Palmar locking plates for corrective osteotomy of latent malunion of dorsally tilted distal radial fractures without structural bone grafting

The purpose of this retrospective study was to investigate the clinical and radiological outcomes following corrective osteotomy for nascent malunion of distal radial fractures with dorsal tilt using palmar-locking plates without using autologous structural bone grafting for dorsal cortex support. The fractures were dorsally angulated distal radial fractures (AO types A2, A3, and C1) with neglected or delayed treatment for 5 to 8 weeks. Fractures were repaired using 2.4-mm palmar locking plates. Dorsal cortical defects at the osteotomy sites were filled with incipient healing callus. Radiographs were obtained before correction and at 2 and 6 weeks and 3, 4.5, 6, and 12 months postoperatively. Palmar tilt, radial inclination, and ulnar variance were measured. There were no cases of loss reduction, implant failure, or delayed fracture union without structural bone graft and casting. Clinical assessments included active range of motion of the wrist and function based on the Mayo Wrist Score. Even with wrist immobilization for >1 month preoperatively, all patients had excellent Mayo Wrist Scores at 4.5 months due to early postoperative rehabilitation. No further changes were apparent between 4.5- and 12-month follow-up.The palmar locking plates provided sufficient stability for corrective osteotomy within 8 weeks of injury without the need for structural bone grafting. Furthermore, casting immobilization was also unnecessary, and a good wrist range of motion was restored early after rehabilitation.     

Volar fixation for dorsally angulated extra-articular fractures of the distal radius: a biomechanical study

PURPOSE: To compare the biomechanical properties of 10 volar plate-fixation designs in 2 fracture models (dorsal wedge osteotomy, segmental resection osteotomy models). METHODS: Forty-eight radiuses were used in this study including 8 pairs. In 40 specimens a 15-mm dorsally based wedge osteotomy was performed and the volar cortex was fractured manually. They were arranged into 10 fixation groups with 5 different fixation designs (test 1). In the contralateral specimens of 8 paired radiuses a 10-mm segment of bone was excised (test 2). Four of the 10 fixation systems were chosen for these specimens. Cadaver hands and the proximal radiuses were potted in polymethylmethacrylate and tested with a servohydraulic materials testing machine with 300 N of axial compression load at 1 N/s initially and after each 1,000 cycles up to 5,000 cycles. After cyclic loading the specimens were loaded to failure in axial compression at 2 mm/min. The stiffness, failure peak load, and failure mode of each specimen were recorded. RESULTS: In test 1 in the wedge osteotomy specimens the T plate was the stiffest and the Synthes titanium plate was the least stiff; however, all specimens completed the 5,000 cycles of loading with no failures. There was no significant difference between the 10 fixation groups in failure peak load and only 7 of 40 failed at the distal portion of the hardware in the final load to failure testing. In test 2 the resection osteotomy specimens were less stiff and failed at a lower failure peak load compared with the wedge osteotomy specimens. Failure at the distal portion of the fixation system was seen in 7 of 8 specimens; nonlocking screws loosened and tines compressed the surrounding bone, resulting in tine-hole enlargement. CONCLUSIONS: All of the plate-fixation systems delivered sufficient stability to permit the simulated postoperative regimen of 1 week of immobilization followed by 5 weeks of early mobilization until expected union at 6 weeks after surgery. Based on these results a preferable volar fixation system would appear to benefit from the following: (1) sufficient plate strength to support the distal fragment from the volar side, (2) a locking system with sufficient strength to remain locked during the healing process, and (3) a distal design that does not affect the bone adversely. The anatomic reduction of the volar cortex in the wedge osteotomy specimens added stability to the construct.     

Mechanical characteristics of locking and compression plate constructs applied dorsally to distal radius fractures

PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.     

Locking versus nonlocking T-plates for dorsal and volar fixation of dorsally comminuted distal radius fractures: a biomechanical study

PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.     

Corrective osteotomies of the radius: Grafting or not?

AIM:To review the current literature regarding corrective osteotomies to provide the best evidence of the rule of bone grafting.METHODS:Our MEDLINE literature search included 280 studies using the following key words "Malunited distal radius fracture" and 150 studies using key words "Corrective osteotomy of the distal radius".Inclusion criteria were:Malunited distal radial,extra articular fracture,volar locking plate,use of iliac bone graft(cancellous or corticocancellous),non-use of bone graft.Twelve studies met the inclusion criteria.RESULTS:Seven of the 12 studies considered,described the use of a graft;the remaining five studies didn't use any graft.Type of malunion was dorsal in most of the studies.The healing time was comparable using the graft or not(mean 12.5 wk),ranging from 7.5 to 16 wk.The mean disabilities of the arm,shoulder and hand score improvement was 23 points both in the studies that used the graft and in those not using the graft.CONCLUSION:This review demonstrated that corrective osteotomy of extra-articular malunited fractures of the distal radius treated by volar locking plate does not necessarily require bone graft.     

Biomechanical Comparison of Different Volar Fracture Fixation Plates for Distal Radius Fractures

The purpose of this study was to compare the biomechanical properties of four volar fixed-angle fracture fixation plate designs in a novel sawbones model as well as in cadavers. Four volar fixed angle plating systems (Hand Innovations DVR-A, Avanta SCS/V, Wright Medical Lo-Con VLS, and Synthes stainless volar locking) were tested on sawbones models using an osteotomy gap model to simulate a distal radius fracture. Based on a power analysis, six plates from each system were tested to failure in axial compression. To simulate loads with physiologic wrist motion, six plates of each type were then tested to failure following 10,000 cycles applying 100N of compression. To compare plate failure behavior, two plates of each type were implanted in cadaver wrists and similar testing applied. All plate constructs were loaded to failure. All failed with in apex volar angulation.The Hand Innovations DVR-A plate demonstrated significantly more strength in peak load to failure and failure after fatigue cycling (p value < 0.001 for single load and fatigue failure). However, there was no significant difference in stiffness among the four plates in synthetic bone. The cadaveric model demonstrated the same mode of failure as the sawbones. None of the volar plates demonstrated screw breakage or pullout, except the tine plate (Avanta SCS/V) with 1 mm of pullout in 2 of 12 plates. This study demonstrates the utility of sawbones in biomechanical testing and indicates that volar fixation of unstable distal radius fractures with a fixed angle device is a reliable means of stabilization.     

Correction osteotomy of distal radius malunion stabilised with dorsal locking plates without grafting

The purpose of this study was to evaluate the results of our correction osteotomies of distal radial malunions without a bone graft. Eleven consecutive patients (mean age 52 years, range 18–71) were treated. A dorsal approach was utilised to perform an opening-wedge osteotomy which then was stabilised with two dorsal columnar plates without filling the osteotomy gap. All patients went on to radiographic union with a filling of the osteotomy gap within a mean period of 3 months (range 2–6 months). All patients had satisfactory results in terms of function and pain. Correction osteotomy and stabilisation with bicolumnar locked plate fixation without a bone graft provides sufficient stability to allow the highly vascularised metaphysis to heal. In patients without risk factors predisposing to non-union, this procedure is safe and feasible.     

Volar versus dorsal fixed-angle fixation of dorsally unstable extra-articular distal radius fractures: a biomechanic study

PURPOSE: To evaluate and compare the biomechanic rigidity and strength of 3 fixed-angle plates used to treat extra-articular distal radius fractures that are dorsally unstable. Volar fixed-angle plates were compared with a dorsal fixed-angle nail plate. METHODS: Three plate constructs were tested: the dorsal nail plate (DNP), distal volar radius (DVR) plate, and locking compression plate (LCP) volar distal radius plate. With anatomic, third-generation, artificial composite radii, dorsally unstable extra-articular distal radius fracture models were made by cutting a wedge osteotomy with an 8-mm dorsal gap 1 cm from the articular surface. These models were then fixed with the 3 implants by the method recommended by the manufacturer. The proximal radii of each specimen were attached to the base of a materials testing machine with a probe centered at the radial side of the lunate fossa. The specimens were loaded at a constant rate to failure under axial compression. Load and displacement were plotted graphically, and the resulting rigidities and strengths of each plate were assessed statistically. RESULTS: The DVR group had significantly greater stiffness than the LCP group. The DVR group had significantly higher maximum loads than both the DNP and LCP groups. There were no significant differences in yield loads. Both the DNP and DVR groups had significantly less displacement at yield than the LCP group. CONCLUSIONS: These 3 groups had similar yield loads. However, the LCP was less stiff than the DVR and had more displacement at yield than both the DVR and DNP. The yield load of all 3 implants was much higher than previously described loads for active wrist and finger motion.     

Fixation of long bone segmental defects: a biomechanical study

OBJECTIVES: 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. METHODS: 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. RESULTS: 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). CONCLUSION: 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.     

A mechanical comparison of the locking compression plate (LCP) and the low contact-dynamic compression plate (DCP) in an osteoporotic bone model

OBJECTIVE: To determine if locking compression plates (LCP) are mechanically advantageous compared to low-contact dynamic compression plates (DCP) when used as a bridging plate in a synthetic model of osteoporotic bone. METHODS: Five synthetic bars (Synbone Osteoporotic bone) were initially tested in compression and the Young's modulus determined. It was found to be comparable to that of tibial cancellous bone in an 80-year-old woman; thus, the synthetic bars were deemed usable to simulate some properties of osteoporotic bone. Six bars were then instrumented with an 8-hole narrow large fragment DCP with six 4.5-mm cortical screws (placed in holes 1-3 and holes 6-8). Six bars were instrumented with a narrow 8-hole LCP using four 5-mm locking screws (placed in the 1st, 3rd, 6th, and 8th holes). In a third group, 6 synbone bars were instrumented with a narrow 8-hole large fragment DCP. Cortical screws were placed in holes 2-3 and holes 6-7. In holes 1 and 8, two 6.5 fully threaded cancellous screws were inserted. A 1-cm osteotomy was created in the Synbone at the center of each plate to represent a comminuted fracture. Initially, quasi-static testing was carried out on all specimens in compression to a maximum load of 450 N. Then 4-point bend tests were carried out in two planes (0 degrees and 90 degrees) with the maximum bending moment at 3.5 Nm. Finally, torsional testing was done to a maximum load of 3.5 Nm. The specimens were then cycled in axial compression 350 N at 5 Hz for 30,000 cycles. The static nondestructive tests were repeated. The slope of the load deformation curve indicated the relative stiffness of the construct. The slopes were determined pre- and postcycling and the loss of stiffness in each group compared. Statistical analysis was carried out using the paired t-test. The specimens were then loaded to failure in compression. RESULTS: There was no statistical difference in the stiffness of the LCP or in the osteotomy gap postcycling. All specimens in the DCP groups failed initial static testing in axial compression. No fatigue testing could be undertaken in this group. CONCLUSIONS: In a synthetic model, the LCP was mechanically superior to the DCP when used as a bridging plate and tested in axial compression.     

Biomechanical stability of a retrotubercle opening-wedge high tibial osteotomy

In recent years, opening-wedge osteotomy has gained popularity. However, the complication rate reported is high. Opening-wedge osteotomy was modified to remedy the problems seen with the conventional technique including loss of correction, delayed healing, and patella infera. This biomechanical study evaluates the response of a new opening-wedge osteotomy in a static and dynamic mode of human cadavers. Results were compared to the stability of the conventional technique. Six preserved pairs of human cadaveric knees were tested. Specimens of the same pair were randomly assigned to either the modified or conventional osteotomy. Internal fixation was used to ensure precise correction and prevent bone collapse. Each tibia was loaded on a material testing system from 0 to 700 N for 10,000 cycles to simulate immediate full weight bearing in a walking individual. Specimens were then loaded to failure to determine ultimate load and stiffness of the construct. Displacement of the articular fragment and stiffness were measured during dynamic loading. Load to failure, displacement, and stiffness were measured during static testing. The modified osteotomy provided significantly greater stiffness (1392 N/mm) and smaller loss of correction (.68 mm) than the conventional osteotomy (741 N/mm; 1.76 mm) under cyclic loading conditions (P<.05). The modified retrotubercle osteotomy provides greater stiffness than the conventional osteotomy, increasing stability by 62% and minimizing loss of correction to <1 mm. The modified osteotomy eliminates the need for bone graft and provides additional strength to allow accelerated rehabilitation.     

Different osteosyntheses for Colles' fracture

Background and purpose In recent years several different plate designs for internal fixation of fractures of the distal radius have been developed. However, few biomechanical studies have been performed to compare these new implants. The purpose of this study was to compare the mechanical properties of 5 different commercially available plates (3 volar and 2 dorsal) with standard K-wire fixation using a distal radial cadaver model.

Material and methods 42 human radial bones from 26 cadavers were included. The bone mineral density (BMD) was measured by DEXA in all bones, and the radial bones were assigned to 6 equiv alent groups based on bone density and total amount of mineral. A distal radial osteotomy was done and a dorsal 30-degree wedge of bone was removed. 1 K-wire fixation group and 5 plate groups were tested for rigidity, yield load, and maximum load.

Results When data from dorsally and volarly applied plates were pooled, we did not find any statistically significant differences between them regarding stiffness, yield load, and maximum load. The K-wire group showed significantly lower yield load than 3 of the plate groups. There were no statistically significant differences in yield load between the 5 plate groups. The K-wire group showed lower rigidity than the plate groups. The K-wire group and 1 plate group failed at a statistically significant lower maximum load than the 4 other plate groups.

Interpretation The volar plates had the same mechanical stability as the dorsally applied plates, and they are therefore a good alternative to dorsally applied plates. K-wire osteosynthesis was inferior to plate osteosyntheses regarding all mechanical properties.     

Comparison of three different plating techniques for the dorsum of the distal radius: a biomechanical study

Three different plating techniques were used on experimentally produced dorsally displaced distal radius fractures in cadavers and were tested in 4-point bending: a AO 3.5-mm T plate (group 1), two 2. 0-mm titanium plates 60 degrees to each other (group 2), and the AO pi plate (group 3). A metaphyseal defect was simulated by a dorsally open wedge osteotomy. The tests show that the 2-mm double-plating technique has superior stiffness and statistically equivalent bending and bone gap to failure compared with the AO 3.5-mm T plate or the pi plate when applied to the unstable distal radius fracture model. (J Hand Surg 2000; 25A:29-33.     

Surgical correction of dorsally angulated distal radius malunions with fixed angle volar plating: a case series

PURPOSE: To report our experience using a fixed-angle volar plate in conjunction with a corrective osteotomy and cancellous bone graft for the treatment of distal radius malunions with dorsal angulation in 4 patients. METHODS: Four consecutive patients had a volarly based opening wedge osteotomy with a fixed angle volar plate and cancellous bone grafting for the treatment of a dorsally angulated distal radius malunion. Data collected retrospectively included a visual analog pain scale, grip strength, range of motion, radiographic parameters, and each patient's subjective functional outcomes as measured by the Disabilities of the Arm, Shoulder, and Hand questionnaire. Motion, strength, and radiographic values were compared with the contralateral arm for each patient. RESULTS: The average time from initial fracture to corrective osteotomy was 346 days. The average length of follow-up evaluation was 13.5 months. The flexion-extension arc of motion increased an average of 21 degrees to a value of 84% of the contralateral side; the pronation-supination arc of motion increased an average of 20 degrees to a value of 98% of the contralateral side. The average tilt of the radius improved from 26 degrees extension to 2 degrees extension; the average radial inclination improved from 22 degrees to 24 degrees; the average ulnar variance excluding the 1 patient who had a distal ulna resection improved from 5 mm to 1 mm. The average retrospective Disabilities of the Arm, Shoulder, and Hand score improved from 30 to 7; the average retrospective visual analog pain scale score improved from 4.5 to 1. The average grip strength increased from 20 to 29 kg, which corresponded to 73% of the contralateral extremity. CONCLUSIONS: The rigid characteristics of fixed angle volar plates can provide an alternative to the traditional techniques of distal radius osteotomy including structural bone grafting and dorsal plate fixation or external fixation. In addition these plates are strong enough to allow for early postoperative motion. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic, Level IV.     

Mechanical comparison in cadaver specimens of three different 90-degree double-plate osteosyntheses for simulated C2-type distal humerus fractures with varying bone densities

OBJECTIVES: To investigate the bone-implant-anchorage of 90-degree double-plate osteosynthesis in simulated complete intra-articular distal humerus fractures using conventional reconstruction plates (CRP), locking compression plates (LCP), and distal humerus plates (DHP), depending on the bone mineral density (BMD) of the cadaver specimens. METHODS: Groups (CRP, LCP, DHP, n=8; LCP, DHP, n=13) in distal humerus cadaver bones were created based on BMD. The fracture model was an unstable intraarticular distal humerus fracture with a transverse osteotomy gap representing metaphyseal comminution (AO type 13-C2.3). Flexion and extension stiffness as well as cycles until failure due to screw pullout under cyclic loading were evaluated. Estimates of BMD values, below which failure was likely to occur, were determined. RESULTS: Stiffness values were not significantly different between groups (extension: P=0.881, flexion: P=0.547). Under cyclic loading, consistent screw pullout failure occurred at BMD values below about 400 mg/cm for CRP and below about 300 mg/cm for LCP constructs. Comparing BMD-matched groups of 8 and 13 specimens respectively, the failure rate was significantly lower for the DHP (0/8) than for the CRP (5/8; P=0.026) and tended to be lower for the DHP (0/13) as compared to the LCP (4/13; P=0.096). CONCLUSION: Bone-implant anchorage was different between locking and nonlocking plate constructs and depended on BMD. While in good bone quality implant choice was not critical, both locking plates provided superior resistance against screw loosening as compared to the CRP at low BMD values (<420 mg/cm). Based on our laboratory results, we conclude that locking plates such as the LCP and DHP are constructs designed to keep anatomical reduction in the presence of comminution and poor bone quality in a low intra-articular fracture of the distal humerus.     

Plate selection for fixation of extra-articular distal humerus fractures: A biomechanical comparison of three different implants

Operative fixation of extra-articular distal humerus using a single posterolateral column plate has been described but the biomechanical properties or limits of this technique is undefined. The purpose of this study was to evaluate the mechanical properties of distal humerus fracture fixation using three standard fixation constructs.Two equal groups were created from forty sawbones humeri. Osteotomies were created at 80 mm or 50 mm from the tip of the trochlea. In the proximal osteotomy group, sawbones were fixed with an 8-hole 3.5 mm LCP or with a 6-hole posterolateral plate. In the distal group, sawbones were fixed with 9-hole medial and lateral 3.5 mm distal humerus plates and ten sawbones were fixed with a 6-hole posterolateral plate. Biomechanical testing was performed using a servohydraulic testing machine. Testing in extension as well as internal and external rotation was performed. Destructive testing was also performed with failure being defined as hardware pullout, sawbone failure or cortical contact at the osteotomy.In the proximal osteotomy group, the average bending stiffness and torsional stiffness was significantly greater with the posterolateral plate than with the 3.5 mm LCP. In the distal osteotomy group, the average bending stiffness and torsional stiffness was significantly greater with the posterolateral plate than the 3.5 mm LCP. In extension testing, the yield strength was significantly greater with the posterolateral plate in the proximal osteotomy specimens, and the dual plating construct in the distal osteotomy specimens. The yield strength of specimens in axial torsion was significantly greater with the posterolateral plate in the proximal osteotomy specimens, and the dual plating construct in the distal osteotomy specimens.Limited biomechanical data to support the use of a pre-contoured posterolateral distal humerus LCP for fixation of extra-articular distal humerus exists. We have found that this implant provided significantly greater bending stiffness, torsional stiffness, and yield strength than a single 3.5 mm LCP plate for osteotomies created 80 mm from the trochlea. At the more distal osteotomy, dual plating was biomechanically superior. Our results suggest that single posterolateral column fixation of extra-articular humerus fractures is appropriate for more proximal fractures but that dual plate fixation is superior for more distal fractures.     

Supplemental medial small fragment fixation adds stability to distal femur fixation: A biomechanical study

Introduction: Bridge plating of distal femur fractures with lateral locking plates is susceptible to varus collapse, fixation failure, and nonunion. While medial and lateral dual plating has been described in clinical series, the biomechanical effects of dual plating of distal femur fractures have yet to be clearly defined. The purpose of this study was to compare dual plating to lateral locked bridge plating alone in a cadaveric distal femur gap osteotomy model.Materials and Methods: Gap osteotomies were created in eight matched pairs of cadaveric female distal femurs (average age: 64 yrs (standard deviation ± 4.4 yrs); age range: 57–68 yrs;) to simulate comminuted extraarticular distal femur fractures (AO/OTA 33A). Eight femurs underwent fixation with lateral locked plates alone and were matched with eight femurs treated with dual plating: lateral locked plates with supplemental medial small fragment non-locking fixation. Mechanical testing was performed on an ElectroPuls E10000 materials testing system using a 10 kN/100 Nm biaxial load cell. Specimens were subject to 25,000 cycles of cyclic loading from 100-1000 N at 2 Hz.Results: Two (2/8) specimens in the lateral only group failed catastrophically prior to completion of testing. All dual plated specimens survived the testing regimen. Dual plated specimens demonstrated significantly less coronal plane displacement (median 0.2 degrees, interquartile range [IQR], 0.0–0.5 degrees) compared to 2.0 degrees (IQR 1.9-3.3, p = 0.02) in the lateral plate only group. Dual plated specimens demonstrated greater bending stiffness compared to the lateral plated group (median 29.0 kN/degree, IQR 1.5–68.2 kN/degree vs median 0.50 kN/degree, IQR 0.23–2.28 kN/degree, p = 0.03).Conclusion: Contemporary fixation methods with a distal femur fractures are susceptible to mechanical failure and nonunion with lateral plates alone. Dual plate fixation in a cadaveric model of distal femur fractures underwent significantly less displacement under simulated weight bearing conditions and demonstrated greater stiffness than lateral plating alone. Given the significant clinical failure rates of lateral bridge plating in distal femur fractures, supplemental fixation should be considered, and dual plating of distal femurs augments mechanical stability in a clinically relevant magnitude.     

Primary stability with tibial press-fit fixation of patellar ligament graft: An experimental study in ovine knees

Purpose: To investigate the initial fixation strength and to assess the value of tibial press-fit fixation of the bone-tendon-bone graft in anterior cruciate ligament reconstruction. Type of Study: Nonrandomized control trial. Methods: For tibial press-fit fixation, the tibial bone block of the bone-tendon-bone graft is countersunk in a bony groove at the distal tunnel outlet and fixed over a bone bridge with 2 No. 6 Ethibond sutures. The bone cylinder harvested from the tibial tunnel using an oscillating hollow saw is plugged into the tibial tunnel parallel to the graft, thus providing for additional anchoring of the graft by tibial press-fit fixation. In a comparative experimental study in 46 ovine knees, this fixation method was assessed for its value in anterior cruciate ligament reconstruction. A tibial bone tunnel was placed in routine manner in each ovine tibia using a target drill unit and an oscillating hollow saw. The complete patellar ligament, proximally attached to the patella and distally to a cylindrical bone block (20 × 8.4 mm), served as graft. Tibial fixation in group A (n = 10) was done using a titanium interference screw (20 × 8 mm), in group B (n = 10) using a titanium staple, in group C (n = 12) using suture fixation over a bone bridge, and in group D (n = 14) using the press-fit fixation described above. In a materials testing machine, all specimens were subjected to continuously increasing load until failure at a velocity of 1 mm/second. Ultimate failure load, stiffness, stress-strain characteristics, and failure mode were evaluated. Results: Ultimate load to failure was 572 N (range, 473 to 680 N) in group A, corresponding to a fixation stiffness of 17.68 N/mm. For group B, ultimate load to failure was 608.4 N (range, 511 to 727 N) and stiffness of 19.92 N/mm. Bone block dislocation was the failure mode in groups A and B. Group C with exclusive suture fixation showed an ultimate load to failure of 304.5 N (range, 120 to 327 N) and a stiffness of only 6.96 N/mm. The mode of failure was suture cutout caused by the bone block in 9 of the cases and untying of the suture knot in 3 cases. Group D with press-fit fixation showed a significantly higher primary stability of 758 N (range, 513 to 993 N) relative to group C, with a corresponding stiffness of 25.12 N/mm (P < .02). In this group, the mode of failure was ligamentous rupture from the bone block. Regarding mechanical properties, no significant differences were seen between groups A, B, and D. Conclusions: Tibial press-fit fixation allows for metal-free fixation with high primary stability. By refilling the bone tunnel, the ligament (with a rather small cross-sectional diameter compared with hamstrings) is safely fixed within the bone tunnel to prevent potential postoperative tunnel enlargement due to movement of the graft within the tunnel. Anchoring the graft at the entrance into the joint, it provides for reduced graft length and adequate elasticity and accomplishes the requirements of fixation at the correct anatomic insertion site.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 17, No 9 (November-December), 2001: pp 963–970     

A biomechanical comparison of two volar locked plates in a dorsally unstable distal radius fracture model

BACKGROUND: This study compares the biomechanical stability of two volar locked plate systems for fixation of unstable, extra-articular distal radius fractures. METHODS: In six matched pairs of fresh frozen cadaveric specimens, a simulated unstable, extra-articular distal radius fracture was created. The fractures were stabilized with one of two types of volar locked plates. Specimens were axially loaded at five different positions: central, volar, dorsal, radial, and ulnar. Initial (precyclic loading) stiffness of each locked plate system was calculated. Each specimen was then loaded for 5,000 cycles with an 80 N central load. Finally, specimens were axially loaded at the same five positions to calculate the postcyclic loading stiffness of each volar locked plate system. Main outcome measurements were precyclic loading stiffness, postcyclic loading stiffness, maintenance of stiffness after cyclic loading, and amount of fracture displacement between the two volar locked plate systems. RESULTS: There were no differences in maintenance of stiffness and fracture displacement following cyclical loading between the two volar plate systems. After cyclic loading, the distal volar radius (DVR) locked plate was significantly stiffer than the Synthes volar locked plate in volar loading only (p < 0.01). CONCLUSION: Materials properties and design differences between these systems did not provide enough biomechanical difference to support use of either implant over the other. With this in vitro model, both implants provided adequate stability to resist physiologic loads expected during therapy in the initial postoperative period.     

Internal fixation of dorsally displaced fractures of the distal part of the radius. A biomechanical analysis of volar plate fracture stability

BACKGROUND: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.