Biomedical subjects

Jinn Lin

Publications and source records attributed to Jinn Lin.

16 recordsLinked to original sources

PubMed2006

Increasing bending strength of tibial locking screws: mechanical tests and finite element analyses.

BACKGROUND: Healing of tibial fractures treated by locked nailing is threatened by locking screw failure. However, the effects of the design factors of the screws on their mechanical strength have rarely been studied. METHOD: Three-point bending tests and finite element analyses were used to investigate the bending strength of five types of commercially available tibial locking screws and two types of specially designed screws. Yielding strength and fatigue life measured in bending tests were correlated to total strain energy and maximal tensile stress computed in finite element analyses. Parametric analysis and design optimization were done according to the Taguchi method. Validation studies to assess the stress rising effect of the threads on the fatigue strength were conducted in two types of new screws made of either stainless steel or titanium alloy. FINDINGS: The yielding strength of the screws was closely related to their total strain energy, and the logarithm of the fatigue life was closely related to the maximal tensile stress with correlation coefficients of -0.95 and -0.90, respectively. Parametric studies indicated that fatigue strength of the screws was affected mainly by inner diameter (contribution, 63.8%) and root radius (27.8%). The yielding strength was determined primarily by inner diameter (88.5%). Titanium screws had a longer fatigue life than stainless steel screws, especially in screws with larger root radii. INTERPRETATION: A screw's strength is closely related to its design factors. Finite element models, which can reliably reflect the mechanical strength of screws can save time and effort during screw design. Larger root radius can effectively improve the fatigue strength, especially for titanium screws as compared with stainless steel screws.

Biomechanical Phenomena↗

PubMed2006

Multiobjective optimization of tibial locking screw design using a genetic algorithm: Evaluation of mechanical performance.

Breakage or loosening of locking screws may impair fracture fixation or bone healing in locked nailing of tibial fractures. Bending strength and bone holding power, two important design objectives of locking screws, may conflict with each other. The present study used multiobjective optimization with a genetic algorithm to investigate the optimal designs with respect to these two objectives. Three-dimensional finite element models for analyzing bending strength and bone holding power of locking screws were created first. Through use of a Taguchi L25 orthogonal array, two objective functions were developed by least-squares regression analyses. Then, the trade-off solutions between the two objectives known as Pareto optima were explored by a weighted-sum aggregating approach under geometric constraints. The objective functions, reliably reflecting the finite element results, were valid for multiobjective studies. The Pareto fronts of the screws with 4.5-mm and 5.0-mm outer diameters were similar. The "knee" region of the Pareto front, characterized by the fact that a small improvement in either objective will cause a large deterioration in the other objective, might be the favored choice of optimal designs. The commercially available locking screws compared with the Pareto optima were found to be dominated designs and could be improved. In conclusion, the multiobjective optimization with a genetic algorithm was useful for optimization of locking screw design with many variables and conflicting objectives. Choosing an optimal design requires a thorough knowledge of the inherent problems. This method could reduce the time, cost, and labor associated with the screw development process.

Algorithms↗

PubMed2006

Effectiveness of completely round nails with both-ends-threaded locking screws for tibial shaft fractures.

BACKGROUND: Completely round nails, in contrast to conventional locked nails with surface grooves, for postoperative endosteal revascularization may increase the nail rigidity and decrease the manufacture cost. Both-ends-threaded screws with higher fatigue strength require smaller nail holes and can further increase the mechanical strength of the nails. METHODS: In this study, both-ends-threaded locking screws were used to treat 68 tibial fractures, including 56 acute fractures in 54 patients and 12 nonunions in 12 patients. There were 41 men and 25 women with a mean age of 39.6 years, and the average follow-up was 24 months. For acute fractures, there were 11 type I, 9 type II, 5 type IIIA, and 3 type IIIB open fractures. Acute fractures were treated with closed nailing. Five hypertrophic nonunions were treated with closed exchanged nailing, and seven oligotrophic nonunions were treated with open nailing and iliac bone grafting. RESULTS: With a single nailing procedure, 53 acute fractures and all nonunions achieved union with mean times of 17.4 weeks and 18.4 weeks, respectively. Three patients underwent exchange nailing and bone grafting and had eventual fracture union. Three fractures with compartment syndrome were treated with fasciotomy. Deep infection occurred in two open fractures but was successfully treated. Nail breakage occurred in one distal fracture and screw backout occurred in another, but fracture union was not affected. Recovery of joint motion was essentially normal in patients without knee or ankle injury. CONCLUSIONS: This study showed that completely round nails with both-ends-threaded locking screws could effectively treat tibial fractures. Completely round nails have the advantages of high mechanical strength and low manufacturing cost.

Adult↗

PubMed2006

Effectiveness of locked nailing for displaced three-part proximal humeral fractures.

BACKGROUND: Published reports about locked nailing for displaced comminuted proximal humeral fractures are few and the results contradictory. METHODS: Locked nailing was used to treat 27 selective patients with displaced three-part proximal humeral fractures. The average age of patients was 54.3 years. The operative indications were persistent severe displacement, intact or minimally displaced lesser tuberosity, tolerance of anesthesia, and adherence to rehabilitation programs. Three patients had associated shoulder dislocation and two had fractures with diaphyseal extension. By transdeltoid approach, the fractures were reduced and then fixed by antegrade nailing with either upward or downward locking screws. The patients were prospectively followed up for an average of 24 months. RESULTS: All fractures achieved eventual union. Three patients with proximal screw loosening required screw removal. On the basis of Neer criteria, excellent or satisfactory results were obtained in 21 patients whose scores averaged 87.5 points. Six patients had unsatisfactory outcomes, with an average of 75.8 points. Two patients with the complication of avascular necrosis still had a satisfactory outcome. Varus deformity of shoulder joints, deformity of the greater tuberosity, collapse of the humeral head, and old age could adversely affect shoulder elevation. However, the anatomic abnormalities might have limited effects on the pain scale, muscle power, and shoulder stability. CONCLUSIONS: Locked nailing can be an effective treatment for selected severely displaced three-part proximal humeral fractures. It is particularly useful for fractures with diaphyseal involvement. Familiarity with the fracture deformity and experience with the surgical techniques are critical for successful treatment results.

Adult↗

PubMed2004

Increase of pullout strength of spinal pedicle screws with conical core: biomechanical tests and finite element analyses.

Screw loosening can threaten pedicle screw fixation of the spine. Conical screws can improve the bending strength, but studies of their pullout strength as compared with that of cylindrical screws have shown wide variation. In the present study, polyurethane foam with two different densities (0.32 and 0.16 gm/cm3) was used to compare the pullout strength and stripping torque among three kinds of pedicle screws with different degrees of core tapering. Three-dimensional finite element models were also developed to compare the structural performance of these screws and to predict their pullout strength. In the mechanical tests, pullout strength was consistently higher in the higher density foam and was closely related to screw insertion torque (r=0.87 and 0.81 for the high and low density foam, respectively) and stripping torque (r=0.92 and 0.78, respectively). Conical core screws with effective foam compaction had significantly higher pullout strength and insertion torque than cylindrical core screws (p<0.05). The results of finite element analyses were closely related to those of the mechanical tests in both situations with or without foam compaction. This study led to three conclusions: polyurethane foam bone yielded consistent experimental results; screws with a conical core could significantly increase pullout strength and insertion torque over cylindrical; and finite element models could reliably reflect the results of mechanical tests.

Bone Screws↗

PubMed2004

Mechanical tests and finite element models for bone holding power of tibial locking screws.

OBJECTIVE: To investigate the bone holding power of tibial locking screws. DESIGN: The bone holding power was assessed by mechanical testing and finite element analysis. BACKGROUND: Screw loosening might threaten fracture fixation and bone healing. METHODS: In mechanical tests, six types of different tibial locking screws were inserted into low-density polyurethane foam tubes, which simulated osteoporotic bone. The screws were pushed out of the foam bone by an axial load, and the maximal pushout load was recorded. In finite element analysis, three-dimensional finite element models with a nonlinear contact interface between the screws and the bones were created to simulate the mechanical testing. The total strain energy of the bone and total reaction force of the screws were recorded. The contribution of the design factors was analyzed by the Taguchi method. RESULTS: In the mechanical tests, foam bone was stripped by the screw threads without screw deformation. The testing results were closely related to those of finite element analysis. The Taguchi analysis showed that the descending order of contribution of the design factors was outer diameter, pitch, half angle, and inner diameter. Root radius and thread width had minimal effects. CONCLUSIONS: The bone holding power of the screws could be reliably assessed by finite element models, which could analyze the effects of all the design factors independently and were potentially applicable to screws with irregular thread patterns.

Analysis of Variance↗

PubMed2004

Therapeutic effects of hyaluronic acid on osteoarthritis of the knee. A meta-analysis of randomized controlled trials.

BACKGROUND: The magnitude of the therapeutic effects of intra-articular injection of hyaluronic acid on osteoarthritis of the knee is still in question. The aim of this meta-analysis was to elucidate the therapeutic efficacy and safety of intra-articular injection of hyaluronic acid for osteoarthritis of the knee. METHODS: We conducted a meta-analysis of twenty blinded randomized controlled trials that compared the therapeutic effect of intra-articular injection of hyaluronic acid with that of intra-articular injection of a placebo to treat osteoarthritis of the knee. The outcome end points were classified into three categories: pain with activities, pain without activities, and function. The outcome measures of the efficacy of hyaluronic acid were the mean differences in the efficacy scores between the hyaluronic acid and placebo groups. The outcome measure of the safety of hyaluronic acid was the relative risk of adverse events. RESULTS: Intra-articular injection of hyaluronic acid can decrease symptoms of osteoarthritis of the knee. We found significant improvements in pain and functional outcomes with few adverse events. However, there was significant between-study heterogeneity in the estimates of the efficacy of hyaluronic acid. Subgroup analysis and meta-regression analysis showed that lower methodological quality such as a single-blind or single-center design resulted in higher estimates of hyaluronic acid efficacy, that introduction of acetaminophen as an escape analgesic in the trial resulted in lower estimates of hyaluronic acid efficacy, and that patients older than sixty-five years of age and those with the most advanced radiographic stage of osteoarthritis (complete loss of the joint space) were less likely to benefit from intra-articular injection of hyaluronic acid. CONCLUSIONS: This meta-analysis confirmed the therapeutic efficacy and safety of intra-articular injection of hyaluronic acid for the treatment of osteoarthritis of the knee. Additional well-designed randomized controlled trials with high methodological quality are needed to resolve the continued uncertainty about the therapeutic effects of different types of hyaluronic acid products on osteoarthritis of the knee in various clinical situations and patient populations. LEVEL OF EVIDENCE: Therapeutic study, Level II-3b (systematic review; nonhomogeneous Level-I studies). See Instructions to Authors for a complete description of levels of evidence.

Activities of Daily Living↗

PubMed2004

Biomechanical and clinical effects of adding interfragmentary wiring to locked nailing for humeral nonunions.

BACKGROUND AND PURPOSE: The use of locked nailing for the treatment of humeral nonunions is threatened by the potential of initial instability which may result in residual fracture gap and motion and is detrimental to fracture healing. This study investigated the biomechanical and clinical effects of adding interfragmentary wiring to reduce the initial instability in the treatment of humeral nonunion. METHODS: The biomechanical study compared the mechanical properties of 3 fixation methods: locked nail alone, with staple, and with interfragmentary wiring. Composite humeri were transected to simulate nonunion and were retrograde nailed. Nail-bone constructs were examined by non-destructive bending tests and destructive torsional tests. The initial instability, fixation stiffness and strength were measured and compared. The clinical study compared 21 nonunions treated by locked nailing alone and 30 nonunions treated by locked nailing with interfragmentary wiring. The indication for wiring was persistent nonunion gap or motion during operation. The union rate, time to union, functional recovery of the adjacent joints and the time for functional recovery were compared between the treatment groups. RESULTS: Biomechanically, in both bending and torsional tests, locked nailing with a staple or wiring resulted in significantly less initial instability than locked nailing alone. Test results for bending stiffness, torsional stiffness, or torsional strength did not differ significantly among the 3 fixation methods. In the clinical study, interfragmentary wiring had the advantage of providing tight nonunion compression, which was beneficial for nonunion healing and promoted early postoperative exercise. Patients treated with locked nailing with interfragmentary wiring had significantly shorter time to union and faster shoulder functional recovery (p < 0.05). CONCLUSIONS: Adding interfragmentary wiring was an effective and safe procedure in humeral nonunions treated with locked nailing.

Biomechanical Phenomena↗

PubMed2003

Locked nailing of severely comminuted or segmental humeral fractures.

Some comminuted or segmental humeral fractures have been well-treated by functional bracing, but some also have been reported to have a bad outcome. If surgery is required, unlocked nailing has the disadvantage of unstable fixation, and plating has the disadvantage of extensive soft tissue injury. In the current study, closed locked nailing was used to treat 23 Orthopaedic Trauma Association Type C humeral fractures (C1, five; C2, three; C3, 15). The patients were 12 men and 11 women with a mean age of 42.4 years. There were 16 closed fractures and four Type I, two Type II, and one Type IIIA open fractures. Eight fractures were in the proximal third, seven in the middle third, and eight in the distal third. With one nailing, 21 of 23 (91%) fractures achieved solid union in an average of 13.2 weeks. The two nonunions eventually united after another revision nailing and bone grafting. No patients had significant impairment of elbow function. Excellent or satisfactory shoulder function was obtained in 20 patients. Closed locked nailing showed reliable treatment results for severely comminuted or segmental humeral fractures. The keys to success include compression of the fractures, static locking, postoperative external support, and experienced surgical technique.

Adult↗

PubMed2003

Open exchange locked nailing in humeral nonunions after intramedullary nailing.

Humeral nonunions after cannulated intramedullary nailing have been difficult to reconstruct. In the current study, 23 consecutive patients were treated by open exchange locked nailing with bone grafting. There were 16 men and seven women with a mean age of 46.2 years. The nonunions followed humeral locked nailing in eight patients, Seidel nailing in 13, and Küntscher nailing in two. The average nonunion time was 14.7 months. The nonunions, located at the proximal (1/3) in four humeri, middle (1/3) in 15, and distal (1/3) in four, were antegrade nailed in 10 and retrograde nailed in 13. Nineteen had 8-mm nails and four had 7-mm nails. Supplementary wiring was used in 19 patients. The average followup was 21.4 months. With one surgery, all but one patient (96%) achieved osseous union in, on average, 16.3 weeks. One patient with chronic renal dialysis had persistent nonunion and an osteolytic supracondylar fracture. Other complications included one postoperative radial nerve palsy, one brachial artery injury, and one wire infection. At followup, all patients with solid union had excellent or satisfactory recovery of shoulder function. The average postoperative Neer score (90.7) was significantly better than the average preoperative score (68.5). Two patients had losses of elbow motion of 10 degrees and 20 degrees, respectively. This study shows that humeral nonunion after cannulated intramedullary nailing can be treated effectively by open exchange locked nailing with bone grafting. Supplementary wiring can compress the nonunion and facilitate bone healing.

Adult↗

PubMed2003

Complications of locked nailing in humeral shaft fractures.

BACKGROUND: The purpose of this study was to investigate the complications of humeral locked nailing. METHODS: Between 1994 and 2000, 161 humeral shaft fractures (98 acute fractures and 63 delayed unions or nonunions) in 159 patients treated with humeral locked nails were followed up for an average of 25.4 months. There were 89 men and 70 women, with an average age of 53.5 years. Acute fractures included 68 closed, 18 type I, 8 type II, 3 type IIIA, and 1 type IIIB open fractures. Thirty-six nonunions had previous operations. In general, acute fractures were treated with closed nailing and nonunions were treated with open nailing with bone grafting. Since 1998, interfragmentary wiring has been added in nonunions to compress the fracture. RESULTS: In total, 30 patients had 31 significant complications. Nine of them were persistent nonunions, six from acute fractures and three from nonunions. Fracture gap was associated with a significantly higher risk of nonunion. The risk of operative comminution was significantly higher in retrograde nailing, and operative comminution resulted in a significantly higher risk of nonunion. Seven of the nine nonunions underwent revisional nailing and achieved eventual union. Removal of the protruded screws was performed in two cases. Other complications included shoulder impairment, elbow impairment, angular malunion, and post-nailing radial nerve palsy. CONCLUSION: Many complications of humeral locked nailing can be prevented by improving the implant design or surgical techniques. The patients with persistent nonunion can be reliably treated by revisional nailing and bone grafting.

Adult↗

PubMed2003

Locked-nail treatment of humeral surgical neck nonunions.

OBJECTIVE: The authors' purpose was to report their experience with the use of locked nails in treating humeral surgical neck nonunions. Locked nailing has the advantages of minimal soft tissue trauma, automatic fracture reduction, and stable fracture fixation. METHODS: Excluding 3 patients with severe medical illness, a total of 15 consecutive patients with 15 nonunions were treated by humeral locked nailing and bone grafting. Delay from trauma to surgery averaged 13.8 months, and 10 patients had previous operations. The average age of patients was 55.1 years; average follow-up time was 22.4 months. There were two hypertrophic and 13 atrophic nonunions. The average preoperative Neer score for shoulder joints was 53.5. All but three cases had varus deformity, with an average angle of 32.3 degrees. RESULTS: Seven nonunions were nailed with 8-mm nails and eight with 7-mm nails. With a single operation, all but one patient achieved osseous union in an average of 5.4 months. This one patient, who had a Neer score of 72, refused further surgery. At follow-up, 13 of the 15 patients had excellent or good functional recovery of shoulder joints, with an average Neer score of 86.7. Four patients had residual varus angulation averaging 15.5 degrees. For patients with solid union, the average range of shoulder motion was 152.3 degrees in flexion and 146.4 degrees in abduction. No patients had significant limitation of elbow motion. Three patients had occasional shoulder pain and no patients had evident shoulder impingement. CONCLUSION: For humeral surgical neck nonunions in which the head fragment still preserves the greater tuberosity, locked nailing with transfixing screws appeared to be a useful alternative, especially in fractures with osteoporosis, severe varus deformity, or severe soft tissue scarring.

Adult↗

PubMed2002

Locked nailing of spiral humeral fractures with or without radial nerve entrapment.

The experience of locked nailing of spiral humeral fractures and the perioperative conditions of the radial nerve are reported. The nerve is at risk of entrapment after such a fracture, and severe injury may occur during closed nailing. Among 162 humeral fractures treated by locked nailing, there were 21 spiral fractures: 18 acute fractures, and three delayed unions. The distribution of the fractures was two at the middle and 19 at the distal (1/3). Twelve patients had preoperative radial nerve palsy. All fractures excluding one middle fracture were retrograde nailed, and all patients had radial nerve exploration. Thirteen fractures were locked statically, seven were locked distally and had cerclage wiring, and one was locked distally only. Fisher's exact tests showed that the risk of radial nerve entrapment significantly increased in fractures with varus angulation or resulting from high-energy trauma. All the patients achieved fracture union and regained satisfactory joint functions. The author suggests that in external rotational spiral humeral fractures, radial nerve exploration should be done if nerve entrapment is highly suspected, irrespective of the fracture location or nerve palsy. Locked nailing with transfixing screws or cerclage wire could be a reliable treatment method for these fractures.

Adult↗

PubMed2002

Bending strength and holding power of a prototype tibial locking screw.

To improve mechanical performance, a prototype tibial locking screw with two components was developed for the current study: a both-ends-threaded screw with a smooth shank and a small set screw inserted obliquely through the cap of the both-ends-threaded screw. The bending strength and holding power of this prototype screw were compared with that of five commercially available tibial locking screws: Synthes, Howmedica, Richards, Osteo AG, and Zimmer. To test bending strength, the screws were inserted into a polyethylene tube and loaded at their midpoint to simulate a three-point bending test. Single-loading yielding strength and cyclic-loading fatigue life then were measured. To test holding power, the screws were inserted into polyurethane foam tubes, and stripping torque and pushout strength were measured. The results showed that the yielding strength and the fatigue life were related closely to the inner diameter of the fully threaded screws. The stripping torque reflected the pushout strength, which also was estimated by the formula D[0.5 + 0.57735 (D - d)/2p] (D, outer diameter; d, inner diameter; p, pitch). Even though, among all of the tested screws, the prototype had the smallest outer diameter at its middle, it had the highest fatigue strength, and simultaneously preserved its high bone-holding power. A clinical trial using this prototype screw is warranted, one in which the difficult surgical technique of inserting the set screws should be investigated.

Bone Screws↗

PubMed2002

Locked nailing with interfragmentary wiring for humeral nonunions.

OBJECTIVE: Locked nailing for humeral nonunions is threatened by residual fracture gap and fracture motion. This article describes the clinical experience of using interfragmentary wiring to solve these problems. METHODS: Interfragmentary wiring was used in 21 consecutive humeral nonunions treated with humeral locked nails. The average age of patients was 49.5 years, with an average nonunion duration of 14.4 months. Eighteen patients had previous operations. Nonunions were located at the proximal third in 4, the middle third in 10, and the distal third in 7. Antegrade nailing was used in 11 and retrograde nailing in 10. Sixteen nonunions were nailed with 8-mm nails and five with 7-mm nails. Interfragmentary wiring was applied to either the posterior or the lateral cortex of humeri in a figure-of-eight configuration. Bone grafting was performed in all and average follow-up time was 22 months. RESULTS: With a single operation, all patients achieved osseous union in, on average, 18.3 weeks. One patient with segmental nonunion suffered acute renal failure 4 months after operation, but fracture healing was not affected. Wire infection occurred in one patient with preoperative infection at the nail entry site and was treated by implant removal. Other complications including two transient radial nerve palsies and one brachial artery injury did not affect the final outcome. At follow-up, all but four patients had complete recovery of shoulder flexion and abduction. The average postoperative Neer score (91.1 points) was significantly better than the average preoperative score (65.5 points). All but three patients had complete recovery of elbow motion. CONCLUSION: Interfragmentary wiring, a safe procedure if properly performed, could effectively decrease the residual fracture gap and fracture motion in locked nailing of humeral nonunions. Further biomechanical studies and prospective, randomized, controlled studies are warranted.

Adult↗

PubMedDate not supplied

Mechanical strength, fatigue life, and failure analysis of two prototypes and five conventional tibial locking screws.

OBJECTIVE: To investigate the effects of the design and microstructure on the mechanical strength of tibial locking devices. DESIGN AND METHODS: The mechanical strength of two prototypes of specially developed locking devices (a both-ends-threaded screw and an unthreaded bolt) was tested and compared with that of five types of commercially available tibial locking screws (Synthes, Howmedica, Richards, Osteo AG, and Zimmer) with similar dimensions. The devices were inserted into a polyethylene tube and loaded at their midpoint by a materials testing machine to simulate a three-point bending test. Single-loading yielding strength and cyclic-loading fatigue life were then measured. Failure analysis of the fractured screws was performed to investigate the microstructure and potential causes of the fatigue fracture. RESULTS: Test results showed that both yielding strength and fatigue life were closely related to the section modulus of the inner diameter of screws. Among the threaded screws, the both-ends-threaded screws had a higher yielding strength and longer fatigue life than the Osteo AG, Howmedica, Richards, and Zimmer screws. The unthreaded bolts had a lower yielding strength than Synthes screws, but they demonstrated the longest fatigue life among all. In failure analysis of broken screws, no metallurgical or manufacturing defects were found except for surface microimperfections. CONCLUSIONS: The implants investigated in this study are manufactured with high-quality materials and manufacturing processes. The main cause of hardware failure was mechanical overloading. The five commercially used tibial locking screws had a relatively short fatigue life under high loading. Removing the screw threads might substantially increase the fatigue life of the locking devices. In unthreaded bolts, this increase might be tenfold to a hundredfold.

Bone Screws↗