Background and objective Mortality in patients with community-acquired pneumonia (CAP) continues to be high. Predictors of disease severity are required to improve patient management. This study investigated blood eosinophil levels at hospital admission as an independent biomarker for predicting severity of CAP.

This study documents the gross and histologic structure of the infrapatellar plica, and fat pad, and adds to an earlier report to the COA. The important new findings are that the femoral attachment...

Anterior knee pain (AKP), a multifactorial symptom complex, can be successfully treated surgically. A specific diagnosis often cannot be made, but the pain is linked to an unrecognized common factor in most patients: the mechanical behavior of the non-isometric contents of the anterior compartment of the knee-the fat pad (FP) and infrapatellar plica (IPP). The objective of this presentation is to describe an effective arthroscopic technique that treats AKP by addressing this common factor. The operation consists of release or resection of the IPP, or ligamentum mucosum, which tethers the FP. These highly innervated tissues act together as a hydraulic shock absorber, filling the anterior compartment. They stretch and deform at the extremes of knee motion because of constraint centrally by the non-isometric IPP. These dynamic changes in shape are eliminated when the plica is released or resected. Pain perception is from perturbed nociceptive nerves: pain relief results from de-tensioning these contained nerves by untethering the fat pad. Ascribing pain causation is problematic because morphologic change, such as inflammation, fibrosis, or contracture of these structures, is only present in a minority of cases. Nonetheless, AKP is both physically linked to these central, pain-sensitive structures and relieved by this operation.

We have described the infrapatellar plica (IPP) of the knee as a non-isometric ligament, attaching the fat pad (FP) to the femur. We had noted during knee arthroscopy that the IPP showed mechanical behavior, stretching and relaxing with motion, and holding the FP against the distal femur. We sought to visualize the kinematics of this behavior using fluoroscopy in cadavers and, in an Institutional Review Board approved study of human volunteers undergoing arthroscopy. With radiographic contrast injected in the IPP, we demonstrated in cadavers and in vivo, that the FP, highly innervated central body (CB), and IPP rotate around the femoral attachment (FA) of the IPP. The fluoroscopic films show a sequence starting in flexion, of stretch and distortion of the IPP and CB, then relaxation throughout mid arc and, remarkable stretch and distortion approaching full extension. This confirmed the non-isometric nature of the IPP. The overlying FP as seen in the second figure was tethered centrally by the IPP, and distorted throughout. Release of the IPP at the FA, which has been shown to reduce or eliminate anterior knee pain (AKP), eliminated the distortion of the FP. This kinematic, demonstrating mechanical perturbation of innervated central structures in the knee, introduces a new central vector, altering traditional patellofemoral biomechanics and suggests an altered concept in the causation of knee pain.

The infrapatellar plica (IPP) is considered to be an embryological remnant, a synovial fold of no mechanical importance. Its tissue characterization has not been described in the English literature. We had noted during knee arthroscopy that the IPP appeared ligament-like, and showed mechanical behavior, stretching and relaxing with motion, and holding the FP against the distal femur. Seeking to determine its gross and microscopic structure and link it to the observed behavior, we dissected 12 cadaver knees, noting for each the gross anatomy, histology of the IPP and attached fat pad (FP). According to the classification by Kim, the IPP types were: 8 separate, 1 split, 2 fenestrated, and 1 vertical septum. The IPP is a non-isometric ligament, with typical ligamentous structure at its femoral attachment (FA), a typical enthesis, and its rope-like central zone (CZ), primarily dense fibrous bundles of collagenous tissue. The structure of the attachment of the IPP to the FP at the central body (CB) is unique and consists of a splaying out of finger-like collagenous septa that merge with those of the FP. There is abundant elastase staining consistent with the distortion associated with knee motion. Lodged in the axillae of these septa are fat lobules similar to those of the FP, but containing a rich plexus of neurovascular bundles, which show wavy redundancy also correlating with the observed mechanical behavior. The IPP/CB/FP complex can be linked to chronic anterior knee pain in that arthroscopic release of the FA relieves the pain in most.

Axial torsional loads representative of gait and stair climbing conditions were applied to transverse sections of 8 uncemented postmortem retrievals and a high-resolution imaging system with digital image correlation was used to measure local micromotion along the bone-implant interface. For 7 components that were radiographically stable, there was limited micromotion for gait loading (1.42 ± 1.33 μm) that increased significantly (P = .0032) for stair climb loading (7.32 ± 9.96 μm). A radiographically loose component had motions on the order of 2.3 mm with gait loading. There was a strong inverse relationship between the amount of bone-implant contact (contact fraction) (P = .001) and micromotion. The uncemented components had greater contact fraction (41.8% ± 14.4% vs 11.5% ± 10.2%, P = .0033) and less median micromotion (0.81 ± 0.79 μm vs 28.8 ± 51.1 μm) compared to a previously reported study of cemented retrievals.

Purpose Anterior knee pain has been relieved by resection of the infrapatellar plica (IPP). The question is: How? The hypothesis is: the IPP acts as an intra-articular ligament, a mechanical link between the forces of knee motion, the fat pad (FP) and the distal femur, holding the FP captive through the arc of motion. Release of the IPP severs this link, allowing the highly innervated FP to move freely. This may allow any underlying pathologic process to heal. Method Anatomic dissection: In 12 knees, the extensor apparatus was released from the femur and retracted distally allowing relationships to be examined. Cadaver studies: Lateral fluoroscopy was used as well as direct arthroscopic visualization to control implantation of tantalum beads or radiographic contrast material in the FP and IPP. The knee was taken through the arc of motion repeatedly. The femoral attachment of the IPP was then released and knee motion repeated. Traction on the extensor apparatus simulated active motion. In-Vivo Study: The IRB approved study of 12 volunteers undergoing planned knee arthroscopy under local anesthesia. Contrast was placed in the FP and IPP under lateral fluoroscopic control. Passive, then active motion then a quads-set manoeuvre was performed. The IPP was resected and knee motion again recorded. Results Knees without IPP (4) demonstrated FPs that were lobular, with lateral bodies, and a central process. The fibrous synovial layer of the capsule bypassed the FP inserting on the superior aspect of the menisci. Knees with an IPP (8) showed a FP that was covered by fibrous synovium. The fibrous elements of the capsule coalesced on either side of the patellar in folds that merged with the alar folds. These fibrous elements ramified over and through the FP and were continuous with the upper portion of the IPP medially and laterally. Inferiorly the lower portion of the IPP merged with fibrous synovium that attached to the superior aspect of the menisci and the inter-meniscal ligament. The cadaver studies demonstrated that the IPP elongated with FP distortion as the knee approached full extension and flexion, and that the IPP was lax through mid arc. Release of the IPP at the femur eliminated almost all of the distortion through the full arc. The In-Vivo study replicated the cadaver observations for passive and active motion. The quads set manoeuvre caused further distortion of the FP with the patella moving one cm proximally. Release of the IPP eliminated FP distortion. Conclusion The IPP seems to act as a true ligamentum mucosum. By virtue of its central femoral attachment if captures the FP against the end of the femur, loosely in mid arc, but with distortion of the FP and stretch of the IPP approaching full flexion and extension. This has been demonstrated in both cadavers and in in-vivo for the first time. Any pathologic process affecting the highly innervated FP will likely be improved by removal of the capture effect of the IPP.

Cementless fixation for the tibial component in total knee arthroplasty (TKA) remains problematic. Peri-Apatite (PA), a solution-deposited hydroxyapatite, is under investigation as an option for improving the fixation of cementless tibial components. In this study, radiostereometric analysis was used to document implant migration in 48 dogs that underwent TKA with cementless, PA-coated, or cemented tibial components. Migration at 12 weeks was similar in the 2 groups. At 12 months, there was greater migration in the PA-coated group, but the difference between the 2 groups was below the threshold considered clinically significant. In this canine TKA model, cementless fixation with PA performed less well than did cemented fixation, but not to a degree that would make a clinical difference in the short term.

The “damage accumulation” phenomenon has not been quantitatively demonstrated in clinical cement mantles surrounding femoral hip stems. We stained transverse sections of 11 postmortem retrieved femoral hip components fixed with cement using fluorescent dye-penetrant and quantified cement damage, voids, and cement–bone interface gaps in epifluorescence and white light micrographs. Crack density (Cr.Dn), crack length-density (Cr.Ln.Dn), porosity, and cement–bone interface gap fraction (c/b-gap%) were calculated, normalized by mantle area. Multiple regression tests showed that cement damage (Cr.Ln.Dn. & Cr.Dn.) was significantly positively correlated (r2=0.98, p<0.001) with “duration of use” and body mass index (“BMI”) but not cement mantle “porosity”. There were significant interactions: “duration of use”⁎“BMI” was strongly predictive (p<0.005) of Cr.Dn.; and “duration of use”⁎“porosity” was predictive (p=0.04) of Cr.Ln.Dn. Stem related cracks accounted for approximately one fifth of Cr.Dn and one third of Cr.Ln.Dn. The mean c/b-gap% was 13.8% but it did not correlate (r2=0.01, p=0.8) with duration of use. We concluded that duration-dependent fatigue damage accumulation occurred during in vivo use. BMI strongly influenced cement crack length and the rate of new crack formation over time. Voids did not increase the rate of crack initiation but appeared to have promoted crack growth over time. Although not progressive, substantial bone resorption at the cement–bone interface appeared to be common.

There is continued interest in the maintenance and functional response of the cement-bone interface to loads that act across the interface. Recent experimental work has found that the interface is quite compliant (~10 microns/MPa) with sliding and opening occurring from shear and tensile loading conditions, respectively. In addition, this interface becomes more compliant following in vivo service (~50 microns/MPa). The question remains as to whether this micromotion is loading angle dependent. To address this question we performed multiloading angle experiments on cement-bone interface specimens. We asked three research questions: (1) does interface compliance depend on loading angle?, (2) are there appreciable coupled transverse motions?, and (3) can interface compliance be explained by contact fraction between cement and bone and source of bone (lab prepared or postmortem retrieval)?

Nonbiologic and mechanical effects of hydroxyapatite coatings have received little evaluation. Hydroxyapatite coatings give porous metal the appearance of decreased roughness. We hypothesized that this apparent decrease in surface roughness would result in diminished initial implant stability. We measured the initial stability of titanium plasma sprayed press-fit femoral stems with and without HA. Stems were implanted into cadaver and synthetic femora and subjected to aggressive stair-climbing loads. Migrations (retroversion and subsidence) and cyclic motions were recorded. Hydroxyapatite coating significantly reduced retroversion (P =.0007) and cyclic subsidence (P =.0086). Scanning electron microscopy imaging revealed that HA coating appeared to have reduced roughness on a millimeter scale but increased roughness on a micrometer scale. We concluded that HA coating improves initial stability through mechanical means, before biological action.

Have you previously submitted this study for another congress?: Yes Which Congress?: Canadian Orthopaedic Association Annual Meeting, July 2011; 15th ESSKA Congress Presentation Method Preference: Oral or E-Poster INTRODUCTION: Wachtler3 in 1979 described the histology of the IPP and discussed its function. Beyond the histology, he injected the fat pad (FP) and noted from his observations that “...from a mechanical and teleological point of view, the IPP may have little relevance...” By contrast, anterior knee pain has been relieved by resection of the infrapatellar plica (IPP)1,2. The question is: How? The hypothesis is: that the IPP acts as an intra-articular ligament, a mechanical link between the motors of knee motion, the fat pad (FP) and the distal femur, holding the FP captive through the arc of motion. Release of the IPP severs this link, allowing the highly innervated FP to move freely. This study reports on replication of Wachtler's study with the addition of in-vivo verification. The remarkable videos are at variance with Wachtler's opinion and suggest a distinct mechanical role for this structure. OBJECTIVES: In cadaver knees to inject the FP and IPP with radiographic contrast, and observe passive motion through lateral fluorscopy. In awake volunteers undergoing arthroscopy, to repeat the experiment with active motion and a quads set manouevre. METHODS: Cadaver studies: In 2 embalmed cadaver knees arthroscopy was performed to verify normal anatomy and the presence of an IPP. Direct arthroscopic visualization was used to control implantation of contrast material in the FP and IPP. The knee was taken through the arc of motion and recorded through lateral fluoroscopy. The femoral attachment of the IPP was then released and knee motion repeated and recorded. In-Vivo Study: In an IRB approved study of 12 volunteers undergoing planned knee arthroscopy under local anesthesia, contrast was placed in the FP and IPP under lateral fluoroscopic control. Passive, then active motion then a quads-set manoeuvre was performed. The IPP was resected and knee motion again recorded. RESULTS: Videos from the cadaver studies demonstrated that the IPP elongated with FP distortion as the knee approached full extension and flexion, and that the IPP was lax through mid arc. Release of the IPP at the femur eliminated almost all of the distortion through the full arc. Success was achieved in only 4 patients in the In-Vivo Study. However, the videos replicated the cadaver observations for passive and, for the first time in living patients, active motion. The quads set manoeuvre caused further distortion of the FP with the patella moving one cm proximally. Release of the IPP eliminated FP distortion. CONCLUSION: Knee motion was recording by lateral fluoroscopy in 2 cadaver, and 4 in-vivo knees. The videos showed in all instances stretch and deformation of the FP and IPP as the knees approached full extension and flexion. This unexpected non-isometric mechanical behaviour of the IPP shows that by virtue of is central attachment it holds the FP captive against the femur. Release of the IPP eliminates the mechanical effect of the IPP on the FP. Pain relief can be through denervation, or through release of the innervated central body of the FP. REFERENCES: 1. Boyd CR, Eakin C, Matheson GO. Infrapatellar plica as a cause of anterior knee pain. Clinical Journal of Sport Medicine. 2005;15:98-103. 2. Demirag B, Ozturk C, Karakayali M. Symptomatic infrapatellar plica. Knee Surgery, Sports Traumatology, Arthroscopy. 2006;14:156-160. 3. Wachtler F. Plica synovialis infrapatellaris in man. Acta Anat (Basel). 1979;104:451-459.

Maintaining adequate fixation between cement and bone is important for successful long term survival of cemented total joint replacements. Mixed-mode loading conditions (combination of tension/compression and shear) are present during in vivo loading, but the micromotion response of the interface to these conditions is not fully understood.Non-destructive, multi-axial loading experiments were conducted on laboratory prepared (n = 6) and postmortem (n = 6) human cement-bone interfaces. Specimens were mounted in custom loading discs and loaded at 0 degrees, 30 degrees, 60 degrees, and 90 degrees relative to the interface plane where 0 degrees represents normal loading to the interface, and 90 degrees represents shear loading along the longitudinal axis of the femur. Axial compliance did not depend on loading angle for laboratory prepared (p = 0.96) or postmortem specimens (p = 0.62). The cement-bone interface was more compliant under tensile than compressive loading at the 0(degrees) loading angle only (p = 0.024). The coupled transverse to axial compliance ratio, which is a measure of the coupled motion, was small for laboratory prepared (0.115 +/- 0.115) and postmortem specimens (0.142 +/- 0.101). There was a moderately strong inverse relationship between interface compliance and contact index (r(2) = 0.65).From a computational modeling perspective, the results of the current study support the concept that the cement-bone interface could be numerically implemented as a compliant layer with the same initial stiffness in tension and shear directions. The magnitude of the compliance could be modified to simulate immediate post-operative conditions (using laboratory prepared data set) or long-term remodeling (using postmortem data set). (C) 2010 Elsevier Ltd. All rights reserved.

Background and purpose Despite the longstanding use of micro-motion as a measure of implant stability, direct measurement of the micromechanics of implant/bone interfaces from en bloc human retrievals has not been performed. The purpose of this study was to determine the stem-cement and cement-bone micromechanics of functionally loaded, en-bloc retrieved, cemented femoral hip components.Methods 11 fresh frozen proximal femurs with cemented implants were retrieved at autopsy. Specimens were sectioned transversely into 10-mm slabs and fixed to a loading device where functional torsional loads were applied to the stem. A digital image correlation technique was used to document micromotions at stem-cement and cement-bone interfaces during loading.Results There was a wide range of responses with stem-cement micromotions ranging from 0.0006 mm to 0.83 mm (mean 0.17 mm, SD 0.29) and cement-bone micromotions ranging from 0.0022 mm to 0.73 mm (mean 0.092 mm, SD 0.22). There was a strong (linear-log) inverse correlation between apposition fraction and micromotion at the stem-cement interface (r(2) = 0.71, p < 0.001). There was a strong inverse log-log correlation between apposition fraction at the cement-bone interface and micromotion (r(2) = 0.85, p < 0.001). Components that were radiographically well-fixed had a relatively narrow range of micromotions at the stem-cement (0.0006-0.057 mm) and cement-bone (0.0022-0.029 mm) interfaces.Interpretatation Minimizing gaps at the stem-cement interface and encouraging bony apposition at the cement-bone interface would be clinically desirable. The cement-bone interface does not act as a bonded interface in actual use, even in radiographically well-fixed components. Rather, the interface is quite compliant, with sliding and opening motions between the cement and bone surfaces.

We have developed a technique to directly observe the micromechanics of the stem–cement and cement–bone interfaces of cemented femoral stems under physiologically relevant loading conditions. Thick transverse sections of a stem–cement–femur construct were fixed to the base of a test frame. Ante- and retro-verting torques were applied to the femoral stem by screwing the stem (via a pair of through holes) to an axle, which was turned using a lever arm actuated by the test frame cross-head. The surface of each transverse section was serially digitally imaged during loading. The displacements of the stem, cement and bone were determined using digital image correlation. These data were then used to calculate the relative displacements across the interfaces. This method provides a path to more thorough understanding of load-transfer from femoral stem to femur.