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Association of sagittal alignment of tibial and femoral components with clinical outcome in total knee arthroplasty: A prospective cohort study
∗Corresponding author: Vijay Kumar Jain. drvijayortho@gmail.com
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Received: ,
Accepted: ,
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Abstract
In total knee replacement component alignment is a very crucial parameter to achieve better clinical outcomes. Only a few studies exist in the literature on the association between sagittal alignment of components and clinical outcomes. The study aimed to measure the functional outcome and association between the sagittal alignment of total knee replacement components and their clinical outcome.
Prospectively we collected data of 81 knees (cases) following total knee replacement. The sagittal femoral angle, anterior and posterior tibial slopes were assessed on 2nd postoperative week using a lateral radiograph. Based on these measures 2 groups were made. Group A comprises of the femoral component which was further divided into A1 (41 cases) and A2 (40 cases) based on the component's sagittal femoral angle in flexion or extension.
Group B comprises of Tibial component subgrouped based on the degree of Tibal angle as the posterior tibial slope or anterior tibial slopes. The B1 subgroup has posterior tibial slope of more than 5° (23 cases), B2 posterior tibial slope within 5° (53 cases), and B3 anterior tibial slope (5 cases). Preoperative and follow-ups at one month, 6 months, and 3 year; the functional assessment was performed using the American Knee Society score and Oxford knee scores. The duration to raise the leg straight (in days) was also measured.
52 patients (81 total knee replacement cases) with a mean age of 62.88 ± 8.21 were enrolled. Results showed significant improvement in mean American Knee Society score (preoperative 32.91 ± 2.61 to 86.68 ± 2.52 postoperatively at 3 years; P < 0.001) and mean Oxford knee score (preoperative 34.69 ± 1.06 to 19.20 ± 1.91 postoperatively at 3-years; P < 0.001). The correlation of American Knee Society score between the femoral component angle and tibial component angle suggested that the maximum correlation was between Group A2 (Femoral angle = 91 to 95) and Group B2 (Tibal angle = 86 to 90), with p-value <0.0001.
There is a positive association between the proper sagittal alignment of femoral component and tibial component in total knee replacement with clinical outcome. The functional outcome (in terms of mean American Knee Society score) is better when the femoral component is positioned in extension and the posterior tibial slope of less than 5° is achieved.
Keywords
Alignment
Sagittal alignment
AKSS
OKSS
Tibial component
Total knee replacement
Tibial angle
Femoral angle
1 Introduction
The correct alignment of tibial component (TC) and femoral component (FC) in the coronal, sagittal, and axial planes is desirable for optimum clinical outcome, patient satisfaction, and longevity of the implants in Total knee arthroplasty (TKA). Traditionally a lot of emphasis has been placed on coronal as well as rotational alignment of the FC and TC. Various investigation has been done on its influence on the clinical outcome of TKA.1,2 The accurate sagittal alignment has been reportedly difficult to obtain2,3.
After TKA, range of motion (ROM) is an important measure of the procedure's success. According to kinematic studies, for the swing phase of gait, 67° of knee flexion is required, 83° for ascending stairs, 90° for descending steps, and 93° for rising from a chair. There is general agreement that 90° of knee flexion is the minimum required for daily activity.4
Hyperextension between the FCs and TCs increases the chances of osteolysis5,6 and anterior tibial post-impingement with posterior-stabilized (PS) prostheses.7 As a result, measuring the alignment of the sagittal component is crucial.
Previously it was believed that the sagittal orientation of components has a slight effect on the range of motion and implant survival. Later, it was documented that a flexed FC caused the loosening of the TC by impingement of the femoral cam on the tibial post.8 Reduced flexion, a notched anterior cortex, osteolysis, and a possible supracondylar fracture are all consequences of a hyperextended FC.9
The femur has a natural curvature with a variable distal femoral flexion angle. The intramedullary guide used for the FC is straight and does not match the curvature. Thus, there is a possibility of sagittal malalignment. It is documented that FC within 0–3° of flexion with a mechanical axis performs well.10 The accepted sagittal alignment of the TC is 0–7° flexion for optimum survival for an implant. A TC in extension would produce impingement of post on cam in cruciate sacrificing design and further restrict the knee flexion. A TC in greater than 7° of flexion would have a restriction of extension.5,11 Since Indian patients require higher degrees of knee flexion for squatting, cross leg sitting and other purposes a proper sagittal alignment of components is required during TKA. The purpose of our study was to assess the sagittal alignment of TC and FC and its effect on clinical outcomes.
2 Materials and methods
Prospectively this study was done in the Orthopedics surgery department at our institute after obtaining ethical clearance (TP(MD/MS) (42/2017)/IEC/PGIMER/RMLH 1770/17). The sample size of the study was 81 knees in 52 patients, 29 patients were operated with bilateral TKR. Patients suffering from primary or secondary osteoarthritis (stage III and stage IV Kellgren and Lawrence grades), and inflammatory arthritis of either sex and age ≥50 years were included. Patients with coronal plane knee deformity (≥30°), neurovascular diseases of the same limb, any systemic or local contraindications for surgery, revision TKR, and any prior history of osteotomy involving knee joints were excluded.
At the screening visit, after obtaining a proper history a thorough physical examination was performed. The demographic details of patients such as age, gender, and systemic comorbidities were noted. Preoperatively knee ROM was measured using standard clinical goniometers. Preoperatively functional scores such as AKSS (American Knee Society Score), and OKS (Oxford Knee Score) were noted.12
A radiograph of the bilateral knee was taken while the patient was standing, with a true lateral view at 100% magnification. Patients were operated by two surgeons with a midline medial para-patellar approach under a tourniquet.
2.1 Postoperative management and follow-up
Patients were mobilized with the help of a walker on the 2nd day or as soon as pain was tolerated. Post-operatively at 2nd week follow-up a lateral radiograph of knee was done. The anatomical axis of both femur and tibia was marked on the radiograph (Fig. 1).
The measurement of FC and TC placement in the sagittal plane regarding femoral and tibial anatomical axes correspondingly was done by the method described by the Knee Society TKA radiographic evaluation.13,14
The angle between the line running across the bottom of the femoral implant and the anatomical axis of the femoral shaft was used to determine the FC's alignment and represented as the Femoral angle (FA). FA ≤90° relates to FC in flexion and FA>90° corresponds to an extension of the FC.5,12,15
The angle between the line running down the bottom of the tibial plate and the anatomical axis of the tibial shaft was used to determine the TC alignment and represented as the Tibial angle (TA). The anterior tibial slope (ATS) was represented by TA > 90°, while the posterior tibial slope (PTS) was represented by TA ≤ 90°.5,12,15
For analysis, we divided the patients into 2 groups based on obtained measures.
Group A comprises of the FC which was further divided into A1 and A2 based on components sagittal FA in flexion or extension.Group A1 - FC in flexion (in degrees)Group A2 - FC in extension (in degrees)
Group B comprises of TC which was further divided into three categories based on TA as of PTS or ATS.Group B1 - TC with a PTS of more than 5°Group B2 - TC with PTS within 5°Group B3 - TC with ATS
Functional assessment was done using the AKSS and OKS at one month, 6 months, and 3 years. Separately VAS was not included in the study because pain is a component of AKSS. In addition, the time taken for straight leg raising (in the number of days) was observed during the postoperative period.
2.2 Statistical analysis
Continuous variables were reported as mean SD and median, whereas categorical variables were presented as number and percentage (%). The Kolmogorov-Smirnov test was used to determine the normality of the data. A non-parametric test was applied if the normality was denied. When the data sets were not normally distributed, the unpaired t-test/Mann-Whitney test was used to compare quantitative variables across the two groups, and the paired t-test/Wilcoxon rank-sum test was used to compare quantitative variables across follow-up within the group. The Chi-Square/Fisher's exact test was used to determine the correlation between qualitative variables. A p-value of <0.05 was regarded as statistically significant. The Statistical Package for Social Sciences (SPSS) version 21.0 was used to analyze the data.
We also compared mean AKSS by allotting patients into 5 groups according to FA and TA (in degree) of components.Group A1 - FC in flexion. (FA = 86° to 90°)
This group included 41 cases.Group A2 - FC in extension. (FA = 91° to 95°)
This group included 40 cases.Group B1 - TC with a PTS of more than 5°. (TA = 81° to 85°)
This group included 23 cases.Group B2 - TC with PTS within 5°. (TA = 86°–90°)
This group included 53 cases.Group B3 - TC with ATS. (TA = 91°–95°)
This group included 5 cases.
2.3 Observations and result
The current study comprised a total of 52 patients. Bilateral TKA was performed in 29 patients. The average age of the patients were 62 years with females outnumbered male. All patients were operated using posterior stabilized implants, no tibial stems were used in any cases. The demographic features of the patients are shown in (Table 1).
| Demographic parameter | Value |
| Age: (In Years) | Age range: 44-83Median age: 62Mean ± SD 62.88 ± 8.21 |
| Sex: | Male: 11 (21.2%)Female: 41 (78.8%0 |
| Side: | Left 37 (45.7%)Right 44 (54.3%) |
| Femoral Angle: (In degree) | Mean ± SD Median Min-Max90.63 ± 1.97 90 86-95 |
| Tibial Angle: (In degree) | Mean ± SD Median Min-Max87.23 ± 2.78 87 82-95 |
The measured values of FAs and TAs in all 81 cases are shown in (Table 2). The mean FA of the patients considered in this study was 90.63 ± 1.97 with the minimum angle being 86° and the maximum angle being 95°. Similarly, the mean TA of the cases considered in this study was 87.23 ± 2.78 with the minimum angle being 82° and the maximum angle being 95°. The FA of maximum patients was in the group of 88°–93° with the most being 90° in 19 (23.5%) cases.
| Angle | Frequency for FA | Frequency for TA |
| 82 | 0 | 3 (3.7%) |
| 83 | 0 | 3 (3.7%) |
| 84 | 0 | 8 (9.9%) |
| 85 | 0 | 9 (11.1%) |
| 86 | 1 (1.2%) | 12 (14.8%) |
| 87 | 3 (3.7%) | 10 (12.3%) |
| 88 | 8 (9.9%) | 10 (12.3%) |
| 89 | 10 (12.3%) | 4 (4.9%) |
| 90 | 19 (23.5%) | 17 (21.0%) |
| 91 | 12 (14.8%) | 1 (1.2%) |
| 92 | 14 (17.3%) | 0 |
| 93 | 9 (11.1%) | 2 (2.5%) |
| 94 | 2 (2.5%) | 1 (1.2%) |
| 95 | 3 (3.7%) | 1 (1.2%) |
| Total cases | 81 | 81 |
Tibial angles of maximum patients were between 84 and 90° with the most being in 90° in 17(21%) cases.
3 American knee society scoring system (AKSS)
The mean AKSS score pre-operatively was 32.91 ± 2.61. During follow-up in the first month, the mean AKSS score was 61.93 ± 3.66. At the follow-up of the 6th month, the mean AKSS score was 81.70 ± 2.68. After 3 years AKSS was 86.68 ± 2.52 (Table 3). The p-value was highly significant i.e., <0.01. The rising trend of AKSS following TKA is shown below (Fig. 2).
| Parameters | Duration | ||||
| Preoperative | 4th Week | 6th month | 3 years | P-Value | |
| AKSS | 32.91 ± 2.61 | 61.93 ± 3.66 | 81.70 ± 2.68 | 86.68 ± 2.52 | <0.001 |
| OKSS | 34.69 ± 1.06 | 30.30 ± 1.78 | 21.31 ± 1.62 | 19.20 ± 1.91 | <0.001 |
4 Oxford knee society score (OKS)
The mean OKS score pre-operatively was 34.69 ± 1.06. During follow-up in the first month, the mean OKS score was 30.30 ± 1.78. At the follow-up of the 6th month, the mean OKS score was 21.31 ± 1.62. After 3 years OKS score was 19.20 ± 1.91. The p-value was highly significant i.e., <0.01 (Table 3). The declining trend of OKS following TKA is shown below (Fig. 2).
5 Regain of straight leg raise (SLR)
Time in the number of days taken for the regain of straight leg raising was noted due to no extension lag. In the study, the earliest regain of SLR was on the 1st day and the delay was on the 7th day. Most of the patients regained SLR on 3rd day. (Fig. 3). The overall mean time taken to regain SLR was 2.67 ± 0.89, with a median of 3, and the range was a minimum of 1 day to a maximum of 7 days.
Firstly, the results of the statistical correlation between AKSS and different groups of FA and TA of components were done individually.
Group A:
Group A1 - FC in flexion. (FA = 86° to 90°).
This group included 41 cases. Mean AKSS increased to 60.88 ± 4.12 at 1 month from the preoperative score of 32.39 ± 2.42 which further increased to 80.9 ± 2.39 and 85.6 ± 2.273 at the end of the 6th month and 3rd year respectively.
Group A2 - FC in extension. (FA = 91° to 95°).
This group included 40 cases. Mean AKSS increased to 63.00 ± 2.77 at 1 month from a preoperative score of 33.45 ± 2.72 which further increased to 82.5 ± 2.74 and 87.75 ± 2.31 at the end of the 6th month and 3rd year respectively.
Group B:
Group B1 - TC with a PTS of more than 5°. (TA = 81° to 85°).
This group included 23 cases. Mean AKSS increased to 60.74 ± 4.00 at 1 month from a preoperative score of 32.70 ± 2.23 which further increased to 80.52 ± 2.43 and 84.52 ± 3.03 at the end of the 6th month and 3rd year respectively.
Group B2 - TC with PTS within 5°. (TA = 86° to 90°).
This group included 53 cases. Mean AKSS increased to 62.13 ± 3.41 at 1 month from a preoperative score of 32.94 ± 2.79 which further increased to 82.15 ± 2.74 and 87.03 ± 2.18 at the end of the 6th month and 3rd year respectively.
Group B3 - TC with ATS. (TA = 91° to 95°).
This group included 5 cases.
Mean AKSS increased to 65.20 ± 2.39 at 1 month from a preoperative score of 33.60 ± 2.61 which further increased to 82.4 ± 1.67 and 83.6 ± 0.89 at the end of the 6th month and 3rd year respectively. Higher AKSS was seen in subgroup A2 of group A, whereas subgroup B2 of group B had higher AKSS.
Secondly; the correlation of AKSS between the FA and TA of component was also calculated among different groups and the results showed that the maximum correlation was between Group A2 (FA = 91° to 95°) and Group B2 (TA = 86° to 90°), with p-value <0.0001. Hence the clinical outcome was better with FC in extension and PTS within 5° (Table 4).
| Group A (FA = 86 to 90) | Group B (FA = 91 to 95) | P-Value | |
| Group C (TA = 81 to 85) | 0.9999 | 0.9997 | <0.0001 |
| Group D (TA = 86 to 90) | 0.999961 | 0.999983 | |
| Group E (TA = 91 to 95) | 0.9956 | 0.9952 |
6 Discussion
The sagittal alignment of FC and TC in knee arthroplasty has been given less attention in the literature. The improper sagittal alignment can cause instability, implant loosening, and poor functional outcome.
The current study from India demonstrates a good correlation between sagittal alignments with AKSS. A better outcome can be obtained if the FC is in the extension and the PTS is within 5°. The outcome will be poor in patients with FC in extension but ATS.
In a study by Faris et al.,15 it was noted that there was no relationship between the sagittal plane position of the FC with the final knee ROM when the component position is in between 20-degree flexion to 20-degree extension whereas in this study proper FC alignment had increased final knee range of motion and hence final mean AKSS.
A study by Longstaff et al.16 conducted on 159 TKAs showed that a good coronal, sagittal, and rotational alignment of FC and TC increases mean AKSS on follow-ups (the highest follow-up period is 1 year) and hence a better clinical outcome. These patients were rehabilitated more quickly and their duration of hospital stay was lesser too.
Peng Y et al.17 did a study on 29 cases of the bi-cruciate retaining implant. After one year of follow-up, there was a significant improvement in Knee society score (KSS) (preoperative 58.1 ±11.8 to postoperative 87.9 ±16.7, p < 0.001). The PTS was the only significant factor associated with the postoperative KSS following regression analysis adjusted for baseline KSS (p = 0.006).
In our study, with good alignment of TKA components in the sagittal plane, the preoperative mean AKSS of 32.91 ± 2.61 increased to 61.93 ± 3.66 on the 4th postoperative week which further increased to 81.70 ± 2.68 at the end of the 6th month and the end of 3 years 86.68 ± 2.52. Further, it is noted that clinical outcome is better with the FC placed in extension and maintaining PTS within 5°.
The majority of the study does not show any correlation between proper sagittal alignment and OKS. Ahmad I et al.18 conducted a study on 474 cases and found no significant difference between the OKS scores of aligned, flexed, and extended FCs. There was also no significant difference in the OKS score of aligned and misaligned TCs.
Scott C·H.E et al.19 in a study of 297 patients; found 73 patients with anterior knee pain with 10 years's follow-up. The patients with anterior knee pain had FC in flexion (−1.5 to 0.3°) in comparison to those without knee pain 0.9–2°). The angle of the PTS was 3.8–5.2° in the patients having anterior knee pain as compared to the non-pain group (5.3–5.9). Their OKS were worse at the follow-up on 1,5 and 10 years.
Ziv YB et al.20 in a retrospective study 225 out of 337 patients with PTS above 5° and 112 had PTS less than 5°. In the follow-up of 3.47 years authors found no significant difference in both groups in terms of VAS, OKS, and Knee Injury and Osteoarthritis Outcome Score.
In our study, with good alignment of TKA components in the sagittal plane, the preoperative mean OKS of 34.69 ± 1.06 decreased to 30.30 ± 1.78 on the 4th postoperative week which further decreased to 21.31 ± 1.62 at the end of 6th month and the end of 3 years 19.20 ± 1.91 with a significant p-value <0.01. The sagittal alignment is necessary for long-term outcomes21. A better outcome can be achieved when FC will be 0–3° of flexion and PTS between o to 7°.22
6.1 Limitations
A few limitations were applied to the study. Firstly, there are fewer patients in the study the sample should have been more. Secondly, for greater precision, measurements ought to have been made using computerized tomography images. Thirdly, a single observer made the measurements of the angles. Lastly surgery was performed by two surgeons.
7 Conclusion
The results of study showed the significant improvement in mean AKSS and mean OKS, hence for the better functional outcome proper sagittal alignment of FC and TC in TKA is necessary. Thus, this study concluded that there is a positive association between the proper sagittal alignment of FC and TC in TKA with clinical outcomes. The functional outcome (in terms of mean AKSS) is better when the FC is placed in extension up to 95° and the PTS of less than 5° is achieved.
Ethical statement
All patients and studies were conducted under ethical conditions. The ethical board gave the permission.
Disclosure statement
We declare that there was no financial support and sponsorship from any type of source or company. The abstract of this study is submitted for presentation in DOACON 2023.
Patient consent for publication
Not applicable.
Authorship contribution
MS, GH, AKN, VKJ: Methodology, Formal analysis, and
Investigation, Writing - original draft preparation, making of the table; MS.
Conceptualization, Methodology, Writing - review, and editing; MS, GH, AKN, VKJ.
Methodology, Writing - review and editing, Resources; and VKJ, AKN.
Conceptualization, Methodology, Writing - review and editing, Resources, Supervision.
Data availability
We have all the patient-related data in an Excel sheet.
Use of AI tool
None.
References
- The use of accelerometer-based navigation for coronal TKA alignment: a prospective, single surgeon comparative study. Arch Orthop Trauma Surg. 2020;140:1169-1174.
- [Google Scholar]
- The influence of postoperative coronal alignment on tibial migration after total knee arthroplasty in preoperative varus and valgus knees: a secondary analysis of 10 randomized controlled trials using radiostereometric analysis. J Bone Joint Surg Am. 2021 Dec 15;103(24):2281-2290.
- [Google Scholar]
- The effect ofpost-operative mechanical axis alignment on the survival of primarytotal knee replacements after a follow-up of 15 years. J Bone JointSurg Br. 2011;93(9):1217-1222.
- [Google Scholar]
- Clinical profile of patients with osteoarthritis underwent total knee arthroplasty. International Journal of Orthopaedics. 2020;6(2):851-853.
- [Google Scholar]
- The relationship between the survival of total knee arthroplasty and postoperative coronal, sagittal and rotational alignment of knee prosthesis. Int Orthop. 2014;38:379-385.
- [Google Scholar]
- Does computer-assisted surgery improve postoperative leg alignment and implant positioning following total knee arthroplasty? A meta-analysis of randomized controlled trials? Knee Surg Sports Traumatol Arthrosc. 2012 Jul;20(7):1307-1322.
- [Google Scholar]
- Anterior tibial post impingement in a posterior stabilized total knee arthroplasty. J Orthop Res. 2005;23:536-541.
- [Google Scholar]
- The John Insall Award: control-matched evaluation of painful patellar Crepitus after total knee arthroplasty. Clin Orthop. 2011;469(1):10-17.
- [Google Scholar]
- The effect of alignment and BMI on failure of total knee replacement. J Bone Joint Surg. 2011;93(17):1588-1596.
- [Google Scholar]
- Femoral flexion position is a highly variable factor in total knee arthroplasty: an analysis of 593 conventionally aligned total knee replacements. Knee Surg Sports Traumatol Arthrosc. 2020;28:1014-1022.
- [Google Scholar]
- Relationship between the femoral and tibial component positions and postoperative knee range of motion after posterior-stabilized total knee arthroplasty in varus-aligned knees. J Knee Surg 2022 Sep 8
- [Google Scholar]
- Validation of a prediction model that allows direct comparison of the Oxford Knee Score and American Knee Society clinical rating system. The Bone & Joint Journal. 2015 Apr;97(4):503-509.
- [Google Scholar]
- Radiographic evaluation of alignment following TKA, a systematic review. Maedica (Bucur).. 2017 Sep;12(3):214-218.
- [Google Scholar]
- The Knee Society total knee arthroplasty roentgenographic evaluation and scoring system. Clin Orthop Relat Res. 1989;248:9-12.
- [Google Scholar]
- Sagittal plane positioning of the femoral component in total knee arthroplasty. J Arthroplasty. 1988;3(4):355-358.
- [Google Scholar]
- Good alignment after total knee arthroplasty leads to faster rehabilitation and better function. J Arthroplasty. 2009;24(4):570-578.
- [Google Scholar]
- Does component alignment affect patient reported outcomes following bicruciate retaining total knee arthroplasty? An in vivo three-dimensional analysis. J Knee Surg. 2020 Aug;33(8):798-803.
- [Google Scholar]
- Tibial component sizing and alignment of TKR components does not significantly affect patient reported outcome measures at six months. A case series of 474 participants. Int J Surg. 2018 Apr;52:67-73.
- [Google Scholar]
- Association between femoral component sagittal positioning and anterior knee pain in total knee arthroplasty: a 10-year case-control follow-up study of a cruciate-retaining single-radius design. J Bone Joint Surg Am. 2019 Sep 4;101(17):1575-1585.
- [Google Scholar]
- Excessive sagittal slope of the tibia component during kinematic alignment-safety and functionality at a minimum 2-year follow-up. J Personalized Med. 2022 Aug 30;12(9):1407.
- [Google Scholar]
- Component alignment in total knee replacement. Orthoped Rheumatol Open Access J. 2018;911:3-6.
- [Google Scholar]
- Variation in optimal sagittal alignment of the femoral component in total knee arthroplasty. Orthopedics. 2017;40(2):102-106.
- [Google Scholar]