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Purpose The purpose of the study was to evaluate the frontal gait patterns in patients with chronic patellofemoral instability compared to healthy controls. The hypothesis was that internal-rotation–adduction moment of the knee as altered dynamic Q-angle is evident in patients and correlates positively with increased femoral torsion. Methods Thirty-five patients with symptomatic recurrent patellofemoral instability requiring surgical treatment were matched for average age, sex, and body mass index with 15 healthy controls (30 knees). Several clinical and radiographic measurements were taken from each participant: internal and external rotation (hipIR, hipER), Q-angle, tubercle sulcus angle (TS-angle), femoral antetorsion (femAT), tibial tubercle–trochlear groove (TT-TG) distance, and frontal leg axis. Additionally, three frontal gait patterns were defined and recorded: (1) internal-rotation–adduction moment of the knee during normal walking, (2) dynamic valgus of the knee, and (3) Trendelenburg’s sign in a single-leg squat. Randomized videography was evaluated by three independent blinded observers. Statistical analysis was performed using regression models and comparisons of gait patterns and clinical and radiological measurements. Furthermore, observer reliability was correlated to gradings of radiological parameters. Results Patients showed altered dynamic Q-angle gait pattern during normal walking ( p  < 0.001) compared to healthy controls (interrater kappa = 0.61), whereas highest observer agreement was reported if femAT was greater than 20° (kappa = 0.85). Logistic regression model revealed higher femAT (18.2° ± 12.5 versus 11.9° ± 7.0 ( p  = 0.004) as a significant variable, as well as lower TT–TG distance (23.6 mm ± 2.8 vs. 16.6 mm ± 4.9, p  = 0.004) on evident dynamic Q-angle gait pattern. Dynamic valgus in a single-leg squat was observed significantly more often in patients ( p  < 0.001) compared to controls (interrater kappa = 0.7). However, besides the static measured Q-angle as the only significant variable on evident dynamic valgus pattern (13.6° ± 4.6 vs. 10.3° ± 5.2, p  = 0.003), no radiological parameter was detected to correlate significantly with dynamic valgus and Trendelenburg's sign (n.s.). Conclusions Clinical detection of pathologic torsion and bony alignment may be difficult in patients with patellofemoral instability. The present study demonstrated that dynamic Q-angle gait pattern is significantly altered in patients with chronic patellofemoral instability compared to healthy controls. Moreover, dynamic Q-angle correlates positively with higher femoral torsion and negatively with higher TT–TG distance. Therefore, clinical and radiological assessment of maltorsion should be added to the standard diagnostic workup in cases of patellofemoral instability. Level of evidence Level II.

Background The present study aims to describe the imaging features in incident radiographic patellofemoral osteoarthritis (RPFOA) population in a Chinese suburban area. Methods The Beijing Shunyi osteoarthritis (BJS) study was a population-based, longitudinal and prospective study. Residents were recruited by randomized cluster sampling in 2014 and were followed 3 years later. Home interviews and clinical examinations were performed; weight-bearing posterior-anterior semi-flexed (45-degree) views of the tibiofemoral (TF) joints and skyline (45-degree) views of the patellofemoral (PF) joints were included. For each batch of study films ( n  = 100), 20 films from the year 2014 and 20 previously read PF radiographs were fed back to test inter−/intra-reader repeatability. The imaging features of incident RPFOA were analyzed. Narrative statistics, independent-sample t-tests, and nonparametric tests were performed. Results A total of 1295 participants (2590 knees) were recruited at baseline in 2014, and 967 (74.7%) residents were followed in 2017. Of all the knees ( n  = 1537) without RPFOA at baseline, 139 knees (13.3%) across 119 people developed incident RPFOA. Compared with the whole population, age ( p  = 0.031), body mass index (BMI, p  = 0.042), and incidence of knee pain symptoms ( p  < 0.01) were significantly different in the incident RPFOA population, while range of motion (ROM, p  = 0.052) and gender (0/1, p  = 0.203) showed no significance. In the incident population, the changes of each imaging indicator grade were evaluated—lateral patellofemoral osteophyte (LPOST, increased by 1.02), medial patellofemoral osteophyte (MPOST, increased by 0.49), lateral joint space narrowing (LJSN, increased by 0.30), medial joint space narrowing (MJSN, increased by 0.06); indicator grade progress decreases, respectively. The progress of LPOST was the fastest among the four indicators ( p  < 0.01). Conclusions In this population-based longitudinal study, among the incident RPFOA population, the imaging indicators show that marginal patellofemoral osteophyte is more pronounced than patellofemoral joint space narrowing. LPOST is the fastest-progressing indicator among all the radiographic features, which is also the most common imaging manifestation of RPFOA. In the incident RPFOA population, the proportion of elders, women, higher-BMI individuals, and people suffering knee pain is more than the normal population.

This work aimed to assess inter-rater reliability and agreement of a magnetic resonance imaging (MRI)-based Kellgren and Lawrence (K&L) grading for patellofemoral joint osteoarthritis (OA) and to validate it against the MRI Osteoarthritis Knee Score (MOAKS). MRI scans from people aged 45 to 75 years with chronic knee pain participating in a randomised clinical trial evaluating dietary supplements were utilised. Fifty participants were randomly selected and scored using the MRI-based K&L grading using axial and sagittal MRI scans. Raters conducted inter-rater reliability, blinded to clinical information, radiology reports and other rater results. Intra- and inter-rater reliability and agreement were evaluated using the intra-class correlation coefficient (ICC) and Cohen’s weighted kappa. There was a 2-week interval between the first and second readings for intra-rater reliability. Validity was assessed using the MOAKS and evaluated using Spearman’s correlation coefficient. Intra-rater reliability of the K&L system was excellent: ICC 0.91 (95% CI 0.82–0.95); weighted kappa (ĸ = 0.69). Inter-rater reliability was high (ICC 0.88; 95% CI 0.79–0.93), while agreement between raters was moderate (ĸ = 0.49–0.57). Validity analysis demonstrated a strong correlation between the total MOAKS features score and the K&L grading system (ρ = 0.62–0.67) but weak correlations when compared with individual MOAKS features (ρ = 0.19–0.61). The high reliability and good agreement show consistency in grading the severity of patellofemoral OA with the MRI-based K&L score. Our validity results suggest that the scale may be useful, particularly in the clinical environment. Future research should validate this method against clinical findings.

Background The use of the suprapatellar approach for intramedullary nailing has recently become popular for the treatment of tibial fractures. This study aimed to investigate the effectiveness of using the Chinese Aircraft-shaped Sleeve (CASS) system on the clinical outcomes of tibial intermedullary nailing using a suprapatellar approach for the treatment of tibial fractures in a cohort of adult Chinese patients. Methods Magnetic resonance images (MRI) of the knee joints of 212 healthy adults with normal lower limb function from May 2011 to May 2015 were obtained from a level I Chinese regional trauma centre. Sixty inpatients at the same trauma centre who underwent treatment for tibial shaft fractures from June 2015 to June 2018 were enrolled. Tibial intramedullary nailing fixation of tibial shaft fractures via the suprapatellar approach was performed with either a CASS system or a conventional sleeve. The measurements of patellofemoral joint anatomy, the surgical time, the assessments of the patellofemoral joint cartilage conditions, and information of residual debris based on arthroscopic analysis were subsequently collected. Results The mean patellar angle (PA), sulcus angle (SA), sulcus width (SW) and sulcus depth (SD) were 135.40 ± 6.20°, 142.37 ± 5.33°, 33.37 ± 2.73 mm, and 4.29 ± 0.63 mm, respectively. The surgical time until entry reaming commencement and the irrigation time were significantly lower in the CASS group ( P  < 0.001). The difference in cartilage damage rate between groups was statistically significant ( P  = 0.031); the difference in residual debris conditions was not statistically significant ( P  = 0.1967). Conclusion The use of the CASS system could improve clinical outcomes of intramedullary nailing via suprapatellar approach for patients with a small patellofemoral joint space.

Purpose Several anatomic risk factors associated with patellofemoral disorders have been described. The purpose of this study was to analyze the relationship between bony parameters commonly used to analyze and define patellofemoral malalignment. Methods Patients with patellofemoral disorders presenting between 2016 and 2018 who underwent a standardized radiographic workup including conventional radiographs, weight bearing full-leg radiographs, magnetic resonance imaging (MRI) of the knee, and torsional analysis using hip–knee–ankle MRI were initially included. Patients with a history of lower extremity fracture and a history of surgical procedures affecting bony alignment or partial/total arthroplasty were subsequently excluded. Radiographs and MRI of all included patients were analyzed by four independent observers. Parameters of interest were: femoral torsion, tibial torsion, trochlear dysplasia, tibial tuberosity–trochlear groove (TT–TG) distance, and frontal mechanical axis. All parameters were compared between patients with low grade and high grade trochlear dysplasia as well as between female and male patients. Correlation of continuous variables was assessed with the Pearson correlation coefficient. A binary logistic regression model was used for the calculation of odds ratio between different parameters. Interclass correlation coefficients (ICC) were calculated to determine the interobserver reproducibility. Results A total of 151 patients could be included for detailed analysis. Group comparison revealed that patients with high grade trochlear dysplasia showed significantly higher values for femoral torsion (low grade: 9.8° ± 11.0°, high grade: 16.8° ± 11.5°; p  < 0.001) and significantly higher values for TT–TG distance (low grade: 19.0 mm ± 5.0 mm, high grade: 21.9 mm ± 5.4 mm; p  = 0.002). No significant difference was found for age, tibial torsion, and frontal mechanical axis. With regard to gender, female patients had higher values for femoral torsion (female: 15.6° ± 11.3°, male: 11.0° ± 12.7°; p  = 0.044). The correlation analysis found significant correlation between femoral torsion and tibial torsion ( r  = 0.244, p  = 0.003), femoral torsion and TT–TG distance ( r  = 0.328, p  < 0.001), femoral torsion and frontal mechanical axis ( r  = 0.291, p  < 0.001), and tibial torsion and TT–TG distance ( r  = 0.182, p  = 0.026). Conclusion Bony malalignment in patients with patellofemoral disorder is a complex problem given the significant correlation between femoral and tibial torsion, trochlear dysplasia, TT–TG distance, and frontal mechanical axis. Advanced imaging to analyze rotational and frontal plane alignment is recommended in patients with trochlear dysplasia and/or increased TT–TG on standard radiographs and knee MRI. Understanding of the bony pathology in patellofemoral disorders is key to improve the therapeutic and surgical decision. Level of evidence III, retrospective cohort study.

Background Porous tantalum is reportedly a good substitute for structural bone graft in several applications. So far, its use has not been reported in tibial tuberosity anteriorization (TTA) for treatment of isolated degenerative chondral lesions of the patellofemoral joint. Questions/Purposes We asked whether the use of this material would produce similar standardized functional scores, pain (VAS), fusion rates, complications, and patient satisfaction to those for bone graft. Patients and Methods We performed a randomized, controlled trial in 101 patients (108 knees) scheduled for TTA comparing a porous tantalum implant (57 knees) with an autologous local tibial bone graft (51 knees). The minimum followup was 5 years (mean, 6.2 years; range, 5–8 years). Results At the last followup, clinical scores, fusion rates, and maintenance of the anteriorization either were better or similar for the TTA using the tantalum implant depending on the respective parameter. The operative technique was easier and shorter with the tantalum device. Complication and failure rates were greater using bone graft. Patient satisfaction was greater using the tantalum implant. Conclusions Porous tantalum provided a reasonable alternative to bone graft in TTA. Level of Evidence Level I, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Purpose Tibiofemoral rotation through the knee joint, specifically relative external tibial rotation, has been identified as a potential contributing factor to patellar instability. The purpose of this study is to investigate the relationship between severity of instability with degree of tibiofemoral rotation in three clinical cohorts: fixed or obligatory dislocators (in which the patella either is constantly laterally dislocated or laterally dislocates with every instance of knee flexion, respectively), standard traumatic instability patients, and normal controls. Methods A retrospective study was performed with three cohorts from April 2009 to February 2019: fixed or obligatory dislocators, standard traumatic instability patients, and controls with normal magnetic resonance imaging (MRI) of the knee. All fixed or obligatory dislocation patients from the study time frame were analyzed; controls and standard traumatic instability patients were randomly selected. Inclusion criteria were age under 18 years and qualifying diagnosis; exclusion criteria were outside institution MRI and previous MPFL reconstruction or tibial tubercle osteotomy. Tibiofemoral rotation was measured blindly on initial axial MRI using the posterior femoral and tibial condylar lines. Tibial tubercle to trochlear groove distance (TT–TG) was measured. Intraclass correlation coefficient (ICC) was calculated among four measurers. Results A total of 100 patients were included, 20 fixed or obligatory dislocators, 40 standard traumatic instability patients, and 40 controls. Median age was 13.2 years (range 10–17 years), with 55 females. Age was significantly higher in the standard traumatic instability group than both the control ( p  < 0.001) and fixed or obligatory dislocator groups ( p  = 0.003). ICC for TT–TG and tibiofemoral rotation were 0.92 and 0.96, respectively. Fixed or obligatory dislocator patients averaged 8.5° external tibiofemoral rotation, standard traumatic instability patients 1.6° external tibiofemoral rotation, and controls 3.8° internal tibiofemoral rotation. Both tibiofemoral rotation and TT–TG were highest in the fixed or obligatory dislocator cohort, followed by the standard traumatic instability cohort, and lowest in the controls ( p  < 0.0001 for tibiofemoral rotation and TT–TG). Multivariate analysis showed no correlation between age and tibiofemoral rotation. Conclusions Measurement of tibiofemoral rotation was reproducible with excellent interrater reliability. The degree of tibiofemoral rotation is correlated with severity of patellar instability, with the greatest external tibiofemoral rotation in fixed or obligatory dislocator patients, followed by standard traumatic instability patients, and slight internal tibiofemoral rotation in controls. High external tibiofemoral rotation may be an important pathoanatomic factor in fixed or obligatory dislocators, and with further understanding may become a prognostic factor or surgical target. Level of evidence III.

Purpose External rotation of femoral component in total knee arthroplasty (TKA) with reference to the posterior condyles is recommended in mechanical alignment (MA) to ensure optimum patella tracking. In kinematic knee alignment (KA) technique, femoral component is more internally rotated as the femoral resection is based on flexion–extension axis. This study aims to investigate the clinical and radiological outcomes of the patellofemoral joint in patients who underwent TKA using KA versus mechanical alignment. Methods A review of prospectively collected registry data of 378 consecutive cruciate retaining primary TKAs (P.F.C. ® Total Knee System, DePuy Synthes, Massachusetts, United States) was performed. Propensity scoring was performed matching patients who received KA TKA ( n  = 93) to MA TKA ( n  = 93). Oxford Knee Score (OKS), Knee Society Score (KSS), Short-Form 36 (SF-36), range of motion as well as radiographs assessing patella tilt were compared at 6 months and 2 years after surgery. All patients received the same implant and had their patella resurfaced. Results OKS, KSS, physical component of SF-36 and satisfaction rates were comparable at both 6 months and 2 years after surgery. There was moderate association between preoperative and postoperative patella tilt in KA TKA (Cramer’s V  = 0.260, p  < 0.05). Postoperatively, KA group had a greater number of patients with lateral patella tilt compared to the mechanical group (12 [12.9%] vs 1 [1.1%], p  < 0.001). Patella tilts, however, resolved two years after surgery. Conclusion The relative internal rotation of the femoral component in KA TKA results in greater incidence of lateral patella tilt postoperatively. Nevertheless, patella tilt resolution was noted at 2 years. Level of evidence Level III Evidence—Retrospective Cohort Study.

Purpose To investigate the effect of proximal tibial tubercle osteotomy (PTO) and distal tibial tubercle osteotomy (DTO) in medial opening wedge high tibial osteotomy on patellofemoral alignment, patellofemoral osteoarthritis and clinical outcomes. Methods PTO ( n  = 41) and DTO ( n  = 43) for the same surgical indications were included. Radiographic measurements of the Caton-Deschamps index, patellar tilt and shift, and arthroscopic cartilage evaluation at the patellofemoral joint were performed at osteotomy and plate removal. The Knee Society Score (KSS) was evaluated preoperatively and at the latest follow-up. Results The follow-up period was longer in the PTO group (33.7 months; range 23–40 years) than in the DTO group (22.2 months; range 18–29 months) ( p  < 0.0001), whereas the period from osteotomy to plate removal was not different between the groups. The Caton-Deschamps index of the DTO group was unchanged from 0.9 (range 0.7–1.2) to 0.9 (range 0.6–1.4), whereas that of the PTO group changed from 0.9 (0.7–1.2) to 0.7 (0.5–1.0) ( p  < 0.0001). There were fewer deteriorated cases of cartilage status in the trochlear groove in the DTO group (20.9%) than in the PTO group (56.1%, p  < 0.05). There were more improved cases in the DTO group (23.3%) than in the PTO group (4.9%, p  < 0.05). Postoperative KSS was better in the DTO group than in the PTO group ( p  < 0.05). Conclusion DTO is associated not only with reduced deterioration but also with increased improvement of cartilage status in the trochlear groove and better KSS as compared with PTO. Level of evidence IV.

Abnormal patellofemoral joint (PFJ) stress (defined as the PFJ reaction force divided by the PFJ contact area) may be contributory to early-onset PFJ osteoarthritis in persons who have undergone anterior cruciate ligament reconstruction (ACLr). Using a model of the PFJ that takes into consideration subject-specific contact area, the purpose of this study was to compare peak PFJ stress during functional tasks between females who have undergone ACLr and healthy controls. It was hypothesized that persons post-ACLr would exhibit higher peak PFJ stress during walking, running, and drop landing tasks and that increased PFJ stress would be driven primarily by reduced PFJ contact area. Forty female athletes between the ages of 18–35 who participated in field or court sports participated. Twenty had previously undergone ACLr during the last 6–12 months and 20 were matched to healthy controls. Participants completed two phases of data collection: 1) loaded MRI assessment of the PFJ (35 % bwt) to quantify contact area, and 2) biomechanical assessment of walking, running and a single leg drop land task. A previously described subject-specific model of the PFJ was used to calculate PFJ stress. Peak PFJ stress did not differ between females post-ACLr and healthy controls across tasks. Lower PFJ reaction forces at the time of peak stress were observed in the ACLr group for each task, however this was offset by significantly lower utilized PFJ contact area. Large variability in peak stress was observed in the ACLr group suggesting that a subset of individuals may be at risk of overloading of the PFJ.