Morphology and matrix composition during early tendon to bone healing

Study of bone-tendon interface healing in an animal model using a synthetic scaffold and PRP

PURPOSE

Biological matrices have been used to reinforce large rotator cuff tear repairs. However, rapid resorption and initial immune reactions presented challenges in clinical practice. This study evaluates whether a resorbable synthetic matrix (scaffold), used alone or with platelet-rich plasma (PRP), impacts repair processes at microscopic, ultrasound, and biomechanical levels in a rabbit model of induced tendon-bone interface injury.

METHODS

An experimental study was performed on 24 rabbits. Two experimental groups (n = 12 each) and a control group (n = 24) were defined. In the first group (BioP), the internal gastrocnemius tendon was sectioned and repaired to bone using double-row sutures, reinforced with a PLC (poly-L-lactic-co-ε-caprolactone) and PLA (polylactic acid) scaffold. In the second group (BioP + PRP), autologous PRP was added to the repair. The control group received no scaffold or PRP. Euthanasia was performed at 8 weeks, followed by microscopic, ultrasound, and biomechanical evaluations.

RESULTS

Microscopically, a granulomatous reaction limited to the foreign body was observed in both scaffold groups. The healing process was not altered in any group, showing good biocompatibility of the scaffold. Echographically, a greater sagittal diameter was observed in the group without PRP compared to the other groups. Biomechanically, no significant differences in rupture zones were found across groups, but the scaffold-only group required a higher maximum applied force before rupture.

CONCLUSIONS

At 8 weeks, using a degradable synthetic PLC and PLA scaffold as support at the bone-tendon interface did not significantly alter the normal repair process, showed echographic and biomechanical benefits, and PRP did not show additional benefits in our experimental model.

Advances focusing on the application of decellularization methods in tendon-bone healing

BACKGROUND

The tendon or ligament is attached to the bone by a triphasic but continuous area of heterogeneous tissue called the tendon-bone interface (TBI). The rapid and functional regeneration of TBI is challenging owing to its complex composition and difficulty in self-healing. The development of new technologies, such as decellularization, has shown promise in the regeneration of TBI. Several ex vivo and in vivo studies have shown that decellularized grafts and decellularized biomaterial scaffolds achieved better efficacy in enhancing TBI healing. However further information on the type of review that is available is needed.

AIM OF THE REVIEW

In this review, we discuss the current application of decellularization biomaterials in promoting TBI healing and the possible mechanisms involved. With this work, we would like to reveal how tissues or biomaterials that have been decellularized can improve tendon-bone healing and to provide a theoretical basis for future related studies.

KEY SCIENTIFIC CONCEPTS OF THE REVIEW

Decellularization is an emerging technology that utilizes various chemical, enzymatic and/or physical strategies to remove cellular components from tissues while retaining the structure and composition of the extracellular matrix (ECM). After decellularization, the cellular components of the tissue that cause an immune response are removed, while various biologically active biofactors are retained. This review further explores how tissues or biomaterials that have been decellularized improve TBI healing.

Biologic Impact of Anterior Cruciate Ligament Injury and Reconstruction

Surgical intervention after anterior cruciate ligament (ACL) tears is typically required because of the limited healing capacity of the ACL. However, mechanical factors and the inflammatory response triggered by the injury and surgery can impact patient outcomes. This review explores key aspects of ACL injury and reconstruction biology, including the inflammatory response, limited spontaneous healing, secondary inflammation after reconstruction, and graft healing processes. Understanding these biologic mechanisms is crucial for developing new treatment strategies and enhancing patient well-being. By shedding light on these aspects, clinicians and researchers can work toward improving quality of life for individuals affected by ACL tears.

External stimulation: A potential therapeutic strategy for tendon-bone healing

Injuries at the tendon-bone interface are very common in the field of sports medicine, and healing at the tendon-bone interface is complex. Injuries to the tendon-bone interface can seriously affect a patient’s quality of life, so it is essential to restore stability and promote healing of the tendon-bone interface. In addition to surgical treatment, the healing of tendons and bones can also be properly combined with extracorporeal stimulation therapy during the recovery process. In this review, we discuss the effects of extracorporeal shock waves (ESWs), low-intensity pulsed ultrasound (LIPUS), and mechanical stress on tendon-bone healing, focusing on the possible mechanisms of action of mechanical stress on tendon-bone healing in terms of transcription factors and biomolecules. The aim is to provide possible therapeutic approaches for subsequent clinical treatment.

Multiparity and Aging Impact Chondrogenic and Osteogenic Potential at Symphyseal Enthesis: New Insights into Interpubic Joint Remodeling

Pregnancy and childbirth cause adaptations to the birth canal to allow for delivery and fast recovery. To accommodate delivery through the birth canal, the pubic symphysis undergoes changes that lead to the interpubic ligament (IpL) and enthesis formation in primiparous mice. However, successive deliveries influence joint recovery. We aimed to understand tissue morphology and chondrogenic and osteogenic potential at symphyseal enthesis during pregnancy and postpartum in primiparous and multiparous senescent female mice. Morphological and molecular differences were found at the symphyseal enthesis among the study groups. Despite the apparent incapacity to restore cartilage in multiparous senescent animals, the symphyseal enthesis cells are active. However, these cells have reduced expression of chondrogenic and osteogenic markers and are immersed in densely packed collagen fibers contiguous to the persistent IpL. These findings may indicate alterations of key molecules in the progenitor cell population maintenance of the chondrocytic and osteogenic lineages at the symphyseal enthesis in multiparous senescent animals, possibly compromising the mouse joint histoarchitecture recovery. This sheds light on the distention of the birth canal and the pelvic floor that may play a role in pubic symphysis diastasis (PSD) and pelvic organ prolapse (POP), both in orthopedic and urogynecological practice in women.

Simvastatin promotes rat Achilles tendon-bone interface healing by promoting osteogenesis and chondrogenic differentiation of stem cells

To investigate the effect and mechanism of simvastatin on cell components of tendon-bone healing interface. The tendon-bone healing model was established by inserting the end of the Achilles tendon into the tibial tunnel on 24 rats, and simvastatin was used locally at the tendon-bone interface. Healing was evaluated at 8 weeks by mechanical testing, micro-CT, and qualitative histology including H&E, Toluidine blue, and immunohistochemical staining. In vitro, bone marrow stromal cells (BMSCs) and tendon-derived mesenchymal stem cells (TDSCs) underwent osteogenic and chondrogenic differentiation respectively by plate co-culture. An analysis was performed on days 7 and 14 of cell differentiation. Biomechanical testing demonstrated a significant increase in maximum stiffness in the simvastatin-treated group. Micro-CT analysis showed that the bone tunnels in the simvastatin group were smaller in diameter and had higher bone density. H&E and Toluidine blue staining demonstrated that tendon-bone healing was significantly greater with better tissue arrangement and more extracellular matrix in the simvastatin-treated group than that in the control group, and immunohistochemical staining showed the expression of VEGF in simvastatin group was significantly higher. Histological staining and RT-PCR confirmed that simvastatin could promote the differentiation of co-cultured BMSCs and TDSCs into osteoblasts and chondroblasts, respectively. The effect of promoting osteogenic differentiation was more tremendous at 14 days, while its effect on promoting chondroblast differentiation was more evident on the 7th day of differentiation. In conclusion, local administration of simvastatin can promote the tendon-bone healing by enhancing neovascularization, chondrogenesis, and osteogenesis in different stages of the tendon-bone healing process.

Smaller Gap Formation With Suture Anchor Fixation Than Traditional Transpatellar Sutures in Patella and Quadriceps Tendon Rupture: A Systematic Review

PURPOSE

The purpose of this study is to compare the biomechanical properties between traditional transosseous tunnel and suture anchor technique repair for extensor mechanism ruptures and assess for differences in the mechanism of failure of both techniques.

METHODS

A multi-database search (PubMed, EMBASE, and Medline) was performed according to PRISMA guidelines on November 14, 2021. All articles comparing biomechanical properties of transpatellar and suture anchor technique for extensor mechanism ruptures were included. Abstracts, reviews, case reports, studies without biomechanical analysis, conference proceedings, and non-English language studies were excluded. Outcomes pursued included gap formation, load to failure, and mechanism of failure. Relevant data from studies meeting inclusion criteria were extracted and analyzed. Study methodology was assessed using the Methodological Index for Non-Randomized Studies score.

RESULTS

A total of 212 knees were biomechanically assessed, including 98 patella and 114 quadricep tendon ruptures. Five patellar tendon studies were included, and all of them reported significantly smaller gap formation in suture anchor group. Gap formation for suture anchors ranged from .9 mm to 4.1 mm, while that of transpatellar group ranged from 2.9 mm to 10.3 mm. One study reported a significantly higher load to failure in the suture anchor group, while the remaining four studies reported no significant difference. Load to failure for suture anchor ranged from 259 N to 779 N, while that of the transpatellar group ranged from 287 N to 763 N. The most common mechanism of failure was anchor pullout in suture anchor and knot failure in the transpatellar group. Five quadriceps tendon studies were included, and three studies reported statistically significant smaller gap formation in the suture anchor group. Gap formation for suture anchor ranged from 1.5 mm to 5.0 mm, while that of transpatellar group ranged from 3.1 mm to 33.3 mm. Two studies reported a significantly higher load to failure in the suture anchor group, while one study reported a higher load to failure in the transpatellar repair group. Load to failure for suture anchor ranged from 286 N to 740 N, while that of transpatellar group ranged from 251 N to 691 N. The most common mechanism of failure was suture failure in the suture anchor and knot failure in the transpatellar group.

CONCLUSION

Suture anchor fixation displays a better biomechanical profile than traditional transpatellar techniques in terms of smaller gap formations in the repair of both patella and quadriceps tendon injuries. Anchor pullout in suture anchor fixation was present mainly with the use of titanium anchors.

CLINICAL RELEVANCE

These findings above may result in better retention of tendon approximation in patella and quadriceps tendon fixation postoperatively, which may result in earlier recovery. Further randomized controlled clinical trials to compare these techniques are required.

Time-series biological responses toward decellularized bovine tendon graft and autograft for 52 consecutive weeks after rat anterior cruciate ligament reconstruction

There is an essential demand for developing biocompatible grafts for knee anterior cruciate ligament reconstruction (ACLR). This study investigated cell infiltration into decellularized bovine tendon xenografts using a rat knee ACLR model. Twelve-week-old Sprague–Dawley rats were used. At weeks 1, 2, 4, 8, 16, 26, and 52 (each period, n = 6) after ACLR, rats receiving decellularized bovine tendon (group D, n = 42) or autologous tendon (group A, n = 42) as grafts underwent peritibial bone tunnel bone mineral density (BMD), histological, and immunohistological assessments. BMD increased over time in both the groups until week 16 and then remained unchanged without exhibiting significant differences between the groups. Initially, cellularity in group D was lower than that in group A; however, by weeks 4–8, both the groups were comparable to the native anterior cruciate ligament group and cellularity remained unchanged until week 52. Initially, group A had more M1 macrophages, indicating inflammation, whereas group D had more M2 macrophages, indicating tissue regeneration. Nonetheless, the M1 and M2 macrophage counts of both the groups were comparable at most times. This study revealed the excellent recellularization and tendon–bone integration abilities of decellularized tendons using a cross-species model.

Tackling the Challenges of Graft Healing After Anterior Cruciate Ligament Reconstruction-Thinking From the Endpoint

Anterior cruciate ligament (ACL) tear is common in sports and accidents, and accounts for over 50% of all knee injuries. ACL reconstruction (ACLR) is commonly indicated to restore the knee stability, prevent anterior–posterior translation, and reduce the risk of developing post-traumatic osteoarthritis. However, the outcome of biological graft healing is not satisfactory with graft failure after ACLR. Tendon graft-to-bone tunnel healing and graft mid-substance remodeling are two key challenges of biological graft healing after ACLR. Mounting evidence supports excessive inflammation due to ACL injury and ACLR, and tendon graft-to-bone tunnel motion negatively influences these two key processes. To tackle the problem of biological graft healing, we believe that an inductive approach should be adopted, starting from the endpoint that we expected after ACLR, even though the results may not be achievable at present, followed by developing clinically practical strategies to achieve this ultimate goal. We believe that mineralization of tunnel graft and ligamentization of graft mid-substance to restore the ultrastructure and anatomy of the original ACL are the ultimate targets of ACLR. Hence, strategies that are osteoinductive, angiogenic, or anti-inflammatory should drive graft healing toward the targets. This paper reviews pre-clinical and clinical literature supporting this claim and the role of inflammation in negatively influencing graft healing. The practical considerations when developing a biological therapy to promote ACLR for future clinical translation are also discussed.

Anatomy and histomorphology of the flexor digitorum profundus enthesis: functional implications for tissue engineering and surgery

Background

The enthesis possesses morphological adaptations across the soft-hard tissue junction which are not fully restored during surgical avulsion repairs. This loss of anatomical structure, highly related to function, contributes to poor clinical outcomes. Investigating the native macro- and micro-structure of a specific enthesis can provide functional and biomechanical insights to develop specialised, novel tissue-engineered therapeutic options and potentially improve current surgical treatments for avulsion injuries.

Methods

This study examines the anatomy and histomorphology of the flexor digitorum profundus (FDP) enthesis in 96 fresh-frozen human cadaveric fingers, quantitatively and qualitatively analyzing the shape, size, angle of tendon fibres and histological architecture, and explores differences in sex, finger and distance along the enthesis using linear mixed effects models.

Results

Macroscopically, results showed a consistent trapezoidal insertion shape of 29.29 ± 2.35 mm² mean surface area, but with significant morphometric size differences influenced primarily by the smaller dimensions of the little finger. Microscopically, a fibrocartilaginous enthesis was apparent with a 30.05 ± 0.72^o mean angle of inserting tendon fibres, although regional variation in fibrocartilage and the angle change of tendon fibres before insertion existed.

Conclusions

The implication of these findings on native and specific FDP enthesis function is discussed whilst providing recommendations for optimal FDP enthesis recreation for interfacial tissue engineers and hand surgeons. The study emphasizes the importance of region-specific knowledge whilst also describing methods applicable to assessing any soft tissue insertion.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04922-1.

The role of tendon derived stem/progenitor cells and extracellular matrix components in the bone tendon junction repair

Fibrocartilage enthesis is the junction between bone and tendon with a typical characteristics of fibrocartilage transition zones. The regeneration of this transition zone is the bottleneck for functional restoration of bone tendon junction (BTJ). Biomimetic approaches, especially decellularized extracellular matrix (ECM) materials, are strategies which aim to mimic the components of tissues to the utmost extent, and are becoming popular in BTJ healing because of their ability not only to provide scaffolds to allow cells to attach and migrate, but also to provide a microenvironment to guide stem/progenitor cells lineage-specific differentiation. However, the cellular and molecular mechanisms of those approaches, especially the ECM proteins, remain unclear. For BTJ reconstruction, fibrocartilage regeneration is the key for good integrity of bone and tendon as well as its mechanical recovery, so the components which can guide stem cells to a chondrogenic commitment in biomimetic approaches might well be the key for fibrocartilage regeneration and eventually for the better BTJ healing. In this review, we firstly discuss the importance of cartilage-like formation in the healing process of BTJ. Next, we explore the possibility of tendon-derived stem/progenitor cells as cell sources for BTJ regeneration due to their multi-differentiation potential. Finally, we summarize the role of extracellular matrix components of BTJ in guiding stem cell fate to a chondrogenic commitment, so as to provide cues for understanding the mechanisms of lineage-specific potential of biomimetic approaches as well as to inspire researchers to incorporate unique ECM components that facilitate BTJ repair into design.

Stable Gastric Pentadecapeptide BPC 157 as a Therapy for the Disable Myotendinous Junctions in Rats

(1) Aim: The stable gastric pentadecapeptide BPC 157 is known to heal transected muscle, tendon, and ligament. Thereby, in this study, we investigated the effect of BPC 157 on the dissection of the quadriceps tendon from the quadriceps muscle in rats. (2) Materials and Methods: Myotendinous junction defect, which cannot heal spontaneously in rats, as evidenced with consistent macro/microscopic, biomechanical, functional assessments, eNOS, and COX-2 mRNA levels and oxidative stress and NO-levels in the myotendinous junctions. BPC 157 (10 µg/kg, 10 ng/kg) regimen was given (i) intraperitoneally, first application immediately after surgery, last 24 h before sacrifice; (ii) per-orally, in drinking water (0.16 µg/mL, 0.16 ng/mL, 12 mL/rat/day), till the sacrifice at 7, 14, 28 and 42 postoperative days. (3) Results: These BPC 157 regimens document prominent therapy effects (macro/microscopic, biomechanical, functional much like eNOS and COX-2 mRNA levels and counteracted oxidative stress and NO-levels in the myotendinous junctions), while controls have a poor presentation. Especially, in rats with the disabled myotendinous junction, along with full functional recovery, BPC 157 counteracts muscle atrophy that is regularly progressive and brings muscle presentation close to normal. Accordingly, unlike the perilous course in controls, those rats, when receiving BPC 157 therapy, exhibit a smaller defect, and finally defects completely disappear. Microscopically, there are no more inflammatory infiltrate, well-oriented recovered tissue of musculotendon junction appears in BPC 157 treated rats at the 28 days and 42 days. (4) Conclusions: BPC 157 restores myotendinous junction in accordance with the healing of the transected muscle, tendon, and ligament.

Stem cell therapies in tendon-bone healing

Tendon-bone insertion injuries such as rotator cuff and anterior cruciate ligament injuries are currently highly common and severe. The key method of treating this kind of injury is the reconstruction operation. The success of this reconstructive process depends on the ability of the graft to incorporate into the bone. Recently, there has been substantial discussion about how to enhance the integration of tendon and bone through biological methods. Stem cells like bone marrow mesenchymal stem cells (MSCs), tendon stem/progenitor cells, synovium-derived MSCs, adipose-derived stem cells, or periosteum-derived periosteal stem cells can self-regenerate and potentially differentiate into different cell types, which have been widely used in tissue repair and regeneration. Thus, we concentrate in this review on the current circumstances of tendon-bone healing using stem cell therapy.

Does Demineralized Bone Matrix Enhance Tendon-to-Bone Healing after Rotator Cuff Repair in a Rabbit Model?

Backgroud

The purpose of this study was to compare the histologic outcomes of rotator cuff (RC) repair with demineralized bone matrix (DBM) augmentation and those without DBM augmentation and to evaluate the role of DBM for tendon-to-bone (TB) healing in a rabbit model.

Methods

Twenty-six adult male New Zealand white rabbits were randomly allocated to the control group (n = 13) or the DBM group (n = 13). Repair was performed 8 weeks after complete transection of the right supraspinatus tendon of all rabbits. In the control group, RC repair was achieved by a standard transosseous technique. In the DBM group, RC repair was achieved using the same technique, and DBM was interposed between the cuff and bone. After 8 weeks, the RC tendon entheses from all rabbits were processed for gross and histologic examination.

Results

On gross TB healing, 2 of 11 specimens in the control group were unhealed and no specimen was grossly unhealed in the DBM group (p = 0.421). In the control group, the tendon midsubstance was disorganized with randomly and loosely arranged collagen fibers and rounded fibroblastic nuclei. The TB interface was predominantly fibrous with small regions of fibrocartilage, especially mineralized fibrocartilage. In the DBM group, the tendon midsubstance appeared normal and comprised densely arranged collagen fibers, with orientated crimped collagen fibers running in the longitudinal direction of the tendon. These fibers were interspersed with elongated fibroblast nuclei. The TB interface consisted of organized collagen fibers with large quantities of fibrocartilage and mineralized fibrocartilage.

Conclusions

The use of DBM for TB interface healing in rabbit experiments showed good results in gross and histologic analysis. However, it is difficult to draw a solid conclusion because the sample size is small. Further evaluation in the in vivo setting is necessary to determine clinical recommendations.

FGF2: a key regulator augmenting tendon-to-bone healing and cartilage repair

Ligament/tendon and cartilage injuries are clinically common diseases that perplex most clinicians. Because of the lack of blood vessels and nerves, their self-repairing abilities are rather poor. Therefore, surgeries are necessary and also widely used to treat ligament/tendon or cartilage injuries. However, after surgery, there are still many problems that affect healing. In recent years, it has been found that exogenous FGF2 plays an important role in the repair of ligament/tendon and cartilage injuries and exerts a synergistic effect with endogenous FGF2. Therefore, FGF2 can be used as a new type of biomolecule to accelerate tendon-to-bone healing and cartilage repair after injury.

Guided versus freehand acromioplasty during rotator cuff repair. A randomized prospective study

INTRODUCTION

There is no consensus on how to perform acromioplasty, particularly regarding the level and extent of bone resection, which depend on scapular and humeral morphologies.

HYPOTHESIS

We aimed to determine whether computer-assisted acromioplasty planning helps surgeons remove impinging bone, reduce unnecessary resections, and improve short-term outcomes of rotator cuff tears (RCR).

PATIENTS AND METHODS

We randomized 64 patients undergoing RCR of full-thickness supraspinatus tears into two groups: 'guided acromioplasty' (GA) and 'freehand acromioplasty' (FA). The pre- and post-operative scapula models were reconstructed using computed-tomography scans to quantify impinging bone removal, unnecessary bone resections, and identify zones of acromial bone removal. All patients were evaluated preoperatively and at 6 months to assess their range of motion (ROM), functional scores and tendon integrity using ultrasound.

RESULTS

The two groups did not differ in demographics, clinical or morphologic characteristics. Compared to FA, GA tended to lower impinging bone removal (55±26% vs. 43±27%, p=0.087) and to increase unnecessary resection of the total bone removed (49±22% vs. 57±27%, p=0.248). GA resulted in significant anterior under-resection, while FA resulted in significant medial over-resection. Clinical outcomes and ROM improved significantly for all patients, except for internal rotation in the GA group. There were no other significant differences between the two groups, neither in terms of post-operative scores nor in terms of clinical net improvements, nor tendon repair integrity.

CONCLUSIONS

This computer-assisted planning for acromioplasty during RCR proved no benefits in terms of bone removal, tendon healing, or clinical outcomes. Nonetheless such planning tools could help less experienced surgeons improve the efficacy of acromioplasty.

LEVEL OF PROOF

I, Randomized controlled trial (Therapeutic study).

Flexor digitorum longus tendon transfer to the navicular: tendon-to-tendon repair is stronger compared with interference screw fixation

PURPOSE

To assess whether early rehabilitation could be safe after flexor digitorum longus (FDL) tendon transfer, the current biomechanical study aimed to measure tendon displacement under cyclic loading and load to failure, comparing a traditional tendon-to-tendon (TT) repair with interference screw fixation (ISF).

METHODS

24 fresh-frozen cadaveric below knee specimens underwent FDL tendon transfer. In 12 specimens a TT repair was performed via a navicular bone tunnel. In a further 12 specimens ISF was performed. Using a materials testing machine, the FDL tendon was cycled 1000 times to 150 N and tendon displacement at the insertion site measured. A final load to failure test was then performed. Statistical analysis was performed using two-way ANOVA and an independent t test, with a significance level of p < 0.05.

RESULT

No significant difference in tendon displacement occurred after cyclic loading, with mean tendon displacements of 1.9 ± 1.2 mm (mean ± SD) in the TT group and 1.8 ± 1.5 mm in the ISF group (n.s.). Two early failures occurred in the ISF group, none in the TT group. Mean load to failure was significantly greater following TT repair (459 ± 96 N), compared with ISF (327 ± 76 N), p = 0.002.

CONCLUSION

Minimal tendon displacement of less than 2 mm occurred during cyclic testing in both groups. The two premature failures and significantly reduced load to failure observed in the ISF group, however, indicate that the traditional TT technique is more robust. Regarding clinical relevance, this study suggests that early active range of motion and protected weight bearing may be safe following FDL tendon transfer for stage 2 tibialis posterior tendon dysfunction.

Anterior Cruciate Ligament Reconstruction in a Rabbit Model Using a Decellularized Allogenic Semitendinous Tendon Combined with Autologous Bone Marrow-Derived Mesenchymal Stem Cells

As a regular adoptable material for anterior cruciate ligament (ACL) reconstruction, free tendon allograft exhibits unsatisfactory outcomes, such as retarded ligamentization and tendon–bone integration. The application of bone marrow‐derived mesenchymal stem cells (BMSCs), as well as a decellularized free tendon allograft developed by our group, was proven to be effective in improving ACL reconstruction results. This study aimed to investigate the efficacy and feasibility of decellularized allogenic semitendinous tendon (ST) combined with autologous BMSCs used as a substitute to free tendon allograft in a rabbit model. This study finally shows that the decellularized allogenic ST combined with autologous BMSCs could significantly improve ACL reconstruction results compared with allograft. stem cells translational medicine2019;8:971&982

Cell Therapies in Tendon, Ligament, and Musculoskeletal System Repair

In the last few decades, several techniques have been used to optimize tendon, ligament, and musculoskeletal healing. The evidence in favor of these techniques is still not proven, and level I studies are lacking. We performed an analysis of the therapeutic strategies and tissue engineering projects recently published in this field. Here, we try to give an insight into the current status of cell therapies and the latest techniques of bioengineering applied to the field of orthopedic surgery. The future areas for research in the management of musculoskeletal injuries are outlined. There are emerging technologies developing into substantial clinical treatment options that need to be critically evaluated. Mechanical stimulation of the constructs reproduces a more propitious environment for effective healing.

Comparison of Bone Tunnel and Cortical Surface Tendon-to-Bone Healing in a Rabbit Model of Biceps Tenodesis

BACKGROUND

Many orthopaedic surgical procedures involve reattachment of a single tendon to bone. Whether tendon-to-bone healing is better facilitated by tendon fixation within a bone tunnel or on a cortical surface is unknown. The purpose of this study was to evaluate tendon-healing within a bone tunnel compared with that on the cortical surface in a rabbit model of biceps tenodesis.

METHODS

Thirty-two rabbits (24 weeks of age) underwent unilateral proximal biceps tenodesis with tendon fixation within a bone tunnel (BT group) or on the cortical surface (SA [surface attachment] group). Postoperatively, rabbits were allowed free-cage activity without immobilization. All rabbits were killed 8 weeks after surgery. Healing was assessed by biomechanical testing, microcomputed tomography (micro-CT), and histomorphometric analysis.

RESULTS

Biomechanical testing demonstrated no significant difference between the groups in mean failure loads (BT: 56.8 ± 28.8 N, SA: 55.8 ± 14.9 N; p = 0.92) or stiffness (BT: 26.3 ± 16.6 N/mm, SA: 32.3 ± 9.6 N/mm; p = 0.34). Micro-CT analysis demonstrated no significant difference between the groups in mean volume of newly formed bone (BT: 69.3 ± 13.9 mm, SA: 65.5 ± 21.9 mm; p = 0.70) or tissue mineral density of newly formed bone (BT: 721.4 ± 10.9 mg/cm, SA: 698.6 ± 26.2 mg/cm; p = 0.07). On average, newly formed bone within the tunnel represented only 5% of the total new bone formed in the BT specimens. Histological analysis demonstrated tendon-bone interdigitation and early fibrocartilaginous zone formation on the outer cortical surface in both groups. In contrast, minimal tendon-bone bonding was observed within the tunnel in the BT specimens.

CONCLUSIONS

Tendon fixation in a bone tunnel and on the cortical surface resulted in similar healing profiles. For tendons placed within a bone tunnel, intratunnel healing was minimal compared with the healing outside the tunnel on the cortical surface.

CLINICAL RELEVANCE

The creation of large bone tunnels, which can lead to stress risers and increase the risk of fracture, may not be necessary for biceps tenodesis procedures.

Demineralized Bone Matrix to Augment Tendon-Bone Healing: A Systematic Review

Background:

Following injury to the rotator cuff and anterior cruciate ligament, a direct enthesis is not regenerated, and healing occurs with biomechanically inferior fibrous tissue. Demineralized bone matrix (DBM) is a collagen scaffold that contains growth factors and is a promising biological material for tendon and ligament repair because it can regenerate a direct fibrocartilaginous insertion via endochondral ossification.

Purpose:

To provide a comprehensive review of the literature investigating the use of DBM to augment tendon-bone healing in tendon repair and anterior cruciate ligament reconstruction (ACLR).

Study Design:

Systematic review.

Methods:

Electronic databases (MEDLINE and EMBASE) were searched for preclinical and clinical studies that evaluated the use of DBM in tendon repair and ACLR. Search terms included the following: (“demineralized bone matrix” OR “demineralized cortical bone”) AND (“tissue scaffold” OR “tissue engineering” OR “ligament” OR “tendon” OR “anterior cruciate ligament” OR “rotator cuff”). Peer-reviewed articles written in English were included, and no date restriction was applied (searches performed February 10, 2017). Methodological quality was assessed with peer-reviewed scoring criteria.

Results:

The search strategy identified 339 articles. After removal of duplicates and screening according to inclusion criteria, 8 studies were included for full review (tendon repair, n = 4; ACLR, n = 4). No human clinical studies were identified. All 8 studies were preclinical animal studies with good methodological quality. Five studies compared DBM augmentation with non-DBM controls, of which 4 (80%) reported positive findings in terms of histological and biomechanical outcomes.

Conclusion:

Preclinical evidence indicates that DBM can improve tendon-bone healing, although clinical studies are lacking. A range of animal models of tendon repair and ACLR showed that DBM can re-create a direct fibrocartilaginous enthesis, although the animal models are not without limitations. Before clinical trials are justified, research is required that determines the best source of DBM (allogenic vs xenogenic) and the best form of DBM (demineralized cortical bone vs DBM paste) to be used in them.

Early Graft Tunnel Healing After Anterior Cruciate Ligament Reconstruction With Intratunnel Injection of Bone Marrow Mesenchymal Stem Cells and Vascular Endothelial Growth Factor

Background:

Bone marrow mesenchymal stem cells (BM-MSCs) are multipotent adult stem cells and have become an important source of cells for engineering tissue repair and cell therapy. Vascular endothelial growth factor (VEGF) promotes angiogenesis and contributes fibrous integration between tendon and bone during the early postoperative stage. Both MSCs and VEGF can stimulate cell proliferation, differentiation, and matrix deposition by enhancing angiogenesis and osteogenesis of the graft in the tunnel.

Hypothesis:

Injection of intratunnel BM-MSCs and VEGF enhances the early healing process of a tendon graft.

Study Design:

Controlled laboratory study.

Methods:

In this controlled animal laboratory study, each of 4 groups of rabbits underwent unilateral anterior cruciate ligament (ACL) reconstruction with use of the ipsilateral semitendinosus tendon. The rabbits received intratunnel injection of BM-MSCs and VEGF with a fibrin glue seal covering the distal tunnel at the articular site. Evaluation using magnetic resonance imaging (MRI), collagen type III expression, and biomechanical analyses were performed at 3- and 6-week intervals.

Results:

All parameters using MRI, collagen type III expression, and biomechanical analysis of pullout strength of the graft showed that application of intratunnel BM-MSCs and VEGF enhanced tendon-to-bone healing after ACL reconstruction.

Conclusion:

Intratunnel injections of BM-MSCs and VEGF after ACL reconstruction enhanced graft tunnel healing. Overall, the femoral tunnel that received BM-MSCs and VEGF had better advanced healing with increased collagen type III fibers and better outcomes on MRI and biomechanical analysis. MRI is the most reliable tool for clinical use in evaluating stages of ACL healing after reconstruction, since biopsy is an invasive procedure.

Anatomic Anterior Cruciate Ligament Reconstruction via Independent Tunnel Drilling: A Systematic Review of Randomized Controlled Trials Comparing Patellar Tendon and Hamstring Autografts

PURPOSE

To collect the highest level of evidence comparing anatomic anterior cruciate ligament (ACL) reconstruction via independent tunnel drilling using bone-patellar tendon-bone (BTB) and hamstring tendon (HT) autografts in terms of clinical outcome and failure rate.

METHODS

We performed a systematic review of clinical trials that randomized patients to ACL reconstruction with either BTB or HT autografts with a minimum 2-year follow-up. Only trials using independent tunnel drilling, including outside-in and anteromedial portal techniques, for both autografts were eligible for inclusion, whereas all transtibial studies were excluded. Study design, demographics, surgical technique, rehabilitation protocol, and clinical outcomes were compiled. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed. Quality assessment was performed using the Coleman Methodological Scale (CMS).

RESULTS

Six published studies reporting on 5 randomized controlled trials (RCTs) met the inclusion criteria. No study reported a difference in rerupture rate between BTB and HT. BTB-reconstructed knees experienced a greater incidence of anterior knee pain or crepitus in 2/7 trials and radiographic evidence of degenerative change in 3/7 trials. HT-reconstructed knees had increased instrumented laxity in 2/7 trials and less knee flexion strength postoperatively.

CONCLUSIONS

This study collects all available Level I and II evidence for anatomic ACL reconstruction using BTB and HT grafts. According to the data presented in these studies, clinical outcome scores and failure rates showed no differences for anatomic reconstruction using either autograft. However, in some studies, BTB-reconstructed knees experienced a greater incidence of anterior knee pain and radiographic evidence of degenerative change, and in others, HT-reconstructed knees had increased laxity and less knee flexion strength. In our opinion, both BTB and HT autografts remain valid options for ACL reconstruction when using anatomic drilling techniques, providing a stable knee with reliable return to activity.

LEVEL OF EVIDENCE

Level II, systematic review of Level I and II studies.

Meniscal Allograft Transplantation With Soft Tissue in Bone Socket Fixation: Arthroscopic Technique With Technical Pearls

Meniscal allograft transplantation may slow the progression of degenerative changes in the meniscus-deficient knee. The current literature suggests patients can experience good early to mid-term satisfaction and patient-reported outcomes with reasonable expectations of return to work. More ambitious applications in athletes have also shown good results although long-term data are lacking. Traditionally, meniscal allograft transplantation has been considered an open procedure with incorporation of bone blocks from the allograft source. However, as arthroscopic techniques have advanced, it has become possible to perform this procedure through a predominantly arthroscopic approach while securing the soft tissue graft in bone tunnels. The current demonstration provides this background and technical pearls for success in arthroscopic meniscal allograft transplantation.

P2 porous titanium implants improve tendon healing in an acute rat supraspinatus repair model

BACKGROUND

Current techniques in rotator cuff repair often lack structural integrity. P² porous titanium-coated constructs (DJO Surgical, Austin, TX, USA) promote osseointegration and soft tissue ingrowth. This study examined the ability of this material to improve the structural integrity of supraspinatus tendon repair in a rat model. We hypothesized that P² implants placed at the tendon-to-bone interface would improve mechanical and histologic measures of supraspinatus healing.

METHODS

Forty rats underwent supraspinatus repairs with P² implants in 1 shoulder and standard repair in the other. Rats were humanely killed at time 0 (n = 3), 2 weeks (n = 8), 4 weeks (n = 15), and 12 weeks (n = 14). Tendon-to-bone composite specimens were harvested and evaluated mechanically and histologically.

RESULTS

Tendon cross-sectional area was decreased in the P² implant group at 4 weeks, percentage of relaxation was increased at 2 weeks, elastic modulus was increased at 4 weeks, and maximum load and maximum stress were both increased at 2 and 4 weeks. Histologic analysis revealed no foreign body reactions within or around the P² implant, and healthy viable bone was visible within the P² implant.

CONCLUSION

The results support our hypothesis, specifically in early healing, in this randomized controlled animal study. These data support the use of P² porous titanium implants to improve tendon-to-bone healing.

Hamstring Graft Biological Preparation for Anterior Cruciate Ligament Reconstruction

The all-inside anterior cruciate ligament reconstruction (ACLR) success depends on biologic integration of the graft in the bone tunnel. Sutures wrapping the tendon in the bone tunnel may affect tendon-bone healing in shorter bone tunnels. To achieve better graft integration, we propose a variation of the graft link suture technique wherein the graft is linked chain-like to the femoral and tibial TightRope (Arthrex), which increases the tendon-bone contact area by eliminating sutures from the noose of the graft and thus may allow better graft integration.

Surgical Management of Rectus Femoris Avulsion Among Professional Soccer Players

BACKGROUND

Rectus femoris injuries are common among athletes, especially in kicking sports such as soccer; however, proximal rectus femoris avulsions in athletes are a relatively rare entity.

PURPOSE/HYPOTHESIS

The purpose of this study was to describe and report the results of an original technique of surgical excision of the proximal tendon remnant followed by a muscular suture repair. Our hypothesis was that this technique limits the risk of recurrence in high-level athletes and allows for rapid recovery without loss of quadriceps strength.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Our retrospective series included 5 players aged 31.8 ± 3.9 years with acute proximal rectus femoris avulsion injuries who underwent a surgical resection of the proximal tendon between March 2012 and June 2014. Four of these players had recurrent rectus femoris injuries in the 9 months before surgery, while 1 player had surgery after a first injury. Mean follow-up was 18.2 ± 12.6 months, and minimum follow-up was 9 months. We analyzed the age, sex distribution, physical examination outcomes, type and mechanism of injury, diagnosis, treatment and complications during surgery, postoperative follow-up, and time to return to play. The Lower Extremity Functional Scale (LEFS) and Marx scores were obtained at 3-month follow-up, and isokinetic tests were performed before return to sports. A telephone interview was completed to determine the presence of recurrence at an average follow-up of 18.2 months.

RESULTS

At 3-month follow-up, all patients had Marx activity scores of 16 and LEFS scores of 80. Return to the previous level of play occurred at a mean of 15.8 ± 2.6 weeks after surgery, and none of the athletes suffered a recurrence. Isokinetic test results were comparable between both sides.

CONCLUSION

The surgical treatment of proximal rectus femoris avulsions, consisting of resection of the tendinous part of the muscle, is a reliable and safe technique allowing a fast recovery in professional athletes.

The Biology of Bone and Ligament Healing

This review describes the normal healing process for bone, ligaments, and tendons, including primary and secondary healing as well as bone-to-bone fusion. It depicts the important mediators and cell types involved in the inflammatory, reparative, and remodeling stages of each healing process. It also describes the main challenges for clinicians when trying to repair bone, ligaments, and tendons with a specific emphasis on Charcot neuropathy, fifth metatarsal fractures, arthrodesis, and tendon sheath and adhesions. Current treatment options and research areas are also reviewed.

Femoral Aperture Fixation Improves Anterior Cruciate Ligament Graft Function When Added to Cortical Suspensory Fixation: An In Vivo Computer Navigation Study

Background:

Recommendations for bone tunnel placement during anterior cruciate ligament (ACL) reconstruction have become more precise. However, these recommendations differ neither with the choice of graft nor with the method of fixation used. The influence of the method of femoral fixation used on the biomechanical function of a soft tissue ACL graft remains unknown.

Hypothesis:

Our null hypothesis was that adding femoral aperture fixation to femoral cortical fixation, using the same bone tunnels, will not alter the control of anterior translation (AT) and internal rotation (IR) during ACL reconstruction using a hamstring graft.

Study Design:

Controlled laboratory study.

Methods:

A total of 22 patients with an acute isolated ACL rupture underwent reconstruction using a single-bundle autologous hamstring graft. Computer navigation was used intraoperatively to plot the AT and IR during the pivot-shift test before reconstruction, after ACL reconstruction using cortical suspensory fixation, and after the addition of femoral aperture fixation. Statistical analysis (analysis of variance) was used to compare the AT and IR during the pivot shift at each stage in the procedure.

Results:

Before ACL reconstruction, the mean (±SD) AT was 14.2 ± 7.3 mm and mean IR was 17.2° ± 5.5°. After reconstruction using femoral cortical suspension, these figures were significantly reduced to 6.2 ± 3.5 mm and 12.5° ± 3.20°, respectively (P < .001). The addition of the aperture fixation was associated with a further significant reduction to 4.6 ± 3.2 mm and 10.4° ± 2.7°, respectively (P < .001).

Conclusion:

The addition of femoral aperture fixation to suspensory fixation results in a significant reduction in both the AT and IR that occurs during the pivot-shift assessment immediately after ACL reconstruction using autologous hamstring graft.

Clinical Relevance:

The most precise positioning of bone tunnels during soft tissue ACL reconstruction needs to take into consideration the type of fixation being used.

Factors Expressed in an Animal Model of Anteroinferior Glenohumeral Instability

Background:

There is little information on the molecular factors important in healing and changes that occur in the glenoid labrum in response to injury. Using a novel animal model of acute anterior shoulder dislocation, this study characterizes the factors expressed in the glenoid labrum in response to injury and correlates their expression to glenohumeral stability.

Purpose:

To study the response of the glenoid labrum to injury both biomechanically and with immunohistochemical testing.

Methods:

An injury to the anteroinferior labrum was surgically induced in 50 male Lewis rats. Rats were sacrificed at 3, 7, 14, 28, or 42 days. Immunolocalization experiments were performed to localize the expression of growth factors and cytokines. For biomechanical testing, dynamic stiffness for anterior and posterior laxity, load to failure, stiffness, and maximum load were recorded. Statistical differences were determined at P < .05.

Study Design:

Descriptive laboratory study.

Results:

Expression of interleukin–1 beta (IL-1β), transforming growth factor–beta 1 (TGF-β1), matrix metalloproteinase 3 (MMP3), and matrix metalloproteinase 13 (MMP13) were increased in injured compared with uninjured specimens. Collagen III expression was increased early and decreased with time. Biomechanical testing verified instability by demonstrating increased anterior displacement and decreased stiffness in injured shoulders at all time points.

Conclusion:

This novel animal model of acute anterior shoulder dislocation showed increased expression of IL-1β, TGF-β1, MMP3, MMP13, and collagen III in the injured labral tissue at early time points. Increased anterior laxity and decreased stiffness and maximum load to failure were seen after anterior labral injury, supporting the model’s ability to re-create anterior glenohumeral instability. These data provide important information on the temporal changes occurring in a rat model of anterior glenohumeral dislocation.

Clinical Relevance:

Identification of factors expressed in the anterior capsule and glenoid labrum in response to injury may lead to the development of novel agents that can be used to augment glenoid labrum healing and ultimately improve both surgical and nonsurgical treatment of this common shoulder injury.

Tendon to bone tunnel healing--a study on the time-dependent changes in biomechanics, bone remodeling, and histology in a rat model

Tendons and ligaments attach to bone through a transitional connective tissue with complex biomechanical properties. This unique tissue is not regenerated during healing, and surgical reattachment therefore often fails. The present study was designed to evaluate tendon healing in a bone tunnel and to evaluate the utilized rat model. Wistar rats (n = 61) were operated with the Achilles tendon through a bone tunnel in the distal tibia. Healing was evaluated at 2, 3, 4, and 12 weeks by biomechanical testing, bone mineral density and histology. After 2 weeks median (interquartile range) pull-out force was 2.2 N (1.9). The pull-out force increased chronologically, by 12 weeks fivefold to 11.2 N (11.4). Energy absorption, stiffness, and bone mineral density increased similarly. The histological analyses showed inflammation at early stages with increasing callus by time. Our data showed a slow healing response the first 4 weeks followed by an accelerated healing period, favoring that most of the gain in mechanical strength occurred later than 4 weeks postoperatively. These findings support the concern of a vulnerable tendon bone tunnel interface in the early stages of healing.

Mechano-regulation of collagen biosynthesis in periodontal ligament

Periodontal ligament (PDL) plays critical roles in the development and maintenance of periodontium such as tooth eruption and dissipation of masticatory force. The mechanical properties of PDL are mainly derived from fibrillar type I collagen, the most abundant extracellular component. The biosynthesis of type I collagen is a long, complex process including a number of intra- and extracellular post-translational modifications. The final modification step is the formation of covalent intra- and intermolecular cross-links that provide collagen fibrils with stability and connectivity. It is now clear that collagen post-translational modifications are regulated by groups of specific enzymes and associated molecules in a tissue-specific manner; and these modifications appear to change in response to mechanical force. This review focuses on the effect of mechanical loading on collagen biosynthesis and fibrillogenesis in PDL with emphasis on the post-translational modifications of collagens, which is an important molecular aspect to understand in the field of prosthetic dentistry.

The role of acromioplasty for rotator cuff problems

Acromioplasty is a well-described technique used throughout the wide spectrum of treatment options for shoulder impingement and rotator cuff pathology. Several randomized prospective studies have described clinical outcomes that are statistically similar when comparing patients undergoing rotator cuff repair either with or without concomitant acromioplasty. This article reviews the current evidence for use of acromioplasty in patients with subacromial impingement syndrome and during arthroscopic rotator cuff repair. Despite recently published studies, more long-term data, especially with regard to failure rates and return-to-surgery rates over time, are needed to better determine the role of acromioplasty.

Use of a strontium-enriched calcium phosphate cement in accelerating the healing of soft-tissue tendon graft within the bone tunnel in a rabbit model of anterior cruciate ligament reconstruction

We investigated whether strontium-enriched calcium phosphate cement (Sr-CPC)-treated soft-tissue tendon graft results in accelerated healing within the bone tunnel in reconstruction of the anterior cruciate ligament (ACL). A total of 30 single-bundle ACL reconstructions using tendo Achillis allograft were performed in 15 rabbits. The graft on the tested limb was treated with Sr-CPC, whereas that on the contralateral limb was untreated and served as a control. At timepoints three, six, nine, 12 and 24 weeks after surgery, three animals were killed for histological examination. At six weeks, the graft–bone interface in the control group was filled in with fibrovascular tissue. However, the gap in the Sr-CPC group had already been completely filled in with new bone, and there was evidence of the early formation of Sharpey fibres. At 24 weeks, remodelling into a normal ACL–bone-like insertion was found in the Sr-CPC group. Coating of Sr-CPC on soft tissue tendon allograft leads to accelerated graft healing within the bone tunnel in a rabbit model of ACL reconstruction using Achilles tendon allograft.

Cite this article: Bone Joint J 2013;95-B:923–8.

Functional attachment of soft tissues to bone: development, healing, and tissue engineering

Connective tissues such as tendons or ligaments attach to bone across a multitissue interface with spatial gradients in composition, structure, and mechanical properties. These gradients minimize stress concentrations and mediate load transfer between the soft and hard tissues. Given the high incidence of tendon and ligament injuries and the lack of integrative solutions for their repair, interface regeneration remains a significant clinical challenge. This review begins with a description of the developmental processes and the resultant structure-function relationships that translate into the functional grading necessary for stress transfer between soft tissue and bone. It then discusses the interface healing response, with a focus on the influence of mechanical loading and the role of cell-cell interactions. The review continues with a description of current efforts in interface tissue engineering, highlighting key strategies for the regeneration of the soft tissue-to-bone interface, and concludes with a summary of challenges and future directions.

Effect of bone morphogenetic protein-2 on tendon-bone integration in an in vitro cell culture

The goal of this study was to evaluate the influence of bone morphogenetic protein-2 (BMP-2) on tendon-bone integration in a bovine in vitro cell culture. Seventy-two bovine tendons were cultivated over 3 months. The effects of BMP-2 were evaluated by generation in 4 subgroups. The groups differed in 2 parameters: the application of BMP-2 and the application of primary bovine osteoblasts. Results were analyzed biochemically by determining alkaline phosphatase activity and histologic tendon calcification, both markers for graft incorporation. Histological analysis demonstrated a positive effect of BMP-2 on the production of extracellular matrix and therefore the induction of osteogenesis. In addition, the results showed a superior cell ingrowth on the tendon in the BMP-2-stimulated groups. Calcium carbonate-like structures and organized ossification zones could only be detected in the BMP-2-stimulated tendons. The histological results matched those of the biochemical alkaline phosphatase analysis. The highest alkaline phosphatase activity was detected using BMP-2 stimulation in the first month (P<.001). High alkaline phosphatase values suggest high osteoblast activity and a high potential for mineralization. Furthermore, a positive effect of BMP-2 on fibroblasts existed with regard to the overall integration process. These results confirm the positive influence and triggering effect of BMP-2 on the mineralization process. Bone morphogenetic protein-2 seems to accelerate and optimize tendon-bone integration in the early process of graft incorporation. Besides the influence of BMP-2 on bovine osteoblasts, an additional positive effect of BMP-2 on bovine fibroblasts was detected; therefore, graft incorporation may be carried out by osteoblasts and fibroblasts.

Extracorporeal shockwave therapy for treatment of delayed tendon-bone insertion healing in a rabbit model: a dose-response study

BACKGROUND

Tendon-bone insertion (TBI) consists of both hard and soft tissues. TBI injury with delayed repair is not uncommon. High-dose extracorporeal shockwave (ESW) is effective for treating nonunion fracture, whereas low-dose ESW is used for tendinopathy therapy. The dosing effect of ESW on delayed TBI healing is lacking.

HYPOTHESIS

Low-dose ESW might have a healing enhancement effect comparable to that of high-dose ESW in treating delayed TBI healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Partial patellectomy was adopted to create a delayed TBI healing model by shielding the healing interface between tendon and bone. Ninety-six female New Zealand White rabbits with unilateral delayed TBI healing at the knee joint were divided into 3 groups: controls, low-dose ESW (LD-ESW; 0.06 mJ/mm(2), 4 Hz, 1500 impulses), and high-dose ESW (HD-ESW; 0.43 mJ/mm(2), 4 Hz, 1500 impulses). The TBI shielding was removed at week 4 after partial patellectomy, followed by treatment with control or ESW at week 6. The rabbits were euthanized at week 8 and week 12 for radiological, microarchitectural, histological, and mechanical assessments of healing tissues.

RESULTS

Radiologically, both the LD-ESW group and the HD-ESW group showed larger new bone area than the controls at week 8 and week 12. Microarchitectural measurements showed that the LD-ESW and HD-ESW groups had larger new bone volume than the controls at week 12. Histological assessments confirmed osteogenesis enhancement. Both the LD-ESW and HD-ESW groups showed significantly higher failure load at the TBI healing complex than the control group at week 12. No significant difference was detected between the 2 ESW treatment groups at week 8 or week 12.

CONCLUSION

Extracorporeal shockwave, a unique noninvasive physical modality, had similar effects between the low and high dose for treating delayed TBI healing.

CLINICAL RELEVANCE

Low-dose ESW for TBI delayed healing might be more desirable and have better compliance in clinical applications.

Extracorporeal shock wave therapy is not useful after arthroscopic rotator cuff repair

PURPOSE

Extracorporeal shock wave therapy (ESWT) is known to accelerate the healing of musculoskeletal tissue. The purpose of this study was to test the hypothesis that ESWT stimulates rotator cuff healing after arthroscopic repair.

METHODS

Seventy-one consecutive patients with a small- to large-sized rotator cuff tear underwent arthroscopic rotator cuff repair. The patients were randomized into two groups: 35 patients underwent ESWT at 6 weeks after surgery (ESWT group) and 36 patients did not (control group). Cuff integrity was evaluated with computed tomographic arthrography at 6 months after surgery. Constant and UCLA scores were measurable outcomes.

RESULTS

All patients were available for a minimum one-year follow-up. The mean age of the ESWT and control groups was 59.4 (SD: 7.7) and 58.6 years (SD: 7.8) (n.s.). There were no significant differences in tear size and repair method between the two groups (n.s.). The mean Constant and UCLA scores, respectively, increased from 54.6 to 90.6 (P < 0.001) and from 18.5 to 27.4 (P < 0.001) in the ESWT group, and from 58.9 to 89.3 (P < 0.001) and 18.5 to 27.4 in the control group. Computed tomographic arthrography was performed in 26 patients from the ESWT group and 24 from the control group, and cuff integrity was maintained in 46 out of 50 patients. Definite re-tear was observed in two patients of the ESWT group and four of the controls. There were no complications associated with ESWT.

CONCLUSION

This study failed to prove that ESWT stimulates rotator cuff healing after arthroscopic rotator cuff repair. Additional ESWT after rotator cuff repair could theoretically be advantageous, and it was proven to be safe in this study.

LEVEL OF EVIDENCE

II.

Biologically based strategies to augment rotator cuff tears

Lesions of the rotator cuff (RC) are among the most frequent tendon injuries. In spite of the developments in both open and arthroscopic surgery, RC repair still very often fails. In order to reduce the failure rate after surgery, several experimental in vitro and in vivo therapy methods have been developed for biological improvement of the reinsertion. This article provides an overview of the current evidence for augmentation of RC reconstruction with growth factors. Furthermore, potential future therapeutic approaches are discussed. We performed a comprehensive search of the PubMed database using various combinations of the keywords “tendon,” “rotator cuff,” “augmentation,” “growth factor,” “platelet-rich fibrin,” and “platelet-rich plasma” for publications up to 2011. Given the linguistic capabilities of the research team, we considered publications in English, German, French, and Spanish. We excluded literature reviews, case reports, and letters to the editor.

Chronological changes in the collagen-type composition at tendon-bone interface in rabbits

Objectives

The purpose of this study was to evaluate chronological changes in the collagen-type composition at tendon–bone interface during tendon–bone healing and to clarify the continuity between Sharpey-like fibres and inner fibres of the tendon.

Methods

Male white rabbits were used to create an extra-articular bone–tendon graft model by grafting the extensor digitorum longus into a bone tunnel. Three rabbits were killed at two, four, eight, 12 and 26 weeks post-operatively. Elastica van Gieson staining was used to colour 5 µm coronal sections, which were examined under optical and polarised light microscopy. Immunostaining for type I, II and III collagen was also performed.

Results

Sharpey-like fibres comprised of type III collagen in the early phase were gradually replaced by type I collagen from 12 weeks onwards, until continuity between the Sharpey-like fibres and inner fibres of the tendon was achieved by 26 weeks.

Conclusions

Even in rabbits, which heal faster than humans, an observation period of at least 12 to 26 weeks is required, because the collagen-type composition of the Sharpey-like fibre bone–tendon connection may have insufficient pullout strength during this period. These results suggest that caution is necessary when permitting post-operative activity in humans who have undergone intra-bone tunnel grafts.

The efficacy of acromioplasty in the arthroscopic repair of small- to medium-sized rotator cuff tears without acromial spur: prospective comparative study

PURPOSE

To assess the role of acromioplasty in the arthroscopic repair of small- to medium-sized rotator cuff tears.

METHODS

A prospective randomized trial of 120 patients who had small- to medium-sized rotator cuff tears and various types of acromions without spurs were included. Sixty patients received arthroscopic rotator cuff repair with acromioplasty (group I), and another sixty received the same procedure without acromioplasty (group II). The mean age at surgery was 57.8 ± 9.3 years in group I and 55.8 ± 8.0 years in group II. The shape of the acromion was flat in 18 patients, curved in 32, and hooked in 10 in group I, and it was flat in 15 patients, curved in 36, and hooked in 9 in group II. The mean tear size was similar in the two groups (14.6 ± 5.2 mm in group I and 15.3 ± 7.0 mm in group II). Pain and satisfaction were estimated and range of motion was measured at a mean of 35 months after surgery. Functional outcomes were assessed with American Shoulder and Elbow Surgeons: Constant; and University of California, Los Angeles scores. Tendon healing was evaluated by magnetic resonance imaging postoperatively.

RESULTS

Clinical outcome was significantly improved in both groups after arthroscopic rotator cuff repair (P < .05). There were no significant differences with respect to pain and range of motion between the groups at the final follow-up (1.1 ± 0.9 v 1.3 ± 1.4 on visual analog scale). Functional outcomes also showed no significant differences between the 2 groups (American Shoulder and Elbow Surgeons score, 90.7 ± 13.1 v 87.5 ± 12.0; Constant score, 85.0 ± 11.3 v 83.3 ± 13.0; and University of California, Los Angeles score, 33.4 ± 3.3 v 32.3 ± 3.5). Postoperative imaging showed that the retear rate was 17% in group I and 20% in group II (P = .475).

CONCLUSIONS

Arthroscopic repair of small- to medium-sized rotator cuff tears provided pain relief and improved functional outcome with or without acromioplasty. Clinical outcomes were not significantly different, and acromioplasty may not be necessary in the operative treatment of patients with small- to medium-sized rotator cuff tears in the absence of acromial spurs.

LEVEL OF EVIDENCE

Level II, prospective comparative study.

The effect of tendon surface treatment on cell attachment for potential enhancement of tendon graft healing: an ex vivo model

For both tendon allografts and autografts, the surface, initially optimized for gliding, may not be ideal to facilitate tissue integration for graft healing to host tendon or bone. As a prelude to studying tendon-bone integration, we investigated the effect of surface treatments with trypsin or mechanical abrasion on cell attachment to the tendon surface in a canine ex vivo intrasynovial tendon tissue culture model. Intrasynovial tendon allograft surfaces were seeded with cells after the following treatments: (1) no treatment, (2) mechanical abrasion, (3) trypsin, and (4) abrasion and trypsin. The area covered by cells was determined using confocal laser microscopy at one and two weeks. Results were compared to untreated extrasynovial tendon. Additional tendons were characterized with scanning electron microscopy. Tendons with trypsin treatment had significantly more surface coverage with cells than the other groups, after both one and two weeks of culture. In terms of the cellular shape and size, cells on tendons with trypsin treatment spread more and were more polygonal in shape, whereas tendons with mechanical abrasion with/without trypsin treatment contained smaller, more spindle-like cells. Surface roughening can affect cell behavior with topographical stimulation. Trypsin surface digestion exposes a mesh-like structure on the tendon surface, which could enhance cell adherence and, possibly, tendon/bone healing.

Acceleration of tendon–bone healing in anterior cruciate ligament reconstruction using an enamel matrix derivative in a rat model

We examined whether enamel matrix derivative (EMD) could improve healing of the tendon–bone interface following reconstruction of the anterior cruciate ligament (ACL) using a hamstring tendon in a rat model. ACL reconstruction was performed in both knees of 30 Sprague-Dawley rats using the flexor digitorum tendon. The effect of commercially available EMD (EMDOGAIN), a preparation of matrix proteins from developing porcine teeth, was evaluated. In the left knee joint the space around the tendon–bone interface was filled with 40 µl of EMD mixed with propylene glycol alginate (PGA). In the right knee joint PGA alone was used. The ligament reconstructions were evaluated histologically and biomechanically at four, eight and 12 weeks (n = 5 at each time point). At eight weeks, EMD had induced a significant increase in collagen fibres connecting to bone at the tendon–bone interface (p = 0.047), whereas the control group had few fibres and the tendon–bone interface was composed of cellular and vascular fibrous tissues. At both eight and 12 weeks, the mean load to failure in the treated specimens was higher than in the controls (p = 0.009). EMD improved histological tendon–bone healing at eight weeks and biomechanical healing at both eight and 12 weeks. EMD might therefore have a human application to enhance tendon–bone repair in ACL reconstruction.

Tissue engineering strategies in ligament regeneration

Ligaments are dense fibrous connective tissues that connect bones to other bones and their injuries are frequently encountered in the clinic. The current clinical approaches in ligament repair and regeneration are limited to autografts, as the gold standard, and allografts. Both of these techniques have their own drawbacks that limit the success in clinical setting; therefore, new strategies are being developed in order to be able to solve the current problems of ligament grafting. Tissue engineering is a novel promising technique that aims to solve these problems, by producing viable artificial ligament substitutes in the laboratory conditions with the potential of transplantation to the patients with a high success rate. Direct cell and/or growth factor injection to the defect site is another current approach aiming to enhance the repair process of the native tissue. This review summarizes the current approaches in ligament tissue engineering strategies including the use of scaffolds, their modification techniques, as well as the use of bioreactors to achieve enhanced regeneration rates, while also discussing the advances in growth factor and cell therapy applications towards obtaining enhanced ligament regeneration.

Higher BMP receptor expression and BMP-2-induced osteogenic differentiation in tendon-derived stem cells compared with bone-marrow-derived mesenchymal stem cells

PURPOSE

Surgical reattachment of tendon to bone often fails due to regeneration failure of the specialised tendon-bone junction (TBJ). The use of mesenchymal stem cells for TBJ regeneration has been reported with promising results. Tendon-derived stem cells (TDSCs) with high proliferative and multi-lineage differentiation potential have been isolated. As stem cells residing in tendons, TDSCs can be considered a new cell source for TBJ repair. Bone morphogenic protein 2 (BMP-2) is a potent osteogenic factor with roles in normal bone healing and pathological ectopic bone formation in soft tissues. The use of BMP-2 to promote TBJ repair has been well reported. This study aimed to compare TDSCs to the gold standard bone-marrow-derived mesenchymal stem cells (BMSCs) with respect to osteogenic response to BMP-2 in vitro.

METHOD

The clonogenicity and multi-differentiation potential of TDSCs and BMSCs were identified by colony-forming-unit assay, osteogenic, adipogenic and chondrogenic differentiation assays. Their osteogenic response to BMP-2 in vitro was examined by alkaline phosphatase (ALP) cytochemical staining, ALP activity assay and Alizarin red S staining of calcium nodule formation. Messenger RNA (mRNA) and BMP receptor (types IA, IB and II) protein expression were examined by quantitative real-time reverse-transcriptase polymerase chain reaction (qRT-PCR) and Western blotting.

RESULTS

Our results showed that both TDSCs and BMSCs exhibited stem cell properties, including clonogenicity and multi-differentiation potential. TDSCs expressed higher mRNA and protein levels of BMP receptors IA, IB and II. They also exhibited higher osteogenic differentiation with and without BMP-2 stimulation compared with BMSCs.

CONCLUSIONS

TDSCs with/without BMP-2 might be an attractive source for TBJ repair compared with BMSCs.

Application of layered poly (L-lactic acid) cell free scaffold in a rabbit rotator cuff defect model

Background

This study evaluated the application of a layered cell free poly (L-lactic acid) (PLLA) scaffold to regenerate an infraspinatus tendon defect in a rabbit model. We hypothesized that PLLA scaffold without cultivated cells would lead to regeneration of tissue with mechanical properties similar to reattached infraspinatus without tendon defects.

Methods

Layered PLLA fabric with a smooth surface on one side and a pile-finished surface on the other side was used. Novel form of layered PLLA scaffold was created by superimposing 2 PLLA fabrics. Defects of the infraspinatus tendon were created in 32 rabbits and the PLLA scaffolds were transplanted, four rabbits were used as normal control. Contralateral infraspinatus tendons were reattached to humeral head without scaffold implantation. Histological and mechanical evaluations were performed at 4, 8, and 16 weeks after operation.

Results

At 4 weeks postoperatively, cell migration was observed in the interstice of the PLLA fibers. Regenerated tissue was directly connected to the bone composed mainly of type III collagen, at 16 weeks postoperatively. The ultimate failure load increased in a time-dependent manner and no statistical difference was seen between normal infraspinatus tendon and scaffold group at 8 and 16 weeks postoperatively. There were no differences between scaffold group and reattach group at each time of point. The stiffness did not improve significantly in both groups.

Conclusions

A novel form of layered PLLA scaffold has the potential to induce cell migration into the scaffold and to bridge the tendon defect with mechanical properties similar to reattached infraspinatus tendon model.

Biology and augmentation of tendon-bone insertion repair

Surgical reattachment of tendon and bone such as in rotator cuff repair, patellar-patella tendon repair and anterior cruciate ligament (ACL) reconstruction often fails due to the failure of regeneration of the specialized tissue ("enthesis") which connects tendon to bone. Tendon-to-bone healing taking place between inhomogenous tissues is a slow process compared to healing within homogenous tissue, such as tendon to tendon or bone to bone healing. Therefore special attention must be paid to augment tendon to bone insertion (TBI) healing. Apart from surgical fixation, biological and biophysical interventions have been studied aiming at regeneration of TBI healing complex, especially the regeneration of interpositioned fibrocartilage and new bone at the healing junction. This paper described the biology and the factors influencing TBI healing using patella-patellar tendon (PPT) healing and tendon graft to bone tunnel healing in ACL reconstruction as examples. Recent development in the improvement of TBI healing and directions for future studies were also reviewed and discussed.