Fatty infiltration of the torn rotator cuff worsens over time in a rabbit model.

PURPOSE: The purpose of this investigation is to document quantitatively and qualitatively the changes that occur over time in the rotator cuff muscle after surgical detachment, simulating a chronic, unrepaired rotator cuff tear.
METHODS: The supraspinatus muscle was unilaterally detached from the greater tuberosity in 20 New Zealand white rabbits. All tendons were tagged and retracted from the insertion on the greater tuberosity. Five rabbits were killed at each designated time interval of 6 weeks, 3 months, 6 months, or 1 year after surgery. All animals underwent whole-body perfusion at the time of death for tissue preservation. Gross and histologic evaluations were performed to quantify the progression of fatty infiltration over time.
RESULTS: Loss of muscle and fatty infiltration were evident 6 weeks after detachment of the supraspinatus tendon. The fatty infiltration increased over time from 6 weeks to 1 year (P = .002, analysis of variance). The fatty infiltration was most pronounced near the supraspinatus insertion, and it progressed from the musculotendinous junction toward the muscle origin (Pearson correlation, r = -0.51; P < .0001).
CONCLUSIONS: In this rabbit model of a surgically created rotator cuff tear, fatty infiltration is a progressive, infiltrative process that increases over time in the unrepaired rotator cuff. In addition, the muscle atrophy and fatty infiltration seen in rotator cuff tears progress from the musculotendinous junction toward the muscle origin. CLINICAL RELEVANCE: This animal model of a chronic rotator cuff tear shows that fatty infiltration of the supraspinatus muscle appears as early as 6 weeks and worsens over time in the unrepaired rotator cuff. This may have implications on both the timing and management of rotator cuff tears.