JBJS | The Effects of Ulnar Axial Malalignment on Supination and Pronation*

The Journal of Bone & Joint Surgery, Volume 82, Issue 12

Articles | December 01, 2000

The Effects of Ulnar Axial Malalignment on Supination and Pronation*

Martin C. Tynan, M.D.†; Stefan Fornalski, M.D.†; Patrick J. McMahon, M.D.†; Ali Utkan, M.D.†; Stuart A. Gree, M.D.†; Thay Q. Lee, Ph.D.†

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Investigation performed at Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, Long Beach, California
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Funds were received in total or partial support of the research or clinical study presented in this article. The funding source was the Veterans Affairs Rehabilitation Research and Development Grant, California Orthopaedic Research Institute, John C. Griswold Foundation.
†Orthopaedic Biomechanics Laboratory-VA Long Beach Healthcare System, 5901 East 7th Street, Long Beach, California 90822. E-mail address for T. Q. Lee: tqlee@med.va.gov.

The Journal of Bone & Joint Surgery. 2000; 82:1726-1726

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Abstract

Background: Forearm fractures are common injuries in both adults and children. Despite efforts to obtain anatomical alignment, axial rotational malunions occur, resulting in a decreased range of motion and a poor appearance. The objective of this study was to quantify loss of forearm rotation after simulation of ulnar malunions in supination and pronation.

Methods: Six fresh-frozen cadaveric upper extremities (mean age at the time of death, 79.4 ± 2.8 years) were used to quantify loss of forearm rotation after simulation of axial rotational malunions of the ulna. First, maximum forearm rotation in supination and pronation was measured at torques of 6.8, 13.6, and 20.4 kilograms-centimeter applied with use of a custom jig. Following a midshaft ulnar osteotomy, a custom adjustable internal fixation plate was used to simulate axial rotational malunions of the ulna of 0, 15, 30, and 45 degrees in both directions. Measurements in supination and pronation were then repeated at the prespecified torques. Analysis of variance, with a p value of 0.05, was used for statistical analysis.

Results: In all instances, a decrease in forearm rotation after simulation of the ulnar rotational malunion was accompanied by an increase in rotation in the opposite direction. Supination and pronation were significantly influenced, whereas the total arc of rotation was not affected by ulnar rotational malunion. At a torque of 20.4 kilograms-centimeter, pronation malunions of 15, 30, and 45 degrees resulted in a mean loss of supination (and standard error of the mean) of 5 ± 1, 11 ± 1, and 20 ± 1 degrees, respectively, and supination malunions of 15, 30, and 45 degrees resulted in a mean loss of pronation of 4 ± 1, 10 ± 2, and 18 ± 4 degrees, respectively. The ratio of the simulated rotational malunion to the loss of motion was larger than one.

Conclusions: Ulnar rotational malunions do not lead to a significant change in the total arc of forearm rotation. Instead, loss of motion in one direction is accompanied by increased motion in the opposite direction. Even with a 45-degree ulnar rotational malunion, forearm rotation decreases no more than 20 degrees.

Clinical Relevance: Ulnar rotational malunions have less effect on forearm rotation than that reported after radial malunions. This may be a consideration when treating forearm fractures or correcting rotational malunion of the forearm.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

Forearm rotation, comprised of supination and pronation, results from a complex interaction of osseous articulations and soft-tissue structures, including the radiocapitellar joint, the proximal radioulnar joint, the interosseous membrane, the distal radioulnar joint, and the muscles that attach to the bones^3,7,16,18. This rotation occurs around an axis along the length of the forearm and is in the transverse plane with one degree of freedom around a longitudinal axis (Fig. 1)^3,7,18. The axis consists of a longitudinal line extending from the center of the radial head proximally through the middle of the ulnar head distally ((Fig. 1))^10,18. In full supination, the two bones of the forearm are parallel. With pronation, the mobile radius progressively crosses over the ulna. The ulna has a stable articulation with the humerus, producing negligible movement proximally and minimal motion distally during forearm rotation, and it also functions as an important stabilizer of the forearm^2,4,9. Both the distal radioulnar joint and the interosseous membrane are crucial for proper forearm function^12,15.

Normal forearm rotation is important in activities of daily living as it allows a multitude of complex hand positions. The range of forearm rotation was shown by Boone and Azen to be 82 ± 3.8 degrees of supination and 75.8 ± 5.1 degrees of pronation, with the neutral point being with the forearm in midposition¹. It is important for the surgeon to consider the forearm as one interconnected functioning unit because any abnormality anywhere along the forearm axis can affect forearm rotation. Fifty degrees of supination and 50 degrees of pronation are usually needed for activities of daily living, and a loss of up to 20 degrees of either supination or pronation is usually considered acceptable^7,13.

Diaphyseal ulnar fractures are often treated (in adults) with closed reduction and cast immobilization^8,11,14. Prior study of the effect of malunion of forearm bones has focused on loss of forearm rotation after simulation of radial or both-bone malunions^6,13,17. The objective of our study was to quantify loss of forearm rotation after simulation of axial rotational malunion of the ulna, as can occur after diaphyseal fracture of the ulna. The null hypothesis was that ulnar rotational malunions of 15, 30, and 45 degrees in either supination or pronation would not have any effect on maximum forearm supination or pronation or on the total arc of forearm rotation.

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Fig. 1:: Schematic drawings showing the forearm in full supination and full pronation. AOR = axis of rotation of forearm, PRUJ = proximal radioulnar joint, IOM = interosseous membrane, and DRUJ = distal radioulnar joint.

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Fig. 2:: Illustration showing the experimental setup for the study. A right arm showing the volar surface is depicted. Although all skin and muscles of the forearm specimens were left intact in the experiment, they are not shown here to allow demonstration of hardware placement. DOF = degrees of freedom.

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Fig. 3:: Histograms showing the effects of pronation and supination rotational malunion of the ulna on supination, pronation, and total rotation of the forearm at torques of 6.8, 13.6, and 20.4 kilograms-centimeter. The full vertical bar represents the total range of forearm motion (ROM). The measurements before and after the osteotomy are shown at neutral.

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Fig. 4-A:: Radiograph of a specimen after completion of testing with the hardware intact (Fig. 4-A). The osteotomy site was stabilized with a custom internal fixator. The schematic of this fixator illustrates two views (Fig. 4-B). The narrow portion of the device is fixed to the proximal ulnar segment, while the distal, wide-slotted portion is fixed to the distal ulnar segment. This slotted setup permits rotation of the distal ulnar segment relative to the proximal ulnar segment.

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Fig. 4-B:: Radiograph of a specimen after completion of testing with the hardware intact (Fig. 4-A). The osteotomy site was stabilized with a custom internal fixator. The schematic of this fixator illustrates two views (Fig. 4-B). The narrow portion of the device is fixed to the proximal ulnar segment, while the distal, wide-slotted portion is fixed to the distal ulnar segment. This slotted setup permits rotation of the distal ulnar segment relative to the proximal ulnar segment.

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Table I: Effects of Supination and Pronation Malunion of the Ulna on Forearm Supination and Pronation at Three Levels of Torque

*The change is in relation to the range of motion after the osteotomy without rotation. The values are given as the mean and the standard error of the mean, with a plus value signifying an increase in motion and a minus value signifying a decrease in motion.

	Change in Range of Motion of Forearm* (degrees)
Supination Malunion		Pronation Malunion
Supination	Pronation	Supination	Pronation
6.8 kg-cm torque
15-degree malunion	4 ± 1	-6 ± 2	-4 ± 1	5 ± 1
30-degree malunion	10 ± 2	-12 ± 4	-12 ± 2	9 ± 1
45-degree malunion	12 ± 2	-19 ± 5	-22 ± 1	11 ± 2
13.6 kg-cm torque
15-degree malunion	7 ± 1	-3 ± 1	-4 ± 1	5 ± 1
30-degree malunion	13 ± 1	-10 ± 2	-13 ± 2	8 ± 1
45-degree malunion	16 ± 1	-11 ± 7	-22 ± 2	10 ± 1
20.4 kg-cm torque
15-degree malunion	9 ± 2	-4 ± 1	-5 ± 1	5 ± 1
30-degree malunion	13 ± 2	-10 ± 2	-11 ± 1	9 ± 1
45-degree malunion	19 ± 2	-18 ± 4	-20 ± 1	12 ± 1

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Table I: Effects of Supination and Pronation Malunion of the Ulna on Forearm Supination and Pronation at Three Levels of Torque

	Change in Range of Motion of Forearm* (degrees)
Supination Malunion		Pronation Malunion
Supination	Pronation	Supination	Pronation
6.8 kg-cm torque
15-degree malunion	4 ± 1	-6 ± 2	-4 ± 1	5 ± 1
30-degree malunion	10 ± 2	-12 ± 4	-12 ± 2	9 ± 1
45-degree malunion	12 ± 2	-19 ± 5	-22 ± 1	11 ± 2
13.6 kg-cm torque
15-degree malunion	7 ± 1	-3 ± 1	-4 ± 1	5 ± 1
30-degree malunion	13 ± 1	-10 ± 2	-13 ± 2	8 ± 1
45-degree malunion	16 ± 1	-11 ± 7	-22 ± 2	10 ± 1
20.4 kg-cm torque
15-degree malunion	9 ± 2	-4 ± 1	-5 ± 1	5 ± 1
30-degree malunion	13 ± 2	-10 ± 2	-11 ± 1	9 ± 1
45-degree malunion	19 ± 2	-18 ± 4	-20 ± 1	12 ± 1

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

Six fresh-frozen cadaveric upper extremities were used. All specimens were macroscopically intact without pathological changes. The mean age of the donors at the time of death was 79.4 2.8 years. All specimens were transected at the midpart of the humerus, and forearm tissue including the proximal and distal radioulnar joints was left intact. A posterior approach was used by carefully dissecting between the extensor carpi ulnaris and flexor carpi ulnaris muscles to allow access to the midpart of the ulnar shaft. Once bone had been exposed, a periosteal elevator was used to clean periosteum and all other tissue to accommodate placement of a custom adjustable internal fixation plate. This device had precalculated markings for simulating supination and pronation rotational malunions of the ulna.

The specimens were rigidly fixed to a freely adjustable custom jig that accommodated multiple specimen sizes (Fig. 2). This setup permitted the application of torque about the axis of the ulna resulting in supination and pronation of the forearm. The specimen was clamped to the custom jig, and the elbow was fixed in 90 degrees of flexion by drilling a pin through the olecranon and into the humeral intramedullary canal. Another pin, functioning as the point of torque application, was placed perpendicularly into the distal part of the radius. Next, the torque bar of the jig, which was continuous with a pulley, was fixed to the torque pin in the distal part of the radius. To minimize restriction of movement, three degrees of freedom were allowed at the interface of the torque pin (specimen) and torque bar (jig). The forearm was moved through the full range of supination and pronation, and the middle of this range of motion was designated the neutral point. A goniometer (fixed to the base of the custom jig) was then positioned so that zero on the goniometer was aligned with the neutral point of supination and pronation. Next, a proximal stabilization pin was placed in the ulna. Supination and pronation were manually rechecked on the jig to ensure that none of the pins limited or interfered with the range of motion.

Each specimen was preconditioned through ten supination-pronation cycles to minimize viscoelastic effects. Before the osteotomy, control measurements of maximum supination and pronation were made at three specified torques of 6.8, 13.6, and 20.4 kilograms-centimeter. The midpoint of this range of motion was the previously determined neutral position. Forearm rotation was measured with a goniometer. Preliminary study with our jig indicated repeatability of pronation-supination range-of-motion measurements within 2 degrees. While the ulna was still on the jig, an external fixator was affixed to it across the planned osteotomy site to maintain orientation of the proximal and distal ulnar segments. Next, a midshaft ulnar osteotomy was made with a handheld oscillating saw. The custom adjustable internal fixation plate, which had slots marked to allow fixation of the ulna in 0, 15, 30, and 45 degrees of axial rotational malunion in both directions, was used to fix the osteotomy site. The external fixator was then removed.

Forearm rotation was produced by applying torques of 6.8, 13.6, and 20.4 kilograms-centimeter through cables attached to the pulley wheel. Following the osteotomy without malposition of the osteotomy site, maximum forearm rotation in both supination and pronation was measured and compared with the preosteotomy values to ensure that there was no change. All torques were tested with 0, 15, 30, and 45 degrees of supination and pronation malunion, and maximum supination and pronation were recorded (Fig. 3). A constant time of one minute for tissue deformation was allowed before each measurement.

After completion of testing, all hardware was left intact and anteroposterior and lateral radiographs were made to rule out prior fracture and osteoarthritis and to confirm that hardware placement did not interfere with rotational motion of the forearm (Fig. 4-A and Fig. 4-B).

Results

Introduction | Materials and Methods | Results | Discussion | References

Simulated axial rotational malunions of the ulna did not have a significant effect on the total arc of forearm rotation. At all torques (6.8, 13.6, and 20.4 kilograms-centimeter), forearm pronation increased with pronation malunion of the ulna and decreased with supination malunion of the ulna (Fig. 3 and Table I). At the highest torque tested, ulnar supination malunions of 15, 30, and 45 degrees resulted in losses of pronation (mean and standard error of the mean) of 4 ± 1, 10 ± 2, and 18 ± 4 degrees, respectively.

At all torques, forearm supination decreased with ulnar pronation malunion and increased with ulnar supination malunion (Fig. 3 and Table I). At the highest torque tested, ulnar pronation malunions of 15, 30, and 45 degrees resulted in losses of supination of 5 ± 1, 11 ± 1, and 20 ± 1 degrees, respectively.

In all cases, the loss of either supination or pronation of the forearm was not as great as the amount of simulated axial rotational malunion of the ulna. The degree of simulated rotational malunion did not directly parallel loss of supination or pronation; rather, the ratio of the degree of rotational malunion to loss of either supination or pronation was larger than one.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

In this study, we evaluated the effect of rotational malunion of the ulna on supination, pronation, and the total arc of rotation of the forearm. With increasing amounts of ulnar pronation malunion, a progressive increase of pronation and a progressive decrease of supination were observed. Conversely, with increasing ulnar supination malunion, a progressive decrease of pronation and a progressive increase of supination were observed. At the highest torque tested, simulated pronation malunion of 45 degrees resulted in a mean loss of supination of 20 degrees and simulated supination malunion of 45 degrees resulted in a mean loss of pronation of 18 degrees. Previous studies have shown that up to a 20-degree loss of supination or pronation does not inhibit the performance of activities of daily living^7,13.

Interestingly, at 20.4 kilograms-centimeter of torque, the increase in supination resulting from a 45-degree supination malunion of the ulna was almost twice as large as the increase in pronation seen with a 45-degree pronation malunion of the ulna. This probably resulted from the anatomical relationship between the radial and ulnar bones. In supination, the forearm bones are parallel; however, in pronation, the radius crosses over the ulna, producing interference and limitation of pronation. Change in tension of the supporting soft tissue may be another limiting factor. Rotational malunion results in changes in the lengths of the interosseous membrane and the muscle-tendon units. At maximum supination and pronation, these length changes may have meaningful effects.

The results of this study also demonstrate that experimental rotational malunion of the ulna does not significantly decrease the total arc of forearm rotation. Rather, the arc traveled by the distal part of the radius during forearm rotation showed a characteristic shift toward more pronation with pronation malunion of the ulna and toward more supination with supination malunion. A decrease in supination or pronation is compensated for by a reciprocal increase in pronation or supination. Also, the magnitude of simulated axial malunion did not directly correlate with the loss of supination or pronation.

Our results are consistent with those of prior studies that have demonstrated loss of forearm rotation after simulation of radial or both-bone malunions. Matthews et al. reported little loss of supination and pronation after mid-diaphyseal ulnar and radial angular malunions of 10 degrees, but they reported a functionally important loss of rotation after angular malunions of 20 degrees⁶. Sarmiento et al. reported that ulnar or radial angulation of 10 degrees limited pronation and supination within an acceptable range of 24 degrees, and 10 degrees of angulation of both the ulna and the radius limited pronation and supination by 18 percent¹³. Tarr et al. studied both angular and rotational malunions¹⁷. They reported that 10-degree angular malunions of the middle and distal thirds of the radius, ulna, or both bones resulted in acceptable limitation of supination and pronation. They also reported that 10-degree rotational malunions of the middle and distal thirds of the radius resulted in acceptable limitation of rotation and stated that the degree of rotational malunion paralleled the loss of pronation and supination.

The finding by Tarr et al. that rotational malunion of the radius produced losses of rotation equal to the degree of the malunion¹⁷ differed from the results of our study of axial rotational malunions of the ulna. We found that the loss of supination or pronation did not directly correlate with the amount of axial rotational malunion of the ulna. This difference may be due to several factors, including the anatomical and functional difference between the straight ulna and the curved radius. In addition, at the distal radioulnar joint, the head of the ulna is at the center of axial rotation of the forearm and thus may minimally affect total pronation and supination in comparison with the mobile radius, which rotates and translates around the head of the ulna.

In our study, the experimental model was designed to measure and reproduce forearm rotation accurately. Normally, forearm rotation is an interaction between osseous articulations and soft-tissue constraints. For this reason, specimens were kept as intact as possible, without dissection of skin or muscle except as needed for production of the osteotomy and placement of the internal fixator. In our study and a prior study¹⁷, the forces normally producing forearm rotation were simplified by applying a single torque upon the distal part of the radius to produce the rotation. However, forearm rotation normally is the result of a complex interaction between multiple forearm muscles and soft-tissue constraints. With this simplified model, some of the natural stabilizers were most likely lost.

In conclusion, the results of this study suggest that ulnar rotational malunions do not significantly affect total forearm rotation. Loss of motion in one direction was accompanied by increased motion in the opposite direction. The degree of rotational malunion did not parallel the degree of loss of supination or pronation. Even with ulnar rotational malunion of 45 degrees, the arc of rotation was still within the 20-degree range of acceptable loss. This finding supports the current practice of treating nondisplaced mid-diaphyseal ulnar fractures with closed reduction and immobilization. Finally, the results of our study and that by Tarr et al.¹⁷ suggest that forearm rotation is affected less by ulnar rotational malunion than it is by radial malunion. This may be an important consideration in the treatment of diaphyseal two-bone forearm fractures or rotational malunion of the forearm.

References

Introduction | Materials and Methods | Results | Discussion | References

Boone, D. C., and Azen, S. P.: Normal range of motion of joints in male subjects. J. Bone and Joint Surg.,61-A: 756-759, July 1979 .61-A756 1979

Campbell's Operative Orthopaedics. Ed. 8, pp. 1025-1053. Edited by A. H. Crenshaw. St. Louis, Mosby-Year Book, 1992

Graham, T. J.; Fischer, T. J.; Hotchkiss, R. N.; and Kleinman, W. B.: Disorders of the forearm axis. Hand Clin.,14: 305-316, 1998 .14305 1998 [PubMed]

Jones, D. J.; Henley, M. B.; Schemitsch, E. H.; and Tencer, A. F.: A biomechanical comparison of two methods of fixation of fractures of the forearm. J. Orthop. Trauma,9: 198-206, 1995 .9198 1995 [PubMed]

McAuliffe, J. A.: Forearm fixation. Hand Clin.,,13: 689-701, 1997 .13689 1997

Matthews, L. S.; Kaufer, H.; Garver, D. F.; and Sonstegard, D. A.: The effect on supination-pronation of angular malalignment of fractures of both bones of the forearm. An experimental study. J. Bone and Joint Surg.,64-A: 14-17, Jan 1982 .64-A14 1982

Morrey, B. F.; Askew, L. J.; An, K. N.; and Chao, E. Y.: A biomechanical study of normal functional elbow motion. J. Bone and Joint Surg.,63-A: 872-877, July 1981 .63-A872 1981

Ostermann, P. A.; Ekkernkamp, A.; Henry, S. L.; and Muhr, G.: Bracing of stable shaft fractures of the ulna. J. Orthop. Trauma,8: 245-248, 1994 .8245 1994 [PubMed]

Palmer, A. K., and Werner, F. W.: Biomechanics of the distal radioulnar joint. Clin. Orthop.,187: 26-35, 1984 .18726 1984 [PubMed]

Peimer, C. A.: Surgery of the Hand and Upper Extremity. Vol. 1, pp. 599-749. New York, McGraw-Hill Health Professions Division, 1995

Pollock, F. H.; Pankovich, A. M.; Prieto, J. J.; and Lorenz, M.: The isolated fracture of the ulnar shaft. Treatment without immobilization. J. Bone and Joint Surg.,65: 339-342, March 1983 .65339 1983

Rabinowitz, R. S.; Light, T. R.; Havey, R. M.; Gourineni, P.; Patwardhan, A. G.; Sartori, M. J.; and Vrbos, L.: The role of the interosseous membrane and triangular fibrocartilage complex in forearm stability. J. Hand Surg.,19A: 385-393, 1994 .19A385 1994

Sarmiento, A.; Ebramzadeh, E.; Brys, D.; and Tarr, R.: Angular deformities and forearm function. J. Orthop. Res.,,10: 121-133, 1992 .10121 1992

Sarmiento, A.; Latta, L. L.; Zych, G.; McKeever, P.; and Zagorski, J. P.: Isolated ulnar shaft fractures treated with functional braces. J. Orthop. Trauma,12: 420-424, 1998 .12420 1998 [PubMed]

Skahen, J. R., III; Palmer, A. K.; Werner, F. W.; and Fortino, M. D.: The interosseous membrane of the forearm: anatomy and function. J. Hand Surg.,22A: 981-985, 1997 .22A981 1997

Stroyan, M., and Wilk, K. E.: The functional anatomy of the elbow complex. J. Orthop. and Sports Phys. Ther.,17: 279-288, 1993 .17279 1993

Tarr, R. R.; Garfinkel, A. I.; and Sarmiento, A.: The effects of angular and rotational deformities of both bones of the forearm. An in vitro study. J. Bone and Joint Surg.,66-A: 65-70, Jan 1984 .66-A65 1984

Werner, F. W., and An, K. N.: Biomechanics of the elbow and forearm. Hand Clin.,10: 357-373, 1994.10357 1994 [PubMed]

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Table I: Effects of Supination and Pronation Malunion of the Ulna on Forearm Supination and Pronation at Three Levels of Torque

	Change in Range of Motion of Forearm* (degrees)
Supination Malunion		Pronation Malunion
Supination	Pronation	Supination	Pronation
6.8 kg-cm torque
15-degree malunion	4 ± 1	-6 ± 2	-4 ± 1	5 ± 1
30-degree malunion	10 ± 2	-12 ± 4	-12 ± 2	9 ± 1
45-degree malunion	12 ± 2	-19 ± 5	-22 ± 1	11 ± 2
13.6 kg-cm torque
15-degree malunion	7 ± 1	-3 ± 1	-4 ± 1	5 ± 1
30-degree malunion	13 ± 1	-10 ± 2	-13 ± 2	8 ± 1
45-degree malunion	16 ± 1	-11 ± 7	-22 ± 2	10 ± 1
20.4 kg-cm torque
15-degree malunion	9 ± 2	-4 ± 1	-5 ± 1	5 ± 1
30-degree malunion	13 ± 2	-10 ± 2	-11 ± 1	9 ± 1
45-degree malunion	19 ± 2	-18 ± 4	-20 ± 1	12 ± 1

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Table I: Effects of Supination and Pronation Malunion of the Ulna on Forearm Supination and Pronation at Three Levels of Torque

	Change in Range of Motion of Forearm* (degrees)
Supination Malunion		Pronation Malunion
Supination	Pronation	Supination	Pronation
6.8 kg-cm torque
15-degree malunion	4 ± 1	-6 ± 2	-4 ± 1	5 ± 1
30-degree malunion	10 ± 2	-12 ± 4	-12 ± 2	9 ± 1
45-degree malunion	12 ± 2	-19 ± 5	-22 ± 1	11 ± 2
13.6 kg-cm torque
15-degree malunion	7 ± 1	-3 ± 1	-4 ± 1	5 ± 1
30-degree malunion	13 ± 1	-10 ± 2	-13 ± 2	8 ± 1
45-degree malunion	16 ± 1	-11 ± 7	-22 ± 2	10 ± 1
20.4 kg-cm torque
15-degree malunion	9 ± 2	-4 ± 1	-5 ± 1	5 ± 1
30-degree malunion	13 ± 2	-10 ± 2	-11 ± 1	9 ± 1
45-degree malunion	19 ± 2	-18 ± 4	-20 ± 1	12 ± 1