Reproducibility in modeling and simulation of the knee: Academic, industry, and regulatory perspectives.

Stakeholders in the modeling and simulation (M&S) community organized a workshop at the 2019 Annual Meeting of the Orthopaedic Research Society (ORS) entitled "Reproducibility in Modeling and Simulation of the Knee: Academic, Industry, and Regulatory Perspectives." The goal was to discuss efforts among these stakeholders to address irreproducibility in M&S focusing on the knee joint. An academic representative from a leading orthopedic hospital in the United States described a multi-institutional, open effort funded by the National Institutes of Health to assess model reproducibility in computational knee biomechanics. A regulatory representative from the United States Food and Drug Administration indicated the necessity of standards for reproducibility to increase utility of M&S in the regulatory setting. An industry representative from a major orthopedic implant company emphasized improving reproducibility by addressing indeterminacy in personalized modeling through sensitivity analyses, thereby enhancing preclinical evaluation of joint replacement technology. Thought leaders in the M&S community stressed the importance of data sharing to minimize duplication of efforts. A survey comprised 103 attendees revealed strong support for the workshop and for increasing emphasis on computational modeling at future ORS meetings. Nearly all survey respondents (97%) considered reproducibility to be an important issue. Almost half of respondents (45%) tried and failed to reproduce the work of others. Two-thirds of respondents (67%) declared that individual laboratories are most responsible for ensuring reproducible research whereas 44% thought that journals are most responsible. Thought leaders and survey respondents emphasized that computational models must be reproducible and credible to advance knee M&S.

A Mid-Level Constrained Insert Reduces Coupled Axial Rotation but Not Coronal Mid-Flexion Laxity Induced by Joint Line Elevation in Posterior-Stabilized Total Knee Arthroplasty: A Computational Study.

BACKGROUND: Surgeons may resect additional distal femur during primary posterior-stabilized (PS) total knee arthroplasty (TKA) to correct a flexion contracture. However, the resultant joint line elevation (JLE) increases mid-flexion laxity. We determined whether a mid-level constraint (MLC) insert reduced mid-flexion laxity after JLE. METHODS: Six computational knee models were developed using computed tomography scans and average soft tissue properties yielding balanced extension gaps but with a 10° flexion contracture. Distal femoral resections of +2 and +4 mm were simulated with PS and MLC inserts. Varus-valgus ±10 Nm moments were applied at 30°, 45°, and 60° of flexion. Coronal laxity (the sum of varus-valgus angulation) and coupled axial rotation (the sum of internal/external rotation) were measured and compared between insert models. RESULTS: At 30° of flexion, coronal laxities with the PS insert at the +2 and +4 mm resections averaged 7.9° ± 0.6° and 11.3° ± 0.6°, respectively, and decreased by 0.8° (P = .06) and 1.0° (P = .07), respectively, with the MLC insert. PS rotational laxities at the +2 and +4 mm resections averaged 11.1° ± 3.9° and 12.5° ± 4.6°, respectively, and decreased by 5.6° (P = .01) and 7.1° (P = .02), respectively, with the MLC insert. Similar patterns were observed at 45° and 60° of flexion. CONCLUSION: With additional distal femoral resections to alleviate a flexion contracture, utilizing an MLC insert substantially reduced coupled axial rotation but had a minimal impact on coronal laxity compared to a PS insert. Efforts should be taken to avoid JLE in primary total knee arthroplasty as even MLC inserts may not mitigate coronal laxity.

Arthroplasty Surgeons Differ in Their Intraoperative Soft Tissue Assessments: A Study in Human Cadavers to Quantify Surgical Decision-making in TKA.

BACKGROUND: In TKA, soft tissue balancing is assessed through manual intraoperative trialing. This assessment is a physical examination via manually applied forces at the ankle, generating varus and valgus moments at the knee while the surgeon visualizes the lateral and medial gaps at the joint line. Based on this examination, important surgical decisions are made that influence knee stability, such as choosing the polyethylene insert thickness. Yet, the applied forces and the assessed gaps in this examination represent a qualitative art that relies on each surgeon's intuition, experience, and training. Therefore, the extent of variation among surgeons in conducting this exam, in terms of applied loads and assessed gaps, is unknown. Moreover, whether variability in the applied loads yields different surgical decisions, such as choice of insert thickness, is also unclear. Thus, surgeons and developers have no basis for deciding to what extent the applied loads need to be standardized and controlled during a knee balance exam in TKA. QUESTIONS/PURPOSES: (1) Do the applied moments in soft tissue assessment differ among surgeons? (2) Do the assessed gaps in soft tissue assessment differ among surgeons? (3) Is the choice of insert thickness associated with the applied moments? METHODS: Seven independent human cadaveric nonarthritic lower extremities from pelvis to toe were acquired (including five females and two males with a mean age of 73 ± 7 years and a mean BMI of 25.8 ± 3.8 kg/m 2 ). Posterior cruciate ligament substituting (posterior stabilized) TKA was performed only on the right knees. Five fellowship-trained knee surgeons (with 24, 15, 15, 7, and 6 years of clinical experience) and one chief orthopaedic resident independently examined soft tissue balance in each knee in extension (0° of flexion), midflexion (30° of flexion), and flexion (90° of flexion) and selected a polyethylene insert based on their assessment. Pliable force sensors were wrapped around the leg to measure the loads applied by each surgeon. A three-dimensional (3D) motion capture system was used to measure knee kinematics and a dynamic analysis software was used to estimate the medial and lateral gaps. We assessed (1) whether surgeons applied different moments by comparing the mean applied moment by surgeons in extension, midflexion, and flexion using repeated measures (RM)-ANOVA (p < 0.05 was assumed significantly different); (2) whether surgeons assessed different gaps by comparing the mean medial and lateral gaps in extension, midflexion, and flexion using RM-ANOVA (p < 0.05 was assumed significantly different); and (3) whether the applied moments in extension, midflexion, and flexion were associated with the insert thickness choice using a generalized estimating equation (p < 0.05 was assumed a significant association). RESULTS: The applied moments differed among surgeons, with the largest mean differences occurring in varus in midflexion (16.5 Nm; p = 0.02) and flexion (7.9 Nm; p < 0.001). The measured gaps differed among surgeons at all flexion angles, with the largest mean difference occurring in flexion (1.1 ± 0.4 mm; p < 0.001). In all knees except one, the choice of insert thickness varied by l mm among surgeons. The choice of insert thickness was weakly associated with the applied moments in varus (ß = -0.06 ± 0.02 [95% confidence interval -0.11 to -0.01]; p = 0.03) and valgus (ß = -0.09 ± 0.03 [95% CI -0.18 to -0.01]; p= 0.03) in extension and in varus in flexion (ß = -0.11 ± 0.04 [95% CI -0.22 to 0.00]; p = 0.04). To put our findings in context, the greatest regression coefficient (ß = -0.11) indicates that for every 9-Nm increase in the applied varus moment (that is, 22 N of force applied to the foot assuming a shank length of 0.4 m), the choice of insert thickness decreased by 1 mm. CONCLUSION: In TKA soft tissue assessment in a human cadaver model, five surgeons and one chief resident applied different moments in midflexion and flexion and targeted different gaps in extension, midflexion, and flexion. A weak association between the applied moments in extension and flexion and the insert choice was observed. Our results indicate that in the manual assessment of soft tissue, changes in the applied moments of 9 and 11 Nm (22 to 27 N on the surgeons' hands) in flexion and extension, respectively, yielded at least a 1-mm change in choice of insert thickness. The choice of insert thickness may be more sensitive to the applied moments in in vivo surgery because the surgeon is allowed a greater array of choices beyond insert thickness. CLINICAL RELEVANCE: Among five arthroplasty surgeons with different levels of experience and a chief resident, subjective soft tissue assessment yielded 1 to 2 mm of variation in their choice of insert thickness. Therefore, developers of tools to standardize soft tissue assessment in TKA should consider controlling the force applied by the surgeon to better control for variations in insert selection.

Additional distal femoral resection increases mid-flexion coronal laxity in posterior-stabilized total knee arthroplasty with flexion contracture : a computational study.

AIMS: Surgeons commonly resect additional distal femur during primary total knee arthroplasty (TKA) to correct a flexion contracture, which leads to femoral joint line elevation. There is a paucity of data describing the effect of joint line elevation on mid-flexion stability and knee kinematics. Thus, the goal of this study was to quantify the effect of joint line elevation on mid-flexion laxity. METHODS: Six computational knee models with cadaver-specific capsular and collateral ligament properties were implanted with a posterior-stabilized (PS) TKA. A 10° flexion contracture was created in each model to simulate a capsular contracture. Distal femoral resections of + 2 mm and + 4 mm were then simulated for each knee. The knee models were then extended under a standard moment. Subsequently, varus and valgus moments of 10 Nm were applied as the knee was flexed from 0° to 90° at baseline and repeated after each of the two distal resections. Coronal laxity (the sum of varus and valgus angulation with respective maximum moments) was measured throughout flexion. RESULTS: With + 2 mm resection at 30° and 45° of flexion, mean coronal laxity increased by a mean of 3.1° (SD 0.18°) (p < 0.001) and 2.7° (SD 0.30°) (p < 0.001), respectively. With + 4 mm resection at 30° and 45° of flexion, mean coronal laxity increased by 6.5° (SD 0.56°) (p < 0.001) and 5.5° (SD 0.72°) (p < 0.001), respectively. Maximum increased coronal laxity for a + 4 mm resection occurred at a mean 15.7° (11° to 33°) of flexion with a mean increase of 7.8° (SD 0.2°) from baseline. CONCLUSION: With joint line elevation in primary PS TKA, coronal laxity peaks early (about 16°) with a maximum laxity of 8°. Surgeons should restore the joint line if possible; however, if joint line elevation is necessary, we recommend assessment of coronal laxity at 15° to 30° of knee flexion to assess for mid-flexion instability. Further in vivo studies are warranted to understand if this mid-flexion coronal laxity has negative clinical implications. Cite this article: Bone Joint J 2021;103-B(6 Supple A):87-93.

Simulation of preoperative flexion contracture in a computational model of total knee arthroplasty: Development and evaluation.

Preoperative flexion contracture is a risk factor for patient dissatisfaction following primary total knee arthroplasty (TKA). Previous studies utilizing surgical navigation technology and cadaveric models attempted to identify operative techniques to correct knees with flexion contracture and minimize undesirable outcomes such as knee instability. However, no consensus has emerged on a surgical strategy to treat this clinical condition. Therefore, the purpose of this study was to develop and evaluate a computational model of TKA with flexion contracture that can be used to devise surgical strategies that restore knee extension and to understand factors that cause negative outcomes. We developed six computational models of knees implanted with a posteriorly stabilized TKA using a measured resection technique. We incorporated tensions in the collateral ligaments representative of those achieved in TKA using reference data from a cadaveric experiment and determined tensions in the posterior capsule elements in knees with flexion contracture by simulating a passive extension exam. Subject-specific extension moments were calculated and used to evaluate the amount of knee extension that would be restored after incrementally resecting the distal femur. Model predictions of the extension angle after resecting the distal femur by 2 and 4 mm were within 1.2° (p ≥ 0.32) and 1.6° (p ≥ 0.25), respectively, of previous studies. Accordingly, the presented computational method could be a credible surrogate to study the mechanical impact of flexion contracture in TKA and to evaluate its surgical treatment.

A geometric ratio to predict the flexion gap in total knee arthroplasty.

Measured resection is a common technique for obtaining symmetric flexion and extension gaps in posterior-stabilized (PS) total knee arthroplasty (TKA). A known limitation of measured resection, however, is its reliance on osseous landmarks to guide bone resection and component alignment while ignoring the geometry of the surrounding soft tissues such as the medial collateral ligament (MCL), a possible reason for knee instability. To address this clinical concern, we introduce a new geometric proportion, the MCL ratio, which incorporates features of condylar geometry and MCL anterior fibers. The goal of this study was to determine whether the MCL ratio can predict the flexion gaps and to determine whether a range of MCL ratio corresponds to balanced gaps. Six computational knee models each implanted with PS TKA were utilized. Medial and lateral gaps were measured in response to varus and valgus loads at extension and flexion. The MCL ratio was related to the measured gaps for each knee. We found that the MCL ratio was associated with the flexion gaps and had a stronger association with the medial gap (ß = -7.2 ± 3.05, P < .001) than with the lateral gap (ß = 3.9 ± 7.26, P = .04). In addition, an MCL ratio ranging between 1.1 and 1.25 corresponded to balanced flexion gaps in the six knee models. Future studies will focus on defining MCL ratio targets after accounting for variations in ligament properties in TKA patients. Our results suggest that the MCL ratio could help guide femoral bone resections in measured resection TKA, but further clinical validation is required.

Neither Anterior nor Posterior Referencing Consistently Balances the Flexion Gap in Measured Resection Total Knee Arthroplasty: A Computational Analysis.

BACKGROUND: Whether anterior referencing (AR) or posterior referencing (PR) produces a more balanced flexion gap in total knee arthroplasty (TKA) using measured resection remains controversial. Our goal was to compare AR and PR in terms of (1) medial and lateral gaps at full extension and 90° of flexion, and (2) maximum medial and lateral collateral ligament (MCL and LCL) forces in flexion. METHODS: Computational models of 6 knees implanted with posterior-stabilized TKA were virtually positioned with both AR and PR techniques. The ligament properties were standardized to achieve a balanced knee at full extension. Medial-lateral gaps were measured in response to varus and valgus loading at full extension and 90° of flexion; MCL and LCL forces were estimated during passive flexion. RESULTS: At full extension, the maximum difference in the medial-lateral gap for both AR and PR was <1 mm in all 6 knee models. However, in flexion, only 3 AR and 3 PR models produced a difference in medial-lateral gap <2 mm. During passive flexion, the maximum MCL force ranged from 2 N to 87 N in AR and from 17 N to 127 N in PR models. The LCL was unloaded at >25° of flexion in all models. CONCLUSION: In measured resection TKA, neither AR nor PR better balance the ligaments and produce symmetrical gaps in flexion. Alternative bone resection techniques and rotation alignment targets are needed to achieve more predictable knee balance.

Finite Element Study to Evaluate the Biomechanical Performance of the Spine After Augmenting Percutaneous Pedicle Screw Fixation With Kyphoplasty in the Treatment of Burst Fractures.

Percutaneous pedicle screw fixation (PPSF) is a well-known minimally invasive surgery (MIS) employed in the treatment of thoracolumbar burst fractures (TBF). However, hardware failure and loss of angular correction are common limitations caused by the poor support of the anterior column of the spine. Balloon kyphoplasty (KP) is another MIS that was successfully used in the treatment of compression fractures by augmenting the injured vertebral body with cement. To overcome the limitations of stand-alone PPSF, it was suggested to augment PPSF with KP as a surgical treatment of TBF. Yet, little is known about the biomechanical alteration occurred to the spine after performing such procedure. The objective of this study was to evaluate and compare the immediate post-operative biomechanical performance of stand-alone PPSF, stand-alone-KP, and KP-augmented PPSF procedures. Novel three-dimensional (3D) finite element (FE) models of the thoracolumbar junction that describes the fractured spine and the three investigated procedures were developed and tested under mechanical loading conditions. The spinal stiffness, stresses at the implanted hardware, and the intradiscal pressure at the upper and lower segments were measured and compared. The results showed no major differences in the measured parameters between stand-alone PPSF and KP-augmented PPSF procedures, and demonstrated that the stand-alone KP may restore the stiffness of the intact spine. Accordingly, there was no immediate post-operative biomechanical advantage in augmenting PPSF with KP when compared to stand-alone PPSF, and fatigue testing may be required to evaluate the long-term biomechanical performance of such procedures.