- Email: [email protected]
Bone tunnel remodeling at the site of biodegradable interference screws used for anterior cruciate ligament reconstruction
Bone Tunnel Remodeling at the Site of Biodegradable Interference Screws Used for Anterior Cruciate Ligament Reconstruction: 5-Year Follow-up Georg Lajtai, M.D., Gu¨nter Schmiedhuber, M.D., Franz Unger, M.D., Gernot Aitzetmu¨ller, M.D., Markus Klein, C.M., Irene Noszian, M.D., and Ernst Orthner, M.D.
Purpose: The purpose of this prospective study was to review, using expanded clinical-assessment tools, the long-term results of the local effects of a bioabsorbable interference screw (copolymer 85/15 D,L lactide/glycolide) in anterior cruciate ligament (ACL) reconstruction. Type of Study: This prospective study was initiated in May 1993. The inclusion criteria for patient selection included rupture of the ACL in athletic patients without involvement of the collateral ligaments, arthroscopic ACL reconstruction using middle third of the ligamentum patella, and magnetic resonance imaging (MRI) and plain radiographic examinations of the knee joint during follow-up. Materials: Between May 1993 and October 1994, 32 patients were enlisted in the study; 48 patients did not fit the inclusion criteria. There were 25 men 7 women. The average age was 29.1 years (range, 19 to 50 years). There were 21 right knees and 11 left knees. The follow-up examinations were performed by an independent examiner. There were 28 patients available for follow-up at a medium of 5.2 years (range, 4.1 to 6.4 years). The evaluation included various testing systems (i.e., OAK, IKDC, Lysholm) as well as MRI and plain radiographic studies to investigate the longevity of the implant and potential adverse effects of this new bioabsorbable material. Results: The clinical results were good. The OAK score (Orthopa¨dische Arbeitsgruppe Knie) showed 93% excellent and good results, and 7% fair results. The IKDC and Lysholm scores were 92% and 96% good and excellent results, respectively. MRI showed bone remodeling and new bone formations at the site of the implant in the femoral as well as in the tibial bone tunnel at follow-up. No cystic or osteolytic changes where seen on MRI or plain radiographs. Conclusions: This study showed the correlation between histology and MRI: there was minimal surgical-site edema, minimal reaction to this material, and complete replacement by new bone formation of the previous site of this implant. At 5 years, this bioabsorbable interference screw appeared clinically safe and effective for fixation of bone blocks during ACL reconstruction and MRI showed complete absorption and replacement with new bone. Key Words: Long-term results—Interference screw—Copolymer lactide/glycolide—Bone remodeling—Magnetic resonance imaging—ACL reconstruction—Patellar tendon graft.
B
iodegradable implants have become more commonly used over the past few years.1,2 Recent studies have shown the biocompatibility of different
From the Departments of Traumatology and Radiology (I.N.), AKH–Wels, Wels, Austria. Address correspondence and reprint requests to Georg Lajtai, M.D., Department of Traumatology, AKH–Wels, Grieskirchnerstraße 42, A-4600 Wels, Austria. E-mail: [email protected] © 2001 by the Arthroscopy Association of North America 0749-8063/01/1706-2562$35.00/0 doi:10.1053/jars.2001.21535
implants over a short follow-up period.3,4 Not all bioabsorbable materials are the same in composition, absorption rate, or tissue reaction. It is necessary for studies on such materials to extend beyond the time expected for device degradation. Studies have been reported on poly L-lactide implants, one of which examined the histology before anticipated degradation and, as expected, reported no tissue reaction to a certain suture anchor.5 The implication was that this device would produce no tissue reaction. The assertion was true for the time interval of the study but, unfortunately, the results were not known at or after
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the time of anticipated device degradation. There have been few reports of the long-term fate and adverse tissue reaction of poly L-lactide in bone.6,7 Heretofore, the long-term effects of 85/15 D,L lactide/glycolide have not been reported. The use of metal interference screws in anterior cruciate ligament (ACL) reconstruction has produced good clinical results8,9 They are widely accepted because of their ease of handling and effective fixation, but there are some potential disadvantages. The presence of the metal may limit the subsequent use of magnetic resonance imaging (MRI) as a postoperative assessment tool10 and may require either a planned or unplanned second operation for removal. Bone remodeling at the femoral or at the tibial bone tunnel is not possible, as long as the metal interference screws are in place. For these reasons, a bioabsorbable interference screw has been introduced for graft fixation in ACL reconstruction. Bioabsorbable polymers have been used for suture,11-13 vascular clips,14 and fixation implants for both intra-articular fractures15 and malleolar fractures.16 Controversy exists in the medical literature concerning the use of bioabsorbable implants in orthopaedic surgery.5,15,17-19 The purpose of this prospective study was to review the long-term results of a specific bioabsorbable interference screw, the copolymer 85/15 D,L lactide/glycolide composite, Biologically Quiet Screw (Instrument Makar, Okemos, MI) with an expanded clinical assessment after use in ACL reconstruction. It was hypothesized that the previous site of the implant would be replaced by new bone formation and bone tunnel remodeling without adverse long-term clinical effects. METHODS This prospective study was initiated in May 1993. In a previous study, we reported on the medium-term results of our patients.20 The inclusion criteria for patient selection included rupture of the ACL in athletic patients without involvement of the collateral ligaments, arthroscopic ACL reconstruction using the middle third of the ligamentum patella, and MRI and plain radiographic examinations of the knee joint during the follow-up. Between May 1993 and October 1994, 32 patients were enlisted in the study (48 patients had been excluded because they did not fit the inclusion criteria).20 The objective measurements included the OAK,21 IKDC,22 and the Lysholm scores,23 plain radiographs, and MRI.
Customary Treatment Protocol After the diagnosis of a torn ACL was established by physical examination,24 the customary treatment of patients without fracture was to perform a diagnostic arthroscopy in the first few days after injury. The ruptured ACL was resected using an Ho-YAG laser or with a motorized shaver. In this series, the ACL reconstruction was performed after an average period of 5 weeks (range, 2 to 6 weeks). All patients had a full range of motion before their ACL surgery. Surgical Procedure The middle third of the patellar ligament was inserted under arthroscopic control after bone tunnels were made using compaction. The biodegradable screw was 9 ⫻ 9.0 ⫻ 25 mm and made from the copolymer of 85/15 D,L lactide/glycolide by injection molding. Follow-up Assessment After a follow-up of 5.2 years (range, 4.1 to 6.4 years) 28 patients (87.5%) returned for evaluation. One patient was unable to come to the follow-up examination for geographic reasons and another patient had died in a car accident. Two patients, who had had no complaints at their previous visit, did not wish to come for personal reasons. MRI The MRI studies were performed at average follow-up of 5.2 years. A custom evaluation concept was created by the authors to evaluate the MRI check ups.25 All studies were performed on a 1.0-T MRI unit (Magnetom Expert; Siemens, Vienna, Austria). A dedicated knee coil was used with an 18-cm field of view. T1 images (TR 760, TE 20) were obtained in axial, coronal, and parasagittal planes. Additionally, a STIR sequence (TR 6320, TE 60) was performed in a coronal and parasagittal plane. The parasagittal plane was chosen along the plane of the neoligament 4-mm thick sections using 336 ⫻ 5,120 matrix for both coronal and oblique sagittal images. Observations were made for the presence and/or absence of the screw by change in intensity relative to soft tissue. The bone marrow was inspected for the presence of edema, either diffuse or localized. In addition to the plain-film radiographs, the MRIs were reviewed for maintenance of bone block position of the graft.
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remodel within 5 years. The new cancellous bone in the bone tunnels could be easily detected because the signal of the bone formations was different from that of the surrounding bone (Fig 2). There was never complete bone remodeling in the femoral or in the tibial bone tunnel where the neoligament was in place (Figs 3 and 4). Unlike earlier interval studies,20,25 there were no edematous collections seen in this series at the operative site. Second-Look Arthroscopy: There was one second-look arthroscopy because of reinjury that showed a radial rupture of the posterior segment of the medial meniscus. The ACL tendon graft was torn. The patient reported no clinical signs of instability and had regained his preoperative athletic sport level. There was no evidence of adverse reaction due to the implant. A biopsy examination of the implant site was not performed in this case.
For objective evaluation, the IKDC,22 OAK,21 and the Lysholm scores23 were obtained at follow-up. The results are presented in Fig 1. Radiographic Studies: All patients underwent a radiographic study at follow-up. There was no osteolysis or cystic bone formation detected. The tibial bone tunnel was visible in 89% of patients and the femoral bone tunnel in 11%. Four patients showed a slight sign of osteoarthritis on postoperative plain radiographs compared with their preoperative reports. MRI Studies: There was no MRI evidence of the screw in either the femur or the tibia. The MRIs showed no edema in the distal femur and proximal tibia adjacent to the drill holes. Localized collections of fluid were observed at the top of the femoral bone tunnel on MRI signal of varying diameter in a former study,25 but this was not observed in this series. The original 10-mm bone tunnels showed enlargement in the postoperative course. On follow-up MRI, partial enlargements of the bone tunnel could be measured. The enlargement of the femoral bone tunnel was greater than that of the tibial bone tunnel.20,25 The bone tunnel began to increase in size in the tibia from the distal end and in the femur from the proximal end. The bone remodeling of the tunnel is affected by the surgical position of the bone block in the respective tunnel. Complete bone tunnel remodeling occurred only where the bone blocks were located. For instance, if the bone graft was proximal in the femur and distal in the tibia, the remainder of the tunnel spanned by the soft tissue neoligament would not
FIGURE 2. Sagittal T1 MRI sequence 6 years postoperatively. New bone formation is seen in the femoral and the tibial bone tunnel
FIGURE 1. Lysholm, IKDC, and OAK score at median of 5.2 years (range, 4.1 to 6.4 years) follow-up.
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G. LAJTAI ET AL. and recently, interference expansion plugs.26 Because of the differences between different biodegradable implants, we emphasize that the long-term results reported here are specific to this material (copolymer 85/15 D,L lactide/glycolide), this screw, and this technique. In this study, the site of the 85/15 D,L lactide/ glycolide copolymer material was replaced by new bone formation and there was bone tunnel remodeling at 5 years, thereby confirming the hypothesis. It is clear from this and previous reports20,25 that there was no adverse tissue reaction and that this implant had fully degraded.27 Animal studies by others confirm the minimal reaction to this material in bone and replacement of the implant with new bone formation.28 The maintenance of the physical integrity of this implant for 1 month exceeds the time necessary for biological bone healing.29 This human study not only shows no
FIGURE 3. Coronal T1 MRI sequence 6 years postoperatively. New cancellous bone is seen at the top of the femoral bone tunnel.
DISCUSSION Biodegradable interference screws became popular for ACL reconstruction in connection with the advent of patellar-tendon transplants, yet there are no longterm results published related to the fate of these new materials or their effects on bone remodeling. To our knowledge, this is the first long-term study on one of these biodegradable interference screws. It is necessary that studies on bioabsorbable implants be material- and device-specific. Not all bioabsorbable materials are the same in composition, absorption rate, or tissue reaction. There are many different commonly used bioabsorbable materials used for interference screws; polyglycolic acid (PGA), polylactic acid (PLA), polyparadioxanone (PDS), polymer of PGA/PLA, and various stereoisomers of the lactic acid (PDLA) molecule. In addition to screws used in interference applications, a stereoisomer of polylactic acid, PLLA, is used in rods, plates, anchors,
FIGURE 4. Sagittal T1 MRI sequence 5 years postoperatively. Neoligament and new cancellous bone is clearly seen in the femoral and the tibial bone tunnels. Complete bone tunnel remodeling occurred only where the bone blocks were located.
BONE TUNNEL REMODELING AT SCREW SITE adverse clinical reactions, but the use of this biodegradable material produced no adverse reaction in the surrounding cancellous bone or the neoligament. Ideally, a biodegradable interference screw would degrade with minimal or no host-bone reaction. This and previous studies show this to be true for this material and device.20 In addition, replacement of the operative site with new bone formation would complete the restoration. PLLA implants degrade slower than a copolymer DL 85/15. It is reasonable to assume that the faster a material degrades, the earlier the osseus replacement takes place26,27,30 While an early replacement with fibrous granulation tissue takes place during degradation,31-36 until now little has been known about the long-term fate of the former implant site and its osseous replacement. A study of the tissue reaction of these materials requires that the implant be in place for a sufficient time to undergo degradation. This criterion was met in this study. A study on a poly L-lactide implant reported no tissue reaction, but this study was concluded before the time necessary for the material to undergo degradation.5 Tissue reaction occurs only during and after degradation of the implant. There have been few reports of the long-term fate and adverse tissue reaction of poly L-lactide in bone.6,7 MRI provides a noninvasive method of determining the physical status of a bioabsorbable implant and its absorption status in human subjects. The expansion of the clinical assessment to include the MRI investigation was facilitated by the absence of artefacts with the bioabsorbable interference screw as compared with a metal implant.10 The MRI study was helpful in determining the longevity of the physical properties of this screw in humans. Correlative MRI and gross physical inspection in canine pilot studies showed this screw to maintain its physical properties for 3 weeks and be dissolved and replaced by bone by 6 months.28 Comparison MRIs in this study showed that the bioabsorbable interference screw was not visible at the longterm follow-up. The MRI longitudinal studies helped clarify the safety issues raised in a previous report from this clinic concerning collection of fluid.25 All patients in the previous report and in this study had fluid collections shown by MRI, but they were not accompanied by any adverse clinical symptoms or signs. The immediate postoperative fluid collections were adjacent to the tibial and femoral drill holes and resolved after surgery. Subsequently, there was another area of fluid collection at the top of the femoral bone tunnel reported
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in our previous series.25 The fluid collections disappeared spontaneously and completely without therapy. The collections of fluid that subsequently accumulated around the implant were not associated with any adverse clinical finding or result. At long-term followup, we have not seen any fluid residue on MRI or potential negative affected clinic signs in our patient collective. Those areas showed new cancellous bone on MRI. In a previous report, a container phenomenon appeared as liquid in a container in the proximal femoral bone tunnel.20 This potential space was created in bone by the compaction method, which formed the walls of the container. Although it is known that the compaction method creates walls of dense bone, it was not known what effect bone compaction had on creating the container phenomenon. It was also not known if this area would be regenerated and remodeled with cancellous bone. Our findings show clearly that there is a complete regeneration of cancellous bone in these areas as well. None of our MRI studies performed for this long-term follow-up showed any signs of container phenomenon. MRI shows these areas to be filled with normal cancellous bone without any pathologic signals. In our former series, we reported about bone tunnel enlargement. The enlargement of the femoral bone tunnel was statistically significantly greater than that of the tibial bone tunnel.20,25 The bone tunnels began to increase in size in the tibia from the distal end and in the femur from the proximal end. Remodeling of the bone tunnel depends on the positioning of the bone blocks during ACL reconstruction. The bone remodeling of the tunnel is affected by the position of the bone block in the respective tunnel. Complete bone tunnel remodeling occurred only where the bone blocks were fixed. For instance, if the bone graft was proximal in the femur and distal in the tibia, the remainder of the tunnel spanned by the neoligament would require 5 years for osseous remolding. There was never, even after long-term follow-up, complete bone remodeling seen in the femoral or tibial bone tunnels where the neoligament was in place, except in the regions where the bone blocks were located. This study did not have correlative biopsy studies to confirm the histologic tissue status, but the assumption that the MRI interpretations reflect true new bone formation is supported by recent animal studies.28 This study shows the correlation between histology and MRI, which indicated that there was minimal surgical-site edema, minimal reaction to this material,
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and complete replacement by new bone formation of the previous site of this implant. Acknowledgment: The authors express their appreciation to Lanny L. Johnson, M.D., for reviewing the manuscript. Special thanks to my family Mona, Julian, and Nikolaus Lajtai for their personal support.
19. 20.
21.
REFERENCES 1. Barber FA, Elrod FE, McGuire DA, Paulos LE. Preliminary results of an interference screw. Arthroscopy 1995;11:537548. 2. Johnson LL, van Dyk GE. Metal and biodegradable interference screw: Comparison of failure strength. Arthroscopy 1996; 12:452-456. 3. Warden WH, Friedman R, Teresi LM, Jackson DW. Magnetic resonance imaging of bioabsorbable polylactic acid interference screws during the first 2 year after anterior cruciate ligament reconstruction. Arthroscopy 1999;15:474-480. 4. McGuire DA, Barber FA, Elrod BF, Paulos LE. Bioabsorbable interference screws for graft fixation in anterior cruciate ligament reconstruction. Arthroscopy 1999;15:463-473. 5. Barber FA, Deck MA. The in vivo histology of an absorbable suture anchor: A preliminary report. Arthroscopy 1995;11:7781. 6. Bergsma JE, de Bruijn WC, Rozema FR, Bos RR, Boering G. Late degradation tissue response to poly(L-lactide) bone plates and screws. Biomaterials 1995;16:25-31. 7. B¨ostman OM, Pihlajamaki HK. Late foreign-body reaction to an intraosseous bioabsorbable polylactic acid screw. A case report. J Bone Joint Surg Am 1998;80:1791-1794. 8. Jomha NM, Pinczewski LA, Clingeleffer A, Otto DD. Arthroscopic reconstruction of the anterior cruciate ligament with patellar-tendon autograft and interference screw fixation. The results at seven years. J Bone Joint Surg Br 1999;81:775-779. 9. Aglietti P, Buzzi R, D’Andria S, et al. Long-term study of the anterior cruciate ligament reconstruction for chronic instability using the central one-third patellar tendon and a lateral extraarticular tenodesis. Am J Sports Med 1992;20:38-45. 10. Shellock FG, Mink JH, Curtin S, Friedmann MJ. MR imaging and metallic implants for anterior cruciate ligament reconstruction: Assessment of ferromagnetism and artifact. J Magn Reson Imaging 1992;2:225-228. 11. Craig PH, Williams JA, Davis KW, et al. A biologic comparison of polyglactic 910 and polyglycolic acid synthetic absorbable sutures. Surg Gynecol Obset 1975;141:1-10. 12. Postlethwait RW. Polyglycolic acid surgical suture. Arch Surg 1970;110:489-494. 13. Ray JA, Doddi N, Regula D, et al. Polydioxanone (PDS), a novel monofilament synthetic absorbable suture. Surg Gynecol Obset 1981;153:497-507. 14. Schaefer CJ, Colombani PM, Geelhoed GW. Absorbable ligating clips. Surg Gynecol Obset 1982;154:513-516. 15. Hollinger JO, Battistone GC. Biodegradable bone repair materials: Synthetic polymers and ceramics. Clin Orthop 1986; 207:290-305. 16. B¨ostman O, Vainionp¨aa¨ S, Hirvensalo E, et al. Biodegradable internal fixation for malleolar fracture. A prospective randomised study. J Bone Joint Surg Br 1987;69:615-619. 17. B¨ostman O. Osteolytic changes accompanying degradation of absorbable fracture fixation implants. J Bone Joint Surg Br 1991;73:679-682. 18. Johnson LL, van Dyk GE. Metal and biodegradable interfer-
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ence screw: Comparison of failure strength. Arthroscopy 1996; 12:452-456. Johnson LL. Comparison of bioabsorbable and metal interference screw in anterior cruciate reconstruction: A clinical trial. Arthroscopy 1995;11:349 (abstr). Lajtai G, Humer K, Aitzetm¨uller G, Unger F, Noszian I, Orthner E. Serial magnetic resonance imaging evaluation of a bioabsorbable interference screw and the adjacent bone. Arthroscopy 1999;15:481-488. M¨uller W, Biedert R, Hefti F, et al. OAK knee evaluation: A new way to assess knee ligament injuries. Clin Orthop 1988; 232:37-50. Anderson AF. Rating scales. In: Fu FH, Harner CD, Vince KG, eds. Knee surgery. Vol 1. Baltimore: Williams & Wilkins, 1994;275-296. Lysholm J, Gillquist J. Evaluation of knee ligament surgery results with special emphasis on use of a scoring scale. Am J Sports Med 1982;10:150-154. Anderson A, Lipscomp B. Preoperative instrumented testing of anterior and posterior knee laxity. Am J Sports Med 1989; 17:387-392. Lajtai G, Noszian I, Humer K, Unger F, Aitzetm¨uller G, Orthner E. Serial magnetic resonance imaging evaluation of operative site after fixation of patellar tendon graft with bioabsorbable interference screws in anterior cruciate ligament reconstruction. Arthroscopy 1999;15:709-718. Hovis WD, Buchholz RW. Polyglycolide bioabsorbable screws in the treatment of ankle fractures. Foot Ankle Int 1997;18:128-131. Lajtai G, Balon R, Humer K, Aitzetm¨uller G, Unger F, Orthner E. Resorbierbare Interferenzschrauben: Histologische Untersuchung 4,5 Jahre postoperativ. Unfallchirurg 1998;101:866869. Balch OK, Collier MA, DeBault LE, Johnson, LL. Bioabsorbable suture anchor (copolymer 85/15 D,L lactide/glycolide) implanted in bone: Correlation of physical/mechanical properties, magnetic resonance imaging, and histological response. Arthroscopy 1999;15:691-708. Arnoczky SP, Johnson LL, Nemezk JA. Compaction drilling: A new technique for creating bone tunnels. Presented at the Annual Meeting of the American Academy of Orthopaedic Surgeons, New Orleans, 1994. Stahelin A, Weiler A, R¨ufenacht H, Hoffmann R, Geissmann A, Feinstein R. Clinical degradation and biocompatibility of different bioabsorbable interference screws: A report of six cases. Arthroscopy 1997;13:238-244. Majola A. Fixation of experimental osteotomies with absorbable polylactic acid screws. Ann Chir Gynaecol 1991;80:274281. Weiler A, Helling H, Kirch U, Zirbes T, Rehm K. Foreign body reactions and the course of osteolysis after polyglycolide implants for fracture fixation—Experimental study in sheep. J Bone Joint Surg Br 1996;73:369-376. Vainionp¨aa¨ S. Biodegradation of polyglycolic acid in bone tissue: An experimental study in rabbits. Arch Orthop Trauma Surg 1986;104:333-338. Majola A, Vainionp¨aa¨ S, Vihtonen K, Vasenius J, T¨orm¨al¨a P, Rokkanen P. Intramedullary fixation of cortical bone osteotomies with self-reinforced polylactic rods in rabbits. Int Orthop 1992;16:101-108. B¨ostman OM, P¨aiv¨arinta U, Partio E, et al. The tissue-implant interface during degradation of absorbable polyglycolide fracture fixation screws in the rabbit femur. Clin Orthop 1992; 285:263-272. Nordst¨om P, Pihlajam¨aki H, Toivonen T, T¨orm¨al¨a P, Rokkanen P. Tissue response to polyglycolide and polylactide pins in cancellous bone. Arch Orthop Trauma Surg 1998;117: 197-204.
Purpose: The purpose of this prospective study was to review, using expanded clinical-assessment tools, the long-term results of the local effects of a bioabsorbable interference screw (copolymer 85/15 D,L lactide/glycolide) in anterior cruciate ligament (ACL) reconstruction. Type of Study: This prospective study was initiated in May 1993. The inclusion criteria for patient selection included rupture of the ACL in athletic patients without involvement of the collateral ligaments, arthroscopic ACL reconstruction using middle third of the ligamentum patella, and magnetic resonance imaging (MRI) and plain radiographic examinations of the knee joint during follow-up. Materials: Between May 1993 and October 1994, 32 patients were enlisted in the study; 48 patients did not fit the inclusion criteria. There were 25 men 7 women. The average age was 29.1 years (range, 19 to 50 years). There were 21 right knees and 11 left knees. The follow-up examinations were performed by an independent examiner. There were 28 patients available for follow-up at a medium of 5.2 years (range, 4.1 to 6.4 years). The evaluation included various testing systems (i.e., OAK, IKDC, Lysholm) as well as MRI and plain radiographic studies to investigate the longevity of the implant and potential adverse effects of this new bioabsorbable material. Results: The clinical results were good. The OAK score (Orthopa¨dische Arbeitsgruppe Knie) showed 93% excellent and good results, and 7% fair results. The IKDC and Lysholm scores were 92% and 96% good and excellent results, respectively. MRI showed bone remodeling and new bone formations at the site of the implant in the femoral as well as in the tibial bone tunnel at follow-up. No cystic or osteolytic changes where seen on MRI or plain radiographs. Conclusions: This study showed the correlation between histology and MRI: there was minimal surgical-site edema, minimal reaction to this material, and complete replacement by new bone formation of the previous site of this implant. At 5 years, this bioabsorbable interference screw appeared clinically safe and effective for fixation of bone blocks during ACL reconstruction and MRI showed complete absorption and replacement with new bone. Key Words: Long-term results—Interference screw—Copolymer lactide/glycolide—Bone remodeling—Magnetic resonance imaging—ACL reconstruction—Patellar tendon graft.
B
iodegradable implants have become more commonly used over the past few years.1,2 Recent studies have shown the biocompatibility of different
From the Departments of Traumatology and Radiology (I.N.), AKH–Wels, Wels, Austria. Address correspondence and reprint requests to Georg Lajtai, M.D., Department of Traumatology, AKH–Wels, Grieskirchnerstraße 42, A-4600 Wels, Austria. E-mail: [email protected] © 2001 by the Arthroscopy Association of North America 0749-8063/01/1706-2562$35.00/0 doi:10.1053/jars.2001.21535
implants over a short follow-up period.3,4 Not all bioabsorbable materials are the same in composition, absorption rate, or tissue reaction. It is necessary for studies on such materials to extend beyond the time expected for device degradation. Studies have been reported on poly L-lactide implants, one of which examined the histology before anticipated degradation and, as expected, reported no tissue reaction to a certain suture anchor.5 The implication was that this device would produce no tissue reaction. The assertion was true for the time interval of the study but, unfortunately, the results were not known at or after
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 17, No 6 (July-August), 2001: pp 597– 602
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the time of anticipated device degradation. There have been few reports of the long-term fate and adverse tissue reaction of poly L-lactide in bone.6,7 Heretofore, the long-term effects of 85/15 D,L lactide/glycolide have not been reported. The use of metal interference screws in anterior cruciate ligament (ACL) reconstruction has produced good clinical results8,9 They are widely accepted because of their ease of handling and effective fixation, but there are some potential disadvantages. The presence of the metal may limit the subsequent use of magnetic resonance imaging (MRI) as a postoperative assessment tool10 and may require either a planned or unplanned second operation for removal. Bone remodeling at the femoral or at the tibial bone tunnel is not possible, as long as the metal interference screws are in place. For these reasons, a bioabsorbable interference screw has been introduced for graft fixation in ACL reconstruction. Bioabsorbable polymers have been used for suture,11-13 vascular clips,14 and fixation implants for both intra-articular fractures15 and malleolar fractures.16 Controversy exists in the medical literature concerning the use of bioabsorbable implants in orthopaedic surgery.5,15,17-19 The purpose of this prospective study was to review the long-term results of a specific bioabsorbable interference screw, the copolymer 85/15 D,L lactide/glycolide composite, Biologically Quiet Screw (Instrument Makar, Okemos, MI) with an expanded clinical assessment after use in ACL reconstruction. It was hypothesized that the previous site of the implant would be replaced by new bone formation and bone tunnel remodeling without adverse long-term clinical effects. METHODS This prospective study was initiated in May 1993. In a previous study, we reported on the medium-term results of our patients.20 The inclusion criteria for patient selection included rupture of the ACL in athletic patients without involvement of the collateral ligaments, arthroscopic ACL reconstruction using the middle third of the ligamentum patella, and MRI and plain radiographic examinations of the knee joint during the follow-up. Between May 1993 and October 1994, 32 patients were enlisted in the study (48 patients had been excluded because they did not fit the inclusion criteria).20 The objective measurements included the OAK,21 IKDC,22 and the Lysholm scores,23 plain radiographs, and MRI.
Customary Treatment Protocol After the diagnosis of a torn ACL was established by physical examination,24 the customary treatment of patients without fracture was to perform a diagnostic arthroscopy in the first few days after injury. The ruptured ACL was resected using an Ho-YAG laser or with a motorized shaver. In this series, the ACL reconstruction was performed after an average period of 5 weeks (range, 2 to 6 weeks). All patients had a full range of motion before their ACL surgery. Surgical Procedure The middle third of the patellar ligament was inserted under arthroscopic control after bone tunnels were made using compaction. The biodegradable screw was 9 ⫻ 9.0 ⫻ 25 mm and made from the copolymer of 85/15 D,L lactide/glycolide by injection molding. Follow-up Assessment After a follow-up of 5.2 years (range, 4.1 to 6.4 years) 28 patients (87.5%) returned for evaluation. One patient was unable to come to the follow-up examination for geographic reasons and another patient had died in a car accident. Two patients, who had had no complaints at their previous visit, did not wish to come for personal reasons. MRI The MRI studies were performed at average follow-up of 5.2 years. A custom evaluation concept was created by the authors to evaluate the MRI check ups.25 All studies were performed on a 1.0-T MRI unit (Magnetom Expert; Siemens, Vienna, Austria). A dedicated knee coil was used with an 18-cm field of view. T1 images (TR 760, TE 20) were obtained in axial, coronal, and parasagittal planes. Additionally, a STIR sequence (TR 6320, TE 60) was performed in a coronal and parasagittal plane. The parasagittal plane was chosen along the plane of the neoligament 4-mm thick sections using 336 ⫻ 5,120 matrix for both coronal and oblique sagittal images. Observations were made for the presence and/or absence of the screw by change in intensity relative to soft tissue. The bone marrow was inspected for the presence of edema, either diffuse or localized. In addition to the plain-film radiographs, the MRIs were reviewed for maintenance of bone block position of the graft.
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Clinical Assessment
remodel within 5 years. The new cancellous bone in the bone tunnels could be easily detected because the signal of the bone formations was different from that of the surrounding bone (Fig 2). There was never complete bone remodeling in the femoral or in the tibial bone tunnel where the neoligament was in place (Figs 3 and 4). Unlike earlier interval studies,20,25 there were no edematous collections seen in this series at the operative site. Second-Look Arthroscopy: There was one second-look arthroscopy because of reinjury that showed a radial rupture of the posterior segment of the medial meniscus. The ACL tendon graft was torn. The patient reported no clinical signs of instability and had regained his preoperative athletic sport level. There was no evidence of adverse reaction due to the implant. A biopsy examination of the implant site was not performed in this case.
For objective evaluation, the IKDC,22 OAK,21 and the Lysholm scores23 were obtained at follow-up. The results are presented in Fig 1. Radiographic Studies: All patients underwent a radiographic study at follow-up. There was no osteolysis or cystic bone formation detected. The tibial bone tunnel was visible in 89% of patients and the femoral bone tunnel in 11%. Four patients showed a slight sign of osteoarthritis on postoperative plain radiographs compared with their preoperative reports. MRI Studies: There was no MRI evidence of the screw in either the femur or the tibia. The MRIs showed no edema in the distal femur and proximal tibia adjacent to the drill holes. Localized collections of fluid were observed at the top of the femoral bone tunnel on MRI signal of varying diameter in a former study,25 but this was not observed in this series. The original 10-mm bone tunnels showed enlargement in the postoperative course. On follow-up MRI, partial enlargements of the bone tunnel could be measured. The enlargement of the femoral bone tunnel was greater than that of the tibial bone tunnel.20,25 The bone tunnel began to increase in size in the tibia from the distal end and in the femur from the proximal end. The bone remodeling of the tunnel is affected by the surgical position of the bone block in the respective tunnel. Complete bone tunnel remodeling occurred only where the bone blocks were located. For instance, if the bone graft was proximal in the femur and distal in the tibia, the remainder of the tunnel spanned by the soft tissue neoligament would not
FIGURE 2. Sagittal T1 MRI sequence 6 years postoperatively. New bone formation is seen in the femoral and the tibial bone tunnel
FIGURE 1. Lysholm, IKDC, and OAK score at median of 5.2 years (range, 4.1 to 6.4 years) follow-up.
RESULTS
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G. LAJTAI ET AL. and recently, interference expansion plugs.26 Because of the differences between different biodegradable implants, we emphasize that the long-term results reported here are specific to this material (copolymer 85/15 D,L lactide/glycolide), this screw, and this technique. In this study, the site of the 85/15 D,L lactide/ glycolide copolymer material was replaced by new bone formation and there was bone tunnel remodeling at 5 years, thereby confirming the hypothesis. It is clear from this and previous reports20,25 that there was no adverse tissue reaction and that this implant had fully degraded.27 Animal studies by others confirm the minimal reaction to this material in bone and replacement of the implant with new bone formation.28 The maintenance of the physical integrity of this implant for 1 month exceeds the time necessary for biological bone healing.29 This human study not only shows no
FIGURE 3. Coronal T1 MRI sequence 6 years postoperatively. New cancellous bone is seen at the top of the femoral bone tunnel.
DISCUSSION Biodegradable interference screws became popular for ACL reconstruction in connection with the advent of patellar-tendon transplants, yet there are no longterm results published related to the fate of these new materials or their effects on bone remodeling. To our knowledge, this is the first long-term study on one of these biodegradable interference screws. It is necessary that studies on bioabsorbable implants be material- and device-specific. Not all bioabsorbable materials are the same in composition, absorption rate, or tissue reaction. There are many different commonly used bioabsorbable materials used for interference screws; polyglycolic acid (PGA), polylactic acid (PLA), polyparadioxanone (PDS), polymer of PGA/PLA, and various stereoisomers of the lactic acid (PDLA) molecule. In addition to screws used in interference applications, a stereoisomer of polylactic acid, PLLA, is used in rods, plates, anchors,
FIGURE 4. Sagittal T1 MRI sequence 5 years postoperatively. Neoligament and new cancellous bone is clearly seen in the femoral and the tibial bone tunnels. Complete bone tunnel remodeling occurred only where the bone blocks were located.
BONE TUNNEL REMODELING AT SCREW SITE adverse clinical reactions, but the use of this biodegradable material produced no adverse reaction in the surrounding cancellous bone or the neoligament. Ideally, a biodegradable interference screw would degrade with minimal or no host-bone reaction. This and previous studies show this to be true for this material and device.20 In addition, replacement of the operative site with new bone formation would complete the restoration. PLLA implants degrade slower than a copolymer DL 85/15. It is reasonable to assume that the faster a material degrades, the earlier the osseus replacement takes place26,27,30 While an early replacement with fibrous granulation tissue takes place during degradation,31-36 until now little has been known about the long-term fate of the former implant site and its osseous replacement. A study of the tissue reaction of these materials requires that the implant be in place for a sufficient time to undergo degradation. This criterion was met in this study. A study on a poly L-lactide implant reported no tissue reaction, but this study was concluded before the time necessary for the material to undergo degradation.5 Tissue reaction occurs only during and after degradation of the implant. There have been few reports of the long-term fate and adverse tissue reaction of poly L-lactide in bone.6,7 MRI provides a noninvasive method of determining the physical status of a bioabsorbable implant and its absorption status in human subjects. The expansion of the clinical assessment to include the MRI investigation was facilitated by the absence of artefacts with the bioabsorbable interference screw as compared with a metal implant.10 The MRI study was helpful in determining the longevity of the physical properties of this screw in humans. Correlative MRI and gross physical inspection in canine pilot studies showed this screw to maintain its physical properties for 3 weeks and be dissolved and replaced by bone by 6 months.28 Comparison MRIs in this study showed that the bioabsorbable interference screw was not visible at the longterm follow-up. The MRI longitudinal studies helped clarify the safety issues raised in a previous report from this clinic concerning collection of fluid.25 All patients in the previous report and in this study had fluid collections shown by MRI, but they were not accompanied by any adverse clinical symptoms or signs. The immediate postoperative fluid collections were adjacent to the tibial and femoral drill holes and resolved after surgery. Subsequently, there was another area of fluid collection at the top of the femoral bone tunnel reported
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in our previous series.25 The fluid collections disappeared spontaneously and completely without therapy. The collections of fluid that subsequently accumulated around the implant were not associated with any adverse clinical finding or result. At long-term followup, we have not seen any fluid residue on MRI or potential negative affected clinic signs in our patient collective. Those areas showed new cancellous bone on MRI. In a previous report, a container phenomenon appeared as liquid in a container in the proximal femoral bone tunnel.20 This potential space was created in bone by the compaction method, which formed the walls of the container. Although it is known that the compaction method creates walls of dense bone, it was not known what effect bone compaction had on creating the container phenomenon. It was also not known if this area would be regenerated and remodeled with cancellous bone. Our findings show clearly that there is a complete regeneration of cancellous bone in these areas as well. None of our MRI studies performed for this long-term follow-up showed any signs of container phenomenon. MRI shows these areas to be filled with normal cancellous bone without any pathologic signals. In our former series, we reported about bone tunnel enlargement. The enlargement of the femoral bone tunnel was statistically significantly greater than that of the tibial bone tunnel.20,25 The bone tunnels began to increase in size in the tibia from the distal end and in the femur from the proximal end. Remodeling of the bone tunnel depends on the positioning of the bone blocks during ACL reconstruction. The bone remodeling of the tunnel is affected by the position of the bone block in the respective tunnel. Complete bone tunnel remodeling occurred only where the bone blocks were fixed. For instance, if the bone graft was proximal in the femur and distal in the tibia, the remainder of the tunnel spanned by the neoligament would require 5 years for osseous remolding. There was never, even after long-term follow-up, complete bone remodeling seen in the femoral or tibial bone tunnels where the neoligament was in place, except in the regions where the bone blocks were located. This study did not have correlative biopsy studies to confirm the histologic tissue status, but the assumption that the MRI interpretations reflect true new bone formation is supported by recent animal studies.28 This study shows the correlation between histology and MRI, which indicated that there was minimal surgical-site edema, minimal reaction to this material,
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and complete replacement by new bone formation of the previous site of this implant. Acknowledgment: The authors express their appreciation to Lanny L. Johnson, M.D., for reviewing the manuscript. Special thanks to my family Mona, Julian, and Nikolaus Lajtai for their personal support.
19. 20.
21.
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