Introduction

Modular neck (MN) components in total hip arthroplasty (THA) offer intraoperative flexibility, but adverse local tissue reactions (ALTR) due to tribocorrosion at modular junctions are a potential complication of such designs. Serum ion levels and metal artifact reduction sequence (MARS) MRI are used to assess ALTR following modular THA. This study investigates serum ion levels and MARS MRI findings in a series of hips with MN components and differing articulating surfaces.

Introduction

Clinical examination for stability in knee replacement involves the anterior drawer test. This test has been used to help in the diagnosis of flexion instability when used at 90 degrees and midflexion instability at 30 degrees. We sought to determine the inter-rater reliability of this test when compared to motion capture data.

Introduction

Recent literature has sought to quantify pre-operative work associated with total joint arthroplasty. These studies have utilized surveys or self-reported time logs to estimate the Pre-op Optimization Work (POW) completed by the surgical team. The purpose of this study was to objectively quantify POW associated with total hip arthroplasty (THA) using electronic medical record (EMR) activity audit logs.

Introduction

Golf is a recommended form of physical activity for older adults. However, clinicians have no evidence-based research regarding the demands on the hips of older adults during golf. The purpose of our in vivoobservational study was to quantify the hip biomechanics of older adult golfers.

Introduction

In November 2017, the Center for Medicare and Medicaid Services (CMS) finalized the 2018 Medicare Outpatient Prospective Payment System rule that removed total knee arthroplasty (TKA) procedures from the Medicare inpatient-only (IPO) list of procedures. This action had significant and unexpected consequences.

For several years, CMS has utilized a rule called the “Two-Midnight Rule” to define outpatient status for all procedures not on the IPO list. CMS made TKA subject to the “Two-Midnight Rule” in conjunction with the decision to move TKA off the IPO list. According to the “Two-Midnight Rule,” a hospital admission should be expected to span at least two midnights in order to be covered as an inpatient procedure. If it can be reliably expected that the patient will not require at least two midnights in the hospital, the “Two-Midnight Rule” suggests that the patient is considered an outpatient and is therefore subject to outpatient payment policies. Under prior guidance related to the “Two-Midnight Rule;” however, CMS also states that Medicare may treat some admissions spanning less than two midnights as inpatient procedures if the patient record contains documentation of medical need. The final rule was clear in stating CMS's expectation was that the great majority of TKAs would continue to be provided in an inpatient setting.

Introduction

The Centers for Medicare and Medicaid Services (CMS) removed total knee arthroplasty (TKA) from inpatient-only status in 2018. Our goal was to measure the adoption of outpatient TKAs, the impact on re-treatment rates, and the economic implications for hospitals.

Periprosthetic joint infections (PJI) continue to be a diagnostic challenge for orthopedic surgeons. Chronic PJI are sometimes difficult to diagnose and occasionally present in a subclinical fashion with normal CRP/ESR and/or normal joint aspiration. Some institutions advocate for routine use of intraoperative culture swabs at the time of all revision surgeries to definitively rule out infection. The purpose of this study is to determine whether routine intraoperative cultures is an appropriate and cost effective method of diagnosing subclinical chronic PJI in revision joint replacement patients with a low clinical suspicion for infection.

We performed a retrospective chart review and identified 33 patients that underwent revision hip or knee replacement from a single surgeon over a five-month period. The AAOS guidelines for preoperative PJI workup were followed. 13 patients were diagnosed preoperatively with infection and excluded from the study. 20 patients underwent revision joint replacement and three separate cultures swabs were taken for each patient to help in determining true-positive cultures. Infectious Disease was consulted for all patients with any positive culture. Culture results were reviewed. At our hospital, the cost billed to insurance for a single culture is $1,458.58. We did not calculate the cost of the consultant fee.

Three (15%) of the 20 revision arthroplasty patients had a single positive culture. Infectious Disease consultants diagnosed all three of these positive cultures as contaminants. None of the patients had a true-positive intraoperative culture. The total cost billed by the hospital to obtain these cultures in all 20 patients was $87,514.80

In our study, obtaining a set of three intraoperative cultures for those patients with a negative preoperative infection workup was not only cost prohibitive but did not diagnose a single subclinical infection. Studies to find other more reliable, accurate, and cost effective alternatives to diagnose PJI are warranted.

In patients undergoing revision hip or knee arthroplasty with a low preoperative clinical suspicion for infection, it does not seem that routine intraoperative culture swabs are necessary or cost effective method for diagnosing subclinical periprosthetic joint infection.

Introduction: An open-chain model was used to investigate the kinematics during isometric extension between normal knees and knees replaced with a tricompartmental prosthesis.

Methods: Ten cadaver legs were skeletonized while preserving the knee joint capsule, quadriceps and hamstring tendons. CT scans of the extremity were converted to CAD models that precisely related the bone surfaces to radio-opaque motion analysis markers. The limbs were mounted in a custom open-chain extremity rig [1]. Tibial motion was produced by a linear actuator attached to the quadriceps tendon in the direction of the vector addition of the absent quadriceps muscles. Tendon force was measured with an in-line force transducer and recorded at 300 Hz during the motion. Three-dimensional kinematic data of the isometric extension motion of the knee were recorded at 30 Hz using a motion capture camera system and combined with CAD models of the extremity to evaluate joint kinematics through virtual animations, contact points, and kinematic profiles. After collecting data on normal knee kinematics, each specimen underwent total knee replacement with commercially available implants. Anatomic and implant coordinates were registered to the motion capture data and the captured motion was imposed on the virtual model. The femoral anatomic axis was defined as a line from the center of the femoral head to the posterior cruciate ligament (PCL) femoral insertion point [2]. The tibial anatomic axis was defined as a line from the center of the line connecting the proximal tibial prominences to the center of the distal tibial articular surface [2]. The femoral internal/external (IE) rotation reference was a line connecting the peaks of the medial and lateral epicondyles [2]. The tibial IE rotation reference was a line defined by the anterior boundaries of the articular surfaces [3]. IE rotation angle was defined as the angle between these two reference lines, on a plane perpendicular to the tibial axis. Contact points between the femur and tibia, or corresponding components for the implanted knee, were determined in 30° increments between full extension and 120° flexion [4]. Animations of the virtual CAD models were created for visualization of the motion data.

Results: Tibio-femoral contact points for the normal knee indicate stable behavior on the medial compartment and progressive posterior motion of contact on the lateral side with increasing flexion. The normal knees demonstrated anterior contact on both the medial and lateral sides at full extension (0°). Within the first 30° of flexion, the contact point moves backwards on both medial and lateral sides of the joint, but markedly more so on the lateral. From then on, the contact point stays stable in the mid portion of the medial tibial plateau and more posterior on the lateral demonstrating medial pivoting kinematics. The replaced knee does not demonstrate the “screw-home” from 0°–30° but does demonstrate a stable medial contact point in the mid portion of the tibial plateau and gradual posterior movement of the contact point on the lateral side through 120°, indicating medial pivoting kinematics similar to the normal. These patterns were virtually identical across all specimens. Contact point translation data after knee replacement was consistent with the behavior of the normal knee. The anterior-posterior translation of each condyle for each specimen was normalized and averaged. The replaced knee demonstrated equal or smaller displacement values in all but one category (lateral deep flexion) and maintained similar profiles in all flexion ranges. These results indicate that the replaced knee is stable medially throughout the range of motion wth controlled lateral translation. The contact point AP position was compared at discreet flexion angles between normal and replaced knees. On the medial side, from 0°–110°, there was no statistical significant difference between the two cases with the p-values ranging from 0.45 to 0.79. However at 115° of flexion, the p-value was 0.04 indicating a statistical difference between the normal and replaced knees. The lateral condylar comparison yielded three flexion angles with a statistical difference, 60°, 105°, and 115° with pvalue of 0.05, 0.03, and 0.01 respectively. The mobility of the normal lateral compartment and the more constrained motion path of the replaced component are a factor of these differences.

Kinematic profiles of internal-external rotation and adduction-abduction for normal knees were consistent in shape among all specimens. Replaced knee kinematic profiles varied from normal but were consistent across specimens. The peak quadriceps tendon load for all specimens occurred at 65° with a decrease as the leg progressed to full extension. Tendon load of the implanted knee reached a maximum at 65° which then remained nearly constant through 15°. Tendon loads at 65° are within 10% of the normal knee loads (−4.5% ± 5.6) with two of the three specimens having greater than 10% decreases in tendon load.

Discussion and Conclusion: The normal knee kinematics appear to be driven by the bone geometry and the physical constraints of the soft tissues. The replaced knee kinematics are dependent mostly on the designed geometry of the implants since both cruciate ligaments and cartilage are absent from these trials. The total knee prosthesis implanted was designed as a ballin-socket on the medial side with a “ball-in-arcuate groove” on the lateral side. This design was intended to mimic the stable medial side of the normal knee while allowing the lateral side to rotate around it. In this open chain model, both normal and replaced knees indicate a stable medial side and free motion on the lateral side, demonstrating medial pivoting kinematics. The replaced knees also closely approximate the surface kinematics of the normal knees. Variation in kinematic profiles between the normal and replaced knees are partially attributed to surgical alignment correction. The quadriceps load necessary to move the knee at the same rate through the same range of motion were similar for the replaced knee compared to the normal knee exceeding the normal load by a maximum of 2%.

Introduction: Many attempts have been made to describe the flexion axis of the knee based on landmarks or simple geometric representations of the anatomy. An alternative approach is to use kinematic data to describe the axis of motion of the joint. The helical axis is one kinematic parameter that can accomplish this. The purpose of this study was to compare the correlation between kinematic and anatomic axes of motion.

Methods: Six cadaver lower extremities were skeletonized except for the knee joint. Passive navigation markers were implanted, and CT scans obtained. The limbs were then placed in an open-chain lower extremity rig that allows full range of knee motion. Threedimensional kinematic data were recorded using a camera and the helical axis of motion was calculated. Anatomic landmarks were placed on CT derived CAD models of the extremities consisting of spherical and cylindrical fits of the femoral condyles and a trans-epicondylar axis. Data for the normal knee was processed, by comparison of the helical axis to the landmark axes over varying ranges of flexion and the variation in helical axis direction within that range was also calculated.

Results: The flexion range with the minimum variation of anatomic parameters to the helical axis was 30–100°. Helical axis variation in this range was 5.489 ± 1.173, while variation between the helical axis and those axis defined by spherical, TEA, and cylindrical landmarks were 5.115 ± 2.129°, 3.127 ± 2.029°, and 5.111 ± 1.710°, respectively. A students t-test was performed on each data set with the null hypothesis that the angular difference between the anatomically defined axes and the helical axis is zero. All axes were found to be significantly different from the average helical axis in the range of 30–100° (P= 0.002, 0.013, and 0.001, respectively). The tightest variation in the helical axis occurred at 40–50° of flexion 2.89 ± 0.722.

Conclusion/Discussion/Summary: None of the anatomic landmarks considered in this study represent a consistently valid approximation of the kinematic flexion axis of the knee. The TEA represents the closest approximation of the three with a 95% CI between 0.998 and 5.256°. The range of 30–100° represented the tightest variation over the largest range of flexion. Extension was defined at approximately 30° based on kinematic profiles of internal/external rotation which show a “screw-home” tendency beginning at 30° through extension. This behavior is consistent with an increase in helical axis variation in ranges that were less than 30° of flexion. In a previous open-chain model, both compartments of the joint were spinning around 45 degrees of flexion, which is consistent with the smallest helical axis variation observed in the 40–50° range.

Purpose: A study was undertaken to determine the current prevalence of revisions of total knee arthroplasty (TKA) following minimal incision surgery (MIS) and to compare revisions of MIS TKA procedures to revisions of TKA performed following a standard surgical approach.

Method: A consecutive series of revision TKA performed at three centers by five surgeons over a three year time period was reviewed. Revisions performed for infection and re-revisions were excluded. Review of clinical and radiographic data determined incision type, gender, age, time to revision, and primary diagnosis at time of revision.

Results: Two hundred and thirty-seven first time revision TKAs were performed of which 44 (18.6%) had been a MIS primary TKA and 193 (81.4%) had been a standard primary TKA. Patients with MIS were younger (62.1 years versus 66.2 years, p=.02). There was a trend towards a higher percentage of females in the MIS group (75% versus 63%), although this difference was not significant (p=0.12). Most striking was the difference in time to revision which was significantly shorter for the MIS group (14.8 months versus 80 months, p< .001). The MIS group was much more likely to fail at < 12 months (37% versus 5%, p< .001) and at < 24 months (81% versus 22%, p< .001).

Conclusion: MIS TKA accounted for a substantial percentage of revision TKA in recent years at these centers. The high prevalence of MIS failures occurring within 24 months is disturbing and warrants further investigation.

Kneeling is an important aspect of daily living. Our goal was to describe the in vivo tibiofemoral kinematics during standing and kneeling after total knee arthroplasty (TKA).

Ten posterior substituting (PS) and 10 cruciate retaining (CR) TKA designs were studied in 18 patients. Radiographs were taken when standing, kneeling at 90°, and kneeling at maximal flexion. An image matching technique provided three-dimensional measurements of the femoral component position relative to the AP midpoint of the tibial baseplate.

When standing, the CR tibiofemoral contact position (medial: 7 mm ± 3; lateral: 6 mm ± 3) was more posterior than the PS design (medial: 5 mm ± 2; lateral: 5 mm ± 2). Movement from standing to kneeling at 90° produced different responses. CR knees translated anteriorly (medial: 4 mm ± 4; lateral: 2 mm ± 6), while PS knees translated posteriorly (medial: 0.2 mm ± 3; lateral: 1 mm ± 4). During kneeling, movement from 90° to maximum flexion produced posterior translation of the femur (CR medial: 5 mm ± 4: CR lateral: 5 mm ± 4; PS medial: 6 mm ± 4; PS lateral: 6 mm ± 3). The relationship between the tibiofemoral contact position and flexion angle during kneeling was more variable for CR knees (r2=0.38) than PS knees (r2=0.64), indicating that PS knees provide a more reliable AP position than CR knees.

PS knees dislocate when the arch of the femoral cam slides over the tibial post; CR knees sublux when the femoral contact position translates beyond the edge of the tibial baseplate. The distance to dislocation averaged 13 mm ± 2 for PS knees, and 20 mm±4 for CR knees.

Many patients wish to resume normal activities, including kneeling after TKA. This study provides information for surgeons and patients considering kneeling after TKA.