Equation predicting tibial-tuberosity to trochlear-groove distance following supratubercle osteotomy: Radiographic proof of concept

BACKGROUND

Supratubercle tibial rotational osteotomies are useful in patellar stabilizing procedures with high tibial-tuberosity to trochlear-groove distance caused by excessive external tibial torsion. An investigation determined one degree of internal tibial rotation results in 0.68 mm reduction of tibial-tuberosity to trochlear-groove distance, but did not account for anatomical variability.

METHODS

This is a radiographic proof of concept for equation validation. We compared two different derived equations, a complex four-variable and simplified two-variable equation, to the literature relationship and true measured value from CT imaging. Bilateral pre-operative CTs of 37 patients, evaluated for malalignment, were reviewed retrospectively. We virtually simulated derotations of five, ten and fifteen degrees, and compared the reduction in tibial-tuberosity to trochlear-groove distance measured radiologically from CTs to the one predicted by our equation.

FINDINGS

The difference between the true change in tibial-tuberosity to trochlear-groove distance and that obtained using our four-variable was statistically insignificant for all derotation angles (p > 0.05), and the two-variable equation it was statistically insignificant for five and fifteen degrees of derotation (p > 0.05). Conversely, the true values were statistically different from those found using the published relationship (p < 0.05 for all).

INTERPRETATION

This new equation accounts for individual patient anatomy, for a more accurate relationship between internal rotation of the distal segment of the tibia and the subsequent decrease in the tibial-tuberosity to trochlear-groove distance. The change was overestimated using the linear relationship, which may result in under correction. Future studies will assess true post-operative distance change following osteotomy.

Limited evidence for graft selection in pediatric ACL reconstruction: a narrative review

Anterior cruciate ligament reconstruction is the preferred treatment to anterior cruciate ligament injury. With the increase in anterior cruciate ligament injuries in both adults and skeletally immature patients comes the need for individualized anterior cruciate ligament reconstruction graft selection whether it is the type of graft (auto vs. allograft) or the harvesting site (hamstrings, iliotibial band, quadriceps, patella). Several factors need to be considered preoperatively in order to optimize the patients’ recovery and restore anterior cruciate ligament strength and function. These include age and bone maturity, preoperative knee flexor/extensor strength, sport participation, patient’s needs and anatomical characteristics. This paper aims at bringing evidence supporting the use of a personalized approach in graft selection for faster and more efficient return to sport and propose a theoretical framework to support the approach.

Variable expressivity in a family with an aggrecanopathy

Background

Osteochondritis dissecans is a condition wherein there is a subchondral bone lesion that causes pain, inflammation, and cartilage damage. Dominant Familial Osteochondritis Dissecans is a rare and severe form of osteochondritis dissecans (OCD). It is caused by heterozygous pathogenic variants in the gene encoding Aggrecan; ACAN. Aggrecan, a proteoglycan, is an essential component of the articular and growth plate cartilage.

Methods

Herein, we report three individuals from one family; the proband who presented with short stature, a lower limb bone exostosis, and bilateral knee and elbow OCD at the age of 13 years old. His twin brother presented with isolated short stature and his father with short stature and lumbar disc herniation.

Results

Next‐generation sequencing of the ACAN gene in the proband identified a frameshift variant which is also present in the brother and father with short stature. The proband was treated surgically with bilateral elbow microfracture, after the failure of conservative therapy.

Conclusion

To the best of our knowledge, this is the first patient with an aggrecanopathy who presents with osteochondritis dissecans due to a frameshift variant. This family presents with variable expressivity which might be attributed to modifier genes.

Can a Knee Brace Prevent ACL Reinjury: A Systematic Review

This systematic review aimed to investigate whether the use of a knee brace when returning to sport (RTS) could prevent a second injury after anterior cruciate ligament reconstruction (ACLR). This study was registered with the PROSPERO database and followed PRISMA guidelines. A systematic search of PubMed, Ovid Medline, Ovid All EBM Reviews, Ovid Embase, EBSCO Sportdiscus and ISI Web of Science databases for meta-analysis, randomized controlled trials and prospective cohort studies published before July 2020 was undertaken. The inclusion criteria were: (1) Comparing with and without a brace at RTS, (2) follow up of at least 18 months after ACLR, (3) reinjury rates included in the outcomes. Two reviewers independently extracted the data. Quality appraisal analyses were performed for each study using the Cochrane Collaboration tools for randomized and nonrandomized trials. A total of 1196 patients in three studies were included. One study showed a lower rate of reinjury when wearing a knee brace at RTS. One study found the knee brace to have a significant protective effect for younger patients (≤17 years). The effectiveness of knee bracing when RTS remains ambiguous. Current data cannot support that using a knee brace when RTS will decrease the rate of reinjury after ACL reconstruction.

Arthroscopy Association of Canada Position Statement on Exercise for Knee Osteoarthritis: A Systematic Review of Guidelines

BACKGROUND

Exercise is widely regarded to improve pain and function in patients with knee osteoarthritis (OA) through building supportive muscle mass, facilitating weight loss, and through the other beneficial effects associated with it.

PURPOSE

To explore literature that presents clinical guidelines for the use of exercise in the treatment of knee OA to inform an evidence-based position statement for the Arthroscopy Association of Canada.

STUDY DESIGN

Position statement.

METHODS

PubMed, MEDLINE, Embase, and Cochrane databases were searched for guidelines commenting on the role of exercise for knee OA. The search was limited to guidelines published in the last 10 years. Articles were screened for relevance, focusing on recently published research with clinical guidelines. Inclusion criteria involved all articles providing clinical guidelines for exercise and knee OA.

RESULTS

Eight guidelines were identified. All eight recommended exercise as an important component of treatment for knee OA, with 6/8 strongly recommending it.

CONCLUSION

Exercise is an effective and important component of the non-pharmacological management of knee OA. The Arthroscopy Association of Canada strongly recommends the use of exercise in the management of knee OA.

Management of common elective paediatric orthopaedic conditions during the COVID-19 pandemic: the Montreal experience

PURPOSE

To explore safe delays for the treatment of common paediatric orthopaedic conditions when faced with a life-threatening pandemic, COVID-19, and to propose a categorization system to address this question.

METHODS

Review of the literature related to acceptable delays for treatment of common orthopaedic conditions, experience of healthcare professionals from low resource communities and expertise of experienced surgeons.

RESULTS

Guidelines for the management of cancellations of elective surgeries during a period of resource reallocation are proposed. Elective cases must not be postponed indefinitely as adverse outcomes may result. Triage of waiting lists should include continuous monitoring of the patient and close communication with families despite social distancing and travel restrictions. Telehealth becomes a necessity. Common orthopaedic conditions are triaged into four groups according to urgency and safe and acceptable delay. Categories proposed are Emergent (life and limb threatening conditions), Urgent (within seven days), Semi-elective (postponed for three months) and Elective (postponed for three to 12 months). In total, 25 common orthopaedic conditions are reviewed and categorized.

CONCLUSION

Given the uncertainty within healthcare during a pandemic, it is necessary to determine acceptable delays for elective conditions. We report our experience in developing guidelines and propose categorizing elective cases into four categories, based on the length of delay. Telemedicine plays a key role in determining the gravity of each situation and hence the amount of delay. These guidelines will assist others dealing with elective cases in the midst of a crisis. This paper initiates a coordinated effort to develop a consensus statement on safe delays.Published without peer review.

Knee Morphological Risk Factors for Anterior Cruciate Ligament Injury: A Systematic Review

BACKGROUND

Anterior cruciate ligament (ACL) reconstruction incidence has increased substantially in the past 25 years. Recently, there has been a focus on knee morphology as a contributor to ACL injury risk. The purpose of this study was to systematically review the literature to assess the influence of knee morphology on ACL injury.

METHODS

In accordance with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, PubMed, Embase, and MEDLINE were searched in September 2017 for studies reporting on knee morphology and ACL injury. The search was updated in June 2018. The following inclusion criteria were used: English language; full text available; Level-I, II, or III evidence; human studies; and skeletally mature patients.

RESULTS

After systematically screening 6,208 studies, 65 studies met the inclusion/exclusion criteria. Three additional studies were identified in the search update, for a total of 68 studies comprising 5,834 ACL-injured knees. Intercondylar notch stenosis, most commonly defined by an "A-shaped" notch, decreased notch width, or decreased notch width index, was the most commonly reported femoral morphological risk factor for ACL injury. Increased femoral condylar offset ratio (>63%) and decreased condylar radius of curvature also were associated with an increased risk of ACL injury. Increased medial and lateral tibial slopes were the most commonly reported tibial risk factors. A smaller tibial eminence, reduced ACL size, and poor tibiofemoral congruity were also associated with increased injury risk.

CONCLUSIONS

Intercondylar notch stenosis, variations in sagittal condylar shape, increased tibial slope, reduced tibial eminence size, poor tibiofemoral congruity, and reduced ACL size are substantial risk factors for ACL injury. In future research, it would be valuable to identify a slope beyond which slope correction should be performed concomitantly with ACL reconstruction, and to determine whether an optimal relationship of notch size to graft size exists. To achieve optimal outcomes, the osseous morphological risk factors should be considered in individualized anatomic ACL reconstructions.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

The effect of adipose-derived stem cells on enthesis healing after repair of acute and chronic massive rotator cuff tears in rats

BACKGROUND

Chronic massive rotator cuff tears heal poorly and often retear. This study investigated the effect of adipose-derived stem cells (ADSCs) and transforming growth factor-β3 (TGF-β3) delivered in 1 of 2 hydrogels (fibrin or gelatin methacrylate [GelMA]) on enthesis healing after repair of acute or chronic massive rotator cuff tears in rats.

METHODS

Adult male Lewis rats underwent bilateral transection of the supraspinatus and infraspinatus tendons with intramuscular injection of botulinum toxin A (n = 48 rats). After 8 weeks, animals received 1 of 8 interventions (n = 12 shoulders/group): (1) no repair, (2) repair only, or repair augmented with (3) fibrin, (4) GelMA, (5) fibrin + ADSCs, (6) GelMA + ADSCs, (7) fibrin + ADSCs + TGF-β3, or (8) GelMA + ADSCs + TGF-β3. An equal number of animals underwent acute tendon transection and immediate application of 1 of 8 interventions. Enthesis healing was evaluated 4 weeks after the repair by microcomputed tomography, histology, and mechanical testing.

RESULTS

Increased bone loss and reduced structural properties were seen in chronic compared with acute tears. Bone mineral density of the proximal humerus was higher in repairs of chronic tears augmented with fibrin + ADSCs and GelMA + ADSCs than in unrepaired chronic tears. Similar improvement was not seen in acute tears. No intervention enhanced histologic appearance or structural properties in acute or chronic tears.

CONCLUSIONS

Surgical repair augmented with ADSCs may provide more benefit in chronic tears compared with acute tears, although there was no added benefit to supplementing ADSCs with TGF-β3.

Utility and costs of radiologist interpretation of perioperative imaging in patients with traumatic single-level thoracolumbar fractures

OBJECTIVE The cost of spine management is rising. As diagnostic imaging accounts for approximately 10% of total patient care spending, there is interest in determining if economies could be made with regard to the routine consultation of radiology for image interpretation. In the context of spine trauma, both the spine surgeon and the radiologist interpret perioperative imaging. Authors of the present study investigated the impact of radiologist interpretation of perioperative imaging from patients with traumatic single-level thoracolumbar fractures given that spine surgeons are expected to be comfortable interpreting pathologies of the musculoskeletal system. METHODS The authors conducted a retrospective review of all patients presenting with a single-level thoracolumbar fracture treated at the McGill University Health Centre in the period from January 2003 to December 2010. The time between image capture and radiologist interpretation as well as the number of extraskeletal and/or incidental findings was extracted from the radiology reports on all perioperative images including radiographic, fluoroscopic, and CT images. The cost of interpretation was obtained from the provincial health insurance entity of Quebec. RESULTS Eighty-two patients met the study inclusion criteria. Radiologists took a median of 1 day (IQR 0-5.5 days) to interpret preoperative radiographs. Intraoperative fluoroscopic images and postoperative radiographs were read by the radiologist a median of 19 days (IQR 4-56.75 days) and 34 days (IQR 1-137.5 days) after capture, respectively (p < 0.05). Preoperative radiologist dictations reported extraskeletal and/or incidental findings for 8.1% of radiographs; there were no intraoperative or postoperative extraskeletal findings beyond those previously reported on the preoperative radiographs. Radiologists took a median of 1 day (IQR 0-1 day) to read both preoperative and postoperative CT scans; extraskeletal and/or incidental findings were present in 46.2% of preoperative reports and 4.5% of postoperative reports. There were no intraoperative or postoperative radiological findings that provoked reoperation. A total of 66 intraoperative fluoroscopy images and 225 postoperative radiographs were read for a cost of $1399.20 and $1867.50 (Canadian dollars), respectively, for radiologist interpretation. This cost amounted to 40.3% of all perioperative image interpretation spending. CONCLUSIONS In the management of single-level thoracolumbar fractures, radiologists add information to the diagnostic picture when interpreting preoperative radiographs and perioperative CT scans; however, the interpretation of intraoperative fluoroscopic images and postoperative radiographs comes with significant delay, does not add additional information, and represents an area of potential cost and professional-resource reduction.

The Rotator Cuff Organ: Integrating Developmental Biology, Tissue Engineering, and Surgical Considerations to Treat Chronic Massive Rotator Cuff Tears

The torn rotator cuff remains a persistent orthopedic challenge, with poor outcomes disproportionately associated with chronic, massive tears. Degenerative changes in the tissues that comprise the rotator cuff organ, including muscle, tendon, and bone, contribute to the poor healing capacity of chronic tears, resulting in poor function and an increased risk for repair failure. Tissue engineering strategies to augment rotator cuff repair have been developed in an effort to improve rotator cuff healing and have focused on three principal aims: (1) immediate mechanical augmentation of the surgical repair, (2) restoration of muscle quality and contractility, and (3) regeneration of native enthesis structure. Work in these areas will be reviewed in sequence, highlighting the relevant pathophysiology, developmental biology, and biomechanics, which must be considered when designing therapeutic applications. While the independent use of these strategies has shown promise, synergistic benefits may emerge from their combined application given the interdependence of the tissues that constitute the rotator cuff organ. Furthermore, controlled mobilization of augmented rotator cuff repairs during postoperative rehabilitation may provide mechanotransductive cues capable of guiding tissue regeneration and restoration of rotator cuff function. Present challenges and future possibilities will be identified, which if realized, may provide solutions to the vexing condition of chronic massive rotator cuff tears.

Technical Considerations in Revision Anterior Cruciate Ligament (ACL) Reconstruction for Operative Techniques in Orthopaedics

As the incidence of anterior cruciate ligament (ACL) reconstruction continues to increase, the rate of revision surgery continues to climb. Revision surgery has inherent challenges that must be addressed in order to achieve successful results. The cause of the primary ACL reconstruction failure should be determined, and careful preoperative planning should be performed to address the cause(s) of failure. Each patient undergoing revision surgery should undergo a thorough history and physical examination, receive full length alignment radiographs, lateral radiographs, 45-degree flexion weight-bearing postero-anterior radiographs, and patellofemoral radiographs. 3-dimensional computed topography (CT) scan should be performed to assess tunnel position and widening. Magnetic resonance imaging (MRI) should be used to assess for intra-articular soft tissue pathology. Meniscal tears, meniscal deficiency, anterolateral capsule injuries, bony morphology, age, activity level, connective tissue diseases, infection, graft choice, and tunnel position can all impact the success of ACL reconstruction surgery. Meniscal lesions should be repaired, and in cases of persistent rotatory instability, extra-articular procedures may be indicated. Furthermore, osteotomies may be needed to correct malalignment or excess posterior tibial slope. Depending on the placement and condition of the original femoral and tibial tunnels, revision surgery may be performed in a single procedure or in a staged manner. In most cases, the surgery can be performed in one procedure. Regardless, the surgeon must communicate with the patient openly regarding the implications of revision ACL surgery and the treatment plan should be developed in a shared fashion between the surgeon and the patient.

Systematic Review of Surgical Literature from Resource-Limited Countries: Developing Strategies for Success

BACKGROUND

Injuries and surgical diseases are leading causes of global mortality. We sought to identify successful strategies to augment surgical capacity and research endeavors in low-income countries (LIC's) based on existing peer-reviewed literature.

METHODS

A systematic review of literature from or pertaining to LIC's from January 2002 to December 2011 was performed. Variables analyzed included type of intervention performed, research methodology, and publication demographics such as surgical specialty, partnerships involved, authorship contribution, place and journal of publication.

FINDINGS

A total of 2049 articles met the inclusion criteria between 2002 and 2011. The two most common study methodologies performed were case series (44%) and case reports (18%). A total of 43% of publications were without outcome measures. Only 21% of all publications were authored by a collaboration of authors from low-income countries and developed country nationals. The five most common countries represented were Nepal (429), United States (408), England (170), Bangladesh (158), and Kenya (134). Furthermore, of countries evaluated, Nepal and Bangladesh were the only two with a specific national journal.

INTERPRETATION

Based on the results of this research, the following recommendations were made: (1) Describe, develop, and stimulate surgical research through national peer-reviewed journals, (2) Foster centers of excellence to promote robust research competencies, (3) Endorse partnerships across regions and institutions in the promotion of global surgery, and (4) Build on outcome-directed research.

A Validated Orthopaedic Surgical Simulation Model for Training and Evaluation of Basic Arthroscopic Skills

BACKGROUND

To our knowledge, there is currently no validated educational model to evaluate and teach basic arthroscopic skills that is widely accessible to orthopaedic residency training programs. The primary objective was to design and to validate a surgical simulation model by demonstrating that subjects with increasing level of training perform better on basic arthroscopic simulation tasks. The secondary objective was to evaluate inter-rater and intra-rater reliability of the model.

METHODS

Prospectively recruited participants were divided by level of training into four groups. Subjects performed six basic arthroscopic tasks using a box model: (1) probing, (2) grasping, (3) tissue resection, (4) shaving, (5) tissue liberation and suture-passing, and (6) knot-tying. A score was calculated according to time required to complete each task and deductions for technical errors. A priori total global score, of a possible 100 points, was calculated by averaging scores from all six tasks using equal weights.

RESULTS

A total of forty-nine participants were recruited for this study. Participants were grouped by level of training: Group 1 (novice: fifteen medical students and interns), Group 2 (junior residents: twelve postgraduate year-2 or postgraduate year-3 residents), Group 3 (senior residents: sixteen postgraduate year-4 or postgraduate year-5 residents), and Group 4 (six arthroscopic surgeons). The mean total global score (and standard deviation) differed significantly between groups (p < 0.001): 29.0 ± 13.6 points for Group 1, 40.3 ± 12.1 points for Group 2, 57.6 ± 7.4 points for Group 3, and 72.4 ± 3.0 points for Group 4. Pairwise comparison with Tukey correction confirmed construct validity by showing significant improvement in overall performance by increasing level of training between all groups (p < 0.05). The model proved to be highly reliable with an intraclass correlation coefficient of 0.99 for both inter-rater and intra-rater reliability.

CONCLUSIONS

A simulation model was successfully designed to teach and evaluate basic arthroscopic skills showing good construct validity. This arthroscopic simulation model is inexpensive, valid, and reliable and has the potential to be implemented in other training programs.

Management of femoral neck fractures in the young patient: A critical analysis review

Femoral neck fractures account for nearly half of all hip fractures with the vast majority occurring in elderly patients after simple falls. Currently there may be sufficient evidence to support the routine use of hip replacement surgery for low demand elderly patients in all but non-displaced and valgus impacted femoral neck fractures. However, for the physiologically young patients, preservation of the natural hip anatomy and mechanics is a priority in management because of their high functional demands. The biomechanical challenges of femoral neck fixation and the vulnerability of the femoral head blood supply lead to a high incidence of non-union and osteonecrosis of the femoral head after internal fixation of displaced femoral neck fractures. Anatomic reduction and stable internal fixation are essentials in achieving the goals of treatment in this young patient population. Furthermore, other management variables such as surgical timing, the role of capsulotomy and the choice of implant for fixation remain controversial. This review will focus both on the demographics and injury profile of young patients with femoral neck fractures and the current evidence behind the surgical management of these injuries as well as their major secondary complications.

Tissue response to the components of a hydroxyapatite-coated composite femoral implant

Bone loss around femoral implants used for THA is a persistent clinical concern. It may be caused by stress shielding, generally attributed to a mismatch in stiffness between the implants and host bone. In this regard, a fatigue resistant, carbon fiber (CF) composite femoral implant with bone-matching stiffness has been developed. This study evaluated the tissue response to the three material components of this implant in normal and textured (blasted with 24 grit alumina) surfaces: the hydroxyapatite (HA) coating, the CF composite and the intermediate crystalline HA particulate composite layer to bond to the HA coating (blended). Sprague-Dawley rats underwent bilateral femoral implantation each receiving two rod-like implants. Bone apposition to the HA (37%) and textured Ti (41%) implants was not significantly different. Bone apposition to the untextured CF (14%) and blended (19%) implants and polished Ti (8%) implants was significantly lower. Bone apposition to the textured CF (9%) and blended (11%) implants was lower (but not statistically from the as received or untextured counterparts). Nearly all sections from femurs containing CF implants presented CF debris. There was no evidence of localized bone loss or any strong immune response associated with any of the implant materials. All materials were well tolerated with minimal inflammation despite the presence of particulate debris. The high degree of bone apposition to the HA-coated composite implants and the lack of short-term inflammation and adverse tissue response to the three material implant component support continued evaluation of this composite technology for use in THA.

Effects of workers' compensation on the diagnosis and surgical treatment of patients with hand and wrist disorders

BACKGROUND

Workers' Compensation differs from standard insurance, and it is unclear how or if Workers' Compensation insurance influences the diagnosis and treatment of hand and wrist disorders. The aim of this study was to compare the diagnosis and course of treatment of hand disorders between patients with Workers' Compensation insurance and patients with standard insurance.

METHODS

The complete medical records of patients who visited an academic orthopaedic hand clinic between January 2005 and January 2007 were reviewed, and information on patient history, utilization of diagnostic tests, diagnosis, surgery, and wait-time to surgery was collected. Patients with Workers' Compensation insurance and those with other, third-party coverage were analyzed and compared. Patients without insurance were excluded from this study.

RESULTS

1413 patients (representing 2121 diagnoses) were included in the study. One hundred and sixteen patients (8%) had Workers' Compensation insurance and 1297 patients (92%) had standard insurance. Patients with Workers' Compensation insurance were younger than patients with standard insurance (mean age, forty-three years compared with fifty years, respectively; p < 0.05) and were also more likely to be male (50% compared with 40%, respectively; p = 0.04). Generally, Workers' Compensation patients more often had neurological conditions (p < 0.01), but there was no significant difference in the most common diagnoses between the two groups. Patients with Workers' Compensation underwent surgery slightly more often than did patients with standard insurance (44% compared with 35%, respectively; p = 0.07) and had a higher average number of visits before undergoing surgery (2.3 visits compared with 1.2 visits, respectively; p < 0.05). Twenty-three (45%) of the fifty-one patients with Workers' Compensation insurance who received a diagnosis indicating the need for surgery underwent surgery after the first visit, compared with 316 (69%) of 458 patients with standard insurance (p < 0.05). Patients with Workers' Compensation insurance were more likely than patients with standard insurance to undergo electrodiagnostic testing (26% compared with 15%, respectively; p < 0.01) or magnetic resonance imaging (16% compared with 9%, respectively; p = 0.02).

CONCLUSIONS

Compared with patients receiving standard insurance, patients receiving Workers' Compensation insurance have a greater number of clinic visits before undergoing surgery and receive more diagnostic testing. More research is needed to explore these differences and their potential clinical and economic consequences.

TRPV4-dependent dilation of peripheral resistance arteries influences arterial pressure

Transient receptor potential vanilloid 4 (TRPV4) channels have been implicated as mediators of calcium influx in both endothelial and vascular smooth muscle cells and are potentially important modulators of vascular tone. However, very little is known about the functional roles of TRPV4 in the resistance vasculature or how these channels influence hemodynamic properties. In the present study, we examined arterial vasomotor activity in vitro and recorded blood pressure dynamics in vivo using TRPV4 knockout (KO) mice. Acetylcholine-induced hyperpolarization and vasodilation were reduced by approximately 75% in mesenteric resistance arteries from TRPV4 KO versus wild-type (WT) mice. Furthermore, 11,12-epoxyeicosatrienoic acid (EET), a putative endothelium-derived hyperpolarizing factor, activated a TRPV4-like cation current and hyperpolarized the membrane of vascular smooth muscle cells, resulting in the dilation of mesenteric arteries from WT mice. In contrast, 11,12-EET had no effect on membrane potential, diameter, or ionic currents in the mesenteric arteries from TRPV4 KO mice. A disruption of the endothelium reduced 11,12-EET-induced hyperpolarization and vasodilatation by approximately 50%. A similar inhibition of these responses was observed following the block of endothelial (small and intermediate conductance) or smooth muscle (large conductance) K(+) channels, suggesting a link between 11,12-EET activity, TRPV4, and K(+) channels in endothelial and smooth muscle cells. Finally, we found that hypertension induced by the inhibition of nitric oxide synthase was greater in TRPV4 KO compared with WT mice. These results support the conclusion that both endothelial and smooth muscle TRPV4 channels are critically involved in the vasodilation of mesenteric arteries in response to endothelial-derived factors and suggest that in vivo this mechanism opposes the effects of hypertensive stimuli.

Genetic and fluorescence studies of affinity maturation in related antibodies

Affinity maturation, the process by which an organism's response to infection becomes more specific and more effective over time, occurs after somatic hypermutation of antibody genes in B-cells. This increase in affinity might be a result of the evolution of either specific interactions between antigen and antibody over time (enthalpic factors) or antibody binding site rigidification (entropic factors) or both. Here, monoclonal antibodies, derived from antibodies elicited at different points in the murine immune response after inoculation with the same diketone hapten, have been characterized both genetically and functionally. Though this hapten has previously been shown to produce the catalytic aldolase antibody 38C2, antibodies described here are not catalytic and unlike 38C2, form no covalent enzyme-substrate complex. Thus, they provide a system in which to assess contributions to the evolution of binding affinity. The genes for these non-catalytic antibodies have been sequenced and analyzed both with regard to their relationships to germ line genes, to each other, and to two commercially available catalytic aldolase antibodies. Consequences of particular mutations for antigen binding behavior are discussed. The protein products of these genes have been expressed, purified, and binding properties measured by two complementary techniques: the hapten-induced quenching of the native antibody fluorescence and the changes in the anisotropy of Prodan (6-propionyl-2-(dimethylamino)naphthalene), a fluorescent hapten analogue. Differences in binding affinity are related back to differences in the lengths and amino acid sequences of the complementary determining region 3 (CDR3) binding loop. Taken together with our earlier results on binding site heterogeneity from tryptophan lifetime analysis [Mohan, G.S., Chiu, P.T., Southern, C.A., O'Hara, P.B., 2004. Steady-state and multifrequency phase fluorometry studies of binding site flexibility in related antibodies. J. Phys. Chem. A 108, 7871-7877], affinity appears to be modulated by a combination of entropic and enthalpic factors, and not dominated by one or the other. Because these antibodies are not related to the same germ line gene, however, these results do not provide evidence for the dominance of enthalpy or entropy in evolving binding affinity in this system.