Many surgical procedures have been used torealign the knee extensor mechanism. Proximally,Insall realignment or variations with imbrication ofthe vastus medialis obliquis (VMO) and medialpatellar retinaculum, combined with a lateralrelease, have been used extensively to improvepatellar tracking.1 Distal realignment, in which thetibial tubercle is typically moved medially toimprove patellar alignment, is the other commonapproach to extensor mechanism realignment.

Some tibial tubercle procedures, such as theHauser2 technique, have moved the tibial tubercleposteriorly “down” the medial slope of the tibia asthe tibial tubercle is moved medially. Unfortunately,this type of procedure can increase loads on analready compromised patella. Others, such as theEmslie-Trillat3 procedure, use a flat osteotomy cutbehind the tibial tubercle and subsequent straightmedial tibial tubercle displacement to realign theextensor mechanism. The importance of prevent-ing overload on the realigned patella cannot beoveremphasized. The frequently noted “benign” or“normal” chondrosis (often found in even asymp-

tomatic individuals along the medial facet of thepatella) may not be benign if it is subjected toincreased forces after a straight medializationprocedure. Furthermore, increased force onto amedial facet lesion sustained at the time of adislocation may contribute to further chondraldeterioration or increased symptoms.

Bandi4 and Maquet5 described procedures toreduce contact stress on the patella by elevatingthe tibial tubercle anteriorly. This has been helpfulto many patients with patellar arthrosis. The originalprocedure attempted to unload the patella inpatients with arthrosis and was not specific forthose with concomitant malalignment.

The concept of anteromedial tibial tubercletransfer, as described by Fulkerson6, combinesthe benefit of extensor mechanism realignmentwith unloading of the patellofemoral articulationthrough tibial tubercle elevation. An obliqueosteotomy posterior to the tibial tubercle permitstibial tubercle displacement along a smoothosteotomy plane in an anterior and medial direction. Thus, anteromedialization (AMZ) is anatural evolution from those earlier procedures. Inaddition to combining realignment with elevation,distant bone graft harvest is avoided. The compli-cation rate with anterior medialization has beenlower than with straight anteriorization and no

Surgical Technique for Anteromedialization

of the Tibial Tubercle with the

Tracker™ AMZ Guide System

Jack Farr, MD, Indianapolis, INReviewed and approved by

John P. Fulkerson, MD, Farmington, CT

report of a skin slough or compartment syndromehas been found.

Following 13 patients more than 10 years afteranteromedial tibial tubercle transfer, Buuck andFulkerson reported that 12 out of 13 had good orexcellent results.7 The average modified Lysholmscore was 83.5 out of 100. Ten of these patientsimproved or were the same as one year postop-eratively. This shows properly performed antero-medial tibial tubercle transfer gives sustainedbenefit in carefully selected patients.

PREOPERATIVE EVALUATION

Preoperatively evaluate the patient with patellarpain in an organized, systematic manner. Includea detailed history and physical examination, payingparticular attention to the entire kinetic chain,from hip to foot, with obvious emphasis on thepatella. “Malalignment” is a general term andmust be evaluated in each component of thechain in each axis plane—that is x, y and z.Standard patellofemoral views, such as theMerchant view, used with the clinical trackingassessment, are usually adequate. In complicatedcases, CT or MRI patellar tracking studies maybe of assistance.

With this preoperative information in mind, formulate an initial plan using the Fulkerson classification (Table 1). At the time of surgery, thecorrelation to the Fulkerson classification may befurther modified after the lateral release. (Forexample, there is variation in the movement ofthe patella medially after isolated lateral releasefrom none to a moderate amount.) In addition toclassification of patellofemoral mechanics, makefurther modifications of the planned technique onthe basis of not only the depth and grade of thechondrosis, but also on the location of the chon-drosis as recently described by Fulkerson et. al(Table 2). As well as potentially decreasing andmedializing loads, it is important to rememberthat loads after AMZ are also transferred to more

proximal areas of the patella earlier during rangeof motion.

Patients with diffuse patellar articular degener-ation, proximal crush injury or nonspecific anteriorknee pain are generally not candidates for thisprocedure. Patients with predominant sulcuschondrosis should be approached cautiously.

PROCEDURE

After arthroscopic evaluation and treatment,perform the lateral release and reassess tracking.Make a skinincision from themid-patella levelthrough theanterolateralportal in anoblique, slightlymedial manner,ending about 5to 10cm distal tothe tibial tuber-cle (Figure 1).Divide thesubcutaneoustissues in linewith the skinand obtainhemostasis.

Continue the lateral release from its distalextent along the lateral aspect of the patellar tendon.Inspect the patella and trochlea to correlate theopen and arthroscopic findings. This exposureallows fixation of chondral or osteochondral fragments or additional debridement.

Continue this lateral release extension alongthe lateral aspect of the tibial tubercle at the borderof the anterior compartment, which is now bluntlyelevated in a subperiosteal manner. Place thecustom anterior compartment muscle retractor(Cat. No. 219454) subperiosteally with blunt endsdirectly adjacent to the posterior tibia,

2

Figure 1: The skin incision begins near theanterolateral portal and courses slightly mediallyto end distal to the tibial tubercle.

M L

11

Tracker™ AMZ Guide System

Module

Positioning Card

Retractor

Cutting Block

Anchor Pins

Anchor Pins

Anchor Pin Puller

Bone Clamp

10

A 41-year-old female, C.M., had ten years ofpatellofemoral pain, with the majority of her pain in the leftknee. She had a history of right and left patellar dislocations,and then subsequent subluxation with no further dislocations.Five to ten years pre-op, she had increased effusions pro-portional to activity, along with grinding, catching, giving wayand extreme pain while climbing stairs. She failed to respondto conservative treatment.

Weightbearing AP and flex knee PA radiographs revealedmaintenance of tibiofemoral joint space, and the Merchantview demonstrated moderately shallow morphololgy withsubluxation.

She had full range of motion, with no increased laxity ortibiofemoral pain. Her maximum pain was at the lateral facet,which was greater than direct patellofemoral pain. As sus-pected preoperatively, there was PF chondrosis (medialpatellar facet and central sulcus), thus AMZ was selectedrather than straight medialization.

Post-op radiographs revealed the desired elevation. TheMerchant view demonstrated a centralized patella. Full painrelief occurred six months post-op.

C.H. is a 47-year-old female who had progressivepatellofemoral pain for 10 years. Both patellofemoral jointshad chronic patellar subluxation with degenerative changesand clinical lateral compression syndrome. She failed torespond to conservative management. The less-involvedknee was treated first with AMZ and debridement. At fourweeks post-op, C.H. had full motion, minimal discomfort andgood quad function. At that point, the contralateral kneeunderwent AMZ and debridement. Both surgeries were performed on an outpatient basis under local anesthetic.C.H.’s postoperative course has been uncomplicated. She ispain-free on the less arthritic knee and has activity-relatedaching on the more arthritic knee.

The postoperative Merchant views illustrate that whenadequate lateral patellofemoral articular surface remainsafter anteromedialization, that surface will support the lateralaspect and the patella will appear centralized. However, asimilar AMZ performed on a patient with exposed bone onthe lateral trochlea and patella will not have lateral cartilagesupport; therefore, even though the patella is dynamicallycentralized and load-bearing is more medial, the lack ofchondral support at the lateral aspect of the joint results inthe appearance of an under-corrected subluxation/tilt. Suchis the case in this patient. The surgery was performed correctly, the patient is happy, but the surgeon would like thepostoperative x-rays to “look better”.

CASE STUDY ONE

CASE STUDY TWO

Preoperative Merchant View —C.M.

Postoperative Merchant View —C.M.

Left Preoperative

Merchant View —C.M.Right Preoperative

Merchant View —C.M.

Left Postoperative

Merchant View —C.M.

Right Postoperative

Merchant View —C.M.

3

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A ... -ordnohcon,tnemngilalamoN...A aicalam

B ... -ordnohc,tnemngilalamoN...A Isedarg(tnedivesiaicalam...A )IIdna

C ... sitirhtraoetso,tnemngilalamoN...A )VIdnaIIIsedarg(tneserpsi

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Modified Version(Dimensions Separate)1. Softening2. Fibrillation fissures partial

(<50% thickness)3. Fibrillation fissures deep partial

(>50% thickness)4. Bone exposed

Table 1* Sports Medicine and Arthroscopy Review,Vol. 2, No. 3, 1994** OrthoClinic, NA, 17:235-248, 1986

M L

M L

M L

M L

M L

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Table 1* Sports Medicine and Arthroscopy Review,Vol. 2, No. 3, 1994** OrthoClinic, NA, 17:235-248, 1986

M L

M L

M L

M L

M L

M L

M L

M L

Variable asrelated toarea, depth,and possibly,patellar positionM L

SPECIAL PRECAUTIONS

1. Patient Expectations—As with many aspectsof life, expectations play a very important rolein satisfaction. Even after a technically correctprocedure, some degree of discomfort is notuncommon, since the degenerative changesremain. Take extra time to explain that theknee joint will have the same “worn out” partsafter surgery. The patella will be in a new posi-tion in an attempt to decrease patellofemoralforce, which usually decreases pain, but thepatellofemoral joint will still have degenerativechanges. Crepitus and “popping” may remainpostoperatively, so make sure to alert patientsduring preoperative counseling. A realisticgoal is improved comfort and endurance, nottotal pain relief. High level sports may not bepossible.

2. Quad Strength—Continue emphasis on thepatient’s responsibility in rehabilitation.Communicate that optimal comfort will not beachieved until full quadriceps (and entireextremity) strength has been restored. In theearly post-op period, do not hesitate to usephysical therapy, functional electrical stimula-tion or biofeedback to “jump-start” quadricepstrengthening and function.

3. Psychologic Profile—As in cosmetic surgerycases, be certain the cause of knee pain is theknee and not a focus for other problems.

4. Smokers—As with other procedures whichincrease tension on the skin, the vascularsupply may become borderline. The plasticsurgery literature demonstrates that nicotinefurther compromises blood flow. Thus, smok-ers should quit several weeks before surgeryand abstain postoperatively.

5. RSD—Sympathetic pain may be observedpost-op. Atypical pain may be evaluated bydifferential blockade and treated appropriately.

6. Secondary Gain—Secondary factors must beseparated from organic factors. All patello-femoral surgery must be approached withcaution when there is potential for secondarygain, and when patient motivation for rehabili-tation is low.

7. “Dashboard” Injuries—As the proximal pole isoften involved, the prognosis after any surgicalprocedure is highly guarded in these patients.

SPECIAL PROCEDURES

1. Straight Anteriorization—In patients with centraltracking and patellofemoral arthritis, straightanteriorization can be achieved using theTracker AMZ Guide System. After all bonycuts are made, the tubercle fragment is firsttemporarily anteromedialized. It is then movedlaterally to a central position to effect a“straight anteriorization” by a locally obtainedoffset graft as previously described byFulkerson.

2. Anterolateralization—Patients who are experi-encing degenerative change and pain after aprior medialization, such as a prior Hauserprocedure, may be treated by reversing theposteromedialization. The medial facet can beunloaded and the tibial tubercle elevated tofurther unload the patella through anterolater-alization. The placement of the Tracker GuideSystem is such that the slope permits antero-lateral shift of the tibial tubercle.

3. Local Anesthetic Option—Through meticuloususe of subperiosteal local anesthetic, in addi-tion to standard soft tissue anesthetic, themajority of the procedure—including bonycuts—may be performed under local anes-thetic with supplemental I.V. sedation.

9

Optionally, this free fragment may be hand heldfor assessing patellar tracking and for drilling.Place the knee through its range of motion toassess tracking, and adjust the tubercle toachieve desired elevation and central tracking.

If tracking remains too lateral, the tibial tuberclecan be further medialized at this point. If thetracking is too medial but has the desired amountof elevation, a local offset bone graft may beused. This was previously described by Fulkersonas a way to maintain anteriorization whiledecreasing or fully neutralizing the amount ofmedialization. Move the tibial tubercle proximally ordistally for concomitant problems with baja oralta, respectively.

Use two 4.5mm ACE Medical Company corticalbone screws of the appropriate length to purchasethe posterior cortex using an interfragmentarytechnique. With direct, precise measurement,and countersinking as appropriate, the proximalscrew is secured first.

The bone clamp may then be removed toallow insertion of the drill sleeve at the distal holeand completion of interfragmentary fixation of thetubercle. At least one of the screws should be

perpendicular to the osteotomy (Figure 12).There is usually a sharp edge of medial bone

at the proximal extent of the transferred tubercle.After measuring the elevation, cautiously andconservatively round this sharp region with arongeur so it does not impinge on the patellartendon through range of motion. (Note: this maydiminish the measured radiographic elevation

appearance of the tibial tubercle elevation post-operatively.)

The procedure may be performed with or with-out a tourniquet to this point. If the procedure hasbeen performed with a tourniquet, deflate thetourniquet at this time and pay close attention toachieving hemostasis, especially in the region ofthe fat pad and the geniculate branches.

Postoperatively, place the patient in a standardcompressive knee dressing using a compressionice wrap. Use a drain for the immediate postoper-ative period.

POSTOPERATIVE MANAGEMENT

Control swelling by continuously cooling andelevating the limb. Begin immediate quadricep-setting exercises to maintain quadricep control.Encourage a normal gait with foot flat/minimalweightbearing for the first six weeks using twocrutches.8

Continue to encourage the patient to maintainquadricep function and strength, then proceedwith range of motion and further strengthening byusing an exercise bicycle on low resistance.

Counsel the family to help avoid potential fallsby freeing the living area of area rugs, unrulypets underfoot, etc. At six weeks, check radiographs of the osteotomy. As determined bythe radiographic and clinical evaluation, progressively increase weightbearing as tolerated,so the patient is full weightbearing and off crutchesby eight weeks. Since the osteotomy will serveas a stress riser to the tibia, give specific instruc-tions to the patient about avoiding twisting orturning of the extremity to prevent fractures.Thepatient should progressively advance activities ofdaily living, avoiding stairs until optimal quadricepstrength is reestablished.

8

Figure 12: With the proximal screw in place, the bone clamp is removedfrom the distal hole to completely secure the bone fragment.

protecting the neurovascularstructures, (anteriortibial artery anddeep peronealnerves are immedi-ately behind theposterolateral tibia)(Figure 2).

Expose theentire tibial tuber-cle by gentlyretracting the skinmedially while

minimizing dissection of soft tissue attachments.Incise the retinaculum longitudinally at the medialaspect of the patellar tendon along its distal threecentimeters. This allows full medial and lateralvisualization of the patellar tendon before theosteotomy as it attaches to the tibial tubercle andunconstrained elevation after the osteotomy.

Using the cutting block position card (Cat. No.219458), select the site of the anteromedialperiosteal cut along the medial aspect of the tib-ial tubercle. The position of this cut depends uponthe desired slope angle, as referenced in theFulkerson classification chart (Table 1). For example,the steeper the desired slope, the closer this anteriorcut will be to the patellar tendon. On the otherhand, a gentle slope will place this cut moremedially. The extreme example would be thehorizontal cut of a straight medialization.

The slope selector arm (Cat. No .219455) fitsover either end of the cutting block position cardto estimate where a sloped osteotomy would exitposterolaterally (Figure 3).

Use a marking pen to trace the planned cut.The obliquity of the cut should be determinedsuch that the proximal posterolateral corner ofthe osteotomy will end at least 5-10mm anteriorto the posterolateral tibial cortex. The cuttingblock, either with or without the pivot base, (Cat.Nos. 219453 or 219452, respectively), is then

slipped over thecutting blockposition card.Once comfort-able with theprocedure, youmay choose todiscontinue useof the position-ing card.

When usingthe cutting blockwith the pivotbase, attach theends of thebase to the tibiaby using a 2mmdrill (Cat. No.219460) andunicorticalshort anchorpins (Cat. No.219465)(Figure 4).Unicortical predrilling prior to pin insertion isrequired. Proximally, one or two pins may beinserted for attachment, while only the medial pinwill be used distally because of block overhangdue to the distal tibia’s apex shape and obliquecourse of the planned cut.

With the pivot base secured, pivot the cuttingblock guide on the base to the desired slopeusing the slope selector arm. Remember to taperthe osteotomy anteriorly as the osteotomy planeis continued distally. Alternatively, the cuttingblock alone may also be held in position freehand(Figure 5). The choice of Tracker™ System cutting blocks is based on surgeon preference

5

Figure 2: Custom retractor positioned subperiostally below the tibia.

Figure 3: Positioning card with slope selectorarm attached.

Figure 4: Appropriate length unicorticalanchor pins securing pivot base to tibia.

Proposed oblique ostetomy exit

and shouldreflect the surgeon’sexperiencelevel andfamiliarity withthe procedure.

Attach theslope selectorarm assembly(Cat. No.219455) to thecutting blockby inserting

the slope selector cannula into the desired holeon the drill guide. The slope selector arm will beadjacent to the tibia’s exposed lateral wall, whichis the exit site of the osteotomy (Figure 6). Thispredetermines the eventual, final posterior cutexit level and the resulting slope. (Special Note:Unlike the Restore™ ACL Tibial Guide, the slopeselector is not designed to be rigidly secured tothe tibia. The Tracker Slope Selector must behand held in the desired exit position with gentle

pressure tomaintain posi-tion whendrilling.)

Orient theosteotomyplane so thatno drill bit,osteotome orsaw breaksthrough theposterior tibia.This can beprevented by

carefully planning the osteotomy plane with theslope selector arm. The system allows any of thecutting block guide holes to be used, based onsurgeon preference.

Use a 3.2mm drill bit (Cat. No. 219461) to bothtemporarily fix the block and to confirm anosteotomy exit site as the drill bit tip exits (underdirect observation) at the slope selector tip.

The drill is removed from the drill bit (whichremains tohold the blockin place(Figure 7). The2.0mm drill isthen used tomake holes inthe tuberclethrough theextreme proxi-mal and distalholes of thecutting block(unicorticalproximally andbi-cortical distally). Anchor pins are inserted inthese holes to hold the block securely. As familiarity with the system increases, the 3.2mmdrill step may be skipped.

(Note: To further minimize the potential ofdeflection, only use new, sharp drill bits andapply low, even pressure while drilling).

When com-fortable withthe accuracyof the plannedsaw cut (dou-ble check withthe slopeselector), usean oscillatingsaw throughthe cuttingblock sawguide. Beginthe cut distally

6

Figure 6: Slope selector attached to cuttingblock, guiding the 3.2 mm drill pin posteriorlyto the exit site on the tibia.

Figure 8: If an osteotome will be used, makemultiple drill holes with the cutting block firmlyin place. No holes are needed if the oblique cutwill be made with a saw blade. Note the anterior taper of the osteotomy distally.

Figure 7: A 3.2mm drill bit in the middledrill hole secures the cutting block before distaland proximal anchor pins are placed

Figure 5: Cutting block without pivot baseheld in position freehand and then fixed aboewith unicortical and below with biocortical2.0mm anchor pins.

so the saw blade is easy to see as it exits thetibia along the slope (Figure 8). Proceed withcaution proximally where it is more difficult to seethe saw blade. Note that posterior structures areprotected by the retractor as long as the retractoris in proper position, but saw only when full visu-alization is maintained.

The original technique described by Fulkersonis to make multiple 4.5mm drill holes through anaiming block and then allow an osteotome or sawblade and “connect the dots”. With a properlyplaced and secured cutting block, this generallyis not necessary. Dr. Fulkerson now typically usesa saw through the block.

Remove the cutting block from the tibia bypulling the anchor pins using the Anchor PinPuller (Cat. No. 219456) (Figure 9).

To free thetibial tubercle,connect theproximal pos-terior cut withthe proximalanterior cut byusing two link-ing cuts atslightly differ-ent angles.Angle the firstcut from theproximal pos-terolateral

aspect of the osteotomy and gently continueproximally and anteriorly. End the cut just proxi-mal to the lateral aspect of the patellar tendoninsertion. To allow rotation, make a gentle, proxi-mally angled second cut directed from this lateralsite to the osteotomy site proximal and medial tothe patellar tendon insertion (Figure 10). The cutscan be made with any appropriately sizedosteotome or sagittal saw, but great care must betaken to avoid injuring the patellar tendon and itsinsertion.

As is com-mon in totaljoint recon-struction, usethe previoussaw cut trackas a “capturedguide” to finishthe primaryosteotomyplane cutproximally anddistally.Osteoclasiscan then easily be performed through a very thinlayer of cortex distally. A smooth anterior taper ofthe osteotomy distally may decrease the stressriser effect at the distal aspect of the osteotomy.

Next, loosen the tibial tubercle fragment withan osteotome and rotate anteromedially. To tem-porarily secure this fragment, drill a distal 4.5mmhole in the tubercle fragment only, through whichthe Tracker Bone Clamp (Cat. No. 219457) willfirmly hold it. With hard tibial bone, the other siteof the clamp fixation may require superficialdrilling to establish a foothold. Use an anchor pinproximally, which is placed lateral and adjacent tothe free tibial tubercle (without exiting the posteriorcortex) to further stabilize the fragment (Figure11). This is superficial, temporary fixation only.

7

Figure 9: The Anchor Pin Puller captures thehead of the anchor pin to remove the cuttingblock.

Figure 11: The bone clamp secures the fragment distally, while ananchor pin stabilizes the fragment proximally. First approximation, 12-18mm desired elevation.

Figure 10: The Proximal posterior cut is connected to the proximal anterior cut using twolinking cuts at slightly different angles proximal(above) to the patellar tendon insertion.

First Cut

Second Cut

Mitek, Tracker and Restore are trademarks of ETHICON, Inc., a Johnson & Johnson company, or its Mitek Products Division. U.S. Patents 5,613,971, 5,112,337. Other U.S. and foreign patents are pending. All rights reserved. Printed in the USA. © Mitek Products, a Division of Ethicon, Inc. P/N 900455 Rev B, 08/00.

For more information, call your Mitek representative at 1– 800–382 – 4682 or visit www.mitek.com.Mitek Products, Division of ETHICON, Inc., 60 Glacier Drive, Westwood, Massachusetts 02090

Contraindications : None known

Caution: Federal law (USA) restricts this device to sale by oron the order of a physician.

REFERENCES

1. Insall, J.N.: Surgery of the Knee, Second Edition, New York,Churchill Livingstone, 1993.

2. Hauser, H.: Total transplant for slipping patella, Surgery,Gynecology and Obstetrics, 66:199-214, 1938.

3. Trillat, A. Dejour, H. and Couette A.: Diagnostic et traite-ment des subluxations recidivantes de la rotule; Revue DeChirurgie Orthopedique et Reparatrice De L Appareil Moteur;50:813-24, 1964 .

4. Bandi, W.: Chondromalacia patellae and femoro-patellararthrosis, etiology, clinical aspects and therapy. HelveticaChirurgica Acta; 39:Suppl. 11:1-70, 1972.

5. Maquet, P.: Advancement of the tibial tuberosity, ClinicalOrthopaedics and Related Research; No. 115:225-230,March/April 1976.

6. Fulkerson, J.: Anteromedialization of the tibial tuberosity forpatellofemoral malalignment, Clinical Orthopaedics andRelated Research; No. 177:176-81, July/August 1983.

7. Presentation by John Fulkerson, MD, and David Buuck, MD,at the July 1995 American Orthopedic Society of SportsMedicine in Toronto, Canada.

8. Presentation by W.B. Stetson, MD, M.J. Friedman, MD, J.P.Fulkerson, MD, M. Cheng and D. Buuck, MD, at the April1996 Athroscopy Association of North America inWashington, D.C.