Robotic-arm-assisted lateral unicompartmental knee arthroplasty leads to high implant survival and patient satisfaction at mean 10-year follow-up.

BACKGROUND: There is a lack of literature reporting on long-term outcomes following robotic-arm-assisted lateral unicompartmental knee arthroplasty (UKA). This study assessed the long-term survivorship, patient-reported satisfaction and pain scores following robotic-arm-assisted lateral UKA for lateral compartment osteoarthritis (OA). METHODS: A single surgeon's database was reviewed to identify all patients who underwent robotic-arm-assisted lateral UKA with a cemented, fixed-bearing prosthesis prior to May 2015. Patients were contacted to determine implant survivorship, satisfaction and pain. Kaplan-Meier models were applied to analyse survival. RESULTS: A total of 77 knees (70 patients) with a mean follow-up of 10.2 ± 1.5 years (range: 8.1-13.3) were included. Five knees were revised, corresponding to a 10-year survivorship of 96.1% and estimated survival time of 12.7 ± 0.3 years (95% confidence interval: 12.2-13.2) with all-cause revision as the endpoint. Unexplained pain (40.0%) and progression of OA (40.0%) in contralateral compartments were the most reported reasons for revision. Among patients without revision, 94.4% were either satisfied or very satisfied with their lateral UKA and the average pain score was 1.1. CONCLUSION: Robotic-arm-assisted lateral UKA led to high implant survivorship and patient satisfaction, and low pain scores at long-term follow-up. Progression of OA in contralateral compartments and unexplained pain were the most frequent reasons for revision. These findings support the continued use of robotic-arm-assisted lateral UKA for lateral compartment OA; however, its clinical value over conventional techniques remains to be established in prospective comparative studies. LEVEL OF EVIDENCE: Therapeutic Level IV.

A Consecutive Series of Vancouver B2 Periprosthetic Femur Fractures Treated With Contemporary Monoblock Versus Modular Revision Stems: Clinical and Radiographic Outcomes.

BACKGROUND: Tapered fluted titanium (TFT) stems are the implant design of choice for managing Vancouver B2 periprosthetic femur fractures (PFFs), producing reliable results over the past few decades. The aim of this study was to compare the radiographic and clinical outcomes of Vancouver B2 PFFs treated with contemporary monoblock versus modular TFTs. METHODS: A consecutive series of 113 patients (72 women, 64%, mean age 70 years [range, 26 to 96]) who had a B2 PFF were treated with either a monoblock (n = 42) or modular (n = 71) TFT stem between 2008 and 2021. The mean body mass index was 30 ± 7. The mean follow-up was 2.9 years. A radiographic review was performed to assess leg length and offset restoration, endosteal cortical contact length, and stem subsidence. Kaplan-Meier analyses were used to determine survivorship without revision, reoperation, or dislocation. RESULTS: There was no difference in the restoration of leg length (0.3 ± 8.0 mm) or offset (2.8 ± 8.2 mm) between the monoblock and modular cohorts (P > .05). Mean endosteal cortical contact length (47.2 ± 26.6 versus 46.7 ± 2 6.4 mm, P = .89) and stem subsidence (2.7 ± 3.5 versus 2.4 ± 3.2 mm, P = .66) did not differ. No difference in patient-reported outcome measures (Hip Disability and Osteoarthritis Outcome Score-Joint Replacement; Veterans RAND 12 Item Health Survey Physical and Mental; visual analog score; and Lower Extremity Activity Scale) between the groups was observed. Survivorship at 2 years free from reoperation, revision, and dislocation was 90.4, 90.3, and 97.6%, respectively, for the monoblock cohort; and 84.0, 86.9, and 90.0%, respectively, for the modular cohort. CONCLUSIONS: No significant differences in radiographic or clinical outcomes were observed between patients treated with monoblock or modular TFTs in this large series of B2 PFFs.

Rapid lumbar MRI protocol using 3D imaging and deep learning reconstruction.

BACKGROUND AND PURPOSE: Three-dimensional (3D) imaging of the spine, augmented with AI-enabled image enhancement and denoising, has the potential to reduce imaging times without compromising image quality or diagnostic performance. This work evaluates the time savings afforded by a novel, rapid lumbar spine MRI protocol as well as image quality and diagnostic differences stemming from the use of an AI-enhanced 3D T2 sequence combined with a single Dixon acquisition. MATERIALS AND METHODS: Thirty-five subjects underwent MRI using standard 2D lumbar imaging in addition to a "rapid protocol" consisting of 3D imaging, enhanced and denoised using a prototype DL reconstruction algorithm as well as a two-point Dixon sequence. Images were graded by subspecialized radiologists and imaging times were collected. Comparison was made between 2D sagittal T1 and Dixon fat images for neural foraminal stenosis, intraosseous lesions, and fracture detection. RESULTS: This study demonstrated a 54% reduction in total acquisition time of a 3D AI-enhanced imaging lumbar spine MRI rapid protocol combined with a sagittal 2D Dixon sequence, compared to a 2D standard-of-care protocol. The rapid protocol also demonstrated strong agreement with the standard-of-care protocol with respect to osseous lesions (κ = 0.88), fracture detection (κ = 0.96), and neural foraminal stenosis (ICC > 0.9 at all levels). CONCLUSION: 3D imaging of the lumbar spine with AI-enhanced DL reconstruction and Dixon imaging demonstrated a significant reduction in imaging time with similar performance for common diagnostic metrics. Although previously limited by long postprocessing times, this technique has the potential to enhance patient throughput in busy radiology practices while providing similar or improved image quality.

Proximal bone block with distal screw trajectory improves mechanical stability during distalization tibial tubercle osteotomy.

PURPOSE: The purpose of this study was to quantify differences in mechanical stability of a wedge-shaped distalization tibial tubercle osteotomy (TTO) with a standard technique, versus a modified technique with use of a proximal bone block and distally angled screw trajectory. METHODS: Ten fresh-frozen cadaver lower extremity specimens (five matched pairs) were utilized. Within each specimen pair, one specimen was randomly assigned to undergo a standard distalization osteotomy fixed with two bicortical 4.5-mm screws oriented perpendicular to the long axis of the tibia, and the other to undergo a distalization osteotomy with modified fixation utilizing a proximal bone block and distally angled screw trajectory. Each specimen's patella and tibia were mounted on a servo-hydraulic load frame using custom fixtures (MTS Instron). The patellar tendon was dynamically loaded to 400 N at a rate of 200 N/second for 500 cycles. Following the cyclic loading, loading to failure was done at 25 mm/min. RESULTS: The modified distalization TTO technique demonstrated significantly higher average load to failure compared to the standard distalization TTO technique (1339 N vs. 844.1 N, p < 0.001). Average maximum tibial tubercle displacement during cyclic loading was significantly smaller in the modified TTO technique group compared to the standard TTO technique (1.1 mm vs. 4.7 mm, p < 0.001). CONCLUSION: This study demonstrates that distalization TTO utilizing a modified technique with a proximal bone block and distally aimed screws is biomechanically superior to standard distalization TTO without proximal bone block and screw trajectory perpendicular to the long axis of the tibia. This increased stability may aid in reducing the reported higher complication rates (including loss of fixation, delayed union and nonunion) following distalization TTO, although future clinical outcome studies are warranted.

The Risk Assessment and Prediction Tool (RAPT) Score Predicts Discharge Destination, Length of Stay, and Postoperative Mobility After Total Joint Arthroplasty.

BACKGROUND: Predicting an arthroplasty patient's discharge disposition, length of stay (LOS), and physical function is helpful because it allows for preoperative patient optimization, expectation management, and discharge planning. The goal of this study was to evaluate the ability of the Risk Assessment and Prediction Tool (RAPT) score to predict discharge destination, LOS, and postoperative mobility in patients undergoing primary total knee arthroplasty (TKA) and total hip arthroplasty (THA). METHODS: Primary unilateral TKAs (n = 9,064) and THAs (n = 8,649) performed for primary osteoarthritis at our institution from 2018 to 2021 (excluding March to June 2020) were identified using a prospectively maintained institutional registry. We evaluated the associations between preoperative RAPT score and (1) discharge destination, (2) LOS, and postoperative mobility as measured by (3) successful ambulation on the day of surgery and (4) Activity Measure for Post-Acute Care (AM-PAC) "6-Clicks" score. RESULTS: On multivariable analyses adjusting for multiple covariates, every one-point increase in RAPT score among TKA patients was associated with a 1.82-fold increased odds of home discharge (P < .001), 0.22 days shorter LOS (P < .001), 1.13-fold increased odds of ambulating on postoperative day 0 (P < .001), and 0.25-point higher Activity Measure for Post-Acute Care score (P < .001). Similar findings were seen among THAs. A RAPT score of 8 or higher was the most sensitive and specific cutoff to predict home discharge. CONCLUSION: Among nearly 18,000 TKA and THA patients, RAPT score was predictive of discharge disposition, LOS, and postoperative mobility. A RAPT score of 8 or higher was the most sensitive and specific cutoff to predict discharge to home. In contrast to prior studies of the RAPT score which have grouped TKAs and THAs together, this study ran separate analyses for TKAs and THAs and found that THA patients seemed to perform better than TKA patients with equal RAPT scores, suggesting that RAPT may behave differently between TKAs and THAs, particularly in the intermediate risk RAPT range.

Ultrasound of the distal biceps brachii tendon using four approaches: reproducibility and reader preference.

OBJECTIVES: To determine which sonographic appearance of the distal biceps brachii tendon (DBBT) is preferred by readers, and if images obtained by two different operators are reproducible. METHODS: We performed an IRB-approved prospective sonographic evaluation of the DBBT in 50 healthy elbows using four different approaches (anterior, lateral, medial, posterior) performed by two operators. Five musculoskeletal radiologists independently reviewed the images, and ranked the four approaches based on overall appearance of echogenicity of the tendon, visualized length, and visualization of the insertion. RESULTS: The medial approach was preferred in 79.6% of elbows, anterior in 17.6%, lateral in 2.8%, and the posterior approach was never preferred. The difference was statistically significant (P < 0.001). Kappa values for the five readers were 0.61 to 0.8 for choosing the images produced by the medial approach. CONCLUSION: The appearance of the DBBT using the medial approach is preferred by readers and is reproducible between different operators.

The Arthroscopic Surgery Skill Evaluation Tool Global Rating Scale is a Valid and Reliable Adjunct Measure of Performance on a Virtual Reality Simulator for Hip Arthroscopy.

PURPOSE: The purpose of this study is to further evaluate the construct validity and interobserver reliability of a hip arthroscopy virtual simulator using the Arthroscopic Surgery Skill Evaluation Tool (ASSET) global rating scale. METHODS: Thirty participants (23 male/7 female) completed a diagnostic arthroscopy and a loose body retrieval simulation on the VirtaMed Arthros Hip Simulator (Zurich, Switzerland) twice at a minimum of 1 week apart. Subjects consisted of 12 novices (medical students, postgraduate year [PGY] 1-2), 5 intermediate trainees (PGY3-4), 9 senior trainees (PGY5 and fellows), and 4 attending faculty. Simulator metrics were recorded and then compiled to generate a total simulator score (TSS). The loose body retrieval was graded using the ASSET scoring tool. Inter-rater and intrarater reliability for the ASSET for 2 blinded raters and construct validity of the ASSET and the TSS were calculated. Correlation between the TSS, ASSET and individual simulator metrics was determined. RESULTS: Prior simulation experience (P ≤ 0.01) correlated with higher TSS and higher ASSET, while video game experience correlated with higher TSS on the diagnostic module only (P = 0.004). There was a significant difference in ASSET score among all experience groups (P < 0.04). Novices had the lowest mean ASSET whereas experts had the highest mean ASSET with a difference of 17.4 points. Overall performance on the surgical module significantly correlated with the ASSET score (r = 0.444, P = 0.016). There was a significant positive correlation among higher ASSET and number of loose bodies retrieved, operation time, camera path and grasper path length, and percentage of cartilage injury. ASSET demonstrated excellent intrarater reliability and showed substantial or better inter-reliability in 8 of 9 domains. CONCLUSION: The VirtaMed hip arthroscopy simulator demonstrated good construct validity and excellent reliability for simulator-based metrics and ASSET score. Use of both simulator metrics and ASSET offers a more comprehensive performance assessment on hip arthroscopy simulation than either measure alone. CLINICAL RELEVANCE: As virtual reality simulation for arthroscopy becomes more commonplace in orthopaedic training, evaluation of the most effective objective and subjective measures of performance is necessary to optimize simulation training.

The AAHKS Best Podium Presentation Research Award: Comparing the Efficacy of Irrigation Solutions on Staphylococcal Biofilm Formed on Arthroplasty Surfaces.

BACKGROUND: A diverse array of antibacterial solutions is utilized by orthopedic surgeons in an attempt to disperse bacterial biofilm. Few studies compare these agents against biofilm grown on clinically relevant orthopedic biomaterials, such as plastic, acrylic cement, and porous titanium. METHODS: MSSA biofilm was grown on plastic 48-well plates, polymethylmethacrylate cement beads and porous Ti-6Al-4V acetabular screw caps. Antibacterial solutions were tested according to manufacturer guidance and included: isotonic saline, vancomycin (1 mg/mL), polymyxin-bacitracin (500,000 U/L-50,000 U/L), povidone-iodine 0.3%, povidone-iodine 10%, a 1:1 combination of povidone-iodine 10% & 4% hydrogen peroxide, polyhexamethylene biguanide (PHMB) and betaine 0.04%, a commercial solution containing chlorhexidine gluconate (CHG) 0.05%, and a commercial solution containing benzalkonium chloride and ethanol. Twenty four and 72-hour biofilms were exposed to solutions for 3 minutes to reproduce intraoperative conditions. Solution efficacy was measured through sonication of treated surfaces followed by counting colony forming units and validated with a resazurin assay to assess cell viability. Experiments were performed in triplicate and repeated at least once. A three-fold log reduction in CFU counts versus controls was considered as a measure of solution efficacy. RESULTS: Saline, vancomycin and polymyxin-bacitracin were ineffective compared to other solutions against planktonic MSSA. Povidone-iodine 10% and a 1:1 solution of povidone-iodine 10% and 4% hydrogen peroxide were the only effective solutions against biofilm across all three surfaces and time points. CONCLUSION: Commercial antibacterial solutions vary significantly in their efficacy against MSSA biofilm. Efficacy globally decreased as biofilm maturity increased. Increased solution cost did not confer increased efficacy.

Early Recovery Outcomes in Patients Undergoing Total Hip Arthroplasty Through a Posterior Approach With Modified Postoperative Precautions.

BACKGROUND: Recent data suggest that a modified, more lenient set of precautions after total hip arthroplasty (THA) performed through the posterolateral approach may safely allow more patient movement and exercise in the immediate postoperative period. We hypothesize that 1) patients undergoing THA given modified precautions will demonstrate a fast-track return to functional activity and 2) wrist-based activity trackers will provide valuable information on postoperative activity levels. METHODS: We prospectively enrolled patients undergoing THA. Patients were given a wrist-based, commercially available activity tracker to wear 1 week preoperatively and 6 weeks postoperatively. Postoperative hip precautions included only the avoidance of the "leg-shaving" position of combined hip flexion, adduction, and internal rotation. Linear mixed models were used to analyze the change in steps and Hip Disability and Osteoarthritis Outcome Score-Junior (HOOS)-JR data. Pearson correlation coefficients were used to describe the relationship between average steps and HOOS-JR scores over time. RESULTS: Eighty-two patients were enrolled. Seventy-four percent returned to work by week 4. Seventy-six percent of left THA patients returned to driving by week 4. At 6 weeks, 23% of survey respondents were taking pain medication and 26% were using assistive devices. Average daily steps were 1098 at week 1, 2491 at week 2, 4130 at week 3, 4850 at week 4, 5712 at week 5, and 6069 at week 6. A significant correlation (R: -0.981) was found between increased weekly steps and improved HOOS-JR scores after THA (P < .001). CONCLUSION: Defining expected recovery timelines for patients undergoing THA helps surgeons counsel their patients preoperatively. Our study demonstrates an expected pathway for recovery after THA by using modified precautions that will be more clearly outlined with ongoing clinical data analysis.

Medial Patellofemoral Ligament Isometry in the Setting of Patella Alta.

PURPOSE: To investigate alterations in technique for medial patellofemoral ligament (MPFL) reconstruction in the setting of patella alta and describe the effect of these alterations on MPFL anatomometry. METHODS: Ten cadaveric knees were used. Four candidate femoral attachment sites of MPFL were tested. The attachment sites were Schottle's point (SP), 5 mm distal to SP, 5 mm proximal to SP, and 10 mm proximal to SP. A suture anchor was placed at the upper 40% of the medial border of the patella with the emanating suture used to simulate the reconstructed ligament. MPFL maximum length change was calculated through a range of motion between 0° and 110°. Recordings at all 4 candidate femoral attachments sites were repeated after a flat tibial tubercle osteotomy and transfer to achieve alta as measured by the Caton-Deschamps Index (CDI) of 1.3, 1.4, and 1.5. RESULTS: The 10 specimens had an average CDI of 0.99, range 0.87 to 1.16. In the native tibial tubercle condition, SP was more isometric through 20° to 70° range of motion, or anatomometric, than any other candidate femoral attachment location. With patella alta with a CDI of 1.3 and 1.4, attachment site 5 mm proximal to SP exhibited more anatomometry than SP. With patella alta with a CDI of 1.5, attachment site 10 mm proximal to SP exhibited more anatomometry than SP. CONCLUSIONS: Increased patella alta significantly alters MPFL anatomometry. With increasing degrees of patella alta, more proximal candidate femoral attachment sites demonstrate decreased change in length compared with SP. None of the varied femoral attachments produced anatomometry over the entirety of the flexion range from 20° to 70°, suggesting that in cases of significant patella alta, proximalization the femoral attachment site of MPFL reconstruction may be necessary to achieve an anatomometric MPFL reconstruction. CLINICAL RELEVANCE: A standardized, isolated MPFL reconstruction may be prone to failure in the setting of patella alta, given the anisometry demonstrated. Alternative femoral attachment sites for MPFL reconstruction should be considered in these patients.

Aseptic Loosening at the Tibia in Total Knee Arthroplasty: A Function of Cement Mantle Quality?

BACKGROUND: Aseptic loosening remains one of the leading causes for failure of total knee arthroplasty (TKA). We sought to identify early radiographic measures that may associate with aseptic tibial component loosening, emphasizing systematic evaluation of the cement mantle. METHODS: All TKA revisions from 2007 to 2015 with the primary indication of tibial aseptic loosening were identified using in an institutional implant retrieval database. After exclusion criteria, 61 TKAs comprised the study group. A matched control group of 59 TKAs that had not failed at a minimum of 3 years was identified for comparison. Radiographic analysis on all 6-week postoperative radiographs included angulation of components, cement penetration depth, and presence of radiolucency at the implant-cement and bone-cement interfaces. Groups were compared with Student's t-test, chi-squared test, and Mann-Whitney U-test. A final multivariable logistic regression model was formed for the outcome of aseptic loosening. RESULTS: On multivariable analysis, failure was associated with a greater number of zones with cement penetration <2 mm (5.6 vs 3.4 zones, odds ratio [OR] 1.89, P < .001), increasing percent involvement of radiolucency at the implant-cement interface (8.7% vs 3.1%, OR = 1.15, P = .001), and increased varus alignment of the tibial component (1.5° vs 0°, OR = 1.35, P = .014). A greater number of zones with a radiolucent line at the bone-cement interface did not significantly associate (1.1 vs 0.3, P = .091). CONCLUSION: Our results suggest that radiographic indicators of poor cement mantle quality associate with later aseptic loosening. This emphasizes the need for surgeons to perform careful cement technique in order to reduce the risk of TKA failure. LEVEL OF EVIDENCE: III (Case-control).

High-Sensitivity C-Reactive Protein: Retrospective Study of Potential Blood Biomarker of Inflammation in Acute Mild Traumatic Brain Injury.

OBJECTIVE: A panel of biomarkers is needed to definitively diagnose mild traumatic brain injury (mTBI). There is a clear role for the inclusion of an inflammatory biomarker. This study looked to find a relationship between high sensitivity C-reactive protein (hsCRP), an inflammatory biomarker, and mTBI. SETTING: Neurology department of high-volume tertiary orthopedic hospital. PARTICIPANTS: Individuals diagnosed with mTBI (n = 311, age 21 ± 12 years, 53% female). DESIGN: Retrospective cohort study. MAIN MEASURES: hsCRP levels; postconcussive symptoms; demographics. RESULTS: Continuous hsCRP levels were transformed into quartiles, as defined by less than 0.200 mg/L for quartile 1 (Q1); 0.200 to 0.415 mg/L for quartile 2 (Q2); 0.415 to 1.100 mg/L for quartile 3 (Q3); and greater than 1.100 mg/L for quartile 4 (Q4). Mean hsCRP was elevated in the cohort of individuals who presented within 1 week of injury and was found to significantly decrease between the first visit and 4 weeks postinjury (P = .016). Initial hsCRP level was positively correlated with age (r = 0.163, P = .004), and age significantly increased between quartiles (P = .013). Patients with increased age (odds ratio: 3.48) and those who endorsed headache (odds ratio: 3.48) or fatigue (odds ratio: 2.16) were significantly associated with increased risk of having an hsCRP level in Q4. CONCLUSION: hsCRP may be a viable addition to acute and longitudinal biomarker panels for diagnosis and prognosis of mTBI.

Head Impact Burden and Change in Neurocognitive Function During a Season of Youth Football.

OBJECTIVE: To determine the association of repetitive subconcussive head impacts with functional outcomes in primary and high school tackle football players. SETTING: Youth football fields and an outpatient sports neurology clinic. PARTICIPANTS: A total of 112 primary school (n = 55, age 9-12 years) and high school (n = 57, age 15-18 years) football players. DESIGN: A prospective cohort study. MAIN MEASURES: Helmet-based sensors were used to record head impacts during practices and games during the 2016 football season. Impact g-forces were summed to yield a measure of cumulative impact. History of self-reported premorbid medical diagnoses was obtained preseason. Players completed assessments of a variety of outcomes both pre- and postseason: neuropsychological test performance, symptoms, vestibular and ocular-motor screening, balance, parent-completed attention-deficit hyperactivity disorder (ADHD) symptoms, and self-reported behavioral adjustment. RESULTS: Average cumulative impact was 3700 (standard deviation = 2700) g-forces for the season and did not differ between age groups (P = .594). Cumulative impact did not predict pre- to postseason change scores on any outcome measures (all P > .05). Instead, younger age group and reported history of premorbid ADHD predicted change scores on several cognitive testing measures and parent-reported ADHD symptoms, while reported history of premorbid anxiety and depression predicted change scores on symptom reporting. CONCLUSIONS: In youth tackle football, subconcussive head impacts sustained over the course of a single season may not be associated with neurocognitive functional outcomes. The absence of a significant association may reflect the relatively short follow-up interval, and signals the need for studies across multiple seasons.

Risk Factors for Nerve Injury After Total Hip Arthroplasty: A Case-Control Study.

BACKGROUND: Postsurgical acute nerve injury is rare but potentially devastating following total hip arthroplasty (THA). Previous literature suggests a wide range of incidence from 0.1% to 7.6%. Confirmed risk factors for these injuries remain unclear. METHODS: THA patients at our institution who developed nerve injury during their admission for THA between January 1, 1998, and December 31, 2013, were systematically identified and matched with 2 control subjects by surgical date. Relevant patient and surgical data were obtained through review of patient charts and electronic health records. We identified potential risk factors and calculated odds ratios (OR) using a conditional logistic regression model with a parsimonious stepwise approach. RESULTS: We identified 93 nerve injuries in 43,761 THAs (0.21%). The mean age of cases was 63 years. Adjusting for other factors in the model, patients <45 years were found to be at increased risk of developing nerve injury (OR, 7.17; P = .033). Similarly, patients with a history of tobacco use (OR, 1.90; P = .030) and a history of spinal surgery or disease (OR, 10.06; P < .001) were also associated with increased risk of nerve injury. For every 30-minute increase in surgery time after 1 hour, risk of nerve injury risk increased (OR, 1.48; P = .034). Assignment as first operative case of the morning was associated with a decreased risk of nerve injury (OR, 0.37, P = .043). CONCLUSION: This study demonstrates that nerve injury is a rare complication following THA at our institution. We found risk factors that are possibly modifiable factors such as lumbar spine disease, smoking, and time of surgical scheduling.

Risk factors for acute nerve injury after total knee arthroplasty.

INTRODUCTION: In this we study identified potential risk factors for post-total knee arthroplasty (TKA) nerve injury, a catastrophic complication with a reported incidence of 0.3%-1.3%. METHODS: Patients who developed post-TKA nerve injury from 1998 to 2013 were identified, and each was matched with 2 controls. A multivariable logistic regression model was built to calculate odds ratios (ORs). RESULTS: Sixty-five nerve injury cases were identified in 39,990 TKAs (0.16%). Females (OR 3.28, P = 0.003) and patients with history of lumbar pathology (OR 6.12, P = 0.026) were associated with increased risk of nerve injury. Tourniquet pressure < 300 mm Hg and longer duration of anesthesia may also be risk factors. DISCUSSION: Surgical planning for females and patients with lumbar pathology should be modified to mitigate their higher risk of neurologic complications after TKA. Our finding that lower tourniquet pressure was associated with higher risk of nerve injury was unexpected and requires further investigation. Muscle Nerve 57: 946-950, 2018.

Anisometry of Medial Patellofemoral Ligament Reconstruction in the Setting of Increased Tibial Tubercle-Trochlear Groove Distance and Patella Alta.

PURPOSE: To assess the impact elevated tibial tubercle-trochlear groove (TT-TG) distance and patella height, as measured by the Caton-Deschamps Index (CDI), have on the isometry of a reconstructed medial patellofemoral ligament (MPFL). METHODS: Nine fresh-frozen cadaveric knees were placed on a custom testing fixture, with a fixed femur and a mobile tibia. A suture fixed to the MPFL origin on the patella and free to move at the Schöttle point on the femur represented a reconstructed MPFL. A local coordinate system was established, and retroreflective markers attached to the suture quantified MPFL length changes by use of a 3-dimensional motion capture system. The tubercle was transferred to create TT-TG distances of 20 mm and 25 mm and CDIs of 1.2 and 1.4 (patella alta). Recordings of the MPFL suture length change as the knee was brought through a range of motion were made using all combinations of tubercle anatomy in a randomized order for each specimen. A generalized estimating equation modeling technique was used to analyze and control for the clustered nature of the data. RESULTS: Knees with native tibial tubercle anatomy showed MPFL isometry through 20° to 70° range of motion. Tibial tubercle lateralization (increased TT-TG distance) significantly altered MPFL isometry with a TT-TG distance of 20 mm (P < .0001). Patella alta significantly altered MPFL isometry with a CDI of 1.2 (P = .0182). The interaction of tibial tubercle lateralization combined with patella alta significantly increased the amount of anisometry seen in the reconstructed MPFL (P < .001). CONCLUSIONS: Increased tibial tubercle lateralization and patella alta produce anisometry in an MPFL reconstruction using currently recommended landmarks, leading to potentially increased graft tension and potential failure. CLINICAL RELEVANCE: Tibial tubercle transfer should be considered when performing an MPFL reconstruction for recurrent patellofemoral instability in the setting of significant patella alta and an elevated TT-TG distance-especially when both are present-because an isolated MPFL reconstruction will be prone to failure given the anisometry shown in this study.

Magnetic Resonance Imaging Validation of Tibial Tubercle Transfer Distance in the Fulkerson Osteotomy: A Clinical and Cadaveric Study.

PURPOSE: To validate the medialization and anteriorization distances, and the osteotomy angle of anteromedialization tibial tubercle osteotomies using postoperative axial imaging. METHODS: From March 2004 to August 2015, 117 consecutive patients who underwent anteromedialization osteotomies of the tibial tubercle by a single surgeon were identified. Only patients with pre- and postoperative magnetic resonance imaging (MRI) studies were included. Using MRI multiplanar reformats, distances that the tibial tubercle was translated medially (medialization) and anteriorly (anteriorization) were measured. In addition, the osteotomy angle was measured on the postoperative MRI. The measured values were compared with intraoperative estimates. Tibial tubercle osteotomies were then performed on 3 cadaveric knee specimens and imaged with pre- and postprocedure MRIs to correlate intraoperative measurements with MRI findings. RESULTS: A total of 40 patients (41 knees) (34.2%) had both pre- and postoperative MRIs and were included. Compared with intraoperative assessment, MRI measured medialization values average 94.7% (standard deviation [SD] 37.7) of dictated values (P = .1). MRI measured anteriorization averaged less than half of dictated values (48.9%, SD 18.2%, P < .0001). MRI measured osteotomy angles averaged 67.2% of dictated values (SD 50.3%, P < .0001). The steepest osteotomy angle that could be performed without violating the posterior cortex and/or endangering the posterior neurovascular structures was 46.3°. CONCLUSIONS: Surgeons often overestimate both the anteriorization distance and the osteotomy angle in anteromedialization tibial tubercle osteotomies. The steepest osteotomy angle is less than the 60° described in the literature. Modifications should be considered when more anteriorization is desired with tubercle transfers. LEVEL OF EVIDENCE: Level IV, retrospective case series.

Midterm Survivorship and Patient Satisfaction of Robotic-Arm-Assisted Medial Unicompartmental Knee Arthroplasty: A Multicenter Study.

BACKGROUND: Studies have showed improved accuracy of lower leg alignment, precise component position, and soft-tissue balance with robotic-assisted unicompartmental knee arthroplasty (UKA). No studies, however, have assessed the effect on midterm survivorship. Therefore, the purpose of this prospective, multicenter study was to determine midtem survivorship, modes of failure, and satisfaction of robotic-assisted medial UKA. METHODS: A total of 473 consecutive patients (528 knees) underwent robotic-arm-assisted medial UKA surgery at 4 separate institutions between March 2009 and December 2011. All patients received a fixed-bearing, metal-backed onlay tibial component. Each patient was contacted at minimum 5-year follow-up and asked a series of questions to determine survival and satisfaction. Kaplan-Meier method was used to determine survivorship. RESULTS: Data were collected for 384 patients (432 knees) with a mean follow-up of 5.7 years (5.0-7.7). The follow-up rate was 81.2%. In total, 13 revisions were performed, of which 11 knees were converted to total knee arthroplasty and in 2 cases 1 UKA component was revised, resulting in 97% survivorship. The mean time to revision was 2.27 years. The most common failure mode was aseptic loosening (7/13). Fourteen reoperations were reported. Of all unrevised patients, 91% was either very satisfied or satisfied with their knee function. CONCLUSION: Robotic-arm-assisted medial UKA showed high survivorship and satisfaction at midterm follow-up in this prospective, multicenter study. However, in spite of the robotic technique, early fixation failure remains the primary cause for revision with cemented implants. Comparative studies are necessary to confirm these findings and compare to conventional implanted UKA and total knee arthroplasty.

Low Vitamin D Levels are Associated With Need for Surgical Correction of Pediatric Fractures.

BACKGROUND: There is growing concern over the relationship between the severity of pediatric fractures and low vitamin D [25-hydroxyvitaminD (25(OH)D)] status. OBJECTIVE: Compare 25(OH)D levels and lifestyle of children with fractures to nonfracture controls to determine if 25(OH)D levels are associated with fractures and if there is a 25(OH)D fragility fracture threshold. METHODS: Pediatric fracture and nonfracture controls were included. Bone health survey and medical record data were analyzed. Fractures were categorized using the Abbreviated Injury Scale (AIS). AIS 3 fractures were identified as fractures that required surgical intervention. Univariate and multivariable ordinal regression analyses were performed to identify potential risk factors for increased fracture severity. RESULTS: A total of 369 fracture patients and 662 nonfracture controls aged 18 years and younger were included. Both groups' 25(OH)D levels were comparable. 25(OH)D was 27.5±8.9 in the fracture group compared with 27.4±9.1 ng/mL in nonfracture controls (P=0.914). AIS 3 fractures had lower 25(OH)D levels (24.6±9.3 ng/mL) versus AIS 1 and 2 (30.0±10.8 and 28.3±8.4, respectively, P=0.001). Univariate correlations for AIS severity were found with age (P=0.015) and outdoor playtime (P=0.042). Adjusted odds ratios for 25(OH)D levels <12 ng/mL was 55.4 (P=0.037), 25(OH)D between 12 and 20 ng/mL was 6.7 (P=0.039), 25(OH)D between 20 and 30 ng/mL was 2.8 (P=0.208), and 25(OH)D between 30 and 40 was 1.7 (P=0.518). CLINICAL RELEVANCE: Occurrence of a pediatric fracture was not associated with 25(OH)D levels in our study. However, children with lower vitamin D levels were found to be at higher risk for more severe fractures. Early evidence suggests that the target serum level for 25(OH)D should be at least 40 ng/mL in patients less than 18 years of age as the relative risk of more severe fractures increased as 25(OH)D levels decreased <40 ng/mL. LEVEL OF EVIDENCE: Level III.

Focal osteonecrosis in the femoral head following stable anatomic fixation of displaced femoral neck fractures.

INTRODUCTION: Femoral head (FH) osteonecrosis (ON) and subsequent segmental collapse is a major concern following displaced femoral neck fractures (FNF). We aimed to quantify residual perfusion to the FH following FNF and evaluate the viability of the FH overtime after surgical fixation. MATERIALS AND METHODS: Twenty-three patients with FNF underwent dynamic contrast-enhanced (DCE)-MRI to estimate bone perfusion in the FH, using the contralateral side as control. Following open anatomic reduction and a length/angle-stable fixation, a special MRI sequence evaluated the FH for ON changes over time at 3 and 12 months after surgery. RESULTS: We found significant compromise of both arterial inflow [83.1%-initial area under the curve (IAUC) and 73.8%-peak) and venous outflow (243.2%-elimination rate (K el)] in the FH of the fractured side. The supero-medial quadrant suffered the greatest decrease in arterial inflow with a significant decrease of 71.6% (IAUC) and 68.5% (peak). Post-operative MRI revealed a high rate (87%-20/23) of small ON segments within the FH, and all developed in the anterior aspect of the supero-medial quadrants. Fracture characteristics, including subcapital FNF, varus deformity, posterior roll-off ≥20° and Pauwel's angle of 30°-50° demonstrated a greater decrease in perfusion compared to contralateral controls. CONCLUSION: FNF significantly impaired the vascular supply to the FH, resulting in high incidence of small ON segments in the supero-medial quadrant of the FH. However, maintained perfusion, probably through the inferior retinacular system, coupled with urgent open anatomic reduction and stable fixation resulted in excellent clinical and radiographic outcomes despite a high rate of small ON segments noted on MRI. LEVEL OF EVIDENCE: Level I: Prognostic Investigation.