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linical Outcome of Double-Bundlenterior Cruciate Ligament Reconstructionillem M. van der Merwe, MD, and Richard P.B. von Bormann, MD

Clinical outcomes assessment in double-bundle anterior cruciate ligament (ACL) recon-struction surgery is an essential tool in the quest for continuous improvement in surgicalcare. This is a review of the literature and current thinking concerning the methods ofassessing clinical outcomes.There are a number of key issues when single-bundle and double-bundle ACL outcomesare assessed and compared. Firstly, a double-bundle ACL reconstruction is not nec-essarily an “anatomic” reconstruction. An incorrectly placed double bundle is asnonanatomical as an incorrectly positioned single bundle. It is also crucial to specifywhich outcome is being assessed and its relevance. Surgery that results in early returnto function does not necessarily produce normal biomechanics or long term protectionfrom osteoarthritis.Traditional clinical tests of knee stability do not show a difference between the twotechniques. There is however, new evidence that this is because traditional testing is notsufficiently accurate or sensitive. In-vivo testing and laboratory studies using new methodsof assessing dynamic 3D kinematics of the knee consistently show that anatomic double-bundle ACL reconstruction more closely reproduces normal biomechanics.Oper Tech Sports Med 16:171-175 © 2008 Elsevier Inc. All rights reserved.

KEYWORDS anterior cruciate ligament, double bundle, clinical outcome

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Half of what we know is wrong, we just don’t know whichhalf—Prof. Tim Noakes, Head of Sport Science Instituteof South Africa

ur patients empirically expect the best treatment whenthey come and see us with knee injuries. For us to

rovide this treatment, we need to know what outcome cane expected from a certain intervention. Emphasis is increas-

ngly being placed on patient-based outcomes and not onubjective parameters that have little relevance to patient’sbjective symptoms and functions.This emphasis should lead to the cycle of continuous im-

rovement and involves the use of practice guidelines basedn research, which in turn is based on patient-based out-omes. This improves outcomes and leads to a continuousmprovement in quality of care (Fig. 1).

Given that clinical practice modification is based on out-ome studies, the ability to measure clinical results is thus

ports Science Orthopaedic Clinic, Sports Science Centre, Cape Town,South Africa.

ddress reprint requests to Richard P.B. von Bormann, MD, 26 Glenwaters,St Fillians Road, Camps Bay, 8004, South Africa. E-mail: richard@

agrucox.com.

060-1872/08/$-see front matter © 2008 Elsevier Inc. All rights reserved.oi:10.1053/j.otsm.2008.10.011

ital. There are 3 methods to measure clinical results. Therst is randomized clinical trials, which remain the gold stan-ard for the evaluation of therapeutic interventions.1 How-ver, these studies are more illuminating when not only thentervention and the outcome, but also the assessment pe-iod, are well defined.

The second method is meta-analysis, the technique cur-ently used to evaluate a large body of literature.2 With meta-nalysis, after performing a critical review of the literature,he data from studies meeting specific inclusion criteria areooled. The net result is that the sample size swells, thus

ncreasing the validity of the results.Retrospective case studies, the third method for assess-ent of the performance of a therapeutic intervention, are

raught with the potential for bias. These reports are fre-uently from a single surgeon or center and represent thexperience of a specialist surgeon. These reports are noteadily applicable to the generalist orthopaedic community,here most anterior cruciate ligament (ACL) reconstructions

re done by surgeons performing fewer than 10 per year.urthermore, the investigator may be the inventor of theevice or procedure, which introduces conflict of interest

nd the potential for bias.

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172 W.M. van der Merwe and R.P.B. von Bormann

itfalls Whenssessing Clinical Outcomesimple correlation between 2 entities does not mean that

he one causes the other. A correlation simply means that aelationship exists between 2 factors, but it tells you nothingbout the direction of the relationship.

Consider the folk-tale of the Czar who learned that theost disease-ridden province in his empire was also therovince with the most doctors. His solution? He promptlyrdered all the doctors shot.To make sense of outcomes, it is vital to pick the outcomeeasures carefully. Also fundamental is the awareness that

ny given intervention will not necessarily be beneficial for allutcomes measured. For example, the procedure that has theest outcome regarding return to high demand sport mightot have the best outcome regarding protection from long-erm degenerative changes.

Surgeons are always looking for the complete answer, butt may be that the procedure that gets the patient back toerforming in a high-level sport is not the best for their knee

n the long term. With this in mind, we need to know exactlyhat an outcome measure tells us about a certain procedure

nabling us to inform our patients accurately about the prosnd cons.

hat Is Being Compared?his to me is where the biggest problem lies. The need toeassess ACL reconstruction technique arose from the facthat many surgeons felt that although we were restoring con-rol of anteroposterior (AP) translation, we are failing to con-rol the pivot shift, which is a function of the rotational sta-

igure 1 The cycle of continuous quality improvement.

ility of the knee.3 w

Jonsson and coworkers4 showed that there is little relation-hip between the restoration of AP translation and functionalutcomes. Importantly, this study and others also demon-trated that rotational instability leads to worse functionalutcomes.4,5

Numerous articles have been published on the anatomynd biomechanical behavior of the anteromedial and pos-erolateral bundles of the native ACL.6,7 These studies showhat better control of in vitro rotational stability could bechieved with a posterolateral bundle.

In an attempt to create a more anatomical ACL, Jepsen andolleagues8 showed that bringing the femoral tunnel downn the wall of the femoral notch improved biomechanicalarameters in the laboratory as well as functional outcomes

n vivo.9

Anatomic ACL reconstruction followed, and the double-undle ACL reconstruction was perfected. This allowed for airect comparison of the double-bundle and single-bundleCL reconstruction.There are 2 issues here. The first is the concept of anatomic

CL reconstruction. It has been clearly shown that a morenatomic placement of the tunnels, to best mirror the nativeCL position, leads to better rotational stability and func-

ional results.8,10 The next, although I think it a separatessue, is whether the ACL can be reconstructed anatomicallyith 1 bundle or whether we in fact need 2 bundles. ACL

econstruction can therefore be anatomical or nonanatomicalith single or multiple tunnels or bundles. Double-bundle

econstruction is not synonymous with anatomic ACL recon-truction (Fig. 2).

This is an important concept to understand when we arenalyzing studies comparing different techniques and a cau-ion to the occasional ACL surgeon. Studies that show noifference between single- and double-bundle ACL recon-tructions do not justify nonanatomic single-bundle recon-truction, the so-called “vertical graft.”9

Another potential problem is consistent tunnel placement.n a study that we presented at the International Society ofrthroscopy, Knee Surgery, and Orthopaedic Sports Medi-ine (ISAKOS) meeting in Florence in May 2007, we used 3DRI analysis to evaluate our tunnel position in patients post-

peratively. The results showed that although our clock po-ition was repeatable, our deep or shallow position varied.-rays, however, did not accurately predict tunnel position.

n other words, are our tunnels really where we think weave made them?

linical Outcomes

ouble Bundle, Doublerouble—Does Double-Bundle ACLeconstruction Lead to More Complications?ears have been expressed as to whether double-bundle sur-ery has an inherently greater risk of complications and fail-re.11 The first concern was for iatrogenic injury associated

ith the posterolateral tunnel. Neven and colleagues12

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Clinical outcome of double-bundle ACL reconstruction 173

howed in cadaver studies that there is no risk of iatrogenicesion to the lateral collateral ligament, lateral gastrocnemiusendon, or popliteus tendon with a posterolateral tunnelrilled through a low anteromedial portal in high flexion.Yasuda and colleagues13 pointed out to the relative high

ailure rate of the postero-lateral bundle and its tendency torevent full extension. However, Zantop and colleagues ex-lain that this is a result of technique, namely not tighteninghe PL bundle in full extension, and not concept.7,13

Concerns over the larger cross-sectional area of the dou-le-bundle ACL in the notch have been refuted by Nishimorind colleagues,14 who showed in a magnetic resonance im-ging (MRI) study that the incidence of PCL impingement onhe ACL graft is the same.

We know of no study showing higher rates of surgicalomplications with double-bundle as compared with single-undle ACL reconstruction. In addition, although potentialroblems with more tunnels have been mentioned when itomes to revision surgery, these have not been reported.hus, with no evidence of greater complication rates; “double

unnel— same trouble.”

igure 2 The concept of anatomical ACL reconstruction.

Figure 3 Summary of scenarios when measuring rotation in the

s There a Difference inechanical Stability Between Single-

nd Double-Bundle ACL Reconstruction?nteroposterior Laxitynteroposterior laxity can be evaluated by use of the Lach-an test, anterior draw test, and the KT 1000. Anteroposte-

ior laxity is still the most popular diagnostic as well as out-ome measure. In a meta-analysis study done by Meredicknd colleagues, it was shown that there is no statistical dif-erence between single and double bundle ACL reconstruc-ion regarding AP translation.15

otational Laxityhe Pivot shift is the most widely used test to assess rotational

axity, but it has been criticized because of the subjectiveature of the grading system and its dependence on the skillf the examiner to perform the test and detect movement ofhe bone beneath the skin.

However, there are quite a few studies to show that dou-le-bundle ACL reconstruction restores control of the pivothift better than single-bundle reconstruction.16 There arelso studies showing no difference.7,13 Interestingly, there areo studies to show that single-bundle ACL reconstructionestores pivot shift control better than double-bundle sur-ery.

Restoring rotational stability to the knee is a very impor-ant outcome to measure but, unfortunately, the complexityf the movement makes it difficult to quantify. To quantifyotational stability, we need to quantify the force that wepply, in both magnitude and direction, and then accuratelyeasure the amount that the tibia rotates in relation to the

emur (summarized in Fig. 3).The Pittsburgh group have developed a device to quantify

otation of the knee. A walking boot is used to control footnd ankle motion, a universal force moment sensor measurespplied forces and torques, and an electromagnetic trackingevices attached to the skin measures motion of the tibia

knee.

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174 W.M. van der Merwe and R.P.B. von Bormann

elative to the femur. Fuller, Liu and colleagues have shownhat these skin markers are as reliable as bone markers refut-ng previous concerns over their accuracy.17 The reliability ofhe device has been established, and we await clinical studies.

At the Sports Science Institute of South Africa, we haveeveloped a device for measuring the movement of the tibiaelative to the femur using MRI. The patient’s foot is held in aalking boot with a rotating base plate, and the hip is left free

o rotate. A rotational force, controlled by a transducer andorrected for body weight, is applied to the knee through theoot. MRI scans are then taken with the knee in neutral,aximal internal rotation, and maximal external rotation.his sequence is completed with the knee first in 10°, and

hen 80° of flexion. The scans can then be converted to 3Dmages with the use of Mimics software (Materialise NV, Leu-en, Belgium). The repeatability of the studies at both 10 and0° of flexion has been validated.18

In normal or uninjured knees, we found a great variationn tibial rotation relative to the femur, from 13° to 28°. Theibial rotation was greater in flexion than extension. Thether pattern that emerged was a bell curve distribution oformal, with hypermobile and stiff knees respectively at eachnd of the spectrum of normal.

In ACL-deficient knees after an injury, the total range ofibial, rotation in flexion increases on average by 6°. Single-undle reconstruction returns rotational stability to within 2°f the uninjured side. However, because of the large range ofotation values in the normal knees, assessing only the me-ian value for rotation in the post-ACL reconstruction kneesoes not tell the whole story. Some knees had less rotationhan the contra lateral or normal knee, whereas others weretill “loose” in flexion. This brought our attention to the facthat we might be over-constraining some knees from theypermobile group with the single-bundle reconstruction.Recently, the importance of maintaining full range of mo-

ion, namely flexion and extension, after ACL reconstructionas been shown.19 Clinical function as well as osteoarthritisas been shown to correlate to lack of full range of motion.20

The relationship of a restriction of rotational move-ent—or over-constraining of the knee—to function and

steoarthritis, has not been fully investigated.In summary, rotational stability of the knee is very impor-

ant but also very complex. In the future, computer-assistedavigation will help us in assessing rotational parametersfter ACL injury and reconstruction.21

The importance of loading the knee while assessing theotation is apparent and an increasing number of studies andnstruments are becoming available that will help us explainunctional rotational abnormalities.15,22 I believe this is moremportant and relevant than AP translation.

D Kinematicst the Sports Science Institute of South Africa, we recentlyompleted a study to compare the rotational stability afteringle- or double-bundle ACL reconstruction (paper to beresented at the ISAKOS Congress, Osaka, Japan, 2009).17

his study showed no statistical difference in rotational sta-

ility after single- or double-bundle ACL reconstruction. t

owever, what we did find was that the axis of rotation hadhifted in the single-bundle reconstruction, with the poten-ial to put more shear forces on the medial compartment.his finding fits with work by Hagemeister and Tashman,howing that although single-bundle reconstruction restoresP translation and rotation, the 3D kinematics of the knee areot in fact normal.23,24

Tashman and coworkers23 have developed dynamic 3Dtereoradiographic methods for precisely measuring motionf the knee. Their method makes use of 2 high-speed fluo-oscopy units to precisely measure kinematics and joint con-act areas during dynamic movements. Because this methodirectly measures position and motion of the bones, it is morerecise than motion analysis systems that are based on mark-rs affixed to the skin.

Dynamic stereoradiographic methods to measure joint ki-ematics may be sensitive enough to detect subtle advantagesf anatomic double-bundle ACL reconstruction over tradi-ional single bundle methods in controlling the 3D kinemat-cs of the knee.

As we have shown in this section, there seems to be aifference in mechanical stability between single- andouble-bundle ACL reconstructions. However, some ofhe changes are difficult to pick up with conventionaleasuring devices and as instruments that are more pre-

ise are developed hopefully this question can be an-wered more clearly.

s There a Difference in Clinical Outcome?here are no long-term studies yet, but all the short-termesults show no clinical difference in outcome measured withhe Tegner activity scores, IKDC knee score, or Lysholmcore. What we need is an objective score that allows us toeasure the performance of the athlete not only at the reha-

ilitation facility, but also on the field. We are currently con-ucting a multicenter study driven by Hayden Morris fromhe Park Clinic, Melbourne, Australia, to develop just such acore. To conclude, no difference in clinical outcome haseen demonstrated but, thus far, the follow-up periods areoo short to draw any conclusive findings and we are awaitingong-term results.

onclusionslthough the concept of anatomic ACL reconstruction is wellstablished, the question remains as to whether this surgeryequires two tunnels or is one accurately placed tunnel suf-cient. The jury is still out but undoubtedly, the evidence isounting that at least in some cases we need two bundles to

estore normal kinematics to the knee.25

Will restoring normal kinematics to the knee prevent os-eoarthritis in the long term? I think this is a separate questionnd the answer is probably no. I believe the articular cartilagend subchondral bone damage at the time of the originalnjury will lead to osteoarthritis even in a well functioningnee. Will restoring normal kinematics lead to better func-

ioning knees and fewer complications? We hope so.

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Clinical outcome of double-bundle ACL reconstruction 175

In future, we will have true “a-la carte” ACL surgery. Someill be single bundle, some will be double bundle, and even

he tunnel positions will vary according to the patients needs.ot only will the ACL reconstruction of the future be tailorade for the individual morphology and kinematics, but itill also be tailor made for a specific outcome.3D imaging techniques will tell us more about the inser-

ion site anatomy. 3D kinematics testing devices will tell usow the knee moves and what ligament is required to restorehe “normal” movement under load. We will thus use theatient’s uninjured knee as a template to customize the ACLeconstruction.

Dr. Freddie Fu, chairman of the Pittsburgh group, hasostulated that the bony morphology of the knee controls theattern of knee movement and, hence, the ligaments thatevelop to guide this specific movement. At our institute, weave examined bony morphology of the knee and found aorrelation between the height of the lateral condyle and themount of rotation—this is ongoing research.26

Finally, in recent research at the Sports Science Institute ofouth Africa, we have isolated a gene that is expressed in thenormal” collagen matrix. Our evidence suggests that indi-iduals that do not have this “protective” gene are more likelyo have ACL injuries.24 Interestingly, we found that womennd men younger than 21 years of age who had sustainedCL injuries do not have this “protective gene.” Experienceas shown that these 2 groups have exceedingly high rate ofe-rupture. Perhaps in future we will be able to do a geneticcreen, predict the high-risk patient, and give appropriateounseling.

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4. Jonsson H, Riklund-Ahlström K, Lind J: Positive pivot shift after ACLreconstruction predicts later osteoarthrosis: 63 patients followed 5-9years after surgery. Acta Orthop Scand 75:594-599, 2004

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6. Colombet P, Robinson J, Christel P, et al: Morphology of anterior cru-ciate ligament attachments for anatomic reconstruction: A cadavericdissection and radiographic study. Arthroscopy 22:984-992, 2006

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1. Hemmerich A, Vaughn K, van der Merwe W: Prospective randomizedstudy to compare single bundle versus double bundle ACL reconstruc-tion in restoring rotational 3D kinematics of the knee. Presented at the7th Biennial ISAKOS Congress, Osaka, Japan, April 5-9, 2009

2. Posthumus M, Schwellnus M, van der Merwe W: Type 5 collagen geneis associated with ACL ruptures. ISAKOS, Osaka, 2009

3. Tashman S, Collon D, Anderson K, et al: Abnormal rotational kneemotion during running after anterior cruciate ligament reconstruction.Am J Sports Med 32:975-983, 2004

4. Hagemeister N, Long N, Duval N, et al: Quantitative comparison ofthree different types of anterior cruciate ligament reconstruction meth-ods: Laxity and 3-D kinematic measurements. Biomed Mater Eng 12:47-57, 2002

5. Tsai AG, Musahl V, Steckel H, et al: Rotational knee laxity: reliability ofa simple measurement device in vivo. BMC Musculoskelet Disord 9:35,2008

6. von Bormann R, Vaugh K, van der Merwe W: Association betweendistal femur morphometry and knee kinematics under torsional load-

ing. Isakos, Osaka, 2009