Arthroscopic Findings Associated with Roof Impingement of an Anterior Cruciate Ligament Graft

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1 /95/ $02.00/0 THE AMERICAN JOURNAL OF SPORTS MEDICINE, Vol. 23, No American Orthopaedic Society for Sports Medicine Arthroscopic Findings Associated with Roof Impingement of an Anterior Cruciate Ligament Graft Bruce M. Watanabe,* MD, and Stephen M. Howell, LTC, MC, USAFR From the *University of Texas Medical Branch, Division of Orthopedic Surgery, Galveston, Texas, and the Clinical investigation Facility (CIF), David Grant Medical Center, Travis Air Force Base, California ABSTRACT Nineteen patients with roof impingement of an anterior cruciate ligament graft had their grafts inspected during second-look arthroscopy. The diagnosis of roof im-pingement was suspected from the clinical findings of an effusion, extension deficit, recurrent instability, or anterior knee pain. The diagnosis was confirmed when a portion of the tibial tunnel was anterior to the tibial intersection of the slope of the intercondylar roof on a lateral roentgenogram of the fully extended knee. During second-look arthroscopy the impinged anterior cruciate ligament graft had one or more of the following features: fractured bundles, guillotined remnants at the tibial insertion, parallel fragmentation of an uninterrupted graft, fibrous nodule, or an extrusion of graft material at the outlet of the notch. We hypothesize that these changes in the integrity of the anterior cruciate ligament graft are caused by mechanical injury from roof impingement. Clinical Relevance. One should suspect that a patient with an effusion, extension deficit, recurrent instability, or anterior knee pain after an anterior cruciate ligament reconstruction may have roof impingement. A lateral roentgenogram in full extension is diagnostic if the tibial tunnel is anterior to the intercondylar roof. The surgeon should be aware that impinged grafts can have a variety of arthroscopic appearances in addition to the previously reported fibrous nodule or Cyclops lesion. Intercondylar roof impingement, caused by anterior placement of the tibial tunnel, can compromise the outcome of Address correspondence and reprint requests to Stephen M. Howell, MD, 8100 Timberlake Way, Suite F, Sacramento, CA The views expressed herein are those of the authors and do not reflect the official policy or position of the United States Department of Defense or the United States Government. One author has commercial affiliation with a product named and used in this study. an ACL reconstruction. 3,7,10,13,16-19,21 Clinically, roof impingement causes effusions, extension deficits, recurrent instability, or anterior knee pain, 3,6,7,10,13,16-18,21 Arthroscopic observations have shown that roof impingement can injure the anterior portion of the graft causing it to degenerate into a fibrous nodule 6,18 or Cyclops lesion The purpose of this study was to review the clinical find-ings associated with an impinged ACL graft, present a simple, inexpensive roentgenographic technique to diagnose roof impingement, and to describe the arthroscopic features of an impinged graft. We were able to define four additional graft injury patterns in addition to the fibrous nodule or Cyclops lesion that we hypothesize are caused by roof impingement. MATERIALS AND METHODS Selection Criteria and Clinical Evaluation Our study population comprised patients with reconstructed knees that had an effusion, extension deficit, recurrent instability, or anterior knee pain. An extension deficit existed when the passive extension of the recon-structed knee was less than the normal knee. 11,16 Recurrent anterior instability was diagnosed by a KT-1000 arthrometer (MedMetric, San Diego, California) when a 3-mm or greater increase in anterior translation was measured in the reconstructed knee compared with the normal knee by using a manual maximum test. 2 The diagnosis of roof impingement was determined from a lateral roentgenogram of the fully extended knee before performing the second-look arthroscopy. The arthroscopic appearance of the graft was determined by a review of the operative note and either the intraoperative photographs or videotape. Patient Profile Nineteen patients who had been operated on between

2 Vol. 23, No. 5, 1995 Arthroscopic Findings in an ACL Graft 617 December 1989 and February 1994 fulfilled the clinical selection criteria; from their lateral roentgenograms it was determined that they had roof impingement. There were 2 female and 17 male patients with an average age of 27 years. Five patients were reconstructed by the senior author (SMH) and 14 had their primary ACL reconstructions done by other surgeons. Eighteen knees were reconstructed with autogenous tissues: 13 received a bone-patellar tendon-bone graft and 5 received a double-looped semitendinosus-gracilis hamstring graft. One patient had a fresh-frozen, nonirradiated, Achilles tendon allograft. Roentgenographic Diagnosis of Roof Impingement The lateral roentgenogram of the fully extended knee was analyzed to calculate the percentage of roof impingement, to determine the sagittal location of the tibial tunnel, and to measure the roof angle. The plane of the tibial plateau was defined by a line between the most superior points of the anterior and posterior margins of the proximal end of the tibia. The amount of impingement by the roof was calculated by measuring the distance on the plane of the tibial plateau from the intersection of the anterior border of the tibial tunnel with the tibial plateau to the interection of the line of the slope of the intercondylar roof and the tibial plateau. This distance was then divided by the width of the tibial tunnel and the result was expressed as a percentage. A positive result was used to indicate impingement and a negative one indicated an unimpinged location. 11,12,16 A correction was required in the calculation of the amount of roof impingement when the reconstructed knee did not fully extend. The difference in knee extension was measured using a goniometer. The calculation of the percentage of roof impingement was increased 3% for each degree of extension loss to correct for the underestimation of the roof impingement that is caused by a flexion contracture. 16 The location of the central axis of the tibial tunnel was calculated by extending the line of the central axis of the tibial tunnel to its intersection with the line of the tibial plateau. The distance from this intersection to the anterior end of the line of the tibial plateau was then measured. This distance was then divided by the length of the line of the tibial plateau, and the result was expressed as a percentage. The slope of the intercondylar roof was measured as the angle subtended by the line of the slope of the intercondylar roof with the line of the long axis of the femur. 11,12,15,16 Magnetic Resonance Imaging Diagnosis of Roof Impingement The roentgenographic diagnosis of roof impingement was confirmed by magnetic resonance imaging (MRI) in 11 patients. Roof impingement existed when the graft demonstrated a regionalized signal increase confined to the distal two-thirds of the intraarticular portion of the graft. Posterior deformation of the graft caused by direct contact of the intercondylar roof against the anterior surface of the graft was also used as a sign of impingement. 10,12,13,15,16 We specifically inspected each MR scan for evidence of frac-tured bundles and fibrous nodules. 18 The MR scan was used to confirm the roentgenographic diagnosis of roof impingement but was not a requirement to be included in the study. Arthroscopic Appearance of Impinged ACL Grafts Both authors independently reviewed each patient s operative notes, and intraoperative photographs or videotape. We agreed on four new arthroscopic patterns of graft injury that we believed to be associated with roof impingement, in addition to the fibrous nodule or Cyclops lesion. 7,17 These injury patterns were 1) fractured bundles, identified by a rupture of a portion of the graft at its midsection; 2) guillotined fibers, identified by shorter, 3 to 4 mm in length, graft fibers amputated more distally at the entrance of the tibial tunnel into the notch; 3) parallel fragmentation, identified by multiple, lax, parallel, uninterrupted bundles; and 4) extrusion, identified by molding of the graft by the distal end of the notch. Both authors then rereviewed each graft s arthroscopic appearance and recorded the incidence of each injury pattern. Reason for Second-Look Arthroscopy The second-look arthroscopy was undertaken to regain knee extension in 12 patients with stable knees, or to replace a lax or torn ACL graft in 7 patients with unstable knees. Extension was regained by performing a delayed roofplasty. 8 The time from primary reconstruction to second-look arthroscopy ranged from 2 to 55 months, with an average of 15 months. Data Analysis The clinical findings, roentgenographic measurements, and the arthroscopic appearance of the graft were analyzed using descriptive statistics. Multiple regression analysis with step-wise removal of insignificant variables was done to determine if roof angle, percent impingement, and extension deficit were predictive of the stability of the knee at the time of the second-look arthroscopy. Data reduction was performed on a personal computer (Macintosh 840 AV; Apple Computer, Cupertino, California) using Statview II (Abacus Concepts, Berkeley, California). RESULTS Clinical Findings Six (32%) of the 19 patients with roof impingement were noted to complain of effusions, 12 (63%) complained of an extension loss. Eight (42%) of the knees had recurrent anterior instability and 8 (42%) had anterior knee pain. The average extension loss was 9 ± 10 (Table 1). Nine of 11(82%) of the patients with reconstructed knees

3 618 Watanabe and Howell American Journal of Sports Medicine TABLE 1 Preoperative Results and Arthroscopic Findings Findings Graft a Subjective Objective Pain Effusion Extension Instability KT1000 b Extension c % impingment loss PTB Yes No Yes Yes DLSTG Yes No Yes Yes PTB Yes Yes Yes No PTB Yes No Yes No DLSTG No Yes No No PTB Yes No No Yes DLSTG No No No Yes PTB No No Yes No PTB No No Yes No PTB No No Yes No DLSTG Yes No Yes No ATA No No No Yes PTB No Yes No Yes PTB Yes Yes Yes No PTB No No No Yes PTB No Yes Yes No DLSTG No No Yes No PTB Yes Yes Yes No PTB No No No Yes Total ± = ± 24 a PTB, patellar tendon-bone; DLSTG, double-looped semitendinosus/gracilis; ATA, Achilles tendon allograft. b KT-1000 arthrometer translation (reconstructed-normal) difference at manual maximum. c Difference in extension: values greater than zero indicate extension deficit of reconstructed site. with extension deficits had stable knees. Six of eight (75%) of the patients whose knees had regained full extension had unstable knees. Therefore, the stability of the reconstructed knee with roof impingement can be predicted by knowing whether the reconstructed knee has full extension or an extension deficit (r 2 = 0.46, P = ) (Fig. 1). Roentgenographic Analysis In all knees that we studied, the lateral roentgenogram of the knee in maximal extension revealed that a portion of the tibial tunnel was anterior to the slope of the intercondylar roof (Fig. 2). The mean percentage of roof impingement was 57% (range, 20% to 100%). The mean location for the center of the tibial tunnel was 32% ± 8% (range, 20% to 44%) from the anterior edge of the tibia. The average roof angle was 34 (range, 22 to 45 ) (Table 1). MRI Analysis An impinged ACL graft was determined on every MR scan by the pathognomonic finding of a regionalized signal increase within the distal two-thirds of the intraarticular pathway of the graft. One patient demonstrated a fractured anterior bundle that was displaced into the notch. No fibrous nodules were identified. Arthroscopic Appearance of Impinged ACL Grafts The following descriptions characterize and differentiate the five injury patterns that we believe are associated with roof impingement of an ACL graft. Fractured Bundles. A bundle of graft material was separated from the main body of the graft. The injury involved the anterior portion of the graft, and the fracture occurred near the midpoint (Fig. 3). The injury did not occur near the femoral origin or the tibial insertion. The posterior portion of the graft was usually undamaged and continued to provide stability in the majority of knees. The ends of the fractured bundle were not remodeled or rounded off, making them distinct from the fibrous nodule 6,18 and Cyclops lesion. 7,17 Ten (53%) of the knees had fractured bundles, establishing this injury pattern as the most common. Guillotined Graft Remnants. The anterior fibers of the graft were amputated within 3 to 5 mm of exiting the tibial tunnel and entering the intercondylar notch. This left short, stubby graft remnants that stood up like closely cropped hair. These are distinct from fractured bundles, which are more substantial in length and girth, and which are injured in the middle rather than the distal third of the graft. As was the case with fractured bundles, only the anterior fibers were primarily affected with minimal involvement of the posterior portion of the graft (Fig. 4). Seven (37%) of the reconstructions had guillotined graft fibers. Parallel Fragmentation. In parallel fragmentation the original tubular or rectangular graft was separated into a series of continuous, smaller bundles that remained in continuity but were elongated (Fig. 5). If the fragmentation was confined to the anterior portion of the graft, the knee was stable. If the fragmentation extended and included the entire graft,

4 Vol. 23, No. 5, 1995 Arthroscopic Findings in an ACL Graft 619 the knee was found to be unstable. Six (32%) of the knees had parallel fragmentation, and half of these knees were unstable. Parallel fragmentation differs from fractured bundles, guillotined remnants, and the fibrous nodule because the graft is not ruptured but remains continuous. Fibrous Nodule. The fibrous nodule or Cyclops lesion is a single, large, remodeled bundle of fibrous tissue that varies from 1 X 1 cm to 2 X 3 cm in size. It arises from the anterior or anterolateral aspect of the distal third of the ACL graft. 6,7,17,18 We observed that the fibrous nodule was always associated with other graft injury patterns (Figs. 3 and 5). Six (32%) of the knees had fibrous nodules. Extrusion of Graft. The extruded graft differs from an unimpinged graft because the distal third of the graft extends beyond the distal opening of the notch. The graft has the same shape as the distal outlet of the intercondylar notch. This is different from the fibrous nodule because the graft remains uninterrupted and does not develop a distinct nodular lesion (Fig. 6). Two (11%) of the knees had graft extrusion, making this the least common injury pattern. Combination Lesions. Twelve (63%) of the knees had a combination of injury patterns. Seven (37%) of the knees had just one arthroscopic finding of graft injury associated with roof impingement. Extrusion of the graft was seen as an isolated lesion in only two patients (11%) (Table 1). DISCUSSION TABLE 1 Continued Findings Arthroscopic Fractured Guillotined Fibrous Parallel Extrusion bundles nodule fragment No Yes No Yes No No Yes Yes No No Yes No Yes No No No Yes No Yes No Yes Yes No No No No No No No Yes No Yes Yes No No No No No No No Yes Yes No Yes No Yes No Yes No No Yes No Yes No No Yes No No No No Yes No No Yes No No No No No Yes No No Yes Yes No Yes No No Yes No Yes No No No No No Yes No No No Yes No No No No The patients in our study group with impinged ACL grafts were identified by their clinical findings of extension deficits, effusions, instability, or anterior knee pain. These findings have been observed in earlier studies that included impinged grafts. Extension deficits are common in grafts Figure 1. The side-to-side difference in knee extension (I-N) (degrees) is compared with the side-to-side difference in anterior tibial translation measured by the arthrometer during the application of the manual maximum test. Knees with flexion contractures were almost always stable. Knees with impinged grafts that regained full extension were always unstable. inserted with roof impingement. 5,6,10,15,16,18,19 Effusions were observed by Fisher and Shelbourne 4 in their patients with symptomatic extension block caused by impingement of a patellar tendon graft, by Ferkel et al 3 in their patients with impinged GORE-TEX grafts and by Yamamoto et al 21 in their patients with an impinged ligament augmentation device. Instability can result if the graft is severely impinged, 16 Anterior knee pain often occurs in patients with an impinged ACL graft. 10,18 A patient seen after an ACL reconstruction with an extension deficit, effusion, recurrent instability, or anterior knee pain should be evaluated with a lateral roentgenogram with the knee in maximal extension to determine if the graft is being traumatized by roof impingement. The lateral roentgenogram of the reconstructed knee in full extension is an inexpensive, sensitive, and specific technique for diagnosing roof impingement and can be rou-tinely performed in any roentgenographic suite.11,13,15,16 If the roentgenogram is taken with the knee in flexion, the roof impingement can be missed (Fig. 2). If a patient fails to regain full extension by 2 months after the reconstruc-tion, we routinely perform a lateral roentgenogram of the maximally extended knee to be certain that the graft is not impinged. Magnetic resonance imaging is also effective for diagnosing roof impingement but it is costly, which prevents it from being routinely used as a method to analyze the graft and the placement of the tibial tunnel. The pathognomonic findings of an impinged graft on MR scanning are a re-gionalized signal increase confined to the distal two-thirds of the graft, and posterior bowing of the graft caused by direct contact of the graft against the intercondylar roof, or both. 10,12-16 Eleven (58%) of the knees in this study had an MRI scan, and all demonstrated an increased signal in the distal two-thirds of the graft, verifying the roentgeno-graphic diagnosis of roof impingement.

5 620 Watanabe and Howell American Journal of Sports Medicine Figure 2. A, roof impingement cannot be diagnosed or quantitated if the lateral roentgenogram is taken with the knee in flexion. B, the roentgenogram of the extended knee shows that the tibial tunnel is anterior to the slope of the intercondylar roof, establishing the diagnosis of roof impingement. The percentage of roof impingement in this knee was 75%. If this knee were found to have a flexion contracture when compared with the extension of the normal knee, then the percentage of roof impingement would be increased 3% for each degree of extension loss. Five distinct arthroscopic appearances of the impinged graft were observed that we hypothesize represent differ-ent patterns of mechanical injury to the graft caused by roof impingement. Because these distinct graft appearances may represent different points on a continuum of graft damage, these distinct injury patterns were more likely to occur in combination rather than in isolation. For example, in Figure 3, A through D, the anterior bundles of the graft may have initially fractured and subsequently remodeled into a fibrous nodule while the middle bundles were initially protected and have subsequently fractured. The posterior fibers remain protected and are intact. Fractured bundles was the most common injury pattern that we found and this always involved the anterior portion of the graft. This is consistent with our observations that the intercondylar roof damaged the anterior surface of the graft first. These fibers may rupture with repeated knee extension. The posterior fibers were often spared and remained uninterrupted, explaining why 70% of these knees with fractured bundles were stable at the time of presentation. In cases of moderate or severe impingement, the injury pattern may extend to the posterior fibers, causing them to rupture and rendering the knee unstable. Injury to the graft as it entered the intercondylar notch from the tibial tunnel was thought to be caused by guillotining of the graft by the distal end of the intercondylar roof. Guillotined fibers were only 3 to 5 mm in length and protruded like closely cropped hair from the intraarticular entrance of the tibial tunnel. The localization of this injury pattern to the anterior surface of the graft is consistent with the roof impingement hypothesis of graft injury. In parallel fragmentation, the anterior fibers were al-ways involved. They remained in continuity but were elon-gated and lax when probed. When the fragmentation was confined to only the anterior fibers, the knees were stable. When the injury involved the entire body of the graft, the knees were unstable. For roof impingement to cause parallel fragmentation, the graft would have to avoid fracturing, which could occur if the impingement caused the graft to stretch early after implantation. Laxity of the anterior surface of the graft would minimize abrasion yet allow flexing of the graft, which could cause separation of several strands from the main body of the graft, producing parallel fragments. Disruption of the parallel fibers would convert this injury pattern to fractured bundles. Formation of a fibrous nodule or Cyclops lesion could occur if the fractured bundles coalesced and remodeled into an organized bundle of fibrous tissue. The last injury pattern, graft extrusion, can be explained

6 Vol. 23, No. 5, 1995 Arthroscopic Findings in an ACL Graft 621 E Figure 3. It was common to observe a combination of injury patterns in the graft subjected to roof impingement. A, the fractured bundle occurs in the midportion of the graft and involves the anterior surface of the graft. B, the posterior portion of the graft is in continuity and not attenuated, which explains why this knee remained stable on clinical and arthrometric testing. C, impingement of the anterior surface of the graft by the intercondylar roof is noted with the knee at 30 of flexion. D, in maximal extension, the graft is impinged and a portion of the fractured bundles has coalesced and remodeled to form a fibrous nodule. E, the illustration of the knee in the sagittal plane localizes the fracture to the midsection of the anterior portion of the graft. The bundle is displaced anterior into the notch and may cause a clunk during knee extension. by a mismatch in the diameter of the graft and the volume of the intercondylar notch. An inadequate notchplasty, or the insertion of an oversized graft, may force the graft to slowly extrude from the notch as the knee tries to regain extension. This can occur only if the graft remains in continuity, which is likely if the impingement is less severe and the abrasive affects of impingement are minimal. Our observations are consistent with a previous study in which knees with intercondylar roof impingement that had an extension deficit were likely to remain stable, and knees that regained extension were likely to become unstable16 (Fig. 1). Minimal levels of roof impingement can result in an extension deficit preserv-

7 622 Watanabe and Howell American Journal of Sports Medicine E Figure 4. A, the main body of the graft is stable to probing. B, with the knee in 10 of flexion the graft is impinged. C and D, the anterior portion of this graft has been guillotined by the intercondylar roof as the graft enters the notch through the tibial tunnel. The guillotined graft fibers are 3 to 5 mm in length and stand up like closely cropped hair. E, the illustration of the knee in the sagittal plane shows that only the anterior portion of the graft is guillotined. Loss of this small portion of the graft has allowed this knee to regain full extension. The rest of the graft is unaffected and continues to provide stability to the knee. ing enough graft so that the knee remains stable. 10,15,16 When roof impingement is more severe, the knee can regain extension but only by the graft elongating 16 or rupturing. Aggressive physical therapy has been recommended to treat patients with extension deficits after ACL reconstruction. 4 This treatment should only be prescribed after the knee has been evaluated with a lateral roentgenogram with the knee in full extension. If the patient has an impinged graft,

8 Vol. 23, No. 5, 1995 Arthroscopic Findings in an ACL Graft 623 E Figure 5. A, in flexion, a fibrous nodule is seen on the anterior portion of the graft. B through D, the remaining graft has parallel fragmentation. These fibers are subdivided from the original body of the graft and elongated, which explains why the reconstructed knee is unstable. E, the illustration of the knee in the sagittal plane shows that the entire graft is elongated with multiple parallel bundles, and remains in continuity. This knee was unstable because the entire graft was lax. a delayed roofplasty should be performed to prevent further injury to the graft before resuming physical therapy. 5,10,15,18 A principle that we learned from our experience is to avoid roof impingement at the time of graft implantation to prevent the injury to the graft that this article has described. One method the surgeon can use to help avoid roof impinge-

9 624 Watanabe and Howell American Journal of Sports Medicine C Figure 6. A, at 30 of flexion, the ACL graft appears to flare out at its base. B, in maximal extension, the flaring of the graft appears to have resulted from extrusion of the graft by the intercondylar roof (arrow). Because the graft is in continuity and not elongated, this knee remains stable but has a 10 flexion contracture compared with the unoperated knee. C, the illustration of the knee in the sagittal plane shows that the distal anterior portion of the graft has been extruded from the intercondylar notch. As opposed to the fibrous nodule, the extruded graft has the same shape as the distal outlet of the intercondylar notch and is in continuity with the remainder of the graft. Extrusion prevents the knee from regaining full extension. ment is to obtain a lateral roentgenogram with the knee in maximum extension in the operating room with the tibial guide pin in place. The guide pin should be 4 to 5 mm posterior and parallel to the slope of the intercondylar roof with the knee fully extended. The sagittal location and inclination of the pin will vary considerably between knees because the slope of the intercondylar roof and knee extension vary widely between patients. 1,11,20 The technique that we currently use customizes the location for the tibial tunnel and checks for roof impingement without the inconvenience and expense of an intraoperative roentgenogram. 8,10 To be certain that the notch has been expanded to account for the three-dimensional volume of the graft, we favor the use of an impingement rod to check the extent of the roofplasty before inserting the graft. The impingement rod, which is the same diameter as the graft, should freely pass into the notch and through the tibial tunnel with the knee in maximum extension. REFERENCES 1. Brattström H: Patela alta in non-dislocating knee joints. Acta Orthop Scand 41: , Daniel DM, Akeson WH, O Connor JJ (eds): Knee Ligaments: Structure, Function, Repair. New York, Raven Press, Ferkel RD, Fox JM, Wood D, et al: Arthroscopic second look at the GORE-TEX ligament. Am J Sports Med 17: , Fisher SE, Shelbourne KD: Arthroscopic treatment of symptomatic extension block complicating anterior cruciate ligament reconstruction. Am J Sports Med 21: , 1993

10 Vol. 23, No. 5, 1995 Arthroscopic Findings in an ACL Graft Fullerton LR, Andrews JR: Mechanical block to extension following augmentation of the anterior cruciate ligament: A case report. Am J Sports Med 12: , Gachter A: Arthroscopic shaving following cruciate ligamentplasty. Orthopade 79: , Greenfield MA, Scott WN: The Cyclops syndrome in anterior cruciate ligament reconstruction using iliotibial band. Am J Knee Surg 7: 39-41, Howell SM: Roof impingement of ACL grafts: Diagnosis, causes, prevention, and late surgical correction, in Feagin JA (ed): The Crucial Ligaments; Diagnosis and Treatment of Ligamentous Injuries About the Knee. New York, Churchill Livingstone, 1994, pp Howell SM: Arlhroscopic ACL reconstruction using double-looped semi-tendinosus and gracilis autogenous hamstring graft. Oper Tech Sports Med 1: 58-65, Howell SM: Arthroscopic roofplasty: A method for correcting an extension deficit caused by roof impingement of an anterior cruciate ligament graft, Arthroscopy 8: , Howell SM, Barad SJ: Knee extension and its relationship to the slope of the intercondylar roof. Am J Sports Med 23: , Howell SM, Berns GS, Farley TE: Unimpinged and impinged anterior cruciate ligament grafts: MR signal intensity measurements. Radiology 179: , Howell SM, Clark JA: Tibial tunnel placement in anterior cruciate ligament reconstructions and graft impingement. Clin Orthop,283: , Howell SM, Clark JA, Blasier RD: Serial magnetic resonance imaging of hamstring anterior cruciate ligament autografts during the first year of implantation: A preliminary study. Am J Sports Med 19: 42-47, Howell SM, Clark JA, Farley TE: Serial magnetic resonance study assessing the effects of impingement on the MR image of the patellar tendon graft. Arthroscopy 8; , Howell SM, Taylor MA: Failure of reconstruction of the anterior cruciate ligament due to impingement by the intercondylar roof. J Bone Joint Surg 75A: , Jackson DW, Schaefer RK: Cyclops syndrome: Loss of extension following intra-articular anterior cruciate ligament reconstruction. Arthroscopy 6: , Marzo JM, Bowen MK, Warren RF, et al: lntraarticular fibrous nodule as a cause of loss of extension following anterior cruciate ligament reconstruction. Arthroscopy 8: 10-18, Romano VM, Graf BK, Keene JS, et al: Anterior cruciate ligament reconstruction. The effect of tibial tunnel placement on range of motion. Am J Sports Med 21: , Scuden GR: The femoral intercondylar roof angle: Radiographic and MRI measurement Am J Knee Surg 6: 10-14, Yamamoto H, lshibashi T, Muneta T, et al: Effusions after anterior cruciate ligament reconstruction using the ligament augmentation device. Arthroscopy 8: , 1992