Poster Session 2: Human studies 444 NEUROPHYSIOLOGICAL CHARACTERIZATION OF POSTHERNIORRHAPHY PAIN E.K. Aasvang * ,a,b , B. Brandsborg c , B. Christensen c , T.S. Jensen c,d , H. Kehlet a a Section of Surgical Pathophysiology, The Juliane Marie Centre, Denmark b Department of Anaesthesia, Centre of Head and Orthopedics, Rigshospitalet, Copenhagen, Denmark c Danish Pain Research Center, Denmark d Department of Neurology, Aarhus University Hospital, Denmark Background. Chronic pain affecting everyday activi- ties are reported in 10% of patients following inguinal herniorrhaphy. However, the neurophysiological changes and underlying pathophysiological mechanisms are not known in detail. Methods. The primary endpoint was to identify sen- sory disturbances specific for chronic postherniorrha- phy pain patients. Thirty-five patients reporting chronic post-herniorrhaphy pain were compared with a control group of 10 patients without postoperative pain. Sensory tests were carried bilaterally and included detection and pain thresholds to thermal and mechani- cal stimuli and response to repetitive pinprick stimula- tion. Side to side and inter-group differences were compared. Results. Sensory disturbances on the operated side were found in patients and controls. Thermal and tactile detection thresholds were sig- nificantly increased in the pain group compared to controls. Direct pressure pain detection threshold was significantly lower in pain-patients compared with controls. Evoked/increased pain to repetitive punctuate stimulation was found only in the pain- patient group and only on the operated side. After- sensations to repetitive pinprick stimulation were reported by 11/35 (28%) pain patients and not by the controls. Conclusion. Similar to other types of chronic postoper- ative pain syndromes (i.e. mastectomy) we found that sensory disturbances are present including sensitization indicating that this is a neuropathic pain state. The find- ing that pressure pain detection was significantly decreased only in the pain group suggests that the origin of pain is from deeper structures rather than the skin. However, whether the underlying pathophysiological mechanisms are related to an intraoperative nerve injury or inflammation of nervous tissue remains to be explored. doi:10.1016/j.ejpain.2007.03.459 445 TEMPORAL SUMMATION OF PAIN – REPRO- DUCIBILITY IN NORMAL VOLUNTEERS A. Bet *, J. Acosta-Guillen, R. Lecybyl, M. Hanna Pain Clinical Research Hub, King’s College Hospital, King’s College London, UK Background and aims. The phenomenon of Temporal Summation refers to an increase in the experienced intensity of pain as a consequence of repeated stimulation. The aim of our study was to investigate the relation- ship between stimulus intensity and the stimulus fre- quency required to evoke pain as well as the reproducibility of repetitive stimulation for evaluation of pain. Methods. Two groups of 12 healthy male volunteers participated in a two-visit study. A constant current electrical stimulator (Digitimer) was used to produce 1 ms square wave pulses that were applied to the area above the right sural nerve. Detection threshold (DT), pain threshold (PT) and pain tolerance threshold (PTT) were established in the beginning of each ses- sion. Temporal summation of pain was induced by repeated electrical stimuli and temporal summation threshold (TST) determined for different stimulus fre- quency and intensity. Pain was assessed by NRS and VAS. Results. In all subjects, but one, TST was obtainable and reproducible. We also observed that it is dependent on the intensity and the frequency of stimuli. DT showed the greatest intrasubject variability. PT and PTT showed a low intrasubject variability. Intrasubject variability for PT, PTT and TST indicated that the sample size required to detect a 25% difference is approximately 7, 3 and 14 subjects, respectively. Conclusions. Using single 1 ms electrical pulses we were able to demonstrate good intrasubject correlation for PT, PTT and TST. The present study supports the use of this model for evaluation of TS in healthy individ- uals and pharmacological characterization. doi:10.1016/j.ejpain.2007.03.460 446 A PROSPECTIVE STUDY OF PAIN AFTER HYS- TERECTOMY IN WOMEN WITH BENIGN UTER- INE DISORDERS B. Brandsborg * ,a , M. Dueholm b , L. Nikolajsen a , L. de Lasson c , H. Kehlet d , T.S. Jensen a Poster Presentations / Human studies / European Journal of Pain 11(S1) (2007) S59–S207 S197