Into-Tunnel Repair Versus Onto-Surface Repair for Rotator Cuff Tears in a Rabbit Model

Comparison of 3 Different Surgical Techniques for Rotator Cuff Repair in a Rabbit Model: Direct Suture, Inlay Suture, and Polyether Ether Ketone (PEEK) Suture Anchor

BACKGROUND

Rotator cuff tears have been repaired using the transosseous method for decades. The direct suture (DS) technique has been widely used for rotator cuff tears; however, the retear rate is relatively high. Suture anchors are now used frequently for rotator cuff repair (RCR) in accordance with recent developments in materials. However, polyether ether ketone (PEEK) may still cause complications such as the formation of cysts and osteophytes. Some studies have developed the inlay suture (IS) technique for RCR.

PURPOSE/HYPOTHESIS

To compare how 3 different surgical techniques-namely, the DS, IS, and PEEK suture anchor (PSA)-affect tendon-bone healing after RCR. We hypothesized that the IS technique would lead to better tendon-to-bone healing and that the repaired structure would be similar to the normal enthesis.

STUDY DESIGN

Controlled laboratory study.

METHODS

Acute infraspinatus tendon tears were created in 36 six-month-old male rabbits, which were divided into 3 groups based on the technique used for RCR: DS, IS, and PSA. Animals were euthanized at 6 and 12 weeks postoperatively and underwent a histological assessment and imaging. The expression of related proteins was demonstrated by immunohistochemistry and immunofluorescence staining. Mechanical properties were evaluated by biomechanical testing.

RESULTS

At 12 weeks, regeneration of the enthesis was observed in the 3 groups. However, the DS group showed a lower type I collagen content than the PSA and IS groups, which was similar to the results for scleraxis. The DS group displayed a significantly inferior type II collagen expression and proteoglycan deposition after safranin O/fast green and sirius red staining. With regard to runt-related transcription factor 2 and alkaline phosphatase, the IS group showed upregulated expression levels compared with the other 2 groups.

CONCLUSION

Compared with the DS technique, the PSA and IS techniques contributed to the improved maturation of tendons and fibrocartilage regeneration, while the IS technique particularly promoted osteogenesis at the enthesis.

CLINICAL RELEVANCE

The IS and PSA techniques may be more beneficial for tendon-bone healing after RCR.

Semi-Bone Tunnel Technique Using Double-Row Suture Bridge Combined With Platelet-Rich Plasma Hydrogel for Rotator Cuff Repair in a Rabbit Model

BACKGROUND

The approach to managing the footprint area and reconstructing the tendon-bone interface (TBI) is critical for optimal healing.

PURPOSE

To evaluate the outcomes of the semi-bone tunnel (SBT) technique using a double-row suture bridge combined with platelet-rich plasma (PRP) hydrogel for rotator cuff repair in a rabbit model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 48 New Zealand White rabbits were divided into 4 groups. The supraspinatus tendons were severed at the footprint to create a rotator cuff tear model in the surgical groups. Rabbits were treated with the traditional onto-surface repair (control group), SBT technique (SBT group), and SBT technique combined with PRP hydrogel implantation (SBT+PRP group). The rabbits without surgery were the normal group. At 8 weeks after surgery, macroscopic observation, magnetic resonance imaging (MRI) and micro-computed tomography (μCT) examinations, histological evaluations, and biomechanical tests were performed to assess the curative effects of the given treatments.

RESULTS

The MRI results showed that the repaired supraspinatus tendon presented a uniform signal, minimal inflammatory response, and the lowest signal-to-noise quotient value in the SBT+PRP group. The μCT results suggested that the SBT technique did not reduce the local bone mineral density in the TBI area compared with the onto-surface repair technique. The histological staining results showed that the regenerated TBI in the SBT+PRP group had a 4-layer structure similar to the natural tissue. The highest values for biomechanical properties were observed in the SBT+PRP group, and there was no significant difference between the SBT+PRP group and normal group.

CONCLUSION

The SBT technique presented a better tendon-bone healing effect for rotator cuff tear in the rabbit model compared with the traditional onto-surface repair technique. The specimens in the SBT+PRP group had a similar TBI structure and biomechanical properties to the natural tissue.

CLINICAL RELEVANCE

The SBT technique can be an alternative surgical approach for rotator cuff repair, especially for moderate to large tears and cases requiring scaffold implantation.

Losartan in Combination With Bone Marrow Stimulation Showed Synergistic Effects on Load to Failure and Tendon Matrix Organization in a Rabbit Model

PURPOSE

To investigate the effects of combining bone marrow stimulation (BMS) with oral losartan to block transforming growth factor β1 (TGF-β1) on biomechanical repair strength in a rabbit chronic injury model.

METHODS

Forty rabbits were randomly allocated into 4 groups (10 in each group). The supraspinatus tendon was detached and left alone for 6 weeks to establish a rabbit chronic injury model and was then repaired in a surgical procedure using a transosseous, linked, crossing repair construct. The animals were divided into the following groups: control group (group C), surgical repair only; BMS group (group B), surgical repair with BMS of the tuberosity; losartan group (group L), surgical repair plus oral losartan (TGF-β1 blocker) for 8 weeks; and BMS-plus-losartan group (group BL), surgical repair plus BMS plus oral losartan for 8 weeks. At 8 weeks after repair, biomechanical and histologic evaluations were performed.

RESULTS

The biomechanical testing results showed significantly higher ultimate load to failure in group BL than in group B (P = .029) but not compared with group C or group L. A 2 × 2 analysis-of-variance model found that the effect of losartan on ultimate load significantly depended on whether BMS was performed (interaction term F1,28 = 5.78, P = .018). No difference was found between the other groups. No difference in stiffness was found between any groups. On histologic assessment, groups B, L, and BL showed improved tendon morphology and an organized type I collagen matrix with less type III collagen compared with group C. Group BL showed the most highly organized tendon matrix with more type I collagen and less type III collagen, which indicates less fibrosis. Similar results were found at the bone-tendon interface.

CONCLUSIONS

Rotator cuff repair combined with oral losartan and BMS of the greater tuberosity showed improved pullout strength and a highly organized tendon matrix in this rabbit chronic injury model.

CLINICAL RELEVANCE

Tendon healing or scarring is accompanied by the formation of fibrosis, which has been shown to result in compromised biomechanical properties, and is therefore a potential limiting factor in healing after rotator cuff repair. TGF-β1 expression has been shown to play an important role in the formation of fibrosis. Recent studies focusing on muscle healing and cartilage repair have found that the downregulation of TGF-β1 by losartan intake can reduce fibrosis and improve tissue regeneration in animal models.

Superior capsular reconstruction using the long head of the biceps to treat massive rotator cuff tears improves patients shoulder pain, mobility and function

PURPOSE

Arthroscopic superior capsule reconstruction (SCR) with the long head of the biceps (LHBT) was performed to restore structural stability, force couple balance, and shoulder joint function. This study aimed to evaluate the functional outcomes of SCR using the LHBT over at least 24 months of follow-up.

METHOD

This retrospective study included 89 patients with massive rotator cuff tears who underwent SCR using the LHBT, met the inclusion criteria and underwent follow up for at least 24 months. The preoperative and postoperative shoulder range of motion (forward flexion, external rotation, and abduction), acromiohumeral interval (AHI), visual analog scale (VAS) score, American Shoulder and Elbow Surgeons (ASES) score and Constant-Murley score were obtained, and the tear size, and Goutallier and Hamada grades were also investigated.

RESULTS

Compared with those measured preoperatively, the range of motion, AHI, and VAS, Constant-Murley, and ASES scores were significantly improved immediately postoperatively (P < 0.001) and at the 6-month, 12-month, and final follow-ups (P < 0.001). At the last follow-up, the postoperative ASES score and Constant-Murley score increased from 42.8 ± 7.6 to 87.4 ± 6.1, and 42.3 ± 8.9 to 84.9 ± 10.7, respectively; with improvements of 51 ± 21.7 in forward flexion, 21.0 ± 8.1 in external rotation, and 58.5 ± 22.5 in abduction. The AHI increased 2.1 ± 0.8 mm and the VAS score significantly changed from 6.0 (5.0, 7.0) to 1.0 (0.0, 1.0), at the final follow-up. Eleven of the 89 patients experienced retears, and one patient needed reoperation.

CONCLUSION

In this study with at least 24-months of follow-up, SCR using the LHBT for massive rotator cuff tears could effectively relieve shoulder pain, restore shoulder function and increase shoulder mobility to some extent.

LEVEL OF EVIDENCE

IV.

Transcriptional time course after rotator cuff repair in 6 month old female rabbits

Introduction: Rotator cuff tears are prevalent in the population above the age of 60. The disease progression leads to muscle atrophy, fibrosis, and fatty infiltration, which is not improved upon with surgical repair, highlighting the need to better understand the underlying biology impairing more favorable outcomes. Methods: In this study, we collected supraspinatus muscle tissue from 6 month old female rabbits who had undergone unilateral tenotomy for 8 weeks at 1, 2, 4, or 8 weeks post-repair (n = 4/group). RNA sequencing and enrichment analyses were performed to identify a transcriptional timeline of rotator cuff muscle adaptations and related morphological sequelae. Results: There were differentially expressed (DE) genes at 1 (819 up/210 down), 2 (776/120), and 4 (63/27) weeks post-repair, with none at 8 week post-repair. Of the time points with DE genes, there were 1092 unique DE genes and 442 shared genes, highlighting that there are changing processes in the muscle at each time point. Broadly, 1-week post-repair differentially expressed genes were significantly enriched in pathways of metabolism and energetic activity, binding, and regulation. Many were also significantly enriched at 2 weeks, with the addition of NIF/NF-kappaB signaling, transcription in response to hypoxia, and mRNA stability alongside many additional pathways. There was also a shift in transcriptional activity at 4 weeks post-repair with significantly enriched pathways for lipids, hormones, apoptosis, and cytokine activity, despite an overall decrease in the number of differentially expressed genes. At 8 weeks post-repair there were no DE genes when compared to control. These transcriptional profiles were correlated with the histological findings of increased fat, degeneration, and fibrosis. Specifically, correlated gene sets were enriched for fatty acid metabolism, TGF-B-related, and other pathways. Discussion: This study identifies the timeline of transcriptional changes in muscle after RC repair, which by itself, does not induce a growth/regenerative response as desired. Instead, it is predominately related to metabolism/energetics changes at 1 week post-repair, unclear or asynchronous transcriptional diversity at 2 weeks post-repair, increased adipogenesis at 4 weeks post-repair, and a low transcriptional steady state or a dysregulated stress response at 8 weeks post-repair.

A Knitted PET Patch Enhances the Maturation of Regenerated Tendons in Bridging Reconstruction of Massive Rotator Cuff Tears in a Rabbit Model

BACKGROUND

Although nondegradable synthetic grafts for bridging reconstruction of massive rotator cuff tears (MRCTs) have shown satisfactory clinical outcomes, their function and details on graft-tendon healing and enthesis regeneration have not been fully studied.

HYPOTHESIS

The knitted polyethylene terephthalate (PET) patch as a nondegradable synthetic graft could provide sustained mechanical support, facilitating enthesis and tendon regeneration in the treatment of MRCTs.

STUDY DESIGN

Controlled laboratory study.

METHODS

A knitted PET patch was fabricated for bridging reconstruction (PET group) in a New Zealand White rabbit model of MRCTs (negative control group), and an autologous Achilles tendon was used as a control (autograft group). The animals were sacrificed, and tissue samples were harvested for gross observation as well as histological and biomechanical analyses at 4, 8, and 12 weeks postoperatively.

RESULTS

Histological analysis showed no significant difference in the graft-bone interface score between the PET and autograft groups at 4, 8, and 12 weeks postoperatively. Interestingly, in the PET group, Sharpey-like fibers were observed at 8 weeks, while fibrocartilage formation and the ingrowth of chondrocytes were recognized at 12 weeks. Meanwhile, the tendon maturing score was significantly higher in the PET group than in the autograft group (19.7 ± 1.5 vs 15.3 ± 1.2, respectively; P = .008) at 12 weeks, with parallel-oriented collagen fibers around the knitted PET patch. Moreover, the ultimate failure load of the PET group was similar to that of a healthy rabbit tendon at 8 weeks (125.6 ± 13.6 vs 130.8 ± 28.6 N, respectively; P > .05) and no different from that of the autograft group at 4, 8, and 12 weeks.

CONCLUSION

The knitted PET patch could not only immediately reconstruct the mechanical support for the torn tendon postoperatively in the rabbit model of MRCTs but also enhanced maturation of the regenerated tendon by fibrocartilage formation and improved the organization of collagen fibers. Herein, the knitted PET patch could be a promising candidate graft adopted in bridging reconstruction of MRCTs.

CLINICAL RELEVANCE

A nondegradable knitted PET patch can safely bridge MRCTs with satisfactory mechanical strength and the promotion of tissue regeneration.

Bioprinted living tissue constructs with layer-specific, growth factor-loaded microspheres for improved enthesis healing of a rotator cuff

Substantial challenges remain in constructing the native tendon-to-bone interface for rotator cuff healing owing to the enthesis tissues' highly organized structural and compositional gradients. Herein, we propose to bioprint living tissue constructs with layer-specific growth factors (GFs) to promote enthesis regeneration by guiding the zonal differentiation of the loaded stem cells in situ. The sustained release of tenogenic, chondrogenic, and osteogenic GFs was achieved via microsphere-based delivery carriers embedded in the bioprinted constructs. Compared to the basal construct without GFs, the layer-specific tissue analogs realized region-specific differentiation of stem cells in vitro. More importantly, bioprinted living tissue constructs with layer-specific GFs rapidly enhanced the enthesis regeneration in a rabbit rotator cuff tear model in terms of biomechanical restoration, collagen deposition, and alignment, showing gradient interface of fibrocartilage structures with aligned collagen fibrils and an ultimate load failure of 154.3 ± 9.5 N resembling those of native enthesis tissues in 12 weeks. This exploration provides a feasible strategy to engineer living tissue constructions with region-specific differentiation potentials for the functional repair of gradient enthesis tissues. STATEMENT OF SIGNIFICANCE: Previous studies that employed acellular layer-specific scaffolds or stem cells for the reconstruction of the rotator cuff faced challenges due to their insufficient capability to rebuild the anisotropic compositional and structural gradients of native enthesis tissues. This manuscript proposed a living tissue construct with layer-specific, GFs-loaded µS, which can direct in situ and region-specific differentiation of the embedded stem cells to tenogenic, chondrogenic, and osteogenic lineages for functional regeneration of the enthesis tissues. This bioprinted living tissue construct with the unique capability to reduce fibrovascular scar tissue formation and simultaneously facilitate enthesis tissue remodeling might provide a promising strategy to repair complex and gradient tissues in the future.

Biomechanical and Histological Results of Dual-Suspensory Reconstruction Using Banded Tendon Graft to Bridge Massive Rotator Cuff Tears in a Chronic Rabbit Model

BACKGROUND

Bridging rotator cuff tendon defects with a patch is a reasonable treatment for massive rotator cuff tears (MRCTs). However, the poor outcomes associated with routine patch repair have prompted exploration into superior bridging techniques and graft structures.

PURPOSE

To detect whether dual-suspensory reconstruction using a banded graft would be superior to routine bridging using a patch graft to treat MRCTs and to detect the comparative effectiveness of patellar tendon (PT) and fascia lata (FL) grafts in dual-suspensory reconstruction.

STUDY DESIGN

Controlled laboratory study.

METHODS

Unilateral chronic MRCTs were created in 72 mature male New Zealand White rabbits, which were randomly divided into 3 groups: (1) patch bridging repair using rectangular FL autograft (PR-FL), (2) dual-suspensory bridging reconstruction using banded FL autograft (DSR-FL), and (3) dual-suspensory bridging reconstruction using banded PT autograft (DSR-PT). In each group, the mean failure load and stiffness of the cuff-graft-humerus (C-G-H) complexes of 6-week and 12-week specimens were recorded, with the failure modes and sites noted. Moreover, cuff-to-graft and graft-to-bone interface healing and graft substance remodeling of the complexes were histologically evaluated (via hematoxylin and eosin, Picrosirius red, Masson trichrome, and Safranin O/fast green staining) at 6 and 12 weeks to assess integrations between the bridging constructs and the native bone or rotator cuff tendons.

RESULTS

The DSR-PT group had the greatest mean failure loads and stiffness of the C-G-H complexes at 6 and 12 weeks (41.81 ± 7.00 N, 10.34 ± 2.68 N/mm; 87.62 ± 9.20 N, 17.98 ± 1.57 N/mm, respectively), followed by the DSR-FL group (32.04 ± 5.49 N, 8.20 ± 2.27 N/mm; 75.30 ± 7.31 N, 14.39 ± 3.29 N/mm, respectively). In the DSR-PT and DSR-FL groups, fewer specimens failed at the graft-to-bone junction and more failed at the cuff-to-graft junction, but both groups had higher median failure loads at 6 and 12 weeks (DSR-PT: cuff-to-graft junction, 37.80 and 83.76 N; graft-to-bone junction, 45.46 and 95.86 N) (DSR-FL: cuff-to-graft junction, 28.52 and 67.68 N; graft-to-bone junction, 37.92 and 82.18 N) compared with PR-FL (cuff-to-graft junction, 27.17 and 60.04 N; graft-to-bone junction, 30.12 and 55.95 N). At 12 weeks, the DSR-FL group had higher median failure loads at graft substance (72.26 N) than the PR-FL group (61.27 N). Moreover, the PR-FL group showed more inflammatory responses at the 2 healing interfaces and the graft substance in the 6-week specimens and subsequently displayed poorer interface healing (assessed via collagen organization, collagen maturity, and fibrocartilage regeneration) and graft substance remodeling (assessed via collagen organization and maturity) in 12-week specimens compared with the DSR-PT and DSR-FL groups. Superior interface healing and substance remodeling processes were observed in the DSR-PT group compared with the DSR-FL group.

CONCLUSION

When compared with routine patch repair, the dual-suspensory reconstructions optimized biomechanical properties and improved interface healing and graft substance remodeling for bridging MRCTs. Furthermore, the dual-suspensory technique using the PT graft presented superior histological and biomechanical characteristics than that using FL.

CLINICAL RELEVANCE

The dual-suspensory reconstruction technique using banded tendon grafts may enhance bridging constructs for MRCTs in humans, warranting further investigations of clinical outcomes.

The Plug-Type Patch Results in Immediate and Postoperative Advantages in Graft-to-Bone Integration for Bridging Massive Rotator Cuff Tears in a Chronic Rabbit Model

BACKGROUND

Various patches have been used to bridge massive rotator cuff tears (MRCTs) by reconnecting the cuff tendons to the humeral head, but the outcomes continue to be suboptimal. Notably, the graft-bone junction is a vulnerable site for failure, which requires optimization in patch design and techniques to enhance initial and postoperative fixation strength at the graft-bone interface.

HYPOTHESIS

The plug-type patch (Plug-Pat) through intratunnel fixation would optimize mechanical characteristics in initial graft-to-bone fixation and subsequently improve postoperative biomechanical and histological properties in graft-to-bone healing when compared with the routine rectangular patch (Rect-Pat).

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 60 mature male New Zealand White rabbits underwent acute rotator cuff defects to create chronic models with MRCTs. The fascia lata autograft was then harvested to prepare a Plug-Pat, which was distally rooted in the bone tunnel and proximally sutured to native tendons in a horizontal mattress fashion to reconnect the humeral head and cuff tendons. The control group was repaired with a routine Rect-Pat that was secured onto the bone surface for graft-bone fixation. After surgery, the cuff-graft-bone complexes of rabbits in both groups were harvested immediately (0 weeks) for time-zero initial fixation strength and refreshed contact area assessment, and at 6 or 12 weeks for postoperative biomechanical and histological evaluation.

RESULTS

The Plug-Pat significantly enhanced initial fixation strength in comparison with the Rect-Pat (mean ± SD; failure load, 36.79 ± 4.53 N vs 24.15 ± 2.76 N; P < .001) and decreased failure at the graft-bone interface of the construct at 0 weeks, with a significantly increased refreshed bone bed contact area (52.63 ± 2.97 mm² vs 18.28 ± 1.60 mm²; P < .001) between the graft and bone. At 6 and 12 weeks postoperatively, the Plug-Pat similarly resulted in greater failure load (43.15 ± 4.53 N vs 33.74 ± 2.58 N at 6 weeks; P = .001; 76.65 ± 5.04 N vs 58.17 ± 5.06 N at 12 weeks; P < .001) and stiffness (10.77 ± 2.67 N/mm vs 8.43 ± 0.86 N/mm at 6 weeks; P = .066; 16.98 ± 2.47 N/mm vs 13.21 ± 1.66 N/mm at 12 weeks; P = .011), with less specimen failure at the graft-bone interface than the Rect-Pat. In histological analyses, the Plug-Pat had a higher postoperative graft-bone integration score than the Rect-Pat, showing a more mature intratunnel healing interface with fibrocartilage tidemark formation, improved collagen properties, and more oriented cells when compared with those at the surface healing interface in the Rect-Pat.

CONCLUSION

The Plug-Pat enhanced initial fixation strength and enlarged the refreshed contact area for graft-bone connection at time zero and subsequently improved postoperative biomechanical properties and graft-bone integration at the graft-bone healing interface when compared with the Rect-Pat.

CLINICAL RELEVANCE

The Plug-Pat using intratunnel fixation may be a promising strategy for patch design to optimize its initial and postoperative graft-bone connection for bridging reconstruction of MRCTs.

H-loop Knotless Double-Row Repair Versus Knotted Suture Bridge for Rotator Cuff Tears: A Biomechanical and Histological Study in an Animal Model [Formula: see text]

BACKGROUND

Knotted suture bridge repair (KSBR) has been widely proven to be an effective method for rotator cuff repairs. However, the occurrence of type 2 failure after suture bridge repair remains a frequent problem because of the stress concentration and disturbance of tendon perfusion in the medial row. The authors have developed the H-loop knotless double-row repair (HLDR) to counteract these problems.

PURPOSE

To compare the biomechanical and histological outcomes of HLDR and KSBR for rotator cuff tear in the rabbit model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Acute bilateral supraspinatus tears were created on the shoulders of 46 New Zealand White rabbits. HLDR and KSBR were randomly performed on the left side or right side. Thirteen animals each were sacrificed at 2, 4, and 8 weeks after surgery (n = 39), with 6 rabbits used for histological evaluation and the other 7 rabbits for biomechanical testing. The remaining 7 animals from the original 46 were only used for initial biomechanical evaluation at week 0.

RESULTS

Macroscopically, all repaired tendons were connected to their footprint on the greater tuberosity without postoperative complications at 8 weeks after surgery. The HLDR group had significantly better histological bone-to-tendon integration compared with the KSBR group in terms of fibrocartilage regeneration, collagen composition, and fiber organization. The biomechanical outcomes in the HLDR group were demonstrated to be better than those of the KSBR group at time 0 and 8 weeks after surgery.

CONCLUSION

Both repair techniques were effective for rotator cuff tears in a rabbit rotator cuff tear model; however, HLDR demonstrated more advantages in improving biomechanical properties and histological tendon-to-bone healing compared with KSBR.

CLINICAL RELEVANCE

This animal study suggested that HLDR might be an alternative choice for rotator cuff tears in humans to increase tendon-to-bone healing and reduce the rate of failure to heal.

An Arthroscopy-Assisted Mini-Invasive Technique to Create a Chronic Rabbit Model With Massive and Retracted Supraspinatus Rotator Cuff Tears

Understanding the pathophysiology of rotator cuff tears (RCTs) in animal models is of great importance, as it helps in the development of repair strategies and therapeutic treatments for rotator cuff diseases in humans. This Technical Note describes a comprehensive step-by-step description of an arthroscopic-assisted minimally invasive RCT model in rabbits. This technique is beneficial because the rabbit has rotator cuffs anatomically similar to those of humans, and it has been widely used as a preclinical animal model in the basic science literature. Compared with other small animals (e.g., mice and rats), the advantage of the rabbit model is that it can test the effectiveness and healing process of new surgical repair techniques that require relatively larger anatomical structures. Moreover, it is more cost-effective compared with larger animal models, such as sheep and canines. This arthroscopic-assisted mini-invasive technique to create an RCT model may have a better effect on simulating the degenerative and chronic RCT state in humans than the commonly used open surgery, along with an earlier return to activities, less scarring and tissue adhesion, fewer injuries to the deltoid, and fewer complications.

The “Second Hit” of Repair in a Rabbit Model of Chronic Rotator Cuff Tear

The rabbit supraspinatus is a useful translational model for rotator cuff (RC) repair because it recapitulates muscle atrophy and fat accumulation observed in humans after a chronic tear (the “first hit”). However, a timeline of RC tissue response after repair, especially with regard to recent evidence of muscle degeneration and lack of regeneration, is currently unavailable. Thus, the purpose of this study was to characterize the progression of muscle and fat changes over time after the repair of a chronic RC tear in the rabbit model. Two rounds of experiments were conducted in 2017–2018 and 2019–2020 with N = 18 and 16 skeletally mature New Zealand White rabbits, respectively. Animals underwent left supraspinatus tenotomy with repair 8 weeks later. The unoperated right shoulder served as control. The rabbits were sacrificed at 1-, 2-, 4-, and 8-weeks post-repair for histological and biochemical analysis. Atrophy, measured by fiber cross-sectional area and muscle mass, was greatest around 2 weeks after repair. Active muscle degeneration peaked at the same time, involving 8% of slide areas. There was no significant regeneration at any timepoint. Fat accumulation and fibrosis were significantly increased across all time points compared to contralateral. Statement of Clinical Significance: These results demonstrate model reproducibility and a “second hit” phenomenon of repair-induced muscle atrophy and degeneration which partially recovers after a short time, while increased fat and fibrosis persist.

The Biomechanical and Histological Processes of Rerouting Biceps to Treat Chronic Irreparable Rotator Cuff Tears in a Rabbit Model

BACKGROUND

Recently, the biceps was rerouted into a newly fabricated bicipital groove for in situ superior capsular reconstruction (SCR), resulting in promising time-zero cadaveric and clinical outcomes. However, no studies have determined the in vivo biomechanical and histological processes after the biceps is transposed to a nonanatomic position.

PURPOSE

To explore the in vivo biomechanical and histological processes of the rerouting biceps tendon to treat chronic irreparable rotator cuff tears (IRCTs) in a rabbit model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 94 skeletally mature male rabbits were used to create a chronic IRCT model in the supraspinatus tendon. Then, the biceps rerouting procedures were performed in rabbits with chronic IRCT. Eighteen rabbits were sacrificed at 1, 3, 6, 9, and 12 weeks postoperatively for biomechanical testing, micro-computed tomography scanning, and histological analysis. The biomechanical and histological changes of intra- and extra-articular portions of the rerouting biceps were evaluated at each time point, with the contralateral native superior capsule (NSC) and the native biceps (NB) as controls, respectively. The morphology and bone formation of the fabricated bicipital grooves were evaluated, with native grooves as controls.

RESULTS

The intra-articular rerouting biceps tendon was progressively remodeled over time, displaying denser fibers and more mature collagen than those of the NSC, with gradual improvements in the tendon-to-bone healing interface from 6 to 12 weeks. Consequently, the failure load and stiffness of the intra-articular rerouting biceps portion increased with time and were significantly higher than those of the NSC from 9 weeks. Similarly, the extra-articular portion of the rerouting biceps progressively healed into a new bicipital groove, as demonstrated by a smaller tendon-to-bone interface from 6 to 12 weeks, resulting in greater failure load and stiffness at 9 and 12 weeks than those of the NB attachment. The newly fabricated bicipital groove showed similar morphology to that of the native groove with sufficient trabecular bone formed underneath.

CONCLUSION

The rerouting biceps could progressively remodel and heal into the newly fabricated bicipital groove over time, resulting in greater biomechanical performances in intra- and extra-articular portions than the NSC and the NB attachment.

CLINICAL RELEVANCE

The biceps rerouting technique may be a feasible procedure to perform in situ SCR to treat IRCT in the future clinical practice; however, more clinical evidence is required.

Biceps Augmentation Outperforms Tear Completion Repair or In Situ Repair for Bursal-Sided Partial-Thickness Rotator Cuff Tears in a Rabbit Model

BACKGROUND

There is an ongoing debate on the treatment of bursal-sided partial-thickness rotator cuff tears (PTRCTs), including ideal repair techniques. Augmentation using a collagen patch has been introduced as a new surgical approach to treat PTRCTs, while the effect of autogenous biceps augmentation (BA) has not been investigated.

PURPOSE

To analyze the effects of BA on bursal-sided PTRCTs and compare its histological and biomechanical results with those of tear completion followed by repair and in situ repair (ISR).

STUDY DESIGN

Controlled laboratory study.

METHODS

Unilateral chronic PTRCTs were created in 96 mature New Zealand White rabbits, which were randomly divided into 4 groups: no repair, tear completion repair (TCR), ISR, and BA. A new bicipital groove was fabricated in BA for the biceps tendon that was transferred to augment the bursal-sided PTRCT repair. In each group, we sacrificed 6 rabbits for biomechanical testing of the whole tendon-to-bone complex (WTBC) and 6 for histological evaluation of bursal- and articular-sided layers at 6 and 12 weeks postoperatively. Healing responses between the biceps and new bicipital groove in the BA group were determined using histological analysis, and final groove morphologies were evaluated using micro-computed tomography.

RESULTS

The remaining tendon and enthesis in bursal-sided PTRCTs progressively degenerated over time. WTBCs of ISR exhibited a larger failure load than those of TCR, although better healing properties in the bursal-sided repaired site were achieved using TCR based on histological scores and superior articular-sided histological scores were observed using ISR. However, WTBCs of BA displayed the best biomechanical results and superior histological scores for bursal- and articular-sided regions. The new bicipital groove in BA remodeled over time and formed similar morphologies to a native groove, which provided a mature bone bed for transferred biceps tendon healing to augment bursal-sided PTRCTs.

CONCLUSION

BA achieved better biomechanical and histological results for repairing bursal-sided PTRCTs as compared with TCR and ISR. When compared with that of TCR, the WTBC of ISR exhibited a higher failure load, showing histological superiority in the articular-sided repair and inferiority in the bursal-sided repair.

CLINICAL RELEVANCE

BA may be an approach to improve bursal-sided PTRCT repair in humans, which warrants further clinical investigation.

Postoperative malrotation of humerus shaft fracture causes degeneration of rotator cuff and cartilage

We hypothesized that postoperative malrotation of humeral shaft fractures can alter the bio-mechanical environment of the shoulder; thus, rotator cuff and cartilage degeneration could be induced. Therefore, we designed an animal experiment to evaluate the impact of malrotation deformities after minimally invasive surgery for humeral fractures on the rotator cuff and cartilage, which has rarely been described in previous studies. Twenty-four New Zealand white rabbits were randomly divided into the sham control group (A), negative control group (B) and malrotated group (C). A sham operation with surgical exposure alone was performed in group A. Humeral shaft osteotomy was performed in Group B and C. In Group B, the fractures were fixed in situ with plate -screw system. While in Group C, iatrogenic rotational deformity was created after the proximal end of the fracture being internally rotated by 20 degrees and then subsequently fixed. The animals with bone healing were sacrificed for pathological and biochemical examination. In group C, the modified Mankin scale for cartilage pathology evaluation and the modified Movin scale for tendon both showed highest score among groups with statistical significance (P < 0.05); Disordered alignment and proportion of collagen I/III of rotator cuff were confirmed with picrosirius red staining; Transmission electron microscopy also showed ultrastructural tendon damage. Immunohistochemistry showed that both MMP-1 and MMP-13 expression were significantly higher in group C than groups A and B(P < 0.05). Minimally invasive techniques for humerus shaft fracture might be cosmetically advantageous, but the consequent postoperative malrotation could increase the risk of rotator cuff and cartilage degeneration. This conclusion is supported here by primary evidence from animal experiments.

The Effect of Antiosteoporosis Therapy With Risedronate on Rotator Cuff Healing in an Osteoporotic Rat Model

BACKGROUND

Osteoporosis increases the revision rate of rotator cuff repair (RCR). Weak fixation might not be the only cause of high RCR failure rates. The biological mechanism associated with tendon-to-bone healing after RCR in osteoporosis should be investigated.

HYPOTHESIS

(1) Osteoporosis would impair rotator cuff healing through the high osteoclastic activity at the repaired interface. (2) Risedronate would promote rotator cuff healing by reducing osteoclastic activity at the repaired interface.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 84 female Sprague Dawley rats were randomly treated using ovariectomy or sham surgeries to establish osteoporotic and nonosteoporotic rat models. After confirming osteoporosis, a chronic rotator cuff tear model was created and RCR was performed. Postoperatively, osteoporotic rats were randomly divided into osteoporosis (OP) and osteoporosis with risedronate administration (OP+RIS) groups. Nonosteoporotic rats were used as the control (CON) group. Osteoclastic activity was measured at 1 and 3 weeks after RCR, and histologic analysis of the tendon-to-bone interface, bone morphometric evaluation, and biomechanical tests were performed at 4 and 8 weeks.

RESULTS

At the early healing stages of 1 and 3 weeks after RCR, the OP group showed the highest osteoclast density at the repaired interface. Compared with the OP group, risedronate administration significantly decreased osteoclast density in the OP+RIS group. At 8 weeks, histologic scores were greater in the OP+RIS group than in the OP group but still lower than in the CON group. Histologic scores at 8 weeks were negatively correlated with osteoclast density at the early healing stage. Additionally, the OP+RIS group showed better bone morphometric parameters and biomechanical properties than did the OP group.

CONCLUSION

Osteoporosis impaired rotator cuff healing, which might be related to the high osteoclast density at the repaired interface at the early healing stage. Postoperative risedronate administration decreased osteoclast density and enhanced rotator cuff healing in osteoporotic rats, although the effect was inferior to that in nonosteoporotic rats.

CLINICAL RELEVANCE

Postoperative risedronate administration can be considered a potential therapy to enhance rotator cuff healing in patients with postmenopausal osteoporosis. However, this needs to be verified in a clinical setting.

Arthroscopic Humeral Bone Tunnel-Based Tendon Grafting and Trapezius Transfer for Irreparable Posterior Superior Rotator Cuff Tear

Irreparable posterior rotator cuff tears pose challenges to orthopaedic surgeons, especially when the medial remaining rotator cuff is not reusable. Trapezius transfer is biomechanically favorable due to the similar vector of the transferred muscle to the native posterior superior rotator cuff. Regarding combined tendon grafting in trapezius transfer, onto-surface tendon attachment to the humerus was reported in most previous reports. For better tendon-humeral head connection, we introduce an humeral bone tunnel-based tendon grafting technique. In this technique, we use the hamstring tendons and the anterior half of the peroneus tendon to make 3 grafts. The most critical steps of this technique are the proper creation of the humeral tunnels and graft implantation. We consider the introduction of this technique will shed light in the field of trapezius transfer for Irreparable posterior rotator cuff tears.

Rooting Rotator Cuff Reconstruction for Irreparable Posterior-Superior Rotator Cuff Tear

Irreparable posterior-superior rotator cuff tear is encountered quite often in clinical practice. Bridging the tendon defect with various materials is reasonable. However, optimal bridging structures and techniques are still being pursued. We introduce a rotator cuff bridging technique, rooting rotator cuff reconstruction. In this technique, autogenous tendon is used to make grafts. On the medial side, the graft tendons are suspended on the rotator cuff tendon. On the lateral side, the graft tendons are placed into tunnels through the tuberosities. The most critical steps of this technique are properly fabricating the humeral tunnels and suspending the graft tendons onto the rotator cuff tendon. We believe this technique will shed light on rotator cuff reconstruction.

Assessment of whether the rabbit subscapularis tendon model is suitable for studying the human chronic rotator cuff pathology: Discovery of a new ligament connecting the glenoid and subscapularis tendon

OBJECTIVE

This study aimed to investigate the anatomical relationship between the subscapularis tendon and glenosubscapularal ligament (GSL) that we accidentally identified from our previous study on a rabbit shoulder model and to determine whether this anatomical relationship has an impact on the rabbit shoulder model for studying the human chronic rotator cuff pathology.

METHODS

In this study, 15 male New Zealand rabbits aged 12 weeks and weighing 2.5 kg were used. Moreover, 3 rabbits were sacrificed for the anatomical and histological investigation of the relationship between the subscapularis tendon and GSL at baseline. The remaining 12 rabbits underwent the subscapularis tendon tenotomy from the lesser tuberosity using a standardized procedure. The GSL was cut on the left side and preserved on the right side. For histomorphometric analysis, 6 rabbits were first sacrificed at 6 weeks and then the remaining 6 rabbits at 12 weeks.

RESULTS

In all the rabbits, GSL was identified, connecting the upper portion of glenoid and subscapularis muscle-tendon junction. The mean thickness of the middle portion of GSL was 1.1±0.2 mm; the mean length of GSL was 8.4±2.3 mm. The mean widths of the proximal and distal attachments were 2.4±0.3 and 4.2±0.5 mm, respectively. The mean size of the native subscapularis muscle fibers was 122.6±4.3 μm2. The mean size of the muscle fibers in shoulders with tenotomy alone was 112.6±6.2 and 102.6±4.8 μm2 at 6 and 12 weeks, respectively. The mean size of the muscle fibers in shoulders with tenotomy plus GSL cut severing was 88.3±9.7 and 56.4±5.2 μm2 at 6 and 12 weeks, respectively. The significant muscle atrophy was observed both at 6 and 12 weeks in the shoulders with tenotomy plus GSL cut compared with those with tenotomy alone as well as those with the native subscapularis. However, the muscle atrophy was not significantly different in the shoulders with tenotomy alone at different time points.

CONCLUSION

Because GSL may prevent the subscapularis retraction, the rabbit subscapularis tendon model may not be suitable for studying the human chronic rotator cuff pathology if GSL is neglected or preserved.

Tear Completion Versus In Situ Repair for 50% Partial-Thickness Bursal-Side Rotator Cuff Tears: A Biomechanical and Histological Study in an Animal Model

BACKGROUND

Tear completion followed by repair (TCR) and in situ repair (ISR) have been widely used for bursal-side partial-thickness rotator cuff tears (PTRCTs). Both techniques have shown favorable results; however, controversy continues in terms of the best management.

PURPOSE

To compare the histological and biomechanical outcomes of these 2 techniques for 50% partial-thickness bursal-side rotator cuff tear repair in a rabbit model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 27 rabbits were used in this experimental study. Seven rabbits were sacrificed at the beginning of the study to form an intact tendon control group. A chronic 50% partial-thickness bursal-side tear model was created in 20 rabbits, and 5 rabbits were sacrificed for biomechanical testing of chronic partial-thickness tears (control group) without repair. In 15 rabbits, partial-thickness tears were repaired after 8 weeks. Partial-thickness tears in the right shoulders were completed to full thickness and repaired; in contrast, left shoulders were repaired in situ. All rabbits were euthanized 8 weeks after the repair. The tendons were tested biomechanically for ultimate failure, linear stiffness, and displacement. Histological evaluations of tendon-to-bone healing were performed via the modified Watkins score.

RESULTS

Macroscopically, all repaired tendons were attached to the greater tuberosity. The TCR group had a higher failure load than the ISR group, with mean values of 140.4 ± 13.8 N and 108.1 ± 16.6 N, respectively (P = .001). The modified Watkins score was significantly higher in the TCR group (23.5; range, 22-27) than in the ISR group (19.5; range, 16-22) (P = .009).

CONCLUSION

Both repair techniques are effective for 50% partial-thickness bursal-side rotator cuff tears; however, TCR yields significantly superior biomechanical and histological characteristics compared with ISR.

CLINICAL RELEVANCE

Tear completion and repair technique may increase tendon-to-bone healing and thereby reduce re-rupture rate in the partial thickness bursal side rotator cuff tears.

Suprascapular nerve neuropathy leads to supraspinatus tendon degeneration

BACKGROUND

Nowadays most of attention regarding rotator cuff is payed to how to reduce the failure after rotator cuff surgical repair rather than how to prevent the rotator cuff tear before surgery. The etiologies of rotator cuff tear are still unclear. As we all know, the nerve system include brain, spinal cord, sensory organs and all the neurons allover our body coordinates the homoeostasis of our body. We hypothesis that the nerve injury proximal to suprascapular nerve can leads to rotator cuff degeneration even tear.

METHODS

Thirty-six SD rats were used. A defect on the suprascapular nerve was made on the right side and a sham surgery on the nerve (expose nerve only) at the left side. The insertion of supraspinatus tendon and supraspinatus muscle were harvested for testing. Twelve rats were sacrificed for biomechanical (six rats) and histological (six rats) properties were evaluated at 3, 6, and 9 weeks after surgery, respectively.

RESULTS

Significant inferior biomechanical properties of rotator cuff were found in nerve injured side compared to the nerve intact side at 6-9 weeks. Significant muscle atrophy was found at nerve injured side from 3 to 9 weeks. The enthesis of nerve injured side showed significant excessive cell maturity, reduced cellularity, smaller metachromasia area and more type-III collagen especially at 9 weeks after surgery.

CONCLUSIONS

The neuropathy proximal to suprascapular nerve can leads to rotator cuff degeneration even tear. The nerve dysfunction maybe an important etiology for rotator cuff tear.

Suprascapular nerve injury affects rotator cuff healing: A paired controlled study in a rat model

Purpose

We designed a paired controlled study to investigate the role of the suprascapular nerve (SSN) in rotator cuff healing using a rat tear model, and we hypothesised that rotator cuff healing is impaired in the absence of a healthy SSN.

Methods

Bilateral supraspinatus tenotomy from the great tuberosity was performed for 36 Wistar rats, which was then repaired immediately. A defect on the SSN was made on the right side, and a sham surgery was performed on the SSN at the left side. Twelve rats were sacrificed for biomechanical (six rats) and histological (six rats) testing, evaluated at 3, 6, and 9 weeks after surgery.

Results

The bone–tendon junction on the nerve-intact side showed significantly better biomechanical characteristics than the nerve-injured side in terms of maximum load, maximum stress over time, stiffness at 9 weeks, and Young's modulus at 3 and 9 weeks. On the nerve-injured side, significantly smaller fibrocartilage layers and muscle fibres could be obtained over time. In addition, on the nerve-injured side, inferior bone–tendon interface formation was obtained in terms of cell maturity, cell alignment, collagen orientation, and the occurrence of tidemark and Sharpey's fibres through 9 weeks. In addition, neuropeptide Y was secreted in the nerve-intact group at 6 and 9 weeks.

Conclusion

This study showed the inferior healing of the bone–tendon junction on the nerve-injured side compared with the nerve-intact side, which indicates that the SSN plays an important role in rotator cuff healing. Surgeons should pay more attention to SSN injury when treating patients with rotator cuff tear.

Comparison of bone surface and trough fixation on bone-tendon healing in a rabbit patella-patellar tendon injury model

BACKGROUND

Many orthopedic surgical procedures involve reattachment between tendon and bone. Whether bone-tendon healing is better facilitated by tendon fixation on a bone surface or within a tunnel is unknown. The purpose of this study was to comparatively evaluate the effects of bone surface versus bone trough fixation on bone-tendon healing in a rabbit patella-patellar tendon (PPT) injury model.

METHODS

The rabbits underwent partial patellectomy with patellar-tendon fixation on the osteotomy surface (bone surface fixation, BSF group) (n = 28) or within a bone trough (bone trough fixation, BTF group) (n = 28). The PPT interface was evaluated by macroscopic observation, micro-computed tomography scanning, histological analysis, and biomechanical testing at postoperative week 8 or week 16.

RESULTS

Macroscopically, no signs of infection or osteoarthritis were observed, and the regenerated tissue bridging the residual patella and patellar tendon showed no obvious difference between the two groups. There were significantly higher bone mineral density ​and trabecular thickness ​in BSF group compared with BTF group at week 8 (p ​< ​0.05 for both). However, the bone volume fraction (BVF), bone mineral density and trabecular thickness in BSF group were significantly lower than those in BTF group (p ​< ​0.05 for all) at week 16. Histological analysis demonstrated that new bone was formed at the proximal patella and reattached to the residual patellar tendon through a regenerated fibrocartilage-like tissue in both groups. There was more formation and better remodelling of fibrocartilage-like tissue in BTF group than BSF group at week 8 and week 16 (p ​< ​0.05 for both). Biomechanical testing revealed that there was higher failure load and stiffness at the PPT interface in BTF group than BSF group at week 16 (p ​< ​0.05 for both).

CONCLUSIONS

These results suggested that raptured tendon fixation in a bone trough resulted in superior bone-tendon healing in comparison with tendon fixation on bone surface in a rabbit PPT injury model.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

Although the structural and functional difference of knee joint between human and rabbit limit the results to be directly used in clinical, our research does offer a valuable reference for the improvement of reattachment between bone and tendon.

A more flattened bone tunnel has a positive effect on tendon-bone healing in the early period after ACL reconstruction

PURPOSE

The purpose of this study was to evaluate whether a flattened bone tunnel has a positive effect on the tendon-bone healing (TBH) process in the early period after anterior cruciate ligament (ACL) reconstruction.

METHODS

Seventy-two New Zealand White rabbits were randomly allocated into two groups, the flattened tunnel (FT) group and the conventional round tunnel (RT) group. We compared the cross-sectional areas and diameters of the bone tunnels between the two groups through computed tomography (CT) scanning. TBH results between the two groups were assessed by histological analysis, micro-CT scanning and biomechanical tests at 4 weeks, 8 weeks and 12 weeks after operation.

RESULTS

The cross-sectional areas of the bone tunnels between the two groups were almost the same. However, the shape of bone tunnels in the FT group was more flattened. A faster cellular and collagen remoulding process were found in the FT group. Semiquantitative histological analysis of Safranin O staining showed that there was more fibrocartilage formation in the interface region in the FT group (P < 0.05). Sirius Red staining showed that the tissues in the interface areas were more intense in the FT group. Micro-CT scanning showed that more new bone formation could be found in the interface region in the FT group. The biomechanical tests also showed that FT ACL reconstruction will result in a stronger regenerated tendon-bone interface.

CONCLUSIONS

Our study found that a flattened bone tunnel accelerated TBH in the early period after ACL reconstruction surgery in a rabbit model, which lays the groundwork for further clinical practice of this ACL reconstruction method.

Animal modeling in bone research-Should we follow the White Rabbit?

Animal models are live subjects applied to translational research. They provide insights into human diseases and enhance biomedical knowledge. Livestock production has favored the pace of human social development over millennia. Today's society is more aware of animal welfare than past generations. The general public has marked objections to animal research and many species are falling into disuse. The search for an ideal methodology to replace animal use is on, but animal modeling still holds great importance to human health. Bone research, in particular, has unmet requirements that in vitro technologies cannot yet fully address. In that sense, standardizing novel models remains necessary and rabbits are gaining in popularity as potential bone models. Our aim here is to provide a broad overview of animal modeling and its ethical implications, followed by a narrower focus on bone research and the role rabbits are playing in the current scenario.

How Long Should We Wait to Create the Goutallier Stage 2 Fatty Infiltrations in the Rabbit Shoulder for Repairable Rotator Cuff Tear Model?

Background

Significant proportion of rotator cuff tears (RCTs) in clinical field are of a kind of repairable tear wherein the degree of fatty infiltration is of Goutallier stage 1 or stage 2. Therefore, the animal model, showing similar fatty infiltration, seems preferable for researches. The purpose of this study is to find out the proper time frame in which there is Goutallier stage 1 or stage 2 fatty infiltration in the rabbit RCT model for the research of repairable RCT in humans.

Methods

Supraspinatus tendon tears were created in forty male New Zealand white rabbits at their right shoulder (n= 8 for each group), and a sham operation on the left shoulder. Rabbits were divided into five groups (2nd, 4th, 6th, 8th, and 12th weeks). Specimens were harvested from the central portion of the supraspinatus muscle for haematoxylin and eosin (H &E) staining, followed by histological and Goutallier grading evaluation. Results are expressed as mean ± standard deviation by Sigma Plot software (version 7.0).

Results

At two weeks, mainly lipoblasts were observed around the muscle fibers, and at four weeks these lipoblasts were replaced by mature adipocytes with fatty infiltration amount (2.13 ± 0.35). The degree of muscle atrophy was (1.50 ± 0.53) at four weeks compared to sham group (0.88 ± 0.64) with significant difference (p < 0.05). The inflammatory process appeared as two phases. At two weeks, it was increased with grading value (1.88 ± 0.35). However, in the four-week group, it showed a sharp decrease (0.50 ± 0.53). At six weeks, inflammation reappeared to increase (1.13 ± 0.83). Then, a gradual decline appeared at eight weeks (0.88 ± 0.83) and at 12 weeks (0.50 ± 0.92).

Conclusions

At two and four weeks, both fat distribution in rabbit supraspinatus muscles and Goutallier grading scale mostly appeared as grade 2. Therefore, we can consider four weeks to be a suitable period for making a repairable RCT animal model for the human research, considering the early acute tissue reaction at 2 weeks after the tendon tears.

Effect of Low-Intensity Pulsed Ultrasound After Autologous Adipose-Derived Stromal Cell Transplantation for Bone-Tendon Healing in a Rabbit Model

BACKGROUND

Low-intensity pulsed ultrasound (LIPUS), as a safe biophysiotherapy, can enhance bone-tendon (B-T) healing in vivo and induce osteogenic or chondrogenic differentiation of mesenchymal stromal cells in vitro. This study aimed to determine whether LIPUS can improve the efficacy of transplanted mesenchymal stromal cells on B-T healing.

HYPOTHESIS

LIPUS can induce lineage-specific differentiation of transplanted adipose-derived stromal cells (ASCs) at the B-T healing site, thus resulting in superior healing quality when compared with LIPUS or ASCs alone.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 112 mature rabbits with partial patellectomy in the hindlimb were randomly assigned into mock sonication without ASCs (control), ultrasonication without ASCs (LIPUS), mock sonication with ASCs (ASCs), and ultrasonication with ASCs (LIPUS + ASCs). The treatment time of the mock sonication or ultrasonication was 20 minutes per day. Autologous ASCs were transplanted to the healing site by fibrin glue during the operation, and LIPUS was delivered daily starting at postoperative day 3 until euthanasia. The patella-patellar tendon junctions were postoperatively harvested at 8 and 16 weeks for radiological, histological, and mechanical evaluations. Additionally, 9 animals were used for ASC tracking with mCherry protein.

RESULTS

Radiologically, there was more new bone formation and remodeling in the LIPUS + ASCs group as compared with the other groups. Synchrotron radiation micro-computed tomography showed that the LIPUS + ASCs group significantly increased bone volume fraction, trabecular thickness, and trabecular number at the healing site as compared with the other groups at postoperative 8 weeks ( P < .05 for all). Histologically, immunohistochemical staining confirmed that the transplanted mCherry-ASCs can differentiate into osteoblasts and fibrochondrocytic-like cells. Meanwhile, as compared with the other groups, the LIPUS + ASCs group showed more formation and maturity of the fibrocartilage layer and new bone at postoperative weeks 8 and 16 ( P < .05 for all). Biomechanically, the LIPUS + ASCs group showed significantly higher failure load and stiffness versus the other groups at postoperative weeks 8 and 16 ( P < .05 for all).

CONCLUSION

Autologous ASC transplantation stimulated with LIPUS can result in superior B-T healing quality when compared with LIPUS or ASCs alone.

CLINICAL RELEVANCE

This study demonstrates the effectiveness of using ASC transplantation stimulated with LIPUS for B-T healing and provides a foundation for future clinical studies.