Anteroposterior Translational Malalignment of Ankle Arthrodesis Alters Foot Biomechanics in Cadaveric Gait Simulation.

Tibiotalar arthrodesis is a common surgical treatment for end-stage ankle arthritis. Proper ankle alignment is important as malalignment can lead to complications that may require revision surgery. This study aimed to determine how anteroposterior (AP) translational malalignment of ankle arthrodesis affects distal foot joint kinematics and plantar pressure. Ankle arthrodesis was performed on 10 cadaveric foot specimens using a custom fixture that could fuse the ankle neutrally and induce discrete malalignments (3, 6, and 9 mm) anteriorly and posteriorly. Gait was simulated under each alignment with a robotic gait simulator, and foot bone motion and plantar pressure were quantified. AP translational malalignment did not substantially affect plantar pressure or joint range of motion, but there were several significant differences in joint position throughout stance phase. Differences were seen in five joints (talocalcaneal, talonavicular, calcaneocuboid, fifth tarsometatarsal, and first metatarsophalangeal) and in the position of the first metatarsal relative to the talus. The most extreme effects occurred when the talus was displaced 6 mm or more posteriorly. In vivo, this may lead to aberrant joint loading, which could negatively impact patient outcomes. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:450-458, 2020.

Enchondroma Protuberans of the Ulna in a Pediatric Patient: A Case Report.

CASE: We report the case of a 3-year-old boy who presented with a distal ulnar fracture through a mixed sclerotic and lytic expansile lesion. The underlying lesion, an enchondroma protuberans, can mimic either benign or malignant bone tumors. It was successfully treated with casting and intralesional treatment. CONCLUSION: Enchondroma protuberans is a rare entity that mimics enchondroma, osteochondroma, periosteal chondroma, or chondrosarcoma. Diagnosis is typically made through both radiographic and histologic means. In this case, the pathologic fracture was successfully treated with casting followed by intralesional curettage and bone-grafting. There was no evidence of recurrence at 18 months.

The effects of patellar tendon advancement on the immature proximal tibia.

PURPOSE: The aim of this study is to examine the short-term effects of patellar tendon advancement on the proximal tibial slope in the skeletally immature patient. METHODS: A retrospective, non-randomized, comparative cohort design was used. Koshino indices and tibial slopes were assessed pre-operatively and post-operatively and compared with age- and sex-matched controls. RESULTS: Nine children with 17 patellar tendon advancements were analyzed for changes in Koshino indices. Of these 17 tibiae, radiographs on changes in tibial slope were available for 16 tibiae which were also compared with controls. Children aged <11 years had a greater initial posterior tibial slope (69.8° ± 3.5°) than age-matched controls (80.3° ± 2.7°). A decrease in posterior slope was seen in these younger patients (average change 10.3° ± 4.8°) at an average of 1.6 years of follow-up. Of the nine apophyses in children aged <11 years of age, seven had undergone premature closure. CONCLUSION: Patellar tendon advancement appears to have an unreported effect on the proximal tibial growth in the young patient (<11 years old). These patients appear to be susceptible to apophyseal closure, resulting in subsequent loss of posterior tibial slope. Surgeons should be aware of this effect and monitor younger patients with radiographs if performing this procedure.

Variation in external rotation moment arms among subregions of supraspinatus, infraspinatus, and teres minor muscles.

A rotator cuff tear causes morphologic changes in rotator cuff muscles and tendons and reduced shoulder strength. The mechanisms by which these changes affect joint strength are not understood. This study's purpose was to empirically determine rotation moment arms for subregions of supraspinatus, infraspinatus, and for teres minor, and to test the hypothesis that subregions of the cuff tendons increase their effective moment arms through connections to other subregions. Tendon excursions were measured for full ranges of rotation on 10 independent glenohumeral specimens with the humerus abducted in the scapular plane at 10 and 60 degrees . Supraspinatus and infraspinatus tendons were divided into equal width subregions. Two conditions were tested: tendon divided to the musculotendinous junction, and tendon divided to the insertion on the humerus. Moment arms were determined from tendon excursion via the principle of virtual work. Moment arms for the infraspinatus (p < 0.001) and supraspinatus (p < 0.001) were significantly greater when the tendon was only divided to the musculotendinous junction versus division to the humeral head. Moment arms across subregions of infraspinatus (p < 0.001) and supraspinatus (p < 0.001) were significantly different. A difference in teres minor moment arm was not found for the two cuff tendon conditions. Moment arm differences between muscle subregions and for tendon division conditions have clinical implications. Interaction between cuff regions could explain why some subjects retain strength after a small cuff tear. This finding helps explain why a partial cuff repair may be beneficial when a complete repair is not possible. Data presented here can help differentiate between cuff tear cases that would benefit from cuff repair and cases for which cuff repair might not be as favorable.

Variability in isometric force and moment generating capacity of glenohumeral external rotator muscles.

BACKGROUND: Muscles which cause glenohumeral external rotation possess varying ability for generating force and moment due to differences in muscle architecture, moment arm, and the interaction of these two factors. This study's purpose was to determine a complete dataset of muscle-tendon parameters for predicting the moment generating capacity and force-length dependence for external rotation of infraspinatus, supraspinatus and teres minor muscles. METHODS: Muscle fascicle length, sarcomere length, pennation angle, and muscle volume were measured for sub-regions of infraspinatus and supraspinatus, and teres minor from 10 glenohumeral specimens. Tendon excursion was measured for glenohumeral rotation. From these parameter measurements, optimal fascicle length, physiological cross-sectional area, muscle force-length dependence, and maximum isometric moment generating capacity were calculated. FINDINGS: Substantial differences were found for optimal muscle length, physiologic cross-sectional area, and tendon length for the 10 specimens of this study. Muscle sub-region had a significant effect on the force-length relationship for infraspinatus (P<0.001), but was not significant for supraspinatus (P=0.49). For infraspinatus and supraspinatus, maximum isometric rotation moment capacity was greater at 10 degrees versus 60 degrees abduction (P<0.001). Maximum isometric rotation moment capacity for the teres minor was greater at 10 degrees versus 60 degrees abduction (P<0.01). Sub-regions demonstrated significant differences in isometric moment capacity (P<0.001). INTERPRETATION: Functional capabilities of these muscles depend on muscle architecture and moment arm as well as their combined effects. The results allow for development of stochastic and deterministic models of glenohumeral external rotation strength which can be used for prediction of muscle forces and joint moments.