Research Review by Dr. Shawn Thistle©


Dec. 2007

Study Title:

The audible pop from thoracic spine thrust manipulation and its relation to short-term outcomes in patients with neck pain


Cleland JA, Flynn TW, Childs JD, Eberhart S

Publication Information:

Journal of Manual & Manipulative Therapy 2007; 15(3): 143-154.


Neck pain is very common and costly. The lifetime prevalence of neck pain is roughly 70%, with 15-22% of individuals experiencing pain beyond 5 years. Manual medicine practitioners utilize a number of interventions to treat mechanical neck pain, including joint mobilization/manipulation, traction, therapeutic exercise, acupuncture, and various electromodalities. Recently, evidence has emerged suggesting that low-amplitude, high-velocity spinal manipulation directed at the thoracic spine can be effective for treating mechanical neck pain. Many clinicians believe that the success of such manipulative interventions is directly related to achieving an audible “pop”, or joint cavitation, despite any evidence to support this tenet.

Recent studies on lumbopelvic manipulation have suggested that achieving an audible “pop” is not related to short-term (2-4 days)1 or longer-term (4 weeks)2 outcomes. This study aimed to investigate the relationship between the audible pop and patient-centered outcomes in patients with mechanical neck pain undergoing a regimen of thrust manipulation directed at the thoracic spine.

This prospective cohort study included 78 patients between the ages of 18 and 65 (average age 42) with mechanical neck pain, with or without unilateral upper extremity symptoms, and an initial Neck Disability Index level of at least 10%. Exclusion criteria were standard, and included:
  • presence of any medical red flag suggesting a non-musculoskeletal origin of neck symptoms
  • history of whiplash injury in the previous 6 weeks
  • CNS involvement
  • diagnosis of cervical spine stenosis
  • signs of nerve root compression
All patients underwent a standardized physical examination including: neurological screening, cervical ROM and postural assessment, upper quarter muscle testing, deep neck flexor strength testing, special tests (Spurling, ROOS, neurodynamic, neck distraction), and segmental mobility testing. Patients also provided demographic information and completed the following outcome measures:
  1. Neck Disability Index (NDI)
  2. 11-point Numeric Pain Rating Scale – rating pain over the last 24 hours from 0 (no pain) to 10 (worst pain imaginable)
  3. Fear Avoidance Beliefs Questionnaire
  4. Global Rating of Change (GROC) – completed on follow-up only; a 15-point scale from -7 (a very great deal worse) to +7 (a very great deal better)
All outcome measures were repeated at follow-up, which occurred 2-4 days after the treatment (note: no long term follow-up was conducted in this study).

All patients were treated with the same regimen of thoracic spine manipulations as follows:
  1. Distraction Manipulation – performed with the patient seated and the therapist behind the patient. The therapist placed their upper chest in the middle thoracic spine and grasped the patient’s elbows (hands clasped behind the neck) – a distraction thrust was then delivered.
  2. Upper Thoracic Spine Manipulation – a more traditional “anterior” adjustment directed at T1-T4 with the patient supine.
  3. Lower Thoracic Spine Manipulation – identical to 2) but directed below T4.
All three manipulation procedures were performed twice (totaling 6 manipulations per patient), regardless of the presence or absence of cavitation on the first attempt. Audible pops were operationally defined as “an audible sound heard by either the patient or therapist”. The therapist recorded the presence or absence of a pop after each manipulation. For statistical analysis, patients were divided into two groups – arbitrarily set as those with ≤ 3 pops and those with > 3 pops. (NOTE: if multiple cavitations occurred with one manipulation, it was counted as one “pop”). The relationship between the total number of pops and the scores for pain, disability, and ROM were measured using Pearson correlation coefficients.

Pertinent results of this study include:
  • subjects had experienced neck pain for an average of 80 days (note a large standard deviation of 70.6 days though)
  • the average number of “pops” experienced across the entire group was 3.8; 21 patients experienced ≤3 pops and 51 experienced > 3 pops
  • there were no significant baseline differences between the ≤3/>3 pops groups for pain, disability, and neck ROM
  • the only significant relations were found between the number of pops and cervical side-bending-right (r = -0.27), right rotation (r = -0.27), and left rotation (r = -0.34) – note these correlations are inverse – hence, more pops resulted in less cervical motion
  • between group (≤3/>3 pops) differences for the NDI and NPRS did not reach clinically significant values (that is, no group showed superior results)
  • of the patients with ≤3 pops, 33% experienced self-rated successful outcomes (between +5 and +7 on the GROC), while in the > 3 pops group, 31% had similar results (this difference was non-significant)
  • the odds ratio for those with ≤3 pops achieving successful outcome was 1.3 (although non-significant, this suggests these patients were more likely to improve)

Conclusions & Practical Application:

It has traditionally been thought that in order for spinal manipulation to be successful, an audible pop must be heard. This study provides preliminary evidence that this tenet may not be true. Interestingly overlooked by the authors, this study also provided further evidence that thoracic spine manipulation can be effective for treating mechanical neck pain (this of course wasn’t the purpose of the study, and there was no control group – that being said, all patients in general improved with this intervention). The results of this study should be considered in light of some general design weaknesses and practical considerations:
  • Only short-term follow-up was conducted. Future studies should extend this period to more closely mimic clinical practice.
  • Cervical spine thrust manipulation was not used – the model for this study was based on the previous work indicating that thoracic manipulation is effective for treating neck pain. Therefore these results cannot be extrapolated to cervical manipulation.
  • The operational definition of a pop was admittedly subjective and dichotomized as yes/no. The authors acknowledge that it is not practical to ask therapists or patients to count multiple pops that may occur with one manipulation. In practice (and most likely in the study), manipulation often results in multiple pops – this study design had no way to account for the potentially greater neurological or mechanical effect(s) of this phenomenon.
  • No attempt was made to identify which segments were popping. One previous study has suggested that the pop only originates from the “targeted segment” 53% of the time anyway – which in itself challenged another long-held tenet in manual therapy: specificity of manipulation.
  • It has been documented that a refractory period exists between possible cavitations in a single joint. As all 6 manipulations were administered in succession, joints may have “already popped”, thus preventing them from cavitating on subsequent thrusts.
This concept is a difficult one to study, providing many challenges to researchers. This particular group of authors has done a commendable amount of work in this area to date, with more on the way. To date, their work as a whole suggests that the popping sound associated with spinal manipulation may not be as important as once thought for determining the clinical outcome of manipulation.

Additional References:

  1. Flynn TW, Fritz JM, Wainner R et al. The audible pop is not necessary for successful high velocity thrust manipulation in individuals with low back pain. Arch Phys Med Rehabil 2003; 87: 1057-1060.
  2. Flynn TW, Childs JD, & Fritz JM. The audible pop from high-velocity thrust manipulation and outcome in individuals with low back pain. J Manipulative Physiol Ther 2006; 29: 40-45.
  3. Ross JK, Bereznick DE, McGill SM. Determining cavitation location during lumbar and thoracic spinal manipulation: Is spinal manipulation accurate and specific? Spine 2004; 29: 1452-1457.