Roentgen Stereophotogrammetric Analysis (RSA) is the gold standard for measuring implant micromotion thereby predicting implant loosening. Early migration has been associated with the risk of long-term clinical failure. We used RSA to assess the stability of the Australian designed cementless hip stem (Paragon TM) and now report our 5-year results. Fifty-three patients were prospectively and consecutively enrolled to receive a Paragon hip replacement. Tantalum beads were inserted into the bone as per RSA protocol and in the implant. RSA x-rays were taken at baseline 1–4 days post-surgery, at 6 weeks, 6 months, 12 months, 2 years, and 5 years. RSA was completed by an experienced, independent assessor. We reported the 2-year results on 46 hips (ANZJS 91 (3) March 2021 p398) and now present the 5-year results on 27 hips. From the 2-year cohort 5 patients had died, 8 patients were uncontactable, 1 patient was too unwell to attend, 5 patients had relocated too far away and declined. At 5 years the mean axial subsidence of the stem was 0.66mm (0.05 to 2.96); the mean rotation into retroversion was 0.49˚ (−0.78˚ to 2.09˚), rotation of the stem into valgus was −0.23˚ (−0.627˚ to 1.56˚). There was no detectable increase in subsidence or rotation between 6 weeks and 5 years. We compared our data to that published for the Corail cementless stem and a similar pattern of migration was noted, however greater rotational stability was achieved with the Paragon stem over a comparable follow-up period. The RSA results confirm that any minor motion of the Paragon cementless stem occurs in the first 6 weeks after which there is sustained stability for the next 5 years. The combination of a bi-planar wedge and transverse rectangular geometry provide excellent implant stability that is comparable to or better than other leading cementless stems

Introduction. Reverse Shoulder Arthroplasty (RSA) improves the mechanics of rotator cuff deficient shoulders. To optimize functional outcomes and minimize failures of the RSA manufacturers have recently made innovative design modifications with lateralized components. However, these innovations have their own set of biomechanical trade-offs, such as increased shear forces along the glenoid bone interface. The objective of this study was to develop an efficient musculoskeletal model to evaluate and compare both the muscle forces and joint reactive force of a normal shoulder to those implanted with varied RSA implant designs. We believe these findings will provide valuable insight into possible advantages or shortcomings of this new RSA design. Methods. A kinematic model of a normal shoulder joint was adapted from publically available musculoskeletal modeling software. Static optimizations then allowed for calculation of the individual muscle forces, moment arms and joint reactive forces relative to net joint moments. An accurate 3D computer models of humeral lateralized design (HLD) (Equinoxe, Exactech, Gainesville FL, USA), glenoid lateral design (GLD) (Encore, DJO Global, Vista CA, USA), and Grammont design (GD) (Aequalis, Tornier, Amsterdam, NV) reverse shoulder prostheses was also developed and parametric studies were performed based on the numerical simulation platform. Results. As expected, there were decreases in muscle forces in all RSA models (Table 1). These decreases were greatest in the middle deltoid of the HLD model for abduction and flexion (Figure 1) and in the rotator cuff muscles under both internal and external rotation (Figure 2). In all RSA models the muscle forces of the rotator cuff were diminished to near zero in all range of motions. The joint reactive forces in abduction and flexion decreased similarly for all RSA models compared to the normal shoulder model, with the greatest decrease again seen in the HLD model (Table 1). Conclusion. These findings demonstrate that the design characteristics implicit in these modified RSA prostheses result in kinematic differences most prominently seen in the deltoid muscle and overall joint reactive forces. These differences could have a profound effect on the ultimate clinical success and long term outcomes for RSA. These results can help guide continued optimization of RSA design and clinical outcomes. The developed innovative shoulder modeling simulation could serve as a prototype for testing of future implant design concepts

Purpose. The purpose of this study was to examine the influence of weight-bearing on the measurement of in vivo wear of total knee replacements using model-based RSA at 1 and 2 years following surgery. Methods. Model-based RSA radiographs were collected for 106 patients who underwent primary TKR at a single institution. Supine RSA radiographs were obtained post-operatively and at 6-, 12-, and 24-months. Standing (weight-bearing) RSA radiographs were obtained at 12-months (n=45) and 24-months (n=48). All patients received the same knee design with a fixed, conventional PE insert of either a cruciate retaining or posterior stabilized design. Ethics approval for this study was obtained. In order to assess in vivo wear, a highly accurate 3-dimensional virtual model of each in vivoTKA was developed. Coordinate data from RSA radiographs (mbRSA v3.41, RSACore) were applied to digital implant models to reconstruct each patient's replaced knee joint in a virtual environment (Geomagic Studio, 3D Systems). Wear was assessed volumetrically (digital model overlap) on medial and lateral condyles separately, across each follow-up. Annual rate of wear was calculated for each patient as the slope of the linear best fit between wear and time-point. The influence of weight-bearing was assessed as the difference in annual wear rate between standing and supine exams. Age, BMI, and Oxford-12 knee improvement were measured against wear rates to determine correlations. Results. Weight bearing wear measurement was most consistent and prevalent in the medial condyle with 0–4% of calculated wear rates being negative compared to 29–39% negative wear rates for the lateral condyle. For the medial condyle, standing exams revealed higher mean wear rates at 1 and 2 years; supine, 16.3 mm. 3. /yr (SD: 27.8) and 11.2 mm. 3. /yr (SD: 18.5) versus standing, 51.3 mm. 3. /yr (SD: 55.9) and 32.7 mm. 3. /yr (SD: 31.7). The addition of weight-bearing increased the measured volume of wear for 78% of patients at 1 year (Avg: 32.4 mm. 3. /yr) and 71% of patients at 2 years (Avg: 48.9 mm. 3. /yr). There were no significant (95% CI) correlations between patient demographics and wear rates. Discussion and Conclusion. This study demonstrated TKA wear to occur at a rate of approximately 10 mm. 3. /year and 39 mm. 3. /year in patients imaged supine versus standing, respectively, averaged over 2 years of clinical follow-up. In an effort to eliminate the effect of PE creep and deformation, wear was also calculated between 12 and 24 months as 9.3 mm. 3. (standing examinations), This value is comparable to wear rates obtained from retrieved TKRs. Weight-bearing exams produced better wear data with fewer negative wear rates and reduced variance. Limitations of this study include: supine patient imaging performed at post-op, no knee flexion performed, and unknown patient activity level. Strengths of this study include: large sample size of a single TKR system, linear regression of wear measurements and no requirement for implanted RSA beads with this method. Based on these results, in vivo volumetric wear of total knee replacement polyethylene can be reliably measured using model-based RSA and weight-bearing examinations in the short- to mid–term. For any figures or tables, please contact authors directly

The philosophy of cemented total hip arthroplasty (THA) femoral components has become polarised. At one extreme are polished, collarless, tapered devices that are expected to subside; at the other extreme are roughened, non-tapered implants with a collar designed not to subside. Radiostereometric analysis (RSA) allows the accurate measurement of implant movement and has been extensively used for measurement of the in vivo migration of implants. The degree of migration as measured by RSA during the first years after surgery has been shown to correlate with the long-term performance of cemented femoral implants. The purpose of this study was to review the two-year RSA results of two different designs of primary cemented THA stems. Data from two previous prospective RSA trials with two-year follow-up were pooled. The first group included 36 patients who received a Spectron (Smith & Nephew, Memphis, USA) cemented stem. The second group included 13 patients who received an Exeter (Stryker, Mahwah, USA) cemented stem, and 15 patients who received a CPCS (Smith & Nephew, Memphis, USA) cemented stem. All patients underwent RSA examinations shortly post-operation, at 6 weeks, 3 months, 6 months, 1 years, and 2 years. Migration and rotation of the femoral stems was measured at each time point relative to the post-operative exam, and compared between the two groups. There was no difference in age at surgery (Spectron 78 ± 6 years, Exeter/CPCS 77 ± 5 years, p = 0.43), BMI (Spectron and Exeter/CPCS 28 ± 5 kg/m2, p = 0.92), or percentage of male patients (Spectron 23% male, Exeter/CPCS 21% male) between the implant groups. Subsidence was significantly greater (p < 0.0001) at all time points from three months to two years for the Exeter and CPCS stems (0.94 ± 0.39 mm at two years) compared to the Spectron stem (0.05 ± 0.16 mm at two years). There was no significant difference between the stem types for medial-lateral translation (p = 0.07) or anterior-posterior translation (p = 0.49), or for anterior-posterior tilt (p = 0.15), internal-external rotation (p = 0.89), or varus-valgus rotation (p = 0.05). Implant material, design, and surface finish are all factors in the long-term performance of cemented femoral hip implants. In this study, both femoral stem designs had a magnitude of sub-sidence that was within the limits of what is considered to be safe with respect to long-term performance. The continuous subsidence of the Exeter and CPCS stems is consistent with previous reports in the literature

Introduction. In vitro studies showed that the anti-oxidative properties of vitamin E stabilize free radicals while retaining the mechanical strength of UHMWPE. The purpose was to evaluate vitamin E diffused polyethylene (VEPE) wear and stability of femoral components using RSA. Patient reported outcome measures (PROMs) were evaluated to determine the clinical outcome at 5 years. Methods. 48 patients (52 hips), with osteoarthritis, participated in a 5 year RSA study. Each patient received a VEPE liner, a porous titanium coated shell, and an uncemented stem with a 32mm head. Tantalum beads were inserted into the VEPE and the femur to measure head wear and stem stability using RSA. RSA and PROM follow-up was obtained postoperatively, 6 months, 1, 2, 3, and 5 years after surgery. The Wilcoxon signed-ranks test determined if changes in penetration or migration were significant (p≤0.05). Results. 47 hips were followed at 3 years, and 35 at 5 years. The median± standard error (SE) superior head penetration into the polyethylene was 0.05±0.01mm at 3 years and 0.06±0.01 mm at 5 years. There was no difference after 2 years. The median± SE distal stem migration was 0.06±0.21mm at 3 years, and 0.06±0.29mm at 5 years with no significant differences over time. All PROMs improved significantly from the preoperative to all other intervals (p<0.001 for all). Discussion. The VEPE liners show low head penetration at 5 years. The early head penetration, probably due to creep, is lower relative to that reported for non-VEPE measured by RSA. While most stems were stable, the high standard error results from one stem that migrated substantially by 6 months (9.4mm), which has since stabilized. This study documents the longest-term evaluation of in vivo wear performance of vitamin E stabilized UHMWPE. The low wear and the stability of the femoral stem shows promise for long-term survivorship

Reverse shoulder arthroplasty (RSA) was released into the United States market in 2004 for the indication of Rotator Cuff Tear Arthropathy. Since that time the indications have widened and now include massive rotator cuff tears that are not deemed to be surgically repairable. This diagnosis includes patients that are considered young in terms of shoulder replacement surgery. These patients do not have the radiographic changes of arthropathy, but most have undergone multiple surgical procedures in the past to attempt to repair the rotator cuff deficiency. These younger patients have a different post-op expectation than the patient with advanced arthropathy over the age of 70. The complication rate seen in this younger patient population is higher than seen in the older population undergoing RSA. The post-operative survey for satisfaction is also considerably lower in the younger population group. RSA for massive rotator cuff tears in a younger population under the age of 65 years gives a lower patient satisfaction result and a higher complication rate than age-matched patients older than 65 years. Although this is still the best procedure available for this difficult diagnosis, patients younger than 65 years should be consulted as to what their expectations are post-operatively. Pain relief is still the main reason to undergo an RSA

The Rizzoli Orthopaedic Institute has been involved in RSA since 1998. During last 25 years, several investigations have been carried on to evaluate both implant fixation and poliethylene deformation in unicompartmental and total knee replacements. Nevertheless, RSA has also been used to investigate the relative micromotions and the kinematic modifications in cadaveric models of ankles with ligamentous injuries. RSA evaluation has demonstrated that in a particular TKR implant, with mobile half-bearings, the threshold for loosening was 1.3° for rotation about the longitudinal axis and 0.5 mm for medio-lateral translation. Moreover, RSA has revealed cold flow to be concentrated in the posterior region of the medial half-bearing. This has lead to further improvement in polyethilene and implant design. RSA has also demonstrated that in all-poly tibial UKR, poliwear does not impair tibial component fixation and that deformation of the all-poly tibial component is strictly correlated to implant loosening. Moreover, RSA has been used to investigate stress-inducible displacement of the tibial component in all-poly UKRs. It has been demonstrated that rotations around the transverse axis of the knee joint are the most common form of stress-inducible displacement, while stress-induced translations are negligible. Moreover, stress-inducible translational displacement has reached significantly higher values for those patients with unexplained painful UKR, despite no sign of loosening on conventional radiographic and standard supine RSA evaluations. Further application of RSA has focused on the kinematic evaluation of poliethilene motion pattern modifications throughout a 3 years follow-up period after a mobile-bearing TKR. Patients have been investigated in weight-bearing conditions and results demonstrated that longitudinal rotations and medio-lateral translations tended to increase at last follow-up, while sagittal translations dod not show any significant modification over time. At present, a new device has been installed at the Istituto Ortopedico Rizzoli. It was specifically designed and made for RSA, static and fluoroscopic. This device can work both in mono- and bi-planar configuration as required by the RSA protocols. Moreover it is able to acquire image stacks in order to study the in-vivo and real time kinematics of a joint. he theoretical biomechanical resolution of a static RSA followup tests is 0.2 mm for translation and 0.3° for rotation. In fluoroscopic configuration the theoretical resolution is 1 mm for translation and 1° for rotations, depending on the used frame rate and on the joint movement speed. A kinematic comparison of different prosthetic designs is currently ongoing, to evaluate different motion patterns under dynamic weight-bearing conditions and to compare them with passive kinematics acquired intra-operatively using a navigation system

Background:. The rising number of morbidly obese patients may have significant consequences on the health care system. It may alter the effectiveness, safety as well as cost of certain surgical procedures. Reverse shoulder arthroplasty (RSA) is rapidly gaining in popularity. We investigated the effect of morbid obesity on outcomes, complications, disposition and cost in morbidly obese patients undergoing RSA in a 1: 3 case control series. Methods:. Our joint registry was searched for all patients undergoing primary RSA (excluding fractures) with a minimum of 24 months follow-up from 2003–2010; 21 patients with Body Mass Index (BMI) > 35 were identified (follow-up 45 ± 16 months, 17 females and 4 males, age 69 ± 7) and compared to 63 matched control patients with BMI<30 (follow-up 48 ± 20, 50 females, age 71 ± 6). Outcome data was obtained pre- and postoperatively. Patients' Charlson-Deyo comorbidity index (CDI), total comorbidities, operative time, blood loss (EBL), hospitalization length, disposition, cost and complications were recorded. Results:. There were significant (p < 0.05 for all) and comparable improvements in clinical outcomes, i.e. ASES 32→69 versus 40→78) and range-of-motion (i.e. elevation 61°→140° versus 74°→153°). Obese patients had less notching (1/21 versus 5/63, p = 0.007). Obese patients had more total comorbidities excluding obesity (6 versus 4, p = 0.001), higher CDI (2 versus 1, p = 0.025) and higher rates of obstructive sleep apnea (48% versus 3%, p = 0.0001). They had longer operative time by 13 minutes (p = 0.014) and higher EBL by 40 ml (p = 0.008). Length of stay was similar (3.1 versus 2.6 days, p = 0.21) but a 6-fold higher rate of discharge to facilities (6/21 versus 3/63, p = 0.007) and a higher readmission rate (2 versus 0, p = 0.06) was seen in obese patients. Hospital cost was higher by $2,958.00 (p = 0.02). Major (n = 4 versus 8) and minor complication rates (n = 3 versus 14) were similar (p = 0.479 and 0.440, respectively). No intraoperative complications or mechanical device failures were noted in either group. Conclusions:. RSA was as safe and effective in morbidly obese patients, but an increased cost, disposition to facilities and needs after discharge was observed

This study aimed to compare the early clinical results and stem subsidence between three consecutive series of revision hip replacement cases with femoral impaction bone grafting to evaluate the effects of developments in technique. In the original series 1 (n=23), bone graft was irradiated at 25kG. I n series 2 (n=12) non-irradiated double washed graft and long stems were used as required. In series 3 (n=21) modular tamps were used. Sensitive radiographic analysis techniques, EBRA and RSA, were used to measure stem subsidence. Major stem re-revision was required in five hips in series one, one hip in series two and no hips in series three. Two periprosthetic fractures occurred in series one. There was a statistically significant reduction in stem subsidence at the cement-bone interface at 12 months between series one and series two and three (p<0.05). In series three there was negligible stem subsidence at the cement-bone interface. Technique developments in femoral impaction grafting, including the use of modular tamps designed to simply the procedure, yields excellent early clinical and radiographic results. Using RSA, we have shown that the fixation of the stems in bone is comparable to that achieved in primary hip replacement

The main purpose of the present study was to determine long-term implant fixation of 15 unicompartmental knee arthroplasty (UKAs) with an all-poly tibial component using Roentgen stereophotogrammetric analysis (RSA) at a mean 10-year follow-up. The secondary purpose was to investigate whether the progressive loss of implant's fixation correlates with a reduction in Knee society score (KSS). Fifteen non-consecutive patients with primary knee osteoarthritis received a UKA with an all-poly tibial component were assessed using KSS scores pre-operatively and post-operatively and RSA on day 2 after surgery, then at 3, 6, and 12 months and yearly thereafter. The mean last follow-up was 10 years. An increase in maximum total point motion (MTPM) values from 6 months to 1 year post-operatively was found respect to post-operative reference. Implants’ displacement values were always 2 mm during the first 6 months, and then, two different trends were noticed in revised and non-revised implants. MTPM increase between 1 and 2 years of follow-up in non-revised UKAs was always 0.2 mm, whereas it was [0.2 mm in revised UKAs. A linear and negative correlation with statistical significance was found between MTPM and both clinical and functional KSS scores (p 0.001). Also in a long-term follow-up evaluation, RSA is an effective tool to predict functional results after an all-poly UKA providing also a relevant predictive value at 1 year follow-up, and this can be very useful for both patients and surgeons

Purpose. The purpose of the study was to determine the rate of conversion from RSA to THR in a number of Canadian centers performing resurfacings. Method. Retrospective review was undertaken in 12 Canadian Centers to determine the rate of revision and reason for conversion from RSA to THR. Averages and cross-tabulation with Chi-Squared analysis was performed. kaplan Meier survivorship was calculated. Results. A total of 2810 resurfacings were performed up to December 2008. 770 hips had a minimum of 5 year follow-up. The overall survivorship of this group was 97.8%. 80 patients underwent conversion to THR. Five resurfacing systems were used. The reason for failure is reported: 21 were for femoral neck fracture, 25 were for loosening, 9 were for deep infection, 3 foravn, 4 pseudotumors, 2 for impingement, 6 for groin pain and 10 for other reasons. The cumulative conversion rate is 2.8%. The survivorship was significantly different analyzed by gender. The 5 year female survivorship was 95.4% and for males was 97.7%. Surgeon experience proved to be a significant factor in conversion rates. Conclusion. The revision rate to date with this new technology suggests that with increasing experience hip resurfacing arthroplasty remains an acceptable option for the treatment of hip arthritis

Introduction. Osteolysis caused by wear of the ultrahigh molecular weight polyethylene (UHMWPE) often leads to failure. Cross-linking improves wear, but also produces residual free radicals that decrease oxidative stability. In vitro studies have shown that the anti-oxidative properties of vitamin E UHMWPE stabilize free radicals while retaining the physical and chemical properties of UHMWPE. The porous surface of the Regenerex™ shell was developed for improved bone in-growth fixation. The increased porosity of the Regenerex™ shell promotes early bony in-growth with the goal of greater long-term stability. The purpose of this study was to evaluate vitamin E infused polyethylene (VEPE) wear and stability of acetabular and femoral components using RSA. Methods. 58 patients (64 observed hips), all with osteoarthritis, gave informed consent to participate in a 5 year RSA study. Each patient received a VEPE liner, a Regenerex™ acetabular shell, and an uncemented stem with either a 32mm or 36 mm cobalt chrome femoral head. Tantalum beads were inserted into the VEPE, the pelvic and the femoral bone to measure head penetration into the polyethylene, and shell and stem stability over time, using RSA. RSA radiographs were scheduled immediately postoperatively (up to 6 weeks) and 6 months, 1, 2, 3, and 5 years after surgery. The Wilcoxon signed-ranks nonparametric test was used to determine if changes in penetration or migration were significant over time at p≤0.05. Results. 58 hips have been followed for 6 months, 55 at 1 year, 52 at 2 years, 47 at 3 years and 18 at 5 years. The 36mm cohort data is not reported at this time due to insufficient follow-up. The median± standard error (SE) superior head penetration into the polyethylene was 0.05±0.01mm at 2 years, 0.05±0.01mm at 3 years, and 0.05±0.02 mm at 5 years. The acetabular components had a median± SE cup translation in the proximal direction of 0.09±0.03mm at 2 years, 0.04±0.04mm at 3 years, and 0.06±0.06mm at 5 years. The median± SE cup rotation was −0.09±0.16 degrees at 2 years, −0.02±0.15 degrees at 3 years, and 0.30±0.20 degrees at 5 years. There was a statistically significant difference in cup rotation between the 6 month and 1 year intervals (p=0.007), but no significant differences in translation or head penetration. The median± SE stem distal migration was 0.08±0.07mm at 2 years, 0.05±0.23mm at 3 years, and 0.02±0.17mm at 5 years, with a significant difference between the 6 month and 3 year intervals (p=0.029). Discussion. The VEPE liners show low head penetration at 5 years. The early head penetration, probably due to creep, is substantially lower relative to that reported for non-vitamin E stabilized UHMWPE measured by similar techniques. At 5 years, all acetabular components were stable, with the early significant difference in rotation at 1 year likely due to early settling of the cup. This study documents the longest-term evaluation of in vivo wear performance of vitamin E stabilized UHMWPE. The stability of the Regenerex™ shell and femoral stem shows promise for long-term survivorship

Introduction. Stem geometry is known to influence the outcome in THA; however it is unknown whether the material properties, stiffness in particular can influence the stem stability and outcome. The aim of this study was to measure the influence of stem material properties on micromotion and migration using Roentgen Stereophotogrammetric Analysis (RSA) system. Methods. 41 patients were implanted with a collarless polished tapered (CPT) femoral stem (Zimmer, Warsaw, Indiana), which was made of either cobalt-chromium (CoCr) (n=21) or stainless steel (n=20). RSA was used to measure dynamically inducible micromotion (DIMM: difference in stem position in going from double-leg stance (DLS) to single leg stance (SLS)), prosthesis bending (difference in the head-tip distance when going from DLS to SLS), and mean migration of the head, tip and the cement restrictor. DIMM and bending were measured at 3 months, migration at 6, 12 and 24 months. All analyses were carried out using SPSS for windows (v.15.0.0, Chicago. IL, USA). Results were reported as mean ± 95% confidence interval (CI) and regarded as significant when p < 0.05. Results. Preliminary analysis showed that DIMM of head was significantly (p = 0.02) greater for CoCr (0.97mm ± 0.6mm) than stainless steel (0.27mm ± 0.6mm). The mean stem bending for CoCr was 0.08mm (± 0.06mm) and for stainless steel 0.15mm (± 0.06mm) (p =0.77). Both implants heads migrated posteriorly, medially and distally. The mean subsidence for the cobalt-chromium and stainless steel stems was 1.02mm (±0.19mm) (p < 0.001) and 1.12mm (± 0.34mm) (p=0.001) (p= 0.07) at 24 months. Conclusion. Dynamically induced micromotion was greater for the stiffer stem, however there were no differences in terms of over all migration, indicating that survival (in terms of loosening) should be the similar for both stainless steel and CoCr versions of this implant

Introduction. The most common method for accurate kinematic analysis of the knee arthroplasty uses bi-planar fluoroscopy and model-based RSA. The main challenge is to have access to reverse-engineered CAD models of the implant components, if not provided by the company, making this method impractical for a clinical study involving many types or sizes of implants. An alternative could be to reconstruct the 3D primitive features of the implant, such as cylindrical pegs, flat surfaces and circular boundaries, based on their 2D projections. This method was applied by Kaptein et al. (2006) for hip implants. However, despite its broad potential, it has not yet been applied for studying TKA kinematics. This study develops a methodology for feature-based RSA of TKA and investigates the range of accuracies in comparison to model-based RSA. Methods. Joint-3D software was developed in the MATLAB programming language to segment and fit elementary 2D features such as circles, lines, and ellipses to the edges of the parts on the radiographs (Figure 1). The software has the capability to reconstruct the 3D location and orientation of the components based on their 2D projections. To test the accuracy of the system a standard primary knee replacement system (Zimmer NexGen) was implanted on bone replica models, and positioned at 0° to 120° flexion at 30° intervals, simulating a lunge activity. For each pose, a multi-planar radiography system developed in our lab (Amiri et al., 2011) was used to take a sagittal and a 15° distally rotated radiograph (Figure 2a). Figure 1 shows the features C, L, and E segmented on the tibia and femur. The 3D reconstruction is performed based on a number of functions: Functions ‘f’ and ‘g’ reconstruct a 3D point or line based on their 2D projections. Function ‘h’ finds the plane containing the 3D circular edge based on its two projection ellipses. Function ‘i’ finds the 3D location of a line based on one projection line, and a known 3D vector normal to the solution 3D line. Based on these, the coordinate systems of the components were reconstructed (Figure 2b):. Femur_Origin=f(C1A,C1B);. Femur_Anteroposterior=g(L1A, L1B);. Femur_Proximodistal=g(L2A,L2B);. Femur_Mediolateral=i(L,C1A–C1B),{L=L1: if flexion<45°; L=L2: if flexion>45°};. E_3D=h(E1A,E1B);. Tibia_Origin=f(E1A_Centre,E1B_Centre);. Tibia_Anteroposterior=g(L3A,L3B);. Tibia_Mediolateral=cross(E_3D, Tibia_Anteroposterior);. Tibia_Proximodistal=cross(Tibia_Anteroposterior, Tibia_Mediolateral). To determine the errors, model-based RSA measures were used as the reference using the reverse-engineered models of the components in JointTrack software (University of Florida). Results. The overall accuracies in terms of bias (the mean error) and precision (standard deviation of the errors) are shown in Figure 3. The bias was within 0.5–1 mm and 0.9–1.2°, and the calculated precision was in the range of 0.4–0.6 mm and 0.7–1.0°. The overall accuracy was 0.8±0.6 mm and 1±0.7°. Discussion. The very good accuracies obtained show the practicality of the methodology. The methodology can be easily worked out for any type of implant based on the primitive geometric features at the bone-implant interface. This method can be extremely useful in a large clinical study by eliminating the need for having the 3D models of many types and sizes of the implant available

Reverse total shoulder arthroplasty was developed to address the treatment of patients with Cuff Tear Arthropathy. Despite of the clinical improvements seen with initial reverse shoulder replacements, several mechanical problems remain. Scapular notching has been reported between 24.5% and 96% of cases. Patients have also exhibited limited external rotation, either from impingement or slackening of remaining cuff musculature. Additionally, by medializing and moving the humerus distally, patients note a loss of the normal deltoid contour leading not only to cosmetic concerns, but possibly decreasing deltoid efficiency and creating a prosthesis with less inherent stability. Finally, although mechanical failure on the glenoid side initially was thought to be uncommon, various glenoid sided problems have been reported.

Recognition of these problems led to clinical and basic science studies aimed at improving surgical technique and the design of reverse shoulder implants. During the last 10 years, our institution has been conducting biomechanical research examining the forces across the glenohumeral joint. Several different models have been created to replicate mechanical failures by integrating biomechanical information with our clinical investigations, including altering the position of the implant (tilt), the type of fixation of the implant (screw or peg), and glenoid-sided bone loss. We were able to address glenoid component failure (with initial rates of 10% in our clinical studies) by recommending locking screws to neutralize forces at the fixation site. These discoveries have reduced glenoid-sided fixation failures to less than 0.1%.

In vitro kinematic function and factors that affect impingement free glenohumeral motion of reversed implants is another area of interest. The clinical relevance of impingement includes scapular-notching, pain from impingement, instability and excessive prosthetic wear. Several models that include motion in three different planes (flexion-extension, abduction-adduction and internal-external rotation) have been developed to study multiple prosthetic, technique and anatomic factors which can result from varying degrees of impingement. By integrating the results from these models into our clinical practice (e.g., selecting a more lateralized glenosphere, selecting a varus humeral component and inferiorly translating the glenoid component on the glenoid surface), we have been able to maintain low rates of notching (∼10% at 8 year follow-up). Finally, our current work involves development of a model that attempts to understand which factors might be influential in causing instability and stiffness. Thus, biomechanics research offers an excellent opportunity for interdisciplinary collaboration to solve complex clinical problems.

Is there an optimal way to place a glenoid in reverse total shoulder arthroplasty (RTSA)? Four of the six parameters that a surgeon can control in a RTSA involve the glenoid. The parameters are: inferior tilt, increased lateral or inferior offset and increased glenosphere diameter. The theoretical challenges are further complicated by the normal variations that exist in the bony anatomy of the scapula and pathological abnormalities prevalent in as many as 40% of patients undergoing RTSA. Over the last 5 years there has been a growing body of data and study on the biomechanics, clinical outcomes and complications of this prosthesis. What have we learned? How does a surgeon incorporate this into their practice? The goal of this talk is to briefly review the current status of biomechanics on the impact of glenosphere positioning and offset on the outcome of reverse arthroplasty.

Introduction

Recent literature has shown that RSAs successfully improve pain and functionality, however variability in range of motion and high complication rates persist. Biomechanical studies suggest that tensioning of the deltoid, resulting from deltoid lengthening, improves range of motion by increasing the moment arm. This study aims to provide clinical significance for deltoid tensioning by comparing postoperative range of motion measurements with deltoid length for 93 patients.

4 years of follow-up study on 27 patients who had biological reverse total shoulder replacement 12 patients who had Bio-RSA by using Tonier Aequalis reversed implants with bone graft extracted from the head of humerus before humeral shaft was prepared. The average age of this group of patients is 77. The average pre-operative shoulder abduction on the affected side is 52 degrees and forward flexion of 90 degrees. Indication for surgery in all those cases are due to cuff tear. The average post-operative abduction is 90 degrees and forward flexion of 97 degrees. The average follow-up period is 9 months with a range from 4 to 18 months. Two patients from this group failed to make an improvement in the range of their shoulder movements post-operatively.

15 underwent Bio-RSA by using Delta XTEND reverse shoulder system without bone graft. The average age of this group of patients is 73. The average pre-operative shoulder abduction is 35 degrees and forward flexion of 37 degrees. Indication for surgery again in most of the cases is due to cuff tear, except one case was due to proximal humeral fracture. The average post-operative abduction is 96 degrees and forward flexion of 101 degrees. The average follow-up period is 19 months with a range of 4–42 months. Only one patient failed to make an improvement post-operatively. This is the patient who had Bio-RSA due to a proximal humeral fracture. 6 patients out of this group also had previous resurfacing which has failed in comparison to the bone graft group which none had previous resurfacing surgery.

The mobile-bearing variant of a single-radius design is assumed to provide more freedom of motion compared to the fixed-bearing variant because the insert does not restrict the natural movements of the femoral component. This would reduce the contact stresses and wear which in turn may have a positive effect on the fixation of the prosthesis to the bone and thereby decreases the risk for loosening. The aim of this prospective randomized study was to evaluate early migration of the tibial component and kinematics of a mobile-bearing and fixed-bearing total knee prosthesis of the same single-radius design.

According to a prospective randomized protocol 20 Triathlon single-radius posterior- stabilized knee prostheses were implanted (9 mobile-bearing and 11 fixed-bearing). Fluoroscopy and roentgen stereophotogrammetric analysis were performed 6 and 12 months post-operatively.

The 1 year post-operative roentgen stereophotogrammetric analysis results showed considerable early migrations in 3 mobile-bearing patients and 1 fixed-bearing patient. The range of knee flexion was the same for the mobile-bearing and fixed- bearing group. The mobile insert was following the femoral component during motion.

This study showed no apparent distinction in early migration and kinematics between mobile-bearing and fixed-bearing single-radius total knee prostheses. Des- pite the mobile insert was following the femoral component during motion, and therefore performed as intended, no kinematic advantages of the mobile-bearing total knee prosthesis were seen. It is concluded that a mobile insert in single-radius total knee prostheses is redundant and will not lead to additional benefits.

Introduction

Within the reconstruction of unicondylar femoral bone defects with morselized bone grafts in revision total knee arthroplasty (TKA), a stem extension appears to be critical to obtain adequate mechanical stability. Whether the stability is still secured by this reconstruction technique in bicondylar defects has not been assessed. Long, rigid stem extensions have been advocated to maximize the stability in revision TKAs. The disadvantage of relatively stiff stem extensions is that bone resorption is promoted due to stress shielding. Therefore, we developed a relatively thin intramedullary stem which allowed for axial sliding movements of the articulating part relative to the intramedullary stem. The hypothesis behind the design is that compressive contact forces are directly transmitted to the distal femoral bone, whereas adequate stability is provided by the sliding intramedullary stem. A prototype was made of this new knee revision design and applied to the reconstruction of uncontained bicondylar femoral bone defects.