Location of the posterior interosseous nerve in relation to common lateral approaches to the elbow.

PURPOSE: The risk of posterior interosseous nerve (PIN) injury during surgical approaches to the lateral elbow varies depending on the chosen approach, level of dissection, and rotational position of the forearm. Previous studies evaluated the trajectory of the PIN in specific surgical applications to reduce iatrogenic nerve injuries. The goal of this study is to examine the location of the PIN using common lateral approaches with varying forearm rotation. METHODS: The Kaplan, extensor digitorum communis (EDC) split, and Kocher approaches were performed on 18 cadaveric upper extremity specimens. Measurements were recorded with a digital caliper from the radiocapitellar (RC) joint and the lateral epicondyle to the point where the PIN crosses the approach in full supination, neutral, and full pronation with the elbow at 90°. The ratio of the nerve's location in relation to the entire length of the radius was also evaluated to account for different-sized specimens. RESULTS: The PIN was not encountered in the Kocher interval. For Kaplan and EDC split, with the forearm in full supination, the mean distance from the lateral epicondyle to the PIN was 52.0 ± 6.1 mm and 59.1 ± 5.5 mm, respectively, and the mean distance from the RC joint to the PIN was 34.7 ± 5.5 mm and 39.3 ± 4.7 mm, respectively; with the forearm in full pronation, the mean distance from the lateral epicondyle to the PIN was 63.3 ± 9.7 mm and 71.4 ± 8.3 mm, respectively, and the mean distance from the RC joint to the PIN was 44.2 ± 7.7 mm and 51.1 ± 8.7 mm, respectively. CONCLUSIONS: The PIN is closer to the lateral epicondyle and RC joint in the Kaplan than EDC split approach and is not encountered during the Kocher approach. The PIN was not encountered within 26 mm from the RC joint and 39 mm from the lateral epicondyle in any approach and forearm position and is generally safe from iatrogenic injury within these distances.

Lower trapezius tendon transfer for irreparable rotator cuff injuries: a scoping review.

Background: Rotator cuff tears are a common source of shoulder pain and dysfunction. An irreparable rotator cuff tear poses a particular treatment challenge. There have been few studies reporting the outcomes of lower trapezius tendon (LTT) transfer for irreparable rotator cuff injuries. Therefore, the purpose of this review is to summarize the postoperative functional outcomes and complications of patients undergoing a LTT transfer for massive irreparable rotator cuff injuries. Methods: A scoping review was performed using the Medline, Embase, Cochrane Central Register of Controlled Trials, and Google Scholar databases with the search terms "trapezius" AND "transfer." Of 362 studies included for initial screening, 37 full-text citations were reviewed, with 5 studies meeting all the inclusion criteria to be included in the review. Two reviewers extracted data on study design, patient demographics, surgical technique, functional outcomes, range of motion (ROM), and complications for each study according to the predefined criteria. Results: Improvements in the preoperative to postoperative functional status, identified using the Disabilities of the Arm, Shoulder, and Hand (50.34 to 18), The American Shoulder and Elbow Surgeons Score (48.56 to 80.24), Visual Analog Scale (5.8 to 1.89), Single Assessment Numeric Evaluation (34.22 to 69.86), and Subjective Shoulder Value (52.24 to 77.66), were evident across all 5 studies. Preoperative to postoperative increases in ROM were seen for flexion (85 to 135), external rotation (18 to 52), and abduction (50 to 98). The overall complication rate was 18%, with seroma formation (8%) as the most common postoperative complication. Discussion/Conclusion: Our analysis showed that LTT transfer improved postoperative function, ROM, and pain for patients with irreparable rotator cuff tears with an overall complication rate of 18%. Future controlled studies are required to directly compare LTT transfer to other tendon transfers and other surgical techniques for irreparable rotator cuff tears.

Avoiding the posterior interosseous nerve during 2-incision distal biceps tendon repair: an anatomic study.

BACKGROUND: The posterior interosseous nerve (PIN) is the most commonly injured motor nerve during distal biceps tendon repair resulting in severe functional deficits. Anatomic studies of distal biceps tendon repairs have evaluated the proximity of the PIN to the anterior radial shaft in supination, but limited studies have evaluated the location of the PIN in relation to the radial tuberosity (RT), and none have examined its relation to the subcutaneous border of the ulna (SBU) with varying forearm rotation. This study evaluates the location of the PIN in relation to the RT and SBU to help guide surgeons in safe placement of the dorsal incision and the safest zones of dissection. METHODS: The PIN was dissected from arcade of Frohse to 2 cm distal to the RT in 18 cadaver specimens. Four lines were drawn perpendicular to the radial shaft at the proximal, middle, and distal aspect of and 1 cm distal to the RT in the lateral view. Measurements were recorded with a digital caliper along these lines to quantify the distance between the SBU and RT to the PIN with the forearm in neutral, supination, and pronation with the elbow at 90° flexion. Measurements were also made along the length of the radius at the volar, middle, and dorsal surfaces at the distal aspect of the RT to assess its proximity to the PIN. RESULTS: Mean distances to the PIN were greater in pronation than supination and neutral. The PIN crossed the volar surface of the distal aspect of the RT -6.9 ± 4.3 mm (-13, -3.0) in supination, -0.4 ± 5.8 mm (-9.9, 2.5) in neutral, and 8.5 ± 9.9 mm (-2.7, 13) in pronation. One centimeter distal to the RT, mean distance to the PIN was 0.54 ± 4.3 mm (-4.5, 8.8) in supination, 8.5 ± 3.1 mm (3.2, 14) in neutral, and 10 ± 2.7 mm (4.9, 16) in pronation. In pronation, mean distances from the SBU to the PIN at points A, B, C, and D were 41.3 ± 4.2, 38.1 ± 4.4, 34.9 ± 4.2, and 30.8 ± 3.9 mm, respectively. CONCLUSION: PIN location is quite variable, and to avoid iatrogenic injury during 2-incision distal biceps tendon repair, we recommend placement of the dorsal incision no more than 25 mm anterior to the SBU and carrying out deep dissection proximally first to identify the RT before continuing the dissection distally to expose the tendon footprint. The PIN was at risk of injury along the volar surface at the distal aspect of the RT in 50% with neutral rotation and 17% with full pronation.

Stress shielding following stemless anatomic total shoulder arthroplasty.

Background: Finite element analysis has suggested that stemless implants may theoretically decrease stress shielding. The purpose of this study was to assess the radiographic proximal humeral bone adaptations seen following stemless anatomic total shoulder arthroplasty. Methods: A retrospective review of 152 prospectively followed stemless total shoulder arthroplasty utilizing a single implant design was performed. Anteroposterior and lateral radiographs were reviewed at standard time points. Stress shielding was graded as mild, moderate, and severe. The effect of stress shielding on clinical and functional outcomes was assessed. Also, the influence of subscapularis management on the occurrence of stress shielding was determined. Results: At 2 years postoperatively, stress shielding was noted in 61 (41%) shoulders. A total of 11 (7%) shoulders demonstrated severe stress shielding with 6 occurring along the medial calcar. There was one instance of greater tuberosity resorption. At the final follow-up, no humeral implants were radiographically loose or migrated. There was no statistically significant difference in clinical and functional outcomes between shoulders with and without stress shielding. Patients undergoing a lesser tuberosity osteotomy had lower rates of stress shielding, which was statistically significant (p = 0.021). Discussion: Stress shielding does occur at higher rates than anticipated following stemless total shoulder arthroplasty, but was not associated with implant migration or failure at 2 years follow-up. Level of evidence: IV, Case series.

Trabecular bone density distribution in the scapula of patients undergoing reverse shoulder arthroplasty.

BACKGROUND: To improve implant survival after reverse shoulder arthroplasty (RSA), surgeons need to maximize screw fixation. However, bone density variation and distribution within the scapula are not well understood as they relate to RSA. The three columns of bone in the scapula surrounding the glenoid fossa are the lateral border, the base of the coracoid process, and the spine of the scapula. In our previous study by Daalder et al on cadaveric specimens, the coracoid column was significantly less dense than the lateral border and spine. This study's objective was to verify whether these results are consistent with computer tomography (CT) scan information from patients undergoing RSA. METHODS: Two-dimensional axial CT images from twelve patients were segmented, and a three-dimensional digital model of the scapula was subsequently created using Mimics 17.0 Materialise Software (Leuven, Belgium). Hounsfield unit (HU) values representing cortical bone were filtered out to determine the distributions of trabecular bone density. An analysis of variance with post hoc Bonferroni tests determined the differences in bone density between the columns of bone in the scapula. RESULTS: The coracoid superolateral (270 ± 45.6 HU) to the suprascapular notch was significantly less dense than the inferior (356 ± 63.6 HU, P = .03, ds = 1.54) and anterosuperior portion of the lateral border (353 ± 68.9 HU, P = .04, ds = 1.42) and the posterior (368 ± 70 HU, P = .007, ds = 1.65) and anterior spine (370 ± 78.9 HU, P = .006, ds = 1.54). DISCUSSION/CONCLUSION: The higher-density bone in the spine and lateral border compared with the coracoid region may provide better bone purchase for screws when fixing the glenoid baseplate in RSA. This is in agreement with our previous study and indicates that the previous cadaveric results are applicable to clinical CT scan data. When these studies are taken together, they provide robust evidence for clinical applications, including having surgeons aim screws for higher-density regions to increase screw fixation, which may decrease micromotion and improve implant longevity.

The coronoid opening angle: a novel radiographic technique to assess bone loss in coronoid trauma.

BACKGROUND: Elbow fracture dislocations are complex injuries that often require surgical treatment in order to obtain a stable and congruent elbow joint. The coronoid plays a key role in the stability of this joint. Accurately identifying the degree of coronoid bone loss in the setting of traumatic elbow injuries is challenging. The purpose of this study is to describe a new radiographic measure, the coronoid opening angle (COA), to assist in estimating bone loss in these challenging fractures. METHODS: Radiographs were drawn from a regional database in a consecutive fashion. Candidate radiographs were excluded on the basis of radiographic evidence of degenerative changes, previous surgery or injury, bony deformity, and inadequate lateral view of the elbow. Normal COA, coronoid height, and calculated COA at varying amounts of bone loss were determined by 3 reviewers. RESULTS: A total of 120 subjects were included. The normal coronoid opening angle was 34° (95% CI 32.9°-34.0°) and the coronoid height, 18.8 mm (18.1-19.6). Ninety-five percent of the population had an opening angle greater than 29° (95% CI 27.2°-29°). The COA limit was calculated at 20%, 33%, and 50% of baseline coronoid height corresponding to degree of bone loss. Coronoid opening angles of 24°, 20°, and 16°, respectively, indicate the minimum bone loss of interest in 95% of the population. The intraclass correlation coefficient was found to be 0.89 or higher. CONCLUSION: In the setting of elbow trauma, it is often challenging to predict the amount of coronoid bone loss. The coronoid opening angle is a new technique and an adjunct for lateral elbow radiographs to predict the minimum coronoid bone loss. This can be used to guide clinical decision making, aid in predicting instability, and guide treatment. Future research will aim to validate this tool in the clinical trauma setting.

Central fixation element type and length affect glenoid baseplate micromotion in reverse shoulder arthroplasty.

BACKGROUND: Reverse shoulder arthroplasty (RSA) is commonly used to treat patients with rotator cuff tear arthropathy. Loosening of the glenoid component remains one of the principal modes of failure and represents a significant complication that requires revision surgery. This study assessed the effects of various factors on glenoid baseplate micromotion for primary fixation of RSA. MATERIALS AND METHODS: A half-fractional factorial design of experiment was used to assess 4 factors: central element type (central peg or screw), central cortical engagement according to length (13.5 or 23.5 mm), anterior-posterior peripheral screw type (nonlocking or locking), and cancellous bone surrogate density (160 or 400 kg/m3, 10 or 25 PCF). Glenoid baseplates were implanted into high- or low-density Sawbones rigid polyurethane foam blocks and cyclically loaded at 60° for 1000 cycles (500-N compressive force range) using a custom-designed loading apparatus. Micromotion at the 4 peripheral screw positions was recorded using linear variable differential transformers. RESULTS: Central peg fixation generated 358% greater micromotion at all peripheral screw positions compared with central screw fixation (P < .001). Baseplates with short central elements that lacked cortical bone engagement generated 328% greater micromotion than those with long central elements (P = .001). No significant effects were observed when varying anterior-posterior peripheral screw type or bone surrogate density. There were significant interactions between central element type and length (P < .001). DISCUSSION: A central screw and a long central element that engaged cortical bone reduced RSA baseplate micromotion. These findings serve to inform surgical decision making regarding baseplate fixation elements to minimize the risk of glenoid loosening and, thus, the need for revision surgery.

A multicenter, prospective 2-year analysis of the Sidus stem-free shoulder arthroplasty system.

BACKGROUND: The purpose of this multicenter, prospective study was to evaluate the efficacy and safety of a stemless total shoulder arthroplasty compared with a traditional stemmed control. METHODS: Ninety-five shoulders were selected for participation in this Food and Drug Administration investigational device exemption clinical trial and underwent stemless total shoulder arthroplasty. Subjects returned for follow-up at 6 weeks, 6 months, 12 months, and 2 years postoperatively. Outcome measures included pain; range of motion; American Shoulder and Elbow Surgeons, Western Ontario Osteoarthritis of the Shoulder, and Short Form 12 scores; and radiographic review. Baseline data were compared with 2-year follow-up data to determine the rate of composite clinical success compared with the stemmed control. RESULTS: All outcome assessments demonstrated significant improvements (P ≤ .007). The mean American Shoulder and Elbow Surgeons score improved from 20 to 89 (P < .0001), and the mean shoulder pain score decreased from 8.3 ± 1.6 to 0.7 ± 1.5 (P < .0001). The mean Western Ontario Osteoarthritis of the Shoulder score decreased from 1443 ± 256 to 203 ± 267 (P < .0001). On the Short Form 12, the mean physical health score increased from 33 ± 7 to 48 ± 9 (P < .0001) and the mean mental health score increased from 50 ± 13 to 54 ± 8 (P = .007). Mean active forward elevation increased from 97° ± 27° to 143° ± 25° (P < .0001), and mean active external rotation increased from 21° ± 16° to 53° ± 18° (P < .0001). Kaplan-Meier analysis showed an implant survivorship rate of 98% at 2 years. The composite clinical success rate was 87% compared with 85% for the stemmed control. CONCLUSIONS: This study showed that a stemless rough-blasted humeral implant with metaphyseal bone fixation provides good clinical and radiographic outcomes and survivorship at 2 years, with outcomes comparable to a traditional stemmed implant.

Three-dimensional scapular morphology is associated with rotator cuff tears and alters the abduction moment arm of the supraspinatus.

BACKGROUND: Numerous studies have reported an association between rotator cuff injury and two-dimensional measures of scapular morphology. However, the mechanical underpinnings explaining how these shape features affect glenohumeral joint function and lead to injury are poorly understood. We hypothesized that three-dimensional features of scapular morphology differentiate asymptomatic shoulders from those with rotator cuff tears, and that these features would alter the mechanical advantage of the supraspinatus. METHODS: Twenty-four individuals with supraspinatus tears and twenty-seven age-matched controls were recruited. A statistical shape analysis identified scapular features distinguishing symptomatic patients from asymptomatic controls. We examined the effect of injury-associated morphology on mechanics by developing a morphable model driven by six degree-of-freedom biplanar videoradiography data. We used the model to simulate abduction for a range of shapes and computed the supraspinatus moment arm. FINDINGS: Rotator cuff injury was associated with a cranial orientation of the glenoid and scapular spine (P = .011, d = 0.75) and/or decreased subacromial space (P = .001, d = 0.94). The shape analysis also identified previously undocumented features associated with superior inclination and subacromial narrowing. In our computational model, warping the scapula from a cranial to a lateral orientation increased the supraspinatus moment arm at 20° of abduction and decreased the moment arm at 160° of abduction. INTERPRETATIONS: Three-dimensional analysis of scapular morphology indicates a stronger relationship between morphology and cuff tears than two-dimensional measures. Insight into how morphological features affect rotator cuff mechanics may improve patient-specific strategies for prevention and treatment of cuff tears.

Reliability of a novel 3-dimensional computed tomography method for reverse shoulder arthroplasty postoperative evaluation.

BACKGROUND: Long-term function and survival of reverse shoulder arthroplasties (RSAs) are reliant on component positioning and fixation. Conventional postoperative analysis is performed using plain radiographs or 2-dimensional (2D) computed tomography (CT) images. Although 3-dimensional (3D) CT would be preferred, its use is limited by metal artifacts. This study proposes a new 3D CT method for postoperative RSA evaluation and compares its interobserver reliability with conventional methods. MATERIALS AND METHODS: Preoperative and postoperative CT scans, as well as postoperative radiographs, were obtained from 18 patients who underwent RSA implantation; the scapula, implant, and screws were reconstructed as 3D CT models. The postoperative 3D scapula and implant were imported into preoperative coordinates and matched to the preoperative scapula. Standardized scapula coordinates were defined, in which the glenoid baseplate version and inclination angle were measured. The percentage of screw volume in bone was measured from a Boolean intersection operation between the preoperative scapula and screw models. Four independent reviewers performed the measurements using 3D CT and conventional 2D methods. Intraclass correlation coefficients (ICCs) were used to compare the reliability of the methods. RESULTS: The 3D CT method showed excellent reliability (ICC > 0.75) in baseplate inclination (ICC = 0.92), version (ICC = 0.97), and screw volume in bone (ICC = 0.99). Conventional 2D methods demonstrated poor reliability (ICC < 0.4). For radiographs, inclination showed poor reliability (ICC = 0.09) and the screw percentage in bone showed fair reliability (ICC = 0.54). Version was not measured with plain radiographs. For 2D CT slice measurements, inclination showed poor reliability (ICC = 0.02), version showed excellent reliability (ICC = 0.81), and the screw percentage in bone showed poor reliability (ICC = 0.28). CONCLUSION: The new 3D CT-based method for evaluating RSA glenoid implant positioning and screw volume in bone showed excellent reliability and overcame the metal-artifact limitation of postoperative CT and 3D CT reconstruction.

Subscapularis management in stemless total shoulder arthroplasty: tenotomy versus peel versus lesser tuberosity osteotomy.

BACKGROUND: It is unknown whether subscapularis management technique has an influence on the outcomes and complications of stemless total shoulder arthroplasty. The purpose of this study, therefore, was to compare outcomes and complications between subscapularis tenotomy, peel, and lesser tuberosity osteotomy used during stemless shoulder arthroplasty. METHODS: We reviewed 188 stemless anatomic total shoulder arthroplasties and compared clinical and functional outcomes between those performed through a subscapularis tenotomy (n = 68), subscapularis peel (n = 65), or lesser tuberosity osteotomy (n = 55). Patients were followed up clinically and radiographically at 6 months, 1 year, and 2 years postoperatively. RESULTS: At 2 years postoperatively, no statistically significant differences in visual analog scale pain scores, American Shoulder and Elbow Surgeons scores, or patient-reported instability (P ≥ .19) were found between groups. Active external rotation was greater in the peel group (P = .006) than in the tenotomy group but was not different compared with the lesser tuberosity osteotomy group (P = .07). No statistically significant difference in clinical subscapularis failures was noted between groups (P = .11); however, 2 patients in the peel group sustained a subscapularis failure requiring reoperation. DISCUSSION: The results of this multicenter comparative analysis show that all 3 subscapularis management techniques are effective and safe in the short term when used with stemless anatomic total shoulder arthroplasty.

Factors contributing to glenoid baseplate micromotion in reverse shoulder arthroplasty: a biomechanical study.

BACKGROUND: Reverse shoulder arthroplasty (RSA) is typically performed in patients with cuff tear arthropathy. A common type of RSA baseplate has a central peg and 4 peripheral screws inserting into the glenoid surface. Baseplate failure is a significant postoperative complication that reduces prosthetic longevity and usually requires revision surgery. This study evaluated the contribution of mechanical factors on initial baseplate fixation. MATERIALS AND METHODS: This study simulated glenoid baseplate loading in a RSA. A half-fractional factorial design was used to test 5 factors: bone density (160 or 400 kg/m3), screw length (18 or 36 mm), number of screws (2 or 4), screw angle (neutral or diverging), and central peg length (13.5 or 23.5 mm). Trials were cyclically loaded at a 60° angle with 500 N for 1000 cycles. Micromotion at 4 peripheral screw positions was analyzed using a multifactorial analysis of variance (P < .05). RESULTS: We found an increase in micromotion with 3 scenarios: (1) lower bone density at all screw positions; (2) shorter central peg length at the inferior, superior and anterior screws; and (3) shorter screw length at the inferior and anterior screws. There were interactions between bone density and screw length at the inferior and anterior screws and between bone density and central peg length at the inferior, superior, and anterior screws. DISCUSSION: Greater bone density, a longer central peg, and longer screws provide improved initial glenoid fixation in an RSA, whereas the number of screws, and the angle of screw insertion do not. These findings may help minimize baseplate failure and revision operations.

3D Printed Anatomy-Specific Fixture for Consistent Glenoid Cavity Position in Shoulder Simulator.

Purpose: Fixation methods for consistent anatomical structure positioning in biomechanical testing can be challenging. Image-based 3D printing is an attractive method for fabrication of biomechanical supports of anatomical structure due to its ability to precisely locate anatomical features with respect to the loading system. Method: A case study is presented to provide a design guide for fixation block fabrication. The anatomy of interest was CT scanned and reconstructed in 3D. The model was imported into commercially available CAD software and modified into a solid object and to create the fixture block. The CAD fixture block is standardized such that anatomical features are always in the same position for the testing system by subtracting the anatomy from a base fixture block. Results: This method allowed a strong immobilization of anatomical specimens and a controlled and consistent positioning feature with respect to the testing system. Furthermore, the fixture block can be easily modified and adapted to anatomical structures of interest using CAD software. Conclusion: This approach allows preservation of the bony anatomy integrity and provides a repeatable and consistent anatomical positioning with respect to the testing system. It can be adapted for other anatomical structures in various other biomechanical settings.

Trabecular bone density distribution in the scapula relevant to reverse shoulder arthroplasty.

BACKGROUND: How trabecular bone density varies within the scapula and how this may lead to more optimal reverse shoulder arthroplasty (RSA) screw placement has not been addressed in the scientific literature. The 3 columns of trabecular bone within the scapula adjacent to the glenoid fossa, one extending through the lateral border, a second into the base of the coracoid process, and a third extending into the spine of the scapula, were hypothesized to be of relatively similar density. METHODS: Two-dimensional axial computed tomography (CT) images of 19 fresh frozen cadaver specimens were obtained. Digital Imaging and Communications in Medicine (DICOM; National Electrical Manufacturers Association, Rosslyn, VA, USA) image files of the CT scanned scapulae were imported into Mimics 17.0 Materialise Software (Leuven, Belgium) for segmentation and 3-dimensional digital model generation. To determine the distribution of trabecular bone density, Hounsfield unit (HU) values in the scapulae gray value files obtained from Mimics were filtered to remove any cortical bone. HU values of 650 define the corticocancellous interface in CT image data and were considered to be cortical bone. Analyses of variance with post hoc Bonferroni tests were used to determine statistical differences between the intra- and inter-regions of bone density comparisons. RESULTS: The base of the coracoid process was statistically significantly less dense than the spine and the lateral border of the scapulae examined (P < .05). DISCUSSION/CONCLUSION: The higher-quality bone in the spine and lateral border, compared with the coracoid regions, may provide better bone purchase for screws when fixing the glenoid baseplate in RSA.

Outcomes following long head of biceps tendon tenodesis.

Lesions of the proximal long head of the biceps tendon (LHB) have been considered as a major cause of shoulder pain and dysfunction. The role of the LHB in causing pain has been a source of controversy for many years, and extensive literature is available discussing anatomy, function, pathology, and most importantly appropriate treatment. Despite this, there is a lack of consensus in the literature regarding the management of biceps-related pathology. Biceps tenotomy and tenodesis are common surgical treatment options when dealing with LHB-related pathology. In this review, a brief discussion on surgical options is provided while focusing on the different options for biceps tenodesis including outcomes and complications.

Effect of implant geometry on range of motion in reverse shoulder arthroplasty assessed using glenohumeral separation distance.

BACKGROUND: Whereas reverse shoulder arthroplasty has been successful in treating patients with cuff tear arthropathy, implant impingement after the procedure often causes complications, including reduced range of motion, bone loss, and instability. Attempts to simulate this problem in vitro typically rely on subjective visual methods to detect impingement. The purpose of this study was to determine the effect of humeral neck-shaft angle, implant diameter, humeral cup depth, and glenoid component eccentricity on minimum abduction angle and range of motion using an implant-tracking method for impingement detection. METHODS: Tests were performed in a kinematic shoulder simulator with actuated cables representing the deltoid. The humerus was manually adducted and abducted past the point of impingement in either direction. Centers of the implant components were tracked with optical motion capture and processed with a thresholding algorithm to determine the minimum abduction angle where impingement occurred. RESULTS: Humeral cup depth had the largest effect on minimum abduction angle and range of motion, with a retentive cup reducing range of motion by 26°. A decreased neck-shaft angle reduced minimum abduction angle by 10° but had little effect on overall range of motion. Diameter and eccentricity had little effect. CONCLUSION: A reduced neck-shaft angle reduces minimum abduction angle but does not improve overall range of motion. A more retentive humeral cup increases minimum abduction angle significantly. Although retentive cups are intended to improve joint stability, the reduced range of motion that they impart to the joint may partly counteract the benefits of increased constraint.

From the unstable painful shoulder to multidirectional instability in the young athlete.

In conclusion, instability as a cause of shoulder pain in the young athlete is a difficult and often missed diagnosis. These young patients often seek treatment of shoulder pain but do not recall any episodes of shoulder instability. As a result, these uncommon, poorly described forms of instability are often misdiagnosed. A heightened clinical suspicion and an accurate, prompt diagnosis of instability is of paramount importance in this athletic group. It dictates appropriate treatment of the condition, avoids treatment delays and failure, provides better outcomes, and ensures timely return to play. UPS and MDI are two forms of this diagnosis. In UPS, patients at risk are young hyperlax athletes with a history of direct trauma or forceful overextension of the shoulder. They have shoulder pain that is described as deep anterior, reproduced with an anterior apprehension test and relieved with a relocation test. Soft tissue and/or bony lesions consistent with instability (observed on imaging or at arthroscopy) are necessary to confirm the diagnosis of UPS. Once the diagnosis is made, standard arthroscopic techniques with labrum reinsertion and/or anteroinferior capsule plication can lead to predictable good results and return to sport. In MDI, patients at risk are also young hyperlax athletes. However, these patients often do not have a history of trauma. They have shoulder pain that is often somewhat vague in location and is reproduced with a sulcus and/or hyper abduction test. Soft tissue and/or bony lesions consistent with instability are uncommon, with the exception of capsular laxity. The mainstay of treatment is physiotherapy rehabilitation. When surgery is necessary, open capsular shift and arthroscopic capsular plication are effective.

Factors affecting the stability of reverse shoulder arthroplasty: a biomechanical study.

BACKGROUND: Despite the success of reverse shoulder arthroplasty (RSA) in treating patients with painful pseudoparalytic shoulders, instability is a common complication and currently the factors affecting stability are not well understood. The objective of this study was to investigate a number of factors as well as the interactions between factors to determine how they affect the stability of the prosthesis. These factors included: active arm posture (abduction and abduction plane angles), loading direction, glenosphere diameter and eccentricity, and humeral socket constraint. METHODS: Force required to dislocate the joint, determined using a biomechanical shoulder simulator, was used as a measure of stability. A factorial design experiment was implemented to examine the factors and interactions. RESULTS: Actively increasing the abduction angle by 15° leads to a 30% increase in stability and use of an inferior-offset rather than a centered glenosphere improved stability by 17%. Use of a more constrained humeral socket also increased stability; but the effect was dependent on loading direction, with a 88% improvement for superior loading, 66% for posterior, 36% for anterior, and no change for inferior loading. Abduction plane angle and glenosphere diameter had no effect on stability. CONCLUSION: Increased glenohumeral abduction and the use of an inferior-offset glenosphere were found to increase the stability of RSA. Additionally, use of a more constrained humeral socket increased stability for anterior, posterior, and superior loading. These identified factor effects have the potential to decrease the risk of dislocation following RSA.

The unstable painful shoulder (UPS) as a cause of pain from unrecognized anteroinferior instability in the young athlete.

HYPOTHESIS: The etiology of shoulder pain in the overhead athlete is often difficult to determine. This study hypothesized that (1) instability can present in a purely painful form, without any apparent history of instability, but with anatomic lesions indicative of instability, termed unstable painful shoulder (UPS), and that (2) arthroscopic shoulder stabilization is effective. MATERIALS AND METHODS: The study evaluated 20 patients (mean age, 22 ± 8 years) at a mean of 38 months postoperatively (range, 24-69 months). Inclusion criteria were painful shoulder with lesions indicative of instability on imaging or at surgery, minimum 2-year follow-up. Exclusion criteria were recognized instability, other associated pathologies, and previous shoulder surgery. RESULTS: Patients were young, hyperlax athletes who complained of deep, anterior shoulder pain and denied any instability. Pain was reproduced with the arm in an anterior apprehension position and relieved by a relocation test; however, no actual apprehension was experienced. Patients often had glenohumeral laxity and hyperlaxity. Lesions indicative of instability confirmed that at least 1 unapparent shoulder subluxation occurred. The Rowe, Walch-Duplay, and University of California, Los Angeles scores improved significantly (P < .05); 19 patients (95%) were satisfied, and 15 (75%) returned to their previous level of sports. DISCUSSION: The diagnosis of UPS is often missed but is important to consider in the young hyperlax athlete. Soft tissue and/or bony lesions consistent with instability are necessary to confirm the diagnosis. Arthroscopy certainly deserves a significant place in this form of anteroinferior instability because it allows both the assessment of lesions (ie, diagnosis) and a satisfactory functional result and return to sport.