Young Wan Moon

Bony Landmarks for Determining the Mechanical Axis of the Femur in the Sagittal Plane during Total Knee Arthroplasty

Background There is no accepted landmark for the mechanical axis of the femoral axis in sagittal plane in conventional total knee arthroplasty. Methods As palpable anatomic landmarks of the femur, lateral epicondyle, and anterior margin of the greater trochanter were identified. The line connecting these two landmarks was defined as the palpable sagittal axis. The mechanical axis of the femur was compared with the palpable sagittal axis and the distal femoral anterior cortex axis. These axes were also compared with sagittal bowing of the femur. Results The distal femoral anterior cortex axis and the palpable sagittal axis were flexed by 4.1° and 2.4° more than the sagittal mechanical axes, respectively (p < 0.05). However, the palpable sagittal axis was not correlated with sagittal bowing of the femur (Spearmans rs, 0.17; p = 0.14). Conclusions The palpable sagittal axis showed a consistent relationship with the sagittal mechanical femoral axes regardless of the severity of the sagittal bowing of the femur.

Comparison of robot-assisted and conventional total knee arthroplasty: A controlled cadaver study using multiparameter quantitative three-dimensional CT assessment of alignment

Introduction: A functional total knee replacement has to be well aligned, which implies that it should lie along the mechanical axis and in the correct axial and rotational planes. Incorrect alignment will lead to abnormal wear, early mechanical loosening, and patellofemoral problems. There has been increased interest of late in total knee arthroplasty with robotic assistance. This study was conducted to determine whether robot-assisted total knee arthroplasty is superior to the conventional surgical method with regard to the precision of implant positioning. Materials and Methods: Twenty knee replacements, comprising ten robot-assisted procedures and ten conventional operations, were performed on ten cadavers. Two experienced surgeons performed the surgeries. Both procedures on each cadaver were performed by the same surgeon. The choice of which procedure was to be performed first was randomized. Following implantation of the prosthesis, the mechanical axis deviation, femoral coronal angle, tibial coronal angle, femoral sagittal angle, tibial sagittal angle, and femoral rotational alignment were measured via 3D CT scanning. These variables were then compared with the preoperatively planned values. Results: In the knees that underwent robot-assisted surgery, the mechanical axis deviation ranged from −1.94° to 2.13° (mean: −0.21°), the femoral coronal angle from 88.08° to 90.99° (mean: 89.81°), the tibial coronal angle from 89.01° to 92.36° (mean: 90.42°), the tibial sagittal angle from 81.72° to 86.24° (mean: 83.20°), and the femoral rotational alignment from 0.02° to 1.15° (mean: 0.52°) in relation to the transepicondylar axis. In the knees that underwent conventional surgery, the mechanical axis deviation ranged from −3.19° to 3.84° (mean: −0.48°), the femoral coronal angle from 88.36° to 92.29° (mean: 90.50°), the tibial coronal angle from 88.15° to 91.51° (mean: 89.83°), the tibial sagittal angle from 80.06° to 87.34° (mean: 84.50°), and the femoral rotational alignment from 0.32° to 4.13° (mean: 2.76°) in relation to the transepicondylar axis. In the conventional knee replacement group, there were two instances of outliers outside the range of 3° varus/valgus for the mechanical axis deviation. The robot-assisted knee replacements showed significantly superior femoral rotational alignment results compared with conventional surgery (pu2009=u20090.006). There was no statistically significant difference between robot-assisted and conventional total knee arthroplasty with regard to the other variables. All the measurements showed high intra-observer and inter-observer reliability. Conclusion: Robot-assisted total knee arthroplasty showed excellent precision in the sagittal and coronal planes of the 3D CT scan. In particular, the robot-assisted technique showed better accuracy in femoral rotational alignment compared to the conventional surgery, despite the fact that the surgeons who performed the operations were more experienced and familiar with the conventional method than with robot-assisted surgery. It can thus be concluded that robot-assisted total knee arthroplasty is superior to conventional total knee arthroplasty.

Are Navigation Systems Accurate Enough to Predict the Correction Angle During High Tibial Osteotomy? Comparison of Navigation Systems With 3-Dimensional Computed Tomography and Standing Radiographs

Background: Unpredicted overcorrection of the mechanical axis can occur during navigation-assisted high tibial osteotomy (HTO). It is not clear whether the erroneous overcorrection stems from the navigation system itself or from other causes. Purpose: To evaluate the accuracy of the navigation system in HTO by comparing the change in the femorotibial angle provided by the navigation system with the bony correction angle of the proximal tibia on 3-dimensional computed tomography (3D CT) and with the change in mechanical femorotibial alignment on standing whole-leg radiographs. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: A total of 16 knees underwent navigation-assisted HTO, and their alignment data were obtained before and after correction. For comparison, preoperative and follow-up standing whole-leg anteroposterior radiographs, lateral knee radiographs, and preoperative and postoperative 3D CT scans were taken. The medial proximal tibial angle (MPTA), posterior tibial slope, and mechanical femorotibial angle (mFTA) were measured in these images, and the 3 coronal and 3 sagittal correction angles were compared with each other. Results: In the coronal plane, the mean correction angle of the navigation system was 9.3° ± 2.0° valgus (range, 6°-13°), and the mean MPTA on 3D CT increased 9.7° ± 2.0° (range, 6.7°-13.8°) after correction. The mean correction angle of the mFTA on standing radiographs was 11.9° ± 3.2° valgus (range, 6.9°-16.5°). There was no statistical significance between the navigation system and 3D CT (P = .187), but there was a statistically significant difference between the navigation system and standing radiographs (P = .001). The results of the correction angle in the sagittal plane were similar to those in the coronal plane. Conclusion: The correction of the femorotibial angle by the navigation system was not different from the bony correction angle on 3D CT. There was a discrepancy between the correction angle of the navigation system and that of the standing radiograph. Clinical Significance: Surgeons must be cautious about the tension of soft tissue, even when using the navigation system during HTO.

Robot-assisted Implantation Improves the Precision of Component Position in Minimally Invasive TKA

Minimally invasive and robot-assisted procedures have potential advantages when used for total knee arthroplasty (TKA). The purpose of this cadaveric study was to examine whether robot-assisted minimally invasive procedures improve TKA alignment after modifying the robotic techniques and instruments. Total knee arthroplasties were performed on 10 pairs of fresh cadaveric femora. Ten knees were replaced using the robot-assisted minimally invasive technique and 10 using the conventional minimally invasive technique. After prosthesis implantation, limb and prosthesis alignments were investigated by measuring mechanical axis deviation, femoral and tibial sagittal and coronal inclination, and femoral rotational alignment with 3-dimensional computed tomography scans. Postoperative alignment accuracy of the implanted prostheses was better in the robot-assisted minimally invasive TKA group than in the conventional minimally invasive TKA group as judged by the rotational alignment of the femoral component (0.7°±″.3° vs 3.6°±2.2°, respectively) and the tibial component sagittal angle (7.8°±1.1° vs 5.5°±3.6°, respectively). One sagittal inclination outlier for the tibial side existed in the robotic minimally invasive TKA group, and 2 outliers for the mechanical axis, 2 for the tibial side sagittal inclination, and 2 for the femoral rotational alignment existed in the conventional minimally invasive TKA group. Higher implanted prostheses accuracy and fewer outliers in postoperative radiographic alignments can be attained with robot-assisted TKA. Minimally invasive TKA in combination with an improved robot-assisted technique is an alternative option to compensate for the shortcomings of conventional minimally invasive TKA.

Factors Correlated with the Reducibility of Varus Deformity in Knee Osteoarthritis: An Analysis Using Navigation Guided TKA

Background We hypothesized that a number of clinical and radiologic parameters could influence the reducibility of varus deformity in total knee arthroplasty. The aim of this study was to identify the factors correlated with reducibility of varus deformity and predict more accurately the amount of medial soft tissue release required in varus deformity total knee arthroplasty. Methods One hundred forty-three knees with preoperative varus alignment and medial osteoarthritis were included in this retrospective study. The total knee arthroplasties were performed using a navigation system (OrthoPilot) by single surgeon. To assess varus deformity, the authors measured preoperative mechanical axis angles and valgus stress angles. Mechanical tibial angles, mechanical femoral angles, femoral osteophyte sizes, and tibial osteophyte sizes were measured. The Ahlbäck grading scale was applied for radiologic parameters, and clinical parameters (age, body mass index, sex, duration of pain, and preoperative range of motion) were documented. Correlations between these factors and preoperative valgus stress angle were analyzed. Results A negative correlation was found between preoperative mechanical axis angle and preoperative valgus stress angle (p < 0.01, r = -0.38), and a positive correlation was found between the preoperative mechanical tibial angle and preoperative valgus stress angle (p = 0.01, r = 0.19). Conclusions The present study shows that preoperative varus deformity and proximal tibial vara (measured by preoperative mechanical axis angle and mechanical tibial angle, respectively) are correlated with reducibility of varus deformity (measured by preoperative valgus stress angle), and clinical parameters (age, range of motion, duration of pain and body mass index) and other radiologic parameters (osteophyte size, severity of osteoarthritis and angulation of distal femoral joint surface) were not significantly correlated with reducibility of varus deformity.

Analysis of medial flexion gap after medial release for varus deformity by navigation-guided TKA.

The goal of this study was to analyze medial flexion gaps after medial release for varus deformity by navigation-guided total knee arthroplasty (TKA). In each patient, a preoperative standing anteroposterior (AP) radiograph of the lower extremity and an AP valgus stress radiograph of the knee were used to measure preoperative mechanical axis angle and valgus stress angle, respectively. The correlation between preoperative varus deformities and medial flexion gap increases as measured by navigation was examined. Patients were assigned to 2 groups: group A (25 knees), in which the difference between the lateral flexion gap (LFG) and the medial flexion gap (MFG) (LFG-MFG) was ≤ 1 mm; and group B (73 knees), with an LFG-MFG of >1 mm.Mean preoperative mechanical axis angles in groups A and B were 13.21° ± 5.01° varus (range, 3.7°-23.6°) and 10.05° ± 3.70° varus (range, 1.9° - 23.7°), respectively. Mean preoperative valgus stress angles in groups A and B were 1.72° ± 0.89° valgus (range, 0.1° - 4.0°) and 4.84° ± 2.61° valgus (range, 0.1° - 11.7°), respectively. A significant difference was observed between the groups in terms of mechanical axis angle (P = .002) and valgus stress angle (P<.001). Furthermore, valgus stress angle was found to be more strongly correlated with medial flexion gap increase than mechanical axis angle. The cutoff values of mechanical axis angle and valgus stress angle in group A were 13.4° and 2.45°, respectively.This study shows that preoperative valgus stress angle measurements can be used to predict the extent of medial release for varus deformity.

Determination of an Applicable FRAX Model in Korean Women

We investigated which of the three FRAX fracture risk assessment tool models is most applicable to Korean women. For 306 postmenopausal women (mean age, 77 yr) with a hip fracture, fracture probabilities were calculated using FRAX models from Japan, Turkey and China. Data on bone mineral density (BMD) at the femoral neck were available for 103 patients. Significant differences existed among the models, independent of the inclusion of BMD in the calculation of fracture probabilities. The probabilities of both major osteoporotic fractures and hip fractures were significantly higher in the Japanese model than in the Turkish or Chinese models. In all of the models, the probabilities of a major osteoporotic fracture, but not of a hip fracture, decreased significantly if calculated without BMD values. By applying the Japanese model, the ten-year probabilities for major osteoporotic and hip fractures increased significantly with age. Our results suggest that the Japanese FRAX model might be the most appropriate for Korean women.

Is Total Knee Arthroplasty a Viable Treatment Option in Octogenarians with Advanced Osteoarthritis

Purpose This study directly compared clinical assessment scores and short-term systemic complications after total knee arthroplasty (TKA) between a group of patients aged 80 or older (141 patients) and another group of patients aged between 65 and 70 years (616 patients) with advanced osteoarthritis. Materials and Methods We retrospectively investigated 757 osteoarthritic patients who underwent primary TKA from January 2007 to January 2011 with a follow-up of 1 year. The surgery was performed using an extramedullary alignment guide instrument without invasion of the intramedullary canal to decrease embolic load and blood loss. Results At 1 year after surgery, the mean Knee Society knee score was improved in both groups (from 63.6 to 83.2 in octogenarians and from 68.3 to 89.0 in the younger group) and the level of satisfaction was excellent in both groups (8 in octogenarians and 8.3 in the younger group), even though there was no notable change in function score in the octogenarians (from 61.0 to 61.9 in the octogenarians and from 62.3 to 73.6 in the younger group). The total incidence of systemic complications (3.4% vs. 1.2%, p=0.400) and surgical complications (2.1% vs. 0.5%, p=0.229) showed no significant difference between groups. Conclusions TKA yielded favorable clinical outcomes with a comparatively low postoperative complication rate in octogenarians despite the negligible functional improvement.

Serial Changes of Quadriceps and Hamstring Muscle Strength Following Total Knee Arthroplasty: A Meta-Analysis

This meta-analysis was performed to analyze serial changes in thigh muscles, including quadriceps and hamstring muscles, from before to one year after total knee arthroplasty (TKA). All studies sequentially comparing isokinetic quadriceps and hamstring muscle strengths between the TKA side and the contralateral uninjured limb were included in this meta-analysis. Five studies with 7 cohorts were included in this meta-analysis. The mean differences in the strengths of quadriceps and hamstring muscles between the TKA and uninjured sides were greatest three months after surgery (26.8 N∙m, 12.8 N∙m, P<0.001), but were similar to preoperative level at six months (18.4 N∙m, 7.4 N∙m P<0.001) and were maintained for up to one year (15.9 N∙m, 4.1 N∙m P<0.001). The pooled mean differences in changes in quadriceps and hamstring strengths relative to preoperative levels were 9.2 N∙m and 4.9 N∙m, respectively, three months postoperatively (P = 0.041), but were no longer significant after six months and one year. During the year after TKA, quadriceps and hamstring muscle strengths were lowest after 3 months, recovering to preoperative level after six months, but not reaching the muscle strength on the contralateral side. Relative to preoperative levels, the difference in muscle strength between the TKA and contralateral knees was only significant at three months. Because decrease of strength of the quadriceps was significantly greater than decrease in hamstring muscle strength at postoperative three months, early rehabilitation after TKA should focus on recovery of quadriceps muscle strength.

Comparison of soft tissue balancing, femoral component rotation, and joint line change between the gap balancing and measured resection techniques in primary total knee arthroplasty A meta-analysis

Background:This meta-analysis was designed to compare the accuracy of soft tissue balancing and femoral component rotation as well as change in joint line positions, between the measured resection and gap balancing techniques in primary total knee arthroplasty. Methods:Studies were included in the meta-analysis if they compared soft tissue balancing and/or radiologic outcomes in patients who underwent total knee arthroplasty with the gap balancing and measured resection techniques. Comparisons included differences in flexion/extension, medial/lateral flexion, and medial/lateral extension gaps (LEGs), femoral component rotation, and change in joint line positions. Finally, 8 studies identified via electronic (MEDLINE, EMBASE, and the Cochrane Library) and manual searches were included. All 8 studies showed a low risk of selection bias and provided detailed demographic data. There was some inherent heterogeneity due to uncontrolled bias, because all included studies were observational comparison studies. Results:The pooled mean difference in gap differences between the gap balancing and measured resection techniques did not differ significantly (−0.09u200amm, 95% confidence interval [CI]: −0.40 to +0.21u200amm; P = 0.55), except that the medial/LEG difference was 0.58u200amm greater for measured resection than gap balancing (95% CI: −1.01 to −0.15u200amm; P = 0.008). Conversely, the pooled mean difference in femoral component external rotation (0.77°, 95% CI: 0.18° to 1.35°; P = 0.01) and joint line change (1.17u200amm, 95% CI: 0.82 to 1.52u200amm; Pu200a<u200a0.001) were significantly greater for the gap balancing than the measured resection technique. Conclusion:The gap balancing and measured resection techniques showed similar soft tissue balancing, except for medial/LEG difference. However, the femoral component was more externally rotated and the joint line was more elevated with gap balancing than measured resection. These differences were minimal (around 1u200amm or 1°) and therefore may have little effect on the biomechanics of the knee joint. This suggests that the gap balancing and measured resection techniques are not mutually exclusive.