BACKGROUND The purpose of this paper was to determine whether acromial morphology influences anteroposterior shoulder stability. We hypothesized that a more horizontal and higher position of the acromion in the sagittal plane would be associated with posterior instability. METHODS In this retrospective study, patients with unidirectional posterior instability were age and sex-matched to a cohort of patients with unidirectional anterior instability. Both cohorts were compared with a control group of patients with no instability and no degenerative glenohumeral (rotator cuff and/or joint surface) or acromial changes. Measurements on radiographs included posterior acromial tilt, anterior and posterior acromial coverage (AAC and PAC), posterior acromial height (PAH), and the critical shoulder angle (CSA). RESULTS The number of patients enrolled in each instability group was 41, based on a priori power analysis. The control group consisted of 53 shoulders. Of the measured anatomic factors, PAH showed the most significant association with posterior instability (odds ratio [OR] = 1.8; p < 0.001) in the logistic regression model. PAH was significantly greater in the posterior instability group compared with the anterior instability group (30.9 versus 19.5 mm; p < 0.001). With a cutoff value of PAH of 23 mm, the OR for posterior instability was 39. Shoulders with posterior instability were also significantly different from normal shoulders with regard to PAH (p < 0.001), AAC (p < 0.001), and PAC (p < 0.001) whereas, in the shoulders with anterior instability, all of these values except the AAC (p = 0.011) did not differ from those of normal shoulders. CONCLUSIONS Specific acromial morphology is significantly associated with the direction of glenohumeral instability. In shoulders with posterior instability, the acromion is situated higher and is oriented more horizontally in the sagittal plane than in normal shoulders and those with anterior instability; this acromial position may provide less osseous restraint against posterior humeral head translation. A steep "Swiss chalet roof-type" acromion virtually excluded recurrent posterior instability in an albeit relatively small cohort of patients. Additional investigation is needed to determine the relevance of these findings for future treatment. LEVEL OF EVIDENCE Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Background: Chronic pseudoparalysis is generally defined as the inability to actively elevate the arm above 90° with free passive range of motion and no neurological deficits. It has been suggested that this arbitrary cutoff needs to be refined. Purpose: To analyze whether there are structural and biomechanical differences in patients with chronic pseudoparalysis and those with chronic pseudoparesis. Study Design: Case-control study; Level of evidence, 3. Methods: In this retrospective study, 50 patients with chronic massive rotator cuff tears (mRCTs; ≥2 tendons) and free passive and active scapular plane abduction <90° were divided into 2 groups: pseudoparalysis group (n = 24; active scapular plane abduction, <45°) and pseudoparesis group (n = 26; active scapular plane abduction, >45° and <90°). Radiographic measurements included the critical shoulder angle, acromiohumeral distance, posterior acromial tilt, anterior and posterior acromial coverages, and posterior acromial height on outlet views. Measurements on magnetic resonance imaging (MRI) included fatty infiltration of the rotator cuff muscles, anterior (subscapularis) and posterior (infraspinatus/teres minor) tear extensions, and global (anterior + posterior) tear extension in the parasagittal plane. A published musculoskeletal model was used to simulate the effect of different mRCTs on the muscle force required for scapular plane abduction. Results: Plain radiographs revealed no differences between patients with chronic pseudoparalysis and those with pseudoparesis. MRI assessment showed significant differences between patients with chronic pseudoparalysis and those with pseudoparesis with respect to fatty infiltration of the subscapularis (2.9 vs 1.6; P < .001) and infraspinatus (3.6 vs 3.0; P < .001) muscles, and anterior (−23° vs 4°; P < .001), posterior (−23° vs −14°; P = .034), and global rotator cuff (225° vs 190°; P < .001) tear extensions. The anterior tear extension in patients with chronic pseudoparalysis always involved more than 50% of the subscapularis, which was associated with an odds ratio of 5 for inability to actively abduct more than 45°. The biomechanical model was unable to find a combination of muscles that could balance the arm in space when the tear extended beyond the supraspinatus and the cranial subscapularis. Conclusion: This study confirms that chronic pseudoparalysis and pseudoparesis are associated with different structural lesions. In the setting of a chronic mRCT, involvement of more than 50% of the subscapularis tendon with fatty infiltration of stage 3 is associated with pseudoparalysis of active scapular plane abduction <45°. The key function of the subscapularis was confirmed in the biomechanical model.

Background: It is unclear which structural parameters determine the development or the absence of chronic pseudoparalysis (PP) in patients with massive rotator cuff tears (mRCTs). Purpose: To determine whether scapular morphologic characteristics and extent of rotator cuff tearing are independent factors associated with chronic PP. Study Design: Case-control study; Level of evidence, 3. Methods: In this retrospective case-control study, 50 patients with chronic mRCT (≥2 fully detached tendons) and active scapular plane abduction less than 90° (PP group) were age- and sex-matched with a cohort of 50 patients with chronic mRCT and an active scapular plane abduction greater than 90° (non-PP; NPP group). Analysis of standardized, plain radiographs included measurement of the critical shoulder angle (CSA) and the acromiohumeral distance (ACHD) on anteroposterior views and measurement of posterior acromial tilt, anterior and posterior acromial coverage, and posterior acromial height on standardized outlet views. Measurements on magnetic resonance imaging included fatty muscle infiltration, anterior (subscapularis) and posterior (infraspinatus/teres minor) tear extension, and global tear extension (anterior + posterior tear extension) in the parasagittal plane. Results: Overall, no significant difference was found in patients’ demographic characteristics ( P > .05). Univariate analyses confirmed significant differences between the PP and NPP groups in active scapular plane abduction (51°± 22° vs 135°± 29°; P < .001). Multivariate analyses revealed independent factors associated with PP compared with the NPP group: CSA (38.2°± 4.6° vs 35.2°± 3.7°; P = .001); ACHD (4.7 ± 2.2 vs 7.3 ± 2.6 mm; P < .001); posterior acromial height (22 ± 10 vs 17 ± 7 mm; P = .005); and anterior (–9°± 21° vs 25°± 12°; P < .001) and posterior (–18°± 14° vs 2°± 14°; P < .001) tear extension. The NPP group had significantly less involvement and fatty infiltration of the subscapularis (1.4 ± 0.6) compared with the PP group (2.2 ± 0.9) ( P < .001). Conclusion: This study confirms that global RCT extension and the quality of the inferior half of the subscapularis are significantly associated with chronic pseudoparalysis. The study further shows that acromial morphologic characteristics are relevant in the development of pseudoparalysis. Patients with pseudoparalysis have a larger CSA, less ACHD, and a higher positioned acromion in the sagittal plane.

Purpose The aim of this work is to evaluate the effectiveness of training with the low-fidelity ArthroBox ® regarding performance of different basic arthroscopy tasks using a validated high-fidelity virtual reality simulator of the knee. Methods Nineteen volunteers (14 females and 5 males) without any previous experience in arthroscopy were randomly assigned either to the ArthroBox ® training group (n =10) or the non-training group (n =9). The training group underwent a supervised ArthroBox ® training consisting of a daily 60-min session for three consecutive days. Both groups completed the basic and the final assessment using a validated virtual reality-based passive haptic knee arthroscopy simulator (ArthroS, VirtaMed™). The following three factors were measured in different exercises (explained in "Materials and methods"): amount of time to finish the task, length of camera and scope path within the joint. Furthermore, the volunteers' demographics (age, sex, dexterity, video game experience, sport activities and profession) was assessed but showed no differences between the groups. Results There were no significant differences between the training and non-training group regarding the above-mentioned demographic factors. However, the training group showed significant improvement from baseline to follow-up in most activities (e.g. task performance time in seconds, intra-articular camera and grasp distance in centimetres; see Table 1) in comparison to the non-training group. Conclusions The results from this study demonstrate that training for three consecutive days using a portable and versatile low-fidelity simulator significantly improves arthroscopy performance when using a validated high-fidelity virtual knee simulator. Arthroscopic triangulation training outside the operating theatre with a portable, low-cost simulator has proven to be a valuable educational tool to improve the arthroscopic skills of trainee surgeons. Level of evidence Diagnostic study, Level II.

Background: The treatment of unstable (Neer type IIB and V) extra-articular distal clavicle fractures remains challenging, especially when encountering a small lateral fragment which does not allow for sufficient screw purchase. It was the purpose of this study to present the clinical and radiologic outcome of a consecutive series of patients treated by a stand-alone coracoclavicular stabilization using a so-called cow-hitch technique with a suture anchor. Methods: Nineteen patients were treated with a specific surgical technique for distal clavicle fractures (11 left, 8 right) with either rupture or bony avulsion of the coracoclavicular ligaments. Fourteen patients were examined in our outpatient clinic for the purpose of this study after a mean follow-up of 5 years (1-12.2 years). The examination included scoring according to Constant Murley score (CMS), the American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES), the Subjective Shoulder Value (SSV), and follow-up radiographs. Two additional patients were amenable to a telephone interview. Results: All patients reported very good subjective results, with a mean SSV of 92% and a mean ASES score of 96%. The CMS resulted in average absolute values of 92 points. Fractures consolidated in 95% of cases. One patient developed an asymptomatic pseudarthrosis. The coracoclavicular distance was restored from 21 mm preoperatively to 11 mm at the final follow-up and finally showed an average side-to-side difference of þ1.8 mm. Sports activities were fully resumed after an average of 4.7 months. Conclusion:The coracoclavicular stand-alone cow-hitch suture repair for unstable distal clavicle fractures is a minimally invasive fixation technique without prominent hardware that allows for an anatomic reduction and stable fixation with a low complication and high bony union rate. Both radiographic and clinical long-term results are very satisfactory.

Background Primarily posterior bone deficient (dysplastic) (Walch type C) or secondarily eroded (Walch type B2 or B3) glenoids represent a surgical challenge for shoulder arthroplasty. Due to the posteriorly static decentered head, reverse total shoulder arthroplasty (RTSA) is often considered as the treatment of choice. The purpose of this study is to report the clinical and radiographic outcomes, complications and reoperations of RTSA for posteriorly deficient glenoids. Materials and methods All patients who underwent RTSA for osteoarthritis secondary to underlying glenoid deficiency (Walch type B2, B3 and C) between 2005 and 2018 (study group), were identified from our institutional shoulder arthroplasty database and gender- and age-matched to a cohort of patients with normal glenoid bone stock (control group). Longitudinal pre- and postoperative clinical [Constant–Murley (CS) score, Subjective Shoulder Value (SSV)] and radiographic outcomes were assessed. Results We included 188 patients (94 in each group). The median follow-up was 43 ± 26 (24–144) months in the study group and 59 ± 32 (24–124) months in the control group. The glenoid deficiency was addressed by using glenoid bone reconstruction. The surgical site complication and revision rate of RTSA in patients with bony deficient glenoids were 17% and 7%. Although glenoid loosening was slightly higher in the study group (5 vs. 2), overall no significant differences were found between the study and control groups in satisfaction scores, preoperative and postoperative absolute and relative Constant scores, complication and revision rates, respectively. Conclusion Reverse total shoulder arthroplasty (RTSA) seems to be a valuable treatment option for patients with primary (dysplasia) or secondary (wear) posterior glenoid deficiency. Although severe glenoid bone loss seems to be a risk factor for glenoid component failure, the overall complication and revision rates as well as clinical and radiographic outcome are comparable to RTSA in patients without compromised glenoid bone stock. Level of evidence Level III: case–control study

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