by Elizabeth Hofheinz, M.P.H., M.Ed., September 18, 2019
How much is, “I can bend my leg more” in concrete terms? What does, “I am a lot steadier on my feet” look like in scientific terms? Richard Guyer, M.D., Chairman, Texas Back Institute Research Foundation knows. Working with Ram Haddas, Ph.D., Director of the Spine Biomechanics Lab at Texas Back Institute, they are transforming what is traditionally a subjective arena into a dynamic one that yields objective information.
Dr. Guyer told OSN,
“This facility, the first U.S. spine-related human movement biomechanics lab
within a private spine practice, is capable of delivering information beyond
the typical imaging and patient-reported data that surgeons must rely on. At
the outset, we primarily worked with scoliosis patients, but have now expanded
to work with those patients undergoing surgery for cervical myelopathy, SI
joint dysfunction, degenerative spinal disease, both cervical and lumbar
artificial disc replacement, and chronic low back pain.” 
Body temp, pulse rate, respiration rate, BP, and…gait!
“Doing a gait analysis is a bit like having a 5th vital sign to work with because it is objective,” states Dr. Guyer. “You can use all of the patient-reported outcomes à la ‘I am a 6 out of 10’ on the pain scale, but gait along with function analysis are measures that the patient has little control over (they largely occur on an unconscious level). We put motion sensors and dynamic EMG electrodes and record the information by high-speed cameras. Then a structural human model analysis is carried out with the computer software that determines the level of function including walking speed, length of steps, balance including sway, etc.”
Digging deeper, he notes, “Electromyography (EMG) is used to measure muscle activity and to determine the extent to which these muscles are contributing to any gait issues. Again, we know what normal looks like, so when the muscles fire, the sensors allow us to see which muscles are functioning at what point during the gait cycle. In addition, we can assess how much energy someone expends (and whether or not they are expending more energy than normal). We then use this information to compare with their pre and post op measurements.”
How big is your cone of economy?
“As for balance, we know what a normal cone of stability looks like and in balance analysis we determine the patient’s cone of economy measurement. If someone has a narrow cone of economy, then that is the most energy efficient way of maintaining posture and increased stability. How much a patient sways and increases his or her cone size, makes them less efficient and less stable. The balance analysis reveals a wealth of information. Using these tools allows us to quantify and compare the patient’s “cone of economy” and balance before and after surgery. Dr Haddas and his team were the first to describe this.”
What the body generates…
“To quantify balance, gait, and other biomechanical functional parameters, we use force plates on the floor and pressure sensors on chairs. This allows us to quantify how much pressure is being put on the surface at any one time and to determine the load symmetry. And when someone rises from a sitting position, it can determine if he or she is favoring one side or another.”
Referring to Cervical Myelopathy patients, Dr. Guyer says, “Dr. Haddas and his team recently published a study indicating that changes in ground reaction forces (delayed heel contact, increased force magnitude, etc.) may suggest why these individuals have difficulty maintaining balance while walking.”
All of this gives patients a sense of empowerment, as well as peace of mind, says Dr. Guyer. “A patient might have the sense that their speed has not accelerated, but the gait analysis says that his or her cadence is faster and that they are taking longer steps. On the surgeon end of things, doing such measurements pre- and postop affords the physician a greater depth of knowledge with which to approach treatment. Gait analysis provides more refined, accurate results than the many outcome measures, including the Oswestry Disability Index.”
Dr. Guyer: “There is an immense psychological benefit for patients to see concrete pre- and postoperative evidence of how they are faring. The extent to which their muscles are functioning, how much their ROM has increased, etc. All of this represents a critical collaboration of the worlds of biomechanics and engineering and spine.”