Utility of dynamic ultrasound in the assessment of patellar instability (158)

Objectives: Few imaging modalities currently exist that allow for dynamic assessment of the patellofemoral joint. Dynamic evaluation of patellar instability is typically based on physical examination using the Glide test to assess and quantify lateral patellar translation. However, this method can be limited for inexperienced examiners, and precise quantification with this method remains difficult. Therefore, this study aimed to utilize ultrasound imaging to quantify patellar position and translation under dynamic loading conditions to compare knees with and without injury to the medial soft tissue restraints. Methods: 10 fresh frozen, unpaired cadaveric knee specimens underwent assessment of lateral patellar translation using a portable ultrasound device. The probe was positioned 1cm above the medial joint line, and measurements were performed based on the distance between the articular edge of the medial patellar facet and the most prominent edge of the medial trochlear facet. Using an electronic force gauge, two standardized loading conditions were created: (1) Unloaded (0N of force), and (2) loaded with 20N of laterally directed force on the patella to mimic the Glide test. Patellar translation in the lateral direction was assessed from 0-40 degrees of knee flexion at 10 degree increments using a hand held goniometer. Measurements were performed in intact knees and were repeated after arthroscopic transection of the medial soft tissue restraints (both medial patellofemoral ligament [MPFL] and medial quadriceps tendon-femoral ligament [MQTFL]). All measurements were performed using Image J. Paired t-test was used to compare the findings of the intact vs injured states. Sensitivity, specificity, accuracy, negative, and positive predictive value for the injury state were determined based on the values from the intact state +2 standard deviations (SD). P-value <0.05 was considered statistically significant. Results: Compared with the intact state, significant increases in lateralized patellar position and translation were observed when the MPFL and MQTFL were transected, at all flexion angles between 0 and 40 degrees ( p values ranging from .005 to <.001). Results are listed in Table 1. The greatest difference was noted with a laterally directed force of 20N at 20 degrees knee flexion, where a 32.8% (6mm) increase in lateral translation was observed in the injured state, when compared to the intact state. Based on 2 SD from normal values at 20 and 30 degrees, the optimal cutoff point to identify MPFL/MQTFL injury was 17.5 mm of distance from the medial trochlea to the medial patellar facet (sensitivity 95.1%; specificity 86.7%; accuracy 90%). Conclusions: Under dynamic ultrasonographic assessment, the integrity of the medial patellar restraints can be effectively evaluated based on measurements of patellar position and translation, with patellar position >17.5mm from the medial trochlea at 20 and 30 degrees knee flexion indicating the presence of injury. As dynamic ultrasound can be performed without radiation or invasive testing in multiple clinical settings, further studies are recommended to assess the utility of ultrasound based assessments in the evaluation and management of patellar instability.

Examination of the proximodistal patellar position in small dogs in relation to anatomical features of the distal femur and medial patellar luxation

Objective To determine the influence of anatomical features of the distal femur on the proximodistal patellar position and compare the proximodistal patellar position between dogs with and without medial patellar luxation (MPL). Study design Retrospective case series (n = 71). Methods Mediolateral-view radiographs of clinical cases of dogs weighing less than 15 kg were obtained. The stifle joint angle, patellar ligament length, patellar length, size of the femoral condyle, trochlear length, and trochlear angle were measured and included in multiple linear regression analyses to ascertain their effects on the proximodistal patellar position. Radiographs were divided into MPL and control groups. The effects of MPL on the proximodistal patellar position and morphological factors were also examined. Results The final model for the proximodistal patellar position revealed that the patella became distal as the ratio of the patellar ligament length to patellar length decreased, the trochlear angle relative to the femur increased, the trochlear length relative to the patellar length increased, or the trochlear length relative to the femoral condyle width decreased. The proximodistal patellar position in the MPL group was not significantly different from that in the control group despite the trend towards a distally positioned patella (p = 0.073). The MPL group showed a significantly shorter trochlea (p<0.001) and greater trochlear angle relative to the femur (p = 0.029) than the control group. Conclusion The proximodistal patellar position depends on multiple factors, and its determination based on PLL/PL alone may not be appropriate. Dogs with MPL did not have a proximally positioned patella compared with dogs without MPL. Although hindlimbs with MPL had a shorter trochlea than those without patellar luxation, this difference did not appear to be sufficient to displace the patellar position proximally in small dogs, possibly compensated by increased trochlear angle relative to the femur.

Comparison of Patellofemoral Kinematics and Stability After Medial Patellofemoral Ligament and Medial Quadriceps Tendon–Femoral Ligament Reconstruction

Background: There is a lack of evidence regarding the optimum extensor-sided fixation method for medial patellofemoral ligament (MPFL) reconstruction. There is increased interest in avoiding patellar drilling via soft tissue–only fixation to the distal quadriceps, thus reconstructing the medial quadriceps tendon–femoral ligament (MQTFL). The biomechanical implications of differing extensor-sided fixation constructs remain unknown. Hypothesis: The null hypothesis was there would be no differences between traditional MPFL reconstruction and MQTFL reconstruction with respect to resistance to lateral translation, patellar position, or patellofemoral contact pressures. Study Design: Controlled laboratory study. Methods: Nine adult knee specimens were mounted on a jig that applied static, physiologic loads to the quadriceps tendons. Patellar position and orientation, knee flexion angle, and patellofemoral pressure were recorded at 8 different flexion angles between 0° and 110°. Additionally, a lateral patellar excursion test was conducted wherein a load was applied directly to the patella in the lateral direction with the knee at 30° of flexion and subjected to 2-N quadriceps loads. Testing was conducted under 4 conditions: intact, transected MPFL, MQTFL reconstruction, and MPFL reconstruction. For MQTFL reconstruction, the surgical technique established by Fulkerson was employed. For MPFL reconstruction, a traditional technique was utilized. Results: The patellar excursion test showed no significant difference between the MQTFL and intact states with respect to lateral translation. MPFL reconstruction led to significantly less lateral translation ( P < .05) than all other states. There were no significant differences between MPFL and MQTFL reconstructions with respect to peak patellofemoral contact pressure. MPFL and MQTFL reconstructions both resulted in increased internal rotation of the patella with the knee in full extension. Conclusion: Soft tissue-only extensor-sided fixation to the distal quadriceps (MQTFL) during patella stabilization appears to re-create native stability in this time 0 cadaver model. Fixation to the patella (MPFL) was associated with increased resistance to lateral translation. Clinical Relevance: Evolving anatomic knowledge and concern for patellar fracture has led to increased interest in MQTFL reconstruction. Both MQTFL and MPFL reconstructions restored patellofemoral stability to lateral translation without increasing contact pressures under appropriate graft tensioning, with MQTFL more closely restoring native resistance to lateral translation at the time of surgery.

Different Patellar Indices and Their Role in Decision-Making: An MRI-Based Study

Magnetic resonance imaging (MRI) of knee has become the integral part of knee evaluation, hence any MRI based study adds more value if it helps in the decision-making process, especially for surgery in treating patellofemoral pain. We tried to determine normal patellar indices using knee MR images and the correlation between them and also compared the results with different ethnic population. We analyzed the prospectively collected MR images of 117 knees/patients, and Insall–Salvati (IS) index, modified IS index, patellotrochlear (PT) index, and patellophyseal (PP) index were calculated. Two standard deviations from the mean were used to define the normal and abnormal patellar position. Cohen's kappa values were used to assess the agreement between the indices and the correlation between them was analyzed using Pearson's correlation. The mean values for IS index, modified IS index, PT index, and PP index were 1.00, 1.53, 0.40, and 0.58, respectively. There was very good agreement between PT index and PP index. There was weak correlation between all the indices except the one between PT and PP indices which had a strong negative correlation. Based on commonly used methodology, there were 4% of asymptomatic patients who were outside the standardized cut-off values and different indices classified different knees as abnormal. This indicates patellar position should be one among the many other factors, not as a sole factor when making a surgical decision in patellofemoral pain. We also noted that the indices compared fairly with other populations. Further research is needed to determine the clinical applicability of these indices.

Agreement and Reliability of Lateral Patellar Tilt and Displacement following Total Knee Arthroplasty with Patellar Resurfacing

Patellar position and alignment may be measured on routine axial radiographs by various techniques; however, the agreement and reliability of such measurements with a resurfaced patella remain unknown. This study evaluated the range and reliability of lateral patellar tilt and lateral patellar displacement following total knee arthroplasty (TKA) with a resurfaced patella among three observers on 45° Merchant view in 139 TKAs. Intraclass correlation coefficient (ICCs) were used to evaluate intraobserver agreement (IOA) and inter-rater reliability (IRR). IRR was high between each of the observers for lateral patellar tilt (ICC = 0.8) and lateral patellar displacement (ICC = 0.87). IOA was also high upon repeat measurement for the same observer for lateral patellar tilt (ICC ≥ 0.90) and lateral patellar displacement (ICC ≥ 0.86). Therefore, lateral patellar tilt and lateral patellar displacement are reproducible measurements of patellar position on a Merchant axial radiograph following a well-functioning TKA with a resurfaced patella.

The Effect of Diacutaneous Fibrolysis on Patellar Position Measured Using Ultrasound Scanning in Patients With Patellofemoral Pain Syndrome

Context: Tightness or lack of flexibility of several muscles of the thigh has been associated with patellofemoral joint pain. A tight iliotibial band can lead to laterally located patella and an abnormal patellar tracking pattern. Diacutaneous fibrolysis (DF) is commonly used to reduce muscle tightness, but no studies have evaluated the effects of this technique in the treatment of patients with patellofemoral pain syndrome. Objective: To assess the effect of DF on patellar position in patients with patellofemoral pain syndrome. Design: A single-group, pretest–posttest clinical trial. Setting: University of Zaragoza. Participants: A total of 46 subjects with patellofemoral pain (20 males, 26 females; age: 27.8 [6.9] y). Intervention: Three sessions of DF. Main Outcome Measures: Patellar position measurement using real-time ultrasound scanning; pain intensity measured with visual analog scale and function measured with the Anterior Knee Pain Scale. Results: The application of 3 sessions of DF significantly increased the patellar position at posttreatment evaluation (P < .001) and at 1-week follow-up (P < .001). There was not a significant difference on patellar position between posttreatment and follow-up measurements (P = .28). There were also a statistically significant decrease in pain and increase in function at posttreatment and at 1-week follow-up measurements (P < .001). Conclusion: This study found that patellar position, pain intensity, and function were significantly improved after 3 sessions of DF and at 1-week follow-up.