Results of total knee arthroplasty using the femoral condyle rotational and the valgus cut angle

The valgus cut angle is the angle between mechanical and anatomical axis of the femur (FMA and FAA), and femoral condyle rotation is the angle between surgical trans-epicondylar axis and posterior condylar axis (sTEA and PCA). We used these indexes in total knee arthroplasty.

RESULTS OF TOTAL KNEE ARTHROPLASTY USING

THE FEMORAL CONDYLE ROTATIONAL AND THE VALGUS CUT ANGLE

Huy Phuong Nguyen, Dung Tran Trung

Hanoi Medical University

We conducted a prospective study of 48 patients with 54 diagnoses of osteoarthritis of the knee All patients were underwent knee MRI and long leg radiograph pre-operatively The valgus cut angle is the angle between mechanical and anatomical axis of the femur (FMA and FAA), and femoral condyle rotation

is the angle between surgical trans-epicondylar axis and posterior condylar axis (sTEA and PCA) We used these indexes in total knee arthroplasty The results of total knee arthroplasty, based on imaging criteria and KSS scale (KS and KFS) following up post-surgery to 15 months, are as follows: the mean of valgus cut and femoral condyle rotational angle were 7.47º ± 1.25º and 3.52º ± 1.86º, respectively There were no differences between men and women The mean of mechanical axis post-surgery was 1.22º ± 0.45º (0.02º

- 5.05º) The mean of pre-operative and post-operative KS scoring and KFS scoring were 32.74 ± 10.36 and 88.8 ± 9.3, 39.35 ± 12.36 and 82.77 ± 15.63, respectively Applying femoral condyle rotational and valgus cut angles as indexes for surgery can improve the precision and outcomes of total knee arthroplasty.

I INTRODUCTION

Keywords: femoral condyle rotational, valgus cut angle, knee osteoarthritis, total knee arthroplasty.

Osteoarthritis of the knee is a common

disease leading to disability among the elderly

According to the epidemiology studies, about

13 % of people aged 60 and above report

having symptoms of knee osteoarthritis [1]

Total knee arthroplasty (TKA) is a surgery in

which damaged articular cartilage is removed

and replaced by artificial components Restoring

the lower limb axis and correctly placing the

artificial components are basic requirements

of total knee arthroplasty There are many

techniques which are used to determine the femoral condyle rotation, however they are mainly based on landmarks of femoral condyle [2] The anatomical landmarks which are normally used to achieve correct rotational alignment of the femoral component during surgery are the posterior condylar axis (PCA), anteroposterior axis (AP axis), and epicondylar axis (TEA) The surgical trans-epicondylar axis (sTEA) has been evaluated

as an axis that reflects exactly the knee flexion axis and perpendicular to mechanical axis

of femur [3] Studies in Europe and America have shown that the line connecting posterior edges of femoral condyle rotates about 3º in comparison with sTEA which means that the femoral rotation is 3º to the horizontal knee axis [4; 5]

Corresponding author: Nguyen Huy Phuong,

Department of Surgery, Hanoi Medical University

Email: drhuyphuong@gmail.com

Received: 27/11/2018

Accepted: 12/03/2019

Figure 1 Diagram demonstrating the TEA,

APA and PCA, axes.

The 3º femoral rotation angle is currently

being used in Vietnam However, several

studies in Asian populations have showed

that this angle ranges from 1.7º to 9.7º [6]

Moreover, the recovery of the lower limb axis

post-surgery can be better when the axis

is close to 0º It also depends on the distal

femoral cut and valgus cut angle, which are

created by mechanical axis and anatomical

axis of the femur (figure 2) This angle is also

different between patients

Figure 2 The anatomical and mechanical

axis of the femur

Therefore, we conducted this research

on Vietnamese patients with the following 2

purposes:

1 To identify the femoral condyle rotation and valgus cut angle in knee osteoarthritic patients who have indicated total knee arthroplasty

2 To evaluate the results of total knee arthroplasty which was applied femoral condyle rotational and valgus cut angle technique

II METHODS

1 Materials

1.1 Subject Inclusion criteria

- The osteoarthritis patients have indications for total knee arthroplasty

- The patients underwent MRI (Magnetic resonance imaging) and long leg radiograph before surgery

- The patient who participated in the research

Exclusion criteria

- Osteoarthritis patients who do not have indications or who have contraindications to total knee arthroplasty

- Patients who had various axes cannot be identified in MRI and long leg radiograph

- Patients who had bone fractures or general surgical interventions of the knee before

Sample size

We used total population sampling type (purposive sampling), recruiting 48 patients with 54 osteoarthritic knees in which total knee arthroplasty surgery was appropriate

1.2 Study Design

Prospective cross-sectional study

1.3 Place

Department of Orthopedic and Trauma and Department of Radiology in Saint Paul Hospital

and Hanoi Medical University Hospital.

1.4 Duration

From July, 2016 to May, 2018

1.5 Variable research

- Age and gender; the femoral rotated angle

(sTEA and PCA)

- The valgus cut angle (FMA - Femoral

mechanical-anatomical angle, and FAA -

Femoral anteversion angle); the mechanical

axis of lower limb post-surgery

- KSS score (including KS - Knee score, and KFS - Knee functional score) before and after surgery

2 Methods

MRI scanning system 1.5 Tesla which was made in Florida, USA, in November, 2009, serial 037255, thin slice cut 1mm, 256 slices and X-rays machine

Simple Angle Measurement software and eFILM to measure the angle

Figure 3 Demonstrating measure rotation and valgus cut angle by the software

Figure 4 Distal cutting slice based on

valgus cut angle

Figure 5 Anterior and posterior cutting slice based on femoral rotated angle

2.1 Surgical technique applying femoral

condyle rotation and valgus cut angle

- Distal cutting slice based on intramedullary

and valgus cut angle (the angle between

mechanical axis and anatomical axis) (FMA

and FAA)

- Anterior and posterior cutting slice based

on the angle between sTEA and PCA

- Other cutting slices is similar to normal total knee arthroplasty

2 The femoral condyle rotational and the valgus cut angle

Table 1 The mean of rotation and valgus cut angle

Mean

Rotation angle 3.52º ± 1.86º (0.09º - 6.79º)

Valgus angle 7.47º ± 1.25º (4.24º - 10.23º)

The mean rotation and valgus angle were 3.52º and 7.47º respectively

Table 2 The mean of rotation angle in respect of gender

Rotation angle

The mean rotation angle in male and female were 3.28º and 3,57º respectively There is no statistically significant difference

Table 3 The mean of valgus angle in relation to gender

Valgus cut angle

There is no statistically significant difference between male and female (p = 0.5)

Table 4 Mechanical axis between pre – operation and post - operation

Mechanical axis p-value

(T-test)

The mechanical axis between pre-operation and post-operation are statistically significant difference (p = 0.003)

2.2 Collecting the data

The variable research was collected

following a medical record pattern

3 Statistical analysis

STATA 12.0 software to calculate p-value,

T-test

III RESULTS

1 Age and sex characteristics

The youngest patient is 55 years and oldest patient is 78 years The mean of age is 68.47

± 12,06 years The ratio of male/female was 4/44

Table 5 The improvement in terms of KSS scoring

KS score KFS score p-value

Pre-Op 32.74 ± 0.36 39.35 ± 12.36 <0.001 (T-test)

Post-Op 88.8 ± 9.3 82.77 ± 15.63 <0.001 (T-test)

KS and KFS score are better after operation in comparison with pre-operation

Table 6 General result evaluation, in terms of KSS scoring

General result evaluation is very good, account for 77,2%

IV DISCUSSION

In this study, 54 knees in 48 patients with the

average of age of 68,47 ± 12,06 were observed

The ratio of male/female was 4/44, this means

that women are more likely to experience knee

osteoarthritis and total knee replacement than

men This difference due to the menopause

through which period women have a decrease

in estrogen levels and osteoporosis

Several studies which were based on

mechanical and kinematic alignment have

shown that sTEA axis reflexes exactly with the

horizontal axis of the knee This means that

anterior-posterior slice cuts need to be parallel

with sTEA in order to obtain the best result

However, many studies have reported that

the determination of this axis in surgery tend to

be difficult, resulting in many inaccuracies[2]

Besides that, surgical instruments mainly based

on PCA axis Therefore, identifying the angle

between sTEA and PCA axis is very important,

it helps define the rotation angle of

anterior-posterior slice cut In America and Europe,

a majority of research that has evaluated

the valgus angle to be 3º However, some

research in Asian populations have showed

that this angle varies from 1,7º to 9,7º [7 - 9]

In particular, the mean of Japanese rotation cut angle is 5º [8],[9] In our research, the mean

of rotation angle (sTEA and PCA) was 3.52º ± 1.86º (vary from 0.09º to 6.79º), which means there is a significant difference among patients During surgery, we set up the tool which can cut anterior-posterior slice based on the angle between sTEA and PCA which is measured pre-operation vary from 0º to 6º

Beside the rotation cut angle, the valgus cut angle is an essential factor for total knee replacement This angle determines the accuracy of cutting distal to the femur and the recovery of the mechanical axis of the limb mostly depends on this slice cut [11 - 13]

We cut the distal femur by intramedullary guide according to femur anatomical axis and valgus cut angle to help the cutting slice of distal femur perpendicular to the mechanical axis of femur The average of mechanical axis based on X-rays after surgery is 1.22º ± 0.45º, this means that applying valgus cut angle might help the patient to recover the mechanical axis better

General evaluation according to KSS score through the duration of 15 months after surgery, the outcome of the patients is very

good (77.2 %), good (17.1 %), fair (5.7 %) and

bad (0%) However, this is just initial outcome,

it should be carried out further with a larger

number of patients to evaluate the effective of

valgus cut angle application

V CONCLUSION

Applying the femoral rotation and valgus cut

angle in total knee arthroplasty can improve

the precision of surgery and help patients to

restore the mechanical axis of the lower limb

after surgery

Acknowledgement

A completed study would not be done

without any assistance Therefore, the authors

who conducted this research gratefully give

acknowledgement to Department of Orthopedic

and Trauma and Department of Radiology

in Saint Paul University Hospital and Hanoi

Medical University Hospital

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