Background

The purpose of this study was to assess the overall clinical and radiographic outcomes of unicompartmental knee arthroplasty (UKA) in the 2–10 year postoperative period. The secondary goal was to compare outcomes between fixed- (FB) and mobile-bearing (MB) implant designs.

Computer navigation has been advocated as a means to improve limb and component alignment and reduce the number of outliers after total knee arthroplasty (TKA). We aimed to determine the alignment outcomes of 1500 consecutive computer-assisted TKAs performed by a single surgeon, using the same implant, with a minimum 1 year follow-up, and to analyze the outliers. Based on radiographic analysis, 112 limbs (7.5%) in 109 patients with mechanical axis malalignment of > 3° were identified and analyzed.

The indication for TKA was osteoarthritis in 107 patients and rheumatoid arthritis in 2 patients. Fifty-eight patients (53%) had undergone simultaneous bilateral TKA and 13 patients (12%) had a BMI >30. Preoperative varus deformity was seen in 100 limbs and valgus deformity in 12 limbs. Thirty limbs (27%) had an extra-articular deformity (2 post HTO limbs, 3 malunited fractures, 1 stress fracture, 21 severe femoral bowing and 3 tibial bowing) and 21 limbs (19%) had severe lateral laxity or subluxation. Thirty-eight limbs (34%) had a preoperative deformity of =10° and 24 limbs (21.5%) had varus or valgus deformity of >20°.

Postoperatively, 11 limbs were malaligned at ±3°, 74 limbs at ±4°, 22 limbs at ±5°, 2 limbs at ±6°, and 2 limbs at ±7°. Coronal plane malalignment of > ±3° of the femoral component was seen in 28 limbs, tibial component in 32 limbs, and both femoral and tibial components in 13 limbs. Twenty-six limbs with preoperative varus deformity had a postoperative valgus alignment of >183° and 3 limbs with valgus deformity had a postoperative varus alignment of <177°.

The incidence of outliers for postoperative limb alignment was low at 7.5% with the tibial component showing a higher incidence of coronal malalignment. Malalignment may be more common in cases of simultaneous bilateral procedures, preoperative limb alignment of =10°, limbs with extra-articular deformities and severe lateral instability. There was a tendency towards over-correction of the hip-knee-ankle axis in both varus- and valgus-deformed knees. Further detailed statistical analysis of the data will be presented.

This is the largest single-surgeon series of consecutive navigated TKAs and consequently the largest analysis of outliers that highlights which knees are likely to fall outside the +3 degrees of acceptable alignment and which therefore behoove the surgeon to exercise greater caution.

Introduction

In total hip arthroplasty, a high radiographic inclination angle (RI) of the acetabular component has been linked to short- and long-term complications. There are several factors that lead to RI outliers including cup version, pelvic orientation and angle of the cup introducer relative to the floor. The primary aim of this study was to analyse what increases the risk of having a cup with an RI outside the target zone when controlling cup orientation with a digital inclinometer.

Computer-assisted orthopaedic surgery (CAOS) improves mechanical alignment and the accuracy of surgical cuts in the context of total knee arthroplasty. A simplified, CAOS enhanced instrumentation system was assessed to determine if the same effects could be achieved through the use of a less intrusive system. Two cohorts of surgeons (experienced and trainees) performed a series of total knee arthroplasty resections in knee models with and without navigation-enhanced instrumentation. The percentage of resections that deviated from the planned cut by more than 2°or 2mm (outliers) was determined by post-resection advanced imaging for six unique outcome metrics. Within each experience level, the use of the CAOS enhanced system significantly reduced the total percentage of outliers as compared to conventional instrumentation (Figure 1). The experienced users improved from 35% to 4% outliers overall (p < .001) and the trainees from 34% to 10% outliers (p < .001). Comparing across experience levels, the experienced surgeons performed significantly better in only a single resection metric with conventional instrumentation (Figure 2A), varus/valgus tibial alignment, with 8.3% outliers compared to the trainee's 63% outliers (p = .004). The use of CAOS enhanced instrumentation eliminated any differences between the two user groups for all measured resections (Figure 2B). Comparing CAOS enhanced to conventional instrumentation specifically between anatomical deformity types revealed that there is significant improvement (p < .05) with the use of enhanced instrumentation for all three deformity types (Figure 3). These results suggest that non-intrusive CAOS enhanced instrumentation is a viable alternative to conventional instrumentation with possible benefits. This trial also demonstrates that additional experience may not correlate to improved surgical accuracy, and outliers may be less a result of individual surgeon ability or specific anatomic deformities, and more so related to limitations of the instrumentation used or other yet unidentified factors.

The most reported benefit of TKA navigation technologies has been the reduction in limb and component alignment outliers. This improvement has not been shown to effect clinical outcomes. This study was designed to compare the functional outcomes between computer assisted techniques and manual techniques.

Each group had 60 patients with similar demographics. The average functional outcomes (SF-36, WOMAC, range of motion, pain relief, and knee society score) were the same.

The average scores of the SF-36, Knee Society Score, WOMAC were similar for the two groups. However, fewer patients in Group II reported visual analog pain scores greater than 40 at 6 wks, 3 mos and 6 mos. At 1 yr, the pain scores of the two groups were similar. Fewer patients in Group II had KSS scores less than 70 at 3 months, 80 at 6 months, and 90 at one year, than those in Group I. The average range of motion in Group II was greater by 8 degrees at 4 wks and 3 mos, but equal to the average ROM in Group I at 6 and 12 mos. However, the number of patients with less than 90 degrees of motion at each follow-up period was less in Group II than in Group I at each follow-up period. There were fewer superficial wound infections in Group II than in Group I.

The average functional outcomes were similar; the results indicate a consistent reduction in outliers in most measured parameters of functional outcomes. In particular, the guidelines for administering pain medication and providing physical therapy were similar for the two groups. The results of this study are parallel to the radiographic results comparing TKA’s performed with manual and computer assisted instrumentation. In those studies, a reduction in outliers was consistently associated with the use of computer assisted techniques.

Background

Coronal malalignment has been proposed as a risk factor for mechanical failure after total knee arthroplasty (TKA). In response to these concerns, technologies that provide intraoperative feedback to the surgeon about component positioning have been developed with the goal of reducing rates of coronal plane malalignment and improving TKA longevity. Imageless hand-held portable accelerometer technology has been developed to address some the limitations associated with other computer assisted navigation devices including line-of-sight problems, preoperative imaging requirements, extra pin sites, up-font capital expenditures, and learning curve. The purpose of this study was to compare the accuracy and precision of a hand-held portable navigation system versus conventional instrumentation for tibial and femoral resections in TKA.

Introduction

The conventional bone resection technique in TKA is recognized as less accurate than computer-assisted surgery (CAS) and patient-matched instrumentation (PMI). However, these systems are not available to all surgeons performing TKAs. Furthermore, it was recently reported that PMI accuracy is not always better than that of the conventional bone resection technique. As such, most surgeons use the conventional technique for distal femur and proximal tibia resection, and efforts to improve bone resection accuracy with conventional technique are necessary. Here, we examined intraoperative X-rays after bone resection of the distal femur and proximal tibia with conventional bone resection technique. If the cutting angle was not good and the difference from preoperative planning was over 3º, we considered re-cutting the bone to correct the angle.

Minimally invasive total knee replacement (MIS-TKR) has been reported to have better early recovery than conventional TKR. Quadriceps-sparing (QS) TKR is the least invasive MIS procedure, but it is technically demanding with higher reported rates of complications and outliers. This study was designed to compare the early clinical and radiological outcomes of TKR performed by an experienced surgeon using the QS approach with or without navigational assistance (NA), or using a mini-medial parapatellar (MP) approach. In all, 100 patients completed a minimum two-year follow-up: 30 in the NA-QS group, 35 in the QS group, and 35 in the MP group. There were no significant differences in clinical outcome in terms of ability to perform a straight-leg raise at 24 hours (p = 0.700), knee score (p = 0.952), functional score (p = 0.229) and range of movement (p = 0.732) among the groups. The number of outliers for all three radiological parameters of mechanical axis, frontal femoral component alignment and frontal tibial component alignment was significantly lower in the NA-QS group than in the QS group (p = 0.008), but no outlier was found in the MP group.

In conclusion, even after the surgeon completed a substantial number of cases before the commencement of this study, the supplementary intra-operative use of computer-assisted navigation with QS-TKR still gave inferior radiological results and longer operating time, with a similar outcome at two years when compared with a MP approach.

Cite this article: Bone Joint J 2013;95-B:906–10.

Eligible patients were randomly allocated to PMI or standard intramedullary jigs. Smith and Nephew's patient specific cutting blocks (Visionaire) were used for PMI. Postoperative component positioning was investigated using the ‘Perth CT protocol’. Deviation of more than 3° from the recommended position was regarded as an outlier. Exact Mann-Whitney U test was used to compare component positioning and difference in proportion of outliers was calculated using Chi Squared analysis. Fifty-five knees were enrolled in the standard instrumentation group and fifty-two knees in the PMI group. Coronal femoral alignment was 0.7 ± 1.9° (standard) vs 0.5 ± 1.6° (PMI) (P=0.33). Outliers 9.4% vs 7.4% (P=0.71). Coronal tibial alignment was 0.4 ± 1.5° (standard) vs 0.6 ± 1.4° (PMI) (P=0.56). Outliers 1.9% vs 1.9% (P=0.99). Sagittal femoral alignment was 0.6 ± 1.5° (standard) vs 1.3 ± 1.9° (PMI) (P=0.07). Outliers 3.8% vs 13.2% (P=0.09). Tibial slope was 1.7 ± 1.9 ° (standard) vs 1.8 ± 2.7° (PMI) (P=0.88). Outliers 13.2% vs 24.1% (P=0.15). External rotation of femoral component was 0.6 ± 1.4° (standard) vs 0.2 ± 1.8° (PMI) (P=0.14). Outliers: 3.8% vs 5.6% (P=0.66). Compared to standard intramedullary jigs, patient matched instrumentation does not improve component positioning or reduce alignment outliers

Aims. Traditionally, acetabular component insertion during total hip arthroplasty (THA) is visually assisted in the posterior approach and fluoroscopically assisted in the anterior approach. The present study examined the accuracy of a new surgeon during anterior (NSA) and posterior (NSP) THA using robotic arm-assisted technology compared to two experienced surgeons using traditional methods. Methods. Prospectively collected data was reviewed for 120 patients at two institutions. Data were collected on the first 30 anterior approach and the first 30 posterior approach surgeries performed by a newly graduated arthroplasty surgeon (all using robotic arm-assisted technology) and was compared to standard THA by an experienced anterior (SSA) and posterior surgeon (SSP). Acetabular component inclination, version, and leg length were calculated postoperatively and differences calculated based on postoperative film measurement. Results. Demographic data were similar between groups with the exception of BMI being lower in the NSA group (27.98 vs 25.2; p = 0.005). Operating time and total time in operating room (TTOR) was lower in the SSA (p < 0.001) and TTOR was higher in the NSP group (p = 0.014). Planned versus postoperative leg length discrepancy were similar among both anterior and posterior surgeries (p > 0.104). Planned versus postoperative abduction and anteversion were similar among the NSA and SSA (p > 0.425), whereas planned versus postoperative abduction and anteversion were lower in the NSP (p < 0.001). Outliers > 10 mm from planned leg length were present in one case of the SSP and NSP, with none in the anterior groups. There were no outliers > 10° in anterior or posterior for abduction in all surgeons. The SSP had six outliers > 10° in anteversion while the NSP had none (p = 0.004); the SSA had no outliers for anteversion while the NSA had one (p = 0.500). Conclusion. Robotic arm-assisted technology allowed a newly trained surgeon to produce similarly accurate results and outcomes as experienced surgeons in anterior and posterior hip arthroplasty. Cite this article: Bone Jt Open 2021;2(6):365–370

A predictive model for final kyphosis was tested by evaluating the radiographs of forty-three patients with traumatic burst fractures. Since clinical outcomes are related to final kyphosis in the ambulatory patient rather than on the initial supine injury radiograph, the ability to predict final kyphosis is beneficial in determining treatment. This study demonstrated that in the appropriately selected patient for conservative care, the limit of final-kyphosis(Kf) can be predicted from the intial-kyphosis(KI) , such that Kf= < KI+.5KI . Outliers from this equation were patients who had unrecognized posterior column fractures, superior and inferior end-plate fractures, and/or multiple level of injury. The purpose of this study was to define a prediction model that afforded clinicians the ability to define final kyphosis from initial supine films in order to guide the management of stable burst fractures. This study has demonstrated that as a rule of thumb, the final absolute kyphosis for stable burst fractures can be expected to be up to Ki (initial absolute kyphosis) + 1.5Ki. Outliers were found to be fractures with unrecognized posterior element injury, both superior and inferior endplate fractures and multiple level injuries. The final kyphosis is clinically more relevant than the initial kyphosis in terms of functional outcome after conservative management. A prediction model for final kyphosis based on initial injury films can help guide the clinician for optimal management. Retrospective radiographic analysis was performed on forty-three patients with a minimum follow up six months. All patients suffered traumatic burst fractures, which were deemed stable as to be satisfactorily managed in a brace. Serial radiographs were used to determine initial (Ki) and final (Kf), Kyphosis angles. Predicted Kf was determined using the equation Kf =Ki + 1.5 Ki. The initial absolute kyphosis was the measured kyphosis using the Cobb technique and including the loss of the expected normal lordosis of that spinal segment. Inclusion criteria included burst fractures at between levels T10 – L3 in the neurologically intact patient. The equation accurately predicted the final outcome , Kf, in 70 % of the cases. In 20% of the cases, the Kf was less than expected. (Acceptable clinical result). In 10% of the cases, Kf was greater than predicted or achieved a clinically unacceptable kyphotic angulation requiring secondary surgery. In this group of outliers, post-hoc analysis identified unrecognized posterior element injury, both superior and inferior endplate fractures and multiple level injuries. In traumatic burst fractures, the goal of management is to protect the spine during healing while maintaining an acceptable alignment, which will not lead to late pain and deformity. A final absolute kyphosis angle, Kf, from twenty to thirty degrees has been variably regarded as a threshold to obtain a good clinical outcome. Criteria for stability have been previously documented, however variables are based on initial presentation. Aside from careful classification of the fracture type, the current “rule of thumb” prediction model for Kf may further help the clinician with management decisions

BACKGROUND. The aim of Patient-specific instrumentation surgery is to improve accuracy and limit the range of surgical variability. The main purpose of this study is to summarize and compare the radiographic outcomes of TKA performed using Patient-specific instrumentation compared with conventional techniques. PURPOSES. In this study, we compared varus/valgus of the individual prosthesis components, rotation of femoral components and posterior slope of tibial components of 40 TKAs performed using a patient-specific technique with values from a matched control group of patients who were operated on by conventional intramedullary alignment technique. METHODS. We retrospectively evaluated 55 primary TKAs performed for osteoarthritis: conventional instrumentation using the PFC Sigma (n = 15) patient-specific instrumentation using GMK MyKnee© (n = 40). Varus/valgus of the individual prosthesis components, rotation of femoral components and posterior slope of tibial components were measured from CT images taken post operation, whether there were more outliers with one of the two methods. The fraction of outliers (> 3°) was determined. RESULTS. There was excellent reliability with low standard deviations for the determination of femoral component rotation and varus/valgus of the tibial components. There were significantly more outliers in the conventional (26.7%) group than in the patient-specific instrument group (10.0%). Outliers in Varus/valgus of femoral components were comparable between groups (7.5% in the patient-specific instrument group and 6.7% in the conventional instrument group). Other parameters such as posterior slope of tibial components did not differ in terms of outliers. CONCLUSIONS. In this study, Patient-specific instrument was effective in significantly reducing outliers of rotational femoral component and varus/valgus of the tibial components alignment during TKA. Therefore, additional studies are needed to determine whether patient-specific instrumentation improves clinical function or patient satisfaction

Introduction. The limited field of view with less-invasive hip approaches for total hip arthroplasty can make a reliable cup positioning more challenging. The aim of this study was to evaluate the accuracy of cup placement between the traditional transgluteal approach and the anterior approach in a routine setting. Objectives. We asked if the (1) accuracy, (2) precision, and (3) number of outliers of the prosthetic cup orientation differed between three study groups: the anterior approach in supine position, the anterior approach in lateral decubitus position, and the transgluteal approach in lateral decubitus position. Methods. In a retrospective comparative study we compared the inclination and anteversion of the cup after total hip arthroplasty (THA) in a consecutive series of 325 patients (350 hips). The transgluteal approach group consisted of 67 hips operated in lateral decubitus position; the anterior approach in supine position consisted of 127 operated and the anterior approach in lateral decubitus position consisted of 156 hips. The aim of the cup orientation was Lewinnek's safe zone defined by an inclination of 40±10° and an anteversion of 15°±10°. The postoperative cup orientation was determined using a validated computer-assisted method based on statistical shape modeling. This method allows the virtual creation of an accurate three-dimensional pelvic model for each individual patient based on the two-dimensional anteroposterior pelvic radiograph. The inclination and anteversion was then calculated relative to the anterior pelvic plane – a natural reference plane for the calculation of inclination and anteversion. Accuracy was defined as the difference from the cup orientation to Lewinnek's target value. Precision was defined as the standard deviation of the two angles. Outliers were characterized by an anteversion or inclination angle outside of Lewinnek's safe zone. Results. (1) The accuracy of the anterior approach in supine position did not differ compared to the transgluteal approach, but differed to the anterior approach in supine position for inclination (p=0.882; p<0.001) (Figure 1) and anteversion (p = 0.014; p<0.001) (Figure 2). (2) The precision of the anterior approach in supine position was significantly higher compared to the transgluteal approach (p<0.001) and the anterior approach in lateral decubitus position for anteversion (p<0.001 for both groups) and inclination (p<0.001 for both groups) (Figure 3). (3) There was a significantly reduced number of outliers for the anterior approach in supine position compared to the anterior approach in lateral position (p=0.001) but not in comparison to the transgluteal approach (p=0.999) (Figure 2). Conclusions. The anterior approach in supine position results in a more precise placement of the prosthetic cup both for inclination and anteversion. Cup placement with less-invasive approaches does not lead to a higher variability of cup placement despite the more limited surgical field of view. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

In this study we randomised 140 patients who were due to undergo primary total knee arthroplasty (TKA) to have the procedure performed using either patient-specific cutting guides (PSCG) or conventional instrumentation (CI). . The primary outcome measure was the mechanical axis, as measured at three months on a standing long-leg radiograph by the hip–knee–ankle (HKA) angle. This was undertaken by an independent observer who was blinded to the instrumentation. Secondary outcome measures were component positioning, operating time, Knee Society and Oxford knee scores, blood loss and length of hospital stay. A total of 126 patients (67 in the CI group and 59 in the PSCG group) had complete clinical and radiological data. There were 88 females and 52 males with a mean age of 69.3 years (47 to 84) and a mean BMI of 28.6 kg/m. 2. (20.2 to 40.8). The mean HKA angle was 178.9° (172.5 to 183.4) in the CI group and 178.2° (172.4 to 183.4) in the PSCG group (p = 0.34). Outliers were identified in 22 of 67 knees (32.8%) in the CI group and 19 of 59 knees (32.2%) in the PSCG group (p = 0.99). There was no significant difference in the clinical results (p = 0.95 and 0.59, respectively). Operating time, blood loss and length of hospital stay were not significantly reduced (p = 0.09, 0.58 and 0.50, respectively) when using PSCG. . The use of PSCG in primary TKA did not reduce the proportion of outliers as measured by post-operative coronal alignment. . Cite this article: Bone Joint J 2015;97-B:56–63

Aim:. AIS causes a loss of trunk height. This paper documents this loss against sitting height standards and assesses formulae for adjusting height loss back to the standard. Methods:. A total of 334 patients (84% female) with AIS and no other known systemic disease had sitting height measured. This was compared to standards of sitting height with age and the ratio of height to sitting height with age (HSH). The corrected height was calculated using published formulae and replotted against these standards. Results:. Both sexes had significant numbers of patients under the 5th centile compared to those above the 95th centile for sitting height (p<0.05 in males and females) and for HSH centiles (p<0.05 in males and females). All formulae increased the sitting height back to within the standards. In males only the Ylikoski formula demonstrated any significant difference in sitting height and HSH. In females the Kono formula gave the least significant difference between those above and below the 95th and 5. th. centiles for sitting height and the Hwang formula for HSH. Discussion:. Scoliosis causes a loss of sitting height seen with the centile standards for sitting height and height to sitting height ratios. This can be corrected, the most accurate formula being Hwang, correcting the data to lie between the 5th and 95th centiles for sitting height with no significant difference between the number of outliers to these centiles. Outliers after use of this formula may suggest alternative pathology. Conflict Of Interest Statement: No conflict of interest

Purpose. 182 AMIS Total Hip Replacements were analysed for implant placement using the IMATRI system to evaluate the accuracy of the minimal invasive technique. These hips were done in two different periods to assess if the measurement and analyses of the implant placement improved over time. Methods. 182 Consecutive AMIS Total Hip Replacements were performed during two different periods. Postoperative X-rays were done on all cases in the recovery room and the images were all uploaded to the IMATRI system. Leg length discrepancy, acetabular cup inclinations and anteversion were measured using predetermined morphing systems. Data were then analysed to define accuracy of implant placement. Outliers were also analysed to explain possible reasons. Summary. 70% of the cases had leg lengths within 5mm of the opposite hip with range of −9 to +25 mm leg length difference. Acetabular cup anteversion varied from 5° to 30° with 72% between 10° and 20° anteversion. Acetabular cup inclination varied from 27° to 58° with 87% between 35° and 55°. Implant positioning improved during the second period, especially in the degree of anteversion with 77% of prosthesis between 5° and 25°deg anteversion. NO DISCLOSURES

Purpose Of Study. The study was started in 2004 to determine the best bearing surface in the long term, and to measure the metal ion levels generated by each of the bearing surfaces. We present the latest updated results. Material and methods. A prospective randomised study was started in 2004 to compare the wear characteristics of Ceramic on X linked Polyethylene (C.O.P.), Ceramic on Ceramic (C.O.C), Ceramic on Metal (C.O.M.) and Metal on Metal (M.O.M) bearings. The level of Cobalt and Chrome ions in red blood cells have been documented at serial intervals, using the ICP – MS method. Aside from the bearing surfaces the rest of the implant is standard, using a Pinnacle Cup, Corail Stem and 28mm heads. 256 Cases were enrolled on the study. To date 71 cases have been lost due to death (26), revision (9) and lost to follow up (36), leaving us with 185 for follow-up. An even spread of cases in each bearing surface are still available for follow up, viz. 46 C.O.P, 48 C.O.C., 44 C.O.M. and 47 M.O.M. Average follow up is currently 4.8 years, ranging up to 9 years. Results. To date no difference could be determined on the wear properties, with all bearings being acceptable. The only wear that could be measured was with C.O.P. bearings. Metal ion levels at no stage have been raised in the C.O.P. and C.O.C. bearings. Initially C.O.M. bearings had lower levels than M.O.M. bearings, but by 36 months were virtually the same with the mean below the 2ug/L level. At 60 month follow up values on almost half of the cases show markedly lower metal ions in the C.O.M. group. Outliers in both groups were associated with poorly placed cups, with the C.O.M. bearing being more forgiving that the M.O.M. group. Conclusion. To date the C.O.P. and C.O.M. bearings are performing the best of the 4 bearing combinations. NO DISCLOSURES

Aim: Preliminary results and complications of AGC Total knee Arthroplasty with early results are presented. Materials and Methods: 51 AGC Total Knee Arthroplasties were undertaken between October 2005 and September 2006. There were 22 males and 28 females. Indication for Total Knee Arthroplasty was Primary and Traumatic Osteoarthris. Brain Lab Implant dedicated Navigation was used. Results: Outliers were significantly reduced. Complications including superficial infection, late rehabilitation, and stiffness are reported. No revision was undertaken. Tips and pearls regarding navigated Arthroplasty with reference to learning curve are discussed. Discussion: Each navigation system type has its advantages and disadvantages and can be used with minimally invasive surgery (MIS) total knee arthroplasty (TKA). In addition, concerns for computer glitches, training of personnel, extra time requirements, cost and ability to demonstrate improvements in technique and results are discussed. Conclusions: Navigated Knee Arthroplasty using AGC-Biomet implant is recommended. Early experience is reported. Salient features of early learning curve are discussed. The current paper shows how the anatomic approach can influence soft tissue tension and support the surgeon during release of soft tissues in leg axis deformities

Introduction. It is widely accepted that computer navigation more reliably restores neutral mechanical alignment than conventional instrumentation in total knee arthroplasty (TKA) surgery. Recently, magnetic resonance (MR) based instrumentation has been introduced to the market with a rapid growth in usage. However, a paucity of comparative data still exists on the precision of magnetic resonance (MR) based instruments in achieving acceptable lower limb alignment when compared to other validated techniques. In this analysis, we compare the radiographic outcomes of 3 techniques to achieve satisfactory prosthetic alignment by 2 surgeons using the same prosthesis and surgical technique. Methods. A series of 180 patients who had undergone TKA surgery were included in this study. Two fellowship-trained knee surgeons performed all surgeries using the same cemented, posterior stabilized implants (NexGen, Zimmer, Warsaw, In). Patients were stratified in to 3 groups according to the technique used to align the knee; 1. Conventional Intra-medullary Instrumentation, 2. Computer Navigation (Orthosoft), and 3. MR-based guides (Zimmer PSI). All patients underwent a post-operative CT Perth Protocol to assess coronal, sagittal and rotational alignment of the femoral and tibial implants. A radiographer who was blinded to the alignment technique used performed all radiographic measurements. Outliers were defined at a deviation of more than 3 degrees from the mechanical axis in all planes of motion. Results. The radiographic outcome measures will be presented to highlight the significant differences between 3 groups. In addition, the early surgical experience with the introduction of MR based instruments will be reviewed along with the early problems encountered from tibial sagittal alignment that became apparent with time. Conclusion. The rapid introduction of MR based instruments in to the market by several prosthetic companies has occurred without adequate pre-release analysis. This study will allow surgeons to make an informed decision on whether to use this technology based on validated radiographic measures, when compared to both conventional alignment techniques and computer navigation

Aims

The aim of this study was to compare the biomechanical models of two frequently used techniques for reconstructing severe acetabular defects with pelvic discontinuity in revision total hip arthroplasty (THA) – the Trabecular Metal Acetabular Revision System (TMARS) and custom triflange acetabular components (CTACs) – using virtual modelling.