Patellar Tendon Injury Research Articles

Impact of elevated serum advanced glycation end products and exercise on intact and injured murine tendons

ABSTRACT Overview: Delayed tendon healing is a significant clinical challenge for those with diabetes. We explored the role of advanced glycation end-products (AGEs), a protein modification present at elevated levels in serum of individuals with diabetes, on injured and intact tendons using a mouse model. Cell proliferation following tissue injury is a vital component of healing. Based on our previous work demonstrating that AGEs limit cell proliferation, we proposed that AGEs are responsible for the delayed healing process commonly observed in diabetic patients. Further, in pursuit of interventional strategies, we suggested that moderate treadmill exercise may support a healing environment in the presence of AGEs as exercise has been shown to stimulate cell proliferation in tendon tissue. Materials and Methods: Mice began receiving daily intraperitoneal injections of bovine serum albumin (BSA)-Control or AGE-BSA injections (200μg/ml) at 16-weeks of age. A tendon injury was created in the central third of both patellar tendons. Animals assigned to an exercise group began a moderate treadmill protocol one week following injury. The intact Achilles tendon and soleus muscle were also evaluated to assess the effect of BSA and AGE-BSA on un-injured muscle and tendon. Results: We demonstrate that our injection dosing and schedule lead to an increase in serum AGEs. Our findings imply that AGEs indeed modulate gene expression following a patellar tendon injury and have modest effects on gene expression in intact muscle and tendon. Conclusions: While additional biomechanical analysis is warranted, these data suggest that elevated serum AGEs in persons with diabetes may impact tendon health.

Collagen V deficiency during murine tendon healing results in distinct healing outcomes based on knockdown severity

Tendon function is dependent on proper organization and maintenance of the collagen I tissue matrix. Collagen V is a critical regulator of collagen I fibrils, and while prior studies have shown a negative impact of collagen V deficiency on tendon healing outcomes, these studies are confounded by collagen V deficiency through tendon development. The specific role of collagen V in regulating healing tendon properties is therefore unknown. By using inducible Col5a1 knockdown models and analyzing gene expression, fibril and histological tendon morphology, and tendon mechanical properties, this study defines the isolated role of collagen V through tendon healing. Patellar tendon injury caused large changes in tendon gene expression, and Col5a1 knockdown resulted in dysregulated expression of several genes through tendon healing. Col5a1 knockdown also impacted collagen fibril size and shape without observable changes in scar tissue formation. Surprisingly, heterozygous Col5a1 knockdown resulted in improved stiffness of healing tendons that was not observed with homozygous Col5a1 knockdown. Together, these results present an unexpected and dynamic role of collagen V deficiency on tendon healing outcomes following injury. This work suggests a model of tendon healing in which quasi-static mechanics may be improved through titration of collagen fibril size and shape with modulation of collagen V expression and activity.

Patellar Tendon Injury: A Bibliometric Analysis of the Most-Cited Articles Demonstrates Relatively High Overall Level of Evidence

PurposeTo identify and analyze the 50 most-cited articles in patellar tendon injury research.MethodsThe ISI Web of Science and SCOPUS databases were used to conduct a search for articles pertaining to patellar tendon injury. For the top 50 most-cited articles, bibliometric data (title, first and senior author, citation count, journal, publication year, citation density, country of origin, Level of Evidence [LOE]) and topic of article were recorded.ResultsThe mean number of citations was 172.0 ± 88.2 (range 101-546). There was a statistically significant correlation between publication year and citation density (r = 0.61, P < .01). The earliest article was the third most-cited article (362 citations), published by Blazina et al. in 1973, which discussed the epidemiology of patellar tendinopathy. The first and second most-cited articles (546 and 466 citations, respectively) covered surgical outcomes of patellar tendinopathy and prevalence of patellar tendinopathy among elite athletes. A total of 14 articles (28%) discussed nonoperative management, whereas only 5 articles discussed surgical management (10%). The most frequent LOE category was a LOE of IV (n = 18, 36%), but 19 studies (38%) were LOE I or LOE II.ConclusionsAmong the top 50 most-cited studies regarding patellar tendon injury, a relatively high number were of a high LOE (19 Level I or II, 38%), affirming that these articles in patellar tendon injury research are not only influential, but also of high-quality evidence.Clinical RelevanceThis bibliometric analysis provides an efficient tool for educators, researchers, and evidence-based practitioners to identify and evaluate the most influential articles in patellar tendon injury research.

Treatment of Distal Patellar Tendon Chronic Rupture: The X-Wave Technique

Injuries to the patellar tendon (PT) are associated with knee function deterioration and loss of the capacity to perform daily and sports activities. Patellar tendon injury is often misdiagnosed at emergency rooms, leading to chronic proximal retraction and a challenging clinical scenario. Proximal PT injuries are more common, while distal ones, which can involve tibial bone avulsion fractures or direct tendon avulsion, are rarer. The low incidence of distal PT rupture and the variety of injury patterns make a personal approach reasonable when based on the intraoperative findings and the surgeon's experience. Our purpose is to describe a surgical technique to restore the knee extensor mechanism after chronic distal PT rupture using two kinds of graft, one as a waveform augmentation of the native tendon and the other as reinforcement in a letter X aspect.

Extensor mechanism ruptures.

Native patellar tendon injuries are seen in younger patients compared to quadriceps tendon ruptures.Up to a third of the patients may have local (antecedent tendinopathy and cortisone injections) or systemic risk factors (obesity, diabetes, hyperparathyroidism, chronic renal failure, fluoroquinolone or statin use) of injury, these are more frequent in bilateral disruptions.Complete extensor mechanism disruptions should be repaired surgically. Although isolated primary repair has been reported to have good outcomes in younger patients with acute tears and good tendon quality, augmentation of the repair with autograft, allograft or synthetic material should be considered in patients with poor tendon quality, chronic tears or tendon defects.High rates of return to work/sports have been reported in native patellar and quadriceps tendon tears, with re-rupture rates <5%.Extensor mechanism disruptions in patients with a total knee arthroplasty are challenging due to older age, systemic co-morbidities and poor local conditions, resulting in inferior outcomes compared to native extensor mechanism injuries. Some form of augmentation with autograft, allograft or synthetics is advisable in all cases. Salvage procedures such as whole extensor mechanism allografts provide acceptable outcomes in multiply operated knees with extensive bone and soft tissue deficits.

Double-Row Suture Anchor Fixation and Achilles Allograft Augmentation for Chronic Patellar Tendon Rupture Repair

Patellar tendon ruptures are functionally devastating injuries that result in failure of the knee extensor mechanism and can lead to a loss of ambulation. Chronic patellar tendon injuries are defined as tears greater than 2 weeks old and are typically more complex to manage than acute tears. Recently, the use of double-row suture anchor configurations has been explored as a technique to provide improved strength in addition to tendon-to-bone compression at the anatomic footprint. The purpose of this article is to describe a surgical technique involving chronic patellar tendon rupture repair using a double-row suture construct augmented with Achilles allograft. Our technique offers a variety of benefits and permits early postoperative mobilization.

Eugenol-Preconditioned Mesenchymal Stem Cell-Derived Extracellular Vesicles Promote Antioxidant Capacity of Tendon Stem Cells In Vitro and In Vivo.

Tendon stem cells (TSCs) are often exposed to oxidative stress at tendon injury sites, which impairs their physiological effect as well as therapeutic application. Recently, extracellular vesicles (EVs) derived from bone marrow mesenchymal stem cells (BMSCs) were shown to mediate cell protection and survival under stress conditions. The function of BMSC-EVs may be affected by pretreatment with various factors such as eugenol (EUG)—a powerful antioxidant. In our previous study, we found that H2O2 significantly impaired TSC proliferation and tenogenic differentiation capabilities. Apoptosis and intracellular ROS accumulation in TSCs were induced by H2O2. However, such H2O2-induced damage was prevented by treatment with EUG-BMSC-EVs. Furthermore, EUG-BMSC-EVs activated the Nrf2/HO-1 pathway to counteract H2O2-induced damage in TSCs. In a rat patellar tendon injury model, the ROS level was significantly higher than that in the normal tendon and TSCs not pretreated showed a poor therapeutic effect. However, EUG-BMSC-EV-pretreated TSCs significantly improved tenogenesis and matrix regeneration during tendon healing. Additionally, the EUG-BMSC-EV group had a significantly improved fiber arrangement. Overall, EUG-BMSC-EVs protected TSCs against oxidative stress and enhanced their functions in tendon injury. These findings provide a basis for potential clinical use of EUG-BMSC-EVs as a new therapeutic vehicle to facilitate TSC therapies for tendon regeneration.

Nonwoven-based gelatin/polycaprolactone membrane loaded with ERK inhibitor U0126 for treatment of tendon defects

BackgroundTendon is a major component of musculoskeletal system connecting the muscles to the bone. Tendon injuries are very common orthopedics problems leading to impeded motion. Up to now, there still lacks effective treatments for tendon diseases.MethodsTendon stem/progenitor cells (TSPCs) were isolated from the patellar tendons of SD rats. The expression levels of genes were evaluated by quantitative RT-PCR. Immunohistochemistry staining was performed to confirm the presence of tendon markers in tendon tissues. Bioinformatics analysis of data acquired by RNA-seq was used to find out the differentially expressed genes. Rat patellar tendon injury model was used to evaluate the effect of U0126 on tendon injury healing. Biomechanical testing was applied to evaluate the mechanical properties of newly formed tendon tissues.ResultsIn this study, we have shown that ERK inhibitor U0126 rather PD98059 could effectively increase the expression of tendon-related genes and promote the tenogenesis of TSPCs in vitro. To explore the underlying mechanisms, RNA sequencing was performed to identify the molecular difference between U0126-treated and control TSPCs. The result showed that GDF6 was significantly increased by U0126, which is an important factor of the TGFβ superfamily regulating tendon development and tenogenesis. In addition, NBM (nonwoven-based gelatin/polycaprolactone membrane) which mimics the native microenvironment of the tendon tissue was used as an acellular scaffold to carry U0126. The results demonstrated that when NBM was used in combination with U0126, tendon healing was significantly promoted with better histological staining outcomes and mechanical properties.ConclusionTaken together, we have found U0126 promoted tenogenesis in TSPCs through activating GDF6, and NBM loaded with U0126 significantly promoted tendon defect healing, which provides a new treatment for tendon injury.

Enhanced tendon healing by a tough hydrogel with an adhesive side and high drug-loading capacity.

Hydrogels that provide mechanical support and sustainedly release therapeutics have been used to treat tendon injuries. However, most hydrogels are insufficiently tough, release drugs in bursts, and require cell infiltration or suturing to integrate with surrounding tissue. Here, we report that a hydrogel serving as a high-capacity drug depot and combining a dissipative tough matrix on one side and a chitosan adhesive surface on the other side supports tendon gliding and strong adhesion (larger than 1,000 J/m2) to tendon on opposite surfaces of the hydrogel, as we show with porcine and human tendon preparations during cyclic-friction loadings. The hydrogel is biocompatible, strongly adheres to patellar, supraspinatus and Achilles tendons of live rats, boosted healing and reduced scar formation in a rat model of Achilles-tendon rupture, and sustainedly released the corticosteroid triamcinolone acetonide in a rat model of patellar tendon injury, reducing inflammation, modulating chemokine secretion, recruiting tendon stem and progenitor cells, and promoting macrophage polarization to the M2 phenotype. Hydrogels with ‘Janus’ surfaces and sustained-drug-release functionality could be designed for a range of biomedical applications.

Patellar Tendon Injury Associated with a Contralateral Achilles Tendon Injury. Case Report

Patellar Tendon Injury Associated with a Contralateral Achilles Tendon Injury. Case Report

Do intra-articular knee injuries detected by preoperative MRI affect the clinical management of extensor mechanism ruptures?

Objectives:We sought to determine the prevalence of intra-articular findings at the time of extensor mechanism injury that required subsequent surgical intervention.Design:Retrospective cohort study.Setting:Level 1 academic trauma center.Patients/participants:Sixty-seven knees in 66 nonconsecutive patients (mean age 53.6 years, 95.6% male) with extensor mechanism injury and preoperative magnetic resonance imaging (MRI) before undergoing open primary surgical repair.Main outcome measurements:Patellar or quadriceps tendon rupture, high or low injury energy level, and age above or below 45 years were used to stratify patients. The primary outcome was additional surgery for intra-articular injury. Demographics, comorbidities, mechanism and location of injury, and internal derangements based on MRI findings were also collected.Results:Fifty-one knees (76.1%) had quadriceps tendon injury, 13 knees (19.4%) had patellar tendon injury, and 3 knees (4.6%) had both. Thirty-four knees (50.7%) had intra-articular pathology and 3 (4.5%) required additional surgery, including 1 knee (7.7%) with patellar tendon injury and 2 knees (3.9%) with quadriceps tendon injury. Patellar tendon injuries were more commonly associated with cruciate ligament injury (P < .01) and occurred in younger patients (P < .001) than quadriceps tendon injury.Conclusions:50.7% of cases with extensor mechanism injury had intra-articular pathology but only 4.5% required additional surgery. The results of our study suggest that preoperative MRI is unlikely to be of significant clinical utility in most extensor mechanism injuries but should be considered in cases of patellar tendon rupture in younger patients where the incidence of concomitant cruciate ligament injury is higher.Level of evidence:Diagnostic Level III.

Adipogenic differentiation was inhibited by downregulation of PPAR\u03b3 signaling pathway in aging tendon stem/progenitor cells

BackgroundTendon stem/progenitor cells (TSPCs) play a vital role in tendon repair and regeneration. Previously we found more adipocytes accumulated in the patellar tendon injury sites in aging rats compared with the young ones, of which the mechanism is still unknown. Here, we want to identify whether erroneous differentiation of TSPCs by aging accounts for the adipocyte accumulation.MethodsTSPCs from young and aging rats were isolated and propagated. Both young and aging TSPCs were induced to differentiate into adipocytes, and Oil red O staining, quantitative real-time polymerase chain reaction (qRT-PCR), western-blot and immunofluorescent staining were used to evaluate the capability of TSPCs. RNA sequencing was utilized to screen out different genes and signaling pathways related to adipogenesis between young and aging TSPCs.ResultsThe Oil red O staining showed there were more adipocytes formed in young TSPCs. Besides, adipogenic markers perilipin, peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer-binding proteins alpha (C/EBPα) and Fatty acid-binding protein 4 (FABP4) were elevated both at gene and protein level. PPARγ signaling pathway was selected as our target via RNA sequencing. After adding the signaling activators, Rosiglitazone maleate (RM), inhibited adipogenesis of aging TSCs was reversed.ConclusionsIn conclusion, aging inhibited adipogenesis of TSPCs by down‐regulating PPARγ signaling. It is not likely that the adipocyte accumulation in aging tendon during repair was due to the aging of TSPCs. This may provide new targets for curing aging tendon injuries or tendinopathies.

Morbid obesity is not a contraindication to lower limb arthroplasty

There are concerns that increased BMI is associated with a greater length of stay (LOS) and perioperative complications following total knee (TKR) and total hip replacements (THR). We analysed data from a six-month period to see if there was a correlation between BMI and LOS. We performed a subgroup analysis for patients with morbid obesity (BMI &gt;40) looking at perioperative complications. 285 TKRs and 195 THRs were analysed. For TKRs, the average length of stay was 2.7 days. The average BMI was 32.4. There was no significant correlation between BMI and LOS (r=-0.0447, p=0.2267). The morbidly obese category (n=33) had the shortest LOS (2.5 days) compared to other BMI categories. 30- day readmission rate was 6%. 90-day re-admission rate was 12%. Six patients had minor wound issues requiring no intervention or antibiotics only. The was one prosthetic joint infection, one stitch abscess, one DVT and one patellar tendon injury. For THRs, the average LOS was 2.9 days. The average BMI was 29.9. There was no significant correlation between BMI and LOS (r=0.007, p=0.4613). The morbid obese category (n=9) had the shortest LOS (1.9 days) compared to other BMI categories. No patients were readmitted within 90 days or had documented complications. We have shown that for TKRs and THRs, increased BMI is not associated with increased LOS. The morbidly obese were found to have the shortest LOS. Re-admission rates and complications were commendable for patients with morbid obesity. BMI &gt;40 is not a contraindication to TKR or THR.

Patellar Tendon Allograft Reconstruction

Background: Chronic patellar tendon injuries can cause significant functional deficits due to anterior knee pain, extension weakness, and extensor lag. With chronic injuries, the tissue is inadequate and of poor quality. Chronic injuries require autograft or allograft for augmentation or reconstruction. We present reconstruction of a chronic patellar tendon injury with Achilles tendon allograft. Indications: Chronic patellar tendon injuries causing functional deficits, including knee extension weakness, extensor lag, and anterior knee pain. Technique Description: A longitudinal incision is made over the patellar tendon, and the patellar tendon is excised. Two guide pins are drilled in a retrograde fashion through the patella and are overdrilled with a reamer. A trough is made at the tibial tubercle using an oscillating saw. The Achilles allograft calcaneal bone block is contoured to the appropriate size, and then press fit into the trough. Two 4.0-mm fully threaded cannulated screws with washers are used to secure the bone block. The fresh frozen Achilles allograft is doubled over, and a double Krackow running locking suture is placed. A V-Y advancement of the quadriceps tendon is performed to ensure adequate advancement of the patella. The limbs of the Krackow suture are pulled through the patella drill holes and tied with knee in full extension. Results: At 1 year, patients can expect near full range of motion with minimal extensor lag. Reconstruction results in improved pain and function as compared with preoperatively, as well as return to activities. Conclusion: Achilles tendon allograft is a good option for reconstructing chronic patellar tendon injuries. Advantages of the Achilles allograft include the bone-to-bone healing at the tibia, lack of donor site morbidity, and the large amount of tissue available for reconstruction.

272 Morbid Obesity in Lower Limb Arthroplasty: Short Length of Stay and Favourable One-Year Outcomes

Abstract Introduction There are concerns that BMI is associated with a greater length of stay (LOS) and perioperative complications in lower limb arthroplasty. Method We analysed data from a six-month period to see if there was a correlation between BMI and LOS. We performed a subgroup analysis for patients with morbid obesity (BMI &amp;gt;40). Results 285 TKRs and 195 THRs were analysed. For TKRs, the average length of stay was 2.7 days. There was no significant correlation between BMI and LOS (r=-0.0447, p = 0.2267). The morbidly obese category (n = 33) had the shortest LOS (2.5 days) compared to other BMI categories. 30-day readmission rate was 6%. 90-day re-admission rate was 12%. Six patients had minor wound issues requiring no intervention or antibiotics only. The was one prosthetic joint infection, one stitch abscess, one DVT and one patellar tendon injury. For THRs, the average LOS was 2.9 days. There was no significant correlation between BMI and LOS (r = 0.007, p = 0.4613). The morbid obese category (n = 9) had the shortest LOS (1.9 days) compared to other BMI categories. No patients were readmitted within 90 days or had documented complications. Conclusions Increased BMI is not associated with increased LOS. The morbidly obese had the shortest LOS, and commendable complication and re-admission rates.

The Impact of Hypercholesterolemia on Tendon Injury Repair

Background Hypercholesterolemia is a condition characterized by high blood cholesterol levels and is associated with tendon xanthomas (cholesterol deposits found on superficial tendons). Lipid accumulation in the tendon's extracellular spaces1 may disrupt the parallel organization of collagen substructures within the tendon, and negatively affect its mechano-sensing and mechanical properties, which may lead to injury. We hypothesized that tendon strength and metabolism would be inferior in a high cholesterol environment and attenuate the tendon's ability to repair after injury. Methods 50 Sprague-Dawley (SD, control) and 50 apolipoprotein E knock-out rats (ApoE, Envigo, IL, USA) rats bred in-house were subject to a unilateral patellar tendon (PT) injury at 12 weeks of age; the uninjured limb served as a control. Animals were euthanased at 3, 14 or 42 days post-injury, time-points chosen to represent tendon inflammatory, reparative and remodelling repair phases, respectively. Animals were randomly assigned for investigating gene expression (SD/ApoE per timepoint n=4/4), tissue histology (n=6/6), biomechanical testing (n=10/10; 14 and 42 days only). Equal male/female ratios were used where possible (total SD M23/F27, ApoE M23/F26). Results ApoE total cholesterol was over double that of SD rats (mean 2.12 vs 0.99 mg/ml, p<0.001). Despite this, there was little histological evidence of lipid content (Oil Red-O staining) in tendons of either group, and no apparent differences in tendon mechanical or material properties (Fig. 1). However, there were differences in gene expression (Fig. 2). ApoE rats demonstrated significantly greater COX2 expression than SD; other inflammatory markers (TGFβ, IL-1, IL-6) did not differ between groups. COL1A1, SCX, LOXα were significantly upregulated 14 days post injury in SD compared to ApoE. A greater COL3A1 response was also observed in ApoE compared to SD rats. Discussion We found differences in injury repair at the cellular level, using an ApoE high cholesterol model. There was little evidence of lipid accumulation at the tissue level, therefore the PT may have been a poor choice for an injury study in this instance and it is not surprising that biomechanical differences were not found. Moreover, ApoE rats were recently found to demonstrate only modest early atherosclerotic characteristics2, thus the young age of our cohort may be a primary factor in the lack of physical evidence of lipid accumulation. Nonetheless, our results indicate that even with a mild phenotype, high cholesterol significantly modulates tendon inflammatory and healing cellular activity, as indicated by altered mRNA levels, which may contribute to the known consequences of tendon cholesterol on tendons in humans. References 1Grewal et al. 2014. Accumulation of oxidized LDL in the tendon tissues of C57BL/6 or apolipoprotein E knock-out mice that consume a high fat diet: potential impact on tendon health. PLoS One 9(12): e114214. 2Rune et al., 2018. Long-term Western diet fed apolipoprotein E-deficient rats exhibit only modest early atherosclerotic characteristics. Sci Rep 8(1): 5416.

Technique for Fixation of Semitendinosus to the Patella in Patellar Tendon Reconstruction

Chronic patellar tendon injuries are rare yet challenging to treat. Timing of surgery and graft choices are debatable. Many techniques and methods of fixation have been described with pros and cons. Functional impairment of the extensor mechanism and postoperative complications triggers the quest for finding the ideal technique. In this Technical Note, we use distally based semitendinosus (ST) looped over 2 ETHIBOND sutures. The ETHIBOND is passed through 2 vertical tunnels in the patella and retrieved proximally, docking the ST in a blind tunnel created in the lower pole of the patella. The whip-stitched free ST end is passed through a tunnel behind the tibial tubercle and sutured back to its base. A polyester tape is used to augment the repair in a circumferential manner. Postoperatively full weight bearing is allowed as tolerated in a hinged knee brace locked in extension with only passive range of motion of 0-90° allowed for 6 weeks.

Patellar tendon reconstruction with hamstring autograft for the treatment of chronic irreparable patellar tendon injuries

BackgroundPatellar tendon injuries not amenable to primary repair present a challenging problem for surgeons and patients alike. No standard surgical technique exists for these injuries and few studies report outcomes after surgical treatment. MethodsA retrospective analysis was conducted for patients undergoing surgical treatment for irreparable patellar tendon tears. Patients were treated with an indirect tendon reconstruction technique using high-strength suture to set initial patellar height and hamstring autograft for biologic augmentation. Patients who underwent this procedure between 2012 and 2018 and met minimum two-year follow-up with completion of all outcome measurements including KOOS, PROMIS, VAS pain and satisfaction scores were included. ResultsEleven patients met inclusion criteria. Ten of eleven patients (91%) had intact repairs and final patient outcomes were collected at a mean of 54.9 ± 23.1 months after surgery. Only one patient experienced extensor lag at final follow-up (p < 0.001). The preoperative Caton–Dechamps ratio was 1.77 ± 0.58, which decreased to 0.98 ± 0.25 after surgery (p < 0.001). The mean postoperative KOOS ADL score was 61.5. The mean postoperative PROMIS Global Mental and Physical Health scores were 46.9 ± 8.7 and 42.0 ± 9.8. Post-operative mean VAS satisfaction score was 5.6 ± 3.4. ConclusionsPatellar tendon reconstruction with autologous hamstring tendon graft and suture augmentation allows for acceptable outcomes in the setting of patellar tendon disruption with segmental defects when direct repair is not possible.

Safety of the application of Rigidfix cross-pin system via different tibial tunnels for tibial fixation during anterior cruciate ligament reconstruction

BackgroundWe investigate the safety of the application of the Rigidfix cross-pin system via different tibial tunnels in the tibial fixation during anterior cruciate ligament (ACL) reconstruction.MethodsFive adult fresh cadaver knees were fixed with the Rigidfix cross-pins in the tibial fixation site during ACL reconstruction. Two different tibial tunnel groups were established: in group A, the tunnel external aperture was placed at the 25° angle of coronal section; in group B, the tunnel external aperture was placed at the 45° angle of coronal section. The guide was placed at the plane 0.5 mm below articular facet through the tibial tunnel, with three rotation positions set at 0°, 30°, and 60° slopes. The incidences of iatrogenic injuries at tibial plateau cartilage (TPC), medial collateral ligament (MCL), and patellar tendon in three different slope angles were calculated in groups A and B and the results were analyzed by using chi square test.ResultsThe iatrogenic injuries at MCL, TPC, and patellar tendon could occur after the Rigidfix cross-pin system was placed 5 mm below tibial plateau cartilage for ACL reconstruction. The incidences of TPC injury (χ2 = 5.662, P = 0.017) and MCL injury (P = 0.048, Fisher exact probability method) were significantly lower in group A than in group B. However, the incidence of patellar tendon injury showed no significant difference between these two groups (χ2 = 0.120, P = 0.729).ConclusionsWhen the Rigidfix cross-pin system is used for ACL reconstruction at the tibial fixation site, the external aperture of tibial tunnel should not be placed at the excessively posterosuperior site, to avoid MCL and TPC injuries.

Hypoxia-Induced Mesenchymal Stem Cells Exhibit Stronger Tenogenic Differentiation Capacities and Promote Patellar Tendon Repair in Rabbits.

Tendon injury is a common but tough medical problem. Unsatisfactory clinical results have been reported in tendon repair using mesenchymal stem cell (MSC) therapy, creating a need for a better strategy to induce MSCs to tenogenic differentiation. This study was designed to examine the effect of hypoxia on the tenogenic differentiation of different MSCs and their tenogenic differentiation capacities under hypoxia condition in vitro and to investigate the in vivo inductility of hypoxia in tenogenesis. Adipose tissue-derived MSCs (AMSCs) and bone marrow-derived MSCs (BMSCs) were isolated and characterized. The expression of hypoxia-induced factor-1 alpha (Hif-1α) was examined to confirm the establishment of hypoxia condition. qRT-PCR, western blot, and immunofluorescence staining were used to evaluate the expression of tendon-associated marker Col-1a1, Col-3a1, Dcn, and Tnmd in AMSCs and BMSCs under hypoxia condition, compared with Tgf-β1 induction. In vivo, a patellar tendon injury model was established. Normoxic and hypoxic BMSCs were cultured and implanted. Histological, biomechanical, and transmission electron microscopy analyses were performed to assess the improved healing effect of hypoxic BMSCs on tendon injury. Our in vitro results showed that hypoxia remarkably increased the expression of Hif-1α and that hypoxia not only promoted a significant increase in tenogenic markers in both AMSCs and BMSCs compared with the normoxia group but also showed higher inductility compared with Tgf-β1. In addition, hypoxic BMSCs exhibited higher potential of tenogenic differentiation than hypoxic AMSCs. Our in vivo results demonstrated that hypoxic BMSCs possessed better histological and biomechanical properties than normoxic BMSCs, as evidenced by histological scores, patellar tendon biomechanical parameters, and the range and average of collagen fibril diameters. These findings suggested that hypoxia may be a practical and reliable strategy to induce tenogenic differentiation of BMSCs for tendon repair and could enhance the effectiveness of MSCs therapy in treating tendon injury.