Senile kyphosis arises from anterior ‘wedge’ deformity of thoracolumbar vertebrae, often in the absence of trauma. It is difficult to reproduce these deformities in cadaveric spines, because a vertebral endplate usually fails first. We hypothesise that endplate fracture concentrates sufficient loading on to the anterior cortex that a wedge deformity develops subsequently under physiological repetitive loading. Thirty-four cadaveric thoracolumbar “motion segments,” aged 70–97 yrs, were overloaded in combined bending and compression. Physiologically-reasonable cyclic loading was then applied, at progressively higher loads, for up to 2 hrs. Before and after fracture, and again after cyclic loading the Introduction
Methods
Osteoporotic vertebral fractures can cause severe vertebral wedging and kyphotic deformity. This study tested the hypothesis that kyphoplasty restores vertebral height, shape and mechanical function to a greater extent than vertebroplasty following severe wedge fractures. Pairs of thoracolumbar “motion segments” from seventeen cadavers (70–97 yrs) were compressed to failure in moderate flexion and then cyclically loaded to create severe wedge deformity. One of each pair underwent vertebroplasty and the other kyphoplasty. Specimens were then creep loaded at 1.0kN for 1 hour. At each stage of the experiment the following parameters were measured: vertebral height and wedge angle from radiographs, motion segment compressive stiffness, and stress distributions within the intervertebral discs. The latter indicated intra-discal pressure (IDP) and neural arch load-bearing (FN).Introduction
Methods
Senile kyphosis arises from anterior ‘wedge’ deformity of thoracolumbar vertebrae, often in the absence of trauma. It is difficult to reproduce these deformities in cadaveric spines, because a vertebral endplate usually fails first. We hypothesise that endplate fracture concentrates sufficient loading on to the anterior cortex that a wedge deformity develops subsequently under physiological repetitive loading. Thirty-four cadaveric thoracolumbar “motion segments,” aged 70–97 yrs, were overloaded in combined bending and compression. Physiologically-reasonable cyclic loading was then applied, at progressively higher loads, for up to 2 hrs. Before and after fracture, and again after cyclic loading the distribution of compressive loading on the vertebral body was assessed from recordings of compressive stress along the sagittal mid-plane of the adjacent intervertebral disc. Vertebral deformity was assessed from radiographs at the beginning and end of testing.Introduction
Methods
Paratenonitis describes inflammation of the paratenon and commonly presents as an overuse injury. The paratenon is the connective tissue sheath that surrounds tendons - including tendo Achilles, and serves to minimise friction with the outer layer of the tendon, the epitenon. Whilst this conjunction allows the tendon to glide smoothly on muscular contraction, the presentation of paratenonitis typically follows periods of frequent, repetitive musculoskeletal movements; hence, paratenonitis commonly afflicts the elite and, albeit to a lesser extent, amateur athlete. The extent to which friction at the epitenon-paratenon juncture contributes to this tendinopathy remains unclear, and this study is therefore concerned with the coefficient of friction and the lubrication regime. By using a specially designed and validated apparatus, the in vivo paratenon-epitenon conjunction was approximated using bovine flexor tendon paratenon and a glass disc; this is being an equivalent experimental set-up to that used in other studies exploring soft tissue contacts. Bovine synovial fluid was used to lubricate the conjunction at 37 deg C, and the frictional characteristics were analysed over a range of sliding speeds and loads. The coefficient of friction was found to generally lie between 0.1 – 0.01. This range suggests that a system of mixed lubrication applies - where the synovial fluid is causing partial separation of the two surfaces. However, when the data is plotted in the form of a Stribeck curve, the trend suggests that boundary lubrication prevails - where lubrication is determined by surface-bound proteins. The coefficient of friction at the epitenon-paratenon interface appears to be approximately one order of magnitude greater than that typically reported within the healthy synovial joint. Additionally, the synovial joint is thought to exhibit some fluid film lubrication (i.e. total surface separation), whereas the epitenon-paratenon lubrication regime appears to vary only between the inferior mixed and boundary systems - depending on the specific biomechanical conditions. This data would suggest that the coefficient of friction at the epitenon-paratenon interface is relatively high and thus is potentially significant in the incidence of paratenonitis. Such a hypothesis could be of particular interest to sports-medicine and orthopaedic specialists.
