Many recent knee prostheses are designed aiming to the physiological knee kinematics on tibiofemoral joint, which means the femoral rollback and medial pivot motion. However, there have been few studies how to design a patellar component. Since patella and tibia are connected by a patellar tendon, tibiofemoral and patellofemoral motion or contact forces might affect each other. In this study, we aimed to discuss the optimal design of patellar component and simulated the knee flexion using four types of patellar shape during deep knee flexion. Our simulation model calculates the position/orientation, contact points and contact forces by inputting knee flexion angle, muscle forces and external forces. It can be separated into patellofemoral and tibiofemoral joints. On each joint, calculations are performed using the condition of point contact and force/moment equilibrium. First, patellofemoral was calculated and output patellar tendon force, and tibiofemoral was calculated with patellar tendon force as external force. Then patellofemoral was calculated again, and the calculation was repeated until the position/orientation of tibia converged. We tried four types of patellar shape, circular dome, cylinder, plate and anatomical. Femoral and tibial surfaces are created from Scorpio NRG PS (Stryker Co.). Condition of knee flexion was passive, with constant muscle forces and varying external force acting on tibia. Knee flexion angle was from 80 to 150 degrees. As a result, the internal rotation of tibia varied much by using anatomical or plate patella than dome or cylinder shape. Although patellar contact force did not change much, tibial contact balances were better on dome and cylinder patella and the medial contact forces were larger than lateral on anatomical and plate patella. Thus, the results could be divided into two types, dome/cylinder and plate/anatomical. It might be caused by the variations of patellar rotation angle were large on anatomical and plate patella, though patellar tilt angles were similar in all the cases. We have already reported that the anatomical shape of patella would contact in good medial-lateral balance when tibia moved physiologically, therefore we have predicted the anatomical patella might facilitate the physiological tibiofemoral motion. However, the results were not as we predicted. Actually our previous and this study are not in the same condition; we used a posterior-stabilized type of prosthesis, and the post and cam mechanism could not make the femur roll back during deep knee flexion. It might be better to choose dome or cylinder patella to obtain the stability of tibiofemoral joint, and to choose anatomical or plate to the mobility.
The effect of each step of medial soft tissue releases on the external rotation angle of the femoral component was assessed during posterior stabilized total knee arthroplasty (PS-TKA) with modified gap control technique. Consecutive 840 knees were assessed. During PS-TKA, medial soft tissue release was done to obtain rectangular gap in extension using tensors/balancers. The deep fiber of medial collateral ligament (MCL) was released in all cases. No more release was done in 464 knees. Only anterior fiber of superficial MCL was released in 49 knees, and only posterior fiber of superficial MCL was released in 129 knees. Both fibers were released in 169 knees. Additional pes anserinus was released in 29 knees. Rotation angle of the femoral component was decided based on the flexion gap angle. The angle was compared among the five groups.Introduction
Methods
The hip-knee-ankle (HKA) angle between the mechanical axis of the femur (FM) and the mechanical axis of the tibia (TM) is the standard parameter to assess the coronal alignment of the lower extremity. TM is the line between the center of the tibial spines notch (Point T) and the center of the tibial plafond. However, this theory is based on the premise that TM coincides the anatomical axis of the tibia (TA). Fig.1a shows typical varus knee with medial shift of the tibial articular surface. In this case, TM does not coincide TA. Fig. 2 demonstrates the error of HKA angle when Point T locates medial to TA. Fig.2a shows normal alignment. Fig.2b shows varus alignment. Fig. 2c shows the tibia with medial shift of the tibial articular surface. The tibia has 7 degrees varus articular inclination in Fig.2b and 2c. However, HKA angle is 0 degree in Fig.2c. HKA angle underestimates varus deformity in knees with medial shift of the tibial articular surface. However, the degree of medial shift of the tibial articular surface is obscure. In this study, detailed anatomical configuration of the proximal tibia was evaluated. The effect of the value of HKA angle on the coronal alignment in TKA was then discussed. This study consists of 117 knees. On the AP view radiograph of the tibia, three distance and two angle parameters were measured. Those were tibial articular surface width, distance between medial edge of the tibial articular surface and Point T, distance from TA to Point T. Angle between TM and TA, and the varus inclination angle of the tibial articular surface relative to the perpendicular line to TA.Introduction
Methods
The extension and flexion gaps are affected by different factors in total knee arthroplasty (TKA). Flexion but not extension gap measurements are influenced by posterior cruciate ligament (PCL) preservation or resection and patella reduction or eversion and thigh weight. If the flexion gap is measured with the thigh placed on the tibia, the measurement results must include the thigh weight; nevertheless, there is no detailed report regarding the thigh weight influence on the flexion gap. In this study, we investigated how thigh weight affected flexion gap measurement. Four knees of whole-body fresh-frozen cadavers (Mongolian race) were investigated. The femur and tibia were dissected with a standard measured resection technique. After the femoral component was set, the flexion gap was measured with a knee balancer. The distraction force of 20, 30, and 40 pounds were loaded at the joint level. For each measurement, the influences of the patella reduced or everted (PR or PE) and the PCL preserved or resected (CR or PS) were estimated. The flexion gap was measured five times in four different categories (CR/PR, CR/PE, PS/PR, PS/PE) and the thigh weight was reduced by weights (0, 0.5, 1.0, 2.0, 3.0 kg) using a string and pulley system. During measurement, the femur was just placed on the tibia, and the knee flexion angle was maintained at 90 degrees with a goniometer. After all measurements, the lower limbs were resected, and the thighs were weighed with a scale. Steel-Dwasstest (non-parametric multiple comparison test) were performed for statistical analysis, and p < 0.05 was considered significant.INTRODUCTION
METHODS
Factors influencing flexion angle of the knee before and after PS-TKA were assessed. In 368 PS-TKA cases (71 males and 297 females) by means of modified gap control technique with Stryker NRG system, multi-variance analysis was performed to assess factors influencing flexion angle before TKA and flexion angle 3 weeks after TKA. Their mean age was 74.1 years old. Operative techniques and angle of the components were included as the factors.Purpose
Methods
The aim of this study was to evaluate the shape of patella relative to the femoral epicondylar axis and to find sex differences. Computed tomography (CT) images of 100 knees with tibiofemoral osteoarthritis in 100 patients were prospectively collected. All patients were diagnosed as varus-type osteoarthritis with no destructive patellar deformity. Fifty patients were male and 50 female. The average male age was 70.8±14.6 (mean ± SD) years and the average female age was 73.3±6.7 years. Forty nine knees were right and 51 knees were left. The average height of males was 162.6±7.4 cm and that of females 149.6±5.7 cm. Males were significantly taller than females. The CT scan was performed with 2mm-interval slices in the vertical plane to the long axis of femoral shaft. Every CT image was examined to determine the maximum distance between the medial and lateral femoral epicondyle (inter-epicondylar distance, IED) along the epicondylar axis. The maximum patellar width and thickness were also measured at the image which had these maximum distances, while patellar cartilage thickness in anteroposterior diameter was not measured in this study. For evaluating the patellar size, each measured value was divided by IED and calculated each ratio. The ratio of patellar width to patellar thickness was also calculated. All parameters were compared between males and females. Statistical software Statview ver.5.0 (SAS Institute Inc.) was used for all analyses with significance being set at the 5% level.Objective
Materials and methods
Postoperative functional outcomes and patients’ satisfaction after total knee arthroplasty are associated with postoperative range of motion. Severe deformities require surgical correction such as soft tissue release and appropriate bone resection. The goal of surgery is to correct the contracture and bring the knee to good range of motion. Using gap-balancing technique is one of the major techniques to obtain good range of motion. Although the gaps are well balanced, the thickness of tibial insert would affect the range of motion. In this study, we analyzed the difference between intraoperative extension joint gap and the thickness of implanted insert (DJI). The objective of this study was to investigate whether DJI affected the postoperative extension of the knee. A total of 155 knees were analyzed retrospectively. Subject included 27 males and 128 females with an average of 72.7 ± 7.0 years. The mean preoperative knee flexion angle was 136.1 ± 20.0°and the mean preoperative knee extension deficit was 4.0 ± 6.1°. All the patients had a diagnosis of varus-type osteoarthritis, identical prostheses (Stryker NRG posterior-stabilized type) implanted with a modified gap-balancing technique and no postoperative complications which may have affected the range of motion. Range of motion was measured using a goniometer before surgery and 12 months after surgery. Joint gap between femoral component and proximal tibia in full extension was measured by a tensor/ balancer device which added joint gap an expansion force by 30 inch pounds intra-operatively. Although we empirically regarded the appropriate DJI was 5 mm for this prosthesis, we determined the thickness of the tibial inserts considering preoperative range of motion. Thinner inserts compared with the joint gap was implanted for knees with flexion contracture and thicker inserts was implanted for knees with hyperextension. In this study, to determine the relationship of DJI and flexion contracture, the correlation coefficient between DJI and extension deficit was calculated. The diagram of DJI and postoperative extension angle is shown in Figure 1. The correlation coefficient between DJI and postoperative extension deficit was 0.24, which showed that DJI slightly affected the postoperative extension of the knee. Flexion contracture cannot be corrected by simply adjusting DJI.
The effect of each step of medial soft tissue release was assessed taking the expansion strength and patellar condition into account in five fresh frozen normal cadaver specimens. In each cadaver specimen, only proximal tibia was cut. Then, ACL was cut, and deep MCL fiber was released. This condition was set as “the basic”. Joint gap distance and angle were measured at full extension, 30°, 60°, 90°, 120° flexion and in full flexion. The measurement was firstly done with the standard tensor/balancer with the patella everted, and the next with the offset tensor/balancer with the patella reduced. The torque of 10, 20 and 30 inch-pounds were applied through the specialized torque wrench. After the measurement in “the basic”, PCL, MCL superficial fibres, pes anserinus and semi-membranosus were released step by step. Measuring the joint gap distance and angle with the same scheme above were conducted after the each step.Introduction
Methods
Mobility at insert-tray articulations in mobile bearing knee implant accommodates lower cross-shear at polyethylene (PE) insert, which in turn reduces wear and delamination as well as decreasing constraint forces at implant-bone interfaces. Though, clinical studies disclosed damage due to wear has occurred at these mobile bearing articulations. The primary goal of this study is to investigate the effect of second articulations bearing mobility and surface friction at insert-tray interfaces to stress states at tibial post during deep flexion motion. Figure 1 shows the 3-D computational aided drawing model and finite element model of implant used in this study. LS-DYNA software was employed to develop the dynamic model. Four conditions of models were tested including fixed bearing, as well as models with coefficients of friction of 0.04, 0.10 and 0.15 at tibial-tray interfaces to represent healthy and with debris appearance. A pair of nonlinear springs was positioned both anteriorly and posteriorly to represent ligamentous constraint. The dynamic model was developed to perform position driven motion from 0° to 135° of flexion angle with 0°, 10° and 15° of tibial rotation. The prosthesis components were subjected with a deep squatting force.Introduction
Method & Analysis
Differences in the sizes of femoral and tibial components between females and males, between osteoarthritis (OA) and rheumatoid arthritis (RA), and between measured bone resection and the gap control technique during TKA were assessed. 500 PS-TKAswith the Stryker NRG system in 408 cases were assessed. There were 83 male knees and 417 female knees, and 472 OA knees and 28 RA knees. This study was performed in Japan, and almost all OA knees had varus deformities. In each case, the sizes of the femoral and tibial components were measured on radiographs. The measured sizes represented those of the measured bone resection. TKA was performed by the gap control technique using a tensor/balancer with 30 inch-pounds expansion strength, and the sizes of the femoral and tibial components (used size) were recorded.Purpose:
Method:
Accurate measurement of the extension and flexion gap is important in total knee arthroplasty (TKA). Particularly, the flexion gap may be influenced by several factors; therefore, tension of the posterior cruciate ligament (PCL), knee extensor mechanism, and the thigh weight may need to be considered while estimating the flexion gap. However, there is no comprehensive study on the flexion gap, including an assessment of the influence of gravity on the gap. The purpose of this study is to investigate the influence of PCL, knee extensor mechanism, and thigh weight on the flexion gap by using a fresh frozen cadaver. A fresh frozen lower limb that included the pelvis was used for the assessments. The knee was resected by a measured resection technique and a femoral component was implanted to estimate the component gap. The knee was flexed by precisely 90 degrees using a computer navigation system. The flexion gap was measured in different situations: group A, PCL preserved and patella reduced; group B, PCL preserved and patella everted; group C, PCL resected and patella reduced; and group D, PCL resected and patella everted. In each group, the measurements were obtained under 3 different conditions: 1, knee flexed and the lower limb on the operation table under gravity, as is usually done in TKA; 2, hip and knee flexed 90 degrees to avoid the influence of gravity; and 3, knee set in the same position as in condition 1 and the thigh was held by hand to reduce the influence of the thigh weight.Objective:
Methods:
Following total knee arthroplasty (TKA), some patients show patella baja. It is possible that patella baja after posterior stabilized (PS)-type TKA causes the patellar clunk syndrome and limitation of flexion. The purpose of this study was to examine patellar height before and after PS-type TKA and identify the factors related to the change in patellar height. Lateral X-ray films were taken at 90 degrees flexion before and after TKA using fluoroscopy in 87 patients (95 knees) (Fig. 1a, b). The components and surgical technique for TKA were Scorpio NRG (Stryker) and the modified gap control technique, respectively. The Insall-Salvati ratio (ISR) and the Labelle-Laurin method (LL) were measured as parameters of patellar height (Fig. 1c, d). Posterior condylar offset (PCO) (Fig. 1e), the distance from the anterior femoral line to the tibial tuberosity (TA), and the distance from the tibial tuberosity to the posterior condyle of the femur [TP; {TA-F (the length of the femoral condyle)}] (Fig. 1f) were examined as parameters that could be associated with the change in patellar height. All parameters were divided by patellar length to compensate for the expansion rate in each photograph. The mean LL/P, PCO/P, TA/P, and TP/P before TKA were set at 100%.Introduction
Methods
In varus knee, posterior cruciate ligament (PCL) release has been reported to result in the increase of the flexion gap without significant effect on the extension gap. However, the effect of release on gap angle is still obscure. On the other hand, gap angle and distance measured with the tension devices may vary due to different distraction forces. In this study, difference of gap angle and distance before and after PCL resection in knee extension and 90° flexion was inspected. Effect of different distraction force on gap was also assessed. Fifty cases with medial osteoarthritis undergoing PS-TKA were included in the study. PCL of all the cases were identified intact before resection.INTRODUCTION:
OBJECTIVES:
Total elbow joint arthroplasty has limited longevity and is therefore not appropriate for younger rheumatoid arthritis patients. Arthroplasty using an inter-positional membrane may be another surgical option for this population. However, clinical results for joint arthroplasty using the inter-positional membrane have not traditionally been favorable because rheumatoid activity could not be controlled. Today, rheumatoid activity can be controlled with biologics; therefore, the utility of the inter-positional membrane procedure was re-evaluated. An 8×6 cm sheet of fascia was detached from the patient's tensor fascia lata muscle to produce a JK membrane. The fascia was stretched on a frame and kept in a 2% chromic acid potassium solution for 24 hours. Then, the fascia was exposed to direct sunlight in order to reduce the dichromic acid. The fascia was washed out in running water for 24 hours and was then stored in phenol with the addition of 70% alcohol. Elbow arthroplasties were performed on three elbow joints in two young female patients. The first case had a significantly damaged right elbow joint with severe joint dysfunction. A JK membrane arthroplasty was done for the first case in 2003, when this patient was 34 years old. Biologics were administered with methotrexate after the surgery. The second case demonstrated bilateral ankylosed elbows due to idiopathic juvenile arthritis. Bilateral JK membrane arthroplasties were performed in 2010, when this patient was 32 years old. Several operative and manual manipulations were necessary in order to increase the range of motion following surgery. Biologics were administered with cyclosporine.Objective:
Methods:
Reliability of a gap control technique with the tensor/balancer during PS-TKA was assessed by means of fluoroscopic images after TKA. Thirty-one subjects were selected for assessment. The mean age of the subjects was 73.0 years old. During PS-TKA, a parapatellar approach was used. Cruciate ligaments were excised, and distal femoral and proximal tibial cuts were made. After all osteophytes were removed, the joint gap angle and distance were measured in full extension and at 90° flexion using a tensor/balancer. Medial soft tissue releases were performed and soft tissue balancing was obtained in full extension so that the joint gap angle was 3° or less than 3°. The joint gap angle and distance between femoral and tibial cut surfaces in full extension, and between a tangent to the posterior femoral condyles and tibial cut surface at 90° flexion were measured. The external rotation angle of the anterior and posterior cuts of the femur was decided based on the joint gap angle at 90° flexion. The size of the femoral component was decided based on the joint gap distance in full extension and at 90° flexion. Then only the trial femoral component was inserted. The joint gap angle and distance between the tangent to the condyles of the trial femoral component and tibial cut surface in full extension and at 90° flexion were measured. More than one month after TKA, the fluoroscopic images of the prostheses were taken during knee extension/flexion. Then, a torque of about 5 Nm was applied to the lower leg in order to assess the varus/valgus flexibility during flexion. The pattern matching method was used to measure the 3D movements of the prostheses from the fluoroscopic images. The joint gap angle was calculated in full extension and at 90° flexion. The varus/valgus flexibility at each flexion angle was also assessed.Introduction
Methods
