Determining the Optimal Intramedullary Screw Canal Fill Ratio in Length Unstable Metacarpal Fractures: A Biomechanical Investigation.

PURPOSE: Intramedullary (IM) screw fixation is gaining popularity in the treatment of metacarpal fractures. Despite its rapid adoption, there is a paucity of evidence regarding parameters to optimize effectiveness. This study aimed to quantify the relationship between stability, IM screw size, and canal fill using a cadaveric model. METHODS: Thirty cadaveric metacarpals (14 index, 13 middle, and three ring fingers; mean age: 58.3 years, range: 48-70) were selected to allow for canal fill ratios of 0.7-1.1 for screws sized 3.0, 3.5, and 4.5 mm. Metacarpals underwent a 45° volar-dorsal osteotomy at the midpoint before fixation with an IM screw. Specimens were subjected to 100 cycles of loading at 10 N, 20 N, and 30 N before load-to-failure testing. Correlation coefficients for angular displacement on the final cycle at each load, peak load to failure, and average stiffness were assessed. RESULTS: Correlation coefficients for the angular displacement on the 100th cycle were as follows: 10 N, R = 0.62, 20 N, R = 0.57, and 30N, R = 0.58. Correlation values for peak load to failure as a function of canal fit were as follows: 3.0 mm, R = 0.5, 3.5 mm, R = 0.17, and 4.5 mm, R = 0.44. The canal fill ratio that intersected the line-of-best fit at an angular deformity of 10° was 0.74. Average peak forces for 3.0-, 3.5-, and 4.5-mm screws were 79.5, 136.5, and 179.6 N, respectively. Average stiffness for each caliber was 14.8, 33.4, and 52.3 N/mm. CONCLUSIONS: Increasing screw diameter and IM fill resulted in more stable fixation, but marginal gains were seen in ratios >0.9. A minimum fill ratio of 0.74 was sufficient to withstand forces of early active motion with angular deformity <10°. CLINICAL RELEVANCE: An understanding of the relationship of IM fill ratio of metacarpal screws to fracture stability may provide a framework for clinicians to optimally size these implants.

Interfascicular Anatomy of the Motor Branch of the Ulnar Nerve: A Cadaveric Study.

PURPOSE: The motor branch of the ulnar nerve contains fascicles that innervate the intrinsic musculature of the hand. This cadaveric study aimed to describe the organization and consistency of the internal topography of the motor branch of the ulnar nerve. METHODS: Five fresh-frozen cadaveric specimens with an average age of 74 years (range, 65-88 years) were dissected. The ulnar nerve was exposed and transfixed to the underlying tissues to maintain its orientation throughout the dissection. The dorsal cutaneous branch (DCB) and the volar sensory branch were identified and reflected to expose the motor branch. The fascicles to the first dorsal interosseus (FDI), flexor pollicis brevis, and abductor digiti minimi (ADM) were identified. Internal neurolysis was performed distal to proximal to identify the interfascicular arrangement of these fascicles within the motor branch. The organization of these fascicles was noted, and the branch points of the DCB, FDI, and ADM were measured relative to the pisiform using a handheld electronic caliper. RESULTS: The internal topography of the motor branch was consistent among all specimens. Proximal to the pisiform, the arrangement from radial to ulnar was as follows: volar sensory branch, flexor pollicis brevis, FDI/intrinsic muscles, ADM, and DCB. The position of these branches remained consistent as the deep motor branch curved radially within the palm and traveled to the terminal musculature. The locations of the average branch points of the FDI, ADM, and DCB with respect to the pisiform were as follows: FDI, 4.6 cm distal (range, 4.1-4.9 cm), 4.5 cm radial (range, 4.1-4.9 cm); ADM, 0.65 cm distal (range, 0.3-1.1 cm), 0.7 cm radial (range, 0.3-1.1 cm), DCB, 7.7 cm proximal (range, 4.2-10.1 cm), and 0.4 cm ulnar (range, 0.3-0.8 cm). CONCLUSIONS: The internal topography of the ulnar nerve motor branch was consistent among the specimens studied. The topography of the motor branches was maintained as the motor branch turns radially within the palm. CLINICAL RELEVANCE: This study provides further understanding of the internal topography of the ulnar nerve motor branch at the wrist level.

Strength Comparison of Fibrin Glue and Suture Constructs in Upper Extremity Peripheral Nerve Coaptations: An In Vitro Study.

PURPOSE: To compare in vitro failure loads of nerve coaptations using fibrin glue alone, a suture alone, and a combination of fibrin glue and a suture. METHODS: The median, radial, and ulnar nerves of 15 fresh-frozen cadaveric upper extremity specimens (45 nerves in total) were dissected in vitro and transected 5 cm proximal to the wrist crease to simulate an injury requiring coaptation. Three coaptation techniques were used: fibrin glue alone, a suture alone, and a suture augmented with fibrin glue. The load to failure of each repair was measured using a linear servo-actuator with an in-line force sensor. The results were analyzed using 2-way repeated measures analysis of variance tests and pairwise comparisons with Bonferroni correction. RESULTS: Both the nerve coaptation technique and the specific nerve that was repaired had a significant effect on failure load. Suture-glue repair had the highest load to failure, 11.2 ± 2.9 N, and significantly increased the load to failure by 2.9 ± 1.7 N compared with glue repair alone. There was no significant difference between suture-glue repair and suture repair alone or between glue repair alone and suture repair alone. CONCLUSIONS: In this in vitro cadaveric model, nerve injury coaptation using both a suture and fibrin glue resulted in the strongest repair. The addition of fibrin glue may provide some benefit when used to augment suture repair, but when used in isolation, it is inferior to combined suture-and-glue constructs. CLINICAL RELEVANCE: Combined suture-and-glue nerve coaptations might be useful in the early postoperative period in increasing nerve repair strength and potentially reducing rupture rates.

The Impact of Scaphoid Malunion on Radioscaphoid Joint Contact: A Computational Analysis.

PURPOSE: The clinical relevance of scaphoid malunion is controversial because the biomechanical sequelae remain poorly understood. In this computational study, the effect of increasing scaphoid malunion on radioscaphoid joint contact was assessed. METHODS: Six computational wrist models of active wrist flexion-extension were used to examine 6 scaphoid malunions of varying severities. The malunions were computationally created using 3-dimensional imaging software. Each scaphoid was shortened at the waist by 2 mm to simulate fracture comminution and the distal pole was angulated volarly from 15° to 55° in 10° intervals to create a total of 6 scaphoid malunion models per specimen. Each malunion model was then assessed at 3 wrist positions: neutral, 40° flexion, and 40° extension. The radioscaphoid contact area, as well as the contact centroid, was calculated. RESULTS: There was a statistically significant association between malunion severity and a wider area of contact at the radiocar: pal joint. The centroid of this radioscaphoid contact area also moved in an ulnar direction for all tested wrist positions. In the extended wrist position, the centroid also moved volarly. CONCLUSIONS: In this computational model, the amount of radioscaphoid joint contact was significantly increased with progressive scaphoid malunion severity. Furthermore, the position of the contact centroid had a significant change in position in the ulnar direction in all wrist positions with increasing scaphoid malunion. The clinical importance of this contact is yet to be elucidated, but this computational model serves as a basis for understanding the biomechanical consequences of scaphoid humpback deformities. CLINICAL RELEVANCE: This study provides a computational analysis examining changes at the radioscaphoid joint that may occur within the wrist with the scaphoid malunited.

Scaphoid Malunion Clinical and Radiographic Outcomes at a Minimum of 4 Years Follow-Up.

PURPOSE: To evaluate the radiographic and clinical outcomes of patients with scaphoid malunion after acute fracture at a mean of 7 years after injury. METHODS: Patients with scaphoid malunion were identified from a departmental database of acute scaphoid fractures. Patients with a scaphoid height-to-length ratio greater than 0.6 on final follow-up computed tomography (CT) scan were considered malunited. These patients were contacted to return for CT imaging and clinical assessment. A total of 22 patients were included (4 females and 18 males). Average age of the group was 41 years (range, 16-64 years) and average length of follow-up was 7.4 years (range, 4.4-11.8 years) after injury. RESULTS: Ten patients who underwent CT imaging demonstrated arthritic changes at the radial styloid, scaphoid fossa, or scaphotrapeziotrapezoid joint(s). Despite this, patients had good clinical function that was not significantly different compared with the uninjured side. Patients reported minimal pain and disability based on patient-reported outcome measures, and there was a moderate correlation between passive range of motion and height-to-length ratio. CONCLUSIONS: Nearly half of all patients with malunited acute scaphoid fractures demonstrated radiographic findings of early arthritis on CT imaging but overall good clinical results on midterm follow-up. TYPE OF STUDY/LEVEL OF EVIDENCE: Prognostic IV.

Anterior Interosseus to Ulnar Motor Nerve Transfers: A Canadian Perspective.

BACKGROUND: The anterior interosseus nerve (AIN) to ulnar motor nerve transfer has been popularized as an adjunct to surgical decompression in patients with severe cubital tunnel syndrome (CuTS) and high ulnar nerve injuries. The factors influencing its implementation in Canada have yet to be described. METHODS: An electronic survey was distributed to all members of the Canadian Society of Plastic Surgery (CSPS) using REDCap software. The survey examined 4 themes: previous training/experience, practice volume of nerve pathologies, experience with nerve transfers, and approach to the treatment of CuTS and high ulnar nerve injuries. RESULTS: A total of 49 responses were collected (12% response rate). Of all, 62% of surgeons would use an AIN to ulnar motor supercharge end-to-side (SETS) transfer for a high ulnar nerve injury. For patients with CuTS and signs of intrinsic atrophy, 75% of surgeons would add an AIN-SETS transfer to a cubital tunnel decompression. Sixty-five percent would also release Guyon's canal, and the majority (56%) use a perineurial window for their end-to-side repair. Eighteen percent of surgeons did not believe the transfer would improve outcomes, 3% cited lack of training, and 3% would preferentially use tendon transfers. Surgeons with hand fellowship training and those less than 30 years in practice were more likely to use nerve transfers in the treatment of CuTS (P < .05). CONCLUSIONS: Most CSPS members would use an AIN-SETS transfer in the treatment of both a high ulnar nerve injury and severe CuTS with intrinsic atrophy.

Adherence of Burn Outpatient Clinic Referrals to ABA Criteria in a Tertiary Center: Creating Unnecessary Referrals?

Initial assessment and triage of burns are guided by the American Burn Association criteria for referral to a burn center. These criteria are sensitive but not specific and can potentially lead to over-triage and "unnecessary" clinic visits. We are a Level 1 trauma center with burn subspecialty care, and due to the COVID-19 pandemic, referrals to our multidisciplinary outpatient burn clinic required triaging for virtual care appointments. In order to improve the triage process, we retrospectively reviewed our outpatient burn clinic referrals over a 2-year period, 2018 to 2019, for adherence to American Burn Association criteria. We collected data pertaining to patient and burn characteristics, as well as treatment outcome, to characterize referrals not requiring an in-person appointment. Of the 244 patients referred, 73% met the referral criteria, with 45% of these patients being healed at the first visit and 14.6% requiring surgical management. Mean time from injury to first visit was 9.7 days (mode 6), and the average number of visits was 2. Overall, mean burn size was 2%, with the majority of injuries being partial thickness (71%), located in the hand or extremity (77%). There was a fairly equal distribution of contact (36%), flame (21%), and scald (26%) burns. This study highlights the nonspecific nature of the American Burn Association referral criteria. We found that pediatric and hand burns in particular were over-triaged and lead to "unnecessary" appointments. This information is useful to help adjust referral criteria and to guide triaging of appointments with the evolution of telehealth and virtual care.

The effect of four-corner fusion and proximal row carpectomy on uniplanar and multiplanar wrist motion: A biomechanical study.

PURPOSE: To compare changes in wrist kinematics after scaphoidectomy and four-corner fusion (4CF), and proximal row carpectomy (PRC). METHODS: Six cadaveric specimens underwent flexion-extension, radial-ulnar deviation and circumduction in an active motion wrist simulator. Native state, "anatomic 4CF", "radial 4CF", and PRC were compared. RESULTS: Radial 4CF reduced wrist extension, while PRC reduced radial deviation. Fusion groups had similar motion profiles. 44%, 41%, and 32% of native circumduction was maintained in PRC, anatomic, and radial 4CF. CONCLUSIONS: Both fusion positions resulted in comparable motion outcomes. Anatomic 4CF was restricted in wrist extension compared to PRC but provided favourable radial deviation.

The Impact of Scaphoid Malunion on Carpal Motion: An In-Vitro Analysis.

Background: The clinical significance of scaphoid malunion is debated and its effect on wrist kinematics is poorly understood. Alterations to scaphoid morphology in other pathologies result in significant sequelae and arthrosis. By understanding the impact of scaphoid malunion on carpal kinematics, better insight can be garnered to inform models of wrist motion and clinical treatment of this injury. Methods: Seven cadaveric upper extremities underwent active wrist flexion and extension in a custom motion wrist simulator with scaphoid kinematics being captured with respect to the distal radius. A three-stage protocol of progressive simulated malunion severity was performed [intact, 10° malunion (Mal 10°), 20° malunion (Mal 20°)] with data analyzed from 45° wrist extension to 45° wrist flexion. Scaphoid malunions were modelled by creating successive volar wedge osteotomies and reducing the resultant scaphoid fragments with two 0.062" Kirshner wires. Motion of the scaphoid, lunate, trapezium-trapezoid was recorded using optical trackers. Results: Increasing scaphoid malunion severity did not significantly affect scaphoid or trapezium-trapezoid motion (p > 0.05); however, it did significantly alter lunate motion (p < 0.001). Increasing malunion severity resulted in progressive lunate extension across wrist motion (Intact - Mal 10°: mean difference (mean dif.) = 7.1° ± 1.6, p < 0.05; Intact - Mal 20°: mean dif. = 10.2° ± 2.0, p < 0.05). Conclusions: In this in-vitro model, increasing scaphoid malunion severity was associated with progressive extension of the lunate in all wrist positions. The clinical significance of this motion change is yet to be elucidated, but this model serves as a basis for understanding the kinematic consequences of scaphoid malunion deformities.

Loading at the distal radius and ulna during active simulated dart throw motion.

Loading at the distal forearm during dart throw motion (DTM) has been examined under static loads but there is no consensus on how loading is affected by active motion. In this work two implants were designed to measure forearm loading in a cadaveric model of wrist motion. Loads through the radius and ulna were significantly greater in reverse DTM than forward DTM. Radius loads were greatest in extended and radial deviated positions, and ulnar loads were greatest in flexed and ulnar deviated position. This work gives insight into the biomechanics of loading of the forearm to guide further studies.

Validation of an effective, low cost, Free/open access 3D-printed stethoscope.

The modern acoustic stethoscope is a useful clinical tool used to detect subtle, pathological changes in cardiac, pulmonary and vascular sounds. Currently, brand-name stethoscopes are expensive despite limited innovations in design or fabrication in recent decades. Consequently, the high cost of high quality, brand name models serves as a barrier to clinicians practicing in various settings, especially in low- and middle-income countries. In this publication, we describe the design and validation of a low-cost open-access (Free/Libre) 3D-printed stethoscope which is comparable to the Littmann Cardiology III for use in low-access clinics.