Procedural skills in spinal manipulation: do prerequisites matter?

Assessment of forces during side-posture adjustment with the use of a table-embedded force plate: Reference values for education

OBJECTIVE

Force-sensing treatment tables are becoming more commonly used by chiropractic educational institutions. However, when a table-embedded force platform is the sole measurement method, there is little information available about what force-time values instructors and students should expect for side-posture spinal manipulative thrusts. The purpose of this report is to provide force-time values recorded with such a system during side-posture manipulation with human recipients.

METHODS

Student volunteers were examined by and received lumbar or pelvic side-posture manipulation from experienced chiropractors who were diplomates of the Gonstead Clinical Studies Society. Forces were recorded using proprietary software of a Bertec force platform; force and time data were analyzed with a custom-programmed software tool in Excel.

RESULTS

Seven doctors of chiropractic performed 24 thrusts on 23 student recipients. Preload forces, averaging 69.7 N, and thrust loading duration, averaging 167 milliseconds, were similar to previous studies of side-posture manipulation. Peak loads were higher than previous studies, averaging 1010.9 N. Other variables included prethrust liftoff force, times from thrust onset to peak force and peak load to resolution of thrust, and average rates of force loading and unloading.

CONCLUSION

The values we found will be used for reference at our institution and may be useful to instructors at other chiropractic educational institutions, in the teaching of lumbar side-posture manipulation. A caveat is that the values of this study reflect multiple sources of applied force, not solely the force applied directly to the spine.

Developing spinal manipulation psychomotor skills competency: A systematic review of teaching methods

OBJECTIVE

To update the state of the art regarding the acquisition of spinal high-velocity low-amplitude psychomotor skills competency among chiropractors and chiropractic students.

METHODS

Available electronic articles from 5 databases, published between June 2015 and August 2020, were obtained. Eligible studies underwent methodological quality assessments using the Joanna Briggs Institute Critical Appraisal Checklists and Cochrane Collaboration's Risk of Bias Tools.

RESULTS

Fourteen critically appraised studies were identified, including 10 cohort studies and 4 randomized controlled trials. There was no literature excluded due to high risk of bias. The type of augmented devices included a mannequin on a force platform, a computer-connected device, a human analogue mannequin, and a 3-dimensional electrogoniometer with an instrumented spatial linkage.

CONCLUSION

The use of augmented feedback devices such as human analogue mannequins with force-sensing table technology and computer-connected devices is potentially beneficial in the chiropractic curricula and may facilitate student learning and improvement of spinal manipulation. More studies are required to determine whether psychomotor skill aids translate directly into raised competency levels in novice clinicians.

Reliability and accuracy of an expert physical therapist as a reference standard for a manual therapy joint mobilization trial

Objective: Previous studies on learning joint mobilization techniques have used expert practitioners as the reference standard as there is no current evidence on what ideal forces would be for effective mobilizations. However, none of these trials have documented the reliability or accuracy of the reference standard. Therefore, the purpose of this study was to report both the reliability and accuracy of an expert physical therapist (PT) acting as a reference standard for a manual therapy joint mobilization trial.Methods: A secondary analysis was performed using data from a published randomized, controlled, crossover study. The mobilization technique studied was the central posterior to anterior (PA) joint mobilization of the L3 vertebra. Reliability and accuracy data for the reference standard were collected over four time periods spanning 16 weeks.Results: Intrarater reliability of the expert PT for R1 and R2 joint forces was excellent (R1 Force ICC_3,3 0.95, 95%CI 0.76-0.99 and R2 Force ICC_3,3 0.90, 95%CI 0.49-0.99). Additionally, the expert PT was 92.3% accurate (mean % error±SD, 7.7 ± 5.5) when finding Grade III mean peak mobilization force and 85.1% accurate (mean % error±SD, 14.9 ± 8.3) when finding Grade IV mean peak mobilization force. Finally, correlations between actual applied forces and computed ideal forces were excellent (Pearson r 0.79-0.92, n = 24, P < 0.01 for all correlations).Discussion: The expert PT in this manual therapy joint mobilization trial showed excellent reliability and accuracy as the reference standard. The study supports the use of implementing quantitative feedback devices into the teaching of joint mobilization when a reliable and accurate reference standard has been identified.Level of Evidence: 2b.

High-velocity, low-amplitude spinal manipulation training of prescribed forces and thrust duration: A pilot study

OBJECTIVE

High-velocity, low-amplitude spinal manipulation (HVLA-SM) may generate different therapeutic effects depending on force and duration characteristics. Variability among clinicians suggests training to target specific thrust duration and force levels is necessary to standardize dosing. This pilot study assessed an HVLA-SM training program using prescribed force and thrust characteristics.

METHODS

Over 4 weeks, chiropractors and students at a chiropractic college delivered thoracic region HVLA-SM to a prone mannequin in six training sessions, each 30 minutes in duration. Force plates embedded in a treatment table were used to measure force over time. Training goals were 350 and 550 Newtons (N) for peak force and ≤150 ms for thrust duration. Verbal and visual feedback was provided after each training thrust. Assessments included 10 consecutive thrusts for each force target without feedback. Mixed-model regression was used to analyze assessments measured before, immediately following, and 1, 4, and 8 weeks after training.

RESULTS

Error from peak force target, expressed as adjusted mean constant error (standard deviation), went from 107 N (127) at baseline, to 0.2 N (41) immediately after training, and 32 N (53) 8 weeks after training for the 350 N target, and 63 N (148), -6 N (58), and 9 N (87) for the 550 N target. Student median values met thrust duration target, but doctors' were >150 ms immediately after training.

CONCLUSION

After participation in an HVLA-SM training program, participants more accurately delivered two prescribed peak forces, but accuracy decreased 1 week afterwards. Future HVLA-SM training research should include follow-up of 1 week or more to assess skill retention.

Measurement and Analysis of Biomechanical Outcomes of Chiropractic Adjustment Performance in Chiropractic Education and Practice

OBJECTIVE

The purpose of this study was to compare biomechanical measures of chiropractic adjustment performance of the McTimoney toggle-torque-recoil (MTTR) technique among students and chiropractors.

METHODS

Fifty-three participants (15 year-3 [Y3] and 16 year-5 chiropractic students and 22 McTimoney chiropractors [DCs]) participated in this study. Each applied 10 MTTR thrusts to a dynamic load cell, 5 each with their left and right hands. Biomechanical variables including preload force, peak force, time to peak force, thrust duration, and total thrust time were computed from each of the force-time histories and compared within groups using a series of 2-way analysis of variance to evaluate the effects of sex and handedness, and between groups to determine the effect of experience using a series of 3-way analysis of variance. The Games-Howell post hoc test was used to further assess pairwise comparisons.

RESULTS

Mean time to peak force was more than 3 × shorter for DCs (69.96 ms) compared with Y3 students (230.36 ms) (P = .030). Likewise, mean thrust duration was also found to be nearly 2.5-fold significantly shorter for DCs (117.77 ms) compared with Y3 students (283.84 ms) (P = .030). The DCs took significantly less total thrust time (mean = 1.27 seconds) in administering MTTR thrusts than Y3 students (1.89 seconds) (P = .006). No significant differences were found among any of the 3 clinician groups for peak force or in time to peak force or thrust duration for comparisons of all 10 MTTR thrusts among year-5 students and DCs. Higher peak forces were observed for thrusts delivered with clinicians' dominant hands (P = .001), and the fastest thrusts were found for the dominant hands of DCs (P = .001). Sex had no significant effect on biomechanical variables. The Y3 students had significant greater variability in thrust times for each hand and for analyses of both hands combined (P = .001).

CONCLUSION

Training and experience were found to result in shorter MTTR thrust times and other biomechanical variables that have been identified as important factors in the mechanisms of chiropractic adjustments. Identification of such biomechanical markers as performance outcomes may be of assistance in providing feedback for training in chiropractic education and technique application.

The effect of real-time feedback on learning lumbar spine joint mobilization by entry-level doctor of physical therapy students: a randomized, controlled, crossover trial

OBJECTIVE

To examine the effects of real-time, objective feedback on learning lumbar spine joint mobilization techniques by entry-level Doctor of Physical Therapy (DPT) students.

METHODS

A randomized, controlled, crossover design was used. Twenty-four 1st Year DPT students were randomized into two groups. Group 1 (n = 12) practiced with the real-time feedback device first and then without it, while Group 2 (n = 12) practiced without the device first and then with it. Both practice periods with and without the device were 4 weeks long. Data were collected at Baseline, 5 weeks, 11 weeks, and 16 weeks. The crossover period was 5 weeks long, during which neither group practiced with or without the device. Eight force parameters were measured: R1 force; R2 force; Grade III and Grade IV mean peak force, frequency, and amplitude.

RESULTS

When students practiced with the real-time feedback device, they more closely matched the reference standard for two outcomes: 1) the mean difference in R2 force between student and reference standard was better with device (38.0 ± 26.7 N) than without it (51.0 ± 38.5 N); P = .013; and 2) the mean difference in Grade III peak to peak amplitude force was also better with device (8.9 ± 9.3 N) than without it (11.8 ± 11.0); P = .026. All other force parameters improved when students practiced with the real-time feedback device, however, the differences between when they practiced without the device were not statistically significant.

DISCUSSION

Real-time, objective feedback using a direct force measurement device improved learning for some aspects of lumbar spine joint mobilization by entry-level physical therapy students.

LEVEL OF EVIDENCE

2b.

Does the application site of spinal manipulative therapy alter spinal tissues loading?

BACKGROUND CONTEXT

Previous studies found that the intervertebral disc (IVD) experiences the greatest loads during spinal manipulation therapy (SMT).

PURPOSE

Based on that, this study aimed to determine if loads experienced by spinal tissues are significantly altered when the application site of SMT is changed.

STUDY DESIGN

A biomechanical robotic serial dissection study.

SAMPLE

Thirteen porcine cadaveric motion segments.

OUTCOME MEASURES

Forces experienced by lumbar spinal tissues.

METHODS

A servo-controlled linear actuator provided standardized 300 N SMT simulations to six different cutaneous locations of the porcine lumbar spine: L2-L3 and L3-L4 facet joints (FJ), L3 and L4 transverse processes (TVP), and the space between the FJs and the TVPs (BTW). Vertebral kinematics were tracked optically using indwelling bone pins; the motion segment was removed and mounted in a parallel robot equipped with a six-axis load cell. Movements of each SMT application at each site were replayed by the robot with the intact specimen and following the sequential removal of spinal ligaments, FJs and IVD. Forces induced by SMT were recorded, and specific axes were analyzed using linear mixed models.

RESULTS

Analyses yielded a significant difference (p<.05) in spinal structures loads as a function of the application site. Spinal manipulative therapy application at the L3 vertebra caused vertebral movements and forces between L3 and L4 spinal segment in the opposite direction to when SMT was applied at L4 vertebra. Additionally, SMT applications over the soft tissue between adjacent vertebrae significantly decreased spinal structure loads.

CONCLUSION

Applying SMT with a constant force at different spinal levels creates different relative kinetics of the spinal segments and load spinal tissues in significantly different magnitudes.

Learning spinal manipulation: A best-evidence synthesis of teaching methods

OBJECTIVE

The purpose of this study was to evaluate the effectiveness of different reported methods used to teach spinal manipulative therapy to chiropractic students.

METHODS

For this best-evidence literature synthesis, 5 electronic databases were searched from 1900 to 2015. Eligible studies were critically appraised using the criteria of the Scottish Intercollegiate Guidelines Network. Scientifically admissible studies were synthesized following best-evidence synthesis principles.

RESULTS

Twenty articles were critically appraised, including 9 randomized clinical trials, 9 cohort studies, and 2 systematic reviews/meta-analyses. Eleven articles were accepted as scientifically admissible. The type of teaching method aids included a Thrust in Motion cervical manikin, instrumented cardiopulmonary reanimation manikin, padded contact with a load cell, instrumented treatment table with force sensor/transducer, and Dynadjust instrument.

CONCLUSIONS

Several different methods exist in the literature for teaching spinal manipulative therapy techniques; however, future research in this developing area of chiropractic education is proposed. It is suggested that various teaching methods be included in the regular curricula of chiropractic colleges to aid in developing manipulation skills, efficiency, and knowledge of performance.

How should we teach lumbar manipulation? A consensus study

BACKGROUND

Spinal manipulation is an effective intervention for low back pain, yet there is little consistency in how this skill is taught.

OBJECTIVES

The purpose of this study was to identify what educators and clinicians believe are important characteristics of the patient and operator position prior to side-lying lumbar manipulation and the patient position and operator motion during the manipulative thrust.

DESIGN

A multi-disciplinary correspondence-based Delphi method.

METHODS

Three rounds of questionnaires were sent to physical therapists, osteopaths and chiropractors. Consensus was established in Round 3 if at least 75% of respondents identified a characteristic as very important/extremely important on a 5-point Likert scale.

RESULTS

265 educators and clinicians completed the three rounds of questioning. There was consensus that localization to target segment, patient comfort, table height, and logrolling the patient towards the operator are important characteristics of patient position during the preparatory phase. During the manipulation phase, respondents agreed that it is important to maintain localization to the segment and rotate the patient's pelvis and lumbar spine. For the operator characteristics, consensus was reached for the following items; moving up and over the patient, maintaining contact using forearms, and close contact between the operator and patient (preparatory phase); generating force through the body and legs, dropping the body downwards, maintaining localization, and providing a high-velocity and low-amplitude thrust (manipulation phase).

CONCLUSIONS

This Delphi study successfully identified key characteristics of patient position and operator position and motion for effective delivery of side-lying lumbar spine manipulations.

Methods of Muscle Activation Onset Timing Recorded During Spinal Manipulation

OBJECTIVE

The purpose of this study was to determine electromyographic threshold parameters that most reliably characterize the muscular response to spinal manipulation and compare 2 methods that detect muscle activity onset delay: the double-threshold method and cross-correlation method.

METHODS

Surface and indwelling electromyography were recorded during lumbar side-lying manipulations in 17 asymptomatic participants. Muscle activity onset delays in relation to the thrusting force were compared across methods and muscles using a generalized linear model.

RESULTS

The threshold combinations that resulted in the lowest Detection Failures were the "8 SD-0 milliseconds" threshold (Detection Failures = 8) and the "8 SD-10 milliseconds" threshold (Detection Failures = 9). The average muscle activity onset delay for the double-threshold method across all participants was 149 ± 152 milliseconds for the multifidus and 252 ± 204 milliseconds for the erector spinae. The average onset delay for the cross-correlation method was 26 ± 101 for the multifidus and 67 ± 116 for the erector spinae. There were no statistical interactions, and a main effect of method demonstrated that the delays were higher when using the double-threshold method compared with cross-correlation.

CONCLUSIONS

The threshold parameters that best characterized activity onset delays were an 8-SD amplitude and a 10-millisecond duration threshold. The double-threshold method correlated well with visual supervision of muscle activity. The cross-correlation method provides several advantages in signal processing; however, supervision was required for some results, negating this advantage. These results help standardize methods when recording neuromuscular responses of spinal manipulation and improve comparisons within and across investigations.

Differential displacement of soft tissue layers from manual therapy loading

BACKGROUND

Understanding the biomechanics of spinal manipulative therapy requires knowing how loads are transmitted to deeper structures. This investigation monitored displacement at sequential depths in thoracic paraspinal tissues parallel with surface load directions.

METHODS

Participants were prone and a typical preload maneuver was applied to thoracic tissues. Ultrasound speckle tracking synchronously monitored displacement and shear deformation of tissue layers in a region of interest adjacent to load application to a depth of 4 cm. Cumulative and shearing displacements along with myoelectric activity were quantitatively estimated adjacent to loading site.

FINDINGS

The cephalocaudal cumulative displacement in layers parallel to the surface were, in order of depth, 1.27 (SD=0.03), 1.18 (SD=0.02), and 1.06 (SD=0.01) mm (P<0.000), respectively. The superficial/intermediate shear was 2.1 ± 2.3% whereas the intermediate/deep shear was 4.4% (SE=3.7, P=0.014). Correlation of tissue layers was stronger with application site displacement at the surface (0.87<r<0.89) than with muscle activation (0.65<r<0.67).

INTERPRETATION

Surface loading of the torso in combined posteroanterior and caudocephalic directions result in both displacement of tissues anteriorly and in shearing between tissue layers in the plane of the tissues strata to depths that could plausibly affect spinal tissues. Displacements of tissues more likely arise passively, consistent with load transmitted by the retinacula cutis and epimuscular force pathways. Displacements are similar in magnitude to those known to evoke biologically relevant responses in both animal and human studies.

Staging the use of teaching aids in the development of manipulation skill

Skill development in manual therapies is influenced by a number of factors. The effects of the training program organization, mentor coaching, feedback in various forms, and electromechanical training aids are factors that have been studied. A significant gap exists in understanding when teaching aids might be most effective within a defined curriculum structure. This project used the ratio of instructional theory and laboratory practice to define the learning context. An electromechanical training aid (Dynadjust™) was introduced at different stages (year 2 and year 4) of training for high-velocity, low-amplitude (HVLA) manipulation. Learners were assigned to either the Aid group or the NoAid group. Independent assessment of skill was evaluated before and after 6 weeks by means of recording force-time profiles of HVLA performance. Repeated measures analysis of variance (ANOVA) evaluated change scores in the force amplitude and rate of rise in force. Program features were dominated by a low ratio of laboratory practice to didactic foundational education components. Use of the aid was not associated with any measurable gains for participants when used in year 2. Later participation in year 4 suggested enhanced development in rate of rise for force (p < 0.0597) and for peak force (p < 0.0303). Careful attention should be given to the sequencing of content and laboratory work in designing curricula for training programs. For programs using lower ratios of laboratory contact hours, teaching aids to augment practice may result in better performance gains when introduced later than if added early in the curriculum.

Physiological responses to spinal manipulation therapy: investigation of the relationship between electromyographic responses and peak force

OBJECTIVE

It is believed that systematic modulation of spinal manipulative therapy (SMT) parameters should yield varying levels of physiological responses and eventually a range of clinical responses. However, investigation of SMT dose-physiological response relationship is recent and has mostly been conducted using animal or cadaveric models. The main objective of the present study is to investigate SMT dose-physiological response relation in humans by determining how different levels of force can modify electromyographic (EMG) responses to spinal manipulation.

METHODS

Twenty-six participants were subjected to 2 trials of 4 different SMT force-time profiles using a servo-controlled linear actuator motor. Normalized EMG activity of paraspinal muscles (left and right muscles at level T6 and T8) was recorded during and after SMT, and EMG values were compared across the varying levels of force.

RESULTS

Increasing the level of force yielded an increase in paraspinal muscle EMG activity during the thrust phase of SMT but also in the two 250-millisecond time windows after the spinal manipulation impulse. These muscle activations quickly attenuated (500 milliseconds after spinal manipulation impulse).

CONCLUSION

The study confirmed the presence of a local paraspinal EMG response after SMT and highlighted the linear relationship between the SMT peak force and paraspinal muscle activation.

Relationship between Biomechanical Characteristics of Spinal Manipulation and Neural Responses in an Animal Model: Effect of Linear Control of Thrust Displacement versus Force, Thrust Amplitude, Thrust Duration, and Thrust Rate

High velocity low amplitude spinal manipulation (HVLA-SM) is used frequently to treat musculoskeletal complaints. Little is known about the intervention's biomechanical characteristics that determine its clinical benefit. Using an animal preparation, we determined how neural activity from lumbar muscle spindles during a lumbar HVLA-SM is affected by the type of thrust control and by the thrust's amplitude, duration, and rate. A mechanical device was used to apply a linear increase in thrust displacement or force and to control thrust duration. Under displacement control, neural responses during the HVLA-SM increased in a fashion graded with thrust amplitude. Under force control neural responses were similar regardless of the thrust amplitude. Decreasing thrust durations at all thrust amplitudes except the smallest thrust displacement had an overall significant effect on increasing muscle spindle activity during the HVLA-SMs. Under force control, spindle responses specifically and significantly increased between thrust durations of 75 and 150 ms suggesting the presence of a threshold value. Thrust velocities greater than 20-30 mm/s and thrust rates greater than 300 N/s tended to maximize the spindle responses. This study provides a basis for considering biomechanical characteristics of an HVLA-SM that should be measured and reported in clinical efficacy studies to help define effective clinical dosages.

Effects of visual feedback on manipulation performance and patient ratings

OBJECTIVE

This study examined the explicit targeted outcome (a criterion standard) and visual feedback on the immediate change in and the short-term retention of performance by novice operators for a high-velocity, low-amplitude procedure under realistic conditions.

METHODS

This study used a single-blind randomized experimental design. Forty healthy male (n = 26) and female (n = 14) chiropractic student volunteers with no formal training in spinal manipulative therapy participated. Biomechanical parameters of an L4 mammillary push spinal manipulation procedure performed by novice operators were quantified. Participants were randomly assigned to 2 groups and paired. One group received visual feedback from load-time histories of their performance compared with a criterion standard before a repeat performance. Participants then performed a 10-minute distractive exercise consisting of National Board of Chiropractic Examiners review questions. The second group received no feedback. An independent rating of performance was conducted for each participant by his/her partner. Results were analyzed separately for biomechanical parameters for partner ratings using the Student t test with levels of significance (P < .01) adjusted for repeated testing.

RESULTS

Expressed in percent change for each individual, visual feedback was associated with change in the biomechanical performance of group 2, a minimum of 14% and a maximum of 32%. Statistical analysis rating of the performance favored the feedback group on 4 of the parameters (fast, P < .0008; force, P < .0056; precision, P < .0034; and composite, P < .0016).

CONCLUSION

Quantitative feedback, based on a tangible conceptualization of the target performance, resulted in immediate and significant improvement in all measured parameters. Newly developed skills were retained at least over short intervals even after distractive tasks. Learning what to do with feedback on one's own performance may be more important than the classic teaching of how to do it.