Orthopaedic Research Laboratory Alumni Council

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Board of Directors

Richard Debski, Ph.D. President
Caroline Wang, M.S. Secretary
Jamie Pfaeffle, M.D., Ph.D. Treasurer
Doug Boardman, M.D.
Thay Lee, Ph.D.
Patrick McMahon, M.D.
Karen Ohland, M.S.
Christos Papgeorgiou, M.D.
Masataka Sakane, M.D.
Sven Scheffler, M.D.
Jennifer Wayne, Ph.D.

2006 Mr. & Mrs. Kwok-Chong Woo Research Grant

Matthew Chakan
University of Pittsburgh

Proprioception of the Metacarpophalangeal Joint of the Index Finger


Matthew & his advisor Dr. Li with their testing apparatus

FINAL REPORT

Introduction

Carpal tunnel syndrome (CTS) is a degenerative disease that results from the compression of the median nerve in the wrist.   Afflicted patients often experience clumsiness and frequently report unexplainable object dropping.   It is possible that these complications may be partially explained by a reduced awareness of limb position, which may result in misplacement of stabilizing forces during gripping tasks.   Proprioception has been shown to heavily rely on muscle spindle sensory input [1], so degeneration of the neurological pathway should decrease proprioceptive accuracy.   Since the first lumbrical muscle is innervated by the median nerve and acts on the index finger metacarpo-phalangeal joint (MCP), it is likely that proprioception at this joint will be reduced in CTS patients.   This study was performed to quantify the proprioceptive acuity of CTS patients and controls at the MCP of the index finger.   It was hypothesized that CTS patients would have a larger average error than the control group.

Materials & Methods

Nineteen right-handed subjects (nine male, ten female), with an average age of 35.3±14.1 years, without any disorders in the right arm, and three 53.3±1.5 year old right-handed and right-hand affected carpal tunnel syndrome subjects were tested in this study.  The dominant hand was prepared for testing by neutrally splinting the index finger interphalangeal joints, visually estimating the MCP center-of-rotation, and fixing a spindle above the MCP center.  Next, the hand was placed below the testing apparatus, with the wrist in the neutral position, the thumb radially abducted, and the middle, ring, and little fingers in 0° of flexion at all joints.   The subject was then instructed to match the position of their index finger with that of a target, located on the top of the apparatus, by only moving their index MCP and without being able to visualize their finger.   The target was moved to twelve randomly ordered angles, each differing by 10°, from -20° to 90° of flexion.   The subject and target positions were monitored by a customized LabVIEW program (National Instruments, Austin, TX) which interfaced with potentiometers that were attached to rods fixed above the MCP center-of-rotation and the target center-of-rotation.   Two trials were gathered for each subject and the average angular accuracy was calculated at each target angle.   A repeated-measures ANOVA was performed using MINITAB statistical software (Minitab 15, State College, PA) to determine if the normal angular accuracy was dependent on the target angle.  Lastly, the normal population joint accuracy data were compared to the CTS accuracy data.

Results

The nineteen normal subjects were consistent in matching the target (Figure 1), with the majority of subjects exhibiting an absolute error below 10°.  Compared with the finger target, the subjects tended to over-flex their MCP below 40° (p<0.05), while they also tended to under-flex (i.e. over-extend) their MCP above 40° (p<0.05).

Figure 1 .   The nineteen normal subjects' flexion angles (solid lines), compared to the target flexion angles (dashed line).

As Figure 2 shows, the mean normal subject error was low except when the target was positioned above 40°.  The CTS subject error also approximates that of the normal subjects, with little difference between the normal and CTS data.

Figure 2.   Mean angular error of normal subjects (light, solid line) and CTS subjects (heavy, solid line), compared to target accuracies (dashed line).

Discussion

The normal subject results indicate that a subject's proprioceptive accuracy is largely dependent on the target position and that the accuracy is high until the MCP is past 40° of flexion.  Beyond 40°, the normal subjects tended to perceive their index as being more flexed than it actually was.    These same trends were qualitatively observed in the CTS population, despite that the CTS population was too few to allow for statistical comparison against normals.   It seems that proprioceptive capability is not severely affected by CTS, although a large sample size is needed to obtain more conclusive results.   One must be wary of these conclusions, however, as the apparatus was shown to have an error of the same magnitude as the joint angular error [2].

Acknowledgements

The authors thank Margaret Chakan and Sebastian Gehrmann for help with subject recruitment, and the Orthopaedic Research Laboratory Alumni Council for financial support.

References

•  Gandevia, S. et al. (1976). J. Physiology, 260, 387-407.

•  Chakan et al. (2007) Pittsburgh Orthopaedic J. (in press).

 


Matthew with his advisor Dr. Zong-Ming Li

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