Biomechanical analysis of lateral pin placements for pediatric supracondylar humerus fractures.

AIM: Several clinical studies have shown that lateral pinning alone is of equal stability to crossed pins in the treatment of supracondylar fractures. The aim of this study was to compare the stability of parallel and varied divergent lateral pin configurations to provide an easily reproducible technique for optimal pin placement. METHODS: Twelve third-generation synthetic composite humeri were osteotomized at the level of the coronoid and olecranon fossae to simulate a humeral supracondylar fracture. Each fracture was reduced and fixed using two 1.6 mm (0.062 inches) Kirschner wires (1 fixed, 1 varied) in 4 different positions (from parallel to divergent with respect to fixed wire), and sequentially tested in extension, varus, and valgus as well as internal and external rotations using an MTS 858 Minibionix materials testing load frame (MTS Corporation, Eden Prairie, MN). A 2-way analysis of variance was carried out to compare construct stiffness in all 5 modes of testing according to both pin position and testing sequence. A level of P<0.05 was considered statistically significant. RESULTS: The best torsional, valgus, and extension resistances were found with position 4, which was the most divergent configuration. For both internal and external rotations, position 4 showed statistically higher stiffness as compared with all other configurations (P<0.05). In resistance to extension, both positions 3 and 4 were stiffer than either position 1 or 2 (P<0.05). For resistance in varus testing, position 3 showed statistically greater stiffness than all other pin positions (P<0.05). Although there was no statistical difference between all the 4 positions in valgus testing, position 4 showed greater resistance when compared with other positions. CONCLUSIONS: The lateral pin placed parallel to the metaphyseal flare of the lateral humeral cortex, in combination with a second diverging pin crossing the fracture site at the medial edge of the coronoid fossa (position 4), provided the optimum fixation for supracondylar fractures of the humerus. CLINICAL RELEVANCE: Using these readily available landmarks, the treating surgeon can reproducibly provide appropriate pinning treatment for most of these fractures.

The effect of posterior capsular tightening on peak subacromial contact pressure during simulated active abduction in the scapular plane.

HYPOTHESIS: Our hypothesis was that tightening of the posterior capsule would lead to increased subacromial pressure and increased superior translation during active abduction in the scapular plane. BACKGROUND: Subacromial impingement syndrome is a painful condition that occurs during overhead activities as the rotator cuff is compressed in the subacromial space. Unrecognized secondary causes of subacromial impingement may lead to treatment failure. Posterior capsular tightness, believed to alter glenohumeral joint kinematics, is often cited as a secondary cause of SI; however, scientific evidence is lacking. The primary objective of this study was to evaluate the effect of posterior capsular tightening on peak subacromial pressure during abduction in the scapular plane. MATERIALS AND METHODS: Ten fresh frozen shoulder specimens from deceased donors were mounted on a custom shoulder simulator. With the scapula fixed, the deltoid and rotator cuff muscles were loaded in discrete static steps with a constant ratio to elevate the humerus in the scapular plane. The treatment order (no tightening, 1-cm, and 2-cm tightening of the posterior capsule) was randomly assigned to each specimen. Peak subacromial contact pressure and glenohumeral kinematics at the peak pressure position were compared using a repeated measures analysis of variance. RESULTS: Peak subacromial pressures (mean +/- standard deviation) were similar between treatment groups: 345 +/- 152, 410 +/- 213, and 330 +/- 164 kPa for no tightening, 1-cm, and 2-cm tightening of the posterior capsule respectively (P > .05). No significant differences were found for superior or anterior translations at the peak pressure position (P > .05). DISCUSSION: Posterior capsular tightening, as a sole variable, did not contribute to a significant increase in peak subacromial pressure during abduction in the scapular plane. A similar study simulating active forward flexion is necessary to fully characterize the contribution of posterior capsular tightness to subacromial impingement. CONCLUSION: Tightening of the posterior capsule did not increase subacromial pressure, or increase superior or anterior translation during abduction in the scapular plane.

Genipin cross-linked fibrin hydrogels for in vitro human articular cartilage tissue-engineered regeneration.

Our objective was to examine the potential of a genipin cross-linked human fibrin hydrogel system as a scaffold for articular cartilage tissue engineering. Human articular chondrocytes were incorporated into modified human fibrin gels and evaluated for mechanical properties, cell viability, gene expression, extracellular matrix production and subcutaneous biodegradation. Genipin, a naturally occurring compound used in the treatment of inflammation, was used as a cross-linker. Genipin cross-linking did not significantly affect cell viability, but significantly increased the dynamic compression and shear moduli of the hydrogel. The ratio of the change in collagen II versus collagen I expression increased more than 8-fold over 5 weeks as detected with real-time RT-PCR. Accumulation of collagen II and aggrecan in hydrogel extracellular matrix was observed after 5 weeks in cell culture. Overall, our results indicate that genipin appeared to inhibit the inflammatory reaction observed 3 weeks after subcutaneous implantation of the fibrin into rats. Therefore, genipin cross-linked fibrin hydrogels can be used as cell-compatible tissue engineering scaffolds for articular cartilage regeneration, for utility in autologous treatments that eliminate the risk of tissue rejection and viral infection.

Fibrin sealants from fresh or fresh/frozen plasma as scaffolds for in vitro articular cartilage regeneration.

Our objective was to evaluate human CryoSeal fibrin glue derived from single units of plasma as scaffolds for articular cartilage tissue engineering. Human articular chondrocytes were encapsulated into genipin cross-linked fibrin glue derived from individual units of fresh or frozen plasma using the CryoSeal fibrin sealant (FS) system. The constructs were cultured for up to 7 weeks in vitro under low (5%) or normal (21%) oxygen. Chondrocyte viability was >90% within the fibrin gels. Hypoxia induced significant increases in collagen II and Sox9 gene expression and a significant decrease in collagen I. A significant increase in collagen II was detected in fresh plasma-derived cultures, while only collagen I was significantly increased in frozen plasma cultures. Significant increases in total glycosaminoglycan and collagen were detected in the extracellular matrix secreted by the encapsulated chondrocytes. A significant increase in compression modulus was only observed for fresh plasma-derived gels, which is likely explained by a greater amount of collagen type I detected after 7 weeks in frozen compared to fresh plasma gels. Our results indicate that CryoSeal fibrin glue derived from fresh plasma is suitable as a tissue engineering scaffold for human articular chondrocytes, and therefore should be evaluated for autologous articular cartilage regeneration.

2008 Otto Aufranc Award: component design and technique affect cement penetration in hip resurfacing.

Either excessive or insufficient cement penetration within the femoral head after hip resurfacing influences the risk of femoral failures. However, the factors controlling cement penetration are not yet fully understood. We determined the effect of femoral component design and cementation technique on cement penetration. Six retrieved femoral heads were resurfaced for each implant (BHR, ASR, Conserve Plus, DuROM, ReCAP) using the manufacturers' recommendations for implantation. In addition, the BHR was implanted using the Conserve Plus high-viscosity cementation technique, "BHR/hvt," and vice versa for the Conserve, "Conserve/lvt." The average cement penetration was highest with BHR (65.62% +/- 15.16%) compared with ASR (12.25% +/- 5.12%), Conserve Plus(R) (19.43% +/- 5.28%), DuROM (17.73% +/- 3.96%), and ReCAP (26.09% +/- 5.20%). Cement penetration in BHR/hvt remained higher than all other implants equaling 36.7% +/- 6.6%. Greater femoral component design clearance correlated with cement mantle thickness. Femoral component design in hip resurfacing plays a major role in cement penetration.

Use of an internet "viral" marketing software platform in health promotion.

BACKGROUND: Health-related websites have become a common tool for public health authorities to inform the general public of their health promotion information and programs. However, building traffic in the cluttered health Internet universe is becoming increasingly complex, costly, and challenging for governmental health promotion websites. In 2006, the Canadian Health Network (CHN), a cooperative program made up of the Public Health Agency of Canada (PHAC) and some 20 health non-governmental organizations (NGOs), was looking for an affordable marketing tool for the promotion of its website and contents to specific populations. OBJECTIVE: To test new and innovative marketing tools for a health promotion website in Canada. METHODS: Within the context and constraints of a governmental health promotion website, an adaptation of a commercial Internet viral marketing software platform was developed and implemented under the name "The Crazy Race". This process was done interactively between seven NGOs and the CHN staff. The communication objectives were (a) to provide a meaningful visit that could communicate important public health messages, and (b) to increase subscriptions to its e-newsletter. A nine-step standardized Web-user experience (Internet path) was thus defined and experimented with under a pre-determined operating budget of less then Can$50,000, mainly paid for by participating organizations on a pay-per-performance basis. RESULTS: An initial group of 215 people were sent an invitation to participate in the campaign. Over its 15-day duration, the campaign generated by itself and without any media support a total of 110,200 Web user participants who registered and sent a total of 439,275 invitations (2% of the Canadian Web-user population of 21.8 million in 2006). The epidemic self-dissemination of the campaign occurred in both French and English populations and spread across all age groups. Two-thirds of the participants were women. CONCLUSIONS: The use of an Internet viral marketing platform proved to be effective in bringing thousands of Web users to discover and explore a governmental health promotion website. The exponential growth of the person-to-person dissemination generated by the campaign indicates that public health messages have high viral propagation potential on the Internet ("virulence") when they are presented in the context of an enjoyable online game. This could constitute a promising method to create affordable mass audience public health campaigns, both in Canada and internationally.

Femoral component sizing and positioning in hip resurfacing arthroplasty.

Hip resurfacing arthroplasty is now being done on a regular basis with excellent short-term results. Although the technologic improvements are important in achieving improved clinical results, surgical technique and implant positioning are also critical. To minimize the risk of impingement and preserve acetabular bone stock during hip resurfacing arthroplasty, it is important for orthopaedic surgeons to be familiar with the current principles of femoral component sizing and positioning.

Comparison of the stability of various internal fixators used in the treatment of osteochondritis dissecans--a mechanical model.

The purpose of this study was to determine what characteristics of fixation devices used in the treatment of osteochondritis dissecans (OCD) contribute to improved stability to resist shear loading. An OCD model was designed using rigid polyurethane foam. Each specimen consisted of two components, an osteochondral fragment and a corresponding defect. A total of 40 specimens were prepared and assigned to one of four groups: control (no extrinsic stabilizer); two 2-mm-diameter Kirschner wires (K-wires), 40 mm in length; one threaded washer and a 28-mm screw; and one threaded washer and a 38 mm screw. Each specimen was mounted onto an Iosipescu shear test fixture and subjected to shear loads at a pseudo-static displacement rate of 0.075 mm/s. All groups demonstrated some stability; controls were significantly less stable than all other groups. The group with the threaded washer and 38-mm screw demonstrated the greatest stability (p < 0.001), and no difference was noted between the K-wire and 28-mm screw groups. These results suggest that, in this OCD model, friction conferred some intrinsic stability to resist loads in shear. However, stability was improved with the use of long implants that compressed the fragments together.

Internal plate fixation of fractures: short history and recent developments.

Metal plates for internal fixation of fractures have been used for more than 100 years. Although initial shortcomings such as corrosion and insufficient strength have been overcome, more recent designs have not solved all problems. Further research is needed to develop a plate that accelerates fracture healing while not interfering with bone physiology. The introduction of rigid plates had by far the greatest impact on plate fixation of fractures. However, it led to cortical porosis, delayed bridging, and refractures after plate removal. These unwarranted effects were said to be caused by bone-plate contact interfering with cortical perfusion. Consequently, further plate modifications aimed to reduce this contact area to minimize necrosis and subsequent porosis. The advocates of limited-contact plates have not published measurements of the contact area or proof of the temporary nature of the porosis. Moreover, clinical studies of newer plate types have failed to show a superior outcome. Histomor-phometric measurements of the cortex showed no difference in the extent of necrosis under plates having different contact areas. Necrosis was predominant in the periosteal cortical half, whereas porosis occurred mostly in the endosteal cortical half. No positive correlation was found between either. The scientific evidence to date strongly suggests that bone loss is caused by stress shielding and not interference with cortical perfusion secondary to bone-plate contact. Consequently, an axially compressible plate (ACP) incorporating polylactide (PLA) inserts press-fit around screw holes was designed. The bioresorbable inserts should allow for (1) increased micromotion in the axial plane to promote healing during the union phase and (2) gradual degradation over time to decrease stress shielding during the remodeling phase. Results of ongoing experimental results are encouraging. Only plates allowing dynamic compression in the axial plane can lead to a revolution in fracture fixation.

Dual cryogenic fixation for mechanical testing of soft musculoskeletal tissues.

Mechanical testing of soft musculoskeletal structures like tendons and ligaments are essential to medical advances. A long-standing limitation for testing these structures in isolation has been the ability to solidly fix both ends of the tendon. Cryogenic fixation technology was leveraged into the development of a dual cryogenic fixation (DCF) device. Results of the study show that the DCF allows tendons to be tested in isolation, at physiologic temperatures, with excellent reproducibility.

The effect of the wafer procedure on pressure in the distal radioulnar joint.

PURPOSE: To investigate the effect of the wafer procedure on pressure within the distal radioulnar joint. METHODS: The effect of increasing transverse distal ulnar head resection with preservation of the ulnar styloid was evaluated in 4 fresh frozen cadaver arms. Specimens were tested in neutral rotation. A standard transaxial load was applied from the radius to the ulna and the distal radioulnar joint intra-articular pressure was evaluated. RESULTS: Increasing amounts of distal ulnar resection led to a linear increase in pressure in the distal radioulnar articulation. CONCLUSION: The wafer procedure leads to an increase in pressure in the distal radioulnar joint that may lead to the early onset of osteoarthritis.