ORIGINAL ARTICLE
What is the Best Material for Molding Casts in Children? Steven B. Daines, MD,* David D. Aronsson, MD,* Bruce D. Beynnon, PhD,* Daniel R. Sturnick, BS,* Jennifer W. Lisle, MD,* and Shelly Naud, PhDw
Background: Casts are used to treat clubfeet, developmental dysplasia of the hip (DDH), forearm fractures, and femur fractures. The ability of a cast to maintain a desired shape is termed moldability. Clinicians use plaster, fiberglass, and soft casts. To our knowledge the biomechanical molding characteristics of these 3 materials have never been reported. We hypothesized that moldability of plaster would be better than fiberglass and fiberglass would be better than soft cast. Methods: We compared 12.7 cm wide casts of plaster, fiberglass, and soft cast. Casts were 5 layers thick, prepared in 401C water, and placed over 2 layers of cotton padding on 5.1 cm and 15.2 cm diameter foam cylinders. A loading device simulated loads applied by clinicians when molding casts for 4 conditions: clubfoot (thumb-shaped 50 N load on 5.1 cm model), DDH (thumb-shaped 100 N load on 15.2 cm model), forearm fracture (palm-shaped 50 N load on 5.1 cm model), and femur fracture (palm-shaped 100 N load on 15.2 cm model). The loading device applied molding for 7 minutes. Five casts of each material were made for each model. Casts were removed, photographed, and the area of maximal deformation was compared with an unmolded cast. A large area of maximal deformation meant that the deformation was spread out over a large area, less precise molding. Results: In the clubfoot model, plaster was more precise than fiberglass (P = 0.002) and soft cast (P < 0.0001). In the DDH model, plaster was more precise than fiberglass (P < 0.0001) and soft cast (P < 0.0001) and fiberglass was more precise than soft cast (P < 0.0001).In the femur fracture model, plaster was more precise than fiberglass (P = 0.001) and soft cast (P = 0.001). Conclusions: The moldability of plaster is better than fiberglass and soft cast and fiberglass is better than soft cast. Clinical Relevance: If precise molding is required, plaster has the best moldability. In cases not requiring precise molding, fiberglass and soft cast are lightweight, waterproof, and available in child-friendly colors.
From the Departments of *Orthopaedics & Rehabilitation; and wMedical Biostatistics, University of Vermont College of Medicine, Burlington, VT. Supported by the McClure Musculoskeletal Research Center, University of Vermont College of Medicine. The authors declare no conflicts of interest. Reprints: David D. Aronsson, MD, Department of Orthopaedics & Rehabilitation, University of Vermont College of Medicine, Robert T. Stafford Hall, Room 434B, Burlington, VT 05405. E-mail: david. [email protected]. Copyright r 2014 by Lippincott Williams & Wilkins
J Pediatr Orthop
Key Words: cast moldability, cast biomechanical properties, cast material properties, cast treatment for clubfoot, DDH, forearm fractures and femur fractures (J Pediatr Orthop 2014;34:743–748)
P
laster casts have become a staple tool of orthopaedic surgeons in emergency rooms and clinics throughout the world. The fiberglass cast, introduced in the 1970s, had several innovative advances including being robust, lightweight, water resistant, and more radiolucent. In addition, the setting temperatures of synthetic casts are lower than plaster, markedly decreasing the risk of burning the skin.1,2 The development of waterproof cast liners allowed patients to bathe, shower, and swim while wearing a cast. In addition to being waterproof, fiberglass casts were available in many colors making them popular for treating children’s fractures despite the higher cost. Subsequently, waterproof soft casts were developed with the advantages of being lighter and more flexible than fiberglass, creating a more comfortable and custom fit. In addition, a soft cast can be removed by the family at home negating the necessity of a follow-up appointment to remove the cast. When cast materials are setting, they remain pliable and shapeable. Depending on the type of cast, clinicians use thumbs, fingers, and hands to mold the cast into a particular shape. The ability of various casting materials to retain the desired shape is referred to as moldability. In children, there are numerous clinical settings where precise cast molding is imperative to achieve a satisfactory outcome including clubfeet, developmental dysplasia of the hip (DDH), forearm fractures, and femur fractures.3–11 Clinicians are increasingly using newer materials such as fiberglass and soft cast rather than plaster. This has been motivated by improved material properties including wear resistance, bending strength, tensile and yield strength, elastic modulus, setting time, and decreasing the release of exothermic heat.12–18 Clinicians intuitively believe that plaster has the benefit of being more moldable than fiberglass or soft cast and plaster expands rather than constricts when setting.19 To our knowledge, the molding characteristics of different cast materials have never been reported. We studied the molding characteristics of 3 cast materials (plaster, fiberglass, and soft cast) on 4 models simulating 4 clinical problems; clubfoot, DDH, forearm fracture, and femur fracture. Our hypothesis was molding would be more precise with plaster than fiberglass and more precise with fiberglass than soft cast.
Volume 34, Number 7, October/November 2014
www.pedorthopaedics.com |
743
J Pediatr Orthop
Daines et al
METHODS A model designed to simulate a child’s clubfoot or forearm fracture was created using a 5.1 cm (2 inches) foam cylinder to replicate the soft tissues with a 1.9 cm (3⁄4 inches) wooden dowel center to replicate the bone. A second model designed to simulate DDH or a child’s femur fracture was created using a 15.2 cm (6 inches) foam cylinder to replicate the soft tissues with a 2.5 cm (1 inches) wooden dowel center to replicate the bone (Stitches Afloat, Shelburne, VT). The foam cylinders replicated the compliance of human soft tissue and were similar to the compliance of the foam used as a soft tissue substitute by Erickson et al.20 To determine the forces that clinicians apply while molding a cast, 2 pediatric orthopaedists were recruited to the laboratory to push on a digital force plate (Chatillon; AMETEK, Berwyn, PA) with the force that they typically use to mold a clubfoot cast, maintain the reduction of DDH, maintain the reduction of a forearm fracture, and maintain the reduction of a femur fracture. The clinicians pushed with approximately 50 N to mold the clubfoot and forearm fracture cast and 100 N to mold the DDH and femur fracture cast. A custom loading device was developed to simulate the loads applied by clinicians when molding casts for the 4 clinical conditions: clubfoot [thumb shaped 50 N on 5.1 cm (2 inches) foam], DDH [thumb shaped 100 N on 15.2 cm (6 inches) foam], forearm fracture [palm shaped 50 N on 5.1 cm (2 inches) foam], and femur fracture [palm
Volume 34, Number 7, October/November 2014
shaped 100 N on 15.2 cm (6 inches) foam]. The loading device used weights to apply the desired loads to the cast through wooden models, approximating the shape of a thumb or palm for 7 minutes while casts set (Fig. 1). We compared 12.7 cm (5 inches) wide casts of plaster (Specialist, BSN Medical, Rutherford College, NC), fiberglass (Scotchcast Plus, 3M, St. Paul, MN) and soft cast (Soft Cast, 3M, St. Paul, MN). Each cast was 5 layers thick, dipped in 401C water, and placed over 2 layers of cotton padding (Webril, Covidien, Mansfield, MA). The casts were applied on 5.1 cm (2 inches) and 15.2 cm (6 inches) diameter foam cylinders with 1.9 cm (3⁄4 inches) and 2.5 cm (1 inch) wooden dowel centers, respectively. The loading device applied a compressive load normal to the surface of the cast without shear loads in a manner similar to that used in the clinical environment. Five casts of each of the 3 cast materials were made for each of the 4 models (60 total casts). After 7 minutes, when the casts had set, they were removed from the foam cylinders and photographed with a camera that was aligned collinear with the inside of the cast (axial view) with a scaling reference placed at the level of maximal deformation depth. The images were then digitized for molding shape comparison. The precision of molding (moldability) was analyzed by calculating the 2-dimensional area of maximal deformation (AMD) that developed in the molded cast compared with an unmolded cast. If the cast was not molded, there would be no deformation and the cast would remain circular (Fig. 2, semi-circular grey line of an unmolded cast). If the molding was precise, a small AMD would indicate that the cast molded exactly to the shape of the thumb or palm (Fig. 2, dashed line with corresponding AMD). If the molding was less precise, a large AMD would indicate that the cast did not mold exactly to the shape of the thumb or palm and the deformation of the cast was spread out over a large area.
Statistical Analysis The AMDs of the 3 cast materials (plaster, fiberglass, and soft cast) for the 4 clinical models (clubfoot, DDH, forearm fracture, and femur fracture) were com-
FIGURE 1. An image showing the custom loading device developed to replicate the forces applied by clinicians when molding casts. The device applied a 50 or 100 N load to the cast through a thumb-shaped or palm-shaped wooden model.
744 | www.pedorthopaedics.com
FIGURE 2. A drawing of the inside of a cast (axial view) at the level of maximal deformation showing how the molding was analyzed by the 2-dimensional area of maximal deformation (AMD). If the cast was not molded, there would be no AMD and the cast would remain circular (semi-circular grey). If the molding was precise (dashed line), a small AMD would indicate that the cast molded exactly to the thumb or palm shape. r
2014 Lippincott Williams & Wilkins
J Pediatr Orthop
Volume 34, Number 7, October/November 2014
Moldability of Plaster, Fiberglass and Soft Casts
TABLE 1. Mean Area of Maximum Deviation (AMD) for Plaster (P), Fiberglass (F), and Soft Cast (S) ± SD and Comparison P-values for Clubfoot, DDH, Forearm Fracture, and Femur Fracture Cast Models Clubfoot Cast Material
DDH Cast Mean ± SD
Material
Average area (mm2) of maximal deformation (AMD) P 560 ± 45 P F 726 ± 67 F S 1018 ± 172 S Comparison
P
Comparison
Plaster, fiberglass and soft cast comparisons P-F 0.002* P-F P-S < 0.0001* P-S F-S 0.01 F-S
Forearm Fracture Cast
Femur Fracture Cast
Mean ± SD
Material
Mean ± SD
Material
Mean ± SD
2986 ± 266 5282 ± 235 6873 ± 457
P F S
563 ± 107 526 ± 169 578 ± 45
P F S
3195 ± 563 4904 ± 519 5037 ± 546
P
Comparison
P
Comparison
P
< 0.0001* < 0.0001* 0.0001*
P-F P-S F-S
0.7 0.8 0.5
P-F P-S F-S
0.001* 0.001* 0.7
DDH indicates developmental dysplasia of the hip.
pared using t tests. To correct for multiple comparisons, the significance level was adjusted using the Bonferroni method (0.05/12 = 0.004). Results with a P-value of 0.8 (poorly molded cast) the redisplacement rate was 26%.7 The possibility of redisplacement and concerns about loss of pronation or supination has caused many clinicians to recommend surgery for forearm fractures in children. This trend toward surgery was documented in an 11-year study involving 2297 fractures. The authors reported a 7-fold increase in operative management between the first and last year of the study: 2 of 143 patients in the first year (1.4%) and 28 of 270 patients in the last year (10.4%).24 We believe that most forearm fractures can be successfully managed with a closed reduction under sedation and application of a properly molded cast. Femur fractures with
What is the Best Material for Molding Casts in Children? Steven B. Daines, MD,* David D. Aronsson, MD,* Bruce D. Beynnon, PhD,* Daniel R. Sturnick, BS,* Jennifer W. Lisle, MD,* and Shelly Naud, PhDw
Background: Casts are used to treat clubfeet, developmental dysplasia of the hip (DDH), forearm fractures, and femur fractures. The ability of a cast to maintain a desired shape is termed moldability. Clinicians use plaster, fiberglass, and soft casts. To our knowledge the biomechanical molding characteristics of these 3 materials have never been reported. We hypothesized that moldability of plaster would be better than fiberglass and fiberglass would be better than soft cast. Methods: We compared 12.7 cm wide casts of plaster, fiberglass, and soft cast. Casts were 5 layers thick, prepared in 401C water, and placed over 2 layers of cotton padding on 5.1 cm and 15.2 cm diameter foam cylinders. A loading device simulated loads applied by clinicians when molding casts for 4 conditions: clubfoot (thumb-shaped 50 N load on 5.1 cm model), DDH (thumb-shaped 100 N load on 15.2 cm model), forearm fracture (palm-shaped 50 N load on 5.1 cm model), and femur fracture (palm-shaped 100 N load on 15.2 cm model). The loading device applied molding for 7 minutes. Five casts of each material were made for each model. Casts were removed, photographed, and the area of maximal deformation was compared with an unmolded cast. A large area of maximal deformation meant that the deformation was spread out over a large area, less precise molding. Results: In the clubfoot model, plaster was more precise than fiberglass (P = 0.002) and soft cast (P < 0.0001). In the DDH model, plaster was more precise than fiberglass (P < 0.0001) and soft cast (P < 0.0001) and fiberglass was more precise than soft cast (P < 0.0001).In the femur fracture model, plaster was more precise than fiberglass (P = 0.001) and soft cast (P = 0.001). Conclusions: The moldability of plaster is better than fiberglass and soft cast and fiberglass is better than soft cast. Clinical Relevance: If precise molding is required, plaster has the best moldability. In cases not requiring precise molding, fiberglass and soft cast are lightweight, waterproof, and available in child-friendly colors.
From the Departments of *Orthopaedics & Rehabilitation; and wMedical Biostatistics, University of Vermont College of Medicine, Burlington, VT. Supported by the McClure Musculoskeletal Research Center, University of Vermont College of Medicine. The authors declare no conflicts of interest. Reprints: David D. Aronsson, MD, Department of Orthopaedics & Rehabilitation, University of Vermont College of Medicine, Robert T. Stafford Hall, Room 434B, Burlington, VT 05405. E-mail: david. [email protected]. Copyright r 2014 by Lippincott Williams & Wilkins
J Pediatr Orthop
Key Words: cast moldability, cast biomechanical properties, cast material properties, cast treatment for clubfoot, DDH, forearm fractures and femur fractures (J Pediatr Orthop 2014;34:743–748)
P
laster casts have become a staple tool of orthopaedic surgeons in emergency rooms and clinics throughout the world. The fiberglass cast, introduced in the 1970s, had several innovative advances including being robust, lightweight, water resistant, and more radiolucent. In addition, the setting temperatures of synthetic casts are lower than plaster, markedly decreasing the risk of burning the skin.1,2 The development of waterproof cast liners allowed patients to bathe, shower, and swim while wearing a cast. In addition to being waterproof, fiberglass casts were available in many colors making them popular for treating children’s fractures despite the higher cost. Subsequently, waterproof soft casts were developed with the advantages of being lighter and more flexible than fiberglass, creating a more comfortable and custom fit. In addition, a soft cast can be removed by the family at home negating the necessity of a follow-up appointment to remove the cast. When cast materials are setting, they remain pliable and shapeable. Depending on the type of cast, clinicians use thumbs, fingers, and hands to mold the cast into a particular shape. The ability of various casting materials to retain the desired shape is referred to as moldability. In children, there are numerous clinical settings where precise cast molding is imperative to achieve a satisfactory outcome including clubfeet, developmental dysplasia of the hip (DDH), forearm fractures, and femur fractures.3–11 Clinicians are increasingly using newer materials such as fiberglass and soft cast rather than plaster. This has been motivated by improved material properties including wear resistance, bending strength, tensile and yield strength, elastic modulus, setting time, and decreasing the release of exothermic heat.12–18 Clinicians intuitively believe that plaster has the benefit of being more moldable than fiberglass or soft cast and plaster expands rather than constricts when setting.19 To our knowledge, the molding characteristics of different cast materials have never been reported. We studied the molding characteristics of 3 cast materials (plaster, fiberglass, and soft cast) on 4 models simulating 4 clinical problems; clubfoot, DDH, forearm fracture, and femur fracture. Our hypothesis was molding would be more precise with plaster than fiberglass and more precise with fiberglass than soft cast.
Volume 34, Number 7, October/November 2014
www.pedorthopaedics.com |
743
J Pediatr Orthop
Daines et al
METHODS A model designed to simulate a child’s clubfoot or forearm fracture was created using a 5.1 cm (2 inches) foam cylinder to replicate the soft tissues with a 1.9 cm (3⁄4 inches) wooden dowel center to replicate the bone. A second model designed to simulate DDH or a child’s femur fracture was created using a 15.2 cm (6 inches) foam cylinder to replicate the soft tissues with a 2.5 cm (1 inches) wooden dowel center to replicate the bone (Stitches Afloat, Shelburne, VT). The foam cylinders replicated the compliance of human soft tissue and were similar to the compliance of the foam used as a soft tissue substitute by Erickson et al.20 To determine the forces that clinicians apply while molding a cast, 2 pediatric orthopaedists were recruited to the laboratory to push on a digital force plate (Chatillon; AMETEK, Berwyn, PA) with the force that they typically use to mold a clubfoot cast, maintain the reduction of DDH, maintain the reduction of a forearm fracture, and maintain the reduction of a femur fracture. The clinicians pushed with approximately 50 N to mold the clubfoot and forearm fracture cast and 100 N to mold the DDH and femur fracture cast. A custom loading device was developed to simulate the loads applied by clinicians when molding casts for the 4 clinical conditions: clubfoot [thumb shaped 50 N on 5.1 cm (2 inches) foam], DDH [thumb shaped 100 N on 15.2 cm (6 inches) foam], forearm fracture [palm shaped 50 N on 5.1 cm (2 inches) foam], and femur fracture [palm
Volume 34, Number 7, October/November 2014
shaped 100 N on 15.2 cm (6 inches) foam]. The loading device used weights to apply the desired loads to the cast through wooden models, approximating the shape of a thumb or palm for 7 minutes while casts set (Fig. 1). We compared 12.7 cm (5 inches) wide casts of plaster (Specialist, BSN Medical, Rutherford College, NC), fiberglass (Scotchcast Plus, 3M, St. Paul, MN) and soft cast (Soft Cast, 3M, St. Paul, MN). Each cast was 5 layers thick, dipped in 401C water, and placed over 2 layers of cotton padding (Webril, Covidien, Mansfield, MA). The casts were applied on 5.1 cm (2 inches) and 15.2 cm (6 inches) diameter foam cylinders with 1.9 cm (3⁄4 inches) and 2.5 cm (1 inch) wooden dowel centers, respectively. The loading device applied a compressive load normal to the surface of the cast without shear loads in a manner similar to that used in the clinical environment. Five casts of each of the 3 cast materials were made for each of the 4 models (60 total casts). After 7 minutes, when the casts had set, they were removed from the foam cylinders and photographed with a camera that was aligned collinear with the inside of the cast (axial view) with a scaling reference placed at the level of maximal deformation depth. The images were then digitized for molding shape comparison. The precision of molding (moldability) was analyzed by calculating the 2-dimensional area of maximal deformation (AMD) that developed in the molded cast compared with an unmolded cast. If the cast was not molded, there would be no deformation and the cast would remain circular (Fig. 2, semi-circular grey line of an unmolded cast). If the molding was precise, a small AMD would indicate that the cast molded exactly to the shape of the thumb or palm (Fig. 2, dashed line with corresponding AMD). If the molding was less precise, a large AMD would indicate that the cast did not mold exactly to the shape of the thumb or palm and the deformation of the cast was spread out over a large area.
Statistical Analysis The AMDs of the 3 cast materials (plaster, fiberglass, and soft cast) for the 4 clinical models (clubfoot, DDH, forearm fracture, and femur fracture) were com-
FIGURE 1. An image showing the custom loading device developed to replicate the forces applied by clinicians when molding casts. The device applied a 50 or 100 N load to the cast through a thumb-shaped or palm-shaped wooden model.
744 | www.pedorthopaedics.com
FIGURE 2. A drawing of the inside of a cast (axial view) at the level of maximal deformation showing how the molding was analyzed by the 2-dimensional area of maximal deformation (AMD). If the cast was not molded, there would be no AMD and the cast would remain circular (semi-circular grey). If the molding was precise (dashed line), a small AMD would indicate that the cast molded exactly to the thumb or palm shape. r
2014 Lippincott Williams & Wilkins
J Pediatr Orthop
Volume 34, Number 7, October/November 2014
Moldability of Plaster, Fiberglass and Soft Casts
TABLE 1. Mean Area of Maximum Deviation (AMD) for Plaster (P), Fiberglass (F), and Soft Cast (S) ± SD and Comparison P-values for Clubfoot, DDH, Forearm Fracture, and Femur Fracture Cast Models Clubfoot Cast Material
DDH Cast Mean ± SD
Material
Average area (mm2) of maximal deformation (AMD) P 560 ± 45 P F 726 ± 67 F S 1018 ± 172 S Comparison
P
Comparison
Plaster, fiberglass and soft cast comparisons P-F 0.002* P-F P-S < 0.0001* P-S F-S 0.01 F-S
Forearm Fracture Cast
Femur Fracture Cast
Mean ± SD
Material
Mean ± SD
Material
Mean ± SD
2986 ± 266 5282 ± 235 6873 ± 457
P F S
563 ± 107 526 ± 169 578 ± 45
P F S
3195 ± 563 4904 ± 519 5037 ± 546
P
Comparison
P
Comparison
P
< 0.0001* < 0.0001* 0.0001*
P-F P-S F-S
0.7 0.8 0.5
P-F P-S F-S
0.001* 0.001* 0.7
DDH indicates developmental dysplasia of the hip.
pared using t tests. To correct for multiple comparisons, the significance level was adjusted using the Bonferroni method (0.05/12 = 0.004). Results with a P-value of 0.8 (poorly molded cast) the redisplacement rate was 26%.7 The possibility of redisplacement and concerns about loss of pronation or supination has caused many clinicians to recommend surgery for forearm fractures in children. This trend toward surgery was documented in an 11-year study involving 2297 fractures. The authors reported a 7-fold increase in operative management between the first and last year of the study: 2 of 143 patients in the first year (1.4%) and 28 of 270 patients in the last year (10.4%).24 We believe that most forearm fractures can be successfully managed with a closed reduction under sedation and application of a properly molded cast. Femur fractures with
