JBJS | Biomechanical Evaluation of Fixation of Intra-Articular Fractures of the Distal Part of the Radius in Cadavera: Kirschner Wires Compared with Calcium-Phosphate Bone Cement*

The Journal of Bone & Joint Surgery, Volume 81, Issue 3

Articles | March 01, 1999

Biomechanical Evaluation of Fixation of Intra-Articular Fractures of the Distal Part of the Radius in Cadavera: Kirschner Wires Compared with Calcium-Phosphate Bone Cement*

DURAN N. YETKINLER, M.D., PH.D.†; AMY L. LADD, M.D.‡; ROBERT D. POSER, D.V.M.†; BRENT R. CONSTANTZ, PH.D.§; DENNIS CARTER, PH.D.§, CUPERTINO, CALIFORNIA

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Investigation performed at the Biomechanics Laboratory, Norian Corporation, Cupertino

The Journal of Bone & Joint Surgery. 1999; 81:391-9

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Abstract

Background: The purpose of this study was to compare the biomechanical efficacy of an injectable calcium-phosphate bone cement (Skeletal Repair System [SRS]) with that of Kirschner wires for the fixation of intra-articular fractures of the distal part of the radius.Methods: Colles fractures (AO pattern, C2.1) were produced in ten pairs of fresh-frozen human cadaveric radii. One radius from each pair was randomly chosen for stabilization with SRS bone cement. These ten radii were treated with open incision, impaction of loose cancellous bone with use of a Freer elevator, and placement of the SRS bone cement by injection. In the ten control specimens, the fracture was stabilized with use of two horizontal and two oblique Kirschner wires. The specimens were cyclically loaded to a peak load of 200 newtons for 2000 cycles to evaluate the amount of settling, or radial shortening, under conditions simulating postoperative loading with the limb in a cast. Each specimen then was loaded to failure to determine its ultimate strength.Results: The amount of radial shortening was highly variable among the specimens, but it was consistently higher in the Kirschner-wire constructs than in the bone fixed with SRS bone cement within each pair of radii. The range of shortening for all twenty specimens was 0.18 to 4.51 millimeters. The average amount of shortening in the SRS constructs was 50 percent of that in the Kirschner-wire constructs (0.51 ± 0.34 compared with 1.01 ± 1.23 millimeters; p = 0.015). With the numbers available, no significant difference in ultimate strength was detected between the two fixation groups.Conclusions: This study showed that fixation of an intra-articular fracture of the distal part of a cadaveric radius with biocompatible calcium-phosphate bone cement produced results that were biomechanically comparable with those produced by fixation with Kirschner wires. However, the constructs that were fixed with calcium-phosphate bone cement demonstrated less shortening under simulated cyclic load-bearing.Clinical Relevance: A calcium-phosphate bone cement with high compressive strength may provide adequate stability of the fracture and therefore serve as an alternative to Kirschner wires with their associated complications.

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Introduction

Introduction | Materials and Methods | Results | Discussion | References

Distal radial fractures, often referred to as Colles fractures, frequently occur in women who are more than forty-five years old and who have fallen on an outstretched hand. The fall creates a compressive load that fractures the dorsal cortex, typically with comminution. The fracture may also include a tensile failure of the volar cortex⁵. Even though most Colles fractures are considered to be low-energy extra-articular injuries that occur in osteopenic bone, intra-articular fractures often are also classified as Colles fractures. The radiographic findings include dorsal angulation and displacement, radial shortening, impaction, and comminution; there also may be a fracture of the ulnar styloid process, carpal instability, and soft-tissue injury²².

The objectives of treatment of a Colles fracture are to restore and maintain the anatomy of the wrist in order to obtain early, painless function²⁸. The current methods of treatment often do not fulfill these goals. The traditional method of closed reduction and use of a cast is indicated for fractures that have little or no displacement or comminution^4,5,8,18. If a cast alone is used to treat an unstable distal radial fracture characterized by comminution, marked displacement of the fragments, and interposition of soft tissue, the fracture has a tendency to redisplace within about two weeks^8,18,29. Percutaneous pins, external fixation, and operative reduction and internal fixation therefore are often used to stabilize an unstable fracture¹. However, these treatment methods have their own inherent problems.

Rayhack, in a study of displaced distal radial fractures that had been treated with use of percutaneous pins, reported complications that included loss of reduction, pin-track infection, broken pins, migration of pins, tendon irritation and irritation of the radial sensory nerve, rupture of the extensor tendon, and Sudeck atrophy²³. Although external fixation may provide more predictable restoration of radial length, the rate of complications has been as high as 70 percent (thirty-one of forty-four patients in one series¹⁰), mainly because of the extended period of immobilization. These complications have included pin-track infection; fracture through pin sites; radial sensory neuritis; reflex sympathetic dystrophy; and, most importantly, disuse atrophy and stiffness of the joint^5,10,11,25. Sommerkamp et al. attempted to decrease morbidity related to immobilization by using dynamic external fixators, but they encountered insufficient stability at the fracture site, with more settling and other complications²⁷. Despite the increasing popularity of more invasive techniques (open reduction and internal fixation) for the treatment of distal radial fractures, serious complications can occur; these include loss of fixation, neuritis of the median nerve, reflex sympathetic dystrophy, wound infection, and late posttraumatic arthritis¹¹.

Intra-articular fractures in particular present several problems. Incomplete reduction usually results in a poor outcome¹⁵. Joint stiffness, articular incongruity, and posttraumatic arthritis also can occur⁵. Invasive treatment such as bone-grafting and internal fixation may often be needed because of the complex nature of these fractures.

Fernandez and Jupiter suggested the use of Kirschner wires as an effective method for fixation of simple intra-articular compression-type fractures of the distal part of the radius, which usually do not need bone-grafting⁵. An alternative method of fixation of these fractures was biomechanically evaluated in the current in vitro study. We compared the use of SRS (Skeletal Repair System) injectable calcium-phosphate bone cement (Norian, Cupertino, California) with that of Kirschner wires.

*One or more of the authors has received or will receive benefits for personal or professional use 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 Norian Corporation, Cupertino, California.

†Norian Corporation, 10260 Bubb Road, Cupertino, California 95014-4166. E-mail address: duran_yetkinler@norian.com.

‡900 Welch Road, Suite 15, Palo Alto, California 94304.

§Division of Biomechanical Engineering, Terman Building, Rooms 550 (B. R. C.) and 561 (D. C.), Stanford University, Stanford, California 94305.

†Norian Corporation, 10260 Bubb Road, Cupertino, California 95014-4166. E-mail address: duran_yetkinler@norian.com.

‡900 Welch Road, Suite 15, Palo Alto, California 94304.

§Division of Biomechanical Engineering, Terman Building, Rooms 550 (B. R. C.) and 561 (D. C.), Stanford University, Stanford, California 94305.

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FIG1:: Fig. 1 Drawing showing the articular surface (A) and an anteroposterior view (B) of the desired Colles fracture (AO pattern, C2.1).

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FIG2:: Fig. 2 Drawing showing Kirschner-wire fixation of a three-part intra-articular distal radial fracture. Two Kirschner wires were placed horizontally across the sagittal fracture line, and an additional two wires were placed in an oblique pattern across the horizontal fracture line.

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FIG3-A:: Fig. 3-A: Radiograph showing fixation of a fracture with Kirschner wires.

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FIG3-B:: Fig. 3-B: Radiograph showing fixation of a fracture with SRS bone cement.

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FIG4:: Fig. 4 Drawing showing top and side views of the placement of the linear variable differential transducers (LVDT) around the distal fragments of the distal radial fracture for measurement of movement of the fragments in the axial direction. The data that were obtained were used to calculate settling of the lunate and scaphoid fossae as well as dorsal and volar step-off. (Only linear variable differential transducer 5 is shown in the side view for the purpose of simplification.)

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FIG5:: Fig. 5 Graph showing settling of the entire articular surface of the Kirschner-wire (K-wire) constructs compared with that of the SRS constructs. Each data point represents one pair of specimens.

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FIG6:: Fig. 6 Graph showing settling of the scaphoid and lunate fossae in the Kirschner-wire (K-wire) constructs compared with that in the SRS constructs. Each data point represents one pair of specimens.

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FIG7:: Fig. 7 Graph showing volar and dorsal step-off in the Kirschner-wire (K-wire) constructs compared with that in the SRS constructs. Each data point represents one pair of specimens.

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TABLE I DATA ON OVERALL DISPLACEMENT (SETTLING) AND ULTIMATE LOAD TO FAILURE

*SRS = Skeletal Repair System bone cement (Norian, Cupertino, California).

Specimen Pair	Type of Construct*	Overall Displacement (mm)	Ultimate Load to Failure (N)
1	Kirschner-wire	-0.61	-1745
	SRS	-0.38	-860
2	Kirschner-wire	-1.35	-2150
	SRS	-0.49	-2410
3	Kirschner-wire	-0.37	-2790
	SRS	-0.19	-5660
4	Kirschner-wire	-0.60	-1930
	SRS	-0.46	-1890
5	Kirschner-wire	-4.51	-694
	SRS	-1.29	-953
6	Kirschner-wire	-1.28	-1110
	SRS	-1.01	-1220
7	Kirschner-wire	-0.55	-3130
	SRS	-0.43	-2030
8	Kirschner-wire	-0.18	-1300
	SRS	-0.24	-1060
9	Kirschner-wire	-0.33	-2440
	SRS	-0.33	-2420
10	Kirschner-wire	-0.28	-1130
	SRS	-0.26	-1460
Average and standard deviation	Kirschner-wire	-1.01 ± 1.23	-1842 ± 796
SRS	-0.51 ± 0.34	-1996 ± 1413

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TABLE I DATA ON OVERALL DISPLACEMENT (SETTLING) AND ULTIMATE LOAD TO FAILURE

*SRS = Skeletal Repair System bone cement (Norian, Cupertino, California).

Specimen Pair	Type of Construct*	Overall Displacement (mm)	Ultimate Load to Failure (N)
1	Kirschner-wire	-0.61	-1745
	SRS	-0.38	-860
2	Kirschner-wire	-1.35	-2150
	SRS	-0.49	-2410
3	Kirschner-wire	-0.37	-2790
	SRS	-0.19	-5660
4	Kirschner-wire	-0.60	-1930
	SRS	-0.46	-1890
5	Kirschner-wire	-4.51	-694
	SRS	-1.29	-953
6	Kirschner-wire	-1.28	-1110
	SRS	-1.01	-1220
7	Kirschner-wire	-0.55	-3130
	SRS	-0.43	-2030
8	Kirschner-wire	-0.18	-1300
	SRS	-0.24	-1060
9	Kirschner-wire	-0.33	-2440
	SRS	-0.33	-2420
10	Kirschner-wire	-0.28	-1130
	SRS	-0.26	-1460
Average and standard deviation	Kirschner-wire	-1.01 ± 1.23	-1842 ± 796
SRS	-0.51 ± 0.34	-1996 ± 1413

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TABLE II DISPLACEMENT OF THE INDIVIDUAL LINEAR VARIABLE DIFFERENTIAL TRANSDUCERS AND SETTLING OF THE SCAPHOID AND LUNATE FOSSAE*

*The values are given in millimeters. †SRS = Skeletal Repair System bone cement (Norian, Cupertino, California).

Specimen Pair	Type of Construct†	Displacement of Linear Variable Differential Transducer						Settling of Scaphoid Fossa	Settling of Lunate Fossa
1: Volar Scaphoid	2: Lateral Scaphoid	3: Dorsal Scaphoid	4: Dorsal Lunate	5: Medial Lunate	6: Volar Lunate
1	Kirschner-wire	-0.24	-1.89	-1.54	-0.70	-0.87	-1.02	-1.22	-0.86
	SRS	-0.46	-0.06	0.05	0.29	0.14	-0.04	-0.16	0.13
2	Kirschner-wire	-0.65	-1.11	-1.65	-1.49	-1.14	0.00	-1.14	-0.88
	SRS	0.00	-0.08	0.00	0.16	-0.03	-0.08	-0.02	0.02
3	Kirschner-wire	-0.61	-1.90	-0.18	-0.35	-0.19	-0.01	-0.90	-0.18
	SRS	-0.14	-0.02	-0.29	-0.03	0.09	-0.02	-0.15	0.03
4	Kirschner-wire	-0.66	-0.85	-0.42	-0.43	0.26	0.40	-0.64	0.08
	SRS	-0.10	-0.32	0.06	0.20	-0.79	-0.62	-0.12	-0.40
5	Kirschner-wire	-3.59	-5.26	-4.68	-6.29	0.38	-6.79	-4.51	-4.23
	SRS	-2.80	-0.83	-0.26	-0.58	-0.23	0.10	-1.30	-0.24
6	Kirschner-wire	-1.57	-2.05	-0.28	0.28	0.03	0.00	-1.30	0.10
	SRS	0.00	0.18	-0.70	0.69	-1.34	-1.69	-0.18	-0.78
7	Kirschner-wire	-0.14	-0.25	-0.41	0.11	-0.07	-0.62	-0.27	-0.20
	SRS	0.06	-0.33	-0.29	0.03	0.11	-0.46	-0.19	-0.11
8	Kirschner-wire	-0.11	0.18	-0.27	-0.64	-0.64	0.21	-0.07	-0.36
	SRS	0.38	-0.02	-0.72	-0.69	-0.16	0.32	-0.12	-0.18
9	Kirschner-wire	-0.06	-0.10	-0.31	-0.30	-0.18	0.20	-0.16	-0.09
	SRS	-0.51	-0.31	-0.05	-0.06	-0.14	0.02	-0.29	0.03
10	Kirschner-wire	0.07	-0.50	-0.96	-0.29	-1.26	0.43	-0.47	-0.37
	SRS	0.01	-0.26	-0.29	-0.27	-0.32	0.00	-0.18	-0.20
Average and standard deviation	Kirschner-wire	-0.76 ± 1.10	-1.37 ± 1.58	-1.07 ± 1.38	-1.01 ± 1.92	-0.37 ± 0.58	-0.72 ± 2.18	-1.07 ± 1.29	-0.70 ± 1.29
SRS	-0.36 ± 0.90	-0.21 ± 0.28	-0.25 ± 0.28	-0.02 ± 0.41	-0.27 ± 0.47	-0.25 ± 0.57	-0.27 ± 0.37	-0.17 ± 0.27

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TABLE II DISPLACEMENT OF THE INDIVIDUAL LINEAR VARIABLE DIFFERENTIAL TRANSDUCERS AND SETTLING OF THE SCAPHOID AND LUNATE FOSSAE*

*The values are given in millimeters. †SRS = Skeletal Repair System bone cement (Norian, Cupertino, California).

Specimen Pair	Type of Construct†	Displacement of Linear Variable Differential Transducer						Settling of Scaphoid Fossa	Settling of Lunate Fossa
1: Volar Scaphoid	2: Lateral Scaphoid	3: Dorsal Scaphoid	4: Dorsal Lunate	5: Medial Lunate	6: Volar Lunate
1	Kirschner-wire	-0.24	-1.89	-1.54	-0.70	-0.87	-1.02	-1.22	-0.86
	SRS	-0.46	-0.06	0.05	0.29	0.14	-0.04	-0.16	0.13
2	Kirschner-wire	-0.65	-1.11	-1.65	-1.49	-1.14	0.00	-1.14	-0.88
	SRS	0.00	-0.08	0.00	0.16	-0.03	-0.08	-0.02	0.02
3	Kirschner-wire	-0.61	-1.90	-0.18	-0.35	-0.19	-0.01	-0.90	-0.18
	SRS	-0.14	-0.02	-0.29	-0.03	0.09	-0.02	-0.15	0.03
4	Kirschner-wire	-0.66	-0.85	-0.42	-0.43	0.26	0.40	-0.64	0.08
	SRS	-0.10	-0.32	0.06	0.20	-0.79	-0.62	-0.12	-0.40
5	Kirschner-wire	-3.59	-5.26	-4.68	-6.29	0.38	-6.79	-4.51	-4.23
	SRS	-2.80	-0.83	-0.26	-0.58	-0.23	0.10	-1.30	-0.24
6	Kirschner-wire	-1.57	-2.05	-0.28	0.28	0.03	0.00	-1.30	0.10
	SRS	0.00	0.18	-0.70	0.69	-1.34	-1.69	-0.18	-0.78
7	Kirschner-wire	-0.14	-0.25	-0.41	0.11	-0.07	-0.62	-0.27	-0.20
	SRS	0.06	-0.33	-0.29	0.03	0.11	-0.46	-0.19	-0.11
8	Kirschner-wire	-0.11	0.18	-0.27	-0.64	-0.64	0.21	-0.07	-0.36
	SRS	0.38	-0.02	-0.72	-0.69	-0.16	0.32	-0.12	-0.18
9	Kirschner-wire	-0.06	-0.10	-0.31	-0.30	-0.18	0.20	-0.16	-0.09
	SRS	-0.51	-0.31	-0.05	-0.06	-0.14	0.02	-0.29	0.03
10	Kirschner-wire	0.07	-0.50	-0.96	-0.29	-1.26	0.43	-0.47	-0.37
	SRS	0.01	-0.26	-0.29	-0.27	-0.32	0.00	-0.18	-0.20
Average and standard deviation	Kirschner-wire	-0.76 ± 1.10	-1.37 ± 1.58	-1.07 ± 1.38	-1.01 ± 1.92	-0.37 ± 0.58	-0.72 ± 2.18	-1.07 ± 1.29	-0.70 ± 1.29
SRS	-0.36 ± 0.90	-0.21 ± 0.28	-0.25 ± 0.28	-0.02 ± 0.41	-0.27 ± 0.47	-0.25 ± 0.57	-0.27 ± 0.37	-0.17 ± 0.27

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TABLE III DATA ON VOLAR AND DORSAL STEP-OFF

*SRS = Skeletal Repair System bone cement (Norian, Cupertino, California). †The average of the differences between the two groups.

Specimen Pair	Type of Construct*	Volar Step-off (mm)	Dorsal Step-off (mm)
1	Kirschner-wire	0.78	0.84
	SRS	0.42	0.24
	Difference	-0.36	-0.60
2	Kirschner-wire	0.65	0.16
	SRS	0.08	0.16
	Difference	-0.57	0.00
3	Kirschner-wire	0.60	0.17
	SRS	0.11	0.32
	Difference	-0.49	0.15
4	Kirschner-wire	1.07	0.01
	SRS	0.52	0.14
	Difference	-0.55	0.13
5	Kirschner-wire	3.20	1.61
	SRS	2.91	0.32
	Difference	-0.29	-1.29
6	Kirschner-wire	1.56	0.56
	SRS	1.68	1.39
	Difference	0.12	0.83
7	Kirschner-wire	0.48	0.52
	SRS	0.52	0.32
	Difference	0.04	-0.20
8	Kirschner-wire	0.32	0.37
	SRS	0.06	0.03
	Difference	-0.26	-0.34
9	Kirschner-wire	0.26	0.01
	SRS	0.53	0.01
	Difference	0.27	0.00
10	Kirschner-wire	0.36	0.67
	SRS	0.01	0.02
	Difference	-0.35	-0.65
Average and standard deviation	Kirschner-wire	0.93 ± 0.89	0.49 ± 0.48
SRS	0.68 ± 0.92	0.30 ± 0.41
Difference†		-0.24 ± 0.29	-0.20 ± 0.57

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TABLE III DATA ON VOLAR AND DORSAL STEP-OFF

*SRS = Skeletal Repair System bone cement (Norian, Cupertino, California). †The average of the differences between the two groups.

Specimen Pair	Type of Construct*	Volar Step-off (mm)	Dorsal Step-off (mm)
1	Kirschner-wire	0.78	0.84
	SRS	0.42	0.24
	Difference	-0.36	-0.60
2	Kirschner-wire	0.65	0.16
	SRS	0.08	0.16
	Difference	-0.57	0.00
3	Kirschner-wire	0.60	0.17
	SRS	0.11	0.32
	Difference	-0.49	0.15
4	Kirschner-wire	1.07	0.01
	SRS	0.52	0.14
	Difference	-0.55	0.13
5	Kirschner-wire	3.20	1.61
	SRS	2.91	0.32
	Difference	-0.29	-1.29
6	Kirschner-wire	1.56	0.56
	SRS	1.68	1.39
	Difference	0.12	0.83
7	Kirschner-wire	0.48	0.52
	SRS	0.52	0.32
	Difference	0.04	-0.20
8	Kirschner-wire	0.32	0.37
	SRS	0.06	0.03
	Difference	-0.26	-0.34
9	Kirschner-wire	0.26	0.01
	SRS	0.53	0.01
	Difference	0.27	0.00
10	Kirschner-wire	0.36	0.67
	SRS	0.01	0.02
	Difference	-0.35	-0.65
Average and standard deviation	Kirschner-wire	0.93 ± 0.89	0.49 ± 0.48
SRS	0.68 ± 0.92	0.30 ± 0.41
Difference†		-0.24 ± 0.29	-0.20 ± 0.57

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

Ten pairs of radii from human cadavera were cleaned of soft tissue. A fracture then was created in each radius with use of a servohydraulic materials testing machine (MTS, Minneapolis, Minnesota). One radius, randomly chosen from each pair, was stabilized with SRS bone cement, and the contralateral radius was stabilized with Kirschner wires. Settling of the scaphoid and lunate fossae and of the entire articular surface was recorded while the fracture constructs were cyclically loaded under conditions simulating intermittent postoperative loading that would occur in a patient. The specimens then were loaded to failure to determine the ultimate strength of the constructs.

Material

SRS bone cement is percutaneously injectable and fast-setting; it cures in vivo to form a carbonated apatite with a low crystalline order and a small grain size similar to the mineral phase of bone³. This cement has been reported to be replaced by host bone through an osteoclast-mediated process similar to normal bone-remodeling^3,6. The cementitious paste was formed by mixing calcium source powder consisting of calcium carbonate (CaCO₃) and a-tricalcium phosphate (Ca₃[PO4]₂) and phosphate source powder containing monocalcium phosphate monohydrate (Ca[H₂PO₄]₂·H₂O) with phosphate-buffered solution. After the material has been implanted, it equilibrates to body temperature, accelerating the formation of carbonated apatite. It hardens ten minutes after implantation and achieves 50 percent of its ultimate compressive strength by one hour. Full compressive strength of fifty-five megapascals is attained by approximately twelve hours after implantation³.

Selection and Preparation of the Specimens

Ten pairs of fresh-frozen forearms from human adult cadavera were prescreened with use of plain posteroanterior radiographs to detect gross anatomical abnormalities. Bone-mineral-density measurements of the ultradistal, mid-distal, and one-third distal regions were obtained with use of dual-energy x-ray absorptiometry (Hologic QDR-4500A; Hologic, Waltham, Massachusetts). The average difference between the bone-mineral-density values of the SRS constructs (0.639 ± 0.183 gram per square centimeter) and the Kirschner-wire constructs (0.648 ± 0.199 gram per square centimeter) was 0.009 gram per square centimeter; with the numbers available, this difference was not found to be significant (p = 0.717).

The radii were removed from the forearms by careful dissection of the soft tissue around the bone. All radii were wrapped in towels that had been soaked in saline solution and were stored in tightly sealed plastic bags at -20 degrees Celsius or less. All specimens were thawed at room temperature for at least seven hours before the fractures were created.

Each radius was cleaned of all soft tissue and cut to a standard length of fifteen centimeters from the distal end. The shaft (diaphyseal) end was potted in an aluminum tube with use of dental acrylic polymer (PERM Reline and Repair Resin; Hygenic, Akron, Ohio). In addition, an acrylic mold was made of each articular surface of each radius. Biplanar contact radiographs of the radius and acrylic imprints of the proximal region of the radius were made to provide a template to ensure accurate reduction during fixation of the fracture.

Creation of the Fractures

The specimens were placed vertically with 75 degrees of dorsiflexion and 10 degrees of ulnar deviation on an MTS table to simulate the position of the radius during a fall^7,20. Stress-risers were created with a combination of drilling (1.6-millimeter-diameter drill-holes spaced two millimeters apart) and scoring of the cortical bone around the desired three-part intra-articular fracture line¹⁹. The fractures were created by impaction of the specimens, in the same orientation as just described, against the load-cell in an MTS minibionix servohydraulic materials testing machine at twenty-five millimeters per second, and were compressed until a fifteen-millimeter displacement of the actuator was achieved²⁰. If the desired intra-articular fracture line (Fig. 1) was not created, then an osteotome was used to complete the fracture. The reproducible three-part intra-articular fractures that were made with this method were consistent with the fracture types treated with Kirschner wires as described by Fernandez and Jupiter⁵.

Fixation of the Fractures

One radius from each pair was randomly chosen for fixation with 1.6-millimeter Kirschner wires (Figs. 2 and 3-A)⁵. The contralateral radius was stabilized with SRS bone cement (Fig. 3-B).

Before fixation with the SRS bone cement, the loose cancellous-bone fragments were compressed with a Freer elevator onto the periphery of the fracture void in order to create a firm cancellous bed as recommended by the manufacturer. Although impaction of the fragments increased the size of the void and normally would increase the instability of the fracture, subsequent injection with SRS bone cement filled the space that had been created, which was thought to be beneficial for achieving stability. The SRS bone cement was prepared for use according to the manufacturer's directions and was injected through a 12-gauge needle. A paraffin film was wrapped around the radius to simulate soft tissue.

The operative technique for the control specimens, after the fractures had been appropriately reduced, involved insertion of two horizontal and two oblique Kirschner wires.

An orthopaedic surgeon specializing in hand surgery reduced and fixed all of the specimens. Both specimens of each pair were wrapped in a plastic bag and were incubated in 100 percent humidity at 37 degrees Celsius in order to simulate physiological body conditions and to allow curing of the SRS bone cement. The specimens were incubated for twelve to twenty-four hours before testing. No specimens were refrozen after fixation and before testing.

Calculations of Force on the Distal Part of the Radius

The current study involved simulation of immediate postoperative weight-bearing on the distal part of the radius. When a patient's arm is in a cast, compressive forces may occur on the wrist joint and at the fracture site because of flexion of the digits. Two major muscle-tendon units cross over the wrist joint in order to flex the digits; these are the flexor digitorum profundus and the flexor digitorum superficialis². In vivo measurements of the tendon forces on these muscles have been reported while the digits were in flexion². These forces ranged from thirty-nine to 196 newtons and from twelve to 147 newtons for the flexor digitorum profundus and the flexor digitorum superficialis, respectively². (The force values were converted from the original mass equivalent.) If the minimum tendon forces are thirty-nine and twelve newtons, then the total force is fifty-one newtons. It has been demonstrated that only 80 percent of the load is transferred by the distal part of the radius at the wrist joint³⁰; thus, 80 percent of fifty-one newtons (40.8 newtons) is the force that will be applied to the distal part of the radius by flexion of each digit. In the current study, a zero to 200-newton cyclic load (the approximate load due to flexion of five digits) was used to simulate the immediate postoperative load borne by the distal part of the radius.

Biomechanical Testing of the Fracture Constructs

After the SRS bone cement had cured, the specimens were placed vertically on the MTS minibionix servohydraulic materials testing machine (Fig. 4). The molded acrylic template that was formed from the individual articular surface of each radius was used to maximize the load-bearing contact area across the radiocarpal joint after fixation. Six linear variable differential transducers were placed around the potting tube and were used to measure the axial displacement of the two distal fracture fragments at six different anatomical sites (Fig. 4). Data with regard to time, displacement (of the linear variable differential transducers and the MTS crosshead), and load were collected with Teststar (Minneapolis, Minnesota) on an Excel-5.0 spreadsheet (Microsoft, Redmond, Washington) with use of an HP Vectra N2 4/33si computer (Hewlett-Packard, Palo Alto, California).

The specimens first were loaded sinusoidally for 2000 cycles at one hertz. It was assumed that a patient would use the digits fifty times a day while the arm was immobilized in the cast. The cast is worn for approximately six weeks; therefore, the digits would be flexed approximately 2000 times during this immediate postoperative load-bearing period. The data points at minimum and maximum load levels were recorded for each cycle. The values for settling (displacement of the linear variable differential transducers and the MTS crosshead) were calculated as the difference between the value at the resting position before the first cycle and that after 2000 cycles.

Posteroanterior and lateral radiographs were made after cycling. The linear variable differential transducers then were removed, and the specimen was loaded to failure at twenty-five millimeters per second with a maximum displacement of fifteen millimeters. The values for force and crosshead displacement were sampled and recorded at 100 hertz during the load-to-failure part of the experiment. Final posteroanterior and lateral radiographs were made.

Analysis of the Data

Outcome Parameters

Settling due to the simulated immediate postoperative load-bearing of the distal part of the radius was measured by displacement of the MTS crosshead. Settling of the lunate and scaphoid fossae was calculated by averaging the measurements of the displacement of the three linear variable differential transducers around each anatomical fossa (Fig. 4). Linear variable differential transducers 1, 2, and 3 were used for calculations for the scaphoid fossa, and linear variable differential transducers 4, 5, and 6 were used for calculations for the lunate fossa. The step-off at the volar and dorsal sides of the distal part of the radius was calculated according to the absolute value of the difference between the displacement measurements from two adjacent linear variable differential transducers across the intra-articular fracture line (Fig. 4). Linear variable differential transducers 1 and 6 determined the volar step-off, and linear variable differential transducers 3 and 4 determined the dorsal step-off. Finally, after cyclic loading, the ultimate load to failure was determined according to the applied peak force during static loading.

Statistical Analysis

A nonparametric analysis, the Wilcoxon signed-rank test, was used to determine differences between the two types of fixation. Our null hypothesis was that there was no significant difference (p > 0.05) between the outcome parameters measured in the specimens that had been stabilized with Kirschner wires and those measured in the specimens that had been stabilized with calcium-phosphate bone cement (SRS).

Results

Introduction | Materials and Methods | Results | Discussion | References

Overall, there was significantly more displacement (settling) in the Kirschner-wire constructs than in the SRS constructs (range, 0.18 to 4.51 millimeters compared with 0.19 to 1.29 millimeters; p = 0.015) (Table I and Fig. 5). With the numbers available, no significant difference in ultimate strength was detected between the SRS constructs and the Kirschner-wire constructs (average [and standard deviation], 1996 ± 1413 newtons compared with 1842 ± 796 newtons; p = 0.721) (Table I).

Measurements of displacement of the individual linear variable differential transducers showed generally more settling in the Kirschner-wire constructs than in the SRS constructs (Table II). When the displacement data for the scaphoid and lunate fossae were examined separately, it was found that there was significantly more settling of the scaphoid fossa of the Kirschner-wire constructs than there was of the scaphoid fossa of the SRS constructs (average, 1.07 ± 1.29 millimeters compared with 0.27 ± 0.37 millimeters; p = 0.017) (Fig. 6). With the number of specimens used in our experiment, we were not able to detect a significant difference in terms of settling of the lunate fossa between the Kirschner-wire constructs and the SRS constructs (p = 0.139). In both test groups, the scaphoid fossa settled slightly more than did the lunate fossa (p = 0.452) (Table II). The settling of the scaphoid fossa of the Kirschner-wire constructs was correlated linearly with that of the SRS constructs (r² = 0.802) (Fig. 6). No linear correlation was observed in a similar analysis of settling of the lunate fossa (r² = 0.007).

The step-off data revealed no significant difference, with the numbers available, between the Kirschner-wire constructs and the SRS constructs with regard to articular incongruity at the dorsal cortex (0.49 ± 0.48 millimeter compared with 0.30 ± 0.41 millimeter; p = 0.333); however, there was a significant difference between the two constructs with regard to the incongruity at the volar cortex (0.93 ± 0.89 millimeter compared with 0.68 ± 0.92 millimeter; p = 0.037) (Table III and Fig. 7). With the number of specimens used in this experiment, we could not demonstrate that articular incongruity was more prominent on the volar side than it was on the dorsal side regardless of the type of treatment (p = 0.071). The amount of step-off on the volar side of the Kirschner-wire constructs was linearly correlated with that on the volar side of the SRS constructs (r² = 0.901) (Fig. 7). No linear correlation was observed in a similar analysis of dorsal step-off (r² = 0.033). All of the SRS constructs remained intact throughout the cyclic-loading experiment.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

The findings in this study demonstrated that the fracture fragments of the SRS constructs settled significantly less than did those of the Kirschner-wire constructs. From a practical point of view, these data indicate that SRS bone cement can provide initial stability that is comparable with or better than that achieved with use of Kirschner-wire fixation.

Clinically, when the radius settles, the ulna carries more load, thereby altering the normal biomechanics of the wrist. This phenomenon is known as ulnar impaction syndrome and is diagnosed on the basis of radiographic changes, associated pain, decreased grip strength, and limited rotation of the forearm^26,31. In a clinical study of distal radial fractures, Hutchinson et al. found that treatment with pins and plaster caused an average of 2.5 millimeters of shortening of the radius at four months¹⁰. In the current study of cadavera, the amount of settling in the Kirschner-wire constructs ranged from 0.18 to 4.51 millimeters. In both study groups, the scaphoid fossa settled slightly more than did the lunate fossa, suggesting that the scaphoid fossa may be more important in terms of load transfer under the loading conditions that were imposed. This finding is supported by those of previous reports indicating that most of the force (50 percent more than that in the lunate fossa) is transmitted through the scaphoid fossa³⁰.

There was more volar articular incongruity in the Kirschner-wire constructs than in the SRS constructs. The volar cortex was more prone to have articular step-off than was the dorsal cortex in both test groups. This finding confirms that a major portion of the load is transferred by the volar cortex³⁰. Failure to achieve an anatomical reduction (an articular step-off of less than one to two millimeters) of intra-articular fragments has been associated with radiographic evidence of arthritis in most if not all patients¹⁵. In a study of young adults, twenty-two (92 percent) of twenty-four patients who had articular step-off were symptomatic¹⁵. With an adequate and properly maintained reduction, the rate of radiocarpal arthritis may be reduced to 5 to 10 percent (one of thirteen patients in one study¹² and three [10 percent] of thirty-one in another study⁹), even in patients who have a severely comminuted fracture.

Unstable distal radial fractures involving osteopenic bone may not be amenable to open treatment with metal fixation devices because of the low bone strength. However, the problem of attaining stability without an extended period of immobilization remains. Insertion of a structural material that can transfer load without causing a loss of stability at the fracture site is an attractive alternative for the treatment of these comminuted fractures. An intramedullary core of acrylic bone cement has been used in this manner for primary fixation of distal radial fractures involving osteopenic bone^14,21,24. The patients have been able to use the hand immediately postoperatively without the need for additional fixation. Periosteal bone formation has occurred and osseous union has been established within six to seven weeks after this procedure¹⁶. The incompatible nature of acrylic bone cements as well as late loosening as a result of the progression of osteoporosis make the use of polymeric materials unattractive for the treatment of distal radial fractures. The same immediate postoperative stability may be achieved with SRS bone cement without compromising fracture-healing or long-term structural integrity.

Jupiter et al. reported that SRS bone cement can be administered percutaneously and can support the reduction of the fracture by countering compressive forces that occur in the comminuted metaphyseal region of the fractured distal part of the radius¹³. Those authors concluded that the material is biocompatible and that it did not cause any serious complications. Kopylov et al., in another clinical study, found that distal radial fractures that were treated with SRS bone cement needed a shorter period of immobilization because of the stability that was attained by the filling of the metaphyseal bone defects¹⁷.

A related issue that was not addressed in the current study is the substantial effect that even short-term exposure to the aqueous biological milieu has on the degradation of the bone cement, resulting in the immediate loss of stabilization within the bone. The effectiveness with which the cement can be implanted in the laboratory setting is not likely to be duplicated in a clinical situation. There is a question as to whether the experimental methodology that we used to determine settling had the necessary precision to reveal small differences in the amounts of settling between the two treatment groups.

Operative treatment with use of SRS bone cement necessitates an open incision and impaction of loose cancellous-bone fragments, and this might increase the operative time and the rate of complications compared with those associated with Kirschner-wire fixation. In addition, the specimens in the current study required twelve to twenty-four hours of incubation in 100 percent humidity at 37 degrees Celsius, and this might have had a negative impact on both treatment groups, especially the Kirschner-wire specimens.

In conclusion, the findings in the current study suggest that use of a minimum operative exposure to prepare the fracture void properly as well as filling of regions of cancellous-bone voids with a biocompatible calcium-phosphate (SRS) bone cement provides adequate fixation to maintain reduction of intra-articular distal radial fractures. Patients may start to use the affected limb soon after the operation in order to restore the function of the hand to the prefracture level.

References

Introduction | Materials and Methods | Results | Discussion | References

Abbaszadegan, H.; Jonsson, U.; and von Sivers, K.: Prediction of instability of Colles' fractures. Acta Orthop. Scandinavica,60: 646-650, 1989.60646 1989

Chao, E. Y. S.; An, K.-N.; Cooney, W. P., III; and Linscheid, R. L.: Muscle and joint forces in the hand. In Biomechanics of the Hand, pp. 53-72. Singapore, World Scientific, 1989.

Constantz, B. R.; Ison, I. C.; Fulmer, M. T.; Poser, R. D.; Smith, S. T.; VanWagoner, M.; Ross, J.; Goldstein, S. A.; Jupiter, J. B.; and Rosenthal, D. I.: Skeletal repair in situ formation of the mineral phase of bone. Science,267: 1796-1799, 1995.2671796 1995 [PubMed]

Cooney, W. P., III; Linscheid, R. L.; and Dobyns, J. H.: External pin fixation for unstable Colles' fractures. J. Bone and Joint Surg.,61-A: 840-845, Sept. 1979.61-A840 1979

Fernandez, D. L., and Jupiter, J. B.: Epidemiology, mechanism, classification. In Fractures of the Distal Radius: A Practical Approach to Management, pp. 23-52. New York, Springer, 1996.

Frankenburg, E. P.; Goldstein, S. A.; Bauer, T. W.; Harris, S. A.; and Poser, R. D.: Biomechanical and histological evaluation of a calcium phosphate cement. J. Bone and Joint Surg.,80-A: 1112-1124, Aug. 1998.80-A1112 1998

Frykman, G.: Fracture of the distal radius including sequelae—shoulder-hand-finger syndrome, disturbance in the distal radio-ulnar joint and impairment of nerve function. A clinical and experimental study. Acta Orthop. Scandinavica, Supplementum 108, 1967.

Gartland, J. J., and Werley, C. W.: Evaluation of healed Colles' fractures. J. Bone and Joint Surg.,33-A: 895-907, Oct. 1951.33-A895 1951

Geissler, W. B., and Fernandez, D. L.: Percutaneous and limited open reduction of the articular surface of the distal radius. J. Orthop. Trauma,5: 255-264, 1991.5255 1991 [PubMed]

Hutchinson, D. T.; Strenz, G. O.; and Cautilli, R. A.: Pins and plaster vs external fixation in the treatment of unstable distal radial fractures. A randomized prospective study. J. Hand Surg.,20-B: 365-372, 1995.20-B365 1995

Jupiter, J. B.: Current concepts review. Fractures of the distal end of the radius. J. Bone and Joint Surg.,73-A: 461-469, March 1991.73-A461 1991

Jupiter, J. B., and Lipton, H.: Operative treatment of intraarticular fractures of the distal radius. Clin. Orthop.,292: 48-61, 1993.29248 1993 [PubMed]

Jupiter, J. B.; Winter, S.; Sigman, S.; Lowe, C.; Pappas, C.; Ladd, A. L.; Van Wagoner, M.; and Smith, S. T.: Repair of five distal radius fractures with an investigational cancellous bone cement: a preliminary report. J. Orthop. Trauma,11: 110-116, 1997.11110 1997 [PubMed]

Kiyoshige, Y.: Bone cementing of distal radial fractures in the elderly. In Fractures of the Distal Radius, pp. 84-88. Edited by P. Saffar and W. P. Cooney, III. Philadelphia, J. B. Lippincott, 1995.

Knirk, J. L., and Jupiter, J. B.: Intra-articular fractures of the distal end of the radius in young adults. J. Bone and Joint Surg.,68-A: 647-659, June 1986.68-A647 1986

Kofoed, H.: Comminuted displaced Colles' fracture. Treatment with intramedullary methylmethacrylate stabilisation. Acta Orthop. Scandinavica,54: 307-311, 1983.54307 1983

Kopylov, P.; Jonsson, K.; Thorngren, K. G.; and Aspenberg, P.: Injectable calcium phosphate in the treatment of distal radial fractures. J. Hand Surg.,21-B: 768-771, 1996.21-B768 1996

Lidstrom, A.: Fractures of the distal end of the radius. A clinical and statistical study of end results. Acta Orthop. Scandinavica, Supplementum 41, 1959.

Muller, M. E.; Nazarian, S.; Koch, P.; and Schatzker, J.: Principles of the classification of fractures; radius/ulna, distal segment, the groups, the subgroups and their qualifications. In The Comprehensive Classification of Fractures of Long Bones, pp. 5-9, 106-115. New York, Springer, 1990.

Myers, E. R.; Sebeny, E. A.; Hecker, A. T.; Corcoran, T. A.; Hipp, J. A.; Greenspan, S. L.; and Hayes, W. C.: Correlations between photon absorption properties and failure load of the distal radius in vitro. Calcif. Tissue Internat.,49: 292-297, 1991.49292 1991

Nilsson, M. H.: Bone cementing in the treatment of Colles' fracture. Opuscula Medica,24: 123-125, 1979.24123 1979

Pool, C.: Colles's fracture. A prospective study of treatment. J. Bone and Joint Surg.,55-B(3): 540-544, 1973.55-B(3)540 1973

Rayhack, J. M.: The history and evolution of percutaneous pinning of displaced distal radius fractures. Orthop. Clin. North America,24: 287-300, 1993.24287 1993

Schmalholz, A.: Bone cement for redislocated Colles' fracture. A prospective comparison with closed treatment. Acta Orthop. Scandinavica,60: 212-217, 1989.60212 1989

Seitz, W. H., Jr.; Froimson, A. I.; and Leb, R. B.: Reduction of treatment-related complications in the external fixation of complex distal radius fractures. Orthop. Rev.,20: 169-177, 1991.20169 1991 [PubMed]

Short, W. H.; Palmer, A. K.; Werner, F. W.; and Murphy, D. J.: A biomechanical study of distal radial fractures. J. Hand Surg.,12A: 529-534, 1987.12A529 1987

Sommerkamp, T. G.; Seeman, M.; Silliman, J.; Jones, A.; Patterson, S.; Walker, J.; Semmler, M.; Browne, R.; and Ezaki, M.: Dynamic external fixation of unstable fractures of the distal part of the radius. A prospective, randomized comparison with static external fixation. J. Bone and Joint Surg.,76-A: 1149-1161, Aug. 1994.76-A1149 1994

Szabo, R. M., and Weber, S. C.: Comminuted intraarticular fractures of the distal radius. Clin. Orthop.,230: 39-48, 1988.23039 1988 [PubMed]

Szabo, R. M.: Extra-articular fractures of the distal radius. Orthop. Clin. North America,24: 229-237, 1993.24229 1993

Werner, F. W.; An, K.-N.; Palmer, A. K.; and Chao, E. Y. S.: Force analysis. In Biomechanics of the Wrist Joint, pp. 77-97. Edited by K.-N. An, R. A. Berger, and W. P. Cooney, III. New York, Springer, 1991.

Zabinski, S. J., and Weiland, A. J.: Fracture of the distal radius. In Orthopaedic Knowledge Update: Trauma, pp. 67-82. Edited by A. M. Levine. Rosemont, Illinois, American Academy of Orthopaedic Surgeons, 1996.

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FIG1:: Fig. 1 Drawing showing the articular surface (A) and an anteroposterior view (B) of the desired Colles fracture (AO pattern, C2.1).

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FIG3-A:: Fig. 3-A: Radiograph showing fixation of a fracture with Kirschner wires.

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FIG3-B:: Fig. 3-B: Radiograph showing fixation of a fracture with SRS bone cement.

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FIG7:: Fig. 7 Graph showing volar and dorsal step-off in the Kirschner-wire (K-wire) constructs compared with that in the SRS constructs. Each data point represents one pair of specimens.

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TABLE I DATA ON OVERALL DISPLACEMENT (SETTLING) AND ULTIMATE LOAD TO FAILURE

*SRS = Skeletal Repair System bone cement (Norian, Cupertino, California).

Specimen Pair	Type of Construct*	Overall Displacement (mm)	Ultimate Load to Failure (N)
1	Kirschner-wire	-0.61	-1745
	SRS	-0.38	-860
2	Kirschner-wire	-1.35	-2150
	SRS	-0.49	-2410
3	Kirschner-wire	-0.37	-2790
	SRS	-0.19	-5660
4	Kirschner-wire	-0.60	-1930
	SRS	-0.46	-1890
5	Kirschner-wire	-4.51	-694
	SRS	-1.29	-953
6	Kirschner-wire	-1.28	-1110
	SRS	-1.01	-1220
7	Kirschner-wire	-0.55	-3130
	SRS	-0.43	-2030
8	Kirschner-wire	-0.18	-1300
	SRS	-0.24	-1060
9	Kirschner-wire	-0.33	-2440
	SRS	-0.33	-2420
10	Kirschner-wire	-0.28	-1130
	SRS	-0.26	-1460
Average and standard deviation	Kirschner-wire	-1.01 ± 1.23	-1842 ± 796
SRS	-0.51 ± 0.34	-1996 ± 1413

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TABLE I DATA ON OVERALL DISPLACEMENT (SETTLING) AND ULTIMATE LOAD TO FAILURE

*SRS = Skeletal Repair System bone cement (Norian, Cupertino, California).

Specimen Pair	Type of Construct*	Overall Displacement (mm)	Ultimate Load to Failure (N)
1	Kirschner-wire	-0.61	-1745
	SRS	-0.38	-860
2	Kirschner-wire	-1.35	-2150
	SRS	-0.49	-2410
3	Kirschner-wire	-0.37	-2790
	SRS	-0.19	-5660
4	Kirschner-wire	-0.60	-1930
	SRS	-0.46	-1890
5	Kirschner-wire	-4.51	-694
	SRS	-1.29	-953
6	Kirschner-wire	-1.28	-1110
	SRS	-1.01	-1220
7	Kirschner-wire	-0.55	-3130
	SRS	-0.43	-2030
8	Kirschner-wire	-0.18	-1300
	SRS	-0.24	-1060
9	Kirschner-wire	-0.33	-2440
	SRS	-0.33	-2420
10	Kirschner-wire	-0.28	-1130
	SRS	-0.26	-1460
Average and standard deviation	Kirschner-wire	-1.01 ± 1.23	-1842 ± 796
SRS	-0.51 ± 0.34	-1996 ± 1413

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TABLE II DISPLACEMENT OF THE INDIVIDUAL LINEAR VARIABLE DIFFERENTIAL TRANSDUCERS AND SETTLING OF THE SCAPHOID AND LUNATE FOSSAE*

*The values are given in millimeters. †SRS = Skeletal Repair System bone cement (Norian, Cupertino, California).

Specimen Pair	Type of Construct†	Displacement of Linear Variable Differential Transducer						Settling of Scaphoid Fossa	Settling of Lunate Fossa
1: Volar Scaphoid	2: Lateral Scaphoid	3: Dorsal Scaphoid	4: Dorsal Lunate	5: Medial Lunate	6: Volar Lunate
1	Kirschner-wire	-0.24	-1.89	-1.54	-0.70	-0.87	-1.02	-1.22	-0.86
	SRS	-0.46	-0.06	0.05	0.29	0.14	-0.04	-0.16	0.13
2	Kirschner-wire	-0.65	-1.11	-1.65	-1.49	-1.14	0.00	-1.14	-0.88
	SRS	0.00	-0.08	0.00	0.16	-0.03	-0.08	-0.02	0.02
3	Kirschner-wire	-0.61	-1.90	-0.18	-0.35	-0.19	-0.01	-0.90	-0.18
	SRS	-0.14	-0.02	-0.29	-0.03	0.09	-0.02	-0.15	0.03
4	Kirschner-wire	-0.66	-0.85	-0.42	-0.43	0.26	0.40	-0.64	0.08
	SRS	-0.10	-0.32	0.06	0.20	-0.79	-0.62	-0.12	-0.40
5	Kirschner-wire	-3.59	-5.26	-4.68	-6.29	0.38	-6.79	-4.51	-4.23
	SRS	-2.80	-0.83	-0.26	-0.58	-0.23	0.10	-1.30	-0.24
6	Kirschner-wire	-1.57	-2.05	-0.28	0.28	0.03	0.00	-1.30	0.10
	SRS	0.00	0.18	-0.70	0.69	-1.34	-1.69	-0.18	-0.78
7	Kirschner-wire	-0.14	-0.25	-0.41	0.11	-0.07	-0.62	-0.27	-0.20
	SRS	0.06	-0.33	-0.29	0.03	0.11	-0.46	-0.19	-0.11
8	Kirschner-wire	-0.11	0.18	-0.27	-0.64	-0.64	0.21	-0.07	-0.36
	SRS	0.38	-0.02	-0.72	-0.69	-0.16	0.32	-0.12	-0.18
9	Kirschner-wire	-0.06	-0.10	-0.31	-0.30	-0.18	0.20	-0.16	-0.09
	SRS	-0.51	-0.31	-0.05	-0.06	-0.14	0.02	-0.29	0.03
10	Kirschner-wire	0.07	-0.50	-0.96	-0.29	-1.26	0.43	-0.47	-0.37
	SRS	0.01	-0.26	-0.29	-0.27	-0.32	0.00	-0.18	-0.20
Average and standard deviation	Kirschner-wire	-0.76 ± 1.10	-1.37 ± 1.58	-1.07 ± 1.38	-1.01 ± 1.92	-0.37 ± 0.58	-0.72 ± 2.18	-1.07 ± 1.29	-0.70 ± 1.29
SRS	-0.36 ± 0.90	-0.21 ± 0.28	-0.25 ± 0.28	-0.02 ± 0.41	-0.27 ± 0.47	-0.25 ± 0.57	-0.27 ± 0.37	-0.17 ± 0.27

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TABLE II DISPLACEMENT OF THE INDIVIDUAL LINEAR VARIABLE DIFFERENTIAL TRANSDUCERS AND SETTLING OF THE SCAPHOID AND LUNATE FOSSAE*

*The values are given in millimeters. †SRS = Skeletal Repair System bone cement (Norian, Cupertino, California).

Specimen Pair	Type of Construct†	Displacement of Linear Variable Differential Transducer						Settling of Scaphoid Fossa	Settling of Lunate Fossa
1: Volar Scaphoid	2: Lateral Scaphoid	3: Dorsal Scaphoid	4: Dorsal Lunate	5: Medial Lunate	6: Volar Lunate
1	Kirschner-wire	-0.24	-1.89	-1.54	-0.70	-0.87	-1.02	-1.22	-0.86
	SRS	-0.46	-0.06	0.05	0.29	0.14	-0.04	-0.16	0.13
2	Kirschner-wire	-0.65	-1.11	-1.65	-1.49	-1.14	0.00	-1.14	-0.88
	SRS	0.00	-0.08	0.00	0.16	-0.03	-0.08	-0.02	0.02
3	Kirschner-wire	-0.61	-1.90	-0.18	-0.35	-0.19	-0.01	-0.90	-0.18
	SRS	-0.14	-0.02	-0.29	-0.03	0.09	-0.02	-0.15	0.03
4	Kirschner-wire	-0.66	-0.85	-0.42	-0.43	0.26	0.40	-0.64	0.08
	SRS	-0.10	-0.32	0.06	0.20	-0.79	-0.62	-0.12	-0.40
5	Kirschner-wire	-3.59	-5.26	-4.68	-6.29	0.38	-6.79	-4.51	-4.23
	SRS	-2.80	-0.83	-0.26	-0.58	-0.23	0.10	-1.30	-0.24
6	Kirschner-wire	-1.57	-2.05	-0.28	0.28	0.03	0.00	-1.30	0.10
	SRS	0.00	0.18	-0.70	0.69	-1.34	-1.69	-0.18	-0.78
7	Kirschner-wire	-0.14	-0.25	-0.41	0.11	-0.07	-0.62	-0.27	-0.20
	SRS	0.06	-0.33	-0.29	0.03	0.11	-0.46	-0.19	-0.11
8	Kirschner-wire	-0.11	0.18	-0.27	-0.64	-0.64	0.21	-0.07	-0.36
	SRS	0.38	-0.02	-0.72	-0.69	-0.16	0.32	-0.12	-0.18
9	Kirschner-wire	-0.06	-0.10	-0.31	-0.30	-0.18	0.20	-0.16	-0.09
	SRS	-0.51	-0.31	-0.05	-0.06	-0.14	0.02	-0.29	0.03
10	Kirschner-wire	0.07	-0.50	-0.96	-0.29	-1.26	0.43	-0.47	-0.37
	SRS	0.01	-0.26	-0.29	-0.27	-0.32	0.00	-0.18	-0.20
Average and standard deviation	Kirschner-wire	-0.76 ± 1.10	-1.37 ± 1.58	-1.07 ± 1.38	-1.01 ± 1.92	-0.37 ± 0.58	-0.72 ± 2.18	-1.07 ± 1.29	-0.70 ± 1.29
SRS	-0.36 ± 0.90	-0.21 ± 0.28	-0.25 ± 0.28	-0.02 ± 0.41	-0.27 ± 0.47	-0.25 ± 0.57	-0.27 ± 0.37	-0.17 ± 0.27

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TABLE III DATA ON VOLAR AND DORSAL STEP-OFF

*SRS = Skeletal Repair System bone cement (Norian, Cupertino, California). †The average of the differences between the two groups.

Specimen Pair	Type of Construct*	Volar Step-off (mm)	Dorsal Step-off (mm)
1	Kirschner-wire	0.78	0.84
	SRS	0.42	0.24
	Difference	-0.36	-0.60
2	Kirschner-wire	0.65	0.16
	SRS	0.08	0.16
	Difference	-0.57	0.00
3	Kirschner-wire	0.60	0.17
	SRS	0.11	0.32
	Difference	-0.49	0.15
4	Kirschner-wire	1.07	0.01
	SRS	0.52	0.14
	Difference	-0.55	0.13
5	Kirschner-wire	3.20	1.61
	SRS	2.91	0.32
	Difference	-0.29	-1.29
6	Kirschner-wire	1.56	0.56
	SRS	1.68	1.39
	Difference	0.12	0.83
7	Kirschner-wire	0.48	0.52
	SRS	0.52	0.32
	Difference	0.04	-0.20
8	Kirschner-wire	0.32	0.37
	SRS	0.06	0.03
	Difference	-0.26	-0.34
9	Kirschner-wire	0.26	0.01
	SRS	0.53	0.01
	Difference	0.27	0.00
10	Kirschner-wire	0.36	0.67
	SRS	0.01	0.02
	Difference	-0.35	-0.65
Average and standard deviation	Kirschner-wire	0.93 ± 0.89	0.49 ± 0.48
SRS	0.68 ± 0.92	0.30 ± 0.41
Difference†		-0.24 ± 0.29	-0.20 ± 0.57

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TABLE III DATA ON VOLAR AND DORSAL STEP-OFF

*SRS = Skeletal Repair System bone cement (Norian, Cupertino, California). †The average of the differences between the two groups.

Specimen Pair	Type of Construct*	Volar Step-off (mm)	Dorsal Step-off (mm)
1	Kirschner-wire	0.78	0.84
	SRS	0.42	0.24
	Difference	-0.36	-0.60
2	Kirschner-wire	0.65	0.16
	SRS	0.08	0.16
	Difference	-0.57	0.00
3	Kirschner-wire	0.60	0.17
	SRS	0.11	0.32
	Difference	-0.49	0.15
4	Kirschner-wire	1.07	0.01
	SRS	0.52	0.14
	Difference	-0.55	0.13
5	Kirschner-wire	3.20	1.61
	SRS	2.91	0.32
	Difference	-0.29	-1.29
6	Kirschner-wire	1.56	0.56
	SRS	1.68	1.39
	Difference	0.12	0.83
7	Kirschner-wire	0.48	0.52
	SRS	0.52	0.32
	Difference	0.04	-0.20
8	Kirschner-wire	0.32	0.37
	SRS	0.06	0.03
	Difference	-0.26	-0.34
9	Kirschner-wire	0.26	0.01
	SRS	0.53	0.01
	Difference	0.27	0.00
10	Kirschner-wire	0.36	0.67
	SRS	0.01	0.02
	Difference	-0.35	-0.65
Average and standard deviation	Kirschner-wire	0.93 ± 0.89	0.49 ± 0.48
SRS	0.68 ± 0.92	0.30 ± 0.41
Difference†		-0.24 ± 0.29	-0.20 ± 0.57