journal of clinical orthopaedics and trauma 6 (2015) 240–243
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/jcot
Original Article
Distal femoral rotational alignment in the Indian population – An important consideration in total knee arthroplasty Tul B. Pun a, Vignesh P. Krishnamoorthy b, Ravi J. Korula c, Pradeep M. Poonnoose c,* a
Resident, Department of Orthopaedics, Christian Medical College, Vellore 632004, Tamil Nadu, India Associate Professor, Department of Orthopaedics, Christian Medical College, Vellore 632004, Tamil Nadu, India c Professor, Department of Orthopaedics, Christian Medical College, Vellore 632004, Tamil Nadu, India b
article info
abstract
Article history:
Objective: To measure the angular relationships of distal femoral rotational axes in the
Received 28 January 2015
normal Indian population.
Accepted 14 April 2015
Materials and methods: Magnetic Resonance Imaging (MRI) scans of the knee of 40 Indian
Available online 15 May 2015
subjects were used to define the posterior condylar axis, the transepicondylar axis and the
Keywords:
between the posterior condylar axis and the transepicondylar axis, and the Whiteside-
Whiteside's line
epicondylar angle (W-EP angle) were then calculated.
Whiteside's line (anteroposterior axis). The posterior condylar angle (PCA) – the angle
Posterior condylar axis
Results: The mean posterior condylar angle in the Indian knee was 4.678 and the mean
Transepicondylar line
Whiteside-epicondylar angle was 92.78.
Indian knees
Conclusion: There are differences in the distal femoral rotational axes among various races.
Total knee arthroplasty
The mean PCA and the W-EP angle are more externally rotated in the Indian than in the Western, population, but similar to the Chinese. Using fixed values to define the angular relationships between the axes could lead to malrotation of the femoral component. An understanding of the racial differences is essential while designing implants for the Indian population. # 2015 Delhi Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
Key message The Posterior condylar angle and Whiteside-epicondylar angle are more externally rotated in the Indian knees than in the
Western population. Using Western values to define the angular relationships between the axes could lead to malrotation of the femoral component. An understanding of the racial differences is essential while designing implants for the Indian population.
* Corresponding author. Tel.: +91 416 2282081; fax: +91 416 2232035. E-mail address: [email protected] (P.M. Poonnoose). http://dx.doi.org/10.1016/j.jcot.2015.04.002 0976-5662/# 2015 Delhi Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
journal of clinical orthopaedics and trauma 6 (2015) 240–243
1.
Introduction
241
was drawn by joining the deepest point of the patellar groove to the midpoint of the intercondylar notch. The angle between the posterior condylar axis and the transepicondylar axis was measured as the posterior condylar angle (PCA) (Fig. 1). The angle between the Whiteside's line and the transepicondylar axis was measured as the Whiteside-epicondylar angle (W-EP angle) (Fig. 2).
The anatomy of the distal femur plays a crucial role in the normal kinematics of the knee joint. The accuracy of the femoral component rotation in total knee arthroplasty (TKA) affects patello-femoral tracking, soft tissue balancing in flexion, rotational alignment of the tibia in extension and also helps in preventing anterior femoral notching.1,2 The three commonly used landmarks for referencing rotational orientation of the femoral component in TKA are – the posterior condylar axis, the transepicondylar axis and the anteroposterior axis (Whiteside's line). There is a wide variation in these axes among different racial groups as proven by various studies.3–10 We propose to define the angular relationships of these axes in the normal Indian population using Magnetic Resonance Imaging (MRI) scans of the knee joint. These values may help factor in changes in the design of TKA implants for the Indian population.
The MRI scans of 40 knees were analysed. The mean age of the subjects was 29.45 years with a range from 20 to 45 years. The mean PCA (posterior condylar angle) was 4.678 (SD 1.368) with a range of 1.68–7.88. Of the 40 knees, 39.1% of them had a PCA that was greater than 58. The mean W-EP angle was 92.78 (SD 1.328), with a range from 908 to 96.38. Forty percent of the knees had a WEP angle greater than 938, indicating more than 38 of internal rotation of the epicondylar axis.
2.
4.
Material and methods
MRI scans of the knee joint of 40 subjects that were done to rule out soft tissue injuries (ligament and meniscal injuries) were analysed for this study. Patients with a previous history of fracture, infection and knees with arthritic changes were excluded from the study. The MRI images were analysed in a PACS (Picture Archiving & Communication System) monitor, using GE Centricity software (Version 3.0). An axial MRI image, in which the femoral epicondyles were most prominent, was used for measurement of the various angles. The posterior condylar axis was defined as a tangential line joining both the femoral condyles, touching its posterior articular surface. The transepicondylar axis was drawn by joining the most prominent part of the lateral epicondyle and the centre of the medial epicondylar sulcus. The Whiteside's line (anteroposterior axis)
[(Fig._1)TD$IG]
3.
Discussion
The importance of rotational alignment of the femoral component in TKA is now increasingly recognized. It not only affects the medio-lateral stability during knee flexion, but also influences patellar tracking.1,5,11 External rotation also affects polyethylene wear in the patellar component and may affect anterior knee pain after TKA.4 Measured resection technique, when based on a single landmark or axis as the sole reference for femoral component rotation in total knee arthroplasty, is often inaccurate. In knees with severe valgus deformity, the use of the posterior condylar axis as the reference axis may lead to malrotation due to lateral femoral condylar hypoplasia.6 The transepicondylar axis may be difficult to define, due to difficulty in finding the most prominent point or the sulcus of the medial epicondyle.7 There are two types of epicondylar axes: the surgical axis – drawn between the lateral epicondyle and the centre of the medial epicondylar sulcus, and the clinical axiswhich is drawn between the most prominent part of the lateral and medial epicondyle.9,10 Berger et al.10 regarded the former axis to be more reliable, though it is more difficult to define clinically.6 The Whiteside's line could be difficult to define in deformed knees – due to erosion of the anterior portion of the lateral or medial femoral condyles.3 Therefore, while determining rotational alignment of the femoral component in total knee arthroplasty, it is essential take into consideration all the relevant axes.
5.
Fig. 1 – Showing the transepicondylar axis, the posterior condylar axis and the posterior condylar angle (PCA).
Results
Posterior condylar angle (PCA)
Western studies suggest that the Posterior condylar angle (PCA) is about 38 – (Griffin et al.8 – 3.118, Boisgard et al.9 2.658, Berger et al.10 – 3.58). Most proprietary jigs used in measured resection, place the anterior and posterior femoral cuts at 38 of external rotation to the posterior condylar axis. According to our study, the PCA in the Indian knee is about 4.678 – which is greater than in the Western knees – but slightly less than the
242
journal of clinical orthopaedics and trauma 6 (2015) 240–243
[(Fig._2)TD$IG]
Table 2 – Whiteside–Epicondylar (W–EP) angle in different ethnic populations. Population
Mean Whiteside–Epicondylar (W–EP) angle
Indian – Our study Western5 Japanese3 Chinese4
Fig. 2 – Showing the Whiteside's line and the Whitesideepicondylar angle (W–EP angle).
Japanese3 (5.88) and Chinese4 (5.18 in males and 5.88 in females). Mullaji et al. also described a PCA of 58 in Indian knees6 (Table 1). This suggests that the use of standard femoral jigs with 38 inbuilt external rotation with reference to the posterior condylar axis in total knee arthroplasty can result in internal rotation of the femoral component in Indian knees.
6.
Whiteside–Epicondylar (W–EP) angle
The mean W-EP angle was more externally rotated in the Indian population (92.78) than in the Western and Japanese population (Table 2). The Japanese population3 was older than our study group (mean age of 50.2 years Vs 29.45 years) and the Western study5 was done in cadavers. This implies that if we take the perpendicular to the AP axis or the Whiteside's line as the reference during total knee arthroplasty, the femoral component would be placed in a more externally rotated position. The W–EP angle in the study done by Amaranath et al.11 was 92.8 2.48, which is comparable to our study. They showed that gender, age and mechanical alignment had no significant effect on altering the relationship of transepicon-
92.78
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/jcot
Original Article
Distal femoral rotational alignment in the Indian population – An important consideration in total knee arthroplasty Tul B. Pun a, Vignesh P. Krishnamoorthy b, Ravi J. Korula c, Pradeep M. Poonnoose c,* a
Resident, Department of Orthopaedics, Christian Medical College, Vellore 632004, Tamil Nadu, India Associate Professor, Department of Orthopaedics, Christian Medical College, Vellore 632004, Tamil Nadu, India c Professor, Department of Orthopaedics, Christian Medical College, Vellore 632004, Tamil Nadu, India b
article info
abstract
Article history:
Objective: To measure the angular relationships of distal femoral rotational axes in the
Received 28 January 2015
normal Indian population.
Accepted 14 April 2015
Materials and methods: Magnetic Resonance Imaging (MRI) scans of the knee of 40 Indian
Available online 15 May 2015
subjects were used to define the posterior condylar axis, the transepicondylar axis and the
Keywords:
between the posterior condylar axis and the transepicondylar axis, and the Whiteside-
Whiteside's line
epicondylar angle (W-EP angle) were then calculated.
Whiteside's line (anteroposterior axis). The posterior condylar angle (PCA) – the angle
Posterior condylar axis
Results: The mean posterior condylar angle in the Indian knee was 4.678 and the mean
Transepicondylar line
Whiteside-epicondylar angle was 92.78.
Indian knees
Conclusion: There are differences in the distal femoral rotational axes among various races.
Total knee arthroplasty
The mean PCA and the W-EP angle are more externally rotated in the Indian than in the Western, population, but similar to the Chinese. Using fixed values to define the angular relationships between the axes could lead to malrotation of the femoral component. An understanding of the racial differences is essential while designing implants for the Indian population. # 2015 Delhi Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
Key message The Posterior condylar angle and Whiteside-epicondylar angle are more externally rotated in the Indian knees than in the
Western population. Using Western values to define the angular relationships between the axes could lead to malrotation of the femoral component. An understanding of the racial differences is essential while designing implants for the Indian population.
* Corresponding author. Tel.: +91 416 2282081; fax: +91 416 2232035. E-mail address: [email protected] (P.M. Poonnoose). http://dx.doi.org/10.1016/j.jcot.2015.04.002 0976-5662/# 2015 Delhi Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
journal of clinical orthopaedics and trauma 6 (2015) 240–243
1.
Introduction
241
was drawn by joining the deepest point of the patellar groove to the midpoint of the intercondylar notch. The angle between the posterior condylar axis and the transepicondylar axis was measured as the posterior condylar angle (PCA) (Fig. 1). The angle between the Whiteside's line and the transepicondylar axis was measured as the Whiteside-epicondylar angle (W-EP angle) (Fig. 2).
The anatomy of the distal femur plays a crucial role in the normal kinematics of the knee joint. The accuracy of the femoral component rotation in total knee arthroplasty (TKA) affects patello-femoral tracking, soft tissue balancing in flexion, rotational alignment of the tibia in extension and also helps in preventing anterior femoral notching.1,2 The three commonly used landmarks for referencing rotational orientation of the femoral component in TKA are – the posterior condylar axis, the transepicondylar axis and the anteroposterior axis (Whiteside's line). There is a wide variation in these axes among different racial groups as proven by various studies.3–10 We propose to define the angular relationships of these axes in the normal Indian population using Magnetic Resonance Imaging (MRI) scans of the knee joint. These values may help factor in changes in the design of TKA implants for the Indian population.
The MRI scans of 40 knees were analysed. The mean age of the subjects was 29.45 years with a range from 20 to 45 years. The mean PCA (posterior condylar angle) was 4.678 (SD 1.368) with a range of 1.68–7.88. Of the 40 knees, 39.1% of them had a PCA that was greater than 58. The mean W-EP angle was 92.78 (SD 1.328), with a range from 908 to 96.38. Forty percent of the knees had a WEP angle greater than 938, indicating more than 38 of internal rotation of the epicondylar axis.
2.
4.
Material and methods
MRI scans of the knee joint of 40 subjects that were done to rule out soft tissue injuries (ligament and meniscal injuries) were analysed for this study. Patients with a previous history of fracture, infection and knees with arthritic changes were excluded from the study. The MRI images were analysed in a PACS (Picture Archiving & Communication System) monitor, using GE Centricity software (Version 3.0). An axial MRI image, in which the femoral epicondyles were most prominent, was used for measurement of the various angles. The posterior condylar axis was defined as a tangential line joining both the femoral condyles, touching its posterior articular surface. The transepicondylar axis was drawn by joining the most prominent part of the lateral epicondyle and the centre of the medial epicondylar sulcus. The Whiteside's line (anteroposterior axis)
[(Fig._1)TD$IG]
3.
Discussion
The importance of rotational alignment of the femoral component in TKA is now increasingly recognized. It not only affects the medio-lateral stability during knee flexion, but also influences patellar tracking.1,5,11 External rotation also affects polyethylene wear in the patellar component and may affect anterior knee pain after TKA.4 Measured resection technique, when based on a single landmark or axis as the sole reference for femoral component rotation in total knee arthroplasty, is often inaccurate. In knees with severe valgus deformity, the use of the posterior condylar axis as the reference axis may lead to malrotation due to lateral femoral condylar hypoplasia.6 The transepicondylar axis may be difficult to define, due to difficulty in finding the most prominent point or the sulcus of the medial epicondyle.7 There are two types of epicondylar axes: the surgical axis – drawn between the lateral epicondyle and the centre of the medial epicondylar sulcus, and the clinical axiswhich is drawn between the most prominent part of the lateral and medial epicondyle.9,10 Berger et al.10 regarded the former axis to be more reliable, though it is more difficult to define clinically.6 The Whiteside's line could be difficult to define in deformed knees – due to erosion of the anterior portion of the lateral or medial femoral condyles.3 Therefore, while determining rotational alignment of the femoral component in total knee arthroplasty, it is essential take into consideration all the relevant axes.
5.
Fig. 1 – Showing the transepicondylar axis, the posterior condylar axis and the posterior condylar angle (PCA).
Results
Posterior condylar angle (PCA)
Western studies suggest that the Posterior condylar angle (PCA) is about 38 – (Griffin et al.8 – 3.118, Boisgard et al.9 2.658, Berger et al.10 – 3.58). Most proprietary jigs used in measured resection, place the anterior and posterior femoral cuts at 38 of external rotation to the posterior condylar axis. According to our study, the PCA in the Indian knee is about 4.678 – which is greater than in the Western knees – but slightly less than the
242
journal of clinical orthopaedics and trauma 6 (2015) 240–243
[(Fig._2)TD$IG]
Table 2 – Whiteside–Epicondylar (W–EP) angle in different ethnic populations. Population
Mean Whiteside–Epicondylar (W–EP) angle
Indian – Our study Western5 Japanese3 Chinese4
Fig. 2 – Showing the Whiteside's line and the Whitesideepicondylar angle (W–EP angle).
Japanese3 (5.88) and Chinese4 (5.18 in males and 5.88 in females). Mullaji et al. also described a PCA of 58 in Indian knees6 (Table 1). This suggests that the use of standard femoral jigs with 38 inbuilt external rotation with reference to the posterior condylar axis in total knee arthroplasty can result in internal rotation of the femoral component in Indian knees.
6.
Whiteside–Epicondylar (W–EP) angle
The mean W-EP angle was more externally rotated in the Indian population (92.78) than in the Western and Japanese population (Table 2). The Japanese population3 was older than our study group (mean age of 50.2 years Vs 29.45 years) and the Western study5 was done in cadavers. This implies that if we take the perpendicular to the AP axis or the Whiteside's line as the reference during total knee arthroplasty, the femoral component would be placed in a more externally rotated position. The W–EP angle in the study done by Amaranath et al.11 was 92.8 2.48, which is comparable to our study. They showed that gender, age and mechanical alignment had no significant effect on altering the relationship of transepicon-
92.78
