Fixed-bearing Medial Unicompartmental Knee Arthroplasty Restores Neither the Medial Pivoting Behavior Nor the Ligament Forces of the Intact Knee in Passive Flexion

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° flexion, but occurred from 30° to 90° 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

A review of the surgical conversion rate and independent management of spinal extended scope practitioners in a secondary care setting

INTRODUCTION Spinal orthopaedic triage aims to reduce unnecessary referrals to surgical consultants, thereby reducing waiting times to be seen by a surgeon and to surgical intervention. This paper presents an evaluation of a spinal orthopaedic triage service in the third largest spinal unit in the UK. METHODS A retrospective service evaluation spanning 2012 to 2014 was undertaken by members of the extended scope practitioner (ESP) team to evaluate the ESPs’ ability to manage patient care independently and triage surgical referrals appropriately. Data collected included rates of independent management, referral rates for surgical consideration and conversion to surgery. Patient satisfaction rates were evaluated retrospectively from questionnaires given to 5% of discharged patients. RESULTS A total of 2,651 patients were seen. The vast majority (92%) of all referrals seen by ESPs were managed independently. Only 8% required either a discussion with a surgeon to confirm management or for surgical review. Of the latter, 81% were considered to be suitable surgical referrals. A 99% satisfaction rate was reported by discharged patients. CONCLUSIONS ESP services in a specialist spinal service are effective in managing spinal conditions conservatively and identifying surgical candidates appropriately. Further research is needed to confirm ESPs’ diagnostic accuracy, patient outcomes and cost effectiveness

The Infrared Array Camera (IRAC) for the Spitzer Space Telescope

The Infrared Array Camera (IRAC) is one of three focal plane instruments in the Spitzer Space Telescope. IRAC is a four-channel camera that obtains simultaneous broad-band images at 3.6, 4.5, 5.8, and 8.0 microns. Two nearly adjacent 5.2x5.2 arcmin fields of view in the focal plane are viewed by the four channels in pairs (3.6 and 5.8 microns; 4.5 and 8 microns). All four detector arrays in the camera are 256x256 pixels in size, with the two shorter wavelength channels using InSb and the two longer wavelength channels using Si:As IBC detectors. IRAC is a powerful survey instrument because of its high sensitivity, large field of view, and four-color imaging. This paper summarizes the in-flight scientific, technical, and operational performance of IRAC.Comment: 7 pages, 3 figures. Accepted for publication in the ApJS. A higher resolution version is at http://cfa-www.harvard.edu/irac/publication

Validation of the HOOS, JR: A Short-form Hip Replacement Survey

BACKGROUND: Patient-reported outcome measures (PROMs) are increasingly in demand for outcomes evaluation by hospitals, administrators, and policymakers. However, assessing total hip arthroplasty (THA) through such instruments is challenging because most existing measures of hip health are lengthy and/or proprietary. QUESTIONS/PURPOSES: The objective of this study was to derive a patient-relevant short-form survey based on the Hip disability and Osteoarthritis Outcome Score (HOOS), focusing specifically on outcomes after THA. METHODS: We retrospectively evaluated patients with hip osteoarthritis who underwent primary unilateral THA and who had completed preoperative and 2-year postoperative PROMs using our hospital\u27s hip replacement registry. The 2-year followup in this population was 81% (4308 of 5351 patients). Of these, 2371 completed every item on the HOOS before surgery and at 2 years, making them eligible for the formal item reduction analysis. Through semistructured interviews with 30 patients, we identified items in the HOOS deemed qualitatively most important to patients with hip osteoarthritis. The original HOOS has 40 items, the four quality-of-life items were excluded a priori, five were excluded for being redundant, and one was excluded based on patient-relevance surveys. The remaining 30 items were evaluated using Rasch modeling to yield a final six-item HOOS, Joint Replacement (HOOS, JR), representing a single construct of hip health. We calculated HOOS, JR scores for the Hospital for Special Surgery (HSS) cohort and validated this new score for internal consistency, external validity (versus HOOS and WOMAC domains), responsiveness to THA, and floor and ceiling effects. Additional external validation was performed using calculated HOOS, JR scores in collaboration with the Function and Outcomes Research for Comparative Effectiveness in Total Joint Replacement (FORCE-TJR) nationally representative joint replacement registry (n = 910). RESULTS: The resulting six-item PROM (HOOS, JR) retained items only from the pain and activities of daily living domains. It showed high internal consistency (Person Separation Index, 0.86 [HSS]; 0.87 [FORCE]), moderate to excellent external validity against other hip surveys (Spearman\u27s correlation coefficient, 0.60-0.94), very high responsiveness (standardized response means, 2.03 [95% CI, 1.84-2.22] [FORCE]; and 2.38 [95% CI, 2.27-2.49] [HSS]), and favorable floor (0.6%-1.9%) and ceiling (37%-46%) effects. External validity was highest for the HOOS pain (Spearman\u27s correlation coefficient, 0.87 [95% CI, 0.86-0.89] [HSS]; and 0.87 [95% CI, 0.84-0.90] [FORCE]) and HOOS activities of daily living (Spearman\u27s correlation coefficient, 0.94 [95% CI, 0.93-0.95] [HSS]; and 0.94 [95% CI, 0.93-0.96] [FORCE]) domains in the HSS validation cohort and the FORCE-TJR cohort. CONCLUSIONS: The HOOS, JR provides a valid, reliable, and responsive measure of hip health for patients undergoing THA. This short-form PROM is patient relevant and efficient. LEVEL OF EVIDENCE: Level III, diagnostic study