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The effect of metallic radial head arthroplasty on radiocapitellar joint contact area
Clinical Biomechanics 18 (2003) 115–118 www.elsevier.com/locate/clinbiomech
The effect of metallic radial head arthroplasty on radiocapitellar joint contact area Victor S. Liew, Ian C. Cooper, Louis M. Ferreira, James A. Johnson, Graham J.W. King
*
Bioengineering Research Laboratory, Division of Orthopaedic Surgery, Hand and Upper Limb Centre, Lawson Health Research Institute, St. JosephÕs Health Care London, The University of Western Ontario, 268 Grosvenor Street, London, ON, Canada N6A 4L6 Received 25 June 2002; accepted 31 October 2002
Abstract Objective. This study determined the effect of metallic radial head arthroplasty on radiocapitellar joint contact area. Design. The contact area of eight intact radiocapitellar joints was assessed during simulated compressive loading. Subsequently, the same experiments were repeated after reconstruction with three different radial head implant sizes. Background. There has been an increasing use of metal radial head implants relative to silicone implants. However, the contact characteristics with the metal reconstruction have not been determined. Methods. A 100 N compressive load was applied to the radiocapitellar joint at three different flexion angles for the native joint and three different sizes of a metal head implant. An impression material was employed to quantify joint contact area. Results. Following metallic radial head arthroplasty, the contact area decreased by approximately two-thirds relative to the native radiocapitellar joint (P < 0:001). Smaller implant sizes resulted in slightly larger contact areas (P < 0:05). In addition, contact area decreased as joint flexion angle increased (P < 0:04). Conclusions. Selection of radial head implant size is likely not a significant factor with regard to contact area mechanics of the radiocapitellar articulation. Relevance The effect of radial head implant size on the contact area produced with the native capitellum is not known. This study shows that the design or selection of a metallic radial head implant from the viewpoint of size is likely not an important factor with regard to minimizing joint contact stresses. Ó 2003 Elsevier Science Ltd. All rights reserved. Keywords: Metal radial head implant; Radial head fracture; Elbow joint contact mechanics; Joint casting
1. Introduction Radial head fractures are the most common fractures of the elbow. Treatment options include non-operative management, open reduction and internal fixation, radial head excision, and radial head arthroplasty (Boulas and Morrey, 1998; Furry and Clinkscales, 1998; Harrington et al., 2001). The latter alternative is indicated for management of non-reconstructable radial head fractures with a concomitant injury of the collateral ligaments, interosseus ligament, or an associated elbow dislocation. Silicone implants were the preferred option *
Corresponding author. E-mail address: [email protected] (G.J.W. King).
for arthroplasty in the past. However, there have been many well-documented complications including prosthesis failure, adverse tissue reaction, and poor load transfer (Morrey et al., 1981; Vanderwilde et al., 1994; Worsing et al., 1986). As such, there has been an increasing use of metal implants more recently, with encouraging short to medium-term results (Harrington et al., 2001; Knight et al., 1993; Moro et al., 2001). The utilization of metal prostheses, however, raise important questions regarding the effect of both the implant and implant sizing on alteration of contact mechanics. While there have been reports on radiocapitellar joint contact patterns in the intact joint (Caputo et al., 1998; Goel et al., 1982; Stormont et al., 1985), the effect of radial head arthroplasty on contact area is unknown.
0268-0033/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 8 - 0 0 3 3 ( 0 2 ) 0 0 1 7 2 - 9
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Fig. 1. The loading apparatus used to produce radio-capitellar compression at three angles of flexion.
The purposes of this study were to quantify the contact area of the radiocapitellar joint before and after radial head arthroplasty with a metal implant and to determine the effect of implant size on joint contact area. Our hypotheses were that radiocapitellar joint contact area would decrease after metallic radial head arthroplasty and that implant size would have little influence on contact area.
2. Methods The distal humerus and proximal radius were resected from eight previously frozen upper extremities, dissected of all soft tissue, and potted in polymethylmethacrylate bone cement (5 males, 3 females; average age ¼ 68 ðSD 13Þ years). Bovine calf serum was used to maintain proper hydration of the articular surfaces. A custommade apparatus was used that allowed the joint to be reproducibly tested at different flexion angles (Fig. 1). After application of the casting material to the radial head, the joint was loaded with 100 N of compressive force. Testing was performed at 60°, 90°, and 120° of flexion in neutral rotation. This protocol was followed for the intact radial head, then subsequently with an undersized metal implant, an optimally sized implant, and an over-sized implant (Evolveâ , Wright Medical–– Arlington, TN, USA). The optimally sized implant was carefully selected according to the dimensions of the native radial head. The under- and over-sized implants were 2 mm smaller and larger in diameter than the optimally sized implant, respectively. Reprosilâ (D E N T S P L Y International Inc.––Milford, DE, USA)––a vinyl polysiloxane dental impression material––was used to quantify the contact area of the radiocapitellar joint (Fig. 2). In order to maintain consistent viscosity of the casting material, testing was done at an ambient room temperature of 24 1 °C and mixing and application of the casting material to the joint was accomplished within 60 s. After the impression material had cured for 12 min, the corresponding cast was removed from the joint. Subsequently, images of each cast were taken using a digital scanner at a reso-
Fig. 2. A silicone cast following polymerization and retrieval from the (intact) joint.
lution of 200 dpi. SigmaScanâ (Version 2.0, SPSS Science––Chicago, IL, USA) was used to calculate the contact area from the casts (Fig. 2), by tracing the inner edge of the digitized casts. In order to verify the reproducibility of the casting method, five casts of the radiocapitellar joint were made for a randomly chosen condition (i.e. native radial head at 60° of joint flexion). The contact area of each cast was then calculated and compared. To quantify the reproducibility of the measurement technique using the digitization software, five different individuals calculated the contact area from the same cast five times. Two-way repeated measures analyses of variance were employed for statistical purposes with the Student– Newman–Keuls method utilized for post-hoc analysis (Sigmastatâ Version 2.03, SPSS Science). Reproducibility of the casting method and measurement technique was assessed by means of a coefficient of variation.
3. Results Radiocapitellar contact area decreased significantly after an optimally sized metallic radial head arthro-
V.S. Liew et al. / Clinical Biomechanics 18 (2003) 115–118
Fig. 3. Joint contact area for the intact and three radial head implant sizes. Contact area decreased following metallic radial head arthroplasty (P < 0:001) and with increasing implant size (P < 0:05).
Fig. 4. Joint contact area at the three angles of flexion tested for the four conditions of the radial head. Contact area decreased as joint flexion angle increased (P < 0:04).
plasty. This effect was similar after under- and oversized radial head arthroplasty (Fig. 3, P < 0:001). On further analysis of implant size, we found a small but significant decrease in contact area as implant size increased (Fig. 3, P < 0:05). Overall, there was a small but significant effect of joint flexion angle, with a decrease in contact area at larger flexion angles (Fig. 4, P < 0:04). Regarding the reproducibility of our casting method, <6% variability was found. The interobserver variability of the measurement technique was <1%.
4. Discussion Various methods of determining joint contact area have been described in the literature, including wax casting, cement casting, reversible cartilage staining, and the use of pressure-sensitive films. The silicone casting technique employed in this study has been found to be reproducible, as reported by Stormont et al. (1985) and as verified in this investigation. Furthermore, this particular casting material has been used extensively in dental applications, and has been demonstrated to be highly accurate (Council on Dental Materials, Instruments, and Equipment, 1990; Federick and Caputo,
117
1997). An additional advantage of this technique is that it is non-invasive with respect to the articulation. Disadvantages of this method are that it is limited to static measurements and contact pressure is not quantified. While Stormont et al. (1985), Goel et al. (1982) and Caputo et al. (1998) have reported on radiocapitellar joint contact patterns of the native articulation, this study is the first investigation quantifying the contact area of the reconstructed radiocapitellar joint. We found that optimally sized metallic radial head arthroplasty decreased radiocapitellar joint contact area by an average of 68% relative to the native radial head. The two major factors affecting the contact area of an articulation are stiffness (or modulus) of the materials and the conformity of the two surfaces. It is likely that the most influential factor related to the reduction in contact area with the use of a metal implant is the increased stiffness of the metal relative to the native radial head. With regard to conformity, the radius of curvature decreases with smaller implants, and results in a more conforming interface at the radiocapitellar joint and consequently, a greater contact area. While this may seem to advocate the use of a better fitting, and hence constrained, device in an effort to reproduce normal contact areas, implant loosening may become an important issue, as was reported with earlier designs of total knee prostheses (Peterson et al., 1979). Overall, we found the influence of implant size to be less prominent than the effect of implant stiffness. As such, selection of implant size in order to maximize contact area likely will not have a significant effect on joint contact stresses. Regarding the effect of joint flexion angle, we found a decrease in joint contact area as flexion angle increased. This seems to be contrary to the findings of Goel et al. (1982) who reported an increase in radiocapitellar joint contact area as the elbow moved from extension to flexion. It should be noted, however, that in the above investigation, the joint was tested at full extension, 90°, and full flexion as opposed to the three angles (60°, 90°, and 120°) tested in this study. The effect of joint angle on joint contact area is, in all likelihood, due to changes in the topography of the capitellum at the different angles. Harrington et al. (2001), Knight et al. (1993) and Moro et al. (2001) have reported on the medium-term outcomes of titanium and vitallium radial head implants, respectively, with good to excellent results in 75% of subjects in both series. Harrington and coworkers found elbow arthritis to be a significant complication in approximately 15% of his subjects, however, the degeneration was confined to the ulnohumeral joint only (Harrington et al., 2001). This is may be a result of the severity of the initial injury though, and not a direct consequence of metallic radial head arthroplasty. Not surprisingly, metallic radial head arthroplasty decreases joint contact area at the radiocapitellar joint, resulting in greater contact pressures. This may have implications
118
V.S. Liew et al. / Clinical Biomechanics 18 (2003) 115–118
with respect to cartilage wear on the capitellum, particularly at long-term follow-up. Although the reduction in contact area (and hence the increase in contact pressure) that occurs with a metal arthroplasty does not appear to be detrimental with regard to joint cartilage wear in the medium term, the long-term effect of metallic radial head arthroplasty requires further assessment. 5. Conclusions We found that radiocapitellar joint contact area decreases by approximately two-thirds relative to the native joint following metallic radial head arthroplasty. In addition, we found that smaller implants slightly increase contact area at the joint and that contact area decreases as joint flexion angle increases. Future work in this field should include dynamic measurements of contact mechanics, quantification of pressure parameters, and in-situ testing with soft-tissue constraints of the joint kept intact. Acknowledgements This investigation was supported by grants from the Lawson Health Research Institute Pooled Research Trust Fund and the Canadian Institute for Health Research. The assistance of Julie Allard in the preparation of this manuscript is gratefully acknowledged. References Boulas, H.J., Morrey, B.F., 1998. Biomechanical evaluation of the elbow following radial head fracture. Comparison of open reduc-
tion and internal fixation vs. excision, silastic replacement, and non-operative management. Chir Main 17, 314–320. Caputo, A.E., Mazzocca, A.D., Nowak, M.D., 1998. Joint contact patterns of the radiocapitellar joint with forearm rotation in a cadaveric model. In: Transactions of the 44th Annual Meeting of the Orthopaedic Research Society, New Orleans, p. 1153. Council on Dental Materials, Instruments, and Equipment. 1990. Vinyl polysiloxane impression materials: A status report. J. Am. Dent. Assoc. 120, 595–596. Federick, D.R., Caputo, A., 1997. Comparing the accuracy of reversible hydrocolloid and elastomeric impression materials. J. Am. Dent. Assoc. 128, 183–188. Furry, K.L., Clinkscales, C.M., 1998. Comminuted fractures of the radial head. Arthroplasty versus internal fixation. Clin. Orthop. 353, 40–52. Goel, V.K., Singh, D., Bijlani, V., 1982. Contact areas in human elbow joints. J. Biomech. Eng. 104, 169–175. Harrington, I.J., Sekyi-Otu, A., Barrington, T.W., Evans, D.C., Tuli, V., 2001. The functional outcome with metallic radial head implants in the treatment of unstable elbow fractures: A long-term review. J. Trauma 50, 46–52. Knight, D.J., Rymaszewski, L.A., Amis, A.A., Miller, J.H., 1993. Primary replacement of the fractured radial head with a metal prosthesis. J. Bone Joint Surg. Br. 75, 572–576. Moro, J.K., Werier, J., MacDermid, J.C., Patterson, S.D., King, G.J.W., 2001. Arthroplasty with a metal radial head for unreconstructable fractures of the radial head. J. Bone Joint Surg. Am. 83A, 1201–1211. Morrey, B.F., Askew, L., Chao, E.Y., 1981. Silastic prosthetic replacement for the radial head. J. Bone Joint Surg. Am. 63, 454–458. Peterson, L.F., Fitzgerald Jr., R.H., Johnson Jr., E.W., 1979. Total joint arthroplasty. The knee. Mayo Clin. Proc. 54, 564–569. Stormont, T.J., An, K.N., Morrey, B.F., Chao, E.Y., 1985. Elbow joint contact study: Comparison of techniques. J. Biomech. 18, 329–336. Vanderwilde, R.S., Morrey, B.F., Melberg, M.W., Vinh, T.N., 1994. Inflammatory arthritis after failure of silicone rubber replacement of the radial head. J. Bone Joint Surg. Br. 76, 78–81. Worsing Jr., R.A., Engber, W.D., Lange, T.A., 1986. Reactive synovitis from particulate silastic. J. Bone Joint Surg. Am. 64, 581–585.
The effect of metallic radial head arthroplasty on radiocapitellar joint contact area Victor S. Liew, Ian C. Cooper, Louis M. Ferreira, James A. Johnson, Graham J.W. King
*
Bioengineering Research Laboratory, Division of Orthopaedic Surgery, Hand and Upper Limb Centre, Lawson Health Research Institute, St. JosephÕs Health Care London, The University of Western Ontario, 268 Grosvenor Street, London, ON, Canada N6A 4L6 Received 25 June 2002; accepted 31 October 2002
Abstract Objective. This study determined the effect of metallic radial head arthroplasty on radiocapitellar joint contact area. Design. The contact area of eight intact radiocapitellar joints was assessed during simulated compressive loading. Subsequently, the same experiments were repeated after reconstruction with three different radial head implant sizes. Background. There has been an increasing use of metal radial head implants relative to silicone implants. However, the contact characteristics with the metal reconstruction have not been determined. Methods. A 100 N compressive load was applied to the radiocapitellar joint at three different flexion angles for the native joint and three different sizes of a metal head implant. An impression material was employed to quantify joint contact area. Results. Following metallic radial head arthroplasty, the contact area decreased by approximately two-thirds relative to the native radiocapitellar joint (P < 0:001). Smaller implant sizes resulted in slightly larger contact areas (P < 0:05). In addition, contact area decreased as joint flexion angle increased (P < 0:04). Conclusions. Selection of radial head implant size is likely not a significant factor with regard to contact area mechanics of the radiocapitellar articulation. Relevance The effect of radial head implant size on the contact area produced with the native capitellum is not known. This study shows that the design or selection of a metallic radial head implant from the viewpoint of size is likely not an important factor with regard to minimizing joint contact stresses. Ó 2003 Elsevier Science Ltd. All rights reserved. Keywords: Metal radial head implant; Radial head fracture; Elbow joint contact mechanics; Joint casting
1. Introduction Radial head fractures are the most common fractures of the elbow. Treatment options include non-operative management, open reduction and internal fixation, radial head excision, and radial head arthroplasty (Boulas and Morrey, 1998; Furry and Clinkscales, 1998; Harrington et al., 2001). The latter alternative is indicated for management of non-reconstructable radial head fractures with a concomitant injury of the collateral ligaments, interosseus ligament, or an associated elbow dislocation. Silicone implants were the preferred option *
Corresponding author. E-mail address: [email protected] (G.J.W. King).
for arthroplasty in the past. However, there have been many well-documented complications including prosthesis failure, adverse tissue reaction, and poor load transfer (Morrey et al., 1981; Vanderwilde et al., 1994; Worsing et al., 1986). As such, there has been an increasing use of metal implants more recently, with encouraging short to medium-term results (Harrington et al., 2001; Knight et al., 1993; Moro et al., 2001). The utilization of metal prostheses, however, raise important questions regarding the effect of both the implant and implant sizing on alteration of contact mechanics. While there have been reports on radiocapitellar joint contact patterns in the intact joint (Caputo et al., 1998; Goel et al., 1982; Stormont et al., 1985), the effect of radial head arthroplasty on contact area is unknown.
0268-0033/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 8 - 0 0 3 3 ( 0 2 ) 0 0 1 7 2 - 9
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V.S. Liew et al. / Clinical Biomechanics 18 (2003) 115–118
Fig. 1. The loading apparatus used to produce radio-capitellar compression at three angles of flexion.
The purposes of this study were to quantify the contact area of the radiocapitellar joint before and after radial head arthroplasty with a metal implant and to determine the effect of implant size on joint contact area. Our hypotheses were that radiocapitellar joint contact area would decrease after metallic radial head arthroplasty and that implant size would have little influence on contact area.
2. Methods The distal humerus and proximal radius were resected from eight previously frozen upper extremities, dissected of all soft tissue, and potted in polymethylmethacrylate bone cement (5 males, 3 females; average age ¼ 68 ðSD 13Þ years). Bovine calf serum was used to maintain proper hydration of the articular surfaces. A custommade apparatus was used that allowed the joint to be reproducibly tested at different flexion angles (Fig. 1). After application of the casting material to the radial head, the joint was loaded with 100 N of compressive force. Testing was performed at 60°, 90°, and 120° of flexion in neutral rotation. This protocol was followed for the intact radial head, then subsequently with an undersized metal implant, an optimally sized implant, and an over-sized implant (Evolveâ , Wright Medical–– Arlington, TN, USA). The optimally sized implant was carefully selected according to the dimensions of the native radial head. The under- and over-sized implants were 2 mm smaller and larger in diameter than the optimally sized implant, respectively. Reprosilâ (D E N T S P L Y International Inc.––Milford, DE, USA)––a vinyl polysiloxane dental impression material––was used to quantify the contact area of the radiocapitellar joint (Fig. 2). In order to maintain consistent viscosity of the casting material, testing was done at an ambient room temperature of 24 1 °C and mixing and application of the casting material to the joint was accomplished within 60 s. After the impression material had cured for 12 min, the corresponding cast was removed from the joint. Subsequently, images of each cast were taken using a digital scanner at a reso-
Fig. 2. A silicone cast following polymerization and retrieval from the (intact) joint.
lution of 200 dpi. SigmaScanâ (Version 2.0, SPSS Science––Chicago, IL, USA) was used to calculate the contact area from the casts (Fig. 2), by tracing the inner edge of the digitized casts. In order to verify the reproducibility of the casting method, five casts of the radiocapitellar joint were made for a randomly chosen condition (i.e. native radial head at 60° of joint flexion). The contact area of each cast was then calculated and compared. To quantify the reproducibility of the measurement technique using the digitization software, five different individuals calculated the contact area from the same cast five times. Two-way repeated measures analyses of variance were employed for statistical purposes with the Student– Newman–Keuls method utilized for post-hoc analysis (Sigmastatâ Version 2.03, SPSS Science). Reproducibility of the casting method and measurement technique was assessed by means of a coefficient of variation.
3. Results Radiocapitellar contact area decreased significantly after an optimally sized metallic radial head arthro-
V.S. Liew et al. / Clinical Biomechanics 18 (2003) 115–118
Fig. 3. Joint contact area for the intact and three radial head implant sizes. Contact area decreased following metallic radial head arthroplasty (P < 0:001) and with increasing implant size (P < 0:05).
Fig. 4. Joint contact area at the three angles of flexion tested for the four conditions of the radial head. Contact area decreased as joint flexion angle increased (P < 0:04).
plasty. This effect was similar after under- and oversized radial head arthroplasty (Fig. 3, P < 0:001). On further analysis of implant size, we found a small but significant decrease in contact area as implant size increased (Fig. 3, P < 0:05). Overall, there was a small but significant effect of joint flexion angle, with a decrease in contact area at larger flexion angles (Fig. 4, P < 0:04). Regarding the reproducibility of our casting method, <6% variability was found. The interobserver variability of the measurement technique was <1%.
4. Discussion Various methods of determining joint contact area have been described in the literature, including wax casting, cement casting, reversible cartilage staining, and the use of pressure-sensitive films. The silicone casting technique employed in this study has been found to be reproducible, as reported by Stormont et al. (1985) and as verified in this investigation. Furthermore, this particular casting material has been used extensively in dental applications, and has been demonstrated to be highly accurate (Council on Dental Materials, Instruments, and Equipment, 1990; Federick and Caputo,
117
1997). An additional advantage of this technique is that it is non-invasive with respect to the articulation. Disadvantages of this method are that it is limited to static measurements and contact pressure is not quantified. While Stormont et al. (1985), Goel et al. (1982) and Caputo et al. (1998) have reported on radiocapitellar joint contact patterns of the native articulation, this study is the first investigation quantifying the contact area of the reconstructed radiocapitellar joint. We found that optimally sized metallic radial head arthroplasty decreased radiocapitellar joint contact area by an average of 68% relative to the native radial head. The two major factors affecting the contact area of an articulation are stiffness (or modulus) of the materials and the conformity of the two surfaces. It is likely that the most influential factor related to the reduction in contact area with the use of a metal implant is the increased stiffness of the metal relative to the native radial head. With regard to conformity, the radius of curvature decreases with smaller implants, and results in a more conforming interface at the radiocapitellar joint and consequently, a greater contact area. While this may seem to advocate the use of a better fitting, and hence constrained, device in an effort to reproduce normal contact areas, implant loosening may become an important issue, as was reported with earlier designs of total knee prostheses (Peterson et al., 1979). Overall, we found the influence of implant size to be less prominent than the effect of implant stiffness. As such, selection of implant size in order to maximize contact area likely will not have a significant effect on joint contact stresses. Regarding the effect of joint flexion angle, we found a decrease in joint contact area as flexion angle increased. This seems to be contrary to the findings of Goel et al. (1982) who reported an increase in radiocapitellar joint contact area as the elbow moved from extension to flexion. It should be noted, however, that in the above investigation, the joint was tested at full extension, 90°, and full flexion as opposed to the three angles (60°, 90°, and 120°) tested in this study. The effect of joint angle on joint contact area is, in all likelihood, due to changes in the topography of the capitellum at the different angles. Harrington et al. (2001), Knight et al. (1993) and Moro et al. (2001) have reported on the medium-term outcomes of titanium and vitallium radial head implants, respectively, with good to excellent results in 75% of subjects in both series. Harrington and coworkers found elbow arthritis to be a significant complication in approximately 15% of his subjects, however, the degeneration was confined to the ulnohumeral joint only (Harrington et al., 2001). This is may be a result of the severity of the initial injury though, and not a direct consequence of metallic radial head arthroplasty. Not surprisingly, metallic radial head arthroplasty decreases joint contact area at the radiocapitellar joint, resulting in greater contact pressures. This may have implications
118
V.S. Liew et al. / Clinical Biomechanics 18 (2003) 115–118
with respect to cartilage wear on the capitellum, particularly at long-term follow-up. Although the reduction in contact area (and hence the increase in contact pressure) that occurs with a metal arthroplasty does not appear to be detrimental with regard to joint cartilage wear in the medium term, the long-term effect of metallic radial head arthroplasty requires further assessment. 5. Conclusions We found that radiocapitellar joint contact area decreases by approximately two-thirds relative to the native joint following metallic radial head arthroplasty. In addition, we found that smaller implants slightly increase contact area at the joint and that contact area decreases as joint flexion angle increases. Future work in this field should include dynamic measurements of contact mechanics, quantification of pressure parameters, and in-situ testing with soft-tissue constraints of the joint kept intact. Acknowledgements This investigation was supported by grants from the Lawson Health Research Institute Pooled Research Trust Fund and the Canadian Institute for Health Research. The assistance of Julie Allard in the preparation of this manuscript is gratefully acknowledged. References Boulas, H.J., Morrey, B.F., 1998. Biomechanical evaluation of the elbow following radial head fracture. Comparison of open reduc-
tion and internal fixation vs. excision, silastic replacement, and non-operative management. Chir Main 17, 314–320. Caputo, A.E., Mazzocca, A.D., Nowak, M.D., 1998. Joint contact patterns of the radiocapitellar joint with forearm rotation in a cadaveric model. In: Transactions of the 44th Annual Meeting of the Orthopaedic Research Society, New Orleans, p. 1153. Council on Dental Materials, Instruments, and Equipment. 1990. Vinyl polysiloxane impression materials: A status report. J. Am. Dent. Assoc. 120, 595–596. Federick, D.R., Caputo, A., 1997. Comparing the accuracy of reversible hydrocolloid and elastomeric impression materials. J. Am. Dent. Assoc. 128, 183–188. Furry, K.L., Clinkscales, C.M., 1998. Comminuted fractures of the radial head. Arthroplasty versus internal fixation. Clin. Orthop. 353, 40–52. Goel, V.K., Singh, D., Bijlani, V., 1982. Contact areas in human elbow joints. J. Biomech. Eng. 104, 169–175. Harrington, I.J., Sekyi-Otu, A., Barrington, T.W., Evans, D.C., Tuli, V., 2001. The functional outcome with metallic radial head implants in the treatment of unstable elbow fractures: A long-term review. J. Trauma 50, 46–52. Knight, D.J., Rymaszewski, L.A., Amis, A.A., Miller, J.H., 1993. Primary replacement of the fractured radial head with a metal prosthesis. J. Bone Joint Surg. Br. 75, 572–576. Moro, J.K., Werier, J., MacDermid, J.C., Patterson, S.D., King, G.J.W., 2001. Arthroplasty with a metal radial head for unreconstructable fractures of the radial head. J. Bone Joint Surg. Am. 83A, 1201–1211. Morrey, B.F., Askew, L., Chao, E.Y., 1981. Silastic prosthetic replacement for the radial head. J. Bone Joint Surg. Am. 63, 454–458. Peterson, L.F., Fitzgerald Jr., R.H., Johnson Jr., E.W., 1979. Total joint arthroplasty. The knee. Mayo Clin. Proc. 54, 564–569. Stormont, T.J., An, K.N., Morrey, B.F., Chao, E.Y., 1985. Elbow joint contact study: Comparison of techniques. J. Biomech. 18, 329–336. Vanderwilde, R.S., Morrey, B.F., Melberg, M.W., Vinh, T.N., 1994. Inflammatory arthritis after failure of silicone rubber replacement of the radial head. J. Bone Joint Surg. Br. 76, 78–81. Worsing Jr., R.A., Engber, W.D., Lange, T.A., 1986. Reactive synovitis from particulate silastic. J. Bone Joint Surg. Am. 64, 581–585.