SCIENTIFIC ARTICLE
The Effect of Distal Radius Translation in the Coronal Plane on Forearm Rotation: A Cadaveric Study of Distal Radius Fractures C. Tate Hepper, MD, Michael A. Tsai, BS, Brent G. Parks, MS, Norman H. Dubin, PhD, Kenneth R. Means, Jr, MD
Purpose To determine the effect of lateral translation of the distal radius in the coronal plane on forearm rotation after distal radius fracture. Methods Ten fresh cadaveric limbs underwent distal radius osteotomy just proximal to the distal radial-ulnar joint to simulate an extra-articular distal radius fracture. We used an Agee Wrist Jack external fixator to create increasing magnitudes of distal fragment lateral translation in 2-mm increments. Forearm rotation was measured using a 3-dimensional camera at each magnitude of lateral translation. Results Total forearm rotation for the intact specimen and 2, 4, 6, and 8 mm (maximal) radial translations was 186 53 , 188 54 , 189 55 , 190 57 , and 193 59 , respectively. There was no significant difference for any magnitude of radial translation. The average maximal radial translation possible before radioulnar abutment was 8 0.5 mm. Conclusions In this cadaveric model, translation of the distal radius fragment in the lateral direction had no effect on forearm rotation. Clinical relevance At the level of the proximal border of the distal radioulnar joint, isolated distalradius translation does not significantly affect forearm rotation. (J Hand Surg Am. 2014; 39(4):651e655. Copyright Ó 2014 by the American Society for Surgery of the Hand. All rights reserved.) Key words Distal radius fractures, forearm rotation, radial translation.
A
POTENTIAL COMPLICATION in the treatment of distal radius fractures is malunion resulting in altered wrist mechanics,1 loss of function, and the possible need for corrective osteotomy.2
From the Curtis National Hand Center, MedStar Union Memorial Hospital, Baltimore, MD. Received for publication July 23, 2013; accepted in revised form January 9, 2014. This research was funded by the Raymond M. Curtis Research Foundation, the Curtis National Hand Center. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Corresponding author: Kenneth R. Means, Jr, MD, care of Anne Mattson, Curtis National Hand Center, 3333 North Calvert Street, Baltimore, MD 21218; e-mail: anne. [email protected]. 0363-5023/14/3904-0007$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2014.01.010
Radiographic parameters identified as predictive of functional outcome include radial height, radial inclination, ulnar variance, dorsal-palmar tilt, carpal alignment, and articular congruity.3 To date, little attention has been paid to translation in the coronal plane. In extra-articular distal radius fractures (AO 23eA2), the pull of the brachioradialis is a deforming force resulting in lateral translation of the distal fragment.4 This deformity can be difficult to treat closed, although various techniques have been suggested.5 Bronstein et al6 performed a cadaveric analysis on the effects of a variety of distal radius fracture deformities on forearm rotation. In their limited model assessing a number of variables, 5 or 10 mm of lateral translation did not produce a significant change in
Ó 2014 ASSH
r
Published by Elsevier, Inc. All rights reserved.
r
651
652
DISTAL RADIUS TRANSLATION
forearm rotation. In our study, we aimed to test the hypothesis that extra-articular distal radius fractures with lateral translation of the distal fragment in the coronal plane result in restricted forearm rotation in a cadaveric model. MATERIALS AND METHODS Cadaveric model We used 10 paired, fresh-frozen cadaver upper limbs from 5 cadaveric donors with intact hands, wrists, and elbows. There were 2 male and 3 female cadaver donors. Average age was 76 years (range, 55e92 y). Each specimen was thawed and screened radiographically for evidence of prior fracture or other bony abnormality. One specimen had evidence of a prior distal radius fracture with old screw holes from a volar plate, which was healed in anatomic alignment and had no baseline passive range of motion deficit, and was therefore included in the study. The specimens were sectioned at the level of the proximal humerus. We inserted a large threaded rod into the humerus to assist in mounting the extremity. We then applied an Agee WristJack Fracture Reduction System (Hand Biomechanics Lab, Inc, Sacramento, CA) external fixator directly to the lateral aspect of the radius. Two pins were placed into the radial shaft. A single pin was placed into the distal radius using fluoroscopic assistance (Figs. 1, 2). The carpus and hand were left free. Baseline forearm rotation measurements were then taken as described in detail subsequently. We made a transverse dorsal incision directly over the planned osteotomy site. The third and fourth extensor compartment tendons were retracted medially. The second extensor compartment tendons were retracted laterally to expose the entire dorsal surface of the distal radius. We used a sagittal saw to create a complete distal radius cut that exited the medial border of the radius just proximal to the sigmoid notch and immediately adjacent to the distal radioulnar joint (Fig. 2). Special care was taken to avoid damaging the surrounding soft tissues. Using the functionality of the Agee WristJack external fixator, we were able to laterally translate the distal radius fragment in 2-mm increments. Maximum translation occurred when the ulnar head and neck impinged on the radial shaft (Fig. 3). Translation was measured radiographically with a mini C-arm image intensifer. The external fixator translation screw was turned several turns, and translation was checked with the C-arm. We added turns of the translation screw until we arrived at each J Hand Surg Am.
FIGURE 1: Experimental setup with external fixator applied to the distal radius. Camera markers are affixed to the external fixator via a rigid frame. The humerus is secured with a large intramedullary metal rod to facilitate mounting the specimen.
FIGURE 2: Radiograph before translation of the distal fragment. The osteotomy has been performed just proximal to the DRUJ. A radiopaque marker is present as a reference to measure the magnitude of translation. A single pin is present in the distal fragment. Two pins are placed in the shaft (not pictured).
2-mm increment of translation. A 12.7-mm-diameter radiopaque stainless-steel ballbearing marker was used to control for image magnification. The bearing was attached to each specimen in the same spot and was included in every C-arm image. We used a stainless-steel ruler to take scaled measurements directly on the screen of the C-arm image intensifer in real time. All images were saved digitally as Digital Imaging and Communications in Medicine files for possible later analysis. We saw no noteworthy motion r
Vol. 39, April 2014
DISTAL RADIUS TRANSLATION
measure 6 degrees of freedom in 3-dimensional motion. Each marker is composed of 3 distinct points, which the camera detects at the intersection of black and white regions (Fig. 1). Measurement data are reported at the centroid of the triad. The system has a measurement rate of 20 Hz, a processing time of 15 to 20 ms/frame, factory calibration accuracy of 0.35 mm root mean square, and validation testing accuracy of 0.18 mm root mean square. We created a rigid frame to attach the markers to each specimen to minimize variation in marker placement between specimens. A total of 4 markers, 2 on the specimen and 2 on the turntable platform, were measured to maximize accuracy. The camera was mounted on a tripod that was locked in place above the test apparatus and looked directly downward at the test surface (Fig. 4). The camera remained in place for the duration of testing and resulted in precise measurements. The camera system has been measured by validation testing in our laboratory to be accurate within 0.5 . A standard IEEE 1394 cable supplied power to the camera and also facilitated communication with the controlling computer. A minimum of 50 frames of data were collected and averaged at each forearm position. The angles of pronation and supination were calculated relative to the angle corresponding to neutral position. Neutral forearm rotation was defined as perpendicular to the humeral epicondylar axis. Degrees of supination and pronation from neutral and total arc of motion were measured and recorded for each specimen in the intact forearm and for 2, 4, 6, and 8 mm (or maximum) lateral translation.
FIGURE 3: Maximal lateral translation has occurred with abutment of the ulnar neck against the radial shaft.
of the distal fragment in any other plane. Fluoroscopic images were taken after each specimen was tested, to confirm that the applied torque was not creating unwanted deformity. Biomechanical testing The rod fixed in the distal humerus was first mounted to the testing apparatus. The elbow and forearm were positioned beneath the humerus so that they could swing freely with the forearm in a dependent position. We then loosely connected the external fixator to a turnstile located directly under the specimen. A 1.4-kg mass was used to apply torque to the turnstile in either supination or pronation (Fig. 4). The mass was attached to the turnstile via a steel cable in 1 of 2 locations to create either a supination or pronation torque. The steel cable ran over a pulley attached to the side of the table to avoid friction between the table and the steel cable. The external fixator was not rigidly fixed to the turnstile to allow some minor degrees of freedom of rotation (ie, it was impossible to exactly align the axes of forearm and turnstile rotations). The biomechanical testing procedure was repeated for each magnitude of translation of the distal radius. We measured forearm rotation using the MicronTracker 2 (Claron Technology, Inc, Toronto, Canada), a fully passive motion tracking system that is able to J Hand Surg Am.
653
Statistics Average forearm rotation, 95% confidence intervals, and standard deviation were calculated for each magnitude of lateral translation. Analysis of variance with repeated measures was used to determine whether there were significant changes in supination, pronation, or total arc of motion. We calculated average translation and standard deviation to radioulnar abutment. Significance was set to P < .05. We determined that a sample size of 10 would have 80% power to detect a difference in means of 15 , assuming a standard deviation of 15 , using a paired t test with a .05 2-sided significance level. RESULTS Pronation for the intact specimen and 2, 4, and 6 mm and maximal radial translation was 84 22 , 85 23 , 84 24 , 86 23 , and 85 23 (mean SD), respectively. There was no significant difference r
Vol. 39, April 2014
654
DISTAL RADIUS TRANSLATION
FIGURE 4: Experimental setup with a 3-dimensional motion camera mounted over the specimen and the limb mounted on the testing apparatus. The external fixator is attached to the turnstile, which is rotated by a 1.4-kg mass.
(P ¼ .92) for any magnitude of radial translation. Supination for the intact specimen and 2, 4, and 6 mm, and maximal radial translation was 102 35 , 102 35 , 104 36 , 104 40 , and 107 43 , respectively. We found no significant differences for any magnitude of lateral translation (P ¼ .32). Total forearm rotation for the intact specimen was 186 53 . For 2, 4, and 6 mm and maximal lateral translation, total forearm rotation increased by 2 , 3 , 4 , and 7 , respectively. Again, there was no significant difference for any magnitude of lateral translation (P ¼ .30). Figure 5 represents the means and 95% confidence intervals for total arc of rotation at each magnitude of lateral translation. The average maximal lateral translation possible before radioulnar abutment was 8 0.5 mm. Six of the 10 specimens demonstrated 8 mm radial translation. No specimen had a maximal translation less than 7 mm.
transverse extra-articular distal radius fracture affected forearm rotation in a cadaveric model. A limited study by Bronstein et al6 demonstrated no change in forearm rotation with lateral translation of the distal fragment. Similarly, in our study, we found no significant difference in forearm rotation with varying magnitudes of distal radius translation. Bronstein et al used a similar cadaveric model, with the exception that they measured rotation directly using a protractor rather than a 3-dimensional tracking system. They also tested multiple planes of deformity including 5 and 10 mm lateral translation, which had no effect on forearm rotation in their model. Medial translation of the distal fragment produced a 23% decrease in pronation in their study. We also found that the distal fragment could be translated 8 mm on average before the proximal radial shaft abutted the ulnar head and neck. It was our observation in this model of extra-articular distal radius fractures with intact distal radioulnar joint (DRUJ) ligaments that the distal radius fragment and ulna moved as a unit. In reality, creating distal radius fragment translation actually creates translation of the radial shaft ulnarly in relation to the intact distal
DISCUSSION In this study, we aimed to determine whether lateral translation of the distal fragment in a simple, J Hand Surg Am.
r
Vol. 39, April 2014
DISTAL RADIUS TRANSLATION
655
FIGURE 5: Total forearm rotation means and 95% confidence intervals.
radius and ulna unit. This observation may have implications for reducing this deformity in the clinical setting. Our study had several weaknesses. We only measured passive forearm rotation in a cadaveric model. Of course, many other factors determine clinical results for patients with distal radius fractures. Distal radius translation could affect other wrist motions, pain, DRUJ and radiocarpal joint biomechanics, function of the pronator quadratus, and the appearance of the wrist. Also, this is a cadaveric model in which we simulated forearm rotation by applying a torque to the forearm via an external fixator. Results may have been different if forearm rotation had been accomplished via the musculotendinous units of the forearm to more closely resemble the clinical situation. We also used a sagittal saw to simulate a fracture and to limit damage to the surrounding soft tissues. In the clinical scenario, associated soft tissue injuries, such as the interosseous membrane, DRUJ capsule, and triangular fibrocartilage complex, may have a role in forearm rotation. Finally, in the clinical scenario, deformity is almost always multiplaner and may involve rotation of the distal fragment in relation to the shaft. Our cadaveric model specifically only examined pure lateral translation without rotation. Rotation through
J Hand Surg Am.
the fracture that appears as translation radiographically may have an effect on forearm rotation clinically. Distal radius translation of an extra-articular distal radius fragment in the lateral direction does not affect passive forearm rotation in a cadaveric model. Distal radius translation may have an effect on other clinical parameters not assessed in our study. Further study is needed to determine acceptable magnitudes of lateral translation of the distal radius in the clinical setting. REFERENCES 1. Pogue DJ, Viegas SF, Patterson RM, et al. Effects of distal radius fracture malunion on wrist joint mechanics. J Hand Surg Am. 1990; 15(5):721e727. 2. Bushnell BD, Bynum DK. Malunion of the distal radius. J Am Acad Orthop Surg. 2007;15(1):27e40. 3. Ng CY, McQueen MM. What are the radiological predictors of functional outcome following fractures of the distal radius? J Bone Joint Surg Br. 2011;93(2):145e150. 4. Koh S, Andersen CR, Buford WL Jr, Patterson RM, Viegas SF. Anatomy of the distal brachioradialis and its potential relationship to distal radius fracture. J Hand Surg Am. 2006;31(1):2e8. 5. Rapley JH, Kearny JP, Schrayer A, Viegas SF. Ulnar translation, a commonly overlooked, unrecognized deformity of distal radius fractures: techniques to correct the malalignment. Tech Hand Up Extrem Surg. 2008;12(3):166e169. 6. Bronstein AJ, Trumble TE, Tencer AF. The effects of distal radius fracture malalignment on forearm rotation: a cadaveric study. J Hand Surg Am. 1997;22(2):258e262.
r
Vol. 39, April 2014
The Effect of Distal Radius Translation in the Coronal Plane on Forearm Rotation: A Cadaveric Study of Distal Radius Fractures C. Tate Hepper, MD, Michael A. Tsai, BS, Brent G. Parks, MS, Norman H. Dubin, PhD, Kenneth R. Means, Jr, MD
Purpose To determine the effect of lateral translation of the distal radius in the coronal plane on forearm rotation after distal radius fracture. Methods Ten fresh cadaveric limbs underwent distal radius osteotomy just proximal to the distal radial-ulnar joint to simulate an extra-articular distal radius fracture. We used an Agee Wrist Jack external fixator to create increasing magnitudes of distal fragment lateral translation in 2-mm increments. Forearm rotation was measured using a 3-dimensional camera at each magnitude of lateral translation. Results Total forearm rotation for the intact specimen and 2, 4, 6, and 8 mm (maximal) radial translations was 186 53 , 188 54 , 189 55 , 190 57 , and 193 59 , respectively. There was no significant difference for any magnitude of radial translation. The average maximal radial translation possible before radioulnar abutment was 8 0.5 mm. Conclusions In this cadaveric model, translation of the distal radius fragment in the lateral direction had no effect on forearm rotation. Clinical relevance At the level of the proximal border of the distal radioulnar joint, isolated distalradius translation does not significantly affect forearm rotation. (J Hand Surg Am. 2014; 39(4):651e655. Copyright Ó 2014 by the American Society for Surgery of the Hand. All rights reserved.) Key words Distal radius fractures, forearm rotation, radial translation.
A
POTENTIAL COMPLICATION in the treatment of distal radius fractures is malunion resulting in altered wrist mechanics,1 loss of function, and the possible need for corrective osteotomy.2
From the Curtis National Hand Center, MedStar Union Memorial Hospital, Baltimore, MD. Received for publication July 23, 2013; accepted in revised form January 9, 2014. This research was funded by the Raymond M. Curtis Research Foundation, the Curtis National Hand Center. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Corresponding author: Kenneth R. Means, Jr, MD, care of Anne Mattson, Curtis National Hand Center, 3333 North Calvert Street, Baltimore, MD 21218; e-mail: anne. [email protected]. 0363-5023/14/3904-0007$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2014.01.010
Radiographic parameters identified as predictive of functional outcome include radial height, radial inclination, ulnar variance, dorsal-palmar tilt, carpal alignment, and articular congruity.3 To date, little attention has been paid to translation in the coronal plane. In extra-articular distal radius fractures (AO 23eA2), the pull of the brachioradialis is a deforming force resulting in lateral translation of the distal fragment.4 This deformity can be difficult to treat closed, although various techniques have been suggested.5 Bronstein et al6 performed a cadaveric analysis on the effects of a variety of distal radius fracture deformities on forearm rotation. In their limited model assessing a number of variables, 5 or 10 mm of lateral translation did not produce a significant change in
Ó 2014 ASSH
r
Published by Elsevier, Inc. All rights reserved.
r
651
652
DISTAL RADIUS TRANSLATION
forearm rotation. In our study, we aimed to test the hypothesis that extra-articular distal radius fractures with lateral translation of the distal fragment in the coronal plane result in restricted forearm rotation in a cadaveric model. MATERIALS AND METHODS Cadaveric model We used 10 paired, fresh-frozen cadaver upper limbs from 5 cadaveric donors with intact hands, wrists, and elbows. There were 2 male and 3 female cadaver donors. Average age was 76 years (range, 55e92 y). Each specimen was thawed and screened radiographically for evidence of prior fracture or other bony abnormality. One specimen had evidence of a prior distal radius fracture with old screw holes from a volar plate, which was healed in anatomic alignment and had no baseline passive range of motion deficit, and was therefore included in the study. The specimens were sectioned at the level of the proximal humerus. We inserted a large threaded rod into the humerus to assist in mounting the extremity. We then applied an Agee WristJack Fracture Reduction System (Hand Biomechanics Lab, Inc, Sacramento, CA) external fixator directly to the lateral aspect of the radius. Two pins were placed into the radial shaft. A single pin was placed into the distal radius using fluoroscopic assistance (Figs. 1, 2). The carpus and hand were left free. Baseline forearm rotation measurements were then taken as described in detail subsequently. We made a transverse dorsal incision directly over the planned osteotomy site. The third and fourth extensor compartment tendons were retracted medially. The second extensor compartment tendons were retracted laterally to expose the entire dorsal surface of the distal radius. We used a sagittal saw to create a complete distal radius cut that exited the medial border of the radius just proximal to the sigmoid notch and immediately adjacent to the distal radioulnar joint (Fig. 2). Special care was taken to avoid damaging the surrounding soft tissues. Using the functionality of the Agee WristJack external fixator, we were able to laterally translate the distal radius fragment in 2-mm increments. Maximum translation occurred when the ulnar head and neck impinged on the radial shaft (Fig. 3). Translation was measured radiographically with a mini C-arm image intensifer. The external fixator translation screw was turned several turns, and translation was checked with the C-arm. We added turns of the translation screw until we arrived at each J Hand Surg Am.
FIGURE 1: Experimental setup with external fixator applied to the distal radius. Camera markers are affixed to the external fixator via a rigid frame. The humerus is secured with a large intramedullary metal rod to facilitate mounting the specimen.
FIGURE 2: Radiograph before translation of the distal fragment. The osteotomy has been performed just proximal to the DRUJ. A radiopaque marker is present as a reference to measure the magnitude of translation. A single pin is present in the distal fragment. Two pins are placed in the shaft (not pictured).
2-mm increment of translation. A 12.7-mm-diameter radiopaque stainless-steel ballbearing marker was used to control for image magnification. The bearing was attached to each specimen in the same spot and was included in every C-arm image. We used a stainless-steel ruler to take scaled measurements directly on the screen of the C-arm image intensifer in real time. All images were saved digitally as Digital Imaging and Communications in Medicine files for possible later analysis. We saw no noteworthy motion r
Vol. 39, April 2014
DISTAL RADIUS TRANSLATION
measure 6 degrees of freedom in 3-dimensional motion. Each marker is composed of 3 distinct points, which the camera detects at the intersection of black and white regions (Fig. 1). Measurement data are reported at the centroid of the triad. The system has a measurement rate of 20 Hz, a processing time of 15 to 20 ms/frame, factory calibration accuracy of 0.35 mm root mean square, and validation testing accuracy of 0.18 mm root mean square. We created a rigid frame to attach the markers to each specimen to minimize variation in marker placement between specimens. A total of 4 markers, 2 on the specimen and 2 on the turntable platform, were measured to maximize accuracy. The camera was mounted on a tripod that was locked in place above the test apparatus and looked directly downward at the test surface (Fig. 4). The camera remained in place for the duration of testing and resulted in precise measurements. The camera system has been measured by validation testing in our laboratory to be accurate within 0.5 . A standard IEEE 1394 cable supplied power to the camera and also facilitated communication with the controlling computer. A minimum of 50 frames of data were collected and averaged at each forearm position. The angles of pronation and supination were calculated relative to the angle corresponding to neutral position. Neutral forearm rotation was defined as perpendicular to the humeral epicondylar axis. Degrees of supination and pronation from neutral and total arc of motion were measured and recorded for each specimen in the intact forearm and for 2, 4, 6, and 8 mm (or maximum) lateral translation.
FIGURE 3: Maximal lateral translation has occurred with abutment of the ulnar neck against the radial shaft.
of the distal fragment in any other plane. Fluoroscopic images were taken after each specimen was tested, to confirm that the applied torque was not creating unwanted deformity. Biomechanical testing The rod fixed in the distal humerus was first mounted to the testing apparatus. The elbow and forearm were positioned beneath the humerus so that they could swing freely with the forearm in a dependent position. We then loosely connected the external fixator to a turnstile located directly under the specimen. A 1.4-kg mass was used to apply torque to the turnstile in either supination or pronation (Fig. 4). The mass was attached to the turnstile via a steel cable in 1 of 2 locations to create either a supination or pronation torque. The steel cable ran over a pulley attached to the side of the table to avoid friction between the table and the steel cable. The external fixator was not rigidly fixed to the turnstile to allow some minor degrees of freedom of rotation (ie, it was impossible to exactly align the axes of forearm and turnstile rotations). The biomechanical testing procedure was repeated for each magnitude of translation of the distal radius. We measured forearm rotation using the MicronTracker 2 (Claron Technology, Inc, Toronto, Canada), a fully passive motion tracking system that is able to J Hand Surg Am.
653
Statistics Average forearm rotation, 95% confidence intervals, and standard deviation were calculated for each magnitude of lateral translation. Analysis of variance with repeated measures was used to determine whether there were significant changes in supination, pronation, or total arc of motion. We calculated average translation and standard deviation to radioulnar abutment. Significance was set to P < .05. We determined that a sample size of 10 would have 80% power to detect a difference in means of 15 , assuming a standard deviation of 15 , using a paired t test with a .05 2-sided significance level. RESULTS Pronation for the intact specimen and 2, 4, and 6 mm and maximal radial translation was 84 22 , 85 23 , 84 24 , 86 23 , and 85 23 (mean SD), respectively. There was no significant difference r
Vol. 39, April 2014
654
DISTAL RADIUS TRANSLATION
FIGURE 4: Experimental setup with a 3-dimensional motion camera mounted over the specimen and the limb mounted on the testing apparatus. The external fixator is attached to the turnstile, which is rotated by a 1.4-kg mass.
(P ¼ .92) for any magnitude of radial translation. Supination for the intact specimen and 2, 4, and 6 mm, and maximal radial translation was 102 35 , 102 35 , 104 36 , 104 40 , and 107 43 , respectively. We found no significant differences for any magnitude of lateral translation (P ¼ .32). Total forearm rotation for the intact specimen was 186 53 . For 2, 4, and 6 mm and maximal lateral translation, total forearm rotation increased by 2 , 3 , 4 , and 7 , respectively. Again, there was no significant difference for any magnitude of lateral translation (P ¼ .30). Figure 5 represents the means and 95% confidence intervals for total arc of rotation at each magnitude of lateral translation. The average maximal lateral translation possible before radioulnar abutment was 8 0.5 mm. Six of the 10 specimens demonstrated 8 mm radial translation. No specimen had a maximal translation less than 7 mm.
transverse extra-articular distal radius fracture affected forearm rotation in a cadaveric model. A limited study by Bronstein et al6 demonstrated no change in forearm rotation with lateral translation of the distal fragment. Similarly, in our study, we found no significant difference in forearm rotation with varying magnitudes of distal radius translation. Bronstein et al used a similar cadaveric model, with the exception that they measured rotation directly using a protractor rather than a 3-dimensional tracking system. They also tested multiple planes of deformity including 5 and 10 mm lateral translation, which had no effect on forearm rotation in their model. Medial translation of the distal fragment produced a 23% decrease in pronation in their study. We also found that the distal fragment could be translated 8 mm on average before the proximal radial shaft abutted the ulnar head and neck. It was our observation in this model of extra-articular distal radius fractures with intact distal radioulnar joint (DRUJ) ligaments that the distal radius fragment and ulna moved as a unit. In reality, creating distal radius fragment translation actually creates translation of the radial shaft ulnarly in relation to the intact distal
DISCUSSION In this study, we aimed to determine whether lateral translation of the distal fragment in a simple, J Hand Surg Am.
r
Vol. 39, April 2014
DISTAL RADIUS TRANSLATION
655
FIGURE 5: Total forearm rotation means and 95% confidence intervals.
radius and ulna unit. This observation may have implications for reducing this deformity in the clinical setting. Our study had several weaknesses. We only measured passive forearm rotation in a cadaveric model. Of course, many other factors determine clinical results for patients with distal radius fractures. Distal radius translation could affect other wrist motions, pain, DRUJ and radiocarpal joint biomechanics, function of the pronator quadratus, and the appearance of the wrist. Also, this is a cadaveric model in which we simulated forearm rotation by applying a torque to the forearm via an external fixator. Results may have been different if forearm rotation had been accomplished via the musculotendinous units of the forearm to more closely resemble the clinical situation. We also used a sagittal saw to simulate a fracture and to limit damage to the surrounding soft tissues. In the clinical scenario, associated soft tissue injuries, such as the interosseous membrane, DRUJ capsule, and triangular fibrocartilage complex, may have a role in forearm rotation. Finally, in the clinical scenario, deformity is almost always multiplaner and may involve rotation of the distal fragment in relation to the shaft. Our cadaveric model specifically only examined pure lateral translation without rotation. Rotation through
J Hand Surg Am.
the fracture that appears as translation radiographically may have an effect on forearm rotation clinically. Distal radius translation of an extra-articular distal radius fragment in the lateral direction does not affect passive forearm rotation in a cadaveric model. Distal radius translation may have an effect on other clinical parameters not assessed in our study. Further study is needed to determine acceptable magnitudes of lateral translation of the distal radius in the clinical setting. REFERENCES 1. Pogue DJ, Viegas SF, Patterson RM, et al. Effects of distal radius fracture malunion on wrist joint mechanics. J Hand Surg Am. 1990; 15(5):721e727. 2. Bushnell BD, Bynum DK. Malunion of the distal radius. J Am Acad Orthop Surg. 2007;15(1):27e40. 3. Ng CY, McQueen MM. What are the radiological predictors of functional outcome following fractures of the distal radius? J Bone Joint Surg Br. 2011;93(2):145e150. 4. Koh S, Andersen CR, Buford WL Jr, Patterson RM, Viegas SF. Anatomy of the distal brachioradialis and its potential relationship to distal radius fracture. J Hand Surg Am. 2006;31(1):2e8. 5. Rapley JH, Kearny JP, Schrayer A, Viegas SF. Ulnar translation, a commonly overlooked, unrecognized deformity of distal radius fractures: techniques to correct the malalignment. Tech Hand Up Extrem Surg. 2008;12(3):166e169. 6. Bronstein AJ, Trumble TE, Tencer AF. The effects of distal radius fracture malalignment on forearm rotation: a cadaveric study. J Hand Surg Am. 1997;22(2):258e262.
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Vol. 39, April 2014
