Comparison of muscle tightness between knees in individuals with unilateral osteoarthritis and its relationship with pain and function

Abstract

BACKGROUND:

Unilateral osteoarthritis (OA) affects single knees and presents a unique scenario where individuals experience varying degrees of symptoms between their affected and unaffected knees.

OBJECTIVE:

This study aims to investigate differences in muscle tightness between symptomatic and asymptomatic knees in individuals with unilateral knee OA while exploring the interplay among pain, functionality, and muscle tightness.

METHODS:

In this cross-sectional study, thirty knee OA patients underwent assessments for hamstring (Active Knee Extension, Straight Leg Raise), iliotibial band (Ober Test), and quadriceps tightness (Modified Thomas Test). Pain intensity was measured using the Visual Analog Scale (VAS), and functional limitations were evaluated via the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC).

RESULTS:

A negative correlation was observed between participants’ pain and AKE ( $p=$ 0.004, $r=-$ 0.515), ASLR ( $p=$ 0.27, $r=-$ 0.403), Ober ( $p=$ 0.010, $r=-$ 0.461) values. However, no significant correlation was found with the Modified Thomas value ( $p=$ 0.204, $r=-$ 0.239). There was also a negative correlation between participants’ WOMAC scores and AKE ( $p=$ 0.019, $r=-$ 0.427), OBER ( $p=$ 0.004, $r=-$ 0.510), and Modified Thomas ( $p=$ 0.022, $r=-$ 0.416) values, while ASLR ( $p=$ 0.286, $r=-$ 0.202) values showed no significant correlation. Comparisons between AKE, Ober, and Modified Thomas values showed higher values in asymptomatic extremities (AKE: $p=$ 0.025, Ober: $p=$ 0.021, Modified Thomas: $p=$ 0.030).

CONCLUSION:

This study emphasizes the significance of muscle tightness in the symptomatic extremities of individuals with unilateral knee OA. The results indicate that increased muscle tightness makes pain worse and limits movement. It’s crucial for healthcare providers treating OA to focus on improving muscle flexibility, reducing pain, and enhancing overall function.

Keywords

Hamstring muscles knee muscle tightness osteoarthritis quadriceps muscle

1. Introduction

Arthritis is one of the leading causes of disability in adults over the age of 55 [1]. The knee, one of the major joints that supports body weight, is the most commonly affected joint by osteoarthritis (OA) [2]. Clinical features of knee OA include joint pain, stiffness, crepitus, and limited range of motion, leading to functional limitations in knee movements [3]. Surgical, pharmacological, and various physiotherapeutic options are used in people with knee OA, depending on the extent of the disease. Non-surgical treatments for OA include weight control, exercise, manipulation, electrotherapy, non-steroidal drugs, and intra-articular steroids [4, 5].

Patients with knee OA often modify their gait to relieve knee pain [6]. Common changes include decreased stride length and walking speed, decreased knee flexion and range of motion, and changes in ankle and hip joint moments [7, 8]. In people with OA, the joint capsule and surrounding muscles lose their flexibility as a result of restricted knee flexion and extension angles. In OA, the chondrocytes in the cartilage do not function properly potentially affecting the flexibility of the hamstring muscles [9]. Insufficient flexibility in the iliotibial band, hamstrings, and quadriceps muscle groups can lead to a less fluid knee movement, potentially increasing the risk of injury and musculoskeletal issues for the individual [10, 11]. Muscle spasm develops in the knee musculature in 1st and 2nd grade knee OA. The extensors of the knee joint, quadriceps, are prone to weakness, while the flexors of the knee joint, hamstrings, experience tightness. The stiffness observed in early-stage knee OA is reported in the literature to stem from spasms in the biceps femoris muscle due to pain and the flexor reflex [12, 13]. Therefore, along with strengthening, it is necessary to stretch the muscles around the joint [12].

Many biomechanical studies of knee OA limit their analysis to a single extremity [14, 15]. However, few studies have examined whether this is representative of both limbs, and whether unilateral and bilateral disease result in similar alterations.

There is an association between lower extremity muscle weakness and knee pain, but the literature is unclear as to which muscle tightness is responsible for pain in this knee region. In the light of this information, the hypothesis of this study is that symptomatic lower extremity muscle tightness significantly higher in individuals with unilateral knee OA than in asymptomatic extremities. In addition, there is a relationship between lower extremity muscle tightness and pain and function [9, 10, 16]. The aim of this study was to determine whether there is an association between lower extremity muscle shortening and pain and function in individuals with knee OA.

2. Materials and methods

2.1 Protocol

This study was designed as a cross-sectional prospective investigation and received approval from the Research Ethics Committee of the Faculty of Medicine at KTO Karatay University (decision no. 2022/055). The research was conducted between January and July 2023 at a private hospital, involving 30 volunteers diagnosed with unilateral knee OA. Prior to their participation, all participants were required to provide informed consent. The study adhered rigorously to the principles outlined in the Declaration of Helsinki throughout all stages of the research process. The findings of this study were meticulously reported in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement to ensure the highest quality of reporting.

2.2 Participants

The study included a total of 30 participants diagnosed with unilateral knee OA within the age range of 49–64, comprising 8 males and 22 females. The research was conducted at a private hospital in Konya between January and July 2023. Inclusion criteria for the study encompassed having a diagnosis of unilateral knee OA, experiencing knee pain with radiological evidence of OA, being between the ages of 40–65, voluntary participation, and reporting lower back pain with a pain intensity $>$ 3 on the Visual Analog Scale (VAS) persisting for at least 3 months. Exclusion criteria for the study involved patients with bilateral knee OA, a history of knee surgery, acute arthritis (inflammation, effusion), infectious arthritis, osteomyelitis, malignancies, severe osteoporosis, joint ankylosis, hypermobile joints, advanced degenerative changes, rheumatoid arthritis, and other progressive rheumatological diseases.

2.3 Sample size

In the pre-study phase, a total of 10 individuals with unilateral knee OA were included in the study. The G ${{}^{*}}$ Power software package (Version 3.0.10, Franz Faul, Kiel University, Germany) was used to calculate the required sample size for this study. The statistical findings indicate that, based on the pain values observed in this pilot study, an effect size of $r=$ 0.48, $\alpha=$ 0.05 for the type I error rate, and $\beta=$ 0.20 for the type II error rate would necessitate a minimum of 27 participants with unilateral knee osteoarthritis to achieve 80% statistical power. To accommodate potential data loss or participant attrition, a further 10 percent of individuals were included in this study.

2.4 Outcome measures

2.4.1 Sociodemographic information

Information about the age, gender, height and weight of the participants was collected using the Sociodemographic Information Collection tool prepared by the researchers.

2.4.2 Pain assessment of participants

Pain levels among the participants were evaluated utilizing the Visual Analog Scale (VAS). A ten-centimeter line with numerical markings from zero to ten was presented, accompanied by detailed explanations to ensure clarity. On this scale, “0” denoted the absence of pain, whereas “10” signified the highest level of pain intensity experienced. Participants were instructed to indicate their pain levels during both rest and activity by marking the corresponding points on the ten-centimeter line [17].

2.4.3 Functional assessment of participants

The participants’ functional status will be evaluated employing the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), a scale validated for use in Turkish populations. This scale ranges from a minimum score of “0” to a maximum score of “96”. Higher scores on the scale indicate greater impairment and limitations in functional abilities, reflecting a lower quality of daily life [18].

2.4.4 Hamstring muscle tightness assessment

To evaluate hamstring muscle tightness, the Active Knee Extension (AKE) test was employed. Participants were positioned in the supine posture following the AKE testing protocol. The non-evaluated leg remained extended straight, and a strap was used to secure the pelvis to the bed, passing over the anterior superior iliac spine. A horizontal bar, set at a 90 ${{}^{\circ}}$ angle, was placed over the participant’s hip joint, and the distal part of the thigh made contact with the bar. The participant was then instructed to actively extend the knee while maintaining a neutral ankle position. A smartphone inclinometer, positioned at the midpoint of the tibia, was used to measure the angle. Participants were guided to extend the knee until they experienced discomfort while ensuring a 90-degree hip flexion angle. The range of motion was recorded as the most stable measure in both pre- and post-test assessments. In this context, the knee joint was considered to have a 180 ${{}^{\circ}}$ angle in the vertical plane when the hip was flexed at 90 ${{}^{\circ}}$ [19, 20].

Another assessment utilized to measure hamstring muscle tightness was the Active Straight Leg Raise (ASLR) test, which was conducted on both legs. During this test, participants were instructed to lie supine and perform hip flexion while keeping the knee in full extension. They were asked to raise their legs until the point of discomfort. The hip flexion angle was measured using a smartphone inclinometer app positioned at the midpoint of the femur [21].

2.4.5 Iliotibial band tightness assessment

In the evaluation of iliotibial band tightness, the Ober Test, a reliable and valid method, was utilized. Patients diagnosed with knee OA were positioned in a lateral lying posture with their hips and knees bent, ensuring alignment of shoulders, hips, and ankles. The leg to be assessed was placed on top, and one hand flexed the upper leg to form a 90-degree angle, while the other hand provided stabilization for the pelvis. Allowing the assessed leg to naturally adduct due to gravity, the angle of hip adduction was measured. A smartphone inclinometer, placed at the midpoint of the lateral surface of the femur, was used to measure this angle accurately [22, 23].

2.4.6 Quadriceps muscle tightness assessment

To evaluate the flexibility of the knee extensors, the Modified Thomas Test was employed. For measuring quadriceps muscle flexibility, participants were instructed to lie supine at the edge of the bed and bring both knees towards the chest. This action straightened the lumbar vertebrae and caused posterior pelvic rotation. Using their arms, participants lowered the tested limb towards the floor while keeping the contralateral hip maximally flexed. A smartphone positioned at the midpoint of the femur was utilized to measure the angle accurately [22, 24].

2.5 Statistical analysis

SPSS 29 (IBM Corp., Armonk, NY, USA) statistical package program was used to evaluate the data. The descriptive statistics (mean, standard deviation, number, and percentile) were given for the categorical and continuous variables. The conformity of variables to normal distribution was examined using the Shapiro–Wilk test and histogram method. To compare measurements between groups, paired samples $t$ -test was used for data fitting the normal distribution. Pearson correlation analysis was used to evaluate the relationship between pain, function and muscles tightness. The strength of correlations was categorized as strong ( $>$ 0.5), moderate (0.3–0.5), weak (0.1–0.3), or very weak ( $<$ 0.1) according to $r$ value $p<$ 0.05 was accepted as the significance level.

Table 1
Sociodemographic information

Gender
	X $\pm$ SD / $n$ (%)
Age (year)	58.83 $\pm$ 4.06
BMI (kg/m²)	31.26 $\pm$ 2.55
WOMAC	46.59 $\pm$ 17.22
VAS	5.23 $\pm$ 0.91
Male	8 (26.7)
Female	22 (73.3)

X: mean, SD: standard deviation, $n$ : number, %: percentange, BMI: body mass index, WOMAC: western ontario and mcmaster universities osteoarthritis index, VAS: visual analog scale.

3. Results

3.1 Sociodemographic

Sociodemographic information of the participants is given in Table 1.

When comparing the AKE values of the affected extremities with those of the healthy extremities, the AKE values of the healthy extremities were higher ( $p=$ 0.025, 95% CI $=-$ 6.41, $-$ 0.45, $d=$ 0.595). When comparing the OBER values of the affected extremities with those of the healthy extremities, the OBER values of the healthy extremities were higher ( $p=$ 0.021, 95% CI $=-$ 4.55, $-$ 0.38, $d=$ 0.611). When comparing the Modified Thomas values of the affected extremities with those of the healthy extremities, the Modified Thomas values of the healthy extremities were higher ( $p=$ 0.030, 95% CI $=-$ 5.32, $-$ 0.28, $d=$ 0.575). The ASLR values of the affected extremities were similar to those of the healthy extremities ( $p=$ 0.242, 95% CI $=-$ 3.05, 0.79, $d=$ 0.305) (Table 2).

Table 2
Comparison of symptomatic and asymptomatic extremities

	Knee with OA	Knee without OA	%95 CI		$p$
	X $\pm$ SD	X $\pm$ SD	Lower	Upper
AKE	151.73 $\pm$ 5.56	155.17 $\pm$ 5.97	$-$ 6.41	$-$ 0.45	0.025^*
ASLR	64.63 $\pm$ 3.74	65.77 $\pm$ 3.69	$-$ 3.05	0.79	0.242
Ober	21.83 $\pm$ 4.07	24.30 $\pm$ 4.01	$-$ 4.55	$-$ 0.38	0.021^*
Modified thomas	11.23 $\pm$ 4.68	14.03 $\pm$ 5.05	$-$ 5.32	$-$ 0.28	0.030^*

X: mean, SD: standard deviation, AKE: active knee extansor, ASLR: active straight leg raise, independent sample $t$ test, $p<$ 0.05.

There was a negative strong correlation between participants’ pain and AKE ( $p=$ 0.004, $r=-$ 0.515). There was a negative moderate correlation between participants’ pain and ASLR ( $p=$ 0.27, $r=-$ 0.403), OBER ( $p=$ 0.010, $r=-$ 0.461) values, while there was no significant correlation with the Modified Thomas value ( $p=$ 0.204, $r=-$ 0.239) (Table 3).

Table 3

The relationship between pain and muscle tightness in symptomatic extremity

	VAS	AKE	ASLR	OBER	Modified thomas
VAS	1
AKE	$-$ 0.515^**	1
ASLR	$-$ 0.403^*	0.659^**	1
OBER	$-$ 0.461^*	0.492^**	0.195	1
Modified thomas	$-$ 0.239	0.317	0.220	0.237	1

ASLR: active straight leg raise, AKE: active knee extension test, VAS: visual analog scale, pearson correlation, ^*: $p<$ 0.05, ^**: $p<$ 0.01.

There was a negative strong correlation between participants’ WOMAC scores and OBER ( $p=$ 0.004, $r=-$ 0.510). There was negative moderate correlation between participants’ WOMAC scores and AKE ( $p=$ 0.019, $r=-$ 0.427), Modified Thomas ( $p=$ 0.022, $r=-$ 0.416) values, while there was no significant correlation between WOMAC scores and ASLR ( $p=$ 0.286, $r=-$ 0.202) values (Table 4).

Table 4

The relationship between functionality and muscle tightness in symptomatic extremity

	WOMAC	AKE	ASLR	OBER	Modified thomas
WOMAC	1
AKE	$-$ 0.427^*	1
ASLR	$-$ 0.202	0.659^**	1
OBER	$-$ 0.510^**	0.492^**	0.195	1
Modified thomas	$-$ 0.416^*	0.317	0.220	0.237	1

ASLR: active straight leg raise, AKE: active knee extension test, WOMAC: western ontario and mcmaster universities osteoarthritis index, pearson correlation, ^*: $p<$ 0.05, ^**: $p<$ 0.01

4. Discussion

This study investigated the relationships between hamstring, quadriceps, and ITB tightness, pain and function in individuals with unilateral knee OA and obtained useful results for researchers and clinicians. The findings of this study revealed that increased hamstring, iliotibial band and knee extensor muscle tightness in the symptomatic limb was associated with lower active knee extension, Ober test and Modified Thomas test values compared to asymptomatic limbs. These results suggest that increased muscle tightness in individuals with unilateral knee OA may lead to limitations in range of motion, impaired muscle function and pain in the symptomatic extremity. In light of the study results, which revealed a negative correlation between participants’ pain and AKE, it is evident that hamstring flexibility plays a crucial role in influencing pain levels among individuals with knee OA. This finding aligns with existing literature that emphasizes the significance of assessing muscle tightness in the context of knee OA [25, 26]. The observed correlation supports the notion that reduced hamstring flexibility, as measured by AKE, is associated with increased pain in individuals with knee OA. Previous research has consistently shown altered gait patterns, reduced range of motion, and muscle weakness in joints affected by knee OA [8, 27, 28]. One of the contributing factors to these changes is often muscle tightness, especially in the hamstring muscles [10]. Considering the significant association identified in this study between pain, and AKE, interventions aimed at improving hamstring flexibility may prove valuable in managing and alleviating pain in individuals with knee OA. These results underscore the importance of addressing muscle tightness, particularly in the hamstring muscles, as a potential target for more effective and targeted interventions in the management of knee OA symptoms. Further research could explore specific exercises or therapies that focus on improving hamstring flexibility to better inform evidence-based interventions for individuals dealing with knee OA.

Figure 1.

Flowchart.

In this study, increased iliotibial band tightness was observed in symptomatic extremities of individuals with unilateral knee OA. The iliotibial band is a significant structure affecting both the hip and knee joints [29]. The findings of this study demonstrated a negative correlation between OBER test and the severity of knee pain in individuals with unilateral knee OA, supporting the direct relationship between iliotibial band tightness and pain, as previously shown in the literatüre [11, 30]. The increased tightness in the iliotibial band could affect the stability around the knee joint, potentially increasing pain intensity and functional limitations [11]. This relationship allows us to understand the connection between stability and pain. However, more comprehensive studies incorporating the anatomical and biomechanical effects of the iliotibial band are needed to clarify this relationship. Such studies would provide a clearer understanding of the direct impact of iliotibial band tightness on the symptoms of knee OA. A more comprehensive examination of the anatomical and biomechanical effects of the iliotibial band is necessary to clarify the impact of its tightness on the symptoms of knee OA. Such detailed studies could contribute to the development of more targeted and effective interventions for individuals dealing with knee OA.

Focusing on the results of the modified Thomas test, lower values were observed in affected extremities compared to healthy extremities. This indicates that limitations in knee flexion angles could contribute to increased muscle tightness in the affected extremity [16]. Lower values in the Modified Thomas test might signify restrictions in the anterior portion of the femur in individuals with knee OA, potentially affecting quadriceps muscle tightness and complicating knee extension [22, 24]. The lower values observed in the Modified Thomas test among individuals with knee OA suggest a potential association between restricted knee flexion angles and limitations in the anterior portion of the femur [22, 24]. These findings imply that compromised flexibility in the quadriceps muscle, influenced by femur restrictions, may contribute to heightened muscle tightness and further complicate the extension of the knee joint. This intricate interplay between reduced knee flexion and its impact on quadriceps muscle function highlights the importance of addressing both aspects in the management and rehabilitation of individuals with knee OA. Future research could explore targeted interventions aimed at improving both knee flexion and quadriceps muscle flexibility to alleviate the complications associated with knee extension in this population.

The observed negative correlations between hamstring, quadriceps, and ITB tightness tests and pain in this study align with previous research highlighting the impact of muscle tightness on pain perception [12, 25]. Hamstring, quadriceps, and ITB with limited flexibility can create additional stress on the joints, potentially exacerbating pain. This finding emphasizes the importance of addressing muscle tightness as part of pain management strategies in individuals with knee OA.

Furthermore, the significant negative correlations identified between participants’ WOMAC scores and the outcomes of the OBER, AKE, and Modified Thomas tests shed light on the intricate relationship between functional impairment and specific musculoskeletal factors in individuals with knee OA. These findings are consistent with existing literature suggesting that impaired lower extremity muscle flexibility can significantly impact the ability to perform daily activities and jeopardize overall functional capacity [25, 31]. The strong negative correlation with OBER indicates that increased iliotibial band tightness is associated with higher WOMAC scores, suggesting that limitations in hip abduction could contribute to the overall functional impairment reported by participants [32]. Furthermore, the moderate negative correlations observed between WOMAC scores and AKE, as well as Modified Thomas values, underscore the impact of reduced hamstring flexibility and limitations in knee flexion angles on the severity of symptoms reported by individuals with knee OA. These findings suggest that addressing hamstring flexibility and femur restrictions may be crucial in mitigating the functional limitations and pain experienced by these individuals [31]. Interestingly, no significant correlation was found between WOMAC scores and ASLR values. WOMAC scores encompass a broader spectrum of knee-related symptoms, while the ASLR test specifically evaluates aspects of lumbar spine stability and pelvic tilt. It’s possible that the observed symptoms in knee OA patients may not be directly influenced by the specific factors assessed by the ASLR test [33]. It is essential to recognize the specificity of these correlations, as they highlight distinct aspects of musculoskeletal function contributing to the overall symptomatology of knee OA.

This study has several implications for clinical practice. Firstly, healthcare professionals should consider evaluating muscle tightness in both extremities of individuals with unilateral knee OA, as differences in muscle tightness between limbs could influence the overall management approach. Secondly, interventions aimed at improving muscle flexibility, such as targeted stretching exercises and physical therapy, could be incorporated into the treatment plans of patients with knee OA. These interventions have the potential to alleviate pain, enhance joint function, and increase overall mobility.

However, it is important to acknowledge the limitations of this study. The relatively small sample size might restrict the generalizability of this study. Additionally, this study focused solely on muscle tightness without considering other biomechanical and anatomical factors that could influence knee OA symptoms. Future research with larger sample sizes and comprehensive assessments of various musculoskeletal factors can provide a more holistic understanding of the relationship between muscle tightness, pain, and function in individuals with knee OA.

5. Conclusion

The findings of this study indicate an association between increased muscle tightness in the symptomatic extremity and specific tests. Notably, substantial differences in muscle tightness were evident between affected and unaffected knees, revealing negative correlation with pain and functional limitations. However, the underlying mechanisms of this relationship and its clinical significance should be further explored in-depth. Further research on this topic will contribute to a better understanding of the relevant mechanisms and the clinical outcomes of the condition.

Author contributions

All listed authors made valuable contributions to the development of this manuscript. Conception and design: BSU, OT; Methodology: BSU, OT, HG; Investigation: BSU, MST; Resources: OT, OE; Data collecting: OT, OE; Analysis and interpretation of the data: BSU, HG; Supervision: BSU, MST; Writing – original draft: BSU, OT, HG, MST, OE; Writing – review & editing: BSU, OT, HG, MST, OE. All authors read and approved the final version of the manuscript and agreed with the order of presentation of the authors.

Data availability statement

Data will be made available from the corresponding author upon request.

Ethical approval

The study was approved by the Drug and Non-Medical Device Research Ethics Committee of KTO Karatay University, Faculty of Medicine (decision number 2022/055).

Funding

The authors report no funding.

Informed consent

Informed consent was obtained from all patients to be included in the study.

Footnotes

Acknowledgments

The authors thank all participants.

Conflict of interest

The authors have no conflict of interest to declare related to this article.

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