Hemi shoulder arthroplasty is a rather successful procedure although revision surgery due to secondary glenoid erosion is reported in more than 25%. The downside of common shoulder arthroplasty is that in a deltopectoral approach the subscapularis tendon needs to be detached for exposure of the humeral head. Refixation of subscapularis tendon is associated with a retear rate of 4%, furthermore with progressing fatty muscle infiltration and loss of function. In case of revision surgery a second subscapularis tendon detachment is even more associated with worse function. Thus, arthroscopic humeral head resurfacing is an expedient alternative for minimal invasive humeral head arthroplasty without compromising subscapularis function. The purpose of this study was to report first clinical and subjective results after arthroscopic-assisted resurfacing of the humeral head. For this prospective case series, 24 patients (7 females, 17 males; mean age 59 years, range 42–73 years) undergoing arthroscopic-assisted partial shoulder resurfacing with the partial eclipse prosthesis were included in the study. Clinical conditions and subjective assessments were evaluated before surgery and annually thereafter using the Constant score (CS), active range of motion (ROM), visual analog scale (VAS) for pain, and the American Shoulder and Elbow Surgeons scale (ASES). Radiological outcomes and major complications were monitored. The mean CS for all patients improved significantly from 51 points preoperatively to 83 points 12 months after surgery (p=0.005). Trends towards increasing ROMs were detected. Subjective scores significantly improved from baseline to the 1-year follow-up (VAS: from 6.4 to 2.5, p=0.010; ASES: from 47 to 76, p=0.026). The majority of patients (88%) stated that they would undergo the procedure again. Revisions were indicated in 17% due to progression of osteoarthritis. Arthroscopic-assisted partial humeral head resurfacing as a minimal invasive procedure with the advantages of bone stock preservation and intact subscapularis tendon allowed immediate postoperative active mobilization and provided significant improvements in subjective outcome. In case of revision surgery a primary situation was encountered with postoperative results comparable to primary arthroplasty

Introduction. Shoulder arthroplasty is used to treat several common pathologies of the shoulder, including osteoarthritis, post-traumatic arthritis, and avascular necrosis. In replacement of the humeral head, modular components allow for anatomical variations, including retroversion angle and head-neck angle. Surgical options include an anatomic cut or a guide-assisted cut at a fixed retroversion and head-neck angle, which can vary the dimensions of the cut humeral head (height, anteroposterior (AP), and superoinferior (SI) diameters) and lead to negative long term clinical results. This study measures the effect of guide-assisted osteotomies on humeral head dimensions compared to anatomic dimensions. Methods. Computed tomography (CT) scans from 20 cadaveric shoulder specimens (10 male, 10 female; 10 left) were converted to three-dimensional models using medical imaging software. An anatomic humeral head cut plane was placed at the anatomic head – neck junction of all shoulders by a fellowship trained shoulder surgeon. Cut planes were generated for each of the standard implant head-neck angles (125°, 130°, 135°, and 140°) and retroversion angles (20°, 30°, and 40°) in commercial cutting guides. Each cut plane was positioned to favour the anterior humeral head-neck junction while preserving the posterior cuff insertion. The humeral head height and diameter were measured in both the AP plane and the SI plane for the anatomic and guide-assisted osteotomy planes. Differences were compared using separate two-way repeated measures ANOVA for each dependent variable and deviations were shown using box plot and whisker diagrams. Results. Guide-assisted cuts tend to be smaller than the anatomic humeral head dimensions. Retroversion angle showed a significant effect on head height, AP, and SI diameters (p=0.002). The effect of head-neck angle was only significant for SI diameter (p<0.001). The largest dimensional deviation was observed at 20 degrees of retroversion and resulted in a 2.5mm decrease in humeral head height, averaged over the range of head-neck values. Conclusion. Where patient's natural anatomy falls outside the range of commercial cutting guides, resection according to the template may result in a deviation from the natural dimensions of the humeral head, which impacts the sizing of the implant head component. This has implications for both manufacturers to create a template that has a larger range of retroversion angles, as well as surgeons' choices in intra-operative planning

Reverse shoulder arthroplasty (RSA) has an increasing effective use in the treatment of patients with a variety of diagnoses, including rotator cuff deficiency, inflammatory arthritis, or failed shoulder prostheses. Glenoid bone loss is not uncommonly encountered in these cases due to the significant wear. Severe bone loss can compromise glenoid baseplate positioning and fixation, consequently increasing the risk for early component loosening, instability, and scapular notching. To manage severe glenoid bone deficiencies, bone grafts are commonly used. Although, many studies report outcome of bone grafting in revision RSA, the literature on humeral head autograft for glenoid bone loss in primary RSA is less robust. The purpose of this study is to evaluate the clinical and radiographic outcomes of primary RSA with humeral head autograft for glenoid bone loss at our institution. Institutional review board approval was obtained to retrospectively review the records of 22 consecutive primary RTSA surgeries in 21 patients with humeral head autograft for glenoid bone loss between January 2008 and December 2016. Five patients died during follow-up, three were unable to be contacted and one refused to participate, leaving a final study cohort of 12 patients with 13 shoulders that underwent RSA. All patients had a clinical evaluation including detailed ROM and clinical evaluation using the American Shoulder and Elbow Surgeons (ASES) Score, Constant Score, Western Ontario Osteoarthritis of the Shoulder Index (WOOS), and Short Form-12 (SF-12) questionnaires. Preoperative and postoperative plain radiographs and CT scans were assessed for component position, loosening, scapular notching, as well as graft incorporation, resorption, or collapse. There were 6 males and 6 females, with an average age of 74 ± 6.8 years. The average BMI was 31.7 ± 5.3, and the median ASA score was 3. Average follow-up was 3.4 ± 1.1 years. The average postoperative range of motion measurements for the operative arm are: flexion = 120 ± 37, abduction = 106 ± 23, external rotation = 14 ± 12, internal rotation at 90 degrees of abduction = 49 ± 7, external rotation at 90 degrees of abduction = 50 ± 28. Average functional scores are: ASES: 76.9 ± 19.2, WOOS: 456 ± 347, SF12 physical: 34.2 ± 8.2, SF12 mental: 54.1 ± 10.2, Constant Score: 64.6 ± 14. No evidence of hardware loosening or evidence of bone graft resorption were encountered. On CT, the average of pre operative B-angle was 79.3 ± 9.3 while the pre operative reverse shoulder angle was 101.4 ± 28. Glenoid retroversion average on CT was 13.3 ± 16.6. Post operative baseplate inclination average was 82 ± 7.4 while the baseplate version 7.8 ±10. The operative technique was able to achieve up to 30 degrees of inclination correction and up to 50 degrees of version correction. In conclusion, primary reverse shoulder arthroplasty with humeral head autograft for glenoid bone loss provides excellent ROM and functional outcomes at mid-term follow-up. This technique has a high rate of bone incorporation and small risk of bone resorption at mid term follow up

A secure taper connection in shoulder arthroplasty is mandatory to avoid loosening and fretting. This study's objective was to determine the amount of in situ force used by surgeons to seat a humeral head and to determine the disengagement force of the taper connection. The influence of 1) material type, 2) head size, and 3) surgeon on the impaction force and the fixation (pulloff force) of the sample was examined. Methods. Impaction data was collected from experienced shoulder surgeons (n=5) during a cadaver lab. Testing groups (n=5 each) were: 1) small ceramic, 2) big ceramic, 3)small metal and 4) large metal. Twenty centric, anatomic humeral heads (DJO surgical, Vista, CA, TURONTM, material: CoCrMo or BIOLOX®delta, size: 38×14mm or 54×22mm) were paired with a corresponding humeral neck (TURON™, DJO surgical, type: neutral modular, material: CoCrMo). Each taper was always used with the same humeral head throughout testing. The impaction force sequence was recorded using an instrumented impactor (Piezo sensor, model 208 C05, PCB PIEZOTRONICSINC, Depew, NY, ±1%). The surgeons impacted all samples into the cadaver using their typical pattern of hammer strikes (Figure 1). The engaged humeral head and taper were removed by hand and then disengaged using an instrumented (U93, HBM, Darmstadt, Germany, load limit: 5kN) hand-held pulloff-device. Statistics and data analysis were performed in MATLAB (2014b, Mathworks, Natick, MA, α=0.05). Two-tailed, pearson's linear correlation coefficients are reported. Group differences were determined using Kruskal Wallis test. Pair-wise comparisons were performed using a Tukey correction. Results. Extremely high and variable impaction forces were measured (Table 1, Figure 2). The maximum force was nearly 27 kN; however, that value reduced to ∼18kN when the data from an outlier surgeon was removed. Maximum impaction forces were 12.45±4.36 kN, and the average was 10.47±3.63 kN. The pulloff force ranged from 0.94 kN to 5.54 kN with an average of 2.76±1.19 kN. Higher impaction forces required higher pulloff forces to disengage the taper connection (p<0.001, R>−0.608). Ceramic humeral heads showed a 24% higher fixation strength (p=0.004) under similar engagement conditions (p=0.18) in comparison to metal components. Head size does not appear to influence either the magnitude of the impaction force surgeons use (p>0.20) nor the force needed to disengage the taper (p=0.25). The surgeon performing the insertion had a significant influence on the impaction strike timing (p<0.001), number of strikes (p<0.001), and the impaction forces (p<0.03) and the pulloff force (p<0.001). Conclusions. Impaction forces were markedly larger than those recorded for taper engagement in hip arthroplasty. The ceramic humeral component showed greater fixation strength in comparison to the metal for similar impaction forces. Pulloff forces were approximately 25% of the impaction force. Potentially, this low taper efficiency resulted from the cadaver absorbing much of the energy rather than the taper connection. The influence of the patient and the clinical situation on the taper efficiency is unknown. Variations between surgeons greatly influenced the impaction and the fixation force. Therefore, individual surgeon practices may substantially influence clinical fixation strength of tapered shoulder implants

Background. Humeral version is the twist angle of the humeral head relative to the distal humerus. Pre-operatively, it is most commonly measured referencing the transepicondylar axis, although various techniques are described in literature (Matsumura et al. 2014, Edelson 1999, Boileau et al., 2008). Accurate estimation of the version angle is important for humeral head osteotomy in preparation for shoulder arthroplasty, as deviations from native version can result in prosthesis malalignment. Most humeral head osteotomy guides instruct the surgeon to reference the ulnar axis with the elbow flexed at 90°. Average version values have been reported at 17.6° relative to the transepicondylar axis and 28.8° relative to the ulnar axis (Hernigou, Duparc, and Hernigou 2014), although it is highly variable and has been reported to range from 10° to 55° (Pearl and Volk 1999). These studies used 2D CT images; however, 2D has been shown to be unreliable for many glenohumeral measurements (Terrier 2015, Jacxsens 2015, Budge 2011). Three-dimensional (3D) modeling is now widely available and may improve the accuracy of version measurements. This study evaluated the effects of sex and measurement system on 3D version measurements made using the transepicondylar and ulnar axis methods, and additionally a flexion-extension axis commonly used in biomechanics. Methods. Computed tomography (CT) scans of 51 cadaveric shoulders (26 male, 25 female; 32 left) were converted to 3D models using medical imaging software. The ulna was reduced to 90° flexion to replicate the arm position during intra-operative version measurement. Geometry was extracted to determine landmarks and co-ordinate systems for the humeral long axis, epicondylar axis, flexion-extension axis (centered through the capitellum and trochlear groove), and ulnar long axis. An anatomic humeral head cut plane was placed at the head-neck junction of all shoulders by a fellowship trained shoulder surgeon. Retroversion was measured with custom Matlab code that analysed the humeral head cut plane relative to a reference system based on the long axis of the humerus and each elbow axis. Effects of measurement systems were analyzed using separate 1-way RM ANOVAs for males and females. Sex differences were analyzed using unpaired t-tests for each measurement system. Results. Changing the measurement reference significantly affected version (p<0.001). The ulnar axis method consistently resulted in higher measured version than either flexion-extension axis (males 9±1°, females 14±1°, p<0.001) or epicondylar axis (males 8±1°, females 12±1°, p<0.001). See Figure 1. Version in males (38±11°) was 7° greater than females (31±12°) when referencing the flexion-extension axis (p=0.048). Conclusion. Different measurement systems produce different values of version. This is important for humeral osteotomies; if version is assessed using the epicondyles pre-operatively and subsequently by the ulna intra-operatively, then the osteotomy will be approximately 10° over-retroverted. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction. Total shoulder arthroplasty (TSA) is an effective treatment to restore shoulder function and alleviate pain in the case of glenohumeral arthritis [1]. Stress shielding, which occurs when bone stress is reduced due to the replacement of bone with a stiffer metallic implant, causes bone resorption of up to 9% of the humeral cortical thickness following TSA [2]. Shorter length stems and smaller overall geometries may reduce stress shielding [3], however the effect of humeral head backside contact with the resection plane has not yet been fully investigated on bone stress. Therefore, the purpose of this study was to quantify the effect of humeral head contact conditions on bone stresses following TSA. Methods. 3D models of eight male left cadaveric humeri (68±6 years) were generated from CT data using MIMICS. These were then virtually prepared for reconstruction by an orthopaedic surgeon to accept a short-stem humeral implant (Exactech Equinoxe® Preserve) that was optimally sized and placed centrally in the humeral canal. The humeral head was positioned in the inferior-medial position such that contact was achieved on the medial cortex, and no contact existed on the lateral cortex. Three different humeral head backside contact conditions were investigated (Figure 1); full backside contact (FULL), contact with only the inferior-medial half of the resection (INF), and contact with only the superior-lateral half of the resection (SUP). Cortical bone was assigned an elastic modulus of 20 GPa and a Poisson's ratio of 0.3. Trabecular bone was assigned varying stiffness based on CT attenuation [4]. A joint reaction force was then applied representing 45˚ and 75˚ of abduction [5]. Changes in bone stress, as well as the expected bone response based on change in strain energy density [6] was then compared between the intact and reconstructed states. Results. For cortical bone, the full backside contact altered bone stress by 28.9±5.5% compared to intact, which was significantly less than the superior (37.0±3.9%, P=0.022) and inferior (53.4±3.9%, P<0.001) backside contact conditions. Similar trends were observed for changes in trabecular bone stress relative to the intact state, where the full backside contact altered bone stress by 86.3±27.9% compared to intact, compared to the superior and inferior contact conditions, which altered bone stress by 115.2±45.0% (P=0.309) and 197.4±80.2% (P=0.024), respectively. In terms of expected bone response, both the superior and inferior contact resulted in an increase in bone volume with resorbing potential compared to the full contact (Figure 2). Discussion and Conclusions. The results of this study show that full humeral head backside contact with the humeral resection plane is preferable for short stem humeral TSA implants with the head in the inferior-medial position. As expected, the superior contact typically increased resorption potential in the medial quadrant due to the lack of load transfer, however interestingly the inferior contact increased resorption potential in both the lateral and medial quadrants. Analysis of implant micromotion showed that medial liftoff of the implant occurred, which resulted in a lack of load transfer in the most medial aspect of the resection plane. For any figures or tables, please contact the authors directly

Background. Partial humeral head resurfacing using a stemless implant is a bone-conserving option in treatment of focal chondral defects. We report our experience using the Arthrosurface HemiCAP® device. Methods. This is a retrospective study of patients with focal chondral defects of the humeral head, treated with partial resurfacing arthroplasty, with a minimum follow-up of 2 years. Mean patient age was 45.4 years (range 27–76). Patients were analyzed in 2 groups: those who underwent HemiCAP for an isolated humeral head defect, and those who had HemiCAP combined with biologic resurfacing of concomitant glenoid disease. Results. 39 patients met inclusion criteria, 5 of whom had concomitant biologic glenoid resurfacing. 24 of 34 shoulders (70.6%) with HemiCAP alone demonstrated functional improvement and decreased pain. Mean forward flexion showed some improvement from 131 degrees pre-operatively to 158 degrees post-operatively (p=0.004). Mean Subjective Shoulder Value improved from 35.0% to 83.6% (p< 0.001). ASES score improved from 29.8 to 77.7(p< 0.001). However, follow-up radiographs showed progression of glenoid disease in 20.6%(7 shoulders). 5 shoulders(14.7%) failed and were revised: 3 to total shoulder arthroplasty, 1 to hemiarthroplasty, and 1 patient underwent glenohumeral fusion. 5 (14.7%) had some pain at latest follow-up but were pursuing a course of conservative management. In the group with associated biologic glenoid resurfacing, all 5 patients had ongoing pain and progression of glenohumeral arthritis requiring revision or glenohumeral fusion. Conclusion. While 70% of patients with an isolated humeral head chondral defect had significant improvement in pain and function after HemiCAP, the outcomes were not superior to those published for complete humeral head resurfacing, or for stemmed prostheses. HemiCAP was not successful for patients with concomitant glenoid disease. Results for these patients were inferior to those published for total shoulder arthroplasty, and ultimately all were revised to a stemmed prosthesis or fused

In shoulder arthroplasty, humeral resurfacing or short stem devices rely on the proximal humeral bone for fixation and load transfer. For resurfacing designs, the fixation takes place above the anatomical neck, whilst for short stem designs the resection is made at the anatomical neck and fixation is achieved in the bone distal to that resection. The aim of the study is to investigate the bone density in these proximal areas to provide information for implant design and guidance on appropriate positions to place implant fixation entities. CT scans of healthy humeri were used to map bone density distribution in the humeral head. CT scans were manually segmented and a solid model of the proximal humerus was discretised into 1mm tetrahedral elements. Each element centroid was then assigned an apparent bone density based on CT scan Grey values. Matlab was used to sort data in spatial groups according to element centroid position to map bone density distribution. The humeral head was divided into twenty 2mm thick slices parallel to the humeral neck starting from the most proximal region of the humeral head to distal regions beneath epiphyseal plate (Fig 1a). Each slice was then radially divided into 30 concentric circles and each circle was angularly divided into 12 regions (Fig 1b). The bone density for each of these regions was calculated by averaging density values of element centroid residing in each region. Average bone density in each slice indicates that bone density decreases from proximal region to distal regions below the epiphyseal plate and higher bone density was measured proximal to the anatomical neck of the humerus (Fig2). Figure 3 shows that, both above and below the anatomical neck, bone density increases from central to peripheral regions where eventually cortical bone occupies the space. This trend is more pronounced in regions below the anatomical neck and above the epiphyseal plate. In distal slices below the anatomical neck, a higher bone density distribution in inferior (calcar) regions was also observed. Current generation short stem designs require a resection at the anatomical neck of the humerus and a cruciform keel to fix the implant in the distal bone. In the example in Figure 3, the anatomical neck resection corresponds to the 18 mm slice, with the central cruciform keel engaging between slices 18 mm and 27 mm. The data indicates that this keel should make use of the denser bone by the calcar for fixation, suggesting a crucifix orientation as highlighted in Figure 3. The current generation of proximally fixed humeral components are less invasive than conventional long-stemmed designs, but the disadvantage is that they must achieve fixation over a smaller surface area and with a less advantageous lever arm down the shaft of the humerus. By presenting a spatial density map of the proximal humerus, the current study may help improve fixation of proximally fixed designs, with a simple modification of implant rotational orientation to make use of the denser bone in the calcar region for fixation and load transfer

Shoulder arthroplasty is used to treat osteoarthritis, post-traumatic arthritis, and avascular necrosis. Modular components allow for natural variability in shoulder anatomy, including retroversion and head-neck angles. Surgical options include anatomic or guide-assisted cut at a fixed retroversion and head-neck angle. The purpose of this study was to determine the variability between head height (HH) and anteroposterior (AP) and superoinferior (SI) diameters using anatomic and guide-assisted humeral head cuts. Computed tomography scans of 10 cadaveric shoulder specimens (5 male, 5 female) were converted to 3D models. An anatomic humeral head cut plane was placed at the anatomic head–neck junction maintaining the posterior cuff insertion for all shoulders by a fellowship trained shoulder surgeon. Cut planes were generated for standard implant head neck angles (125°,130°,135°, and 140°) and retroversion angles (20°,30°, and 40°) in commercial cutting guides, for a combination of 12 repeated cut conditions per specimen. The humeral HH and the head diameter were measured in the AP and the SI planes for anatomic and guide-assisted osteotomy planes. Differences were compared using a separate two-way repeated measures ANOVA for each dependent variable. Guide-assisted cuts showed no significant effect on HH due to head-neck (p=0.205) or retroversion angles (p=0.190). These results persisted by gender (male: head-neck p=0.659 and retroversion p=0.386; female: head-neck p=0.204 and retroversion p=0.190). SI diameter increased by 1.3 mm with increasing head-neck angle (p<0.001), but there was no effect due to retroversion (p=0.148). A head-neck angle of 125° caused the greatest decrease in SI diameter of −2.8 mm compared to the anatomic cut, averaged over the retroversion range. The greatest reduction of SI diameter, −3.4 mm compared to anatomic, occurred with 125° head-neck angle and 20° retroversion. By gender, males showed a significant effect from head-neck angle (p=0.008), but females did not (p=0.077). There was no significant difference from retroversion in either gender group (male p=0.792; female p=0.057). There was no significant difference in AP diameter by head-neck (p=0.192) or retroversion angles (p=0.168). These results persisted in the males (head-neck p=0.420 and retroversion p=0.780). In females, there was no effect from head-neck angle (p=0.232); however, retroversion angle trended toward significance (p=0.050). For patients whose natural anatomy falls outside the range of the commercial cut guides, templated resection may result in deviation from natural humeral head dimensions. Due to the large variability in anatomic retroversion and head-neck angles in the subjects of this study, further study with a larger sample size is needed to investigate observed trends. These preliminary results have implications for manufacturers to create guides to represent a larger segment of the population, and surgeons' intra-operative choice

The numbers of anatomic total shoulder joint replacements (ATSR) is increasing during the past years with encouraging clinical results. However, the survivorship of ATSR is lower as compared to total knee and hip replacements. Although the reasons for revision surgery are multifactorial, wear-associated problems like loosening are well-known causes for long-term failure of ATSR. Furthermore there is lack of valid experimental wear tests for ATSR. Therefore the purpose of this study was to define experimental wear testing parameters for ATSR and to perform a wear study comparing ceramic and metallic humeral heads. Kinetic and kinematic data were adopted from in-vivo loading measurements of the shoulder joint (. orthoload.com. ) and from several clinical studies on shoulder joint kinematics. As activity an ab/adduction motion of 0 to 90° in combination with an ante/retroversion while lifting a load of 2 kg has been chosen. Also a superior-inferior translation of the humeral head has been considered. The wear assessment was performed using a force controlled AMTI joint simulator for 3×10. 6. cycles (Fig. 1) and polyethylene wear has been assed gravimetrically. The studied ATSR (Turon. TM. , DJO Surgical, USA) resulted in a polyethylene wear rate of 62.75 ± 1.60 mg/10. 6. cycles in combination with metallic heads. The ceramic heads significantly reduced the wear rate by 26.7 % to 45.99 ± 1.31 mg/10. 6. (p<0.01). The wear scars dimensions were in good agreement to clinical retrievals. This study is the first that experimentally studied the wear behavior of ATSR based on clinical and biomechanical data under load controlled conditions. In term of wear the analyzed ATSR could clearly benefit from ceramic humeral heads. However, in comparison to experimental wear studies of total knee and hip replacements the wear rate of the studied ATSR was relatively high. Therefore further research may focus on optimized wear conditions of ATSR and the hereby described method may serve as a tool to evaluate a wear optimization process

Introduction. The treatment of glenohumeral arthritis in a young patient poses a significant challenge. Factors that affect decision making include higher activity levels, greater expectations, and concerns of implant longevity. Conflicting results have been reported in the literature. The purpose of this study is to report on our results for resurfacing of the humeral head combined with a biologic glenoid resurfacing using a soft tissue allograft for the treatment of glenohumeral osteoarthritis. Methods. From 2003 to 2009 a retrospective multi-center review of 15 humeral and biologic glenoid resurfacing procedures with a mean age of 36.5 yrs. was performed. Indications for surgery included a diagnosis of glenohumeral arthritis non-responsive to conservative treatment. Exclusion criteria included major glenoid osseous deficiency, advanced rheumatoid arthritis, and chronic infection. Results. Mean follow-up of 57.1 months showed that on average active forward elevation improved from 126.8° to 136° and external rotation improved from 27.1° to 35.3°. The mean pre-operative and post-operative VAS score only improved from 7.9 to 5.1. Five (29%) patients were converted a total shoulder arthroplasty (TSA) at an average of 24 months with no complications in the remaining patients. Discussion. The clinical outcome of humeral head resurfacing with soft tissue resurfacing of the glenoid has not yielded encouraging results, as both pain and function are not significantly improved. Due to the disappointing results of this procedure and high revision rate, it is no longer these authors primary treatment option for OA in the young. Determining the optimal treatment for osteoarthritis in the young patient is still being investigated

An understanding of forces that act on the shoulder joint is important for designing, testing, and evaluating shoulder arthroplasty products. Last year, we presented data describing upper arm motion during eight in-situ hours of occupational and recreational tasks. Using that data the associated humeral head joint forces were calculated with an upper extremity model in OpenSim. Five subjects from a nonrandom sampling of occupations wore the Inertial Measurment Units during a four hour period while at their work place performing their normal work duties and then during the four hour period of non-work activities immediately following. An unscented Kalman filter (UKF) was used to produce the 3D humeral – thoracic angles at 128 Hz from the IMU data. Because of the very large number of data points collected with the IMUs, ninety samples of twenty second duration were randomly selected from each four hour collection period. Using the sampled files, the time scales of the sampled files were scaled by a factor of five and then analyzed with the SUEM static optimization and joint reaction features. Not every sample file could be modeled resulting in an average number of sampled files of 66.7 per subject and condition (work/recreation). The humeral – thoracic angles were then used as input to the Stanford Upper Extremity Model (SUEM) in the OpenSim environment. The SUEM model allowed 2 rotation degree of freedom (rdof) for the forearm (flexion twist), 3 rdof at the humeral – scapular joint, and predicted scapular motion based on the humeral – thoracic elevation angle. All models were run for an assumed 80 kg body weight and included the bone mass of the scapula, clavical, humerus, radius, and ulna, but none of the soft tissue mass. Shoulder muscles were represented by 15 actuators: three heads for each of the deltoid, latissimus dorsi, and pectoralis, and 1 head each for the coracobrachialis, infraspinatous, subscapularis, supraspinatous, termes major, and teres minor. The 5. th. , 50. th. , and 95. th. percentile values of each force component acting on the humeral head from each sampled file for each subject and condition were calculated and the distribution of forces was plotted as a histogram. The overall mean and standard deviation for the 5. th. , 50. th. , and 95. th. percentile values were also determined. Of the A-P and S-I force components, anterior and inferior directed force components were larger than the posterior and superior directed force components. For the M-L force component, the forces were nearly exclusively directed in the medial direction. The 5. th. and 95. th. percentile forces during these subjects' ADL were generally lower than those described by Westerhoff 2009, suggesting that within the limitations of the modeling assumptions, loading experienced during in-situ ADL may be different than loading during laboratory simulation of representative motions

Purpose. The presence of a Hill-Sachs lesion is a major contributor to failure of surgical intervention following anterior shoulder dislocation. The relationship between lesion size, measured on pre-operative MRI, and risk of recurrent instability after surgery has not previously been defined. Hypothesis: We hypothesized that the size of Hill-Sachs lesions on pre-op MRI would be greater among patients who failed soft tissue stabilization when compared to patients who did not fail. We also hypothesized that the existence of a glenoid lesion would lead to failure with smaller Hill-Sachs lesions. Method. Nested case-control analysis of 114 patients was performed to evaluate incidence of failure after soft tissue stabilization. Successful follow-up of at least 24 months was made with 91 patients (80%). Patients with recurrent instability after surgery were compared to randomly selected age and sex matched controls in a 1:1 ratio. Pre-operative sagittal and axial MRI series were analyzed for presence of Hill-Sachs lesions, and maximum edge-to-edge length and depth as well as location of the lesion related to the bicipital groove (axial) and humeral shaft (sagittal) were measured. Results. Of 91 patients included in analysis, 77 (84.6%) had identifiable Hill-Sachs lesions. 32 patients (35.2%) suffered from failure of soft tissue stabilization (redislocation 22.0%; subjective instability 13.2%). Ten of these patients (11.0%) underwent further surgery. When comparing the age and sex matched failure and control groups, statistically significant differences in unadjusted data were found for axial edge-to-edge length (p = 0.01), axial depth (p = 0.01), and sagittal edge-to-edge length (p = 0.04), with larger sized lesions found in the failure group (Figure 1). Differences trended towards significant for sagittal depth and angle from the bicipital groove. Conclusion. In this retrospective case-control study, humeral head defect size was positively correlated with recurrent instability after soft-tissue stabilization. Larger Hill-Sachs lesions, as measured on pre-op MRI, were found in patients who failure surgical intervention when compared to patients who did not fail. These data and future studies may help determine pre-operative clinical guidelines for the treatment of anterior shoulder dislocation

Shoulder resurfacing arthroplasty is a bone conserving option for patients with glenohumeral arthritis. We report the early results of this procedure at our unit with a minimum follow up of 2 years (mean follow up of 36 months). A historical analysis of prospectively collected clinical data was reviewed on a consecutive series of 22 patients (mean age of 73 years) with end stage gleno-humeral arthrosis who had undergone humeral resurfacing hemiarthroplasty performed by a single surgeon. Pain and function were assessed using the Oxford shoulder score and patient satisfaction was recorded. Radiographs were evaluated for implant loosening. 82% of patients had significant improvement in their oxford shoulder score from pre-operatively to two years post-operatively. Complications included one case of intra-operative conversion to a stemmed hemiarthroplasty due to fracture of the humeral head, one case of adhesive capsulitis that required MUA and arthroscopic capsular release and two cases of revision to a total shoulder replacement for pain. Humeral resurfacing arthroplasty is a viable treatment option for glenohumeral arthritis with good short term results

Massive irreparable rotator cuff tears often lead to superior migration of the humeral head, which can markedly impair glenohumeral kinematics and function. Although treatments currently exist for treating such pathology, no clear choice exists for the middle-aged patient demographic. Therefore, a metallic subacromial implant was developed for the purpose of restoring normal glenohumeral kinematics and function. The objective of this study was to determine this implant's ability in restoring normal humeral head position. It was hypothesized that (1) the implant would restore near normal humeral head position and (2) the implant shape could be optimized to improve restoration of the normal humeral head position. A titanium implant was designed and 3D printed. It consisted of four design variables that varied in both implant thickness (5mm and 8mm) and curvature of the humeral articulating surface (high constraint and low constraint. To assess these different designs, these implants were sequentially assessed in a cadaver-based biomechanical testing protocol. Eight cadaver specimens (64 ± 13 years old) were loaded at 0, 30, and 60 degrees of glenohumeral abduction using a previously developed shoulder simulator. An 80N load was equally distributed across all three deltoid heads while a 10N load was applied to each rotator cuff muscle. Testing states included a fully intact rotator cuff state, a posterosuperior massive rotator cuff tear state (cuff deficient state), and the four implant designs. An optical tracking system (Northern Digital, Ontario, Canada) was used to record the translation of the humeral head relative to the glenoid in both superior-inferior and anterior-posterior directions. Superior-Inferior Translation. The creation of a posterosuperior massive rotator cuff tear resulted in significant superior translation of the humeral head relative to the intact cuff state (P=0.016). No significant differences were observed between each implant design and the intact cuff state as all implants decreased the superior migration of the humeral head that was observed in the cuff deficient state. On average, the 5mm low and high constraint implant models were most effective at restoring normal humeral head position to that of the intact cuff state (-1.3 ± 2.0mm, P=0.223; and −1.5 ± 2.3mm, P=0.928 respectively). Anterior-Posterior Translation. No significant differences were observed across all test states for anterior-posterior translation of the humeral head. The cuff deficient on average resulted in posterior translation of the humeral head, however, this was not statistically significant (P=0.128). Both low and high constraint implant designs were found to be most effective at restoring humeral head position to that of the intact cuff state, on average resulting in a small anterior offset (5mm high constraint: 2.0 ± 4.7mm, P=1.000; 8mm high constraint: 1.6 ± 4.9mm, P=1.000). The 5mm high constraint implant was most effective in restoring normal humeral head position in both the superior-inferior and anterior-posterior directions. The results from this study suggest the implant may be an effective treatment for restoring normal glenohumeral kinematics and function in patients with massive irreparable rotator cuff tears. Future studies are needed to address the mechanical efficiency related to arm abduction which is a significant issue related to patient outcomes

Total shoulder arthroplasty implants have evolved to include more anatomically shaped components that replicate the native state. The geometry of the humeral head is non-spherical, with the sagittal diameter of the base of the head being up to 6% (or 2.1-3.9 mm) larger than the frontal diameter. Despite this, many TSA humeral head implants are spherical, meaning that the diameter must be oversized to achieve complete coverage, resulting in articular overhang, or portions of the resection plane will remain uncovered. It is suspected that implant-bone load transfer between the backside of the humeral head and the cortex on the resection plane may yield better load-transfer characteristics if resection coverage was properly matched without overhang, thereby mitigating proximal stress shielding. Eight paired cadaveric humeri were prepared for reconstruction with a short stem total shoulder arthroplasty by an orthopaedic surgeon who selected and prepared the anatomic humeral resection plane using a cutting guide and a reciprocating sagittal saw. The humeral head was resected, and the resulting cortical boundary of the resection plane was digitized using a stylus and an optical tracking system with a submillimeter accuracy (Optotrak,NDI,Waterloo,ON). A plane was fit to the trace and the viewpoint was transformed to be perpendicular to the plane. To simulate optimal sizing of both circular and elliptical humeral heads, both circles and ellipses were fit to the filtered traces using the sum of least squares error method. Two extreme scenarios were also investigated: upsizing until 100% total coverage and downsizing until 0% overhang. Total resection plane coverage for the fitted ellipses was found to be 98.2±0.6% and fitted circles was 95.9±0.9%Cortical coverage was found to be 79.8 ±8.2% and 60.4±6.9% for ellipses and circles respectively. By switching to an ellipsoid humeral head, a small 2.3±0.3% (P < 0.001) increase in total coverage led to a 19.5±1.3%(P < 0.001) increase in cortical coverage. The overhang for fitted ellipses and circles was 1.7 ±0.7% and 3.8 ±0.8% respectively, defined as a percentage of the total enclosed area that exceeded the bounds of the humerus resections. Using circular heads results in 2.0 ±0.1% (P < 0.001) greater overhang. Upsizing until 100% resection coverage, the ellipse produced 5.4 ±3.5% (P < 0.001) less overhang than the circle. When upsizing the overhang increases less rapidly for the ellipsoid humeral head that the circular one (Figure 1). Full coverage for the head is achieved more rapidly when up-sizing with an ellipsoid head as well. Downsizing until 0% overhang, total coverage and cortical coverage were 7.5 ±2.8% (P < 0.001) and 7.9 ±8.2% (P = 0.01) greater for the ellipse, respectively. Cortical coverage exhibits a crossover point at −2.25% downsizing, where further downsizing led to the circular head providing more cortical coverage. Reconstruction with ellipsoids can provide greater total resection and cortical coverage than circular humeral heads while avoiding excessive overhang. Elliptical head cortical coverage can be inferior when undersized. These initial findings suggest resection-matched humeral heads may yield benefits worth pursuing in the next generation of TSA implant design. For any figures or tables, please contact the authors directly

We compared the rate of revision of two classes of primary anatomic shoulder arthroplasty, stemmed (aTSA) and stemless (sTSA) undertaken with cemented all polyethylene glenoid components. A large national arthroplasty registry identified two cohort groups for comparison, aTSA and sTSA between 1. st. January 2011 and 31. st. December 2020. A sub-analysis from 1 January 2017 captured additional patient demographics. The cumulative percentage revision (CPR) was determined using Kaplan-Meier estimates of survivorship and hazard ratios (HR) from Cox proportional hazard models adjusted for age and gender. Of the 7,533 aTSA procedures, the CPR at 8 years was 5.3% and for 2,567 sTSA procedures was 4.0%. There was no difference in the risk of revision between study groups (p=0.128). There was an increased risk of revision for aTSA and sTSA undertaken with humeral head sizes <44mm (p=0.006 and p=0.002 respectively). Low mean surgeon volume (MSV) (<10 cases per annum) was a revision risk for aTSA (p=0.033) but not sTSA (p=0.926). For primary diagnosis osteoarthritis since 2017, low MSV was associated with an increased revision risk for aTSA vs sTSA in the first year (p=0.048). Conversely, low MSV was associated with a decreased revision risk for sTSA in the first 6 months (p<0.001). Predominantly aTSA was revised for loosening (28.8%) and sTSA for instability/dislocation (40.6%). Revision risk of aTSA and sTSA was associated with humeral head size and mean surgeon volume but not patient characteristics. Inexperienced shoulder arthroplasty surgeons experience lower early revision rates with sTSA in the setting of osteoarthritis. Revision of aTSA and sTSA occurred for differing reasons

Background. The current use of a spherical prosthetic humeral head in total shoulder arthroplasty results in an imprecise restoration of the native geometry and improper placement of the center of rotation, maintained in a constant position, in comparison to the native head and regardless of glenoid component conformity. A radially-mismatched spherical head to allow gleno-humeral translation is a trade-off that decreases the contact area on the glenoid component, which may cause glenoid component wear. This finding suggests that the use of a non-spherical head with a more conforming glenoid component may reduce the risk of glenoid component wear by allowing gleno-humeral translation while increasing the contact area. A non-spherical prosthetic head more accurately replicates the head shape, rotational range of motion and gleno-humeral joint kinematics than a spherical prosthetic head, compared with the native humeral head. The combination of inversion of the bearing materials with the non-spherical configuration of the humeral head may thus decrease polyethylene wear. Aim of the present study is to evaluate in vitro wear behaviour of an all-polyethylene elliptical humeral head component against a metallic glenoid component in an anatomic configuration. Material and methods. The prosthetic components tested are from the Mirai. ®. Modular Shoulder System by Permedica S.p.A.. The prosthetic bearing components were tested in their anatomic configuration: the humeral head rubbing against the glenoid inlay, assembled over the glenoid base-plate. The glenoid insert is made of Ti6Al4V alloy coated with TiNbN. The glenoid insert, as the glenoid base-plate have the same shape which reproduce the native shape of the glenoid. Moreover, the glenoid insert has a concave articular surface described by two different radii on orthogonal planes. The vitamin E-blended UHMWPE humeral head is not spherical but elliptic-shaped with an articular surface described by two different profiles in sagittal and coronal plane. The component sizes combination tested have the greatest radial mismatches allowed between humeral head and glenoid insert. The test was performed up to 2.5 million of cycles applying a constant axial load of 756 N. Results. After 2.500.000 cycles the mean mass loss from the humeral head was 0.68 mg. The mean wear rate of the humeral head was 0.28 mg/Mc (SD 0.45 mg/Mc). The surface of the humeral heads showed an elliptical worn area with matt and polished areas with scratching. The surface of the TiNbN-coated glenoid insert counterparts did not show wear signs. Conclusion. The tested prosthetic humeral head has a non-spherical shape with an elliptical base and 2 different radii on sagittal and coronal plane. Also the tested glenoid insert has 2 different radii on sagittal and coronal planes. This components geometry leads to a radial mismatch between head and glenoid on sagittal and coronal planes. A different kinematics, allowing gleno-humeral translation while increasing the contact area, radial mismatch in different planes and the inversion of bearing materials may have a role in reducing component wear and may explain the extremely low wear rate found in the present study

Introduction. For anatomical reconstruction in shoulder arthroplasty, it is important to understand normal glenohumeral geometry. Unfortunately, however, the details of the glenohumeral joint in Asian populations have not been sufficiently evaluated. There is a racial difference in body size, and this difference probably results in a difference in glenohumeral size. The purpose of this study was to evaluate three-dimensional geometry of the glenohumeral joint in the normal Asian population and to clarify its morphologic features. Methods. Anthropometric analysis of the glenohumeral joint was performed using computed tomography scans of 160 normal shoulders from healthy volunteers in age from 20 to 40 years. Using OsiriX MD, Geomagic Studio, and AVIZO software, the dimensions of humeral head width, humeral head diameter, glenoid height, glenoid width, and glenoid diameter were analyzed three-dimensionally (Figure 1). In diameter analyses, the humeral head was assumed to be a sphere and the glenoid was to fit a sphere (Figure 2–3). Sex differences in height, humeral length, humeral head width, humeral head diameter, glenoid height, glenoid width, and glenoid diameter were compared using Mann-Whitney U tests. The correlations between sides and among the respective parameters in the glenohumeral dimensions were evaluated with Spearman rank correlation tests. The significance level was set at 0.05 for all analyses. Results. Average height and humeral length of the volunteers were 164.7 ± 9.7 cm and 29.1 ± 1.8 cm respectively. The normal Asian glenohumeral joint has average humeral head width of 41.4 ± 3.7 mm, humeral head diameter of 42.9 ± 3.6 mm, glenoid height of 31.5 ± 2.8 mm, glenoid width of 23.1 ± 2.4 mm, and glenoid diameter of 62.0 ± 6.8 mm. The humeral head and glenoid were significantly larger in males than in females (p<0.001 in all analyses). The average radius difference between the glenoid and the humeral head was 9.6 ± 2.8 mm, and there was no sex difference (p=0.359). The average ratio of the glenoid radius to the humeral head radius was 144.9% ± 12.2%, and the ratio was significantly larger in females than in males (p=0.026). The glenohumeral size was well correlated between the two sides, and there were direct correlations among the heights, humeral length, humeral head size, and glenoid size (p<0.001 in all analyses). Conclusions. The present study revealed that the values of glenohumeral dimensions were uniform in both males and females with a strong correlation between the dominant shoulder and the nondominant shoulder. Since there are direct correlations among height, humeral length, and the size of the glenohumeral joint, we can also predict the glenohumeral size of patients from their respective heights. The present results would be useful to determine the size of implants and to improve clinical outcomes of shoulder arthroplasty for glenohumeral joints of Asian patients. The size of the Asian glenohumeral joint was obviously smaller than that reported in the past literature including black and Caucasian populations. Some shoulder prostheses that are designed in Europe or America and are widely used worldwide could be oversized for small females

Glenoid failure remains the most common mode of total shoulder arthroplasty failures. Porous tantalum metal (Trabecular Metal™, Zimmer) have grown in popularity in hip and knee arthroplasty. First-generation porous tantalum metal-backed glenoid components demonstrated metal debris, resulted in failure, and were revised to second-generation glenoid implants. Evidence for second-generation porous tantalum metal implants in shoulder arthroplasty is sparse.1–4 The purpose of this study was to assess clinical and radiographic outcomes in a series of patients with second-generation porous tantalum glenoid components at a minimum two-years postoperative. We retrospectively reviewed the clinical and radiographic outcomes of patients who received a second-generation porous tantalum glenoid component anatomic shoulder arthroplasty between May 2009 and December 2017 with minimum 24 months follow-up. The shoulder arthroplasties were performed by one of two senior fellowship-trained surgeons. We collected postoperative clinical outcome indicators: EQ5D visual analog scale (VAS), Western Ontario Osteoarthritis of the Shoulder (WOOS) Index, American Shoulder and Elbow Surgeons (ASES) Score, and Constant Score (CS). Radiographic review was performed by an independent fellowship-trained surgeon. The Endrizzi metal debris grading system1 was utilized to grade metal debris. We computed descriptive statistics and compared outcome scores between groups via the non-parametric Wilcoxon rank-sum test, with group-wise comparisons defined by: metal debris and humeral head migration (secondary analyses). Thirty-five patients [23 male (65.7%) and 12 female (34.3%)] with 40 shoulder replacements participated in the study. Forty of 61 shoulders (65.6%) had an average of 64 ± 20.3 months follow-up (range 31 to 95). Average BMI was 27.5 ± 4.4 kg/m2 (range 19.5 to 39.1). The average postoperative EQ5D VAS at final follow-up was 74.6 ± 22.5, WOOS Index 87.9 ± 16.6, ASES Score 88.3 ± 10.9, and CS 80.4 ± 13. At final follow-up, 18 of 40 shoulders (45%) had metal debris [15 of 40 (37.5%) Endrizzi grade 1 and three of 40 (7.5%) Endrizzi grade 2], and 22 of 40 shoulders (55%) did not show evidence of metal debris. There was one non-revision reoperation (open subscapularis exploration), one shoulder with anterosuperior escape, three shoulders with glenoid radiolucencies indicative of possible glenoid loosening, and nine shoulders with superior migration of the humeral head (>2mm migration at final follow-up compared to immediate postoperative). When comparing postoperative scores between patients with vs without metal debris, we found no statistically significant difference in the EQ5D VAS, WOOS Index, ASES Score and CS. On further analyses, when comparing superior migration of the humeral head and postoperative outcomes scores, we found no statistically significant difference. We report the longest published follow-up with clinical and radiographic outcomes of second-generation porous tantalum glenoid anatomic shoulder arthroplasties. In this series of patients, 45% of total shoulder arthroplasties with a second-generation porous tantalum glenoid implant had radiographic evidence of metal debris. This metal debris was not statistically associated with poorer postoperative outcomes. Further investigation and ongoing follow-up are warranted