Tuesday, June 23, 2009

Grades of mobilization by PA technique: Inter-therapist variances

There is no gold standard for measurement of magnitude of force applied or joint displacement. Many scientific tools & methodologies have been used to measure quantity of force applied by manual therapy procedures and joint displacement thus caused. Among these equipments some serve to mobilize the spine others serve as measurement tools for mobilization.

Different grades of mobilization have helped manual therapists to compartmentalize the quality & quantity of the energy package they provide to the receptive tissue. Having said so the general feeling is that, grades of mobilization helps in this regard only partially, because standardization of delivery can not be warranted for it is individualistic and dependant on the therapist. Therapist centered module delivery is dependant on many factors so inter-therapist variance is quite inevitable.

The PA mobilization: PA technique of spinal mobilization is both a diagnostic & therapeutic tool. Both subject & instrument oriented tests for the reliability of physical therapists' ability to detect intervertebral motion have confirmed unreliable testing in the face of documented efficacy of manual treatment via PA spinal mobilization.

However, despite the widespread use of spinal mobilization, little is known about the forces used or the accuracy of therapists in estimating the forces they use in administering the technique (1). In the following discussion we would like to throw light on the issue.

1. Study of Simmonds & colleagues (1995): In this study therapist applied oscillatory posteroanterior (PA) mobilizations to the mechanical model under three different conditions of stiffness for following purposes:

  • To quantify the forces used by therapists
  • To determine the accuracy of therapists in applying these forces

The findings are as follows:

  • Average forces across grades and stiffness levels = (57.59 to 178.27) Newton
  • Lower the stiffness lower is the force applied
  • Displacement varied with stiffness and mobilization grade. In the least stiff condition, the mean displacement varied between 2.25 and 3.45 mm for grades 1 to 4, respectively.

2. Review of Snodgrass & colleagues (2006): Snodgrass & colleagues reviewed 6 electronic databases up to April 2005 comprising of 20 studies of quantitative measurement of applied force during a PA mobilization technique mostly focusing on the lumbar spine in order to find out

  • Evaluate the consistency of force application by manual therapists when carrying out posterior-to-anterior (PA) mobilization techniques.
  • Factors that influence the application and measurement of mobilization forces.

They found when defined by magnitude, frequency, amplitude, and displacement:

  • PA mobilization forces are extremely variable among clinicians applying the same manual technique.
  • Variability is attributed to differences in techniques, measurement or reporting procedures, or variations between therapists or between patients.


1. Inter-therapist variability is high in manual therapy procedures be it a commonly applied technique i.e. PA mobilization (1,2). This further warranty improvement in the clinical standardization of manual force application.
2. There is a systematic bias in underestimating the magnitude of applied force and in overestimating motion. The variability in force application and the general overestimation of motion detection leads to poor reliability of measurements obtained with clinical tests based on motion palpation (1).

Addressing the research gap:

Future research on mobilization should include forces applied to the cervical and thoracic spines in addition to the lumbar spine while thoroughly describing force parameters and measurement methods to facilitate comparison between studies (2).

References: 1. Simmonds MJ et al; Phys Ther. 1995 Mar;75(3):212-22. 2. Snodgrass SJ et al; J Manipulative Physiol Ther. 2006 May;29(4):316-29. 3. Björnsdóttir SV et al; Disabil Rehabil. 1997 Feb;19(2):39-46.

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