Cement augmentation of the acetabulum for revision total hip arthroplasty for infection.

Antibiotic-loaded cement spacers in first-stage revision hip arthroplasty for infection are associated with a high dislocation and fracture rate. This technical note describes a novel surgical technique, utilizing screws and cement, improving acetabular coverage and reducing the risk of mechanical failure. Fifteen infected hip prostheses underwent removal, cement acetabular augmentation and insertion of a femoral cement spacer. Eleven hips had successful infection eradication and subsequently underwent a second stage revision procedure a mean duration of 15 weeks (9-48) after the first stage. No dislocations or fractures of the cement spacers were observed. This technique affords the potential to reduce the duration of time cement spacers remaining in situ, provides enhanced mechanical stability and improved antibiotic elution through cement-on-cement articulation.

Modulation of motor unit discharge rate and H-reflex amplitude during submaximal fatigue of the human soleus muscle.

Declining motor unit discharge rates and H-reflex amplitude have been observed in separate experiments during fatiguing submaximal contractions in humans. The purpose of this experiment was to investigate motor unit discharge rate, H-reflex amplitude, and twitch contractile properties concurrently during a fatiguing submaximal isometric contraction of the ankle plantarflexors. Eleven healthy subjects performed fatiguing contractions of low force (25% maximal voluntary contraction (MVC)) or high force (42-66% MVC). Hoffmann (H)-reflexes, muscle compound action potentials (M-waves), twitch contractile properties, and motor unit discharges were recorded from the soleus muscle. In the low-force fatigue task, motor unit firing rate increased gradually over time, whereas the resting H-reflex was significantly depressed at 15% of endurance time and remained quasiconstant for the rest of the task. This suggests that the processes mediating the resting H-reflex depression are relatively independent of those modulating the motor unit firing rate during a low-force fatigue task. In the high-force fatigue task, a decline in the average motor unit discharge rate was accompanied by a decrease in the resting H-reflex amplitude and a prolongation of the twitch half-relaxation time (HRT) at the completion of the fatigue task. Overall, motor unit firing rate was modulated in parallel with changes in the twitch HRT, consistent with the muscle wisdom hypothesis.