Patella tracking and patellofemoral pain syndrome

NewsBot · Dec 1, 2006

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Patellofemoral Joint Kinematics in Individuals with and without Patellofemoral Pain Syndrome
N.J. MacIntyre, N.A. Hill, R.A. Fellows, R.E. Ellis, and D.R. Wilson
The Journal of Bone and Joint Surgery (American). 2006;88:2596-2605.

Background: Patellofemoral pain syndrome is a prevalent condition in young people. While it is widely believed that abnormal patellar tracking plays a role in the development of patellofemoral pain syndrome, this link has not been established. The purpose of this cross-sectional case-control study was to test the hypothesis that patterns of patellar spin, tilt, and lateral translation make it possible to distinguish individuals with patellofemoral pain syndrome and clinical evidence of patellar malalignment from those with patellofemoral pain syndrome and no clinical evidence of malalignment and from individuals with no knee problems.

Methods: Three-dimensional patellofemoral joint kinematics in one knee of each of sixty volunteers (twenty in each group described above) were assessed with use of a new, validated magnetic resonance imaging-based method. Static low-resolution scans of the loaded knee were acquired at five different angles of knee flexion (ranging between –4° and 60°). High-resolution geometric models of the patella, femur, and tibia and associated coordinate axes were registered to the bone positions on the low-resolution scans to determine the patellar motion as a function of knee flexion angle. Hierarchical modeling was used to identify group differences in patterns of patellar spin, tilt, and lateral translation.

Results: No differences in the overall pattern of patellar motion were observed among groups (p > 0.08 for all global maximum likelihood ratio tests). Features of patellar spin and tilt patterns varied greatly between subjects across all three groups, and no significant group differences were detected. At 19° of knee flexion, the patellae in the group with patellofemoral pain and clinical evidence of malalignment were positioned an average of 2.25 mm more laterally than the patellae in the control group, and this difference was marginally significant (p = 0.049). Other features of the pattern of lateral translation did not differ, and large overlaps in values were observed across all groups.

Conclusions: It cannot be determined from our cross-sectional study whether the more lateral position of the patella in the group with clinical evidence of malalignment preceded or followed the onset of symptoms. It is clear from the data that an individual with patellofemoral pain syndrome cannot be distinguished from a control subject by examining patterns of spin, tilt, or lateral translation of the patella, even when clinical evidence of mechanical abnormality was observed.

Clinical Relevance: Since most patients with patellofemoral pain syndrome did not demonstrate abnormalities in patellar tracking during loaded knee flexion, other causative mechanisms must be explored to develop effective diagnostic and treatment strategies for this common musculoskeletal condition.
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Admin2 · Dec 1, 2006

Related threads:
Foot pronation and knee pain
Knee abduction impulses and patellofemoral pain
Patellofemoral pain and asymmetrical hip rotation

NewsBot · Nov 13, 2010

Patellar Maltracking Correlates With Vastus Medialis Activation Delay in Patellofemoral Pain Patients
Saikat Pal, Christine E. Draper, Michael Fredericson, Gary E. Gold, Scott L. Delp, Gary S. Beaupre, Thor F. Besier
American Journal of Sports Medicine

Background: Delayed onset of vastus medialis (VM) activity compared with vastus lateralis activity is a reported cause for patellofemoral pain. The delayed onset of VM activity in patellofemoral pain patients likely causes an imbalance in muscle forces and lateral maltracking of the patella; however, evidence relating VM activation delay to patellar maltracking is sparse. The aim of this study was to investigate the relationship between VM activation delay and patellar maltracking measures in pain-free controls and patellofemoral pain patients.

Hypothesis: Patellar tilt and bisect offset, measures of patellar tracking, correlate with VM activation delay in patellofemoral pain patients classified as maltrackers.

Study Design: Case control study; Level of evidence, 3.

Methods: Vasti muscle activations were recorded in pain-free (n = 15) and patellofemoral pain (n = 40) participants during walking and jogging. All participants were scanned in an open-configuration magnetic resonance scanner in an upright weightbearing position to acquire the position of the patella with respect to the femur. Patellar tilt and bisect offset were measured, and patellofemoral pain participants were classified into normal tracking and maltracking groups.

Results: Correlations between VM activation delay and patellar maltracking measures were statistically significant in only the patellofemoral pain participants classified as maltrackers with both abnormal tilt and abnormal bisect offset (R 2 = .89, P < .001, with patellar tilt during walking; R 2 = .75, P = .012, with bisect offset during jogging). There were no differences between the means of activation delays in pain-free and all patellofemoral pain participants during walking (P = .516) or jogging (P = .731).

Conclusion: There was a relationship between VM activation delay and patellar maltracking in the subgroup of patellofemoral pain participants classified as maltrackers with both abnormal tilt and abnormal bisect offset.

Clinical Relevance: A clinical intervention such as VM retraining may be effective in only a subset of patellofemoral pain participants—namely, those with excessive tilt and excessive bisect offset measures. The results highlight the importance of appropriate classification of patellofemoral pain patients before selection of a clinical intervention.
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NewsBot · Aug 20, 2011

From the latest LER:
PFP: Vasti revisited

Research presented in August at the annual meeting of the American Society of Biomechanics in Long Beach, CA, adds support to the increasingly popular idea that patellofemoral pain syndrome arises from different mechanisms—and therefore should be managed differently—in different subgroups of patients.

The findings also call into question the popular theory that patellar maltracking stems primarily from strength or activation imbalances in the vasti muscles. They suggest instead that vasti function is only one of multiple factors contributing to patellar maltracking, and it’s the other factors that may prove more useful for differentiating one PFPS subgroup from another.
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Full story

NewsBot · Sep 1, 2012

Electromechanical Delay of the Vastus Medialis Obliquus and Vastus Lateralis in Individuals With Patellofemoral Pain Syndrome
Han-Yu Chen, Chia-Chen Chien, Shyi-Kuen Wu, Jiann-Jong Liau, Mei-Hwa Jan
J Orthop Sports Phys Ther 2012;42(9):791-796,

STUDY DESIGN: Case-control study.

OBJECTIVE: To examine electromechanical delay (EMD) of the vastus medialis obliquus (VMO) and the vastus lateralis (VL) in individuals with patellofemoral pain syndrome (PFPS).

BACKGROUND: EMD is a mechanical property of muscles related to protective reflex and sports performance. The time duration of the EMD can be shortened with strength training and, conversely, can be lengthened secondary to immobilization. However, it is unclear if EMD between various components of the quadriceps is affected in individuals with PFPS.

METHODS: Twenty-six individuals with PFPS and 26 healthy volunteers were studied. The VMO and VL were electrically stimulated to evoke muscle twitches. Ultrasound was used to assess patellar movement elicited by the muscle twitch. The time from the onset of electrical stimulation to the onset of patellar movement was measured as the EMD. The EMDs of the VMO and VL were compared between groups using a mixed-model analysis of variance.

RESULTS: Subsequent to a significant interaction (P<.001), post hoc analysis indicated that the EMD of the VMO was longer (PFPS, 37.3 ± 0.7 milliseconds; control, 25.9 ± 0.7 milliseconds; P<.001) and the EMD of the VL was shorter (PFPS, 18.4 ± 0.5 milliseconds; control, 25.1 ± 0.5 milliseconds; P<.001) in the PFPS group. Therefore, in the individuals with PFPS, the EMD of the VMO was significantly longer than that of the VL (P<.001), which was not the case for those in the control group (P = .20).

CONCLUSION: The mechanical properties of the VMO and VL may be altered in patients with PFPS.
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NewsBot · Dec 29, 2012

Muscle Functional MRI to Evaluate Quadriceps Dysfunction in Patellofemoral Pain
Pattyn, Els; Verdonk, Peter; Steyaert, Adelheid; Van Tiggelen, Damien; Witvrouw, Erik
Medicine & Science in Sports & Exercise; 27 December 2012

Purpose: A dysfunction of the quadriceps muscle group has often been suggested to play an important role in the pathophysiology of patellofemoral pain (PFP). However, consensus is lacking regarding the quadriceps recruitment pattern of patients with PFP. The aim of this study is to examine by muscle functional magnetic resonance imaging (mfMRI) if PFP patients actually exhibit an altered activation of the muscles that play a significant role in the dynamic balance of the patella.

Methods: Forty-six patients with PFP (25 female and 21 male, mean age 25.0 +/- 7.4 years) and 30 healthy control subjects (17 female and 13 male, mean age 21.6 +/- 4.5 years) underwent MRI of the quadriceps before and immediately after a squat exercise. The transverse relaxation time (T2) and the T2 shift were calculated for the vasti muscles.

Results: There were no significant differences in the T2 values at rest and the T2 shift values between the patient and the control group, except for the T2 rest value of the VMVI of females (P=0.007). The T2 shift of the VL was significantly smaller than the T2 shift of the VMVI in both study groups (male P<0.001 and female P=0.044), while in females, the T2 shift of the VMO was also significantly smaller than the T2 shift of the VMVI (P=0.027).

Conclusions: The activation pattern of the quadriceps is not altered in patients with PFP for both males and females. As the relative contribution of the quadriceps muscles to a functional activity has not been modified, there is no evidence for quadriceps dysfunction.
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NewsBot · May 14, 2013

The role of muscle strength & activation patterns in patellofemoral pain
H. Toumi et al
Clinical Biomechanics; Available online 8 May 2013

Background
To investigate the extent to which quadriceps muscle activation and strength are responsible for patellofemoral pain.

Methods
A pain on–off switch system synchronized with a force transducer and surface electromyography was utilized on 32 volunteer patellofemoral pain patients during maximal isometric and squat exercises.

Findings
There were 26 patients out of the 32 tested who complained of pain during the squat or isometric test, of these 20 subjects presented a significant advantage for the vastus lateralis compared to the vastus medialis obliquis activation and 12 patients had decreased quadriceps strength of the symptomatic compared to the non symptomatic leg. All patients who demonstrated weak vastus medialis obliquis activation during the isometric exercise possessed the same symptoms during the squat. On the other hand, 9 patients who showed diminished vastus medialis obliquis activation during the squat displayed equal activation between the vastus medialis obliquis and the vastus lateralis during the isometric task. With regard to the timing for the onset of muscle activation, there were only 4 patients who had a difference (P = 0.03) between the symptomatic (0.042 s) and non-symptomatic legs (0.011 s).

Interpretation
Causes for patellofemoral pain vary and are not necessarily a result of quadriceps strength deficit or vastus medialis obliquis activation weakness. Patellofemoral pain patients who possess lower vastus medialis obliquis activation compared to the vastus lateralis do not necessarily have quadriceps weakness while patients presenting with quadriceps strength deficits do not always have an imbalance between vastus medialis obliquis and vastus lateralis activation.
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NewsBot · Jun 25, 2013

Between-limb Gait and Muscle Strength Asymmetry in Runners with Patellofemoral Pain Syndrome
Webber, Talia
MSC Thesis 2013 University of Calgary

Purpose: To investigate between-limb gait and muscle strength asymmetry in patellofemoral pain syndrome (PFPS) subjects and controls.

Methods: Three-dimensional hip, knee, and ankle joint kinematics were collected during treadmill running. Maximum voluntary isometric contractions of the hip musculature were collected using a force dynamometer. PFPS subjects completed a 6-week strengthening program. Discrete variable asymmetry was calculated using analysis of variance and waveform kinematic asymmetry was calculated using coefficients of multiple correlation and root mean square error.

Results: PFPS exhibited between-limb asymmetry of hip and knee transverse plane waveform kinematics, while controls exhibited asymmetry of hip frontal plane waveform kinematics. PFPS subjects exhibited decreased hip transverse plane and increased knee transverse plane waveform kinematic asymmetry following rehabilitation.

Conclusion: PFPS subjects demonstrate a different pattern of gait asymmetry than controls. Increases in hip muscle strength results in between-limb asymmetry of PFPS subjects to more closely resemble that of healthy controls.
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NewsBot · Jul 16, 2013

COMPARISON OF ELECTRICAL ACTIVITY OF PATELLA STABILIZER MUSCLES BETWEEN ATHLETESWITH AND WITHOUT PATELLOFEMORAL PAIN SYNDROME
Nahid Khoshraftar Yazdi; Majid Mehdikhani
1st Annual International Interdisciplinary Conference, AIIC 2013, 24-26 April, Azores, Portugal -Proceedings- 679

The aim of this study was to compare the electrical activity of the Tensor fascia lata (TFL) and Vastus lateralis (VL) muscles as lateral stabilizers and the Vastus medialis oblique (VMO) muscle as medial stabilizer of the patella in athletes with and without patellofemoral pain syndrome (PFPS). Eleven healthy athletes (4 women, 7 men) and 9 athletes with PFPS (3 women, 6 men) ranging in age from 20 to 30 years performed the submaximal isometric knee extension contraction initiated from 45°of flexion and an extended position to 30° and 15°angles. The activation amplitude of the TFL, VL and VMO muscles were quantified from the recorded electromyographic (EMG) signals. The results showed that Electrical activity of the VMO muscle at 30° and 45° angles for the patients was significantly greater than those of the control subjects. No significant differences were demonstrated in VMO: VL and VMO: TFL across all knee flexion angles between groups. However, the mean value of the ratio of VMO: (TFL + VL) at an angle of 30° for the subjects with PFPS was significantly greater than that of the control group. It may be assumed that the higher electrical activity of the VMO at 30° angle in PFPS patients is an effort to prevent more lateral patella tracking. Since the TFL and VL muscles produce lateral force on the patella, both of them should be studied for consideration of lateral stabilizers of the patella in the patients with PFPS.
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NewsBot · Dec 24, 2013

Coupling Angle Variability in Healthy and Patellofemoral Pain Runners
Tommy J. Cunningham et al
Clinical Biomechanics; Available online 17 December 2013

Background
Patellofemoral pain is hypothesized to result in less joint coordination variability. The ability to relate coordination variability to patellofemoral pain pathology could have many clinical uses; however, evidence to support its clinical application is lacking. The aim was to determine if vector coding’s coupling angle variability, as a measure of joint coordination variability, was less for runners with patellofemoral pain than healthy controls as is commonly postulated.
Methods
Nineteen female recreational runners with patellofemoral pain and eleven healthy controls performed a treadmill acclimation protocol then ran at a self-selected pace for fifteen minutes. 3-D kinematics, force plate kinetics, knee pain and rating of perceived exertion were recorded each minute. Data were selected for the: pain group at the highest pain reached (pain ≥ 3/10) in a non-exerted state (exertion < 14/20), and; non-exerted healthy group from the eleventh minute. Coupling angle variability was calculated over several portions of the stride for six knee-ankle combinations during five non-consecutive strides.
Findings
46 of 48 coupling angle variability measures were greater for the pain group, with 7 significantly greater (p < .05).
Interpretation
These findings oppose the theory that less coupling angle variability is indicative of a pathological coordinate state during running. Greater coupling angle variability may be characteristic of patellofemoral pain in female treadmill running when a larger threshold of pain is reached than previously observed. A predictable and directional response of coupling angle variability measures in relation to knee pathology is not yet clear and requires further investigation prior to considerations for clinical utility
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NewsBot · Oct 7, 2014

Re-evaluating the functional implications of the Q-angle and its relationship to in-vivo patellofemoral kinematics
Benjamin R. Freedman, Timothy J. Brindle, Frances T. Sheehan
Clinical Biomechanics; Articles in Press

Highlights
•The data from the current study question the validity and utility of the Q-angle as it (1) does not represent the true “line-of-application the quadriceps force,” (2) has low to moderate reliability, (3) does not strongly correlate to in vivo PF kinematics, (4) has weak to moderate correlations with patellar kinematics indicating exactly the opposite of that believed clinically (medial displacement in increased Q-angle), and (5) was not different between cohorts.
•PF interventions are likely best guided by directly measuring in vivo patellar kinematics acquired during tasks requiring active quadriceps control using accurate dynamic measurement techniques.
•Clinicians may want to consider other clinical measures, such as the clinical patellar tilt angle, that have demonstrated greater reliability and stronger correlations to patellar kinematics.
•These study results lead to the recommendation that the clinical Q-angle not be used as a surrogate for the patellar kinematics. Future research should focus on developing clinical markers that have a strong relationship to patellar kinematics and/or PF pain.
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Background
The Q-angle is widely used clinically to evaluate individuals with anterior knee pain. Recent studies have questioned the utility of this measure and have suggested that a large Q-angle may not be associated with lateral patellofemoral translation, as often assumed. The objective of this study was to determine: 1) how accurately the Q-angle represents the line-of-action of the quadriceps and 2) if adding active quadriceps contraction or a bent knee position to the measurement of the Q-angle improves its reliability, accuracy, and association with patellofemoral kinematics.

Design
Cross-sectional cohort study.

Methods
The study included individuals diagnosed with chronic idiopathic patellofemoral pain and control subjects (n = 43 and n = 30 knees). Three measures of the clinical Q-angle (straight- and bent-knee with relaxed quadriceps and straight-knee with maximum isometric quadriceps contraction) were obtained with a goniometer and compared to a fourth MR-based measure of Q-angle. Patellofemoral kinematics were derived from dynamic cine-phase contrast images, acquired while subjects extended/flexed their knee from approximately 0° and 45°.

Findings
The Q-angle did not represent the line-of-action of the quadriceps. The average difference between each clinical and the MR-based Q-angle ranged from 5° to 8°. These differences varied greatly across subjects (range: -28.5° to 3.9o). Adding an active quadriceps contraction or a bent knee position, did not improve the reliability of the Q-angle. An increased Q-angle correlated to medial patellar displacement and tilt (r = 0.38-0.54, p <0.001) in the cohort with anterior knee pain.

Interpretation
Clinicians are cautioned against using the Q-angle to infer patellofemoral kinematics.
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NewsBot · Apr 14, 2016

Q-angle in patellofemoral pain: relationship with dynamic knee valgus, hip abductor torque, pain and function.
Almeida GP et al
Rev Bras Ortop. 2016 Feb 9;51(2):181-6.

OBJECTIVE:
To investigate the relationship between the q-angle and anterior knee pain severity, functional capacity, dynamic knee valgus and hip abductor torque in women with patellofemoral pain syndrome (PFPS).
METHODS:
This study included 22 women with PFPS. The q-angle was assessed using goniometry: the participants were positioned in dorsal decubitus with the knee and hip extended, and the hip and foot in neutral rotation. Anterior knee pain severity was assessed using a visual analog scale, and functional capacity was assessed using the anterior knee pain scale. Dynamic valgus was evaluated using the frontal plane projection angle (FPPA) of the knee, which was recorded using a digital camera during step down, and hip abductor peak torque was recorded using a handheld dynamometer.
RESULTS:
The q-angle did not present any significant correlation with severity of knee pain (r = -0.29; p = 0.19), functional capacity (r = -0.08; p = 0.72), FPPA (r = -0.28; p = 0.19) or isometric peak torque of the abductor muscles (r = -0.21; p = 0.35).
CONCLUSION:
The q-angle did not present any relationship with pain intensity, functional capacity, FPPA, or hip abductor peak torque in the patients with PFPS.
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NewsBot · May 24, 2016

Structural Abnormalities on Magnetic Resonance Imaging in Patients With Patellofemoral Pain
A Cross-sectional Case-Control Study
Rianne A. van der Heijden et al
Am J Sports Med May 20, 2016

Background: Structural abnormalities of the patellofemoral joint might play a role in the pathogenesis of patellofemoral pain (PFP), a common knee problem among young and physically active individuals. No previous study has investigated if PFP is associated with structural abnormalities of the patellofemoral joint using high-resolution magnetic resonance imaging (MRI).
Purpose: To investigate the presence of structural abnormalities of the patellofemoral joint on high-resolution MRI in patients with PFP compared with healthy control subjects.
Study Design: Cross-sectional study; Level of evidence, 3.
Methods: Patients with PFP and healthy control subjects between 14 and 40 years of age underwent high-resolution 3-T MRI. All images were scored using the Magnetic Resonance Imaging Osteoarthritis Knee Score with the addition of specific patellofemoral features. Associations between PFP and the presence of structural abnormalities were analyzed using logistic regression analyses adjusted for age, body mass index (BMI), sex, and sports participation.
Results: A total of 64 patients and 70 control subjects were included in the study. Mean ? SD age was 23.2 ? 6.4 years, mean BMI ? SD was 22.9 ? 3.4 kg/m2, and 56.7% were female. Full-thickness cartilage loss was not present. Minor patellar cartilage defects, patellar bone marrow lesions, and high signal intensity of the Hoffa fat pad were frequently seen in both patients (23%, 53%, and 58%, respectively) and control subjects (21%, 51%, and 51%, respectively). After adjustment for age, BMI, sex, and sports participation, none of the structural abnormalities were statistically significantly associated with PFP.
Conclusion: Structural abnormalities of the patellofemoral joint have been hypothesized as a factor in the pathogenesis of PFP, but the study findings suggest that structural abnormalities of the patellofemoral joint on MRI are not associated with PFP.
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NewsBot · Oct 22, 2016

Relationship between Duration of Patellofemorall Pain Syndrome and Patellar Alignment
Zohre Ebrahimi et al
Journal of Clinical Physiotherapy Research Vol 1, No 2 (2016)

Introduction: Patellofemoral Pain Syndrome (PFPS) is one of the most common musculoskeletal disorders. The cause of PFPS has been reported to be multifactorial. Patellar malalignments are accepted as the leading causes of PF pain and PF joint disorders. The purpose of the present study was to assess the relationship between duration of PFPS and patellar alignment.
Method and Materials: The patellar alignment of participants was compared in three groups: patients with 2-3 month PFPS duration, patients with 12-15 months PFPS duration, and matched healthy participants. Congruence angle, Q angle, Patella height (Insall-Salvati index), Lateral patellar tilt angle, and Pain and Function score were measured among these three groups.
Results: The patella height (Insall-Salvati index) (r=0.32), lateral patellar tilt angle (r=0.28), Visual Analogy Scale (r=0.77), and function score (r=-0.80) correlated with duration of PFPS. The patella height (Insall-Salvati index), lateral patellar tilt angle, and pain in patients group with 12-15 months of PFPS duration were significantly greater and function score was less than those of the control group. The patella height (Insall-Salvati index) and pain in patients group with 2-3 months of PFPS duration were significantly greater and function score was less than those of the control group. There was no significant difference in other measurements among the three groups.
Conclusions: It can be concluded that duration of PFPS affects alignment of patella and knee joint function score. Therefore, early and complete treatment of PFPS is recommended.
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NewsBot · Jan 20, 2017

Patellofemoral Pain & the Vastus Medialis Myth

NewsBot · May 2, 2017

VASTUS LATERALIS OBLIQUE ACTIVITY DURING GAIT OF SUBJECTS WITH PATELLOFEMORAL PAIN
Gilmar Moraes Santos et al
Rev Bras Med Esporte vol.23 no.2 São Paulo Mar./Apr. 2017

Introduction:
So far, little is known about the behavior of electromyographic activity of vastus lateralis oblique muscle during treadmill gait in subjects with and without patellofemoral pain syndrome.

Objective:
The purpose of this study was to investigate the electromyographic activity of the patellar stabilizers muscles and the angle of the knee joint flexion in subjects with and without patellofemoral pain syndrome.

Method:
Fifteen subjects without (21 ± 3 years) and 12 with patellofemoral pain syndrome (20 ± 2 years) were evaluated. The electromyographic activity and flexion angle of the knee joint were obtained during gait on the treadmill with a 5 degree inclination.

Results:
The knee flexion angle was significantly lower in the subjects with patellofemoral pain syndrome when compared with the healthy controls. The electromyographic activity of vastus lateralis longus was significantly greater during gait on the treadmill with inclination in subjects with patellofemoral pain syndrome. The results also showed that the electromyographic activity of vastus lateralis oblique and vastus medialis oblique were similar in both groups, regardless of the condition (with/without inclination).

Conclusion:
We have shown that knee kinematics during gait differs among patients with and without patellofemoral pain syndrome and healthy controls and that a different motor strategy persists even when the pain is no longer present. In addition, the findings suggested that the vastus lateralis oblique has a minor role in patellar stability during gait.
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NewsBot · Feb 13, 2018

Vastus lateralis motor unit firing rate is higher in females with patellofemoral pain
Alessio Gallina et al
Archives of Physical Medicine and Rehabilitation Article in Press

Objective
To compare neural drive, determined from motor unit firing rate, to the vastus medialis and lateralis in females with and without patellofemoral pain.

Design
Cross-sectional study.

Setting
University research laboratory.

Participants
Females (N=56) 19-35 years old, 36 with patellofemoral pain and 20 controls. Interventions: Not applicable.

Main Outcome Measure(s)
Participants sustained an isometric knee extension contraction at 10% of their maximal voluntary effort for 70s. Motor units (N=414) were identified using high-density surface electromyography. Average firing rate was calculated between 5 and 35s after recruitment for each motor unit. Initial firing rate was the inverse of the first three motor unit inter-spike intervals.

Results
In control participants, vastus medialis motor units discharged at higher rates than vastus lateralis (p=0.001). This was not observed in females with patellofemoral pain (p=0.78) due to a higher discharge rate of vastus lateralis compared to control participants (p=0.002). No between-group differences were observed for vastus medialis (p=0.93). Similar results were obtained for the initial motor unit firing rate.

Conclusions
These findings suggest that females with patellofemoral pain have a higher neural drive to vastus lateralis but not vastus medialis, which may be a contributor of the altered patellar kinematics observed in some studies. The different neural drive may be an adaptation to patellofemoral pain, possibly to compensate for decreased quadriceps force production, or a precursor of patellofemoral pain.
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NewsBot · Feb 28, 2018

Runners with Patellofemoral Pain Exhibit Greater Peak Patella Cartilage Stress Compared to Pain-Free Runners
Tzu-Chieh Liao et al
Journal of Applied Biomechanics

The purpose of this study is to determine whether recreational runners with patellofemoral pain (PFP) exhibit greater peak patella cartilage stress compared to pain-free runners. A secondary purpose was to determine the kinematic and/or kinetic predictors of peak patella cartilage stress during running. Twenty-two female recreational runners participated (12 with PFP and 10 pain-free controls). Patella cartilage stress profiles were quantified using subject-specific finite element models simulating the maximum knee flexion angle during stance phase of running. Input parameters to the finite element model included subject-specific patellofemoral joint geometry, quadriceps muscle forces, and lower extremity kinematics in the frontal and transverse planes. Tibiofemoral joint kinematics and kinetics were quantified to determine the best predictor of stress using stepwise regression analysis. Compared to the pain-free runners, those with PFP exhibited greater peak hydrostatic pressure (PFP vs. control, 21.2 ± 5.6 MPa vs. 16.5 ± 4.6 MPa) and maximum shear stress (11.3 ± 4.6 MPa vs. 8.7 ± 2.3 MPa). Knee external rotation was the best predictor of peak hydrostatic pressure and peak maximum shear stress (38% and 25% of variances, respectively) followed by the knee extensor moment (21% and 25% of variances, respectively). Runners with PFP exhibit greater peak patella cartilage stress during running compared to pain-free individuals. The combination of knee external rotation and a high knee extensor moment best predicted elevated peak stress during running.
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NewsBot · Sep 28, 2018

Patellofemoral Joint Stress during Incline and Decline Running
Kai-Yu Ho et al
Phys Ther Sport; Article in Press

Highlights
1.First study assessing the effects of gradients on patellofemoral joint stress
2.Decline running significantly increases patellofemoral joint stress
3.Incline running does not alter patellofemoral joint stress
4.Elevated joint stress during decline running is mainly driven by less trunk flexion
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Objectives
To compare patellofemoral joint (PFJ) stress between level, incline, and decline running.

Design
Experimental study.

Setting
University laboratory.

Participants
Twenty recreational runners.

Main Outcome Measures
Kinematics and kinetics of the trunk and lower extremity were obtained under 3 treadmill conditions: level, 6° incline, and 6° decline. PFJ stress, PFJ reaction force, and PFJ contact area were determined using a biomechanical model. One-way ANOVAs with repeated measures and post-hoc analyses were used to compare outcome variables across the 3 conditions.

Results
Peak PFJ stress and PFJ stress-time integral (cumulative PFJ stress over the stance phase) during decline running were significantly higher than during level and incline running. There was no difference in peak PFJ stress and PFJ stress-time integral between level and incline running. The increased peak PFJ stress during decline running was related to increased PFJ reaction force, resulting from a decrease in trunk flexion angle.

Conclusions
Running on a decline treadmill resulted in higher peak PFJ stress and stress-time integral. Peak PFJ stress and PFJ stress-time integral were similar during level and incline running. Results from this study may be used to prevent excessive PFJ stress during decline running, by targeting a postural strategy utilizing increased trunk flexion.
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NewsBot · May 5, 2020

Individuals with patellofemoral pain syndrome have altered inter-leg force coordination
Bernard X.W.Liew et al
Gait & Posture; Volume 79, June 2020, Pages 65-70

Highlights
•Patellofemoral pain syndrome (PFPS) is a common overuse leg injury.
•Greater inter-leg motor abundance may encourage greater inter-leg force sharing.
•PFPS impairs inter-leg motor abundance during bilateral hopping.
•Motor deficits occur during periods of shock absorption and peak bodyweight support.
•Impaired inter-leg force sharing may prolong pain in individuals with PFPS.
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Background
Patellofemoral pain syndrome (PFPS) is one of the most common musculoskeletal disorders. Pain may be further exacerbated by atypical motor coordination strategies. It has been thought that low coordination variability may concentrate loads onto painful knee tissues.

Research question
To investigate if inter-limb force coordination is altered between individuals with and without PFPS.

Methods
31 individuals (control = 17, PFPS = 14) performed bilateral vertical hopping, on two force plates at three frequencies (2.2, 2.6, 3.0 Hz). Uncontrolled manifold analysis (UCM) was used to provide an index of motor abundance (IMA) in the coordination of inter-limb forces to stabilize the two-limb’s total force. UCM was applied to the study of forces in each plane (medial-lateral (ML), anterior-posterior (AP), vertical). Bayesian Functional Data Analysis was used for statistical inference. We calculated the mean () with 95 % credible interval (CrI) of the difference between the two groups. We also calculated the probability .

Results
Individuals with PFPS had the greatest significant decrement from controls at 6% of stance hopping at 2.6 Hz by a mean difference of -0.23 for ML GRF; at 19 % of stance hopping at 2.2 Hz by a mean difference of -0.14 for AP GRF; and 52 % of stance hopping at 2.6 Hz by a mean difference of -0.14 for vertical GRF. For vertical GRF, there was a > 0.95 probability that controls had greater IMA than individuals with PFPS hopping between 12–13% of stance at 2.2 Hz, and between 48–55% at 2.6 Hz.

Significance
Individuals with PFPS have reduced inter-leg force coordination for impact force attenuation and body support, compared to asymptomatic controls. The present study provides insights into a plausible mechanism underpinning persistent knee pain which could be used in the development of novel rehabilitative approaches for individuals with PFPS.
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