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This feasibility study used novel accelerometry (vibration) and microphone (sound) methods to assess crepitus originating from the lumbar spine before and after side-posture spinal manipulative therapy (SMT).
Methods
This study included 5 healthy and 5 low back pain (LBP) participants. Nine accelerometers and 1 specialized directional microphone were applied to the lumbar region, allowing assessment of crepitus. Each participant underwent full lumbar ranges of motion (ROM), bilateral lumbar SMT, and repeated full ROM. After full ROMs the participants received side-posture lumbar SMT on both sides by a licensed doctor of chiropractic. Accelerometer and microphone recordings were made during all pre- and post-SMT ROMs. Primary outcome was a descriptive report of crepitus prevalence (average number of crepitus events/participant). Participants were also divided into 3 age groups for comparisons (18-25, 26-45, and 46-65 years).
Results
Overall, crepitus prevalence decreased pre–post SMT (average pre = 1.4 crepitus/participant vs post = 0.9). Prevalence progressively increased from the youngest to oldest age groups (pre-SMT = 0.0, 1.67, and 2.0, respectively; and post-SMT = 0.5, 0.83, and 1.5). Prevalence was higher in LBP participants compared with healthy (pre-SMT–LBP = 2.0, vs pre-SMT–healthy = 0.8; post-SMT–LBP = 1.0 vs post-SMT–healthy = 0.8), even though healthy participants were older than LBP participants (40.8 years vs 27.8 years); accounting for age: pre-SMT–LBP = 2.0 vs pre-SMT–healthy = 0.0; post-SMT–LBP = 1.0 vs post-SMT–healthy = 0.3.
Conclusions
Our findings indicated that a larger study is feasible. Other findings included that crepitus prevalence increased with age, was higher in participants with LBP than in healthy participants, and overall decreased after SMT. This study indicated that crepitus assessment using accelerometers has the potential of being an outcome measure or biomarker for assessing spinal joint (facet/zygapophyseal joint) function during movement and the effects of LBP treatments (eg, SMT) on zygapophyseal joint function.
Crepitus (audible sound arising from tissues during normal motion) originating from the vertebral column has been associated with degeneration of the posterior joints of the spine (facet joints/zygapophyseal [Z] joints).
made an interesting observation: “The noises of normal and abnormal [Z] joints are built into the nature of the structures. To ignore these noises would be foolish, as they might be used to help determine the effectiveness of treatment.”
Conway P, Herzog W, Zhang Y, Hasler E. Identification of the mechanical factors required to cause cavitation during spinal manipulation in the thoracic spine. International Conference on Spinal Manipulation. May 15-17, 1992; Chicago, IL: 281-284.
Conway P, Herzog W, Zhang Y, Hasler E. Identification of the mechanical factors required to cause cavitation during spinal manipulation in the thoracic spine. International Conference on Spinal Manipulation. May 15-17, 1992; Chicago, IL: 281-284.
One theory of the mechanism of the anatomic and biomechanical beneficial effects of SMT is depicted in Figure 1. Briefly, connective tissue adhesions develop in hypomobile Z joints,
Conway P, Herzog W, Zhang Y, Hasler E. Identification of the mechanical factors required to cause cavitation during spinal manipulation in the thoracic spine. International Conference on Spinal Manipulation. May 15-17, 1992; Chicago, IL: 281-284.
Over time (weeks to months) this would lead to decreased joint vibrations and sounds during motion (decreased crepitus).
Fig 1Flowchart showing a model of putatively beneficial anatomic and biomechanical effects of spinal manipulation, including the theoretical relationships of crepitus and cavitation to the model.
In addition, we hypothesize that LBP participants would have more crepitus than healthy participants because of increased muscle tightness of LBP participants, leading to relative compression of the articular surfaces making up the Z joints. Such compression could conceivably interrupt the normal smooth gliding motion of the Z joints, resulting in crepitus vibrations. We also hypothesize that older participants would have more crepitus than younger ones because of decreased joint lubrication and increased joint degeneration in older Z joints, resulting in more crepitus vibrations/sounds.
A few studies have been conducted to explore the mechanisms and consequences of cavitation during SMT.
However, there have been no studies assessing lumbar crepitus. In addition, the peer-reviewed literature has no record of a study assessing tissue characteristics of the spine using acoustics or a study comparing accelerometers with microphones in assessing acoustic data originating from the spine (including data associated with Z joint crepitus).
In addition, analysis of vibration and sound waves recorded from accelerometers and microphones have been used rather extensively to assess sounds as a type of biomarker associated with temporomandibular joint dysfunction,
This feasibility study (N = 10) was designed to continue the process of addressing the current gaps of knowledge by further developing previous methods and evaluating additional methods to assess and localize Z joint crepitus recorded during lumbar motion both before and after SMT. More specifically, this study evaluated recordings made simultaneously from accelerometers and a specialized directional microphone. Recordings were made from both healthy (n = 5) and low back pain (LBP, n = 5) participants of different age groups. The reason for using both accelerometers and a microphone is that each may produce unique and complementary information.
A comparison between mechanomyographic condenser microphone and accelerometer measurements during submaximal isometric, concentric and eccentric contractions.
If successful, joint crepitus identified during lumbar motion could be used as an outcome measure (biomarker) to assess the mechanisms of SMT.
Methods
Participant Screening and Enrollment
This project was approved by the National University of Health Sciences IRB. Five healthy participants and 5 participants with low back pain (n = 10) were sought from 3 age ranges: 18 to 25, 26 to 45, and 46 to 65 years. More participants (n = 8) were sought from the older 2 age groups to better assess crepitus. In addition, an equal distribution of men and women was also sought. Participants were recruited from the student, faculty, and staff population of a complementary and integrative health institution through posters, flyers, and e-mail announcements. Those who passed the initial screening were scheduled for an examination where a research chiropractic physician conducted a thorough history and physical examination that included orthopedic and neurologic tests to ensure participants were selected who met stringent inclusion and had none of the exclusion criteria. Separate criteria that had been previously developed and implemented for healthy
Magnetic resonance imaging zygapophyseal joint space changes (gapping) in low back pain patients following spinal manipulation and side-posture positioning: a randomized controlled mechanisms trial with blinding.
were used in this study. Generally, healthy participants had no current LBP; no known spinal pathologic conditions or spinal surgery; and no previous history of LBP lasting more than 2 weeks or no more than 3 episodes of LBP of brief duration (1 week) in any given year. Low back pain participants had current LBP and a history of an episode of LBP lasting for more than 2 weeks or more than 3 episodes of back pain of brief duration (1 week) in any given year. Participants were excluded if they reported having had spinal surgery or having been previously been diagnosed with disc degeneration, significant osteoarthritis, scoliosis of >5 degrees or other known significant pathologic condition. Current pain was assessed using a 100-mm visual analog scale and scores were converted to a 0 to 10 numeric pain rating, with 0 being no pain and 10 being worst pain imaginable.
Chiropractic chronic low back pain sufferers and self-report assessment methods. Part I. A reliability study of the Visual Analogue Scale, the Pain Drawing, and the McGill Pain Questionnaire.
Participants completing the study received a $10 gift card or (if preferred by a student) University Service credit equivalent to the number of hours of participation.
Placement of Accelerometers and Microphone
After completing the informed consent process, enrolled participants were scheduled for an accelerometry and microphone visit. During this visit, patients were initially asked if they had received SMT in the previous 24 hours or if their health had changed significantly after the examination visit (all participants answered no to both questions). Seven accelerometers (Bruel & Kjaer 2693, Naerum, Denmark) were then taped with elastic kinesiology tape (Rock Tape, Campbell, CA) in position in the midline over the L1-S2 spinous processes and sacral tubercles (Fig 2; color versions of Fig 2, Fig 3, Fig 4, Fig 5, Fig 6, Fig 7 can be viewed in the online version). An additional 2 accelerometers (total of 9) were taped lateral to the midline accelerometers: one 3 cm to the left and one 3 cm to the right of the mid-distance between the L4 and L5 midline accelerometers. A microphone (PCB Piezotronics 130A40, Depew, NY) was then taped 4 cm to the left of the T12 spinous process. Spinous process landmarks were verified using diagnostic ultrasound. Data were collected using a LabView program (National Instruments, Austin, TX) written for a previous project
and modified to record from an additional channel to accommodate the microphone. Recordings were displayed on and recorded from a computer-based oscilloscope.
Fig 2Placement of accelerometers and specialized directional microphone: (A) participant with the 9 accelerometers and microphone taped in place for recording; (B) close-up of one of the accelerometers; (C) close-up of the microphone; (D) illustration showing placement of 9 accelerometers (solid circles) and the microphone. See online version for color figure.
Fig 3Accelerometer and microphone recordings were taken during 6 ranges of motion, including flexion (A), extension, right and left (B) rotation, and right and left (C) lateral flexion. See online version for color figure.
Fig 4Spinal manipulation was performed with the accelerometers and microphone in place. Ultrasound of the right L3/4 Z joint is shown being conducted simultaneously for another component of the project that will be reported separately. See online version for color figure.
Fig 5Example of crepitus detected by accelerometers and microphone (see online version for color figure). (A) LabView oscilloscope recording of crepitus taken during left lateral flexion in a 55-year-old man. The flat baseline can be seen at the far left, followed by the sharp response of several accelerometers and the distinct, broad waveform of the microphone. (B) Expanded (by ~100×) timeline of the same crepitus. Again, notice that the accelerometers are at their individual baselines at the far left, followed by a dramatic simultaneous shift from the baseline of several accelerometers. The L2 (red) and L3 (green) accelerometers leave their baselines first, followed by L4 (gray) and the left accelerometer (dark blue). This was crepitus at the left L2/3 zygapophyseal (Z) joint. The microphone (light blue) has a very broad wave pattern that is best seen with the more contracted timeline (A). This distinct wave pattern from the microphone was rare. (C) Recording of an artifact of the L1 and S2 accelerometers, which may have been caused by the patient’s gown bumping the accelerometers.
Fig 6(A and B) Crepitus taken during motions before spinal manipulation (pre-SMT); (C and D) report crepitus taken during motions after spinal manipulation (post-SMT). (A and C) Individual zygapophyseal (Z) joints from which crepitus were recorded during full ranges of motion. Joints from which crepitus was recorded during more than one movement or multiple times during the same movement were counted only once in A and C. (B and D) Crepitus was recorded during multiple movements of the same joint, or multiple times during the same movement, each incidence of crepitus was counted. Results for healthy participants are reported in bold typeface and those for low back pain (LBP) participants are reported in italics. See online version for color figure.
were then conducted during full ranges of motion (ROMs, Fig 3). The motions were forward flexion, extension, left and right lateral flexion, and left and right axial rotation. Participants were asked to stop the motion if or when she or he felt pain. After each motion, participants were asked if any sounds or vibrations related to joint movement were heard or felt in the spine during the motion.
Spinal Manipulation
After full ROMs the participants received side-posture lumbar SMT on both sides. Healthy participants began with the left side up and LBP participants began with the most painful side up. The accelerometers and microphone remained in place during the SMTs (Fig 4). A slightly modified general SMT (hypothenar ilium technique)
directed at the L3/L4-L5/S1 segmental levels was used. The modification was to the clinician’s “contact hand” (thrusting hand), which was moved from the usual up-side posterior superior iliac spine to the inferolateral sacrum. The modification was to avoid contact with accelerometer wires and had been developed for previous studies that used accelerometers to assess cavitation during SMT.
Recordings were then conducted post-SMT during full ROMs. Again, after each motion participants were asked if they heard or felt any sounds or vibrations related to joint movement in the spine during the motion.
Accelerometer placement and taping were examined after each set of ROMs and after SMT. If contact between the skin and an accelerometer appeared to have loosened during the motions and SMT, the accelerometer tape was adjusted until proper contact was made. Occasionally new tape was used to ensure accelerometer skin contact.
Assessment of Recordings
The data collected from the accelerometers were assessed using methods previously found to be reliable and valid for cavitation.
Cramer GD, Ross K, Pocius J, et al. Assessing cavitation and Z joint gapping following side-posture spinal adjusting: a feasibility case series. Thirteenth Annual Research Agenda Conference, March 13-15, 2008. Washington, DC. J Chiropr Educ. 22:54.
In this study, 2 observers, each of whom had more than 2 years of experience reading accelerometer and microphone recordings in our lab, assessed each recording and reached consensus to identify crepitus and determine the Z joint of origin for each instance of crepitus. Amplitude (measured as the change of voltage generated in the piezoelectric accelerometers) from the 2 primary accelerometers involved in a crepitus event (eg, L2 and L3 accelerometers for either a left or right L2/3 crepitus) was also recorded, and the average of the 2 values was used as the amplitude for each crepitus. The accelerometer results were qualitatively compared with simultaneous recordings from the microphone to determine similarities and differences between the 2 acoustic methods and to determine the usefulness of the microphone in assessing crepitus.
Data Analysis
Data were analyzed descriptively to determine distribution of crepitus (ie, the specific Z joints from which crepitus originated); crepitus prevalence (primary outcome, average number of crepitus events/participant); comparison of crepitus prevalence from participants of different age groups; comparison of crepitus prevalence in healthy and LBP participants; crepitus amplitude (overall and for healthy and LBP participants); crepitus recorded during each range of motion to determine the motions that produced the most and least crepitus; and agreement between participant report of crepitus and accelerometer recordings. In addition, comparison of crepitus before and after SMT was made for all of the groups of participants (ie, age groups, LBP participants, and healthy participants).
Results
Participants
Ten participants were enrolled. Distribution of participants by age and sex is shown in Table 1. The difference between the ages of healthy vs LBP participants (healthy > LBP) was 13.0 ± 7.01 (P = .0504). Pain was rated as 3 (±1) for LBP participants and 0 (±0) for healthy participants. No adverse events were reported during the study.
The accelerometry and acoustic methods were successfully implemented on all participants, with simultaneous recordings from the accelerometers and the microphone being accomplished. Crepitus was identified as simultaneous deviations from baseline of multiple accelerometers (Figs 5A and 5B). As in previous work, artifacts had a distinct appearance (Fig 5C) and were easily distinguished from crepitus.
The microphone was somewhat useful in helping to differentiate crepitus from artifacts; however, it was erratic in recording crepitus.
Distribution of Crepitus
Figure 6 summarizes the incidence and distribution of crepitus before and after SMT. Overall, 23 instances of crepitus (Figs 6B and 6D) were recorded from 15 different Z joints (Figs 6A and 6C). Pre-SMT there were 14 instances of crepitus (Fig 6B) recorded from 7 joints (Fig 6A). Post-SMT there were 9 instances of crepitus (Fig 6D) recorded from 8 joints (Fig 6C). Crepitus could be recorded from the same joint of the same participant during different motions. For example, if crepitus was recorded from a participant’s right (R) L4/5 Z joint during flexion and left lateral flexion, this would be counted as 2 instances of crepitus (shown in Figs 6B and 6D) from 1 Z joint (shown in Figs 6A and 6C). Such multiple instances from the same Z joint but during different motions occurred from 2 Z joints recorded from 2 different participants, 1 pre-SMT healthy, and 1 post-SMT LBP (1 Z joint for each participant).
Also, multiple instances of crepitus were counted for Figures 6B and 6D if crepitus was recorded from the same Z joint during different times of the same motion (eg, flexion) with all recordings reaching the baseline between instances. This occurred for 2 joints (2 different LBP participants, both pre-SMT).
Generally, crepitus was recorded from different joints pre-SMT vs post-SMT. There were only 2 exceptions to this, 1 in a healthy participant and 1 in an LBP participant, when crepitus was recorded from the same joint before and after SMT. The amplitude was the same before and after SMT for the Z joint (L L4/5) of the healthy participant (0.01 mV). However, the exception in the LBP participant was unique in that 6 instances of crepitus were recorded from the R L4/5 Z joint during flexion pre-SMT (accelerometer recordings went to baseline between instances of crepitus) and only 1 was recorded post-SMT. The average amplitude of the 6 pre-SMT recordings was 0.10 mV and the amplitude of the single post-SMT R L4/5 recording was 0.04 mV.
Crepitus Prevalence
Table 2 presents the prevalence of crepitus. Overall crepitus prevalence (last column in Table 2) decreased pre-post SMT (average pre = 1.4 crepitus/participant, range 0-7 crepitus/participant, vs post = 0.9, range 0-2).
Table 2Total Crepitus (and Crepitus Prevalence) by Age Group Pre- and Post-SMT
Prevalence progressively increased from the youngest to oldest age groups (pre-SMT = 0.0, 1.67, and 2.0, respectively, range 0-10; and post-SMT = 0.5, 0.83, and 1.5, range 1-5).
Prevalence was higher in LBP participants than healthy participants (pre-SMT–LBP = 2.0, range 0-7, vs pre-SMT–healthy = 0.8, range 0-4; post-SMT–LBP = 1.0, range 0-2, vs post-SMT–healthy = 0.8, range 0-2), even though healthy participants were older than LBP (40.8 years vs 27.8 years). Accounting for differences in age of the healthy vs LBP participant groups by removing healthy 46- to 65-year-old participants (n = 2, no LBP participants in this age group), prevalence of healthy participants decreased (pre-SMT–LBP = 2.0, range 0-7, vs pre-SMT–healthy = 0.0, no range; post-SMT–LBP = 1.0, range 0-2 vs post-SMT–healthy = 0.3, range 0-1).
Amplitude of Crepitus
With the exception of 1 LBP post-SMT crepitus of the left SI joint that had the amplitude of a cavitation (1.66 mV), crepitus amplitude was <0.16 mV. Average pre-SMT crepitus amplitude was 0.08 mV, which was greater than post-SMT crepitus, which was 0.03 mV, excluding the outlier mentioned earlier. Excluding the 1 outlier, the pre- vs post-SMT crepitus difference was greater in LBP (pre-SMT 0.09 mV, post-SMT 0.04) than healthy participants (pre-SMT 0.04 mV, post-SMT 0.03 mV).
Crepitus During ROMs
Figure 7 reports pre-SMT, post-SMT, and overall crepitus recorded during each motion. The most crepitus was recorded during flexion (pre-SMT 8, 57.1%, post-SMT 6, 66.7%, and overall 14, 60.9%). For pre-SMT, flexion was followed by right lateral flexion (3, 21.4%) with extension, left lateral flexion, and left rotation all producing the same amount of crepitus (1 each, 7.1%). Post-SMT flexion was followed by extension (2, 22.2%) and right rotation (1, 11.1%), with no crepitus recorded in the other motions.
Agreement Between Participant Report of Crepitus and Recording of Crepitus
Participants were more often in agreement with the recordings; however, this is largely accounted for by 94 instances of a possible 120 when the participants heard no crepitus and none were recorded (78.3%). There were 3 instances (2.5%) when crepitus was heard or felt by the participant and recorded by the accelerometers. There were 23 (19.2%) instances when crepitus was either recorded but not heard or felt by the participant or heard or felt by the participant but not recorded.
Discussion
Summary of Main Findings
This feasibility study successfully collected crepitus data from the lumbar region of 10 participants (5 healthy, 5 LBP) from 3 different age ranges. Overall, crepitus prevalence decreased after SMT. In addition, prevalence progressively increased from the youngest to oldest age groups and was higher in LBP compared with healthy participants. The majority of crepitus was recorded during flexion and participants generally did not hear or feel the recorded crepitus.
The research extended previous work on cavitation during SMT
by evaluating recordings of crepitus made from both accelerometers and from a specialized directional microphone during full ROMs. These methods are novel to the assessment of spinal crepitus, and the peer-reviewed literature has no record of a study assessing spinal crepitus by any means.
Accelerometers vs Microphone
Even though the amplitude of crepitus was approximately one-tenth that of cavitation, the accelerometers performed well in this study and crepitus was identified as distinct events of multiple accelerometers responding in such a way that the specific Z joints of origin could be identified.
Previous reports using both accelerometers and a microphone indicated that each produced unique and complementary information in the assessment of other tissues
A comparison between mechanomyographic condenser microphone and accelerometer measurements during submaximal isometric, concentric and eccentric contractions.
However, in this study, even though the microphone recordings did move from the baseline during crepitus, the response was erratic. The amplitude of the microphone signal was close to baseline in all artifacts, which contrasted with the movement from baseline identified in crepitus. The artifacts in this study were very similar to those identified in previous research assessing cavitation and were usually the result of a participant’s gown or shorts bumping 1 or more accelerometers. This created a distinct appearance on the accelerometer recordings (Fig 5C).
As mentioned, the artifacts could have been identified without the use of a microphone. The microphone may not have been useful in this crepitus study because the amplitude of crepitus was markedly less than that previously recorded for cavitations.
The low amplitude, combined with the location of the microphone a considerable distance from most of the recorded crepitus, likely precluded adequate assessment of crepitus by the microphone. The microphone was positioned at T12 to avoid contact with any of the 9 accelerometers. Future studies of crepitus by our group will probably not include microphone recordings.
Z Joints as the Origin of Crepitus
Although other anatomic structures (eg, muscles, ligaments) cannot be completely ruled out as the possible source of the recorded vibrations (crepitus), the Z joints are the most likely source of the recorded crepitus for 2 primary reasons. First, similar waveforms were identified from artificially produced crepitus conducted during validity testing of the methods
(unpublished data). These experiments were conducted on a spine embedded in silicone and vibrations originating directly from the Z joints were produced and recorded. Second, recordings not matching the types of waveforms previously reported from cavitations (only with lower amplitudes)
and artificial crepitus (unpublished data), produced in reliability testing, were not included as crepitus in this study. Consequently, crepitus may have potentially been underreported in this study; however, the methods increased the confidence that reported crepitus was of Z joint origin.
Age
Crepitus increased with age. This is consistent with the theory that crepitus increases with arthritic changes
Although 8 participants were enrolled from the older 2 age groups, as was the goal, no LBP participants were enrolled from the oldest age group.
Crepitus in Healthy and LBP Participants Pre- and Post-SMT
The finding that more crepitus was recorded in pre-SMT LBP than in healthy participants in spite of the younger age of the LBP participants was interesting. After SMT (post-SMT), the number of crepitus events (both total crepitus and joints producing crepitus) in LBP and healthy participants was almost identical (Figs 6C and 6D). One hypothesis to explain the difference in pre-SMT crepitus is that increased muscle tightness of the LBP participants led to relative compression of the articular surfaces making up the Z joints. Such compression could conceivably cause the normal smooth gliding motion of the Z joints to change to a series of small rapid motions, which could result in crepitus vibrations. The results of 1 LBP participant in the study may provide an example that supports this hypothesis. In this participant, crepitus was recorded from the same joint (right L4/5) 6 times throughout the 4 seconds of pre-SMT flexion. The accelerometer recordings went completely to baseline between each instance of crepitus. After SMT there was only 1 crepitus recorded from this joint during flexion. The average amplitude of the 6 pre-SMT recordings was 0.10 mV and the amplitude of the single post-SMT R L4/5 recording was 0.04 mV. This would suggest the joint was moving in a more regular (smooth) pattern after SMT. The small number of participants in this feasibility study prevents further speculation on this issue.
Participant Report of Crepitus vs Recorded Crepitus
Overall, participant report of crepitus was not an indicator of whether or not a crepitus was recorded. This finding is quite different from previous studies on cavitation during SMT, where participant (and clinician) report of cavitation was closely related to recorded cavitation.
As discussed previously, the wave magnitude of crepitus was markedly less than that of a typical cavitation. The more subtle crepitus vibrations detected by the accelerometers likely went undetected by the participants in this study. There were also 12 instances when the participant heard or felt a sound or vibration during a motion, but none was recorded. At first this seemed more difficult to explain. However, in a previous study there was an instance where a participant responded that she or he heard a cavitation but none was recorded.
We hypothesized that the cavitation in this instance occurred above the lumbar level and therefore was not recorded by the lumbar accelerometers. The same phenomenon may very well be occurring in this study, one difference being that during the full ROM recordings, the thoracic region was going through full ROMs along with the lumbar region, whereas during the SMT cavitation study, the SMT force was directed to the lumbar region, resulting primarily in lumbar segmental motion.
Consequently, much more motion occurred in the thoracic region in this study than in previous ones, and we hypothesize that some of the crepitus heard and felt by the participants was originating from the thoracic region and the lumbar-placed accelerometers did not respond to the subtle thoracic crepitus. Participants were asked about sounds and vibrations in the spine and most likely responded “yes” if any sound or vibration was heard or felt in the thoracic region. To further assess this issue, future studies should use procedures to minimize thoracic motion during ROM recordings and ask specific questions to verify the location of the reported sound or vibration.
Ranges of Motion
Flexion was without question the motion that produced the most crepitus (60.9% overall). This result probably is due to the lumbar region having considerably more motion in flexion (60°) than any other motion.
Future studies using crepitus as a secondary outcome measure could perhaps be limited to recordings taken during flexion only in order to use time most efficiently. However, because crepitus was recorded during all 6 motions (Fig 7), research using crepitus as a primary outcome should continue to record during all ROMs.
SMT and Crepitus
Spinal manipulative therapy had an effect on crepitus in this study, both the Z joints producing crepitus and the amplitude of crepitus (overall less amplitude post-SMT). However, the results indicate that the relationship between crepitus and SMT may be complex. Total crepitus was reduced after SMT in this study; however, 9 instances of crepitus from 8 Z joints were recorded post-SMT (Fig 6). Interestingly, with only 2 exceptions, the Z joints producing crepitus post-SMT were different from those that produced crepitus pre-SMT. This would seem to indicate a change beyond that of mere chance.
There may be several reasons for the pre–post SMT differences. The Z joint movement (gapping) produced by SMT
Magnetic resonance imaging zygapophyseal joint space changes (gapping) in low back pain patients following spinal manipulation and side-posture positioning: a randomized controlled mechanisms trial with blinding.
may have added sufficient mobility to the pre-SMT crepitus-producing joints that they moved more freely and did not produce crepitus post-SMT. On the other hand, the SMT force on pre-SMT non–crepitus-producing joints that were somewhat hypomobile may have induced enough motion that they began to move into a range that had not been used immediately pre-SMT; consequently, the joint surfaces may have been contacting in facetal areas that were not as well lubricated (ie, less synovial fluid in these regions) as the more frequently used facetal regions, thus creating crepitus as the joints entered the previously hypomobile zones. Much more work is needed to assess the veracity of this speculation.
Future research on larger numbers of healthy and LBP participants from different ages would help to clarify the effects of SMT on crepitus. Combining studies assessing crepitus with imaging of the Z joints could potentially help to study the relationship between Z joint degeneration and crepitus that has been alluded to by other authors.
would be an appealing candidate for complementary use with the accelerometry outcomes in future clinical mechanistic research. We are currently assessing the feasibility of adding ultrasound to future studies.
Limitations and Future Research
This was a feasibility study on a small number of participants. Therefore, the results cannot be generalized to a larger population but may be used to inform future studies. In addition, largely because of the convenience sample of faculty, staff, and students from a complementary and integrative health university, there were no LBP participants in the 46 to 65 age group; consequently, the LBP participants were younger than the healthy participants. In addition, they had only mild LBP (3 of 10). Even with these limitations, differences in crepitus were found for age, LBP vs healthy participants, the effects of SMT on crepitus, and the motions that produced crepitus.
Although reliability and validity studies have been completed for the phenomenon of cavitation during SMT,
further validity studies of the subtler phenomenon of crepitus are currently underway.
The findings of this small feasibility study indicate that further research in this area is merited. Crepitus in healthy and LBP participants and in participants from different age ranges and with Z joints of different levels of degeneration
should be evaluated in studies fully powered to allow for generalizability of data to larger populations. Such studies should recruit from a larger population, as has been done in previous, larger clinical trials conducted by our research group.
Magnetic resonance imaging zygapophyseal joint space changes (gapping) in low back pain patients following spinal manipulation and side-posture positioning: a randomized controlled mechanisms trial with blinding.
Reliability of zygapophysial joint space measurements made from magnetic resonance imaging scans of acute low back pain participants: comparison of 2 statistical methods.
The effects of side-posture adjusting on the lumbar zygapophysial joints of low back pain patients as evaluated by magnetic resonance imaging: a preliminary study.
The broader recruiting methods will likely lead to more LBP participants from the older age group. In addition, the larger studies would allow for further assessment of SMT on crepitus, possibly shedding further light on the complex relationships between these 2 variables.
A power analysis was conducted using PROC POWER in SAS 9.4 (SAS Institute Inc., Cary, NC) to determine the number of participants needed for future clinical investigation. The sample size estimates were based on means and standard deviations from the descriptive statistics of this feasibility study. All power analyses conducted assumed 2-sided tests, β = 0.80, α = 0.05, and a normal distribution of the data. Power analysis to compare pre- and post-SMT measures of crepitus, which would be the primary study objective, that was done using a paired t test (SD = 1.8; assuming r = 0.5) indicated that 28 participants would be needed to complete the study to detect a mean difference of 1, which is hypothesized to identify a meaningful change. Secondary objectives would be to determine if there are differences in mean crepitus between healthy and LBP participants, as well as in younger participants and older participants (2-sample t test assuming equal variances; mean difference = 1 crepitus/participant – large effect). To compare crepitus pre-SMT in healthy vs LBP participants (SD = 2.5), 100 participants would need to be in each group. To compare pre-SMT crepitus in adults aged 26 to 45 years with adults aged 46 to 65 years (SD = 2.7), 116 participants would be needed in each group. Consequently, the ideal study would be 232 participants with 116 LBP and 116 healthy participants and the same numbers (ie, 116) between the ages of 26 to 45 and between the ages of 46 and 65. Studies assessing purely the effects of SMT on crepitus could be conducted on many fewer (ie, 28) total participants.
In addition, the accelerometry methods could be further enhanced through the process of automation. The methods for analyzing each recording were extremely time consuming. Each recording took approximately 1 hour for a well-trained researcher to assess, and there were 12 recordings per participant, 1 for each of 6 motions both pre- and post-SMT. In addition, to increase reliability, 2 observers assessed each recording independently and then came to consensus. Therefore, approximately 240 hours were required to assess the recordings. Automation of the methods is feasible (personal communications with P. K. Raju, PhD, and D. Marghitu, PhD, professors of acoustics at Auburn University),
and accomplishing such automation would allow for more rapid assessment and quantification of the data. Increasing the speed of crepitus analysis would aid in future clinical studies.
Biomarkers are essential to the advancement of research into complementary and integrative health therapies, including manual therapies.
If the accelerometry analysis automation and studies outlined earlier are successful, joint vibrations (crepitus) identified during lumbar motion could eventually be used as an outcome measure (biomarker) to assess Z joint function and to assess the effects of LBP treatments, including SMT, on the Z joints. Such new information could potentially help with the important efforts of identifying subpopulations of LBP patients who respond best to various types of treatments.
In this feasibility study, data collected from accelerometers provided useful information indicating the prevalence of crepitus increased with age, was higher in LBP than healthy participants, and decreased overall after SMT. Consequently, crepitus assessment using accelerometers has the potential of being an outcome measure or biomarker for providing meaningful information on Z joint function during movement and for providing information on the effects of LBP treatments (eg, SMT) on Z joint function. Further research on larger numbers of participants is warranted to assess crepitus in healthy and LBP participants of different age ranges and different severities of degeneration. In addition, assessment of the effects of SMT on crepitus is also warranted.
Funding Sources and Conflicts of Interest
This project was partially funded by NIH/NCCIH Grant # 3R01AT000123-06S2. No conflicts of interest were reported for this study.
Contributorship Information
Concept development (provided idea for the research): G.C.
Design (planned the methods to generate the results): G.C., K.R.
Supervision (provided oversight, responsible for organization and implementation, writing of the manuscript): G.C.
Data collection/processing (responsible for experiments, patient management, organization, or reporting data): G.C., M.B., P.B.
Analysis/interpretation (responsible for statistical analysis, evaluation, and presentation of the results): G.C., M.B., P.B., K.R.
Literature search (performed the literature search): G.C., M.B., P.B.
Writing (responsible for writing a substantive part of the manuscript): G.C.
Critical review (revised manuscript for intellectual content, this does not relate to spelling and grammar checking): G.C., K.R.
Practical Applications
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Data collected from accelerometers provided useful information in this pilot study.
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Crepitus prevalence increased with age.
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Crepitus prevalence was higher in LBP than healthy subjects.
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Overall crepitus prevalence decreased following SMT.
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Crepitus assessment using accelerometers has the potential of being an outcome measure/biomarker for zygapophyseal joint function, including before and after LBP treatments (eg, SMT).
Acknowledgments
The authors acknowledge Jennifer Dexheimer, BS, Clinical Research Coordinator, for coordinating the clinical component of this project; Nathan Miller, DC, for performing the spinal manipulation; Dana Madigan, DC, MPH, for performing the power analysis discussed in Future Research; Lynn Zoufal, MBA, for help with project management; both Dr. Madigan and Judith Pocius, MS, for reviewing late drafts of the manuscript; and Robert Hansen for producing the illustrations and graph.
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