Cause Of Patellofemoral Pain Syndrome Research Articles

Effect of strengthening exercises in individuals with patellofemoral pain syndrome: a randomised controlled trial

Background/Aims Muscle imbalance in patella stabilisers leads to patellar lateral glide and can cause patellofemoral pain syndrome. This study investigated the effect of progressive strengthening exercises of the vastus medialis oblique on pain and patellar alignment in patients with patellofemoral pain syndrome and patellar lateral glide. Methods A double-blind, randomised controlled trial was conducted with 40 individuals with patellofemoral pain syndrome with patellar lateral glide aged 20–40 years. The study group received vastus medialis oblique-specific strengthening exercises and routine physiotherapy treatment, and the control group received routine physiotherapy treatment only (stretching exercises, gluteal and quadriceps isometric exercises and conventional transcutaneous electrical nerve stimulation). Participants performed these exercises three times a week for 8 weeks. Pain intensity was measured before and after the intervention using a visual analogue scale and patellar alignment was measured using ultrasonographic parameters, including the trochlear angle, patella offset angle and distance between patellar tip and trochlear groove. Results In the between-groups comparison, there was a significant decrease in pain intensity in both the study and control groups, although the study group had a greater decrease (study group before intervention: 71.15 ± 1.54, study group after intervention: 22.21 ± 0.35, P=0.001); control group before intervention: 70.09 ± 1.22, control group after intervention: 31.82 ± 0.36 (P=0.001)) and patella offset angle (in the study group compared to the control group after 8 weeks of intervention. In within-groups comparison, a significant decrease of the patella offset angle in the study group was observed (before intervention: 16.2 ± 1.53; after intervention: 13.2 ± 1.87, P=0.001). No significant differences were found for the other parameters. Conclusions Specific strengthening of the vastus medialis oblique muscle in patients with patellofemoral pain syndrome and patellar lateral glide can lead to pain reduction and improvement of patellar alignment to correct lateralisation. This change may delay the process of patellofemoral joint degeneration. Including vastus medialis oblique-specific strengthening exercises in standard physiotherapy treatments may help to reduce pain levels in people with patellofemoral pain syndrome. Implications for practice Investigating the main cause of patellofemoral pain syndrome could have an essential role in the rehabilitation treatment of patients.

Distal Approaches in Patellofemoral Pain: A Systematic Review, Part I

Purpose: Increased patellofemoral joint reaction force is the main cause of patellofemoral pain syndrome. Foot pronation causes faulty joint coupling of the lower limb and increases the patellofemoral joint reaction force; accordingly, this study aims to systematically review the effect of the distal interventions on the clinical symptoms and kinematics of patients with patellofemoral pain. Methods: The search strategy was applied to Google Scholar, PubMed, Science Direct, Medline, Web of Science, and Scopus databases. The search was limited to the English language. The studies were from 2000 to 2022. In 4 stages, the selected articles were screened for systematic review. The quality of the study was evaluated by the Downs and Black scale. Meanwhile, the articles were classified into 3 categories as follows: High, medium, and low quality. Results: A total of 12 articles were screened for this systematic review. The quality of the study was medium. Meanwhile, 5 articles had medium quality and 7 articles had high quality. The results of the systematic review showed that distal interventions are effective in improving clinical symptoms and correcting the faulty kinematics of the lower limb. Conclusion: Distal interventions by correcting the faulty joint coupling reduce the patellofemoral joint reaction force and pain. As a result, distal interventions in combination with proximal exercise have a better effect on clinical symptoms.

Patellofemoral Chondropathy Areas in Folk Dancers: An MRI Study.

Patellofemoral chondropathy (PFC) is one of the most important causes of patellofemoral pain syndrome. PFC may occur as a result of anatomic reasons such as patellar malalignment and/or increased patellofemoral joint stresses. Most research on this subject has involved sports injuries and anatomic variations. The literature is scarce on PFC related to the dance. Fourteen dancers (14 knees, all male) were found to have PFC based on MRI evaluations and clinical examinations between January 2010 and December 2019 (3 dancers were excluded due to prior surgeries of the knee). Age, sex, side of injury, range of motion, Q angle, types of dances, body mass index, and patellar specifics (alta, baja, Wiberg) were recorded for 11 dancers included in the study. We observed PFC at the femoral contact areas (FCA) and patellar contact areas (PCA) of Goodfellow description. Chondral lesions were observed at Gooodfellow areas FCA-3 in 2 dancers, FCA-4 in 5 dancers, PCA-2 in 10 dancers, PCA-3 in 10 dancers, and PCA-4 in 9 dancers. Dance styles that include frequent deep flexions and strolling on a flexed knee joint may be risk factors for chondral lesions in the contact area of the femur in male dancers.

Static and Dynamic Quadriceps Stretching Exercises in Patients With Patellofemoral Pain: A Randomized Controlled Trial.

Limited data are available on the effect of stretching exercise in patients with patellofemoral pain (PFP) who have inflexible quadriceps, which is one of the various causes of PFP syndrome. This study compares quadriceps flexibility, strength, muscle activation time, and patient-reported outcomes after static and dynamic quadriceps stretching exercises in patients with PFP who had inflexible quadriceps. Quadriceps flexibility and strength, muscle activation time, and patient-reported outcomes would improve with dynamic quadriceps stretching as compared with static quadriceps stretching exercises. Randomized controlled trial. Level 2. Of the 44 patients included in the study, 20 performed static stretching and 24 performed dynamic stretching. Quadriceps flexibility was assessed by measuring the knee flexion angle during knee flexion in the prone position (the Ely test). Muscle strength and muscle activation time were measured using an isokinetic device. The patient-reported outcomes were evaluated using the visual analogue scale for pain and anterior knee pain scale. No significant differences in quadriceps flexibility and strength, muscle activation time, and patient-reported outcomes in the involved knees were found between the 2 groups (P values > 0.05). Quadriceps flexibility and strength, muscle activation time, and patient-reported outcomes in patients with PFP who had inflexible quadriceps showed no significant differences between the static and dynamic quadriceps stretching exercise groups. Both static and dynamic stretching exercises may be effective for improving pain and function in patients with PFP who have inflexible quadriceps.

Electromyographic analysis of VMO and VL across straight leg raise, short arc quad, medial tibial rotation and hip adduction in normal individuals.

The lateral malalignment of patella is considered to be the main cause of patellofemoral pain syndrome (PFPS). PFPS, in an occupational setup, is aggravated by prolonged sitting, climbing stairs, squatting, and kneeling. Strengthening of vastus medialis oblique (VMO) opposes the lateral force produced by vastus lateralis (VL) and helps in stabilizing patella. The main objective was to compare six common rehabilitation exercises (REs) and to identify those which could possibly activate VMO selectively to alleviate PFPS of occupational workers. Ten subjects, having no history of PFPS, performed six REs, namely, straight leg raise with neutral hip position (SLRN), straight leg raise with externally rotated hip position (SLRER), short arc quad with neutral hip position (SAQN), short arc quad with externally rotated hip position (SAQER), medial tibial rotation and hip adduction (HA). REs were compared on the basis of integrated electromyographic activity of VMO and VL. Results demonstrated that VMO activity was more than that of VL during all REs. However, this difference was not statistically significant in any of the six REs. HA produced significantly higher VMO activity than SLRN, SLRER and SAQN. The results provided a wider range of options for selecting apposite REs for treating patients diagnosed with PFPS.

Prevalence and sensitivity of trigger points in lumbo-pelvic-hip muscles in patients with patellofemoral pain syndrome

ObjectivesChanges in the activity of the lumbo-pelvic-hip muscles have been established as a major cause of patellofemoral pain syndrome (PFPS), a common orthopedic problem. The present study aimed to compare the prevalence and sensitivity of myofascial trigger points (MTrPs) in lumbo-pelvic-hip muscles in persons with and without PFPS. MethodsThirty women with PFPS and 30 healthy women 18–40 years old were recruited for this study. The prevalence of MTrPs was assessed by palpation, and pressure algometry was used to measure the pressure pain threshold. This study evaluated the areas where MTrPs are most commonly found in the lumbar muscles (internal oblique, erector spinae and quadratus lumborum), pelvic muscles (gluteus maximus, gluteus medius, gluteus minimus and piriformis), and hip muscles (hip adductor, quadriceps, hamstring, tensor fascia lata and sartorius). Independent t-tests were used to compare mean pressure pain thresholds between the two groups. Chi-squared tests were used to compare the prevalence of MTrPs. ResultsThe prevalence of MTrPs was significantly higher in most of the lumbo-pelvic-hip muscles in patients with PFPS compared to healthy persons. However, there were no significant differences between groups in the prevalence of MTrPs in the gluteus minimus or adductor muscles. The pressure pain threshold in lumbo-pelvic-hip muscles was lower in patients with PFPS compared to healthy participants. ConclusionIn patients with PFPS the prevalence of MTrPs in the lumbo-pelvic-hip region was higher, and the pressure pain threshold was lower, than in healthy people. Thus therapy to treat PFPS should target the lumbo-pelvic-hip muscles.

Activation level of vastus medialis muscle in different rehabilitation exercises

Excessive lateralization, which often occurs by the weakening of Vastus Medialis (VM) muscle of the patella, is one of the causes of Patellofemoral Pain Syndrome (PFPS) For prevention and rehabilitation of PFPS, the VM strength is essential. Objective: The aim of the study was to compare the VM activation level in four different exercises used in the prevention and rehabilitation of PFPS that are isometric knee extension at 30° and 60° and isometric squat at 60° with or without hip adduction. Methods: A sample of 14 sedentary healthy subjects, aged between 20 and 40 years was included. The EMG signal of VM muscle was collected during Maximal Voluntary Isometric Contraction with duration of five seconds for each exercise. From the captured EMG signal, a period of three seconds was cut and thereafter the Root Mean Square value for each exercise was obtained. Results: The results showed that there was significantly greater activation in VM extension exercises compared to squat exercises. However, there was no significant difference between the two extension exercises, as well as between squat exercises. Conclusion: It can be concluded that the best exercises to maximize the activation of the VM are the isometric knee extension, regardless of the rated angle, since they have greater VM activation level, essential for the prevention and rehabilitation of PFPS

Inter- and intra-rater reliability of patellofemoral kinematic and contact area quantification by fast spin echo MRI and correlation with cartilage health by quantitative T1ρ MRI

BackgroundPatellar maltracking is a leading cause of patellofemoral pain syndrome (PFPS). The aim of this study was to determine the inter- and intra-rater reliability of a semi-automated program for magnetic resonance imaging (MRI) based patellofemoral kinematics. MethodsSixteen subjects (10 with PFPS [mean age 32.3; SD 5.2; eight females] and six controls without PFPS 19 [mean age 28.6; SD 2.8; three females]) participated in the study. One set of T2-weighted, fat-saturated fast spin-echo (FSE) MRIs were acquired from each subject in full extension and 30° of knee flexion. MRI including axial T1ρ relaxation time mapping sequences was also performed on each knee. Following image acquisitions, regions of interest for kinematic MRI, and patellar and trochlear cartilage were segmented and quantified with in-house designed spline- based MATLAB semi-automated software. ResultsIntraclass Correlations Coefficients (ICC) of calculated kinematic parameters were good to excellent, ICC > 0.8 in patellar flexion, rotation, tilt, and translation (anterior -posterior, medial -lateral, and superior -inferior), and contact area translation. Only patellar tilt in the flexed position and motion from extended to flexed state was significantly different between PFPS and control patients (p=0.002 and p=0.006, respectively). No significant correlations were identified between patellofemoral kinematics and contact area with T1ρ relaxation times. ConclusionsA semi-automated, spline-based kinematic MRI technique for patellofemoral kinematic and contact area quantification is highly reproducible with the potential to help better understand the role of patellofemoral maltracking in PFPS and other knee disorders. Level of EvidenceLevel IV

Biomechanics Associated with Patellofemoral Pain and ACL Injuries in Sports

Knee injuries are prevalent among a variety of competitive sports and can impact an athlete's ability to continue to participate in their sport or, in the worst case, end an athlete's career. The aim was to evaluate biomechanics associated with both patellofemoral pain syndrome (PFPS) and anterior cruciate ligament (ACL) injuries (in sports involving landing, change in direction, or rapid deceleration) across the three time points frequently reported in the literature: pre-injury, at the time of injury, and following injury. A search of the literature was conducted for research evaluating biomechanics associated with ACL injury and PFPS. The Web of Science, SPORTDiscus, EBSCO, PubMed, and CINAHL databases, to March 2015, were searched, and journal articles focused on ACL injuries and PFPS in sports that met the inclusion criteria were reviewed. The search methodology was created with the intent of extracting case-control, case, and cohort studies of knee injury in athletic populations. The search strategy was restricted to only full-text articles published in English. These articles were included in the review if they met all of the required selection criteria. The following inclusion criteria were used: (1) The study must report lower extremity biomechanics in one of the following settings: (a) a comparison of currently injured and uninjured participants, (b) a prospective study evaluating risk factors for injury, or (c) a study reporting on the injury event itself. (2) The study must include only currently active participants who were similar at baseline (i.e. healthy, high school level basketball players currently in-season) and include biomechanical analysis of either landing, change in direction, or rapid deceleration. (3) The study must include currently injured participants. The studies were graded on the basis of quality, which served as an indication of risk of bias. An adapted version of the 'Strengthening the Reporting of Observational Studies in Epidemiology' (STROBE) guidelines was used to rate observational research. Fifteen journal articles focusing on ACL injuries and PFPS in sports met the inclusion criteria. These included three associated with both ACL injuries and PFPS across multiple time points. There was limited evidence for an association between ankle biomechanics and knee injury, with only one ACL injury study identifying decreased plantar flexion in association with injury. Only prospective studies can determine biomechanical risk factors associated with ACL injuries and PFPS. Case studies and case-control studies do not allow for the determination of risk factors associated with both ACL injuries and PFPS as there is no certainty regarding the presence of the observed biomechanics prior to the onset of injury. Further, each study design has its own set of limitations. Lastly, the majority of the studies included in this review had adult female participants. By evaluating several different study designs looking at knee injuries during high-risk manoeuvres, we were able to obtain a holistic perspective of biomechanics associated with PFPS and ACL injuries. Looking at different biomechanical research approaches allowed us to assess not only the mechanism of injury, but also to look for commonalities in biomechanics (in particular, altered frontal plane mechanics at the knee and altered sagittal plane mechanics at the knee and hip) between injured and uninjured participants pre-injury, at the time of injury, and following injury, to better understand potential causes of PFPS and ACL injury. Development of injury prevention programmes should focus on correcting these mechanics observed across the three time points during high-risk manoeuvres as this may help decrease the prevalence of ACL injury and PFPS. Programmes focusing not only on neuromuscular training, but also skill-specific training focused on correcting mechanics during these high-risk manoeuvres may be of greatest benefit regarding prevention. Future research should consider the impact of cumulative loading on knee injury risk. Additionally, better techniques for assessing mechanics in-game are needed in order to facilitate injury prevention and screening strategies.

Ultrasound investigation of vastus medialis oblique muscle architecture: an in vivo study.

There is thought to be a link between vastus medialis oblique (VMO) architecture and patellofemoral pain syndrome (PFPS). Historical data are largely derived from older populations, whereas PFPS commonly affects younger populations. The aim of this study was to gather data on VMO architecture in young asymptomatic adults, to provide baseline values for comparison with symptomatic sufferers. VMO maximum fiber angle and insertion ratio were measured with ultrasound. The insertion ratio represents the proportion (%) of the patella which has the muscle fibers attaching to its medial border. Eighty knees from 40 healthy young subjects (18 males, 22 females, and age 20-30) were assessed. Individual Tegner scores were recorded to assess participants' level of physical activity. Results were compared with data in the literature for PFPS sufferers and normal older individuals. Mean fiber angle and insertion ratio were 56.6° and 57.8%, respectively. There was no significant difference between age groups. The insertion ratio was higher among females (61.2% F:53.6% M). There was some evidence of increased fiber angle and decreased insertion ratio with increased Tegner score. There was some overlap in fiber angle between healthy knees in this study and values reported elsewhere for pathological knees. VMO fiber angle and insertion ratio are not age-related. The overlap in fiber angle values between healthy and pathological knees suggests that the cause of PFPS is multifactorial. An individual's VMO architecture may be affected by their physical activity level, which could have important implications for PFPS.

Gait biomechanics and hip muscular strength in patients with patellofemoral osteoarthritis

A significant number of patients with patellofemoral osteoarthritis (PFOA) have described a history of patellofemoral pain syndrome (PFPS). This leads to speculation that the underpinning mechanical causes of PFPS and PFOA may be similar. Although alterations in gait biomechanics and hip strength have been reported in PFPS, this relationship has not yet been explored in PFOA. Therefore the purpose of this study was compare gait biomechanics and hip muscular strength between PFOA patients and a healthy control group. Fifteen patients with symptomatic, radiographic PFOA and 15 controls participated. All patients underwent a walking gait analysis and maximal hip strength testing. Biomechanical variables of interest included the peak angular values of contra-lateral pelvic drop, hip adduction and hip internal rotation during the stance phase. Hip abduction and external rotation strength were assessed using maximal voluntary isometric contractions. The PFOA group demonstrated significantly lower hip abduction strength compared to controls but no difference in hip external rotation strength. There were no statistical differences between the PFOA and control groups for contra-lateral pelvic drop, hip adduction and hip internal rotation angles during walking. Despite patients with PFOA exhibiting weaker hip abductor muscle strength compared to their healthy counterparts they did not demonstrate alterations in pelvis or hip biomechanics during gait. These preliminary data suggests that weaker hip abductor strength does not result in biomechanical alterations during gait in this population.

The Effects of Quadriceps Strengthening on Pain, Function, and Patellofemoral Joint Contact Area in Persons with Patellofemoral Pain

Patellar malalignment is a major cause of patellofemoral pain syndrome (PFPS), but the relationship between clinical symptoms and changes in patellar position and knee muscle strength has not been confirmed. This study examined the effect of weight training on hip and knee muscle strength, patellofemoral joint contact area, and patellar tilt on subjects with and without PFPS, hoping to develop an optimal rehabilitation protocol for subjects with PFPS. The study uses a prospective independent group comparison. Fifteen subjects with and without PFPS were assessed for knee strength, patellofemoral joint contact area, and patellar tilt angle using magnetic resonance imaging. The subjects with PFPS were also examined and given a numeric pain rating score and a Kujala patellofemoral score. The subjects performed lower-limb weight training 3 times/wk for 8 wks, and the outcomes were assessed both before and after training. Subjects with PFPS have increased their patellofemoral joint contact area after weight training (P < 0.001). No statistical significant change was found on the patellar tilt angle. The isometric and isokinetic knee strength in subjects with and without PFPS have increased after weight training (P value increased from 0.007 to 0.05). Both numeric pain rating and Kujala patellofemoral score in the PFPS group improved after training (P < 0.001). Weight-training exercise increased knee muscle strength and the patellofemoral joint contact area, which could reduce mechanical stress in the joint, improving pain and function in subjects with PFPS.

Is there any relationship between Q-angle and lower extremity malalignment?

The aim of this study was to assess the relationship between Q-angle and lower extremity alignment in women with unilateral patellofemoral pain syndrome (PFPS). Eighty-five women with unilateral patellofemoral pain participated in the study, with each subject acting as their own internal control using the unaffected limb. Lower extremity alignment and Q-angles of the affected and unaffected knees were compared. There was a significant difference in the Q-angle between the affected (19.61±4.35) and the unaffected (17.63±4.29) side (p=0.00). There was also a significant difference in the lateral distal femoral angle (LDFA) (81.00±2.58 vs. 81.83±3.03; p=0.03) and no significant difference in the medial proximal tibial angle (MPTA) (87.88±2.63 vs. 87.60±3.29; p=0.51) between the affected and the unaffected side. There was no relationship between the Q-angle and LDFA (r=0.001, p=0.99), and MPTA (r=-0.051, p=0.64) in the affected side of the patients. There was also no relationship between the Q-angle and LDFA (r=0.179, p=0.64), and MPTA (r=-0.146, p=0.18) in the unaffected side of the patients. Increased Q-angle and decreased LDFA may be associated with PFPS although cause or effect cannot be established. There was no relationship between the Q-angle and lower extremity malalignment. Large prospective longitudinal studies are needed to detect changes in the femoral anteversion and toe-in gait and to establish if these features are a cause of PFPS.

Vastus Medialis Obliquus Atrophy

Background: Quadriceps atrophy and in particular atrophy of the vastus medialis obliquus (VMO) muscle have been frequently related with patellofemoral pain syndrome (PFPS), despite very little objective evidence. Hypothesis: Patients with PFPS exhibit atrophy of the VMO in comparison with healthy controls. Study Design: Case-control study; Level of evidence, 3. Methods: Forty-six patients with PFPS and 30 healthy control persons with similar age, gender, body mass index, and activity index distributions underwent magnetic resonance imaging (MRI) of the quadriceps. The muscle size was determined by calculating the cross-sectional area of the total quadriceps and its components. Results: The cross-sectional area (CSA) of the VMO was significantly smaller in the PFPS group than in the control group (16.67 ± 4.97 cm2 vs 18.36 ± 5.25 cm2) (P = .040). A tendency was noted for a smaller total quadriceps CSA for the PFPS patients at midthigh level (66.99 ± 15.06 cm2 vs 70.83 ± 15.30 cm2) (P = .074). Conclusion: This is the first study to examine VMO size in PFPS patients by MRI. Patients with patellofemoral problems exhibited atrophy of the VMO. Although it is not clear whether this atrophy is a result or a cause of PFPS, the results of this study do show that atrophy of the VMO is a contributing factor in PFPS. Longitudinal, prospective studies are needed to establish the cause-effect relation of VMO atrophy and PFPS.

Women with patellofemoral pain syndrome have quadriceps femoris volume and strength deficiency

the aim of this study was to assess muscle torque, total volume, and cross-sectional area, and lower limb function of the quadriceps muscle in women with unilateral patellofemoral pain syndrome (PFPS). twenty-four women with unilateral patellofemoral pain participated in the study, with each subject acting as their own internal control by using the unaffected limb. quadriceps muscle torque was measured with the Isomed 2000. The total volume and cross-sectional area (CSA) of the quadriceps muscle were measured by using magnetic resonance imaging. Lower limb function was assessed by hop and step-down tests. there was a significant difference in the total volume (P < 0.05) and in the cross-sectional area (P < 0.05) of the quadriceps muscle between affected and unaffected sides. There was a significant difference in the peak torque of the quadriceps muscle at 60°/s between affected and unaffected sides (P < 0.05). There were significant correlations between quadriceps largest CSA and volume on the affected side (P < 0.05) and on the unaffected side (P < 0.05). There were significant negative correlations between the smallest CSA and the peak torque at 180°/s (P < 0.05) and at 60°/s (P < 0.05) on the affected side. decreased torque, total volume, and CSA of the quadriceps muscle are presented in unilateral with PFPS although cause or effect cannot be established. Large prospective longitudinal studies are needed to detect the changes in the muscle structure and to establish whether these features are a cause of PFPS.

Delayed onset of electromyographic activity of vastus medialis obliquus relative to vastus lateralis in subjects with patellofemoral pain syndrome

Patellofemoral Pain Syndrome (PFPS) is a common musculoskeletal complaint. The presence of a delay between vastus medialis obliquus (VMO) and vastus lateralis (VL) muscle onset has been suggested in the literature as a possible cause of PFPS, with poor agreement amongst authors on the value of the delay. In this study we computed the delay in the activation of VMO and VL in 15 PFPS patients and 20 age-matched controls (Ctrls) during the following tasks: sit to stand, stand to sit, squat, step up and step down. Activation instants were detected from surface EMG data by a double-threshold statistical detector. In order to compare the muscle activity throughout the task, we computed the delay between the instants in which the VMO and VL normalised envelopes reached subsequent normalised amplitude levels, until the envelope peak. In all investigated tasks but sit to stand, the onset delay was lower or equal then 0.02 s, without group differences. Similarly, no differences between Ctrls and PFPS timing were found throughout all tasks, until the peak. Our results do not support the hypothesis that an onset delay between VMO and VL can be one of the causes of PFPS.

Evaluation of a computational model used to predict the patellofemoral contact pressure distribution

One possible cause of patellofemoral pain syndrome is excessive lateral force acting on the patella. Although several treatment methods focus on decreasing the lateral force acting on the patella, the relationship between the lateral force and the patellofemoral contact pressure distribution is unclear. A computational model has been developed to determine how loading variations alter the patellofemoral force and pressure distributions for individual knees. The model allows variation in the quadriceps and patella tendon forces, and calculates the predicted contact pressure distribution using the discrete element analysis technique. To characterize the accuracy of the model, four cadaver knees were flexed on a knee simulator with three initial Q-angles, while recording the force and pressure distributions with a pressure sensor. A model of each knee was created from CT data. Using the external force applied to the knee, the geometry of the knee, and the quadriceps origin as input, the pressure distribution was calculated during flexion. Similar trends were noted for the computational and experimental results. The percentage of the total force applied to the lateral cartilage increased with the Q-angle. The maximum contact pressure increased during flexion. The maximum lateral contact pressure increased with the Q-angle for three knees. For the other knee, increasing the Q-angle decreased the maximum lateral pressure. The maximum medial contact pressure decreased as the Q-angle increased. By characterizing the influence of patellofemoral loading on the force and pressure distributions, the computational model could be used to evaluate treatment methods prescribed for patellofemoral pain.

Patellofemoral Pain Syndrome

There is no clear consensus in the literature concerning the terminology, aetiology and treatment for pain in the anterior part of the knee. The term 'anterior knee pain' is suggested to encompass all pain-related problems. By excluding anterior knee pain due to intra-articular pathology, peripatellar tendinitis or bursitis, plica syndromes, Sinding Larsen's disease, Osgood Schlatter's disease, neuromas and other rarely occurring pathologies, it is suggested that remaining patients with a clinical presentation of anterior knee pain could be diagnosed with patello-femoral pain syndrome (PFPS). Three major contributing factors of PFPS are discussed: (i) malalignment of the lower extremity and/or the patella; (ii) muscular imbalance of the lower extremity; and (iii) overactivity. The significance of lower extremity alignment factors and pathological limits needs further investigation. It is possible that the definitions used for malalignment should be re-evaluated, as the scientific support is very weak for determining when alignment is normal and when there is malalignment. Consequently, pathological limits must be clarified, along with evaluation of risk factors for acquiring PFPS. Muscle tightness and muscular imbalance of the lower extremity muscles with decreased strength due to hypotrophy or inhibition have been suggested, but remain unclear as potential causes of PFPS. Decreased knee extensor strength is a common finding in patients with PFPS. Various patterns of weaknesses have been reported, with selective weakness in eccentric muscle strength, within the quadriceps muscle and in terminal knee extension. The significance of muscle function in a closed versus open kinetic chain has been discussed, but is far from well investigated. It is clear that further studies are necessary in order to establish the significance of various strength deficits and muscular imbalances, and to clarify whether a specific disturbance in muscular activation is a cause or an effect (or both) of PFPS. The most common symptoms in patients with PFPS are pain during and after physical activity, during bodyweight loading of the lower extremities in walking up/down stairs and squatting, and in sitting with the knees flexed. However, the source of patellofemoral pain in patients with PFPS cannot be sufficiently explained. There are several types of clinical manifestation of pain, and therefore a differentiated documentation of the patient's pain symptoms is necessary. The connection between strength, pain and inhibition, as well as between personality and pain, needs further investigation. Many different treatment protocols are described in the literature and recent studies advocate a comprehensive treatment approach allowing for an individual and specifically designed treatment. Surgical treatment is rarely indicated. It is strongly suggested that, when presenting studies on PFPS, a detailed description should be provided of the diagnosis, inclusion and exclusion criteria of the patients should be specified along with a detailed methodology, and the conclusions drawn should be compared with those of other studies in the published literature. As this is not the case in most studies on PFPS found in the literature, it is only possible to make general comparisons. In order to further develop treatment models for PFPS we advocate prospective, randomised, controlled, long term studies using validated outcome measures. However, there is a strong need for basic research on the nature and aetiology of PFPS in order to better understand this mysterious syndrome.