Precision of Palpatory Location of Skeletal Landmarks in Three Dimensions

Eric Potocki, BS
Edward Owens, MS, DCABSTRACT

Introduction: Surveys of chiropractors have shown that palpation methods are in common use and are relied on for making clinical decisions related to patient care (1). At least three different palpatory methods have been traditionally used by chiropractors as indicators of the need for chiropractic adjustment: static palpation of vertebral alignment and tenderness, motion palpation for passive movement characteristics and muscle palpation to detect muscle tone imbalances. The reliability and validity of motion palpation (MP) has been frequently studied. While MP seems to have good face validity, it is considered to have limited objectivity. Keating performed a meta-analysis of the available literature on MP in 1989 and concluded that no strong claims for the objectivity of lumbar motion palpation could be made at that time (2). Keating showed that studies of MP demonstrated very little reliability, were limited in their number of examiners, and suffered from an over reliance on asymptomatic students as palpatory subjects.

An interesting finding from reliability studies is that while inter-examiner reliability is typically low, intra-examiner agreement is generally good, i.e. assessors often agree with their own measures. Breen suggested that some of the error might be due to examiners simply misnaming the involved segment (3). Panzer came to similar conclusions in a more recent review of the motion palpation literature, and offered the suggestion that improved standardization of palpatory techniques be carried out (4).

One study performed at this institution found poor inter-examiner and intra-examiner reliability for a particular type of muscle palpation that is used in the curriculum as a way to assign vertebral misalignment listings (5). As a follow-up to that study, we are considering the palpation procedure as two separate tasks: locating the structure of interest, and sensing the tissue texture or joint flexibility. In the current pilot study we have developed a way to test examiners' ability to locate skeletal landmarks by palpation.

Methods: Four students were asked to digitize the locations of the left and right mastoid processes and the external occipital protuberance (EOP) on a student volunteer using a three dimensional digitizer, the Microscribe 3D, [Immersion Corporation, San Jose, CA]. The subject was positioned prone on a HI-LO table adjacent to the Microscribe. The students were given instructions into the proper usage and limitations of the arm of the digitizer before the test and were allowed to warm up or practice finding and digitizing points on a variety of objects until they felt comfortable using the equipment while palpating. With the stylus tip of the digitizer placed on the palpation finger, students found and marked what they felt were the desired points, then depressed a footpad to insert a three dimensional coordinate into an excel spreadsheet. These points of interest were found from left to right i.e. left mastoid, EOP, right mastoid. Each student had four attempts to locate the desired points, two warm-up trials and two test trials. After this simple procedure the collected data were plotted and analyzed for precision of point location between all the students. Results: Preliminary findings on bony landmark location indicate a good degree of inter-examiner precision. On nearly all the points of interest students were within a five-millimeter range. Table 1 provides the statistical description of the 3D locations for each landmark that was digitized. Figure 1 is a plot of two dimensions (x and y, the horizontal plane) of the digitized locations. In this figure all eight attempts overlaid. Notice the tight clustering of the locations.

Structure x-coord (range mm) y-coord (range mm) z-coord (range mm)
Left Mastoid 5.81 2.97 6.98
EOP 2.62 3.60 2.21
Right Mastoid 2.87 2.02 8.07

Discussion: Preliminary results show that our method of digitizing works well for determining where individual examiners perceive the points in question to be located on a subject. As our data shows, the information can be readily used to cross-examine palpation findings to enhance precision. For prominent bony landmarks our test-palpators, all fourth-quarter students, seemed to be able to recognize the same five mm area. Our plan is to test examiner precision on consecutively less prominent structures such as points of muscle attachment, transverse processes of cervical vertebrae or even recognition of cervical segmental level (associated with TPs or spinouses).

Conclusion: Based on our test results so far we feel that the Microscribe 3D is a novel and effective tool for more precise understanding of what structures chiropractors are palpating when performing a spinal exam. We feel that this knowledge will better our understanding of the frequent inter-examiner palpation discrepancies so that ultimately improvements can be made in the reliability of palpation as a tool for subluxation analysis.


  1. Walker BF. Most Common Methods Used in Combination to Detect Spinal Subluxation. A Survey of Chiropractors in Victoria. Australasian Chiropractic & Osteopathy. 1998 NOV. 7(3). pp 109-11.
  2. Keating J. Inter-examiner reliability of motion palpation of the lumbar spine: a review of the quantitative literature. Am J Chiropractic Med 1989;2:107-110.
  3. Breen A. The reliability of palpation and other diagnostic methods. Journal of Manipulative And Physiological Therapeutics. 1992; 15(1): 54-56.
  4. Panzer DM. The reliability of lumbar motion palpation. Journal of Manipulative And Physiological Therapeutics. 1992; 15(8): 518-523.