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PubMed2007

Soft tissue tendon graft fixation in serially dilated or extraction-drilled tibial tunnels: a porcine model study using high-resolution quantitative computerized tomography.

BACKGROUND: Tibial tunnel preparation may contribute to improved soft tissue graft fixation. HYPOTHESIS: Step dilation produces greater tunnel wall bone volume than does extraction drilling and increases fixation strength. Bioabsorbable interference screw divergence decreases fixation strength, regardless of tunnel preparation method. STUDY DESIGN: Controlled laboratory study. METHODS: Twenty porcine tibias were divided into 2 groups of 10 with matching mean apparent bone mineral density. One group received 9-mm-diameter extraction-drilled tunnels, and the other group received 7-mm-diameter extraction-drilled tunnels followed by step dilation to 9 mm. High-resolution quantitative computerized tomography scans and voxel analysis techniques determined tunnel wall bone volume fraction. Screws secured 8.5-mm-diameter porcine grafts in the tunnels. Repeat scans were used to determine screw divergence. Cyclic loading was performed in a servohydraulic device before load to failure testing. RESULTS: The step dilation group had greater tunnel wall bone volume/total volume than did the extraction drilled group; however, a significant increase in fixation strength was not detected. Specimens with screw divergence angles less than 15 degrees had superior fixation and insertion torques compared with specimens with angles 15 degrees or more. Screw divergence correlated more strongly with fixation strength than did mean apparent bone mineral density or screw insertion torque. CONCLUSION: Step dilation increased tunnel wall bone volume/total volume, but fixation strength did not improve. Screw divergence >or=15 degrees decreases graft-bone tunnel fixation whether or not step dilation is performed. CLINICAL RELEVANCE: Screw alignment plays a greater role in anterior cruciate ligament graft fixation than does extraction drilling or step dilation tunnel preparation methods in healthy bone.

Absorbable Implants↗
PubMed1994

[A study on fixatives for the simultaneous histological estimation of the gastric mucous gel layer and mucous cells in rat gastric surface mucosa].

We examined the special characteristics of various kinds of fixatives and tried to find the most suitable method for simultaneous histological estimation of the mucous gel layer and mucous cells in rat gastric paraffin sections stained with Alcian blue (pH2.5)-periodic acid Schiff (AB-PAS). The tested fixatives were (group in parentheses): absolute ethanol at -80 degrees C (A), absolute methanol at -80 degrees C (B), Carnoy's solution (C), formalin-ethanol (D) and formalin-Tyrode (E). The thickness of the mucous gel layer (ML) and the numbers of AB- and PAS-positive cells (AB cells, PAS cells) of both the fundic gland area (F. area) and pyloric gland area (P. area) were measured microscopically (x 200). ML in the F. area was found in the order of (A) > (B) > (C) > (D) = (E). AB cells were in the order of (A) > (E) > (B) > (C) > (D); and PAS cells were in the order of (B) > (A) > (E) > (C) > (D). Effects of various fixatives in the P. area showed the same trend as the F. area. Apart from above mentioned procedures, we observed the effects of ethanol at various temperatures: -80 degrees C, -25 degrees C, -4 degrees C and 20 degrees C. ML, AB and PAS cells showed the highest level at -80 degrees C. Moreover, to confirm that these fixatives retain the mucus, we evaluated the hexose and hexosamine contents contained in the fixative solution after fixation. As a result of various fixations, the hexose and hexosamine values in the fixative solution were the smallest for ethanol at -80 degrees C. In conclusion, ethanol at -80 degrees C was the most suitable fixative for histological estimation of mucous gel and mucous cells in rat gastric surface mucosa.

Animals↗
PubMed2002

Biomechanical evaluation of proximal humeral fracture fixation supplemented with calcium phosphate cement.

BACKGROUND: Proximal humeral fractures are common injuries, and numerous surgical methods have been described for their treatment. The biomechanical characteristics of various internal fixation devices that are used to treat these fractures have not been extensively studied, nor has the potential beneficial effect of calcium phosphate cement supplementation. METHODS: We used a cadaveric three-part proximal humeral osteotomy model to perform a biomechanical evaluation of three types of internal fixation devices: a cloverleaf plate, an angled blade-plate, and Kirschner wires. The effect of supplementing the fixation with SRS (Skeletal Repair System) calcium phosphate cement was evaluated as well. Eighteen pairs of fresh-frozen humeri were obtained, and the bone-mineral density of each specimen was measured. In each pair, one specimen was secured with internal fixation alone and the contralateral specimen was secured with internal fixation combined with calcium phosphate cement. The specimens were tested cyclically in abduction and in external rotation for 250 cycles to evaluate interfragmentary motion. The specimens were then loaded to failure in external rotation to measure torsional load to failure and torsional stiffness. RESULTS: Overall, there were no significant differences between the specimens treated with the blade and cloverleaf plates, whereas the specimens treated with Kirschner wires demonstrated more interfragmentary motion, less stiffness, and lower torque to failure. In general, supplementation with calcium phosphate cement led to significant improvements in the mechanical performance of all three forms of internal fixation as demonstrated by a significant decrease in interfragmentary motion, a significant increase in torque to failure, and a significant increase in torsional stiffness. The addition of calcium phosphate cement increased the stiffness of even the most osteoporotic specimens to levels that were higher than those of the most osteodense specimens that had been treated with internal fixation alone. CONCLUSION: The initial biomechanical properties of internal fixation as measured with use of a proximal humeral osteotomy model and three methods of fixation were significantly improved by the addition of calcium phosphate cement.

Aged↗
PubMed2003

Internal fixation compared with arthroplasty for displaced fractures of the femoral neck. A meta-analysis.

BACKGROUND: The optimal choice for the stabilization of displaced femoral neck fractures remains controversial, with alternatives including arthroplasty and internal fixation. Our objective was to determine the effect of arthroplasty (hemiarthroplasty, bipolar arthroplasty, and total hip arthroplasty), compared with that of internal fixation, on rates of mortality, revision, pain, function, operating time, and wound infection in patients with a displaced femoral neck fracture. METHODS: We searched computerized databases for randomized clinical trials published between 1969 and 2002, and we identified additional studies through hand searches of major orthopaedic journals, bibliographies of major orthopaedic textbooks, and personal files. Of 140 citations initially identified, fourteen met all eligibility criteria. Three investigators independently graded study quality and abstracted relevant data, including information on revision and mortality rates. RESULTS: Nine trials, which included a total of 1162 patients, provided detailed information on mortality rates over the first four postoperative months, which ranged from 0% to 20%. We found a trend toward an increase in the relative risk of death in the first four months after arthroplasty compared with the risk in the first four months after internal fixation (relative risk, 1.27). At one year, the relative risk of death was 1.04. The risk of death after arthroplasty appeared to be higher than that after fixation with a compression screw and side-plate but not higher than that after internal fixation with use of screws only (relative risk = 1.75 and 0.86, respectively; p < 0.05). Fourteen trials that included a total of 1901 patients provided data on revision surgery. The relative risk of revision surgery after arthroplasty compared with the risk after internal fixation was 0.23 (p = 0.0003). Pain relief and the attainment of overall good function were similar in patients treated with arthroplasty and those treated with internal fixation (relative risk, 1.12 for pain relief and 0.99 for function). Infection rates ranged from 0% to 18%, and arthroplasty significantly increased the risk of infection (relative risk, 1.81; p = 0.009). In addition, patients who underwent arthroplasty had greater blood loss and longer operative times than those who were treated with internal fixation. CONCLUSIONS: In comparison with internal fixation, arthroplasty for the treatment of a displaced femoral neck fracture significantly reduces the risk of revision surgery, at the cost of greater infection rates, blood loss, and operative time and possibly an increase in early mortality rates. Only larger trials will resolve the critical question of the impact on early mortality.

Arthroplasty↗
PubMed1996

Effects of fixation and tissue processing on immunohistochemical demonstration of specific antigens.

Identification of biomarkers in archival tissues using immunochemistry is becoming increasingly important for determining the diagnosis and prognosis of tumors, for characterizing preinvasive neoplastic changes in glandular tissues such as prostate, for evaluating the response of tumors and preinvasive neoplastic changes to certain therapies (i.e., as a surrogate intermediate end point), for selecting patients who are candidates for specific therapies (e.g., immunotherapy) and for retrospective studies. For detecting specific biomarkers it is important to understand the limitations imposed by the fixation methods and processing of the tissues. This study was designed to determine the effects of fixation on the detection in archival paraffin blocks of selected antigens postulated to be important in tumor biology. We evaluated the antigens TGF alpha, p185erbB-2, broad spectrum keratins, p53, and TAG-72 (B72.3). Fixatives evaluated included standard preparations of neutral buffered formalin, acid formalin, zinc formalin, alcoholic formalin, ethanol, methanol, and Bouin's fixative. We found that in general neutral buffered formalin is the poorest fixative for maintaining antigen recognition by immunohistochemistry and that no single fixative was best for all antigens. The dehydrating (coagulant) fixatives (e.g., ethanol and methanol) preserved immunorecognition of p53 and broad spectrum keratins best while the slow cross-linking fixatives (e.g., unbuffered zinc formalin) were best for demonstrating TGF alpha and p185erbB-2. Fixatives other than neutral buffered formalin produced equivalent recognition of the epitope of TAG-72 by B72.3. In formalin fixed archival tissues, only a portion of the antigen signal can be detected by routine immunohistologic methods.

Antigens, Neoplasm↗
PubMed1983

In vitro effects of external fixation on intact and osteotomized tibiae. A biomechanical study.

In order to study the in vitro mechanical effects of external fixation on intact and osteotomized bone, human and rabbit tibiae were tested in three-point bending in an Instron testing machine. Intact tibiae were loaded in the elastic range before and after application of an external fixation device. In the human specimens the Vidal-Adrey double frame was used, and in the rabbit specimens the external mini-fixation. The bone deformation in the anteroposterior direction was measured with a linear voltage differential transformer. After application of external fixation a median bone elastic stiffness of 110.2 per cent in human tibiae and of 106.1 per cent in rabbit tibiae was found, in relation to the stiffness of intact tibiae without external fixation. The stiffness increase was significant in human specimens, but not significant in rabbit specimens. In osteotomized human tibiae fixed with the Vidal-Adrey double frame a median stiffness of 8.5 per cent of the stiffness of intact bones was found when compression was not applied, compared to 19.9 per cent when compression was applied. In rabbit tibiae a median stiffness of osteotomized bones with external mini-fixation was 8.9 per cent of the stiffness of intact bones. There was a good agreement between the results in rabbit tibiae with the mini-fixation and human tibiae with external fixation without compression. The external mini-fixation thus seems to be a suitable model for the study of bone healing in rabbit tibiae.

Aged↗
PubMed1999

The acetabular component in total hip arthroplasty. Evaluation of different fixation principles.

Initial stability is necessary for permanent fixation of acetabular cups. Biologic reactions to submicron particles such as localized bone resorption may lead to implant failure. The aim of the study was to evaluate different fixation principles of acetabular components. Four randomized studies and one case-control study were performed to evaluate different bone cements, different cup designs, use of ceramic coating or not, different type of screws and the need of additional screw fixation or not. Radiostereometry (RSA) makes it possible to analyze small translations and rotations of implants with a high accuracy. This method is suitable for evaluation of early stability and was used in four of the studies. Clinical and radiological follow-up were performed regularly. The cements were tested in the laboratory. 30 patients (mean age 71 years, range: 63-76) received total hip arthroplasties and were randomised to fixation with Boneloc (14) or Palacos cum gentamicin (16) bone cement. The curing temperature was 23 degrees lower for the Boneloc cement but the tensile strength was reduced and the elastic modulus was lower compared to Palacos. The proximal cup migration was greater in the Boneloc group up to 12 months (p 0.04) and these cups migrated medially in contrast to a small lateral migration seen in the Palacos group (p 0.04). Radiolucencies were more pronounced in the Boneloc group at 12 months (p 0.04). 155 patients (171 hips, mean age 50 years, range: 24-64) received uncemented hip arthroplasties. 84 hips were randomised to the PCA and 87 to the Harris-Galante I designs. The 10-year survival rates were 85% for the PCA and 99% for the Harris-Galante I cups (revision as end-point). The wear and clinical results did not differ. 43 patients (mean age 60 years, range 44-68) received uncemented porous cups with a titanium mesh in pure titanium (Harris-Galante II) and were randomised to additional fixation with either biodegradable screws (23, poly-L-lactic acid, PLLA) or screws made of titanium alloy (20). Increased proximal and medial-lateral translations (p 0.02, 0.04) but less rotation around the longitudinal axis (p 0.04) were seen in the PLLA group up to 2 years. There were also more pronounced radiolucencies anteriorly in this group at 2 years. The clinical results did not differ. 23 uncemented porous cups (Harris-Galante II) with hydroxyapatite-tricalciumphosphate coating (HA/TCP) were pair-wise matched to uncoated cups. Up to 2 years, decreased rotations around the horizontal axis were recorded in the HA/TCP-coated cups. Central postoperative gaps were more frequently seen in the HA/TCP group (p < 0.01), but at 2 years radiolucencies were more pronounced in the uncoated group (p < 0.01). The wear and clinical results did not differ. 62 patients (64 hips, mean age 56 years, range: 32-75) were randomized to porous Trilogy cups with (30) and without (34) cluster holes for additional screw fixation. Up to 2 years there were no differences in migration, wear, radiographic findings or clinical results. In conclusion Boneloc cement was associated with poor fixation due to inferior mechanical properties. The PLLA screws did not provide sufficient stability. Unacceptably high failure rates were recorded for the PCA cup. HA/TCP coating improved the fixation and the interface of porous cups. HA/TCP coated porous cups can be fixed without adjunctive screw fixation.

Absorbable Implants↗
PubMed2002

[Treatment of complex bone nonunion with external skeletal fixation].

OBJECTIVES: To summarize the experience in the treatment of 112 cases of complex bone nonunion from 1982 to 1999 in our department and introduce the technique of external skeletal fixation. METHODS: The two fragment ends of all cases were fixed under pressure with half-ring sulcated external skeletal fixator. Those cases complicated by bone defect or limb shortening were operated on with epiphysiotomy to restore the length of the limb in the period of compressive fixation or after the occurrence of bone union according to the condition of complicated infection and the length of the limb shortened. RESULTS: The nonunion of the 112 cases was united eventually. The infection in 34 cases was eradicated. Bone union in cases without infection took 3 approximately 7 months (average 5.2 months) and in cases with infection took 5 approximately 11 months (average 5.5 months). The length of the limb in 11 cases with bone defect was restored in the same period of compressive external fixation and another 8 cases achieved after bone union. The length between the injured and healthy limbs was balanced. CONCLUSIONS: When external skeletal fixation is employed to treat those troublesome cases of bone nonunion, the pins for fixation are inserted in sites far from the lesions and the non-united fragment ends are exposed only in the area without scars. Consequently, there is little interference with the blood circulation and the osteogenic potency of the fragment ends. The sclerotic bone tissue is not excised, the marrow cavity is not chased to be open and the fragment ends are only moderately modified. As a result, the stability of fixation is increased and further shortening of the limb avoided. External skeletal fixation using small pins with cross penetration results in plastic fixation and promotes bone healing. Bone lengthening with epiphysiotomy can restore the balance of the limbs.

Adolescent↗
PubMed1992

Effects of different ocular fixation conditions on A-scan ultrasound biometry measurements.

A-scan readings must be taken along the visual axis for accurate axial length measurement. Various fixation targets, which ideally should not induce accommodation, are used to limit eye movements. In this study results using the Humphrey biometer under different fixation conditions were compared to establish the most suitable target. We also investigated corneal applanation effects by comparing optical and ultrasonic measurements of anterior chamber depth. We examined 12 randomly selected normal eyes of 12 young subjects. Three A-scans were recorded for each of five fixation conditions: spotlight at 6 m; Snellen letter at 6 m; solid probe's built-in green fixation target; Snellen letter at 6 m viewed through a -4.00 DS lens; spotlight at 6 m under cycloplegia (the comparison condition). Variability 'within' each fixation condition, estimated by the standard deviation for each subject, was equal throughout the 12 subjects for each fixation condition. Also variation was independent of size of the ocular dimension. The good agreement between the comparison condition and optical anterior chamber depth measurements indicated that the solid probe produced little applanation. Differences 'between' fixation conditions were investigated. It was concluded that a spotlight or letter at 6 m provides a suitable fixation target for biometry. Built-in fixation targets can produce significant errors.

Adult↗
PubMed2004

[Fixation points and retinal sensitivity observed in reading text by patients with bilateral macular atrophy].

PURPOSE: To study by use of a scanning laser ophthalmoscope(SLO). How patients with bilateral macular atrophy use their retinas in reading Japanese sentences of varying sizes. METHODS: Thirty-eight eyes of 19 patients with bilateral macular atrophy were examined. Sentences of a fixed length (MNREAD-J sentences) were projected onto the patients' retinas with the SLO, and the size of the letters was varied. Patients were asked to read aloud the sentences slowly, and both their voices and retinal images were recorded simultaneously on videotape so that we could locate the retinal area they were using for reading. We compared these fixation points in reading with simple fixation points obtained by SLO microperimetry. RESULTS: In 21 eyes, the patients used the same area of the retina in all measurements. In 15 eyes, the fixation points for reading differed from the fixation area measured by microperimetry. In 8 of the 15 eyes, the fixation area for reading changed as the letter size was altered. In 2 eyes, oral reading was impossible, and no fixation point was established. CONCLUSIONS: The combination of SLO with reading evaluation clarified the fixation area for oral reading. Multiple fixation points were thought to be present quite commonly in eyes with macular degeneration. The fixation point was thought to be determined by the macular condition and the size of the letters being read.

Adult↗
PubMed1992

Stability of an ankle arthrodesis fixed by cancellous-bone screws compared with that fixed by an external fixator. A biomechanical study.

Twenty-three fresh-frozen human specimens were subjected to ankle arthrodesis and fixation with two cancellous-bone screws. The specimens were then subjected to four newton-meters of manually applied tibial torque, plantar flexion-dorsiflexion moment, and medial-lateral bending moment; relative rotation between the tibia and the talus was recorded for each mode of testing. A Calandruccio triangular compression device was then applied to threaded pins penetrating the tibia and talus, the screws were removed, and the test sequence was repeated. Tibiotalar motions recorded with both systems of fixation were markedly affected by the quality of the bone. When less than 2 degrees of total tibiotalar rotation was recorded in response to four newton-meters of manually applied internal-external tibial torque, all specimens demonstrated less torsional rotation with the screw fixation than with the external fixator. The mean rotations produced by medial-lateral bending moment were equivalent for both systems of fixation. When torsional rotations with the use of screw fixation were greater than 2 degrees, all specimens demonstrated more torsional rotation with the screws than with the external fixator, and all but one specimen had more medial-lateral rotation with the screws than with the fixator. For applied plantar flexion-dorsiflexion moment, twenty-two of the twenty-three specimens demonstrated more rotation with the Calandruccio fixator than with the screws; this was due in part to motion permitted at the hinge points of the frame itself.

Aged↗
PubMed2005

[Arthrodesis of interphalangeal joints by means of external frame fixation].

PURPOSE OF THE STUDY: The indications for arthrodesis of interphalangeal joints include pain, instability, deformity or irreparable damage to the relevant flexor or extensor tendon. The general principle of arthrodesis is to resect the affected joint ends in the flexion desired so that a highest possible surface of contact may be provided. Subsequently, retention by means of internal or external fixation is performed. The aim of this study is to evaluate our method of interphalangeal joint arthrodesis, using an external frame fixator, to present the results and to point out the advantages of this method, thus showing its applicability for relevant surgical indication. MATERIAL: Arthrodesis by external fixation was carried out in 37 patients. The group included 21 men and 16 women at an average age of 49.6 years (range, 30 to 67 years). The method was used in the patients who differed in the etiology of lesions of interphalangeal joints. Twenty-two patients had previously experienced purulent arthritis, six had post-traumatic arthritis and joint instability, five had rheumatoid arthritis, two had primary arthritis and two had an inveterate rupture of the extensor aponeurosis. METHODS: We used a simple frame fixator whose stability was based on two to four Kirschner's wires inserted and maintained in clamps on rods, 4 cm or 7.5 cm long, each having a double anti-clockwise thread that facilitates compression, distraction and correction in one plane. The surgical procedure was carried out under axillary block with the use of a tourniquet. It involved making an S-shaped incision dorsally, severing the extensor apparatus, resecting articular surfaces in the desired flexion position, inserting parallel wires and fixing them in clamps on rods, achieving compression, checking the position of articular surfaces and suturing. Included in the group assessment were the gender and age of the patients, etiology of articular disease, number of the digits and joints affected, limb laterality, wound healing, stability of fixation, maintenance of a correct arthrodesis position and signs of healing on X-ray images. Time required for bony union and the shortening of the digit due to surgery were also included in the evaluation. RESULTS: The 35 followed-up patients showed healing of the wound and arthrodesis, with firm bony union being achieved at an average of 6.7 weeks. In one patient after removal of the fixator, septic pseudoarthrosis developed at the site of the resected distal interphalangeal joint. Another patient developed ischemia of the distal phalanx of the thumb treated, which required release and subsequent removal of the external fixator, with vasodilatation therapy. After a prolonged topical therapy, painless fibrous ankylosis developed in that interphalangeal joint and the thumb was salvaged. DISCUSSION: The aim of arthrodesis is to achieve firm and painless bony union in a correct functional position at a reasonable time. Arthrodesis in our patients healed at an average time of 6.7 weeks. The high effectivity of the compression technique in achieving firm bony fusion is the factor emphasized in the literature, particularly in situations where there is a reduced contact surface, poor coverage by soft tissue, infection or the presence of a systemic disease, such as rheumatoid arthritis or diabetes mellitus. This all is in agreement with the results of this study. CONCLUSIONS: This study shows advantages of the compression technique of arthrodesis by means of external frame fixation based on insertion of wires beyond the site of inflammation. Compression and stability result in rapid osseous union, immobilization in plaster cast is not necessary, free joints of the hand can be exercised, the fixator is removed in an outpatient department and the minimal presence of metal material does not interfere with good healing of soft tissues. Therefore this method has all merits to be used for surgery in a terrain affected by rheumatic, inflammatory or potentially inflammatory lesions.

Adult↗
PubMed2005

[Use of a hybrid external fixator for treatment of tibial fractures].

PURPOSE OF THE STUDY: The study deals with treatment of the articular ends of the tibia, using a hybrid external fixator. A group of patients treated in the years 2001-2003 is retrospectively evaluated. MATERIAL: Between 2001 and 2003, 21 patients (16 men and 5 women) with a fracture of either the distal or the proximal end of the tibia were treated, using a Synthes external hybrid fixator, at the Department of Orthopedics and Traumatology, Faculty of Medicine, Charles University, Plzen. The average age of the patients was 49.2 years. The fractures, evaluated by the AO classification, included five type A3 fractures and 16 type C1 or C2 fractures. In 14 patients the fracture was associated with multiple trauma or polytrauma and in seven it was a single injury. Open fractures were treated in five patients (grade 2 in two and grade 3 in three patients), closed fractures in 16 patients (Type CII in 12 and type CIII in four patients, as assessed by Tscherne's classification). Fifteen patients had fracture of the proximal tibia and six had distal tibial fracture. A hybrid external fixator was used alone in six patients, and in combination with miniosteosynthesis in 15 patients. METHODS: The first aim was to perform closed reduction or reduction from a minimal approach with an intraoperative image intensifier. Subsequently, the fracture was temporarily stabilized with pelvic reduction forceps or Ki wires and, if indicated, the articular ends were stabilized by miniosteosynthesis. When the outer ankle was fractured, plate osteosynthesis was carried out. Finally, a hybrid external fixator was applied. In the case of an open fracture, this procedure was preceded by soft tissue debridement. RESULTS: The evaluation, based on clinical and radiographic findings and subjective complaints of the patients, was made with the use of the Rasmussen and Bray scoring system. Nineteen patients were followed up, two failed to turn up. The results were excellent in five, very good in six, satisfactory in five and poor in three patients. Two repeat operations were necessary. DISCUSSION: The treatment of injury to the articular ends of the tibia, with the use of a hybrid external fixator, is one of the options for stabilization of both open and closed fractures. This method enables us to stabilize fractures of the tibial metaphysis as well as intra-articular fractures. Application of a hybrid external fixator is indicated in type A and type C fractures (AO classification). The state of crural soft tissues must be taken into consideration. The advantage of this method is the use of Kirschner wires, as fixation components, stretched in a circular frame. The fixation components require only minimum space for insertion in the metaphysis or epiphysis, the implant is stable and permits easy treatment of soft tissues. Another advantage is the possibility of early rehabilitation of the adjacent joints and loading of the extremity. Relatively frequent "pin infection" and therefore more frequent visits to the outpatient department can be considered a disadvantage. CONCLUSIONS: The method described here is, in addition to other options of fracture osteosynthesis, suitable for treatment of fractured ends of the tibia. External fixator application can be used with advantage for treatment of supra or infra-articular fractures of the tibia and fractures associated with marked swelling of soft tissues, for which internal osteosynthesis is not indicated, and in open fractures as well.

Adolescent↗
PubMed2006

[The biomechanical study of craniovertebral junction fixation with posterior transarticular screw].

OBJECTIVE: To evaluate the stability of biomechanics of occipitoatlantoaxial reconstruction with transarticular screw fixation. METHODS: Twelve fresh human cadaveric occipitocervical spine specimens were mounted in a custom-designed, spine-testing machine that applied pure moments while recording the three-dimensional angular movement at occiput (Oc)-C(1) and C(1 - 2) segments. The specimens were tested under seven different conditions: the intact (intact group), the occipitoatlantoaxial instability (Destabilized group), fixation with Ti-cable plus bone graft group (cable + graf group), fixation with the transarticular fixation (CTS group), fixation with SUMMIT occitocervical spinal fixation system (SUMMIT group), fixation with transarticular screw plus bone graft (CTS + graf group), and fixation with SMMIT system and plus graft group (SUMMIT + graf group). The data obtained were statistically analyzed. RESULTS: The CTS group reduced motion to well within the normal rang. In the Oc-C(1) segment, The CTS group and SUMMIT group allowed a very small rang of motion (ROM) and neutral zone (NZ) during lateral bending and axial rotation. The ROM and NZ during flexion and extension of the SUMMIT group, were significantly smaller than those of cable + graf group and CTS group (6.64 degrees +/- 0.59 degrees, 2.49 degrees +/- 0.26 degrees, 0.50 degrees +/- 0.03 degrees, 0.21 degrees +/- 0.01 degrees, 0.27 degrees +/- 0.07 degrees, 0.13 degrees +/- 0.01 degrees vs 10.01 degrees +/- 1.26 degrees, 3.80 degrees +/- 0.79 degrees, 7.93 degrees +/- 1.34 degrees, 3.18 degrees +/- 0.95 degrees, 9.54 degrees +/- 0.87 degrees, 5.93 degrees +/- 0.74 degrees, P < 0.05). In the C(1 - 2) segment, ROM and NZ in all directions of CTS group were smaller in rotation than SUMMIT group (1.64 degrees +/- 0.39 degrees, 0.61 degrees +/- 0.15 degrees, 0.14 degrees +/- 0.05 degrees, 0.02 degrees +/- 0.01 degrees, 0.32 degrees +/- 0.04 degrees, 0.08 degrees +/- 0.01 degrees, vs 0.21 degrees +/- 0.04 degrees, 0.07 degrees +/- 0.03 degrees, 0.21 degrees +/- 0.12 degrees, 0.10 degrees +/- 0.02 degrees, 2.92 degrees +/- 0.28 degrees, 1.27 degrees +/- 0.11 degrees, all P < 0.05). There was no significant difference in ROM and NZ in all directions between CTS + graf group and SUMMIT + Graf group (P > 0.05). CONCLUSION: In vivo biomechanics studies show that posterior occipitocervical transarticular fixation has unique features in reconstructing dynamic stability of the occipitoatlantoaxis, especially in controlling stability of rotation and lateral flexion, thus ensuring successful fusion of the implanted bone and allowing for clinical use of the technique.

Adult↗
PubMed1990

Retinal fixation point location in the foveal avascular zone.

The site of normal fixation is often assumed to be centered in the foveal avascular zone (FAZ). This assumed anatomic relationship is used during photocoagulation therapy as an objective guide to avoid damaging critical retinal structures on or near fixation. With laser therapy being directed closer and closer to the center of the FAZ, the accuracy with which the center of the FAZ locates the retinal point of fixation becomes an important therapeutic issue. Using an optimized technique for visualizing the retinal vasculature entoptically, the authors determined the location of the retinal point of fixation with respect to the foveal area vasculature in 26 eyes of 14 healthy subjects. In 23 eyes (12 subjects), a traditional FAZ was observed, the other three eyes (two subjects) had capillaries near or crossing the center of fixation. Of the 23 eyes with a traditional FAZ, 20 had centers of fixation located eccentric to the center but in the FAZ, (average deviation from the center of the FAZ, 66.5 +/- 49.5 microns) with the direction of deviation from the FAZ center appearing random. Consequently, when following protocols that advocate photocoagulation treatment with spot centers closer to the FAZ center than 300 microns, the center of the FAZ is a poor locator of a subject's retinal point of fixation. When using the FAZ as a reference, the resulting uncertainty in the location of the subject's retinal point of fixation increases the probability of significant damage to the actual point of fixation by up to 20%.

Adolescent↗
PubMed1989

Internal fixation of malar fractures: an experimental biophysical study.

Open reduction and internal fixation of displaced zygoma fractures are necessary to avoid immediate and delayed facial disfigurement. Interosseous wires, Kirschner wires, and more recently, rigid metallic miniplates have been recommended for fixation of these and other midfacial fractures. However, the precise physical stability of the zygoma with respect to wire versus miniplate fixation methods and with respect to the number and location of miniplates applied is not known. Noncomminuted zygoma fractures were simulated by saw osteotomy in eight fresh human cadaver heads (16 zygoma "fractures"). Each zygoma was sequentially fixated with three miniplates, two miniplates, one miniplate, and three interosseous wires across the orbital rim and arch "fractures". Static and oscillating loads simulating maximal physiologic masticatory stresses were applied to the fixated zygoma along the lines of action of the masseter muscle by means of a tensometer. The stability and adequacy of each pattern of fixation were recorded. Double-miniplate fixation across the orbital rim of simulated noncomminuted zygoma "fractures" is sufficient to withstand static and oscillating loading similar to physiologic masticatory forces. Neither single-miniplate fixation nor triple-wire fixation are sufficient to stabilize the zygoma against similar forces.

Biophysical Phenomena↗
PubMed1988

Eccentric fixation with macular scotoma.

People with macular scotoma tend to read and visually scan more slowly than others with equivalently reduced visual acuity but intact central fields. We measured fixation eye movements and considered the contribution of fixation variability and centripetal eye drift to poor visual performance. These factors might confound efforts to consistently use an optimum retinal locus outside of the macula. We measured monocular horizontal and vertical eye movements using a search coil eyetracker while subjects with naturally occurring central scotomata or control subjects with simulated scotomata eccentrically fixated a single character that was sized to their visual acuity. Motivated subjects with long-standing stable maculopathies were chosen to estimate attainable performance limits. During attempts to eccentrically fixate, an ubiquitous foveal pursuit or centripetal drift tendency was not found; rather a pattern of drift was idiosyncratic from subject to subject. This finding was confirmed by an analysis of eye drift of 32 eyes with long-standing bilateral macular scotomata. Moreover, the eye drift speeds (15-200 minarc/sec) were too low to be of functional significance. Drift speeds during eccentric fixation with a visible target were not significantly different than those after the target was extinguished; however, drift speeds were greater than during foveal fixation. This suggests that the fovea has a specialized control of slow eye movements. Fixation variability increased with scotoma size for both simulated and real scotomata, with an abrupt rise when scotomata diameters exceeded 20 degrees C. A significant minority of subjects (39%) adopted two or more distinct preferred retinal loci (PRL) during fixation. Multiple PRL were also more likely if scotoma size exceeded 20 degrees C. Reasonably steady fixation is thus attainable when central scotoma sizes are smaller than approximately 20 degrees C.

Adult↗
PubMed1977

Fixation disparity and stereopsis.

The magnitude of fixation disparity has been proposed to be uncorrelated with stereoscopic sensitivity. Studies on this relationship have been confined to the effects of vergence-induced fixation disparity on stereoacuity: some subjects exhibited decreased stereoacuity with induced fixation disparity. The present study was designed to determine whether prismatic correction of naturally occurring horizontal fixation disparity would result in increased stereoacuity. Five subjects with eso and 5 with exo fixation disparity had their fixation disparity curves and stereothresholds evaluated before and after wearing corrective lenses and prisms that neutralized the fixation disparity. Five subjects with no fixation disparity served as controls. After 1 month most subjects showed no change in their fixation disparity curves and stereothresholds.

Depth Perception↗