Early micromotion of joint prostheses with respect to the bone can be assessed very accurately by a method called Roentgen Stereophotogrammetric Analysis (RSA); a method that uses two simultaneous X-ray exposures of the joint and has an accuracy of 0.1 mm for translations and 0.3 degree for rotations [. 1. ]. In order to reach this accuracy, metallic markers are inserted into the bone and attached to the surface of the prosthesis. These markers can then be identified automatically in the two radiographs [. 2. ]. Since the adjustments to the prosthesis are difficult, time-consuming and expensive, RSA has only been applied in a limited number of clinical trials. In a previous study we have developed a Model-based RSA algorithm, which does not require the attachment of markers to the prosthesis [. 3. ]. This algorithm is based on minimisation of the non-overlapping area (NOA) between the automatically detected contour of the prosthesis from the roentgen image, with the virtually projected contour of a three-dimensional model of the prosthesis. Because the accuracy of this NOA algorithm was not as high as the accuracy of the currently used Marker-based RSA, we have studied alternative algorithms for Model-based RSA. From a simulation study in which we used models of the Interax Total Knee Prosthesis (Stryker-Howmedica) and the G2 Hip Prosthesis (Johnson & John-son), we found that the results of the NOA algorithm can be improved substantially. The newly developed Model-based RSA algorithm is based on minimisation of the mean distance between the points of the actual contour and the virtually projected contour. The simulation study shows that the new algorithm is superior to the NOA-algorithm in situations where part of the contour is occluded, as well as in situations where the contour is distorted by noise. With the new algorithm, the residual position error can be reduced to 0.1 mm. and also the residual orientation error can be reduced to 0.3 degree, making Model-based RSA a future alternative to Marker-based RSA

Roentgen stereophotogrammetric analysis (RSA) is the most accurate radiographic technique for the assessment of three-dimensional micromotion in joints. RSA has been used previously to study the kinematics of the anterior cruciate ligament (ACL)-deficient knee and to measure knee laxity after bone-tendon-bone (BTB) reconstructions. There is no published evidence on its use in assessing hamstring grafts in vivo, in comparing hamstring versus BTB reconstruction, or in-depth analyses of graft performance. The aim of this project was to use RSA to measure laxity in both BTB and hamstring reconstructions, and to attempt a detailed analysis of graft behaviour in both reconstructions, with particular attention to graft stretching and slippage of the bony attachments. A prospective study was undertaken on 14 patients who underwent ACL reconstruction. Seven had BTB reconstruction, and seven had four-stranded semitendinosus/gracilis (STG). Tantalum markers were inserted at the time of surgery, into distal femur and proximal tibia, and also directly into the graft itself. Stress radiographs (90N anterior and 90N posterior force) were taken early post-operatively, and then at 6 weeks, and 3, 6 and 12 months. In addition to measuring total anteroposterior knee laxity, a detailed analysis of the graft itself was possible. The BTB grafts had stretched by an average of 1.54%, and the bone plugs had migrated by 0.50 mm at the femoral end and by 0.61mm at the tibial end. The hamstring grafts had stretched on average 3.94%, and the intraosseous ends had migrated by 3.96mm at the femoral end and by 7.10mm at the tibial end. This is believed to be the most detailed application of RSA in analysing the performance of the two commonly used grafts in ACL reconstruction. Details such as graft stretching and fixation slippage have not been available previously; the data obtained in this study may have implications for clinical practice

Model-based Roentgen Stereophotogrammetric Analysis (RSA) measures micromotion of an orthopaedic implant with respect to its surrounding bone, without the use of markers on the implant. In previous studies with a total knee prosthesis, Model-based RSA showed to be very accurate. In this study, Model-based RSA is validated in a phantom experiment of a total hip prosthesis. A metal backed, elliptical shaped EP-FIT PLUS ®cup was used in combination with a SL-PLUS ® hip-stem from PLUS Endoprothetik AG. In vivo conditions were simulated by using sawbones and perspex plates to mimic the bones and soft tissue. Virtual projections of the CAD models of the implant were fitted on the automatically detected contours in nine RSA radiographs and the error inmigration calculation was determined. The standard deviations of the error in translation for the cup were: 0.03, 0.05, and 0.21 mm. (x, y, z-direction) The standard deviations of the error in orientation were respectively 0.56, 0.48, and 0.18 degrees (n = 10). For the stem, the standard deviations of the error in translation are: 0.09, 0.11, and 0.29 mm and for the orientation: 0.63, 2.03, and 0.24 degrees (n = 0). The results for the cup are satisfactory, and make Model-based RSA a good alternative for conventional RSA. Especially for this type of metal backed, non hemispherical cup for which no markerless alternative is available. The error in orientation around the y-axis of the stem is of concern. Experiments with models from Reversed Engineering had similar low accuracy. We expect that the cause of these inaccuracies is the rectangular cross sectional shape of this specific hip stem, and we expect better results from experiments with differently shaped stems. The results of this study make very clear that Model-based RSA is avaluable and accurate technique, but phantom studies are always necessary to validate the accuracy for a specific implant shape

Introduction Roentgen stereophotogrammetric analysis (RSA) is the most accurate radiographic technique for measuring three-dimensional micromotion in joints, and is now being developed for the study of anterior cruciate ligament (ACL) injury and outcome after surgical reconstruction. Using RSA a prospective study of ACL reconstruction is being undertaken. The aim is to obtain accurate information on the performance of both bone-patellar tendon-bone (BPTB) and hamstring grafts post-operatively. Materials and methods 14 patients with a unilateral ACL tear who underwent ACL reconstruction have been studied prospectively. Seven had BPTB grafts, and seven had four-stranded semitendinosus/gracilis. Tantalum markers were inserted at the time of surgery, 4 each into the femur and tibia, and 8 into the graft, at regular intervals along the length. Stress stereo radiographs (90N anterior and posterior draw forces) were taken at 1, 6, 12 and 24 weeks post-operatively. They were analysed using Medis RSA software. Results Initial results suggest that in addition to measuring total anteroposterior knee laxity, detailed analysis of the graft itself is possible. Beads placed in the bone blocks of the BPTB grafts, and in the intraosseous ends of the hamstrings, enable calculation of slippage of the fixation. The BPTB bone plugs moved 0.6 to 1.2mm by 12 weeks, the Hamstrings fixation was more variable. Beads placed in the intraarticular graft may enable measurement of any post-operative stretching, but are also somewhat erratic. Identification of the site of stretching – around the tunnel entrances, or intraarticularly, should be possible. Conclusions We believe that this detailed application of RSA in analysing the performance of the two commonly used grafts in ACL reconstruction has not been previously described. We hope to gain valuable insight into the behaviour of both graft types and reasons for graft failure. This presentation will demonstrate the methods developed and include the technical difficulties encountered in this on-going study

There is no non-invasive gold standard for measuring gap formation following rotator cuff repair; re-tears are reported both on MRI and Ultrasound. Roentgen Stereophotogrammetric Analysis (RSA) has previously been used to monitor microscopic migration of markers in rigid bodies. We present a novel RSA technique using a combination of 1mm tantalum beads and metal sutures to allow accurate monitoring of gap formation following rotator cuff repair. The RSA system combines a commercially made calibration cage with software developed at Imperial College. We verified the RSA system by analysing a movable glass phantom and comparing the data with precise physical measurements of the same object: it identified a 2mm distraction of the phantom to within 0.05mm. In vitro work involved cadaveric human shoulders. We placed three 1mm RSA tantalum beads in the greater tuberosity and three metal sutures in supraspinatus tendon. We then created a tear in supraspinatus at its insertion into the greater tuberosity. We were able to show that RSA images taken before and after the tear correlated closely with direct measurements. The processed data demonstrated movement associated with gap formation. We have performed two open rotator cuff repairs using trans-osseous sutures. During surgery RSA markers were inserted into the shoulder to allow post-operative monitoring of the repair (guided by the in vitro work). Direct measurements of the distance between markers each side of the repair were taken intra-operatively (T=O). RSA images were taken immediately post-operatively (T=1 hours), day 3, day 14, and day 84. The RSA data suggests gapping of typically 3mm may have occurred at the repair sites in both patients. Ultrasound imaging was performed at the same intervals by consultant musculoskeletal radiologists blinded to the RSA data. Preliminary results correlating the two modalities suggest that ultrasound can visualise gap formation accurately even immediately post-operatively

Aim of many surgical operations on the spine is very often to achieve a solid fusion between two or more vertebrae (arthrodesis). Describing lumbar spine mobility radiographically has been determined to be very imprecise with measurement errors of three to six mm in the sagittal plane. Using roentgen stereophotogrammetric analysis (RSA) it is possible to perform clinical kinematic lumbar studies with high accuracy. Many experimental studies have presented basic data on the stabilising implant effect in human cadaver lumbar spines, but no study compared the in vivo stabilising effect in different types of implant. The RSA was performed in a radiographic set-up with two 40° angulated roentgen tubes with simultaneous exposures. A combined reference plate and calibration device with 0.8 mm tantalum balls at known positions was situated between the patient and the uniplanar film cassette, enabling simultaneous calibration and patient examination. At each RSA the patients were examined in supine and erect positions without corset. The translatory movements, induced by the change in position, of the 0.8 mm tantalum balls implanted into the fused vertebrae were calculated by computed data processing. These translations visualised the movements of the most proximal vertebra of the fusion in relation to the most distal. The present study has demonstrated the in vivo stability of lumbar fusion augmented with transpedicular screws to be adequate. Sagittal translation seems to be easier to elicit than movements along the other three-dimensional axes. A widely decompressed and destabilised vertebra without screw fixation increases the risk for persisting intervertebral translations. The RSA technique described seems to be a good way for comparing the in vivo behaviour of different implant systems

Background. Roentgen Stereophotogrammetric Analysis (RSA) represents nowadays an excellent solution for high-accuracy fixation measurement of UKAs. To date, to the best of our knowledge, no previous study has investigated long-term micromotions of a UKA using RSA. For this reason, the main purpose of the present study is to determine long-term implant fixation of 15 UKAs with all-poly tibial component using RSA at a mean 10-years follow-up. The secondary purpose was to investigate whether the progressive loss of implant's fixation correlates with a reduction of KSS scores. Methods. Fifteen non-consecutive patients with primary knee osteoarthritis received a UKA with an all-poly tibial component between January 1995 and April 2003 in the Authors' institution. Pre and post-operative KSS scores were recorded. RSA evaluation was performed on day 2 after surgery, than at 3, 6, and 12 months and yearly thereafter. The patients were evaluated with a mean follow-up of 10 years. Results. An increase of MTPM (Maximum Total Point Motion) values from 6 months to 1 year post-operatively was found respect to post-operative reference. Implants' displacement values were always less than 2 mm during the first 6 months, than two different trends were noticed in revised and non-revised implants. A linear and inverse correlation with statistical significance was found between MTPM and both clinical and functional KSS scores. Conclusion. Also in a long term follow up evaluation, RSA is an effective tool to predict functional results after an all-poly UKA

Objective: There is no non-invasive gold standard for measuring gap formation following rotator cuff repair; re-tears are reported both on MRI and Ultrasound. We present a novel RSA technique using a combination of 1mm tantalum beads and metal sutures to allow monitoring of gap formation following rotator cuff repair.

Methodology: We carried out ten open rotator cuff repairs with using trans-osseous sutures on patients with moderate to massive tears. During surgery RSA markers were inserted into the shoulder to allow postoperative monitoring of the repair. These markers took the form of 1mm RSA tantalum beads in the greater tuberosity, distal to the repair site, and three metal sutures in tendon, proximal to the repair site. Direct measurements of the distance between the markers each side of the repair were taken intra-operatively (T=O). RSA images were taken of the repair immediately postoperatively (T=1–2 hours), day 3, 2 weeks, 3 months and 1 year post-operatively. Ultrasound imaging was performed at the same intervals by consultant musculo-skeletal radiologists blinded to the RSA data.

Results: At the 3 month stage post-operatively RSA data shows an increase in the average gap between the 2 sets of markers, with considerable variation between patients (5mm to 19mm).

Conclusion: The results are highly suggestive of gap formation in the repair. The greatest increase in gap formation has been seen between 2 weeks and 3 months. During this time patients come out of their abduction arm sling and commence physiotherapy. It may be that due to excessive loading on the repair before it has fully healed has causes failure in some cases.

Introdution:

Over the last years research has focused on attempts to achieve better fixation in knee prosthesis by improving cementing techniques and prosthetic designs; thus prosthetic fixation is critical while loosening at the bone-cement interface is still an important matter for the orthopaedic surgeon.

Aims: To study prospectively the characteristic migration of four different cemented femoral stems using Radiostereometry. Methods: 96 patients undergoing cemented femoral hip replacement for osteoarthritis were randomised to receive an Exeter (Howmedica Stryker), Ultima Tapered Polished Stem [TPS], Ultima straight stem [USS] (Johnson and Johnson) or Charnley Elite (Depuy/Johnson and Johnson) stem. RSA migration measurements were performed postoperatively and at 6,12,18 and 24 months post surgery using the UMRSA system. Results: Two signiþcantly distinct patterns of distal migration in the y direction (subsidence) were seen, compatible with previous studies. Tapered stems subsided rapidly by six months, Exeter 0.85mm (±0.15) UTPS 0.85mm (±0.15), stabilising by 2 years, Exeter 1.3mm (±0.35), UTPS 1.2mm (±0.25). The USS and Elite designs showed lower migrations of 0.1mm (±0.1) and 0.15 (±0.15) mm at six and 0.25mm (±0.15) and 0.35mm (±0.15) at 24 months. For migrations and rotations in other directions, differences were seen between prostheses with the same design concept. Whilst both the UTPS and Exeter exhibited posterior migration of the head, by 24 months this was expressed as a rotation about the transverse axis for the TPS and the axial axis for the Exeter. The Elite and USS differed in rates of posterior migration and varus tilt. Conclusions: Patterns of migration for stems with the same design concept may vary due to subtle differences in prosthesis shape. These variations produce a distinct migration Ç signature È for each stem.

Introduction: In total knee arthroplasty (TKA) it remains a topic if cementless designs offer long-term stability equivalent to cemented procedures and if the components should be coated with calciumphosphate to enhance fixation. This study compares the three-dimensional migration patters of cemented and uncoated and periapatite (PA) coated tibial trays during a 2-year clinical follow-up study using roentgen stereophotogram-metric analysis (RSA) measurements as a predictor of long-term implant loosening (Ryds definition).

Methods: A double blind randomized prospective study was performed on 101 osteoarhtritic patients receiving 115 Duracon TKA. The tibial tray was either cemented (25), uncoated and uncemented (46) or PA-coated and uncemented (44). The groups were matched for sex, age, BMI and pre-op Insall score. Patients were evaluated at 1 week, 3, 6, 12 and 24 months post-operatively using standard radiographs and Insall scores. At each evaluation RSA measurements determined the translational (medial-lateral (ML), caudal-cranial (CC), anterior-posterior(AP)) and rotational (anterior tilt, external and valgus rotation) displacements of the tibial tray.

Results: Insall scores were not statistically different between the groups. Average component displacement was low for the cemented components in all directions. For the uncemented trays migration was highest in the CC direction (subsidence) and steep during the first 6 weeks. At two years the uncoated trays showed significantly more subsidence (−0.5 0.63 mm, range: −2.1 to 0.5 mm) than the cemented components (0.1 0.17 m, range: −0.2 to 0.4 mm, p< 0.05) and the PA-coated group (−0.1 0.60 mm, range: −2.8 to 0.3 mm, p< 0.05). Average subsidence of the cemented and PA-coated implants was nearly the same but variability was higher for the coated trays (p=0.01). Displacements in all other directions were not significantly different between the groups. Using Ryds definition, a total of 10 tibial trays from the cemented group (40%), 29 trays from the uncoated group (63%) and 11 trays from the PA-coated group (26%) were identified to be at risk for long-term loosening. In seven cases (all cemented) component tilt was critical.

Conclusion: At 2 years no clinical differences were found between cemented, uncoated and PA-coated tibial trays. However, RSA measurements showed significantly different migration patterns and predictions for long-term implant stability. Steep initial subsidence before stabilisation seems an inherent characteristics of uncemented fixation. In contrast, the cement layer below cemented trays can lead to AP tilt. Uncoated uncemented components migrate significantly indicating a high risk of late loosening. PA-coating reduces tray migration and the risk of long-term failure to levels equivalent to cemented fixation.

Introduction

The Accolade II taper stem incorporates design features which maximize proximal stem fit and bone contact and avoids more distal taper engagement which has been shown to be problematic. RSA was used in this study to analyze stem micromotion to 2 years post-surgery, providing an indication of long-term fixation. Pain, function and health-related quality of life were also compared before and after total hip arthroplasty (THA.)

Objectives

An important measure for the diagnosis and monitoring of knee osteoarthritis is the minimum joint space width (mJSW). This requires accurate alignment of the x-ray beam with the tibial plateau, which may not be accomplished in practice. We investigate the feasibility of a new mJSW measurement method from stereo radiographs using 3D statistical shape models (SSM) and evaluate its sensitivity to changes in the mJSW and its robustness to variations in patient positioning and bone geometry.

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

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

Roentgen stereophotogrammetric analysis (RSA) is a tool that can provide quantitative information for objective evaluation and comparison of implant migration. The purpose of this study was to develop and validate a new method to determine the position and orientation of an implant with RSA that does not require the implant modification or acquisition of accurate 3D implant models. This method utilizes information from certain common features of implant geometry. This method has demonstrated in-vitro precision and accuracy of 0.005 !0.059 mm in position and 0.09 ! 0.166° in orientation which is equivalent to both marker and model based RSA methods. Roentgen stereophotogrammetric analysis (RSA) is a tool that can provide quantitative information for objective evaluation and comparison of implant migration. RSA measures have demonstrated the ability to both predict premature implant failure before clinical or standard radiological signs appear, and to elucidate implant wear which is considered a major causal factor in failure. To provide this functionality, RSA requires either the modification of each implant by the addition of spherical markers or the acquisition of accurate 3D models of each implant. These approaches can significantly limit the application of the RSA method. The purpose of this study was to develop and validate a new method to determine the position and orientation of an implant with RSA that does not require the modifying or acquiring accurate 3D models of each implant. This method is based on the geometric inter-relationship between the pair of RSA images and geometric information from the projected outlines of certain paired (visible in both views) features of implant geometry. Evaluations were performed on a metallic acetabular cup modified with spherical markers. The implant features used in this case where the hemispherical shell and the planar circle at the base of the acetabular cup. This method has demonstrated an average in-vitro precision and accuracy of 0.005 !0.059 mm in position and 0.09 ! 0.166° in orientation which was equivalent to that achieved with the marker based method and equivalent to published model based RSA results. Funding: NSERC, GEOIDE, University of Calgary

Introduction. Primary mechanical stability is important with uncemented THR because early migration is reduced, leading to more rapid osseointegration between the implant and bone. Such primary mechanical stability is provided by the design features of the device. The aim of this study was to compare the migration patterns of two uncemented hip stems, the Furlong Active and the Furlong HAC stem; the study was designed as a randomised control trial. The implants were the Furlong HAC, which is an established implant with good long term results, and the Furlong Active, which is a modified version of the Furlong HAC designed to minimise stress concentrations between the implant and bone, and thus to improve fixation. Materials and methods. The migration of 43 uncemented femoral components for total hip replacement was measured in a randomised control trial using Roentgen Stereophotogrammetric Analysis (RSA) over two years. Twenty-three Furlong HAC and twenty Furlong Active stems were implanted into 43 patients. RSA examinations were carried out post-operatively, and at six months, 12 months and 24 months post-operatively. The patients stood in-front of a purpose made calibration frame which contained accurately positioned radio-opaque markers. From the obtained images, the 3-D positions of the prosthesis and the host bone were reconstructed. Geometrical algorithms were used to identify the components of the implant. These algorithms allowed the femoral component to be studied without the need to attach markers to the prosthesis. The migration was calculated relative to the femoral coordinate system representing the anterior-posterior (A-P), medial-lateral (M-L) and proximal-distal (P-D) directions respectively. Distal migration was termed subsidence. Results. Both stems subsided significantly during the first six months following surgery but almost all stems did not progressively subside thereafter. The Furlong Active stem experienced approximately three times the amount of subsidence of the Furlong HAC stem; this difference was significant (p = 0.02). There was one subsidence outlier (four standard deviations from the mean) for the Furlong Active stem between one and two years post-operatively. Both the stems migrated laterally and rotated into valgus. Lateral migration was greater for the Furlong Active stem; at 12 and 24 months there was a significant migration of the Furlong Active head laterally of 0.51 mm (p = 0.012) and 0.58 mm (p = 0.013) respectively. There was no significant difference in clinical scores between the implants at any RSA examination post-operatively. Discussion. The initial fixation of the Furlong Active stem was not as good as the established stem making it less likely to integrate effectively with the bone. In this study, the theoretical design of a hip replacement to minimise the stress concentration between the implant and bone and thus improve fixation actually resulted in worse implant fixation. Stems designed theoretically to improve fixation may not achieve this. Therefore we recommend that new devices should be tested using Roentgen Stereophotogrammetric Analysis. Acknowledgments This work was funded by the Furlong Charitable Research Foundation

Over the past 30 years, cemented, cementless, and hybrid fixation options have been utilised with various total knee arthroplasty (TKA) implant systems. While cemented components are widely used and considered the most reliable method of fixation, historical results may not be applicable to contemporary patients, who are increasingly younger than 65 years of age. Moreover, the literature is not definitive on which method of TKA fixation obtains the best clinical, functional, and radiographic results. A recent Cochrane meta-analysis on roentgen stereophotogrammetric analysis (RSA) included five randomised clinical trials (RCTs) in 297 participants. The authors observed that cemented fixation of tibial components demonstrated smaller displacement in relation to cementless fixation. However, the risk of future aseptic loosening with uncemented fixation was approximately half that of cemented fixation (risk ratio = 0.47, 95% CI 0.24 to 0.92) with a 16% absolute risk difference between groups. Almost all included studies recorded functional measures of Knee Society and Hospital for Special Surgery knee scores, but the authors of each study found no significant difference between the groups. Recently, highly porous metals have become an attractive fixation option in TKA due to their biomechanical properties. In a large RCT of 397 patients, Pulido et al found that uncemented highly porous metal tibias provided comparably durable fixation and reliable pain relief and restoration of function when compared with traditional cemented modular tibias. While longer term studies are needed, cementless TKAs may be a durable and reliable alternative with highly porous metals, particularly in younger patients

Total knee replacements are being more commonly performed in active younger and obese patients. Fifteen-year survivorship studies demonstrate that cemented total knee replacements have excellent survivorship, with reports of 85 to 97%. Cemented knee arthroplasties are doomed to failure due to loss of cement-bone interlock over time. Inferior survivorship occurs in younger patients and obese patients who would be expected to place increased stress on the bone-cement interfaces. Roentgen stereophotogrammetric analysis (RSA) studies have indicated that cementless fixation should perform better than cemented fixation. However, cementless fixation for total knee replacement has not gained widespread utilization due to the plethora of poor results reported in early series. The poor initial results with cementless total knee replacement have occurred due to poor implant designs such as cobalt chrome porous interfaces, poor initial tibial component stability, lack of continuous porous coating, poor polyethylene, and use of metal-backed patellae. I have used cementless fixation for total knee replacements for young, active, and heavy patients since 1986 when durability over 20 years is desirable. My series of over 1,300 cementless TKAs represents about 20% of the 6,500 total knees I have performed from 1986 to 2017. I have seen initial failures in my series due to the use of metal-backed patellae with thin polyethylene, older generation polyethylene, and use of screws with the tibial components which provide access to the metaphyseal bone for polyethylene wear debris. Overall implant fixation failures were still significantly low due to the use of a highly porous titanium surface on both the tibial and femoral components. With the advent of utilizing implants with continuous porous surfaces and highly crosslinked polyethylene, and elimination of use of metal-backed patellae and tibial screws, I have only had one revision due to aseptic loosening or osteolysis in the last 1,071 cases performed since 2002. Almost 50% of total knees are now performed on patients under the age of 65. A 55-year-old patient has a 30 year life expectancy. Modern total knee replacement design has made biological fixation predictable for young and heavy patients. Because it is a biological interface, it should respond better than cement to the increased stresses that will be applied over many years by our younger, more active and heavier total knee population