Intra-articular depth gauge increases accuracy in measuring rotator cuff tears

Cadaveric and clinical study finds the device is more useful than existing methods.

Issue: September 2006

HOLLYWOOD, Fla. — The common algorithms for measuring partial-thickness rotator cuff tears are losing ground as surgeons turn to devices, like the intra-articular depth gauge, for more accurate measurements.

Many such algorithms are based on historic anatomic data. For example, one conventional method assumes total tendon thickness is always 12 mm. Surgeons repair partial-thickness rotator cuff tears if the exposed footprint represents more than 50% of the total tendon thickness, or 6 mm, according to Ian K.Y. Lo, MD, of the University of Calgary in Alberta, Canada.

However, he added, the wide range of tendon thicknesses and variability in footprint anatomy can lead to improper decision-making with such algorithms.

"Our current recommendation really should be scrutinized — the 50% rule, the 6-mm rule — because these were based on comparison to a normal size," Lo said at the Arthroscopy Association of North America 25th Annual Meeting.

Cadaveric and clinical studies

In a cadaveric and clinical study comparing a conventional method with a method using the intra-articular depth gauge, Lo found that the device was more accurate and more useful in a clinical setting for individualized treatment.

The intra-articular depth gauge consists of two pieces, including a pointed inner rod, Lo said.

Using that rod, surgeons can penetrate the lateral intact portion of the rotator cuff, while the other position on the guide allows the surgeon to determine the total tendon thickness.

Lo first performed a cadaver study on eight fresh-frozen shoulders, creating partial-thickness rotator cuff tears of different sizes. Another surgeon arthroscopically evaluated each tear by comparing to a shaver and by using an intra-articular depth gauge. He noted the amount of footprint exposed, the total tendon thickness and the percentage of tendon thickness torn, Lo said.

Lo then dissected the shoulders and determined their true anatomic measurements. He found the mean true amount of footprint exposed was 7 mm (range, 5 mm to 10 mm), the mean true total tendon thickness was 13 mm (range, 10 mm to 22 mm), and the mean true percentage of tendon thickness torn was 54% (range, 33% to 70%).

Upon comparison, the conventional treatment algorithm measurements and the true measurements were close for measuring the exposed footprint, Lo said. But total tendon thickness and percentage of thickness involved did not correlate well between the conventional method and true measurements.

"However, when you use the intra-articular depth gauge vs. the true measurement, we were good at measuring the exposed footprint, relatively good at measuring the total tendon thickness and also relatively good at measuring the total tendon thickness involved," Lo said.

For the clinical study, Lo identified 32 patients — mostly men — with partial-thickness rotator cuff tears and found measurements similar to those in the cadaveric study.

Using the intra-articular depth gauge, Lo found the mean exposed footprint was 10 mm (range, 0 mm to 18 mm), the mean total tendon thickness was 14 mm (range, 10 mm to 19 mm) and the mean percentage of tendon thickness torn was 65% (range, 0 % to 95%).

Treatment algorithm changed

"When we used the intra-articular depth gauge in contrast to the use of a standard measurement tool, we changed our treatment algorithm," Lo said. "That is, four of our patients were actually debrided instead of repaired and three were repaired instead of debrided ... This information may be useful for individualized treatment."

Lo said he plans to conduct a randomized trial on the intra-articular depth gauge and provide a recommendation for using the device to treat partial-thickness rotator cuff tears.

For more information:
Lo IKY. The use of an intra-articular depth gauge in the measurement of partial thickness rotator cuff tears. #SS-25. Presented at the Arthroscopy Association of North America 25th Annual Meeting. May 18-21, 2006. Hollywood, Fla.