Hand injuries during COVID-19: Lessons from lockdown.

The two-month nationwide lockdown implemented in Australia in response to COVID-19 involved restrictions on social gatherings and non-essential services, resulting in marked changes to the distribution of time spent at home and in the workplace. Given the likelihood of future lockdowns, this study aimed to investigate whether the lockdown was associated with an alteration in the pattern of acute hand injuries admitted to Sydney Hospital Hand Unit relative to the same period in 2019, and whether target areas for preventative strategies could be identified. During the lockdown period in 2020, 332 acute presentations were noted, and in the same period in 2019, 310 cases were noted. The mean patient age was higher in 2020, largely due to a 327% increase in do-it-yourself (DIY) injuries. Workplace injuries increased in 2020 despite a 9.5% reduction in hours-worked, reflecting a redistribution of workers into manual labour jobs with a higher risk for hand injuries. Patients who suffered low-energy injuries at work were also significantly younger in 2020, suggesting this effect was most pronounced in younger age-groups, probably due to the shutdown of hospitality-based industries. Domestic violence-related injuries increased in 2020, highlighting the need to maintain resources to provide support in such cases at subspecialty hand units, which are often largely outpatient-centred. This study, therefore, identified a number of key areas that could be targeted in the event of future lockdowns, including messages regarding safe DIY activities, and more stringent requirements regarding worksite briefing and safety for people commencing labour-based jobs, especially if transferring from another industry.

Structural Failure Mechanisms of Common Flexor Tendon Repairs.

BACKGROUND: This study investigated the exact failure mechanisms of the most commonly used conventional tendon repair techniques. A new method, radiographing repair constructs in antero-posterior and lateral projections before and after tensioning was used. This allowed to precisely analyse failure mechanisms in regards to geometrical changes in all three dimensions. Additionally the biomechanical stability focusing on gapping was tested. METHODS: Sheep fore limb deep flexor tendons were harvested and divided in eight groups of ten tendons. Three common variants of the Kessler repair method and four common 4-strand repair techniques were tested. Additionally a new modification of the Adelaide repair was tested. RESULTS: Biomechanical testing showed no significant differences in gapping for the three tested 2-strand Kessler repair groups. Once a double Kessler or 4-strand Kessler repair was performed the stability of the repair improved significantly. Further significant improvements in biomechanical stability could be achieved by using cross locks in the repair like in the Adelaide repair method. Qualitative analysis using radiographs showed that all Kessler repair variants unfolded via rotations around the transverse suturing component, no matter which variant was used. CONCLUSIONS: Additional to the commonly described constriction of the repair construct, the rotating deformation is the main reason for repair site gapping in Kessler tendon repair methods. The term "locking" in a Kessler repair is misleading. The cruciate repairs tended to loose grip and drag (cheese-wire) through the tendon and therefore lead to gapping. The most stable repair constructs in all three dimensions were the Adelaide repair and its interlocking modification. This is due to the superior anchoring qualities of its cross locks and three dimensional stability.

Tendon to bone healing and its implications for surgery.

Entheses are complex structures which act to reduce stress concentrations between tendon and skeleton tissues. Understanding the development and function of the enthesis organ has implications for surgical repair, particularly in regards to healing and the regulation of tendon to bone engraftment. In this paper we review the development and function of entheses as well as the enthesis organ concept. Next we examine the process of tendon to bone healing and how this can be regulated, before addressing implications for surgical repair and post-operative care.

Influence of locking stitch size in a four-strand cross-locked cruciate flexor tendon repair.

PURPOSE: The 4-strand cross-locked cruciate technique (Adelaide technique) for repairing flexor tendons in zone II is a favorable method in terms of strength and simplicity. The purpose of this study was to investigate the effects of varying the cross-lock stitch size in this repair technique. Outcomes measured were load to failure and gap formation. METHODS: We harvested 22 deep flexor tendons from adult pig forelimbs and randomly allocated them into 2 groups. After cutting the tendons at a standard point, we performed a 4-strand cross-locked cruciate repair using 3-0 braided polyester with either 2-mm cross-locks (n = 11) or 4-mm cross-locks (n = 11). All repairs were completed with a simple running peripheral suture using 6-0 polypropylene. Repaired tendons were loaded to failure and the mechanism of failure, load to failure, stiffness, and load to 2-mm gap formation were determined. RESULTS: All repairs failed by suture breakage; we noted no suture pullout. There was no difference in load to failure (71.7-71.1 N; p = .89) or stiffness (4.1-4.6 N/mm; p = .23) between the 2-mm cross-lock and the 4-mm cross-lock groups. There was a trend toward higher resistance to 2-mm gap formation with the 4-mm cross-locks (55-62.2 N; p = .07). CONCLUSIONS: Four-strand cross-locked cruciate repairs with cross-lock sizes of 2 and 4 mm provide high tensile strength and are resistant to pullout. Repairs with 4-mm cross-locks tend to provide a more central load distribution and better gapping resistance than repairs with 2-mm cross-locks.

A biomechanical assessment of repair versus nonrepair of sheep flexor tendons lacerated to 75 percent.

PURPOSE: The benefit of repairing a 75% partial flexor tendon laceration remains controversial. The purpose of this study was to assess the degree of gap formation with and without repair when the 75% lacerated tendon is subjected to cyclic loading. Repair with only a peripheral suture was compared to that using a core and peripheral repair technique. METHODS: Sixteen deep flexor tendons from sheep hind limbs were lacerated to 75% of the tendon diameter. The cut tendons were loaded for 100 cycles from 3 N up to 30 N and then back to 3 N, at a rate of 0.2 Hz. Gap formation was measured at 0 and 100 cycles. Tendons were then randomized into 2 repair groups of 8 each: group 1 was repaired with only a simple, running peripheral suture (6-0 polypropylene monofilament), whereas group 2 was repaired with a modified Kessler core suture (4-0 silicone-coated braided polyester) plus a peripheral suture (6-0 polypropylene monofilament). Repaired tendons were tested for 500 cycles, and the gap was measured at 0, 100, and 500 cycles. After cycling, gap was measured at 100 N load, and the peak loads were determined on static failure testing. RESULTS: The 75% partially lacerated tendons had >2 mm gap at 100 cycles. This gap was significantly reduced by peripheral or peripheral plus core repairs (p < .001). There was no difference in gap formation between tendons with peripheral repair only and those with both peripheral and core repairs. Gap formation in repaired tendons remained

In vitro comparison of lagged and nonlagged screw fixation of metacarpal fractures in cadavers.

PURPOSE: Lag screw fixation is reported to provide the most biomechanically stable construct for fixation of oblique or spiral metacarpal fractures. Lag screws are inserted after overdrilling the proximal cortex, resulting in compression at the fracture site. Minor drilling errors can result in poor screw purchase, instability, and ultimately impaired fracture healing. In an in vitro study, we compared construct stability provided by nonlagged and lagged screw fixation. METHODS: A cadaveric human metacarpal model was used. After removing the soft tissue, long oblique osteotomies were made in 24 metacarpals, which were then randomized to lagged or nonlagged fixation. Nonlagged fixation was performed through a newly introduced reduction system. Fixed specimens were subjected to biomechanical analysis by way of cantilevered bending to failure, and calculations were made for axial stress and normalized stiffness. RESULTS: All specimens failed in a typical manner through the proximal screw site. Nonlagged compared with lagged screw fixation resulted in a higher axial stress and normalized stiffness, although the differences did not reach statistical significance. CONCLUSIONS: Nonlagged screw fixation with use of a precompression device provided comparable fracture site stiffness and biomechanical stability without use of lag screws while removing the requirement for overdrilling, thus simplifying the technique.

Pediatric treadmill injuries: a public health issue.

BACKGROUND: Treadmill injuries in children tend to be severe and are becoming increasingly common. We present an overview of this problem to promote public awareness, education, and to advocate a prevention strategy for this preventable injury. METHODS: Medical records of all children with treadmill-related injuries during a 6-year period (January 2001-November 2006) from 2 tertiary pediatric hospitals were reviewed. Data on patient demographics, injury related data, types of surgical procedure, and outcome of treatment were collected. RESULTS: Forty-four children with treadmill-related injuries were admitted in a 6-year period (2001-2006). Each year, the incidence increased with 17 (39%) cases occurring in 2006 so far. The median age of injury at the time of incident was 2.8 years (range, 8 months-12 years). There was a higher incidence in males (55%) compared with females (45%). Most of these injuries were to the hand (75%), full-thickness burns (59%), <1% of total burn surface area (TBSA) (73%), and occurred while the treadmill was in use by an adult (34%). Twenty-one (47%) children required skin grafting surgery. CONCLUSION: Treadmill-related burn injuries in children are a serious public health issue and warrants considerable attention. Adult supervision is paramount, and prevention strategies should include child safety features in equipment designs.

Growth factor expression following clinical mandibular distraction osteogenesis in humans and its comparison with existing animal studies.

AIM: Lengthening the mandible by distraction osteogenesis (DO) is nowadays a well recognized technique in maxillofacial surgery. In this study growth factor expression profiles were examined in biopsies taken from six patients undergoing mandibular DO and compared with findings from a sheep model for mandibular DO. STUDY DESIGN: In all patients (and sheep), the ascending ramus was distracted 10-15 mm at a rate of 1mm/day using an intraoral device. Biopsies were taken from the centre of the distraction zone 21 days after completion of distraction. Using standard immunohistochemical techniques, samples were stained for platelet-derived growth factor (PDGF), transforming growth factor beta (TGF-beta), basic fibroblast growth factor (bFGF) and bone morphogenetic proteins-2, -4 and -7 (BMP-2, -4, -7), matrix metalloproteinases-1 and -3 (MMP-1, -3), the vascular endothelial growth factor (VEGF), a marker for endothelial cells (CD-31) and type IV collagen (Col IV). RESULTS: Positive staining for PDGF, bFGF, TGF-beta, BMP-2, -4, and -7 was noted in cells and matrix components. There was intense staining for MMP-1. Strong staining for CD-31 and COL IV was observed adjacent to vessels. VEGF staining was less specific. Similar findings were noted in the sheep model. CONCLUSION: Growth factor expression in the human distraction site is similar to that in the sheep model.

The effect of rate of distraction osteogenesis on structure and function of anterior digastric muscle fibers.

The authors hypothesized that distraction at a rate of 3 mm/day, compared with mandibular distraction at a rate of 1 mm/day, would produce a maladaptive response in adjacent muscles of mastication. The authors further hypothesized that the maladaptive response would manifest at the single fiber level by means of increased sarcomeric heterogeneity, decreased maximum force output, and increased susceptibility to stretch-induced injury. In an ovine model, distraction osteogenesis of the right hemimandible was performed at either 1 mm/day for 21 days (n = 2) or 3 mm/day for 7 days (n = 2) to achieve a total distraction distance of 21 mm. The left hemimandibles served as controls. After a consolidation period of 2 days, the anterior digastric muscles were harvested; in six randomly selected single fibers from each muscle, maximum calcium-activated force (Po) was measured at optimal sarcomere length. The amount of damage to the sarcomeres in each fiber was assessed microscopically. To test susceptibility to contraction-induced injury, each fiber was given an activated stretch of 20 percent. Compared with control fibers and fibers distracted at 1 mm/day, maximum tetanic force (Po) was significantly lower in fibers distracted at 3 mm/day. Compared with control fibers, specific Po (Po/cross-sectional area) was lower in fibers distracted at 3 mm/day. The number of sarcomeres appearing damaged in fibers distracted at 3 mm/day was significantly higher than in control fibers or in fibers distracted at 1 mm/day. A greater deficit in Po was observed after a single activated stretch in fibers distracted at 3 mm/day than in control fibers or in fibers distracted at 1 mm/day. The authors conclude that distraction of the anterior digastric muscle in sheep at 3 mm/day produces a maladaptive response in the muscle fibers but a rate of 1 mm/day is tolerated by the muscle fibers. These data are consistent with the hypothesis that distraction of skeletal muscle at high rates results in increased heterogeneity of sarcomere lengths and that this increase in heterogeneity is the most likely potential mechanism resulting in whole muscle force deficits and in increased susceptibility to stretch-induced injury in distracted muscles.

The role of nerve growth factor and brain-derived neurotrophic factor in inferior alveolar nerve regeneration in distraction osteogenesis.

Distraction osteogenesis (DO) has become the mainstay of treatment of mandibular hypoplasias. Despite the clinical acceptance of the technique in the last decade, little is known of the biological mechanism of bone and soft tissue regeneration. The biological response of peripheral nerves to distraction has not been well documented. This study examined the role of two neurotrophic molecules, nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), in DO on nerve regeneration of the inferior alveolar nerve (IAN) in an ovine mandible model. Twelve animals were randomly divided into three groups and distracted at 5, 10, and 15 days using a mandibular osteotomy and uniaxial external distractor. The mental nerves and the IAN from the distracted site were harvested at the end of the distraction period and examined for the presence of NGF and BDNF using immunohistochemistry. Nerve growth factor expression was increased at both sites, whereas BDNF was only expressed at the mental nerve on the distracted side. Nerve growth factor and BDNF are involved in the response of the peripheral nerves to injury. Mechanical force applied to the IAN by distraction may lead to detachment of Schwann cells from their axons, leading to segmental degeneration. The resulting myelin sheath debris may serve as a trigger for higher expression of NGF and BDNF, facilitating Schwann cell proliferation and remyelination of the affected segment. Distraction of the mandible may serve as a source of subacute injury to the IAN and influence NGF and BDNF.