The statistical analysis was achieved by the SPSS 19.0 statistical software (IBM Corp., Armonk, NY, USA). We chose the mean and standard deviation (SD) to describe normally distributed measurement data, as well as median, along with minimum and maximum values for describing measurement data that were not normally distributed. Number of cases and percentage were used to describe counted data. The angles of alignment were presented in absolute values. The hypothesis of counted data was analyzed by Chi-square test. Multiple linear regression analysis was applied to analyze factors related to the overall alignment of the lower extremity. Two-tailed P < 0.05 was considered statistically significant.
Data were collected continuously between June 2014 and December 2014, from 195 patients who underwent primary TKA at Peking University Third Hospital. Seven patients were excluded due to low quality full-length lower extremity radiographs 2 weeks after surgery; therefore, 188 cases were included in the study. Among 188 patients included in the study, 22 were male and 166 were female. The average age was 65.8 years (range 49–85 years). A total of 212 TKAs were completed. Left- and right-sided procedures were equally represented. In the study group, 196 cases had varus knee preoperatively, with the varus angle (mean ± SD) 11.78 ± 5.54°, and 16 cases had valgus knee, with the valgus angle 10.28 ± 8.36° [Table 1].
Radiographs of all 212 TKAs were measured. Coronal alignment was within the range of ±3° in 144 cases with femoral side prostheses alignment and 191 cases with tibial side prostheses alignment. Satisfactory rates were 67.9% and 90.1%, respectively. The paired Chi-square test on the satisfactory rate of the two groups showed that the difference was statistically significant (P = 0.02) [Table 2].
Multiple linear regression analysis was applied, where dependent variables were determined by postoperative coronal alignment of the lower extremities, and independent variables were set as the coronal prosthetic alignment on the femoral and tibial sides. Results showed that femoral side prosthesis alignment had greater effect on overall lower extremity alignment than the tibial side. The standardized regression coefficient for femoral side was 0.666 and for tibial side was 0.414 (P < 0.001). Subgroup analysis was conducted based on the varus or valgus status of the prostheses. In case of both femoral and tibial side varus, the standardized regression coefficients were as follows: femoral side = 0.658 (P < 0.001) and tibial side = 0.377 (P < 0.001). In case of both femoral and tibial side valgus, the standardized regression coefficients were as follows: femoral side = 0.555 (P = 0.010) and tibial side = 0.030 (P = 0.880). In case of the femoral side varus and the tibial side valgus, the standardized regression coefficients were as follows: femoral side = 0.702 (P < 0.001) and tibial side = 0.211 (P = 0.034). Finally, in case of the femoral side valgus and the tibial side varus, the standardized regression coefficients were as follows: femoral side = 0.416 (P = 0.043) and tibial side = 0.287 (P = 0.153). Analysis of each subgroup showed that femoral side alignment had greater effect on the postoperative coronal alignment of the lower extremity [Table 3].
A good prosthesis alignment after TKA is an important factor to ensure postoperative function, patient satisfaction, and prosthesis longevity. Precise bone cutting is the prerequisite for achieving good prosthetic alignment. Conventional TKA techniques rely on IM guide system on femoral side and EM guide system on tibial side. To the best of our knowledge, no studies comparing the effects of these two different methods on postoperative lower extremity coronal alignment exist.
Using the medial third of tibial tuberosity and the anterior tibial tendon as the proximal and distal reference marks is a common method used currently for tibial EM resection. A good postoperative alignment been reported in literature using this method. Chiu et al. defined satisfactory alignment as within the range of ±3°, and the rate of satisfactory alignment was 78.7%. Among scholars who defined satisfactory alignment as within the range of ±4°, Ishii et al. reported a rate of satisfactory alignment in 88% of cases, Teter et al. in 92% of cases, and Maestro et al. in 84% of cases. We defined satisfactory coronal alignment as within ±3°, and we had 90.1% of patients with satisfactory postoperative alignment, which was consistent with previous literature reports.
It is generally believed that IM guide has higher accuracy compared with EM system at the same site. Reed et al. found in their analysis of 100 cases of TKA radiographs that tibial side IM-guided resection had an accuracy rate of 85%, but EM-guided resection had an accuracy rate of 65%. Cashman et al. also showed that tibial IM-guided resection had significantly more accurate postoperative coronal alignment compared with the EM. However, comparison between femoral side IM guide and tibial side EM guide failed to show the expected superior rate of satisfactory postoperative alignment. Moon et al. reported that in their study of 154 surgical cases, in which IM guide was used, 34 cases had unsatisfactory femoral side postoperative alignment, and the rate of satisfactory alignment was 77%. Although Laskin et al. reported that 96% of patients with IM-guided resection had satisfactory femoral side alignment, this rate decreased to 72% in obese patients or patients with large medullary cavities. Our rate of satisfactory postoperative coronal alignment was 67.9%, which was significantly inferior to the results of the tibial side.
Previous studies investigated the causes of unsatisfactory femoral side alignment. Teter et al. reported that the curve in the distal third of the femur could cause inaccuracies in IM-guided resection. The study by Yau et al. supports this conclusion. They also noted a higher incidence of this type of coronal femoral curve in Chinese patients with end-stage osteoarthritis. This may be a possible cause for the unsatisfactory femoral prosthetic alignment in our study. Locating the femoral medullary entry point can also cause errors in bone cutting, leading to unsatisfactory postoperative alignment. By measuring 40 lower extremity radiographs, Reed et al. noted that 6.6 mm medial to the trochlear notch is the ideal medullary entry point in line with the coronal anatomical axis. The studies from Mihalko et al. on cadavers showed that only the sagittal alignment of the prosthesis was affected in case of three different medullar entry points on the same femoral anteroposterior axis. The coronal alignments, on the other hand, did not show any statistical difference. Novotny et al. conducted studies on 45 cadavers and pointed out that the ideal coronal medullary entry point is where the ratio of the distance between the entry point and the distal lateral femoral cortex, and the overall diameter equals 0.53. In addition, effects of sex and lower extremity alignment on orientation of knee have been discussed in previous study, which indicated that the entry point of femur might be different between men and women. We selected a fixed position based on the clinical experience of surgeon as an entry point of femur, which might be a potential reason causing the error of bone cutting. Measuring the femoral morphology in the front view of X-ray to adjust the position of entry point is a method worth considering; more studies need to be done to confirm this assumption in further time. The diameter and length of the IM rods are other factors that can affect the accuracy of femoral coronal alignment. In Novotny et al.'s study, an increase in the diameter of the IM rod from 8 mm to 9 mm and length from 101.6 mm to 228.6 mm can decrease the coronal alignment maximum potential error from 5.78° to 0.66°. Thus, many factors can affect the accuracy of femoral IM-guided resection.
The results of this study showed that whether it is the overall alignment or various scenarios of the subgroups, postoperative coronal alignment is mainly affected by femoral side IM-guided resection. Noteworthy study results showed that when femoral prostheses had valgus placement, tibial side alignment had no effect on lower extremity postoperative coronal alignment (P > 0.05, clearly no statistical significance). Insufficient sample size after subdividing may have affected the results. Therefore, this conclusion will need to be confirmed by further studies with a larger sample size.
The significance of this retrospective, observational study is that it analyzed, for the first time, the effect of femoral and tibial side bone cutting on postoperative alignment, and noted that postoperative coronal alignment is mainly affected by femoral side IM-guided resection. In addition, our preliminary results suggest that the incidence of unsatisfactory postoperative femoral side alignment may be higher. Different factors, such as the distal curve of the femur, wrong medullary entry point, and inappropriate IM rod diameter and length, may all contribute to unsatisfactory femoral side alignment. Given that femoral side IM guide procedure is affected by so many factors, surgeons should pay closer attention. The X-ray films in this study were affected by the rotation of lower extremity and the preoperative contraction of knee extension. Although we controlled the quality of our radiographs, as a retrospective study, we were unable to completely eliminate this effect on our results. Therefore, this study has certain limitations. In future, the results with a larger sample size should be analyzed by the difference valgus angle of femoral cutting guide and the preoperative contraction of knee extension in subdivided groups, to avoid the improper conclusion caused by the deviation data.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
1. Ritter MA, Faris PM, Keating EM, Meding JB. Postoperative alignment of total knee replacement. Its effect on survival Clin Orthop Relat Res. 1994;299:153–6 doi: 10.1097/00003086-199402000-00021
2. Longstaff LM, Sloan K, Stamp N, Scaddan M, Beaver R. Good alignment after total knee arthroplasty
leads to faster rehabilitation and better function J Arthroplasty. 2009;24:570–8 doi: 10.1016/j.arth.2008.03.002
3. Cashman JP, Carty FL, Synnott K, Kenny PJ. Intramedullary versus extramedullary alignment of the tibial component in the triathlon knee J Orthop Surg Res. 2011;6:44 doi: 10.1186/1749-799X-6-44
4. Matsuda S, Kawahara S, Okazaki K, Tashiro Y, Iwamoto Y. Postoperative alignment and ROM affect patient satisfaction after TKA Clin Orthop Relat Res. 2013;471:127–33 doi: 10.1007/s11999-012-2533-y
5. Bourne RB, Chesworth BM, Davis AM, Mahomed NN, Charron KD. Patient satisfaction after total knee arthroplasty
: Who is satisfied and who is not? Clin Orthop Relat Res. 2010;468:57–63 doi: 10.1007/s11999-009-1119-9
6. Chiu KY, Yau WP, Ng TP, Tang WM. The accuracy
of extramedullary guides for tibial component placement in total knee arthroplasty
Int Orthop. 2008;32:467–71 doi: 10.1007/s00264-007-0354-5
7. Ishii Y, Ohmori G, Bechtold JE, Gustilo RB. Extramedullary versus intramedullary alignment guides in total knee arthroplasty
Clin Orthop Relat Res. 1995;318:167–75
8. Teter KE, Bregman D, Colwell CW Jr. Accuracy
of intramedullary versus extramedullary tibial alignment cutting systems in total knee arthroplasty
Clin Orthop Relat Res. 1995;321:106–10 doi: 10.1097/00003086-199512000-00016
9. Maestro A, Harwin SF, Sandoval MG, Vaquero DH, Murcia A. Influence of intramedullary versus extramedullary alignment guides on final total knee arthroplasty
component position: A radiographic analysis J Arthroplasty. 1998;13:552–8 doi: 10.1016/S0883-5403(98)90055-9
10. Reed MR, Bliss W, Sher JL, Emmerson KP, Jones SM, Partington PF. Extramedullary or intramedullary tibial alignment guides: A randomised, prospective trial of radiological alignment J Bone Joint Surg Br. 2002;84:858–60 doi: 10.1302/0301-620X.84B6.12702
11. Moon YW, Han JH, Lee KH, Jang SW, Seo JG. Clinical outcome of IM-guided total knee arthroplasty
with inappropriate femoral resection in coronal plane Knee Surg Relat Res. 2013;25:19–24 doi: 10.5792/ksrr.2013.25.1.19
12. Laskin RS. RMC total knee replacement. A review of 166 cases J Arthroplasty. 1986;1:11–19
13. Yau WP, Chiu KY, Tang WM, Ng TP. Coronal bowing of the femur and tibia in Chinese: its incidence and effects on total knee arthroplasty
planning J Orthop Surg (Hong Kong). 2007;15:32–36
14. Reed SC, Gollish J. The accuracy
of femoral intramedullary guides in total knee arthroplasty
J Arthroplasty. 1997;12:677–682
15. Mihalko WM, Boyle J, Clark LD, Krackow KA. The variability of intramedullary alignment of the femoral component during total knee arthroplasty
J Arthroplasty. 2005;20:25–8 doi: 10.1016/j.arth.2004.10.011
16. Novotny J, Gonzalez MH, Amirouche FM, Li YC. Geometric analysis of potential error in using femoral intramedullary guides in total knee arthroplasty
J Arthroplasty. 2001;16:641–7 doi: 10.1054/arth.2001.23714
17. Zeng YM, Wang Y, Zhu ZA, Dai KR. Effects of sex and lower extremity alignment on orientation of the knee joint line in knee surgery Chin Med J. 2012;125:2126–31 doi: 10.3760/cma.j.issn.0366-6999.2012.12.009
18. Teter KE, Bregman D, Colwell CW Jr. The efficacy of intramedullary femoral alignment in total knee replacement Clin Orthop Relat Res. 1995;321:117–21
Edited by: Li-Shao Guo
Keywords:© 2016 Chinese Medical Association
Accuracy; Conventional Resection; Extramedullary Guide; Intramedullary Guide; Prosthetic Coronal Alignment; Total Knee Arthroplasty