Chapter 17

D. Longino, N. Clerk, P.J. Fowler, J.R. Giffi n

Technique in ACL reconstruction:

hamstring reconstruction

History

A nterior cruciate ligament (ACL) reconstruc-tion remains one of the most common pro-cedures performed by orthopaedic surgeons.

Reconstructive techniques continue to evolve asongoing research advances our understanding of the complexities of the native ACL. ACL recon-struction with anatomical positioning of single-bundle grafts using anteromedial portal drilling techniques as well as a heightened interest in dou-ble-bundle reconstruction are recent reflections of flthe ongoing attempt to replicate more accurately the anatomy, biomechanics, and function of thenormal ACL.

Preoperative planning

In most cases, a thorough history and physical examination are suffi cient to make the diagnosis ffiof complete ACL rupture. However, partial ACL rupture, with sparing of some fibers of either the fiposterolateral or the anteromedial bundles, should be suspected in individuals who present with a history typical for ACL injury and have asymmet-rical laxity on some, but not all, of the ACL stabil-ity tests (i.e., Lachman, anterior drawer, and pivot shift tests) when compared to the uninjured knee. Care must be taken to identify any additional liga-mentous laxity that may require repair or recon-struction concurrently with ACL surgery.Preoperative imaging includes (1) bilateral stand-ing anteroposterior (AP) radiographs with the knee in full extension and in 30° of fl exion (tun-flnel view), (2) a lateral radiograph with the knee in 30° of fl exion, and (3) a skyline view of the patel-fllofemoral joint. Th e tunnel view provides a gross Thdepiction of notch morphology. It also helps toidentify any subtle degenerative changes that may, depending on the chronicity of the injury, predateor have occurred subsequent to ACL rupture. If any clinical or radiographic concern exists regard-ing varus or valgus lower extremity alignment, 3-ft standing views are obtained to determine whether

a concurrent or staged osteotomy may be required. Although magnetic resonance imaging (MRI) accu-rately diagnoses ACL rupture and identifies con-ficomitant meniscal or chondral injuries, it is not routinely obtained prior to proceeding with sur-gery, as it may unnecessarily delay treatment. Any associated pathology in these structures will be identifi ed and treated at the time of arthroscopic fiACL reconstruction.Patients routinely receive 1 g of cefazolin intra-venously 30 min prior to the operation. If allergy concerns dictate, vancomycin or clindamycin can be substituted.

Surgical technique

Patient positioning

Th e patient is positioned supine on the operatingThtable. An examination under anesthetic is per-formed. A lateral side post is placed at the level of the tourniquet, and a foot rest is used to place the knee in a self-supported position of 80–90° of flex-flion (Fig. 1). Th is is the working position for ten-Thdon harvest, notch preparation, and drilling of the tibial tunnel. A tourniquet is applied proximally on the thigh and set to between 250 and 300 mm Hg.

Fig. 1 – Patient positioning.

et al., The Knee Joint © Springer-Verlag France, Paris 2012M. Bonnin

196 The Traumatic Knee

riorly away from the underlying tibia. A 15 blade or Metzenbaum scissors are used to puncture the sartorial fascia. A bursal plane is opened between the elevated sartorial fascia, with the semitendi-nosus and gracilis tendons adherent to its under-surface, and the underlying fibers of the superfifi -ficial medial collateral ligament (MCL). A retractoris placed within this plane to retract the sartorial fascia medially.Th e gracilis tendon is the proximal of two tendons Thvisualized on the underside of the retracted sarto-rial fascia. It is retrieved from the wound with a tendon hook leaving it attached at its distal inser-tion. Any attachments or bands to the overlying fascia are cut under direct visualization with scis-sors. Care is taken not to blindly run the scissors up the superior surface of the tendon as this may risk damage to the saphenous nerve. Fingertip palpation of the tendon confirms it has been ade-fiquately freed of adhesions. An open-ended tendon harvester is then used to harvest the gracilis ten-don taking care to strip directly in line with the orientation of the tendon (Fig. 3).Gentle, steady pressure is used to advance the har-vester while avoiding the temptation to pull exces-sively on the distal tendon. Should significant resis-fitance be encountered, the harvester is removed and the tendon rechecked for any residual fascialattachments. Once the tendon has been stripped from the muscle belly and pulled free of the wound, the tendon stripper is carefully removed along the same orientation, as it was inserted to minimize the risk of inadvertent damage to adjacent neuro-vascular structures. Th e semitendinosus tendon is Thharvested in a similar fashion. Care must be taken to identify and cut a large band of tissue, present in most individuals, originating from the medial head of the gastrocnemius and attaching to the semitendinosus tendon just proximal to its tibial insertion. Failure to release this band can result in premature amputation of the graft.A 15 blade is used to peel the common insertion of both tendons as a unit off the proximal tibia. Thff eThgraft is immediately placed in a bowl of saline andtransferred to the back table for preparation.

Th e tourniquet is not routinely inflTh ated during theflcase unless poor visualization is encountered sec-ondary to bleeding.Clippers are used to shave the knee from 5 cmabove the proximal pole of the patella to 5 cm dis-tal to the tibial tubercle, taking care to incorporatethe areas of potential incisions for any meniscal repairs. Th e locations for a standard superior-me-Thdial outfl ow portal and anteromedial and anterolat-fleral para-patellar portals are marked. The incision Thfor hamstring harvest and drilling of the tibial tun-nel is outlined approximately 2 cm in length and one thumb breadth medial and slightly distal to the tibial tubercle (Fig. 2). Th e hamstring tendons canThoften be palpated in this area, and care should betaken to approximate the proximal extent of the incision such that the tendons can be visualized and approached slightly proximal to their insertion.Th e leg is washed and the sites of proposed incisionsThare pre-injected with 20 mL of 0.25% sensorcaine with 1:200,000 (5 mg/mL) epinephrine. Intra-artic-ular injection is avoided. Th e leg is prepped with a Thchlorhexidine solution and allowed to air-dry before sterile drapes are applied. An iodophor-impregnatedadhesive drape is then applied to the surgical site.

Graft harvest

A 10 blade is used to incise the skin. Elevation of the skin edges with two rakes facilitates subcu-taneous dissection, performed with a 15 blade. Th e sartorial fascia is identifiTh ed, and the graci-filis and semitendinosus tendons should be easily palpable. Toothed forceps lift the sartorial fascia, proximal to the hamstring tendon insertion, ante-

Fig. 2 – Sites of arthroscopy portals and graft harvest incision. Fig. 3 – Gracilis harvest with tendon stripper.

Technique in ACL reconstruction: hamstring reconstruction 197

than the anteromedial portal to aid visualization during preparation and drilling of the tibial tun-nel. Th e anteromedial portal should hug the patel-Thlar tendon and be just proximal to the level of the medial meniscus in order to give instruments the best access for notch debridement. Occasionally, an accessory medial portal is required for femoral tunnel placement while viewing through the anter-omedial portal. A diagnostic arthroscopy is per-formed and additional joint pathology addressed.An eff ort is made to preserve any intact functioning fffffi bers of the ACL during notch debridement. Often fithe residual ACL stump has scarred to the posterior cruciate ligament (PCL). Sufficient tissue is removed ffito allow unimpeded access to the femoral insertion of the ACL. Leaving some residual fibers of the finative ACL, however, may have some benefits. Thfi eThpresence of these can aid in correctly identifyingthe location of the tibial insertion site. Addition-ally, these fi bers in theory act as a source of vascular fiingrowth to revascularize the tendon graft and serve to seal the aperture of the tibial tunnel, preventing tunnel exposure to synovial fluid, a potential bio-fllogical contributor to tunnel widening (1).

Femoral tunnel preparation

A 4.5-mm full radius shaver is used to debride the remnants of the femoral attachment of the native ACL to the lateral femoral condyle. Only the femo-ral footprint of anteromedial and posterolateral bundle attachments of the ACL need to be cleared (Fig. 5). Limiting the amount of soft tissue strip-ping to this focal area provides visual feedback to the surgeon on the ideal placement of the femoral tunnel, regardless of the knee fl exion angle.flIt has also been suggested that anatomic landmarkssuch as the lateral intercondylar ridge and lateralbifurcate ridge can aid in identifying these inser-tion sites (2). Th ese landmarks may not be obvi-Th

Graft preparation

Even in short-stature patients, the hamstrings are usually of suffi cient length to allow a quadrupleffitendon graft of at least 10–12 cm in length. By utilizing an anteromedial portal for drilling, fem-oral tunnel lengths between 35 and 40 mm are consistently achieved. Th e 15 mm second-genera-Thtion (continuous loop) EndoButton CL (Smith &Nephew Endoscopy Inc., Andover, Massachusetts) serves to maximize the length of graft presentwithin the femoral tunnel.A preloaded EndoButton CL can be used or one can be loaded with a 0 absorbable monofilament fifl ipping suture on one end and two number 2 flbraided composite polyester pulling sutures on theother. Th e EndoButton is mounted in the Acufex ThGraftMaster II Table (Smith & Nephew Endoscopy Inc., Andover, Massachusetts), and the two ten-dons, still attached at their pes anserine conflu-flence, are placed through the continuous loop of the EndoButton. A number 1 absorbable suture locks the free ends of the tendons together underequal tension and attaches them to the GraftMas-ter. Th e tendon ends opposite the EndoButton are Thwhip-stitched together with a non-locking baseball stitch using a number 2 braided composite poly-ester suture. Th e whip stitch need only extend a Thquarter of the length of the graft to ensure no non-absorbable suture will remain within the knee joint once the graft is passed. Th e remainder of the graft This tubularized using a whip stitch of 2.0 absorbable suture that serves to ease graft passage. Th e graftThis then passed through a series of calibrated cyl-inders to determine its diameter in 0.5-mm incre-ments. A moist sponge covers the graft after it hasbeen tensioned to 20 lb (Fig. 4).

Diagnostic arthroscopy and notch preparation

A standard three-portal technique is utilized, with two main para-patellar tendon working portalsand a superior medial portal created for an outflow flcannula. Th e anteromedial and anterolateral por-Thtals are made in a vertical fashion with an 11 blade.Th e anterolateral portal is placed slightly higher Th

Fig. 4 – Graft tensioning after fi nal preparation in the Acufex GraftMaster II. Fig. 5 – Debridement of the lateral wall is limited to the ACL femoral inser-tion site.

198 The Traumatic Knee

Th e graft is marked in two locations from its proxi-Thmal extent (EndoButton). The fiTh rst mark corre-fisponds to the length of the femoral tunnel as read from the 4.5-mm calibrated drill or depth gauge. TheThsecond mark is the length of the femoral tunnel plus 10 mm, which roughly corresponds to the fl ippingfldistance required by the EndoButton. These mark-Th

ous in all individuals (depending on from which portal the lateral wall is visualized from) and may be distorted with notch wall debridement using a mechanical shaver. Furthermore, descriptions of the femoral insertion site anatomy based on a clock face (10 o’clock for right knee and 2 o’clock for the left knee) that have become popular in theliterature are ambiguous and vary depending on the degree of knee fl exion and the surgeon’s point flof reference (e.g., back or front of the notch) at thetime of surgery. We now routinely visualize themost posterior aspect of the femoral notch to iden-tify the proximal extent of the articular cartilage on the lateral femoral condyle. With the knee in 90° of fl exion, our starting position for the femoral tun-flnel in most cases is positioned 4–5 mm (dependingon graft diameter) forward from this landmark.Once this position has be identified and cleared, fia 45° Steadman awl is used to mark the startingpoint of the femoral tunnel (Fig. 6). The position of Ththe tunnel is somewhat eccentrically placed toward the anteromedial portion of the native ACL femo-ral insertion. Prior to drilling, correct poisoningof this point is confi rmed by placing the arthro-fiscope in the anteromedial portal, which provides abroader view of the posterior aspect of the lateralfemoral condyle (Fig. 7).Depending on graft diameter, an appropriate size femoral off set guide (usually a 4- or 5-mm) is placed ffffthrough the anteromedial portal (Fig. 8). The kneeThis then fl exed greater than 130° while maintaining flvisualization of the position of the off set guide in ffffrelation to the previously marked starting point.While off set guides are not necessary, we have fffffound them useful in protecting the medial femo-ral condyle while drilling the guidewire as well as in directing the guidewire through the portal inorder to gain adequate femoral tunnel length. A 2.7-mm Beath pin is drilled out the lateral cortex of the femur and snapped with a Kelly. With the knee remaining in a hyperflexed position, the offfl -ffffset guide is removed and a final check is made that fithe guidewire position will allow femoral tunnel creation without breaching the posterior or infe-rior aspect of the lateral femoral condyle.A calibrated 4.5-mm EndoButton drill is passed over the Beath pin. Th e depth at which the 4.5-mm drillThpasses through the lateral femoral cortex is noted. If required, a cannulated depth gauge can also be used to confi rm tunnel length. Thfi e appropriately sized Thcalibrated femoral drill is drilled over the Beath pinto 7 mm short of the lateral femoral cortex. Th isThdrill is advanced manually, the last few millimetersin reverse to avoid breaching the cortex. A loop of 0non-absorbable suture is threaded through the Beathpin. Th e pin and one end of the suture are retrieved Thfrom the lateral femur. Th e shaver is used to clear the Thnotch and femoral tunnel of any residual reamings.

Fig. 6 – Starting hole placement as viewed from the anterolateral portal with the knee in 90° of fl exion.

Fig. 7 – Starting hole placement as viewed from the anteromedial portal with the knee in 90° of fl exion.

Fig. 8 – Femoral off set guide for femoral tunnel guidewire placement placed through the anteromedial portal.

Technique in ACL reconstruction: hamstring reconstruction 199

Fig. 9 – Acufex tibial elbow drill guide positioned for drilling of the tibialtunnel guidewire.

Fig. 11 – Intra-operative lateral fl uoroscopy of tibial guidewire.

ings can be visualized arthroscopically at the time of graft passage to judge if the graft is adequately positioned to allow the EndoButton to fl ip.fl

Tibial tunnel preparation

An Acufex tibial elbow drill guide (Smith & Nephew Endoscopy Inc., Andover, Massachusetts) set at 45° of inclination is inserted through the anteromedialportal. Care is taken to place the tibial tunnel ante-riorly in the ACL footprint, corresponding more tothe site of anteromedial fi ber insertion. Typically, fisome residual fi bers of the native ACL tibial inser-fition remain after notch debridement to aid guideplacement on the tibia. If these are not present,one should position the guide to a point in line withthe posterior border of the anterior horn of the lat-eral meniscus in the sagital plane and just medial to the midpoint between the medial and lateral tibial spines in the coronal plane (Fig. 9). Th e startingThpoint for the drill should be just lateral to the ante-rior fi bers of the superfifi cial MCL. Thfi e guidewire is Thadvanced until its tip is visualized within the joint.It is advanced 2 cm further using a mallet. TheThguidewire should not impinge on the PCL, the wall of the notch, or the roof of the notch as the kneeis extended. Guide pin position is confirmed withfiintra-operative fl uoroscopy. Thfl e pin should mirror Ththe slope of the medial tibial spine on the AP view (Fig. 10) and run slightly posterior but parallel to Blumensaat’s line on the lateral view (Fig. 11).Th e scope is reintroduced into the knee, and the tib-Thial tunnel is drilled using the appropriate graft tun-nel sizer as a protecting sleeve. Any residual debrisin the tunnel is cleared with the shaver, and a rasp is used to smooth its posterior aspect. A crochet hook is used to retrieve the previously passed non-absorb-able suture from the tibial tunnel. Th e periosteum Thjust distal to the tibial tunnel is incised with cautery and cleared with a curette to allow the graft to bestapled directly to the anterior aspect of the tibia.

Graft passage

Th e EndoButton sutures are shuttled through the Thknee using the previously passed non-absorbablesuture, and the graft is advanced into the knee. TheThEndoButton is fl ipped, and with manual tension onflthe distal end of the graft, the knee is cycled. TheTharthroscope is reinserted into the knee. Th e graft is Thvisualized while the knee is brought into full exten-sion to ensure it does not impinge against the roof of the notch. With the knee in 90° of fl exion, a tri-flangular space should be visible at the apex of the notch (3). Th e boundaries of the triangle consist of Ththe roof of the notch, the anteromedially directed

Fig. 10 – Intra-operative AP fl uoroscopy of tibial guidewire.

200 The Traumatic Knee

interference screw can be utilized or the sutures can be posted for additional fixation. An examina-fition under anesthetic is repeated to ensure any lax-ity has been corrected.Th e passing sutures are retrieved from the femur and Ththe tibial incision is irrigated and closed with inter-rupted 2.0 absorbable suture followed by a running 3.0 absorbable stitch and steristrips. Th e superome-Thdial outfl ow cannula is used to insert an intra-artic-flular drain. Th e portals are injected with 20 mL of Th0.25% sensorcaine with 1:200,000 epinephrine, and sterile dressings and cooling devices are applied.

Pearls

Femoral insertion site visualization

Poor visualization of the femoral ACL insertion site can be frustrating and lead to compromises in tun-nel positioning. Portal placement is important, as an anterolateral viewing portal that has been placed too far lateral can cause or exacerbate this situation. An individual with a narrow notch, sometimes pre-dicted based on the preoperative tunnel view, can also present this dilemma. While uncommon, a conservative notchplasty in this latter case may be warranted. Alternatively, one can consider using a standard anteromedial portal to view and an acces-sory medial portal to drill the femoral tunnel.

Femoral tunnel preparation

Historically, techniques in ACL surgery have been developed around creating a more non-anatomical (isometric) ACL reconstruction (4). More recently, there has been a realization that replication of the anatomical insertion sites of the native ACL may be paramount to success. Traditionally, single-bundle techniques have focused on reproduction of the anteromedial bundle of the ACL, with trans-tibial drilling of the femoral tunnel being the most com-mon technique used during reconstruction. Trans-tibial drilling techniques, however, dictate femoral socket starting position and have the potential to cause femoral tunnel placement too high in the intercondylar notch (5). Th e ability to consistently Threproduce an anatomic femoral insertion site may only occur if one is willing to accept a more poste-rior position of the tibial tunnel (6). Th is compro-Thmise in tunnel position, being more representativeof the tibial insertion of the posterolateral bundle of the ACL than that of the anteromedial bundle, is likely to have deleterious eff ects on graft function ffff(7,8). For this reason it is strongly recommended

fi bers of the PCL, and the posterolaterally directed fifi bers of the ACL graft (Fig. 12). Thfi e presence of Ththis triangle confirms correct femoral tunnelfiplacement and subsequent ACL graft orientation to avoid PCL impingement.

Graft fi xationfi

The graft is then manually tensioned to 20 lb and Thfi xed distally to the tibia in 0° of knee flfi exion with fla 3M stabilizer gun and 5 staples (Fig. 13). If the graft tapers creating a graft tunnel mismatch, an

Fig. 12 – Probe within the triangular space as viewed from the anterolat-eral portal with the knee in 90° of fl exion.

Fig. 13 – AP radiograph showing femoral and tibial fi xation.

Technique in ACL reconstruction: hamstring reconstruction 201

case. An extra 2–2.5 cm of graft material can beobtained during harvest by releasing the common insertion site of the two tendons on the anteriortibia with a large sleeve of attached periosteum. In some cases this can aff ord enough extra length ffffto proceed with the reconstruction as planned. An interference screw may, however, be required for fi xation on the tibia because insuffifi cient graft ffiremains for staple fixation.fi

Graft contamination

While extremely uncommon, graft contamination during ACL reconstruction can occur, and to date, no clear consensus has been reached regarding appropriate management (9). Our current pro-tocol requires the graft be soaked for 30 min in a solution of 500 mL 0.9% normal saline containing Penicillin G (2 million units), Bacitracin (50,000 units), and Gentamycin (80 mg). This is followed Thby serial dilution baths in normal saline to further decrease the risk of contamination and cleanse the graft of the initial antibiotic solution. Bacterial swabs are then taken prior to implantation.

Lateral femoral cortex breach

If the lateral femoral cortex is breached with the fi nal femoral reamer one may (a) still attempt to fiuse EndoButton fi xation if the tunnel diameter is fi6.5 mm or less as the EndoButton will often still engage on the lateral the cortex, (b) use an Xten-dobutton (XtendoButton™, Smith and Nephew, Corp., Andover, MA) or femoral interference screw as alternative fi xation, and (c) use a two-incision fitechnique to secure the sutures around a femoral post.

Postoperative care

Th e patient is placed on protected weight-bearing Thcrutches for 2–4 weeks following surgery. If no meniscal work has been performed, the patient does not require bracing and may start range-of-motion exercises immediately. Dressing change and drain removal occurs on postoperative day one in clinic. Th e patient is weaned offTh crutches when he ffor she demonstrates suffi cient quadriceps function ffiand can walk unaided with a normal gait. Focus of the fi rst 3 months of rehabilitation is on obtain-fiing full range of motion with gentle strengthening exercises. A more aggressive strengthening pro-gram is instituted after 3 months when the graft is more securely incorporated. Return to high-risk

that drilling of the femoral tunnel be performed through the anteromedial portal (or a rear entry guide system), which allows easy access to the ACL insertion on the lateral femoral condyle indepen-dent of tibial tunnel location.It is also recommended that the fi nal reamer for thefifemoral tunnel be passed over the Beath pin and drilled manually. Th is reduces the risk of damage to Ththe medial femoral condyle and PCL during drill pas-sage. Th e femur can also be scored a few millimeters Thto determine the amount of the back wall that willbe preserved prior to reaming the remainder of thetunnel. Finally, the technique minimizes the risk of breaching the lateral femoral cortex when drilling.

Tibial tunnel preparation

Proper placement of the tibial guidewire is basedon a combination of intra-articular landmarks,absence of graft impingement with knee motion, and intra-operative fl uoroscopic imaging. Signififl -ficant guidewire malpositioning requires redrilling.Smaller magnitude adjustments can be made using a parallel pin guide. More commonly, however, only a minor correction in guidewire placement,on the order of 1–2 mm, is required. This can beThaccomplished by overdrilling the original 2.7-mm guidewire with the 4.5-mm cannulated EndoBut-ton drill. Th e guidewire can now be eccentrically Thpositioned in this 4.5-mm bone tunnel. This allowsThan almost 2-mm modifi cation of guidewire place-fiment, in any direction, from its original location. Th e repositioned 2.7-mm guidewire is impactedThinto the notch to maintain its position prior tooverdrillling with the final tibial tunnel drill.fi

Graft passage

Care is taken during graft passage to ensure that the EndoButton is rotated in such a manner thatthe fl ipping suture, when tensioned, will pull the fldistal extent of the vertically oriented EndoButtonin a lateral direction. Because of the angle at which it exits the femur, this will serve to minimize thedistance the EndoButton needs to be pulled out of the lateral femoral cortex before it can be fl ipped.fl

Complications

Short graft

Amputating the graft prematurely at the time of harvest can add signifi cant time and anxiety to the fi

202 The Traumatic Knee

Zavras T, Race A, Bull AM, 4. et al. (2001) A comparative study of ‘isometric’points for anterior cruciate ligament graft attachment. Knee Surg Sports Traumatol Arthrosc9:28–33Golish S, Baumfeld J, Schoderbeck RJ, 5. et al. (2007) TheTheff ect of tibial tunnel starting position on tunnel length ffffin anterior cruciate ligament reconstruction: a cadavericstudy. Arthroscopy 23(11):1187–1192Pombo M, Kopf S, Irrgang J,6. et al. (2008) Th e ability of Thtranstibial tunnel drilling in ACL reconstruction to restore the anatomic femoral insertion site: a prospective study. Pittsbg Orthop J 19:95Ekdahl M, Nozaki M, Ferretti M,7. et al. (2008) Healing andbiomechanical properties of tendon grafts using differ-ffffent ACL reconstruction techniques: a goat model. Pittsbg Orthop J 19:78–79Ekdahl M, Nozaki M, Ferretti M, 8. et al. (2008) The effTh ectffffof tunnel placement on bone-tendon healing of anterior cruciate ligament reconstruction in a goat model. Pittsbg Orthop J 19:80–81Izquierdo R, Cadet E, Bauer R, 9. et al. (2005) A survey of sports medicine specialists investigating the manage-ment of anterior cruciate ligament grafts. Arthroscopy 21(11):1348–1353

sports can occur after 6 months of rehabilitation at the earliest if strengthening and propriocep-tive parameters have been maximized. Standard follow-up visits occur at 2, 6, and 12 weeks postop-eratively and then at 6, 12, and 24 months prior to release from care.

References

Wilson T, Kantaras A, Atay A, 1. et al. (2004) Tunnel enlarge-ment after anterior cruciate ligament surgery. Am J Sports Med 32(2):543–549

Ferretti M, Ekdahl M, Shen W,2. et al. (2007) Osseous land-marks of the femoral attachment of the anterior cruciateligament: an anatomic study. Arthroscopy 23(11):1218–1225Lawhorn K, Howell SM (2008) Avoiding ACL graft3. impingement: principles for tunnel placement using thetranstibial tunnel technique. In: Jackson DW, editor. Mas-ter techniques in orthopaedic surgery: reconstructive kneesurgery. Philadelphia: Lippincott Williams & Williams