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Editorial Commentary: Fixation of Soft-Tissue Anterior Cruciate Ligament Grafts in Osteoporotic Bone
Editorial Commentary: Fixation of Soft-Tissue Anterior Cruciate Ligament Grafts in Osteoporotic Bone Robert A. Pedowitz, M.D., Ph.D.
Abstract: Tibial-side fixation of soft-tissue grafts in osteoporotic bone has become an important concern, as anterior cruciate ligament reconstruction indications push toward older patients. Although soft-tissue fixation with an interference screw and cortical button may be statistically stronger than graft fixation with a screw or button alone, this hybrid construct is probably not optimized from a clinical perspective.
See related article on page 1694
S
o, what is the question? Is it statistically better? Is it a clinical improvement? Is it optimized for your patients? These are important considerations when extrapolating from biomechanical studies to real-life clinical decision making. Domnick, Herbort, Raschke, Habermann, Schliemann, Petersen, and Weimann,1 in an article entitled “Anterior Cruciate Ligament Soft Tissue Graft Fixation in the ElderlydIs There a Reason to Use Interference Screws?,” address the topic of tibial-side fixation for osteoporotic bone during anterior cruciate ligament (ACL) reconstruction using soft-tissue grafts. As they correctly note, this is an important issue because an increasing percentage of ACL reconstructions are being performed in older and/or female patients, in whom bone mineral density can significantly affect fixation strength. It is also a controversial concern because there are many graft choices and fixation options, and simple interference screw fixation remains a popular and convenient alternative. It must be emphasized that the vast majority of biomechanical data pertaining to ACL fixation come from research in normal bone (or similar surrogates), and virtually all randomized prospective clinical studies of ACL graft fixation have been performed in younger patient
University of California, Los Angeles The author reports the following potential conflict of interest or source of funding: Virtamed. Consultant and employee. Full ICMJE author disclosure forms are available for this article online, as supplementary material. Ó 2017 by the Arthroscopy Association of North America 0749-8063/17408/$36.00 http://dx.doi.org/10.1016/j.arthro.2017.03.032
populations. There is little to go on when it comes to graft fixation for soft bone. Domnick et al.1 show that fixation of soft-tissue grafts in osteoporotic tibial bone is statistically better with hybrid fixation (interference screws plus an extracortical button) compared with interference fixation alone or extracortical button fixation alone. They should be congratulated for their biomechanical design, which included single load-to-failure testing and a cyclic loading protocol. Their methods and analyses were clear. But did they ask the right questions, and can we extrapolate the data? Let us dig in. With single load-to-failure testing, the best construct (hybrid fixation) had a yield load of 283.4 86.9 N and a maximum load of 407.9 102.3 N.1 As the authors note, these mean failure loads were below the typical ACL graft loads to be expected during postoperative activities of daily living (ADL), estimated to be about 450 N.2 Given the substantial variability of the data (reflected by the large standard deviations), a very high percentage of these constructs failed way below anticipated postoperative ADL graft loads. The cyclic loading data were even more concerning. After 2,000 cycles of progressive loading (to a maximum of 100 N), displacement of the hybrid fixation constructs at the yield load was 12.9 2.7 mm! I assume that the yield load was lower after the cyclic loading protocol than after a single pull to failure, although it was not delineated in the article. It does not matter much for the point I am trying to make. After 2,000 cycles (not a large number of cycles compared with what would be expected postoperatively prior to graft incorporation) with a very low cyclic load (no more than 100 N), a
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 33, No 9 (September), 2017: pp 1701-1702
1701
1702
EDITORIAL COMMENTARY
below-ADL yield load was associated with displacement that correlates with complete graft failure. Was the construct clinically sufficient? I do not think so, even for the best construct in the study by Domnick et al.1 Reviewing this article induced some déjà vu because I came to similar conclusions after publication of a relevant biomechanical study about 10 years ago.3 In that study, we evaluated characteristics of soft-tissue grafts fixed with interference screws in hard porcine bone as a function of loading angle relative to the femoral graft socket. Grafts were cyclically loaded to 150 N for 200 cycles and then loaded to failure. Under in-line loading conditions (similar to tibial graft fixation conditions in vivo), load to failure averaged 285.7 69.1 N. I was surprised by our data because other studies showed higher loads to failure for soft-tissue grafts fixed with interference screws. But our laboratory findings changed my clinical practice. I shifted to alternatives for soft-tissue graft fixation on the tibial side, using an interference screweandesheath combination4 or an interference screw backed up with a bone staple or a cortical screw with a washer. I became much more concerned about soft-tissue fixation in softer bone, as data emerged about the subject5 and we began to push our ACL reconstruction indications into the later decades. And it just did not feel solid. So, déjà vu. Back to the questions. Is this surgical technique optimized for individual patients? Domnick et al.1 suggest that we consider a change in the postoperative rehabilitation protocol to protect soft-tissue grafts fixed with screw-plus-button fixation. I infer this means crutches and/or a brace for 12 weeks, until the soft tissue incorporates within the bone tunnel, but I doubt this would be well received by most patients and surgeons. Given what we know about patient compliance with our rehabilitation instructions, this probably would not be a reliable solution for inadequate fixation. An alternative was stronger suture for attachment to the button because the failure mode was always breakage of the No. 2 polyethylene suture. This is probably a good idea. It would have been nice to include data so that we would know if it makes a clinically relevant difference in construct performance. But in my opinion, the strongest recommendation would be to avoid soft-tissue ACL graft fixation in osteoporotic tibial bone with any of the constructs studied by Domnick et al.1 Why use a construct that has a mean failure load below ADL loads when there are viable alternatives? Tibial soft-tissue graft fixation can be enhanced by interference screwesheath combinations, distal cortical screws with soft-tissue or suturepost washers, or cortical staples, although there are
few data about these options for osteoporotic bone, specifically. Admittedly, some of these implants can be a nuisance under the skin and may require later removal. But is this not preferable to a complete loss of graft fixation? Another option would be to perform reconstruction in older patients with bone-ligamentbone allograft or autograft fixed with interference screws to achieve bone-bone interlocking. Clinical outcomes, specifically in patients with osteoporosis, are needed so that we can understand the clinical impact of these surgical decisions. But my intuition (Level VI evidence) tells me that there must be stronger fixation alternatives for osteoporotic tibial bone than those described in the current study. To summarize: Are the findings of this study statistically significant? Yes. Is it clinically sufficient to use an interference screw plus cortical button with No. 2 polyethylene suture for soft-tissue grafts in the setting of soft tibial bone? Maybe not. The data suggest that it is a risky proposition with routine ACL rehabilitation. What is the optimal graft fixation method for ACL reconstruction in patients with osteoporosis? We cannot say from this study. But the authors raise an important clinical question that deserves our attention.1
References 1. Domnick C, Herbort M, Raschke MJ, et al. Anterior cruciate ligament soft tissue graft fixation in the elderly: Is there a reason to use interference screws? A human cadaver study. Arthroscopy 2017;33:1694-1700. 2. Noyes FR, Butler DL, Grood ES, Zernicke RF, Hefzy MS. Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions. J Bone Joint Surg Am 1984;66:344-352. 3. Zhang AL, Lewicky YM, Oka R, Mahar A, Pedowitz R. Biomechanical analysis of femoral tunnel pull-out angles for anterior cruciate ligament reconstruction with bioabsorbable and metal interference screws. Am J Sports Med 2007;35:637-642. 4. Kousa P, Järvinen TL, Vihavainen M, Kannus P, Järvinen M. The fixation strength of six hamstring tendon graft fixation devices in anterior cruciate ligament reconstruction. Part II: Tibial site. Am J Sports Med 2003;31: 182-188. 5. Brand JC Jr, Pienkowski D, Steenlage E, Hamilton D, Johnson DL, Caborn DN. Interference screw fixation strength of a quadrupled hamstring tendon graft is directly related to bone mineral density and insertion torque. Am J Sports Med 2000;28:705-710.
Abstract: Tibial-side fixation of soft-tissue grafts in osteoporotic bone has become an important concern, as anterior cruciate ligament reconstruction indications push toward older patients. Although soft-tissue fixation with an interference screw and cortical button may be statistically stronger than graft fixation with a screw or button alone, this hybrid construct is probably not optimized from a clinical perspective.
See related article on page 1694
S
o, what is the question? Is it statistically better? Is it a clinical improvement? Is it optimized for your patients? These are important considerations when extrapolating from biomechanical studies to real-life clinical decision making. Domnick, Herbort, Raschke, Habermann, Schliemann, Petersen, and Weimann,1 in an article entitled “Anterior Cruciate Ligament Soft Tissue Graft Fixation in the ElderlydIs There a Reason to Use Interference Screws?,” address the topic of tibial-side fixation for osteoporotic bone during anterior cruciate ligament (ACL) reconstruction using soft-tissue grafts. As they correctly note, this is an important issue because an increasing percentage of ACL reconstructions are being performed in older and/or female patients, in whom bone mineral density can significantly affect fixation strength. It is also a controversial concern because there are many graft choices and fixation options, and simple interference screw fixation remains a popular and convenient alternative. It must be emphasized that the vast majority of biomechanical data pertaining to ACL fixation come from research in normal bone (or similar surrogates), and virtually all randomized prospective clinical studies of ACL graft fixation have been performed in younger patient
University of California, Los Angeles The author reports the following potential conflict of interest or source of funding: Virtamed. Consultant and employee. Full ICMJE author disclosure forms are available for this article online, as supplementary material. Ó 2017 by the Arthroscopy Association of North America 0749-8063/17408/$36.00 http://dx.doi.org/10.1016/j.arthro.2017.03.032
populations. There is little to go on when it comes to graft fixation for soft bone. Domnick et al.1 show that fixation of soft-tissue grafts in osteoporotic tibial bone is statistically better with hybrid fixation (interference screws plus an extracortical button) compared with interference fixation alone or extracortical button fixation alone. They should be congratulated for their biomechanical design, which included single load-to-failure testing and a cyclic loading protocol. Their methods and analyses were clear. But did they ask the right questions, and can we extrapolate the data? Let us dig in. With single load-to-failure testing, the best construct (hybrid fixation) had a yield load of 283.4 86.9 N and a maximum load of 407.9 102.3 N.1 As the authors note, these mean failure loads were below the typical ACL graft loads to be expected during postoperative activities of daily living (ADL), estimated to be about 450 N.2 Given the substantial variability of the data (reflected by the large standard deviations), a very high percentage of these constructs failed way below anticipated postoperative ADL graft loads. The cyclic loading data were even more concerning. After 2,000 cycles of progressive loading (to a maximum of 100 N), displacement of the hybrid fixation constructs at the yield load was 12.9 2.7 mm! I assume that the yield load was lower after the cyclic loading protocol than after a single pull to failure, although it was not delineated in the article. It does not matter much for the point I am trying to make. After 2,000 cycles (not a large number of cycles compared with what would be expected postoperatively prior to graft incorporation) with a very low cyclic load (no more than 100 N), a
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 33, No 9 (September), 2017: pp 1701-1702
1701
1702
EDITORIAL COMMENTARY
below-ADL yield load was associated with displacement that correlates with complete graft failure. Was the construct clinically sufficient? I do not think so, even for the best construct in the study by Domnick et al.1 Reviewing this article induced some déjà vu because I came to similar conclusions after publication of a relevant biomechanical study about 10 years ago.3 In that study, we evaluated characteristics of soft-tissue grafts fixed with interference screws in hard porcine bone as a function of loading angle relative to the femoral graft socket. Grafts were cyclically loaded to 150 N for 200 cycles and then loaded to failure. Under in-line loading conditions (similar to tibial graft fixation conditions in vivo), load to failure averaged 285.7 69.1 N. I was surprised by our data because other studies showed higher loads to failure for soft-tissue grafts fixed with interference screws. But our laboratory findings changed my clinical practice. I shifted to alternatives for soft-tissue graft fixation on the tibial side, using an interference screweandesheath combination4 or an interference screw backed up with a bone staple or a cortical screw with a washer. I became much more concerned about soft-tissue fixation in softer bone, as data emerged about the subject5 and we began to push our ACL reconstruction indications into the later decades. And it just did not feel solid. So, déjà vu. Back to the questions. Is this surgical technique optimized for individual patients? Domnick et al.1 suggest that we consider a change in the postoperative rehabilitation protocol to protect soft-tissue grafts fixed with screw-plus-button fixation. I infer this means crutches and/or a brace for 12 weeks, until the soft tissue incorporates within the bone tunnel, but I doubt this would be well received by most patients and surgeons. Given what we know about patient compliance with our rehabilitation instructions, this probably would not be a reliable solution for inadequate fixation. An alternative was stronger suture for attachment to the button because the failure mode was always breakage of the No. 2 polyethylene suture. This is probably a good idea. It would have been nice to include data so that we would know if it makes a clinically relevant difference in construct performance. But in my opinion, the strongest recommendation would be to avoid soft-tissue ACL graft fixation in osteoporotic tibial bone with any of the constructs studied by Domnick et al.1 Why use a construct that has a mean failure load below ADL loads when there are viable alternatives? Tibial soft-tissue graft fixation can be enhanced by interference screwesheath combinations, distal cortical screws with soft-tissue or suturepost washers, or cortical staples, although there are
few data about these options for osteoporotic bone, specifically. Admittedly, some of these implants can be a nuisance under the skin and may require later removal. But is this not preferable to a complete loss of graft fixation? Another option would be to perform reconstruction in older patients with bone-ligamentbone allograft or autograft fixed with interference screws to achieve bone-bone interlocking. Clinical outcomes, specifically in patients with osteoporosis, are needed so that we can understand the clinical impact of these surgical decisions. But my intuition (Level VI evidence) tells me that there must be stronger fixation alternatives for osteoporotic tibial bone than those described in the current study. To summarize: Are the findings of this study statistically significant? Yes. Is it clinically sufficient to use an interference screw plus cortical button with No. 2 polyethylene suture for soft-tissue grafts in the setting of soft tibial bone? Maybe not. The data suggest that it is a risky proposition with routine ACL rehabilitation. What is the optimal graft fixation method for ACL reconstruction in patients with osteoporosis? We cannot say from this study. But the authors raise an important clinical question that deserves our attention.1
References 1. Domnick C, Herbort M, Raschke MJ, et al. Anterior cruciate ligament soft tissue graft fixation in the elderly: Is there a reason to use interference screws? A human cadaver study. Arthroscopy 2017;33:1694-1700. 2. Noyes FR, Butler DL, Grood ES, Zernicke RF, Hefzy MS. Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions. J Bone Joint Surg Am 1984;66:344-352. 3. Zhang AL, Lewicky YM, Oka R, Mahar A, Pedowitz R. Biomechanical analysis of femoral tunnel pull-out angles for anterior cruciate ligament reconstruction with bioabsorbable and metal interference screws. Am J Sports Med 2007;35:637-642. 4. Kousa P, Järvinen TL, Vihavainen M, Kannus P, Järvinen M. The fixation strength of six hamstring tendon graft fixation devices in anterior cruciate ligament reconstruction. Part II: Tibial site. Am J Sports Med 2003;31: 182-188. 5. Brand JC Jr, Pienkowski D, Steenlage E, Hamilton D, Johnson DL, Caborn DN. Interference screw fixation strength of a quadrupled hamstring tendon graft is directly related to bone mineral density and insertion torque. Am J Sports Med 2000;28:705-710.