The quantification of muscle activities during arm elevation following reverse shoulder arthroplasty or superior capsular reconstruction for irreparable rotator cuff tears using positron emission tomography.

BACKGROUND: Reverse shoulder arthroplasty (RSA) and superior capsular reconstruction (SCR) are recognized as surgical options for an irreparable rotator cuff tear. However, the postoperative changes of the muscle activity patterns remain unclear. The purpose of this study was to investigate the quantified muscle activities on shoulder elevation in patients treated with RSA or SCR using fluorine-18-labelled fluorodeoxyglucose-positron emission tomography. METHODS: Asymptomatic shoulders that underwent RSA or SCR and those without a rotator cuff tear were analyzed as the RSA, SCR, and control groups. All subjects underwent shoulder elevation exercise, followed by a fluorine-18-labelled fluorodeoxyglucose-positron emission tomography examination. Using previously established methods to quantify the uptake of each muscle on positron emission tomography images, the standard uptake values (SUVs) for 16 portions of the deltoid, rotator cuff, and periscapular muscles were obtained to compare the muscle activity patterns among 3 groups. RESULTS: The deltoid muscle showed the most characteristic differences according to the surgeries. The mean SUVs of the anterior, middle, and posterior deltoid were 3.3, 3.7, and 1.5 for the RSA group; 2.7, 4.2, and 1.5 for the SCR group; and 1.3, 2.0, and 0.9 for the control group, respectively. In comparison to the control group, both the RSA and SCR groups showed significantly increased SUVs at all portions of the deltoid muscle. The RSA group showed similar SUVs for the anterior and middle deltoid, whereas the SCR and control groups showed greatest SUVs at the middle deltoid. In addition, the serratus anterior, levator scapulae, and upper portion of the trapezius in the RSA group showed greater SUVs than in the control group. CONCLUSION: The deltoid muscle showed increased activity in the RSA and SCR groups. The middle deltoid was mainly used in the SCR group, whereas the anterior and middle deltoid, as well as the upward rotator muscles of the scapula, were mainly used in the RSA group.

Three-dimensional quantitative measurements of atrophy and fat infiltration in sub-regions of the supraspinatus muscle show heterogeneous distributions: a cadaveric study.

INTRODUCTION: Rotator cuff tears are common in the older population. Atrophy and fat infiltration develop un-evenly in torn supraspinatus (SSP) muscles leading to pre- and post-surgical complications. The purpose of the current study was twofold: first, to implement a volumetric and quantitative magnetic resonance imaging (MRI) approach to quantify the degree of muscle atrophy and fat infiltration within the SSP muscle and its four sub-regions (AS, PS, AD, and PD); second to compare 3-D MRI outcomes to the standard 2-D assessment and investigate their relationship with tear size. MATERIALS AND METHODS: Fifteen cadaveric shoulders were obtained and MRI performed. Quantitative 3-D outcomes included SSP muscle volume, fossa volume, fat-free muscle volume, and fat fraction for the whole SSP muscle and its four sub-regions. 2-D and qualitative measurements included tear size, 2-D fat infiltration using the Goutallier classification, tangent sign, and occupation ratio. RESULTS: Linear regression outcomes with tear size were not significant for both cross-sectional area (r = - 0.494, p = 0.061) and occupation ratio (r = - 0.011, p = 0.969). Tear size negatively correlated with fat-free muscle volume for both AS and PS sub-regions (AS: r = - 0.78, p < 0.001; PS: r = - 0.68, p = 0.005, respectively) while showing no significant correlation with fat fraction outcomes. AD and PD sub-regions positively correlated with tear size and fat fraction outcomes (AD: r = 0.70, p = 0.017; PD: r = 0.52, p = 0.045, respectively), while no significant correlation was observed between tear size and fat-free muscle volumes. CONCLUSION: Quantitative 3-D volumetric assessment of muscle degeneration resulted in better outcomes compared to the standard 2-D evaluation. The superficial supraspinatus muscle sub-regions primarily presented muscle atrophy, while the deep sub-regions were mainly affected by fat infiltration. 3-D assessments could be used pre-surgically to determine the best course of treatment and to estimate the muscles' regenerative capacity and function.

Mechanism and patterns of bone loss in patients with anterior shoulder dislocation.

BACKGROUND: Bony defects are common injuries associated with anterior shoulder dislocation. It is generally thought that these bony defects are created at the time of dislocation. However, there have been no biomechanical reports demonstrating the exact time point when these lesions occur. The purpose of this study was to clarify when, how, and which types of bony defects were created during experimental dislocation in cadaveric shoulders. METHODS: Fifteen fresh-frozen cadaveric shoulders (mean age at the time of death, 79 years) were fixed in a custom testing machine. First, the glenohumeral joint was inspected by arthroscopy. Then, the arm was held at 60° of abduction and maximum external rotation and was manually extended horizontally under fluoroscopy until an anterior dislocation occurred. Next, a force of 800 N was applied to a Kirschner wire inserted in the humeral head in the direction of the pectoralis major with use of an air cylinder. We waited until the arm came to equilibrium under this condition. Finally, the glenohumeral joint was arthroscopically examined. We further performed x-ray micro-computed tomography and histologic examination in 1 shoulder with a bipolar lesion. RESULTS: After the anterior dislocation, a Bankart lesion was created in 9 of 15 shoulders and a fragment-type glenoid defect (avulsion fracture) was created in 4. A Hill-Sachs lesion, on the other hand, was not observed after the dislocation. The equilibrium arm position was 40° ± 17° in flexion, 45° ± 22° in abduction, and 27° ± 19° in external rotation. In this arm position, newly created lesions were Hill-Sachs lesions in 6 shoulders and erosion-type glenoid defects (compression fracture) in 7. Micro-computed tomography, performed in a single specimen, showed a flattened anterior glenoid rim with collapse of trabecular bone. Histologic analysis of nondecalcified sections using hematoxylin-eosin staining indicated that the anterior rim of the glenoid was compressed and flattened. The cortex of the anterior glenoid rim could be clearly observed. CONCLUSION: The fragment-type glenoid defect (avulsion fracture) was observed at the time of dislocation, whereas the erosion-type defect (compression fracture) was observed when the arm came to equilibrium in the midrange of motion. Hill-Sachs lesions were created not at the time of dislocation but after the arm came to equilibrium.

Shoulder arthroplasty in patients with immunosuppression following solid organ transplantation.

BACKGROUND: The purpose was to determine the risk and outcomes of primary shoulder arthroplasties in patients with immunosuppression who had undergone solid organ transplantation. METHODS: Using a single institution's total joint registry, we reviewed 30 primary shoulder arthroplasties in 25 post-transplantation patients, including 12 total shoulder arthroplasties, 10 hemiarthroplasties, and 8 reverse shoulder arthroplasties, between 1985 and 2012. Therapy and patient variables were recorded, including immunosuppressive therapy protocols, the date of preceding solid organ transplantation, and specific medications taken in the perioperative period. We matched a cohort of control patients for age, sex, type of implant, and year of surgery at a ratio of 4:1. Two groups were compared regarding mortality risk, complications, and clinical outcomes (pain score, range of motion, and American Shoulder and Elbow Surgeons score). RESULTS: No periprosthetic infections occurred in the post-transplantation group at a mean follow-up of 39 months. However, the post-transplantation group showed an increased risk of periprosthetic fractures compared with the control group (hazard ratio, 8.18; 95% confidence interval, 1.22-70.98; P = .03). Despite the increase in fractures, the overall number of complications did not differ between the groups. Furthermore, postoperative shoulder function and outcome scores were not significantly different between patients who had a prior transplant and those who did not. CONCLUSION: Primary shoulder arthroplasty in patients with immunosuppression who underwent solid organ transplantation is a successful procedure to treat glenohumeral arthritis. In contrast, there may be an increased risk of periprosthetic fractures in patients with a history of a solid organ transplant.

Comparison of best-fit circle versus contralateral comparison methods to quantify glenoid bone defect.

BACKGROUND: Several measurement techniques have been reported to quantify glenoid bone defect in patients with anterior shoulder instability. Among them, the method that uses a best-fit circle and another that uses the contralateral glenoid as a control are most commonly used. However, to our knowledge, no study has been reported that compared the reliability of these methods. The purpose of this study, therefore, was to determine which of these methods has higher reproducibility. METHOD: In this study, 3-dimensional computed tomography data from 94 patients (mean age 29 years) with unilateral anterior shoulder instability were used. Three examiners measured the glenoid bone defect of each patient 3 times using 2 techniques: the best-fit circle method and the contralateral comparison method. Intra- and interobserver reliabilities were measured using intraclass correlation coefficient (ICC). RESULTS: The intraobserver reliability was found to be 0.91 for the best-fit circle method and 0.98 for the contralateral comparison method. The interobserver reliability was 0.77 for the best-fit circle method and 0.88 for the contralateral method. The percentage of glenoid defect was 11.5% when using the best-fit circle and 10.7% with the contralateral method. CONCLUSION: The contralateral comparison method was more reliable than the best-fit circle method for quantifying the amount of glenoid bone loss.

Curved-guide system is useful in achieving optimized trajectory for the most inferior suture anchor during arthroscopic Bankart repair.

BACKGROUND: A curved-drill guide system was recently introduced to achieve a better trajectory for a low anteroinferior anchor during arthroscopic Bankart repair. However, the clinical performance of such a device remains unclear. The purpose of this study was to evaluate the trajectory and position of the low anteroinferior suture anchor with use of the curved-guide system in clinical cases. METHODS: We enrolled 41 cases of arthroscopic Bankart repair in this study. Of these cases, 9 were repaired using the curved drill guide whereas 32 were repaired using a conventional straight guide. Postoperative computed tomography scans were obtained, and 3-dimensional models of the scapula were reconstructed. Notable perforations of the opposite cortex by the most inferior anchors were recorded. The clock-face angle, insertion angle, and insertion distance were measured. RESULTS: The anchor perforation rate in the curved-guide group (11%) was significantly lower than that in the straight-guide group (56%) (P = .02). The insertion distance in the curved-guide group was significantly shorter than that in the straight-guide group (4.0 ± 1.6 mm vs. 7.0 ± 2.4 mm, P < .01). The clock-face angle and insertion angle were significantly greater in the perforated straight-guide group than in the nonperforated groups. The percentage of anchors in the absolute safe zone (clock-face angle > 135° and < 165° and insertion angle < 100°), where no anchors perforated, was greater in the curved-guide group than the straight-guide group. CONCLUSION: Compared with the conventional straight guide, the curved-guide system provides better placement of the most inferior suture anchor during arthroscopic Bankart repair.

Efficacy of collagenase Clostridium histolyticum injection for Dupuytren's contracture in East-Asian population.

BACKGROUND: Treatment with injection of collagenase Clostridium histolyticum (CCH) has been recognized as an effective option for the Dupuytren's contracture (DC) in Europe and North America. However, there are no studies describing mid-term efficacy of CCH treatment in East-Asian population. The purpose of this study was to assess 2-year outcomes following CCH treatment in Japanese patients. METHODS: Twenty hands (28 joints) from 18 DC patients underwent CCH injection with manipulation according to the product specifications with 2-year follow-up. Patients were assessed for extension deficit on treated metacarpophalangeal (MCP) and/or proximal interphalangeal (PIP) joints before treatment, at 4 weeks and 2 years after the treatment. RESULTS: At 4 weeks after CCH treatment, contracture of treated joints significantly improved from the mean extension deficit of 45° before treatment to 3° for MCP joints, and from 41° to 14° for PIP joints (P < 0.001, <0.001, respectively). Improved contracture was maintained with 4° and 23° at 2 years after CCH treatment (P < 0.001, <0.05, respectively). Successful correction defined as ≤ 5° extension deficit was obtained in 14/16 MCP and 5/12 PIP joints at 4 weeks; of these, 11 MCP and 1 PIP joints maintained the corrected range of motion at 2-year follow-up. CONCLUSION: CCH treatment could be a useful option to improve contracture in Japanese patients. During 2-year follow-up, this treatment could provide comparable effect durability to previous studies from Western countries. Moreover, our results support the evidence that better correction of the contracture can be obtained in the MCP joints than PIP joints after CCH treatment.

Intramuscular fat infiltration evaluated by magnetic resonance imaging predicts the extensibility of the supraspinatus muscle.

INTRODUCTION: Rotator cuff (RC) tears result in muscle atrophy and fat infiltration within the RC muscles. An estimation of muscle quality and deformation, or extensibility, is useful in selecting the most appropriate surgical procedure. We determined if noninvasive quantitative assessment of intramuscular fat using MRI could be used to predict extensibility of the supraspinatus muscle. METHODS: Seventeen cadaveric shoulders were imaged to assess intramuscular fat infiltration. Extensibility and histological evaluations were then performed. RESULTS: Quantitative fat infiltration positively correlated with histological findings and presented a positive correlation with muscle extensibility (r = 0.69; P = 0.002). Extensibility was not significantly different between shoulders graded with a higher fat content versus those with low fat when implementing qualitative methods. DISCUSSION: A noninvasive prediction of whole-muscle extensibility may directly guide pre-operative planning to determine if the torn edge could efficiently cover the original footprint while aiding in postoperative evaluation of RC repair. Muscle Nerve 57: 129-135, 2018.

Critical shoulder angle in an East Asian population: correlation to the incidence of rotator cuff tear and glenohumeral osteoarthritis.

BACKGROUND: Focus has recently been on the critical shoulder angle (CSA) as a factor related to rotator cuff tear and osteoarthritis (OA) in the European population. However, whether this relationship is observed in the Asian population is unclear. METHODS: The correlation between the CSAs measured on anteroposterior radiographs and the presence or absence of rotator cuff tears or OA changes was assessed in 295 patients. Rotator cuff tears were diagnosed with magnetic resonance imaging or ultrasonography. OA findings were classified using the Samilson-Prieto classification. The CSAs among the patients with rotator cuff tears, OA changes, and those without pathologies were compared. Multivariable analyses were used to clarify the potential risks for these pathologies. RESULTS: The mean CSA with rotator cuff tear (33.9° ± 4.1°) was significantly greater than that without a rotator cuff tear (32.3° ± 4.5°; P = .002). Multivariable analysis also showed that a greater CSA had a significantly increased risk of rotator cuff tears, with the odds ratio of 1.08 per degree. OA findings showed no significant correlation to the CSAs. CONCLUSIONS: Our study demonstrates that the CSA is greater in those with a rotator cuff tear than in those without a tear or OA changes, which may be an independent risk factor for the incidence of rotator cuff tears in the Japanese population.

Glenoid bone grafting in primary reverse total shoulder arthroplasty.

BACKGROUND: Severe glenoid bone loss remains a challenge in patients requiring shoulder arthroplasty and may necessitate glenoid bone grafting. The purpose of this study was to determine results, complications, and rates of failure of glenoid bone grafting in primary reverse shoulder arthroplasty. METHODS: Forty-one shoulders that underwent primary reverse arthroplasty between 2006 and 2013 with a minimum follow-up of 2 years (mean, 2.8 years; range, 2-6 years) were reviewed. Thirty-four (83%) received corticocancellous grafts and 7 (17%) structural grafts. RESULTS: Active range of motion and pain levels were significantly improved (P < .001), with mean American Shoulder and Elbow Surgeons score of 77, Simple Shoulder Test score of 9, and patient satisfaction of 93% at the most recent follow-up. Preoperative severe glenoid erosion and increasing body mass index were significantly associated with worse American Shoulder and Elbow Surgeons scores (P = .04). On radiographic evaluation, 7 patients (18%) had grade 1 or grade 2 glenoid lucency. Glenoid bone graft incorporation was observed in 31 patients (78%). Twelve patients (30%) suffered from grade 1 or grade 2 scapular notching. All of the patients with structural grafts showed graft incorporation and no signs of glenoid lucency. CONCLUSION: Although glenoid lucency, glenoid graft resorption, and scapular notching were present at short-term to midterm follow-up, none of the patients needed revision surgery. Primary reverse shoulder arthroplasty with glenoid reconstruction using bone graft relieved pain and restored shoulder function and stability.

Is previous nonarthroplasty surgery a risk factor for periprosthetic infection in primary shoulder arthroplasty?

BACKGROUND: The purpose of this study was to determine the risk of periprosthetic infection after primary shoulder arthroplasty (SA) in patients undergoing previous nonarthroplasty shoulder surgery compared with those without previous surgery. MATERIALS AND METHODS: All patients undergoing primary SA at our institution between 1970 and 2012 were included in this study. The cohort consisted of 4577 patients treated with 2890 total SAs, 1233 hemiarthroplasties, and 454 reverse SAs; 813 (18%) patients had undergone prior nonarthroplasty shoulder surgery on the operative side. Patients with and without previous surgery were compared for postoperative periprosthetic infection. Univariate and multivariable analyses were used. RESULTS: Deep postoperative infection of the shoulder was diagnosed in 68 patients (1.49%). Of the 813 patients who had undergone previous surgery, 20 (2.46%) developed a deep postoperative infection. However, of the 3764 patients who did not have previous shoulder surgery, 48 patients (1.28%) sustained deep shoulder infection. This difference was significant in both the univariate (P = .0094) and multivariate analyses (P = .0390). In addition, older age and female gender were significantly associated with a lower risk of deep postoperative infection (P = .0150 and P = .0074, respectively). A higher number of previous surgeries was also significantly associated with an increased risk of deep postoperative infection (P = .0272). CONCLUSIONS: The risk of infection after primary SA is significantly higher in patients with a history of prior non-arthroplasty-related surgery. This finding should be discussed with the patients before their surgery, and potential preoperative and intraoperative workup should be undertaken to identify at-risk patients.

Effect of smoking on complications following primary shoulder arthroplasty.

BACKGROUND: The purpose of this study was to examine the effect of smoking on the incidence of complications after primary anatomic total shoulder arthroplasty (TSA) and reverse shoulder arthroplasty (RSA). METHODS: All patients who underwent primary TSA or RSA at our institution between 2002 and 2011 and had a minimum 2-year follow-up were included. Smoking status was assessed at the time of surgery. Current smokers, former smokers, and nonsmokers were compared for periprosthetic infection, fractures (intraoperative and postoperative), and loosening after surgery. RESULTS: The cohort included 1834 shoulders in 1614 patients (814 in smokers and 1020 in nonsmokers). Complications occurred in 73 patients (75 shoulders; 44 in smokers and 31 in nonsmokers). There were 20 periprosthetic infections (16 in smokers and 4 in nonsmokers), 27 periprosthetic fractures (14 in smokers and 13 in nonsmokers), and 28 loosenings (14 in smokers and 14 in nonsmokers). Smokers had lower periprosthetic infection-free survival rates (95.3%-99.4% at 10 years; P = .001) and overall complication-free survival rates (78.4%-90.2%; P = .012) than nonsmokers. Multivariable analyses showed that both current and former smokers had significantly higher risk of periprosthetic infection in comparison with nonsmokers (hazard ratio [HR], 7.27 and 4.56, respectively). In addition, current smokers showed a higher risk of postoperative fractures than both former smokers (HR, 3.63) and nonsmokers (HR, 6.99). CONCLUSIONS: This study demonstrates that smoking is a significant risk factor of complications after TSA and RSA. These findings emphasize the need for preoperative collaborative interventions, including smoking cessation programs.

Comfort and acceptability of various immobilization positions using a shoulder external rotation and abduction brace.

BACKGROUND: Immobilization with shoulder braces is used for conservative treatment of an initial shoulder dislocation. Various arm positions have been investigated to determine optimal position in terms of the anatomical reduction of the Bankart lesion. Recently, the effect of immobilization in shoulder abduction as well as in external rotation has been reported. However, there are few studies assessing subjects' acceptability of the brace in various arm positions. We hypothesized that a certain arm position regarding abduction or external rotation for immobilization would induce significant discomfort during activities of daily living. METHODS: A dominant arm of 20 healthy participants was immobilized with a shoulder brace in 4 different positions; adduction and internal rotation (Add-IR), adduction and external rotation (Add-ER), 30° of abduction and 30° of external rotation (Abd-30ER), and 30° of abduction and 60° of external rotation (Abd-60ER). After completing immobilization for 24 h, subjects were asked to assess the discomfort of bracing for overall and individual activities, using a visual analogue scale. Data were compared among the four positions. RESULTS: For overall activities and several activities (eating, reading books, and removing and putting on pants), Abd-60ER was significantly more uncomfortable than adducted arm positions. Abd-30ER did not show any differences compared to the other arm positions. CONCLUSION: Immobilization in abduction and external rotation seems to be acceptable although the arm position in 30° of abduction and 60° of external rotation is less comfortable than the others. Our results might be useful in determining and developing the ideal shoulder brace which could keep patients' compliance and improve their outcomes.

Comparison of Passive Stiffness Changes in the Supraspinatus Muscle After Double-Row and Knotless Transosseous-Equivalent Rotator Cuff Repair Techniques: A Cadaveric Study.

PURPOSE: To investigate the alteration of passive stiffness in the supraspinatus muscle after double-row (DR) and knotless transosseous-equivalent (KL-TOE) repair techniques, using shear wave elastography (SWE) in cadavers with rotator cuff tears. We also aimed to compare altered muscular stiffness after these repairs to that obtained from shoulders with intact rotator cuff tendon. METHODS: Twelve fresh-frozen cadaveric shoulders with rotator cuff tear (tear size: small [6], medium-large [6]) were used. Passive stiffness of 4 anatomic regions in the supraspinatus muscle was measured based on an established SWE method. Each specimen underwent DR and KL-TOE footprint repairs at 30° glenohumeral abduction. SWE values, obtained at 0°, 10°, 20°, 30°, 60°, and 90° abduction, were assessed in 3 different conditions: preoperative (torn) and postoperative conditions with the 2 techniques. The increased ratio of SWE values after repair was compared among the 4 regions to assess stiffness distribution. In addition, SWE values were obtained on 12 shoulders with intact rotator cuff tendons as control. RESULTS: In shoulders with medium-large-sized tears, supraspinatus muscles showed an increased passive stiffness after rotator cuff repairs, and this was significantly observed at adducted positions. KL-TOE repair showed uniform stiffness changes among the 4 regions of the supraspinatus muscle (mean, 189% to 218% increase after repair), whereas DR repair caused a significantly heterogeneous stiffness distribution within the muscle (mean, 187% to 319% after repair, P = .002). Although a repair-induced increase in muscle stiffness was observed also in small-sized tears, there were no significant differences in repaired stiffness changes between DR and KL-TOE (mean, 127% to 138% and 127% to 130% after repairs, respectively). Shoulders with intact rotator cuff tendon showed uniform SWE values among the 4 regions of the supraspinatus muscle (mean, 38.2 to 43.0 kPa). CONCLUSIONS: Passive stiffness of the supraspinatus muscle increases after rotator cuff repairs for medium-large-sized tears. KL-TOE technique for the medium-large-sized tear provided a more uniform stiffness distribution across the repaired supraspinatus muscles compared with the DR technique. CLINICAL RELEVANCE: Based on this insight, investigating rotator cuff muscle stiffness changes, further studies using SWE may determine the optimal repair technique for various sizes of rotator cuff tears.

Association between acromioclavicular joint pain and capsular bulging in adolescent baseball players.

PURPOSE: The purpose of this study was to investigate the association between acromioclavicular (AC) joint pain and superior capsular bulging assessed by ultrasound in adolescent baseball players. METHODS: One hundred and fifty players (1st-8th graders) were examined. All subjects underwent physical examinations, including assessment of tenderness on the AC joint and provocative tests (the Buchberger's test and the cross-body adduction stress test). Bilateral AC joints with the arm in both the resting and the cross-body positions were examined by ultrasound. RESULTS: Twelve of 150 players (8 %) had AC symptoms with both positive tenderness and positive provocative tests. Interestingly, their prevalence increased with age-one of the 70 (1.4 %) 1st-3rd graders, six of 46 (13 %) 4th-6th graders and five of 34 (15 %) 7th-8th graders. Ultrasonography of AC joints in the cross-body position showed that the difference in superior capsular bulging between the throwing and non-throwing sides was significantly greater in symptomatic players (1.6 ± 1.2 mm) than in asymptomatic players (0.2 ± 0.8 mm) (p = 0.002). CONCLUSION: The prevalence of superior capsular bulging was significantly higher in adolescent baseball players with AC joint pain than in those without it. In adolescent baseball players with shoulder pain, AC joint symptoms should be considered amongst potential causes. Careful observation of these patients is suggested in cases of superior capsular bulging of the AC joint as determined by ultrasonography. LEVEL OF EVIDENCE: III.

The role of an octacalcium phosphate in the re-formation of infraspinatus tendon insertion.

BACKGROUND: To improve the success rate of rotator cuff repair, we investigated whether octacalcium phosphate (OCP) with gelatin (Gel) vehicle had a positive effect on tendon-to-bone healing. METHODS: We assessed the histologic characteristics of the tendon-to-bone healing using the rabbit rotator cuff repair model. We divided the shoulders into 3 groups: control (without OCP/Gel composite), OCP/Gel composite (OCP+group), and Gel alone without OCP (Gel group) to evaluate the effectiveness of gelatin. RESULTS: Both the number of newly formed tendon fibers and the Sharpey fibers at the repair site increased in the OCP+group compared with those in the other 2 groups on hematoxylin-eosin staining (P < .05). On immunohistochemical evaluation, both the bone and the fibers in the OCP+group demonstrated that type I collagen was picked up, whereas the newly formed tendon fibers and Sharpey fibers revealed type III collagen. CONCLUSION: Treatment with OCP made collagen fibers and the Sharpey fibers, constituted by type I and type III collagens, increase at the tendon-to-bone insertion. It might be beneficial for the healing of rotator cuff tendon to bone.

Feasibility assessment of shear wave elastography to rotator cuff muscle.

Pre-surgical measurement of supraspinatus muscle extensibility is important for rotator cuff repair. The purpose of the present study was to explore the potential feasibility of a shear wave ultrasound elastography (SWE)-based method, combined with B-mode ultrasound, to measure the in vivo stiffness of the supraspinatus muscle non-invasively and thus obtain key information about supraspinatus muscle extensibility. Our investigation comprised two steps. First, we determined the orientation of the supraspinatus muscle fibers in cadaveric shoulders without rotator cuff tear in order to optimize the ultrasound probe positions for SWE imaging. Second, we investigated the feasibility of quantifying the stiffness of the normal supraspinatus muscle by SWE in vivo. The supraspinatus muscle was divided into four anatomical regions: anterior superficial (AS), posterior superficial (PS), anterior deep (AD), and posterior deep (PD). Each region was examined by SWE. The SWE stiffnesses of AD, AS, PD, and PS were 40.0 ± 12.4, 34.0 ± 9.9, 32.7 ± 12.7, 39.1 ± 15.7 kPa, respectively. SWE combined with B-Mode ultrasound imaging could be a feasible method for quantifying the local stiffness of the rotator cuff muscles.

In vivo measurement of rotator cuff tendon strain with ultrasound elastography: an investigation using a porcine model.

OBJECTIVES: To clarify the relationship between the strain ratio measured by ultrasound elastography and the mechanical properties of the tendon measured by a universal testing machine. We also attempted to determine the effect of the type and depth of soft tissue overlying the tendon on the elastographic measurement. METHODS: Twelve fresh porcine shoulders were prepared. Elastographic measurement was performed on the infraspinatus tendon by manually applying repetitive compressions from an ultrasound probe with an acoustic coupler consisting of an elastomer with definite elasticity as a reference material. The strain ratio, defined as tendon/reference strain, was obtained by 4 different approaches: with the probe placed on the skin, on the subcutaneous fat after removing the skin, on the muscle after removing the subcutaneous fat, and directly on the tendon. The strain ratios measured by these approaches were compared statistically. The relationship between the depth of the tendon measured on elastography and the strain ratio was also investigated. We also attempted to clarify the relationship between the strain ratio of the tendon and its elastic property. The tendon was mounted on a testing machine, and compressive force was applied. Tendon compliance was calculated as the reciprocal of the Young modulus in the range of 5% to 10% strain, which was compared to its strain ratio. RESULTS: The tendon/reference strain ratio significantly correlated with the tendon compliance (r = 0.73; P < .01). The strain ratio was not affected by differences in the measuring approaches (P = .4) or by the depth to the tendon level (P = .8). CONCLUSIONS: Our results indicated that the strain ratio of the rotator cuff tendon could be measured with minimal influence by overlying soft tissues if its depth from the skin was less than 22 mm. We believe that ultrasound elastography would be a useful tool for assessment of tendon elasticity in clinical practice.

Stress distribution inside bone after suture anchor insertion: simulation using a three-dimensional finite element method.

PURPOSE: To define stress distribution patterns inside a bone around suture anchors inserted at different angles using a three-dimensional finite element (FE) method. METHODS: An isotropic cube model (Young's modulus, 1,380 MPa; Poisson's ratio, 0.3) was designed on a computer to standardize analysis conditions. A virtual Twinfix anchor was inserted into the cube at two different angles (45° and 90°) against the top surface. A traction force (100 N) was applied to the anchor at six different angles (15°, 30°, 45°, 60°, 75° and 90°) against the top surface. Elastic analysis was performed, and the distribution of the von Mises equivalent stress inside the cube was calculated. The highest value of the equivalent stress at each traction angle was compared between the 45° and 90° anchor insertion settings. RESULTS: Stress concentration was most evident around proximal anchor threads, particularly on the traction side. Interestingly, stress gradually declined with an increase in traction angle only for the 90° insertion setting. At 15° and 90° traction angles, the equivalent stress was lower for the 45° insertion setting than for the 90° insertion setting. In contrast, the 90° insertion setting exhibited lower equivalent stress than the 45° insertion setting at 30°, 45° and 60° traction angles. CONCLUSIONS: Insertion of an anchor at 90° might reduce the stress concentration around the proximal anchor threads on the traction side and provide lower equivalent stress in the middle range of traction angles (30°-60°) than insertion at 45°. This could avoid early postoperative anchor failure.