Orthopaedic Research Laboratory Alumni Council

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Visit the research laboratories of the alumni of Dr. Woo.

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.

2008 Mr. & Mrs. Kwok-Chong Woo Research Grant

Andrew Brown
University of Pittsburgh

Measurement of In Vivo Glenohumeral Joint Translations


Andrew with his advisor, Dr. Rich Debski

Acknowledgement

I believe that establishing an objective physical exam for diagnosing shoulder pathologies remains challenging, however many of the obstacles we face today are similar to those faced in the development of the Lachman test and the KT-1000 many years ago. Thus, I would like to thank ORLAC and the Woo family for enabling me to perform this exciting and important research over the summer of 2008 with the goal of ultimately overcoming the challenges that this research faces. I would also like to thank everyone else at the MSRC for serving as early research subjects and providing me with invaluable feedback throughout all stages of this study.

Final Report

Significance and Objectives

Surgical repair for shoulder instability has a high rate of poor patient outcome following surgical repair, which may be due largely to the numerous types and varying extents of joint pathologies resulting from dislocation and the difficulty in accurately diagnosing them. [1,2,3] The location and extent of many of these injuries cannot be determined using diagnostic imaging techniques. Thus, clinicians perform physical diagnostic exams by applying a force to the humerus and attempting to measure the translation with respect to the scapula. However, these tests are highly subjective and may result in incorrect or insufficient diagnoses and consequently ineffective surgical repairs [4].

In order to improve clinicians' diagnostic proficiency, an exam must be developed that is standardized, to allow comparisons across clinicians and examinations, sensitive, in order to detect pathologies when it exists and specific, in order to detect the type and extent of the pathology present. Establishing the actual diagnostic criteria for this will involve performing this optimal test on a wide population with both normal and injured shoulders, which will require the measurement of joint translation in an accurate and repeatable fashion.

My goal for this project was to develop a motion analysis based methodology capable of accurately and repeatably measuring in vivo glenohumeral joint translations at the millimeter level. My specific objectives were to:

  • Determine the appropriate motion analysis system for measuring translations in a clinical environment
  • Construct a shoulder positioning device to fix the joint to a standardized orientation
  • Quantify the accuracy and repeatability of the motion tracking protocol during simulated clinical exams

Development of Motionn Analysis System and Shoulder Positioning Device

Flock of Birds, a magnetic based motion tracking system was used to measure shoulder motion. The system could be set up so that the major axes of measurement corresponded to the anatomical axes of the test subjects allowing simplification of translation calculations. The z-displacement of the Flock of Birds receiver was considered to represent anterior-posterior (A/P) humeral translation with respect to the thorax and was the only translation component studied. (Figure 1)


Figure 1: Binding free energy of the complexes of CaM and Fas over the 30 ns molecular dynamics simulations with the exclusion of the entropy term.

A device to stabilize the arm was an important requirement of accurately tracking humeral motion. The major design criteria of the Shoulder Positioning Apparatus (SPAR) were to repeatably position a subject's arm at a variety of joint angles, to stabilize and support various sized arms to allow muscle relaxation and to be metal-free. (Figure 2) Given these criteria, PVC pipe was chosen because it is non-metallic, easily adjusted to various rotations and inexpensive, allowing various size pieces to be used for varying arm lengths The elbow and armrest portion of the SPAR is completely adjustable allowing for subjects' full ranges of internal/external rotation to be examined, while varying the position and vertical support pipe length of the SPAR allowed different sized arms to be tested.


Figure 2. Experimental setup with the Shoulder Positioning Apparatus seen in blue.

Repeatability of Simulated Clinical Exam

Using a constant shoulder position of 90 abduction and neutral rotation and, a single clinician placed a Flock of Birds receiver on the bicipital groove of the humerus. The receiver was then fully depressed into the skin and 6 cycles of A/P loading were performed. The clinician attempted to limit forces in other directions as this would affect the magnitude of translation measured This procedure was repeated for a total of three trials. A total of four subjects (2 Male/2 Female, Age 23 ± 1.3) were examined. Intra-observer repeatability was determined to be 1.7mm by calculating the standard deviation of the three reported translations for each subject.

Conclusions

Flock of Birds was found to be capable of accurately performing in the experimental environment and was non-invasive for both the patient and clinician. A shoulder positioning apparatus was designed to stabilize the arm and performed satisfactorily in preliminary tests. Finally, clinical exams were simulated on four shoulders and it was determined that using the current methodology, the clinical exams were repeatable to under 2mm of anterior-posterior humeral translation. Additionally, our measured translations compare well with those found in the literature. [6,7]

While we found that we were displacing the Flock of Birds receiver in a repeatable manner, it is unknown how much of this displacement was truly glenohumeral translation and how much was due to the effects of soft tissue, lack of stabilization of the scapula and differences in applied load. This remains a significant challenge to accurately measuring glenohumeral translations in vivo and diagnosing instability.

Future directions will include addressing the limitations of the SPAR and examining the effect that factors, such as joint position, gender, age or activity level have on glenohumeral translations. Finally, we hope to use this system to determine the difference between injured and non-injured shoulders in order to create objective diagnostic criteria that will allow surgeons to better detect and treat shoulder pathologies following dislocation.

References

  1. L Hovelius. Clin Orthop, 1982.
  2. SRA Arciero et al. AJSM, 1994.
  3. HL McLaughlin, DI MacLellan. J Trauma, 1967.
  4. L Hovelius et al. JBJS Am, 1996.
  5. M Bahk et al. AJSM, 2006.
  6. D Magit et al. AJSM, 2008.
  7. MT Reis et al. CORR, 2002.

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