Pre-milling technique improves the accuracy of posterior femoral condyle cut and reduces the tibial recut in Oxford unicompartmental knee arthroplasty.

BACKGROUND: Recuts are sometimes needed in UKA because of inadequate posterior tibial cut thickness. We investigated the efficacy of a pre-milling technique (the first milling is done prior to the posterior condylar cut) in Oxford unicompartmental knee arthroplasty to enhance bone cut thickness and to minimize tibial recuts. PATIENTS AND METHODS: Between January 2021 and January 2023, a posterior condyle cut was made before milling in 213 knees in 152 patients (conventional group), while the pre-milling technique was used in 198 knees in 140 patients (pre-milling group). The thickness of the posterior condyle and the rate of tibial recuts were compared between the groups. RESULTS: The bone cut thickness was thinner in the conventional group than in the pre-milling group in small-size (4.7 mm ± 0.6 mm and 5.0 mm ± 0.6 mm, P = 0.0001) and in medium-size (5.1 mm ± 0.5 mm and 5.4 mm ± 0.5 mm, 0.0001) femoral components, whereas there was no difference in large-size femoral components. However, the thickness was still less than the component thickness (5.17 mm for small, 5.57 mm for medium and 6.17 mm for large) in both groups. Tibial recuts were more prevalent in the conventional group than in the pre-milling group (14 knees, 7%, 3 knees 2%, P = 0.002). CONCLUSIONS: The pre-milling technique was found to increase the bone cut thickness in small and medium femoral components, reducing the need for tibial recuts. Further research is warranted to optimize the pre-milling technique and to investigate its long-term impact on patient outcomes.

Propensity of the tight mid-flexion and loose flexion gap despite the adjustment of extension and flexion gaps in Oxford unicompartmental knee arthroplasty: retrospective study.

PURPOSE: A well-balanced joint gap is necessary in Oxford unicompartmental knee arthroplasty (OUKA) to prevent mobile-bearing dislocation. While the gaps between 20° (extension) and 100° (flexion) are precisely adjusted using the incremental mill system, there has been insufficient evaluation of gaps in other angles. We hypothesized that the gap is not always the same in other angles. This retrospective study aimed to evaluate the gap in full-extension (0°), mid-flexion (60°) and deep flexion (130°) for comparison with those in extension and flexion gaps. METHODS: We evaluated 119 knees in 83 patients (51 females, 31 males, aged 71.9 years). The full-extension and mid-flexion gaps were compared with the extension gap, and the deep flexion gap was contrasted with the flexion gap. Each gap was classified into isometric, tight or loose, for evaluation of contributing factors. RESULTS: Although the full-extension gap tended to be isometric (45%), the mid-flexion tended to be tight (48%), whereas the deep-flexion was loose in most knees (84%) (P = 0.002). The tight mid-flexion and loose deep flexion gap pattern accounted for 44% of the total knees, especially so with smaller femoral components (P = 0.004). CONCLUSION: Our results highlight the propensity of tight mid-flexion and loose flexion gap despite the adjustment of extension and flexion gaps in OUKA. Although the effect of such a minor gap imbalance is still unknown, the pattern was more prevalent in patients with smaller-sized femoral components. Use of a larger femoral component may equalize the gap throughout the motion arc.

Preoperative Arithmetic Hip-Knee-Ankle Angle as a Predictor of Postoperative Leg Alignment in Medial Oxford Unicompartmental Knee Arthroplasty.

Introduction This study aimed to evaluate whether the arithmetic hip-knee-ankle angle (aHKA) can be used to predict the postoperative HKA. Methods This study included 248 knees in 166 patients who underwent Oxford unicompartmental knee arthroplasty (UKA) between February 2021 and November 2022. Through preoperative and postoperative long-leg radiography, the medial proximal tibial angle (MPTA) and the lateral distal femoral angle (LDFA) were expressed as the deviation from the perpendicular line to the mechanical axes, and the mechanical HKA (mHKA) was defined as the angle between the femoral and tibial mechanical axes. Using the MPTA and LDFA, the arithmetic HKA (aHKA; MPTA + LDFA) and the joint line obliquity (JLO; MPTA - LDFA) were calculated, and the preoperative and postoperative values were compared. Results The preoperative aHKA and the postoperative mHKA values were similar (-0.38° ± 2.96°) and significantly smaller than the difference between the preoperative and postoperative mHKAs (4.58° ± 3.60°, P < 0.05). Meanwhile, the MPTA tended to be varus, and the LDFA tended to be valgus. Eventually, the JLO inclined more medially from -6.33° ± 3.42° preoperatively to -8.97° ± 3.92° postoperatively, representing a significant difference (P < 0.05). Conclusion The preoperative aHKA was similar to the postoperative mHKA. Therefore, it can be regarded as a predictor of postoperative leg alignment after Oxford UKA. Meanwhile, there was a medial incline of the joint line. Further investigation is required to evaluate the effect of such a joint line alteration.

Tibial Lateral Condyle Fracture After Cementless Oxford Unicompartmental Knee Arthroplasty (UKA): A Report of Four Cases.

Cementless unicompartmental knee arthroplasty (UKA) has a lower rate of radiolucency in postoperative follow-up than cemented UKA. However, the rate of tibial plateau fracture, one of the complications, has been reported to be higher in cementless UKA than in cemented UKA. We report four cases of postoperative tibial lateral condyle fractures after cementless Oxford UKA. Four patients underwent cementless Oxford UKA. Immediate postoperative radiography and CT showed no fracture lines. At five to six weeks postoperatively, MRI showed a fracture line from the intersection of the longitudinal and transverse tibial osteotomies through the lateral pinhole to the end of the lateral tibial diaphysis. At three months, bone union was observed without surgical treatments. Lateral tibial fracture after cementless Oxford UKA has a good clinical course without the need for surgical intervention. Medial fractures should thus be more actively prevented. MRI is useful for less symptomatic tibial lateral condyle fractures.

Caliper-Based Restricted Kinematic Alignment Total Knee Arthroplasty.

Restricted kinematic alignment total knee arthroplasty (rKA-TKA) is a reasonable selection for avoiding an extreme alignment that has been conceded to induce implant failure. However, computer-aided devices (CAS), such as navigation, robotics, and patient-specific instrumentation, are necessary to perform rKA-TKA. This paper reports on the surgical technique of kinematic alignment total knee arthroplasty (KA-TKA) using mechanical instruments. The lateral distal femoral angle (LDFA) and the medial proximal tibial angle (MPTA) are measured from preoperative long radiographs or CT of the lower limb, and the arithmetic hip-knee-ankle angle (aHKA) is calculated from the MPTA - LDFA. The predefined restriction boundaries are used to determine the osteotomy angle. In our practice, the LDFA is 85° to 93°, the MPTA is 85° to 90°, and the aHKA is 5° varus to 3° valgus. If correction of the femoral osteotomy is required, this can be achieved by changing the thickness of the paddle set on the distal articular surface or by adjusting the angle of the variable angle femoral cutting guide. For the tibia, the distal end of the extramedullary rod, with the proximal part placed in the center of the knee joint, should be adjusted so that it does not exceed the lateral malleolus. This limits the medial tilt of the osteotomy plane to within 5.5°. These techniques allow restricted KA to be performed with existing mechanical instruments without using CAS.

Synthesis and biological activity of photostable and persistent abscisic acid analogs.

The plant hormone abscisic acid (ABA) plays a critical role in various environmental stress responses and has long been expected to be used in agriculture. However, the practical use of ABA has been limited, mainly because of its photoinstability and rapid biodegradation. We previously developed photostable ABA agonists, BP2A and Me 1',4'-trans-diol BP2A, in which the dienoic acid side chain of ABA was replaced with phenylacetic acid. This finding validated our structure-based approach in designing photostable agonists and provided a basis for developing a more potent or long-lasting ABA agonist. In this study, we synthesized novel BP2A analogs in which the cyclohexenone ring was modified to avoid catabolism by the ABA metabolic enzyme, ABA 8'-hydroxylase. All synthesized analogs showed higher photostability than BP2A under sunlight. In an Arabidopsis seed germination assay, (+)-compounds 5 and 6 with a tetralone ring displayed significantly stronger ABA agonist activity than (+)-BP2A. In contrast, in the in vitro phosphatase assays, both compounds showed comparable or weaker ABA receptor (PYL1) agonistic activity than (+)-BP2A, suggesting that the stronger ABA-like activity of (+)-5 and (+)-6 may arise from their metabolic stability in vivo. This study provides data relevant to designing photostable and persistent ABA agonists.

Restricted Kinematically Aligned Total Knee Arthroplasty Following Failed Oxford Unicompartmental Knee Arthroplasty.

In this report, we describe how to revise a failed Oxford unicompartmental knee arthroplasty to kinematically aligned total knee arthroplasty (TKA). Its benefits are the maintenance of the native joint line along with the avoidance of supplemental parts, such as metal augments and stems. This can be applied to patients whose medial tibial cortex is well preserved. The distal cutting plane and rotation alignment are decided before the removal of the femoral component. The tibial cutting plane is up to 12 mm below the lateral joint surface and the varus is up to 5° below the extramedullary rod. Eventually, the native joint line and alignment along with the soft tissue envelope can be well maintained, similar to the restricted kinematically aligned TKA.

Kinematically Aligned Oxford Unicompartmental Knee Arthroplasty Using the Microplasty Instrumentation System.

This technical note demonstrates kinematically aligned Oxford unicompartmental knee arthroplasty using the Microplasty instrumentation system with custom-made devices. The medial joint line is evaluated preoperatively; if it is aligned and parallel with the lateral joint line, they are considered to comprise the coronal knee joint line (CJL). In this case, the coronal inclination of a spoon gauge inserted into the medial joint space indicates the CJL. Otherwise, an accessory spoon is inserted and connected to the medial spoon to refer to the posterior condylar line, which is considered the CJL. The tibial cutting block is then connected without changing the inclination of the spoon and the coronal tilt of the tibial extramedullary rod is adjusted, which is implemented with a custom-made ankle yoke. The remainder of the steps is then identical to the conventional Microplasty procedure. This technique can imitate the cutting line to the CJL, which might be considered ideal from mechanical and kinematic perspectives.

Incomplete Screw Thread Engagement of Proximal Fragment: A Possible Failure Risk After Internal Fixation for Femoral Neck Fractures.

Background For successful internal fixation for femoral neck fracture, the sliding mechanism of the screw is important because it can induce inter-fragmental compression. The thread should penetrate the fracture line and be located within the proximal fragment. If screw thread engagement is incomplete and a part of the thread remains within the distal fragment, the screw sliding can be disturbed, potentially leading to fixation failure. We hypothesized that screw thread in the fracture is a risk of fixation failure. Methods We studied 133 hips that underwent internal fixation for femoral neck fracture using dual sliding and compression screws (DSCS) with 20 mm threads. The existence of incomplete thread engagement and fixation failure (cut out, perforation, pseudoarthrosis, or femoral neck shortening) were evaluated on anteroposterior hip radiography postoperatively. The distances from the thread end to the fracture line, screw head to the femoral head cortex, and femoral head diameter were measured to analyze their relationships with any incomplete thread engagement and fixation failure. Differences in evaluation data were assessed using Fisher's exact test, Student's t-test, and receiver operating characteristic (ROC) analysis. Results Forty-six cases had at least one screw with incomplete thread engagement, and the other 87 hips had a complete engagement. The failure rate in the group of hips with incomplete thread engagement was significantly higher (7/46, 15.2%) than that in the group of hips with complete thread engagement (3/87, 3.4%) (P = 0.032). Incomplete thread engagement was found in 59 out of 266 screws (22.2%), and a femoral head ≤ 43.9 mm in diameter was associated with an increased risk of incomplete thread engagement. Most incomplete thread engagement screws (81.4%) had < 5 mm thread length within the distal fragment. Conclusion A partially threaded screw is a significant risk of fixation failure after internal fixation for a femoral neck fracture. The smaller femoral head diameter increases the possibility of incomplete thread engagement. Shortening the thread length by 5 mm may help to avoid incomplete thread engagement.

Bearings can dislocate with smaller femoral components and thicker bearings in Oxford™ medial unicompartmental knee arthroplasty.

BACKGROUND: A mobile bearing can dislocate when joint laxity is larger than jumping height, the height difference between the bottom and the peak of the bearing (the highest point of the upper bearing surface on each side). Significant laxity due to improper gap balancing should therefore be avoided. However, once the bearing rotates vertically on the tibial component, the bearing can dislocate with smaller laxity than the jumping height. We mathematically calculated the required laxity for dislocation (RLD) and the required rotation of the bearing for dislocation (RRD). The current study addressed the question: 1) could the femoral component size and the bearing thickness affect the RLD and RRD? HYPOTHESIS: The femoral component size and the bearing thickness could affect the MLD and MRD. METHODS: The RLD and RRD were calculated using the bearing dimensions provided by the manufacturer with femoral component size, bearing thickness, and directions (anterior, posterior, and medial/lateral) as the variables on a two-dimensional basis. RESULTS: The RLD was 3.4 to 5.5mm in the anterior, 2.3 to 3.8mm in the posterior, and 1.4 to 2.4mm in the medial or lateral directions. The RLD decreased with a smaller femoral size or a thicker bearing. Similarly, the RRD decreased with a smaller femoral size or a thicker bearing thickness in all directions. CONCLUSIONS: Increased bearing thickness and decreased femoral component size deceased the RLD and RRD, which would relate to an increased risk of dislocation. Selecting the femoral component as large as possible and the bearing as thin as possible would therefore be helpful in the prevention of dislocation. LEVEL OF EVIDENCE: III; comparative computer simulation study.

Intraoperative avulsion fracture of the intercondylar eminence in Oxford mobile-bearing unicompartmental knee arthroplasty: Case report.

BACKGROUND: Unicompartmental knee arthroplasty (UKA) can provide good postoperative results and long term survival, but there may be complications. We present a rare case of avulsion fracture of the intercondylar eminence during UKA surgery. CASE PRESENTATION: An 88-year-old man had right-knee pain with anteromedial osteoarthritis. Oxford partial knee UKA (Zimmer Biomet, Warsaw, IN) was performed by the senior author by the under-vastus approach using Microplasty instruments. During the final check of the range of motion, an avulsion fracture of the intercondylar eminence occurred at the terminal extension. A 4.0 mm cannulated cancellous screw was inserted into the intercondylar eminence from just in front of the anterior cruciate ligament to the posterior tibial cortex. Six months postoperatively, bony fusion was confirmed by lateral radiography. Two years after the surgery, the patient was fully satisfied. The flexion angle was 125°, but still with an extension limit of 10°. DISCUSSION: Avulsion fracture of the intercondylar eminence can be caused by hyperextension and/or the ACL becoming tighter in full extension of the knee. In this patient, avulsion fracture also probably occurred due to increased tension of the ACL in the fully extended position. After making the horizontal cut, we inserted a thin metal plate to prevent deeper vertical cuts, but an excessive horizontal cut was a possible cause of the fracture. As treatment for avulsion fracture of the intercondylar eminence, fixation of the cannulated cancellous screw resulted in uneventful bone fusion. We recommend having a cannulated cancellous screw at hand for such complications and for other potential intraoperative problems, such as tibial plateau fracture. Further investigation into limited postoperative extension might be needed. CONCLUSION: Our patient had intraoperative avulsion fracture of the intercondylar eminence, a relatively rare complication of Oxford UKA which is probably caused by the extension being tight and/or an excessive horizontal cut. Having a cannulated cancellous screw at hand is advised, and attention should be paid to postoperative limit of extension.

The Lateral Malleolus Is a Simple and Reliable Landmark that Can Be Used to Reliably Perform Restricted Kinematically Aligned Total Knee Arthroplasty-Anatomical and Clinical Studies in Japanese Population.

In restricted kinematic alignment total knee arthroplasty (TKA), bone resection is performed within a safe range to help protect against failure from extreme alignments. Patient-specific instrumentation, navigations, and robotics are often required for restricting bone cuts within a specified safe zone. We hypothesized that the lateral malleolus could be used as a landmark for restricting the tibial osteotomy using a mechanical jig. Here, we examine its feasibility in anatomical and clinical settings. We studied long-leg standing radiographs of 114 consecutive patients (228 knees) who underwent knee arthroplasty in our institution. We measured the lateral malleolus angle (LMA), the angle between the tibial axis and the line between the center of the knee and the lateral surface of the lateral malleolus. The medial proximal tibial angle was also measured before and after restricted kinematic alignment TKA under restriction with reference to the lateral malleolus. Mean LMA was 5.5 ± 0.5 degrees. This was relatively consistent and independent of patient's height, weight, and body mass index. The lateral malleolus is a reliable bone landmark that can be used to recognize approximately 5.5 degrees of varus intraoperatively. A surgeon can use this as a restriction of the tibial varus cut up to 6 degrees without the requirement for expensive assistive technologies.

Kinematic Alignment Bi-unicompartmental Knee Arthroplasty With Oxford Partial Knees: A Technical Note.

Bi-unicompartmental knee arthroplasty (BiUKA) is an alternative to total knee arthroplasty for selected patients. Although it is thought to be technically demanding, the technique has not been previously described in detail. Kinematic alignment (KA) implantation and bone cuts parallel to the native joint line would be beneficial to ensure optimal mechanical loading. Here, we detail a technique for KA-BiUKA using the Oxford partial knees. The joint line is identified using the spoon of the microplasty instrumentation system with/without the accessory spoons. The tibia is cut parallel with the joint line using a side-slidable ankle yoke so that the inclination of the cutting block is parallel with the spoon surface. After defining the horizontal bone-cutting lines, the predominantly affected condyle is operated upon, followed by the lesser affected condyle. Although custom-made devices are required, the technique is useful and reproducible in the performance of KA-BiUKA with the Oxford partial knees.

Varus placement of the tibial component of Oxford unicompartmental knee arthroplasty decreases the risk of postoperative tibial fracture.

AIMS: A fracture of the medial tibial plateau is a serious complication of Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). The risk of these fractures is reportedly lower when using components with a longer keel-cortex distance (KCDs). The aim of this study was to examine how slight varus placement of the tibial component might affect the KCDs, and the rate of tibial plateau fracture, in a clinical setting. METHODS: This retrospective study included 255 patients who underwent 305 OUKAs with cementless tibial components. There were 52 males and 203 females. Their mean age was 73.1 years (47 to 91), and the mean follow-up was 1.9 years (1.0 to 2.0). In 217 knees in 187 patients in the conventional group, tibial cuts were made orthogonally to the tibial axis. The varus group included 88 knees in 68 patients, and tibial cuts were made slightly varus using a new osteotomy guide. Anterior and posterior KCDs and the origins of fracture lines were assessed using 3D CT scans one week postoperatively. The KCDs and rate of fracture were compared between the two groups. RESULTS: Medial tibial fractures occurred after surgery in 15 patients (15 OUKAs) in the conventional group, but only one patient (one OUKA) had a tibial fracture after surgery in the varus group. This difference was significant (6.9% vs 1.1%; p = 0.029). The mean posterior KCD was significantly shorter in the conventional group (5.0 mm (SD 1.7)) than in the varus group (6.1 mm (SD 2.1); p = 0.002). CONCLUSION: In OUKA, the distance between the keel and posterior tibial cortex was longer in our patients with slight varus alignment of the tibial component, which seems to decrease the risk of postoperative tibial fracture.Cite this article: Bone Joint J 2022;104-B(10):1118-1125.

Current concept of kinematic alignment total knee arthroplasty and its derivatives.

The kinematic alignment (KA) approach to total knee arthroplasty (TKA) has recently increased in popularity. Accordingly, a number of derivatives have arisen and have caused confusion. Clarification is therefore needed for a better understanding of KA-TKA. Calipered (or true, pure) KA is performed by cutting the bone parallel to the articular surface, compensating for cartilage wear. In soft-tissue respecting KA, the tibial cutting surface is decided parallel to the femoral cutting surface (or trial component) with in-line traction. These approaches are categorized as unrestricted KA because there is no consideration of leg alignment or component orientation. Restricted KA is an approach where the periarthritic joint surface is replicated within a safe range, due to concerns about extreme alignments that have been considered 'alignment outliers' in the neutral mechanical alignment approach. More recently, functional alignment and inverse kinematic alignment have been advocated, where bone cuts are made following intraoperative planning, using intraoperative measurements acquired with computer assistance to fulfill good coordination of soft-tissue balance and alignment. The KA-TKA approach aims to restore the patients' own harmony of three knee elements (morphology, soft-tissue balance, and alignment) and eventually the patients' own kinematics. The respective approaches start from different points corresponding to one of the elements, yet each aim for the same goal, although the existing implants and techniques have not yet perfectly fulfilled that goal.

Approximately 80% of Japanese osteoarthritic patients fall out of the safety range in restricted kinematically-aligned total knee arthroplasty in an analysis of preoperative long-leg radiograms.

BACKGROUND: Restricted kinematically-aligned total knee arthroplasty (KA-TKA) is a reasonable modification to avoid the alignment outlier that may cause implant failure. However, despite a noted high incidence of constitutional varus in Japanese individuals, there has been no investigation into how many knees require the restriction in restricted KA-TKA (RKA-TKA) among Japanese patients. Therefore, we conducted a study using preoperative long-leg radiograms. METHODS: We studied long-leg radiographs of 228 knees in 114 consecutive patients. The numbers of knees within the safety range and their corrective osteotomy angle in the restriction algorithms advocated by Almaawi et al. (2017) and MacDessi et al. (2020) were evaluated. RESULTS: According to the algorithms used by Almaawi et al. and MacDessi et al., out of 228 knees, 46 (20%) and 39 (17%) fell within the safety range, respectively. The mean correction angles of the hip-knee-ankle angle, lateral distal femoral angle and medial proximal tibial angle were 2.8 ± 3.4°, 0.4 ± 1.4° and 2.4 ± 2.8° in the algorithm used by Almaawi et al., while they were -4.9 ± 4.7°, 1.1 ± 2.5° and -6.0 ± 3.4° in the algorithm used by MacDessi et al. Most of the knees needed to be restricted in order to perform RKA-TKA, regardless of the algorithm used. CONCLUSIONS: Based on a preoperative analysis of long-leg radiograms in a Japanese population, most knees fall out of the safety range in RKA-TKA. Surgeons must consider whether to allow component outlier or to perform corrective osteotomy that likely requires soft tissue release.

Bearing Separation From the Lateral Wall of the Tibial Component Is a Risk of Anterior Dislocation of the Mobile Bearing in Oxford Unicompartmental Knee Arthroplasty.

BACKGROUND: Bearing dislocation is a serious complication after Oxford unicompartmental knee arthroplasty. Bearing separation from the lateral wall can cause it to spin (90° horizontal rotation) and eventually dislocate because there is just a 2 mm difference in height in both the lateral and medial sides from the bottom of the bearing, compared with the anterior (5 mm) and posterior (3 mm) sides. The details of this problem have not been previously examined. METHODS: Twenty-one dislocations in 12 patients were retrospectively analyzed. Bearing separation was defined as the bearing position being sufficiently distant from the lateral wall of the tibial component to allow spinning. We analyzed the incidence of separation, the direction and the recurrence of the dislocations, and their causes and treatments. RESULTS: Five of the 12 patients had separation. Of the total of 21 dislocations, 11 occurred in cases of separation (52%). Seven of 11 anterior dislocations were found to have separation, whereas nine of 13 posterior dislocations occurred without separation (P = .0237). Three of 5 patients with separation had recurrence of dislocation, and eventually 2 underwent revision to fixed-bearing unicompartmental knee arthroplasty. CONCLUSION: Bearing separation from the lateral wall of the tibial component can cause bearing dislocation, especially in an anterior direction. To prevent separation, the wall-bearing distance should be evaluated before the keel slot preparation, with manipulation as necessary. Conversely, posterior dislocation was predominant in our nonseparation cases.

ORAC and DPPH assay comparison to assess antioxidant capacity of tea infusions: relationship between total polyphenol and individual catechin content.

Commercially available tea infusions are the major source of catechins for preparing bottled tea beverages and tea supplements available in the market today. In the present study, we analyzed five tea infusions to measure the total antioxidant capacity (TAC) by oxygen radical absorbance capacity (ORAC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity (DRSC) assays, total polyphenol content by the colorimetric method and individual catechin content by high-performance liquid chromatography. Four major tea catechins were also analyzed for their TAC to reveal differential antioxidant behavior of the tea infusions, resulting in the ORAC and DRSC methods. The correlation coefficients between DRSC and the total polyphenol or total catechin content of the tea infusions were 1.0 and 0.99. However, the values fall to 0.73 and 0.69, respectively, while the ORAC activity was correlated with total polyphenol and total catechin content. Determining the TAC of individual tea catechins showed that ORAC of epicatechin was seven-fold higher than that of epigallocatechin gallate; on the contrary, epigallocatechin gallate showed significantly (P < 0.05) stronger DRSC activity than epicatechin. By evaluating the structure-activity relationship, this study further revealed that OH substitution at the 3' position in pyrogallol moieties contributes to the lower ORAC value of epigallocatechin and epigallocatechin gallate comparing with their non-3'-OH counterparts, such as epicatechin and epicatechin gallate, respectively. Also, numbers of OH substitutions were poorly correlated with the observed ORAC value unlike the DRSC. Overall, results of this study enabled us to hypothesize that substances having a lower TAC value in the ORAC assay compared with that in DPPH assays may pertain to a pro-oxidant effect by generating reactive oxygen species in an aqueous buffer, at a physiological pH. We also propose that substances exhibiting lower TAC value in the ORAC assay compared with that in the DPPH assay are powerful pro-oxidants compared with the substances showing a higher TAC value in the ORAC assay than that in the DPPH assay.