Arthrometry for Measuring Shoulder Laxity
February 1, 2000 3 minutes read
Arthrometry for Measuring Shoulder Laxity
Abstract & Commentary
Synopsis: KT-1000 arthrometer testing in the shoulder was evaluated with mixed results.
Source: Pizzari T, et al. Measurement of anterior-to-posterior translation of the glenohumeral joint using the KT-1000. J Orthop Sports Phys Ther 1999;29(10):602-608.
While knee laxity has been measured somewhat "objectively" with arthrometry for some time, shoulder laxity or instability has not. The purpose of this study was to determine if glenohumeral laxity could be reliably measured with an arthrometer that is traditionally used for knees. First, the KT-1000 arthrometer was modified by adding 25 mm to the proximal sensor pad by attaching a wooden block to the pad. A single examiner underwent eight hours of training on the arthrometer before the study began. Each subject was placed in the prone position with the arm abducted to 90° and positioned in neutral rotation. The proximal sensor pad of the arthrometer was just distal to the joint line and the distal pad was placed over the scapula (in this position, the pad traditionally called the proximal pad for knee measurements became the distal pad on the arm). Anterior-to-posterior translation was evaluated using a posterior pull (as the patient was positioned prone, this was an upward pull on the arthrometer) with a force of 67 N (15 lb). Two measures were taken that were not recorded to familiarize the subject with the procedure, followed by three recorded measures.
Twenty-eight volunteer subjects were measured bilaterally twice (16 females and 12 males; mean age, 22.1 ± 2.9 years). Analysis included intraclass correlation coefficients (ICCs) to determine test-retest reliability for one examiner (intratester). Dominant shoulder ICC was 0.67, while nondominant shoulder ICC was 0.76. Other findings included large (95%) confidence intervals, which possibly indicate "relatively large amounts of random error." In addition, a two-way analysis of variance (ANOVA) was performed to compare males to females and dominant to nondominant shoulders. Results of this revealed a significant difference between sexes, but no difference with respect to dominance.
Comment by Clayton F. Holmes, EdD, PT, ATC
This study is a good first attempt at quantifying glenohumeral laxity, a clinical condition that has long been difficult to assess and quantify objectively. However, the subject number was low and the confidence intervals too high. In addition, the tester was not blinded at all, to the data or to the subject. This may have contributed significantly to increased intratester reliability. I also take exception to Pizzari and colleagues’ characterization of reliability as "moderate" or "good."
All of these weaknesses notwithstanding, this study is an introduction to a creative and possibly effective way to measure and quantify glenohumeral laxity. Knee arthrometers are readily available and in wide use in outpatient physical therapy settings. However, as Pizzari et al also pointed out, further research is necessary to determine if this arthrometer is applicable to the shoulder. For example, it would be beneficial to assess intertester reliability as well as to evaluate validity by comparing this method of measurement with MRI, fluoroscopy, electromagnetic spatial trackers, ultrasound, and stress radiography. Pizzari et al also must demonstrate the ability to measure anterior laxity, which is the direction most commonly encountered clinically. Then we could better determine whether arthrometry would have a place in the shoulder evaluation.
According to an arthrometry assessment of shoulder laxity, which of the following statements is/are true?
a. The glenohumeral joint is more lax in males.
b. The dominant shoulder is more lax than the nondominant.
c. There was a difference between males and females.
d. a and c are true
e. a, b, and c are true
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