Patellofemoral Joint Contact Forces Research Articles

Skipping has lower knee joint contact forces and higher metabolic cost compared to running

BackgroundThe health benefits of running based exercise programs are plentiful however the high rate of injury in these programs often reduces or eliminates exercise participation. Skipping has shorter steps, reduced vertical ground reaction forces (GRFs), and lower knee extensor torques, compared to running forming the basis of the present hypothesis that skipping would have lower tibio-femoral and patello-femoral joint contact forces. Research questionThe purpose of this study was to compare knee contact forces between skipping and running at the same speed. We also compared metabolic cost of these two gaits to examine the idea that the larger vertical displacement in skipping is a primary factor in its previously reported high metabolic cost. MethodsThe study evaluated joint contact forces through musculoskeletal modeling with GRF and 3D kinematic data and metabolic cost using oxygen consumption data from 20 young, healthy, trained participants as they skipped and ran on an instrumented treadmill at 2.68 m/s. Results: Skipping, compared to running, had substantially lower tibio-femoral and patello-femoral joint contact forces and linear impulses on both per-step and per-kilometer (i.e. lower cumulative loads) bases and also 30% higher metabolic cost. The lower joint loads in skipping were directly associated with its shorter steps and the higher metabolic cost was directly associated to its larger vertical displacement through the stride. SignificanceAs joint loads may predispose individuals to running related injuries, skipping presents an attractive alternative exercise modality with additional increased aerobic benefits.

Hip- and patellofemoral-joint loading during gait are increased in children with idiopathic torsional deformities

BackgroundTorsional deformities of the femur and tibia are associated with gait impairments and joint pain. Several studies have investigated these gait deviations in children with cerebral palsy. However, relatively little is known about gait deviations in children with idiopathic torsion and debate ensues about the management of these patients. Research questionWhat are the effects of idiopathic increased femoral neck anteversion and external tibial torsion on lower-limb kinematics, kinetics and joint loading during gait in children and adolescents. MethodsPatient-specific musculoskeletal models were created for 12 children/adolescents (mean age of 14 years) with torsional deformities using low-dose biplane radiographic imaging and 3D gait analysis. Comparisons of joint motion and net joint torques during gait were made to an age-matched control group with no torsional deformities. The effects of torsional deformities on muscle and joint contact forces were investigated using two personalised musculoskeletal models: one with normal torsion and another with patient-specific torsion. ResultsFemoral neck anteversion and external tibial torsion for the patients were (mean ± SD) 38° ± 9° and 40° ± 10°, respectively. Patients had increased internal hip rotation and external knee rotation as well as increased pelvic tilt during gait. Additionally, the efficacy of the plantarflexor-knee extension mechanism was diminished. Hip joint contact force was higher in the model with patient-specific torsion. The mediolateral component of the patellofemoral joint contact force was also increased despite the magnitude of the resultant patellofemoral contact force being unchanged. SignificanceIt has been previously established that idiopathic lower-limb torsional deformities alter gait kinematics. However, this study also showed that loading of the hip and patellofemoral joints are increased. This is an important insight for the clinical management of these patients and highlights that idiopathic lower-limb torsional deformities are not a purely cosmetic issue.

Effects Of Load Carriage and Step Length Manipulation on Knee Loads During Walking

PURPOSE: Effects of load carriage on medial tibiofemoral joint (mTFJ) and patellofemoral joint (PFJ) contact forces were evaluated using preferred, 7.5% shorter and 7.5% longer step lengths. METHODS: Sixteen male Army ROTC Cadets (20.1 ±2.5 years, 77.4 ±13.4 kg) completed walking treadmill trials (1.3 m/s) with and without 20-kg load carriage. Trials were then collected with altered step lengths (±7.5%) with load carriage. Joint contact forces normalized to body weight (BW) per step and per 1-km were estimated for the mTFJ and PFJ via musculoskeletal modeling. RESULTS: At preferred step length, the load carriage increased peak mTFJ contact force per step by 19.3% (p<0.001, d=1.33) and mTFJ impulse per 1-km by 22% or 89 additional BW*s per km (p<0.001, d=1.49). Relative to body mass, the load carriage increased peak PFJ contact force per step by 14.2% (p<0.001, d=0.66) and PFJ impulse per km by +18.7% or 19 additional BW*s per km (p<0.001, d=0.69). There was a 1:2 relationship between the load carriage and absolute peak mTFJ contact force increase versus a more modest 1:1 relationship between load carriage and absolute peak PFJ contact force increase. Compared with preferred step length with load carriage, a short step with load carriage did not alter mTFJ or PFJ contact forces (all p>0.05). In contrast, a long step magnified the effect of load carriage on all metrics of mTFJ and PFJ contact forces. Specifically, a long step with load carriage increased peak mTFJ contact force by 9.0% (p<0.004, d=0.63) and mTFJ impulse per 1-km by 6.6% or 32.8 additional BW*s per km (p=0.001, d=0.48). A long step increased peak PFJ contact force by 26.6% (p=0.004, d=0.68) and PFJ impulse per 1-km by 22.7% or 27.1 additional BW*s impulse per km (p=0.001, d=0.48) compared with preferred step length with load carriage. A long step with load carriage resulted in 1:3.2 and 1:2.4 relationship between added load weight and absolute increases in peak mTFJ and PFJ contact forces, respectively. CONCLUSIONS: The added load carriage was preferentially borne by the mTFJ with a smaller increase in PFJ contact forces. A short step was not an effective strategy to reduce mTFJ and PFJ loads. A longer than preferred step length, often observed in shorter individuals during formation marching, increased both mTFJ and PFJ contact forces with greatest increases noted in the PFJ.

Are contemporary femoral components sizing and design likely to affect functional results in TKA? A mathematical model of an implanted knee to predict knee forces.

This study is aimed to investigate the effects of the choice of femoral and tibial components on several mechanical outputs that might be associated with total knee replacement surgery outcomes using a validated computational model: the Kansas knee simulator. Two models from the same range of implants were taken into account: Model 1, the femoral component fitted the femoral epiphysis, with physiological positioning of the articulating surface using a 10-mm-thick tibial component, and in Model 2, the femoral component was 4mm smaller than in Model 1, and a 14-mm-thick tibial component was used with a similar tibial resection and the tibio-femoral joint line was 4mm more proximal to compensate the increased posterior bone resection and maintain proper soft-tissue tension in flexion. Changes in reaction forces and contact pressures between the components, changes in extensor muscle forces and changes in patello-femoral joint kinematics during walking gait have been studied. While the computational model predicted that most kinematic and kinetic outputs, including tibio-femoral and patello-femoral joint motions, contact forces, pressures and areas, were similar for Model 1 and Model 2, and a dramatic difference has been found in the extensor muscle forces necessary to flex and extend the knee. To reproduce the same knee motion with a knee reconstructed as in Model 2, a patient would need to generate approximately 40% greater extensor muscle force throughout the gait cycle in order to do so. As a consequence of such a large increase in the extensor muscle force, the knee motions would probably be compromised and, subsequently, a patient with a knee reconstructed as in Model 2 would be less likely to be able to reproduce normal knee function and therefore more likely to report poor outcome.

Reliability and Minimal Detectable Change Values for Predictions of Knee Forces during Gait and Stair Ascent Derived from the FreeBody Musculoskeletal Model of the Lower Limb.

FreeBody is a musculoskeletal model of the lower limb used to calculate predictions of muscle and joint contact forces. The validation of FreeBody has been described in a number of publications; however, its reliability has yet to be established. The purpose of this study was, therefore, to establish the test–retest reliability of FreeBody in a population of healthy adults in order to add support to previous and future research using FreeBody that demonstrates differences between cohorts after an intervention. We hypothesized that test–retest estimations of knee contact forces from FreeBody would demonstrate a high intra-class correlation. Kinematic and kinetic data from nine older participants (4 men: mean age = 63 ± 11 years; 5 women: mean age = 49 ± 4 years) performing level walking and stair ascent was collected on consecutive days and then analyzed using FreeBody. There was a good level of intra-session agreement between the waveforms for the individual trials of each activity during testing session 1 (R = 0.79–0.97). Similarly, overall there was a good inter-session agreement within subjects (R = 0.69–0.97) although some subjects showed better agreement than others. There was a high level of agreement between the group mean waveforms of the two sessions for all variables (R = 0.882–0.997). The intra-class correlation coefficients (ICC) were very high for peak tibiofemoral joint contact forces (TFJ) and hamstring forces during gait, for peak patellofemoral joint contact forces and quadriceps forces during stair ascent and for peak lateral TFJ and the proportion of TFJ accounted for by the medial compartment during both tasks (ICC = 0.86–0.96). Minimal detectable change (MDC) of the peak knee forces during gait ranged between 0.43 and 1.53 × body weight (18–170% of the mean peak values). The smallest MDCs were found for medial TFJ share (4.1 and 5.8% for walking and stair ascent, respectively, or 4.8 and 6.7% of the mean peak values). In conclusion, the results of this study support the use of FreeBody to investigate the effect of interventions on muscle and joint contact forces at the cohort level, but care should be taken if using FreeBody at the subject level.

Normalized patellofemoral joint reaction force is greater in individuals with patellofemoral pain

Patellofemoral pain is a disabling, highly prevalent pathology. Altered patellofemoral contact forces are theorized to contribute to this pain. Musculoskeletal modeling has been employed to better understand the etiology of patellofemoral pain. Currently, there are no data on the effective quadriceps moment arm for individuals with patellofemoral pain, forcing researchers to apply normative values when modeling such individuals. In addition, the ratio of patellofemoral reaction force to quadriceps force is often used as a surrogate for patellofemoral joint contact force, ignoring the fact that the quadriceps efficiency can vary with pathology and intervention. Thus, the purposes of this study were to: (1) quantify the effective quadriceps moment arm in individuals with patellofemoral pain and compare this value to a control cohort and (2) develop a novel methodology for quantifying the normalized patellofemoral joint reaction force in vivo during dynamic activities. Dynamic MR data were captured as subjects with patellofemoral pain (30F/3M) cyclically flexed their knee from 10° to 40°. Data for control subjects (29F/9M) were taken from a previous study. The moment arm data acquired across a large cohort of individuals with patellofemoral pain should help advance musculoskeletal modeling. The primary finding of this study was an increased mean normalized patellofemoral reaction force of 14.9% (maximum values at a knee angle of 10°) in individuals with patellofemoral pain. Understanding changes in the normalized patellofemoral reaction force with pathology may lead to improvements in clinical decision making, and consequently treatments, by providing a more direct measure of altered patellofemoral joint forces.

Anterior referencing of tibial slope in total knee arthroplasty considerably influences knee kinematics: a musculoskeletal simulation study

PurposeIn total knee arthroplasty (TKA), the posterior tibial slope is not always reconstructed correctly, and the knee ligaments may become too tight in flexion. To release a tight flexion gap, surgeons can increase the posterior tibial slope using two surgical resection techniques: the anterior tibial cortex (ACR) or the centre of tibial plateau (CPR) referencing. It is not known how this choice affects the knee laxity and function during activities of daily living. The aim of this study was to investigate the effect of tibial slope on knee laxity, kinematics and forces during a squatting activity using computer simulation techniques. We hypothesised that the effects depend on the referencing technique utilised.MethodsA validated musculoskeletal model of TKA was used. Knee laxity tests were simulated in flexion and extension. Then, a squat motion was simulated to calculate: movement of the tibiofemoral joint (TFJ) contact points and patello-femoral joint (PFJ) contact force. All analyses were repeated with more anterior (−3°), neutral (0°), and more posterior tibial slope (+3°, +6°, +9°), and with two referencing techniques (ACR, CPR).ResultsKnee laxities increased dramatically with more posterior slope with the ACR technique (up to 400%), both in flexion and in extension. The CPR technique, instead, had much smaller effects (up to 42% variations). During squatting, more slope with the ACR technique resulted in larger movements of the TFJ contact point. The PFJ contact force decreased considerably with more slope with the CPR technique (12% body weight reduction every 3° more posterior slope), thanks to the preservation of the patellar height and quadriceps–femur load sharing.ConclusionACR technique alters considerably the knee laxity, both in flexion and extensions, and surgeons should be cautious about its use. More slope with CPR technique induces more favourable TFJ kinematics and loading of the knee extensor apparatus and does not substantially alter knee laxity. Preferably, the tibial slope resection should be pre-planned thoroughly and performed using CPR technique as accurately as possible. Surgeons can directly translate the results of this study into the clinical practice.

Reduced step length reduces knee joint contact forces during running following anterior cruciate ligament reconstruction but does not alter inter-limb asymmetry

BackgroundAnterior cruciate ligament reconstruction is associated with early onset knee osteoarthritis. Running is a typical activity following this surgery, but elevated knee joint contact forces are thought to contribute to osteoarthritis degenerative processes. It is therefore clinically relevant to identify interventions to reduce contact forces during running among individuals after anterior cruciate ligament reconstruction. The primary purpose of this study was to evaluate the effect of reducing step length during running on patellofemoral and tibiofemoral joint contact forces among people with a history of anterior cruciate ligament reconstruction. Inter limb knee joint contact force differences during running were also examined. Methods18 individuals at an average of 54.8months after unilateral anterior cruciate ligament reconstruction ran in 3 step length conditions (preferred, −5%, −10%). Bilateral patellofemoral, tibiofemoral, and medial tibiofemoral compartment peak force, loading rate, impulse, and impulse per kilometer were evaluated between step length conditions and limbs using separate 2 factor analyses of variance. FindingsReducing step length 5% decreased patellofemoral, tibiofemoral, and medial tibiofemoral compartment peak force, impulse, and impulse per kilometer bilaterally. A 10% step length reduction further decreased peak forces and force impulses, but did not further reduce force impulses per kilometer. Tibiofemoral joint impulse, impulse per kilometer, and patellofemoral joint loading rate were lower in the previously injured limb compared to the contralateral limb. InterpretationRunning with a shorter step length is a feasible clinical intervention to reduce knee joint contact forces during running among people with a history of anterior cruciate ligament reconstruction.

Individual muscle contributions to ground reaction and to joint contact, ligament and bone forces during normal gait

Recent developments in musculoskeletal modelling have enabled numerous studies to explore how individual muscles contribute to progression, support and mechanical loading during gait. However, the literature still lacks data on the contributions of musculo-tendon forces to several structures, making it difficult to determine the primary contributors. The aim of the present study was thus to provide a comprehensive investigation of individual muscle contributions to ground reaction (i.e. 3D ground reaction force and moment), and to joint contact, ligament and bone (i.e. compression?traction of bony segments) forces during normal gait. We used a 3D lower limb musculoskeletal model coupled with a static optimisation method using a pseudo-inverse, which indeed yielded data on individual muscle contributions currently missing from the literature. We report the individual muscle contributions to (i) 3D ground reaction force and moment, (ii) hip, tibiofemoral, patellofemoral and ankle joint contact forces, (iii) tibiofemoral and ankle ligament forces, and (iv) femur, patella and tibia bone forces. In line with the recent literature, the primary contributors are the vastii, gluteus medius, soleus, rectus femoris, gemellus, quadratus femoris, gluteus maximus, and adductors. While the current observations are made on a generic model, the present method offers a comprehension tool that can shed light on the underlying mechanisms governing the musculoskeletal system.

Dosimétrie des mesures de torsion et d’antéversion des membres inférieurs utilisant l’EOS et le scanner

Torsional deformities of the femur and tibia are associated with gait impairments and joint pain. Several studies have investigated these gait deviations in children with cerebral palsy. However, relatively little is known about gait deviations in children with idiopathic torsion and debate ensues about the management of these patients.What are the effects of idiopathic increased femoral neck anteversion and external tibial torsion on lower-limb kinematics, kinetics and joint loading during gait in children and adolescents.Patient-specific musculoskeletal models were created for 12 children/adolescents (mean age of 14 years) with torsional deformities using low-dose biplane radiographic imaging and 3D gait analysis. Comparisons of joint motion and net joint torques during gait were made to an age-matched control group with no torsional deformities. The effects of torsional deformities on muscle and joint contact forces were investigated using two personalised musculoskeletal models: one with normal torsion and another with patient-specific torsion.Femoral neck anteversion and external tibial torsion for the patients were (mean ± SD) 38° ± 9° and 40° ± 10°, respectively. Patients had increased internal hip rotation and external knee rotation as well as increased pelvic tilt during gait. Additionally, the efficacy of the plantarflexor-knee extension mechanism was diminished. Hip joint contact force was higher in the model with patient-specific torsion. The mediolateral component of the patellofemoral joint contact force was also increased despite the magnitude of the resultant patellofemoral contact force being unchanged.It has been previously established that idiopathic lower-limb torsional deformities alter gait kinematics. However, this study also showed that loading of the hip and patellofemoral joints are increased. This is an important insight for the clinical management of these patients and highlights that idiopathic lower-limb torsional deformities are not a purely cosmetic issue.

Patellofemoral joint contact forces during activities with high knee flexion

The patellofemoral (PF) joint plays an essential role in knee function, but little is known about the in vivo loading conditions at the joint. We hypothesized that the forces at the PF joint exceed the tibiofemoral (TF) forces during activities with high knee flexion. Motion analysis was performed in two patients with telemetric knee implants during walking, stair climbing, sit-to-stand, and squat. TF and PF forces were calculated using a musculoskeletal model, which was validated against the simultaneously measured in vivo TF forces, with mean errors of 10% and 21% for the two subjects. The in vivo peak TF forces of 2.9-3.4 bodyweight (BW) varied little across activities, while the peak PF forces showed significant variability, ranging from less than 1 BW during walking to more than 3 BW during high flexion activities, exceeding the TF forces. Together with previous in vivo measurements at the hip and knee, the PF forces determined here provide evidence that peak forces across these joints reach values of around 3 BW during high flexion activities, also suggesting that the in vivo loading conditions at the knee can only be fully understood if the forces at the TF and the PF joints are considered together.

Knee and hip joint forces – sensitivity to the degrees of freedom classification at the knee

Previous research has demonstrated that the number of degrees of freedom (DOF) modelled at a given joint affects the antagonistic muscle activity predicted by inverse dynamics optimization techniques. This higher level of muscle activity in turn results in greater joint contact forces. For instance, modelling the knee as a 3 DOF joint has been shown to result in higher hip and knee joint forces commensurate with a higher level of muscular activity than when the knee is modelled with 1 DOF. In this study, a previously described musculoskeletal model of the lower limb was used to evaluate the sensitivity of the knee and hip joint contact forces to the DOF at the knee during vertical jumping in both a 1 and a 3 DOF knee model. The 3 DOF knee was found to predict higher tibiofemoral and hip joint contact forces and lower patellofemoral joint contact forces. The magnitude of the difference in hip contact force was at least as significant as that found in previous research exploring the effect of subject-specific hip geometry on hip contact force. This study therefore demonstrates a key sensitivity of knee and hip joint contact force calculations to the DOF at the knee. Finally, it is argued that the results of this study highlight an important physiological question with practical implications for the loading of the structures of the knee; that is, the relative interaction of muscular, ligamentous, and articular structures in creating moment equilibrium at the knee.

Lower-extremity musculoskeletal geometry affects the calculation of patellofemoral forces in vertical jumping and weightlifting

The calculation of the patellofemoral joint contact force using three-dimensional (3D) modelling techniques requires a description of the musculoskeletal geometry of the lower limb. In this study, the influence of the complexity of the muscle model was studied by considering two different muscle models, the Delp and Horsman models. Both models were used to calculate the patellofemoral force during standing, vertical jumping, and Olympic-style weightlifting. The patellofemoral forces predicted by the Horsman model were markedly lower than those predicted by the Delp model in all activities and represented more realistic values when compared with previous work. This was found to be a result of a lower level of redundancy in the Delp model, which forced a higher level of muscular activation in order to allow a viable solution. The higher level of complexity in the Horsman model resulted in a greater degree of redundancy and consequently lower activation and patellofemoral forces. The results of this work demonstrate that a well-posed muscle model must have an adequate degree of complexity to create a sufficient independence, variability, and number of moment arms in order to ensure adequate redundancy of the force-sharing problem such that muscle forces are not overstated.

Joint line elevation in revision TKA leads to increased patellofemoral contact forces

One difficulty in revision total knee arthroplasty (TKA) is the management of distal femoral bone defects in which a joint line elevation (JLE) is likely to occur. Although JLE has been associated with inferior clinical results, the effect that an elevated joint line has on knee contact forces has not been investigated. To understand the clinical observations and elaborate the potential risk associated with a JLE, we performed a virtual TKA on the musculoskeletal models of four subjects. Tibio- and patellofemoral joint contact forces (JCF) were calculated for walking and stair climbing, varying the location of the joint line. An elevation of the joint line primarily affected the patellofemoral joint with JCF increases of as much as 60% of the patient's body weight (BW) at 10-mm JLE and 90% BW at 15-mm JLE, while the largest increase in tibiofemoral JCF was only 14% BW. This data demonstrates the importance of restoring the joint line, as it plays a critical role for the magnitudes of the JCFs, particularly for the patellofemoral joint. JLE caused by managing distal femoral defects with downsizing and proximalizing the femoral component could increase the patellofemoral contact forces, and may be a contributing factor to postoperative complications such as pain, polyethylene wear, and limited function.

How accurate is Whiteside's line as a reference axis in total knee arthroplasty?

There is an increasing focus on the precision with which prostheses in the knee are inserted with advent of computer assisted surgery. Much attention has been paid to the differences between this and conventional alignment jig techniques. Both techniques however rely on accurate identification of bony morphology and utilising this information to correctly orientate the prosthesis. Correct rotational alignment of the femoral prosthesis in total knee arthroplasty is important for correct patella tracking, patellofemoral joint contact forces, varus–valgus positioning in flexion, correct rotational alignment of the tibia in extension and the avoidance of anterior femoral notching. Whiteside's line is considered to be perpendicular to the epicondylar axis and therefore a reliable axis of reference. A cadaveric study was performed to assess the reliability and reproducibility of Whiteside's line in 50 cadaveric distal femora. Our results have shown that Whiteside's line is perpendicular to the epicondylar axis in the majority of cases (mean of 91°). However the variation of values about the mean (range 80–102°), and a SD of 4.7° suggests that this should not be used alone as a rotational assessment guide. Rotation should ideally be checked against several axes to avoid errors in rotation positioning of the femoral prosthesis.

Knee and hip kinetics during normal stair climbing.

Understanding joint kinetics during activities of daily living furthers our understanding of the factors involved in joint pathology and the effects of treatment. In this study, we examined hip and knee joint kinetics during stair climbing in 35 young healthy subjects using a subject-specific knee model to estimate bone-on-bone tibiofemoral and patello-femoral joint contact forces. The net knee forces were below one body weight while the peak posterior-anterior contact force was close to one body weight. The peak distal-proximal contact force was on average 3 times body weight and could be as high as 6 times body weight. These contact forces occurred at a high degree of knee flexion where there is a smaller joint contact area resulting in high contact stresses. The peak knee adduction moment was 0.42 (0.15) Nm/kg while the flexion moment was 1.16 (0.24) Nm/kg. Similar peak moment values, but different curve profiles, were found for the hip. The hip and knee posterior-anterior shear forces and the knee flexion moment were higher during stair climbing than during level walking. The most striking difference between stair ascent and level walking was that the peak patello-femoral contact force was 8 times higher during stair ascent. These data can be used as baseline measures in pathology studies, as input to theoretical joint models, and as input to mechanical joint simulators.

Patellofemoral stresses during open and closed kinetic chain exercises. An analysis using computer simulation.

Rehabilitation of the symptomatic patellofemoral joint aims to strengthen the quadriceps muscles while limiting stresses on the articular cartilage. Some investigators have advocated closed kinetic chain exercises, such as squats, because open kinetic chain exercises, such as leg extensions, have been suspected of placing supraphysiologic stresses on patellofemoral cartilage. We performed computer simulations on geometric data from five cadaveric knees to compare three types of open kinetic chain leg extension exercises (no external load on the ankle, 25-N ankle load, and 100-N ankle load) with closed kinetic chain knee-bend exercises in the range of 20 degrees to 90 degrees of flexion. The exercises were compared in terms of the quadriceps muscle forces, patellofemoral joint contact forces and stresses, and "benefit indices" (the ratio of the quadriceps muscle force to the contact stress). The study revealed that, throughout the entire flexion range, the open kinetic chain stresses were not supraphysiologic nor significantly higher than the closed kinetic chain exercise stresses. These findings are important for patients who have undergone an operation and may feel too unstable on their feet to do closed chain kinetic chain exercises. Open kinetic chain exercises at low flexion angles are also recommended for patients whose proximal patellar lesions preclude loading the patellofemoral joint in deeper flexion.

Influence of patellar thickness on patellar tracking and patellofemoral contact characteristics after total knee arthroplasty

Although total knee arthroplasty (TKA) has become a very common procedure, patellar problems remain a major cause of disability. Patellar thickness is one of the most challenging factors. The influence of patellar thickness on patellofemoral kinematics and contact characteristics following TKA was investigated. Seven unembalmed whole-lower-extremity cadaveric specimens were used. The kinematics was measured with a magnetic tracking device (3Space Tracker System, Polhemus Navigation Sciences Division, Colchester, VT). Contact area was calculated from the kinematic data and the digitized joint surface geometries based on a theoretical method. The patellofemoral joint contact force was measured directly using a uniaxial force transducer. Kinematically, the influence of patellar thickness on patellar flexion, rotation, and proximodistal shift was not significant. Orthopaedic surgeons are often challenged by derangement of the patellofemoral joint, especially following TKA. It is commonly assumed that restoration of overall patellar thickness is most desirable. A thin patella can reduce the contact force, but it also poses the potential risks of stress fracture and anteroposterior instability. Increasing patellar thickness might be expected to increase the effective quadriceps moment arm at low flexion angles of the knee, but potentially reduces the range of motion of the knee and predisposes to patellar subluxation. Either a thicker or a thinner patella had a smaller contact area than intact and normal-thickness patella. Therefore, the surgical technique of patellar resurfacing during TKA should attempt to reproduce the original patellar thickness.

Surgery simulation analysis of anterior advancement of the tibial tuberosity

The objective of this study is to evaluate the surgical outcome of anterior displacement of the tibial tuberosity (Maquet procedure) for reducing patellofemoral joint contact force. The in-vivo experimental knee joint geometric data with a biomechanical model was used to do the simulation of the Maquet procedure. Six healthy young adults performed weight-bearing knee flexion-extension by ascending a one-step stair. Dynamic X-ray images of the knee were continuously recorded by a video-fluoroscopic system. These X-ray images were analysed on a computerized digitizing system to get the knee joint geometric data. Based on the continuous in-vivo geometric data, computer surgery simulation was studied on six right knees with advancement of 3, 5,10,15, and 20 degrees of the patellar tendon insertion. Evaluation of the simulation consequences from a biomechanical view point showed that the Maquet procedure reduced the patellofemoral joint reaction force only up to 20% at 90 degrees of knee flexion angle. The patellofemoral joint reaction force had 50% reduction only when the knee flexion angle less than 20 degrees, and only when the patellar tendon was moved out by 15 or 20 degrees. This represented nearly 1 in. of the anterior displacement of the tibial tuberosity. The results also showed that the Maquet procedure would decrease up to 20% of the force transmission efficiency of the patellofemoral mechanism, which would cause the mechanical consequences of the operation to be only minor at larger knee flexion angles more than 20 degrees. These findings suggest that the Maquet procedure is only favourable to less active or older patients having small knee flexion angle activities.

Effects of retinacular release and tibial tubercle elevation in patellofemoral degenerative joint disease

Release of the patellar retinaculum and tibial tubercle elevation have both been advocated for the treatment of patellofemoral degeneration. Questions remain, however, regarding the magnitude and predictability of such effects in diseased joints. Using cadaver knee joints exhibiting a range of patellofemoral cartilage degeneration, we investigated the effects on joint contact pressures on release of the patellar retinaculum, followed by tibial tubercle elevations of 1.25 and 2.5 cm. Retinacular release failed to alter the joint-loading parameters significantly. Tibial tubercle elevation reduced the patello-femoral joint contact area and contact force, but failed to cause a consistent change in contact pressure. Tibial tubercle elevation also caused a migration of the joint contact area superolaterally on the retropatellar surface. This migration occurred in conjunction with ventral tilting of the inferior pole of the patella as the tubercle was elevated, suggesting that significant changes in joint kinematics may result from this procedure.