IntroductionPatient specific instruments (PSI) and computer-assisted surgery (CAS) are innovative technologies that offer the potential to improve the accuracy and reproducibility with which a total knee arthroplasty (TKA) is performed. It has not been established whether clinical, functional, or radiographic outcomes between PSI, CAS, and manual TKA differ in the hands of an experienced TKA surgeon. The purpose of this study was to evaluate clinical, functional and radiographic outcomes between TKA performed with PSI, CAS, and manual instruments at short-term follow-up. Our hypothesis was that at early follow-up, we would be unable to elucidate any significant differences between the groups using the most commonly utilized outcomes measures.Methods40 PSI, 38 CAS, and 40 manual TKA were performed by a single surgeon. The groups were similar in regards to age, sex, and preoperative diagnosis. The Knee Society Scoring System was used to evaluate patient clinical and functional outcome scores preoperatively ...

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...

Purpose To compare the biomechanical strengths of 5 surgical techniques for treatment of traumatic hyperextension instability of the proximal interphalangeal (PIP) joint.Methods Thirty-six cadaveric fingers were randomly assigned to 6 groups: normal control, volar plate repair, flexor digitorum superficialis tenodesis (FDST), single lateral band transfer (SLBT), double lateral band transfer, and dual split lateral band transfer. For each experimental specimen, the volar plate and accessory collateral ligaments were transected, the PEP joint was hyperextended to 900, and a PIP joint stabilizing procedure was completed. The ultimate strength of each procedure was ascertained by loading to failure, and the fingers were dissected to determine the pathoanatomy of failure. Force-displacement curves were used to estimate the stiffness of each group, and multiple pairwise statistical comparisons were performed.Results The mean PIP joint stiffness in the control group was significantly greater than the mean PIP joint stiffness in the FDST and SLBT groups, but not significantly different from the mean PIP joint stiffness in the other 3 groups. There were no significant differences in the mean PIP joint stiffness between the 5 joint stabilizing techniques. The SLBT, double lateral band transfer, and dual split lateral band transfer repairs all failed by massive disruption of the flexor tendon sheath, whereas the volar plate repairs and FDST repairs failed by either suture anchor pullout or suture breakage.Conclusions The stiffness of 5 surgical techniques to stabilize a traumatic hyperextensible PIP joint did not vary significantly. Clinical relevance The 5 described techniques to stabilize a posttraumatic PIP joint hyperextension deformity may provide for equal restraint to PIP joint hyperextension instability in the early postoperative period. The choice of procedure should take into consideration other factors not studied, including the potential for PIP joint flexion contracture and long-term durability. Copyright (C) 2015 by the American Society for Surgery of the Hand. All rights reserved.

Background The purpose of this study was to evaluate (1) patient preferences regarding iPad and paper-based questionnaires, (2) the efficacy of iPad and paper questionnaires in a hand surgery practice, (3) the influence of questionnaire length on patient preferences and data collection, and (4) patient characteristics associated with a preference for iPad-based questionnaires. Methods Two hundred total patients in a single hand surgery practice were randomly assigned to one of four groups. Each group completed either the Michigan Hand Questionnaire (MHQ) or QuickDASH (QD) using either an iPad or pen and paper. Patient preferences, questionnaire completion and timing, and demographic data were analyzed. Results The use of an iPad was associated with a statistically stronger preference for the same delivery format in the future compared to paper for the MHQ (93.9 vs 52.1 %, p < 0.001) and QD (90.0 vs 41.7 %, p < 0.001). The MHQ iPad group found the survey “physically easy” more often compared to the MHQ paper group, while no difference was found among QD groups. Questionnaire timing between iPad and paper groups was similar for the MHQ but statistically longer with the iPad for QD. A significantly higher proportion of patients who preferred the iPad were under the age of 50 compared to those who preferred paper. Conclusions The addition of an iPad is an efficient and preferable questionnaire format for functional outcome assessment in a hand and upper extremity surgery practice setting. The iPad is particularly preferable for longer outcome questionnaires and for patients under the age of 50.

PSI software adjusts preoperative planning to accommodate differences in implant design. Such adjustments may influence the accuracy of intraoperative jig placement, bone resection, or component placement. Our purpose was to determine whether implant design influences PSI accuracy. 96 and 123 PSI TKA were performed by a single surgeon using two different implant systems and identical PSI software. Femoral coronal alignment outliers were greater for Implant 1 (23.9% Implant 1 vs. 13.4% Implant 2; P=0.050). Tibial coronal alignment outliers were greater for Implant 2 (10.9% Implant 1 vs. 22.7% Implant 2; P=0.025). There was no difference in overall mechanical axes. Differences in implant design can influence bone resection and component alignment. PSI software rationale must align with surgeons’ intraoperative goals.

Proper femoral component rotation is crucial in successful total knee arthroplasty. Rotation using anatomic landmarks has traditionally referenced the transepicondylar axis (TEA), Whiteside's Line (WSL), or posterior condylar axis (PCA). TEA is thought to best approximate the flexion-axis of the knee, however WSL or PCA are common surrogates in the operating room. This study evaluated 560 knees using MRI-based planning software to assess the relationship of WSL and PCA to the TEA and determine if the relationships were influenced by pre-operative coronal deformity. Results showed the WSL-TEA relationship has more variability than PCA-TEA and that the PCA is more internally rotated in females and valgus knees. Axis options and historical assumptions about axis relationships may need to be reassessed as imaging technology advances.

Background The purpose of the present study is to evaluate a single surgeon’s short, intermediate, and long-term clinical, functional, and radiographic outcomes with a trapeziectomy with flexor carpi radialis (FCR) suspension arthroplasty without tendon interposition (LRSA). Methods Twenty-one patients underwent 26 FCR suspension arthroplasties without tendon interposition by a single senior surgeon. All patients had Eaton stage III and IV carpometacarpal (CMC) osteoarthritis. The Patient-Rated Wrist and Hand Evaluation (PRWHE) and Quick Disabilities of Arm, Shoulder, and Hand (QuickDASH) were used to evaluate functional outcomes. A comprehensive strength and range of motion evaluation was performed to evaluate clinical outcomes. Plain radiographs at rest and with maximal pinch were performed to evaluate for arthroplasty space subsidence. Results The LRSA exhibited consistent clinical and functional outcomes throughout postoperative follow-up. As the average patient age and time from surgery increased, range of motion (ROM) and PRWHE scores stayed relatively constant, while lateral tip and tip pinch strength deteriorated with time. The LRSA prevented the proximal migration of the first metacarpal in all but one patient. No patients required revision arthroplasty following LRSA. Conclusions This study demonstrates the consistent short, intermediate, and long-term clinical, functional, and radiographic outcomes following a trapeziectomy with FCR suspension arthroplasty.

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 surgeon9s 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.

PURPOSE:The purpose of this study was to evaluate clinical, functional, and radiographic outcomes following total knee arthroplasty (TKA) performed with patient-specific instrumentation (PSI), computer-assisted surgery (CAS), and manual instruments at short-term follow-up.METHODS:122 TKAs were performed by a single surgeon: 42 with PSI, 38 with CAS, and 40 with manual instrumentation. Preoperative, 1-month, and 6-month clinical and functional outcomes were measured using the Knee Society scoring system (knee score, function score, range of motion, and pain score). Improvements in clinical and functional outcomes from the preoperative to postoperative period were analyzed. Preoperative and postoperative radiographs were measured to evaluate limb and component alignment.RESULTS:Preoperative, 1-month postoperative, and 6-month postoperative knee scores, function scores, range of motion, and pain scores were highest in the PSI group compared to CAS and manual instrumentation. At 6-month follow-up, PSI TKA was associated with a statistically significant improvement in functional score when compared to manual TKA. Otherwise, there were no statistically significant differences in improvements among PSI, CAS, and manual TKA groups.CONCLUSION:The higher preoperative scores in the PSI group limits the ability to draw definitive conclusions from the raw postoperative scores, but analyzing the changes in scores revealed that PSI was associated with a statistically significant improvement in Knee Society Functional score at 6-month post-TKA as compared to CAS or manual TKA. This may be attributable to improvements in component rotation and positioning, improved component size accuracy, or other factors that are not discernible on plain radiograph.

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 patient9s 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.

The purpose of this study was to determine whether differences in clinical, functional, or radiographic outcomes existed at 5-year follow-up between patients who underwent computer-assisted or manual total knee arthroplasty (TKA). Seventy-eight consecutive TKAs were performed by a single surgeon who had extensive experience performing computer-assisted and manual TKA. The manual group (n=40) and computer-assisted group (n=38) were similar with regard to age, sex, diagnosis, body mass index, surgical technique, implants, perioperative management, Knee Society scores, and anteroposterior mechanical axis. Sixty-three (manual group, n=34; computer-assisted group, n=29) patients were available for final follow-up. At 5-year follow-up, no statistically significant differences were found in Knee Society knee score (P=.289), function score (P=.272), range of motion (P=.284), pain score (P=.432), or UCLA activity score (P=.109) between the 2 groups. Postoperative radiographs showed a significant difference in the mechanical axis (P=.004) between the 2 groups; however, both groups achieved a neutral mechanical axis of ±3° (computer-assisted group mean, 2.0°; manual group mean, -0.24°).When TKA was performed by an experienced surgeon, no significant difference was identified at 5-year follow-up between patients who underwent computer-assisted vs manual TKA.

Introduction: The use of computer-assisted surgery (CAS) offers the experienced surgeon the ability to improve limb and implant alignment and reduce outliers. Two recent high quality meta-analyses have demonstrated that CAS can produce more accurate and precise limb alignment results. It has not been clearly established within the literature whether these benefits translate to improved patient outcomes. A previous case-controlled study by this author demonstrated no significant difference in clinical, functional, or radiographic outcomes between CAS and manual TKA at short term follow-up. We attributed these results to the improvements in the performance of manual TKA that had been realized through the learning effects afforded by working extensively with an intraoperative navigation system. The purpose of the present study was to determine whether any differences in clinical, functional, or radiographic outcomes could be elicited between patients who underwent either CAS or manual TKA at 5 year follow-up.

Introduction Patient specific instruments (PSI) and computer-assisted surgery (CAS) are innovative technologies that offer the potential to improve the accuracy and reproducibility with which a total knee arthroplasty (TKA) is performed. It has not been established whether clinical, functional, or radiographic outcomes between PSI, CAS, and manual TKA differ in the hands of an experienced TKA surgeon. The purpose of this study was to evaluate clinical, functional and radiographic outcomes between TKA performed with PSI, CAS, and manual instruments at short-term follow-up. Our hypothesis was that at early follow-up, we would be unable to elucidate any significant differences between the groups using the most commonly utilized outcomes measures. Methods 40 PSI, 38 CAS, and 40 manual TKA were performed by a single surgeon. The groups were similar in regards to age, sex, and preoperative diagnosis. The Knee Society Scoring System was used to evaluate patient clinical and functional outcome scores preoperatively and at 1 and 6 months postoperatively. Long-standing AP radiographs were obtained pre and postoperative to evaluate mechanical axis alignment. Results PSI, CAS, and manual TKA produced similar interval improvements in clinical and functional outcomes at both 1 and 6-months postoperative. Knee Society Knee scores were on average 88.5, 72.5, and 69.3 for PSI, CAS, and manual TKA at 1 month and 99.4, 83.4, and 84.6 at 6 months postoperative. Knee Society Function scores were on average 65.9, 49.3, and 48.4 for PSI, CAS, and manual TKA at 1 month and 86.3, 66.2, and 61.2 at 6 months postoperative. Although PSI tended to have higher absolute Knee and Function scores at 1 and 6 months postoperative, the interval change from preoperative to postoperative between each group was similar. Postoperative mechanical axis alignment was not significantly different between PSI, CAS, and manual TKA (1.0âi?½°, 2.0âi?½°, and −0.2âi?½°, respectively). Discussion This study suggests that in the hands of an experienced arthroplasty surgeon, PSI, CAS and manual TKA produce similar interval improvements in clinical, functional, and radiographic outcomes at short-term follow-up. These results may reflect the ability of an arthroplasty-trained academic surgeon to perform a TKA accurately with multiple technologies. These findings may also represent the lack of sensitivity and inability of commonly utilized evaluation tools, like plain radiographs and the Knee Society Scoring System, to adequately differentiate small differences in outcomes and limb alignment, if differences do indeed exist. Long-term follow-up will help establish whether these TKA technologies continue to demonstrate equivalent clinical and functional interval improvements.

Introduction Computer-assisted surgery (CAS) is a tool developed to allow accurate limb and implant alignment in TKA. The strength of the technology is that it allows the surgeon to assess soft tissue balance and ligament laxity in flexion and extension. The accuracy of this ligament balancing technology depends upon an accurate determination of femoral component size. This size is established with intraoperative surface registration techniques. Customized instrumentation (CI) is a measured resection technique in which component size is established on preoperative 3D MRI reconstructions. The purpose of this study is to determine how these two computer-based technologies compare with regard to the accuracy with which femoral component size is established in TKA. Methods 67 TKA were performed using CI and 30 TKA were performed using CAS by a single surgeon. CI-predicted and CAS-predicted femoral component size were compared to actual component selection. The process by which CI and CAS perform an anatomic registration was evaluated. Results The CI and CAS systems accurately predicted surgeon-selected femoral component size in 89% and 43% of cases, respectively (p Discussion The CI system was both more accurate and more precise than the CAS navigation system in predicting femoral component size in TKA. CI utilizes preoperative MR imaging to generate femoral component sizing based on optimizing medial-lateral fit with a measured posterior femoral bone resection. CAS utilizes surface registration techniques based on anatomic site registration that may be subject to intraoperative measurement error due to difficult visualization (femoral epicondyles), inherent subjectivity (Whiteside9s line) or anatomic variation (hypoplastic posterior condyles). CI bases implant sizing solely on reproducing an anatomical fit and a measured resection technique, whereas CAS attempts to balance an anatomic fit with optimal soft tissue balancing. In this study, the surgeon9s final component selection was more likely to be in accordance with the CI rather than the CAS sizing algorithm. This study suggests that intraoperative surface registration may not be as accurate as preoperative 3D MRI reconstructions for establishing optimal femoral component sizing. Surgeons using intraoperative navigation based surface registration need to be aware of this when they are making femoral component size selection, establishing ligament balance, and determining femoral rotation.

Introduction Most surgeons utilize one of three axis options in conventional total knee arthroplasty (TKA), the transepicondylar axis (TEA), Whiteside9s line (WSL) or the posterior condylar axis (PCA) with an external rotation correction factor. Each option has limitations and no clear algorithm has been determined for which option to use and when. Many surgeons believe the TEA to be the gold standard for determining rotation however it can be difficult to access intraoperatively. WSL and PCA have been used as surrogates for determining axial rotation in conventional TKA but may also be prone to error. MRI based preoperative planning systems overcome intraoperative limitations while accounting for the individual anatomy of each patient, thus helping optimize femoral component rotation. The goal of this study was to examine if coronal plane deformity had any effect on the relationship of conventional referencing options such as WSL and PCA to the TEA. Methods Utilizing a preoperative planning software based on MRI, we compared the preoperative posterior femoral condyle resections for three different axis options in 176 TKA. The difference in bone resection amount was used to determine the rotational differences between the axis options in all knees. Assuming that the TEA was the ideal rotational axis, we compared the TEA to both WSL and PCA. A 1-sample t-test and paired t-test were then used to determine if there was a significant rotational difference between the various axis options when accounting for degree and direction of preoperative deformity in the coronal plane. Results In the overall population of 176 knees (42 valgus, 134 varus), neither WSL or PCA approximated the TEA accurately (p=0.016 and 0.001). In valgus deformity, WSL was found to approximate the TEA (p=0.68) better than the PCA (p=0.21). Minor varus deformity ( 6 degrees) deformity favored use of PCA due to lower variability. For complete results see Figure 2. Conclusion Based on MRI data, our study indicates that preoperative coronal plane deformity should help determine the specific referencing option utilized for femoral component rotation in TKA. Broad application of either WSL or the PCA to all patients regardless of preoperative deformity did not accurately approximate TEA in femoral component rotation. Rather, analysis of the degree and direction of preoperative coronal plane deformity indicates that WSL and PCA should be used in specific scenarios to approximate the TEA. When WSL or PCA either both approximate or do not approximate the TEA, we recommend using the option with a lower standard deviation, and thus less variability. Although this MRI based technology is not in widespread use, we believe our findings (Figure 1) can assist the majority of surgeons determine when to use WSL or the PCA based on preoperative coronal plane deformity.

Computer-assisted surgery (CAS) is a tool developed to allow accurate limb and implant alignment in total knee arthroplasty [TKA]. The strength of the technology is that it allows the surgeon to assess soft tissue balance and ligament laxity in flexion and extension. The accuracy of this ligament balancing technology depends upon an accurate determination of femoral component size. This size is established with intraoperative surface registration techniques. Customised instrumentation (CI) is a measured resection technique in which component size is established on preoperative 3D MRI reconstructions. The purpose of this study is to determine how these two computer-based technologies compare with regard to the accuracy with which femoral component size is established in TKA. 67 TKA were performed using CI and 30 TKA were performed using CAS by a single surgeon. CI-predicted and CAS-predicted femoral component size were compared to actual component selection. The process by which CI and CAS perform an anatomic registration was evaluated. The CI and CAS systems accurately predicted surgeon-selected femoral component size in 89% and 43% of cases, respectively (p The CI system was both more accurate and more precise than the CAS navigation system in predicting femoral component size in TKA. CI utilises preoperative MR imaging to generate femoral component sizing based on optimizing medial-lateral fit with a measured posterior femoral bone resection. CAS utilises surface registration techniques based on anatomic site registration that may be subject to intraoperative measurement error due to difficult visualization (femoral epicondyles), inherent subjectivity (Whiteside9s line) or anatomic variation (hypoplastic posterior condyles). CI bases implant sizing solely on reproducing an anatomical fit and a measured resection technique, whereas CAS attempts to balance an anatomic fit with optimal soft tissue balancing. In this study, the surgeon9s final component selection was more likely to be in accordance with the CI rather than the CAS sizing algorithm. The CI system was capable of accurate femoral component placement in TKA. This study suggests that intraoperative surface registration may not be as accurate as preoperative 3D MRI reconstructions for establishing optimal femoral component sizing. Surgeons using intraoperative navigation based surface registration need to be aware of this when making femoral component size selection, establishing ligament balance, and determining femoral rotation.

Custom instrumentation in TKA utilises pre-operative imaging to generate a customised guide for cutting block placement. The surgeon is able to modify the plan using three-dimensional software. Although this technology is increasingly gaining acceptance, there is a paucity of clinical data supporting it. One hundred and eleven patients underwent primary TKA using the Zimmer Patient-Specific Instrumentation (PSI) system, in 28 of the cases surgical navigation was used to validate the PSI-generated cuts. Alignment measurements included long-leg alignment and biplanar distal femoral and proximal tibial cuts. Further measurements evaluated femoral implant placement in the AP plane, femoral component rotation, measured bone resection and implant sizing accuracy. The mean final limb alignment as recorded by computer-assisted surgical (CAS) tools was 0.3° of varus. Only two limbs were malaligned by greater than 3°. The femoral component had a mean alignment of 0.3° of valgus and 4.5° of flexion (PSI plan 3° flexion). The predicted femoral size was accurate in 89% of cases and the anterior femoral cut was congruent with the anterior cortex in 92% of cases. The PSI-directed femoral component rotation was consistent with the surgeon9s perceived rotation in 95% of cases. The posterior condylar bone resection had a mean difference of The tibial component had a mean alignment of 0.5° of varus and 8.5° of posterior slope (PSI plan 7° posterior slope). The only statistically significant deviation in alignment was the increased tibial slope (p = 0.046). The tibial component size was accurately predicted in 66% of cases. Custom instrumentation in total knee arthroplasty accurately achieved implant and limb alignment in our study. The plan was more reproducible on the femoral slide. The overestimation of tibial slope and tibial sizing incongruity were related to some of the reference points for the software. A potential benefit of this technology is improved mid-flexion stability by accurately determining femoral component size, placement, and rotation. Further studies will need to be conducted to determine the efficiency and cost-effectiveness of this technology.

Introduction Custom instrumentation in TKA utilizes pre-operative imaging to generate a customized guide for cutting block placement (Figure 1). The surgeon is able to modify the plan using three-dimensional software (Figure 2). Although this technology is increasingly gaining acceptance, there is a paucity of clinical data supporting it. Methods One hundred and eleven patients underwent primary TKA using the Patient-Specific Instrumentation (PSI) system, in twenty-eight of the cases surgical navigation was used to validate the PSI-generated cuts. Alignment measurements included long-leg alignment and biplanar distal femoral and proximal tibial cuts. Further measurements evaluated femoral implant placement in the AP plane, femoral component rotation, measured bone resection and implant sizing accuracy. Results The mean final limb alignment as recorded by computer-assisted surgical (CAS) tools was 0.3° of varus. Only two limbs were malaligned by greater than 3° (Figure 3). The femoral component had a mean alignment of 0.3° of valgus and 4.5° of flexion (PSI plan 3° flexion). The predicted femoral size was accurate in 89% of cases and the anterior femoral cut was congruent with the anterior cortex in 92% of cases. The PSI-directed femoral component rotation was consistent with the surgeon9s perceived rotation in 95% of cases. The posterior condylar bone resection had a mean difference of The tibial component had a mean alignment of 0.5° of varus and 8.5° of posterior slope (PSI plan 7° posterior slope). The only statistically significant deviation in alignment was the increased tibial slope (p=0.046) (Figure4). The tibial component size was accurately predicted in 66% of cases. Discussion Custom instrumentation in total knee arthroplasty accurately achieved implant and limb alignment in our study. The plan was more reproducible on the femoral slide. The overestimation of tibial slope and tibial sizing incongruity were related to some of the reference points for the software. A potential benefit of this technology is improved mid-flexion stability by accurately determining femoral component size, placement, and rotation. Further studies are needed to determine the efficiency and cost-effectiveness of this technology.