Early healing of flexor tendon insertion site injuries: Tunnel repair is mechanically and histologically inferior to surface repair in a canine model

Abstract

Orthopedic injuries often require surgical reattachment of tendon to bone. Tendon ends can be sutured to bone by direct apposition to the bone surface or by placement within a bone tunnel. Our objective was to compare early healing of a traditional surface versus a novel tunnel method for repair of the flexor digitorum profundus (FDP) tendon insertion site in a canine model. A total of 70 tendon-bone specimens were analyzed 0, 5, 10 or 21 days after injury and repair, using tensile and range of motion mechanical testing, histology and densitometry. Ultimate force (a measure of repair strength) did not differ between surface and tunnel repairs at day 0. Both repair types had reduced strength at 10 and 21 days compared to 0 days, indicative of deterioration of suture grasping strength (tendon softening). At 21 days, tendons repaired in a bone tunnel had 38% lower ultimate force compared to surface repairs (p ¼ 0.017). Histological findings were comparable between repair groups at 5 and 10 days but differed at 21 days, when we saw evidence of maturation of the tendonbone interface in the surface repairs compared to an immature fibrous interface with no evidence of tendon-bone integration in the tunnel repairs. After accounting for bone removed by the tunnel, no difference in bone mineral density or trabecular bone volume existed between surface and tunnel repairs. If the results of our animal study extend to healing of the human FDP insertion, they indicate that FDP tendons should be reattached to the distal phalanx by suture to the cortical surface rather than suture in a bone tunnel. ß

Alendronate prevents bone loss and improves tendon‐to‐bone repair strength in a canine model

“…20 We previously demonstrated significant bone loss and decreased mechanical properties of the repaired tendon-bone complex in the first 21 days after flexor tendon insertion site injury and repair in a canine model. 4,6 We also observed increased osteoclast surface and normal rates of bone formation, indicating that bone loss was due to excessive bone resorption. Therefore, our goal in this study was to suppress bone loss after insertion site repair using alendronate 18 in an attempt to prevent the decrease in biomechanical properties.…”

“…6 All animal procedures complied with the Animal Studies Committee of Washington University and with the policies of the NIH. Each dog had the second and fifth FDP tendons injured and repaired.…”

“…Although this proximal tendon cut reduces the clinical impact of this initial study, it was done to remove repair site tension as a variable 8 and to match the conditions of the control group. 6 Postoperatively, forelimbs were subjected to passive motion rehabilitation. 6 Dogs received a daily oral dose of alendronate (2 mg/kg).…”

“…4,5 Experimental studies on flexor tendon to distal phalanx repair indicate that mechanical properties decline over the first 21 days of healing. 4,6 These findings demonstrate the need for improvement in the treatment of flexor digitorum profundus (FDP) tendon-to-bone insertion site injuries. The first 3 weeks of healing are especially critical, as the repair is prone to gap formation and failure during this interval.…”

“…Therefore, our goal in this study was to suppress bone loss after insertion site repair using alendronate 18 in an attempt to prevent the decrease in biomechanical properties. We hypothesized that: (1) systemic alendronate would reduce bone loss and lead to improved biomechanical properties compared to historical controls not treated with alendronate, 6 and (2) the addition of a local dose of alendronate 20 would have an additional effect in suppressing bone loss leading to a further improvement in biomechanical properties.…”