Does phasic dopamine release cause policy updates?

Phasic dopamine activity is believed to both encode reward-prediction errors (RPEs) and to cause the adaptations that these errors engender. If so, a rat working for optogenetic stimulation of dopamine neurons will repeatedly update its policy and/or action values, thus iteratively increasing its work rate. Here, we challenge this view by demonstrating stable, non-maximal work rates in the face of repeated optogenetic stimulation of midbrain dopamine neurons. Furthermore, we show that rats learn to discriminate between world states distinguished only by their history of dopamine activation. Comparison of these results to reinforcement learning simulations suggests that the induced dopamine transients acted more as rewards than RPEs. However, pursuit of dopaminergic stimulation drifted upwards over a time scale of days and weeks, despite its stability within trials. To reconcile the results with prior findings, we consider multiple roles for dopamine signalling.

Subscapularis function after primary tendon to tendon repair in patients after replacement arthroplasty of the shoulder.

HYPOTHESIS: We studied the results of tendon-to-tendon repair of the subscapularis during total shoulder arthroplasty (TSA) to compare its clinical results relative to more recent studies looking at osteotomy of the lesser tuberosity. MATERIALS AND METHODS: This study analyzed the postoperative integrity of the subscapularis by a tendon-to-tendon repair in 45 arthroplasties in 43 patients. RESULTS: Preoperatively, 23 patients had a negative lift-off test; 22 could not perform the test. Postoperatively, 41 patients had a negative lift-off test; four could not reach behind themselves to do the test. All 45 shoulders had a negative belly-press test pre-operatively and post-operatively. DISCUSSION: Tendon-to-tendon repair is simpler, quicker, and avoids the possibility of an osteotomy nonunion. Tendon-to-tendon repair of the subscapularis tenotomy in shoulder arthroplasty remains an option in the presence of reasonable quality tendon, utilizing relaxing sutures (partial closure of the lateral rotator interval), and limiting early postoperative passive external rotation. LEVEL OF EVIDENCE: Level 4; Retrospective case series, no control group.

Preoperative cardiac evaluation of patients with acute hip fracture.

The goals of the present study were to assess if there is an association between preoperative cardiac evaluation and surgery timing in patients with a hip fracture, to evaluate the relationship between surgery timing and postoperative morbidity and mortality, and to determine if the proper patients are being selected for noninvasive cardiac testing based on the practice guidelines published by the American College of Cardiology/American Heart Association Task Force. Surgery delay secondary to cardiac clearance may be a risk factor for increased postoperative complications that is independent of a patient's general medical condition. Surgical treatment of acute hip fractures may be delayed by many factors besides preoperative cardiac clearance, but it is the job of the orthopedic surgeon, who best understands the importance of timely surgery for a hip fracture, to minimize delays. Careful screening of patients who have sustained a hip fracture can improve overall outcomes by minimizing the number of patients whose surgical treatment is unnecessarily delayed for cardiac clearance.

Multidirectional instability of the shoulder in elite female gymnasts.

Multidirectional instability (MDI) of the shoulder is symptomatic laxity in 2 or more directions, 1 of which is inferior. MDI is well described in overhead athletes (eg, baseball players, tennis players, swimmers) but not in gymnasts. We conducted this study to estimate the incidence of any type of shoulder pathology in elite gymnasts, to estimate MDI incidence in this population, and to determine which if any circumstances place these gymnasts at higher risk for developing MDI. An 18-question multiple-choice questionnaire was administered to 70 female US collegiate gymnastics teams. Potential risk factors were cross-matched against those gymnasts with traumatic shoulder injuries and again against those gymnasts who met MDI study inclusion criteria. Of the 1115 questionnaires distributed, 457 (34 teams) were returned. Twenty-two percent of gymnasts suffered from a traumatic shoulder injury, and 11% met study inclusion criteria. There was a statistically significant (P =.02) relationship between generalized ligamentous laxity and traumatic shoulder instability but not MDI. Incidence of atraumatic or traumatic shoulder injuries in gymnasts is higher than previously recognized. Although this study did not reveal any potential risk factors, it does provide several avenues for more specific research.