Intra-articular biomechanical environment following modified Bristow and Latarjet procedures in shoulders with large glenoid defects: relationship with postoperative complications.

BACKGROUND: Although coracoid transfers including the modified Bristow and Latarjet procedures are widely used to treat anterior shoulder instability, the influence of the choice of procedure on the biomechanical outcomes is not well characterized. We aimed to clarify the intra-articular stress distribution following these 2 procedures using 3-dimensional finite-element analysis and to investigate the role of stress distribution in the pathophysiology of postoperative complications. METHODS: Overall, 6 male patients aged 17-47 years with unilateral anterior shoulder instability were recruited. Computed tomographic digital imaging and communications in medicine (CT-DICOM) data of the contralateral (healthy) shoulder of each patient was obtained and used for developing the 3-dimensional normal glenohumeral joint model. A 25% bony defect was created in the anterior glenoid rim where the coracoid process was transferred in the standing and lying-down positions to create the Bristow and Latarjet models, respectively. The arm position was set as 0° or 90° abduction. The Young moduli of the humerus and scapula were calculated using CT data, and set as 35.0 MPa and 113.8 GPa for the articular cartilage and inserted screw, respectively. A compressive load (50 N) was applied to the greater tuberosity toward the center of the glenoid, and a tensile load (20 N) was applied to the tip of the coracoid in the direction of conjoint tendon. Elastic analysis was used to determine the equivalent stress distribution. RESULTS: A significant reduction in mean equivalent stress was observed within the glenoid cartilage for both models (P = .031); however, a new stress concentration appeared within the grafted coracoid-facing region of the humeral-head cartilage in both models. The proximal half of the coracoid graft exhibited lower equivalent stress than the distal half in 5 of the 6 Latarjet models, whereas the proximal half showed higher equivalent stress than the distal half in all 6 Bristow models. High stress concentration was identified at the midpoint of the inserted screw in Bristow models. DISCUSSION AND CONCLUSIONS: Intra-articular stress distribution may explain the different rates of postoperative complications associated with the modified Bristow and Latarjet procedures. New stress concentration within the humeral-head cartilage might contribute to the development of glenohumeral osteoarthritis following both procedures. Stress shielding in the proximal part of the coracoid graft might contribute to osteolysis following the Latarjet procedure. Surgeons should be aware of the risk of breakage of the inserted screw following the modified Bristow procedure.

Comparison between single and double suture passing techniques in the suture bridge rotator cuff repair with a 2-mm tape: A simulation study using a three-dimensional finite element method.

BACKGROUND: Suture bridge repair has been widely used as one of the standard procedures in the arthroscopic rotator cuff repair. We compared the intratendinous stress distribution between single and double suture passing techniques in the suture bridge repair using a 2-mm tape and clarified the roles of tensioning in this procedure. METHODS: A board-like model of the supraspinatus tendon and humeral head was used in order to standardize conditions and exclude the influence of anatomical variations between individuals. Reattachment of the supraspinatus tendon to the bone was simulated using both single and double suture passing techniques for the suture bridge repair using a 2-mm tape. A tensile load was applied to the medial end of the tendon, and the stress distribution pattern was observed. Elastic analysis enabled comparison of the von Mises equivalent and maximum principal stresses between the single and double suture passing techniques. The tape configuration was subsequently translated 1 mm toward the insertion points of lateral anchors to simulate the tensioning maneuver. RESULTS: Although the distribution pattern of both the equivalent and the maximum principal stresses was similar for both models, areas with a high stress concentration were smaller in the single suture passing model than those in the double suture passing model. The equivalent stress concentrated within the tendon beneath the tapes as well as in the area between the crossing tapes and the lateral end of the tendon, whereas the maximum principal stress concentrated medial to the sites of suture penetration. CONCLUSIONS: Single suture passing technique can reduce the extent of intratendinous stress concentration compared with double suture passing technique, which might be beneficial to reduce the incidence of type 2 retear after suture bridge repair of rotator cuff tendon using a 2-mm tape.

Muscle activities during shoulder internal rotation differ in arm position: a preliminary quantitative analysis using positron emission tomography.

OBJECTIVE: To investigate the muscle activity patterns of the glenohumeral joint during internal rotation both with the arm at 0° and 90° of abduction using 2-deoxy-2-[18F] fluoro-D-glucose (FDG) positron emission tomography (PET) and magnetic resonance imaging (MRI). MATERIALS AND METHODS: Six healthy male volunteers underwent PET examination after performing active glenohumeral internal rotation exercise using an elastic band both with the arm at 0° and 90° of abduction. As a control, PET scan under resting condition was also performed. The exercise was performed before and after 18 fluorodeoxyglucose injection. Each PET image was fused to the corresponding MRI to identify each muscle. The standardized uptake value (SUV) of each muscle was compared between the two arm positions. RESULTS: With the arm at 0° of abduction, the SUV increased significantly after exercise both in the middle and inferior 1/3 of the subscapularis, which were significantly higher than that of the superior 1/3 of the subscapularis (P < 0.05). The SUV of the inferior 1/3 of the subscapularis was significantly higher at 90° of abduction than at 0° of abduction and was significantly higher than that of the superior 1/3 at 90° of abduction (P < 0.01). The SUV after exercise in the inferior infraspinatus and teres minor increased. CONCLUSIONS: The middle and inferior parts of the subscapularis are the main shoulder internal rotators in 0° of abduction, whereas the inferior part of the subscapularis is the main internal rotator in 90° of abduction.

Proximal-medial part in the coracoid graft demonstrates the most evident stress shielding following the Latarjet procedure: a simulation study using the 3-dimensional finite element method.

BACKGROUND: Although the osteolysis of the coracoid graft is frequently observed after the Latarjet procedure particularly in its proximal part, its pathomechanism is not well understood. METHODS: Three-dimensional finite element glenohumeral joint models were developed using CT-DICOM data of 10 normal shoulders. A 25% bony defect was created on the anterior glenoid rim, and the coracoid process was transferred flush with the glenoid cartilage using 2 half-threaded screws. In the hanging arm as well as in the 90° abducted positions, a compressive load (50 N) was applied to the greater tuberosity toward the center of the glenoid and a tensile force (20 N) was applied to the coracoid tip along the direction of the conjoint tendon. Next, elastic analysis was performed, and the distribution patterns of the equivalent stress as well as the maximum principal stress were compared among 4 parts (proximal/distal and medial/lateral) of the coracoid graft. RESULTS: Both the equivalent stress and the maximum principal stress were reduced in the proximal half of the coracoid graft. A high stress concentration was observed in the lateral aspect of the coracoid graft particularly in the 90° abducted position. The proximal-medial part demonstrated the lowest equivalent stress as well as the maximum principal stress for both arm positions, which were significantly lower than those in the distal 2 parts. CONCLUSION: In the Latarjet procedure, the proximal-medial part of the coracoid graft demonstrated the most evident stress shielding, which may play an important role in postoperative osteolysis.

Representative survey of frozen shoulder questionnaire responses from the Japan Shoulder Society: What are the appropriate diagnostic terms for primary idiopathic frozen shoulder, stiff shoulder or frozen shoulder?

BACKGROUND: Primary frozen shoulder has unknown etiology and significant restriction of active and passive motion. The distinction between frozen shoulder and stiff shoulder has been unclear. Therefore, the purposes of this study were to perform a survey regarding definition and classification of frozen shoulder proposed by the American Academy of Orthopedic Surgeons (AAOS) among the members of the Japan Shoulder Society (JSS) and to compare the results with those obtained among the members of the American Shoulder and Elbow Surgeons (ASES). METHODS: The Scientific Research Project Committee of the JSS prepared the questionnaire for frozen shoulder and stiff shoulder. Surveys were sent by e-mail on Jan 14, 2016 to JSS registered members and the response dead-line was set on March 13, 2016. RESULTS: The number of respondents was 230, including all directors, councilors, and senior doctors. Agreement with the definition of primary frozen shoulder was 67%, the classification of primary or secondary frozen shoulder was 53%, and the 3 divisions of secondary frozen shoulder was 53%. Diagnostic terms for the cases of shoulder stiffness with unknown etiology were as follows: frozen shoulder (31%), stiff shoulder (22%), periarthritis scapulohumeralis (16%), so called "Gojukata" in Japan, which means shoulder problems in their fifties (16%), idiopathic frozen shoulder (6%), primary frozen shoulder (4%), adhesive capsulitis (3%), others (2%). CONCLUSION: The survey shows lower rates of agreement among the JSS members than the ASES members for the definition of primary frozen shoulder, the classification of primary and secondary frozen shoulder, and the divisions of secondary frozen shoulder. To avoid confusion between stiff shoulder and frozen shoulder, the committee agrees to the ISAKOS recommendation that the term "frozen shoulder" should be used exclusively for primary idiopathic stiff shoulder.

A biomechanical study on suture anchor insertion angle: Which is better, 90° or 45°?

INTRODUCTION: The purpose of this study was to compare the pullout strength of anchors inserted at 90° and 45° to the bone surface using synthetic bones and porcine humeri. SUBJECTS AND METHODS: Pullout tests were performed by universal testing machine. Synthetic cancellous bones of 0.08, 0.16, and 0.24 g/cm3 (defining as low, medium and high density, respectively) with 2-mm-thick cortical bone model attached on one side and the greater tuberosity of porcine humeri (average bone density, 270 mg/cm3) were chosen for pullout tests. Metallic anchors were inserted at 90° or 45° to the surface and pulled at 90° or 45° from the surface. The maximum load to failure for each condition was recorded. Differences in pullout failure loads between insertion angle, pulling angle, and bone density were analyzed. RESULTS: When the sutures were pulled at 90° in low, medium, high density bones, and porcine humeri, 90°-inserted-anchors showed higher pullout strength than the 45°-inserted-anchors (534.6 ± 28.9 N vs. 488.1 ± 25.3 N (p < 0.05), 636.8 ± 25.3 N vs. 517.5 ± 27.4 N (p < 0.01), 735.6 ± 45.1 N vs. 557.0 ± 42.5 N (p < 0.01), and 285.6 ± 47.2 N vs. 181.4 ± 31.3 N (p < 0.01), respectively). When the sutures were pulled at 45° in low, medium density bones and porcine humeri, 90°-inserted-anchors showed higher pullout strength than the 45°-inserted-anchors (651.1 ± 38.3 N vs. 529.4 ± 37.6 N (p < 0.01), 711.4 ± 25.3 N vs. 599.2 ± 29.8 N (p < 0.01), and 265.3 ± 49.0 N vs. 181.5 ± 29.4 N (p < 0.01), respectively). CONCLUSION: Pullout strength of the anchors inserted at 90° to the bone surface was greater than the anchors inserted at 45° regardless of the bone density.

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.

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.

Comparison of fixation properties between coil-type and screw-type anchors for rotator cuff repair: A virtual pullout testing using 3-dimensional finite element method.

BACKGROUND: Pullout of inserted anchor constitutes one of the pathomechanisms of re-tearing after rotator cuff repair. The purpose of the present study was to investigate the fixation properties of suture anchors using 3-dimensional finite element method. METHODS: The computer models of three types of anchors (TwinFix Ti, HEALICOIL PK and HEALICOIL RG) were inserted into the isotropic cube model that simulated cancellous bone. In the virtual pullout testing, a tensile load (500 N) along the long axis of the inserted anchor was applied to the site of suture thread attachment to simulate a traction force. The distribution of von Mises equivalent stress, the failure patterns of elements inside the cube and the anchor displacement were compared among the three anchors. RESULTS: In TwinFix Ti, the highest stress concentration was seen around the anchor threads close to the surface of the cube, which caused element failure at this site. On the other hand, both HEALICOIL PK and HEALICOIL RG demonstrated a high stress concentration as well as element failure around the anchor tip. Comparing the anchor displacement, HEALICOIL RG showed the smallest displacement among the three anchors. The tensile loads that required a 0.1-mm displacement for TwinFix Ti, HEALICOIL PK and HEALICOIL RG were 400 N, 370 N, and greater than 500 N, respectively. CONCLUSIONS: The bony structures close to the footprint surface may be damaged during surgery due to preparation for the bony bed as well as the insertion of anchors. Thus, we assumed that HEALICOIL RG represented the best initial fixation properties among the three anchors tested. Virtual pullout testing using 3-dimensional finite element method could reveal the detailed biomechanical characteristics of each suture anchor, which would be important for shoulder surgeons to improve the clinical outcomes of rotator cuff repair.

Prediction of pathological fracture of the femoral shaft with an osteolytic lesion using a computed tomography-based nonlinear three-dimensional finite element method.

BACKGROUND: Physicians radiologically estimate the reduction in bone strength based on the size or location of bone tumors. The goal of this study was to clarify the relationship between the size or location of a bony defect and its mechanical strength using a computed tomography-based three-dimensional finite element method. METHODS: Computed tomography data of the right femur from two volunteers (one healthy male and one female patient with primary osteoporosis) were used for the present study. A spherical defect of various sizes and locations at the level of the isthmus of the femoral shaft was created on the three-dimensional finite element models to simulate the osteolytic bone tumor. We classified these defects into three types: inner erosion, cortical disruption, and outer erosion. Two types of mechanical testing were performed: axial compression and torsion. RESULTS: In the axial compression testing of the healthy male subject, the correlation coefficients between the defect rate and the failure load in the cortical disruption type, inner erosion type, and outer erosion type were -0.916, -0.358, and -0.106, respectively. In the torsion testing, they were -0.8744, -0.9001, and -0.8907, respectively. In the axial compression testing of the osteoporotic female subject, the correlation coefficients in the cortical disruption type, inner erosion type, and outer erosion type were -0.754, -0.621, and -0.158, respectively. In the torsion testing, they were -0.9199, -0.5098, and -0.8363, respectively. In both tests, the defect rate of the cortex increased and the bone strength decreased, especially in the cortical disruption type. CONCLUSION: The results of the present study demonstrate that osteolytic bone tumors can weaken the bone strength, particularly when perforation of the cortex occurs via tumor invasion. These results may be useful for risk assessment of pathological fractures due to primary and metastatic osteolytic bone tumors in clinical practice.

Patient trends in orthopedic traumas and related disorders after tsunami caused by the Great East Japan Earthquake: An experience in the primary referral medical center.

BACKGROUND: In the Great East Japan Earthquake, the Japanese Red Cross Ishinomaki Hospital played an important role as a principal referral center within the Ishinomaki region, one of the most severely affected areas in eastern Japan. The present study describes the patient population, clinical characteristics, and time courses of the medical problems observed at this hospital. METHODS: A retrospective survey of medical logs and records was conducted on the first 2 weeks after the earthquake to characterize orthopedic traumas and related disorders treated during this catastrophe. Patient number, severity of injuries, number of patients secondarily transported to the referral medical centers in the inland area, and the number of surgeries performed during the study period were investigated. RESULTS: Totally, 7686 patients visited the hospital. Of which, 1807 patients suffered from exogenous diseases, such as trauma, burns, crush syndrome, deep venous thrombosis, and infectious diseases. Patients who suffered from hypothermia were the most frequently seen within the first 2 weeks after the earthquake. Interestingly, most patients' conditions were not severe and required only simple treatments. Four patients (0.2% of patients with exogenous diseases) were secondarily transported to the referral medical centers in the inland area and only four patients were surgically treated because of a lack of available implants, surgical devices, and electric power supply. DISCUSSION AND CONCLUSIONS: The Great East Japan Earthquake and subsequent tsunami, which occurred during an early spring afternoon, resulted in a unique orthopedic patient population, which included few severely injured patients compared with numerous deaths. We believe that each coastal region hospital should develop its own emergency medical care system to address future tsunami events while considering their surrounding environment. The information described in the present study should be important for preparation toward future events involving massive earthquakes followed by tsunami disasters.

Ultrasound elastography-based assessment of the elasticity of the supraspinatus muscle and tendon during muscle contraction.

BACKGROUND: Although elasticity of the supraspinatus muscle and tendon is a useful parameter to represent the conditions of the supraspinatus muscle and tendon, assessment of the elasticity in clinical settings has not been established. The purpose of this study was to determine the elasticity of the supraspinatus muscle belly and tendon under different muscle contraction conditions using ultrasound real-time tissue elastography (RTE). METHODS: Twenty-three healthy individuals participated in this study. Ultrasound RTE was used for elasticity measurements of the muscle belly and tendon of the supraspinatus muscle. The elasticity was defined as the ratio of strain in the tissues to that in an acoustic coupler (reference). A greater ratio indicated that the tissue was softer. Measurements were performed with study subjects in the lateral decubitus position at 10° of shoulder abduction under conditions of (1) no contraction, (2) isometric contraction without a weight, and (3) isometric contraction with a 1-kg weight. RESULTS: The intraclass correlation coefficient (ICC1,3) of 3 measurements under each condition ranged from 0.931 to 0.998, showing high intraobserver reliability. Strain ratios for both the supraspinatus muscle belly and tendon significantly decreased with increases in muscle contraction (P < .001). CONCLUSIONS: Ultrasound RTE with the acoustic coupler has the potential to noninvasively detect changes in the elasticity of the supraspinatus muscle belly and tendon that accompany varying levels of muscle contraction in clinical practice.

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.

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.

Venous thromboembolism after elective shoulder surgery: a prospective cohort study of 175 patients.

BACKGROUND: The purpose of this study was to investigate the incidence of venous thromboembolism (VTE) after elective arthroscopic shoulder surgery. MATERIALS AND METHODS: One hundred seventy-five consecutive patients who underwent arthroscopic shoulder surgery were enrolled (mean age, 61 years). Patients who had VTE preoperatively and underwent trauma surgery or arthroplasty were excluded. All the patients used foot pumps or elastic stockings after surgery for deep venous thrombosis (DVT) prophylaxis. DVT in the 4 limbs was assessed by ultrasound before and after surgery. Pulmonary embolism was diagnosed by computed tomography pulmonary angiography. Risk factors related to DVT were assessed. RESULTS: The overall incidence of DVT was 10 of 175 patients (5.7%). Most of the DVT cases were detected at 1 to 2 days after surgery. All patients were asymptomatic. There were no patients who had symptomatic pulmonary embolism. However, an asymptomatic pulmonary embolus developed in 1 patient during the 3-month follow-up period. There were no significant differences between the DVT and non-DVT groups regarding the risk factors. DISCUSSION AND CONCLUSION: Our data have shown that symptomatic VTE is rare after elective arthroscopic shoulder surgery. However, asymptomatic VTE may occur even with DVT preventive measures. Because most of the DVTs were found in the calf veins, we recommend that surgeons pay attention to the possibility of DVT in the lower extremities even after arthroscopic shoulder surgery. The incidence of asymptomatic VTE after elective arthroscopic shoulder surgery was 5.7%. All patients were asymptomatic, and most of the DVTs occurred 1 or 2 days after surgery.

Contribution of oxidative stress to the degeneration of rotator cuff entheses.

BACKGROUND: Rotator cuff degeneration is one of the multiple factors that lead to rotator cuff tears; however, the precise mechanism of such degeneration still remains unclear. In this study, we investigated the supraspinatus tendon enthesis to clarify the link between rotator cuff degeneration and oxidative stress in antioxidant enzyme superoxide dismutase 1 (Sod1)-deficient mice (Sod1(-/-)). METHODS: The supraspinatus tendon and humeral head were isolated and fixed to prepare histologic sections from wild-type and Sod1(-/-) male mice at 20 weeks of age. Hematoxylin-eosin staining was performed to assess the histomorphologic structure. To investigate the collagen fibers, we examined spatially aligned collagen fibers using a polarizing microscope and assessed the amount of collagen using immunohistochemical staining. To analyze the tissue elasticity, we measured the tissue acoustic properties using scanning acoustic microscopy. RESULTS: The Sod1(-/-) mice showed histologic changes, such as a misaligned 4-layered structure and fragmented tidemark, in the enthesis. Sod1 loss also decreased the amount of brightly diffracted light and type I collagen, indicating collagen downregulation. The scanning acoustic microscopy analysis showed that the speed and attenuation of sound were increased in the nonmineralized fibrocartilage of the Sod1(-/-) mice, suggesting decreased mechanical properties in the supraspinatus enthesis. CONCLUSION: Sod1 deficiency-induced degeneration is associated with impaired elasticity in the supraspinatus tendon enthesis, recapitulating human rotator cuff degeneration. These results suggest that intracellular oxidative stress contributes to the degeneration of rotator cuff entheses.

Differences in muscle activities during shoulder elevation in patients with symptomatic and asymptomatic rotator cuff tears: analysis by positron emission tomography.

BACKGROUND: Differences in muscle activity patterns between patients with symptomatic and asymptomatic full-thickness rotator cuff tears have not yet been fully clarified. The purpose of this study was to investigate the muscle activity pattern by use of positron emission tomography (PET) in patients with symptomatic and asymptomatic rotator cuff tears. METHODS: Ten shoulders of 9 patients with full-thickness rotator cuff tears were divided into 2 groups by a numerical pain rating scale (0-10), symptomatic (≥2) and asymptomatic (0 or 1), with 5 shoulders each. Scaption exercise of bilateral arms (200 repetitions in 10 minutes) with a weight of 0.25 kg each was performed before and after injection of fluorodeoxyglucose. After PET examination, the standardized uptake value of each muscle was calculated to quantify its activity and compared between the two groups. RESULTS: The activity of the anterior and middle deltoid was significantly decreased in the symptomatic group compared with the asymptomatic group (anterior deltoid, P = .02; middle deltoid, P = .03). In contrast, the activity of the superior trapezius was significantly increased in the symptomatic group compared with the asymptomatic group (P = .02). CONCLUSION: In patients with a symptomatic tear, the deltoid activity was decreased and the trapezius activity was increased. It is likely that they might have moved the painful glenohumeral joint less and instead moved the painless scapulothoracic joint more during the prescribed exercise. We conclude that patients with painful rotator cuff tears use the parascapular muscles more than those without pain do during arm elevation.

Muscle activity pattern of the shoulder external rotators differs in adduction and abduction: an analysis using positron emission tomography.

BACKGROUND: The muscle activity pattern during shoulder external rotation has not been fully clarified. This study aimed to determine the activities involved in external rotation in the adducted and abducted positions using positron emission tomography (PET). METHODS: Seven healthy volunteers underwent PET examinations after performing external rotation using an elastic band at both 0° and 90° of shoulder abduction in the frontal plane. External rotation exercise was performed before and after injection of fluorine 18 fluorodeoxyglucose, which was followed by PET examination. The protocols for external rotation exercise were identical between the 2 shoulder positions. To obtain control data, PET examination was also performed under resting conditions. The order of these 3 PET examinations was randomized, and they were performed at intervals of 1 week or greater. Each PET image was fused to the corresponding magnetic resonance image to identify each shoulder muscle. After this, the standardized uptake value was calculated in each muscle and was compared between the 2 shoulder positions. RESULTS: The infraspinatus showed the greatest muscle activity during external rotation at 0° of abduction, whereas the teres minor showed the greatest activity at 90° of abduction. The teres minor-infraspinatus ratio at 90° of abduction (mean ± SD, 1.21 ± 0.23) was significantly higher than that at 0° of abduction (0.84 ± 0.15) (P < .01). CONCLUSION: The infraspinatus and teres minor are the main shoulder external rotators. The teres minor is more important as an external rotator in abduction than in adduction.

Radiolucent zone of the patella following total knee arthroplasty without patellar resurfacing.

BACKGROUND: The radiolucent zones in the patella are sometimes observed in patients who have undergone total knee arthroplasty (TKA) without patellar resurfacing. On the basis of radiological findings from our clinical experience, we hypothesize that the pathogenesis of this lesion may be similar to that of the lesions of spontaneous osteonecrosis, and this lesion may be due to both osteoporosis and stress concentration. The present study aimed to determine the incidence of the radiolucent zone after TKA without patellar resurfacing. Moreover, the roles of osteoporosis and patellar morphology, which are related to the stress distribution in the patella, were also investigated. METHODS: We studied 48 knees of 38 patients who underwent primary TKA using the Genesis II prosthesis. Axial radiographs taken 1 year postoperatively were used to assess the incidence of the radiolucent zone. The World Health Organization fracture risk assessment tool (FRAX) score and the preoperative patellar facet angle were compared between patients with and without the radiolucent zones. RESULTS: Five patellae (10.4%) showed the radiolucent zones postoperatively (the radiolucent group), whereas no such lesions were found in the remaining 43 patellae (the normal group). The major osteoporotic fracture risk of the radiolucent group calculated using the FRAX was 24.8% and significantly higher than that in the normal group (14.7%; p = 0.01). The average patellar facet angle in the radiolucent group was 123.6°, which was significantly smaller than that in the normal group (133.6°; p = 0.003). DISCUSSION AND CONCLUSIONS: The results of the present study suggest that both underlying osteoporosis and a steep patellar facet angle may play an important role in the pathogenesis of the radiolucent zones in patellae after TKA without patellar resurfacing. Patellar resurfacing may be considered, particularly in osteoporotic patients who have a steep patellar facet angle, to avoid the appearance of the postoperative radiolucent zone in the patella.