SUMMARY Normal subjects performed bilaterally symmetric rapid elbow flexions or extensions ("focal movements") while standing. Specific patterns of electromyographic activity in leg and trunk muscles ("associated postural adjustments") were seen for each type of movement. The biomechanical significance of these postural adjustments was analysed by means of the ground reaction forces and motion of the various body segments. Experimental data were compared with that from a theoretical model of the body consisting of a six segment kinetic chain with rigid links. Distinct patterns of the ground reaction forces with elbow flexion were opposite in direction to those seen with elbow extension. Movements of the various body segments were small and specific for a certain focal movement. Dynamic perturbations arising from the arm movement in an anteroposterior direction were found to be compensated by postural adjustments, whereas vertical perturbations were not compensated. The muscular activity acting about different joints in the different movements was found to correlate with the predictions of activity needed to compensate for net joint reaction moments arising from the focal movement. Motion of the various body segments could be understood as resulting from the interplay of the net reaction moments and the net muscular moments at the different joints. Dynamic postural requirements are accomplished by a precise active compensation initiated before the focal movement.Leg and trunk muscles are active in association with fast voluntary elbow movements in standing human subjects. This postural muscle activity associated with arm movements has several characteristic features. EMG activity in leg and trunk muscles precedes that of the prime mover of the displaced segment.' 2-6 Activity depends on the condition of postural support' 5 7 including weightlessness.8 It also adapts rapidly to changes in the environmental context. l s 8 9In our own previous study, subjects made bilaterally symmetrical rapid elbow flexions or extensions ("focal movements") in either free standing or when supported by being strapped to a firm wall behind them. EMG activity in erector spinae, rectus abdominis, quadriceps femoris, hamstrings, tibialis anterior and gastrocnemius ("postural movements") began prior to activity in the arm muscles in a distal-toproximal order of activation and demonstrated specific patterns for each type of movement. These patterns in the postural muscles were characterised by alternating activity in antagonist pairs similar to the triphasic pattern seen in the arm muscles with rapid or "ballistic" movements.' o-12 Postural "agonists" and "antagonists" were defined by this pattern according to the order of activation, but the kinesiology of the postural movements was not known.Questions arise as to the function of this muscle activity in postural muscles preceding and during voluntary arm movements. Evidence of the nature of postural strategies associated with limb displacements 232

Background: Pediatric orthopaedic fellowship directors (FDs) have a valuable impact on the education of trainees and future leaders in the field. There is currently no research on the characteristics of pediatric orthopaedic FDs. Methods: Programs were identified using the Pediatric Orthopaedic Society of North America fellowship directory. Operative, nonoperative, and specialty programs were included. Data was collected through Qualtrics survey, e-mail, telephone, and online searches. Variables included demographics (age, sex, race/ ethnicity), Hirsch index (h-index) as a measure of research productivity, graduate education, residency and fellowship training, years of hire at current institution and as FD, and leadership roles. Results: Fifty-five FDs were identified. The majority (49/55, 89%) were male and 77% (27/35) were Caucasian. The mean age at survey was 51.1 ± 8.2 years. The mean h-index was 17.2. Older age correlated with higher h-index (r = 0.48, P = 0.0002). The average duration from fellowship graduation to FD appointment was 9.6 ± 6.7 and 6.9 ± 6.1 years from institutional hire. Sixteen FDs (29%) had additional graduate level degrees. Almost all (52/55, 95%) FDs completed orthopaedic surgery residencies and all graduated fellowship training. Twenty-nine percent (16/55) completed more than 1 fellowship. Most FDs (51/55, 93%) completed a fellowship in pediatric orthopaedic surgery. Ten FDs (18%) completed pediatric orthopaedic surgery fellowships that included spine-specific training. One-third of all current FDs were fellowship-trained at either Boston Children's Hospital (9/55, 16%) or Texas Scottish Rite Hospital for Children (9/55, 16%). Conclusions: Pediatric orthopaedic FDs are typically early-career to mid-career when appointed, with a strong research background. Nearly a third completed additional graduate degrees or multiple fellowships. Although male dominated, there are more female FDs leading pediatric orthopaedic programs compared with adult reconstruction, trauma, and spine fellowships. As fellowships continue to grow and diversify, this research will provide a baseline to determine changes in FD leadership.

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Background: The risk of surgical site infection in pediatric posterior spine fusion (PSF) is up to 4.3% in idiopathic populations and 24% in patients with neuromuscular disease. Twenty-three percent of pediatric PSF tissue cultures are positive before closure, with a higher rate in neuromuscular patients. Our primary aim was to evaluate the feasibility of a complete randomized controlled trial to study the efficacy of surgical site irrigation with povidone-iodine (PVP-I) compared with sterile saline (SS) to reduce the bacterial contamination rate before closure in children undergoing PSF. Methods: One hundred seventy-five subjects undergoing PSF were enrolled in a multicenter, single-blind, pilot randomized controlled trial. We recruited patients at low-risk (LR) and high-risk (HR) for infection 3:1, respectively. Before closure, a wound culture was collected. Nonviable tissues were debrided and the wound was soaked with 0.35% PVP-I or SS for 3 minutes. The wound was then irrigated with 2 L of saline and a second sample was collected. Results: One hundred fifty-three subjects completed the protocol. Seventy-seven subjects were allocated to PVP-I (18 HR, 59 LR) and 76 to SS (19 HR, 57 LR). Cultures were positive in 18% (14/77) of PVP-I samples (2 HR, 12 LR) and in 17% (13/76) of SS samples (3 HR, 10 LR) preirrigation and in 16% (12/77) of PVP-I samples (5 HR, 7 LR) and in 18% (14/76) of SS samples (4 HR, 10 LR) postirrigation. Eight percent (3/37) HR subjects (1 PVP-I, 2 SS) experienced infection at 30 days postoperative. No LR subjects experienced infection. Conclusions: Positive cultures were similar across treatment and risk groups. The bacterial contamination of wounds before closure remains high regardless of irrigation type. A complete randomized controlled trial would be challenging to adequately power given the similarity of tissue positivity across groups. Level of Evidence: Level II—pilot randomized controlled trial.