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| Revision Knee Arthroplasty: the Case for Metaphyseal Sleeves |
| Authors: Issaq Ahmed, Rohit Maheshwari, Phil Walmsley, Ivan Brenkel Department of Trauma and Orthopaedics, Fife Acute Hospital Trust, Victoria Hospital, Kirkcaldy |
| Immediate Effects of a Knee Brace with a Constraint to Knee Extension on Knee Kinematics and Ground Reaction Forces in a Stop-Jump Task |
| Authors: Bing Yu,*†, Daniel Herman† Jennifer Preston†, William Lu‡, Donald T. Kirkendall†, and William E. Garrett† †From the University of North Carolina at Chapel Hill, ‡the University of Hong Kong, Hong Kong |
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Revision Knee Arthroplasty: the Case for Metaphyseal Sleeves
A total knee replacement (TKR) is a successful surgical treatment for patients with end-stage arthritis. The national joint registries for the UK estimate that more than 63,000 replacements of the knee were carried out in 20091,2. Although the clinical results of primary TKR continue to be excellent, the number of revision procedures required is increasing1,2. In the UK alone 3,798 revisions were performed between 2007/082.
The goals of revision arthroplasty are pain relief, restoration of the anatomical alignment and functional stability and accurate re establishment of the joint line. These revision arthroplasties can be challenging with the need to deal with bone defects, ligament stability and fixation. Careful selection of the appropriate implant is important and should be based on the severity of bone loss and on the status of the ligamentous and soft tissue stabilising structures.
Several systems of classification have been proposed for assessing bone loss prior to revision. The most commonly-used is that of the Anderson Orthopaedic Research Institute (AORI) which classifies the femur (F) and tibia (T) separately3. Type 1 defects are those with an intact cortical rim with localised metaphyseal defects which will not compromise the stability of a revision component. In type 2 there is damaged metaphyseal bone with loss of cancellous bone in the metaphyseal segment. Defects can occur in one femoral condyle or tibial plateau (2A) or in both condyles or plateaux (2B). Finally in type 3 there is deficient metaphyseal bone and cortical rim. Bone loss comprises a major portion of either condyle or plateau. These defects are occasionally associated with detachment of the collateral or patellar ligaments and usually require long-stemmed revision implants with bone grafts or a custom-made hinged prosthesis.
Ideally, the revision knee replacement system will offer the options of adjunctive stem fixation, methods to manage bone loss and various levels of prosthetic constraint. Current treatment options for tibial and femoral bone loss in the revision setting include cement, morselized or structural allograft, metal wedges and augments, and custom or hinge/tumour prostheses. The use of stem extensions and offset stems can assist with component position, supplement fixation, decrease stress at the bone-implant interface, and help address asymmetric bone defects. There are currently no comparative studies to guide the revision surgeon with regards to choice of revision option in managing bone loss. The aim of this article is to describe a relatively new technique in revision knee arthroplasty which specifically addresses large metaphyseal defects which can be associated with both complex primary knee arthroplasty and during revision knee arthroplasty.
The mobile bearing tray revision systemAuthors: Issaq Ahmed, Rohit Maheshwari, Phil Walmsley, Ivan Brenkel Department of Trauma and Orthopaedics, Fife Acute Hospital Trust, Victoria Hospital, Kirkcaldy During the past 2 years we have been using the mobile bearing tray (MBT) revision knee system with metaphyseal sleeves (DePuy Orthopaedics, Warsaw, USA) in all of our revision cases and in complex primaries associated with significant bone loss. The MBT revision tray provides a stable and versatile foundation in the revision knee setting by offering a wide array of intraoperative options to assist the revision knee surgeon when handling bony and soft-tissue deficiencies. There are multiple sizes of tibial components to allow for proximal tibial coverage. Stepped metaphyseal sleeves allow for the filling of bony defects and superior metaphyseal compressive loading. Trial sleeves are sequentially broached until bony defects are overcome and solid fixation in the metaphyseal bone is achieved. Tibial augmentations are also available to manage uncontained bony defects, allowing the surgeon to achieve a stable platform on good bone for excellent fixation. Cemented or uncemented tibial diaphyseal stems are available in various lengths and diameters. The mobile-bearing tibial revision tray allows the revision surgeon to accomplish the goals of filling substantial bony defects, restoring the joint line, and providing a strong platform for solid fixation with compressive loading of bone.
The following is a brief description of the surgical technique that we currently employ when using this revision tray system. All procedures have been carried out by the 2 senior authors (IJB and PW). Preoperative Planning Revision total knee arthroplasty begins with thorough clinical and radiography evaluations. Physical evaluation includes examining the soft tissues and noting previous incisions. Range of motion, ligamentous stability and integrity of the extensor mechanism are evaluated. Patients are also requested to complete functional assessment questionnaires. Radiographic evaluation includes weight bearing biplanar views of the knees and tangential views of the patella to assess the present implant and evaluate bone stock, its alignment as compared to the extremity, location of the anatomic joint line and evaluation of the tibial and femoral bone stock. We do not routinely obtain full length radiographs but these can be helpful in assessing overall alignment. Radiological assessment using standard anteroposterior and lateral views is known to underestimate bone loss5 and therefore in all cases we ensure that allograft is available. Exposure When possible, we prefer to use the scar from the primary procedure. Where parallel incisions are present, the more lateral is usually preferred, because the blood supply to the extensor surface is medially dominant. Fibrous adhesions are carefully released to re-establish the suprapatellar pouch and medial and lateral gutters Where patellar mobilisation difficulties persist, a quadriceps snip, a proximal inverted quadriceps incision (modified V-Y), or a tibial-tubercle osteotomy may be indicated. Multiple intra-operative cultures are obtained at every revision. Extraction of Implants Care is taken to preserve as much bone as possible. We use a selection of tools including thin osteotomes, an oscillating saw, a Gigli saw and various extraction devices. The bone/cement or bone/prosthesis interface is carefully disrupted before extraction is attempted. The implanted components are disengaged and extracted as gently as possible to avoid fracture and unnecessary sacrifice of bone stock. When the entire prosthesis is to be replaced, we remove the femoral component first, because this will enhance access to the proximal tibia. All residual bone cement is cleared. Accurate assessment of the quantity and location of remaining cortical and cancellous bone can now be accurately graded using the AORI system3 and considered in the final assessment of whether augments and sleeves are required to supplement the revision. The most common scenario that we have encountered in our series is a large uncontained osseous defect of the medial tibial plateau with varying amounts of the lateral tibial plateau remaining for structural support. Tibial Preparation For purposes of alignment, we prepare the proximal tibial with reference to the position of an intramedullary (IM) reference guide. The location of the medullary canal is approximated, and the medullary canal is sequentially reamed with progressively larger reamers until firm endosteal engagement is established. The proximal tibia is then prepared using the metaphyseal sleeve broach attached to the appropriate trial stem. The broach is carefully impacted into the tibia until the top surface of the broach is at the desired proximal tibial resection level. If the broach is unstable or if any defect is unfilled, the procedure is repeated with consecutively larger broaches until the desired fit is achieved. Any remaining areas or voids between the periphery of the sleeve and the adjacent bone of the proximal part of the tibia are filled with morselized cancellous bone graft. The broach handle is removed, leaving the last broach in place (Figure 3). The proximal tibia is now resected using the top of the broach as a guide. The trial tibial base plate is assembled with the appropriate-sized trial metaphyseal sleeve and trial stem and inserted.
The joint space is evaluated with spacer blocks to determine the flexion-extension gaps. The balance and symmetry of both the flexion and extension gaps are established as well as whether augments are needed. With the tibia sized and the approximate joint line established, the preliminary femoral component size can be selected by evaluating the explanted component or by sizing against the cutting guide. To decrease the flexion gap without affecting the extension gap, a larger femoral component is applied with the addition of posterior augmentation. This is particularly important where a stem extension is indicated, because the stem extension will determine the anteroposterior positioning of the component and the consequent flexion gap. The alternative is additional distal femoral resection and use of a thicker tibial insert to tighten the flexion gap. However this is generally not recommended, because considerable bone stock has already been sacrificed in the primary procedure, and it is important that additional resection of the distal femur be avoided. To decrease the extension gap without affecting the flexion gap, the distal femur is augmented. It is important to note that this will lower the joint line, which is usually desirable because it is generally found to be elevated in knee revision patients. Femoral Preparation The midline of the femoral trochlea is identified, and the medullary canal drilled to a depth of 3-5 cm. The medullary canal is opened sequentially with reamers of progressively larger size until firm endosteal engagement is established. Femoral metaphyseal sleeves are also available. These are used when severe bone loss is encountered in the femoral notch. Much like tibial metaphyseal sleeves, they allow for the filling of bony defects and give the femoral component a stable base for solid fixation to the metaphyseal bone. The femur is sequentially broached to the desired dimension. Care is taken to ensure that the broach remains centred in the path of the reamers. This will keep the metaphyseal sleeve in the desired anteroposterior position. For femoral rotation, the tibial trial functions as a reference point. In a knee with competent collateral ligaments, we use a spacer block that references the tibial plateau and creates a quadrilateral flexion gap. Anterior resection is performed through the anterior slot. Posterior resection is performed through the slot designated zero or, where there is posterior condyle deficiency, the appropriate 4-mm or 8-mm slot is used to accommodate posterior augments. In most cases, little if any bone is removed from the distal femur, because the joint line is effectively elevated with the removal of the primary femoral component. Each condyle is cut only to the level required to establish a viable surface, with augmentation used to correct imbalance. Final femoral preparation involves notch and chamfer resection. Where augmentation is planned, the appropriate augment buttons are inserted into their receptacles on the finishing guide. The length of the intercondylar box differs for the Sigma stabilised and TC3 femoral components and this needs to be taken into consideration when making the notch cut. Both are indicated on the anterior surface of the guide. The trial femoral component is now assembled and inserted. Once the appropriate thickness polyethylene trial insert is in place, the knee is taken through a range of motion to verify function and stability. We do not routinely replace or revise the patella unless there is established or suspected infection or if it is obviously loose. At this point, the trial components are removed and the final implants are inserted. Implantation of the components Before final implantation of the components the site is thoroughly cleansed with pulsatile lavage and dried. The final appropriate-sized trial metaphyseal sleeve is impacted in the proximal tibial. Next bone cement is prepared and applied to the proximal tibial surface or directly to the underside of the tibial tray component which has been previously attached to the stem. These are then impacted into place and any extruded cement cleared. Attention is then turned to the femur. As with the tibia the metaphyseal sleeve component is impacted into the distal femur. Cement is then applied to the anterior, anterior chamfer and distal surfaces of the femur and the internal posterior and posterior chamfer surfaces of the femoral component. Care is taken to ensure that the medullary canal remains free of cement. The femoral component is then impacted. Once the cement is set the trial insert is removed and the definitive mobile bearing insert introduced into the implanted tibial tray. The freedom to rotate allows the implant to bring the bearing surfaces into congruent low wear contact. Early experience
Immediate Effects of a Knee Brace with a Constraint to Knee Extension on Knee Kinematics and Ground Reaction Forces in a Stop-Jump Task
Authors: Bing Yu,*†, Daniel Herman† Jennifer Preston†, William Lu‡, Donald T. Kirkendall†, and William E. Garrett† †From the University of North Carolina at Chapel Hill, ‡the University of Hong Kong, Hong Kong Introduction Acute ACL injuries are common knee injuries in sports participants.12,25,29 An ACL injury has a devastating effect on the individual, resulting in high levels of short-term disability and increasing the likelihood of secondary knee disorders, such as osteoarthritis, in later life.19,26,29,30,32 In sports, women have an ACL injury rate 3 to 10 times higher than the rate in men.2,8,20,22 The primary mechanism of the injury is non-contact in nature; that is, there is no physical contact between the patient and other people at the time of injury.4,24,26 The non-contact nature of the majority of ACL injuries suggests that the intrinsic forces generated by patients themselves are likely to be an important cause.10,15,16,30 Previous studies have shown that non-contact ACL injuries mainly occur in the performance of certain athletic tasks, such as stop-jump, landing, and cutting.1,2,4,11,14 Previous studies have also shown that female recreational athletes have lower extremity motor controls that may increase the load on their ACLs in specific athletic tasks, in comparison with their male counterparts.7,21 For our long-term studies on the prevention of non-contact ACL injuries, we therefore hypothesised that women tend to have altered lower extremity motor controls that, in specific athletic tasks, frequently bring them close to positions in which non-contact ACL injuries may occur, thereby increasing their risk for non-contact ACL injuries. One of the characteristics of female recreational athletes’ movement is their small knee flexion angle in landing tasks that are preceded with horizontal movements, such as stop-jump tasks.7,21 Regarding biomechanics, decreasing the knee flexion angle at landing increases the loading on the ACL5,13,23,28,31 and thereby increases the risk for ACL injuries. As a natural continuation of our preliminary studies, the purpose of this study was to address the effects of constraining knee extension on lower extremity kinematics and kinetics by having recreational athletes wear a specially designed knee brace during a stop-jump task. It was hypothesized for this study that the specially designed knee brace would significantly increase the knee flexion angle at the landing of the stop-jump task and that the maximum ground reaction forces would be reduced as the knee flexion angle at landing increased.Materials and Methods Twelve male and 12 female healthy recreational athletes between 18 and 28 years of age without known histories of knee disorders were recruited as the subjects for this study (Table 1). A recreational athlete was defined as a person who plays sports 2 to 3 times per week regularly without following a professionally designed training scheme. All subjects were recruited through advertising from the general student population on a university campus. The use of human subjects was approved by the institution’s internal review board.
The newly designed knee brace with a constraint to knee extension was constructed using an existing functional knee brace (4titude; dj Orthopedics, LLC, Vista, Calif). The brace frame was made of 6061-T6 aluminum with upright upper thigh and lower calf cuffs. Hook-and-loop straps are used to attach the brace to the leg (Figure 1). The medium-size brace weighs 20 oz. The new design uses a spring mechanism to constrain knee extension. The resistance mechanism in the hinge (Figure 1) engages at 40° of knee flexion and applies a gradually increasing resistance to knee extension motion up to 10° of knee flexion, at which point a rigid stop prevents further knee extension. The resistive torque is adjustable with a maximum of 3 N•m at 10° of knee flexion. A total of 8 such braces were made for right and left sides in each of the 4 sizes: small, medium, large, and extra large. The athletic task tested in this study was a vertical stop-jump task frequently performed in basketball and volleyball games. This task consists of an approach run, with up to 5 steps, and a 2-footed landing followed by a 2-footed takeoff for the maximum height (Figure 2). A recent review of more than 100 ACL injury cases on videotape3 revealed that 70% of non-contact ACL injuries occurred in stop-jump–related tasks. All subjects underwent testing in the Motion Analysis Laboratory of the Center for Human Movement Science of the University of North Carolina at Chapel Hill. Subjects signed informed consent forms before data collection. Subjects were instructed to have a 10-minute warm-up before data collection. The stop-jump task and the knee braces were described to the subject; demonstration of the task was avoided to minimise coaching effects. All subjects were blinded to the hypothesis of this study. Passive reflective markers were placed on each subject bilaterally at the anterior superior iliac spine, lateral malleolus, upper anterior aspect of the tibia, and lower anterior aspect of the tibia. A marker was also placed on the lower spine at the L4-L5 joint.17 The subjects performed the stop-jump task with the above-described markers. Each subject performed 5 successful trials of the stop-jump task at the maximum approach run speed and vertical jump effort he/she felt comfortable with for each of the 2 brace conditions: (1) without brace and (2) with the specially designed knee brace with a constraint to knee extension. The order of the 2 conditions was randomised. The newly designed knee brace, in the appropriate size, was applied to the dominant leg of each subject. The dominant leg was defined as the leg the subject used for single-leg jumping. Three-dimensional (3D) videographic and force plate data were collected for each subject in the stop-jump task for the 2 brace conditions. Six infrared video cameras were used to collect the trajectories of reflective markers on the subject at a frame rate of 120 frames/s. The 6 infrared cameras were calibrated for a 2.5 m long x 1.5 m wide x 2.5 m high space (calibration volume), in which the subject performed the stop-jump task. Two Type 4060A Bertec force plates (Bertec Corp,Worthington, Ohio) were used to collect the ground reaction force signals at a sample rate of 1200 samples/channel/s. The videographic and ground reaction force signals were recorded by the Peak Performance Motus videographic and analog data acquisition system (Peak Performance Technology Inc, Englewood, Colo). The videographic and force plate data collection was time synchronized to 1200 frames/s and 1200 samples/channel/s. Additional 3-D videographic data were collected in a standing trial after all the stop-jump trials. Additional passive reflective markers were placed bilaterally at the medial malleolus and medial and lateral femur condyles. These additional markers were used to estimate the locations of those critical body landmarks that were needed for calculating joint centers but that were not clearly visible when the subjects were performing the stop-jump task. Each subject was asked to stand in the middle of the calibration volume. The 3-D videographic data of all reflective markers were collected. The collected 3-D coordinates of the markers during each stop-jump trial were filtered through a Butterworth lower-pass digital filter at estimated optimum cutoff frequencies.33 The 3-D local coordinates of the medial and lateral femur condyles and medial malleolus were estimated from the 3-D coordinates of markers on the tibia in the standing trial. The 3-D coordinates of the hip joint centers in stop-jump trials were estimated from the 3-D coordinates of the reflective markers on the right and left anterior superior iliac spines and L4-L5 joints and on anatomical data.3 The 3-D coordinates of the medial and lateral femur condyles and medial malleolus in stop-jump trials were estimated from the local coordinates of the corresponding markers in the standing trials, and the direction cosine matrices of the tibia was defined by the 3-D coordinates of the markers on the tibia in stop-jump trials. The knee joint center was defined as the middle point between the medial and lateral femur condyles. The ankle joint center was defined as the middle point between the medial and lateral malleolus. The 3-D coordinates of the knee and ankle joint centers and medial and lateral malleolus were used to define the tibia reference frame. The 3-D coordinates of the knee and hip joint centers and medial and lateral femur condyles were used to define the femur reference frame. The knee joint angles were determined as Euler angles of the tibia reference frame relative to the femur reference frame rotated in order of (1) flexion-extension (z-axis), (2) varus-valgus (y-axis), and (3) internal-external rotation (x-axis).4 The electric signals from the force plates were converted to forces. All signal processing and data reduction were performed using a MotionSoft 3-D motion data reduction program package version 5.5 (MotionSoft Inc, Chapel Hill, NC). The validity and reliability of estimated joint centers and angles can be found in other studies.3,6,17,18,34 The stance phase of the stop-jump task was defined as the duration from the time of landing to the time of takeoff. The time of landing was defined as the time represented by the first frame in which the vertical ground reaction force was greater than zero after the approach run. The time of takeoff was defined as the time represented by the first frame in which the vertical ground reaction force was zero after the landing. The entire stance phase of the stop-jump task was divided into 2 phases: landing and jumping phases. The landing phase was defined as the duration from the time of landing to the time of the maximum knee flexion angle. The jumping phase was defined as the time of the maximum knee flexion angle to the time of takeoff. The approach run speed, knee flexion angle at the landing, maximum knee flexion angle, range of knee flexion motion, and maximum posterior, medial, and vertical ground reaction forces during the landing phase were identified for each trial. The approach run speed was defined as the magnitude of the mean horizontal velocity of the hip joint centers at the time of landing. The range of the knee flexion motion during the landing phase was defined as the difference between the maximum knee flexion angle during the stance phase of the stop-jump task and the knee flexion angle at the landing. The data from the first 3 successful trials in each condition were used for data analysis. Analyses of variation with mixed design were conducted to compare the knee flexion angle at the landing, maximum knee flexion angle, and range of knee flexion motion with maximum posterior, medial, and vertical ground reaction forces during the landing phase of the stop-jump task. The brace condition was treated as a repeated measure, whereas gender was considered an independent measure. In case of a significant brace condition by gender interaction effect on a given dependent variable, analyses of variance were conducted to compare the dependent variable between brace conditions as a repeated measure for each gender and between genders as independent groups for each brace condition. A type I error rate of .05 was chosen to indicate statistical significance in each analysis. All statistical analyses were performed using the SYSTAT computer program package, version 5.0 (SYSTAT Inc, Evanston, Ill). Results There was no significant difference in approach run speed and jump height between brace conditions (P = .825 and .681, respectively). Male subjects’ approach run speed and jump height were significantly greater than those of female subjects (P = .000) (Figures 3 and 4). The specially designed knee brace significantly increased knee flexion angle at the landing in the stop-jump task on average from 27.4° to 32.5° for male subjects and from 22.3° to 27.6° for female subjects (P = .001) (Figure 5). Female subjects had significantly smaller knee flexion angles at the landing in the stop-jump task than did male subjects in both brace and nonbrace conditions (P = .003) (Figure 5). There was no significant effect on the maximum knee flexion angle in the stop-jump task (P = .508) in the knee brace condition (Figure 6). Female subjects had significantly smaller maximum knee flexion angles in the stop-jump task than did male subjects in both brace and nonbrace conditions (P = .001) (Figure 6). The specially designed knee brace significantly reduced the angle of the range of knee flexion motion in the stop-jump task on average from 49.4° to 41.3° for male subjects and from 46.3° to 41.9° for female subjects (P = .015) (Figure 7). There was no significant difference in the range of knee flexion motion in the stop-jump task between male and female subjects (P = .498) (Figure 7). There was no significant effect on the maximum posterior ground reaction force in the stop-jump task from the knee breace (P = .588) (Figure 8). Female subjects had significantly greater posterior ground reaction force in the stop-jump task than did male subjects in both brace and nonbrace conditions (P = .007) (Figure 8). There was no significant effect on the maximum medial ground reaction force in the stop-jump task (P = .708) in the knee brace condition (Figure 9). Female subjects had significantly greater medial ground reaction forces in the stop-jump task than did male subjects in both brace and non-brace conditions (P = .000) (Figure 9). There was no significant effect on the maximum vertical ground reaction force in the stop-jump task (P = .708) in the knee brace condition (Figure 10). Female subjects had significantly greater vertical ground reaction forces in the stop-jump task than did male subjects in both brace and nonbrace conditions (P = .003) (Figure 10).
Discussion The specially designed knee brace did not significantly affect subjects’ performances in the stop-jump tasks. The effect on performances and comfort are common concerns when wearing knee braces in sports. The results of this study show that the mean approach run speed and jump height in the stop-jump task were essentially the same with and without the brace for both male and female subjects. These results suggest that the knee brace used in this study did not consistently affect subjects’ running and jumping performances in a positive or a negative way. To a certain degree, these results indicate that wearing the specially designed knee brace used in this study was not uncomfortable or that the discomfort of wearing the brace was within the range of tolerance. The desired function of the mechanism to constrain knee extension while wearing the specially designed knee brace was to modify lower extremity kinematics and kinetics and to reduce the load on the ACL in athletic tasks by increasing the knee flexion angle at the landing. The results of this study supported our hypothesis that the knee brace would significantly increase the knee flexion angle at the landing in the stop-jump task, but they did not support our hypothesis that the knee brace would significantly reduce the maximum ground reaction forces in the stop-jump task. The significant increase in the knee flexion angle at the landing with the specially designed brace was not likely the effect of approach run speed because there was no significant difference in the approach speeds between the brace and nonbrace conditions. The results of this study also suggested that the specially designed knee brace did not significantly affect the maximum knee flexion angle in the stop-jump task. The significant decrease in the range of knee flexion motion in the stop-jump task with the knee brace was mainly due to the increase in the knee flexion angle at the landing in the knee brace condition. It is likely that the specially designed knee brace did not significantly affect the knee joint resultant forces and moments in this study. These forces and moments are mainly determined by the ground reaction forces and moments because of the relatively small masses and moment of inertia of the foot and shank. There are not likely to be significant differences in knee joint resultant forces and moments if there are no significant differences in ground reaction forces. These results combined together indicated that the specially designed knee brace significantly increased the knee flexion angle at the landing in the stop-jump task, as it was designed to do, but it did not significantly modify other lower extremity kinematics and kinetics in the stop-jump task as it was expected to. Although the specially designed brace did not significantly reduce the maximum ground reaction forces, it should still have served the overall purpose of the design — to reduce the load on the ACL —because increased knee flexion angle at the landing should assist in reducing the anterior shear force applied on the tibia through the patellar tendon. Studies repeatedly have shown that the anterior shear force applied on the tibia through the patellar tendon is a function of the knee flexion angle.4,13,23,28,31 The anterior shear force applied on the tibia through the patellar tendon decreases as the patellar tendon–tibia shaft angle decreases, whereas the patellar tendon–tibia shaft angle decreases as the knee flexion angle increases. Therefore, anterior shear force applied on the tibia through the patellar tendon decreases as the knee flexion angle increases. According to the results of a recent study by Nunley et al,27 the patellar tendon–tibia shaft angle, on average, will be decreased from 19.0° to 17.4° for women and from 13.8° to 12.3° for men when their knee flexion angles increase from 22.3° to 27.6° and from 27.4° to 32.5°, respectively. This means that the anterior shear force applied on the tibia through the patellar tendon, on average, will be reduced by 9% for women and by 13% for men if they increase their knee flexion angles from 22.3° to 27.6° and from 27.4° to 32.5°, respectively. The decrease in the anterior shear force on the tibia should significantly reduce the load on the ACL if other conditions remain the same. The results of this study indicate that increased knee flexion angle at the landing does not necessarily mean a soft landing. A study by DeVita and Skelly 9 showed that subjects had increased knee flexion angles at the landing and decreased maximum vertical ground reaction forces in a drop landing task when using the soft landing technique in comparison with the knee flexion angles and vertical ground forces when using the hard landing technique. An increase in the knee flexion angle at the landing was recommended to reduce the maximum vertical ground reaction force in the landing. The results of our study, however, indicated that increased knee flexion angle was not likely the cause of the decreased maximum ground reaction force in the study by DeVita and Skelly 9 and, therefore, may not be a critical kinematic characteristic of a soft landing. The results of this study are in agreement with the literature. Malinzak et al21 and Chappell et al7 reported that female recreational athletes had decreased knee flexion angles at the landings of running, cutting, drop landing, and stop-jump tasks in comparison with their male counterparts. The results of the present study showed that female subjects had a smaller knee flexion angle at landing than did male subjects at the landing in the stop-jump task. Chappell et al7 reported that female recreational athletes showed increased maximum anterior shear force at the proximal tibia at the landing in 3 stop-jump tasks in comparison with their male counterparts. The posterior ground reaction force is a major contributor to the anterior shear force at the proximal tibia. The results of the present study showed that female subjects, on average, had increased posterior ground reaction force at the landing in the stop-jump task. Chappell et al7 reported that female recreational athletes on average had a valgus moment at the knee, whereas male recreational athletes on average had a varus moment at the knee at the landings of 3 stop-jump tasks. A medial ground reaction force and a valgus knee are contributors to the knee valgus moment. The results of the present study showed that female subjects had increased medial ground reaction force compared with that of male subjects at the landing in the stop-jump task, whereas Malinzak et al21 reported that female recreational athletes on average had valgus knee and male recreational athletes on average had slightly varus knee at the landings of selected athletic tasks. Further studies are needed to fully understand the effects of the specially designed knee brace with constraint to knee extension on the lower extremity kinematics and kinetics in athletic tasks and potential clinical applications. Although in the present study the subjects increased their knee flexion angles at the landing of the stop-jump tasks, it is not clear if the increased knee flexion angles were due to the effect of constraining the knee extension or the effect of knee bracing. We did not find evidence in our extensive literature review showing that knee braces without constraint to knee extension assist in reducing knee flexion angle at landings in athletic tasks. Further studies are needed to determine the effects of constraining the knee extension and of purely knee bracing on the lower extremity kinematics and kinetics in athletic tasks. Also, the results of the present study only showed the immediate effects of the specially designed brace on the knee kinematics and kinetics in the stop-jump task. Further studies are needed to determine the long-term training effects of wearing the specially designed knee brace on the lower extremity kinematics and kinetics as compared with not wearing the brace. The present study only investigated the effects of the specially designed knee brace on ground reaction forces. Although the results of the present study showed that wearing the specially designed knee brace did not significantly affect the performance and ground reaction forces in the stop-jump task, and may not affect knee joint resultant moments in the stop-jump task, it is still possible that wearing a knee brace may affect the muscle contraction patterns and techniques to perform athletic tasks. Further studies are needed to compare knee muscle contraction patterns in the stop-jump task with and without the specially designed knee brace. The results of the present study showed a potential to apply the specially designed knee brace in the rehabilitation of ACL injury patients. The present study, however, only tested the immediate effects of the specially designed brace on the knee kinematics and kinetics of healthy recreational athletes without knee injuries. Further studies are needed to determine the effects of the specially designed knee brace on the lower extremity kinematics and kinetics of patients with ACL injuries in post-injury rehabilitation programs. The results of this study appear to warrant the following conclusions:
Acknowledgements The authors would like to thank dj Orthopedics, LLC, for providing the specially designed knee braces that were used this study. Orthopaedic Product News would like to thank The American Journal of Sports Medicine, from whom this article has been reprinted with permission. References
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