Stem Fixation Research Articles

Numerical evaluation of bone remodelling and adaptation considering different hip prosthesis designs

BackgroundThe change in mechanical properties of femoral cortical bone tissue surrounding the stem of the hip endoprosthesis is one of the causes of implant instability. We present an analysis used to determine the best conditions for long-term functioning of the bone–implant system, which will lead to improvement of treatment results. MethodsIn the present paper, a finite element method coupled with a bone remodelling model is used to evaluate how different three-dimensional prosthesis models influence distribution of the density of bone tissue. The remodelling process begins after the density field is obtained from a computed tomography scan. Then, an isotropic Stanford model is employed to solve the bone remodelling process and verify bone tissue adaptation in relation to different prosthesis models. FindingsThe study results show that the long-stem models tend not to transmit loads to proximal regions of bone, which causes the stress-shielding effect. Short stems or application in the calcar region provide a favourable environment for transfer of loads to the proximal region, which allows for maintenance of bone density and, in some cases, for a positive variation, which causes absence of the aseptic loosening of an implant. In the case of hip resurfacing, bone mineral density changes slightly and is closest to an intact femur. InterpretationInstallation of an implant modifies density distribution and stress field in the bone. Thus, bone tissue is stimulated in a different way than before total hip replacement, which evidences Wolff's law, according to which bone tissue adapts itself to the loads imposed on it. The results suggest that potential stress shielding in the proximal femur and cortical hypertrophy in the distal femur may, in part, be reduced through the use of shorter stems, instead of long ones, provided stem fixation is adequate.

Up to seven years' follow-up of short cemented stems in complex primary total knee arthroplasty: A prospective study

BackgroundAlthough primary total knee arthroplasty (TKA) shows good clinical, functional and radiological results, it can be complicated by certain conditions or pathologies. The main objective of this study was to evaluate the global performance of short cemented metaphyseal stem components in patients undergoing complex primary TKA. MethodsThis is a single-surgeon prospective case series of 91 patients who underwent complex primary TKA requiring short stem fixation between January 2009 and October 2014. Knee Society Scores, physical examinations, and radiological assessments were performed pre- and postoperatively at six weeks, three months, six months, 12months, and annually thereafter. ResultsThere were 40 females (46 TKAs) and 40 males (45 TKAs) in the study cohort. The left knee accounted for 52.7% of the surgeries. The average body-mass index (BMI) was 31.8kg/m2. Knee Society Scores obtained at the latest follow-up showed 96.4% and 95.5% good-to-excellent results respectively for the Knee and Function sub-scores. Radiological assessment showed that all Knee Society roentgenographic scores were below 10, without any evidence of impending or possible failure. Only one revision was required in this cohort for a patient suffering a deep chronic infection. At seven years, the Kaplan–Meier survivorship analysis revealed a 100% survivorship for aseptic loosening and a 98.9% survivorship for infection and revision of the components for any reason. ConclusionThis study demonstrated that TKA with short cemented stems resulted in good functional, clinical, and radiological outcomes for up to seven years for patients requiring complex TKA.

Short-Term Results of Ultra-Short Anatomic vs Ultra-Short Non-Anatomic Proximal Loading Uncemented Femoral Stems

BackgroundQuestion arises as to whether rigid fixation of ultra-short anatomic or ultra-short non-anatomic proximal loading uncemented femoral stem can be obtained without diaphyseal stem fixation. The purpose of this study is to compare the short-term clinical results, radiographic results, revision and survival rates, and complication rates of ultra-short anatomic versus ultra-short non-anatomic uncemented femoral stems. MethodsThis study consisted of 50 patients (56 hips) in the ultra-short anatomic uncemented stem group (mean age 61.4 ± 14.7 years) and 50 patients (56 hips) in the ultra-short non-anatomic uncemented stem group (mean age 59.5 ± 15.2 years). The mean follow-up was 3.4 years (range 3-4) in the ultra-short anatomic stem group and 3.5 years (range 3-4) in the ultra-short non-anatomic stem group. ResultsAt the final follow-up, the mean Harris hip scores (92 vs 93 points), Western Ontario and McMaster Universities Osteoarthritis scores (16 vs 15 points), University of California at Los Angeles activity scores (6.5 vs 6.8 points), the incidence of thigh pain (0% vs 4%), revision rates (0% vs 4%), aseptic loosening rate (0% vs 2%), and complication rates (2% vs 4%) were not significantly different between 2 groups. ConclusionBoth ultra-short anatomic and ultra-short non-anatomic proximal loading uncemented femoral stems obtained rigid fixation without diaphyseal stem fixation in the short-term follow-up. This finding suggests that an ultra-short anatomic uncemented femoral stem can be replaced with an ultra-short non-anatomic uncemented stem to reduce inventory of the femoral stems, and consequently reduce manufacturing and delivery cost of these femoral stems.

Do Porous Tantalum Metaphyseal Cones Improve Outcomes in Revision Total Knee Arthroplasty?

BackgroundSome authors have advocated for use of porous tantalum metaphyseal cones to manage bone defects during revision total knee arthroplasty (TKA). The purpose of this study is to compare results with porous metaphyseal cones to results with traditional hybrid stem fixation in revision TKA. MethodsForty-nine patients undergoing revision TKA with femoral and/or tibial metaphyseal cones (39 tibial only, 3 femoral only, 7 both) were matched by surgical indication to 49 patients undergoing revision TKA with a traditional hybrid stem (non-cone) technique. Clinical and radiographic outcomes were compared at a minimum of two-year follow-up (mean 3.5 years) with adjustment for baseline characteristics. ResultsPre-revision bone defects and most baseline demographics were similar between the cone and non-cone cohorts suggesting appropriate matching. Patients in the non-cone cohort had greater pre- to post-operative increases in Knee Society Score (37.2 ± 18.6 vs 28.4 ± 17.8, P = .010) and Knee Society Functional Score (30.4 ± 24.3 vs 13.1 ± 27.6, P = .003). The cohorts did not differ with respect to complications, subsequent reoperation, subsequent revision, patient satisfaction, tibial overhang, the presence of radio-sclerotic lines, cortical hypertrophy around the stems, or tibial subsidence. ConclusionIn this series, metaphyseal cones were not associated with superior outcomes at short-term follow-up. Given the increased cost associated with use of cones compared to traditional techniques, this study cannot support the routine use of metaphyseal cones in revision TKA. Longer-term follow-up will be necessary to determine if construct durability differs over the long term.

Revision Total Hip Arthroplasty With a Monoblock Splined Tapered Grit-Blasted Titanium Stem

BackgroundIn revision total hip arthroplasty (THA), proximal femoral bone loss creates a challenge of achieving adequate stem fixation. The purpose of this study was to examine the outcomes of a monoblock, splined, tapered femoral stem in revision THA. MethodsOutcomes of revision THA using a nonmodular, splined, tapered femoral stem from a single surgeon were reviewed. With a minimum of 2-year follow-up, there were 68 cases (67 patients). Paprosky classification was 3A or greater in 85% of the cases. Preoperative and postoperative Harris Hip Scores (HHS), radiographic subsidence and osseointegration, limb length discrepancy, complications, and reoperations were analyzed. ResultsThe Harris Hip Score improved from 37.4 ± SD 19.4 preoperatively to 64.6 ± SD 21.8 at final follow-up (P < .001). There were 16 revision procedures—8 for septic indications and 8 for aseptic indications. Subsidence occurred at a rate of 3.0% and dislocation at 7.4%. Limb length discrepancy of more than 1 cm after revision was noted in 13.6% of patients. Bone ingrowth was observed in all but 4 patients (94.1%). At 4-year follow-up, Kaplan-Meier estimated survival was 72.9% (95% confidence interval [CI] 57.0-83.8) for all causes of revision, 86.6% (95% CI 72.0-93.9) for all aseptic revision, and 95.5% (95% CI 86.8-98.5) for aseptic femoral revision. ConclusionAlthough complications were significant, revision for femoral aseptic loosening occurred in only 3 patients. Given the ability of this monoblock splined tapered stem to adequately provide fixation during complex revision THA, it remains a viable option in the setting of substantial femoral bone defects.

Optimizing Mechanical Alignment With Modular Stems in Revision TKA

BackgroundAlthough mechanical alignment is critical for optimal function and long-term implant durability, the role of modular stems in achieving ideal alignment is unclear. MethodsWe identified 319 revision total knee arthroplasty from 2003-2013, for which stem length, stem diameter, and stem fixation method were recorded prospectively. Three-dimensional canal-filling ratio, the product of canal-filling ratio at the stem tip in both the anteroposterior and lateral planes, and alignment were measured radiographically. ResultsIdeal alignment of the femur was considered to be 95° in the anteroposterior (AP) plane and from 1° of extension to 4° of flexion in the lateral plane, and ideal tibial alignment was considered to be 90° in the AP plane. Even after accounting for difference in stem size and canal-fill, ideal AP alignment was more reliably achieved with press-fit stems. ConclusionFurthermore, increased engagement of the diaphysis and its anatomical axis with canal-filling stems facilitates accurate alignment.

Aseptic loosening of total ankle replacement : One-stage revision ankle arthroplasty

To revise one or both loosened prosthesis components, to achieve postoperative pain relief, and preserve ankle range of motion. Aseptic loosening of the tibial and/or talar ankle prosthesis components without substantial bone defect of the tibial or talar bone stock. General surgical or anesthesiological risks, infections, critical soft tissue conditions, nonmanageable hindfoot instability, neurovascular impairment of the lower extremity, neuroarthropathy (e. g. Charcot arthropathy), substantial nonreconstructable osseous defects with or without cysts on the tibial and/or talar side, non-compliance, patients with primary total ankle replacement (TAR) using intramedullary fixation (stem fixation), patients with severely reduced bone quality, insulin-dependent diabetes mellitus, smoking, unrealistic patient expectations, patients with high activity in sports. Exposure of the ankle joint using the previous incision (anterior or lateral transfibular approach). Mobilization and removal of loosened prosthesis component. Careful debridement of bone stock at bone-prosthesis interface. Determination of prosthesis component size. Implantation of definitive prosthesis components. Wound closure in layers. Asoft wound dressing is used. Thromboprophylaxis is recommended. Patient mobilization starts at postoperative day1 with 15 kg partial weight bearing using astabilizing walking boot or cast for 6weeks. Following clinical and radiographic follow-up at 6weeks, full weight bearing is initiated gradually. Between January 2007 and December 2012 aone-stage revision TAR was performed in 14patients with amean age of 52.7± 12.0years (29.8-70.5years). The indication for revision surgery was aseptic loosening of one or both prosthesis components. The mean time between the initial TAR and revision surgery was 5.9± 2.9years (2.0-11.5years). In 2patients atibiotalocalcaneal arthrodesis was performed due to painful aseptic loosening of revision TAR. In all patients asignificant pain relief was observed.

Effect of Stem Size and Fixation Method on Mechanical Failure After Revision Total Knee Arthroplasty

BackgroundAlthough the need for stemmed components is well accepted to improve mechanical survival in revision total knee arthroplasty (TKA), the ideal fixation method and stem design remain controversial. MethodsWe performed a retrospective review of 223 patients who underwent revision TKA in whom stemmed components had not been used previously and with a mean follow-up of 61.6 months, including 108 components with fully cemented stems and 316 components with “hybrid” press-fit stems. ResultsBased on a time to event model, risk for mechanical failure was equivalent for both cemented and hybrid stems (relative risk, 0.991; P = .98). Young age was the single greatest risk factor for mechanical failure (P = .006). Although there was a trend toward increased failure with cemented stems in patients aged <65 years, there was no significant difference in risk after accounting for covariates (relative risk, 1.4; P = .50). Intramedullary canal fill, not stem length or diameter, was the strongest predictor of failure with hybrid stems, and risk was reduced by 41.2% for each additional 10% canal fill. ConclusionIn conclusion, both cemented and hybrid modular stems are viable options in revision TKA. Surgeons should attempt to maximize canal filling of hybrid stems to obtain a solid press-fit. In addition, further studies are needed to evaluate the long-term survival of cemented stem fixation in young patients.

Tapered modular fluted titanium stems for femoral fixation in revision total knee arthroplasty

Consensus regarding femoral stem fixation options in revision total knee arthroplasty remains controversial. Tapered, modular, fluted titanium (TMFT) stems have an excellent track record in total hip arthroplasty for their ability to provide axial and rotational stability in situations of compromised host bone. We present 3 successfully treated cases in which the Food & Drug Administration granted permission to use custom TMFT stems in situations of failed femoral fixation in multiple revised knees. These stems hold promise to achieve stable fixation in revision total knee arthroplasty where host metadiaphyseal bone is deficient. Implant manufactures should consider dedicating future resources to create adapters that can link existing successful TMFT stems currently used in hip arthroplasty to revision total knee components when host bone is severely compromised.

Outcome in design-specific comparisons between highly crosslinked and conventional polyethylene in total hip arthroplasty

Background and purpose — Most registry studies regarding highly crosslinked polyethylene (XLPE) have focused on the overall revision risk. We compared the risk of cup and/or liner revision for specific cup and liner designs made of either XLPE or conventional polyethylene (CPE), regarding revision for any reason and revision due to aseptic loosening and/or osteolysis.Patients and methods — Using the Nordic Arthroplasty Register Association (NARA) database, we identified cup and liner designs where either XLPE or CPE had been used in more than 500 THAs performed for primary hip osteoarthritis. We assessed risk of revision for any reason and for aseptic loosening using Cox regression adjusted for age, sex, femoral head material and size, surgical approach, stem fixation, and presence of hydroxyapatite coating (uncemented cups).Results — The CPE version of the ZCA cup had a risk of revision for any reason similar to that of the XLPE version (p = 0.09), but showed a 6-fold higher risk of revision for aseptic loosening (p < 0.001). The CPE version of the Reflection All Poly cup had an 8-fold elevated risk of revision for any reason (p < 0.001) and a 5-fold increased risk of revision for aseptic loosening (p < 0.001). The Charnley Elite Ogee/Marathon cup and the Trilogy cup did not show such differences.Interpretation — Whether XLPE has any advantage over CPE regarding revision risk may depend on the properties of the polyethylene materials being compared, as well as the respective cup designs, fixation type, and follow-up times. Further research is needed to elucidate how cup design factors interact with polyethylene type to affect the risk of revision.

The effect of cement on hip stem fixation: a biomechanical study.

This study presents the numerical analysis of stem fixation in hip surgery using with/without cement methods since the use of cement is still controversial based on the clinical studies in the literature. Many different factors such as stress shielding, aseptic loosening, material properties of the stem, surgeon experiences etc. play an important role in the failure of the stem fixations. The stem fixation methods, cemented and uncemented, were evaluated in terms of mechanical failure aspects using computerized finite element method. For the modeling processes, three dimensional (3D) femur model was generated from computerized tomography (CT) images taken from a patient using the MIMICS Software. The design of the stem was also generated as 3D CAD model using the design parameters taken from the manufacturer catalogue. These 3D CAD models were generated and combined with/without cement considering the surgical procedure using SolidWorks program and then imported into ANSYS Workbench Software. Two different material properties, CoCrMo and Ti6Al4V, for the stem model and Poly Methyl Methacrylate (PMMA) for the cement were assigned. The material properties of the femur were described according to a density calculated from the CT images. Body weight and muscle forces were applied on the femur and the distal femur was fixed for the boundary conditions. The calculations of the stress distributions of the models including cement and relative movements of the contacts examined to evaluate the effects of the cement and different stem material usage on the failure of stem fixation. According to the results, the use of cement for the stem fixation reduces the stress shielding but increases the aseptic loosening depending on the cement crack formations. Additionally, using the stiffer material for the stem reduces the cement stress but increases the stress shielding. Based on the results obtained in the study, even when taking the disadvantages into account, the cement usage is more suitable for the hip fixations.

Isolated acetabular revision with femoral stem retention after bipolar hip arthroplasty.

In bipolar hemiarthroplasty, migration of the outer cup component into the acetabular cup, with evidence of severe osteolysis in the acetabulum, commonly occurs without loosening of the femoral component. The merits of retaining the stable femoral component in these cases have been debated. Our study aimed to determine whether revision of the acetabular component in isolation could be successfully performed. The data of 54 patients (61 hips), 44 women, and 10 men, aged 67.7 (range 47-86) years at the time of the index revision, were analyzed. The average time from primary operation to revision surgery was 14.9 (range 1.0-27.0) years, with an average follow-up time after revision of 5.2 (range, 1.0-18.7) years. Indications for acetabular revision included migration of the outer cup component (N = 55), disassembly of the bipolar cup (N = 4), and recurrent dislocation (N = 2). Fixation of the femoral stem was cementless in 49 hips and cemented in 12. Bone grafting for osteolysis of the proximal femur around the stem was performed in six hips. An acetabular reinforcement ring with a cemented cup was used in 31 hips, with cementless cup fixation in 29 hips, and cemented cup in one case. On average, the Harris hip score improved from 57.0 ± 21.6 to 87.4 ± 6.40 points after revision. Two cases of femoral periprosthetic fracture were treated with osteosynthesis 3year post-revision. There was no evidence of loosening of the femoral stem or subsidence, with a non-progressive radiolucent line <2mm identified in one case. There was no incidence of dislocation or deep infection, and all components were judged to be stable at the final follow-up. Isolated acetabular revision can be reliably performed in cases of failed bipolar hemiarthroplasty with a well-fixed femoral component.

Is the humeral stem useful in anatomic total shoulder arthroplasty?

PurposeTraditionally and since Neer, the humeral side of shoulder arthroplasty consisted of a stemmed component but the real need for stem fixation in total shoulder arthroplasty (TSA) has barely been investigated. The current study evaluated the clinical and radiological outcomes with a stemless TSA.MethodsForty-seven patients, 20 female and 27 male patients with an average age of 63, were selected in four orthopaedic centres during a four year period, and implanted with a humeral head prosthesis with a three-fin design and titanium coating. Aetiologies were: primary osteoarthritis (29), fracture sequelae (12) and avascular osteonecrosis (6). Minimum follow-up was two years (range 24–51 months). The patients were evaluated with the Constant score (CS) and radiological exams.ResultsTwo patients had revision of the implants, one for persistent pain and one for secondary massive rotator cuff tear. At the final follow-up, the mean CS was 69, with an average gain of 36. All parameters improved with a foremost in pain relief. Mean satisfaction rate was 87%. Average anterior active elevation was 131° with a gain of 48. Radiologic evaluations showed stable implants in all cases. However, 17 cases demonstrated radiolucent areas, particularly superior and lateral to the implant, which neither decreased nor increased with time. No revisions were related to humeral component loosening.ConclusionsStemless TSA provides the same results as compared to TSA with a humeral stem. We are still unsure as to the nature of the lucent zones and we are continuing our investigation to better understand this radiological phenomenon.

Tapered uncemented HA-coated femoral stems: a radiological study

INTRODUCTION: Numerous national joint registries demonstrate a trend towards the use of uncemented femoral components in total hip arthroplasty. While the results of first-generation uncemented, and some of the second-generation uncemented implants have been unacceptably poor, others, including the fully hydroxyapatite (HA) coated femoral stems, have been excellent with survival rates of greater than 95% at 20 years. Component longevity is largely related to robust stem fixation to native bone. Adequate stem fixation to the native bone can be determined by clinical assessment and radiological signs of osteointegration. The absence of these radiological signs might be an indication of early loosening. With this in mind, we performed a radiological analysis of the osteointegration of uncemented fully HA-coated femoral stems inserted at our arthroplasty unit. MATERIALS AND METHODS: We performed a retrospective chart and radiological review of patients who had undergone total hip replacement with an uncemented fully HA-coated femoral component over a five-year period. Between March 2003 and March 2008, 80 patients met the criteria used, and radiological changes around the femoral stem were analysed. The mean patient age at the time of surgery was 59 years, and the most common presenting pathology was avascular necrosis (43%). The immediate post-operative, six-week, six-month, one-year and five-year radiographs were evaluated. RESULTS: There were no revisions for stem-related complications. The earliest radiological signs of osteointegration, which included remodelling and trabecular bone formation, were noticed as early as six weeks post-operatively in 4%. At six months and one year, these had increased to 63% and 100% respectively. Thereafter, the radiographs demonstrated minimal change and maintained so-called 'radiological silence'. CONCLUSION: Osteointegration of fully HA-coated stems occurs in a predictable manner, and is noted in radiographs as early as the six-week follow-up period. Signs of osteointegration can be used as reliable indicators of solid femoral stem fixation after total hip replacement

Porous Femoral Fixation in Total Hip Arthroplasty with Short Anatomical Stem: Radiographic Evaluation.

BackgroundHip prostheses with short anatomical stems were designed for metaphyseal fixation and to spare bone stock. We present a study of a short anatomical femoral stem used in all age groups of patients with Dorr A and B type of femora.MethodsWe reviewed radiographs of 85 hips in 74 patients who had a cementless total hip arthroplasty with a short anatomical 80 mm femoral stem designed to achieve pure metaphyseal fixation. A ream-only technique was used for femoral canal preparation in all patients. At each follow-up, radiological evaluation was performed for stem alignment, proximal metaphyseal fill, subsidence, status of biological fixation of the femoral stem, heterotrophic ossification, radiolucency, osteolysis, and limb length discrepancy of the stem. Acetabular components were evaluated for positioning, acetabular bone coverage, and radiolucent and osteolytic lesions.ResultsThe final mean alignment of femoral stem was 2° valgus. The average intramedullary fill by the stem at the proximal level of the lesser trochanter was 93% in the coronal plane and 88% in the sagittal plane. No components were considered to be undersized. Thirteen hips (15.2%) presented radiolucent lines (10 hips < 1 mm in width and 3 hips [3.5%] 2 mm in width) and 100% of them were not progressive with respect to the last follow-up radiograph. All of the stems had excellent fixation by demonstrating bone ingrowth at the latest follow-up. At the last follow-up, heterotopic ossification was noted in 5 hips. The mean preoperative limb length discrepancy was 9.3 mm and the mean postoperative discrepancy was 3.8 mm. The mean acetabular component angle of the 85 components was 41.2° with a mean anteversion of 22.1°. At the last follow-up, there were no revisions of the femoral component. One patient, 25 months after the index operation, required an acetabular component revision because of recurrent hip dislocation. There were no radiological signs of loosening in any of the short-stem prostheses at the last examination.ConclusionsThe short, metaphyseal-fitting anatomic cementless femoral stem provided stable fixation without relying on diaphyseal fixation.

Survivorship of Metaphyseal Sleeves in Revision Total Knee Arthroplasty

BackgroundMetaphyseal fixation has promising early results in providing component stability and fixation in revision total knee arthroplasty (TKA). However, there are limited studies on midterm results of metaphyseal sleeves. We analyzed complications, rerevisions, and survivorship free of revision for aseptic loosening of metaphyseal sleeves in revision TKA. MethodsTwo hundred eighty patients with 393 metaphyseal sleeves (144 femoral, 249 tibial) implanted during revision TKA from 2006-2014 were reviewed. Sleeves were most commonly cemented (55% femoral, 72% tibial). Mean follow-up was 3 years, mean age was 66 years, and mean body mass index was 34 kg/m2. Indications for revision TKA included 2-stage reimplantation for deep infection (37%), aseptic loosening of the tibia (14%), femur (12%), or both components (9%), and instability (14%). ResultsThere was a 12% rate of perioperative complications, most commonly intraoperative fracture (6.5%). Eight sleeves (2.5%) required removal: 6 (2%) during component resection for deep infection (all were well-fixed at removal) as well as 1 (0.8%) femoral sleeve and 1 (0.8%) tibial sleeve for aseptic loosening. Five-year survivorship free of revision for aseptic loosening was 96% and 99.5% for femoral and tibial sleeves, respectively. Level of constraint, bone loss, sleeve and/or stem fixation, and revision indication did not significantly affect outcomes. ConclusionMetaphyseal sleeve fixation to enhance component stability during revision TKA has a 5-year survivorship free of revision for aseptic loosening of 96% and 99.5% in femoral and tibial sleeves, respectively. Both cemented and cementless sleeve fixation provides reliable durability at intermediate follow-up.

Not all cemented femoral stems are created equal: A selection algorithm

Cementless femoral stem fixation predominates in total hip arthroplasty with North America and includes various designs designated as fit and fill or double taper proximally porous coated stems, parallel sided taper wedge or “blade” stems, tapered rectangular cross-section Zweymuller-type stems, fully-porous coated cylindrical stems, Wagner-style conical shape splined titanium stems, and modular proximal sleeve stems. Regardless of the stem type, the essential tenets of long-term fixation and osseointegration remain obtaining adequate mechanical stability and intimate prosthesis contact with viable host bone. This manuscript will detail a selection an algorithm for selection of an appropriate femoral stem for a given patient anatomy.

Primary stability of unicompartmental knee arthroplasty under dynamic flexion movement in human femora

BackgroundThe objective of our study was to evaluate the impact of a trabecular stem fixation versus a cortical teeth fixation technique on the primary stability of cemented unicompartmental femoral components under dynamic flexion movement loading conditions in human femora. MethodsTen fresh-frozen human knees of a mean donor age of 73.9years were used to perform medial unicompartmental knee arthroplasty under a less invasive parapatellar surgical approach. The femora were divided into two groups of matched pairs based on comparable trabecular bone mineral density. To assess the primary stability, a new method based on a combination of dynamic flexion movement, double-peak loading simulating stair climbing, kinematic analysis of the femoral component migration relative to the bone and an evaluation of the cement layer by fragments cut through the implant-cement-bone interface in the sagittal plane of the medial condyle was introduced. FindingsFor the “trabecular stem fixation” technique the mean load to failure was 2340 (SD 650) N and for “cortical teeth fixation” it was 1080 (SD 455) N, with a substantially enhanced dynamic fixation strength for the “trabecular stem fixation” (p=0.008). In the distal area the cement layer of the “trabecular stem fixation” showed a significant decreased thickness compared to the “cortical teeth fixation” (p=0.029), while a substantially deeper cement penetration (p=0.044) has been achieved for the “trabecular stem fixation”. InterpretationFrom our observations, we conclude that there is a significantly enhanced primary stability with a “trabecular stem fixation” compared to a “cortical teeth fixation” technique of cemented unicompartmental femoral components, in terms of dynamic failure load and migration characteristics.

No Difference in Implant Micromotion Between Hybrid Fixation and Fully Cemented Revision Total Knee Arthroplasty: A Randomized Controlled Trial with Radiostereometric Analysis of Patients with Mild-to-Moderate Bone Loss.

In revision total knee arthroplasty (TKA), the femoral component and tibial baseplate are usually cemented. However, stems can be fixed either with cement or with a press-fit technique, with the latter resulting in hybrid fixation. There is no consensus on the preferred stem fixation technique. Therefore, we compared the stability of cemented TKA implants with the stability of TKA implants fixed with the hybrid technique in a prospective randomized trial using radiostereometric analysis (RSA). Thirty-two patients with a Type-I or II bone defect who needed revision TKA and were randomly allocated at the time of surgery into either the cemented or hybrid-fixation group were included in the study. The radiographs for the RSA were obtained during hospitalization (baseline); at 6 weeks; and at 3, 6, 12, and 24 months. Migration of the femoral and tibial implants was measured using model-based RSA and expressed along or around the 3 orthogonal axes and as total translation (TT) and total rotation (TR). Clinical results were evaluated using the Knee Society Score (KSS), the Knee injury and Osteoarthritis Outcome Score (KOOS), active flexion, and visual analog scale (VAS) scores for pain and satisfaction. Mann-Whitney and chi-square tests were used to compare migration and clinical outcomes between the cement and hybrid techniques. At 24 months, no difference in median migration or the number of migrating components was found between the cemented and hybrid-fixation groups. In each group, approximately one-third of the tibial components had total rotation of >1°. The clinical scores did not differ between the techniques. At 24 months after revision TKAs, cemented and hybrid-fixation replacements were equally stable. Unexpectedly, both groups had implants with >1 mm or >1° of micromotion although there were no clinical or radiographic signs of loosening. Whether these findings indicate the possibility of loosening with longer follow-up remains to be investigated. Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Satisfactory Results of the Exeter Revision Femoral Stem Used for Primary Total Hip Arthroplasty

BackgroundThe Exeter cemented femoral stem has demonstrated excellent clinical and radiographic outcomes as well as long-term survivorship free from aseptic loosening. A shorter revision stem (125 mm) with a 44 offset became available for the purpose of cement-in-cement revision situations. In certain cases, this shorter revision stem may be used for various primary total hip arthroplasties (THAs) where the standard length stem would require distally reaming the femoral canal. We sought to report on the early to midterm results of this specific stem when used for primary THA regarding (1) clinical and radiographic outcomes, (2) complications, and (3) survivorship. MethodsTwenty-nine patients (33 hips) underwent a hybrid THA using the smaller revision Exeter cemented femoral stem. Twenty-five patients (28 hips) had at least 2 years of follow-up and were assessed for clinical and radiographic outcomes. All 33 hips were included in the analysis of complications and survivorship. The Kaplan-Meier survivorship was performed using revision for all causes and for aseptic loosening as the end points. ResultsThe average clinical follow-up was 4 years (range, 2-7). Harris Hip Scores improved from a mean preoperative value of 56 (range, 23-96) to 90 (range, 51-100) at the latest follow-up. All patients demonstrated superior cement mantles with no signs of loosening. One patient suffered a B2 periprosthetic fracture and 1 patient experienced 2 episodes of instability. The 5-year Kaplan-Meier survivorship was 96.7% for all causes of revision and was 100% using aseptic loosening as the end point. ConclusionThe shorter Exeter revision cemented femoral stem has favorable early to midterm clinical and radiographic outcomes when used for primary THA with a low complication rate and is a viable option in patients with narrow femoral canals where uncemented stem fixation is not desired.