Diabetes mellitus impairs tendon-bone healing after rotator cuff repair

Abstract

Introduction: Studies have demonstrated a significant decrease in skeletal mass, bone mineral density, and impaired fracture healing in the diabetic population. However, the effect of sustained hyperglycemia on tendon-to-bone healing is unknown.

Materials and methods: Forty-eight male, Lewis rats underwent unilateral detachment of the supraspinatus tendon followed by immediate anatomic repair with transosseous fixation. In the experimental group (n = 24), diabetes was induced preoperatively via intraperitoneal injection of streptozotocin (STZ, 65 mg/kg) and confirmed with both pre- and post-STZ injection intraperitoneal glucose tolerance tests (IPGTT). Animals were sacrificed at 1 and 2 weeks postoperatively for biomechanical, histomorphometric, and immunohistochemical analysis. Serum hemoglobin A1c (HbA1c) levels were measured at 2 weeks postoperatively. Statistical comparisons were performed using Student t tests with significance set at P < .05.

Results: IPGTT analysis demonstrated a significant impairment of glycemic control in the diabetic compared to control animals (P < .05). Mean HbA1c level at 2 weeks postoperatively was 10.6 ± 2.7% and 6.0 ± 1.0% for the diabetic and control groups, respectively (P < .05). Diabetic animals demonstrated significantly less fibrocartilage and organized collagen, and increased AGE deposition at the tendon-bone interface (P < .05). The healing enthesis of diabetic animals demonstrated a significantly reduced ultimate load-to-failure (4.79 ± 1.33 N vs 1.60 ± 1.67 N and 13.63 ± 2.33 N vs 6.0 ± 3.24 N for control versus diabetic animals at 1 and 2 weeks, respectively) and stiffness compared to control animals (P < .05).

Discussion: Sustained hyperglycemia impairs tendon-bone healing after rotator cuff repair in this rodent model. These findings have significant clinical implications for the expected outcomes of soft tissue repair or reconstructive procedures in diabetic patients with poor glycemic control.

Figure 1

Study design. SS, supraspinatus; STZ, streptozotocin; IPGTT, Intraperitoneal Glucose Tolerance Test; IHC, immunohistochemistry, HBA1c – hemoglobin A1c.

Figure 2

Acute rotator cuff repair model. (A) The acromioclavicular joint is divided and the deltoid is split in-line with its fibers to allow atraumatic exposure and isolation of the supraspinatus tendon. (B) A modified Mason-Allen stitch is placed with a 4-0 Ethibond suture in the distal supraspinatus tendon. (C) The tendon is divided directly off the greater tuberosity and the footprint is defined and gently debrided of any residual debris. (D) The sutures are passed via the crossed transosseous bone tunnels and tied over the humeral metaphysis to achieve an anatomic rotator cuff repair.

Figure 3

Induction of diabetes. (A) Area under the curve (AUC) analysis of intraperitoneal glucose tolerance tests (IPGTT) provided a quantitative index of the severity of hyperglycemia. Mean AUC was significantly greater in the diabetic (21, 510 ± 2826) compared to control animals (9,826 ± 1366) (*P = .0001). (B) Mean HbA1c level at 2 weeks postoperatively was significantly greater in the experimental compared to control group and consistent with the diabetic phenotype (10.6 ± 2.7% vs 6.0 ± 1.0%, respectively) (*P = .0001).

Figure 4

Gross appearance of tendon. At the time of sacrifice, the supraspinatus tendon (red arrow) was friable, atrophic, and demonstrated a yellowish discoloration in diabetic animals (A) compared to a more robust, healthy tendon tissue observed in control animals (B).

Figure 5

Fibrocartilage formation. (A) Control enthesis (2 weeks, 40× magnification). (B) Diabetic enthesis (2 weeks, 40× magnification). (C) Quantitative histomorphometry revealed that the diabetic animals had significantly reduced fibrocartilage at the healing enthesis compared to control animals at both 1 and 2 weeks postoperatively (17254 ± 14957µm² versus 61724 ± 10493 µm² and 25025 ± 14705 µm² vs 61000 ± 9175 µm² for 1 and 2 weeks, respectively) (*P < .05).

Figure 6

Collagen birefringence. (A) Control enthesis (2 weeks, 100× magnification). (B) Diabetic enthesis (2 weeks, 40× magnification). (C) Evaluation of collagen birefringence with polarized light microscopy revealed significantly less organized collagen at the tendon-bone interface in the diabetic group compared to control animals at both 1 and 2 weeks postoperatively (13.81 ± 2.28 vs 94.30 ± 13.13 and 30.75 ± 4.97 vs 70.82 ± 11.04 for 1 and 2 weeks, respectively) (*P < .05).

Figure 7. Advanced glycosylation endproducts

Immunohistochemistry was performed to evaluate for differences in the quantity and distribution of advanced glycosylation endproducts (AGEs) in the supraspinatus muscle belly and healing enthesis of (A) control (2 weeks, 100× magnification) and (B) diabetic animals (2 weeks, 100× magnification). Significantly greater advanced glycosylation endproducts (AGE) were noted in both the supraspinatus muscle and its repaired enthesis of diabetic compared to control animals (P < .05).

Figure 8

Ultimate load-to-failure. The tendon-bone complex of diabetic animals demonstrated a significantly reduced mean load-to-failure compared to control animals at both 1 and 2 weeks postoperatively (4.79 ± 1.33N vs 1.60 ± 1.67N and 13.63 ± 2.33N vs 6.0 ± 3.24N respectively) (*P < .05).