Histologic Differences in Human Rotator CuffMuscle Based on Tear Characteristics

These authors suggest that fatty accumulation in the rotator cuff is associated with shoulder dysfunction and a risk of failure of rotator cuff repair. They sought to (1) describe cellular findings in rotator cuff muscles in patients presenting with varying degrees of rotator cuff tendon pathology by examining fat content and myofiber cross-sectional area of rotator cuff muscles and (2) correlate histologic features to magnetic resonance imaging (MRI) grades according to the Goutallier classification.

Rotator cuff muscle biopsies were performed in a consecutive series of 27 patients with rotator cuff tears undergoing arthroscopic shoulder surgery. Rotator cuffs were graded according to the Goutallier classification and labeled as either partial-thickness or fullthickness.

12 patients without a rotator cuff tear undergoing arthroscopic surgery and having muscle biopsies served as controls.

Patients in the control cohort were younger (mean, 46 years) than those in the study group (mean, 60 years, p < 0.01).

Within the study group, 12 and 15 patients were recorded as having partial and full-thickness rotator cuff tears, respectively.

Lipid accumulation visualized at the cellular level was fairly-to moderately correlated with the Goutallier classification on MRI. Muscle biopsy specimens with a Goutallier grade of 2+ had significantly more lipid accumulation than those with grade-0 or grade-1 fatty accumulation.

Muscle biopsies at the sites of full-thickness tears showed significantly greater lipid accumulation than those associated with either partial or no tears. Partial thickness rotator cuff tears had no difference in lipid accumulation in comparison to the control group.

Muscle biopsy specimens from full-thickness tears had significantly smaller myofiber cross-sectional area when compared with partial thickness tears and controls.

The authors concluded that

(1) cellular lipid accumulation correlates with the MRI Goutallier grade of fatty accumulation;

(2) muscle biopsy specimens from partial-thickness tears are more similar to controls than to those from full-thickness tears, and

(3) full-thickness tears of all sizes showed significantly greater lipid content and smaller myofiber cross-sectional area compared with partial-thickness tears and controls. The residual attachment of partial thickness tears may protect the muscle from fatty accumulation.

Comment: The mechanism for cuff-tear associated muscle deterioration is not known: nerve traction? the effect of aging? disuse? collagen abnormality? If this degeneration is to be prevented, its cause must be better understood. Prevention is important because, as the article below points out, muscle degeneration does not appear reversible after cuff repair.