Validation of a 3D CT imaging method for quantifying implant migration following anatomic total shoulder arthroplasty.

Glenoid component loosening remains a common complication following anatomic total shoulder arthroplasty (TSA); however, plain radiographs are unable to accurately detect early implant migration. The purpose of this study was to validate the accuracy of a method of postoperative, three-dimensional (3D) computed tomography (CT) imaging with metal artifact reduction (MAR) to detect glenoid component migration following anatomic TSA. Tantalum bead markers were inserted into polyethylene glenoid components for implant detection on 3D CT. In-vitro validation was performed using a glenoid component placed into a scapula sawbone and incrementally translated and rotated, with MAR 3D CT acquired at each test position. Accuracy was evaluated by root mean square error (RMSE). In-vivo validation was performed on six patients who underwent anatomic TSA, with two postoperative CT scans acquired in each patient and marker-based radiostereometric analysis (RSA) performed on the same days. Glenoid component migration was calculated relative to a scapular coordinate system for both MAR 3D CT and RSA. Accuracy was evaluated by RMSE and paired Student's t-tests. The largest RMSE on in-vitro testing was 0.24 mm in translation and 0.11° in rotation, and on in-vivo testing was 0.47 mm in translation and 1.04° in rotation. There were no significant differences between MAR 3D CT and RSA measurement methods. MAR 3D CT imaging is capable of quantifying glenoid component migration with a high level of accuracy. MAR 3D CT imaging is advantageous over RSA because it is readily available clinically and can also be used to evaluate the implant-bone interface.

Dynamic in-vivo assessment of navicular drop while running in barefoot, minimalist, and motion control footwear conditions.

Running-related injuries are common and previous research has suggested that the magnitude and/or rate of pronation may contribute to the development of these injuries. Accurately and directly measuring pronation can be challenging, and therefore previous research has often relied on navicular drop (under both static and dynamic conditions) as an indirect assessment of pronation. The objectives of this study were to use dynamic, biplane X-ray imaging to assess the effects of three footwear conditions (barefoot, minimalist shoes, motion control shoes) on the magnitude and rate of navicular drop during running, and to determine the association between static and dynamic measures of navicular drop. Twelve healthy distance runners participated in this study. The magnitude and rate of navicular drop were determined by tracking the 3D position of the navicular from biplane radiographic images acquired at 60Hz during the stance phase of overground running. Static assessments of navicular drop and foot posture were also recorded in each subject. Footwear condition was not found to have a significant effect on the magnitude of navicular drop (p=0.22), but motion control shoes had a slower navicular drop rate than running barefoot (p=0.05) or in minimalist shoes (p=0.05). In an exploratory analysis, static assessments of navicular drop and foot posture were found to be poor predictors of dynamic navicular drop in all footwear conditions (p>0.18).

Effects of footwear on three-dimensional tibiotalar and subtalar joint motion during running.

Running is a popular form of recreation, but injuries are common and may be associated with abnormal joint motion. The objective of this study was to determine the effect of three footwear conditions - barefoot (BF), an ultraflexible training shoe (FREE), and a motion control shoe (MC) - on 3D foot and ankle motion. Dynamic, biplane radiographic images were acquired from 12 runners during overground running. 3D rotations of the tibiotalar and subtalar joints were quantified in terms of plantarflexion/dorsiflexion (PF/DF), inversion/eversion (IN/EV) and internal/external rotation (IR/ER). Across the early stance phase (defined as footstrike to heel-off), BF running demonstrated greater tibiotalar joint range of motion for PF/DF (28.2 ± 8.3°) and IR/ER (7.0 ± 1.4°) than the shod conditions (FREE: PF/DF=15.1 ± 5.9°, IR/ER=4.8 ± 2.1°; MC: PF/DF=15.0 ± 6.2°, IR/ER=4.3 ± 0.7°). Also at the tibiotalar joint, BF running resulted in a position significantly more plantarflexed (BF: 2.0 ± 12.5°, FREE: 15.7 ± 12.2°, MC: 16.5 ± 9.3°) and internally rotated (BF: 12.9 ± 4.5°, FREE: 10.7 ± 4.3°, MC: 10.6 ± 3.9°) at footstrike compared to both shod conditions. No differences were detected between the shod conditions at any point in the early stance phase at the tibiotalar joint. The MC condition demonstrated significant differences compared to FREE at several points throughout the early stance phase at the subtalar joint, with the greatest differences seen at 30% in PF/DF (MC -1.4 ± 8.8°: FREE: -0.5 ± 9.0°), IN/EV (MC -8.1 ± 5.7°: FREE -6.3 ± 5.5°) and IR/ER (MC -9.5 ± 5.3°: FREE: -8.7 ± 5.2°). These findings indicate that footwear has subtle effects on joint motion mainly between BF and shod conditions at the tibiotalar joint and between shod conditions at the subtalar joint.

Associations among shoulder strength, glenohumeral joint motion, and clinical outcome after rotator cuff repair.

Rotator cuff tears are a common condition causing pain and disability, but the relationships among clinical measures of shoulder function and measures of glenohumeral joint (GHJ) function are not well known. In the study reported here, dynamic in vivo GHJ motion was measured during abduction from biplane radiographs in 22 rotator cuff repair (RCR) patients and 36 control subjects. Isometric shoulder strength was measured and clinical outcomes were assessed using the Western Ontario Rotator Cuff (WORC) Index. Associations among WORC, GHJ motion, and several shoulder strength ratios were assessed with linear regression. An association was detected between higher ER/ABD (external rotation/coronal-plane abduction) strength ratio and a humerus positioned more inferiorly relative to the glenoid in control subjects and RCR patients. Higher ER/ABD strength ratio was also associated with better clinical outcome in RCR patients. These findings suggest a relationship between ER/ABD strength ratio and a more centrally located average superior/inferior contact center in RCR patients and control subjects. The ER/ABD strength ratio can be easily measured in a clinical setting and therefore can be used in larger studies to investigate its relation to clinical outcomes over time or perhaps to predict superior migration of the humeral head.

Bracing improves clinical outcomes but does not affect the medial knee joint space in osteoarthritic patients during gait.

PURPOSE: Osteoarthritis (OA) of the knee is commonly treated through the use of medial compartment unloading braces which have been shown to improve clinical symptoms. The objective of this study was to assess the effects of a medial compartment unloading brace on biomechanical measurements and clinical outcomes. We hypothesized that brace usage would lead to increased medial joint space and improved clinical outcomes. METHODS: Ten patients with medial compartment OA were prescribed a medial compartment unloading brace and underwent dynamic biplane radiograph imaging while walking with and without the brace. The Western Ontario and McMaster University Osteoarthritis (WOMAC) Index was used to assess pain before brace wear and at the time of testing. The 3D position and orientation of the femur and tibia were determined using a model-based tracking technique. RESULTS: Patients saw an average improvement of 33 % in their WOMAC scores (p = 0.01). This study failed to detect any statistically significant changes in the functional joint space, knee kinematics, or contact centre location between the braced and unbraced condition (n.s.). CONCLUSION: The data from this study, using a highly accurate (±0.6 mm and ±0.6°) 3D radiograph analysis of dynamic tibiofemoral motion, suggest that the brace is ineffective at increasing joint space. However, it was shown to be effective in improving clinical outcome and therefore should continue to be prescribed to patients even though the mechanism of its effectiveness remains unknown. LEVEL OF EVIDENCE: IV.

Validation of a novel method for quantifying and comparing regional ACL elongations during uniaxial tensile loading.

Given the complex three-dimensional (3D) knee joint loading associated with anterior cruciate ligament (ACL) injuries, accurate site- and bundle-specific strain measurements are critical. The purpose of this study was to quantify tensile load-induced migrations of radio-opaque markers injected directly into the ACL, as a first step in validating a roentgen stereophotogrammetric analysis-based method for measuring ligament strain. Small markers were inserted into the femur and tibia, as well as injected into the antero-medial bundle of the ACL of eight (42-56 yrs) femur-ACL-tibia complexes (FATCs). The FATCs were then loaded under tension along the ligament's longitudinal axis by a material testing machine from 10 N to 50 N, 100 N, 125 N, and 150 N, each over 10 load-unload cycles. Complexes were imaged before the loading protocol, between each loading sequence, and after the protocol via biplane radiography. Marker migrations within the ACL tissue were quantified as the difference in their 3D positions between the pre- and each post-loading condition. Negligible migration was evident, with the lowest average root mean square values observed along the longitudinal axis of the ACL, ranging from 0.128 to 0.219 mm. Further, neither marker location nor load magnitude significantly affected migration values. This innovative method, therefore, presents as a plausible means to measure global and regional ACL strains, as small as 0.75% strain. In particular, it may provide important new insights in ACL strain behaviors during complex 3D knee load states associated with ligament injury.