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Background Although dynamic knee valgus can be visually identified using the 2D frontal plane projection angle (FPPA), the validity of the FPPA in terms of predicting frontal plane knee kinematics has been questioned. The biomechanical utility of the FPPA may lie in its ability to predict frontal plane knee moments. Hypothesis/Purpose The purpose of the current study was to comprehensively evaluate the ability of the FPPA to predict the frontal plane knee kinetics (peak moment, average moment, and moment at peak knee flexion) across a wide range of tasks (stepping, landing, and change of direction). Design Crossover Study Design. Methods Three-dimensional lower-extremity kinetics and 2D video were obtained from 39 healthy athletes (15 males and 24 females) during execution of six tasks (step down, drop jump, lateral shuffle, deceleration, triple hop, side-step-cut). Linear regression analysis was performed to determine if the 2D FPPA at peak knee flexion predicted frontal plane knee moment variables during the deceleration phase of each task (peak moment, average moment, moment at peak knee flexion). Results The FPPA was found to significantly predict the peak frontal plane knee moment for two tasks (deceleration and side-step-cut, R² = 12% to 25%), average frontal plane knee moment for five tasks (drop jump, shuffle, deceleration, triple hop, side-step-cut, R² = 15% to 40%), and frontal plane knee moment at peak knee flexion for five tasks (drop jump, shuffle, deceleration, triple hop, side-step-cut, R² = 16% to 45%). Conclusion An increased FPPA (medial knee collapse) predicted increased knee valgus moments (or decreased knee varus moments) during landing and change of direction tasks (but not stepping). However, the predictive ability of the FPPA was weak to moderate. [ABSTRACT FROM AUTHOR]

This work aimed to develop a novel multipurpose device for guided knee flexion-extension, both passively using a motorized pneumatic system and actively (muscle-driven) with the joint unloaded or loaded during dynamic MRI. Secondary objectives were to characterize the participant experience during device use, and present preliminary dynamic MRI data to demonstrate the different device capabilities. Self-reported outcomes were used to characterize the pain, physical exertion and discomfort levels experienced by 10 healthy male participants during four different active knee motion and loading protocols using the novel device. Knee angular data were recorded during the protocols to determine the maximum knee range of motion achievable. Dynamic MRI was acquired for three healthy volunteers during passive, unloaded knee motion using 2D Cartesian TSE, 2D radial GRE and 3D UTE sequences; and during active, unloaded and loaded knee motion using 2D radial GRE imaging. Because of the different MRI sequences used, spatial resolution was inherently lower for active knee motion than for passive motion acquisitions. Depending on the protocol, some participants reported slight pain, mild discomfort and varying levels of physical exertion. On average, participants achieved ∼40° of knee flexion; loaded conditions can create knee moments up to 27 Nm. High quality imaging data were obtained during different motion and loading conditions. Dynamic 3D data allowed to retrospectively extract arbitrarily oriented slices. A novel multipurpose device for guided, physiologically relevant knee motion and loading during dynamic MRI was developed. Device use was well tolerated and suitable for acquiring high quality images during different motion and loading conditions. Different bone positions between loaded and unloaded conditions were likely due to out-of-plane motion, particularly because image registration was not performed. Ultimately, this device could be used to advance our understanding of physiological and pathological joint mechanics. [ABSTRACT FROM AUTHOR]

To assess a relationship between lower limb muscle activity and the frontal plane knee kinematics during a single-legged drop jump. Correlation study; Functional Anatomy Laboratory. 35 healthy collegiate male athletes. Muscle activity (%MVIC) of gluteus maximus, gluteus medius, biceps femoris, semitendinosus, vastus medialis quadriceps, vastus lateralis quadriceps, medial gastrocnemius and lateral gastrocnemius; peak knee frontal plane projection angle; and Pearson's correlation coefficients between muscle activity and peak knee frontal plane projection angle. All outcomes were assessed for both dominant and non-dominant limbs. Significant correlations (r = 0.46–0.60, P < 0.05) were found between the muscle activities of the gluteus maximus, gluteus medius, biceps femoris, and semitendinosus, when compared to the knee frontal plane projection angle. Gluteal muscles and hamstring muscles are associated with the peak knee frontal plane projection angle during a single-legged drop jump test. Thus, gluteal and hamstring muscle activities should be considered when developing rehabilitation or injury prevention programs. • Gluteal muscles and hamstring muscle activity is associated with peak knee frontal plane projection angle. • Vastus medalis and vastus lateralis muscles activity is not related to peak knee frontal plane projection angle. • Gastrocnemius muscles activity correlation with peak knee frontal plane projection angle is unclear. • Muscle activity must be considered if the aim is to control knee valgus. [ABSTRACT FROM AUTHOR]

In this article the biomechanics of the tibiofemoral joint, patellofemoral joint and menisci are discussed. Normal knee kinematics depend on soft tissue and bony structures working closely together. Implant manufacturers have considered this interaction in order to design and develop a broad spectrum of total knee replacement (TKR) implant solutions. These designs include anatomic and functional considerations, asymmetric or symmetric implants, mobile or fixed bearing offerings and 'high flexion' designs, as well as designs with a single or multiple radii of curvature. Substantial differences in outcome between these designs remains unproven and TKR design selection at present is therefore often based on other factors, such as cost and the surgeon's familiarity with a particular knee system. An understanding of knee biomechanics pertaining to implant design will help surgeons with implant selection and help refine the method of implantation to optimize patient outcomes. [ABSTRACT FROM AUTHOR]

This article covers the current understanding of human knee biomechanics and how these data are used in the assessment and development of knee replacement implants. Extensive and well corroborated data is available to the surgeon and engineer implant designer to aid in the design of new implant systems. The forces acting on the human knee joint have been measured experimentally from both external methods and permanently implanted telemetric devices. Motions of the knee are well understood for both the healthy knee as well as all commercially available total knee replacements today. Implant designers are now compelled to use these data in the design and testing of new implant systems. We now have 45 years in the modern age of knee replacement, with many lessons learned to-date, and repeating mistakes can now be avoided with just a fundamental understanding of the available published data on biomechanics and motion of the knee joint. To-date most implant designers have settled upon an averaging approach to the design of implant systems. We have now entered into an age where it is possible to customize implants for each individual patient yet respect all of the hard learned lessons of the past 45 years. [ABSTRACT FROM AUTHOR]

Background: Patellofemoral complications are one of the main problems after total knee arthroplasty (TKA). The design of the TKA component may affect the patellar biomechanics, which may be associated with this postoperative complication. The purpose of this study was to assess the influence of TKA and prosthesis designs on the patellar kinematics and patellofemoral pressure.Methods: Using fresh-frozen cadavers, we measured the patellofemoral pressure, patella offset, and patella tilt in the following 4 conditions: normal knee (patella replacement only), cruciate-retaining TKA, condylar-stabilizing TKA, and posterior-stabilized TKA.Results: The patellofemoral pressure increased significantly after the cruciate-retaining TKA and condylar-stabilizing TKA compared with the normal knee. The patella offset in the normal knee decreased with increasing knee flexion angles, while the patella offset in the TKA knees did not change significantly through the full range of motion. The amount of lateral patella tilt in the normal knee was significantly larger than the TKA knees in the full range of motion.Conclusion: Although the femoral components are designed to reproduce an anatomical patellar tracking, the physiological patellar kinematics were not observed. Relatively high patellofemoral pressure and kinematic change after TKA may be associated with postoperative complications such as the anterior knee pain. [ABSTRACT FROM AUTHOR]

Background: Total knee arthroplasty and its relation to gait abduction or adduction moment has not been fully described.Methods: Gait analysis was performed on 25 patients (27 knees) preoperatively, 6 months and 1 year after total knee arthroplasty. Reflective markers were placed on the lower extremity, and motion data were collected at 60 Hz using 6 infrared cameras. Ground reaction forces were recorded at 960 Hz with a force plate. Stance phase was divided into braking and propulsive phases. Coronal knee angles and moments were calculated. Repeated-measures analysis of variance was used to compare frontal plane knee impulse over time and between the braking and propulsive phases of stance.Results: In varus knees, static alignment was corrected from 2.2° varus to 3.3° valgus and in valgus knees from 15.2° valgus to 2.7° valgus (P < .010). Braking phase adduction impulse decreased from 0.145 to 0.111 at 6 months but increased to 0.126 Nm/kg s (P > .05) at 1 year. Propulsive phase impulse changed from 0.129 to 0.085 and persisted at 1 year. Impulse changed from 0.01 (abduction) to 0.11 Nm/kg s (adduction) at 6 months and persisted (P = .01).Conclusion: Restoration of anatomic alignment and soft tissue balancing changes the lateral loading conditions of valgus knees. Both cases, between 6 months and 1 year, increased peak moment. [ABSTRACT FROM AUTHOR]

Background: ACL injuries are common in sports, which has resulted in the development of risk screening and injury prevention programs to target modifiable neuromuscular risk factors. Previous studies which have analyzed single-leg cutting tasks have reported that the anticipation status of the task (pre-planned vs. unanticipated) has a significant effect on the mechanics of the knee. Hypothesis/Purpose: The purpose of this systematic review is to assess the effect of anticipation on the mechanics of the knee in the sagittal, frontal, and transverse planes during tasks which athletes frequently perform during competition. Study Design: Systematic Review Methods: The following databases were searched using relevant key words and search limits: Pub Med, SPORTDiscus, CINAHL, and Web of Science. A modified version of the Downs and Black checklist was used to assess the methodological quality of the articles by two independent reviewers. Results: 284 articles were identified during the initial database search. After a screening process, 34 articles underwent further review. Of these articles, 13 met the criteria for inclusion in this systematic review. Conclusions: It appears that tasks which do not allow a subject to pre-plan their movement strategy promote knee mechanics which may increase an athlete's risk of injury. Clinical Relevance: Clinicians involved in the development and implementation of ACL injury risk screening and prevention programs may want to consider incorporating tasks which do not allow time for preplanning. These unanticipated tasks may more closely mimic the demands of the sports environment and may promote mechanics which increase the risk of injury. [ABSTRACT FROM AUTHOR]

The mechanical wear and tear of soft connective tissue from repetitive joint loading is a primary factor in degenerative joint disease, and therefore methods are needed to accurately characterize wear in joint structures. Here, we evaluate the accuracy of using a structured light 3D optical scanning system and modeling software to quantify and visualize volume loss in whole human meniscus subjected to in vitro joint loading. Using 3D printed meniscus replicas with known wear volumes, we determined that this novel imaging method has a mean accuracy of approximately 13 mm3, corresponding to a mean error of less than 7% when measuring meniscal volumetric changes of 0.2 cm3 (size of a pea). The imaging method was then applied to measure the in vitro wear of whole human menisci at four time points when a single cadaveric knee was subjected to one million cycles of controlled joint loading. The medial and lateral menisci reached steady state volumetric reductions of 0.72 cm3 and 0.34 cm3 per million cycles, respectively. Colorimetric maps of linear wear depth revealed high wear and deformation in the posterior regions of both the medial and lateral menisci. For the first time, this study has developed a method to accurately characterize volume loss in whole meniscus subjected to in vitro joint loading. This 3D scanning method offers researchers a new investigative tool to study mechanical wear and joint degeneration in meniscus, and other soft connective tissues. [Display omitted] [ABSTRACT FROM AUTHOR]

Background: A smaller knee flexion angle and larger knee valgus angle during weight-bearing activities have been identified as risk factors for non-contact anterior cruciate ligament (ACL) injuries. To prevent such injuries, attention has been focused on the role of hip strength in knee motion control. However, gender differences in the relationship between hip strength and knee kinematics during weight-bearing activities in the frontal plane have not been evaluated. Hypothesis/Purpose: The purpose of this study was to determine the influence of hip strength on knee kinematics in both genders during a single-legged landing task in the frontal plane. The hypotheses were that 1) subjects with a greater hip strength would demonstrate larger knee flexion and smaller knee valgus and internal rotation angles and 2) no gender differences would exist during the single-legged landing task. Methods: Forty-three Japanese collegiate basketball players (20 males, 23 females) participated in this study. Three-dimensional motion analysis was used to evaluate knee kinematics during a single-legged medial drop landing (SML). A hand-held dynamometer was used to assess hip extensor (HEXT), abductor (HAB), and external rotator (in two positions: seated position [SHER] and prone [PHER]) isometric strength. Spearman rank correlation coefficients (ρ) were determined for correlations between hip strength and knee kinematics at initial contact (IC) and peak (PK) during SML (p < 0.05). Results: Negative correlations were observed between the knee valgus angle at IC and HEXT (ρ = -0.48, p = 0.02), HAB (ρ = -0.46, p = 0.03) and PHER (ρ = -0.44, p = 0.04) strength in females. In addition, a significant positive correlation was observed between the knee flexion angle at PK and HEXT strength (ρ = 0.61, p = 0.004) in males. Conclusions: Significant correlations between hip strength and knee kinematics during SML were observed in both genders. Hip strength may, therefore, play an important role in knee motion control during sports activities, suggesting that increased hip strength may help to prevent non-contact ACL injuries in athletes of both genders. Moreover, gender-specific programs maybe needed to control abnormal knee motion, as the influence of hip strength on knee kinematics may differ based on gender. [ABSTRACT FROM AUTHOR]

Abstract: Aseptic loosening and other wear-related complications are some of the most frequent late reasons for revision of total knee arthroplasty (TKA). Periprosthetic osteolysis (PPOL) pre-dates aseptic loosening in many cases, indicating the clinical significance of this pathogenic mechanism. A variety of implant-, surgery- and host-related factors have been delineated to explain the development of PPOL. These factors influence the development of PPOL because of changes in mechanical stresses within the vicinity of the prosthetic device, excessive wear of the polyethylene liner, and joint fluid pressure and flow acting on the peri-implant bone. The process of aseptic loosening is initially governed by factors such as implant/limb alignment, device fixation quality and muscle coordination/strength. Later, large numbers of wear particles detached from TKA trigger and perpetuate particle disease, as highlighted by progressive growth of inflammatory/granulomatous tissue around the joint cavity. An increased accumulation of osteoclasts at the bone–implant interface, impairment of osteoblast function, mechanical stresses and increased production of joint fluid contribute to bone resorption and subsequent loosening of the implant. In addition, hypersensitivity and adverse reactions to metal debris may contribute to aseptic TKA failure, but should be determined more precisely. Patient activity level appears to be the most important factor when the long-term development of PPOL is considered. Surgical technique, implant design and material factors are the most important preventative factors, because they influence both the generation of wear debris and excessive mechanical stresses. New generations of bearing surfaces and designs for TKA should carefully address these important issues in extensive preclinical studies. Currently, there is little evidence that PPOL can be prevented by pharmacological intervention. [Copyright &y& Elsevier]

Summary: Objective: Previous studies have shown that meniscectomy results in an increase of local load transmission and may cause degeneration of the knee cartilage. Using 3D reconstructed T2 mapping, we examined the influence on the femoral cartilage under loading after medial meniscectomy. Design: Ten porcine knees were imaged using a pressure device and a 3.0-T magnetic resonance imaging (MRI) system. Consecutive sagittal T2 maps were obtained in neutral alignment with and without compression, and under compression at 10° varus alignment. After medial meniscectomy, the aforementioned MRI was repeated. Cartilage T2 before and after meniscectomy under each condition were compared at the 12 regions of interest (ROIs) defined on the 3D weight-bearing area of the femoral cartilage. Results: Before meniscectomy, large decreases in T2 under neutral compression were mainly seen at the anterior and central ROIs of the medial cartilage, which shifted to the posterior ROIs after meniscectomy. There were significant differences in decrease in T2 ratio with loading before and after meniscectomy (9.8%/4.3% at the anterior zone, 4.0%/11.4% at the posterior zone, P < 0.05). By applying varus compression, a more remarkable decrease in the cartilage T2 in posterior ROIs after meniscectomy was achieved. (Before/after meniscectomy: 8.7%/2.5% at the anterior zone, 7.2%/18.7% at the posterior zone, P < 0.05). Conclusions: Assuming a decrease in T2 with loading correlated with the applied pressure, a deficiency of the medial meniscus resulted in a shift of the primary area with a maximal decrease of cartilage T2 with loading posteriorly in the porcine knee joint, presumably reflecting the intraarticular environment of load transmission. [Copyright &y& Elsevier]

Abstract: Biomechanical studies have shown that external rotation of the femoral TKA component improves patellar tracking but does not restore it to physiologic values. We hypothesized that this could be due to differences in the trochlear groove geometry of TKA and normal knees. This was investigated via a virtual TKA procedure that mounted femoral components on to 3-dimensional models of healthy femurs, followed by measurement of the trochlear geometry before and after the simulated TKA. The results showed that (1) external rotation of the component brought the trochlear groove closer to normal anatomy than no external rotation; (2) however, even with external rotation, the trochlear anatomy was only partially restored to normal. Further work is needed to determine implications for patellofemoral complications observed with current TKA designs. [ABSTRACT FROM AUTHOR]

Summary: Background: Total meniscectomy has been shown to cause early-onset arthritis in the underlying cartilage and bone in the knee joint, demonstrating that the meniscus plays an important protective role in the load carrying capacity. Relationships between friction and wear in synovial joints are complex due to the biphasic nature of articular cartilage and the time dependency of tribological responses. Determination of friction and wear in the whole natural joint in vitro or in vivo is technically difficult and the tribological effect of meniscectomy has not been previously studied in an articulating knee joint. Objective: The aim of this study was to use a tribological simulation of the medial compartmental bovine knee, to investigate friction and wear, with and without the meniscus. We hypothesised that meniscectomy would lead to elevated contact stress and frictional coefficient across the joint. Methods: Skeletally mature bovine medial compartmental knee joints were dissected and mounted in a pendulum friction simulator, which was used to apply physiologically relevant loading and motion. Wear was quantified using micro-MRI scans and surface profilometry. Results: Knees tested with the intact meniscus showed no change in surface roughness and no detectable cartilage loss or deformation. However, increased contact stress and frictional coefficient upon removal of the meniscus, led to immediate surface fibrillation, biomechanical wear and permanent deformation of cartilage. Conclusions: This study presents, for the first time, an in vitro model simulation system to investigate the tribological effects of meniscectomy and meniscus repair and regeneration. [Copyright &y& Elsevier]

Purpose: The purpose of this study was to measure changes in anterior-posterior (AP) laxity and graft forces after cutting the posterolateral (PL) bundle of the anterior cruciate ligament (ACL). Methods: Twelve fresh-frozen cadaveric knees underwent AP laxity testing at ± 100 N of applied tibial force. Resultant forces in the ACL were recorded during passive extension from 120° to 0° with no tibial force, 100 N of anterior tibial force, 100 N of quadriceps force, and 5 Nm of internal tibial torque. The femoral origin of the PL bundle was identified, the ligament fibers were dissected from bone, and tests were repeated. Results: Cutting the PL bundle significantly increased mean laxity by +1.3 mm (at 0°), +1.1 mm (at 10°), and +0.5 mm (at 30°). For the passive knee extension tests, cutting the PL bundle significantly decreased mean ACL force at 0° for all loading modes; the mean decreases were 31 N (with no tibial force), 50 N (with 100 N of anterior force), 33 N (with 100 N of quadriceps force), and 40 N (with 5 Nm of internal torque). Conclusions: The decreases in ACL force at 0° from cutting the PL bundle are consistent with the commonly accepted view that the PL bundle tightens with knee extension. Cutting the taut PL bundle did significantly increase AP laxity between 0° and 30°, but the increases were relatively small. Therefore we conclude that the PL bundle plays a relatively minor role in controlling anterior tibial translation. Clinical Relevance: In view of our findings, the need to reconstruct the PL bundle for better restoration of a normal AP laxity profile is questioned. [Copyright &y& Elsevier]

Purpose: The purpose of this study was to dynamically assess the native strain patterns of the anteromedial bundle (AMB) and posterolateral bundle (PLB) of the anterior cruciate ligament (ACL) and compare these findings with graft bundle strain patterns after double-bundle (DB) ACL reconstruction with tibial fixation under 40 N of tension at 75° knee flexion (AMB) and under 20 N of tension at 20° knee flexion (PLB) and after single-bundle (SB) reconstruction with tibial fixation under 40 N of tension at 20° knee flexion. Methods: The mean strain pattern of the AMB and PLB of the native ACL of 4 cadaveric knees was measured via differential variable reluctance transducers and 2-dimensional kinematic analysis during passive manual knee flexion-extension under a constant axial compression load. Measurements were repeated after DB and SB ACL reconstruction. Celeration line assessments with a split-middle technique were performed to quantify percent strain/knee flexion-extension angle change at reciprocating bundle function transition points. Results: The DB ACL reconstruction technique displayed reciprocating AMB and PLB strain patterns that more closely replicated those of the native ACL. The SB ACL reconstruction technique tended to replicate AMB strain patterns, suggesting poor bundle function differentiation. Conclusions: The DB ACL reconstruction with differential AMB and PLB tensioning more closely replicated native ACL strain patterns than the SB ACL reconstruction. The SB ACL reconstruction that we used closely simulated native ACL AMB strain patterns; however, PLB function was not restored. Clinical Relevance: The DB ACL reconstruction more closely replicated the AMB and PLB strain patterns of the native ACL. [Copyright &y& Elsevier]

Purpose: Our purpose was to evaluate the role of the posteromedial (PM) bundle of the native posterior cruciate ligament (PCL) in restraining posterior tibial translation and the effects of sectioning of the PM bundle on PCL forces. Methods: The PCL’s femoral origin was mechanically isolated by use of a cylindrical coring cutter, and a cap of bone containing the ligament fibers was attached to a load cell that recorded resultant force in the ligament as the knee was passively extended from 120° to 0° without and with simulated tibial loading conditions. Anteroposterior laxity was also measured after load cell installation. The PM bundle was cut at its femoral origin, and all tests were repeated. Results: Cutting the PM bundle produced small but statistically significant increases in mean laxity at 0° (+1.06 mm) and 10° (+0.83 mm) of flexion; mean laxities at 30°, 45°, 70°, and 90° were unchanged. Forces in the remaining anterolateral bundle were not significantly different from those in the intact ligament for any mode of tibial loading, with the exception of the valgus moment, where sectioning of the PM bundle significantly reduced the PCL force at 0° and 5° of flexion. Conclusions: The relatively small increases in mean laxity after cutting of the PM bundle show that it plays a minor role in restraining posterior tibial translation. The minor changes in ligament force profiles after cutting of the PM bundle indicate that the remaining anterolateral bundle fibers continued to be loaded in a near-normal fashion. Clinical Relevance: This study helps to elucidate the function of the PM bundle in the native PCL. Because only small changes were seen in the biomechanical parameters tested, the rationale for reconstructing this bundle of the PCL could be questioned. [Copyright &y& Elsevier]

Abstract: This study examined the kinematics of a cruciate-retaining (CR) total knee arthroplasty (TKA) component that attempts to enhance knee flexion by improving posterior tibiofemoral articular contact at high-flexion angles. Using an in vitro robotic experimental setup, medial and lateral femoral translations of this CR design were compared with that of a conventional CR TKA design and intact knee under a combined quadriceps and hamstring muscle load. Both CR TKA designs showed similar kinematics throughout the range of flexion (0°-150°). The TKAs restored nearly 80% of the posterior femoral translation of the intact knee at 150°. The posterior cruciate ligament (PCL) forces measured for the high-flexion CR TKA component indicate that the PCL is important in the mid-flexion range but has little effect on knee kinematics at high flexion. [Copyright &y& Elsevier]