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Quantifying impaired thumb movement in CTS

By Jay D. Lenn

OREF grant recipient seeks new treatment approaches

Carpal tunnel syndrome (CTS) is a common hand disorder that affects an estimated 3.7 percent of the general population in the United States. Although the disorder rarely causes serious disability, it can disrupt common daily activities, require time off from work, and result in substantial medical expenses.

Currently, a diagnosis of CTS relies largely on subjective, qualitative, or nonspecific methods. Zong-Ming Li, PhD, formerly director of the Hand Research Laboratory at the University of Pittsburgh and now with the Cleveland Clinic, received the 2007 Frank E. Raymond Memorial Orthopaedic Research and Education Foundation (OREF) Research Grant for an investigation that may lead to the development of quantitative strategies for diagnosis, rehabilitation, and treatment of CTS. Robert J. Goitz, MD, chief, division of hand and upper extremity surgery, University of Pittsburgh, is co-principal investigator for Dr. Li’s study.

Impaired sensation and motion
CTS occurs when the median nerve is compressed where it passes through the carpal tunnel. The median nerve controls sensation in the palm side of the thumb, index finger, middle finger, and a portion of the ring finger. It also innervates one muscle of the index finger, one muscle of the middle finger, and three muscles controlling the thumb. Compression of the median nerve may cause numbness, tingling, or pain, as well as clumsiness or a lack of dexterity in the hand.

Dr. Li and his colleagues have conducted a number of studies that employ innovative engineering methods to determine the impact of CTS on sensation, muscle function, and sensorimotor integration.

“There’s a lack of quantification about fine motor control in the hand. But it’s so important. We grasp things and pick up things. People with carpal tunnel syndrome drop them for reasons we don’t yet understand,” Dr. Li noted.

With his OREF funding, Dr. Li’s research team is studying thumb kinematics and the impact of CTS on those movements. Their research employs a motion analysis system that can detect and quantify three-dimensional movement of the thumb.

Zong-Ming Li, PhD

Thumb movement—one muscle at a time
The thumb plays a critical role in hand function and provides the motion and strength for grasping and other prehensile tasks.

“This motion results from complicated combinations of flexion/extension, abduction/adduction, and axial rotation of the thumb joints. It requires a delicate coordination of a number of muscles both intrinsic and extrinsic to the hand,” Dr. Li explained.

To break down this complicated activity into individual components, Dr. Li’s research team has devised a cadaveric model to describe thumb motion created by each muscle (Fig. 1).

Fig. 1 Reflective markers attached to a cadaveric thumb enable researchers to isolate and record the function of a single muscle in thumb movement. Courtesy of the University of Pittsburgh and Cleveland Clinic

Cadaveric arm specimens are dissected to expose the eight muscles controlling movement of the thumb. Each muscle-tendon group is overlaid with a pulley system connected by a thread that follows the line of action of that muscle. Tension applied to one pulley system at a time, therefore, simulates the function of a single muscle in thumb movement.

During the experiment, the arm, wrist, and fingers are secured to replicate a neutral, “at-rest” position. Light-sensitive markers, strategically placed on the surface of the thumb and hand, enable a motion analysis system to record the movement of the thumb in three dimensions. The team found that each muscle produced movements in multiple joints and/or in multiple anatomic directions. The distinctive patterns of thumb movement associated with each muscle may subsequently provide relevant data for quantifying impairments in thumb function.

Thumb movement—live
Dr. Li’s study also uses the motion analysis system in clinical tests that record movement of the thumb in patients diagnosed with CTS and age-matched controls. Each participant is tested with the right forearm and wrist secured to ensure uniformity in arm and hand positions. Reflective markers are attached to the skin of each participant in the same pattern as used in the cadaveric study.

Each person performs a specified number of repetitions of two movements (Fig. 2). First, the person starts with the thumb fully extended and then performs opposition by moving it to touch the palm at the base of the little finger and returns it to the original position. The second movement is multiple circular motions performed by rotating the thumb in a large circle.

Fig. 2 A human subject performs specific thumb movements while a motion capture system records the thumb’s kinematics. Courtesy of the University of Pittsburgh and Cleveland Clinic

The comparison of data from the study and control groups enables the researchers to quantify impaired movement associated with CTS. The data analysis also provides methods for judging healthy and impaired joint coordination during movement, such as possible changes in the timing of key events in a movement cycle.

The researchers are also correlating the outcome of motion analysis of the thumb with traditional clinical tools used to diagnose CTS and monitor functional abilities.

Mechanics and the patient
Dr. Li’s education was in engineering mechanics with a focus on musculoskeletal biomechanics and movement science.

“To be able to apply my engineering knowledge to clinical problems—that is the most satisfying thing,” he said.

Dr. Li noted that funding from OREF has played a critical role in advancing his goal of translating data from engineering research models into improved clinical outcomes.

“The pilot data we’re collecting and the insight we have gained will help us tremendously to design a study that is important for the science and important for the clinical obligation of a grant from the National Institutes of Health,” he said.

Jay D. Lenn is a contributing writer for OREF and can be reached at communications@oref.org

To review the AAOS clinical practice guidelines on the diagnosis and treatment of carpal tunnel syndrome, visit www.aaos.org/guidelines

September 2010 Issue