Torsional stability of fixation methods in basicervical femoral neck fractures: a biomechanical study.

BACKGROUND: Basicervical femoral neck fracture is a rare proximal femur fracture with a high implant failure rate. Biomechanical comparisons between cephalomedullary nails (CMNs) and dynamic hip screws (DHSs) under torsion loading are lacking. This study compared the biomechanical performance of three fixations for basicervical femoral neck fractures under torsion load during early ambulation. METHODS: The biomechanical study models used three fixations: a DHS, a DHS with an anti-rotation screw, and a short CMN. Finite element analysis was used to simulate hip rotation with muscle forces related to leg swing applied to the femur. The equivalent von Mises stress (EQV) on fixation, fragment displacement, and strain energy density at the proximal cancellous bone were monitored for fixation stability. RESULTS: The EQV of the short CMN construct (304.63 MPa) was comparable to that of the titanium DHS construct (293.39 MPa) and greater than that of the titanium DHS with an anti-rotation screw construct (200.94 MPa). The proximal fragment displacement in the short CMN construct was approximately 0.13 mm, the greatest among the constructs. The risk of screw cutout for the lag screw in short CMNs was 3.1-5.8 times greater than that for DHSs and DHSs with anti-rotation screw constructs. CONCLUSIONS: Titanium DHS combined with an anti-rotation screw provided lower fragment displacement, stress, and strain energy density in the femoral head than the other fixations under torsion load. Basicervical femoral neck fracture treated with CMNs may increase the risk of lag screw cutout.

Analysis of Stress Distribution and Displacement Based on the Miniscrew Positions of the Palatal Slope Bone-borne Expander: A Finite Element Study.

OBJECTIVES: This study aimed to investigate the stress distribution pattern of the palatal slope bone-borne expander on the maxillary area according to a different anteroposterior position of anchored miniscrews using finite element analysis. MATERIALS AND METHODS: Nasomaxillary stereolithography files with three different anteroposterior anchored miniscrew positions of the palatal slope bone-borne expander were determined as model A, B, and C. Each model consists of four supported miniscrews. Model A: two anterior miniscrews were located between the maxillary canine and the first premolar, and two posteriors between the second premolar and the first molar. Model B: two anteriors were between the lateral incisor and the canine, and two posteriors were the same as in model A. Model C: two anteriors were the same as in model A, and two posteriors were distal to the first molar. One turn of expander screws was applied. Maximum principal stress, equivalent elastic strain, equivalent von Mises stress, and transverse displacement were evaluated. RESULTS: The maximum principal stress was mostly found at the bone-miniscrew interface. Model A exhibited an intersecting area of stress between the supported miniscrews. The highest value of principal stress was in model B, while model C showed a uniform distribution pattern. The elastic strain pattern was similar to the principal stress in all models. The highest value of equivalent von Mises stress was located on the expander screw. The largest amount of transverse displacement of teeth was in model A, while model C exhibited a more consistent transverse displacement than other models. Vertical displacement of posterior teeth was also noticed. CONCLUSION: Based on the result, it revealed that the various anteroposterior miniscrew placements of the palatal slope bone-borne expander had various patterns of stress distribution and resulted in various outcomes. It may be inferred that model A's miniscrew location was advantageous for obtaining expansion quantities, but model C's miniscrew position was advantageous for maintaining consistent biomechanics.

Clinical challenges of biomechanical performance of narrow-diameter implants in maxillary posterior teeth in aging patients: A finite element analysis.

This study evaluated the biomechanical performance of narrow-diameter implant (NDI) treatment in atrophic maxillary posterior teeth in aging patients by finite element analysis. The upper left posterior bone segment with first and second premolar teeth missing obtained from a patient's cone beam computed tomography data was simulated with cortical bone thicknesses of 0.5 and 1.0 mm. Three model groups were analyzed. The Regimen group had NDIs of 3.3 × 10 mm in length with non-splinted crowns. Experimental-1 group had NDIs of 3.0 × 10 mm in length with non-splinted crowns and Experimental-2 group had NDIs of 3.0 × 10 mm in length with splinted crowns. The applied load was 56.9 N in three directions: axial (along the implant axis), oblique at 30° (30° to the bucco-palatal plane compared to the vertical axis of the tooth), and lateral load at 90° (90° in the bucco-palatal plane compared to the vertical axis of the tooth). The results of the von Mises stress on the implant fixture, the elastic strain, and principal value of stress on the crestal marginal bone were analyzed. The axial load direction was comparable in the von Mises stress values in all groups, which indicated it was not necessary to use splinted crowns. The elastic strain values in the axial and oblique directions were within the limits of Frost's mechanostat theory. The principal value of stress in all groups were under the threshold of the compressive stress and tensile strength of cortical bone. In the oblique and lateral directions, the splinted crown showed better results for both the von Mises stress, elastic strain, and principal value of stress than the non-splinted crown. In conclusion, category 2 NDIs can be used in the upper premolar region of aging patients in the case of insufficient bone for category 3 NDI restorations.

The application of inverted lateral clavicle locking compression plate for medial clavicle fractures: biomechanical study and clinical implementation.

BACKGROUND: There has been no absolute consensus on the optimal implant for fixation of medial clavicle fracture. The purpose of the present study was to test the biomechanical efficacy of inverted lateral clavicle locking compression plate (LCP-LC) in fixation of this specific fracture location by finite element analysis. METHODS: Transverse and comminuted medial clavicle fracture simulated models stabilized by three different devices including inverted LCP-LC, superior clavicle LCP (LCP-SC), and dual reconstruction (LCP-RP) with LCP-SC were investigated biomechanical performance under three loading conditions, i.e., axial compression, inferior bending, and axial torsion. RESULTS: EQV stress exhibited on implant and elastic strain at fracture site under inferior bending was greater than other loading cases. LCP-SC construct represented the greatest EQV stress and elastic strain. The inverted LCP-LC construct demonstrated lower EQV stress than the LCP-SC construct and was comparable to dual plating. Under axial compression and axial torsion, elastic strain produced from the inverted LCP-LC construct was comparable to dual plating, but greater than dual plating when subjected to inferior bending. CONCLUSION: By the results of FE analysis, inverted LCP-LC could be a potential application for fixation of clavicle fracture with short medial fragment.

Comparative study of mechanical performance of various fixation constructs in multifragmentary distal humeral shaft fracture: a finite element analysis.

BACKGROUND: There has been no scientific mechanical assessment demonstrating the optimal fixation technique in multifragmentary fractures of the distal humeral shaft. The purpose of the present study was to compare the biomechanical performance of 5 fixation constructs as used in minimally invasive plating osteosynthesis (MIPO) for distal humeral shaft fractures. METHODS: Three-dimensional (3D) humerus model with 20 mm distal humeral shaft fracture gap simulating multifragmentary fracture was created from computed tomography data and virtually fixed by 5 fixation techniques as MIPO, i.e., anterior narrow dynamic compression plate (DCP), anterior narrow locking compression plate (LCP), anterior reversed proximal humeral internal locking system (R-PHILOS), extra-articular distal humerus locking compression plate (LCP-EADH), and anteromedial LCP. All constructs were biomechanically tested under 6 loading conditions by means of finite element analysis, i.e., 250-N axial compression, 7.5-N m internal rotation, 7.5-N m external rotation, 10-N m posterior bending, 10-N m valgus rotation, and 10-N m varus rotation. In addition, A 3D model of each construct was fabricated as 3D printed models. Fixations were applied to the 3D printing model which were later mechanically tested to validate the FE results. RESULTS: EQV stress exhibited on anterior narrow LCP and anterior R-PHILOS were comparable which were lower than other constructs under axial compression and valgus-varus bending. Anterior R-PHILOS produced lower EQV stress than other constructs under internal-external rotation and posterior bending. On the whole, R-PHILOS demonstrated a comparable fracture displacement to those LCP with anterior or anteromedial approaches, that achieved the lowest displacement values. In addition, the experimental mechanical test values shared a correlation with the FE model results. CONCLUSION: Overall, the anterior R-PHILOS was considered as a potential candidate for multifragmentary distal humeral shaft fractures. It demonstrated efficacious biomechanical performance in terms of implant stress and distal fragment displacement.

Nonvascularized fibular graft with locking screw fixation for metaphyseal bone loss of distal femur: biomechanical assessment validated by a clinical case series.

BACKGROUND: The optimal modality to surgically treat significant bone loss of distal femur remains inconclusive. The objectives of the present study were to assess the mechanical performance of nonvascularized fibular graft (NVFG) with locking screw fixation in distal femur fixation construct by finite element analysis and to retrospectively describe the outcomes of the present technique in clinical cases. METHODS: Four constructs which the fractured femur was stabilized by LCP-DF alone, dual plating, LCP-DF combined with NVFG, and LCP-DF combined with NVFG (LCP-DF-NVFG-S) with locking screw were assessed the biomechanical performance under physiological loads. For the clinical case series, 12 patients with open intercondylar fracture with metaphyseal bone loss of distal femur were operated by LCP-DF-NVFG-S. The collected data included fracture consolidation, length of NVFG, perioperative complications and objective clinical results. RESULTS: LCP-DF-NVFG-S demonstrated lower implant equivalent von Mises stress (EQV) stress and better fracture stability than other constructs. A locking screw presented its essence in maintaining the NVFG in the required position and subsequently enhancing the fracture stability. In regard to the clinical series, all fractures were consolidated with an average duration of 27.8 weeks (range 20-32). An average NVFG length was 7.8 cm (range 6-12). No perioperative complication was demonstrated. By the Knee Society score, 1 was considered to be excellent, 9 to be good and 2 to be poor. CONCLUSION: Based on the results of mechanical assessment and case series, LCP-DF-NVFG-S can be an effective technique in the management of metaphyseal bone loss of distal femur.

Biomechanical evaluation of two internal fixation systems for the treatment of mandibular symphyseal fracture.

Due to the disadvantage of maxillomandibular fixation, the semi-rigid and rigid internal fixations have been employed to provide early mouth motion. To find the proper fixation and adequate stability, the biomechanical performance of these systems was assessed using Finite Element (FE) method. The 3D mandible model with a symphyseal fracture, teeth, periodontal ligament, and fixation devices were created for the FE analyzes. The bone structure was determined as a transverse isotropic whereas the fixation devices were titanium. The load includes Masseter, Medial Pterygoid, and Temporalis muscular forces as well as the occlusal forces acting on first molars, canines, and incisors. The maximum stress occurs at the center of fixation devices at symphyseal fracture. The maximum stress values were 877.4 MPa for the reconstruction plate and 646.8 MPa for the mini-plates. The plates maintained the fracture width at mid-region better than superior and inferior. The maximum fracture gap were 1.10 and 0.78 mm for reconstruction plate and mini-plates, respectively. The fracture site's elastic strain stabilized with the reconstruction plate was 1089.0 microstrains and with the mini-plates was 399.6 microstrains. The treatment of a mandibular symphyseal fracture using a mini-plates provides more adequate fracture stability for new bone formation and mechanically safer than locking reconstruction plate. Mini-plates fixation was able to control the fracture gap better than the reconstruction plate. Mini-plates technique was considered as the first choice of internal fixation, however, a reconstruction plate can also be used in case of unavailability and complication related to mini-plating.

Dual plating for fixation failure of the distal femur: Finite element analysis and a clinical series.

BACKGROUND: The optimal technique for managing distal femur fixation failure remains inconclusive. The author studied the efficacy of a combined proximal humerus locking compression plate (LCP-PH) and 3.5 mm reconstruction plate (LCP-RP) by finite element (FE) analysis and retrospectively described the clinical outcomes of the present technique in such difficult circumstances. METHODS: Biomechanical study setting included FE models of the distal femur with remaining holes from previous distal femur LCP (LCP-DF) fixation stabilized with three different constructs i.e., LCP-DF alone, LCP-DF-and-LCP-RP, as well as LCP-PH-and-LCP-RP. All settings were analyzed by using FE under physiological loads. Regarding the clinical series, the outcomes of 8 LCP-DF fixation failures operated on by the present technique were retrospectively reviewed. RESULTS: High Implant stress of 911.2 MPa and elastic strain at fracture site of 200.8 µÉ› were found when stabilized with LCP-DF. The constructs of LCP-DF-and-LCP-RP, and LCP-PH-and-LCP-RP presented lower implant stress compared to LCP-DF, 511.5, and 617.5 MPa, respectively. The elastic strain of both dual plating constructs was also 4-5 times lower than LCP-DF and differed from each other by approximately 10 µÉ›. Regarding the clinical series, bony consolidation was achieved in all cases with a mean duration of 28.5 weeks (range 24-36). An average ROM of the affected knee was 115° (range 105-140). Regarding the KSS, 1 was determined to be excellent and 7 to be good. CONCLUSION: By the biomechanical analysis and the clinical results, the construct of LCP-PH-and-LCP-RP could be an effective technique for revision surgery of LCP-DF fixation failure.

Comparative biomechanical performance of two configurations of screw constructs and types used to stabilize different sites of unstable Pauwels type II femoral neck fractures: A finite element analysis.

BACKGROUND: A smaller dimension of the femoral neck in the Asian population may have difficulty placing inverted triangle multiple screws configuration for treatment. Posterior triangle configuration, which is suitable in limited space of the femoral neck, is a promising alternative treatment approach. This study aimed to investigate the biomechanical performance of inverted and posterior triangles of multiple screws fixation configuration for both cannulated and standard solid-core screws in stabilizing Pauwels type II femoral neck fracture sub-capital, mid-cervical, and basilar regions using Finite Element (FE) method. METHODS: A 3D femur model was created for Pauwels type II femoral neck fractures. The fracture sites were in the mid-cervical, sub-capital, and basilar regions, with a spacing of 7 mm between adjacent fracture lines. Both cannulated and solid-core screws were configured in the inverted and posterior triangle patterns. The applied physiological loads to the FE models included muscle and hip contact forces. Equivalent von Mises (EQV) stresses were used to monitor fixation strength whereas elastic strain of each configuration indicated the degree of stability of a fracture site. RESULTS: EQV stress on the screws for posterior and inverted triangle configuration ranged from 212.1 to 290.2 MPa, and 224.4-314.8 MPa, respectively. The EQV stress the posterior triangle configuration was lower than the inverted triangle configuration by 5.5-10.8%. The stress exhibited on the screw was greatest when the fracture site was at basilar regions, 1.1-1.3 times greater than fracture in sub-capital region. Elastic strain at fractures retained by cannulated screw was greater than solid-core screw with maximum difference of 68 microstrains. Cannulated screw provided less stability than the solid-core screw. CONCLUSIONS: The screws used in the posterior triangle configuration exhibits lower screw stress in all fracture regions of the femoral neck. The solid-core screw shows superior biomechanical properties compared with cannulated screw with lower EQV stress and better fracture stability. Posterior triangle configuration is considered an alternative treatment of choice for the patient with a small dimension of the femoral neck.

Effects of miniscrew location on biomechanical performances of bone-borne rapid palatal expander to midpalatal suture: A finite element study.

This study investigated the effects of miniscrew location on biomechanical performance of bone-borne rapid palatal expander (B-RPE) to midpalatal suture, using finite element (FE). Three cases of B-RPE with different miniscrew locations (3 and 6 mm from midpalatal suture and palatal interdental site) were simulated activations in partly ossified midpalatal suture maturation. This study compared the expansion amount and pattern along the suture line. Equivalent von Mises (EQV) stresses at appliance, miniscrew, midpalatal sutures, and elastic strain at the bone around miniscrew were evaluated. In all cases, they could not break the midpalatal suture of palatine bone. However, midpalatal suture at the maxilla was expanded. The expansion amount and unparallel expanding pattern were increased when miniscrews were positioned away from the suture. The interdental miniscrew position extended the suture more than the other 2 cases, but the pattern was unparallel. When the miniscrews were positioned away from the suture, the EQV stress at the appliance and elastic strain at the bone around the miniscrew were reduced. In the case of the palatal interdental miniscrew, all parameters were of lower magnitude. All cases could expand the partly ossified midpalatal suture maturation. The distance between the midpalatal suture and the miniscrew influenced appliance EQV stress, elastic strain at the bone around the miniscrew, and expansion characteristics.

Finite element analysis between Hunsuck/Epker and novel modification of Low Z plasty technique of mandibular sagittal split osteotomy.

A novel modification of the Low Z plasty (NM-Low Z) technique for bilateral sagittal split osteotomy was recently proposed. The osteotomy line was modified more inferiorly than in the conventional Hunsuck-Epker (HE) approach. The NM-Low Z technique enhances the mandibular setback distance and degree of rotation in severe skeletal discrepancies. This study aimed to investigate the biomechanical behavior under simulated forces, and to compare the NM-Low Z and HE techniques on the mandible with Class III skeletal deformity at 1 week, 3 weeks, and 6 weeks post-operation. Physiological muscular and occlusal loads were simulated using the finite element (FE) method. Stresses on the miniplate, screws, and bone were observed and compared between the two models. The elastic strain at the fracture site was observed for the optimal bone-healing capacity. The NM-Low Z model exhibited a lower stress than the HE model at every stage post-operation. Both models demonstrated elastic strains within the normal range for bone healing. In summary, the biomechanical behavior of the NM-Low Z technique is comparable to that of the conventional EH technique. NM-Low Z could facilitate post-operation skeletal stability by reducing the stress on fixation materials during bone healing.

Biomechanical performance of short and long cephalomedullary nail constructs for stabilizing different levels of subtrochanteric fracture.

INTRODUCTION: The aim of this study was to assess biomechanical performance of short and long Cephalomedullary nail constructs consisting of different number of distal screw for stabilizing different levels of subtrochanteric fracture. MATERIALS AND METHODS: The femur obtained from computed tomography scanner was used to create a transverse fracture at 15 mm (level A), 35 mm (level B), and 55 mm (level C) below the lesser trochanter. Short and long Cephalomedullary nails were virtually inserted to the fractured femur. Four-node tetrahedral element was used to build up finite element (FE) models for biomechanical analysis. The analysis focused on post-operative stage of partial weight-bearing. RESULTS: Stress on the implant localized at the surface between lag screw/nail and distal screw/nail. Short Cephalomedullary nail exhibited higher stress than long Cephalomedullary nail. The stress in short Cephalomedullary nail could be reduced by using two distal screws fixation and the fracture at level A produced less stress than that of level B and C. Either short or long nail with two distal screws is sufficient to withstand the stress magnitude produced from the physiologic load. When single dynamic distal screw was used, stress on implant, elastic strain at fracture gap, and bone stress reached the high values. Elastic strain of the fracture gap at level C were less than that of level A and B, but no statistically significant difference. There was no proximal cancellous bone damage observed from the FE analysis. CONCLUSIONS: Long Cephalomedullary nail with at least two distal locking screws remains a proper implant for subtrochanteric fracture fixation in overall locations. However, short Cephalomedullary nail with two distal screws may be a candidate for a high subtrochanteric fracture. Single dynamic screw insertion is strongly not recommended with either short or long nail regarding implant failure.

Single lag screw and reverse distal femur locking compression plate for concurrent cervicotrochanteric and shaft fractures of the femur: biomechanical study validated with a clinical series.

BACKGROUND: The optimal surgical management of concurrent cervicotrochanteric and shaft fractures of the femur has not been consensual. The authors investigated the reliability of combined single lag screw and reverse distal femur locking compression plate (LCP-DF) by finite element (FE) study and retrospectively described the present technique for these dual fractures. METHOD: Intact femurs were derived from CT data, and the implant models were created by using CAD software. The fractured femur and implant models were virtually aligned based on the surgical techniques before converting to the FE model. In the FE model, applied boundary conditions included body weight, muscle forces, and constraint of the joints. Regarding clinical series, three patients with these dual fractures of the femur and 2 with cervicotrochanteric fractures with subtrochanteric extension were operated on by the proposed technique. The collected data include operative time, postoperative complications, union times, and clinical outcomes. RESULTS: Equivalent von Mises stress exhibited on dynamic hip screws with an anti-rotational screw was higher than the other techniques, close to the yield stress of the material. Multiple screw fixation produced better stability for transcervical fractures whereas the proposed technique of combined single lag screw and reverse LCP-DF provided better stability for intertrochanteric fractures. No significant difference in cortical bone stress was found between multiple screw construct and the proposed technique. The proposed technique presented a lower risk of secondary fractures, as the strain energy density (SED) in cancellous bone was lower than multiple screw construct. Regarding clinical series, all fractures were united with a mean union time of-16.1 weeks (range 12-20). There were no any postoperative complications. Regarding the Harris score, 1 was determined to be excellent value, and 4 to be good. CONCLUSION: By the FE results, a combination of a single lag screw and reverse LCP-DF is an effective technique for fixation of cervicotrochanteric fractures. Empowered by the clinical results, this proposed technique could be an alternative for concurrent cervicotrochanteric and shaft fractures of the femur especially when either single-system or dual-system devices seem not to be suitable.

Comparison of canine stifle kinematic analysis after two types of total knee arthroplasty: A cadaveric study.

BACKGROUND AND AIM: Osteoarthritis is a common consequence of cranial cruciate ligament rupture (CCLR) in the canine stifle. Total knee replacement is a valuable method for managing end-stage osteoarthritis. MATERIALS AND METHODS: Two new designs of total knee replacement implants were fabricated with information from computed tomography scans. Canine hind limbs of cadavers were tested with a biomechanical testing machine with C-arm fluoroscopy. The four groups tested were as follows: Intact stifles (INTACT), CCLR, total knee arthroplasty (TKA) with a peg on top of the tibial component (TKAP), and TKA with no peg on top of the tibial component (TKAN). Extension, flexion, adduction, abduction, internal rotation, external rotation, cranial translation, caudal translation, and range of motion were measured. RESULTS: The cranial translation of the tibia relative to the femur increased significantly after cutting off the cranial cruciate ligament. After arthroplasty, adduction/abduction and cranial/caudal translation within the TKAN group was increased compared with the intact stifle group. In the TKAP group, only adduction was greater than it was in the intact stifle group. CONCLUSION: The design of the prosthesis used for the TKAP group was more appropriate for total knee replacement in dogs than the design of the prosthesis for the TKAN group.

Preoperative planning of medial opening wedge high tibial osteotomy using 3D computer-aided design weight-bearing simulated guidance: Technique and preliminary result.

BACKGROUND: High tibial osteotomy (HTO) is an established treatment for uni-compartmental osteoarthritis with varus deformity in relatively active young patients with good knee mobility. The most important factor for success and low complications of HTO is the precise correction of osteotomy. The objective of this study was to evaluate the accuracy of pre-operative planning of open-wedge HTO using t3D computer-aided design (CAD) weight-bearing simulated guidance technique for the succession of surgery. MATERIALS AND METHODS: Nineteen patients who met the inclusion criteria were recruited between July 2013 and June 2014. 3D CAD weight-bearing simulated guidance technique was obtained from standard anterior-posterior, lateral of hip-to-ankle full leg standing radiographs, and computed tomography (CT) scan provided the weight-bearing corrective axis of preoperative planning and predictive corrective mechanical axis value. Post-operative mechanical axis value was obtained after surgery. RESULTS: This comparative study between the predictive corrective, using 3D CAD weight-bearing simulated guidance technique, and post-operative mechanical axis value, analysed with t-test statistical analysis, showed the insignificant difference ( p > 0.05). CONCLUSION: We conclude that the 3D CAD weight-bearing simulated guidance technique has good accuracy as preoperative planning of open-wedge HTO for succession surgery.

3D CAD/reverse engineering technique for assessment of Thai morphology: Proximal femur and acetabulum.

PURPOSE: To assess morphological parameters of proximal femur and acetabulum in Thai population with three-dimensional measurement technique, and to analysis of collateral side symmetric, gender difference, and correlation between morphometric parameters. METHODS: Investigation was performed in 240 femurs. All three-dimensional femur models were acquitted from 64-slice spiral CT scanner. Morphometric parameters under consideration included acetabular diameter, femoral head diameter, shaft isthmus location, intramedullary canal diameter, diaphyseal diameter, femoral head height, femoral neck isthmus, femoral neck length, neck shaft angle, bow angle, and anteversion angle. All parameters were measured based on functions and least-square regression function in CAD software. Obtained measured data were then used for analysis of collateral side symmetric, gender difference, correlation between morphometric parameters, and compared with other populations. RESULTS: Female had a smaller dimension compared with male in most of the parameters. No significant difference was observed between left and right femurs. High correlation pairs of morphometric parameters included femoral head diameter-acetabular diameter, femoral head diameter-neck isthmus diameter, femoral head diameter-diaphyseal diameter at shaft isthmus level, acetabular diameter-neck isthmus diameter, neck isthmus diameter-diaphyseal diameter at shaft isthmus level, and acetabular diameter-diaphyseal diameter at shaft isthmus level. Some morphometric parameters of Thai are smaller than other Caucasian, and some Asian nation, i.e. femoral head diameter, femoral neck length, and femoral head height. CONCLUSIONS: This study provides essential morphometric data for various orthopedic implant designs relating to proximal femur region.

Biomechanical performance of retrograde nail for supracondylar fractures stabilization.

The study compared the biomechanical performance of retrograde nail used to stabilize supracondylar fracture (three different levels) by means of finite element analysis. Three different nail lengths (200, 260, and 300 mm) of stainless steel and titanium nails were under consideration. Intact femur model was reconstructed from Digital Imaging and Communications in Medicine images of Thai cadaveric femur scanned by computed tomography spiral scanner, whereas geometry of retrograde nail was reconstructed with the data obtained from three-dimensional laser scanner. The retrograde nail was virtually attached to the femur before nodes and elements were generated for finite element model. The finite element models were analyzed in two stages, the early stage of fracture healing and the stage after fracture healing. The finding indicated that purchasing proximal locking screw in the bowing region of the femur may be at risk due to the high stresses at the implant and bone. There were no differences in stress level, elastic strain at a fracture gap, and bone stress between stainless steel and titanium implant. Since the intramedullary canal requires reaming to accommodate the retrograde nail, the length of retrograde nail should be as long as necessary. However, in case that the retrograde nail can be accommodated into the intramedullary canal without reaming, the longer retrograde nail can be used.

Rapid-prototype endoprosthesis for palliative reconstruction of an upper extremity after resection of bone metastasis.

PURPOSE: To present a rapid-prototype (RP) endoprosthesis replacement after tumor resection in patients with bone metastasis of the upper extremity. The short-term complications and functional outcomes were evaluated as well as the survival of patients and endoprosthesis. METHODS: Bone metastasis patients who required bone resection and endoprosthesis replacement were enrolled and consented before operation. Custom-made endoprosthesis was fabricated from polymethyl methacrylate assisted by RP technology. After surgery was performed, patients were followed up daily until discharge and monthly until 6 months postoperatively for immediate post-operative complications and for signs of endoprosthesis failure. The functional outcome was evaluated 6 months postoperatively by the Musculoskeletal Tumor Society score (MTSS) and the Mankin score. Thereafter, patients' survival and arm condition were monitored every 3 months. RESULTS: Sixteen cases participated on this study. There were nine proximal-, four total- and two distal humerus, and one proximal ulna replacement. The median follow-up period was 486 days. The mean MTSS was 55 % and the Mankin score was good in 64 % and fair in 36 % of the patients. Glenohumeral subluxation was observed in 23 % of the patients; however, a stable shoulder was achieved in all cases. There were no prosthesis failure or systemic breakage. CONCLUSIONS: An RP endoprosthesis may have significant advantages when the entire humerus needs to be replaced, or periarticular sites are involved. This technique offers custom-made endoprosthesis with enough durability, and in a relatively short production time at reasonable costs which are suitable for palliative reconstruction.

Lateral condylar prominence, post corrective osteotomy of cubitus varus: a study using three-dimensional reverse engineering technique.

Lateral condylar prominence is a common problem after corrective osteotomy of the cubitus varus, which is believed to result from unequal opposing cut surfaces of lateral-based wedge osteotomy using a medial hinge. This study investigated this issue using a 3-dimensional CT data set consisting of images of the deformed elbow and the normal elbow of a patient with cubitus varus deformity who was scheduled for corrective osteotomy A CT scan was performed with 3mm slice thickness and a reconstruction was done with 1mm interpolated slice thickness on both the left and right humerus. The CT-data set was then manipulated using reverse engineering software. Three-dimensional models of both the deformed and normal humeri were studied. Several locations or levels of medial hinge placement, each with 4-degree-tilt wedge osteotomy cut options, were then virtually performed and evaluated. The degree of correction was determined from the varus angle plus the normal carrying angle of the normal side. From the study, it was found that the degree of lateral condylar prominence is directly proportional to the distance of placement of the medial hinge above the joint. Differences in the lengths of the osteotomy surfaces have no effect on condylar prominence; only the step-off phenomenon affects condylar prominence. According to our findings, placement of the medial hinge close to the joint with a 10-degree distal osteotomy cut just above the olecranon fossa will result in optimal minimization of condylar prominence or the step-off phenomenon.

Optional entry point for retrograde femoral nailing: an anatomical study using the reverse engineering method.

OBJECTIVE: To investigate the optimal entry point for retrograde femoral nailing using medical imaging and reverse engineering technologies. MATERIAL AND METHOD: One hundred and eight adult cadaveric femurs were scanned using a computed tomography (CT) scanner. To obtain three-dimensional models, medical imaging and reverse engineering technologies were used. The insertion assessment was performed using computer aided design (CAD) software. The curve representing the mid-line in the intramedullary canal in the mid-shaft region was approximated using regression analysis. The curve was extended tangentially toward the femoral condyle, where the intersection between the curve and the condylar surface is the insertion site. The location of the insertion site was determined using the center of the anterior most of the intercodylar notch as a reference point. The measured distances were presented in medial-lateral and anterior-posterior perspectives from the reference point. RESULTS: Average insertion site for Thai population was 0.56 mm lateral to and 12.67 mm medial to the anterior most of the intercondylar notch. The distance measured from intercondylar notch to the insertion site in the anterior-posterior direction was not significantly different between males and females; however a significant difference in the insertion site was found in medial-lateral directions. CONCLUSION: The insertion site can be clinically approximated lying on the anterior-posterior axis, since the distance from the anterior-posterior axis to the insertion site is relatively small. The insertion site for the Thai population was found to be 12 mm anterior to the center of the anterior most of the intercondylar notch.