Unicompartmental knee arthroplasty approximates healthy knee kinematics more closely than total knee arthroplasty.

Total knee arthroplasty (TKA) and unicompartmental knee arthroplasty (UKA) are effective surgeries to treat end-stage knee osteoarthritis. Clinicians assume that TKA alters knee kinematics while UKA preserves native knee kinematics; however, few studies of in vivo kinematics have evaluated this assumption. This study used biplane radiography to compare side-to-side tibiofemoral kinematics during chair rise, stair ascent, and walking in 16 patients who received either TKA or UKA. We hypothesized that TKA knees would have significant kinematic changes and increased asymmetry with the contralateral knee, while UKA knee kinematics would not change after surgery and preoperative knee symmetry would be maintained. Native bone and implant motion were tracked using a volumetric model-based tracking technique. Six degrees of freedom kinematics were calculated throughout each motion. Kinematics were compared between the operated and contralateral knees pre- and post-surgery using a linear mixed-effects model. TKA knees became less varus with the tibia more medial, posterior, and distal relative to the femur. UKA knees became less varus with the tibia less lateral on average. Postoperative TKA knees were in less varus than UKA knees on average and at low flexion angles, with an internally rotated tibia during chair rise and stair ascent. At high flexion angles, the tibia was more medial and posterior after TKA than UKA. Side-to-side kinematic symmetry worsened after TKA but was maintained or improved after UKA. Greater understanding of kinematic differences between operated and contralateral knees after surgery may help surgeons understand why some patients remain unsatisfied with their new knees.

Hydrogen Peroxide, Povidone-Iodine and Chlorhexidine Fail to Eradicate Staphylococcus aureus Biofilm from Infected Implant Materials.

Hydrogen peroxide, povidone-iodine, and chlorhexidine are antiseptics that are commonly added to irrigants to either prevent or treat infection. There are little clinical data available that demonstrate efficacy of adding antiseptics to irrigants in the treatment of periprosthetic joint infection after biofilm establishment. The objective of the study was to assess the bactericidal activity of the antiseptics on S. aureus planktonic and biofilm. For planktonic irrigation, S. aureus was exposed to different concentrations of antiseptics. S. aureus biofilm was developed by submerging a Kirschner wire into normalized bacteria and allowing it to grow for forty-eight hours. The Kirschner wire was then treated with irrigation solutions and plated for CFU analysis. Hydrogen peroxide, povidone-iodine, and chlorhexidine were bactericidal against planktonic bacteria with over a 3 log reduction (p < 0.0001). Unlike cefazolin, the antiseptics were not bactericidal (less than 3 log reduction) against biofilm bacteria but did have a statistical reduction in biofilm as compared to the initial time point (p < 0.0001). As compared to cefazolin treatment alone, the addition of hydrogen peroxide or povidone-iodine to cefazolin treatment only additionally reduced the biofilm burden by less than 1 log. The antiseptics demonstrated bactericidal properties with planktonic S. aureus; however, when used to irrigate S. aureus biofilms, these antiseptics were unable to decrease biofilm mass below a 3 log reduction, suggesting that S. aureus biofilm has a tolerance to antiseptics. This information should be considered when considering antibiotic tolerance in established S. aureus biofilm treatment.

An Analysis of Radiographic Leg Length Discrepancy and Hip Offset in Patients at Risk of Developing Osteoarthritis.

Background: Leg length and hip offset are important principles in total hip arthroplasty (THA). Patients may endorse leg length differences (LLD) postoperatively that may be anatomical or functional. The objective of this study was to determine the normal radiographic variation in leg length and hip offset in a preosteoarthritic population without a THA. Methods: A retrospective study was completed using data from the Osteoarthritis Initiative, a prospective longitudinal study. Patients at risk of developing or with early osteoarthritis without inflammatory arthritis or prior THA were included. Measurements were made from full limb length anterior-posterior (AP) radiographs. Multiple linear regression models were employed to predict side-to-side differences in LLD, Δ femoral offset (FO), Δ abductor muscle length (AML), Δ abductor lever arm, and Δ AP pelvic offset. Results: The mean radiographic LLD was 4.6 mm, with 12 mm within 1 standard deviation. No significant differences were detected between LLD and sex, age, body mass index, or height. The median radiographic differences in FO, AML, abductor lever arm, and AP pelvic offset were 3.2 mm, 4.8 mm, 3.6 mm, and 3.3 mm, respectively. Height was predictive of Δ FO, while both height and age were predictive of Δ AML. Conclusions: Radiographic leg length variations in a population without symptomatic or radiographic osteoarthritis exist. FO and AML are dependent on patient characteristics. Preoperative radiographic LLD is not predicted by age, gender, body mass index, or height. It should be stressed that anatomic reconstruction is one of the many goals of arthroplasty and can stand in conflict with the priority and primary goals of stability and fixation, which should be prioritized.

Dose optimization in surgical prophylaxis: sub-inhibitory dosing of vancomycin increases rates of biofilm formation and the rates of surgical site infection.

Antibiotic stewardship is viewed as having great public health benefit with limited direct benefit to the patient at the time of administration. The objective of our study was to determine if inappropriate administration of antibiotics could create conditions that would increase the rates of surgical infection. We hypothesized that sub-MIC levels of vancomycin would increase Staphylococcus aureus growth, biofilm formation, and rates of infection. S. aureus MRSA and MSSA strains were used for all experiments. Bacteria were grown planktonically and monitored using spectrophotometry. Quantitative agar culture was used to measure planktonic and biofilm bacterial burden. A mouse abscess model was used to confirm phenotypes in vivo. In the planktonic growth assay, increases in bacterial burden at » MIC vancomycin were observed in USA300 JE2 by 72 h. Similar findings were observed with ½ MIC in Newman and SH1000. For biofilm formation, USA300 JE2 at » and ½ MIC vancomycin increased biofilm formation by approximately 1.3- and 2.3-fold respectively at 72 h as compared to untreated controls. Similar findings were observed with Newman and SH1000 with a 2.4-fold increase in biofilm formation at ½ MIC vancomycin. In a mouse abscess model, there was a 1.2-fold increase with sub-MIC vancomycin at 3 days post infection. Our study showed that Sub-optimal vancomycin dosing promoted S. aureus planktonic growth and biofilm formation, phenotypic measures of bacterial virulence. This phenotype induced by sub-MIC levels of vancomycin was also observed to increase rates of infection and pathogenesis in our mouse model. Risks of exposure to sub-MIC concentrations with vancomycin in surgical procedures are greater as there is decreased bioavailability in tissue in comparison to other antibiotics. This highlights the importance of proper antibiotic selection, stewardship, and dosing for both surgical prophylaxis and treatment of infection.

How well does intra-operative contact path predict post-operative contact path during activities of daily living after medial unicompartmental knee arthroplasty?

Robot-assisted surgical systems can predict post-operative kinematics based upon intra-operative passive kinematics, planned implant position and alignment, and soft-tissue tension. It is currently unknown how well the intra-operative passive kinematics replicate the post-surgical weight bearing active kinematics. This study compared intra-operative and post-operative tibiofemoral implant contact paths after medial unicompartmental knee arthroplasty (mUKA). Passive intraoperative and active postoperative tibiofemoral contact path data was collected from eight patients who underwent mUKA. Intraoperative contact path data was measured using a navigation system. Postoperative contact path data was measured during walking, chair rise, stair ascent, and stair descent using a biplane radiography system and a validated tracking process. A total of 86 movement trials were included in the analysis. The contact point on the femur implant was up to 9.8 mm more medial and up to 8.3 mm less anterior at low flexion angles during activities of daily living than during passive extension intra-operatively, and the contact point on the tibia implant was up to 13.8 mm less lateral and up to 5.8 mm less posterior at low flexion angles during activities of daily living than during intra-operative passive extension. Femoral contact paths primarily differed between 3° and 42° of flexion; and tibial contact paths differed between 3° and 50° of flexion. This pilot study is the first to compare intra-operative and post-operative weight bearing contact paths. The primary conclusions from this study are that contact points on the femur implant are more medial and less anterior at low flexion angles during activities of daily living than during passive extension intra-operatively, and that the contact points on the tibia implant are less lateral at low flexion angles during activities of daily living than during intra-operative passive extension.

Medial Unicompartmental Knee Arthroplasty Restores Native Knee Kinematics During Activities of Daily Living: A Pilot Study.

The ability of unicompartmental knee arthroplasty (UKA) to restore native knee kinematics during activities of daily living remains unclear. The objectives of this prospective study were to identify changes in knee kinematics after medial UKA (mUKA) and to determine if mUKA restores native knee kinematics during activities of daily living. We hypothesized that kinematics are different between the mUKA knee and contralateral knee before surgery, that mUKA restores native knee kinematics, and that mUKA does not affect lateral compartment dynamic joint space. Nine participants performed walking, chair rise, stair ascent and stair descent within a biplane radiography system before and after mUKA. Bilateral knee kinematics were determined for each activity using a validated tracking process that matched subject-specific bones and implants to the biplane radiographs. Compared to contralateral knee, the pre-UKA knee was more adducted (p ≤ 0.019), and more laterally translated (p ≤ 0.008) during all four activities. Additionally, compared to contralateral knee, pre-UKA knee was less internally rotated (p ≤ 0.044) during chair rise and stair ascent. Lateral compartment dynamic joint space did not change during any activity from pre to post mUKA. Our results indicate that mUKA generally restores native kinematics during activities of daily living without altering lateral compartment dynamic joint space.

In vivo changes in adjacent segment kinematics after lumbar decompression and fusion.

The pathogenesis of lumbar adjacent segment disease is thought to be secondary to altered biomechanics resulting from fusion. Direct in vivo evidence for altered biomechanics following lumbar fusion is lacking. This study's aim was to describe in vivo kinematics of the superior adjacent segment relative to the fused segment before and after lumbar fusion. This study analyzed seven patients with symptomatic lumbar degenerative spondylolisthesis (5 M, 2F; age 65 ± 5.1 years) using a biplane radiographic imaging system. Each subject performed two to three trials of continuous flexion of their torso according to established protocols. Synchronized biplane radiographs were acquired at 20 images per second one month before and six months after single-level fusion at L4-L5 or L5-S1, or two-level fusion at L3-L5 or L4-S1. A previously validated volumetric model-based tracking process was used to track the position and orientation of vertebrae in the radiographic images. Intervertebral flexion/extension and AP translation (slip) at the superior adjacent segment were calculated over the entire dynamic flexion activity. Skin-mounted surface markers were tracked using conventional motion analysis and used to determine torso flexion. Change in adjacent segment kinematics after fusion was determined at corresponding angles of dynamic torso flexion. Changes in adjacent segment motion varied across patients, however, all patients maintained or increased the amount of adjacent segment slip or intervertebral flexion/extension. No patients demonstrated both decreased adjacent segment slip and decreased rotation. This study suggests that short-term changes in kinematics at the superior adjacent segment after lumbar fusion appear to be patient-specific.

Crossing the Cervicothoracic Junction in Cervical Arthrodesis Results in Lower Rates of Adjacent Segment Disease Without Affecting Operative Risks or Patient-Reported Outcomes.

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: To evaluate the risks and benefits of crossing the cervicothoracic junction (CTJ) in cervical arthrodesis. SUMMARY OF BACKGROUND DATA: Whether the CTJ should be crossed in cervical arthrodesis remains up for debate. Keeping C7 as the distal end of the fusion risks adjacent segment disease (ASD) and can result in myelopathy or radiculopathy. Longer fusions are thought to increase operative risk and complexity but result in lower rates of ASD. MATERIALS AND METHODS: Patients undergoing cervical spine fusion surgery ending at C7 or T1 with ≥1-year follow-up were included. To evaluate operative risk, estimated blood loss (EBL), operative time, and length of hospital stay were collected. To evaluate patient-reported outcomes (PROs), Neck Disability Index (NDI) and SF-12 questionnaires (PCS12 and MCS12) were obtained at follow-up. Revision surgery data were also obtained. RESULTS: A total of 168 patients were included and divided into a C7 end-of-fusion cohort (NC7=59) and a T1 end-of-fusion cohort (NT1=109). Multivariate regression analysis adjusting for age, sex, race, surgical approach, and number of levels fused showed that EBL (P=0.12), operative time (P=0.07), and length of hospital stay (P=0.06) are not significantly different in the C7 and T1 end-of-fusion cohorts. Multivariate regression of PROs showed no significant difference in NDI (P=0.70), PCS12 (P=0.23), or MCS12 (P=0.15) between cohorts. Fisher analysis showed significantly higher revision rates in the C7 end-of-fusion cohort (7/59 for C7 vs. 2/109 for T1; odds ratio, 6.4; 95% confidence interval, 1.2-65.1; P=0.01). CONCLUSIONS: Crossing the CTJ in cervical arthrodesis does not increase operative risk as measured by blood loss, operative time, and length of hospital stay. However, it leads to lower revision rates, likely because of the avoidance of ASD, and comparable PROs. Thus, crossing the CTJ may help prevent ASD without negatively affecting operative risk or long-term PROs.

Porogen-based solid freeform fabrication of polycaprolactone-calcium phosphate scaffolds for tissue engineering.

Drop on demand printing (DDP) is a solid freeform fabrication (SFF) technique capable of generating microscale physical features required for tissue engineering scaffolds. Here, we report results toward the development of a reproducible manufacturing process for tissue engineering scaffolds based on injectable porogens fabricated by DDP. Thermoplastic porogens were designed using Pro/Engineer and fabricated with a commercially available DDP machine. Scaffolds composed of either pure polycaprolactone (PCL) or homogeneous composites of PCL and calcium phosphate (CaP, 10% or 20% w/w) were subsequently fabricated by injection molding of molten polymer-ceramic composites, followed by porogen dissolution with ethanol. Scaffold pore sizes, as small as 200 microm, were attainable using the indirect (porogen-based) method. Scaffold structure and porosity were analyzed by scanning electron microscopy (SEM) and microcomputed tomography, respectively. We characterized the compressive strength of 90:10 and 80:20 PCL-CaP composite materials (19.5+/-1.4 and 24.8+/-1.3 Mpa, respectively) according to ASTM standards, as well as pure PCL scaffolds (2.77+/-0.26 MPa) fabricated using our process. Human embryonic palatal mesenchymal (HEPM) cells attached and proliferated on all scaffolds, as evidenced by fluorescent nuclear staining with Hoechst 33258 and the Alamar Blue assay, with increased proliferation observed on 80:20 PCL-CaP scaffolds. SEM revealed multilayer assembly of HEPM cells on 80:20 PCL-CaP composite, but not pure PCL, scaffolds. In summary, we have developed an SFF-based injection molding process for the fabrication of PCL and PCL-CaP scaffolds that display in vitro cytocompatibility and suitable mechanical properties for hard tissue repair.