Image Rotation Alters Apparent Fibula Length: An Evaluation of Talocrural Angle, Shenton Line, and Dime Sign.

BACKGROUND: Fibula shortening can compromise ankle stability and force transmission, thereby impacting clinical outcomes. Because radiographs depict 3-dimensional anatomy in 2 dimensions, accurate radiographic assessment of fibula length is a commonly encountered clinical challenge. The talocrural angle (TCA), Shenton line, and dime sign are useful parameters of fibula length. Yet, the impact of 3-dimensional limb positioning on these radiographic parameters is not established. METHODS: Bone models were constructed from CT scans of 30 lower limbs. Fibula length was computationally manipulated, and digitally reconstructed radiographs were generated reflecting 1-degree increments of sagittal and axial plane rotation of each limb for each fibula length condition. The TCA was computationally measured on each image. The presence of an aligned mortise view, intact Shenton line, and intact dime sign was assessed by 2 observers. RESULTS: The mean TCA, which was 78.0 (95% CI ± 1.6) degrees for a true mortise projection with anatomic fibula length, changed by approximately 1 degree per millimeter of fibula length change. On average, 14.7 degrees of caudal rotation obscured 2 mm of fibular shortening by virtue of producing the same TCA as a true mortise view with anatomic fibula length, designated a false positive view. Axial rotation had a comparatively small effect. Observers 1 and 2 were, respectively, 91% and 88% less likely to accurately judge the image alignment of the false positive images compared to true mortise images. Moreover, intraobserver agreement was poor to moderate (mean 0.47, range 0.13-0.59) and interobserver agreement was uniformly poor (mean 0.08, range 0.01-0.20). CONCLUSION: In our study using digitally reconstructed radiographs from CT scans of 30 limbs, we found that sagittal plane rotation impacts the radiographic appearance of fibula length as measured by the TCA. Limb axial rotation had a comparatively small effect. Further study of human perception of Shenton line and dime sign is needed before the effect of rotation on these parameters can be fully understood. LEVEL OF EVIDENCE: Level IV, case series.

The Center-Center Image Closely Approximates Other Methods for Syndesmosis Reduction Clamp Placement.

BACKGROUND: The optimal placement for a syndesmosis reduction clamp remains an open question. This study compared the center-center axis, which localizes clamp placement using only an internally rotated lateral ankle X-ray, with other common approaches, whose accuracy can only be confirmed using computed tomography (CT). METHODS: Bone models of anatomically aligned (n = 6) and malreduced (n = 48) limbs were generated from CT scans of cadaveric specimens. Four axes for guiding clamp placement (center-center, centroid, B2, and trans-syndesmotic) were then analyzed, using digitally reconstructed radiographs derived from the bone models. Each axis' location was defined using angle-height pairs that describe axis orientation along the full anatomical region where syndesmosis fixation occurs. RESULTS: In anatomically aligned limbs, the center-center axis was located on average (±95% CI [confidence interval]), 0.64° (±0.50°) internal rotation, 1.03° (±0.73°) internal rotation, and 2.09° (±7.29°) external rotation from the centroid, B2, and trans-syndesmotic axes, respectively. Fibular displacement altered the magnitude of limb rotation needed to identify the center-center axis. CONCLUSION: The center-center technique is a valid method that closely approximates previously described methods for syndesmosis clamp placement without using CT, and the magnitude of C-arm rotation needed to transition from a talar dome lateral to a center-center view may be a potential method for assessing syndesmosis reduction. LEVELS OF EVIDENCE: Level III: Retrospective comparative study.

Syndesmosis Injury Contributes a Large Negative Effect on Clinical Outcomes: A Systematic Review.

INTRODUCTION: The literature largely addresses questions of diagnostic accuracy and therapeutic accuracy. However, the magnitude of the clinical impact of syndesmosis injury is commonly described in intuitive yet qualitative terms. This systematic review aimed to quantify the impact of syndesmosis injury. METHODS: Published clinical outcomes data were used to compute an effect size reflecting the impact of syndesmosis injury. This was done within the clinical contexts of isolated syndesmosis injury and syndesmosis injury with concomitant ankle fracture. Clinical outcomes data included Olerud-Molander (OM) and American Orthopaedic Foot and Ankle Society (AOFAS) scores, visual analog scale for pain, and days missed from sport competition. Parametric data were compared with Student t tests. Effect size was computed using Cohen's d. RESULTS: In ankle fracture patients, syndesmosis injury demonstrated a large effect size for OM (d = 0.96) and AOFAS (d = 0.83) scores. In athletic populations without concomitant ankle fracture, syndesmosis injury demonstrated a large effect size on days missed from competition (d = 2.32). DISCUSSION: These findings confirm the magnitude of the negative impact of syndesmosis injury in athletic populations with isolated injury and in ankle fracture patients. In ankle fracture patients, this large negative effect remains despite surgery. Thus, syndesmosis repair may not fully mitigate the impact of the injury. LEVELS OF EVIDENCE: Level III: Systematic review.

Computed Tomographic Validation of the Center-Center Radiographic Technique for Syndesmosis Fixation Axis Alignment in Normal Ankles.

BACKGROUND: Ankle syndesmotic ligament injury is an important factor affecting clinical outcome after lower extremity injury with as little as 2 mm of syndesmotic displacement leading to worse clinical outcome. One important factor is the appropriate placement of clamps and fixation across the syndesmosis. When not ideally aligned, these can result in malalignment of the fibula in the incisura. This study sought to provide computer validation of using the center-center technique to identify an ideal centroid axis for placement of syndesmotic implants. METHODS: Thirty computed tomography (CT) scans of patients from July 1, 2016, to June 30, 2018, with normal syndesmoses were evaluated. Center-center and centroid measurements were drawn and compared on the axial CT images at 10, 20, and 30 mm superior to the tibial plafond. Three observers recorded measurements for the same 50 patients in order to compare interobserver reliability. RESULTS: The difference between the centroid and center-center axis at each height level was a mean 0.4 degrees (range, 0.3-0.5 degrees). The center-center and centroid axis change by externally rotating as the height increases away from the tibial plafond with mean, 3 degrees (range, 0-6.1 degrees). Intraclass correlation coefficients (ICCs) were measured at 0.98, thus demonstrating excellent intraobserver and interobserver reliability on these measurements. CONCLUSION: The center-center technique can be used to identify the centroid axis within an acceptable degree of rotation at heights above the tibial plafond that are relevant to an operating surgeon placing syndesmotic fixation. CLINICAL RELEVANCE: Theoretically, this aligns the centroids of the fibula and tibia, which achieves the same ideal patient-specific alignment and raises the question as to the extent to which the centroid and center-center axes correlate in the general population. If present, a strong correlation has potentially high clinical importance when planning syndesmotic fixation.

Compensatory Motion of the Subtalar Joint Following Tibiotalar Arthrodesis: An in Vivo Dual-Fluoroscopy Imaging Study.

BACKGROUND: Tibiotalar arthrodesis is a common treatment for end-stage tibiotalar osteoarthritis, and is associated with a long-term risk of concomitant subtalar osteoarthritis. It has been clinically hypothesized that subtalar osteoarthritis following tibiotalar arthrodesis is the product of compensatory subtalar joint hypermobility. However, in vivo measurements of subtalar joint motion following tibiotalar arthrodesis have not been quantified. Using dual-fluoroscopy motion capture, we tested the hypothesis that the subtalar joint of the limb with a tibiotalar arthrodesis would demonstrate differences in kinematics and increased range of motion compared with the subtalar joint of the contralateral, asymptomatic, untreated ankle. METHODS: Ten asymptomatic patients who had undergone unilateral tibiotalar arthrodesis at a mean (and standard deviation) of 4.0 ± 1.8 years previously were evaluated during overground walking and a double heel-rise task. The evaluation involved markerless tracking with use of dual fluoroscopy integrated with 3-dimensional computed tomography, which allowed for dynamic measurements of subtalar and tibiotalar dorsiflexion-plantar flexion, inversion-eversion, and internal-external rotation. Range of motion, stance time, swing time, step length, and step width were also measured. RESULTS: During the early stance phase of walking, the subtalar joint of the limb that had been treated with arthrodesis was plantar flexed (-4.7° ± 3.3°), whereas the subtalar joint of the untreated limb was dorsiflexed (4.6° ± 2.2°). Also, during the early stance phase of walking, eversion of the subtalar joint of the surgically treated limb (0.2° ± 2.3°) was less than that of the untreated limb (4.5° ± 3.2°). During double heel-rise, the treated limb exhibited increased peak subtalar plantar flexion (-7.1° ± 4.1°) compared with the untreated limb (0.2° ± 1.8°). CONCLUSIONS: A significant increase in subtalar joint plantar flexion was found to be a primary compensation during overground walking and a double heel-rise activity following tibiotalar arthrodesis. CLINICAL RELEVANCE: Significant subtalar joint plantar flexion compensations appear to occur following tibiotalar arthrodesis. We found an increase in subtalar plantar flexion and considered the potential relationship of this finding with the increased rate of subtalar osteoarthritis that occurs following ankle arthrodesis.

Connecting the wrist to the hand: A simulation study exploring changes in thumb-tip endpoint force following wrist surgery.

The wrist is essential for hand function. Yet, due to the complexity of the wrist and hand, studies often examine their biomechanical features in isolation. This approach is insufficient for understanding links between orthopaedic surgery at the wrist and concomitant functional impairments at the hand. We hypothesize that clinical reports of reduced force production by the hand following wrist surgeries can be explained by the surgically-induced, biomechanical changes to the system, even when those changes are isolated to the wrist. This study develops dynamic simulations of lateral pinch force following two common surgeries for wrist osteoarthritis: scaphoid-excision four-corner fusion (SE4CF) and proximal row carpectomy (PRC). Simulations of lateral pinch force production in the nonimpaired, SE4CF, and PRC conditions were developed by adapting published models of the nonimpaired wrist and thumb. Our simulations and biomechanical analyses demonstrate how the increased torque-generating requirements at the wrist imposed by the orthopaedic surgeries influence force production to such an extent that changes in motor control strategy are required to generate well-directed thumb-tip end-point forces. The novel implications of our work include identifying the need for surgeries that optimize the configuration of wrist axes of rotation, rehabilitation strategies that improve post-operative wrist strength, and scientific evaluation of motor control strategies following surgery. Our simulations of SE4CF and PRC replicate surgically-imposed decreases in pinch strength, and also identify the wrist's torque-generating capacity and the adaptability of muscle coordination patterns as key research areas to improve post-operative hand function.

Surgical Simulations Based on Limited Quantitative Data: Understanding How Musculoskeletal Models Can Be Used to Predict Moment Arms and Guide Experimental Design.

The utility of biomechanical models and simulations to examine clinical problems is currently limited by the need for extensive amounts of experimental data describing how a given procedure or disease affects the musculoskeletal system. Methods capable of predicting how individual biomechanical parameters are altered by surgery are necessary for the efficient development of surgical simulations. In this study, we evaluate to what extent models based on limited amounts of quantitative data can be used to predict how surgery influences muscle moment arms, a critical parameter that defines how muscle force is transformed into joint torque. We specifically examine proximal row carpectomy and scaphoid-excision four-corner fusion, two common surgeries to treat wrist osteoarthritis. Using models of these surgeries, which are based on limited data and many assumptions, we perform simulations to formulate a hypothesis regarding how these wrist surgeries influence muscle moment arms. Importantly, the hypothesis is based on analysis of only the primary wrist muscles. We then test the simulation-based hypothesis using a cadaveric experiment that measures moment arms of both the primary wrist and extrinsic thumb muscles. The measured moment arms of the primary wrist muscles are used to verify the hypothesis, while those of the extrinsic thumb muscles are used as cross-validation to test whether the hypothesis is generalizable. The moment arms estimated by the models and measured in the cadaveric experiment both indicate that a critical difference between the surgeries is how they alter radial-ulnar deviation versus flexion-extension moment arms at the wrist. Thus, our results demonstrate that models based on limited quantitative data can provide novel insights. This work also highlights that synergistically utilizing simulation and experimental methods can aid the design of experiments and make it possible to test the predictive limits of current computer simulation techniques.

Reduction in DNA synthesis during two-photon microscopy of intrinsic reduced nicotinamide adenine dinucleotide fluorescence.

Two-photon laser scanning microscopy (TPLSM) of endogenous reduced nicotinamide adenine dinucleotide (NAD(P)H) provides important information regarding the cellular metabolic state. When imaging the punctate mitochondrial fluorescence originating from NAD(P)H in a rat basophilic leukemia (RBL) cell at low laser powers, no morphological changes are evident, and photobleaching is not observed when many images are taken. At higher powers, mitochondrial NAD(P)H fluorescence bleaches rapidly. To assess the limitations of this technique and to quantify the extent of photodamage, we have measured the effect of TPLSM on DNA synthesis. Although previous reports have indicated a threshold power for "safe" two-photon imaging, we find the laser power to be an insufficient indicator of photodamage. A more meaningful metric is a two-photon-absorbed dose that is proportional to the number of absorbed photon pairs. A temporary reduction of DNA synthesis in RBL cells occurs whenever a threshold dose of approximately 2 x 10(53) photon2 cm-4 s-1 is exceeded. This threshold is independent of laser intensity when imaging with average powers ranging from 5 to 17 mW at 740 nm. Beyond this threshold, the extent of the reduction is intensity dependent. DNA synthesis returns to control levels after a recovery period of several hours.