Femoral Component Position Research Articles

Avoidance of Patello-Femoral Overstuffing

Reconstruction of the patello-femoral compartment and by that avoidance of an overstuffing is one of the important steps for a successful TKA. A revision rate of around 15 % due to problems of the patello-femoral compartment demonstrates that this is not achieved in all cases. There can be many reasons for an overstuffing and also the symptoms can be very variable, showing sometimes a limited flexion, patello-femoral maltracking or anterior knee pain. Due to its relevance the following paper demonstrates the different reasons for a patello-femoral overstuffing. Further possible solutions for avoidance of overstuffing are described. The reasons for patello-femoral overstuffing are multiple. The majority is caused on the femoral side, however additional patellar and tibial reasons exist. During positioning of the femora resection blocks, the distal resection plane (extension/flexion) as well as the AP block for sizing is crucial. For that a pre-op analysis and implant planning in the lateral view of the X-ray should be performed in order to optimise implant size and position. For the patella the correct resection height and plane are important to avoid an overstuffing. A lateral patella component position can be another reason for an overstuffing. In conclusion, it can be stated that an anatomic reconstruction of the patello-femoral compartment is an important part of TKA surgery. The avoidance of a patello-femoral overstuffing can be achieved by exact pre-op planning of the femoral component size and position, and by precise surgery with sufficient bone resection.

The effect of femoral neck osteotomy on femoral component position of a primary cementless total hip arthroplasty.

The aim of this study was to quantify the femoral canal diameter and version at different femoral neck osteotomy locations, and to investigate the effect of the osteotomy plane on femoral component position in total hip arthroplasty (THA). Preoperative and postoperative three-dimensional models were reconstructed in 15 patients (19 hips) who underwent primary cementless THA with tapered non-anatomical femoral stem. On the pre-operative models, the osteotomy plane was simulated at different levels (-5, 0, 5, and 10 mm from the femoral saddle [piriformis fossa]) and angles (30, 40, 50, and 60° from the femoral anatomical axis). Medullary canal version and mediolateral diameter were measured on the osteotomy surfaces. On the postoperative models, the femoral neck osteotomy plane, stem anteversion and alignment were measured. The average canal diameter ranged from 22.8 to 26.3 mm at different osteotomy levels and from 20.8 to 29.0 mm at different osteotomy angles. The average canal version ranged from 11.4 to 23.2° at different resection levels and from 12.8 to 21° at different resection angles. The femoral stem anteversion was correlated with neck osteotomy angle (R = 0.72), whereas stem alignment in frontal plane (varus/valgus) was correlated with neck osteotomy level (R = 0.87). The femoral neck osteotomy plane in THA affects the postoperative stem position due to the complex morphology of the proximal femoral medullary canal, suggesting that both femoral neck resection level and angle should be considered in optimizing femoral component alignment in THA patients.

A novel standardized algorithm using SPECT/CT evaluating unhappy patients after unicondylar knee arthroplasty--a combined analysis of tracer uptake distribution and component position.

BackgroundThe introduction of a standardized SPECT/CT algorithm including a localization scheme, which allows accurate identification of specific patterns and thresholds of SPECT/CT tracer uptake, could lead to a better understanding of the bone remodeling and specific failure modes of unicondylar knee arthroplasty (UKA). The purpose of the present study was to introduce a novel standardized SPECT/CT algorithm for patients after UKA and evaluate its clinical applicability, usefulness and inter- and intra-observer reliability.MethodsTc-HDP-SPECT/CT images of consecutive patients (median age 65, range 48–84 years) with 21 knees after UKA were prospectively evaluated. The tracer activity on SPECT/CT was localized using a specific standardized UKA localization scheme. For tracer uptake analysis (intensity and anatomical distribution pattern) a 3D volumetric quantification method was used. The maximum intensity values were recorded for each anatomical area. In addition, ratios between the respective value in the measured area and the background tracer activity were calculated. The femoral and tibial component position (varus-valgus, flexion-extension, internal and external rotation) was determined in 3D-CT. The inter- and intraobserver reliability of the localization scheme, grading of the tracer activity and component measurements were determined by calculating the intraclass correlation coefficients (ICC).ResultsThe localization scheme, grading of the tracer activity and component measurements showed high inter- and intra-observer reliabilities for all regions (tibia, femur and patella). For measurement of component position there was strong agreement between the readings of the two observers; the ICC for the orientation of the femoral component was 0.73-1.00 (intra-observer reliability) and 0.91-1.00 (inter-observer reliability). The ICC for the orientation of the tibial component was 0.75-1.00 (intra-observer reliability) and 0.77-1.00 (inter-observer reliability).ConclusionsThe SPECT/CT algorithm presented combining the mechanical information on UKA component position, alignment and metabolic data is highly reliable and proved to be a valuable, consistent and useful tool for analysing postoperative knees after UKA. Using this standardized approach in clinical studies might be helpful in establishing the diagnosis in patients with pain after UKA.

Evaluation of fixed-bearing arthroplasty in primary total knee replacement

Background Fixed-bearing primary total knee replacement is a well-established method of treatment for advanced arthritic knee joint. Aim of the study This study evaluated the clinical, functional, and radiological outcomes after the use of fixed-bearing total knee arthroplasty in cases of primary total knee replacement. Patients and method This prospective study was conducted on 14 patients (six male and eight female) who attended Suez Canal University Hospitals between January 2012 and January 2013, and the mean age was 60 years (range 50-72 years) at the time of surgery. The patients included in the study had advanced unilateral knee osteoarthritis with severe pain and functional disability with failure of conservative measures. Preoperative clinical and radiological evaluation was carried out and the knee society clinical and functional rating system (KSS) was used to evaluate the patients preoperatively and postoperatively at 1-year follow-up. The scoring system combines a relatively objective knee score that is based on the clinical parameters and a functional score based on how patients perceive their knee function in relation to specific activities. Radiological evaluation was carried out to determine the alignment of the knee and the femoral and tibial component positions. Results There was significant difference between preoperative and postoperative clinical and functional scores. The mean postoperative clinical assessment score for pain was 44.9, for range of motion it was 115.9, and for stability it was 23.5. Postoperative mean knee society clinical assessment score was 90.7 and the mean functional assessment score for knee function was 87.5. According to the knee society clinical and functional score, 85% of patients had excellent results and 15% of patients had good results. As regards radiological results, all knees were well-aligned at 1 year postoperatively and no periprosthetic loosening or radiolucent line around either component was found. Conclusion Primary total knee arthroplasty using fixed-bearing prosthesis is an effective procedure with good clinical and functional results and early mobilization.

Novel computer-assisted method for revision arthroplasty of the knee.

To introduce the navigation system of software and instruments designed specifically for revision total knee arthroplasty (TKA). We present an imageless navigation system for revision TKA, with optical point and tracker identification to assess kinematic and anatomical landmarks. The system automatically positions the cutting guides with a motorized cutting unit. The cutting unit is placed on the distal femur with a femoral clamp and acts as a rigid body and the base for all femoral cuts. The surgical technique for using the navigation system for revision TKA is based on the technique used in primary TKA. However, there are some important differences. The most notable are: (1) differences in estimation of the position of the primary implant relative to the bone and the mechanical axes; (2) the specific possibilities the revision navigation software offers in terms of optimal joint level positioning; and (3) the suggested "best fit" position, in which the clock position, stem position and offset, femoral component size, and mediolateral position of the femoral component are taken into account to find the optimal femoral component position. We assessed the surgical technique, and accompanying software procedural steps, of the system, identifying any advantages or disadvantages that they present. The system aims to visualize critical steps of the procedure and is intended as a tool to support the surgeon in surgical decision-making. Combining a computer-assisted cutting device with navigation makes it possible to carry out precise cuts without pinning. Furthermore, the femoral clamp provides a stable fixation mechanism for the motorized cutting unit. A stable clamp is paramount in the presence of periarticular bony defects. The system allows the position of the primary implant relative to the bone and mechanical axes to be estimated, at which point any malalignments can be corrected. It also offers an optimal joint level position for implantation, and suggests a "best fit" position, in which the clock position, stem position and offset, femoral component size, and mediolateral position of the femoral component are considered. The surgeon can therefore make decisions intraoperatively to maximise alignment and, hence, outcomes. Based on the intraoperative findings of joint stability, the surgeon can modify the preoperative plan and switch from a constrained condylar system to a hinged version, or vice versa. The system is flexible and easy to learn and allows improvements in workflow during TKA.

Is the Surgical Epicondylar Axis the Center of Rotation in the Osteoarthritic Knee?

The relationship between the surgical epicondylar axis (SEA) and the rotational axis of the distal femur remains unclear. We investigated the relationship between the SEA and the distal femur and whether the SEA can be used as the rotational axis of the knee. Angular and linear measurements of 70 femora at 0°, 30°, 60°, 90°, and 120° of flexion were recorded. Results showed that the SEA was a logical and appropriate parameter as a principal axis for knee flexion at least between 0° and 60° of flexion. The study has important implications for the design and positioning of femoral components in total knee arthroplasty.

Should we aim at undercorrection when doing a total knee arthroplasty?

Restoration of neutral mechanical alignment is traditionally considered as one of the prerequisites for successful total knee replacement. The purpose of this study was to investigate whether a certain bias towards undercorrection exists with conventional total knee arthroplasty (TKA) instruments. A cohort of 456 consecutive patients, who underwent the same standardised TKA with restoration of neutral mechanical alignment as target, was studied. Based on the preoperative alignment, patients were stratified into three categories: valgus, neutral and varus. Component and limb alignment were compared between these groups. The mean post-operative hip-knee-ankle angle was -0.7° (SD 2.5) in valgus knees, 0.2° (SD 1.9) in neutral knees and 2.4° (SD 3.9) in varus knees (p < 0.001). About 39.8% of the varus knees remained in >3° of varus post-operative and 20.2% of the valgus knees remained in <-3° of valgus. A systematic unintentional undercorrection was noted in varus knees, which was proportional to the preoperative varus deformity and which was caused by varus positioning of both the femoral and tibial components. In valgus knees, the undercorrection was caused almost exclusively by valgus bias of the femoral component's position. This study showed that conventional TKA instruments are associated with a systematic unintentional bias towards undercorrection of the pre-existing deformity. The clinical relevance of this study is that intentionally aiming at slight undercorrection of the deformity may lead to excessive undercorrection in reality in case the surgeon does not recognise the automatic bias that already exists with standard instruments. Therapeutic study, Level III.

MRI-detected osteophyte is a predictor for receiving total knee arthroplasty in patients with end-stage knee osteoarthritis

in 84 knees and rheumatoid arthritis in 6 knees. The pre-operative mechanical alignment of the lower limbwas in 13.4 6.3 (0-30) varus. The knees were randomized in 1:1:1 ratio into one of the three groups conventional instruments (CON), computer navigation (NAV) and patient specific instruments (PSI). They were also randomized with regard to the 3 surgeons. Each surgeon performed 10 CON, 10 NAV and 10 PSI TKA. The three groups were matched, except there were more male patients in the PSI group. The prostheses and surgical routines were standardized. Post-operative standing long films of the entire lower limbs were taken.We recorded the tourniquet time and the operative time (skin-to-skin). We measured the femoral and tibial component positions in the coronal and axial planes and the overall lower limb alignment of the lower limb after TKA. Results: The mean tourniquet times were 49.2 12.7 minutes for CON, 68.6 14.8 minutes for NAV and 49.1 15.3 minutes for PSI groups (p < 0.001, Oneway ANOVA). Conventional instrument was more likely to result in an excessively flexed femoral component (p 1⁄4 0.001, Oneway ANOVA). Number of outliers in postoperative lower limb alignment, and other components positions in the coronal and sagittal plane showed no statistically significant difference. Conclusion: We found that the tourniquet time and operation time of using patient specific instrument in TKA were similar to that of conventional instrument, and shorten than computer navigation. The postoperative lower limb alignment and individual component positions were similar in all 3 groups except in sagittal plane where conventional instrument resulted in a significantly flexed femoral component. Although statistical significance was not achieved, the incidence of outliers was the highest in the conventional instrument group, followed by patient specific instrument and finally computer navigation. The current studied identifiedmarginal benefit of PSI in isolated component position compared to conventional instrument. A prospective study with a larger sample size and better post-op imaging modality (e.g. CT or MRI) may be needed to prove the efficacy of PSI. 860 MRI-DETECTED OSTEOPHYTE IS A PREDICTOR FOR RECEIVING TOTAL KNEE ARTHROPLASTY IN PATIENTS WITH END-STAGE KNEE OSTEOARTHRITIS L. Liu y,z, H. Kaneko y, R. Sadatsuki y, S. Hada y, A. Yusup y, M. Kinoshita y, I. Futami y, Y. Shimura x, H. Kurosawa x, Y. Saita y, Y. Takazawa y, H. Ikeda y, K. Kaneko y,z, M. Ishijima y,z. yDept. of Med. for Orthopaedics and Motor Organ, Juntendo Univ. Graduate Sch. of Med., Tokyo, Japan; z Sportology Ctr., Juntendo Univ. Graduate Sch. of Med., Tokyo, Japan; xDept. of Orthopaedic Surgery, Juntendo Tokyo Metropolitan Koto Geriatric Med. Ctr., Tokyo, Japan

Do we need intraoperative radiographs for positioning the femoral component in total hip arthroplasty?

Poor long-term results of total hip arthroplasty (THA) can result from femoral component misalignment. There are few reports that discuss the effectiveness of intraoperative radiographs for placing femoral components. This study is a retrospective review to find out the usefulness of intraoperative radiographs in detecting and improving the femoral component misalignment in posterior-approached primary THA. The study group included 150 primary THAs performed between September 2009 and April 2012. After the trial component insertion in lateral decubitus position, intraoperative radiography was performed. The surgeon assessed the femoral component position in three aspects: alignment, leg length, and offset. If it is not following the preoperative template, the surgeon makes the intraoperative adjustments to change the femoral component position. After the operation, postoperative radiograph was taken; the same parameters were measured and were compared to intraoperative findings. The changes in each parameter were classified into three categories: satisfactory, no change, and unsatisfactory. Among the three parameters, if one is satisfactory and the others are not unsatisfactory, we defined it as accurate positioning of the femoral component. Intraoperative adjustments were made in 122 cases (81.3%). The adjustments included changes in the component size (35.3%), component alignment (38.6%), femoral offset (14.0%), and additional femoral neck cuts (56.0%). As a result, accurate positioning was successfully achieved in 112 cases (91.8%) by taking intraoperative radiographs. Our data suggest that intraoperative radiography is a useful method for detecting the errors of placing the femoral components, and the success of a surgeon to correct those errors after detecting them intraoperatively.

Anterior Referencing versus Posterior Referencing in Total Knee Arthroplasty

Appropriate femoral component positioning and sizing is essential for proper kinematic function in total knee arthroplasty (TKA). Anterior or posterior referencing (AR or PR) are two major techniques for setting center of rotation and for balancing the sagittal plane of the arthroplasty. Both techniques have advantages and disadvantages. Minimally invasive surgical (MIS) TKA has added yet another aspect to intraoperative techniques and postoperative outcomes. A total of 100 consecutive patients undergoing unilateral MIS TKA were prospectively randomized to either AR or PR. Knee Society Scores, range of motion, SF-12, and strength testing by Cybex dynamometer were evaluated at standardized intervals postoperatively for 2 years. There were no statistically significant differences in surgical (incision length, surgical release, blood loss, surgical time, and length of stay) or clinical outcomes between two groups at all postoperative intervals (2 and 6 weeks, 3 and 6 months, and 1 and 2 years). Results demonstrate that both AR and PR are effective and can be used successfully during MIS TKA.

Our Midterm Results of the Birmingham Hip Resurfacing With and Without Navigation

We reviewed 148 consecutive hip resurfacings in order to assess the clinical outcomes of the BHR at midterm follow-up and to compare the accuracy of the navigation in the positioning of femoral component. We retrospectively analyzed 85 hips using the conventional jig to implant the femoral component and we prospectively followed 63 hips operated on by navigation. At a mean follow-up of 50.54months, the Harris hip score improved significantly from 44.66 preoperatively to 98.45 postoperatively without any differences between the groups. Radiologically, we classic navigated group. Our clinical outcomes are excellent at midterm follow-up and the navigation definitely improves the implant position in both planes.

Use of Intraoperative X-rays to Optimize Component Position and Leg Length During Total Hip Arthroplasty

Proper femoral and acetabular component position and leg length equality are important intraoperative considerations during total hip arthroplasty. Unfortunately, traditional surgical techniques often lead to suboptimal component position, and such deviations have been associated with increased rates of prosthetic wear, dislocation, component loosening, and patient dissatisfaction. Although surgical navigation has been shown to improve reproducibility of component alignment, such technology is not universally available and is associated with significant costs and additional surgical/anesthetic time. In the current study, we found that a routine intraoperative pelvic radiograph could successfully identify malpositioned components and leg length inequalities and could allow for successful correction of identified problems. Unexpected component malposition and leg length inequality occurred in only 1.5% of cases where an intraoperative pelvic radiograph was utilized.

Radiographic accuracy in TKA with a CT-based patient-specific cutting block technique

Patient-specific instrumentation (PSI) technology for the implantation of total knee arthroplasty (TKA) has a rising interest in the orthopaedic community. Data of PSI are controversially discussed. The hypothesis of this paper is that the radiological accuracy of CT-based PSI is similar to the one of navigated TKA published in the literature. Since 2010, all 301 consecutively performed PSI TKAs (GMK MyKnee©) were included in this study. The radiological assessment consisted in a preoperative and postoperative standard X-ray and long-standing X-ray. Changes from the planned to the definitively implanted component size were documented. Postoperative analysis included limb alignment and position of femoral and tibial components (for varus/valgus and flexion or tibial slope). The postoperative average hip-knee-ankle angle was 180.1° ± 2.0°. In the frontal plane a total of 12.4 % of outliers >3°, for the tibial components 4.1 % of outliers >3° and for the femoral components 4.8 % of outliers >3° were measured. A total of 12.3 % of outliers for posterior tibial slope and 9 % of outliers >3° for the femoral flexion were noted. 10.8 % of the 602 planned size components were adapted intraoperatively. Although it is still unknown which limb axis is the correct one for the best clinical result, a technology providing the aimed axis in a most precise way should be chosen. Comparing the outcome of the current study with the data from the literature, there does not seem to be any difference compared to computer-assisted surgery. IV.

Impact of a mobile-bearing total knee arthroplasty design on non-resurfaced patellar tracking ( comparative study with fixed-bearing total knee arthroplasty)

Background Unlike fixed-bearing total knee arthroplasty (TKA), mobile-bearing TKA is designed to accommodate for small mismatches in the rotational position of the femoral and tibial components owing to mobility of the bearing insert. Thereby, central patellar tracking is potentially facilitated. The aim of this study is to determine whether the incidence of lateral retinacular release would be lower in knees replaced with a mobile-bearing TKA as compared with a fixed-bearing TKA design. Patients and methods A standardized surgical technique was applied in 64 consecutive cases with advanced varus osteoarthritis. A single cruciate-substituting knee design was used in all patients. The selection of a fixed-bearing versus mobile-bearing TKA was made primarily on the basis of knee stability, age, and lifestyle activities. There were 39 women and 25 men in the study, mean age 64.5 years (range, 56–77 years). A mobile-bearing TKA design was implanted in half of the cases (32) and a fixed-bearing design was equally implanted in the other half. Results The overall lateral retinacular release rate in this study was 12.5% (eight of 64 knees). The incidence of lateral retinacular release was higher (P Conclusion In conclusion, the current study showed that decreased incidence of lateral retinacular release could be one potential advantage of the mobile-bearing TKA design. However, further long-term follow-up studies are still required to document other theoretical benefits of mobile-bearing TKA with respect to reduced polyethylene wear, durable long-term fixation, and patellofemoral performance.

Total knee arthroplasty using anatomic alignment can produce mid-flexion laxity

BackgroundModern total knee arthroplasty offers two different alignment techniques, anatomic or mechanical, based on the bone axes selected for implantation of the prosthetic components. This study examined the axes of both during simulated physiologic knee joint motion, as well as the relationship between these axes and the implication of medial–lateral soft tissue balance in total knee arthroplasty. MethodsSeven fresh-frozen, lower limb specimens were stripped at a level 15cm from joint line, leaving the joint capsule, quadriceps muscle, hamstring tendons and ligamentous structures intact. Specimens were anatomically marked to track precise movements of the tibia and femur — from which both alignment axes were determined. Medial and lateral joint spacings were tracked to determine collateral ligament laxity. A kneeling simulator jig produced physiologic knee motion. FindingsMeasurements of medial and lateral joint spacings revealed statistically significant differences at all flexion angles between the two alignment axes. The anatomic alignment axes' pattern demonstrates mid-flexion lateral opening and late-flexion medial joint space opening — mechanical axes revealing a consistent 2–3mm larger lateral than medial joint space. InterpretationIn an effort to produce a more natural feeling knee replacement, understanding the normal kinematic soft tissue balance can serve as a useful reference point, and mid flexion laxity is an important clinical concern. With currently available total knee arthroplasty designs, mechanical alignment is preferable to anatomic alignment because it creates consistent spacing, which can be addressed by ligament lengthening or adjustments in femoral component positioning.

The First SICOT Oral Presentation Award 2011: Imageless computer-assisted femoral component positioning in hip resurfacing: a prospective randomised trial

The aim of the study was to evaluate the effects of imageless computer-assisted surgery (CAS) on the accuracy of positioning of the femoral component and on the short-term clinical outcome in hip resurfacing (HR) using a randomised prospective design. A total of 75 consecutive patients undergoing HR were randomly allocated to CAS and conventional implantation, respectively. Preoperatively and six months post-operatively standardised pelvic anteroposterior X-ray images, the total Western Ontario and McMaster Universities Osteoarthritis Index, the Harris Hip Score and the EQ-5D utility index were evaluated in a blinded manner. The primary end point of the study was a post-operative femoral component malpositioning in five degrees or more either varus or valgus absolute deviation from the planned stem shaft angle. Patient demographics and algofunctional scores did not differ between the CAS and conventional implantation samples. Using CAS fewer femoral components were positioned in five or more degrees absolute deviation (4/37 vs 12/38, Fisher's exact p = 0.047; 95 % confidence interval for the primary end point's incidence difference: +3 %; +39 %); the respective incidences of five or more degrees of varus deviation were 0/37 vs 5/38. One conversion to a stemmed prosthesis (CAS group) was performed for periprosthetic femoral neck fracture. Radiological signs of superolateral femoral neck/implant impingement were observed in two cases (one CAS-based and one conventional implantation). The accuracy of femoral HR component positioning was significantly improved using CAS. However, one major complication necessitated early revision in the CAS group at six months of observation. Apart from that adverse event no inter-group differences were observed for the short-term clinical outcome. Future studies need to address the clinical long-term relevance of CAS in HR.

Piriformis fossa approach in optimising femoral neck osteotomy and component positioning in hemiarthroplasty surgery for intracapsular fractured neck of femur

Figure 3 The femoral rasp inserted to a sufficient depth in the canal via the piriformis fossa. The rasp acts as a guide while diathermy is used to demarcate the angle of neck osteotomy. lies medial to the greater trochanter of the proximal femur (Fig 2). This ensures only a blunt instrument is used to create an initial passage for the femoral rasp, minimising the risk of femoral perforation. With the neck still intact, a box chisel is used to create the necessary opening for rasp insertion. The rasp is sufficiently inserted to act as a visual guide for the neck cut. Monopolar diathermy outlines the neck osteotomy (Fig 3) and, following osteotomy and head removal, the rasp is inserted to the required depth.

Piriformis fossa approach in optimising femoral neck osteotomy and component positioning in hemiarthroplasty surgery for intracapsular fractured neck of femur

Piriformis fossa approach in optimising femoral neck osteotomy and component positioning in hemiarthroplasty surgery for intracapsular fractured neck of femur

More accurate component alignment in navigated total knee arthroplasty has no clinical benefit at 5-year follow-up

Background and purpose Computer navigation in total knee arthroplasty is somewhat controversial. We have previously shown that femoral component positioning is more accurate with computed navigation than with conventional implantation techniques, but the clinical impact of this is unknown. We now report the 5-year outcome of our previously reported 2-year outcome study.Methods 78 of initially 84 patients (80 of 86 knees) were clinically and radiographically reassessed 5 (5.1–5.9) years after conventional, image-based, and image-free total knee arthroplasty. The methodology was identical to that used preoperatively and at 2 years, including the Knee Society score (KSS) and the functional score (FS), and AP and true lateral standard radiographs.Results Although a more accurate femoral component positioning in the navigated groups was obtained, clinical outcome, number of reoperations, KSS, FS, and range of motion were similar between the groups.Interpretation The increased costs and time for navigated techniques did not translate into better functional and subjective medium-term outcome compared to conventional techniques.

Improved femoral component rotation in TKA using patient-specific instrumentation

BackgroundPatient-specific instrumentation (PSI) was introduced in an attempt to reduce positional outliers of components in total knee arthroplasty (TKA). It was hypothesized that PSI could help with the positioning of femoral components in optimal rotational alignment. MethodsA magnetic resonance imaging (MRI) analysis of 94 patients following TKA was conducted. Of these, 46 operations were performed using PSI and 48 using conventional instrumentation. The rotation of the femoral components was determined in the MRI and deviations >3° were considered outliers. Data were analyzed for positional outliers, observer reliability, and a variance comparison between implant groups. ResultsThere was excellent inter- and intraobserver reliability with low standard deviations for the determination of femoral component rotation. There were significantly more outliers in the conventional (22.9%) group than in the PSI group (2.2%, p=0.003). ConclusionIn this setup, PSI was effective in significantly reducing outliers of optimal rotational femoral component alignment during TKA.