Total Knee Arthroplasty Kinematics Predict Patient-Reported Outcome Measures: Implications for Clinical Kinematic Examinations.

BACKGROUND: A core tenet of total knee arthroplasty (TKA) is that achieving more natural kinematics will lead to superior patient outcomes. Yet this relationship has not been proven for large representative cohorts of TKA patients because accurately measuring 3-dimensional TKA kinematics is time-consuming and expensive. But advanced imaging systems and machine learning-enhanced analysis software will soon make it practical to measure knee kinematics preoperatively and postoperatively in the clinic using radiographic methods. The purpose of this study was to assess the reported relationships between TKA kinematics and outcomes and distill those findings into a proposal for a clinically practical protocol for a clinical kinematic exam. METHODS: This study reviewed the recent literature relating TKA kinematics to patient outcomes. There were 10 studies that reported statistical associations between TKA kinematics and patient outcome scores utilizing a range of functional activities. We stratified these activities by the complexity of the radiographic examination to create a proposed examination protocol, and we generated a list of requirements and characteristics for a practical TKA clinical kinematic examination. RESULTS: Given considerations for a clinically practical kinematic exam, including equipment, time and other resources, we propose 3 exam levels. With basic radiographs, we suggest studying single-leg stance in extension, lunge or squat, and kneeling. For fluoroscopic systems with X-ray pulses up to 20 ms, we propose chair-rise or stair ascent to provide additional dynamic information. For fluoroscopic systems with X-ray pulses of less than 10 ms, we propose rapid open-chain knee flexion-extension to simulate the highly dynamic swing phase of gait. CONCLUSIONS: It is our hope that this proposed examination protocol spurs discussion and debate so that there can be a consensus approach to clinical examination of knee and TKA kinematics when the rapidly advancing hardware and software capabilities are in place to do so.

Robotic-assisted Total Knee Arthroplasty Technology Provides a Repeatable and Reproducible Method of Assessing Soft Tissue Balance.

Soft-tissue balancing is an important factor in primary total knee arthroplasty (TKA), with 30 to 50% of TKA revisions attributed to technical operative factors including soft-tissue balancing. Robotic-assisted TKA (RATKA) offers opportunities for improved soft-tissue balancing methods. This study aimed to evaluate the repeatability and reproducibility of ligamentous laxity assessments during RATKA using a digital tensioner.Three experienced RATKA surgeons assessed preresection and trialing phases of 12 human cadaveric knees with varying degrees of arthritis. Ligamentous laxity was assessed with manual varus and valgus stresses in extension and flexion, with a digital tensioner providing feedback on the change of laxity displacement. Intraclass correlation coefficient (ICC) analyses were used to determine the repeatability within a single surgeon and reproducibility between the three surgeons.The results showed excellent repeatability and reproducibility in ligamentous laxity assessment during RATKA. Surgeons had excellent repeatability for preresection and trialing assessments, with median ICC values representing excellent reproducibility between surgeons. Surgeons were repeatable within 1 or 1.5 mm for preresection and trialing assessments. On average, the variation within a surgeon was 0.33 ± 0.26 mm during preresection and 0.29 ± 0.28 mm during trialing. When comparing surgeons to each other, they were reproducible within an average of 0.69 ± 0.33 mm for preresection and 0.65 ± 0.31 mm for trialing.This study demonstrated the reliability of robotic-assisted soft-tissue balancing techniques, providing control over ligamentous laxity assessments, and potentially leading to better patient outcomes. The digital tensioner used in this study provided excellent repeatability and reproducibility in ligamentous laxity assessment during RATKA, highlighting the potential benefits of incorporating robotics in TKA procedures.

Posterior Compartment Debridement and Varus Deformity Correction in Total Knee Arthroplasty.

BACKGROUND: Restoration of joint-line position and deformity correction remain important tenets for preserving stability and function after total knee arthroplasty (TKA). We sought to characterize the role of posterior osteophytes in the correction of alignment deformity during TKA. METHODS: We evaluated 57 patients (57 TKAs) who participated in a trial of robotic-arm assisted TKA outcomes. Weight-bearing and fixed preoperative alignment was measured using long-standing radiographs and tools of the robotic-arm tracking system, respectively. Total volume (cm3) of posterior osteophytes was quantified using preoperative planning computed tomography scans. Joint-line position was evaluated using bone resection thicknesses measured using a caliper. RESULTS: The mean (minimum to maximum) initial fixed deformity was 4 degrees (range, 0 to 11) of varus. All patients showed asymmetric posterior osteophytes. Mean total osteophyte volume was 3 cm3 (range, 1 to 9). Total osteophyte volume was positively correlated with severity of fixed deformity (r = 0.48, P = .0001). Removal of osteophytes allowed for the correction of functional alignment to within 3 degrees of neutral in all cases (mean 0 degree), with none requiring release of the superficial medial collateral ligament. Tibial joint-line position was restored to within 3 millimeters in all but 2 cases (mean increase of height, 0.6 [range, -4 to +5]). CONCLUSION: In the end-stage diseased knee, posterior osteophytes typically occupy space in the posterior capsule on the concave side of the deformity. Thorough debridement of posterior osteophytes may help facilitate management of modest varus deformity with decreased need for soft-tissue releases or adjustments to planned bone resection.

Mid-Term Performance of the First Mass-Produced Three-Dimensional Printed Cementless Tibia in the United States as Reported in the American Joint Replacement Registry.

BACKGROUND: Cementless tibial components have shown improvements in clinical performance compared to predicate designs, though evidence supporting mid-term performance and fixation is scarce. The purpose of this study is to determine the mid-term survivorships, revision rates, and reasons why 3-dimensional printed cementless tibial baseplates (3DTKAs) failed compared to other cementless as well as cemented tibial baseplates reported from the American Joint Replacement Registry (AJRR) data. METHODS: All primary total knee arthroplasty (TKA) cases performed in patients 65 years of age or older within the AJRR from January 2, 2012 through June 30, 2020 were queried. A total of 28,631 3DTKAs were identified from 428 institutions. These were compared to all other "aggregated cementless tibia" (n = 7,577) and "aggregated cemented tibia" (n = 550,133) cases. Centers for Medicare & Medicaid Services data over the same time period were merged with AJRR data to determine survivorship and patient-timed incident revision rates per 1,000 years. Failure reasons were tracked during this study period. RESULTS: At 60 months, Kaplan-Meier implant survivorship was 98.9% (CI 98.7-99.0), 98.3% (CI 97.9-98.6), and 98.4% (CI 98.4-98.5) in the 3DTKA, aggregate cementless, and cemented knee cohorts, respectively (P < .0001). Patient-timed incident revision rates were 3.11 (CI 2.75-3.53), 3.99 (CI 3.34-4.76), and 3.35 (CI 3.28-3.42) for those cohorts, which corresponds to a revision rate of 0.31%, 0.40%, and 0.34% per year. CONCLUSION: In this analysis, 3DTKA had favorable survivorship and lower revision rates compared to aggregate cementless and cemented TKAs implanted from the same national database during the same time period.

Return to Work and Driving After Robotic Arm-Assisted Total Knee Arthroplasty.

Background: Robotic arm-assisted total knee arthroplasty (RATKA) has demonstrated improved patient-reported outcome measures. Less evidence has been reported on how frequently patients return to complex activities of daily living. Our purposes were to investigate (1) hospital lengths of stay (LOSs) (2) discharge dispositions and (3) the rates and postoperative time intervals at which patients returned to driving and working. Methods: A total of 50 RATKA patients who were employed prior to surgery were included. Outcomes included hospital LOS, discharge dispositions, return to driving, and return to work. Results: A total of 48 patients (96%) were discharged home with self-care or health aid discharge after a mean LOS of 1.2 ± 0.6 days. Twelve patients (24%) returned to driving within 3 weeks of surgery. In our study, 100% of patients who underwent RATKA returned to driving after a mean of 29 days (range, 4 to 62 days). Forty-five patients (90%) returned to their preoperative level of work after a mean of 46 days (range, 2 to 96 days). Nineteen patients (38%) returned to work within 3 weeks. Conclusions: This study showed fast recovery after RATKA, with >90% returning to driving and working at full capacity within 2 months. Many (38%) returned to work within 3 weeks. Further studies to demonstrate the value of RATKA with respect to recovery of complex activities are needed. Compared to controls from previously published literature on manual total knee arthroplasties, it appears that patients who undergo RATKA have similar or better outcomes in reference to return to driving.

Increased Prevalence of Posterior Cruciate Ligament Dysfunction Noted With 3-Dimensional Intraoperative Kinematic Evaluation in Total Knee Arthroplasty.

BACKGROUND: Poor restoration of cruciate-driven kinematics after total knee arthroplasty may result from technical difficulties, but the ligament may also be functionally compromised by the presence of arthritis. We asked whether the function of the posterior cruciate ligament (PCL) could be assessed intraoperatively to predict the quality of the resulting posterior cruciate kinematics. METHODS: PCL integrity was assessed using intraoperative infrared trackers to monitor knee kinematics in 73 patients. Three-dimensional images of the femur and tibia were projected onto a screen, allowing the surgeon to visualize kinematic relationships in real time. We measured femoral rollback (distance of femoral contact as a percentage of antero-posterior tray width) from images captured by the robotic system during initial kinematic assessment, gap balancing, and assessment of the final construct and from lateral flexion radiographs obtained 2 years after surgery. Associations were characterized using Pearson's correlation and graphical methods. RESULTS: Thirty-six knees (49%) showed rollback <60% during gap balancing, indicative of PCL insufficiency. The rollback during gap balancing was positively correlated with that seen in the final cruciate retaining constructs (r = 0.60, P < .001), which in turn predicted rollback 2 years after surgery on lateral flexion X-rays (r = 0.50, P = .006). CONCLUSION: Intraoperative functional evaluations can allow the surgeon to identify cases where rollback is not consistent with desirable knee kinematics, and posterior stabilization may lead to a better outcome for those patients.

Improved Component Placement Accuracy with Robotic-Arm Assisted Total Knee Arthroplasty.

Component position of total knee arthroplasty (TKA) has been shown to influence prosthetic survivorships and clinical outcomes. Our objective was to compare the three-dimensional accuracy to plan of robotic-arm assisted TKA (RATKA) with conventional TKA for component position. We conducted a nonrandomized, prospective study comparing 143 RATKA with 86 conventional TKA operated at four U.S. centers between July 2016 and October 2018. Computed tomography (CT) scans obtained approximately 6 weeks postoperatively were analyzed using anatomical landmarks. Absolute deviation from surgical plans were defined as the absolute value of the difference between the CT measurements and surgeons' femoral and tibial component mechanical varus/valgus alignment, tibial component posterior slope, and femoral component internal/external rotation. Differences of absolute deviations were tested using stratified Wilcoxon's tests that controlled for study center. Patient-reported outcome measures collected through 1 postoperative year were modeled using multiple regression controlling for age, sex, body mass index, study center, and the preoperative score. RATKA demonstrated greater accuracy for tibial component alignment (median [25th, 75th percentiles] absolute deviation from plan of all centers combined for conventional vs. RA, 1.7 [0.9, 2.9] vs. 0.9 [0.4, 1.9] degrees, p < 0.001), femoral component rotation (1.5 [0.9, 2.5] vs. 1.3 [0.6, 2.5] degrees, p = 0.015), and tibial slope (2.9 [1.5, 5.0] vs. 1.1 [0.6, 2.0] degrees, p < 0.001). In multivariable analyses, RATKA showed significantly greater Veterans RAND 12-item health survey (VR-12) physical component scores (adjusted mean difference [95% confidence interval (CI)]: 2.4 [0.2, 4.5] points, p = 0.034) and qualitatively greater Knee Society (KS) composite functional scores (3.5 [-1.3, 8.2] points, p = 0.159), though not statistically significant. Compared with conventional instrumentation, RATKA demonstrated greater three-dimensional accuracy to plan for various component positioning parameters and clinical improvements in physical status and function with no major safety concerns during the first postoperative year. These results may be attributed to the preoperative CT scan planning, real-time intraoperative feedback, and stereotactic-guided cutting that takes into consideration patient-specific bony anatomy. These findings support the use of RATKA for enhanced arthroplasty outcomes.

Lower limb kinematics of unicompartmental knee arthroplasty individuals during stair ascent.

OBJECTIVE: Purpose of the study was to compare lower-limb kinematics and interlimb asymmetry during stair ascent in individuals post-medial or lateral unicompartmental knee arthroplasty (UKA). METHODS: 60 patients (20 medial; 10 lateral) post-UKA and 30 matched healthy controls performed stair ascent. Spatio-temporal, lower-limb kinematics and interlimb asymmetries during stair ascent were compared. RESULTS: Medial-UKA group displayed 5° less knee extension of the UKA limb than controls (p = 0.005) and 2° less than the contralateral limb during stance phase. No interlimb asymmetries were found for lateral-UKA. CONCLUSION: Patients post-UKA demonstrate satisfactory lower-limb kinematics and minimal interlimb asymmetry during stair ascent compared to healthy individuals.

Patient-Reported Functional and Satisfaction Outcomes after Robotic-Arm-Assisted Total Knee Arthroplasty: Early Results of a Prospective Multicenter Investigation.

The purpose of this study was to perform a 3-month interim comparative analysis on outcomes between robotic-arm-assisted total knee arthroplasty (RATKA) and manual TKA patients. Specifically, we evaluated (1) patient self-reported symptoms, (2) expectations and satisfaction, and (3) functional activities, based on the 2011 Knee Society Scoring System. Between June 1, 2016, and March 31, 2018, 252 patients (102 manual and 150 robotic) were enrolled into a prospective, nonrandomized, open-label, multicenter comparative cohort study. Functional activity scores, patient-reported symptoms, as well as satisfaction and expectation scores were obtained from the 2011 Knee Society Scoring System preoperatively, at 4 to 6 weeks, and at 3 months postoperatively. Student's t-tests, Wilcoxon rank-sum tests, and chi-square tests with α set at 0.05 were used to compare between-group mean improvements from baseline. At 4 to 6 weeks postoperatively, RATKA patients were found to have significantly larger improvements in walking and standing (1.4 vs. -1.2 points; p = 0.019). RATKA patients were also found to have larger improvements in advanced activities (1.3 vs. 2.3 points), pain with walking (3.3 vs. 3.2 points), satisfaction score (12.4 vs. 12 points), and expectations score (5.1 vs. 4.4 points) when compared with manual TKA patients. At 3 months, RATKA patients were also found to have larger improvements in walking and standing (6.0 vs. 4.8 points), standard activities (11.4 vs. 10.1 points), advanced activities (6.2 vs. 4.6 points), functional activities total score (22.8 vs. 21.2 points), pain with walking (4.3 vs. 4.1 points), total symptoms score (10.5 vs. 10.3 points), satisfaction score (17.0 vs. 15.5 points), expectations score (4.8 vs. 4.0 points) when compared with manual TKA patients. The data indicate RATKA patients to have equal or greater improvements in 9 out of 10 of the Knee Society Scoring System components assessed at 3 months postoperatively, though not all findings were statistically significant. Since this is an early results report, this study will be continued for a longer follow-up, but we are encouraged by these interim results.

Robotic-Arm Assisted Total Knee Arthroplasty More Accurately Restored the Posterior Condylar Offset Ratio and the Insall-Salvati Index Compared to the Manual Technique; A Cohort-Matched Study.

INTRODUCTION: Despite the demonstrated success of modern total knee arthroplasty (TKA), it remains a procedure that involves sophisticated preoperative planning and meticulous technique to reconstruct the mechanical axis, achieve ideal joint balance, and restore maximal range-of-motion (ROM). Recently, robotic-arm assisted TKAs have emerged as a promising new technology offering several technical advantages, and it is achieving excellent radiological results, including establishing the posterior condylar offset ratio (PCOR) and the Insall-Salvati Index (ISI). Studies have demonstrated that these parameters are surgically modifiable, and their accurate restoration (fewer mean differences) correlate with improved final joint range-of-motion. However, there is a paucity of studies that evaluate these parameters in light of performing robotic-arm assisted TKA. Therefore, in this study, we aimed to compare: 1) PCOR and 2) ISI restoration in a cohort of patients who underwent robotic-arm assisted versus manual TKA. MATERIALS AND METHODS: We evaluated a series of 43 consecutive robotic-arm assisted (mean age 67 years; range, 46 to 79 years) and 39 manual total knee arthroplasties (mean age 66 years; range, 48 to 78 years) performed by seven fellowship-trained joint reconstructive surgeons. All surgeries were performed using medial para-patellar approaches by high-volume surgeons. Using the Knee Society Radiographic Evaluation System, preoperative and four-to six-week postoperative radiographs were analyzed to determine the PCOR and patella height based on the ISI. RESULTS: The mean postoperative PCOR was larger in manual TKA when compared to the robotic-assisted cohort (0.53 vs. 0.49; p=0.024). The absolute mean difference between pre- and postoperative PCOR was larger in manual when compared to robotic-arm assisted TKA (0.03 vs. 0.004; p=0.01). In addition, the number of patients who had postoperative ISI outside of the normal range (0.8 to 0.12) was higher in the manual cohort (12 vs. 4). CONCLUSION: Patients who underwent TKA using robotic-arm assisted technology had smaller mean differences in PCOR which has been previously shown to correlate with better joint ROM at one year following surgery. In addition, these patients were less likely to have values outside of normal ISI, which means they are less likely to develop patella baja, a condition in which the patella would impinge onto the patellar component, leading to restricted flexion and overall decreased ROM.

Disease Progression After Lateral and Medial Unicondylar Knee Arthroplasty.

BACKGROUND: Medial unicompartmental knee arthroplasty (UKA) has been a successful option for treatment of arthritis in patients with a healthy lateral compartment. However, lateral UKA is less common and results are less consistent. The purpose of this study is to compare progression of radiographically evident osteoarthritis in unoperated compartments during 5 years after lateral and medial UKA. METHODS: We undertook serial radiographic evaluation of 20 lateral and 114 medial UKA performed by the senior author during calendar years 2007-2008. Anteroposterior, lateral, and skyline radiographs obtained preoperatively and 1 and 5+ (mean, 5.3; range, 5.1-6.4) years postoperatively were independently graded for osteoarthritis in the unoperated tibiofemoral (TF) and patellofemoral (PF) compartments using established scales of Kellgren (0-4 point global scale for osteoarthritis), Ahlbäck (0-5 point scale based on joint space narrowing), and Altman (0-12 point composite criteria score). Rates of disease progression were compared between lateral and medial UKA groups using bivariate methods and multilevel growth models that adjusted for baseline characteristics. RESULTS: All mean disease grades for the TF and PF compartments increased (worsened) over time. The adjusted rate of Kellgren grade change was statistically (P < .05) faster for lateral UKA in the TF and PF compartments, as was Ahlbäck change in the TF compartment. Kellgren grade for the TF compartment of lateral and medial UKA groups increased 1.1 vs 0.6 points on average over 5 years adjusted for age, sex, and body mass index (P < .001). CONCLUSION: Surgeons should consider the propensity for faster disease progression after UKA in evaluating patients with isolated lateral compartment disease. LEVEL OF EVIDENCE: Level III, therapeutic study.

Knee strength, power and stair performance of the elderly 5 years after unicompartmental knee arthroplasty.

BACKGROUND: Unicompartmental knee arthroplasty (UKA) has been shown to demonstrate some satisfactory short-term outcomes. However, to our knowledge, there have been no reports on midterm or long-term knee extensor strength and leg extensor power post-UKA. AIMS: Therefore, the purposes of this study were: (1) to assess the isokinetic knee extensor strength, leg extensor power and stair performance of elderly participants at 5 years UKA post-operation; (2) to compare the differences in knee extensor strength and leg extensor power between the UKA and contralateral healthy limbs. METHODS: Nineteen elderly participants (75 ± 5 years) who had a medial or a lateral compartment UKA at 5 years post-operation were recruited. The isokinetic knee extensor strength and leg extensor power were measured. The stair performance was tested on a 4-step stair, and ascent and descent velocities were calculated. The pain level was assessed. RESULTS: The UKA limbs' knee extensor strength and leg extensor power were 1.01 ± 0.39 Nm/kg and 0.98 ± 0.27 W/kg, respectively. The stair ascent and descent velocities were 0.37 ± 0.07 and 0.38 ± 0.11 m/s, respectively. In addition, the UKA limbs exhibited comparable knee strength and leg power relative to the contralateral limbs. DISCUSSION: In general, the knee extensor strength and leg extensor power exhibited by the UKA limbs at 5 years post-operation may be typical in comparison with the normative data. CONCLUSIONS: We suggest that UKA is a satisfactory treatment in regard to the recovery of knee strength, leg power and ability to climb up and down stairs.

Balanced Flexion and Extension Gaps Are Not Always of Equal Size.

BACKGROUND: It has been widely accepted in total knee arthroplasty (TKA) that flexion and extension gaps in the disarticulated knee during surgery should be equalized. We hypothesized that tensioning during assessment of the flexion gap can induce temporary widening of the gap due to posterior tibial translation. We aimed to describe posterior tibial translation at flexion gap (90°) assessments and assess the correlation of tibial translation with laxity (flexion space increase) using constrained and non-constrained inserts. METHODS: Imageless navigation was used to measure flexion angle, tibial position relative to the femoral axis, and lateral/medial laxity in 30 patients undergoing primary TKA. Trialing was conducted using posteriorly stabilized and cruciate retaining trials of the same size to elucidate the association of posterior tibial translation with changes in joint capsule laxity at 90° knee flexion. RESULTS: All patients demonstrated posterior tibial translation during flexion gap assessment relative to their subsequent final implantation [mean ± standard deviation (range), 11.3 ± 4.4 (4-21) mm]. Positive linear correlation [r = 0.69, 95% confidence interval (CI) 0.44-0.84, P ≤ .001] was demonstrated between translations [8.7 ± 2.4 (3-13) mm] and laxity changes [2.9° ± 2.0° (-0.7° to 7.4°)] at 90° of flexion. CONCLUSION: Posterior tibial translation can cause artifactual widening of the flexion gap during gap balancing in posteriorly stabilized TKA, which can be of sufficient magnitude to alter femoral component size selection for some patients. Recognition and management of these intra-operative dynamics for optimal kinematics could be feasible with the advent of robotic applications.

Knee moments after unicompartmental knee arthroplasty during stair ascent.

BACKGROUND: For unicompartmental knee arthroplasty (UKA), abnormal loading on the tibiofemoral joint could exacerbate knee osteoarthritis or implant wear. Joint moments are an indirect measure of such loading. However, little is known about knee moments of patients with UKA, tempering enthusiasm for its use. QUESTIONS/PURPOSES: In patients with UKAs performing stair ascent, we (1) determined whether interlimb differences for knee moments are demonstrated, (2) described the knee kinetics of patients with medial and lateral UKAs, and (3) investigated possible factors that might influence the knee abductor moments. METHODS: In our cross-sectional study, we recruited 26 patients with UKA with nondiseased contralateral limbs who performed stair ascent. Seventeen patients had medial UKAs and nine had lateral UKAs. Paired t-tests and CIs were applied to determine interlimb differences within each UKA group for peak knee moments and times to peak moments. RESULTS: During stair ascent, the medial UKA group displayed greater peak extensor moments for the nondiseased compared to the UKA limb (p = 0.030), whereas the lateral UKA group did not (p = 0.087). For both medial and lateral UKA groups, the UKA limb demonstrated greater internal peak abductor moments (p = 0.005 and 0.013, respectively). Both UKA groups exhibited knee moments similar to those in the literature. Limb dominance and postoperative time were correlated for both UKA groups. CONCLUSIONS: Reduced knee extensor moments of limbs with UKA displayed by some participants may indicate less compressive loading on the tibiofemoral joint surfaces, whereas the increased abductor moments suggest increased compression on the medial compartment. These findings suggest UKA knees may not be subjected to excessive loads regardless of the side reconstructed.

Can squeaking with ceramic-on-ceramic hip articulations in total hip arthroplasty be avoided?

Squeaking is a recognized complication of total hip arthroplasty with ceramic on ceramic bearings but the etiology has not been well identified. We evaluated 183 hips in 148 patients who had undergone ceramic-on-ceramic noncemented total hip arthroplasties at one center between 1997-2007 by standardized telephone interviews and radiographic review. Audible squeaking was reported from 22 hips (12% of 183) of 19 patients. Prevalence of squeaking was associated with younger age; obesity; lateralized cup position; use of beta titanium alloy femoral components and shortened head length options; and higher reported activity level, greater pain, and decreased satisfaction at the time of the interview. Squeaking was described as having little personal significance by most patients. Squeaking might be preventable in part through medialization of the acetabular cup and avoidance of the use of shortened femoral necks.

Does interlimb knee symmetry exist after unicompartmental knee arthroplasty?

BACKGROUND: Unicompartmental knee arthroplasty (UKA) has long been a treatment option for patients with disease limited primarily to one compartment with small, correctable deformities. However, some surgeons presume that normal kinematics of a lateral compartment UKA are difficult to achieve. Furthermore, it is unclear whether UKA restores normal knee kinematics and interlimb symmetry. QUESTIONS/PURPOSES: We determined knee kinematics exhibited during stair ascent by patients with medial- (MED-UKA) or lateral-UKA (LAT-UKA) and if the knee kinematics of the operated and nonoperated limbs were symmetrical. METHODS: Participants were 17 individuals with MED-UKA and nine with LAT-UKA, all with nondiseased contralateral limbs. For each limb, participants walked up four stairs for five trials while a motion-capture system obtained reflective marker locations. Temporal events were determined by force platform signals. Interlimb symmetry was classified for temporal gait and knee angular kinematics by comparing observed interlimb differences with clinically meaningful differences set at 5% of stride time for temporal variables and 5° for angular variables. The minimum postoperative followup was 6 months (median, 24 months; range, 6-53 months). RESULTS: Neither group demonstrated clinically meaningful mean interlimb differences. However, approximately half of participants of each UKA group displayed asymmetry favoring the operative or nonoperative limb with similar frequency. CONCLUSIONS: Many patients undergoing UKA demonstrate kinematic interlimb symmetry during stair ascent. Interlimb asymmetry may be affected by a variety of factors unrelated to the UKA. CLINICAL RELEVANCE: A MED- or LAT-UKA can potentially restore normal knee function for a demanding task of daily life.

Cementation of tibial inserts into nonmatching base plates in revision total knee arthroplasty.

UNLABELLED: We describe the use of a novel technique for adapting nonmatching tibial inserts into tibial trays in revision total knee arthroplasty. From 1998 to 2003, the senior author performed 7 revision total knee arthroplasty procedures, during which a nonmatching tibial insert was cemented into a tibial tray to retain a well-fixed but incompatible opposite component. Bench tests were undertaken to confirm the stability of cement as a locking mechanism substitute. Three components completed 1 000 000 cycles of loading under simulated physiologic stresses with no evidence of fixation failure. There have been no clinical failures at 18 to 69 months in vivo follow-up (mean, 49 months). This technique provided durable fixation while avoiding host bone damage that might have occurred needlessly had the well-fixed implant been extracted. LEVEL OF EVIDENCE: level IV therapeutic study, case series.

The John Insall Award: no functional advantage of a mobile bearing posterior stabilized TKA.

BACKGROUND: Mobile bearing (MB) total knee design has been advocated as a means to enhance the functional characteristics and decrease the wear rates of condylar total knee arthroplasty (TKA). However, it is unclear if these designs achieve these goals. QUESTIONS/PURPOSES: We asked whether function of patients or survivorship would be greater or complications would be lesser in groups of patients with MB compared with fixed bearing (FB) TKA. We also sought to describe retrieval findings. METHODS: We randomized 507 primary TKAs in 416 eligible patients to receive MB (n = 252) or FB (n = 255) devices from November 2001 to August 2007 (Investigational Device Exemption G000180, ClinicalTrials.gov registration number NCT00946075). Patients were blinded to treatment allocation. WOMAC Index, SF-12 Health Survey, knee range of motion, and Knee Society scores were collected and compared preoperatively and at 6, 12, and 24 months postoperatively. We recorded device failures and complications until October 2009. Kaplan-Meier survivorship was compared using the log rank test. Twelve retrieved MB devices underwent pathologic analysis. The minimum postoperative time was 2.2 years (mean, 5.9 years; range, 2.2-7.9 years). RESULTS: We found no differences in mean clinical assessment scores or mean score changes from baseline at any postoperative interval through 2 postoperative years. Nineteen of the 252 MB and 13 of the 255 FB knees had undergone revision of any component. Estimated survival at 6 postoperative years was similar for the two devices: 90.1% (95% confidence interval [CI], 84.1-93.9) for MB and 94.2% (95% CI, 90.1-96.6) for FB. Two MB and no FB tibial components were revised for loosening. There was one case of MB insert dislocation. Retrieved MB devices demonstrated no unexpected wear or mechanical device failures. CONCLUSION: We found no evidence of functional advantage of the MB design. Survivorship was similar, although the study is limited by short duration of followup.