationship to technical considerations during total knee arthroplasty. Clin Orthop Relat Res 1994;299:31. 26. Goldberg VM, Figgie III HE, Figgie MP. Technical considerations in total knee surgery: management of patella problems. Orthop Clin North Am 1989;20:189. 27. Cheng T, Zhang G, Zhang X. Clinical and radiographic outcomes of image-based computer-assisted total knee arthroplasty: an evidence-based evaluation. Surg Innov 2010;18(1):15. 28. Mason JB, Fehring TK, Estok R, et al. Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty 2007;22(8): 1097. 29. Stockl B, Nogler M, Rosiek R, et al. Navigation improves accuracy of rotational alignment in total knee arthroplasty. Clin Orthop Relat Res 2004;426:180. 30. Sarmah SS, Patel S, Hossain FS, et al. The radiological assessment of total and unicompartmental knee replacements. J Bone Joint Surg Br 2012;94(10): 1321.