Elbow motion patterns during daily activity.

BACKGROUND: This in vivo kinematic study was developed to ascertain (1) elbow posture and motion during daily activities and (2) to compare motions of the dominant and nondominant elbows. METHODS: Forty-six subjects wore a custom instrumented shirt to continuously measure elbow posture and motion for the waking hours of 1 day. The 3D orientations of each of the forearm and humerus sensors enabled calculation of elbow flexion-extension and pronation-supination angles. RESULTS: The elbow flexion-extension postures that were most common ranged from 60°-100° for both the dominant and nondominant extremities averaging 44% ± 4% and 35% ± 4% of the day, respectively. When elbow flexion motions were calculated, there were a large number of motions over a wide distribution of flexion angles, with the dominant side exhibiting significantly more motions per hour than the nondominant side. CONCLUSION: Both flexion-extension and pronation-supination motions occur more commonly in the dominant arm, and the dominant arm is more commonly in pronation. These data provide a baseline for assessing treatment outcomes, ergonomic studies, and elbow arthroplasty wear testing.

Comparing daily shoulder motion and frequency after anatomic and reverse shoulder arthroplasty.

BACKGROUND: Both anatomic (TSA) and reverse total shoulder arthroplasty (RTSA) are common interventions for glenohumeral arthrosis, with the goal of relieving pain and restoring mobility. Understanding shoulder arthroplasty motion and frequency is of interest in evaluating effectiveness and in predicting bearing wear for implant development and optimization. The purpose of this study was to measure and compare the total daily shoulder motion of patients after TSA and RTSA. METHODS: Thirty-six human subjects who had undergone shoulder arthroplasty wore a custom instrumented garment that tracked upper extremity motion for the waking hours of 1 day. The 3-dimensional orientation of each humeral sensor was transformed with respect to the torso to calculate total joint motion and frequency, with comparison of TSA to RTSA. In addition, the yearly motion of the shoulder was extrapolated. RESULTS: The majority of shoulder motion occurred below 80° of elevation (P < .001), totaling on average 821 ± 45 and 783 ± 27 motions per hour for TSA and RTSA, respectively. Conversely, elevations >80° were significantly less frequent, totaling only 52 ± 44 (P < .001) and 38 ± 27 (P < .001) motions per hour for TSA and RTSA, respectively. No significant differences were detected between TSA and RTSA shoulders (P = .22) or their respective contralateral asymptomatic sides (P = .64, P = .62). When extrapolated, it was estimated that each TSA and RTSA shoulder elevated above 60° approximately 1 million and 0.75 million cycles per year, respectively. DISCUSSION: Mean shoulder motions after TSA or RTSA were not significantly different from the contralateral asymptomatic side. In addition, no significant differences were detected in shoulder motion or frequency between TSA and RTSA.

Multiple Periprosthetic Joint Infections: Evidence for Decreasing Prevalence.

BACKGROUND: Multiple periprosthetic joint infections (MPJIs) are uncommon. We determine the prevalence of developing a second-site periprosthetic joint infection. METHODS: Our institutional arthroplasty database was reviewed. Those who developed a second-site infection had a retrospective chart review to determine the pathogen, timing of infection, comorbidities, and results of treatment. RESULTS: Thirteen of 206 (6.3%) patients at-risk for MPJI experienced a second periprosthetic joint infection. Mode of the second infection was hematogenous in 6, all of whom were being treated for the index periprosthetic joint infection. Seven secondary infections did not relate to the index infection. Two patients were lost to follow-up, 5 continued on suppressive antibiotics, and 6 successfully cleared infection. CONCLUSION: The prevalence of MPJI has decreased compared with previous reports.

Regional variations in radial head bone volume and density: implications for fracture patterns and fixation.

BACKGROUND: Fractures of the radial head are common with most partial articular fractures resulting in an anterolateral fragment. The exact mechanism of radial head fracture is unknown; however, forces transmitted and variations in local bone density are believed important. This study quantifies the regional variations in bone density and volume of the radial head to better understand the pathomechanics of fracture patterns. METHODS: Computer tomography scan data of 18 cadaver elbows were imported into imaging analysis software. The radial head was divided into quadrants based on neutral forearm rotation. Bone density and volume were calculated and compared between quadrants. RESULTS: The regional densities of bone expressed in Hounsfield units (HU) were posteromedial quadrant (PM) 496 ± 87 HU, anteromedial quadrant (AM) 443 ± 72 HU, anterolateral quadrant (AL) 409 ± 60 HU, and posterolateral quadrant (PL) 406 ± 57 HU. The volume of bone in descending order was PM 1138 ± 179 mm(3), PL 1013 ± 213 mm(3), AM 1010 ± 210 mm(3), and AL 938 ± 175 mm(3). The PM quadrant was significantly denser than the AM, AL, and PL quadrants, (P = .001) and the AM quadrant was significantly denser than the AL and PL quadrants (P = .006 and .009). The PM quadrant had significantly more bone volume when compared to the AM, AL, and PL (P = .001). The AM and PL quadrants had significantly greater bone volume compared to AL quadrant (P = .023 and .018, respectively). CONCLUSION: Radial head bone volume and density is highest in the posteromedial quadrant and lowest in the anterolateral quadrant where fractures occur more frequently.