DISCUSSION
In this multidimensional study which investigated the presence of
sarcopenia in patients with osteoarthritis, the rate of sarcopenia in
knee OA patients was found to be approximately 12%. Sarcopenic OA
patients were found to be older, weaker, thinner, malnourished, and had
limited physical activity levels. Unlike other studies, the presence of
sarcopenia in a multidimensional way, including body composition
parameters, ultrasonographic muscle structure evaluations, isometric
muscle strength evaluations, handgrip strength and walking speed
evaluations, biochemical evaluations, anthropometric measurements and
comprehensive functional evaluation tests measured by DEXA were
examined. As far as we know, this is the first study in the literature
to use all of these parameters at the same time. In this study, all
parameters except biochemical parameters were found to have predictive
value in diagnosing sarcopenia.
Kemmler et al. in their study with elderly individuals over the age of
70, found the prevalence of sarcopenia to be 4.5% and reported that
patients with hip and lower extremity OA were more likely to have
sarcopenia than those without osteoarthritis (9.1% with OA; 3.5%
without OA) (16). The rate of sarcopenia found in our study appears to
be similar to Kemmler et al. Clinical evidence suggests that the link
between OA and sarcopenia occurs through functional and cellular
pathways. It has been reported that patients with OA and rheumatoid
arthritis are more prone to the development of sarcopenia due to the
increased cytokines (5).
Baumgartner et al., for the diagnosis of sarcopenia, used the
appendicular muscle mass (ASM) and skeletal muscle mass index (SMI)
calculated by DEXA and reported the prevalence of sarcopenia as 13-24%
under the age of 70 and > 50% in those aged 80 and over.
Studies have found a strong correlation between DEXA and body
composition measurements in elderly individuals with MR and CT
measurements, which are gold standard methods (17).
In recent years, it has been suggested that muscle ultrasonography can
be used as a practical, easily accessible and inexpensive method in the
evaluation of sarcopenia. In the literature reviews, 4 studies were
found in which DEXA and US were used together to diagnose sarcopenia. In
all of these studies, ultrasonographic measurements of muscle thickness
from many regions and thighs were found to be consistent with muscle
mass values measured by DEXA.(18-21). In our study, the relationship
between left gastrocnemius pennation angle and isokinetic muscle
strength (peak torque extensor at an isokinetic 180 ° angular velocity)
and appendicular lean body mass measured by DEXA was shown. The
relationship between the angle of pennation of the right gastrocnemius
muscle were found to be correlated with muscle strength (peak torque at
an isokinetic 180-degree angular velocity and peak torque/body weight
extensor ). A strong positive correlation was found between SMI and
bilateral gastrocnemius medialis muscle thickness also.
The advantage of using DEXA in the diagnosis of sarcopenia is the better
evaluation of SMI and skeletal muscle mass which was found to be
associated with physical disability (22). Handgrip strength and
quadriceps muscle strength are associated independently with predicting
disability (23). Isometric handgrip strength, lower extremity muscle
strength was found to be strongly correlated with knee extension torque
and thigh cross-sectional muscle area (24). In our study, bilateral
extensor isokinetic 60 degrees angular velocities of the knee joint were
found to be statistically lower in the sarcopenic group compared to the
other 2 groups. In functional evaluations, bilateral handgrip strength
was found to be decreased in the sarcopenic group. Bilateral handgrip
strength and bilateral knee extension strengths were positively
correlated as moderate and with respect to several health outcomes.
Additionally, in this study, sarcopenia was found to be significantly
associated with physical dependence, regardless of age, ethnic
difference, comorbidities, health-related behaviours and fat mass (25).
Gait speed plays an important role in the evaluation of sarcopenia. Gait
speed is the first functional assessment to be considered in the
evaluation of sarcopenia (26).
Active muscle strength test in the elderly is difficult to perform due
to the reasons such as immobilization, pain, injury, surgical procedure,
cognitive impairment, and technical complexity. The cross-sectional area
of the muscles shows muscle mass and is related to muscle strength.
Therefore, the cross-sectional area can be evaluated in order to have an
idea about muscle strength in clinical applications. It has been stated
that in intensive care patients, muscle loss can be monitored with
rectus femoris and vastus intermedius muscle thickness (27). Although
the quadriceps femoris pennation angle was not found to be significantly
correlated with functional muscle parameters, in the study conducted by
Strasser et al. with 26 healthy elderly individuals, the pennation angle
was found to be lower than the control group consisting of 26 healthy
young individuals (27). In our study, bilateral measurements were
including in 3 regions by ultrasonograph. Fascicular length and
pennation angle of the gastrocnemius muscle were evaluated as well as
muscle thickness, and non-sarcopenic patients and healthy volunteers
were included in the study as well as sarcopenic patients. In our study,
it was found that bilateral gastrocnemius fascicle lengths and
right-sided gastrocnemius pennate angle were lower in sarcopenic
patients than those without and in the control group, and there was no
significant difference between bilateral rectus femoris subcutaneous
tissue and muscle thickness.
Decreased muscle quality and muscle mass can be considered as the most
important factors in OA pathogenesis (28). At the same time, the painful
joint can cause a decrease in muscle tone and consequently a decrease in
muscle mass. When the relationship between OA and sarcopenia was
examined, it could not be understood whether OA is a risk factor or a
direct result of sarcopenia. For this, it may be recommended to conduct
a systematic study investigating the development of sarcopenia in the
ipsilateral extremity with OA occurring in a single joint and its effect
on physical functions (29). In our study, the WOMAC function and total
score evaluated in the sarcopenia group were found to be statistically
significantly higher than the other two groups. The decrease in muscle
mass and muscle quality caused by sarcopenia in patients with OA may
explain the increasingng in WOMAC scores. In addition, a negative
correlation between WOMAC function and total score and left-hand grip
strength was found as an indicator of upper extremity muscle function in
our function studies. This suggests that sarcopenia may affect not only
the lower extremity but the whole body in these patients.
In our study, a relationship between rectus abdominis subcutaneous
tissue thickness and right-hand grip strength, and between rectus
abdominis muscle thickness and FMI was found. Although Abe et al. did
not find a correlation between BMI and body mass with abdominal muscle
thickness (2-3 cm from the side of the umbilicus, lower part of the
rectus abdominis) measured by ultrasound, a correlation with handgrip
strength and standing up test performance was found. The body mass with
the appendicular lean soft tissue mass (ALM) parameter measured by DEXA
was evaluated (30). In another study using BIA in patients with
metabolic syndrome, a positive correlation was found between rectus
abdominis muscle thickness and skeletal muscle mass index (SMI) (31). In
a cross-sectional study conducted by Kara et al. with 30 healthy
volunteers, low vitamin D levels were found to be associated with
decreased muscle strength (especially knee and ankle extensors), but no
relationship was found with muscle architecture (32). In our study, a
positive correlation was found between bilateral gastrocnemius medius
muscle thickness and SMI and vitamin D levels. Therefore, it can be
thought that Vitamin D supplementation may increase muscle mass and
decrease sarcopenia in these patients.
In the study conducted by Kositsawat et al. where 1826 people were
studied; a relationship was found between low vitamin D levels and the
decreased walking speed (33). In our study, a negative relationship was
found between gait speed, and FM measured by DEXA, and a positive
relationship with vitamin D level. Although there was no significant
difference between vitamin D levels in our study, the average vitamin D
levels in the sarcopenic group were determined to be 19 ng/mL. These
levels can be considered as a deficiency in the literature and may
explain the relationship between vitamin D levels and walking speed in
this study. Additionally, in our study, a cross-sectional relationship
between increased BMI index and decreased walking speed and a positive
correlation between increased leptin levels and BMI was found. In
another study, although no relationship was found between the thigh
muscle cross-sectional area and the decrease in walking speed, a
relationship was found between the change in the thigh muscle area and
the change in walking speed. The total amount of fat and muscle fat
infiltration has been reported to be important predictors for a
reduction in walking speed (34). This report may likewise explain our
findings.
As shown in our study, it is an expected result that sarcopenic patients
are weaker (low body weight and BMI) and their bilateral hand grip
strength, walking speed, waist and hip circumference, upper-middle arm
circumference, calf and thigh circumferences are lower compared to
non-sarcopenic patients. Similar to our findings, in a study conducted
by Marini et al. with 207 sarcopenic people between the ages of 65-93,
it was found that waist circumference, upper middle arm and calf
circumference, weight and BMIs were significantly lower in both genders
compared to those without sarcopenia (35).
The relation of sarcopenia and malnutrition has been shown in many
studies (36, 37). In their study Velazquez et al. which involved 90
elderly women with an average age of 78, it was found that the
prevalence of sarcopenia was 41%, when the nutritional status was
evaluated according to MNA founded that 7.1% of those with normal,
45.9% of those with malnutrition risk, and 77.2% of those with
nutritional deficiency were sarcopenic (38). In our study, MNA was used
for malnutrition assessment and it was found that sarcopenic patients
were significantly malnourished compared to non-sarcopenic and control
groups. Therefore, it is our understanding that improving the
nutritional status of OA patients may be beneficial in increasing muscle
mass and preventing sarcopenia in these patients.
Leptin has been found to be increased in the cartilages of patients with
OA, and although it is mainly synthesized from adipocytes, it is also
synthesized from chondrocytes (18). A positive correlation has been
found between the leptin level measured in synovial fluid and BMI, and
it has been stated that this may be one of the metabolic factors
explaining the role of obesity in the pathogenesis of OA (5). The
function of leptin in OA is not fully determined but it has a biphasic
effect which facilitates cartilage synthesis at low levels and causes
inflammation and degeneration of cartilage at high levels (39). In our
study, the relationship between sarcopenia, plasma leptin and
adiponectin levels were evaluated and the relationship between leptin
and adiponectin levels and muscle ultrasound and isokinetic evaluations
of the patients were studied. A weak and low positive correlation was
found between leptin levels and subcutaneous tissue thickness of the
gastrocnemius and rectus femoris muscle in the muscle ultrasound
evaluation performed in the non-sarcopenic knee OA group. This link may
be due to the correlation between leptin and obesity.
In our study, although the serum leptin level was found to be lower in
the sarcopenia group compared to the group without sarcopenia, there was
no statistically significant difference between the two groups.
Moreover, there were significantly different BMIs between these two
groups. The BMI values in the sarcopenic group were significantly lower
than the group 2 and 3 The lower serum leptin levels in the sarcopenia
group compared to the group without sarcopenia may be related to lower
BMI. The studies of Toussirot et al. and Sarı et al. stated that the low
leptin levels found in patients with ankylosing spondylitis could be
attributed to the low BMI values of the patient group in furtherance to
our study (40, 41). In our study, the FM value measured by DEXA in
sarcopenic patients was found to be lower than the other two groups. The
low level of leptin in the sarcopenic group compared to the other two
groups may be related to the low FM value.
Adiponectin plays a role in many processes such as energy metabolism,
insulin resistance, and vascular physiology. High molecular weight
adiponectin is the most active form of adiponectin which is the most
sensitive marker reflecting insulin resistance and metabolic rate (42).
High adiponectin levels have been recognized as a predictor for bone
mineral density loss (43). In addition, high adiponectin levels have
been shown to contribute to physical disability in a prospective cohort
in which the effect of adiponectin on physical functions was
investigated (44). In our study, a negative correlation was found
between adiponectin levels and the VAS score in motion. This
relationship was found in the sarcopenic group. The fact that
adiponectin is seen as more determinant in terms of pain intensity in
patients with low BMI, especially biomechanical factors, may be related
to its role in inflammatory pathology. In our study, the relationship
between adiponectin level and quality of life were also studied. In our
study, the quality of life of the patients was evaluated using the SF-36
scoring system. When SF-36 sub-scores were compared with adiponectin
levels in the OA group, a moderate negative correlation was observed
between the pain sub-score. Quality of life can be affected by
conditions such as disease activation, pain status, and the presence of
comorbidities. It is a predictable situation that a more serious disease
state will progress when quality of life worsens.
One of the limitations of our study is that the limit cut-off value for
DEXA measurement was used according to the values calculated in previous
studies. Since there is no muscle mass limit value determined for
Turkish society, our evaluations was based on the studies with the
highest number of patients and the values suggested by EWSGOP. In our
study, only female patients, thinking that they would create a more
homogeneous group, were included. Most previous studies investigating
sarcopenia in OA patients also included only women in literature.