Jayme C. Burket

Spatial Variation in Osteonal Bone Properties Relative to Tissue and Animal Age

Little is known about osteonal bone mineral and matrix properties, although these properties are of major importance for the understanding of bone alterations related to age and bone diseases such as osteoporosis. During aging, bone undergoes modifications that compromise their structural integrity as shown clinically by the increase of fracture incidence with age. Based on Fourier transform infrared (FTIR) analysis from baboons between 0 and 32 yr of age, consistent systematic variations in bone properties as a function of tissue age are reported within osteons. The patterns observed were independent of animal age and positively correlated with bone tissue elastic behavior measured by nano‐indentation. As long as tissue age is expressed as a percentage of the entire osteon radius, osteonal analyses can be used to characterize disease changes independent of the size of the osteon. These mineral and matrix analyses can be used to explain bone fragility. The mineral content (mineral‐to‐matrix ratio) was correlated with the animal age in both old (interstitial) and newly formed bone tissue, showing for the first time that age‐related changes in BMC can be explain by an alteration in the mineralization process itself and not only by an imbalance in the remodeling process.

Microstructure and nanomechanical properties in osteons relate to tissue and animal age

Material property changes in bone tissue with ageing are a crucial missing component in our ability to understand and predict age-related fracture. Cortical bone osteons contain a natural gradient in tissue age, providing an ideal location to examine these effects. This study utilized osteons from baboons aged 0-32 years (n=12 females), representing the baboon lifespan, to examine effects of tissue and animal age on mechanical properties and composition of the material. Tissue mechanical properties (indentation modulus and hardness), composition (mineral-to-matrix ratio, carbonate substitution, and crystallinity), and aligned collagen content (aligned collagen peak height ratio) were sampled along three radial lines in three osteons per sample by nanoindentation, Raman spectroscopy, and second harmonic generation microscopy, respectively. Indentation modulus, hardness, mineral-to-matrix ratio, carbonate substitution, and aligned collagen peak height ratio followed biphasic relationships with animal age, increasing sharply during rapid growth before leveling off at sexual maturity. Mineral-to-matrix ratio and carbonate substitution increased 12% and 6.7%, respectively, per year across young animals during growth, corresponding with a nearly 7% increase in stiffness and hardness. Carbonate substitution and aligned collagen peak height ratio both increased with tissue age, increasing 6-12% across the osteon radii. Indentation modulus most strongly correlated with mineral-to-matrix ratio, which explained 78% of the variation in indentation modulus. Overall, the measured compositional and mechanical parameters were the lowest in tissue of the youngest animals. These results demonstrate that composition and mechanical function are closely related and influenced by tissue and animal age.

Otto Aufranc Award: Large Heads Do Not Increase Damage at the Head-neck Taper of Metal-on-polyethylene Total Hip Arthroplasties

BackgroundFretting and corrosion at head-neck junctions of total hip arthroplasties (THAs) have been associated with adverse local tissue reactions in patients with both metal-on-polyethylene (MoP) and metal-on-metal (MoM) prostheses. Femoral head size contributes to the severity of fretting and corrosion in large-diameter MoM THAs, but its impact on such damage in MoP THAs remains unknown.Questions/purposes(1) Is femoral head size associated with increased fretting or corrosion at the head-neck junction in MoP total hips? (2) Is duration of implantation associated with increased fretting or corrosion?MethodsThe severity of fretting/corrosion on surfaces of head tapers and stem trunnions was visually examined in 154 MoP THAs retrieved as part of 3282 revision surgeries performed at our institution between January 1, 2007, and December 31, 2013. Fretting and corrosion damage were subjectively graded by two independent observers on a 1 to 4 scale, and their relations to head size, alloy combinations, taper/trunnion design, length of implantation (LOI), and location were investigated. Differences in scores never exceeded one grade, and this occurred in only 17% of examined implants. With the available implants, the study provided 88% power to detect differences of 0.5 in fretting or corrosion scores in these analyses.ResultsFretting and corrosion of the tapers and the trunnions were not affected by head size (p = 0.247, p = 0.471, p = 0.837, and p = 0.868, respectively), although taper/trunnion design affected taper fretting (p = 0.005) and corrosion (p = 0.0031) and trunnion fretting (p = 0.0028). Head taper fretting (observed in 73% of heads) increased with LOI, but head taper corrosion (noted in 93% of heads) was not affected. Trunnion fretting (observed in 86% of stems) was more severe in mixed-alloy combinations and with increased LOI and was more severe proximally. Trunnion corrosion (noted in 72% of stems) was also location-dependent with greater corrosion distally.ConclusionsFretting and corrosion are regular occurrences in MoP THAs, but neither damage type was related to femoral head size. Conversely, taper design, LOI, and alloy combination affected the severity of both fretting and corrosion.Clinical RelevanceAlthough it has been suggested that trunnion corrosion seen in MoP bearings is a function of larger diameter heads, our data suggest that larger femoral heads may be used for increased damage at the modular junction of MoP THAs.

Variations in nanomechanical properties and tissue composition within trabeculae from an ovine model of osteoporosis and treatment.

Osteoporosis and treatment may affect both composition and nanomechanical properties and their spatial distributions within the individual trabeculae of cancellous bone at length scales that cannot be captured by bulk measurements. This study utilized 25 mature adult ewes divided into 5 treatment groups. Four treatment groups were given a dietary model for human high-turnover osteoporosis, and two of these were treated with antiresorptive drugs, either zoledronate (ZOL) or raloxifene (RAL), to examine their effects on bulk tissue properties and nanoscale tissue composition and mechanical properties within trabeculae. Treatment effects were most pronounced at the nanoscale, where RAL increased indentation modulus and hardness throughout trabeculae by 10% relative to the osteoporosis model. In comparison, ZOL increased these properties exclusively at the surfaces of trabeculae (indentation modulus +12%, hardness +16%). Nanomechanical alterations correlated with changes in tissue mineralization, carbonate substitution, crystallinity, and aligned collagen. Despite only minimal changes in bulk tissue tBMD, the nanomechanical improvements within trabeculae with both treatments greatly improved the predicted theoretical bending stiffness of individual trabeculae when idealized as cylindrical struts. Hence, small tissue-level alterations in critical locations for resisting trabecular failure could account for some of the discrepancy between the large reductions in fracture risk and the only modest changes in BMD with antiresorptive treatments.

Return to Sports and Physical Activities After Primary Partial Arthrodesis for Lisfranc Injuries in Young Patients

Background: Research regarding outcomes in sports and physical activities after primary partial arthrodesis for Lisfranc injuries has been sparse. The purposes of this study were to assess various sports and physical activities in young patients following primary partial arthrodesis for Lisfranc injuries and to compare these with clinical outcomes. Methods: Patients who underwent primary partial arthrodesis for a Lisfranc injury were identified by a retrospective registry review. Thirty-eight of 46 eligible patients (83%) responded for follow-up at a mean of 5.2 (range, 1.0 to 9.3) years with a mean age at surgery of 31.8 (range, 16.8 to 50.3) years. Physical activity participation was assessed with a new sports-specific, patient-administered questionnaire. Clinical outcomes were assessed with the Foot and Ankle Outcome Score (FAOS). Results: Patients participated in 29 different and 155 total physical activities preoperatively, and 27 different and 145 total physical activities postoperatively. Preoperatively, 47.1% were high impact, and postoperatively, 44.8% were high impact. The most common activities were walking, bicycling, running, and weightlifting. Compared to preoperatively, difficulty was the same in 66% and increased in 34% of physical activities. Participation levels were improved in 11%, the same in 64%, and impaired in 25% of physical activities. Patients spent on average 4.2 (range, 0.0 to 19.8) hours per week exercising postoperatively. In regard to return to physical activity, 97% of respondents were satisfied with their operative outcome. Mean postoperative FAOS subscores were significantly worse for patients who had increased physical activity difficulty. Conclusion: Most patients were able to return to their previous physical activities following primary partial arthrodesis for a Lisfranc injury, many of which were high-impact. However, the decreased participation or increase in difficulty of some activities suggests that some patients experienced postoperative limitations in exercise. Future studies could compare sports outcomes between primary partial arthrodesis and open reduction internal fixation for Lisfranc injuries. Level of Evidence: Level IV, retrospective case series.

Risk Factors for Posttraumatic Synostosis and Outcomes Following Operative Treatment of Ankle Fractures

Background: Distal tibiofibular synostosis is a known but poorly described complication of ankle fractures. The objective of this study was to evaluate the relationship between ankle fracture fixation method and other risk factors in the development of synostosis in posttraumatic operative ankle fractures. Outcomes of patients with no synostosis, incomplete bony bridging, or complete synostosis also were compared. Methods: All operative ankle fractures from a single surgeon’s prospectively collected clinical database were evaluated for the presence of distal tibiofibular synostosis not earlier than 3 months postoperatively. All fractures were treated in a fracture-specific and ligament-specific fashion. Syndesmotic screws, when used, were routinely removed no sooner than 4 months after operation. Patient demographic and medical history data as well as injury and fixation profile were evaluated. Incidence of complications was also reviewed. Foot and Ankle Outcome Score (FAOS) and range of motion (ROM) were compared between the groups. Results: Of the 564 ankle fractures included in the study, 91 demonstrated complete synostosis and 46 demonstrated incomplete bony bridging. Multivariate analysis revealed male sex (odds ratio [OR] = 2.82, P < .001), syndesmotic screw fixation (OR = 2.46, P < .001), and tibiotalar dislocation (OR = 1.74, P = .032) to remain significant independent risk factors for the development of incomplete bony bridging or complete synostosis while adjusting for confounding risk factors. Ankles with synostosis also demonstrated significant reduction in dorsiflexion (P = .017), plantarflexion (P = .024), and inversion (P < .001), though patient-reported outcome measures were equivalent with patients without synostosis. Conclusion: Syndesmotic screw fixation, male sex, and tibiotalar dislocation were significant risk factors in the formation of postoperative distal tibiofibular synostosis, though patient-reported outcome measures seemed equivalent among patients with and without synostosis. Level of Evidence: Level III, case control study of prospectively collected registry data.

Correlation of Talar Anatomy and Subtalar Joint Alignment on Weightbearing Computed Tomography With Radiographic Flatfoot Parameters

Background: Underlying bony deformity may be related to development of adult-acquired flatfoot deformity (AAFD). Multiplanar weightbearing (MP-WB) computed tomography can be used to identify subtalar deformity which may contribute to valgus hindfoot alignment. On coronal MP-WB images, 2 angles reliably evaluate the subtalar joint axis: the angle between the inferior facet of the talus and the horizontal (inftal-hor) and the angle between the inferior and superior facets of the talus (inftal-suptal). Although these angles have been shown to differ significantly between flatfoot patients and controls, no study has investigated their relationships with other components of AAFD. We hypothesized that these angles would correlate strongly with commonly used radiographic measures of AAFD. Methods: Forty-five patients with stage II AAFD and 17 control patients underwent MP-WB imaging and standard weightbearing radiographs. MP-WB measurements were correlated with standard radiographic measurements of AAFD. Differences between AAFD and control patients were assessed using independent samples t tests and Mann-Whitney U tests. To assess correlations between each MP-WB measurement and radiographic measurement, factorial generalized linear models (GLMs) were constructed. Results: Patients with AAFD differed from the controls in all measured angles (P ≤ .001 for each). After accounting for differences between flatfoot and control patients, inftal-hor was not significantly correlated with any of the radiographic angles. Inftal-suptal, however, correlated with the AP coverage angle, AP talar–first metatarsal angle, calcaneal pitch, Meary’s angle, medial column height, and hindfoot alignment after accounting for differences between flatfoot patients and controls. Meary’s angle alone explained 48% of the variation in inftal-suptal angles. Conclusion: As measured on coronal MP-WB images, patients with stage II AAFD had more innate valgus in their talar anatomy as well as more valgus alignment of their subtalar joints than did control patients. It is possible that this information could be used to identify patients likely to have progression of deformity and may ultimately guide the approach to operative reconstruction. Level of Evidence: Level III, case-control study.

New radiographic parameter assessing hindfoot alignment in stage II adult-acquired flatfoot deformity.

Background: The hindfoot moment arm is a reliable measurement of hindfoot valgus deformity in stage II adult-acquired flatfoot deformity (AAFD) and can be used to guide intraoperative correction of the hindfoot. There is currently little understanding of how the hindfoot moment arm relates to angular measurements of hindfoot alignment. The purpose of this study was to develop a new hindfoot alignment angle that can reliably quantify hindfoot valgus in patients with AAFD and to establish the relationship of this angle with the hindfoot moment arm. Methods: Preoperative hindfoot alignment radiographs were reviewed for 10 consecutive patients (10 feet) who were indicated for reconstruction for stage II AAFD. A second group of 10 patients (10 feet) without flatfoot were identified to serve as normal controls. The hindfoot moment arm and the new hindfoot alignment angle were measured in blinded fashion by 2 readers. Reliability was assessed using intraclass correlation coefficients (ICCs). The difference in angle between normal and flatfoot patients was assessed with a Mann-Whitney U test. A linear regression model was used to assess the relationship between hindfoot moment arm and the new hindfoot alignment angle. Results: Intra- and interrater reliability for the hindfoot alignment angle was excellent (ICC = 0.979 and 0.965, respectively). Flatfoot patients had greater mean angles than did normal patients (22.5 ± 4.9 vs 5.6 ± 5.4 degrees, P < .001). The hindfoot moment arm was correlated significantly with the hindfoot alignment angle (P < .001), increasing by 0.81 mm for every degree increase in angle (adjusted R2 = 0.9046). Conclusion: These results indicate that the new hindfoot alignment angle is a reliable measure of hindfoot valgus and can differentiate between flatfoot and normal patients. In addition, the strong linear relationship between the hindfoot alignment angle and moment arm may allow for the use of this angle in the intraoperative correction of hindfoot valgus. Level of Evidence: Level III, retrospective case control study.

Effect of Obesity on Clinical and Radiographic Outcomes Following Reconstruction of Stage II Adult Acquired Flatfoot Deformity

Background: Obesity is a known risk factor for the development of adult acquired flatfoot deformity (AAFD), but obesity’s effects on outcomes following AAFD reconstruction are unknown. We hypothesized that obesity would negatively impact outcomes following joint-preserving stage II AAFD reconstruction. Methods: This retrospective study compared the outcomes of normal-weight (18.5 kg/m2 ≤ BMI < 25 kg/m2), overweight (25 kg/m2 ≤ BMI < 30 kg/m2), and obese (BMI ≥ 30 kg/m2) patients after AAFD reconstruction. Clinical outcome measures included the Foot and Ankle Outcome Score (FAOS), Short-Form 12 (SF-12), and Numeric Rating Scale of Pain (NRS Pain) administered preoperatively and at least 1 year postoperatively. Anteroposterior and lateral radiographs were taken preoperatively and at least 6 months postoperatively. Pre- to postoperative changes in outcome measures were assessed within BMI classes. Preoperative, postoperative, and pre- to postoperative changes in outcomes were compared among BMI classes. There were 41 normal-weight patients, 39 overweight patients, and 44 obese patients with a mean age of 56 years, FAOS follow-up of 2.9 years, and radiographic follow-up of 2.1 years. Demographics and reconstructive procedures were comparable among the 3 BMI classes. Results: All outcomes significantly increased pre- to postoperatively in the 3 groups with the exception of the FAOS Symptoms subscale for normal-weight patients (P = .340) and SF-12 Mental Component score for all 3 BMI classes (P > .999). Preoperatively, obese patients had more symptoms than normal-weight patients, scoring 12 points lower on the FAOS Symptoms subscore (P = .008). Obese patients also scored 11 points lower preoperatively on the SF-12 Overall score (P = .028) and had 31% greater pain than normal-weight patients (P = .003). There were no differences among the 3 BMI classes in any postoperative outcomes assessed. Conclusion: Although obese patients had significantly worse symptoms, overall health, and NRS pain scores preoperatively, the short-term clinical and radiographic outcomes of stage II AAFD reconstruction were similar for normal-weight, overweight, and obese patients. We suggest that joint-preserving reconstruction remains a viable alternative to fusion of the triple joint complex for the treatment of overweight and obese stage II AAFD patients. Level of Evidence: Level III, retrospective cohort study.

Altered distributions of bone tissue mineral and collagen properties in women with fragility fractures

Heterogeneity of bone tissue properties is emerging as a potential indicator of altered bone quality in pathologic tissue. The objective of this study was to compare the distributions of tissue properties in women with and without histories of fragility fractures using Fourier transform infrared (FTIR) imaging. We extended a prior study that examined the relationship of the mean FTIR properties to fracture risk by analyzing in detail the widths and the tails of the distributions of FTIR properties in biopsies from fracture and non-fracture cohorts. The mineral and matrix properties of cortical and trabecular iliac crest tissue were compared in biopsies from women with a history of fragility fracture (+Fx; n=21, age: mean 54±SD 15y) and with no history of fragility fracture (-Fx; n=12, age: 57±5y). A subset of the patients included in the -Fx group were taking estrogen-plus-progestin hormone replacement therapy (HRT) (-Fx+HRT n=8, age: 58±5y) and were analyzed separately from patients with no history of HRT (-Fx-HRT n=4, age: 56±7y). When the FTIR parameter mean values were examined by treatment group, the trabecular tissue of -Fx-HRT patients had a lower mineral:matrix ratio (M:M) and collagen maturity (XLR) than that of -Fx+HRT patients (-22% M:M, -18% XLR) and +Fx patients (-17% M:M, -18% XLR). Across multiple FTIR parameters, tissue from the -Fx-HRT group had smaller low-tail (5th percentile) values than that from the -Fx+HRT or +Fx groups. In trabecular collagen maturity and crystallinity (XST), the -Fx-HRT group had smaller low-tail values than those in the -Fx+HRT group (-16% XLR, -5% XST) and the +Fx group (-17% XLR, -7% XST). The relatively low values of trabecular mineral:matrix ratio and collagen maturity and smaller low-tail values of collagen maturity and crystallinity observed in the -Fx-HRT group are characteristic of younger tissue. Taken together, our data suggest that the presence of newly formed tissue that includes small/imperfect crystals and immature crosslinks, as well as moderately mature tissue, is an important characteristic of healthy, fracture-resistant bone. Finally, the larger mean and low-tail values of mineral:matrix ratio and collagen maturity noted in our -Fx+HRT vs. -Fx-HRT biopsies are consistent with greater tissue age and greater BMD arising from decreased osteoclastic resorption in HRT-treated patients.