The purpose of this study is to report the parameter characteristics of the femoral anteversion angle (FAA) and tibial tubercle-trochlear groove (TT-TG) distance in patients with patellar instability compared to healthy individuals and to evaluate their reliability in predicting patellar dislocation, providing potential indications for osteotomy.

A retrospective collection of consecutive patients with patellar instability constituted the study group, while individuals without patellofemoral disorder served as the control group. Measurement of the FAA and TT-TG distance were conducted by lower extremity computed tomography scans and knees with true patellar dislocation were recorded. The diagnostic capability of the FAA and TT-TG distance was assessed using receiver operating characteristic curves and area under the curve (AUC), determining the pathological values by sensitivity and specificity.

The FAA (21.6 ± 9.0°) and TT-TG distance (20.1 ± 4.8 mm) in the study group were significantly greater than the control group (10.6 ± 7.9° and 15.6 ± 4.6 mm, respectively) (p < 0.001). The AUCs for patellar dislocation were 0.869 for FAA and 0.712 for TT-TG distance, with pathological cut-off values of 18.2° and 18.2 mm, respectively. The odds ratios for FAA and TT-TG distance were 1.185 and 1.125, respectively (p < 0.05).

Patients with patellar instability exhibited significantly greater FAA and TT-TG distance compared to healthy individuals. The FAA demonstrated superior predictive capability for patellar dislocation compared to the TT-TG distance. The FAA (>18.2°) measured by surgical transepicondylar axis and TT-TG distance (>18.2 mm) were the potential pathological thresholds. Additionally, an increase of 1° in FAA and 1 mm in TT-TG distance was associated with a 18.5% and 12.5% increased risk of patellar dislocation, respectively. Surgeons should be aware of the risk of patellar dislocation associated with rotational malalignment.

Level III.

The aim of this study was to analyse sex-specific differences contributing to dynamic valgus in competitive soccer players before and after a standardised fatiguing protocol.

Thirty-nine healthy female and male competitive soccer players (19 females and 20 males) were recruited for the purpose of this study. Bilateral medial knee displacement (MKD) was assessed during drop jump landings using a three-dimensional motion capture system before and after a standardised fatiguing protocol. In addition, all soccer players underwent clinical examinations, including rotational hip range of motion (ROM), isokinetic strength testing and magnetic resonance imaging (MRI) of the hip and knee. Sex-specific and fatigue-dependent differences were reported, and the influence of demographic, clinical and radiographic factors on MKD was analysed via multiple linear regression models.

Compared with male soccer players, female soccer players demonstrated a tendency towards increased MKD during drop jump landings before (p = 0.09) and after the fatiguing protocol (p = 0.04). Sex-specific differences included increased hip internal rotation (IR) ROM, decreased hip external rotation (ER) strength and increased femoral torsion in females (all p < 0.002). According to the multiple linear regression models (stepwise method), increased hip IR ROM (90° of flexion) and the non-dominant leg remained the sole independent predictors of increased MKD during drop jump landings before (p < 0.01 and p = 0.02, respectively) and after fatigue (p < 0.01 and p < 0.01, respectively). An increase in hip IR ROM in females was linearly related to MKD after fatigue (R2 = 0.25; p < 0.01).

Female soccer players exhibited increased dynamic valgus before and after fatigue, which is likely attributed to joint mobility, as well as muscular and anatomical differences, such as increased hip IR ROM, reduced hip ER strength and increased femoral torsion. In particular, females with increased hip IR ROM were more susceptible to effects of fatigue on MKD, which may increase their risk for anterior cruciate ligament injury.

Level III.

The purpose of this study was to evaluate pre- to postoperative changes in clinical and functional outcomes as well as gait patterns in patients who underwent surgery for chronic patellofemoral instability (PFI).

Patients who underwent surgery for the treatment of recurrent PFI according to an individual risk factor analysis were included. Pre- and minimum 12 months postoperatively, patient-reported outcome measures (PROM; Kujala score, Lysholm score, Tegner Activity Scale [TAS] and Visual Analog Scale for pain) as well as gait (dynamic Q-angle) and function (dynamic valgus and dynamic Trendelenburg during single-leg squat) via videography were evaluated. Subgroup analysis was performed based on whether or not patients underwent concomitant distal femoral osteotomy (DFO) due to coronal and/or torsional malalignment.

Twenty-three patients were included (follow-up: 12.5 [12.1-13.0] months), of which 60.9% patients underwent a concomitant DFO. All PROM improved significantly (p < 0.05). Overall, dynamic Q-angle (p = 0.016) and dynamic valgus (p = 0.041) were observed significantly less frequently postoperatively when to compared to preoperatively. Subgroup analysis showed that only the group that underwent DFO had a significant improvement of dynamic Q-angle (p = 0.041). Dynamic Trendelenburg did not improve (p > 0.05). Regression analysis showed that the presence of a postoperative dynamic Q-angle was associated with a worse postoperative Kujala score (p = 0.042) and TAS (p = 0.049).

Patient-individualized surgery for PFI improved gait patterns and functional testing, especially in patients who also underwent DFO. The presence of dynamic Q-angle postoperatively was associated with significantly worse functional outcome and sporting ability.

Level III.

To compare the odds of patellofemoral instability events requiring subsequent surgery and revision surgical intervention in patients with joint hypermobility syndromes (JHS) to that of a matched cohort.

This is a retrospective cohort study using the PearlDiver Mariner Database. Records were queried between 2010 and 2021 with a diagnosis of JHS, including Ehlers-Danlos syndrome (EDS) and Marfan syndrome. Propensity matching was performed with a randomly generated control cohort without a diagnosis of JHS to account for age, sex, Charlson comorbidity index, diabetes, and obesity. Multivariable logistic regression was used to compare rates of patellar dislocation over a 1- and 2-year period between the 2 cohorts while controlling for previous knee injury or surgery. Patients who sustained a patellar dislocation over the 2-year period were followed to calculate rates of surgical intervention and subsequent revision.

In a population of 91,747, those with JHS experienced patellofemoral instability at a significantly increased rate at both a 1-year (adjusted odds ratio [aOR] 11.40; 95% confidence interval 9.23-14.25, P < .001) and 2-year (aOR 8.73; 7.36-10.44, P < .001) periods. The greatest risk was observed in patients with EDS at 1 year (aOR 16.32; 12.54-21.67, P < .001). Of those with an instability event, patients with JHS experienced a significantly increased rate of surgery at 1 year (aOR 3.20; 1.61-7.28, P = .002) and 2 years (aOR 3.18; 1.70-6.62, P < .001). Of those treated with surgery, there was no significant difference in the rates of revision surgical intervention between the JHS and control cohorts.

Patients with JHS experienced significantly increased rates of patellofemoral instability and subsequent surgery. However, of those treated with surgery, there was no difference in rates of revision surgical intervention between those with or without joint hypermobility syndromes.

Level III, retrospective cohort study.

Patellofemoral instability is influenced by morphological factors and associated with compensational alterations in gait pattern. Recent simulation studies investigated the impact of knee morphology on the stability and loading of the patellofemoral joint but neglected the patient-specific gait pattern. The aim of this study was to investigate the impact of patient-specific gait pattern on muscle forces and joint loading in individuals with patellofemoral instability. Musculoskeletal simulations with a model including a twelve degrees of freedom knee joint were performed based on three-dimensional motion capture data of 21 individuals with chronic patellofemoral instability and 17 healthy control participants. The patellofemoral instability group walked with a less flexed knee joint and reduced knee flexion and abduction moments compared to the control group, which required less quadriceps muscle forces. Lower quadriceps muscle forces resulted in a reduction of tibiofemoral and patellofemoral joint contact forces despite similar walking velocities between both groups. Furthermore, we observed decreased lateralizing patella forces in subjects with patella instability, which could potentially reduce the risk of patella dislocation. Our findings highlight the importance of accounting for the patient-specific gait pattern when analysing knee loads in individuals with patellofemoral instability.

The orientation of the quadriceps femoris can be represented by the quadriceps angle (Q-angle) has not yet been approved because of the high incidence of patellar instability. In this study, the correlations among components of the quadriceps femoris and the Q-angle using the plain radiographic technique were assessed. This retrospective study aims to use the radiographic technique to clarify these doubts from anatomic viewpoints.

One hundred consecutive young adult patients (50 men and 50 women; aged, 34 ± 5 and 33 ± 6 years, respectively) who sustained chronic unilateral lower extremity injuries (unilateral femoral, tibial nonunions or malunions) were enrolled. The contralateral intact lower extremity was used for the study. The full-length standing scanogram (FLSS) was used to evaluate the rectus Q-angle (R-Q angle), vastus Q-angle (V-Q angle), and clinical Q-angle (C-Q angle; i.e., known as the Q-angle). The three Q-angles were compared statistically. The Mann-Whitney U test and the Kruskal-Wallis test were used for comparison among groups. The Spearman rank correlation coefficient was used to evaluate the degree of relationship between two groups.

The C-Q angle or the V-Q angle was statistically different from the R-Q angle (p < 0.001). The C-Q angle between sexes was not different (p = 0.25). High correlation occurred among the C-Q angle, the R-Q angle, and the V-Q angles (correlation coefficient, 0.886-0.979). The multiple linear regression revealed of C-Q angle = 0.72; R-Q angle, p < 0.001 + 0.21; and V-Q angle, (p = 0.009) + 2.61° in 100 patients.

Orientation of the quadriceps femoris can be represented by the Q-angle. Compared to the rectus femoris, the three vastus muscles of the quadriceps femoris are more correlated to the Q-angle.

The aim of this study was to evaluate the clinical effect of derotational femoral osteotomy combined with medial patellofemoral ligament reconstruction for patellar dislocation and the effect of the distribution of femoral torsion at different segments on postoperative function.

Forty-two patients with patellar dislocation who underwent derotational femoral osteotomy from 2017 to 2021 were retrospectively analysed. All patients received computed tomography scans from the hip to the knee to evaluate correction of the femoral anteversion (FA) angle, patellar tilt angle (PTA) and congruence angle (CA) after derotational femoral osteotomy. Subjective scores, such as the Kujala, Lysholm, International Knee Documentation Committee (IKDC), Tegner and visual analog scale (VAS) scores, were used to evaluate knee function before and after the operation. Patients with supracondylar torsion > distal torsion were categorized into the supracondylar torsion group and patients with distal torsion > supracondylar torsion were categorized into the distal torsion group. Subgroup analyses were performed.

No presentation of redislocation occurred in these patients at the minimum 2-year follow-up visit. The mean preoperative FA angle in the supracondylar torsion group was 30.2° ± 4.2°, and the mean postoperative FA angle was 14.5° ± 2.5° (p < 0.001). The mean preoperative FA angle was 26.7° ± 1.4° and the mean postoperative FA angle was 14.1° ± 1.4° in the distal torsion group. In addition, postoperative PTA and CA were significantly corrected in both groups (p < 0.001). The postoperative Kujala, Lysholm, IKDC, Tegner and VAS scores were significantly improved in both groups (p < 0.001). Subgroup analyses showed a higher preoperative FA in the supracondylar torsion group and a higher occurrence of high-grade trochlear dysplasia in the distal torsion group. However, there was no significant difference in their postoperative clinical outcomes.

Through a minimum of 2-year follow-up visits of patients with patellar dislocation and increased FA, it was found that derotational femoral osteotomy could significantly reduce FA and improve subjective knee function. The pattern of torsion distribution did not significantly affect the clinical outcomes of derotational femoral osteotomy. These findings readvised orthopaedic surgeons that derotational femoral osteotomy remains the preferred procedure for correcting rotational malalignment, but that they should be more cautious about its indications.

Level IV.

Pain-associated knee joint disorders are common in daily life. Practically, knee pain should be divided into the origin from the isolated tibiofemoral (TF), isolated patellofemoral (PF) joint, or a combination thereof. The TF joint controls the actions of level walking, while the PF joint controls knee flexion-extension. Owing to its sufficient inherent stability, non-traumatic disorders of the isolated TF joint in young individuals are uncommon. In contrast, because of its insufficient inherent stability, non-traumatic disorders of the isolated PF joint are common in young individuals. Patellar malalignment (PM) associated with knee pain is common in all age groups, and the most common predisposing factor is imbalanced peripatellar soft-tissue tension. The outward forces acting on the patella are caused by pulling from the quadriceps femoris during knee flexion to extension (manifested by the quadriceps angle [Q-angle]), and sliding backward of the iliotibial band (ITB) during knee extension to flexion. Once the muscle power of the vastus medialis (especially the vastus medialis obliquus [VMO]) decreases, which lowers the counteracting effect against outward forces, the patella displaces or rotates laterally. The reduced contact surface between the patella and the femoral condyle significantly increases the compressive pressure and injures the articular cartilage. Subsequently, progressive PF degeneration occurs. Although other factors may also cause PM, they are relatively uncommon. In principle, nonsurgical treatment of PM should be considered first, while surgical treatment should follow established indications. Some nonsurgical techniques are currently widely used that feature high satisfaction rates. Surgical techniques are continuously being developed, and their success rates have gradually improved. This study aimed to review the current literature for relevant studies and report related publications of the author's institution to emphasize the universality and importance of PM management. Conceptually, simply focusing on problems of the TF joint cannot treat all knee disorders.

Q-angle is an important parameter to assess quadriceps muscle's function and its effect on knee. The present study aims to investigate the potential relationships between Q-angle, muscle strength, and balance in both athlete and non-athlete populations.

Fifty-six athletes and non-athletes aged between 18 and 20 were included in this cross-sectional study. The Q-angle of each participant was measured using a universal goniometer. Muscle strength was evaluated using hand-held dynamometer, and static and dynamic balance were assessed using the one-leg stand test and Y balance test, respectively.

Our findings revealed that athletes had a significantly smaller Q angle than non-athletes (p < 0.05). Furthermore, male participants had both higher muscle strength and better static balance with eyes closed than female participants (p < 0.05). Similarly, athletes had both higher muscle strength and better static balance than non-athletes (p < 0.05). Moreover, we found that the dominant limb had a significantly smaller Q angle than the non-dominant limb (p < 0.05). However, we did not observe a significant relationship between Q angle and dynamic balance (p > 0.05).

Our study suggests that individuals who participate in sports have lower Q angle values than those who do not participate in sports. Additionally, gender differences may exist in muscle strength and static balance. Furthermore, the Q angle was found to be lower in the non-dominant extremity compared to the dominant extremity. Finally, our study revealed a significant association between Q angle and knee muscle strength and static balance. Further research is needed to elucidate the underlying mechanisms of these relationships.

Impaired hip kinematics and kinetics may incite patellar instability. This study tested the hypothesis that hip adduction and internal rotation angles during gait are higher in adolescents with recurrent patellar dislocations compared to healthy controls.

Case-control study. Eighty-eight knees (67 patients) with recurrent patellar dislocation (mean age 14.8 years ± 2.8 SD) were compared to 54 healthy knees (27 individuals, 14.9 years ± 2.4 SD). Peak hip, knee and pelvis kinematics and kinetics were captured using 3D-gait analysis (VICON, 12 cameras, 200 Hz, Plug-in-Gait, two force plates) and compared between the two groups. One cycle (100%) consisted of 51 data points. The mean of six trials was computed.

Peak hip adduction angles and abduction moments were significantly higher in patients with recurrent patellar dislocation compared to the control group (p < 0.001 and 0.002, respectively). Peak internal hip rotation did not differ significantly.

Elevated hip adduction angles and higher hip abduction moments in gait of adolescents with recurrent patellar dislocation may indicate an impaired function of hip abductors that contributes to patellar instability.

Q-angle represents the resultant force vector of the quadriceps and patellar tendons acting on the patella. An increased Q-angle has been considered a risk factor for many disorders and injuries. This literature review challenges the clinical value of static Q-angle and recommends a more dynamic movement evaluation for making clinical decisions. Although there are many articles about static Q-angle, few have assessed the value of dynamic Q-angle. We searched Scopus and PubMed (until September 2021) to identify and summarize English-language articles evaluating static and dynamic Q-angle, including articles for dynamic knee valgus (DKV) and frontal plane projection angle. We also used textbooks and articles from references to related articles. Although static Q-angle measurement is used systematically in clinical practice for critical clinical decisions, its interpretation and clinical translation present fundamental and intractable limitations. To date, it is acceptable that mechanisms that cause patellofemoral pain and athletic injuries have a stronger correlation with dynamic loading conditions. Dynamic Q-angle has the following three dynamic elements: frontal plane (hip adduction, knee abduction), transverse plane (hip internal rotation and tibia external rotation), and patella behavior. Measuring one out of three elements (frontal plane) illustrates only one-third of this concept. Static Q-angle lacks biomechanical meaning and utility for dynamic activities. Although DKV is accompanied by hip and tibia rotation, it remains a frontal plane measurement, which provides no information about the transverse plane and patella movement. However, given the acceptable reliability and the better differentiation capability, DKV assessment is recommended in clinical practice.

The knee is a complex structure composed of bone, cartilage, menisci, ligaments and muscles, which all work synergistically to optimize congruence, stability, and function. Osteotomies are procedures addressing an abnormal joint alignment, shifting the mechanical load from a diseased joint compartment to a healthier one. Preoperative planning is an important art of identifying the source of abnormal load distribution to the joint, enabling the surgeon to simulate a deformity correction ahead of the surgical procedure.