Aims. Patient-specific instrumentation of total knee arthroplasty (TKA) is a technique permitting the targeting of individual kinematic alignment, but deviation from a neutral mechanical axis may have implications on implant fixation and therefore survivorship. The primary objective of this randomized controlled study was to compare the fixation of tibial components implanted with patient-specific instrumentation targeting kinematic alignment (KA+PSI) versus components placed using computer-assisted surgery targeting neutral mechanical alignment (MA+CAS). Tibial component migration measured by radiostereometric analysis was the primary outcome measure (compared longitudinally between groups and to published acceptable thresholds). Secondary outcome measures were inducible displacement after one year and patient-reported outcome measures (PROMS) over two years. The secondary objective was to assess the relationship between alignment and both tibial component migration and inducible displacement. Patients and Methods. A total of 47 patients due to undergo TKA were randomized to KA+PSI (n = 24) or MA+CAS (n = 23). In the KA+PSI group, there were 16 female and eight male patients with a mean age of 64 years (. sd. 8). In the MA+CAS group, there were 17 female and six male patients with a mean age of 63 years (. sd. 7). Surgery was performed using cemented, cruciate-retaining Triathlon total knees with patellar resurfacing, and patients were followed up for two years. The effect of alignment on tibial component migration and inducible displacement was analyzed irrespective of study group. Results. There was no difference over two years in longitudinal migration of the tibial component between the KA+PSI and MA+CAS groups (reaching median maximum total point motion migration at two years of 0.40 mm for the KA+PSI group and 0.37 mm for the MA+CAS group, p = 0.82; p = 0.68 adjusted for age, sex, and body mass index (BMI) for all follow-ups). Both groups had mean migrations below acceptable thresholds. There was no difference in inducible displacement (p = 0.34) or PROMS (p = 0.61 for the Oxford Knee Score) between groups. There was no correlation between alignment and tibial component migration or alignment and inducible displacement. These findings support non-neutral alignment as a viable option with this component, with no evidence that it compromises fixation. Conclusion. Kinematic alignment using patient-specific instrumentation in TKA was associated with acceptable tibial component migration, indicating stable fixation. These results are supportive of future investigations of kinematic alignment. Cite this article: Bone Joint J 2019;101-B:929–940

Aims. The purpose of the present study was to compare patient-specific instrumentation (PSI) and conventional surgical instrumentation (CSI) for total knee arthroplasty (TKA) in terms of early implant migration, alignment, surgical resources, patient outcomes, and costs. . Patients and Methods. The study was a prospective, randomized controlled trial of 50 patients undergoing TKA. There were 25 patients in each of the PSI and CSI groups. There were 12 male patients in the PSI group and seven male patients in the CSI group. The patients had a mean age of 69.0 years (. sd. 8.4) in the PSI group and 69.4 years (. sd. 8.4) in the CSI group. All patients received the same TKA implant. Intraoperative surgical resources and any surgical waste generated were recorded. Patients underwent radiostereometric analysis (RSA) studies to measure femoral and tibial component migration over two years. Outcome measures were recorded pre- and postoperatively. Overall costs were calculated for each group. Results. There were no differences (p > 0.05) in any measurement of migration at two years for either the tibial or femoral components. Movement between one and two years was < 0.2 mm, indicating stable fixation. There were no differences in coronal or sagittal alignment between the two groups. The PSI group took a mean 6.1 minutes longer (p = 0.04) and used a mean 3.4 less trays (p < 0.0001). Total waste generated was similar (10 kg) between the two groups. The PSI group cost a mean CAD$1787 more per case (p < 0.01). Conclusion. RSA criteria suggest that both groups will have revision rates of approximately 3% at five years. The advantages of PSI were minimal or absent for surgical resources used and waste eliminated, and for meeting target alignment, yet had significantly greater costs. Therefore, we conclude that PSI may not offer any advantage over CSI for routine primary TKA cases. Cite this article: Bone Joint J 2019;101-B:565–572

We conducted a meta-analysis, including randomised controlled trials (RCTs) and cohort studies, to examine the effect of patient-specific instruments (PSI) on radiological outcomes after total knee replacement (TKR) including: mechanical axis alignment and malalignment of the femoral and tibial components in the coronal, sagittal and axial planes, at a threshold of > 3º from neutral. Relative risks (RR) for malalignment were determined for all studies and for RCTs and cohort studies separately.

Of 325 studies initially identified, 16 met the eligibility criteria, including eight RCTs and eight cohort studies. There was no significant difference in the likelihood of mechanical axis malalignment with PSI versus conventional TKR across all studies (RR = 0.84, p = 0.304), in the RCTs (RR = 1.14, p = 0.445) or in the cohort studies (RR = 0.70, p = 0.289). The results for the alignment of the tibial component were significantly worse using PSI TKR than conventional TKR in the coronal and sagittal planes (RR = 1.75, p = 0.028; and RR = 1.34, p = 0.019, respectively, on pooled analysis). PSI TKR showed a significant advantage over conventional TKR for alignment of the femoral component in the coronal plane (RR = 0.65, p = 0.028 on pooled analysis), but not in the sagittal plane (RR = 1.12, p = 0.437). Axial alignment of the tibial (p = 0.460) and femoral components (p = 0.127) was not significantly different.

We conclude that PSI does not improve the accuracy of alignment of the components in TKR compared with conventional instrumentation.

Cite this article: Bone Joint J 2014; 96-B:1052–61.

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. Total knee arthroplasty is effective for the management of osteoarthritis of the knee. Conventional techniques utilizing manual instrumentation (MI) make use of intramedullary femoral guides and either extramedullary or intramedullary tibial guides. While MI techniques can achieve excellent results in the majority of patients, those with ipsilateral hardware, post-traumatic deformity or abnormal anatomy may be technically more challenging, resulting in poorer outcomes. Computer-assisted navigation (CAN) is an alternative that utilizes fixed trackers and anatomic registration points, foregoing the need for intramedullary guides. This technique has been shown to yield excellent results including superior alignment outcomes compared to MI with fewer outliers. However, studies report a high learning curve, increased expenses and increased operative times. As a result, few surgeons are trained and comfortable utilizing CAN. Patient-specific instrumentation is an alternative innovation for total knee arthroplasty. Custom guide blocks are fabricated based on a patient's unique anatomy, allowing for the benefits of CAN but without the increased operative times or the high learning curve. In this study we sought to evaluate the accuracy of PSI techniques in patients with previous ipsilateral hardware of the femur. Methods. After reviewing our database of 300 PSI total knee arthroplasty patients, 16 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 [Figure 1], 1 had a sliding hip screw, and 1 patient had a cephalomedullary nail. Postoperative mechanical axis alignment measurements were performed using plain long-standing radiographs [Figure 2]. 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 [Table 1]. 11 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 7.9°(1.5°–15.7°). The average value of a deformity identified via preoperative radiographs was 10.1°(2.2°–14.7°). Average postoperative mechanical axis was 3.1° (1°–5.3°) measured from plain radiographs. Average angle between the FMA and femoral component was 90.0° (85.3°–94.1°). The average angle between the TMA and tibial component was 90.6°(87.6°–92.9°). The average difference between the femoral mechanical and anatomic axes was 5.9°(3.4°–7.0°). The average discrepancy between medial and lateral joint space on an anterior-posterior standing radiograph was 0.4mm(0.0mm–1.1mm). At an average of 4.5 months follow-up, American Knee Society knee scores show an aggregate average score of 82.94. Conclusions. Patient specific instrumentation (PSI) 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 otherwise 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. Patient-specific instrumentation (PSI) is a contemporary method to optimize accuracy of alignment in total knee arthroplasty (TKA). As the potential benefits come at the cost of increased economic and logistic expenses, there is great scientific and practical interest in the actual advantages and reliability of such systems. Therefore, the purpose of the present study was to compare clinical results, radiological limb alignment, and three-dimensional (3D)-component positioning between conventional instrumentation (CVI) and a computed tomographic (CT)-based PSI in primary TKA. Methods. Two-hundred-ninety consecutive patients (300 knees) with severe, debilitating osteoarthritis scheduled for TKA were included in this study using either CVI (n=150) or PSI (n=150). Patients were clinically assessed according to the Knee Society Score (KSS), range of motion (ROM), and visual analog scale for pain (VAS) before and two years after surgery. Hip-knee-ankle angle (HKA) and 3D-component positioning were assessed on postoperative radiographs and CT to evaluate accuracy of CVI and PSI. Results. Data of 222 knees (CVI: n=108, PSI: n=114) were available for analysis after a mean follow up of 28.6±5.2 months. Clinical (KSS knee and function, ROM, VAS) and radiological parameters (HKA) improved significantly from pre to postoperative in both groups. At the early follow up, clinical outcome was comparable between the two groups, whereas KSS function and VAS for pain were significantly better in the PSI group. Mean HKA deviation from the targeted neutral mechanical axis (CVI: 2.2°±1.7°; PSI: 1.5°±1.4°; p<0.001), rates of outliers (CVI: 22.2%; PSI: 9.6%; p=0.016), and 3D-component positioning outliers were significantly lower in the PSI group. Additionally, the accuracy of femoral and tibial component positioning was significantly higher in all planes. At early follow up, all clinical scores were significantly better in the subgroup of HKA non-outliers (HKA: 180°±3°) compared to HKA outliers. Conclusions. CT-based PSI compared to CVI improves accuracy of mechanical alignment restoration and 3D-component positioning in primary TKA. While clinical outcome was comparable between the two instrumentation groups at early follow up, significantly inferior outcome was detected in the subgroup of HKA-outliers

Introduction. Total Knee Arthroplasty (TKA) is highly successful in treatment of end-stage degenerative arthritis of the knee. CT-based Patient-Specific Instrumentation (PSI) utilizes a CT scan of the lower extremity to create a three-dimensional model of the patient's anatomy, plan the surgery, and provide unique patient-specific resection blocks for the surgery. There are few published studies utilizing CT-PSI. The present study prospectively evaluates clinical, operative, and radiographic outcomes from 100 CT-based TKAs using this technology (MyKnee®, Medacta International S.A., Castel San Pietro, Switzerland). Materials and Methods. 100 consecutive eligible knees (94 patients) of the senior author underwent TKA using CT-based PSI technology. The primary outcome of the study was to compare the planned pre-operative femoral and proximal tibial resections to the actual intra-operative measured resections. Clinical outcomes included pre- and post-operative Knee Society Scores, Range-of-Motion (ROM, measured by goniometer), and complication data. Pre- and 6-week post-operative long-leg standing radiographs were obtained to assess HKA alignment. The femoral component angle (FCA) in the coronal plane, the tibial component angle (TCA), and posterior slope of the tibia were also assessed. Additionally, 10 patients were selected at random to undergo a post-operative CT scan for comparison to radiographic measurements. Results. 94 patients were enrolled representing 51 left and 49 right TKAs. Average follow up was 3.9 years (range 3.5 – 4.4 years). Average Knee Society Score (KSS) improved from 44.3 to 81.8 while KSS Function Score improved from 59.1 to 81.8 at 1 year. ROM arc of the patients was 110.5 (range 0–130) pre-operatively and was 111.3 (range 0–130) post-operatively. Two patients had a post-operative infection requiring surgical intervention. There were no thromboembolic complications and no revisions in study patients. No patient required a manipulation under anesthesia for post-operative stiffness. No intraoperative complications occurred nor were there any cases of abandoning the PSI blocks for standard technique. The actual bony resections achieved during surgery were strongly correlated to the planned resections of all 6 bone fragments measured. Each achieved statistical significance (p<0.001). Average post-operative alignment was 179.36° (range 175°–186°). Alignment was 180 ± 3° in 94% of patients post-operatively. Ten patients underwent a post-operative CT scan for HKA verification. The average post-operative HKA was 179.9° (range, 176.9°–180.9°) with a standard deviation of 1.31°. When comparing our pre-operative alignment by x-ray vs. CT, we found only 0.09° (p<0.001) average difference between them. Post-operatively, we continued to show very similar results showing x-ray HKA measurement of 180.1° vs. CT measurement of 179.9° (p<0.001). Discussion. The pre-operative CT reconstruction can accurately predict the intra-operative resection depths as demonstrated here. All 6 bony resections measured to within 1mm of the predicted value in the aggregate of our series. The restoration of mechanical axis to 179.9° as measured by CT scans demonstrates the efficacy of the blocks. Conclusion. The present study demonstrates efficacy in the use of CT-based PSI - showing that the planning can accurately predict bony resections, be used safely, and achieve precise radiographic outcomes. Consequently, we routinely support the use of CT-based PSI in TKA

Patient-specific instrumentation (PSI) has been greatly marketed in knee endoprosthetics for the past few years. By utilising PSI, the prosthesis´ accuracy of fit should be improved. Besides, both surgical time and hospital costs should be reduced. Whether these proposed advantages are achieved in medial UKA remains unclear yet. The aim of this study was to evaluate the preoperative planning accuracy, time saving, and cost effectiveness utilising PSI in UKA. Data from 22 patients (24 knees) with isolated medial unicompartmental knee osteoarthritis were analysed retrospectively. The sample comprised sixteen men and six women (mean age 61 ± 8 years) who were electively provided with a UKA utilising PSI between June 2012 and October 2014. For evaluation of preoperative planning accuracy (1) planned vs. implanted femoral component size, (2) planned vs. implanted tibial component size, and (3) planned vs. implanted polyethylene insert size were analysed. Since UKA is a less common, technically demanding surgery, depending in large part on the surgeon´s experience, preoperative planning reliability was also evaluated with regard to surgeon experience. Moreover, actual surgical time and cost effectiveness utilising PSI was evaluated. Preoperative planning had to be modified intraoperatively to a wide extend for gaining an optimal outcome. The femoral component had to be adjusted in 41.7% of all cases, the tibial component in 58.3%, and the insert in 87.5%. Less experienced surgeons had to change preoperative planning more often than experienced surgeons. Utilising PSI increased surgical time regardless of experience. Linear regression revealed PSI-planning and surgeon inexperience as main predictors for increased surgical time. Additionally, PSI increased surgical costs due to e.g. enlarged surgical time, license fees and extraordinary expenditure for MRI scans. The preoperative planning accuracy depends on many different factors. The advertised advantages of PSI could not be fully supported in case of UKA on the basis of the here presented data – especially not for the inexperienced surgeon

Introduction. Increased accuracy of pre-operative imaging in patient-specific instrumentation (PSI) can result in longer-term savings, and reduced accumulated dose of radiation by eliminating the need for post-operative imaging or revision surgery. The benefits and drawbacks of CT vs MRI for use in PSI is a source of ongoing debate. This study reviews all currently available evidence regarding accuracy of CT vs MRI for pre-operative imaging in PSI. Methods. The MEDLINE and EMBASE databases were searched between 1990 and 2013 to identify relevant studies. As most studies available focus on validation of a single technique rather than a direct comparison, the data from several clinical studies was assimilated to allow comparison of accuracy. Overall accuracy of each modality was calculated as proportion of outliers >3 % in the coronal plane. Results. Seven studies matched our inclusion criteria. Outlier incidence was 12.5% (9.27–17.4%) with CT and 16.96% (1.2–44%) with MRI (p>0.05). Conclusions. Current evidence shows comparable accuracy with both imaging modalities for PSI. Outlier incidence is slightly lower in the CT group with lower variation but this was not significant. At present there is not enough published data to convincingly conclude in favour of CT or MRI for accuracy of component alignment. It is our conclusion that CT is more favourable at present due to reduced scanning times, increased availability, and cheaper cost

The present IRB approved study evaluates the early results of 100 TKAs using CT-based Patient-Specific Instrumentation (PSI) (MyKnee®, Medacta International, SA, Castel San Pietro, Switzerland). For this technique, a CT scan of the lower extremity is obtained, and from these images, the knee is reconstructed 3-dimensionally. Surgical and implant-size planning are performed according to surgeon preference, with the goal to create a neutral mechanical axis. Once planned and approved, the blocks are made. Outcomes measured for the present study include surgical factors such as Tourniquet Time (TT) as a measure of surgical efficiency, the actual intraoperative bony resection thicknesses to be compared to the planned resections from the CT scan, and complication data. Furthermore, pre- and post-operative long standing alignment and Knee Society Scores (KSS) were obtained. During surgery, the PSI cutting block is registered on the femur first and secured with smooth pins. No osteophytes are removed as the blocks use the positive topography of the osteophytes for registration. The distal femoral resection is performed directly through the block. An appropriate sized 4-in-1 block is placed and the remaining resections are performed. The tibial resection block is registered and resection performed. Final bone preparation, patella resurfacing, and trialing is performed as is standard to all surgical techniques. There were 50 Left and 50 Right TKA's performed in 61 females and 39 males. All patients had diagnosis of osteoarthritis. The average BMI was 31.1 and average age was 64.5 (range 41–90). 79 patients had pre-operative varus deformities with Hip Knee Angle (HKA) average of 174.7° (range 167°–179.5°). 19 patients had pre-operative valgus deformities averaging 184.4° (range 180.5°–190°). Three patients were neutral. Average TT was 31.2 minutes (range 21–51 minutes). With regard to the bony resections, the actual vs. planned resections for the distal medial femoral resection was 8.7 mm vs. 8.9 mm respectively. Further actual vs. planned femoral resections include distal lateral 7.2 vs. 6.7 mm; posterior medial 8.3 vs. 8.9 mm; and posterior lateral 6.2 vs. 6.8 mm. The actual vs. planned tibial resections recorded include medial 6.4 vs. 6.3 mm and lateral 8.3 vs. 8.2. The planned vs. actual bony cuts are strongly correlated, and highly predictive for all 6 measured cuts (p=<.001). No intraoperative complications occurred. Average KSS improved from 45.9 to 81.4, and KSS Function Score improved from 57.7 to 73.5 at 6 weeks postoperative visit. There were no thromboembolic complications. Two patients had a post-operative infection requiring surgical intervention. Post-operative alignment was 179.36° (range 175°–186°) for all patients. Alignment was neutral, within 3° in 95.9% of patients. There were only 4 outliers with maximal post-operative angulation of 6°. In conclusion, these early results demonstrate efficacy of CT-based PSI for TKA. The surgery can be performed efficiently, accurately, and safely. Furthermore, excellent short term clinical and radiographic results can be achieved

The present IRB approved study evaluates the early results of 100 TKAs using CT-based Patient-Specific Instrumentation (PSI) (MyKnee®, Medacta International, SA, Castel San Pietro, Switzerland). For this technique, a CT scan of the lower extremity is obtained, and from these images, the knee is reconstructed 3-dimensionally. Surgical and implant-size planning are performed according to surgeon preference, with the goal to create a neutral mechanical axis. Once planned and approved, the blocks are made [Fig. 1]. Outcomes measured for the present study include surgical factors such as Tourniquet Time (TT) as a measure of surgical efficiency, the actual intraoperative bony resection thicknesses to be compared to the planned resections from the CT scan, and complication data. Furthermore, pre- and post-operative long standing alignment and Knee Society Scores (KSS) were obtained. During surgery, the PSI cutting block is registered on the femur first and secured with smooth pins. No osteophytes are removed as the blocks use the positive topography of the osteophytes for registration. The distal femoral resection is performed directly through the block. An appropriate sized 4-in-1 block is placed and the remaining resections are performed. The tibial resection block is registered and resection performed. Final bone preparation, patella resurfacing, and trialing is performed as is standard to all surgical techniques. There were 50 Left and 50 Right TKA's performed in 61 females and 39 males. All patients had diagnosis of osteoarthritis. The average BMI was 31.1 and average age was 64.5 (range 41–90). 79 patients had pre-operative varus deformities with Hip Knee Angle (HKA) average of 174.7° (range 167°–179.5°). 19 patients had pre-operative valgus deformities averaging 184.4° (range 180.5°–190°). Three patients were neutral. Average TT was 31.2 minutes (range 21–51 minutes). With regard to the bony resections, the actual vs. planned resections for the distal medial femoral resection was 8.7 mm vs. 8.9 mm respectively. Further actual vs. planned femoral resections include distal lateral 7.2 vs. 6.7 mm; posterior medial 8.3 vs. 8.9 mm; and posterior lateral 6.2 vs. 6.8 mm. The actual vs. planned tibial resections recorded include medial 6.4 vs. 6.3 mm and lateral 8.3 vs. 8.2. The planned vs. actual bony cuts are strongly correlated, and highly predictive for all 6 measured cuts (p=<.001) [Fig. 3]. No intraoperative complications occurred. Average KSS improved from 45.9 to 81.4, and KSS Function Score improved from 57.7 to 73.5 at 6 weeks postoperative visit. There were no thromboembolic complications. Two patients had a post-operative infection requiring surgical intervention. Post-operative alignment was 179.36° (range 175°–186°) for all patients. Alignment was neutral, within 3° in 95.9% of patients. There were only 4 outliers with maximal post-operative angulation of 6° [Fig. 2]. In conclusion, these early results demonstrate efficacy of CT-based PSI for TKA. The surgery can be performed efficiently, accurately, and safely. Furthermore, excellent short term clinical and radiographic results can be achieved

Background. To improve implant positioning in total knee arthroplasty (TKA) patient-specific instrumentation (PSI) has been introduced as alternative for conventional instrumentation (CI). Though the PSI technique offers interesting opportunities in TKA, there is no consensus about the effectiveness of PSI in comparison with CI and results concerning soft-tissue balancing remain unclear. Therefore, the primary aim of the present study was to investigate the varus-valgus laxity in extension and flexion in patients receiving a TKA using PSI compared with CI. Additionally, radiological, clinical and functional outcomes were assessed. Methods. In this prospective randomization controlled trial, 42 patients with osteoarthritis received a Genesis II PS (Smith & Nephew, Memphis, Tennessee), with either PSI (Visionaire, Smith & Nephew) or CI (Smith & Nephew). Patients visited the hospital preoperative and postoperative after 6 weeks, 3 and 12 months. One-year postoperative varus-valgus laxity was measured in extension and flexion on stress radiographs. Additional assessments included: the hip-knee-ankle angle on long-leg radiographs, femoral and tibia component rotation on CT-scans, radiolucency, the Knee Society Score (KSS), VAS pain, VAS Satisfaction, Knee injury and Osteoarthritis Outcome score (KOOS), Patella score (Kujala), the University of California Los Angeles activity score (UCLA), the anterior-posterior laxity in 20° and 90° knee flexion, adverse events and complications. The outcome measures were compared using independent t-tests, non-parametric alternatives and repeated measurements, with a significance level of p<0.05. Results. In four cases intra-operative modifications were needed, since the PSI did not fit correctly on the tibia and/or femur. No significant differences were found between the two groups for varus-valgus laxity in both extension and flexion (figure 1), as well as for the other radiological outcomes. Both groups improved significantly on clinical and functional outcomes over time. No significant differences were found between the groups one year postoperatively. Finally, the PSI group received a thinner insert than the CI group (p=0.04). Conclusion. In conclusion, PSI in TKA does not result in better varus-valgus laxity, and clinical and functional outcomes compared with CI, one year postoperative. Since the PSI group received a thinner insert, the pre-operative surgery plan developed for he PSI probably provides more conservative bone cuts compared with CI. The thinner insert might be beneficial in the long-term; however, further research is needed to gain more insight in the long-term results of PSI

Hardware in or about the knee joint presents a number of challenges to the surgeon in performance of Total Knee Arthroplasty (TKA). Conventional instrumentation usually requires a modification of technique or removal of the metallic implants. Computer-Assisted TKA (CAOS) is another option, but adds complexity and time to the procedure. MRI-based Patient-Specific Instrumentation (PSI) cannot be used as metal causes unwanted artifact and renders the images for planning, useless. However, CT scans are not affected by metal and thus CT-based PSI can be used in TKA patients with pre-existing hardware. The present IRB approved study evaluates 12 consecutive knees (10 patients) with pre-existing hardware using CT-based PSI (MyKnee®, Medacta International, SA, Castel San Pietro, Switzerland). In this technique, CT scan of the lower extremity is obtained, and from these images, the knee is reconstructed 3-dimensionally. Surgical and implant-size planning are performed according to surgeon preference, with the goal to create a neutral mechanical axis. Once planned and approved, the blocks are made [Fig 1]. During surgery, the PSI cutting block is registered on the femur first and secured with smooth pins. The distal femoral resection is performed directly through the block. An appropriate sized 4-in-1 block is placed and the remaining femoral resections are performed. The tibial resection block is registered and resection performed. Final bone preparation, patella resurfacing, and trialing is performed as is standard to all surgical techniques. Of the 12 TKAs, there were 5 left and 7 right knees performed in 6 females and 6 males. The average BMI was 33.19 and average age was 53 (range 44–63). All diagnoses were either osteoarthritis or post-traumatic osteoarthritis. Follow-up averaged 59 weeks (range 18.6–113.7). Nine patients had pre-operative varus deformities with HKA deformities average of 171.9° (range 154°–178.5°). One patient had pre-operative valgus deformity of 184.5°. Two patients were neutral (180°). Post-operative alignment for all patients (n = 11) was 179° (range 177°–180°). All patients were within 3° neutral, post operatively. Four patients measured 180°, 4 measured at 179°, 2 measured at 178°, and only one at 177°. Hardware consisted of 5 patients with femur or tibia staples, 3 with plate(s) and screws [Fig. 2], 3 patients with ACL interference screws, and one titanium rod. No hardware was removed unless necessary for implantation. Only 3 patients required some hardware removal. The pre-operative Range of Motion (ROM) averaged 2.9° to 98.3° (Extension range 0–15° and flexion range 30–115°). Post-operative ROM was 2.9° to 101.3°. (Extension range 0–5° and flexion range 65–125°). Knee Society Score (KSS) improved from 42.3 to 82.3, and KSS Function Score improved from 52.1 to 77.5. No intraoperative complications were recorded. Average tourniquet time was 42.1 minutes (range 28–102). Regardless of the deformity, the patient's post-operative mechanical axes HKA averaged 179° (range 177–180). Clinical scores were typical for TKA patients with improvement in both KSS and ROM. In conclusion, early results using PSI in patients with pre-existing hardware in or about the joint, is safe, efficient, and accurate in performance of TKA

Hardware in or about the knee joint presents a number of challenges to the surgeon in performance of Total Knee Arthroplasty (TKA). Conventional instrumentation usually requires a modification of technique or removal of the metallic implants. Computer-Assisted TKA (CAOS) is another option, but adds complexity and time to the procedure. MRI-based Patient-Specific Instrumentation (PSI) cannot be used as metal causes unwanted artifact and renders the images for planning, useless. However, CT scans are not affected by metal and thus CT-based PSI can be used in TKA patients with pre-existing hardware. The present IRB approved study evaluates 12 consecutive knees (10 patients) with pre-existing hardware using CT-based PSI (MyKnee®, Medacta International, SA, Castel San Pietro, Switzerland). In this technique, CT scan of the lower extremity is obtained, and from these images, the knee is reconstructed 3-dimensionally. Surgical and implant-size planning are performed according to surgeon preference, with the goal to create a neutral mechanical axis. Once planned and approved, the blocks are made. During surgery, the PSI cutting block is registered on the femur first and secured with smooth pins. The distal femoral resection is performed directly through the block. An appropriate sized 4-in-1 block is placed and the remaining femoral resections are performed. The tibial resection block is registered and resection performed. Final bone preparation, patella resurfacing, and trialing is performed as is standard to all surgical techniques. Of the 12 TKAs, there were 5 left and 7 right knees performed in 6 females and 6 males. The average BMI was 33.19 and average age was 53 (range 44–63). All diagnoses were either osteoarthritis or post-traumatic osteoarthritis. Follow-up averaged 59 weeks (range 18.6–113.7). Nine patients had pre-operative varus deformities with HKA deformities average of 171.9° (range 154°–178.5°). One patient had pre-operative valgus deformity of 184.5°. Two patients were neutral (180°). Post-operative alignment for all patients (n=11) was 179° (range 177°–180°). All patients were within 3° neutral, post operatively. Four patients measured 180°, 4 measured at 179°, 2 measured at 178°, and only one at 177°. Hardware consisted of 5 patients with femur or tibia staples, 3 with plate(s) and screws, 3 patients with ACL interference screws, and one titanium rod. No hardware was removed unless necessary for implantation. Only 3 patients required some hardware removal. The pre-operative Range of Motion (ROM) averaged 2.9° to 98.3° (Extension range 0–15° and flexion range 30–115°). Post-operative ROM was 2.9° to 101.3°. (Extension range 0–5° and flexion range 65–125°). Knee Society Score (KSS) improved from 42.3 to 82.3, and KSS Function Score improved from 52.1 to 77.5. No intraoperative complications were recorded. Average tourniquet time was 42.1 minutes (range 28–102). Regardless of the deformity, the patient's post-operative mechanical axes HKA averaged 179° (range 177–180). Clinical scores were typical for TKA patients with improvement in both KSS and ROM. In conclusion, early results using PSI in patients with pre-existing hardware in or about the joint, is safe, efficient, and accurate in performance of TKA

Objective. Patient-specific instrumentation (PSI) is a novel technique in total knee arthroplasty (TKA) which potentially permits more accurate alignment of the components; however, there is no consensus in literature regarding the accuracy and reliability of PSI as many studies have shown controversial and inconsistent results of various PSI systems. A 24-month follow-up study was carried out to compare perioperative clinical outcomes, radiological limb alignment and component positioning, as well as functional outcomes following TKA between PSI and conventional instrumentation (CI). Methods. During September 2011 and August 2012, 90 consecutive patients were scheduled to undergo unilateral TKA with either PSI or CI. TruMatch® Personalised Solutions was used in this study, and a senior surgeon performed all operations. Patients were clinically assessed before, 6-month and 24-month after surgery. Results. There were 42 patients who underwent TKA with PSI and 48 patients with CI, with no preoperative demographic and clinical difference. There was significant improvement in maximal extension for both groups at both of the two follow-ups, compared to baseline. While the CI group maintained similar maximal flexion angle, PSI group had significant decrease in maximal flexion angle, at both follow-ups. Overall, there was no significant improvement in the range of motion for both groups over the 24-month period after surgery. At 6 and 24 months postoperatively, there were similarly significant improvements in the mean scores of Oxford Knee Score, Knee Society Score, and Physical Component Sscore of the SF-36 Health Survey for both groups. At 24 months postoperatively, no significant differences were detected between PSI and CI groups in all clinical and functional outcomes. Radiographic results showed that the lower limb mechanical alignment and coronal component positioning were satisfactory and similar between the two groups. There were no differences in operating time, haemoglobin loss, transfusion rate and length of hospitalisation between PSI and CI, perioperatively. Conclusion. In conclusion, CT-based PSI showed comparable clinical and functional outcomes at 24 months after TKA compared with CI. There were no significant differences between the two types of instruments in achieving alignment restoration, component positioning, and perioperative clinical outcomes in terms of operating time and blood loss

Introduction & aims

Patient specific instrumentation (PSI) is a useful tool to execute pre-operatively planned surgical cuts and reduce the number of trays in surgery. Debate currently exists around improved accuracy, efficacy and patient outcomes when using PSI cutting guides compared to conventional instruments. Unicompartmental Knee Arthroplasty (UKA) revision to Total Knee Arthroplasty (TKA) represents a complex scenario in which traditional bone landmarks, and patient specific axes that are routinely utilised for component placement may no longer be easily identifiable with either conventional instruments or navigation. PSI guides are uniquely placed to solve this issue by allowing detailed analysis of the patient morphology outside the operating theatre. Here we present a tibia and femur PSI guide for TKA on patients with UKA.

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.

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.

Total knee arthroplasty is a successful procedure that reduces knee pain and improves function in most patients with knee osteoarthritis. Patient dissatisfaction however remains high, and along with implant longevity, may be affected by component positioning. Surgery in obese patients is more technically challenging with difficulty identifying appropriate landmarks for alignment and more difficult exposure of the joint. Patient specific instrumentation (PSI) has been introduced with the goal to increase accuracy of component positioning by custom fitting cutting guides to the patient using advanced imaging. A strong criticism of this new technology however, is the cost associated. The purpose of this study was to determine, using a prospective, randomized-controlled trial, the cost-effectiveness of PSI compared to standard instrumentation for total knee arthroplasty in an obese patient population.

Patients with a body mass index greater than 30 with osteoarthritis and undergoing a primary total knee arthroplasty were included in this study. We randomized patients to have their procedure with either standard instrumentation (SOC) or PSI. At 12-weeks post-surgery patients completed a self-reported cost questionnaire and the Western Ontario and McMaster Osteoarthritis Index (WOMAC). We performed a cost-effectiveness analyses from a public health payer and societal perspective. As we do not know the true cost of the PSI instrumentation, we estimated a value of $100 for our base case analysis and used one-way sensitivity analyses to determine the effect of different values (ranging from $0 to $500) would have on our conclusions.

A total of 173 patients were enrolled in the study with 86 patients randomized to the PSI group and 87 to the SOC group. We found the PSI group to be both less effective and more costly than SOC when using a public payer perspective, regardless of the cost of the PSI. From a societal perspective, PSI was both less costly, but also less effective, regardless of the cost of the PSI. The mean difference in effect between the two groups was −1.61 (95% CI −3.48, 026, p=0.091). The incremental cost-effectiveness ratio was $485.71 per point increase in the WOMAC, or $7285.58 per clinically meaningful difference (15 points) in the WOMAC.

Overall, our results suggest that PSI is not cost-effective compared to standard of care from a public payer perspective. From a societal perspective, there is some question as to whether the decreased effect found with the PSI group is worth the reduced cost. The main driver of the cost difference appears to be time off of volunteer work, which will need to be investigated further. In future, we will continue to follow these patients out to one year to collect cost and effectiveness data to investigate whether these results remain past 12 weeks post-surgery.

Patient specific instrumentation (PSI) is the latest advancement in total knee arthroplasty (TKA), which claims to improve alignment, simplify the surgical process, forecasts the component size and reduces the operating time. We discuss our experience of preoperative planning using default settings and making changes where necessary.

We analysed prospectively collected data in 100 consecutive PSI knee replacements (Zimmer®) performed in our institute during the period February to August 2012. All patients underwent MRI scans of the ipsilateral hip, knee and ankle joints. From the images, Materialise® (Leuven, Belgium) provided 3D model of the knee on which preoperative planning was done using PSI software. All default plans were checked and appropriate changes were made before the senior author approved final plan for preparation of patient specific moulds.

We made 636 changes (6.36 changes per knee) preoperatively from the default settings. In only 4% of the patients, the primary cuts needed revision. Thus in 96% of the cases, the primary cuts allowed optimal alignment and gap balancing with appropriate soft tissue release. Our preoperative planning predicted 99% of femoral and 98% of tibial component sizes definitively implanted.

Our results show the importance of the surgeon's input in approving preoperative planning with this technique.