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DOI: 10.1148/radiol.2252010357
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(Radiology 2002;225:541-550.)
© RSNA, 2002

Musculoskeletal Imaging

Anterior Cruciate Ligament Reconstruction with Bioabsorbable Polyglycolic Acid Interference Screws: MR Imaging Follow-up1

Fabienne D. Bach, MD, Robert Y. Carlier, MD, Jean B. Elis, MD, Dominique M. Mompoint, MD, Antoine Feydy, MD, Olivia Judet, MD, Philippe Beaufils, MD and Christian Vallée, MD

1 From the Departments of Diagnostic Imaging (F.D.B., R.Y.C., D.M.M., A.F., C.V.) and Orthopedic Surgery (J.B.E.), Raymond Poincaré Hospital University Teaching Hospital, 104 Boulevard Raymond Poincaré, 92380 Garches, France; Department of Diagnostic Imaging, American Hospital of Paris, Neuilly sur Seine, France (O.J.); and Department of Orthopedic Surgery, A. Mignot Hospital, Versailles, France (P.B.). Received January 24, 2001; revision requested March 12; final revision received February 19, 2002; accepted March 1. Address correspondence to R.Y.C. (e-mail: robert.carlier@rpc.ap-hop-paris.fr).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
PURPOSE: To examine at magnetic resonance (MR) imaging the degradation of an interference screw made of polyglycolic acid (67.5%) and trimethylene carbonate (32.5%) and compare the MR findings with the clinical evaluation results.

MATERIALS AND METHODS: Clinical and MR imaging studies were performed concomitantly 6 months (in 20 patients), 1 year (in 10 patients), and 2 years (in eight patients) after surgery. Screw resorption rate, tibial tunnel appearance and contents, epiphyseal reaction, reconstructed ligament appearance, bone plug healing, joint effusion, and synovitis were evaluated.

RESULTS: The screw was observed to be partially resorbed (by approximately one-third) at 6 months and totally resorbed at 1 year. Enhancement of the tunnel content, which can be linked to bone healing and screw replacement, was seen without a surrounding inflammatory reaction. Bone tunnel enlargement was observed and remained stable over time; this phenomenon has often been reported with metallic or polylactic acid interference screws and could be due to the position of the screw within the tunnel. The tissue that was seen at MR imaging to be replacing the screw was either fibrous or fatty and fibrous but never bone.

CONCLUSION: Resorption of the screw does not appear to be related to clinical results.

© RSNA, 2002

Index terms: Knee, CT, 452.12111 • Knee, injuries, 452.252, 452.4857 • Knee, ligaments, menisci, and cartilage, 452.252, 452.4857 • Knee, MR, 452.12141, 452.12143 • Knee, prostheses, 452.1267, 452.1269 • Knee, surgery, 452.45


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Disruption of the anterior cruciate ligament (ACL) is a common knee injury, and subsequent functional instability is often noted. Surgical reconstruction of the ACL may be indicated to reduce the morbidity associated with this injury. Fixation of bone-to–patellar tendon–to-bone autografts with metallic or bioabsorbable interference screws has produced good clinical results (1–15).

The initial use of metallic interference screws can complicate revision surgery (16) and hinder magnetic resonance (MR) imaging (17,18). For these reasons, bioabsorbable interference screws have been developed. To our knowledge, the first bioabsorbable interference screws were made of poly-L–lactic acid or lactide glycolide copolymers.

The aim of this prospective study was to examine the degradation of an interference screw (Endofix; Acufex, Mansfield, Mass) made of polyglycolic acid (67.5%) and trimethylene carbonate (32.5%) at MR imaging and compare the MR imaging findings with the clinical evaluation results.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
This prospective study was conducted in accordance with the recommendations of the local ethics committee at Poincaré Hospital University Teaching Hospital, and written informed consent was obtained from each patient. Between September 1994 and May 1995, the same surgeon (P.B.) performed arthroscopic ACL reconstruction in 20 patients by using a bone-to–patellar tendon–to–central third patellar tendon–to–tibial bone implant. These were not consecutive patients.

The following patient inclusion criteria were used: age between 16 and 50 years and closed epiphyses, ACL injury of one knee that required surgical replacement with a bone-to–patellar tendon–to-bone autograft, and signed informed consent with agreement to attend follow-up visits. The following exclusion criteria were used: additional ligament laxities with a grade higher than 2 (according to European classification of frontal laxity) in the affected knee, previous ACL surgery of either knee, previous cruciate ligament injury of the unaffected knee, stage 4 articular cartilage defects, need for concomitant procedures in the affected knee exclusive of meniscal repair or intercondylar notch plasty, chronic muscle disorders, inability or unwillingness to follow the rehabilitation protocol, and known active articular infection, metabolic bone disease, neoplastic disease, or inflammatory joint disease. There were 14 male and six female patients, and their average age was 32 years (age range, 16–47 years). ACL reconstruction was performed, on average, 16 months after the knee trauma (range, 2 months to 12 years).

Fixation of the autograft was performed with bioabsorbable interference screws (Endofix) made of a polyglycolic acid and trimethylene carbonate copolymer. The size of the interference screws (length, 20 or 25 mm; width, 7 or 9 mm) and the diameter of the tibial tunnel (1.06 cm) were determined from the surgical reports.

Clinical evaluation and MR imaging were performed concomitantly 6 months, 1 year, and 2 years after surgery in 20, 10, and eight patients, respectively. All studies were performed with a 0.5-T MR imaging unit (MR Max; GE Medical Systems, Milwaukee, Wis). A dedicated knee coil was used with a 15-cm field of view. T1-weighted MR images (repetition time msec/echo time msec, 400/20) were obtained in oblique sagittal and oblique transverse planes without and following the intravenous injection of 0.1 mL of gadopentetate dimeglumine (Dotarem; Guerbet, Aulnay-sous-Bois, France) per kilogram of body weight. Five-millimeter-thick sections and a 192 x 192 matrix were used, and two signals were acquired. The oblique sagittal plane was chosen parallel to the tibial tunnel and enabled study of the reconstructed ligament on one section and of the tibial tunnel or the screw in a longitudinal plane. The oblique transverse plane permitted the study of the tibial tunnel and the screw in a transverse plane.

An initial MR study was performed to assess visibility of the screw and accuracy of the screw measurements, which were close to 0.01 cm. For an in vitro study, we performed transverse and sagittal T2-weighted imaging of the screw placed in a container filled with water.

Two skeletal radiologists (O.J., C.V.) in consensus studied the following parameters on successive MR images: morphologic features, signal intensity, length, and diameter of the screw; diameter, shape (ie, parallel, conelike, or cavity-like in the sagittal plane or shaped like the letter O or an 8 in the transverse plane), and contents (ie, fibrous tissue, fat, or combination of the two; enhancement after contrast material administration) of the tibial tunnel; bone reaction around the tunnel (ie, marrow edema with enhancement after contrast material administration); appearance of the reconstructed ligament (ie, normal, thin and irregular, or distended); bone plug healing (ie, disappearance of the low-signal-intensity interface between the graft and the osseous tunnel); joint effusion (ie, small when it was limited to the suprapatellar synovial bursa and large when it included the entire joint cavity); and synovial reaction (ie, enhancement after contrast material administration). The radiologists calculated the screw resorption rate on the basis of changes in screw length and width and compared resorption with clinical results. The images were displayed on film for interpretation. The 1- and 2-year MR imaging review studies were analyzed independently of any previous comparative studies.

In the eight patients who were examined 2 years after surgery, unenhanced computed tomographic (CT) examinations were performed by using 5-mm-thick sections in a plane orthogonal to the tibial tunnel and high-spatial-resolution bone study parameters. With this method, we evaluated the screw resorption, the rim (for osteosclerosis) and contents of the tibial tunnel (ie, tissue, fat, or combination of the two), the appearance and healing of the bone plug, and the appearance of the reconstructed ligament and then compared these results with the MR imaging results.

The orthopedic surgeon (P.B.) documented the pre- and postoperative clinical evaluation results at 6 months, 1 year, and 2 years after surgery by using several scoring methods. Two subjective evaluation tools were used. The Lysholm knee scoring scale (19) is used to assess knee function on the basis of the presence of pain, swelling, a limp, locking, and/or instability and the ability to climb stairs and squat, and a grade of 0–100 is assigned. A grade of 0–64 indicates a poor result; 65–83, an intermediate result; 84–90, a good result; and 91–100, a very good result. The Tegner activity level scale (20) has grades from 0, which indicates infirmity, to 10, which indicates ability to participate in competitive sports. Results were considered good if the level of activity was the same as, very good if the level of activity was better than, or poor if the level of activity was worse than that before the causative trauma.

The scoring system of the International Knee Documentation Committee (21) involves the use of subjective evaluation tools, symptoms, objective functional testing (ie, Lachman test, range of motion), and radiologic analysis. With this system, knees are given a grade of A to indicate normal, B to indicate almost normal, C to indicate abnormal, or D to indicate very abnormal. For the purposes of this study, clinical results were considered to be poor (grade C or D), good (grade B), or very good (grade A).

The correlation between the clinical results and the MR imaging findings of screw resorption, tunnel enlargement, and reconstructed ligament appearance was determined by calculating the Spearman rank correlation coefficient.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The bioabsorbable interference screw was depicted, free of artifact, with postoperative MR imaging, at which the screw was well differentiated from the surrounding tissue as a low-signal-intensity area at T1-weighted sequences.

Screw Resorption
The mean percentage of screw resorption, in either length or diameter, was observed to be approximately one-third at 6 months (31.0% in length and 35.5% in diameter), with an SD of 31.34 for resorption of length and of 6.89 for resorption of diameter (Table 1).


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  		TABLE 1. Screw Evaluation 6 Months after Surgery

 
At 1-year follow-up, the screw was no longer detectable (Fig 1). Nonmeasurable traces of the length of the screw were observed in only four patients, and resorption of the width of the screw was always greater than 50% (Table 2).



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  		Figure 1a. Oblique sagittal T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) of the center of the knee after ACL reconstruction obtained (a, c) before and (b, d) after intravenous contrast material administration. (a) Six months after surgery, the interference screw (short arrow) is still detectable in a parallel tibial tunnel. The reconstructed ligament (long arrow) has low signal intensity and is well defined. (b) Contrast enhancement (arrows) is seen within the tunnel and intercondylar notch. (c, d) On MR images obtained at the same level as in a and b 1 year after surgery, the screw is undetectable. Enhancement (arrow in d) within the tibial tunnel after intravenous contrast material administration persists.

 


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  		Figure 1b. Oblique sagittal T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) of the center of the knee after ACL reconstruction obtained (a, c) before and (b, d) after intravenous contrast material administration. (a) Six months after surgery, the interference screw (short arrow) is still detectable in a parallel tibial tunnel. The reconstructed ligament (long arrow) has low signal intensity and is well defined. (b) Contrast enhancement (arrows) is seen within the tunnel and intercondylar notch. (c, d) On MR images obtained at the same level as in a and b 1 year after surgery, the screw is undetectable. Enhancement (arrow in d) within the tibial tunnel after intravenous contrast material administration persists.

 


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  		Figure 1c. Oblique sagittal T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) of the center of the knee after ACL reconstruction obtained (a, c) before and (b, d) after intravenous contrast material administration. (a) Six months after surgery, the interference screw (short arrow) is still detectable in a parallel tibial tunnel. The reconstructed ligament (long arrow) has low signal intensity and is well defined. (b) Contrast enhancement (arrows) is seen within the tunnel and intercondylar notch. (c, d) On MR images obtained at the same level as in a and b 1 year after surgery, the screw is undetectable. Enhancement (arrow in d) within the tibial tunnel after intravenous contrast material administration persists.

 


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  		Figure 1d. Oblique sagittal T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) of the center of the knee after ACL reconstruction obtained (a, c) before and (b, d) after intravenous contrast material administration. (a) Six months after surgery, the interference screw (short arrow) is still detectable in a parallel tibial tunnel. The reconstructed ligament (long arrow) has low signal intensity and is well defined. (b) Contrast enhancement (arrows) is seen within the tunnel and intercondylar notch. (c, d) On MR images obtained at the same level as in a and b 1 year after surgery, the screw is undetectable. Enhancement (arrow in d) within the tibial tunnel after intravenous contrast material administration persists.

 

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  		TABLE 2. Results 1 Year after Surgery

 
At all 2-year follow-up CT or MR imaging examinations, the screw was totally resorbed (Table 3). No correlation between screw resorption rate and clinical results was noted (P > .05). We observed good clinical results at 6 months in 95% (n = 19) of the patients, even though the mean resorption rate reached 30%. Important variations in mean rate of screw length resorption, between 6% and 100% (SD, 31.34), were observed.


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  		TABLE 3. Results 2 Years after Surgery

 
Tibial Tunnel
Tunnel enlargement was observed in 18 of 20 patients after the 6-month interval, as compared with the intraoperative size of the tibial tunnel (Table 4). There was a mean enlargement of 40%. The mean area size was 1.27 cm2 (SD, 0.28), whereas the mean intraoperative section size was 0.88 cm2 (mean diameter, 1.66 cm). In six cases, accurate measurement at 1-year follow-up could not be performed owing to osseous incorporation, which hampered the precise delineation of the tunnel limits. In the other four cases, the tunnels were enlarged, with a mean area of 1.33 cm2. There was no change in tunnel size between the 6-month, 1-year, and 2-year follow-ups.


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  		TABLE 4. Tunnel, ACL, and Joint Findings 6 Months after Surgery

 
Different tunnel shapes were noted at 6 months. In the sagittal plane, the limits of the tunnel were parallel in eight, conelike in nine, and cavity-like in three patients (Fig 2). In the transverse plane, the tunnel was shaped like an O in eight cases and like an 8 in 12 (Fig 3). The O-shaped tunnels had parallel edges in most cases, whereas the 8-shaped tunnels were conelike in seven, cavity-like in three, and parallel in two patients. There was no change in tunnel shape between the 6-month and 2-year follow-up examinations. Neither tunnel enlargement nor shape modification was observed to be related to any clinical result, including laxity (P > .05).



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  		Figure 2a. Oblique sagittal T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) of the center of the knee. (a) Parallel, (b) conelike, and (c) cavity-like tibial tunnels (arrows) are seen.

 


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  		Figure 2b. Oblique sagittal T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) of the center of the knee. (a) Parallel, (b) conelike, and (c) cavity-like tibial tunnels (arrows) are seen.

 


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  		Figure 2c. Oblique sagittal T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) of the center of the knee. (a) Parallel, (b) conelike, and (c) cavity-like tibial tunnels (arrows) are seen.

 


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  		Figure 3a. Oblique transverse T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) of the knee. Enlarged tibial tunnels (arrows) shaped like (a) an O and (b) an 8 are seen.

 


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  		Figure 3b. Oblique transverse T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) of the knee. Enlarged tibial tunnels (arrows) shaped like (a) an O and (b) an 8 are seen.

 
Combined CT and MR imaging studies performed in eight patients after a 2-year period permitted a better evaluation of the tunnel contents (Table 3). Replacement of the screw with tissue was evaluated. In five patients, a structure with a tissue attenuation of 70 HU at CT and an isointense signal at T1-weighted MR imaging was observed (Fig 4). In the three remaining patients, the same structure was associated with a rim of fatty tissue (-60 HU at CT and high signal intensity at T1-weighted MR imaging) (Fig 5).



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  		Figure 4a. (a, b) Oblique transverse T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) obtained (a) before and (b) after contrast material administration. (c) Oblique transverse CT scan of a clinically normal knee obtained 2 years after surgery. (a) MR image shows the screw is totally resorbed in an enlarged tunnel shaped like an 8 (thin black arrows). A structure (solid white arrow) with an isointense signal compared with that of muscle has replaced the screw. Bone plug healing, with disappearance of the low-signal-intensity interface between the graft and the osseous tunnel (thick black arrow), has been achieved. The low-signal-intensity structure (open arrow) corresponds to the cortical part of the bone plug on the CT image. (b) MR image obtained at the same level as in a shows enhancement (arrow), which corresponds to hypervascularity at the screw site, within the tunnel. (c) CT scan shows the tissue (solid arrow), which has an attenuation of 70 HU, that has replaced the screw. The cortical part (open arrow) of the bone plug has high attenuation.

 


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  		Figure 4b. (a, b) Oblique transverse T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) obtained (a) before and (b) after contrast material administration. (c) Oblique transverse CT scan of a clinically normal knee obtained 2 years after surgery. (a) MR image shows the screw is totally resorbed in an enlarged tunnel shaped like an 8 (thin black arrows). A structure (solid white arrow) with an isointense signal compared with that of muscle has replaced the screw. Bone plug healing, with disappearance of the low-signal-intensity interface between the graft and the osseous tunnel (thick black arrow), has been achieved. The low-signal-intensity structure (open arrow) corresponds to the cortical part of the bone plug on the CT image. (b) MR image obtained at the same level as in a shows enhancement (arrow), which corresponds to hypervascularity at the screw site, within the tunnel. (c) CT scan shows the tissue (solid arrow), which has an attenuation of 70 HU, that has replaced the screw. The cortical part (open arrow) of the bone plug has high attenuation.

 


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  		Figure 4c. (a, b) Oblique transverse T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) obtained (a) before and (b) after contrast material administration. (c) Oblique transverse CT scan of a clinically normal knee obtained 2 years after surgery. (a) MR image shows the screw is totally resorbed in an enlarged tunnel shaped like an 8 (thin black arrows). A structure (solid white arrow) with an isointense signal compared with that of muscle has replaced the screw. Bone plug healing, with disappearance of the low-signal-intensity interface between the graft and the osseous tunnel (thick black arrow), has been achieved. The low-signal-intensity structure (open arrow) corresponds to the cortical part of the bone plug on the CT image. (b) MR image obtained at the same level as in a shows enhancement (arrow), which corresponds to hypervascularity at the screw site, within the tunnel. (c) CT scan shows the tissue (solid arrow), which has an attenuation of 70 HU, that has replaced the screw. The cortical part (open arrow) of the bone plug has high attenuation.

 


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  		Figure 5a. (a, b) Oblique transverse T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) obtained (a) before and (b) after contrast material administration. (c) Oblique transverse CT scan of a clinically normal knee, obtained 2 years after surgery. In a, the MR image shows the screw is totally resorbed in an enlarged tunnel, which is shaped like an 8 (small short arrows), and has been replaced by a structure (large long arrow) with an isointense signal compared with that of the muscles in the center of the screw site. The structure is associated with a peripheral hyperintense rim, which is consistent with fatty tissue (thick short solid arrow). The sclerotic bone plug (open arrow) has hypointense signal. In b, the MR image shows the central structure (arrow) at the screw site is enhanced. In c, the CT scan shows that a central tissular structure (70 HU) (long arrow) associated with a rim of fatty tissue (-60 HU) (short solid arrow) has replaced the screw within the tunnel. The bone plug (open arrow) is partially healed and has a pediculated and sclerotic appearance.

 


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  		Figure 5b. (a, b) Oblique transverse T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) obtained (a) before and (b) after contrast material administration. (c) Oblique transverse CT scan of a clinically normal knee, obtained 2 years after surgery. In a, the MR image shows the screw is totally resorbed in an enlarged tunnel, which is shaped like an 8 (small short arrows), and has been replaced by a structure (large long arrow) with an isointense signal compared with that of the muscles in the center of the screw site. The structure is associated with a peripheral hyperintense rim, which is consistent with fatty tissue (thick short solid arrow). The sclerotic bone plug (open arrow) has hypointense signal. In b, the MR image shows the central structure (arrow) at the screw site is enhanced. In c, the CT scan shows that a central tissular structure (70 HU) (long arrow) associated with a rim of fatty tissue (-60 HU) (short solid arrow) has replaced the screw within the tunnel. The bone plug (open arrow) is partially healed and has a pediculated and sclerotic appearance.

 


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  		Figure 5c. (a, b) Oblique transverse T1-weighted MR images (400/20, 5-mm section thickness, 192 x 192 matrix, two signals acquired, 15-cm field of view) obtained (a) before and (b) after contrast material administration. (c) Oblique transverse CT scan of a clinically normal knee, obtained 2 years after surgery. In a, the MR image shows the screw is totally resorbed in an enlarged tunnel, which is shaped like an 8 (small short arrows), and has been replaced by a structure (large long arrow) with an isointense signal compared with that of the muscles in the center of the screw site. The structure is associated with a peripheral hyperintense rim, which is consistent with fatty tissue (thick short solid arrow). The sclerotic bone plug (open arrow) has hypointense signal. In b, the MR image shows the central structure (arrow) at the screw site is enhanced. In c, the CT scan shows that a central tissular structure (70 HU) (long arrow) associated with a rim of fatty tissue (-60 HU) (short solid arrow) has replaced the screw within the tunnel. The bone plug (open arrow) is partially healed and has a pediculated and sclerotic appearance.

 
In 17 of 20 patients, enhancement after intravenous injection of gadolinium-based contrast material, which corresponded to hypervascularity at the screw site, was observed within the tunnel at 6 months (Table 4). This enhancement was noted in eight of 10 patients at 1-year follow-up (Table 2) and persisted in seven of eight patients at 2-year follow-up (Table 3).

Surrounding Cancellous Bone
At 6 months, a thin line of enhancement encircling the tunnel was present in only four patients (Table 4). No signal intensity modification was noted in the surrounding cancellous bone of the 16 other patients. In all but one patient, this phenomenon disappeared without any treatment after 1 year and may have been related to the surgical procedure (Table 2). The 2-year follow-up CT images obtained in eight patients revealed thin peripheral osteosclerosis, which was not seen on the MR images (Table 3).

Bone Plug Healing
After an interval of 6 months, bone-to-bone healing, with disappearance of the low-signal-intensity interface between the graft and the osseous tunnel, was complete in 10 of 20 patients (Fig 4) (Table 4). Bone healing was complete in eight of 10 patients after 1 year (Table 2). After 2 years, pediculated and sclerotic bone plugs were seen in two patients (Fig 5), and a lytic plug was seen in one patient. These findings did not correlate with the clinical results (Table 3). The five other bone plugs were healed.

Joint Effusion
After 6 months, only one large effusion and five small effusions were noted (Table 4). At 1 year, only one small effusion persisted (Table 2). The effusion had spontaneously disappeared by the 2-year follow-up (Table 3).

Synovial Reaction
At 6-month follow-up, synovial enhancement in the intercondylar notch was seen in 18 patients (Table 4). It persisted in seven of 10 patients after 1 year (Table 2) but disappeared spontaneously after 2 years (Table 3).

Graft Appearance
The patellar tendon graft was identified in its entirety on a single section and had various MR appearances. The most common pattern, seen in 17 of 20 patients at 6 months, was a thick and well-defined low-signal-intensity band on T1-weighted oblique sagittal MR images (Table 4). The graft was thin and irregular in two patients and thin and distended in one patient. These three abnormal reconstructed ligaments had the same appearance 1 year after surgery (Table 2).

After 2 years, the reconstructed ligament was poorly depicted on CT images. It appeared to be normal at MR imaging, however, in six of the eight patients examined, distended in one patient, and degraded in one patient, as compared with the appearance of the ligament at previous studies (Table 3). No consistent relationship between reconstructed ligament appearance and clinical results was observed (P > .05).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Like most bioabsorbable implants, the described interference screw (Endofix), which is made of polyglycolic acid and trimethylene carbonate, is nonferromagnetic and can be studied at postoperative MR imaging without artifact.

Initial reports about the clinical use of biodegradable interference screws have shown that these devices facilitate clinical outcomes that are identical to those with metallic screws (1,2,4–6,9–12,14,22). The most frequently reported complication associated with the use of biodegradable interference screws is screw breakage during insertion, but this can be avoided by adjusting the surgical technique (2).

The described interference screw provides secure initial strength for graft fixation. It degrades more quickly than do screws made of lactic acid, the degradation of which has been reported to occur after more than 2 years (2,23). Our study results show that signs of screw degradation are present at 6 months and screw resorption is complete at 1 year in almost all cases. These findings seem to have no influence on clinical results.

We observed enhancement of the tunnel contents after contrast material injection in 17 of 20 patients at 6 months, in eight of 10 patients at 1 year, and in seven of eight patients at 2 years, with no enhancement in the surrounding cancellous bone. These findings reflect the absence of any substantial inflammatory response and are evidence of the safety of this screw. Hypervascularization within the tunnel may be linked to a physiologic phenomenon of bone-to-bone healing and to replacement of the screw by vascularized tissue rather than by bone.

Combined CT and MR examination permitted a better analysis of the contents and limits of the tunnel. At 2-year follow-up we observed a fibrous tissue component in five of eight patients and a mixed fibrous tissue–fat component in the remaining three patients. No histologic study was performed, however. Stähelin et al (24) studied the tibial biopsy findings in six patients 3 weeks to 20 months after ACL reconstruction performed with bioabsorbable interference screws made of lactic or glycolic acid. They observed a preponderance of fibrous tissue but also traces of new lamellar bone.

Tibial and femoral tunnel enlargement has often been observed after ACL reconstruction with absorbable interference screws or metallic screws (25–27). This enlargement was observed often in our study: in 18 of 20 patients at 6 months and in all 10 patients at 1 year. There appeared to be no increased frequency of this phenomenon over time; however, accurate measurements could not be performed at 1- and 2-year follow-up examinations because of bone plug healing. Moreover, the tunnel shape modifications (parallel, conelike, or cavity-like) usually became stable over time without intensifying.

Fahey and Indelicato (25) proposed possible explanations for this enlargement, which included an immune response with resorption and stress shielding proximal to the interference screw that results in resorption or an inflammatory response by the synovium in the tunnel. Peyrache et al (27) studied 18 ACL reconstructions achieved with metallic interference screws and observed the same enlargement and shape modifications. They proposed the explanation of bone resorption due to micromotion of the graft relative to the tunnel wall, inflammatory response in the tunnel, or stress shielding of the tunnel wall proximal to the interference screw.

Another explanation is suggested by the results of our studies in the transverse oblique plane. In the tunnel, a screw and a bone plug must be inserted, but the screw diameter is only slightly smaller than the tunnel diameter. Thus, the screw has to push the cancellous bone around the tunnel, either parallel to the drilling axis of the tunnel or in a different axis; this phenomenon explains the cone- or cavity-like radiologic appearance. When the tunnel has an O shape, the screw is totally within the tunnel and enlargement is parallel. When the tunnel has an 8 shape, the screw is partially or totally inserted out of the tunnel, and this explains the possibility of cone- or cavity-like enlargement. Similar to Fahey and Indelicato (25) and Peyrache et al (27), we observed no correlation between tunnel enlargement and clinical results.

A potential problem associated with the degradation of interference screws is compromised biocompatibility, even though few complications occur with the clinical use of these devices. Inflammatory foreign-body reactions, including a discharging sinus without infection, have been encountered in many published clinical studies of the use of absorbable fracture fixation implants made of polyglycolide, lactide-glycolide, or poly-L-lactic acid (28–34). Because the time to polylactide degradation is longer, this complication occurs much later than reactions to devices made of polyglycolic acid (29–32). The reported prevalence of macroscopically manifested nonbacterial inflammatory reactions in clinical series has varied from 5.0% to 22.5% (30). The degree of tissue responses has ranged from a small solitary discharging sinus of short duration to an intense reaction that required repeated surgical drainage procedures.

Böstman et al (30,32) studied the nature of these reactions at histologic examination and observed a nonspecific foreign-body reaction that consisted mainly of neutrophilic polymorphonuclear leukocytes and foreign-body giant cells phagocytizing the broken-down implant material. Osteolytic areas are statistically associated with this reaction. Böstman (28) suggested that increased pressure within the cavity during degradation of the screw may force the liquid polymeric debris through the skin if other routes of absorption or expulsion are not accessible.

No clinical inflammatory reaction has been observed in most studies performed after ACL reconstruction with bioabsorbable interference screws (2,5,6,8,24,25,27,35). Martinek and Friederich (36) reported a case of osteolytic tibial enlargement in association with pretibial cyst formation 8 months after ACL graft fixation with a poly-D,L lactide interference screw. It seems to be the first obvious adverse reaction reported. Neither joint inflammatory reaction nor graft insufficiency was observed, and the histologic examination revealed no inflammatory response. Stähelin et al (24) studied six tibial biopsy specimens after ACL reconstructions performed by using interference screws made of polylactic acid, polyglycolic acid, or a polylactic acid–polyglycolic acid copolymer. They observed the presence of foreign-body giant cells in only one case, with no clinical inflammatory reaction. Furthermore, Lajtai et al (37) performed biopsy 41/2 years after implantation of a degradable interference screw made of a lactide-glycolide copolymer and detected no foreign-body reaction or signs of inflammation at histologic analysis.

In the present study, we did not perform biopsy and thus cannot empirically exclude that the enhancement observed within the tunnel corresponds to a foreign-body reaction with phagocytosis of screw debris. However, no inflammatory clinical complication was observed. No increased signal intensity surrounding the screws suggestive of substantial inflammatory reaction was observed. A subtle thin line of enhancement surrounding the tunnel in four patients could be seen after a 6-month interval. This line spontaneously disappeared 1 year after surgery. Warden et al (22) reported a similar area of high signal intensity surrounding the tunnel at T2-weighted MR imaging 8 months after polylactic acid interference screw implantation. They thought that these changes represented a general reaction to surgical insult rather than to the screws because similar changes were noted at the patellar harvest site. In the same way, it is likely that the joint effusions and synovial reaction that we observed were a response to the surgical procedure because they spontaneously resolved over time.

We concur with the results in former series (38–46), because no close relationship between the clinical findings and the MR imaging appearance of the graft after ACL reconstruction was observed. Most cases of clinically intact reconstructed ACLs were intact at MR imaging according to the same criteria used to establish the integrity of the normal native ACL. However, at 6 months, there were two cases of clinically stable knees in which MR imaging did not depict a uniform graft structure. Yamato and Yamagishi (46) and Cheung et al (39) considered that these autograft changes might be the result of fibrosis, variation in the amount of fatty tissue investing the reconstructed ligament, tendon graft healing resulting from synovial proliferation, and/or revascularization of the graft.

In conclusion, our MR imaging study results confirm that with the described interference screw, postoperative MR imaging can be performed without artifacts and that the bioabsorption of this screw is much more rapid than that of screws made of lactic acid (which have a 1-year degradation time range). We did not observe any correlation between the rapidity of screw resorption and the clinical results, which were very good in most patients. The tissue replacing the screw was fibrous or fibrous and fatty but never bone.

Patient tolerance of the screw was highly satisfactory. No substantial inflammatory reaction was observed in the epiphyseal bone around the tunnel, and we suggest a mechanical explanation for the tibial tunnel enlargement. Because no histologic examination was performed, however, the absence of a microscopic inflammatory foreign-body reaction could not be confirmed.


   FOOTNOTES
 
Abbreviation: ACL = anterior cruciate ligament

Author contributions: Guarantors of integrity of entire study, C.V., F.D.B., R.Y.C.; study concepts, C.V., O.J., P.B.; study design, C.V., F.D.B., R.Y.C.; literature research, F.D.B., J.B.E., R.Y.C.; clinical studies, A.F., J.B.E., P.B., F.D.B.; experimental studies, C.V., O.J., P.B.; data acquisition, F.D.B., R.Y.C., J.B.E., A.F.; data analysis/interpretation, O.J., C.V.; statistical analysis, F.D.B., J.B.E., R.Y.C.; manuscript preparation, D.M.M., F.D.B., R.Y.C.; manuscript definition of intellectual content, C.V., F.D.B., R.Y.C.; manuscript editing, F.D.B., R.Y.C., D.M.M.; manuscript revision/review and final version approval, R.Y.C., C.V.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Abate JA, Fadale PD, Hulstyn MJ, Walsh WR. Initial fixation strength of polylactic acid interference screws in anterior cruciate ligament reconstruction. Arthroscopy 1998; 14:278-284.[Medline]
  2. Barber FA, Elrod BF, McGuire DA, Paulos LE. Preliminary results of an absorbable interference screw. Arthroscopy 1995; 11:537-548.[Medline]
  3. Brown CH, Hecker AT, Hipp JA, Myers ER, Hayes WC. The biomechanics of interference screw fixation of patellar tendon anterior cruciate ligament grafts. Am J Sports Med 1993; 21:880-886.[Abstract/Free Full Text]
  4. Johnson LL, VanDick GE. Metal and biodegradable interference screws: comparison of failure strength. Arthroscopy 1996; 12:452-456.[Medline]
  5. Kousa P, Järvinen TLN, Pohjonen T, Kannus P, Kotikoski M, Järvinen M. Fixation strength of a biodegradable screw in anterior cruciate ligament reconstruction. J Bone Joint Surg Br 1995; 77:901-905.
  6. Lajtai G, Humer K, Aitzetmuller G, Unger F, Ramadani F, Orthner E. Results of reconstruction of anterior cruciate ligament ruptures: use of resorbable interference screws (minimum follow-up of 2.5 years). Unfallchirurg 1999; 102:35-42[German].[CrossRef][Medline]
  7. Marti C, Imhoff A, Bahrs C, Romero J. Metallic versus bioabsorbable interference screw for fixation of bone–patellar tendon–bone autograft in arthroscopic anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 1997; 5:217-221.[CrossRef][Medline]
  8. McGuire DA, Barber FA, Elrod BF, Paulos LE. Bioabsorbable interference screws for graft fixation in anterior cruciate ligament reconstruction. Arthroscopy 1999; 15:463-473.[Medline]
  9. Pena F, Grontvedt T, Brown GA, Aune AK, Engebretsen L. Comparison of failure strength between metallic and absorbable interference screws. Am J Sports Med 1996; 24:329-334.[Abstract/Free Full Text]
  10. Rupp S, Krauss PW, Fritsch EW. Fixation strength of a biodegradable interference screw and a press-fit technique in anterior cruciate ligament reconstruction with a BPTB graft. Arthroscopy 1997; 13:61-65.[Medline]
  11. Rupp S, Seil R, Schneider A, Kohn DM. Ligament graft initial fixation strength using biodegradable interference screws. J Biomed Mater Res 1999; 48:70-74.[CrossRef][Medline]
  12. Seil R, Rupp S, Krauss PW, Benz A, Kohn DM. Comparison of initial fixation strength between biodegradable and metallic interference screws and a press-fit fixation technique in a porcine model. Am J Sports Med 1998; 26:815-819.[Abstract/Free Full Text]
  13. Stähelin AC, Feinstein R, Friederich NF. Clinical experience using a bioabsorbable interference screw for ACL reconstruction. Orthop Trans 1995; 19:287-288.
  14. Tuompo P, Partio E, Rokkanen P. Absorbable fixation in bone-tendon-bone reconstruction of anterior cruciate ligament. J Bone Joint Surg Br 1997; 79:189.
  15. Weiler A, Windhagen H, Raschke M, Laumeyer A, Hoffmann R. Biodegradable interference screw fixation exhibits pull-out force and stiffness similar to titanium screws. Am J Sports Med 1998; 26:119-128.[Abstract/Free Full Text]
  16. Kurzweil PR, Frogameni AD, Jackson DW. Tibial interference screw removal following anterior cruciate ligament reconstruction. Arthroscopy 1995; 11:289-291.[Medline]
  17. Miller MD. Revision cruciate ligament surgery with retention of femoral interference screws. Arthroscopy 1998; 14:111-114.[Medline]
  18. Shellock FG, Mink JH, Curtin S, Friedman MJ. MR imaging and metallic implants for anterior cruciate ligament reconstruction: assessment of ferromagnetism and artifact. J Magn Reson Imaging 1992; 2:225-228.[Medline]
  19. 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.[Abstract/Free Full Text]
  20. Tegner J, Lysholm J. Rating systems in the evaluation of knee ligament injuries. Clin Orthop 1985; 198:43-49.
  21. Hefti F, Müller W, Jacob RP, Stäubli HU. Evaluation of knee ligament injuries with the IKDC form. Knee Surg Sports Traumatol Arthrosc 1993; 1:226-230.[CrossRef][Medline]
  22. Warden WH, Friedman R, Teresi LM, Jackson DW. Magnetic resonance imaging of bioabsorbable polylactic acid interference screws during the 2 two years after anterior cruciate ligament reconstruction. Arthroscopy 1999; 15:474-480.[Medline]
  23. Lohman M, Partio EK, Vehmas T, Kivisaari A, Kivisaari L. MR imaging in biofix-osteosynthesis. Acta Radiol 1999; 40:415-417.[Medline]
  24. Stähelin AC, Weiler A, Rüfenacht 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.[Medline]
  25. Fahey M, Indelicato PA. Bone tunnel enlargement after anterior cruciate ligament replacement. Am J Sports Med 1994; 22:410-414.[Abstract/Free Full Text]
  26. Loubignac F, Lecuire F, Rubini J, Basso M. Evolution radiologique inquiétante après fixation des plasties de ligament croisé antérieur par vis d’interférence résorbables. Acta Orthop Belg 1998; 64:47-51.[Medline]
  27. Peyrache MD, Djian P, Christel P, Witwoët J. Tibial tunnel enlargement after anterior cruciate ligament reconstruction by autogenous bone-patellar tendon-bone graft. Knee Surg Sports Traumatol Arthrosc 1996; 4:2-8.[CrossRef][Medline]
  28. Böstman OM. Osteolytic changes accompanying degradation of absorbable fracture fixation implants. J Bone Joint Surg Br 1991; 73:679-682.
  29. Böstman OM. Current concepts review: absorbable implants for the fixation of fractures. J Bone Joint Surg Am 1991; 73:148-153.[Free Full Text]
  30. Böstman OM. Intense granulomatous inflammatory lesions associated with absorbable internal fixation devices made of polyglycolide in ankle fractures. Clin Orthop 1992; 278:193-199.
  31. Böstman OM. Osteoarthritis of the ankle after foreign-body reaction to absorbable pins and screws. J Bone Joint Surg Br 1998; 80:333-338.
  32. Böstman O, Hirvensalo E, Mäkinen J, Rokkanen P. Foreign-body reactions to fracture fixation implants of biodegradable synthetic polymers. J Bone Joint Surg Br 1990; 72:592-596.
  33. Böstman O, Päivärinta U, Partio E, Vasenius J, Manninen M, Rokkanen P. Degradation and tissue replacement of an absorbable polyglycolide screw in the fixation of rabbit femoral osteotomies. J Bone Joint Surg Am 1992; 74:1021-1031.[Abstract/Free Full Text]
  34. Böstman O, Partio E, Hirvensalo E, Rokkanen P. Foreign-body reactions to polyglycolide screws. Acta Orthop Scand 1992; 63:173-176.[Medline]
  35. Lajtai G, Humer K, Aitzetmuller 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.[Medline]
  36. Martinek V, Friederich NF. Tibial and pretibial cyst formation after anterior cruciate ligament reconstruction with bioabsorbable interference screw fixation. Arthroscopy 1999; 15:317-320.[Medline]
  37. Lajtai G, Balon R, Humer K, Aitzetmuller G, Unger F, Orthner E. Resorbable interference screws: histologic study 4.5 years postoperative. Unfallchirurg 1998; 101:866-869[German].[CrossRef][Medline]
  38. Autz G, Goodwin C, Singson RD. Magnetic resonance evaluation of anterior cruciate ligament repair using the patellar tendon double bone block technique. Skeletal Radiol 1991; 20:585-588.[CrossRef][Medline]
  39. Cheung Y, Magee TH, Rosenberg ZS, Rose DJ. MRI of anterior cruciate ligament reconstruction. J Comput Assist Tomogr 1992; 16:134-137.[Medline]
  40. Djian P, Christel P, Roger B, Witwoët J. Evaluation radiologique et IRM des ligamentoplasties intra-articulaires utilisant le tendon rotulien. Rev Chir Orthop 1994; 80:403-412.
  41. Maywood RM, Murphy BJ, Uribe JW, Hechtman KS. Evaluation of arthroscopic anterior cruciate ligament reconstruction using magnetic resonance imaging. Am J Sports Med 1993; 21:523-527.[Abstract/Free Full Text]
  42. Moeser P, Bechtold RE, Clark T, Rovere G, Karstaedt N, Wolfman N. MR Imaging of anterior cruciate ligament repair. J Comput Assist Tomogr 1989; 13:105-109.[Medline]
  43. Rak KM, Gillogly SD, Schaefer RA, Yakes WF, Liljedahl RR. Anterior cruciate ligament reconstruction: evaluation with MR Imaging. Radiology 1991; 178:553-556.[Abstract/Free Full Text]
  44. Sanchis-Alfonso V, Martinez-Sanjuan V, Gastaldi-Orquin E. The value of MRI in the evaluation of the ACL deficient knee and in the post-operative evaluation after ACL reconstruction. Eur J Radiol 1993; 16:126-130.[CrossRef][Medline]
  45. Schiavone Panni A, Lucania L, Milano G. Absorbable screw fixation in ACL reconstruction: a clinical, CT and MRI follow-up study. J Bone Joint Surg Br 1997; 79:189.
  46. Yamato M, Yamagishi T. MRI of patellar tendon anterior cruciate ligament autografts. J Comput Assist Tomogr 1992; 16:604-607.[Medline]



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