Introduction

There have been many attempts to reduce the risk of femoral component loosening.

Using a tapered stem having a highly polished stem surface results in stem stabilization subsequent to debonding and stem-cement taper-lock and is consistent with force-closed fixation design.

Introduction

Excellent long-term survival rates associated with the absence of stem subsidence have been achieved with total hip arthroplasty (THA) using femoral components cemented line-to-line (“French Paradox”). Recently, short stems have been introduced in order to preserve diaphyseal bone and to accommodate to minimal invasive THA and a variety of clinical situations. The aim of the current study was to quantify the rotational and tilting stability of a Kerboull stem of varying length after line-to-line cementation using a validated in-vitro model.

Introduction:

Extensive bone defects of the proximal femur e.g. due to aseptic loosening might require the implantation of megaprostheses. In the literature high loosening rates of such megaprostheses have been reported. However, different fixation methods have been developed to achieve adequate implant stability, which is reflected by differing design characteristics of the commonly used implants. Yet, a biomechanical comparison of these designs has not been reported.

The aim of our study was to analyse potential differences in the biomechanical behaviour of three megaprostheses with different designs by measuring the primary rotational stability in vitro.

Introduction

The Exeter cemented polished tapered stem design was introduced into clinical practice in the early 1970's. [i] Design and cement visco-elastic properties define clinical results [ii]; a recent study by Carrington et al. reported the Exeter stem has 100% survivorship at 7 years. [iii] Exeter stems with offsets 37.5–56 mm have length 150 mm (shoulder to tip). Shorter stems, lengths 95–125 mm, exist in offsets 30–35.5 mm. The Australian National Joint Replacement Registry recently published that at 7 years the shorter stems are performing as well as longer stems on the registry [iv]. Clinical observation indicates in some cases of shorter, narrower femora that fully seating a 150 mm stem's rasp in the canal can be difficult, which may affect procedural efficiency. This study investigates the comparative risk of rasp distal contact for the Exeter 150 mm stem or a 125 mm stem.

Introduction

Resorptive bone remodeling secondary to stress shielding has been a concern associated with cementless total hip arthroplasty (THA). At present, various types of cementless implants are commercially available. The difference in femoral stem design may affect the degree of postoperative stress shielding. In the present study, we aimed to compare the difference in bone mineral density (BMD) change postoperatively in femurs after the use of 1 of the 3 types of cementless stems.

Shoulder arthroplasty humeral stem design has evolved to accommodate patient anatomy characteristics. As a result, stems are available in numerous shapes, coatings, lengths, sizes, and vary by fixation method. This abundance of stem options creates a surgical paradox of choice. Metrics describing stem stability, including a stem's resistance to subsidence and micromotion, are important factors that should influence stem selection, but have yet to be assessed in response to the diametral (i.e., thickness) sizing of short stem humeral implants. Eight paired cadaveric humeri (age = 75±15 years) were reconstructed with surgeon selected ‘standard’ sized short-stemmed humeral implants, as well as 2mm ‘oversized’ implants. Stem sizing conditions were randomized to left and right humeral pairs. Following implantation, an anteroposterior radiograph was taken of each stem and the metaphyseal and diaphyseal fill ratios were quantified. Each humerus was then potted in polymethyl methacrylate bone cement and subjected to 2000 cycles of 90º forward flexion loading. At regular intervals during loading, stem subsidence and micromotion were assessed using a validated system of two optical markers attached to the stem and humeral pot (accuracy of <15µm). The metaphyseal fill ratio did not differ significantly between the oversized and standard stems (0.50±0.06 vs 0.50±0.10; P = 0.997, Power = 0.05); however, the diaphyseal fill ratio did (0.52±0.06 vs 0.45±0.07; P < 0.001, Power = 1.0). Neither fill ratio correlated significantly with stem subsidence or micromotion. Stem subsidence and micromotion were found to plateau following 400 cycles of loading. Oversizing stem thickness prevented implant head-back contact in all but one specimen with the least dense metaphyseal bone, while standard sizing only yielded incomplete head-back contact in the two subjects with the densest bone. Oversized stems subsided significantly less than their standard counterparts (standard: 1.4±0.6mm, oversized: 0.5±0.5mm; P = 0.018, Power = 0.748;), and resulted in slightly more micromotion (standard: 169±59µm, oversized: 187±52µm, P = 0.506, Power = 0.094,). Short stem diametral sizing (i.e., thickness) has an impact on stem subsidence and micromotion following humeral arthroplasty. In both cases, the resulting three-dimensional stem micromotion exceeded, the 150µm limit suggested for bone ingrowth, although that limit was derived from a uniaxial assessment. Though not statistically significant, the increased stem micromotion associated with stem oversizing may in-part be attributed to over-compacting the cancellous bed during broaching, which creates a denser, potentially smoother, interface, though this influence requires further assessment. The findings of the present investigation highlight the importance of proper short stem diametral sizing, as even a relatively small, 2mm, increase can negatively impact the subsidence and micromotion of the stem-bone construct. Future work should focus on developing tools and methods to support surgeons in what is currently a subjective process of stem selection

Introduction. Stem geometry is known to influence the outcome in THA; however it is unknown whether the material properties, stiffness in particular can influence the stem stability and outcome. The aim of this study was to measure the influence of stem material properties on micromotion and migration using Roentgen Stereophotogrammetric Analysis (RSA) system. Methods. 41 patients were implanted with a collarless polished tapered (CPT) femoral stem (Zimmer, Warsaw, Indiana), which was made of either cobalt-chromium (CoCr) (n=21) or stainless steel (n=20). RSA was used to measure dynamically inducible micromotion (DIMM: difference in stem position in going from double-leg stance (DLS) to single leg stance (SLS)), prosthesis bending (difference in the head-tip distance when going from DLS to SLS), and mean migration of the head, tip and the cement restrictor. DIMM and bending were measured at 3 months, migration at 6, 12 and 24 months. All analyses were carried out using SPSS for windows (v.15.0.0, Chicago. IL, USA). Results were reported as mean ± 95% confidence interval (CI) and regarded as significant when p < 0.05. Results. Preliminary analysis showed that DIMM of head was significantly (p = 0.02) greater for CoCr (0.97mm ± 0.6mm) than stainless steel (0.27mm ± 0.6mm). The mean stem bending for CoCr was 0.08mm (± 0.06mm) and for stainless steel 0.15mm (± 0.06mm) (p =0.77). Both implants heads migrated posteriorly, medially and distally. The mean subsidence for the cobalt-chromium and stainless steel stems was 1.02mm (±0.19mm) (p < 0.001) and 1.12mm (± 0.34mm) (p=0.001) (p= 0.07) at 24 months. Conclusion. Dynamically induced micromotion was greater for the stiffer stem, however there were no differences in terms of over all migration, indicating that survival (in terms of loosening) should be the similar for both stainless steel and CoCr versions of this implant

Stem geometry is known to influence the outcome in THA; however it is unknown whether the material properties, stiffness in particular can influence the stem stability and outcome. The aim of this study was to measure the influence of stem material properties on micromotion and migration using Roentgen Stereophotogrammetric Analysis (RSA) system. 41 patients were implanted with a collarless polished tapered (CPT) femoral stem (Zimmer, Warsaw, Indiana), which was made of either cobalt-chromium (CoCr) (n=21) or stainless steel (n=20). RSA was used to measure dynamically inducible micromotion (DIMM: difference in stem position in going from double-leg stance (DLS) to single leg stance (SLS)), prosthesis bending (difference in the head-tip distance when going from DLS to SLS), and mean migration of the head, tip and the cement restrictor. DIMM and bending were measured at 3 months, migration at 6, 12 and 24 months. All analyses were carried out using SPSS for windows (v.15.0.0, Chicago. IL, USA). Results were reported as mean ± 95% confidence interval (CI) and regarded as significant when p < 0.05. Preliminary analysis showed that total head DIMM was significantly (p = 0.02) greater for CoCr (0.97mm ± 0.6mm) than stainless steel (0.27mm ± 0.6mm). The mean stem bending for CoCr was 0.08mm (± 0.06mm) and for stainless steel 0.15mm (± 0.06mm) (p =0.77). Both implants heads migrated posteriorly, medially and distally. The mean subsidence for the cobalt-chromium and stainless steel stems was 1.02mm (± 0.19mm) (p < 0.001) and 1.12mm (± 0.34mm) (p=0.001) (p= 0.07) at 24 months. It was interesting to note that the dynamically induced micromotion was greater for the stiffer stem, however there were no differences in terms of overall migration, indicating that survival (in terms of loosening) should be the similar for both steel and CoCr versions of this implant

Patients, and their femurs, come in all shapes, sizes, and types. Fortunately, so do cementless femoral stems! A simple approach is to separately consider A) the part inside the bone and B) the part outside the bone. The inner-cortical geometry (Dorr type), bone density, and presence of any deformity, influence selection of stem shape, length, and extent of ingrowth surface (the part inside the bone). Restoration of limb length and offset is a function of the neck angle and length (the part outside the bone). Clinical data indicates that undersizing of cementless stems increases the risk of revision for aseptic loosening while restoration of limb length and offset favorably affects patient satisfaction and function

Background. Impaction bone grafting (IBG) using a circumferential metal mesh is one of the options that allow restoration of the femoral bone stock and stability of the implant in hip arthroplasty. Here we examined the clinical and radiographic outcome of this procedure with a cemented stem and analyzed experimentally the initial stability of mesh–grafted bone–cemented stem complexes. Methods. We retrospectively reviewed 6 hips (6 patients) that had undergone femoral revisions with a circumferential metal mesh, impacted bone allografts, and a cemented stem. The mean follow-up period was 2.9 years (range, 1.4–3.8 years). Hip joint function was evaluated with the Japanese Orthopaedic Association hip score, and radiographic changes were determined from radiographs. The initial resistance of cemented stem complexes to axial and rotational force was measured in a composite bone model with various segmental losses of the proximal femur. Results. The hip score improved from 50 (range, 10–84) preoperatively to a mean of 74 (range, 67–88) at the final follow-up. The overall implant survival rate was 100% at 4 years when radiological loosening or revision for any reason was used as the endpoint. No stem subsided more than 3 mm vertically within 1 year after implantation. Computed tomography showed reconstitution of the femoral canal in a metal mesh. In mechanical analyses, there was no influence on the stem stability to axial compression during the repeated axial compression test between IBG reconstruction rates. On the other hand, for IBG reconstruction rate of 66.7%, grafted bone-Sawbone juntion was buckled under the axial breaking force. In contrast, under rotational load, the rotation angles of the stainless mesh were strongly affected by the IBG reconstruction rate. Conclusions. The short-term results show good outcomes for reconstruction of proximal bone loss with impaction bone allografts and a circumferential mesh. The procedure should be applied in cases where the circumferential proximal bone loss is less than half of the stem length implanted

INTRODUCTION. Modular knee implants are used to manage large bone defects in revision total knee arthroplasty. These implants are confronted with varying fixation characteristics, changes in load transfer or stiffen the bone. In spite of their current clinical use, the influence of modularity on the biomechanical implant-bone behavior (e.g. implant fixation, flexibility, etc.) still is inadequately investigated. Aim of this study is to analyze, if the modularity of a tibial implant could change the biomechanical implant fixation behavior and the implant-bone flexibility. MATERIAL & METHODS. Nine different stem and sleeve combinations of the clinically used tibial revision system Sigma TC3 (DePuy) were compared, each implanted standardized with n=4 in a total of 36 synthetic tibial bones. Four additional un-implanted bones served as reference. Two different cyclic load situations were applied on the implant: 1. Axial torque of ±7Nm around the longitudinal stem axis to determine the rotational implant stability. 2. Varus-valgus-torque of ±3,5Nm to determine the bending behavior of the stem. A high precision optical 3D measurement system allowed simultaneous measuring of spatial micromotions of implant and bone. Based on these micromotions, relative motions at the implant-bone-interface and implant flexibility could be calculated. RESULTS. Lowest relative micromotions were measured along the tibial base component and the sleeve; however, these motions varied depending on the implant construct used. Maximum relative micromotions were detected at the distal end of the implant for all groups, indicating a more proximal fixation of all modular combinations. Regarding varus-valgus-torque measurement, all groups showed a deviant flexibility behavior compared to the reference group. When referred to the un-implanted bone, implants without stems revealed the highest flexibility, whereas implants with shorter stems had lowest flexibility. DISCUSSION & CONCLUSION. All groups showed a more proximal fixation behavior; moreover, both extent and location of fixation could be influenced by varying the modular combination. Larger stems seemed to support a more distal fixation behavior, whereas the implant fixation moved proximal while extending the sleeve. Here the influence of the sleeve on fixation behavior seemed to be dominant compared to the influence of the stem. Concerning varus-valgus-torque, a strong connection between the used stem and implant-bone flexibility seemed to exist. In addition, the influence of the sleeve on flexibility seemed to be rather low. This study showed, that modularity can influence the biomechanical behavior of tibial implants. If these results can be transferred to other tibial implants still remains to be seen

Introduction. Recent implant design trends have renewed concerns regarding metal wear debris release from modular connections in THA. Previous studies regarding modular head-neck taper corrosion were largely based on cobalt chrome (CoCr) alloy femoral heads. Comparatively little is known about head-neck taper corrosion with ceramic femoral heads or about how taper angle clearance influences taper corrosion. This study addressed the following research questions: 1) Could ceramic heads mitigate electrochemical processes of taper corrosion compared to CoCr heads? 2) Which factors influence stem taper corrosion with ceramic heads? 3) What is the influence of taper angle clearance on taper corrosion in THA?. Methods. 100 femoral head-stem pairs were analyzed for evidence of fretting and corrosion. A matched cohort design was employed in which 50 ceramic head-stem pairs were matched with 50 CoCr head-stem pairs based on implantation time, lateral offset, stem design and flexural rigidity. Fretting corrosion was assessed using a semi-quantitative scoring scale where a score of 1 was given for little to no damage and a score of 4 was given for severe fretting corrosion. The head and trunnion taper angles were measured using a roundness machine (Talyrond 585, Taylor Hobson, UK). Taper angle clearance is defined as the difference between the head and trunnion taper angles. Results. The fretting corrosion scores were significantly lower for the stems in the ceramic head cohort when compared with the CoCr cohort. Stem alloy and stem flexural rigidity were predictors of stem fretting and corrosion damage in the ceramic head cohort, however not for the CoCr cohort. The mechanism of mechanically assisted crevice corrosion was the same in the two cohorts, with the exception being that, only one of the two surfaces (i.e., the trunnion) engaged in the oxide abrasion and repassivation process in the ceramic cohort. There was no significant correlation observed between taper angle clearance and visual fretting-corrosion scores for trunnions in the ceramic cohort (Rho=−0.17), trunnions in the CoCr cohort (Rho=0.24), or the femoral head tapers in the metal cohort (Rho=−0.05) (Figure 1). Additionally, visual fretting-corrosion scores in the metal cohort were similar between components with distal contact (negative taper angle clearance) and components with proximal contact (positive taper angle clearance) (p=0.43 and 0.56 for head and trunnion scores, respectively). Conclusions. The results suggest that by using a ceramic femoral head, CoCr fretting and corrosion from the modular head-neck taper may be mitigated, but not completely eliminated. The findings of this study support further study of the role of ceramic heads in potentially reducing femoral taper corrosion. Taper angle clearance was not correlated with the visual fretting-corrosion scores in the ceramic or CoCr cohort in the present study. The effects of taper angle clearance may not be significant compared to other factors leading to material loss or the lack of correlation may be due to the limitations in the visual scoring method. Research is underway quantify the volume of material release from explants to better understand the reasons for reduced fretting and corrosion observed in the ceramic head cohort

Purpose. CentPillar GB HA stem (stryker®) is developed as the stem fitting the Japanese femur, and now there is CentPillar TMZF HA stem (stryker®) as the improvement type of the stem by coating the PureFix HA with plasma spray. We observed the factors which influenced on the stem subsidence between the two-type stems. Materials and Methods. We intended for 26 hips 23 patients that we performed total hip arthroplasty (THA) during the period between January 2005 and June 2009 and were able to follow up more than three years. 10 males 11 hips and 13 females 15 hips, the mean age at the time of surgery was 56.5 (range, 29–74) years old, and primary diseases were osteoarthritis (OA) in 17 hips, Idiopathic Osteonecrosis of Femoral Head (ION) in six hips, and rheumatoid arthritis (RA) in three hips. 16 hips were treated with the CentPillar GB HA stem (G group), and 10 hips were performed with the CentPillar TMZF HA stem (T group). The examination items are the stem size, the canal fill ratio of the stem (the top of lesser trochanter, the bottom of lesser trochanter, the distal portion of the stem) and the stem alignment (on anteroposterior radiograph and Lauenstein view). Results. The mean stem subsidence was 1.75 mm (range, 0–8.9 mm) in the G group, and 0.87 mm (range, 0–2.9 mm) in the T group. Although there was no significant difference, it accepted the tendency that the stem subsidence in the G group was larger than its in T group. The case in which the stem subsidence more than 2 mm was found at were 7 hips in the G group, whereas it was only one hip in the T group. The stem size, the canal fill ratio of the stem and the stem alignment were no meaningful effect on the stem subsidence. In F-test, the stem subsidence of the G group had significantly large dispersion compared with the T group (P<0.01). Discussion and Conclusion. Although there were no significant differences in the stem subsidence between the two groups, the variation of the stem subsidence was significantly small in the T group. We examined the factor which affected the stem subsidence, but neither item recognized meaningful relation, and the influence such as differences of the surface processing was considered. In fact, the strength of the TMZF HA stem improved for the GB HA stem with TMZF titanium alloy, the contact area with the bone spread by coating the PureFix HA with plasma spray, the elasticity of TMZF became closer to the bone, and the strong proximal fixation were enabled. In THA with the GB HA stem, variation of the stem subsidence was significantly large, so considerable attention for the excessive stem subsidence was required