Resurfacing with chemically modified hyaluronic acid and lubricin for flexor tendon reconstruction

We assessed surface coating with carbodiimide derivatized hyaluronic acid combined with lubricin (cd‐HA‐Lubricin) as a way to improve extrasynovial tendon surface quality and, consequently, the functional results in flexor tendon reconstruction, using a canine in vivo model. The second and fifth flexor digitorum profundus tendons from 14 dogs were reconstructed with autologs peroneus longus (PL) tendons 6 weeks after a failed primary repair. One digit was treated with cd‐HA‐Lubricin, and the other was treated with saline as the control. Six weeks following grafting, the digits and graft tendons were functionally and histologically evaluated. Adhesion score, normalized work of flexion, graft friction in zone II, and adhesion breaking strength at the proximal repair site in zone III were all lower in the cd‐HA‐Lubricin treated group compared to the control group. The strength at the distal tendon/bone interface was decreased in the cd‐HA‐Lubricin treated grafts compared to the control grafts. Histology showed inferior healing in the cd‐HA‐Lubricin group at both proximal and distal repair sites. However, cd‐HA‐Lubricin treatment did not result in any gap or rupture at either the proximal or distal repair sites. These results demonstrate that cd‐HA‐Lubricin can eliminate graft adhesions and improve digit function, but that treatment may have an adverse effect on tendon healing. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 969–975, 2013     

Enhanced flexor tendon healing through controlled delivery of PDGF‐BB

A fibrin/heparin‐based delivery system was used to provide controlled delivery of platelet derived growth factor BB (PDGF‐BB) in an animal model of intrasynovial flexor tendon repair. We hypothesized that PDGF‐BB, administered in this manner, would stimulate cell proliferation and matrix remodeling, leading to improvements in the sutured tendon's functional and structural properties. Fifty‐six flexor digitorum profundus tendons were injured and repaired in 28 dogs. Three groups were compared: (1) controlled delivery of PDGF‐BB using a fibrin/heparin‐based delivery system; (2) delivery system carrier control; and (3) repair‐ only control. The operated forelimbs were treated with controlled passive motion rehabilitation. The animals were euthanized at 7, 14, and 42 days, at which time the tendons were assessed using histologic (hyaluronic acid content, cellularity, and inflammation), biochemical (total DNA and reducible collagen crosslink levels), and biomechanical (gliding and tensile properties) assays. We found that cell activity (as determined by total DNA, collagen crosslink analyses, and hyaluronic acid content) was accelerated due to PDGF‐BB at 14 days. Proximal interphalangeal joint rotation and tendon excursion (i.e., tendon gliding properties) were significantly higher for the PDGF‐BB‐treated tendons compared to the repair‐alone tendons at 42 days. Improvements in tensile properties were not achieved, possibly due to suboptimal release kinetics or other factors. In conclusion, PDGF‐BB treatment consistently improved the functional but not the structural properties of sutured intrasynovial tendons through 42 days following repair. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res     

Effect of hyaluronic acid/chondroitin sulfate on healing of full-thickness tendon lacerations in rabbits

Viscoat, a high-molecular-weight, highly purified hyaluronic acid (HA) and chondroitin sulfate (CS) compound, was instilled around rabbit plantaris tendon following full-thickness laceration and surgical repair. After 3 weeks of immobilization, no significant difference in adhesion strength or tensile strength of the healing tendons existed between Viscoat-treated tendons and controls. This contradicts previous studies which suggest that hyaluronic acid reduces postoperative tendon adhesions. Further studies examining tendon adhesions after less severe degrees of tendon injury and using direct, quantitative measurement techniques are warranted to demonstrate whether HA has a beneficial effect on tendon healing.     

Seprafilm interposition for preventing adhesion formation after tenolysis. An experimental study on the chicken flexor tendons

BACKGROUND: Hyaluronic acid and its derivatives have become increasingly popular for preventing adhesions in primary tendon repair. Their use in tenolysis, however, has not been established yet. The purpose of the current study was to evaluate the efficacy of Seprafilm, a combination of carboxymethylcellulose membrane and hyaluronate, in prevention of adhesion formation after tenolysis. MATERIALS AND METHODS: Thirty chickens were initially operated on their right central toes in order to constitute an experimental setting of postoperative flexor tendon adhesion. They were then randomly assigned to 3 groups at 6 weeks. Group 1 received no further procedure, group 2 underwent simple tenolysis with physiologic saline injection, and group 3 had tenolysis with Seprafilm interposition. RESULTS: Group 3 scored a significantly higher average gliding excursion value than the other groups. Histologic examination corroborated the biomechanical data. CONCLUSION: Seprafilm was effective in preventing adhesions after tenolysis.     

Tendon‐derived progenitor cells improve healing of collagenase‐induced flexor tendinitis

Tendinitis is a common and a performance‐limiting injury in athletes. This study describes the value of intralesional tendon‐derived progenitor cell (TDPC) injections in equine flexor tendinitis. Collagenase‐induced tendinitis was created in both front superficial digital flexor (SDF) tendons. Four weeks later, the forelimb tendon lesions were treated with 1 × 10⁷ autogenous TDPCs or saline. Tendinitis was also induced by collagenase in one hind SDF tendon, to study the survival and distribution of DiI‐labeled TDPCs 1, 2, 4, and 6 weeks after injection. The remaining normal tendon was used as a “control.” Twelve weeks after forelimb TDPC injections, tendons were harvested for assessment of matrix gene expression, biochemical, biomechanical, and histological characteristics. DiI‐labeled TDPCs were abundant 1 week after injection but gradually declined over time and were undetectable after 6 weeks. Twelve weeks after TDPC injection, collagens I and III, COMP and tenomodulin mRNA levels were similar (p = 0.3) in both TDPC and saline groups and higher (p < 0.05) than normal tendon. Yield and maximal stresses of the TDPC group were significantly greater (p = 0.005) than the saline group's and similar (p = 0.6) to normal tendon. However, the elastic modulus of the TDPC and saline groups were not significantly different (p = 0.32). Histological assessment of the repair tissues with Fourier transform‐second harmonic generation imaging demonstrated that collagen alignment was significantly better (p = 0.02) in TDPC group than in the saline controls. In summary, treating collagenase‐induced flexor tendon lesions with TDPCs improved the tensile strength and collagen fiber alignment of the repair tissue. Study Design © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2162–2171, 2016.     

Effects of corticosteroids and hyaluronic acid on torn rotator cuff tendons in vitro and in rats

Corticosteroids (CS) or hyaluronic acid (HA) is used in subacromial injection for the conservative treatment of rotator cuff tears (RCT); this study addresses the question of how CS and HA affect the tendon tissue and fibroblasts in vitro and in rats. Cell proliferation assays were performed in human tendon fibroblasts from RCT. Rats underwent surgery to create RCT, and the surgical sites were injected with CS or HA. The rotator cuff tendons were subjected to biomechanical testing, microscopic and immunohistochemical analysis of proliferating cell nuclear antigen (PCNA), and ultrastructural analysis. Cell proliferation was significantly decreased with CS in vitro (p < 0.05). Maximal load of CS‐treated tendons was significantly decreased compared with that of HA‐treated tendons (p < 0.05), as well as PCNA⁺ cells at 2 weeks (p < 0.05). Ultrastructural observations of the CS‐treated rats detected apoptosis of tendon fibroblasts 24 h after surgery. Histological and biomechanical data 4 weeks after surgery were not significant among the three groups. Unlike HA, CS caused cell death, and inhibition of the proliferation of tendon fibroblasts, leading to a delay of tendon healing involved and a subsequent decrease of biomechanical strength at the surgical site. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1523–1530, 2015.     

The effect of muscle loading on flexor tendon‐to‐bone healing in a canine model

Previous tendon and ligament studies have demonstrated a role for mechanical loading in tissue homeostasis and healing. In uninjured musculoskeletal tissues, increased loading leads to an increase in mechanical properties, whereas decreased loading leads to a decrease in mechanical properties. The role of loading on healing tissues is less clear. We studied tendon‐to‐bone healing in a canine flexor tendon‐to‐bone injury and repair model. To examine the effect of muscle loading on tendon‐to‐bone healing, repaired tendons were either cut proximally (unloaded group) to remove all load from the distal phalanx repair site or left intact proximally (loaded group). All paws were casted postoperatively and subjected to daily passive motion rehabilitation. Specimens were tested to determine functional properties, biomechanical properties, repair‐site gapping, and bone mineral density. Loading across the repair site led to improved functional and biomechanical properties (e.g., stiffness for the loaded group was 8.2 ± 3.9 versus 5.1 ± 2.5 N/mm for the unloaded group). Loading did not affect bone mineral density or gapping. The formation of a gap between the healing tendon and bone correlated with failure properties. Using a clinically relevant model of flexor tendon injury and repair, we found that muscle loading was beneficial to healing. Complete removal of load by proximal transection resulted in tendon‐to‐bone repairs with less range of motion and lower biomechanical properties compared to repairs in which the muscle‐tendon‐bone unit was left intact. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res     

The tensile strength of various peripheral circumferential repair techniques in canine flexor tendons

The purpose of this study was to evaluate the tensile strength of six peripheral circumferential suture techniques, using a variable number of suture strands. Transverse lacerations were made in 184 fresh frozen canine flexor profundus tendons and repaired using only a 6-0 Prolene circumferential suture. The six running suture techniques were: Simple, Simple-locking, Lembert, Halsted, Cross-stitch and Lin-locking, and 6, 10, 14, and 20 suture strands were used. For each technique, the tensile strength gradually increased with the increased number of suture strands. The tensile strength of the Lin-locking technique (19–34 N) was greater than that of the other techniques, followed by Cross-stitch (16–33 N), Halsted (10–25 N), Lembert (8–23 N), Simple (6–12 N), and Simple-locking (5–8 N). The Lin-locking had the best holding power, but it was technically the most complicated to place. The Cross-stitch had good tensile strength values. The Simple and the Simple-locking had the lowest tensile strengths. From the viewpoints of tensile strength and technical skill, the Cross-stitch may be preferable to other suture techniques.     

Effects of lubricant and autologous bone marrow stromal cell augmentation on immobilized flexor tendon repairs

The purpose of the study was to test a novel treatment that carbodiimide‐derivatized‐hyaluronic acid‐lubricin (cd‐HA‐lubricin) combined cell‐based therapy in an immobilized flexor tendon repair in a canine model. Seventy‐eight flexor tendons from 39 dogs were transected. One tendon was treated with cd‐HA‐lubricin plus an interpositional graft of 8 × 10⁵ BMSCs and GDF‐5. The other tendon was repaired without treatment. After 21 day of immobilization, 19 dogs were sacrificed; the remaining 20 dogs underwent a 21‐day rehabilitation protocol before euthanasia. The work of flexion, tendon gliding resistance, and adhesion score in treated tendons were significantly less than the untreated tendons (p < 0.05). The failure strength of the untreated tendons was higher than the treated tendons at 21 and 42 days (p < 0.05). However, there is no significant difference in stiffness between two groups at day 42. Histologic analysis of treated tendons showed a smooth surface and viable transplanted cells 42 days after the repair, whereas untreated tendons showed severe adhesion formation around the repair site. The combination of lubricant and cell treatment resulted in significantly improved digit function, reduced adhesion formation. This novel treatment can address the unmet needs of patients who are unable to commence an early mobilization protocol after flexor tendon repair. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:154–160, 2016.     

Early healing of flexor tendon insertion site injuries: Tunnel repair is mechanically and histologically inferior to surface repair in a canine model.

Orthopedic injuries often require surgical reattachment of tendon to bone. Tendon ends can be sutured to bone by direct apposition to the bone surface or by placement within a bone tunnel. Our objective was to compare early healing of a traditional surface versus a novel tunnel method for repair of the flexor digitorum profundus (FDP) tendon insertion site in a canine model. A total of 70 tendon-bone specimens were analyzed 0, 5, 10 or 21 days after injury and repair, using tensile and range of motion mechanical testing, histology and densitometry. Ultimate force (a measure of repair strength) did not differ between surface and tunnel repairs at day 0. Both repair types had reduced strength at 10 and 21 days compared to 0 days, indicative of deterioration of suture grasping strength (tendon softening). At 21 days, tendons repaired in a bone tunnel had 38% lower ultimate force compared to surface repairs (p = 0.017). Histological findings were comparable between repair groups at 5 and 10 days but differed at 21 days, when we saw evidence of maturation of the tendon-bone interface in the surface repairs compared to an immature fibrous interface with no evidence of tendon-bone integration in the tunnel repairs. After accounting for bone removed by the tunnel, no difference in bone mineral density or trabecular bone volume existed between surface and tunnel repairs. If the results of our animal study extend to healing of the human FDP insertion, they indicate that FDP tendons should be reattached to the distal phalanx by suture to the cortical surface rather than suture in a bone tunnel.     

Quantification of regional blood flow to canine flexor tendons

Although the blood supply and the microcirculation of flexor tendons have been studied and defined extensively using qualitative methods, the quantitative assessment of blood flow has been lacking because of the limitations of the available experimental techniques. We studied the regional blood supply to the flexor tendons of dogs by the technique of radionuclide-labeled microspheres. Seven adult mongrel dogs were used. Microsphere injection and tissue-counting techniques previously used for other tissues were applied. Samples of proximal, isthmus, and distal portions of the profundus and superficialis flexor tendons were harvested from each digital unit of available limbs from each dog. Mean (+/- SE) flows (ml/100 g dry tissue/min) were proximal profundus 1.78 +/- 0.60 and superficialis 7.10 +/- 1.50. The differences were significant (p less than 0.01). The study suggests that regional variation in blood flow to canine digital flexor tendons exists, so that a single value for blood flow to these tendons is not relevant. Furthermore, the study supports the concept of dual (vascular and synovial) nutrition to the digital flexor tendons in dogs. These observations may have implications regarding tendon repair techniques.     

Establishment of an in vivo turkey model for the study of flexor tendon repair

Flexor tendon injuries are common and pose a clinical challenge for functional restoration. The purpose of our study was to assess the adequacy of the turkey as a large animal model for flexor tendon injuries in vivo. Twenty‐four male turkeys underwent surgical flexor tendon cut and repair. Turkeys were allocated to five groups postoperatively: (1) foot casted in extension and sacrificed after 3 weeks; (2) foot casted in extension and sacrificed after 6 weeks; (3) foot casted in flexion and sacrificed after 3 weeks; (4) foot casted in flexion and sacrificed after 6 weeks; and (5) foot casted in flexion for 6 weeks and then free roaming allowed for an additional 3 weeks before sacrifice. After sacrifice, digits were collected and analyzed for adhesion formation, healing at the macrolevel and histologically, and biomechanical properties—including friction, work of flexion, stiffness, and strength of repair. All turkeys survived anesthesia and surgery. Tendon rupture occurred in all extension casts and in 11% of those casted in flexion. Friction and work of flexion were significantly higher in the repaired digit than the control digit. There was a correlation between duration of immobilization and repair strength. Histologically, the tendon healed with tenocytes migrating into the gap and producing collagen fibers. We have, for the first time, studied flexor tendon injury and repair using turkeys in terms of anesthesia, surgical procedures, postoperative care, and animal husbandry. The findings regarding functional and histological results from this novel avian model were comparable to the most commonly used mammal model. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2497–2505, 2018.

     

Tissue reactions of adenoviral, adeno-associated viral, and liposome-plasmid vectors in tendons and comparison with early-stage healing responses of injured flexor tendons

PURPOSE: Delivery of growth factor genes that may substantially increase the healing rate of injured digital flexor tendons is a new application of gene therapy. Adenoviral, adeno-associated viral (AAV), and liposome-plasmid vectors have been used to deliver genes to tendons, but the tendon reactions to these vectors--particularly in contrast to the healing responses in the injured tendons--were unknown. This study was designed to compare the tissue reactions of the earlier-mentioned vectors in tendons with the healing responses of injured flexor tendons. METHODS: Forty-two flexor digitorum profundus tendons of 6 New Zealand white rabbits were used. Eighteen tendons were divided into 3 groups of 6 each and injected with different vectors: adenoviral vector, AAV2-luciferase vector, or pCMV-beta vector with liposome. Another 12 tendons were cut and repaired. At 3, 7, and 14 days, the tendons were harvested and stained with hematoxylin and eosin. Normal flexor tendons were harvested as controls. RESULTS: The tissue reactions of the liposome-plasmid vector in tendons were the most prominent among the 3 vectors tested. The adenoviral vector elicited a moderate degree of tissue reaction. The AAV2 vector caused remarkable reactions in epitenon but almost no reactions in endotenon. Early-stage tissue reactions were more robust in the injured tendons. Compared with early-stage inflammatory and healing responses, the reactions elicited by these vectors were less severe. CONCLUSIONS: The 3 gene delivery systems tested elicit less severe tissue reactions in flexor tendons compared with early-stage inflammatory changes in injured tendons. Adenoviral and AAV vectors elicit less severe tissue reactions than liposome-plasmid vectors. The AAV2 vector appears to cause almost no reaction in endotenon. In terms of tissue reactions, the adenoviral and AAV2 vectors, in particular AAV2, are suitable gene delivery systems for future gene transfer to the tendon in vivo.     

Adhesions in a murine flexor tendon graft model: Autograft versus allograft reconstruction

Reconstruction of flexor tendons often results in adhesions that compromise joint flexion. Little is known about the factors involved in the formation of flexor tendon graft adhesions. In this study, we developed and characterized a novel mouse model of flexor digitorum longus (FDL) tendon reconstruction with live autografts or reconstituted freeze‐dried allografts. Grafted tendons were evaluated at multiple time points up to 84 days post‐reconstruction. To assess the flexion range of the metatarsophalangeal joint, we developed a quantitative outcome measure proportional to the resistance to tendon gliding due to adhesions, which we termed the Gliding Coefficient. At 14 days post‐grafting, the Gliding Coefficient was 29‐ and 26‐fold greater than normal FDL tendon for both autografts and allografts, respectively (p < 0.001), and subsequently doubled for 28‐day autografts. Interestingly, there were no significant differences in maximum tensile force or stiffness between live autograft and freeze‐dried allograft repairs over time. Histologically, autograft healing was characterized by extensive remodeling and exuberant scarring around both the ends and the body of the graft, whereas allograft scarring was abundant only near the graft–host junctions. Gene expression of GDF‐5 and VEGF were significantly increased in 28‐day autografts compared to allografts and to normal tendons. These results suggest that the biomechanical advantages for tendon reconstruction using live autografts over devitalized allografts are minimal. This mouse model can be useful in elucidating the molecular mechanisms in tendon repair and can aid in preliminary screening of molecular treatments of flexor tendon adhesions. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:824–833, 2008     

Growth factor and protease expression during different phases of healing after rabbit deep flexor tendon repair

The purpose of the study was to contribute to the mapping of molecular events during flexor tendon healing, in particular the growth factors insulin‐like growth factor‐1 (IGF‐1), vascular endothelial growth factor (VEGF) and nerve growth factor (NGF), matrix metalloproteinases (MMP‐3 and MMP‐13) and their inhibitors (tissue inhibitors of metalloproteinases, TIMP‐1 and TIMP‐3, and the protease cathepsin K. In a rabbit model of flexor tendon injury, the mRNA expression for the growth factors, MMPs and TIMPs were measured in tendon and tendon sheath tissue at several time points (3, 6, 21, and 42 days) representing different phases of the healing process. We found that MMP‐13 remained increased during the study period, whereas MMP‐3 returned to normal levels within the first week after injury. TIMP‐3 was down‐regulated in the tendon sheaths. Cathepsin K was up‐regulated in tendons and sheaths after injury. NGF was present in both tendons and sheaths, but unaltered. IGF‐1 exhibited a late increase in the tendons, while VEGF was down‐regulated at the later time points. In conclusion, we have demonstrated the presence of NGF in flexor tendons. MMP‐13 expression appears to play a more protracted role in flexor tendon healing than MMP‐3. The relatively low levels of endogenous IGF‐1 and VEGF mRNA following injury support their potential beneficial role as exogenous modulators to optimize tendon healing and strength without increasing adhesion formation. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:886–892     

可吸收防粘连膜在预防上肢屈肌腱粘连中的应用

目的观察局部应用可吸收防粘连膜在预防上肢屈肌腱粘连中的应用及疗效。方法回顾性总结2004年3月～2006年2月间手及前臂屈肌腱损伤患者53例共89条肌腱，其中27例（45条屈肌腱）吻合肌腱后，采用成都迪康公司生产的可吸收防粘连膜包绕肌腱吻合端缝合固定，作为实验组；余26例（44条屈肌腱）同法修复但术中不使用可吸收防粘连膜，以作为对照。两组均在术后6个月随访。并参照中华医学会手外科学会手部肌腱修复后评定标准，按手指总主动活动度（TAM）法加以检测伤手功能以评估疗效。结果可吸收防粘连膜组随访39条肌腱，效果优良者34条，优良率87．2％，未用可吸收防粘连膜对照组，随访44条肌腱，效果优良者为29条，优良率为65．9％，两者差异有显著性（χ^2=5．1，P〈0．05）。结论手及前臂屈肌腱损伤术中应用可吸收防粘连膜可预防和减轻屈肌腱术后粘连，效果显著。     

透明质酸外敷膜对大鼠手术切口愈合

目的　探讨透明质酸外敷膜对手术切口愈合的影响。方法　选用纯系SD大鼠 4 8只 ,随机分为 8组 ,每组 6只。采用背部两侧切口 ,左侧外敷透明质酸膜 ,为实验组 ;右侧外敷生理盐水纱条作为对照。分别对术后 1～ 2 8d切口愈合情况进行组织学观察。结果　实验组炎症反应轻 ,表皮愈合快 ,成纤维细胞发生退行样变化 ,胶原纤维较纤细 ,排列较疏松。结论　透明质酸外敷膜在切口愈合早期 ,有较强的透皮作用 ;并可促进表皮层愈合、延缓角化层形成。