Results

Table I shows the percentages of adverse conditions for a particular location and angle of the nail placement. For a better overview, the results in table I were illustrated in graphs (Graphs 1-4). Each graph represents the incidence of one of the four adverse conditions for each position and angle of the nail insertion. Then, the results have been statistically processed in tables (Tables II - IV).

Graphs 1 and 2 show that the screws penetration into the radiocarpal joint and its non-subchondral displacement depend mainly on the distance of the entry point of the nail from the tip of the radial styloid process. The incidence of these two adverse conditions was at its least with the nail insertion at the distance of 1.0 cm from the tip of the radial styloid. There was high incidence (50 - 100%) of screw penetration into the radiocarpal joint with the nail insertion at the distance of 0.5 cm from the tip of the radial styloid. High incidence (80 – 100%) of non-subchondral screw displacement was observed in the cases of the nail insertion at the distance of 1.5 cm from the tip of the radial styloid. These two adverse conditions were affected the least by the angle of the nail rotation to the transverse axis of the distal radius The screw penetration into the radiocarpal joint, (Fig. 24), causes

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destruction of the articular cartilage, pain of the wrist; subsequently, stiffness, and arthritis of the radiocarpal joint. With non-subchondral displacement of the screws, the fracture fixation is less stable, which can cause its secondary dislocation.

Table I. The percentages of the adverse conditions; the percentages of penetration of distal screws into the radiocarpal joint, into the dorsal or volar surface of distal radius and the percentages of there non-subchondral placement of all 20 trials for each position. Columns represent the distance from the tip of radial styloid (in cm) for each variant; rows represent the angle of Micronail rotation.

Between APL and

EPB (I. extensor

compartment)

Between APL- EPB and ECRL (between I.

and II. extensor

compartments)

Between ECRL and ECRB (II. extensor compartment) 0.5 1.0 1.5 0.5 1.0 1.5 0.5 1.0 1.5 Penetration into the radiocarpal joint 20°dorsal _{100 15 0 90 15 0 85 15 0} 10°dorsal _{100 10 0 95 10 0 85 5 0} 0° 95 5 0 90 0 0 95 5 0 10°volar 50 5 0 85 5 0 95 5 0 20°volar _{85 5 0 85 5 0 90 0 0} Penetration to the dorsal surface of radius 20°dorsal _{0 0 0 0 0 0 0 0 5} 10°dorsal _{0 5 10 5 5 10 10 10 20} 0° 5 5 20 10 10 25 20 20 30 10°volar _{30 35 40 55 55 65 60 70 85} 20°volar _{75 80 90 90 95 100 95 100 100} Penetration to the volar surface of radius 20°dorsal 95 100 100 95 100 100 80 90 100 10°dorsal _{90 95 100 40 45 60 30 50 70} 0° 15 20 30 5 5 15 0 5 15 10°volar 5 5 10 0 0 5 0 0 5 20°volar _{0 0 0 0 0 0 0 0 0} Non- subcho- ndral placem-ent of screws 20°dorsal 100 15 90 90 15 85 85 15 90 10°dorsal _{100 10 80 95 10 85 85 10 90} 0° 95 5 90 90 5 90 95 10 95 10°volar 95 5 100 85 10 100 95 10 100 20°volar _{85 0 100 85 100 100 90 10 100}

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Graph 1. The percentage of the penetration of the fixed-angle locking screws into the radiocarpal joint of the 20 trials for each variant

Graph 2. The percentage of cases of the non-subchondral screw displacement of the fixed-angle locking screws of the 20 trials for each variant

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Figure 24. The screw penetration into the radiocarpal joint, P: screw penetration, S: scaphoid, R: radius, LT: Lister's tubercle, EPL: dislocated tendon of EPL to expose screw penetration.

Graphs 3 and 4 show that the screws penetration into the dorsal or volar sides of the distal radius depends mainly on the nail rotation in the transverse plane. The incidence of these two adverse conditions was at its least with the nail insertions with 0° rotation to the transverse axis of the radius. There was high incidence (75 - 100%) of screw penetration into the dorsal side of the radius with the nail insertions with 20° volar rotation to the transverse axis of the radius. Also, high incidence (30 – 85%) of these adverse conditions was observed with the nail position of 10° volar rotation to the transverse axis of the radius. High incidence (80 – 100%) of volar screw penetration was observed in the cases of the nail insertion with 20°dorsal rotation to the transverse axis of the radius. Also, in the cases of nail position in 10° dorsal rotation to the transverse axis of the radius, the incidence of penetration into the volar side of the radius was high (30 – 90%). In the case of screws penetration into the dorsal surface of the radius (Fig. 25), there is a risk of injury of the extensor tendons in the III., IV. and V. extensor compartments, mainly EDC tendon, which lies on the ulnar half of dorsal surface of the distal radius. In the case of the screws penetration into the volar surface (Fig. 26), there is a risk of injury in m. pronator quadrates that is not significant. Rough drilling or use of screws much longer than needed may cause injury of the flexor digitorum profundus tendon. Injuries

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of the m. flexor pollicis longus tendon and the median nerve are unlikely. There was no case of penetration into DRUJ in all positions of Micronail in all trials.

Graph 3. The percentage of the penetration of the fixed-angle locking screws into the dorsal surface of the distal radius in 20 trials for each variant

Graph 4. The percentage of the penetration of the fixed-angle locking screws to the volar surface of the distal radius in 20 trials for each variant

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Figure 25. The penetration into the dorsal side of the radius, P: screw penetration, I-IV: extensor compartments, S: scaphoid, RC: radiocarpal joint, L: lunate, LT: Lister's tubercle

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Table II is a summary of the adverse conditions for each variant of nail insertion. It shows the percentage of all adverse conditions in each trial (i.e. each entry position). The three positions of the entry point that have low incidence of adverse conditions were in the distance of 1.0 cm from tip of the radial styloid process with 0° rotation to the transverse axis of the radius regardless of the location in dorso-volar direction of the distal radius. The safest of the aforementioned three positions, with incidence of adverse conditions of 5%, was that between the. I. and II. extensor compartments.

Table II. The percentages of the total share of the adverse conditions in each position

Between APL and EPB (I. extensor compartment)

Between I. and II. extensor compartments

Between ECRL and ECRB (II. extensor compartment)

0,5cm 1cm 1,5cm 0,5cm 1cm 1,5cm 0,5cm 1cm 1,5cm 20°dors. 73.75% 32.50% 46.25% 68.75% 32.50% 46.25% 62.50% 30.00% 48.75% 10°dors. 72.50% 30.00% 46.25% 58.75% 17.50% 38.75% 52.50% 18.75% 45.00% 0° 52.50% 8.75% 33.75% 48.75% 5.00% 32.50% 52.50% 10.00% 35.00% 10°vol. 45.00% 12.50% 35.00% 56.25% 17.50% 42.50% 62.50% 21.25% 47.50% 20°vol. 61.25% 21.25% 46.25% 65.00% 50.00% 50.00% 68.75% 27.50% 50.00%

Since the individual penetrations do not result in side effects of same severity and Table II does not, indeed, reflect the real severity of each, it is advisable to take decisions in accordance with the recalculated values (more reflective) (Table III). The screw penetration into the joint space is considered the most serious, thus it is assigned the value of 1.0. For the same reason, the penetration into the dorsal side was given the value of 0.9; the value of 0.85 for the penetration into the volar side and the value of 0.75 for non-subchondral screws displacement. For a better overview, the results in table III were illustrated in graph 5.

Table III. The percentages of all adverse conditions in teach attempt in accordance with recalculated values (see text)

Between APL and EPB (I. extensor compartment)

Between I. and II. extensor compartments

Between ECRL and ECRB (II. extensor compartment) 0,5cm 1cm 1,5cm 0,5cm 1cm 1,5cm 0,5cm 1cm 1,5cm 20°dors. 63,94% 27,81% 37,19% 59,56% 27,81% 37,19% 54,19% 25,69% 39,25% 10°dors. 62,88% 25,69% 37,44% 51,19% 15,06% 30,94% 45,81% 16,00% 36,25% 0° 45,88% 7,56% 26,63% 42,69% 4,25% 25,69% 46,06% 8,69% 27,75% 10°vol. 38,13% 11,13% 27,81% 49,56% 15,50% 34,44% 55,06% 18,88% 38,94% 20°vol. 54,06% 19,25% 38,06% 57,44% 41,38% 41,25% 60,75% 24,38% 41,25%

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Graph 5. Illustration of the values in Table III

Finally, the results of each variant of the nail positions were compared with the results of the variant of the nail entry point with the least incidence of the adverse conditions, which was between I. and II. extensor compartments, 1.0 cm proximal to the apex of the radial styloid process, and in 0° nail rotation to the transverse axis of the radius. The significance of differences between two sets of data was estimated using the student t-test. A favorable condition (without screw penetration or subchondral displacement) was given value 0; an adverse condition value 1. The results of the student t-test with the p value less than 0.05 were considered to be significant. The p values were not significant in only two positions of the entry point into the distal radius (Table IV). These positions were in the distance of 1.0 cm from the apex of the radial styloid process, between APL and EPB (in the I. compartment) or between ECRL and ECRB (in the II. compartment), and in 0° rotation to the transverse axis of the distal radius. P values of > 0.05 mean, here, that there are no significant differences between the two compared sets. Therefore, it can be stated that these two positions have, also, low incidence of the adverse conditions, but slightly more than the position of 1.0 cm proximal to the apex of the radial styloid process, between I. and II. extensor compartments, and in 0° nail rotation to the transverse axis of the radius.

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Table IV: p values of the results of each variant of the nail positions compared with the results of the variant of the nail position with the least incidence of the adverse conditions

between APL and EPB (I. extensor compartment)

Between I. and II. Extensor compartment

between ECRL and ECRB (II. extensor compartment)

0.5 cm 1.0 cm 1.5 cm 0.5 cm 1.0 cm 1.5 cm 0.5 cm 1.0 cm 1.5 cm 20°dorsal < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 10°dorsal < 0.001 < 0.001 < 0.001 < 0.001 0.006 < 0.001 < 0.001 < 0.001 < 0.001 0° < 0.001 0.176 < 0.001 < 0.001 < 0.001 < 0.001 0.116 < 0.001 10°volar < 0.001 0.047 < 0.001 < 0.001 0.006 < 0.001 < 0.001 0.001 < 0.001 20°volar < 0.001 0.001 < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 < 0.001

To sum up, the results show that the best location of the cortical window (entry point) of Micronail is between I. and II. extensor compartments and 1 cm from the tip of the radial styloid process with insertion at 0° rotation in the transverse plane. For an ideal position of the cortical window, the best location of the skin incision is on the dorsal third of the altitude of the radial side of distal radius. It begins 0.5 cm proximal to the tip of radial styloid process and continues proximally 2.0 cm. In the subcutaneous tissue, it is necessary to isolate the superficial branch of the radial nerve cautiously. The nerve should remain uninjured on the dorsal side of approach.

According to this experimental study, the optimal position of the entry point differs from that recommended in the manual of Micronail in distance from the tip of the radial styloid process. In the manual, this distance is about 3-4 mm. However, in this location, the risk of screw penetration into the radiocarpal joint is great according to this study.