Linear correlation between patellar positioning and rotation of the lower limb in radiographic imaging: a 3D simulation study.

PURPOSE: The purpose of this study was to quantify changes in rotation of the lower limb between image pairs based on patellar position. Additionally, we investigated the differences in alignment between centralized patellar and orthograde-positioned condyles. METHODS: Three-dimensional models of 30 paired legs were aligned in neutral position with condyles orthogonal to the sagittal axis and then rotated internally and externally in 1° increments up to 15°. For each rotation, the deviation of the patella and the subsequent changes in alignment parameters were calculated and plotted using a linear regression model. Differences between neutral position and patellar centralization were analysed qualitatively. RESULTS: A linear relationship between lower limb rotation and patellar position can be postulated. The regression model (R2 = 0.99) calculated a change of the patellar position of - 0.9 mm per degree rotation and alignment parameters showed small changes due to rotation. The physiological lateralization of the patella at neutral position was on average - 8.3 mm (SD: ± 5.4 mm). From neutral position, internal rotation that led to a centralized patella was on average - 9.8° (SD: ± 5.2°). CONCLUSION: The approximately linear dependence of the patellar position on rotation allows an inverse estimation of the rotation during image acquisition and its influence on the alignment parameters. As there is still no absolute consensus about lower limb positioning during image acquisition, data about the impact of a centralized patella compared to an orthograde condyle positioning on alignment parameters was provided. LEVEL OF EVIDENCE: IV.

Elbow flexion and forearm supination strength in a healthy population.

BACKGROUND AND HYPOTHESIS: Despite the lack of representative data of a healthy population, many clinical trials concerning the measurement of postoperative elbow flexion or forearm supination strength use the contralateral side as a control. We hypothesized that there are no differences in elbow flexion and supination strength between the dominant and nondominant sides in healthy volunteers. METHODS: The study was performed on a cross-sectional cohort of healthy subjects without any prior injuries or surgical interventions of the upper extremities. Isometric elbow flexion strength and supination strength were measured on both the dominant and nondominant sides. The results were analyzed for the entire group and subanalyzed for female vs. male, for different age groups, and according to handedness and regular practice of overhead sports. RESULTS: A total of 150 subjects (75 female and 75 male subjects; mean age, 44 ± 15 years [range, 18-72 years]) were included in this study. Within the entire collective, no significant differences concerning the elbow flexion strength between the dominant and nondominant sides could be detected, whereas the supination strength was 7% higher on the dominant side (P = .010). Women, right-hand-dominant subjects, and subjects who do not regularly practice overhead sports have a significant 8% higher supination strength on the dominant side compared with the nondominant side (P < .05). Left-hand-dominant subjects have an 8% higher elbow flexion strength on the nondominant right side (P < .05). CONCLUSION: Elbow flexion strength and forearm supination strength differ between the dominant and nondominant sides. The contralateral upper extremity cannot be used as a matched control without some adjustments.

Challenging the Current Concept of Critical Glenoid Bone Loss in Shoulder Instability: Does the Size Measurement Really Tell It All?

BACKGROUND: Bone loss at the anterior glenoid rim is a main reason for failure of soft-tissue based surgical stabilization procedures in patients with anterior shoulder instability. PURPOSE: To evaluate the capability of conventional glenoid bone loss measurement techniques to provide an adequate estimation of the actual biomechanical effect of glenoid defects. STUDY DESIGN: Descriptive laboratory study. METHODS: Thirty consecutive patients with unilateral anterior shoulder instability and varying degrees of glenoid defect were included. Patient-specific computer tomography-based 3-dimensional shoulder models of the affected and unaffected sides were created. The bony shoulder stability ratio (SR) was determined in various potential dislocation directions with finite element analysis. Values obtained from conventional glenoid defect size measurement techniques (Pico and Sugaya) were correlated with the finite element analysis results. Additionally, a mathematical model was developed to theoretically analyze the correlation between glenoid defect size measurements and the SR. RESULTS: The authors found substantial interindividual differences of the SR of the unaffected shoulders in all directions of measurement. Bone loss at the anterior glenoid rim significantly reduced the SR in the 2-o'clock ( P = .011), 3-o'clock ( P < .001), and 4-o'clock ( P < .001) directions referring to a right shoulder. The correlation between the defect size measurements and the SR for the 2-o'clock (rho = -0.522 and -0.580), 3-o'clock (rho = -0.597 and -0.580), and 4-o'clock (rho = -0.527 and -0.522) directions was statistically significant. However, it showed only moderate strength and was nonlinear as well as dependent on the inherent shape of the concavity. As shown by the mathematical model, bone loss has the most considerable effect at the edge of the glenoid rim, and an increasingly concave-shaped glenoid leads to an increase in loss of SR provoked by the same extent of bone loss. CONCLUSION: Current glenoid bone loss measurements are unable to provide an adequate estimation on the actual biomechanical effect of glenoid defects because (1) the relation between the glenoid defect size and its biomechanical effect is nonlinear and (2) patients with shoulder instability have constitutional biomechanically relevant glenoid concavity shape differences. CLINICAL RELEVANCE: These findings challenge the current concept of setting a general threshold for critical glenoid bone loss, which requires bony reconstruction surgery.

The Arthroscopic Bankart-Plus Procedure for Treatment of Anterior Shoulder Instability With Small to Intermediate Glenoid Defects.

To date, specific surgical procedures are available for the treatment of anterior shoulder instability with substantial bony glenoid defects, as well as for patients without osseous lesions. However, specific treatment options are lacking for the frequently observed small to intermediate glenoid defects, which may not necessitate glenoid reconstruction surgery according to current guidelines but can still jeopardize the outcome after mere soft-tissue stabilization procedures. This article describes the so-called arthroscopic Bankart-Plus procedure for the treatment of anterior shoulder instability with small to intermediate bony glenoid defects. In addition to the conventional capsulolabral repair, an allogeneic demineralized spongy bone matrix is inserted between the glenoid neck and the labrum with the aim of compensating for the glenoid bone loss by increasing the volume of the labrum and thus its stabilizing effect.

Use of shoulder pacemaker for treatment of functional shoulder instability: Proof of concept.

BACKGROUND: Functional shoulder instability (polar type III) is caused by underactivity of rotator cuff and periscapular muscles, which leads to subluxation or dislocation during shoulder movement. While surgical treatment has shown no benefits, aggravates pain, and frequently diminishes function even further, conservative treatment is often ineffective as well. OBJECTIVES: The aim was to investigate the effectiveness of a "shoulder pacemaker" device that stimulates underactive muscles in patients with functional instability during shoulder movement in order to re-establish glenohumeral stability. PATIENTS AND METHODS: Three patients with unsuccessfully treated functional shoulder instability causing pain, emotional stress, as well as limitations during daily activities and sports participation were enrolled in this pilot project. The device was used to stimulate the external rotators of the shoulder and retractors of the scapula. Pain level, subjective shoulder instability, range of motion, visible aberrant muscle activation, and signs of dislocation were compared when the device was switched on and off. RESULTS: No changes were observed when the device was attached but switched off. When the device was switched on, all patients were able to move their arms freely without pain, discomfort, or subjective or objective signs of instability. All patients rated this as an excellent experience and volunteered to train further with the device. No complications were observed. CONCLUSION: The electric stimulation of hypoactive rotator cuff and periscapular muscles by means of the shoulder pacemaker successfully re-establishes stability in patients with functional shoulder instability during the time of application. VIDEO ONLINE: The online version of this article (doi: 10.1007/s11678-017-0399-z) contains the video: "The Shoulder-Pacemaker: treatment of functional shoulder instability with pathological muscle activation pattern". Video by courtesy of P. Moroder, M. Minkus, E. Böhm, V. Danzinger, C. Gerhardt and M. Scheibel, Charité Universitätsmedizin Berlin 2017, all rights reserved.