Assessment of abdominal muscle function during a simulated unilateral weight-bearing task using ultrasound imaging

STUDY DESIGN: Cross-sectional study. OBJECTIVE: To investigate the function of the transversus abdominis (TrA) and internal oblique (10) muscles bilaterally during a simulated weight-bearing task using ultrasound imaging. BACKGROUND: An important aspect of neuromuscular control at the lumbopelvic region is stabilization. Biomechanical models have predicted that activation of transversely oriented muscles, such as the TrA and 10 muscles, can stiffen the sacroiliac joints and actively stabilize the pelvis for weight bearing. METHODS AND MEASURES: Nineteen healthy subjects were positioned in supine lying with their right heel against a footplate linked to a force transducer. Each subject performed a static simulated weight-bearing task of the right lower extremity. Ultrasound imaging was used to assess resultant changes in thickness of the 10 and TrA muscles, as well as the lateral slide of the anterior abdominal fascia on each side of the abdomen alternately. Muscle thickness and slide of the fascia were assessed at standardized force levels (0% and 25% of body weight). RESULTS: Substantial increases (P < .0001) in mean (+/- SD) thickness of the 10 (18.5% +/- 9.7%) and TrA (24.7% +/- 175%) muscles during the weight-bearing task were measured. Lateral movement (slide) of the anterior abdominal fascia of the TrA muscle also occurred (mean +/- SD, 1.3 +/- 2.0 mm; P = .014) with weight bearing. Changes in muscle thickness and amount of slide were similar for the left and right side of the abdomen (P > or = .11). CONCLUSION: The findings are consistent with biomechanical models that predicted symmetrical activation of the deep transversely oriented lumbopelvic muscles in healthy subjects in response to a unilateral functional weight-bearing task. Ultrasound imaging as a measurement tool represents a noninvasive method for measuring abdominal muscle function in functional axial loading.     

Observed changes in lateral abdominal muscle thickness after spinal manipulation: a case series using rehabilitative ultrasound imaging

STUDY DESIGN: Case series. BACKGROUND: A clinical prediction rule (CPR) has been developed and validated that accurately identifies a subgroup of patients with low back pain (LBP) likely to benefit from spinal manipulation; however, the mechanism of spinal manipulation remains unclear. The purpose of this case series was to describe changes in lateral abdominal muscle thickness using rehabilitative ultrasound imaging (RUSI) immediately following spinal manipulation in a subgroup of patients positive on the rule. CASE DESCRIPTIONS: Data from 9 patients (5 female, 4 male; 18-53 years of age) with a primary complaint of LBP are presented. All patients had symptoms for less than 16 days (range, 3-14 days) and did not have symptoms distal to the knee, satisfying the 2-factor rule for predicting successful outcome from spinal manipulation. The Oswestry Disability Index scores ranged from 8% to 52%. Lateral abdominal muscle thickness was assessed with the patient at-rest and while contracted during an abdominal drawing-in maneuver (ADIM) using RUSI. Measurements were taken before and immediately after spinal manipulation. Patients completed a 15-minute training session of the ADIM prior to assessment, to mitigate the potential for a learning effect to occur. OUTCOMES: Based on changes that exceeded the threshold for measurement error, 6 of 9 patients demonstrated an improved ability (11.5%-27.9%) to increase transversus abdominis (TrA) muscle thickness during the ADIM postmanipulation. Additionally, TrA muscle thickness at-rest postmanipulation decreased for 5 patients (11.5%-25.9%), while at-rest internal oblique muscle thickness decreased for 4 patients (6.4%-12.2%). DISCUSSION: This case series describes short-term changes in lateral abdominal muscle thickness post spinal manipulation. Although case series have significant limitations, including the fact that no cause-and-effect claims can be made, the decrease in muscle thickness at rest and the greater increase in muscle thickness during the ADIM postmanipulation observed in some of the patients could suggest an improvement in muscular function. Future research is needed to determine if increased muscle thickness is associated with improvements in pain and disability and to further explore neurophysiologic mechanisms of spinal manipulation.     

Intrarater and interrater reliability of assessment of lumbar multifidus muscle thickness using rehabilitative ultrasound imaging

STUDY DESIGN: Within-session intrarater and interrater reliability study. OBJECTIVE: To establish the intrarater and interrater reliability of thickness measurements of the multifidus muscle in a parasagittal plane, conducted by an experienced ultrasound operator and a novice assessor. BACKGROUND: There is considerable evidence for the important role of the multifidus muscle in segmental stabilization of the lumbar spine. The cross-sectional area of the multifidus muscle has been assessed in healthy subjects and patients with low back pain using real-time ultrasound imaging. However, few studies have measured the thickness of the multifidus muscle using a parasagittal view. METHODS AND MEASURES: The thickness of the multifidus muscle was measured at rest, using real-time ultrasound imaging, in 10 subjects without a history of low back pain, at the levels of the L2-3 and L4-5 zygapophyseal joints. The measure was carried out 3 times at each level by 2 assessors (1 experienced, 1 novice). Intrarater (model 3) and interrater (model 2) reliability was assessed by calculation of an F statistic (analysis of variance), the intraclass correlation coefficient (ICC), and the standard error of measurement (SEM). RESULTS: On the basis of an average of 3 trials, the 2 operators showed very high interrater agreement on the measurement of thicknesses at the L2-3 level (ICC2,3 = 0.96; 95% CI: 0.84 to 0.99) and the L4-5 vertebral level (ICC2,3 = 0.97; 95% CI: 0.87 to 0.99), with no systematic differences in muscle size across operators (P > .05). Interrater reliability was relatively lower for the L2-3 level (ICC2,1 = 0.85; 95% CI: 0.51 to 0.96) than the L4-5 level (ICC2,1 = 0.87; 95% CI: 0.52 to 0.97) when a single trial per rater was used, but these values still indicated a high level of agreement. In addition, the novice and experienced operator produced reliable intrarater measurements at L2-3 (ICC3,1 = 0.89; 95% CI: 0.72 to 0.97 and 0.94; 95% CI: 0.86 to 0.99) and at L4-5 (ICC3,1 = 0.88; 95% CI: 0.68 to 0.97 and 0.95; 95% CI: 0.86 to 0.99), with no systematic differences in muscle size across trials (P > .05). The consistently low SEM values also indicate low measurement error. CONCLUSION: A novice and an experienced assessor were both able to reliably perform this measure at rest for 2 vertebral levels using real-time ultrasound imaging. An average of 3 trials produced higher interrater reliability scores, though using a single trial per rater was also reliable.     

Effects of specific exercise instructions on abdominal muscle activity during trunk curl exercises

STUDY DESIGN: A repeated-measures, counterbalanced design. OBJECTIVES: To test whether subjects could learn and retain the ability to alter the relative activity of abdominal muscle groups when performing trunk curl exercises. BACKGROUND: Although trunk curl exercises are widely prescribed, a disadvantage of trunk curls is that they primarily activate rectus abdominis, while the internal and external oblique abdominis muscles are considered to be more important contributors to lumbar stability. METHODS AND MEASURES: A convenience sample of 25 subjects performed trunk curl exercises in accordance with 3 different sets of instructions: nonspecific instructions (NS), instructions intended to emphasize rectus abdominis activity (RE), and instructions intended to emphasize oblique abdominis activity (OE). Electromyographic (EMG) activity was recorded from the upper and lower rectus and the internal and external oblique abdominis muscles while a physical target was used to insure that the trunk was raised to the same height for all conditions. Normalized root-mean-square EMG amplitude measures were used to test for instruction-dependent changes in the relative EMG activity of the rectus and oblique muscle groups. RESULTS: Following a single, brief, instruction session, subjects performing trunk curls had significantly greater normalized oblique:rectus EMG ratios when following OE instructions (mean [+/- SD] oblique-rectus ratio, 1.45 +/- 0.34) than when following RE (mean [+/- SD] oblique-rectus ratio, 0.76 +/- 0.24) or NS (mean [ISD] oblique-rectus ratio, 0.63 +/- 0.23) instructions. Retesting 1 week later indicated that subjects retained this skill. CONCLUSIONS: With minimal instruction, subjects are able to volitionally alter the relative activity of the oblique and rectus abdominis muscles when performing trunk curls. Incorporating instructions emphasizing oblique abdominis activity into lumbar stabilization programs appears promising and has potential advantages over other approaches to altering abdominal muscle activity during trunk     

Rehabilitative ultrasound imaging of the abdominal muscles

Rehabilitative ultrasound imaging (RUSI) of the abdominal muscles is increasingly being used in the management of conditions involving musculoskeletal dysfunctions associated with the abdominal muscles, including certain types of low back and pelvic pain. This commentary provides an overview of current concepts and evidence related to RUSI of the abdominal musculature, including issues addressing the potential role of ultrasound imaging in the assessment and training of these muscles. Both quantitative and qualitative aspects associated with clinical and research applications are considered, as are the possible limitations related to the interpretation of measurements made with RUSI. Research to date has utilized a range of methodological approaches, including different transducer placements and imaging techniques. The pros and cons of the various methods are discussed, and guidelines for future investigations are presented. Potential implications and opportunities for clinical use of RUSI to enhance evidence-based practice are outlined, as are suggestions for future research to further clarify the possible role of RUSI in the evaluation and treatment of abdominal muscular morphology and function.     

The use of real-time ultrasound feedback in teaching abdominal hollowing exercises to healthy subjects

STUDY DESIGN: Randomized controlled trial. OBJECTIVES: To determine if supplementing typical clinical instruction with real-time ultrasound feedback facilitates performance and retention of the abdominal hollowing exercise (AHE). BACKGROUND: Increasingly clinicians are using real-time ultrasound imaging as a form of feedback when teaching patients trunk stabilization exercises; however, there has been no justification for this practice. METHODS AND MEASURES: Forty-eight subjects were divided randomly into 3 groups that received different types of feedback: group 1 received minimal verbal feedback, group 2 received verbal and palpatory feedback, and group 3 received real-time ultrasound, verbal, and palpatory feedback. If the subject performed 3 consecutive correct AHEs during the initial session, she/he returned for a retention test. The performance of 3 consecutive, correct AHEs was the criterion measure; the number of trials to criterion was also recorded during the initial and retention test sessions. RESULTS: The ability to perform the AHE differed among groups (P<.001). During the initial session, 12.5% of subjects in group 1, 50.0% of subjects in group 2, and 87.5% of subjects in group 3 were able to perform 3 consecutive AHEs. Group 3 subjects achieved the criterion in fewer trials than the other 2 groups (P = .0006). No differences among groups were found for the retention testing; however, low power due to fewer subjects precluded a strong interpretation of this finding. CONCLUSION: Real-time ultrasound feedback can decrease the number of trials needed to consistently perform the AHE; however, the data are inconclusive with regard to retention of this skill.     

Standardized ultrasound method for assessing detrusor muscle thickness in children

PURPOSE: We standardized transabdominal ultrasound measurement of bladder wall thickness in children and evaluated its reliability. MATERIALS AND METHODS: Using ultrasonography we measured the thickness of the low echogenic layer of the ventral and dorsal bladder walls at increasing degrees of bladder fullness in the setting of voiding cystourethrography. For assessing intra-observer variability an observer blinded to the numerical values of the measurements studied 38 patients 0.2 to 13.7 years old (median age 1. 5). Measurements were performed as pairs of replicates at well-defined sites with reference to the urachal remnant, and rectal impression and/or contour. For assessing interobserver variability 3 independent observers measured the same child. Eight children 0.3 to 10.5 years old (median age 6.4) were evaluated at 2 degrees of bladder fullness per child. RESULTS: The thickness of the low echogenic layer of the ventral and dorsal walls was 0.4 to 2.9 (median 0.9) and 0.4 to 2.8 mm. (median 1.1). The dorsal wall was slightly thicker than the ventral wall. The intra-observer and interobserver variability of measurements (standard deviation) was 0. 2 mm. for each wall part. There was a small systematic difference among observers. CONCLUSIONS: It is possible to determine the thickness of the low echogenic layer of the bladder wall with a systematic and anatomically defined method of acceptably reliable measurements. The ventral and dorsal walls should continue to be measured until more is known about their pathological appearance.     

Prehospital ultrasound imaging improves management of abdominal trauma

BACKGROUND: Blunt abdominal trauma with intra-abdominal bleeding is often underdiagnosed or even overlooked at trauma scenes. The purpose of this prospective, multicentre study was to compare the accuracy of physical examination and prehospital focused abdominal sonography for trauma (PFAST) to detect abdominal bleeding. METHODS: Six rescue centres took part in the study from December 2002 to December 2003, including 230 patients with suspected abdominal injury. The accuracy of physical examination at the scene and PFAST were compared. Later examinations in the emergency department (ultrasonography and/or computed tomography) were used as the reference standard. RESULTS: The complete protocol and follow-up was obtained in 202 patients. The sensitivity, specificity and accuracy of PFAST were 93 per cent, 99 per cent and 99 per cent, respectively, compared with 93 per cent, 52 per cent and 57 per cent for physical examination at the scene. Scanning with PFAST occurred a mean(s.d.) 35(13) min earlier than ultrasound in the emergency department. Abdominal bleeding was detected in 14 per cent of patients. Using PFAST led to a change in either prehospital therapy or management in 30 per cent of patients, and a change to admitting hospital in 22 per cent. CONCLUSION: In this study, PFAST was a useful and reliable diagnostic tool when used as part of surgical triage at the trauma scene.     

Ultrasound imaging assessment of abdominal muscle function during drawing-in of the abdominal wall: an intrarater reliability study

STUDY DESIGN: Test-retest intrarater reliability study. OBJECTIVE: To examine reliability of abdominal musculature measurements across a broad range of conditions for a physical therapist newly trained in assessment using rehabilitative ultrasound imaging (RUSI). BACKGROUND: RUSI has previously been used to assess abdominal muscle function during a drawing-in maneuver of the anterior abdominal wall, and measurements conducted by an experienced assessor have been validated by comparison with magnetic resonance imaging. Few studies have examined the reliability of less experienced operators, and only in isolated measurement conditions. METHODS AND MEASURES: Nineteen subjects (11 female, 8 male) without a history of low back pain performed the abdominal drawing-in maneuver in a supine hook-lying position. RUSI was used bilaterally to assess the thickness of the internal oblique (IO) and transversus abdominis (TrA) muscles at rest and on contraction, as well as changes in the length of the TrA muscle (indicated by slide of the anterior abdominal fascia). The reliability of a novice rater who received 8 hours of training was examined (a) across 3 measurements of the same ultrasound image, (b) across 3 separate ultrasound images (averaged for days and sides of abdomen), and (c) across 2 days (averaged for images and sides). RESULTS: Reliability of assessing muscle thickness was very high across 3 measurements of the sale image (intrarater correlation coefficients [ICC3.1] were all greater than 0.97), fair to high across 3 images (ICC(3,4) = 0.62-0.82), and fair to high across 2 days (ICC(3,6) = 0.63-0.85). Reliability of measuring the slide of the anterior abdominal fascia was very high across measurements from the same image (ICC(3,1) = 0.98) but very low across images (ICC(3,4) = 0.44) and across 2 days (ICC(3,6) = 0.36). CONCLUSIONS: High reliability of a novice rater was demonstrated for some measurement conditions. Measures of reliability for recapturing the image and repetition across days ranged from low to high. Inconsistencies in the pattern of results suggest that for a novice assessor using RUSI, training should be performed and reliability assessed for each abdominal muscle and measurement condition intended to be used for research and clinical practice.     

Monitoring of skeletal muscle oxygenation using near-infrared spectroscopy during abdominal aortic surgery

Purpose. To examine the utility of near-infrared spectroscopy (NIRS) in assessing lower-leg perfusion, NIRS was performed on the calf muscles of patients who underwent abdominal aortic surgery. Methods. Thirty patients undergoing elective infrarenal abdominal aortic surgery for abdominal aortic aneurysm (AAA group; n = 16) and aorto-occlusive disease (AOD group; n = 14) were studied. Before induction of anesthesia, NIRS probes were placed over both calf muscles, and muscle oxygen saturation (S_tO2) was continuously monitored throughout the surgery. Results. The preoperative S_tO2 value was significantly lower in the AOD group (57.0 ± 11.2%) than in the AAA group (68.7 ± 7.0%). In both groups, S_tO2 significantly decreased after aortic cross-clamping; the maximal ischemic value of S_tO2 in the AAA group (17.8 ± 7.2%) was significantly lower than that in the AOD group (46.7 ± 17.1%). The time taken to reach maximal ischemia was significantly longer in the AAA group (30 ± 12 min) than in the AOD group (19 ± 12 min). After release of the aortic clamp, the decreased S_tO2 returned to the preoperative level in the AAA group, whereas it increased above the preoperative value in the AOD group. Conclusion. NIRS performed on the calf muscles is a useful method for assessing the changes in lower-leg perfusion during and after abdominal aortic surgery. Received: June 6, 2001 / Accepted: December 5, 2001     

Co-activation of the abdominal and pelvic floor muscles during voluntary exercises

The response of the abdominal muscles to voluntary contraction of the pelvic floor (PF) muscles was investigated in women with no history of symptoms of stress urinary incontinence to determine whether there is co-activation of the muscles surrounding the abdominal cavity during exercises for the PF muscles. Electromyographic (EMG) activity of each of the abdominal muscles was recorded with fine-wire electrodes in seven parous females. Subjects contracted the PF muscles maximally in three lumbar spine positions while lying supine. In all subjects, the EMG activity of the abdominal muscles was increased above the baseline level during contractions of the PF muscles in at least one of the spinal positions. The amplitude of the increase in EMG activity of obliquus externus abdominis was greatest when the spine was positioned in flexion and the increase in activity of transversus abdominis was greater than that of rectus abdominis and obliquus externus abdominis when the spine was positioned in extension. In an additional pilot experiment, EMG recordings were made from the pubococcygeus and the abdominal muscles with fine-wire electrodes in two subjects during the performance of three different sub-maximal isometric abdominal muscle maneuvers. Both subjects showed an increase in EMG activity of the pubococcygeus with each abdominal muscle contraction. The results of these experiments indicate that abdominal muscle activity is a normal response to PF exercise in subjects with no symptoms of PF muscle dysfunction and provide preliminary evidence that specific abdominal exercises activate the PF muscles.     

Characterization of lateral abdominal muscle thickness in persons with lower extremity amputations

STUDY DESIGN: Retrospective review. OBJECTIVES: To describe bilateral thickness of the lateral abdominal muscles at baseline and during an abdominal drawing-in maneuver (ADIM) in individuals with unilateral transtibial (TTA) or transfemoral (TFA) amputations. BACKGROUND: Although side-to-side symmetry of lateral abdominal muscle thickness has been established in healthy individuals, the degree of symmetry in those with unilateral lower extremity amputations remains unknown. Differences in lateral abdominal muscle thickness may exist based on prior findings of asymmetry and differences measured based on level of amputation in both the size and function of the iliopsoas and back extensor muscles. METHODS AND MEASURES: Seventy patients (69 males, 1 female) with traumatic unilateral lower extremity amputations (TTA, n = 39; TFA, n = 31) received a rehabilitative ultrasound imaging examination. Absolute thickness of the transversus abdominis (TrA) and the external and internal oblique muscles combined (EO+IO) were assessed bilaterally at baseline and during the ADIM. Symmetry was assessed using relative muscle thickness values at baseline. Percent increase in muscle thickness during the ADIM was used to investigate muscle function. Separate 2-by-2 mixed-model ANOVAs were used to compare both within-group (side of amputation versus nonamputated side) and between-group (TTA versus TFA) differences for thickness and function of the TrA and the EO+IO muscles. RESULTS: On the side of the amputation, the relative baseline thickness of the EO+IO measurement was greater (P < .05), while the relative baseline thickness of the TrA muscle was smaller (P < .05). But the mean differences side to side were small (1.3%) and unlikely to be clinically significant. Further, there were no differences in baseline muscle thickness between groups for the TrA (P = .95) or the EO+IO (P = .94) muscles. For thickness measurements during the ADIM, the TrA showed no side-to-side (P = .74) or group (P = .07) differences. Similarly, no side-to-side (P = .60) or group (P = .09) differences were found in the EO+IO thickness during the ADIM. CONCLUSIONS: Despite the limitations of retrospective review, these findings provide an initial reference data set for future studies. Bilateral symmetry of the lateral abdominal wall muscle thicknesses at baseline and during the ADIM for those with unilateral lower extremity amputations is comparable to healthy individuals. Future studies should consider the potential influences of low back pain and gait training on symmetry of muscle thickness and muscle function based on level of amputation.