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The Gross Morphology of Torn Human Anterior Cruciate Ligaments in Unstable Knees
The Gross Morphology of Torn Human Anterior Cruciate Ligaments in Unstable Knees Ian K. Y. Lo, M.D., Gerardus H. R. de Maat, Jody W. Valk, and Cyril B. Frank, M.D., F.R.C.S.C.
Summary: To evaluate the presence and incidence of reattachments of torn human anterior cruciate ligaments (ACL), we prospectively investigated 101 patients undergoing arthroscopic ACL reconstruction to study the intra-articular morphology of ACLs under circumstances in which functional healing had failed. Results showed that roughly 72% of these unstable knees had reattachment of the torn ACL to the posterior cruciate ligament (PCL). Eighteen percent had no signs of ACL reattachment but only 2% of previously torn ACLs were absent. These results suggest that even in chronic situations in which the knee remains functionally unstable, human ACLs rarely resorb. It also suggests that torn human ACLs commonly reattach in the knee, mainly to the PCL via a process that is consistent with scarring. While the function of these reattachments is clearly inadequate in people with unstable knees because of a combination of reattachment location, scar quantity, or quality, these results nonetheless show that the intra-articular environment in humans often maintains ACL stumps and it is not totally inhibitory to ACL reattachment via some biological process. Key Words: Anterior cruciate ligament—Ligament—Knee.
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omplete tears of the anterior cruciate ligament (ACL) commonly lead to anterior instability and knee dysfunction.1-6 Reconstruction of the ACL using autograft or allograft tissue has become commonplace because of the poor functional outcomes with nonoperative treatment and primary repair.1-3 Poor results have been attributed to the poor healing potential of the ACL and to the hostile intra-articular environment. This has led some authors to either state or imply that the ACL does not heal at all.1,7-11 During arthroscopic evaluation of an ACL disruption, however, it has been noted that the ACL sometimes appears to have reattached to the posterior From the Division of Orthopaedics, the University of Calgary, Calgary, Alberta, Canada (C.B.F.); the Department of Orthopaedics, University of Western Ontario, London, Ontario, Canada (I.K.Y.L.); and the Faculty of Medicine, The University of Utrecht, The Netherlands (G.H.R.d.M, J.W.V.). Address correspondence and reprint requests to C. B. Frank, M.D., F.R.C.S.C., Department of Surgery, the University of Calgary, 3330 Hospital Dr NW, Calgary, Alberta T2N 4N1, Canada. E-mail: [email protected] r 1999 by the Arthroscopy Association of North America 0749-8063/99/1503-1910$3.00/0
cruciate ligament (PCL) substance. Several authors have recognized this and other configurations of ACL disruptions including intrasynovial ruptures, horsehairlike tearing, bony avulsions, rounded ACL stumps, and complete resorption of the ligament.12-14 However, few have prospectively documented their incidence. In 1987, Fowler and Regan15 reported on 49 patients with chronic ACL insufficiency whom they had treated with minimal arthroscopic surgery and rehabilitation. In 7 cases they noted that a portion of the ACL remnant had reattached to the PCL. In 1991, Vahey et al.16 reported magnetic resonance imaging (MRI) findings and correlated them to arthroscopic results. Thirty percent of their cases involved ACL reattachment to the PCL, which led to difficulties in MRI interpretations. Others have reported on the possible function of this reattachment suggesting it may provide some restraint to anterior tibial translation.17 Our purpose in this study was to document the prevalence of this PCL reattachment versus other configurations of the ACL in patients who had symptoms and signs of ACL deficiency and who were undergoing ACL reconstruction
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at our institution. Our hypothesis was that very few ACLs would be found to be attached within the joint in this population of patients who remained unstable and who had thus failed to heal from a clinical point of view. METHODS From the period October 1995 to October 1996, 101 patients undergoing ACL reconstruction at the Sport Medicine Centre of the University of Calgary were studied. All patients had typical symptoms and signs of ACL insufficiency, with functional instability and positive pivot shifts. There were 60 male and 41 female patients with a mean age of 26.9 years (range, 13 to 45 years). The right knee was involved 69 times and the left knee 32 times. The mean time from initial injury to reconstruction was 29.4 months (range, 1 to 240 months). All procedures were performed by four experienced knee surgeons. Standard anteromedial and anterolateral portals were used for each knee arthroscopy. While viewing through each anterior portal, the gross morphology of the ACL remnant was determined both by observation and palpation with a probe. The classification of ACL attachments used by all surgeons was a modification of that proposed by Gachter12 (Fig 1). In this classification, class A (mop-end type) was characterized by frayed or mop-like torn ends of the disrupted ACL. Class B was defined as an intrasynovial or insubstance tear of the ACL. In these cases, the investing synovium appeared intact and the ACL may appear scarred and elongated underneath. Class C
was a bony avulsion of the ACL from the tibial eminence; class D was differentiated by retracted, torn ACL remnants with round or clubhead-like distention. Class E represented scarring or clear reattachment of the ACL to the PCL, either anteriorly, posteriorly, or both. Class F was characterized by complete resorption of the ACL with usually only a small portion of the tibial attachment recognizable. Class G represented apparent scarring of the torn ACL ends to each other; in these cases, there was no reattachment of the ACL to the PCL and the ACL remnant appeared elongated. Patients who were classifiable into more than one group were categorized as class H. To minimize bias, the surgeons were not made aware of any particular purpose to this study. Rather, they were simply asked to use the modified Gatcher classification12 to carefully evaluate ACL morphology in every case. In addition, patients were grouped into two broad categories. Those with intra-articular reattachments (class B, E, G) suggesting possible scarring or healing of the ACL remnants and those without intra-articular reattachments (class A, C, D, F) suggesting the absence of a scarring or healing response. Classification was confirmed by at least one other observer. After classification, each patient underwent reconstruction by that surgeon’s preferred technique. Data were analyzed with the assistance of a consulting statistician. Statistical significance was set at P ⬍ .05. Unpaired t tests were used to compare differences between sexes to define potential gender differences in the intra-articular classification of ACL disruptions and also to compare differences between classification,
FIGURE 1. Classification of the intra-articular morphology of anterior cruciate ligament disruptions. Note that Class H (not shown) is defined as a combination of 2 or more classes.
GROSS MORPHOLOGY OF TORN HUMAN ACL time from injury, and those patients with and without intra-articular reattachments.
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ments (class B, E, G) were seen 28.4 ⫾ 41.3 and 33.1 ⫾ 32.8 months (mean ⫾ SD). These intervals were not statistically different (P ⫽ .63).
RESULTS No significant differences were found between observers for the classification of ligament morphology. The overall distribution of intra-articular morphology seen at a mean of 29.4 months after initial injury (range, 1 to 240 months) from the pooled observations is shown in Fig 2. The vast majority (66%) of cases were class E, representing reattachment of the ACL remnant to the PCL. In 9 cases, the ACL could be classified into more than one class (class H). In 6 of these 9 cases, this represented a combination of class E with another. Thus, combined with the pure class E results, there were roughly 72% of patients with some reattachments of the torn ACL to the PCL. Not surprisingly, there were no patients in this series of chronic reconstructions which were classified as C (bony avulsions). Such avulsions are normally treated acutely by internal fixation in our centre. The distribution of morphology by sex is listed in Table 1, showing no significant differences. The mean time from injury to reconstruction is also summarized in Table 1. There was no consistent trend that correlated time from injury to grade or progression of classification (r2 ⫽ .05). Class B and G were seen earlier after injury that other classes (P ⬍ .0001), but the numbers are small. Patients with (class B, E, G) and without (class A, C, D, F) intra-articular reattach-
FIGURE 2. Distribution of disrupted anterior cruciate ligament morphology.
DISCUSSION This study evaluated the morphology of the disrupted ACL in patients who had failed nonoperative treatment and were undergoing ACL reconstruction. By definition, because all patients were undergoing surgical reconstruction for symptoms of ACL insufficiency, all of them had failed to heal functionally. Therefore, any ACL reattachments that were seen in this series must be noted to clearly represent functional failures of any healing response. As such, these results could simply be used to support the well-known clinical concept that ACL healing results are often mechanically deficient.1 Further consideration, however, suggests the important distinction that this deficiency is not attributable to resorption of the damaged ACL or to a total lack of any repair response around the torn ACL. Specifically, even in this series of unstable knees, nearly three quarters of disrupted ACLs showed some intra-articular reattachment. The majority of cases (66%) showed new attachments of the ACL to the PCL alone (class E) (Fig 3), or reattachment to the PCL plus new attachments elsewhere. All reattachments were substantial enough to require the surgeon to cut or shave the reattached ACL away from the PCL, or from its other locations in the joint. No other specific test of the quality or functionality of ACL attachments was attempted. In 16% of cases (class A and D), torn ends of semiacutely torn ACLs were still free. It was perhaps still too soon after their injury for these particular patients to have had their torn ACL reach a morphological endpoint; ACLs in those 16% could thus still either resorb (class F) or attach to the PCL (class E) with time. In 7 % of cases, loose but present ACL remnants were seen to be in continuity between normal ACL insertion sites (class B and G). These lesions could have occurred as a result of incomplete ACL injuries. Alternatively, however, ends of completely torn ACLs could have scarred together and remained, or become (by stretching), functionally loose. Importantly, very few (2%) ACLs in this series had actually resorbed, despite the fact that the vast majority represented chronic lesions at an average of 29.4 months after ACL injury. This observation of ACL reattachments after injury is, in itself, not unique. As noted above, other groups have commented previously on ACL reattachments.
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I.K.Y. LO ET AL. TABLE 1. Classification and Time From Injury of Disrupted ACLs by Sex Female
Male
Male and Female
Classification
No. (%)
Mean TSI
No. (%)
Mean TSI
Overall Mean TSI
SD
A B C D E F G H
4 (9.8) 2 (4.9) 0 (0.0) 4 (9.8) 26 (63.4) 1 (2.4) 1 (2.4) 3 (7.3)
54.0 8.0 0.0 32.3 25.6 72.0 15.0 64.8
3 (5.0) 2 (3.3) 0 (0.0) 5 (8.3) 41 (68.3) 1 (1.7) 2 (3.3) 6 (10.0)
16.0 10.0 0.0 30.5 32.7 20.0 12.0 4.4
37.7 9.0 0.0 31.3 29.9 46.0 13.0 24.5
30.0 1.5 0.0 38.2 42.5 36.1 2.0 54.8
Abbreviations: TSI, time since injury (months); SD, standard deviation.
However, when data in this current study are compared to such reports,15,16 the incidence of intra-articular reattachments documented here is higher. Fowler and Regan15 and Vahey et al.16 reported incidences of ACL reattachment to the PCL of only 14% and 30%, respectively. The difference between these reports and our study, we speculate, is not due to unique populations but rather to study design. Both previous reports15,16 were retrospective reviews in which the surgeon was not specifically observing and classifying the disrupted ACL morphology. In fact, a more recent series of conservatively treated ACL disruptions reported by Ihara et al.18,19 that underwent arthroscopy 3 months after injury with a view toward defining ACL morphology (more analogous to the purpose of this study), found that 78% of ligaments remained ‘‘in continuity.’’ Without evidence of complete ACL tears
FIGURE 3. Arthroscopic appearance of the tibial remnant of an anterior cruciate ligament disruption reattached to roof of the notch and the posterior cruciate ligament (open arrow). The femoral end of the ACL (solid arrow) is also seen to be attached to the convergence of the ACL stump and the PCL (Class E).
and/or proof of abnormal (i.e., new) attachments of torn ACLs in that series,18,19 it is not clear that Ihara’s results represent true reattachments, as opposed to partial injuries. While we did not document the completeness of ACL injury at the original episode, our demonstration of abnormal sites of ACL reattachment, on the other hand, almost completely rules out the possibility that ACL morphologies resulted from partial ACL injuries. What is perhaps the most interesting observation in the current clinical series of functionally deficient, complete ACL injuries, is that very few torn ACLs had resorbed. Instead, most had formed some sort of new intra-articular attachments. This appears to contradict the clinical notion that ACLs do not heal functionally because of the implied absence of any intra-articular healing response.7-10 In 1938, Palmer10 stated that ‘‘as a rule, total rupture of a cruciate band is probably incapable of healing spontaneously.’’ Arnoczky7 , in 1990, concluded that ‘‘although the anterior cruciate ligament is capable of a vascular response after injury, spontaneous repair (or healing by second intention) does not occur.’’ In 1994, Woo et al.11 stated that ‘‘midsubstance ACL tears usually do not heal’’ and Fu et al.9 suggested that ‘‘a torn anterior cruciate ligament often fails to show any healing response.’’ Our results most clearly contradict at least the last of these statements in that, despite their failure to heal functionally, some healing (reattachment) processes can and do occur in many torn ACLs. While all reattachments were functionally inadequate in the series of patients we studied (which were actually selected for surgery based on functional failure), the presence of some ACL healing responses is worth noting. We believe that this is an important distinction, because no ACL healing response implies that reattachment is virtually impossible.
GROSS MORPHOLOGY OF TORN HUMAN ACL Reattachment itself, of course, cannot be used to imply function, as any functionally reconnected ligament should perform a mechanical or physiological function (i.e., carry some tensile load). In the case of the ACL, the load-carrying function of intra-articular reattachments similar to those observed here, have, in fact, been tested by Crain et al.20 In a study of 48 patients undergoing ACL reconstruction, they documented the gross morphology of the ACL remnant and measured KT-1000 displacement before and after resection of ACL reattachments. They reported four different morphologies and noted differential changes in KT-1000 measurements according to ACL morphology. Patients with reattachments to the lateral or anterior intercondylar notch had the largest changes in laxity, but patients with ACLs scarred to the PCL also showed differences. This provides some evidence that reattachents can contribute to the stability of the human knee. Interestingly, these results in humans appear to be different than results of ACL transections in several animals, supporting the concept that humans may have a more favorable biological response to ACL injury.21-24 In animal models, as opposed to any ACL reattachment, complete ACL resorption after an injury is apparently very common.25-27 In the canine model, for example, O’Donoghue et al.25,26 reported that in ACLs that were completely transected and treated without repair, 23 of 24 ACLs retracted and resorbed. In 1 case, the ACL was reattached to the lateral portion of the intercondylar notch. More recently, Hefti et al.23 reported that 22 of 24 rabbit ACLs failed to regenerate after complete transection. In only two animals the ACL remnant reattached to the PCL. These apparent differences in intra-articular morphology between these models and human results may represent differences in study designs or in mechanisms of injury, but may also indicate differences between healing responses in animal and human ACLs, which remain to be defined. Finally, while we must again make it clear that all patients in the current series clearly did not exhibit a functional healing response, we believe that the fact that most exhibited some reattachment response is a very important distinction for two reasons. First, this suggests that if some patients formed new attachments with more appropriate qualities or quantities, in more appropriate locations within the joint, some may actually reattach functionally without reconstruction. This could explain why some documented ACL injury patients are able to cope without surgery.1,19 Second, while clinical data clearly show that current primary ACL repair techniques do not reliably promote func-
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tional ACL healing over time1-3, results of this study suggest that other means of promoting functional reattachment of torn ACLs by enhancing these endogenous biological responses should still be explored. Acknowledgment: We thank Dr. G.D. Bell, Dr. R. Bray, and Dr. N. Mohtadi for their valuable contributions in this study.
REFERENCES 1. Frank C, Jackson DW. The science of reconstruction of the anterior cruciate ligament. J Bone Joint Surg Am 1997;79:15561576. 2. Hawkins RJ, Misamore GW, Merritt T. Follow-up of the acute non-operative isolated anterior cruciate ligament tear. Am J Sports Med 1986;14:205-210. 3. Johnson RJ, Beynnon BD, Nichols CE et al. The treatment of injuries of the anterior cruciate ligament. J Bone Joint Surg Am 1992;74:140-151. 4. Kannus P, Jarvinen M. Conservatively treated tears of the anterior cruciate ligament. J Bone Joint Surg Am 1987;69:10071012. 5. Odensten M, Hamberg P, Nordin M et al. Surgical or conservative treatment of the acutely torn anterior cruciate ligament. Clin Orthop 1985;198:87-93. 6. Pattee GA, Fox JM, Del Pizzo W et al. Four to ten year follow-up of unreconstructed anterior cruciate ligament tears. Am J Sports Med 1989;17:430-435. 7. Arnoczky SP. Basic science of anterior cruciate ligament repair and reconstruction. AAOS Instr Course Lect 1990;40:201-212. 8. Frank CB. Ligament healing: current knowledge and clinical applications. J Am Acad Orthop Surg 1996;4:74-83. 9. Fu FH, Harner CD, Johnson DL. Biomechanics of knee ligaments: Basic concepts and clinical applications. Instr Course Lect 1994;43:137-150. 10. Palmer I. On the injuries of the ligaments of the knee joint: a clinical study. Acta Chir Scand (Suppl) 1938;53:1-282. 11. Woo SLY, An KN, Arnoczky SP, et al. Anatomy, biology and biomechanics of tendon, ligament, and meniscus. In: Simon SR. ed. Orthopaedic basic science. Park Ridge, IL: American Academy of Orthopaedic Surgeons, 1994;45-88. 12. Gachter A. The various faces of anterior cruciate ligament tears during arthroscopic examination. In: Jakob RP, Staubli HU, eds. The knee and the cruciate ligaments. Berlin: SpringerVerlag, 1992;190-192. 13. Jackson RW, Dandy DJ. Arthroscopy of the knee., New York: Grune & Stratton, 1976. 14. Johnson LL. Diagnostic and surgical arthroscopy. St. Louis, CV Mosby, 1981. 15. Fowler PJ, Regan WD. The patient with symptomatic chronic anterior cruciate ligament insufficiency. Results of minimal arthroscopic surgery and rehabilitation. Am J Sports Med 1987;15:321-325. 16. Vahey TN, Broome DR, Kowmas JK et al. Acute and chronic tears of the anterior cruciate ligament: Differential features at MR imaging. Radiology 1991;181:251- 253. 17. Kurzweil PR, Jackson DW. Chronic anterior cruciate ligaments. In Fu FH, Harner CD, Vince KG, eds. Knee surgery. Vol 1. Baltimore: Williams & Wilkins, 1994;731-747. 18. Ihara H, Megumi M, Takayanagi K, et al. Acute torn meniscus combined with acute cruciate ligament injury. Second look arthroscopy after 3-month conservative treatment. Clin Orthop 1994;307:146-154. 19. Ihara H, Miwa M, Deya K, et al. MRI of anterior cruciate ligament healing. J Comput Assist Tomogr 1995;20:317-321.
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20. Crain EH, Fithian DC, Daniel DM. Variation in ACL scar pattern: Does this contribute to anterior stability in ACL deficient knees? Presented at the Annual Meeting of the Arthroscopy Association of North America, San Diego, CA, 1997. 21. Deie M, Ochi M, Ikuta Y. High intrinsic healing potential of human anterior cruciate ligament. Acta Orthop Scand 1995;66: 28-32. 22. Hefti F. Healing process. In Jakob RP, Staubli HU, eds. The knee and the cruciate ligaments. Berlin: Springer-Verlag, 1992;257-261. 23. Hefti FL, Cress A, Fasel J et al. Healing of the transected anterior cruciate ligament in the rabbit. J Bone Joint Surg Am 1991;73:373-383.
24. Kleiner JB, Roux RD, Amiel D, et al. Primary healing of the anterior cruciate ligament. Presented at the 32nd Annual Meeting of the Orthopedic Research Society, New Orleans, LA, 1986. 25. O’Donoghue DH, Frank GR, Jeter WJ, et al. Repair and reconstruction of the anterior cruciate ligament in dogs. J Bone Joint Surg Am 1971;53:710-718. 26. O’Donoghue DH, Rockwood CA, Frank GR et al. Repair of the anterior cruciate ligament in dogs. J Bone Joint Surg Am 1966;48:503-519. 27. Woo SLY, Young EP, Ohland KJ et al. The effects of transection of the anterior cruciate ligament on healing of the medial collateral ligament: A biomechanical study of the knee in dogs. J Bone Joint Surg Am 1990;72:382-392.
Summary: To evaluate the presence and incidence of reattachments of torn human anterior cruciate ligaments (ACL), we prospectively investigated 101 patients undergoing arthroscopic ACL reconstruction to study the intra-articular morphology of ACLs under circumstances in which functional healing had failed. Results showed that roughly 72% of these unstable knees had reattachment of the torn ACL to the posterior cruciate ligament (PCL). Eighteen percent had no signs of ACL reattachment but only 2% of previously torn ACLs were absent. These results suggest that even in chronic situations in which the knee remains functionally unstable, human ACLs rarely resorb. It also suggests that torn human ACLs commonly reattach in the knee, mainly to the PCL via a process that is consistent with scarring. While the function of these reattachments is clearly inadequate in people with unstable knees because of a combination of reattachment location, scar quantity, or quality, these results nonetheless show that the intra-articular environment in humans often maintains ACL stumps and it is not totally inhibitory to ACL reattachment via some biological process. Key Words: Anterior cruciate ligament—Ligament—Knee.
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omplete tears of the anterior cruciate ligament (ACL) commonly lead to anterior instability and knee dysfunction.1-6 Reconstruction of the ACL using autograft or allograft tissue has become commonplace because of the poor functional outcomes with nonoperative treatment and primary repair.1-3 Poor results have been attributed to the poor healing potential of the ACL and to the hostile intra-articular environment. This has led some authors to either state or imply that the ACL does not heal at all.1,7-11 During arthroscopic evaluation of an ACL disruption, however, it has been noted that the ACL sometimes appears to have reattached to the posterior From the Division of Orthopaedics, the University of Calgary, Calgary, Alberta, Canada (C.B.F.); the Department of Orthopaedics, University of Western Ontario, London, Ontario, Canada (I.K.Y.L.); and the Faculty of Medicine, The University of Utrecht, The Netherlands (G.H.R.d.M, J.W.V.). Address correspondence and reprint requests to C. B. Frank, M.D., F.R.C.S.C., Department of Surgery, the University of Calgary, 3330 Hospital Dr NW, Calgary, Alberta T2N 4N1, Canada. E-mail: [email protected] r 1999 by the Arthroscopy Association of North America 0749-8063/99/1503-1910$3.00/0
cruciate ligament (PCL) substance. Several authors have recognized this and other configurations of ACL disruptions including intrasynovial ruptures, horsehairlike tearing, bony avulsions, rounded ACL stumps, and complete resorption of the ligament.12-14 However, few have prospectively documented their incidence. In 1987, Fowler and Regan15 reported on 49 patients with chronic ACL insufficiency whom they had treated with minimal arthroscopic surgery and rehabilitation. In 7 cases they noted that a portion of the ACL remnant had reattached to the PCL. In 1991, Vahey et al.16 reported magnetic resonance imaging (MRI) findings and correlated them to arthroscopic results. Thirty percent of their cases involved ACL reattachment to the PCL, which led to difficulties in MRI interpretations. Others have reported on the possible function of this reattachment suggesting it may provide some restraint to anterior tibial translation.17 Our purpose in this study was to document the prevalence of this PCL reattachment versus other configurations of the ACL in patients who had symptoms and signs of ACL deficiency and who were undergoing ACL reconstruction
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at our institution. Our hypothesis was that very few ACLs would be found to be attached within the joint in this population of patients who remained unstable and who had thus failed to heal from a clinical point of view. METHODS From the period October 1995 to October 1996, 101 patients undergoing ACL reconstruction at the Sport Medicine Centre of the University of Calgary were studied. All patients had typical symptoms and signs of ACL insufficiency, with functional instability and positive pivot shifts. There were 60 male and 41 female patients with a mean age of 26.9 years (range, 13 to 45 years). The right knee was involved 69 times and the left knee 32 times. The mean time from initial injury to reconstruction was 29.4 months (range, 1 to 240 months). All procedures were performed by four experienced knee surgeons. Standard anteromedial and anterolateral portals were used for each knee arthroscopy. While viewing through each anterior portal, the gross morphology of the ACL remnant was determined both by observation and palpation with a probe. The classification of ACL attachments used by all surgeons was a modification of that proposed by Gachter12 (Fig 1). In this classification, class A (mop-end type) was characterized by frayed or mop-like torn ends of the disrupted ACL. Class B was defined as an intrasynovial or insubstance tear of the ACL. In these cases, the investing synovium appeared intact and the ACL may appear scarred and elongated underneath. Class C
was a bony avulsion of the ACL from the tibial eminence; class D was differentiated by retracted, torn ACL remnants with round or clubhead-like distention. Class E represented scarring or clear reattachment of the ACL to the PCL, either anteriorly, posteriorly, or both. Class F was characterized by complete resorption of the ACL with usually only a small portion of the tibial attachment recognizable. Class G represented apparent scarring of the torn ACL ends to each other; in these cases, there was no reattachment of the ACL to the PCL and the ACL remnant appeared elongated. Patients who were classifiable into more than one group were categorized as class H. To minimize bias, the surgeons were not made aware of any particular purpose to this study. Rather, they were simply asked to use the modified Gatcher classification12 to carefully evaluate ACL morphology in every case. In addition, patients were grouped into two broad categories. Those with intra-articular reattachments (class B, E, G) suggesting possible scarring or healing of the ACL remnants and those without intra-articular reattachments (class A, C, D, F) suggesting the absence of a scarring or healing response. Classification was confirmed by at least one other observer. After classification, each patient underwent reconstruction by that surgeon’s preferred technique. Data were analyzed with the assistance of a consulting statistician. Statistical significance was set at P ⬍ .05. Unpaired t tests were used to compare differences between sexes to define potential gender differences in the intra-articular classification of ACL disruptions and also to compare differences between classification,
FIGURE 1. Classification of the intra-articular morphology of anterior cruciate ligament disruptions. Note that Class H (not shown) is defined as a combination of 2 or more classes.
GROSS MORPHOLOGY OF TORN HUMAN ACL time from injury, and those patients with and without intra-articular reattachments.
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ments (class B, E, G) were seen 28.4 ⫾ 41.3 and 33.1 ⫾ 32.8 months (mean ⫾ SD). These intervals were not statistically different (P ⫽ .63).
RESULTS No significant differences were found between observers for the classification of ligament morphology. The overall distribution of intra-articular morphology seen at a mean of 29.4 months after initial injury (range, 1 to 240 months) from the pooled observations is shown in Fig 2. The vast majority (66%) of cases were class E, representing reattachment of the ACL remnant to the PCL. In 9 cases, the ACL could be classified into more than one class (class H). In 6 of these 9 cases, this represented a combination of class E with another. Thus, combined with the pure class E results, there were roughly 72% of patients with some reattachments of the torn ACL to the PCL. Not surprisingly, there were no patients in this series of chronic reconstructions which were classified as C (bony avulsions). Such avulsions are normally treated acutely by internal fixation in our centre. The distribution of morphology by sex is listed in Table 1, showing no significant differences. The mean time from injury to reconstruction is also summarized in Table 1. There was no consistent trend that correlated time from injury to grade or progression of classification (r2 ⫽ .05). Class B and G were seen earlier after injury that other classes (P ⬍ .0001), but the numbers are small. Patients with (class B, E, G) and without (class A, C, D, F) intra-articular reattach-
FIGURE 2. Distribution of disrupted anterior cruciate ligament morphology.
DISCUSSION This study evaluated the morphology of the disrupted ACL in patients who had failed nonoperative treatment and were undergoing ACL reconstruction. By definition, because all patients were undergoing surgical reconstruction for symptoms of ACL insufficiency, all of them had failed to heal functionally. Therefore, any ACL reattachments that were seen in this series must be noted to clearly represent functional failures of any healing response. As such, these results could simply be used to support the well-known clinical concept that ACL healing results are often mechanically deficient.1 Further consideration, however, suggests the important distinction that this deficiency is not attributable to resorption of the damaged ACL or to a total lack of any repair response around the torn ACL. Specifically, even in this series of unstable knees, nearly three quarters of disrupted ACLs showed some intra-articular reattachment. The majority of cases (66%) showed new attachments of the ACL to the PCL alone (class E) (Fig 3), or reattachment to the PCL plus new attachments elsewhere. All reattachments were substantial enough to require the surgeon to cut or shave the reattached ACL away from the PCL, or from its other locations in the joint. No other specific test of the quality or functionality of ACL attachments was attempted. In 16% of cases (class A and D), torn ends of semiacutely torn ACLs were still free. It was perhaps still too soon after their injury for these particular patients to have had their torn ACL reach a morphological endpoint; ACLs in those 16% could thus still either resorb (class F) or attach to the PCL (class E) with time. In 7 % of cases, loose but present ACL remnants were seen to be in continuity between normal ACL insertion sites (class B and G). These lesions could have occurred as a result of incomplete ACL injuries. Alternatively, however, ends of completely torn ACLs could have scarred together and remained, or become (by stretching), functionally loose. Importantly, very few (2%) ACLs in this series had actually resorbed, despite the fact that the vast majority represented chronic lesions at an average of 29.4 months after ACL injury. This observation of ACL reattachments after injury is, in itself, not unique. As noted above, other groups have commented previously on ACL reattachments.
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I.K.Y. LO ET AL. TABLE 1. Classification and Time From Injury of Disrupted ACLs by Sex Female
Male
Male and Female
Classification
No. (%)
Mean TSI
No. (%)
Mean TSI
Overall Mean TSI
SD
A B C D E F G H
4 (9.8) 2 (4.9) 0 (0.0) 4 (9.8) 26 (63.4) 1 (2.4) 1 (2.4) 3 (7.3)
54.0 8.0 0.0 32.3 25.6 72.0 15.0 64.8
3 (5.0) 2 (3.3) 0 (0.0) 5 (8.3) 41 (68.3) 1 (1.7) 2 (3.3) 6 (10.0)
16.0 10.0 0.0 30.5 32.7 20.0 12.0 4.4
37.7 9.0 0.0 31.3 29.9 46.0 13.0 24.5
30.0 1.5 0.0 38.2 42.5 36.1 2.0 54.8
Abbreviations: TSI, time since injury (months); SD, standard deviation.
However, when data in this current study are compared to such reports,15,16 the incidence of intra-articular reattachments documented here is higher. Fowler and Regan15 and Vahey et al.16 reported incidences of ACL reattachment to the PCL of only 14% and 30%, respectively. The difference between these reports and our study, we speculate, is not due to unique populations but rather to study design. Both previous reports15,16 were retrospective reviews in which the surgeon was not specifically observing and classifying the disrupted ACL morphology. In fact, a more recent series of conservatively treated ACL disruptions reported by Ihara et al.18,19 that underwent arthroscopy 3 months after injury with a view toward defining ACL morphology (more analogous to the purpose of this study), found that 78% of ligaments remained ‘‘in continuity.’’ Without evidence of complete ACL tears
FIGURE 3. Arthroscopic appearance of the tibial remnant of an anterior cruciate ligament disruption reattached to roof of the notch and the posterior cruciate ligament (open arrow). The femoral end of the ACL (solid arrow) is also seen to be attached to the convergence of the ACL stump and the PCL (Class E).
and/or proof of abnormal (i.e., new) attachments of torn ACLs in that series,18,19 it is not clear that Ihara’s results represent true reattachments, as opposed to partial injuries. While we did not document the completeness of ACL injury at the original episode, our demonstration of abnormal sites of ACL reattachment, on the other hand, almost completely rules out the possibility that ACL morphologies resulted from partial ACL injuries. What is perhaps the most interesting observation in the current clinical series of functionally deficient, complete ACL injuries, is that very few torn ACLs had resorbed. Instead, most had formed some sort of new intra-articular attachments. This appears to contradict the clinical notion that ACLs do not heal functionally because of the implied absence of any intra-articular healing response.7-10 In 1938, Palmer10 stated that ‘‘as a rule, total rupture of a cruciate band is probably incapable of healing spontaneously.’’ Arnoczky7 , in 1990, concluded that ‘‘although the anterior cruciate ligament is capable of a vascular response after injury, spontaneous repair (or healing by second intention) does not occur.’’ In 1994, Woo et al.11 stated that ‘‘midsubstance ACL tears usually do not heal’’ and Fu et al.9 suggested that ‘‘a torn anterior cruciate ligament often fails to show any healing response.’’ Our results most clearly contradict at least the last of these statements in that, despite their failure to heal functionally, some healing (reattachment) processes can and do occur in many torn ACLs. While all reattachments were functionally inadequate in the series of patients we studied (which were actually selected for surgery based on functional failure), the presence of some ACL healing responses is worth noting. We believe that this is an important distinction, because no ACL healing response implies that reattachment is virtually impossible.
GROSS MORPHOLOGY OF TORN HUMAN ACL Reattachment itself, of course, cannot be used to imply function, as any functionally reconnected ligament should perform a mechanical or physiological function (i.e., carry some tensile load). In the case of the ACL, the load-carrying function of intra-articular reattachments similar to those observed here, have, in fact, been tested by Crain et al.20 In a study of 48 patients undergoing ACL reconstruction, they documented the gross morphology of the ACL remnant and measured KT-1000 displacement before and after resection of ACL reattachments. They reported four different morphologies and noted differential changes in KT-1000 measurements according to ACL morphology. Patients with reattachments to the lateral or anterior intercondylar notch had the largest changes in laxity, but patients with ACLs scarred to the PCL also showed differences. This provides some evidence that reattachents can contribute to the stability of the human knee. Interestingly, these results in humans appear to be different than results of ACL transections in several animals, supporting the concept that humans may have a more favorable biological response to ACL injury.21-24 In animal models, as opposed to any ACL reattachment, complete ACL resorption after an injury is apparently very common.25-27 In the canine model, for example, O’Donoghue et al.25,26 reported that in ACLs that were completely transected and treated without repair, 23 of 24 ACLs retracted and resorbed. In 1 case, the ACL was reattached to the lateral portion of the intercondylar notch. More recently, Hefti et al.23 reported that 22 of 24 rabbit ACLs failed to regenerate after complete transection. In only two animals the ACL remnant reattached to the PCL. These apparent differences in intra-articular morphology between these models and human results may represent differences in study designs or in mechanisms of injury, but may also indicate differences between healing responses in animal and human ACLs, which remain to be defined. Finally, while we must again make it clear that all patients in the current series clearly did not exhibit a functional healing response, we believe that the fact that most exhibited some reattachment response is a very important distinction for two reasons. First, this suggests that if some patients formed new attachments with more appropriate qualities or quantities, in more appropriate locations within the joint, some may actually reattach functionally without reconstruction. This could explain why some documented ACL injury patients are able to cope without surgery.1,19 Second, while clinical data clearly show that current primary ACL repair techniques do not reliably promote func-
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tional ACL healing over time1-3, results of this study suggest that other means of promoting functional reattachment of torn ACLs by enhancing these endogenous biological responses should still be explored. Acknowledgment: We thank Dr. G.D. Bell, Dr. R. Bray, and Dr. N. Mohtadi for their valuable contributions in this study.
REFERENCES 1. Frank C, Jackson DW. The science of reconstruction of the anterior cruciate ligament. J Bone Joint Surg Am 1997;79:15561576. 2. Hawkins RJ, Misamore GW, Merritt T. Follow-up of the acute non-operative isolated anterior cruciate ligament tear. Am J Sports Med 1986;14:205-210. 3. Johnson RJ, Beynnon BD, Nichols CE et al. The treatment of injuries of the anterior cruciate ligament. J Bone Joint Surg Am 1992;74:140-151. 4. Kannus P, Jarvinen M. Conservatively treated tears of the anterior cruciate ligament. J Bone Joint Surg Am 1987;69:10071012. 5. Odensten M, Hamberg P, Nordin M et al. Surgical or conservative treatment of the acutely torn anterior cruciate ligament. Clin Orthop 1985;198:87-93. 6. Pattee GA, Fox JM, Del Pizzo W et al. Four to ten year follow-up of unreconstructed anterior cruciate ligament tears. Am J Sports Med 1989;17:430-435. 7. Arnoczky SP. Basic science of anterior cruciate ligament repair and reconstruction. AAOS Instr Course Lect 1990;40:201-212. 8. Frank CB. Ligament healing: current knowledge and clinical applications. J Am Acad Orthop Surg 1996;4:74-83. 9. Fu FH, Harner CD, Johnson DL. Biomechanics of knee ligaments: Basic concepts and clinical applications. Instr Course Lect 1994;43:137-150. 10. Palmer I. On the injuries of the ligaments of the knee joint: a clinical study. Acta Chir Scand (Suppl) 1938;53:1-282. 11. Woo SLY, An KN, Arnoczky SP, et al. Anatomy, biology and biomechanics of tendon, ligament, and meniscus. In: Simon SR. ed. Orthopaedic basic science. Park Ridge, IL: American Academy of Orthopaedic Surgeons, 1994;45-88. 12. Gachter A. The various faces of anterior cruciate ligament tears during arthroscopic examination. In: Jakob RP, Staubli HU, eds. The knee and the cruciate ligaments. Berlin: SpringerVerlag, 1992;190-192. 13. Jackson RW, Dandy DJ. Arthroscopy of the knee., New York: Grune & Stratton, 1976. 14. Johnson LL. Diagnostic and surgical arthroscopy. St. Louis, CV Mosby, 1981. 15. Fowler PJ, Regan WD. The patient with symptomatic chronic anterior cruciate ligament insufficiency. Results of minimal arthroscopic surgery and rehabilitation. Am J Sports Med 1987;15:321-325. 16. Vahey TN, Broome DR, Kowmas JK et al. Acute and chronic tears of the anterior cruciate ligament: Differential features at MR imaging. Radiology 1991;181:251- 253. 17. Kurzweil PR, Jackson DW. Chronic anterior cruciate ligaments. In Fu FH, Harner CD, Vince KG, eds. Knee surgery. Vol 1. Baltimore: Williams & Wilkins, 1994;731-747. 18. Ihara H, Megumi M, Takayanagi K, et al. Acute torn meniscus combined with acute cruciate ligament injury. Second look arthroscopy after 3-month conservative treatment. Clin Orthop 1994;307:146-154. 19. Ihara H, Miwa M, Deya K, et al. MRI of anterior cruciate ligament healing. J Comput Assist Tomogr 1995;20:317-321.
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20. Crain EH, Fithian DC, Daniel DM. Variation in ACL scar pattern: Does this contribute to anterior stability in ACL deficient knees? Presented at the Annual Meeting of the Arthroscopy Association of North America, San Diego, CA, 1997. 21. Deie M, Ochi M, Ikuta Y. High intrinsic healing potential of human anterior cruciate ligament. Acta Orthop Scand 1995;66: 28-32. 22. Hefti F. Healing process. In Jakob RP, Staubli HU, eds. The knee and the cruciate ligaments. Berlin: Springer-Verlag, 1992;257-261. 23. Hefti FL, Cress A, Fasel J et al. Healing of the transected anterior cruciate ligament in the rabbit. J Bone Joint Surg Am 1991;73:373-383.
24. Kleiner JB, Roux RD, Amiel D, et al. Primary healing of the anterior cruciate ligament. Presented at the 32nd Annual Meeting of the Orthopedic Research Society, New Orleans, LA, 1986. 25. O’Donoghue DH, Frank GR, Jeter WJ, et al. Repair and reconstruction of the anterior cruciate ligament in dogs. J Bone Joint Surg Am 1971;53:710-718. 26. O’Donoghue DH, Rockwood CA, Frank GR et al. Repair of the anterior cruciate ligament in dogs. J Bone Joint Surg Am 1966;48:503-519. 27. Woo SLY, Young EP, Ohland KJ et al. The effects of transection of the anterior cruciate ligament on healing of the medial collateral ligament: A biomechanical study of the knee in dogs. J Bone Joint Surg Am 1990;72:382-392.