Background: A well-defined, reproducible small animal model that allows quantitative assessment of musculotendinous changes would be desirable for investigations concerning rotator cuff pathology.
Methods: The supraspinatus tendon was released by osteotomy of the greater tuberosity in seven New Zealand rabbits. The musculotendinous unit was then allowed to retract during 6 weeks. Retraction was monitored with computed tomography (CT). At sacrifice, CT measurements of retraction were validated by measurement of the total length of the musculotendinous unit after sacrifice and by correlation with functional and structural properties of the musculotendinous unit at tendon release and at sacrifice.
Results: Mean(SD) retraction of the musculotendinous unit was 1.8 (0.2) cm on CT, precisely, and negatively correlated with the total length of the retracted musculotendinous unit at sacrifice (r = −0.87, p = 0.011) but not significantly correlated with CT measurements of atrophy (r = 0.20, p = 0.699) or fatty infiltration (r = 0.13, p = 0.78). Mean (SD) muscle work decreased from 1.6 (0.23) Nm to 1.2 (1) Nm (p = 0.056). Mean (SD) muscle fibre diameter decreased from 65 (10) µm to 48 (16) µm (p = 0.063). This decrease was significantly correlated with the amount of fatty infiltration (r = 0.79, p = 0.033).
Discussion: Tendon release using osteotomy of the rabbit greater tuberosity allows precise measurement of musculotendinous retraction and offers the possibility for functional muscular testing. Changes in the rabbit supraspinatus muscle caused by myotendinous retraction correspond to those observed in established sheep models.