A secure taper connection in shoulder arthroplasty is mandatory to avoid loosening and fretting. This study's objective was to determine the amount of Impaction data was collected from experienced shoulder surgeons (n=5) during a cadaver lab. Testing groups (n=5 each) were: 1) The 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. 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).Methods
Results
The complex 3D geometry of the scapula and the variability among individuals makes it difficult to precisely quantify its morphometric features. Recently, the scapular neck has been recognized as an important morphometric parameter particularly due to the role it plays in scapular notching, which occurs when the humeral component of a reverse shoulder arthroplasty (RSA) prosthesis engages the posterior column of the scapula causing mechanical impingement and osseous wear. Prosthetic design and positioning of the glenoid component have been accepted as two major factors associated with the onset of notching in the RSA patient population. The present image-based study aimed to develop an objective 3D approach of measuring scapular neck, which when measured pre-operatively, may identify individuals at risk for notching. A group of 81 subjects (41 M, 69.7 ± 8.9 yrs.; 40 F, 70.9 ± 8.1 yrs.) treated with RSA were evaluated in this study. The 3D point-cloud of the scapular geometry was obtained from pre-operative computed tomography (CT) scans and rendered in Mimics. Subsequently, a subject-specific glenoid coordinate system was established, using the extracted glenoid surface of each scapula as a coordinate reference. The principal component analysis approach was used to establish three orthogonal coordinate axes in the geometric center of the glenoid. Utilization of glenoid-specific reference planes (glenoid, major axis, and minor axis plane) were selected in order to remove subjectivity in assessing “true” anterior/posterior and profile views of the scapula. The scapular neck length was defined as the orthogonal distance between the glenoid surface and the point on the posterior column with the significant change of curvature (Fig. 1). In addition, the angle between the glenoid plane, area center of the glenoid, and the point of significant change of the curvature were assessed (Fig. 2). This new parameter was developed to serve as a predictive critical value for the occurrence of notching. The incidence of notching increases as the value of the notching angle decreases. In order to evaluate relationships between glenoid and scapular neck, the glenoid width and height was also measured at the glenoid plane.Introduction:
Materials and Methods:
Currently, there are a variety of different reverse shoulder implant designs but few anatomic studies to support the optimal selection of prosthetic size. This study analyzed the glenohumeral relationships of patients who underwent reverse shoulder arthroplasty (RSA). Ninety-two shoulders of patients undergoing primary RSA for a massive rotator cuff tear without bony deformity or deficiency and 10 shoulders of healthy volunteers (controls) were evaluated using three-dimensional CT reconstructions and computer aided design (CAD) software. Anatomic landmarks were used to define scapular and humeral planes in addition to articular centers. After aligning the humeral center of rotation with the glenoid center, multiple glenohumeral relationships were measured and evaluated for linearity and size stratification. The correction required to transform the shoulder from its existing state (CT scan) to a realigned image (CAD model) was compared between the RSA and control groups. Size stratification was verified for statistical significance between groups. Generalized linear modeling was used to investigate if glenoid height, coronal humeral head diameter and gender were predictive of greater tuberosity positions.Background:
Methods:
Accurate placement of glenoid components in reverse and total shoulder arthroplasty has been shown to reduce the risk of implant failure (1, 2, 6). Surgical techniques and literature describe methods to determine favorable positions for implant placement (3, 4, 5) but achieving that position surgically remains a challenge. Placement of glenoid components is faced with the challenge of variable glenoid morphology on which conventional instrumentation does not always provide a reliable reference (6, 7, 8). Limited surgical exposure is another challenge since many anatomic landmarks are not visible to the surgeon to use as spacial reference. Anatomic landmarks and angles can be more reliabily selected on CT scans with 3-dimentional reconstruction (9,10) yet few methods allow for the reproducible translation of these plans to surgery. Navigation has produced better accuracy and lower variability than conventional instrumentation (11), yet its regular usage remains limited, especially in the shoulder. A patient specific planning and guiding system has been developed for glenoid implant placement of total and reverse shoulder arthoplasty procedures. This method allows for preoperative planning on a patient specific virtual 3D model of the scapula derived from CT images (Figure 1), and guided placement of a pin which which serves as the central axis for determining proper implant position. An initial implant position was presented on the virtual model based on the methods described by the surgical technique of the corresponding procedure. These plans were either approved or adapted to a desired position within the planning software by the surgeons. Using this planned position as input, patient specific surgical guides were created which fit onto the exposed anatomy and guide the drilling of the pin (Figure 1). This method was tested on 14 cadavers, with attention directed to translation of the starting point from the original plan, the ability to reproduce the intended degree of inferior tilt, and the ability to reproduce the glenoid version angle.Background and Motivation
Methods
While reverse shoulder arthroplasty has shown successful outcomes for a variety of shoulder pathologies, postoperative instability continues to be one of the most common complications limiting outcomes. In the literature, reports of instability range from 2.4%–31%. Many authors recommend an initial attempt at closed reduction followed by a period of immobilization for management of the initial dislocation episode while others may seek to rule out infection or other secondary causes; however there is little data to support either practice. The purpose of this study was to evaluate the outcomes of patients with postoperative dislocation following reverse shoulder arthroplasty managed with closed reduction. A retrospective review of all reverse shoulder arthroplasties performed by a single surgeon (MF) from 2002-present was performed to identify all patients treated for postoperative dislocation treated with closed reduction, either in the office setting or under anesthesia in the operating room. A total of 21 patients were identified. Preoperative patient characteristics, implant selection, and time to initial dislocation episode were recorded. Final outcomes including recurrent instability need for revision surgery, ASES outcome score, and range of motion were evaluated.Background:
Methods:
Reverse shoulder arthroplasty (RSA) has proven to be a useful tool to manage a variety of pathologic conditions. However, inconsistent improvement in motion occurs in patients who have undergone RSA for revision shoulder arthroplasty, proximal humeral fracture sequelae, and treatment of infection. Additional factors that have been suggested to produce poor postoperative range of motion (ROM) may be associated with patient's factors such as poor preoperative range of motion and surgical factors such as inability to lengthen the arm. The purpose of this study was to analyze multiple factors which may be responsible in predicting motion after RSA. It is our hypothesis that intraoperative ROM is most predictive of postoperative ROM. Between February 2003 and April 2011 566 patients (225 male and 341 female) treated with a RSA for 1) acute proximal humeral fracture (11), 2) Sequeala of proximal humeral fractures (31), 3) cuff tear arthropathy (278), 4) massive cuff tear without arthritis (78), 5) failed shoulder arthroplasty (168) and 6) infection (29) were evaluated with preoperative range of motion, intraoperative range of motion and range of motion at a minimum of 2-year postoperative follow up. A single observer recorded intraoperative flexion (IFF) in 30° increments. Preoperative and postoperative ROM was recorded by patient video or a previously validated patient performed outcome measure. Preoperative diagnosis was confirmed by radiographic and intraoperative information. 477 patients had preoperative and postoperative radiographs available for analysis of acromial-greater tuberosity distance change (AGT) which was utilized to calculate arm lengthening. A regression analysis was then performed to determine which factors were most influential in predicting postoperative active range of motion.Introduction:
Methods:
Subchondral bone density (SBD) distribution is an important parameter regarding that may be important when considering implant stability. This parameter is a reflection of the loading experienced by the joint throughout the lifetime and may be useful in pre-surgical planning and implant design. Clinically, the question of the glenoid surface preparation for TSA/RSA remains controversial, despite numerous published studies on glenoid bone morphology. To address this question, there exists a need to develop a 3D quantitative method capable of analyzing the complex glenoid bone morphology at different depths from the surface. Computed tomographic osteoabsoptiomery (CT-OAM) evaluates SBD based on the Housfield Unit (HU) value of each pixel. In this pilot study, we aimed to analyze SBD distribution of the glenoid at different depths by means of CT-OAM in male TSA subjects. A study group of twenty male TSA patients (61–69y.o) were included in this study. Each subject obtained a pre-operative CT scan following a standardized protocol on the same CT scanner (1.25 mm slice thickness). Resultant DICOM 2D images were processed in custom-written program (VC++) and the surface of every glenoid was manually traced from the axial slices. Care was taken during the manual tracing process to exclude osteophytes and cyst formations from the resultant surface. Values of HU at every selected pixel on the surface of the glenoid were recorded. Subsequently, the layer of pixels at a 0.5 mm distance from the previous surface was virtually scraped and the HU values of new layer of pixels were recorded. This routine was repeated up to a depth of 5 mm from the glenoid surface, taking measurements on 11 virtual 3D surfaces with a thickness of 0.5 mm. Mean SBD distribution was reported for each layer and differences were compared using ANOVA and Fisher's post-hoc test.Introduction:
Materials and Methods:
Reverse total shoulder arthroplasty was developed to address the treatment of patients with Cuff Tear Arthropathy. Despite of the clinical improvements seen with initial reverse shoulder replacements, several mechanical problems remain. Scapular notching has been reported between 24.5% and 96% of cases. Patients have also exhibited limited external rotation, either from impingement or slackening of remaining cuff musculature. Additionally, by medializing and moving the humerus distally, patients note a loss of the normal deltoid contour leading not only to cosmetic concerns, but possibly decreasing deltoid efficiency and creating a prosthesis with less inherent stability. Finally, although mechanical failure on the glenoid side initially was thought to be uncommon, various glenoid sided problems have been reported. Recognition of these problems led to clinical and basic science studies aimed at improving surgical technique and the design of reverse shoulder implants. During the last 10 years, our institution has been conducting biomechanical research examining the forces across the glenohumeral joint. Several different models have been created to replicate mechanical failures by integrating biomechanical information with our clinical investigations, including altering the position of the implant (tilt), the type of fixation of the implant (screw or peg), and glenoid-sided bone loss. We were able to address glenoid component failure (with initial rates of 10% in our clinical studies) by recommending locking screws to neutralize forces at the fixation site. These discoveries have reduced glenoid-sided fixation failures to less than 0.1%. In vitro kinematic function and factors that affect impingement free glenohumeral motion of reversed implants is another area of interest. The clinical relevance of impingement includes scapular-notching, pain from impingement, instability and excessive prosthetic wear. Several models that include motion in three different planes (flexion-extension, abduction-adduction and internal-external rotation) have been developed to study multiple prosthetic, technique and anatomic factors which can result from varying degrees of impingement. By integrating the results from these models into our clinical practice (e.g., selecting a more lateralized glenosphere, selecting a varus humeral component and inferiorly translating the glenoid component on the glenoid surface), we have been able to maintain low rates of notching (∼10% at 8 year follow-up). Finally, our current work involves development of a model that attempts to understand which factors might be influential in causing instability and stiffness. Thus, biomechanics research offers an excellent opportunity for interdisciplinary collaboration to solve complex clinical problems.
While reverse shoulder arthroplasty (RSA) has shown successful outcomes for a variety of shoulder pathologies, postoperative scapula fractures continue to be one of the most common complications limiting outcomes with rates reported between 0.8–7.2%. Previous literature has shown that postoperative scapula fractures have a deleterious effect on elevation and outcomes scores, however these studies were all performed at short-term follow-up from the fracture. It has also not been shown whether postoperative scapular fractures increases risk of revision surgery. The purpose of this study was to determine the effect of postoperative scapula fracture on the outcomes following RSA at minimum 1 year follow-up from the fracture. A retrospective, case-control study of 25 nonoperatively treated postoperative scapula fractures following RSA in a single surgeon's practice was analyzed with minimum 2 year follow-up from surgery and 1 year follow-up from fracture. Patients with postoperative scapula fractures were matched 1: 4 to a control group for age, sex, total follow-up time, indication for surgery, and primary versus revision surgery. Outcome measures including revision surgery, ASES score, and change in range of motion were compared between fracture cases and controls. Radiographic features including fracture location (acromion vs. scapular spine) and healing of fracture was also analyzed with respect to outcome.Background:
Methods:
We report the use of the reverse shoulder prosthesis in the revision of a failed shoulder hemiarthroplasty in 19 shoulders in 18 patients (7 men, 11 women) with severe pain and loss of function. The primary procedure had been undertaken for glenohumeral arthritis associated with severe rotator cuff deficiency. Statistically significant improvements were seen in pain and functional outcome. After a mean follow-up of 44 months (24 to 89), mean forward flexion improved by 26.4° and mean abduction improved by 35°. There were six prosthesis-related complications in six shoulders (32%), five of which had severe bone loss of the glenoid, proximal humerus or both. Three shoulders (16%) had non-prosthesis related complications. The use of the reverse shoulder prosthesis provides improvement in pain and function for patients with failure of a hemiarthroplasty for glenohumeral arthritis and rotator cuff deficiency. However, high rates of complications were associated with glenoid and proximal humeral bone loss.
Outcomes for a RSP to treat either a previous operated shoulder (revision procedure) was compared to a primary RSP. Twenty primary RSP (6M, 14F) for an irreparable rotator cuff tear (IRCT) with glenohumeral arthritis /anterior superior arch deficiency and 31 revision RSP (10M, 21F) (previous rotator or cuff surgery, hemi or total shoulder arthroplasty) were evaluated at an average of 24 months postoperatively. Mean age at the time of RSP was 72.3 for primaries 67.2 for revisions. Assessment with pre- and postoperatively SF-36, SST, ASES scores, physical exam, satisfaction surveys, and radiographs was performed. Primary RSP improvements /Revision RSP improvements were: 9.4 sf-36 PCS/ 6.3 sf-36 PCS, 1.8 SST/ 1.6 SST,31.8ASES / 17.5ASES (p<
0.05),49.2 elevation/ 14.2 elevation (p<
0.05) and 57.8 external rotation/ 30 external rotation. 71.3% Excellent/good/. 56% Excellent/ good (p<
0.05), 21.4% satisfactory/ 33.3% satisfactory, 7.1% unsatisfactory outcome/ 9.5% unsatisfactory outcome. Complications only occurred in the revisions including component disassociation, glenoid loosening, recurrent instability, and infection Primary RSP provides predictable improvements in pain and function with minimal complications. Revision RSP has a higher complication rate and improvements in pain and function are less reliable. Conventional shoulder arthroplasty for patients with IRCT with gle-nohumeral arthritis/anterior superior arch deficiency has resulted in adequate pain relief but functional improvement has not been predictable. Thus, the initial operative selection for these patients must consider the effect of a failed reconstructive attempt on patient outcomes.
There are multiple proximal prosthetic geometries available for a surgeon to select when humeral head replacement is indicated for four-part proximal humerus fractures. We compared different proximal prosthetic geometries in stable and unstable fracture patterns, with a standard tuberosity fixation method. Simulated four-part fractures were created with an oscillating saw in six synthetic shoulder models. Three different proximal prosthetic geometries used polymetylmethacrelate (PMMA) – a smooth circular shape (SCS), a diamond shape (DS) and an irregular multiple fin shape (IMFS) prostheses. A standardised fixation method using vertical, and horizontal straps along with a medial based cerclage strap was performed. Passive motion was then carried out using a robotic articulator. Interfragmentary displacement was measured from tuberosity to tuberosity as well as tuberosity to shaft using mercury strain gauges. The least amount of interfragmentary motion occurred when an IMFS was used in a stable fracture pattern. This geometry provided more interfragmentary stability even with the unstable fracture pattern than the DS or SCS. The least stable construct was the SCS prosthesis with an unstable fracture pattern. Prosthetic geometry does affect stability of tuberosity reconstruction in proximal humerus fractures. An irregular shaped prosthesis augments the fixation construct. When using a smooth prosthetic design a stable fracture pattern must be achieved to prevent excessive interfragmentary motion. A smooth prosthetic design for tuberosity reconstruction is not recommended.
