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A Biomechanical Comparison of Repair Techniques for Anterior Cruciate Ligament Tibial Avulsion Fracture Under Cyclic Loading
A Biomechanical Comparison of Repair Techniques for Anterior Cruciate Ligament Tibial Avulsion Fracture Under Cyclic Loading Harehiko Tsukada, M.D., Yasuyuki Ishibashi, M.D., Eiichi Tsuda, M.D., Yasuharu Hiraga, M.D., and Satoshi Toh, M.D.
Purpose: Although several technical developments for arthroscopic treatment of anterior cruciate ligament (ACL) avulsion fracture have been reported, it remains unclear which fixation technique is most effective to obtain the best initial fixation strength. The objectives of this study were to compare the initial fixation strength in response to a cyclic tensile load between different fixation techniques for ACL avulsion fractures. Type of Study: Cadaveric biomechanical evaluation. Methods: Using 15 fresh-frozen cadaveric human knees, 3 different fixation techniques for noncomminuted ACL avulsion fractures were compared by measuring the anterior tibial translation (ATT) under 500 cycles of 0 to 100 N of anterior tibial load: (1) antegrade screw fixation, (2) retrograde screw fixation, and (3) pullout suture fixation. Results: The increase in the ATT after the cyclic loading for the pullout suture fixation (2.2 ⫾ 0.8 mm) was significantly larger than that for the antegrade screw fixation (1.0 ⫾ 0.2 mm). The ATT increase in the retrograde fixation group (2.0 ⫾ 0.6 mm) was not significantly different compared with the other groups. Conclusions: All methods were effective and there was a slight biomechanical advantage to antegrade screw fixation over pullout suture fixation. Clinical Relevance: Antegrade screw fixation is more effective in obtaining initial rigid fixation than pullout suture fixation for ACL avulsion fractures. Key Words: Anterior cruciate ligament— Avulsion fracture—Biomechanical study—Cyclic loading.
A
vulsion fracture of the tibial attachment of the anterior cruciate ligament (ACL) results in anterior knee instability and occasionally anterior impingement during knee extension, when the avulsion fragment is displaced.1-5 In addition, subsequent histologic degenerative change of the ACL substance caused by the decreased tension has been reported in the chronic course.6 Therefore, immediate anatomic reduction and fixation of the fragment are widely recommended for type III and IV displaced fractures
From the Department of Orthopaedic Surgery, Hirosaki University School of Medicine, Hirosaki, Aomori, Japan. Address correspondence and reprint requests to Harehiko Tsukada, M.D., Department of Orthopaedic Surgery, Hirosaki University School of Medicine, 5 Zaifu-cho, Hirosaki, Aomori 036-8562, Japan. E-mail: [email protected] © 2005 by the Arthroscopy Association of North America 0749-8063/05/2110-3946$30.00/0 doi:10.1016/j.arthro.2005.06.020
as classified by Meyers and McKeever,7 whereas undisplaced or minimal displaced fragment should be treated conservatively.8 Most of the early studies proposed open reduction and internal fixation (ORIF) of the displaced fragment (e.g., Lee’s method9). Recently, several technical developments for arthroscopic reduction and internal fixation (ARIF) have been reported.10-19 ARIF has been classified as pullout suture fixation modified from the Lee’s method and as pin or screw fixation driven in an antegrade or retrograde direction. Although previous studies have reported the successful outcome of primary repair of the avulsion fracture of ACL attachment in children,1,4,20 the outcome in adults varies, and several postoperative complications have been reported. Good and excellent results in adult patients treated with ARIF were reported by Osti et al.17 and Senekovicˇ and Veselko,21 whereas Berg10 and Montgomery et al.22 reported
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 21, No 10 (October), 2005: pp 1197-1201
1197
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H. TSUKADA ET AL. grade screw fixation, (2) retrograde screw fixation, and (3) pullout suture fixation. METHODS
FIGURE 1. flexion.
The testing system with the knee joint at 30° of
postoperative loss of knee motion as the most frequent complication after ARIF. Limited preoperative range of motion and prolonged postoperative immobilization were raised as the risk factors of loss of knee motion.1 Because the necessity of postoperative immobilization greatly depends on the initial strength at the fixation site, rigid fixation of the avulsion fragment of the ACL attachment is the key to reduce the motion complication. However, it remains unclear which fixation technique is most effective to obtain the best initial fixation strength. Therefore, the objectives of this study were to compare the initial fixation strength in response to a cyclic load between 3 different fixation techniques for ACL avulsion fractures: (1) ante-
Fifteen fresh-frozen human cadaveric knees with an age range of 31 to 83 years (mean, 58.6 years) were used for this study. Specimens were stored at ⫺20°C, thawed at room temperature 24 hours before testing, and kept moist with saline irrigation throughout the preparation and mechanical testing.23 Soft-tissue structures were removed to expose the bone, leaving ligaments, capsule, and popliteal muscle and tendon intact. The proximal part of the femur and the distal part of the tibia were placed in molds of polymethylmethacrylate for gripping to test the fixture’s rigidly. The specimen was mounted on the materials testing machine (Instron 4465; Instron Corp, Canton, MA) at 30° of knee flexion and neutral internal-external and varus-valgus rotation, without restricting the other 3 degrees of freedom (anterior-posterior, medial-lateral, and proximal-distal translation) (Fig 1). Before creating the ACL avulsion fracture, the neutral anteriorposterior position of intact knee was determined and used as a reference position throughout the testing. It was defined as the position midway between the 2 zero load points of the load-displacement hysteresis loop by imposing a ⫾50-N drawer cycle. On the testing machine, the tibial eminence, including the whole area of the ACL tibial attachment, was completely isolated from the tibial plateau with an osteotome to produce the type-III fracture with 90° of knee flexion. The bottom of the fragment was made round shaped to mimic the clinical fracture pattern (Fig 2A). Specimens were divided into 3 groups of 5 knees so that the average age of 3 groups would be matched.
FIGURE 2. Illustrations of the repair techniques for ACL avulsion fracture: (A) created ACL avulsion fracture, (B) antegrade screw fixation, (C) retrograde screw fixation, and (D) pullout suture fixation.
BIOMECHANICAL STUDY OF ACL AVULSION FRACTURE Antegrade Screw Fixation After the avulsion fragment was reduced anatomically, a small guide pin was drilled from the center of the avulsion fragment to the posterolateral cortex. The 4-mm diameter titanium cannulated cancellous screw with spiked washer (Depuy ACE, Warsaw, IN) was inserted from the joint surface through the guide pin, penetrating the distal tibial cortex (Fig 2B). Retrograde Screw Fixation The fragment was held using the ACL tibial guide so as not to be displaced or pushed up until completion of the screw insertion. A small guide pin was drilled from the anteromedial cortex to the center of the avulsion fragment, and the titanium cannulated cancellous screw described above was inserted in a retrograde fashion to fix the fragment. The tip of the screw protruded slightly above the joint surface (Fig 2C). Pullout Suture Fixation Two drill holes 2 mm in diameter were created from just medial and lateral of the repositioned fragment to the anteromedial cortex of the proximal tibia. The distal outlet of the 2 drill holes was more than 10 mm apart. Using a 24-gauge wire loop, doubled No. 2 Ethibond suture (Ethicon, Somerville, NJ) was penetrated into the ACL just proximal to the avulsion fragment. Then the wire loop was advanced into each drill hole to pass the doubled suture through the holes. The doubled sutures were pulled out tightly and tied over the tibial bone bridge (Fig 2D). Biomechanical Testing The repaired knee was repositioned at 30° of knee flexion and, throughout the preparation, the knee was kept mounted on the materials testing machine. The repaired knee was subjected to 500 cycles of 0 to 100 N cyclic anterior tibial loads at a crosshead speed of 100 mm/min and load-displacement curve was recorded in 20 Hz of sampling rate. The direction of the load mimics a Lachman test. The loading conditions used in this study were determined based on estimated loads in the ACL graft that had been reported in previous literatures. Morrison24 calculated the mean peak force in the ACL during level walking to be 157 N. Zheng et al.25 calculated the peak force in the ACL to be 142 N during seated knee extension (open chain exercise). Toutoungi et al.26 calculated the mean peak force in the ACL during isokinetic/isometric extension at knee angles of 35° to 40° to be 0.55 ⫻
1199
body weight. The anterior load of 100 N that we selected was intended to mimic early rehabilitation exercises such as continuous passive motion and partial weight bearing. The anterior tibial translation (ATT) in response to an anterior load of 100 N before and after 500 cycles of the loading was determined in reference to the neutral anteroposterior position defined in the intact knee. To quantify the loss of graft fixation, the parameter “laxity increase” introduced by Scheffler et al.27 was determined as the change in the tibial position at load pickup between the first cycle and the last cycle of cyclic loading. The laxity increase is a permanent elongation of the graft constructs and consists of graft slippage from the fixation device and plastic deformation of the linkage materials and knot tightening. In other words, the ATT consists of the laxity increase and the recoverable elongation of the tendon graft itself. Statistical Analysis The increase in the ATT obtained from the 3 different fixation techniques as well as the laxity increase in response to cyclic loading were compared. Based on our data of the first 9 knees (3 knees in each group), a power analysis was performed (power ⫽ 0.80, significance level ⫽ 0.05) so differences of 2 mm for the increase in the ATT could be detected. It was determined that 5 knee specimens in each group were required for this study. We used the Scheffé test for statistical analysis; significance was set at P ⬍ .05. RESULTS The average age of the specimens was 59.8 years (range, 31 to 83 years) for antegrade screw fixation, 60.4 years (range, 41 to 77 years) for retrograde screw fixation, and 55.8 years (range, 31 to 83 years) for pullout suture fixation, representing no statistically significant difference. No macroscopic crack of the fragment or injury of ACL-tibia junction was observed after the testing. Furthermore, no fixation failure such as implant failure or screw backing out was observed. The size of the fragment was consistently 15 ⫻ 15 ⫻ 7 mm throughout the study groups. In all groups, the increase in the ATT was observed after cyclic loading. The increase in the ATT between before and after 500 cycles of the loading in pullout suture fixation (2.2 ⫾ 0.8 mm) was significantly larger than that in antegrade screw fixation (1.0 ⫾ 0.2 mm) (P ⬍ .05). The ATT in retrograde screw fixation increased by 2.0 ⫾ 0.6 mm after the cyclic loading,
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FIGURE 3. Change in ATT and laxity increase of repaired ACL avulsion fractures of the knee during cyclic loading.
which tended to be larger than antegrade screw fixation, although no significant differences were detected compared with the other 2 groups. No significant differences in the laxity increase were detected among groups; however, the laxity increase in pullout suture fixation (1.8 ⫾ 1.0 mm) and retrograde screw fixation (1.7 ⫾ 0.6 mm) tended to be larger than that in antegrade screw fixation (0.9 ⫾ 0.2 mm) (Fig 3). DISCUSSION There are several reports of poor outcomes in ACL tibial avulsion fractures.2,6,7,10,22 Concomitant injury of the ACL substance may result in persistent ACL deficiency, even if anatomic restoration of the avulsion fracture is achieved. The status of the ACL substance should be evaluated using magnetic resonance imaging to determine the ideal treatment. The fixation technique is another issue crucial to the success of primary repair of ACL tibial avulsion.10-19 In this study, after 500 cycles of 0 to 100 N, the ATT for pullout suture fixation was significantly increased compared with antegrade screw fixation. Also, the laxity increase for pullout suture fixation tended to be greater than antegrade screw fixation. This suggests that the laxity that occurred in pullout suture fixation resulted from tightening or slippage at the suture knot or the suture cutting into the tibial bone bridge. Use of a metal wire or larger suture may reduce the risk of these types of fixation failure and contribute to reducing the increase in laxity. In contrast, antegrade screw fixation with a washer was the most effective technique to obtain initial rigid fixation. These results support the successful clinical outcome of antegrade
screw and washer fixation reported by Senekovicˇ et al.21 The increase of the ATT and the laxity increase for retrograde screw fixation tended to be larger than that for antegrade screw fixation. Because the tip of the screw must penetrate into the fragment to obtain rigid fixation in retrograde screw fixation, the use of this fixation technique might be restricted when the fragment is thin or comminuted. There were several limitations in this study. The first was the lack of a quantitative method to evaluate the bone density of the tested specimens, which were from individuals whose average age was relatively old. Osteoporotic bone quality of older human specimens could potentially predispose to failure at the fixation site. The second limitation was that the avulsion fragment was produced en bloc. It was not shown whether repair techniques were effective to obtain rigid fixation for the comminuted fragment. CONCLUSIONS The results of this study show that antegrade screw fixation was more effective to obtain initial rigid fixation than pullout suture fixation for ACL avulsion fractures. Acknowledgment: The authors acknowledge the contribution of Yuji Yamamoto, M.D., and Kan-ichiro Wada, M.D., for data analysis.
REFERENCES 1. Baxter MP, Wiley JJ. Fractures of the tibial spine in children: An evaluation of knee stability. J Bone Joint Surg Br 1988; 70:228-230. 2. Kendall NS, Hsu SYC, Chan K. Fracture of tibial spine in adults and children. J Bone Joint Surg Br 1992;74:848-852. 3. Keys GW, Walters J. Nonunion of intercondylar eminence fracture of the tibia. J Trauma 1988;28:870-871. 4. Wiley JJ, Baxter MP. Tibial spine fractures in children. Clin Orthop Rel Res 1990;255:54-60. 5. Zaricznyj B. Avulsion fracture of the tibial eminence: Treatment by open reduction and pinning. J Bone Joint Surg Am 1977;59:1111-1114. 6. Horibe S, Shi K, Mitsuoka T, Hamada M, Matsumoto N, Toritsuka Y. Nonunited avulsion fractures of the intercondylar eminence of the tibia. Arthroscopy 2000;16:757-762. 7. Meyers MH, McKeever FM. Fracture of the intercondylar eminence of the tibia. J Bone Joint Surg Am 1970;52:1677-1684. 8. Molander ML, Wallin G, Wikstad I. Fracture of the intercondylar eminence of the tibia: A review of 35 patients. J Bone Joint Surg Am 1981;63:89-91. 9. Lee HG. Avulsion fracture of the tibial attachments of the crucial ligaments: Treatment by operative reduction. J Bone Joint Surg 1937;19:460-468. 10. Berg EE. Comminuted tibial eminence anterior cruciate ligament avulsion fractures: Failure of arthroscopic treatment. Arthroscopy 1993;9:446-450.
BIOMECHANICAL STUDY OF ACL AVULSION FRACTURE 11. Berg EE. Pediatric tibial eminence fractures: Arthroscopic cannulated screw fixation. Arthroscopy 1995;11:328-331. 12. Carro LP, Suarez GG, Cimiano FG. The arthroscopic knot technique for fracture of the tibia in children. Arthroscopy 1994;10:698-699. 13. Kogan MG, Marks P, Amendola A. Technique for arthroscopic suture fixation of displaced tibial intercondylar eminence fractures. Arthroscopy 1997;13:301-306. 14. Lubowitz JH, Grauer JD. Arthroscopic treatment of anterior cruciate ligament avulsion. Clin Orthop Rel Res 1993;294: 242-246. 15. Matthews DE, Geissler WB. Arthroscopic suture fixation of displaced tibial eminence fractures. Arthroscopy 1994;10:418-423. 16. McLennan JG. The role of arthroscopic surgery in the treatment of fractures of the intercondylar eminence of the tibia. J Bone Joint Surg Br 1982;64:477-480. 17. Osti L, Merlo F, Liu SH, Bocchi L. A simple modified arthroscopic procedure for fixation of displaced tibial eminence fractures. Arthroscopy 2000;16:379-382. 18. Van Loon T, Marti RK. A fracture of the intercondylar eminence of the tibia treated by arthroscopic fixation. Arthroscopy 1991;7:385-388. 19. Veselko M, Senekovicˇ V, Tonin M. Simple and safe arthroscopic placement and removal of cannulated screw and washer for fixation of tibial avulsion fracture of the anterior cruciate ligament. Arthroscopy 1996;12:259-262.
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20. Willis RB, Blokker C, Stoll TM, Paterson DC, Galpin RD. Long-term follow-up of anterior tibial eminence fractures. J Pediatr Orthop 1993;13:361-364. 21. Senekovicˇ V, Veselko M. Anterograde arthroscopic fixation of avulsion fractures of the tibial eminence with a cannulated screw: Five-year results. Arthroscopy 2003;19:54-61. 22. Montogomery KD, Cavanaugh J, Cohen S, Wickiewicz TL, Warren RF, Blevens F. Motion complications after arthroscopic repair of anterior cruciate ligament avulsion fractures in the adult. Arthroscopy 2002;18:171-176. 23. Woo SL-Y, Orlando CA, Camp JF, Akeson WH. Effects of postmortem storage by freezing on ligament tensile behavior. J Biomech 1986;19:399-404. 24. Morrison JB. Mechanics of the knee joint in relation to normal walking. J Biomech 1970;3:51-61. 25. Zheng N, Fleisig GS, Escamilla RF, Barrentine SW. An analytical model of the knee for estimation of internal forces during exercise. J Biomech 1998;31:963-967. 26. Toutoungi DE, Lu TW, Leardini A, Catani F, O’Connor JJ. Cruciate ligament forces in the human knee during rehabilitation exercise. Clin Biomech 2000;15:176-187. 27. Scheffler SU, Südkamp, NP, Göckenjan A, Hoffman RFG, Weiler A. Biomechanical comparison of hamstring and patellar tendon graft anterior cruciate ligament reconstruction techniques: The impact of fixation level and fixation method under cyclic loading. Arthroscopy 2002;18:304-315.
Purpose: Although several technical developments for arthroscopic treatment of anterior cruciate ligament (ACL) avulsion fracture have been reported, it remains unclear which fixation technique is most effective to obtain the best initial fixation strength. The objectives of this study were to compare the initial fixation strength in response to a cyclic tensile load between different fixation techniques for ACL avulsion fractures. Type of Study: Cadaveric biomechanical evaluation. Methods: Using 15 fresh-frozen cadaveric human knees, 3 different fixation techniques for noncomminuted ACL avulsion fractures were compared by measuring the anterior tibial translation (ATT) under 500 cycles of 0 to 100 N of anterior tibial load: (1) antegrade screw fixation, (2) retrograde screw fixation, and (3) pullout suture fixation. Results: The increase in the ATT after the cyclic loading for the pullout suture fixation (2.2 ⫾ 0.8 mm) was significantly larger than that for the antegrade screw fixation (1.0 ⫾ 0.2 mm). The ATT increase in the retrograde fixation group (2.0 ⫾ 0.6 mm) was not significantly different compared with the other groups. Conclusions: All methods were effective and there was a slight biomechanical advantage to antegrade screw fixation over pullout suture fixation. Clinical Relevance: Antegrade screw fixation is more effective in obtaining initial rigid fixation than pullout suture fixation for ACL avulsion fractures. Key Words: Anterior cruciate ligament— Avulsion fracture—Biomechanical study—Cyclic loading.
A
vulsion fracture of the tibial attachment of the anterior cruciate ligament (ACL) results in anterior knee instability and occasionally anterior impingement during knee extension, when the avulsion fragment is displaced.1-5 In addition, subsequent histologic degenerative change of the ACL substance caused by the decreased tension has been reported in the chronic course.6 Therefore, immediate anatomic reduction and fixation of the fragment are widely recommended for type III and IV displaced fractures
From the Department of Orthopaedic Surgery, Hirosaki University School of Medicine, Hirosaki, Aomori, Japan. Address correspondence and reprint requests to Harehiko Tsukada, M.D., Department of Orthopaedic Surgery, Hirosaki University School of Medicine, 5 Zaifu-cho, Hirosaki, Aomori 036-8562, Japan. E-mail: [email protected] © 2005 by the Arthroscopy Association of North America 0749-8063/05/2110-3946$30.00/0 doi:10.1016/j.arthro.2005.06.020
as classified by Meyers and McKeever,7 whereas undisplaced or minimal displaced fragment should be treated conservatively.8 Most of the early studies proposed open reduction and internal fixation (ORIF) of the displaced fragment (e.g., Lee’s method9). Recently, several technical developments for arthroscopic reduction and internal fixation (ARIF) have been reported.10-19 ARIF has been classified as pullout suture fixation modified from the Lee’s method and as pin or screw fixation driven in an antegrade or retrograde direction. Although previous studies have reported the successful outcome of primary repair of the avulsion fracture of ACL attachment in children,1,4,20 the outcome in adults varies, and several postoperative complications have been reported. Good and excellent results in adult patients treated with ARIF were reported by Osti et al.17 and Senekovicˇ and Veselko,21 whereas Berg10 and Montgomery et al.22 reported
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 21, No 10 (October), 2005: pp 1197-1201
1197
1198
H. TSUKADA ET AL. grade screw fixation, (2) retrograde screw fixation, and (3) pullout suture fixation. METHODS
FIGURE 1. flexion.
The testing system with the knee joint at 30° of
postoperative loss of knee motion as the most frequent complication after ARIF. Limited preoperative range of motion and prolonged postoperative immobilization were raised as the risk factors of loss of knee motion.1 Because the necessity of postoperative immobilization greatly depends on the initial strength at the fixation site, rigid fixation of the avulsion fragment of the ACL attachment is the key to reduce the motion complication. However, it remains unclear which fixation technique is most effective to obtain the best initial fixation strength. Therefore, the objectives of this study were to compare the initial fixation strength in response to a cyclic load between 3 different fixation techniques for ACL avulsion fractures: (1) ante-
Fifteen fresh-frozen human cadaveric knees with an age range of 31 to 83 years (mean, 58.6 years) were used for this study. Specimens were stored at ⫺20°C, thawed at room temperature 24 hours before testing, and kept moist with saline irrigation throughout the preparation and mechanical testing.23 Soft-tissue structures were removed to expose the bone, leaving ligaments, capsule, and popliteal muscle and tendon intact. The proximal part of the femur and the distal part of the tibia were placed in molds of polymethylmethacrylate for gripping to test the fixture’s rigidly. The specimen was mounted on the materials testing machine (Instron 4465; Instron Corp, Canton, MA) at 30° of knee flexion and neutral internal-external and varus-valgus rotation, without restricting the other 3 degrees of freedom (anterior-posterior, medial-lateral, and proximal-distal translation) (Fig 1). Before creating the ACL avulsion fracture, the neutral anteriorposterior position of intact knee was determined and used as a reference position throughout the testing. It was defined as the position midway between the 2 zero load points of the load-displacement hysteresis loop by imposing a ⫾50-N drawer cycle. On the testing machine, the tibial eminence, including the whole area of the ACL tibial attachment, was completely isolated from the tibial plateau with an osteotome to produce the type-III fracture with 90° of knee flexion. The bottom of the fragment was made round shaped to mimic the clinical fracture pattern (Fig 2A). Specimens were divided into 3 groups of 5 knees so that the average age of 3 groups would be matched.
FIGURE 2. Illustrations of the repair techniques for ACL avulsion fracture: (A) created ACL avulsion fracture, (B) antegrade screw fixation, (C) retrograde screw fixation, and (D) pullout suture fixation.
BIOMECHANICAL STUDY OF ACL AVULSION FRACTURE Antegrade Screw Fixation After the avulsion fragment was reduced anatomically, a small guide pin was drilled from the center of the avulsion fragment to the posterolateral cortex. The 4-mm diameter titanium cannulated cancellous screw with spiked washer (Depuy ACE, Warsaw, IN) was inserted from the joint surface through the guide pin, penetrating the distal tibial cortex (Fig 2B). Retrograde Screw Fixation The fragment was held using the ACL tibial guide so as not to be displaced or pushed up until completion of the screw insertion. A small guide pin was drilled from the anteromedial cortex to the center of the avulsion fragment, and the titanium cannulated cancellous screw described above was inserted in a retrograde fashion to fix the fragment. The tip of the screw protruded slightly above the joint surface (Fig 2C). Pullout Suture Fixation Two drill holes 2 mm in diameter were created from just medial and lateral of the repositioned fragment to the anteromedial cortex of the proximal tibia. The distal outlet of the 2 drill holes was more than 10 mm apart. Using a 24-gauge wire loop, doubled No. 2 Ethibond suture (Ethicon, Somerville, NJ) was penetrated into the ACL just proximal to the avulsion fragment. Then the wire loop was advanced into each drill hole to pass the doubled suture through the holes. The doubled sutures were pulled out tightly and tied over the tibial bone bridge (Fig 2D). Biomechanical Testing The repaired knee was repositioned at 30° of knee flexion and, throughout the preparation, the knee was kept mounted on the materials testing machine. The repaired knee was subjected to 500 cycles of 0 to 100 N cyclic anterior tibial loads at a crosshead speed of 100 mm/min and load-displacement curve was recorded in 20 Hz of sampling rate. The direction of the load mimics a Lachman test. The loading conditions used in this study were determined based on estimated loads in the ACL graft that had been reported in previous literatures. Morrison24 calculated the mean peak force in the ACL during level walking to be 157 N. Zheng et al.25 calculated the peak force in the ACL to be 142 N during seated knee extension (open chain exercise). Toutoungi et al.26 calculated the mean peak force in the ACL during isokinetic/isometric extension at knee angles of 35° to 40° to be 0.55 ⫻
1199
body weight. The anterior load of 100 N that we selected was intended to mimic early rehabilitation exercises such as continuous passive motion and partial weight bearing. The anterior tibial translation (ATT) in response to an anterior load of 100 N before and after 500 cycles of the loading was determined in reference to the neutral anteroposterior position defined in the intact knee. To quantify the loss of graft fixation, the parameter “laxity increase” introduced by Scheffler et al.27 was determined as the change in the tibial position at load pickup between the first cycle and the last cycle of cyclic loading. The laxity increase is a permanent elongation of the graft constructs and consists of graft slippage from the fixation device and plastic deformation of the linkage materials and knot tightening. In other words, the ATT consists of the laxity increase and the recoverable elongation of the tendon graft itself. Statistical Analysis The increase in the ATT obtained from the 3 different fixation techniques as well as the laxity increase in response to cyclic loading were compared. Based on our data of the first 9 knees (3 knees in each group), a power analysis was performed (power ⫽ 0.80, significance level ⫽ 0.05) so differences of 2 mm for the increase in the ATT could be detected. It was determined that 5 knee specimens in each group were required for this study. We used the Scheffé test for statistical analysis; significance was set at P ⬍ .05. RESULTS The average age of the specimens was 59.8 years (range, 31 to 83 years) for antegrade screw fixation, 60.4 years (range, 41 to 77 years) for retrograde screw fixation, and 55.8 years (range, 31 to 83 years) for pullout suture fixation, representing no statistically significant difference. No macroscopic crack of the fragment or injury of ACL-tibia junction was observed after the testing. Furthermore, no fixation failure such as implant failure or screw backing out was observed. The size of the fragment was consistently 15 ⫻ 15 ⫻ 7 mm throughout the study groups. In all groups, the increase in the ATT was observed after cyclic loading. The increase in the ATT between before and after 500 cycles of the loading in pullout suture fixation (2.2 ⫾ 0.8 mm) was significantly larger than that in antegrade screw fixation (1.0 ⫾ 0.2 mm) (P ⬍ .05). The ATT in retrograde screw fixation increased by 2.0 ⫾ 0.6 mm after the cyclic loading,
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H. TSUKADA ET AL.
FIGURE 3. Change in ATT and laxity increase of repaired ACL avulsion fractures of the knee during cyclic loading.
which tended to be larger than antegrade screw fixation, although no significant differences were detected compared with the other 2 groups. No significant differences in the laxity increase were detected among groups; however, the laxity increase in pullout suture fixation (1.8 ⫾ 1.0 mm) and retrograde screw fixation (1.7 ⫾ 0.6 mm) tended to be larger than that in antegrade screw fixation (0.9 ⫾ 0.2 mm) (Fig 3). DISCUSSION There are several reports of poor outcomes in ACL tibial avulsion fractures.2,6,7,10,22 Concomitant injury of the ACL substance may result in persistent ACL deficiency, even if anatomic restoration of the avulsion fracture is achieved. The status of the ACL substance should be evaluated using magnetic resonance imaging to determine the ideal treatment. The fixation technique is another issue crucial to the success of primary repair of ACL tibial avulsion.10-19 In this study, after 500 cycles of 0 to 100 N, the ATT for pullout suture fixation was significantly increased compared with antegrade screw fixation. Also, the laxity increase for pullout suture fixation tended to be greater than antegrade screw fixation. This suggests that the laxity that occurred in pullout suture fixation resulted from tightening or slippage at the suture knot or the suture cutting into the tibial bone bridge. Use of a metal wire or larger suture may reduce the risk of these types of fixation failure and contribute to reducing the increase in laxity. In contrast, antegrade screw fixation with a washer was the most effective technique to obtain initial rigid fixation. These results support the successful clinical outcome of antegrade
screw and washer fixation reported by Senekovicˇ et al.21 The increase of the ATT and the laxity increase for retrograde screw fixation tended to be larger than that for antegrade screw fixation. Because the tip of the screw must penetrate into the fragment to obtain rigid fixation in retrograde screw fixation, the use of this fixation technique might be restricted when the fragment is thin or comminuted. There were several limitations in this study. The first was the lack of a quantitative method to evaluate the bone density of the tested specimens, which were from individuals whose average age was relatively old. Osteoporotic bone quality of older human specimens could potentially predispose to failure at the fixation site. The second limitation was that the avulsion fragment was produced en bloc. It was not shown whether repair techniques were effective to obtain rigid fixation for the comminuted fragment. CONCLUSIONS The results of this study show that antegrade screw fixation was more effective to obtain initial rigid fixation than pullout suture fixation for ACL avulsion fractures. Acknowledgment: The authors acknowledge the contribution of Yuji Yamamoto, M.D., and Kan-ichiro Wada, M.D., for data analysis.
REFERENCES 1. Baxter MP, Wiley JJ. Fractures of the tibial spine in children: An evaluation of knee stability. J Bone Joint Surg Br 1988; 70:228-230. 2. Kendall NS, Hsu SYC, Chan K. Fracture of tibial spine in adults and children. J Bone Joint Surg Br 1992;74:848-852. 3. Keys GW, Walters J. Nonunion of intercondylar eminence fracture of the tibia. J Trauma 1988;28:870-871. 4. Wiley JJ, Baxter MP. Tibial spine fractures in children. Clin Orthop Rel Res 1990;255:54-60. 5. Zaricznyj B. Avulsion fracture of the tibial eminence: Treatment by open reduction and pinning. J Bone Joint Surg Am 1977;59:1111-1114. 6. Horibe S, Shi K, Mitsuoka T, Hamada M, Matsumoto N, Toritsuka Y. Nonunited avulsion fractures of the intercondylar eminence of the tibia. Arthroscopy 2000;16:757-762. 7. Meyers MH, McKeever FM. Fracture of the intercondylar eminence of the tibia. J Bone Joint Surg Am 1970;52:1677-1684. 8. Molander ML, Wallin G, Wikstad I. Fracture of the intercondylar eminence of the tibia: A review of 35 patients. J Bone Joint Surg Am 1981;63:89-91. 9. Lee HG. Avulsion fracture of the tibial attachments of the crucial ligaments: Treatment by operative reduction. J Bone Joint Surg 1937;19:460-468. 10. Berg EE. Comminuted tibial eminence anterior cruciate ligament avulsion fractures: Failure of arthroscopic treatment. Arthroscopy 1993;9:446-450.
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