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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.

High-grade knee laxity is associated with early anterior cruciate ligament (ACL) graft failure, poor function, and compromised clinical outcome. Yet, the specific ligaments and ligament properties driving knee laxity remain poorly understood. We described a Bayesian calibration methodology for predicting unknown ligament properties in a computational knee model. Then, we applied the method to estimate unknown ligament properties with uncertainty bounds using tibiofemoral kinematics and ACL force measurements from two cadaver knees that spanned a range of laxities; these knees were tested using a robotic manipulator. The unknown ligament properties were from the Bayesian set of plausible ligament properties, as specified by their posterior distribution. Finally, we developed a calibrated predictor of tibiofemoral kinematics and ACL force with their own uncertainty bounds. The calibrated predictor was developed by first collecting the posterior draws of the kinematics and ACL force that are induced by the posterior draws of the ligament properties and model parameters. Bayesian calibration identified unique ligament slack lengths for the two knee models and produced ACL force and kinematic predictions that were closer to the corresponding in vitro measurement than those from a standard optimization technique. This Bayesian framework quantifies uncertainty in both ligament properties and model outputs; an important step towards developing subject-specific computational models to improve treatment for ACL injury.

In TKA, soft tissue balancing is assessed through manual intraoperative trialing. This assessment is a physical examination via manually applied forces at the ankle, generating varus and valgus moments at the knee while the surgeon visualizes the lateral and medial gaps at the joint line. Based on this examination, important surgical decisions are made that influence knee stability, such as choosing the polyethylene insert thickness. Yet, the applied forces and the assessed gaps in this examination represent a qualitative art that relies on each surgeon's intuition, experience, and training. Therefore, the extent of variation among surgeons in conducting this exam, in terms of applied loads and assessed gaps, is unknown. Moreover, whether variability in the applied loads yields different surgical decisions, such as choice of insert thickness, is also unclear. Thus, surgeons and developers have no basis for deciding to what extent the applied loads need to be standardized and controlled during a knee balance exam in TKA.(1) Do the applied moments in soft tissue assessment differ among surgeons? (2) Do the assessed gaps in soft tissue assessment differ among surgeons? (3) Is the choice of insert thickness associated with the applied moments?Seven independent human cadaveric nonarthritic lower extremities from pelvis to toe were acquired (including five females and two males with a mean age of 73 ± 7 years and a mean BMI of 25.8 ± 3.8 kg/m 2 ). Posterior cruciate ligament substituting (posterior stabilized) TKA was performed only on the right knees. Five fellowship-trained knee surgeons (with 24, 15, 15, 7, and 6 years of clinical experience) and one chief orthopaedic resident independently examined soft tissue balance in each knee in extension (0° of flexion), midflexion (30° of flexion), and flexion (90° of flexion) and selected a polyethylene insert based on their assessment. Pliable force sensors were wrapped around the leg to measure the loads applied by each surgeon. A three-dimensional (3D) motion capture system was used to measure knee kinematics and a dynamic analysis software was used to estimate the medial and lateral gaps. We assessed (1) whether surgeons applied different moments by comparing the mean applied moment by surgeons in extension, midflexion, and flexion using repeated measures (RM)-ANOVA (p0.05 was assumed significantly different); (2) whether surgeons assessed different gaps by comparing the mean medial and lateral gaps in extension, midflexion, and flexion using RM-ANOVA (p0.05 was assumed significantly different); and (3) whether the applied moments in extension, midflexion, and flexion were associated with the insert thickness choice using a generalized estimating equation (p0.05 was assumed a significant association).The applied moments differed among surgeons, with the largest mean differences occurring in varus in midflexion (16.5 Nm; p = 0.02) and flexion (7.9 Nm; p0.001). The measured gaps differed among surgeons at all flexion angles, with the largest mean difference occurring in flexion (1.1 ± 0.4 mm; p0.001). In all knees except one, the choice of insert thickness varied by l mm among surgeons. The choice of insert thickness was weakly associated with the applied moments in varus (β = -0.06 ± 0.02 [95% confidence interval -0.11 to -0.01]; p = 0.03) and valgus (β = -0.09 ± 0.03 [95% CI -0.18 to -0.01]; p= 0.03) in extension and in varus in flexion (β = -0.11 ± 0.04 [95% CI -0.22 to 0.00]; p = 0.04). To put our findings in context, the greatest regression coefficient (β = -0.11) indicates that for every 9-Nm increase in the applied varus moment (that is, 22 N of force applied to the foot assuming a shank length of 0.4 m), the choice of insert thickness decreased by 1 mm.In TKA soft tissue assessment in a human cadaver model, five surgeons and one chief resident applied different moments in midflexion and flexion and targeted different gaps in extension, midflexion, and flexion. A weak association between the applied moments in extension and flexion and the insert choice was observed. Our results indicate that in the manual assessment of soft tissue, changes in the applied moments of 9 and 11 Nm (22 to 27 N on the surgeons' hands) in flexion and extension, respectively, yielded at least a 1-mm change in choice of insert thickness. The choice of insert thickness may be more sensitive to the applied moments in in vivo surgery because the surgeon is allowed a greater array of choices beyond insert thickness.Among five arthroplasty surgeons with different levels of experience and a chief resident, subjective soft tissue assessment yielded 1 to 2 mm of variation in their choice of insert thickness. Therefore, developers of tools to standardize soft tissue assessment in TKA should consider controlling the force applied by the surgeon to better control for variations in insert selection.

Background: Long-term patient-reported outcome measures (PROMs), rates of return to sport, and revision risk after anterior cruciate ligament (ACL) reconstruction (ACLR) are not well understood. Purpose: To provide long-term follow-up of PROMs, return-to-sport rates, and revision rates after ACLR and to identify predictors for poor outcome. Study Design: Case-control study; Level of evidence, 3. Methods: A total of 2042 patients were included in an institutional ACL registry (2009-2013) and longitudinally followed. PROMs were completed preoperatively and at all follow-up time points. Questions regarding return to sport and knee stability were completed at final follow-up. Predictors for poor outcome on the International Knee Documentation Committee (IKDC) score were estimated in a regression model incorporating risk factors such as patient characteristics, graft choice, and concomitant injuries. Revision rates and risk of subsequent non-ACL surgeries were calculated. Results: Autografts were used in 76% of the patients (patellar tendon, 62%; hamstring grafts, 38%). Allografts were used in 24% of patients. The questionnaires were returned by 1045 (51.2%) patients at a mean of 7.2 years (range, 5.0-9.8 years) after surgery. Improvements in IKDC score of >30 points were sustained for all patient categories. The strongest predictor for lesser improvement in IKDC score was a cartilage lesion >2 cm2 identified during surgery. Male sex and college education completion were associated with improved IKDC scores. Meniscal lesions did not predict change) in the IKDC score. A total of 69% of patients had returned to sport after 8.1 years (range, 6.7-9.8 years). The main reason for not returning to sport was fear of reinjury. The revision rate was 7.2% after 9 years (range, 8-11 years), 13% of patients needed subsequent ipsilateral non-ACL surgery, and 6% underwent contralateral ACLR. The absence of a meniscal tear, younger age, and male sex were predictors for revision. Graft choice did not predict PROM results or revision risk. Conclusion: Improvements in IKDC scores were sustained 7 years after ACLR. The strongest predictor for poor outcome was a cartilage lesion >2 cm2. Patients can expect a 70% return-to-sport rate and an 87% chance of their knee feeling stable during daily and athletic activities after 8 years. Young male patients have better PROM scores but a higher risk of revision. There is a 26% chance of subsequent knee surgery within 9 years, including a revision rate of 7%, subsequent non-ACL surgery to the operated knee in 13%, and a 6% chance of contralateral ACLR.

Background: Robotic-assisted total knee arthroplasty (rTKA) has emerged as a patient-specific customizable tool that enables 3-dimensional preoperative planning, intraoperative adjustment, robotic-assisted bone preparation, and soft-tissue protection. Haptic rTKA may enhance component positioning, but only a few small studies have examined patient satisfaction and clinical outcomes after haptic rTKA. Purpose: In patients who underwent haptic rTKA, we sought to evaluate (1) the discrepancy in alignment between the executed surgical plan and implanted alignment in the coronal and sagittal planes 1 year postoperatively and (2) patient-reported outcomes 2 years postoperatively. Methods: From a prospectively collected database, we reviewed 105 patients who underwent haptic rTKA from August 2016 to May 2017. Two fellowship-trained arthroplasty surgeons independently reviewed hip-to-ankle standing biplanar radiographs to measure overall limb alignment and individual tibial and femoral component alignment relative to the mechanical axis and compared this to the executed surgical plan. Patient-reported outcomes were collected preoperatively and at 2 years postoperatively using the Lower Activity Extremity Score (LEAS), Knee Injury and Osteoarthritis Outcome Score Junior (KOOS Jr.), and Numeric Pain Rating Scale (NPRS). Results: Mean patient age was 62.4 years, and mean body mass index was 30.6 kg/m2. Interobserver reliability was significant with a κ of 0.89. Absolute mean deviations in postoperative coronal alignment compared to intraoperative alignment were 0.625° ± 0.70° and 0.45° ± 0.50° for the tibia and femur, respectively. Absolute mean deviations in postoperative tibial sagittal alignment were 0.47° ± 0.76°. Overall mechanical alignment was 0.97° ± 1.79°. Outcomes in LEAS, KOOS Jr., and NPRS changed from 8 to 10, 78 to 88.3, and 8 to 1, respectively. Conclusions: Haptic rTKA demonstrated high reliability and accuracy (less than 1°) of tibial coronal, femoral coronal, and tibial sagittal component alignment postoperatively compared to the surgical plan. Patient-reported outcomes improved, as well. A more rigorous study on long-term outcomes is warranted.

Background: Limited data exist regarding the association of tibiofemoral bony and soft tissue geometry and knee laxity with risk of first-time noncontact anterior cruciate ligament (ACL) rupture. Purpose: To determine associations of tibiofemoral geometry and anteroposterior (AP) knee laxity with risk of first-time noncontact ACL injury in high school and collegiate athletes. Study Design: Cohort study; Level of evidence, 2. Methods: Over a 4-year period, noncontact ACL injury events were identified as they occurred in 86 high school and collegiate athletes (59 female, 27 male). Sex- and age-matched control participants were selected from the same team. AP laxity of the uninjured knee was measured using a KT-2000 arthrometer. Magnetic resonance imaging was taken on ipsilateral and contralateral knees, and articular geometries were measured. Sex-specific general additive models were implemented to investigate associations between injury risk and 6 features: ACL volume, meniscus–bone wedge angle in the lateral compartment of the tibia, articular cartilage slope at the middle region of the lateral compartment of the tibia, femoral notch width at the anterior outlet, body weight, and AP displacement of the tibia relative to the femur. Importance scores (in percentages) were calculated to rank the relative contribution of each variable. Results: In the female cohort, the 2 features with the highest importance scores were tibial cartilage slope (8.6%) and notch width (8.1%). In the male cohort, the 2 top-ranked features were AP laxity (5.6%) and tibial cartilage slope (4.8%). In female patients, injury risk increased by 25.5% with lateral middle cartilage slope becoming more posteroinferior from –6.2° to –2.0° and by 17.5% with lateral meniscus–bone wedge angle increasing from 27.3° to 28.2°. In males, an increase in AP displacement from 12.5 to 14.4 mm in response to a 133-N anterior-directed load was associated with a 16.7% increase in risk. Conclusion: Of the 6 variables studied, there was no single dominant geometric or laxity risk factor for ACL injury in either the female or male cohort. In males, AP laxity >13 to 14 mm was associated with sharply increased risk of noncontact ACL injury. In females, lateral meniscus–bone wedge angle >28° was associated with a sharply decreased risk of noncontact ACL injury.

Aims Limited evidence is available on mid-term outcomes of robotic-arm assisted (RA) partial knee arthroplasty (PKA). Therefore, the purpose of this study was to evaluate mid-term survivorship, modes of failure, and patient-reported outcomes of RA PKA. Methods A retrospective review of patients who underwent RA PKA between June 2007 and August 2016 was performed. Patients received a fixed-bearing medial or lateral unicompartmental knee arthroplasty (UKA), patellofemoral arthroplasty (PFA), or bicompartmental knee arthroplasty (BiKA; PFA plus medial UKA). All patients completed a questionnaire regarding revision surgery, reoperations, and level of satisfaction. Knee Injury and Osteoarthritis Outcome Scores (KOOS) were assessed using the KOOS for Joint Replacement Junior survey. Results Mean follow-up was 4.7 years (2.0 to 10.8). Five-year survivorship of medial UKA (n = 802), lateral UKA (n = 171), and PFA/BiKA (n = 35/10) was 97.8%, 97.7%, and 93.3%, respectively. Component loosening and progression of osteoarthritis (OA) were the most common reasons for revision. Mean KOOS scores after medial UKA, lateral UKA, and PFA/BiKA were 84.3 (SD 15.9), 85.6 (SD 14.3), and 78.2 (SD 14.2), respectively. The vast majority of the patients reported high satisfaction levels after RA PKA. Subgroup analyses suggested tibial component design, body mass index (BMI), and age affects RA PKA outcomes. Five-year survivorship was 98.4% (95% confidence interval (CI) 97.2 to 99.5) for onlay medial UKA (n = 742) and 99.1% (95% CI 97.9 to 100) for onlay medial UKA in patients with a BMI < 30 kg/m2 (n = 479). Conclusion This large single-surgeon study showed high mid-term survivorship, satisfaction levels, and functional outcomes in RA UKA using metal-backed tibial onlay components. In addition, favourable results were reported in RA PFA and BiKA. Cite this article: Bone Joint J 2020;102-B(1):108–116

Purpose: The purpose of this study was to evaluate the effectiveness of day-case unicompartmental knee arthroplasty (UKA) by assessment of successful same-day discharge (SDD), readmission, complication and reoperation rates in the recent literature. Methods: For this systematic review and meta-analysis, PubMed, Embase and Cochrane Library were comprehensively searched to identify all eligible studies reporting outcomes of day-case UKA. Studies with intended same-day home discharge after UKA were included. A meta-analysis of proportions, using a random-effects model, was performed to estimate overall rates of successful SDD and adverse events. Subgroup analyses were performed for studies including selected patients (i.e., patients had to meet certain patient-specific criteria to be eligible for day-case UKA) and unselected patients (i.e., no additional criteria for day-case UKA), as well as for clinical and registry-based studies. Additional outcomes included reasons for the failure of SDD and patient satisfaction. Results: A total of 29 studies and 9694 patients were included with a mean age of 66 ± 9 years and mean follow-up of 59 days (mean range 30–270 days). Based on 24 studies (2733 patients), the overall successful SDD rate was 88% (95% confidence interval [CI] 80–92). These rates were 91% (95% CI 84–95) across studies with selected patients and 76% (95% CI 55–89) across studies with unselected patients. Overall readmission, complication and reoperation rates were 3% (95% CI 1.9–4.4), 4% (95% CI 2.8–5.2) and 1% (95% CI 0.8–1.3), respectively. Inability to mobilize, nausea and uncontrolled pain were frequently reported reasons for failed SDD. The overall patient satisfaction rate was 94%. Conclusion: This systematic review with meta-analysis found an overall successful SDD rate of 88% after UKA in a heterogeneous cohort of selected and unselected patients. Readmission, complication and reoperation rates suggest UKA can be performed safely and effectively as a same-day discharge procedure. Level of evidence: Level IV, systematic review of level III and IV studies.

Background: Loss to follow-up in registry studies might affect generalizability and interpretation of results. Purpose: To evaluate the effect of nonresponder bias in our anterior cruciate ligament (ACL) registry. Study Design: Case-control study; Level of evidence, 3. Methods: A total of 2042 patients with ACL reconstruction in the Hospital for Special Surgery ACL Registry between 2009 and 2013 were included in the study. Patients who completed the patient-reported outcome measures at 2 or 5 years were considered responders (n = 808). Baseline data and patient characteristics were compared between responders and nonresponders (n = 1234). Both responders and nonresponders were contacted and invited to complete the International Knee Documentation Committee (IKDC) and Marx scores electronically and respond to questions regarding return to sports and subsequent surgeries. Nonresponders who completed the questionnaires after reminders were considered late responders. The remaining nonresponders were considered never-responders. The late responders (n = 367) completed the questionnaires after a mean follow-up of 7.8 years (range, 6.7-9.6 years), while follow-up for the responders was 6.8 years (range, 5.0-9.7 years). Responders and late responders were then compared in terms of differences in IKDC and Marx scores from baseline to final follow-up. Results: Nonresponders were younger (28.5 vs 31.5 years; P < .001) and more often male (60% vs 53%; P = .003) compared with responders. Responders had a higher level of education and were more likely to be White (79% vs 74%; P = .04). There were no substantial differences in patient characteristics or baseline IKDC and Marx scores between the late responders and never-responders. There were no statistically significant differences in patient-reported outcomes, return to sports, or subsequent surgeries between responders and late responders at a mean follow-up time of 8.8 years (range, 6.7-9.7 years). Repeat email reminders and telephone calls increased response rate by 18% (from 40% to 58%). Conclusion: There was no difference in clinical outcome as evaluated using IKDC and Marx scores between responders and late responders.

BACKGROUND: Decisions regarding care for osteoarthritis involve physicians helping patients understand likely benefits and harms of treatment. Little work has directly compared patient and surgeon risk-taking attitudes, which may help inform strategies for shared decision-making and improve patient satisfaction. METHODS: We surveyed patients contemplating total joint arthroplasty visiting a high-volume specialty hospital regarding general questions about risk taking, as well as willingness to undergo surgery under hypothetical likelihoods of moderate improvement and complications. We compared to responses from surgeons answering similar questions about willingness to recommend surgery. RESULTS: Altogether 82% (162/197) of patients responded, as did 65% (30/46) of joint replacement surgeons. Mean age among patients was 66.4 years; 58% were female. Surgeons averaged 399 surgeries in 2019. Responses were similar between groups for general, health, career, financial, and sports/leisure risk-taking (p>0.20); surgeons were marginally more risk taking in driving (p=0.05). For willingness to have or recommend surgery, as the chance of benefit decreased, or the chance of harm increased, the percentage willing to have or recommend surgery decreased. Between a 70% and 95% chance of moderate improvement (for a 2% complication risk), as well as between a 90% and 95% chance of moderate improvement (for 4% and 6% complication risks), the percentage willing to have or recommend surgery was indistinguishable between patients and surgeons. However, for lower likelihoods of improvement, a higher percentage of patients were willing to undergo surgery than surgeons recommended. Patients were also more often indifferent between complication risks. CONCLUSION: Although patients and surgeons were often willing to have or recommend joint replacement surgery at similar rates, they diverged for lower-benefit higher-harm scenarios.

Background:There is concern that utilization of lateral extra-articular tenodesis (LET) in conjunction with anterior cruciate ligament (ACL) reconstruction (ACLR) may disturb lateral compartment contact mechanics and contribute to joint degeneration.Hypothesis:ACLR augmented with LET will alter lateral compartment contact mechanics in response to simulated pivoting maneuvers.Study Design:Controlled laboratory study.Methods:Loads simulating a pivot shift were applied to 7 cadaveric knees (4 male; mean age, 39 ± 12 years; range, 28-54 years) using a robotic manipulator. Each knee was tested with the ACL intact, sectioned, reconstructed (via patellar tendon autograft), and, finally, after augmenting ACLR with LET (using a modified Lemaire technique) in the presence of a sectioned anterolateral ligament and Kaplan fibers. Lateral compartment contact mechanics were measured using a contact stress transducer. Outcome measures were anteroposterior location of the center of contact stress (CCS), contact force from anterior to posterior, and peak and mean contact stress.Results:On average, augmenting ACLR with LET shifted the lateral compartment CCS anteriorly compared with the intact knee and compared with ACLR in isolation by a maximum of 5.4 ± 2.3 mm ( P < .001) and 6.0 ± 2.6 mm ( P < .001), respectively. ACLR augmented with LET also increased contact force anteriorly on the lateral tibial plateau compared with the intact knee and compared with isolated ACLR by a maximum of 12 ± 6 N ( P = .001) and 17 ± 10 N ( P = .002), respectively. Compared with ACLR in isolation, ACLR augmented with LET increased peak and mean lateral compartment contact stress by 0.7 ± 0.5 MPa ( P = .005) and by 0.17 ± 0.12 ( P = .006), respectively, at 15° of flexion.Conclusion:Under simulated pivoting loads, adding LET to ACLR anteriorized the CCS on the lateral tibial plateau, thereby increasing contact force anteriorly. Compared with ACLR in isolation, ACLR augmented with LET increased peak and mean lateral compartment contact stress at 15° of flexion.Clinical Relevance:The clinical and biological effect of increased anterior loading of the lateral compartment after LET merits further investigation. The ability of LET to anteriorize contact stress on the lateral compartment may be useful in knees with passive anterior subluxation of the lateral tibia.

Aims Uncemented mobile bearing designs in medial unicompartmental knee arthroplasty (UKA) have seen an increase over the last decade. However, there are a lack of large-scale studies comparing survivorship of these specific designs to commonly used cemented mobile and fixed bearing designs. The aim of this study was to evaluate the survivorship of these designs. Methods A total of 21,610 medial UKAs from 2007 to 2018 were selected from the Dutch Arthroplasty Register. Multivariate Cox regression analyses were used to compare uncemented mobile bearings with cemented mobile and fixed bearings. Adjustments were made for patient and surgical factors, with their interactions being considered. Reasons and type of revision in the first two years after surgery were assessed. Results In hospitals performing less than 100 cases per year, cemented mobile bearings reported comparable adjusted risks of revision as uncemented mobile bearings. However, in hospitals performing more than 100 cases per year, the adjusted risk of revision was higher for cemented mobile bearings compared to uncemented mobile bearings (hazard ratio 1.78 (95% confidence interval 1.34 to 2.35)). The adjusted risk of revision between cemented fixed bearing and uncemented mobile bearing was comparable, independent of annual hospital volume. In addition, 12.3% of uncemented mobile bearing, 20.3% of cemented mobile bearing, and 41.5% of uncemented fixed bearing revisions were for tibial component loosening. The figures for instability were 23.6%, 14.5% and 11.7%, respectively, and for periprosthetic fractures were 10.0%, 2.8%, and 3.5%. Bearing exchange was the type of revision in 40% of uncemented mobile bearing, 24.3% of cemented mobile bearing, and 5.3% cemented fixed bearing revisions. Conclusion The findings of this study demonstrated improved survival with use of uncemented compared to cemented mobile bearings in medial UKA, only in those hospitals performing more than 100 cases per year. Cemented fixed bearings reported comparable survival results as uncemented mobile bearings, regardless of the annual hospital volume. The high rates of instability, periprosthetic fractures, and bearing exchange in uncemented mobile bearings emphasize the need for further research. Cite this article: Bone Joint J 2021;103-B(7):1261–1269.

BACKGROUND: It has been suggested that the degree of anterior tibial translation (ATT) as measured passively on imaging studies (static ATT) after an anterior cruciate ligament (ACL) injury may influence outcomes after ACL reconstruction. However, there is a lack of evidence supporting these suggestions. QUESTIONS/PURPOSES: The purpose of this retrospective prognostic study was to assess the predictive value of pre-operative static ATT in knees with ACL injury on return to sport and in satisfaction after ACL reconstruction. Our hypothesis was that greater static ATT would be associated with lower rates of return to sport and lower levels of satisfaction. METHODS: Patients treated with ACL reconstruction were identified from an institutional registry and assigned to one of three groups according to their ACL injury type: acute ACL injury, chronic ACL injury, and failed ACL reconstruction. ATT in each knee compartment was measured using magnetic resonance imaging, and a retrospective telephone questionnaire was used to investigate post-ACL reconstruction return to sport and subjects’ satisfaction. RESULTS: One hundred thirty patients (52 acute with ACL injury, 29 with chronic ACL injury, and 49 with failed ACL reconstruction) completed the questionnaire, with a mean follow-up of 5.67 years. Ninety-seven patients (74.6%) returned to their primary sport, of whom 63 (65%) returned to the same level of sport. The mean time to return to sport was 10.1 months (range, 2 to 24 months). Overall, 113 patients (87%) were either very satisfied or satisfied with their outcomes. No difference in medial or lateral ATT was found between patients who returned to sport and those who did not. The failed-ACL reconstruction group had significantly lower rates of return to sport than did acutely and chronically injured patients (60.4% versus 88.5% and 75.9%, respectively). CONCLUSION: The degree of pre-operative ATT in an ACL-deficient knee was not correlated with return to sport or satisfaction after ACL reconstruction. In this study cohort, only failed-ACL reconstruction patients undergoing revision ACL reconstruction were significantly less likely to return to their main sport. They were also less likely to return to sport at their pre-operative level, if they did return to sport. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s11420-019-09724-9) contains supplementary material, which is available to authorized users.

There is controversy as to whether the presence of degenerative changes and malalignment of the patellofemoral joint is a contraindication to medial unicompartmental knee arthroplasty. Therefore, the aim of the present study was to examine the influence of preoperative radiographic patellofemoral joint osteoarthritis and alignment on intermediate-term knee and patellofemoral joint-specific patient-reported outcomes following fixed-bearing medial unicompartmental knee arthroplasty.We performed a retrospective review of the records on a consecutive series of patients who had undergone robotic arm-assisted fixed-bearing onlay medial unicompartmental knee arthroplasty and had a minimum duration of follow-up of 2 years. All records were collected from a single surgeon's arthroplasty registry. Patients with severe bone loss or grooving of the lateral patellar facet were excluded. Radiographic assessment was performed with use of the Kellgren-Lawrence and Altman classification systems as well as with patellofemoral joint alignment measurements. The latest follow-up consisted of a patient-reported questionnaire, including the Kujala (Anterior Knee Pain Scale) score, the Knee Injury and Osteoarthritis Outcome Score (KOOS), Junior (JR), and satisfaction levels.A total of 536 patients (639 knees) were included. After a mean duration of follow-up (and standard deviation) of 4.3 ± 1.6 years (range, 2.0 to 9.2 years), good-to-excellent Kujala scores were reported independent of the presence of patellofemoral joint osteoarthritis preoperatively (Kellgren-Lawrence grade 0 compared with ≥1, p = 0.82; grade ≤1 compared with ≥2, p = 0.84). Similar findings were found when osteoarthritis was present in either the medial or lateral side of the patellofemoral joint as defined by an Altman score of ≥2 (medial, p = 0.81; lateral, p = 0.90). KOOS scores and satisfaction also were not affected by degenerative patellofemoral joint changes. Furthermore, neither the patellar tilt angle nor the congruence angle influenced patient-reported outcomes.Preoperative radiographic mild to moderate patellofemoral joint degeneration (Kellgren-Lawrence grades 1 through 3) and/or malalignment did not compromise intermediate-term knee and patellofemoral joint-specific patient-reported outcomes in patients managed with fixed-bearing medial unicompartmental knee arthroplasty. On the basis of the results of the present study, we believe that neither mild to moderate patellofemoral degeneration nor abnormal patellar tilt or congruence should be considered a contraindication to fixed-bearing medial unicompartmental knee arthroplasty.Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Outpatient surgery is an increasingly attractive option for patients undergoing procedures with established, acceptable risk profiles. Benefits of outpatient surgery include cost savings, enhanced patient experience and improved resource allocation at busy hospitals. The purpose of this study was to compare 90-day complication and readmission rates for patients undergoing unicompartmental knee arthroplasty (UKA) in the outpatient as opposed to the inpatient setting.Patients who underwent UKA (CPT code 27446) between 2007 and 2016 were retrospectively selected from a national private insurance database. Patients were defined as ambulatory if their coded location of procedure was in an ambulatory surgery center or as an in-hospital outpatient. Postoperative complications were identified using the Reportable Center for Medicare Services (CMS) Complication Measures. Risks of complications were compared between the inpatient and outpatient cohorts using multivariate logistic regression controlling for age, gender, and comorbidities.2600 patients undergoing ambulatory UKA and 5084 patients undergoing inpatient UKA were identified. The percentage of UKA procedures performed on an outpatient basis significantly increased over the course of the study (14.5% to 58.1%, p 0.001). After adjusting for age, gender, and comorbidities, ambulatory surgery was found to be associated with a decreased risk of postoperative transfusion (OR 0.28; p 0.001) and pneumonia (OR 0.23; p = 0.008) and there was a trend towards decreased 90-day readmission risk (OR = 0.83; p = 0.062).Ambulatory discharge following UKA is increasing in popularity, does not increase risk for perioperative complications or readmission, and may even portend a safer post-operative course.

Introduction The purpose was to compare robotic assisted (RA), computer navigated (CN), and conventional UKA techniques. Methods Databases were queried for data on study characteristics, UKA systems, complications, and tibiofemoral alignment. Results Four RA and six CN RCTs were identified. No significant differences were found in operative time, tibiofemoral alignment, and reoperation rates when comparing RA or CN to conventional UKA. RA UKA resulted in a significantly lower risk of complications compared to conventional UKA. Conclusions RA UKA results in fewer complications than conventional UKA with a clinically significant increase in operative time. All groups were similar in remaining evaluated parameters.

Purpose (I) To determine the incidence of periprosthetic tibial fractures in cemented and cementless unicompartmental knee arthroplasty (UKA) and (II) to summarize the existing evidence on characteristics and risk factors of periprosthetic fractures in UKA. Methods Pubmed, Cochrane and Embase databases were comprehensively searched. Any clinical, laboratory or case report study describing information on proportion, characteristics or risk factors of periprosthetic tibial fractures in UKA was included. Proportion meta-analysis was performed to estimate the incidence of fractures only using data from clinical studies. Information on characteristics and risk factors was evaluated and summarized. Results A total of 81 studies were considered to be eligible for inclusion. Based on 41 clinical studies, incidences of fractures were 1.24% (95%CI 0.64–2.41) for cementless and 1.58% (95%CI 1.06–2.36) for cemented UKAs (9451 UKAs). The majority of fractures in the current literature occurred during surgery or presented within 3 months postoperatively (91 of 127; 72%) and were non-traumatic (95 of 113; 84%). Six different fracture types were observed in 21 available radiographs. Laboratory studies revealed that an excessive interference fit (press fit), excessive tibial bone resection, a sagittal cut too deep posteriorly and low bone mineral density (BMD) reduce the force required for a periprosthetic tibial fracture to occur. Clinical studies showed that periprosthetic tibial fractures were associated with increased body mass index and postoperative alignment angles, advanced age, decreased BMD, female gender, and a very overhanging medial tibial condyle. Conclusion Comparable low incidences of periprosthetic tibial fractures in cementless and cemented UKA can be achieved. However, surgeons should be aware that an excessive interference fit in cementless UKAs in combination with an impaction technique may introduce an additional risk, and could therefore be less forgiving to surgical errors and patients who are at higher risk of periprosthetic tibial fractures. Level of evidence V.

Background: Anterior cruciate ligament (ACL) injuries are occurring with increasing frequency in the adolescent population. Outcomes after ACL reconstruction (ACLR) are inconsistently reported in homogeneous patient populations. Purpose/Hypothesis: To evaluate outcomes after bone–patellar tendon–bone (BTB) autograft ACLR in competitive high school–aged athletes by examining return to sport (RTS), patient satisfaction, and reinjury rates. Our hypothesis was that RTS rates and satisfaction will be high and reinjury rates will be low. Study Design: Case series; Level of evidence, 4. Methods: An institutional ACL registry was utilized to identify competitive high school–aged athletes (14-18 years old) who underwent primary ACLR using BTB autograft with a minimum 2-year follow-up. A postoperative questionnaire was administered to determine rates and types of RTS, quality of sports performance, reinjury, and satisfaction. Uni- and multivariable analyses were used to identify demographic, sport-specific, and clinical factors related to RTS. Results: A total of 53 patients were included (mean ± SD age at the time of surgery, 16.6 ± 1.34 years). Mean follow-up was 3.78 ± 0.70 years (range, 2.60-4.94 years). The overall ipsilateral ACL retear rate was 7.5% (n = 4). There were 10 subsequent ACL tears to the contralateral knee (19%). Forty-four (83%) patients successfully returned to at least their prior level of sport at a mean 10.5 ± 8.7 months (range, 3-48 months). Overall satisfaction was high, with 91% of patients very satisfied with the outcome. Higher confidence levels regarding performance of the reconstructed knee were associated with increased probability of RTS on multivariate analysis. Conclusion: BTB autograft ACLR results in high rates of RTS and satisfaction and low rates of subsequent ipsilateral ACL injuries in competitive high school–aged athletes. Patients with higher confidence in performance of the reconstructed knee are more likely to return to at least their prior level of sport.

Purpose To describe the complications that occur following biologic therapeutic injections. Methods We queried physician members of the Biologic Association, a multidisciplinary organization dedicated to providing a unified voice for all matters related to musculoskeletal biologics and regenerative medicine. Patients included in this study must have (1) received a biologic injection, (2) sustained an adverse reaction, and (3) had a minimum of 1-year follow-up after the injection. Patient demographic information, medical comorbidities, diagnoses, and previous treatments were recorded. The type of injection, injection setting, injection manufacturers, and specific details about the complication and outcome were collected. Results In total, 14 patients were identified across 6 institutions in the United States (mean age 63 years, range: 36-83 years). The most common injections in this series were intra-articular knee injections (50%), followed intra-articular shoulder injections (21.4%). The most common underlying diagnosis was osteoarthritis (78.5%). Types of injections included umbilical cord blood, platelet-rich plasma, bone marrow aspirate concentrate, placental tissue, and unspecified “stem cell” injections. Complications included infection (50%), suspected sterile inflammatory response (42.9%), and a combination of both (7.1%). The most common pathogen identified from infection cases was Escherichia coli (n = 4). All patients who had isolated infections underwent treatment with at least one subsequent surgical intervention (mean: 3.6, range: 1-12) and intravenous antibiotic therapy. Conclusions This study demonstrates that serious complications can occur following treatment with biologic injections, including infections requiring multiple surgical procedures and inflammatory reactions. Level of Evidence Level IV, case series.

The pivot shift and Lachman examinations are "teammates" with complementary but distinct roles in the successful diagnosis and treatment of anterior cruciate ligament rupture and injury to the surrounding soft-tissue envelope of the knee. The Lachman test measures anterior tibial translation in response to an applied anterior tibial load. This test assesses the integrity of the native or reconstructed anterior cruciate ligament and the secondary medial restraints including the medial meniscus and medial collateral ligament. In contrast, the pivot shift exam creates coupled tibiofemoral motions in response to a complex combination of multiplanar loads. This test assesses the stabilizing role of the native or reconstructed anterior cruciate ligament and the secondary lateral restraints including the lateral meniscus and anterolateral complex. The pivot shift grade depends not only on the soft the tissue stabilizers of the knee but also on the shape of the proximal tibia and the distal femur including lateral tibial slope and femoral condylar offset. Both examinations have unique strengths and weaknesses, but when combined as diagnostic tools, they achieve far more collectively than what each can achieve alone.

Background:The biomechanical effect of lateral extra-articular tenodesis (LET) performed in conjunction with anterior cruciate ligament (ACL) reconstruction (ACLR) on load sharing between the ACL graft and the LET and on knee kinematics is not clear.Purpose/Hypothesis:The purpose was to quantify the effect of LET on (1) forces carried by both the ACL graft and the LET and (2) tibiofemoral kinematics in response to simulated pivot shift and anterior laxity tests. We hypothesized that LET would decrease forces carried by the ACL graft and anterior tibial translation (ATT) in response to simulated pivoting maneuvers and during simulated tests of anterior laxity.Study Design:Controlled laboratory study.Methods:Seven cadaveric knees (mean age, 39 ± 12 years [range, 28-54 years]; 4 male) were mounted to a robotic manipulator. The robot simulated clinical pivoting maneuvers and tests of anterior laxity: namely, the Lachman and anterior drawer tests. Each knee was assessed in the following states: ACL intact, ACL sectioned, ACL reconstructed (using a bone–patellar tendon–bone autograft), and after performing LET (the modified Lemaire technique after sectioning of the anterolateral ligament and Kaplan fibers). Resultant forces carried by the ACL graft and LET at the peak applied loads were determined via superposition. ATT was determined in response to the applied loads.Results:With the applied pivoting loads, performing LET decreased ACL graft force up to 80% (44 ± 12 N; P < .001) and decreased ATT of the lateral compartment compared with that of the intact knee up to 7.6 ± 2.9 mm ( P < .001). The LET carried up to 91% of the force generated in the ACL graft during isolated ACLR (without LET). For simulated tests of anterior laxity, performing LET decreased ACL graft force by 70% (40 ± 20 N; P = .001) for the anterior drawer test with no significant difference detected for the Lachman test. No differences in ATT were deteced between ACLR with LET and the intact knee on both the Lachman and the anterior drawer tests ( P = .409). LET reduced ATT compared with isolated ACLR on the simulated anterior drawer test by 2.4 ± 1.8 mm ( P = .032) but not on the simulated Lachman test.Conclusion:In a cadaveric model, LET in combination with ACLR transferred loads from the ACL graft to the LET and reduced ATT with applied pivoting loads and during the simulated anterior drawer test. The effect of LET on ACL graft force and ATT was less pronounced on the simulated Lachman test.Clinical Relevance:LET in addition to ACLR may be a suitable option to offload the ACL graft and to reduce ATT in the lateral compartment to magnitudes less than that of the intact knee with clinical pivoting maneuvers. In contrast, LET did not offload the ACL graft or add to the anterior restraint provided by the ACL graft during the Lachman test.

Introduction: Opioid misuse and overprescription have contributed to a national public health crisis in the United States. Postoperatively, patients are often left with unused opioids, which pose a risk for diversion if not appropriately disposed of. Patients are infrequently provided instructions on safe disposal methods of surplus opioids. Purpose: We sought to determine the current rates of disposal of unused opioids and the reported disposal mechanisms for unused opioids that were prescribed for acute postoperative pain control. Methods: A systematic review was performed of the PubMed, Cochrane, and Embase databases for relevant articles from their earliest entries through October 2, 2019. We used the search terms “opioid” or “narcotic” and “disposal” and “surgery.” Studies were considered for inclusion if they reported the rate of disposal of unused opioids following surgery. A screening strategy was used to identify relevant articles using Covidence. For studies meeting inclusion criteria, relevant information was extracted. Results: Sixteen studies met inclusion criteria. We found that surplus opioid disposal rates varied widely, from 4.9% to 87.0%. Among studies with no intervention (opioid disposal education or drug disposal kit/bag), rates of opioid disposal ranged from 4.9% to 46.5%. While 7 studies used opioid disposal education as an intervention, only 3 showed a significant increase in surplus opioid disposal compared with standard care. All 3 studies that used an opioid disposal kit or bag as an intervention demonstrated significant increases in opioid disposal. Conclusions: Baseline rates of surplus opioid disposal are relatively low in the postoperative setting. Our findings suggest that opioid disposal kits significantly increase rates of surplus opioid disposal postoperatively. Further research, including a large-scale cost-benefit analysis, will be necessary prior to recommending widespread implementation of drug disposal kits or bags.

Aims It remains controversial whether patellofemoral joint pathology is a contraindication to lateral unicompartmental knee arthroplasty (UKA). This study aimed to evaluate the effect of preoperative radiological degenerative changes and alignment on patient-reported outcome scores (PROMs) after lateral UKA. Secondarily, the influence of lateral UKA on the alignment of the patellofemoral joint was studied. Methods A consecutive series of patients who underwent robotic arm-assisted fixed-bearing lateral UKA with at least two-year follow-up were retrospectively reviewed. Radiological evaluation was conducted to obtain a Kellgren Lawrence (KL) grade, an Altman score, and alignment measurements for each knee. Postoperative PROMs were assessed using the Kujala (Anterior Knee Pain Scale) score, Knee Injury and Osteoarthritis Outcome Score Joint Replacement (KOOS JR), and satisfaction levels. Results A total of 140 knees (130 patients) were identified for analysis. At mean 4.1 years (2.0 to 8.5) follow-up, good to excellent Kujala scores were reported. The presence of mild to moderate preoperative patellofemoral joint osteoarthritis had no impact on these scores (KL grade 0 vs 1 to 3, p = 0.203; grade 0 to 1 vs 2 to 3, p = 0.674). Comparable scores were reported by patients with osteoarthritis (Altman score of ≥ 2) evident on either the medial or lateral patellofemoral joint facet (medial, p = 0.600 and lateral, p = 0.950). Patients with abnormal patellar congruence and tilt angles (≥ 17° and ≥ 14°, respectively) reported good to excellent Kujala scores. Furthermore, lateral UKA resulted in improvements to patellofemoral alignment. Conclusion This is the first study demonstrating that mild to moderate preoperative radiological degenerative changes and malalignment of the patellofemoral joint are not associated with poor patient-reported outcomes at mid-term follow-up after lateral fixed-bearing UKA. Our data suggest that this may be explained by realignment of the patella and thereby redistribution of loads across the patellofemoral joint. Cite this article: Bone Joint J 2020;102-B(6):727–735.

Background:Return to sports is an important outcome in ensuring patient satisfaction after knee-replacement surgery. However, few studies have directly compared unicompartmental knee arthroplasty (UKA), total knee arthroplasty (TKA), and patellofemoral arthroplasty (PFA).Hypothesis:TKA will result in lower rates of return to sports than either UKA and PFA due to increased complexity and invasiveness.Study Design:Cohort study; Level of evidence, 3.Methods:Patients who underwent UKA, TKA, or PFA with 1 to 2 years of follow-up were sent a questionnaire regarding return to sports, satisfaction with return to sports, pain, the University of California, Los Angeles activity scale, and the High Activity Arthroplasty Score (HAAS). The patients who underwent either TKA or UKA were matched 2:1 with regard to age and sex to patients who underwent PFA. Differences were compared using analysis of variance, t tests, and chi-square tests.Results:A total of 202 patients were eligible. After matching, the final cohort consisted of 23 PFA patients, 46 UKA patients, and 46 TKA patients. The majority of patients were female (87%), and the mean ± SD age was 56 ± 9.1 years. The UKA group had higher HAAS values than the TKA group pre- and postoperatively (9.9 vs 7.1 [ P = .001] and 12.4 vs 9.5 [ P < .001], respectively). Patients with UKA had higher rates of return to sports after surgery than those with TKA or PFA (UKA, 80.5%; TKA, 71.7%; PFA, 69.5%; P = 0.08). In addition, the UKA group had the highest satisfaction with this outcome. Improvement between pre- and postoperative scores was similar in all 3 groups.Conclusion:Patients who underwent UKA reported better activity scores and return-to-sports rates than patients who had TKA and PFA. No differences were found in improvement after surgery, suggesting that preoperative differences were reflected postoperatively. These findings inform shared decision making and can help to manage patient expectations after surgery.

Background: The purpose of this study was to evaluate early postoperative outcomes in patients following UKA (unicompartmental knee arthroplasty) compared to a matched cohort of TKA (total knee arthroplasty) patients. Methods: Patients who met radiographic criteria for a medial UKA who underwent either a TKA or UKA at a single institution were matched based on age, gender, and BMI. Results: One hundredy and fifty UKA in 138 patients and 150 TKA in 148 patients were included in this retrospective analysis. Mean age was 62.6 ± 9 years and 65.2 ± 9 years in the UKA and TKA groups respectively (p = .01). Patients who underwent UKA had significantly less pain at two and six weeks postoperatively compared to TKA patients with mean Numeric Pain Rating Scale (NPRS) scores of 3.7 ± 1.1 vs. 7.8 ± 1.2, p < .001 and 2.6 ± 1.3 vs. 4.6 ± 1.6, p < .001 respectively. Knee Society Scores (KSS) were higher in the UKA group at six weeks and two years postoperative (86.5 ± 2.8 vs. 81.4 ± 3.6, p < .001 and 89.5 ± 2.4 vs. 84.5 ± 3.3, p < .001 respectively). Return to work was faster in the UKA group (mean 20.6 ± 7.89 vs. 38.6 ± 6.23 days, p < .001). The UKA group also had higher mean Forgotten Joint Scores of 90.5 ± 3.6 vs. 79.5 ± 9.5 (p < .001). Conclusions: Patients with primarily medial compartment OA who underwent UKA had less postoperative pain, earlier return to work, and higher KSS compared to a matched group who underwent TKA.

BACKGROUND Anterior cruciate ligament (ACL) graft position within the anatomic femoral footprint of the native ACL and the flexion angle at which the graft is fixed (i.e., fixation angle) are important considerations in ACL reconstruction surgery. However, their combined effect on ACL graft force remains less well understood. HYPOTHESIS During passive flexion, grafts placed high within the femoral footprint carry lower forces than grafts placed low within the femoral footprint (i.e., high and low grafts, respectively). Forces carried by high grafts are independent of fixation angle. All reconstructions impart higher forces on the graft than those carried by the native ACL. STUDY DESIGN Controlled laboratory study. METHODS Five fresh-frozen cadaveric knees were mounted to a robotic manipulator and flexed from full extension to 90° of flexion. The ACL was sectioned and ACL force was calculated via superposition. ACL reconstructions were then performed using a patellar tendon autograft. For each knee, four different reconstruction permutations were tested: high and low femoral graft positions fixed at 15° and at 30° of flexion. Graft forces were calculated from full extension to 90° of flexion for each combination of femoral graft position and fixation angle again via superposition. Native ACL and ACL graft forces were compared through early flexion (by averaging tissue force from 0 to 30° of flexion) and in 5° increments from full extension to 90° of flexion. RESULTS When fixed at 30° of flexion, high grafts carried less force than low grafts through early flexion bearing a respective 64 ± 19 N and 88 ± 11 N (p = 0.02). Increasing fixation angle from 15° to 30° caused graft forces through early flexion to increase 40 ± 13 N in low grafts and 23 ± 6 N in high grafts (p

Increased posterior-inferior directed slope of the subchondral bone of the lateral tibial plateau is a risk factor for noncontact rupture of the anterior cruciate ligament (ACL). Previous measures of lateral tibial slope, however, vary from study to study and often lack documentation of their accuracy. These factors impede identifying the magnitude of lateral tibial slope that increases risk of noncontact ACL rupture. Therefore, we developed and evaluated a new method that (1) requires minimal user input; (2) employs 3D renderings of the tibia that are referenced to a 3D anatomic coordinate system; and (3) is precise, reliable, and accurate. The user first isolated the proximal tibia from computed tomography (CT) scans. Then, the algorithm placed the proximal tibia in an automatically generated tibial coordinate system. Next, it identified points along the rim of subchondral bone around the lateral tibial plateau, iteratively fit a plane to this rim of points, and, finally, referenced the plane to the tibial coordinate system. Precision and reliability of the lateral slope measurements were respectively assessed via standard deviation and intra- and inter-class correlation coefficients using CT scans of three cadaveric tibia. Accuracy was quantified by comparing changes in lateral tibial slope calculated by our algorithm to predefined in silico changes in slope. Precision, reliability, and accuracy were ≤0.18°, ≥0.998, and ≤0.13°, respectively. We will use our novel method to better understand the relationship between lateral tibial slope and knee biomechanics towards preventing ACL rupture and improving its treatment.

Background Unicompartmental knee arthroplasty is a successful treatment for unicompartmental knee osteoarthritis that has lower complication rates, faster recovery, and a more natural feeling knee compared to total knee arthroplasty. However, long-term survival has been a persistent concern. As more surgeon-controlled variables have been linked to survival, interest in robotic-assisted surgery has continued to grow. Methods A review and synthesis of the literature on the subject of robotic-assisted unicompartmental knee arthroplasty was performed. Results We present the driving factors behind the development of robotic-assisted techniques in unicompartmental knee arthroplasty and the current state-of-the art. The ability of surgeons to achieve intraoperative targets with robotic assistance and the outcomes of robotic-assisted surgery are also described. Conclusion Robotic-assisted surgery has become increasingly popular in unicompartmental knee arthroplasty, as it allows surgeons to more accurately and reproducibly plan and achieve operative targets during surgery. Cost remains a concern, and it remains to be seen whether robotic-assisted surgery will improve long-term survivorship after unicompartmental knee arthroplasty.

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.

Background: Recent epidemiologic reports have demonstrated rising injury rates in Major League Baseball (MLB) and Minor League Baseball (MiLB). Although several studies have recently been published on specific injuries, the majority of injuries have not yet been formally studied. Purpose: The purpose of this study is to (1) generate a summative analysis of all injuries that occur in MLB and MiLB, (2) identify the 50 most common injuries, and (3) generate focused reports and fact sheets on the characteristics of each of those diagnoses. Study Design: Case series; Level of evidence, 4. Methods: The MLB Health and Injury Tracking System was used to identify injuries occurring in MLB and MiLB players from 2011 to 2016. Injuries were defined as those that occurred during normal baseball activity and resulted in at least 1 day out of play. A multitude of player and injury characteristics were analyzed, and detailed reports of the 50 most commonly occurring injuries were generated. Results: A total of 49,955 injuries occurred during the study period; 45,123 were non–season ending, and they resulted in 722,176 days out of play. The mean (median) days missed per injury was 16 (6) days. Overall, 39.1% of all injuries occurred in pitchers. The upper extremity was involved in 39% of injuries, while 35% occurred in the hip/groin/lower extremity. Surgery was required in 6.5% of cases, and 9.7% of injuries were season ending. Hamstring strains were the most common injury (n = 3337), followed by rotator cuff strain/tear (n = 1874), paralumbar muscle strain (n = 1313), biceps tendinitis (n = 1264), oblique strain (n = 1249), and elbow ulnar collateral ligament injury (n = 1191). The diagnoses that were most likely to end a player’s season were elbow ulnar collateral ligament injury (60% season ending) and superior labrum anterior and posterior tear (50.9% season ending). Conclusion: Contrary to prior reports relying on disabled list data, the annual number of injuries in professional baseball remained steady from 2011 to 2016. Similar trends were noted for the annual number of days missed and mean days missed per injury. Although the mean days missed per injury was high (16), the median was much lower at 6 days.

Medial unicompartmental knee arthroplasty (UKA) is an accepted treatment for isolated medial osteoarthritis. However, using an improper thickness for the tibial component may contribute to early failure of the prosthesis or disease progression in the unreplaced lateral compartment. Little is known of the effect of insert thickness on both knee kinematics and ligament forces. Therefore, a computational model of the tibiofemoral joint was used to determine how non-conforming, fixed bearing medial UKA affects tibiofemoral kinematics, and tension in the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL) during passive knee flexion. Fixed bearing medial UKA could not maintain the medial pivoting that occurred in the intact knee from 0° to 30° of passive flexion. Abnormal anterior-posterior (AP) translations of the femoral condyles relative to the tibia delayed coupled internal tibial rotation, which occurred in the intact knee from 0° to 30° of flexion, but occurred from 30° to 90° of flexion following UKA. Increasing or decreasing tibial insert thickness following medial UKA also failed to restore the medial pivoting behavior of the intact knee despite modulating MCL and ACL forces. Reduced AP constraint in non-conforming medial UKA relative to the intact knee leads to abnormal condylar translations regardless of insert thickness even with intact cruciate and collateral ligaments. This finding suggests that the conformity of the medial compartment as driven by the medial meniscus and articular morphology plays an important role in controlling AP condylar translations in the intact tibiofemoral joint during passive flexion. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1868-1875, 2018.

Background Due to disappointing historical outcomes of unicompartmental knee arthroplasty (UKA), Kozinn and Scott proposed strict selection criteria, including preoperative varus alignment of ≤15°, to improve the outcomes of UKA. No studies to date, however, have assessed the feasibility of correcting large preoperative varus deformities with UKA surgery. The study goals were therefore to (1) assess to what extent patients with large varus deformities could be corrected and (2) determine radiographic parameters to predict sufficient correction. Methods In 200 consecutive robotic-arm assisted medial UKA patients with large preoperative varus deformities (≥7°), the mechanical axis angle (MAA) and joint line convergence angle (JLCA) were measured on hip-knee-ankle radiographs. It was assessed what number of patients were corrected to optimal (≤4°) and acceptable (5°-7°) alignment, and whether the feasibility of this correction could be predicted using an estimated MAA (eMAA, preoperative MAA−JLCA) using regression analyses. Results Mean preoperative MAA was 10° of varus (range, 7°-18°), JLCA was 5° (1°-12°), postoperative MAA was 4° of varus (−3° to 8°), and correction was 6° (1°-14°). Postoperative optimal alignment was achieved in 62% and acceptable alignment in 36%. The eMAA was a significant predictor for optimal postoperative alignment, when corrected for age and gender (P Conclusion Patients with large preoperative varus deformities (7°-18°) could be considered candidates for medial UKA, as 98% was corrected to optimal or acceptable alignment, although cautious approach is needed in deformities >15°. Furthermore, it was noted that the feasibility of achieving optimal alignment could be predicted using the preoperative MAA, JLCA, and age.

BackgroundThe correct amount of external rotation of the femoral component during TKA is controversial because the resulting changes in biomechanical knee function associated with varying degrees of femoral component rotation are not well understood. We addressed this question using a comput

Background: Understanding specific risk profiles for each patient and their propensity to experience clinically meaningful improvement after anterior cruciate ligament reconstruction (ACLR) is important for preoperative patient counseling and management of expectations. Purpose: To develop machine learning algorithms to predict achievement of the minimal clinically important difference (MCID) on the International Knee Documentation Committee (IKDC) score at a minimum 2-year follow-up after ACLR. Study Design: Case-control study; Level of evidence, 3. Methods: An ACLR registry of patients from 27 fellowship-trained sports medicine surgeons at a large academic institution was retrospectively analyzed. Thirty-six variables were tested for predictive value. The study population was randomly partitioned into training and independent testing sets using a 70:30 split. Six machine learning algorithms (stochastic gradient boosting, random forest, neural network, support vector machine, adaptive gradient boosting, and elastic-net penalized logistic regression [ENPLR]) were trained using 10-fold cross-validation 3 times and internally validated on the independent set of patients. Algorithm performance was assessed using discrimination, calibration, Brier score, and decision-curve analysis. Results: A total of 442 patients, of whom 39 (8.8%) did not achieve the MCID, were included. The 5 most predictive features of achieving the MCID were body mass index ≤27.4, grade 0 medial collateral ligament examination (compared with other grades), intratunnel femoral tunnel fixation (compared with suspensory), no history of previous contralateral knee surgery, and achieving full knee extension preoperatively. The ENPLR algorithm had the best relative performance (C-statistic, 0.82; calibration intercept, 0.10; calibration slope, 1.15; Brier score, 0.068), demonstrating excellent predictive ability in the study’s data set. Conclusion: Machine learning, specifically the ENPLR algorithm, demonstrated good performance for predicting a patient’s propensity to achieve the MCID for the IKDC score after ACLR based on preoperative and intraoperative factors. The femoral tunnel fixation method was the only significant intraoperative variable. Range of motion and medial collateral ligament integrity were found to be important physical examination parameters. Increased body mass index and prior contralateral surgery were also significantly predictive of outcome.

Femoral and tibial radiolucent lines (RLL) after unicompartmental knee arthroplasty (UKA) can be categorized in physiological and pathological radiolucencies. Although physiological tibial radiolucency is assessed extensively in literature, studies reporting femoral radiolucency are lacking. Therefore, a retrospective study was performed to assess physiological femoral RLL and its relationship to short-term functional outcomes.A total of 352 patients were included who underwent robotic-assisted medial UKA surgery and received a fixed-bearing metal-backed cemented medial UKA. Radiographic follow-up consisted of standard anteroposterior and lateral radiographs. Functional outcomes, using the Western Ontario and McMaster Universities Arthritis Index questionnaire, of patients with RLL were compared with a matched cohort, based on gender, age, and body mass index.In this cohort, 101 patients (28.8%) had physiological regional radiolucency around the femoral (10.3%) and/or tibial (25.3%) components, of which 6.8% concerned both components. Tibial RLL were more frequently seen compared with femoral RLL (P.001). Our data suggest that the time of onset of femoral radiolucency develops later (1.36 years) than tibial radiolucency (1.00 years, P = .02). No difference in short-term functional outcomes was found between the RLL group and the matched cohort group without radiolucency.This study acknowledges that tibial and femoral physiological radiolucencies may develop after cemented medial UKA. Furthermore, this was the first study showing that physiological femoral RLL occur later than tibial RLL. Prospective studies with longer follow-up and larger numbers are necessary to compare radiolucency in different UKA designs and the relationship to outcomes.

Knee laxity, defined as the net translation or rotation of the tibia relative to the femur in a given direction in response to an applied load, is highly variable from person to person. High levels of knee laxity as assessed during routine clinical exams are associated with first-time ligament injury and graft reinjury following reconstruction. During laxity exams, ligaments carry force to resist the applied load; however, relationships between intersubject variations in knee laxity and variations in how ligaments carry force as the knee moves through its passive envelope of motion, which we refer to as ligament engagement, are not well established. Thus, the objectives of this study were, first, to define parameters describing ligament engagement and, then, to link variations in ligament engagement and variations in laxity across a group of knees. We used a robotic manipulator in a cadaveric knee model (n = 20) to quantify how important knee stabilizers, namely the anterior and posterior cruciate ligaments (ACL and PCL, respectively), as well as the medial collateral ligament (MCL) engage during respective tests of anterior, posterior, and valgus laxity. Ligament engagement was quantified using three parameters: (1) in situ slack, defined as the relative tibiofemoral motion from the neutral position of the joint to the position where the ligament began to carry force; (2) in situ stiffness, defined as the slope of the linear portion of the ligament force–tibial motion response; and (3) ligament force at the peak applied load. Knee laxity was related to parameters of ligament engagement using univariate and multivariate regression models. Variations in the in situ slack of the ACL and PCL predicted anterior and posterior laxity, while variations in both in situ slack and in situ stiffness of the MCL predicted valgus laxity. Parameters of ligament engagement may be useful to further characterize the in situ biomechanical function of ligaments and ligament grafts.

Anterolateral ligament (ALL) reconstruction as an adjunct to anterior cruciate ligament (ACL) reconstruction remains a subject of clinical debate. This uncertainty may be driven in part by a lack of knowledge regarding where, within the range of knee motion, the ALL begins to carry force (engages). (1) Does the ALL engage in the ACL-intact knee; and (2) where within the range of anterior tibial translation occurring in the ACL-sectioned knee does the ALL engage? A robotic manipulator was used to measure anterior tibial translation, ACL forces, and ALL forces in 10 fresh-frozen cadaveric knees (10 donors; mean age, 41 ± 16 years; range, 20-64 years; eight male) in response to applied multiplanar torques. The engagement point of the ALL was defined as the anterior tibial translation at which the ALL began to carry at least 15% of the force carried by the native ACL; a threshold of 15% minimized the sensitivity of the engagement point of the ALL. This engagement point was compared with the maximum anterior tibial translation permitted in the ACL-intact condition using a paired Wilcoxon signed-rank test (p < 0.05). Normality of each outcome measure was confirmed using Kolmogorov-Smirnov tests (p < 0.05). The ALL engaged in five and four of 10 ACL-intact knees in response to multiplanar torques at 15° and 30° of flexion, respectively. Among the nine of 10 knees in which the ALL engaged with the ACL sectioned, the ACL-intact motion limit, and ALL engagement point, respectively, averaged 1.5 ± 1.1 mm and 5.4 ± 4.1 mm at 15° of flexion and 2.0 ± 1.3 mm and 5.7 ± 2.7 mm at 30° of flexion. Thus, the ALL engaged 3.8 ± 3.1 mm (95% confidence interval [CI], 1.4-6.3 mm; p = 0.027) and 3.7 ± 2.4 mm (95% CI, 2.1-5.3 mm; p = 0.008) beyond the maximum anterior tibial translation of the ACL-intact knee at 15° and 30° of flexion, respectively. In this in vitro, cadaveric study, the ALL engaged in up to half of the ACL-intact knees. In the ACL-sectioned knees, the ALL engaged beyond the ACL-intact limit of anterior subluxation on average in response to multiplanar torques, albeit with variability that likely reflects interspecimen heterogeneity in ALL anatomy. The findings suggest that surgical variables such as the joint position and tension at which lateral extraarticular grafts and tenodeses are fixed might be able to be tuned to control where within the range of knee motion the graft tissue is engaged to restrain joint motion on a patient-specific basis.