Femoral sizing in total knee arthroplasty is rotation dependant

Efficacy of the Pre-operative Three-Dimensional (3D) CT Scan Templating in Predicting Accurate Implant Size and Alignment in Robot Assisted Total Knee Arthroplasty

Background

Nearly 20% of Total knee Arthroplasty patients remain dissatisfied. This is a major concern in twenty-first century arthroplasty practice. Accurate implant sizing is shown to improve the implant survival, knee balance and patient reported outcome. Aim of the current study is to assess the efficacy of pre-operative three-dimensional (3D) CT scan templating in a robot-assisted TKA in predicting the correct implant sizes and alignment.

Materials and methods

Prospectively collected data in a single center from 30 RA-TKAs was assessed. Inclusion criterion was patients with end stage arthritis (both osteoarthritis and rheumatoid arthritis) undergoing primary TKA. Patients undergoing revision TKA and patients not willing to participate in the study were excluded. Preliminary study of ten patients had indicated almost 100% accuracy in determining the implant size and position. Sample size was estimated to be 28 for 90% reduction in implant size and position error with α error of 0.05 and beta error of 0.20 with power of study being 80. Post-operative radiographs were assessed by an independent observer with respect to implant size and position. The accuracy of femoral and tibial component sizing in the study was compared with the historic control with Chi-squared test. The p value < 0.05 was considered significant.

Results

The pre-operative CT scan 3D templating accuracy was 100% (30 out of 30 knees) for femoral component and 96.67% (29 out of 30 knees) for tibial component. The implant position and limb alignment was accurate in 100% of patients. The accuracy of femoral component and tibial component sizing is statistically significant (Chi-squared test, p value 0.0105 and 0.0461, respectively).

Conclusion

The study results show the effectiveness of pre-operative 3 D CT scan planning in predicting the implant sizes and implant positioning. This may have a potential to improve the implant longevity, clinical outcomes and patient satisfaction.

Preoperative Virtual Total Knee Arthroplasty Surgery Using a Computed Tomography-based 3-dimensional Model With Variation in Reference Points and Target Alignment to Predict Femoral Component Sizing

Background

The purpose of this study was to investigate the size differences of 19 different femoral component placements from the standard position in total knee arthroplasty using 3-dimensional virtual surgery.

Methods

Three-dimensional bone models were reconstructed from the computed tomography data of 101 varus osteoarthritic knees. The distal femoral bone was cut perpendicular to the femoral mechanical axis (MA) in the coronal plane. Twenty different component placements consisting of 5 cutting directions (perpendicular to MA, 3° and 5° extension relative to MA [3°E-MA and 5°E-MA, respectively], and 3° and 5° flexion relative to MA [3°F-MA and 5°F-MA, respectively]) in the sagittal plane, 2 rotational alignments (clinical epicondylar axis [CEA] and surgical epicondylar axis [SEA]), and 2 rotational types of anterior reference guide (central [CR] and medial [MR]) were simulated.

Results

The mean anteroposterior dimension of femur ranged from 54.3 mm (5°F-MA, SEA, CR) to 62.5 mm (5°E-MA, CEA, MR). The largest and smallest differences of anteroposterior dimension from the standard position (3°F-MA, SEA, and CR) were 7.1 ± 1.3 mm (5°E-MA, CEA, and MR) and −1.2 ± 0.2 mm (5°F-MA, SEA, and CR), respectively. Multiple regression analysis revealed that flexion cutting direction, SEA, and CR were associated with smaller component size.

Conclusions

The femoral component size can be affected easily by not only cutting direction but also the reference guide type and the target alignment. Our findings could provide surgeons with clinically useful information to fine-tune for unintended loose or tight joint gaps by adjusting the component size.

Do optional implants improve the femoral fit during total knee arthroplasty in Asians? Comparison of the femoral fit between single- and dual-option implants

BACKGROUND

The purpose of this study was to evaluate the femoral fit in Asian patients during total knee arthroplasty by examining whether (1) the advanced single-option implant improves the fit of the femoral component in both the anterior flange and distal cutting surface and (2) the dual-option implants show better fit than the advanced single-option implant.

METHODS

A total of 950 knees that underwent primary total knee arthroplasty were included. Two types of single-option implant systems (Optetrak Logic and Truliant) and three types of dual-option implant systems (Anthem, Attune, and Persona) were used. The difference between the resected surface of the femur and femoral component dimensions was analyzed in predefined six zones. Appropriateness of fit (good-fit, over-hang, under-hang) was also evaluated.

RESULTS

The advanced single-option implant showed higher rates of good-fit and lower rates of over-hang and under-hang in almost all distinct zones than the old version single-option implant. The advanced single-option implant demonstrated similar good-fit, higher over-hang and lower under-hang rates than the dual-option implants. All single-option implants showed significantly higher over-hang rate (P < 0.05) and lower under-hang rate (P < 0.05) than all dual-option implant systems in the anterior flange transverse area. The narrow option was only selected in 12-20% of all cases.

CONCLUSIONS

The advanced single-option implant system improved the fit of the femoral component when compared with the old version and showed similar good-fit rates when compared with the dual-option implant systems. The narrow option of the dual-option implant systems was used less frequently than expected in Asian knees.

Which is better? Anterior or posterior referencing for femoral component position in total knee arthroplasty

When sizing the femoral component or determining its placement in total knee arthroplasty (TKA), if the anterior-posterior diameter of the femoral condyle is between component sizes, the selected size will differ depending on whether anterior referencing (AR) or posterior referencing (PR) is used. As a result, the amount of resected bone will also vary. In the present prospective study, we compared the two referencing methods to determine which is more suitable for individual patients. We recruited 58 patients (92 joints) who received TKA using the standard technique with intermediate-size components. AR was used in 26 joints, and PR in 23 joints. Seventeen of the patients underwent same-day bilateral TKA in which components of different sizes were used for the left and right joints. AR resulted in significantly smaller anterior and posterior offsets than PR. Preoperative clinical evaluation revealed no significant differences among cases in which intermediate-size components were indicated, or those in which components of different sizes were indicated. When an intermediate-sized component was indicated using the AR method, moving the sizer forward resulted in a larger posterior gap, but this technique was nevertheless considered acceptable. AR is likely to be more suitable than PR as it achieves more physiological anterior clearance.

Does increased femoral component size options reduce anterior femoral notching in total knee replacement?

OBJECTIVE

Total knee arthroplasty (TKA) is currently the best option for management of advanced knee arthritis for patients who have exhausted conservative management. There have been significant implant design improvements and this is a continuing process to help the surgeon replicate patient anatomy and kinematics. Amongst the many variables in implantation to achieve a well-functioning TKA, getting optimal femoral component sizing is one. Every implant system has certain discreet implant sizes and the surgeon has to strive to obtain the best fit possible for the patient and attain a well aligned and stable TKA. The aim of this study was to assess the frequency of various femoral component sizes being implanted with a system which has 2.5 mm antero-posterior increment between sizes, and to assess the incidence of anterior femoral notching when using a posterior referencing system.

MATERIALS AND METHODS

A retrospective analysis of 739 TKAs implanted in 532 patients between January 2013 and January 2016 at a single center using a single posterior stabilized implant system was done. Patient demographics and femur component size used was obtained from hospital patient records. Immediate post-operative radiographs were analyzed to look for anterior femoral notching and presence of this was classified according to Tayside classification. A telephonic follow up at minimum 2 tears post-surgery was done to interview for occurrence of supracondylar femur fracture or revision for any other causes.

RESULTS

There were 207 bilateral and 325 unilateral TKAs performed in 532 patients during the study period. There were 245 males and 287 females with an average age of 61.3 years (43-81 years, SD = 7.2). The most commonly used femoral component was 60 mm and an intermediate size prosthesis was used in 43.11% patients. The incidence of femoral notching ranged from 0 to 6.3%. No patient had sustained a supracondylar condylar fracture at minimum 2 years follow up.

CONCLUSION

The availability of a larger number of femoral components in a TKA system allows the surgeon the modularity to choose and obtain the best fit possible. Restoration of posterior condylar offset, preventing anterior notching, medio-lateral overhang and patellofemoral joint stuffing are greatly dependent on correct femoral component sizing. The findings from our study underscore the need to use an implant system with as many femoral size options as possible with lesser increments in between sizes to minimize anterior femoral notching when using a posterior referencing technique.

Morphometric Assessment of Resected Femoral Cut Surface in Korean Knees and Its Fitting With Western-Designed Femoral Components

BACKGROUND

This study aimed at assessing the morphometry of resected femurs in Korean patients during total knee arthroplasty (TKA) and comparing these measurements with current Western-designed femoral component dimensions.

METHODS

This single-blind, prospective, randomized, controlled trial involved intraoperative measurements for 271 femoral component implantations from 3 contemporary TKA systems, with 2 systems offering narrow sizing options. The difference between femoral component dimensions and the resected surface of distal femur was measured in millimeters at 5 distinct zones.

RESULTS

Overhang of standard femoral component was common in the anterior-medial condyle and anterior-lateral condyle ranging from 50.8% to 99.0% and 21.5% to 88.0%, respectively. With narrow femoral components, the rate of overhang reduced to 21.5%-30.2% and 9.2%-32.1%. Conversely, underhang rates were higher over the anterior flange width, middle medial-lateral and posterior medial-lateral zones. Standard components displayed higher underhang rates at these zones compared to narrow components. The good fit rate for femoral component was low among the 3 systems ranging from 1.0% to 56.0%. System with narrow option sizing increases the underhang rates in males, while improving the component fit among females at similar zones with rate ranging from 5.2% to 52.9%.

CONCLUSION

Currently available TKA implant designs may not provide a perfect match for the distal femoral shape of the Korean population. The availability of implants with standard and narrow options can substantially improve the optimal fitting of femoral components in the Korean population.

Effect of the Referencing System on the Posterior Condylar Offset and Anterior Flange-Bone Contact in Posterior Cruciate-Substituting Total Knee Arthroplasty

BACKGROUND

The effect of referencing system on posterior condylar offset (PCO) after total knee arthroplasty (TKA) is still controversial. Moreover, there is a lack of concern about the anterior flange-bone contact according to the referencing system.

METHODS

One hundred four TKAs using the anterior referencing (AR) system and 107 TKAs using the posterior referencing (PR) system were analyzed with 2-year follow-up. The PCO, PCO ratio (PCOR), and contact at the anterior flange-bone interface were compared between the 2 groups. The flexion and extension gaps and the degree of medial release were measured, and clinical outcomes were evaluated. Finally, the correlation between changes in PCO and knee flexion angle was analyzed.

RESULTS

The mean postoperative PCO and PCOR were significantly larger in the PR group than in the AR group. Incomplete contact between the anterior flange and anterior femur occurred more frequently in the AR group than in the PR group (48.1% vs 13.1%, P < .001). The medial and lateral flexion gaps were significantly larger in the AR group than in the PR group. The groups showed no differences in soft tissue release, degree of flexion, and clinical scores. In both groups, there was no correlation between postoperative change of PCO and improvement in flexion.

CONCLUSION

The PR system produced larger PCO and PCOR, and smaller flexion gap compared to the AR system. Additionally, the PR group showed more favorable contact between the anterior flange and anterior femur. However, these differences were not related to the degree of soft tissue release and clinical outcomes.

Comparison of patellofemoral outcomes after TKA using two prostheses with different patellofemoral design features

PURPOSE

The purpose of the present study was to compare the clinical and radiographic results after TKA using two prostheses with different sagittal patellofemoral design features, including outcomes related to compatibility of the patellofemoral joint.

METHODS

The clinical and radiographic results of 81 patients (100 knees) who underwent TKA using the specific prosthesis (group A) were compared with those in a control group who underwent TKA using the other prosthesis (group B). The presence of anterior knee joint pain, patellar crepitation, and patellar clunk syndrome was also checked.

RESULTS

The function score and maximum flexion angle at the last follow-up were slightly better in group A than those in group B (92.0 ± 2.3 vs. 90.6 ± 4.2) (133.6° ± 8.4° vs. 129.6° ± 11.4°). Anterior knee pain was observed in 6 knees and patellar crepitation in four knees in group A. In group B, these symptoms were observed in 22 knees and 18 knees, respectively. There was no patellar clunk syndrome in either group. The alignment was corrected with satisfactory positioning of components. The patellar height remained unchanged after TKA in the two groups. The differences between preoperative and postoperative patellar tilt angle and patellar translation were small.

CONCLUSION

When comparing the clinical and radiographic results after TKA using two prostheses with different sagittal patellofemoral design features, TKA using the specific prosthesis provided satisfactory results with less clinical symptoms related to the patellofemoral kinematics with TKA using the other prosthesis.

LEVEL OF EVIDENCE

III.

Mediolateral femoral component position in TKA significantly alters patella shift and femoral roll-back

PURPOSE

Increased retropatellar pressure and altered kinematics are associated with anterior knee pain and unsatisfied patients after total knee arthroplasty (TKA). Since malposition of the implant is believed to contribute to postoperative pain, we performed this in vitro study to evaluate the influence of mediolateral femoral component position on retropatellar pressure as well as tibio-femoral and patella kinematics.

METHODS

For the test, a fixed-bearing TKA was implanted in eight fresh frozen cadaver specimens. To determine the impact of mediolateral (ML) position, three variants of femoral components (3-mm medialization, neutral position and 3-mm lateralization) were produced using rapid prototyping replicas. In a knee rig, a loaded squat from 20° to 120° of flexion was applied. Retropatellar pressure distribution was measured with a pressure-sensitive film. Additionally, an ultrasonic-based three-dimensional motion analysis system was used to register patello- and tibio-femoral kinematics.

RESULTS

ML translation of the femoral component by 3 mm did not lead to a significant alteration in retropatellar peak pressure (medial 6.5 ± 2.5 MPa vs. lateral 6.0 ± 2.4 MPa). Following the ML translation of the femoral component, the patella was significantly shifted and tilted in the same directions. Varying the ML femoral component position also led to a significant alteration in femoral roll-back.

CONCLUSION

In day-by-day use, ML position should be chosen with care since there is a significant influence on patella shift and femoral roll-back. Retropatellar pressure is not significantly altered, so there is no clear evidence of an impact on anterior knee pain.

Anthropometric measurements of the femur change with component positioning in total knee arthroplasty

BACKGROUND

To analyze aspect ratio (AP size/ (ML) size) of osteoarthritic knees at four different areas of the femur and to observe if proximalization of the femoral cut would change the ML size as well as confirm that external rotation increases the measurements for the AP dimensions of the femur.

METHOD

From the available MyKnee database (Medacta International, Castel San Pietro, Switzerland) 1030 patients were randomly selected within 20° of deformity consisting of 400 men with a mean (SD) age of 67.5 (9) years and 630 women with a mean (SD) age of 69 (10) years (p<0.0001). A specific software program was developed to measure AP and ML dimensions of the femur on CT-scans for (3D) planning in four areas. The AP femoral size was measured with neutral axial rotation following the epicondylar axis and without accepting anterolateral notching.

RESULTS

Proximalization of the femur resulted in no changes except for a larger ML3 area in men. Increased axial rotation increased the AP dimensions for the same femur by a mean (SD) 2.5 (1) mm for males and females.

CONCLUSIONS

The crucial area for overhang of the femoral component is the anterior region (ML1) with an aspect ratio of about ±, but with an important range. Proximalization of the femoral cut is not accompanied by narrowing of the anterior femur but ML widening of the more posterior femur in men. Increased external rotation leads to a measurement of bigger AP size leading to an AP versus ML mismatch and change in aspect ratio.

Changes in femoral posterior condylar offset and knee flexion after PCL-substituting total knee arthroplasty: comparison of anterior and posterior referencing systems

PURPOSE

Anterior referencing and posterior referencing are two major techniques for positioning femoral components and balancing the sagittal plane during total knee arthroplasty (TKA). The purpose of this study was to evaluate the changes in medial and lateral posterior condylar offset (PCO) after bilateral TKA using anterior referencing (AR) or posterior referencing (PR) systems and compare the effect of the PCO changes on knee flexion.

METHODS

Twenty female patients (mean age, 68.6 years) underwent bilateral TKA using the AR technique in one knee and the PR technique in the contralateral knee. Three-dimensional reconstructed computed tomographic images from the sagittal plane were used to evaluate PCO before and after arthroplasty. Knee Society scores and range of motion were evaluated postoperatively at a mean of 2.9 years.

RESULTS

Postoperative medial and lateral PCOs were significantly greater (p < 0.001 and p = 0.048, respectively) in the AR group (30.9 ± 2.2 and 29.1 ± 1.5 mm, respectively) than those in the PR group (29.1 ± 2.7 and 27.3 ± 2.3 mm, respectively). In addition, the degree of change in the PCO after TKA was greater in the AR group than in the PR group. On the final follow-up, no differences in the degree of knee flexion were observed between the two groups (124.7° for AR and 124.5° for PR). Knee Society scores were similar in the two groups both preoperatively and postoperatively. On the final follow-up, individual changes in the medial and lateral PCO were not associated with changes in the knee flexion angle.

CONCLUSIONS

Restoration of PCO after TKA was more accurate with the PR technique than with the AR technique. However, the postoperative differences in PCO showed no correlation with changes in knee flexion 2 years after PCL-substituting TKA.

LEVEL OF EVIDENCE

Therapeutic study, Level I.

Posterior reference guides do not always maintain the size of posterior femoral condyles in TKA

PURPOSE

Posterior reference guides are provided by many manufacturers. However, the true posterior femoral condyle bone resection thicknesses using posterior reference guides are not stated by the manufacturers. The purpose of this study was to analyse the influence of the posterior reference guide designs on the posterior femoral condyle bone resection thickness.

METHODS

Thickness of posterior femoral condyle bone resection and thickness of prostheses were investigated in 8 types of total knee prostheses using the production drawings provided by the manufacturers.

RESULTS

Posterior femoral condyle bone resection thickness differed between prostheses. Change in size of the medial posterior condyle ranged from -0.5 to 1.4 mm at 0° external rotation, from -2.9 to 1.4 mm at 3° external rotation, and from -5.3 to 1.4 mm at 6° external rotation. Change in size of lateral posterior condyle ranged from -0.5 to 1.4 mm at 0° external rotation, from -0.4 to 3.4 mm at 3° external rotation, and from -0.4 to 5.3 mm at 6° external rotation.

CONCLUSIONS

This study showed that posterior femoral condyle bone resection thickness was different for each posterior reference guide. The rotation centre of posterior reference guides influenced the bone resection thickness in the posterior femoral condyle. The size of the posterior femoral condyles increased in some guides but decreased in other guides. The maximum differences in size changes of the posterior femoral condyles between the guides were 1.9 mm at 0° external rotation, 4.1 mm at 3° external rotation, and 6.3 mm at 6° external rotation. To control the size of posterior femoral condyles, the posterior reference guide design should be checked before use.