Highly Porous Titanium Cups Frequently Presenting with Radiolucent Lines in Cementless Primary Total Hip Arthroplasty: A Retrospective Cohort Study.

Background/Objectives: A highly porous titanium cup with a three-dimensional metal interface was recently introduced to improve biological fixation and survival. However, radiography has revealed concerns regarding these cups, despite their excellent short- and mid-term clinical outcomes. This study compared the clinical and radiographic results of a highly porous titanium cup with those of a hydroxyapatite-coated porous titanium cup after primary total hip arthroplasty (THA). Methods: Fifty-one primary THAs were investigated. A highly porous titanium cup was used in 17 hips, and a hydroxyapatite-coated porous titanium cup was used in 34 hips. No significant differences in preoperative patient demographic characteristics were observed between the two groups. The 2-year postoperative clinical and radiographic results were compared. Results: Radiolucent lines were observed in 13 (76%) of 17 hips with highly porous titanium cups and in none (0%) of 34 hips with hydroxyapatite-coated porous titanium cups (p < 0.001). In the highly porous titanium cup group, radiolucent lines were observed in five hips (29%) in one zone, two hips (11%) in two zones, and six hips (35%) in three zones. No cup loosening was observed in either group. Conclusions: Radiolucent lines were significantly more frequent in highly porous titanium cups. This study suggests that, compared to the three-dimensional structure of porous titanium, the hydroxyapatite coating of porous titanium had a greater influence on bone ingrowth in the short term. The meaning of these findings in the long-term is unclear yet.

Protocol of a pilot randomized clinical trial to evaluate nutritional support and rehabilitation on prevention of skeletal muscle mass loss during neoadjuvant chemotherapy in patients with esophageal cancer.

BACKGROUND: Subtotal esophagectomy with lymph node dissection followed by neoadjuvant chemotherapy (NAC) is the standard treatment for stage II-III esophageal cancer. Esophagectomy is still associated with high morbidity rates, and reducing these rates remains challenging. Among several complications, postoperative pneumonia (PP) is sometimes fatal, which has been reportedly caused by sarcopenia. Thus, nutritional support and rehabilitation may be promising for preventing skeletal muscle mass loss and reduce the incidence of PP. METHODS: This single-center, randomized, open-label, pilot trial will randomize a total of 40 patients with esophageal cancer in a 1:1 ratio either to ISOCAL Clear + rehabilitation arm or only rehabilitation arm. Although all patients will be educated about rehabilitation by a specialized physician and will be asked to undergo the prespecified rehabilitation program, patients treated with ISOCAL Clear + rehabilitation arm will be supplemented by 400 mL of ISOCAL Clear (Nestlé Japan Ltd, Tokyo, Japan) per day during two courses of NAC with docetaxel, cisplatin, and fluorouracil. Body composition will be assessed using Inbody (Inbody Co., Ltd., Tokyo, Japan) just before starting NAC and surgery. The primary endpoint is the change of skeletal muscle index (SMI) during NAC. Secondary endpoints include (i) body weight, total skeletal muscle mass, appendicular skeletal muscle mass, and lean body mass index changes; (ii) the percentage of ISOCAL Clear continuation; (iii) appetite evaluation; (iv) the percentage of targeted calorie achievement; (v) adverse events of NAC; (vi) postoperative complication rates; and (vii) postoperative hospital stay. DISCUSSION: This prospective trial assesses the efficacy of nutritional support in addition to rehabilitation during NAC for patients with esophageal cancer. The results will be utilized in assessing whether the effects of nutritional support by ISOCAL Clear are promising or not and in planning future larger clinical trials.

Efficacy of Early Rehabilitation for Severe Coronavirus Disease 2019 Pneumonia: Factor Analysis Using Machine Learning.

Objectives: Patients with severe coronavirus disease 2019 (COVID-19) who develop pneumonia face the risk of ventilatory muscle disuse in the acute phase, which can result in persistent respiratory impairments in the subacute phase. Although rehabilitation during the acute phase is considered effective, there are limited reports on this topic. Therefore, this study aimed to investigate the effectiveness of acute-phase rehabilitation in patients with severe COVID-19. Methods: The study included 57 patients (45 men and 12 women; mean age: 63.2±12.1 years) admitted between April and June 2021, all of whom required intubation for respiratory management. Among them, 34 patients underwent acute-phase rehabilitation interventions based on the early goal-directed mobilization protocol. The primary objectives were to assess the occurrence of medical accidents related to acute-phase rehabilitation and evaluate their impact on survival and mobility upon hospital discharge. Statistical techniques and machine learning algorithms were employed for data analysis. Results: Remarkably, no medical accidents occurred during the acute-phase rehabilitation among the patients. Furthermore, our findings indicated that acute-phase rehabilitation did not influence survival outcomes. However, it did have a positive impact on the mobility of patients upon hospital discharge. Conclusions: Acute-phase rehabilitation can be safely administered to patients with severe COVID-19 by following an early goal-directed mobilization protocol. This approach may also contribute to improved activities of daily living after discharge.

The modification of bone cut angle and joint line obliquity did not change the tibiofemoral kinematics and stability of knee joint after total knee arthroplasty.

INTRODUCTION: Previous reports using cadaveric knees and musculoskeletal computer simulation have shown that kinematically aligned (KA) total knee arthroplasty (TKA) provides more natural and physiological tibiofemoral kinematic patterns than mechanically aligned (MA) TKA. These reports suggested that the modification of joint line obliquity improve the knee kinematics. This study aimed to determine whether joint line obliquity change the intraoperative tibiofemoral kinematics in TKA candidates with knee osteoarthritis. METHODS: Thirty consecutive knees with varus osteoarthritis that underwent TKA using a navigation system were evaluated. Two types of trial components were prepared: (1) MA TKA model: component trial in which articulating surface was parallel to the bone cut surface (2) KA TKA model: the femoral component trial, which mimicked the KA TKA method of Dossett et al. was designed 3° valgus and 3° internal rotation to the femoral bone cut surface, and the tibial component trial was designed 3° varus to the tibial bone cut surface. These two trials were set on the same knees during the operation, and the tibiofemoral rotational kinematics and varus-valgus laxity were measured from 0° to 120° of knee flexion using a navigation system. RESULTS: The joint gap was 20 ± 2 mm and 3° ± 1° varus in extension and 20 ± 2 mm and 3° ± 1°varus in flexion. The differences in femoral component rotation between KA TKA and MA TKA were not statistically significant for any knee flexion angle. The differences in varus-valgus laxity between KA TKA and MA TKA were also not statistically significant for any knee flexion angle. CONCLUSION: Although the degree of joint line obliquity varies widely in various KA TKA methods, this study, which mimicked the method of Dossett et al. showed that the modification of joint line obliquity did not change the tibiofemoral kinematics and stability of the knee joint in TKA candidates with knee osteoarthritis.

A cemented mobile-bearing total knee prosthesis prevents peri-prosthetic bone mineral density loss around the femoral component: a consecutive follow-up at a mean of 11 years.

PURPOSE: Research has shown that a cemented mobile-bearing component has a favorable effect on the bone mineral density (BMD) of the distal femur at 2 years after total knee arthroplasty (TKA). This study was performed to determine whether the advantage on BMD of a cemented mobile-bearing TKA over a conventional cemented fixed-bearing TKA changes with time. This report is an update of a matched cohort study initiated in 2004 and for which the 2-year results have been published. METHODS: Twenty-eight knees that were treated with a fixed-bearing posterior stabilized (PS) prosthesis and 28 matched knees from a database of 76 knees that were treated with a mobile-bearing PS prosthesis in the same period were investigated. All knees underwent dual-energy X-ray absorptiometry (DEXA) scans around the femoral component preoperatively, 2 weeks postoperatively, 5 years postoperatively, and annually thereafter. Eighteen knees with a cemented mobile-bearing PS prosthesis and 20 knees with a cemented fixed-bearing PS prosthesis were investigated for more than 6 years. The mean follow-up period was 11 years. RESULTS: The range of motion, Knee Society Score, BMD of the lumbar spine, and follow-up period were not significantly different preoperatively and postoperatively in the two groups. In the fixed-bearing group, the BMD of the anterior part of the femoral condyle decreased postoperatively. In the mobile-bearing group, the BMD of the posterior part of the femoral condyle increased postoperatively. The postoperative change in the BMD at 5 years and the latest follow-up period was statistically significant in the two groups. CONCLUSIONS: This DEXA study revealed that a cemented mobile-bearing component had a favorable effect on the BMD of the distal femur after TKA even at a mean of 11 years postoperatively. LEVEL OF EVIDENCE: Therapeutic study, level II, prospective comparative study.

Medial peg position of cementless porous tantalum tibial component affects bone mineral density around the prosthesis after total knee arthroplasty: 2-year follow-up study.

BACKGROUND: Use of a porous tantalum tibial component for total knee arthroplasty (TKA) was reported to have beneficial effects on periprosthetic bone mineral density (BMD). In some cases, hexagonal peg is placed close to or in contact with the tibial cortex, which may result in stress-shielding around the peg. However, no studies have analyzed the relationship between peg position and BMD. The aim of this study was to compare the peg position and BMD around the peg in a porous tantalum tibial component after TKA. METHODS: Twenty-seven patients (27 knees) who underwent primary TKA with a cementless porous tantalum tibial component were investigated. BMD was measured by dual-energy X-ray absorptiometry for 2 years after the operation. The distance between the peg and the tibial cortex (peg distance) was measured on the medial and lateral sides. RESULTS: BMD was decreased in the medial region after the operation (p < 0.01). Relative change in BMD was lower in the medial region than in the central and lateral regions (p < 0.01). Multiple regression analysis showed that medial peg distance was negatively correlated with relative change of BMD in the medial part of the tibia (p = 0.04, R = 0.402). CONCLUSIONS: The medial peg position affected the postoperative relative change of BMD in the medial part of the tibia, but did not affect the longevity of the implant. As the tibial medial peg became closer to the medial tibial cortex, the BMD loss became larger in the medial part of the tibia at 2 years postoperatively.

Is the Anterolateral or Posterolateral Approach More Effective for Early Postoperative Recovery after Minimally Invasive Total Hip Arthroplasty?

Currently, various minimally invasive surgical techniques are applied for total hip arthroplasty (THA). There are few studies comparing the early postoperative clinical outcomes of minimally invasive THA between anterolateral and posterolateral approaches. In this retrospective study, 62 patients underwent minimally invasive THA via either the anterolateral approach with an intermuscular exposure using the modified Watson-Jones approach (MIS-AL, 34 hips) or mini-incision THA with a posterolateral approach (MIS-PL, 28 hips). We analyzed intraoperative data, postoperative hematological data, postoperative radiographic findings, and the postoperative recovery of muscle strength. The mean surgical time was significantly longer in the MIS-PL than in the MIS-AL group. The mean postoperative serum C-reactive protein level was significantly higher in the MIS-PL group than in the MIS-AL group only on postoperative day 3. There were no significant between-group differences in the postoperative recovery rate of muscle strength during hip abduction. The recovery rate of muscle strength during hip extension was better in the MIS-AL group than in the MIS-PL group only on postoperative day 3. In conclusion, we found no obvious advantage in early postoperative recovery between the MIS-AL and MIS-PL approaches. Therefore, the benefit of rapid postoperative recovery was comparable between the MIS-AL and MIS-PL approaches.

Periprosthetic Loss of Bone Mineral Density After Cementless Porous Tantalum and Cemented Total Knee Arthroplasties: A Mean of 11-Year Concise Follow-Up of a Previous Report.

BACKGROUND: Our previous study showed that the decrease in relative change of bone mineral density (BMD) in the lateral part of the tibia was significantly less in the group treated with the cementless porous tantalum component than in the group treated with the cemented cobalt-chromium tibial component up to 5 years after the operation. However, the long-term benefits of porous tantalum tibial component on BMD have not been proven. The aim of this study was to update a matched cohort study at a minimum of 6 years' follow-up period. METHODS: Twenty patients with a porous tantalum tibial component and 18 patients with a cemented cobalt-chromium-alloy tibial component were investigated for more than 6 years in the present study. The mean follow-up period was 11.4 years. Dual X-ray absorptiometry was used to measure the BMD. RESULTS: The decrease in relative change of BMD in the lateral aspect of the tibia was significantly less with the porous tantalum tibial component than that with the cemented cobalt-chromium tibial component up to 5 years. However, at the final follow-up period, no significant difference was observed in the relative change of BMD between the 2 groups. No prosthetic migration or periprosthetic fracture was detected in either group. CONCLUSION: The present study is one of the studies with the longest follow-up period on BMD after total knee arthroplasty. Porous tantalum tibial component did not have a favorable effect on the BMD of the proximal tibia after total knee arthroplasty for long term.

Changes in viscoelastic properties of articular cartilage in early stage of osteoarthritis, as determined by optical coherence tomography-based strain rate tomography.

BACKGROUND: Biomechanical changes in articular cartilage are associated with the onset of osteoarthritis. We developed an optical coherence tomography-based strain rate tomography method: stress relaxation optical coherence straingraphy (SR-OCSA). The purpose of this study was to establish an approach for measuring mechanical properties of articular cartilage using SR-OCSA, and to investigate the distribution of viscoelastic properties of articular cartilage in early osteoarthritis. METHODS: Anterior cruciate ligament transection surgery was performed on the left knees of 8-9-month-old New Zealand white rabbits. SR-OCSA was used to visualize and measure the viscoelastic properties of articular cartilage via attenuation coefficient of strain rate (ACSR). Using the same conditions as in the SR-OCSA test, an indentation test was conducted, and relaxation time was measured to evaluate the relationship between ACSR and relaxation time. RESULTS: SR-OCSA could nondestructively detect and visualize changes in the distribution of viscoelastic properties of articular cartilage in early osteoarthritis. SR-OCSA captured significant increases in ACSR in cartilage at 2 weeks after surgery, when a histologically slight osteoarthritis sign was present. As cartilage degeneration progressed, ACSR increased, whereas relaxation time decreased in a time-dependent manner. Moreover, ACSR negatively correlated with relaxation time. In particular, ACSR was elevated around the tidemark and the elevation tended to move as cartilage degeneration progressed. CONCLUSIONS: SR-OCSA could tomographically and nondestructively detect and visualize changes in the distribution of viscoelastic properties of articular cartilage in early osteoarthritis. The mechanical properties around the tidemark were degraded as cartilage degeneration progressed. Thus, SR-OCSA provides important data needed to understand the biomechanics of early osteoarthritis.

Impingement of the patellar component against the tibial post depends on the design of the post-cam mechanism: Comparison between 12 posterior stabilized total knee prostheses.

BACKGROUND: Patella-post impingement (PPI), contact of the patellar component with the tibial post, occurs during deep knee flexion after posterior stabilized total knee arthroplasty (TKA). In a previous pilot study, only two product lines were investigated. The aim of this study was to compare PPI between 12 contemporary posterior stabilized knee prostheses. METHODS: Twelve posterior stabilized knee prostheses were implanted in full-length sawbone models of the femur and tibia using a navigation system. The distance between the lower edge of the patellar component and the cut surface of the tibia was defined as the tibial-patellar clearance (TPC), which represents the length of the patellar tendon. The TPC was set from 20 to 40 mm and the knee was moved from full extension to deep flexion while the knee angle at which PPI occurred (PPI angle) was recorded. RESULTS: The PPI angle differed between prostheses (P < 0.05). Shorter TPCs resulted in smaller PPI angles and longer TPCs resulted in larger PPI angles (P < 0.05). To achieve more than 130° of flexion without PPI, the TPC should be prepared at a minimum of 20 mm for the NexGen LPS-Flex, Persona PS, Legion PS, and Evolution PS, 22 mm for the Attune RP and Journey II, 24 mm for the Triathlon PS, PFC Sigma PS, and Attune PS, and 26 mm for the NRG PS, Vanguard PS, and Vanguard RP. CONCLUSIONS: The design of the tibial post significantly affects the PPI angle. To avoid PPI during deep flexion, appropriate TPC should be prepared during surgery.

Asymmetric Tibial Component Improved the Coverage and Rotation of the Tibial Component in a Medial Pivot Total Knee Prosthesis.

Malrotation of tibial components is one of the important causes of failure in total knee arthroplasty. The aim of this study is to determine the relationship between tibial rotational positioning and coverage of the tibial surface during the operation, using a symmetric and newly introduced asymmetric medial pivot tibial components. The coverage and overhang were compared between a symmetric component (Advance medial pivot) and a newly introduced asymmetric medial pivot tibial component (Evolution medial pivot) in 31 knees during the operation. When the tibial component was placed parallel to the anteroposterior (AP) axis, the uncovered width in the posteromedial part using a symmetric design was larger than that using an asymmetric design (p < 0.01). Overhang in the posterolateral part was observed in 42% for a symmetric design and 3% for an asymmetric design (p < 0.01). When the component was placed in malrotation (10 degrees internal to the AP axis), overhang in the posteromedial part was observed in 6% for a symmetric design and in 71% for an asymmetric design (p < 0.01). The tibial rotation parallel to the AP axis and maximizing coverage of the tibial surface conflict in a symmetric design, but are compatible in an asymmetric design. An asymmetric tibial component is expected to improve the coverage and the rotational positioning of medial pivot total knee prosthesis.

Comparison of in vivo polyethylene wear particles between mobile- and fixed-bearing TKA in the same patients.

PURPOSE: Polyethylene wear particle generation is one of the most important factors that affects the mid- to long-term results of total knee arthroplasties (TKA). Mobile-bearing total knee prostheses were developed to reduce polyethylene wear generation. However, whether mobile-bearing prostheses actually generate fewer polyethylene wear particles than fixed-bearing prostheses remains controversial. The aim of this study was to compare, within individual patients, the in vivo polyethylene wear particles created by a newly introduced mobile-bearing prosthesis in one knee and a conventional fixed-bearing prosthesis in other knee. METHODS: Eighteen patients receiving bilateral TKAs to treat osteoarthritis were included. The synovial fluid was obtained from 36 knees at an average of 3.5 years after the operation. The in vivo polyethylene wear particles were isolated from the synovial fluid using a previously validated method and examined using a scanning electron microscope and an image analyser. RESULTS: The size and shape of the polyethylene wear particles from the mobile-bearing prostheses were similar to those from the conventional fixed-bearing prostheses. Although the number of wear particles from the mobile-bearing prosthesis (1.63 × 107 counts/knee) appeared smaller than that from the fixed-bearing prosthesis (2.16 × 107 counts/knee), the difference was not statistically significant. CONCLUSIONS: The current in vivo study shows that no statistically significant differences were found between the polyethylene wear particles generated by a newly introduced mobile-bearing PS prosthesis and a conventional fixed-bearing PS prosthesis during the early clinical stage after implantation. LEVEL OF EVIDENCE: Therapeutic study, Level III.

Anatomical analysis of the relation between human ligamentum flavum and posterior spinal bony prominence.

BACKGROUND: Posterior spinal bony prominences are commonly used as landmarks during posterior spinal surgery; however, the exact relationship of these structures with ligamentum flavum (LF) borders and attachments has not been clarified. MATERIALS AND METHODS: Whole spines were removed en bloc from 20 embalmed human cadavers. Plain radiographs and computed tomography (CT) scans of each whole spine were taken, and then the spine was divided in two parts along the pedicle bases. The LFs were painted with contrast dye, and second radiographs and CT scans were taken again. Radiographic data were analyzed using CT image analyzer. RESULTS: The craniolateral border of LF at four upper lumbar levels (from L1/2 to L4/5) located cranial to isthmus in both sides (3.5 mm), meanwhile, it located at or below isthmus in both sides at L5-S1 level (0.5 mm). In the midline, LF attached below the isthmus levels at four upper lumbar levels (4 mm), though it located in the same level of isthmus at L5-S1 (1 mm). The mean distance between medial border of pedicles and lateral border of LF increased from upper to the lower lumbar levels (6.5 mm at L1/2 - 11.4 mm at L5-S1). Distance between interlaminar space and cranial border of LF at the midline gradually increased from 8.2 mm at L1 toward 11.1 mm at L4, it was 9.3 mm in L5. CONCLUSIONS: From the data of new analytical method using contrasted LF and reconstructed CT, the detailed relations between bony prominence and the border of LF were uncovered. Based on these findings and reconstructed LF images superimposed on lamina, surgeons would design safe and adequate lumbar spinal decompression with imagination of overall pictures of the LF from the dorsal side.

Mobile-bearing TKA improved the anteroposterior joint stability in mid-flexion range comparing to fixed-bearing TKA.

INTRODUCTION: Proper anteroposterior (AP) joint displacement is an important indicator of good clinical outcome following total knee arthroplasty (TKA). We hypothesized that a newly introduced mobile-bearing posterior stabilized (PS) prosthesis reduces the AP joint displacement. The aim of this study is to compare the AP joint displacement between a newly introduced mobile-bearing PS TKA in one knee and a conventional fixed-bearing PS TKA in other knee. MATERIALS AND METHODS: 82 knees in 41 patients who had bilateral TKAs were investigated. All the patients received a conventional fixed-bearing PS prosthesis in one knee and a highly congruent mobile-bearing PS prosthesis in the other knee. AP joint displacement was measured using the KT-2000 arthrometer, at 30° and 75° in flexion, at average of 3.3 years after the operation. RESULTS: AP joint displacements at 30° in flexion were 6 ± 3 mm in the knees with the mobile-bearing PS prosthesis and 9 ± 4 mm in the knee with fixed-bearing PS prosthesis (p < 0.001). AP joint displacements at 75° in flexion were 4 ± 2 mm in the knees with the mobile-bearing PS prosthesis and 6 ± 3 mm in the knee with fixed-bearing PS prosthesis (p < 0.001). CONCLUSIONS: This study suggested that the design of the prosthesis can improve the AP joint stability in mid-flexion range.

Anatomical landmarks of the distal femoral condyles are not always parallel to the tibial bone cut surface in flexion during total knee arthroplasty.

BACKGROUND: Soft tissue balancing is crucial to the success of total knee arthroplasty (TKA). To create a rectangular flexion joint gap, the rotation of the femoral component is important. The purpose of this study is to determine whether or not anatomical landmarks of the distal femoral condyles are parallel to the tibial bone cut surface in flexion. METHODS: Forty-eight patients (three male and 45 female) with a mean age of 74years were examined. During the operation, we estimated the flexion joint gap with the following three techniques. 1) a three degree external cut to the posterior condylar line (MR1), 2) a parallel cut to the surgical transepicondylar axis (MR2), and 3) a parallel cut to the anatomical transepicondylar axis (MR3). RESULTS: The flexion joint gap was 1.1±3.0° (mean±standard deviation (SD)) in internal rotation in the case of MR1, 0.9±3.4° in internal rotation in the case of MR2, and 2.1±3.4° in external rotation in the case of MR3. An outlier (flexion joint gap >3.0°) was observed in 12 cases (25%) in MR1, 13 cases (27%) in MR2, and 15 cases (31%) in MR3. CONCLUSIONS: The anatomical landmarks of the distal femoral condyles are not always parallel to the tibial bone cut surface in flexion. To create a rectangular flexion joint gap, the rotation of the femoral component rotation is based not only on the anatomical landmarks but also on the ligament balance.

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.

In vivo wear particles of remelted highly crosslinked polyethylene after total hip arthroplasty: report of four cases.

This is the first report of in vivo wear particles from four total hip arthroplasties using remelted highly crosslinked polyethylene. The number of particles was (1.51 ± 0.45) × 10(7) g(-1) (mean ± standard error); particle size (equivalent circle diameter), 0.72 ± 0.15 µm; and roundness, 1.45 ± 0.05. Remelted highly crosslinked polyethylene generates fewer, rounder, equivalently sized particles compared with corresponding reported values for particles generated from conventional polyethylene.

Mobile-bearing prosthesis and intraoperative gap balancing are not predictors of superior knee flexion: a prospective randomized study.

PURPOSE: Range of motion is a crucial measure of the outcome of total knee arthroplasty. Gap balancing technique and mobile-bearing prosthesis can improve postoperative range of motion. The purpose of this study was to determine the factors that are predictive of the postoperative range of motion. METHODS: A total of 94 knees with varus osteoarthritis were prospectively randomized to receive either a posterior-stabilized mobile-bearing or a posterior-stabilized fixed-bearing prosthesis. All preoperative and postoperative protocols and operative techniques were identical in the two groups. Extension and flexion joint gaps were measured using a tensor device during the operation. Multiple regression analysis was conducted to determine the best predictors of the knee flexion angle 2 years after the operation. The independent variables were type of prosthesis (mobile-bearing or fixed-bearing), difference between flexion and extension joint gaps (mm), age, gender, body mass index (BMI), preoperative and intraoperative knee flexion angles, change in posterior condylar offset, and posterior tilt of the tibial plateau. RESULTS: The mean difference between flexion and extension joint gaps was 0.8 ± 1.3 (mean ± SD) mm for mobile-bearing and 0.8 ± 1.9 mm for fixed-bearing prosthesis. The mean flexion angle for mobile-bearing and fixed-bearing groups was 120 ± 16° and 116 ± 20° preoperatively (n.s.), 142 ± 9° and 141 ± 12° intraoperatively (n.s.), and 129 ± 10° and 128 ± 13° at 2 years postoperatively (p = 0.773), respectively. Predictors were identified in the following three categories: (1) preoperative flexion angle, (2) intraoperative radiographic flexion angle, and (3) BMI (R = 0.603, p < 0.001). CONCLUSIONS: Mobile-bearing prosthesis and optimal gap balancing did not result in superior postoperative flexion angle. Better preoperative and intraoperative flexion angles and lower BMI were the significant predictors for better postoperative flexion angle. LEVEL OF EVIDENCE: Therapeutic study, Level I.

Advantages of externally powered prosthesis with feedback system using pseudo-cineplasty.

Externally powered upper-limb prostheses are difficult to use because of the lack of sensory feedback. Neuroprostheses have recently been developed for people with upper-limb amputation but are complicated, expensive, and still developing. We therefore designed a simple system by combining pseudo-cineplasty with extended physiological proprioception to provide sensory feedback to the body. We penetrated the palmaris longus tendon percutaneously with a metal ring, similar to that used in body piercing, in a nondisabled subject as a pseudo-cineplasty. The tendon and ring were connected to the system, and a sensory feedback experiment was performed. We investigated the ability of the user to determine the size of an object grasped by the prosthetic hand without visual information. The subject could distinguish between large and small objects with 100% accuracy and between small, medium, and large objects with 80% accuracy. In pseudo-cineplasty, control and sensory feedback are natural because the prosthetic hand is controlled by muscle contraction. Tension transmitted from the prosthetic hand is sensed via muscle spindles and skin sensors. This technique allows only partial sensory feedback but appears to offer several advantages over other human-machine interfaces.

No difference in in vivo polyethylene wear particles between oxidized zirconium and cobalt-chromium femoral component in total knee arthroplasty.

PURPOSE: Polyethylene wear particle generation is one of the most important factors affecting mid- to long-term results of total knee arthroplasties. Oxidized zirconium was introduced as a material for femoral components to reduce polyethylene wear generation. However, an in vivo advantage of oxidized zirconium on polyethylene wear particle generation is still controversial. The purpose of this study was to compare in vivo polyethylene wear particles between oxidized zirconium total knee prosthesis and conventional cobalt-chromium (Co-Cr) total knee prosthesis. METHODS: Synovial fluid was obtained from the knees of 6 patients with oxidized zirconium total knee prosthesis and from 6 patients with conventional cobalt-chromium (Co-Cr) total knee prosthesis 12 months after the operation. Polyethylene particles were isolated and examined using a scanning electron microscope and image analyser. RESULTS: Total number of particles in each knee was 3.3 ± 1.3 × 10(7) in the case of oxidized zirconium (mean ± SD) and 3.4 ± 1.2 × 10(7) in that of Co-Cr (n.s.). The particle size (equivalent circle diameter) was 0.8 ± 0.3 µm in the case of oxidized zirconium and 0.6 ± 0.1 µm in that of Co-Cr (n.s.). The particle shape (aspect ratio) was 1.4 ± 0.0 in the case of oxidized zirconium and 1.4 ± 0.0 in that of metal Co-Cr (n.s). CONCLUSIONS: Although newly introduced oxidized zirconium femoral component did not reduce the in vivo polyethylene wear particles in early clinical stage, there was no adverse effect of newly introduced material. At this moment, there is no need to abandon oxidized zirconium femoral component. However, further follow-up of polyethylene wear particle generation should be performed to confirm the advantage of the oxidized zirconium femoral component. LEVEL OF EVIDENCE: Therapeutic study, Level III.