Patients receiving reverse total shoulder arthroplasty (RTSA) often have osseous erosions because of glenohumeral arthritis, leading to increased surgical complexity. Glenoid implant fixation is a primary predictor of the success of RTSA and affects micromotion at the bone-implant interface. Augmented implants which incorporate specific geometry to address superior erosion are currently available, but the clinical outcomes of these implants are still considered short-term. The objective of this study was to investigate micromotion at the glenoid-baseplate interface for a standard, 3 mm and 6 mm lateralized baseplates, half-wedge, and full-wedge baseplates. It was hypothesized that the mechanism of load distribution from the baseplate to the glenoid will differ between implants, and these varying mechanisms will affect overall baseplate micromotion. Clinical CT scans of seven shoulders (mean age 69 years, 10°-19° glenoid inclinations) that were classified as having E2-type glenoid erosions were used to generate 3D scapula models using MIMICS image processing software (Materialise, Belgium) with a 0.75 mm mesh size. Each scapula was then repeatedly virtually reconstructed with the five implant types (standard,3mm,6mm lateralized, and half/full wedge; Fig.1) positioned in neutral version and inclination with full backside contact. The reconstructed scapulae were then imported into ABAQUS (SIMULIA, U.S.) finite element software and loads were applied simulating 15°,30°,45°,60°,75°, and 90° of abduction based on published instrumented in-vivo implant data. The micromotion normal and tangential to the bone surface, and effective load transfer area were recorded for each implant and abduction angle. A repeated measures ANOVA was used to perform statistical analysis. Maximum normal micromotion was found to be significantly less when using the standard baseplate (5±4 μm), as opposed to the full-wedge (16±7 μm, p=0.004), 3 mm lateralized (10±6 μm, p=0.017), and 6 mm lateralized (16±8 μm, p=0.007) baseplates (Fig.2). The half-wedge baseplate (11±7 μm) also produced significantly less micromotion than the full-wedge (p=0.003), and the 3 mm lateralized produced less micromotion than the full wedge (p=0.026) and 6 mm lateralized (p=0.003). Similarly, maximum tangential micromotion was found to be significantly less when using the standard baseplate (7±4 μm), as opposed to the half-wedge (12±5 μm, p=0.014), 3 mm lateralized (10±5 μm, p=0.003), and 6 mm lateralized (13±6 μm, p=0.003) baseplates (Fig.2). The full wedge (11±3 μm), half-wedge, and 3 mm lateralized baseplate also produced significantly less micromotion than the 6 mm lateralized (p=0.027, p=012, p=0.02, respectively). Both normal and tangential micromotion were highest at the 30° and 45° abduction angles (Fig.2). The effective load transfer area (ELTA) was lowest for the full wedge, followed by the half wedge, 6mm, 3mm, and standard baseplates (Fig.3) and increased with abduction angle. Glenoid baseplates with reduced lateralization and flat backside geometries resulted in the best outcomes with regards to normal and tangential micromotion. However, these types of implants are not always feasible due to the required amount of bone removal, and medialization of the bone-implant interface. Future work should study the acceptable levels of bone removal for patients with E-type glenoid erosion and the corresponding best implant selections for such cases. For any figures or tables, please contact the authors directly

Reverse shoulder arthroplasty (RSA) is commonly used to treat patients with rotator cuff tear arthropathy. Loosening of the glenoid component remains one of the principal modes of failure and is the main complication leading to revision. For optimal RSA implant osseointegration to occur, the micromotion between the baseplate and the bone must not exceed a threshold of 150 µm. Excess micromotion contributes to glenoid loosening. This study assessed the effects of various factors on glenoid baseplate micromotion for primary fixation of RSA. A half-fractional factorial experiment design (2k-1) was used to assess four factors: central element type (central peg or screw), central element cortical engagement according to length (13.5 or 23.5 mm), anterior-posterior (A-P) peripheral screw type (nonlocking or locking), and bone surrogate density (10 or 25 pounds per cubic foot [pcf]). This created eight unique conditions, each repeated five times for 40 total runs. Glenoid baseplates were implanted into high- or low-density Sawbones™ rigid polyurethane (PU) foam blocks and cyclically loaded at 60 degrees for 1000 cycles (500 N compressive force range) using a custom designed loading apparatus. Micromotion at the four peripheral screw positions was recorded using linear variable displacement transducers (LVDTs). Maximum micromotion was quantified as the displacement range at the implant-PU interface, averaged over the last 10 cycles of loading. Baseplates with short central elements that lacked cortical bone engagement generated 373% greater maximum micromotion at all peripheral screw positions compared to those with long central elements (p < 0.001). Central peg fixation generated 360% greater maximum micromotion than central screw fixation (p < 0.001). No significant effects were observed when varying A-P peripheral screw type or bone surrogate density. There were significant interactions between central element length and type (p < 0.001). An interaction existed between central element type and level of cortical engagement. A central screw and a long central element that engaged cortical bone reduced RSA baseplate micromotion. These findings serve to inform surgical decision-making regarding baseplate fixation elements to minimize the risk of glenoid loosening and thus, the need for revision surgery

Introduction. Model-based radiostereometric analysis (MBRSA) allows the in vivo measurement of implant loosening (i.e. migration) from a host bone by acquiring a pair of biplanar radiographs of the patient's implant over time. Focusing on total knee replacement patients, the accuracy of MBRSA in calculating tibial baseplate migration depends on the accuracy in registering a 3D model onto the biplanar radiographs; thus, the shape of the baseplate and its orientation relative to the imaging planes is pertinent. Conventionally, the baseplate coordinate system is aligned with the laboratory coordinate system, however, this reference orientation is unnecessary and may hide unique baseplate features resulting in less accurate registration (Figure 1). Therefore, the primary objective of this study was to determine the optimal baseplate orientation for improving accuracy during MBRSA, and an acceptable range of orientations for clinical use. A second objective was to demonstrate that a custom knee positioning guide repeatably oriented the baseplate within the acceptable range of orientations. Materials and Methods. A tibia phantom consisting of a baseplate rigidly fixed to a sawbone was placed in 24 orientations (combination of six rotations about X (i.e. knee flexion) and four rotations about Z (i.e. hip abduction)) with three pairs of radiographs acquired at each orientation. The radiographs were processed in MBRSA software, and the mean maximum total point motion (MTPM), an indicator of bias error during model registration, was plotted as a function of the two rotations to determine the optimal orientation and a range of acceptable orientations (Figure 2). A custom knee positioning guide was manufactured with the goal of orienting the baseplate close to the optimal orientation and within the acceptable range of orientations (Figure 3). Ten independent pairs of biplanar radiographs were acquired by repeatedly placing a knee model in the knee positioning guide, and the images were processed in MBRSA software to determine the baseplate orientation. Results and Discussion. Results showed an 85% decrease in bias error between the reference orientation (i.e. no rotation) and the optimal orientation (10° rotation about X and 5° rotation about Z). An acceptable range of orientations from 5° − 20° rotation about an axis perpendicular to the sagittal imaging plane and from 5° − 15° rotation about an axis perpendicular to the coronal imaging plane was defined as these orientations decreased the bias error by more than 50%. Additionally, the custom knee positioning guide controlled the mean orientation ± one standard deviation within the acceptable range of orientations. Conclusions. The accuracy of MBRSA is significantly improved if the tibial baseplate is placed in the range of acceptable orientations as opposed to the conventional reference orientation. A custom knee positioning guide can be used during a clinical study to repeatably position the patient's knee within the range of acceptable orientations. For any figures or tables, please contact the authors directly

Reverse total shoulder arthroplasty (RTSA) has a proven track record as an effective treatment for a variety of rotator cuff deficient conditions. However, glenoid erosion associated with the arthritic component of these conditions can present a challenge for the shoulder arthroplasty surgeon. Options for treatment of glenoid wear include partial reaming with incomplete baseplate seating, bony augmentation using structural or impaction grafting techniques, and augmented baseplates. Augmented components have the advantage of accommodating glenoid deformity with a durable material and also ream less subchondral bone; both of which may offer an advantage over traditional bone grafting. Biomechanical and early clinical studies of augmented glenoid baseplates suggest they are a reasonable treatment option, though posteriorly augmented baseplates have shown better performance than superiorly augmented implants. However, there are no mid- or late-term studies comparing augmented baseplates to bone grafting or partial reaming. We present a live surgical demonstration of RTSA for a patient with advanced glenoid erosion being treated with an augmented glenoid baseplate that can be dialed in the direction of any deformity (superior, posterior, etc.). This versatility allows the surgeon to place the augment in any direction and is not confined to the traditional concepts of glenoid wear in a single vector. Clearly, longer term follow up studies are needed to determine the ultimate effectiveness of these devices in treating glenoid deformity in RTSA

Introduction. Little guidance exists regarding the minimum screw length and number necessary to achieve fixation with reverse shoulder arthroplasty (rTSA). The goal of this study is to quantify the pre- and post-cyclic baseplate displacements associated with two baseplate designs of different sizes using multiple screw lengths and numbers in a low density polyurethane bone substitute model. Methods. The test was conducted according to ASTM F 2028–17. The baseplate displacements of standard and small reverse shoulder constructs (Equinoxe, Exactech, Inc.) were quantified in a 15pcf polyurethane block (Pacific Research, Inc.) before and after cyclic testing with an applied load of 750N for 10,000 cycles. Baseplates were constructed using 2 or 4 screws with 3 different poly-axial locking compression screw lengths: 4.5×18mm, 4.5×30mm, and 4.5×46mm. Five of each configuration were tested for a total of 30 specimens for each baseplate. A two-tailed, unpaired student's t-test (p<0.05) compared baseplate displacements before and after cyclic loading in both the superior-inferior (S/I) and anterior-posterior (A/P) directions. The standard and small results were then compared. Results. All standard and small reverse glenoid baseplates remained well-fixed after cyclic loading in the low-density bone substitute model regardless of screw length or number. The average pre- and post-cyclic displacement for baseplates with 2 screws was significantly greater than that of baseplates with 4 screws in both the A/P and S/I directions. The average pre- and post-cyclic displacements for baseplates with 18mm screws were significantly greater than baseplates with 46mm screws in the A/P and S/I directions, post-cyclic displacement with 18mm screws was significantly greater than with 30mm screws in the A/P and S/I directions, and post-cyclic displacement with 30mm screws was significantly greater than with 46mm screws in the S/I direction only. Few differences in fixation were observed between baseplate sizes. Statistically significant difference was reached for post cyclic S/I displacement for 30mm (small baseplate superior) and 46mm screws (standard baseplate superior). Discussion and Conclusions. The results demonstrate that rTSA glenoid displacement is impacted by both the number and length of screws for both standard and small baseplate sizes. Regardless of the number of screws, the use of longer screws was associated with significantly better initial fixation. Additionally, the use of more screws was associated with significantly better fixation irrespective of screw length in the A/P direction. None of the tested devices catastrophically failed, demonstrating that adequate fixation can be achieved with as little as two 18mm screws for the baseplates utilized. However, this screw configuration was associated with the largest pre- and post-cyclic displacements, so it is assumed to be at a greater risk for aseptic loosening. If using 4 screws is not feasible in a given case, the results suggest that using longer screws can be used to improve fixation. The results of the small and standard baseplates were comparable for the given lengths and quantities of screws, suggesting that the reduced surface area of the small baseplate has no detrimental impact on fixation. Care should be made when extrapolating these results to glenoid defects. For any figures or tables, please contact authors directly

Purpose. Total knee replacement is the one of the most performed surgeries. However, patient's satisfaction rate is around 70–90 % only. The sacrifice of cruciate ligament might be the main reason, especially in young and active patients. ACL stabilizes the knee by countering the anterior displacing and pivoting force, absorbs the shock and provides proprioception of the knee. However, CR knees has been plagued by injury of PCL during the surgery and preservation of the ACL is a demanding technique. Stiffness is more common comparing to PS designed knee. To insert a tibial baseplate with PE is usually thicker than 8 mm comparing to 2–4 mm of removed tibial bone. The stuffing of joint space may put undue tension on preserved ACL and PCL. Modern designed BCR has been pushed onto market with more sophisticated design and instrumentation. However, early results showed high early loosening rate. Failure to bring the tibia forward during cementing may be the main cause. The bone island where ACL footprint locates is frequently weak, intraoperative fracture happens frequently. A new design was developed by controlled elevation and reattachment of the ACL footprint to meet all the challenges. Method. A new tibial baseplate with a keel was designed. The central part of the baseplate accommodates elevated bony island with ACL footprint. The fenestrations at the central part is designed for reattachment of bony island under proper tension with heavy sutures and fixed at anterior edge of the baseplate in suture bridge fashion and also for autograft to promote bony healing after reattachment. The suture bridge method has been used by arthroscopists for ACL avulsion fracture without the need of immobilization. The elevation of bony island release the tension in the ACL which come from stuffing of baseplate and PE insert and greatly facilitate cementing of the baseplate. The keel improve the weakness of traditional U shape design of BCR knees. Instead of keeping the bony island intact by separately cutting the medial and lateral tibial plateau in BCR knees in the past, we choose to saw the tibial plateau in one stroke as in PS knees, then removes the two condyles. The bony island includes the footprint both ACL and PCL. The central part of tibial baseplate will push the bony island upward which release the undue tension in the cruciate ligaments. Summary. We proposed a new solution for the kinematic conflict in the present bi-cruciate knee designs by elevation and re- attachment of bony island with ACL footprint at the same time simplify the ACL preservation. The simple tibial cutting procedure also facilitate the process. The technique protects PCL from injury during tibial bone cutting in CR knees. We believe the new BCR design has the potential to replace CR knee in term of function and longevity in the future

Background. Use of a baseplate with a smaller diameter in reverse shoulder arthroplasty has been recommended, especially in patients with a small glenoid or insufficient bony stock due to severe glenoid wear. However, effect of a smaller baseplate on stability of the glenoid component has not been evaluated. The purpose of this study was to determine whether a smaller baseplate (25 mm) is beneficial to the initial primary stability of the glenoid component compared to that with a baseplate of a commonly used size (29 mm) by finite element analysis. Methods. Computed tomography (CT) scans of fourteen scapulae were acquired from cadavers with no apparent deformity or degenerative change. Glenoid diameter corresponding to the diameter of the inferior circle of glenoid was measured using a caliper and classified into the small and large glenoid groups based on 25mm diameter. CT slices were used to construct 3-dimensional models with Mimics (Materialise, Leuven, Belgium). A corresponding 3D Tornier Aequalis® Reversed Shoulder prosthesis model was generated by laser scanning (Rexcan 3D Laser Scanner, Solutionix, Seoul, Korea). Glenoid components with 25mm and 28mm diameter of the baseplate were implanted into the scapular of small and large glenoid group, respectively. Finite element models were constructed using Hypermesh 11.0 (Altair Engineering, Troy, MI, USA) and a reverse engineering program (Rapidform 3D Systems, Inc., Rock Hill, SC, USA). Abaqus 6.10 (Dassault Systemes, Waltham, MA) was used to simulate 30. o. , 60. o. , and 90. o. glenohumeral abduction in the scapular plane. Single axial loads of 686N (1 BW) at angles of 30. o. , 60. o. , and 90. o. abduction were applied to the center of the glenosphere parallel to the long axis of the humeral stem. Relative micromotion at the middle and inferior thirds bone–glenoid component interface, and distribution of bone stress under the glenoid component and around the screws were analyzed. Wilcoxon's rank-sum test was used for statistical comparison and p < 0.05 was considered as a minimum level of statistical significance. Results. In small glenoid group, micromotion at the middle and inferior thirds of the glenoid-glenosphere interface at angles of 30. o. and 60. o. abduction were significantly greater in the 29mm baseplate than in the 25mm baseplate. There was no significant difference in micromotion at angle of 90. o. abduction between 25mm and 29mm baseplate. In large glenoid group, there was no statistically significant difference in micromotion between 25mm and 29mm baseplate at all angles of abduction. In small glenoid group, maximum bone stress was measured at the point of cortical engagement of the inferior screw and was statistically greater in the 29mm baseplate than in the 25mm baseplate. In large glenoid group, there was no statistically significant difference of maximum bone stress around the inferior screw between 25mm and 29mm baseplates. Conclusions. Use of a baseplate with a smaller diameter (25 mm) in reverse shoulder arthroplasty is suitable for improving the primary stability of the glenoid component, especially in small glenoid

Introduction. Proper positioning of the baseplate and optimal screw placement are necessary to avoid loosening or failure of the glenoid component in RTSA. Several in vitro and anatomic studies have documented ideal number, size, length and angulation of baseplate screws. However, such fixation can often be tenuous, as the anatomy of scapula bone varies. Furthermore, it can be difficult to identify regions with the best bone stock intraoperatively even though surgeons have an understanding of scapular anatomy with potential screw trajectories in mind. This often leads to variable screw lengths and angulations in the clinical setting. The purpose of this study was to measure optimal screw lengths and angles to reach ideal regions in cadaveric scapulae and to compare the clinical experiences of three surgeons with each other and against a cadaveric model with screw lengths and angulations. Materials and Methods. Seven cadaveric scapulae were used as the template for optimal screw angulation and length for baseplate implantation. Total 21 cases (seven cases of each 3 surgeons) of reverse total shoulder arthroplasty using the Aequalis®-Reversed shoulder prosthesis (Tornier, France) were included. Measurement of screw angulation was done on the AP and axillary views to account for the superior-inferior and the antero-posterior angulations, respectively. The screw lengths used on each scapula was recorded prior to insertion in cadavers and retrieved from the operative records in clinical cases. Screws directed anteriorly and superiorly were recorded as positive values while posteriorly and inferiorly directed screws were designated negative values. The significant differences in degrees of screw angulation and screw lengths among the 3 surgeon groups were calculated using the ANOVA, with the p value at 0.05. The Mann-Whitney U test was performed to evaluate the cadaver group against the surgeon groups. Results. In cadaveric specimens, the averages of the screw lengths used were 29.4 mm (anterior screw), 15.4 mm (posterior screw), 36.0 mm (superior screw), and 46.70 mm (inferior screw). The anterior screw was directed 6.9° inferior and 7.5° degrees posterior in reference to the central peg. The posterior screw direction was inferior (−5.0°) and posterior (−1.7°); Superior screw was directed superiorly (30.1°) and anteriorly (22.2°), while the inferior screw was aimed inferiorly (−15.3°) and posteriorly (−8.3°). In clinical cases, the differences in screw length among the 3 surgeon groups were not statistically significant. There was no significant difference in screw angulation among the 3 surgeons except posterior screw. Comparing cadaveric specimens from the clinical cases, the anterior screws were shorter and directed more superiorly and anteriorly in the patients, and the superior and inferior screws were directed less superiorly and inferiorly in the patient. Conclusion. We concluded that more vertical screw placement of the superior and inferior screws is necessary to obtain the ideal baseplate fixation

Introduction. Proper positioning of the baseplate and optimal screw placement are necessary to avoid loosening or failure of the glenoid component in RTSA. Several in vitro and anatomic studies have documented ideal number, size, length and angulation of baseplate screws. However, such fixation can often be tenuous, as the anatomy of scapula bone varies. Furthermore, it can be difficult to identify regions with the best bone stock intraoperatively even though surgeons have an understanding of scapular anatomy with potential screw trajectories in mind. This often leads to variable screw lengths and angulations in the clinical setting. The purpose of this study was to measure optimal screw lengths and angles to reach ideal regions in cadaveric scapulae and to compare the clinical experiences of three surgeons with each other and against a cadaveric model with screw lengths and angulations. Materials and Methods. Seven cadaveric scapulae were used as the template for optimal screw angulation and length for baseplate implantation. Total 21 cases (seven cases of each 3 surgeons) of reverse total shoulder arthroplasty using the Aequalis®-Reversed shoulder prosthesis (Tornier, France) were included. Measurement of screw angulation was done on the AP and axillary views to account for the superior-inferior and the antero-posterior angulations, respectively. The screw lengths used on each scapula was recorded prior to insertion in cadavers and retrieved from the operative records in clinical cases. Screws directed anteriorly and superiorly were recorded as positive values while posteriorly and inferiorly directed screws were designated negative values. The significant differences in degrees of screw angulation and screw lengths among the 3 surgeon groups were calculated using the ANOVA, with the p value at 0.05. The Mann-Whitney U test was performed to evaluate the cadaver group against the surgeon groups. Results. In cadaveric specimens, the averages of the screw lengths used were 29.4 mm (anterior screw), 15.4 mm (posterior screw), 36.0 mm (superior screw), and 46.70 mm (inferior screw). The anterior screw was directed 6.9° inferior and 7.5° degrees posterior in reference to the central peg. The posterior screw direction was inferior (−5.0°) and posterior (−1.7°); Superior screw was directed superiorly (30.1°) and anteriorly (22.2°), while the inferior screw was aimed inferiorly (−15.3°) and posteriorly (−8.3°). In clinical cases, the differences in screw length among the 3 surgeon groups were not statistically significant. There was no significant difference in screw angulation among the 3 surgeons except posterior screw. Comparing cadaveric specimens from the clinical cases, the anterior screws were shorter and directed more superiorly and anteriorly in the patients, and the superior and inferior screws were directed less superiorly and inferiorly in the patient. Conclusion. We concluded that more vertical screw placement of the superior and inferior screws is necessary to obtain the ideal baseplate fixation

Introduction. The use of cementless TKA's has been gradually increasing over the past several years given the increasing life expectancy of our patient population. Cementless TKA's have not been rapidly adopted due to the challenges and uncertainty of tibial fixation especially in elderly patients. With the advent of new technologies, the results of cementless TKA's with the potential for long term biologic fixation may now be equivalent or better than cemented TKA's. A highly porous tibial baseplate was developed based on proximal tibial anatomy using CT scans using 3D printing technology with focus on length, location and design of press-fit pegs. Objectives. The purpose of this study was to review the early results with respect to fixation and complications using a new, highly porous cementless tibial baseplate designed for biologic fixation. Methods. One hundred primary cementless TKAs were retrospectively reviewed using a highly porous titanium tibial baseplate. The femoral and patella components were also press-fit using peri-apetite beaded technology. Patients were evaluated at 2 weeks, 3 months, 1 and 2 year for clinical and radiographic outcomes along with any early (within 90 day) and 2 year complications. Postoperative protocol consisted of immediate full weightbearing, as tolerated. Radiographs were evaluated for biological fixation and radiolucent lines. Results. There were 68 females and 32 males with 7 undergoing bilateral TKA. The mean age was 63.8 yrs (range 40–84). The mean BMI was 33.7. Diagnosis in all patients was osteoarthritis. The mean follow up was 24.8 months (range 15 to 33). The mean hospital length of stay was 3.2 days (range 2–7). The mean pre operative flexion was 105.8 degrees which improved to 117.9 degrees at latest follow up. KSS scores improved significantly in all patients. There were no postoperative transfusions in this group. All patients developed good radiographic fixation and stability of the tibial baseplate (Figure 1). There were no cases of loosening of the baseplate or infections in this series. Within 90 days, one patient developed a non fatal DVT and one patient was revised due to instability from a CR to a PS femur with the baseplate intact. At 8 months post-op, one patient had a liner exchange for MPFL rupture with a subluxating patella. At 18 months post-op, one patient had a liner exchange due to instability and extensor mechanism rupture. In both cases the baseplate was not revised. Conclusions. Study results indicate cementless fixation using this baseplate is a viable option with good short term clinical results and no cases of aseptic loosening at 2 years. Early stability, pain relief and good ROM were shown. Long term data will be required to determine the overall benefits of this highly porous TKA with biologic fixation versus cemented arthroplasty

Purpose. Previous retrieval studies demonstrate increased tibial baseplate roughness leads to higher polyethylene backside wear in total knee arthroplasty (TKA). Micromotion between the polyethylene backside and baseplate is affected by the locking mechanism design and can further increase backside wear. This study's purpose was to examine modern locking mechanisms influence, in the setting of both polished and non-polished tibial baseplates, on backside tibial polyethylene damage and wear. Methods. Five TKA models were selected with different tibial baseplate and/or locking mechanism designs. Six retrieval tibial polyethylenes from each TKA model were matched based on time in vivo (TIV), age at TKA revision, BMI, gender, number of times revised, and revision reason. Two observers visually assessed each polyethylene. Primary outcomes were visual damage scores, individual visual damage modes, and linear wear rates determined on micro-computed tomography (micro-CT) scan in mm/year. Demographics were compared by one-way ANOVA. Damage scores, damage modes, and linear wear were analyzed by the Kruskal-Wallis test and Dunn's multiple comparisons test. Results. There were no differences among the groups based on TIV (p=0.962), age (p=0.609), BMI (p=0.951), gender, revision number, or reason for revision. There was a significant difference across groups for visual total damage score (p=0.031). The polished tibial design with a partial peripheral capture locking mechanism and anterior constraint demonstrated a significantly lower score compared to one of the non-polished tibial designs with a complete peripheral-rim locking mechanism (13.0 vs. 22.0, p=0.019). Otherwise, mean total damage scores were not significant between groups. There were identifiable differences among the groups based on abrasions (p=0.006). The polished design with a tongue-in-groove locking mechanism demonstrated a significantly higher score compared to one of the designs with a non-polished baseplate (5.83 vs. 0.83, p=0.016). Only the two designs with non-polished baseplates demonstrated dimpling (5.67 and 8.67), which was significant when compared against all other groups (p<0.0001), but not against each other (p>0.99). No other significant differences were identified when examining burnishing, cold flow, scratching, or pitting. No polyethylene components exhibited embedded debris or delamination. There was a significant difference among groups for linear wear on micro-CT scanning (p=0.003). Two of the polished baseplate designs, one with the partial peripheral rim capture and one with the tongue-in-groove locking mechanism, demonstrated significantly lower wear rates than the non-polished design with a complete peripheral-rim locking mechanism (p=0.008 and p=0.032, respectively). There were no other differences in wear rates between groups. Conclusions. Total damage scores and wear rates were similar between all groups except when comparing two of the polished TKA designs to one of the non-polished baseplate designs. The other TKA model with a non-polished tibial baseplate had similar damage scores and wear rates to the polished designs, likely due to its updated locking mechanism. Dimpling was specific for non-polished tibial baseplates while abrasions were identified in the design with a tongue-in-groove locking mechanism. Our study showed even in the setting of a non-polished tibial baseplate, modern locking mechanisms can decrease backside damage and wear similar to that of other current generation TKA designs. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

A pain free motion of the patella after total knee arthroplasty (TKA) is still a challenge for surgeons and TKA-designers today. After TKA, the restricted guidance of the patella and kinematic alterations of the femorotibial joint results in increased retropatellar pressure and unphysiological patellar tracking. The alignment of the prosthetic components can influence patellofemoral stresses and tracking of the patella. The aim of this study was to demonstrate the consequences of different alignments of the tibial baseplate on patellar stress and knee kinematics. Different alignments of the tibial baseplate were simulated with five different UHMWPE-Inlets. Inserts with medial and lateral translation (±3mm; Figure 1A) as well as internal and external rotation (±3°; Figure 1B) were manufactured. Original inlays were used to define the neutral position. Eight human knee specimens without TKA were tested in a custom made knee rig. This rig mimics a loaded squat from approximately 20°−120° of flexion under six degrees of freedom in the knee joint. Retropatellar pressure (IScan, Tekscan, USA) as well as knee kinematics (CMS 20, Zebris, Germany) were recorded during squatting. Afterwards, TKA components were implanted in a neutral position via subvastus approach in tibia first technique. Each of the 5 tibial inlets was tested consecutively with the knee rig under the same conditions. Results were compared using mixed effects models with a random intercept per specimen. Component alignment as well as moving direction (flexion/extension) and flexion degree were defined as fixed effects in our model (SPSS, IBM, USA). After TKA in neutral position, retropatellar peak pressure increased by 0.71MPa (p<0.01), femorotibial rollback was reduced (−2.24mm; p<0.01) and the patella kinematics, in particular patella flexion (−2.02°; p<0.01) and rotation (−0.97°; p<0.01), were changed during squatting. Compared to the neutral position, internal rotation of the tibial baseplate increased retropatellar pressure by 0.20 MPa, while an external rotation provided a reduction of −0.24 MPa (p<0.01). In contrast a medialization or lateralization showed no effect on retropatellar pressure (p=0.09). Both, rotation and translation of the tibial baseplate influenced tibiofemoral kinematics significantly. A reduction of the femorotibial rollback was measured in external alignment (rotation and lateral translation; both p<0.01). An internal rotation showed more femoral rollback (0.93mm p<0.01). Patellar kinematics was changed primarily by component translation rather than rotation. A lateralisation of the tibial baseplate resulted in a medial shift of the patella by −0.43mm and vice versa (p<0.01). Rotation of the tibial baseplate had no influence on the patella shift (p=0.8). The findings in this study suggest that the alignment of the tibial baseplate influences patellar biomechanics significantly in vitro. An external rotation of the tibial baseplate decreased retropatellar pressure and patella kinematics tend more to the in situ situation of a natural knee. An internal alignment of the tibial baseplate seems to reconstruct natural tibiofemoral rollback in parts. However, studies (i.e. Nicoll et al.) show higher anterior knee pain by an internal alignment and a higher rollback after TKA might lead to higher wear

Previous retrieval studies demonstrate increased tibial baseplate roughness leads to higher polyethylene backside wear in total knee arthroplasty (TKA). Micromotion between the polyethylene backside and tibial baseplate is affected by the locking mechanism design and can further increase backside wear. The purpose of this study was to examine modern locking mechanisms, in the setting of both roughened and polished tibial baseplates, on backside tibial polyethylene wear. Five TKA models were selected, all with different tibial baseplate and/or locking mechanism designs. Six retrieval tibial polyethylenes from each TKA model were matched based on time in vivo (TIV), age at TKA revision, BMI, gender, number of times revised, and revision reason. Two observers scored each polyethylene backside according to a visual damage score and individual damage modes. Primary outcomes were mean damage score and individual damage modes. Demographics were compared by one-way ANOVA. Damage scores and modes were analysed by the Kruskal-Wallis test and Dunn's multiple comparisons test. There were no differences among the groups based on TIV (p=0.962), age (p=0.651), BMI (p=0.951), gender, revision number, or reason for revision. There was a significant difference across groups for mean total damage score (p=0.029). The polished tibial design with a partial peripheral capture locking mechanism and anterior constraint demonstrated a significantly lower score compared to one of the roughened tibial designs with a complete peripheral-rim locking mechanism (13.0 vs. 22.1, p=0.018). Otherwise, mean total damage scores were not significant between groups. As far as modes of wear, there were identifiable differences among the groups based on abrasions (p=0.005). The polished design with a tongue-in-groove locking mechanism demonstrated a significantly higher score compared to both groups with roughened tibial baseplates (5.83 vs. 0.83, p=0.024 and 5.83 vs. 0.92, p=0.033). Only the two designs with roughened tibial baseplates demonstrated dimpling (5.67 and 8.67) which was significant when compared against all other groups (p0.99). No other significant differences were identified when examining burnishing, cold flow, scratching, or pitting. No polyethylene components exhibited embedded debris or delamination. Total damage scores were similar between all groups except when comparing one of the polished TKA design to one of the roughened designs. The other TKA model with a roughened tibial baseplate had similar damage scores to the polished designs, likely due to its updated locking mechanism. Dimpling wear patterns were specific for roughened tibial baseplates while abrasive wear patterns were identified in the design with a tongue-in-groove locking mechanism. Our study showed even in the setting of a roughened tibial baseplate, modern locking mechanisms decrease backside wear similar to that of other current generation TKA designs

Introduction. The General Social Survey estimates that 19 million Americans shoot firearms, with 10% of this population being over the age of 65. More reverse total shoulder arthroplasty (rTSA) are seeking to return to physical activity after surgery, but the effects of shooting a firearm on the fixation of a rTSA implant are unknown. This study will seek to examine the recoil effect of a firearm on a rTSA baseplate fixation, by recording the forces absorbed by a shooter and applying these forces to a rTSA implant assembly in laboratory conditions. Methods. A total of 5 shooters over a range of heights and bodyweights fired a single action 12 gauge shotgun with 3 ounce slugs 5 times each. An accelerometer was rigidly fixated to the barrel of the firearm to record impulse values upon firing. 8 reverse shoulder baseplate/glenosphere assemblies (Equinoxe, Exactech, Inc) were fixated to 15 lb/ft3 density rigid polyurethane bone substitute blocks for drop tower testing. Displacement was measured before and after testing using digital displacement indicators by applying a physiologically relevant 357N shear load parallel to the face of the glenosphere, and a nominal 50N compressive axial load perpendicular to the glenosphere as shown in Figure 1. Measurements were taken for the S/I axis, and the sample was rotated 90 degrees for the A/P axis. The glenosphere/baseplate assemblies were loaded in a drop tower apparatus at 0° of abduction and 90° flexion to replicate the orientation of the joint seen while shooting. The drop tower utilized a 1.079kg weight set at 8” with a rubber impulse specific materil between the weight and impactor to reproduce the highest average impulse seen in shooting. A total of 50 drops were performed, to simulate two rounds of trap shooting at 25 shots each. A Student's one-tailed, paired t-test was used to identify whether or not significant loosening occurred, where p<0.05 denoted a significant difference. Results. The average shooting values for each shooter are presented in Table 1. Displacement measurements in the A/P and S/I axes before and after drop tower testing are presented in Table 2. All 8 samples remained well fixed after drop tower testing, and neither A/P nor S/I directions showed significant difference in displacement (p≤.279, p≤.158) with an average displacement of 4 and 10 microns, respectively. Discussion and Conclusions. This testing replicates a worst case scenario, as the combination of both round size and number of shots taken is not likely to be paired together while shooting recreationally. Additionally, the foam block used mimics an immediate postoperative scenario, where in reality a patient is unlikely to shoot again until recovering from the procedure. Shooting form also seemed to play a role, as shots that were considered “poor form” recorded up to 30% higher recoil values than those with “good form”. For these reasons, early results indicate chance of implant loosening due to the forces from shooting firearms is low, especially if the patient is a former experienced shooter who wishes to return to the sport. To view tables/figures, please contact authors directly

Adequate fixation of implant components is an important goal for all arthroplasty procedures. Aseptic loosening is one of the leading causes of revision surgery in total knee arthroplasty. Radiostereometric analysis (RSA) is an imaging technique to measure implant migration, with established migration thresholds for well-fixed, at risk, and unacceptably migrating components. The purpose of the present study was to examine the long-term fixation of a cemented titanium fixed bearing polished tibial baseplate. Patients enrolled in a previous two-year prospective trial were recalled at ten years. All patients received a cemented, posterior-stabilised total knee replacement of the same design implanted by one of three surgeons. Of the original 35 patients, 16 were available for long-term follow-up, with one patient lost to follow-up, nine patients deceased, and a further nine patients unwilling to return to the clinic. Each patient underwent RSA imaging in a supine position using a conventional RSA protocol. Migration of the tibial component in all planes as well as maximum total point motion (MTPM) was compared between all time points (baseline, six weeks, three months, six months, one year, two years) up to the ten year follow-up visits. Outcome scores including the Knee Society Score (KSS), WOMAC, SF-12, and UCLA Activity Score were recorded. At ten years, the mean migrations of the tibial component were less than 0.1 mm and 0.1 degree in all planes relative to the post-operative RSA exam. There was no significant difference in tibial component migration between time points. However, MTPM increased significantly over time (p = 0.002), from 0.23 ± 0.18 mm at six weeks to 0.42 ± 0.20 mm at ten years. At one year, 13 patients had an acceptable MTPM level, three patients had an ‘at risk’ level, and no patient had an ‘unacceptable’ level. No patients were revised at ten years. WOMAC and KSS were significantly improved (p < 0.0001) at the latest follow-up compared to pre-operatively, but there was no difference in SF-12. The median UCLA Activity Score at latest follow-up was six (range, two to eight). The tibial baseplate demonstrated solid fixation at ten years. No patients had an unacceptable MTPM level at one year and no patients were revised at ten years, supporting the use of RSA to predict long-term loosening risk. The low level of tibial baseplate migration found in the present study correlates to the low rate of revision for this implant as reported in individual studies and in joint replacement registries

Nowadays, initial fixation and relative movements of the tibial baseplate with respect to the bone are not a hot topic anymore. Most surgeons have already accepted cement fixation and don't aim for bone ingrowth anymore. This might change if the trend towards implants that offer always a deeper flexion persists. These implants tend to load the tibial baseplate more posteriorly during deep flexion potentially causing a higher risk of lift_off and thus loosening. The ideal concept pushing our team was the search for a design of either a stem or other fixation features able to hold the baseplate to the bone keeping the amount of bone that needs to be removed within acceptable limits. The Profix tibial baseplate (Smith & Nephew) has a wide range of fixation techniques available. It can be cemented or used cementless and, in both cases, several stem designs are available. One of these is the so-called Omega stem. It has the advantage of being thin (in fact it is a stem and a chisel at the same time) but also stiff, withstanding bending loads due to its curvature in the transversal plane. It is also relatively short compared to other stems and it is thus bone-sparing and suitable for MIS

Introduction. The Rotational alignment is an important factor for survival total knee Arthroplasty. Rotational malalignment causes knee pain, global instability, and wear of the polyethylene inlay. Also, the anterior cortex line was reported that more reliable and more easily identifiable landmark for correct tibial component alignment. The aims of the current study is to identify effect of inserting the tibial baseplate of using anterior cortex line landmark of TKA on stress/strain distributions within cortical bone and bone cement. Through the current study, final aim is to suggest an alternative position of tibia baseplate for reduction of TKA failures with surgical convenience. Materials and Method. A three-dimensional tibia FE model with TKA was generated based on a traditional TKA surgical guideline. Here, a commercialized TKA (LOSPA, Corentc, Korea) was considered corresponded to a patient specific tibia morphology. Tibia baseplate was positioned at anterior cortex line. Alternative two positions were also considered based on tibia tuberosity 1/3 line and tibia tuberosity end line known as a gold standard (Fig. 1-A). Loading and boundary conditions for the FE analysis were determined based on five activities of daily life of persons with TKA (Fig. 1-B). FE model was additionally validated comparing with an actual mechanical test. Results and Discussions. The, through comparing with strain distribution on the cortical bone measured from the actual mechanical test considering 0°, 30° 60°, 90°, 120° and 140° flexion with femoral rollback phenomenon (Fig. 2). Stress/strain on the cortical bone (medial region) of the proximal tibia for the baseplate positioned at anterior cortex line were a little better distributed than those at tibia tuberosity 1/3 line and tibia tuberosity end line although the stress/stain values were similar to each other (Fig. 3-A). Potential fracture risk of the bone cement for the baseplate positioned at anterior cortex line was lower than that at tibia tuberosity 1/3 line and tibia tuberosity end line, considering safety factor (N=3). Particularly, Potential fracture risk of the bone cement for the baseplate positioned at tibia tuberosity 1/3 line known as a gold standard was highest (over 20MPa for stair down activity) (Fig. 3-B). Conclusion. Our results suggested that anterior cortex line landmark was feasible to apply positioning method on the tibial baseplate in terms of mechanical characteristics which were compared to tibia tuberosity 1/3 line and tibia tuberosity end line known as a gold standard. This study may be valuable by suggesting for the first time an alternative baseplate position for reduction of TKA failures with surgical convenience

INTRODUCTION. Total knee arthroplasty (TKA) is typically performed using cement to secure the prosthesis to bone. There are complications associated with cementing that include intra-operative hypotension, third-body abrasive wear, and loosening at the cement interfaces. A cementless prosthesis using a novel keeled trabecular metal tibial baseplate was developed to eliminate the need for cementing the tibial component in TKA. METHODS. A retrospective chart review was performed on patients who underwent TKA using cementless tibial and femoral components between August, 2013 and January, 2014. Patients with minimum two-year follow-up including radiographs were included in the analysis. Patient demographics as well as preoperative and postoperative range of motion (ROM) and function were measured using the Knee Society Scoring system (KSS). Post-operative radiographs were assessed for signs of osteolysis, loosening, or subsidence. Paired T-tests were used to identify differences in preoperative and postoperative ROM and KSS. RESULTS. Thirty-three patients underwent 48 TKAs in the study period. Of those, 20 patients (29 knees) completed two-year follow-up. The mean patient age was 69.0 ±8.4 years and mean BMI was 29.9 ±4.3. The average time of follow-up was 24.6 months (range 24–29). Preoperative ROM was on average 4.3–117.3°±6.7 and the preoperative KSS knee scores and functional scores were 43.8 ±8.6 and 49.8 ±12.6, respectively. Postoperatively, there were statistically significant improvements in ROM (0–130.7°±7.3), and postoperative KSS knee (98.4 ±3.2) and functional scores (99.3 ±2.6), at two years, respectively. None of the radiographs demonstrated evidence of osteolysis, loosening, migration, or subsidence. DISCUSSION and CONCLUSION. The two-year results of TKA utilizing a cementless tibial baseplate demonstrate excellent results in terms of knee ROM and function. The radiographic evidence of osteointegration without evidence of loosening, subsidence, or migration of the tibial components is promising. Further follow up is necessary to ensure that these implants will provide a satisfactory long-term alternative to cement fixation

While reverse shoulder arthroplasty (RSA) is a reliable treatment option for patients with rotator cuff deficiency, loss of glenoid baseplate fixation often occurs due to screw loosening. We questioned whether an analysis of the trabecular bone density distribution in the scapula would indicate more optimal sites for screw placement. As such, the purpose of this study was to determine the anatomic distribution of trabecular bone density in regions of the scapula available for screw placement in RSA. Seven cadaveric shoulders were computed tomography (CT) scanned, and then voxels of the scapulae were isolated from the CT volume (Mimics 15.0 Materialise, Leuven, Belgium). Analyses were conducted in a common, 3D coordinate system. Volumetric regions of interest (ROI) within the scapula were identified based on potential baseplate screw sites. ROIs included areas at the base of the coracoid process lateral and inferior to the suprascapular notch, in the posterior and anterior lateral spine and in the anterosuperior and posteroinferior lateral border. Hounsfield Units (HU) were extracted from voxels corresponding to trabecular bone within each ROI. Overall bone density was summarised as the frequency of HU values above 80% of the ROI's maximum density value. Paired, two-tailed t-tests assuming unequal variance were used for pairwise comparisons (P≤0.05). Intra-region analyses compared two ROIs within the same broad anatomical structure; inter-region analyses compared ROIs between anatomical structures. Areas of the spine and lateral border of the scapula appeared to be denser than the coracoid process. Intra-region comparisons indicated no significant differences within ROI: coracoid P=0.43, spine P=0.95, lateral border P=0.41. ROI inferior to the suprascapular notch were on average 3.78% (P=0.08) and 6% (P=0.04) less dense than the anterosuperior and posteroinferior lateral border and 7.59% (P=0.006) and 7.72% (P=0.01) less dense than the anterior and posterior lateral spine. ROI lateral to the suprascapular notch were 6% (P=0.05) and 8.21% (P=0.02) less dense than the anterosuperior and posteroinferior lateral border and 9.8% (P=0.006) and 9.94% (P=0.008) less dense than the anterior and posterior lateral spine. There was no significant difference between the anterior spine and anterosuperior and posteroinferior lateral border (P=0.12, P=0.58), nor between the posterior spine and anterosuperior and posteroinferior lateral border (P=0.14, P=0.57). Results from this study indicate that the spine and lateral border of the scapula contain denser trabecular bone relative to regions in the coracoid. The higher quality bone of the spine and lateral border should be favoured over the coracoid process when fixing the glenoid baseplate in RSA. Further research may support the redesign of the glenoid baseplate geometry to better integrate the anatomy of the scapula and improve implant survival

Introduction. In total knee arthroplasty (TKA), non-cemented implants rely on initial fixation to stabilize the implant in order to facilitate biologic fixation. The initial fixation can be affected by several different factors from type of implant surface, implant design, patient factors, and surgical technique. The initial fixation is traditionally quantified by measuring the motion between the implant and underlying bone during loading (micromotion). Extraction force has also been quantified for cementless devices. The question remains does an increase or decrease in extraction force affect micromotion based on the fact that most loading at the knee joint is in compression. The objective of this research is to investigate if there is any correlation between extraction force and implant micromotion. Methods. The relationship between extraction force and micromotion was evaluated by performing a series of experiments using a synthetic bone analog and a tibial baseplate with hexagon pegs. Tunnels for the hexagon pegs were machined into the synthetic bone analog with different diameters, from 9.7 to 11.7 mm. The smaller diameter tunnels increase the press fit between the peg and bone. Sixty-six implants were tested to determine maximum extraction force. The implants were extracted using an electro-mechanical testing frame at a rate of 0.4 inches / minute. Two different types of bone analogs were used for this evaluation. One was an open-cell foam with a density of 12.5 lb/ft. 3. and the other was a closed-cell foam with a density of 20 lb/ft. 3. . Twelve TKA implants were tested to determine the maximum anterior-lift off micromotion during a posterior load application. A posterior stabilized polyethylene insert and mating femoral component were used during the loading. The posterior load cycled from 90 to 900 N for 500 cycles. The micromotion was evaluated with the femur at 90 degrees of flexion. Differential Variable Reluctance Transducers (DVRTs) were located under the four corners of the implant to quantify the superior-inferior motion of the implant. A composite synthetic bone analog was used for this evaluation, with open-cell foam (12.5 lb/ft. 3. ) on the inside and closed-cell foam (50 lb/ft. 3. ) on the outside. Results. The extraction force was higher for the denser closed-cell foam (Figure 1A). The extraction force generally increased with decreasing tunnel diameter, but there was a plateau of extraction force between 10.9 mm and 10.1 mm for the open-cell foam and peaked at 10.7mm for the closed-cell foam. The micromotion in both posterior DVRTs were found to be similar for all tunnel diameters. The micromotion in both anterior DVRTs increased slightly when increasing tunnels diameters from 10.2 mm to 10.7 and 11.2 mm, but increased dramatically when increasing the tunnel diameter to 11.7 mm. Discussion. In this study using a synthetic bone model, a decrease in extraction force was found to correlate with an increase in anterior lift-off micromotion (Figure 2). Next steps are to confirm these results from this simplified model in a more physiologic model with cadaveric bone and activity based loading. For any figures or tables, please contact authors directly (see Info & Metrics tab above).