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clinmed/2000010002v1 (January 10, 2000)
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Transcondylar screw fixation in ACL reconstruction

Pier P Mariani, Gianluca Camillieri, Fabrizio Margheritini, Ezio Adriani, and Gaetano Maresca

Orthopaedic Department University La Sapienza Rome, Laboratory of Arthroscopic and Joint Surgery

Introduction

Several alternatives are available for reconstruction of the anterior cruciate ligament: different grafts, auto or allografts, and different methods of fixation, intra or extra-articular. In the first category, the interference screw method is still one of the most commonly performed, but is associated with a variety of possible complications1,2 including screw divergence3, intra-operative graft damage4, damage to the dorsal cortical bone5, and the presence of intra-articular hardware6 which must be removed if revision becomes necessary or in cases of acute septic arthritis onset. For these complications, alternative extra-articular methods of fixation have been developed7,8 and several experimental and clinical studies have shown the validity of these methods9,10,11 .Unfortunately, some practical disadvantages are reported using these methods12,13 : incomplete "grab" of the femoral lateral cortex, interposition of soft tissue between the device and femoral cortex, ruptured connecting sutures, and the so-called "bungee effect".

An intermediate method between intra and extra-articular fixation is the transcondylar system. Fixation is achieved by a blunt-nosed transverse screw, which enters the femoral tunnel from the lateral cortex, pushing the bone plug against the medial wall of the tunnel. To our knowledge, no reports have been previously described in the literature concerning clinical validity of this method.

The aim of this study is to analyze final outcome after transverse fixation in arthroscopically-assisted ACL reconstruction. Two groups of ACL reconstruction were prospectively compared: in one group endoscopic fixation was achieved with an interference screw, and the other group with a transverse screw.

Materials and Methods

From June 1996 to September 1997, a prospective randomized study was undertaken in order to assess two groups of patients undergoing ACL reconstruction. Group A (endoscopic technique) consisted of 24 patients (17 men and 7 women) with an average age of 24.4 years (range: 18 to 42 years). Group B (transcondylar technique) consisted of 31 patients (23 men and 8 women) with an average age of 24.7 years (range: 18 to 40 years). Subjects were randomly assigned to one of the two treatments groups and randomization was achieved using the heads and tails method. This explains the different dimensions of the two groups. The two groups were evenly matched in age, sex, time from injury to reconstruction, meniscal injuries, and type of meniscal procedures. Exclusion criteria included acute tears (less than 2 months old), significant multiple ligament injuries, controlateral knee instability, and degenerative joint diseases. Patients were evaluated at 29 months follow-up (range: 24 to 39 months) with the International Knee Documentation Committee (IKDC) form14. Knee laxity was recorded pre- and postoperatively using the KT-2000 arthrometer15 (Medmetric Inc., San Diego, CA). Both knees were tested and anterior displacement was measured at 15, 20, and 30 lbs. Maximum manual translation and side-to-side differences were also recorded. The Lysholm-II16 form and Tegner16 scoring system were also utilized.

Statistical analysis consisted of independent sample t tests to assess group differences in surgical technique. Statistical significance was set at P< 0.05.

Surgical Technique

All surgeries were performed by the same surgeon (PPM). In both groups the central third of the patellar tendon is harvested from the distal pole of the patella to the tibial tubercle. The patellar bone block prepared for insertion into the femoral tunnel ranges between 20 and 25 mm in length. Endoscopic technique is performed in the usual manner. The tibial tunnel in both groups is reamed in extension, using the One-Step drill guide (Arthrotek, Ontario, CA). The transcondylar technique is based on a U-shaped drill guide to position the transcondylar blunt-nosed interference screw perpendicular to the femoral bone plug graft. After reaming the femoral tunnel in standard fashion, the U-shaped drill guide is inserted into the femoral and tibial tunnels. A 2.4 mm drill bit is inserted into the bullet and lateral femoral condyle until it contacts the insertion rod of the drill guide. At this moment, the drill guide is removed, and the arthroscope is introduced into the anteromedial portal. After verification of the drill bit crossing the center of the tunnel, a transcondylar tunnel is made with a cannulated reamer. A cannulated blunt-nosed interference screw (9 mm in diameter) is advanced until it is seen entering the femoral tunnel. The graft is passed through the femoral tunnel using a looped K-wire. The screw is tightened 1-2.5 turns, corresponding to 4-6 mm of screw advancement. The graft is tensioned and the leg is put through full range of movement several times. This is done to confirm adequate femoral fixation. Tibial fixation is achieved with a standard interference screw and the knee flexed at 30 degrees.

Postoperative Rehabilitation

The same postoperative rehabilitation protocol was used in all patients. On the second day postoperative, drains are removed and weight bearing is allowed with a postoperative brace. At the second post-operative day, sutures are removed and continuous passive motion is begun in order to obtain sufficient R.O.M. (0-100 degrees). All patients receive a videotaped rehabilitation program in order to continue the same protocol at rehabilitation units outside the hospital. One month postoperatively, the knee brace is completely removed and rehabilitation is continued until the third post-operative month. After this period, the patient begins athletic training for his individual sport. Full sport activity is allowed between four and five months postoperatively based on risk level. Patients are asked to return for routine postoperative evaluation at 2-week intervals until the sixth postoperative month, and thereafter at 6-month intervals.

Results

All patients entered in this study were available for follow-up. All examinations and results were evaluated by a single independent examiner (GC) not involved in the surgery. The average injury to surgery time was 442 days in Group A (range, 65 to 3362 days), and in 477 days in Group B (range, 75 to 4880 days). Five patients in Group A underwent partial medial meniscectomy and one patient underwent lateral meniscectomy. Six patients (19.3%) in group B underwent partial medial meniscectomy, and three patients (9.6%) underwent partial lateral meniscectomy. An "all-inside" suture of the posterior horn was performed in four patients (12.9%) of Group B. Preoperative IKDC evaluation revealed 6 patients (10,9%) with grade A, 8 patients (14.5%) with grade B, 18 patients (32.7%) with grade C and 23 patients (41.8%) were graded D.

Subjective assessment: at final follow-up ten patients (41.6%) from Group A and 10 (32.3%) patients from Group B considered their reconstructed knee normal, and 19 patients (61.3%) from Group B and 9 patients (37.5%) from Group A rated their reconstructive knee nearly normal. Two patients (8.3%) in Group A and no patient in Group B rated their knee as abnormal. Only one patient in Group A reported his knee as severely abnormal.

Activity Level: In Group A, 18 patients (75%) returned to the same preinjury activity level while 6 patients (25%) returned to a lower sports activity level. No statistical differences were detected between the two groups. In Group B, 23 patients (74.2%) returned to the same preinjury activity level while 6 patients (19.3%) patients returned to a lower sports level. Two patients (6.4%) were able to increase their activity to level I. No statistical differences were detected between the two groups.

Range of Motion: Only three (12.5%) patients in Group A and two (6.4%) patients in Group B had decreased flexion between 6 and 15. No deficit in extension was detected in either group.

Ligament Evaluation: In Group A, 17 (70.8%) patients demonstrated a Lachman test of +1 and 7 (29.1%) of +2 preoperatively. In Group B, the Lachman test resulted in +1 in 21 (67.7%) patients and +2 in 10 (32.2%) patients. In Group A, the pivot shift was +1 in 15 (62.5%) patients, +2 in 7 (29.1%), and +3 in 2 (8.3%) patients, whereas in Group B pivot shift distribution showed +1 in 20 (64.5%) patients, +2 in 8 (25.8%), and +3 in 3 (9.7%) patients. Postoperatively, a firm endpoint Lachman test was noted in 12 (50%) patients in Group A and in 18 (58.1%) patients in Group B. Increased excursion with a firm endpoint was noted in 9 patients (37.5%) in Group A and 11 patients (35.5%) in Group B. A soft endpoint was noted in 2 (8.3%) patients in Group A, and 2 (6.4%) patients in Group B. A markedly positive displacement was seen in only one (4.1%) patient in Group A. At final follow-up, no patient had a grossly positive pivot shift, although 4 (16.6%) patients in Group A and 2 (6.4%) in Group B showed a +1 pivot shift. Only one patient (4.2%) in Group A had a +2 pivot shift.

Preoperatively, utilizing the KT-2000, anterior displacement in all patients in Groups A and B was greater than 5 mm, with a side-to-side difference of 5.86 mm (SD 2.83) for Group A and 6.18 mm (SD 3.69) for Group B. At final follow-up the injured versus normal (I-N) side-to-side difference at maximal manual loading was 3.68 mm (SD 1.71) in Group A and 1.64 (SD 2.05) in Group B with P<0.0001 (Tab. 1). Mean absolute displacement was 12.25 mm (SD 2.82) in Group A and 9.7 mm (SD 3.1) in Group B with a statistically significant difference (P<0.005).

At overall final IKDC evaluation, in Group A no patient was graded A, 15 patients (62.5%) graded B, 6 patients (25%) graded C, and 3 (12.5%) graded D. In Group B, 9 (29.1%) patients were graded A, 17 (54.8%) patients graded B, 4 (12.9%) patients graded C, and only one patient (3.2%) graded D (Tab. 2). The difference was statistically significant (P<0.05).

Clinical Rating Scales: preoperatively, the Lysholm II score was 45.12 (min 20, max 65, SD 4.34) in Group A and 46.78 (min 23, max 60, SD 4.06) in Group B. All patients were rated poor; one was rated fair. The postoperative Lysholm II score was 94.65 (min 83, max 100, SD 5.1) in Group A, and 96.7 in Group B (min 81, max 100, SD 4.7), without statistically significant differences. In Group A, 15 patients (62.5%) were rated excellent, 6 patients (25%) good, 2 patients (8.3%) fair, and one poor (4.1%). In Group B, 21 patients (67.7%) were rated excellent, 8 patients (25.8%) good, and 2 patients (6.4%) fair. The mean preinjury Tegner score was 6.7 (range, 4 to 9) in Group A, and 7 (range, 5 to 9) in Group B. After injury and prereconstruction, the mean Tegner score was 3.4 (range, 0 to 6) in Group A, and 3.5 (range, 0 to 7) in Group B. Postoperatively, the mean Tegner score was 6.2 (range, 2 to 9) in Group A, and 6.4 (range, 2 to 9) in Group B. No statistical differences were recognized regarding Tegner evaluation.

Discussion

The optimal method for bone-patellar tendon-bone (B-PT-B) graft fixation remains unknown. Endoscopic interference screw fixation17,18,19 is the most widely used and considered the gold standard. However, complications have been reported in the literature with this method1,2,3,20,21, necessitating alternative methods of femoral fixation. Transcondylar fixation is a newly available method. Experimental studies, testing biomechanical validity of this method, (Fatigue testing of Arthrotek Set Screws using the U-guide technique. R Olsen, R Wiley, Arthrotek, Ontario, CA), have shown no difference in terms of pull-out22 strength between the interference and transverse screws. No clinical studies have been reported, thus this study was designed to evaluate its clinical validity. We did not find any statistically significant differences in clinical outcome, nor the Lysholm II and Tegner scoring systems, between patients who underwent ACL reconstruction with transcondylar fixation and those with interference screw fixation, even if the KT-2000 maximal manual measurements were significantly better using transcondylar fixation. Better results achieved with this technique may be attributed to the type of fixation (the only differing step between the two procedures).

Transcondylar fixation offers different advantages, most importantly increased space for biological fixation23,24, which allows a more aggressive rehabilitation25. The hardware of an interference screw hinders bony regrowth into the tunnel, especially if the screw is not against the cortical side of the plug26,27. Theoretically, faster integration of the bone block would be expected if the screw was placed transversely and the rate of bone regrowth on the femoral side was documented with serial Tc 99 bone scans. However, we were unable to carry out this investigation in all patients due to lack of patient acceptance. In spite of this, we noticed complete reduction of femoral bone scan activity three months after ACL reconstruction. Another advantages of transcondylar fixation is reduction of interference screw-related complications1,2,3,20,21, allowing firm fixation of the bone plug even when the posterior cortical rim is blown out, and avoidance of graft damage. Moreover, the transcondylar screw, which fixates the bone plug against the medial wall of the tunnel, avoids problems of graft advancement within the tunnel secondary to mismatched tunnels or suture lacerations. The blunt-nosed transcondylar screw minimizes bony surface contact, thus reducing hardware and biological tissue interface. In cases of septic arthritis following ACL surgery, avoidance of screw removal in order to preserve the graft during the arthroscopic debridement is possible. The three cases of septic arthritis (0.3%), occurred in our casistique and not included in this series, underwent arthroscopic debridement and antibiotic therapy without screw removal. When an interference screw has been used in a primary ACL reconstruction, its removal leaves a wider tunnel that may not allow an immediate graft replacement. In ACL revision surgery, removal of the transcondylar screw appears more difficult than the interference screw. However, if properly sized, the head of the screw is usually superficial enough to be removed easily without the aid of fluoroscopy. In one case, not included in this series, an ACL revision surgery for a secondary instability was performed with removal of the transcondylar interference screw. Because the femoral and tibial tunnels were in correct position, a similar transcondylar method using the Bone-Mulch Screw (Arthrotek, Ontario, CA) with hamstrings graft was used.

We have experienced few complications with this technique, which were not in this study. In two cases, the drill bit and, in one case, the screw driver broke due to instrument metal fatigue. In only two cases, the bone block slipped off while tensioning prior to tibial fixation, allowing repositioning and fixation of the bone plug. There were no cases of bone block fracturing by the transcondylar screw. The amount of screw pressure still depends on surgeon "sensibility", making improved instrumentation useful for the less experienced surgeon.

In conclusion, the transcondylar screw allows stable and durable fixation of the B-T-B graft in ACL reconstruction. The concept of a compressed-fit, perpendicularly-oriented plug, insures greater contact and compression between the bone plug and femoral bone, and avoidance of the previously mentioned interference screw complications.

References

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