Introduction. The Flexible Nichidai Knee (FNK) System (Nakashima Medical, Japan) was designed to fit Asian knees. Especially, the posterior stabilized(PS) prosthesis was designed as semi-constrained posterior stabilized system that had a large tibial post and femoral articulation. We hypothesized that the semi-constrained PS implant design would have a positive influence on vivo kinematics after total knee arthroplasty (TKA). Materials and Methods. A total of 16 patients (21 knees) who had undergone TKA using PS implant were randomly recruited from our database. Of the 16 patients, all patients were women. Fourteen patients had osteoarthritis and 2 patients had rheumatoid arthritis. The average age was 72.3± 9.5 years, and the average postoperative duration was 23.4 ± 19.3 months. The subject performed sequential deep knee bends under WB from 0° to maximum flexion under fluoroscopic monitoring in the sagittal plane. Conversely, under NWB, the patient sat on a chair and was asked to perform active assisted knee flexion. To estimate spatial position and orientation of the artificial knee prosthesis, a 2D to 3D registration technique was used. We evaluated knee range of motion, femoral axial rotation relative to the tibial component, and anteroposterior translation of the femorotibial contact point for both medial and lateral sides. Closest distances between femoral cam and tibial post engagement were measured,. Results. Range of Motion. The mean full extension angle between femoral and tibial components, was −8.1±8.8°and −7.5±5.5°in WB and NWB, respectively. The mean maximum-flexion angle was 110.0±18.1°and 119.3±8.9°in WB and NWB, respectively. Femoral Axial Rotation. Fig.1 shows the mean degree of femoral axial rotation relative to the tibial components in WB and NWB. The femur was externally rotated 0.7±3.9°and 0.3±4.7°at 0° degree in WB and NWB, respectively. The external rotation increased to 4.8±5.2°and 6.2±5.9°at 120°flexion in WB and NWB, respectively. Anteroposterior Translation. The mean femorotibial contact point under WB and NWB was shown in Fig.2 for medial contact and Fig. 3 for lateral contact. Under WB, the mean medial contact point moved posteriorly from −1.6±2.0mm at 0° flexion. The point then moved gradually anteriorly with flexion to −9.3±1.5mm at 120°flexion. The mean lateral contact point moved posteriorly from −1.9±1.7mm at 0° flexion, and then moved anteriorly to at −8.9±2.7mm 120° flexion. Under NWB conditions, the mean medial contact point moved posteriorly from −1.1±1.8mm at 0° flexion. The point then moved gradually posteriorly with flexion to −6.6±2.8mm at 120° flexion. The mean lateral contact point in PS TKA moved posteriorly from −4.4±3.3mm at 0° flexion, and then moved posteriorly to −12.3±3.6mm at 120°flexion. Post-Cam Engagement. The mean knee flexion angle at initial post-cam engagement was 61.9 ± 15.9° under WB and 57.5 ± 16.0° under NWB. Discussion. Our study showed external rotation and bycondylar posterior rollback pattern in the entire range of knee flexion. The reason for this might be that the post cam design was high(20mm), which does not allow for high external rotation. The in vivo kinematics of the semi-constrained PS FNK prosthesis showed similar kinematic patterns due to the development concept of the implant design

Introduction

Tibiofemoral constraint in patients with total knee replacements (TKR) is dependent on both implant geometry and the surrounding soft tissue structures. Choosing more highly constrained geometries can reduce the contribution of soft tissue necessary to maintain joint stability [1]. Often when knee revision surgeries are required, the soft tissue and bone are compromised leading to the use of more constrained implants to ensure knee stability [2]. The current study quantifies the differences in varus-valgus (VV) and internal-external (IE) constraint between two types of total knee revision systems: SIGMA® TC3© and ATTUNE® REVISION.

Introduction. The interaction between the mobile components of total elbow replacements (TER) provides additional constraint to the elbow motion. Semi-constrained TER depend on a mechanical linkage to avoid dislocation and have greater constraint than unconstrained TER that rely primarily in soft tissue for joint stability. Greater constraint increases the load transfer to the implant interfaces and the stresses in the polyethylene components. Both of these phenomena are detrimental to the longevity of TER, as they may result in implant loosening and increased damage to the polyethylene components, respectively[1]. The objective of this work was to compare the constraint profile in varus-valgus and internal-external rotation and the polyethylene stresses under loads from a common daily activity between two semi-constrained TER, Coonrad/Morrey (Zimmer-Biomet) and Discovery® (DJO), and an unconstrained TER, TEMA (LimaCorporate). Methods. We developed finite element (FE) models of the three TER mechanisms. To reduce computational cost, we did not include the humeral and ulnar stems. Materials were linear-elastic for the metallic components (E. Ti6Al4V. =114.3 GPa, E. CoCr. =210 GPa, v=0.33) and linear elastic-plastic for the polyethylene components (E=618 MPa, v=0.46; S. Y. =22 MPa; S. U. =230.6 MPa; ε. U. =1.5 mm/mm). The models were meshed with linear tetrahedral elements of sizes 0.4–0.6 mm. We assumed a friction coefficient of 0.02 between metal and polyethylene. In all simulations, the ulnar component was fixed and the humeral component loaded. We computed the constraint profiles in full extension by simulating each mechanism from 8° varus to 8° valgus and from 8° internal to 8° external rotation. All other degrees-of-freedom except for flexion extension were unconstrained. Then, we identified the instant during feeding that generated the highest moments at the elbow[2], and we applied the joint forces and moments to each TER to evaluate the stresses in the polyethylene. To validate the FE results, we experimentally evaluated the constraint of the design with highest polyethylene stresses in pure internal-external rotation and compared the results against those from a FE model that reproduced the experimental setup (Fig.1-a). Results. For each design, the constraint profiles in varus-valgus (Fig.2-a) were similar to internal-external rotation (Fig.2-b). All designs showed a lax zone in which the mechanisms rotated freely and an engagement zone in which the mobile components contacted, resulting in load transfer. The laxity of the Coonrad/Morrey and the Discovery® was similar and lower than that of the TEMA. After engagement, the stiffness of the TEMA was less than that of the Discovery® and the Coonrad/Morrey. The TEMA showed the lowest polyethylene stresses of all three designs under demanding loads during feeding. Only Discovery® and Coonrad/Morrey had zones reaching permanent deformation (Fig.3). For the Coonrad/Morrey, with the highest polyethylene stresses, the experimental and computational constraint profiles were similar (Fig.1-b). Discussion. The TEMA unconstrained design transferred less moment than semi-constrained designs, reducing the burden on the implant interfaces. Moreover, the TEMA design had lower stresses in the polyethylene components due to the combination of less constraint and a lack of sharp edges on the articular surfaces. For any figures or tables, please contact the authors directly

Total elbow arthroplasty (TEA) usage is increasing owing to expanded surgical indications, better implant designs, and improved long-term survival. Correct humeral implant positioning has been shown to diminish stem loading in vitro, and radiographic loosening in in the long-term. Replication of the native elbow centre of rotation is thought to restore normal muscle moment arms and has been suggested to improve elbow strength and function. While much of the focus has been on humeral component positioning, little is known about the effect of positioning of the ulnar stem on post-operative range of motion and clinical outcomes. The purpose of this study is to determine the effect of the sagittal alignment and positioning of the humeral and ulnar components on the functional outcomes after TEA. Between 2003 and 2016, 173 semi-constrained TEAs (Wright-Tornier Latitude/Latitude EV, Memphis, TN, USA) were performed at our institution, and our preliminary analysis includes 46 elbows in 41 patients (39 female, 7 male). Patients were excluded if they had severe elbow deformity precluding reliable measurement, experienced a major complication related to an ipsilateral upper limb procedure, or underwent revision TEA. For each elbow, saggital alignment was compared pre- and post-operatively. A best fit circle of the trochlea and capitellum was drawn, with its centre representing the rotation axis. Ninety degree tangent lines from the intramedullary axes of the ulna and humerus, and from the olecranon tip to the centre of rotation were drawn and measured relative to the rotation axis, representing the ulna posterior offset, humerus offset, and ulna proximal offset, respectively. In addition, we measured the ulna stem angle (angle subtended by the implant and the intramedullary axis of the ulna), as well as radial neck offset (the length of a 90o tangent line from the intramedullary axis of the radial neck and the centre of rotation) in patients with retained or replaced radial heads. Our primary outcome measure was the quickDASH score recorded at the latest follow-up for each patient. Our secondary outcome measures were postoperative flexion, extension, pronation and supination measured at the same timepoints. Each variable was tested for linear correlation with the primary and secondary outcome measures using the Pearson two-tailed test. At an average follow-up of 6.8 years (range 2–14 years), there was a strong positive correlation between anterior radial neck offset and the quickDASH (r=0.60, p=0.001). There was also a weak negative correlation between the posterior offset of the ulnar component and the qDASH (r=0.39, p=0.031), and a moderate positive correlation between the change in humeral offset and elbow supination (r=0.41, p=0.044). The ulna proximal offset and ulna stem angle were not correlated with either the primary, or secondary outcome measures. When performing primary TEA with radial head retention, or replacement, care should be taken to ensure that the ulnar component is correctly positioned such that intramedullary axis of the radial neck lines up with the centre of elbow rotation, as this strongly correlates with better function and less pain after surgery

Total shoulder arthroplasty has gone through several generations, as instruments and implant designs have given surgeons both more options in the alignment of the components and more guidance in the best choices to make. However, while the measurement of alignment has become more sophisticated, the importance of particular aspects of alignment to actual patient comfort and function has been less completely characterised. Overstuffing of the joint and proud humeral heads have been most associated with clinical failure. The efforts to avoid this can be divided into two camps: 1.) The anatomic school, who believe an experienced surgeon can divine the correct anatomy that existed before the distortions of arthritis began, and that the surgeon should make free-hand cuts and alignments to restore the normal anatomy. 2.) The cutting-guide school, who believe that average versions and positions avoid error and that soft-tissue balancing requires occasional deviations from “normal” anatomy. Reverse total shoulder replacement in contrast is a semi-constrained implant, with built-in “internal impingement” at the extremes of motion, which can cause notching and/or instability (levering out). Initial European experience favored placing the humeral component in 0 degrees, but most surgeons have gravitated toward 15–20 degrees of retroversion to allow easy conversion from/to a hemiarthroplasty as needed. Increased retroversion may block internal rotation, and increased anteversion limits external rotation

Introduction. Reverse total shoulder arthroplasty (RTSA) is a semi-constrained joint replacement with an articulating cobalt-chromium glenosphere and ultra-high molecular weight polyethylene (PE). Because of its limited load bearing, surgeons and implant manufacturers have not elicited the use of highly cross-linked PE in the shoulder, and to date have not considered excessive PE wear in the reverse shoulder a primary concern. As the number of shoulder procedures is expected to grow exponentially in the next decade, however, it is important to evaluate how new designs and bearing materials interact and to have an understanding of what is normal in well-functioning joint replacements. Currently, no in vivo investigation into RTSA PE wear has been conducted, with limited retrieval and simulation studies. In vitro and in silico studies demonstrate a large range in expected wear rates, from 14.3 mm. 3. /million cycles (MC) to 126 mm. 3. /MC, with no obvious relationship between wear rate and polyethylene diameter. The purpose of this study is to evaluate, for the first time, both volumetric and linear wear rates in reverse shoulder patients, with a minimum six-year follow-up using stereo radiographic techniques. Methods. To date, seven patients with a self-reported well-functioning Aequalis Reversed II (Wright Medical Group, Edina, MN, USA) RTSA implant system have been imaged (mean years from surgery = 7.0, range = 6.2 to 9). Using stereo radiographs, patients were imaged at the extents of their range of motion in internal and external rotation, lateral abduction, forward flexion, and with their arm at the side. Multiple arm positions were used to account for the multiple wear vectors associated with activities of daily living and the shoulder's six degrees of motion. Using proprietary software, the position and orientation of the polyethylene and glenosphere components were identified and their transformation matrices recorded. These transformation matrices were then applied to the CAD models of each component, respectively, and the apparent intersection of the glenosphere into the PE recorded. Using previously validated in-house software, volumetric and maximum linear wear depth measurements were obtained. Linear regression was used to identify wear rates. Results. The volumetric and linear wear rates for the 36 mm PE liners (n = 5) were 39 mm. 3. /y (r. 2. = 0.86, range = 24 to 42 mm. 3. /y) and 0.09 mm/y (r. 2. = 0.96, range = 0.08 to 0.11 mm/y), respectively. Only two patients with 42 mm PE liners were evaluated. For these, volumetric and linear wear rates were 110 mm. 3. /y (r. 2. = 0.81, range = 83 to 145 mm. 3. /y) and 0.17 mm/y (r. 2. = 0.99, range = 1.12 to 1.15 mm/y), respectively. Conclusion. For the first time, PE wear was evaluated in the reverse shoulder in vivo. More patients are required for conclusive statements, but preliminary results suggest first order volumetric and linear wear rates within those predicted by simulation studies. It is interesting to note the increased wear with larger PE size, likely due to the increased contact area between congruent faces and the potential for increased sliding distance during arm motion

The aim of the study was to assess the results of treating knee osteoarthrosis with total knee arthroplasty (TKA) after previous tibia and/or femur fractures resulting in axial limb deformities. Thirty-six knees (34 patients) were operated on. At the most recent follow-up, 4.8 years after surgery, all but one patient demonstrated an improvement in both clinical and functional KSS. This male patient required revision after 2 years due to tibial component aseptic loosening. Improved range of motion was generally noted, especially extension, however, two patients with both tibia and femur fractures had worse results. TKA is an effective method of treatment for patients with arthrosis after a previous femur or tibia fractures. When deformity is severe semi-constrained or constrained, implants with extensions may be necessary

Controversy remains regarding the optimal treatment for iatrogenic injury to the medial collateral ligament (MCL) during primary total knee arthroplasty (TKA). Some authors have recommended converting to a prosthesis that provides varus/valgus constraint while others have recommended primary repair. In this study we report the results of a 45 patients who sustained intra-operative MCL injuries during primary TKA that were treated with primary repair. Of 3922 consecutive primary TKA there were 48 (1.2%) intra-operative MCL lacerations or avulsions. One patient was lost and one died before 24-month follow-up. All but one patient underwent primary repair with placement of components without varus/valgus constraint. This left 45 knees with a mean follow up of 89 months (range, 24 – 214 months). The mean HSS knee scores increased from 47 to 85 points (p<0.001). No patients had subjective complaints of instability. No patients had excessive varus/valgus laxity when tested in full extension and 30 degrees of flexion. The range of motion at the time of final follow-up averaged 110 degrees (range, 85 – 130 degrees). Five knees required treatment for stiffness with 4 knees undergoing manipulation under anesthesia and 1 knee undergoing open lysis of adhesions with polyethylene articular surface exchange. Two knees underwent revision for aseptic loosening of the tibial component. In the three knees that underwent open revision, the MCL was noted to be in continuity and without laxity. Primary repair with 6 weeks of post-operative hinged bracing after iatrogenic injury to the MCL during primary TKA was successful at preventing instability although stiffness was seen in approximately 10% of patients. The increased morbidity associated with implantation of a semi-constrained or constrained implant may be unwarranted in this situation

Controversy remains regarding the optimal treatment for iatrogenic injury to the medial collateral ligament (MCL) during primary total knee arthroplasty (TKA). Some authors have recommended converting to a prosthesis that provides varus/valgus constraint while others have recommended primary repair. In this study, we report the results of 45 patients who sustained intra-operative MCL injuries during primary TKA that were treated with primary repair. Of 3922 consecutive primary TKA there were 48 (1.2%) intra-operative MCL lacerations or avulsions. One patient was lost and one died before 24 months follow up. All but one patient underwent primary repair with placement of components without varus/valgus constraint. This left 45 knees with a mean follow up of 89 months (range, 24 to 214 months). The mean HSS knee scores increased from 47 to 85 points (p<0.001). No patients had subjective complaints of instability. No patients had excessive varus/valgus laxity when tested in full extension and 30 degrees of flexion. The range of motion at the time of final follow-up averaged 110 degrees (range, 85 to 130 degrees). Five knees required treatment for stiffness with 4 knees undergoing manipulation under anaesthesia and 1 knee undergoing open lysis of adhesions with polyethylene articular surface exchange. Two knees underwent revision for aseptic loosening of the tibial component. In the three knees that underwent open revision, the MCL was noted to be in continuity and without laxity. Primary repair with 6 weeks of post-operative hinged bracing after iatrogenic injury to the MCL during primary TKA was successful at preventing instability although stiffness was seen in approximately 10% of patients. The increased morbidity associated with implantation of a semi-constrained or constrained implant may be unwarranted in this situation

Purpose. Clinical outocome of revision total elbow arthroplasty(TEA) in rheumatoid arthritis(RA) patients were evaluated. Methods. Clinical outocome of revision TEA that underwent between 2005 and 2013 were evaluated. Causes of revision, implanted revised prosthesis, a clinical score (the Japanese Orthopaedic Association (JOA) elbow assessment score), the arc of motion and complications were investigated. Totally, 6 patients underwent revision TEA. The patients were females with a mean age of 60.4 years (range, 32 to 72). Results. Seventy-two primary TEAs were done in corresponding period. Six out of 72 (8.3%) TEAs were revised. Causes of revision were loosening, instability (dislocation) and breakage of a component in 3, 2 and 1 cases, respectively. A mean duration from initial TEA to revision surgery was 10.3 years (range, 1 to 13). Semi-constrained arthroplasties (5 Coonrad-Morrey, 1 Discovery) were used for revision surgery. A mean JOA elbow assessment score improved from 59 to 81 point at the time of follow up. The mean ROM, flexion was improved 125 degrees, to 131 degrees. Extension, supination and pronation was not changed. A fracture at the time of implant withdrawal occurred as an intraoperative complication. The fractures were recovered by wiring with autologous bone graft from the ilium and a good bone union was achieved in 2 out of 3 cases. However, a re-revision surgery with plate was required in the remaining case. Conclusions. Revision TEA provided a satisfactory functional outcome. An intraoperative fracture was a critical complication in this procedure

In primary TKA, non- or semi-constrained TKA implants might have their limitations in the absence of collateral ligaments, severe deformity, large osseous defects and gross flexion-extension instability. Although most primary TKA indications can be solved with modular, non-hinged implants, an adequate balancing might require a relevant soft tissue release. This consequently adds complexity and operative time with less predictable results in the elderly patient. The current literature reporting on short- to mid-term results of rotating hinged implants in primary osteoarthritis shows some quite diverse results and consequently different interpretations of this implant type in primary knee arthroplasty. Although some authors were able to show good and excellent clinical results in 91% of patients and consequent survival rates of a rotating hinge implant after 15 years up to 96% in primary indications, others found high complication rates of up to 25% of all operated patients, which remains unclear for us and is inconsistent with our clinical results in primary and revision TKA in over 30 years of experience with the ENDO-Model rotating hinge implant. Our potential indications in the elderly for a rotating or pure hinged implant in primary TKA include: Complete MCL instability; Severe varus or valgus deformity (>20 degrees) with necessary relevant soft tissue release; Relevant bone loss including insertions of collaterals; Gross flexion-extension gap imbalance; Ankylosis; One staged implantation with specific antibiotics after PJI. Due to general limited soft tissues or hyperlaxity, patients with neuropathic joints, or lack of extensor mechanism should be considered for a complete hinged implant. The ENDO-model hinge has only been minimally adapted since its development in the 70´s, including fully cemented long stems, in modular and non-modular versions. We strictly reserve a rotational hinge in primary indications for patients >70 years with a combined varus alignment, whereas in severe valgus deformities, a complete hinged implant version should be used for our implant design

Thirty years ago, rotator cuff surgery was exceedingly uncommon and shoulder arthroplasty almost unknown. Surgery for shoulder instability was largely empirical, non-anatomical and frequently unsuccessful. With the help of arthroscopy and MR scanning, a complex array of labral, ligament and tendon pathologies can now be recognised and treated, precisely and predictably. Anatomy-restoring arthroscopic techniques have largely replaced open stabilisation surgery. As life expectancy rises and citizens remain active into their seventh and eighth decades, the call for rotator cuff surgery has risen dramatically. Complex tendon transfers have expanded the indications for cuff surgery. Open repair has in part been supplanted by increasingly sophisticated arthroscopic techniques. The potential use of orthobiologics and stem cells promises further advances in the foreseeable future. Following the successful development of humeral hemiarthroplasty, and later of total shoulder replacement, surgical techniques and clinical indications for arthroplasty are now well refined. Predictable outcomes have been further enhanced by the present generation of ‘anatomic’ prostheses. More recently, the ‘rediscovery’ and improvement of semi-constrained (reverse) prostheses has transformed the previously dismal outlook for sufferers of cuff arthropathy and similar conditions. Many Australian Orthopaedic Association trainees undertake post-specialisation fellowships in shoulder surgery, both at home and abroad, and there is a steady flow of young overseas fellows through Australian shoulder units. The Shoulder and Elbow Society of Australia, founded in 1990 as a loose grouping of interested colleagues, now boasts over 70 active members. Australian surgeons and researchers are well represented in the prestigious Journal of Shoulder and Elbow Surgery and Australian shoulder surgery has come of age

The Mathys. ¯. finger joint replacement system offers a novel fixation method into the proximal and distal medullary canals and a semi-constrained articulation. This comprises a separable, form-fit joint with a distal/proximal play of 0.7 mm, a lateral excursion of 10°, and rotation of up to 6°. This has theoretical advantages of increased radio-ulnar stability, preventing ulnar drift in patients with rheumatoid disease, and enhanced osseointegration offering implant longevity. In our unit, however, high failure rates were noted, prompting a review of cases to quantify our suspicions. Case notes of all patients who underwent finger joint replacement using the Mathys. ¯. implant between 1999 and 2005 were retrieved. Twenty-two devices were implanted by a single surgeon during this period. Four were in finger proximal interphalangeal joints, 17 in finger metacarpophalangeal joints and one in a thumb carpometacarpal joint (CMCJ). Indications for joint replacement included sixteen for rheumatoid arthritis (RA) and five for post-traumatic joint problems. The only thumb CMCJ was replaced for primary osteoarthritis. Patients were reviewed regularly and implant performance assessed critically along with survival of the implant to revision, infection or death of the patient. Mean follow up was 30 months. Sixteen implants failed including the only thumb CMCJ. Modes of failure were rotation (11), poor range of motion (two), infection (two) and dislocation (the CMCJ). Similar ball and socket designs for uncemented thumb CMCJ replacement, such as the Ledoux prosthesis, have previously shown poor survival and have been withdrawn from the market. Of the finger implants in RA patients (n=16), 12 implants failed of which ten were due to rotation. Time to failure ranged from two to 48 months (mean 15 months). The authors do not recommend the use of this implant, especially in cases of rheumatoid arthritis

Introduction and aims. Recently many implants for ankle arthroplasty have been developed around the world, and especially some mobile bearing, three-component implants have good results. Nevertheless, at our institution fixed two-component, semi-constrained alumina ceramic total ankle arthroplasty (TAA) with TNK Ankle had been performed since 1991 and led to improved outcomes. We report clinical results and in vivo kinematic analyses for TNK Ankle. Method. Between 1991 and 2006, total ankle arthroplasties with TNK Ankle were performed with 102 patients (106 ankles) with osteoarthritis at our institution. There were 91 women and 11 men. The mean age was 69 years and mean follow-up was 5.4 years. These cases were evaluated clinically and radiographically. Besides in vivo kinematics, in TNK Ankle was analysed using 3D-2D model registration technique with fluoroscopic images. Between 2007 and 2008, prospectively ten TAA cases examined with fluoroscopy at postoperative one year. Results. In clinical results, excellent were 48 cases, good were 31 cases, fair were 10 cases, poor were nine cases, and death and loss to follow-up were 10 cases. Reoperations are performed on eight cases, one was arthrodesis, seven were talar component revision or talar revision with ceramic whole talus prosthesis. TNK Ankle have the rough surfaces by beadworks, and added surface treatment with hydroxyapatite granules, calcium phosphate paste or tissue engineered mesenchymal cells. Recently, only talar components were fixed with bone cement. Loosening has been more frequent in talar than tibial, whereas no reoperation was on cemented talar component cases. According to 3D-2D model registration, both components rotated a little each other and the contact region between both components variously sifted during weight bearing flexion of ankle. It was supposed that replaced position and angle of components concerned with the contact region. Conclusions. TAA with TNK Ankle have led to better results with improvement for surface treatments. Kinematics of ankle prostheses was derived by 3D-2D model registration, more appropriate position and angle to replace

Non- or semi-constraint TKA implants do have their limitations in the absence of collateral ligaments, severe deformity, large osseous defects and gross flexion - extension instability or mismatch, even in primary TKA. Additionally instability is increasingly recognised as a major failure factor in primary and revision TKA. Historically most of the first pure hinged TKA implants have shown disappointing results, due to early loosening based on excessive force transmission from the hinge mechanism to the bone-cement interface, used the use of all metal articulation, suboptimal instrumentation or design. Consequently a hinged design was abandoned by most US surgeons. However, some European centres continued with the use of some early European designed pure- and rotating hinged implants. Although most indication in primary TKA can be solved with modular non- or semi-constrained implants, an adequate balancing might require a relevant soft tissue release or reconstruction with allografts. This consequently increases the complexity and operative time with less predictable results in the elderly patient with principal less healing potential, desirable early post-operative full weightbearing and full range of motion. Thus potential indications in the elderly for a rotating- or pure hinged implant in primary TKA include: . –. Complete MCL instability. –. Severe varus or valgus deformity (>25°) with necessary relevant soft tissue release. –. Relevant bone loss with insertions of collaterals. –. Gross flexion-extension in balance. –. Post-traumatic with distal femur or proximal tibia fracture. –. Stiff knee. –. Severe osteoporosis in the old patient. –. Post infectious for a one staged implantation with specific antibiotics in cement. While some authors showed excellent survival rates in of 96% after 15 years in primary TKA, some recent studies revealed high complication rates of up to 25%, including a high infection rate of 2.9%. This remains inconsistent with our clinical results in primary TKA, which revealed an overall survival rate in patients over 60 years of 94% after 13 years, while patients < 60 years revealed a survival rate of only 77%. Correlation between survival rate and deformity revealed in varus alignment a survival rate of 97%, whereas in valgus only a rate of 79%. Consequently we strictly reserve a rotational hinge for patients > 60 years with a combined varus alignment, whereas in severe valgus deformities a pure hinged should be used for our implant design. Limitations of most hinged implants are relatively rare. In our hands the main limitation is hyperextension and weak extensor mechanism, because this leads to early loosenings

Introduction:. Reverse total shoulder arthroplasty (RTSA) has become instrumental in relieving pain and returning function to patients with end-stage rotator cuff disease. A distalized and medialized center of rotation in addition to a semi-constrained implant design allows the deltoid to substitute for the non-functioning rotator cuff. The purpose of this study was to examine the relationship between specific deltoid and rotator cuff muscle parameters and functional outcomes following RTSA. Methods:. Patients undergoing RTSA by a single surgeon were enrolled in a prospective, IRB approved RTSA outcomes registry. Inclusion criteria were diagnosis of cuff tear arthropathy or massive rotator cuff tear, a minimum 2-year follow-up, and a preoperative shoulder MRI. We excluded patients undergoing revision arthroplasty, fracture, and a history of previous open shoulder surgery. For the 28 patients meeting our criteria, the cross-sectional area (CSA) of the anterior, middle, and posterior deltoid were measured on an axial MRI (Figure 1). Fatty infiltration (FI) of the deltoid, supraspinatus (SS), infraspinatus (IS), teres minor, and subscapularis were assessed on sagittal T1-MRI quantitatively via image processing and qualitatively on the 5-point Fuchs scale by a fellowship-trained musculoskeletal radiologist. Outcome measures included active forward elevation (aFE), active external rotation (aER), active internal rotation (aIR), strength in abduction, Constant-Murley score (CMS), Subjective Shoulder Value (SSV), Visual Analogue Scale (VAS) pain, and American Shoulder and Elbow Surgeons (ASES) total and ASES activities of daily living (ADL) scores as assessed by a trained, clinical research nurse. Correlation of deltoid CSA and FI with outcomes measures was analyzed with a Spearman rank correlation coefficient (ρ) with significance at P < .05. Results:. The correlations between preoperative deltoid size and quantitative deltoid FI to postoperative function are shown in Table 1. The total deltoid CSA showed the most significant, positive correlations with outcome measures. The anterior deltoid CSA showed the strongest correlation to postoperative strength in abduction. Quantitative FI of the deltoid was negatively associated with several outcome measures (Table 1). Quantitative FI of the SS and IS demonstrated a significant negative correlation with aER (ρ = −.732, P = .039 and ρ = −.790, P = .004, respectively). The grade of FI, as assessed using the Fuchs scale, did not correlate to any clinical outcome data. Discussion and Conclusion:. Preoperative deltoid size and FI of the deltoid and the rotator cuff muscles correlate to 2-year functional outcomes following RTSA. The anterior, posterior, and total CSA of the deltoid had significant, positive associations with several outcome measures, whereas FI of the deltoid, SS, and IS had significant, negative associations, particularly with humeral rotation. In the future, optimization of deltoid and rotator cuff muscle function preoperatively may improve functional outcomes in RTSA

Introduction. Total knee arthroplasty (TKA) prostheses are semi-constrained artificial joints. Femorotibial constraint is a key property of a TKA prosthesis and should be designed to match the device's intended function. Cruciate Retaining (CR) prostheses are usually used for patients with a functioning posterior cruciate ligament (PCL). For patients without a fully functioning PCL, CR-Constrained (CRC) prostheses may be used. A CRC tibial insert usually has a more conforming sagittal profile especially in the anterior aspect to provide increased constraint to prevent paradoxical femoral translation during knee flexion. A quantitative understanding of the constraint behavior of a prosthesis design is critical to ensure its functional outcome. Using a validated computer simulation, this study evaluated the anterior-posterior (AP) constraint of two types of tibial inserts (CR and CRC) from a same TKA product family. Methods. Both the CR and CRC prostheses are from the same TKA product family (Optetrak Logic, Exactech, USA). Three sizes (sizes 1, 3, and 5) from each product line were included in this study. Computer simulations using finite element analysis (FEA) were performed at 0° flexion per ASTM F1223 standard [1] (Figure 1). The simulation has been validated with physical testing (more details submitted in a separate abstract to ISTA 2013). Briefly, FEA models were created with all materials considered linear elastic. The tibial baseplate was distally fixed and a constant compressive force (710 N) was applied to the femoral component. Nonlinear Surface-Surface-Contact was established at the articulating surfaces. A coefficient of friction of 0.1 was assumed for all articulations [2]. The femoral component was driven under a displacement-controlled scheme to slide along AP direction on the tibial insert. Constraint force occurring at the articulation was derived from the reaction force at the distal fixation. A nonlinear FEA solver was used to solve the simulations. Results. The force-displacement curves predicted by the simulation exhibited the hysteresis loop appearance for both CR and CRC inserts (Figure 2). The anterior aspect of the CRC curves showed a steeper raise than the CR curves, and the trend was consistent across sizes. Taking the slope from 0 to 5 mm range, the anterior constraint of the CRC insert was significantly greater than the CR insert, while the posterior constraint of the CRC insert was also slightly greater (Figure 3). Discussion/Conclusion. The increased AP constraint of the CRC insert revealed in the study is consistent with the design geometry and functional intent of the device. With a much increased anterior lip, the CRC insert is expected to provide substantially greater anterior constraint than the CR insert to prevent paradoxical femoral translation for patients without a fully functioning PCL. The CRC insert is also expected to provide slightly increased posterior constraint due to its gently elevated posterior lip. This study quantitatively demonstrated the effect of design geometry on the outcome constraint function of different TKA prostheses

Introduction. Ideally, a patient receiving a unicondylar knee replacement will have fully functional anterior and posterior cruciate ligaments. When at least one of the cruciate ligaments is not fully functional, femoral and tibial implant contact position can potentially increase along the anterior-posterior (AP) axis. Where unicondylar implant wear testing typically uses AP resistance assuming fully functional cruciate ligaments, the authors used reduced AP resistance intended to simulate deficient cruciate ligaments. Methods. Optetrak Logic® Uni (Exactech Inc, Gainesville, FL USA) unicondylar test specimens featuring an all-UHMWPE tibial component and a cobalt chromium femoral component were used in this study. The system has a semi-constrained articular geometry. Testing was conducted at an independent testing facility (EndoLab GMBH, Thansau, Rosenheim, Germany). A four-station knee simulator was used (EndoLab knee simulator) with two unicondylar knee implants per station, giving a total of eight test specimens. Two different tibial fixation designs (keeled and peg) with identical articulating surfaces were tested. Tibial test specimens were 6 mm in thickness. Unloaded soak controls were stored in distilled water at 37°C. The test was conducted according to ISO 14243–1: 2009 [1]. Test specimens were immersed in calf serum (PAA GmBH, Cölbe, LOT B00111-5126) with a protein content of 20 g/l. Custom polyurethane molds allowed for individual component measurement. Per the ISO 14243-1, a 7% medial offset was incorporated into the set-up. The unicondylar knee implants were set at neutral position in extension. Tibial rotational restraint was 0.36 Nm/° and zero when the test specimen was within ± 6° of the reference position. This test was conducted with an AP resistance of 9.3N/mm to maximize AP displacement and simulate deficient cruciate ligaments. Typical unicondylar knee wear testing is conducted with an AP resistance of 44N/mm, which assumes functional cruciate ligaments. Results. Wear data was separated by component design (keeled and peg) as well as for medial and lateral placement [Table 1]. There was no significant difference between lateral components but there was for medial components. This difference could be due to the small sample size. Contact area of the UHMWPE tibial components was elliptical, with the longer portion along the AP axis. Mean wear rates were comparable to historical unicondylar knee systems tested at the same laboratory using the standard AP resistance (i.e., 44 N/mm). Discussion/Conclusion. This study demonstrated using an AP resistance 9.3 N/mm to simulate the presence of deficient cruciate ligaments in a unicondylar knee wear test produced similar wear rates and greater AP displacement when compared to testing using an AP resistance of 44 N/mm, which assumes functioning ligaments. This being said, design and material information about historical unicondylar knee systems tested are not known, so a direct comparison cannot be made. Performing unicondylar knee wear tests with reduced AP resistance could provide realistic wear information for devices implanted in patients without fully functioning cruciate ligaments

Introduction. Total knee arthroplasty (TKA) prostheses are semi-constrained artificial joints. A well-functioning TKA prosthesis should be designed with a good balance between stability and mobility, meaning the femorotibial constraint of the artificial joint should be appropriate for the device's function. To assess the constraint behavior of a TKA prosthesis, physical testing is typically required, and an industrial testing standard has been developed for this purpose [1]. Computer simulation has become increasingly useful in many industries, including medical device research and development where finite element analysis (FEA) has been extensively used in stress analysis and structural evaluation. This study presents an FEA-based simulation to evaluate the femorotibial constraint behavior of TKA prosthesis, and demonstrated the effectiveness of the method by validating through physical testing. Methods. A Cruciate Retaining (CR) TKA prosthesis design (Optetrak Logic CR, Exactech, USA) was used in this study. CAD models of the implants assembled at 0° of flexion were used for the simulation. Finite element models were generated using with all materials assumed linear elastic. Boundary conditions were set up according to the ASTM F1223 standard (Figure 1). The tibial baseplate was fixed distally. A constant compressive force (710 N) was applied on the femoral component. Nonlinear Surface-Surface-Contact was defined at the femorotibial articulating surfaces. Coefficient of friction was determined from physical test. The femoral component was driven under a displacement-controlled scheme to slide along the anterior-posterior (AP) direction on the tibial insert. At each time step, constraint force occurring at the articulating surface was derived from the reaction force at the distal fixation of the tibial baseplate. A nonlinear FEA solver (NX Nastran SOL601, Siemens, USA) was used to solve the simulation. In addition, five samples of the prostheses were physically tested, and the results were compared with the simulation. Results. The simulation successfully captured the movement of contact location and pressure along the movement of the femoral component (Figure 2). The force-displacement curve predicted by the simulation exhibited a very close hysteresis loop profile as the results of physical testing (Figure 3). Using the curve slope from 0 to 5 mm to characterize the linear constraint, the simulation predicted 45.7 N/mm anteriorly and 36.4 N/mm posteriorly, which are less than 10% different from the physical testing results (46.4 N/mm anteriorly and 39.6 N/mm posteriorly). Discussion/Conclusion. This study demonstrated that the simulation was able to closely predict the femorotibial constraint behavior of the TKA prosthesis under ASTM F1223 testing. The simulation results resembled the physical testing results not only in the general curve profile but also in the magnitude of slope values. The increased difference at the far anterior region could be related to the fact that no material nonlinearity was currently considered, which could be improved in future studies. A validated simulation method could be very useful in TKA prosthesis design. Since no physical prototypes are required, design evaluation and optimization can be achieved in a much easier and faster manner

Implant designs for hip and knee arthroplasty have undergone a continual improvement process, but development of implants for total elbow arthroplasty (TEA) have lagged behind despite the marked mechanical burden placed on these implants. TEA is not as durable with failure rates approaching thirty percent at five years. The Coonrad-Morrey (Zimmer, Warsaw, IN), a linked design, remains the standard-bearer, employing polyethylene bushings through which a metal axle passes. A common failure mode is bushing wear and deformation, causing decreased joint function as the bushing-axle constraint decreases and osteolysis secondary to release of large volumes of wear debris. Improving upon this poor performance requires determining which factors most influence failure, so that failure can be avoided through design improvements. The approach integrates clinical observations of failed TEAs with implant retrieval analysis, followed by measurements of loads across the elbow for use in stress analyses to assess the performance of previous designs, and, finally, new design approaches to improve performance. Examination of the clinical failures of more than seventy Coonrad-Morrey TEAs revealed patterns of decreased constraint and stem loosening. Implant retrieval analysis from more than thirty of these cases showed excessive bushing deformation and wear and burnishing of the fixation stems consistent with varus moments across the joint. To determine loads across the elbow, motion analysis data were collected from eight TEA patients performing various activities of daily living. The kinematic data were input into a computational model to calculate contact forces on the total elbow replacement. The motion that produced the maximum contact force was a feeding motion with the humerus in 90° of abduction. For this motion, the joint reaction forces and moments at the point of maximum contact were determined from a computational model. We applied these loads to numerical models of the articulating bushings and axle of the Coonrad-Morrey to examine polyethylene strains as measures of damage and wear. Strain patterns in response to the large varus moment applied to the elbow during feeding activities showed extensive plastic deformation in the locations at which deformation and wear damage were observed in our retrieved implants (Fig. 1). Finally, we examined a new semi-constrained design concept intended to meet two goals: transfer contact loads away from the center of the joint, thus allowing contact to provide a larger internal moment to resist the large external varus moment; and reduce polyethylene strains by utilizing curved contacting surfaces on both the axle and the bushings (Fig. 2). After a sensitivity analysis to determine optimal dimensional choices (e.g., bushing and axle radii), we compared the resulting polyethylene strains between the Coonrad-Morrey and new design at locations that experienced the largest strains (Fig. 3). Substantial decreases were achieved, suggesting far less deformation and wear, which should relate to marked improvements in performance. Currently, we are incorporating this new design concept, along with alterations in stem design achieved from examination of load transfer at the fixation interfaces based on the same loading conditions, to achieve an implant system intended to improve the performance of TEA