- Research article
- Open Access
Unilateral-dominant reduction in muscle volume in female knee osteoarthritis patients: computed tomography-based analysis of bilateral sides
Journal of Orthopaedic Surgery and Research volume 15, Article number: 543 (2020)
Muscle weakness is associated with osteoarthritis pathology. A recent study demonstrated that measuring muscle volume using computed tomography (CT)-based analysis and comparing bilateral muscles in the same patient allowed for accurate evaluation of muscle volume in unilateral hip osteoarthritis (OA) patients. Here, we evaluated muscle volume using CT-based analysis and compared bilateral muscles in knee OA (KOA) patients.
CT images were obtained from 35 female radiographic KOA patients the day prior to total knee replacement surgery. Muscle volume (MV) was semi-automatically analyzed. Knee extension muscle strength (MS) was determined using a hand-held dynamometer. The severity of KOA patients’ clinical symptoms was examined using four domains of the Japanese Orthopedic Association (JOA) score. We compared the difference in MS (ΔMS) and MV (ΔMV) between the operated side (OS), which exhibited severe radiographic OA or severe pain, and the contralateral side (CS).
JOA score was significantly lower in the OS than CS. MV and MS were also significantly lower in the OS than CS. There was no correlation between MV and MS or between MV and MS as a percentage of body weight on either side. However, ΔMV was positively correlated with ΔMS and pain on walking in the JOA.
We evaluated MV and MS using bilateral CT images of the legs of KOA patients. A reduction in MV was observed on the OS, and was correlated with a reduction in MS and pain on walking. Bilateral CT image analysis may be useful for evaluating the relationship between OA pathology and muscle atrophy.
Knee osteoarthritis (KOA) is a well-known musculoskeletal disorder and a key cause of disability, particularly in elderly individuals . A number of biomechanical pathways likely play major roles in KOA. For example, excessive mechanical stress arising from either a reduction in load-bearing area on the surface of a joint or applying a heavy load can halt the repair of damaged joint tissue . Muscle weakness is a key measure of the extent of disability in OA patients . A number of reports have demonstrated that a reduction in lean mass in the lower limbs is common in OA patients , and this reduction is correlated with a heightened risk of falls [5,6,7]. Therefore, accurate evaluation of the muscles of KOA patients is important to better understand the relationship between the muscle and OA pathology.
Previous studies have proposed that translational studies that fill the gap between basic and clinical research using three-dimensional imaging data provide a basis for creating anatomical models of the human anatomy and may allow orthopedic surgeons to determine ideal practices before orthopedic surgery [8,9,10]. Computed tomography (CT) is used for various applications, including the evaluation of orthopedic tumors  and fractures , and preoperative planning of orthopedic surgery . CT is also regularly used to quantify muscle volume (MV) at regions around the knee and hip [14,15,16]. In particular, the cross-sectional area (CSA) of the affected region determined from CT images is measured to evaluate MV [14,15,16]. However, these measurements vary widely and are dependent on the location at which the section is taken. In addition, muscle mass varies greatly from person to person due to differences in height or body mass index (BMI), making it difficult to conduct comparisons and accurately elucidate the effect of KOA on muscle mass. A recent study showed that muscle volume in unilateral hip OA patients could be accurately evaluated by measuring muscle volume using CT-based analysis and comparing bilateral muscles in the same patient .
Here, we evaluated muscle volume using CT-based analysis and conducted comparisons between bilateral muscles in KOA patients.
The study protocol received ethics approval from the Institutional Review Board (IRB) for Clinical Research and Treatment of Kitasato University (IRB approval number: B20-133).
According to power analysis conducted with α = 0.05 and power = 0.80 using G*POWER3, 34, and 17 samples were needed to obtain a statistically significant difference in muscle strength (MS) and MV, respectively, between the operated and contralateral sides. Therefore, we obtained CT images from 35 female patients with radiographic KOA the day prior to total knee replacement surgery. Four domains of the Japanese Orthopedic Association (JOA) score, namely, pain on walking (domain I), pain on ascending or descending stairs (domain II), range of motion (domain III), and joint effusion (domain IV) , were used to evaluate symptom severity (Table 1).
Knee extension MS was determined using a hand-held dynamometer (μTas F-1; Anima, Tokyo) as participants were seated on a chair with their hips and knees flexed at 90°. Knee extension MS was expressed as the raw value in Newtons (N) and as a percentage of body weight (% BW). The difference in MS (ΔMS) between the operated side (OS), which exhibited severe radiographic OA or severe pain, and the contralateral side (CS) was calculated using the following equation:
CT-based analysis of femoral muscle volume
Axial CT images were used to measure patients’ femoral MV. CT images comprising a 10-mm region of interest were taken 200 mm above the knee joint at 1-mm thickness and semi-automatically analyzed using the MIMICS® software (Materialise Japan Co., Ltd., Yokohama, Japan) (Fig. 1). Femoral MV was compared between OS and CS. Differences in MV between OS and CS were calculated using the following equation:
Differences between OS and CS were examined using paired t test. The relationship between MV and MS was evaluated using Spearman’s correlation coefficient. A P value of < 0.05 was considered statistically significant. Statistical analysis was performed using the SPPSS software (Version 25.0; SPSS, IBM, Armonk, NY, USA).
Study participant’s demographic information
The participants’ demographic and clinical information are provided in Table 2. Participants’ mean age was 72.4 ± 7.4 years and body mass index was 26.1 ± 4.1 kg/m2. There was no difference in the ratio of Kellgren/Lawrence (K/L) grades between the OS and CS. Total JOA score and the score for all four domains (pain on walking, pain on ascending or descending stairs, range of motion, and joint effusion) were significantly lower in the OS than CS.
Muscle strength and volume
MS and MS as a percentage of body weight were significantly reduced in the OS compared to CS (P = 0.001; Table 3). MV was also significantly reduced in the OS compared to CS (P = 0.001; Table 3). No correlation was found between MV and MS (Fig. 2a) or MV and MS as a percentage of body weight on the OS (Fig. 2b). However, ΔMV was positively correlated with ΔMS on the OS (r = 0.651, P < 0.001; Fig. 2c).
Relationship between clinical score, muscle strength, and muscle volume
There was no correlation between the total JOA score and the score for three domains (pain on ascending or descending stairs, range of motion, and joint effusion) and ΔMS (Fig. 3a, c–e) or ΔMV (Fig. 4a, c–e). In contrast, both ΔMS and ΔMV were significantly correlated with domain I (pain on walking) in JOA (ΔMS, r = 0.342, P = 0.044, Fig. 3b; ΔMV, r = 0.375, P = 0.026; Fig. 4b).
Previous studies have shown that KOA patients exhibit a reduction in muscle mass in the lower limbs compared to age-matched healthy controls [6, 19, 20]. However, a cohort study reported a weak association between bone mass, measured based on bioimpedance analysis (BIA) using a body composition analyzer, on muscle strength in KOA patients . Consistent with previous reports, we found no correlation between MS and MV. However, bilateral MV analysis using CT images taken from KOA subjects showed a unilateral decrease in MV on the side with severe OA and that this reduction was strongly correlated with a reduction in MS. CT-based analysis of bilateral sides may therefore be a useful tool for evaluating muscle weakness in KOA patients due to the exclusion of parameters such as age and BMI, which affect muscle mass and strength (Table 4).
There is a logical biomechanical explanation for the association between leg muscle mass and knee symptoms. Periarticular muscles, which keep injured and degenerated knees structurally stable and supported, with greater mass relative to total body mass provide better stability, resulting in less pain. Several studies examining changes to the muscles in the lower limbs have shown that low impact exercises like swimming and cycling are beneficial for reducing pain in patients with KOA [21, 22]. Therefore, low impact therapeutic approaches may be important for relieving pain in KOA patients.
Several reports have suggested that unilateral mechanical unloading is a cause of muscle reduction [23,24,25]. Studies in humans have reported that, as a result of unilateral lower limb unloading, there is a 7% decrease in muscle CSA after 21 days  and a 16% decrease after 35 days [23, 25]. In the present study, MV was reduced by approximately 6% on the side with severe OA, and this reduction was associated with pain on walking. Underuse of the muscle due to pain may therefore explain the unilateral reduction in MV in KOA patients.
This study has several limitations (Table 4). First, the analyzed muscle comprises several different muscles, including the rectus femoris, biceps femoris, and adductor longus. Assessment of individual muscles is necessary to obtain a practical understanding of functional disability in patients with KOA. Second, our study was a cross-sectional study. Longitudinal studies are needed to clarify the relationship between OA development and muscle reduction. Finally, patients with bilateral KOA were included among the participants in this study.
We evaluated MV using bilateral CT images of the legs of patients with severe knee pain. MV was reduced on the side with severe OA and this reduction was correlated with a decrease in MS and pain. Bilateral CT image analysis may be useful for evaluating the link between OA and muscle pathology due to the ability to exclude parameters such as age and BMI, which affect muscle mass and strength. Further investigation using a longitudinal study may clarify the relationship between OA development and muscle reduction.
Availability of data and materials
The datasets supporting the conclusions of this article are included within the article. The raw data can be requested from the corresponding author.
Bone mass index
Institutional Review Board
Japanese Orthopedic Association
Percentage of body weight
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We thank Ms. Yuko Onuki for her help with CT image analysis.
This study was supported in part by research grants from the Parents’ Association of Kitasato University School of Medicine.
Ethics approval and consent to participate
All experimental protocols were approved by the Ethics Review Board of Kitasato University (Permission number: B20-133).
Consent for publication
The authors declare that they have no competing interests.
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Tsukada, A., Uchida, K., Aikawa, J. et al. Unilateral-dominant reduction in muscle volume in female knee osteoarthritis patients: computed tomography-based analysis of bilateral sides. J Orthop Surg Res 15, 543 (2020). https://doi.org/10.1186/s13018-020-02074-x
- Computed tomography
- Muscle volume
- Muscle strength