Abstract:Short stem prostheses provide conservative surgery and favorable metaphyseal load transmission. However, clinical longterm results are lacking. Therefore, in vitro trials can be used to predict bone-implant performance. In this in vitro study, primary stability and stress shielding of a new cementless short stem implant was evaluated in comparison to a straight stem using nine pairs of human cadaver femurs. Primary stability, including reversible micromotion and irreversible migration, was assessed in a hip si… Show more
“…This finding is consistent with those of previous biomechanical studies examining different types of femoral stems, such as anatomic, straight, custom made, short, and low modulus stems [7,16,[29][30][31][32]. The distal part of the anatomical stem is likely to support the load because of a proximal-distal mismatch (tight distal fit and fill), which may lead to proximal bone resorption and cortical hypertrophy [33].…”
Section: Discussionsupporting
confidence: 91%
“…Second, our test did not take into consideration dynamic loading cycle. The initial stability describes the reversible implant-bone micromotion during dynamic loading and early irreversible migration [16,34]. The presented relative axial displacements and rotations would include the elastic and irreversible motion.…”
Section: Discussionmentioning
confidence: 99%
“…The equivalent load where this moment was reached was calculated for each bone. In intact femur, the equivalent load was 1600 N [16]. In operated femurs, the equivalent load ranged from 1455 to 2111 N according to the altered head position after stem insertion.…”
Section: Loading Proceduresmentioning
confidence: 99%
“…Several reports indicate that short stems have good clinical performance [8,[10][11][12], reduced intraoperative complications [13], and stable fixation in osteoporotic bone [14,15]. Biomechanical studies of short stems have demonstrated a sufficient initial stability and an improved proximal load transfer [6,7,16]. These reports would help to expand the indications for short femoral stems; however, the abovementioned advantages of short stems are controversial.…”
“…This finding is consistent with those of previous biomechanical studies examining different types of femoral stems, such as anatomic, straight, custom made, short, and low modulus stems [7,16,[29][30][31][32]. The distal part of the anatomical stem is likely to support the load because of a proximal-distal mismatch (tight distal fit and fill), which may lead to proximal bone resorption and cortical hypertrophy [33].…”
Section: Discussionsupporting
confidence: 91%
“…Second, our test did not take into consideration dynamic loading cycle. The initial stability describes the reversible implant-bone micromotion during dynamic loading and early irreversible migration [16,34]. The presented relative axial displacements and rotations would include the elastic and irreversible motion.…”
Section: Discussionmentioning
confidence: 99%
“…The equivalent load where this moment was reached was calculated for each bone. In intact femur, the equivalent load was 1600 N [16]. In operated femurs, the equivalent load ranged from 1455 to 2111 N according to the altered head position after stem insertion.…”
Section: Loading Proceduresmentioning
confidence: 99%
“…Several reports indicate that short stems have good clinical performance [8,[10][11][12], reduced intraoperative complications [13], and stable fixation in osteoporotic bone [14,15]. Biomechanical studies of short stems have demonstrated a sufficient initial stability and an improved proximal load transfer [6,7,16]. These reports would help to expand the indications for short femoral stems; however, the abovementioned advantages of short stems are controversial.…”
“…Both variables can be measured precisely with experiments. For example, some biomechanical studies measured implant related stress with strain gauges [23–26] or implant-bone relative micromotions with inductive sensors [23, 26, 27]. However, implant fixation and bone flexibility of tibial revision knee implant modularity with regards to using sleeve and stem fixation individually and in combination has not yet been analyzed.…”
IntroductionRevision total knee arthoplasty often requires modular implants to treat bone defects of varying severity. In some cases, it may not be clear which module size and implant combination (e.g. sleeve and stem) should be chosen for a specific defect. When balancing implant stability and osseointegration against stress-shielding, it is important to choose an appropriate implant combination in order to match the given level of bone loss. Therefore, the necessity of stems in less extensive tibial defects and the advantage of different stems (lengths and stiffnesses) in combination with large metaphyseal sleeves on implant fixation and bone flexibility using a modular tibial revision knee system, were analyzed.Materials and methodsFour different stem combinations for a tibial revision implant (Sigma TC3, DePuy) were compared to an intact bone. Standardized implantation with n = 4 synthetic tibial bones was performed after generating an Anderson Orthopaedic Research Institute (AORI) Type T1 bone defect. Axial torques around the longitudinal stem axis and varus-valgus torques were separately applied to the implant. Micromotions of bone and implant were tracked using a digital image correlation system to calculate relative micromotions at the implant-bone-interface and bone deformation.ResultsOverall, using stems reduced the proximal micromotions of tray and sleeve compared to no stem, while reducing bone deformation proximally at the same time, indicating some potential for proximal stress-shielding compared to no stem. The potential for increased proximal stress-shield due to reduced proximal deformation appeared to be greater when using the longer stems. The location of lowest relative micromotions was also more distal when using long stems as opposed to short stems. A short stem (especially a smaller diameter short stem which still achieves diaphyseal fixation) displayed less potential for stress-shielding, but greater bone deformation distal to the tip of the stem than in the natural model.DiscussionIn the case of tibial revision implants with metaphyseal sleeves in a simple fully contained Type I defect, the absence of a stem provides for more natural bone deformation. However, adding a stem reduces overall relative micromotions, while introducing some risk of proximal stress-shielding due to increased diaphyseal fixation. Increasing stem length intensifies this effect. Short stems offered a balance between reduced micromotions and more proximal bone deformation that reduced the potential for stress-shielding when compared to long stems. A short stem with slightly smaller diameter (simulating a less stiff stem which still has diaphyseal fixation) increased the proximal bone deformation, but also tended to increase the bone deformation even further at the distal stem’s tip.ConclusionIn conclusion, further investigation should be conducted on fully contained Type I defects and the addition of a stem to offer better initial stability, taking into account stem length (i.e. shorter or more flexible stems) to su...
Cementless-surface-replacement-arthroplasty (CSRA) of the shoulder aims for functional joint restoration with minimal bone loss. Good clinical results have been reported, but due to the radiopaque metal shell no data is available on the structure, osseous integration, and bone stock under the implant. 14 hemi-CSRAs (4 manufacturers) with two geometries (crown [n ¼ 7]/ stem [n ¼ 7] fixation) were retrieved from patients undergoing revision due to glenoidal erosion. Histological sections cutting through the implant centre and bone were analysed. Quantitative histomorphometry evaluated the bone-implant-contact and compared the bone-area to native humeral retrievals (n ¼ 7). The boneimplant-interface was further assessed by scanning-electron-microscopy (SEM) and energy-dispersive-x-ray (EDX). Qualitative histology revealed a reduced and inhomogeneous bone stock. Obvious signs of stress shielding were observed with bone predominantly visible at the stem and implant rim. Quantitative histomorphometry confirmed the significantly reduced bone-area (9.2 AE 3.9% [crown 9.9 AE 4.3%, stem 8.6 AE 3.6%]) compared to native humeri (21.2 AE 9.1%; p < 0.05). Bone-implant-contact was 20.5 AE 5.8% (crown 21.8 AE 6.2%, stem 19.2 AE 5.6%) which was confirmed by SEM and EDX. Altogether, CRSA shows satisfactory bone ingrowth at the interface suggesting sufficient primary stability to allow osseous integration. However, clear signs of stress shielding with an inhomogeneous and reduced bone stock were observed. The impact on the long-termresults is unclear requiring further investigation. ß
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