Effects of trypsinization and mineralization on intrasynovial tendon allograft healing to bone

The purpose of the current study was to develop a novel technology to enhance tendon‐to‐bone interface healing by trypsinizing and mineralizing (TM) an intrasynovial tendon allograft in a rabbit bone tunnel model. Eight rabbit flexor digitorum profundus (FDP) tendons were used to optimize the trypsinization process. An additional 24 FDP tendons were stratified into control and TM groups; in each group, 4 tendons were used for in vitro evaluation of TM and 8 were transplanted into proximal tibial bone tunnels in rabbits. The samples were evaluated histologically and with mechanical testing at postoperative week 8. Maximum failure strength and linear stiffness were not significantly different between the control and TM tendons. A thin fibrous band of scar tissue formed at the graft‐to‐bone interface in the control group. However, only the TM group showed obvious new bone formation inside the tendon graft and a visible fibrocartilage layer at the bone tunnel entrance. This study is the first to explore effects of TM on the intrasynovial allograft healing to a bone tunnel. TM showed beneficial effects on chondrogenesis, osteogenesis, and integration of the intrasynovial tendon graft, but mechanical strength was the same as the control tendons in this short‐term in vivo study. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:468–474, 2015.     

Distal attachment of flexor tendon allograft: A biomechanical study of different reconstruction techniques in human cadaver hands

We compared the mechanical force of tendon‐to‐bone repair techniques for flexor tendon reconstruction. Thirty‐six flexor digitorum profundus (FDP) tendons were divided into three groups based upon the repair technique: (1) suture/button repair using FDP tendon (Pullout button group), (2) suture bony anchor using FDP tendon (Suture anchor group), and (3) suture/button repair using FDP tendon with its bony attachment preserved (Bony attachment group). The repair failure force and stiffness were measured. The mean load to failure and stiffness in the bony attachment group were significantly higher than that in the pullout button and suture anchor groups. No significant difference was found in failure force and stiffness between the pullout button and suture anchor groups. An intrasynovial flexor tendon graft with its bony attachment has significantly improved tensile properties at the distal repair site when compared with a typical tendon‐to‐bone attachment with a button or suture anchor. The improvement in the tensile properties at the repair site may facilitate postoperative rehabilitation and reduce the risk of graft rupture. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:1720–1724, 2013     

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.     

Local administration of alendronate reduced peri‐tunnel bone loss and promoted graft‐bone tunnel healing with minimal systemic effect on bone in contralateral knee

Continued systemic administration of alendronate was reported to reduce peri‐tunnel bone resorption and promoted graft‐bone tunnel healing at the early stage post‐anterior cruciate ligament (ACL) reconstruction. However, systemic increase in bone mineral density (BMD) in the contralateral intact knee was observed. We tested if single local administration of alendronate into the bone tunnel during ACL reconstruction could achieve similar benefits yet without the systemic effect on bone. Seventy‐two rats with unilateral ACL reconstruction were divided into three groups: saline, low‐dose (6 μg/kg) and mid‐dose (60 μg/kg) alendronate. For local administration, alendronate was applied to the bone tunnels for 2 min before graft insertion and repair. At weeks 2 and 6, the reconstructed complex was harvested for high‐resolution computed tomography (vivaCT) imaging followed by biomechanical test or histology. Our results showed that local administration of low‐dose alendronate showed comparable benefits on the reduction of peri‐tunnel bone loss, enhancement of bone tunnel mineralization, tunnel graft integrity, graft osteointegration and mechanical strength of the reconstructed complex at early stage post‐reconstruction, yet with minimal systemic effect on mineralized tissue at the contralateral intact knee. A single local administration of alendronate at the low‐dose therefore might be used to promote early tunnel graft healing post‐reconstruction. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:1897–1906, 2013     

Tendon and Ligament Healing and Current Approaches to Tendon and Ligament Regeneration

Ligament and tendon injuries are common problems in orthopedics. There is a need for treatments that can expedite nonoperative healing or improve the efficacy of surgical repair or reconstruction of ligaments and tendons. Successful biologically-based attempts at repair and reconstruction would require a thorough understanding of normal tendon and ligament healing. The inflammatory, proliferative, and remodeling phases, and the cells involved in tendon and ligament healing will be reviewed. Then, current research efforts focusing on biologically-based treatments of ligament and tendon injuries will be summarized, with a focus on stem cells endogenous to tendons and ligaments. Statement of clinical significance: This paper details mechanisms of ligament and tendon healing, as well as attempts to apply stem cells to ligament and tendon healing. Understanding of these topics could lead to more efficacious therapies to treat ligament and tendon injuries. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:7–12, 2020     

Development of the supraspinatus tendon‐to‐bone insertion: Localized expression of extracellular matrix and growth factor genes

The adult healing response of the rotator cuff tendon‐to‐bone insertion site differs from the ordered process of insertion site development. Healing is characterized by disorganized scar and a lack of fibrocartilage formation, in contrast to the well organized fibrocartilaginous transition which forms during the normal development of the tendon‐to‐bone insertion. The purpose of this study was to localize the expression of a number of extracellular matrix and growth factor genes during insertion site development in order to guide future strategies for augmenting adult rotator cuff healing. The rotator cuff was morphologically distinct at 13.5 dpc (days postconception). Neo‐tendon was evident as a condensation of cells adjacent to bone. The interface between tendon and bone did not form into a mature fibrocartilaginous insertion until 21‐days postnatally, based upon the appearance of four distinct zones with a mineralized humeral head. Fibroblasts of the supraspinatus tendon expressed type I collagen at all timepoints. Type II collagen was first expressed by chondrocytes in the fibrocartilage and mineralized fibrocartilage at 7 days and persisted in the mineralized fibrocartilage at 56 days. Type X collagen was first expressed by the chondrocytes in the mineralized fibrocartilage at 14 days and persisted in the mineralized fibrocartilage at 56 days. A shift from TGF‐β3 to TGF‐β1 expression occurred at 15.5 dpc. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1621–1628, 2007     

The quadriga effect revisited: Designing a “safety incision” to prevent tendon repair rupture and gap formation in a canine model in vitro

Loss of experimental animals due to tendon repair failure results in the need for additional animals to complete the study. We designed a relief proximal to the flexor digitorum profundus (FDP) tendon repair site to serve as a “safety incision” to prevent repair site ruptures and maximize safety incision‐to‐suture strength. The FDP tendons were dissected in 24 canine forepaws. The 2nd and 5th tendons were lacerated at the proximal interphalangeal joint level and sutured using a modified Kessler technique and peripheral running suture. Tendon width was measured where the FDP tendon separates into each individual digit and a safety incision, equal to the 2nd and 5th tendon widths, was performed 3, 4, or 5 mm (Groups 1, 2, and 3) proximal to the separation. The tendons were pulled at a rate of 1 mm/s until either the “safety incision” ruptured or the repair failed. There was no gap formation at the repair site in Groups 1 and 2. However, all Group 3 tendons failed by repair site rupture with the safety incision intact. An adequate safety incision to protect repair gap and rupture and maintain tendon tension for the FDP animal model should be about 4 mm from where the FDP tendon separates. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:1482–1489, 2010     

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     

Indian hedgehog signaling and the role of graft tension in tendon‐to‐bone healing: Evaluation in a rat ACL reconstruction model

The structure and composition of the native enthesis is not recapitulated following tendon‐to‐bone repair. Indian Hedgehog (IHH) signaling has recently been shown to be important in enthesis development in a mouse model but no studies have evaluated IHH signaling in a healing model. Fourteen adult male rats underwent ACL reconstruction using a flexor tendon graft. Rats were assigned to two groups based on whether or not they received 0N or 10N of pre‐tension of the graft. Specimens were evaluated at 3 and 6 weeks post‐operatively using immunohistochemistry for three different protein markers of IHH signaling. Quantitative analysis of staining area and intensity using custom software demonstrated that IHH signaling was active in interface tissue formed at the healing tendon‐bone interface. We also found increased staining area and intensity of IHH signaling proteins at 3 weeks in animals that received a pre‐tensioned tendon graft. No significant differences were seen between the 3‐week and 6‐week time points. Our data suggests that the IHH signaling pathway is active during the tendon‐bone healing process and appears to be mechanosensitive, as pre‐tensioning of the graft at the time of surgery resulted in increased IHH signaling at three weeks. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:641–649, 2016.     

Comparative Evaluation of the Book‐Type Acellular Bone Scaffold and Fibrocartilage Scaffold for Bone‐Tendon Healing

Bone‐tendon (B‐T) healing is a clinical challenge due to its limited regeneration capability. Fibrocartilage regeneration and bone formation at the healing site are two critical factors for B‐T healing. Promoting fibrocartilage regeneration and bone formation by tissue‐engineering may be a promising treatment strategy. In this study, we innovatively fabricated two kinds of acellular scaffolds from bone or fibrocartilage tissues, namely the book‐type the acellular bone scaffold (BABS) and the book‐type acellular fibrocartilage scaffold (BAFS). Histologically, the two scaffolds well preserved the native extracellular matrix (ECM) structure without cellular components. In vitro studies showed BABS is superior in osteogenic inducibility, while BAFS has good chondrogenic inducibility. To comparatively investigate the efficacy on B‐T healing, the BABS or BAFS were, respectively, implanted into a rabbit partial patellectomy model. Macroscopically, a regenerated bone‐tendon insertion (BTI) was bridging the residual patella and patellar‐tendon with no signs of infection and osteoarthritis. Radiologically, more new bone was formed at the healing interface in the BABS group as compared with the BAFS or control (CTL) groups (p < 0.05). Histologically, at postoperative week 16, histological scores were significantly better for regenerated fibrocartilage in the BAFS group or BABS group compared with the CTL group, but the BAFS group showed a significantly larger score than the BABS groups (p < 0.05). Biomechanical evaluation indicated a higher failure load and stiffness were shown in the BAFS group than those in the BABS or CTL groups at week 16 (p < 0.05). This study indicated that the BAFS is a more promising scaffold for B‐T healing in comparison with the BABS. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1709–1722, 2019     

Revitalized and synovialized allograft for intrasynovial flexor tendon reconstruction in an in vivo canine model

This study was to test our hypothesis that flexor tendon reconstruction with an allograft revitalized with bone marrow stromal cells (BMSCs) and synovialized with carbodiimide derivatized autologous synovial fluid (cd‐SYN) would result in better digit functional restoration than the conventional allograft tendon. A total of 32 flexor digital profundus tendons from the second and fifth digit of 16 dogs were created a repair failure model first. Then, failed‐repaired tendons were reconstructed with either a revitalized‐synovialized allograft tendon or a clinical standard autograft tendon (control group). The allograft tendon was seeded with autologous BMSCs in multiple slits and the graft surface was coated with cd‐SYN. A 6 weeks after tendon reconstruction, the digits were harvested and evaluated for digit function, adhesion status, tendon gliding resistance, attachment strength, cell viability, and histologic factors. The allograft group had significantly improved digit function compared with the control group through decreased work of flexion, increased digit range of motion under 2‐Newton force, and less adhesion score (p < .05). However, the distal attachment‐site strength and stiffness in the allograft tendon were significantly weaker than the autografts (p < .05). No significant difference was found for gliding resistance. Histologically, allograft tendons coated with allograft had smoother surfaces and showed tendon‐to‐bone and tendon‐to‐tendon incorporation. Viable BMSCs were found in the tendon slits 6 weeks after the graft. In conclusion, cellular lubricant‐based modification of allograft tendons improved digit function and reduced the adhesions compared with autograft for flexor tendon reconstruction. However, improvement of graft‐to‐host tendon healing is still challenging. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2218–2227, 2018.

     

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     

Smad8/BMP2‐engineered mesenchymal stem cells induce accelerated recovery of the biomechanical properties of the achilles tendon

Tendon tissue regeneration is an important goal for orthopedic medicine. We hypothesized that implantation of Smad8/BMP2‐engineered MSCs in a full‐thickness defect of the Achilles tendon (AT) would induce regeneration of tissue with improved biomechanical properties. A 2 mm defect was created in the distal region of murine ATs. The injured tendons were then sutured together or given implants of genetically engineered MSCs (GE group), non‐engineered MSCs (CH3 group), or fibrin gel containing no cells (FG group). Three weeks later the mice were killed, and their healing tendons were excised and processed for histological or biomechanical analysis. A biomechanical analysis showed that tendons that received implants of genetically engineered MSCs had the highest effective stiffness (>70% greater than natural healing, p < 0.001) and elastic modulus. There were no significant differences in either ultimate load or maximum stress among the treatment groups. Histological analysis revealed a tendon‐like structure with elongated cells mainly in the GE group. ATs that had been implanted with Smad8/BMP2‐engineered stem cells displayed a better material distribution and functional recovery than control groups. While additional study is required to determine long‐term effects of GE MSCs on tendon healing, we conclude that genetically engineered MSCs may be a promising therapeutic tool for accelerating short‐term functional recovery in the treatment of tendon injuries. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1932–1939, 2012     

Ⅱd区屈趾肌腱损伤早期修复的形态学和生物力学研究

目的 为探索Ⅱd区不同伤情下肌腱的合理修复方法,进行动物实验,以提供对临床有用的参考依据。方法 选用正常白色来亨鸡24只,每组12只24趾。A组为单纯切割伤组,左侧修复双腱,右侧切除浅腱修复深腱;B组为严重挫伤组,修复同前。直接关闭腱鞘,术后3周控制性主、被动活动,术后6周进行修复的屈趾深肌腱的生物力学测定(滑动距离、屈曲功),并观察和测量各修复组织间的粘连性状和粘连面积。结果 单纯切割伤组两种修复方法之间的滑动距离、屈曲功、粘连性状和粘连面积在统计学上没有显著差异;而在严重挫伤组,双腱修复侧的滑动距离小于浅腱切除单纯修复深腱侧,屈曲功和粘连面积大于单纯修复深腱侧,粘连程度较大,在统计学上有显著性差异(p<0.05)。结论 本研究提示:临床上对Ⅱd亚区的浅、深屈趾肌腱单纯切割伤,应修复双腱;严重挫伤时,则应切除浅腱而只修复深腱。     

Effects of superficialis tendon repairs on lacerated profundus tendons within or proximal to the A2 pulley: an in vivo study in chickens

PURPOSE: In a flexor tendon injury model in chickens we undertook a study to evaluate effects of the flexor digitorum superficialis (FDS) tendon repairs on excursions, work of flexion, and adhesions of the repaired flexor digitorum profundus (FDP) tendon after their injuries within or proximal to the equivalent of the A2 pulley and early tendon motion. METHODS: Thirty-five leghorn chickens were divided into 3 groups. In group 1 the FDS and FDP tendons of the long toes on both sides were transected in the area covered by the pulley. In group 2 the tendons were transected proximal to the pulley. In the first 2 groups, both tendons were repaired on the left feet, and only the profundus was repaired with superficialis excision on the right. The operated toes underwent simulated passive flexion for 3 weeks and results were evaluated 8 weeks after surgery. Chickens in group 3 were unoperated and served as the controls. RESULTS: When the tendons were cut within the pulley the FDP excursions and work of flexion were significantly better in the toes in which the FDS was excised than in those with both tendon repairs. When they were cut proximal to the pulley the repairs of both tendons had outcomes similar to that with excision of the FDS. Adhesions were more severe when both tendons were repaired under the pulley as compared with those after repair of a single tendon. CONCLUSIONS: This study showed different effects of the surgical repair or excision of the FDS on the FDP tendon within or proximal to a major pulley. Repair of both tendons worsens the gliding of the FDP tendon and increases adhesions within the major pulley; however, repair of both tendons yields outcomes equivalent to that after repair of only the FDP tendon proximal to the pulley.     

Integrating soft and hard tissues via interface tissue engineering

The enthesis, or interface between bone and soft tissues such as ligament and tendon, is prone to injury and often does not heal, even post surgical intervention. Interface tissue engineering represents an integrative strategy for regenerating the native enthesis by functionally connecting soft and hard tissues and thereby improving clinical outcome. This review focuses on integrative and cell‐instructive scaffold designs that target the healing of the two most commonly injured soft tissue‐bone junctions: tendon‐bone interface (e.g., rotator cuff) and ligament‐bone interface (e.g., anterior cruciate ligament). The inherent connectivity between soft and hard tissues is instrumental for musculoskeletal motion and is therefore a key design criterion for soft tissue regeneration. To this end, scaffold design for soft tissue regeneration have progressed from single tissue systems to the emerging focus on pre‐integrated and functional composite tissue units. Specifically, a multifaceted, bioinspired approach has been pursued wherein scaffolds are tailored to stimulate relevant cell responses using spatially patterned structural and chemical cues, growth factors, and/or mechanical stimulation. Moreover, current efforts to elucidate the essential scaffold design criteria via strategic biomimicry are emphasized as these will reduce complexity in composite tissue regeneration and ease the related burden for clinical translation. These innovative studies underscore the clinical relevance of engineering connective tissue integration and have broader impact in the formation of complex tissues and total joint regeneration. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1069–1077, 2018.

     

Sexual dimorphism in the effect of GDF‐6 deficiency on murine tendon

Three members of the growth/differentiation factor (GDF) subfamily of bone morphogenetic proteins (BMPs), GDFs‐5, ‐6, and ‐7, have demonstrated the potential to augment tendon and ligament repair. To gain further insight into the in vivo role of these molecules, previous studies have characterized intact and healing tendons in mice with functional null mutations in GDF‐5 and ‐7. The primary goal of the present study was to perform a detailed characterization of the intact tendon phenotype in 4‐ and 16‐week‐old male and female GDF6?/? mice and their +/+ littermates. The results demonstrate that GDF6 deficiency was associated with an altered tendon phenotype that persisted into adulthood. Among males, GDF6?/? tail tendon fascicles had significantly less collagen and glycosaminoglycan content, and these compositional differences were associated with compromised material properties. The effect of GDF6 deficiency on tendon was sexually dimorphic, however, for among female GDF6?/? mice, neither differences in tendon composition nor in material properties were detected. The tendon phenotype that was observed in males appeared to be stronger in the tail site than in the Achilles tendon site, where some compositional differences were present, but no material property differences were detected. These data support existing in vitro studies, which suggest a potential role for BMP‐13 (the human homologue to GDF‐6) in tendon matrix modeling and/or remodeling. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1603–1611, 2009     

Auto‐crosslinked hyaluronic acid gel accelerates healing of rabbit flexor tendons in vivo

This study's purpose was to assess the in vivo effect of auto‐crosslinked hyaluronic acid (HA) gel, a natural HA derivative with increased viscosity and tissue residence time, on adhesions and healing of injured and surgically repaired rabbit digital flexor tendons. The second and third right deep digital flexor tendons from 48 rabbits (n = 96 tendons) were cut and repaired with a modified Kessler and running peripheral suture. Animals were randomized to two groups, receiving either HA gel or saline injected around both freshly repaired tendons. After 2, 3, 6, and 12 weeks, six rabbits in each group were euthanized. Tendon pull‐out force and breaking strength were measured as a value for adhesion formation and tendon healing, respectively. A histological assessment of adhesions and healing was related to the mechanical results. A significantly faster increase in breaking strength was found in HA gel‐treated compared to saline‐treated tendons; this coincided with a significantly accelerated tissue repair response after injury. No significant difference in adhesion formation was found between the two groups at any time. Our results indicate a significant acceleration of in vivo healing of tendons treated with HA gel. Adhesion formation was unaffected. These results could have important clinical value in promoting rehabilitation after tendon injury. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:408–415, 2009     

Semitendinosus tendon regeneration after anterior cruciate ligament reconstruction: can we use it twice?

Purpose

It has been demonstrated that the semitendinosus tendon can regenerate after being harvested in its whole length and thickness for anterior cruciate ligament (ACL) reconstruction. Ultrasound studies and guided biopsies of the regenerated tendon have shown compatibility and resembling features of the normal tendon. The question is if this neo-tendon is biologically and functionally adequate for re-use?

Methods

Two randomised groups of 150 volunteers were followed up for two years after harvesting the semitendinosus only (25) or the semitendinosus and gracilis tendons (25) in ACL reconstruction. The patients were followed up with clinical and ultrasound examinations, biopsies and histological tests. Surgical exploration was done in three patients for macroscopic verification. The injected arteries of four lower limbs were dissected and the tendon’s arterial supplies were examined.

Results

Seventy-two percent of the cases showed regeneration of the semitendinosus tendons. The neotendons were inserted mostly below the knee joint (83.3 %) where they had fused with the gracilis tendon, and above the joint (60 %) when the gracilis was harvested as well. The isokinetic strength of the hamstrings and quadriceps was not significantly diminished on the operated side. A macroscopic and histological analysis of the regenerated tendons demonstrates close resemblance to normal anatomy, with focal areas of fibrosis. In one patient the regenerated tendon was used for medial patellofemoral ligament reconstruction.

Conclusion

The semitendinosus muscle can recover and the tendon has great potential to regenerate after harvesting for ACL reconstruction. Our data suggest that the regenerated tendons could be used for iterative ligament reconstruction.