Electrophysiological And Performance Changes Of The Lumbar Paraspinal Muscle After Posterior Lumbar Interbody Fusion

During recent decades, posterior lumbar interbody fusion (PLIF) has been performed increasingly. However, the posterior access and the implant’s position cause paraspinal muscle damage, which may lead to instability and a reduced capacity. Previous studies have noted over the paraspinal muscle after surgery, including a loss in muscle thickness on computer tomograph, edematous and fatty changes on magnetic resonance imaging. The success of an operation is thus still primarily made conditional on the radiological result, although it is only in the event of substantial correction losses that there is a correlation with occurring pain. Morphological factors (bones, intervertebral discs) are typically blamed for chronic pain syndromes in the literature, while less importance is attached to functional factors (nerves and muscles). The link between postoperative low back pain, denervation of lumbar paraspinal muscle, and the observed changes in muscle functions, such as weakness or fatigue, have not yet been clearly defined. The aims of this study was to follow PLIF patients suffering from postsurgery disability and low back problems (pain group) in everyday tasks by studying muscle EMG and factions changes in lumbar paraspinal muscle and compare them with postoperatively well-improved patients (control group). This study includes two parts. In the first part, the denervation condition of the multifidus in pain group was compared with control group. In the second part, the evaluation was performed by comparing the strength and endurance capacity of the lumbar paraspinal muscle in pain group and in control group as well as link between denervation of paraspinal muscle, muscle functions, and postoperative low back pain was investigated.Part one. Denervation of Lumbar Multifidus After Posterior Lumbar Interbody FusionObjective. To determine the effect of posterior lumbar interbody fusion on paraspinal muscle by means of electrophysiological.Methods. Of86patients who had undergone PLIF,40patients with good recovery and46patients with poor recovery but no evidence of abnormality on plain film, CT, and MRI were divided into control group and pain group respectively. Postoperative electromyography examination was performed.Results. In pain group, the spontaneous activity(consisting of positive waves and fibrillation) in multifidus presented a significant difference when compared with in control group (P<0.01). All spontaneous activity located in surgery region. In pain group, spontaneous activity presented a significantly higher in the fusion segment than in adjacent regions (P<0.01). Spontaneous activity in laminectomy side did not presented a significant difference when campared with in contralateral side (P=0.45)Conclusion. This results demonstrated that posterior lumbar interbody fusion resulted in spontaneous activity in multifidus. Denervation condition of multifidus in pain group was much severer than in control group.Part two. Performance Changes of the Lumbar Paraspinal Muscle After PLIF and Risk Factors of Postoperative PainObjective. To determine the difference in muscle strength, muscle fatigue between pain group and control group and investigate the link between denervation of paraspinal muscle, muscle functions, and postoperative low back pain.Methods. Maximum voluntary isometric contractions strength of trunk extension and flexion as well as flexion/extension strength ratio were investigated on Tergumed lumbar training devices. Concurrent surface electromyograms were detected from paraspinal muscles during sustained isometric contractions at80%MVIC force level of trunk extension. Slope of median frequency(MFs parameters of the EMG power density spectrum were monitored to quantify localized muscle fatigue. The relationship between these factor (spontaneous activity score, muscle strength, flexion/extension strength ratio, MFs) and postoperative low back pain was investigated by the correlation analysis.Results. The group with low back pain showed significant lower extension strength than control group(P<0.01). The muscle performance test did not demonstrate a significant difference in flexion strength (P=0.75). Pain group presented a significant higher flexion/extension strength ratio and MFs than control group(P<0.01). Logistic regression analysis revealed that there was positive correlation of postoperative low back pain with spontaneous activity score and negative correlation with extension strength.Conclusion. Strength of paraspinal muscles in pain group decreased significantly after PLIF surgery. Denervation of multifidus can influence significantly extension strength and be one risk for postoperative low back pain. Nevertheless, extension strength can be a protect factor for postoperative low back pain.