The quantitative results indicate that the unloading of the 28-day tail suspension induced changes in both surface roughness and thickness of patellar articular cartilage and the LA stimulation to ST-36 and KI-1 acupoints could subside these changes.
Our previous study found that 28-day unloading affected articular cartilage site-dependently in ultrasound parameters [17
]. Relatively severe alterations were found in patella including cartilage thinning and the increase of surface roughness. Hence, this study selected patellar articular cartilage as study samples. The therapeutic effects of LA on patellar articular cartilage subjected to unloading were assessed by using a high-frequency UBM system. Comparing the diagnostic ability of different ultrasound parameters, the coefficients related to ultrasound reflection or backscatter tend to be sensitive for the investigation of cartilage matrix structural changes [12
], whereas URI is a recently introduced parameter of assessing the surface irregularity of the cartilage tissue [15
]. Another ultrasound parameter is attenuation that could reflect more information on the tissue composition (PG, collagen, or water content) and mechanical properties (stiffness) [27
]. Based on those previous studies, the acoustic parameters correlated with the morphologic and mechanical properties of the degraded cartilage tissue were investigated in recent studies [13
]. This study therefore chose URI, IRC, IBC, cartilage thickness, and ultrasonographic grade as the parameters to evaluate the effect of unloading and the corresponding countermeasure effect of LA on patellar cartilage. Using UBM, the impact of disuse on the surface morphology (surface roughness measured by URI) and the apparent morphology (cartilage thickness) are clearly demonstrated, whereas the impact on the composition changes measured by the reflection coefficients (IRC, IBC) of both the cartilage surface and the cartilage-bone interface was not significant. The cartilage thickness and URI of the cartilage surface could be more sensitive indexes to indicate the disuse changes in articular cartilage than IRC, IBC. In addition, the quantitative analysis of the morphology parameters (cartilage thickness and surface roughness) might be more sensitive than the semiquantitative evaluation of the UBM images (sonographic grade).
The UBM finding for changes in the thickness and URI of patellar cartilage supports findings of previous studies [17
]. Following LA treatment there was a significant lower value in URI and a higher value in cartilage thickness compared with group T (). The results indicated the retaining of ultrasonic characteristics of patellar articular cartilage by daily LA treatment. The exact mechanism of LA effect cannot be answered by this study. However, to eliminate the local effect of LA, LA treatment was only applied to the left hindlimb while results were examined in both patellae. The results showed no significant difference between the left and right sides. This suggests that LA retains ultrasonic characteristics of patellar articular cartilage through a systemic regulation rather than a local effect.
In light of traditional Chinese medicine (TCM), life is governed by the interaction of Yin
is the vital energy flowing through the meridians to keep Yin-Yang
in balance. When Yin
are in imbalance and Qi
is obstructed, it results in diseases. In an ancient TCM book, Inner Classic of the Yellow Emperor
, which was written around third century B.C., needle acupuncture was already mentioned as an important therapy to rebalance Yin-Yang
and circulate Qi
clearly in the meridians. With the most recent technologic development, LA has been introduced. Without insertion into the skin, the laser probe is placed at acupoints to generate the low-intensity, nonthermal laser irradiation. It is found that the therapeutic efficacy of LA depends on the depth of laser energy transmission [33
]. Some studies demonstrated the similarity between LA stimulation and the stimulation of traditional needle acupuncture or electroacupuncture (EA). Litscher [10
] reported that the LA-generated light stimulus was analogous to mechanical pressure by manipulating the needle. Komori et al. [34
] provided evidence that both needle acupuncture and LA therapy had similar effects on microcirculation. Hsieh et al. [35
] pointed out that the frequency-dependent brain-area activation stimulated by LA was similar to that induced by electroacupuncture (EA). With the worldwide training and provision of acupuncture care in the recent two decades, an increasing attention has been paid to the scientific evaluation of acupuncture treatment of various diseases including OA pain [36
However, few studies have reported on LA countermeasure of cartilage degeneration. The present study selected KI-1 and ST-36 as treatment sites and found the therapeutic effect of LA on the acoustic and morphological properties of patellar articular cartilage subjected to unloading. KI-1 (Yong Quan-Bubbling Spring) is the first acupoint of the Kidney meridian, where life begins to gush, coiling up through the body. The Inner Classic of the Yellow Emperor
notes that kidney strength manifests in strong bones. KI-1 acupuncture strengthens kidney function. Hsieh et al. [35
] conducted a study to investigate the possible mechanism of LA at KI-1. Their results demonstrated that its mechanism concerns the nervous system (afferent sensory information processing) and the circulatory system (hemodynamic properties). The Stomach takes Yang
(taking in food) and also shows Yin
(assimilation and nourishment). Thus the Stomach channel is important for balancing Yin-Yang
. ST-36 (Zu San Li) is a key point of the Stomach meridian and frequently used in acupuncture therapy. For example, Zhang et al. [8
] needled at ST-36 and SP-6 (San Yin Jiao) to effectively prevent bone loss in ovariectomized rats and Guo et al. [11
] stimulated ST-36 and KI-1 to improve intestinal calcium absorption to counter the inhibitory effect of microgravity on bones [38
]. It was also found by Yin et al. [39
] that glycometabolism in the hypothalamus had a rise by ST-36 acupuncture. Those studies demonstrate that ST-36 acupuncture enhances the digestion function and provides wholistic care to promote health, balance, and vitality.
There are several limitations in this study. A limitation of the study design is that the laser beam spot size is large relative to the anatomical size of hindlimbs of rats. The responses to laser acupuncture treatment may not be specific to ST36 and KI1. Further studies using laser with smaller beam spot size are needed to address the question whether the laser acupuncture treatment at the other body regions or points which are not necessary on the meridians would show the same responses. In addition, stratified laser output levels can be tested to determine a dose-effect threshold and the optimal laser dose parameter. Another limitation of this study is that the experiment is an in vitro
laboratory research. Because of the low thickness and anatomical location of articular cartilage, monitoring the tissue in vivo
has been a challenge. Recently, the arthroscopic ultrasound appears to be a promising method for in vivo
investigation on articular cartilage [4
]. The study design can be improved by using in vivo
arthroscopic ultrasound imaging to evaluate the articular cartilage in larger animals such as dogs.
In conclusion, the present study used the UBM system to evaluate the alterations in patellar articular cartilage induced by unloading and the therapeutic effects of LA therapy on the cartilage tissue in rats. The results indicate that 28-day unloading induced significant changes in cartilage thickness and URI and insignificant changes in IRC, IBC, and ultrasonographic score. The daily LA therapy improved the acoustic and morphological properties of the cartilage tissue and prevented the cartilage degeneration. This study suggests that LA therapy would be a simple and safe non-pharmacological countermeasure for unloading-induced cartilage degeneration and the UBM system has potential to be a sensitive, specific tool for quantitative assessment of articular cartilage.