A comparison of select trunk muscle thickness change between subjects with low back pain classified in the treatment-based classification system and asymptomatic controls.

Study Design: Cross-sectional descriptive.

Objectives: To investigate if muscle thickness change, as measured with rehabilitative ultrasound imaging (RUSI), is different across subgroups of patients with low back pain (LBP), classified in the Treatment-Based Classification (TBC) system, when compared to controls.

Background: Researchers have demonstrated that subgroups of patients with LBP exist and respond differently to treatment, challenging the assertion that LBP is "nonspecific." The TBC system uses 4 categories (stabilization, mobilization, direction specific exercise, or traction) to subgroup patients. Recently, researchers have demonstrated impairments of the transverse abdominis (TrA) and lumbar multifidus (LM) in those with LBP, regardless of classification. Although distinct differences in impairments have been identified between subgroups, TrA and LM impairments have not been studied and may be present across categories of the TBC system.

Methods And Measures: RUSI was utilized to measure percent thickness change from rest to contracted state during a voluntary task of the TrA and during an upper extremity task known to activate the LM in 56 subjects classified in the TBC system and 20 controls.

Results: During the prone upper extremity lifting task with a hand weight, there was a significant group difference for the LM at L4-L5 (P = .03) and at L5-S1 (P = .04), and during volitional activation for the TrA (P < .01). Post hoc testing revealed the differences were between controls and both the direction specific and stabilization categories at the L4-L5 level, between control and direction specific category for the L5-S1 level, and between controls and all 3 categories for the TrA.

Conclusion: Deficits in the ability to generate muscle thickness changes in the TrA and LM occurred across categories of the TBC system. Intervention studies should be performed to determine if intervention can correct these deficits and if deficit corrections are related to outcomes.