Are you using PRECISE measures?

Ankle Anterior Drawer in Prone

Are you using PRECISE measures?



Orthopedics is about precision.  Why do we wiggle a joint and subjectively draw a conclusion about its instability?  We need to do better.  Research has demonstrated digital inclinometers are a more accurate method of assessment (6° minimum significant difference) of knee range of motion than long arm goniometers (minimum significant different of 10°).1  Likewise, studies have shown that handheld dynamometry is superior to isokinetic testing, manual muscle testing, and externally fixed dynamometry.2,3    Handheld dynamometers are portable and cost effective with strong concurrent validity and excellent reliability for isometric muscle strength assessment.2,3  As a clinician, I have found handheld dynamometers to be invaluable for strength testing.  Muscle testing grades of 4(-), 4, 4(+), and 5 are highly variable.  Numbers displayed on a dynamometer are much more discerning when it comes to assessing both current status and progress.  Being able to calculate a percentage of strength deficits and improvements in strength gains allow for the documentation of objective data.  These are both examples demonstrate how technology can provide precise measurements for better orthopedic care.


The desire to contribute to the enhancement of objectivity in orthopedics has led me along a fascinating (and somewhat tumultuous) journey to develop the Mobil-Aider arthrometer.  Through years of teaching orthopedic manual skills and clinical practice, I struggled with the fact that there was no device to quantify joint mobility.  Studies have reported fair to good intra-rater reliability but poor inter-rater reliability.  Thus, each person may be consistent but between people, there is great variability.  Replicating techniques become a significant problem when trying to assess the effectiveness of manual therapy interventions.  If you take a CPR course, you do manual compressions until you hear a “click.”  That auditory feedback lets you know you are pushing to sufficient depth.  If you don’t hear a “click,” you know to push harder.  Immediate auditory or visual feedback is very important in skill acquisition.4  So why can’t we quantify joint mobility? 


My experience in the academic lab included instructing students in manual techniques. I demonstrated the task.  They mimic what I did while I provided feedback. 

Problem 1: I had no way of knowing the feel of their grip or the magnitude of the translation if they were not do the technique on me. 

Problem 2: I had no way of knowing what they were feeling and they struggled to explain it. 

Imagine a student (or novice clinician) doing an inferior glide of the shoulder.  I would ask, “Do you feel the capsular endfeel?”  “Do you feel how the inferior glide comes to a soft stop but as you maintain consistent pressure, the glide creeps a little more?”  Of course, if you have felt this before, you understand the description and how to perform the task.  However, if you have not, it can be challenging to appreciate the “feel.”  If the student had a device interfaced between their hands and the patient (or lab partner) and if one were able to say, “when you get to 5 mm of translation, do you feel how you begin to encounter some resistance to the inferior glide?”  The student would then be instructed to maintain the pressure and watch the numbers on the arthrometer increase by 0.5 to 1 mm as the “creep” of the capsular endfeel occurs.  With the “coaching” and the visual feedback, the mastery of the psychomotor task is enhanced.  Equally as important, the student would now have a way to continue to practice correctly when the faculty member is not present.  This was the driving force for the development of the Mobil-Aider arthrometer.


Through the development process (funded by the National Science Foundation), I learned about customer acquisition and the value of listening to the pain points of the consumer.  This is where the scope of the Mobil-Aider expanded into ligamentous stability testing.  We have published 8 studies on the validity and reliability to date.  I would like to highlight two studies that are important in appreciating the value of technology and obtaining objective data. 


Mobil-Aider kneeOne study5 was “Use of a New Arthrometer to Assess Knee Pathology.”  The Lachman test was used with the Mobil-Aider to examine ACL laxity.  The mean difference between the involved and uninvolved knees were -0.18, 2.05, and 3.38 mm for intact, partial tear, and complete tear as identified on MRI, respectively.  Thus, the Mobil-Aider allowed the user to distinguish millimeters of differences between extremities.  This is valuable information.  Many of you may remember the KT1000 device.  It was a large apparatus (fit in a roller bag type case) that could only be used on the knee.  It also had several problems.  There was a hard plastic piece that had to be pressed down onto the patella for stabilization and the handle used for the tibial translation pulled the device away for the tibia (introducing measurement error).  The Mobil-Aider design addressed these points and is valid within 5% of measurement.


Ankle Anterior Drawer in ProneLikewise, a study6 entitled “Assessing Lateral Ankle Sprains with a New Arthrometer” identified significant differences between the control and grade I and grade II ankle sprain groups.  There was ± 0.31 mm difference in anterior translation (anterior drawer) between healthy ankles. Whereas there was 1.11 mm and 2.16 mm difference between ankles in grade I and grade II sprains, respectively.  This is consistent with stress radiographs.  Despite the manual anterior drawer test being convenient, the subjectivity makes it unreliable.  A difference of a bit over 1 millimeter could impact the clinical decision to treat with an aircast versus a boot.  By comparing the data of the injured to uninjured extremity, we mitigate the variability of what is “normal.”


Both of these studies are just the beginning of the potential to populate the literature with objective data about joint mobility/laxity.  The use of the Mobil-Aider arthrometer is the future of evidence-based orthopedics.  If you would like to learn more about the Mobil-Aider arthrometer, please visit:


  1. Hancock GE, Hepworth T, Wembridge K. Accuracy and reliability of knee goniometer methods. BMC Musculoskeletal Disorders. 2013;14(17)
  2. Cadogan A, Laslett M, Hing W, McNair P, Williams M. Reliability of a new hand-held dynamometer in measuring shoulder range of motion and strength. Manual Therapy. 2011; 16(1):97–101.
  3. Romero-Franco N, Fernandez-Dominguez JC, Montano-Munuera JA, Romero-Franco J, Jimenez-Reyes P. Validity and reliability of a low-cost dynamometer to assess maximal isometric strength of upper limb. Journal of Sports Science. 2019;37(15):1787–1793.
  4. Wulf G, Shea C, Lewthwaite R. Motor skills learning and performance: A review of influential factors. Medical Education. 2010;44(1):75-84.
  5. Hammoud S, Palombaro K, Gulick DT. Use of a New Arthrometer to Assess Knee Pathology. Global Journal of Orthopedic Research. January 2022
  6. Taweel NR, Gulick DT, Palombaro KM. Assessing Lateral Ankle Sprains with a New Arthrometer. March 2022, publication pending


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