Healing of the Achilles tendon: an experimental study

Chronologic Changes in the Elastic Modulus of a Healing Achilles Tendon Rupture Measured Using Shear Wave Elastography

BACKGROUND

Shear wave elastography (SWE) has been used to examine the elasticity of a ruptured Achilles tendon; however, the healing process of a ruptured tendon has not been studied yet. This study aimed to detail the change in mechanical properties of a healing Achilles tendon rupture managed conservatively or surgically using SWE.

METHODS

Using a prospective cohort study design, we evaluated the patients treated conservatively (conservative group) and surgically (surgical group) with the "gift-box" technique for an isolated index acute Achilles tendon rupture during their healing process. SWE measurements were taken of both the injured and uninjured sides every 4 weeks up to 24, 36, and 48 weeks after treatment. Additionally, tendon thickness and power Doppler (PD) grade were measured at the same time points as SWE measurements. The American Orthopaedic Foot & Ankle Society (AOFAS) ankle-hindfoot rating system score and Achilles tendon Total Rupture Score (ATRS) were compared at 24 and 48 weeks.

RESULTS

The ruptured Achilles tendon obtained an SWE value comparable with the unruptured side at 12 weeks in the conservative group and at 4 weeks with surgical group. The surgical group had significantly higher SWE values up to 24 weeks compared with the conservative group. Additionally, this group had a significantly larger increase in tendon thickness in nearly all periods. Both treatment groups were comparable regarding the PD grade, AOFAS score, and ATRS.

CONCLUSION

SWE is a convenient noninvasive method to determine the progress of the healing process after tendon injury. Our analysis using SWE has revealed the detailed chronologic changes in SWE values and related mechanical properties of a healing Achilles tendon rupture, which can be used for devising appropriate rehabilitation protocols.

LEVEL OF EVIDENCE

Level II, prospective cohort study.

Intrinsic Tendon Regeneration After Application of Purified Exosome Product: An In Vivo Study

Background:

Tendons are primarily acellular, limiting their intrinsic regenerative capabilities. This limited regenerative potential contributes to delayed healing, rupture, and adhesion formation after tendon injury.

Purpose:

To determine if a tendon’s intrinsic regenerative potential could be improved after the application of a purified exosome product (PEP) when loaded onto a collagen scaffold.

Study Design:

Controlled laboratory study.

Methods:

An in vivo rabbit Achilles tendon model was used and consisted of 3 groups: (1) Achilles tenotomy with suture repair, (2) Achilles tenotomy with suture repair and collagen scaffold, and (3) Achilles tenotomy with suture repair and collagen scaffold loaded with PEP at 1 × 10¹² exosomes/mL. Each group consisted of 15 rabbits for a total of 45 specimens. Mechanical and histologic analyses were performed at both 3 and 6 weeks.

Results:

The load to failure and ultimate tensile stress were found to be similar across all groups (P ≥ .15). The tendon cross-sectional area was significantly smaller for tendons treated with PEP compared with the control groups at 6 weeks, which was primarily related to an absence of external adhesions (P = .04). Histologic analysis confirmed these findings, demonstrating significantly lower adhesion grade both macroscopically (P = .0006) and microscopically (P = .0062) when tendons were treated with PEP. Immunohistochemical staining showed a greater intensity for type 1 collagen for PEP-treated tendons compared with collagen-only or control tendons.

Conclusion:

Mechanical and histologic results suggested that healing in the PEP-treated group favored intrinsic healing (absence of adhesions) while control animals and animals treated with collagen only healed primarily via extrinsic scar formation. Despite a smaller cross-sectional area, treated tendons had the same ultimate tensile stress. This pilot investigation shows promise for PEP as a means of effectively treating tendon injuries and enhancing intrinsic healing.

Clinical Relevance:

The production of a cell-free, off-the-shelf product that can promote tendon regeneration would provide a viable solution for physicians and patients to enhance tendon healing and decrease adhesions as well as shorten the time required to return to work or sports.

Tendon injury and repair - A perspective on the basic mechanisms of tendon disease and future clinical therapy

Tendon is an intricately organized connective tissue that efficiently transfers muscle force to the bony skeleton. Its structure, function, and physiology reflect the extreme, repetitive mechanical stresses that tendon tissues bear. These mechanical demands also lie beneath high clinical rates of tendon disorders, and present daunting challenges for clinical treatment of these ailments. This article aims to provide perspective on the most urgent frontiers of tendon research and therapeutic development. We start by broadly introducing essential elements of current understanding about tendon structure, function, physiology, damage, and repair. We then introduce and describe a novel paradigm explaining tendon disease progression from initial accumulation of damage in the tendon core to eventual vascular recruitment from the surrounding synovial tissues. We conclude with a perspective on the important role that biomaterials will play in translating research discoveries to the patient.

STATEMENT OF SIGNIFICANCE

Tendon and ligament problems represent the most frequent musculoskeletal complaints for which patients seek medical attention. Current therapeutic options for addressing tendon disorders are often ineffective, and the need for improved understanding of tendon physiology is urgent. This perspective article summarizes essential elements of our current knowledge on tendon structure, function, physiology, damage, and repair. It also describes a novel framework to understand tendon physiology and pathophysiology that may be useful in pushing the field forward.

A review on animal models and treatments for the reconstruction of Achilles and flexor tendons

Tendon is a connective tissue mainly composed of collagen fibers with peculiar mechanical properties essential to functional movements. The increasing incidence of tendon traumatic injuries and ruptures-associated or not with the loss of tissue-falls on the growing interest in the field of tissue engineering and regenerative medicine. The use of animal models is mandatory to deepen the knowledge of the tendon healing response to severe damages or acute transections. Thus, the selection of preclinical models is crucial to ensure a successful translation of effective and safe innovative treatments to the clinical practice. The current review is focused on animal models of tendon ruptures and lacerations or defective injuries with large tissue loss that require surgical approaches or grafting procedures. Data published between 2000 and 2016 were examined. The analyzed articles were compiled from Pub Med-NCBI using search terms, including animal model(s) AND tendon augmentation OR tendon substitute(s) OR tendon substitution OR tendon replacement OR tendon graft(s) OR tendon defect(s) OR tendon rupture(s). This article presents the existing preclinical models - considering their advantages and disadvantages-in which translational progresses have been made by using bioactive sutures or tissue engineering that combines biomaterials with cells and growth factors to efficiently treat transections or large defects of Achilles and flexor tendons.

Quantitative US Elastography Can Be Used to Quantify Mechanical and Histologic Tendon Healing in a Rabbit Model of Achilles Tendon Transection

Purpose To determine the time-dependent change in strain ratios (SRs) at the healing site of an Achilles tendon rupture in a rabbit model of tendon transection and to assess the correlation between SRs and the mechanical and histologic properties of the healing tissue. Materials and Methods Experimental methods were approved by the institutional animal care and use committee. The Achilles tendons of 24 New Zealand white rabbits (48 limbs) were surgically transected. The SRs of Achilles tendons were calculated by using compression-based quantitative ultrasonographic elastography measurements obtained 2, 4, 8, and 12 weeks after transection. After in vivo elastography, the left Achilles tendon was harvested for mechanical testing of ultimate load, ultimate stress, elastic modulus, and linear stiffness, and the right tendons were harvested for tissue histologic analysis with the Bonar scale. Time-dependent changes in SRs, mechanical parameters, and Bonar scale scores were evaluated by using repeated-measures analysis of variance. The correlation between SRs and each measured variable was evaluated by using the Spearman rank correlation coefficient. Results Mean SRs and Bonar scale values decreased as a function of time after transection, whereas mechanical parameters increased (P < .001). SR correlated with ultimate stress (ρ = 0.68, P <.001,) elastic modulus (ρ = 0.74, P <.001), and the Bonar scale (ρ = 0.87, P <.001). Conclusion Quantitative elastography could be a useful method with which to evaluate mechanical and histologic properties of the healing tendon. ^© RSNA, 2017 Online supplemental material is available for this article.

Prospective Use of a Standardized Nonoperative Early Weightbearing Protocol for Achilles Tendon Rupture: 17 Years of Experience

BACKGROUND

Acute traumatic rupture of the Achilles tendon can be treated operatively or nonoperatively. Throughout the literature, there is no consensus regarding the optimal treatment protocol.

PURPOSE

To report on 17 years of experience with treating this injury with a standardized nonoperative treatment protocol.

STUDY DESIGN

Case Series; Level of evidence, 4.

METHODS

The treatment protocol was based on a combination of an equinus cast and rehabilitation boot, which promoted immediate full weightbearing and early functional rehabilitation. A total of 171 patients were consecutively treated and prospectively followed from 1996 to 2013. Assessed were subjective parameters such as pain, loss of strength, return to previous activity level, meteosensitivity, and general satisfaction with the treatment outcome. Clinical assessment included testing of plantar flexion strength and endurance, calf circumference, and tendon length. Subjective and clinical parameters were then used to calculate a modified Thermann score. The correlation between tendon lengthening and function was calculated using the Pearson correlation coefficient.

RESULTS

A total of 114 patients were followed for a minimum of 12 months (mean, 27 ± 20 months; range, 12-88 months). The mean Thermann score was 82 ± 13 (range, 41-100), and subjective satisfaction was rated "very good" and "good" in 90%. An inverse correlation was found between tendon length and muscle strength (R = -0.3). There were 11 reruptures (8 with and 3 without an adequate trauma). General complications were 5 deep venous thromboses, 1 complex regional pain syndrome, and minor problems such as transient heel pain (n = 3), heel numbness (n = 1), and cast-associated skin abrasions (n = 4).

CONCLUSION

Seventeen years of experience with a nonoperative treatment protocol for acute rupture of the Achilles tendon confirmed good functional outcome and patient satisfaction. Reruptures mostly occurred with new traumatic events in the vulnerable phase from 6 to 12 weeks after the initial injury. Muscle strength correlated to tendon length, making its assessment a crucial follow-up parameter. The protective equinus cast and boot can protect against excessive tendon lengthening during the healing process.

Effects of botulinum toxin A injection on healing and tensile strength of ruptured rabbit Achilles tendons

BACKGROUND

Tendon lacerations are most commonly managed with surgical repair. Postoperative complications such as adhesions and ruptures often occur with immobilization. Early postoperative mobilization is therefore advised to minimize complications and time required to return to daily life. The aim of this study was to evaluate whether botulinum neurotoxin type-A (BoNT-A) can be used to enhance healing and prevent rupture in mobilized animals with Achilles tenotomy.

METHODS

Twenty-seven rabbits were divided into 3 groups, namely, I, II, and III, after surgical 1-sided Achilles tenotomy and end-to-end repair. The control group for biomechanical comparisons consisted of randomly selected contralateral (unoperated) healthy Achilles tendons. Group I received BoNT-A (4 U/kg) injection into the calf muscles. One week later, electromyographical confirmation was performed to establish the effects of injection. Surgery was then performed. Animals in the second group (n = 9, group II) were immobilized with a cast postoperatively. The third group (n = 9, group III) was mobilized immediately with no cast or BoNT-A. Tendons were harvested and gap formation or ruptures as well as strength of the repaired tendon were assessed 6 weeks after surgery.

RESULTS

Achilles tendons healed in all animals injected with BoNT-A, whereas all were ruptured in group III. All Achilles tendons of animals in groups I and II healed. However, group I repaired tendons were biomechanically equivalent to healthy tendons, whereas group II repaired tendons demonstrated significantly decreased tensile strength (P = 0.009).

CONCLUSIONS

The present study suggests that local injection of BoNT-A can be used for treatment of tendon rupture and may replace the use of cast for immobilization. However, further studies are needed to determine whether BoNT-A injection can have a beneficial effect on the healing of tendon repairs in humans.

The past, present and future in scaffold-based tendon treatments

Tendon injuries represent a significant clinical burden on healthcare systems worldwide. As the human population ages and the life expectancy increases, tendon injuries will become more prevalent, especially among young individuals with long life ahead of them. Advancements in engineering, chemistry and biology have made available an array of three-dimensional scaffold-based intervention strategies, natural or synthetic in origin. Further, functionalisation strategies, based on biophysical, biochemical and biological cues, offer control over cellular functions; localisation and sustained release of therapeutics/biologics; and the ability to positively interact with the host to promote repair and regeneration. Herein, we critically discuss current therapies and emerging technologies that aim to transform tendon treatments in the years to come.

Nonoperative, dynamic treatment of acute achilles tendon rupture: influence of early weightbearing on biomechanical properties of the plantar flexor muscle-tendon complex-a blinded, randomized, controlled trial

Acute Achilles tendon rupture alters the biomechanical properties of the plantar flexor muscle-tendon complex that can affect functional performance and the risk of repeat injury. The purpose of the present study was to compare the biomechanical properties of the plantar flexor muscle-tendon complex in patients randomized to early weightbearing or non-weightbearing in the nonoperative treatment of Achilles tendon rupture. A total of 60 patients were randomized to full weightbearing from day 1 of treatment or non-weightbearing for 6 weeks. After 6 and 12 months, the peak passive torque at 20° dorsiflexion, the stiffness during slow stretching, and the maximal strength were measured in both limbs. The stiffness of the plantar flexor muscle-tendon complex in the terminal part of dorsiflexion was significantly increased (p = .024) in the non-weightbearing group at 12 months. The peak passive torque was significantly lower for the affected limb at 6 months (91%; p = .01), and the stiffness was significantly lower for the affected limb during the early part of dorsiflexion at 6 (67%; p < .001) and 12 (77%; p < .001) months. In conclusion, an increased stiffness of the plantar flexor muscle-tendon complex in the terminal part of dorsiflexion was found in the non-weightbearing group. The altered stiffness and strength in the affected limb could affect the coordination of gait and running.

Healing of the Achilles tendon in rabbits--evaluation by magnetic resonance imaging and histopathology

Background

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) could provide valuable findings for tendon regeneration. A non-invasive image method that can effectively evaluate the quality of the scar tissue has not yet been employed.

Methods

Thirteen New Zealand rabbits were divided into two groups: group 1—non-treated control (n = 4); group 2—surgical intervention (n = 9). The central portion of the Achilles tendon was resected, and after 30 days, DCE-MRI was performed. Contrast enhancement methods were applied using the region of interest (ROI) technique. In the medium third of the Achilles tendon, the intra-substantial signal intensity and the presence of hyper-intense intra-tendon focus points and of signal heterogeneity were evaluated. Antero-posterior and transversal diameters of the tendon were measured. The Achilles tendon was removed and dissected free from other tissues. Sections from the central part of the tendon were stained for histological analysis.

Results

The difference between the contrast enhancement curves of the control and surgical groups (p < 0.0001) was observed. The surgical group had an intense contrast enhancement in the contrast sequences, enlargement of the diameter and intra-substantial signal intensity alteration, with hyper-signal focus points and widening of the tendon sheath, which presented irregular contours and intense contrast enhancement. On histology, the Achilles tendon presented diffuse widening of the tendon sheath and wedge-shaped areas with scarring tissue rich in disordered collagen fibres. These findings were related to alteration in the intra-substantial signal intensity, with hyper-signal focus points in the DCE-MRI.

Conclusions

MRI with perfusion could be a useful technique for evaluating tissue and fibrous scarring in tendons.

Simple suture and anchor in rabbit hips

Objective

Using biomechanical studies, this research aims to compare hip capsulorrhaphy in rabbits, carried out with two different techniques: capsulorrhaphy with simple sutures and with anchors.

Method

Thirteen New Zealand Albino (Oryctolaguscuniculus) male rabbits, twenty-six hip joints, were used. First, a pilot project was performed with three rabbits (six hip joints). This experiment consisted of ten rabbits divided into two groups: group 1 underwent capsulorrhaphy on both right and left hips with simple suture using polyglycolic acid absorbable thread, and group 2 underwent capsulorrhaphy with titanium anchors. After a four-week postoperative period, the animals were euthanized and the hip joints were frozen. On the same day of the biomechanical studies, after the hip joints were previously unfrozen, the following parameters were evaluated: rigidity, maximum force, maximum deformity and energy.

Results

There was no relevant statistical difference in rigidity, maximum force, maximum deformity and energy between the simple suture and anchor groups.

Conclusion

Through biomechanical analyses, using parameters of rigidity, maximum force, maximum deformity and energy, it has been shown that capsulorrhaphy with simple suture and with anchors has similar results in rabbit hip joints. Level of Evidence II, Prospective Comparative Study.

Biomechanical properties of Achilles tendon repair augmented with a bioadhesive-coated scaffold

The Achilles tendon is the most frequently ruptured tendon. Both acute and chronic (neglected) tendon ruptures can dramatically affect a patient's quality of life, and require a prolonged period of recovery before return to pre-injury activity levels. This paper describes the use of an adhesive-coated biologic scaffold to augment primary suture repair of transected Achilles tendons. The adhesive portion consisted of a synthetic mimic of mussel adhesive proteins that can adhere to various surfaces in a wet environment, including biologic tissues. When combined with biologic scaffolds such as bovine pericardium or porcine dermal tissues, these adhesive constructs demonstrated lap shear adhesive strengths significantly greater than that of fibrin glue, while reaching up to 60% of the strength of a cyanoacrylate-based adhesive. These adhesive constructs were wrapped around transected cadaveric porcine Achilles tendons repaired with a combination of parallel and three-loop suture patterns. Tensile mechanical testing of the augmented repairs exhibited significantly higher stiffness (22-34%), failure load (24-44%), and energy to failure (27-63%) when compared to control tendons with suture repair alone. Potential clinical implications of this novel adhesive biomaterial are discussed.

Biomechanical evaluation on tendon reinsertion by comparing trans-osseous suture and suture anchor at different stages of healing: experimental study on rabbits

BACKGROUND

Through an experimental biomechanical study on rabbits, tendon reinsertion by means of trans-osseous suture on a spongy bone bed and suture anchor were evaluated comparatively at different phases of healing.

METHODS

Twenty-four New Zealand White rabbits were used: 2 as pilots, 4 as the control group, and 18 as the experimental group. These 18 animals underwent sectioning and reinsertion of the Achilles tendon bilaterally, using the technique of trans-osseous suture on 1 side and suture anchor on the other. All the pelvic limbs that underwent the procedure were then immobilized for 3 weeks. The experimental group was divided into 3 groups that were sacrificed, respectively, 3, 6, and 12 weeks later. The tendon-bone complex was subjected to biomechanical tests to evaluate the parameters of maximum strength, stiffness, and yield strength.

RESULTS

There was no statistically significant difference between the suture anchor group and the trans-osseous suture group, in relation to yield strength (3 weeks, P = .222; 6 weeks, P = .465; and 12 weeks, P = .200) or maximum strength (3 weeks, P = .222; 6 weeks, P = .076; and 12 weeks, P = .078). In relation to stiffness, the suture anchor group showed a statistically significant difference only at 3 weeks of healing (P = .032) over the trans-osseous suture group.

CONCLUSION

The technique of suturing with an anchor was shown to be similar to the technique of trans-osseous suture for the studied parameters.

Restoration of strength despite low stress and abnormal imaging after Achilles injury

PURPOSE

To determine the usefulness of clinical imaging in predicting the mechanical properties of rabbit Achilles tendons after acute injury.

METHODS

We created a 2 x 7-mm full-thickness central tendon defect in one Achilles tendon of healthy rabbits. Rabbits in groups of 10 were killed immediately and 4 and 8 wk after surgery (n = 30). We then performed magnetic resonance (MR) imaging, ultrasonography (US), bone mineral densitometry (BMD), and mechanical testing to failure using a dual-cryofixation assembly on experimental and contralateral tendons. The main outcome measures included tendon dimensions, optical density (OD) of T1-weighted, proton density (PD), and T2-weighted MR sequences, US focal abnormalities, BMD of the calcaneus, and stress and peak load to failure.

RESULTS

On MR imaging and US, all dimensions of the injured tendons after 2 wk and more were greater than those of the contralateral tendons (P < 0.05). The mean T1-weighted OD was greater at 4 wk (256 +/- 53) and 8 wk (184 +/- 24) than immediately after surgery (149 +/- 15). Mechanical stress was markedly lower in the experimental than in the contralateral tendons at both 4 wk (39 +/- 9 vs 77 +/- 16 N x mm(-2)) and 8 wk (58 +/- 6 vs 94 +/- 26 N x mm(-2); P < 0.05). Mean peak load to failure was significantly lower immediately after surgery (332 +/- 128 N) than at 4 and 8 wk (712 +/- 106 and 836 +/- 90 N, respectively). Both high T1-weighted OD (r = -0.73) and PD OD (r = -0.69) correlated with lower mechanical stress (P < 0.05). In the experimental tendons, higher T1-weighted OD correlated with lower peak load (r = -0.46; P < 0.05).

CONCLUSIONS

Normal peak loads 4 wk after injury were withstood by an enlarged tendon of lower stress. These findings support progressive physical loading 4 wk after an Achilles tendon injury. T1-weighted OD constituted a marker of tendon mechanical recovery.

Achilles tendon suture deteriorates tendon capillary blood flow with sustained tissue oxygen saturation - an animal study

BACKGROUND

Treatment of ruptured Achilles tendons currently constitutes of conservative early functional treatment or surgical treatment either by open or minimal invasive techniques. We hypothesize that an experimental Achilles tendon suture in an animal model significantly deteriorates Achilles tendon microcirculation immediately following suturing.

METHODS

Fifteen Achilles tendons of eight male Wistar rats (275-325 g) were included. After preparation of the Achilles tendon with a medial paratendinous approach, Achilles tendon microcirculation was assessed using combined Laser-Doppler and spectrophotometry (Oxygen-to-see) regarding:- tendinous capillary blood flow [arbitrary units AU]- tendinous tissue oxygen saturation [%]- tendinous venous filling pressure [rAU]The main body of the Achilles tendon was measured in the center of the suture with 50 Hz. 10 minutes after Achilles tendon suture (6-0 Prolene), a second assessment of microcirculatory parameters was performed.

RESULTS

Achilles tendon capillary blood flow decreased by 57% following the suture (70 +/- 30 AU vs. 31 +/- 16 AU; p < 0.001). Tendinous tissue oxygen saturation remained at the same level before and after suture (78 +/- 17% vs. 77 +/- 22%; p = 0.904). Tendinous venous filling pressure increased by 33% (54 +/- 16 AU vs. 72 +/- 20 AU; p = 0.019) after suture.

CONCLUSION

Achilles tendon suture in anaesthetised rats causes an acute loss of capillary perfusion and increases postcapillary venous filling pressures indicating venous stasis. The primary hypothesis of this study was confirmed. In contrast, tendinous tissue oxygen saturation remains unchanged excluding acute intratendinous hypoxia within the first 10 minutes after suture. Further changes of oxygen saturation remain unclear. Furthermore, it remains to be determined to what extent reduced capillary blood flow as well as increased postcapillary stasis might influence tendon healing from a microcirculatory point of view in this animal setting.

Treatment of acute Achilles tendon rupture: fibrin glue versus fibrin glue augmented with the plantaris longus tendon

In the surgical repair of Achilles tendon ruptures, suturing is standard, although fibrin glue also has been used for repair since the 1980s. Augmentation with the plantaris longus tendon is also a popular technique; however, no study has yet compared the outcome of augmented versus only glued repair of ruptured Achilles tendons. This study compares the long-term results of surgical repair of Achilles tendon rupture with fibrin glue versus fibrin glue augmented with the plantaris longus tendon. Forty patients who had undergone Achilles tendon repair with fibrin glue took part in a follow-up examination after an average of 11.5 years. The fibrin group consisted of 16 patients and the fibrin glue augmented with plantaris longus tendon group consisted of 15 patients. The modified Thermann score (adapted from Weber) and results of an isokinetic force measurement were the same in both groups, whereas complications in the 2 groups also did not differ. We conclude that augmentation with the plantaris longus tendon is not necessary when operatively treating acute ruptured Achilles tendons with fibrin glue.

LEVEL OF CLINICAL EVIDENCE

2.

Long-term results after operatively treated Achilles tendon rupture: fibrin glue versus suture

The use of fibrin glue for repairing Achilles tendon ruptures was introduced in the 1980s. Although fibrin glue has been in regular use since that time, suturing remains the standard for surgical repair. Studies have indicated that, in the short term, fibrin glue is as effective as suturing. To date, there have been no long-term studies comparing the outcomes of these 2 techniques. This study compares the long-term results of surgical repair of Achilles tendon rupture with sutures versus fibrin glue. Forty-two patients who had undergone Achilles tendon repair with either suture or fibrin glue took part in a follow-up examination after an average of 12.1 years. The fibrin group consisted of 31 patients and the suture group consisted of 11 patients. Patients treated with fibrin glue reached a higher modified Thermann score (adapted from Weber), achieved equal results in an isokinetic force measurement, and showed fewer complications. The authors concluded that the use of fibrin glue for the repair of ruptured Achilles tendon is a suitable alternative to traditional sutures.

LEVEL OF CLINICAL EVIDENCE

2.

Static and dynamic biomechanical properties of the regenerating rabbit Achilles tendon

BACKGROUND

Since tendons show viscoelastic behavior, dynamic viscoelastic properties should be assessed in addition to static biomechanical properties. We evaluated differences between static and dynamic biomechanical properties of the regenerating rabbit Achilles tendon following tenotomy.

METHODS

At 3, 6, or 12 weeks after right Achilles tenotomy, the right (regenerating) and left (control) tendons were collected with the calcaneus from 49 rabbits. A unidirectional failure test and a dynamic viscoelastic test were conducted.

FINDINGS

Tensile strength and Young's modulus (static biomechanical properties) in the regenerating group at Week 6 were significantly greater than at Week 3, while at Week 12, these were significantly greater than at Week 6. However, even at Week 12, both parameters were less than in the control group. The value of tan delta represents dynamic viscoelasticity, a smaller tan delta indicates greater elasticity. tan delta for the regenerating group was significantly greater than for the control group at Week 3, but regenerating and control groups did not significantly differ at Week 6. No marked change was seen from Weeks 6 to 12 in the regenerating group, and no significant difference in tan delta was evident between the regenerating and control groups at Week 12.

INTERPRETATION

Dynamic biomechanical properties of regenerating rabbit Achilles tendons may improve more rapidly than static biomechanical properties. Ability to tolerate dynamic movement in the healing Achilles tendon may improve more rapidly than ability to withstand static stresses.

Mechanical alterations of rabbit Achilles' tendon after immobilization correlate with bone mineral density but not with magnetic resonance or ultrasound imaging

OBJECTIVE

To assess the usefulness of magnetic resonance imaging (MRI), ultrasound (US) imaging, or bone mineral density (BMD) in predicting the mechanical properties of immobilized rabbit Achilles' tendons.

DESIGN

Experimental study.

SETTING

Basic university laboratory.

ANIMALS

Twenty-eight rabbits.

INTERVENTIONS

Twelve rabbits had 1 hindlimb casted for 4 weeks and 10 rabbits were casted for 8 weeks. Contralateral legs and 12 normal hindlimbs served as controls.

MAIN OUTCOME MEASURES

Achilles' tendon dimensions on MRI and US, T1- and T2-signal intensities on MRI, classification of abnormalities on MRI and US; BMD of the calcaneus with dual-energy x-ray absorptiometry. Biomechanic measures consisted of peak load, stiffness, and stress. Imaging variables were correlated with biomechanic alterations.

RESULTS

Immobilized Achilles' tendons were weaker and showed decreased mechanical stress compared with their contralateral legs and controls (all P<.05). MRI and US revealed larger Achilles' tendons after immobilization. However, neither increased MRI nor US signal abnormality was found. BMD was lower in immobilized calcanei and larger in contralateral legs than controls. Only BMD correlated with both the decreased peak load (R2=.42, P<.05) and stress (R2=.54, P<.05) of immobilized Achilles' tendon.

CONCLUSIONS

This study established weakened mechanical properties of immobilized Achilles' tendons. BMD of the calcaneus, but not MRI and US, was predictive of the mechanical alterations in immobilized Achilles' tendons. BMD may be a useful biomarker to monitor disease and recovery in Achilles' tendons.

Arthroscopically assisted percutaneous repair of fresh closed achilles tendon rupture by Kessler's suture

BACKGROUND

Achilles tendon ruptures are difficult to repair, and the healing rate is low due to this structure's anatomic and physiological characteristics. It is essential to develop new techniques to increase the healing rate and decrease the rate of complications.

OBJECTIVE

To propose and evaluate a new percutaneous method of repairing fresh closed Achilles tendon ruptures by Kessler's suture under arthroscopy.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Twenty patients were followed at least 12 months in this study. First, the torn ends of the Achilles tendon were debrided during arthroscopy. Then percutaneous repair of the Achilles tendon was performed using Kessler's suture by an inside-out technique. All cases were followed up for an average range of 21 months (range, 12-36 months). All patients were evaluated by clinical examination, magnetic resonance imaging, and the Lindholm scale.

RESULTS

The torn ends were well aligned and sutured after the debridement under arthroscopy. According to the Lindholm scale, excellent results were seen in 15 cases and good in 5 cases. No patients had complications such as nerve injury, infection, or re-rupture at follow-up. Magnetic resonance imaging results showed that the ruptured Achilles tendons were repaired and remodeled very well in all patients.

CONCLUSION

The present method is an effective surgical technique for repair of a closed rupture of the Achilles tendon. The short-term follow-up results were good, and recovery time was short. Few complications were found in our study cases.

The Effects of Substance P on the Biomechanic Properties of Ruptured Rat Achilles’ Tendon

OBJECTIVE

To determine whether injection of substance P into the paratendinous region of a ruptured and subsequently sutured rat Achilles' tendon alters the biomechanic properties of the tendon.

DESIGN

Interventional animal study.

SETTING

Animal laboratory at a university hospital.

ANIMALS

Ninety-six 2-month-old, male Sprague-Dawley rats.

INTERVENTION

Injection of saline, substance P (10(-6)micromol/kg of body weight [BW] or 10(-8)micromol/kg BW) associated with neutral endopeptidase inhibitors, or neutral endopeptidase inhibitors alone into the paratendinous region of ruptured and subsequently sutured rat Achilles' tendons from the second until the sixth day postoperatively.

MAIN OUTCOME MEASURES

Stress at maximal load and work to maximal load and stiffness.

RESULTS

Stress at maximal load was higher in the groups injected with substance P than in the saline group in the first, second, and sixth weeks. Work to maximal load was higher from the second until the sixth weeks in the substance P-treated groups than in the saline group. Stiffness did not differ between the 4 groups in any of the weeks.

CONCLUSIONS

Injection of substance P into the paratendinous region of ruptured and subsequently sutured rat Achilles' tendons improved tendon healing by enhancing stress at maximal load and work to maximal load. However, stiffness was not significantly affected.

Suture holding capacity of the Achilles tendon during the healing period: an in vivo experimental study in rabbits

BACKGROUND

Early motion and weightbearing is known to promote the healing of Achilles tendon repair. It is important to be informed about the repair strength for a secure rehabilitation. There are reports about the initial repair strength of Achilles tendons; however, they are mainly in vitro studies that represent the time zero strength of the repair. Softening of the tendon observed during the biological process of the tendon healing, which may effect the suture holding capacity and in turn the repair strength of the tendon has not been evaluated before.

METHODS

In the current study, the suture holding capacity of rabbit Achilles tendon was observed at various times during the healing period.

RESULTS

The suture holding capacity of the tendon at the end of the first and third weeks after surgery was found to be similar within 30% of the control tendon. However, at the end of the fourth week it was doubled reaching 65% of the control tendon.

CONCLUSIONS

Intrinsic tendon insufficiency which causes a decrease in the suture holding capacity of the tendon may lead to pull-out of the suture material during the postoperative third week. This period is precarious for early motion and weightbearing since the suture holding capacity of the tendon doubled relative to the previous three weeks.

Biomechanical and histologic comparison of Achilles tendon ruptures reinforced with intratendinous and peritendinous plantaris tendon grafts in rabbits: an experimental study

INTRODUCTION

We hypothesized that the closer the reinforcing graft was to the repair zone, the more strength the healed tendon would achieved. Therefore, we compared the ruptured rabbit Achilles tendons reinforced with intratendinous and peritendinous plantaris grafts.

MATERIALS AND METHODS

The experimental study was performed on Achilles tendons of 20 rabbits. First, they were divided into two groups: group I (n=10) underwent intratendinous graft and end-to-end tenorraphy, and group P (n=10) were repaired end-to-end and then reinforced with a peritendinous plantaris graft. An above-knee cast was applied during 6 weeks postoperatively. The two groups were compared to each other biomechanically and histologically. Seven randomly selected rabbits from each group were used for biomechanical evaluation. The remaining six rabbits (three from each group) were used for histologic comparison. Non-operated sides (n=20) served as the control group.

RESULTS

The mean maximum load at rupture of the repaired and control groups was 159.9+/-31 N, 83+/-7.5 N, and 207.5+/-35 N for group I, group P, and the control group, respectively. Values between groups were significantly different considering maximum load and absorbed energy to rupture. There was no significant difference between groups I and P in respect to strain. Control group tendons (groups I-C and P-C) had significantly more lengthening capability than operated tendons. Macroscopically, group I tendons were thicker and stiffer than group P tendons. Histologically, differences between the group I and group P specimens revealed that the healing process was faster in tendons augmented intratendinously.

CONCLUSIONS

In reinforcing Achilles tendon repair, the site of the tendon graft affected the result. When the graft was used intratendinously, the healed tendon was more similar biomechanically to normal tendon and had more graft-tendon orientation histologically than the tendon augmented peritendinously.

Nonoperative treatment of acute rupture of the achilles tendon: results of a new protocol and comparison with operative treatment

BACKGROUND

Excellent results are reported from both nonoperative and operative treatment of Achilles tendon rupture.

PURPOSE

To describe a new nonoperative treatment protocol for Achilles tendon ruptures and compare outcomes with operative treatment.

STUDY DESIGN

Retrospective cohort study.

METHODS

We treated 23 patients nonoperatively with an equinus ankle cast and boot and compared their outcome with that of a group of 24 patients previously treated operatively. Muscle strengthening and walking with full weightbearing were started as soon as tolerated in both groups. Follow-up examinations were performed for 18 nonoperatively treated patients after 23 months and for 15 operatively treated patients after 49 months.

RESULTS

Subsidence of pain, return to unaided walking, and return to work was faster in the nonoperatively treated group. Patient satisfaction, return to sports, and ultimate strength was the same for both groups. The complication rate was similar, except for reruptures: four early in the nonoperative group and one late in the operative group. Two types of reruptures occurred in the nonoperative group: 1). normally healing tendon subjected to new trauma, rerupturing in the healing zone, and achieving a good result with continued nonoperative treatment; and 2). tendon failing proximal to the initial rupture at the muscle-tendon junction, without trauma, requiring operative repair and augmentation.

CONCLUSIONS

Results of operative and nonoperative treatment were equivalent.