Structural/postural corrective based Chiropractors endeavor to return the abnormal spine back towards an accepted normal via the physiological process of ligamentous re-modeling. Ligamentous re-modeling is based on the fact that the resting length of a ligament can be altered by the application of a structurally specific traction or exercise. But how does this process really work?
In this article, I will discuss four main viscoelastic properties of spinal ligaments and their importance in the therapeutic rehabilitation of human spinal structure and global posture.
Visco-elastic Properties of Ligaments
The general response of ligaments to a traction load or a repetitive structural/postural corrective exercise is influenced by several phenomena which are time-dependent, such as hysteresis, creep, recovery and plastic deformation.
Ligamentous hysteresis is defined as the energy lost (as heat) within the tissue between loading and unloading. When the ligament is stimulated repetitively with constant peak load, hysteresis develops and the ligament length limits increase with each cycle. Thus the repetitive use of the same force produces greater and greater ligamentous deformation (creep). This is why postural/structural corrective exercises work and should always be done first, before the patient is adjusted or has any traction performed. The exercises “heat-up” the ligaments, increase their length and reduce their internal tension. This “sets-up” the spine to better receive any corrective spinal manipulation or traction. Also, if you can increase the peak load during the patients corrective exercise session you will increase tissue hysteresis. The use of a device such as the Pro-Lordotic Neck Exerciser™ provides 20-50 pounds of force into the lower, middle and/or upper anterior neck structures while the patient performs their corrective neck extension exercises. SeeFigure 1.
It is important the peak force be delivered into the region of the spine that most needs re-modeling. If the patient has a lower cervical kyphosis, that is the region that should receive most of the structural corrective exercise.
Figure 1. Pro-Lordotic Neck Exercise.
- Ligament Creep
Ligament creep is defined as the time dependent elongation of a ligament when subjected to a constant stress. Ligament creep is not linear in nature. Most of the ligament elongation occurs during the first 15-20 minutes of a traction load. This is why at least 10-20 minutes of structural corrective traction is usual recommended. But how long does is take the ligament to recover from the elongating force and return to its original length?
In a human in vivo study, following 20 minutes of deep flexion, a 25-minute rest period was required in order to achieve 50% recovery and a 50-minute rest period was required to achieve 70% recovery from the resulting creep.1 Recent evidence demonstrate that both creep and tension-relaxation induced in 20-50 minutes of loading or stretching a ligament, respectively, demonstrated 40-60% recovery in the first hour of rest, whereas full recovery is a very slow process which may require 24-48 hours.1 Also, hysteresis recovery following creep deformation was more prolonged and less complete in older subjects.2 From these studies, we can see that performing corrective procedures on your patients (in-office) three times per week with 48 hours or more between sessions will not be very successful if the patient is not also performing some type of ligamentous rehabilitation at home on a daily basis. Having them re-stretch the soft tissues in-between the in-office therapy sessions with postural/structural corrective exercises and devices like the Pro-Lordotic Neck Exerciser™, the Cervical Remodeling Collar™ (Figure 2.)and/or a Denneroll™ (Figure 3.) are essential for a good structural corrective outcome.
Figure 2. Cervical Remodeling Collar.
Figure 3. Cervical Denneroll.
- Frequency or Time-History
Ligament behavior is also dependent on the frequency of load application and unloading or strain rate. Cyclic loading of a ligament with the same peak load, but at a higher frequency, results in larger creep development and longer time for the full recovery of the creep to occur.1 So having your patient perform their corrective exercises in a slightly faster, but still controlled, manner is better than a slow methodical fashion.
Ligament length-tension (strain-stress) behavior is also temperature-dependent, exhibiting reduced capability and therefore increased deformation at higher temperatures.1 The main point to understand from this statement is to not perform corrective procedures in a cold room or with a cold patient. It also re-iterates the importance of heating-up the tissues with exercise before other corrective procedures are performed.
So a person could ask: How do you get the ligaments to stay elongated if they recover so quickly? This is accomplished by getting the ligament stretched out to a length that moves it out of its elastic capability and into its plastic (viscous) range. Plastic deformation of a ligament can occur all at once, such as in athletic injuries where an extremely large force is applied, or through what is called “repetitive overwhelm”. Repetitive overwhelm is when a sub-maximal physical stress is applied so often, that it causes a micro-failure of the ligamentous cross-links, resulting in permanent deformation of the ligament. The main factors that affect plastic deformation are the amount, duration and frequency of the applied force.3 In one reference involving the posterior cruciate ligament of the knee, it was found that “Slow stretching of the ligament results in elongation up to 30% before any plastic deformation”.4
Understanding ligament physiology is essential to achieving consistent positive changes in your patient’s posture and structure. This information presented above emphasizes the importance of giving the patient a “home rehab kit” that includes the Pro-Lordotic Neck Exerciser™ and some form of corrective home traction (Denneroll or Cervical Remodeling Collar).
I hope this information helps you improve your patient’s corrective care and health outcomes.
1. Solomonow, M. Ligaments: A source of musculoskeletal disorders. Anatomy, physiology, pathophysiology review. Journal of Bodywork and Movement Therapies 2009 (13):136-154.
2. Twomey L, Taylor J. Flexion creep deformation and hysteresis in the lumbar vertebral column.Spine. 1982 Mar-Apr; 7(2):116-22.
3. Christensen, K. Plastic deformation and long-term support. Dynamic Chiropractic. December 15, 1999 (17).
Chow JCY. Advanced Arthroscopy. Springer-Verlag Publishing, New York, 2001: pg. 522.