Christopher Plaskos

Sequential versus automated cutting guides in computer-assisted total knee arthroplasty

The accuracy and efficiency of automated cutting guides in CAS systems have not been previously compared with conventional CAS techniques. Therefore, it is not yet clear if these more advanced technologies are warranted. We hypothesized that a novel automated cutting guide with CAS for total knee arthroplasty would be more efficient and more accurate than conventional navigation with sequential cutting blocks. Twelve cadaver legs were used in total. Each leg was randomly assigned to either an automated guide positioning or a conventional freehand computer-navigated guide positioning. The guide positions postosseous fixation and the final bone-cut surfaces were digitized and compared to the targeted cutting planes. The final location of the impacted trial implant was also digitized and compared to the planned implant location. The time for each step and the total time taken to prepare the femur were measured for both groups. The mean femoral preparation time was shorter with the automated cutting guide than the conventional method (5.5 min versus 13.8 min, p<0.001). The average deviation in the final bone resections from the planned resections was significantly lower for the automated cutting guide in the frontal/rotational plane (0.55° versus 1.1°), sagittal plane (0.75° versus 2.0°), and cut height direction (0.56 mm versus 1.6 mm). Therefore, based on these results, we concluded that automated cutting-guide positioning resulted in more efficient and more accurate femoral cuts in comparison to the conventional navigation method in a cadaveric model.

Recutting the distal femur to increase maximal knee extension during TKA causes coronal plane laxity in mid-flexion

BACKGROUND The aim of this study was to quantify the effects of distal femoral cut height on maximal knee extension and coronal plane knee laxity. METHODS Seven fresh-frozen cadaver legs from hip-to-toe underwent a posterior stabilized TKA using a measured resection technique with a computer navigation system equipped with a robotic cutting guide. After the initial femoral resections were performed, the posterior joint capsule was sutured until a 10° flexion contracture was obtained with the trial components in place. Two distal femoral recuts of +2mm each were then subsequently made and the trials were reinserted. The navigation system was used to measure the maximum extension angle achieved and overall coronal plane laxity [in degrees] at maximum extension, 30°, 60° and 90° of flexion, when applying a standardized varus/valgus load of 9.8 [Nm] across the knee. RESULTS For a 10 degree flexion contracture, performing the first distal recut of +2mm increased overall coronal plane laxity by approximately 4.0° at 30° of flexion (p=0.002) and 1.9° at 60° of flexion (p=0.126). Performing the second +2mm recut of the distal femur increased mid-flexion laxity by 6.4° (p<0.0001) at 30° and 4.0° at 60° of flexion (p=0.01), compared to the 9 mm baseline resection (control). Maximum knee extension increased from 10° of flexion to 6.4° (± 2.5° SD, p<0.005) and to 1.4° (± 1.8° SD, p<0.001) of flexion with each 2mm recut of the distal femur. CONCLUSIONS Recutting the distal femur not only increases the maximum knee extension achieved but also increases coronal plane laxity in midflexion.

Adjustable Cutting Blocks for Computer-Navigated Total Knee Arthroplasty: A Cadaver Study

Computer-navigation in total knee arthroplasty has been reported to increase accuracy but also procedure duration. We compared surgical time and precision using a novel adjustable cutting block vs freehand navigation with conventional blocks on 12 bilateral cadaver tibiae. The mean time required was significantly less to position the adjustable block than the conventional block (2 minutes 10 seconds vs 6 minutes 35 seconds, P = .006). Guide positioning precision (standard deviation) for the adjustable block vs conventional block was as follows: varus/valgus, 0.24 degrees vs 1.16 degrees (P = .015); posterior slope, 0.35 degrees vs 0.74 degrees (P = .13); and cut height, 0.37 vs 1.41 mm (P = .010). There were no significant differences in the final bone cut accuracy between the 2 groups. The use of adjustable cutting blocks simplifies navigated procedures and may reduce the time required to perform a navigated total knee arthroplasty.

Software for compartmental translation analysis and virtual three-dimensional visualization of the pivot shift phenomenon.

Anterior cruciate ligament (ACL) injury may cause knee instability and may result in damage to the menisci and the articular cartilage. The pivot shift test is commonly used to identify rotational instability of the knee following injury to the ACL. The magnitude of lateral compartment translation correlates well with the grade of the pivot shift. However, commonly used navigation systems do not readily provide individualized compartmental translation. We aimed to develop software to (a) quantify individual medial and lateral compartmental translation in the knee during the pivot shift test, and (b) generate animated three-dimensional renderings of recorded pivot shift examinations. Twelve paired cadaveric knees were used to test the software. Three mechanized pivot shift tests were performed on each knee with the ACL intact and again after sectioning the ACL. Using the Pivot Shift Processor, we successfully analyzed the data recorded using the navigation system. After sectioning the ACL, there was a greater increase in tibiofemoral translation in the lateral compartment compared to the medial compartment. The Pivot Shift Visualizer successfully produced a 3D rendering of the knee joint and the recorded pivot shift maneuvers. This virtual representation of the pivot shift phenomenon from multiple points of view allows for efficient side-by-side comparison of tibiofemoral motion tracking across conditions, which is not possible in the in vivo / in vitro settings. This, in turn, could lead to a better understanding of the kinematics in play during the pivot shift phenomenon.

The effect of medial condylar bone loss of the knee on coronal plane stability—A cadaveric study

INTRODUCTION The quantitative effects of medial bone loss of the knee on both leg alignment and coronal plane stability are poorly understood. MATERIALS AND METHODS Utilizing computer navigation, 5mm bone defects of the medial distal femur (MDF), medial posterior femoral condyle (MPF), and medial tibial plateau (MT) were simulated in 10 cadaveric limbs, and alignment of the knee at various degrees of flexion were analyzed when applying standardized varus and valgus loads. RESULTS The 5mm MPF defect significantly increased varus laxity at 90° of flexion by 3.3° ± 1.2° (p=0.019), a 5mm MDF defect resulted in a 2.2° ± 1.7° (p=0.037) and a 2.1° ± 1.3° (p=0.023) increase in laxity at 0° and 30° of flexion, respectively, and a 5mm MT defect increased varus laxity at all flexion angles by 4.0° to 7.0°, but was only statistically significant at 30° (p=0.026). DISCUSSION This study confirms and quantifies the theories of flexion and extension gap balancing, and pseudolaxity of the medial collateral ligament in the varus knee, the results of which can be used in preoperative planning and intraoperative decision making for both total knee and unicondylar arthroplasty.

A navigated 8-in-1 femoral cutting guide for total knee arthroplasty technical development and cadaveric evaluation.

The goals of this study were to determine the precision of femoral component placement using a novel computes assisted surgery (CAS)-enabled 8-in-1 cutting guide in cadaver limbs and to identify errors generated at various stages of the cutting process. The cutting guide placement was on average within 1 degrees or millimeter of the target position in the varus/valgus, axial rotation, and cut height directions and within 2 degrees or millimeters, in all other directions. The difference between the desired femoral component and the impacted trial component position, defined as the execution error, averaged 0.9 degrees +/- 1.7 degrees of varus rotation, 0.8 +/- 2.3 mm of lateral translation, and 0.3 +/- 1 mm of proximal translation in the coronal plane (+/-SD). In the sagittal and axial planes, the execution error averaged 2.8 degrees +/- 2.5 degrees of flexion, 3.4 +/- 1.3 mm of anterior translation, and 0.7 degrees +/- 2.7 degrees of external rotation. CAS permits accurate placement of 8-in-1 jigs for valgus/varus, axial rotation, and cut height but is less accurate in the sagittal plane. Care should be taken when executing the cuts, which can affect precision in the sagittal plane more than actual positioning of the jig.

Laxity Profiles in the Native and Replaced Knee—Application to Robotic-Assisted Gap-Balancing Total Knee Arthroplasty

BACKGROUND The traditional goal of the gap-balancing method in total knee arthroplasty is to create equal and symmetric knee laxity throughout the arc of flexion. The purpose of this study was to (1) quantify the laxity in the native and the replaced knee throughout the range of flexion in gap-balancing total knee arthroplasty (TKA) and (2) quantify the precision in achieving a targeted gap profile throughout flexion using a robotic-assisted technique with active ligament tensioning. METHODS Robotic-assisted, gap-balancing TKA was performed in 14 cadaver specimens. The proximal tibia was resected, and the native tibiofemoral gaps were measured using a robotic tensioner that dynamically tensioned the soft-tissue envelope throughout the arc of flexion. The femoral implant was then aligned to balance the gaps at 0° and 90° of flexion. The postoperative gaps were then measured during final trialing with the robotic tensioner and compared with the planned gaps. RESULTS The native gaps increased by 3.4 ± 1.7 mm medially and 3.7 ± 2.1 mm laterally from full extension to 20° of flexion (P < .001) and then remained consistent through the remaining arc of flexion. Gap balancing after TKA produced equal gaps at 0° and 90° of flexion, but the gap laxity in midflexion was 2-4 mm greater than at 0° and 90° (P < .001). The root mean square error between the planned gaps and actual measured postoperative gaps was 1.6 mm medially and 1.7 mm laterally throughout the range of motion. CONCLUSION Aiming for equal gaps at 0° and 90° of flexion produced equal gaps in extension and flexion with larger gaps in midflexion. Consistent soft-tissue balance to a planned gap profile could be achieved by using controlled ligament tensioning in robotic-assisted TKA.