BACKGROUND:Shear forces on the patella can lead to patellar loosening and failure in total knee arthroplasty (TKA). Our objectives were as follows: (1) evaluate the mechanical load-to-shear failure in a unique cohort of cemented patellar components in well-functioning postmortem TKAs and (2) determine the influence of clinical and radiographic factors on load-to-shear failure. METHODS:There were 22 patellae that were harvested from well-functioning postmortem TKAs (mean implantation duration 9.1 years [range, 1.7 to 19.6]). There were three all-polyethylene 3-peg onlay patellar designs evaluated. The patellae were evaluated for polyethylene damage, implant-to-bone size ratios, microarchitectural parameters, and implant-cement-bone interface. Patellar specimens were loaded with isolated shear stress using a servo-hydraulic test frame until failure. Univariate and multivariable linear regression models were used to analyze the influence of clinical and radiographic factors on load-to-shear failure. RESULTS:The mean load-to-shear failure was 1,881 ± 621 N. There were nine patellae that failed at the bone-cement interface, seven that failed at the implant-cement interface, and six that involved both interfaces. There were no failures at the peg-implant junction. On multivariable analyses, load to failure was positively associated with bone volume fraction and negatively associated with body mass index, duration of implantation, and implant-to-bone surface area coverage. Load-to-shear failure was not associated with surface damage or radiographic parameters and did not differ across the three patellar implant designs. CONCLUSIONS:In this novel cohort of cemented patellar buttons from well-functioning postmortem TKAs, load-to-shear failure was higher than previously reported in buttons cemented in cadaver native patellae. The amount of bony coverage by the patellar button was inversely associated with shear strength after accounting for other pertinent factors. When choosing between two patellar button sizes, surgeons should consider opting for the smaller size, which may improve the maximum shear strength of the patellar construct.

Background Treatment of stiffness following total knee arthroplasty (TKA) is complicated by a lack of a specific diagnosis for arthrofibrosis. Magnetic resonance imaging (MRI) provides a noninvasive means to generate and evaluate clinically diagnostic images of deep structures within the knee. The purpose of this study was to assess how the severity and location of arthrofibrosis observed on MRI relate to MRI synovial classifications and range of motion in primary TKA patients undergoing revision surgery. Methods There were 137 patients (140 knees) scheduled for TKA revision surgery who underwent preoperative MRI and were assigned a global synovial classification (normal, abnormal, arthrofibrosis, infection, focal scarring, polymeric) and severity of arthrofibrosis (none, mild, moderate, severe) within the individual anterior and posterior compartments. Passive joint flexion and extension measurements were recorded intraoperatively. Results The global synovial classification of arthrofibrosis had a greater prevalence of severe fibrosis within the anterior (25 of 42) and posterior (16 of 42) compartments as compared to other classifications (P < 0.0001). Reduced flexion and extension were found in patients who had a global synovial classification of arthrofibrosis (P < 0.0001). Reduced knee flexion was observed with greater anterior fibrosis severity, and reduced knee extension was observed with greater posterior fibrosis severity (P < 0.0001). Conclusions Anterior and posterior fibrosis severity differs across MRI synovial classifications. Further, the extent of joint flexion and extension differs by MRI synovial classifications and severity of compartment arthrofibrosis. The results of this study support that MRI presents an effective and noninvasive means to discern global and local synovial reactions within individuals undergoing revision TKA.

Background: Open reduction and internal fixation for fractures of the subchondral bone (including articular impaction fractures, insufficiency fractures, and early-collapse in avascular necrosis) is difficult or impossible in difficult-to-reach anatomic regions. Indirect reduction methods utilizing calcium phosphate cementation has been tried with a near 50% failure rate and 22% conversion to arthroplasty. On the other hand, open impaction bone grafting has been employed with success. Here we present the first cadaveric series demonstrating fracture reduction by minimally-invasive impaction grafting using chain-milled partially-demineralized allograft bone. Methods: Thirteen cadaveric proximal femur specimens were used for this study. A 2 cm diameter by 2 cm deep osteochondral core was drilled into the weightbearing portion of the femoral head. A 1cm deep portion of the core was morselized to simulate subchondral fracture with an intact osteochondral cap. Force-control loading of this defect was performed using 800N approximating body mass with the resultant stiffness and displacement recorded (pre-repair). A metaphyseal-entry retrograde fluoroscopic approach using a 5mm trochar cannula was used to perform MIS allograft impaction grafting to effect fracture reduction. 2cc of chain-milled partially-demineralized allograft bone was used per cadaveric specimen (LENOSS OsteoPearl, MTF Biologics). Linear loading was repeated using the same force-control protocol (800N) to again measure stiffness and displacement (post-repair). Surface volumetric displacement was evaluated by 3D surface scanning on the femoral head surface before and after grafting. Baseline and post-grafting computed tomography (CT) was performed to evaluate defect filling. Results: All specimens successfully underwent MIS impaction grafting. Qualitatively, upon impaction of the chain-milled allograft, graft material uniformly fills the bony defect apparently following paths of least resistance and powerfully reduces the osteochondral cap. The osteochondral cap biomechanically demonstrated a 2.4-fold increase in stiffness under compression as compared to pre-repair and importantly, almost no plastic deformation following repair with a final depression of 1.0 ±1.3mm (SD), as compared to 4.1 ±1.5mm pre-repair. Conclusion: This is a cadaveric study demonstrating biomechanical advantages of subchondral impaction grafting using chain-milled, partially-demineralized allograft bone through a minimally-invasive approach. Unlike subchondral cement augmentation, impaction grafting has the apparent benefits of: 1. Ability to generate mechanical power to effect fracture reduction; 2. Graft tends to follow paths of least resistance to reinforce a fracture plane; 3. No-leakage; and 4. Subchondral mechanical reinforcement of the osteochondral fragment. This positions partially-demineralized chain-milled allograft impaction grafting as a prime method for the treatment of pre- and early-osteochondral collapse.

BACKGROUND:At our institution, surgeons were observing cases of failed total knee arthroplasties (TKAs) with surface delamination of the tibial insert fabricated by direct compression molding. The increase in unexpected failure led us to investigate the prevalence of delamination and its causes through the use of retrieval analysis and reviews of clinical, demographic, and radiographic data. METHODS:Between 2000 and 2019, a total of 519 Exactech Optetrak posterior-stabilized direct-compression-molded polyethylene inserts had been retrieved. To determine prevalence, we utilized institutional usage data, manufacturer sales to our institution, and hospital records to determine the delamination rate. Eighty-six retrieved specimens (16 with delamination) were assessed for oxidation with use of infrared spectroscopy. RESULTS:Sixty-four (12%) of the 519 inserts had delamination. The delamination rate was 0.36% across the 20-year period. Osteolysis was the reason for revision in 25% of delaminated cases, compared with 4% of non-delaminated cases. The mean oxidation index of the delaminated inserts was 2.67 ± 1.4 (range, 1.2 to 6.6). Delamination was not associated with surgical factors (cement viscosity and tibial insert thickness) or processes associated with manufacturing and implantation of the inserts into the patients (implantation year, shelf life, and packaging and sterilization dates). CONCLUSIONS:The lack of causative factors for the increase in delamination was perplexing. In 2021, following the completion of our study, the manufacturer determined that since 2004, polyethylene inserts were packaged in "non-conforming" vacuum bags that were missing a secondary barrier layer intended to markedly lessen oxygen permeation. The use of non-conforming bags apparently increased the risk of premature oxidation, delamination, and associated osteolysis. LEVEL OF EVIDENCE:Prognostic Level IV . See Instructions for Authors for a complete description of levels of evidence.

BACKGROUND:Medially conforming (MC) total knee arthroplasty (TKA) has seen increased clinical utilization. This design allows for either retention or resection of the posterior cruciate ligament (PCL); however, the impact of the PCL on femoral rollback and posterior tibial sag is unknown. Therefore, we developed a computational model to quantify how the PCL affects femoral rollback and posterior sag in MC-TKA. METHODS:Computational models of 10 cadaver knees were virtually implanted with MC-TKAs. Clinical tests of passive flexion and posterior sag were simulated, and femoral rollback and posterior tibial translation (PTT) were quantified. These tests were simulated in MC-TKA with the PCL retained, partially resected, and completely resected. We then assessed how increasing the tibial insert thickness in PCL-resected MC-TKA and switching to posterior-stabilized (PS)-TKA impacted posterior sag. RESULTS:Femoral rollback decreased medially by a median of 2.4 mm (P ≤ 0.001) and laterally by a median of 3.3 mm (P ≤ 0.001) with simulated PCL resection. For the simulated sag test, PTT increased by a median of 4.2 (P ≤ 0.05) and 7.4 mm (P ≤ 0.001) with partial and complete PCL resection, respectively. Moreover, PTT was reduced by a median of 7.1 mm (P ≤ 0.01) when converting a PCL-resected MC-TKA to a PS-TKA. CONCLUSIONS:In a computational model, MC-TKA does not fully compensate for the function of the PCL, which facilitates femoral rollback in passive flexion and resists PTT during a posterior sag test. Resecting the antero-lateral bundle, with preservation of the postero-medial bundle of the PCL, yields more femoral rollback and less PTT than complete PCL resection in MC-TKA. Increasing tibial insert thickness in MC-TKA also does not account for the role of the PCL in reducing PTT during a sag test, while a PS-TKA does.

BACKGROUND:Assessing intraoperative ligament balance in the posterior cruciate ligament (PCL)-retaining total knee arthroplasty (TKA) can be achieved by quantifying tibio-femoral contact forces. Ligament balancing may involve selectively releasing PCL fibers; however, the effects of the extent and location of PCL release on compartmental contact forces are not well understood. To investigate these effects, we developed a computational model to quantify changes in medial and lateral contact forces resulting from targeted PCL fiber release. METHODS:Computational models of 10 cadaver knees (five men and five women with a mean age of 63 years) were virtually implanted with a cruciate-retaining TKA. Passive knee flexion was simulated under three PCL conditions: all PCL fibers retained, all PCL fibers resected, and only the central PCL fibers released. Tibio-femoral contact forces in the medial and lateral compartments at 90° of flexion were measured for each PCL condition. RESULTS:Resecting the PCL resulted in a reduction of contact forces by a median of 24.2 N (P ≤ 0.01) medially and a median of 11.1 N (P ≤ 0.01) laterally. Selective release of only the central PCL fibers reduced medial and lateral contact forces by medians of 11.5 N (P ≤ 0.05) and 4.5 N (P ≤ 0.05), representing 47 and 50% of the reduction observed with complete PCL resection, respectively. CONCLUSIONS:Resecting the PCL asymmetrically impacts compartmental contact forces, with a greater reduction observed in the medial compartment. Given the contribution of the releasing PCL's central portion to the reduction in compartmental contact forces, surgeons may consider first focusing on this region when conducting intraoperative releases to achieve ligament balance via PCL resection in cruciate-retaining TKA.

BACKGROUND:Prosthetic impingement after total hip arthroplasty (THA) has been associated with instability and may be a cause of accelerated polyethylene wear and pain. Previous retrieval studies report a high prevalence of impingement in acetabular liners. Robotic technology has the potential to reduce THA instability as it enables technical precision and optimizes implant positioning. However, whether robotics can improve impingement prevalence is unknown. Thus, the objectives of this study were to: (1) determine the prevalence and severity of acetabular liner impingement with robotic navigation; and (2) compare impingement prevalence with a control cohort of manually placed THA liners. METHODS:There were 18 robotic-assisted liners and 11 non-robotic controls scored for the presence and severity of impingement. Radiographic measurements of acetabular inclination and anteversion were assessed using prerevision standing radiographs. Femoral head size (36 being the most common), length of implantation, revision indication, age, gender, and body mass index were recorded. RESULTS:Of the robotic liners, 61% showed impingement, while 45% of the non-robotic liners showed impingement (P = 0.14). The robotic group demonstrated a lower variance of inclination (robotic: 41.7° ± 3.9, control: 42.8° ± 7.1, P = 0.64) and lower anteversion variance (robotic: 22.8° ± 2.8, control: 20.8° ± 7.9, P = 0.43), but mean values did not differ between the groups. Impingement presence and severity were not related to head size, length of implantation, or other demographic variables. CONCLUSIONS:This study suggests that the use of robotic-assisted technology employing modern-day implants with larger diameter heads does not reduce the prevalence or severity of prosthetic impingement in retrieved acetabular liners from revision THA.

Patient-specific flanged acetabular components are utilized to treat failed total hip arthroplasties with severe acetabular defects. We previously developed and published a finite element model that investigated the impact of hip joint center lateralization on construct biomechanics during gait conditions. This model consisted of a patient-specific implant designed to address a superior-medial defect created in a standard pelvic geometry. This study aims to utilize the same model and examine how cortical shell thickness and ischial cancellous bone density affect the strain distribution in the bone and bone-implant micromotion. Using published studies and bone density analyses of patients who had undergone total hip arthroplasties with flanged acetabular components, we established a thickness range for the cortical shell (1.5, 1, and 0.75 mm) and two levels of ischial cancellous bone density (100% and 25%). We compared the resulting bone strains against the fatigue strength of the bone (0.3% strain) as a criterion for local bone failure and the bone-implant micromotion against the threshold associated with bone ingrowth (20 µm). A thinner pelvic cortical shell and lower ischial cancellous bone density increased areas of bone at risk of failure, particularly at the ischial screws (from 6% to 38%), and decreased areas compatible with bone ingrowth. These findings agree with our clinical knowledge that compromised ischial bone and inadequate ischial fixation negatively impact the survivorship of flanged acetabular components. This series establishes our modeling approach of a computational model that can be utilized to guide implant design to best treat unique acetabular defects.

BACKGROUND:Compromised function is a common reason for patient dissatisfaction after total knee arthroplasty. However, objectively evaluating function often requires costly, time-consuming, and highly specialized data collection and analysis in a dedicated motion analysis laboratory. To overcome this practical barrier, we developed a radiographic-based method to quantify knee joint moments in routine clinical care and to explore the relationship between knee moments in the sagittal plane and the Knee Osteoarthritis Outcomes Score for Joint Replacement (KOOS JR). METHODS:Motion analysis was performed on 20 patients (nine women, aged: 38 to 76 years; body mass index: 22.1 to 31.6) during level ground walking preoperatively and 6 weeks after total knee arthroplasty. At the same time points, patients underwent frontal and lateral biplane radiographs that were synchronized spatially and temporally with ground force measurements during bipedal and single leg stances on the operated leg. The knee adduction moment (KAM), in percent body weight times height (%BW·H), was calculated in the coronal plane as the product of the ground force and the perpendicular distance between the force's line of action and the knee center. The dynamic KAM during walking was compared to the radiographic KAM and related to KOOS JR. RESULTS:The peak dynamic KAM range was -0.5 to 4.3% BW·H preoperatively and 1 to 4.4% BW·H postoperatively. The static KAM, particularly during single leg stance, was strongly correlated with the peak dynamic KAM; however, the KAM was not correlated with KOOS JR. CONCLUSIONS:The radiographic KAM, particularly during single leg stance, was an excellent surrogate metric for the peak dynamic KAM. The KAM was not correlated with KOOS JR; however, our follow-up was short, and we did not consider additional kinetic metrics, like the knee flexion moment. The proposed methodology allows routine clinical evaluation of knee kinetic markers of functional recovery that can complement patient-reported outcome measures.

Osteoarthritis (OA) treatment is limited by the lack of effective nonsurgical interventions to slow disease progression. Here, we examined the contributions of the subchondral bone properties to OA development. We used parathyroid hormone (PTH) to modulate bone mass before OA initiation and alendronate (ALN) to inhibit bone remodeling during OA progression. We examined the spatiotemporal progression of joint damage by combining histopathological and transcriptomic analyses across joint tissues. The additive effect of PTH pretreatment before OA initiation and ALN treatment during OA progression most effectively attenuated load-induced OA pathology. Individually, PTH directly improved cartilage health and slowed the development of cartilage damage, whereas ALN primarily attenuated subchondral bone changes associated with OA progression. Joint damage reflected early transcriptomic changes. With both treatments, the structural changes were associated with early modulation of immunoregulation and immunoresponse pathways that may contribute to disease mechanisms. Overall, our results demonstrate the potential of subchondral bone-modifying therapies to slow the progression of OA.

BACKGROUND:Cementless total knee arthroplasty (TKA) has regained interest for its potential for long-term biologic fixation. The density of the bone is related to its ability to resist static and cyclic loading and can affect long-term implant fixation; however, little is known about the density distribution of periarticular bone in TKA patients. Thus, we sought to characterize the bone mineral density (BMD) of the proximal tibia in TKA patients. METHODS:We included 42 women and 50 men (mean age 63 years, range: 50 to 87; mean body mass index 31.6, range: 20.5 to 49.1) who underwent robotic-assisted TKA and had preoperative computed tomography scans with a BMD calibration phantom. Using the robotic surgical plan, we computed the BMD distribution at 1 mm-spaced cross-sections parallel to the tibial cut from 2 mm above the cut to 10 mm below. The BMD was analyzed with respect to patient sex, age, preoperative alignment, and type of fixation. RESULTS:The BMD decreased from proximal to distal. The greatest changes occurred within ± 2 mm of the tibial cut. Age did not affect BMD for men; however, women between 60 and 70 years had higher BMD than women ≥ 70 years for the total cut (P = .03) and the medial half of the cut (P = .03). Cemented implants were used in 1 86-year-old man and 18 women (seven < 60 years, seven 60 to 70 years, and four ≥ 70 year old). We found only BMD differences between cemented or cementless fixation for women < 60 years. CONCLUSIONS:To our knowledge, this is the first study to characterize the preoperative BMD distribution in TKA patients relative to the intraoperative tibial cut. Our results indicate that while sex and age may be useful surrogates of BMD, the clinically relevant thresholds for cementless knees remain unclear, offering an area for future studies.

Background: Anterior cervical discectomy and fusion (ACDF) is known to elicit adverse biomechanical effects on immediately adjacent segments; however, its impact on the kinematics of the remaining nonadjacent cervical levels has not been understood. This study aimed to explore the biomechanical impact of ACDF on kinematics beyond the immediate fusion site. We hypothesized that compensatory motion following single- level ACDF is not predictably distributed to adjacent segments due to compensation from noncontiguous levels. Methods: Six fresh- frozen cervical spines (C2-T1) underwent fluoroscopic screening and sagittal and coronal reformats from computed tomography scans and were utilized to grade segmental degeneration. Each specimen was tested to 30 degrees of flexion and extension intact and following single- level ACDF at the C5-C6 level. The motions of each vertebral body were tracked using 3- dimensional (3D) motion capture into an inverse kinematics model, facilitating correlations between the 3D reconstruction from computed tomography images and the 3D motion capture data. This model was used to calculate each level's flexion/extension range of motion (ROM). Results: Single- level fusion at the C5-C6 level across all specimens resulted in a significant motion reduction of-6.8 degrees (P P = 0.002). No significant change in ROM occurred in the immediate adjacent segments C4-C5 (P P = 0.07) or C6-C7 (P P = 0.15). Hypermobility was observed in 2 specimens (33%) exclusively in adjacent segments. In contrast, the other 4 spines (66%) displayed hypermobility at noncontiguous segments. Hypermobility occurred in 42% (5/12) of the adjacent segments, 28% (5/18) of the noncontiguous segments, and 50% (3/6) of the cervicothoracic segments. Conclusion: Single- level ACDF impacts ROM beyond adjacent segments, extending to noncontiguous levels. Compensatory motion, not limited to adjacent levels, may be influenced by degenerative changes in noncontiguous segments. Surprisingly, hypermobility may not occur in adjacent segments after ACDF. Clinical Relevance: Overall, the multifaceted biomechanical effects of ACDF underscore the need for a comprehensive understanding of cervical spine dynamics beyond immediate adjacency, and it needs to be taken into consideration when planning single- level ACDF. Level of Evidence: 4.

BACKGROUND:Modular connections in total hip arthroplasty (THA) offer surgical advantages, but can contribute to implant fretting and corrosion due to micromotion at the head-stem interface. Previous studies implicated lower flexural rigidity as a key contributing factor to THA corrosion and fretting, but none associated flexural rigidity with direct histological evaluation or magnetic resonance imaging (MRI) outcomes. The purpose of this study was to determine how implant flexural rigidity is associated with MRI imaging metrics and histopathological outcomes in patients who have a failed THA. METHODS:Patients requiring revision THA surgery underwent preoperative MRIs with 3-dimensional multispectral imaging techniques to suppress metal artifacts. The MRI images were graded for adverse local tissue reactions. For each hip, trunnion flexural rigidity was measured from the retrieved femoral stem, and a periprosthetic tissue sample was retrieved and evaluated using semiquantitative histology. Generalized linear models and analyses of variance were used to assess associations between flexural rigidity and MRI and histology outcomes. RESULTS:A total of 106 THA stems were retrieved (46 women and 60 men, age: 68 years (range, 60 to 73 years). After adjustment for length of implantation, flexural rigidity was negatively correlated with histologic aseptic lymphocyte-dominant vasculitis-associated lesion severity (β = -26.27, P = .018), Fujishiro lymphocyte grading (β = -13.4, P = .039), perivascular lymphocyte layers (β = -17.8, P = .022), the grade of tissue organization (β = -22.5, P = .009), the presence of diffuse synovitis (β = -66.5, P = .003), and the presence of lymphoid aggregates (β = -75.9, P = .022). No association was found between MRI metrics and flexural rigidity. CONCLUSIONS:Among these implants, decreased trunnion stiffness was associated with increased histologic features of adverse host-mediated soft tissue reactions.

Patient-specific flanged acetabular components are utilized to treat failed total hip arthroplasties with large acetabular defects. Previous clinical studies from our institution showed that these implants tend to lateralize the acetabular center of rotation. However, the clinical impact of lateralization on implant survivorship is debated. Our goal was to develop a finite element model to quantify how lateralization of the native hip center affects periprosthetic strain and implant-bone micromotion distributions in a static level gait loading condition. To build the model, we computationally created a superomedial acetabular defect in a computed tomography 3D reconstruction of a native pelvis and designed a flanged acetabular implant to address this simulated bone defect. We modeled two implants, one with ~1 cm and a second with ~2 cm of hip center lateralization. We applied the maximum hip contact force and corresponding abductor force observed during level gait. The resulting strains were compared to bone fatigue strength (0.3% strain) and the micromotions were compared to the threshold for bone ingrowth (20 µm). Overall, the model demonstrated that the additional lateralization only slightly increased the area of bone at risk of failure and decreased the areas compatible with bone ingrowth. This computational study of patient-specific acetabular implants establishes the utility of our modeling approach. Further refinement will yield a model that can explore a multitude of variables and could be used to develop a biomechanically-based acetabular bone loss classification system to guide the development of patient-specific implants in the treatment of large acetabular bone defects.

BACKGROUND:Dislocation after total hip arthroplasty (THA) is a primary reason for THA revision. During THA through the direct anterior approach (DAA), the iliofemoral ligament, which provides the main resistance to external rotation (ER) of the hip, is commonly partially transected. We asked: (1) what is the contribution of the medial iliofemoral ligament to resisting ER after DAA THA? and (2) how much resistance to ER can be restored by repairing the ligament? METHODS:A fellowship-trained surgeon performed DAA THA on 9 cadaveric specimens. The specimens were computed tomography scanned before and after implantation. Prior to testing, the ER range of motion of each specimen to impingement in neutral and 10° of extension was computationally predicted. Each specimen was tested on a 6-degrees-of-freedom robotic manipulator. The pelvis was placed in neutral and 10° of extension. The femur was externally rotated until it reached the specimen's impingement target. Total ER torque was recorded with the medial iliofemoral ligament intact, after transecting the ligament, and after repair. Torque at extremes of motion was calculated for each condition. To isolate the contribution of the native ligament, the torque for the transected state was subtracted from both the native and repaired conditions. RESULTS:The medial iliofemoral ligament contributed an average of 68% (range, 34 to 87) of the total torque at the extreme of motion in neutral and 80% (58 to 97) in 10⁰ of extension. The repaired ligament contributed 17% (1 to 54) of the total torque at the extreme of motion in neutral and 14% (5 to 38) in 10⁰ of extension, restoring on average 18 to 25% of the native resistance against ER. CONCLUSIONS:The medial iliofemoral ligament was an important contributor to the hip torque at the extreme of motion during ER. Repairing the ligament restored a fraction of its ability to generate torque to resist ER.

Computational studies of total knee arthroplasty (TKA) often focus on either joint mechanics (kinematics and forces) or implant fixation mechanics. However, such disconnect between joint and fixation mechanics hinders our understanding of overall TKA biomechanical function by preventing identification of key relationships between these two levels of TKA mechanics. We developed a computational workflow to holistically assess TKA biomechanics by integrating musculoskeletal and finite element (FE) models. For our initial study using the workflow, we investigated how tibiofemoral contact mechanics affected the risk of failure due to debonding at the implant-cement interface using the four available subjects from the Grand Challenge Competitions to Predict In Vivo Knee Loads. We used a musculoskeletal model with a 12 degrees-of-freedom knee joint to simulate the stance phase of gait for each subject. The computed tibiofemoral joint forces at each node in contact were direct inputs to FE simulations of the same subjects. We found that the peak risk of failure did not coincide with the peak joint forces or the extreme tibiofemoral contact positions. Moreover, despite the consistency of joint forces across subjects, we observed important variability in the profile of the risk of failure during gait. Thus, by a combined evaluation of the joint and implant fixation mechanics of TKA, we could identify subject-specific effects of joint kinematics and forces on implant fixation that would otherwise have gone unnoticed. We intend to apply our workflow to evaluate the impact of implant alignment and design on TKA biomechanics.

BACKGROUND:Partial or total release of the posterior cruciate ligament (PCL) is often performed intraoperatively in cruciate-retaining total knee arthroplasty (CR-TKA) to alleviate excessive femoral rollback. However, the effect of the release of selected fibers of the PCL on femoral rollback in CR-TKA is not well understood. Therefore, we used a computational model to quantify the effect of selective PCL fiber releases on femoral rollback in CR-TKA. METHODS:Computational models of 9 cadaveric knees (age: 63 years, range 47 to 79) were virtually implanted with a CR-TKA. Passive flexion was simulated with the PCL retained and after serially releasing each individual fiber of the PCL, starting with the one located most anteriorly and laterally on the femoral notch and finishing with the one located most posteriorly on the medial femoral condyle. The experiment was repeated after releasing only the central PCL fiber. The femoral rollback of each condyle was defined as the anterior-posterior distance between tibiofemoral contact points at 0° and 90° of flexion. RESULTS:Release of the central PCL fiber in combination with the anterolateral (AL) fibers, reduced femoral rollback a median of 1.5 [0.8, 2.1] mm (P = .01) medially and by 2.0 [1.2, 2.5] mm (P = .04) laterally. Releasing the central fiber alone reduced the rollback by 0.7 [0.4, 1.1] mm (P < .01) medially and by 1.0 [0.5, 1.1] mm (P < .01) laterally, accounting for 47 and 50% of the reduction when released in combination with the AL fibers. CONCLUSIONS:Releasing the central fibers of the PCL had the largest impact on reducing femoral rollback, either alone or in combination with the release of the entire AL bundle. Thus, our findings provide clinical guidance regarding the regions of the PCL that surgeons should target to reduce femoral rollback in CR-TKA.

The evaluation, classification, and treatment of significant bone loss after total knee arthroplasty (TKA) continue to be a complex and debated topic in revision TKA (rTKA). Despite the introduction of new evidence and innovative technologies aimed at addressing the approach and care of severe bone loss in rTKA, there is no single document that systematically incorporates these newer surgical approaches. Therefore, a comprehensive review of the treatment of severe bone loss in rTKA is necessary. The Stavros Niarchos Foundation Complex Joint Reconstruction Center Hospital for Special Surgery, dedicated to clinical care and research primarily in revision hip and knee replacement, convened a Management of Bone Loss in Revision TKA symposium on June 24, 2022. At this meeting, the 42 international invited experts were divided into groups; each group was assigned to discuss questions related to 1 of the 4 topics: (1) assessing preoperative workup and imaging, anticipated bone loss, classification system, and implant surveillance; (2) achieving durable fixation in the setting of significant bone loss in revision TKA; (3) managing patellar bone loss and the extensor mechanism in cases of severe bone loss; and (4) considering the use of complex modular replacement systems: hinges, distal femoral, and proximal tibial replacements. Each group came to consensus, when possible, based on an extensive literature review and interactive discussion on their group topic. This document reviews each these 4 areas, the consensus of each group, and directions for future research.

BACKGROUND:Knee instability in midflexion may contribute to patient dissatisfaction following total knee arthroplasty (TKA). Midflexion instability involves abnormal motions and tissue loading in multiple planes. Therefore, we quantified and compared the tensions carried by the medial and lateral collateral ligaments (MCL and LCL) following posterior-stabilized (PS) TKA through knee flexion, and then compared these tensions with those carried by the native knee. Finally, we examined the relationships between collateral ligament tensions and anterior tibial translation (ATT). METHODS:Eight cadaveric knees (from 5 male and 3 female donors with a mean age of 62.6 years and standard deviation of 10.9 years) underwent PS TKA. Each specimen was mounted to a robotic manipulator and flexed to 90°. ATT was quantified by applying 30 N of anterior force to the tibia. Tensions carried by the collateral ligaments were determined via serial sectioning. Robotic testing was also conducted on a cohort of 15 healthy native cadaveric knees (from 9 male and 6 female donors with a mean age of 36 years and standard deviation of 11 years). Relationships between collateral ligament tensions during passive flexion and ATT were assessed via linear and nonlinear regressions. RESULTS:MCL tensions were greater following PS TKA than in the native knee at 15° and 30° of passive flexion, by a median of ≥27 N (p = 0.002), while the LCL tensions did not differ. Median tensions following PS TKA were greater in the MCL than in the LCL at 15°, 30°, and 90° of flexion, by ≥4 N (p ≤ 0.02). Median tensions in the MCL of the native knee were small (≤11 N) and did not exceed those in the LCL (p ≥ 0.25). A logarithmic relationship was identified between MCL tension and ATT following TKA. CONCLUSIONS:MCL tensions were greater following PS TKA with this typical nonconforming PS implant than in the native knee. Anterior laxity at 30° of flexion was highly sensitive to MCL tension during passive flexion following PS TKA but not in the native knee. CLINICAL RELEVANCE:Surgeons face competing objectives when performing PS TKA: they can either impart supraphysiological MCL tension to reduce anterior-posterior laxity or maintain native MCL tensions that lead to heightened anterior-posterior laxity, as shown in this study.