Small Subchondral Drill Holes Improve Marrow Stimulation of Rotator Cuff Repair in a Rabbit Model of Chronic Rotator Cuff Tear

Background: Microfracture of the greater tuberosity has been proved effective for enhancing tendon-to-bone healing after rotator cuff repair. However, no standard diameter for the microfracture has been established. Purpose/Hypothesis: This study aimed to assess treatment with large- and small-diameter microfractures to enhance healing during rotator cuff repair surgery in a rabbit model of chronic rotator cuff tear. It was hypothesized that a small-diameter microfracture had advantages in terms of tendon-to-bone integration, bone-tendon interface maturity, microfracture healing, and biomechanical properties compared with a large-diameter microfracture. Study Design: Controlled laboratory study. Methods: Bilateral supraspinatus tenotomy from the greater tuberosity was performed on 21 New Zealand White rabbits. Bilateral supraspinatus repair was performed 6 weeks later. Small-diameter (0.5 mm) microfracture and large-diameter microfracture (1 mm) were performed on the left side and right side, respectively, in 14 rabbits as a study group, and simple repair without microfracture was performed in 7 rabbits as a control group. At 12 weeks later, 7 of 14 rabbits in the study group were sacrificed for micro-computed tomography evaluation and biomechanical testing. Another 6 rabbits were sacrificed for histological evaluation. In the control group, 3 of the 7 rabbits were sacrificed for histological evaluation and the remaining rabbits were sacrificed for biomechanical testing. Results: Significantly better bone-to-tendon integration was observed in the small-diameter microfracture group. Better histological formation and maturity of the bone-tendon interface corresponding to better biomechanical results (maximum load to failure and stiffness) were obtained on the small-diameter microfracture side compared with the large-diameter side and the control group. The large-diameter microfracture showed worse radiographic and histological properties for healing of the microfracture holes on the greater tuberosity. Additionally, the large-diameter microfracture showed inferior biomechanical properties but similar histological results compared with the control group. Conclusion: Small-diameter microfracture showed advantages with enhanced rotator cuff healing for biomechanical, histological, and radiographic outcomes compared with large-diameter microfracture, and large-diameter microfracture may worsen the rotator cuff healing.