Three-dimensional characterization of the anterior cruciate ligament's femoral footprint.

There is increasing use of three-dimensional (3D) computed tomography (CT) for researching anterior cruciate ligament (ACL) reconstructions and tunnel placement. However, there is limited 3D CT data on the ACL footprint. The purpose of this study is to define the native ACL femoral footprint using 3D surface reconstructions of computed tomography (CT) imaging of cadaveric knees. The femoral insertion of the ACL was meticulously dissected and marked with drill holes in seven cadaveric knees. CT scans were performed on each specimen, and 3D computer models were created. Distance from the condyle edges to the margins of the footprint were referenced to the total condylar size. This was performed both parallel and perpendicular to the femoral axis as well as the intercondylar notch. The mean condylar depth (c/C) ratios along the axis of the femur were 0.45 ± 0.06 for the anterior border, 0.44 ± 0.08 for the posterior border, 0.26 ± 0.07 for the proximal border, and 0.63 ± 0.08 for the distal border. The mean notch (n/N) ratios for the four margins were 0.37 ± 0.04 for the anterior border, 0.67 ± 0.08 for the posterior border, 0.49 ± 0.07 for the proximal margin, and 0.50 ± 0.06 for the distal border. The mean c/C ratios parallel the intercondylar notch measured 0.23 ± 0.03 for the anterior border, 0.27 ± 0.04 for the posterior border, 0.37 ± 0.04 for the proximal border, and 0.12 ± 0.02 for the distal border. The mean n/N ratios perpendicular to the intercondylar notch measured 0.11 ± 0.06 for the anterior border, 0.52 ± 0.09 the posterior border, 0.29 ± 0.06 for the proximal border, and 0.30 ± 0.06 for the distal border. This study provides reference measures of the femoral footprint of the ACL using 3D CT. It will assist future studies that use advanced imaging to evaluate accuracy of ACL reconstruction.

Three-dimensional characterization of the femoral footprint of the posterior cruciate ligament.

PURPOSE: The purpose of this study was to define an anatomic standard for the femoral footprint of the posterior cruciate ligament (PCL) based on 3-dimensional (3D) surface reconstructions of computed tomography (CT) scans of cadaveric knees. METHODS: The femoral insertion of the PCL was identified and marked with drill holes in 7 cadaveric knees. CT scans were performed on each specimen, and 3D computer models were generated. The distance from the condyle edges to the margins of the footprint were referenced to the total condylar size parallel and perpendicular to the femoral axis and intercondylar notch. RESULTS: The mean ratio of the anteroposterior width of the medial femoral condyle referenced parallel to the intercondylar notch measured 0.08 ± 0.02 for the anterior border, 0.60 ± 0.08 for the posterior border, 0.16 ± 0.05 for the proximal border, and 0.44 ± 0.06 for the distal border. The mean ratio of the superior-inferior height of the medial femoral condyle with respect to the apex of the intercondylar notch corrected and referenced perpendicular to the intercondylar notch measured 0.14 ± 0.04 for the anterior border, 0.44 ± 0.07 for the posterior border, 0.03 ± 0.02 for the proximal border, and 0.56 ± 0.07 for the distal border. CONCLUSIONS: This cadaveric study provides an anatomic reference for mathematical analysis of the femoral PCL footprint using CT-based 3D topographic modeling. The average PCL center point is located 25% down from the roof of the notch and 38% from anterior to posterior from the anterior condyle with regard to total medial femoral condyle length. CLINICAL RELEVANCE: This study provides a standard of measurement for future studies that use advanced imaging to evaluate the accuracy of PCL reconstruction.

Metaphyseal and diaphyseal bone loss in the tibia following transient muscle paralysis are spatiotemporally distinct resorption events.

When the skeleton is catabolically challenged, there is great variability in the timing and extent of bone resorption observed at cancellous and cortical bone sites. It remains unclear whether this resorptive heterogeneity, which is often evident within a single bone, arises from increased permissiveness of specific sites to bone resorption or localized resorptive events of varied robustness. To explore this question, we used the mouse model of calf paralysis induced bone loss, which results in metaphyseal and diaphyseal bone resorption of different timing and magnitude. Given this phenotypic pattern of resorption, we hypothesized that bone loss in the proximal tibia metaphysis and diaphysis occurs through resorption events that are spatially and temporally distinct. To test this hypothesis, we undertook three complimentary in vivo/µCT imaging studies. Specifically, we defined spatiotemporal variations in endocortical bone resorption during the 3weeks following calf paralysis, applied a novel image registration approach to determine the location where bone resorption initiates within the proximal tibia metaphysis, and explored the role of varied basal osteoclast activity on the magnitude of bone loss initiation in the metaphysis using µCT based bone resorption parameters. A differential response of metaphyseal and diaphyseal bone resorption was observed throughout each study. Acute endocortical bone loss following muscle paralysis occurred almost exclusively within the metaphyseal compartment (96.5% of total endocortical bone loss within 6days). Using our trabecular image registration approach, we further resolved the initiation of metaphyseal bone loss to a focused region of significant basal osteoclast function (0.03mm(3)) adjacent to the growth plate. This correlative observation of paralysis induced bone loss mediated by basal growth plate cell dynamics was supported by the acute metaphyseal osteoclastic response of 5-week vs. 13-month-old mice. Specifically, µCT based bone resorption rates normalized to initial trabecular surface (BRRBS) were 3.7-fold greater in young vs. aged mice (2.27±0.27µm(3)/µm(2)/day vs. 0.60±0.44µm(3)/µm(2)/day). In contrast to the focused bone loss initiation in the metaphysis, diaphyseal bone loss initiated homogeneously throughout the long axis of the tibia predominantly in the second week following paralysis (81.3% of diaphyseal endocortical expansion between days 6 and 13). The timing and homogenous nature are consistent with de novo osteoclastogenesis mediating the diaphyseal resorption. Taken together, our data suggests that tibial metaphyseal and diaphyseal bone loss induced by transient calf paralysis are spatially and temporally discrete events. In a broader context, these findings are an essential first step toward clarifying the timing and origins of multiple resorptive events that would require targeting to fully inhibit bone loss following neuromuscular trauma.

Epidural steroid injections for the treatment of cervical radiculopathy in elite wrestlers: case series and literature review.

BACKGROUND: Elite wrestlers place tremendous stress through their cervical spine. These athletes are at risk for cervical trauma and may develop radiculopathy from recurrent episodes of injury. Team physicians and athletic trainers are faced with the challenge of treating these injuries in such a way as to allow the athlete to safely and expeditiously return to competition. Epidural steroid injections can be a successful complement to a conservative treatment algorithm for these complex injuries. STUDY DESIGN: Case Series. METHODS: Five upper-level NCAA collegiate wrestlers who experienced symptomatic cervical radiculopathy were identified from an archival review. The majority of the athletes had MRI evidence of cervical disc disease, with corresponding subjective complaints and physical examination findings including pain and weakness that precluded continued competition. All athletes were treated conservatively with initial activity modification, strengthening, rehabilitation, NSAIDs, and, ultimately, cervical epidural steroid injections. RESULTS: All five athletes successfully returned to competition without negative clinical sequelae or need for operative intervention. The athletes demonstrated subjective improvement in their symptoms and strength, and all were able to return to a high level of competition. The cervical epidural steroid injections were found to be safe, effective, and well tolerated in all of the athletes. CONCLUSIONS: Elite wrestlers with cervical radiculopathy can be effectively and safely managed with a conservative regimen that includes cervical epidural steroid injections, which may allow them to continue to compete at a high level.

Relationships between in vivo microdamage and the remarkable regional material and strain heterogeneity of cortical bone of adult deer, elk, sheep and horse calcanei.

Natural loading of the calcanei of deer, elk, sheep and horses produces marked regional differences in prevalent/predominant strain modes: compression in the dorsal cortex, shear in medial-lateral cortices, and tension/shear in the plantar cortex. This consistent non-uniform strain distribution is useful for investigating mechanisms that mediate the development of the remarkable regional material variations of these bones (e.g. collagen orientation, mineralization, remodeling rates and secondary osteon morphotypes, size and population density). Regional differences in strain-mode-specific microdamage prevalence and/or morphology might evoke and sustain the remodeling that produces this material heterogeneity in accordance with local strain characteristics. Adult calcanei from 11 animals of each species (deer, elk, sheep and horses) were transversely sectioned and examined using light and confocal microscopy. With light microscopy, 20 linear microcracks were identified (deer: 10; elk: six; horse: four; sheep: none), and with confocal microscopy substantially more microdamage with typically non-linear morphology was identified (deer: 45; elk: 24; horse: 15; sheep: none). No clear regional patterns of strain-mode-specific microdamage were found in the three species with microdamage. In these species, the highest overall concentrations occurred in the plantar cortex. This might reflect increased susceptibility of microdamage in habitual tension/shear. Absence of detectable microdamage in sheep calcanei may represent the (presumably) relatively greater physical activity of deer, elk and horses. Absence of differences in microdamage prevalence/morphology between dorsal, medial and lateral cortices of these bones, and the general absence of spatial patterns of strain-mode-specific microdamage, might reflect the prior emergence of non-uniform osteon-mediated adaptations that reduce deleterious concentrations of microdamage by the adult stage of bone development.

The osteoporosis self-assessment screening tool: a useful tool for the orthopaedic surgeon.

BACKGROUND: Simple and effective methods are needed to identify patients at risk for osteoporosis or osteoporosis-related fracture so that they can be screened with use of dual x-ray absorptiometry and counseled for treatment. Currently, we use a cumbersome survey assessing thirty-two risk factors. A much simpler score based on the Osteoporosis Self-Assessment Screening Tool (OST score) has been established as highly sensitive and specific in women, but similar data are lacking for men. This score is calculated by subtracting the age of the patient in years from the weight in kilograms and multiplying the result by 0.2. Our goal was to test the hypothesis that the OST score is more sensitive and specific than our extensive risk-assessment survey in men. METHODS: Using axial dual x-ray absorptiometry analysis, we evaluated a cohort of men who had either responded to our newspaper advertisement or were seen as patients in our orthopaedic clinic. Patients filled out the risk-assessment survey at the time of scanning. Osteoporosis was defined as a T-score of -2.5 or less in the lumbar spine, hip, or femoral neck. RESULTS: Twenty-seven (17%) of 158 white men, with a mean age of 67.5 years and a mean weight of 85.3 kg, had osteoporosis. After analysis of the thirty-two risk factors, two remained as significant independent predictors in the final multivariable model (p = 0.042 and p = 0.015). This model had an area under the receiver operating characteristic curve of 0.68 (>0.70 is considered to provide acceptable discrimination). The OST scores ranged from -6 (greatest risk) to 16 (least risk). With use of the OST score to predict osteoporosis, the area under the receiver operating characteristic curve was 0.76. The cutoff of an OST score of <2 provided the largest area under the receiver operating characteristic curve (0.74), with test characteristics for an OST score of <2 including a sensitivity of 85%, specificity of 64%, positive predictive value of 31%, and negative predictive value of 96%. CONCLUSIONS: The Osteoporosis Self-Assessment Screening Tool score is superior to a broad risk-factor analysis in the identification of men at risk for osteoporosis or osteoporotic fractures. We have found it simple to use in our clinic to determine which patients should undergo dual x-ray absorptiometry screening. LEVEL OF EVIDENCE: Diagnostic Level I. See Instructions to Authors for a complete description of levels of evidence.

The influence of collagen fiber orientation and other histocompositional characteristics on the mechanical properties of equine cortical bone.

This study examined relative influences of predominant collagen fiber orientation (CFO), mineralization (% ash), and other microstructural characteristics on the mechanical properties of equine cortical bone. Using strain-mode-specific (S-M-S) testing (compression testing of bone habitually loaded in compression; tension testing of bone habitually loaded in tension), the relative mechanical importance of CFO and other material characteristics were examined in equine third metacarpals (MC3s). This model was chosen since it had a consistent non-uniform strain distribution estimated by finite element analysis (FEA) near mid-diaphysis of a thoroughbred horse, net tension in the dorsal/lateral cortices and net compression in the palmar/medial cortices. Bone specimens from regions habitually loaded in tension or compression were: (1) tested to failure in both axial compression and tension in order to contrast S-M-S vs non-S-M-S behavior, and (2) analyzed for CFO, % ash, porosity, fractional area of secondary osteonal bone, osteon cross-sectional area, and population densities of secondary osteons and osteocyte lacunae. Multivariate multiple regression analyses revealed that in S-M-S compression testing, CFO most strongly influenced total energy (pre-yield elastic energy plus post-yield plastic energy); in S-M-S tension testing CFO most strongly influenced post-yield energy and total energy. CFO was less important in explaining S-M-S elastic modulus, and yield and ultimate stress. Therefore, in S-M-S loading CFO appears to be important in influencing energy absorption, whereas the other characteristics have a more dominant influence in elastic modulus, pre-yield behavior and strength. These data generally support the hypothesis that differentially affecting S-M-S energy absorption may be an important consequence of regional histocompositional heterogeneity in the equine MC3. Data inconsistent with the hypothesis, including the lack of highly longitudinal collagen in the dorsal-lateral ;tension' region, paradoxical histologic organization in some locations, and lack of significantly improved S-M-S properties in some locations, might reflect the absence of a similar habitual strain distribution in all bones. An alternative strain distribution based on in vivo strain measurements, without FEA, on non-Thoroughbreds showing net compression along the dorsal-palmar axis might be more characteristic of the habitual loading of some of the bones that we examined. In turn, some inconsistencies might also reflect the complex torsion/bending loading regime that the MC3 sustains when the animal undergoes a variety of gaits and activities, which may be representative of only a portion of our animals, again reflecting the possibility that not all of the bones examined had similar habitual loading histories.

Regional differences in cortical bone organization and microdamage prevalence in Rocky Mountain mule deer.

The limb bones of cursorial mammals may exhibit regional structural/material variations for local mechanical requirements. For example, it has been hypothesized that mineral content (%ash) and secondary osteon population density (OPD) progressively change from proximal (e.g., humerus) to distal (e.g., phalanx), in accordance with corresponding progressive changes in stress and mechanical/metabolic cost of functional use (both greatest in the distal limb). We tested this hypothesis in wild-shot Rocky Mountain mule deer by examining transverse segments from mid-diaphyses of medial proximal phalanges, principal metacarpals, radii, and humeri, as well as the lateral aspects of sixth ribs from each of 11 mature males. Quantified structural parameters included the section modulus (Z), polar moment of inertia (J), cortical area/total area ratio (CA/TA), bone girth, and cortical thickness. In addition, %ash and the prevalence of in vivo microcracks were measured in each bone. Thin sections from seven animals were further examined for OPD and population densities of new remodeling events (NREs). Results showed a significant progressive decrease in %ash from the humerus (75.4% +/- 0.9%) to the phalanx (69.4% +/- 1.1%) (P < 0.0001), with general proximal-to-distal increases in OPD and general decreases in J and Z. Thirteen microcracks were identified in the rib sections, and only two were observed in the limb bones. Although the ribs had considerably greater NREs, no significant differences in NREs were found between the limb bones, indicating that they had similar remodeling rates. Equivalent microcrack prevalence, but nonequivalent structural/material organization, suggests that there are regional adaptations that minimize microcrack production in locations with differences in loading conditions. The progressive proximal-to-distal decrease in %ash (up to 6%); moderate-to-high correlations between OPD, %ash, J, and CA/TA; and additional moderate-to-high correlations of these parameters with each bone's radius of gyration support the possibility that these variations are adaptations for regional loading conditions.

Are uniform regional safety factors an objective of adaptive modeling/remodeling in cortical bone?

It has been hypothesized that a major objective of morphological adaptation in limb-bone diaphyses is the achievement of uniform regional safety factors between discrete cortical locations (e.g. between cranial and caudal cortices at mid-diaphysis). This hypothesis has been tested, and appears to be supported in the diaphyses of ovine and equine radii. The present study more rigorously examined this question using the equine third metacarpal (MC3), which has had functionally generated intracortical strains estimated by a sophisticated finite element model. Mechanical properties of multiple mid-diaphyseal specimens were evaluated in both tension and compression, allowing for testing of habitually tensed or compressed regions in their respective habitual loading mode ("strain-mode-specific" loading). Elastic modulus, and yield and ultimate strength and strain, were correlated with in vivo strain data from a previously published finite element model. Mechanical tests revealed minor variations in elastic modulus, and yield and ultimate strength in both tension and compression loading, while physiological strains varied significantly between the cortices. Contrary to the hypothesis of uniform safety factors, the MC3 has a broad range of tension (caudo-medial, 4.0; cranio-lateral, 37.7) and compression (caudo-medial, 5.7; cranio-lateral, 68.9) safety factors.