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Background: Anterior cruciate ligament (ACL) grafts that are placed for reconstruction are subject to complex forces. Current “anatomic” ACL reconstruction techniques may result in greater in situ graft forces. The biological effect of changing magnitudes of ACL graft force on graft-tunnel osseointegration is not well understood. Purpose: The research objective is to determine how mechanical force on the ACL graft during knee motion affects tendon healing in the tunnel. Study Design: Controlled laboratory study. Methods: Male rats (N = 120) underwent unilateral ACL reconstruction with a soft tissue flexor tendon autograft. ACL graft force was modulated by different femoral tunnel positions at the time of surgery to create different graft force patterns with knee motion. External fixators were used to eliminate graft load during cage activity. A custom knee flexion device was used to deliver graft load through controlled daily knee motion. Graft-tunnel healing was then assessed via biomechanical, micro–computed tomography, and histological analyses. Results: ACL graft-tunnel healing was sensitive to dynamic changes in graft forces with postoperative knee motion. High ACL graft force with joint motion resulted in early inferior ACL graft load to failure as compared with knees that had low-force ACL grafts and joint motion and knees that were immobilized (mean ± SD: 5.50 ± 2.30 N vs 9.91 ± 3.54 N [P = .013] and 10.90 ± 2.8 N [P = .001], respectively). Greater femoral bone volume fraction was seen in immobilized knees and knees with low-force ACL grafts when compared with high-force ACL grafts at 3 and 6 weeks. Conclusion: The authors were able to demonstrate that ACL graft-tunnel incorporation is sensitive to dynamic changes in ACL graft force with joint motion. Early high forces on the ACL graft appear to impair graft-tunnel osseointegration. Clinical Relevance: Current “anatomic” techniques of ACL reconstruction may result in greater graft excursion and force with knee motion. Our results suggest that the postoperative rehabilitation regimen may need to be modified during the early phase of healing to protect the reconstruction. [ABSTRACT FROM AUTHOR]

Background: Moderate graft pretensioning in anterior cruciate ligament (ACL) reconstruction is paramount to restore knee stability and normalize knee kinematics. However, little is known about the effect of graft pretensioning on graft-to-bone healing after ACL reconstruction. Hypothesis: Moderate graft pretensioning will improve bone formation within the bone tunnel after ACL reconstruction, resulting in superior load to failure. Study Design: Controlled laboratory study. Methods: 67 male Sprague-Dawley rats underwent unilateral ACL reconstruction with a flexor digitorum longus tendon autograft. The graft was subjected to pretensioning forces of 0 N, 5 N, or 10 N. Custom-made external fixators were used for knee immobilization postoperatively. Rats were euthanized for biomechanical load-to-failure testing (n = 45) and micro–computed tomography (μCT) examination (n = 22) at 3 and 6 weeks after surgery. Three regions of each femoral and tibial bone tunnel (aperture, middle, and tunnel exit) were chosen for measurement of tunnel diameter and new bone formation. Results: Biomechanical tests revealed significantly higher load-to-failure in the 5-N graft pretensioned group compared with the 0- and 10-N groups at 3 weeks (8.58 ± 2.67 N vs 3.96 ± 1.83 N and 4.46 ± 2.62 N, respectively) and 6 weeks (16.56 ± 3.50 N vs 10.82 ± 1.97 N and 7.35 ± 2.85 N, respectively) after surgery (P < .05). The mean bone tunnel diameters at each of the 3 regions were significantly smaller in the 5-N group, at both the femoral and tibial tunnel sites, than in the 0- and 10-N groups (P < .05). At 3 and 6 weeks postoperatively, the bone mineral density, bone volume fraction, and connectivity density around the aperture and middle regions of the tibial bone tunnels were all significantly higher in the 5-N group compared with the 0- and 10-N groups (P < .05). In the aperture and middle regions of the femoral bone tunnels, pretensioning at either 5 or 10 N resulted in increased bone formation compared with the nonpretensioned group at 3 weeks postoperatively. No differences were found in bone formation between any of the 3 femoral tunnel regions at 6 weeks. Conclusion: Graft pretensioning can stimulate new bone formation and improve tendon-to-bone tunnel healing after ACL reconstruction. Clinical Relevance: Optimal graft pretensioning force in ACL reconstruction can improve bone tunnel healing. Further study is necessary to understand the mechanisms underlying the effect of graft pretensioning on healing at the bone-tunnel interface. [ABSTRACT FROM AUTHOR]

The article discusses a study that evaluated the effect of low-magnitude load and delayed loading on the healing of tendon-to-bone injury in a rat model. Unilateral patellar tendon detachment were conducted on 192 rats then were repaired and external fixator placed with the loading controlled for immobilized rats. Conclusions indicated stronger tendon-bone complex, organized tendon-bone interface and less scar tissue with immobilization than with other loading regimens.

The article evaluates the effect of vitamin D deficiency on rotator cuff healing using biomechanical, radiographic and histological analyses in a rat model. It looks at the role of vitamin D in maintaining cellular proliferation and differentiation as it regulates phosphate within muscle cells. It is found that decreased vitamin D levels affect failure load of rotator cuff repair during the acute phase of tendon healing. The role of vitamin D metabolism in healing enthesis is also discussed.

Background: Rotator cuffs heal through a scar tissue interface after repair that makes them prone to failure. Scleraxis (Scx) is a basic helix-loop-helix transcription factor that is thought to direct tendon development during embryogenesis. The purpose of this study was to determine if the application of mesenchymal stem cells (MSCs) transduced with adenoviral-mediated scleraxis (Ad-Scx) could improve regeneration of the tendon-bone insertion site in a rat rotator cuff repair model.Hypothesis: Bone marrow–derived cells transduced with Scx would improve the structure of the healing tendon-bone interface and result in increased tendon attachment strength.Study Design: Controlled laboratory study.Methods: Sixty Lewis rats underwent unilateral detachment and repair of the supraspinatus tendon. Thirty animals received MSCs in a fibrin glue carrier, and 30 received Ad-Scx-transduced MSCs. Animals were sacrificed at 2 weeks and 4 weeks and evaluated for the presence of fibrocartilage and collagen fiber organization at the insertion. Biomechanical testing was performed to determine the structural and material properties of the repaired tissue. Statistical analysis was performed with a Wilcoxon rank sum test with significance set at P = .05.Results: There were no differences between the Scx and MSC groups in terms of histologic appearance at 2 weeks. However, the Scx group had higher ultimate stress-to-failure (2.6 ± 0.9 vs 1.7 ± 0.3 MPa; P = .03) and stiffness (8.4 ± 2.9 vs 5.0 ± 1.9 N/mm; P = .01) compared with the MSC group. At 4 weeks, the Scx group had more fibrocartilage (728.7 ± 50.4 vs 342.6 ± 217.0 mm2; P = .04), higher ultimate load to failure (26.7 ± 4.6 vs 20.8 ± 4.4 N; P = .01), higher ultimate stress to failure (4.7 ± 1.3 vs 3.5 ± 1.0 MPa; P < .04), and higher stiffness values (15.3 ± 3.4 vs 9.3 ± 2.2 N/mm; P < .001) as compared with the MSC group.Conclusion: Mesenchymal stem cells genetically modified with Scx can augment rotator cuff healing at early time points.Clinical Relevance: Biologic augmentation of acutely injured rotator cuffs with Scx-transduced MSCs may improve rotator cuff tendon healing and reduce the incidence of re-tears. However, further studies are needed to determine if this remains safe and effective in larger models. [ABSTRACT FROM AUTHOR]

Background: Rotator cuff tendon heals by formation of an interposed zone of fibrovascular scar tissue. Recent studies demonstrate that transforming growth factor—beta 3 (TGF-β 3) is associated with tissue regeneration and ‘‘scarless’’ healing, in contrast to scar-mediated healing that occurs with TGF-β 1.Hypothesis: Delivery of TGF-β3 in an injectable calcium-phosphate matrix to the healing tendon-bone interface after rotator cuff repair will result in increased attachment strength secondary to improved bone formation and collagen organization and reduced scar formation of the healing enthesis.Study Design: Controlled laboratory study.Methods: Ninety-six male Sprague-Dawley rats underwent unilateral detachment of the supraspinatus tendon followed by acute repair using transosseous suture fixation. Animals were allocated into 1 of 3 groups: (1) repair alone (controls, n = 32), (2) repair augmented by application of an osteoconductive calcium-phosphate (Ca-P) matrix only (n = 32), or (3) repair augmented with Ca-P matrix + TGF-β 3 (2.75 μg) at the tendon-bone interface (n = 32). Animals were euthanized at either 2 weeks or 4 weeks postoperatively. Biomechanical testing of the supraspinatus tendon-bone complex was performed at 2 and 4 weeks (n = 8 per group). Microcomputed tomography was utilized to quantitate bone microstructure at the repair site. The healing tendon-bone interface was evaluated with histomorphometry and immunohistochemical localization of collagen types I (COLI) and III (COLIII). Statistical analysis was performed using 2-way analysis of variance with significance set at P < .05.Results: There was significantly greater load to failure of the Ca-P matrix + TGF-β3 group compared with matrix alone or untreated controls at 4 weeks postoperatively (P = .04). At 2 weeks, microcomputed tomography revealed a larger volume of newly formed bone present at the healing enthesis in both experimental groups compared with the control group. By 4 weeks, this newly formed, woven bone had matured into calcified, lamellar bone. Histomorphometric analysis demonstrated significantly greater fibrocartilage and increased collagen organization at the healing tendon-bone insertion site in both experimental groups compared with the control group at 2 weeks (P = .04). Over time, TGF-β3 delivery led to greater COLI expression compared with COLIII at the healing enthesis, indicating a more favorable COLI to COLIII ratio with administration of TGF-β3.Conclusion: Augmentation with an osteoconductive Ca-P matrix at the tendon-bone repair site is associated with new bone formation, increased fibrocartilage, and improved collagen organization at the healing tendon-bone interface in the early postoperative period after rotator cuff repair. The addition of TGF-β3 significantly improved strength of the repair at 4 weeks postoperatively and resulted in a more favorable COLI/COLIII ratio.Clinical Relevance: The delivery of TGF-β3 with an injectable Ca-P matrix at the supraspinatus tendon footprint has promise to improve healing after soft tissue repair. [ABSTRACT FROM AUTHOR]

Background: Previous studies have documented increased posteromedial contact forces with the elbow at lower flexion angles associated with valgus extension overload; however, the authors believe that posteromedial elbow impingement in association with valgus laxity is a complex pathological process that may occur throughout the entire throwing motion in the form of ulnohumeral chondral and ligamentous overload.Hypothesis: Valgus laxity with the elbow at 90° of flexion may lead to chondromalacia secondary to a subtle shift in the contact point between the tip of the olecranon and the distal humeral trochlea.Study Design: Controlled laboratory study.Methods: Six fresh human cadaveric elbows were dissected and subjected to a static valgus load. Pressure-sensitive Fuji film measured the contact pressure, contact area, and shift in contact area across the posteromedial elbow before and after sectioning the anterior bundle of the ulnar collateral ligament.Results: The contact pressure between the tip of the olecranon process and the medial crista of the posterior humeral trochlea significantly increased, from an average of 0.27 ± 0.06 kg/cm2 to 0.40 ± 0.08 kg/cm2. The contact area also significantly decreased, from an average of 30.34 ± 9.17 mm2 to 24.59 ± 6.44 mm2, and shifted medially on the medial humeral crista, which corresponds to the position of the posteromedial chondral lesions that was observed in throwing athletes in the authors’ clinical practice.Conclusion: While simulating the early acceleration phase of the throwing motion with the elbow in 90° of flexion, the results illustrate that abnormal contact may occur as a result of valgus laxity through increased contact pressures across the posteromedial elbow between the medial tip of the olecranon and medial crista of the humeral trochlea. In addition, congruency of the ulnohumeral joint changed, as there was a statistically significant medial shift of the olecranon on the posterior humeral trochlea with the elbow at 90° of flexion after sectioning the anterior bundle of the ulnar collateral ligament.Clinical Relevance: In the throwing athlete who continues the repetitive, throwing motion despite valgus laxity from ulnar collateral ligament insufficiency, the authors believe that these results provide a plausible mechanism for injury throughout the entire throwing motion secondary to ulnohumeral chondral and ligamentous overload. As throwing athletes may produce a tremendous amount of force and subsequent chondromalacia within the posteromedial aspect of the elbow, the findings of this study illustrate the importance of prompt clinical recognition of ulnar collateral ligament insufficiency. [ABSTRACT FROM AUTHOR]