Rasch analysis of the anterior knee pain scale in adolescents with patellofemoral pain.

OBJECTIVE: The aim of this study was to evaluate the Anterior Knee Pain Scale in a cohort of adolescents being treated conservatively for patellofemoral pain using Rasch analysis. DESIGN: This is a psychometric study. SETTING: Physical therapy clinics of a large pediatric hospital in Columbus, Ohio (United States). SUBJECTS: A total of 646 adolescent patients with patellofemoral pain (76% female, 14.6 ± 1.6 years old). INTERVENTION: Not applicable. MAIN MEASURE: The Anterior Knee Pain Scale. RESULTS: The median Anterior Knee Pain Scale score was 73 (interquartile range 64-81), with scores ranging from 7 to 100 on the 100-point scale. The Rasch person reliability for the Anterior Knee Pain Scale was 0.74 and the Cronbach's alpha was 0.75, representing an acceptable person reliability. Principal component analysis revealed a ratio of 5.2:1 demonstrating acceptable unidimensionality of the Anterior Knee Pain Scale. A significant misfit was observed in the item "Abnormal Painful Kneecap Movements" (Outfit Means Square 2.74, Infit Means Square 1.41). Ordering of item responses was unsatisfactory as only five of the 13 items demonstrated appropriate distinction between each of the responses. There was no differential item functioning for sex or age for all items of the Anterior Knee Pain Scale, based upon the criterion of ⩾ 0.5 logit difference. CONCLUSION: The Anterior Knee Pain Scale does not meet interval-level measurement criteria and should be considered ordinal level data.

Classifying individuals with and without patellofemoral pain syndrome using ground force profiles - Development of a method using functional data boosting.

BACKGROUND: Predictors of recovery in patellofemoral pain syndrome (PFPS) currently used in prognostic models are scalar in nature, despite many physiological measures originally lying on the functional scale. Traditional modelling techniques cannot harness the potential predictive value of functional physiological variables. RESEARCH QUESTION: What is the classification performance of PFPS status of a statistical model when using functional ground reaction force (GRF) time-series? METHODS: Thirty-one individuals (control = 17, PFPS = 14) performed maximal countermovement jumps, on two force plates. The three-dimensional components of the GRF profiles were time-normalized between the start of the eccentric phase and take-off, and used as functional predictors. A statistical model was developed using functional data boosting (FDboost), for binary classification of PFPS statuses (control vs PFPS). The area under the Receiver Operating Characteristic curve (AUC) was used to quantify the model's ability to discriminate the two groups. RESULTS: The three predictors of GRF waveform achieved an average out-of-bag AUC of 93.7 %. A 1 % increase in applied medial force reduced the log odds of being in the PFPS group by 0.68 at 87 % of jump cycle. In the AP direction, a 1 % reduction in applied posterior force increased the log odds of being classified as PFPS by 1.10 at 70 % jump cycle. For the vertical GRF, a 1 % increase in applied force reduced the log odds of being classified in the PFPS group by 0.12 at 44 % of the jump cycle. SIGNIFICANCE: Using simple functional GRF variables collected during functionally relevant task, in conjunction with FDboost, produced clinically interpretable models that retain excellent classification performance in individuals with PFPS. FDboost may be an invaluable tool to be used in longitudinal cohort prognostic studies, especially when scalar and functional predictors are collected.

Targeted Treatment Protocol in Patellofemoral Pain: Does Treatment Designed According to Subgroups Improve Clinical Outcomes in Patients Unresponsive to Multimodal Treatment?

BACKGROUND: Targeted intervention for subgroups is a promising approach for the management of patellofemoral pain. HYPOTHESIS: Treatment designed according to subgroups will improve clinical outcomes in patients unresponsive to multimodal treatment. STUDY DESIGN: Prospective crossover intervention. LEVEL OF EVIDENCE: Level 3. METHODS: Patients with patellofemoral pain (PFP; n = 61; mean age, 27 ± 9 years) were enrolled. Patients with PFP received standard multimodal treatment 3 times a week for 6 weeks. Patients not responding to multimodal treatment were then classified into 1 of 3 subgroups (strong, weak and tight, and weak and pronated foot) using 6 simple clinical tests. They were subsequently administered 6 further weeks of targeted intervention, designed according to subgroup characteristics. Visual analog scale (VAS), perception of recovery scale (PRS), 5-Level European Quality 5 Dimensions (EQ-5D-5L), and self-reported version of the Leeds Assessment of Neuropathic Symptoms and Signs scale (S-LANSS) were used to assess pain, knee function, and quality of life before and after the interventions. RESULTS: In total, 34% (n = 21) of patients demonstrated recovery after multimodal treatment. However, over 70% (n = 29/40) of nonresponders demonstrated recovery after targeted treatment. The VAS, PRS, S-LANSS, and EQ-5D-5L scores improved significantly after targeted intervention compared with after multimodal treatment (P < 0.001). The VAS score at rest was significantly lower in the "weak and pronated foot" and the "weak and tight" subgroups (P = 0.011 and P = 0.008, respectively). Posttreatment pain intensity on activity was significantly lower in the "strong" subgroup (P = 0.006). CONCLUSION: Targeted treatment designed according to subgroup characteristics improves clinical outcomes in patients unresponsive to multimodal treatment. CLINICAL RELEVANCE: Targeted intervention could be easily implemented after 6 simple clinical assessment tests to subgroup patients into 1 of 3 subgroups (strong, weak and tight, and weak and pronated foot). Targeted interventions applied according to the characteristics of these subgroups have more beneficial treatment effects than a current multimodal treatment program.

Toward the Development of Data-Driven Diagnostic Subgroups for People With Patellofemoral Pain Using Modifiable Clinical, Biomechanical, and Imaging Features.

BACKGROUND: Unfavorable treatment outcomes for people with patellofemoral pain (PFP) have been attributed to the potential existence of subgroups that respond differently to treatment. OBJECTIVES: This study aimed to identify subgroups within PFP by combining modifiable clinical, biomechanical, and imaging features and exploring the prognosis of these subgroups. METHODS: This was a longitudinal cohort study, with baseline cluster analyses. Baseline data were analyzed using a 2-stage cluster analysis; 10 features were analyzed within 4 health domains before being combined at the second stage. Prognosis of the subgroups was assessed at 12 months, with subgroup differences reported as global rating of change and analyzed with an exploratory logistic regression adjusted for known confounders. RESULTS: Seventy participants were included (mean age, 31 years; 43 [61%] female). Cluster analysis revealed 4 subgroups: "strong," "pronation and malalignment," "weak," and "active and flexible." Descriptively, compared to the strong subgroup (55% favorable), the odds of a favorable outcome were lower in the weak subgroup (31% favorable; adjusted odds ratio [OR] = 0.30; 95% confidence interval [CI]: 0.07, 1.36) and the pronation and malalignment subgroup (50%; OR = 0.64; 95% CI: 0.11, 3.66), and higher in the active and flexible subgroup (63%; OR = 1.24; 95% CI: 0.20, 7.51). After adjustment, compared to the strong subgroup, differences between some subgroups remained substantive, but none were statistically significant. CONCLUSION: In this relatively small cohort, 4 PFP subgroups were identified that show potentially different outcomes at 12 months. Further research is required to determine whether a stratified treatment approach using these subgroups would improve outcomes for people with PFP. LEVEL OF EVIDENCE: Diagnosis, level 2b. J Orthop Sports Phys Ther 2019;49(7):536-547. doi:10.2519/jospt.2019.8607.

Are there three main subgroups within the patellofemoral pain population? A detailed characterisation study of 127 patients to help develop targeted intervention (TIPPs).

BACKGROUND: Current multimodal approaches for the management of non-specific patellofemoral pain are not optimal, however, targeted intervention for subgroups could improve patient outcomes. This study explores whether subgrouping of non-specific patellofemoral pain patients, using a series of low cost simple clinical tests, is possible. METHOD: The exclusivity and clinical importance of potential subgroups was assessed by applying à priori test thresholds (1 SD) from seven clinical tests in a sample of adult patients with non-specific patellofemoral pain. Hierarchical clustering and latent profile analysis, were used to gain additional insights into subgroups using data from the same clinical tests. RESULTS: 130 participants were recruited, 127 had complete data: 84 (66%) female, mean age 26 years (SD 5.7) and mean body mass index 25.4 (SD 5.83), median (IQR) time between onset of pain and assessment was 24 (7-60) months. Potential subgroups defined by the à priori test thresholds were not mutually exclusive and patients frequently fell into multiple subgroups. Using hierarchical clustering and latent profile analysis three subgroups were identified using 6 of the 7 clinical tests. These subgroups were given the following nomenclature: (1) 'strong', (2) 'weak and tighter' and (3) 'weak and pronated foot'. CONCLUSIONS: We conclude that three subgroups of patellofemoral patients may exist based on the results of six clinical tests which are feasible to perform in routine clinical practice. Further research is needed to validate these findings in other data sets and, if supported by external validation, to see if targeted interventions for these subgroups improve patient outcomes.

Pattern classification of kinematic and kinetic running data to distinguish gender, shod/barefoot and injury groups with feature ranking.

The identification of differences between groups is often important in biomechanics. This paper presents group classification tasks using kinetic and kinematic data from a prospective running injury study. Groups composed of gender, of shod/barefoot running and of runners who developed patellofemoral pain syndrome (PFPS) during the study, and asymptotic runners were classified. The features computed from the biomechanical data were deliberately chosen to be generic. Therefore, they were suited for different biomechanical measurements and classification tasks without adaptation to the input signals. Feature ranking was applied to reveal the relevance of each feature to the classification task. Data from 80 runners were analysed for gender and shod/barefoot classification, while 12 runners were investigated in the injury classification task. Gender groups could be differentiated with 84.7%, shod/barefoot running with 98.3%, and PFPS with 100% classification rate. For the latter group, one single variable could be identified that alone allowed discrimination.

Management of patients with patellofemoral pain syndrome using a multimodal approach: a case series.

STUDY DESIGN: A case series of consecutive patients referred to physical therapy with patellofemoral pain syndrome (PFPS). BACKGROUND: Physical therapists often treat patients with PFPS, yet there is currently no consensus as to the most effective management strategies. The purpose of this case series is to describe the outcomes of patients referred to physical therapy with PFPS who were treated with a multimodal approach. CASE DESCRIPTION: Five patients were treated with a combination of thrust and nonthrust manipulation directed at the joints of the lower quarter, trunk and hip stabilization exercises, patellar taping, and foot orthotics. Outcome measures used to capture change in patient status included the Numeric Pain Rating Scale, the Kujala Anterior Knee Pain Scale, the Lower Extremity Functional Scale, and the Global Rating of Change. OUTCOMES: Five patients (median age, 15 years; range, 14-50 years) with a median duration of knee pain for 8 months (range, 3-24 months) were included in this prospective case series. Four (80%) of the 5 patients demonstrated decreased pain and a clinically significant improvement in function. These gains in function were maintained at a 6-month follow-up. DISCUSSION: Although a cause-and-effect relationship cannot be inferred from a case series, the outcomes achieved by the patients are consistent with studies incorporating manual physical therapy, exercise, patellar taping, and orthotic prescription to the management of conditions of the lower extremity. Further randomized controlled trials should be performed to determine the effectiveness of this multimodal approach for the management of individuals with PFPS.

Is pain in patellofemoral pain syndrome neuropathic?

OBJECTIVE: There is no consensus among experts regarding the etiology or management of patellofemoral pain syndrome (PFPS). Observations indicating dysfunction of the peripheral nervous system around the patellae have been reported. To what extent these sensory abnormalities cause pain has so far not been investigated. The aim of this study was to assess whether a subgroup of patients with unilateral PFPS have neuropathic pain related to the painful knee. METHOD: A total of 91 patients with unilateral PFPS, between 18 and 40 years of age, and a comparable group of 23 healthy participants aged 18 to 44 years were included. Level of knee function, pain intensity, and qualities were assessed. Somatosensory assessments were carried out by bedside neurologic tests and quantitative sensory testing, assessing thermal, tactile, and vibration thresholds. RESULTS: Ample signs of sensory aberrations with considerable heterogeneity and overlap regarding the degree and type of dysfunction of the nervous system were found in the painful area of the PFPS patients. No clear subgroup of patients with neuropathic pain or clustering of features related to neuropathic pain was identified. DISCUSSION: This study hypothesizes that the observed sensory aberrations may cause neuropathic pain in patients with PFPS. There is no validated method for subgrouping patients with possible neuropathic pain and in this study considerable heterogeneity and overlap regarding signs and symptoms of neuropathic pain made subgrouping even more difficult. A mechanism-based understanding of the pain is, however, essential for the selection of adequate treatment strategies in painful musculoskeletal disorders.

Anterior knee pain in children with cerebral palsy.

Anterior knee pain arising from the patellofemoral joint may be a significant problem in the cerebral palsy (CP) population. The aim of this study was to classify patients with anterior knee pain based on etiology and organize orthopaedic management based on this classification. This study was a retrospective chart review of patients with CP and anterior knee pain admitted to the orthopaedic outpatient clinic between 1991 and 2003. Children with CP who had intractable anterior knee pain despite 6 months of conservative treatment with at least 2 years' follow-up were identified and included. The medical records, radiographs, and treatment protocols were screened. Patients were classified into 3 groups according to pathology. Group I consisted of 7 children with patella alta only. Group II consisted of 7 children with patellar inferior pole fractures. Group III consisted of 13 children with subluxated or dislocated patellas. Conservative treatment methods such as anti-inflammatory drugs, local ice packs, stretching exercises, and braces should be the first step in treatment. For those patients in whom conservative treatment was not effective, surgical treatment alternatives were discussed. Knee pain resolved in all patients after surgical treatment of the underlying pathology. Gait analysis can be performed for patients with patellofemoral subluxations to evaluate the rotational malalignment of the tibia and femur. In conclusion, anterior knee pain arising from the patellofemoral joint in patients with CP should be evaluated and treated to prevent future functional deterioration.

Development of a clinical prediction rule for classifying patients with patellofemoral pain syndrome who respond to patellar taping.

STUDY DESIGN: Predictive validity/diagnostic test study. OBJECTIVE: To determine the predictive validity and interrater reliability of selected clinical exam items and to develop a clinical prediction rule (CPR) to determine which patients respond successfully to patellar taping. BACKGROUND: Patellar taping is often used to treat patients with PFPS. However, the characteristics of the patients who respond best to patellar taping intervention have not been identified. METHODS AND MEASURES: Fifty volunteers (27 males, 23 females) with PFPS underwent a standardized clinical examination. Diagnosis of PFPS was based on the complaint of retropatellar pain that was provoked by a partial squat or stair ascent/descent. Subjects performed 3 functional activities and rated their pain during each activity on a numerical rating scale (NPRS). All subjects received treatment with a medial glide patellar-taping technique and repeated the functional activities and pain ratings. An immediate 50% reduction in pain or moderate improvement on a global rating of change (GRC) questionnaire was considered a treatment success. Likelihood ratios (LRs) were calculated to determine which examination items were most predictive of treatment outcome. Logistic regression analysis identified items included in the CPR. RESULTS: Twenty-six subjects (52%) had an immediate successful response to the intervention. Two examination items (positive patellar tilt test or tibial varum greater than 5 degrees, +LR = 4.4) comprised the CPR. Application of the CPR improved the probability of a successful outcome from 52% to 83%. Fifty-eight percent of the lower extremity measures were associated with moderate to good reliability (reliability coefficient range, 0.52-0.84). The reliability coefficients for the items that comprised the CPR were 0.49 (patellar tilt) and 0.66 (tibial varum). CONCLUSION: A CPR was developed to predict an immediate successful response to a medial glide patellar taping technique. Validation of the CPR in an independent sample is necessary before widespread clinical use can be recommended.

Primary cartilage lesions and outcome among subjects with patellofemoral pain syndrome.

We investigated the association between cartilage lesion and future symptoms in two groups of subjects with patellofemoral pain syndrome (PFPS). Group A consisted of 31 men (mean age 20.9 years, range 19-32) and group B of 28 consecutive patients (12 men and 16 women; mean age 27.8 years, range 15-50) operated on for PFPS. The mean follow-up time was 3.4 (range 1-7) years in group A and 4.9 (range 1-6) years in group B. At follow-up the subjects in group A with severe cartilage lesion (n = 10) reported more knee symptoms as measured by their Kujala score (mean 75.1, SE 3.6 vs. 88.5, SE 2.4) than those with minor cartilage lesion (n = 21) (age and follow-up time-adjusted P < 0.01). In group B the subjects with severe cartilage lesion tended to report more knee symptoms according to their Kujala score (mean 71.0, SE 7.0 vs. 86.1, SE 5.9; age, sex and follow-up time-adjusted P = 0.15) and VAS score (mean 51.8, SE 11.8 vs. 12.7, SE 10.4; adjusted P = 0.04) than the subjects without cartilage lesion. Our study shows that among the patients with PFPS, the subjects with severe cartilage lesion of the patella or femoral trochlea reported more subjective symptoms and functional limitations at follow-up than those without or with small cartilage lesion of the patella or femoral trochlea.

Clinical classification of patellofemoral pain syndrome: guidelines for non-operative treatment.

The patellofemoral pain syndrome (PFPS) remains a challenging musculoskeletal entity encountered by clinicians. Reviewing the literature, conflicting data seem to exist regarding the effect of non-operative treatment in PFPS patients. A possible explanation may be lack of a clear classification system of patients with PFPS. It is our opinion that the term PFPS still is a 'wastebasket', which probably comprises several different entities. Therefore, it seems important to subdivide this broad group of patients into different categories with a specific rehabilitation approach. In this study, we introduce a classification system, which reflects a consensus reached by the European Rehabilitation Panel. This classification system should help the clinicians to identify the cause(s) of patellofemoral pain, and consequently help to select the most appropriate non-operative treatment. The authors are aware that no rehabilitation protocol will work for all PFPS patients, since the underlying mosaic of pathophysiology and tissue-healing responses are unique. Therefore, the aim of this study with a classification system was to guide the clinician through clinical examination in order to develop a non-operative treatment protocol, specific for each individual with PFPS.