Tissue memory in healing tendons: short loading episodes stimulate healing

Dexamethasone treatment influences tendon healing through altered resolution and a direct effect on tendon cells

Inflammation, corticosteroids, and loading all affect tendon healing, with an interaction between them. However, underlying mechanisms behind the effect of corticosteroids and the interaction with loading remain unclear. The aim of this study was to investigate the role of dexamethasone during tendon healing, including specific effects on tendon cells. Rats (n = 36) were randomized to heavy loading or mild loading, the Achilles tendon was transected, and animals were treated with dexamethasone or saline. Gene and protein analyses of the healing tendon were performed for extracellular matrix-, inflammation-, and tendon cell markers. We further tested specific effects of dexamethasone on tendon cells in vitro. Dexamethasone increased mRNA levels of S100A4 and decreased levels of ACTA2/α-SMA, irrespective of load level. Heavy loading + dexamethasone reduced mRNA levels of FN1 and TenC (p < 0.05), while resolution-related genes were unaltered (p > 0.05). In contrast, mild loading + dexamethasone increased mRNA levels of resolution-related genes ANXA1, MRC1, PDPN, and PTGES (p < 0.03). Altered protein levels were confirmed in tendons with mild loading. Dexamethasone treatment in vitro prevented tendon construct formation, increased mRNA levels of S100A4 and decreased levels of SCX and collagens. Dexamethasone during tendon healing appears to act through immunomodulation by promoting resolution, but also through an effect on tendon cells.

Nanofiber matrix formulations for the delivery of Exendin-4 for tendon regeneration: In vitro and in vivo assessment

Tendon and ligament injuries are the most common musculoskeletal injuries, which not only impact the quality of life but result in a massive economic burden. Surgical interventions for tendon/ligament injuries utilize biological and/or engineered grafts to reconstruct damaged tissue, but these have limitations. Engineered matrices confer superior physicochemical properties over biological grafts but lack desirable bioactivity to promote tissue healing. While incorporating drugs can enhance bioactivity, large matrix surface areas and hydrophobicity can lead to uncontrolled burst release and/or incomplete release due to binding. To overcome these limitations, we evaluated the delivery of a peptide growth factor (exendin-4; Ex-4) using an enhanced nanofiber matrix in a tendon injury model. To overcome drug surface binding due to matrix hydrophobicity of poly(caprolactone) (PCL)-which would be expected to enhance cell-material interactions-we blended PCL and cellulose acetate (CA) and electrospun nanofiber matrices with fiber diameters ranging from 600 to 1000 nm. To avoid burst release and protect the drug, we encapsulated Ex-4 in the open lumen of halloysite nanotubes (HNTs), sealed the HNT tube endings with a polymer blend, and mixed Ex-4-loaded HNTs into the polymer mixture before electrospinning. This reduced burst release from ∼75% to ∼40%, but did not alter matrix morphology, fiber diameter, or tensile properties. We evaluated the bioactivity of the Ex-4 nanofiber formulation by culturing human mesenchymal stem cells (hMSCs) on matrix surfaces for 21 days and measuring tenogenic differentiation, compared with nanofiber matrices in basal media alone. Strikingly, we observed that Ex-4 nanofiber matrices accelerated the hMSC proliferation rate and elevated levels of sulfated glycosaminoglycan, tendon-related genes (Scx, Mkx, and Tnmd), and ECM-related genes (Col-I, Col-III, and Dcn), compared to control. We then assessed the safety and efficacy of Ex-4 nanofiber matrices in a full-thickness rat Achilles tendon defect with histology, marker expression, functional walking track analysis, and mechanical testing. Our analysis confirmed that Ex-4 nanofiber matrices enhanced tendon healing and reduced fibrocartilage formation versus nanofiber matrices alone. These findings implicate Ex-4 as a potentially valuable tool for tendon tissue engineering.

Does mechanical loading restore ligament biomechanics after injury? A systematic review of studies using animal models

BACKGROUND

Mechanical loading is purported to restore ligament biomechanics post-injury. But this is difficult to corroborate in clinical research when key ligament tissue properties (e.g. strength, stiffness), cannot be accurately measured. We reviewed experimental animal models, to evaluate if post-injury loading restores tissue biomechanics more favourably than immobilisation or unloading. Our second objective was to explore if outcomes are moderated by loading parameters (e.g. nature, magnitude, duration, frequency of loading).

METHODS

Electronic and supplemental searches were performed in April 2021 and updated in May 2023. We included controlled trials using injured animal ligament models, where at least one group was subjected to a mechanical loading intervention postinjury. There were no restrictions on the dose, time of initiation, intensity, or nature of the load. Animals with concomitant fractures or tendon injuries were excluded. Prespecified primary and secondary outcomes were force/stress at ligament failure, stiffness, laxity/deformation. The Systematic Review Center for Laboratory animal Experimentation tool was used to assess the risk of bias.

RESULTS

There were seven eligible studies; all had a high risk of bias. All studies used surgically induced injury to the medial collateral ligament of the rat or rabbit knee. Three studies recorded large effects in favour of ad libitum loading postinjury (vs. unloading), for force at failure and stiffness at 12-week follow up. However, loaded ligaments had greater laxity at initial recruitment (vs. unloaded) at 6 and 12 weeks postinjury. There were trends from two studies that adding structured exercise intervention (short bouts of daily swimming) to ad libitum activity further enhances ligament behaviour under high loads (force at failure, stiffness). Only one study compared different loading parameters (e.g. type, frequency); reporting that an increase in loading duration (from 5 to 15 min/day) had minimal effect on biomechanical outcomes.

CONCLUSION

There is preliminary evidence that post-injury loading results in stronger, stiffer ligament tissue, but has a negative effect on low load extensibility. Findings are preliminary due to high risk of bias in animal models, and the optimal loading dose for healing ligaments remains unclear.

Secretome from In Vitro Mechanically Loaded Myoblasts Induces Tenocyte Migration, Transition to a Fibroblastic Phenotype and Suppression of Collagen Production

It is known that mechanical loading of muscles increases the strength of healing tendon tissue, but the mechanism involved remains elusive. We hypothesized that the secretome from myoblasts in co-culture with tenocytes affects tenocyte migration, cell phenotype, and collagen (Col) production and that the effect is dependent on different types of mechanical loading of myoblasts. To test this, we used an in vitro indirect transwell co-culture system. Myoblasts were mechanically loaded using the FlexCell^® Tension system. Tenocyte cell migration, proliferation, apoptosis, collagen production, and several tenocyte markers were measured. The secretome from myoblasts decreased the Col I/III ratio and increased the expression of tenocyte specific markers as compared with tenocytes cultured alone. The secretome from statically loaded myoblasts significantly enhanced tenocyte migration and Col I/III ratio as compared with dynamic loading and controls. In addition, the secretome from statically loaded myoblasts induced tenocytes towards a myofibroblast-like phenotype. Taken together, these results demonstrate that the secretome from statically loaded myoblasts has a profound influence on tenocytes, affecting parameters that are related to the tendon healing process.

Predicting the effect of reduced load level and cell infiltration on spatio-temporal Achilles tendon healing

Mechanobiology plays an important role in tendon healing. However, the relationship between mechanical loading and spatial and temporal evolution of tendon properties during healing is not well understood. This study builds on a recently presented mechanoregulatory computational framework that couples mechanobiological tendon healing to tissue production and collagen orientation. In this study, we investigated how different magnitudes of mechanical stimulation (principal strain) affect the spatio-temporal evolution of tissue production and the temporal evolution of elastic and viscoelastic mechanical parameters. Specifically, we examined the effect of cell infiltration (mimicking migration and proliferation) in the callus on the resulting tissue production by modeling production to depend on local cell density. The model predictions were carefully compared with experimental data from Achilles tendons in rats, at 1, 2 and 4 weeks of healing. In the experiments, the rat tendons had been subjected to free cage activity or reduced load levels through intramuscular botox injections. The simulations that included cell infiltration and strain-regulated collagen production predicted spatio-temporal tissue distributions and mechanical properties similarly to that observed experimentally. In addition, lack of matrix-producing cells in the tendon core during early healing may result in reduced collagen content, regardless of the daily load level. This framework is the first to computationally investigate mechanobiological mechanisms underlying spatial and temporal variations during tendon healing for various magnitudes of loading. This framework will allow further characterization of biomechanical, biological, or mechanobiological processes underlying tendon healing.

The Influence of Early Weightearing, Controlled Motion, and Timing of Orthosis Removal on the Nonoperative Management of Achilles Tendon Rupture: A Systematic Review

This is a systematic review of the non-operative treatment for Achilles tendon rupture aimed at assessing the effect of early weightbearing, controlled motion and orthosis removal on 5 outcome measures. The literature was searched for relevant RCTs and prospective cohort studies. The primary outcome measure was the re-rupture rate. The secondary outcome measures were the rates for DVT, duration before return to work (RTW), return to sports (RTS) and the mean Achilles Tendon Rupture Score (ATRS). Eighteen publications reporting a total of 1068 patients were reviewed. The pooled rates were: re-rupture: 7.3%, DVT: 5.5%, RTW: 10.3 weeks, RTS: 47.7% and ATRS: 78.7. Early compared to late weightbearing was associated with significantly lower rates of DVT, RTW and ATRS but no difference in the rates of re-rupture and RTS. Early controlled motion compared to no motion was associated with significantly lower rates of re-rupture, RTW and ATRS but no difference in the rates of DVT and RTS. Early compared to late orthosis removal was associated with significantly higher rates of re-rupture and ATRS as well as a lower rate of RTW but no difference in the rates of DVT and RTS. The findings relating to re-rupture, DVT, RTW and RTS support the adoption of early weightbearing and controlled motion in the non-operative treatment for Achilles tendon rupture. Early removal of orthosis is not advisable due to an increased risk of re-rupture. The ATRS results were considered inconclusive probably due to inconsistencies in the reporting or heterogeneity in the study population.

Early functional rehabilitation compared with traditional immobilization for acute Achilles tendon ruptures : a meta-analysis

AIMS

The aim of this meta-analysis was to assess the prognosis after early functional rehabilitation or traditional immobilization in patients who underwent operative or nonoperative treatment for rupture of the Achilles tendon.

METHODS

PubMed, Embase, Web of Science, and Cochrane Library were searched for randomized controlled trials (RCTs) from their inception to 3 June 2020, using keywords related to rupture of the Achilles tendon and rehabilitation. Data extraction was undertaken by independent reviewers and subgroup analyses were performed based on the form of treatment. Risk ratios (RRs) and weighted mean differences (WMDs) (with 95% confidence intervals (CIs)) were used as summary association measures.

RESULTS

We included 19 trials with a total of 1,758 patients. There was no difference between the re-rupture rate (RR 0.84 (95% CI 0.56 to 1.28); p = 0.423), time to return to work (WMD -1.29 (95% CI -2.63 to 0.05); p = 0.060), and sporting activity (WMD -1.50 (95% CI -4.36 to 1.37); p = 0.306) between the early functional rehabilitation and the traditional immobilization treatment strategies. Early rehabilitation up to 12 weeks yielded significantly better Achilles tendon Total Rupture Scores ((ATRS) WMD 5.11 (95% CI 2.10 to 8.12); p < 0.001). Patients who underwent functional rehabilitation had significantly lower limb symmetry index of heel-rise work ((HRW) WMD -4.19 (95% CI -8.20 to 0.17); p = 0.041) at one year.

CONCLUSION

Early functional rehabilitation is safe and provides better early function and the same functional outcome in the longer term. Cite this article: Bone Joint J 2021;103-B(6):1021-1030.

A numerical framework for mechano-regulated tendon healing-Simulation of early regeneration of the Achilles tendon

Mechano-regulation during tendon healing, i.e. the relationship between mechanical stimuli and cellular response, has received more attention recently. However, the basic mechanobiological mechanisms governing tendon healing after a rupture are still not well-understood. Literature has reported spatial and temporal variations in the healing of ruptured tendon tissue. In this study, we explored a computational modeling approach to describe tendon healing. In particular, a novel 3D mechano-regulatory framework was developed to investigate spatio-temporal evolution of collagen content and orientation, and temporal evolution of tendon stiffness during early tendon healing. Based on an extensive literature search, two possible relationships were proposed to connect levels of mechanical stimuli to collagen production. Since literature remains unclear on strain-dependent collagen production at high levels of strain, the two investigated production laws explored the presence or absence of collagen production upon non-physiologically high levels of strain (>15%). Implementation in a finite element framework, pointed to large spatial variations in strain magnitudes within the callus tissue, which resulted in predictions of distinct spatial distributions of collagen over time. The simulations showed that the magnitude of strain was highest in the tendon core along the central axis, and decreased towards the outer periphery. Consequently, decreased levels of collagen production for high levels of tensile strain were shown to accurately predict the experimentally observed delayed collagen production in the tendon core. In addition, our healing framework predicted evolution of collagen orientation towards alignment with the tendon axis and the overall predicted tendon stiffness agreed well with experimental data. In this study, we explored the capability of a numerical model to describe spatial and temporal variations in tendon healing and we identified that understanding mechano-regulated collagen production can play a key role in explaining heterogeneities observed during tendon healing.

Achilles Tendon Rupture: Mechanisms of Injury, Principles of Rehabilitation and Return to Play

The Achilles tendon is the thickest, strongest and largest tendon in the human body, but despite its size and tensile strength, it frequently gets injured. Achilles tendon ruptures (ATRs) mainly occur during sports activities, and their incidence has increased over the last few decades. Achilles tendon tears necessitate a prolonged recovery time, sometimes leaving long-term functional limitations. Treatment options include conservative treatment and surgical repair. There is no consensus on which is the best treatment for ATRs, and their management is still controversial. Limited scientific evidence is available for optimized rehabilitation regimen and on the course of recovery after ATRs. Furthermore, there are no universally accepted outcomes regarding the return to play (RTP) process. Therefore, the aim of this narrative review is to give an insight into the mechanism of injuries of an ATR, related principles of rehabilitation, and RTP.

Resistance Exercises in Early Functional Rehabilitation for Achilles Tendon Ruptures Are Poorly Described: A Scoping Review

OBJECTIVES

To (1) describe which resistance exercises are used in the first 8 weeks of treatment for acute Achilles tendon rupture and (2) assess the completeness of reporting of the exercise descriptions.

DESIGN

Scoping review.

LITERATURE SEARCH

We searched the MEDLINE, Embase, CINAHL, Cochrane Library, and Physiotherapy Evidence Database (PEDro) databases.

STUDY SELECTION CRITERIA

Randomized controlled trials, cohort studies, and case series (10 or more participants) that reported using resistance exercise in the immobilization period in the first 8 weeks of treatment for acute Achilles tendon rupture were included.

DATA SYNTHESIS

Completeness of exercise description was assessed with the Consensus on Exercise Reporting Template (CERT) and the Toigo and Boutellier exercise descriptor framework.

RESULTS

Thirty-eight studies were included. Fifty-one resistance exercises were extracted and categorized as isometric exercises (n = 20), heel raises (n = 6), strengthening with external resistance (n = 13), or unspecified (n = 12). A median of 8 (interquartile range, 6-10) of a possible 19 CERT items was reported. The amount of items described of the 13 Toigo and and Boutellier exercise descriptors ranged from 0 to 11.

CONCLUSION

A variety of resistance exercises targeted at the ankle plantar flexors were used as part of early functional rehabilitation after Achilles tendon rupture. However, most studies provided inadequate description of resistance exercise interventions. J Orthop Sports Phys Ther 2020;50(12):681-691. Epub 23 Oct 2020. doi:10.2519/jospt.2020.9463.

Comparison of Tendon Lengthening With Traditional Versus Accelerated Rehabilitation After Achilles Tendon Repair: A Prospective Randomized Controlled Trial

BACKGROUND

Early weightbearing protocols after Achilles tendon repair promote mobilization, yet little is known about their effect on tendon lengthening.

PURPOSE

To evaluate tendon lengthening after Achilles tendon repair with accelerated rehabilitation.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

Patients undergoing primary repair for acute Achilles tendon ruptures consented to have tantalum beads placed within the tendon. Patients were randomized into either a traditional (weightbearing at 6 weeks) or accelerated (graduated weightbearing at 2 weeks) rehabilitation group. The primary outcome of the study was postoperative tendon elongation as measured by radiostereometric beads. Secondary outcomes included Achilles Tendon Total Rupture Score (ATRS) and Patient-Reported Outcomes Measurement Information System Pain Interference Short Form (PROMIS PI-SF) score.

RESULTS

All 18 patients included in the final analysis were found to have significant tendon lengthening after surgery, with a mean lengthening of 15.9 mm. No significant differences were found in overall lengthening between the traditional and accelerated rehabilitation groups (15.3 ± 4.5 vs 16.4 ± 4.7 mm, respectively; P = .33) at final follow-up. The repair site in each group was found to lengthen more than the intratendinous site (traditional group, 13.2 vs 2.1 mm; accelerated group, 16.8 vs -0.4 mm); however, no difference in lengthening was seen between groups (P = .82 and P = .31, respectively). The greatest amount of lengthening occurred between 2 and 6 weeks, and the least amount of lengthening occurred between 6 and 12 weeks, with no difference between the traditional and accelerated groups at these time points (P = .84 and P = .38, respectively). No differences were noted in ankle range of motion (dorsiflexion, P = .16; plantarflexion, P = .08) or outcome scores (ATRS, P = .56; PROMIS PI-SF, P = .54).

CONCLUSION

This study's findings demonstrate that all patients undergoing operative repair of Achilles tendon ruptures had lengthening after surgery. No difference was found in tendon lengthening (repair site or intratendinous) at any time point between patients undergoing traditional versus accelerated rehabilitation postoperatively. The greatest amount of lengthening was found to occur between 2 and 6 weeks postoperatively, and tendon lengthening decreased significantly after 6 weeks.

REGISTRATION

NCT04050748 (ClinicalTrials.gov identifier).

The Effect of Ankle Foot Orthosis' Design and Degree of Dorsiflexion on Achilles Tendon Biomechanics—Tendon Displacement, Lower Leg Muscle Activation, and Plantar Pressure During Walking

Background: Following an Achilles tendon rupture, ankle foot orthoses (AFO) of different designs are used to protect the healing tendon. They are generally designed to protect against re-rupture by preventing undesired dorsiflexion and to prevent elongation by achieving plantarflexion in the ankle. There is limited knowledge of the biomechanical effects of different AFO designs and ankle angles on the tendon and lower leg muscles.

Hypothesis: The hypothesis was that non-uniform displacement in the Achilles tendon, lower leg muscle activity, and plantar pressure distribution would be affected differently in different designs of AFO and by varying the degree of dorsiflexion limitation.

Study Design: Controlled laboratory study.

Methods: Ultrasound of the Achilles tendon, EMG of the lower leg muscles and plantar pressure distribution were recorded in 16 healthy subjects during walking on a treadmill unbraced and wearing three designs of AFO. Ultrasound speckle tracking was used to estimate motion within the tendon. The tested AFO designs were a rigid AFO and a dorsal brace used together with wedges and an AFO with an adjustable ankle angle restricting dorsiflexion to various degrees.

Results: There were no significant differences in non-uniform tendon displacement or muscle activity between the different designs of AFO. For the rigid AFO and the adjustable AFO there was a significant reduction in non-uniform displacement within the tendon and soleus muscle activity as restriction in dorsiflexion increased.

Conclusion: The degree of dorsiflexion allowed within an AFO had greater effects on Achilles tendon displacement patterns and muscle activity in the calf than differences in AFO design. AFO settings that allowed ankle dorsiflexion to neutral resulted in displacement patterns in the Achilles tendon and muscle activity in the lower leg which were close to those observed during unbraced walking.

Response to mechanical loading in rat Achilles tendon healing is influenced by the microbiome

We have previously shown that changes in the microbiome influence how the healing tendon responds to different treatments. The aim of this study was to investigate if changes in the microbiome influence the response to mechanical loading during tendon healing. 90 Sprague-Dawley rats were used. Specific Opportunist and Pathogen Free (SOPF) rats were co-housed with Specific Pathogen Free (SPF) rats, carrying Staphylococcus aureus and other opportunistic microbes. After 6 weeks of co-housing, the SOPF rats were contaminated which was confirmed by Staphylococcus aureus growth. Clean SOPF rats were used as controls. The rats were randomized to full loading or partial unloading by Botox injections in their calf muscles followed by complete Achilles tendon transection. Eight days later, the healing tendons were tested mechanically. The results were analysed by a 2-way ANOVA with interaction between loading and contamination on peak force as the primary outcome and there was an interaction for both peak force (p = 0.049) and stiffness (p = 0.033). Furthermore, partial unloading had a profound effect on most outcome variables. In conclusion, the response to mechanical loading during tendon healing is influenced by changes in the microbiome. Studies aiming for clinical relevance should therefore consider the microbiome of laboratory animals.

Defining Components of Early Functional Rehabilitation for Acute Achilles Tendon Rupture: A Systematic Review

BACKGROUND

Early functional rehabilitation is frequently discussed in treating Achilles tendon rupture. A consistent definition of what constitutes early functional rehabilitation has not been established across the literature, despite studies supporting its efficacy. A standardized definition would be helpful to pool data across studies, allow for between-study comparisons, and ultimately work toward developing clinical guidelines.

PURPOSE

To define early functional rehabilitation (including when it is initiated and what it entails) when used to treat Achilles tendon rupture and to identify outcome measures for evaluating the effect of treatment.

STUDY DESIGN

Systematic review; Level of evidence, 4.

METHODS

Ovid MEDLINE, EMBASE, PEDro, CINAHL, and Cochrane databases were searched for relevant studies. Eligibility criteria for selecting studies consisted of randomized controlled trials, cohort studies, and case series (≥10 participants) including weightbearing or exercise-based interventions within 8 weeks after Achilles tendon rupture.

RESULTS

A total of 174 studies published between 1979 and 2018 were included. Studies were rated a median (interquartile range [IQR]) of 17 (15-20) on the Downs & Black checklist and included 9098 participants. Early functional rehabilitation incorporated weightbearing (95%), range of motion (73%), and isometric/strengthening exercises (50%). Weightbearing was initiated within the first week, whereas exercise (eg, ankle range of motion, strengthening, whole-body conditioning) was initiated in the second week. Initiation of exercises varied based on whether treatment was nonsurgical (mean, 3.0 weeks; IQR, 2.0-4.0 weeks) or simple (mean, 2.0 weeks; IQR, 0.0-2.3 weeks) or augmented surgical repair (mean, 0.5 weeks; IQR, 0.0-2.8 weeks) (P = .017). Functional outcomes including ankle range of motion (n = 84) and strength (n = 76) were reported in 130 studies. Other outcome domains included patient-reported outcomes (n = 89), survey-based functional outcomes (n = 50), and tendon properties (n = 53).

CONCLUSION

Early functional rehabilitation includes weightbearing and a variety of exercise-based interventions initiated within the first 2 weeks after acute Achilles tendon rupture/repair. Because early functional rehabilitation has lacked a standardized definition, interventions and outcome measures are highly variable, and pooling data across studies should be done with attention paid to what was included in the intervention and how treatment was assessed.

Tendon morphology and mechanical properties assessed by ultrasound show change early in recovery and potential prognostic ability for 6-month outcomes

PURPOSE

Optimizing tendon structural recovery during the first 12 weeks after Achilles tendon rupture is a prime target to improve patient outcomes, but a comprehensive understanding of biomarkers is needed to track early healing. The purpose of this study was to observe healing of tendon structure over time using ultrasound-based, tendon-specific measures and to identify relationships between tendon structural characteristics and clinical measures of gait and strength.

METHODS

Twenty-seven participants (21 males, mean (SD) age 39 (11) years) were assessed at 4, 8, 12, and 24 weeks after injury or surgery using ultrasound imaging techniques. Gait analysis and strength testing were added at the later time points.

RESULTS

Ruptured tendons had significantly lower dynamic shear modulus (p < 0.001), greater tendon cross-sectional area (p < 0.001), and greater length (p < 0.001) than the uninjured side. Dynamic shear modulus, cross-sectional area, and length were found to increase over time (p < 0.01). Tendon structure at 4 weeks post-injury [cross-sectional area symmetry (r = 0.737, p = 0.002) and dynamic shear modulus (r = 0.518, p = 0.040)] related to stance phase walking symmetry at 24 weeks.

CONCLUSIONS

Tendon structure assessed by ultrasound imaging changes over the first 24 weeks of healing after Achilles tendon rupture, suggesting it could be used as a biomarker to track tendon healing early in recovery. Additionally, tendon structure within the first 12 weeks relates to later walking gait and heel-rise symmetry, which may indicate that tendon structure could have prognostic value in the care of these patients. This study's clinical relevance is in its support for using ultrasound imaging to assess early patient healing and prognosticate later patient outcomes after Achilles tendon rupture.

LEVEL OF EVIDENCE

Level 2, prospective cohort prognostic study.

Effects of immobilization angle on tendon healing after achilles rupture in a rat model

Conservative (non-operative) treatment of Achilles tendon ruptures is a common alternative to operative treatment. Following rupture, ankle immobilization in plantarflexion is thought to aid healing by restoring tendon end-to-end apposition. However, early activity may improve limb function, challenging the role of immobilization position on tendon healing, as it may affect loading across the injury site. This study investigated the effects of ankle immobilization angle in a rat model of Achilles tendon rupture. We hypothesized that manipulating the ankle from full plantarflexion into a more dorsiflexed position during the immobilization period would result in superior hindlimb function and tendon properties, but that prolonged casting in dorsiflexion would result in inferior outcomes. After Achilles tendon transection, animals were randomized into eight immobilization groups ranging from full plantarflexion (160°) to mid-point (90°) to full dorsiflexion (20°), with or without angle manipulation. Tendon properties and ankle function were influenced by ankle immobilization position and time. Tendon lengthening occurred after 1 week at 20° compared to more plantarflexed angles, and was associated with loss of propulsion force. Dorsiflexing the ankle during immobilization from 160° to 90° produced a stiffer, more aligned tendon, but did not lead to functional changes compared to immobilization at 160°. Although more dorsiflexed immobilization can enhance tissue properties and function of healing Achilles tendon following rupture, full dorsiflexion creates significant tendon elongation regardless of application time. This study suggests that the use of moderate plantarflexion and earlier return to activity can provide improved clinical outcomes. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Multiscale computational model of Achilles tendon wound healing: Untangling the effects of repair and loading

Mechanical stimulation of the healing tendon is thought to regulate scar anisotropy and strength and is relatively easy to modulate through physical therapy. However, in vivo studies of various loading protocols in animal models have produced mixed results. To integrate and better understand the available data, we developed a multiscale model of rat Achilles tendon healing that incorporates the effect of changes in the mechanical environment on fibroblast behavior, collagen deposition, and scar formation. We modified an OpenSim model of the rat right hindlimb to estimate physiologic strains in the lateral/medial gastrocnemius and soleus musculo-tendon units during loading and unloading conditions. We used the tendon strains as inputs to a thermodynamic model of stress fiber dynamics that predicts fibroblast alignment, and to determine local collagen synthesis rates according to a response curve derived from in vitro studies. We then used an agent-based model (ABM) of scar formation to integrate these cell-level responses and predict tissue-level collagen alignment and content. We compared our model predictions to experimental data from ten different studies. We found that a single set of cellular response curves can explain features of observed tendon healing across a wide array of reported experiments in rats–including the paradoxical finding that repairing transected tendon reverses the effect of loading on alignment–without fitting model parameters to any data from those experiments. The key to these successful predictions was simulating the specific loading and surgical protocols to predict tissue-level strains, which then guided cellular behaviors according to response curves based on in vitro experiments. Our model results provide a potential explanation for the highly variable responses to mechanical loading reported in the tendon healing literature and may be useful in guiding the design of future experiments and interventions.

Tendons and ligaments transmit force between muscles and bones throughout the body and are comprised of highly aligned collagen fibers that help bear high loads. The Achilles tendon is exposed to exceptionally high loads and is prone to rupture. When damaged Achilles tendons heal, they typically have reduced strength and stiffness, and while most believe that appropriate physical therapy can help improve these mechanical properties, both clinical and animal studies of mechanical loading following injury have produced highly variable and somewhat disappointing results. To help better understand the effects of mechanical loading on tendon healing and potentially guide future therapies, we developed a computational model of rat Achilles tendon healing and showed that we could predict the main effects of different mechanical loading and surgical repair conditions reported across a wide range of published studies. Our model offers potential explanations for some surprising findings of prior studies and for the high variability observed in those studies and may prove useful in designing future therapies or experiments to test new therapies.

The Ruptured Achilles Tendon Elongates for 6 Months After Surgical Repair Regardless of Early or Late Weightbearing in Combination With Ankle Mobilization: A Randomized Clinical Trial

BACKGROUND

Treatment strategies for Achilles tendon rupture vary considerably, and clinical outcome may depend on the magnitude of tendon elongation after surgical repair. The aim of this project was to examine whether tendon elongation, mechanical properties, and functional outcomes during rehabilitation of surgically repaired acute Achilles tendon ruptures were influenced by different rehabilitation regimens during the early postsurgical period.

HYPOTHESIS

Restricted early weightbearing that permits only limited motion about the ankle in the early phase of tendon healing limits tendon elongation and improves functional outcome.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

75 consecutive patients with an acute Achilles tendon rupture were included. They underwent surgical repair, and tantalum beads were placed in the distal and proximal parts of the tendon; thereafter, the patients were randomized into 3 groups. The first group was completely restricted from weightbearing until week 7. The second group was completely restricted from weightbearing until week 7 but performed ankle joint mobilization exercises. The first and second groups were allowed full weightbearing after week 8. The third group was allowed partial weightbearing from day 1 and full weightbearing from week 5. All patients received the same instructions in home exercise guidelines starting from week 9.

RESULTS

The rehabilitation regimen in the initial 8 weeks did not significantly influence any of the measured outcomes including tendon elongation. Achilles tendon elongation and tendon compliance continued for up to 6 months after surgery, and muscle strength, muscle endurance, and patient-reported functional scores did not reach normal values at 12 months.

CONCLUSION

Differences in rehabilitation loading pattern in the initial 8 weeks after the repair of an Achilles tendon rupture did not measurably alter the outcome. The time to recover full function after an Achilles tendon rupture is at least 12 months. Registration: NCT02422004 ( ClinicalTrials.gov identifier).

Different mechanisms activated by mild versus strong loading in rat Achilles tendon healing

Background

Mechanical loading stimulates Achilles tendon healing. However, various degrees of loading appear to have different effects on the mechanical properties of the healing tendon, and strong loading might create microdamage in the tissue. This suggests that different mechanisms might be activated depending on the magnitude of loading. The aim of this study was to investigate these mechanisms further.

Methods

Female rats had their right Achilles tendon cut transversely and divided into three groups: 1) unloading (calf muscle paralysis by Botox injections, combined with joint fixation by a steel-orthosis), 2) mild loading (Botox only), 3) strong loading (free cage activity). Gene expression was analyzed by PCR, 5 days post-injury, and mechanical testing 8 days post-injury. The occurrence of microdamage was analyzed 3, 5, or 14 days post-injury, by measuring leakage of injected fluorescence-labelled albumin in the healing tendon tissue.

Results

Peak force, peak stress, and elastic modulus of the healing tendons gradually improved with increased loading as well as the expression of extracellular matrix genes. In contrast, only strong loading increased transverse area and affected inflammation genes. Strong loading led to higher fluorescence (as a sign of microdamage) compared to mild loading at 3 and 5 days post-injury, but not at 14 days.

Discussion

Our results show that strong loading improves both the quality and quantity of the healing tendon, while mild loading only improves the quality. Strong loading also induces microdamage and alters the inflammatory response. This suggests that mild loading exert its effect via mechanotransduction mechanisms, while strong loading exert its effect both via mechanotransduction and the creation of microdamage.

Conclusion

In conclusion, mild loading is enough to increase the quality of the healing tendon without inducing microdamage and alter the inflammation in the tissue. This supports the general conception that early mobilization of a ruptured tendon in patients is advantageous.

Foot and Ankle Surgery: Common Problems and Solutions

Participation in sports activity has increased significantly during the last several decades. This phenomenon has exposed orthopedic sports medicine surgeons to new challenges regarding the diagnosis and management of common sport-related injuries. Arthroscopy is becoming more commonly used in many of the surgical procedures for these injuries and carries the risk of complications. Wound and nerve complications make up the bulk of complications in most procedures. This article describes these complications associated with the common surgical procedures related to foot and ankle sport-related injuries and how to address and prevent them.

Side-to-side differences in Achilles tendon geometry and mechanical properties following achilles tendon rupture

Background

Recovery of tendon structure has been suggested to play a role in clinical success following Achilles tendon rupture. The purpose of this study was to identify side-to-side differences in tendon geometry and mechanical properties following Achilles tendon rupture and investigate the relationship of tendon structure with clinical outcomes.

Methods

Participants within 1 year post complete rupture were included. Tendon geometry and mechanical properties were quantified using B-mode ultrasound imaging and continuous shear wave elastography (cSWE). Clinical outcomes included the heel-rise test. Participant self-reported function was measured using the Achilles tendon Total Rupture Score, Foot and Ankle Outcome Score - quality of life subscale, and the Physical Activity Scale.

Results

Twenty participants [mean (SD) age: 42.7(13.6) years, 13 managed surgically] were included. Tendon thickness was greater on the ruptured side (p <0.001) [median (IQR) rupture: 1.38(1.21-1.56) cm, non-rupture: 0.49(0.40-0.52)]. Tendon length to the gastrocnemius was longer (p <0.001) on ruptured [22.8 (21.71-24.31) cm] than non-ruptured [21.66(20.74-23.62) cm] sides. Viscosity was lower on the ruptured side (p <0.001) [median (IQR) rupture: 37.7(30.6-43.3) Pa*s, non-rupture: 53.5(48.4-59.6) Pa*s]. Shear modulus was not different between sides. Tendon thickness (rho = 0.675, p = 0.002) and shear modulus (rho = -0.791, p = 0.001) related to total work on the heel-rise test.

Conclusion

Ultrasound imaging, including cSWE, can be used to detect side-to-side differences in tendon structure in individuals with Achilles tendon rupture and tendon structure relates to clinical performance.

Level of evidence

III b.

Different gene response to mechanical loading during early and late phases of rat Achilles tendon healing

Mechanical loading stimulates tendon healing both when applied in the inflammatory phase and in the early remodeling phase of the process, although not necessarily via the same mechanisms. We investigated the gene response to mechanical loading in these two phases of tendon healing. The right Achilles tendon in rats was transected, and the hindlimbs were unloaded by tail suspension. The rats were exposed to 5 min of treadmill running 3 or 14 days after tendon transection. Thereafter, they were resuspended for 15 min or 3 h until euthanasia. The controls were suspended continuously. Gene analysis was first performed by microarray analysis followed by quantitative RT-PCR on selected genes, focusing on inflammation. Fifteen minutes after loading, the most important genes seemed to be the transcription factors EGR1 and C-FOS, regardless of healing phase. These transcription factors might promote tendon cell proliferation and differentiation, stimulate collagen production, and regulate inflammation. Three hours after loading on day 3, inflammation was strongly affected. Seven inflammation-related genes were upregulated according to PCR: CCL20, CCL7, IL-6, NFIL3, PTX3, SOCS1, and TLR2. These genes can be connected to macrophages, T cells, and recruitment of leukocytes. According to Ingenuity Pathway Analysis, the recruitment of leukocytes was increased by loading on day 3, which also was confirmed by histology. This inflammation-related gene response was not seen on day 14 Our results suggest that the immediate gene response after mechanical loading is similar in the early and late phases of healing but the late gene response is different.NEW & NOTEWORTHY This study investigates the direct effect of mechanical loading on gene expression during different healing phases in tendon healing. One isolated episode of mechanical loading was studied in otherwise unloaded healing tendons. This enabled us to study a time sequence, i.e., which genes were the first ones to be regulated after the loading episode.

An in vitro scratch tendon tissue injury model: effects of high frequency low magnitude loading

The healing process of ruptured tendons is suboptimal, taking months to achieve tissue with inferior properties to healthy tendon. Mechanical loading has been shown to positively influence tendon healing. However, high frequency low magnitude (HFLM) loads, which have shown promise in maintaining healthy tendon properties, have not been studied with in vitro injury models. Here, we present and validate an in vitro scratch tendon tissue injury model to investigate effects of HFLM loading on the properties of injured rat tail tendon fascicles (RTTFs). A longitudinal tendon tear was simulated using a needle aseptically to scratch a defined length along individual RTTFs. Tissue viability, biomechanical, and biochemical parameters were investigated before and 7 days after culture . The effects of static, HFLM (20 Hz), and low frequency (1 Hz) cyclic loading or no load were also investigated. Tendon viability was confirmed in damaged RTTFs after 7 days of culture, and the effects of a 0.77 ± 0.06 cm scratch on the mechanical property (tangent modulus) and tissue metabolism in damaged tendons were consistent, showing significant damage severity compared with intact tendons. Damaged tendon fascicles receiving HFLM (20 Hz) loads displayed significantly higher mean tangent modulus than unloaded damaged tendons (212.7 ± 14.94 v 92.7 ± 15.59 MPa), and damaged tendons receiving static loading (117.9 ± 10.65 MPa). HFLM stimulation maintained metabolic activity in 7-day cultured damaged tendons at similar levels to fresh tendons immediately following damage. Only damaged tendons receiving HFLM loads showed significantly higher metabolism than unloaded damaged tendons (relative fluorescence units -7021 ± 635.9 v 3745.1 ± 641.7). These validation data support the use of the custom-made in vitro injury model for investigating the potential of HFLM loading interventions in treating damaged tendons.

Nonsurgical treatment and early return to activity leads to improved Achilles tendon fatigue mechanics and functional outcomes during early healing in an animal model

Achilles tendon ruptures are common and devastating injuries; however, an optimized treatment and rehabilitation protocol has yet to be defined. Therefore, the objective of this study was to investigate the effects of surgical repair and return to activity on joint function and Achilles tendon properties after 3 weeks of healing. Sprague-Dawley rats (N = 100) received unilateral blunt transection of their Achilles tendon. Animals were then randomized into repaired or non-repaired treatments, and further randomized into groups that returned to activity after 1 week (RTA1) or after 3 weeks (RTA3) of limb casting in plantarflexion. Limb function, passive joint mechanics, and tendon properties (mechanical, organizational using high frequency ultrasound, histological, and compositional) were evaluated. Results showed that both treatment and return to activity collectively affected limb function, passive joint mechanics, and tendon properties. Functionally, RTA1 animals had increased dorsiflexion ROM and weight bearing of the injured limb compared to RTA3 animals 3-weeks post-injury. Such functional improvements in RTA1 tendons were evidenced in their mechanical fatigue properties and increased cross sectional area compared to RTA3 tendons. When RTA1 was coupled with nonsurgical treatment, superior fatigue properties were achieved compared to repaired tendons. No differences in cell shape, cellularity, GAG, collagen type I, or TGF-β staining were identified between groups, but collagen type III was elevated in RTA3 repaired tendons. The larger tissue area and increased fatigue resistance created in RTA1 tendons may prove critical for optimized outcomes in early Achilles tendon healing following complete rupture. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2172-2180, 2016.

COX-2 inhibition impairs mechanical stimulation of early tendon healing in rats by reducing the response to microdamage

Early tendon healing can be stimulated by mechanical loading and inhibited by cyclooxygenase (COX) inhibitors (nonsteroidal anti-inflammatory drugs). Therefore, we investigated if impairment of tendon healing by a COX-2 inhibitor (parecoxib) is related to loading. Because loading might infer microdamage, which also stimulates healing, we also investigated if this effect is inhibited by parecoxib. The Achilles tendon was transected in 114 rats. Three degrees of loading were used: full loading, partial unloading, and unloading (no unloading, Botox injections in the plantar flexor muscles, or Botox in combination with tail suspension). For each loading condition, the rats received either parecoxib or saline. In a second experiment, rats were unloaded with Botox, and the tendon was subjected to microdamage by needling combined with either saline or parecoxib. Mechanical testing day 7 showed that there was a significant interaction between loading and parecoxib for peak force at failure (P < 0.01). However, logarithmic values showed no significant interaction, meaning that we could not exclude that the inhibitory effect of parecoxib was proportionate to the degree of loading. Microbleeding was common in the healing tissue, suggesting that loading caused microdamage. Needling increased peak force at failure (P < 0.01), and this effect of microdamage was almost abolished by parecoxib (P < 0.01). Taken together, this suggests that COX-2 inhibition impairs the positive effects of mechanical loading during tendon healing, mainly by reducing the response to microdamage.

Weight bearing the same day versus non-weight bearing for 4 weeks in Achilles tendon rupture

INTRODUCTION

Achilles tendon rupture (ATR) often occurs in 40- to 50-year-old men. Multiple studies discuss the correct treatment strategy based on surgical or nonsurgical intervention, including early mobilization. We aimed to compare the outcomes of bearing weight on the same day with non-weight bearing over a 4-week period of ATR patients.

MATERIALS AND METHOD

Forty-seven ATR patients were conservatively treated and entered into our study. Group 1 consisted of 23 patients treated with partial weight bearing beginning the same day of conservative treatment; Group 2 consisted of 24 patients treated with non-weight bearing after a 4-week period. Patients were at least 18 years old and were followed for 12 months. Evaluation criteria were mechanism of injury, admission time to our clinic, complication rate, and time to return to work. Symptoms and physical activity levels of all patients were assessed on 6 and 12 months after treatment began, according to the Achilles Tendon Total Rupture Score (ATRS), Physical Activity Scale (PAS), and American Orthopedic Foot and Ankle Society (AOFAS) ankle-hindfoot score.

RESULTS

Rerupture rates were rate 17.4% (4 patients) in Group 1 and 12.5% (3 patients) in Group 2 (p = 0.81). Time to return to work was shorter in Group 1 compared with Group 2, but it was not statistically significant (p = 0.86). AOFAS, ATRS, and PAS scores at 6 and 12 months showed no significant differences between groups (p = 0.69, p = 0.59, p = 0.89, p = 0.77, p = 0.94, p = 0.66, respectively).

CONCLUSION

This study showed that a well-conducted early-weight-bearing treatment has good clinical outcomes, with a complication rate no higher than non-weight-bearing treatment.

Early controlled tension improves the material properties of healing human achilles tendons after ruptures: a randomized trial

BACKGROUND

Weightbearing in a fixed brace after acute Achilles tendon ruptures does not necessarily lead to mechanical tension in the tendon. Early motion has a positive effect on the clinical outcome, but it is not clear if this is because of effects on tendon strength or unspecific effects. The aim of this study was to examine if tensional loading leads to an improvement in the mechanical properties of the healing Achilles tendon.

HYPOTHESIS

The elastic modulus of the tendon callus is increased by early tensional loading.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 2.

METHODS

Thirty-five patients with an acute Achilles tendon rupture were recruited consecutively. They underwent surgery with a single suture and received metal markers in the distal and proximal parts of the tendon. After surgery, the patients were randomized to either cast immobilization for 7 weeks or tensional loading. The latter group wore a cast for 2 weeks and then a removable foam walker boot for 5 weeks. They were instructed to remove the boot twice daily and push a special training pedal to produce a predetermined, gradually increasing tensional load on the healing tendon. At 7, 19, and 52 weeks postoperatively, the patients were investigated with roentgen stereophotogrammetric analysis under different loading conditions and computed tomography. The collected data allowed calculation of the modulus of elasticity. At 52 weeks, the clinical outcome was also examined using the Achilles tendon Total Rupture Score (ATRS) and the heel-raise index.

RESULTS

The elastic modulus at 19 and 52 weeks was higher in the tensional loading group. There was no significant difference in the ATRS or heel-raise index at 52 weeks. As in previous studies, there was a significant correlation between the modulus at 7 weeks and the heel-raise index at 52 weeks. There were no signs of tendon elongation.

CONCLUSION

Early tensional loading improves the mechanical properties of the healing Achilles tendon.

Bilateral quadriceps rupture: results with and without platelet-rich plasma

This article presents a 46-year-old man with bilateral atraumatic quadriceps rupture that occurred while he was descending stairs. The patient underwent surgery the day after the accident. In the left knee, quadriceps reinsertion was performed using a conventional technique. In the right knee, platelet-rich plasma (PRP), both in its liquid and semisolid patterns, was added intraoperatively. Ultrasonography and magnetic resonance imaging evaluations were performed 1, 6, and 24 months postoperatively. At 6 and 24 months postoperatively, clinical and functional evaluations also were performed. Clinical examination showed no differences between the knees, and functional scores were the same for both knees. Ultrasonographic evaluation showed bilateral persistent tendon thickening and gross echotexture abnormalities, with no side-to-side differences. Magnetic resonance imaging showed signals of vascularized granulation tissue in both knees, which was more evident in the right (PRP) knee at 1 month postoperatively, along with a better signal of scar tissue in the right knee at 6 and 24 months postoperatively. The use of PRP yielded no better clinical or functional results than the lack of its use. However, a more intense and significant reparative healing process occurred where the PRP was used, thus suggesting a more rapid completion of the healing process, although this effect seems to remain only a radiographic finding with no clinical correlation.

Rerupture rate after early weightbearing in operative versus conservative treatment of Achilles tendon ruptures: a meta-analysis

Whether Achilles tendon rupture benefits from surgery or conservative treatment remains controversial. Moreover, the outcome can be influenced by the rehabilitation protocol. The goal of the present meta-analysis was to compare the rerupture rate after surgical repair of the Achilles tendon followed by weightbearing within 4 weeks versus conservative treatment with weightbearing within 4 weeks. In addition, a secondary analysis was performed to compare the rerupture rates in patients who started weightbearing after 4 weeks. Seven randomized controlled trials published from 2001 to 2012, with 576 adult patients, were included. The primary outcome measure was the rerupture rate. The secondary outcomes were minor and major complications other than rerupture. In the early weightbearing group, 7 of 182 operatively treated patients (4%) experienced rerupture versus 21 of 176 of the conservatively treated patients (12%). A secondary analysis of the patients treated with late weightbearing showed a rerupture rate of 6% (7 of 108) for operatively treated patients versus 10% (11 of 110) for conservatively treated patients. The differences concerning the rerupture rate in both groups were not statistically significant. No differences were found in the occurrence of minor or major complications after early weightbearing in both patient groups. In conclusion, we found no difference in the rerupture rate between the surgically and nonsurgically treated patients followed by early weightbearing. Weightbearing after 4 weeks also resulted in no differences in the rupture rate in the surgical versus conservatively treated patients. However, surgical treatment was associated with a twofold greater complication rate than conservative treatment.

Primary gene response to mechanical loading in healing rat Achilles tendons

Loading can stimulate tendon healing. In healing rat Achilles tendons, we have found more than 150 genes upregulated or downregulated 3 h after one loading episode. We hypothesized that these changes were preceded by a smaller number of regulatory genes and thus performed a microarray 15 min after a short loading episode, to capture the primary response to loading. We transected the Achilles tendon of 54 rats and allowed them to heal. The hind limbs were unloaded by tail-suspension during the entire experiment, except during the loading episode. The healing tendon tissue was analyzed by mechanical testing, microarray, and quantitative real-time polymerase chain reaction (qRT-PCR). Mechanical testing showed that 5 min of loading each day for 4 days created stronger tissue. The microarray analysis after one loading episode identified 15 regulated genes. Ten genes were analyzed in a repeat experiment with new rats using qRT-PCR. This confirmed the increased expression of four genes: early growth response 2 (Egr2), c-Fos, FosB, and regulation of G protein signaling 1 (Rgs1). The other genes were unaltered. We also analyzed the expression of early growth response 1 (Egr1), which is often co-regulated with c-Fos or Egr2, and found that this was also increased after loading. Egr1, Egr2, c-Fos, and FosB are transcription factors that can be triggered by numerous stimuli. However, Egr1 and Egr2 are necessary for normal tendon development, and can induce ectopic expression of tendon markers. The five regulated genes appear to constitute a general activation machinery. The further development of gene regulation might depend on the tissue context.

Controlled treadmill exercise eliminates chondroid deposits and restores tensile properties in a new murine tendinopathy model

Tendinopathy is a widespread and disabling condition characterized by collagen fiber disruption and accumulation of a glycosaminoglycan-rich chondroid matrix. Recent clinical reports have illustrated the potential of mechanical loading (exercise) therapies to successfully treat chronic tendinopathies. We have developed a new murine tendinopathy model which requires a single injection of TGF-β1 into the Achilles tendon midsubstance followed by normal cage activity for 2 weeks. At this time, tendon maximum stress showed a dramatic (66%) reduction relative to that of normal controls and this persisted at four weeks. Loss of material properties was accompanied by abundant chondroid cells within the tendon (closely resembling the changes observed in human samples obtained intra-operatively) and increased expression of Acan, Col1a1, Col2a1, Col3a1, Fn1 and Mmp3. Mice subjected to two weeks of daily treadmill exercise following TGF-β1 injection showed a similar reduction in tendon material properties as the caged group. However, in mice subjected to 4 weeks of treadmill exercise, tendon maximum stress values were similar to those of naive controls. Tendons from the mice exercised for 4 weeks showed essentially no chondroid cells and the expression of Acan, Col1a1, Col2a1, Col3a1, and Mmp3 was significantly reduced relative to the 4-week cage group. This technically simple murine tendinopathy model is highly amenable to detailed mechanistic and translational studies of the biomechanical and cell biological pathways, that could be targeted to enhance healing of tendinopathy.

Structural and biomechanical characteristics after early mobilization in an Achilles tendon rupture model: operative versus nonoperative treatment

Acute Achilles tendon ruptures are common sports injuries; however, treatment remains a clinical challenge. Studies show a superior effect of early mobilization and full weight bearing on tendon healing and clinical outcome; however, few data exist on structural and biomechanical characteristics in the early healing phase. This study investigated the histological and biomechanical characteristics of early mobilization and full weight bearing in an Achilles tendon rupture model. Eighty rats underwent dissection of a hindpaw Achilles tendon; 40 rats were treated conservatively and 40 underwent open repair of the transected Achilles tendon by suturing. Early mobilization and full weight bearing were allowed in both groups. At 1, 2, 4, and 8 weeks after tenotomy, tensile strength, stiffness, thickness, tissue characteristics (histological analysis), and length were determined. Dissected Achilles tendons healed in all animals during full weight-bearing early mobilization. One and 2 weeks after tenotomy, rats in the operative group showed increased tensile strength and stiffness compared with the nonoperative group. Repair-site diameters were increased at 1, 2, and 8 weeks after tenotomy. Tendon length was decreased in the operative group throughout observation, whereas the nonoperative group showed increased structural characteristics on the cellular level and a more homogeneous collagen distribution. Surgical treatment of dissected rat Achilles tendons showed superior biomechanical characteristics within the first 2 weeks. Conservative treatment resulted in superior histological findings but significant lengthening of the tendon in the early healing phase (weeks 1-8).

Low-level mechanical stimulation is sufficient to improve tendon healing in rats

Treatment of tendon injuries often involves immobilization. However, immobilization might not prevent mild involuntary isometric muscle contraction. The effect of weak forces on tendon healing is therefore of clinical interest. Studies of tendon healing with various methods for load reduction in rat Achilles tendon models show a consistent reduction in tendon strength by at least half, compared with voluntary cage activity. Unloading was not complete in any of these models, and the healing tendon was therefore still exposed to mild mechanical stimulation. By reducing the forces acting on the tendon even further, we now studied the effects of this mild stimulation. Rat Achilles tendons were transected and allowed to heal spontaneously under four different loading conditions: 1) normal cage activity; 2) calf muscle paralysis induced by botulinum toxin A (Botox); 3) tail suspension; 4) Botox and tail suspension, combined, to eliminate even mild stimulation. Healing was evaluated by mechanical testing after 8 days. Botox alone and suspension alone both reduced tendon callus size (transverse area), thereby impairing its strength compared with normal cage activity. The combination of Botox and suspension did not further reduce tendon callus size but drastically impaired the material properties of the tendon callus compared with each treatment alone. The peak force was only a fifth of that in the normal cage activity group. The results indicate that also the mild loading that occurs with either Botox or suspension alone stimulates tendon healing. This stimulation appears to affect mainly tissue quality, whereas stronger stimulation also increases callus size.

Augmentation of tendon healing with butyric acid-impregnated sutures: biomechanical evaluation in a rabbit model

BACKGROUND

Butyric acid (BA) has been shown to be angiogenic and to enhance transcriptional activity in tissue. These properties of BA have the potential to augment biological healing of a repaired tendon.

PURPOSE

To evaluate this possibility both biomechanically and histologically in an animal tendon repair model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A rabbit Achilles tendon healing model was used to evaluate the biomechanical strength and histological properties at 6 and 12 weeks after repair. Unilateral tendon defects were created in the middle bundle of the Achilles tendon of each rabbit, which were repaired equivalently with either Ultrabraid BA-impregnated sutures or control Ultrabraid sutures.

RESULTS

After 6 weeks, BA-impregnated suture repairs had a significantly increased (P < .0001) Young's modulus and ultimate tensile strength relative to the control suture repairs. At 12 weeks, no statistical difference was observed between these measures. The histological data at 6 weeks demonstrated significantly increased (P < .005) vessel density within 0.25 mm of the repair suture in the BA-impregnated group. There was also an associated 42% increase in the local number of myofibroblasts in the BA samples relative to the controls at this time. By 12 weeks, these differences were not observed.

CONCLUSION

Tendons repaired with BA-impregnated sutures demonstrated improved biomechanical properties at 6 weeks relative to control sutures, suggesting a neoangiogenic mechanism of enhanced healing through an increased myofibroblast presence.

CLINICAL RELEVANCE

These findings demonstrate that a relatively simple alteration of suture material may augment early tendon healing to create a stronger repair construct during this time.

Etanercept does not impair healing in rat models of tendon or metaphyseal bone injury

BACKGROUND AND PURPOSE

Should blockade of TNF-α be avoided after orthopedic surgery? Healing of injuries in soft tissues and bone starts with a brief inflammatory phase. Modulation of inflammatory signaling might therefore interfere with healing. For example, Cox inhibitors impair healing in animal models of tendon, ligament, and bone injury, as well as in fracture patients. TNF-α is expressed locally at increased levels during early healing of these tissues. We therefore investigated whether blocking of TNF-α with etanercept influences the healing process in established rat models of injury of tendons and metaphyseal bone.

METHODS

Rats were injected with etanercept, 3.5 mg/kg 3 times a week. Healing of transected Achilles tendons and bone healing around screws implanted in the tibial metaphysis were estimated by mechanical testing. Tendons were allowed to heal either with or without mechanical loading. Ectopic bone induction following intramuscular BMP-2 implants has previously been shown to be stimulated by etanercept in rodents. This was now tested as a positive control.

RESULTS

Tendon peak force after 10 days was not significantly influenced by etanercept. Changes exceeding 29% could be excluded with 95% confidence. Likewise, screw pull-out force was not significantly influenced. More than 25% decrease or 18% increase could be excluded with 95% confidence. However, etanercept treatment increased the amount of bone induced by intramuscular BMP-2 implants, as estimated by blind histological scoring.

INTERPRETATION

Etanercept does not appear to impair tendon or metaphyseal bone healing to any substantial degree.

Achilles tendon healing in rats is improved by intermittent mechanical loading during the inflammatory phase

Tendons adapt to changes in mechanical loading, and numerous animal studies show that immobilization of a healing tendon is detrimental to the healing process. The present study addresses whether the effects of a few episodes of mechanical loading are different during different phases of healing. Fifty female rats underwent Achilles tendon transection, and their hind limbs were unloaded by tail suspension on the day after surgery. One group of 10 rats was taken down from suspension to run on a treadmill for 30 min/day, on days 2-5 after transection. They were euthanized on day 8. Another group underwent similar treadmill running on days 8-11 and was euthanized on day 14. Continuously unloaded groups were euthanized on days 8 and 14. Tendon specimens were then evaluated mechanically. The results showed that just four loading episodes increased the strength of the healing tendon. This was evident irrespective of the time point when loading was applied (early or late). The positive effect on early healing was unexpected, considering that the mechanical stimulation was applied during the inflammatory phase, when the calluses were small and fragile. A histological study of additional groups with early loading also showed some increased bleeding in the loaded calluses. Our results indicate that a short episodes of early loading may improve the outcome of tendon healing. This could be of interest to clinical practice.

Autologous platelets have no effect on the healing of human achilles tendon ruptures: a randomized single-blind study

BACKGROUND

Animal studies have shown that local application of platelet-rich plasma (PRP) stimulates tendon repair. Preliminary results from a retrospective case series have shown faster return to sports.

HYPOTHESIS

Autologous PRP stimulates healing of acute Achilles tendon ruptures.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 2.

METHODS

Thirty patients were recruited consecutively. During surgery, tantalum beads were implanted in the Achilles tendon proximal and distal to the rupture. Before skin suture, randomization was performed, and 16 patients were injected with 10 mL PRP (10 times higher platelet concentration than peripheral blood) whereas 14 were not. With 3-dimensional radiographs (roentgen stereophotogrammetric analysis; RSA), the distance between the beads was measured at 7, 19, and 52 weeks while the patient resisted different dorsal flexion moments over the ankle joint, thereby estimating tendon strain per load. An estimate of elasticity modulus was calculated using callus dimensions from computed tomography. At 1 year, functional outcome was evaluated, including the heel raise index and Achilles Tendon Total Rupture Score. The primary effect variables were elasticity modulus at 7 weeks and heel raise index at 1 year.

RESULTS

The mechanical variables showed a large degree of variation between patients that could not be explained by measuring error. No significant group differences in elasticity modulus could be shown. There was no significant difference in heel raise index. The Achilles Tendon Total Rupture Score was lower in the PRP group, suggesting a detrimental effect. There was a correlation between the elasticity modulus at 7 and 19 weeks and the heel raise index at 52 weeks.

CONCLUSION

The results suggest that PRP is not useful for treatment of Achilles tendon ruptures. The variation in elasticity modulus provides biologically relevant information, although it is unclear how early biomechanics is connected to late clinical results.