Portable ultrasonography is increasingly used to evaluate ankle stability at the point of care. This study aims to determine the correlation of portable‐ultrasonographic and fluoroscopic measurements of ankle laxity in a cadaveric ligament transection model of ankle ligament injury. We hypothesize that there is an association between portable‐ultrasonographic and fluoroscopic measurements when performing stress evaluation of lateral ankle instability. Eight fresh‐frozen below‐knee amputated cadaveric specimens with intact proximal fibula underwent ultrasound and fluoroscopic evaluation of the ankle during anterior drawer and talar tilt testing. The assessment was first performed with all lateral ankle ligaments intact and thereafter with sequential transection of the anterior talofibular ligament, calcaneofibular ligament, and posterior talofibular ligament. The anterior drawer test was performed with both 50N and 80N of force, and talar tilt test was performed with 1.7 Nm of torque. Correlations between (1) portable‐ultrasonographic and fluoroscopic measurements and (2) sequential transection of lateral ankle ligaments were evaluated using Spearman's rank correlations. The same statistical test was used to investigate the correlation between the ultrasonographic and the fluoroscopic measurements. The inter‐ and intra‐observer agreement was assessed using the intraclass correlation coefficient through a two‐way mixed‐effects model with absolute agreement. Portable‐ultrasonographic and fluoroscopic measurements increased as additional ligaments of the lateral ankle were transected (Spearman's rank correlation ranged from 0.74 to 0.81, 0.74 to 0.81, p‐values < 0.001). Strong positive correlations between ultrasonographic and fluoroscopic measurements were found during the lateral ankle stability evaluation using anterior drawer and talar tilt testing (Spearman's rank correlation ranged from 0.81 to 0.85, 0.81 to 0.85, p‐values < 0.001). Inter‐rater (0.99, 95% CI: 0.98–0.99) and intra‐rater reliability (0.97, 95% CI: 0.95–0.99) for the ultrasonographic measurements were substantial. In conclusion, there was a strong correlation found between ultrasonographic and fluoroscopic values measured during simulated anterior drawer and talar tilt test in a cadaveric ligament transection model. In this model, the portable‐ultrasonographic measurement was found to be reliable for repeated measurements of the talar translation and the lateral clear space distance. Based on these data, ultrasonography is likely to become a valuable point of care diagnostic tool due to its ability to readily and dynamically evaluate suspected lateral ankle instability. Clinical Significance: The use of dynamic stress ultrasound to assess the anterior translation of the talus and the lateral clear space distance appears to be a reliable and repeatable technique to evaluate lateral ankle stability with a radiation‐free, noninvasive, and low‐cost manner.
Background: Medial patellofemoral complex (MPFC) reconstruction plays an important role in the surgical treatment of patellar instability. Anatomic reconstruction is critical in re-creating the native function of the ligament, which includes minimizing length changes that occur in early flexion. Anatomic risk factors for patellar instability such as trochlear dysplasia, patella alta, and increased tibial tuberosity to trochlear groove (TT-TG) distance have been shown to influence the function of the MPFC graft in cadaveric studies, but the native length change patterns of the MPFC fibers in knees with anatomic risk factors have not been described. Purpose: To describe the in vivo length changes of the MPFC fibers in knees with anatomic risk factors for patellar instability and identify the optimal attachment sites for MPFC reconstruction. Study Design: Controlled laboratory study. Methods: Dynamic computed tomography imaging was performed on the asymptomatic knee in patients with contralateral patellar instability. Three-dimensional digital knee models were created to assess knees between 0° and 50° of flexion in 10° increments. MPFC fiber lengths were calculated at each flexion angle between known anatomic attachment points on the extensor mechanism (quadriceps tendon, MPFC midpoint [M], and patella) and femur (1, 2, and 3, representing the proximal to distal femoral footprint). Changes in MPFC fiber length were compared for each condition and assessed for their relationships to morphologic risk factors (trochlear depth, Caton Deschamps Index [CDI], and TT-TG distance). Results: In 22 knees, native MPFC fibers were found to be longer at 0° than at 20° to 50° of flexion. Length changes observed between 0° and 50° increased with the number of risk factors present. In the central fibers of the MPFC (M-2), 1.7% ± 3.1% length change was noted in knees with no anatomic risk factors, which increased to 5.6% ± 4.6%, 17.0% ± 6.4%, and 26.7% ± 6.8% in the setting of 1, 2, and 3 risk factors, respectively. Nonanatomic patella-based attachments were more likely to demonstrate unfavorable length change patterns, in which length was greater at 50° than 0°. In patellar attachments, an independent relationship was found between increasing length changes and TT-TG distance, while in quadriceps tendon attachments, a trend toward a negative relationship between length changes and CDI was noted. All configurations demonstrated a strong relationship between percentage change in length and number of morphologic risk factors present, with the greatest influence found in patella-based attachments. Conclusion: The MPFC fibers demonstrated increased length changes in knees when a greater number of morphological risk factors for patellar instability were present, which worsened in the setting of nonanatomic configurations. This suggests that the function of the intact MPFC in patients with anatomic risk factors may not reflect previously described findings in anatomically normal knees. Further studies are needed to understand the pathoanatomy related to these changes, as well as the implications for graft placement and assessment of length changes during MPFC reconstruction techniques. Clinical Relevance: MPFC length change patterns vary based on the number of morphologic risk factors for patellar instability present and should be considered during reconstructive procedures.
Background: The use of imaging to diagnose patellofemoral instability is often limited by the inability to dynamically load the joint during assessment. Therefore, the diagnosis is typically based on physical examination using the glide test to assess and quantify lateral patellar translation. However, precise quantification with this technique remains difficult. Purpose: To quantify patellar position using ultrasound imaging under dynamic loading conditions to distinguish between knees with and without medial patellofemoral complex (MPFC) injury. Study Design: Controlled laboratory study. Methods: In 10 cadaveric knees, the medial patellofemoral distance was measured to quantify patellar position from 0° to 40° of knee flexion at 10° increments. Knees were evaluated at each flexion angle under unloaded conditions and with 20 N of laterally directed force on the patella to mimic the glide test. Patellar position measurements were made on ultrasound images obtained before and after MPFC transection and compared for significant differences. To determine the ability of medial patellofemoral measurements to differentiate between MPFC-intact and MPFC-deficient states, area under the receiver operating characteristic (ROC) curve analysis and the Delong test were used. The optimal cutoff value to distinguish between the deficient and intact states was determined using the Youden J statistic. Results: A significant increase in medial patellofemoral distance was observed in the MPFC-deficient state as compared with the intact state at all flexion angles ( P = .005 to P < .001). When compared with the intact state, MPFC deficiency increased medial patellofemoral distance by 32.8% (6 mm) at 20° of knee flexion under 20-N load. Based on ROC analysis and the J statistic, the optimal threshold for identifying MPFC injury was 19.2 mm of medial patellofemoral distance at 20° of flexion under dynamic loading conditions (area under the ROC curve = 0.93, sensitivity = 77.8%, specificity = 100%, accuracy = 88.9%). Conclusion: Using dynamic ultrasound assessment, we found that medial patellofemoral distance significantly increases with disruption of the MPFC. Clinical Relevance: Dynamic ultrasound measurements can be used to accurately detect the presence of complete MPFC injury.
Objectives: Accuracy of femoral tunnel positioning is critical during medial patellofemoral complex (MPFC) reconstruction, as even 5mm of malpositioning has been associated with altered patellofemoral contact pressures. To help identify the appropriate position for femoral tunnel placement, Schottle and others have described radiographic landmarks to identify the MPFC footprint on lateral knee radiographs. These measurements are based on an extension of the posterior cortical line, which can vary based on the length of the femur visible on the radiograph. Because the scope of view can vary between intraoperative imaging modalities, the aim of this study was to assess the effect of femoral length on the accuracy of radiographic landmarks of the MPFC. Methods: In 9 unpaired cadaveric knees, the MPFC footprint was exposed on the medial femur, and the proximal and distal boundaries of the footprint were marked. Lateral fluoroscopic images of the knee were obtained and assessed in 1 cm length increments, beginning 1cm proximal to the posterior condyle and continuing proximally to a femoral length of 8 cms. The MPFC midpoint was described on each image relative to the posterior cortical line of the femur and a line perpendicular to this line, relative to the proximal margin of the posterior condyle. Linear regression analysis was used to assess the effect of femoral length on the radiographic position of the MPFC. ROC curve analysis and Delong test were used to determine ROC curve analysis and Delong test were used, and the minimum amount of femoral length required on radiographs to accurately identify an anatomic femoral tunnel was determined using Youden’s J statistic. Results: Using the posterior cortical line as a reference, the radiographic description of the MPFC footprint moved anteriorly with decreasing femoral length on the radiographs, particularly at 4cm and less. However, no proximal-distal change was seen in relation to the line through the proximal margin of the posterior condyle with changing femoral lengths. Linear regression analysis showed a significant relationship between the femoral length and anterior position of the MPFC on radiographs (R = 0.461, R2 = 0.212, B= -0.636, p < 0.001). The slope coefficient was -0.636 mm, indicating that for every cm decrease in femoral length, the actual anatomic footprint of the MPFC moves anteriorly by 0.636 mm in relation to the posterior cortical line. Furthermore, ROC curve analysis revealed that a minimum of 4 cm of femoral length on lateral radiographs is required to accurately localize the footprint of the MPFC (AUC 0.79; sensitivity 76.7 %; specificity 69 %; p < 0.001). Conclusions: The radiographic landmarks for the MPFC femoral footprint can change depending on the length of the distal femur visible on radiographs. We found that at least 4cm of the femoral shaft should be visible for the radiographic landmarks to be accurate. As fluoroscopy is frequently used intraoperatively for MPFC reconstruction, our findings may serve as a guide for accurate femoral tunnel placement.
Objectives: The medial patellofemoral complex (MPFC) has a broad attachment on the patella and quadriceps tendon. Recent anatomic studies have demonstrated a corresponding elongated footprint on the medial femur in which the proximal fibers constitute the MQTFL and the distal fibers form the MPFL. Reconstruction of the MPFL and MQTFL have traditionally been described using the midpoint of the femoral footprint (Schottle’s point) while varying the graft’s position on the patella or quadriceps tendon. The purpose of this study was to compare graft isometry of MPFL, MQTFL, and MPFC reconstruction when using a standard femoral tunnel versus the corresponding anatomic femoral tunnel, and to identify the morphologic risk factors that influence each reconstruction technique. Methods: 3D digital knee models were created from dynamic CT images of asymptomatic knees of patients with contralateral patellar instability. Knee models were grouped into 10° intervals and graft length, or distance between the defined points on the femur and extensor mechanism were measured in the following conditions: 1) standard MQTFL (sMQTFL), between the midpoint of the femoral footprint and the quadriceps tendon attachment, 2) anatomic MQTFL (aMQTFL), between the proximal femoral footprint and quadriceps tendon attachment, 3) standard MPFL (sMPFL), between the femoral footprint midpoint and the patellar attachment, 4) anatomic MPFL (aMPFL), between the distal femoral footprint and patellar attachment, and 5) MPFC, between the midpoints of the femoral and quadriceps tendon/patellar attachments. Changes in graft length between 0°and 40° flexion were compared for each reconstruction technique and assessed for their relationship to morphologic risk factors using stepwise multiple regression analyses. Results: 12 knees were included in this study (3M, 9F; mean age 23.1+/-8.0y). Mean graft length was significantly greater at 0° than 40° in all reconstructive techniques (p<0.001 to p=0.045). Graft length changes showed no significant differences between reconstructive techniques when using corresponding anatomic femoral tunnels (aMQTFL, aMPFL, aMPFC). When compared to aMPFC (8.8mm), graft length changes were greater in sMQTFL (11.3, p=0.005) and smaller in sMPFL (6.9, p=0.037); however 2/12 (16.7%) of the sMPFL had unfavorable length change patterns that were tighter in flexion than extension. Overall, proximal reconstructions (aMQTFL and sMQTFL) were the most sensitive to the presence of morphologic risk factors (R=.933, R2=0.87 and R=0.898,R2=0.81, respectively) with patella alta having the greatest effect. In contrast, the distal reconstructions (aMPFL and sMPFL) did not have a significant relationship with risk factors but trended toward a significant relationship with TTTG distance (p=0.072 and 0.064, respectively). Conclusions: For MQTFL and MPFL reconstructions, using the corresponding anatomic femoral attachment showed more favorable length change patterns over using the currently described standard femoral tunnel. Overall, graft length changes in proximal (quadriceps tendon) reconstructions were more sensitive to the presence of patella alta, while distal (patellar) reconstructions were influenced by TTTG distance. Further studies are needed to identify the optimal reconstructive technique based on each patient-specific morphologic patterns in the treatment of patellar instability.
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