- Email: [email protected]
Reference Points for Radial Head Prosthesis Size
Reference Points for Radial Head Prosthesis Size Job N. Doornberg, MS, Durk S. Linzel, BS, David Zurakowski, PhD, David Ring, MD From the Department of Orthopaedic Surgery and Biostatistics, Harvard Medical School, Boston, MA; Orthopaedic Hand and Upper Extremity Service, Massachusetts General Hospital, Boston, MA; Department of Biostatistics, Children’s Hospital Boston, Boston, MA.
Purpose: Metallic radial head implants are useful when the radial head cannot be repaired reliably and when either the elbow or the forearm is unstable. Problems arise when the radial head prosthesis is too thick, causing erosions of the capitellum and incongruity of the ulnohumeral joint. We used quantitative 3-dimensional computed tomography analysis to investigate the relative height of the radial head relative to the lateral edge and central ridge of the coronoid process as reference points for optimal insertion of a radial head prosthesis. Methods: Seventeen computed tomography scans of the elbow were analyzed. The anatomic coronal plane of the forearm was determined using 3-dimensional images and a 2-dimensional image bisecting the articular surface of the radial head was created in this plane. The distance between the plane of the articular surface of the radial head and parallel planes at the most proximal aspect of the coronoid (the central ridge) and the lateral edge of the coronoid articular surface were measured. Negative values indicate the radial head is proximal to the coronoid. Results: The average distance between the planes defined by the radial head articular surface and the coronoid central ridge was -0.8 mm. The average distance between the planes defined by the radial head articular surface and the lateral edge of the coronoid articular surface was -0.9 mm. Conclusions: Because the radial head was on average only 0.9 mm more proximal than the lateral edge of the coronoid process and because the key is to not overstuff the joint a useful general guideline would be to place the plane of the articular surface of the radial head even with or just slightly more proximal than the lateral edge of the coronoid articular surface. Considering the substantial variability of the normal height of the articular surface of the radial head with respect to that of the coronoid, preoperative radiographs of the opposite elbow may be useful to avoid overstuffing the elbow. (J Hand Surg 2006;31A:53–57. Copyright © 2006 by the American Society for Surgery of the Hand.) Key words: Coronoid, elbow, fracture, injury patterns.
The radial head has been recognized as an important stabilizer of the elbow.1 Replacement of the fractured radial head with a prosthesis is a useful treatment option when the forearm or elbow are unstable and when internal fixation is tenuous or impossible.2– 4 Silicone rubber implants were popular for a while but now it is well recognized that a metal implant provides greater stability.5,6 Selection of the appropriate radial head implant size can be difficult. No guidelines have been suggested other than attempting to match the size of the resected radial head; the appropriate size is disputed.
One biomechanical study suggested using the thickest radial head implant possible.7 This is in stark contrast to the realization by many elbow surgeons that the major drawback of metal radial head prostheses is the placement of an implant that is too large and causes widening of the lateral side of the ulnotrochear joint space and radiocapitellar wear.8 A prosthesis that is too large also may contribute to persistent elbow instability after surgical repair. The purpose of this study was to quantify the anatomic relationship between the coronoid process and the radial head to determine useful landmarks for The Journal of Hand Surgery
53
54
The Journal of Hand Surgery / Vol. 31A No. 1 January 2006
Figure 1. Three-dimensional computed tomography images were used to determine a plane defined by the distal margins of the articular surface of the radial head. Arrow 1, the central ridge of the coronoid process; arrow 2, the lateral edge of the coronoid process.
insertion of an appropriately sized radial head prosthesis.
ridge) (Fig. 1) and the lateral edge of the coronoid articular surface (the most proximal aspect of the proximal radial ulnar joint) (Fig. 1) were measured with imaging software (OSIRIS Imaging Software; Digital Imaging Unit, University Hospital of Geneva, Switzerland). Negative values indicate the radial head is proximal to the central ridge and lateral edge of the coronoid; positive values indicate the radial head is distal. Although the software is accurate to 0.1 mm the selection of planes and measurement points is somewhat subjective; therefore, 2 observers performed all of the measurements to evaluate the interobserver reliability of the technique. Each observer repeated the measurements 3 times at 2-week intervals to evaluate the intraobserver reliability. With 80% power the sample size of 17 elbows allowed a degree of accuracy of detecting a difference of 1 mm in coronoid height and lateral edge measurements based on assuming an SD of 1 mm across the trials (effect size ⫽ 1) using the F-test in repeated-measures analysis of variance (ANOVA) (version 5.0, nQuery Advisor; Statistical Solutions, Boston, MA). Statistical Methods The Pearson product-moment correlation coefficient (r) was used to measure the level of intraobserver and interobserver reliability. Correlations between 0.70
Materials and Methods Seventeen computed tomography scans of the elbow were analyzed. This represents a single year’s consecutive set of scans obtained for the routine patient care of an isolated fracture of the distal humerus in a skeletally mature patient. There were 8 females and 9 males with an average age of 44 years (range, 15– 84 y). A protocol for the use of these scans was approved by the Human Research Committee. Image manipulation was performed (Vitrea 2 software; Vital Images, Inc., Plymouth, MN). For each patient 3-dimensional computed tomography images were used to determine a plane defined by the margins of the articular surface of the radial head (Fig. 1). A 2-dimensional image was created in a plane orthogonal to the articular surface of the radial head. The rotation of the plane was selected so that it connected 2 points: (1) a point at the center of the radial head (where lines representing the major and minor diameters of the somewhat elliptical radial head cross) and (2) a point on the central ridge of the coronoid at a point representing 50% of the total height of the coronoid process (Fig. 2). By using this image the distance between the plane of the articular surface of the radial head and parallel planes at the most proximal aspect of the coronoid (the central
Figure 2. A 2-dimensional image was created in a plane orthogonal to the articular surface of the radial head. The rotation of the plane was selected so that it connected 2 points: (1) a point at the center of the radial head (where lines representing the major and minor diameters of the somewhat elliptical radial head cross) and (2) a point on the central ridge of the coronoid at a point representing 50% of the total height of the coronoid process.
Doornberg et al / Radial Head Prosthesis Size
55
and 0.89 were regarded as good and r values of 0.90 or greater were considered excellent. Because 3 trials were performed for each observer to determine the distance from the radial head to the central ridge and the lateral edge on the coronoid process of the ulna, repeated-measures ANOVA was applied and the Greenhouse-Geisser F-test was used to indicate whether the measurements between trials were consistent or if they had significant variability. A 95% confidence interval was constructed based on each observer’s 3 trials. Two-tailed p values of less than .05 were regarded as statistically significant. Statistical analysis was performed with statistical software (SPSS version 12.0; SPSS Inc., Chicago, IL).
Results Reliability of Measurements There was good to excellent intraobserver reliability for both observers 1 and 2. Pearson moment correlations for intraobserver agreement showed an average r value of 0.93 among the 3 trials for coronoid height and an r value of 0.89 for lateral edge (p ⬍ .001). With respect to interobserver reliability the average correlation was an r value of 0.91 for the coronoid height (excellent reliability) and an r value of 0.79 for agreement between observers with respect to lateral edge measurements (good reliability). Measurements The distance between the parallel planes defined by the articular surface of the radial head and the central ridge of the coronoid process of the ulna averaged 0.8 mm (SD ⫾ 0.7; range, -0.8 to 2.0 mm) for observer 1 and 0.8 mm (SD ⫾ 0.8; range, -1.3 to 2.2 mm) for observer 2. The negative value indicates that the plane defined by the articular surface of the radial head was proximal to the coronoid ridge (Fig. 3). The distance between the parallel planes at the articular surface of the radial head and the lateral edge of the coronoid process averaged -0.9 mm (SD ⫾ 0.7; range, -2.7 to 0.4 mm) for observer 1 and -0.9 mm (SD ⫾ 0.8; range, -2.8 to 0.5 mm) for observer 2. These values indicate that the radial head is more proximal than the lateral edge of the coronoid in all but 1 case for observer 1 (distance ⫽ ⫹0.1 mm) and in 3 cases for observer 2 (distance ⫽ ⫹0.1, ⫹0.1, ⫹0.2 mm) but to a variable degree (Fig. 4). The F-tests in repeated-measures ANOVA indicated no significant differences in these measurements for both observers at both measurement times.
Discussion Prosthetic replacement of the radial head now is commonplace. Many fractures of the radial head cannot be constructed, and the results of open reduc-
Figure 3. (A) The central ridge of the coronoid process was more proximal than the plane defined by the articular surface of the radial head in most cases (positive value of the measurement). (B) A negative value indicates that the plane defined by the articular surface of the radial head was proximal to the coronoid ridge; this was observed in a few patients.
tion and internal fixation of very complex fractures are poor and unpredictable.4,9,10 Given the importance of contact between the radial head and the capitellum to the stability of the elbow and forearm after a fracture– dislocation, surgeons have become wary of silicone rubber implants and complex surgical repairs prone to early failure and metal prostheses have gained popularity.2,6,11–13 The described techniques for inserting metal prostheses recommend sizing the prosthesis based on the resected head fragments or the radial length14 –16; however, no guidelines are suggested for preventing the placement of a prosthesis that is too thick. The insertion of a prosthesis that is too thick can lead to subluxation of the ulnohumeral joint and capitellar wear, both of which may contribute to pain, synovitis, and restricted motion.8 The suggestion to insert the largest prosthesis that will fit may be suitable in the biomechanics laboratory7 but is not appropriate clinically, particularly in patients with associated el-
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The Journal of Hand Surgery / Vol. 31A No. 1 January 2006
Figure 4. (A) The radial head is more proximal than the lateral edge of the coronoid in most cases as indicated by a negative value. (B) In 2 cases the lateral edge of the coronoid process was slightly more proximal as indicated by a positive value.
bow ligament injuries in whom the instability of the elbow easily will accommodate the insertion of a thick, oversized prosthesis. Studies of the size and shape of the radial head17–22 have focused on the anatomic features of the native radial head for the purposes of prosthesis design.20,21 The excised radial head is available in patients who have arthroplasty for acute fractures for appropriate sizing of the prosthetic head but original radial length is hard to estimate and restore, especially in more comminuted fractures. A common error is to measure the thickness of the prosthesis on the thickest portion of the radial head (the part with the greatest amount of the radial neck on it). Because the prosthesis will rest on the most proximal extension of the neck this technique will result in overstuffing of the joint unless the
neck is planed to the lowest portion of the neck fracture—something that is not performed routinely. Our data indicate that the plane defined by the edges of the proximal articular surface of the radial head is proximal to the lateral edge of the coronoid process in almost all patients but there is substantial variability between patients. The central ridge of the coronoid process may not be as useful a guide for prosthesis size because this point is distal to the proximal articular surface of the radial head in a substantial percentage of patients and also shows substantial variation. Precise restoration of the relative length of the radial head with respect to the coronoid process may need to be patient specific. The contralateral elbow might be useful as a guide for appropriate size but we have not evaluated whether these measurements are consistent in the contralateral arm of the patient. These represent specific measurements made on the computed tomography scans. The technique and area measured and the inability to account for variations in cartilage thickness may limit the usefulness of the measurements clinically; however, we believe that these factors will have a relatively limited influence. Based on shared clinical experience we prefer to err toward a slightly short prosthesis because such prostheses are likely to provide adequate stability while avoiding the problems associated with excessively thick prostheses. Based on our data a good guideline for most patients is to place the prosthesis so that the plane created by the edges of the proximal articular surface roughly is even with the lateral edge of the coronoid process. To avoid overstuffing the elbow joint with an excessively thick radial head prosthesis the surgeon should use the excised radial head fragments (with care taken not to overestimate thickness based on the thickest portion of the head), assess the relationship between the proximal articular surface of the prosthesis and the lateral edge of the coronoid at the lesser sigmoid notch, and perform intraoperative image intensification to examine this relationship and any malalignment of the ulnohumeral joint in the anteroposterior view or substantial changes in ulnar variance at the wrist. Received for publication December 21, 2004; accepted in revised form June 17, 2005. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Supported by an unrestricted research grant from the AO Foundation and Wright Medical, Inc. Corresponding author: David Ring, MD, Orthopaedic Hand and Upper Extremity Service, Massachusetts General Hospital, Yawkey Center, Suite 2100, 55 Fruit St, Boston, MA 02114; e-mail: [email protected]. Copyright © 2006 by the American Society for Surgery of the Hand 0363-5023/06/31A01-0010$32.00/0 doi:10.1016/j.jhsa.2005.06.012
Doornberg et al / Radial Head Prosthesis Size
References 1. Schneeberger AG, Sadowski MM, Jacob HA. Coronoid process and radial head as posterolateral rotatory stabilizers of the elbow. J Bone Joint Surg 2004;86A:975–982. 2. Moro JK, Werier J, MacDermid JC, Patterson SD, King GJ. Arthroplasty with a metal radial head for unreconstructible fractures of the radial head. J Bone Joint Surg 2001;83A: 1201–1211. 3. Ashwood N, Bain GI, Unni R. Management of Mason typeIII radial head fractures with a titanium prosthesis, ligament repair, and early mobilization. J Bone Joint Surg 2004;86A: 274 –280. 4. Ring D, Quintero J, Jupiter JB. Open reduction and internal fixation of fractures of the radial head. J Bone Joint Surg 2002;84A:1811–1815. 5. Gupta GG, Lucas G, Hahn DL. Biomechanical and computer analysis of radial head prostheses. J Shoulder Elbow Surg 1997;6:37– 48. 6. Morrey BF, Askew L, Chao EY. Silastic prosthetic replacement for the radial head. J Bone Joint Surg 1981;63A:454 – 458. 7. Markolf KL, Tejwani SG, O’Neil G, Benhaim P. Loadsharing at the wrist following radial head replacement with a metal implant. A cadaveric study. J Bone Joint Surg 2004;86A:1023–1030. 8. Van Riet RP, Van Glabbeek F, Verborgt O, Gielen J. Capitellar erosion caused by a metal radial head prosthesis. A case report. J Bone Joint Surg 2004;86A:1061–1064. 9. Heim U. Surgical treatment of radial head fracture. Z Unfallchir Versicherungsmed 1992;85:3–11. 10. King GJ, Evans DC, Kellam JF. Open reduction and internal fixation of radial head fractures. J Orthop Trauma 1991;5: 21–28. 11. Harrington IJ, Sekyi-Otu A, Barrington TW, Evans DC, Tuli V. The functional outcome with metallic radial head implants in the treatment of unstable elbow fractures: a longterm review. J Trauma 2001;50:46 –52.
57
12. Harrington IJ, Tountas AA. Replacement of the radial head in the treatment of unstable elbow fractures. Injury 1981;12: 405– 412. 13. Pugh DM, Wild LM, Schemitsch EH, King GJ, McKee MD. Standard surgical protocol to treat elbow dislocations with radial head and coronoid fractures. J Bone Joint Surg 2004; 86A:1122–1130. 14. Skalski K, Swieszkowski W, Pomianowski S, Kedzior K, Kowalik S. Radial head prosthesis with a mobile head. J Shoulder Elbow Surg 2004;13:78 – 85. 15. King G, Patterson S. Evolve modular radial head. Arlington, TN: Wright Medical Technology, 2002. 16. rHeadTM radial implant system. Surgical technique. San Diego, Avanta Orthopaedics, 2002. 17. Captier G, Canovas F, Mercier N, Thomas E, Bonnel F. Biometry of the radial head: biomechanical implications in pronation and supination. Surg Radiol Anat 2002;24:295– 301. 18. Mahaisavariya B, Saekee B, Sitthiseripratip K, Oris P, Tongdee T, Bohez EL, Vander Sloten J. Morphology of the radial head: a reverse engineering based evaluation using threedimensional anatomical data of radial bone. Proc Inst Mech Eng [H] 2004;218:79 – 84. 19. van Riet RP, Van Glabbeek F, Neale PG, Bortier H, An KN, O’Driscoll SW. The noncircular shape of the radial head. J Hand Surg 2003;28A:972–978. 20. Swieszkowski W, Skalski K, Pomianowski S, Kedzior K. The anatomic features of the radial head and their implication for prosthesis design. Clin Biomech 2001;16:880 – 887. 21. King GJ, Zarzour ZD, Patterson SD, Johnson JA. An anthropometric study of the radial head: implications in the design of a prosthesis. J Arthroplasty 2001;16:112–116. 22. Beredjiklian PK, Nalbantoglu U, Potter HG, Hotchkiss RN. Prosthetic radial head components and proximal radial morphology: a mismatch. J Shoulder Elbow Surg 1999;8: 471– 475.
Purpose: Metallic radial head implants are useful when the radial head cannot be repaired reliably and when either the elbow or the forearm is unstable. Problems arise when the radial head prosthesis is too thick, causing erosions of the capitellum and incongruity of the ulnohumeral joint. We used quantitative 3-dimensional computed tomography analysis to investigate the relative height of the radial head relative to the lateral edge and central ridge of the coronoid process as reference points for optimal insertion of a radial head prosthesis. Methods: Seventeen computed tomography scans of the elbow were analyzed. The anatomic coronal plane of the forearm was determined using 3-dimensional images and a 2-dimensional image bisecting the articular surface of the radial head was created in this plane. The distance between the plane of the articular surface of the radial head and parallel planes at the most proximal aspect of the coronoid (the central ridge) and the lateral edge of the coronoid articular surface were measured. Negative values indicate the radial head is proximal to the coronoid. Results: The average distance between the planes defined by the radial head articular surface and the coronoid central ridge was -0.8 mm. The average distance between the planes defined by the radial head articular surface and the lateral edge of the coronoid articular surface was -0.9 mm. Conclusions: Because the radial head was on average only 0.9 mm more proximal than the lateral edge of the coronoid process and because the key is to not overstuff the joint a useful general guideline would be to place the plane of the articular surface of the radial head even with or just slightly more proximal than the lateral edge of the coronoid articular surface. Considering the substantial variability of the normal height of the articular surface of the radial head with respect to that of the coronoid, preoperative radiographs of the opposite elbow may be useful to avoid overstuffing the elbow. (J Hand Surg 2006;31A:53–57. Copyright © 2006 by the American Society for Surgery of the Hand.) Key words: Coronoid, elbow, fracture, injury patterns.
The radial head has been recognized as an important stabilizer of the elbow.1 Replacement of the fractured radial head with a prosthesis is a useful treatment option when the forearm or elbow are unstable and when internal fixation is tenuous or impossible.2– 4 Silicone rubber implants were popular for a while but now it is well recognized that a metal implant provides greater stability.5,6 Selection of the appropriate radial head implant size can be difficult. No guidelines have been suggested other than attempting to match the size of the resected radial head; the appropriate size is disputed.
One biomechanical study suggested using the thickest radial head implant possible.7 This is in stark contrast to the realization by many elbow surgeons that the major drawback of metal radial head prostheses is the placement of an implant that is too large and causes widening of the lateral side of the ulnotrochear joint space and radiocapitellar wear.8 A prosthesis that is too large also may contribute to persistent elbow instability after surgical repair. The purpose of this study was to quantify the anatomic relationship between the coronoid process and the radial head to determine useful landmarks for The Journal of Hand Surgery
53
54
The Journal of Hand Surgery / Vol. 31A No. 1 January 2006
Figure 1. Three-dimensional computed tomography images were used to determine a plane defined by the distal margins of the articular surface of the radial head. Arrow 1, the central ridge of the coronoid process; arrow 2, the lateral edge of the coronoid process.
insertion of an appropriately sized radial head prosthesis.
ridge) (Fig. 1) and the lateral edge of the coronoid articular surface (the most proximal aspect of the proximal radial ulnar joint) (Fig. 1) were measured with imaging software (OSIRIS Imaging Software; Digital Imaging Unit, University Hospital of Geneva, Switzerland). Negative values indicate the radial head is proximal to the central ridge and lateral edge of the coronoid; positive values indicate the radial head is distal. Although the software is accurate to 0.1 mm the selection of planes and measurement points is somewhat subjective; therefore, 2 observers performed all of the measurements to evaluate the interobserver reliability of the technique. Each observer repeated the measurements 3 times at 2-week intervals to evaluate the intraobserver reliability. With 80% power the sample size of 17 elbows allowed a degree of accuracy of detecting a difference of 1 mm in coronoid height and lateral edge measurements based on assuming an SD of 1 mm across the trials (effect size ⫽ 1) using the F-test in repeated-measures analysis of variance (ANOVA) (version 5.0, nQuery Advisor; Statistical Solutions, Boston, MA). Statistical Methods The Pearson product-moment correlation coefficient (r) was used to measure the level of intraobserver and interobserver reliability. Correlations between 0.70
Materials and Methods Seventeen computed tomography scans of the elbow were analyzed. This represents a single year’s consecutive set of scans obtained for the routine patient care of an isolated fracture of the distal humerus in a skeletally mature patient. There were 8 females and 9 males with an average age of 44 years (range, 15– 84 y). A protocol for the use of these scans was approved by the Human Research Committee. Image manipulation was performed (Vitrea 2 software; Vital Images, Inc., Plymouth, MN). For each patient 3-dimensional computed tomography images were used to determine a plane defined by the margins of the articular surface of the radial head (Fig. 1). A 2-dimensional image was created in a plane orthogonal to the articular surface of the radial head. The rotation of the plane was selected so that it connected 2 points: (1) a point at the center of the radial head (where lines representing the major and minor diameters of the somewhat elliptical radial head cross) and (2) a point on the central ridge of the coronoid at a point representing 50% of the total height of the coronoid process (Fig. 2). By using this image the distance between the plane of the articular surface of the radial head and parallel planes at the most proximal aspect of the coronoid (the central
Figure 2. A 2-dimensional image was created in a plane orthogonal to the articular surface of the radial head. The rotation of the plane was selected so that it connected 2 points: (1) a point at the center of the radial head (where lines representing the major and minor diameters of the somewhat elliptical radial head cross) and (2) a point on the central ridge of the coronoid at a point representing 50% of the total height of the coronoid process.
Doornberg et al / Radial Head Prosthesis Size
55
and 0.89 were regarded as good and r values of 0.90 or greater were considered excellent. Because 3 trials were performed for each observer to determine the distance from the radial head to the central ridge and the lateral edge on the coronoid process of the ulna, repeated-measures ANOVA was applied and the Greenhouse-Geisser F-test was used to indicate whether the measurements between trials were consistent or if they had significant variability. A 95% confidence interval was constructed based on each observer’s 3 trials. Two-tailed p values of less than .05 were regarded as statistically significant. Statistical analysis was performed with statistical software (SPSS version 12.0; SPSS Inc., Chicago, IL).
Results Reliability of Measurements There was good to excellent intraobserver reliability for both observers 1 and 2. Pearson moment correlations for intraobserver agreement showed an average r value of 0.93 among the 3 trials for coronoid height and an r value of 0.89 for lateral edge (p ⬍ .001). With respect to interobserver reliability the average correlation was an r value of 0.91 for the coronoid height (excellent reliability) and an r value of 0.79 for agreement between observers with respect to lateral edge measurements (good reliability). Measurements The distance between the parallel planes defined by the articular surface of the radial head and the central ridge of the coronoid process of the ulna averaged 0.8 mm (SD ⫾ 0.7; range, -0.8 to 2.0 mm) for observer 1 and 0.8 mm (SD ⫾ 0.8; range, -1.3 to 2.2 mm) for observer 2. The negative value indicates that the plane defined by the articular surface of the radial head was proximal to the coronoid ridge (Fig. 3). The distance between the parallel planes at the articular surface of the radial head and the lateral edge of the coronoid process averaged -0.9 mm (SD ⫾ 0.7; range, -2.7 to 0.4 mm) for observer 1 and -0.9 mm (SD ⫾ 0.8; range, -2.8 to 0.5 mm) for observer 2. These values indicate that the radial head is more proximal than the lateral edge of the coronoid in all but 1 case for observer 1 (distance ⫽ ⫹0.1 mm) and in 3 cases for observer 2 (distance ⫽ ⫹0.1, ⫹0.1, ⫹0.2 mm) but to a variable degree (Fig. 4). The F-tests in repeated-measures ANOVA indicated no significant differences in these measurements for both observers at both measurement times.
Discussion Prosthetic replacement of the radial head now is commonplace. Many fractures of the radial head cannot be constructed, and the results of open reduc-
Figure 3. (A) The central ridge of the coronoid process was more proximal than the plane defined by the articular surface of the radial head in most cases (positive value of the measurement). (B) A negative value indicates that the plane defined by the articular surface of the radial head was proximal to the coronoid ridge; this was observed in a few patients.
tion and internal fixation of very complex fractures are poor and unpredictable.4,9,10 Given the importance of contact between the radial head and the capitellum to the stability of the elbow and forearm after a fracture– dislocation, surgeons have become wary of silicone rubber implants and complex surgical repairs prone to early failure and metal prostheses have gained popularity.2,6,11–13 The described techniques for inserting metal prostheses recommend sizing the prosthesis based on the resected head fragments or the radial length14 –16; however, no guidelines are suggested for preventing the placement of a prosthesis that is too thick. The insertion of a prosthesis that is too thick can lead to subluxation of the ulnohumeral joint and capitellar wear, both of which may contribute to pain, synovitis, and restricted motion.8 The suggestion to insert the largest prosthesis that will fit may be suitable in the biomechanics laboratory7 but is not appropriate clinically, particularly in patients with associated el-
56
The Journal of Hand Surgery / Vol. 31A No. 1 January 2006
Figure 4. (A) The radial head is more proximal than the lateral edge of the coronoid in most cases as indicated by a negative value. (B) In 2 cases the lateral edge of the coronoid process was slightly more proximal as indicated by a positive value.
bow ligament injuries in whom the instability of the elbow easily will accommodate the insertion of a thick, oversized prosthesis. Studies of the size and shape of the radial head17–22 have focused on the anatomic features of the native radial head for the purposes of prosthesis design.20,21 The excised radial head is available in patients who have arthroplasty for acute fractures for appropriate sizing of the prosthetic head but original radial length is hard to estimate and restore, especially in more comminuted fractures. A common error is to measure the thickness of the prosthesis on the thickest portion of the radial head (the part with the greatest amount of the radial neck on it). Because the prosthesis will rest on the most proximal extension of the neck this technique will result in overstuffing of the joint unless the
neck is planed to the lowest portion of the neck fracture—something that is not performed routinely. Our data indicate that the plane defined by the edges of the proximal articular surface of the radial head is proximal to the lateral edge of the coronoid process in almost all patients but there is substantial variability between patients. The central ridge of the coronoid process may not be as useful a guide for prosthesis size because this point is distal to the proximal articular surface of the radial head in a substantial percentage of patients and also shows substantial variation. Precise restoration of the relative length of the radial head with respect to the coronoid process may need to be patient specific. The contralateral elbow might be useful as a guide for appropriate size but we have not evaluated whether these measurements are consistent in the contralateral arm of the patient. These represent specific measurements made on the computed tomography scans. The technique and area measured and the inability to account for variations in cartilage thickness may limit the usefulness of the measurements clinically; however, we believe that these factors will have a relatively limited influence. Based on shared clinical experience we prefer to err toward a slightly short prosthesis because such prostheses are likely to provide adequate stability while avoiding the problems associated with excessively thick prostheses. Based on our data a good guideline for most patients is to place the prosthesis so that the plane created by the edges of the proximal articular surface roughly is even with the lateral edge of the coronoid process. To avoid overstuffing the elbow joint with an excessively thick radial head prosthesis the surgeon should use the excised radial head fragments (with care taken not to overestimate thickness based on the thickest portion of the head), assess the relationship between the proximal articular surface of the prosthesis and the lateral edge of the coronoid at the lesser sigmoid notch, and perform intraoperative image intensification to examine this relationship and any malalignment of the ulnohumeral joint in the anteroposterior view or substantial changes in ulnar variance at the wrist. Received for publication December 21, 2004; accepted in revised form June 17, 2005. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Supported by an unrestricted research grant from the AO Foundation and Wright Medical, Inc. Corresponding author: David Ring, MD, Orthopaedic Hand and Upper Extremity Service, Massachusetts General Hospital, Yawkey Center, Suite 2100, 55 Fruit St, Boston, MA 02114; e-mail: [email protected]. Copyright © 2006 by the American Society for Surgery of the Hand 0363-5023/06/31A01-0010$32.00/0 doi:10.1016/j.jhsa.2005.06.012
Doornberg et al / Radial Head Prosthesis Size
References 1. Schneeberger AG, Sadowski MM, Jacob HA. Coronoid process and radial head as posterolateral rotatory stabilizers of the elbow. J Bone Joint Surg 2004;86A:975–982. 2. Moro JK, Werier J, MacDermid JC, Patterson SD, King GJ. Arthroplasty with a metal radial head for unreconstructible fractures of the radial head. J Bone Joint Surg 2001;83A: 1201–1211. 3. Ashwood N, Bain GI, Unni R. Management of Mason typeIII radial head fractures with a titanium prosthesis, ligament repair, and early mobilization. J Bone Joint Surg 2004;86A: 274 –280. 4. Ring D, Quintero J, Jupiter JB. Open reduction and internal fixation of fractures of the radial head. J Bone Joint Surg 2002;84A:1811–1815. 5. Gupta GG, Lucas G, Hahn DL. Biomechanical and computer analysis of radial head prostheses. J Shoulder Elbow Surg 1997;6:37– 48. 6. Morrey BF, Askew L, Chao EY. Silastic prosthetic replacement for the radial head. J Bone Joint Surg 1981;63A:454 – 458. 7. Markolf KL, Tejwani SG, O’Neil G, Benhaim P. Loadsharing at the wrist following radial head replacement with a metal implant. A cadaveric study. J Bone Joint Surg 2004;86A:1023–1030. 8. Van Riet RP, Van Glabbeek F, Verborgt O, Gielen J. Capitellar erosion caused by a metal radial head prosthesis. A case report. J Bone Joint Surg 2004;86A:1061–1064. 9. Heim U. Surgical treatment of radial head fracture. Z Unfallchir Versicherungsmed 1992;85:3–11. 10. King GJ, Evans DC, Kellam JF. Open reduction and internal fixation of radial head fractures. J Orthop Trauma 1991;5: 21–28. 11. Harrington IJ, Sekyi-Otu A, Barrington TW, Evans DC, Tuli V. The functional outcome with metallic radial head implants in the treatment of unstable elbow fractures: a longterm review. J Trauma 2001;50:46 –52.
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