Measurement of Hybrid III Head Impact Kinematics Using an Accelerometer and Gyroscope System in Ice Hockey Helmets.

Helmet-based instrumentation is used to study the biomechanics of concussion. The most extensively used systems estimate rotational acceleration from linear acceleration, but new instrumentation measures rotational velocity using gyroscopes, potentially reducing error. This study compared kinematics from an accelerometer and gyroscope-containing system to reference measures. A Hybrid III (HIII) adult male anthropometric test device head and neck was fit with two helmet brands, each instrumented with gForce Tracker (GFT) sensor systems in four locations. Helmets were impacted at various speeds and directions. Regression relationships between GFT-measured and reference peak kinematics were quantified, and influence of impact direction, sensor location, and helmet brand was evaluated. The relationship between the sensor output and the reference acceleration/velocity experienced by the head was strong. Coefficients of determination for data stratified by individual impact directions ranged from 0.77 to 0.99 for peak linear acceleration and from 0.78 to 1.0 for peak rotational velocity. For the data from all impact directions combined, coefficients of determination ranged from 0.60 to 0.80 for peak resultant linear acceleration and 0.83 to 0.91 for peak resultant rotational velocity. As expected, raw peak resultant linear acceleration measures exhibited large percent differences from reference measures. Adjustment using regressions resulted in average absolute errors of 10-15% if regression adjustments were done by impact direction or 25-40% if regressions incorporating data from all impact directions were used. Average absolute percent differences in raw peak resultant rotational velocity were much lower, around 10-15%. It is important to define system accuracy for a particular helmet brand, sensor location, and impact direction in order to interpret real-world data.

Validation of a helmet-based system to measure head impact biomechanics in ice hockey.

PURPOSE: This study aimed to quantify differences between head acceleration measured by a helmet-based accelerometer system for ice hockey and an anthropometric test device (ATD) to validate the system's use in measuring on-ice head impacts. METHODS: A Hybrid III 50th percentile male ATD head and neck was fit with a helmet instrumented with the Head Impact Telemetry (HIT) System for hockey and impacted at various speeds and directions with different interfaces between the head and helmet. Error between the helmet-based and reference peak accelerations was quantified, and the influence of impact direction and helmet-head interface was evaluated. Regression equations were used to reduce error. System-reported impact direction was validated. RESULTS: Nineteen percent of impacts were removed from the data set by the HIT System processing algorithm and were not eligible for analysis. Errors in peak acceleration between the system and ATD varied from 18% to 31% and from 35% to 64% for linear and rotational acceleration, respectively, but were reduced via regression equations. The relationship between HIT System and reference acceleration varied by direction (P < 0.001) and head-helmet interface (P = 0.005). Errors in impact azimuth were approximately 4%, 10%, and 31% for side, back, and oblique back impacts, respectively. CONCLUSIONS: This is the first comprehensive evaluation of peak head acceleration measured by the HIT System for hockey. The HIT System processing algorithm removed 19% of the impacts from the data set, the correlation between HIT System and reference peak resultant acceleration was strong and varied by head surface and impact direction, and the system error was larger than reported for the 6-degree-of-freedom HIT System for football but could be reduced via calibration factors. These findings must be considered when interpreting on-ice data.

Reverse shoulder arthroplasty glenoid fixation: is there a benefit in using four instead of two screws?

BACKGROUND: To allow osseous integration to occur and thus provide long-term stability, initial glenoid baseplate fixation must be sufficiently rigid. A major contributing factor to initial rigid fixation is baseplate screw fixation. Current baseplate designs use a 4-screw fixation construct. However, recent literature suggests adequate fixation can be achieved with fewer than 4 screws. The purpose of the present study was to determine whether a 4-screw construct provides more baseplate stability than a 2-screw construct. METHODS: A flat-backed glenoid baseplate with 4 screw hole options was implanted into 6 matched pairs of cadaver scapulas using standard surgical technique. Within each pair, 2 screws or 4 screws were implanted in a randomized fashion. A glenosphere was attached allowing cyclic loading in an inferior-to-superior direction and in an anterior-to-posterior direction. Baseplate motion was measured using 4 linear voltage displacement transducers evenly spaced around the glenosphere. RESULTS: There was no statistical difference in the average peak central displacements between fixation with 2 or 4 screws (P = .338). Statistical increases in average peak central displacement with increasing load (P < .001) and with repetitive loading (P < .002) were found. CONCLUSION: This study demonstrates no statistical difference in baseplate motion between 2-screw and 4-screw constructs. Therefore, using fewer screws could potentially lead to a reduction in operative time, cost, and risk, with no significant negative effect on overall implant baseplate motion.

Morphology of the cubital tunnel: an anatomical and biomechanical study with implications for treatment of ulnar nerve compression.

PURPOSE: The purpose of this study is to provide a thorough understanding of the anatomy of the cubital tunnel and to outline specific anatomical parameters of the cubital tunnel retinaculum (CuTR) that might aid in the management of ulnar nerve problems. The hypotheses of this study are (1) that the nerve elongates with elbow flexion and (2) that the cross-sectional area of the cubital tunnel is inversely proportional to the degree of elbow flexion. METHODS: Eleven fresh-frozen cadaver arms were dissected at the medial elbow. The CuTR was identified, and its thickness was measured. After excising the CuTR, we measured the elongation of the anterior and posterior aspects of the ulnar nerve, as well as the length of the CuTR origin/insertion, at increasing intervals of elbow flexion (15°, 30°, 45°, 90°, 120°, and 135°). Using 3-dimensional digitization technology, the surface of the cubital tunnel was recorded at 4 positions of elbow flexion (15°, 45°, 90°, and 135°) and analyzed to define the tunnel geometry. RESULTS: The CuTR origin-to-insertion length and the ulnar nerve length both increased significantly with increasing flexion angle. Both lengths at 90°, 120°, and 135° of elbow flexion were greater than at 15° or 30°. The cubital tunnel area was significantly less at 135° compared to either 45° or 90° of flexion. There was a linear relationship between the cubital tunnel area of the different arms with the corresponding nerve cross-sectional area when measured at the level of the epicondyle and when the arm was at 90° of elbow flexion. CONCLUSIONS: The CuTR begins to stretch at 60° of flexion and continues to stretch with increasing flexion. Similarly, the ulnar nerve is more taut in flexion. The area within the cubital tunnel decreases beyond 90° of elbow flexion. CLINICAL RELEVANCE: Understanding the dynamic anatomical relationships of the cubital tunnel might help in the safe treatment of cubital tunnel syndrome when using minimally invasive techniques and instrumentation.

Scaphoid and lunate translation in the intact wrist and following ligament resection: a cadaver study.

PURPOSE: To determine the amount of scaphoid and lunate translation that occurs in normal cadaver wrists during wrist motion, and to quantify the change in ulnar translation when specific dorsal and volar wrist ligaments were sectioned. METHODS: We measured the scaphoid and lunate motion of 37 cadaver wrists during wrist radioulnar deviation and flexion-extension motions using a wrist joint motion simulator. We quantified the location of the centroids of the bones during each motion in the intact wrists and after sectioning either 2 dorsal ligaments along with the scapholunate interosseous ligament or 2 volar ligaments and the scapholunate interosseous ligament. RESULTS: In the intact wrist, the scaphoid and lunate statistically translated radially with wrist ulnar deviation. With wrist flexion, the scaphoid moved volarly and the lunate dorsally. After sectioning either the dorsal or volar ligaments, the scaphoid moved radially. After sectioning the dorsal or volar ligaments, the lunate statistically moved ulnarly and volarly. CONCLUSIONS: Measurable changes in the scaphoid and lunate translation occur with wrist motion and change with ligament sectioning. However, for the ligaments that were sectioned, these changes are small and an attempt to clinically measure these translations of the scaphoid and lunate radiographically may be limited. The results support the conclusion that ulnar translocation does not occur unless multiple ligaments are sectioned. Injury of more than the scapholunate interosseous ligament along with either the dorsal intercarpal and dorsal radiocarpal or the radioscaphocapitate and scaphotrapezial ligaments is needed to have large amounts of volar and ulnar translation.