Physical Therapy Korea

Osteoarthritis is a common disease with an increasing prevalence and is one of the leading causes of disability among the older adults [1]. Epidemiologically, half of the world’s population aged 65 years or older has osteoarthritis, making it a common joint disease [1]. In particular, osteoarthritis of the knee accounts for approximately 4/5ths of the global osteoarthritis burden and is highly associated with obesity and age [2]. The prevalence and incidence of knee osteoarthritis in women and men are approximately 1.69 and 1.39, respectively [2]. The number of arthritis cases reportedly increases with age, with prevalence rates peaking at older ages and incidence rates peaking at 70–79 years [3]. The increasing prevalence of knee arthritis may cause various health problems in a rapidly aging society such as in Korea [3].

The primary symptom of knee osteoarthritis is pain, which is usually induced during activity and relieved at rest [4]. In chronic knee arthritis, pain is caused by the decrease in joint protection by the muscles and is severe enough to wake one from sleep and limit movement during activity [4]. In one year, approximately 25% of the population over the age of 55 years had persistent knee pain, and approximately 1/6th consulted a doctor in the hospital [5]. Approximately > 50% of the patients who self-reported knee pain had radiological knee osteoarthritis [5]. Treatment of osteoarthritis can be divided into four major categories (non-pharmacological, pharmacological, surgical, and complementary or alternative) [6]. Of these, the safest and least invasive treatments must be initiated, followed by the use of invasive methods when symptoms worsen [6]. Aerobic walking and strengthening exercises reportedly improve function in patients with knee osteoarthritis [7]. Additionally, simple home-based and walking exercises improve the quality of life of patients with knee osteoarthritis and decrease pain and disability [8]. However, whether gait training can be used as a therapeutic tool in exercise programs is a reality that must be continually confirmed [8].

The kinematics of the knee joint that appear in the average person during gait are predominantly flexion and extension. The convex–concave mechanism of the articular surfaces causes the tibia to roll and slid forward against the articular ridge of the fibula during leg extension [9]. When standing up from a squatting position with the feet on the ground, the articular ridge of the fibula simultaneously rolls forward and slides backward against the articular surface of the tibia [9]. These movements limit the magnitude of the translational movement of the fibula relative to the tibia [9]. The gastrocnemius muscle aids in rolling the peroneal articular ridge and stabilizing the horizontal transfer forces generated on the semilunar cartilage during sliding [9].

Recent studies have reported that individuals with joint instability and knee osteoarthritis have significantly reduced sagittal and lateral rotational motions of the knee [10]. Reduced rotational motion is thought to be a compensatory mechanism that stabilizes the unstable knee joint and prevents pain [10]. However, this compensation increases the loading and decreases the shock-absorbing capacity, which can cause long-term problems [10]. Several recent studies have used patellar tendon straps to immobilize the patella and provide stability to the knee joint [11]. However, there have been no studies on the effects of patellar tendon straps during gait in patients with knee osteoarthritis. Therefore, this study aimed to investigate the effects of wearing and not wearing patellar tendon straps on joint kinematic and mechanical data and muscle activation levels during walking in patients with bilateral knee osteoarthritis. The hypothesis of this study was that when patients with bilateral knee osteoarthritis wear straps, the kinematics in the sagittal plane would improve.

1. Participants

The experiment was conducted at the Onju General Social Welfare Center in Asan City. Participants were recruited through recruitment literature, and the experiment was explained to them. Thereafter, informed consent was obtained before the research experiment were performed. Study participants were selected based on the following criteria: aged 60–85 years, bilateral knee osteoarthritis, and capable of walking at least 30 m during a single independent walk. The exclusion criteria were as follows: those who had undergone knee joint replacement surgery, were diagnosed with dementia, and were unable to walk independently.

G-power (ver. 3.1.9.7; Franz Faul, Kiel University) was used to determine the number of participants to be recruited, based on an effect size of 0.50, significance level of 0.05, and power of 95%. This resulted in a required sample size of 32 participants. Considering previous studies [12,13] and a dropout rate of 10%, a total of 35 participants were recruited. Among the 35 participants, 12 did not participate because of poor health, six did not have bilateral knee arthritis, three had undergone knee replacement surgery, three had undergone ankle surgery, one had dementia, and two dropped out and were excluded. Finally, nine participants were selected and tested in the research experiment (Figure 1). This study was approved by Hoseo University Institutional Ethics Committee (IRB no. 1041231-220712-HR-148-02), and all participants provided written informed consent.

Figure 1. Flowchart of the study. OP, operation; VMO, vastus medialis oblique; VL, vastus lateralis; BF, biceps femoris; G-max, gluteus maximus.

2. Measurement

Measurements of the quadriceps angle (Q-angle), leg length, and toe bend were used as references to determine the extent to which patients with knee osteoarthritis differed.

The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) assesses pain, stiffness, and function and has been well validated in older adults with knee or hip osteoarthritis [14]. The assessment tool relates to knee joint pain (5 questions), stiffness (2 questions), and physical function (17 questions) and requires the participant to complete the questionnaire with the researcher’s help or independently. All the questions were rated on a 5-point scale (0–4 points): not unpleasant (0 points), slightly unpleasant (1 point), normal (2 points), quite unpleasant (3 points), and very unpleasant (4 points).

For the Q-angle, the participant first comfortably positioned the foot in a supine position, and subsequently, a line was drawn connecting the anterior superior iliac spine (ASIS) to the center of the patella. The Q-angle was measured using an angiometer at the point where the line drawn intersected with the line connecting the tibialis transverse plane and the patella center [15]. The knee bone center point is based on the point at which a line drawn from the medial to the lateral knee bone border intersects that drawn from the inferior to the superior pole [16]. The angle was measured three times, and the average value was considered as the measured value.

For structural leg length measurements, the participant was placed in the supine position on a bed, and a tape measure (Hoechstmass; Hoechstmass) was used to measure the distance from the ASIS to the medial malleolus. For accurate measurements, the participants wore thin shorts. After applying stickers to the ASIS and medial malleolus to ensure uniform measurements, leg length was measured, and the difference between the difference between the right and left leg lengths was calculated. To reduce errors, the same examiner repeated the measurement three times and used the average value [17].

The great toe side-flexion angle was measured using an angle meter (Pocket Goniometers; Seedtech). For the angle meter measurement, a point was displayed on the body of the first metatarsal bone of the first foot and the body of the first metatarsal bone of the great toe to make two vertical lines. The angle formed by the two vertical lines was recorded as the great toe side-flexion angle [18]. The experiment was performed three times, and the average value was recorded.

The three-dimensional motion analysis system attempts to measure kinematic variables of the lower extremities. A miniature inertial measurement unit (IMU) (myoMOTION; Noraxon USA, Inc.) is capable of measuring body-minimal product tracking for three-dimensional angular alignment and has an accuracy of 1.2° for dynamic measurements (Figures 2, 3) [19].

Figure 2. Inertial measurement unit sensor (myoMOTION; Noraxon USA, Inc.).

Figure 3. Inertial measurement unit sensor attachment site. PSIS, posterior superior iliac spine.

The zebris FDM-S multifunction force measuring plate (zebris Medical GmbH) analyzes the static and dynamic force distributions under the foot in the standing posture and during gait, synchronizes with the IMU sensor, and simultaneously measures the force distribution during dynamic balance with the IMU sensor (Figure 4).

Figure 4. The zebris FDM-S multifunction force measuring plate (zebris Medical GmbH).

Surface electromyography (EMG) (Ultium; Noraxon USA, Inc.) was used to measure muscle activity before and after patellar tendon strap application. The attachment sites of the vastus medialis muscles are as follows: 80% of the line between the anterior joint space of the anterior border of the superior-anterior gluteal bursa and the medial ligament in a sitting posture with the knees slightly bent and the upper body slightly bent back. Thus, the direction of EMG electrode should be approximately perpendicular to the line between the anterior joint space of the ASIS and the anterior border of the medial ligament [20]. The vastus medialis attaches at a point 2/3rds of the line from the ASIS higher than the lateral aspect of the patella in a sitting posture with the knee slightly bent and the upper body bent back [20]. The muscle fibers and sensor are attached in the same direction [20]. The gluteus maximus muscle is affixed at approximately 50% of the line between the femur and greater trochanter in the supine position [20]. This position is in line with the largest projection mid-buttocks [20]. The direction of the electrode is in the line from the posterior superior iliac spine to the center of the thigh [20]. The biceps femoris muscle is located at 50% of the line between the pseudolateral superior articular ridge of the tibia and the gluteal tubercle in the supine position, with the knee bent to < 90° and the thigh and foot rotated slightly to the side [20]. The EMG should be in the direction of the line between the pseudolateral superior articular ridge of the tibia and gluteal tuberosity [20]. The electrode size for all muscles was 10 mm, which is the maximum size in the muscle fiber direction, and the the distance between electrodes was 20 mm (Figure 5).

Figure 5. Electromyography attachment.

Age, height, weight, sex, body mass index (BMI), degree and duration of knee pain, Q-angle, length of the leg, and great toe side-flexion angle of all participants with bilateral knee osteoarthritis were recorded to analyze kinematic and mechanical data and the degree of muscle activation of the joint during walking, before and after wearing patellar tendon straps. Other medical history was checked. All participants wore the IMU sensor and EMG, stood on the starting line, performed a 0-point adjustment (calibration), walked in a straight line for a distance of 5 m, turned around, and returned to the original position; this was repeated twice for a total of three times. After each walk, a 3-minute rest period was provided, and if the participant requested more rest time, a longer break was provided. The same walk was performed after wearing the patellar tendon strap (Zamst; Nippon Sigmax Co., Ltd.), and a 5-minute rest period was provided before and after wearing the patellar tendon strap. The strap should be worn such that the pad is positioned inward 5 cm below the center of the patella, while producing moderate pressure (Figure 6).

Figure 6. Patellar tendon strap attachment.

Kinematic data, kinetic data, and muscle activity were evaluated during the gait cycle with and without patellar tendon straps. The experiments were performed three times, and the averages were calculated and analyzed.

For the measured gait, data of the interval between the eight markers were extracted [21]. The marker intervals were based on the left lower extremity: (1) the moment the heel touches the ground (initial contract); (2) the moment the big toe of the opposite leg leaves the ground (loading response); (3) the limb is in the initial support phase, when the tibia of the opposite leg becomes vertical from the ground (mid-stance); (4) the leg is in the second half of the support phase, when the heel of the opposite leg touches the ground (terminal stance); (5) the moment the big toe of the leg is off the ground (pre-swing); (6) the moment when the tibia of the left leg crosses the opposite leg (initial swing); (7) the moment when the tibia of the left leg becomes perpendicular to the ground (mid-swing); and (8) the moment immediately before the heel touches the ground (terminal swing). Gait was measured three times before and after the intervention; the kinematic, kinetic, and muscle activation data were averaged.

3. Statistical Analysis

Statistical analysis was performed using the IBM SPSS for Windows (ver. 20.0; IBM Co.). The Shapiro–Wilk test for normality was used to check whether the variables were normally distributed. Normally distributed variables were subjected to a corresponding sample t-test, a variable test, and variables that were not normally distributed were subjected to the Wilcoxon signed-rank test, a non-variable test, for within-group before and after comparisons. The significance level was set at p < 0.05.

1. Demographic Information

Nine participants, one male and eight females, were included in the study, and the general characteristics of the participants are shown (Table 1). They consisted of age (75.89 ± 7.08 years), height (154.76 ± 5.95 cm), weight (60.82 ± 4.74 kg), and BMI (25.43 ± 2.33 kg2). The total WOMAC index was 40.77 ± 10.72. The visual analog scale for each posture was 1.89 ± 1.36 for sitting still, 3.56 ± 2.30 for standing up while seated, 2.67 ± 1.66 for standing, and 4.11 ± 11.4 for walking (Table 2).

Table 1 . Characteristics of subjects (N = 9).

Variable	Value
Age (y)	75.89 ± 7.08
Height (cm)	154.76 ± 5.95
Weight (kg)	60.82 ± 4.74
BMI (kg/m2)	25.43 ± 2.33
Q-angle Lt. (°)	172.6 ± 2.65
Q-angle Rt. (°)	171.8 ± 3.16
Leg length Lt. (cm)	75.76 ± 2.47
Leg length Rt. (cm)	75.83 ± 3.35
Hallux valgus Lt. (°)	20.03 ± 6.95
Hallux valgus Rt. (°)	22.30 ± 7.87

Values are presented as mean ± standard deviation. Lt., left; Rt., right..

Table 2 . WOMAC scores of subjects (N = 9).

Variable	Value
WOMAC pain	8.77 ± 3.27
WOMAC stiffness	2.23 ± 1.32
WOMAC function	29.66 ± 7.41
WOMAC total	40.77 ± 10.72

WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index..

2. Kinematic Data With and Without Patellar Tendon Straps During Gait Cycle

The kinematic data before and after wearing the patellar strap in this study were as follows: during the terminal stance, maximal left hip spread increased from –3.71° ± 2.82° to –4.53° ± 2.58°, and in the terminal hexagon, maximal right knee flexion angle increased from 24.80° ± 6.01° to 26.63° ± 6.48°. The minimum flexion of the right foot dorsiflexion increased from –13.82° ± 7.94° to –15.87° ± 7.74° during the pre-swing phase. During the initial swing phase, the maximum right dorsiflexion increased from –16.26° ± 7.79° to –18.25° ± 7.77° (Table 3).

Table 3 . Kinematic data of subjects with and without patellar tendon strap during walking (N = 9).

Gait cycle	Variable	Pre	Post	p-value
Terminal stance	Lt. Maximum hip abduction (°)	–3.71 ± 2.82	–4.53 ± 2.58	0.045*
Pre swing	Rt. Minimum ankle dorsiflexion (°)	–13.82 ± 7.94	–15.87 ± 7.74	0.041*
Initial swing	Rt. Minimum ankle dorsiflexion (°)	–16.26 ± 7.79	–18.25 ± 7.77	0.015*
Terminal swing	Rt. Maximum knee flexion (°)	24.80 ± 6.01	26.63 ± 6.48	0.016*

Values are presented as mean ± standard deviation. Lt., left; Rt., right. *p < 0.05..

3. Spatiotemporal Parameters and Muscle Activities With and Without Patellar Straps During Walking

The spatiotemporal parameters in the walking stage in this study were as follows: cadence and speed increased from 97.85 ± 12.17 to 105.86 ± 9.06 steps/min and from 2.51 ± 0.61 to 2.85 ± 0.36 m/s, respectively. Left and right step time decreased from 628.93 ± 97.90 to 573.88 ± 46.19 ms and from 634.38 ± 103.32 to 565.30 ± 46.34 ms, respectively. Stride time also decreased from 1,251.75 ± 188.66 to 1,142.63 ± 94.61 ms (Table 4).

Table 4 . Spatiotemporal parameters of subjects with and without patellar tendon straps (N = 9).

Subject	Pre	Post	p-value
Cadence (steps/min)	97.85 ± 12.17	105.86 ± 9.06	0.032*
Velocity (m/s)	2.51 ± 0.61	2.85 ± 0.36	0.026*
Lt. Step time (ms)	628.93 ± 97.90	573.88 ± 46.19	0.021*
Rt. Step time (ms)	634.38 ± 103.32	565.30 ± 46.34	0.008*
Stride time (ms)	1,251.75 ± 188.66	1,142.63 ± 94.61	0.011*

Values are presented as mean ± standard deviation. Lt., left; Rt., right. *p < 0.05..

The foot force duration was as follows. The left midfoot force duration decreased from 80.47% ± 2.31% to 78.60% ±2.40%, right midfoot force duration decreased from 80.39% ± 2.88% to 78.96% ± 2.20%, and right hindfoot force duration decreased from 72.58% ± 3.88% to 69.59% ± 2.04% (Table 5).

Table 5 . Foot force duration of subjects with and without patellar tendon straps (N = 9).

Subject	Pre	Post	p-value
Lt. Midfoot force duration (%)	80.47 ± 2.31	78.60 ± 2.40	0.013*
Rt. Midfoot force duration (%)	80.39 ± 2.88	78.96 ± 2.20	0.048*
Rt. Hindfoot force duration (%)	72.58 ± 3.88	69.59 ± 2.04	0.022*

Values are presented as mean ± standard deviation. Lt., left; Rt., right. *p < 0.05..

The muscle activity with and without patellar tendon straps was not significantly different.

This study investigated the effect of wearing patellar tendon straps on joint kinematic and mechanical data and muscle activation during gait in patients with bilateral knee osteoarthritis. We hypothesized that patients with bilateral knee osteoarthritis would experience improved sagittal plane kinematics when wearing straps. The results of this study showed the following kinematic data after wearing the patellar tendon straps. Maximum hip widening decreased from –3.71 ± 2.82 to –4.53 ± 2.58 during the terminal stance phase of the left lower extremity, and maximum knee bending increased from 24.80 ± 6.01 to 26.63 ± 6.48 during the terminal swing phase of the right lower extremity. The minimum values of ankle joint dorsal foot flexion decreased from –13.82 ± 7.94 to –15.87 ± 7.74 and from –16.26 ± 7.79 to –18.25 ± 7.77 during the pre- and early swing phase of the right lower extremity, respectively. In terms of space-time measurements, cadence and velocity increased, whereas step time, stride time, and foot force duration decreased. Muscle activity did not show any significant differences.

A previous study showed that patients with knee osteoarthritis had lower plantar flexion during the push-off phase than healthy participants [22]. The present study showed that the minimum mean plantar flexion of patients with knee osteoarthritis during the pre-push-off phase was 13°, which is approximately 2° lower than the average. After wearing the patellar tendon strap, the angle was 15°, which is the normal angle. Plantar flexion of approximately 15° occurred at the moment of toe-off during the initial swing phase, with increased movement from 16° to 18°. In another study, after using patellar tendon straps and sports taping, the visual analog scale was compared after performing leg incline squats, jump tests, etc. in four groups of patients with patellar tendon pain: patellar tendon straps, sports taping, placebo, and as a control group. The study showed a significant reduction in pain during squat execution, with patellar tendon straps being more effective at approximately 80% and sports taping at approximately 72% [23]. Previous studies have shown that when wearing a patellar tendon strap, neurological mechanisms improve disability, and neuromuscular activity around the knee decreases pain and disability [24]. Thus, it can be inferred that the patellar tendon strap alters sensory input, reduces pain, and results in changes in the joint angles.

Motor changes in patients with knee osteoarthritis have been reported to increase the adduction moment of the knee during gait [25]. When walking at slower speeds, the adduction moment can be reduced by decreasing the mechanical load [26]. In a previous study, patients with knee osteoarthritis exhibited an adduction angle, whereas healthy controls were relatively neutral during the initial folding [27]. In the present study, it can be seen that the hip widening increased from –3° to –4° of adduction spread during the terminal stance phase, which can be carefully inferred as an increase in hip adduction with increasing velocity after wearing the patellar tendon straps.

No studies have compared the effects of patellar tendon straps on gait in patients with knee osteoarthritis. Gait analysis has been performed in patients with knee osteoarthritis who were wearing knee braces [27]. The knee brace utilizes a 3-point bracing concept with an airbag [27]. The results of this study showed that when the airbag was inflated, the adduction moment decreased more. However, the brace used in the previous study encompassed the knee except for the patella, which had a different shape than the strap used in this study. Additionally, there was a difference in the force transmitted to the knee, which could have led to the differences in the results.

The knee bending angle during the terminal swing phase with normal gait is approximately 5° [28], with little or no width; however, in this study, the knee bends at 24° before wearing the straps compared with that in normal people. As arthritis progresses, limitation of motion [29] and weakening of the knee labral muscles occur in patients with knee osteoarthritis compared to those without it [30]. Because the participants in this study were selected from those with chronic knee osteoarthritis, it is inferred that flexion of approximately 20° occurs during the terminal swing phase when the knee is not fully extended due to joint restrictions, and that flexion is increased due to backward sliding of the tibia by the patellar strap while the muscles are weakened. However, because these reasons are uncertain, future studies on healthy people are needed to clarify their precise causes.

According to a previous study, spatiotemporal parameters resulted in significantly lower gait speed, cadence, step length, and stride length in patients with arthritis than in those without arthritis [31]. Studies have shown that patients with knee arthritis have decreased stride length and velocity and a longer stance phase time in the gait cycle [32]. Another study found that walking time and cycle were significantly longer in patients with knee osteoarthritis than in healthy individuals [31]. Our results showed that the number of steps per minute increased by approximately 8 steps/min before and after wearing the patellar tendon strap, and the velocity increased by 0.34 m/s. Both step and stride times showed decreased results, and foot force duration also decreased. These results suggest that knee stabilization by immobilizing the tibia with a patellar tendon strap increased walking speed and number of steps, and decreased walking time and foot force duration. However, this requires further clarification.

The limitations of this study are as follows. First, the sample size was small. A dropout rate of 10% was considered; however, more participants dropped out, and the study had to be conducted with a smaller sample size. If more participants are selected in the future, this study will have greater validity. Second, the proportion of males and females differed, making generalization difficult to men. In the future, it would be clearer if we proceeded with the experiment by separating the groups by sex. Third, the experiment was conducted without distinguishing between the degrees of knee osteoarthritis. There was a large bias against arthritis without considering the degree of knee osteoarthritis. Fourth, it is difficult to generalize these results without considering other diseases or healthy participants. Further experiments with healthy participants and participants with other diseases will yield a variety of results.

After the patellar tendon strap was applied, the walking speed and number of steps per minute increased during the gait cycle. This is presumed to be due to an increase in the joint angle in pain decrease owing to a neurological mechanism caused by the patellar tendon strap. Thus, wearing a patellar tendon strap while walking in patients with knee osteoarthritis was found to cause kinematic changes in the sagittal plane of the joint.

None.

This research was supported by the Academic Research Fund of Hoseo University in 2022 (202202420001).

No potential conflicts of interest relevant to this article are reported.

Conceptualization: EJL, KSK, YIH. Data curation: EJL. Formal analysis: EJL, YIH. Funding acquisition: YIH. Investigation: EJL, YIH. Methodology: EJL, KSK, YIH. Project administration: EJL, YIH. Resources: KSK. Software: EJL. Supervision: KSK, YIH. Validation: EJL, KSK, YIH. Visualization: EJL. Writing - original draft: EJL, YIH. Writing - review & editing: KSK, YIH.