Amir Ata Rahnemai-Azar

Development of computer tablet software for clinical quantification of lateral knee compartment translation during the pivot shift test

The pivot shift test is a commonly used clinical examination by orthopedic surgeons to evaluate knee function following injury. However, the test can only be graded subjectively by the examiner. Therefore, the purpose of this study is to develop software for a computer tablet to quantify anterior translation of the lateral knee compartment during the pivot shift test. Based on the simple image analysis method, software for a computer tablet was developed with the following primary design constraint – the software should be easy to use in a clinical setting and it should not slow down an outpatient visit. Translation of the lateral compartment of the intact knee was 2.0 ± 0.2 mm and for the anterior cruciate ligament-deficient knee was 8.9 ± 0.9 mm (p < 0.001). Intra-tester (ICC range = 0.913 to 0.999) and inter-tester (ICC = 0.949) reliability were excellent for the repeatability assessments. Overall, the average percent error of measuring simulated translation of the lateral knee compartment with the tablet parallel to the monitor increased from 2.8% at 50 cm distance to 7.7% at 200 cm. Deviation from the parallel position of the tablet did not have a significant effect until a tablet angle of 45°. Average percent error during anterior translation of the lateral knee compartment of 6mm was 2.2% compared to 6.2% for 2 mm of translation. The software provides reliable, objective, and quantitative data on translation of the lateral knee compartment during the pivot shift test and meets the design constraints posed by the clinical setting.

The Anterolateral Capsule of the Knee Behaves Like a Sheet of Fibrous Tissue

Background: The function of the anterolateral capsule of the knee has not been clearly defined. However, the contribution of this region of the capsule to knee stability in comparison with other anterolateral structures can be determined by the relative force that each structure carries during loading of the knee. Purpose/Hypothesis: The purpose of this study was to determine the forces in the anterolateral structures of the intact and anterior cruciate ligament (ACL)–deficient knee in response to an anterior tibial load and internal tibial torque. It was hypothesized that the anterolateral capsule would not function like a traditional ligament (ie, transmitting forces only along its longitudinal axis). Study Design: Controlled laboratory study. Methods: Loads (134-N anterior tibial load and 7-N·m internal tibial torque) were applied continuously during flexion to 7 fresh-frozen cadaveric knees in the intact and ACL-deficient state using a robotic testing system. The lateral collateral ligament (LCL) and the anterolateral capsule were separated from the surrounding tissue and from each other. This was done by performing 3 vertical incisions: lateral to the LCL, medial to the LCL, and lateral to the Gerdy tubercle. Attachments of the LCL and anterolateral capsule were detached from the underlying tissue (ie, meniscus), leaving the insertions and origins intact. The force distribution in the anterolateral capsule, ACL, and LCL was then determined at 30°, 60°, and 90° of knee flexion using the principle of superposition. Results: In the intact knee, the force in the ACL in response to an anterior tibial load was greater than that in the other structures (P < .001). However, in response to an internal tibial torque, no significant differences were found between the ACL, LCL, and forces transmitted between each region of the anterolateral capsule after capsule separation. The anterolateral capsule experienced smaller forces (~50% less) compared with the other structures (P = .048). For the ACL-deficient knee in response to an anterior tibial load, the force transmitted between each region of the anterolateral capsule was 434% greater than was the force in the anterolateral capsule (P < .001) and 54% greater than the force in the LCL (P = .036) at 30° of flexion. In response to an internal tibial torque at 30°, 60°, or 90° of knee flexion, no significant differences were found between the force transmitted between each region of the anterolateral capsule and the LCL. The force in the anterolateral capsule was significantly smaller than that in the other structures at all knee flexion angles for both loading conditions (P = .004 for anterior tibial load and P = .04 for internal tibial torque). Conclusion: The anterolateral capsule carries negligible forces in the longitudinal direction, and the forces transmitted between regions of the capsule were similar to the forces carried by the other structures at the knee, suggesting that it does not function as a traditional ligament. Thus, the anterolateral capsule should be considered a sheet of tissue. Clinical Relevance: Surgical repair techniques for the anterolateral capsule should restore the ability of the tissue to transmit forces between adjacent regions of the capsule rather than along its longitudinal axis.

Correlation between a 2D simple image analysis method and 3D bony motion during the pivot shift test

BACKGROUND The pivot shift test is the most specific clinical test to detect anterior cruciate ligament injury. The purpose of this study was to determine the correlation between the 2D simple image analysis method and the 3D bony motion of the knee during the pivot shift test and assess the intra- and inter-examiner agreements. METHODS Three orthopedic surgeons performed three trials of the standardized pivot shift test in seven knees. Two devices were used to measure motion of the lateral knee compartment simultaneously: 1) 2D simple image analysis method: translation was determined using a tablet computer with custom motion tracking software that quantified movement of three markers attached to skin over bony landmarks; 2) 3D bony motion: electromagnetic tracking system was used to measure movement of the same bony landmarks. RESULTS The 2D simple image analysis method demonstrated a good correlation with the 3D bony motion (Pearson correlation: 0.75, 0.76 and 0.79). The 3D bony translation increased by 2.7 to 3.5 times for every unit increase measured by the 2D simple image analysis method. The mean intra-class correlation coefficients for the three examiners were 0.6 and 0.75, respectively for 3D bony motion and 2D image analyses, while the inter-examiner agreement was 0.65 and 0.73, respectively. CONCLUSIONS The 2D simple image analysis method results are related to 3D bony motion of the lateral knee compartment, even with skin artifact present. This technique is a non-invasive and repeatable tool to quantify the motion of the lateral knee compartment during the pivot shift test.

Anatomic and Histological Investigation of the Anterolateral Capsular Complex in the Fetal Knee

Background: There is currently disagreement with regard to the presence of a distinct ligament in the anterolateral capsular complex of the knee and its role in the pivot-shift mechanism and rotatory laxity of the knee. Purpose: To investigate the anatomic and histological properties of the anterolateral capsular complex of the fetal knee to determine whether there exists a distinct ligamentous structure running from the lateral femoral epicondyle inserting into the anterolateral tibia. Study Design: Descriptive laboratory study. Methods: Twenty-one unpaired, fresh fetal lower limbs, gestational age 18 to 22 weeks, were used for anatomic investigation. Two experienced orthopaedic surgeons performed the anatomic dissection using loupes (magnification ×3.5). Attention was focused on the anterolateral and lateral structures of the knee. After the skin and superficial fascia were removed, the iliotibial band was carefully separated from underlying structures. The anterolateral capsule was then examined under internal and external rotation and varus-valgus manual loading and at different knee flexion angles for the presence of any ligamentous structures. Eight additional unpaired, fetal lower limbs, gestational age 11 to 23 weeks, were used for histological analysis. Results: This study was not able to prove the presence of a distinct capsular or extracapsular ligamentous structure in the anterolateral capsular complex area. The presence of the fibular collateral ligament, a distal attachment of the biceps femoris, the entire lateral capsule, the iliotibial band, and the popliteus tendon in the anterolateral and lateral area of the knee was confirmed in all the samples. Histological analysis of the anterolateral capsule revealed a loose, hypocellular connective tissue with less organized collagen fibers compared with ligament and tendinous structures. Conclusion: The main finding of this study was that the presence of a distinct ligamentous structure in the anterolateral complex is not supported from a developmental point of view, while all other anatomic structures were present. Clinical Relevance: The inability to prove the existence of a distinct ligamentous structure, called the anterolateral ligament, in the anterolateral knee capsule may indicate that the other components of the anterolateral complex, such as the lateral capsule, the iliotibial band, and its capsule-osseous layer, are more important for knee rotatory stability.

Is Lateral Femoral Notch Depth Associated with Rotatory Instability in ACL Deficient Knees: A Quantitative Pivot Shift Analysis

Objectives: Persistent rotatory knee instability after anterior cruciate ligament (ACL) reconstruction is relatively common. While the causes of this persistent instability are multifactorial, bony morphologic characteristics have been proposed to play a role. Therefore, the purpose of this study was to evaluate the relationship between the well-described lateral femoral notch (LFN) depth and quantitative measures of rotatory knee stability. We hypothesized that greater LFN depth would be associated with increased rotatory knee instability. Methods: A consecutive series of patients undergoing primary ACL reconstruction at our university medical center from June 2014 to April 2016 were analyzed. Inclusion criteria included primary ACL tear, no concurrent ligamentous or bony injury requiring operative treatment, no history of previous knee injury or surgery to the ACL-injured extremity, and no history of injury or surgery to the contralateral knee. A standardized pivot shift test was performed by the senior surgeon preoperatively under anesthesia in both knees and quantified using tablet image analysis software and accelerometer sensors as previously described and validated. Lateral knee radiographs and sagittal magnetic resonance images (MRI) of the injured knee were evaluated for depth of the LFN as previously described. A line tangent to the lateral femoral condyle articular surface was drawn across the notch. Notch depth was measured perpendicular from this line to the deepest point of the LFN. Pearson correlation coefficient was used to analyze correlations between continuous variables. Chi-square test was used to analyze relationships between notch depth and presence/absence of medial or lateral meniscus tears. Analyses were performed with SPSS 22.0 and significance was set at a p<0.05. Results: Fifty patients met inclusion criteria and were included in this study (mean age 24 years, range 13-45; 28 females, 22 males). Mean LFN depth as measured via x-ray was 0.8 mm (SD=0.63, n=50) and via MRI was 1.0 mm (SD=0.73, n=47). Twenty-two (44%) patients had a medial meniscus tear and 27 (54%) had a lateral meniscus tear. LFN on x-ray had moderate but significant positive correlations with ipsilateral lateral compartment acceleration (r=0.402, p=0.004) and acceleration side-to-side differences (r=0.407, p=0.003). LFN depth on MRI had moderate but significant positive correlations with ipsilateral lateral compartment acceleration (r=0.334, p=0.022) and acceleration side-to-side differences (r=0.363, p=0.012). LFN depth on x-ray was significantly associated with the presence of a lateral meniscus tear (p=0.014). There were no significant associations between LFN depth (x-ray or MRI) on ipsilateral or contralateral lateral compartment translation, contralateral lateral compartment acceleration, or the presence of medial meniscus tears. Conclusion: The results from this study demonstrated that a well described bony morphologic feature - LFN depth - was correlated with higher lateral compartment acceleration as measured by quantitative pivot shift analysis. Furthermore, greater LFN depth was associated with an increased incidence of lateral meniscus tears, which supports findings from previous studies. Assessment of LFN depth may help clinicians identify patients with greater rotatory instability prior to ACL reconstruction and potentially direct surgical treatment to account for additional rotatory knee instability. Table 1: Mean Quantitative Pivot Shift Values of the Injured and Uninjured Knee Injured Uninjured Side-to-Side Difference Compartment Acceleration (m/s2) 5.14 (SD=0.73) 3.45 (SD=0.95) 1.68 (SD=2.09) Lateral Compartment Translation (mm) 3.67 (SD=2.30) 1.22 (SD=0.75) 2.46 (SD=2.24)

In Vitro Biomechanical Analysis of Knee Rotational Stability

Several soft tissue structures and inherent anatomical characteristics contribute to stability of the knee. In vitro biomechanical studies provide valuable insight to the role of these factors as well as treatments to address rotational knee laxity by simulating clinical examinations and in vivo activities. The anterior cruciate ligament is a complex structure and is the main restraint for rotational laxity, and thus reconstruction surgeries should aim to restore its native anatomy. Other soft tissue structures such as the anterolateral structures and menisci also contribute as well, and injuries to these structures need to be properly assessed to achieve optimal outcomes. Findings from in vitro studies need to be appropriately coupled with in vivo studies to satisfy the ultimate goal of improving the clinical care of patients with knee ligamentous injuries.