Early Recovery Outcomes in Patients Undergoing Contemporary Posterior Approach Total Hip Arthroplasty: Each Week Shows Progress.

Background: Little is known about patients' postoperative week-by-week progress after undergoing posterior approach total hip arthroplasty (THA) with regard to pain, function, return to work, and driving. Purpose: We sought to evaluate a large cohort of patients undergoing posterior approach THA with modified posterior hip precautions to better understand the trajectory of recovery. Methods: Patients at a single institution undergoing primary posterior approach THA by fellowship-trained arthroplasty surgeons were prospectively enrolled. Patient functional status and early rehabilitation recovery milestones were evaluated preoperatively and each week postoperatively for 6 weeks. Results: Of 312 patients who responded to weekly questionnaires, there were varying response rates per question. At 1 week after surgery, 15% (39/256) of respondents had returned to work, increasing to 57% (129/225) at week 6. At 6 weeks, 77% of patients (174/225) had returned to driving; 25% (56/225) were taking pain medication (including prescription opioids or nonsteroidal anti-inflammatory drugs); and 15% (34/225) were using assistive devices (down from 91%, 78%, 56%, 35%, and 27% at weeks 1, 2, 3, 4, and 5, respectively). Average postoperative Hip dysfunction and Osteoarthritis Outcome Score for Joint Replacement and Lower Extremity Functional Scale scores were significantly higher than preoperative scores. Respondents reported significantly less pain at each week postoperatively than the previous week. Conclusion: These findings suggest that there may be an expected pathway for recovery after posterior THA using perioperative pain protocols, modified postoperative precautions, and physical therapy protocols to improve patient outcomes after THA, with most patients returning to normal at 4 weeks. Defining the expected recovery timeline may help surgeons in counseling patients preoperatively and guiding their recovery.

Radiographic Findings Associated With Mild Hip Dysplasia in 3869 Patients Using a Deep Learning Measurement Tool.

Background: Hip dysplasia is considered one of the leading etiologies contributing to hip degeneration and the eventual need for total hip arthroplasty (THA). We validated a deep learning (DL) algorithm to measure angles relevant to hip dysplasia and applied this algorithm to determine the prevalence of dysplasia in a large population based on incremental radiographic cutoffs. Methods: Patients from the Osteoarthritis Initiative with anteroposterior pelvis radiographs and without previous THAs were included. A DL algorithm automated 3 angles associated with hip dysplasia: modified lateral center-edge angle (LCEA), Tönnis angle, and modified Sharp angle. The algorithm was validated against manual measurements, and all angles were measured in a cohort of 3869 patients (61.2 ± 9.2 years, 57.1% female). The percentile distributions and prevalence of dysplastic hips were analyzed using each angle. Results: The algorithm had no significant difference (P > .05) in measurements (paired difference: 0.3°-0.7°) against readers and had excellent agreement for dysplasia classification (kappa = 0.78-0.88). In 140 minutes, 23,214 measurements were automated for 3869 patients. LCEA and Sharp angles were higher and the Tönnis angle was lower (P < .01) in females. The dysplastic hip prevalence varied from 2.5% to 20% utilizing the following cutoffs: 17.3°-25.5° (LCEA), 9.4°-15.6° (Tönnis), and 41.3°-45.9° (Sharp). Conclusions: A DL algorithm was developed to measure and classify hips with mild hip dysplasia. The reported prevalence of dysplasia in a large patient cohort was dependent on both the measurement and threshold, with 12.4% of patients having dysplasia radiographic indices indicative of higher THA risk.

Anterior-Posterior Laxity in Midflexion After Posterior-Stabilized TKA Is Sensitive to MCL Tension in Passive Flexion: An in Vitro Biomechanical Study.

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.

Impact of Selective Posterior Cruciate Ligament Fiber Release on Femoral Rollback in Cruciate-Retaining Total Knee Arthroplasty: A Computational Study.

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.

Decreased Instability in High-Risk (Hip-Spine 2B) Patients After Modifications of Surgical Planning and Technique.

BACKGROUND: Patients undergoing primary total hip arthroplasty (THA) who have spinal deformity and a stiff spine are the highest-risk group for instability. Despite the increasing use of dual-mobility cups and large femoral heads, dislocation remains a major complication after THA. Preoperative planning becomes a critical aspect of ensuring precise component positioning within a safe zone. The purpose of this study was to investigate dislocation rates over a 9-year period. METHODS: A retrospective review of 4,731 THAs performed by 3 orthopaedic surgeons between January 2014 and March 2023 was performed. Spinopelvic measurements were conducted to determine the hip-spine classification group for each patient. Only patients classified as 2B (pelvic incidence-lumbar lordosis > 10° and Δsacral slope < 10°) were eligible. Both absolute and relative dislocation frequencies were then analyzed using time-series analysis techniques and Fisher's exact tests. RESULTS: A total of 281 hip-spine 2B patients undergoing primary THA were eligible for analysis (57% women; mean age, range: 66 years, 23 to 87; mean body mass index, range: 28, 16 to 45). The overall dislocation rate was 4.3%. Use of femoral head sizes ≥ 40 mm increased from 4% in 2014 to 2019 to 37% in 2020 to 2023 (P < .001), while the use of dual-mobility cups decreased from 100% in 2014 to 2019 to 37% in 2020 to 2023 (P < .001). Acetabular component planning was changed from the supine plane to the standing plane in February 2020. Those changes in surgical practice were notably correlated with a significant decrease in dislocation rates from 6.8% in 2014 to 2019 to 1.5% in 2020 to 2023 (P = .03). CONCLUSIONS: Our study demonstrates that the introduction of advanced preoperative THA planning to the standing plane, coupled with precise intraoperative technology for implant placement, can significantly reduce the risk of instability in high-risk THA patients. Notably, we observed a significant decrease in dislocation rates, which aligned with the shift in surgical practice. LEVEL OF EVIDENCE: IV.

Is Tibial Bone Mineral Density Related to Sex, Age, Preoperative Alignment, or Fixation Method in Primary Total Knee Arthroplasty?

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.

No Difference in Limb Alignment Between Kinematic and Mechanical Alignment Robotic-Assisted Total Knee Arthroplasty.

BACKGROUND: Individualized alignment techniques have gained major interest in an effort to increase satisfaction among total knee arthroplasty patients. This study aimed to compare postoperative alignment between kinematic alignment (KA) and mechanical alignment (MA) and assess whether KA significantly deviates from the principle of aligning the limb as close to neutral alignment as possible. METHODS: There were 234 patients who underwent robotic-assisted total knee arthroplasty using an unrestricted KA and a strict MA technique (KA: 145, MA: 89). The lateral distal femoral angle, medial proximal tibia angle, and the resultant arithmetic hip-knee-ankle angle (aHKA) were measured. The aHKA < 0 indicated varus alignment, while the aHKA > 0 indicated valgus knee alignment. The primary outcome was the frequency of cases that resulted in an aHKA of ± 4° of neutral (0°), as assessed on full-leg standing radiographs obtained at 6 weeks postoperatively. The secondary outcome was the change in coronal plane alignment of the knee classification type from preoperative to postoperative between the MA and KA groups. RESULTS: The mean preoperative aHKA was similar between the 2 groups (P = .19). The KA group had a mean postoperative aHKA of -1.4 ± 2.4°, while the MA group had a mean postoperative aHKA of -0.5 ± 2.1°. No significant difference in limb alignment was identified between KA and MA cases that resulted in hip-knee-ankle angle of ± 4° being neutral (91.7 versus 96.6%, P = .14). There were 97.2% of cases in the KA group that fell within the ± 5° range. The MA group was associated with a significantly higher rate of coronal plane alignment of the knee classification type change from preoperatively to postoperatively (P < .001). CONCLUSIONS: Kinematic alignment achieved similar postoperative aHKA compared to MA, and thus did not significantly deviate from the principle of aligning the limb as close to neutral alignment as possible. Surgeons should feel comfortable starting to introduce individualized alignment techniques. Without being restricted by boundaries, postoperative alignment will be within 5 degrees of neutral 97% of the time.

A novel computational workflow to holistically assess total knee arthroplasty biomechanics identifies subject-specific effects of joint mechanics on implant fixation.

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.

Variability of the femoral mechanical-anatomical axis angle and its implications in primary and revision total knee arthroplasty.

Aims: Distal femoral resection in conventional total knee arthroplasty (TKA) utilizes an intramedullary guide to determine coronal alignment, commonly planned for 5° of valgus. However, a standard 5° resection angle may contribute to malalignment in patients with variability in the femoral anatomical and mechanical axis angle. The purpose of the study was to leverage deep learning (DL) to measure the femoral mechanical-anatomical axis angle (FMAA) in a heterogeneous cohort. Methods: Patients with full-limb radiographs from the Osteoarthritis Initiative were included. A DL workflow was created to measure the FMAA and validated against human measurements. To reflect potential intramedullary guide placement during manual TKA, two different FMAAs were calculated either using a line approximating the entire diaphyseal shaft, and a line connecting the apex of the femoral intercondylar sulcus to the centre of the diaphysis. The proportion of FMAAs outside a range of 5.0° (SD 2.0°) was calculated for both definitions, and FMAA was compared using univariate analyses across sex, BMI, knee alignment, and femur length. Results: The algorithm measured 1,078 radiographs at a rate of 12.6 s/image (2,156 unique measurements in 3.8 hours). There was no significant difference or bias between reader and algorithm measurements for the FMAA (p = 0.130 to 0.563). The FMAA was 6.3° (SD 1.0°; 25% outside range of 5.0° (SD 2.0°)) using definition one and 4.6° (SD 1.3°; 13% outside range of 5.0° (SD 2.0°)) using definition two. Differences between males and females were observed using definition two (males more valgus; p < 0.001). Conclusion: We developed a rapid and accurate DL tool to quantify the FMAA. Considerable variation with different measurement approaches for the FMAA supports that patient-specific anatomy and surgeon-dependent technique must be accounted for when correcting for the FMAA using an intramedullary guide. The angle between the mechanical and anatomical axes of the femur fell outside the range of 5.0° (SD 2.0°) for nearly a quarter of patients.

Changing practice to a new-generation triple-taper collared femoral component reduces periprosthetic fracture rates after primary total hip arthroplasty.

Aims: Periprosthetic femoral fracture (PPF) is a major complication following total hip arthroplasty (THA). Uncemented femoral components are widely preferred in primary THA, but are associated with higher PPF risk than cemented components. Collared components have reduced PPF rates following uncemented primary THA compared to collarless components, while maintaining similar prosthetic designs. The purpose of this study was to analyze PPF rate between collarless and collared component designs in a consecutive cohort of posterior approach THAs performed by two high-volume surgeons. Methods: This retrospective series included 1,888 uncemented primary THAs using the posterior approach performed by two surgeons (PKS, JMV) from January 2016 to December 2022. Both surgeons switched from collarless to collared components in mid-2020, which was the only change in surgical practice. Data related to component design, PPF rate, and requirement for revision surgery were collected. A total of 1,123 patients (59.5%) received a collarless femoral component and 765 (40.5%) received a collared component. PPFs were identified using medical records and radiological imaging. Fracture rates between collared and collarless components were analyzed. Power analysis confirmed 80% power of the sample to detect a significant difference in PPF rates, and a Fisher's exact test was performed to determine an association between collared and collarless component use on PPF rates. Results: Overall, 17 PPFs occurred (0.9%). There were 16 fractures out of 1,123 collarless femoral components (1.42%) and one fracture out of 765 collared components (0.13%; p = 0.002). The majority of fractures (n = 14; 82.4%) occurred within 90 days of primary THA. There were ten reoperations for PPF with collarless components (0.89%) and one reoperation with a collared component (0.13%; p = 0.034). Conclusion: Collared femoral components were associated with significant decreases in PPF rate and reoperation rate for PPF compared to collarless components in uncemented primary THA. Future studies should investigate whether new-generation collared components reduce PPF rates with longer-term follow-up.

What Is the Role of a Periarticular Injection for Knee Arthroplasty Patients Receiving a Multimodal Analgesia Regimen Incorporating Adductor Canal and Infiltration Between the Popliteal Artery and Capsule of the Knee Blocks? A Randomized Blinded Placebo-Controlled Noninferiority Trial.

BACKGROUND: Optimal analgesic protocols for total knee arthroplasty (TKA) patients remain controversial. Multimodal analgesia is advocated, often including peripheral nerve blocks and/or periarticular injections (PAIs). If 2 blocks (adductor canal block [ACB] plus infiltration between the popliteal artery and capsule of the knee [IPACK]) are used, also performing PAI may not be necessary. This noninferiority trial hypothesized that TKA patients with ACB + IPACK + saline PAI (sham infiltration) would have pain scores that were no worse than those of patients with ACB + IPACK + active PAI with local anesthetic. METHODS: A multimodal analgesic protocol of spinal anesthesia, ACB and IPACK blocks, intraoperative ketamine and ketorolac, postoperative ketorolac followed by meloxicam, acetaminophen, duloxetine, and oral opioids was used. Patients undergoing primary unilateral TKA were randomized to receive either active PAI or control PAI. The active PAI included a deep injection, performed before cementation, of bupivacaine 0.25% with epinephrine, 30 mL; morphine; methylprednisolone; cefazolin; with normal saline to bring total volume to 64 mL. A superficial injection of 20 mL bupivacaine, 0.25%, was administered before closure. Control injections were normal saline injected with the same injection technique and volumes. The primary outcome was numeric rating scale pain with ambulation on postoperative day 1. A noninferiority margin of 1.0 was used. RESULTS: Ninety-four patients were randomized. NRS pain with ambulation at POD1 in the ACB + IPACK + saline PAI group was not found to be noninferior to that of the ACB + IPACK + active PAI group (difference = 0.3, 95% confidence interval [CI], [-0.9 to 1.5], P = .120). Pain scores at rest did not differ significantly among groups. No significant difference was observed in opioid consumption between groups. Cumulative oral morphine equivalents through postoperative day 2 were 89 ± 40 mg (mean ± standard deviation), saline PAI, vs 73 ± 52, active PAI, P = .1. No significant differences were observed for worst pain, fraction of time in severe pain, pain interference, side-effects (nausea, drowsiness, itching, dizziness), quality of recovery, satisfaction, length of stay, chronic pain, and orthopedic outcomes. CONCLUSIONS: For TKA patients given a comprehensive analgesic protocol, use of saline PAI did not demonstrate noninferiority compared to active PAI. Neither the primary nor any secondary outcomes demonstrated superiority for active PAI, however. As we cannot claim either technique to be better or worse, there remains flexibility for use of either technique.

Deep-Learning Automation of Preoperative Radiographic Parameters Associated With Early Periprosthetic Femur Fracture After Total Hip Arthroplasty.

BACKGROUND: The radiographic assessment of bone morphology impacts implant selection and fixation type in total hip arthroplasty (THA) and is important to minimize the risk of periprosthetic femur fracture (PFF). We utilized a deep-learning algorithm to automate femoral radiographic parameters and determined which automated parameters were associated with early PFF. METHODS: Radiographs from a publicly available database and from patients undergoing primary cementless THA at a high-volume institution (2016 to 2020) were obtained. A U-Net algorithm was trained to segment femoral landmarks for bone morphology parameter automation. Automated parameters were compared against that of a fellowship-trained surgeon and compared in an independent cohort of 100 patients who underwent THA (50 with early PFF and 50 controls matched by femoral component, age, sex, body mass index, and surgical approach). RESULTS: On the independent cohort, the algorithm generated 1,710 unique measurements for 95 images (5% lesser trochanter identification failure) in 22 minutes. Medullary canal width, femoral cortex width, canal flare index, morphological cortical index, canal bone ratio, and canal calcar ratio had good-to-excellent correlation with surgeon measurements (Pearson's correlation coefficient: 0.76 to 0.96). Canal calcar ratios (0.43 ± 0.08 versus 0.40 ± 0.07) and canal bone ratios (0.39 ± 0.06 versus 0.36 ± 0.06) were higher (P < .05) in the PFF cohort when comparing the automated parameters. CONCLUSIONS: Deep-learning automated parameters demonstrated differences in patients who had and did not have early PFF after cementless primary THA. This algorithm has the potential to complement and improve patient-specific PFF risk-prediction tools.

High degree of alignment precision associated with total knee arthroplasty performed using a surgical robot or handheld navigation.

PURPOSE: The purpose of this study was to compare the precision of bony resections during total knee arthroplasty (TKA) performed using different computer-assisted technologies. METHODS: Patients who underwent a primary TKA using an imageless accelerometer-based handheld navigation system (KneeAlign2®, OrthAlign Inc.) or computed tomography-based large-console surgical robot (Mako®, Stryker Corp.) from 2017 to 2020 were retrospectively reviewed. Templated alignment targets and demographic data were collected. Coronal plane alignment of the femoral and tibial components and tibial slope were measured on postoperative radiographs. Patients with excessive flexion or rotation preventing accurate measurement were excluded. RESULTS: A total of 240 patients who underwent TKA using either a handheld (n = 120) or robotic (n = 120) system were included. There were no statistically significant differences in age, sex, and BMI between groups. A small but statistically significant difference in the precision of the distal femoral resection was observed between the handheld and robotic cohorts (1.5° vs. 1.1° difference between templated and measured alignments, p = 0.024), though this is likely clinically insignificant. There were no significant differences in the precision of the tibial resection between the handheld and robotic groups (coronal plane 0.9° vs. 1.0°, n.s.; sagittal plane 1.2° vs. 1.1°, n.s.). There were no significant differences in the rate of overall precision between cohorts (n.s.). CONCLUSIONS: A high degree of component alignment precision was observed for both imageless handheld navigation and CT-based robotic cohorts. Surgeons considering options for computer-assisted TKA should take other important factors, including surgical principles, templating software, ligament balancing, intraoperative adjustability, equipment logistics, and cost, into account. LEVEL OF EVIDENCE: III.

Posterior-stabilized versus mid-level constraint polyethylene components in total knee arthroplasty.

Aims: Mid-level constraint designs for total knee arthroplasty (TKA) are intended to reduce coronal plane laxity. Our aims were to compare kinematics and ligament forces of the Zimmer Biomet Persona posterior-stabilized (PS) and mid-level designs in the coronal, sagittal, and axial planes under loads simulating clinical exams of the knee in a cadaver model. Methods: We performed TKA on eight cadaveric knees and loaded them using a robotic manipulator. We tested both PS and mid-level designs under loads simulating clinical exams via applied varus and valgus moments, internal-external (IE) rotation moments, and anteroposterior forces at 0°, 30°, and 90° of flexion. We measured the resulting tibiofemoral angulations and translations. We also quantified the forces carried by the medial and lateral collateral ligaments (MCL/LCL) via serial sectioning of these structures and use of the principle of superposition. Results: Mid-level inserts reduced varus angulations compared to PS inserts by a median of 0.4°, 0.9°, and 1.5° at 0°, 30°, and 90° of flexion, respectively, and reduced valgus angulations by a median of 0.3°, 1.0°, and 1.2° (p ≤ 0.027 for all comparisons). Mid-level inserts reduced net IE rotations by a median of 5.6°, 14.7°, and 17.5° at 0°, 30°, and 90°, respectively (p = 0.012). Mid-level inserts reduced anterior tibial translation only at 90° of flexion by a median of 3.0 millimetres (p = 0.036). With an applied varus moment, the mid-level insert decreased LCL force compared to the PS insert at all three flexion angles that were tested (p ≤ 0.036). In contrast, with a valgus moment the mid-level insert did not reduce MCL force. With an applied internal rotation moment, the mid-level insert decreased LCL force at 30° and 90° by a median of 25.7 N and 31.7 N, respectively (p = 0.017 and p = 0.012). With an external rotation moment, the mid-level insert decreased MCL force at 30° and 90° by a median of 45.7 N and 20.0 N, respectively (p ≤ 0.017 for all comparisons). With an applied anterior load, MCL and LCL forces showed no differences between the two inserts at 30° and 90° of flexion. Conclusion: The mid-level insert used in this study decreased coronal and axial plane laxities compared to the PS insert, but its stabilizing benefit in the sagittal plane was limited. Both mid-level and PS inserts depended on the MCL to resist anterior loads during a simulated clinical exam of anterior laxity.

Complication Rate After Primary Total Hip Arthroplasty Using the Posterior Approach and Enabling Technology: A Consecutive Series of 2,888 Hips.

BACKGROUND: Total hip arthroplasty (THA) is a safe and effective procedure; however, complications such as dislocation, fracture, and infection still occur. It is still unclear whether the dislocation rate via the posterior approach (PA) is better, equal, or worse than the direct anterior approach. Our aim was to report the primary THA dislocation rate via the PA using enabling technology in a large consecutive series of patients. METHODS: A retrospective cohort of 2,888 primary THAs were reviewed at a single, high-volume, academic institution from January 2018 to September 2021. All patients underwent a THA by 4 fellowship-trained orthopaedic surgeons through the PA with enabling technology. Overall dislocation and readmission rates within 90 days and up to 3 years were analyzed. RESULTS: Of the 2,888 procedures, a total of 39 patients had complications related to the surgery during the 3-year follow-up period. There were 10 patients (0.35%) who experienced a dislocation, with half undergoing surgical revision. Of the 39 patients who experienced complications, 37 (1.3%) were readmitted and 2 underwent revision during their hospital stay. Postoperative periprosthetic fractures were the most common cause for readmission and reoperation at a rate of 0.52% and 0.52%, respectively. CONCLUSION: The dislocation rate of 0.35% is one of the lowest reported rates via the PA at a mean follow up of 2.1 years and is comparable to previously published rates using alternate approaches. Using contemporary THA with enabling technology, the PA is a reliable approach with respect to dislocation and complication rates after primary THA.

An Interpretable Machine Learning Model for Predicting 10-Year Total Hip Arthroplasty Risk.

BACKGROUND: As the demand for total hip arthroplasty (THA) rises, a predictive model for THA risk may aid patients and clinicians in augmenting shared decision-making. We aimed to develop and validate a model predicting THA within 10 years in patients using demographic, clinical, and deep learning (DL)-automated radiographic measurements. METHODS: Patients enrolled in the osteoarthritis initiative were included. DL algorithms measuring osteoarthritis- and dysplasia-relevant parameters on baseline pelvis radiographs were developed. Demographic, clinical, and radiographic measurement variables were then used to train generalized additive models to predict THA within 10 years from baseline. A total of 4,796 patients were included [9,592 hips; 58% female; 230 THAs (2.4%)]. Model performance using 1) baseline demographic and clinical variables 2) radiographic variables, and 3) all variables was compared. RESULTS: Using 110 demographic and clinical variables, the model had a baseline area under the receiver operating curve (AUROC) of 0.68 and area under the precision recall curve (AUPRC) of 0.08. Using 26 DL-automated hip measurements, the AUROC was 0.77 and AUPRC was 0.22. Combining all variables, the model improved to an AUROC of 0.81 and AUPRC of 0.28. Three of the top five predictive features in the combined model were radiographic variables, including minimum joint space, along with hip pain and analgesic use. Partial dependency plots revealed predictive discontinuities for radiographic measurements consistent with literature thresholds of osteoarthritis progression and hip dysplasia. CONCLUSION: A machine learning model predicting 10-year THA performed more accurately with DL radiographic measurements. The model weighted predictive variables in concordance with clinical THA pathology assessments.

Deep Learning Phenotype Automation and Cohort Analyses of 1,946 Knees Using the Coronal Plane Alignment of the Knee Classification.

BACKGROUND: The Coronal Plane Alignment of the Knee (CPAK) classification allows for knee phenotyping which can be used in preoperative planning prior to total knee arthroplasty. We used deep learning (DL) to automate knee phenotyping and analyzed CPAK distributions in a large patient cohort. METHODS: Patients who had full-limb radiographs from a large arthritis database were retrospectively included. A DL algorithm was developed to automate CPAK knee alignment parameters including the lateral distal femoral, medial proximal tibia, hip-knee-ankle, and joint line obliquity angles. The algorithm was validated against a fellowship-trained arthroplasty surgeon. After applying the algorithm in a large patient cohort (n = 1,946 knees), the distribution of CPAK was compared across patient sex and baseline Kellgren-Lawrence (KL) scores. RESULTS: There was no significant difference in the CPAK angles (n = 140, P = .66-.98, inter-class correlation coefficient = 0.89-0.91) or phenotype classifications made by the algorithm and surgeon (P = .96). The deep learning algorithm measured the entire cohort (n = 1,946 knees, mean age 61 years [range, 46 to 80 years], 51% women) in < 5 hours. Women had more valgus CPAK phenotypes than men (P < .05). Patients who had higher KL grades at baseline (2 to 4) were more varus using the CPAK classification compared to lower KL grades (0 to 1) (P < .05). CONCLUSION: We applied an accurate, automated DL algorithm on a large patient cohort to determine knee phenotypes, helping to validate and strengthen the CPAK classification system. Analyses revealed that sex-specific and major bone loss adjustments may need to be accounted for when using this system.

Leg-Length Discrepancy Variability on Standard Anteroposterior Pelvis Radiographs: An Analysis Using Deep Learning Measurements.

BACKGROUND: Leg-length discrepancy (LLD) is a critical factor in component selection and placement for total hip arthroplasty. However, LLD radiographic measurements are subject to variation based on the femoral/pelvic landmarks chosen. This study leveraged deep learning (DL) to automate LLD measurements on pelvis radiographs and compared LLD based on several anatomically distinct landmarks. METHODS: Patients who had baseline anteroposterior pelvis radiographs from the Osteoarthritis Initiative were included. A DL algorithm was created to identify LLD-relevant landmarks (ie, teardrop (TD), obturator foramen, ischial tuberosity, greater and lesser trochanters) and measure LLD accurately using six landmark combinations. The algorithm was then applied to automate LLD measurements in the entire cohort of patients. Interclass correlation coefficients (ICC) were calculated to assess agreement between different LLD methods. RESULTS: The DL algorithm measurements were first validated in an independent cohort for all six LLD methods (ICC = 0.73-0.98). Images from 3,689 patients (22,134 LLD measurements) were measured in 133 minutes. When using the TD and lesser trochanter landmarks as the standard LLD method, only measuring LLD using the TD and greater trochanter conferred acceptable agreement (ICC = 0.72). When comparing all six LLD methods for agreement, no combination had an ICC>0.90. Only two (13%) combinations had an ICC>0.75 and eight (53%) combinations had a poor ICC (<0.50). CONCLUSION: We leveraged DL to automate LLD measurements in a large patient cohort and found considerable variation in LLD based on the pelvic/femoral landmark selection. This emphasizes the need for the standardization of landmarks for both research and surgical planning.

Novel Arthrometer for Quantifying In Vivo Knee Laxity in Three Planes Following Total Knee Arthroplasty.

BACKGROUND: Knee instability is a leading cause of dissatisfaction following total knee arthroplasty (TKA). Instability can involve abnormal laxity in multiple directions including varus-valgus (VV) angulation, anterior-posterior (AP) translation, and internal-external rotation (IER). No existing arthrometer objectively quantifies knee laxity in all three of these directions. The study objectives were to verify the safety and assess reliability of a novel multiplanar arthrometer. METHODS: The arthrometer utilized a five degree-of-freedom instrumented linkage. Two examiners each conducted two tests on the leg that had received a TKA of 20 patients (mean age 65 years (range, 53-75); 9 men, 11 women), with nine and eleven distinct patients tested at 3-month and 1-year postoperative time points, respectively. AP forces from -10 to 30 Newtons, VV moments of ±3 Newton-meters, and IER moments of ±2.5 Newton-meters were applied to each subject's replaced knee. Severity and location of knee pain during testing were assessed using a visual analog scale. Intraexaminer and interexaminer reliabilities were characterized using intraclass correlation coefficients. RESULTS: All subjects successfully completed testing. Pain during testing averaged 0.7 (out of possible 10; range, 0-2.5). Intraexaminer reliability was >0.77 for all loading directions and examiners. Interexaminer reliability and 95% confidence intervals were 0.85 (0.66-0.94), 0.67 (0.35-0.85), and 0.54 (0.16-0.79) in the VV, IER, and AP directions, respectively. CONCLUSION: The novel arthrometer was safe for evaluating AP, VV, and IER laxities in subjects who had received TKA. This device could be used to examine relationships between laxity and patient perceptions of knee instability.

Does a Uni "Feel Better" than a Total Knee? Not Necessarily, When Using Modern Implant Designs.

Background: When comparing functional outcomes of patients with unicompartmental knee arthroplasty (UKA) versus total knee arthroplasty (TKA), studies often report the UKA as the preferred procedure; however, recent improvements in the design of modern TKA implants have aimed at narrowing this gap. Purpose: We sought to compare the "feel" of modern TKA implants to that of UKA, using the Forgotten Joint Score (FJS), a validated patient-reported outcome measure. Methods: We performed a retrospective review of patients who underwent TKA and UKA at 2 institutions between 2014 and 2017. All UKA procedures were robotic arm-assisted with a single implant, "traditional TKAs" were performed using traditional posterior-stabilized implants, and "modern TKAs" were performed using posterior-stabilized implants with a modern design. Differences in FJS were assessed using 1-way analysis of variance and independent 2-sample t tests. Results: A total of 600 patients were included in our study, with 200 patients in each surgical subcategory. Mean age was 62.8 ± 10.2 years and mean body mass index was 29.9 ± 4.9. Modern TKA and UKA had similar FJS at 1 year. While modern TKA had a significantly higher FJS than traditional TKA, UKA did not have a significantly higher FJS than traditional TKA. Conclusion: Our retrospective analysis found no significant differences in the FJS of patients who underwent UKA and TKA with a modern design; however, both had superior scores than traditional TKA designs. This finding suggests that modern TKA designs may have the potential to achieve the natural feeling that is typically associated with joint-conserving surgeries such as UKA, although longer follow-up is necessary.