Anabolic steroids reduce muscle damage caused by rotator cuff tendon release in an experimental study in rabbits

Poly(ADP-Ribose) Polymerases-Inhibitor Talazoparib Inhibits Muscle Atrophy and Fatty Infiltration in a Tendon Release Infraspinatus Sheep Model: A Pilot Study

Structural muscle changes, including muscle atrophy and fatty infiltration, follow rotator cuff tendon tear and are associated with a high repair failure rate. Despite extensive research efforts, no pharmacological therapy is available to successfully prevent both muscle atrophy and fatty infiltration after tenotomy of tendomuscular unit without surgical repair. Poly(ADP-ribose) polymerases (PARPs) are identified as a key transcription factors involved in the maintenance of cellular homeostasis. PARP inhibitors have been shown to influence muscle degeneration, including mitochondrial hemostasis, oxidative stress, inflammation and metabolic activity, and reduced degenerative changes in a knockout mouse model. Tenotomized infraspinatus were assessed for muscle degeneration for 16 weeks using a Swiss Alpine sheep model (n = 6). All sheep received daily oral administration of 0.5 mg Talazoparib. Due to animal ethics, the treatment group was compared with three different controls from prior studies of our institution. To mitigate potential batch heterogeneity, PARP-I was evaluated in comparison with three distinct control groups (n = 6 per control group) using the same protocol without treatment. The control sheep were treated with an identical study protocol without Talazoparib treatment. Muscle atrophy and fatty infiltration were evaluated at 0, 6 and 16 weeks post-tenotomy using DIXON-MRI. The controls and PARP-I showed a significant (control p < 0.001, PARP-I p = 0.01) decrease in muscle volume after 6 weeks. However, significantly less (p = 0.01) atrophy was observed in PARP-I after 6 weeks (control 1: 76.6 ± 8.7%; control 2: 80.3 ± 9.3%, control 3: 73.8 ± 6.7% vs. PARP-I: 90.8 ± 5.1% of the original volume) and 16 weeks (control 1: 75.7 ± 9.9; control 2: 74.2 ± 5.6%; control 3: 75.3 ± 7.4% vs. PARP-I 93.3 ± 10.6% of the original volume). All experimental groups exhibited a statistically significant (p < 0.001) augmentation in fatty infiltration following a 16-week period when compared to the initial timepoint. However, the PARP-I showed significantly less fatty infiltration (p < 0.003) compared to all controls (control 1: 55.6 ± 6.7%, control 2: 53.4 ± 9.4%, control 3: 52.0 ± 12.8% vs. PARP-I: 33.5 ± 8.4%). Finally, a significantly (p < 0.04) higher proportion and size of fast myosin heavy chain-II fiber type was observed in the treatment group. This study shows that PARP-inhibition with Talazoparib inhibits the progression of both muscle atrophy and fatty infiltration over 16 weeks in retracted sheep musculotendinous units.

Estrogen and testosterone supplementation improves tendon healing and functional recovery after rotator cuff repair

Failure of healing after rotator cuff repair (RCR) is common. The purpose of the current study was to evaluate the effect of systemic estrogen or testosterone supplementation on tendon healing after RCR. Seventy-two adult male mice were utilized for all experiments. The supraspinatus tendon was transected and repaired with 6-0 Prolene suture on the left shoulder of 51 animals. Mice were segregated into three groups postoperative: (1) vehicle group (VG; n = 18), (2) estrogen group (EST; n = 17), and (3) testosterone group (TST; n = 16). An unrepaired control group (unrepaired, n = 21) did not have surgery. Utilizing these animals, histological analysis, activity testing, biomechanical testing and RNA sequencing (RNA-seq) was performed. At 8 weeks post-RCR, TST, and EST supplementation improved the overall histologic structure of the repaired enthesis site. No differences in ultimate failure loads or stiffness were detected between VG, EST, and TST groups after biomechanical testing. RCR caused a reduction in wheel activity compared to unrepaired controls and supplementation with TST restored wheel activity. RNA-seq analysis indicated that estrogen and testosterone regulated different pathways associated with enthesis healing, including a suppression of inflammatory signaling. Supplementation with sex hormones improved the structure of the repaired tendon enthesis and significantly regulated expression of diverse pathways regulating multiple biological processes. Testosterone administration following RCR restored wheel activity without having a detrimental impact on biomechanical strength. Future human studies of sex hormone supplementation after RCR are warranted as supplementation in an animal model may improve tendon enthesis healing.

Interventions used to mitigate muscle fatty degeneration following the repair of massive rotator cuff tears. A systematic review of animal studies

BACKGROUND

Muscle fatty degeneration following rotator cuff tears has been unequivocally associated with poorer functional outcomes and increased risk for retear following rotator cuff repair. Promising results have emerged from animal studies, with the implementation of various interventions for biologic inhibition of this fatty muscle degeneration. The lack of high quality randomized human evidence on this topic, increases the impact of pooled results from animal literature. The aim of the present study was to systematically review the available published literature for animal studies evaluating the ability of several interventions used to mitigate muscle fatty degeneration following the repair of massive rotator cuff tears.

PATIENTS AND METHODS

A comprehensive search was conducted on Pubmed, Scopus and Google Scholar, covering the period from conception until 16th April 2022. Datasets were stratified based on the type of intervention performed. SYRCLE risk of bias instrument was implemented for quality assessment of the included studies.

RESULTS

Rotator cuff repair augmentation with Adipose derived stem cells (ADSC's), Mesenchymal stem cells (MSC's) and Nandrolone was effective against fatty infiltration, but less effective against muscle atrophy. More beneficial effect was shown by the utilization of Beige adipose tissue - Fibroadipogenic progenitors (BAT-FAP) stimulation, using either Amibregon or BAT-FAPs transplantation. Both provided good results in mitigating muscle atrophy, fatty infiltration and fibrosis.

DISCUSSION

ADSC's, MSC's, Nandrolone and BAT-FAP stimulation may have a role in mitigating muscle fatty degeneration following rotator cuff tears. Large scale human studies are required to further elucidate their role in the clinical setting.

LEVEL OF EVIDENCE

V; systematic review of pre-clinical studies.

Abnormal Laboratory Values for Metabolic and Hormonal Syndromes Are Prevalent Among Patients Undergoing Rotator Cuff Repair

Purpose

To determine the prevalence of systemic laboratory abnormalities among patients undergoing rotator cuff repair (RCR).

Methods

Patients who underwent RCR at the authors' institution for 1 year between October 2021 to September 2022 were retrospectively identified. Preoperative laboratory values, including serum sex hormones, vitamin D, hemoglobin A1C, and a lipid panel, were obtained as part of our routine practice during the study period. Demographics and tear characteristics were compared in patients with laboratory data and those without. For included patients with laboratory data, mean laboratory values and percentage of patients with abnormal laboratory values were recorded.

Results

During a 1-year period of time, 135 RCRs were performed, of which preoperative labs were obtained on 105. Of these, 67% were sex hormone deficient, 36% were vitamin D deficient, 45% had an abnormal hemoglobin A1C, and 64% had an abnormal lipid panel. In total 4% had "normal" labs.

Conclusions

In this retrospective study, sex hormone deficiency is highly prevalent among patients undergoing RCR. Nearly all patients undergoing RCR have systemic laboratory abnormalities involving either sex hormone deficiency, vitamin D deficiency, dyslipidemia, and/or prediabetes.

Level of Evidence

Level IV, prognostic case series.

The Effect of Sex Hormone Deficiency on the Incidence of Rotator Cuff Repair: Analysis of a Large Insurance Database

BACKGROUND

The purpose of the present study was to analyze the association between sex hormone deficiency and rotator cuff repair (RCR) with use of data from a large United States insurance database.

METHODS

A retrospective analysis of insured subjects from the Truven Health MarketScan database was conducted, collecting data for RCR cases as well as controls matched for age, sex, and years in the database. Multivariable logistic regression models adjusted for matching variables were utilized to compare RCR status with estrogen deficiency status and testosterone deficiency status. These associations were confirmed with use of data from the Veterans Genealogy Project database, with which the relative risk of RCR was estimated for patients with and without sex hormone deficiency.

RESULTS

The odds of RCR for female patients with estrogen deficiency were 48% higher (odds ratio, 1.48; 95% confidence interval, 1.44 to 1.51; p < 0.001) than for those without estrogen deficiency. The odds of RCR for males with testosterone deficiency were 89% higher (odds ratio, 1.89; 95% confidence interval, 1.82 to 1.96; p < 0.001) than for those without testosterone deficiency. Within the Veterans Genealogy Project database, the relative risk of estrogen deficiency among RCR patients was 2.58 (95% confidence interval, 2.15 to 3.06; p < 0.001) and the relative risk of testosterone deficiency was 3.05 (95% confidence interval, 2.67 to 3.47; p < 0.001).

CONCLUSIONS

Sex hormone deficiency was significantly associated with RCR. Future prospective studies will be necessary to understand the pathophysiology of rotator cuff disease as it relates to sex hormones.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Progression of muscle loss and fat accumulation in a rabbit model of rotator cuff tear

Rotator cuff (RC) tears present a treatment challenge due to muscle atrophy and degeneration, fatty infiltration, and fibrosis. The purpose of this study was to generate a high time-resolution model of RC tear in rabbits and to characterize the progression of architectural and histological changes. Thirty-five female New Zealand White rabbits (age: 6 months) underwent left supraspinatus tenotomy. Five rabbits were used to evaluate immediate muscle architectural changes. The remaining 30 rabbits underwent right shoulder sham surgery and sacrifice at 1, 2, 4, 8, or 16 weeks. Histology was used to quantify muscle fiber cross-sectional area (CSA), muscle degeneration and regeneration, and fat localized to inter- versus intrafascicular regions. Muscle fiber CSA decreased by 26.5% compared to sham at 16 weeks (effect of treatment, p < 0.0001). Muscle degeneration increased after tenotomy (effect of treatment, p = 0.0006) without any change in regeneration. Collagen and fat content increased by 4 weeks and persisted through 16 weeks. Interfascicular fat was increased at all time points, but intrafascicular fat was increased only at 1, 4, and 16 weeks posttenotomy. Intrafascicular fat adjacent to degenerating muscle fibers increased as well (effect of treatment, p < 0.0001; effect of time, p = 0.0102). Statement of clinical relevance: Rabbit supraspinatus tenotomy recapitulates key features of the pathophysiology of human RC tears, including muscle atrophy and degeneration, lack of regeneration, fat accumulation, and fibrosis.

Translational therapy from preclinical animal models for muscle degeneration after rotator cuff injury

Chronic rotator cuff tears are debilitating diseases which significantly affect patients’ quality of life and pose substantial financial burden to the society. The intraoperative reparability of injured tendon and postoperative probability of tendon retear are highly associated with the quality of torn muscles, specifically, the severity of muscle atrophy and fatty infiltration. Animal models that reproduce the characteristic muscle pathology after rotator cuff injury have been developed and used to provide insight into the underlying biology and pathophysiology. In this review, we briefly summarize the current information obtained from preclinical animal studies regarding the degenerative change of cuff muscle subsequent to tendon release and/or suprascapular nerve denervation. Importantly, we focus on the potential translational therapeutic targets or agents for the prevention or reversal of muscle atrophy and fatty infiltration. While further studies are warranted to assess the safety and efficacy of novel therapies derived from these preclinical animal research, we believe that their clinical translation for the treatment of rotator cuff disorders is on the horizon.

The Translational potential of this article

Novel therapeutic strategies described in this review from preclinical animal studies hold a great translational potential for preventing or reversing rotator cuff muscle pathology, while further assessments on their safety and efficacy are warranted.

Nandrolone supplementation does not improve functional recovery in an aged animal model of volumetric muscle loss injury

Aging hinders the effectiveness of regenerative medicine strategies targeting the repair of volumetric muscle loss (VML) injury. Anabolic steroids have been shown to improve several factors which contribute to the age-related decline in muscle's regenerative capacity. In this study, the impact of exogenous nandrolone decanoate (ND) administration on the effectiveness of a VML regenerative repair strategy was explored using an aged animal model. Unilateral tibialis anterior VML injuries were repaired in 18-month-aged animal models (male Fischer 344 rat) using decellularized human skeletal muscle scaffolds supplemented with autologous minced muscle. The contralateral limb was left untreated/uninjured. Following repair, ND(+) or a carrier control (ND-) was delivered via weekly injection for a period of 8 weeks. At 8 weeks, muscle isometric torque, gene expression, and tissue structure were assessed. ND(+) treatment did not improve contractile torque recovery following VML repair when compared to carrier only ND(-) injection controls. Peak isometric torque in the ND(+) VML repair group remained significantly below contralateral uninjured control values (4.69 ± 1.18vs. 7.46 ± 1.53 N mm/kg) and was statistically indistinguishable from carrier only ND(-) VML repair controls (4.47 ± 1.18 N mm/kg). Gene expression for key myogenic genes (Pax7, MyoD, MyoG, IGF-1) were not significantly elevated in response to ND injection, suggesting continued age related myogenic impairment even in the presence of ND(+) treatment. ND injection did reduce the histological appearance of fibrosis at the site of VML repair, and increased expression of the collagen III gene, suggesting some positive effects on repair site matrix regulation. Overall, the results presented in this study suggest that a decline in regenerative capacity with aging may present an obstacle to regenerative medicine strategies targeting VML injury and that the delivery of anabolic stimuli via ND administration was unable to overcome this decline.

Anabolic Androgenic Steroids in Orthopaedic Surgery: Current Concepts and Clinical Applications

Despite the well-documented effects of testosterone and its synthetic derivatives—collectively termed anabolic androgenic steroids (AASs)—on the musculoskeletal system, the therapeutic use of these agents has received limited investigation within the field of orthopaedic surgery. In the last 2 decades, preclinical and clinical research has started to identify promising applications of the short-term use of AASs in the perioperative period. There is evidence to suggest that AASs may improve postoperative recovery after anterior cruciate ligament reconstruction and total joint arthroplasty. In addition, AASs may augment the biological healing environment in specific clinical scenarios including muscle injury, fracture repair, and rotator cuff repair. Current literature fails to present strong evidence for or against the use of AASs in orthopaedics, but there is continuous research on this topic. The purpose of this study was to provide a comprehensive overview of the current status of AAS applications in orthopaedic surgery, with an emphasis on preclinical data, clinical studies, and future directions.

Supraspinatus muscle architecture and physiology in a rabbit model of tenotomy and repair

Chronic rotator cuff tears can cause severe functional deficits. Addressing the chronic fatty and fibrotic muscle changes is of high clinical interest; however, the architectural and physiological consequences of chronic tear and repair are poorly characterized. We present a detailed architectural and physiological analysis of chronic tear and repair (both over 8 and 16 wk) compared with age-matched control rabbit supraspinatus (SSP) muscles. Using female New Zealand White Rabbits (n = 30, n = 6/group) under 2% isoflurane anesthesia, the SSP was surgically isolated and maximum isometric force was measured at four to six muscle lengths. Architectural analysis was performed, and maximum isometric stress was computed. Whole muscle length-tension curves were generated using architectural measurements to compare experimental physiology to theoretical predictions. Architectural measures are consistent with persistent radial and longitudinal atrophy over time in tenotomy that fails to recover after repair. Maximum isometric force was significantly decreased after 16 wk tenotomy and not significantly improved after repair. Peak isometric force reported here are greater than prior reports of rabbit SSP force after tenotomy. Peak stress was not significantly different between groups and consistent with prior literature of SSP stress. Muscle strain during contraction was significantly decreased after 8 wk of tenotomy and repair, indicating effects of tear and repair on muscle function. The experimental length-tension data were overlaid with predicted curves for each experimental group (generated from structural data), exposing the altered structure-function relationship for tenotomy and repair over time. Data presented here contribute to understanding the physiological implications of disease and repair in the rotator cuff.NEW & NOTEWORTHY We utilize an established method to measure the length-tension relationship for the rabbit supraspinatus in normal, torn, and repaired muscles. We then perform architectural analysis to evaluate structural changes after tear and repair. Although peak isometric force is lower in the tear and repair groups, there are no differences in peak stresses across groups. These findings indicate persistent structural changes (both radial and longitudinal atrophy) and physiological deficiencies (decreased peak force and uncoupling structure-function relationship) after tenotomy that do not significantly recover after repair.

Fatty degeneration of the rotator cuff: pathogenesis, clinical implications, and future treatment

Chronic rotator cuff pathology is often complicated by fatty degeneration of the rotator cuff (FDRC) muscles, an insidious process associated with poor prognosis with or without surgical intervention. Currently there is no treatment for FDRC, and many studies have described a natural course for this disease almost always resulting in further degeneration and morbidity. Recapitulating FDRC using animal injury models, and using imaging-based studies of human FDRC, the pathophysiology of this disease continues to be further characterized. Researchers studying mesenchymal stem cell-derived progenitor cells and known fibrogenic and adipogenic signaling pathways implicated in FDRC seek to clarify the underlying processes driving these changes. While new cell- and molecular-based therapies are being developed, currently the strongest available avenue for improved management of FDRC is the use of novel imaging techniques which allow for more accurate and personalized staging of fatty degeneration. This narrative review summarizes the evidence on the molecular and pathophysiologic mechanisms of FDRC and provides a clinical update on the diagnosis and management of this condition based on the existing knowledge. We also sought to examine the role of newer biologic therapies in the management of RC fatty degeneration and to identify areas of future research.

In vivo supraspinatus muscle contractility and architecture in rabbit

The rotator cuff (RC) muscles are crucial in moving and stabilizing the glenohumeral joint, and tears can be functionally devastating. Chronic fatty and fibrotic muscle changes, which are nonresponsive to surgical tendon repair, are a focus of contemporary research. The rabbit model recapitulates key biological features of human RC tears, but function and physiology are poorly characterized; limited force and stress data are inconsistent with literature norms in other mammalian species. Here, we present an improved method to assess the physiology of the rabbit supraspinatus muscle (SSP), and we report values for healthy SSP architecture and physiology. Using female New Zealand White Rabbits (n = 6) under 2% isoflurane anesthesia, we surgically isolated the SSP and maximum isometric force measured at 4-6 muscle lengths. Architectural analysis was performed, and maximum isometric stress was computed. Whole muscle length-tension curves were generated using architectural measurements to compare experimental physiology to theoretical predictions. Maximum isometric force (80.87 ± 5.58 N) was dramatically greater than previous reports (11.06 and 16.1 N; P < 0.05). Architectural measurement of fiber length (34.25 ± 7.18 mm), muscle mass (9.9 ± 0.93 g), pennation angle (23.67 ± 8.32°), and PCSA (2.57 ± 0.20 cm²) were consistent with prior literature. Isometric stress (30.5 ± 3.07 N/cm²) was greater than previous reports of rabbit SSP (3.10 and 4.51 N/cm²), but similar to mammalian skeletal muscles (15.7-30.13 N/cm²). Previous studies underestimated peak force by ∼90%, which has profound implications for interpreting physiological changes as a function of disease state. The data that are presented here enable understanding the physiological implications of disease and repair in the RC of the rabbit.NEW & NOTEWORTHY We introduce an improved method to assess rabbit supraspinatus muscle physiology. Maximum isometric force measured for the rabbit supraspinatus was dramatically greater than previous reports in the literature. Consequently, the isometric contractile stress reported is almost 10 times greater than previous reports of rabbit supraspinatus, but similar to available literature of other mammalian skeletal muscle. We show that previous reports of peak supraspinatus isometric force were subphysiological by ∼90.

Nandrolone decanoate relieves joint pain in hypogonadal men: a novel prospective pilot study and review of the literature

Testosterone is an archetypal androgenic-anabolic steroid (AAS), while its exogenous administration is considered to be the gold standard for the treatment of male hypogonadism. The benefits are not due to its intrinsic nature alone but are due to the result of its interactions with the androgen receptor (AR). As the management of hypogonadism continues to advance into the modern era, it would be preferable for modern andrologists to have multiple tools at their disposal to influence AR activity. Nandrolone, or 19-nortestosterone, is one such compound. In the following review of the literature, we examine the history, pharmacology, and clinical applications of this medication. We also present the results of our novel pilot study examining the favorable effects of nandrolone on joint pain for hypogonadal men.

Evaluation of Muscular Atrophy and Fatty Infiltration Using Time-zero Magnetic Resonance Imaging as Baseline Data, After Rotator Cuff Repair

Background

This study evaluated postoperative changes in the supraspinatus from time-zero to 6 months, using magnetic resonance imaging (MRI). We hypothesized that restoration of the musculotendinous unit of the rotator cuff by tendon repair immediately improves the rotator cuff muscle status, and maintains it months after surgery.

Methods

Totally, 76 patients (29 men, 47 women) with rotator cuff tears involving the supraspinatus tendon who underwent arthroscopic rotator cuff repairs were examined. MRI evaluation showed complete repair with intact integrity of the torn tendon at both time-zero and at 6 months follow-up. All patients underwent standardized MRI at our institution preoperatively, at 1 or 2 days postoperative, and at 6 months after surgery. Supraspinatus muscular (SSP) atrophy (Thomazeau grade) and fatty infiltrations (Goutallier stage) were evaluated by MRI. The cross-sectional area of SSP in the fossa was also measured.

Results

As determined by MRI, the cross-sectional area of SSP significantly decreased 11.41% from time-zero (immediate repair) to 6 months post-surgery, whereas the Goutallier stage and Thomazeau grade showed no significant changes (p < 0.01). Furthermore, compared to the preoperative MRI, the postoperative MRI at 6 months showed a no statistically significant increase of 8.03% in the cross-sectional area. In addition, morphological improvements were observed in patients with high grade Goutallier and Thomazeau at time-zero, whereas morphology of patients with low grade factors were almost similar to before surgery.

Conclusions

Our results indicate that cross-sectional area of the initial repair appears to decrease after a few months postoperatively, possibly due to medial retraction or strained muscle.

How Long Should We Wait to Create the Goutallier Stage 2 Fatty Infiltrations in the Rabbit Shoulder for Repairable Rotator Cuff Tear Model?

Background

Significant proportion of rotator cuff tears (RCTs) in clinical field are of a kind of repairable tear wherein the degree of fatty infiltration is of Goutallier stage 1 or stage 2. Therefore, the animal model, showing similar fatty infiltration, seems preferable for researches. The purpose of this study is to find out the proper time frame in which there is Goutallier stage 1 or stage 2 fatty infiltration in the rabbit RCT model for the research of repairable RCT in humans.

Methods

Supraspinatus tendon tears were created in forty male New Zealand white rabbits at their right shoulder (n= 8 for each group), and a sham operation on the left shoulder. Rabbits were divided into five groups (2nd, 4th, 6th, 8th, and 12th weeks). Specimens were harvested from the central portion of the supraspinatus muscle for haematoxylin and eosin (H &E) staining, followed by histological and Goutallier grading evaluation. Results are expressed as mean ± standard deviation by Sigma Plot software (version 7.0).

Results

At two weeks, mainly lipoblasts were observed around the muscle fibers, and at four weeks these lipoblasts were replaced by mature adipocytes with fatty infiltration amount (2.13 ± 0.35). The degree of muscle atrophy was (1.50 ± 0.53) at four weeks compared to sham group (0.88 ± 0.64) with significant difference (p < 0.05). The inflammatory process appeared as two phases. At two weeks, it was increased with grading value (1.88 ± 0.35). However, in the four-week group, it showed a sharp decrease (0.50 ± 0.53). At six weeks, inflammation reappeared to increase (1.13 ± 0.83). Then, a gradual decline appeared at eight weeks (0.88 ± 0.83) and at 12 weeks (0.50 ± 0.92).

Conclusions

At two and four weeks, both fat distribution in rabbit supraspinatus muscles and Goutallier grading scale mostly appeared as grade 2. Therefore, we can consider four weeks to be a suitable period for making a repairable RCT animal model for the human research, considering the early acute tissue reaction at 2 weeks after the tendon tears.

Anabolic steroids and tendons: A review of their mechanical, structural, and biologic effects

One of the suspected deleterious effects of androgenic-anabolic steroids (AAS) is the increased risk for tendon rupture. However, investigations to date have produced inconsistent results and it is still unclear how AAS influence tendons. A systematic review of the literature was conducted to identify studies that have investigated the mechanical, structural, or biologic effects that AAS have on tendons. In total, 18 highly heterogeneous studies were identified. Small animal studies made up the vast majority of published research, and contradictory results were reported frequently. All of the included studies focused on the potential deleterious effects that AAS have on tendon, which is striking given the recent use of AAS in patients following tendon injury. Rather than providing strong evidence for or against the use of AAS, this review highlights the need for additional research. Future studies investigating the use of AAS as a possible treatment for tendon injury/pathology are supported by reports suggesting that AAS may counteract the irreparable structural/functional changes that occur in the musculotendinous unit following rotator cuff tears, as well as studies suggesting that the purported deleterious effects on tendon may be transient. Other possible areas for future research are discussed in the context of key findings that may have implications for the therapeutic application of AAS. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2830-2841, 2018.

Arthroscopic single-row repair of massive potentially irreparable postero-superior cuff tear

PURPOSE

We retrospectively evaluated the results of complete repair of massive potentially irreparable postero-superior tears in a consecutive cohort of patients. With the increasing and widespread use of superior capsular reconstruction, a complete repair of the superior cuff, also if not functional, may be a valuable option for irreparable cuff lesions.

METHODS

A consecutive case series of massive potentially irreparable postero-superior cuff tears that underwent complete repair was included in the study. Irreparability of cuff tear was defined when on preoperative MRI images, a positive tangent sign, a Goutallier 3-4 stage of fatty infiltration, and an absent acromion-humeral distance were present. A single-row complete repair was performed using triple-loaded titanium suture anchors. Operative time was recorded, as well as intra- and postoperative complications. Patients were followed for 12 months post-op; they were clinically evaluated with the use of constant score (CS) and subjective shoulder value (SSV) at 3, 6, and 12 months; a 12-month postoperative ultrasound evaluation was obtained.

RESULTS

Thirty-two patients satisfying the inclusion criteria were enrolled. The mean age was 52 years (range 41-58). The repair was completed with a mean use of 2.4 triple-loaded suture anchors (range 2-4); the mean operative time was 70 min (range 45-90). The mean preoperative CS was 55 (range 45-75, SD 17), while the SSV was 40 (range 30-70, SD 22). At the final follow-up, the mean CS and SSV were 72 (range 62-85, SD 8) and 80 (range 60-90, SD 10) (p < 0.001 with respect to the preoperative scores), respectively. At the final follow-up, sonography showed a complete healing of the cuff in 20 cases (62.5%). No intra-operative complications occurred; at the final follow-up, five patients (15, 6%) were not satisfied of the results and asked for revision surgery.

CONCLUSIONS

The complete repair of massive potentially irreparable rotator cuff tear in patients younger than 60 years old yielded good results at a short-term follow-up, with a sonographic re-tear rate of about 20%. Even if it is logical to consider a tendon with severe fatty degeneration as non-functional, the superior soft tissue reconstruction we achieved may have at least the same results of a superior capsular reconstruction, with obvious lower costs.

LEVEL OF EVIDENCE

Level 4, case series with no comparison group.

Costamere protein expression and tissue composition of rotator cuff muscle after tendon release in sheep

Previous studies suggested that degradation of contractile tissue requires cleavage of the costamere, a structural protein complex that holds sarcomeres in place. This study examined if costamere turnover is affected by a rotator cuff tear in a previously established ovine model. We found the activity of focal adhesion kinase (FAK), a main regulator of costamere turnover, was unchanged at 2 weeks but decreased by 27% 16 weeks after surgical release of the infraspinatus tendon. This was accompanied by cleavage of the costamere protein talin into a 190 kDa fragment while full length talin remained unchanged. At 2 weeks after tendon release, muscle volume decreased by 17 cm³ from an initial 185 cm³ , the fatty tissue volume was halved, and the contractile tissue volume remained unchanged. After 16 weeks, the muscle volume decreased by 36 cm³ , contractile tissue was quantitatively lost, and the fat content increased by 184%. Nandrolone administration mitigated the loss of contractile tissue by 26% and prevented fat accumulation, alterations in FAK activity, and talin cleavage. Taken together, these findings imply that muscle remodeling after tendon release occurs in two stages. The early decrease of muscle volume is associated with reduction of fat; while, the second stage is characterized by substantial loss of contractile tissue accompanied by massive fat accumulation. Regulation of costamere turnover is associated with the loss of contractile tissue and seems to be impacted by nandrolone treatment. Clinically, the costamere may represent a potential intervention target to mitigate muscle loss after a rotator cuff tear. © 2017 The Authors. Journal of Orthopaedic Research® published by Wiley Periodicals, Inc. on behalf of the Orthopaedic Research Society. J Orthop Res 36:272-281, 2018.

Ten-Year Multicenter Clinical and MRI Evaluation of Isolated Supraspinatus Repairs

BACKGROUND

Early repair of isolated supraspinatus tears could prevent further deterioration of the rotator cuff; however, there is no consensus on the management of such tears because of a lack of long-term outcome studies. The purposes of this study were to report the 10-year outcomes of isolated supraspinatus repairs and to investigate the factors that favor healing and recovery.

METHODS

We retrieved the records of all 511 patients who, in 2003, underwent repair of full-thickness isolated supraspinatus tears, performed by 15 surgeons at 15 centers. In 2014, the patients were asked to return for evaluation at a minimum follow-up of 10 years. One hundred and eighty-eight patients could not be reached, and 35 were excluded because they had a reoperation (17 had a retear, 7 had conversion to an arthroplasty, and 11 had other causes). A total of 288 patients (50% were men) who had a mean age (and standard deviation) at index surgery of 56.5 ± 8.3 years (range, 32 to 77 years) were evaluated clinically, and 210 of them were also evaluated using magnetic resonance imaging (MRI).

RESULTS

Thirty shoulders (10.4%) had complications, including stiffness (20 shoulders), infection (1 shoulder), and other complications (9 shoulders). The total Constant score improved from a mean of 51.8 ± 13.6 points (range, 19 to 87 points) preoperatively to 77.7 ± 12.1 points (range, 37 to 100 points) at 10 years. At the 10-year follow-up evaluation, the mean Subjective Shoulder Value (SSV) was 84.9 ± 14.8 (range, 20 to 100), and the mean Simple Shoulder Test (SST) was 10.1 ± 2.2 (range, 3 to 12). Of the 210 shoulders evaluated using MRI, the repair integrity was Sugaya type I in 26 shoulders (12%), type II in 85 (41%), type III in 59 (28%), type IV in 27 (13%), and type V in 13 (6%). The total Constant score at the final follow-up was significantly associated with tendon healing (p < 0.005) and was inversely associated with preoperative fatty infiltration (p < 0.001). Neither the surgical approach nor the preoperative retraction influenced the outcomes.

CONCLUSIONS

Repairs of isolated supraspinatus tears maintained considerable improvement in clinical and radiographic outcomes at 10 years. Preoperative fatty infiltration and postoperative retear have a significantly detrimental effect on the long-term functional outcome of rotator cuff repair.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

The Rotator Cuff Organ: Integrating Developmental Biology, Tissue Engineering, and Surgical Considerations to Treat Chronic Massive Rotator Cuff Tears

The torn rotator cuff remains a persistent orthopedic challenge, with poor outcomes disproportionately associated with chronic, massive tears. Degenerative changes in the tissues that comprise the rotator cuff organ, including muscle, tendon, and bone, contribute to the poor healing capacity of chronic tears, resulting in poor function and an increased risk for repair failure. Tissue engineering strategies to augment rotator cuff repair have been developed in an effort to improve rotator cuff healing and have focused on three principal aims: (1) immediate mechanical augmentation of the surgical repair, (2) restoration of muscle quality and contractility, and (3) regeneration of native enthesis structure. Work in these areas will be reviewed in sequence, highlighting the relevant pathophysiology, developmental biology, and biomechanics, which must be considered when designing therapeutic applications. While the independent use of these strategies has shown promise, synergistic benefits may emerge from their combined application given the interdependence of the tissues that constitute the rotator cuff organ. Furthermore, controlled mobilization of augmented rotator cuff repairs during postoperative rehabilitation may provide mechanotransductive cues capable of guiding tissue regeneration and restoration of rotator cuff function. Present challenges and future possibilities will be identified, which if realized, may provide solutions to the vexing condition of chronic massive rotator cuff tears.

Mesenchymal Stem Cell Secretome: A Potential Tool for the Prevention of Muscle Degenerative Changes Associated With Chronic Rotator Cuff Tears

BACKGROUND

Massive rotator cuff tears (MRCTs) are usually chronic lesions with pronounced degenerative changes, where advanced fatty degeneration and atrophy can make the tear irreparable. Human mesenchymal stem cells (hMSCs) secrete a range of growth factors and vesicular systems, known as secretome, that mediates regenerative processes in tissues undergoing degeneration.

PURPOSE

To study the effect of hMSC secretome on muscular degenerative changes and shoulder function on a rat MRCT model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A bilateral 2-tendon (supraspinatus and infraspinatus) section was performed to create an MRCT in a rat model. Forty-four Wistar-Han rats were randomly assigned to 6 groups: control group (sham surgery), lesion control group (MRCT), and 4 treated-lesion groups according to the site and periodicity of hMSC secretome injection: single local injection, multiple local injections, single systemic injection, and multiple systemic injections. Forelimb function was analyzed with the staircase test. Atrophy and fatty degeneration of the muscle were evaluated at 8 and 16 weeks after injury. A proteomic analysis was conducted to identify the molecules present in the hMSC secretome that can be associated with muscular degeneration prevention.

RESULTS

When untreated for 8 weeks, the MRCT rats exhibited a significantly higher fat content (0.73% ± 0.19%) compared with rats treated with a single local injection (0.21% ± 0.04%; P < .01) or multiple systemic injections (0.25% ± 0.10%; P < .05) of hMSC secretome. At 16 weeks after injury, a protective effect of the secretome in the multiple systemic injections (0.62% ± 0.14%; P < .001), single local injection (0.76% ± 0.17%; P < .001), and multiple local injections (1.35% ± 0.21%; P < .05) was observed when compared with the untreated MRCT group (2.51% ± 0.42%). Regarding muscle atrophy, 8 weeks after injury, only the single local injection group (0.0993% ± 0.0036%) presented a significantly higher muscle mass than that of the untreated MRCT group (0.0794% ± 0.0047%; P < .05). Finally, the proteomic analysis revealed the presence of important proteins with muscle regeneration, namely, pigment epithelium-derived factor and follistatin.

CONCLUSION

The study data suggest that hMSC secretome effectively decreases the fatty degeneration and atrophy of the rotator cuff muscles.

CLINICAL RELEVANCE

We describe a new approach for decreasing the characteristic muscle degeneration associated with chronic rotator cuff tears. This strategy is particularly important for patients whose tendon healing after later surgical repair could be compromised by the progressing degenerative changes. In addition, both precise intramuscular local injection and multiple systemic secretome injections have been shown to be promising delivery forms for preventing muscle degeneration.

Genomic and lipidomic actions of nandrolone on detached rotator cuff muscle in sheep

Reversal of fatty infiltration of pennate rotator cuff muscle after tendon release is hitherto impossible. The administration of nandrolone starting at the time of tendon release prevents the increase in fat content, but does not revert established fatty infiltration. We hypothesised that tendon release and myotendinous retraction cause alterations in lipid related gene expression leading to fatty muscle infiltration, which can be suppressed by nandrolone through its genomic actions if applied immediately after tendon release. The effects of infraspinatus tendon release and subsequent tendon repair at 16 weeks were studied in six Swiss Alpine sheep. In the interventional groups, 150mg nandrolone was administered weekly after tendon release until sacrifice (N22W, n=6) or starting at the time of repair (N6W, n=6). Infraspinatus volume, composition, expressed transcripts, lipids, and selected proteins were analyzed at baseline, 16 and 22 weeks. Tendon release reduced infraspinatus volume by 22% and increased fat content from 11% to 38%. These changes were not affected by repair. Fatty infiltration was associated with up-regulation of 227 lipid species, and increased levels of the adipocyte differentiation marker PPARG2 (peroxisome proliferator-activated receptor gamma 2). Nandrolone abrogated lipid accumulation, halved the loss in fiber area percentage, and up-regulated androgen receptor levels and transcript expression in the N22W but not the N6W group. The results document that nandrolone mitigates muscle-to-fat transformation after tendon release via a general down-regulation of lipid accumulation concomitantly with up-regulated expression of its nuclear receptor and downstream transcripts in skeletal muscle. Reduced responsiveness of retracted muscle to nandrolone as observed in the N6W group is reflected by a down-regulated transcript response.

Beyond testosterone cypionate: evidence behind the use of nandrolone in male health and wellness

Characterized by low serum testosterone levels and diverse symptoms, male hypogonadism is a common condition. Current medical treatment focuses on testosterone supplementation using multiple modalities such as injections, gels and pellets. Interestingly, while testosterone is considered an anabolic androgenic steroid, it has not been saddled with the social stigma that other, similar medications have. The goal of this review is to highlight an anabolic steroid, 19-nortestosterone (i.e., nandrolone, deca-durabolin) and illustrate prospective therapeutic applications for male health. Containing a chemical structure similar to testosterone, nandrolone has a higher myotrophic: androgenic ratio resulting in improved effects on muscle mass. Animal models have suggested application in the improvement of joint healing following rotator cuff repair. Minimal literature exists regarding the use of nandrolone and, as such, further human studies are required.

Serial MRI evaluation following arthroscopic rotator cuff repair in double-row technique

INTRODUCTION

So far, recurrent rotator cuff defects are described to occur in the early postoperative period after arthroscopic repair. The aim of this study was to evaluate the musculotendinous structure of the supraspinatus, as well as bone marrow edema or osteolysis after arthroscopic double-row repair. Therefore, magnetic resonance (MR) images were performed at defined intervals up to 2 years postoperatively.

STUDY DESIGN

Case series; Level of evidence, 3.

MATERIALS AND METHODS

MR imaging was performed within 7 days, 3, 6, 12, 26, 52 and 108 weeks after surgery. All patients were operated using an arthroscopic modified suture bridge technique. Tendon integrity, tendon retraction ["foot-print-coverage" (FPC)], muscular atrophy and fatty infiltration (signal intensity analysis) were measured at all time points. Furthermore, postoperative bone marrow edema and signs of osteolysis were assessed.

RESULTS

MR images of 13 non-consecutive patients (6f/7m, ∅ age 61.05 ± 7.7 years) could be evaluated at all time points until ∅ 108 weeks postoperatively. 5/6 patients with recurrent defect at final follow-up displayed a time of failure between 12 and 24 months after surgery. Predominant mode of failure was medial cuff failures in 4/6 cases. The initial FPC increased significantly up to 2 years follow-up (p = 0.004). Evaluations of muscular atrophy or fatty infiltration were not significant different comparing the results of all time points (p > 0.05). Postoperative bone marrow edema disappeared completely at 6 months after surgery, whereas signs of osteolysis appeared at 3 months follow-up and increased to final follow-up.

CONCLUSIONS

Recurrent defects after arthroscopic reconstruction of supraspinatus tears in modified suture bridge technique seem to occur between 12 and 24 months after surgery. Serial MRI evaluation shows good muscle structure at all time points. Postoperative bone marrow edema disappears completely several months after surgery. Signs of osteolysis seem to appear caused by bio-absorbable anchor implantations.

Biologic Treatments for Sports Injuries II Think Tank-Current Concepts, Future Research, and Barriers to Advancement, Part 2: Rotator Cuff

Rotator cuff tears are common and result in considerable morbidity. Tears within the tendon substance or at its insertion into the humeral head represent a considerable clinical challenge because of the hostile local environment that precludes healing. Tears often progress without intervention, and current surgical treatments are inadequate. Although surgical implants, instrumentation, and techniques have improved, healing rates have not improved, and a high failure rate remains for large and massive rotator cuff tears. The use of biologic adjuvants that contribute to a regenerative microenvironment have great potential for improving healing rates and function after surgery. This article presents a review of current and emerging biologic approaches to augment rotator cuff tendon and muscle regeneration focusing on the scientific rationale, preclinical, and clinical evidence for efficacy, areas for future research, and current barriers to advancement and implementation.

Efficacy of multimodal analgesia injection combined with corticosteroids after arthroscopic rotator cuff repair

INTRODUCTION

Although arthroscopic rotator cuff repair is minimally invasive, there is still considerable postoperative pain, especially during the first 48 hours. The present study assessed the short-term efficacy and safety of multimodal analgesic (MMA) injection associated to corticosteroids in arthroscopic rotator cuff tear surgery.

MATERIAL AND METHOD

A single-center prospective randomized study included 50 patients undergoing arthroscopic rotator cuff tear surgery. The study group received subacromial injection of a mixture of morphine, ropivacaine and methylprednisolone associated to intra-articular injection of morphine plus methylprednisolone; the control group received only isotonic saline. All patients had had 24 hours self-administered morphine associated to standard analgesia. Postoperative data were recorded at 30 minutes and 1, 2, 4, 6, 12, 18 and 24 hours: pain intensity, morphine intake and side effects, and also time to first morphine bolus and additional analgesic intake. Constant, ASES and SST functional scores were recorded at 3 months.

RESULTS

Postoperative pain was significantly less intense in the MMA group than in controls at 30 min, H1, H4, H6, H12, H18 and H24 (P<0.05). A rebound at D10 occurred in both groups. During the first 24 hours, MMA significantly reduced cumulative resort to morphine (P<0.05 at H1/2, P<0.001 at H1-24). Mean time to first bolus was significantly longer in the MMA group (71.6 vs. 33 min; P<0.05). The rate of opioid-related side effects was similar between groups. At last follow-up, functional scores were similar between groups. There were no cases of infection or delayed skin healing.

CONCLUSION

MMA associated to corticosteroids after arthroscopic rotator cuff tear surgery provided immediate benefit in terms of analgesia and morphine sparing, without apparent risk of infection. The practice is presently little known in France and deserves longer-term assessment, especially as regards functional rehabilitation and tendon healing.

LEVEL OF EVIDENCE

2.

Anabolic Steroids Reduce Muscle Degeneration Associated With Rotator Cuff Tendon Release in Sheep

BACKGROUND

Chronic rotator cuff tendon tearing is associated with irreversible atrophy, fatty infiltration, and interstitial fibrosis of the corresponding muscle.

HYPOTHESES

Anabolic steroids can prevent musculotendinous degeneration during retraction and/or can reverse these changes after operative repair of the retracted musculotendinous unit in sheep.

STUDY DESIGN

Controlled laboratory study.

METHODS

The infraspinatus tendon was released in 18 alpine sheep. All sheep underwent repair of the retracted musculotendinous unit after 16 weeks and were sacrificed after 22 weeks; 6 sheep served as controls, 6 sheep were treated with weekly intramuscular injection of 150 mg of nandrolone decanoate after infraspinatus (ISP) repair (group N6W), and 6 sheep were treated with 150 mg of nandrolone decanoate immediately after tendon release (group N22W). Muscle biopsy specimens were taken before tendon release and after 16 and 22 weeks. Muscle volume and fatty infiltration (on MRI), myotendinous retraction, and muscle density (on computed tomography) were measured immediately after ISP release, after 6 weeks, and before ISP repair and sacrifice.

RESULTS

Muscle volume on MRI decreased to a mean (±SD) of 80% ± 8% of the original volume after 6 weeks, remained stable at 78% ± 11% after 16 weeks, and decreased further to 69% ± 9% after 22 weeks in the control group. These findings were no different from those in group N22W (72% ± 9% at 6 weeks, 73% ± 6% at 16 weeks, and 67% ± 5% at 22 weeks). Conversely, the N6W group did not show a decrease in ISP volume after repair; this finding differed significantly from the response in the control and N22W groups. Fatty infiltration (on MRI) continuously increased in the control group (12% ± 4% at tendon release, 17% ± 4% after 6 weeks, 50% ± 9% after 16 weeks, and 60% ± 8% after 22 weeks) and the N6W group. However, application of anabolic steroids at the time of tendon release (N22W group) significantly reduced fatty infiltration after 16 (16% ± 5%; P < .001) and 22 weeks (22% ± 7%; P < .001).

CONCLUSION

In a sheep model of rotator cuff tendon tear, further muscle atrophy can be prevented with the application of anabolic steroids starting immediately after tendon repair. In addition, fatty muscle infiltration can largely be prevented if the steroids are applied immediately after tendon release.

CLINICAL RELEVANCE

Study findings may lead to the development of treatment strategies to prevent or reduce muscle degeneration caused by rotator cuff tendon tearing.

Tendon response to pharmaco-mechanical stimulation of the chronically retracted rotator cuff in sheep

PURPOSE

Chronic tearing of tendons is associated with molecular and structural alterations causing biomechanical changes, which compromise musculotendinous function and become limiting factors for tendon repair. This study investigated the histological response of chronically retracted sheep rotator cuff tendons to mechanical and pharmacological stimulation in view of tendon repair.

METHODS

Sixteen weeks after experimental release of the infraspinatus tendon in 20 sheep, the retracted musculotendinous unit was subjected to continuous traction either with [anabolic steroids (nandrolone) group/insulin-like growth factor (IGF) group] or without (control group) additional pharmacological treatment during 6 weeks. A new degeneration score for tendinous tissues (DSTT), based on established knowledge on histological changes associated with tendon degeneration, was used for histological analysis at the time of tendon release, at the beginning of continuous re-lengthening and at repair in all animals.

RESULTS

The DSTT score (inter-observer correlation: r = 0.83), quantifiably representing tendon degeneration, improved from 15.5 (SD 1.3) points before to 9.8 (SD 3.8) points after re-lengthening. It improved in a qualitatively and quantitatively similar fashion if pharmacological stimulation was added. The nandrolone group improved from 13.7 (SD 1.6) to 9.8 (SD 1.9) and the IGF group from 13.3 (SD 3.6) to 8.8 (SD 1.8) points.

CONCLUSION

Mechanical stimulation significantly reduced tissue degeneration. However, the addition of a pharmacological stimulation with anabolic steroids or IGF had neither a measurable positive nor negative effect on the degenerative process. Therefore, this investigation does neither support the additional pharmacological use of the anabolic steroid nandrolone or of IGF decanoate for restoration of tendon degeneration, nor otherwise provide evidence for additional tendon damage, if those substances are used to alter the muscular metabolism.

Animal model for chronic massive rotator cuff tear: behavioural and histologic analysis

PURPOSE

Massive rotator cuff tears (MRCT) are usually chronic lesions that present associated degenerative changes of the myotendinous unit that have been implicated in limitations for surgical repair. In order to develop effective therapies, it is important to establish animal models that mimic the hallmarks of the injury itself. Therefore, in the present work, we aimed to (1) optimize a rodent animal model of MRCT that closely reproduces the fatty infiltration of the cuff muscles seen in humans and (2) describe the effects of unilateral or bilateral lesion in terms of histology and behaviour.

METHODS

Massive tear was defined as two rotator cuff tendons-supraspinatus and infraspinatus-section. Twenty-one Wistar rats were randomly assigned to four groups: bilateral lesion (five animals), right-sided unilateral lesion (five animals), left-sided unilateral lesion (five animals) and control (six animals). Behaviour was analyzed with open field and staircase test, 16 weeks after lesion. After that, animals were killed, and the supraspinatus and infraspinatus muscles were processed.

RESULTS

Histologic analysis revealed adipocytes, fatty infiltration and atrophy in the injured side with a greater consistency of these degenerative changes in the bilateral lesion group. Behaviour analysis revealed a significant functional impairment of the fine motor control of the forepaw analyzed in staircase test where the number of eaten pellets was significantly higher in sham animals (sham = 7 ± 5.0; left unilateral = 2.6 ± 3.0; right unilateral = 0 ± 0; and bilateral = 0 ± 0, p < 0.05). A trend to reach a lower level of steps, in more injured animals, was also observed (sham animals = 3 ± 1.6 > left unilateral = 2 ± 2.1 > right unilateral = 0.8 ± 1.3 > bilateral = 0.8 ± 1.1).

CONCLUSIONS

The present study has been able to establish an animal model that disclosed the hallmarks of MRCT. This can now be used as a valuable, cost-effective, pre-clinical instrument to assist in the development of advanced tissue engineered strategies. Moreover, this animal model overcomes some of the limitations of those that have been reported so far and thus represents a more reliable source for the assessment of future therapeutic strategies with potential clinical relevance.

Fatty infiltration and rotator cuff atrophy

Moderate to severe fatty infiltration and rotator cuff atrophy are commonly associated with poor clinical outcomes and failed rotator cuff repair. Numerous animal and human studies have attempted to elucidate the etiology of fatty infiltration and rotator cuff atrophy. Mechanical detachment of the tendon in rotator cuff tears is primarily responsible. Suprascapular nerve injury may also play a role. CT, MRI, and ultrasonography are used to evaluate severity. The Goutallier staging system is most commonly used to evaluate fatty infiltration, and rotator cuff atrophy is measured using multiple techniques. The presence and severity of fatty infiltration have been associated with increasing age, tear size, degree of tendon retraction, number of tendons involved (ie, massive tears), suprascapular neuropathy, and traumatic tears. Fatty infiltration is irreversible and progressive if left untreated. Slight reversal of muscle atrophy has been noted after repair in some studies. Novel therapies are currently being evaluated that may eventually allow clinicians to alter the natural history and improve patient outcomes.

The science of rotator cuff tears: translating animal models to clinical recommendations using simulation analysis

PURPOSE

The purpose of this article is to review basic science studies using various animal models for rotator cuff research and to describe structural, biomechanical, and functional changes to muscle following rotator cuff tears. The use of computational simulations to translate the findings from animal models to human scale is further detailed.

METHODS

A comprehensive review was performed of the basic science literature describing the use of animal models and simulation analysis to examine muscle function following rotator cuff injury and repair in the ageing population.

RESULTS

The findings from various studies of rotator cuff pathology emphasize the importance of preventing permanent muscular changes with detrimental results. In vivo muscle function, electromyography, and passive muscle-tendon unit properties were studied before and after supraspinatus tenotomy in a rodent rotator cuff injury model (acute vs chronic). Then, a series of simulation experiments were conducted using a validated computational human musculoskeletal shoulder model to assess both passive and active tension of rotator cuff repairs based on surgical positioning.

CONCLUSION

Outcomes of rotator cuff repair may be improved by earlier surgical intervention, with lower surgical repair tensions and fewer electromyographic neuromuscular changes. An integrated approach of animal experiments, computer simulation analyses, and clinical studies may allow us to gain a fundamental understanding of the underlying pathology and interpret the results for clinical translation.

Biologics in the management of rotator cuff surgery

The rotator cuff enthesis is not reestablished after a rotator cuff repair. Instead, a scar-mediated healing response occurs at the tendon-bone interface, which is notably weaker than the native enthesis and thus more prone to failure. Biological augmentation through growth factors, AASs, biomimetic scaffolds, or siRNA therapy has the potential to enhance the healing response. The ultimate key, however, is in determining which of these enables a more regenerative healing response of the native tissue rather than enhanced production of scar tissue. In addition, the optimal combination of factors, dosing, and delivery methods remains to be clearly elucidated. Biological augmentation and tissue engineering for tendon healing remains promising, but much work still needs to be done.

Rotator cuff muscles lose responsiveness to anabolic steroids after tendon tear and musculotendinous retraction: an experimental study in sheep

BACKGROUND

Long-standing rotator cuff tendon tearing is associated with retraction, loss of work capacity, irreversible fatty infiltration, and atrophy of the rotator cuff muscles. Although continuous musculotendinous relengthening can experimentally restore muscular architecture, restoration of atrophy and fatty infiltration is hitherto impossible.

HYPOTHESIS

Continuous relengthening with pharmacological stimulation of muscle growth using an anabolic steroid or insulin-like growth factor (IGF) can reverse atrophy and fatty infiltration as well as improve the work capacity of chronically retracted rotator cuff muscles in sheep.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixteen weeks after tenotomy of the infraspinatus (ISP) tendon, atrophy and fatty infiltration had developed in the retracted ISP muscle. The musculotendinous unit was continuously relengthened in 14 sheep during 6 weeks: Four sheep were treated without pharmacological stimulation, 4 with intramuscular administration of an anabolic steroid, and 6 with IGF before final repair and rehabilitation (12 weeks). Changes were documented by intraoperative measurements of muscle work capacity, histology, and computed tomography/magnetic resonance imaging.

RESULTS

Musculotendinous relengthening by continuous traction resulted in gains of length ranging from 0.7 cm in the IGF group to 1.3 cm in the control group. Fatty infiltration progressed in all groups, and the muscle's cross-sectional area ranged from 71% to 74% of the contralateral side at sacrifice and did not show any differences between groups in weight, volume, histological composition, or work capability of the muscle. The contralateral muscles in the anabolic steroid group, however, showed significantly higher (mean ± standard deviation) muscle work capacity of 10 ± 0.9 N·m than the contralateral muscles of the control group (6.8 ± 2.4 N·m) (P < .05). This was accompanied by an increased mean muscle fiber area as well as by an unusual gain in the animals' weight after injection of the anabolic steroid.

CONCLUSION

Subcutaneous continuous relengthening of a chronically retracted musculotendinous unit is feasible and advances the retracted musculotendinous junction toward its original position. This does not change the muscle work capacity. Whereas anabolic steroids have been shown to be effective in preventing classic degenerative muscle changes after tendon tears, neither an anabolic steroid nor IGF contributes to regeneration of the muscle once degenerative changes are established.

CLINICAL RELEVANCE

The findings demonstrate that muscle cells lose reactiveness to an anabolic steroid and IGF once retraction has led to fatty infiltration and atrophy of the muscle. Retraction of the muscle after tendon tears must be avoided by early repair, particularly in an athlete, as no regeneration can be achieved by mechanical or pharmacological means at this time.