Effectsofplatelet-richplasmainjectiononelectricalactivityandbiomechanicsoftheerectorspinaemusclesinlumbarmyofascialpainsyndrome

Low back pain is one of the most common health problems worldwide, and myofascial pain syndrome (MPS) affecting the spinal stabilizer muscles is a frequent cause. MPS is characterized by painful trigger points in muscles that can cause localized pain, restricted movement, and ongoing discomfort. Currently, diagnosing and monitoring MPS relies heavily on subjective methods like manual palpation, which requires experienced clinicians and produces variable results between different assessors. There is a need for objective, reliable tools to measure the physical and electrical changes in muscles affected by MPS.

Additionally, while several treatments exist for MPS including dry needling and trigger point injections, platelet-rich plasma (PRP) has emerged as a promising newer option that uses the body's own growth factors to promote healing. However, its effects on the actual muscle function and structure in lumbar MPS remain unclear. This study aimed to address these gaps by using two objective measurement tools — surface electromyography (sEMG) to assess muscle electrical activity and a handheld device called MyotonPRO to measure muscle biomechanical properties — to better understand what happens in painful versus non-painful muscles and to evaluate whether PRP treatment can improve these measurable abnormalities.

The researchers recruited 40 patients with unilateral lumbar MPS from a hospital rehabilitation department in China between October 2022 and October 2023. All participants had experienced symptoms for more than six months and had pain on only one side of their lower back. The study used a single-group design without randomization or a control group. Before receiving treatment, all 40 participants underwent comprehensive assessments.

Muscle electrical activity was measured using sEMG while participants performed trunk extension exercises, capturing six features including root mean square, mean absolute value, integrated EMG, and waveform length in the time domain, plus median frequency and mean power frequency in the frequency domain. Muscle mechanical properties were measured at rest using MyotonPRO, which records oscillation frequency (muscle tone), dynamic stiffness, logarithmic decrement (elasticity), relaxation time, and creep. Pain levels were rated on a visual analog scale from 0 to 10, and functional disability was measured with the Oswestry Disability Index. After these baseline measurements, 33 of the 40 participants received a single ultrasound-guided PRP injection targeting trigger points in the painful erector spinae muscle.

The PRP was prepared from each patient's own blood through a two-step centrifugation process. Two weeks after the injection, all assessments were repeated in the 33 participants who completed follow-up.

Before treatment, clear differences existed between the painful and non-painful sides. All four sEMG time-domain features were significantly higher on the painful side (RMS, MAV, iEMG, and WL all with p < 0.001 or p = 0.001), indicating greater electrical muscle activity during contraction. However, no differences were found in frequency-domain features (MPF and MDF). On mechanical testing, the painful side showed significantly higher oscillation frequency (p = 0.041) and logarithmic decrement (p = 0.022), meaning the painful muscles had higher resting tone but lower elasticity.

No significant differences were found in stiffness, relaxation time, or creep. After PRP treatment, substantial improvements were observed. Pain scores dropped from 4.3 to 2.2 on the VAS (p < 0.001), and disability scores improved from 20.8 to 13.8 on the ODI (p < 0.001). The excessive electrical activity on the painful side decreased significantly for RMS (77.1 to 67.3, p = 0.001), MAV (60.7 to 53.1, p = 0.001), iEMG (112131.2 to 10666.9, p = 0.001), and WL (9125.4 to 8127.4, p = 0.008).

Notably, the logarithmic decrement on the painful side increased after treatment (1.48 to 1.59, p < 0.001), suggesting improved elasticity. Interestingly, some parameters on the non-painful side also changed after treatment, possibly due to reduced compensatory activity. After treatment, no significant differences remained between sides for any sEMG features.

This study provides valuable preliminary evidence that objective tools can detect the physical abnormalities caused by myofascial pain syndrome and track improvement after treatment. The findings suggest that MPS primarily affects the time-domain electrical features of muscles — essentially how much they activate — rather than their fatigue-related frequency characteristics. The higher muscle tone and reduced elasticity on the painful side align with the 'energy crisis theory' of trigger points, where sustained muscle contraction creates a cycle of pain and dysfunction. For clinicians, this suggests that sEMG and MyotonPRO could potentially serve as useful adjunct tools for diagnosing MPS and monitoring treatment response, though more validation is needed.

The results also support PRP as a promising treatment for lumbar MPS, with a single injection producing measurable improvements in both patient-reported outcomes and objective muscle function within two weeks. However, the lack of a control group means some improvement could reflect natural healing or placebo effects. Patients with chronic low back pain from MPS may find this encouraging, as PRP offers a minimally invasive option using their own biological material. Future research should compare PRP directly against established treatments like dry needling or local anesthetic injections, include longer follow-up periods, and use randomized controlled designs to confirm these preliminary findings.