In vivo length change patterns of the medial and lateral collateral ligaments along the flexion path of the knee

Regional shear wave speeds track regional axial stress in nonuniformly loaded fibrous soft tissues

Ligaments and tendons undergo nonuniform deformation during movement. While deformations can be imaged, it remains challenging to use such information to infer regional tissue loading. Shear wave tensiometry is a promising noninvasive technique to gauge axial stress and is premised on a tensioned beam model. However, it is unknown whether tensiometry can predict regional stress in a nonuniformly loaded structure. The objectives of this study were to (1) determine whether regional shear wave speed tracks regional axial stress in nonuniformly loaded fibrous soft tissues, and (2) determine the sensitivity of regional axial stress and shear wave speed to nonuniform load distribution and fiber alignment. We created a representative set of 12,000 dynamic finite element models of a fibrous soft tissue with probabilistic variations in fiber alignment, stiffness, and aspect ratio. In each model, we applied a randomly selected nonuniform load distribution, and then excited a shear wave and tracked its regional propagation. We found that regional shear wave speed was an excellent predictor of the regional axial stress (RMSE = 0.57 MPa) and that the nature of the regional shear wave speed-stress relationship was consistent with a tensioned beam model (R2 = 0.99). Variations in nonuniform load distribution and fiber alignment did not substantially alter the wave speed-stress relationship, particularly at higher loads. Thus, these findings suggests that shear wave tensiometry could provide a quantitative estimate of regional tissue stress in ligaments and tendons.

Comparison of knee kinematics and ligament forces in single and multi-radius cruciate-retaining total knee arthroplasty: A computer simulation study

BACKGROUND

The single-radius design in total knee arthroplasty has been designed to develop a more fixed flexion-extension axis without mid-flexion instability compared with the multi-radius design. It remains unclear whether differences between the multi-radius and single-radius designs can affect kinematics and collateral ligament forces. This study aimed to simulate knee kinematics and kinetics between single-radius and multi-radius models using a musculoskeletal computer model.

METHODS

The single-radius and multi-radius femoral components were virtually implanted in a computer simulation using the same tibial insert. The effects of implant design on kinematics and medial collateral ligament forces during squatting and gait activities were analyzed.

RESULTS

During squatting, the multi-radius model exhibited paradoxical anterior translation on both the medial and lateral flexion facet center where peak anterior translation was 2.4 mm for medial flexion facet center and 2.2 mm for the lateral flexion facet center, while the peak anterior translation of the single-radius model was less than 1 mm at early flexion. A rapid decrease in medial collateral ligament tension was observed in the early flexion phase in the multi-radius model, which occurred simultaneously with paradoxical anterior translation, whereas the relatively constant medial collateral ligament tension was observed in the single-radius model. During gait activity, the single-radius model exhibited a more posterior position than the multi-radius model.

CONCLUSION

These suggest that abrupt changes in the medial collateral ligament force influence anterior sliding of the femur, and that the single-radius design is a reasonable choice for prevention of mid-flexion instability.

Mechanisms of mobile bearing dislocation in lateral unicompartmental knee replacement

Mobile bearing dislocation occurs in 1- 6% of Oxford Domed Lateral replacements. Dislocations are predominantly medial, but can occur anteriorly or posteriorly. They tend to occur when the knee is flexed. It is not clear how dislocations can be prevented. A previously described mechanical rig for assessing mobile bearing dislocation was updated so as to study dislocation with the knee in flexion. Sub-categories for the description of each type of dislocation were introduced. Dislocation was only possible when the knee was distracted. As the amount of distraction possible in the knee is variable, the risk of dislocation is related to the amount of distraction in the rig necessary for a dislocation. The type of dislocation requiring the least distraction was medial `edge' dislocation in which the edge of the bearing dislocates onto the tibial wall, which is the most common type of dislocation. The amount of distraction necessary decreased the further the bearing was from the wall and with 50% posterior overhang. Rotation of the knee did not influence the amount of distraction. In conclusion dislocation can only occur if the lateral compartment is distracted. To reduce the dislocation risk, surgeons should aim to position the femoral and tibial components so that the bearing is as close as possible to the wall without jamming against it and the tibial component should be positioned flush with the posterior tibial cortex. If, during the surgery, the mobile bearing can easily be dislocated onto the wall the surgeon should consider changing to a fixed bearing. The tibial component should also be positioned flush with the posterior tibial cortex, as if it is too far forward this may contribute to dislocation.

Medial stability and lateral flexibility of the collateral ligaments during mid-range flexion in medial-pivot total knee arthroplasty patients demonstrates favorable postoperative outcomes

PURPOSE

The objectives of the present study were to investigate the length change in different bundles of the superficial medial collateral ligament (sMCL) and lateral collateral ligament (LCL) during lunge, and to evaluate their association with Knee Society Score (KSS) following medial-pivot total knee arthroplasty (MP-TKA).

METHODS

Patients with unilateral MP-TKA knees performed a bilateral single-leg lunge under dual fluoroscopy surveillance to determine the in-vivo six degrees-of-freedom knee kinematics. The contralateral non-operated knees were used as the control group. The attachment sites of the sMCL and LCL were marked to calculate the 3D wrapping length. The sMCL and LCL were divided into anterior, intermediate, and posterior portions (aMCL, iMCL, pMCL, aLCL, iLCL, pLCL). Correlations between lengths/elongation rate of ligament bundles from full extension to 100° flexion and the KSS were examined.

RESULTS

The sMCL and LCL demonstrated relative stability in length at low flexion, but sMCL length decreased whereas LCL increased with further flexion on operated knees. The sMCL length increased at low flexion and remained stable with further flexion, while the LCL length decreased with flexion on the contralateral non-operated knees. The lengths of aMCL, iMCL, and pMCL showed moderate (0.5 < r < 0.7, p < 0.05) negative correlations with the KSS, and the lengths of aLCL, iLCL, and pLCL were positively correlated with the KSS at mid flexion on operated knees (p < 0.05). The elongation rates of aLCL, iLCL, and pLCL were negatively correlated with the KSS at high flexion on operated knees (p < 0.05). However, no significant correlations between the length of different bundles of sMCL or LCL with KSS were found on contralateral non-operated knees.

CONCLUSIONS

The elongation pattern of sMCL/LCL on MP-TKA knees showed differences with contralateral non-operated knees. The sMCL is tense at low to middle flexion and relaxed at high flexion, while LCL is relaxed at low to middle flexion and tense at high flexion following MP-TKA. Medial stability and proper lateral flexibility during mid flexion were associated with favorable postoperative outcomes in MP-TKA patients. In contrast, lateral relaxation at deep flexion should be avoided when applying soft-tissue balancing in MP-TKA.

LEVEL OF EVIDENCE

Level III.

Virtual Joint Motion Simulator Accurately Predicts Effects of Femoral Component Malalignment during TKA

Component alignment accuracy during total knee arthroplasty (TKA) has been improving through the adoption of image-based navigation and robotic surgical systems. The biomechanical implications of resulting component alignment error, however, should be better characterized to better understand how sensitive surgical outcomes are to alignment error. Thus, means for analyzing the relationships between alignment, joint kinematics, and ligament mechanics for candidate prosthesis component design are necessary. We used a digital twin of a commercially available joint motion simulator to evaluate the effects of femoral component rotational alignment. As anticipated, the model showed that an externally rotated femoral component results in a knee which is more varus in flexion, with lower medial collateral ligament tension compared to a TKA knee with a neutrally aligned femoral implant. With the simulation yielding logical results for this relatively simple test scenario, we can have more confidence in the accuracy of its predictions for more complicated scenarios.

Posterior-stabilized total knee arthroplasty kinematics and joint laxity: A hybrid biomechanical study

BACKGROUND

Posterior-stabilized (PS)-total knee arthroplasty (TKA) arose as an alternative to cruciate-retaining (CR)-TKA in the 1970s. Since then, it has become a popularly utilized TKA design with outcomes comparable to CR-TKA. The post-cam mechanism is unique to PS-TKA as it substitutes the function of the posterior cruciate ligament (PCL). The study aimed to understand the kinematic and laxity changes in PS-TKA with under- and overstuffing of the tibiofemoral joint space with the polyethylene (PE) insert.

METHODS

This study employed a hybrid computational-experimental joint motion simulation on a VIVO 6 degrees of freedom (6-DoF) joint motion simulator (AMTI, Watertown, MA, USA). Physical prototypes of a virtually-performed TKA in mechanical alignment (MA) and kinematic alignment (KA) based on cadaveric CT scans and a virtual ligament model were utilized. The reference, understuffed (down 2 mm) and overstuffed (up 2 mm) joint spaces were simulated, neutral flexion and laxity testing loads and motions were performed for each configuration.

RESULTS

The PE insert thickness influenced post-cam engagement, which occurred after 60º in the overstuffed configurations, after 60º-75º in the reference configurations and after 75º in the understuffed configurations. The understuffed configurations, compared to the reference configurations, resulted in a mean 2.0º (28%) and 2.0º (31%) increase in the coronal laxity in MA and KA respectively. The overstuffed configurations, compared to the reference configuration, resulted in an increase in the mean joint compressive forces (JCFs) by 73 N (61%) and 77 N (62%) in MA and KA models, respectively.

CONCLUSIONS

The under- and overstuffing in PS-TKA alter the kinematics with variable effects. Understuffing decreases the stability, JCFs and inverse with overstuffing. Subtle changes in the PE insert thickness alter the post-cam mechanics.

Posterior Tibial Slope Increases Anterior Cruciate Ligament Stress in Bi-Cruciate Retaining Total Knee Arthroplasty: In Vivo Kinematic Analysis

The study design involved here is experimental in nature. The resection of the anterior cruciate ligament (ACL) during conventional total knee arthroplasty (TKA) has been considered a potential factor leading to abnormal in vivo knee kinematics. Bi-cruciate retaining (BCR) TKA designs allow the preservation of the ACL with the potential to restore native knee kinematics. This study aimed to investigate the effect of posterior tibial slope (PTS) on stress experienced by the ACL during weight bearing sit-to-stand (STS) and single-leg deep lunge. The ACL elongation patterns were measured in 30 unilateral BCR TKA patients during weight-bearing STS and single-leg deep lunge using a validated dual fluoroscopic tracking technique. The minimum normalized stress within the anteromedial (AM) and posterolateral (PL) bundle of the ACL during weight-bearing STS and single-leg deep lunge was found at a PTS of 3.7 degrees. The maximum AM and PL bundle stresses were observed at a PTS of 8.5 and 9.3 degrees, respectively during STS and at 8.4, and 9.1 degrees, respectively during single-leg deep lunge. There was a significant positive correlation between PTS and stress observed within the AM and PL bundle of the ACL during weight-bearing STS (R ² = 0.37; p < 0.01; R2  = 0.36; p = 0.01) and single-leg deep lunge (R ² = 0.42; p < 0.01; R ²= 0.40; p < 0.01). The study demonstrates that PTS of operated BCR TKA knees has a significant impact on the stress experienced by the preserved ACL during weight-bearing STS and single-leg deep lunge. This suggests that avoiding excessive PTS may be one of the surgical implant alignment factors to consider during surgery to minimize increased loading of the preserved ACL.

Assessment of knee collateral ligament stiffness by strain ultrasound elastography

BACKGROUND: Knowledge of the biomechanics of the normal collateral ligaments is important to secure optimal stability of the knee following injury. Various in vitro methods have been described in evaluating the biomechanics of these ligaments. However, a method of direct evaluation has not been reported. OBJECTIVE: To determine the stiffness characteristics of the collateral ligaments of the knee using strain ultrasound elastography. METHODS: Strain ultrasound elastography was performed on different components of the collateral ligaments in various angles of knee flexion in 18 healthy males (36 ligaments). We measured relative stiffness of the ligaments using strain ratio (SR = target tissue strain/reference strain). A lower strain ratio indicates higher relative stiffness. RESULTS: There was moderate to excellent intra- and inter-rater agreement for strain ratio measurements in all ligament portions. Strain ratios were lowest at 0° in all three ligaments, indicating high relative stiffness. In the superficial and deep medial collateral ligaments, the strain ratio increased with increasing knee flexion, whereas in the lateral collateral ligament, stiffness showed a tendency to fluctuate. CONCLUSION: Strain ultrasound elastography is a reliable tool for monitoring relative stiffness of the collateral ligaments of the knee and is easily applied to the routine clinical setting.

In vivo stiffness assessment of patellar and quadriceps tendons by strain ultrasound elastography

BACKGROUND:

The patellar and quadriceps tendons are responsible for the extension mechanism of the knee joint and frequently become inflamed during sports. Diagnosis and determination of when an athlete can return to sports following these injuries are usually performed by assessing morphological features and functional outcomes. Nevertheless, mechanical properties are not being assessed.

OBJECTIVE:

To describe the stiffness characteristics of these two tendons over the range of knee flexion and to test the feasibility of using strain ultrasound elastography (SE).

METHODS:

SE with an acoustic coupler as the reference was performed for nine healthy males. Relative stiffness measurements were obtained using the strain ratio (SR = target tissue strain/reference strain) by placing the knee in five different flexion angles. Lower SR indicates higher relative stiffness.

RESULTS:

This study showed reliable measurement with good intra- and inter-rater agreement for SR at 30°. SR of the quadriceps tendon decreases as knee flexion increases, indicating increased relative stiffness. In the patellar tendon, no significant difference was observed between 30° and 60°. Beyond 60°, relative stiffness increased constantly.

CONCLUSIONS:

SE is a reproducible and feasible tool to monitor relative stiffness of the patellar and quadriceps tendons in routine clinical settings.

In Vivo Elongation Patterns of the Collateral Ligaments in Healthy Knees During Functional Activities

BACKGROUND

Improved knowledge of in vivo function of the collateral ligaments is essential for enhancing rehabilitation and guiding surgical reconstruction as well as soft-tissue balancing in total knee arthroplasty. The aim of this study was to quantify in vivo elongation patterns of the collateral ligaments throughout complete cycles of functional activities.

METHODS

Knee kinematics were measured using radiographic images captured with a mobile fluoroscope while healthy subjects performed level walking, downhill walking, and stair descent. The registered in vivo tibiofemoral kinematics were then used to drive subject-specific multibody knee models to track collateral ligament elongation.

RESULTS

The elongation patterns of the medial collateral ligament varied distinctly among its bundles, ranging from lengthening of the anterior fibers to shortening of the posterior bundle with increases in the knee flexion angle. The elongation patterns of the lateral collateral ligament varied considerably among subjects. It showed an average 4% shortening with increasing flexion until 60% to 70% of the gait cycle, and then recovered during the terminal-swing phase until reaching its reference length (defined at heel strike).

CONCLUSIONS

The observed nonuniform elongation of the medial collateral ligament bundles suggests that single-bundle reconstruction techniques may not fully restore healthy ligament function. Moreover, the observed ligament elongation patterns indicate greater varus than valgus laxity in the loaded knee.

CLINICAL RELEVANCE

Through providing key knowledge about the in vivo elongation patterns of the collateral ligaments throughout complete cycles of functional activities, this study offers in vivo evidence for benchmarking ligament reconstruction and soft-tissue balancing in total knee arthroplasty.

WraptMor: Confirmation of an Approach to Estimate Ligament Fiber Length and Reactions With Knee-Specific Morphology

Knee ligament length can be used to infer ligament recruitment during functional activities and subject-specific morphology affects the interplay between ligament recruitment and joint motion. This study presents an approach that estimated ligament fiber insertion-to-insertion lengths with wrapping around subject-specific osseous morphology (WraptMor). This represents an advancement over previous work that utilized surrogate geometry to approximate ligament interaction with bone surfaces. Additionally, the reactions each ligament imparted onto bones were calculated by assigning a force-length relationship (kinetic WraptMor model), which assumed that the insertion-to-insertion lengths were independent of the assigned properties. Confirmation of the approach included comparing WraptMor predicted insertion-to-insertion length and reactions with an equivalent displacement-controlled explicit finite element model. Both models evaluated 10 ligament bundles at 16 different joint positions, which were repeated for five different ligament prestrain values for a total of 80 simulations per bundle. The WraptMor and kinetic WraptMor models yielded length and reaction predictions that were similar to the equivalent finite element model. With a few exceptions, predicted ligament lengths and reactions agreed to within 0.1 mm and 2.0 N, respectively, across all tested joint positions and prestrain values. The primary source of discrepancy between the models appeared to be caused by artifacts in the finite element model. The result is a relatively efficient approach to estimate ligament lengths and reactions that include wrapping around knee-specific bone surfaces.

High-speed fluoroscopic imaging for investigation of three-dimensional knee kinematics before and after marathon running

BACKGROUND

Knee injuries often occur during or shortly after marathon running, and are linked to altered knee kinematics.

RESEARCH QUESTION

The kinematics of healthy knees during pre- and post-marathon running have not been examined with high-speed fluoroscopy. This study aimed to evaluate the effects of marathon running on knee kinematics during walking and running by using a combined high-speed fluoroscopy and MRI technique.

METHODS

Ten healthy runners underwent knee MRI within 24 h before marathon running to construct three-dimensional (3D) knee models. Knee kinematics during treadmill walking and running were evaluated using high-speed fluoroscopy (200hz) within 24 h before and as soon as possible (within 5 h) after marathon running. All pre- and post-marathon measurements were compared.

RESULTS

(1) For post-marathon walking, posterior femoral translation increased 1.4 mm at initial contact (p = 0.015); proximal-distal distance of tibia and femur decreased 0.7 mm and 0.8 mm at initial contact and after contact, respectively (p = 0.039, p = 0.046); and valgus femur rotation increased 1.2° after contact (p = 0.027). (2) For post-marathon running, proximal-distal distance decreased 0.7 mm and 1.0 mm at initial contact and after contact (p = 0.011, p = 0.003) respectively; knee flexion decreased 4.3° before contact (p = 0.007); knee flexion increased 1.8° and 2.6° at initial contact and after contact, respectively (p = 0.038, p = 0.011); external femoral rotation increased 1.2° and 1.8° at initial contact and after contact, respectively (p = 0.012, p = 0.037). Valgus femoral rotation after contact increased 2.3° (p = 0.001).

SIGNIFICANCE

Post-marathon changes in valgus and external femoral rotation, knee flexion, posterior femoral translation, and proximal-distal distance may increase the risk of knee injury. This study provides information to better understand the response of the knee to marathon running.

Measuring stiffness of normal medial collateral ligament in healthy volunteers via shear wave elastography

PURPOSE

We aim to determine a reference data set for normal medial collateral ligament (MCL) stiffness values using shear wave elastography (SWE).

METHODS

Quantitative stiffness of the MCL was measured at three levels: the proximal (MCL area from the level of the medial meniscus to the level of the femoral attachment), the middle (MCL area at the level of the medial meniscus), and the distal (MCL area from the level of the medial meniscus to the level of the tibial attachment) segments of the MCL at a knee position of 0°.

RESULTS

A total of 60 MCL of 30 healthy volunteers (15 female, 15 male) were examined. The mean stiffness values of the proximal, middle, and distal MCL for observer 1 were 32.25 ± 6.44, 34.25 ± 6.84, and 35.47 ± 6.98, respectively. The mean stiffness values of the proximal, middle, and distal MCL for observer 2 were 33.56 ± 6.76, 35.44 ± 6.91, and 36.32 ± 7.04, respectively.

CONCLUSION

SWE has a strong potential to be a method of choice for evaluating MCL stiffness. Our study participants were healthy volunteers and the data can be used as reference data for future studies.

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 Effect of Knee Flexion on Length Changes and Stress Distribution of Ligaments: A Displacement Controlled Finite Element Analysis

The use of dynamic finite element analysis to investigate the biomechanical behavior of the knee joint is mainly based on movement of the joint. Challenges are associated with simulation of knee joint flexion-extension activity. This study investigated changes in the length and stress state of ligaments during lunge with a displacement controlled finite element analysis of the knee joint based on in vivo fluoroscopic kinematic data. The geometric center axis (GCA) was used to represent knee kinematics to quantify femoral motion relative to the tibia. Because the GCA was considered as a functional flexion axis, 2 degrees of freedom could be reduced. Published data on the in vivo fluoroscopic kinematic features of the GCA were used to establish the equations for degrees of freedom. Data for 4 degrees of freedom were obtained simultaneously at every 5° of knee flexion. Displacement and rotation were applied to the femur and tibia to produce relative displacement, and the elongation and stress state of the knee ligaments were computed. The predictions confirmed that lunge affected the biomechanical behavior of ligaments. Displacement controlled finite element analysis of knee flexion can be simulated on the basis of fluoroscopic kinematic data to achieve physiologic movement. [Orthopedics. 2021;44(1):e61-e67.].

Small soft tissue tension changes do not affect patient-reported outcomes one year after primary TKA

BACKGROUND

Adequate soft tissue tension and balance is paramount to achieve favourable outcomes of total knee arthroplasty (TKA). Implant manufacturers offer 1-mm liner increments to fine-tune ligament tension and balance. In this study, we assessed if soft tissue tension changes introduced by minimal changes in liner thicknesses affect early patient reported outcomes.

METHODS

Eighty-nine patients undergoing 99 primary, elective TKAs by a single surgeon were included. After achieving adequate ligament balance, the first 50 knees received an insert that would allow 2-3 mm of medial and lateral opening (control group), whereas the last 49 received an insert which was 1 mm thicker, resulting in a slight increase in ligament tension (study group). Sensor technology was used to record compartmental loads. Knee Society Score (KSS), KOOS Jr., and ROM were recorded pre-operatively, six weeks, four and 12 months post-operatively. The Forgotten Joint Score (FJS) was administered four and 12 months post-operatively.

RESULTS

No differences were observed in demographic variables, pre-operative outcome scores, and ROM measures between groups. Six weeks post-operatively, there was no statistically significant difference in the outcome variables. Four months post-operatively, statistically significant differences were only observed in KOOS Jr. (79 and 73.6; p = 0.05), and FJS (59.9 and 45.5; p < 0.01); all of which favoured the control group. There was no difference in the outcome variables at 12 months.

CONCLUSION

Minor changes in soft tissue tension induced by 1-mm changes in liner thickness resulted in clinically meaningful differences favouring the control group four months post-operatively, but in no clinically noticeable differences 12 months post-operatively. It is possible that lower soft tissue tension may lead to transient improvement in patient-reported early outcomes.

Techniques for In Vivo Measurement of Ligament and Tendon Strain: A Review

The critical clinical and scientific insights achieved through knowledge of in vivo musculoskeletal soft tissue strains has motivated the development of relevant measurement techniques. This review provides a comprehensive summary of the key findings, limitations, and clinical impacts of these techniques to quantify musculoskeletal soft tissue strains during dynamic movements. Current technologies generally leverage three techniques to quantify in vivo strain patterns, including implantable strain sensors, virtual fibre elongation, and ultrasound. (1) Implantable strain sensors enable direct measurements of tissue strains with high accuracy and minimal artefact, but are highly invasive and current designs are not clinically viable. (2) The virtual fibre elongation method tracks the relative displacement of tissue attachments to measure strains in both deep and superficial tissues. However, the associated imaging techniques often require exposure to radiation, limit the activities that can be performed, and only quantify bone-to-bone tissue strains. (3) Ultrasound methods enable safe and non-invasive imaging of soft tissue deformation. However, ultrasound can only image superficial tissues, and measurements are confounded by out-of-plane tissue motion. Finally, all in vivo strain measurement methods are limited in their ability to establish the slack length of musculoskeletal soft tissue structures. Despite the many challenges and limitations of these measurement techniques, knowledge of in vivo soft tissue strain has led to improved clinical treatments for many musculoskeletal pathologies including anterior cruciate ligament reconstruction, Achilles tendon repair, and total knee replacement. This review provides a comprehensive understanding of these measurement techniques and identifies the key features of in vivo strain measurement that can facilitate innovative personalized sports medicine treatment.

Principles of a 3D printed mechanical device for total knee balancing

Implant alignment and soft-tissue balancing are important factors in total knee arthroplasty (TKA). The purpose of this study was to design a mechanical balancing device, which measures deflections resulting from forces applied on each condyle to provide numerical data indicating the extent of ligament release needed, or angular changes in the bone cuts required to achieve a balanced knee. Two mechanical devices were designed and 3D printed, Pistol Grip and In-line. The Pistol Grip design consisted of a lever system that indicated the difference between lateral and medial forces with a single pointer. The In-line design allows for the quantification of the absolute force applied on each individual condyle. The two designs were evaluated on a test rig designed to model balance and imbalance conditions in the knee. For the Pistol Grip design maximum pointer deflection indicates a 2 mm change in elevation per condyle and/or a 3 degrees angular change of the condyles which can be corrected by adjusting the ligament lengths equivalent to 2 mm and/or by modifying the proximal or distal femur bone cut by 3 degrees. For the In-line design, maximum pointer deflection represented a 40 N load on the condyle. Our mechanical balancer designs were successful in providing information that can guide surgeons to accurately achieve balance through ligamentous releases and/or modification to bone cuts. The balancer designs are easy to use, do not require any electronics or software, and can be incorporated into the surgical procedure.

In vivo length change of ligaments of normal knees during dynamic high flexion

Background

Few studies compared the length change of ligaments of normal knees during dynamic activities of daily living. The aim of this study was to investigate in vivo length change of ligaments of the normal knees during high flexion.

Methods

Eight normal knees were investigated. Each volunteer performed squatting, kneeling, and cross-leg motions. Each sequential motion was performed under fluoroscopic surveillance in the sagittal plane. The femoral, tibial, and fibular attachment areas of the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), deep medial collateral ligament (dMCL), superficial medial collateral ligament (sMCL), and lateral collateral ligament (LCL) were determined according to osseous landmarks. After 2D/3D registration, the direct distance from the femoral attachment to the tibial or fibular attachment was measured as the ligament length.

Results

From 20° to 90° with flexion, the ACL was significantly shorter during cross-leg motion than during squatting. For the PCL, dMCL, sMCL, and LCL, there were no significant differences among the 3 motions.

Conclusion

The ACL was shorter during cross-leg motion than during squatting in mid-flexion. This suggests that the ACL is looser during cross-leg motion than during squatting. On the other hand, the length change of the PCL, MCL, and LCL did not change even though the high flexion motions were different.

Elongation Patterns of the Posterior Cruciate Ligament after Total Knee Arthroplasty

This study aimed to understand the ability of fixed-bearing posterior cruciate ligament (PCL)-retaining implants to maintain functionality of the PCL in vivo. To achieve this, elongation of the PCL was examined in six subjects with good clinical and functional outcomes using 3D kinematics reconstructed from video-fluoroscopy, together with multibody modelling of the knee. Here, length-change patterns of the ligament bundles were tracked throughout complete cycles of level walking and stair descent. Throughout both activities, elongation of the anterolateral bundle exhibited a flexion-dependent pattern with more stretching during swing than stance phase (e.g., at 40° flexion, anterolateral bundle experienced 3.9% strain during stance and 9.1% during swing phase of stair descent). The posteromedial bundle remained shorter than its reference length (defined at heel strike of the level gait cycle) during both activities. Compared with loading patterns of the healthy ligament, postoperative elongation patterns indicate a slackening of the ligament at early flexion followed by peak ligament lengths at considerably smaller flexion angles. The reported data provide a novel insight into in vivo PCL function during activities of daily living that has not been captured previously. The findings support previous investigations reporting difficulties in achieving a balanced tension in the retained PCL.

Arthroscopic pie-crusting release of the posteromedial complex of the knee for surgical treatment of medial meniscus injury

Background

An arthroscopic narrow posteromedial gap of the knee may cause failure of a meniscus operation. The posteromedial complex (PMC) of the knee, including the posterior part of the medial collateral ligament (MCL) and the posterior oblique ligament (POL), has a restrictive effect on the opening of the posteromedial gap of the knee in the half-extension position. Thus, we evaluated the radiological and clinical results of pie-crusting release of the PMC for arthroscopic meniscal surgery in tight knees.

Methods

Sixty patients with posterior injury of the medial meniscus were reviewed. All patients accepted arthroscopic pie-crusting release of the PMC. Fourty patients accepted meniscoplasty, and 20 patients accepted meniscal suturing. To evaluate the arthroscopic opening of the medial gap in 20° half-extension under 11-kg valgus stress, the width of the medial space before and after release were measured. During follow-up, the medial stability was evaluated by radiographic measurements of the joint space width (JSW) in 20° half-extension. Magnetic resonance imaging (MRI) was conducted to evaluate healing of the MCL and meniscus. Knee functions were evaluated using VAS (visual analogy score), Lysholm, IKDC (International Knee Documentation Committee) and Tegner scoring systems.

Results

In all patients, meniscus operations were performed without iatrogenic cartilage injury. After PMC release, the arthroscopic width of the medial space was 5.7 ± 0.5 mm, larger than that before release (2.5 ± 0.5 mm, p < 0.01). The follow-up time was 21.93 ± 7.04 months, there was no residual valgus laxity of the knee. The radiographic JSW was 5.97 ± 0.8 mm preoperatively, 9.2 ± 1.1 mm in the 1st week postoperatively, and 6.1 ± 0.9 mm by the 3rd postoperative month, showing no differences between preoperative and 3 months postoperative measurement (p > 0.05). For sutured meniscus, MRI showed healing in 15 patients while five had two-grade abnormal signals. VAS, Lysholm, IKDC and Tegner scores were 1.80 ± 0.51, 80.08 ± 3.74, 82.17 ± 4.64 and 5.48 ± 0.59, respectively, showing significant differences compared with the preoperative scores (5.57 ± 0.69, 48.17 ± 4.22, 51.42 ± 4.02 and 3.20 ± 0.68, respectively, p< 0.01).

Conclusions

Pie-crusting release of the PMC can increase the posteromedial space and improve the visual field of the knee under arthroscopy, while neither causing no residual valgus instability of the knee nor affecting the clinical outcome at the final follow-up.

Length-change patterns of the medial collateral ligament and posterior oblique ligament in relation to their function and surgery

PURPOSE

To define the length-change patterns of the superficial medial collateral ligament (sMCL), deep MCL (dMCL), and posterior oblique ligament (POL) across knee flexion and with applied anterior and rotational loads, and to relate these findings to their functions in knee stability and to surgical repair or reconstruction.

METHODS

Ten cadaveric knees were mounted in a kinematics rig with loaded quadriceps, ITB, and hamstrings. Length changes of the anterior and posterior fibres of the sMCL, dMCL, and POL were recorded from 0° to 100° flexion by use of a linear displacement transducer and normalised to lengths at 0° flexion. Measurements were repeated with no external load, 90 N anterior draw force, and 5 Nm internal and 5 Nm external rotation torque applied.

RESULTS

The anterior sMCL lengthened with flexion (p < 0.01) and further lengthened by external rotation (p < 0.001). The posterior sMCL slackened with flexion (p < 0.001), but was lengthened by internal rotation (p < 0.05). External rotation lengthened the anterior dMCL fibres by 10% throughout flexion (p < 0.001). sMCL release allowed the dMCL to become taut with valgus rotation (p < 0.001). The anterior and posterior POL fibres slackened with flexion (p < 0.001), but were elongated by internal rotation (p < 0.001).

CONCLUSION

The structures of the medial ligament complex react differently to knee flexion and applied loads. Structures attaching posterior to the medial epicondyle are taut in extension, whereas the anterior sMCL, attaching anterior to the epicondyle, is tensioned during flexion. The anterior dMCL is elongated by external rotation. These data offer the basis for MCL repair and reconstruction techniques regarding graft positioning and tensioning.

Anatomical feature of knee joint in Aachen minipig as a novel miniature pig line for experimental research in orthopaedics

BACKGROUND

The pig is a commonly used large animal model, since pigs share anatomical and physiological similarities with humans. In contrast to other experimental pig lines the Aachen minipig, as a robust novel minipig does not require housing with any barrier. To estimate transferability of results to human conditions, pig lines should be thoroughly characterized.

PURPOSE

Therefore, we analyzed the anatomical pecularities of the knee joint of the novel "Aachen minipig" line raised for experimental conditions.

METHODS

Eight knee joints of four adult Aachen minipigs were dissected measuring the dimensions of typical landmarks using a digital caliper. Hybrid pig and human knee joints served as controls. Cartilage of the Aachen minipig (trochlear groove, femoral condyles, menisci) were assessed histologically.

RESULTS

The Aachen minipig shared its knee joint anatomy with the hybrid pig. In comparison to humans, peculiarities of the pig were demonstrated in the Aachen minipig: the lateral meniscus and the lateral tibial joint surface were significantly longer than the medial counterparts. The fibular head was covered by fibrocartilage and completely integrated into the lateral lower joint surface. The cartilage at the joint areas usually used for cartilage repair studies was in average 0.66±0.04mm thick. The porcine anterior cruciate ligament (ACL) attached with two bundles at the anterior tibial plateau separated from each other by the lateral anterior meniscotibial ligament. Aachen minipig articular and meniscal cartilage presented the typical histoarchitecture.

CONCLUSIONS

The Aachen minipig reflects porcine anatomical peculiarities, which should be considered, especially for meniscus and ACL reconstruction.

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.

Effects of femoral component placement on the balancing of a total knee at surgery

Misalignment and soft-tissue imbalance in total knee arthroplasty (TKA) can cause discomfort, pain, inadequate motion and instability that may require revision surgery. Balancing can be defined as equal collateral ligament tensions or equal medial and lateral compartmental forces during the flexion range. Our goal was to study the effects on balancing of linear femoral component misplacements (proximal, distal, anterior, posterior); and different component rotations in mechanical alignment compared to kinematic alignment throughout the flexion path. A test rig was constructed such that the position of a standard femoral component could be adjusted to simulate the linear and rotational positions. With the knee in neutral reference values of the collateral tensions were adjusted to give anatomic contact force patterns, measured with an instrumented tibial trial. The deviations in the forces for each femoral component position were then determined. Compartmental forces were significantly influenced by 2 mm linear errors in the femoral component placement. However, the errors were least for a distal error, equivalent to undercutting the distal femur. The largest errors mainly increase the lateral condyle force, occurred for proximal and posterior component errors. There were only small contact force differences between kinematic and mechanical alignment. Based on these results, surgeons should avoid overcutting the distal femur and undercutting the posterior femur. However, the 2-3 degrees varus slope of the joint line as in kinematic alignment did not have much effect on balancing, so mechanical or kinematic alignment were equivalent.

In-vivo elongation of anterior and posterior cruciate ligament in bi-cruciate retaining total knee arthroplasty

Anterior and posterior cruciate ligament (ACL and PCL) sacrifice in contemporary total knee arthroplasty (TKA) has been considered a potential factor leading to abnormal knee kinematics. Bi-cruciate retaining (BCR) TKA design allows retention of both ACL and PCL. However, there is a limited data on the ACL/PCL in-vivo elongation characteristics of BCR TKA. The study aimed to evaluate and compare the in-vivo elongation patterns of ACL/PCL between BCR TKA and contralateral non-implanted knee and to explore potential factors leading to the changed elongation patterns between limbs. ACL/PCL elongations of both knees during sit-to-stand were measured in 29 unilateral BCR TKA patients using a validated dual fluoroscopic tracking technique. Joint gap changes of the BCR TKA knees relative to the contralateral knee were quantified. BCR TKA and the contralateral non-implanted knee exhibited similar ACL elongation at extension and clinical anterior knee laxity. However, BCR TKA showed significantly greater PCL elongation during flexion than the non-implanted knee. Variation of changed elongation was observed for both ACL and PCL, suggesting a heterogeneous restoration of normal ACL/PCL functions. A significant correlation was found between extension joint gap change and the change of ACL elongation, highlighting the importance of precise joint line restoration and soft tissue balancing during BCR TKA surgery. Our findings suggest that BCR TKA did not fully restore "near-normal" cruciate ligament elongation patterns and anteroposterior stability. Considerable heterogeneity remains in the retained ligament elongation patterns and warrants further investigations of multifactorial factors to optimize ACL/PCL functions in BCR TKA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3239-3246, 2018.

Kinematically aligned total knee arthroplasty limits high tibial forces, differences in tibial forces between compartments, and abnormal tibial contact kinematics during passive flexion

PURPOSE

Following total knee arthroplasty (TKA), high tibial forces, large differences in tibial forces between the medial and lateral compartments, and anterior translation of the contact locations of the femoral component on the tibial component during passive flexion indicate abnormal knee function. Because the goal of kinematically aligned TKA is to restore native knee function without soft tissue release, the objectives were to determine how well kinematically aligned TKA limits high tibial forces, differences in tibial forces between compartments, and anterior translation of the contact locations of the femoral component on the tibial component during passive flexion.

METHODS

Using cruciate retaining components, kinematically aligned TKA was performed on thirteen human cadaveric knee specimens with use of manual instruments without soft tissue release. The tibial forces and tibial contact locations were measured in both the medial and lateral compartments from 0° to 120° of passive flexion using a custom tibial force sensor.

RESULTS

The average total tibial force (i.e. sum of medial + lateral) ranged from 5 to 116 N. The only significant average differences in tibial force between compartments occurred at 0° of flexion (29 N, p = 0.0008). The contact locations in both compartments translated posteriorly in all thirteen kinematically aligned TKAs by an average of 14 mm (p < 0.0001) and 18 mm (p < 0.0001) in the medial and lateral compartments, respectively, from 0° to 120° of flexion.

CONCLUSIONS

After kinematically aligned TKA, average total tibial forces due to the soft tissue restraints were limited to 116 N, average differences in tibial forces between compartments were limited to 29 N, and a net posterior translation of the tibial contact locations was observed in all kinematically aligned TKAs during passive flexion from 0° to 120°, which are similar to what has been measured previously in native knees. While confirmation in vivo is warranted, these findings give surgeons who perform kinematically aligned TKA confidence that the alignment method and surgical technique limit high tibial forces, differences in tibial forces between compartments, and anterior translation of the tibial contact locations during passive flexion.

Step-wise medial collateral ligament needle puncturing in extension leads to a safe and predictable reduction in medial compartment pressure during TKA

PURPOSE

Medial soft tissue release in a varus deformity knee during total knee arthroplasty is essential for accurate balancing of the reconstruction. This study attempts to quantify the effect of sequential needle puncturing of the medial collateral ligament (MCL) using a pressure sensor insert (Verasense by OrthoSensor) and gap measurement under tension.

METHODS

Cruciate-retaining arthroplasties were placed in 14 cadaveric knees. The MCL was elongated by step-wise perforation, in five sets of five perforations, with the use of an 18-gauge needle, followed by valgus stress. Following the fifth set of needle perforations, blade perforation was performed on the remaining tense fibers of the MCL. Following each step-wise perforation, corresponding medial compartment pressures and gap measurements under tension were recorded.

RESULTS

Sensor measurements correlated closely with step-wise tissue release (R = 0.73, p < 0.0001), and a significant decrease in pressure was found in early needle puncturing (mean 49 N after 5, 83 N after 15, p values < 0.05), although changes diminished at later stages of needle perforation (90 N after 20). Gap measurement demonstrated small gradual changes with early puncturing, but showed significant opening in the later stages of release. There was minimal variation in pressure or gap measurements in flexion versus extension. This finding suggests that MCL needle puncture will not lead to unequal gaps between flexion and extension. There were no cases of MCL over-release after 15 punctures, one case after 20 punctures, and three after blade perforation.

CONCLUSION

Needle puncturing of the MCL in extension for up to 15 punctures can be a safe and predictable way to achieve medial opening when balancing a varus knee during TKA as demonstrated in this cadaveric model. Blade perforation should be used with caution to avoid over-release. The needle puncture method can be used by surgeons to achieve reliable reductions in medial compartment pressures, to help achieve a balanced TKA, with minimal risk of over-release.

The evaluation of the role of medial collateral ligament maintaining knee stability by a finite element analysis

Background

A three-dimensional finite element model (FEM) of the knee joint was established to analyze the biomechanical functions of the superficial and deep medial collateral ligaments (MCLs) of knee joints and to investigate the treatment of the knee medial collateral ligament injury.

Methods

The right knee joint of a healthy male volunteer was subjected to CT and MRI scans in the extended position. The scanned data were imported into MIMICS, Geomagic, and ANSYS software to establish a three-dimensional FEM of the human knee joint. The anterior-posterior translation, valgus-varus rotation, and internal-external rotation of knee joints were simulated to observe tibial displacement or valgus angle. In addition, the magnitude and distribution of valgus stress in the superficial and deep layers of the intact MCL as well as the superficial, deep, and overall deficiencies of the MCL were investigated.

Results

In the extended position, the superficial medial collateral ligament (SMCL) would withstand maximum stresses of 48.63, 16.08, 17.23, and 16.08 MPa in resisting the valgus of knee joints, tibial forward displacement, internal rotation, and external rotation, respectively. Meanwhile, the maximum stress tolerated by the SMCL in various ranges of motion mainly focused on the femoral end point, which was located at the anterior and posterior parts of the femur in resisting valgus motion and external rotation, respectively. However, the deep medial collateral ligament could tolerate only minimum stress, which was mainly focused at the femoral start and end points.

Conclusions

This model can effectively analyze the biomechanical functions of the superficial and deep layers of the MCLs of knee joints. The results show that the knee MCL II° injury is the indication of surgical repair.

Loading of the medial meniscus in the ACL deficient knee: A multibody computational study

The menisci of the knee reduce tibiofemoral contact pressures and aid in knee lubrication and nourishment. Meniscal injury occurs in half of knees sustaining anterior cruciate ligament injury and the vast majority of tears in the medial meniscus transpire in the posterior horn region. In this study, computational multibody models of the knee were derived from medical images and passive leg motion for two female subjects. The models were validated against experimental measures available in the literature and then used to evaluate medial meniscus contact force and internal hoop tension. The models predicted that the loss of anterior cruciate ligament (ACL) constraint increased contact and hoop forces in the medial menisci by a factor of 4 when a 100N anterior tibial force was applied. Contact forces were concentrated in the posterior horn and hoop forces were also greater in this region. No differences were found in contact or hoop tension between the intact and ACL deficient (ACLd) knees when only a 5Nm external tibial torque was applied about the long axis of the tibia. Combining a 100N anterior tibial force and a 5Nm external tibial torque increased posterior horn contact and hoop forces, even in the intact knee. The results of this study show that the posterior horn region of the medial meniscus experiences higher contact forces and hoop tension, making this region more susceptible to injury, especially with the loss of anterior tibia motion constraint provided by the ACL. The contribution of the dMCL in constraining posterior medial meniscus motion, at the cost of higher posterior horn hoop tension, is also demonstrated.

THE EFFECT OF COLLATERAL LIGAMENT INJURY ON CARTILAGE CONTACT IN KNEE JOINTS MODELED WITH SIX DEGREES OF FREEDOM

The purpose of this study was to create a kinematic model of the knee joint with six degrees of freedom (DOF) and evaluate the effect of medial collateral ligament (MCL) and lateral collateral ligament (LCL) rupture on cartilage contact point distribution on the tibia during flexion. We hypothesized that collateral ligament contributions vary over six DOF of knee joint articulation and affect the cartilage contact point distribution during joint articulation. The ligament contributions and distribution of joint cartilage contact points cannot be fully assessed with simplified joint models or invasive experiments. Therefore, we developed a new model in which the tibia and femur centers of mass were determined from their surface geometry, and the displacement of the moving tibia was determined from the displacements of the attached ligaments. Compared to the intact knee, the tibia with the LCL removed had higher medial translation and lower valgus rotation. The tibia with the MCL removed had higher lateral translation and higher valgus rotation than the intact knee. At 0[Formula: see text], 30[Formula: see text], and 60[Formula: see text], the tibia with the LCL removed had more internal rotation than the intact knee. Understanding six DOF knee joint kinematics with integration of ligament contributions and cartilage contact positions is useful for the diagnosis of ligament injuries and the design of articulating surfaces for total arthroplasty.

Elongation of the collateral ligaments after cruciate retaining total knee arthroplasty and the maximum flexion of the knee

The mechanisms that affect knee flexion after total knee arthroplasty (TKA) are still debatable. This study investigated the elongation of the superficial medial (sMCL) and lateral collateral ligaments (LCL) before and after a posterior cruciate retaining (CR) TKA. We hypothesized that overstretching of the collateral ligaments in high flexion after TKA could reduce maximal flexion of the knee. Three-dimensional models of 11 osteoarthritic knees of 11 patients including the insertions of the collateral ligaments were created using MR images. Each ligament was divided into three equal portions: anterior, middle and posterior portions. The shortest 3D wrapping length of each ligament portion was determined before and after the TKA surgery along a weight-bearing, single leg flexion path. The relationship between the changes of ligament elongation and the changes of the maximal knee flexion after TKAs was quantitatively analyzed. The sMCL showed significant increases in length only at low flexion after TKA; the LCL showed decreases in length at full extension, but increases with further flexion after TKA. The amount of increases of the maximum flexion angle after TKA was negatively correlated with the increases of the elongations of the anterior portion (p=0.010, r=0.733) and middle portion (p=0.049, r=0.604) of the sMCL as well as the anterior portion (p=0.010, r=0.733) of the LCL at maximal flexion of the knee. The results indicated that the increases of the length of the collateral ligaments at maximal flexion after TKA were associated with the decreases of the maximal flexion of the knee. Our data suggest that collateral ligament management should also be evaluated at higher knee flexion angles in order to optimize maximal flexion of the knee after TKAs.