Results of Low Distal Femur Periprosthetic Fractures.

OBJECTIVES: To compare retrograde intramedullary nail (RIMN) and open reduction internal fixation (ORIF) in very distal periprosthetic distal femur fractures (PDFFs) to determine whether RIMN is an acceptable option for these fractures that are often considered too distal for IMN due to limited bone stock. DESIGN: Retrospective comparative series. SETTING: Level 1 trauma center. PATIENTS: Patients were treated with fracture fixation for a very distal PDFF, defined as the fracture extending to the anterior flange of the implant or distal. Fifty-six patients met inclusion criteria, with 8 excluded for less than 12 months of follow-up. INTERVENTION: The intervention involved fracture fixation with RIMN or ORIF. MAIN OUTCOME MEASUREMENTS: The primary outcome was unplanned return to surgery. Secondary outcomes included fracture union, radiographic alignment, visual analog score, and Patient-Reported Outcome Measurement Information System (PROMIS) Physical Function (PF) and Pain Interference. RESULTS: The mean follow-up period was 27 months. Twelve patients were treated with ORIF and 36 with RIMN. Twenty-one fractures were at the flange, and 27 extended distal to the flange. There were no differences between fixation methods for reoperation, deep infection, nonunion, malunion, visual analog score pain score, and PROMIS Pain Interference score. The mean PROMIS PF score was higher in the RIMN group compared with that in the ORIF group. There were 5 reoperations in the RIMN group (14%) and 3 in the ORIF group (25%). CONCLUSIONS: This is the largest series, to the best of our knowledge, of a subset of very distal PDFFs. The results suggest that RIMN may be an acceptable treatment option for these very difficult fractures. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Is Immediate Weight-Bearing Safe After Single Implant Fixation of Elderly Distal Femur Fractures?

OBJECTIVES: To compare early complications in elderly patients with extra-articular distal femur fractures (DFFs) allowed to weight-bear as tolerated (WBAT) immediately versus patients prescribed initial touchdown weight-bearing (TDWB). DESIGN: Retrospective cohort study. SETTING: Level 1 academic trauma center. PATIENTS: One hundred thirty-five patients 60 years or older who underwent surgical fixation of an extra-articular DFF, including the OTA/AO fracture classification of 33-A1-3, and periprosthetic fractures with a stable knee prosthesis (Lewis and Rorabeck type I or II) with at least 6 months follow-up. INTERVENTION: Immediate WBAT or TDWB after surgical fixation of an extra-articular DFF with either an intramedullary nail or locked plate. MAIN OUTCOME MEASUREMENTS: The primary outcome was a major adverse event within the first 6 months, defined as (1) early fixation failure or change in alignment leading to reoperation, (2) nonunion, or (3) deep infection. Secondary outcomes included postoperative inpatient length of stay, discharge disposition (secondary facility vs. home), malunion, mortality, and patient-reported outcomes. RESULTS: The rate of early adverse events requiring reoperation was similar between the WBAT group (6, 10.7%) and the TDWB group (15, 19.0%; P = 0.23). There was no difference between groups with respect to length of stay, discharge disposition, malunion, and patient-reported outcomes. CONCLUSIONS: This study supports allowing carefully selected elderly patients, based on surgeon preference, to immediately weight-bear after operative fixation of an extra-articular DFF regardless of implant choice. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Mid to distal third tibial shaft fractures caused by gunshots: Characterization and incidence of distal intra-articular extension.

INTRODUCTION: Spiral tibial shaft fractures are known to have a high rate of distal intra-articular extension; however, the risk of joint involvement caused by gunshots has not been thoroughly evaluated. The purpose of this study was to determine the incidence of intra- articular involvement in tibial shaft fractures caused by gunshots. The secondary purpose of this study was to assess the usefulness of ankle radiographs versus computed tomography (CT) scans in identifying these fractures. MATERIALS AND METHODS: Ninety consecutive patients were identified as having a tibia fracture caused by gunshot at a Level-1 trauma center. Forty-four of these patients were fractures of the mid to distal third shaft. Twenty-eight patients had ankle CT scans available for review, and 24 patients had dedicated ankle films. Three orthopaedic surgeons and a radiologist read the radiographs and CT scans. Sensitivity and specificity analysis was performed for the ankle radiographs using ankle CT scans as the gold standard. RESULTS: Seven of the twenty-eight fractures evaluated with a CT scan proved to have intra-articular involvement (Prevalence: 25%, 95% CI: 11.4%-45.2%). One of the seven intra-articular fractures was not seen on dedicated ankle radiographs (14.3%). The sensitivity of diagnosing an intra-articular extension on ankle radiographs was 0.85, 95%CI: 0.42-0.99. The specificity of diagnosing an intra-articular extension on ankle radiographs was 1.00, 95%CI: 0.81-1.00. Of the seven intra-articular fractures, three required additional treatment to address the intra-articular extension. CONCLUSION: The incidence of intra-articular involvement for tibial shaft fractures secondary to gunshot is less than that reported for spiral type fractures (11-45% vs. 25-58%). Although radiographs have a high specificity, the sensitivity is lower than expected, with worse outcomes if a fracture is missed. We recommend that a CT scan should be utilized to determine intra-articular extension in the setting of tibial shaft fractures caused by gunshots.

Ascorbate enhancement of H1 histamine receptor sensitivity coincides with ascorbate oxidation inhibition by histamine receptors.

Ascorbate has previously been shown to enhance both alpha(1)- and beta(2)-adrenergic activity. This activity is mediated by ascorbate binding to the extracellular domain of the adrenergic receptor, which also decreases the oxidation rate of ascorbate. H1 histamine receptors have extracellular agonist or ascorbate binding sites with strong similarities to alpha(1-) and beta(2)-adrenergic receptors. Physiological concentrations of ascorbate (50 microM) significantly enhanced histamine contractions of rabbit aorta on the lower half of the histamine dose-response curve, increasing contractions of 0.1, 0.2, and 0.3 microM histamine by two- to threefold. Increases in ascorbate concentration significantly enhanced 0.2 microM histamine (5-500 microM ascorbate) and 0.3 microM histamine (15-500 microM ascorbate) in a dose-dependent manner. Histamine does not measurably oxidize over 20 h in oxygenated PSS at 37 degrees C. Thus the ascorbate enhancement is independent of ascorbate's antioxidant effects. Ascorbate in solution oxidizes rapidly. Transfected histamine receptor membrane suspension with protein concentration at >3.1 microg/ml (56 nM maximum histamine receptor) decreases the oxidation rate of 392 microM ascorbate, and virtually no ascorbate oxidation occurs at >0.0004 mol histamine receptor/mol ascorbate. Histamine receptor membrane had an initial ascorbate oxidation inhibition rate of 0.094 min.microg protein(-1).ml(-1), compared with rates for transfected ANG II membrane (0.055 min.microg protein(-1).ml(-1)), untransfected membrane (0.052 min.microg protein(-1).ml(-1)), creatine kinase (0.0082 min.microg protein(-1).ml(-1)), keyhole limpet hemocyanin (0.00092 min.microg protein(-1).ml(-1)), and osmotically lysed aortic rings (0.00057 min.microg wet weight(-1).ml(-1)). Ascorbate enhancement of seven-transmembrane-spanning membrane receptor activity occurs in both adrenergic and histaminergic receptors. These receptors may play a significant role in maintaining extracellular ascorbate in a reduced state.

Molecular shielding of electric field complex dissociation.

We have previously demonstrated the ability of electric fields to dissociate ascorbate and catecholamines and shown that the electric field generated by cell membranes is sufficient to produce dissociation of these complexes up to 8 nm from the cell membrane. We show here that this process is applicable to a wide range of biological complexes including small molecules (norepinephrine-morphine sulfate), protein-protein complexes (insulin-glucagon), and small molecule-protein complexes (epinephrine-bovine serum albumin). The extrapolation of the slope of the electric field dependence to zero electric field can be used to estimate the log of the dissociation constant (K(D)) of a complex and, by multiplying the log(K(D)) by -2.303RT, the association energy (E) of the complex. The slope of the electric field dependence is inversely related to the molecular radii, with the best fit of the slope related to E*(1/r1 + 1/r2), where r is the estimated radius of each molecule in the complementary pair. This indicates that the binding site of the pair is shielded by the remaining parts of the molecules, and the larger the molecule the greater the shielding. When the slope of the electric field dependence goes to 0 as r goes to infinity and 1/r goes to 0, the molecular shielding constant is 7.04 x 10(-8) cm2/V. Very large complexes will be minimally affected by the electric field due to molecular shielding and reduced electric field as their radius restricts approach to the membrane. Large protein receptors will deflect the membrane electric field and allow agonist binding.