Dynamic fixation of distal femur fractures using far cortical locking screws: a prospective observational study.

OBJECTIVES: Document fixation and healing of distal femur fractures stabilized by plate osteosynthesis using far cortical locking (FCL) screws. DESIGN: Prospective and observational. SETTING: Two level 1 and 1 level 2 trauma centers. PATIENTS: Thirty-two consecutive patients with 33 distal femur fractures (AO/OTA types 33A, 33C). INTERVENTION: Fractures were stabilized by plate osteosynthesis with MotionLoc FCL screws without supplemental bone graft or bone morphogenic proteins. Patients were followed up for a minimum of 1 year with functional and radiographic assessments obtained at postoperative weeks 6, 12, and 24 and computed tomography scans at week 12. If union was not confirmed within 1 year, follow-up was continued until union or revision surgery. MAIN OUTCOME MEASURES: The primary end point was fracture union in the absence of complications and secondary interventions. Fracture healing was defined by resolution of pain at the fracture site and cortical bridging on biplanar radiographs. Complications were defined by fixation failure, loss of reduction, implant breakage, infection, nonunion, and need for revision. RESULTS: Thirty-one fractures were available for follow-up. None of the 125 FCL screws used for diaphyseal fixation broke or lost fixation. One of the 31 fractures displaced into varus (ΔVarus = 5.8 degrees). Thirty of the 31 fractures healed within 15.6 ± 6.2 weeks. At an average follow-up of 17 ± 4 months, there were 2 revisions: one to correct a malrotation at day 5 and one to treat a nonunion at 6 months. CONCLUSIONS: Absence of implant and fixation failure suggests that dynamic plating of distal femur fractures with FCL screws provides safe and effective fixation.

Rapid cVEMP and oVEMP responses elicited by a novel head striker and recording device.

OBJECTIVE: To develop a reliable, easy to use bedside, office, or field system that allows the rapid measurement of cervical and ocular vestibular evoked myogenic potentials (cVEMP and oVEMP) using a bone-conduction stimulus. STUDY DESIGN: Prospective bioengineering design and proof of concept of the test system with saccular and utricular otolith response studies in human subjects. SETTING: Private practice, tertiary neurotology referral center. SUBJECTS: Twenty healthy adult controls without history of auditory or vestibular dysfunction and 5 preoperative and postoperative patients with confirmed superior canal dehiscence (SCD) participated. INTERVENTIONS: The subjects underwent auditory stimuli-based cVEMP and oVEMP studies using a commercially available system as well as testing with a novel bone-conduction cVEMP and oVEMP head striker system. MAIN OUTCOME MEASURES: Duration of each study, healthy subject and patient comfort, reproducibility, latency, and amplitude of auditory and striker evoked cVEMP and oVEMP responses. RESULTS: The mean age of the healthy controls was 43.8, with a range of 19 to 69 years (10 male and 10 female subjects). The mean age of the SCD patient group was 46, with a range of 25 to 54 years; all female subjects. Although the cVEMP responses were similar using either the auditory or head strike stimuli, the healthy subjects preferred the latter, but the SCD patients became more symptomatic. The oVEMP data showed more consistent responses using the striker system. A statistically significant reduction in latency for the striker-evoked cVEMP occurred compared with the auditory cVEMP evoked response in the 5 SCD preoperative patients. All normalized postoperatively. CONCLUSION: Recording the cVEMP and oVEMP responses using the striker system was much more rapid than with auditory stimuli and was more comfortable for the healthy subjects. The striker system and the acoustic method elicited strong otolithic receptor dysfunction symptoms in all SCD patients; however, they preferred the shorter striker studies. The striker system, because of the statistically shorter latency of p13 during the striker evoked cVEMP, which normalized after SCD closure, suggests that this method may be useful in identifying SCD patients before imaging studies. In addition, based on our biomechanical data, the striker was able to reliably produce a consistent and defined head striker impact.

Far cortical locking enables flexible fixation with periarticular locking plates.

The high stiffness of periarticular locked plating constructs can suppress callus formation and fracture healing. Replacing standard locking screws with far cortical locking (FCL) screws can decrease construct stiffness and can improve fracture healing in diaphyseal plating constructs. However, FCL function has not been tested in conjunction with periarticular plating constructs in which FCL screws are confined to the diaphyseal segment. This biomechanical study evaluated if diaphyseal fixation of a periarticular locking plate with FCL screws reduces construct stiffness and induces parallel interfragmentary motion without decreasing construct strength. Periarticular locking plates were applied to stabilize distal femur fractures in 22 paired femurs using either a standard locked plating approach (LP group) or FCL for diaphyseal fixation (FCL group) using MotionLoc screws (Zimmer, Warsaw, IN). Each specimen was evaluated under quasiphysiological loading to assess construct stiffness, construct durability under dynamic loading, and residual strength after dynamic loading. FCL constructs had an 81% lower initial stiffness than LP constructs. They induced nearly five times more interfragmentary motion than LP constructs under one body weight loading (P < 0.001). FCL constructs generated parallel interfragmentary motion, whereas LP constructs exhibited 48% less motion at the near cortex than at the far cortex (P = 0.002). Seven LP constructs and eight FCL constructs survived 100,000 loading cycles. The residual strength of surviving constructs was 4.9 ± 1.6 kN (LP group) and 5.3 ± 1.1 kN (FCL group, P = 0.73). In summary, FCL screws reduce stiffness, generate parallel interfragmentary motion, and retain the strength of a periarticular locked plating construct. Therefore, FCL fixation may be advisable for stiffness reduction of periarticular plating constructs to promote fracture healing by callus formation.

Biplanar fixation of a locking plate in the diaphysis improves construct strength.

BACKGROUND: Elevation of a locking plate over the bone surface not only supports biological fixation, but also decreases the torsional strength of the fixation construct. Biplanar fixation by means of a staggered screw hole arrangement may combat this decreased torsional strength caused by plate elevation. This biomechanical study evaluated the effect of biplanar fixation on the torsional strength of locking plate fixation in the femoral diaphysis. METHODS: Custom titanium plates were manufactured with either a linear or staggered hole pattern to evaluate planar and biplanar fixation, respectively. Fixation strength under torsional loading was evaluated in surrogates of the femoral diaphysis representative of osteoporotic and non-osteoporotic bone. Furthermore, fixation strength was determined for plate fixation with unicortical or bicortical locking screws. Five specimens per configuration were loaded to failure in torsion to determine their strength, stiffness, and failure mode. FINDINGS: In osteoporotic bone, biplanar fixation was 32% stronger (P=0.01) than planar fixation when unicortical screws were used and 9% stronger (P=0.02) when bicortical screws were used. In non-osteoporotic bone, biplanar fixation was 55% stronger (P<0.001) than planar fixation when unicortical screws were used and 42% (P<0.001) stronger when bicortical screws were used. INTERPRETATION: A biplanar screw configuration improves the torsional strength of diaphyseal plate fixation relative to a planar configuration in both osteoporotic and normal bone. With biplanar fixation, unicortical screws provide the same fixation strength as bicortical screws in non-osteoporotic bone.

Effects of hybrid plating with locked and nonlocked screws on the strength of locked plating constructs in the osteoporotic diaphysis.

BACKGROUND: Hybrid plating (HP) may improve fixation strength of locked plating (LP) constructs by combining the use of locked and nonlocked screws within a bone segment. This biomechanical study evaluated whether a hybrid bridge plating construct provides greater fixation strength than an all-locked construct in the osteoporotic diaphysis. METHODS: LP and HP constructs were applied to a validated surrogate of the osteoporotic femoral diaphysis in a bridge plating configuration. In LP constructs, plates were applied with three locking screws on each side of the fracture gap and remained 1 mm elevated. In HP constructs, plates were applied with two conventional screws complemented by a single locked screw on each side of the fracture. Constructs were tested under dynamic loading to failure in bending, torsion, and axial loading to analyze construct strength and failure mechanism in each loading mode. RESULTS: Compared with the LP construct, the HP construct was 7% stronger in bending (p = 0.17), 42% stronger in torsion (p < 0.001), and 7% weaker in axial compression (p = 0.003). In bending, constructs failed by periprosthetic fracture. In torsion, LP constructs failed by screw breakage, and HP constructs failed by periprosthetic fracture or breakage of the locking screw. In axial compression, all constructs failed by screw migration. CONCLUSIONS: HP delivered similar bending strength and higher torsional strength than an all-locked bridge plating construct, while causing only a small decrease in axial strength. It may therefore provide an attractive alternative to an all-locked construct for plate fixation in the osteoporotic diaphysis.

Far cortical locking can improve healing of fractures stabilized with locking plates.

BACKGROUND: Locked bridge plating relies on secondary bone healing, which requires interfragmentary motion for callus formation. This study evaluated healing of fractures stabilized with a locked plating construct and a far cortical locking construct, which is a modified locked plating approach that promotes interfragmentary motion. The study tested whether far cortical locking constructs can improve fracture-healing compared with standard locked plating constructs. METHODS: In an established ovine tibial osteotomy model with a 3-mm gap size, twelve osteotomies were randomly stabilized with locked plating or far cortical locking constructs applied medially. The far cortical locking constructs were designed to provide 84% lower stiffness than the locked plating constructs and permitted nearly parallel gap motion. Fracture-healing was monitored on weekly radiographs. After the animals were killed at week 9, healed tibiae were analyzed by computed tomography, mechanical testing in torsion, and histological examination. RESULTS: Callus on weekly radiographs was greater in the far cortical locking constructs than in the locked plating constructs. At week 9, the far cortical locking group had a 36% greater callus volume (p = 0.03) and a 44% higher bone mineral content (p = 0.013) than the locked plating group. Callus in the locked plating specimens was asymmetric, having 49% less bone mineral content in the medial callus than in the lateral callus (p = 0.003). In far cortical locking specimens, medial and lateral callus had similar bone mineral content (p = 0.91). The far cortical locking specimens healed to be 54% stronger in torsion (p = 0.023) and sustained 156% greater energy to failure in torsion (p < 0.001) than locked plating specimens. Histologically, three of six locked plating specimens had deficient bridging across the medial cortex, while all remaining cortices had bridged. CONCLUSIONS: Inconsistent and asymmetric callus formation with locked plating constructs is likely due to their high stiffness and asymmetric gap closure. By providing flexible fixation and nearly parallel interfragmentary motion, far cortical locking constructs form more callus and heal to be stronger in torsion than locked plating constructs.

Far cortical locking can reduce stiffness of locked plating constructs while retaining construct strength.

BACKGROUND: Several strategies to reduce construct stiffness have been proposed to promote secondary bone healing following fracture fixation with locked bridge plating constructs. However, stiffness reduction is typically gained at the cost of construct strength. In the present study, we tested whether a novel strategy for stiffness reduction, termed far cortical locking, can significantly reduce the stiffness of a locked plating construct while retaining its strength. METHODS: Locked plating constructs and far cortical locking constructs were tested in a diaphyseal bridge plating model of the non-osteoporotic femoral diaphysis to determine construct stiffness in axial compression, torsion, and bending. Subsequently, constructs were dynamically loaded until failure in each loading mode to determine construct strength and failure modes. Finally, failure tests were repeated in a validated model of the osteoporotic femoral diaphysis to determine construct strength and failure modes in a worst-case scenario of bridge plating in osteoporotic bone. RESULTS: Compared with the locked plating constructs, the initial stiffness of far cortical locking constructs was 88% lower in axial compression (p < 0.001), 58% lower in torsion (p < 0.001), and 29% lower in bending (p < 0.001). Compared with the locked plating constructs, the strength of far cortical locking constructs was 7% lower (p = 0.005) and 16% lower (p < 0.001) under axial compression in the non-osteoporotic and osteoporotic diaphysis, respectively. However, far cortical locking constructs were 54% stronger (p < 0.001) and 9% stronger (p = 0.04) under torsion and 21% stronger (p < 0.001) and 20% stronger (p = 0.02) under bending than locked plating constructs in the non-osteoporotic and osteoporotic diaphysis, respectively. Within the initial stiffness range, far cortical locking constructs generated nearly parallel interfragmentary motion. Locked plating constructs generated significantly less motion at the near cortex adjacent to the plate than at the far cortex (p < 0.01). CONCLUSIONS: Far cortical locking significantly reduces the axial stiffness of a locked plating construct. This gain in flexibility causes only a modest reduction in axial strength and increased torsional and bending strength.

A nonlocking end screw can decrease fracture risk caused by locked plating in the osteoporotic diaphysis.

BACKGROUND: Locking plates transmit load through fixed-angle locking screws instead of relying on plate-to-bone compression. Therefore, locking screws may induce higher stress at the screw-bone interface than that seen with conventional nonlocked plating. This study investigated whether locked plating in osteoporotic diaphyseal bone causes a greater periprosthetic fracture risk than conventional plating because of stress concentrations at the plate end. It further investigated the effect of replacing the locked end screw with a conventional screw on the strength of the fixation construct. METHODS: Three different bridge-plate constructs were applied to a validated surrogate of the osteoporotic femoral diaphysis. Constructs were tested dynamically to failure in bending, torsion, and axial loading to determine failure loads and failure modes. A locked plating construct was compared with a nonlocked conventional plating construct. Subsequently, the outermost locking screw in locked plating constructs was replaced with a conventional screw to reduce stress concentrations at the plate end. RESULTS: Compared with the conventional plating construct, the locked plating construct was 22% weaker in bending (p = 0.013), comparably strong in torsion (p = 0.05), and 15% stronger in axial compression (p = 0.017). Substituting the locked end screw with a conventional screw increased the construct strength by 40% in bending (p = 0.001) but had no significant effect on construct strength under torsion (p = 0.22) and compressive loading (p = 0.53) compared with the locked plating construct. Under bending, all constructs failed by periprosthetic fracture. CONCLUSIONS: Under bending loads, the focused load transfer of locking plates through fixed-angle screws can increase the periprosthetic fracture risk in the osteoporotic diaphysis compared with conventional plates. Replacing the outermost locking screw with a conventional screw reduced the stress concentration at the plate end and significantly increased the bending strength of the plating construct compared with an all-locked construct (p = 0.001).

Relative stability of conventional and locked plating fixation in a model of the osteoporotic femoral diaphysis.

BACKGROUND: This study investigated the stiffness and strength of bridge plating with uni-cortical and bi-cortical locking plate constructs relative to a conventional, non-locked construct in the osteoporotic femoral diaphysis. METHODS: Four bridge plating configurations were applied to a validated model of the osteoporotic femoral diaphysis. A non-locked conventional configuration served as baseline. Locked configurations included bi-cortical locked plating, uni-cortical locked plating and mix-mode locked plating, which combined uni and bi-cortical locking screws. For all configurations, an 11-hole plate was applied with 4.5-mm screws placed in the 1st, 3rd, and 5th plate hole. Five specimens of each configuration were dynamically loaded until failure in torsion, axial compression, and bending to determine construct stiffness, strength and failure modes. FINDINGS: In torsion and bending, locked plating constructs provided a significantly lower stiffness and strength than the conventional construct. The uni-cortical locked construct was 69% weaker (P<0.001) in torsion than the conventional construct, but its torsional strength improved 73% (P<0.001) by adding one bi-cortical locked screw. In axial compression, construct stiffness varied by less than 10% between the four groups. However, the bi-cortical and mixed-mode locked constructs provided a significant increase in strength of 12% (P=0.001) and 11% (P=0.002), respectively, compared to the conventional construct. INTERPRETATIONS: Locked plating in the osteoporotic diaphysis can improve fixation strength under axial loading, but may reduce fixation strength in bending and torsion compared to conventional plating. Adding one bi-cortical locked screw to an otherwise uni-cortical construct is recommended to improve torsional strength.