Acute trunnion failure of a TMZF alloy stem with large diameter femoral heads.

INTRODUCTION: Femoral head-neck modularity in total hip arthroplasty (THA) is advantageous but taper corrosion at the trunnion can result in implant failure. We report two cases of acute catastrophic trunnion failure with a TMZF alloy cementless stem. METHODS: Demographic, clinical, radiographic and operative data including implant retrieval was recorded and is presented. RESULTS: Case 1: A 79 year old farmer presented with sudden onset of hip pain and an inability to weight bear. He underwent a cementless large diameter stemmed metal-on-metal system (MITCH acetabular component, 56mm cobalt chrome head 4.5 lateralised Accolade TMZF, Stryker) nine years previously. He denied symptoms prior to his presentation to the Emergency Department.Case 2: An 86 year old gentleman presented with sudden onset of hip pain and inability to weight bear. He underwent a cementless large diameter stemmed metal-on-poly THA (Trident acetabular component, X3 polyethylene insert, 44mm cobalt chrome head, 4.5 lateralised Accolade TMZF, Stryker)nine years previously. This man had been complaining of mild hip symptoms prior to presentation. CONCLUSION: Patients that have received TMZF alloy cementless stems coupled with CoCr alloy heads are at risk of catastrophic trunnion failure. Importantly, background trunnion corrosion may occur silently and present emergently irrespective of surveillance.

Characterization of a novel capsaicin/heat ongoing pain model.

BACKGROUND: Human experimental pain models provide an important translational link between pre-clinical models and clinical pain. Using topical capsaicin and continuous heat application, the novel capsaicin/heat ongoing pain (CHOP) model induces long-lasting experimental pain of which the perceived intensity can be individually adjusted. METHODS: In the CHOP model, capsaicin or control cream is applied to a 10 × 10 cm skin area and a heating pad is applied over the area after cream removal. Two experiments in healthy participants were performed for model characterization. In Experiment 1, a constant temperature was applied for 60 min; in Experiment 2, temperature was adjusted to maintain a constant perceived intensity for 60 min. RESULTS: Experiment 1: across participants, constant temperature induced initial habituation followed by an increase in sensation back to baseline. Cluster analysis revealed that half the participants sensitized to the constant temperature, while the other half did not. The degree of sensitization was related to the baseline pain unpleasantness, relative to pain intensity. Experiment 2: constant perceived intensity was achieved in the painful and a non-painful control condition. The two conditions did not differ regarding possibly confounding variables, including blood pressure, heart rate, inflammation or physiological stress as measured by surrogate markers. Secondary allodynia and hyperalgesia were reported more following painful compared to control stimulation. Sensitizers as determined in Experiment 1 were also more pain sensitive in Experiment 2. CONCLUSION: The CHOP model reproduces some aspects of clinical pain, such as longer duration, sensitization, secondary allodynia and hyperalgesia. SIGNIFICANCE: Here we demonstrate a novel pain model that can be applied for up to an hour without tissue damage. The CHOP model allows for investigation of primary and secondary hyperalgesia as well as top-down influences on sensitization, thereby providing an experimental model that can be used to assess clinically-oriented questions.

Refolding and purification of a urokinase plasminogen activator fragment by chromatography.

A fragment of recombinant urokinase plasminogen activator (u-PA), was expressed in E. coli in the form of inclusion bodies. Purification and renaturation was achieved in a three-stage process. Capture of the inclusion bodies was achieved by coupling wash steps in Triton X-100 and urea with centrifugation. Solubilised inclusion bodies were then renatured by buffer exchange performed by size-exclusion chromatography (SEPROS). Use of size-exclusion media with higher fractionation ranges resulted in an increase in the recovery of u-PA activity, to a maximum fractionation range of Mr 10000-1500000 after which recovery is reduced, due to a low resolution between the refolded u-PA and denaturant. Fractions of refolded u-PA were concentrated using cation ion-exchange chromatography, which selectively binds correctly folded u-PA. The result is concentrated, active, homogeneous u-PA.