Effect of knee pain on muscles imbalance and physical limitation in individuals with bilateral knee osteoarthritis: A comparative cross-sectional study

INTRODUCTION

Osteoarthritis (OA) of the knee joint accounts for nearly four-fifths of the global burden of OA, and its prevalence increases with age and weight gain.^[1] Globally, knee OA constitutes 20% of all musculoskeletal burdens with its frequency rising as individuals age.^[2] Globally, 9.6% of males and 18% of females aged 60 and above are impacted by symptomatic OA, according to the World Health Organization. Moreover, approximately 80% of individuals with OA experience restricted joint motion, and 25% of those with OA struggle to perform their daily activities. In Asia, the elderly population aged 65 and above reached 7% in 2008 with expectations that it will increase to 16% by 2040.^[3] In Pakistan, the prevalence of knee OA is 28% in rural areas and 25% in urban areas.^[4] This condition is more common among females and older individuals, particularly those aged between 45 and 65.^[5]

The OA can affect any joint but most frequently affects the knee joint.^[6] Knee OA can be characterized using the clinical-radiographic classification criteria established by the American College of Rheumatology, which includes knee pain followed by at least one of the following three symptoms in conjunction with the development of osteophytes visible on knee radiography: Stiffness in the morning lasting for a duration of <30 min, age >50 years, and crepitus during knee movements.^[7] Knee OA has multiple risk factors including advanced age, genetics, overweight or obesity, female sex, knee joint trauma, overuse of the knee, poor muscular strength, low bone mineral density, and prolonged squatting and kneeling positions.^[8]

The pain around the joint and disuse are major factors contributing to the development of muscle imbalance.^[9] Muscle imbalance can also lead to impaired gait rhythm, decreased walking speed, and reduced walking duration in patients with chronic knee OA.^[10] Among the muscles, the quadriceps is the most important in maintaining strength across the knee joint.^[11] Quadricep muscle strength plays a key role in reducing the severity of knee OA, but their weakness can significantly contribute to the advancement of this condition.^[12] The previous studies examining muscle weakness have found that individuals with lateral knee OA and/or medial knee OA are four times more prone to developing muscle weakness compared to healthy counterparts affecting both muscle flexors and extensors.^[13]

A recent study uncovered that individuals with knee extensor weakness face a 1.65 fold increased risk of developing symptomatic knee OA and a 1.58 fold increased risk of radiographic knee OA. Extensor knee muscles provide joint stability and have a cushioning effect. However, reduced muscle power can result in alterations in the joint’s mechanical strain contributing to the onset of knee OA.^[14] Reduced muscle power can lead to abnormal knee joint mechanics. In middle age, the strength and force of knee extensor muscles decrease leading to knee extensor fatigue and reduced muscle activity. This reduction in knee extensor activity is strongly correlated with the advancement of knee OA. It changes the knee flexion angle during walking, especially in individuals with a higher probability of knee OA, post anterior cruciate ligament rupture or pre-existing knee OA.^[15] In 2021, a study observed that patients experiencing knee pain exhibited decreased muscular strength and an increased body mass index (BMI).^[16]

Prior research has predominantly examined the connection between knee pain and quadriceps muscle. Yet, there is a dearth of studies delving into the impact of knee pain on variables such as quadricep muscle strength, hamstring length, and overall physical limitations. This study seeks to address this gap by investigating the influence of knee pain on muscle imbalances and physical limitations, specifically in individuals diagnosed with bilateral knee OA.

MATERIALS AND METHODS

Outcome measures

Pain intensity was evaluated using the NPRS, which ranges from 0 to 10. Here, “0” signifies no pain, while “10” denotes pain of the most severe nature imaginable.^[18] A Camry digital hand-held dynamometer (HHD) was employed to quantify the strength of the quadriceps muscle. A modified HHD is considered a valid and reliable tool for measurement.^[19] For evaluation of knee extensor strength, the patient is asked to perform three to five repetitions of warm-up with 15–90 s of rest with each repetition. The warm-up protocols included marching on spot and half squats exercise. For testing, the patient was seated with 90° of knee flexion. A belt was attached to the leg and was positioned approximately 5 cm proximal to the distal aspect of the lateral malleolus. The other end of the modified belt-stabilizer was set up to position the HHD against the back of a treatment table leg using a flat attachment. When the participant extended his or her knee, the HHD was compressed against the table leg, and force was measured [Figure 1]. Torque is computed by multiplying the force by the distance, which is measured from the center of the knee to the fixation point of the dynamometer.^[20] This torque formula was measured by an online application, “PhysioPhraxis” developed by Scot Morrison (A board-certified orthopedic physical therapist). When the knee is at a 90° angle, in elderly males, the combined torque for knee extension is around 1.77 Nm/kg.^[21] During the assessment of quadriceps strength using HHD, precautions were taken to isolate the muscle group and minimize the influence of other muscles. Participants were positioned appropriately ensuring stabilization of the pelvis and restricting movements of non-target muscles. The HHD device was carefully placed on the distal part of the leg to measure the force generated by the quadriceps specifically. In this study, isometric muscle strength testing was conducted to evaluate the strength of the quadriceps.

Close

Figure 1:

(a and b) Hand-held dynamometer setup for measuring quads strength.

Export to PPT

The hamstring length was evaluated using the active knee extension (AKE) test. Participants were instructed to actively extend the knee with the foot in a relaxed plantar flexion. The test involved stretching the hamstring muscles, and the degree of knee flexion was then recorded by universal goniometer. The benchmarks for AKE angle differ between males and females with a threshold of >33.0° for males and >23.4° for females.^[22] The participants’ physical function was measured utilizing the Western Ontario and McMaster Universities Arthritis Index (WOMAC) Urdu version. This self-administered questionnaire comprises 24 items divided into three subscales: Pain, Stiffness, and Physical Function. Higher WOMAC scores indicate severe functional limitations.^[23]

Official permission letters were obtained from the relevant hospitals for data collection. All willing participants were informed about the study’s purpose and procedures. After obtaining consent, participants were screened based on inclusion and exclusion criteria. Measurements were taken from both knees of each individual. Using the NPRS, a composite pain score (ranging from 0 to 10 points) for both knees was acquired followed by individual scores for each knee to identify the leg experiencing more and less pain. Simultaneously, measurements were taken for quadriceps muscle strength, hamstring length, and physical limitations.

RESULTS

Seventy bilateral knee OA participants with a mean age of 55.25 ± 4.90 years were taken from the Orthopedic Department of Khyber Teaching Hospital and the physiotherapy department of Northwest General Hospital, Peshawar. Out of 70 participants, the frequency and percentage of males were 18 (25.7%) and females were 52 (74.3%). Among the cases of bilateral knee OA, the left knee was more painful with a frequency of 39 (55.5%), then right knee 31 (44.3%). The mean BMI of the participants was 21.7 ± 3.0. The left knee was more severe with a mean and standard deviation (Std) of 2.60 ± 0.5 grade than the right knee [Table 1].

The median interquartile range (IQR) of pain intensity in a more painful knee was 8.00 (1.00) while in a less painful knee was 4.00 (2.00). There was a significant difference between the pain intensity in a more painful knee and a less painful knee with P < 0.01 [Table 2].

The median (IQR) of quadriceps muscle strength in a more painful knee was 0.53 (0.36) while in a less painful knee was 1.35 (0.34). There was a significant difference between the quadriceps strength in a more painful knee and a less painful knee with P < 0.01 [Table 2].

The median (IQR) of hamstring length in a more painful knee was 29.00 (6.00) while in a less painful knee was 11.00 (6.00). A significant difference was found between the hamstring length in a more painful knee and a less painful knee with P < 0.01 [Table 2].

The mean (std) of WOMAC scores in a more painful knee was 50.17 (6.97) while in a less painful knee was 18.47 (6.54). There was a significant difference in WOMAC scores between a more painful and less painful knee with P < 0.01 [Table 2].

DISCUSSION

Individuals with bilateral knee OA showed a significant difference in quadriceps muscle strength between less painful and more painful knees. The quadriceps muscle was weaker in patients having more pain. These findings were consistent with a study that found that there was a decrease in quadriceps muscle cross-sectional area and an increase in adipose tissue in patients with knee OA.^[24] Another study clearly reported that patients with severe knee OA survivors showed a significant decrease in quadriceps rate of force development compared to those with early knee OA.^[25] A previous study shows decreased quadriceps and hamstring strength in individuals with knee OA compared to normal individuals.^[26]

Our study found a significant difference in hamstring length between a less painful knee and a more painful knee. The hamstring length was more compromised in patients having more pain. However, a previous study reported that flexibility of the iliotibial (IT) band and quadriceps muscle strength decreases in grade II and grade III radiographic knee OA. In addition, the flexibility of the IT band and quadriceps muscle strength was more compromised in grades II and III than in grade 0.^[27]

Our study reported that physical limitation was more affected in patients with more knee pain. This finding was reported in a study that the strength of the quadriceps is significantly correlated with pain in the knee and disability of the community. However, psychological activation is considered.^[28] A longitudinal study showed that knee pain was strongly related to quadriceps weakness.^[29] Another study showed that patients with knee OA are associated with functional limitations along with knee instability.^[30] Another study showed that functional limitation increases as muscle strength decreases. In knee OA, muscle weakness is caused by functional limitations.^[31]

This study has certain limitations. First, this study measures the quadriceps strength at a 90° angle of knee flexion while the literature supports that the peak torque value is highest at 60° of knee flexion. Due to feasibility in the clinic, the knee flexion angle was selected at 90°. Second, this study used HHD for strength measurement while a biodex is more valid for measuring quadriceps strength. It is recommended that future studies focus on other muscles for imbalance and its effects on the radiographic severity of knee OA.

CONCLUSION

This study found that individuals experiencing more knee pain demonstrated decreased quadriceps muscle strength and increased hamstring muscle tightness. In addition, those with more painful knees exhibited greater physical limitations in bilateral knee OA.

AUTHORS’ CONTRIBUTIONS

SK and HW contributed to the design, literature search, clinical studies, and data acquisition. UA contributed to concepts, statistical analysis, and manuscript preparation and editing. All authors have critically reviewed and approved the final draft and are responsible for the manuscript’s content and similarity index.