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flexion strength,2,3 and our study also demonstrated no difference between patients whose BR was released or preserved in terms of elbow flexion strength.1 Consequently, we believe that although the BR is repaired after release, this cannot provide more elbow flexion strength than an intact BR. Third, the author stated that BR repair is required for repair of the pronator quadratus (PQ). However, it is difficult to repair the PQ at the radial septum of the radius despite BR repair, because the muscle fascia of the PQ is not strong enough to hold sutures.4 In addition, some studies have shown that PQ repair after volar plate fixation of DRF provided no functional advantage in terms of wrist range of motion, grip strength, and Disabilities of the Hand, Arm, and Shoulder score and visual analog score at 1 year.5,6 The author also mentioned that PQ repair is necessary to prevent flexor tendon complications after volar plate fixation of DRF; however, this is not supported by published evidence. Although we usually do not repair the PQ, we have rarely encountered flexor tendon complications.1 On the other hand, those who routinely repair the PQ still report flexor tendon complications.7,8 Based on a literature review, we believe that flexor tendon complications after volar plate fixation of DRF are not related to PQ repair, but rather to plate position and prominence.6,9 It is reasonable for the author to be concerned regarding nonrepair of the BR after its release during volar plate fixation of DRF, because the need for such repair remains debatable. We hope that further biomechanical studies and randomized clinical trials will address and resolve this issue.
Jae Kwang Kim, MD, PhD Department of Orthopedic Surgery Ewha Womans University, School of Medicine Seoul, South Korea http://dx.doi.org/10.1016/j.jhsa.2015.02.023 REFERENCES 1. Kim JK, Park JS, Shin SJ, Bae H, Kim S-Y. The effect of brachioradialis release during distal radius fracture fixation on elbow flexion strength and wrist function. J Hand Surg Am. 2014;39(11): 2246e2250. 2. Murray WM, Delp SL, Buchanan TS. Variation of muscle moment arms with elbow and forearm position. J Biomech. 1995;28(5): 513e525. 3. Tirrell TF, Franko OI, Bhola S, Hentzen ER, Abrams RA, Lieber RL. Functional consequence of distal brachioradialis tendon release: a biomechanical study. J Hand Surg Am. 2013;38(5):920e926. 4. Nho JH, Gong HS, Song CH, Wi SM, Lee YH, Baek GH. Examination of the pronator quadratus muscle during hardware removal procedures after volar plating for distal radius fractures. Clin Orthop Surg. 2014;6(3):267e272. 5. Hershman SH, Immerman I, Bechtel C, Lekic N, Paksima N, Egol KA. The effects of pronator quadratus repair on outcomes after volar plating of distal radius fractures. J Orthop Trauma. 2013;27(3): 130e133. 6. Tosti R, Ilyas AM. Prospective evaluation of pronator quadratus repair following volar plate fixation of distal radius fractures. J Hand Surg Am. 2013;38(9):1678e1684. 7. Arora R, Lutz M, Hennerbichler A, Krappinger D, Espen D, Gabl M. Complications following internal fixation of unstable distal radius fracture with a palmar locking-plate. J Orthop Trauma. 2007;21(5): 316e322. 8. Soong M, Earp BE, Bishop G, Leung A, Blazar P. Volar locking plate implant prominence and flexor tendon rupture. J Bone Joint Surg Am. 2011;93(4):328e335. 9. White BD, Nydick JA, Karsky D, Williams BD, Hess AV, Stone JD. Incidence and clinical outcomes of tendon rupture following distal radius fracture. J Hand Surg Am. 2012;37(10): 2035e2040.
Letter Regarding “Radiocapitellar Joint Contact Pressures Following Radial Head Arthroplasty” flexion angles in the Zero group (RH replaced at correct length) compared with those in the native RH group. This suggests a spurious finding due to experimental technique. Three experimental studies2e4 have reported less favorable contact mechanics after RH replacement and all 3 have shown that RH replacement results in decreased contact areas and increased contact pressures. One of the studies3 specifically used the same prosthesis as in the current study. Sahu et al.2 showed elevated contact pressures correlates with these decreased contact areas. A study of our own6 has confirmed the findings of those 3 prior reports in this regard.
To the Editor: Cohn and colleagues report the experimental effects of altering the “length” of the radius when replacing the radial head (RH).1 They concluded that 2 mm of radial lengthening is acceptable because it does not significantly increase radiocapitellar contact pressures. For several reasons we think they may have arrived at the wrong conclusion. First, they compared the contact pressures of the “Plus 2” group (prosthetic RH overstuffed by 2 mm) to those of the native RH group. However, Figures 2 and 3 show that there was a consistent trend toward lower mean and maximum contact pressures at all J Hand Surg Am.
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Second, we know from the work of van Glabbeek et al5 that 2.5 mm of lengthening of the radial neck while maintaining the native RH causes a significant increase in radiocapitellar contact pressure. Third, our own studies6 have shown that the Evolve RH prosthesis (Wright Medical Inc., Arlington, TN) that was reported by the authors typically has 2 areas of contact—one fairly centrally and another along its ridge where it makes contact with the lateral trochlear ridge. This latter area typically has abnormally high contact pressures with the Evolve RH prosthesis, and could possibly have gone unrecorded with a single Tekscan 6900 film (Tekscan Inc., South Boston, MA) used as described by the authors. The Tekscan 6900 film covers only 192 mm2, which is insufficient to record contact pressures over the whole Evolve RH (an averaged sized RH of 24 mm has a surface area of 450 mm2). To measure contact over all (or almost all) of the RH one must either use 2 Tekscan 6900 films simultaneously or a larger film (eg, Tekscan 4000, which covers 920 mm2). Fourth, we come to the opposite conclusion using the data reported by the authors. When compared with the Zero group (prosthetic radial head inserted at correct length), the Plus 2 group (prosthetic RH overstuffed by 2 mm) showed significantly higher mean (P ¼ .004) and maximum contact (P ¼ .004) pressures at all flexion angles (Figs. 2 and 3, and Table 1). We recommend correction of the concluding statements made in the abstract and discussion that “up to 2 mm of overlengthening may be tolerated . . . without significantly increasing contact pressure of the radiocapitellar joint”.
3. Liew VS, Cooper IC, Ferreira LM, Johnson JA, King GJ. The effect of metallic radial head arthroplasty on radiocapitellar joint contact area. Clin Biomech (Bristol, Avon). 2003;18(2):115e118. 4. Moungondo F, El Kazzi W, van Riet R, Feipel V, Rooze M, Schuind F. Radiocapitellar joint contacts after bipolar radial head arthroplasty. J Shoulder Elbow Surg. 2010;19(2):230e235. 5. van Glabbeek F, van Riet RP, Baumfeld JA, et al. Detrimental effects of overstuffing or understuffing with a radial head replacement in the medial collateral-ligament deficient elbow. J Bone Joint Surg Am. 2004;86(12):2629e2635. 6. Bachman DR, Thaveepunsan S, Park S, Fitzsimmons JS, An KN, O’Driscoll SW. The effect of prosthetic radial head geometry on the distribution and magnitude of radiocapitellar joint contact pressures. J Hand Surg Am. 2015;40(2):281e288.
In Reply: We thank you for your attention to our study and below are comments to the critique regarding our study. First, we will not correct our concluding statement that “up to 2 mm of over-lengthening may be tolerated.without significantly increasing contact pressures of the radiocapitellar joint”.1 We arrived at this conclusion by examining the native elbow mean and maximum pressures, which showed no statistical significance compared with the “Zero” or “Plus 2” group (Table 1 and Figs. 2 and 3 in original article). The fact that there is a statistically significant increase between the Zero and Plus 2 group is clinically irrelevant because in surgery we replace the patient’s native radiocapitellar joint with a prosthesis and the critique uses our data to extrapolate a clinical situation where a surgeon would replace an already implanted prosthesis to a larger size. As the critique points out, prosthetic implants do not articulate like the native joint and provide an uneven distribution of pressure across the radiocapitellar joint as compared with the native joint. Second, our biomechanical study design was performed in a consistent manner to make any errors equal throughout the data collection process. Although not a perfect model, no biomechanical model can replicate exactly what occurs in vivo. Yes, we could have used a larger Tekscan film to capture a larger area, but we felt that what we used was sufficient in collecting useful data. In addition, van Glabbeek et al2 showed that 2.5 mm of lengthening showed increased pressures and we are sure we would have seen the same if, say, a Plus 3, Plus 4, ad infinitum prosthesis would have been tested—but that was not done. No study is without design flaws and ours is no exception. Our study offers the orthopedic surgeon useful information that they can use in making an educated
Shawn W. O’Driscoll, PhD, MD Daniel R. Bachman, MD Department of Orthopedics Mayo Clinic Rochester, MN http://dx.doi.org/10.1016/j.jhsa.2014.12.048 This work was supported by the Mayo Foundation. S.W.O. receives royalties from Acumed, Aircast, and Tornier. Neither author nor their immediate families has received any financial payments or other benefits from any commercial entity for the preparation of this letter.
REFERENCES 1. Cohn M, Glait SA, Sapienza A, Kwon YW. Radiocapitellar joint contact pressures following radial head arthroplasty. J Hand Surg Am. 2014;39(8):1566e1571. 2. Sahu D, Holmes DM, Fitzsimmons JS, et al. Influence of radial head prosthetic design on radiocapitellar joint contact mechanics. J Shoulder Elbow Surg. 2014;23(4):456e462.
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LETTERS TO THE EDITOR
flexion strength,2,3 and our study also demonstrated no difference between patients whose BR was released or preserved in terms of elbow flexion strength.1 Consequently, we believe that although the BR is repaired after release, this cannot provide more elbow flexion strength than an intact BR. Third, the author stated that BR repair is required for repair of the pronator quadratus (PQ). However, it is difficult to repair the PQ at the radial septum of the radius despite BR repair, because the muscle fascia of the PQ is not strong enough to hold sutures.4 In addition, some studies have shown that PQ repair after volar plate fixation of DRF provided no functional advantage in terms of wrist range of motion, grip strength, and Disabilities of the Hand, Arm, and Shoulder score and visual analog score at 1 year.5,6 The author also mentioned that PQ repair is necessary to prevent flexor tendon complications after volar plate fixation of DRF; however, this is not supported by published evidence. Although we usually do not repair the PQ, we have rarely encountered flexor tendon complications.1 On the other hand, those who routinely repair the PQ still report flexor tendon complications.7,8 Based on a literature review, we believe that flexor tendon complications after volar plate fixation of DRF are not related to PQ repair, but rather to plate position and prominence.6,9 It is reasonable for the author to be concerned regarding nonrepair of the BR after its release during volar plate fixation of DRF, because the need for such repair remains debatable. We hope that further biomechanical studies and randomized clinical trials will address and resolve this issue.
Jae Kwang Kim, MD, PhD Department of Orthopedic Surgery Ewha Womans University, School of Medicine Seoul, South Korea http://dx.doi.org/10.1016/j.jhsa.2015.02.023 REFERENCES 1. Kim JK, Park JS, Shin SJ, Bae H, Kim S-Y. The effect of brachioradialis release during distal radius fracture fixation on elbow flexion strength and wrist function. J Hand Surg Am. 2014;39(11): 2246e2250. 2. Murray WM, Delp SL, Buchanan TS. Variation of muscle moment arms with elbow and forearm position. J Biomech. 1995;28(5): 513e525. 3. Tirrell TF, Franko OI, Bhola S, Hentzen ER, Abrams RA, Lieber RL. Functional consequence of distal brachioradialis tendon release: a biomechanical study. J Hand Surg Am. 2013;38(5):920e926. 4. Nho JH, Gong HS, Song CH, Wi SM, Lee YH, Baek GH. Examination of the pronator quadratus muscle during hardware removal procedures after volar plating for distal radius fractures. Clin Orthop Surg. 2014;6(3):267e272. 5. Hershman SH, Immerman I, Bechtel C, Lekic N, Paksima N, Egol KA. The effects of pronator quadratus repair on outcomes after volar plating of distal radius fractures. J Orthop Trauma. 2013;27(3): 130e133. 6. Tosti R, Ilyas AM. Prospective evaluation of pronator quadratus repair following volar plate fixation of distal radius fractures. J Hand Surg Am. 2013;38(9):1678e1684. 7. Arora R, Lutz M, Hennerbichler A, Krappinger D, Espen D, Gabl M. Complications following internal fixation of unstable distal radius fracture with a palmar locking-plate. J Orthop Trauma. 2007;21(5): 316e322. 8. Soong M, Earp BE, Bishop G, Leung A, Blazar P. Volar locking plate implant prominence and flexor tendon rupture. J Bone Joint Surg Am. 2011;93(4):328e335. 9. White BD, Nydick JA, Karsky D, Williams BD, Hess AV, Stone JD. Incidence and clinical outcomes of tendon rupture following distal radius fracture. J Hand Surg Am. 2012;37(10): 2035e2040.
Letter Regarding “Radiocapitellar Joint Contact Pressures Following Radial Head Arthroplasty” flexion angles in the Zero group (RH replaced at correct length) compared with those in the native RH group. This suggests a spurious finding due to experimental technique. Three experimental studies2e4 have reported less favorable contact mechanics after RH replacement and all 3 have shown that RH replacement results in decreased contact areas and increased contact pressures. One of the studies3 specifically used the same prosthesis as in the current study. Sahu et al.2 showed elevated contact pressures correlates with these decreased contact areas. A study of our own6 has confirmed the findings of those 3 prior reports in this regard.
To the Editor: Cohn and colleagues report the experimental effects of altering the “length” of the radius when replacing the radial head (RH).1 They concluded that 2 mm of radial lengthening is acceptable because it does not significantly increase radiocapitellar contact pressures. For several reasons we think they may have arrived at the wrong conclusion. First, they compared the contact pressures of the “Plus 2” group (prosthetic RH overstuffed by 2 mm) to those of the native RH group. However, Figures 2 and 3 show that there was a consistent trend toward lower mean and maximum contact pressures at all J Hand Surg Am.
r
Vol. 40, April 2015
864
LETTERS TO THE EDITOR
Second, we know from the work of van Glabbeek et al5 that 2.5 mm of lengthening of the radial neck while maintaining the native RH causes a significant increase in radiocapitellar contact pressure. Third, our own studies6 have shown that the Evolve RH prosthesis (Wright Medical Inc., Arlington, TN) that was reported by the authors typically has 2 areas of contact—one fairly centrally and another along its ridge where it makes contact with the lateral trochlear ridge. This latter area typically has abnormally high contact pressures with the Evolve RH prosthesis, and could possibly have gone unrecorded with a single Tekscan 6900 film (Tekscan Inc., South Boston, MA) used as described by the authors. The Tekscan 6900 film covers only 192 mm2, which is insufficient to record contact pressures over the whole Evolve RH (an averaged sized RH of 24 mm has a surface area of 450 mm2). To measure contact over all (or almost all) of the RH one must either use 2 Tekscan 6900 films simultaneously or a larger film (eg, Tekscan 4000, which covers 920 mm2). Fourth, we come to the opposite conclusion using the data reported by the authors. When compared with the Zero group (prosthetic radial head inserted at correct length), the Plus 2 group (prosthetic RH overstuffed by 2 mm) showed significantly higher mean (P ¼ .004) and maximum contact (P ¼ .004) pressures at all flexion angles (Figs. 2 and 3, and Table 1). We recommend correction of the concluding statements made in the abstract and discussion that “up to 2 mm of overlengthening may be tolerated . . . without significantly increasing contact pressure of the radiocapitellar joint”.
3. Liew VS, Cooper IC, Ferreira LM, Johnson JA, King GJ. The effect of metallic radial head arthroplasty on radiocapitellar joint contact area. Clin Biomech (Bristol, Avon). 2003;18(2):115e118. 4. Moungondo F, El Kazzi W, van Riet R, Feipel V, Rooze M, Schuind F. Radiocapitellar joint contacts after bipolar radial head arthroplasty. J Shoulder Elbow Surg. 2010;19(2):230e235. 5. van Glabbeek F, van Riet RP, Baumfeld JA, et al. Detrimental effects of overstuffing or understuffing with a radial head replacement in the medial collateral-ligament deficient elbow. J Bone Joint Surg Am. 2004;86(12):2629e2635. 6. Bachman DR, Thaveepunsan S, Park S, Fitzsimmons JS, An KN, O’Driscoll SW. The effect of prosthetic radial head geometry on the distribution and magnitude of radiocapitellar joint contact pressures. J Hand Surg Am. 2015;40(2):281e288.
In Reply: We thank you for your attention to our study and below are comments to the critique regarding our study. First, we will not correct our concluding statement that “up to 2 mm of over-lengthening may be tolerated.without significantly increasing contact pressures of the radiocapitellar joint”.1 We arrived at this conclusion by examining the native elbow mean and maximum pressures, which showed no statistical significance compared with the “Zero” or “Plus 2” group (Table 1 and Figs. 2 and 3 in original article). The fact that there is a statistically significant increase between the Zero and Plus 2 group is clinically irrelevant because in surgery we replace the patient’s native radiocapitellar joint with a prosthesis and the critique uses our data to extrapolate a clinical situation where a surgeon would replace an already implanted prosthesis to a larger size. As the critique points out, prosthetic implants do not articulate like the native joint and provide an uneven distribution of pressure across the radiocapitellar joint as compared with the native joint. Second, our biomechanical study design was performed in a consistent manner to make any errors equal throughout the data collection process. Although not a perfect model, no biomechanical model can replicate exactly what occurs in vivo. Yes, we could have used a larger Tekscan film to capture a larger area, but we felt that what we used was sufficient in collecting useful data. In addition, van Glabbeek et al2 showed that 2.5 mm of lengthening showed increased pressures and we are sure we would have seen the same if, say, a Plus 3, Plus 4, ad infinitum prosthesis would have been tested—but that was not done. No study is without design flaws and ours is no exception. Our study offers the orthopedic surgeon useful information that they can use in making an educated
Shawn W. O’Driscoll, PhD, MD Daniel R. Bachman, MD Department of Orthopedics Mayo Clinic Rochester, MN http://dx.doi.org/10.1016/j.jhsa.2014.12.048 This work was supported by the Mayo Foundation. S.W.O. receives royalties from Acumed, Aircast, and Tornier. Neither author nor their immediate families has received any financial payments or other benefits from any commercial entity for the preparation of this letter.
REFERENCES 1. Cohn M, Glait SA, Sapienza A, Kwon YW. Radiocapitellar joint contact pressures following radial head arthroplasty. J Hand Surg Am. 2014;39(8):1566e1571. 2. Sahu D, Holmes DM, Fitzsimmons JS, et al. Influence of radial head prosthetic design on radiocapitellar joint contact mechanics. J Shoulder Elbow Surg. 2014;23(4):456e462.
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