Effect of Manual versus Robotic-Assisted Total Knee Arthroplasty on Cervical Spine Static and Dynamic Postures.

This study compared surgeon cervical (C) spine postures and repetitive motions when performing traditional manual total knee arthroplasty (MTKA) versus robotic-assisted TKA (RATKA). Surgeons wore motion trackers on T3 vertebra and the occiput anatomical landmarks to obtain postural and repetitive motion data during MTKA and RATKA performed on cadavers. We assessed (1) flexion-extension at T3 and the occiput anatomical landmarks, (2) range of motion (ROM) as the percentage of time in the flexion-extension angle, (3) repetition rate, defined as the number of the times T3 and the occiput flexion-extension angle exceeded ±10°; and (4) static posture, where T3 or occiput postures exceed 10° for more than 30 seconds. The average T3 flexion-extension angle for MTKA cases was 5-degree larger than for RATKA cases (19 ± 8 vs. 14 ± 8 degrees). The surgeons who performed MTKA cases spent 15% more time in nonneutral C-spine ROM than those who performed RATKA cases (78 ± 25 vs. 63 ± 36%, p < 0.01). The repetition rate at T3 was 4% greater for MTKA than RATKA (14 ± 5 vs. 10 ± 6 reps/min). The percentage of time spent in static T3 posture was 5% greater for overall MTKA cases than for RATKA cases (15 ± 3 vs. 10 ± 3%). In this cadaveric study, we found differences in cervical and thoracic ergonomics between manual and robotic-assisted TKA. Specifically, we found that RATKA may reduce a surgeon's ergonomic strain at both the T3 and occiput locations by reducing the time the surgeon spends in a nonneutral position.

Micromotion Analysis of Various Tibial Constructs in Moderate Tibial Defects in Revision Total Knee Arthroplasty.

BACKGROUND: The purpose of this study is to compare the micromotion of various tibial reconstruction strategies including short cemented and long cementless stems with or without metaphyseal augmentation. METHODS: A moderate tibial bone defect was milled into dual density polyurethane test blocks. Mechanical testing was performed on 4 test constructs: (1) short cemented stem (75-mm total length) alone; (2) short cemented stem with a symmetric metaphyseal cone; (3) a press-fit (175-mm total length) diaphyseal engaging tibial construct without a cone, and (4) the same press-fit tibial construct with a metaphyseal cone augment. Micromotion of the baseplate/cone construct with respect to the tibia block was measured during a stair descent loading profile for 10,000 cycles. The peak-to-peak micromotion of these various tibial constructs was compared. Unpaired t-tests were used to evaluate differences in peak-to-peak micromotion among the various tibial constructs tested. An analysis of variance was performed for final validation. RESULTS: The cemented short stem demonstrated similar varus/valgus displacement, internal/external rotation, compression, and lift-off micromotion values under loading compared to a cementless long stem. A tibial cone improved compression and lift-off micromotion for both cemented and cementless constructs. A short 50-mm cemented stem with a cone demonstrated a lower micromotion at the anterior SI location compared to a press-fit 150-mm cementless stem without a tibial cone. CONCLUSIONS: A short cemented tibial component with a cone achieved similar micromotion during simulated stair descent compared to a cementless diaphyseal press-fit implant in cases of moderate tibial defects.

The Effect of Pelvic Tilt and Femoral Head Size on Hip Range-of-Motion to Impingement.

BACKGROUND: About 50%-70% of dislocators have cups placed within so-called "safe zones." It has been postulated that factors such as femoral head size and pelvic tilt, obliquity, or rotation may influence postoperative stability. Therefore, we assessed varying degrees of pelvic tilt and head sizes on the range of motion (ROM) to impingement. METHODS: A hip simulator was used to import models of 10 subjects who performed object pickup, squatting, and low-chair rising. Parameters were set for pelvic tilt, stem version, and the specific motions as defined by the subjects. Femur-to-pelvis relative motions were determined for abduction/adduction, internal/external rotation, and flexion/extension. Varying tilt angles were tested. Thirty-two millimeter and 36-mm head with a standard cup and 42-mm dual mobility cup were tested. Cup orientations for abduction and anteversion combinations were chosen, and computations of minimum clearances or impingement between components were made. RESULTS: The ROM to impingement varied with the different pelvic tilts and femoral head sizes and with the different motions. The larger the head size, the larger the impingement-free ROM. Negative 10° of pelvic tilt led to the largest impingement-free zone, whereas 10° of forward tilt was associated with fewer impingement-free cup anteversion and abduction angle combinations. Variations in pelvic tilt had the greatest influence on object pickup and affected the impingement-free "safe zone." CONCLUSION: Targets for impingement-free motion may be smaller when considering varying pelvic tilts and femoral head sizes, particularly for certain activities, such as object pickup. These findings may indicate the need for more individualized patient planning.

Development and Verification of Novel Porous Titanium Metaphyseal Cones for Revision Total Knee Arthroplasty.

BACKGROUND: Porous metaphyseal cones are widely used in revision knee arthroplasty. A new system of porous titanium metaphyseal cones has been designed based on the femoral and tibial morphology derived from a computed tomography-based anatomical database. The purpose of this study is to evaluate the initial mechanical stability of the new porous titanium revision cone system by measuring the micromotion under physiologic loading compared with a widely-used existing porous tantalum metaphyseal cone system. METHODS: The new cones were designed to precisely fit the femoral and tibial anatomy, and 3D printing technology was used to manufacture these porous titanium cones. The stability of the new titanium cones and the widely-used tantalum cones were compared under physiologic loading conditions in bench top test model. RESULTS: The stability of the new titanium cones was either equivalent or better than the tantalum cones. The new titanium femoral cone construct had significantly less micromotion compared with the traditional femoral cone construct in 5 of the 12 directions measured (P < .05), whereas no statistical difference was found in 7 directions. The new porous titanium metaphyseal tibial cones demonstrated less micromotion in medial varus/valgus (P = .004) and posterior compressive micromotion (P = .002) compared with the traditional porous tantalum system. CONCLUSION: The findings of this biomechanical study demonstrate satisfactory mechanical stability of an anatomical-based porous titanium metaphyseal cone system for femoral and tibial bone loss as measured by micromotion under physiologic loading. The new cone design, in combination with instrumentation that facilitates surgical efficiency, is encouraging. Long-term clinical follow-up is warranted.

Acetabular Cup Anteversion and Inclination in Hip Range of Motion to Impingement.

BACKGROUND: It is advocated that to avoid complications associated with femoral stem impingement, acetabular positioning should be within a "safe zone." However, instability remains prevalent despite accurate cup positioning, with studies showing dislocations of cups despite positioning within safe zones. We assessed cup position angles associated with impingement in a group of subjects during (1) squatting; (2) object pick-up; and (3) low chair rise. METHODS: Ten subjects (mean age, 69 years; body mass index, 28.4 kg/m(2)) performed object pick up, squatting, and low-chair rising. Femur-to-pelvis relative motions were recorded for flexion/extension, abduction/adduction, and internal/external rotation. A previously reported custom-validated hip range-of-motion 3-dimensional simulator was used, set for neutral pelvic tilt and 15(°) of stem version. Acetabular cup abduction and anteversion combinations were chosen. The software computed minimum clearances between components for any hip position. An idealized tapered wedge stem with a 132° neck angle and a 36-mm femoral head was used. RESULTS: Eight subjects had impingement on squatting between 21(°) and 51(°) of inclination. During object pick-up, 9 subjects had impingement with inclination and anteversion angles within the "safe zone." In low-chair rise, 8 subjects had impingement at cup inclination angles between 14.5(°) and 49.5(°). CONCLUSION: The true acetabular target for impingement-avoidance motion is much smaller than previously believed and varies considerably between patients. Certain activities, such as picking up an object, low-chair rise, and squatting reduce the size of the safe zone. This study supports the need for better individualized preoperative patient-specific planning and intraoperative execution for placement of the components.