Alterations of tendons in patients with diabetes mellitus: a systematic review

Disturbed glycolipid metabolism activates CXCL13-CXCR5 axis in senescent TSCs to promote heterotopic ossification

Heterotopic ossification (HO) occurs as a common complication after injury, while its risk factor and mechanism remain unclear, which restricts the development of pharmacological treatment. Clinical research suggests that diabetes mellitus (DM) patients are prone to developing HO in the tendon, but solid evidence and mechanical research are still needed. Here, we combined the clinical samples and the DM mice model to identify that disordered glycolipid metabolism aggravates the senescence of tendon-derived stem cells (TSCs) and promotes osteogenic differentiation. Then, combining the RNA-seq results of the aging tendon, we detected the abnormally activated autocrine CXCL13-CXCR5 axis in TSCs cultured in a high fat, high glucose (HFHG) environment and also in the aged tendon. Genetic inhibition of CXCL13 successfully alleviated HO formation in DM mice, providing a potential therapeutic target for suppressing HO formation in DM patients after trauma or surgery.

Ultrasound Evaluation of Achilles Tendon Thickness in Diabetic Patients With and Without Foot Complications

Introduction Diabetes mellitus (DM) is a multifaceted metabolic disorder distinguished by elevated blood sugar levels. Type 2-DM (T2DM) stands as a significant contributor to disability due to its widespread occurrence of microvascular and macrovascular complications. According to certain researchers, prolonged elevated blood sugar levels have been observed to trigger a sequence of irregular alterations in the Achilles tendon (AT). AT thickness is one such indicator of these alterations. Methods This was a prospective study carried out on 51 individuals which was further divided into 3 groups (Group A - Normal individuals, Group B - DM without foot complications, Group C - DM with foot complications) with 17 individuals in each as healthy, DM with foot complications and without complications at Sri Devaraj Urs Medical College over a period of one year. The patients' demographics, basic medical records, and laboratory test results were examined and analyzed. Results The mean age of the study participants was 55.41 + 10.25 years. There was no significant difference in age and gender between the three groups. There was a significant difference in mean AT thickness between the groups (p<0.05). The mean thickness of AT was higher in Group C compared to Group B. Group A had the least AT thickness. However, there was no correlation between the variables in individual groups. Conclusions Modifications in the AT's structure may occur before the onset of foot and ankle issues in individuals with diabetes. Hence, the thickening of the AT can be used as an early indicator of impending diabetic foot complications.

Psychological factors show limited association with the severity of Achilles tendinopathy

BACKGROUND

This study aimed to investigate the association between psychosocial factors and the severity of Achilles tendinopathy, along with exploring their potential link to the pain's duration.

METHODS

A cross-sectional study involving 111 individuals with Achilles tendon pain was conducted.

METHODS

A cross-sectional study involving 111 individuals with Achilles tendon pain was conducted. Various psychological factors were assessed using the Pain Catastrophizing Scale, Chronic Pain Self-Efficacy Scale (CPSS), Tampa Scale for Kinesiophobia, and Hospital Anxiety and Depression Scale (HAD). Additionally, the severity of Achilles tendon pain was evaluated using the Victorian Institute of Sport Assessment-Achilles questionnaire (VISA-A-Br). Regression analyses were employed to determine the association of these psychosocial factors with pain severity and duration.

RESULTS

Self-efficacy for chronic pain showed a slight association with Achilles tendon pain severity (β = 0.42 [95% CI: 0.06 to 0.16], p = 0.001), explaining only 19% of the dependent variable. The other variables, including anxiety, depression, pain catastrophizing, and fear of movement, did not exhibit significant associations.

CONCLUSION

The study suggests that psychological factors demonstrate limited association with the severity of Achilles tendinopathy. While self-efficacy for chronic pain was weakly associated, its clinical relevance remains uncertain. Future research, particularly longitudinal studies, should explore the influence of psychosocial factors on treatment adherence and response to enhance management strategies for Achilles tendon pain.

Fibrocartilaginous Tissue: Why Does It Fail to Heal?

Tendons and ligaments are critical components in the function of the musculoskeletal system, as they provide stability and guide motion for the biomechanical transmission of forces into bone. Several common injuries in the foot and ankle require the repair of ruptured or attenuated tendon or ligament to its osseous insertion. Understanding the structure and function of injured ligaments and tendons is complicated by the variability and unpredictable nature of their healing. The healing process at the tendon/ligament to bone interface is challenging and often frustrating to foot and ankle surgeons, as they have a high failure rate necessitating the need for revision.

Insertional Calcific Tendinopathy of the Achilles Tendon and Dysmetabolic Diseases: An Epidemiological Survey

OBJECTIVE

This study reports the incidence of insertional calcific tendinopathy (ICT) of the Achilles tendon in the general population and the percentage of symptomatic patients. The secondary aim is to ascertain whether ICT is associated with diabetes mellitus, thyroid disorders, obesity, and hypercholesterolemia. We hypothesized that metabolic diseases increase the risk of ICT of the Achilles tendon.

DESIGN

Prospective observational study (level III study).

SETTING

Orthopedic Outpatients Clinic and Emergency Department of Tor Vergata University Hospital, Rome, Italy.

PARTICIPANTS

Four hundred thirty-three subjects who met the inclusion criteria.

INTERVENTION METHODS

We collected the plain radiographs of the foot and ankle of patients who attended the hospital. Personal data were recorded [age, sex, and body mass index (BMI)], and comorbidities investigated (diabetes mellitus, hypothyroidism, hyperthyroidism, obesity, and hypercholesterolemia). Multivariate regression analyses were performed to study the predictors of the occurrence of Achilles ICT.

RESULTS

A total of 101 patients (23.3%) showed radiographic evidence of ICT, and 3% (13 patients) were symptomatic. Age [odds ratio (OR) 1.05], diabetes (OR 2.95), hypercholesterolemia (OR 2.27), and hypothyroidism (OR 3.32) were significantly associated with the presence of ICT of the Achilles tendon. Independent predictors of ICT were age, diabetes, hypercholesterolemia, and hypothyroidism. A BMI >30 was associated with a higher incidence of calcifications, and patients with 2 or more comorbidities had more than 10 times higher risk to develop ICT.

CONCLUSION

Insertional calcific tendinopathy of the Achilles tendon is common, but few patients are symptomatic. The incidence of ICT increases with age and is significantly higher in patients with diabetes mellitus and hypothyroidism.

Irregularity in Plantar Fascia, Muscle Edema and Tendon Thickness in Patients with High-Risk for Diabetic Foot

AIM

To investigate the alterations in the plantar fascia (PF), intrinsic muscles, and tendons in the feet of patients at high risk for developing diabetic foot.

METHODS

The healthy feet of 22 patients with type 2 diabetes, who had developed diabetic foot ulcers on a single foot without any pathology on the contralateral extremity, and those of 22 healthy volunteers were evaluated by magnetic resonance imaging. The volume of the Achilles tendon (AT), the surface area of the PF, the thickness of AT, flexor hallucis longus, flexor digitorum longus, tibialis posterior, and peroneus longus tendons, irregularity in the PF, and edema of intrinsic foot muscles were examined.

RESULTS

Nineteen patients (86%) had irregularity in the PF, whereas none of the healthy controls had any (p<0.001). Intrinsic muscle edema was more common in the group with diabetes (p=0.006). The volume of AT and the surface area of PF were decreased in patients with peripheral arterial disease (PAD) (p<0.05). Patients with diabetes mellitus but without PAD had a larger surface area of PF than that of controls (p<0.05). There were no differences in the volume of AT, the surface area of the PF, and other tendon thickness between the groups.

CONCLUSION

Irregularity in the PF and muscle edema may indicate a high risk for the diabetic foot. The presence of PAD may lead to regression in the structure of AT and PF.

Advanced glycation end productions and tendon stem/progenitor cells in pathogenesis of diabetic tendinopathy

Tendinopathy is a challenging complication observed in patients with diabetes mellitus. Tendinopathy usually leads to chronic pain, limited joint motion, and even ruptured tendons. Imaging and histological analyses have revealed pathological changes in various tendons of patients with diabetes, including disorganized arrangement of collagen fibers, microtears, calcium nodules, and advanced glycation end product (AGE) deposition. Tendon-derived stem/ progenitor cells (TSPCs) were found to maintain hemostasis and to participate in the reversal of tendinopathy. We also discovered the aberrant osteochondrogenesis of TSPCs in vitro. However, the relationship between AGEs and TSPCs in diabetic tendinopathy and the underlying mechanism remain unclear. In this review, we summarize the current findings in this field and hypothesize that AGEs could alter the properties of tendons in patients with diabetes by regulating the proliferation and differentiation of TSPCs in vivo.

Clinical results of arthroscopic rotator cuff repair in diabetic and non-diabetic patients

BACKGROUND

Although the clinical outcomes of arthroscopic rotator cuff repair (ARCR) have been reported, few studies have focused on diabetic patients. We investigated and compared the clinical results of ARCR in patients with and without diabetes.

METHODS

This retrospective study involved 195 consecutive patients who underwent ARCR from 2015 to 2018 in our hospital. Twenty-seven and 168 shoulders were assigned to diabetes and non-diabetes groups, respectively. Diabetic patients with poor control were preoperatively hospitalized for perioperative diabetic control. We evaluated range of motion (ROM), Japanese Orthopaedic Association shoulder (JOA) score, Constant Shoulder Score, and University of California, Los Angeles (UCLA) score preoperatively and at 6 months and 1 year post-ARCR. Rates of rotator cuff retear 1 year post-ARCR and preoperative and postoperative stiff shoulder were also evaluated. We compared the results between groups and analyzed them statistically. A p-value of <0.05 was considered statistically significant.

RESULTS

Preoperative ROM, JOA score, Constant Shoulder Score and UCLA scores showed significant improvement at post-ARCR in both groups (p < 0.05). On comparing the groups, although preoperative JOA score and Constant Shoulder Score were significantly lower in diabetes group than in non-diabetes group (diabetic/non-diabetic group; 60.0/65.3 for JOA score; p = 0.003, 59.7/64.2 for Constant Shoulder Score; p = 0.003), there was no significant difference postoperatively (6 months post-ARCR; 88.0/89.7 for JOA score; p = 0.783, 88.1/88.6 for Constant Shoulder Score; p = 0.597, 1 year post-ARCR; 96.7/95.4 for JOA score; p = 0.238, 96.6/95.4 for Constant Shoulder Score; p = 0.248). Furthermore, preoperative and postoperative stiff shoulder and retear rates were not significantly different between groups (p = 0.152, p = 0.344, p = 0.347, and p = 0.563, respectively).

CONCLUSION

Diabetic patients showed comparable clinical results with non-diabetic patients post-ARCR. Perioperative diabetic control may be recommended for preoperatively uncontrolled diabetic patients.

Nesfatin-1 Promotes the Osteogenic Differentiation of Tendon-Derived Stem Cells and the Pathogenesis of Heterotopic Ossification in Rat Tendons via the mTOR Pathway

Heterotopic ossification (HO) is a pathological condition involved in tendinopathy. Adipokines are known to play a key role in HO of tendinopathy. Nesfatin-1, an 82-amino acid adipokine is closely reportedly associated with diabetes mellitus (DM), which, in turn, is closely related to tendinopathy. In the present study, we aimed to investigate the effects of nesfatin-1 on the osteogenic differentiation of tendon-derived stem cells (TDSCs) and the pathogenesis of tendinopathy in rats. In vitro, TDSCs were incubated in osteogenic induction medium for 14 days with different nesfatin-1 concentration. In vivo, Sprague Dawley rats underwent Achilles tenotomy to evaluate the effect of nesfatin-1 on tendinopathy. Our results showed that the expression of nesfatin-1 expression in tendinopathy patients was significantly higher than that in healthy subjects. Nesfatin-1 affected the cytoskeleton and reduced the migration ability of TDSCs in vitro. Furthermore, nesfatin-1 inhibited the expression of Scx, Mkx, and Tnmd and promoted the expression of osteogenic genes, such as COL1a1, ALP, and RUNX2; these results suggested that nesfatin-1 inhibits cell migration, adversely impacts tendon phenotype, promotes osteogenic differentiation of TDSCs and the pathogenesis of HO in rat tendons. Moreover, we observed that nesfatin-1 suppressed autophagy and activated the mammalian target of rapamycin (mTOR) pathway both in vitro and in vivo. The suppression of the mTOR pathway alleviated nesfatin-1-induced HO development in rat tendons. Thus, nesfatin-1 promotes the osteogenic differentiation of TDSC and the pathogenesis of HO in rat tendons via the mTOR pathway; these findings highlight a new potential therapeutic target for tendinopathy.

Management of Achilles and patellar tendinopathy: what we know, what we can do

Tendinopathies are challenging conditions frequent in athletes and in middle-aged overweight patients with no history of increased physical activity. The term “tendinopathy” refers to a clinical condition characterised by pain, swelling, and functional limitations of tendons and nearby structures, the effect of chronic failure of healing response. Tendinopathies give rise to significant morbidity, and, at present, only limited scientifically proven management modalities exist. Achilles and patellar tendons are among the most vulnerable tendons, and among the most frequent lower extremity overuse injuries. Achilles and patellar tendinopathies can be managed primarily conservatively, obtaining good results and clinical outcomes, but, when this approach fails, surgery should be considered. Several surgical procedures have been described for both conditions, and, if performed well, they lead to a relatively high rate of success with few complications. The purpose of this narrative review is to critically examine the recent available scientific literature to provide evidence-based opinions on these two common and troublesome conditions.

Clinical and Structural Outcomes After Rotator Cuff Repair in Patients With Diabetes: A Meta-analysis

Background:

The impact of diabetes on clinical and structural outcomes after rotator cuff repair remains controversial.

Purpose/Hypothesis:

The purpose of this study was to compare clinical outcomes and retear rates after rotator cuff repair in patients with and without diabetes. Our hypotheses were that adequate control of diabetes would decrease the retear rate after rotator cuff repair and that patients with diabetes would have worse clinical outcomes.

Study Design:

Systematic review; Level of evidence, 3.

Methods:

The PubMed, Embase, and Cochrane Library databases were searched for studies comparing outcomes in patients with and without diabetes after full-thickness rotator cuff repair. Clinical outcome analysis included the Constant score, the American Shoulder and Elbow Surgeons (ASES) score, and the University of California–Los Angeles shoulder rating scale; we compared preoperative, postoperative, and change in functional scores from baseline to final follow-up among the included studies. The pooled relative risk was calculated using a random-effects model for retear rates. Clinical outcomes were also pooled using a random-effects model.

Results:

Overall, 10 studies were included. Compared with patients without diabetes, patients with diabetes had a worse preoperative ASES score (P = .009) as well as worse postoperative Constant score (final follow-up range, 9-103 months; P = .0003). However, there was no significant difference in the absolute mean change in clinical outcomes between patients with and without diabetes. Diabetes was associated with a higher retear rate (19.3% in patients without diabetes vs 28.2% in patients with diabetes; P < .0001). The retear rate according to the severity of sustained hyperglycemia in the subgroup analysis was 14.6% in patients without diabetes, versus 22.7% in patients with well-controlled diabetes (<7.0% of preoperative serum HbA1c level; P = .12) and 40.0% in patients with uncontrolled diabetes (HbA1c level ≥7.0%; P < .00001).

Conclusion:

This meta-analysis suggests that diabetes mellitus is associated with an increased risk of retears after rotator cuff repair, and improved blood glucose control may reduce the risk of retears in patients with diabetes mellitus. Although effective glycemic control was associated with a decreased risk of retears in patients with diabetes, we could not prove causation because of potential bias and confounding in the included studies.

Diabetes and Collagen: Interrelations

This review summarizes information on interrelations between diabetes development and collagen metabolism and structure. The growing global problem of diabetes requires the search for new strategies of its complications correction. Among them collagen structure violations and/or its impaired metabolism most often lead to profound disability. Even after several decades of intense studies, pathophysiological mechanisms underlying collagen changes in diabetes mellitus are still not well clear. The main complication is that not only diabetes cause changes in collagen metabolism and structure. Collagens via some mechanisms also may regulate glucose homeostasis, both directly and indirectly. The author also presented the results of own studies on bone and skin type I collagen amino acid composition changes with diabetes. Deepening our understanding of collagen metabolism and diabetes interrelations allows us to optimize approaches to overcome the collagen-mediated consequences of this disease. Recently, it has been clearly demonstrated that use of only antidiabetic agents cannot fully correct such violations. Preparations on the base of flavonoids, collagens and amino acids could be considered as perspective directions in this area of drug development.

Insulin Enhances the In Vitro Osteogenic Capacity of Flexor Tendon-Derived Progenitor Cells

There is increased incidence of tendon disorders and decreased tendon healing capacity in people with diabetes mellitus (DM). Recent studies have also suggested pathological ossification in repair tendon of people with DM. Therefore, the objective of this study is to investigate the effects of insulin supplementation, an important pathophysiologic stimulus of DM, on tendon progenitor cell (TPC) proliferation and in vitro osteogenic capacity. Passage 3 TPCs were isolated from collagenase-digested, equine superficial digital flexor tendons. TPC proliferation was measured via MTT assay after 3 days of monolayer culture in medium supplemented with 0, 0.007, 0.07, and 0.7 nM insulin. In vitro osteogenic capacity of TPCs (Alizarin Red staining, osteogenic mRNA expression, and alkaline phosphatase bioactivity) was assessed with 0, 0.07, and 0.7 nM insulin-supplemented osteogenic induction medium. Insulin (0.7 nM) significantly increased TPC proliferation after 3 days of monolayer culture. Alizarin Red staining of insulin-treated TPC osteogenic cultures demonstrated robust cell aggregation and mineralized matrix secretion, in a dose-dependent manner. Runx2, alkaline phosphatase, and Osteonectin mRNA and alkaline phosphatase bioactivity of insulin-treated TPC cultures were significantly higher at day 14 of osteogenesis compared to untreated controls. Addition of picropodophyllin (PPP), a selective IGF-I receptor inhibitor, mitigated the increased osteogenic capacity of TPCs, indicating that IGF-I signaling plays an important role. Our findings indicate that hyperinsulinemia may alter TPC phenotype and subsequently impact the quality of repair tendon tissue.

Exercise therapy in the treatment of tendinopathies of the lower limbs: a protocol of a systematic review

BACKGROUND

Tendinopathies are specific degenerative conditions of the tendon characterized by pain and disability. The most common tendinopathies of the lower limbs are patellar, Achilles, gluteal, and proximal tendinopathy of the hamstring muscles. Exercise therapy has been studied for the treatment of these tendinopathies; however, different types of muscle contraction, exercise, dose, and intensity are found in the literature, which can make choosing the best treatment option difficult. The purpose of this systematic review is to analyze the available evidence about the effectiveness of exercise therapy in the treatment of patients with lower limb tendinopathies and the effects of different types of exercise therapy in the treatment of these patients.

METHODS

The search strategy will be performed in the following databases: CENTRAL, MEDLINE, EMBASE, PEDro, SPORTDiscus, and CINAHL. The inclusion criteria of the studies will be randomized controlled trials with patients with one of the following tendinopathies: patellar, Achilles, gluteal, and proximal tendinopathy of the hamstring muscles. The primary outcomes will be pain and disability. The intervention will be exercise therapy, and the comparators will be different types of exercise, control groups, or any other type of intervention.

DISCUSSION

Other systematic reviews have been published about the prescription of exercise therapy in the treatment of tendinopathies of the lower limbs. However, the results of these reviews are limited to only one type of tendinopathy or specific exercise. Because some of these reviews are also outdated, this systematic review will investigate whether exercise therapy is more effective than any other type of intervention and if there is a best form of exercise therapy, considering modality, dose, and intensity, for the treatment of lower limb tendinopathies. Furthermore, this study will present data related to the sample size, recruitment period, methodological quality, and visibility of the eligible studies.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO ( CRD42018093011 ).

Effect of photobiomodulation and exercise on early remodeling of the Achilles tendon in streptozotocin-induced diabetic rats

The aim of this study was to compare the treatment effects of laser photobiomodulation (LPBM) therapy and aerobic exercise on the biomechanical properties, tissue morphology and the expression of tendon matrix molecules during early remodeling of Achilles tendon (AT) injury in diabetic rats. Animals were randomly assigned to five groups: injured non diabetic (I, n = 15), injured diabetic (ID, n = 15), injured diabetic plus LPBM (IDL, n = 16), injured diabetic plus aerobic exercise (IDE, n = 16) and injured diabetic plus aerobic exercise and LPBM (IDEAL, n = 17). Type 1 diabetes was induced via a single intravenous injection of Streptozotocin at a dose of 40 mg/kg. A partial tenotomy was performed in the right AT. LPBM was performed with an indium-gallium-aluminum-phosphide 660 nm 10 mW laser device (spot size 0.04 cm2, power density 250 mW/cm2, irradiation duration 16 s, energy 0.16 J, energy density 4 J/cm2) on alternate days for a total of 9 sessions over 3 weeks (total energy 1.44 J), using a stationary contact technique to a single point over the dorsal aspect of the AT. Moderate aerobic exercise was performed on a motorized treadmill (velocity 9 m/min for 60 minutes). At 3 weeks post-injury, biomechanical analyzes as well as assessment of fibroblast number and orientation were performed. Collagen 1 (Col1) and 3 (Col3) and matrix metalloproteinases (MMPs) -3 and 13 protein distributions were studied by immunohistochemistry; while Col1 and Col3 and MMP-2 and 9 gene expression were assessed by quantitative RT-PCR (qRT-PCR). IDEAL exhibited significant increases in several biomechanical parameters in comparison to the other groups. Moreover, IDEAL presented stronger Col1 immunoreactivity when compared to ID, and weaker Col3 immunoreactivity than IDE. Both IDL and IDEAL demonstrated weaker expression of MMP-3 in comparison to I, while IDL presented no expression of MMP-13 when compared to ID. ID, IDL and IDE showed an increased number of fibroblasts in comparison to I, while IDEAL decreased the number of these cells in comparison to ID and IDE. IDL and IDEAL groups exhibited decreased angular dispersion among the fibroblasts when compared to I. The gene expression results showed that IDE demonstrated a downregulation in Col1 mRNA expression in comparison to I and ID. IDEAL demonstrated upregulation of Col1 mRNA expression when compared to IDL or IDE alone and increased MMP-2 expression when compared to IDL and IDE. MMP-9 expression was upregulated in IDEAL when compared to I, IDL and IDE. Our results suggest a beneficial interaction of combining both treatment strategies i.e., aerobic exercise and LPBM, on the biomechanical properties, tissue morphology and the expression of matrix molecules in diabetic tendons.

Impaired function of tendon-derived stem cells in experimental diabetes mellitus rat tendons: implications for cellular mechanism of diabetic tendon disorder

Background

Patients with diabetes mellitus (DM) often suffered with many musculoskeletal disorders, such as tendon rupture and tendinopathy. However, the understanding of the pathogenesis of these alternations is limited. This study was designed to investigate the role of tendon-derived stem cells (TDSCs) in histopathological alterations of DM tendons.

Methods

Forty-two SD rats were randomly and equally divided into a diabetes group (DG) and control group (CG). DM was induced by streptozotocin (65 mg/kg). The patellar tendons were isolated at weeks 1, 2, and 4 for histological analysis. TDSCs were isolated at week 2 for osteo-chondrogenic differentiation analysis. Mann-Whitney U test was used with SPSS. p < 0.050 was statistically significant.

Results

Micro-tears of collagen fibers and altered appearance of tendon cells were observed in DG tendons. DG tendons exhibited significantly higher expression of OPN, OCN, SOX9, and Col II and decreased expression of Col I and tenomodulin (TNMD) at week 2. Diabetic TDSCs (dTDSCs) demonstrated significantly decreased proliferation ability and increased osteogenic and chondrogenic differentiation ability. Osteo-chondrogenic markers BMP2, ALP, OPN, OCN, Col II, and SOX9 were also significantly increased while tenogenic markers Col I and TNMD were decreased in dTDSCs.

Conclusion

These results suggested the erroneous differentiation of dTDSCs might account for the structural and non-tenogenic alternations in DM tendons, which provided new cues for the pathogenesis of tendon disorders in DM.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1108-6) contains supplementary material, which is available to authorized users.

Ultrasonographic Evaluation of Lower Extremity Entheseal Sites in Diabetic Patients Using Glasgow Ultrasound Enthesitis Scoring System Score

Objective

The prevalence of musculoskeletal complications in diabetes mellitus (DM) increases with the duration of disease and with poor glycemic control. Our aim was to evaluate lower extremity musculoskeletal complications in patients with DM using the Glasgow Ultrasound Enthesitis Scoring System, and to reveal the relationship between clinical and sono-graphic findings.

Materials and methods

A total of 67 patients (25 men, 42 women) with DM were included in the study. All the diabetic patients were selected if they did not have any symptom of muscu-loskeletal system in the lower extremities. They were divided into four groups. Ultrasonographic assessment was performed according to the Glasgow Ultrasound Enthesitis Scoring System with an Esaote MyLab 5 device equipped with a 5-13 MHz linear transducer. Correlation between diabetes duration and lower extremity enthesopathy scores were evaluated.

Results

There was a significant correlation between duration of DM and total Glasgow Ultrasound Enthesitis Scoring System scores (p < 0.001). In addition, duration of DM was significantly correlated with enthesophyte scores and erosion scores (both p < 0.001). There was a significant difference among Groups 1 -4 for the mean enthesophyte score and mean erosion score (both, p < 0.001).

Conclusion

Musculoskeletal ultrasonography is an effective, inexpensive, and useful tool without radiation for evaluating diabetic patients for the early diagnosis of musculoskeletal complications.

Type 2 diabetes patients have accelerated cartilage matrix degeneration compared to diabetes free controls: data from the Osteoarthritis Initiative

PURPOSE

Osteoarthritis (OA) and diabetes mellitus (DM) share common risk factors with a potential underlying relationship between both diseases. The purpose of this study was to investigate the longitudinal effects of DM on cartilage deterioration over 24-months with MR-based T2 relaxation time measurements.

METHODS

From the Osteoarthritis Initiative (OAI) cohort 196 diabetics were matched in small sets for age, sex, BMI and Kellgren-Lawrence score with 196 non-diabetic controls. Knee cartilage semi-automatic segmentation was performed on 2D multi-slice multi-echo spin-echo sequences. Texture of cartilage T2 maps was obtained via grey level co-occurrence matrix analysis. Linear regression analysis was used to compare cross-sectional and changes in T2 and texture parameters between the groups.

RESULTS

Both study groups were similar in age (63.3 vs 63.0 years, P = 0.70), BMI (30.9 vs 31.2 kg/m2, P = 0.52), sex (female 53.6% vs 54.1%, P = 0.92) and KL score distribution (P = 0.97). In diabetics, except for the patella, all compartments showed a significantly higher increase in mean T2 values when compared to non-diabetic controls. Global T2 values increased almost twice as much; 1.77ms vs 0.98ms (0.79ms [CI: 0.39,1.19]) (P < 0.001). Additionally, global T2 values showed a significantly higher increase in the bone layer (P = 0.006), and in a separate analysis of the texture parameters, diabetics also showed consistently higher texture values (P < 0.05), indicating a more disordered cartilage composition.

CONCLUSION

Cartilage T2 values in diabetics show a faster increase with a consistently more heterogeneous cartilage texture composition. DM seems to be a risk factor for developing early OA with an accelerated degeneration of the articular cartilage in the knee.

Metalloproteinase Changes in Diabetes

Matrix metalloproteinases (MMPs) constitute a group of over 20 structurally-related proteins which include a Zn(++) ion binding site that is essential for their proteolytic activities. These enzymes play important role in extracellular matrix turnover in order to maintain a proper balance in its synthesis and degradation. MMPs are associated to several physiological and pathophysiological processes, including diabetes mellitus (DM). The mechanisms of DM and its complications is subject of intense research and evidence suggests that MMPs are implicated with the development and progression of diabetic microvascular complications such as nephropathy, cardiomyopathy, retinopathy and peripheral neuropathy. Recent data has associated DM to changes in the tendon structure, including abnormalities in fiber structure and organization, increased tendon thickness, volume and disorganization obtained by image and a tendency of impairing biomechanical properties. Although not fully elucidated, it is believed that DM-induced MMP dysregulation may contribute to structural and biomechanical alterations and impaired process of tendon healing.

The Risk of Achilles or Biceps Tendon Rupture in New Statin Users: A Propensity Score-Matched Sequential Cohort Study

INTRODUCTION

Case reports and pharmacovigilance data reported cases of tendon ruptures in statin users, but evidence from observational studies is scarce and inconclusive. We aimed to assess the association between new statin use and tendon rupture.

METHODS

We performed a propensity score (PS)-matched sequential cohort study, using data from the Clinical Practice Research Datalink. Patients aged ≥45 years with at least one new statin prescription between 1995 and 2014 were PS-matched within 2-year entry blocks to patients without a statin prescription during the block. We followed patients until they had a recorded Achilles or biceps tendon rupture, completed 5 years of follow-up, or were censored for change in exposure status or another censoring criterion. We calculated hazard ratios (HRs) with 95 % confidence intervals (CIs), applying Cox proportional hazard analyses in the overall cohort (crude and multivariable) and in the PS-matched cohort. We performed subgroup analyses by sex, age, treatment duration, and statin dose.

RESULTS

We observed a crude HR of 1.32 (95 % CI 1.21-1.44) in the overall cohort, which attenuated after multivariable adjustment (HR 1.02, 95 % CI 0.92-1.12) and after PS-matching (HR 0.95, 95 % CI 0.84-1.08). Crude HRs were higher in women than in men, but remained around null in both sexes after multivariable adjustment and PS-matching. Subgroup analyses by age, treatment duration, and statin dose revealed null results across all subgroups.

CONCLUSION

The results of this cohort study suggest that statin use does not increase the risk of tendon rupture, irrespective of gender, age, statin dose, or treatment duration.

Resistance jump training may reverse the weakened biomechanical behavior of tendons of diabetic Wistar rats

ABSTRACT Background: resistance training is widely applied in non-diabetic physical protocol showing effectiveness in improving the tendon tissue. To address this gap, we assessed the effects of resistance training on aquatic environment, on the biomechanical properties of the calcaneal tendon of diabetic Wistar rats. Methods: 59 male Wistar rats were evaluated for 60 days, they were randomly divided into the following groups: Sedentary Control Group (SCG, n=15), Sedentary Diabetic Group (SDG, n=15), Trained Control Group (TCG, n=14) and Trained Diabetic Group (TDG, n=15). After randomization the animals from the SDG and the TDG were induced to Diabetes Mellitus by intraperitoneal injection of Streptozotocin (60 mg/kg). The animals on the trained groups performed resistance exercise that consisted of jumping in an aquatic environment. After nine weeks the calcaneal tendons were collected and tractioned on a conventional mechanical testing machine. Results: the analysis of biomechanical parameters showed lower values in elastic modulus (p=0.000), maximum strength tension (p=0.000) and energy/area (p=0.008) in TDG compared to SDG in addition to an increase on the cross-sectional area (p=0.002). There was no difference for the specific deformation variable. Conclusion: the training protocol used restored some biomechanical parameters of the calcaneal tendon in rats induced to diabetes, thus, resulting in an improvement of its mechanical efficiency.

Experimental Diabetes Alters the Morphology and Nano-Structure of the Achilles Tendon

Although of several studies that associate chronic hyperglycemia with tendinopathy, the connection between morphometric changes as witnessed by magnetic resonance (MR) images, nanostructural changes, and inflammatory markers have not yet been fully established. Therefore, the present study has as a hypothesis that the Achilles tendons of rats with diabetes mellitus (DM) exhibit structural changes. The animals were randomly divided into two experimental groups: Control Group (n = 06) injected with a vehicle (sodium citrate buffer solution) and Diabetic Group (n = 06) consisting of rats submitted to intraperitoneal administration of streptozotocin. MR was performed 24 days after the induction of diabetes and images were used for morphometry using ImageJ software. Morphology of the collagen fibers within tendons was examined using Atomic Force microscopy (AFM). An increase in the dimension of the coronal plane area was observed in the diabetic group (8.583 ± 0.646 mm²/100g) when compared to the control group (4.823 ± 0.267 mm²/100g) resulting in a significant difference (p = 0.003) upon evaluating the Achilles tendons. Similarly, our analysis found an increase in the size of the transverse section area in the diabetic group (1.328 ± 0.103 mm²/100g) in comparison to the control group (0.940 ± 0.01 mm²/100g) p = 0.021. The tendons of the diabetic group showed great irregularity in fiber bundles, including modified grain direction and jagged junctions and deformities in the form of collagen fibrils bulges. Despite the morphological changes observed in the Achilles tendon of diabetic animals, IL1 and TNF-α did not change. Our results suggest that DM promotes changes to the Achilles tendon with important structural modifications as seen by MR and AFM, excluding major inflammatory changes.

Changes in Cartilage and Tendon Composition of Patients With Type I Diabetes Mellitus: Identification by Quantitative Sodium Magnetic Resonance Imaging at 7 T

OBJECTIVE

The aim of this study was to investigate possible biochemical alterations in tendons and cartilage caused by type 1 diabetes mellitus (DM1), using quantitative in vivo 7 T sodium magnetic resonance (MR) imaging.

MATERIALS AND METHODS

The institutional review board approved this prospective study, and written informed consent was obtained. Eight DM1 patients with no history of knee trauma and 9 healthy age- and weight-matched volunteers were examined at 7 T using dedicated knee coils.All participants underwent morphological and sodium MR imaging. Region-of-interest analysis was performed manually for the non-weight-bearing area of the femoral condyle cartilage and for the patella tendon. Two readers read the image data sets independently, twice, for intrareader and interreader agreement. Normalized mean sodium signal intensity (NMSI) values were compared between patients and volunteers for each reader using analysis of variance.

RESULTS

On morphological images, cartilage in the non-weight-bearing area and the patellar tendon was intact in all patients. On sodium MR imaging, bivariate analysis of variance showed significantly lower mean NMSI values in the cartilage (P = 0.008) and significantly higher values in the tendons (P = 0.025) of patients compared with those of volunteers.

CONCLUSION

Our study showed significantly different NMSI values between DM1 patients and matched volunteers. Differences observed in the cartilage and tendon might be associated with a DM1-related alteration of biochemical composition that occurs before it can be visualized on morphological MR sequences.

Achilles or biceps tendon rupture in women and men with type 2 diabetes: A population-based case-control study

AIMS

Previous studies suggest that diabetes causes alterations in tendon collagen structure, but evidence on how such findings translate into clinical practice is scarce. We aimed to analyze the association between type 2 diabetes and the risk of tendon rupture.

MATERIALS AND METHODS

We conducted a matched case-control analysis using the UK-based Clinical Practice Research Datalink. Cases (n=7895) were aged 30-89years and had an incident diagnosis of Achilles- or biceps tendon rupture between 1995 and 2013. In multivariable logistic regression analyses we compared the odds of tendon rupture between patients with or without type 2 diabetes, in men and women separately, and taking into account diabetes severity (HbA1c), duration, and antidiabetic drug treatment.

RESULTS

Within 165 (7.1%) female cases with type 2 diabetes, odds ratios (ORs) were increased with poorer diabetes control (OR 2.03, 95% CI 1.20-3.41, HbA1c ≥9% [≥75mmol/mol]), longer disease duration (OR 1.60, 95% CI 0.93-2.74, ≥10years), and current insulin use (OR 2.25, 95% CI 1.30-3.90, ≥20 prescriptions). Among 372 (6.7%) male cases, there was no effect of type 2 diabetes on the risk of tendon rupture.

CONCLUSIONS

Our results suggest that the risk of tendon ruptures may be increased in women with poorly controlled type 2 diabetes, but not in men.

Real-time sonoelastography and ultrasound evaluation of the Achilles tendon in patients with diabetes with or without foot ulcers: a cross sectional study

BACKGROUND

Diabetes mellitus (DM) is an endocrine disease characterized by metabolic abnormalities and long-term complications. The Achilles tendon (AT) plays an important role in foot biomechanics. We aimed to investigate the effect of DM on the Achilles tendon, which may contribute to long-term complications in the foot-ankle complex.

METHODS

Seventy-eight patients with diabetes, with (35 patients, group I) or without (43 patients, group II) foot ulcers were recruited from the endocrinology clinic. Thirty-three age-, gender-, and BMI-matched healthy individuals were selected as controls. All participants underwent ultrasonography and sonoelastography of their AT in order to evaluate Achilles tendon thickness (ATT) and stiffness (ATS). Each patient was also tested for fasting plasma glucose (FPG) and glycosylated hemoglobin (HbA1C) as a measure of diabetes control. Other chronic complications were also evaluated in all patients with diabetes.

RESULTS

The AT was significantly thicker in group I compared to group II and the controls. HbA1C, FPG, and duration of diabetes were higher in group I. We observed that ATT was positively correlated with neuropathy, retinopathy, nephropathy, peripheral arterial disease and coronary arterial disease in group II while this correlation was not detected in group I. ATS was reduced in group I more than group II and control groups.

CONCLUSION

Changes in the structure of the AT may precede foot ankle disorders in patients with diabetes. This is the first study that reported the results of sonoelastosonography of AT in patients with diabetes and revealed the correlation between ATT and other chronic complications of diabetes.

Lower limb complications of diabetes mellitus: a comprehensive review with clinicopathological insights from a dedicated high-risk diabetic foot multidisciplinary team

Diabetic complications in the lower extremity are associated with significant morbidity and mortality, and impact heavily upon the public health system. Early and accurate recognition of these abnormalities is crucial, enabling the early initiation of treatments and thus avoiding or minimizing deformity, dysfunction and amputation. Following careful clinical assessment, radiological imaging is central to the diagnostic and follow-up process. We aim to provide a comprehensive review of diabetic lower limb complications designed to assist radiologists and to contribute to better outcomes for these patients.

The adverse effects of diabetes on osteoarthritis: update on clinical evidence and molecular mechanisms

Projected increases in the prevalence of both diabetes mellitus (DM) and osteoarthritis (OA) ensure their common co-existence. In an era of increasing attention to personalized medicine, understanding the influence of common comorbidities such as DM should result in improved care of patients with OA. In this narrative review, we summarize the literature addressing the interactions between DM and OA spanning the years from 1962 to 2014. We separated studies depending on whether they investigated clinical populations, animal models, or cells and tissues. The clinical literature addressing the influence of DM on OA and its therapeutic outcomes suggests that DM may augment the development and severity of OA and that DM increases risks associated with joint replacement surgery. The few high quality studies using animal models also support an adverse effect of DM on OA. We review strengths and weaknesses of the common rodent models of DM. The heterogeneous literature derived from studies of articular cells and tissues also supports the existence of biochemical and biomechanical changes in articular tissues in DM, and begins to characterize molecular mechanisms activated in diabetic-like environs which may contribute to OA. Increasing evidence from the clinic and the laboratory supports an adverse effect of DM on the development, severity, and therapeutic outcomes for OA. To understand the mechanisms through which DM contributes to OA, further studies are clearly necessary. Future studies of DM-influenced mechanisms may shed light on general mechanisms of OA pathogenesis and result in more specific and effective therapies for all OA patients.

Alterations of tendons in diabetes mellitus: what are the current findings?

As a connective tissue, tendon connects the muscle and bone, and plays the key role in the locomotor system. Some previous studies have shown the pathological alternations in diabetic tendons, which might result in the structural and functional changes, and even accelerate the process of diabetic foot. In this review, we examined the current findings of the diabetic tendons in the form of various aspects, and summarized the clinical presentation, imaging, biomechanical, histopathological, cellular and molecular abnormalities in the diabetic tendons. The progress of diabetic tendon damage is complicated and the main hypotheses include the excessive accumulation of AGEs, the altered inflammatory response, neovascularization and insensitive neuropathy. However, the cellular and molecular mechanisms of these alterations are still ambiguous. Tendon stem/progenitor cells (TSPCs) have been discovered to play important roles in both tendon physiology and tendon pathology. Recently, we identified TSPCs from patellar tendons in our well-established diabetic rat model and found impaired tenogenic differentiation potential of these cells. We proposed a new hypothesis that the impaired cell functions of diabetic TSPCs might be the underlying cellular and molecular mechanism of the diabetic tendon alternations. These findings should be helpful to establish a better therapeutic strategy for diabetic tendon repair and regeneration.

The influence of diabetes mellitus on clinical and structural outcomes after arthroscopic rotator cuff repair

BACKGROUND

The clinical effect of sustained hyperglycemia on tendon-to-bone healing after rotator cuff repair has not been well characterized.

PURPOSE

To compare the clinical and structural outcomes between diabetic and nondiabetic patients after arthroscopic rotator cuff repair and to determine the effect of a diabetic phenotype on tendon-to-bone healing.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

This study retrospectively evaluated a total of 335 shoulders that were available for magnetic resonance imaging (MRI) evaluation at least 6 months after arthroscopic rotator cuff repair using the suture-bridge technique with a minimum follow-up of 1 year. Only patients who had medium- to large-sized tears with supraspinatus of fatty infiltration <2 and no or mild atrophy were enrolled in this study. There were 271 nondiabetic patients (group A) and 64 diabetic patients (group B). The mean age at the time of operation for groups A and B was 57.7 and 58.2 years, respectively, and the mean duration of follow-up after surgery was 27.8 and 24.8 months, respectively.

RESULTS

At the last follow-up, there were no statistically significant differences between the 2 groups with regard to pain at rest and during motion (P = .212 and .336, respectively). Both groups reported statistically significant improvement in Constant and Shoulder Rating Scale of the University of California at Los Angeles scores (P = .323 and .241, respectively), but there was no statistically significant difference between the 2 groups. In assessing the repair integrity with postoperative MRI scans, 39 of 271 cases in group A (14.4%) and 23 of 64 cases in group B (35.9%) had retears, and the difference between the 2 groups was statistically significant (P < .001). In analyzing the retear rates according to the severity of sustained hyperglycemia in group B, retear was found in 16 of 37 (43.2%) uncontrolled diabetic patients with poor glycemic control (≥7.0% of preoperative serum glycosylated hemoglobin [HbA1c] levels) and in 7 of 27 (25.9%) controlled diabetic patients (<7.0%) (P < .001).

CONCLUSION

Pain, range of motion, and function all significantly improved after arthroscopic rotator cuff repair using the suture-bridge technique, regardless of the presence of diabetes. However, sustained hyperglycemia increased the possibility of anatomic failure at the repaired cuff. In diabetic patients, an effective glycemic control was associated with better rate of healing after rotator cuff repair.

Achilles tendons in people with type 2 diabetes show mildly compromised structure: an ultrasound tissue characterisation study

BACKGROUND

Musculotendinous overuse injuries are prevalent in people with type 2 diabetes. Non-enzymatic glycosylation of collagen resulting in tendon stiffening may play a role. In this case-control study we determined whether patients with diabetes had poorer ultrasonographic structure in their Achilles tendons compared to age-matched controls.

METHODS

People with type 1 diabetes or type 2 diabetes, and age-matched controls, had computerised ultrasound tissue characterisation of both Achilles tendons. In contiguous ultrasonographic images of the tendon, echopatterns were quantified and categorised into four echo-types. Tendon abnormality was quantified as sum of echo-types III+IV. Furthermore, skin autofluorescence (AF) of the forearm (AF-value) was gathered.

RESULTS

Twenty four type 2 diabetes patients, 24 controls, 24 type 1 diabetes patients and 20 controls were included. AF-value was higher in type 1 diabetes (1.55±0.17) than in their controls (1.39±0.18, p<0.001) and in type 2 diabetes (2.28±0.38) compared to their controls (1.84±0.32, p<0.001) Achilles tendons of type 2 diabetes patients contained more echo-types III+IV (14.1±7.9%) than matched controls (8.0±5.4%, p<0.001). There was a trend towards a difference in echo-types III+IV between type 1 diabetes patients (9.5±5.3%) and their controls (6.5±3.7%, p=0.055). In a stepwise linear regression analysis, body mass index (BMI) was moderately associated with tendon abnormality in patients with diabetes and controls (β=0.393, p<0.001).

CONCLUSIONS

Type 2, and possibly type 1, diabetes patients showed poorer ultrasonographic Achilles tendon structure that may be a risk factor for tendinopathy. Although markers for accumulation of advanced glycation end products were elevated in both diabetes populations, only BMI was associated with these abnormalities.

TRIAL REGISTRATION NUMBER

NTR2209.

Ultrasound morphology of the Achilles in asymptomatic patients with and without diabetes

BACKGROUND

The prevalence of tendinopathies is increased in subjects with diabetes mellitus. However, there are few data on the structural abnormalities of Achilles tendons in asymptomatic diabetic patients. The aim of the study was to assess the morphologic characteristics of the Achilles tendon in subjects with diabetes in comparison with controls without diabetes.

METHODS

Participants were consecutively recruited from an outpatient population. Ultrasound longitudinal and transverse scans were performed bilaterally along the full length of Achilles tendon from the musculotendinous junction to the insertion. Degenerative features (abnormal fibrillar pattern, hypo-hyperechoic areas), signs of enthesopathy (bony erosion, enthesophytes, and bursitis), and intratendinous neovessel formation were recorded.

RESULTS

Asymptomatic sonographic abnormalities (ASA) were significantly increased in subjects with diabetes (35/136 [25.7%] vs 32/273 [11.7%], P = .0003). Sixty tendons with ASA were observed in the first group and 45 in the latter because ASA were bilateral in 25 and in 13 subjects, respectively. ASA were more frequently localized at the enthesis (32/60 [53.3%] vs 9/45 [20%], P = .0005) in the diabetes group, whereas, on the contrary, they were more prevalent at the midportion in controls (38/45 [84.4%] vs 36/60 [60%], P < .006).

CONCLUSION

Diabetes may predispose to Achilles tendinopathy and particularly to Achilles enthesopathy. Longitudinal studies, evaluating the progression of the lesions not only in the midportion of the tendon but also at the insertion are needed to support this conclusion.

LEVEL OF EVIDENCE

Level III, comparative series.

Functional tissue engineering of tendon: Establishing biological success criteria for improving tendon repair

Improving tendon repair using Functional Tissue Engineering (FTE) principles has been the focus of our laboratory over the last decade. Although our primary goals were initially focused only on mechanical outcomes, we are now carefully assessing the biological properties of our tissue-engineered tendon repairs so as to link biological influences with mechanics. However, given the complexities of tendon development and healing, it remains challenging to determine which aspects of tendon biology are the most important to focus on in the context of tissue engineering. To address this problem, we have formalized a strategy to identify, prioritize, and evaluate potential biological success criteria for tendon repair. We have defined numerous biological properties of normal tendon relative to cellular phenotype, extracellular matrix and tissue ultra-structure that we would like to reproduce in our tissue-engineered repairs and prioritized these biological criteria by examining their relative importance during both normal development and natural tendon healing. Here, we propose three specific biological criteria which we believe are essential for normal tendon function: (1) scleraxis-expressing cells; (2) well-organized and axially-aligned collagen fibrils having bimodal diameter distribution; and (3) a specialized tendon-to-bone insertion site. Moving forward, these biological success criteria will be used in conjunction with our already established mechanical success criteria to evaluate the effectiveness of our tissue-engineered tendon repairs.

Experimental diabetes induces structural, inflammatory and vascular changes of Achilles tendons

This study aims to demonstrate how the state of chronic hyperglycemia from experimental Diabetes Mellitus can influence the homeostatic imbalance of tendons and, consequently, lead to the characteristics of tendinopathy. Twenty animals were randomly divided into two experimental groups: control group, consisting of healthy rats and diabetic group constituted by rats induced to Diabetes Mellitus I. After twenty-four days of the induction of Diabetes type I, the Achilles tendon were removed for morphological evaluation, cellularity, number and cross-sectional area of blood vessel, immunohistochemistry for Collagen type I, VEGF and NF-κB nuclear localization sequence (NLS) and nitrate and nitrite level. The Achilles tendon thickness (µm/100g) of diabetic animals was significantly increased and, similarly, an increase was observed in the density of fibrocytes and mast cells in the tendons of the diabetic group. The average number of blood vessels per field, in peritendinous tissue, was statistically higher in the diabetic group 3.39 (2.98) vessels/field when compared to the control group 0.89 (1.68) vessels/field p = 0.001 and in the intratendinous region, it was observed that blood vessels were extremely rare in the control group 0.035 (0.18) vessels/field and were often present in the tendons of the diabetic group 0.89 (0.99) vessels/field. The immunohistochemistry analysis identified higher density of type 1 collagen and increased expression of VEGF as well as increased immunostaining for NFκB p50 NLS in the nucleus in Achilles tendon of the diabetic group when compared to the control group. Higher levels of nitrite/nitrate were observed in the experimental group induced to diabetes. We conclude that experimental DM induces notable structural, inflammatory and vascular changes in the Achilles tendon which are compatible with the process of chronic tendinopathy.

Continuum model of tendon pathology - where are we now?

Chronic tendon pathology is a common and often disabling condition, the causes of which remain poorly understood. The continuum model of tendon pathology was proposed to provide a model for the staging of tendon pathology and to assist clinicians in managing this often complex condition (Br. J. Sports Med., 43, 2009, 409). The model presents clinical, histological and imaging evidence for the progression of tendon pathology as a three-stage continuum: reactive tendinopathy, tendon disrepair and degenerative tendinopathy. It also provides clinical information to assist in identifying the stage of pathology, in addition to proposed treatment approaches for each stage. The usefulness of such a model is determined by its ability to incorporate and inform new and emerging research. This review examines the degree to which recent research supports or refutes the continuum model and proposes future directions for clinical and research application of the model.