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Objective To determine potential predictive associations between patient-/lesion-specific factors, clinical outcome and anterior ankle impingement in patients that underwent isolated autologous matrix-induced chondrogenesis (AMIC) for an osteochondral lesion of the talus (OLT). Design Thirty-five patients with a mean age of 34.7 ± 15 years who underwent isolated cartilage repair with AMIC for OLTs were evaluated at a mean follow-up of 4.5 ± 1.9 years. Patients completed AOFAS (American Orthopaedic Foot and Ankle Society) scores at final follow-up, as well as Tegner scores at final follow-up and retrospectively for preinjury and presurgery time points. Pearson correlation and multivariate regression models were used to distinguish associations between patient-/lesion-specific factors, the need for subsequent surgery due to anterior ankle impingement and patient-reported outcomes. Results At final follow-up, AOFAS and Tegner scores averaged 92.6 ± 8.3 and 5.1 ± 1.8, respectively. Both body mass index (BMI) and duration of symptoms were independent predictors for postoperative AOFAS and Δ preinjury to postsurgery Tegner with positive smoking status showing a trend toward worse AOFAS scores, but this did not reach statistical significance ( P = 0.054). Nine patients (25.7%) required subsequent surgery due to anterior ankle impingement. Smoking was the only factor that showed significant correlation with postoperative anterior ankle impingement with an odds ratio of 10.61 when adjusted for BMI and duration of symptoms (95% CI, 1.04-108.57; P = 0.047). Conclusion In particular, patients with normal BMI and chronic symptoms benefit from AMIC for the treatment of OLTs. Conversely, smoking cessation should be considered before AMIC due to the increased risk of subsequent surgery and possibly worse clinical outcome seen in active smokers.

Background Meniscus allograft transplantation is a valuable surgical option for post-meniscectomy syndrome. For best results, the selected allograft should be as similar as possible to the original meniscus. Three-dimensional meniscus sizing could be a new approach to improve the accuracy of meniscus matching. The contralateral anatomy might therefore be a suitable reconstruction template. The purpose of this study was to compare the three-dimensional shape of the right and left menisci by bi-planar segmentation of magnetic resonance imaging (MRI) scans. Methods Three-dimensional surface models of healthy menisci were created based on 40 bilateral MRI scans. Manual segmentation was performed on the MRI data in sagittal and coronal planes. For side-to-side comparison, each left meniscus model was mirrored and then superimposed to its corresponding right meniscus model. Differences between the meniscus pairs were assessed by width, length, height and surface distances. Inter-reader reliability, as well as accuracy of bi-planar segmentation was assessed by two different readers. Results The meniscus pairs were not significantly different in terms of width, length and height (P = at least 0.138). Side difference of mean surface distances was 0.76 mm (± 0.13 standard deviation (SD)) for medial and 0.78 mm (± 0.15 SD) for lateral menisci. Inter-reader reliability was good to excellent (0.828–0.987). Conclusion The three-dimensional shapes of the left and right menisci are very similar. Therefore, the contralateral meniscus can be used as a template for three-dimensional meniscus allograft sizing. Three-dimensional meniscus segmentation and sizing can be performed accurately by combination of sagittal and coronal planes.

This study was conducted in order to determine the predictive value of MR arthrography findings for pain relief after glenohumeral corticosteroid injection. This study prospectively enrolled 212 patients (mean age 51.4 years; range 15–90) who underwent fluoroscopy-guided glenohumeral corticosteroid injection. All patients received MR arthrography of the shoulder less than 3 months prior to the infiltration and returned questionnaires which assessed patients’ shoulder pain using the 11-point numeric rating scale (NRS), covering a 1-month follow-up period. MR arthrograms were retrospectively assessed for abnormalities of the rotator cuff, long biceps tendon, glenohumeral bone, cartilage, and labrum as well as for synovitis, bursitis, and signs of adhesive capsulitis. MR arthrography findings were compared to patients’ NRS change using the Mann–Whitney U and Kruskal–Wallis tests for univariate analysis and multiple linear regression for multivariate analysis. Pain reduction of ≥ 2 points was considered to represent clinically relevant improvement, which was seen in 71% of patients 1 week and in 74% of patients 1 month after glenohumeral injection. Univariate analysis of MR findings showed that signs of adhesive capsulitis and an intact labrum were associated with significantly higher NRS reductions after 1 month in comparison to patients without these findings (median 4 vs. 3, p = 0.007 and 4 vs. 2, p = 0.003, respectively). Multivariate analysis proved both factors to be independent predictors of improved outcome after 1 month (beta = 0.176, p = 0.039 and beta = 0.212, p = 0.001, respectively). Glenohumeral corticosteroid injections for pain relief have a high success rate with 74% of patients reporting clinically relevant improvement after 1 month. Signs of adhesive capsulitis and an intact labrum on MR arthrography are independent predictors of a better outcome. • Seventy-four percent of patients report clinically relevant improvement 1 month after glenohumeral corticosteroid injection. • Signs of adhesive capsulitis and an intact labrum on MR arthrography are independent predictors of a high pain level decrease.

Background Progressive collapsing foot deformity (PCFD) is a complex 3-dimensional (3-D) deformity with varying degrees of hindfoot valgus, forefoot abduction, and midfoot varus. The first aim of this study was to perform a 3-D analysis of the talus morphology between symptomatic PCFD patients that underwent operative flatfoot correction and controls. The second aim was to investigate if there is an impact of individual talus morphology on the success of operative flatfoot correction. Methods We reviewed all patients that underwent lateral calcaneal lengthening for correction of PCFD between 2008 and 2018 at our clinic. Radiographic flatfoot parameters on preoperative and postoperative radiographs were assessed. Additionally, 3-D surface models of the tali were generated using computed tomography (CT) data. The talus morphology of 44 flatfeet was compared to 3-D models of 50 controls without foot or ankle pain of any kind. Results Groups were comparable regarding demographics. Talus morphology differed significantly between PCFD and controls in multiple aspects. There was a 2.6° increased plantar flexion (22.3° versus 26°; p = 0.02) and medial deviation (31.7° and 33.5°; p = 0.04) of the talar head in relation to the body in PCFD patients compared to controls. Moreover, PCFD were characterized by an increased valgus (difference of 4.6°; p = 0.01) alignment of the subtalar joint. Satisfactory correction was achieved in all cases, with an improvement of the talometatarsal-angle and the talonavicular uncoverage angle of 5.6° ± 9.7 (p = 0.02) and 9.9° ± 16.3 (p = 0.001), respectively. No statistically significant correlation was found between talus morphology and the correction achieved or loss of correction one year postoperatively. Conclusion The different morphological features mentioned above might be contributing or risk factors for progression to PCFD. However, despite the variety of talar morphology, which is different compared to controls, the surgical outcome of calcaneal lengthening osteotomy was not affected. Level of evidence III.

Background There is evidence that specific variants of scapular morphology are associated with dynamic and static posterior shoulder instability. To this date, observations regarding glenoid and/or acromial variants were analyzed independently, with two-dimensional imaging or without comparison with a healthy control group. Therefore, the purpose of this study was to analyze and describe the three-dimensional (3D) shape of the scapula in healthy and in shoulders with static or dynamic posterior instability using 3D surface models and 3D measurement methods. Methods In this study, 30 patients with unidirectional posterior instability and 20 patients with static posterior humeral head subluxation (static posterior instability, Walch B1) were analyzed. Both cohorts were compared with a control group of 40 patients with stable, centered shoulders and without any clinical symptoms. 3D surface models were obtained through segmentation of computed tomography images and 3D measurements were performed for glenoid (version and inclination) and acromion (tilt, coverage, height). Results Overall, the scapulae of patients with dynamic and static instability differed only marginally among themselves. Compared with the control group, the glenoid was 2.5° (P = .032), respectively, 5.7° (P = .001) more retroverted and 2.9° (P = .025), respectively, 3.7° (P = .014) more downward tilted in dynamic, respectively, static instability. The acromial roof of dynamic instability was significantly higher and on average 6.2° (P = .007) less posterior covering with an increased posterior acromial height of +4.8mm (P = .001). The acromial roof of static instability was on average 4.8° (P = .041) more externally rotated (axial tilt), 7.3° (P = .004) flatter (sagittal tilt), 8.3° (P = .001) less posterior covered with an increased posterior acromial height of +5.8 mm (0.001). Conclusion The scapula of shoulders with dynamic and static posterior instability is characterized by an increased glenoid retroversion and an acromion that is shorter posterolaterally, higher, and more horizontal in the sagittal plane. All these deviations from the normal scapula values were more pronounced in static posterior instability.

Background: In a sheep rotator cuff model, tenotomy predominantly induces fatty infiltration, and denervation induces mostly muscle atrophy. In clinical practice, myotendinous retraction after tendon tear or lateralization after tendon repair tear may lead to traction injury of the nerve. Purpose/Hypothesis: To analyze whether an additional nerve lesion during rotator cuff repair leads to further degeneration of the rotator cuff muscle in the clinical setting. We hypothesized that neurectomy after tendon tear would increase atrophy as well as fatty infiltration and that muscle paralysis after neurectomy would prevent myotendinous retraction after secondary tendon release. Study Design: Controlled laboratory study. Methods: Twelve Swiss alpine sheep were used for this study. For the 6 sheep in the tenotomy/neurectomy (T/N) group, the infraspinatus tendon was released; 8 weeks later, the suprascapular nerve was transected. For the 6 sheep in the neurectomy/tenotomy (N/T) group, neurectomy was performed, and the infraspinatus was tenotomized 8 weeks later. All sheep were sacrificed after 16 weeks. Magnetic resonance imaging (MRI) was performed before the first surgery (baseline) and then after 8 and 16 weeks. The MRI data were used to assess muscle volume, fat fraction, musculotendinous retraction, pennation angle, and muscle fiber length of the infraspinatus muscle. Results: Three sheep (2 in the T/N and 1 in the N/T group) had to be excluded because the neurectomy was incomplete. After 8 weeks, muscle volume decreased significantly less in the T/N group (73% ± 2% of initial volume vs 52% ± 7% in the N/T group; P < .001). After 16 weeks, the mean intramuscular fat increase was higher in the T/N group (36% ± 9%) than in the N/T group (23% ± 6%), without reaching significance (P = .060). After 16 weeks, the muscle volumes of the N/T (52% ± 8%) and T/N (49% ± 3%) groups were the same (P = .732). Conclusion: Secondary neurectomy after tenotomy of a musculotendinous unit increases muscle atrophy. Tenotomy of a denervated muscle is associated with substantial myotendinous retraction but not with an increase of fatty infiltration to the level of the tenotomy first group. Clinical Relevance: Substantial retraction, which is associated with hitherto irrecoverable fatty infiltration, should be prevented, and additional neurogenic injury during repair should be avoided to limit the development of further atrophy., Orthopaedic Journal of Sports Medicine, 9 (8), ISSN:2325-9671

Background Arthroscopic rotator cuff repair techniques have almost replaced open repairs. Short- and mid-term studies have shown comparable outcomes, with no clear superiority of either procedure. The aim of this study was to compare the long-term clinical and imaging outcomes following arthroscopic or open rotator cuff repair. Methods Forty patients with magnetic resonance imaging (MRI)–documented, symptomatic supraspinatus or supraspinatus and infraspinatus tears were randomized to undergo arthroscopic or open rotator cuff repair. Clinical and radiographic follow-up was obtained at 6 weeks, 3 months, 1 year, 2 years, and >10 years postoperatively. Clinical assessment included measurement of active range of motion, visual analog scale score for pain, functional scoring according to the Constant-Murley score (CS), and assessment of the Subjective Shoulder Value. Imaging included conventional radiography and MRI for the assessment of cuff integrity and alteration of the deltoid muscle. Results We enrolled 20 patients with a mean age of 60 years (range, 50-71 years; standard deviation [SD], 6 years) in the arthroscopic surgery group and 20 patients with a mean age of 55 years (range, 39-67 years; SD, 8 years) in the open surgery group. More than 10 years’ follow-up was available for 13 patients in the arthroscopic surgery group and 11 patients in the open surgery group, with mean follow-up periods of 13.8 years (range, 11.9-15.2 years; SD, 1.1 years) and 13.1 years (range, 11.7-15 years; SD, 1.1 years), respectively. No statistically significant differences in clinical outcomes were identified between the 2 groups: The median absolute CS was 79 points (range, 14-84 points) in the arthroscopic surgery group and 84 points (range, 56-90 points) in the open surgery group (P = .177). The median relative CS was 94% (range, 20%-99%) and 96% (range, 65%-111%), respectively (P = .429). The median Subjective Shoulder Value was 93% (range, 20%-100%) and 93% (range, 10%-100%), respectively (P = .976). MRI evaluation showed a retear rate of 30% equally distributed between the 2 groups. Neither fatty infiltration of the deltoid muscle, deltoid muscle volume, nor the deltoid origin were different between the 2 groups. Conclusion In a small cohort of patients, we could not document any difference in clinical and radiographic outcomes at long-term follow-up between arthroscopic and open rotator cuff repair. The postulated harm to the deltoid muscle with the open technique could not be confirmed., JSES International, 4 (4)

Operative management of a coracoid process fracture is indicated in case of painful nonunion, displacement of more than 1 cm, or multiple disruptions of the superior shoulder suspensory complex. Several techniques have been described with open reduction of the fracture and internal fixation using cortical screws with or without additional fixation of the acromioclavicular joint. This Technical Note aims to introduce an alternative safe, minimally invasive method for arthroscopic fixation of a coracoid fracture with simultaneously reduction of the acromioclavicular joint. The described arthroscopic technique might be helpful for shoulder surgeons who want to fix the coracoid process while avoiding the disadvantages of an open approach.

Background Rock climbers are particularly susceptible to shoulder injuries due to repetitive upper-limb movements on vertical or overhanging terrain. However, the long-term effects of prolonged climbing on the shoulder joints are still unknown. Purpose The purpose of this study was to analyze the prevalence of pain and degenerative changes in the shoulder joints after high-level rock climbing over at least 25 years. We hypothesized that specific climber-associated patterns of degeneration would be found. Methods Thirty-one adult male high-level rock climbers were compared to an age- and sex-matched control group of 31 nonclimbers. All participants underwent a detailed interview, standardized clinical examination, and bilateral (climbers) or unilateral (nonclimbers, dominant side) magnetic resonance imaging (MRI) scans. Clinical and MRI findings of the groups were compared. Results The lifetime prevalence of shoulder pain in the rock climbers was 77%. The rock climbers had significantly more abnormalities in the labrum (82% vs. 52%; P = .002), long biceps tendon (53% vs. 23%; P = .006), and cartilage (28% vs. 3%; P = .005). These increased changes positively correlated with climbing intensity. There were no differences between the 2 groups with respect to rotator cuff tendon pathology (68% vs. 58%; P = .331) and acromioclavicular joint degeneration (88% vs. 90%; P = .713). Despite the increased degenerative changes in the rock climbers, their Constant score (CS) was still better than that of the nonclimbers (CS 94, interquartile range [IQR] 92-97, vs. CS 93, IQR 91-95; P = .019). Conclusions Prolonged high-level rock climbing leads to a high prevalence of shoulder pain and increased degenerative changes to the labrum, long biceps tendon, and cartilage. However, it is not related to any restriction in shoulder function.

Background: Long-term results of the arthroscopic Bankart repair in patients older than 40 years are unknown and may be favorable in terms of postoperative glenohumeral arthritis as opposed to the long-term results of the open Latarjet procedure in patients older than 40 years. Purpose: To analyze our long-term results of the arthroscopic Bankart repair for recurrent anterior shoulder instability in patients older than 40 years of age and to compare these results with previously published long-term results of the Latarjet procedure in a cohort of similar age. Study Design: Cohort study; Level of evidence, 3. Methods: A total of 35 consecutive patients (36 shoulders) with a mean age of 47 years (range, 40-69) at time of the arthroscopic Bankart repair were studied at a mean 13.2 years (range, 8-18) after surgery. Clinical and radiographic results were then compared with those of our previous study of 39 consecutive patients (40 shoulders) of a same age group who had been treated for the same pathology with an open Latarjet procedure. Results: Six shoulders (17%) sustained a recurrent shoulder dislocation after a mean 5.3 years; subluxation occurred in 3 shoulders (8%); and apprehension persisted in 3 shoulders (8%). Revision surgery was performed in 8 patients (22%): 2 Bankart and 6 open Latarjet. The relative preoperative Constant score and Subjective Shoulder Value were significantly improved ( P < .001) at final follow-up. Arthropathy of stabilization was advanced in the shoulders of 16 patients (47%) and had progressed by at least 2 grades in 21 patients (62%). There were significantly higher rates of redislocation and subluxation when compared with the open Latarjet procedure (9 vs 3; P = .037), and the mean final Subjective Shoulder Value was significantly lower in the Bankart group (86% vs 91%; P = .011). There were no significant differences in final advanced arthropathy (16 vs 14; P = .334) and revision rates (8 vs 7; P = .409) when compared with the Latarjet procedure. Conclusion: Arthroscopic Bankart repair for recurrent anterior shoulder instability in patients older than 40 years was associated with reliable pain relief and patient satisfaction similar to that after the open Latarjet procedure. Restoration of stability was significantly less successful and development of arthropathy no better than the open Latarjet procedure in patients older than 40 years.

Purpose Selection of a meniscus allograft with a similar three-dimensional (3D) size is essential for good clinical results in meniscus allograft surgery. Direct meniscus sizing by MRI scan is not possible in total meniscectomy and indirect sizing by conventional radiography is often inaccurate. The purpose of this study was to develop a new indirect sizing method, based on the 3D shape of the ipsilateral tibia plateau, which is independent of the meniscus condition. Methods MRI and CT scans of fifty healthy knee joints were used to create 3D surface models of both menisci (MRI) and tibia plateau (CT). 3D bone models of the proximal 10 mm of the entire and half tibia plateau (with / without intercondylar area) were created in a standardized fashion. For each meniscus, the best fitting “allograft” couple out of all other 49 menisci were assessed by the surface distance of the 3D meniscus (best available allograft), of the 3D tibia plateau (3D-CT) and by the radiographic method of Pollard (2D-RX). Results 3D-CT sizing was significantly better by using only the half tibia plateau without the intercondylar area (p Conclusions Automatized, indirect meniscus sizing using the 3D bone models of the tibia plateau is feasible and more precise than the previously described 2D-RX method.. However, further technical improvement is needed to select always the best available allograft.

Background Inaccurate meniscus allograft size is still an important problem of the currently used sizing methods. The purpose of this study was to evaluate a new three-dimensional (3D) meniscus-sizing method to increase the accuracy of the selected allografts. Methods 3D triangular surface models were generated from 280 menisci based on 50 bilateral and 40 unilateral knee joint magnetic resonance imaging (MRI) scans. These models served as an imaginary meniscus allograft tissue bank. Meniscus sizing and allograft selection was simulated for all 50 bilateral knee joints by (1) the closest mean surface distance (MeSD) (3D-MRI sizing with contralateral meniscus), (2) the smallest meniscal width/length difference in MRI (2D-MRI sizing with contralateral meniscus), and (3) conventional radiography as proposed by Pollard (2D-radiograph (RX) sizing with ipsilateral tibia plateau). 3D shape and meniscal width, length, and height were compared between the original meniscus and the selected meniscus using the three sizing methods. Results Allograft selection by MeSD (3D MRI) was superior for all measurement parameters. In particular, the 3D shape was significantly improved (p < 0.001), while the mean differences in meniscal width, length, and height were only slightly better than the allograft selected by the other methods. Outliers were reduced by up to 55% (vs. 2D MRI) and 83% (vs. 2D RX) for the medial meniscus and 39% (vs. 2D MRI) and 56% (vs. 2D RX) for the lateral meniscus. Conclusion 3D-MRI sizing by MeSD using the contralateral meniscus as a reconstruction template can significantly improve meniscus allograft selection. Sizing using conventional radiography should probably not be recommended. Trial registration Kantonale Ethikkommission Zürich had given the approval for the study (BASEC-No. 2018-00856).

Patellofemoral instability can be caused by tibial or femoral torsional deformity. Established surgical treatment options are rotational osteotomies, but the transfer from pre-operative planning to surgical execution can be challenging. Patient-specific instruments (PSI) are proofed to be helpful tools in realignment surgery. However, accuracy of PSI in femoral and tibial rotational osteotomies remains still unknown. Goal of the present study was to evaluate the accuracy of PSI in femoral and tibial rotational osteotomies in a patient population suffering from patellofemoral instability. All patients that underwent femoral or tibial rotational osteotomy using PSI in case of patellofemoral instability from October 2015 until April 2019 in our clinic were included. Twelve knees with twelve supracondylar femoral and seven supratuberositary tibial rotational osteotomies could be included. Accuracy of the correction was assessed using pre- and post-operative CT scans based on conventional measurements and, in 3D, based on 3D bone models of the respective patients. CT measurements revealed an absolute difference between planned and achieved rotation of 4.8° ± 3.1° for femoral and 7.9° ± 3.7° for tibial rotational osteotomies without significant difference (p = 0.069). Regarding 3D assessment, a significant difference could be observed for the residual error between femoral and tibial rotational osteotomies in the 3D angle (p = 0.014) with a higher accuracy for the femoral side. The application of PSI for femoral and tibial rotational osteotomy is a safe surgical treatment option. Accuracy for femoral rotational osteotomies is higher compared with tibial rotational osteotomies using PSI.

Background Anatomic reduction and stable internal fixation of complex proximal humeral fractures in the elderly is challenging. Secondary displacement, screw perforation, and humeral head necrosis are common complications. The outcome of hemiarthroplasty is unpredictable and strongly dependent on the uncertain healing of the greater tuberosity. This multicenter study retrospectively analyzes the midterm results of primary reverse total shoulder arthroplasty for the treatment of acute, complex fractures of the humerus in an elderly population. Methods Fifty-two shoulders in 51 patients with a mean age of 77 years treated with reverse total shoulder arthroplasty for an acute, complex fracture of the proximal humerus were clinically and radiographically analyzed after a mean follow-up period of 35 months (range, 12-90 months). Results There were no intraoperative complications. Revision surgery was performed in 4 shoulders. At final follow-up, the absolute and relative Constant scores averaged 62 points (range, 21-83 points) and 86% (range, 30%-100%), respectively, with a mean Subjective Shoulder Value of 83% (range, 30%-100%). Of the patients, 92% rated the treatment outcome as excellent or good. Patients with a resected or secondarily displaced greater tuberosity had an inferior clinical outcome to those with a healed greater tuberosity. Conclusion The midterm clinical results are predictably good, with low complication rates and a rapid postoperative recovery of painfree everyday function. If secondary displacement of the greater tuberosity occurs, revision surgery may warrant consideration in view of potential improvement of ultimate outcome.

BACKGROUND The pathomechanisms of eccentric osteoarthritis of the shoulder remain unclear. Although there is increasing evidence of bony differences between shoulders with rotator cuff tears and osteoarthritis, analogous differences have not been identified for primary concentric and eccentric osteoarthritis. This study examined the shape and orientation of the acromial roof as a potential risk factor for the development of posterior glenoid wear. METHODS We analyzed computed tomography images of 105 shoulders with primary osteoarthritis. Based on the classification of Walch, 45 shoulders had concentric osteoarthritis (Walch A) and 60 shoulders were affected by eccentric osteoarthritis (Walch B; EOA). A comparison of acromial morphology was performed in a multiplanar reconstruction analysis of computed tomography scans. RESULTS Acromial shape: Acromial length, width, and area were not significantly different. Acromial roof orientation: The acromial roof in EOA was an average of 5° flatter (sagittal tilt; P

Background There is evidence for differences of scapular shape between shoulders with rotator cuff tears (RCT) and osteoarthritic shoulders (OA). This study analyzed orientation and shape of the acromion in patients with massive RCT and concentric OA (COA) in a multiplanar computed tomography (CT) analysis. Methods CT scans of 70 shoulders with degenerative RCT and 45 shoulders with COA undergoing primary shoulder arthroplasty were analyzed. The 2 groups were compared in relation of (1) shape of the acromion, (2) its orientation in space, and (3) the anteroposterior glenoid coverage in relation to the scapular plane. Results Lateral acromial roof extension was an average of 4.6 mm wider and the acromial area was an average of 156 mm2 larger in RCT than in COA (P Conclusions A more externally rotated (axial plane), more downward tilted (coronal plane), and wider posterior covering acromion was more frequent in patients with massive RCT than COA.

It is still unknown whether glenoid inclination or lateral acromial roof extension is a more important determinant for development of rotator cuff tears (RCT) or osteoarthritis (OA) of the shoulder. It was the purpose of this study, to evaluate whether there is a potential predominance of one of these factors in pathogenesis of RCT or concentric OA. We analyzed 70 shoulders with advanced degenerative RCT and 54 shoulders with concentric OA undergoing primary shoulder arthroplasty (anatomical or reverse) using antero-posterior radiography and multiplanar computed tomography. The two groups were compared in relation to glenoid inclination, lateral acromion roof extension, acromial height, and critical shoulder angle (CSA). All measured parameters were highly significantly different between RCT and concentric OA (p < 0.001). Based on Cohen's d effect size, group differences were most distinct in lateral acromial roof extension (1.36x-ray , 0.92ct ) compared with acromial height (1.06x-ray , 0.73ct ) and glenoid inclination (0.60x-ray , 0.61ct ). However, no single factor showed an effect size which was as high as that of the CSA (1.63x-ray ). Interestingly, a ratio of lateral acromion roof extension and acromial height could enhance the effect size (1.60x-ray , 1.16ct ) near to values of the CSA (1.63x-ray ). In summary, lateral acromial roof extension has a greater influence in pathogenesis of degenerative RCT and concentric OA than acromial height or glenoid inclination. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Background Little is known of the mechanisms that lead to the muscle changes associated with rotator cuff disorders. We have observed that the magnetic resonance imaging (MRI) appearance of fatty infiltration (FI) and muscle atrophy (MA) differ between chronic cuff tears and suprascapular neuropathy, suggesting different pathophysiology. This study compares the different MRI changes that occur in chronic cuff tears and suprascapular neuropathy. Methods Two groups were retrospectively identified: (1) RCT group (20 shoulders): patients with chronic tears of the supraspinatus and/or infraspinatus without electromyographic (EMG) evidence of suprascapular neuropathy; (2) neuro group (17 shoulders): patients with EMG documented suprascapular nerve dysfunction and absence of a rotator cuff tear. Magnetic resonance arthrograms were analyzed for the degree of FI and MA, and the morphology of the muscle was assessed, in particular the muscle border, pattern of FI, and extent of involvement. Results The muscle changes that occur following chronic cuff tears differ from that following denervation secondary to suprascapular neuropathy, especially with respect to the muscle border, degree of perineural fat, and overall distribution of FI. Highly specific and characteristic morphological patterns of FI exist for both chronic cuff tears and suprascapular neuropathy. Conclusion Chronic rotator cuff tendon tears and suprascapular neuropathy are both associated with FI and MA of the rotator cuff muscles. The pattern of FI is markedly different in the 2 situations. These findings have diagnostic potential and may serve as a basis for further research concerning type, severity, and evolution of FI under different conditions and after treatment.