Abstract
Context:
Patients with low back pain (LBP) may receive osteopathic manipulative treatment (OMT) to resolve or manage their pain. The indication for OMT for patients with LBP is the presence of somatic dysfunction, diagnosed using palpatory examination. Because palpatory findings commonly have poor interexaminer reliability, the current study used ultrasonography (US) to establish pre-OMT and post-OMT musculoskeletal measurements of relative asymmetry between pelvic and sacral bony landmarks.
Objective:
To document objective musculoskeletal changes that occur in response to OMT using US and to compare palpatory assessment of landmark asymmetry with US assessment.
Methods:
Sixty men and women aged 20 to 55 years with at least 1 episode of LBP in the past 2 weeks were assigned to a seated control, walking control, or OMT group (20 participants per group). Participants received an initial, bilateral US measurement of the skin to posterior superior iliac spine (SPSIS), skin to sacral base position (SBP), and sacral sulcus depth (SSD). Participants in seated control and OMT groups received a palpatory assessment of SBP and SSD prior to initial US assessment. After assessment, the seated control group sat in a waiting room for 30 minutes, the walking control group walked for 5 minutes, and the OMT group received OMT to address sacral base asymmetry using predominantly direct techniques for a maximum of 20 minutes. Participants then received a second US assessment of the same structures.
Results:
Body mass index (BMI) was correlated with SPSIS (r=0.5, P=.001) and SBP (r=0.6, P<.001). More participants in seated control (75%) and OMT (65%) groups had an increase in asymmetry from first to second US assessment for SPSIS compared with participants in the walking control group (35%, P=.05). No significant differences were found between groups for absolute asymmetry or total change in asymmetry (all P>.10). The κ was −0.1 (95% CI, −0.2 to 0.03) for SBP and −0.01 (95% CI, −0.1 to 0.1) for SSD.
Conclusion:
Musculoskeletal changes in SPSIS and SBP measurements related to OMT could not be readily identified using US. The SPSIS and SBP measurements were dependent on BMI, which may have affected the accuracy of US to detect small changes in asymmetry. Qualitative palpatory assessments did not correlate with US measurements. Further study is needed to identify US measurements that demonstrate change with OMT. (ClinicalTrials.gov number NCT02820701)
Numerous studies have demonstrated clinical efficacy of manual medicine techniques, such as osteopathic manipulative treatment (OMT), in patients with low back pain (LBP).
1-4 Clinical efficacy is indicated by reduction of pain, but the anatomical mechanisms of these techniques remain unclear. Clinically, patients are reassessed after OMT for changes in pain level and the presence of somatic dysfunction (tenderness, tissue texture abnormalities, restricted range of motion, and asymmetry). While palpatory assessment of somatic dysfunction before and after OMT is useful clinically, it is less useful as pretreatment and posttreatment outcome measures because of poor interexaminer reliability. Individual examiners are often inaccurate in their identification of bony landmarks,
5-7 so any measurements derived from those findings would not be valid. Therefore, use of objective measurements to assess pretreatment and posttreatment outcomes is desirable.
Most studies objectively assessing somatic dysfunction before and after manual medicine techniques have evaluated changes in tenderness using algometers to measure pressure pain thresholds. Results have indicated that manual medicine increases pressure pain thresholds, meaning tissues tolerate more pressure after manipulation before pain is felt.
8-10 However, this finding may be an indirect effect of technique rather than primary mechanism of action. In other studies, manual medicine techniques induce changes in serum biomarker levels
8,11-15 and muscle activation,
16,17 but these findings may be an indirect effect. A potential mechanism for OMT inducing these physiologic responses is change in bony symmetry around a dysfunctional articulation. Change in symmetry would affect joint range of motion and muscular and ligamentous balance, affecting neurologic proprioceptive responses and neuromuscular processes.
18 Childs et al
19 found improvements in lumbopelvic symmetry after spinal manipulation was associated with pain reduction; however, lumbopelvic symmetry was assessed using palpation. For a better understanding of these mechanisms, an objective measurement of symmetry is needed.
Common choices for objective measurements of bony landmarks include plain film radiography, computed tomography, magnetic resonance imaging, and ultrasonography (US). Radiography and computed tomography expose participants to potentially harmful ionizing radiation, and magnetic resonance imaging is expensive. However, US is inexpensive and radiation-free, which makes it a reasonable choice for obtaining objective outcome measures. Manual medicine studies have used US measurements as outcome measures. Brenner et al
16 measured precontraction and postcontraction lumbar multifidus muscle thickness in the same participant before and after spinal manipulation; manipulation significantly increased change in muscle thickness between precontraction and postcontraction measures, suggesting that the intervention improved the ability of the muscle to contract. Shaw et al
20 used US to assess lumbar vertebral transverse process asymmetry before and after OMT and found that OMT significantly improved symmetry. Ultrasonography is clinically used to identify sacral anomalies in infants and sacral landmarks before caudal epidural injections.
21-25 Lockwood et al
26 used US in an educational setting to assess sacral landmark asymmetry.
The current study used US to quantify changes in asymmetry between pelvic and sacral bony landmarks before and after OMT. We assessed sacral base position and sacral sulcus depth because they are used in palpatory diagnosis.
27 Our objective was to document objective musculoskeletal changes that occur in response to OMT using US. A secondary objective compared palpatory assessment of landmark asymmetry with US assessment. We hypothesized that absolute asymmetry as measured by US would decrease after OMT in participants with a recent history of LBP and remain the same in control groups. To ensure that participants had sacral somatic dysfunction, we recruited participants with a recent history of LBP because studies suggest that people with LBP have greater incidence and severity of somatic dysfunction in lumbar, pelvic, and sacral regions than people without LBP.
28-30
Methods
Participants
From August to December 2016, 60 men and women aged 20 to 55 years with at least 1 episode of LBP in the past 2 weeks were recruited. The first group recruited was randomly assigned using a random number generator to seated control or OMT groups (20 participants/group). The seated control group was used to determine the stability of sacral measurements. The OMT group received OMT to address sacral somatic dysfunction diagnosed through palpation. Three months later, a nonrandomized, substudy was conducted involving a walking control group to investigate the stability of sacral measurements and the effect of walking on sacral base asymmetry. For both studies, potential participants were excluded if they had a body mass index (BMI) over 30, prior spinal surgery, fractures, known congenital anomalies of the lumbar vertebra and sacrum, or OMT in the past week. Participants completed an initial medical history questionnaire: age, date of last pain (today, yesterday, 2-7 days ago, 8-14 days ago, >14 days ago), and frequency of pain in the past 2 weeks. Height and weight were measured at enrollment and BMI was calculated. The study protocol was approved by the local institutional review board, and participants provided informed consent.
Participants in the seated control and OMT groups received palpatory assessment of sacral base position (SBP) and sacral sulcus depth (SSD) before initial US assessment. All participants received initial US assessment of sacral base asymmetry. After assessment, the seated control group waited in another room for approximately 30 minutes. The walking control group walked a defined indoor route for 5 minutes. The OMT group received OMT to address sacral base asymmetry identified by palpation of sacral base positions and sacral sulcus depths. After the intervention (sitting, walking, or OMT), participants received a second US assessment. The ultrasonographer was blinded to seated control vs OMT group assignment.
Palpatory Assessment
To determine SBP using palpation, sacral bases were palpated (K.T.S.) with the participant in the prone position to determine if the right sacral base was anterior, posterior, or equal compared with the left. To determine SSD, relative depth from the posterior surface of the posterior superior iliac spines (PSIS) to the sacral bases was assessed by palpation bilaterally and recorded for the right SSD as deep, shallow, or equal.
US Assessment
For the current study, a portable US machine (Mindray North America M7 with curvilinear transducer C5-2s) was used. A curvilinear transducer provided optimal musculoskeletal visualization for adult sacral base measurements.
31-33 Gain and depth were adjusted individually. Ultrasonographic assessment of 2 bony landmarks, PSIS and sacral base, was performed with participants in a prone position. Imaging was performed by a physician (T.K.) certified by the American Registry for Diagnostic Medical Sonography with 19 years of US experience and 11 years of US teaching experience. The ultrasonographer measured depth from the skin to the posteriormost surface of the PSIS (SPSIS) and depth from the skin to the posteriormost surface of the sacral base (SBP) on both sides before and after intervention (
Figure). For each landmark measurement, the US transducer was placed directly over the bony landmark and consistent contact pressure was used. A third landmark, SSD, was calculated from the other measurements: SSD=SBP−SPSIS.
Osteopathic Manipulative Treatment
The OMT intervention included a brief physical examination to identify somatic dysfunction in lumbar, pelvic, sacral, and lower extremity body regions that treating physicians (C.L.R. or C.R.E. and K.T.S.) considered relevant to the participant's asymmetry of the sacral base position and SSD. Treating physicians were blinded to findings of the US measurements. The OMT was performed to improve sacral asymmetry by treating the sacrum and surrounding regions (lumbar, pelvis, and lower extremities). Improvement in sacral asymmetry was verified (K.T.S.) prior to the postintervention US. The OMT techniques included 1 or more of the following: muscle energy, articular, or high-velocity, low-amplitude as indicated by physical findings and discretion of the treating physician. Additional techniques, such as Still, counterstrain, facilitated positional release, balanced ligamentous tension, and osteopathic cranial manipulative medicine, could be used at the discretion of the treating physician, but total treatment time could not exceed 20 minutes. To encourage participation in the initial study, participants assigned to seated control could receive OMT after the postintervention US assessment.
Statistical Methods
Summary statistics for participants were tabulated: continuous variables were summarized using mean (SD), minimum, and maximum; and categorical variables were summarized using frequencies and percentages. Analysis of variance models were built to compare mean age and BMI across the groups. Correlations between BMI and US measurements were calculated for each landmark (SPSIS, SBP, SSD). Absolute asymmetry between left and right landmark measurements was calculated as follows:
To determine if absolute asymmetry increased, decreased, or stayed the same after intervention, direction of change in asymmetry was calculated as follows:
To account for total change in measurements at both left and right landmarks between the first and second US measurements, total change in asymmetry between first and second US assessments was calculated as follows:
The Fisher exact test was used to test associations between group and direction of change in asymmetry at each landmark. Multiple linear regression models were built to compare mean absolute asymmetry for each landmark measured during the first US assessment between groups while controlling for demographic characteristics, date of last pain, and frequency of pain. Similar multiple linear regression models were built to compare mean total change in asymmetry from first to second US assessment between groups for each landmark between groups.
Mean absolute asymmetry at the first and second US assessments and mean total change in asymmetry for seated control and OMT groups were compared using a 2-sample t test. The walking control group was compared with the seated control and OMT groups for mean absolute asymmetry at the first and second US assessments and for total change in asymmetry using 1-way analysis of variance. To compare qualitative palpatory assessment of SBP and SSD with quantitative US measurements, US measurement of landmark position was first converted to a qualitative assessment as follows:
▪ right anterior SBP or deep SSD = right US measurement > left US measurement
▪ right posterior SBP or shallow SSD = right US measurement < left landmark measurement
▪ equal SBP or SSD = right US measurement = left US measurement
To compare agreement between qualitative palpatory and US assessments of SBP and SSD, κ and associated 95% CIs were calculated. Values less than or equal to 0 indicated no agreement; 0.01 to 0.20, none to slight; 0.21 to 0.40, fair; 0.41 to 0.60, moderate; 0.61 to 0.80, substantial; and 0.81 to 1.00, almost perfect agreement. To determine if US localization of landmarks at the sacral base was reliable, intraclass correlation coefficients (ICC) and associated 95% CIs were calculated for US measurements from the first to second US assessment for each landmark. For ICC, 0.7 to 0.8 was considered good; 0.8 to 0.9, very good; and 0.9 to 1.0, excellent. P≤.05 was considered significant. Data analysis was performed using SAS statistical software version 9.4 (SAS Institute, Inc.).
Results
A total of 60 participants were included in the study (OMT group, n=20; seated control group, n=20; walking control group, n=20). Demographic characteristics of participants are presented in
Table 1. Initially, no differences were found in mean age (
P=.78) or BMI (
P=.34) for the seated control and OMT groups. When adding the walking control group, no differences were found in mean age (
P=.73) or BMI (
P=.48).
Table 1.
Demographic Characteristics of Participants Receiving Pre- and Postintervention US
| Characteristic | All Participants | Seated Control Group (n=20) | Walking Control Group (n=20) | OMT Group (n=20) |
| Femalea | 31 (52) | 10 (50) | 11 (55) | 10 (50) |
| Ageb, y | 29.1 (7.8) 19-56 | 28.9 (8.6) 23-56 | 30.2 (7.6) 24-55 | 28.2 (7.4) 19-52 |
| Date of Last Paina | | | |
| Yesterday or today | 39 (65) | 14 (70) | 13 (65) | 12 (60) |
| ≥2 days ago | 21 (35) | 6 (30) | 7 (35) | 8 (40) |
| Frequency of Paina | | | |
| Daily | 15 (25) | 3 (15) | 7 (35) | 5 (25) |
| Not daily | 45 (75) | 17 (85) | 13 (65) | 15 (75) |
| BMIb | 24.8 (2.1) 19.3-29.6 | 25.3 (1.5) 22.9-28.8 | 24.5 (2.5) 19.3-27.9 | 24.7 (2.3) 19.8-29.6 |
Table 1.
Demographic Characteristics of Participants Receiving Pre- and Postintervention US
| Characteristic | All Participants | Seated Control Group (n=20) | Walking Control Group (n=20) | OMT Group (n=20) |
| Femalea | 31 (52) | 10 (50) | 11 (55) | 10 (50) |
| Ageb, y | 29.1 (7.8) 19-56 | 28.9 (8.6) 23-56 | 30.2 (7.6) 24-55 | 28.2 (7.4) 19-52 |
| Date of Last Paina | | | |
| Yesterday or today | 39 (65) | 14 (70) | 13 (65) | 12 (60) |
| ≥2 days ago | 21 (35) | 6 (30) | 7 (35) | 8 (40) |
| Frequency of Paina | | | |
| Daily | 15 (25) | 3 (15) | 7 (35) | 5 (25) |
| Not daily | 45 (75) | 17 (85) | 13 (65) | 15 (75) |
| BMIb | 24.8 (2.1) 19.3-29.6 | 25.3 (1.5) 22.9-28.8 | 24.5 (2.5) 19.3-27.9 | 24.7 (2.3) 19.8-29.6 |
×
Landmark measurements at first and second US assessments are presented in
Table 2. The BMI was correlated with SPSIS (
r=0.5,
P=.001) and SBP (
r=0.6,
P<.001) but not with SSD (
r=0.2,
P=.24). A significant correlation was found between SPSIS and SBP (
r=0.7,
P<.001).
Table 2.
Landmark Measurements for Each Landmark (N=120) Measured at Both US Assessments
| First US Assessment, mm | Second US Assessment, mm |
| Landmark | Mean (SD) | Range | Mean (SD) | Range |
| SPSIS | | | | |
| Total | 20.5 (7.3) | 7.1-40.0 | 20.2 (7.3) | 6.7-41.0 |
| Left onlya | 21.0 (7.0) | 7.3-40.0 | 20.4 (7.2) | 6.7-37.9 |
| Right onlya | 20.1 (7.7) | 7.1-38.3 | 20.1 (7.5) | 7.7-41.0 |
| SBP | | | | |
| Total | 44.7 (8.5) | 28.6-79.2 | 45.8 (8.5) | 30.2-78.4 |
| Left only | 44.5 (8.4) | 31.1-76.1 | 45.7 (8.9) | 31.5-78.4 |
| Right only | 44.8 (8.7) | 28.6-79.2 | 45.9 (8.2) | 30.2-75.3 |
| SSD | | | | |
| Total | 24.1 (6.3) | 9.1-45.3 | 25.6 (5.9) | 10.4-40.5 |
| Left only | 23.6 (6.0) | 10.7-45.3 | 25.4 (5.8) | 11.7-40.5 |
| Right only | 24.6 (6.5) | 9.1-40.9 | 25.8 (6.2) | 10.4-38.0 |
Table 2.
Landmark Measurements for Each Landmark (N=120) Measured at Both US Assessments
| First US Assessment, mm | Second US Assessment, mm |
| Landmark | Mean (SD) | Range | Mean (SD) | Range |
| SPSIS | | | | |
| Total | 20.5 (7.3) | 7.1-40.0 | 20.2 (7.3) | 6.7-41.0 |
| Left onlya | 21.0 (7.0) | 7.3-40.0 | 20.4 (7.2) | 6.7-37.9 |
| Right onlya | 20.1 (7.7) | 7.1-38.3 | 20.1 (7.5) | 7.7-41.0 |
| SBP | | | | |
| Total | 44.7 (8.5) | 28.6-79.2 | 45.8 (8.5) | 30.2-78.4 |
| Left only | 44.5 (8.4) | 31.1-76.1 | 45.7 (8.9) | 31.5-78.4 |
| Right only | 44.8 (8.7) | 28.6-79.2 | 45.9 (8.2) | 30.2-75.3 |
| SSD | | | | |
| Total | 24.1 (6.3) | 9.1-45.3 | 25.6 (5.9) | 10.4-40.5 |
| Left only | 23.6 (6.0) | 10.7-45.3 | 25.4 (5.8) | 11.7-40.5 |
| Right only | 24.6 (6.5) | 9.1-40.9 | 25.8 (6.2) | 10.4-38.0 |
×
Frequency distributions for direction of change in asymmetry for all landmarks and groups are presented in
Table 3. An association between SPSIS and group was found (
P=.05); asymmetry at SPSIS was more likely to increase after seated control and OMT than after walking control. No associations were found between groups and direction of change in asymmetry for SBP (
P=.35) or SSD (
P=.67).
Table 3.
Frequency Distribution for Direction of Change in US Landmark Asymmetry by Landmark and Study Group
| Direction of Change in Asymmetry, No (%)a | |
| US Landmark | Increased | No Change | Decreased | P Valueb |
| SPSIS | | | | |
| Seated control | 15 (75) | 1 (5) | 4 (20) | .048 |
| Walking control | 7 (35) | 2 (10) | 11 (55) | |
| OMT | 13 (65) | 0 | 7 (35) | |
| SBP | | | | |
| Seated control | 8 (40) | 0 | 12 (60) | .35 |
| Walking control | 12 (60) | 0 | 8 (40) | |
| OMT | 9 (45) | 0 | 11 (55) | |
| SSD | | | | |
| Seated control | 13 (65) | 0 | 7 (35) | .67 |
| Walking control | 13 (65) | 0 | 7 (35) | |
| OMT | 10 (50) | 0 | 10 (50) | |
Table 3.
Frequency Distribution for Direction of Change in US Landmark Asymmetry by Landmark and Study Group
| Direction of Change in Asymmetry, No (%)a | |
| US Landmark | Increased | No Change | Decreased | P Valueb |
| SPSIS | | | | |
| Seated control | 15 (75) | 1 (5) | 4 (20) | .048 |
| Walking control | 7 (35) | 2 (10) | 11 (55) | |
| OMT | 13 (65) | 0 | 7 (35) | |
| SBP | | | | |
| Seated control | 8 (40) | 0 | 12 (60) | .35 |
| Walking control | 12 (60) | 0 | 8 (40) | |
| OMT | 9 (45) | 0 | 11 (55) | |
| SSD | | | | |
| Seated control | 13 (65) | 0 | 7 (35) | .67 |
| Walking control | 13 (65) | 0 | 7 (35) | |
| OMT | 10 (50) | 0 | 10 (50) | |
×
Initially, no differences were found in absolute asymmetry or total change in asymmetry between seated control and OMT groups for any landmark (all
P≥.07). When adding walking control, no differences were found between groups for mean absolute asymmetry (all
P≥.10) or mean total change in asymmetry (all
P≥.19) (
Table 4).
Table 4.
Absolute Asymmetry for Each Landmark Measured at Each US Assessment and Total Change in Asymmetry from First to Second US Assessment
| Absolute Asymmetrya, mm, Mean (95% CI) | |
| US Landmark | Seated Control Group | Walking Control Group | OMT Group | P Valueb |
| SPSIS | | | | |
| First | 3.3 (2.2-4.4) | 3.2 (2.1-4.3) | 2.3 (1.2-3.4) | .35 |
| Second | 4.0 (2.8-5.1) | 3.3 (2.1-4.4) | 2.6 (1.4-3.7) | .26 |
| Changec | 4.6 (3.2-6.0) | 3.1 (1.7-4.5) | 3.0 (1.6-4.4) | .19 |
| SBP | | | | |
| First | 4.0 (2.9-5.1) | 2.4 (1.3-3.4) | 2.8 (1.7-3.9) | .10 |
| Second | 2.8 (1.6-4.0) | 3.8 (2.5-5.1) | 3.0 (1.8-1.1) | .51 |
| Changec | 4.0 (2.5-5.4) | 4.0 (2.7-5.6) | 3.0 (1.6-4.5) | .51 |
| SSD | | | | |
| First | 3.2 (2.1-4.3) | 3.5 (2.4-4.6) | 3.2 (2.1-4.4) | .91 |
| Second | 4.7 (3.3-6.0) | 4.0 (2.7-5.4) | 3.1 (1.8-4.5) | .37 |
| Changec | 4.0 (2.5-5.5) | 3.8 (2.3-5.3) | 4.0 (2.7-5.7) | .94 |
Table 4.
Absolute Asymmetry for Each Landmark Measured at Each US Assessment and Total Change in Asymmetry from First to Second US Assessment
| Absolute Asymmetrya, mm, Mean (95% CI) | |
| US Landmark | Seated Control Group | Walking Control Group | OMT Group | P Valueb |
| SPSIS | | | | |
| First | 3.3 (2.2-4.4) | 3.2 (2.1-4.3) | 2.3 (1.2-3.4) | .35 |
| Second | 4.0 (2.8-5.1) | 3.3 (2.1-4.4) | 2.6 (1.4-3.7) | .26 |
| Changec | 4.6 (3.2-6.0) | 3.1 (1.7-4.5) | 3.0 (1.6-4.4) | .19 |
| SBP | | | | |
| First | 4.0 (2.9-5.1) | 2.4 (1.3-3.4) | 2.8 (1.7-3.9) | .10 |
| Second | 2.8 (1.6-4.0) | 3.8 (2.5-5.1) | 3.0 (1.8-1.1) | .51 |
| Changec | 4.0 (2.5-5.4) | 4.0 (2.7-5.6) | 3.0 (1.6-4.5) | .51 |
| SSD | | | | |
| First | 3.2 (2.1-4.3) | 3.5 (2.4-4.6) | 3.2 (2.1-4.4) | .91 |
| Second | 4.7 (3.3-6.0) | 4.0 (2.7-5.4) | 3.1 (1.8-4.5) | .37 |
| Changec | 4.0 (2.5-5.5) | 3.8 (2.3-5.3) | 4.0 (2.7-5.7) | .94 |
×
When controlling for demographic characteristics, date of last pain, and frequency of pain, no differences were found in absolute asymmetry between groups for SPSIS, SBP, or SSD (all P≥.11) after first US assessment. While still controlling for the same variables, no differences were found in mean total change in asymmetry from first to second US assessment between groups for SPSIS, SBP, or SSD (all P>.06).
Comparison of qualitative palpatory and US assessments of SBP and SSD landmark positions is presented in
Table 5. The κ was −0.1 (95% CI, −0.2 to 0.03) for SBP and −0.01 (95% CI, −0.1 to 0.1) for SSD, indicating no agreement.
Table 5.
Comparison of Qualitative Palpatorya and US Assessments of Landmark Position for Right SBP and SSD Before Seated Control or OMT Interventions (N=40)b
| SBP | SSD |
| US Assessmentc | Posterior | Anterior | Total | Shallow | Deep | Total |
| Anterior or deep | 2 | 17 | 19 | 1 | 17 | 18 |
| Posterior or shallow | 0 | 20 | 20 | 1 | 21 | 22 |
| Equal | 0 | 1 | 1 | 0 | 0 | 0 |
| Total | 2 | 38 | 40 | 2 | 38 | 40 |
Table 5.
Comparison of Qualitative Palpatorya and US Assessments of Landmark Position for Right SBP and SSD Before Seated Control or OMT Interventions (N=40)b
| SBP | SSD |
| US Assessmentc | Posterior | Anterior | Total | Shallow | Deep | Total |
| Anterior or deep | 2 | 17 | 19 | 1 | 17 | 18 |
| Posterior or shallow | 0 | 20 | 20 | 1 | 21 | 22 |
| Equal | 0 | 1 | 1 | 0 | 0 | 0 |
| Total | 2 | 38 | 40 | 2 | 38 | 40 |
×
The ICC between US measurements from the first and second US assessments for groups had very good reliability. For SPSIS, the ICC was 0.83 (95% CI, 0.70-0.91) for the seated control group; 0.80 (95% CI, 0.65-0.89) for the walking control group; and 0.89 (95% CI, 0.79-0.94) for the OMT group. For SBP, ICC was 0.84 (95% CI, 0.71-0.92) for the seated control group; 0.86 (95% CI, 0.75-0.93) for the walking control group; and 0.86 (95% CI, 0.75-0.93) for the OMT group.
Discussion
The current study found that significantly more participants in the seated control and OMT groups had an increase in direction of change in asymmetry for SPSIS compared with participants in the walking control group when using US to quantify changes in asymmetry before and after study interventions. No significant differences were found between groups for absolute asymmetry or total change in asymmetry. The OMT intervention was hypothesized to significantly decrease US-measured asymmetry because palpatory assessment before and after OMT typically finds a decrease in asymmetry between left and right SBP and SSD. Palpatory assessment of these landmarks is a qualitative assessment performed by comparing relative anterior or posterior position of each sacral base with the coronal plane of the patient and by determining the SSD (deep or shallow) through identification of relative depth from the PSIS to sacral base.
27 The current study used US to measure depth from the skin to the sacral base and PSIS and calculated SSD as the difference between the measurements. Because there was no agreement between qualitative palpatory and US assessments of SBP and SSD, US measurements used in the current study may not be representative of palpatory assessments.
Real-time US imaging is well established as a safe and feasible method to evaluate musculoskeletal structures.
20,34,35 Flaum et al
36 found that US assessment of tissue depth to the posterior aspect of the cervical articular pillar did not correlate with palpatory assessment of rotational motion restriction and asymmetry. Our ICC results suggested that US reliably localized landmarks in the sacral region and supported stability of our measurements. However, our US measurements may not be sufficiently precise to detect changes of asymmetry of a few millimeters. The posterior sacral base has an irregular surface, and the PSIS is a rounded landmark; therefore, it may be difficult to measure the same place on each bony landmark repeatedly. Additionally, small changes in US probe pressure on the surface of the skin displace soft tissue, varying the depth of sacral landmarks. Our US reliability when measuring depth from the skin to the bony landmark for SPSIS and SBP had ICCs greater than 0.80, suggesting that measurements from the first and second US assessments were similar. Mean measurements for SPSIS and SBP varied from 20.1 mm to 45.9 mm, and mean absolute asymmetry varied from 2.3 mm to 4.6 mm. Therefore, a 1-mm difference in measured depth from landmark localization or varying probe pressure may have affected our findings.
The current study found that BMI was significantly correlated with SPSIS and SBP, which likely accounted for the significant correlation between SPSIS and SBP. Therefore, soft tissue depth may affect US measurements. Potential participants with BMI greater than 30 were excluded from the current study to minimize the impact of soft tissue depth on measurements, but some US measurement error from soft tissue depth seemed to occur despite the exclusion. Overas et al
37 found that intrarater reliability of US measurements of cervical spine muscle thickness was good for superficial muscles but moderate to poor when measuring deep muscles of the suboccipital area. Osteopathic medical students have been shown to reliably palpate transverse process asymmetry of 4 mm in static models of the lumbar spine covered by 25 mm of upholstery foam.
38 Therefore, palpation may be more sensitive than US when measuring small amounts of asymmetry through soft tissue. The current study found no correlation between BMI and SSD. Because SSD was calculated from 2 bony landmarks, it was less affected by body mass. Future studies should use US measurements between 2 bony landmarks unaffected by soft tissue depth, such as the transverse processes of L5 and the superior aspect of the sacral bases.
The walking control group was added to our study because preliminary analysis of our initial groups indicated that absolute asymmetry of SPSIS and SSD increased between the first and second US assessments for the seated control group compared with the OMT group. This finding suggested that sitting for 30 minutes may increase sacral base asymmetry. Prolonged sitting is an independent risk factor for LBP,
39-41 and sitting time has been positively associated with LBP intensity.
41,42 Likewise, most studies have shown that walking is beneficial for people with LBP.
43,44 Since people with LBP have significantly greater incidence and severity of somatic dysfunction in lumbar, pelvic, and sacral regions than people without LBP, prolonged sitting and walking may cause changes in symmetry. Future studies with greater statistical power are needed to investigate the potential effect of sitting and walking on sacral base asymmetry.
Limitations of the current study included small sample size, the potential effect of prolonged sitting vs walking on sacral base asymmetry, and the potential effect of landmark anatomy and variable probe pressure on measurements of depth from skin to bony landmarks. For comparisons between qualitative palpatory and US assessments, the physical findings of only 1 investigator were used. Additionally, the ultrasonographer was not blinded to participant group during the walking control substudy. Future studies should consider using a larger sample size to increase statistical power to determine between-group effects, a walking control rather than seated control, and measurements between 2 or more bony landmarks unaffected by soft tissue.
Conclusion
Osteopathic manipulation has been effective in treating patients with LBP, but objective measurements of biomechanical changes correlated with palpatory findings have been difficult to establish. Ultrasonography as a safe, cost-effective outcome measure is promising, but the current study could not readily identify musculoskeletal changes attributable to OMT. The measurements of SPSIS and SBP were dependent on BMI, which may have affected the accuracy of US assessments to detect small changes in symmetry. Additionally, qualitative palpatory assessments did not correlate with US measurements. Further study is needed to identify US measurements that demonstrate change with OMT.
Acknowledgments
We thank Deborah Goggin, MA, scientific writer at A.T. Still University, for her editorial assistance. We thank Kathryn Trujillo, BS; Steve Webb, BA, BS; and Dalton Ebel, BA, BS, for their assistance in coordinating the research activities.
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