34 results about "Femur tibia" patented technology

The invention relates to the technical field of finite element modeling, in particular to a kinematics and dynamics index output method based on a human body model, which comprises the following steps of: S1, establishing acceleration modules at the head, the chest, the hip and the lower limbs of the human body model for global and local acceleration and angular velocity output; s2, building displacement modules at the chest, abdomen, knee joints and achilles tendons of the human body model, wherein the displacement modules are used for outputting the compression amount and the elongation amount; and S3, establishing section force modules at the spine, crista iliaca, femur and tibia of the human body model for outputting local force and torque. According to the scheme, the technical problem that kinematics and dynamics indexes of the human body model cannot be effectively extracted in the prior art can be solved, the obtained kinematics and dynamics indexes can be compared with data collected by various sensors in a real physical test, and biological fidelity verification of the human body model is facilitated.

The invention provides a trigger bouncing device and method for a flapping-wing flying robot, and relates to the technical field of bionic robots. The device comprises a bouncing execution mechanism, the bouncing execution mechanism comprises a paw, a tibia and a femur which are connected in sequence, and the tibia and the femur are rotatably connected through a knee joint shaft; the energy storage mechanism comprises an energy storage motor, a lower limiting rod, a fixed pulley, an upper limiting rod, a pulley rope, an energy storage torsion spring and a trigger buckle; wherein the energy storage motor and the lower limiting rod are arranged on the tibia, the knee joint shaft is sleeved with the fixed pulley, the upper limiting rod is arranged on the femur, and the pulley rope sequentially winds the output end of the energy storage motor, the lower limiting rod, the fixed pulley and the upper limiting rod; the two ends of the energy storage torsion spring abut against the tibia and the femur correspondingly, and the trigger buckle can clamp the upper limiting rod at the preset position. Energy is stored through the energy storage torsion spring, the tibia and the femur are pushed to rotate, and bouncing action is conducted. The device achieves a highly bionic effect in appearance, and is more in line with actual leg structures of birds.

The invention provides an osteotomy guider capable of fixing a single condyle and adjusting a gap, and belongs to the technical field of medical apparatuses and instruments. An osteotomy guider upper body; the fixing block is fixedly connected to the lower end of the osteotomy guider upper body; the osteotomy guider lower body is arranged at the lower end of the osteotomy guider upper body; the sliding groove is formed in one side end of the fixing block; the function of adjusting the joint gap and the function of adjusting the thighbone osteotomy amount are added on the basis of an original thighbone osteotomy guider, meanwhile, thighbone single-side fixation is changed into thighbone and tibia double-side fixation, the function of filling the joint gap is achieved without being matched with other instruments for use after modification, the instrument accuracy can be improved, the osteotomy accuracy is guaranteed, and the application range of the thighbone osteotomy guider is widened. Meanwhile, the thighbone and the tibia are fixed on the two sides, so that the stability of the osteotomy position and angle is ensured, and the condition that the osteotomy position and angle deviate is avoided.

The invention discloses an osteotomy plane boundary control method, electronic equipment and a storage medium, and the method comprises the steps: calculating the distance from the center point of an osteotomy pendulum saw to a boundary connecting line of an osteotomy plane, selecting the inward vectors of two edges with the shortest distance, carrying out the weighted summation, taking the weighted summation as a search direction, and carrying out the step-by-step search; the method comprises the following steps of: quickly searching a safe position which is closest to the boundary of a plane position (conforming to the expected movement direction and posture) and is positioned in the boundary of the plane position, and subsequently issuing the safe position to a mechanical arm to drive a surgical tool to move so as to accurately and safely help a doctor to realize osteotomy operation on a thighbone and a tibia. The technical problems that in the prior art, due to the fact that the motion range of an osteotomy swing saw is too large, soft tissue and ligament injuries are caused, and operation precision is reduced are solved.

Bone and joint surface reconstruction methods are disclosed for the therapeutic amelioration of joint defects caused by various conditions, injuries, and diseases to help eliminate or reduce pain and return the joint to its proper bio-mechanical function without the need to replace fully or partially the anatomical joint. The joint may specifically include mammalian joints such as the femorotibial joint, for example. The methods disclosed herein leverage the significant role the subchondral bone plays in the health status of the afflicted joint.

The present application relates to the technical field of medical image processing, and provides a knee femur and tibia segmentation method based on region growing, comprising the following steps: S1, acquiring knee medical images; S2, selecting a growth seed point; S3, coarsely segmenting the knee medical images to obtain knee stem data; S4, finely segmenting the knee medical images to obtain knee connection data; S5, fusing the knee stem data and the knee connection data to obtain knee femur and tibia image data with complete contours; S6, coarsely filling the knee femur and tibia image data to obtain knee femur and tibia image data after coarse filling; and S7, iteratively filling holes in the knee femur and tibia image data by using a three-dimensional sliding window, so as to obtain image data that is consistent with the surrounding data in shape, position and completeness and smoothness. The present application solves the problems of slow segmentation speed, unstable segmentation effect, incomplete segmentation and adhesion in preoperative planning of knee replacement surgery.

The invention relates to the technical field of alloy preparation, and particularly discloses a TC4 alloy, a preparation method thereof and application of the TC4 alloy in preparation of medical thighbone and tibia components. The preparation method of the TC4 alloy specifically comprises the following steps of raw material feeding, electron beam selective melting preparation forming, sand blasting, drying, hot isostatic pressing, heat treatment, grinding and polishing and quality detection. The parameter conditions of hot isostatic pressing are as follows: the temperature is raised to 900-940 DEG C at the temperature raising rate of 8-12 DEG C / min, the pressure is kept at 90-120 MPa, and the temperature and pressure are kept for 90-180 minutes; the parameter conditions of the heat treatment are as follows: first-stage heat preservation is performed for 30-120 minutes under the condition that the temperature is 700-900 DEG C, and then second-stage heat preservation is performed for 3-5 hours under the condition that the temperature is 400-600 DEG C; and argon is filled as protective gas in the whole process. By means of the technical scheme, the anti-fatigue performance of the TC4 alloy can be effectively improved, and the service time of the TC4 alloy thighbone and tibia assembly is prolonged.

The invention discloses a pressurizing positioner for orthopedic surgery, and belongs to the technical field of orthopedic surgery instruments, a non-interference two-dimensional adjusting system is constructed through orthogonal layout of a longitudinal lead screw and a transverse lead screw in combination with a plurality of groups of sliding block-sliding groove matching structures, the longitudinal lead screw is in threaded connection with a first sliding block through a first through hole, and the transverse lead screw is in threaded connection with a second sliding block through a second through hole. Linear adjustment of the upper positioning plate in the vertical direction is achieved, and radial deviation in the adjusting process is eliminated through the limiting effect of the first side sliding groove on the first sliding block. A transverse lead screw drives an upper positioning plate to move horizontally through threaded transmission of a transverse moving block, a second side sliding groove is in sliding fit with a second sliding block to ensure the straightness of horizontal adjustment, meanwhile, a lower positioning plate is in sliding connection with a sliding rod through a fourth sliding block, the position can be adjusted in a self-adaptive mode according to the bone form, cooperative positioning is formed by the lower positioning plate and the upper positioning plate, and the positioning accuracy is improved. And the surgical requirements of irregular bones such as femoral bones and tibia can be accurately met, and the secondary adjustment probability caused by positioning deviation is remarkably reduced.

The invention relates to the technical field of orthopedic physiotherapy lamps, in particular to an irradiation-range-adjustable ultraviolet photocuring lamp for orthopedic surgery, which comprises a mounting frame, two fixed lamp rows are fixedly connected to the outer wall of the bottom of the mounting frame, two symmetrically distributed fixed frames are fixedly connected to the outer wall of the mounting frame, and two limiting slide rails are fixedly connected to the outer walls of the two fixed frames. And two movable lamp rows are arranged below the two limiting sliding rails. The bidirectional rack plate is controlled to move through the rotary knob to drive the gear set and the deformation sliding rod, so that the fixed lamp row and the movable lamp row are changed into rectangular arrangement from square arrangement, the irradiation length is remarkably increased, and the lamp array is suitable for long-range uniform curing of four limbs (such as thighbone, tibia and forearm); the reflector frame is turned over inwards under the action of the torsional spring to reflect light above, the irradiation width is further widened, edge strength attenuation is avoided, and in the lamp array deformation process, the length of the electric wire is dynamically adjusted through the adjusting sliding rod and the spring sliding frame.

An embodiment provides a method for measuring a femoral anterior angle and a tibial torsion angle by using artificial intelligence, the method comprising the steps of: (a) obtaining, by a CT scanner, 2D CT images of the femur, the tibia, and the malleolus of a patient; (b) storing, in a big-data unit, the 2D CT images transmitted from the CT scanner; (c) setting, by an artificial intelligence unit, a first baseline related to the femoral head and neck, a second baseline related to the lower femoral, a third baseline related to the upper tibial, and a fourth baseline related to the malleolus, on the basis of the 2D CT images; and (d) measuring, by an angle measurement unit, a femoral anterior angle formed between the first baseline and the second baseline, and a tibial torsion angle formed between the third baseline and the fourth baseline.

The invention provides a method and a device for determining a postoperative prosthesis sagittal view angle based on a knee joint lateral position film. The method comprises the following steps: acquiring a knee joint lateral position X-ray full-length film; key anatomical mark points of the femur, the tibia and the prosthesis are recognized based on the deep convolution model; fitting a central axis and an anatomical axis based on the key anatomical mark points; and calculating the sagittal view angle of the postoperative prosthesis through the central axis and the anatomical axis. According to the method, based on the knee joint lateral X-ray full-length film, the anatomical axes of the femur and the tibia are accurately fitted through an algorithm, and overall evaluation of the sagittal view angle of the prosthesis is achieved.

The present invention provides a trigger-bouncing device and method for a flapping-wing flying robot, relating to the field of bionic robotics. The device comprises a bouncing actuator comprising a claw, tibia, and femur connected in sequence, the tibia and femur being rotatably connected via a knee joint axis; an energy storage mechanism comprising an energy storage motor, a lower limit rod, a fixed pulley, an upper limit rod, a pulley rope, an energy storage torsion spring, and a trigger trigger. The energy storage motor and lower limit rod are mounted on the tibia, the fixed pulley is mounted on the knee joint axis, and the upper limit rod is mounted on the femur. The pulley rope is sequentially wound around the output end of the energy storage motor, the lower limit rod, the fixed pulley, and the upper limit rod. The two ends of the energy storage torsion spring respectively abut against the tibia and femur, and the trigger trigger can lock the upper limit rod in a preset position. The energy stored in the energy storage torsion spring drives the tibia and femur to rotate, thereby performing a bouncing action. The device achieves a highly bionic appearance, more in line with the actual leg structure of a bird.

The invention relates to a thighbone and tibia gap measuring device and system and a knee joint operation system. The thighbone and tibia gap measuring device comprises an air bag unit, an upper platform unit, a lower platform unit, a limiting unit and a pressure monitoring unit. The femur and tibia gap measuring device has the advantages that the femur and tibia gap measuring device is of an ultra-thin structure and can be conveniently placed in a joint gap of a femur and a tibia before an operation, so that gap measurement before osteotomy is met; through pressure monitoring, the joint gap value can be obtained in real time, so that the osteotomy efficiency is improved, the osteotomy amount is reduced, and excessive osteotomy is avoided; the method is high in universality and can be suitable for different measurement scenes; cost is low, and large-scale popularization and use are facilitated.

The present invention discloses a knee joint positioning method based on deep learning. The invention only needs to input the T1 image of the corresponding knee joint, and can output the corresponding scanning surface parameters to achieve positioning. For the knee joint image, the femur and tibia of the corresponding knee joint are first segmented by Unet; then, based on the segmentation results of the femur and tibia, special points are calculated and positioning lines are drawn; then, based on the type of surface to be positioned, the scanning surface parameters are calculated according to the parameters of the positioning line; finally, the parameters are input into the nuclear magnetic resonance scanning machine to complete the positioning of the knee joint. This method is an end-to-end method that can greatly reduce the workload of doctors. At the same time, experimental results show that this method has good knee joint positioning accuracy.

A method of evaluating a knee joint including a femur, a tibia, and ligaments, includes: inserting into the joint a tensioner-balancer; moving the joint while using the tensioner-balancer to maintain predetermined distraction force or distraction height, and collecting height and force data; deriving ligament displacement data and load data from the height and distraction data; processing the data into a digital model of the joint, including a characterization curve for a plurality of flexion angles; importing into the model implant geometry having femoral and tibial components, each having a back surface; updating the model with a location of femoral and tibial cuts, positioned such that when the components are placed in the joint with their back surfaces against the respective cuts, the implant will position the joint to function in a selected portion of the curve; and storing the model.

A femur-first orthopaedic surgical procedure may include using a surgical navigation system to perform one or more initial measurements on a femur of a patient, a tibia of the patient, or both and to develop a surgical plan for the orthopaedic surgical procedure based on the one or more initial measurements, performing a first resection of the femur, using the surgical navigation system to perform one or more later measurements of the tibia that were inaccessible prior to the first resection of the femur and to confirm the surgical plan based on the one or more later measurements of the tibia, performing a tibial resection of the tibia based on a planned tibial resection plane of the surgical plan after confirming the surgical plan, and performing additional resections of the femur based on planned femoral resection planes of the surgical plan after confirming the surgical plan.

The present invention relates to a cross-replacement artificial knee. A knee prosthesis is capable of moving between an extended position and a flexed position. The knee prosthesis includes: a femoral component configured to be mounted to a femur; a tibial component configured to be mounted to a tibia; a column fixedly connected to one of the femoral component and the tibial component; and a contoured recess defined on the other of the femoral component and the tibial component, the contoured recess configured to be engaged by the column in an extended position or a flexed position of the knee prosthesis. The knee prosthesis may also include an artificial ligament extending between the femoral component and the tibial component. The column and the ligament mimic one of the ACL and the PCL.

A method of evaluating a knee joint which includes a femur, a tibia, and ligaments, includes: inserting into a lateral or medial compartment of the joint a tensioner-balancer having apparatus for applying distraction force; moving the joint within its range of motion; maintaining a predetermined distraction load range or a predetermined distraction height range; collecting distraction height and force data of the femur relative to the tibia; deriving ligament displacement and load data from the height and force data; processing the data to produce a digital geometric model of the joint, the model including a ligament force versus displacement characterization curve for each of a plurality of flexion angles of the femur relative to the tibia; using a software application, evaluating the digital geometric model and selecting a portion of the curve that represents a predetermined desired level of ligament tautness; and storing the digital geometric model.

A method of evaluating a human knee joint including a femur bone, a tibia bone, and ligaments. The method includes: inserting into the joint a tensioner-balancer that includes at least one force sensor; providing an electronic receiving device; moving the knee joint through at least a portion of its range of motion; using the electronic receiving device to collect data from the at least one force sensor; processing the collected force data to produce a digital geometric model of the knee joint, wherein the data includes: a medial spline representing a locus of points of contact of a medial condyle of the femur F with the tensioner-balancer, over a range of knee flexion angles; and a lateral spline representing the locus of points of contact of the femur F with the tensioner-balancer, over a range of knee flexion angles; and storing the digital geometric model for further use.

The present invention discloses a medullary cavity reamer system, including: medullary cavity reamers of several specifications; and a distal reamer, the distal reamer including a distal reamer blade and a distal reamer rod, the distal reamer also including an inner cavity, the inner cavity is opened in the distal reamer, one end of the inner cavity is open, and the open end extends to the end of the distal reamer blade; the medullary cavity reamer can be extended into the inner cavity. The medullary cavity reamer system disclosed by the present invention combines two reamers for reaming, improves the accuracy of the reaming position, and prevents the position difference and reference difference caused by frequent replacement of reamers, reduces the doctor's memory task, and facilitates the progress of the operation; during the operation, the distal reamer always uses the medullary cavity reamer as the reference for penetration, ensuring the same reference, and can be used for both femur and tibia, and the shape of the distal reamer can also be designed according to the shape of the revision prosthesis.

The invention discloses an anti-retreating intramedullary nail, and relates to the technical field of intramedullary nails. The anti-retreating intramedullary nail comprises a main nail body, the main nail body is arranged in a marrow cavity along a femur and a tibia axis, an anti-falling part is arranged at the top of the main nail body, and the anti-falling part is in bent transition connection with the main nail body; a hollow channel is formed in the anti-falling part and the main nail body, a fixing needle is arranged in the hollow channel in a penetrating mode, the fixing needle is a kirschner wire which is commonly used in clinic and has different diameters, and the tail end of the fixing needle can be bent. The nail has the beneficial effects of preventing the nail from falling off and rotating, improving the operation operability, increasing the stability in a marrow cavity and the like. The device can provide a better treatment effect and promote the rehabilitation of a patient in a fracture repair operation.

The present invention relates to the field of motion analysis technology and provides a knee joint motion analysis method, comprising: S1: placing the knee joint in two X-ray devices and continuously taking X-ray images at different times; S2: marking two-dimensional anatomical feature points on the two X-ray images taken at the same time; S3: connecting the virtual X-ray light sources of the two X-ray devices with the two-dimensional anatomical feature points on the images, and using the intersection of the two connecting lines or the midpoint of the line segment with the closest distance between the two connecting lines as a three-dimensional anatomical feature point; S4: repeating step S3 to obtain a set of three-dimensional anatomical feature points of the knee joint; S5: establishing a local coordinate system including the femur, tibia, and patella based on the three-dimensional anatomical feature points in the set, and for any two coordinate systems, calculating the rotation matrix and displacement vector of one coordinate system relative to the other coordinate system to obtain the kinematic parameters of the patellofemoral and tibiofemoral joints. The spatial coordinate system of the bone is directly reconstructed from the feature points of the biplane images, thereby achieving rapid knee joint kinematic analysis.

The adjustable knee rehabilitation brace comprises a rigid supporting framework, an active adjusting module and a flexible follow-up structure, and the rigid supporting framework comprises a thigh support for fixing thighs, a shank support for fixing shanks and a composite hinge mechanism for connecting the thigh support and the shank support. According to the technical scheme, through collaborative design of the composite hinge mechanism, the first angle adjustor and the second angle adjustor, independent and accurate adjustment of a sagittal plane and a frontal plane is achieved, the knee joint varus or valgus force line can be corrected, more complex rehabilitation requirements are met, the bionic air bag array is controlled through three-area independent pressure, and the rehabilitation effect is good. The pressure distribution of a femur-tibia articular surface can be dynamically matched, the risk of secondary injury is effectively reduced, static fixation of the brace is changed into dynamic self-adaptive support, the pressure distribution is adjusted in different activity states, the comfort and the wearing compliance are remarkably improved, and proprioceptive recovery is possibly promoted through pressure feedback.

According to the segmentation and key point detection method and system suitable for the lower limb X-ray full-length film, the terminal and the medium provided by the invention, the model provided by the invention not only can automatically segment areas such as femur, tibia and fibula in the lower limb X-ray full-length film, but also can utilize the segmented areas to assist in identifying anatomical mark points of the lower limb; therefore, intelligent detection of the key points of the two-dimensional screen of the HTO operation and intelligent planning of the HTO operation are realized. According to the invention, operators can be copied, key points can be automatically detected, and the diagnosis efficiency of doctors can be improved. According to the method, the accuracy of the model in segmentation and detection is improved by optimizing a post-processing method of nnU-Net and a data enhancement and threshold screening method in YOLOv5.

The utility model relates to the technical field of experimental injection, in particular to a device suitable for thighbone and tibia injection of experimental animals, which comprises an injection cylinder placing seat, an arc-shaped groove is arranged at the top end of the outer wall of the injection cylinder placing seat, and an injection cylinder main body is arranged at the top end of the outer wall of the injection cylinder placing seat through the arc-shaped groove. The left side of the outer wall of the syringe body is connected with a piston rod in a sliding mode, the right end of the syringe body is communicated with a sliding barrel, the outer wall of the sliding barrel is connected with a sleeve in a sliding mode, and the right side of the outer wall of the syringe containing base is provided with a backward moving component enabling the sleeve to move backwards. A piston rod is extruded through a push rod and a push plate, so that in the liquid discharging process of a needle head, a movable seat is pulled to move through an electric control telescopic rod, the movable seat can drive a sleeve and the needle head to move backwards in the liquid discharging process, and therefore the situation that liquid is sprayed and overflows due to the fact that the internal pressure of the thighbone and the tibia is too large in the liquid injection process can be prevented.

The invention discloses an artificial ligament for cruciate ligament reconstruction, which relates to the technical field of artificial ligaments, and comprises a ligament main body, two ligament support sheaths and two extrusion screws, the ligament body comprises a free section and two longitudinally and transversely woven sections, the ligament body, the free section and the longitudinally and transversely woven sections are all in a circular ring shape, the free section is located between the two longitudinally and transversely woven sections and provided with a plurality of free ligament strips, the longitudinally and transversely woven sections are formed by staggering a plurality of transverse woven strips and longitudinal woven strips, and the end of each free ligament strip is connected with one transverse woven strip and one longitudinal woven strip. Traction members are arranged at the ends, away from the free sections, of the longitudinal-transverse weaving sections A plurality of staggered grooves are formed in the outer side walls of the ligament supporting sheaths, one ends of the ligament supporting sheaths are of an expandable multi-valve structure, internal threaded holes are formed in the ligament supporting sheaths, and the two ligament supporting sheaths are correspondingly arranged in a femur tunnel and a tibia tunnel respectively. The outer side wall of the extrusion screw is provided with an external thread which can be connected with the internal threaded hole and drive the multi-petal structure to open and extrude the inner wall of the bone tunnel. The risk of postoperative ligament loosening can be reduced, and the long-term curative effect of a ligament operation is improved.

The invention discloses an auxiliary distraction device for knee joint surgery, and relates to the technical field of medical auxiliary instruments, the auxiliary distraction device comprises a holding part, a rotating shaft, two distraction arms and a self-adaptive supporting mechanism, and the self-adaptive supporting mechanism comprises a fulcrum block; the force transmission assembly is arranged in the distraction arm, connected with the fulcrum block and used for converting the extrusion force borne by the fulcrum block into linear displacement; and the force feedback assembly is connected with the force transmission assembly and is used for detecting the extrusion force and visualizing the numerical value of the extrusion force. The multiple fulcrum blocks form effective surface contact, concentrated force is dispersed to the multiple supporting points, the peak value of the pressure intensity of the surfaces of the thighbone and the tibia is greatly reduced, the fulcrum blocks are automatically attached to the complex contours of the surfaces of the tibia and the thighbone, then uniform and soft supporting is provided, and through the force feedback assembly, the supporting effect is good. The extrusion force of the fulcrum block on the knee joint tissue can be visualized, and the degree of dependence on doctor experience is reduced.

Methods and systems for performing a knee replacement procedure include analyzing images of a patient's patellofemoral and femoro-tibial joints in multiple flexion positions to identify preoperative knee joint geometry. A statistical patient model predicts prosthetic knee implant performance based on preoperative knee joint geometry and given prosthetic knee implant implantation parameters to calculate an optimized surgical plan for performing the procedure using a computer-assisted surgery system that can use fiducial markers fixed to patient tissue. The model can include optional patient motion for adjusting motion profiles for plan optimization.

A method for imparting tension across a human knee joint which includes a femur bone, a tibia bone, a patella bone, a patellar tendon, and ligaments, wherein the ligaments and patellar tendon are under anatomical tension to connect the femur and tibia together, creating a load-bearing articulating joint. The method includes: providing a tensioning device, including: a baseplate; a top plate; and a linkage interconnecting the baseplate and the top plate and operable to move the tensioning device between retracted and extended positions, wherein the top plate is pivotally connected to the linkage so as to be able to freely pivot about a pivot axis; positioning the tensioning device between the femur and the tibia; applying an actuating force to the linkage to move the tensioning device towards the extended position, so as to impart a controlled separating force driving the femur and tibia apart to extend the ligaments.

The utility model provides a cold and hot kneecap which comprises a kneecap body, and the kneecap body is provided with a cold and hot assembly installation portion and a first fixing portion. A cold and hot assembly is arranged on the cold and hot assembly mounting part; a cold and hot assembly mounting hole is formed in the kneecap body; the cold and hot assembly is provided with a mounting part, the mounting part comprises an extending part and a resisting part, the cold and hot assembly further comprises a fixing piece, and during mounting, the extending part penetrates through the cold and hot assembly mounting hole; the resisting part abuts against the outer side of a cold and hot assembly mounting hole in the kneecap body, and the fixing piece abuts against the inner side of the cold and hot assembly mounting hole. According to the structure, the first fixing part can surround the thigh and is used for assisting in fixing the cold and hot assembly to the knee, the cold and hot assembly can make direct contact with the joint of the patella, the femur and the tibia through the structure, and the cold and hot compress effect is improved; the cold and hot assembly is installed on the kneecap body through the installation part and connected through the fixing piece, and installation and disassembly are convenient. And the kneecap is not provided with a power supply, so that the burden of the leg cannot be increased.