Cementless Femoral Implants Research Articles

Lower Rates of Femoral Fracture and Subsidence with a Morphometric Stem in Cementless Total Hip Arthroplasty.

A "morphometric" tapered femoral stem with size-specific medial curvatures and proportional neck lengths was introduced, attempting to improve fixation and biomechanics in cementless total hip arthroplasty (THA) across a range of femoral sizes and morphotypes. We investigated whether this design reduced complications and better restored anatomy (e.g., limb length and offset) compared to a traditional tapered stem with consistent neck lengths across sizes. We reviewed 389 THAs (340 patients) performed using either of two cementless femoral implants. Records were reviewed for demographics, surgical details, complications, and reoperations. Radiographs were examined for subsidence, biologic fixation, leg lengths, offset, and proximal femoral morphology. The intraoperative fracture rate was lower with this morphometric stem compared to this traditional stem (0 vs. 3.4%), as was the incidence of postoperative subsidence ≥3mm (4.7 vs. 19.2%). With the numbers available, no differences were identified regarding rates of reoperation for periprosthetic femur fracture (0 vs. 1.0%) and femoral fixation failure without fracture (1.1 vs. 0%), or all-cause reoperations (2.7 vs. 2.4%). Limb length and offset restoration were similar with the two implants, but the shortest available femoral head was used less frequently with this morphometric stem compared to this traditional stem (22 vs. 54%). This morphometric stem was associated with decreased rates of intraoperative fracture and postoperative subsidence, along with decreased use of the shortest available head. Nevertheless, both implants demonstrated clinical success, allowing reconstruction of limb length and offset with low rates of femoral fixation failure.

Development of an Instrument to Assess the Stability of Cementless Femoral Implants Using Vibration Analysis During Total Hip Arthroplasty.

Objective: The level of primary implant fixation in cementless total hip arthroplasty is a key factor for the longevity of the implant. Vibration-based methods show promise for providing quantitative information to help surgeons monitor implant fixation intraoperatively. A thorough understanding of what is driving these changes in vibrational behavior is important for further development and improvement of these methods. Additionally, an instrument must be designed to enable surgeons to leverage these methods. This study addresses both of these issues. Method: An augmented system approach was used to develop an instrument that improves the sensitivity of the vibrational method and enables the implementation of the necessary excitation and measurement equipment. The augmented system approach took into account the dynamics of the existing bone-implant system and its interaction with the added instrument. Results: Two instrument designs are proposed, accompanied by a convergence-based method to determine the insertion endpoint. The modal strain energy density distribution was shown to affect the vibrational sensitivity to contact changes in certain areas. Conclusion: The augmented system approach led to an instrument design that improved the sensitivity to changes in the proximal region of the combined bone-implant-instrument system. This fact was confirmed both in silico and in vitro. Clinical Impact: The presented method and instruments address practical intraoperative challenges and provide perspective to objectively support the surgeon’s decision-making process, which will ensure optimal patient treatment.

Are powder-technology-built stems safe? A midterm follow-up registry study

BackgroundPowder technology was developed to bring together the mechanical features and high porosity of titanium. However, the high porosity may theoretically compromise mechanical resistance. Literature is deficient about the use and safety profile of cementless femoral implants built using additive manufacturing (in particular electron beam melting technology, EBM). The purpose of this study was to evaluate the survival rates and the reason for revisions (especially implant breakage) of the first two EBM-built stems at a mid-term follow-up, using a joint arthroplasty registry.MethodsThe registry of Prosthetic Orthopedic Implant (RIPO) was investigated about cementless stems implanted from 2010 to 2017. Stems built with EBM technology (Parva and Pulchra stems; Adler Ortho, Milan, Italy) were compared to all the other cementless stems implanted during the same period, acting as control group. The survival rates and reasons for revision were assessed.ResultsNo stem breakage occurred. At 5-year follow-up, the survival rates of the two cohorts were not statistically different (96.8% EBM stems, 98.0% standard cementless stems; p > 0.05). In the EBM stems, aseptic loosening occurred in 1.7% of the cases at the latest follow-up.ConclusionsThis large cohort showed that mechanical resistance is not a concern in EBM stems at mid-term follow-up. However, larger populations and longer follow-ups are needed to further validate these results.

Clinical Faceoff: Should Orthopaedic Surgeons Have Strict BMI Cutoffs for Performing Primary TKA and THA?

Clinical Faceoff: Should Orthopaedic Surgeons Have Strict BMI Cutoffs for Performing Primary TKA and THA?

The Effect of Prophylactic Cerclage Wires in Primary Total Hip Arthroplasty: A Biomechanical Study

BackgroundDespite literature to support the use of various cerclage techniques to address intraoperative femoral fractures in total hip arthroplasty, there are limited data to support prophylactic cerclage wiring of the femur during cementless implant placement. This study aims to evaluate the effect of prophylactic calcar cerclage wires on the biomechanical parameters required to produce periprosthetic femoral fractures and on the morphology of these fracture patterns in stable cementless femoral implants. MethodsTen pairs of matched fresh frozen cadaveric femurs were implanted with anatomic tapered cementless implants with or without the addition of 2 monofilament calcar wires. Specimens were axially loaded and externally rotated to failure. Initial torsional stiffness, rotation and energy to failure, and torque at failure were measured. Statistical significance was set at P < .05. Fracture patterns were classified according to a well-known classification system. ResultsWired specimens required significantly more rotation (P = .039) and energy to failure (P = .048). No significant difference was detected in initial torsional stiffness (P = .63) or torque at failure (P = .10). All unwired samples developed a Vancouver B2 fracture pattern. Seven of the 8 wired specimens also developed a Vancouver B2 fracture pattern, while the eighth wired specimen developed a Vancouver B1 fracture pattern. ConclusionProphylactic cerclage wire placement increases the rotation and energy to failure in well-fixed press-fit femoral implants. The increase in torsional energy needed for failure may reduce the risk of early periprosthetic fracture. Further studies are needed to evaluate cost vs benefit and long-term outcomes of prophylactic wiring. Based on the results of our study, consideration of prophylactic wiring should be addressed on a case-to-case basis.

Periprosthetic femoral fractures and trying to avoid them: what is the contribution of femoral component design to the increased risk of periprosthetic femoral fracture?

Periprosthetic femoral fractures (PFF) following total hip arthroplasty (THA) are devastating complications that are associated with functional limitations and increased overall mortality. Although cementless implants have been associated with an increased risk of PFF, the precise contribution of implant geometry and design on the risk of both intra-operative and post-operative PFF remains poorly investigated. A systematic review was performed to aggregate all of the PFF literature with specific attention to the femoral implant used. A systematic search strategy of several journal databases and recent proceedings from the American Academy of Orthopaedic Surgeons was performed. Clinical articles were included for analysis if sufficient implant description was provided. All articles were reviewed by two reviewers. A review of fundamental investigations of implant load-to-failure was performed, with the intent of identifying similar conclusions from the clinical and fundamental literature. In total 596 articles were initially identified, with 34 being eligible for analysis. Aggregate analysis of 1691 PFFs in 342 719 primary THAs revealed a significantly higher number of PFFs with cementless femoral implants (p < 0.001). Single-wedge and double-wedge (fit-and-fill) femoral implants were associated with a threefold increase in PFF rates (p < 0.001) compared with anatomical, fully coated and tapered/rounded stems. Within cemented stems, loaded-taper (Exeter) stems were associated with more PFFs than composite-beam (Charnley) stems (p = 0.004). Review of the fundamental literature revealed very few studies comparing cementless component designs. Very few studies within the PFF literature provide detailed implant information. Cementless implants, specifically those of single-wedge and double-wedge, have the highest PFF rates in the literature, with most investigations recommending against their use in older patients with osteoporotic bone. This review illustrates the need for registries and future PFF studies to record implant name and information for future analysis. Furthermore, future biomechanical investigations comparing modern implants are needed to clarify the precise contribution of implant design to PFF risk. Cite this article: Bone Joint J 2017;99-B(1 Supple A):50-9.

Risk Factors for Perioperative Femoral Fractures: Cementless Femoral Implants and the Direct Anterior Approach Using a Fracture Table

BackgroundWith the increased popularity of the direct anterior approach, the issue of periprosthetic femur fractures has come into focus. The purpose of this article is to identify patient- and procedure-related characteristics that are associated with periprosthetic femur fractures in cementless total hip arthroplasties performed through a direct anterior approach using a fracture table. MethodsFive hundred primary total hip arthroplasties performed using cementless femoral implants through a direct anterior approach using a fracture table were evaluated for characteristics associated with perioperative prosthetic femur fracture within the first 3 months of surgery. ResultsTwenty-three hips (4.6%) incurred fractures, 13 (2.6%) intraoperative and 10 (2.0%) postoperative. Bivariate analyses demonstrated females and a body mass index (BMI) >40 with a higher risk of fractures overall and postoperative fractures. A significant difference in DORR ratios was seen in patients with intraoperative fractures and a significant difference seen with implant sizes in patients with postoperative fractures. Multivariable regression analyses demonstrated an increased risk of postoperative fracture with a BMI >40. As the DORR ratio and implant size increased, there was a reduced odds of intraoperative fracture. ConclusionConcern for periprosthetic femur fractures using the direct anterior approach for total hip arthroplasty is high in female patients and in patients with morbid obesity (BMI >40), small DORR ratio, or small implant size.

Cost Comparison of Cementless Versus Cemented Hemiarthroplasty for Displaced Femoral Neck Fractures

Hip hemiarthroplasties are frequently performed for displaced femoral neck fractures. The purpose of this study was to identify the costs associated with cementless and cemented hemiarthroplasties, compare operative times, and identify complications. The hypothesis was that cementless hemiarthroplasties cost less than cemented hemiarthroplasties, require less operative time, and have fewer perioperative complications. A retrospective review was conducted of 2 surgeons' patients admitted for displaced femoral neck fractures between 2006 and 2010. Group 1 included 45 patients who underwent monopolar hemiarthroplasties with cementless femoral components via a standard posterior approach by a single surgeon. Group 2 included 49 patients who underwent monopolar hemiarthroplasties with cemented femoral components via a modified lateral approach by a single surgeon. Surgical and anesthesia times and the cost of implants and accessories were recorded. The cost for cementless components was $3275.60 (femoral stem, $2800; monopolar head, $400; sleeve, $75.60), whereas the cost of cemented components was $3694.47 (femoral stem, $1800; monopolar head, $400; sleeve, $75.60, 3 Simplex with tobramycin cement packets, $1221; cement mixer/irrigator with tip/centralizer and plug/pressurizer, $197.87), a cost savings of 12.7% ($418.87). Operative time was significantly reduced in group 1 vs group 2 (mean, 32.9 vs 56.1 minutes, respectively; P<.01). Anesthesia time was also significantly reduced in group 1 (mean, 82.3 vs 102.9 minutes, respectively; P<.01). The difference in mean anesthetic times demonstrates an overall cost savings of 18.6%, or $1161.30. No difference in complications was noted between the groups perioperatively. Regional cost variances, vendor-hospital contracts, and surgeons' operative times are factors that may influence cost savings. This study demonstrates significantly lower operative and anesthetic times and observable cost savings with cementless femoral implants.

Assessment of a fictitious domain method for patient-specific biomechanical modelling of press-fit orthopaedic implantation

In this article, we discuss an application of a fictitious domain method to the numerical simulation of the mechanical process induced by press-fitting cementless femoral implants in total hip replacement surgeries. Here, the primary goal is to demonstrate the feasibility of the method and its advantages over competing numerical methods for a wide range of applications for which the primary input originates from computed tomography-, magnetic resonance imaging- or other regular-grid medical imaging data. For this class of problems, the fictitious domain method is a natural choice, because it avoids the segmentation, surface reconstruction and meshing phases required by unstructured geometry-conforming simulation methods. We consider the implantation of a press-fit femoral artificial prosthesis as a prototype problem for sketching the application path of the methodology. Of concern is the assessment of the robustness and speed of the methodology, for both factors are critical if one were to consider patient-specific modelling. To this end, we report numerical results that exhibit optimal convergence rates and thus shed a favourable light on the approach.

Foreword

Excellent long-term results have been achieved with cemented implants. However, the profile of the patient presenting for total hip replacement has changed. Pain and disability are no longer the only indications for surgery. The millennium patient, em-powered with information, seeks surgical intervention to restore quality of life. Thus, ever younger cohorts of patients are presenting for total hip replacement. Conservative surgery embraces both soft issue sparing and bone conservation. If the surgeon is confident the hip he is going to use will outlast the patient he should use it. Otherwise he should consider the next operation and conserve bone. Any implant that makes contact with the diaphyseal cortex or is ingrown distally will offload distally with consequent proximal stress protection. Bone conservation is achieved both by taking less bone at the time of surgery and by optimising the physiological loading of the proximal femur to preserve bone in the longer term. This supplement reviews the evolution and the clinical heritage of a short, stemless metaphyseal loading implant the PROXIMA. Elegant biomechanical studies have shown that the PROXIMA is not a 'fit and fill' prosthesis. Excellent axial and rotational stability can be achieved within the cancellous bone, and the implant is suspended in and moves in consort with the surrounding cancellous bone. This reduces the shear stresses at the fixation interface and optimises load transfer in the metaphysis. Bone densitometry demonstrated that the shorter second generation customised Santori stem avoided subtrochanteric buttressing and enhanced the load transfer to the proximal femur with consequent bone remodelling. Using DEXA to compare the periprosthetic bone density of the short stem with a variety of other commercially available cementless femoral implants confirmed that the PROXIMA preferentially loads the metaphyseal bone. The 'round the corner' technique for the insertion of the PROXIMA is ideally suited for minimally invasive surgical approaches. The 'MicroHip' technique uses a section of the anterior Smith-Peterson approach. This is a truly internervous and inter-muscular plane which provides excellent access to the hip joint. Minimal soft tissue disruption, together with bone preservation, makes PROXIMA a truly conservative op-tion for the millennium patient.

Foreword

Excellent long-term results have been achieved with cemented implants. However, the profile of the patient presenting for total hip replacement has changed. Pain and disability are no longer the only indications for surgery. The millennium patient, em-powered with information, seeks surgical intervention to restore quality of life. Thus, ever younger cohorts of patients are presenting for total hip replacement. Conservative surgery embraces both soft issue sparing and bone conservation. If the surgeon is confident the hip he is going to use will outlast the patient he should use it. Otherwise he should consider the next operation and conserve bone. Any implant that makes contact with the diaphyseal cortex or is ingrown distally will offload distally with consequent proximal stress protection. Bone conservation is achieved both by taking less bone at the time of surgery and by optimising the physiological loading of the proximal femur to preserve bone in the longer term. This supplement reviews the evolution and the clinical heritage of a short, stemless metaphyseal loading implant the PROXIMA. Elegant biomechanical studies have shown that the PROXIMA is not a 'fit and fill' prosthesis. Excellent axial and rotational stability can be achieved within the cancellous bone, and the implant is suspended in and moves in consort with the surrounding cancellous bone. This reduces the shear stresses at the fixation interface and optimises load transfer in the metaphysis. Bone densitometry demonstrated that the shorter second generation customised Santori stem avoided subtrochanteric buttressing and enhanced the load transfer to the proximal femur with consequent bone remodelling. Using DEXA to compare the periprosthetic bone density of the short stem with a variety of other commercially available cementless femoral implants confirmed that the PROXIMA preferentially loads the metaphyseal bone. The 'round the corner' technique for the insertion of the PROXIMA is ideally suited for minimally invasive surgical approaches. The 'MicroHip' technique uses a section of the anterior Smith-Peterson approach. This is a truly internervous and inter-muscular plane which provides excellent access to the hip joint. Minimal soft tissue disruption, together with bone preservation, makes PROXIMA a truly conservative op-tion for the millennium patient.

Hydroxyapatite-coated versus grit-blasted femoral stems

We have carried out a prospective, randomised study designed to compare the long-term stability of the stem of cementless femoral implants with differing surface configurations. A total of 50 hips (46 patients) was randomised into two groups, according to whether the medullary stem had been grit blasted (GB) or coated with hydroxyapatite (HA). Both femoral prostheses were of the same geometrical design. We used Ein Bild Roentgen Analyse femoral component analysis (EBRA-FCA) to assess the stability of the stem. The mean follow-up was for 8.66 years. The mean migration of the stem was 1.26 mm in the HA group compared with 2.57 mm in the GB group (Mann-Whitney U test, p = 0.04). A mixed model ANOVA showed that the development of subsidence was statistically different in the two groups during the first 24 months. After this subsidence increased in both groups with no difference between them. Our results indicate that, with the same design of stem, HA coating enhanced the stability of the femoral stem when compared with GB stems.

ＤＸＡ法による大腿骨ステム周囲の骨塩密度の検討

ＤＸＡ法による大腿骨ステム周囲の骨塩密度の検討

Correlation of Computed Finite Element Stresses to Bone Density After Remodeling Around Cementless Femoral Implants

Fundamental to the development of a durable, uncemented femoral component is an understanding of the remodeling process that goes on after implantation. Predicting the bone remodeling that results from the use of a given hip implant would facilitate the design of a prosthesis that would optimize bone adaptation. This report combines the results of finite element stress analysis of the AML prosthesis implanted in vitro into a proximal femur with quantitative bone mineral density measured in vivo in the medial and lateral aspects of human femora at periods after implantation. Unimplanted femora were also analyzed for comparison purposes. Bone density measurements were obtained using dual energy x-ray absorptiometry. Absolute values of the maximum principal stress and maximum shear stress calculated in the femur at the time of implantation accurately predict bone density resulting from remodeling caused by the prosthesis. The calculated initial strain was not found to correlate with resultant bone density. These findings suggest that the results of stress analyses using three dimensional models of femora implanted in vitro can predict bone remodeling around prostheses and may be used to quantitate appropriate design criteria for total hip replacements.

Dual-energy X-ray absorptiometry measurement of bone mineral density around porous-coated cementless femoral implants. Methods and preliminary results.

The measurement of bone mineral density in defined areas around metal implants has improved with the development of dual-energy X-ray absorptiometry. We used this technique to compare the bone mineral density adjacent to metal cementless femoral implants with that of identical regions of bone in normal proximal femora. We studied the anteroposterior views only of 72 femora which contained total hip implants and 34 non-operated femora. We compared the regional bone mineral density of bone adjacent to proximally porous-coated and distally porous-coated implants of one design, to measure the relative differences in the remodelling changes induced by different amounts of porous coating. We also measured differences in bone density with time and with variations in implant size (and therefore stiffness). The greatest decrease in bone mineral density (34.8%) occurred in the most proximal 1 cm of the medial femoral cortex around relatively stiff, extensively porous-coated implants. The next most severe decrease (20% to 25%) was in the next most proximal 6 cm of the medial femoral cortex. Small, progressive decreases in bone mineral density continued for five to seven years after implantation.

The morphology of the proximal femur. A three-dimensional radiographic analysis

Biological fixation of cementless femoral implants requires primary stability by optimal fit in the proximal femur. The anatomy of the bone must then be known precisely. We analysed in vitro the accuracy of bone measurements of 32 femurs and compared the dimensions obtained from radiographs and CT scans with the true anatomical dimensions. Standard radiographs gave only a rough approximation of femoral geometry (mean difference: 2.4 +/- 1.4 mm) insufficiently accurate to allow selection of the best fitting prosthesis from a range of sizes and altogether inadequate to design a custom-made prosthesis. CT scans give greater accuracy (mean difference: 0.8 +/- 0.7 mm) in our experimental conditions, but in clinical practice additional sources of error exist.

Intraoperative Measurement of Rotational Stability of Femoral Components of Total Hip Arthroplasty

High out-of-plane forces acting on the hip joint can produce important rotational micromotion of the femoral component. This micromotion at the prosthesis interface may be detrimental to the stability of the implant. In cementless femoral implants this could prevent bone ingrowth, and in the cemented component this could cause generation of particulate debris, lysis, and loosening. The introduction of the torque wrench micrometer for assessment of intraoperative femoral component stability can quantify the initial stability of primary cementless femoral components and critically evaluate the stability (at either the initial or revision arthroplasty) of both cemented and cementless femoral components. It allows the surgeon to produce a known torque in the direction and magnitude of the out-of-plane forces that load the hip in vivo.