Non-locking Plate Research Articles

Cyclic Loading of Periprosthetic Fracture Fixation Constructs

Femur fractures are a common complication of hip arthroplasty. When the stem is well fixed, fracture fixation is the preferred treatment option. Numerous fixation methods have been advocated, using plates or allograft struts. Vancouver type B1 periprosthetic femur fractures were created distal to a cemented hip stem in 15 third-generation composite femurs. The fractures were fixed with (1) a nonlocking plate and allograft strut, (2) a locking plate and allograft strut, or (3) a locking plate alone. The struts were fixed with cables. After fixation, the constructs underwent cyclic loading for 100,000 cycles. Stiffness of the constructs was determined during bending, torsion, and axial compression before and after cyclic loading. Load to failure was also determined. Overall, cyclic loading had little effect on the mechanical properties of these constructs. The two constructs with allografts were significantly stiffer in bending than the construct consisting of only a locking plate. There were no significant differences in axial or torsional stiffness between the constructs. Load to failure of the two constructs with allografts was significantly greater than the locking plate alone. Allograft strut-plate constructs are stiffer in bending and have a higher load to failure than a stand-alone locking plate. When an allograft plate construct is chosen, locking screw seemed to provide no mechanical advantage. All three constructs tested retained their mechanical characteristics after 100,000 cycles of loading. Our initial concern that the cables fixing the allograft strut would loosen appears unfounded.

Biomechanical Evaluation of Periprosthetic Femoral Fracture Fixation

A variety of methods are available for the fixation of femoral shaft fractures after total hip arthroplasty. However, few studies in the literature have quantified the performance of such repair constructs. The aim of this study was to evaluate biomechanically four different constructs for the fixation of periprosthetic femoral shaft fractures following total hip arthroplasty. Twenty synthetic femora were tested in axial compression, lateral bending, and torsion to determine initial stiffness, as well as stiffness following fixation of a simulated femoral midshaft fracture with and without a bone gap. Four fracture fixation constructs (five specimens per group) were assessed: construct A was a Synthes locked plate (a twelve-hole broad dynamic compression plate) with locked screws; construct B, a Synthes locked plate (a twelve-hole broad dynamic compression plate) with cables and locked screws; construct C, a Zimmer nonlocking (eight-hole) cable plate with cables and nonlocked screws; and construct D, a Zimmer nonlocking (eight-hole) cable plate with allograft strut, cables, and nonlocked screws. Axial stiffness, lateral bending stiffness, and torsional stiffness were assessed with respect to baseline intact specimen values. Axial load to failure was also measured for the specimens. Construct D demonstrated either equivalent or superior stiffness in all testing modes compared with the other constructs in femora with both a midshaft fracture and a bone gap. A comparison of constructs A, B, and C demonstrated equivalent stiffness in all test modes (with one exception) in femora with a midshaft fracture and a bone gap. A combination of a nonlocking plate with an allograft strut (construct D) resulted in the highest stiffness of the constructs examined for treating a periprosthetic fracture around a stable femoral component of a total hip replacement.

Comparative study of distal radial fractures in the elderly treated with locking and non-locking plates

To evaluate the clinical difference of locking and non-locking plates in the treatment of distal radial fractures in the elderly. Forty-nine patients with an average age of 68 years were included. The mean follow-up was 30 months. Five cases were traffic related injury, and others were simple falls. Fractures were classified according to AO classification system: 9 cases of A3, 4 cases of B, 11 cases of C1, 18 cases of C2, 7 cases of C3. Patients were grouped as locking group (29 cases) and non-locking group (20 cases). Significant difference was not found between the two groups in active range of motion, Gartland and Werley score, radiological measurements and score. Locking and non-locking plates have the same clinical outcome in the treatment of distal radial fractures in the elderly.

Fixation of long bone segmental defects: A biomechanical study

Obtaining stable fixation in cases of long bone non-union with segmental bone defects can be challenging. Bone quality is often sub-optimal. Locking plates and structural allografts have both been used clinically in these cases. The objective of this study was to determine the biomechanical characteristics of three constructs that have been employed in this context. A biomechanical study was performed using 3rd Generation Composite Femurs as specimens. A diaphyseal segmental defect was created and fixed with one of three constructs: (1) lateral locking plate (LP); (2) lateral non-locking plate and medial allograft strut (S); (3) lateral non-locking plate and intramedullary fibula allograft (F). The "allografts" were fashioned from 3rd generation composite bones. Axial, torsional and bending stiffness as well as load to failure were determined using a materials testing machine. Overall, construct S was the stiffest and construct LP was the least stiff. Construct F had intermediate characteristics. Axial load to failure for construct S (6108N) and for construct F (5344N) was significantly greater than for construct LP (2855N). When maximal stiffness is desired, a construct with a structural allograft should be chosen over a locking plate. However, biological and anatomic factors must also be taken into account when using these constructs clinically.

Biomechanical comparison of screws and plates for hallux valgus opening-wedge and Ludloff osteotomies

The optimal osteotomy type and fixation method for hallux valgus correction have not been defined. This study examined the mechanical properties of corrective opening-wedge and Ludloff oblique osteotomies under conditions approximating postoperative weight-bearing. Twenty-nine pairs of fresh-frozen metatarsals were divided into three groups. In Group 1, headless screws were compared with standard cortical screws for Ludloff osteotomy fixation. In Groups 2 and 3, Ludloff osteotomies fixed with headless screws were compared with opening-wedge osteotomies fixed with non-locking and locking plates, respectively. Constructs underwent dorsally-directed cantilever loading for 1000 cycles. No significant differences in angulation or stiffness were demonstrable in Group 1. In Group 2, Ludloff/headless screw construct stiffness exceeded non-locking plate construct stiffness. The mean angulation on the 1000th load cycle was greater for plates than for Ludloff/headless screws. In Group 3, locking plate construct stiffness and angulation did not differ from Ludloff/headless screws in early cyclic loading, but fixation failure of the locking plate constructs was common. The results indicate that screw type for Ludloff fixation may be left to surgeon preference and that opening-wedge plates exhibit mechanical properties inferior to that of the Ludloff osteotomy under the tested conditions. Lateral cortex continuity and bone density remain important factors in the performance of opening-wedge osteotomies.

Biomechanical Evaluation of Volar Locking Plates for Distal Radius Fractures

Fixed-angle devices have been a major advancement in orthopedic fracture care and have become an attractive option for fixation of distal radius fractures. Several volar locking plates exist, but there is insufficient literature comparing the strengths of these plates. This study compares the biomechanical strength of two popular volar locking plate systems (Synthes LCP and Hand Innovations DVR-A) along with a nonlocking volar T-plate (Synthes). Twenty-three formalin-fixed cadaveric forearms were divided into three groups with similar ages and bone densities. An unstable extra-articular fracture was created using a standardized osteotomy. Each group was fixed with one of the three plates. Each specimen was loaded in axial compression for 2000 cycles at a force of 400 N. Each specimen that completed cyclic testing was loaded to failure. Stiffness, yield point, and ultimate strength were recorded for each construct. Each fixed-angle construct completed all 2000 cycles. The nonlocking plates failed at an average of 560 cycles. The mean stiffness of the DVR-A, LCP, and the volar T-plates were 277.00, 343.17, and 175.67 N/mm, respectively. There was a statistically significant difference between both fixed-angle plates and the nonlocking plate (p < 0.05). The difference between each fixed-angle construct did not reach significance. Yield point and ultimate strength could only be determined for the two fixed-angle devices. There was no statistically significant difference between the constructs for both yield point (DVR-A = 855.56 N, LCP = 894.15 N) and ultimate strength (DVR-A = 1,021.97 N, LCP = 1,114.87 N). Given our data, fixed-angle constructs withstand cyclical loading representing normal physiologic forces encountered during post-operative rehabilitation. There was no significant biomechanical difference between the two fixed-angle constructs. Our results support that volar fixed-angle locking plates are an effective treatment for unstable extra-articular distal radius fractures, allowing early postoperative rehabilitation to safely be initiated.

Ist die winkelstabile, palmare 3,5-mm-T-Platte die Lösung für dislozierte, distale Radiusfrakturen?

There are many different possibilities for the treatment of the distal radial fracture. According to evidence-based medicine there is no gold standard for the treatment of this fracture. With the development of locking plates, the spectrum of indications for plate osteosynthesis has possibly increased. The aim of our investigation was the evaluation of the clinical results after stabilisation of distal radial fractures with the locking, 3.5 mm T-LCP. In a retrospective study we analysed all patients with distal radial fractures treated with a 3.5 mm T-LCP between 05/02 and 05/04. The complete medical histories and X-rays were analysed and a clinical follow-up examination with the Martini score was performed. 76 from 93 patients (82%) could be examined for the follow-up, the average age was 59 years (17/88). According to the AO classification of Mueller and Nazarian we had 23 A-fractures, 7 B-fractures and 73 C-fractures. After reduction and plate osteosynthesis we found no secondary displacement. The median of the overall results according to the Martini score was 33 from 38 points (9/38). As far as complications were found 1 CRPS, 3 CTS, 2 pseudarthroses, 1 wound infection, 1 delayed bony union, 3 implant failures, and 1 broken plate (after a new injury). In one case the median nerve was cut during operation and a suture was performed. According to our results the 3.5 mm T-LCP is a good implant for the stabilisation of displaced distal radius fractures if the fragments are not too small for the 3.5 mm screws. The anatomic reduction is maintained and the X-rays show very good results. Compared with other investigations we must ask ourselves if the benefit of the locking plates justifies its use as compared with non-locking (conventional) plates.

Biomechanical Analysis of Bicondylar Tibial Plateau Fixation: How Does Lateral Locking Plate Fixation Compare to Dual Plate Fixation?

This study is designed to test the comparative strength of lateral-only locked plating to medial and lateral nonlocked plating in a cadaveric model of a bicondylar proximal tibial plateau fracture. Ten matched pairs of human cadaveric proximal tibia specimens were used for biomechanical testing. Cyclic loading using a materials testing device simulated initial range of motion and load bearing following surgical repair. Subsidence of the medial and the lateral condyles was measured following 10,000 cycles from 100N to 1,000N; the maximum load to failure on the medial condyle for both plate constructs was also measured. On the lateral side, dual plating (DP) allowed an average of 0.68 +/- 0.14 mm of subsidence, compared with 1.03 +/- 0.27 mm for the fixed-angle plate (FAP) (P = 0.077). On the medial side, DP allowed an average of 0.78 +/- 0.15 mm of subsidence, compared with 1.51 +/- 0.32 mm for the FAP (P = 0.045). No significant difference was found in the maximal load to medial condyle fixation failure between either plating construct (P = 0.204). The results of this study demonstrate that dual-plate fixation allows less subsidence in this bicondylar tibial plateau cadaveric model when compared to isolated locked lateral plates. This may raise concerns about the widespread use of isolated lateral locked plate constructs in bicondylar tibial plateau fractures.

Mechanical Characteristics of Locking and Compression Plate Constructs Applied Dorsally to Distal Radius Fractures

Locking plates are thought to have many advantages such as a decreased incidence of loss of reduction secondary to screw toggling and improved bone healing due to an increased periosteal blood supply. We hypothesized that locking plates will also provide increased stiffness and increased load to failure when they are applied dorsally to stabilize dorsally comminuted distal radius fractures. This study compared the stiffness and strength of dorsally applied locking and standard (nonlocking) T-plates applied to a dorsally comminuted distal radius fracture model. Sixteen pairs of embalmed cadaveric human radii were potted, and a standard wedge osteotomy was performed simulating a dorsally comminuted distal radius fracture. The radii were randomized into 2 groups, so that 8 pairs received a 3.5-mm dorsal locking T-plate over the osteotomy on the right radius and 8 pairs received the same on the left radius. A dorsal 3.5-mm standard T-plate was placed over the osteotomy on the contralateral radius in each group. An axial load was used to test the strength and stiffness of each construct. Paired t tests were then used to compare the strength and stiffness of the locking plate with those of the standard plate. A significant difference was found in both the stiffness and the strength between the locking and standard nonlocking plates. The locking T-plate was 33% stiffer than the standard T-plate. The locking T-plate had a 91% increase in the load to failure. Failure for both locking and standard T-plates occurred via volar cortex bone fracture. Locking T-plates increased both the stiffness and strength of dorsally comminuted distal radius fractures compared with standard nonlocking T-plates by a statistically significant margin.

The Evolution of Locked Plates

Kubiak, Erik N. MD; Fulkerson, Eric MD; Strauss, Eric MD; Egol, Kenneth A. MD Author Information

Internal Fixation of Dorsally Displaced Fractures of the Distal Part of the Radius

Volar plate fixation with use of either a locking plate or a neutralization plate has become increasingly popular among surgeons for the treatment of dorsally comminuted extra-articular distal radial fractures. The purpose of the present study was to compare the relative stability of five distal radial plates (four volar and one dorsal), all of which are commonly used for the treatment of dorsally comminuted extra-articular distal radial fractures, under loading conditions simulating the physiologic forces that are experienced during early active rehabilitation. With use of a previously validated Sawbones fracture model, a dorsally comminuted extra-articular distal radial fracture was created. The fracture fixation stability of four volar plates (an AO T-plate, an AO 3.5-mm small-fragment plate, an AO 3.5-mm small-fragment locking plate, and the Hand Innovations DVR locking plate) were compared under axial compression loading and dorsal and volar bending simulating the in vivo stresses that are generated at the fracture site during early unopposed active motion of the wrist and digits. A single dorsal plate (an AO pi plate) was used for comparison, with and without simulated volar cortical comminution. The construct stiffness was measured to assess the resistance to fracture gap motion, and comparisons were made among the implants. The volar AO locking and DVR plates had greater resistance to fracture gap motion (greater stiffness) compared with the volar AO nonlocking and AO T-plates under axial and dorsal loading conditions (p < 0.01), with no significant difference between the AO volar locking and DVR plates. The volar AO locking plate had greater resistance to fracture gap motion than did the volar AO nonlocking plate under axial loading and dorsal bending forces (p < 0.01). The dorsal pi plate had the greatest resistance to fracture gap motion under axial loading and volar and dorsal bending forces (p < 0.01). However, the pi plate was significantly less stable to axial load and dorsal bending forces when the volar cortex was comminuted (p < 0.01). In this model of dorsally comminuted extra-articular distal radial fractures, dorsal pi-plate fixation demonstrated better resistance to fracture gap motion than did the four types of volar plate fixation. The AO volar locking and DVR plates conferred the greatest resistance to fracture gap motion among the four volar plates tested. Volar locking technology conferred a significant increase in resistance to fracture gap motion as compared with nonlocking plate technology.

Failure Strength of 2.0 Locking Versus 2.0 Conventional Synthes Mandibular Plates: A Laboratory Model

This laboratory study compared the performance of locking versus nonlocking Synthes (Synthes, Paoli, PA) 2-mm mandibular fixation plates. The purpose of the study was to determine if there are physical or mechanical properties to support the use of one rigid fixation device over the other. A bovine rib model was selected for this study because they closely approximate characteristics of the human mandible. Two experimental groups composed of 10 locking and 10 nonlocking 2-mm plates were secured to randomly selected osteotomized bovine ribs using 10-mm monocortical screws. The specimens were loaded using a 4-point bending system to the point of failure using a MTS model 309.00 servo-hydraulic testing system (MTS Systems Corp, Eden Prairie, MN) with a custom fabricated fixator. The data was obtained with TestStar 2 version 4.0 and TestWare Sx 4.0 software (MTS Systems Corp), and analyzed to determine if there was any difference in performance between the 2 mandibular plate designs. Overall, there were no statistically significant differences between the locking and conventional 2-mm mandibular plate. Of the 20 samples tested, 1 (nonlocking) had a unique early screw failure (pullout) inconsistent with any other samples and was not analyzed. Of the remaining 19 samples, 17 produced a yield failure, bend, or stretch rather than a plate fracture. Both of the plate fractures occurred in the nonlocking plates. Although the data suggested that this mode of failure was more common in nonlocking plates, the difference between both groups in the mode of failure did not achieve statistical significance (chi2 = 2.0, P = .16). Thus, yield was the predominant mode of failure for both types of devices. The force at which each device failed was also similar in both groups. The force of failure for the nonlocking plates was 559.9 N (SD = 247.9), whereas the locking plate failure strength was 637.8 N (SD = 276.3; t (17) = 0.6, P = .53). The results indicated that there was no suggestion that one plate might be stronger than the other. In this laboratory model, no significant differences were found between the 2 types of mandibular plates. Although studies have shown the locking system to be more rigid, this study suggested that the type and degree of failure are more likely related to bone quality and surgical technique when using the 2-mm mandibular plate. Additional prospective studies are needed to correlate these results in patient models.

A Biomechanical Comparison of Locking and Nonlocking Plates for the Fixation of Calcaneal Fractures

Locking plate systems have been developed in an attempt to increase the strength of fracture fixation and, in so doing, allow earlier mobilization and rehabilitation. The purpose of our study was to compare the mechanical integrity of the locking plate and traditional nonlocking plate fixation for calcaneal fractures in a cadaver model. Our hypothesis was that the locking plate construct provides stronger fixation than the nonlocking plate construct. We created a Sanders type-IIB fracture in 10 pairs of fresh-frozen cadaver feet (bone mineral density, 0.50 +/- 0.14 g/cm2 age, 69 +/- 16 years). One foot of each pair was fixed with a nonlocking calcaneal plate (Synthes, Paoli, PA), and the contralateral foot was fixed with the Locking Calcaneal Plate (Synthes, Paoli, PA). The specimens then were cyclically loaded through the tibia from 0 to 700 N at 1 Hz on a materials testing machine to simulate weightbearing. Fragment displacement was measured with a three-dimensional kinematic analysis system. Significance was set at p < 0.05. There was no significant difference between the two plating systems with respect to the mean (+/- SD) number of cycles to failure (locking plate, 3261 +/- 2355; nonlocking plate, 2271 +/- 2465). In a cadaver model of type-IIB calcaneal fractures, locking plate fixation did not provide a biomechanical advantage over traditional nonlocking plate fixation.

Volar Versus Dorsal Plating in the Management of Intra-Articular Distal Radius Fractures

To compare the complications and functional and radiographic outcomes of volar and dorsal plating of intra-articular distal radius fractures. This retrospective review included 34 patients found by searching a database of 350 patients treated for distal radius fractures. Inclusion criteria were (1) at least 1 year of follow-up data and (2) open reduction and internal fixation of a multifragmentary fragment intra-articular distal radius fracture with either a nonlocking volar or dorsal plate. Twenty patients were treated with a dorsal plate and 14 patients were treated with a volar nonlocking plate. Objective and subjective outcome parameters were compared between the 2 groups. Objective evaluations included wrist range of motion, grip strength, and preoperative and postoperative radiographic parameters (radial inclination, palmar tilt, ulnar variance, fracture pattern). Subjective evaluations were performed using the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire score and the Gartland and Werley score. Volar plating resulted in a significantly better Gartland-Werley score compared with dorsal plating. There were no significant differences in the DASH score. Volar collapse was documented in 5 of the 20 patients in the dorsal plating group, which resulted in a mild loss of pronation compared with the volar plating group. No collapse occurred in the volar plating group. In addition the difference in the percentage of wrist range of motion compared with the contralateral wrist was not significant. Dorsal plating was associated with a ruptured extensor indicis tendon in 1 patient; secondary surgical procedures were required in 4 patients (tenolyses and radial styloidectomy). Volar plating was associated with median nerve neuropathy in 2 patients and intersection syndrome in one. Although both groups of patients had similar DASH scores the functional outcome in terms of Gartland and Werley scores was better in the volar plating group. In addition there was a higher rate of volar collapse and late complications in the dorsal plating group compared with the volar plating group. Therapeutic, Level III.

A randomized comparison of locking and non-locking palmar plating for unstable Colles’ fractures in the elderly

This study compared the effectiveness of locking and non-locking palmar plating for unstable Colles' fractures in the elderly. The patients treated with locking plates included 4 men and 18 women with a mean age of 68 years (Group A) and those treated with non-locking plates included 3 men and 28 women with a mean age of 74 years (Group B). Radiographic parameters, including palmar tilt, radial inclination and radial length were measured before surgery, after surgery and at final followup. There were no significant differences in respect of any of the radiographic parameters between the two groups pre-operatively. After surgery, all of the radiographic parameters were improved in both groups and there were no significant differences between the two groups at final followup.

Locking Versus Nonlocking T-Plates for Dorsal and Volar Fixation of Dorsally Comminuted Distal Radius Fractures: A Biomechanical Study

To see if locking volar plates approach the strength of dorsal plates on a dorsally comminuted distal radius fracture model. Volar plates have been associated with fewer tendon complications than dorsal plates but are thought to have mechanical disadvantages in dorsally comminuted distal radius fractures. Locking plates may increase construct strength and stiffness. This study compares dorsal and volar locking and nonlocking plates in a dorsally comminuted distal radius fracture model. Axial loading was used to test 14 pairs of embalmed radii after an osteotomy simulating dorsal comminution and plating in 1 of 4 configurations: a standard nonlocking 3.5-mm compression T-plate or a 3.5-mm locking compression T-plate applied either dorsally or volarly. Failure was defined as the point of initial load reduction caused by bone breakage or substantial plate bending. No significant differences in stiffness or failure strength were found between volar locked and nonlocked constructs. Although not significant, the stiffness of dorsal locked constructs was 51% greater than that of the nonlocked constructs. Locked or nonlocked dorsal constructs were more than 2 times stiffer than volar constructs. The failure strength of dorsal constructs was 53% higher than that of volar constructs. Failure for both volar locked and nonlocked constructs occurred by plate bending through the unfilled hole at the osteotomy site. Failure for both dorsal locked and nonlocked constructs occurred by bone breakage. Locking plates failed to increase the stiffness or strength of dorsally comminuted distal radius fractures compared with nonlocking plates. Failure strength and stiffness are greater for locked or nonlocked dorsal constructs than for either locked or nonlocked volar constructs. Whether the lower stiffness and failure strength are of clinical significance is unknown. The unfilled hole at the site of comminution or osteotomy is potentially a site of weakness in both volar locked and nonlocked plates.

Unilateral Cervical Facet Dislocation: Biomechanics of Fixation

Unilateral facet dislocation was created in human cadaveric cervical spines. Specimens were sequentially instrumented with posterior or anterior screws and plates, and studied biomechanically. To determine the biomechanical differences between anterior and posterior fixation for stabilization of a reduced unilateral cervical facet dislocation. Although previous studies have compared anterior to posterior instrumentation, no data exist on the biomechanics of either type of stabilization after this particular injury. In 6 human cadaveric cervical spine segments, a reproducible unilateral facet dislocation was created and then unlocked (reduced). Nondestructive torques were applied to specimens that were intact, injured-reduced, fixated using posterior nonlocking lateral mass plates, and fixated using a bone graft plus an anterior nonlocking plate. Flexion, extension, lateral bending, and axial rotation were measured stereophotogrammetrically. Lateral mass plating was more effective than anterior plating in limiting motion after reduction of a unilateral facet dislocation. Averaged, over all loading directions, lateral mass plates reduced the range of motion to 17% of normal; anterior plates reduced range of motion to 89% of normal. In all loading directions, lateral mass plates performed significantly better than anterior plates (P < 0.05, paired Student t-tests). Anterior and posterior plating effectively stabilized a reduced unilateral facet dislocation. Lateral mass fixation provided better immobilization than anterior graft and plate.

A Biomechanical Comparison of a Dorsal 3.5-mm T-Plate and a Volar Fixed-Angle Plate in a Model of Dorsally Unstable Distal Radius Fractures

To compare the biomechanical stability of internal fixation of extra-articular, dorsally unstable distal radius fractures fixed by 1 of 2 methods, either a standard dorsal nonlocked T-plate or a volar locked fixed-angle plate. Biomechanical cadaveric study. Biomechanical testing laboratory. In 6 matched pairs of fresh-frozen cadaveric specimens, a simulated unstable extra-articular distal radius fracture was created. The fractures were stabilized with either a dorsal 3.5-mm stainless steel T-plate or a titanium locked volar fixed-angle plate. Specimens were axially loaded at 5 points (centrally, volarly, dorsally, radially, and ulnarly) and then cyclically loaded for 5000 cycles with an 80 N central load. Postcyclical loading, specimens were once again axially loaded at the 5 points. Initial fixation stiffness and stiffness after midaxial cyclical loading was compared at the 5 points. With the volar locked fixed-angle plate, fixation was significantly stiffer than with the dorsal nonlocked T-plate for ulnar and volar loading in single-cycle testing. After cyclic loading, the locked volar fixed-angle plate maintained more of its initial stiffness than the dorsal nonlocked T-plate. The dorsal 3.5-mm stainless steel T-plate's stiffness when dorsally loaded significantly decreased after cyclical loading. The volar locked fixed-angle plate maintained a greater percentage of its initial stiffness after cyclic loading compared to the dorsal nonlocked plate. Also, the volar locked plate was stiffer than the dorsal nonlocked plate for all loading configurations tested except when subjected to a dorsally applied eccentric load.

Biomechanical analysis of anterior cervical spine plate fixation systems with unicortical and bicortical screw purchase.

Anterior plate fixation with unicortical screw purchase does not involve the risk of posterior cortex penetration and possible injuries of the spinal cord. However, there are very few biomechanical data about the immediate stability of non-locking plate fixation with unicortical or bicortical screw placement. The aim of the present study was to evaluate the immediate biomechanical properties in terms of flexibility of a non-locking anterior plate system with 4.5-mm screw fixation and unicortical or bicortical screw purchase applied to a single destabilized cervical spine motion segment. Using fresh cadaveric cervical spine specimens C3-C7, multidirectional flexibility was measured at the level C4-C5 before and after destabilization and fixation with an anterior plate with either unicortical or bicortical screw purchase. The results showed that fixed cervical spine segments with anterior plate and bicortical screw purchase were more rigid than intact specimens in all modes of testing. The difference was statistically significant for flexion and extension ( P<0.001). Plate fixation with unicortical screw purchase had statistically significant decreased ranges of motion compared to the intact specimen only in extension. Neither unicortical nor bicortical screw purchase decreased the range of motion significantly in axial rotation compared to the intact specimens. This in vitro study documented that neither unicortical nor bicortical screw purchase with non-locking plate fixation can increase stability in all modes of testing, in axial rotation in particular. Direct comparison between the group with uni- and that with bicortical screw fixation did not reveal significant differences, and therefore no advantage was shown for either type of screw fixation. Therefore, we demonstrated that both uni- and bicortical screw purchase with non-locking plate fixation can decrease immediate flexibility of the tested motion segment, with better results for bicortical purchase. No significant differences were found comparing the two groups of screw fixation. These data suggest that unicortical screw fixation can be used for anterior plate fixation with a comparable immediate stability to bicortical screw fixation.

EVOLUTION OF THE INTERNAL FIXATION OF LONG BONE FRACTURES

EVOLUTION OF THE INTERNAL FIXATION OF LONG BONE FRACTURES