A primary goal of shoulder arthroplasty is to place the components in anatomic version. However, traditional instrumentation does not accommodate glenoid wear patterns. Therefore, many investigators have attempted to use computer modeling or CT-based algorithms to create custom targeting guides to achieve this goal. There are some recent studies investigating the use of custom guides. Iannotti et al. published in JBJS-American in 2012 on the use of patient specific instrumentation. There were 31 patients included in the study. The authors found that the planning software and patient specific instrumentation were helpful overall, but particularly of benefit in patients with retroversion in excess of 16 degrees. In this group of patients, the mean deviation was 10 degrees in the standard surgical group and 1.2 degrees in the patient specific instrumentation group. Throckmorton presented a study at the AAOS in 2014 on 70 cadaveric shoulders. There was one high volume surgeon (>100 shoulder arthroplasties a year), two middle volume surgeons (20–50 shoulder arthroplasties a year), and two low volume surgeons (less than 20 shoulder arthroplasties per year). Overall, the custom guide was significantly more accurate than standard instrumentation. The custom guides were found to be especially more accurate among specimens with associated glenoid wear. There were no strong trends to indicate consistent differences between high, medium, and low volume surgeons. The authors concluded that custom guides have narrower standard deviation and fewer significant errors than standard instrumentation. Custom guides continue to evolve for use in shoulder arthroplasty including some guides that allow the surgeon to decide intra-operatively between anatomic shoulder arthroplasty and reverse arthroplasty. Additional studies will be necessary to further define the role of patient specific instrumentation in practice

Introduction:. Total knee arthroplasty (TKA) is an effective operation for the management of osteoarthritis of the knee. Conventional technique utilizing manual instrumentation (MI) allows for reproducible and accurate execution of the procedure. The most common techniques make use of intramedullary femoral guides and either extrameduallary or intrameduallary tibial guides. While these methods can achieve excellent results in the majority of patients, those with ipsilateral hardware, post-traumatic deformity or abnormal anatomy may preclude the accurate use of these techniques. Patient-specific instrumentation (PSI) is an alternative innovation for total knee arthroplasty. Utilizing magnetic resonance imaging (MRI) or computed tomography (CT), custom guide blocks are fabricated based on a patient's unique anatomy. This allows for the benefits of computer assisted navigation (CAN) but without the increased operative times or the high learning curve associated with it. Furthermore it allows the use of familiar cutting blocks and guides to check the accuracy of the PSI guide blocks. In this study we sought to evaluate the accuracy of PSI techniques in patients with previous ipsilateral hardware, which would make the use of MI technically challenging and possibly subject to inaccuracy. Methods:. After reviewing our database of 300 PSI total knee arthroplasty patients, 16 patients were identified (10 male, 6 female) using the Zimmer NexGen Patient Specific Instrumentation System. Fourteen patients included in the study had a preexisting total hip arthroplasty on the ipsilateral side, 1 had a preexisting sliding hip screw, and 1 patient had a preexisting cephalomedullary nail. Postoperative mechanical axis alignment measurements were performed using plain long-standing radiographs. The American Knee Society Score was used to evaluate clinical outcomes postoperatively. Results:. Sixteen total knee arthroplasties were performed using PSI, all in the setting of previous ipsilateral hardware placement. The average age at the time of surgery was 72, with patients ranging from 56 to 85 years of age. Eleven of the included knees had a preoperative varus alignment and 5 had valgus alignment. The average value of a deformity identified via the preoperative planning software was 7.85°. The average value of a deformity identified via preoperative radiographs was 10.1°. Average postoperative mechanical axis was 3.1° measured from plain radiographs. Average angle between the femoral mechanical axis and femoral component was 90.0°. The average angle between the tibial mechanical axis and tibial component was 90.6°. The average difference between the femoral mechanical and anatomic axes was 5.9°. The average discrepancy between medial and lateral joint space on an anterior-posterior standing radiograph was 0.4 mm. At an average of 4.5 months follow-up, American Knee Society knee scores show an aggregate average score of 82.94. Conclusion:. Patient specific instrumentation is an innovative technology in TKA that replaces the use of intramedullary femoral guides and either extramedullary or intramedullary tibial guides. This study demonstrates that PSI is capable of producing favorable radiographic and clinical outcomes despite preexisting ipsilateral hardware, which may preclude the use of customary manual instrumentation. We believe PSI is an accurate and effective tool for use in patients with preexisting ipsilateral hardware

INTRODUCTION:. Despite clear clinical advantages Unicompartimetal Knee Replacement still remain an high demanding and less forgiving surgical procedure. Different Authors in literature pointed out how malalignment increases the rate of aseptic failure even more than in TKR. Computer-assisted surgery has been proposed to improve implant positioning in joint replacement surgery with no need of intramedullary guide despite no still proven clinical advantages. Likewise more recently Patient Specific Instrumentation (PSI) has been suggested, even in partial knee reconstruction, as a new technology capable of new advantages such as shorter surgical times and lower blood losses maintaining at least the same accuracy. Aim of the study is to present a prospective study comparing 2 groups of UKR s using either a computer assisted technique or a CT-based Patient Specific Instrumentation. MATERIALS AND METHODS:. Since January 2010, 54 patients undergoing UKR because medial compartment arthritis were enrolled in the study prospectively. Before surgery patients were alternatively assigned to either computer-assisted alignment (group A) or patient specific instrumentation group (group B). In the group A (27 knees) the implant (Sigma, Depuy Orthopaedics Inc, Warsaw, Indiana, USA) was positioned using a CT-free computer assisted alignment system specifically created for UKR surgery (OrthoKey, Delaware, USA). In group B (27 knees) the implant (GMK Uni, Medacta, Castel San Pietro, Switzerland) was performed using a CT-based PSI technology (MyKnee, Medacta, Castel San Pietro, Switzerland). In both the groups all the implants were cemented and using always a fixed metal backed tibial component. The surgical time and complications were documented in all cases. Six months post-operatively the patients underwent to the same radiological investigation to determine the frontal femoral component angle (FFC), the frontal tibial component angle (FTC), the hip-knee-ankle angle (HKA) and the sagittal orientation (slope) of tibial/femoral components. The number and percentage of outliners for each parameter was determined. In addition the percentage of patients in each group with all 5 parameters within the desired range was calculated. Furthermore the 2 groups were clinically assessed using KSS and Functional score. RESULTS:. There were no differences in the clinical outcome. The mean surgical time was longer in the navigated group of a mean of 5.9 minutes without any statistical differences in complications. The mechanical axes, tibial slope the FTC angle were significantly better aligned in the navigated group. A statistically significant higher number of outliners was seen in the PSI group. The number of implants with all 5 radiological parameters aligned within the desired range was statistically higher in the navigated group. All the implants in the navigated group were correctly aligned in all the planned parameters. Discussion:. To our knowledge this is the first prospective study in literature assessing navigation compared to PSI technique in UKR surgery. Despite a slight not significant longer surgical time in the navigated group, at a short follow-up the results could not demonstrate any clinical differences between the 2 technologies However according to their results the Authors indicate navigation as more helpful in UKR surgery compared to PSI technology in terms of accuracy

Introduction:. Patient specific instrumentation (PSI) is an innovative technology in total knee arthroplasty. With the use of a preoperative MRI or CT scan, custom guide blocks are individually manufactured for each patient. Contrary to other TKA technologies such as computer-assisted surgery, PSI utilizes measured resection technique rather than a primarily ligament balancing technique. This has the potential to negatively affect the operating surgeon's ability to achieve optimal soft tissue balancing, which is especially critical in patients with severe lower extremity malalignment. Despite early research suggesting that PSI is accurate, has a low learning curve, and can reduce OR time, it remains unclear whether a surgeon using PSI can achieve optimal soft tissue balancing using a measured resection technique. The purpose of this study is to evaluate the efficacy of PSI in patients with severe preoperative limb alignment deformities. Methods:. Fifty PSI total knee arthroplasties were performed on 46 patients (21 male, 25 female) using the Zimmer NexGen Patient Specific Instrumentation system. Each patient included in the study had a minimum preoperative deformity of at least 10° varus or valgus measured on preoperative long leg standing radiographs, Zimmer preoperative software or both. Forty-three of the included knees had a varus deformity and 7 had a valgus deformity. Preoperative mechanical axis alignment measurements were obtained using the PSI preoperative planning software and were manually calculated using pre-operative long leg standing radiographs. Postoperative mechanical axis alignment measurements were calculated using plain long leg standing radiographs. The Knee Society Scoring System was used to evaluate clinical and functional outcomes at 1 to 6 months postoperatively. Results:. Average preoperative deformity as calculated with the PSI preoperative planning software and as measured on plain radiographs were 11.5° and 13.3°, respectively. Average postoperative mechanical axis was 3.4° (0.1°–14.4°)-measured from plain radiographs. The average angle between the femoral mechanical axis (FMA) and femoral component was 88.1° (79.3°–93.7°). The average angle between the tibial mechanical axis (TMA) and tibial component was 88.1° (78.4°–90.7°). The average difference between the femoral mechanical and anatomic axes was 6.2° (4.2°–9.1°). The average discrepancy between medial and lateral joint space on an anterior-posterior standing radiograph was 0.1 mm (0–1.9 mm). No patients required soft tissue releases intraoperatively. The American Knee Society criterion showed an aggregate average score of 81.5. Conclusion:. Patient specific instrumentation (PSI) is an innovative technology in TKA utilizing a measured resection technique. It has not been previously established whether or not this technology is effective at restoring optimal soft tissue balance in TKA, particularly in individuals with severe preoperative alignment deformities. This study demonstrates that PSI is capable of producing favorable radiographic and clinical outcomes in a subset of patients with at least 10° of malalignment pre-operatively

Introduction. Patient specific instrumentation (PSI) is an innovative technology in total knee arthroplasty (TKA). With the use of a preoperative MRI or CT scan, custom guide blocks are individually manufactured for each patient. Contrary to other TKA technologies such as computer-assisted surgery, PSI utilises measured resection technique rather than a primarily ligament balancing technique. This has the potential to negatively affect the operating surgeon's ability to achieve optimal soft tissue balancing, which is especially critical in patients with severe lower extremity malalignment. Despite early research suggesting that PSI is accurate, has a low learning curve, and can reduce operating room time, it remains unclear whether a surgeon using PSI can achieve optimal soft tissue balancing using a measured resection technique. The purpose of this study is to evaluate the efficacy of PSI in patients with severe preoperative limb alignment deformities. Methods. Fifty PSI total knee arthroplasties were performed on 46 patients (21 male, 25 female) using the Zimmer NexGen Patient Specific Instrumentation system. Each patient included in the study had a minimum preoperative deformity of at least 10° varus or valgus measured on preoperative long leg standing radiographs, Zimmer preoperative software or both. Forty-three of the included knees had a varus deformity and 7 had a valgus deformity. Preoperative mechanical axis alignment measurements were obtained using the PSI preoperative planning software and were manually calculated using preoperative long leg standing radiographs. Postoperative mechanical axis alignment measurements were calculated using plain long leg standing radiographs. The Knee Society Scoring System was used to evaluate clinical and functional outcomes at 1 to 6 months postoperatively. Results. Average preoperative deformity as calculated with the PSI preoperative planning software and as measured on plain radiographs were 11.5° and 13.3°, respectively. Average postoperative mechanical axis was 3.4° measured from plain radiographs. The average angle between the femoral mechanical axis (FMA) and femoral component, and between the tibial mechanical axis (TMA) and tibial component, was 88.1°. The average difference between the femoral mechanical and anatomic axes was 6.2°. The average discrepancy between medial and lateral joint space on an anterior-posterior standing radiograph was 0.1mm. No patients required soft tissue releases intraoperatively. The American Knee Society criterion showed an aggregate average score of 81.5. Conclusion. Patient specific instrumentation (PSI) is an innovative technology in TKA utilising a measured resection technique. It has not been previously established whether or not this technology is effective at restoring optimal soft tissue balance in TKA, particularly in individuals with severe preoperative alignment deformities. This study demonstrates that PSI is capable of producing favourable radiographic and clinical outcomes in a subset of patients with at least 10° of malalignment pre-operatively. Given the American Knee Society scores as well as the radiographic findings of an average mechanical axis of 3.4° post-operatively, we believe that this technique can achieve comparable results to techniques using intraoperative soft tissue balancing. We believe PSI is an accurate and effective tool for use in patients with severe preoperative angular deformities of the knee

Introduction. Patient Specific Instrumentation (PSI) has the potential to allow surgeons to perform procedures more accurately, at lower cost and faster than conventional instrumentation. However, studies using PSI have failed to convincingly demonstrate any of these benefits clinically. The influence of guide design on the accuracy of placement of PSI has received no attention within the literature. Our experience has suggested that surgeons gain greater benefit from PSI when undertaking procedures they are less familiar with. Lateral unicompartmental knee replacement (UKR) is relatively infrequently performed and may be an example of an operation for which PSI would be of benefit. We aimed to investigate the impact on accuracy of PSI with respect to the area of contact, the nature of the contact (smooth or studded guide surfaces) and the effect of increasing the number of contact points in different planes. Method. A standard anatomy tibial Sawbone was selected for use in the study and a computed tomography scan obtained to facilitate the production of PSI. Nylon PSI guides were printed on the basis of a lateral UKR plan devised by an orthopaedic surgeon. A control PSI guide with similar dimensions to the cutting block of the Oxford Phase 3 UKR tibial guide was produced, contoured to the anterior tibial surface with multiple studs on the tibial contact surface. Variants of this guide were designed to assess the impact of design features on accuracy. These were: a studded guide with a 40% reduction in tibial contact area, a non-studded version of the control guide, the control guide with a shim to provide articular contact, a guide with an extension to allow distal referencing at the ankle and a guide with a distal extension and an articular shim. All guides were designed with an appendage that facilitated direct attachment to a navigation machine (figure 1). 36 volunteers were asked to place each guide on the tibia with reference to a 3D model of the operative plan. The order of placement was varied using a counterbalanced latin square design to limit the impact of the learning effect. The navigation machine recorded deviations from the plan in respect of proximal-distal and medial-lateral translations as well as rotation around all three axes. Statistical analysis was performed on the compound translational and rotational errors for each guide using ANOVA with Bonferroni correction with statistical significance at p<0.05. Results. Contact points in greater than one plane led to a trend for increasing accuracy and precision of PSI guide placement with respect to rotational alignment, this achieved statistical significance relative to the control guide only with the guide that included articular and distal contact points (figure 2). No significant differences were found with respect to translation. Changes in contact area within the same plane and the use of smooth or studded contact points made no significant difference to accuracy. Conclusion. PSI guide design significantly impacts on accuracy of placement. PSI guides for UKR should endeavour to include widely separated reference points in different planes to maximise rotational accuracy

Introduction:. Patient specific instrumentation (PSI) generates customized guides from a magnetic resonance imaging based preoperative plan for use in total knee arthroplasty (TKA). PSI software must be able to accommodate differences in implant design. The purpose of the present study was to determine whether any differences in the accuracy of limb alignment, component alignment, component sizing, or bony resection could be identified in patients undergoing PSI TKA with identical PSI software and one of two different implant systems. Methods:. In this case-control study, two different implant systems from the same manufacturer were evaluated in 37 consecutive PSI TKA (Group 1) and 123 consecutive PSI TKA (Group 2) performed by a single surgeon. A third group (Group 3) consisted of 12 consecutive TKA performed with manual instrumentation and the same implant system as Group 1. Identical software was used to generate a preoperative plan from which planned limb alignment, component alignment, component sizes, and bony resection were determined. Intraoperatively, actual component sizes, bony resection, and recut frequency were determined. Long-standing and lateral radiographs were obtained preoperatively and 4-weeks postoperatively to evaluate limb and component alignment. Results:. Groups were similar with regard to age, gender, BMI, and preoperative alignment. No differences in the accuracy of limb alignment, component alignment, component sizing, or PSI-planned versus actual resection were found between Groups 1 and 2. The rate of recuts required was lower in Group 1 than Group 2 for the proximal tibia (3% vs. 35%; p < 0.05). No differences were found in limb alignment, component alignment, or bony resection between the Groups 1 and 3. Group 1 showed less variation than Group 3 in resection depth of the posterior femur (SD 1.4 mm vs. 2.1 mm) and proximal tibia (SD 1.5 mm vs. 2.3 mm). Discussion:. No discernible differences in the accuracy of limb alignment, component alignment, and component sizing were found between Groups 1 and 2. Group 1 required fewer recuts than Group 2 for the proximal tibia. There may be characteristics of implant design, e.g. the slope of the tibial plateau, that may influence the ability of PSI to accurately determine cut thickness. No differences in limb alignment, component alignment, or bony resection were identified between Groups 1 and 3. Group 1 showed less variability in resection depth than Group 3 in the posterior femur and proximal tibia. This study suggests that PSI can be equally accurate for different implant systems. For a given implant system, PSI shows less variation in resection depth when compared to manual instrumentation

Background. In our pursuit of surgical accuracy and precision we often neglect to evaluate our results objectively. With the use of Computerised Tomography (CT) in pre-operative planning we can use the same technology in order to evaluate surgical accuracy. Hypothesis. The use of Patient Specific Instrumentation (CT based) produces an accurate intra operative guide for precision cutting in knee arthroplasty. Method. A prospective study using Patient Specific Instrumentation (customized cutting blocks) was performed on 35 patients. The small cohort value is due to the high costs of post-operative CT. A CT based software was used to evaluate the pre-operative knee alignment. Surgery was planned and verified on a web based programme with the use of 3D models. Cutting blocks were custom made and used as intra operative guide to make the relevant cuts. Pre and post-operative CT scans were compared for AP and lateral alignment, femoral external rotation and flexion and tibial slope. Knee Society scores were also used to evaluate the clinical outcome. Results. The values for AP and lateral limb alignment, femoral external rotation and flexion were the same as the pre-operative values with no significant deviation (maximum 2 degree difference). The posterior tibial slope was the only value that showed significant deviation from the pre-planned values. Conclusion. There was a significant difference for the posterior tibial slope but otherwise we found no difference in pre and post-operative limb alignment measurements. Pre-operative planning with the use of CT based customised cutting blocks is a reliable and accurate option to obtain optimal alignment and prosthetic orientation in total knee arthroplasty. NO DISCLOSURES

Recent innovations in total ankle replacement (TAR) have led to improvements in implant survivorship, accuracy of component positioning and sizing, and patient outcomes. CT-generated pre-operative plans and cutting guides show promising results in terms of placement enhancement and reproducibility in clinical studies. The purpose of this study was to determine the accuracy of 1) implant sizes used and 2) alignment corrections obtained intraoperatively using the cutting guides provided, compared to what was predicted in the CT generated pre-operative plans.

This is a retrospective study looking at 36 patients who underwent total ankle arthroplasty using a CT generated pre-operative planning system between July 2015 and December 2017. Personalized pre-operative planning data was obtained from the implant company. Two evaluators took measurements of the angle corrected using pre- and post-operative weight bearing ankle AP X-rays. All patients had a minimum three-month follow-up with weightbearing postoperative radiographs. The actual correction calculated from the radiographic assessment was compared with the predicted angles obtained from pre-operative plans. The predicted and predicted alternative component sizes and actual sizes used were also compared. If either a predicted or predicted alternative size was implanted, we considered it to be accurate.

Average age for all patients was 64 years (range 40–83), with a body mass index of 28.2 ± 5.6. All surgeries were performed by two foot and ankle surgeons. The average total surgical time was 110 ± 23 minutes. Pre-operative alignment ranged from 36.7 degrees valgus to 20 degrees varus. Average predicted coronal alignment correction was 0.8 degrees varus ± 9.3 degrees (range, 18.2 degrees valgus to 29 degrees varus) and average correction obtained was 2.1 degrees valgus ± 11.1 degrees. Average post-op alignment was consistently within 5 degrees of neutral. There were no significant differences between the predicted alignments and the postoperative weightbearing alignments. The predicted tibia implant size was accurate in all cases. The predicted sizes were less accurate for talar implants and predicted the actual talar implant size used in 66% of cases. In all cases of predicted talar size mismatch, surgical plans predicted 1 implant size larger than used.

Preliminary analyses of our data is comparable to previous studies looking at similar outcomes. However, our study had higher pre-operative deformities. Despite that, post-op alignments were consistently within 5 degress of neutral with no significant difference between the predicted and actual corrections. Tibial implant sizes are highly accurate while talar implant sizes had a trend of being one size smaller than predicted. Moreover, this effect seems to be more pronounced in the earlier cases likely reflective of increasing surgeon comfort with the implant with each subsequent case. These results confirm that pre-operative cutting guides are indeed helpful in intra-operative implant selection and positioning, however, there is still some room for innovation.

INTRODUCTION

A preoperative planning for accurately predicting the size and alignment of the prosthetic components may allow to perform a precise, efficient and reproducible total knee replacement. The planning can be carried out using as a support digital radiographic images or CT images with three-dimensional reconstruction. Aim of this prospective study is to evaluate and compare the accuracy of two different types of pre-operative planning, in determining the size of the femoral and tibial component in total knee arthroplasty performed with Patient Specific Instrument (PSI). The two compared techniques were: digital radiography and “CT-Based”.

Aims

Accurate placement of the acetabular component during total hip arthroplasty (THA) is an important factor in the success of the procedure. However, the reported accuracy varies greatly and is dependent upon whether free hand or navigated techniques are used. The aim of this study was to assess the accuracy of an instrument system that incorporates 3D printed, patient-specific guides designed to optimise the placement of the acetabular component.

Abstract. Background. Distal femoral osteotomy is an established successful procedure which can delay the progression of arthritis and the need for knee arthroplasty. The surgery, however, is complex and lengthy and consequently it is generally the preserve of highly experienced specialists and thus not widely offered. Patient specific instrumentation is known to reduce procedural complexity, time, and surgeons’ anxiety levels. 1. in proximal tibial osteotomy procedures. This study evaluated a novel patient specific distal femoral osteotomy procedure (Orthoscape, Bath, UK) which aimed to use custom-made implants and instrumentation to provide a precision correction while also simplifying the procedure so that more surgeons would be comfortable offering the procedure. Presenting problem. Three patients (n=3) with early-stage knee arthritis presented with valgus malalignment, the source of which was predominantly located within the distal femur, rather than intraarticular. Using conventional techniques and instrumentation, distal femoral knee osteotomy cases typically require 1.5–2 hours surgery time. The use of bi-planar osteotomy cuts have been shown to improve intraoperative stability as well as bone healing times. 2. This normally also increases surgical complexity; however, multiple cutting slots can be easily incorporated into patient specific instrumentation. Clinical management. All three cases were treated at a high-volume tertiary referral centre (Istituto Ortopedico Rizzoli, Bologna) using medial closing wedge distal femoral knee osteotomies by a team experienced in using patient specific osteotomy systems. 3. Virtual surgical planning was conducted using CT-scans and long-leg weight-bearing x-rays (Orthoscape, Bath, UK). Patient specific surgical guides and custom-made locking plates were design for each case. The guides were designed to allow temporary positioning, drilling and bi-planar saw-cutting. The drills were positioned such that the drills above and below the osteotomy became parallel on closing following osteotomy wedge removal. This gave reassurance of the achieved correction allowed the plate to be located precisely over the drills. All screw lengths were pre-measured. Discussion. The surgical time reduced to approximately 30 minutes by the third procedure. It was evident that surgical time was saved because no intraoperative screw length measurements were required, relatively few x-rays were used to confirm the position of the surgical guide, and the use of custom instrumentation significantly reduced the surgical inventory. The reduced invasiveness and ease of surgery may contribute to faster patient recovery compared to conventional techniques. The final post-operative alignment was within 1° of the planned alignment in all cases. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

The medial opening-wedge high tibial osteotomy (OW-HTO) is an accepted option to treat the isolated medial compartment osteoarthritis (OA) in varus knee. Despite satisfactory outcomes were described in literature, consistent complication rate has been reported and the provided accuracy of coronal alignment correction using conventional HTO techniques falls short. Patient specific instrumentations has been introduced with the aim to reduce complications and to improve the intra-operative accuracy according to the pre-operative plan, which is responsible for the clinical result of the surgery. In this talk, an overview of the clinical results of HTO patient specific instrumentation available in literature will be performed. Moreover, preliminary intra-operative and clinical results of a new customised 3-D printed cutting guide and fixation plate for OW-HTO will be presented

CT-based three-dimensional (3D) pre-operative imaging along with 2D orthogonal sections defined by the plane of the scapula (axial, sagittal and coronal planes) has been demonstrated by many research groups to be a very accurate way to define the bone pathology and alignment/subluxation of the humeral head in relationship to the center line of the scapula or the center of the glenoid fossa. When 3D CT imaging is combined with 3D implant templating the surgeon is best able to define the optimal implant and its location for the desired correction of the bone abnormalities. The use and value of 3D imaging is best when the there is more severe bone pathology and deformity. Transferring the computer-based information of implant location to the surgical site can involve multiple methods. The three methods discussed in the literature to date including use of standard instrumentation in a manner specified by the pre-operative planning, use of single-use patient specific instrumentation and use of reusable patient specific instrumentation. Several cadaver and sawbone studies have demonstrated significant improvement in placement of the glenoid implant with both single use and reusable patient specific instrumentation when compared to use of 2D imaging and standard instrumentation. Randomised clinical trials have also shown that 3D planning and implant templating is very effective in accurate placement of the implant in the desired location using all three types of instrumentation. The optimal use of this technology is dependent upon the severity of the pathology and the experience and preference of the surgeon. With more severe pathology and less surgeon experience 3D pre-operative imaging and templating and use of some level of patient specific instrumentation provides more accurate placement of the glenoid implant

The emergence of patient specific instrumentation has seen an expansion from simple radiographs to plan total knee arthroplasty (TKA) with modern systems using computed tomography (CT) or magnetic resonance imaging scans. Concerns have emerged regarding accuracy of these non-weight bearing modalities to assess true mechanical axis. The aim of our study was to compare coronal alignment on full length standing AP imaging generated by the EOS acquisition system with the CT coronal scout image. Eligible patients underwent unilateral or bilateral primary TKA for osteoarthritis under the care of investigating surgeon between 2017 and 2022, with both EOS X-Ray Imaging Acquisition System and CT scans performed preoperatively. Coronal mechanical alignment was measured on the supine coronal scout CT scan and the standing HKA EOS. Pre-operative lower limb coronal alignment was assessed on 96 knees prior to TKA on the supine coronal scout CT scan and the standing HKA EOS. There were 56 males (56%), and 44 right knees (44%). The mean age was 68 years (range 53-90). The mean coronal alignment was 4.7 degrees (SD 5.3) on CT scan and 4.6 degrees (SD 6.2) on EOS (p=0.70). There was a strong positive correlation of coronal alignment on CT scan and EOS (pearson. 0.927, p=0.001). The mean difference between EOS and CT scan was 0.9 degrees (SD 2.4). Less than 3 degrees variation between measures was observed in 87% of knees. On linear regression for every 1° varus increase in CT HKA alignment, the EOS HKA alignment increased by 0.93° in varus orientation. The model explained 86% of the variability. CT demonstrates excellent reliability for assessing coronal lower limb alignment compared to EOS in osteoarthritic knees. This supports the routine use of CT to plan TKA without further weight bearing imaging in routine cases

Introduction. This is a multi-centre, prospective, observational study of 503 INFINITY fixed bearing total ankle arthroplasties. We report the minimum two-year results of this prosthesis which was introduced to the UK Market in 2014 and is now the most used ankle arthroplasty in the National Joint Registry of England and Wales. Methods. Patients were recruited from 11 centres in the United Kingdom between June 2016 and November 2019. Demographic, radiographic, and functional outcome data (Ankle Osteoarthritis Scale, Manchester Oxford Foot Ankle Questionnaire and Euroquol 5D-5L) were collected preoperatively, at 6 months, 1 year and 2 years and 5 years. The average age was 67.8 (range 23.9 to 88.5) and average BMI 29.3 (18.9 to 48.0). The COFAS grading system was used to stratify deformity. There were 261 (51.9%) COFAS Type 1, 122 (24.2%) COFAS Type 2, 31 (6.2%) COFAS 3 and 89 (17.7%) COFAS type 4. 38 patients (7.6%) presented with inflammatory arthritis. 99 (19.7%) implantations utilised patient specific instrumentation. Complications and reoperations were recorded as adverse events. Radiographs were assessed for lucencies, cysts and/or subsidence. Results. The mean follow up was 34.2 months (range 24–64). 15 patients have died, 8 withdrawn and 3 lost to follow up. 8 implants (1.6%) have been revised. According to the Glazebrook classification there were low grade complications in 6.6%, medium grade in 1.4% and high grade in 1.6%. There have been an additional 13 non revision re-operations (2.6%) at the latest follow up. There was a significant (p < 0.01) improvement across all functional outcome scores at a minimum of 2yr follow up. Discussion and conclusion. This large cohort has shown a low early revision rate and high functional outcomes with a low-profile fixed bearing prosthesis

Aim. To asses the accuracy of total knee replacements performed using CT based patient specific instrumentation by postoperative CT scan. Method. Approval from the Ethics Committee at The University of New South Wales Sydney Australia was granted prior to commencement of this study. 50 patients who had undergone total knee replacement (Evolis, Medacta International) using CT-based patient specific instrumentation (MY KNEE Medacta International) were assessed postoperatively using a CT scan and a validated measurement technique. The mechanical axis of the limb in the coronal plane, the varus/valgus positioning of the femoral component, the varus/valgus positioning of the tibial component, the flexion/extension of the posterior flange of the femoral component and the posterior slope of the tibial base plate were recorded. These results were then compared to each patient's preoperative planning. The percentage of patients found to be within 3 degrees of planned alignment were calculated. This represents the most comprehensive prospective study to utilize CT assessment of postoperative alignment in patient specific instrumentation. All other studies, to our knowledge have utilized scanograms or scout images and not full CT protocol as performed in this study. Results. 96% of patients were within 3 degrees of planned alignment in the coronal plane reproducing the predicted mechanical axis. Predicted coronal plane orientation of the tibial and femoral component was achieved in 100% and 92% of patients, respectively. The flexion/extension of the posterior flange of the femoral component was within 3 degrees in 92% of patients. The planned posterior tibial slope was achieved in 92% of patients. As a result of difficulty in ascertaining the anatomical landmarks during measurement of the rotation of the femoral component, we are currently repeating the measurements using the original 3D software used for preoperative planning, using the same anatomical landmarks. This data will be available at the time of presentation. Conclusion. This study constitutes one of the largest series of patients who have undergone CT assessment following patient specific instrumented knee replacement. We have found that total knee replacement using patient specific instrumentation accurately reproduces preoperative planning in at least 5 out of the 6 parameters measured in this study

Contemporary techniques to perform total knee arthroplasty use either conventional instrumentation with intramedullary and extramedullary referencing or use a computer navigation system that requires insertion of femoral and tibial tracking pins and an intra-operative registration process. Much of the initial enthusiasm for computer navigation in TKA has waned as many of these systems have proved cumbersome, time consuming and expensive with no substantial evidence of a clinical benefit. Patient specific instrumentation is an additional option that is now widely available which seeks to harness some of the accuracy of computer navigation while improving intra-operative surgical efficiency. In 2015 there are now patient specific options available from multiple vendors and these vary in several different ways including: alignment goals; imaging modality; pin guide vs. cutting guide; all plastic vs. metal-plastic composite; and the degree of surgeon input into pre-operative planning. In all systems but one alignment is typically set relative to the mechanical axis; one system uses so-called kinematic alignment. Imaging can be done via CT, MRI, or MRI in conjunction with a hip-knee-ankle radiograph. The guides that are produced are typically made of a plastic material and in some cases are meant only to position pins onto which traditional metal cutting guides are then placed. In some systems the plastic guides come pre-assembled with an integrated metal cutting-guide that allows resection of the distal femur or proximal tibia in one step; in other systems cutting is intended to be carried out through a plastic captured guide. Finally there is wide variability in the degree of surgeon involvement in the pre-operative planning for the guides, ranging from no involvement in the so-called kinematic approach all the way to the ability for surgeons to dictate the depth, location, flexion-extension angle, varus-valgus angle, and rotation in some systems. At this point relatively little comparative data exists to objectively compare one system versus another. Surgeons most likely to find substantial benefit from patient specific instrumentation are those who perform moderate numbers of TKA each year but who have inconsistent surgical scrub teams. For those surgeons, substantial surgical inefficiency can be attributable to the scrub team's unfamiliarity with the complex instrumentation needed for TKA. Patient specific instrumentation can bypass many of those relatively complex instruments and allow the surgeon to complete TKA in a timely and efficient manner. For TKA subspecialists, patient specific instrumentation may have an appeal from a precision standpoint or from an ease-of-room turnover perspective but are unlikely to yield major intra-operative time savings at this point. In the future, combining patient specific instruments with size-specific disposable instruments that are financially and environmentally favorable may make this technology more applicable to even broader groups of surgeons

Introduction. Given the association of osteoarthritis with obesity, the typical patient requiring total knee arthroplasty (TKA) is often obese. Obesity has been shown to negatively influence outcomes following TKA, as it is associated with increased perioperative complications and poorer clinical and functional outcomes. Achieving proper limb alignment can be more difficult in the obese patient, potentially requiring a longer operation compared to non-obese patients. Patient specific instrumentation (PSI), a technique that utilizes MR- or CT-based customized guides for intraoperative cutting block placement, may offer a more efficient alternative to manual instruments for the obese patient. We hypothesize that the additional information provided by a preoperative MRI or CT may allow surgeons to achieve better alignment in less time compared to manual instrumentation. The purpose of this study was to assess whether PSI offers an improved operation length or limb alignment compared to manual instruments for nonmorbidly and morbidly obese patients. Methods. In this retrospective cohort study, we evaluated 77 PSI TKA and 25 manual TKA performed in obese patients (BMI≥30) between February 2013 and May 2015. During this period, all patients underwent PSI TKA unless unable to undergo MR scanning. All cases were performed by a single experienced surgeon and utilized a single implant system (Zimmer Persona™). PSI cases were performed using the MR-based Zimmer Patient Specific Instrumentation system. Tourniquet times were recorded to determine length of operation. Long-standing radiographs were obtained preoperatively and 4-weeks postoperatively to evaluate limb alignment. Cases were subdivided by nonmorbid obesity (30≤BMI<40) and morbid obesity (BMI≥40) to assess the effect of increasing obesity on outcomes. Results. PSI and manual cohorts were similar with regards to age, gender, and preoperative alignment. Tourniquet time was significantly shorter in the PSI group for nonmorbidly obese patients (PSI 49.8 minutes vs manual 58.3 minutes; p=0.005) (Figure 1). Postoperative mechanical axis was similar between groups for both nonmorbidly obese (PSI 1.8° vs manual 2.9°; p=0.338) and morbidly obese patients (PSI 4.0° vs manual 3.6°; p=0.922). Mechanical axis outliers (greater than 3° neutral), though nonsignificant, were fewer in the PSI group for nonmorbidly obese (PSI 21.8% vs manual 35.3%; p=0.318) and morbidly obese patients (PSI 46.1% vs manual 75.0%; p=0.362). Discussion. We found that PSI significantly shortened operation length for nonmorbidly obese patients compared to manual instruments. Obesity is strongly associated with increased perioperative infection rates, as is prolonged operation length. The decreased operation length achieved with PSI in the nonmorbidly obese patient may as a consequence decrease infection rates, though further study is necessary. Though not statistically significant, PSI showed a trend toward decreasing overall mechanical axis outliers for both nonmorbidly obese and morbidly obese patients. The use of patient specific instrumentation compared to manual instruments has been controversial in the literature. However, patient specific instrumentation may be favorable in the obese patient, offering a shorter operation length and possibly improved alignment

Abstract. Background. Conventional TKR aims for neutral mechanical alignment which may result in a smaller lateral distal femoral condyle resection than the implant thickness. We aim to explore the mismatch between implant thickness and bone resection using 3D planning software used for Patient Specific Instrumentation (PSI) TKR. Methods. This is a retrospective anatomical study from pre-operative MRI 3D models for PSI TKR. Cartilage mapping allowed us to recreate the native anatomy, enabling us to quantify the mismatch between the distal lateral femoral condyle resection and the implant thickness. Results. We modelled 292 knees from PSI TKR performed between 2012 and 2015. There were 225 varus knees and 67 valgus knees, with mean supine hip-knee-angle of 5.6±3.1 degrees and 3.6±4.6 degrees, respectively. In varus knees, the mean cartilage loss from medial and lateral femoral condyle was 2.3±0.7mm and 1.1±0.8mm respectively; the mean overstuffing of the lateral condyle 1.9±2.2mm. In valgus knees, the mean cartilage loss from medial and lateral condyle was 1.4±0.8mm and 1.5±0.9mm respectively; the mean overstuffing of the lateral condyle was 4.1±1.9mm. Conclusions. Neutral alignment TKR often results in overstuffing of the lateral condyle. This may increase the patello-femoral pressure at the lateral facet in flexion. Anterior knee pain may be persistent even after patellar resurfacing due to tight lateral retinacular structures. An alternative method of alignment such as anatomic alignment may minimise this problem