Background. Hip resurfacing arthroplasty (HRA) and total hip arthroplasty (THA) are treatments of end-stage hip disease. Gait analysis studies comparing HRA and THA have demonstrated HRA results in a more normal gait than THA. The reasons may include the larger, more anatomic head diameter, the preservation of the femoral neck with restoration of the anatomical hip centre position and normal proprioception. This study investigated (1)whether femoral head size diameter affects gait; (2)whether gait still differs between THA and HRA patients even with comparable head diameters. Methods. We analysed the gait of 33 controls and 50 patients with unilateral hip replacement. Follow-up ranged from 9–68 months. In 27 hips a small femoral head size was used (≤ 36mm); in 23 hips a large head size (>36mm). The small size group consisted of 11 long femoral stem THA and 16 short-stem THA; the large group of 5 long-stem, 8 short-stem THA and 10 HRA patients. There were 14 females/19 males in the control group; 22 females/5 males in the small size group; 13 females/10 males in the large size group. Results. (1) We found a significant difference in step-length between small head sizes and controls (p<0.01) at speeds ranging from 4.0 to 5.5 km/h but no difference between the larger head size and the controls. There was no significant difference in maximum speed, weight acceptance, push-off, mid-stance, impulse and cadence between the groups. (2)Analysis between THA and HRA in the large head size group revealed a significant difference in maximum speed (p=0.021) between long-stem THA (6.338 km/h± 1.542) and HRA (7.756km/h± 0.7604) patients. At 5.5 km/h there was a significantly better weight acceptance (p=0.009) and mid-stance (p=0.041) of HRA compared to short-stems. Impulse was significantly higher for HRA compared to long-stem THA (p<0.05) at all speeds ranging 4 to 5.5 km/h. (3)Males (7.1972 km/h ± .9700) had significantly higher maximum speeds compared to females (6.6524km/h± 1.019) (p=0.017) and lower gait impulse (p<0.01) at speeds ranging from 4 to 5.5km/h. (4)There was no significant difference in Oxford Hip Score (OHS) and EQ-5D of patients in the small compared to large head size group. Conclusions. Gait analysis demonstrated a significant difference in step length between THA patients with head size ≤ 36mm and normal controls. There was no difference in step length between normal controls and THA patients with larger head sizes. Compared to larger head size THA, HRA still revealed higher maximum speeds and better weight acceptance. Males had significantly higher maximum speeds compared to females (controls and hip replacement patients). We could not demonstrate a correlation between better gait and Oxford scores or EQ-5D scores but these are known to have a ceiling effect. In a former study, better gait parameters such as longer step length and higher maximum speed have been associated with higher patient satisfaction

Introduction and Objective. Despite pure alumina have shown excellent long-term results in patients undergoing total hip arthroplasty (THA), alumina matrix composites (AMCs) composed of alumina and zirconium oxide are more commonly used. There are no comparative studies between these two different ceramics. We performed a retrospective case-control study to compare results and associated complications between AMC from two manufacturers and those with pure alumina from another manufacturer. Materials and Methods. 480 uncemented THAs with ceramic on ceramic (CoC) bearing surfaces (288 men and 192 women; mean age of 54.1 ± 12.4 years), were implanted from 2010 to 2015. Group 1: 281 THAs with pure alumina; Group 2A: 142 with AMC bearing in a trabecular titanium cup. Group 2B: 57 hips with AMC bearing with a porous-coated cup. Results. The mean follow-up was 7.3 years. There was one late infection in group 1, eight dislocations, three in group 1 (1.1%), three in group 2A (2.1%), all with a 36 mm femoral head, and two in group 2C (3.5%). Liner malseating was found in one hip in group 1, and in five hips in group 2C, of these, there were four liner fractures (7.0%). Four cups were revised for iliopsoas impingement (three in group 1 and one in group 2B). Two cups were revised for aseptic loosening, one in group 1 and one in group 2A, and four revised femoral stems in group 2A, three for subsidence and another for postoperative periprosthetic B. 2. fracture. The mean preoperative Harris Hip Score was 48.6 ± 3.3 in the whole series and 93.9 ± 7.2 at the end of follow-up. The survival rate of revision for any cause was 98.2% (95% Confidence Interval: 96.6–99.8) at ten years for group 1, 95.8% (95% CI: 92.1–99.5) for group 2A, and 91.1% (95% CI: 83.7–98.5) for group 2B (log-rank 0.030). Conclusions. Outcome of uncemented CoC THA in young patients was satisfactory at mid-term in all three groups. However, liner fractures were frequent in group 2B. All dislocated hips in group 2A had a 36 mm femoral head diameter, and revision due to any cause was less frequent in group 1. Pure alumina CoC THA can be used as a benchmark for comparison with newer CoC THAs

Proximal femur fractures are common in the elderly population. The aim of this study was to determine the relationship between fracture type and proximal femoral geometric parameters. We retrospectively studied the electronic medical records of 85 elderly patients over 60 years of age who were admitted to the orthopedic department with hip fractures between January 2016 and January 2018 in a training and research hospital in Turkey. Age, fracture site, gender, implant type and proximal femoral geometry parameters (neck shaft angle [NSA], center edge angle [CEA], femoral head diameter [FHD], femoral neck diameter [FND], femoral neck axial length [FNAL], hip axial length [HAL], and femoral shaft diameter [FSD]) were recorded. Patients with femoral neck fractures and femur intertrochanteric fractures were divided into two groups. The relationship between proximal femoral geometric parameters and fracture types was examined. SPSS 25.0 (IBM Corparation, Armonk, New York, United States) program was used to analyze the variables. Independent samples t test was used to compare the fracture types according to NSA, FHD, FND and FSD variables. A statistically significant difference was found in FSD (p=0,002) and age (p=0,019). FSD and age were found to be greater in intertrochanteric fractures than neck fractures. Gender, site, CEA, FNAL, HAL, NSA, FHD and FND parametres were not significantly different. In the literature, it is seen that different results have been reached in different studies. In a study conducted in the Chinese population, a significant difference was found between the two groups in NSA, CEA and FNAL measurements. In a study conducted in the Korean population, a significant difference was found only in NSA measurements. The FSD is generally associated with bone mineral densitometry in the literature and has been shown to be a risk factor for fracture formation. However, a study showing that there is a relationship between FSD and fracture type is not available in the literature. In this study; FSD was found to be higher in intertrochanteric fractures (p = 0.002). However, for the clinical significance of this difference, we think that larger patient series and biomechanical studies are needed

In order to reduce the risk of dislocation larger femoral heads in total hip arthroplasty (THA) are being used by surgeons in recent years. The standard head size of 28 mm used in 73% of all hip procedures in 2003 was used in only 29% in 2016; whereas head sizes of 32 mm and 36 mm combined, were used in 70%. The increase of head size effectively reduces the thickness of the acetabular cup, altering the load transfer. Herein, this research work investigates the effect of increasing the femoral head size on the stresses of the periacetabular bone at two selected regions: A1 (superior) and A2 (anterior). Three Finite Element models were developed from CT scan data of a hemipelvis implanted with a cemented all-polyethylene acetabular cup with a 50 mm outer diameter and inner diameter to accommodate three head sizes: 28 mm, 32 mm and 36 mm. The peak reaction force at the hip joint during one leg stand for an overweight patient with a body weight of 100 Kg was simulated for head sizes investigated. We found that highest average von Mises stress was 5.7 MPa and occurred in the cortical bone of region A1 which is located within Zone 1 boundaries (Charnley &DeLee); whereas a lower stress of 4.0 MPa occurred at region A2. In the two regions the stresses were the same for the three head sizes. Periacetabular bone was found to be insensitive to the increase of femoral head diameter in cemented THA

Introduction. Hip resurfacing has become a popular procedure for young active patients with osteonecrosis of the femoral head. However, it is not yet clear exactly how much osteonecrosis would permit this procedure and how much would be a contraindication. The aim of the present study was to analyze the resurfaced femoral head using finite element models and, in particular, to examine the influence of the extent of osteonecrosis and metaphysical stem shaft angles within the femoral head. Methods. We evaluated biomechanical changes at various extents of necrosis and implant alignments, using the finite element analysis method. We established three patterns of necrosis by depth from the surface of femoral head and five stem angles. Extension of necrosis as a quarter of femoral head diameter is type A, from a half is type B, and three-fourths is type C. We set five types of different stem angles from 125 to 145 degrees for the axis of femoral shaft. For these models, we evaluated biomechanical changes associated with the extent of necrosis and the stem alignment. Results. Stress distribution near the bone-cement interface increased with expansion of the necrosis. The stress concentration was particularly evident in the Type C model which had wide cement mantle replacement on the resurfaced femoral head. The maximum stress on the prosthesis was decreased with stem angles ranging from 130 to 140 degrees. Stress concentration at the stem shaft was observed when implanted varus or valgus alignment. Stress concentration of cement was observed at the anterior and inferior edges in each model. Regardless of the extent of necrosis replaced by cement, the stress values at the inferior edge increased as the stem shaft angle became varus. Conclusion. This study suggests that hip resurfacing for patients in whom osteonecrosis extends widely should be considered carefully; increased stress concentration near the bone-cement interface may occur when all the necrotic bone is replaced by cement. Furthermore, excessive varus or valgus implantation of the prosthesis has potentially adverse biomechanical effects for implants and the cement mantle

Tribology and wear of articular cartilage is associated with the mechanical properties, which are governed by the extracellular matrix (ECM). The ECM adapts to resist the loads and motions applied to the tissue. Most investigations take cartilage samples from quadrupeds, where the loading and motions are different to human. However, very few studies have investigated the differences between human and animal femoral head geometry and the mechanical properties of cartilage. This study assessed the differences between human, porcine, ovine and bovine cartilage from the femoral head; in terms of anatomical geometry, thickness, equilibrium elastic modulus and permeability. Diameter of porcine (3-6 months old), bovine (18-24 months old), ovine (4 years old) and human femoral heads were measured (n=6). Plugs taken out of the superior region of each femoral head and creep indentation was performed. The human femoral heads were obtained from surgery due to femoral neck fracture. Cartilage thickness was measured by monitoring the resistive force change as a needle traversed the cartilage and bone at a constant feed rate using a mechanical testing machine. The percentage deformation over time was determined by dividing deformation by thickness. A biphasic finite element model was used to obtain the intrinsic material properties of each plug. Data is presented as the mean ± 95% confidence limits. One-way ANOVA was used to test for significant differences (p < or = 0.05). Significant differences in average femoral head diameter were observed between all animals, where bovine showed the largest femoral head. Human cartilage was found to be significantly thicker than cartilage from all quadrupedal hips. Human cartilage had a significantly larger equilibrium elastic modulus compared to porcine and bovine cartilage. Porcine articular cartilage was measured to be the most permeable which was significantly larger than all the other species. No significant difference in permeability was observed between human and the other two animals: bovine and ovine (Table 1). The current study has shown that articular cartilage mechanical properties, thickness and geometry of the femoral heads differ significantly between different species. Therefore, it is necessary to consider these variations when choosing animal tissue to represent human

A total of 20 pairs of fresh-frozen cadaver femurs were assigned to four alignment groups consisting of relative varus (10° and 20°) and relative valgus (10° and 20°), 75 composite femurs of two neck geometries were also used. In both the cadaver and the composite femurs, placing the component in 20° of valgus resulted in a significant increase in load to failure. Placing the component in 10° of valgus had no appreciable effect on increasing the load to failure except in the composite femurs with varus native femoral necks. Specimens in 10° of varus were significantly weaker than the neutrally-aligned specimens.

The results suggest that retention of the intact proximal femoral strength occurs at an implant angulation of ≥ 142°. However, the benefit of extreme valgus alignment may be outweighed in clinical practice by the risk of superior femoral neck notching, which was avoided in this study.

Finite element analysis was used to examine the initial stability after hip resurfacing and the effect of the procedure on the contact mechanics at the articulating surfaces. Models were created with the components positioned anatomically and loaded physiologically through major muscle forces. Total micromovement of less than 10 μm was predicted for the press-fit acetabular components models, much below the 50 μm limit required to encourage osseointegration. Relatively high compressive acetabular and contact stresses were observed in these models. The press-fit procedure showed a moderate influence on the contact mechanics at the bearing surfaces, but produced marked deformation of the acetabular components. No edge contact was predicted for the acetabular components studied.

It is concluded that the frictional compressive stresses generated by the 1 mm to 2 mm interference-fit acetabular components, together with the minimal micromovement, would provide adequate stability for the implant, at least in the immediate post-operative situation.