Sensitivity of Model-Based Predictions of Post-TKA Kinematic Behavior to Residual Errors in Ultrasound-Based Knee Collateral Ligament Strain Assessment.

Ultrasound-based ligament strain estimation shows promise in non-invasively assessing knee joint collateral ligament behavior and improving ligament balancing procedures. However, the impact of ultrasound-based strain estimation residual errors on in-silico arthroplasty predictions remains unexplored. We investigated the sensitivity of post-arthroplasty kinematic predictions to ultrasound-based strain estimation errors compared to clinical inaccuracies in implant positioning.Two cadaveric legs were submitted to active squatting, and specimen-specific rigid computer models were formulated. Mechanical properties of the ligament model were optimized to reproduce experimentally obtained tibiofemoral kinematics and loads with minimal error. Resulting remaining errors were comparable to the current state-of-the-art. Ultrasound-derived strain residual errors were then introduced by perturbing lateral collateral ligament (LCL) and medial collateral ligament (MCL) stiffness. Afterwards, the implant position was perturbed to match with the current clinical inaccuracies reported in the literature. Finally, the impact on simulated post-arthroplasty tibiofemoral kinematics was compared for both perturbation scenarios. Ultrasound-based errors minimally affected kinematic outcomes (mean differences < 0.73° in rotations, 0.1 mm in translations). Greatest differences occurred in external tibial rotations (-0.61° to 0.73° for MCL, -0.28° to 0.27° for LCL). Comparatively, changes in implant position had larger effects, with mean differences up to 1.95° in external tibial rotation and 0.7 mm in mediolateral translation. In conclusion, our study demonstrated that the ultrasound-based assessment of collateral ligament strains has the potential to enhance current computer-based pre-operative knee arthroplasty planning.

Calibration of Holzapfel-Gasser-Ogden collateral ligament properties in a hybrid post-arthroplasty knee joint model for laxity testing.

Knee collateral ligaments play a vital role in providing frontal-plane stability in post-total knee arthroplasty (TKA) knees. Finite element models can utilize computationally efficient one-dimensional springs or more physiologically accurate three-dimensional continuum elements like the Holzapfel-Gasser-Ogden (HGO) formulation. However, there is limited literature defining subject-specific mechanical properties, particularly for the HGO model. In this study, we propose a co-simulation framework to obtain subject-specific material parameters for an HGO-based finite element ligament model integrated into a rigid-body model of the post-TKA knee. Our approach achieves comparable accuracy to spring formulations while significantly reducing coefficient calibration time and demonstrating improved correlation with reference knee kinematics and ligament strains throughout the tested loading range.

Characterizing the viscoelastic properties of the anterolateral ligament and grafts commonly used in its reconstruction.

BACKGROUND: Current anatomic anterolateral ligament reconstruction is typically performed using either a gracilis tendon or an iliotibial band graft based on their quasi-static behavior. However, there is limited knowledge about their viscoelastic behaviors. This study aimed to characterize the viscoelastic properties of the anterolateral ligament, distal iliotibial band, distal gracilis tendon and proximal gracilis tendon for graft material choice in anterolateral ligament reconstruction. METHODS: All the tissues were harvested from thirteen fresh-frozen cadaveric knees and subjected to preconditioning (3-6 MPa), sinusoidal cycle (1.2-12 MPa), dwell at constant load (12 MPa), and load to failure (3%/s). The quasi-static and viscoelastic properties of the soft tissues were computed and compared using a linear mixed model (p < 0.05). FINDINGS: The hysteresis of anterolateral ligament (mean:0.4 Nm) was comparable with gracilis halves (p > 0.85) but iliotibial band (6 Nm) was significantly higher (p < 0.001,ES = 6.5). In contrast, the dynamic creep of anterolateral ligament (0.5 mm) was similar to iliotibial band (0.7 mm, p > 0.82) whereas both gracilis halves were significantly lower (p < 0.007,ES > 1.4). The elastic modulus of anterolateral ligament (181.4 MPa, p < 0.001,ES > 2.1) was the lowest compared to the grafts materials (distal gracilis tendon:835 MPa, distal gracilis tendon:726 MPa, iliotibial band:910 MPa). Additionally, the failure load of the anterolateral ligament (124.5 N, p < 0.001,ES > 2.9) was also the lowest. INTERPRETATION: The mechanical properties of the gracilis halves and iliotibial band were significantly different from anterolateral ligament, except for hysteresis and dynamic creep, respectively. Our findings showed that the gracilis halves may be a more appropriate graft choice for anterolateral ligament reconstruction due to its low energy dissipation and permanent deformation under dynamic loads.

External rotation of the foot position during plantarflexion increases non-uniform motions of the Achilles tendon.

The medial (GM) and lateral gastrocnemius (GL) muscles enroll to different subparts of the Achilles tendon to form their respective subtendons. The relative gastrocnemii activations during submaximal plantarflexion contraction depend on the position of the foot in the horizontal plane: with toes-in, GL activation increases and GM activation decreases, compared to toes-out. The aim of the current study was to investigate whether horizontal foot position during submaximal isometric plantarflexion contraction differently affects the subtendons within the Achilles tendon in terms of their (i) length at rest, and (ii) elongations and distal motions. Twenty healthy subjects (12 females/8 males) participated in the study. Three-dimensional ultrasound images were taken to capture subtendon lengths at rest and during isometric contraction. Ultrasound images were recorded at the distal end of Achilles tendon (sagittal plane) during ramped contractions and analyzed using a speckle tracking algorithm. All tasks were conducted twice, ones with toes-in and ones with toes-out. At rest, subtendons were shorter with toes-out compared to toes-in. During contraction, the GM subtendon lengthened more in toes-out, compared to the GL, and vice versa (all p <.01). The relative motions within the Achilles tendon (middle minus top layers displacements) were smaller in toes-in compared to toes-out (p =.05) for higher contraction intensity. Our results demonstrated that the horizontal foot position during plantarflexion contraction impacts Achilles tendon motions. Such findings may be relevant in a clinical context, for example in pathologies affecting Achilles tendon motions such as Achilles tendinopathy.

Assessment of in vivo bone activity patterns in medial mobile-bearing unicompartmental knee arthroplasty : a prospective SPECT/CT study.

AIMS: Higher osteoblastic bone activity is expected in aseptic loosening and painful unicompartmental knee arthroplasty (UKA). However, insights into normal bone activity patterns after medial UKAs are lacking. The aim of this study was to identify the evolution in bone activity pattern in well-functioning medial mobile-bearing UKAs. METHODS: In total, 34 patients (13 female, 21 male; mean age 62 years (41 to 79); BMI 29.7 kg/m2 (23.6 to 42.1)) with 38 medial Oxford partial UKAs (20 left, 18 right; 19 cementless, 14 cemented, and five hybrid) were prospectively followed with sequential 99mTc-hydroxymethane diphosphonate single photon emission CT (SPECT)/CT preoperatively, and at one and two years postoperatively. Changes in mean osteoblastic activity were investigated using a tracer localization scheme with volumes of interest (VOIs), reported by normalized mean tracer values. A SPECT/CT registration platform additionally explored cortical tracer evolution in zones of interest identified by previous experimental research. RESULTS: Significant reduction of tracer activity from the preoperative situation was found in femoral and anteromedial tibial VOIs adjacent to the UKA components. Temporarily increased osteoblastic bone activity was observed in VOIs comprising the UKA keel structure at one year postoperatively compared to the preoperative activity. Persistent higher tracer uptake was found in the posterior tibial cortex at final follow-up. Multivariate analysis showed no statistical difference in osteoblastic bone activity underneath cemented or cementless components. CONCLUSION: Well-functioning medial mobile-bearing UKAs showed distinct changes in patterns of normalized bone tracer activity in the different VOIs adjacent to the prosthetic components, regardless of their type of fixation. Compared to the preoperative situation, persistent high bone activity was found underneath the keel and the posterior tibial cortex at final follow-up, with significant reduced activity only being identified in femoral and anteromedial tibial VOIs. Cite this article: Bone Joint J 2022;104-B(1):34-44.

Validated Ultrasound Speckle Tracking Method for Measuring Strains of Knee Collateral Ligaments In-Situ during Varus/Valgus Loading.

Current ultrasound techniques face several challenges to measure strains when translated from large tendon to in-situ knee collateral ligament applications, despite the potential to reduce knee arthroplasty failures attributed to ligament imbalance. Therefore, we developed, optimized and validated an ultrasound speckle tracking method to assess the in-situ strains of the medial and lateral collateral ligaments. Nine cadaveric legs with total knee implants were submitted to varus/valgus loading and divided into two groups: "optimization" and "validation". Reference strains were measured using digital image correlation technique, while ultrasound data were processed with a custom-built speckle tracking approach. Using specimens from the "optimization" group, several tracking parameters were tuned towards an optimized tracking performance. The parameters were ranked according to three comparative measures between the ultrasound-based and reference strains: R2, mean absolute error and strains differences at 40 N. Specimens from the "validation" group, processed with the optimal parameters, showed good correlations, along with small mean absolute differences, with correlation values above 0.99 and 0.89 and differences below 0.57% and 0.27% for the lateral and medial collateral ligaments, respectively. This study showed that ultrasound speckle tracking could assess knee collateral ligaments strains in situ and has the potential to be translated to clinics for knee arthroplasty-related procedures.

SCreg: a registration-based platform to compare unicondylar knee arthroplasty SPECT/CT scans.

BACKGROUND: A combination of conventional computed tomography and single photon emitted computed tomography (SPECT/CT) provides simultaneous data on the intensity and location of osteoblastic activity. Currently, since SPECT/CT scans are not spatially aligned, scans following knee arthroplasty are compared by extracting average and maximal values of osteoblastic activity intensity from large subregions of the structure of interest, which leads to a loss of resolution, and hence, information. Therefore, this paper describes the SPECT/CT registration platform (SCreg) based on the principle of image registration to spatially align SPECT/CT scans following unicondylar knee arthroplasty (UKA) and allow full resolution intra-subject and inter-subject comparisons. METHODS: SPECT-CT scans of 20 patients were acquired before and 1 year after UKA. Firstly, scans were pre-processed to account for differences in voxel sizes and divided in volumes of interest. This was followed by optimization of registration parameters according to their volumetric agreement, and alignment using a combination of rigid, affine and non-rigid registration. Finally, radiotracer uptakes were normalized, and differences between pre-operative and post-operative activity were computed for each voxel. Wilcoxon signed rank sum test was performed to compare Dice similarity coefficients pre- and post-registration. RESULTS: Qualitative and quantitative validation of the platform assessing the correct alignment of SPECT/CT scans resulted in Dice similarity coefficient values over 80% and distances between predefined anatomical landmarks below the fixed threshold of (2;2;0) voxels. Locations of increased and decreased osteoblastic activity obtained during comparisons of osteoblastic activity before and after UKA were mainly consistent with literature. CONCLUSIONS: Thus, a full resolution comparison performed on the platform could assist surgeons and engineers in optimizing surgical parameters in view of bone remodeling, thereby improving UKA survivorship.

Patellar tendon buckling in post-operative total knee arthroplasty patients is more prominent than in healthy controls.

Recent evidence suggests the patellar tendon undergoes buckling during normal knee flexion, which likely contributes to the functioning of the extensor mechanism. Thus, evaluating buckling in patients following total knee arthroplasty (TKA), where extensor mechanism dysfunction remains a common complication, may be relevant. The study goals were to identify whether post-TKA patients exhibit differences in patellar tendon buckling from healthy, similarly-aged adults and whether such buckling correlates with knee and patellar tendon health. Patellar tendon buckling was assessed during passive knee flexion using ultrasound in post-TKA patients (n = 20; 12M, 68 ± 8 years) and compared with previously reported data from healthy adults (n = 12; 12M; 70 ± 8 years). Patients exhibited significantly larger (p < 0.01) buckling magnitude and angles than healthy adults, and reduced distal buckling was linked with better Knee Society Scores (p = 0.04, R2 = 0.24). The greater patellar tendon buckling observed in post-TKA patients could arise due to factors related to the surgery itself (e.g. infrapatellar fat pad resection) or it may be that post-TKA patients had greater patellar tendon buckling before their procedure. Alterations in patellar tendon buckling may predispose individuals to post-surgical complications including instability, anterior knee pain, and extensor mechanism dysfunction, with further work necessary to elucidate potential links.

Non-uniformity in the healthy patellar tendon is greater in males and similar in different age groups.

There is increasing evidence that tendons are heterogeneous and take advantage of structural mechanisms to enhance performance and reduce injury. Fascicle-sliding, for example, is used by energy-storing tendons to enable them to undergo large extensions while protecting the fascicles from damage. Reductions in fascicle-sliding capacity may thus predispose certain populations to tendinopathy. Evidence from the Achilles tendon of significant superficial-to-deep non-uniformity that is reduced with age supports this theory. Similar patellar tendon non-uniformity has been observed, but the effects of age and sex have yet to be assessed. Healthy adults (n = 50, 25M/25F) from a broad range of ages (23-80) were recruited and non-uniformity was quantified using ultrasound speckle-tracking during passive knee extension. Significant superficial-to-deep non-uniformity and proximal/distal variations were observed. No effect of age was found, but males exhibited significantly greater non-uniformity than females (p < 0.05). The results contrast with previous findings in the Achilles tendon; in this study, tendons and tendon regions at high risk for tendinopathy (i.e. males and proximal regions, respectively) exhibited greater non-uniformity, whereas high-risk Achilles tendons (i.e. older adults) previously showed reduced non-uniformity. This suggests that non-uniformity may be dominated by factors other than fascicle-sliding. Anatomically, the varied proximal attachment of the patellar tendon may influence non-uniformity, with quadriceps passive resistance limiting superficial tendon movement, thus linking flexibility, non-uniformity and injury risk. This study also provides evidence of a differential effect of aging on the patellar tendon compared with evidence from prior studies on other tendons necessitating further study to elucidate links between non-uniformity and injury.

Patellar tendon buckling is altered with age.

Recent evidence has revealed that the patellar tendon exhibits buckling during passive knee extension, wherein the tendon folds back onto itself. The clinical relevance of such buckling is unclear, but it has been suggested that it serves to protect the patellar tendon from rupture when subjected to a sudden extreme contraction. Although prior evidence suggests buckling occurs universally, it is poorly understood, and may be influenced by age and sex. Healthy adults (n = 41, aged 21-80 years) were recruited to assess age- and sex-based differences in patellar tendon buckling during passive knee extension. 93% of subjects exhibited buckling in extension, with buckling more prominent in the distal tendon. No age- or sex-based differences in buckling magnitude were observed, but a significant age-based difference in buckling angle was found, with the tendon unbuckling later in flexion in younger adults compared with middle-aged (p = 0.025) and older (p = 0.014) adults. Intrinsic factors were also linked with buckling; for example, smaller maximum knee extension (i.e. less flexibility) correlated with smaller buckling magnitude (p = 0.037, R2 = 0.116), suggesting a link between patellar tendon buckling and joint-level mechanics. These results suggest that buckling is an inherent component of normal knee function that older adults may be failing to take advantage of, predisposing them to injury. Further study will be critical to elucidate the clinical implications of patellar tendon buckling.