Muscle and joint‐contact loading at the glenohumeral joint after reverse total shoulder arthroplasty

The purposes of this study were to determine the contributions of each shoulder muscle to glenohumeral joint force during abduction and flexion in both the anatomical and post‐operative shoulder and to identify factors that may contribute to the incidence of glenoid component loosening/failure and joint instability in the shoulder after reverse shoulder arthroplasty (RSA). Eight cadaveric upper extremities were mounted onto a testing apparatus. Muscle lines of action were measured, and muscle forces and muscle contributions to glenohumeral joint forces were determined during abduction and flexion of the pre‐operative anatomical shoulder and of the shoulder after arthroplasty. Muscle forces in the middle deltoid during abduction and those in the middle and anterior deltoid during flexion were significantly lower in the reverse shoulder than the pre‐operative shoulder (p < 0.017). The resultant glenohumeral joint force in the reverse shoulder was significantly lower than that in the pre‐operative shoulder; however, the superior shear force acting at the glenohumeral joint was significantly higher (p < 0.001). Reverse total shoulder arthroplasty reduces muscle effort in performing lifting and pushing tasks; however, reduced joint compressive force has the potential to compromise joint stability, while an increased superior joint shear force may contribute to component loosening/failure. Because greater superior shear force is generated in flexion than in abduction, care should be taken to avoid excessive shoulder loading in this plane of elevation. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:1850–1858, 2011     

Reverse total shoulder arthroplasty after failed deltoid flap reconstruction

Hypothesis

Reverse shoulder arthroplasty (RSA) yields unsatisfactory results after deltoid flap reconstruction due to defect of the deltoid muscle.

Methods

We retrospectively reviewed the outcome of 19 patients after failed deltoid flap reconstruction treated with RSA. Follow-up was after a mean of 4.5 years.

Results

Seven patients (37 %) had nine postoperative complications requiring totally 16 revision surgeries. Nonetheless, at latest follow-up, 17 patients had no or mild, two had moderate, and none had severe pain. Before RSA; 13 patients had a pseudoparesis. At latest follow-up, none of the patients had a pseudoparesis. Mean flexion was 121° (90°–160°). Abduction strength averaged 2.3 kg (range 0–5.4 kg). The mean constant score was 70 % (range 28–98 %). Of the 19 patients, 15 were very satisfied with the outcome, four were satisfied, and none was dissatisfied. The mean overall subjective shoulder value was 73 % (30–95 %) of the value of a normal shoulder.

Conclusions

Despite of a localized defect of the deltoid muscle after deltoid flap repair, RSA can reliably be associated with a satisfactory outcome.     

Postimpingement instability following reverse shoulder arthroplasty: a parametric finite element analysis

BackgroundInstability following reverse shoulder arthroplasty is influenced by various factors such as component design, component positioning, and soft tissue tensioning. Patients may achieve glenohumeral motion beyond initial scapular impingement during activities of daily living which could further compound instability. However, instability/subluxation risk postscapular impingement is not well documented. Conventional range of motion analysis tools cannot account for the restraining effect of soft tissues or subluxation risk after impingement. Using a previously validated finite element analysis approach, the purpose of this study was to investigate the effects of glenoid component lateralization and humeral component angle of inclination (AOI), with or without simulated subscapularis repair, on postimpingement subluxation. We hypothesized that lack of subscapularis repair, a valgus humeral component AOI, and glenoid medialization would all result in greater postimpingement instability.MethodsA FE model of the shoulder including the subscapularis tendon and middle deltoid was created, incorporating a general representation of a commercial reverse shoulder arthroplasty implant placed under the direction of a fellowship-trained shoulder surgeon. The deltoid and subscapularis were tensioned and wrapped around the reconstructed glenohumeral joint prior to simulating motion. Humeral rotations were then prescribed to simulate external rotation (neutral to 50°), extension (neutral to 50°), adduction (neutral to 30°), and abduction (neutral to 90°). The effects of three glenosphere lateralization offsets (2, 4, and 10 mm) and 2 humeral liner angles of inclination (varus-150° and valgus-155°) on subluxation propensities were investigated with and without the subscapularis tendon present.ResultsSimulated subscapularis repair resulted in 21%-34% less postimpingement subluxation. Presence of the subscapularis provided stability over a greater range of abduction. Impingement-free range of motion was similar regardless of the presence or absence of the subscapularis. The valgus AOI resulted in 23% less subluxation during abduction. During other motions however, the valgus AOI resulted in 67%-110% greater postimpingement subluxation (subscapularis present), which further worsened without the subscapularis.ConclusionImplant design modifications to improve stability may not be beneficial for all motions, highlighting the importance of directionality when investigating instability. Liner-bone impingement appears to compound instability/subluxation and the subscapularis appears to restrain postimpingement instability.Level of evidenceBasic Science Study; Computer Modeling     

Restoration of shoulder abduction function by direct muscular neurotization with the phrenic nerve fascicles and nerve grafts: A case report

In this report, we describe the first case of using the partial phrenic nerve transfer and direct muscular implantation into the deltoid muscle for restoration of the shoulder function and stability. A patient suffering from the partial brachial plexus injury with absent axillary nerve underwent reconstructive surgery by an end‐to‐end nerve coaptation using two fascicles of the phrenic nerve and two autologous nerve grafts, and direct implantation of nerve grafts into the deltoid muscle. Eighteen months after the procedure, we found a functioning biceps with 90° elbow flexion against gravity and 40° shoulder abduction with satisfactory shoulder stability. Electrophysiology revealed reinnervation potentials in the deltoid and biceps muscle. This case demonstrates a satisfactory result after using transfer of the partial ipsilateral phrenic nerve in combination with muscular implantation to restore shoulder abduction and stability. We recommend the described techniques in cases without other reconstructive options. © 2009 Wiley‐Liss, Inc. Microsurgery, 2009.     

Biomechanical analysis of the subscapularis,infraspinatus and teres minor length and moment arm after reverse shoulder arthroplasty: a cadaveric study

BackgroundReverse shoulder arthroplasty (RSA) affects the length and moment arm of the deltoid and rotator cuff. Currently, RSA is commonly considered for cuff-intact conditions, such as primary glenohumeral osteoarthritis. As such, understanding the effect of contemporary lateralized designs on the rotator cuff is paramount. The purpose of this study was to determine changes in length and moment arm of the subscapularis, infraspinatus and teres minor with implantation of one of 3 RSA designs.MethodsA previously validated model was used in 6 hemi-toraces with the shoulder attached. Suture lines were run through pneumatic cylinders from the insertion to the origin of 10 muscles to apply a constant, stabilizing load. Electromagnetic tracking sensors were fixed to the thorax, scapula, and humerus to record 3-dimensional kinematics. Coordinate systems were established according to ISB recommendations. The origin and insertion of the subscapularis, infraspinatus and teres minor were digitized and tracked. Testing consisted of manually rotating the humerus through 5 cycles of its internal-external rotation arc. Kinematic data was collected at 120 Hz. Testing was performed in 3 positions of abduction: 0°, 30°, and 60°. After testing the intact shoulder, RSA was performed using 3 different configurations: an onlay 135-degree humeral component matched with a 2-mm lateralized glenosphere, the same humeral component with a 6-mm lateralized glenosphere, and an inlay 135-degree humeral component matched with a 10 mm lateralized glenosphere. Minimal muscle operative lengths, maximal muscle operative lengths, and muscle moment arms were computed.ResultsWhen compared with the native shoulder, all 3 configurations of RSA resulted in statistically significant increases in both the minimal and maximal operative lengths of the subscapularis in all abduction positions. The teres minor only showed a statistically significant increase in minimal and maximal length at 60° of abduction. The infraspinatus showed a statistically significant increase in tendon excursion at 0° and 30° of abduction. In 40° of abduction and 40° of internal rotation, all RSA configurations translated in a decreased subscapularis internal rotation moment arm. On the contrary, RSA increased the external rotation moment arm of the infraspinatus in neutral rotation and 0° of abduction.ConclusionImplantation of contemporary lateralized RSA implants led to increased length of the subscapularis to a greater extent than the increased length experienced by the infraspinatus and teres minor. The moment arm of the subscapularis decreased, whereas the moment arm of the teres minor in neutral rotation with the arm in abduction increased.Level of EvidenceLevel III; Basic Science, Biomechanics Study     

Changes in deltoid muscle tension after reverse shoulder arthroplasty as quantified by shear wave elastography: relationship with radiographic parameters and functional outcomes

IntroductionImplantation of a reverse shoulder arthroplasty (RSA) impacts deltoid length, shape and tension. Quantification of changes in deltoid muscle tension with implantation of RSA has remained elusive. The purpose of this study was to use shear wave elastography (SWE) to quantify deltoid muscle stiffness preoperatively, intraoperatively and postoperatively in patients undergoing RSA.MethodsTwenty patients scheduled to undergo RSA (ReUnion, Stryker) were prospectively enrolled in this study. A single observer trained in SWE quantified deltoid stiffness preoperatively, intraoperatively, and postoperatively. Clinical evaluation included pain, motion, quickDASH, ASES, Oxford, and subjective shoulder value scores. Preoperative and postoperative radiographs were measured by an independent observer to determine the lateralization and distalization shoulder angles (LSA and DSA). A statistical analysis was then performed to determine whether changes in deltoid muscle stiffness correlated with any of these parameters.ResultsImplantation of a RSA lead to an increase SWE deltoid stiffness value from 22.4 ± 4.2 kPa preoperatively to 29.9 ± 5.23 kPa (P˂ .0001) immediately after surgery, and 26.6 ± 6.6kPa (P= .03) at most recent follow-up. Preoperative SWE deltoid stiffness values did not differ when measured in the office or under anesthesia. Reverse arthroplasty did not significantly change the LSA (P= .051), but did increase the DSA (P< .0001). Greater SWE deltoid stiffness values correlated with better active elevation (P= .0128) better external rotation (P= .0247), and larger DSA (P= .0026). Elevation and external rotation showed a positive correlation with the DSA and a negative correlation with the LSA.ConclusionAfter implantation of one RSA design incorporating glenoid and humeral lateralization, deltoid stiffness as measured with SWE increased significantly. Deltoid stiffness seems to correlate with joint distalization, elevation and external rotation. SWE seems to be reliable to quantify deltoid stiffness after reverse shoulder arthroplasty.Level of EvidenceLevel IV; Diagnostic Study     

The influence of deltoid tensioning on functional outcomes following reverse shoulder arthroplasty

BackgroundWe aimed to investigate the relationship between functional outcomes and radiological and clinical measurements (based on deltoid moment arm length measurements) of reverse total shoulder arthroplasty (RTSA) performed in patients for irreparable rotator cuff tears.MethodsThirty-eight patients who underwent RTSA after irreparable rotator cuff tears between 2016 and 2019 were included in the study. Patients with primary osteoarthritis, rheumatoid arthritis, or post-traumatic RTSA were excluded from the study. The patients were evaluated functionally using the range of motion, Quick DASH, and Constant Scores (CS). Deltoid lengthening was measured both clinically by the difference in upper extremity length (dUEL) and radiologically by the acromiohumeral distance (AHD) and deltoid lever length (DLL). AHD was measured with true anteroposterior radiographs and ultrasound guidance.ResultsThe mean age of the patients was 66.39 ± 7.92 (range, 49–83) years. Of 38 patients, 31 (81.57%) were female and 7 (18.43%) were male. The mean follow-up durations were 26.43 ± 17.05 (range, 12–58) months. The mean active anterior elevation (AAE), abduction (AAB), and external rotation (AER) increased from 57.32°, 41.25°, and 22.32° preoperatively to 149°, 110°, and 34° at the last follow-up, respectively. Preoperatively, the mean QuickDASH score was 58.04, and at the last follow-up, it was 38.19. The mean Constant Score rose from 24.75 preoperatively to 60.64 at the last follow-up. The AHD, DLL, and dUEL mean values were 2.346, 1.89, and 1.746 cm, respectively. There was a significant relation between the DLL and the AAE (P < .01).ConclusionOptimizing deltoid tension plays an essential role in regaining function, and this study demonstrates that lengthening the deltoid increases the patient’s ability to elevate anteriorly, likely by recreating the force-length relationship of the deltoid muscle.     

Standard maximum isometric voluntary contraction tests for normalizing shoulder muscle EMG

A comparison of electromyographic (EMG) activity of muscles between and within subjects, and during separate occasions of testing, requires normalization. The most common way for generating the reference level used for normalizing shoulder EMG data is with a maximum isometric voluntary contraction (MVIC). The purpose of this study was to develop a parsimonious set of standardized tests that generate an MVIC in all the major muscle groups of the shoulder. Twelve muscles of the dominant shoulder of 15 subjects were examined using a combination of surface and intramuscular electrodes during 15 tests. The results indicated that many tests maximally activated more than one muscle simultaneously. Four tests were identified as being sufficient for generating an MVIC in the 12 muscles examined and are recommended as the standard set for normalizing shoulder muscle EMG: abduction 90° with internal rotation (“empty can”), internal rotation in 90° abduction (“internal rotation 90°”), flexion at 125° with scapula resistance (“flexion 125°”), and horizontal adduction at 90° flexion (“palm press”). The use of these shoulder normalization tests will make comparisons between shoulder EMG studies more reliable. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res     

Association between sagittal spinal alignment and postoperative shoulder range of motion following reverse total shoulder arthroplasty

BackgroundThe range of internal rotation sometimes deteriorates after reverse total shoulder arthroplasty; however, the underlying mechanisms remain unclear. This study aimed to investigate the association between sagittal spinal alignment and internal rotation deterioration after reverse total shoulder arthroplasty.MethodsWe retrospectively reviewed 52 patients who underwent reverse total shoulder arthroplasty by a single surgeon between October 2014 and December 2018. The sagittal spine was radiographed, and the sagittal spinal alignment was evaluated based on 10 parameters (e.g. C7-HA: the distance between the plumb line from the center of the seventh cervical vertebral body and the center of the hip axis). We divided the patients into two groups, group A (internal rotation deterioration; 23 patients) and B (without internal rotation deterioration; 29 patients). Logistic regression analysis was performed to analyze the association between sagittal spinal alignment and internal rotation deterioration after reverse total shoulder arthroplasty, and a receiver operating characteristic curve was used to analyse the cutoff value of independent variables that was correlated with IR deterioration.ResultsLogistic regression analysis demonstrated the correlation between C7-HA and internal rotation deterioration (odds ratio, 1.95; 95% confidence interval, 1.33–2.84; P < 0.001). The receiver operating characteristic curve suggested that when C7-HA was at least 2.44 cm, it was strongly correlated with deterioration of internal rotation (sensitivity, 91.3%; specificity, 93.1%; P < 0.001; area under the curve, 0.938). Group A was significantly inferior to group B in not only internal rotation but also flexion and abduction.ConclusionsThis study suggested that a remarkably positive value in C7-HA was a factor that was correlated with deterioration of internal rotation. In addition, the deformation of sagittal spinal alignment would impact on the range of motion after reverse total shoulder arthroplasty.     

The clinical outcomes and tuberosity healing after reverse total shoulder arthroplasty for acute proximal humeral fracture using the turned stem tension band technique

BackgroundRecent studies have reported the clinical effectiveness of tuberosity healing after reverse total shoulder arthroplasty in patients with proximal humeral fractures with respect to joint stability, long-term survival, and postoperative range of motion. However, it is challenging to achieve robust fixation of the fragile bone fragments in elderly patients. This study aimed to report on the radiographic and clinical outcomes of patients who underwent reverse total shoulder arthroplasty for acute proximal humeral fractures using a Turned stem Tension Band technique–a simple suture configuration that can apply a compressive force on both tuberosities at the same time.MethodsEighteen patients who underwent reverse total shoulder arthroplasty for complex proximal humeral fractures (age 80.4 ± 4.7 years, range 70–87 years), using our Turned stem Tension Band technique, were included in this study and evaluated postoperatively for range of motion, American Shoulder and Elbow Surgeons score, Numerical Rating Scale, and tuberosity healing, with minimum 2-years follow-up (mean 34.5 months, range 24–60 months).ResultsAt the final follow-up, mean range of motion results were active flexion, 119 ± 34°; active abduction, 116 ± 35°; active external rotation, 27 ± 12°; and active internal rotation, L3. Six of 11 (55%) patients with 4-part dislocated fractures had neurological disorders from the time of injury; of these, three patients obtained shoulder elevation under 90° at the final follow-up. The mean American Shoulder and Elbow Surgeons score was 77.3 ± 10.7, and the mean Numerical Rating Scale was 1.2 ± 0.9. Fifteen of 18 (83%) patients were satisfied with the results. The tuberosity healing rate was 100% (18 of 18).ConclusionsThe Turned stem Tension Band technique in reverse total shoulder arthroplasty for proximal humeral fractures provides a robust fixation, regardless of the fracture pattern, which results in a high tuberosity healing rate.     

The biomechanics of subscapularis repair in reverse shoulder arthroplasty: The effect of lateralization and insertion site

Functional outcomes of subscapularis (SSc) repair following reverse shoulder arthroplasty (RSA) remains controversial. SSc repair in combination with glenosphere lateralization was reported to yield worse clinical outcomes compared with the non-lateralized glenosphere. The aim of this biomechanical study was to investigate how glenosphere lateralization and different re-insertion sites can affect the biomechanics of the SSc after RSA. Nine patient-specific RSA shoulder models were created from patients' computed tomography scans. Moment arms and SSc length were calculated for abduction, forward flexion, and internal rotation in 20° and 90° abduction for three configurations of glenosphere lateralization (standard/+0, +5, and +10 mm) and three SSc repair sites (native, superior, and inferior) and compared with the native shoulder. When compared with the native shoulder, RSA resulted in large adducting SSc moment arms that were antagonistic to the deltoid. Glenosphere lateralization had no effect on SSc moment arms in any motion. However, lateralization increased SSc tension beyond its anatomic length for +5 and +10 mm of lateralization when attached to its native insertion. A superior SSc repair site created the least adductive moment arm as well as the least amount of SSc lengthening. Increased glenosphere lateralization showed a significant increase in the SSc length, which in combination with its adductive moment arm can be antagonistic to deltoid function. However, a superior SSc repair site may help reduce the adductive SSc moment arm and allow for reduced tension on the repair as its length in that location is less than that of the native SSc. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:888-894, 2020     

Bilateral anatomic total shoulder arthroplasty versus reverse shoulder arthroplasty

The results of anatomic total shoulder arthroplasty and reverse shoulder arthroplasty have previously been reported separately. Although the indications differ, scenarios exist in which a patient may have a total shoulder arthroplasty on 1 shoulder and a reverse shoulder arthroplasty on the contralateral shoulder.Between 1992 and 2009, twelve patients underwent bilateral sequential primary shoulder arthroplasty with a total shoulder arthroplasty on 1 side and reverse shoulder arthroplasty on the contralateral side. Constant score, American Shoulder and Elbow Surgeons (ASES) score, subjective shoulder value, and patient satisfaction were obtained a minimum 1 year postoperatively. Mean postoperative Constant score was 77 after total shoulder arthroplasty and 73 after reverse shoulder arthroplasty (P<.2488). Mean postoperative active forward flexion was similar after total shoulder arthroplasty compared with reverse shoulder arthroplasty (P=.8910). Greater external rotation at the side (43° vs 12°; P<.0001) and internal rotation (T8 vs L1; P<.0001) were observed after total shoulder arthroplasty. Mean ASES score was 89.6 after total shoulder arthroplasty compared with 82.4 after reverse shoulder arthroplasty (P=.0125). Patient satisfaction was 92% for both prostheses, and mean subjective shoulder value was similar (85.4% vs 82.5%; P=.6333).Bilateral shoulder arthroplasty performed with a total shoulder arthroplasty and reverse shoulder arthroplasty on opposite shoulders can provide good functional outcome and high patient satisfaction. Although range of motion is better following total shoulder arthroplasty, no difference was observed in final Constant score or subjective patient assessment.     

Effect of the neck-shaft angle on stability in the onlay type of reverse shoulder arthroplasty: a cadaveric study

BackgroundAlthough reverse shoulder arthroplasty (RSA) has been indicated for treating patients suffering from cuff tear arthropathy, instability is a severe complication. The relationship between the humeral neck-shaft angle and joint stability in RSA as well as the clinical effect of subscapularis tendon repair on postoperative stability after RSA remain controversial. This study is primarily aimed to investigate the relationship between humeral neck-shaft angle and stability using the onlay type of RSA with preserved shoulder girdle muscles using fresh frozen cadavers. Moreover, we aimed to investigate the effect of subscapularis tendon repair after RSA placement.MethodsAn onlay type RSA of not-lateralized glenosphere in a massive rotator cuff tear model with preserved shoulder component muscles was placed on 7 fresh frozen cadavers, and traction tests were performed to dislocate by changing the neck-shaft angle of the stem to 135°, 145°, and 155°. The anterior dislocation force (DF) was evaluated in 6 patterns as follows: 2 patterns at 30° and 60° of abduction and 3 patterns at 30° of internal rotation, in neutral rotation, and 30° of external rotation. DF was recorded at neck-shaft angles of 135°, 145°, and 155° and with and without subscapularis tendon repair.ResultsAt 30° abduction, DF was significantly higher at a neck-shaft angle of 155° regardless of the rotational position (P < .05), and at abduction 60°, there was no difference in DF according to any rotational position and any neck-shaft angle. Regardless of the neck-shaft angle, the DF was significantly higher at 60° abduction than at 30° abduction (P < .05). Furthermore, the DF was significantly higher with subscapularis tendon repair (P < .01).ConclusionOur results showed some relationship between humeral neck-shaft angle and stability in the onlay type of RSA with preserved shoulder component muscles using fresh frozen cadavers. Moreover, a neck-shaft angle of 155° showed the highest anterior DF among neck-shaft angles of 135° and 145° at 30° abduction, and there was no difference at abduction 60° among any neck-shaft angle. Furthermore, subscapularis tendon repair also contributed to anterior stability.     

Function after closed reduction from early unstable reverse shoulder arthroplasty

BackgroundOptimizing deltoid tension during reverse shoulder arthroplasty (RSA) remains a challenge for the shoulder surgeon. Ideal tension likely differs based on patient age, anatomy, size, preoperative diagnosis, and deltoid strength. Excess tension might overstuff the joint and limit range of motion. The aim of this study was to compare the function of patients with early postoperative instability (as a proxy for deltoid tension) and those without instability.MethodsA retrospective cohort study comparing two groups of patients with primary RSA operated on over a 5-year period by a single fellowship-trained shoulder and elbow surgeon using a combination of lateralized and medialized glenoid prosthesis with a 135-degree neck-shaft angle on the humeral side was conducted. The main exposure was shoulder dislocation that did not require revision arthroplasty compared with all other patients in the study period who underwent uneventful primary RSA. Chart review was performed for patient demographics, preoperative diagnosis, operative details, preoperative and postoperative range of motion and pain, reoperation, and instability events. The primary outcome was final clinic visit forward elevation. Outcomes included preoperative, postoperative, and difference in forward elevation and external rotation, as well as pain level.ResultsA total of 79 shoulders treated with primary RSA from 2015 to 2019 were identified. The average follow-up was 9 months (range, 3-47 months). Sixty-seven patients (72 shoulders) underwent uneventful primary RSA. Seven patients (7 shoulders) in the treatment cohort presented to a postoperative visit with complaint of shoulder dislocation that was able to be self-reduced and/or presented with a dislocated shoulder requiring closed reduction without sedation. At the final follow-up, average postoperative forward elevation was 121 ± 27 degrees in stable shoulders versus 145 ± 15 degrees in the unstable group (P = .003). No significant difference in external rotation was shown between stable and unstable RSA (39 ± 12 degrees and 36 ± 14 degrees, respectively). Overall average forward elevation and external rotation improved from 71 to 123 degrees and 19 to 39 degrees, respectively. More than 95% of patients (69/72 uneventful RSA and 6/7 unstable RSA) reported improvement in shoulder pain postoperatively.ConclusionIn the absence of other reasons for instability, early dislocation after RSA is a potential marker of relatively loose deltoid tension. In this study, patients with instability demonstrated higher forward elevation. Patients without instability are likely a mix of those with optimal and suboptimal deltoid tension.Level of evidenceLevel III, Retrospective Comparative Treatment Study     

Assessment of intraoperative joint loads and mobility in reverse total shoulder arthroplasty through a humeral trial sensor

HypothesisThe use of intraoperative glenohumeral load sensors has the potential to facilitate an objective, quantitative assessment of the soft tissue tension during reverse total shoulder arthroplasty.Material and MethodsA reverse total shoulder arthroplasty was performed on eight fresh frozen cadaveric shoulders, creating three different tightness conditions for each shoulder by using various shim thicknesses attached to an instrumented, load-sensing humeral trial component. The glenohumeral loads were recorded during four dynamic maneuvers, consisting of maximum internal/external rotation at 0°, 45° and 90° abduction and forward elevation. The joint kinematics were synchronously recorded using an optical tracking system.ResultsFor normal tightness conditions, 98.3% of the observed loads were below 40 lbf. These loads varied through the range of motion with an increase in glenohumeral loads generally observed towards the limits of the range of motion. With increasing shoulder tightness, the range of motion of the joint was not significantly affected, though the average and maximum glenohumeral load significantly increased (p < 0.01 for all).ConclusionIn a cadaveric setting, higher glenohumeral loads were observed at higher tightness conditions, demonstrating the potential of a load-sensing humeral trial component to quantify intraoperative joint load with reverse total shoulder arthroplasty. The glenohumeral loads are increasing towards the limits of the range of motion, indicating the importance of performing dynamic assessment of stability at the extents of the range of motion during implant trialing.Level of EvidenceBasic Science Study     

反肩置换在老年肱骨近端内固定失败翻修术中的疗效观察

目的：探讨反肩置换术在老年肱骨近端骨折内固定失败后翻修中的应用价值和效果。方法 ：回顾性分析2014年5月至2020年3月肱骨近端骨折内固定失败的患者8例,其中男3例,女5例;年龄65～75岁。8例均行反式肩关节置换术,病程8～16个月。记录并比较手术前和末次随访的关节活动度（range of motion,ROM）、加州大学（University of California at Los Angeles,UCLA）肩关节评分、肩关节视觉模拟评分（visual analogue scale,VAS）、焦虑自评量表（self-rating anxiety scale,SAS）评分、肩关节功能Constant-Murley评分,并分析手术并发症情况。结果：术后8例均获得随访,时间16～28个月。患肩关节活动度（前屈、外旋、外展、内旋）术后明显改善,术后VAS、SAS和UCLA评分也得到改善。肩关节功能Constant-Murley评分中末次随访疼痛、日常活动、活动范围、力量测试评分比术前均有明显提升,且总分比术前提高。1例发生肩胛盂切迹,影像学显示分级为1级,其余患者未发生相关特异性和非特...     

Intermediate to long term results of stemless metaphyseal reverse shoulder arthroplasty: A five to nine year follow-up

BackgroundShoulder arthroplasty incidence is increasing as is the volume of revision surgeries. Revision surgery is easier if humeral bone stock is preserved with minimal bone defects and osteolysis. This has led to an increased focus on the development of various short stemmed and stemless implants which provides stable fixation whilst preserving humeral bone stock.PurposeTo review the medium to long term clinical and radiological outcomes, complications and survival rates of a stemless reverse shoulder prosthesis.Patients and methodPatients with a minimum follow-up of 60 months following a reverse stemless shoulder arthroplasty were deemed eligible. Clinical and radiological data on twenty-one patients operated between 2009 and 2014 were recorded prospectively. Survivorship and patient recorded symptoms with the end point of revision surgery were recorded.ResultsMean follow-up of 78 months (60–114 months). Mean range of active elevation was 136° (80–170°). Mean range of active abduction and active external rotation was 122° (70–170°) and 47° (10–75°) respectively. Mean Oxford score improved from 12 pre-operatively to 44 at final follow up (p < 0.0001). Mean Constant Murley Score improved from 18 to 72 (p < 0.0001). Mean ADLEIR score of 13 pre-operatively increased to 32 post-operatively (p < 0.0001). Notching was seen in 23.5% of cases and no radiolucent areas were observed around the glenoid component. There were two cases of post traumatic peri-prosthetic fractures that were managed conservatively and one case of deep-seated infection that required a washout. The survivorship at the most recent follow-up was 100%.ConclusionThe advantages of bone preservation with the stemless metaphyseal prosthesis combined with encouraging medium to long term clinical and radiological results are very promising, particularly with the improved post-operative patient satisfaction scores. This is the first study that reports the results with a minimum of 5 year follow-up and has the longest mean follow-up period.Clinical relevanceThe reverse stemless shoulder prosthesis is an effective and reliable option for elective shoulder arthroplasty.     

Long-term relation between deltoid muscle volume and clinical outcomes in a reverse shoulder arthroplasty

BackgroundDeltoid muscle function is important in reverse shoulder arthroplasty (RSA). Concerns are raised on the resistance of the deltoid muscle against the postoperative distalization. We hypothesize that a decreased volume of the deltoid muscle is related to worse clinical outcomes after a long-term follow-up. An observational study was conducted to evaluate the relation between volume of the deltoid muscle and clinical outcomes after a long-term follow-up on RSA.MethodsEligible for inclusion was patients who underwent RSA for cuff arthropathy after minimum 3 years follow-up. Fifty-nine patients were enrolled in this study. Preoperative volume was measured on magnetic resonance imaging or computed tomography. Postoperative deltoid volume was evaluated on ultrasonography. Distalization of the humerus was measured on radiographs. Clinical outcomes were measured by the Constant-Murley Score (CMS), Oxford Shoulder Score, and range of motion. Multivariable linear regression models were used to examine the association between the deltoid volume and clinical outcomes, and between distalization and deltoid volume or clinical outcomes.ResultsThe mean follow-up period was 88.7 ± 29.1 months. Postoperative deltoid volume positively correlated with both CMS (P = .045) and abduction strength, in both operated (P = .01) and contralateral side (P < .001). No association between deltoid volume and Oxford Shoulder Score or range of motion, and no association between preoperative volume and postoperative CMS was found. The mean distalization of the humerus was 21.2 mm [95% CI: 19.4-22.9 mm]. Distalization negatively correlated with deltoid volume (P = .012) and CMS (P = .009).ConclusionsPostoperative deltoid volume correlated with clinical outcomes as measured by CMS and abduction strength after a long-term follow-up on RSA.     

The effect of glenoid version on internal and external rotation in reverse total shoulder arthroplasty

BackgroundThere is currently limited understanding of the contribution of glenoid version to postoperative internal (IR) and external rotation (ER) after reverse total shoulder arthroplasty (RTSA). The purpose of this study was to determine the impact of glenoid version on postoperative rotation after RTSA.MethodsForty-five 3-dimensional (3D) computer models of human scapulae were created from de-identified computed tomography (CT) scans. The scapulae were divided into 3 separate groups based on glenoid version: normal (10° to -10°), moderate (-10 to -25°), and severe (< -25°). The scapulae then underwent virtual implantation with a Grammont-style RTSA prosthesis at either 0°, -20°, or -30° of retroversion based on the severity of the native glenoid version (normal, moderate, severe). Internal, external, and total rotation (TR) were determined for each construct at both 30° and 60° of humeral abduction.ResultsGlenoids with a narrow width (< 25 mm) were noted to have minimal bony impingement on rotational testing and were excluded. In the remaining scapulae (n = 34), the achievable TR and IR for the humeral component decreased as glenoid retroversion increased. Changes in rotation for all categories were in general more pronounced at 60° of humeral abduction. Overall, ER generally increased as glenoid retroversion increased, with the largest increase occurring when going from 0° to -20° of retroversion, and minimal increase from -20° to -30° of retroversion regardless of humeral abduction.ConclusionPlacement of the glenoid component in increasing retroversion during RTSA results in a loss of IR and a corresponding increase in ER.Level of EvidenceBasic Science Study     

Moment arms of the shoulder muscles during axial rotation

The objective of the present study was to determine the instantaneous moment arms of 18 major muscle sub‐regions crossing the glenohumeral joint in axial rotation of the humerus during coronal‐plane abduction and sagittal‐plane flexion. The tendon‐excursion method was used to measure instantaneous muscle moment arms in eight entire upper‐extremity cadaver specimens. The results showed that the inferior subscapularis was the largest internal rotator; its rotation moment arm peaks were 24.4 and 27.0 mm during abduction and flexion, respectively. The inferior infraspinatus and teres minor were the greatest external rotators; their respective rotation moment arms peaked at 28.3 and 26.5 mm during abduction, and 23.3 and 22.1 mm during flexion. The two supraspinatus sub‐regions were external rotators during abduction and internal rotators during flexion. The latissimus dorsi and pectoralis major behaved as internal rotators throughout both abduction and flexion, with the three pectoralis major sub‐regions and middle and inferior latissimus dorsi displaying significantly larger internal rotation moment arms with the humerus adducted or flexed than when abducted or extended (p < 0.001). The deltoid behaved either as an internal rotator or an external rotator, depending on the degree of humeral abduction and axial rotation. Knowledge of moment arm differences between muscle sub‐regions may assist in identifying the functional effects of muscle sub‐region tears, assist surgeons in planning tendon transfer surgery, and aid in the development and validation of biomechanical computer models. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:658–667, 2011