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Background: Bone mineral density at the humeral head is reduced in patients with chronic rotator cuff tears. Bone loss in the humeral head is associated with repair failure after rotator cuff reconstruction. Bisphosphonates (eg, zoledronic acid) increase bone mineral density. Hypothesis: Zoledronic acid improves bone mineral density of the humeral head and biomechanical properties of the enthesis after reconstruction of chronic rotator cuff tears in rats. Study Design: Controlled laboratory study. Methods: A total of 32 male Sprague-Dawley rats underwent unilateral (left) supraspinatus tenotomy with delayed transosseous rotator cuff reconstruction after 3 weeks. All rats were sacrificed 8 weeks after rotator cuff repair. Animals were randomly assigned to 1 of 2 groups. At 1 day after rotator cuff reconstruction, the intervention group was treated with a single subcutaneous dose of zoledronic acid at 100 µg/kg bodyweight, and the control group received 1 mL of subcutaneous saline solution. In 12 animals of each group, micro–computed tomography scans of both shoulders were performed as well as biomechanical testing of the supraspinatus enthesis of both sides. In 4 animals of each group, histological analyses were conducted. Results: In the intervention group, bone volume fraction (bone volume/total volume [BV/TV]) of the operated side was higher at the lateral humeral head ( P = .005) and the medial humeral head ( P = .010) compared with the control group. Trabecular number on the operated side was higher at the lateral humeral head ( P = .004) and the medial humeral head ( P = .001) in the intervention group. Maximum load to failure rates on the operated side were higher in the intervention group ( P < .001). Cortical thickness positively correlated with higher maximum load to failure rates in the intervention group ( r = 0.69; P = .026). Histological assessment revealed increased bone formation in the intervention group. Conclusion: Single-dose therapy of zoledronic acid provided an improvement of bone microarchitecture at the humeral head as well as an increase of maximum load to failure rates after transosseous reconstruction of chronic rotator cuff lesions in rats. Clinical Relevance: Zoledronic acid improves bone microarchitecture as well as biomechanical properties after reconstruction of chronic rotator cuff tears in rodents. These results need to be verified in clinical investigations.

Background: Characteristics of chronic rotator cuff tears include continuous loss of tendon structure as well as tendon elasticity, followed by a high failure rate after surgical reconstruction. Several studies have already shown the beneficial effect of extracorporeal shockwave therapy (ESWT) on tissue regeneration in tendon pathologies. Hypothesis: ESWT improves biomechanical tendon properties as well as functional shoulder outcomes in chronic rotator cuff reconstruction in rodents. Study Design: Controlled laboratory study. Methods: After tendon detachment and 3 weeks of degeneration, a subsequent transosseous reattachment of the supraspinatus tendon was performed in 48 adult male Sprague-Dawley rats (n = 16 per group). Rodents were randomly assigned to 3 study groups: no ESWT/control group, intraoperative ESWT (IntraESWT), and intra- and postoperative ESWT (IntraPostESWT). Shoulder joint function, as determined by gait analysis, was assessed repeatedly during the observation period. Eight weeks after tendon reconstruction, the rats were euthanized, and biomechanical and gene expression analyses were performed. Results: Macroscopically, all repairs were intact at the time of euthanasia, with no ruptures detectable. Biomechanical analyses showed significantly improved load-to-failure testing results in both ESWT groups in comparison with the control group (control, 0.629; IntraESWT, 1.102; IntraPostESWT, 0.924; IntraESWT vs control, P≤ .001; IntraPostESWT vs control, P≤ .05). Furthermore, functional gait analyses showed a significant enhancement in intensity measurements for the IntraPostESWT group in comparison with the control group ( P≤ .05). Gene expression analysis revealed no significant differences among the 3 groups. Conclusion: Clearly improved biomechanical results were shown in the single-application and repetitive ESWT groups. Furthermore, functional evaluation showed significantly improved intensity measurements for the repetitive ESWT group. Clinical Relevance: This study underpins a new additional treatment possibility to prevent healing failure. Improved biomechanical stability and functionality may enable faster remobilization as well as an accelerated return to work and sports activities. Furthermore, as shockwave therapy is a noninvasive, easy-to-perform, cost-effective treatment tool with no undesired side effects, this study is of high clinical relevance in orthopaedic surgery. Based on these study results, a clinical study has already been initiated to clinically confirm the improved functionality by ESWT.

Background:Given the unsatisfactory results and reported drawbacks of anterior cruciate ligament (ACL) reconstruction, such as donor site morbidity and the limited choice of grafts in revision surgery, new regenerative approaches based on tissue-engineering strategies are currently under investigation.Purposes:To determine (1) if a novel silk fiber–based ACL scaffold is able to initiate osteointegration in the femoral and tibial bone tunnels under in vivo conditions and (2) if the osteointegration process will be improved by intraoperatively seeding the scaffolds with the autologous stromal vascular fraction, an adipose-derived, stem cell–rich isolate from knee fat pads.Study Design:Controlled laboratory study.Methods:A total of 33 sheep underwent ACL resection and were then randomly assigned to 2 experimental groups: ACL reconstruction with a scaffold alone and ACL reconstruction with a cell-seeded scaffold. Half of the sheep in each group were randomly chosen and euthanized 6 months after surgery and the other half at 12 months. To analyze the integration of the silk-based scaffold in the femoral and tibial bone tunnels, hard tissue histology and micro–computed tomography measurements were performed.Results:Hard tissue histological workup showed that in all treatment groups, with or without the application of the autologous stromal vascular fraction, an interzone of collagen fibers had formed between bone and silk-based graft. This collagen-fiber continuity partly consisted of Sharpey fibers, comparable with tendon-bone healing known for autografts and allografts. Insertion sites were more broad based at 6 months and more concentrated on the slightly protruding, bony knoblike structures at 12 months. Histologically, no differences between the treatment groups were detectable. Analysis of micro–computed tomography measurements revealed a significantly higher tissue density for the cell-seeded scaffold group as compared with the scaffold-alone group in the tibial but not femoral bone tunnel after 12 months of implantation.Conclusion:The novel silk fiber–based scaffold for ACL regeneration demonstrated integration into the bone tunnels via the formation of a fibrous interzone similar to allografts and autografts. Histologically, additional cell seeding did not enhance osteointegration. No significant differences between 6 and 12 months could be detected. After 12 months, there was still a considerable amount of silk present, and a longer observation period is necessary to see if a true ligament-bone enthesis will be formed.Clinical Relevance:ACL regeneration with a silk fiber–based scaffold with and without additional cell seeding may provide an alternative treatment option to current techniques of surgical reconstruction.