Assessing the Outcomes of Spine Surgery Using Global Positioning Systems

Barzilay Yair, MD; Shoval Noam, PhD; Liebergall Meir, MD; Auslander Gail, PhD; Birenboim Amit, MA; Isaacson Michal, MA; Alexander R. Vaccaro, MD, PhD; Kaplan Leon, MD*


Spine. 2011;36(4):E263-E267. 

In This Article

Abstract and Introduction


Study Design. Pilot study.
Objective. To examine whether surgical outcomes can be assessed objectively by advanced tracking technology, based on Global Positioning Systems (GPS).
Summary of Background Data. Outcome studies are the commonest way to assess the results of surgical procedures. The success of these efforts is impeded by a number of factors, including the lack of valid outcome measures, difficulty in assessing changes in patients' expectations (response shift) and confounding effects of secondary gains.
Methods. The measurement of walking speed, distances, and number of walking events per day, claudication index (maximal walking distance), characteristics during motorized trips, and the amount of time spent outdoors were monitored in 2 patients undergoing spine surgery for several weeks using advanced tracking technologies.
Results. In 1 patient, all parameters increased progressively from the time of surgery to the end of the recording period. These findings were consistent with her recovery from surgery. In a second patient, tracking showed the patient's difficulty in mobilizing, leading to the diagnosis of another orthopedic problem, and to total hip replacement surgery.
Conclusion. The technology presented in this pilot appears to be useful in understanding a patient's level and breathe of activity. These data will assist in better understanding the limitations imposed by specific musculoskeletal pathology and in monitoring perioperative function and complications and their related causes. Spatial data may indirectly reflect a patient's social and mental conditions. This interdisciplinary pilot may lead to the development of valid outcome measures for a range of medical conditions. Studies comparing questionnaires to this new outcome measure may shed light on issues like response shifts and secondary gain. Norms and clusters of spatial behaviors in different pathologies may enable better patient selection for medical, mental, and surgical interventions.


The outcome of surgery can be assessed in various ways. Data can be obtained from various persons—the patient, the treating physician, or an independent observer[1] and using various methods (questionnaires, observations, measures of physical performance, radiographs). The quality of data obtained by these methods varies.

Ideally, an outcome tool should be valid, simple, quick, reliable, reproducible, and sensitive to change.[2] One of the most popular ways of measuring outcomes is through the use of self administered questionnaires. They include the following 3 major types: general health,[3] disease specific,[4] and patient satisfaction. Many of the commonly used outcome questionnaires in orthopedic surgery (for example, that of Harris)[5] have never been validated. Moreover, although they may be reliable, patients' self assessments do not necessarily reflect their actual condition. For example, in 1 study, patients with intermittent claudication due to lumbar spinal canal stenosis were asked to assess their walking distances. Although self-reports yielded a wide range of walking abilities, most patients were able to walk the same distance of about 200 m. This raises questions about the validity of patient self-report questionnaires in this area.[6] A response shift is a psychological change in one's perception of the quality of life following a change in health status. The idea goes back to the days of Plato.[7] This phenomenon initially was recognized in patients with terminal diseases who, despite a worsening of the physical condition, did not necessarily report deterioration in quality of life—a positive response shift.[8] Response shift was recently studied in total knee arthroplasty—a negative response shift,[9,10] and the basis for its study in spine surgery has been described,[11] with a review of current data in orthopedic and spine surgery published recently.[12] This psychological process, resulting in a change in the expectations of people when compares between the pre- and the postoperative period, leads to lower scores in commonly used outcome measures and does not "objectively" reflect patients' condition when the problem was not resolved completely by surgery.[12]

Other measures may be more objective, but are dependent on interpretation by skilled diagnosticians and are both costly and technically demanding.[13] Furthermore, most of these tests are carried out in clinical settings under controlled conditions, i.e., controlled speed, flat surface, in the presence of trained staff (for example, Get Up and Go, Shuttle test, walking treadmill test). In order to understand the full impact of the intervention, it is important to obtain data in real-life conditions. These, of course, vary from patient to patient.

In recent years, the rapid development and increased availability of small, inexpensive, and reliable tracking devices have led to a growing volume of spatial research using such technologies.[14] Global Positioning Systems (GPS) devices offer researchers the opportunity for continuous and intensive high-resolution data collection in time (seconds) and space (meters) for long periods of time. GPS and other tracking technologies are now used in a wide variety of fields including tourism,[15,16] environmental health,[17,18] and medical areas such as Alzheimer disease,[19,20] physiology,[21] and peripheral vascular disease.[13] Importantly, they allow to measure patients' behaviors in their natural environment.

The purpose of this pilot study was to examine the ability of GPS technology to serve as a tool to measure outcome of spine surgery regarding out of home activities.