Radiographic analysis of femoral interference screw placement during ACL reconstruction: Endoscopic versus open technique

Arthroscopy: The Journal of Arthroscopic and Related Surgery 9(2):154-158

Published by Raven Press, Ltd. © 1993 Arthroscopy Associationof North America

Radiographic Analysis of Femoral Interference Screw Placement During ACL Reconstruction: Endoscopic Versus Open Technique Mark J. Lemos, M.D., Jeffrey Albert, M.D., Timothy Simon, M.S., and Douglas W. Jackson, M.D.

Summary: Fifty patients with anterior cruciate ligament reconstruction using a bone-patellar tendon-bone autograft performed by two techniques were evaluated roentgenographically to compare the position of the femoral interference screws. Group I consisted of 25 patients in whom the screw was placed using a distal lateral femoral incision (the two-incision technique). Group II patients underwent arthroscopically assisted intraarticular placement qf the screw. These patients were then evaluated with anterior-posterior (AP) and lateral roentgenograms. We observed that the AP and lateral screw angles were significantly different with the two techniques. In addition, the endoscopic placement of the femoral screw had an associated divergence of the screw relative to the bone plug in nine of 25 patients compared with zero of 25 in the open group. In conclusion, radiographic differences do exist between femoral interference screws placed for fixation of an ACL graft using the open approach and those placed endoscopically. Although the clinical significance of these differences is not known, we raise the question of greater divergence in femoral interference screw placement with the newer intraarticular femoral interference screw placement techniques. Key Words: Interference screw--ACL reconstruction--Endoscopic screw placement--Bone-patellar tendon-bone-Screw divergence--ACL complications.

Arthroscopically assisted anterior cruciate ligament (ACL) reconstruction has become the surgical technique of choice for many surgeons. There are multiple graft selections available for reconstruction of the anterior cruciate-deficient knee (1-8). The bone-patellar tendon-bone autograft has had widespread use and is considered to be the gold standard (4). The advantages of the patellar tendon-bone autografts include initial strength that approaches or is greater than the A C L ' s maximum load to failure (9),

immediate interference fixation with pullout strengths >1,000 N (10), biologic bone-to-bone healing (11), and excellent biologic incorporation (12). Interference screw fixation between the bone plugs and osseous tunnels is the choice of many surgeons; other current techniques of fixation for this type of graft include staples, screw and washer, and sutures (13). Interference screw fixation has the advantage of initial high pullout strength, compression of the bone-to-bone surfaces without interfering with bone-to-bone healing, ease of application, and low profile (13). Interference screw fixation in the femoral osseous tunnel may be done either under direct visualization through an incision over the lateral cortex or placed endoscopically through the intercondylar notch. Endoscopic placement has become

From the Southern California Center for Sports Medicine, Long Beach Memorial Medical Center, Long Beach, California, U.S.A. Address correspondence and reprint requests to Douglas W. Jackson, M.D., 2760 Atlantic Avenue, Long Beach, CA 90806, U.S.A.

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E N D O S C O P I C VS. OPEN S C R E W P L A C E M E N T I N A C L S U R G E R Y

more widely used since it eliminates the need for the distal lateral femoral exposure (14). The purpose of this study was to evaluate roentgenographically the two methods of femoral interference screw placement. The roentgenographic screw-bone plug relationship was compared using open femoral interference screw placement versus intraarticular placement under arthroscopic control. MATERIALS AND METHODS All patients who had undergone anterior cruciate reconstruction with a patellar tendon-bone autograft between July 1988 and June 1991 at our institution were singled out. If a patient had associated knee ligamentous pathology requiring additional surgical incisions, they were excluded from the study groups. In Group I interference fixation was placed using exposure of the distal femur through a lateral femoral incision, the vastus lateralis was retracted anteriorly, and the periosteum was elevated over the area of tunnel placement. Once the femoral tunnel was prepared and chamfered, the femoral screw was placed, under direct visualization, into the interval distal to the bone plug and within the osseous tunnel wall. For Group II the femoral interference screw was placed using an endoscopic technique. The interference screw was positioned against the cancellous cylindrical bone plug, forcing the collagenous portion of the graft posteriorly into the osseous tunnel. A cannulated interference screw system was used to position the screw within the joint under arthroscopic visualization through an accessory medial infrapatellar portal. The first 25 patients were selected from alphabetical lists compiled from these two groups in order to collect statistically significant data. All of these patients underwent the same rehabilitation protocol. Follow-up consisted of postoperative visits at I week, 3 weeks, 6 weeks, 3 months, 6 months, and yearly. Radiographic evaluation was obtained at 1 week postsurgery, including anteriorposterior and lateral roentgenograms. In the patients whose graft was fixed with the endoscopic technique radiographs were obtained at the 3-month follow-up appointment. In Group I they were also obtained at 6 months. Screw placement measurements on the anteriorposterior radiographs consisted of recording the angle formed by a line drawn through the axis of the

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screw and a straight line connecting the most distal aspects of the medial and lateral femoral condyles, which defines the joint line (Figs. 1 and 2). Screw measurement for the lateral view radiographs consisted of recording the angle formed by a line drawn through the axis of the screw and a straight line drawn along the femoral shaft axis (Fig. 1). The screw placement ratio was calculated from the anterior-posterior and lateral view radiographs. Figure 3 illustrates the measurements used to calculate the screw placement ratios.

Data analysis Descriptive statistics were calculated using means, standard deviations, and 95% confidence intervals for proportions. Comparative data analysis was accomplished using a two-tailed Student's t test. A p value <0.05 was considered statistically significant. BMDP Statistical Software was used for all calculations (15). RESULTS Statistical differences exist between anteriorposterior and lateral screw angle placement when comparing the open versus endoscopically placed interference screw. The p values, means, and standard deviations are shown in Table 1. No significant divergence was noted in the group of patients with interference screw fixation using the open technique. Endoscopically placed screws showed significant divergence, defined as t>5° difo

ote \

18o °

~/

~

I

\

®0 L

FIG. 1. The screw angle is determined by a line drawn through the long axis of the screw and the joint line (AP view) and axis of the femur (lateral view). M, medial; L, lateral. Arthroscopy, Vol. 9, No. 2, 1993

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2A,B

FIG. 2. Interference screw measurements were made directly from roentgenograms. Representative roentgenograms after femoral interference screw placement using the distal femoral incision (open technique), AP view (A) and lateral view (B).

ference, in nine of 25 screws, for an incidence of 36% (confidence interval of 17-55%) (Tables 2, 3). The screw ratio on the anterior-posterior radiographs showed a statistical difference in location of the femoral screw tip with a p value of 0.00001, whereas no significance was seen with the lateral ratio. Bone incorporation did not show statistical differences between the two methods of screw placement.

ence fixation values by endoscopic fixation, we compared this method of interference screw placement to the open lateral femoral approach. Several significant findings became evident. First, the anterior-posterior and lateral screw angles, as previously defined, are significantly different when comparing the open technique with the endoscopic technique. Second, we noted a significant incidence of screw divergence in our endo-

DISCUSSION Arthroscopic technology and instrumentation continues to improve the orthopaedic surgeon's ability to perform less invasive procedures in the knee. This has resulted in the fixation of arthroscopically placed ACL grafts from within the joint (14). Careful evaluation of any new procedure is necessary to reduce the learning curve before its widespread application. We have found that it is necessary at the time of surgery to convert, intraoperatively, from the endoscopic interference technique to the open technique in - 2 % of our ACL reconstructive procedures. This is because we are unable to get pullout values that resist 40 pounds of pull after cyclic loading of the graft. Because of the occasional failure to achieve high pullout interferArthroscopy, Vot. 9, No. 2, 1993

FIG, 3. The screw placement ratio was calculated from the measurements of d/D for both the AP and lateral radiographs.

E N D O S C O P I C VS. OPEN S C R E W P L A C E M E N T I N A C L S U R G E R Y T A B L E 1. Comparisons of screw angle and screw placement ratios for the open and endoscopic screw placement techniques

Screw angle AP (open) AP (endoscopic LAT (open) LAT (endoscopic) Screw placement ratio AP (open) AP (endoscopic) LAT (open) LAT (endoscopic)

Mean

Standard deviation

48.3 73.5 32.8 18.1

8.2 8.45 10.08 8.02

0.29 0.42 0.36 0.36

0.06 0.05 0.12 0.08

T A B L E 2. Incidence of screw divergence using the

endoscopic and open techniques Divergence angle

Endoscopic

Open

AP >~5° LAT~5 o

7/25~ 3/25a

0/25 0/25

p value

0.000001 0.0005 0.00001 0.99

scopic cases. The confidence interval states that the screws significantly diverge on roentgenograms in one fifth to one half of cases, as seen in Figs. 3 and 4. Other variables, including the lateral screw placement ratio and bone incorporation, were not shown to be statistically significant in these groups. The fact that differences exist in the radiographic appearance of these two techniques is not surprising, but that there is actual screw divergence in more than a third of those placed endoscopically is of concern. Unlike the open technique, where direct visualization and control are easily maintained, the endoscopic technique makes it more difficult to place these screws consistently in a parallel fashion. This radiographic finding may result in weaker initial fixation. Three current endoscopic techniques are used for placement of the interference screw with arthroscopic assistance. The screw fixation may be passed through the anteromedial portal, via an accessory anteromedial portal just over the upper tibial plateau, or through the tibial tunnel. The anteromedial portal theoretically would give the most divergence and the tibial tunnel the least. The disadvantage of the tibial tunnel is the need for additional space for instrumentation in the osseous tunnel. We have used the accessory portal, which allows a more parallel placement of the screw relative to the graft and femoral tunnel when the knee is held fully flexed. Even with this portal we have a significant incidence of divergence, since one does not achieve true parallelism even with the knee maximally flexed. Previously reported endoscopically placed interference screws without divergence showed high pullout values. These values approached those of the ultimate load-to-failure strength of the ligament. We prefer the endoscopictechnique, since it re-

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One patient had divergence in two planes, for a total of nine of 25 patients with divergence in the endoscopic group.

quires less dissection, and since the collagen fibers of the patellar tendon autograft and bone plugs more closely approach a straight line in comparison to the grafts placed through the lateral femoral incision. Theoretically, this would decrease the stresses at the femoral graft junction. However, if the fixation is not acceptable, a more traditional approach is required. A cadaveric study evaluating the biomechanical significance of these differences, as well as the number of threads in contact with the graft required to obtain the desired pullout values, would be helpful. Fulkerson et al. (16) presented data on pullout of divergent screws showing ultimate strength of failure decreasing significantly with screw divergence between 15 and 30°. Their study used adult bovine knees (fresh). They had three groups: group I with no divergence, group II with 15° of divergence, and group III with 30° of divergence. In groups I and II failure occurred at - 2 0 N/mm 2, compared with 4.88 N/ram 2 for group III. The mode of failure for groups I and II was bone fracture and patellar tendon midsubstance when compared with group III, where failures were due to graft pullout. Only one of the nine patients' radiographs with divergence that we evaluated had >15 ° of divergence. We can hypothesize from these data that clinically significant divergence occurred in <5% (one of 25) of the cases evaluated. This finding correlates well with our own experience of conversion from the endoscopic to the open technique for failure of femoral fixation intraoperatively. Evaluation of radiographs of nine endoscopic patients with screw divergence

T A B L E 3. Patient

AP (degrees)

LAT (degrees)

1 2 3 4 5 6 7 8 9

10 10 8 5 11 12 0 7 0

0 0 3 3 9 0 25 0 18

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4A,B

FIG. 4. AP (A) and lateral (13) roentgenograms of endoscopically placed screws. Note the 10° of divergence of the screw from the bone plug in Fig. 4a.

I n c o n c l u s i o n , r a d i o g r a p h i c d i f f e r e n c e s do exist b e t w e e n f e m o r a l i n t e r f e r e n c e s c r e w s p l a c e d for fixa t i o n o f a n A C L graft u s i n g the o p e n a p p r o a c h a n d t h o s e p l a c e d e n d o s c o p i c a l l y . A l t h o u g h the clinical s i g n i f i c a n c e is n o t y e t k n o w n , w e raise the q u e s t i o n o f g r e a t e r d i v e r g e n c e in f e m o r a l i n t e r f e r e n c e s c r e w p l a c e m e n t with the n e w e r e n d o s c o p i c i n t e r f e r e n c e techniques. REFERENCES 1. Butler DL, Grood ES, Noyes FR, et al. Effects of structure and strain measurement techniques on the material properties of young human tendons and fascia. J Biomech 1984;17: 590-6. 2. Grewe RS, Paulos LE. Prosthetic replacement of the anterior cruciate ligament with expanded polytetrafluoroethylene. Am Acad Orthop Surg Instruct Course Lect 1991;40: 213-7. 3. Insall J, Joseph D, Aglietti HP, et al. Bone block iliotibial band transfer for anterior cruciate insufficiency. J Bone Joint Surg 1981;63A:560-9. 4. Jackson DW, Jennings LD. Arthroscopically assisted reconstruction of the anterior cruciate ligament using patella tendon bone autograft. Clin Sports Med 1988;7(4):785-800. 5. Jones KG. Reconstruction of the anterior cruciate ligament: a technique using the central one third of the patellar ligament. J Bone Joint Surg 1970;52A:1302-8. 6. McMaster JH, Weinert CR Jr, Scranton P. The diagnosis and management of isolated anterior cruciate ligament tears: a preliminary report on reconstruction with the gracilis tendon. J Trauma 1974;14:230-5. Arthroscopy, Vol. 9, No. 2, 1993

7. Mott HW. Anatomical reconstruction for cruciate ligament insufficiency. Clin Orthop 1983;172:90-2. 8. Tillberg B. The late repair of torn cruciate ligaments using menisci. J Bone Joint Surg 1977;59B:15-9. 9. Noyes FR, Butler DL, Grood ES, et al. Biomechanical analysis of human ligament grafts used in knee ligament repairs and reconstructions. J Bone Joint Surg 1984;61A:344-52. 10. Shapiro JD, Cohn BT, Jackson DW, Postak PD, Parker RD. The biomechanical effects of geometric configuration of bone-tendon-bone autografts in anterior cruciate ligament reconstruction [Abstract]. Trans Orthop Res Soc 1991;16(2): 590. 11. Noyes FR, Butler DL, Paulos LE, et al. Intra-articular cruciate reconstruction. I. Perspectives on graft strength, vascularization, and immediate motion after replacement. Clin Orthop 1983;172:71-7. 12. Jackson DW, Grood ES, Goldstein J, Rosen MA, Kurzweil PR, Cummings JF, Simon TM. Anterior cruciate ligament reconstruction using patellar tendon autograft and allograft: a comparative study in goats. (in press). 13. Butler DL. Evaluation of fixation methods in cruciate ligament replacement. Am Acad Orthop Surg Instruct Course Lect t987;36:173-8. 14. Jackson DW, Kurzweil PE. Single incision arthroscopic ACL reconstruction technique. A.A.O.S. Videotape. Presented at the 57th Annual AAOS Meeting, New Orleans, 1990. 15. Cohen J. Statistical power analysis for the behavioral sciences, 2nd ed. Hillsdale, New Jersey: Lawrence Erlbaum Associates, 1988. 16. Fulkerson JP, Cautilli R, Hosick WB, Wright J. Divergence angles and their effect on the fixation strength of the Kurosaka screw. Presented at the Jefferson Orthopaedic Society, Philadelphia, November 1991.