Background: More than 450,000 rotator cuff repairs are performed annually, yet healing of tendon to bone often fails. This failure is rooted in the fibrovascular healing response, which does not regenerate the native attachment site. Better healing outcomes may be achieved by targeting inflammation during the early period after repair. Rather than broad inhibition of inflammation, which may impair healing, the current study utilized a molecularly targeted approach to suppress IKKβ, shutting down only the inflammatory arm of the nuclear factor κB (NF-κB) signaling pathway. Purpose: To evaluate the therapeutic potential of IKKβ inhibition in a clinically relevant model of rat rotator cuff repair. Study Design: Controlled laboratory study. Methods: After validating the efficacy of the IKKβ inhibitor in vitro, it was administered orally once a day for 7 days after surgery in a rat rotator cuff repair model. The effect of treatment on reducing inflammation and improving repair quality was evaluated after 3 days and 2, 4, and 8 weeks of healing, using gene expression, biomechanics, bone morphometry, and histology. Results: Inhibition of IKKβ attenuated cytokine and chemokine production in vitro, demonstrating the potential for this inhibitor to reduce inflammation in vivo. Oral treatment with IKKβ inhibitor reduced NF-κB target gene expression by up to 80% compared with a nontreated group at day 3, with a subset of these genes suppressed through 14 days. Furthermore, the IKKβ inhibitor led to enhanced tenogenesis and extracellular matrix production, as demonstrated by gene expression and histological analyses. At 4 weeks, inhibitor treatment led to increased toughness, no effects on failure load and strength, and decreases in stiffness and modulus when compared with vehicle control. At 8 weeks, IKKβ inhibitor treatment led to increased toughness, failure load, and strength compared with control animals. IKKβ inhibitor treatment prevented the bone loss near the tendon attachment that occurred in repairs in control. Conclusion: Pharmacological inhibition of IKKβ successfully suppressed excessive inflammation and enhanced tendon-to-bone healing after rotator cuff repair in a rat model. Clinical Relevance: The NF-κB pathway is a promising target for enhancing outcomes after rotator cuff repair.

Nonunion is defined as the permanent failure of a fractured bone to heal, often necessitating surgical intervention. Atrophic nonunions are a subtype that are particularly difficult to treat. Animal models of atrophic nonunion are available; however, these require surgical or radiation‐induced trauma to disrupt periosteal healing. These methods are invasive and not representative of many clinical nonunions where osseous regeneration has been arrested by a “failure of biology”. We hypothesized that arresting osteoblast cell proliferation after fracture would lead to atrophic nonunion in mice. Using mice that express a thymidine kinase (tk) “suicide gene” driven by the 3.6Col1a1 promoter (Col1‐tk), proliferating osteoblast lineage cells can be ablated upon exposure to the nucleoside analog ganciclovir (GCV). Wild‐type (WT; control) and Col1‐tk littermates were subjected to a full femur fracture and intramedullary fixation at 12 weeks age. We confirmed abundant tk+ cells in fracture callus of Col‐tk mice dosed with water or GCV, specifically many osteoblasts, osteocytes, and chondrocytes at the cartilage‐bone interface. Histologically, we observed altered callus composition in Col1‐tk mice at 2 and 3 weeks postfracture, with significantly less bone and more fibrous tissue. Col1‐tk mice, monitored for 12 weeks with in vivo radiographs and micro–computed tomography (μCT) scans, had delayed bone bridging and reduced callus size. After euthanasia, ex vivo μCT and histology showed failed union with residual bone fragments and fibrous tissue in Col1‐tk mice. Biomechanical testing showed a failure to recover torsional strength in Col1‐tk mice, in contrast to WT. Our data indicates that suppression of proliferating osteoblast‐lineage cells for at least 2 weeks after fracture blunts the formation and remodeling of a mineralized callus leading to a functional nonunion. We propose this as a new murine model of atrophic nonunion. © 2021 American Society for Bone and Mineral Research (ASBMR).

Proximal median nerve compression can be seen in association with cubital tunnel syndrome. Careful evaluation of the reported symptoms as well as thorough clinical examination are the keystone of the correct diagnosis. Also, on the basis of this study, we believe that concurrent decompression can be performed through a single medial incision, though extensive dissection may be required.

Nonunion is defined as the permanent failure of a fractured bone to heal, often necessitating surgical intervention. Atrophic nonunions are a subtype that are particularly difficult to treat. Animal models of atrophic nonunion are available; however, these require surgical or radiation induced trauma to disrupt periosteal healing. While these approaches can result in nonunion, such invasive methods are not representative of many clinical nonunions where osseous regeneration has been arrested by a “failure of biology”. We hypothesized that arresting osteoblast cell proliferation after fracture would lead to atrophic nonunion in mice. Using mice that express a thymidine kinase (tk) ‘suicide gene’ driven by the 3.6Col1a1 promoter (Col1-tk), proliferating osteoblast lineage cells can be ablated upon exposure to the nucleoside analog ganciclovir (GCV). Wild-type (WT; control) and Col1-tk littermates were subjected to a full femur fracture and intramedullary fixation at 12 weeks old. Post injury, mice were dosed with GCV twice daily for 2 or 4 weeks. Histologically, we confirmed abundant tk+ expression in fracture callus, and diminished periosteal cell proliferation in Col1-tk mice at 3 weeks post fracture. Moreover, Col1-tk mice had less osteoclast activity, mineralized callus, and vasculature at the fracture site compared to WT mice. Additional mice were monitored for 12 weeks with in vivo radiographs and microCT scans, which revealed delayed bone bridging and reduced callus size in Col1-tk mice. Following sacrifice, ex vivo microCT and histology demonstrated failed union with residual bone fragments and fibrous tissue in Col1-tk mice. Biomechanical testing demonstrated an inability to recover torsional strength in Col1-tk mice compared to WT. Our data indicates that suppression of proliferating osteoblast-lineage cells for either 2 or 4 weeks after fracture blunts the formation and remodeling of a mineralized callus leading to a functional nonunion. We propose this as a new murine model of atrophic nonunion.

Background: In order to introduce new pharmacological agents with the intent to inhibit the adhesion formation, it is important to test such products on laboratory animals under a protocol that can evaluate the quantitative and qualitative aspects of healing of the tendons. Most experimental models focus on the tensile strength and histological analysis of the tendons, failing to sufficiently quantify the degree of the adhesion formation. Methods: The experiment included six male New Zealand rabbits that underwent surgery of their right forepaws. The deep flexor tendon of the middle finger was transected and repaired and after six weeks the rabbits were killed. In order to assess the extent of adhesions, the functional stiffness of the tendons and the range of motion of the specimens’ fingers was studied using a tensile testing machine. The setup used allowed the simultaneous recording of the specimens’ motion and the pulling force values. Results: The mean values of the left and right forepaws were expressed in the same chart showing a clear difference between the operated and non operated forepaws. Conclusions: Using a relatively simple set up in the laboratory we had the chance to focus on a more elaborate analysis of the data with the help of low cost and accessible software.