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Use of an endoscopic aimer for femoral tunnel placement in anterior cruciate ligament reconstruction
Use of an Endoscopic Aimer for Femoral Tunnel Placement in Anterior Cruciate Ligament Reconstruction David A. McGuire, M.D., Stephen D. Hendricks, and Geri L. Grinstead, Ph.D.
Summary: Accurate placement of the femoral tunnel is a technically difficult aspect of anterior cruciate ligament reconstruction. Various drill guides have been developed to aid in the selection of this site. The purpose of this article is to describe a new drill guide designed to ensure anatomic placement of the femoral tunnel. The guide is used as part of a single-incision arthroscopic anterior cruciate ligament reconstruction technique with a bone-patellar tendon-bone graft secured with interference screws. An intraoperative check of the "pretunnel footprint" can be made to verify correct placement by the remaining cortical margins measurement within an acceptable 1 to 2 mm range before drilling the tunnel to depth. If necessary, minor adjustments to the guidepin location can be made to prevent posterior tunnel margin dimensions of less than 1 mm (troughing) or greater than 2 ram. Key Words: Endoscopic ACL--Femoral tunnel--Graft placement.
nterior cruciate ligament (ACL) reconstruction by arthroscopic means has been volumninously reported. Numerous techniques and instruments have been developed to determine and assist the placement of femoral tunnels, including drilling freehand, using a drill guide, ~6 or a tension isometer. 7-11 The selection of the femoral attachment site for optimal graft insertion is particularly critical 12-~5and current general consensus of the best location is slightly anterior to the "over-the-top" position, at the junction of the intercondylar roof and the intercondylar notch. ~2-19The authors present a method employing an instrument that is used with anatomic references to accurately and consistently select femoral tunnel placement for bone-patellar tendon-bone grafts, in a simple and reliable manner. Femoral tunnel guides are of two basic types defined by tunnel drilling direction: outside-in or inside-out.
A
Private practice. Address correspondence and reprint requests to Stephen D. Hendricks, Research Associate, 4048 Laurel St, Suite 202, Anchorage, A K 99508, U.S.A. © 1996 by the Arthroscopy Association of North America 0749-8063/96/1201-117953.00/0
26
Some surgeons use the standard two-incision technique, which includes the lateral thigh incision employing the outside-in technique. TM Other guides use the inside-out technique. They vary by point of insertion into the knee and the resultant tunnel orientation. Paterson's guide, 6 for example, used the anteromedial incision to drill the femoral tunnel with the knee in hyperflexion. This technique obviates the need for a lateral thigh incision; however, the resultant tunnel axes are nonconcentric in the axial plane and may produce unwanted varus or valgus stresses when tension is applied to the graft (Fig 1). Using the tibial tunnel for reamer access when drilling the femoral tunnel, a current and widely accepted technique, produces concentric tunnel axes. The guide described in this article uses this form of the insideout technique. This design obviates lateral incisions for compartment access of the instrument and there is no requirement to hyperflex the knee during any stage of the drilling process. The endoscopic femoral aimer (EFA) (Fig 2) consists of a case-hardened steel tube assembly fitted with a handle, a tongue, and a spike. The tongue serves as the physical reference to the extreme posterior cortex of the intercondylar notch; the over-the-top ridge (Fig
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 12, No 1 (February), 1996: pp 26-31
ENDOSCOPIC FEMORAL AIMER
]
/
r ]
27
I
~ U.7
/ FIG 1. (A) Tunnels with concentric axes. (B) Tunnel axes that are neither concentric nor parallel. An appropriately tensioned graft within this tunnel configuration would theoretically produce varus stresses. Valgus stresses are also possible with an opposite axes configuration. (C) Tunnel axes that are parallel but not concentric. Theoretical knee stresses associated with this situation would produce lateral forces to the tibia shaft at the joint line. Medial forces are also possible with the axes in an opposite parallel configuration.
3). T h e spike prevents m o v e m e n t o f the E F A once seated into the cortex o f the notch. The space b e t w e e n the tongue and the axis o f the guide pin tube is 7 mm. T h e desired femoral tunnel position is high in the notch with its center a p p r o x i m a t e l y 7 m m anterior to the over-the-top ridge. This p l a c e m e n t results in a tunnel with a i to 2 m m posterior cortical r i m r e m a i n i n g b e t w e e n the f e m o r a l tunnel and the notch for use with the a b o v e d e s c r i b e d b o n e plug dimensions (Fig 4).
TECHNICAL
FIG 3. Operative radiograph. The EFA is positioned through the drilled tibial tunnel with the knee flexed at greater than 50°.
elevated to expose the over-the-top position with an angled curette. The patellar b o n e - t e n d o n - b o n e autograft is harvested with a width o f 10 m m from the tibial tubercle and 11 m m from the patella. B o n e plug pairs with 9 and 10 m m or 11 and 12 m m width dimensions m a y be used instead when a n a t o m i c a l l y appropriate, A tibial guide is used to d e t e r m i n e p l a c e m e n t o f the tibial tunnel. The tibial g u i d e ' s locator pin is p l a c e d at the anatomic center o f the A C L on the tibia. The azimuth used to position the guide for the tibial tunnel corresponds with the 11 o ' c l o c k position for the
SUGGESTIONS
The notchplasty with a resultant width o f at least 2 c m is performed. This notchplasty extends adequately posterior to reveal the posterolateral f e m o r a l cortex and superior to include a portion o f the r o o f o f the notch. The p e r i o s t e u m o f the posterolateral cortex is
handle
guide pin tube
tongueY
I
FIG 2. Diagram of the EFA and the spatial relationship between the tongue and the guide pin tube.
FIG 4. Centered placement of a 2.3 mm (3/32-inch) guide wire. Subsequent 10 or 12 mm drill holes produce 2 and 1 mm cortical margins, respectively. An 11 mm drill hole results in a 1.5 mm margin.
D. A. McGUIRE E T AL.
28
/ 1 el
FIG 6. Endoscopic view of EFA seated in the "over-the-top" position in a left knee.
lectively, these angles impose a knee flexion angle of 55 ° to 60 ° during the drilling of the femoral tunnel using the tibial tunnel for reamer access. The knee m a y require some minor knee flexion angle correction
FIG 5. Axial view, tibial tunnel axis = 30° _+ 5°. Variations to 30° correspond with genu varum and genu valgum.
right knee and the 1 o ' c l o c k position for the left knee, and approximates 30 ° (_+ 5 °) to the tibiofemoral axis (Fig 5). After the tibial tunnel is drilled and its opening into the tibial plateau is chamfered, the knee is positioned -----50 ° and the guide is inserted through the tibial tunnel. The tongue of the guide rests on the posterior femoral cortex, which was previously cleared o f periosteum. Depending on right or left knee reconstruction, the tongue o f the guide, thus the guide pin and the center o f the femoral tunnel, is placed at the 11 or 1 o ' c l o c k position, respectively, using the proximal center of the notch referenced to 12 o'clock. This position corresponds with a tibial tunnel axis oriented 55 ° to 60 ° to the tibial plateau in the saggital plane and 30 ° (_+ 5 °) to the tibiofemoral axis in the axial plane. Col-
FIG 7. EFA in position with 3/32 inch guide wire drilled in place. (Reprinted with permission of Linvatec Corporation, Largo, FL.)
ENDOSCOPIC FEMORAL AIMER
FIG 8. Endoscopic view of pretunnel footprint with guide pin in position. Note space between arrows defined as posterior cortical margin.
during the tongue insertion. Anterior loading of the tibia should be avoided while performing this adjustment. The spike is advanced into the condyle with the knee held securely so as not to bend the tongue of the aimer (Fig 6). Once in place, a guide pin is inserted through the guide tube and drilled to the cortex (Fig 7). After the guide pin is placed, the guide is removed by pulling it back from the condyle and rotating 180 ° clockwise for the right knee or 180 ° counterclockwise for the left knee. This allows the tongue to exit under the condyle and prevents scuffing or damage to adjacent surfaces. An appropriately sized cannulated reamer is advanced over the guide pin. The reamer is advanced approximately 4 to 6 m m to create a "pretunnel footprint" and then withdrawn for inspection. A posterior cortical margin of 1 to 2 m m indicates accurate anatomic placement (Fig 8). If the posterior cortex is less than 1 m m or greater than 2 mm, the guide pin is removed and appropriately repositioned manually and the footprint is again created to verify accuracy before drilling the femoral tunnel to depth. Once appropriate placement is verified, the tunnel is reamed at least 5 m m deeper than the length of the bone plug intended for femoral fixation. A graft pin passer is placed eccentrically in the prox-
29
imal end of the femoral tunnel with anterolateral orientation and is drilled through the femoral cortex. Its exit through the skin of the lateral side of the femur is accomplished manually. The guidewire for the cannulated interference screw is inserted through the anteromedial portal and into the trough of the graft pin passer and exits the lateral thigh. The suture attached to the graft is threaded through the hole in the distal end of the graft pin passer and is subsequently pulled through both tunnels exiting the lateral thigh. The graft is pulled through the tunnels from the distal end of the tibial tunnel, is positioned with the cortical side against the extreme posterior aspect of the femoral tunnel, and is advanced into the femoral tunnel. The guidewire remains anterolateral and the femoral bone plug is secured with a headless cannulated screw placed anterolaterally 2° via the guidewire. The knee is flexed to approximately 90 ° during screw insertion to prevent tissue wrapping around the screw. This placement allows for the screw to be optimally engaged in both the bone block of the graft and the tunnel, thereby increasing pullout strength. The cortical side of the distal end of the graft is positioned against the posterior aspect of the tibial tunnel. After femoral side fixation, tension is placed on the graft by the attached 24 gauge flexible wire in the tibial bone plug. The knee is moved through a range of motion from 0 ° to 120 ° to confirm impingement-free placement without graft pistoning. While maintaining tension, an arthroscopic Lachman's test* is used to verify anterior tibial translation of less than 2 ram. The tibial bone block is then secured with a headless cannulated screw placed anteromedially to the bone block. TECHNICAL CONSIDERATIONS If the cortical margin falls outside of the desired range ( < 1 or > 2 mm) during the footprint inspection, several considerations can be made to assess the cause by separating these types of errors into two groups. The greater than 2 m m (too-anterior) group and the less than 1 m m (too-posterior) group. * An arthroscopic Lachman's test adds a visual component to the manual kinesthetic character of the test. The graft is tensioned manually and the normal relationship between the femur and tibia are viewed arthroscopicallyfor reference. An anterior load is placed in the proximal tibia (Lachman's test) and the position difference from the reference is noted. If the movement is less than 2 mm, the tibial end of the graft is secured. If the movement difference is greater than 2 mm, the tension on the graft is increased and the test is repeated, ff the test is still abnormal (>2 ram), improperlyplaced tunnels are frequently the cause.
30
D. A. M c G U I R E E T AL.
W h e n the remaining cortical margin is greater than 2 mm, the likely reason for this occurance is a bent tongue on the femoral guide. W e have encountered this problem infrequently and attribute this occurance to the weight o f the lower leg resting on the guide while it is in position before or during the insertion of the guide pin. It is possible to prevent the tongue from being bent by holding the leg securely during this phase. Visual inspection of the instrument before each use provides for a back-up protocol. W h e n the remaining cortical margin is less than 1 mm, there are several potential sources o f error; softtissue entrapment or a too-shallow knee angle. While elevating the periosteum sufficiently alleviates the entrapment o f soft tissue most o f the time, tissue debris m a y be caught inadvertantly. Additionally, even when the over-the-top position is properly prepared, there are occasional variations when the over-the-top position is more rounded and this can make it difficult to seat the tongue correctly. If the knee angle is too shallow or if the tibial tunnel is less than 50 ° to the tibial plateau, a posterior cortical " b l o w o u t " or troughing can occur. W e have encountered this problem only once and attribute the occurance to lifting the lower leg, essentially extending the knee, immediately before reaming the femoral tunnel. Holding the knee securely at a constant angle and careful inspection of the footprint before drilling will aid in the prevention of these types of errors. The ease with which cortical margin errors are identified and corrected are a benefit this guide has for femoral tunnel identification. The ability to correct for errors intraoperatively before drilling the tunnel to depth is a distinct advantage over other techniques where postoperative outcome or intraoperative radiographs are the only means of identifying a poorly selected site. A n additional benefit o f this device could be to locate a guide pin or preliminary pilot hole for surgeons who are more comfortable performing a two-incision technique. A rear entry or front entry aimer could then be used in conjunction with the pilot hole or guide pin to reliably create a femoral tunnel, albeit without the pretunnel footprint-verification stage. In summary, this is a simple and time conserving instrument that provides for consistent and reliable anatomic placement o f the femoral tunnel. The design of the instrument obviates the need for a lateral thigh incision, thus reducing the risk of complication and improving cosmetic appeal. The associated surgical technique is considerably less complicated and uses
the validation step of a pretunnel footprint, allowing confirmation of cortical margin dimensions before complete drilling. The accurate positioning of the femoral tunnel by this means eliminates the need for tension isometer use. Finally, the resultant tunnels share a single axis, reducing the aberrant stress concentration factors associated with poor graft placement outcome and subsequent failure. The use o f the E F A results in a procedure that is less invasive and time consuming, and is more uniform with accurate results.
Acknowledgment: The authors thank Linvatec Concept Arthroscopy, Linvatec Corporation, for creating the prototypes and making the modifications necessary to create the final version of the guide. The guide is currently available from Linvatec Concept Arthroscopy as the Bullseye Femoral Guide. REFERENCES 1. Stewart JJ. Athletic injuries particularly to the ligaments of the knee: Diagnosis, repair and physical rehabilitation. Am J Orthop 1969;3:52-57. 2. Rhinelander FW, Brahms MA. Modification of C-clamp for use in restoration of cruciate ligaments. Clin Orthop 1970;71:217218. 3. Lindstrand A, Stenstr~m A, TjOmstrand B. The Lund drill guide: An instrument for repair or reconstruction of the cruciate ligaments. Arch Orthop Trauma Surg 1982;99:231-233. 4. Hewson GF Jr. An improved guide for intra-articnlar cruciate ligament reconstruction and repair. Clin Orthop 1983; 172:119124. 5. Good L, Odensten M, Gillquist J. Precision in reconstruction of the anterior cruciate ligament: A new positioning device compared with hand drilling. Acta Orthop Stand 1987; 58:658-661. 6. Marans HJ, Hendrix MR, Paterson RS. A new femoral drill guide for arthroscopically assisted anterior cruciate ligament replacement. Arthroscopy 1992;8:234-238. 7. Lewis JL, Lew WD, Hill JA, Hanley P, Ohland K, Kirstukas S, Hunter RE. Knee joint motion and ligament forces before and after ACL reconstruction. J Biomech Eng 1989; 111:97-106. 8. Fleming BC, Beynnon BD, Nichols CE, Renstrrm PA, Johnson RJ, Pope MH. An in vivo comparison between intraoperative isometric measurement and local elongation of the graft after reconstruction of the anterior cruciate ligament. J Bone Joint Surg Am 1994;76:511-519. 9. Flandry F, Terry GC, Montgomery RD, Fester MA, Madsen N. Accuracy of clinical isometry and preload testing during anterior cruciate ligament reconstruction. Clin Orthop 1992;279:214222. 10. Sapega AA, Moyer RA, Schneck C, Komalahiranya N. Testing for isometry during reconstruction of the anterior cruciate ligament. J Bone Joint Surg Am 1990;72:259-267. 11. Colville MR, Bowman RR. The significance of isometer measurements and graft position during anterior cruciate ligament reconstruction. Am J Sports Med 1993;21:832-835. 12. Bylski-Austrow DT, Grood ES, Hefzy MS, Holden JP, Butler DL. Anterior cruciate ligament replacement: A mechanical study of femoral attachment location, flexion angle at tensioning, and initial tension. J Orthop Res 1990;8:522-531. 13. Grood ES, Hefzy MS, Butler DL, Suntay WJ, Siegel MG, Noyes
ENDOSCOPIC
14. 15. 16. 17.
FR. On the placement and the initial tension of anterior cruciate ligament substitutes. Trans Orthop Res Soc 1983;29:92. Hefzy MS, Grood ES, Noyes FR. Factors affecting the region of most isometric femoral attachments part II. The anterior cruciate ligament. Am J Sports Med 1989; 17:208-216. Melhom JM, Henning CE. The relationship of the femoral attachment site to the isometric tracking of the anterior cruciate ligament graft. Am J Sports Med 1987; 15:539-542. Odensten M, Gillquist J. Functional anatomy of the anterior cruciate ligament and a rationale for reconstruction. J Bone Joint Surg Am 1985;67:257-262. Penner DA, Daniel DM, Wood P, Mishra D. An in vitro study
FEMORAL
AIMER
31
of anterior cmciate ligament graft placement and isometry. Am J Sports Med 1988; 16:238-243. 18. Sidles JA, Larson RV, Garbini JL, Downey DJ, Matsen FA. Ligament length relationships in the moving knee. J Orthop Res 1988;6:593-610. 19. Larson RV. Graft placement and orientation in ACL reconstruction: Isometry and impingement. In: Book of Abstracts, Instructional Courses and Symposia. Arthroscopy Association of North America, 1 lth Annual Meeting, Boston, MA, 1992. 20. McGuire DA, Grinstead GL. Advances in anterior cruciate ligament surgery. Alaska Med 1990;32:101-105.
Summary: Accurate placement of the femoral tunnel is a technically difficult aspect of anterior cruciate ligament reconstruction. Various drill guides have been developed to aid in the selection of this site. The purpose of this article is to describe a new drill guide designed to ensure anatomic placement of the femoral tunnel. The guide is used as part of a single-incision arthroscopic anterior cruciate ligament reconstruction technique with a bone-patellar tendon-bone graft secured with interference screws. An intraoperative check of the "pretunnel footprint" can be made to verify correct placement by the remaining cortical margins measurement within an acceptable 1 to 2 mm range before drilling the tunnel to depth. If necessary, minor adjustments to the guidepin location can be made to prevent posterior tunnel margin dimensions of less than 1 mm (troughing) or greater than 2 ram. Key Words: Endoscopic ACL--Femoral tunnel--Graft placement.
nterior cruciate ligament (ACL) reconstruction by arthroscopic means has been volumninously reported. Numerous techniques and instruments have been developed to determine and assist the placement of femoral tunnels, including drilling freehand, using a drill guide, ~6 or a tension isometer. 7-11 The selection of the femoral attachment site for optimal graft insertion is particularly critical 12-~5and current general consensus of the best location is slightly anterior to the "over-the-top" position, at the junction of the intercondylar roof and the intercondylar notch. ~2-19The authors present a method employing an instrument that is used with anatomic references to accurately and consistently select femoral tunnel placement for bone-patellar tendon-bone grafts, in a simple and reliable manner. Femoral tunnel guides are of two basic types defined by tunnel drilling direction: outside-in or inside-out.
A
Private practice. Address correspondence and reprint requests to Stephen D. Hendricks, Research Associate, 4048 Laurel St, Suite 202, Anchorage, A K 99508, U.S.A. © 1996 by the Arthroscopy Association of North America 0749-8063/96/1201-117953.00/0
26
Some surgeons use the standard two-incision technique, which includes the lateral thigh incision employing the outside-in technique. TM Other guides use the inside-out technique. They vary by point of insertion into the knee and the resultant tunnel orientation. Paterson's guide, 6 for example, used the anteromedial incision to drill the femoral tunnel with the knee in hyperflexion. This technique obviates the need for a lateral thigh incision; however, the resultant tunnel axes are nonconcentric in the axial plane and may produce unwanted varus or valgus stresses when tension is applied to the graft (Fig 1). Using the tibial tunnel for reamer access when drilling the femoral tunnel, a current and widely accepted technique, produces concentric tunnel axes. The guide described in this article uses this form of the insideout technique. This design obviates lateral incisions for compartment access of the instrument and there is no requirement to hyperflex the knee during any stage of the drilling process. The endoscopic femoral aimer (EFA) (Fig 2) consists of a case-hardened steel tube assembly fitted with a handle, a tongue, and a spike. The tongue serves as the physical reference to the extreme posterior cortex of the intercondylar notch; the over-the-top ridge (Fig
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 12, No 1 (February), 1996: pp 26-31
ENDOSCOPIC FEMORAL AIMER
]
/
r ]
27
I
~ U.7
/ FIG 1. (A) Tunnels with concentric axes. (B) Tunnel axes that are neither concentric nor parallel. An appropriately tensioned graft within this tunnel configuration would theoretically produce varus stresses. Valgus stresses are also possible with an opposite axes configuration. (C) Tunnel axes that are parallel but not concentric. Theoretical knee stresses associated with this situation would produce lateral forces to the tibia shaft at the joint line. Medial forces are also possible with the axes in an opposite parallel configuration.
3). T h e spike prevents m o v e m e n t o f the E F A once seated into the cortex o f the notch. The space b e t w e e n the tongue and the axis o f the guide pin tube is 7 mm. T h e desired femoral tunnel position is high in the notch with its center a p p r o x i m a t e l y 7 m m anterior to the over-the-top ridge. This p l a c e m e n t results in a tunnel with a i to 2 m m posterior cortical r i m r e m a i n i n g b e t w e e n the f e m o r a l tunnel and the notch for use with the a b o v e d e s c r i b e d b o n e plug dimensions (Fig 4).
TECHNICAL
FIG 3. Operative radiograph. The EFA is positioned through the drilled tibial tunnel with the knee flexed at greater than 50°.
elevated to expose the over-the-top position with an angled curette. The patellar b o n e - t e n d o n - b o n e autograft is harvested with a width o f 10 m m from the tibial tubercle and 11 m m from the patella. B o n e plug pairs with 9 and 10 m m or 11 and 12 m m width dimensions m a y be used instead when a n a t o m i c a l l y appropriate, A tibial guide is used to d e t e r m i n e p l a c e m e n t o f the tibial tunnel. The tibial g u i d e ' s locator pin is p l a c e d at the anatomic center o f the A C L on the tibia. The azimuth used to position the guide for the tibial tunnel corresponds with the 11 o ' c l o c k position for the
SUGGESTIONS
The notchplasty with a resultant width o f at least 2 c m is performed. This notchplasty extends adequately posterior to reveal the posterolateral f e m o r a l cortex and superior to include a portion o f the r o o f o f the notch. The p e r i o s t e u m o f the posterolateral cortex is
handle
guide pin tube
tongueY
I
FIG 2. Diagram of the EFA and the spatial relationship between the tongue and the guide pin tube.
FIG 4. Centered placement of a 2.3 mm (3/32-inch) guide wire. Subsequent 10 or 12 mm drill holes produce 2 and 1 mm cortical margins, respectively. An 11 mm drill hole results in a 1.5 mm margin.
D. A. McGUIRE E T AL.
28
/ 1 el
FIG 6. Endoscopic view of EFA seated in the "over-the-top" position in a left knee.
lectively, these angles impose a knee flexion angle of 55 ° to 60 ° during the drilling of the femoral tunnel using the tibial tunnel for reamer access. The knee m a y require some minor knee flexion angle correction
FIG 5. Axial view, tibial tunnel axis = 30° _+ 5°. Variations to 30° correspond with genu varum and genu valgum.
right knee and the 1 o ' c l o c k position for the left knee, and approximates 30 ° (_+ 5 °) to the tibiofemoral axis (Fig 5). After the tibial tunnel is drilled and its opening into the tibial plateau is chamfered, the knee is positioned -----50 ° and the guide is inserted through the tibial tunnel. The tongue of the guide rests on the posterior femoral cortex, which was previously cleared o f periosteum. Depending on right or left knee reconstruction, the tongue o f the guide, thus the guide pin and the center o f the femoral tunnel, is placed at the 11 or 1 o ' c l o c k position, respectively, using the proximal center of the notch referenced to 12 o'clock. This position corresponds with a tibial tunnel axis oriented 55 ° to 60 ° to the tibial plateau in the saggital plane and 30 ° (_+ 5 °) to the tibiofemoral axis in the axial plane. Col-
FIG 7. EFA in position with 3/32 inch guide wire drilled in place. (Reprinted with permission of Linvatec Corporation, Largo, FL.)
ENDOSCOPIC FEMORAL AIMER
FIG 8. Endoscopic view of pretunnel footprint with guide pin in position. Note space between arrows defined as posterior cortical margin.
during the tongue insertion. Anterior loading of the tibia should be avoided while performing this adjustment. The spike is advanced into the condyle with the knee held securely so as not to bend the tongue of the aimer (Fig 6). Once in place, a guide pin is inserted through the guide tube and drilled to the cortex (Fig 7). After the guide pin is placed, the guide is removed by pulling it back from the condyle and rotating 180 ° clockwise for the right knee or 180 ° counterclockwise for the left knee. This allows the tongue to exit under the condyle and prevents scuffing or damage to adjacent surfaces. An appropriately sized cannulated reamer is advanced over the guide pin. The reamer is advanced approximately 4 to 6 m m to create a "pretunnel footprint" and then withdrawn for inspection. A posterior cortical margin of 1 to 2 m m indicates accurate anatomic placement (Fig 8). If the posterior cortex is less than 1 m m or greater than 2 mm, the guide pin is removed and appropriately repositioned manually and the footprint is again created to verify accuracy before drilling the femoral tunnel to depth. Once appropriate placement is verified, the tunnel is reamed at least 5 m m deeper than the length of the bone plug intended for femoral fixation. A graft pin passer is placed eccentrically in the prox-
29
imal end of the femoral tunnel with anterolateral orientation and is drilled through the femoral cortex. Its exit through the skin of the lateral side of the femur is accomplished manually. The guidewire for the cannulated interference screw is inserted through the anteromedial portal and into the trough of the graft pin passer and exits the lateral thigh. The suture attached to the graft is threaded through the hole in the distal end of the graft pin passer and is subsequently pulled through both tunnels exiting the lateral thigh. The graft is pulled through the tunnels from the distal end of the tibial tunnel, is positioned with the cortical side against the extreme posterior aspect of the femoral tunnel, and is advanced into the femoral tunnel. The guidewire remains anterolateral and the femoral bone plug is secured with a headless cannulated screw placed anterolaterally 2° via the guidewire. The knee is flexed to approximately 90 ° during screw insertion to prevent tissue wrapping around the screw. This placement allows for the screw to be optimally engaged in both the bone block of the graft and the tunnel, thereby increasing pullout strength. The cortical side of the distal end of the graft is positioned against the posterior aspect of the tibial tunnel. After femoral side fixation, tension is placed on the graft by the attached 24 gauge flexible wire in the tibial bone plug. The knee is moved through a range of motion from 0 ° to 120 ° to confirm impingement-free placement without graft pistoning. While maintaining tension, an arthroscopic Lachman's test* is used to verify anterior tibial translation of less than 2 ram. The tibial bone block is then secured with a headless cannulated screw placed anteromedially to the bone block. TECHNICAL CONSIDERATIONS If the cortical margin falls outside of the desired range ( < 1 or > 2 mm) during the footprint inspection, several considerations can be made to assess the cause by separating these types of errors into two groups. The greater than 2 m m (too-anterior) group and the less than 1 m m (too-posterior) group. * An arthroscopic Lachman's test adds a visual component to the manual kinesthetic character of the test. The graft is tensioned manually and the normal relationship between the femur and tibia are viewed arthroscopicallyfor reference. An anterior load is placed in the proximal tibia (Lachman's test) and the position difference from the reference is noted. If the movement is less than 2 mm, the tibial end of the graft is secured. If the movement difference is greater than 2 mm, the tension on the graft is increased and the test is repeated, ff the test is still abnormal (>2 ram), improperlyplaced tunnels are frequently the cause.
30
D. A. M c G U I R E E T AL.
W h e n the remaining cortical margin is greater than 2 mm, the likely reason for this occurance is a bent tongue on the femoral guide. W e have encountered this problem infrequently and attribute this occurance to the weight o f the lower leg resting on the guide while it is in position before or during the insertion of the guide pin. It is possible to prevent the tongue from being bent by holding the leg securely during this phase. Visual inspection of the instrument before each use provides for a back-up protocol. W h e n the remaining cortical margin is less than 1 mm, there are several potential sources o f error; softtissue entrapment or a too-shallow knee angle. While elevating the periosteum sufficiently alleviates the entrapment o f soft tissue most o f the time, tissue debris m a y be caught inadvertantly. Additionally, even when the over-the-top position is properly prepared, there are occasional variations when the over-the-top position is more rounded and this can make it difficult to seat the tongue correctly. If the knee angle is too shallow or if the tibial tunnel is less than 50 ° to the tibial plateau, a posterior cortical " b l o w o u t " or troughing can occur. W e have encountered this problem only once and attribute the occurance to lifting the lower leg, essentially extending the knee, immediately before reaming the femoral tunnel. Holding the knee securely at a constant angle and careful inspection of the footprint before drilling will aid in the prevention of these types of errors. The ease with which cortical margin errors are identified and corrected are a benefit this guide has for femoral tunnel identification. The ability to correct for errors intraoperatively before drilling the tunnel to depth is a distinct advantage over other techniques where postoperative outcome or intraoperative radiographs are the only means of identifying a poorly selected site. A n additional benefit o f this device could be to locate a guide pin or preliminary pilot hole for surgeons who are more comfortable performing a two-incision technique. A rear entry or front entry aimer could then be used in conjunction with the pilot hole or guide pin to reliably create a femoral tunnel, albeit without the pretunnel footprint-verification stage. In summary, this is a simple and time conserving instrument that provides for consistent and reliable anatomic placement o f the femoral tunnel. The design of the instrument obviates the need for a lateral thigh incision, thus reducing the risk of complication and improving cosmetic appeal. The associated surgical technique is considerably less complicated and uses
the validation step of a pretunnel footprint, allowing confirmation of cortical margin dimensions before complete drilling. The accurate positioning of the femoral tunnel by this means eliminates the need for tension isometer use. Finally, the resultant tunnels share a single axis, reducing the aberrant stress concentration factors associated with poor graft placement outcome and subsequent failure. The use o f the E F A results in a procedure that is less invasive and time consuming, and is more uniform with accurate results.
Acknowledgment: The authors thank Linvatec Concept Arthroscopy, Linvatec Corporation, for creating the prototypes and making the modifications necessary to create the final version of the guide. The guide is currently available from Linvatec Concept Arthroscopy as the Bullseye Femoral Guide. REFERENCES 1. Stewart JJ. Athletic injuries particularly to the ligaments of the knee: Diagnosis, repair and physical rehabilitation. Am J Orthop 1969;3:52-57. 2. Rhinelander FW, Brahms MA. Modification of C-clamp for use in restoration of cruciate ligaments. Clin Orthop 1970;71:217218. 3. Lindstrand A, Stenstr~m A, TjOmstrand B. The Lund drill guide: An instrument for repair or reconstruction of the cruciate ligaments. Arch Orthop Trauma Surg 1982;99:231-233. 4. Hewson GF Jr. An improved guide for intra-articnlar cruciate ligament reconstruction and repair. Clin Orthop 1983; 172:119124. 5. Good L, Odensten M, Gillquist J. Precision in reconstruction of the anterior cruciate ligament: A new positioning device compared with hand drilling. Acta Orthop Stand 1987; 58:658-661. 6. Marans HJ, Hendrix MR, Paterson RS. A new femoral drill guide for arthroscopically assisted anterior cruciate ligament replacement. Arthroscopy 1992;8:234-238. 7. Lewis JL, Lew WD, Hill JA, Hanley P, Ohland K, Kirstukas S, Hunter RE. Knee joint motion and ligament forces before and after ACL reconstruction. J Biomech Eng 1989; 111:97-106. 8. Fleming BC, Beynnon BD, Nichols CE, Renstrrm PA, Johnson RJ, Pope MH. An in vivo comparison between intraoperative isometric measurement and local elongation of the graft after reconstruction of the anterior cruciate ligament. J Bone Joint Surg Am 1994;76:511-519. 9. Flandry F, Terry GC, Montgomery RD, Fester MA, Madsen N. Accuracy of clinical isometry and preload testing during anterior cruciate ligament reconstruction. Clin Orthop 1992;279:214222. 10. Sapega AA, Moyer RA, Schneck C, Komalahiranya N. Testing for isometry during reconstruction of the anterior cruciate ligament. J Bone Joint Surg Am 1990;72:259-267. 11. Colville MR, Bowman RR. The significance of isometer measurements and graft position during anterior cruciate ligament reconstruction. Am J Sports Med 1993;21:832-835. 12. Bylski-Austrow DT, Grood ES, Hefzy MS, Holden JP, Butler DL. Anterior cruciate ligament replacement: A mechanical study of femoral attachment location, flexion angle at tensioning, and initial tension. J Orthop Res 1990;8:522-531. 13. Grood ES, Hefzy MS, Butler DL, Suntay WJ, Siegel MG, Noyes
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