QUANTITATIVE MORPHOLOGY OF ROTATOR CUFF TEARS AND LONG HEAD OF BICEPS TENDON

Participants: R.E. Hughes, J.E. Kuhn, J.C. Carpenter, L.J. Huston, J. Wening, R. Hollis, J. Langenderfer, A. Mell

Keywords: shoulder, rotator cuff, biceps tendon

Introduction

Research has shown that between 5 to 30% of cadaver shoulders have full-thickness tears of the rotator cuff and partial-thickness tears range from 12 to 20%. Although studies have approximately characterized cuff tear size, no studies have reported careful quantitative characterization of the shape and size of rotator cuff tears in cadaver samples. The level of sophistication used to characterize cuff tears has been to classify them into small, medium, and large sizes (Itoi et al., 1995). While a study has reported the involvement of the infraspinatus, supraspinatus, and subscapularis tendons in a tear, the specific relative areas of the tendons involved in the tear has not been reported.

The long head of the biceps tendon may assist in stabilizing shoulders having chronic rotator cuff tears. If such compensation occurs, the biceps tendon should be hypertrophied. Itoi et al. (1995) showed a correlation between biceps tendon width and size of cuff tear, but they did not associate biceps width with involvement of specific portions of the cuff. There are four specific aims of this project: (1) quantitatively characterize the size and location of rotator cuff tears in a sample of cadaver shoulders; (2) quantitatively characterize the diameter of the biceps tendon in the same shoulders; (3) measure the elastic modulus and estimate the ultimate load of the biceps tendons in shoulders with and without cuff tears; and (4) statistically determine whether there is an association between biceps diameter/material properties and the percentage of the supraspinatus, infraspinatus, and subscapularis tendons involved in cuff tears.

Materials and Methods

Sixty-four cadaveric shoulders were used for this study: 19 pairs had bilateral rotator cuff tears (RCT); 8 pairs had one shoulder with RCT and one shoulder normal; 9 unpaired shoulders with RCT. Two analyses were performed: (1) a comparison of biceps size in matched pairs of shoulders where one shoulder has a cuff tear and the other does not; and (2) an investigation of the association between biceps tendon diameter and cuff tear size. The former analysis used the 8 pairs of shoulders having a cuff tear in only one shoulder; the latter analysis used only one shoulder from each pair of shoulders in order to assure statistical independence between observations. The experimental methods consisted of manual dissection of the cadaveric models to isolate the rotator cuff and the biceps tendon for measurement. The outline of the cuff tear was digitized using a probe attached to the sensor of an electromagnetic tracking system (MotionStar, Ascension Technologies, Burlington, VT). Landmarks on the humerus and scapula were also be digitized. A mathematical model was used to quantitatively characterize the percentage of each tendon involved in the lesion. The dimensions of the biceps tendon were measured using digital calipers. In the matched study, the hypothesis that biceps hypertrophy is associated with the existence of a cuff tear was assessed using a paired t-test. The association between cuff tear size and biceps diameter was assessed using Pearson product moment correlation coefficient.

Progress

All specimens have been digitized and biceps measurements taken. Testing of material properties of the biceps tendon remains to be completed.

Results

The average size for all the tears was 4.42 cm² with a range of 0.073 cm² to 19.17 cm². The location of the tear was not uniformly distributed across the rotator cuff (p<0.001). The comparison of biceps size in involved and uninvolved shoulders showed that the biceps tendon was wider in shoulders with full thickness tears than in shoulders without tears (p=0.044).

References

1. Itoi, E., Hsu, H-C, Carmichael, S.W., Morrey, B.F., and An, K-N (1995) Morphology of the torn rotator cuff. J. Anatomy 186: 429-434.