The current study investigated the effect of treatment with dry needling latent and active MTrPs combined with knee muscle stretching, and it compared that effect with the effect of treatment with oral diclofenac and knee muscle stretching. After treatments, both the groups showed a good effect in knee pain, function, and ROM, However, the DNG showed significantly better results than the DG. Especially in the results ofthe 6-month follow-up, the results of the DNGweresuperior tothose of the DG.
Differentfrompreviousstudiesthat focused on dry needling active trigger points in the treatment of KOA, in this study, in addition to dry needling active trigger points, latent trigger points were also included, and there were several reasons why the latent trigger points dry needle were included. First, latent trigger points have a high prevalence in KOA. The research of Sánchez et al.[10]showed that the prevalence of latent MTrPs varied from 11% to 50% in various muscles of patients with mild to moderate painful KOA.In contrast, the tensor fasciae latae showed the highest prevalence of latent MTrPs (50%). Our study showed a high prevalence of latent trigger points in rectus femoris, vastus lateralis, biceps femoris, and gastrocnemius, all of which wereover 50%, and gastrocnemius wasthe highest(68.8%). The prevalence of latent trigger points in other muscles was also higher than that in Sánchez et al. The reason may be that the participants of the two studies were different. Most of the participants in Sánchez's study were mild to moderate(Kellgren and Lawrence scale between 1–3). However, the subjects included in this study were mostly moderate to severe (Kellgren and Lawrence scale between 2–4). Therefore, it is possible that the more severe the symptoms of KOA patients, the higher the prevalence of latent trigger points.Second, compared with the activate trigger points, latent MTrPs do not produce spontaneous and recognizable pain under stimulation, however, latent MTrPs play a role in limiting the range of motion, reducing muscle strength, accelerating fatigability, and altering muscle contraction patterns[30]. Restricted joint ROM is commonly observed in patients with latent MTPs. The number of latent MTPs has been reported to be negatively correlated with the baseline ROM[31]. Baraja-Vegas[32] observed an increased stiffness in individuals with latent MTPs,andthis increased muscle stiffness alters muscle contractile properties, restricts joint range of motion, provokes muscle weakness, and accelerates fatigability. In addition, Ge et al.[33] found that this motor dysfunction may result in incoherent muscle activation of synergists inducing impaired motor control strategies.Third, in the past, latent trigger points were mostly included in the study of healthy subjects or asymptomatic subject[34,35,36].
However, in recent years, latent trigger points have received attention and have been included in the treatment of various skeletal muscle pain. Calvo Lobo's research showed that dry needling intervention of the latent MTrPwasassociated with the key active MTrP of the infraspinatus reduces pain intensity in the short term in older adults with nonspecific shoulder pain[37]. The results of Sánchez-Infante's study showed that the application of one session of DN over LTrP decreased the pressure pain, dynamic stiffness, and muscle stiffness values at 72h after treatment[38].Another study by Sánchez-Infante showed that one session of DN intervention in latent trigger points of the upper trapezius muscle reduced muscle stiffness and the pressure pain threshold for the dry needling group compared to the sham dry needling group[39]. Latent trigger points have alsobeenincluded in studies of nonspecific chronic low back pain[40]. However, in the trigger point treatment of KOA, no latent trigger point has been involved.
Currently, for the treatment of KOA, the active trigger point is primarily involved, and the active trigger point of quadriceps femoris is primarily included because the referred pain of the quadriceps femoris is near the patellofemoral joint. When activated, there is pain in the patellofemoral joint. Patellofemoral Pain Syndrome(PFPS), as the early lesion of OA, often achieves positive effects by needling the active trigger point of the quadriceps femoris[41,42]. However, only the active trigger point was included in the treatment of KOA, which cannot achieve a positive effect[43,44]. Therefore,latent trigger points may also need to be included in the treatment of KOA, and the reason may be because active and latent MTrPs, as a bundle spasm of muscle fibers, can cause muscle force imbalance, which generates an uneven stress to a certain location in the joint and accelerates cartilage destruction[45]. If it is not treated in time, eventually, this can result in articular dysfunction from synovial stagnation, hypoxia, synovial hyperplasia, biochemical derangements, angiogenesis, effusion, bone remodeling, and inflammation[46].In this study, the muscles involved included the quadriceps, the tensor fasciae latae, the hip adductors, the hip abductors, the hamstrings, and the triceps calf and popliteus muscles. These muscles affect the function and biomechanics of the knee joint. Once the trigger points (latent or active) appears, it may lead to abnormal cartilage load through muscle weakness or tightness, and this may further exacerbate the degenerative process of the knee joint[47,48].
The effects of the included muscles on joint mechanics are as follows:
(1). Quadriceps tightness can lead to an increased compression force of the patellofemoral joint[49,50], or because themedial and lateral components of the quadriceps exert different mediolateral forces at the patella, their unbalancemay alter the pressure distribution across the patellofemoral joint and patellar kinematics[51,41].
(2). The tensor the fascia lata is connected to the patellofemoral through the iliotibial band (ITB) and the sateral patellar retinaculum. The increased tension of the tensor fascia lata increases thepatellar lateral translation and tilt and increases thelateral cartilage pressure[52,53].
(3). The hamstrings, apart frombeing the primary mechanism of knee flexion, also protect the knee from eccentric contraction during the support phase. These both function to cushion the joint and to generate limb deceleration during gait[54]. In addition, as an antagonist of the quadriceps, tightness of the hamstrings may require higher quadriceps force production or cause slight knee flexion, resulting in increased patellofemoral joint reaction forces[55,56].
(4). Inanopen-chain, the gastrocnemius muscle can bend the knee joint and ankle plantar flexion, and the soleus muscle can also bend the ankle plantar flexion. However, inaclosed-chain, the gastrocnemius muscle and soleus muscle pull the lower end of the femur and the lower leg backward to straighten the knee joint[57]. In fact,thegastrocnemius and quadriceps femoris have a co-activation effect when squatting up. However, when the soleus muscle is insufficient, the quadriceps femoris has to use more force to stabilize the knee joint, resulting in strain ofthequadriceps femoris[58].The primary role of the popliteus muscle is to internally rotate the tibia in relation to the femur in open-chain and stabilization of the external rotation of the femur in relation to the tibia in closed chain situations, and the popliteus muscle tightness will cause difficulty in stretching the knee joint[59,60].
(5). The gluteus medius is theprimary abductor of the hip. During walking, weak hip abductors of the stance limb produce a pelvic drop on the swing limb and stance knee varus angulation that shifts the line of gravity (LOG) away from the stance knee. This LOG shift increases the knee adduction moment and the medial joint compressive forces, leading to progressive degeneration. The hip adductor muscles may eccentrically counteract the varus angulation of the knee and consequently might unload the medial tibiofemoral joint[61]. A systematic review identified moderate quality evidence that suggested substantial hip abductor and adductor muscle weakness in people with knee OA[62].
(6). Hip external rotation (the posterior fibers of the gluteus medius and maximus muscles) act eccentrically to control the movements of hip medial rotation during activities with body weight support.The weakness of hip external rotation leads to the internal rotation of the femur, and this contributes to increased lateral forces acting on the patella and greater stress on the lateral patellofemoral joint[63,64].
Previous studies have reported that ROM of the knee joint is decreased gradually in individuals with KOA[65]. It is essential to restore normal length and flexibility to the muscles. Thus, stretching exercises are an effective complementary therapy and play an important role in the treatment of patients with KOA[66,67]. The stretching technique for muscles improved pain ratings, joint stiffness, function, and ROM, and specifically, stretching therapy for the surrounding muscles of the knee can improve muscle flexibility and correct muscle imbalance so as to decrease the stress concentration in the knee. However, one should be careful of achieving this by direct stretching exercises when a muscle is still in pain and spasm. Direct stretching may cause more pain and more spasm in the painful muscle[68]. Therefore, stretching is appropriate after pain relief. In this study, dry needling and oral drugs in the DNG and DG groups significantly reduced pain, and the ROM of both groups significantly improved through treatment combined with stretching. However, the ROM of the DNG group was significantly better than that of the DG group. Similar to this study, previous research has reported improved joint ROM follwing dry needling trigger points[69,70]. The observed changes in joint ROM could be associated with a relaxation of the MTrPs[71]. The reason might be that TrPS can change the structure of the muscle by increasing the stiffness in muscle cells and tissues, and the dry needling can release the contracture nodule of the trigger points, thus decreasing resistance when stretching the muscle[72,73].
Traditionally, clinicians have relied heavily on the use of NSAIDs, including diclofenac sodium to treat the symptoms of KOA, such as inflammatory pain and joint stiffness. Diclofenac is a proven, commonly prescribed nonsteroidal anti-inflammatory drug (NSAID) that has analgesic, anti-inflammatory, and antipyretic properties and has been shown to be effective in treating a variety of acute and chronic pain and inflammatory conditions.Despite its side effects, diclofenac sodium still remains the drug of choice[74]. Clinical studies have repeatedly shown that NSAIDs can alleviate pain and improve function in KOA patients[75]. In terms of the NPRS and WOMAC function, DNG and DG improved significantly in 6-week and 6-month follow-ups compared with pre-treatment. However, the DNG showed advantages in the NPRS and WOMAC function whether in the 6-week or 6-month follow-up. Moreover, DG showed significant regression at the 6-month follow-up compared with the 6-week in NPRs and WOMAC- total. However, DNG showed no significant difference between 6-months follow-up and 6-week. The advantages of dry needling trigger points may be that compared with oral diclofenac, dry acupuncture trigger point can not only alleviate pain, but also restore the mechanical imbalance of the skeletal muscle around the knee joint caused by the trigger point, thus improving the clinical symptoms of knee osteoarthritis.
Limitations
This experiment has certain limitations,one of which is the lack of supervision of the patient’s self-stretching. To cover the ethical and feasibility considerations, this study compared two treatment groups, but no placebo group was used in this experiment. Because current studies have shown no correlation between pain and osteoarthritis classification, this experiment did not analyze and statistics according to the classification of osteoarthritis. Most of our follow-ups were conducted by telephone because the patient was too old and has limited physical mobility. Therefore, no ROM was measured. Finally, previous studies primarily focused on active trigger points, that is, inactivate active trigger points to latent trigger points. However, how to evaluate the effect of dry needling on latent trigger points requires further research to investigate this important issue. The pressure pain threshold (PPT) may have important value for the evaluation of latent trigger points;however, there was no record due to a lack of appropriate instruments.