Biomechanics Of Patellofemoral Joint Research Articles

A finite element analysis of patellofemoral joint biomechanics: Exploring potential causes of postoperative anterior knee pain following unicompartmental knee arthroplasty

PurposeAnterior knee pain is a common complication following unicompartmental knee arthroplasty (UKA). This study aimed to elucidate the mechanism of anterior knee pain after UKA by examining the biomechanical characteristics of the patellofemoral joint. MethodsThis study employs the finite element analysis method. A healthy model of the right lower limb was created using CT scans of an intact right lower limb from a healthy woman. Based on this model, a preoperative pathological model was generated by removing the meniscus and part of the articular cartilage. The UKA prosthesis was then applied to this model with five different bearing thicknesses: 5 mm, 7 mm, 10 mm, 11 mm, and 13 mm. To simulate various degrees of knee joint flexion, the femur was rotated relative to the knee joint's rotational axis, producing lower limb models at flexion angles of 0°, 30°, 60°, 90°, and 120°. We applied a constant force from the center of the femoral head to the center of the ankle joint to simulate lower limb loading during squatting. The simulations were conducted using Ansys 17.0. ResultsBoth overstuffing and understuffing increased the peak stress on the patellar cartilage, with overstuffing having a more pronounced effect. Compared to healthy and balanced models, overstuffed and understuffed models exhibited abnormal stress distribution and stress concentration in the patellar cartilage during knee flexion. ConclusionOverstuffing and understuffing lead to residual varus or valgus deformities after UKA, causing mechanical abnormalities in the patellofemoral joint. These abnormalities, characterized by irregular stress distribution and excessive stress, result in cartilage damage, exacerbate wear in the patellofemoral joint and consequently lead to the occurrence of anterior knee pain.

Lateral release associated with MPFL reconstruction in patients with acute patellar dislocation

ObjectiveMedial patellofemoral ligament (MPFL) injury occurs in the majority of the cases of acute patellar dislocation. The role of concomitant lateral retinaculum release with MPFL reconstruction is not clearly understood. Even though the lateral retinaculum plays a role in both medial and lateral patellofemoral joint stability in MPFL intact knees, studies have shown mixed clinical outcomes following its release during MPFL reconstruction surgery. Better understanding of the biomechanical effects of the release of the lateral retinaculum during MPFL reconstruction is warranted. We hypothesize that performing a lateral release concurrent with MPFL reconstruction will disrupt the patellofemoral joint biomechanics and result in lateral patellar instability.MethodsA previously developed and validated finite element (FE) model of the patellofemoral joint was used to understand the effect of lateral retinaculum release following MPFL reconstruction. Contact pressure (CP), contact area (CA) and lateral patellar displacement were recorded. abstract.ResultsFE modeling and analysis demonstrated that lateral retinacular release following MPFL reconstruction with tibial tuberosity-tibial groove distance (TT-TG) of 12 mm resulted in a 39% decrease in CP, 44% decrease in CA and a 20% increase in lateral patellar displacement when compared to a knee with an intact MPFL. In addition, there was a 45% decrease in CP, 44% decrease in CA and a 21% increase in lateral displacement when compared to a knee that only had an MPFL reconstruction.ConclusionThis FE-based analysis exhibits that concomitant lateral retinaculum release with MPFL reconstruction results in decreased PF CA, CP and increased lateral patellar displacement with increased knee flexion, which may increase the risk of patellar instability.

Biomechanical research on effects of pseudo-patella baja on stress of patellofemoral joint after total knee arthroplasty

To investigate biomechanical effects of pseudo-patella baja on stress of patellofemoral joint after total knee arthroplasty (TKA) by using finite element analysis (FEA). A series of CT and MRI of the left knee joint of two healthy volunteers and three-dimensional (3D) scanned data of TKA prosthesis were taken, and the 3D models of knee before and after TKA were established. The finite element model of pseudo-patella baja, normal patella, and alta patella after TKA were constructed by Insall-Salvafi (IS) ratio and Blackburne-Peel (BP) ratio. The load was applied along the direction of quadriceps femoris. After testing the validity of the finite element model, the high contact stress of patellofemoral joint was measured on the von Mise stress nephogram of pseudo-patella baja, normal patella, and alta patella after TKA when the knee flexion was 30°, 60°, and 90°. The average contact area was calculated according to two volunteers' data. On the finite element model of the normal patella after TKA with knee flexion 30°, 475 N pressure was applied along the direction of quadriceps femoris. The contact stress of patellofemoral joint was (1.29±0.41) MPa, which was similar to the results reported previously. The finite element model was valid. The von Mise stress nephogram showed that the stress mainly focused on the medial patellofemoral articular surface during knee flexion, and the contact point gradually moved up with the knee flexion deepened. The stress on the medial and lateral patellofemoral articular surface increased with the knee flexion deepened but decreased with the increase of patellar height. The effects of patellar height and knee flexion on the high contact stress of patellofemoral joint were similar among the finite element models after TKA based on the data of two volunteers. The high contact stress of patellofemoral joint increased with the knee flexion deepened in the same patellar height models ( P<0.05), but decreased with the increase of patellar height in the same knee flexion models ( P<0.05). The high contact stress of patellofemoral joint of pseudo-patella baja model was significantly higher than normal and alta patella models ( P<0.05). The average contact area of patellofemoral joint of pseudo-patella baja was bigger than normal and alta patella models with the knee flexion deepened. The pseudo-patella baja after TKA has an important effect on the biomechanics of patellofemoral joint. Reserving the joint line and avoiding the occurrence of pseudo-patella baja can decrease the risk of anterior knee pain, patellar arthritis, and other complications caused by the increasing of contact stress of patellofemoral joint.

Electromyographic activity of the lower limb in runners with anterior knee pain while running

Anterior knee pain (AKP) is a common musculoskeletal condition that affects runner athletes of different ages. Lower level and delayed onset electromyographic activity (EMG) of the vastus medialis oblique muscle (VMO) and the vastus lateralis (VL) have been identified in patients with AKP. Recently, it has also been suggested that a delay or decrease in the level of gluteus medius (GM) activation may influence the biomechanics of patellofemoral joint. Thus, this study aimed to compare the EMG patterns of VMO, VL, and GM during treadmill running in recreational runners with AKP. Twelve men with AKP (PG) evaluated by the scale (Scoring of Patellofemoral Disorders) and 20 healthy subjects (CG) participated in this study. The EMG of the muscles was collected during 15 s of running at a speed of 11 km/h. The running cycle was captured by four infrared cameras and 3D visual analysis software. The activation level was measured by the rectified EMG integral and the onset of contraction by the Teager-Kaiser energy operator. The VMO and GM muscles showed significantly shorter pre-activation times and contraction times in the group of runners with pain (p < 0.05). Before the start of the running cycle, only the VMO muscle showed differences, with a lower level for the AKP group. In the other phases of the cycle, there were no significant differences. The results suggest that both the VMO and GM have delay and activation deficits, without changes in the level of activation in patients with AKP, which can contribute to patellar misalignment and consequently to the appearance of pain.

Electromyographic activity of the hip and knee muscles during functional tasks in males with and without patellofemoral pain

BackgroundPatellofemoral pain (PFP) is a common overuse injury in physically active individuals. It is characterized by anterior knee, retropatellar, or prepatellar pain associated with activities that increase patellofemoral joint stress such as squatting, stair ascending and descending, running, jumping, prolonged sitting, and kneeling. The etiology of PFP is believed to be multifactorial. Recently, proximal factors have been shown to influence the biomechanics of patellofemoral joint. ObjectiveThe aim of the study was to assess hip and knee muscle activity during single leg stance and single leg squat in males with PFP and a control group without PFP. MethodsEighteen males with PFP (age 24.2 ± 4.4 years) and 18 healthy subjects as controls (age 23.5 ± 3.8 years) were included. We evaluated gluteus medius, gluteus maximus, vastus medialis oblique (VMO), and vastus lateralis (VL) electromyographic (EMG) activity. The muscle activity and reaction time of the proposed muscles were assessed during single leg stance and single leg squat tasks. Independent t-test was used to identify significant differences between PFP and control groups. ResultsNo difference in activity of the gluteus maximus muscle was found in either task (p > 0.5). Significant differences were found in activity of gluteus medius and VMO in both tasks (p < 0.05). VL muscle activity had significant difference in single leg stance (p = 0.01), however, had no significant difference in single leg squat (p = 0.1). No significant differences were found in reaction time of the four studied muscles during both single leg stance and single leg squat (p > 0.5). ConclusionMales with PFP demonstrated altered gluteus medius, VMO, and VL muscle activity during single leg stance and single leg squat compared to healthy subjects. Gluteus maximus activity did not show any changes between groups. Moreover, muscle recruitment patterns were different between PFP and healthy groups.

DOES MCCONNELL TAPING OR THE STABILITY THROUGH EXTERNAL ROTATION OF THE FEMUR (SERF) STRAP AFFECT REARFOOT PLANTAR LOADING PATTERNS DURING WALKING IN HEALTHY ADULTS?

Background: Changes in patellofemoral joint biomechanics have the potential to influence function of the lower extremity. McConnell taping has been proposed to reduce pain in individuals with patellofemoral pain syndrome (PFPS). It is also believed to improve vastus medialis oblique (VMO) muscle, patellofemoral alignment, and stride length. The stability through external rotation of the femur (SERF) strap has been developed to pull the femur externally to stabilise the patellofemoral joint, in order to reduce patellofemoral pain and improve lower limb kinematics. A lack of literature has examined effects of these two treatment methods on plantar pressures. Therefore, the aim of this study was to investigate the effects of McConnell taping and the SERF strap on rearfoot plantar loading patterns during walking in healthy adults. Materials and Methods: Twenty-three participants (12 males and 11 females, age: 26.52±6.4 years) were randomly tested under 3 conditions: 1) no tape, 2) McConnell taping, and 3) SERF strap. Each participant was instructed to walk on a 2 m pressure plate at their own natural pace. Three valid stance phases of the right foot were recorded for each condition. Maximum pressures of medial heel and lateral heel, contact area of medial heel and lateral heel, initial heel contact, foot axis angle, and centre of pressure were collected. Results: There were significant differences of maximum pressures of lateral heel (p = 0.011) with McConnell taping condition and the SERF strap condition demonstrating higher pressures than the no-tape condition (p = 0.042, p = 0.010 respectively). However, significant differences of other variables were not found. Conclusion: The differences of maximum pressures of lateral heel between the conditions could be a clinical role for McConnell taping or SERF strap use in reducing rearfoot pronation in individuals with lower extremity problems especially PFPS.

Our Experience with Patello femoral joint replacement

Background:Ten to fifteen percent of knee arthritis is reported to be isolated patellofemoral arthritis. Total knee arthroplasty is not recommended for isolated patella femoral arthritis particularly in young patients. We present the retrospective review our series in 7 years.Objectives:The aim of this presentation is to describe our experience in the management of patellofemoral osteoarthritis with the use of the partial patellofemoral arthroplasty, as well as to delineate the pitfalls and causes of revision in our initial series of 153 cases.Methods:between 2009 and 2016, our group performed 157 patellofemoral arthroplasties (PFA) 74% being in women, and 26% in men, the mean age for women was 58 yrs. And 38 yrs. for men, our initial 13 cases were managed with the Avon prosthesis (Stryker Corporation Kalamazoo, Michigan), and then we switched to the Vanguard PF (Zimmer-Biomet Warsaw In), both systems are an On-Lay design that is more flexible for addressing dysplastic trochleas that are more common in our population.Results:We performed a Knee Osteoarthritis Outcome Score (KOOS) for the assessment of the success of the procedure and obtained 87% of patients with excellent results (95 to 100), 10% with fair results (70 to 90) and 3% with poor outcomes (50), we performed a total of 3 revisions due to pain or progress to global arthritis.Conclusion:The PFA is a successful, safe and reproducible surgery that can be used in the group of patients that have isolated patellofemoral osteoarthritis. It requires a thorough knowledge of the patello femoral joint biomechanics, and physiopathology.

Knee biomechanics during walking in recurrent lateral patellar dislocation are normalized by 1year after medial patellofemoral ligament reconstruction.

Gait kinematics and kinetics of the knee before and after medial patellofemoral ligament (MPFL) reconstruction in patients with recurrent lateral patellar dislocation (RPD) are unknown. The purpose of this study was to measure knee kinematics and kinetics during gait before and 1year after anatomical MPFL reconstruction in patients with RPD and compare the results to healthy individuals. Eleven RPD patients were treated using an anatomical MPFL reconstruction procedure. Gait analysis was conducted before and at 3, 6, and 12months after surgery. For comparison, 15 healthy volunteers with no history of orthopaedic problems in their lower limbs were included as the control group. Knee kinematics and kinetics were analysed during gait. Before surgery, the internal knee extension moment in RPD patients was significantly lower than in controls (P=0.025). At 3months post-operatively, there was an additional decrease in knee extension moment compared to before surgery, and so it was still significantly lower than in the control group (P<0.01). Oneyear post-operatively, knee extension moment in the RPD group was significantly increased compared to 3months post-operatively (P<0.01). The knee flexion angle in the early stance phase in the RPD group at 3months post-operatively was significantly lower than that of controls (P<0.01). Knee kinematics and kinetics were similar to that of controls 1year after surgery. Initially, RPD patients had lower knee extension moments during gait compared with controls, but by 1year after MPFL reconstruction, knee kinematics and kinetics of gait in the RPD patients had returned to normal. These observations indicate that MPFL reconstruction may help to delay prospective knee OA as long as possible by restoring the conformation of the patellofemoral joint and gait biomechanics by surgery.

Patellofemoral joint biomechanics in the females with anterior knee pain applying full weight bearing kinematic MRI

Purpose. The aim of the study was to evaluate biomechanics of the patellofemoral joint using full weight bearing kinematic MRI. We postulated that females with unilateral PFP might have greater medial femoral rotation in comparrison to the contralateral knee, also greater lateral patella tilt and displacement. Methods. Forty four females aged 20–40 years with unilateral PFP were included in the study. The kinematic MRI examination was performed with a 1.5 T MRI unit. Full-weight bearing was used. Sagittal and axial images of the patellofemoral joint were acquired with a transmit-receive surface body coil. The study parameters, i. e. bisect offset, patella tilt angle, medial femoral rotation, patellar rotation at 0, 10, 20, 30, 40, 50° of flexion, were measured for both knees. Results. Statistically significant changes were confirmed for greater bisect offset at all angles of flexion. The patella tilt angle increased steadily throughout full extension, but there was no significant difference in the tilt angle at 50° flexion. Greater medial femoral rotation was observed at all degrees of flexion, while patellar rotation showed no difference. Conclusions. Our study has confirmed the growing body of literature, theorizing that the primary cause of PFP pain is altered femur dynamics under relatively stable patella.

In vitro method for assessing the biomechanics of the patellofemoral joint following total knee arthroplasty.

The patellofemoral joint is a common site of pain and failure following total knee arthroplasty. A contributory factor may be adverse patellofemoral biomechanics. Cadaveric investigations are commonly used to assess the biomechanics of the joint, but are associated with high inter-specimen variability and often cannot be carried out at physiological levels of loading. This study aimed to evaluate the suitability of a novel knee simulator for investigating patellofemoral joint biomechanics. This simulator specifically facilitated the extended assessment of patellofemoral joint biomechanics under physiological levels of loading. The simulator allowed the knee to move in 6 degrees of freedom under quadriceps actuation and included a simulation of the action of the hamstrings. Prostheses were implanted on synthetic bones and key soft tissues were modelled with a synthetic analogue. In order to evaluate the physiological relevance and repeatability of the simulator, measurements were made of the quadriceps force and the force, contact area and pressure within the patellofemoral joint using load cells, pressure-sensitive film, and a flexible pressure sensor. The results were in agreement with those previously reported in the literature, confirming that the simulator is able to provide a realistic physiological loading situation. Under physiological loading, average standard deviations of force and area measurements were substantially lower and comparable to those reported in previous cadaveric studies, respectively. The simulator replicates the physiological environment and has been demonstrated to allow the initial investigation of factors affecting patellofemoral biomechanics following total knee arthroplasty.

The effects of the sagittal plane malpositioning of the patella and concomitant quadriceps hypotrophy on the patellofemoral joint: a finite element analysis.

Anterior knee pain is a common symptom after intramedullary nailing in tibia shaft fracture. Moreover, patellofemoral malalignment is also known to be a major reason for anterior knee pain. Patellofemoral malalignment predisposes to increased loading in patellar cartilage. In the previous study, we have demonstrated the quadriceps atrophy and patellofemoral malalignment after intramedullary nailing due to tibia shaft fracture. In this study, our aim was to clarify the effects of quadriceps atrophy and patellofemoral malalignment with the pathologic loading on the joint cartilage. Mesh models of patellofemoral joint were constructed with CT images and integrated with soft tissue components such as menisci and ligaments. Physiological and sagittal tilt models during extension and flexion at 15°, 30° and 60° were created generating eight models. All the models were applied with 137N force to present the effects of normal loading and 115.7N force for the simulation of quadriceps atrophy. Different degrees of loading were applied to evaluate the joint contact area and pressure value with the finite element analysis. There was increased patellofemoral contact area in patellar tilt models with respect to normal models. The similar loading patterns were diagnosed in all models at 0° and 15° knee flexion when 137N force was applied. Higher loading values were obtained at 30° and 60° knee flexions in sagittal tilt models. Furthermore, in the sagittal tilt models, in which the quadriceps atrophy was simulated, the loadings at 30° and 60° knee flexion were higher than in the physiological ones. Sagittal malalignment of the patellofemoral joint is a new concept that results in different loading patterns in the patellofemoral joint biomechanics. This malalignment in sagittal plane leads to increased loading values on the patellofemoral joint at 30° and 60° of the knee flexions. This new concept should be kept in mind during the course of diagnosis and treatment in patients with anterior knee pain. Definition of the exact biomechanical effects of the sagittal tilting will lead to the development of new treatment modalities.

Subject-specific evaluation of patellofemoral joint biomechanics during functional activity

Patellofemoral joint pain is a common problem experienced by active adults. However, relatively little is known about patellofemoral joint load and its distribution across the medial and lateral facets of the patella. In this study, biomechanical experiments and computational modeling were used to study patellofemoral contact mechanics in four healthy adults during stair ambulation. Subject-specific anatomical and gait data were recorded using magnetic resonance imaging, dynamic X-ray fluoroscopy, video motion capture, and multiple force platforms. From these data, in vivo tibiofemoral joint kinematics and knee muscle forces were computed and then applied to a deformable finite-element model of the patellofemoral joint. The contact force acting on the lateral facet of the patella was 4–6 times higher than that acting on the medial facet. The peak average patellofemoral contact stresses were 8.2±1.0MPa and 5.9±1.3MPa for the lateral and medial patellar facets, respectively. Peak normal compressive stress and peak octahedral shear stress occurred near toe-off of the contralateral leg and were higher on the lateral facet than the medial facet; furthermore, the peak compressive stress (11.5±3.0MPa) was higher than the peak octahedral shear stress (5.2±0.9MPa). The dominant stress pattern on the lateral patellar facet corresponded well to the location of maximum cartilage thickness. Higher loading of the lateral facet is also consistent with the clinical observation that the lateral compartment of the patellofemoral joint is more prone to osteoarthritis than the medial compartment. Predicted cartilage contact stress maps near contralateral toe-off showed three distinctly different patterns: peak stresses located on the lateral patellar facet; peak stresses located centrally between the medial and lateral patellar facets; and peak stresses located superiorly on both the medial and lateral patellar facets.

Dynamic KINE-MRI in patellofemoral instability in adolescents

The impact of kinematic MRI (KINE-MRI) in the patellofemoral instability and anterior knee pain of the adolescents is rarely reported. Our special interest was to evaluate the patellofemoral joint biomechanics with KINE-MRI in adolescents with affected and unaffected knees in a case-control study. KINE-MRI was performed in 29 adolescents (affected knee group, n = 29 and unaffected knee group, n = 26) aged 11-16 years with unilateral patellofemoral instability. For the control group, we enrolled ten healthy age- and sex-matched volunteers (healthy knee group, n = 19). The study parameters, bisect offset, lateral patellar displacement, patellar tilt angle, sulcus angle and Insall-Salvati ratio at 0, 10, 20 and 30° of flexion-extension, were measured for the affected knee patients (n = 29), unaffected knee patients (n = 26) and the healthy knee subjects (n = 19). The affected knee and the healthy knee subjects had a significant difference in the bisect offset ratio, lateral patellar displacement test and patellar tilt angle test. In these parameters, the difference between the affected knee patients and the healthy knee subjects progressively increased towards the full extension of the knee. In the affected knee and unaffected knee patients, bisect offset ratio at 0° ranged between 0.50 and 1.20 in both groups, whereas the bisect offset ratio in the healthy knee subjects ranged between 0.33 and 0.75 (p < 0.001). At the 0°, the lateral patellar displacement test ranged between 0 and 10 mm in the affected knee patients and between 0 and 35 mm in the unaffected knee patients, whereas the lateral displacement test ranged between 0 and 5 mm in the healthy knee subjects (p = 0.003). Patellar tilt angle test ranged between -30 and 20° in the affected knee patients and between -30 and 24° in the unaffected knee patients, and in the healthy knee subjects, the patellar tilt angle test ranged between 10 and 24° (p < 0.001). The KINE-MRI was able to detect significant differences in patellofemoral joint kinematics between the patients and the healthy subjects. A new finding with clinical relevance in our work is that the unaffected knee is very similar to the dislocated knee in adolescents and this should be taken in account in rehabilitation of patients. II.

Comparative anatomical measurements of osseous structures in the ovine and human knee

The ovine stifle has been increasingly used as a large animal model for the human knee. Still, comparative anatomical measurements of the knee in sheep and humans are missing. Thus, the purpose of this study was to describe and measure the osseous anatomy of the ovine stifle in comparison to the human knee. Twenty-four stifles of skeletal-mature merino-sheep and 24 human cadaver knees were obtained and distances between selected anatomical structures of the distal femur, the proximal tibia, and the patella were measured digitally and documented. Based on these, intercondylar ratio, tibial aspect ratio, patella aspect ratio and the cortical index were calculated. Regarding epicondylar width, lateral condylar width, medial condylar width and the tibial dimensions, the ovine stifle can be considered as a human knee scaled down by one third. However, sheep have a smaller trochlear width and a narrower femoral intercondylar notch than humans resulting in lower relative values for intercondylar width and intercondylar height. The distal femur's cortical index is the same in both species. In contrast, sheep have a massive bone stock below their tibial plateau and a proximal tibial shaft with remarkably thick cortical bone. The ovine stifle can be regarded as a useful model for the human knee. However, future studies should consider the differences in the femoral intercondylar notch width, the patellofemoral joint's biomechanics and the proximal tibia's cortical bone stock.

Patellar tendon orientation and patellar tracking in male and female knees

Knowledge of patellofemoral joint biomechanics is important for understanding sex-related dimorphism in patellofemoral pathologies and advancement of related treatments. We evaluated the hypotheses that sex differences exist in patellar tendon (PT) orientation and patellar tracking during weight-bearing knee flexion and that they relate to differences in tibiofemoral rotation. The PT orientation and patellar tracking were measured in healthy subjects (18 male, 13 female) during weight-bearing knee flexion, using magnetic resonance and dual fluoroscopic imaging. These data were analyzed for sex differences and correlation with previously reported tibiofemoral rotation data. The results indicated a significant effect of sex on PT orientation, particularly at low flexion angles. In females, the PT was oriented more anteriorly in the sagittal plane, more medially in the coronal plane, and showed greater external tilt in the transverse plane of the tibia (p < 0.05). Significant correlations between tibiofemoral rotation and PT orientation (p < 0.01) indicated that sex differences in coronal and transverse plane orientation of the PT relate to differences in tibiofemoral rotation. Patellar tracking did not show significant sex differences or correlation to tibiofemoral rotation. Further studies are warranted to determine implications for patellofemoral pathologies and treatments like total knee arthroplasty.

Patterns of Patellofemoral Articular Cartilage Wear in Cadavers

Descriptive. Describe and compare patellar and femoral condylar wear patterns, and the wear frequency of both, relative to each other, gender, and sidedness. Studies on normal and pathological patellar cartilage and patellofemoral joint biomechanics are plentiful. However, patellar wear patterns are undefined, as is the relationship of patellar to femoral condylar wear. Articular wear was described for 50 patellae and matching femurs from 26 cadavers. Wear locations were transcribed to gridded templates, and these were compared graphically for frequency, gender, and sidedness of wear. The percent frequency of wear was calculated and areas of wear described. Three patellar and 2 femoral types of wear patterns were observed, and 12 areas of patellar wear and 3 areas of femoral wear described. Patella wear was along the horizontal middle of the patella, with marked medial and odd facet wear. Femoral wear was on the anterior and posterior aspects of the medial condyle, and posterior aspect of the lateral femoral condyle. Patellar and femoral wear frequencies were similar bilaterally, but patellar wear may differ with gender. Patella and distal femur showed distinct wear patterns. The wear area under the patella matches the contact area between the patella and distal femur normally occurring between 45 degrees to 90 degrees of knee flexion. Patellofemoral assessment and treatment may differ for the aged population because of mechanical changes due to wear.

The Effect of Anterior Cruciate Ligament Deficiency and Reconstruction on the Patellofemoral Joint

Background Little is known about the effect of anterior cruciate ligament deficiency and reconstruction on the patellofemoral joint. Hypothesis Anterior cruciate ligament deficiency changes the patellofemoral joint biomechanics. Reconstruction of the ligament does not restore the altered patellofemoral joint function. Study Design Controlled laboratory study. Methods Eight patients with an acute anterior cruciate ligament injury in 1 knee and the contralateral side intact were included in the study. Magnetic resonance and dual-orthogonal fluoroscopic imaging techniques were used to compare the patellofemoral joint function during a single-leg lunge between the intact, the anterior cruciate ligament–injured, and the anterior cruciate ligament–reconstructed knee. Data on the patellar tendon apparent elongation and orientation, patellar tracking and patellofemoral cartilage contact location were collected preoperatively and at 6 months after reconstruction. Results Anterior cruciate ligament deficiency caused a significant apparent elongation and change in orientation of the patellar tendon. It decreased the flexion and increased the valgus rotation and tilt of the patella. Anterior cruciate ligament injury caused a proximal and lateral shift in patellofemoral cartilage contact location. Anterior cruciate ligament reconstruction reduced the abnormal apparent elongation but not the orientation of the patellar tendon, and it restored the patellar flexion and proximal shift in contact. The abnormal patellar rotation, tilt, and lateral shift in cartilage contact persisted after reconstruction. Conclusion The altered function of the patellar tendon in anterior cruciate ligament deficiency resulted in an altered patellar tracking and patellofemoral cartilage contact. Persistent changes in patellofemoral joint function after anterior cruciate ligament reconstruction imply that reconstruction of the anterior cruciate ligament does not restore the normal function of the patellofemoral joint. Clinical Relevance The abnormal kinematics of the patellofemoral joint might predispose the patellofemoral cartilage to degenerative changes associated with anterior cruciate ligament deficiency, even if the ligament is reconstructed in a way that restores anteroposterior knee laxity.

Anterior knee pain

Anterior knee pain is a common complain in all ages athletes. It may be caused by a large variety of injuries. There is a continuum of diagnoses and most of the disorders are closely related. Repeated minor trauma and overuse play an important role for the development of lesions in Hoffa's pad, extensor mechanism, lateral and medial restrain structures or cartilage surface, however usually an increase or change of activity is referred. Although the direct relation of cartilage lesions, especially chondral, and pain is a subject of debate these lesions may be responsible of early osteoarthrosis and can determine athlete's prognosis. The anatomy and biomechanics of patellofemoral joint is complex and symptoms are often unspecific. Transient patellar dislocation has MR distinct features that provide evidence of prior dislocation and rules our complication. However, anterior knee pain more often is related to overuse and repeated minor trauma. Patella and quadriceps tendon have been also implicated in anterior knee pain, as well as lateral or medial restraint structures and Hoffa's pad. US and MR are excellent tools for the diagnosis of superficial tendons, the advantage of MR is that permits to rule out other sources of intraarticular derangements. Due to the complex anatomy and biomechanic of patellofemoral joint maltracking is not fully understood; plain films and CT allow the study of malalignment, new CT and MR kinematic studies have promising results but further studies are needed. Our purpose here is to describe how imaging techniques can be helpful in precisely defining the origin of the patient's complaint and thus improve understanding and management of these injuries.

Patellofemoral contact pressure following high tibial osteotomy: a cadaveric study

Patella infera is a known complication of high tibial osteotomy (HTO) that can cause anterior knee pain due to excessive stresses associated with abnormal patellofemoral (PF) joint biomechanics. However, the translation of these abnormal biomechanics to native cartilage pressure has not been explored. The present study was designed to compare the PF contact pressures of three different HTOs in a human cadaveric model of valgus tibiofemoral correction. Nine fresh cadaveric knees underwent (1) medial opening wedge (OWHTO) with a proximal tuberosity osteotomy (PTO), (2) OWHTO with a distal tuberosity osteotomy (DTO), and (3) a lateral closing wedge (CWHTO). The specimens were mounted in a custom knee simulation rig, with muscle forces being simulated using a pulley system and weights. The PF contact pressure was recorded using an electronic pressure sensor at 15 degrees , 30 degrees , 60 degrees , 90 degrees , and 120 degrees of knee flexion, with results of the intact knees obtained as relative control. Compared to the intact knee, the DTO OWHTO and CWHTO did not significantly (P > 0.05) influence PF pressure at any flexion angle. On the other hand, PTO OWHTO lead to a significant elevation in PF cartilage pressure at 30 degrees (P < 0.05), 60 degrees (P < 0.005), and 90 degrees (P < 0.0005) knee flexion. We conclude from these results that DTO OWHTO maintains normal joint biomechanics and has no significant effect on PF cartilage pressure. In patients who complain of pre-existing anterior knee pain, DTO OWHTO or CWHTO should be considered.

Effect of Patellar Tendon Shortening on Tracking of the Patella

Background Although 10% postoperative patellar tendon shortening after bone–patellar tendon–bone autograft reconstruction of the anterior cruciate ligament has been reported, there are no published studies assessing the effect of shortening on patellofemoral joint biomechanics under physiological loading conditions. Purpose To investigate the influence of patellar tendon shortening on patellofemoral joint biomechanics. Study Design Controlled laboratory study. Methods The authors evaluated the patellofemoral contact area, the location of contact, and the patellofemoral joint reaction force and contact stresses in 7 cadaveric knees before and after 10% patellar tendon shortening. Shortening was achieved using a specially designed device. Experimental conditions simulating those occurring during level walking were employed: physiological quadriceps loads and corresponding angles of tibial rotation were applied at 15 °, 30 °, and 60 ° flexion of the knee. Patellofemoral joint contact areas were measured before and after shortening using the silicone oil–carbon black powder suspension squeeze technique. Results After patellar tendon shortening, patellofemoral joint contact areas were displaced proximally on the patellar surface and distally on the femoral surface. Although the contact area increased by 18% at 15 ° of knee flexion (P=. 04), no significant change occurred at 30 ° or 60 ° of knee flexion (P>. 05). Patellofemoral contact stress remained unchanged after patellar tendon shortening (P>. 05) at each flexion angle. Conclusion Our results suggest that a 10% shortening of the patellar tendon does not alter patellar contact stresses during locomotion. It is not clear whether apparent changes in contact location in all positions and contact area at 15 ° would have clinical consequences.