Can Manual Therapy Alter or Deform Connective Tissue?
The most extensive known research on manual therapy's ability to alter and deform connective tissue (CT) was examined by Joseph Threlkeld, PT, PhD. In this month's Masters In Massage blog we're posting excerpts from his published research article.
The full article can be purchased at https://academic.oup.com/ptj/article-abstract/72/12/893/2728889?redirectedFrom=fulltext
“Manual therapeutic techniques are used to relieve pain and to increase the mobility of joints. The techniques that are specifically utilized to affect connective tissues (CT’s) could be generally categorized as either stretching or compression and include massage, fascial/tendon stretching, traction, and articulation thrust techniques.
One of the principal uses of manual therapy is to produce elongation of the CT structures that may be abnormally restraining arthrokinematic motion.
Microfailure is a desired outcome of some manual stretching techniques that are intended to produce permanent elongation of CT structures.
The result is progressive, permanent (plastic) deformation of the CT structure.
One of the aims of manual therapy is to permanently elongate soft tissues.
The presence of waviness or crimping in the normal collagen bundles represents a variable amount of slack. This slack must be taken out by a tensile force before any individual bundle of collagen is placed on stretch.
In the terminology of manual therapy, the act of elongating CT... is known as 'taking out the slack.'
The physiologic loading region of the stress-strain curve shown in Figure 5 represents the range of forces that usually act on CT in vivo and implies that primarily elastic deformation occurs at these loads.
This idealized stress-strain curve for collagen graphically shows the progression of changes as increasing tensile force (stress) produces ever greater fiber deformation (strain). In the toe region [refers to a region on the graph, not the anatomical toe], very little stress produces a relatively large percentage.
When manual therapeutic techniques are used to decrease joint stiffness, external forces or torques are applied to anatomical structures with the intent of permanently changing the length or mobility of CT.
The resting length of CT is changed through plastic deformation. The mobility of CT is changed by breaking some of the links between adjacent CT bundles.
Mobility might also be improved by restoring the interstitial fluid content of CT structures to normal levels, thereby reestablishing normal frictional resistance between the bundles and adjacent structures.
This gross approximation of the load necessary to cause microfailure (some permanent elongation) can be used to make some educated guesses about how effective the typical forces encountered in manual therapy will be in stretching CT.
Manual therapy is often used to produce a desirable amount of plastic deformation of CT (microfailure of ligaments, fasciae, and so on) and to produce movement of one joint surface with respect to another. Both of these goals require that the medical practitioner apply an external force to the patient. In order for the technique to be safe, effective, and reproducible, the magnitude, velocity, and rate of application of the force must be imparted within relatively narrow limits.
One of the components of manual thrust techniques is to preload a tissue by 'taking out the slack prior to beginning therapeutic movement. This component is often referred to as 'reaching the first point at which resistance is felt.' The same concept is often used in soft tissue stretching techniques by alternating active patient muscle contraction with passive stretching. The end result should allow the collagen fiber crimping to be removed from the CT and for some amount of creep deformation to occur.
In some cases, oscillatory manual techniques are applied to CT with the goal of guiding tissue remodeling and repair and decreasing the randomized arrangement and interlinking of new collagen fibers. Research supports the concept that the application of force to CT during tissue healing and remodeling can improve the extensibility and strength of the tissue.
If 100% of an externally applied force could be transmitted to the long axis of a selected portion of a CT structure, then it could be presumed that forces commonly produced during manual therapy could produce permanent elongation. For example, based on data from the Table, an 18-mm-wide segment of the distal iliotibial band would begin to undergo microfailure at 246 N (25 kg) and macrofailure at 657 N (67 kg). These forces are well within the ranges of forces encountered during thoracic mobilization (Figs. 8-10).
The ability of manual therapy to affect CT has some support in the basic literature of mechanical tissue testing and CT remodeling. Physical forces can and do alter CT.
As yet there is no sound foundation of research to delineate the range or distribution of manually applied forces. This information is needed in order to compare the basic mechanical testing and clinical techniques, to provide a reliable database for testing the efficacy of these techniques, and to assist in the instruction of students in manual therapy. A serious deficiency exists in the manual therapy literature regarding the forces used to move joints and to stretch tissues.
The outcome of manual techniques relies on the skillful application of forces with very definite magnitudes, velocities, accelerations, and directions coupled with specific anatomical sites of application. One could imagine that force could vary depending on the technique used, the region treated, the type of pathology present, and the somatotypes of both patient and therapist.”