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Successful osseointegration of press-fit implants depends on the initial stability, often measured by the micromotions between the implant and bone. A good primary stability can be achieved by optimizing the compressive and frictional forces acting at the bone-implant interface. The frictional properties of the implant-bone interface, which depend on the roughness and porosity of the implant surface coating, can affect the primary stability. Several reversible (elastic) and non-reversible (permanent) deformation processes take place during frictional loading of the implant-bone interface. In case of a rough coating, the asperities of the implant surface are compressed into the bone leading to mechanical interlocking. To optimize fixation of orthopaedic implants it is crucial to understand these complex interactions between coating and bone. The objective of the current study was to gain more insight into the reversible and non-reversible processes acting at the implant-bone interface. Tribological experiments were performed with two types of porous coatings against human cadaveric bone. The results indicated that the coefficient of friction depended on the coating roughness (0.86, 0.95, and 0.45 for an Ra roughness of 41.2, 53.0, and a polished surface, respectively). Larger elastic and permanent displacements were found for the rougher coating, resulting in a lower interface stiffness. The experiments furthermore revealed that relative displacements of up to 35 µm can occur without sliding at the interface. These findings have implications for micromotion thresholds that currently are assumed for osseointegration, and suggest that bone ingrowth actually occurs in the absence of relative sliding at the implant-bone interface.

Background: Optimized surgical fixation and meniscal stabilization during rehabilitation increase healing success. However, the latest generation of all-inside devices has not yet been biomechanically compared with inside-out suture tape (IO-ST) repair. Hypothesis: (1) The contact area of a suture anchor (SA) would compensate for a meniscal defect better than polyether ether ketone anchors (PA); (2) adjustable tensioning for all-inside meniscal repair fixation would result in higher initial load than IO-ST repair; and (3) stiffer constructs would decrease secondary displacement. Study Design: Controlled laboratory study. Methods: This study investigates human menisci (N = 39) via microscopic imaging and a biomechanical testing protocol. For the imaging protocol, needles of an all-inside SA or PA device and an IO-ST device were inserted after staining to measure the iatrogenic defect created by the needle insertion (n = 20) and the length, width, and meniscus contact area of deployed all-inside anchors (n = 6). For biomechanical testing, menisci with longitudinal bucket handle tears were prepared, and single stitches were repaired (each n = 9). After suture tensioning (50 N) and fixation, initial load, initial stiffness, and relief displacement were measured. Constructs underwent cyclic loading between 2 and 20 N, with 10,000 cycles (0.75 Hz), and stiffness and displacement were measured. Ultimate stiffness and load-to-failure were analyzed at 3.15 mm/sec. Results: All-inside needles created greater iatrogenic meniscal defects (P < .001) than IO-ST repair. While PAs were longer (P < .001), SAs were wider with a greater meniscal contact area (both P < .001). IO-ST repair resulted in the lowest initial load (P < .001) and relief displacement (P < .001), whereas SA repair resulted in a higher initial load (P < .007) and stiffness (P < .023) than PA repair. The overall stiffer SA fixation (P < 001) significantly reduced cyclic displacement compared with other repairs (P < .044). The PA group failed due to an anchor fracture at a significantly lower load (84.3 ± 10.7 N; P < .001) than the IO-ST (136.4 ± 10.5 N) and the SA repair (122.1 ± 17.5 N), with a suture-based failure mode. The ultimate stiffness of SA constructs was higher (P < .045) than that of other repairs. Conclusion: While all-inside devices showed improved primary stability, the IO-ST construct demonstrated the highest load-to-failure. In a human cadaveric model, meniscal repair with a more compact and conforming SA was stiffer and reduced cyclic displacement compared with PA and IO-ST repair. Clinical Relevance: All-inside SA repair improved primary stability. Future clinical series will define the overall significance of healing rates.

Background: Primary implant stability is important for successful outcomes after uncemented total ankle replacement (TAR). However, the influence of patient-specific bone density on TAR performance is poorly understood, especially for implants that rely on press-fit for stable primary fixation. Our goal was to evaluate how bone density influences implant-bone interfacial micromotions in 3 press-fit tibial component designs by sampling from a TAR preoperative planning database using finite element analysis (FEA). Methods: FEA was conducted in 4 TAR patients with relatively low-density (n = 2, lowest 10% of a sample including 58 patients) and average-density (n = 2, midrange of sample) bone as assessed from deidentified patient CT scans. Three tibial implant designs were evaluated: a bone-sparing resurfacing implant, a cortex-sparing anterior approach monoblock stemmed implant, and a distal-reaming modular stemmed implant. Implants were inserted into tibia geometries obtained from the CT scans. Press-fit implantation was modeled first, followed by loadings from the stance phase of gait, and the associated micromotions were computed from the FEA output. Results: In general, patients with average-density bone had FEA predicted lower micromotions than patients with low-density bone. FEA suggests that implant fixation features had less influence on micromotions in patients with average-density bone, with peak micromotions ranging from 2 to 23 µm (3.1 ± 1.3 µm average micromotion). For patients with low-density bone, interfacial regions are predicted to experience micromotions exceeding the bony ingrowth threshold of 50 µm only for the resurfacing implant. Conclusion: We investigated the influence of bone density on implant-bone micromotions with varying primary fixation features using FEA. The model predicts that micromotions are less in average-density bone, regardless of implant fixation features. However, both stemmed devices showed lower micromotions in less-dense bone, albeit with the corresponding clinical trade-off of requiring more tibial bone removal. Clinical Relevance: The results presented here implicate the complementary role that local bone density plays in the primary fixation stability of uncemented TAR.

Background: Biomechanical assessment of meniscal repairs is essential for evaluating different meniscal suturing methods and techniques. The continuous meniscal suture technique is a newer method of meniscal repair that may have biomechanical differences compared with traditional techniques. Purpose: To evaluate the displacement, stiffness after cyclical loading, and load to failure for a continuous vertical inside-out meniscal suture versus a traditional vertical inside-out meniscal suture in a porcine medial meniscus. Study Design: Controlled laboratory study. Methods: A total of 28 porcine knees were acquired and divided into 2 test groups of 14 medial meniscus each. A 2.0-cm longitudinal red-white zone cut was made in the body of the medial meniscus for each knee. The continuous suture (CS) group received 4 vertical stitches performed with a continuous vertical meniscal suture technique, and the inside-out suture (IO) group received a traditional vertical suture with 4 stitches. Two traction tapes were passed between the sutures and positioned in the biomechanical testing fixture device. Each specimen underwent load-to-failure testing at 5 mm/s, and displacement, system stiffness, and maximum load to failure were compared between the groups. Results: The displacement after the cyclic test was 0.53 ± 0.12 and 0.48 ± 0.07 mm for the CS and IO groups, respectively. There was no significant difference between the groups (P = .2792). The stiffness at the ultimate load testing was 36.3 ± 1.9 and 35.3 ± 2.4 N/mm for groups CS and IO, respectively, with no significant difference between the groups (P = .2557). In the load-to-failure test, the ultimate load was 218.2 ± 63.9 and 238.3 ± 71.3 N in the CS and IO groups, respectively, with no significant group differences (P = .3062). Conclusion: A continuous vertical meniscal suture created a configuration for treating longitudinal meniscal lesions that was beneficial and biomechanically similar to a traditional vertical suture technique. Clinical Relevance: The study findings indicate that use of the continuous vertical inside-out meniscal suture technique is a possible therapeutic option.

PurposeConventional press-fit technique for anterior cruciate ligament reconstruction (ACLR) is performed with extraction drilling of the femoral bone tunnel and manual shaping of the patellar bone plug. However, the disadvantages of this technique include variation in bone plug size and, thus, the strength of the press-fit fixation, bone loss with debris distribution within the knee joint, potential heat necrosis, and metal wear debris due to abrasion of the guide wire. To overcome these disadvantages, a novel technique involving punching of the femoral bone tunnel and standardized compression of the bone plug was introduced. In this study, the fixation strength and apparent stiffness were tested and compared to that of the gold-standard interference screw fixation technique in three flexion angle configurations (0°/45°/90°) in a porcine model. We hypothesized that the newly developed standardized press fit fixation would not be inferior to the gold standard method.MethodsSixty skeletally mature porcine knees (30 pairs) were used. Full-thickness central third patellar tendon strips were harvested, including a patellar bone cylinder of 9.5 mm in diameter. The specimens were randomly assigned to 10 pairs per loading angle (0°, 45°, 90°). One side of each pair was prepared with the press-fit technique, and the contra-lateral side was prepared with interference screw fixation. Equivalent numbers of left- and right-sided samples were used for both fixation systems. A three-way multifactor ANOVA was carried out to check for the influence of (a) fixation type, (b) flexion angle, and (c) side of the bone pair.ResultsThe primary fixation strength of femoral press-fit graft fixation with punched tunnels and standardized bone plug compression did not differ significantly from that of interference screw fixation (p = 0.51), which had mean loads to failure of 422.4 ± 134.6 N and 445.4 ± 135.8 N, respectively. The flexion angle had a significant influence on the maximal load to failure (p = 0.01). Load values were highest in 45° flexion for both fixations. The anatomical side R/L was not a statistically significant factor (p = 0.79).ConclusionThe primary fixation strength of femoral press-fit graft fixation with punched femoral tunnels and standardized bone plug compression is equivalent to that of interference screw fixation in a porcine model. Therefore, the procedure represents an effective method for ACL reconstruction with patellar or quadriceps tendon autografts including a patellar bone plug.

In cementless Total Hip Arthroplasty (THA), achieving high primary implant fixation is crucial for the long-term survivorship of the femoral stem. While orthopedic surgeons traditionally assess fixation based on their subjective judgement, novel vibration-analysis fixation-monitoring techniques show promising potential in providing the surgeon with objective and quantifiable fixation measurements. This study presents a dynamic response measurement protocol for implant endpoint insertion and evaluates this protocol in the presence of artificial soft tissue. After the artificial femur was prepared in accordance with the THA protocol, the implant was inserted and progressively hammered into the cavity. The Pearson Correlation Coefficient (PCC) and Frequency Response Assurance Criterion (FRAC) corresponding to each insertion hammer hit were derived from the Frequency Response Functions (FRF) corresponding to each insertion step. The protocol was repeated with the artificial femur submerged in artificial soft tissue to imitate the influence of anatomical soft tissue. The FRAC appeared overall more sensitive than the PCC. In the presence of the artificial soft tissue the technique yielded higher PCC and FRAC values earlier in the insertion process. The measurements with artificial soft tissue produced FRFs with fewer peaks, lower resonance frequencies, and overall higher damping factors. The soft tissue appears to limit the fixation-change detection capabilities of the system and a promising potential remedy to this limitation is suggested.

Background The optimal baseplate size for reverse shoulder arthroplasty in patients with varying glenoid dimensions remains controversial. In this study, we evaluated the biomechanical effects of adjusting baseplate size to different glenoid dimensions on primary fixation stability and analyzed the structural relationship between the baseplate and glenoid. Methods We evaluated the primary fixation stability and structural relationship of glenoid components with two circular baseplate sizes (25 mm vs. 29 mm) in different glenoid sizes (small vs. large) using finite element analysis. Three-dimensional finite element models were constructed from 14 cadaveric scapulae and glenoid components with 25‑ and 29‑mm baseplates. The relative micromotion of the bone–baseplate interface at measurement points 1–4, bone stress distribution under the baseplate and around the screws, contact surface area between bone and the baseplate back surface, contact surface area between bone and screws, and length of supporting bone stock (LSBS) for screws were analyzed. Results In small glenoids, relative micromotion and maximum bone stress were significantly greater with the 29‑mm baseplate than with the 25‑mm baseplate. Bone–screw contact surface and LSBS for anterior and posterior screws were significantly greater with the 25‑mm baseplate. In large glenoids, there were no significant differences between baseplate sizes. Conclusions Compared with the 29‑mm baseplate, the 25‑mm baseplate improved primary fixation stability in small glenoids through increased bone–screw contact and LSBS of the anterior and posterior screws. In the large glenoid, baseplate size did not significantly affect the primary fixation stability of the glenoid component. In the small glenoid, adjusting the baseplate size using a small baseplate matching the anatomical size may improve primary fixation stability of the glenoid component. Optimizing bone-screw contact and LSBS is critical for baseplate stability in the small glenoid. However, adjusting the baseplate size to the glenoid does not affect the primary fixation stability in the large glenoid with sufficient bone stock. Baseplate size can be selected with greater flexibility in the large glenoid without compromising primary fixation stability.

Objective: This study evaluated the effects of bony increased offset (BIO) and metallic augments (MAs) on primary reverse shoulder arthroplasty (RSA) baseplate stability in cadaveric specimens with variable bone densities. Methods: Thirty cadaveric specimens were analyzed in an imaging and biomechanical investigation. Computed tomography (CT) scans allowed for preoperative RSA planning and bone density analysis. Three correction methods of the glenoid were used: (1) corrective reaming with a standard baseplate, which served as the reference group (n = 10); (2) MA-RSA (n = 10); and (3) angled BIO-RSA (n = 10). Each augment group consisted of 10° (n = 5) and 20° (n = 5) corrections. Biomechanical testing included cyclic loading in an articulating setup, with optical pre- and post-cyclic micromotion measurements in a rocking horse setup. Results: There were no differences in bone density between groups based on CT scans (p > 0.126). The BIO-RSA group had higher variability in micromotion compared to the MA-RSA and reference groups (p = 0.013), and increased total micromotion compared to the reference group (p = 0.039). Both augmentations using 20° corrections had increased variance in rotational stability compared to the reference group (p = 0.043). Micromotion correlated with the subchondral bone density in the BIO-RSA group (r = −0.63, p = 0.036), but not in the MA-RSA (p > 0.178) or reference (p > 0.117) groups. Conclusions: Time-zero baseplate implant fixation is more variable with BIO-RSA and correlates with bone density. Corrections of 20° with either augmentation approach increase variability in rotational micromotion. The preoperative quantification of bone density may be useful before utilizing 20° of correction, especially when adding a bone graft in BIO-RSAs.

The sequence of reactions in the Calvin cycle, and the biochemical characteristics of the enzymes involved, have been known for some time. However, the extent to which any individual enzyme controls the rate of carbon fixation has been a long standing question. Over the last 10 years, antisense transgenic plants have been used as tools to address this and have revealed some unexpected findings about the Calvin cycle. It was shown that under a range of environmental conditions, the level of Rubisco protein had little impact on the control of carbon fixation. In addition, three of the four thioredoxin regulated enzymes, FBPase, PRKase and GAPDH, had negligible control of the cycle. Unexpectedly, non-regulated enzymes catalysing reversible reactions, aldolase and transketolase, both exerted significant control over carbon flux. Furthermore, under a range of growth conditions SBPase was shown to have a significant level of control over the Calvin cycle. These data led to the hypothesis that increasing the amounts of these enzymes may lead to an increase in photosynthetic carbon assimilation. Remarkably, photosynthetic capacity and growth were increased in tobacco plants expressing a bifunctional SBPase/FBPase enzyme. Future work is discussed which will further our understanding of this complex and important pathway, particularly in relation to the mechanisms that regulate and co-ordinate enzyme activity.

IntroductionTotal hip replacement has been established as a valid treatment option for displaced subcapital fractures. However, insufficient primary fixation may be the reason for early loosening in these osteoporotic patients. Primary fixation of the cup is usually achieved by press-fit fixation that can be enhanced using screws. Locking the screws into their respective cups may seem to improve the primary fixation of the construct, as locked plates proved superior fixation for osteoporotic fractures.MethodsThe study consisted of three groups: in each group, three cups were fixed into blocks of foam bone using press-fit technique. In the first group, no additional screws were used, in the second group two standard screws were inserted, while in the third group two acetabular screws were cemented into the cup to simulate locked screw fixation. Load was applied onto the rim of the acetabular component to cause shearing between the cup and the block. Cup fixation was examined by a loading machine that acquired load versus displacement. The stiffness (load vs. displacement) was calculated.ResultsScrews, either locked or non-locked, enhanced cup fixation by 26 % (p value <0.01). No significant changes were found between the locking and non-locking screws groups.DiscussionThese experimental results indicate that acetabular screws enhance primary cup fixation. This may become significant in conditions where the acetabular bone stock is suboptimal, such as when performing total hip arthroplasty after displaced subcapital fractures. However, there is no superiority for locked screws over standard screw fixation.