Mechanical strength of a new plate compared to six previously tested opening wedge high tibial osteotomy implants.

BACKGROUND: This study aimed to assess the mechanical static and fatigue strength provided by the FlexitSystem plate in medial opening wedge high tibial osteotomies (MOWHTO), and to compare it to six previously tested implants: the TomoFix small stature, the TomoFix standard, the ContourLock, the iBalance, the second generation PEEKPower and the size 2 Activmotion. Thus, this will provide surgeons with data that will help in the choice of the most appropriate implant for MOWHTO. METHODS: Six fourth-generation tibial bone composites underwent a MOWHTO and each was fixed using six FlexitSystem plates, according to standard techniques. The same testing procedure that has already been previously defined, used and published, was used to investigate the static and dynamic strength of the prepared bone-implant constructs. The test consisted of static loading and cyclical loading for fatigue testing. RESULTS: During static testing, the group constituted by the FlexitSystem showed a fracture load higher than the physiological loading of slow walking (3.7 kN > 2.4 kN). Although this fracture load was relatively small compared to the average values for the other Implants from our previous studies, except for the TomoFix small stature and the Contour Lock. During fatigue testing, FlexitSystem group showed the smallest stiffness and higher lifespan than the TomoFix and the PEEKPower groups. CONCLUSIONS: The FlexitSystem plate showed sufficient strength for static loading, and average fatigue strength compared to the previously tested implants. Full body dynamic loading of the tibia after MOWHTO with the investigated implants should be avoided for at least 3 weeks. Implants with a wider T-shaped proximal end, positioned onto the antero-medial side of the tibia head, or inserted in the osteotomy opening in a closed-wedge construction, provided higher mechanical strength than implants with small a T-shaped proximal end, centred onto the medial side of the tibia head.

Numerical comparative study of five currently used implants for high tibial osteotomy: realistic loading including muscle forces versus simplified experimental loading.

BACKGROUND: Many different fixation devices are used to maintain the correction angle after medial open wedge high tibial osteotomy (MOWHTO). Each device must provide at least sufficient mechanical stability to avoid loss of correction and unwanted fracture of the contralateral cortex until the bone heals. In the present study, the mechanical stability of following different implants was compared: the TomoFix small stature (sm), the TomoFix standard (std), the Contour Lock, the iBalance and the second generation PEEKPower. Simplified loading, usually consisting of a vertical load applied to the tibia plateau, is used for experimental testing of fixation devices and also in numerical studies. Therefore, this study additionally compared this simplified experimental loading with a more realistic loading that includes the muscle forces. METHOD: Two types of finite element models, according to the considered loading, were created. The first type numerically simulated the static tests of MOWHTO implants performed in a previous experimental biomechanical study, by applying a vertical compressive load perpendicularly to the plateau of the osteotomized tibia. The second type included muscle forces in finite element models of the lower limb with osteotomized tibiae and simulated the stance phase of normal gait. Section forces in the models were determined and compared. Stresses in the implants and contralateral cortex, and micromovements of the osteotomy wedge, were calculated. RESULTS: For both loading types, the stresses in the implants were lower than the threshold values defined by the material strength. The stresses in the lateral cortex were smaller than the ultimate tensile strength of the cortical bone. The implants iBalance and Contour Lock allowed the smallest micromovements of the wedge, while the PEEKPower allowed the highest. There was a correlation between the micromovements of the wedge, obtained for the simplified loading of the tibia, and the more realistic loading of the lower limb at 15% of the gait cycle (Pearson's value r = 0.982). CONCLUSIONS: An axial compressive load applied perpendicularly to the tibia plateau, with a magnitude equal to the first peak value of the knee joint contact forces, corresponds quite well to a realistic loading of the tibia during the stance phase of normal gait (at 15% of the gait cycle and a knee flexion of about 22 degrees). However, this magnitude of the knee joint contact forces overloads the tibia compared to more realistic calculations, where the muscle forces are considered. The iBalance and Contour Lock implants provide higher rigidity to the bone-implant constructs compared to the TomoFix and the PEEKPower plates.

High Tibial Osteotomy Performed With All-PEEK Implants Demonstrates Similar Outcomes but Less Hardware Removal at Minimum 2-Year Follow-up Compared With Metal Plates.

BACKGROUND: High tibial osteotomy (HTO) is a valuable treatment option in the high-demand patient with chondral damage and an altered mechanical axis. Traditional opening wedge HTO performed with metal plates has several limitations, including hardware irritation, obscuration of detail on magnetic resonance imaging, and complexity of revision surgery. Recently, an all-polyetheretherketone (PEEK) HTO implant was introduced, but no studies to date have evaluated the performance of this implant with minimum 2-year outcomes compared with a traditional metal plate. PURPOSE: To compare patient outcomes and complications of HTO performed using a traditional metal plate with those performed using an all-PEEK implant. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: All patients who underwent HTO by a single surgeon with a minimum 2-year follow-up over a 4-year period were identified. Medical records were reviewed for patient demographics, concomitant procedures, implant used, type and degree of correction, complications, reoperations, and failures. Recorded patient outcomes included EuroQol-5 dimensions (EQ-5D), resiliency, Single Assessment Numeric Evaluation (SANE), Tegner activity level scale, International Knee Documentation Committee (IKDC), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores. HTO performed using a traditional metal plate served as the control group. Statistical analysis was performed using the Student t test for continuous variables and chi-square analysis for nonparametric data, with P < .05 considered significant. RESULTS: A total of 41 patients (21 in the all-PEEK group, 20 in the control group) were identified with greater than 2-year follow-up. The mean patient age was 44 years, and there were no differences between the groups with regard to demographics, degree of correction, or concomitant procedures. In addition, no significant differences were found for any of the patient-reported outcomes. Complications (10% vs 15%, respectively; P = .59), failures (10% vs 5%, respectively; P = .58), and reoperations (10% vs 30%, respectively; P = .10) were similar for the all-PEEK and control groups. However, the all-PEEK group did not have any hardware removal, while 4 patients in the control group underwent hardware removal (P = .03). CONCLUSION: This study suggests that an all-PEEK implant may be safely used with comparable outcomes and complication rates to the traditional method but with less need for hardware removal.

Static and fatigue strength of a novel anatomically contoured implant compared to five current open-wedge high tibial osteotomy plates.

BACKGROUND: The purpose of the present study was to compare the mechanical static and fatigue strength of the size 2 osteotomy plate "Activmotion" with the following five other common implants for the treatment of medial knee joint osteoarthritis: the TomoFix small stature, the TomoFix standard, the Contour Lock, the iBalance and the second generation PEEKPower. METHODS: Six fourth-generation tibial bone composites underwent a medial open-wedge high tibial osteotomy (HTO), according to standard techniques, using size 2 Activmotion osteotomy plates. All bone-implant constructs were subjected to static compression load to failure and load-controlled cyclic fatigue failure testing, according to a previously defined testing protocol. The mechanical stability was investigated by considering different criteria and parameters: maximum forces, the maximum number of loading cycles, stiffness, the permanent plastic deformation of the specimens during the cyclic fatigue tests, and the maximum displacement range in the hysteresis loops of the cyclic loading responses. RESULTS: In each test, all bone-implant constructs with the size 2 Activmotion plate failed with a fracture of the lateral cortex, like with the other five previously tested implants. For the static compression tests the failure occurred in each tested implant above the physiological loading of slow walking (> 2400 N). The load at failure for the Activmotion group was the highest (8200 N). In terms of maximum load and number of cycles performed prior to failure, the size 2 Activmotion plate showed higher results than all the other tested implants except the ContourLock plate. The iBalance implant offered the highest stiffness (3.1 kN/mm) for static loading on the lateral side, while the size 2 Activmotion showed the highest stiffness (4.8 kN/mm) in cyclic loading. CONCLUSIONS: Overall, regarding all of the analysed strength parameters, the size 2 Activmotion plate provided equivalent or higher mechanical stability compared to the previously tested implant. Implants with a metaphyseal slope adapted to the tibia anatomy, and positioned more anteriorly on the proximal medial side of the tibia, should provide good mechanical stability.

High tibial osteotomy for the treatment of medial osteoarthritis of the knee with new iBalance system: 2 years of follow-up.

BACKGROUND: A new system for performing open-wedge high tibial osteotomy (HTO), the iBalance HTO System-Arthrex, has been recently developed in order to make the surgery more reproducible and safe. The aim of this study was to determine the short-term outcomes of the iBalance technique in medial compartment osteoarthritis and varus malalignment of the knee. METHODS: Fifteen patients with a mean age of 50.7 years (SD 5.09), affected by symptomatic varus knee, with medial compartment osteoarthritis (1-2 Ahlbäck degree), were treated with iBalance HTO between July 2011 and February 2012 and evaluated retrospectively. Patients were assessed against the following benchmarks: subjective International Knee Documentation Committee (IKDC) score, Knee injury and Osteoarthritis Outcome Score (KOOS), and VAS for pain and Tegner scores, along with X-rays and MRI, before surgery and after a 2-year follow-up. RESULTS: No severe intraoperative complications or implant failures occurred. The mean preoperative scores were as follows: subjective IKDC 66.8 (SD 1.18), KOOS 61.3 (SD 0.86), Vas for pain 8.6 (SD 1.72) and Tegner 4.1 (SD 2.06), while at follow-up the scores were 73.6 (SD 1.01), 88.1 (SD 1.23), 2.9 (SD 2.35) and 3.1 (SD 1.83), respectively. Correction ranged between 3° and 8°. All patients showed complete articular recovery, no loss of correction, no substantial variation in A/P slope and no hardware problems. CONCLUSIONS: iBalance proved to be effective and safe and produced good overall results. Consolidation and osseointegration of the system took place rapidly, while recovery was precocious, comparable with traditional methods and with no severe complications. LEVEL OF EVIDENCE: Case series, Level IV.

Biomechanical properties of five different currently used implants for open-wedge high tibial osteotomy.

BACKGROUND: As several new tibial osteotomy plates recently appeared on the market, the aim of the present study was to compare mechanical static and fatigue strength of three newly designed plates with gold standard plates for the treatment of medial knee joint osteoarthritis. METHODS: Sixteen fourth-generation tibial bone composites underwent a medial open-wedge high tibial osteotomy (HTO) according to standard techniques, using five TomoFix standard plates, five PEEKPower plates and six iBalance implants. Static compression load to failure and load-controlled cyclic fatigue failure tests were performed. Forces, horizontal and vertical displacements were measured; rotational permanent plastic deformations, maximal displacement ranges in the hysteresis loops of the cyclic loading responses and dynamic stiffness were determined. RESULTS: Static compression load to failure tests revealed that all plates showed sufficient stability up to 2400 N without any signs of opposite cortex fracture, which occurred above this load in all constructs at different load levels. During the fatigue failure tests, screw breakage in the iBalance group and opposite cortex fractures in all constructs occurred only under physiological loading conditions (<2400 N). The highest fatigue strength in terms of maximal load and number of cycles performed prior to failure was observed for the ContourLock group followed by the iBalance implants, the TomoFix standard (std) and small stature (sm) plates. The PEEKPower group showed the lowest fatigue strength. CONCLUSIONS: All plates showed sufficient stability under static loading. Compared to the TomoFix and the PEEKPower plates, the ContourLock plate and iBalance implant showed a higher mechanical fatigue strength during cyclic fatigue testing. These data suggest that both mechanical static and fatigue strength increase with a wider proximal T-shaped plate design together with diverging proximal screws as used in the ContourLock plate or a closed-wedge construction as in the iBalance design. Mechanical strength of the bone-implant constructs decreases with a narrow T-shaped proximal end design and converging proximal screws (TomoFix) or a short vertical plate design (PEEKPower Plate). Whenever high mechanical strength is required, a ContourLock or iBalance plate should be selected.