Limits imposed on glenohumeral motion by joint geometry

Passive shoulder abduction range of motion at 3 months postoperatively is the most important prognostic factor for achieving full recovery of range of motion at 6 months after arthroscopic rotator cuff repair

Background

After arthroscopic rotator cuff repair (ARCR), it is crucial for clinicians to predict the functional recovery in the early postoperative period for considering rehabilitation strategies. The aim of this study was to identify the prognostic factors in the early postoperative period for achieving full recovery of range of motion (ROM) at 6 months after ARCR.

Methods

This study included 184 patients who underwent ARCR. Patients were divided into the full recovery and nonrecovery groups using the Constant ROM score at 6 months postoperatively. The area under the curve for predicting the full recovery group was calculated for all independent variables such as demographic data, ROM, shoulder functional scores at preoperative and 3 months postoperative using receiver operating characteristic curve analysis. Multivariable logistic regression analysis was then performed using candidate variables with an area under the curve of 0.7 or greater to determine prognostic factors for full recovery at 6 months postoperatively. The same analysis as above was also performed by dividing the patients into groups according to their preoperative ROM.

Results

Multivariable logistic regression analysis revealed that preoperative active flexion, 3 months postoperative passive abduction, and internal rotation at 90° abduction ROM were significant prognostic factors of achieving full ROM recovery at 6 months postoperatively. Only passive abduction ROM at 3 months postoperatively was significantly extracted in the preoperative ROM limitation group.

Conclusion

This study demonstrated that passive abduction ROM at 3 months postoperatively was a significant prognostic factor of achieving full recovery of ROM at 6 months after ARCR.

Humeral Resurfacing Arthroplasty: Clinical, Functional and Radiological Assessment at a Mean Follow-Up of 11 Years

Humeral resurfacing arthroplasty (HRA) entails the substitution of the articular surface alone with a prosthetic cap without a humeral stem. It is a more conservative procedure which can be easily converted in a total (anatomical or reverse) arthroplasty, if necessary. The present study aimed to evaluate the clinical and radiographical outcomes in a series of patients treated with HRA by a single surgeon. Thirty-three patients with a mean follow-up of 11 years were clinically (Constant score; disability of the arm, shoulder and hand score, DASH) and radiographically assessed before and after surgery. The Constant and DASH scores improved significantly after surgery, and only two cases needed revision surgery. HRA represents a valid therapeutic option in selected cases to improve the quality of life and prevents the need for more invasive procedures.

Glenohumeral Cartilage Thickness: Implications in Prosthetic Design and Osteochondral Allograft Transplantation

OBJECTIVE

A complete understanding of the glenohumeral joint anatomy is crucial for osteochondral allograft (OCA) transplantation and prosthetic design. However, existing data on the cartilage thickness distribution are not consistent. This study aims to describe the cartilage thickness distribution at both the glenoid cavity and humeral head in males and females.

DESIGN

Sixteen fresh cadaveric shoulder specimens were dissected and separated to expose the glenoid and humeral head articular surfaces. The glenoid and humeral head were cut into 5-mm coronal sections. Sections were imaged and cartilage thickness was measured at 5 standardized points on each section. Measurements were analyzed based on age, sex, and regional location.

RESULTS

For the humeral head, cartilage was thickest centrally (M = 1.77 ± 0.35 mm) and thinnest superiorly and inferiorly (M = 1.42 ± 0.37 mm, 1.42 ± 0.29 mm). At the glenoid cavity, cartilage was thickest in the superior and inferior areas (M = 2.61 ± 0.47 mm, 2.53 ± 0.58 mm) and thinnest centrally (M = 1.69 ± 0.22 mm). Males were found to have thicker cartilage at both the humeral head and glenoid (P = 0.0014, P = 0.0133).

CONCLUSIONS

Articular cartilage thickness distribution of the glenoid and humeral head is nonuniform and reciprocal in nature. These results can be used to further inform prosthetic design and OCA transplantation. We noted a significant difference in cartilage thickness between males and females. This suggests that the sex of the patient should be taken into consideration when matching donors for OCA transplantation.

Manufacture of Soft-Hard Implants from Electrospun Filaments Embedded in 3D Printed Structures

Rotator cuff tendon tears are common injuries of the musculoskeletal system that often require surgical repair. However, re-tearing following repair is a significant clinical problem, with a failure rate of up to 40%, notably at the transition from bone to tendon. The development of biphasic materials consisting of soft and hard components, which can mimic this interface, is therefore promising. Here, a simple manufacturing approach is proposed that combines electrospun filaments and 3D printing to achieve scaffolds made of a soft polydioxanone cuff embedded in a porous polycaprolactone block. The insertion area of the cuff is based on the supraspinatus tendon footprint and the size of the cuff is scaled up from 9 to 270 electrospun filaments to reach a clinically relevant strength of 227N on average. The biological evaluation shows that the biphasic scaffold components are noncytotoxic, and that tendon and bone cells can be grown on the cuff and block, respectively. Overall, these results indicate that combining electrospinning and 3D printing is a feasible and promising approach to create soft-to-hard biphasic scaffolds that can improve the outcomes of rotator cuff repair.

Mid-term outcomes of pyrolytic carbon humeral resurfacing hemiarthroplasty compared with metal humeral resurfacing and metal stemmed hemiarthroplasty for osteoarthritis in young patients: analysis from the Australian Orthopaedic Association National Joint Replacement Registry

BACKGROUND

The optimal surgical management of glenohumeral osteoarthritis in young patients remains an unsolved problem. Humeral resurfacing hemiarthroplasty and stemmed hemiarthroplasty using metallic heads are 2 surgical options that avoid the complications of loosening or wear of the glenoid component seen in total shoulder arthroplasty. Despite the potential benefits, improvement in survivorship has not been demonstrated from joint registry studies or other studies at mid-term follow-up. This is predominantly because of glenoid erosion and pain that occur when the metal resurfaced head articulates with the native glenoid. The use of pyrolytic carbon (pyrocarbon) as a resurfacing material has been proposed as an alternative bearing surface thought to reduce glenoid erosion owing to a marked reduction in wear rates in vitro. This study aimed to compare the survivorship of shoulder hemi-resurfacing using pyrocarbon with shoulder hemi-resurfacing and stemmed hemiarthroplasty using metallic heads.

METHODS

Data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) were analyzed for all patients aged <55 years who had undergone a primary shoulder replacement for osteoarthritis from April 16, 2004, to December 31, 2019. The outcomes of shoulder procedures using pyrocarbon hemi-resurfacing were compared with procedures using metal hemi-resurfacing and metal stemmed hemiarthroplasty. The reasons for revision in each arthroplasty class were analyzed. The analyses were undertaken using Kaplan-Meier estimates of survivorship and hazard ratios (HRs) from Cox proportional hazards models.

RESULTS

We analyzed 393 primary shoulder procedures, of which 163 were pyrocarbon hemi-resurfacing procedures, 163 were metal hemi-resurfacing procedures, and 67 were metal stemmed hemiarthroplasties.The cumulative percentage of revision at 6 years was 8.9% for pyrocarbon hemi-resurfacing, 17.1% for metal hemi-resurfacing, and 17.5% for metal stemmed hemiarthroplasty. Pyrocarbon hemi-resurfacing prostheses had a statistically lower revision rate than other hemi-resurfacing prostheses (HR, 0.41; 95% confidence interval, 0.18-0.93; P = .032). Pain, prosthesis fracture, and infection were the key reasons for revision. No pyrocarbon hemi-resurfacing cases were revised for glenoid erosion. In male patients, pyrocarbon humeral resurfacing had a lower cumulative percentage of revision compared with metal stemmed hemiarthroplasty (HR, 0.32; 95% confidence interval, 0.11-0.93; P = .037).

CONCLUSION

Pyrocarbon humeral resurfacing arthroplasty had statistically lower revision rates at mid-term follow-up in patients aged <55 years compared with other hemi-resurfacing procedures.

Shoulder resurfacing for treatment of focal defects and diffuse osteoarthritis

This article provides a review of the various options for the treatment of osteoarticular pathology of the shoulder. This can range from focal osteochondral defects to diffuse arthritis and can occur at any age. Although total shoulder arthroplasty and hemiarthroplasty are the most frequently used methods, they not generally suitable for younger patients under 60 years old due to the lack of long-term stability and deterioration. If conservative treatment is unsuccessful or not an option, resurfacing is an alternative procedure with good long-term results. The various methods that have been reported for resurfacing and partial resurfacing of the humeral head are described as well as the results of studies on these procedures. In this article the indications, biomechanics, outcomes and complications are outlined for the two resurfacing options preferred by the authors.

Effect of Glenohumeral Internal Rotation Deficit on Shoulder in Baseball Pitchers during Fastball Pitching

Previous studies have reported that pitchers with glenohumeral internal rotation deficit (GIRD) may increase the risk of shoulder injury. However, limited information is available regarding the specific effects of GIRD in baseball pitching. The purpose of this study was to investigate whether baseball pitchers with GIRD change their pitching mechanism. Fifteen baseball pitchers with GIRD and 15 pitchers without GIRD were recruited from university or senior high-school teams. A three-dimensional motion analysis system (Eagle System, Motion Analysis Corporation, Santa Rosa, CA, USA) was used to capture the pitching motion while performing fastball pitches. The kinematics and kinetics of the throwing shoulder and trunk were analyzed based on motion captured data. The Mann-Whitney U test was used to test the differences of the analyzed parameters between two groups. At the instant of ball release, the GIRD group showed lower shoulder external rotation and trunk rotation, and larger shoulder horizontal adduction. In addition, the GIRD group exhibited a significantly larger shoulder inferior force in the cocking and acceleration phase, and a significantly larger internal rotation torque in the acceleration phase. The present results suggested that pitchers with GIRD need stretch training to enlarge joint range of motion, and to improve trunk strength and flexibility to alleviate potential problems associated with pitching in GIRD pitchers.

An interpopulation comparison of 3-dimensional morphometric measurements of the proximal humerus

Background

Precise anatomic reconstruction of the proximal humerus is essential to a favorable outcome of total shoulder arthroplasty. Because of the wide variation in the geometric features of the proximal humerus, prosthetic designs incorporating these disparities are being developed.

Methods

The aim of this study is to use data obtained from cadavers and computed tomographic scans to investigate the 3-dimensional morphometric parameters of the proximal humerus of South African and Swiss samples and make an interpopulation comparison. In addition, the study combines the interarticular variations between populations with the differences in sex and shoulder sides. With the aid of medical imaging techniques and engineering design tools, various geometric features were measured.

Results

The results obtained from these analyses revealed several differences in sex and shoulder sides. On average, the Swiss were larger in most of the measured parameters than the South Africans. The male shoulders of Swiss and South Africans were observed to significantly vary in 4 of the parameters measured. The South African male and female right shoulders varied considerably in one-fourth of the measured shoulder variables. Generally, for both populations, the left and right shoulders of the same individuals were not different in all the measured variables irrespective of sex.

Conclusion

The knowledge acquired in this study is expected to assist in the development of a population-specific shoulder prosthetic design and surgical planning procedures.

Effect of rotator cuff muscle activation on glenohumeral kinematics: A cadaveric study

Healthy shoulder function requires the coordination of the rotator cuff muscles to maintain the humeral head's position in the glenoid. While glenohumeral stability has been studied in various settings, few studies have characterized the effect of dynamic rotator cuff muscle loading on glenohumeral translation during shoulder motion. We hypothesize that dynamic rotator cuff muscle activation decreases joint translation during continuous passive abduction of the humerus in a cadaveric model of scapular plane glenohumeral abduction. The effect of different rotator cuff muscle activity on glenohumeral translation was assessed using a validated shoulder testing system. The Dynamic Load profile is a novel approach, based on musculoskeletal modeling of human subject motion. Passive humeral elevation in the scapular plane was applied via the testing system arm, while the rotator cuff muscles were activated according to the specified force profiles using stepper motors and a proportional control feedback loop. Glenohumeral translation was defined according to the International Society of Biomechanics. The Dynamic load profile minimized superior translation of the humeral head relative to the conventional loading profiles. The total magnitude of translation was not significantly different (0.805) among the loading profiles suggesting that the compressive forces from the rotator cuff primarily alter the direction of humeral head translation, not the magnitude. Rotator cuff muscle loading is an important element of cadaveric shoulder studies that must be considered to accurately simulate glenohumeral motion. A rotator cuff muscle activity profile based on human subject muscle activity reduces superior glenohumeral translation when compared to previous RC loading profiles.

Is posterosuperior contact a normal occurrence in the shoulder?

Posterosuperior (or internal) impingement at the shoulder is defined as contact between the underside of the supraspinatus or infraspinatus tendons with the posterosuperior labrum during extreme external rotation and abduction. In many cases, this contact damages the tendon and causes mirror posterosuperior labrum deterioration. The primary aim of this study was to define whether this contact occurs normally in patients who do not have a rotator cuff tear.

METHODS

We evaluated 100 shoulders in 100 patients. All patients were operated on in the beach chair position. After introducing the scope through the posterior portal, contact between the articular side of the rotator cuff and the posterosuperior labrum was noted as being present or absent when the arm was cocked in 90° abduction and 90° external rotation (90/90) then the arm was cocked in 140° abduction and maximum external rotation (140/Max).

RESULTS

Contact was observed in 69% of patients in the 90/90 cocked position and in 94% of patients in the 140/Max cocked position. We found a correlation between the presence of rotator cuff and/or labrum lesions and the patient regularly performing arm-cock movements (p=0.035).

DISCUSSION

Contact between the underside of the supraspinatus tendon and the posterosuperior labrum occurs physiologically. Repetitive arm-cock movements may contribute to macroscopic lesions of the underside of the rotator cuff and posterosuperior labrum.

LEVEL OF EVIDENCE

IV, basic science study.

Radiographic restoration of native anatomy: a comparison between stemmed and stemless shoulder arthroplasty

BACKGROUND

Shoulder arthroplasty is a reliable procedure for patients with degenerative glenohumeral disease, and reproduction of native shoulder anatomy leads to superior outcomes. The aim of this study was to compare the ability of stemmed and stemless implants to radiographically restore native glenohumeral anatomy.

METHODS

Shoulder arthroplasties were performed in 79 patients, with 58 receiving a stemless implant and 21 receiving a stemmed implant. Preoperative and postoperative radiographs were assessed for humeral head height, humeral head centering, humeral head medial offset, humeral head diameter, humeral neck angle, and lateral humeral offset by 2 independent viewers. Measurements were scored and summed to identify the anatomic reconstruction index (ARI). Radiographic measurements were compared using the Student t test, and significance was set at P < .05 for all statistical analyses. Interobserver agreement of radiographic analyses was assessed using the intraclass correlation coefficient, finding excellent reliability (intraclass correlation coefficient, 0.92).

RESULTS

Five of six radiographic measurements along with the calculated ARI demonstrated no differences between stemmed and stemless shoulder implants (humeral head diameter, P = .651; humeral head height, P = .813; humeral head medial offset, P = .592; lateral humeral offset, P = .311; humeral head centering, P = .414; and ARI, P = .862). Stemless implants showed improved restoration of the native humeral neck angle (0° for stemless vs. -3° for stemmed, P = .017).

CONCLUSION

Radiographic restoration of anatomy is similar for stemmed and stemless shoulder arthroplasty implants.

Three-dimensional measurement of glenoid dimensions and orientations

BACKGROUND

Asians generally have smaller stature than Europeans and Americans, and currently available implants used in reverse shoulder arthroplasty might not fit smaller bony anatomies. However, few articles have reported glenoid geometry in the Asian population. The purpose of this study was to measure the dimensions and orientations of the glenoid from three-dimensional computed tomography reconstructions of elderly Japanese subjects.

METHODS

This study included 100 shoulders (50 males and 50 females with >50 years of age). The mean age was 67 ± 7 years for both sexes, and the mean height was 167 ± 7 cm for males and 154 ± 6 cm for females. Three-dimensional scapular models were created from computed tomographic images, and the glenoid height, glenoid width, glenoid version, glenoid inclination, vault depth, and vault width were measured.

RESULTS

The mean glenoid height and width were 38.6 and 29.4 mm for males and 33.1 and 24.4 mm for females, respectively. Both retroversion and superior inclination were approximately 3° in both sexes. The glenoid vault was deeper in the posterior region with the maximum depth of 26.1 and 23.6 mm in males and females. The vault width was narrower in the anterior region with the anterior width of 2.5 mm at 15 mm medial from the glenoid face in females.

CONCLUSION

Glenoids of Japanese females are small compared to currently available baseplates for reverse shoulder arthroplasty. These results may be helpful to aid design in smaller baseplates that better fit the anatomic geometry of the Asian glenoid.

Assessment of the Spastic Upper Limb with Computational Motion Analysis

This article presents the current status of integrating 3-dimensional motion analysis and electromyography to assess upper extremity function clinically. The authors used their approach to establish a normative database for 5 Shriners Hospital Upper Extremity Evaluation tasks, which provides ranges of motion at the point of task achievement. Also, the inter-joint correlations are provided to understand the movement coordination required for each task. Distal upper extremity motion is strongly related to proximal function, supporting the idea that treatment of the proximal upper extremity deficits may be best preceded by treatment of the more distal upper extremity segments.

Compared to X-ray, three-dimensional computed tomography measurement is a reproducible radiographic method for normal proximal humerus

BACKGROUND

Accurate comprehension of the normal humeral morphology is crucial for anatomical reconstruction in shoulder arthroplasty. However, traditional morphological measurements for humerus were mainly based on cadaver and radiography. The purpose of this study was to provide a series of precise and repeatable parameters of the normal proximal humerus for arthroplasty, based on the three-dimensional (3-D) measurements.

METHODS

Radiographic and 3-D computed tomography (CT) measurements of the proximal humerus were performed in a sample of 120 consecutive adults. Sex differences, two image modalities differences, and correlations of the parameters were evaluated. Intra- and inter-observer reproducibility was evaluated using intraclass correlation coefficients (ICCs).

RESULTS

In the male group, all parameters except the neck-shaft angle of humerus, based on 3-D CT images, were greater than those in the female group (P < 0.05). All variables were significantly different between two image modalities (P < 0.05). In 3-D CT measurement, all parameters expect neck-shaft angle had correlation with each other (P < 0.001), particularly between two diameters of the humeral head (r = 0.907). All parameters in the 3-D CT measurement had excellent reproducibility (ICC range, 0.878 to 0.936) that was higher than those in the radiographs (ICC range, 0.741 to 0.858).

CONCLUSIONS

The present study suggested that 3-D CT was more reproducible than plain radiography in the assessment of morphology of the normal proximal humerus. Therefore, this reproducible modality could be utilized in the preoperative planning. Our data could serve as an effective guideline for humeral component selection and improve the design of shoulder prosthesis.

Assessment of the glenohumeral joint's active and passive axial rotational range

BACKGROUND

Assessment of the range of axial rotation of the glenohumeral joint will improve understanding of shoulder function, with applications in shoulder rehabilitation and sports medicine. However, there is currently no complete description of motion of the joint. The study aimed to develop a reliable protocol to quantify the internal and external axial rotations of the glenohumeral joint during active and passive motion at multiple humeral positions.

METHODS

Optical motion tracking was used to collect kinematic data from 20 healthy subjects. The humerus was positioned at 60°, 90°, and 120° of humerothoracic elevation in the coronal, scapular, and sagittal planes. Internal and external rotations were measured at each position for active and passive motion, where intrasubject standard deviations were used to assess variations in internal-external rotations.

RESULTS

The protocol showed intrasubject variability in the axial rotational range of <5° for active and passive rotations at all humeral positions. Maximum internal rotation was shown to be dependent on humeral position, where a reduced range was measured in the sagittal plane (P < .001) and at 120° elevations (P < .001). Conversely, maximum external rotations were not affected by humeral position.

CONCLUSION

The results describe normal ranges of internal-external rotation of the glenohumeral joint at multiple humeral positions. The protocol's low variability means that it could be used to test whether shoulder pathologic conditions lead to changes in axial rotational range at specific humeral positions.

Optimizing intramedullary entry location on the proximal humerus based on variations of neck-shaft angle

BACKGROUND

The purpose of this study was to define the relationship between the humeral neck-shaft angle (NSA) and variations in the ideal entry portal aligned with the long axis of the intramedullary canal of the proximal humerus.

METHODS

Three-dimensional images of 36 cadaveric humeri with various NSAs were reconstructed by a computerized surgical simulation program. The anteroposterior, mediolateral, and linear distances between a line from the center of the proximal medullary canal to the bicipital groove were measured. Differences among humeri with various NSAs were analyzed.

RESULTS

The intramedullary axis line was located a mean of 9 ± 2 mm posteriorly and 11 ± 3 mm medially from the bicipital groove. The axis line was 9 ± 2 mm posterior and 11 ± 2 mm medial with a standard NSA. The axis line in humeri with a varus NSA was 8 ± 2 mm posteriorly and 9 ± 2 mm medially, whereas the axis line was 10 ± 3 mm posteriorly and 14 ± 3 mm medially with a valgus NSA. The differences in the mediolateral distances between the groups were significant (P < .00009).

CONCLUSION

Care should be taken in choosing the entry portal position in humeri with various NSAs as the entry portal position differs according to the NSA. It is recommended that the location of the entry portal be moved toward the center of the humeral head to align with the centerline of the intramedullary canal in humeri with a valgus NSA in particular.

An evidence-based review of current perceptions with regard to the subacromial space in shoulder impingement syndromes: Is it important and what influences it?

BACKGROUND

Reduction of the subacromial space as a mechanism in the etiology of shoulder impingement syndromes is debated. Although a reduction in this space is associated with shoulder impingement syndromes, it is unclear if this observation is cause or consequence.

METHOD

The purposes of this descriptive review are to provide a broad perspective on the current perceptions with regard to the pathology and pathomechanics of subacromial and internal impingement syndromes, consider the role of the subacromial space in impingement syndromes, describe the intrinsic and extrinsic mechanisms considered to influence the subacromial space, and critique the level of evidence supporting these concepts.

FINDING

Based on the current evidence, the hypothesis that a reduction in subacromial space is an extrinsic cause of impingement syndromes is not conclusively established and the evidence permits no conclusion.

INTERPRETATION

If maintenance of the subacromial space is important in impingement syndromes regardless of whether it is a cause or consequence, research exploring the correlation between biomechanical factors and the subacromial space, using the later as the outcome measure, would be beneficial.

Primary partial humeral head resurfacing: outcomes with the HemiCAP implant

BACKGROUND

Humeral head defects such as degenerative disease or avascular necrosis are often treated with stemmed hemiarthroplasty or total shoulder arthroplasty. Despite its historical and clinical significance, stemmed humeral head replacement poses inherent technical challenges to placing spherical implants at the anatomically correct head height, version, and neck-shaft angle.

PURPOSE

The aim of this study was to assess humeral head inlay arthroplasty as a joint-preserving alternative that maintains the individual head-neck-shaft anatomy. Humeral head inlay arthroplasty also allows intraoperative surface mapping and placement of a contoured articular component that is matched to the patient's defect size, location, and individual surface geometry.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

This retrospective case series included 19 patients (20 shoulders), with an average age of 48.9 years (range, 32-58 years; 16 men, 3 women). Preoperative diagnoses were osteoarthritis in 16 shoulders and osteonecrosis in 4 shoulders. Pre- and postoperative evaluations included physical examination, radiographic assessment, the American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form, the Simple Shoulder Test, a pain visual analog scale, and patient satisfaction rating.

RESULTS

The mean follow-up period was 32.7 months (range, 17-66 months). The mean American Shoulder and Elbow Surgeons score improved from 24.1 to 78.8, mean Simple Shoulder Test score from 3.95 to 9.3, mean visual analog scale score from 8.2 to 2.1, mean forward flexion from 100° to 129°, and mean external rotation from 23° to 43° (P < .001 for all). Radiographic follow-up showed no evidence of periprosthetic fracture, component loosening, osteolysis, or device failure. Patient shoulder self-assessment was 90% poor before surgery and improved to 75% good to excellent at last follow-up; 20% of patients self-rated as somewhat good to somewhat poor, and 5% self-rated as poor. Ninety percent of patients were satisfied with the choice of the procedure. Three patients had postoperative complications unrelated to the implants, including a partial rotator cuff tear treated with physical therapy, preexisting glenoid wear treated with arthroscopic debridement and microfracture, and infection complicated by subscapularis rupture requiring several subsequent surgical procedures but with retention of the implant.

CONCLUSION

Humeral head inlay arthroplasty is effective in providing pain relief, functional improvement, and patient satisfaction. Rather than delaying shoulder arthroplasty to end-stage osteoarthritis, humeral head inlay arthroplasty is a promising new direction in primary shoulder arthroplasty for younger and active patients with earlier stage disease.

Measurement and Description of Three-Dimensional Shoulder Range of Motion With Degrees of Freedom Interactions

The shoulder is the most mobile joint of the human body due to bony constraint scarcity and soft tissue function unlocking several degrees of freedom (DOF). Clinical evaluation of the shoulder range of motion (RoM) is often limited to a few monoplanar measurements where each DOF varies independently. The main objective of this study was to provide a method and its experimental approach to assess shoulder 3D RoM with DOF interactions. Sixteen participants performed four series of active arm movements with maximal amplitude consisting in (1) elevations with fixed arm axial rotations (elevation series), (2) axial rotations at different elevations (rotation series), both in five planes of elevation, (3) free arm movements with the instruction to fill the largest volume in space while varying hand orientation (random series), and (4) a combination of elevation and rotation series (overall series). A motion analysis system combined with an upper limb kinematic model was used to estimate the 3D joint kinematics. Thoracohumeral Euler angles with correction were chosen to represent rotations. The angle-time-histories were treated altogether to analyze their 3D interaction. Then, all 3D angular poses were included into a nonconvex hull representing the RoM space accounting for DOF interactions. The effect of series of movements (n = 4) on RoM volumes was tested with a one-way repeated-measures ANOVA followed by Bonferroni posthoc analysis. A normalized 3D RoM space was defined by including 3D poses common to a maximal number of participants into a hull of average volume. A significant effect of the series of movements (p < 0.001) on the volumes of thoracohumeral RoM was found. The overall series measured the largest RoM with an average volume of 3.46 ± 0.89 million cubic degrees. The main difference between the series of movements was due to axial rotation. A normalized RoM hull with average volume was found by encompassing arm poses common to more than 50% of the participants. In general, the results confirmed and characterized the complex 3D interaction of shoulder RoM between the DOF. The combination of elevation and rotation series (overall series) is recommended to fully evaluate shoulder RoM. The normalized 3D RoM hull is expected to provide a reliable reference to evaluate shoulder function in clinical research and for defining physiologic continuous limits in 3D shoulder computer simulation models.

Scapulothoracic anatomy and snapping scapula syndrome

The scapulothoracic articulation is a sliding junction between the deep aspect of the scapula and thoracic rib cage at the levels of ribs 2 through 7. Motion at this articulation is dynamically stabilized by a variety of muscular attachments, allowing for controlled positioning of the glenoid to assist in glenohumeral joint function. A thorough understanding of the complex anatomic relationships, including the various muscles, and bursa, is critical to the evaluation of patients presenting with scapulothoracic disorders. The snapping scapula syndrome is caused by either osseous lesions or scapulothoracic bursitis and can be difficult to recognize and treat. The purpose of this review is to discuss the anatomy of the scapulothoracic articulation with an emphasis on the pathology associated with snapping scapula syndrome.

Humeral head arthroplasty and its ability to restore original humeral head geometry

BACKGROUND

Modern prosthetic components are designed to enable restoration of proximal humeral morphology, provided that a precise osteotomy of the humeral head at the level of the anatomic neck is performed. To determine whether a simulated osteotomy and replacement arthroplasty with an idealized implant were able to restore original head geometry.

MATERIALS AND METHODS

A handheld digitizer and surface laser scanner were used to digitize 24 humeri. Computer models were used to simulate an osteotomy, performed at the anterior cartilage-metaphyseal interface, and reconstruct the head with a spherical prosthetic head. The head diameter, radius of curvature, and inclination and retroversion angles were calculated for each specimen and compared with the original humeral head.

RESULTS

The simulated osteotomy resulted in a 4.8° decrease in inclination (P < .01) and 11.3° increase in retroversion (P < .001). The radius of curvature in the coronal plane was not significantly different (P = .284). However, in the axial plane, the prosthesis was significantly larger than the original head for both head diameter (P < .001) and radius of curvature (P < .05).

DISCUSSION

The study suggests that the humeral head is not a perfect segment of a sphere and an osteotomy along the anterior cartilage-metaphyseal interface does not remove only the proximal humeral articular surface. Even with a fully adaptable prosthetic implant, replacement arthroplasty is not able to restore original head geometry.

CONCLUSIONS

Alterations to head geometry with the osteotomy described may alter the line of force through the prosthetic joint, producing eccentric loading at the glenoid, and contribute to early failure.

Morphology of the normal and arthritic glenoid

The normal glenoid has a pear-shape aspect and is slightly retroverted. It has a variable orientation in the sagittal plane. The cartilage surface area corresponds to 28 % of the area of the humeral head with a radius of curvature greater than the humeral head. Mechanical properties are significantly higher at the center and posterior edge of the glenoid. With osteoarthritis, the glenoid becomes larger with a greater width and an increasing of the retroversion angle. The wear can be centric or excentric. Mechanical properties are significantly higher at the center and posterior edge of the glenoid.

SURFACE ARTHROPLASTY FOR TREATING PRIMARY AND/OR SECONDARY SHOULDER OSTEOARTHROSIS BY MEANS OF THE HEMICAP-ARTHROSURFACE(®) SYSTEM

Objective: To present the surgical technique for the He-miCAP-Arthrosurface^® system and evaluate our results from this technique for treating primary and/or secondary shoulder osteoarthrosis. Method: Between June 2007 and June 2009, 10 shoulders of 10 patients (nine with primary osteoarthrosis and one with avascular necrosis of the humeral head) underwent surface arthroplasty using the HemiCAP-Arthrosurface^® system to correct the problem. The follow-up time ranged from six to 29 months (mean of 17 months). The patients’ ages ranged from 62 to 73 years (mean of 67.5 years). Six patients were female and four patients were male. The patients were followed up weekly for the first month after the surgical procedure and every three months thereafter. The clinic evaluation was done using the criteria of the University of California at Los Angeles (UCLA) and a visual analogue pain scale. Results: All the patients said that they were satisfied with the results from the surgical treatment, with a mean UCLA score of 30 points and a mean analogue pain score of two points. Conclusion: The HemiCAP-Arthrosurface^® system for shoulder surgery for a specific group of patients is a technique that preserves the bone stock with good functional and antalgic results.

Comparison of shoulder range of motion, strength, and playing time in uninjured high school baseball pitchers who reside in warm- and cold-weather climates

BACKGROUND

There is an assumption that baseball athletes who reside in warm-weather climates experience larger magnitude adaptations in throwing shoulder motion and strength compared with their peers who reside in cold-weather climates.

HYPOTHESES

(1) The warm-weather climate (WWC) group would exhibit more pronounced shoulder motion and strength adaptations than the cold-weather climate (CWC) group, and (2) the WWC group would participate in pitching activities for a greater proportion of the year than the CWC group, with the time spent pitching predicting throwing shoulder motion and strength in both groups.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

One hundred uninjured high school pitchers (50 each WWC, CWC) were recruited. Rotational shoulder motion and isometric strength were measured and participants reported the number of months per year they pitched. To identify differences between groups, t tests were performed; linear regression was used to determine the influence of pitching volume on shoulder motion and strength.

RESULTS

The WWC group pitched more months per year than athletes from the CWC group, with the number of months spent pitching negatively related to internal rotation motion and external rotation strength. The WWC group exhibited greater shoulder range of motion in all planes compared with the CWC group, as well as significantly lower external rotation strength and external/internal rotation strength ratios. There was no difference in internal rotation strength between groups, nor a difference in the magnitude of side-to-side differences for strength or motion measures.

CONCLUSION

Athletes who reside in cold- and warm-weather climates exhibit differences in throwing shoulder motion and strength, related in part to the number of months spent participating in pitching activities. The amount of time spent participating in pitching activities and the magnitude of range of motion and strength adaptations in athletes who reside in warm-weather climates may make these athletes more susceptible to throwing-related injuries.

Glenoid spherical orientation and version

HYPOTHESIS

Glenoid orientation likely plays an important role in shoulder mechanics and has been associated with glenohumeral instability, rotator cuff tears, and total shoulder arthroplasty outcome. Glenoid version and inclination measurements are widely used, but these measurements are 2-dimensional, and orientation of the central face must be inferred from 2 points on the outer rim. This study tested the hypothesis that sphere fitting provides an optimal assessment of glenoid face 3-dimensional orientation, and clinically important differences will exist in some individuals between sphere fit orientation and traditional version measurement.

MATERIALS AND METHODS

Computed tomography scans of 20 normal glenoids were obtained. Glenoid version was measured from resliced, pure transverse images at a series of glenoid heights. Separately, the 3-dimensional surface of each glenoid face was reconstructed. A sphere was fit to the glenoid face, and its orientation was described by 2 angles analogous to version and inclination.

RESULTS

"Sphere fit version" averaged -3.2° ± 3.4° (negative indicating retroversion), and "sphere fit inclination" averaged 1.3° ± 4.7°. Absolute differences between sphere fit version and the standard mid-glenoid version averaged 1.5° (maximum 4.0°) across patients. The glenoids were, on average, 5.5° more retroverted at the 80% height than at the 20% height.

DISCUSSION

Three-dimensional aspects of the glenoid, including the spiraling twist evidenced by increased retroversion superiorly, are accounted for in this novel sphere-fitting approach for assessing glenoid orientation.

CONCLUSIONS

For most normal glenoids, midglenoid version appears to provide an adequate measure of glenoid central face orientation. Sphere fitting has potential utility in optimizing glenoid implant alignment in total shoulder arthroplasty.

Anatomy and mechanics of the shoulder: review of current concepts

This narrative review is intended to provide hand and upper extremity therapists, who occasionally treat patients with shoulder diagnoses, with several current concepts related to normal shoulder anatomy and function. It is hoped that this review will be useful for 1) appreciating patho-anatomy and pathophysiology, 2) planning treatment approaches, and 3) stimulating research aimed at improved understanding of the shoulder.

Shoulder resurfacing

Resurfacing is a type of shoulder arthroplasty that involves replacing the humeral joint surface with a metal covering, or cap, thus preserving the bone of the proximal part of the humerus. If the glenoid is also replaced, a current conventional polyethylene glenoid replacement prosthesis or an interposed soft-tissue graft is used. The potential advantages of humeral resurfacing, as compared with conventional shoulder arthroplasty, are: (1) no osteotomy is performed (and thus the head-shaft angle does not have to be addressed); (2) minimal bone resection; (3) a short operative time; (4) a low prevalence of humeral periprosthetic fractures; and (5) ease of revision to a conventional total shoulder replacement, if needed. Outcomes of surface replacement arthroplasty have been comparable with those of arthroplasties with a stemmed prosthesis in numerous short and mid-term follow-up studies. Future studies are required to assess the long-term outcomes of humeral resurfacing and to evaluate alternative surface bearing materials, especially on the glenoid side. Resurfacing appears to be a viable option for shoulder replacement, especially in young patients.

Shoulder injuries in the overhead athlete

The overhead throwing motion is an extremely skillful and intricate movement. When pitching, the overhead throwing athlete places extraordinary demands on the shoulder complex subsequent to the tremendous forces that are generated. The thrower's shoulder must be lax enough to allow excessive external rotation but stable enough to prevent symptomatic humeral head subluxations, thus requiring a delicate balance between mobility and functional stability. We refer to this as the "thrower's paradox." This balance is frequently compromised and believed to lead to various types of injuries to the surrounding tissues. Frequently, injuries can be successfully treated with a well-structured and carefully implemented nonoperative rehabilitation program. The key to successful nonoperative treatment is a thorough clinical examination and accurate diagnosis. Rehabilitation follows a structured, multiphase approach, with emphasis on controlling inflammation, restoring muscles' balance, improving soft tissue flexibility, enhancing proprioception and neuromuscular control, and efficiently returning the athlete to competitive throwing. Athletes often exhibit numerous adaptive changes that develop from the repetitive microtraumatic stresses occurring during overhead throwing. Treatment should include the restoration of these adaptations.

LEVEL OF EVIDENCE

Level 5.

The area of glenoid asymmetry identified as important contributor to shoulder strength during pushing and pulling in the coronal plane

The geometrical dimensions of the bones that make up the glenohumeral joint could be a key factor in strength predictability. Understanding the mechanical influence of these dimensions (individually or in combination) on shoulder strength could help explain the mechanism of musculoskeletal disorders. The following study shows how a recently discovered geometric parameter, the area of glenoid asymmetry (AGA), is a good indicator of shoulder strength. A comprehensive study was conducted to test whether glenohumeral geometry, as measured through MRI scans, is correlated with upper arm strength. The isometric shoulder strength of 12 subjects during one-handed arm abduction and adduction in the coronal plane, in a range from 5 to 30 degrees , was correlated with the geometries of their glenoid fossae. All subjects were stronger during adduction than abduction for all arm positions. The results revealed a high correlation in the coronal plane between the AGA and mean maximum force and mean maximum moment when an arm was abducted and adducted in a range from 5 degrees to 30 degrees (0.80, p </or= 0.01 and 0.69, p <or= 0.05, respectively during abduction and 0.61, p <or= 0.04 and 0.61, p <or= 0.04, respectively during adduction). This investigation revealed the repercussion of individual glenoid geometry on the maximum acceptable load applied to the hand during arm abduction and adduction in a coronal plane.

The influence of implant articular thickness and glenohumeral conformity on stability of an all-metal glenoid component

The objective of this study was to determine the effect of implant thickness and glenohumeral conformity on fixation of an all-metal glenoid component. A stainless steel glenoid component was designed and implanted in 10 cadaveric scapulae. A testing apparatus capable of producing a loading vector at various angles, magnitudes, and directions was used. The independent variables included 6 directions and 3 angles of joint load, 3 implant thicknesses, and 4 glenohumeral conformities. Implant micromotion relative to bone was measured by use of 4 displacement transducers at the superior, inferior, anterior, and posterior sites. The components displayed a consistent response to loading of ipsilateral compression and contralateral distraction. Stability decreased as the load application angle increased (P < .05). A decrease in the implant thickness and glenohumeral conformity resulted in increased implant stability (P < .05). Decreasing implant thickness and glenohumeral conformity reduce the eccentric component of loading and may improve the durability of glenoid implants.

The influence of medial reattachment of the torn cuff tendon for retracted rotator cuff tears

We reattached the torn rotator cuff medial to the anatomic cuff insertion site if it was retracted. The purpose was to correlate the amount of medial reattachment of the cuff with shoulder function. We evaluated 63 shoulders in which repaired cuffs were followed with magnetic resonance imaging at a mean follow-up of 8 years. The amount of medial reattachment of the cuff tendon was determined by use of a T2-weighted oblique coronal view, which passed through the center of the humeral head, and was defined as the NCA angle (where N indicates the new cuff insertion point, C indicates the center of the humeral head, and A indicates the anatomic cuff insertion point). Theoretically, the more medially the cuff tendon was reattached, the greater the NCA angle. Neither the Japanese Orthopaedic Association shoulder score nor isometric strength of forward elevation was correlated with the NCA angle. The NCA angle was significantly correlated (P = .001) with the active forward elevation angle, which dramatically decreased at 30 degrees of the NCA angle, approximately 13 mm from the original cuff insertion point, assuming a humeral head radius of 25 mm.

An anthropometric study of the bilateral anatomy of the humerus

The purpose of this study was to describe the extramedullary humeral morphology in paired humeri to determine whether geometric differences exist from side to side in the same individual. The anatomic characteristics of 28 paired, dry cadaveric humeri were measured by use of an electromagnetic tracking system. Of the characteristics examined, only the humeral head height was significantly different between right and left humeri in the same individual (P < .005). Most of the characteristics had excellent intra-specimen repeatability. In conclusion, there are few significant differences between contralateral humeral anatomic characteristics. Therefore, the uninjured contralateral humerus can provide a reasonable approximation to the native geometry of the fractured humerus and should be a reliable model for measuring parameters related to implant geometry and optimal positioning during hemiarthroplasty for the treatment of proximal humeral fractures.

Management of elbow osteoarthritis

Primary osteoarthritis of the elbow is characterized by painful stiffness, mechanical symptoms, and the presence of hypertrophic osteophytes. Preservation of the joint space is common and may account for the good results that are usually achieved with nonoperative treatment and nonprosthetic arthroplasty. Elbow osteoarthritis typically affects middle-aged men who engage in strenuous manual activity. Open or arthroscopic capsular release and removal of impinging osteophytes are the primary surgical treatment options. The relative sparing of joint cartilage makes elbow osteoarthritis unique in this regard and amenable to this treatment. Arthroplasty is rarely indicated for primary osteoarthritis of the elbow and should be reserved for elderly individuals with low demands for whom other treatment options have failed.

Arm abduction strength and its relationship to shoulder geometry

This study was conducted to test whether glenohumeral geometry, as measured through MRI scans, is correlated with upper arm strength. The isometric shoulder strength of 12 subjects during one-handed arm abduction in the coronal plane, in a range from 5 degrees to 30 degrees , was correlated with the geometries of their glenoid fossas. Seven parameters describing the glenohumeral joint geometry in the coronal plane were identified as having expected influence on shoulder strength. In addition to these, a new geometric parameter, named the area of glenoid asymmetry (AGA), was considered to reflect the concavity-compression mechanism as well as the inclination of the glenoid surface. As a result of the high correlation between the AGA and mean force and mean moment (0.80, p0.01 and 0.69, p <or= 0.05, respectively) at the glenohumeral joint in a coronal plane, the AGA was distinguished as a factor having influence on shoulder strength when an arm was abducted in a range from 5 degrees to 30 degrees .

Proximal humeral anatomy in shoulder arthroplasty: Implications for prosthetic design and surgical technique

Resurfacing arthroplasty of the glenohumeral joint has been established for several decades as a means to restore comfort and function of the shoulder for many afflictions that derange the normal anatomy. Rigorous study of shoulder anatomy in terms relevant to prosthetic geometry, however, did not begin until the 1990s. It has become apparent that normal anatomy is highly variable from individual to individual and that it is aligned somewhat differently than the early modular prosthetic devices. Multiple studies have shown that retroversion is markedly variable, not only between individuals but also between the left and right sides of the same individual, ranging from 0 degrees to 55 degrees . The inclination of the proximal humeral articular surface relative to the shaft (head shaft angle) is also variable, ranging from 30 degrees to 55 degrees. The center of rotation is variably offset in 3 dimensions. The radius of curvature ranges from 20 to 30 mm and is smaller in women than in men. The thickness of the articular surface, head height, is equally variable but shows a striking proportionality to the radius of curvature. The last decade has seen a proliferation of humeral implants aiming to serve a better understanding of shoulder anatomy and function. A modern understanding of shoulder anatomy and contemporary design features is paramount for surgeons performing shoulder arthroplasty. Head size selection is dependent on multiple factors, the most important of these, other than the patient's original head size, are the osteotomy performed by the surgeon and the inclination angle(s) of the prosthetic system. Systems with variable inclination angles instruct the surgeon to resect the humeral head along the anatomic neck as best possible and then provide either adjustable or variable prosthetic geometries to match the resultant inclination angle. Other prosthetic systems have a fixed inclination angle somewhere within the normal range and instruct the surgeon to make an osteotomy at this inclination, adjusting the fit with additional preparation of the canal and revising the osteotomy as necessary. Over the last decade, most systems have offered heads that are offset by 3 to 4 mm, allowing the surgeon to dial in the most suitable position for the head on the stem. Component design and surgical technique are inextricably intertwined. Most surgeons with experience using modern systems feel a greater sense of predictability in achieving their surgical goals when using these systems as compared with earlier ones. How these developments impact implant longevity will only be known with time and further follow-up.

Total shoulder arthroplasty: glenoid component design

Although Charles Neer's original glenoid component underwent several modifications, the all-polyethylene, keeled component with a radius of curvature that conformed to the humeral radius of curvature and that was implanted with cement became the glenoid implant of choice. Neer reported approximately a 30% incidence of radiolucent lines; however, only 2 of 615 glenoids were revised for loosening. Other surgeons have reported radiolucent lines in up to 90% of glenoid components and have correlated symptoms with increasing radiolucencies. This has led to the development of alternative glenoid components for unconstrained total shoulder arthroplasty. Variations in component design include component shape, articular conformity, method of fixation, and material composition. The purposes of this presentation are to review the performance of the original Neer design, as well as other more recent glenoid designs, to identify factors that may influence the performance of glenoid components, and to provide a rationale for future changes in glenoid component design.

Cementless surface replacement arthroplasty (Copeland CSRA) for osteoarthritis of the shoulder

Clinical experience with the Copeland cementless surface replacement arthroplasty (CSRA) of the shoulder now spans 17 years. Between 1986 and 1997, 79 CSRAs (42 total shoulder replacements and 37 hemiarthroplasties) were performed for primary osteoarthritis of the shoulder. Total shoulder replacement was done in 12 men and 30 women with a mean age of 71.5 years (range, 50-87 years). Hemiarthroplasty was used in 9 men and 28 women; 5 patients had bilateral hemiarthroplasty. The mean age was 73.4 years (range, 53-88 years). Thirty-nine total shoulder arthroplasties and thirty hemiarthroplasties with a follow-up of more than 2 years were available for review. The mean follow-up was 7.6 years (range, 48 months to 13 years) for total shoulder replacement and 4.4 years (range, 24 months to 6.5 years) for hemiarthroplasty. The Constant scores improved from an age-adjusted Constant score of 33.8% (20.0 points) to 94% (61.9 points) for total shoulder replacement and from an age-adjusted Constant score 40.0% (25.3 points) to 91% (58.1 points) for hemiarthroplasty. Active elevation improved by a mean of 59.9 degrees to a mean of 128 degrees for total shoulder replacement and to a mean of 124 degrees for hemiarthroplasty. Of the patients, 89.9% considered the shoulder to be much better or better as a result of the operation. Radiographically, one humeral implant and three glenoid implants had evidence of loosening. Four revisions were performed in the total shoulder replacement group. No revision surgery was needed in the hemiarthroplasty group. The results of this series are at least comparable to those reported for stemmed prostheses with a comparable length of follow-up. The results of total shoulder replacement and hemiarthroplasty in osteoarthritis of the shoulder seem to be comparable. With use of the CSRA prosthesis, several severe complications mainly concerning the humeral shaft and periprosthetic fractures can be avoided. Should the need for revision surgery or arthrodesis arise, these procedures are easily performed, as bone stock has been maintained and no loss of length has been encountered. It does seem that the humeral component does not need a stem or cement for fixation.

Internal impingement of the shoulder in flexion

Contact of the rotator cuff to the superior glenoid with the arm in flexion has been described and postulated to be a source of rotator cuff disease. The goals of the current study were to document the existence of internal impingement in flexion arthroscopically and to determine its prevalence in patients with various diseases. Also, we attempted to determine the clinical significance of internal impingement in flexion by investigating the associations between internal impingement in flexion and the preoperative and intraoperative findings. A consecutive case series of 376 patients having arthroscopy of the shoulder were entered prospectively into this study. During arthroscopy, intraarticular lesions were evaluated and the presence of contact of the rotator cuff to the superior glenoid and the degree of flexion making the contact were noted. Statistical analysis was done with two dependent variables defined: the presence of internal impingement in flexion and the flexion degree making internal impingement in flexion. Of the 376 patients, 277 (74%) had internal impingement in flexion and 99 (26%) did not have internal impingement in flexion. There were no statistically significant differences in the prevalence of internal impingement in flexion according to the primary diagnoses. Statistical analysis revealed that the presence of internal impingement in flexion was associated with Type II superior labrum anterior posterior (SLAP) lesions and the presence of internal impingement of the rotator cuff to the superior glenoid in abduction and external rotation. There was a significant relationship between rotator cuff disease and decreasing angle of contact for internal impingement in flexion. This study showed that internal impingement in flexion is common in a cohort of patients having shoulder surgery, with an overall prevalence of 74%, and that internal impingement in flexion may contribute to the development of Type II SLAP lesions and rotator cuff disease.

The radiographic study in the relationship of the glenohumeral joint

Accurate reproduction of anatomic relationship is important in non-constrained prosthetic arthroplasty. The accurate lateral glenohumeral offset, which indicates a parameter of the lever arm of the deltoid and supraspinatus muscles, is one of the most important elements in achieving the efficient shoulder functions after prosthetic reconstruction. However, to our knowledge, there has been no detailed study on the influence of minute changes in the neck shaft angle, within the normal range, on lateral glenohumeral offset. In this study, we evaluated the relationship between the neck shaft angle and various geometric measurement values in the glenohumeral joint. Radiographs of 471 shoulders without osseous lesions in the glenohumeral joint and greater tuberosity were reviewed. There were 265 males and 206 females, and a mean age was 53.5 years old. The final diagnosis was impingement syndrome in 269 patients, rotator cuff tear in 147, and control group in 55 patients. Eight parameters were measured on true anteroposterior radiographs. The lateral glenohumeral offset correlated with the radius of the curvature of the humeral head and the humeral head diameter. The neck shaft angle was not correlated with the offset value. However, when the offset value was divided by the humeral head diameter, to eliminate the affection of the size of the humeral head toward the offset, a correlation was observed with the neck shaft angle. Based on these correlations, we could obtain the equation of the lateral glenohumeral offset according to the neck shaft angle. Using the equation, when the neck shaft angle is decided, the lateral glenohumeral offset can be estimated based on the correlation between the parameters, which achieve the efficient shoulder functions after prosthetic components. Therefore, inaccurate determination of the neck shaft angle in the humeral head component design and selection may induce dysfunction of the abductor muscles.

Does keel size, the use of screws, and the use of bone cement affect fixation of a metal glenoid implant?

The objective of this study was to determine the effect of screws and keel size on the fixation of an all-metal glenoid component. A prototype stainless-steel glenoid component was designed and implanted in 10 cadaveric scapulae. A testing apparatus capable of producing a loading vector at various angles, magnitudes, and directions was used. The independent variables included six directions and three angles of joint load, and five fixation modalities-three different-sized cross-keels (small, medium, and large), screws, and bone cement. Implant micromotion relative to bone was measured by four displacement transducers at the superior, inferior, anterior, and posterior sites. The components displayed a consistent response to loading of ipsilateral compression and contralateral distraction. Use of progressively larger keels did not significantly improve implant stability. Stability decreased as the angle of load application increased (P <.05). Screw and cement fixation resulted in the most stable fixation (P <.05).

External rotation in the glenohumeral joint during elevation of the arm

OBJECTIVE

To describe patterns of external rotation during humeral elevation, and to compare motion patterns.Design. Patterns of external rotation during forward flexion, scapular abduction and abduction in the frontal plane are described with P-spline curves with an approximately 95% confidence interval.

BACKGROUND

External rotation of the humerus is an essential part of humeral elevation. Standard clinical assessment of external rotation provides insufficient information to describe external rotation patterns which may be essential for insight in shoulder disorders.Methods. The dominant and non-dominant arms of thirty subjects are measured, using a three-dimensional electromagnetic movement recording system.

RESULTS

Overall group patterns demonstrate that humeral elevation in all planes is accompanied by about 55 degrees of external rotation, and each elevation plane has its own typical pattern. The dominant and non-dominant sides are comparable and can be combined.

CONCLUSIONS

There are specific external rotation patterns for each elevation plane. Curves representing the approximately 95% confidence intervals make comparison between groups possible. This method can therefore possibly be used to study the external rotation patterns in groups with certain shoulder disorders to evaluate the results of before and after treatment.

RELEVANCE

The method presented in this paper can be used to study external rotation patterns in healthy shoulders and in shoulders with a specific disorders to gain more insight, to define functional treatment, and to evaluate the results of treatment.