Capsule preservation improves short‐term outcome of hydraulic distension in painful stiff shoulder

The effect of intraarticular hydraulic distension (IHD) for a painful stiff shoulder (or adhesive capsulitis) has been affirmed, but whether rupturing the joint capsule during this process is beneficial remains controversial. By monitoring real‐time pressure–volume (PV) profiles during IHD, we could infuse the largest possible volume without rupturing the capsule. Using the novel technique, we compared the short‐term effects of IHD when the capsule was preserved versus when it was ruptured. Fifty‐four patients with a painful stiff shoulder underwent IHDs intended to preserve or rupture the capsule and then classified into capsule‐ruptured (n = 26) and capsule‐preserved (n = 20) groups, based on the obtained PV profiles. Their profiles were triphasic or biphasic; eight with flat profiles were excluded from the comparison. Clinical outcomes were evaluated at 3‐day and 1‐month follow‐ups, in terms of pain and range of motion (ROM). Although both groups showed significant increase in ROM and decrease in pain after IHD, the improvements were greater in the capsule‐preserved group than in the ruptured group at both follow‐up times, and in triphasic and biphasic cases. In conclusion, the therapeutic effects of IHD in short‐term follow‐ups were enhanced by preserving the capsule. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:1688–1694, 2011     

Capsule function following anterior dislocation: Implications for diagnosis of shoulder instability

During shoulder dislocation, the glenohumeral capsule undergoes non‐recoverable strain, leading to joint instability. Clinicians use physical exams to diagnose injury and direct repair procedures; however, they are subjective and do not provide quantitative information. Our objectives were to: (1) determine the relationship between capsule function following anterior dislocation and non‐recoverable strain; and (2) identify joint positions at which physical exams can be used to detect non‐recoverable strain in specific capsule regions. Physical exams were simulated at three joint positions including external rotation (ER) using robotic technology before and after anterior dislocation. The resulting joint kinematics, strain distribution in the capsule, and non‐recoverable strain were determined. Following dislocation, anterior translation increased by as much as 48% (0° ER: p = 0.03; 30° ER: p = 0.03; 60° ER: p < 0.01). Capsule sub‐regions with less non‐recoverable strain required more ER to detect differences in the strain ratios between the intact and injured joint. Strain ratio changes on the humeral side of the posterior axillary pouch (0.31 ± 0.32) were significant at all joint positions (0° ER: p = 0.03; 30° ER: p = 0.048; 60° ER: p = 0.04), whereas strain ratio differences on the humeral side of the anterior axillary pouch (0.18 ± 0.21) were significant only at 60° of ER (p = 0.03). Therefore, standardizing physical exams for joint position could help surgeons identify specific locations of non‐recoverable strain that may have been ignored. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 962–968, 2013     

Shoulder muscle activation and coordination in patients with a massive rotator cuff tear: an electromyographic study

Adaptive muscle activation strategies following a massive rotator cuff tear (MRCT) are inadequately understood, and the relationship among muscles during everyday activities has not been considered. Thirteen healthy subjects comprised the control group, and 11 subjects with a MRCT the patient group. Upper limb function was assessed using the Functional Impairment test‐hand, neck, shoulder, and arm (FIT‐HaNSA). Electromyography (EMG) was recorded from 13 shoulder muscles, comprising five muscle groups, during a shelf‐lifting task. Mean FIT‐HaNSA scores were significantly lower in MRCT patients (p ≤ 0.001), reflecting a severe functional deficit. In MRCT patients, EMG signal amplitude was significantly higher for the biceps brachii‐brachioradialis (p < 0.001), upper trapezius‐serratus anterior (p = 0.025), muscle groups and for the latissimus dorsi (p = 0.010), and teres major (p = 0.007) muscles. No significant differences in the correlation among muscle groups were identified, pointing to an unchanged neuromuscular strategy following a tear. In MRCT patients, a reorganization of muscle activation strategy along the upper limb kinetic chain is aimed at reducing demand on the glenohumeral joint. Increased activation of the latissimus dorsi and teres major muscles is an attempt to compensate for the deficient rotator cuff. Re‐education towards an alternate neuromuscular control strategy appears necessary to restore function. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1140–1146, 2012     

肩袖撕裂合并冻结肩行手法松解后的关节镜下表现及影响因素分析

目的 观察肩袖撕裂合并冻结肩行手法松解后的关节镜下表现,并分析其影响因素。方法 回顾性分析2017年9月至2019年9月收治的68例肩袖撕裂合并冻结肩病人的病例资料,其中,男35例,女33例,年龄为（52.68±6.54）岁,均行一期麻醉后手法松解联合关节镜检查并肩袖修复术,观察手法松解后的关节镜下表现,比较松解损伤病人和未损伤病人之间的性别、患侧、肩袖撕裂程度差异,分析患肩关节疼痛时间、肩关节活动受限病程和实施手法松解时间与手法松解损伤的相关性。收集病人的数字分级法（numerical rating scale, NRS）疼痛评分、美国肩肘外科医师学会（American Shoulder and Elbow Surgeons, ASES）评分、Constant-Murley评分及丹麦健康与医疗管理局（Danish Health and Medicine Authority）满意度评分。结果 共16例（23.53%）发生手法松解损伤,其中单一损伤者12例,两种及以上损伤者4例,损伤类型为前关节囊撕裂（3例,18.75%）、下关节囊撕裂（6例,37.50%）、盂肱中韧带撕裂（7例,43.75%）、盂肱下韧带肱骨端撕裂（humeral avulsion of the glenohumeral ligament, HAGL）（3例,18.75%）、前盂唇撕裂（2例,12.50%）。松解损伤病人和未损伤病人之间的年龄（P=0.431）、性别（P=0.893）、患侧（P=0.673）、肩袖撕裂程度（P=0.723）、患肩关节疼痛时间（P=0.813）、肩关节活动受限病程（P=0.250）、实施手法松解时间（P=0.125）均未见显著差异。松解损伤组和松解无损伤组术后NRS评分均较术前明显降低,肩关节功能评分较术前明显改善（P均＜0.05）;手术前后的NRS评分、肩关节功能ASES评分、Constant-Murley评分、病人满意度评分比较,差异均无统计学意义（P均＞0.05）。结论 肩袖撕裂合并冻结肩行麻醉后肩关节手法松解联合关节镜下肩袖修复术可能导致单一或合并的镜下损伤表现,年龄、性别、患侧、肩袖撕裂程度、患肩关节疼痛时间、肩关节活动受限病程、实施手法松解时间等因素与发生手法松解损伤无明确相关性。     

盂肱关节腔容量的测量对冻结肩临床分期及治疗影响的研究

目的测量冻结肩（Frozen Shoulder冻结肩）盂肱关节腔容量大小，协助临床分期及治疗。 方法前瞻性收集山西白求恩医院康复科31例冻结肩患者按照临床分期分成两组，一组为渐冻期（Ⅰ期）16例，另一组为冻结期（Ⅱ期）15例，然后在超声引导下进行盂肱关节腔穿刺及容量测量，观察监护仪上压力值间接评估盂肱关节容量。 结果冻结肩Ⅰ期的关节腔起始容量为（10.6±1.7）ml；冻结肩Ⅱ期关节腔起始容量为（6.7±1.5）ml；冻结肩Ⅱ期关节腔扩张时的安全容量为（25.8±1.3）ml。冻结肩Ⅰ期和Ⅱ期的关节腔起始容量差异具有统计学意义（P<0.05）。 结论测量冻结肩盂肱关节腔起始容量可协助量化冻结肩的临床分期；安全容量可为临床行液压扩张治疗提供参考。     

Increased IL‐1β expression and myofibroblast recruitment in subacromial bursa is associated with rotator cuff lesions with shoulder stiffness

We evaluated whether proinflammatory cytokine expression and myofibroblast recruitment in subacromial bursa was linked to rotator cuff lesions with shoulder stiffness. We analyzed expressions of IL‐1β, IL‐6, and TNF‐α in subacromial bursa and joint fluid collected from 14 patients with cuff tears with stiffness as a study group (Group I) and 14 patients with rotator cuff tears without shoulder stiffness as a control group (Group II) using real‐time RT‐PCR, immunohistochemistry, and ELISA. Myofibroblast apoptosis in subacromial bursa was analyzed using terminal deoxynucleotidyl transferase ‐mediated deoxyuridine triphosphate‐biotin nick end‐labeling (TUNEL) and α‐smooth muscle actin immunofluorescence staining. Shoulder function was evaluated using the Constant score. Group I had higher mRNA expression (p < 0.001) and immunoreactivities (p < 0.001) of IL‐1β. They also had higher levels of IL‐1β, IL‐6, and TNF‐α in joint fluid. Increased IL‐1β mRNA expression in the subacromial bursa and IL‐1β levels in joint fluid were correlated with a preoperative deficit in shoulder motion (p < 0.001) and preoperative Constant scores (p < 0.001). Immunofluorescence observations showed that Group I subjects had more myofibroblasts (p < 0.001) than Group II. In Group II, a significant correlation was found between apoptotic myofibroblasts and total myofibroblasts (p = 0.002), but not in Group I (p = 0.510). Increased expression of IL‐1β and myofibroblast recruitment in the subacromial bursa in rotator cuff lesions are linked to shoulder stiffness. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1090–1097, 2008     

Expression analysis of genes involved in collagen cross‐linking and its regulation in traumatic anterior shoulder instability

The molecular alterations involved in the capsule deformation presented in shoulder instability patients are poorly understood. Increased TGFβ1 acts as a signal for production of matrix macromolecules by fibrogenic cells at joint injury sites. TGFβ1, through its receptor TGFβR1, regulates genes involved in collagen cross‐linking, such as LOX, PLOD1, and PLOD2. We evaluated TGFβ1, TGFβR1, LOX, PLOD1, and PLOD2 gene expression in the antero‐inferior (macroscopically injured region), antero‐superior and posterior regions of the glenohumeral capsule of 29 shoulder instability patients and eight controls. We observed that PLOD2 expression was increased in the anterior‐inferior capsule region of the patients compared to controls. LOX expression tended to be increased in the posterior portion of patients. Patients with recurrent shoulder dislocation presented upregulation of TGFβR1 in the antero‐inferior capsule portion and of PLOD2 in the posterior region. Conversely, LOX was increased in the posterior portion of the capsule of patients with a single shoulder dislocation episode. In the antero‐inferior, LOX expression was inversely correlated and TGFβR1 was directly correlated with the duration of symptoms. In the posterior region, PLOD2, TGFβ1, and TGFβR1 were directly correlated with the duration of symptoms. In conclusion, PLOD2 expression was increased in the macroscopically injured region of the capsule of patients. Upregulation of TGFβ1, TGFβR1, and PLOD2 seems to be related with the maintenance of disease symptoms, especially in the posterior region. LOX upregulation seems to occur only in the initial phase of the affection. Therefore, TGFβ1, TGFβR1, LOX, and PLOD2 may play a role in shoulder instability. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:510–517, 2016.     

Normal shoulder muscular activation and co‐ordination during a shoulder elevation task based on activities of daily living: An electromyographic study

Studies of normal shoulder function have often failed to consider the inter‐relationship between different muscle groups in activities relevant to daily life. Upper limb functional status was assessed in 12 healthy male volunteers using the Functional Impairment Test‐Hand, Neck, Shoulder and Arm test (FIT‐HaNSA). Electromyography was then used to study the activity and coordination of 13 muscles (10 by surface electrodes, 3 by fine‐wire intramuscular electrodes) around the shoulder during a dynamic movement task based on the shelf‐lifting task in FIT‐HaNSA. Muscles were grouped for analysis into deltoid (anterior, middle, and posterior divisions), adductors (latissimus dorsi and teres major), rotator cuff (supraspinatus, infraspinatus, and subscapularis), and elbow flexor (brachioradialis, biceps brachii) groups. There were no significant inter‐session effects. Using cross‐correlation analysis to investigate the whole time‐course of activation, there were highly significant positive correlations (p < 0.001) between the deltoid and rotator cuff, the deltoid and adductor and the adductor and rotator cuff groups, and a significant negative correlation between the deltoid and elbow flexor groups (p = 0.031). We conclude that the deltoid, adductor, and rotator cuff muscles all contribute to the muscular component of glenohumeral joint stability. Muscular stability can be adapted as required to meet task‐specific demands. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:53–60, 2012     

关节镜下双后入路结合前方入路盂肱关节囊松解治疗重度原发性冻结肩

目的研究肩关节镜双后入路结合前方入路盂肱关节囊松解治疗重度原发性冻结肩的临床效果。 方法2013年1月至2016年12月南京中医药大学附属医院对16例重度原发性冻结肩患者行关节镜下双后入路结合前方入路盂肱关节囊松解术,男2例、女14例,平均年龄46.6岁,左肩4例、右肩12例。所有患者术前均拍摄肩关节正位片、冈上肌出口位X线片和肩关节MRI检查,全部患者均行双后入路关节镜下盂肱关节囊松解术,所有病例均同时行肩峰下滑囊清理术,分别在术前和末次随访时采用视觉模拟评分（visual analogue scale,VAS）、Constant-Murley评分和美国加利福尼亚大学（University of California, Los Angeles,UCLA）肩关节评分标准进行评价。 结果随访时间10~37个月,平均26个月。术前、术后即刻和末次随访平均UCLA评分分别为（10.3±3.2）分、（28.2±3.3）分和（31.2±5.3）分,差异有统计学意义（P<0.01）;平均Constant-Murley评分为（38.3±4.2）分、（89.2±4.5）分和（95.2±3.3）分;VAS评分平均为（6.3±1.9）分、（1.3±0.3）分和（1.0±0.2）分（P<0.01）。所有患者均对手术效果表示满意。 结论关节镜下双后入路结合前方入路盂肱关节囊松解治疗重度原发性冻结肩,便于术中操作,可以显著地缓解疼痛、恢复肩关节功能。关节镜下双后入路结合前方入路盂肱关节囊松解为治疗重度原发性冻结肩提供有效方法。     

Urethral distension as a novel method to simulate sphincter insufficiency in the porcine animal model

Objectives: To describe a novel animal model of intrinsic sphincter deficiency. Methods: The study was carried out on 10 female pigs. Injury to the urethral sphincter was induced by distension of the urethra. This was obtained by using the balloon of an 18‐F Dufour catheter for 5 min followed by its retraction through the urethra without draining the balloon. The urethral pressure profile was evaluated before injury, immediately postinjury and at day 28 postinjury in the experimental group (n = 5), and on day 1 and day 28 in the control uninjured group (n = 5). The maximal urethral closure pressure, the functional urethral length and the area under curve of the urethral pressure profile were measured. Results: The mean maximal urethral closure pressure at the beginning of the experiment was 32 cmH₂O, and the mean functional urethral length was 4.88 cm. The assessment at day 28 showed a reduction of the maximal urethral closure pressure (50% of the control, P > 0.05), the functional urethral length (52.5% of the control, P < 0.05) and the area under curve (52% of the control, P < 0.05) in injured pigs. Histologically, a fibrosis of the sphincter was detected without rupture of the muscle layer in all the samples. Conclusions: The proposed porcine model can be used to obtain intrinsic sphincter deficiency‐like urodynamic findings without rupturing the sphincter. This methodology can be applied to investigate therapies for intrinsic sphincter deficiency.     

Expression and activity of COX‐1 and 2 and 5‐LOX in joint tissues from dogs with naturally occurring coxofemoral joint osteoarthritis

Understanding the neurobiology of pain in naturally occurring models of osteoarthritis (OA) may improve the understanding of human OA pain. Both COX and LOX have been associated with joint pain. This study evaluated COX‐1, COX‐2, and 5‐LOX expression and activity in a naturally occurring canine model of secondary OA. Hip joint capsule with synovial tissue (HJC) and femoral head subchondral bone (FH) was collected from normal dogs and dogs undergoing total hip replacement for coxofemoral joint OA. Tissues were analyzed for COX‐1, COX‐2, and LOX protein, and PGE₂ and LTB₄. Significantly more COX‐2 protein was present in OA HJC than normal joints (p = 0.0009). There was no significant difference in COX‐1 or LOX protein, although LOX protein was increased (p = 0.069). PGE₂ concentration in normal and OA HJC was similar (p = 1.0). LTB₄ concentration in OA HJC was significantly greater than normal HJC (p = 0.028). Significantly more COX‐1 (p = 0.0098), COX‐2 (p = 0.0028), and LOX (p = 0.0095) protein was present in OA FH tissue compared to normal FH tissue. There were no differences in PGE₂ or LTB₄ concentration in normal and OA FH tissue (p = 0.77 and p = 0.11). Together, these data suggest both COX‐2 and 5‐LOX are appropriate targets for the management of pain associated with naturally occurring OA. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res     

Acute Effects of Intermittent Hemodialysis and Sustained Low-Efficiency Hemodialysis (SLED) on the Pulmonary Function of Patients under Mechanical Ventilation

The effects of hemodialysis (HD) on pulmonary function are still controversial. The objective of this study was to evaluate the effect of intermittent hemodialysis (IHD) and sustained low-efficiency dialysis (SLED) on the respiratory mechanics of ICU patients under invasive mechanical ventilation. We prospectively studied 31 patients. Laboratory and respiratory evaluation (static and dynamic compliance and resistance) was performed pre- and post-HD. Forty HD sessions were studied and grouped in: SLED (n?=?17; Qa?=?200–250 mL/min, Qd?=?300 mL/min) and IHD (n?=?23; Qa =?250–300 mL/min, Qd?=?500 mL/min). There was no difference between the groups according to age, gender, comorbidities, APACHE II, and cause of mechanical ventilation, but pre-HD, patients in the IHD group had higher levels of plasma creatinine (5.4 ± 2.0 vs. 4.2 ± 1.3 mg/dL, p = 0.048) and platelets (286 ± 186 vs. 174 ± 95 10³/mm², p = 0.032) and lower arterial pH (7.37 ± 0.07 vs. 7.42 ± 0.05, p = 0.02). The efficiency of the treatment was similar (p > 0.05) with both types of HD regarding fluid removal, urea reduction rate, and decrease in plasma creatinine. Pre-HD, the ventilatory conditions of both groups were similar (p > 0.05) except for pressure support ventilation and airflow resistance. There were no changes (pre- versus post-HD p > 0.05) induced either by IHD or SLED in the ratio PaO₂/FiO₂ or in any measured ventilatory parameter. In conclusion, neither IHD nor SLED modifies the pulmonary function of patients under mechanical ventilation.     

The frozen shoulder. Diagnosis and management

The differentiation between the stiff and painful shoulder without any joint capsule involvement and with capsule involvement (true adhesive capsulitis) must be established before a rational treatment can be prescribed. Arthrography establishes the correct diagnosis of adhesive capsulitis. Treatment of the stiff and painful shoulder is through prevention and exercise. The treatment of adhesive capsulitis includes prevention, exercises, manipulation, and capsulotomy. Each treatment method is determined by specific criteria. Arthroscopy is not useful for either diagnosis or treatment of adhesive capsulitis but may be useful for recognition of the four stages of the disease.     

Quantitative statistical shape model-based analysis of humeral head migration,Part 2: Shoulder osteoarthritis

We wanted to investigate the quantitative characteristics of humeral head migration (HHM) in shoulder osteoarthritis (OA) and their possible associations with scapular morphology. We quantified CT-scan-based-HHM in 122 patients with a combination of automated 3D scapulohumeral migration (=HHM with respect to the scapula) and glenohumeral migration (=HHM with respect to the glenoid) measurements. We divided OA patients in Group 1 (without HHM), Group 2a (anterior HHM) and Group 2b (posterior HHM). We reconstructed and measured the prearthropathy scapular anatomy with a statistical shape model technique. HHM primarily occurs in the axial plane in shoulder OA. We found “not-perfect” correlation between subluxation distance AP and scapulohumeral migration values (r_s = 0.8, p < 0.001). Group 2b patients had a more expressed prearthropathy glenoid retroversion (13° vs. 7°, p < 0.001) and posterior glenoid translation (4 mm vs. 6 mm, p = 0.003) in comparison to Group 1. Binary logistic regression analysis indicated prearthropathy glenoid version as a significant predictor of HHM (χ² = 27, p < 0.001). Multivariate regression analysis showed that the pathologic version could explain 56% of subluxation distance-AP variance and 75% of the scapulohumeral migration variance (all p < 0.001). Herewith, every degree increase in pathologic glenoid retroversion was associated with an increase of 1% subluxation distance-AP, and scapulohumeral migration. The occurrence of posterior HHM is associated with prearthropathy glenoid retroversion and more posterior glenoid translation. The reported regression values of HHM in the function of the pathologic glenoid version could form a basis toward a more patient-specific correction of HHM.     

Functional integrity of the shoulder joint and pectoralis major following subpectoral implant breast reconstruction

Subpectoral implants for breast reconstruction after mastectomy requires the surgical disinsertion of the sternocostal fiber region of the pectoralis major. This technique is associated with significant shoulder strength and range of motion deficits, but it is unknown how it affects the underlying integrity of the shoulder joint or pectoralis major. The aim of this study was to characterize the long‐term effects of this reconstruction approach on shoulder joint stiffness and pectoralis major material properties. Robot‐assisted measures of shoulder strength and stiffness and ultrasound shear wave elastography images from the pectoralis major were acquired from 14 women an average of 549 days (range: 313–795 days) post reconstruction and 14 healthy, age‐matched controls. Subpectoral implant patients were significantly weaker in shoulder adduction (p < 0.001) and exhibited lower shoulder stiffness when producing submaximal adduction torques (p = 0.004). The underlying material properties of the clavicular fiber region of the pectoralis major were altered in subpectoral implant patients, with significantly reduced shear wave velocities in the clavicular fiber region of the pectoralis major when generating adduction torques (p = 0.023). The clinical significance of these findings are that subpectoral implant patients do not fully recover shoulder strength or stability in the long‐term, despite significant recovery time, and substantial shoulder musculature left intact. The impact of these procedures extends to the remaining, intact volume of the pectoralis major. Optimization of shoulder function should be a key aspect of the post‐reconstruction standard of care. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1610–1619, 2019.     

Coracoid pain test: a new clinical sign of shoulder adhesive capsulitis

Patients with adhesive capsulitis were clinically evaluated to establish whether pain elicited by pressure on the coracoid area may be considered a pathognomonic sign of this condition. The study group included 85 patients with primary adhesive capsulitis, 465 with rotator cuff tear, 48 with calcifying tendonitis, 16 with glenohumeral arthritis, 66 with acromioclavicular arthropathy and 150 asymptomatic subjects. The test was considered positive when pain on the coracoid region was more severe than 3 points (VAS scale) with respect to the acromioclavicular joint and the anterolateral subacromial area. The test was positive in 96.4% of patients with adhesive capsulitis and in 11.1%, 14.5%, 6.2% and 10.6% of patients with the other four conditions, respectively. A positive result was obtained in 3/150 normal subjects (2%). With respect to the other four diseases, the test had a sensitivity of 0.96 and a specificity ranging from 0.87 to 0.89. With respect to controls, the sensitivity and specificity were 0.99 and 0.98, respectively. The coracoid pain test could be considered as a pathognomonic sign in physical examination of patients with stiff and painful shoulder.     

Myofibroblast cells are preferentially expressed early in a rabbit model of joint contracture

Studies have demonstrated increased myofibroblasts in contractures. However, the timeline is largely unknown. The aim of this study was to determine the number of myofibroblasts in contracting joint capsules at 3‐time points over a 24‐week period. Eighteen rabbits subjected to a surgical procedure designed to elicit a knee joint contracture were divided into three groups of six. Rabbits were sacrificed at each respective time point and myofibroblasts in the joint capsules were quantified using immunohistochemistry. The percent of myofibroblasts was significantly elevated in the operated limbs compared to the control limbs at 2 weeks (20% vs. 7%, respectively; p = 0.014). There was no difference in the percent of myofibroblasts between the operated and control limbs at 8 or 24 weeks (p = 0.96 and 0.07, respectively). The percent of myofibroblasts dropped from 20% at 2 weeks to 3.0% at 8 weeks (p < 0.001). The decrease from 8 to 24 weeks was not significant (p = 0.19). A large proportion of myofibroblasts are present in contracted joints at 2 weeks. By week 8, the proportion of myofibroblasts seem to return to normal. Interventions aimed at affecting the myofibroblast cell in order to prevent fibrosis should be instituted early. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:713–719, 2012     

Muscle and Joint Function After Anatomic and Reverse Total Shoulder Arthroplasty Using a Modular Shoulder Prosthesis

Changes in joint architecture and muscle loading resulting from total shoulder arthroplasty (TSA) and reverse total shoulder arthroplasty (RSA) are known to influence joint stability and prosthesis survivorship. This study aimed to measure changes in muscle moment arms, muscle lines of action, as well as muscle and joint loading following TSA and RSA using a metal‐backed uncemented modular shoulder prosthesis. Eight cadaveric upper extremities were assessed using a customized testing rig. Abduction, flexion, and axial rotation muscle moment arms were quantified using the tendon‐excursion method, and muscle line‐of‐force directions evaluated radiographically pre‐operatively, and after TSA and revision RSA. Specimen‐specific musculoskeletal models were used to estimate muscle and joint loading pre‐ and post‐operatively. TSA lateralized the glenohumeral joint center by 4.3 ± 3.2 mm, resulting in small but significant increases in middle deltoid force (2.0%BW) and joint compression during flexion (2.1%BW) (p < 0.05). Revision RSA significantly increased the moment arms of the major abductors, flexors, adductors, and extensors, and reduced their peak forces (p < 0.05). The superior inclination of the deltoid significantly increased while the inferior inclination of the rotator cuff muscles decreased (p < 0.05). TSA using an uncemented metal‐backed modular shoulder prosthesis effectively restores native joint function; however, lateralization of the glenoid component should be minimized intra‐operatively to mitigate increased glenohumeral joint loading and polyethylene liner contact stresses. Revision RSA reduces muscle forces required during shoulder function but produces greater superior joint shear force and less joint compression. The findings may help to guide component selection and placement to mitigate joint instability after arthroplasty. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1988–2003, 2019