FEA, Biomechanical and Clinical Study of R.O. Peritrochanteric Fractures With PFLP vs Cephalomedullary Nail.

Background Hip fractures are the second most common fractures regardless of age . At the same time, the prevalence of these fractures is increasing, with the total number of admissions for hip fractures in the US is estimated to reach 289,000 by 2030 with an increase to 4.5 million by 2050. In the United Kingdom, although there has been an age-weighted decline in hip fractures of 0.5% per year, it is estimated that their incidence in the United Kingdom will double in the next 25 years. In addition, hip fractures are associated with a high risk of mortality, especially in the elderly, as well as reduced mobility. Their consequences in the elderly are significant due primarily to the increased mortality and secondarily to the negative effects on the health of patients resulting in reduced mobility and influence of their quality of life. In a recent review of 38 studies by Dyer et al, hip fracture survivors had significantly affected mobility, independent functionality, health, quality of life, and higher institutionalization rates compared to their respective age control group without fracture. Even with advances in rehabilitation institutes and new scientific protocols for the optimal treatment of hip fragility fractures, the in-hospital mortality rate was 2.4% and the overall mortality, one year postoperatively, was 18.7% and complete recovery or slight reduction of mobility was achieved in 32.1% of patients. In a recent study by the Swedish Hip Fracture Registry, the first-year mortality rate was about 20% for women and 30% for men in a total population study of 289,603 patients with first hip fracture. during a period of 20 years (1998-2017).

The first mobilization after a hip fracture seems to be beneficial for patients as it is associated with reduced complications due to prolonged bed rest and helps the fracture heal. Consequently, the vast majority of fractures require surgical interventions to allow for fast mobilization and loading of the limb. Various osteosynthesis techniques have been proposed and used which fall into three main categories: a) Dynamic Hip Screw (DHS) extramedullary systems, b) Proximal femoral nail N [PN] PFNA], γ-nail [GN] or other implants) and (c) Dynamic Condylar Screw, Angled blade plates, Proximal Femur Locking Plate (PFLP). The type of osteosynthesis is based on the pattern of the fracture, the characteristics of the patient and the preference of the surgeon In our study we will analyze the lateral oblique (reverse oblique) peritrochanteric fractures that are classified as A31-1,2,3 according to AO and extend on the lateral wall of the proximal femur (Figure 1).

In this fracture category we will compare the anatomical locked plate PERI-LOC◊ 4.5mm Proximal Femur Locking Plate (PFLP) (Smith \& Nephew) with cephalomedullary nail [Figure 2]. PFLP is an implant characterized by the ability to place multiple screws in both the head (5) and the femoral diaphysis. It also has an anatomical design, offers immediate reduction of the fracture with the possibility of additional placement of wires while there is a special guide for the transdermal placement of the peripheral screws. In contrast, the cephalic nails, using a transverse screw compressor, allow the linear compression of the descending sections, while providing a high degree of rotational stability.

The common problem with cephalic nails is that they cannot usually align the outwardly displaced central part of the head (Figure 2) and in addition, the posterior slip of the transverse screw is parallel to the fracture line and exacerbates postoperative misalignment. during charging. Biomechanically, however, it is the central part of the nail that resists the sliding forces and holds the further displacement of the fracture. According to the existing literature, there are conflicting data on the stability of PFLP's. Ozkan et al. In a biomechanical study on the stability of PFLPs against intramedullary nails for unstable intertrochanteric fractures (but not reverse oblique ones) they concluded that for subtrochanteric fractures, PFLP's provided greater stability, but the difference was not statistically significant. A retrospective study of the efficacy of PFLP in peritchanteric fractures has shown that it has fewer complications than other methods. At the same time, biomechanical studies suggest that the axial stability of PFLP'S is less than that of intramedullary implants. In studies evaluating the postoperative parameters of peritrochanteric fractures, good results have been reported in terms of anatomical reduction, fracture healing and patient function scores. Nevertheless, it is shown that the intramedullary nails offer greater mechanical stiffness, stabilization and shorter time of onset of porous. It should be noted, however, that a direct comparison of the peri-loc plate with the cephalomedullary nails is not known to have been published in the literature regarding unstable subtrochanteric fractures, while in a study comparing them biomechanically it appears that this material has comparable stability with the TIT (Smith and Nephew) nail.

I. CLINICAL STUDY Purpose of the study The proposed pilot, monocentric, randomized controlled trial is designed to evaluate clinical and radiological parameters as well as quality-of-life indicators in patients with reverse oblique hip fractures (A31-1.3 against AO) undergoing surgery. With the anatomical proximal femur locking plate, against an intermedullary nailing system. Our main assumption is that the plate will provide better radiological and possibly better clinical results compared to the intramedullary nailing system. The biomechanical differences of the two implants will be examined in the biomechanical study.

Primary objective The primary goal of this study is to investigate whether there are statistically significant differences in the main radiological parameters (cut-out, misalignment of the femoral head, loss of alignment, defective posture, non-union), in patients over 65 years of age with reverse oblique hip fractures treated with the classic intramedullary nail system versus PFLP over a 24-week follow-up period.

The second primary goal is to assess the functional status of patients up to 24 weeks postoperatively, using special clinical evaluation scales (Harris Hip score-HHS and Oxford hip score-OHS).

Sub-objectives

Several sub-objectives will also be studied in order to evaluate the efficacy and safety of the above implants, quantifying and drawing evidence from the observed differences between the control groups in the following:

1. Comparison of perioperative and intraoperative surgical data (surgery delay, age-adjusted Carlson comorbidity index, operating time, radioscopy time and dosage, blood loss, length of hospital stay, total dose of analgesics per class of drug (Dual Energy X-ray Absorptiometry) of the healthy hip, the time of fracture healing, the intraoperative complications that depend on the surgeon's manipulations, such as incorrect placement of the compression screw, fracture extension, non-anatomical reduction, osteosynthesis in varus/valgus position, or rotational deformity as well as the assessment of radiological parameters such as the TAD index using postoperative pelvic computed tomography).
2. Quantitative assessment of pain during the perioperative period and at 6, 12 and 24 weeks postoperatively, using the visual analogue scale.
3. Assessment of the patient's general health status before surgery and at 6, 12 and 24 weeks postoperatively using the SF-36 assessment form, the EQ-5D-3L questionnaire, the SARC-F index and the elderly mobility scale (EMS).

Patient selection criteria.

1. A31-1,3 intertrochanteric fracture (AO classification) due to trauma, closed injury
2. Patients over 65 years of age
3. Presentation in the hospital within 7 days from the
4. There are no concomitant injuries or previous operations on the unaffected hip

Patient exclusion criteria

1. Patients with concomitant injuries that affect the treatment and rehabilitation of the affected limb
2. Patients with associated neurovascular injuries requiring immediate surgery
3. Patients with limited Greek language proficiency, including family members
4. Patients who refuse to sign admission consent to the study
5. Patients with severe dementia, bedridden and severe comorbidities that are a contraindication to surgery

Sample size - Statistical analysis This study will use two primary efficacy scales, the Oxford Hip Score and the Harris Hip Score. Minimum clinically significant differences for HHS have been estimated between 7 and 10, while for OHS between 5 and 7. The aim will be to evaluate 15 patients in each group, as this will provide a sufficient sample for 90% strength and for two primary outcome measures. With a projected abandonment rate of 15%, the total number of patients required will be 35. If collection proves problematic during the study, then the target will be reduced and the more common 80% power level will be considered sufficient. For this scenario, the total number of patients required will be 35 (including the 15% non-completion of the study).

The main outcome measure of radiological failure is a binary result (failure / failure). A binary regression accounting model will be performed to estimate the correlation between the 'failure' outcome and the implant type (PFLP, TIT). The complication rate of PFLP versus nail at 24 weeks postoperatively will be compared using the x2 test (with a significance level of 5%). Differences between HHS and OHS between groups will be assessed using the t-test for independent variables at 24 weeks postoperatively with a significance level of 5%. Test levels will be adjusted using Holm-Bonferroni methods to allow multiple comparisons. A linear regression analysis will also be used to quantify the effects of treatment methods on each of the primary outcome measures, after weighing the effects of other important, potentially confusing factors (eg age, gender) recorded for each patient.

II. BIOMECHANICAL STUDY AND ANALYSIS OF PASSED DATA

The experimental test will be performed at the Laboratory of Technology and Strength of Materials of the Department of Mechanical Engineering and Aeronautics of the University of Patras. Two systems of intramedullary implants will be used, the anatomically locked plate PERI-LOC 4.5mm Proximal Femur Locking Plate (S \& N) and a cephalomedullary nailing system.

Our hypothesis is based on the fact that the individual differences between the two osteosynthesis systems for the treatment of two-way fractures may create different patterns of deformation distribution and, consequently, dissimilar biomechanical behaviors. For the purpose of the study, synthetic osteoporotic femurs will be used in which, through osteotomies, the experimental model of an unstable fracture will be created. This will be followed by osteosynthesis of the fracture with the osteostabilization systems under study. The correctness of the implantation of the studied intramedullary systems in the synthetic femurs will be checked radiologically. The implanted bones will be placed in a suitable device, where a static charge will be applied. The induced deformity will be evaluated as it is distributed over the entire surface of the proximal femur with the method of digital image correlation (Digital Image Correlation-DIC) but also the maximum load causing induction of osteosynthesis failure.

In addition to the experimental studies, the biomechanical behavior of the implants under study will be studied using the finite element method. To this end, parametric finite element models of the descending femur and intramedullary implants will be developed. These models, once validated by the mechanical tests, will be used to evaluate possible biomechanical system failure scenarios by performing a detailed bone and/or implant failure analysis.