In-vivo tibiofemoral kinematics of the normal knee during closed and open kinetic chain exercises: A comparative study of box squat and seated knee extension.

A rehabilitation program after anterior cruciate ligament reconstruction is of great importance to obtain a satisfactory prognosis after surgery. However, there is still an onging debate over whether closed kinetic chain or open kinetic chain exercises should be chosen. Our study was designed to compare the in vivo tibiofemoral kinematics during closed kinetic chain and open kinetic chain exercises. Eighteen healthy volunteers were asked to perform box squat and unloaded/10 kg-loaded seated knee extension. In vivo 3-dimensional analysis of tibiofemoral kinematics of different motions were determined using a dual fluoroscopic imaging system. The study found significantly more tibial anterior displacement during loaded seated knee extension than during unloaded seated knee extension from 25°-50° of knee flexion (p ≤ 0.031). The knees exhibited significantly more internal tibial rotation and lateral tibial translation during the box squat than both seated knee extensions during mid-flexion. In addition, the knees showed less internal-external (IE) range of motion (ROM) from 20°- 75° of flexion (p < 0.001) and medial-lateral (ML) ROM from 75° to full extension (p ≤ 0.006) during box squat than both extensions. This knowledge may help optimize rehabilitation plans for patients post ACL reconstruction.

Augmentation of Anterolateral Structures of the Knee Causes Undesirable Tibiofemoral Cartilage Contact in Double-Bundle Anterior Cruciate Ligament Reconstruction-A Randomized In-Vivo Biomechanics Study.

PURPOSE: To analyze the in vivo tibiofemoral cartilage contact patterns in knees undergoing double-bundle anterior cruciate ligament reconstruction(DB-ACLR) with or without anterolateral structure augmentation (ALSA). METHODS: Twenty patients with an ACL-ruptured knee and a healthy contralateral side were included. Nine patients received an isolated DB-ACLR (DB-ACLR group), and 11 patients had a DB-ACLR with ALSA (DB+ALSA group). At 1-year follow-up, a combined computed tomography, magnetic resonance imaging, and dual fluoroscopy imaging system analysis was used to capture a single-legged lunge of both the operated and healthy contralateral side. Tibiofemoral contact points (CPs) of the medial and lateral compartments were compared. CP locations were expressed as anteroposterior (AP, +/-) and medial-lateral (ML, -/+) values according to the tibia. RESULTS: In the DB-ACLR knees, no significant differences were found in CPs when compared with the healthy contralateral knees (P ≥ .31). However, in the DB+ALSA knees, the CPs in the lateral compartment had a significantly more anterior (mean AP: operative, -2.8 mm, 95% confidence interval [CI] -5.0 to-0.7 vs healthy, -5.0 mm, 95% CI -6.7 to -3.2; P = .006) and lateral (mean ML: operative, 23.2 mm, 95% CI 21.9-24.5 vs healthy, 21.8 mm, 95% CI 20.2-23.3; P = .013) location. The CPs in the medial compartment were located significantly more posterior (mean AP: operative, -3.4, 95% CI -5.0 to -1.9 vs healthy, -1.3, 95% CI -2.6 to -0.1; P = .006) and lateral (mean ML: operative, -21.3, 95% CI -22.6 to -20.0 vs healthy, -22.6, 95% CI -24.2 to -21.0; P = .021). CONCLUSIONS: DB-ACLR restored the tibiofemoral cartilage contact mechanics to near-normal values at 1-year follow-up. Adding the ALSA to the DB-ACLR resulted in significantly altered tibiofemoral cartilage contact locations in both the medial and lateral compartments. CLINICAL RELEVANCE: In DB-ACLR knees, the addition of an ALSA may be unfavorable as it caused significantly changed arthrokinematics.

There are isoheight points that measure constant femoral condyle heights along the knee flexion path.

PURPOSE: It is a challenge to evaluate the maintenance of medial and lateral soft tissue balance in total knee arthroplasty (TKA). This study aimed to determine the "isoheight" points and the "isoheight" axis (IHA) that can measure constant medial/lateral condyle heights during flexion of the knee, and compare the IHA with two major anatomical axes, the transepicondylar axis (TEA) and the geometric center axis (GCA). METHODS: Twenty-two healthy human knees were imaged using a combined MRI and dual fluoroscopic imaging system while performing a single-legged lunge (0°-120°). The isoheight points of the medial and lateral femoral condyles were defined as the locations with the least amount of changes in heights during the knee flexion; an IHA is the line connecting the medial and lateral isoheight points. The measured changes of the condyle heights using the IHA were compared with those measured using the TEA and GCA. RESULTS: Overall, the IHA was posterior and distal to the TEA, and anterior to the GCA. The isoheight points measured condyle height changes within 1.2 ± 2.3 mm at the medial and 0.7 ± 3.3 mm at the lateral sides during the knee flexion. Between 0° and 45°, the condyle height changes measured using the GCA (medial: 3.0 ± 1.8 mm, lateral: 2.3 ± 2.0 mm) were significantly larger than those of the IHA and the TEA (p < 0.05). Between 90° and 120°, the changes of the condyle heights measured using the TEA (medial: 5.3 ± 1.8 mm, lateral: 3.3 ± 1.8 mm) were significantly larger than those of the IHA and GCA (p < 0.05). CONCLUSION: There are isoheight points in the medial and lateral femoral condyles that can measure constant heights along the full range of knee flexion and could be used to formulate an "isoheight" axis (IHA) of the femur. The condyle height changes measured by the TEA and GCA were greater than the IHA measurements along the flexion path. These data could be used as a valuable reference to evaluate the condyle height changes after TKA surgeries and help achieve soft tissue balance and optimal knee kinematics along the flexion path. LEVEL OF EVIDENCE: IV.

The Occurrence of Meniscal and Chondral Injury in Two-Stage Revision Anterior Cruciate Ligament Reconstruction: A Consecutive Case Series.

Two-stage revision anterior cruciate ligament (ACL) reconstruction is an effective way to revise suboptimal tunnel-placement allowing for proper graft fixation. However, prolonged increased laxity of the knee may increase the risk of meniscal or chondral injury. It was hypothesized that no additional meniscal or chondral lesions occur in between the two stages of the two-stage revision ACL reconstruction. In this retrospective study, 42 patients undergoing a two-stage revision ACL reconstruction were included. Surgical notes for both stages were screened for meniscal and chondral status, interventions to any concurrent injury, surgery dates, along with basic patient characteristics. In 4 of the 42 patients, a new meniscal tear occurred in between the two stages, of which three required partial meniscectomy during the second stage of the ACL revision. One patient experienced a new small degenerative tear that did not require intervention. Two out of the four menisci that were repaired during the first stage had failed and required partial meniscectomy. No significant difference was found in the time between the two stages with respect to the occurrence of meniscal tears. No significant differences in chondral status were found. In conclusion, approximately 10% of patients developed a new meniscal tear and no difference in macroscopic chondral injury was observed between the first and second stages.

In vivo kinematics and ligamentous function of the knee during weight-bearing flexion: an investigation on mid-range flexion of the knee.

PURPOSE: To investigate the in vivo femoral condyle motion and synergistic function of the ACL/PCL along the weight-bearing knee flexion. METHODS: Twenty-two healthy human knees were imaged using a combined MRI and dual fluoroscopic imaging technique during a single-legged lunge (0°-120°). The medial and lateral femoral condyle translation and rotation (measured using geometric center axis-GCA), and the length changes of the ACL/PCL were analyzed at: low (0°-30°), mid-range (30°-90°) and high (90°-120°) flexion of the knee. RESULTS: At low flexion (0°-30°), the strains of the ACL and the posterior-medial bundle of the PCL decreased. The medial condyle showed anterior translation and lateral condyle posterior translation, accompanied with a sharp increase in external GCA rotation (internal tibial rotation). As the knee continued flexion in mid-range (30°-90°), both ACL and PCL were slack (with negative strain values). The medial condyle moved anteriorly before 60° of flexion and then posteriorly, accompanied with a slow increase of GCA rotation. As the knee flexed in high flexion (90°-120°), only the PCL had increasingly strains. Both medial and lateral condyles moved posteriorly with a rather constant GCA rotation. CONCLUSIONS: The ACL and PCL were shown to play a reciprocal and synergistic role during knee flexion. Mid-range reciprocal anterior-posterior femoral translation or laxity corresponds to minimal constraints of the ACL and PCL, and may represent a natural motion character of normal knees. The data could be used as a valuable reference when managing the mid-range "instability" and enhancing high flexion capability of the knee after TKAs. LEVEL OF EVIDENCE: Level IV.

Who should you be following? The top 100 social media influencers in orthopaedic surgery.

BACKGROUND: Social media has been credited with the potential to transform medicine, and Twitter was recently named "an essential tool" for the academic surgeon. Despite this, peer-to-peer and educational influence on social media has not been studied within orthopaedic surgery. This knowledge is important to identify who is controlling the conversation about orthopaedics to the public. We hypothesized that the plurality of top influencers would be sports medicine surgeons, that social media influence would not be disconnected from academic productivity, and that some of the top social media influencers in orthopaedic surgery would not be orthopaedic surgeons. AIM: To identify the top 100 social media influencers within orthopaedics, characterize who they are, and relate their social media influence to academic influence. METHODS: Twitter influence scores for the topic "orthopaedics" were collected in July 2018 using Right Relevance software. The accounts with the top influence scores were linked to individual names, and the account owners were characterized with respect to specialty, subspecialty, practice setting, location, board certification, and academic Hirsch index (h-index). RESULTS: Seventy-eight percent of top influencers were orthopaedic surgeons. The most common locations included California (13%), Florida (8%), New York (7%), United Kingdom (7%), Colorado (6%), and Minnesota (6%). The mean academic h-index of the top influencers (n = 79) was 13.67 ± 4.12 (mean ± 95%CI) and median 7 (range 1-89) (median reported h-index of academic orthopaedic faculty is 5 and orthopaedic chairpersons is 13). Of the 78 orthopaedic surgeons, the most common subspecialties were sports medicine (54%), hand and upper extremity (18%), and spine (8%). Most influencers worked in private practice (53%), followed by academics (17%), privademics (14%), and hospital-based (9%). All eligible orthopaedic surgeons with publicly-verifiable board certification statuses were board-certified (n = 74). CONCLUSION: The top orthopaedic social media influencers on Twitter were predominantly board-certified, sports-medicine subspecialists working in private practice in the United States. Social media influence was highly concordant with academic productivity as measured by the academic h-index. Though the majority of influencers are orthopaedic surgeons, 22% of top influencers on Twitter are not, which is important to identify given the potential for these individuals to influence patients' perceptions and expectations. This study also provides the top influencer network for other orthopaedic surgeons to engage with on social media to improve their own social media influence.

Anatomic is better than isometric posterior cruciate ligament tunnel placement based upon in vivo simulation.

PURPOSE: To elucidate the effects of various tibial and femoral attachment locations on the theoretical length changes and isometry of PCL grafts in healthy knees during in vivo weightbearing motion. METHODS: The intact knees of 14 patients were imaged using a combined magnetic resonance and dual fluoroscopic imaging technique while the patient performed a quasi-static lunge (0°-120° of flexion). The theoretical end-to-end distances of the 3-dimensional wrapping paths between 165 femoral attachments, including the anatomic anterolateral bundle (ALB), central attachment and posteromedial bundle (PMB) of the PCL, connected to an anterolateral, central, and posteromedial tibial attachment were simulated and measured. A descriptive heatmap was created to demonstrate the length changes on the medial condyle and formal comparisons were made between the length changes of the anatomic PCL and most isometric grafts. RESULTS: The most isometric graft, with approximately 3% length change between 0° and 120° of flexion, was located proximal to the anatomic femoral PCL attachments. Grafts with femoral attachments proximal to the isometric zone decreased in length with increasing flexion angles, whereas grafts with more distal attachments increased in length with increasing flexion angles. The ALB and central single-bundle graft demonstrated a significant elongation from 0° to 120° of flexion (p < 0.001). The PMB decreased in length between 0° and 60° of flexion after which the bundle increased in length to its maximum length at 120° (p < 0.001). No significant differences in length changes were found between either the ALB or PMB and the central graft, and between the ALB and PMB at flexion angles ≥ 60° (n.s.). CONCLUSIONS: The most isometric attachment was proximal to the anatomic PCL footprint and resulted in non-physiological length changes. Moving the femoral attachment locations of the PCL significantly affected length change patterns, whereas moving the tibia locations did not. The importance of anatomically positioned (i.e., distal to the isometric area) femoral PCL reconstruction locations to replicate physiological length changes is highlighted. These data can be used to optimize tunnel positioning in either single- or double-bundle and primary or revision PCL reconstruction cases. LEVEL OF EVIDENCE: IV.

An In Vivo Prediction of Anisometry and Strain in Anterior Cruciate Ligament Reconstruction - A Combined Magnetic Resonance and Dual Fluoroscopic Imaging Analysis.

PURPOSE: To evaluate the in vivo anisometry and strain of theoretical anterior cruciate ligament (ACL) grafts in the healthy knee using various socket locations on both the femur and tibia. METHODS: Eighteen healthy knees were imaged using magnetic resonance imaging and dual fluoroscopic imaging techniques during a step-up and sit-to-stand motion. The anisometry of the medial aspect of the lateral femoral condyle was mapped using 144 theoretical socket positions connected to an anteromedial, central, and posterolateral attachment site on the tibia. The 3-dimensional wrapping paths of each theoretical graft were measured. Comparisons were made between the anatomic, over the top (OTT), and most-isometric (isometric) femoral socket locations, as well as between tibial insertions. RESULTS: The area of least anisometry was found in the proximal-distal direction just posterior to the intercondylar notch. The most isometric attachment site was found midway on the Blumensaat line with approximately 2% and 6% strain during the step-up and sit-to-stand motion, respectively. Posterior femoral attachments resulted in decreased graft lengths with increasing flexion angles, whereas anterodistal attachments yielded increased lengths with increasing flexion angles. The anisometry of the anatomic, OTT and isometric grafts varied between tibial insertions (P < .001). The anatomic graft was significantly more anisometric than the OTT and isometric graft at deeper flexion angles (P < .001). CONCLUSIONS: An area of least anisometry was found in the proximal-distal direction just posterior to the intercondylar notch. ACL reconstruction at the isometric and OTT location resulted in nonanatomic graft behavior, which could overconstrain the knee at deeper flexion angles. Tibial location significantly affected graft strains for the anatomic, OTT, and isometric socket location. CLINICAL RELEVANCE: This study improves the knowledge on ACL anisometry and strain and helps surgeons to better understand the consequences of socket positioning during intra-articular ACL reconstruction.

An in Vivo Simulation of Isometry of the Anterolateral Aspect of the Healthy Knee.

BACKGROUND: To assess the isometry of theoretical lateral extra-articular reconstruction (LER), we evaluated theoretical grafts attached to various points on the lateral femoral condylar area and to either Gerdy's tubercle or the anatomic attachment site of the anterolateral ligament to the tibia. METHODS: In 18 subjects, healthy knees with no history of either injury or surgery involving the lower extremity were studied. The subjects performed a sit-to-stand motion (from approximately 90° of flexion to full extension), and each knee was studied using magnetic resonance and dual fluoroscopic imaging techniques. The 3-dimensional wrapping paths of each theoretical LER graft were measured. Grafts showing the least change in length during the sit-to-stand motion were considered to be the most isometric. RESULTS: The most isometric attachment site on the lateral femoral epicondyle to either of the studied tibial attachment sites was posterior-distal to the femoral attachment site of the fibular collateral ligament. The LER graft had a mean change in length of approximately 3%. Moving the femoral attachment site anteriorly resulted in increased length of the graft with increasing flexion; more posterior attachment sites resulted in decreased length with increasing flexion. Moving the attachment site in the proximal-distal direction had a less profound effect. Moving the tibial attachment site from Gerdy's tubercle to the tibial attachment site of the anterolateral ligament affected the overall isometric distribution on the lateral femoral epicondyle. CONCLUSIONS: The most isometric attachment site on the femur for an LER would be posterior-distal to the femoral attachment site of the fibular collateral ligament. Different length changes for LER grafts were identified with respect to different femoral attachment sites. Desirable graft fixation locations for treating anterolateral rotatory instability were found posterior-proximal to the femoral fibular collateral ligament attachment. CLINICAL RELEVANCE: The present data could be used both in biomechanical studies and in clinical studies as guidelines for planning LER surgical procedures.

The biomechanical effect of tunnel placement on ACL graft forces in double-bundle ACL reconstruction - A 3D computational simulation.

BACKGROUND: The posterolateral (PL) graft experiences a high failure rate in anterior cruciate ligament double-bundle (DB) reconstruction. It is hypothesized that tunnel positions could dramatically affect the graft forces. METHODS: A validated computational model was used to simulate DB reconstruction with various femoral PL tunnel locations (8-11 mm center-center tunnel spacing). Graft fixation was simulated at both 0° and 30°. Knee biomechanics were examined with the knee under a 134 N anterior load and 400 N quadriceps load at 0°, 30°, 60°, and 90° of flexion. Graft forces, tibial translation, and tibial rotation were calculated. RESULTS: PL graft forces at full extension increased with increasing tunnel spacing under both fixation settings, but the knee kinematics was not dramatically affected. CONCLUSION: Small changes in the femoral PL tunnel position could result in large changes in graft forces, implying that precise PL tunnel position is an important factor in a successful DB reconstruction.

In Vivo Anterolateral Ligament Length Change in the Healthy Knee During Functional Activities-A Combined Magnetic Resonance and Dual Fluoroscopic Imaging Analysis.

PURPOSE: To measure the in vivo anterolateral ligament (ALL) length change in healthy knees during step-up and sit-to-stand motions. METHODS: Eighteen healthy knees were imaged using magnetic resonance and dual fluoroscopic imaging techniques during a step-up and sit-to-stand motion. The ALL length change was measured using the shortest three-dimensional wrapping path, with its femoral attachment located slightly anterior-distal (ALL-Claes) or posterior-proximal (ALL-Kennedy) to the fibular collateral ligament attachment. The ALL length measured from the extended knee position of the non-weight-bearing magnetic resonance scan was used as a reference to normalize the length change. RESULTS: During the step-up motion (approximately 55° flexion to full extension), both the ALL-Claes and ALL-Kennedy showed a significant decrease in length of 21.2% (95% confidence interval 18.0-24.4, P < .001) and 24.3% (20.6-28.1, P < .001), respectively. During the sit-to-stand motion (approximately 90° flexion to full extension), both the ALL-Claes and ALL-Kennedy showed a consistent, significant decrease in length of 35.2% (28.8-42.2, P < .001) and 39.2% (32.4-46.0, P < .001), respectively. From approximately 90° to 70° of flexion, a decrease in length of approximately 6% was seen; 70° of flexion to full extension resulted in an approximately 30% decrease in length. CONCLUSIONS: The ALL was found to be a nonisometric structure during the step-up and sit-to-stand motion. The length of the ALL was approximately 35% longer at approximately 90° of knee flexion when compared with full extension and showed decreasing length at lower flexion angles. Similar ALL length change patterns were found with its femoral attachment located slightly anterior-distal or posterior-proximal to the fibular collateral ligament attachment. CLINICAL RELEVANCE: These data suggest that, if performing anatomic ALL reconstruction, graft fixation may be performed beyond 70° flexion to reduce the chance of lateral compartment overconstraint. Anatomic ALL reconstruction may affect the knee kinematics more in high flexion than at low flexion angles.

Postoperative time dependent tibiofemoral articular cartilage contact kinematics during step-up after ACL reconstruction.

This study was to investigate the in vivo tibiofemoral cartilage contact locations before and after anterior cruciate ligament (ACL) reconstruction at 6 and 36 months. Ten patients with unilateral ACL injury were included. A step-up motion was analyzed using a combined magnetic resonance modeling and dual fluoroscopic imaging techniques. The preoperative (i.e. ACL deficient and healthy contralateral) and postoperative cartilage contact locations at 6 and 36 months were analyzed. Similar patterns of the cartilage contact locations during the step-up motion were found for the preoperative and postoperative knee states as compared to the preoperative healthy contralateral side. At the end of step-up motion, the medial contact locations at postoperative 36 months were more anterior when compared to the preoperative healthy contralateral (p=0.02) and 6 months postoperative knee states (p=0.01). The changes of the cartilage contact locations at 36 months after ACL reconstruction compared to the healthy contralateral side were strongly correlated with the changes at 6 months postoperatively. This study showed that the tibiofemoral cartilage contact locations of the knee changes with time after ACL reconstruction, implying an ongoing recovery process within the 36 months after the surgery. There could be an association between the short-term (6 months) and longer-term (36 months) contact kinematics after ACL reconstruction. Future studies need to investigate the intrinsic relationship between knee kinematics at different times after ACL reconstruction.