Jing-Sheng Li

Anteroposterior Stability of the Knee during the Stance Phase of Gait after Anterior Cruciate Ligament Deficiency

Quadriceps avoidance and higher flexion strategies have been assumed as effects of ACL deficiency on knee joint function during gait. However, the effect of ACL deficiency on anteroposterior stability of the knee during gait is not well defined. In this study, 10 patients with unilateral acute ACL ruptures and the contralateral side intact performed gait on a treadmill. Flexion angles and anteroposterior translation of the ACL injured and the intact controlateral knees were measured at every 10% of the stance phase of the gait (from heel strike to toe-off) using a combined MRI and dual fluoroscopic imaging system (DFIS). The data indicated that during the stance phase of the gait, the ACL-deficient knees showed higher flexion angles compared to the intact contralateral side, consistent with the assumption of a higher flexion gait strategy. However, the data also revealed that the ACL-deficient knees had higher anterior tibial translation compared to the intact contralateral side during the stance phase of the gait. The higher flexion gait strategy was not shown to correlate to a reduction of the anterior tibial translation in ACL deficient knees. These data may provide indications for conservative treatment or surgical reconstruction of the ACL injured knees in restoration of the knee kinematics during daily walking activities.

Biomechanical Evaluation of Knee Joint Laxities and Graft Forces After Anterior Cruciate Ligament Reconstruction by Anteromedial Portal, Outside-In, and Transtibial Techniques

Background: Recently, anatomic anterior cruciate ligament (ACL) reconstruction is emphasized to improve joint laxity and to potentially avert initiation of cartilage degeneration. There is a paucity of information on the efficacy of ACL reconstructions by currently practiced tunnel creation techniques in restoring normal joint laxity. Study Design: Controlled laboratory study. Hypothesis: Anterior cruciate ligament reconstruction by the anteromedial (AM) portal technique, outside-in (OI) technique, and modified transtibial (TT) technique can equally restore the normal knee joint laxity and ACL forces. Methods: Eight fresh-frozen human cadaveric knee specimens were tested using a robotic testing system under an anterior tibial load (134 N) at 0°, 30°, 60°, and 90° of flexion and combined torques (10-N·m valgus and 5-N·m internal tibial torques) at 0° and 30° of flexion. Knee joint kinematics, ACL, and ACL graft forces were measured in each knee specimen under 5 different conditions (ACL-intact knee, ACL-deficient knee, ACL-reconstructed knee by AM portal technique, ACL-reconstructed knee by OI technique, and ACL-reconstructed knee by TT technique). Results: Under anterior tibial load, no significant difference was observed between the 3 reconstructions in terms of restoring anterior tibial translation (P > .05). However, none of the 3 ACL reconstruction techniques could completely restore the normal anterior tibial translations (P < .05). Under combined tibial torques, both AM portal and OI techniques closely restored the normal knee anterior tibial translation (P > .05) at 0° of flexion but could not do so at 30° of flexion (P < .05). The ACL reconstruction by the TT technique was unable to restore normal anterior tibial translations at both 0° and 30° of flexion under combined tibial torques (P < .05). Forces experienced by the ACL grafts in the 3 reconstruction techniques were lower than those experienced by normal ACL under both the loading conditions. Conclusion: Anterior cruciate ligament reconstructions by AM portal, OI, and modified TT techniques are biomechanically comparable with each other in restoring normal knee joint laxity and in situ ACL forces. Clinical Relevance: Anterior cruciate ligament reconstructions by AM portal, OI, and modified TT techniques result in similar knee joint laxities. Technical perils and pearls should be carefully considered before choosing a tunnel creating technique.

In vivo kinematics of the knee during weight bearing high flexion

Achieving high flexion is an objective of contemporary total knee arthoplasty; however little is known on the knee biomechanics at high flexion under weight-bearing conditions. This study investigates the 6DOF kinematics and tibiofemoral cartilage contact biomechanics of the knee during weight-bearing flexion from full extension to maximal flexion. Eight knees from seven healthy subjects with no history of injuries or chronic pain were recruited. The knees were MRI scanned to create 3D models of the tibia and femur, including their articular cartilage surfaces. The subjects were then imaged using a dual fluoroscopic image system while performing a weight-bearing quasi-static single-legged lunge from full extension to maximal flexion. The 6DOF kinematics and the articular cartilage contact locations were measured along the flexion path of the knee. The result indicated that the internal tibial rotation increased sharply at low flexion angles (full extension to 30°), maintained a small variation in the middle range of flexion (30-120°, and then sharply increased again at high flexion angles (120° to maximal flexion). The contact point moved similarly in the medial and lateral compartments before 120° of flexion, but less on the medial compartment at high flexion angles. The results indicated that the knee motion could not be described using one character in the entire range of flexion, especially in high flexion. The knee kinematic data in the entire range of flexion of the knee could be instrumental for designing new knee prostheses to achieve physical high flexion and improving rehabilitation protocols after knee injuries.

A novel dual fluoroscopic imaging method for determination of THA kinematics: In-vitro and in-vivo study

Accurate measurement of six-degrees-of-freedom in-vivo kinematics of the total hip arthroplasty (THA) is essential in gaining insights into in-vivo THA performance. The objective of this study was to validate a novel dual fluoroscopy imaging system (DFIS) for determination of the THA kinematics using both in-vitro and in-vivo approaches. The in-vitro validation utilized cadaveric hip specimens to compare the THA motion using the DFIS technique with those measured by a radiostereometric analysis (RSA). The differences between the DFIS technique and the RSA were within 0.33±0.81 mm (mean±SD) in translation and 0.45±0.65° in rotation during dynamic motion of the hips. In the in-vivo validation, the THA kinematics of two patients during a treadmill gait was assessed for the feasibility/repeatability of the DFIS technique in measurement of THA kinematics. The poses of the THAs during the treadmill gait was measured using the DFIS technique with the maximum standard deviation of 0.35 mm in translation and of 0.55° in rotation. This study demonstrated that the DFIS technique has comparable accuracy of the RSA and is highly repeatable for measurement of dynamic THA motion, suggesting that the DFIS is a promising tool in evaluating the in-vivo THA biomechanics during functional activities.

Kinematic characteristics of the tibiofemoral joint during a step-up activity

The step-up activity (stair-ascending) is an important daily function of the knee. This study aimed to investigate the articular cartilage contact kinematics on both tibial and femoral cartilage surfaces and describe the femoral condylar motion using the transepicondylar axis (TEA) and the geometric center axis (GCA) during a step-up activity. Twenty-one healthy subjects were included and their knee joint models were reconstructed using MR images. A single-stair step-up activity was imaged using a dual-fluoroscopic imaging system. Three-dimensional knee joint contact points were determined and projected onto the tibial plateau and femoral condylar surfaces. The contact points on the medial and lateral tibial plateau moved anteriorly (by 13.5±3.2 and 10.7±5.0 mm, respectively, p>0.05) with knee extension. The contact points on the medial and lateral femoral condyle moved from the posterior to the anterior portion (by 32.2±4.9 mm and 25.5±4.2 mm, respectively, p<0.05) and were located on the inner half of the femoral cartilage throughout the activity. The data on articular contact kinematics and the femoral condylar motion described using the TEA and GCA indicated that the medial and lateral compartments had similar motion patterns during the step-up activity. The knee does not demonstrate a medial-pivoting motion character during the step-up activity. The data may provide insight to contemporary TKA development.

In Vivo Patellar Tracking and Patellofemoral Cartilage Contacts during Dynamic Stair Ascending

The knowledge of normal patellar tracking is essential for understanding the knee joint function and for diagnosis of patellar instabilities. This paper investigated the patellar tracking and patellofemoral joint contact locations during a stair ascending activity using a validated dual-fluoroscopic imaging system. The results showed that the patellar flexion angle decreased from 41.9° to 7.5° with knee extension during stair ascending. During first 80% of the activity, the patella shifted medially about 3.9 mm and then slightly shifted laterally during the last 20% of the ascending activity. Anterior translation of 13 mm of the patella was measured at the early 80% of the activity and the patella slightly moved posteriorly by about 2mm at the last 20% of the activity. The path of cartilage contact points was slightly lateral on the cartilage surfaces of patella and femur. On the patellar cartilage surface, the cartilage contact locations were about 2mm laterally from heel strike to 60% of the stair ascending activity and moved laterally and reached 5.3mm at full extension. However, the cartilage contact locations were relatively constant on the femoral cartilage surface (∼5mm lateral). The patellar tracking pattern was consistent with the patellofemoral cartilage contact location pattern. These data could provide baseline knowledge for understanding of normal physiology of the patellofemoral joint and can be used as a reference for clinical evaluation of patellofemoral disorders.

Meniscus Injuries Alter the Kinematics of Knees With Anterior Cruciate Ligament Deficiency

Background: Most knee joint biomechanics studies have involved knees with an isolated anterior cruciate ligament (ACL) injury. However, a large portion of patients with injured ACLs have accompanied meniscus tearing. In this study, the in vivo alteration of knee biomechanics after tearing the ACL with or without combined medial or lateral meniscus tear was investigated during stair-ascending activity. Hypothesis: The kinematic behavior of ACL-deficient knees changes with a combined medial or lateral meniscus tear. Study Design: Controlled laboratory study. Methods: Twenty-one patients with injured ACLs (contralateral side intact) were recruited before undergoing ACL reconstruction. Among these patients, 5 had isolated ACL injuries (group I), 8 had combined ACL and medial meniscus injuries (group II), and 8 had combined ACL and lateral meniscus injuries (group III). Bilateral magnetic resonance scans were obtained on each patient to construct 3-dimensional anatomic knee models. Both knees were then scanned during stair-climbing activity using a dual fluoroscopic imaging system. The knee kinematics during stair climbing were reproduced using a bone model image matching method. Anteroposterior and mediolateral translations and axial tibial rotation of the knee during stair ascent were then compared between the injured and intact contralateral knees of the patients. Results: On average, injured knees in groups I and III showed more than 2 mm increased anterior tibial translation close to full knee extension. In group II, no statistically significant difference was observed between the injured and contralateral side in anteroposterior translation. Near full extension, in groups I and III, injured knees had less than 1 mm of increased medial tibial translation compared with the contralateral side, whereas in group II, a 1.0-mm increase in lateral tibial shift was observed in the injured knees. With regard to axial tibial rotation, group I showed an increased external tibial rotation (approximately 5°), group II had little variation, whereas group III had increased internal tibial rotation (approximately 3°). Conclusion: The results of this study demonstrate that a combined ACL/meniscus injury could alter the kinematics of ACL-injured knees in a different way compared with knees with isolated ACL tears, depending on the pattern of the meniscus tear. Considering the varying effect of meniscus injuries on knee joint kinematics, future studies might focus on specific treatment of patients with combined ACL and meniscus injuries to protect the joint from abnormal kinematics and subsequent postoperative cartilage degeneration.

Gender analysis of the anterior femoral condyle geometry of the knee.

BACKGROUND No study has used 3-D anatomic knee models to investigate the gender differences in anterior femoral condyles. Therefore, this study aims to determine the morphologic differences between genders in anterior femoral condyles of the knees using 3-D anatomic knee models. METHODS Ninety-six male and sixty-five female 3D anatomic knee models were used to measure lateral and medial anterior condyle heights, anterior trochlear groove heights, and anterior condyle width, which were normalized by the anterior-posterior and medial-lateral dimensions of the knee, respectively. The shape of anterior condyle groove was also analyzed. RESULTS The mean lateral anterior condyle height, medial anterior condyle height and anterior condyle width of females were 6.6±1.8 mm, 2.0±2.3 mm, and 44.7±4.2 mm, respectively. These data were significantly smaller (p<0.05) than those of males (7.7±1.8 mm, 2.9±2.0 mm and 50.0±3.4 mm). However, after normalizing by the femur size, the aspect ratios had no gender differences. Both the ranges of lateral and medial condyle of females were significantly smaller than those of males, and the geometry curve of anterior condyle was different between genders. CONCLUSION Although the gender differences in anterior femoral condyle sizes no longer existed after normalization with the femur size, the shape and the peak position of anterior condyle groove still have gender differences. The data may have important implications on the current debate of gender-specific TKAs. CLINICAL RELEVANCE This study provides a better understanding of gender differences in anterior femoral condyle geometry.

Sagittal plane rotation center of lower lumbar spine during a dynamic weight-lifting activity.

This study investigated the center of rotation (COR) of the intervertebral segments of the lower lumbar spine (L4-L5 and L5-S1 segments) in sagittal plane during a weight-lifting (3.6 kg in each hand) extension activity performed with the pelvis constrained. Seven healthy subjects were studied using a dual fluoroscopic imaging technique. Using the non-weightbearing, supine position during MRI scan as a reference, the average intervertebral flexion angles of the L4-L5 and L5-S1 were 6.6° and 5.3° at flexion position of the body, respectively, and were -1.8° and -3.5° at extension position of the body, respectively. The CORs of the lower lumbar spine were found segment-dependent and changed with the body postures. The CORs of the L4-L5 segment were at the location about 75% posterior from the anterior edge of the disc at flexion positions of the body, and moved to about 92% of the posterior portion of the disc at extension positions of the body. The CORs of the L5-S1 segment were at 95% posterior portion of the disc at flexion positions of the body, and moved outside of the posterior edge of the disc by about 12% of the disc length at extension positions of the body. These results could help understand the physiological motion characters of the lower lumbar spine. The data could also provide important insights for future improvement of artificial disc designs and surgical implantation of the discs that are aimed to reproduce normal spinal functions.

Principal component analysis in construction of 3D human knee joint models using a statistical shape model method.

The statistical shape model (SSM) method that uses 2D images of the knee joint to predict the three-dimensional (3D) joint surface model has been reported in the literature. In this study, we constructed a SSM database using 152 human computed tomography (CT) knee joint models, including the femur, tibia and patella and analysed the characteristics of each principal component of the SSM. The surface models of two in vivo knees were predicted using the SSM and their 2D bi-plane fluoroscopic images. The predicted models were compared to their CT joint models. The differences between the predicted 3D knee joint surfaces and the CT image-based surfaces were 0.30 ± 0.81 mm, 0.34 ± 0.79 mm and 0.36 ± 0.59 mm for the femur, tibia and patella, respectively (average ± standard deviation). The computational time for each bone of the knee joint was within 30 s using a personal computer. The analysis of this study indicated that the SSM method could be a useful tool to construct 3D surface models of the knee with sub-millimeter accuracy in real time. Thus, it may have a broad application in computer-assisted knee surgeries that require 3D surface models of the knee.