Approximately 30% of general practice consultations for musculoskeletal pain are related to tendon disorders, causing substantial personal suffering and enormous related healthcare costs. Treatments are often prone to long rehabilitation times, incomplete functional recovery, and secondary complications following surgical repair. Overall, due to their hypocellular and hypovascular nature, the regenerative capacity of tendons is very poor and intrinsically a disorganized scar tissue with inferior biomechanical properties forms after injury. Therefore, advanced therapeutic modalities need to be developed to enable functional tissue regeneration within a degenerative environment, moving beyond pure mechanical repair and overcoming the natural biological limits of tendon healing. Our recent studies have focused on developing biologically augmented treatment strategies for tendon injuries, aiming at restoring a physiological microenvironment and boosting endogenous tissue repair. Along these lines, we have demonstrated that the local application of mesenchymal stromal cell-derived small extracellular vesicles (sEVs) has the potential to improve rotator cuff tendon repair by modulating local inflammation and reduce fibrotic scarring. In another approach, we investigated if the local delivery of the tendon ECM protein SPARC, which we previously demonstrated to be essential for tendon maturation and tissue homeostasis, has the potential to enhance tendon healing. Finally, I will present results demonstrating the utility of nanoparticle-delivered, chemically modified mRNAs (cmRNA) to improve tendon repair

Tendons display poor intrinsic healing properties and are difficult to treat[1]. Prior in vitro studies[2] have shown that, by targeting the Activin A receptor with magnetic nanoparticles (MNPs), it is possible to remotely induce the tenogenic differentiation of human adipose stem cells (hASCs). In this study, we investigated the tenogenic regenerative potential of remotely-activated MNPs-labelled hASCs in an in vivo rat model. We consider the potential for magnetic controlled nanoparticle mediated tendon repair strategies. hASCs were labelled with 250 nm MNPs functionalized with anti-Activin Receptor IIA antibody. Using a rapid curing fibrin gel as delivery method, the MNPs-labelled cells were delivered into a Ø2 mm rat patellar tendon defect. The receptor was then remotely stimulated by exposing the rats to a variable magnetic gradient (1.28T), using a customised magnetic box. The stimulation was performed 1 hour/day, 3 days/week up to 8 weeks. Tenogenesis, iron deposition and collagen alignment were assessed by histological staining and IHC. Inflammation mediators levels were assessed by ELISA and IHC. The presence of human cells in tendons after 4 and 8 weeks was assessed by FISH analysis. Histological staining showed a more organised collagen arrangement in animals treated with MNPs-labelled cells compared to the controls. IHC showed positive expression of tenomodulin and scleraxis in the experimental groups. Immunostaining for CD45 and CD163 did not detect leukocytes locally, which is consistent with the non-significant levels of the inflammatory cytokines analysis performed on plasma. While no iron deposition was detected in the main organs or in plasma, the FISH analysis showed the presence of human donor cells in rat tendons even after 8 weeks from surgery. Our approach demonstrates in vivo proof of concept for remote control stem cell tendon repair which could ultimately provide injectable solutions for future treatment. We are grateful for ERC Advanced Grant support ERC No.789119, ERC CoG MagTendon No.772817 and FCT grant 2020.01157.CEECIND

Macrophages play a critical role in innate immunity by promoting or inhibiting tissue inflammation and repair. Classically, macrophages can differentiate into either pro-inflammatory (M1) or pro-reparative (M2) phenotypes in response to various stimuli. Therefore, this study aimed to address how extracellular vesicles (EVs) derived from polarized macrophages can affect the inflammatory response of tendon cells. For that purpose, human THP-1 cells were stimulated with lipopolysaccharide (LPS), and interleukins -4 and -13 (IL- 4, IL-13), to induce macrophages polarization into M1, M2, and hybrid M1/M2 phenotypes. Subsequently, the EVs were isolated from the culture medium by ultracentrifugation. The impact of these nanovesicles on the inflammation and injury scenarios of human tendon-derived cells (hTDCs), which had previously been stimulated with interleukin- 1 beta (IL-1ß) to mimic an inflammatory scenario, was assessed. We were able to isolate three different nanovesicles populations, showing the typical shape, size and surface markers of EVs. By extensively analyzing the proteomic expression profiles of M1, M2, and M1/M2, distinct proteins that were upregulated in each type of macrophage-derived EVs were identified. Notably, most of the detected pro- inflammatory cytokines and chemokines had higher expression levels in M1-derived EVs and were mostly absent in M2-derived EVs. Hence, by acting as a biological cue, we observed that M2 macrophage-derived EVs increased the expression of the tendon-related marker tenomodulin (TNMD) and tended to reduce the presence of pro-inflammatory markers in hTDCs. Overall, these preliminary results show that EVs derived from polarized macrophages might be a potential tool to modulate the immune system responses becoming a valuable asset in the tendon repair and regeneration fields worthy to be further explored

Summary Statement. The aim of this study was to compare patterns (aligned, random and grid) of electrospun polydioxanone scaffolds for tendon repair. The aligned design was optimal, directing cell shape, orientation and protein expression. Moreover, it naturally crimped, presenting tendon-like morphology. Introduction. Nanofibrous electrospun materials have been previously proposed as potential scaffolds for tendon repair, with emphasis on biomimetic design, postulated to encourage tissue regeneration. In this study, we characterised the interaction of primary tendon-derived cells with polydioxanone (PDO) scaffolds. PDO is a polymer with an excellent in vitro and in vivo biocompatibility, and is specifically compatible with tendon-derived cells. Here, we designed electrospun PDO scaffolds with different fibre orientations, namely aligned, random and grid-like patterns. To evaluate their potential as patches for tendon repair, we grew primary tendon derived cells on these scaffolds, and tested different aspects of cell behavior, including cell shape, proliferation and protein expression. Methods. Scaffolds with different orientations were produced using a single nozzle electrospinning set-up. Human tendon cells were extracted from rotator cuff tissue resected during surgical repair, with appropriate ethical approval. Cells were grown on different scaffolds for at least 14 days. Multiphoton microscopy (MPM) was used to image cells (green, calcein AM, and red, actin-phalloidin). Cell growth was monitored using AlamarBlue assay. Cell length, width and orientation were manually measured from images acquired by fluorescence microscopy. RNA was extracted by Trizol homogenisation in a GentleMACS (Miltenyi Biotec). RNA samples were reversibly transcribed to cDNA and RT QPCR were performed using a ViiA7 (Life Technologies) with QuantiTect primer assays (QIAGEN). Results are in relative expression to GAPDH. Results. MPM enabled the visualization of the scaffolds and viable cells grown for at least 14 days. Images demonstrate the distinct appearance of cells grown on highly aligned scaffold compared to random, grid-orientation and glass control. They also show the crimp-like appearance of the oriented scaffold as well as the cells on these crimped fibres. Interestingly, proliferation was not significantly effected by scaffold pattern. However, cell shape was clearly affected, and cells grown on oriented scaffolds showed higher anisotropy and elongated, narrower cell shape compared to all other groups, presenting a more tendon-like phenotype. This was further supported by a strong increase in the expression of β-actin on the aligned compared to the randomly oriented scaffold, correlating with observed changes in cell length and shape. Conclusion. The aim of this study was to compare patterns (aligned, random and grid) of electrospun polydioxanone scaffolds as templates for tendon repair. Aligned PDO scaffolds significantly affected cell length, width, and orientation. We also found that β-actin expression was significantly increased on aligned polydioxanone scaffolds. Moreover, PDO scaffolds fabricated as aligned/oriented were observed to present crimp-like morphology, similar to native tendon. Taken together, these findings suggest an aligned morphology of polydioxanone may hold the potential to improve tendon healing

Introduction and Aims: In order to evaluate the hypothesis that the ‘temporary and controlled reduction of muscle force protects repair sites come from its safe, active, and passive range of motion and diminishes complications’, a tendon repair model was evaluated. Method: After heel cord tenotomy, Sprague-Dawley rats (n=36) were randomised to Botulinum A Toxin at six units per kilogram or saline and the tendon repaired with a two-strand core suture and a peritenon running suture. The ankles were pinned in equinus for two days, and then the animals were allowed to move freely within their cages. Analysis included gap, rupture rates, electrophysiologic measurements and mechanical testing. Results: The treatment group had a statistically significant lower spontaneous partial or total rupture rate than the control (P=0.38). Tendon electrophysiologic testing showed that the toxin group had lower twitch and tetanus values than the control group (evidence of effective denervation). The toxin group also had better histologic healing and better strength of repair (higher rupture strength values). Histologic assessment showed that the toxin-treated group had more normal histology with less scar. Conclusion: Chemoprotection decreases significantly spontaneous tendon rupture rates following repair in active versus control groups. The active toxin group demonstrated better healing. Decreasing tension across repair sites is equally effective in increasing inastamotic strength and permits active range of motion without rupture

Acute distal biceps tendon repair reduces fatigue-related pain and minimises loss of forearm supination and elbow flexion strength. We report the short- and long-term outcome following repair using an EndoButton technique. Between 2010 – 2018, 102 patients (101 males; mean age 43 years) underwent acute (□6 weeks) distal biceps tendon repair using an EndoButton technique. The primary short-term outcome was complications. The primary long-term outcome was the Quick-DASH (Q-DASH). Secondary outcomes included the Oxford Elbow Score (OES), EuroQol-5D-3L (EQ-5D), return to function and satisfaction. At mean short-term follow-up of 4 months (2.0 – 55.5) eight patients (7.8%) experienced a major complication and 34 patients (33.3%) experienced a minor complication. Major complications included re-rupture (n=3, 2.9%), unrecovered nerve injury (n=4, 3.9%) and surgery for heterotopic ossification excision (n=1, 1.0%). Three patients (2.9%) required surgery for a complication. Minor complications included neuropraxia (n=27, 26.5%) and superficial infection (n=7, 6.9%). At mean follow-up of 5 years (1 – 9.8) outcomes were collected from 86 patients (84.3%). The median Q-DASH, OES, EQ-5D and satisfaction scores were 1.2 (IQR 0 – 5.1), 48 (IQR, 46 – 48), 0.80 (IQR, 0.72 – 1.0) and 100/100 (IQR, 90 – 100) respectively. Most patients returned to sport (82.3%) and employment (97.6%) following surgery. Unrecovered nerve injury was associated with a poor outcome according to the Q-DASH (p< 0.001), although re-rupture and further surgery were not (p > 0.05). Acute distal biceps tendon repair using an EndoButton technique results in excellent patient reported outcomes and health-related quality of life. Although rare, unrecovered nerve injury adversely affects outcome

The biomechanical evaluation of tendon repair with collagen-based scaffolds in rat model is a common method to determine the functional outcome of the tested material. We introduced a magnetic resonance imaging (MRI) approach to verify the biomechanical test data. In present study different collagen scaffolds for tendon repair were examined. Two collagen test materials: based on bovine stabilized collagen, chemically cross-linked with oriented collagenous fibres (material 1) and based on porcine dermal extracellular matrix, with no cross-linking (material 2) were compared. The animal study was approved by the local review board. Surgery was performed on male Sprague-Dawley rats with a body weight of 400 ± 19 g. Each rat underwent a 5 mm transection of the right Achilles tendon. The M. plantaris tendon was removed. The remaining tendon ends were re-joined with a 5 mm scaffold of either the material 1 or 2. Each scaffold material was sutured into place with two single stiches (Vicryl 4–0, Ethicon) each end. A total of 16 rats (n= 8 each group) were observed for 28 days follow up. The animals were sacrificed and hind limbs were transected proximal to the knee joint. MRI was performed using a 7 Tesla scanner (BioSpec 70/30, Bruker). T2-weighted TurboRARE sequences with an in-plane resolution of 0.12 mm and a slice thickness of 0.7 mm were analysed. All soft and hard tissues were removed from the Achilles tendon-calcaneus-foot complex before biomechanical testing. Subsequently, the specimens were fixed in a materials testing machine (Z1.0, Zwick, Ulm, Germany) for tensile testing. All tendons were preloaded with 1 N and subsequently stretched at a rate of 1 mm/s until complete failure was observed. Non-operated tendons were used as a control (n=4). After 28 postoperative days, MRI demonstrated that four scaffolds (material 1: n=2, material 2: n=2) were slightly dislocated in the proximal part of hind limb. In total five failures of reconstruction could be detected in the tendon repairs (material 1: n=3, material 2: n=2). Tendons augmented with the bovine material 1 showed a maximum tensile load of 57.9 ± 17.9 N and tendons with porcine scaffold material 2 of 63.1 ± 19.5 N. The native tendons demonstrated only slightly higher loads of 76.6 ± 11.6 N. Maximum failure load of the tendon-scaffold construct in both groups did not differ significantly (p < 0.05). Stiffness of the tendons treated with the bovine scaffold (9.9 ± 3.6 N/mm) and with the porcine scaffold (10.7 ± 2.7 N/mm) showed no differences. Stiffness of the native healthy tendon of the contralateral site was significantly higher (20.2 ± 6.6 N/mm, p < 0.05). No differences in the mechanical properties between samples of both scaffold groups could be detected, regardless of whether the repaired tendon defect has failed or the scaffold has been dislocated. The results show that MRI is important as an auxiliary tool to verify the biomechanical outcome of tendon repair in animal models

Introduction. Patients with hip abductor tendon tears amenable to endoscopic repair tend to be severely disabled and older. However, low preop baseline patient reported outcome (PRO) and advancing age are each often reported to be a harbinger of poor result with hip arthroscopy. Thus, the purpose of this study is to report the demographic makeup of this population and how these patients faired in terms of preop scores and reaching both Minimal Clinically Important Difference (MCID) and Substantial Clinical Benefit (SCB). Methods. Sixty-six consecutive hips in 64 patients (2 bilateral) undergoing endoscopic abductor tendon repair with a hollow core bioabsorbable suture anchor and having achieved two-year follow-up were prospectively assessed with modified Harris Hip Score (mHHS) and international Hip Outcome Tool (iHOT) scores. The MCID for patients undergoing hip arthroscopy has previously been determined as 8 for the mHHS and 13 for the iHOT. SCB has been determined as 20 for the mHHS and 28 for the iHOT. Subgroups were compared using the independent samples t-test. Results. The average age was 57 years (range 22–83 years) with 59 females and 5 males. Post-operative follow-up averaged 28 months (range 24–60). There were 33 full-thickness and 33 partial-thickness tears; 39 gluteus medius tears, 25 medius and minimus tears, and 2 isolated minimus tears. Among the 66 hips, the average preop mHHS was 48.8 with 98.5% achieving MCID and 93.8% SCB. Among 60 hips that had complete iHOT data, the average preop score was 30.0 with 98.3% achieving MCID and 88.3% SCB. There were no complications. One patient underwent repeat arthroscopy for joint debridement at 12 months following abductor repair, and one subsequently underwent total hip replacement at 11 months following repair. There was no statistically significant difference between subgroups of full thickness/partial thickness tears, or single/two tendon tears. Conclusion. This report of endoscopic abductor tendon repair represents a heterogeneous group of single and two tendon involvement with partial and full thickness tears. Collectively these patients can respond exceptionally well in terms of MCID (98.5% mHHS; 98.3% iHOT) and SCB (93.8% mHHS; 88.3% iHOT), even in the presence of low preop baseline scores (average 48.8 mHHS; 30 iHOT) and older age (average 57 years). For any tables or figures, please contact the authors directly

Extensor tondon lacerations are much more common than flexor tendon injuries. The outcome of this lesions depends on mamy factors including severity of initial trauma, coexisting lesions, of the hand, site of the laceration, experience of the surgeon, and post operative rehabilitation. The aim of this prospective study was to review our results of primary extensor tendon repair with regard to the zone of injury. During a period of 28 months, 32 patients with open extensor tendon laccerations were repaired by modified kessler technique using 4-0 nonabsorbable suture. After tendon repair, immobilization with a volar splint was applied for 4-weeks and physiotherapy was carried out. Patients were followed–up for a mean of 12 months. we used the 5 extensor tendon zones and results were assesed using Miller’s rating system. Patents with closed tendon ruptures or concomitant hand fracture were excluded from the study. Seventy two extensor tendons were repaired. The mean age of patients was 24.6 years (17–46 y). Excellent and good resalts were obtained as the follows: in zone 5(88/4%), zone 3 (84%), zone 2(55.5%), zone 4(42.7%), zone 1(40%). Results were poor in zone 4(42.8%), zone 1(40%), zone 2(22.2%), zone 3(4%), and zone 5(3.9%). No in fection was seen. We found a strong correlation between the site of the repair and outcome. More excellent and good results were obtained when the repair was performed distal to the extensor retinaculum (Zone 3), and above the wrist (Zone 5). Unsatisfactory results were seen when the tendon repair was done at or near DIP joint (zone 1), in the region of complex extensor mechanism (zone 2) or beneth the extensor retinaculum (zone 4). We cocluded the anatomic location of tendon repair has an important effect in outcome

Summary. Tissue grafts fail to recapitulate native tendon function, imposing the need for development of functional regeneration strategies. Herein, we describe advancements in tendon repair and regeneration using functionalised natural and synthetic devices and scaffold-free cell-based therapies. Introduction. Tendon and ligament injuries constitute an unmet clinical need with approximately 100,000 new cases annually in US alone. Tissue grafts are considered the gold standard in clinical practice. However, allografts and xenografts can lead to potential disease transmission, whilst the limited supply of autografts in severe injuries and degenerative conditions restricts their use. To this end, scaffold and scaffold-free therapies are under development to address the tissue grafts shortage. Herein, we describe biophysical, biochemical and biological methods to maintain tendon derived cell phenotype and/or differentiation of other cell types towards tenogenic lineage; development of tendon-equivalent facsimiles; and ultimately functional neotendon formation. Materials and Methods. Growth factor supplementation was assessed as means to either maintain tendon derived stem cell phenotype or differentiate them towards tenocytes. The influence of conditioning media was assessed as means to differentiate skin fibroblasts and stem cells towards tenogenic lineage. Biophysical and biochemical/biological features were assessed as means to maintain tendon derived cell phenotype and directional neotissue formation in rat patellar tendon model. Rich in tendon-specific extracellular matrix cell sheets were produced by appropriate modulation of the in vitro microenvironment. Structural, biophysical and biological analyses were subsequently carried out. Discussion & Future Studies. Treatment with 10 and 100 ng/mL of IGF-1 preserved tendon stem cell multipotency for up to 28 days in culture and minimised changes in marker expression and extracellular matrix molecules production enhancing that way the clinical potential of these cells. Hierarchically assembled collagen scaffolds and anisotropically ordered polymeric substrates of rigidity similar to native tendons facilitate tenocyte phenotype maintenance in vitro, whilst in vivo studies are under way to assess the extent of functional tendon regeneration. Appropriate modulation of the in vitro microenvironment of tenocytes with macromolecules enhances tendon specific extracellular matrix deposition within 6 days in culture, facilitating that way the wide acceptance of cell-sheet technology for tendon repair and regeneration

Introduction and Objective. Zone 2 flexor tendon injuries are still one of the challenges for hand surgeons. It is not always possible to achieve perfect results in hand functions after these injuries. There is no consensus in the literature regarding the treatment of zone 2 flexor tendon injuries, tendon repair and surgical technique to be applied to the A2 pulley. The narrow fibro-osseous canal structure in zone 2 can cause adhesions and loss of motion due to the increase in tendon volume due to surgical repair. Different surgical techniques have been defined to prevent this situation. In our study, in the treatment of zone 2 flexor tendon injuries; Among the surgical techniques to be performed in addition to FDP tendon repair; We aimed to compare the biomechanical results of single FDS slip repair, A2 pulley release and two different pulley plasty methods (Kapandji and V-Y pulley plasty). Materials and Methods. In our study, 12 human upper extremity cadavers preserved with modified Larssen solution (MLS) and amputated at the mid ½ level of the arm were used. A total of 36 fingers (second, third and the fourth fingers were used for each cadaver) were divided into four groups and 9 fingers were used for each group. With the finger fully flexed, the FDS and FDP tendons were cut right in the middle of the A2 pulley and repaired with the cruciate four-strand technique. The surgical techniques described above were applied to the groups. Photographs of fingers with different loads (50 – 700 gr) were taken before and after the application. Proximal interphalangeal (PIP) joint angle, PIP joint maximum flexion angle and bowstring distance were measured. The gliding coefficient was calculated by applying the PIP joint angle to the single-phase exponential association equation. Results. Gliding coefficient after repair increased by %21.46 ± 44.41, %62.71 ± 116.9, %26.8 ± 35.35 and %20.39 ± 28.78 in single FDS slip repair, A2 pulley release, V-Y pulley plasty and Kapandji plasty respectively. The gliding coefficient increased significantly in all groups after surgical applications (p<0.05). PIP joint maximum flexion angle decreased by %3.17 ± 7.92, %12.82 ± 10.94, %8.33 ± 3.29 and %7.35 ± 5.02 in single FDS slip repair, A2 pulley release, V-Y pulley plasty and Kapandji plasty respectively. PIP joint maximum flexion angle decreased significantly after surgery in all groups (p<0.05). However, there was no statistically significant difference between surgical techniques for gliding coefficient and PIP joint maximum flexion angle. Bowstring distance between single FDS slip repair, kapandji pulley plasty and V-Y pulley plasty showed no significant difference in most loads (p>0.05). Bowstring distance was significantly increased in the A2 pulley release group compared to the other three groups (p<0.05). Conclusion. Digital motion was negatively affected after flexor tendon repair. Similar results were found in terms of gliding coefficient and maximum flexion angle among different surgical methods. As single FDS slipe repair preserves the anatomical structure of the A2 pulley therefore we prefer it as an ideal method for zone 2 flexor tendon repair. However, resection of FDS slip may jeopardizes nutrition to the flexor digitorum profundus tendon which weakens the repair site. Therefore the results must be confirmed by an in vivo study before a clinical recommendation can be made. Keywords: Flexor tendon; injury; pulley plasty; cadaver;

Introduction. Hip abductor tendon tears have been referred to as “rotator cuff tears of the hip,” and are a recognized etiology for persistent, often progressive, lateral hip pain, weakness, and limp. Multiple repair techniques and salvage procedures for abductor tendon tears have been reported in the literature; however, re-tear remains a frequent complication following surgical repair. This study compares the short-term outcomes of open abductor tendon repairs with decortication and suture fixation (DSF) compared to a modified technique repair into a bone trough (BT), to determine best surgical results for large abductor tendon avulsions. Additionally, surgical treatment of small tears versus large tears was examined. Methods. The outcomes of 37 consecutive hip abductor tendon repairs treated between January 2009 and December 2017 were retrospectively reviewed. Large tears were defined as detachment of 33–100% of the gluteus medius insertion. There were 15 DSF and 10 BT cases. Postoperative pain, ability to perform single leg stance, hip abduction, and Trendelenburg lurch, were examined. Small tears (12 cases) were defined as having no gluteus medius avulsion from the trochanteric insertion and were comprised of longitudinal tears (repaired side-by-side) and isolated gluteus minimus tears (repaired by tenodesis to the overlying gluteus medius). Standard statistical analyses were utilized. Type I error for all analyses was set at α=0.05. Results. When comparing large tear repair outcomes, repairs into a BT had superior outcomes to repairs with DSF: 0 (BT) versus 6 (DSF, 40%) failure rate (p<0.05), and greater reductions in pain at one-year post surgery (Δ VAS: BT, −5.70±0.97 | DSF: −2.73±0.69; p<0.01), ability to perform a single leg stance and hip abduction (90% and 100% vs 47% and 73%) (p<0.05). Clinical strength ratings were higher for repairs into a BT, but this did not reach statistical significance. When comparing large to small tear repair outcomes, small tears were found to have lower VAS pain scores and higher clinical strength ratings during both the pre-op and 1-year post-op time points (p<0.05). A higher percentage of those with small tears were able to perform a single leg stance and hip abduction (100%) compared to those with large tears (64% and 78% respectively) (p<0.05). A significantly higher frequency of residual lurch was also observed for those with large tears; 56% compared to small tears at 0%. Conclusions. Utilizing a BT repair significantly improved surgical results for large abductor tendon avulsions. Level of evidence: Therapeutic level IV case series

Introduction The four strand cruciate tendon repair has been described as the ideal technique, as it combines simplicity with the biomechanical advantages of four-strands. We wanted to determine if increasing the size of the locking loop increases the repair strength, and the gain in biomechanical integrity that various peripheral techniques provides. Methods Forty-eight deep flexor tendons harvested from sheep hindlimbs were randomly divided into six groups of eight. All tendons were sharply transected. Initially, four groups were repaired using the cruciate core technique without a peripheral suture. The locking loops were set at 50%, 33%, 25%, or 10% of the volar CSA and then tested to failure. The final two groups of tendons were repaired using the established optimal locking loop size. These two groups were combined with either the simple running or the interlocking horizontal mattress (IHM) peripheral suture. These were then tested to failure and biomechanically assessed. Results Repairs with locking loops of 25% had the greatest biomechanical properties; with load to two millimetre gap formation, load to failure and stiffness of 10N, 46.3 and 3.9N/mm respectively. Those with a 33%, 50% and 10% locking loops followed this. Those with 10% locking loops failed due to the suture material sliding out of the tendon. All other groups failed by suture breakage. Using the cruciate core technique with a 25% volar CSA locking loop, the load to two millimetre gap formation, load to failure and stiffness was 32.9N, 47.2N, and 7.6N/mm respectively when combined with the simple running peripheral suture and 46.4N, 79.4N and 9.9N/mm respectively when combined with the IHM repair. The IHM/cruciate combination was significantly better than the simple running/cruciate repair. Using the IHM technique in your tendon repair, this study demonstrates that the peripheral suture can provide approximately 75%, 40% and 60% of the total load to two millimetre gap formation, load to failure and stiffness respectively. Conclusions Unlike the Kessler technique, increasing the size of the locking loop in the cruciate method decreases the repair strength. The ideal sized bite seems to be approximately 25% of the volar cross-sectional area. Additional, the peripheral suture is biomechanically vital to the integrity of the repair. In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source

Tendon injuries constitute a major healthcare burden owing to the limited healing ability of these tissues and the poor clinical outcomes of surgical repair treatments. Recent advances in tendon tissue engineering (TTE) strategies, particularly through the use of biotextile technologies, hold great promise toward the generation of artificial living tendon constructs. We have previously developed a braided construct based on suture threads coated with gelMA:alginate hydrogel encapsulating human tendon cells. These cell-laden composite fibers enabled the replication of cell and tissue-level properties simultaneously. Based on this concept, in this study we explored the use of platelet lysate (PL), a pool of supra-physiological concentrations of growth factors (GFs), to generate a hydrogel layer, which is envisioned to act as a depot of therapeutic factors to induce tenogenic differentiation of encapsulated human adipose stem cells (hASCs). For this purpose, commercially available suture threads were first embedded in a thrombin solution and then incubated in PL containing hASCs. Herein, thrombin induces the gelation of PL and consequent hydrogel formation. After coating suture threads with the mixture of PL-ASCs, cells were found to be viable and homogeneously distributed along the fibers. Strikingly, hASCs encapsulated within the PL hydrogel layer around the suture thread were able to sense chemotactic factors present in PL and to establish connections between adjacent independent fibers, suggesting a tremendous potential of PL cell-laden hydrogel fibers as building blocks in the development of living constructs aimed at tendon repair applications

Purpose: To find if there is any difference in gapping of tendon repair on cylcic loading and energy to failure of tendon repair when the circumferential suture knot is placed on the same side of the core suture knot or to the opposite side of the core suture knot. Methods: Ten pig flexor tendons were repaired using 3 0 braided Polyester (Ethibond) as core suture (modified Kessler) and 6 0 Nylon as circumferential stitch (Hal-stead). Five tendons were repaired with the circumferential suture knot placed on the same side as the core suture (Group I) and the other five placed on the opposite side (Group II). Allocation to either of the groups was random. Using a testing machine the tendons were cyclically loaded and the energy to failure was calculated. Gapping during cylical loading was recorded using digital images. Results: Mean gapping in Group I was 0.01 mm and in Group II was 0.03mm. This was not statistically signifi-cant (2x3 ANOVA, p > 0.3). The mean load to failure in group I was 58.7 N (55 to 65) and in group II was 59.5 N (54 to 67). This was also not statistically significant (p > 0.3 one way ANOVA). Conclusion: There is no difference in gapping and energy to failure of tendon repair when the circumferential suture knot is placed on the same side of the core suture knot or to the opposite side of the core suture knot

Purpose: The purpose is to evaluate the clinical outcome of patients who underwent excision of motion-limiting radioulnar heterotopic ossification (HO) as a complication of a distal biceps tendon repair. The hypothesis is that there are no measurable clinical losses that persist after excision. Method: Between 1996 and 2005, eight consecutive patients were identified. All were treated with heterotopic ossification excision using a standard surgical technique, a single dose of postoperative radiation, four weeks of indomethacin, and a standard rehabilitation protocol. These individuals were studied and compared to a matched cohort of eight patients who underwent a distal biceps tendon repair with a similar surgical technique that was uncomplicated. At minimum follow-up of one year, all patients in both groups completed the Disabilities of the Arm, Shoulder and Hand (DASH) outcomes questionnaire, were tested for range of motion in elbow flexion/extension and forearm supination/pronation, and underwent biceps isokinetic dynamometry strength testing including elbow flexion and forearm supination. Both peak strength as well as muscle fatigue were quantified. Range of motion and strength comparisons were made both between groups and side-to-side within each group. Results: There were no patients lost to follow-up. At mean follow-up of 56 months, there were no cases of nerve palsy, recurrence, or other complications. All patients in the HO group returned to their original occupation without restrictions. Mean arc of forearm rotation in this group increased from 19 to 151 degrees (p=0.01), but pronation (65 degrees) was less than the unaffected arm (p=0.01). There were no side-to-side differences in motion within the control group, or differences in peak strength or fatigue within either group. When comparing the two groups, there was a trend towards worse functional outcomes on DASH in the HO group than the controls (p=0.09). No differences were identified between the HO and control groups with respect to isokinetic torque, endurance strength or range of motion. Conclusion: When patients develop motion-limiting heterotopic ossification after distal biceps tendon repair, surgical resection can safely lead to a functional recovery of elbow and forearm strength and motion. Level III Evidence, Case-control

Purpose: Anatomic repair of an acute distal biceps tear has been demonstrated to improve flexion and supination strength compared with conservative treatment. The most commonly used fixation methods for a distal biceps tendon repair include suture anchors, bioabsorbable screws, and endobutton. The goal of this study was to. perform a radiologic evaluation of bioabsorbable screw tunnel osteolysis and. retrospectively review bioabsorbable-screw related clinical complications. Method: We included twenty (20) consecutive patients who underwent primary anatomic repair of the distal biceps tendon since 2005. We used a 7x23mm biote-nodesis. ®. screw (Arthrex) in 18 cases, and 8x23mm and 8x12mm screws in the other two cases. First, from the x-ray view done in the immediate postoperative period showing the complete screw tunnel, we measured the ratio of the volume of the bone tunnel to the volume of the radius bone section. A mathematical formula for cylindrical volume was used (¶ x r2 x h). We used a relation between two volumes rather than the tunnel volume itself for scaling purposes. Secondly, we calculated the same relation on the x-ray from the last follow-up. We then obtained the percentage of tunnel enlargement by relating the volumetric ratio from the first x-ray to the ratio from the last x-ray. Afterwards, we performed a retrospective chart review noting any bioabsorbable screw-related and postoperative complications. Results: In the group, the average age was forty-six (46) years. All subjects were male. Eighteen (18) cases were acute complete ruptures operated in the first three weeks, one case was a partial rupture and one case was chronic (one year). The average follow up was eighteen (18) months. We found that the average initial relative volume occupied by the screw tunnel was 47 % of the bone section. At the last follow-up, this volume increased to 68%. After our chart review, we found that one patient presented with a broken screw and increased pain and that another patient developed a severe foreign-body reaction with re-rupture of the tendon requiring three reoperations. Conclusion: The use of a bioabsorbable screw for distal biceps tendon fixation results in significant osteolysis of the radial bone at short term follow-up. Consequences of osteolysis in the radius are worrisome since iatro-genic fractures are more likely to occur. Osteolysis can be secondary to an inflammatory reaction to the screw material, bone necrosis secondary to pressure or initial thermal necrosis. We also noted two cases of severe bio-tenodesis screw-related complications among our series of twenty (20) patients. These results call into question the use of the bioabsorbable screw in distal biceps tendon repair and are important to present. Exact volume of bone loss using 3D computed tomography scan analysis as well as quality of life questionnaires and strength testing will be available for presentation

Avulsion of the distal biceps tendon is an uncommon clinical entity accounting for 3% of all biceps tendon injuries. Various surgical techniques for its repair have been reported, however, the optimal technique is unknown. The two-incision technique is used by three upper limb surgeons at North Shore Hospital. There has been some concern regarding the risk of heterotopic bone formation with this technique. We present a review of a series of patients with distal biceps tendon ruptures treated with the modified two-incision technique to identify and describe any complications that we encountered and also assess the clinical, functional and radiological outcomes of our patients. Over a 4-year period from 2002–2006, 42 distal biceps tendons repairs using the two-incision technique were identified from the hospital database. All 42 patients were males with an average age of 51.9 years. Patients were followed-up prospectively and reviewed at a clinic where they filled out the SF-12 questionnaire and a Mayo Elbow Performance Score was assessed. Clinical assessment was carried out with regards to their range of flexion-extension and their pronation-supination. All peripheral nerves were examined. Isokinetic elbow flexion-extension and forearm pronation-supination were measured and compared to the unaffected extremity. X-rays were taken to identify heterotrophic ossification or proximal radioulnar synostoses. Our review, so far, indicates a good clinical and functional outcome in most of our patients. We identified one patient with heterotrophic bone formation requiring excision. Two patients had a transient lateral ante-brachial cutaneous nerve parasthesia and two patients had re-ruptures following surgery. This study represents a relatively large series of patients. Our results reveal that the two-incision technique is an effective surgical option for the repair of ruptured distal biceps tendons. We found that radioulnar synostoses and heterotrophic ossification are rare following the muscle splitting modification of the two-incision technique

Introduction/Aim. Flexor tendon injuries of the hand are common with an incidence of over 3000 per annum in the UK. These injuries can affect hand function significantly. Early treatment with optimal repair is crucial to prevent disability. This study aimed at investigating the re-rupture rate following primary flexor tendon repair at our institution and to identify potential risk factors for re-rupture. Methods. 100 flexor tendons' injuries that underwent primary repair over a one-year period were reviewed retrospectively. Data was collected on age, gender, occupation, co morbidities, injured fingers, hand dominance, smoking status, zone of injury, time to surgery, surgeon grade, type of repair and suture, and antibiotic use on included patients. Causes of re-rupture were examined. We compared primary tendon repairs that had a re-rupture to those that did not re-rupture. Univariate and multivariate analysis was undertaken to identify the most significant risk factors for re-rupture. Results. 11 out of 100 (11%) repaired tendons went on to re-rupture. A significantly higher proportion of tendons re-rupture was noted when the repair was performed on the dominant hand (p-value = 0.009), in Zone 2 (0.001), and when a surgical delay of more than 72 hours from the time of injury occurred (0.01). Multivariate regression analysis identified repairs in Zone 2 to be the most significant predictor of re-rupture. Causes of re-rupture included infection in 5, rupture during rehabilitation exercises in 5 and fall in 1 patient. Conclusions. A re-rupture rate of 11% was noted in our study. Patients with Zone 2 injuries, repair on dominant hand and those with a surgical delay of more than 3 days were at higher risk of re-rupture. Careful consideration of these factors especially zone 2 injuries is crucial to reduce this rate. Providing a fast-track pathway for managing these patients can reduce time to surgery

Digital Ventilated Cages (DVC) offer an innovative technology to obtain accurate movement data from a single mouse over time [1]. Thus, they could be used to determine the occurrence of a tendon damage event as well as inform on tissue regeneration [2,3]. Therefore, using the mouse model of tendon experimental damage, in this study it has been tested whether the recovery of tissue microarchitecture and of extracellular matrix (ECM) correlates with the motion data collected through this technology.

Mice models were used to induce acute injury in Achilles tendons (ATs), while healthy ones were used as control. During the healing process, the mice were housed in DVC cages (Tecniplast) to monitor animal welfare and to study biomechanics assessing movement activity, an indicator of the recovery of tendon tissue functionality. After 28 days, the AT were harvested and assessed for their histological and immunohistochemical properties to obtain a total histological score (TSH) that was then correlated to the movement data.

DVC cages showed the capacity to distinguish activity patterns in groups from the two different conditions. The data collected showed that the mice with access to the mouse wheel had a higher activity as compared to the blocked wheel group, which suggests that the extra movement during tendon healing improved motion ability. The histological results showed a clear difference between different analyzed groups. The bilateral free wheel group showed the best histological recovery, offering the highest TSH score, thus confirming the results of the DVC cages and the correlation between movement activity and structural recovery.

Data obtained showed a correlation between TSH and the DVC cages, displaying structural and movement differences between the tested groups. This successful correlation allows the usage of DVC type cages as a non-invasive method to predict tissue regeneration and recovery.

Acknowledgements: This research is part of the P4FIT project ESR13, funded by the H2020-ITN-EJD MSCA grant agreement No.955685.