Hospital volume and patient outcomes after cholecystectomy in Scotland: retrospective, national population based study.

OBJECTIVES: To define associations between hospital volume and outcomes following cholecystectomy, after adjustment for case mix using a national database. DESIGN: Retrospective, national population based study using multilevel modelling and simulation. SETTING: Locally validated administrative dataset covering all NHS hospitals in Scotland. PARTICIPANTS: All patients undergoing cholecystectomy between 1 January 1998 and 31 December 2007. MAIN OUTCOME MEASURES: Mortality, 30 day reoperation rate, 30 day readmission rate, and length of stay. RESULTS: We identified 59,918 patients who had a cholecystectomy in one of 37 hospitals: five hospitals had high volumes (>244 cholecystectomies/year), 10 had medium volumes (173-244), and 22 had low volumes (<173). Compared with low and medium volume hospitals, high volume hospitals performed more procedures non-electively (17.1% and 19.5% v 32.8%), completed more procedures laparoscopically (64.7% and 73.8% v 80.9%), and used more operative cholangiography (11.2% and 6.3% v 21.2%; χ(2) test, all P<0.001). In a well performing multivariable analysis with bias correction for a low event rate, the odds ratio for death was greater in both the low volume (odds ratio 1.45, 95% confidence interval 1.06 to 2.00, P=0.022) and medium volume (1.52, 1.11 to 2.08, P=0.010) groups than in the high volume group. However, in simulation studies, absolute risk differences between volume groups were clinically negligible for patients with average risk (number needed to treat to harm, low v high volume, 3871, 1963 to 17,118), but were significant in patients with higher risk. In models accounting for the hierarchical structure of patients in hospitals, those in medium volume hospitals were more likely to undergo reoperation (odds ratio 1.74, 1.31 to 2.30, P<0.001) or be readmitted (1.17, 1.04 to 1.31, P=0.008) after cholecystectomy than those in high volume hospitals. Length of stay was shorter in high volume hospitals than in low (hazard ratio for discharge 0.78, 0.76 to 0.79, P<0.001) or medium volume hospitals (0.75, 0.74 to 0.77, P<0.001). These differences were also only of clinical significance in patients at higher risk. CONCLUSIONS: There is wide variation among hospitals in the management of gallstone disease and an association between higher hospital volume and better outcome after a cholecystectomy. The relative risk of death is lower in high volume centres, and although absolute risk differences between volume groups are significant for elderly patients and patients with comorbidity, they are clinically negligible for those at average risk.

Fixed dystonia in complex regional pain syndrome: a descriptive and computational modeling approach.

BACKGROUND: Complex regional pain syndrome (CRPS) may occur after trauma, usually to one limb, and is characterized by pain and disturbed blood flow, temperature regulation and motor control. Approximately 25% of cases develop fixed dystonia. Involvement of dysfunctional GABAergic interneurons has been suggested, however the mechanisms that underpin fixed dystonia are still unknown. We hypothesized that dystonia could be the result of aberrant proprioceptive reflex strengths of position, velocity or force feedback. METHODS: We systematically characterized the pattern of dystonia in 85 CRPS-patients with dystonia according to the posture held at each joint of the affected limb. We compared the patterns with a neuromuscular computer model simulating aberrations of proprioceptive reflexes. The computer model consists of an antagonistic muscle pair with explicit contributions of the musculotendinous system and reflex pathways originating from muscle spindles and Golgi tendon organs, with time delays reflective of neural latencies. Three scenarios were simulated with the model: (i) increased reflex sensitivity (increased sensitivity of the agonistic and antagonistic reflex loops); (ii) imbalanced reflex sensitivity (increased sensitivity of the agonistic reflex loop); (iii) imbalanced reflex offset (an offset to the reflex output of the agonistic proprioceptors). RESULTS: For the arm, fixed postures were present in 123 arms of 77 patients. The dominant pattern involved flexion of the fingers (116/123), the wrists (41/123) and elbows (38/123). For the leg, fixed postures were present in 114 legs of 77 patients. The dominant pattern was plantar flexion of the toes (55/114 legs), plantar flexion and inversion of the ankle (73/114) and flexion of the knee (55/114).Only the computer simulations of imbalanced reflex sensitivity to muscle force from Golgi tendon organs caused patterns that closely resembled the observed patient characteristics. In parallel experiments using robot manipulators we have shown that patients with dystonia were less able to adapt their force feedback strength. CONCLUSIONS: Findings derived from a neuromuscular model suggest that aberrant force feedback regulation from Golgi tendon organs involving an inhibitory interneuron may underpin the typical fixed flexion postures in CRPS patients with dystonia.