Dr. Anthony A. Schepsis

Coastal Orthopedics
Beverly, MA
Professor of Orthopedic Surgery
Boston University School of Medicine

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AMZ publication

JKS-2005-048 Version 1 

 Anteromedialization: Review and Technique 

Jack Farr MD, Anthony Schepsis MD, Brian Cole MD, MBA, John Fulkerson MD, and Paul Lewis 

OrthoIndy: Indianapolis, IN 

Boston Univerisity Orthopaedic Surgical Associates: Boston, MA 

Midwest Orthopaedics at Rush: Chicago, IL 

Orthopedic Associates of Hartford: Hartford, CT 

Midwest Orthopaedics at Rush: Chicago, IL 

Abstract 

Anteromedialization was introduced by Fulkerson as a method to address patellofemoral pain, chondrosis and malalignment. Long-term follow-up demonstrates efficacy. Patellofemoral cartilage extent and region analysis allows for refined indications to optimize results. This article reviews the historical background, technique, results and biomechanical rationale. This overview will assist in optimally integrating the procedure in the treatment armamentarium for patellofemoral disease. 

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Introduction 

Fulkerson originally designed the technique of anteromedialization (AMZ) of the tibial tubercle to address patellofemoral (PF) pain associated with (PF) chondrosis in conjunction with (PF) tilt and/or chronic patellar subluxation while at the same time avoiding the complication rate of the Maquet tibial tubercle elevation15. The AMZ technique transferred areas of patellofemoral loading through: medialization to also improve patellofemoral joint congruity (improved joint contact area) and anteriorization to transfer forces proximally, while theoretically decreasing the absolute magnitude of the PF resultant force14. This theoretical decrease in resultant force and increase in contact area would thus decrease joint surface stress potentially decreasing the condition of overload contributing to pain1

Long-term clinical follow-up, has verified both the efficacy of the procedure and a decrease in the complication rate associated which had been associated with the Maquet technique of anteriorization4

Currently, there has been a renewed interest in AMZ in conjunction with cartilage restoration of the PF compartment. For cartilage restoration treatments, it is imperative that stress on the restoration be optimized/ minimized. In the case of the patellofemoral joint cartilage restoration, the importance of optimizing patellofemoral joint stress was not realized initially. This was demonstrated by the poor results of PF autologous cultured chondrocyte implantation (ACI) for patellofemoral cartilage defects as originally reported by Brittberg and Peterson (that is, patellar malalignment was not corrected in this early series)3. In that series, 5 of the 7 patellofemoral ACI patients did poorly, in contrast with a high rate of success at the tibiofemoral articulation. Subsequently, with attention to alignment and elevation through anteromedialization, the results of PF ACI have approached that of the tibiofemoral joint25,30 . This article will assess AMZ clinical studies, analyze relevant biomechanics and conclude with a review of the technique which includes applications in cartilage restoration. 

Background: Clinical Studies in the Literature 

Fulkerson originally described anteromedial transfer of the tibial tubercle in 198315. He reported further his clinical series in 199014 . He studied outcomes of 30 patients followed for more than 2 years with 12 patients followed for more than 5 years. The authors reported a 93% success rate subjectively, and 89% success rate by objective parameters. In a subgroup of patients with advanced arthrosis, there were 75% good, but no excellent outcomes. 

Piordano and Fulkerson subsequently looked retrospectively at a series of patients over a 10 year period, attempting to compare results relative the to geographic location of the articular cartilage disease31. Eighty seven percent of 23 patients with disease primarily located either in the distal or lateral portion of the patella, had a successful outcome. Of 9 patients with medial disease, there was a 55% success rate, and in 5 patients with either 

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proximal or distal disease, only one (20%), had a satisfactory outcome. They also found a correlation between advanced disease of the central trochlea and a poor outcome. . 

Buuck and Fulkerson reviewed 36 patients (42 knees) at an average of 8.2 years (minimum 4.4 years) follow up4. Eighty-one percent said they were the same or better than at one year follow up and 86 % achieved a good or excellent result. Eighty one percent returned to sports, and 36% returned to running and court sports. Of the 4 poor results, three had large trochlea articular lesions. 

Bellemans, et.al, reported on 29 patients who underwent anteromedialization osteotomies for chronic anterior knee pain2. He divided the patients into 2 subgroups according to radiographic criteria for malalignment. Group 1 had subluxation without tilt and group 2 had subluxation and tilt. 14 patients in group 1 had AMZ alone, and 15 patients in group 2 had an AMZ with a lateral release. All but one patient had a successful outcome by Kujala and Lysholm rating scales. He noted consistent correction of radiographic subluxation in group 1, and subluxation as well as tilt in group 2. 

Naranja and co-authors reported on their results of anteromedialization, although their technique was distinctly different than that described in this article28. They performed a flat osteotomy and then elevated the shingle with a 10mm bone graft, described as the “Elmsie-Trillat-Maquet” procedure. In their series of 55 procedures in 51 patients, they reported an 84% success rate, 73% by the Fulkerson patellar scoring scale. 

Relevant Biomechanics 

To optimally apply the tibial tubercle anteromedialization (AMZ) procedure, a sound understanding of both normal and abnormal patellofemoral biomechanics is essential. By definition, “stress” is contact force divided by the contact area. With abnormalities in PF contact area, PF stress can be elevated with deleterious material (cartilage) and physical (overload pain) effects. The goals of the AMZ procedure are threefold and not mutually exclusive: 1) to transfer the patellar tracking from areas of PF chondrosis to areas of intact (or normal) articular cartilage, 2) to increase the contact area by improving joint congruity and 3) decrease patellofemoral contact force15,24

The summation of all patellofemoral joint forces is the patellofemoral joint reaction force (PFJR). It can be simplistically be thought of as a resultant vector of the quadriceps tendon force vector summed with the patellar tendon force (those portions of each that are perpendicular to the tangent of the PF contact vector). This force may also be defined as the force equal and opposite to the posterior compressive force that the patella exerts on the femoral articulating surface13. As the knee flexes, the PFJR is increased because of: 1) the increasing moment arm of the flexors (i.e., the applied force (center of body mass) is applied farther from the axis of rotation) and 2) as the knee is flexed, the angle between the component forces of the PFJR (i.e., quadriceps and patellar tendon) becomes more acute, increasing the resulting vector21. Calculations of the PFJR have been determined to be 0.5 times the body weight in normal walking and 3.3 times when ascending and descending stairs and even higher with jumping35. During assessment of 

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these forces, it is important to calculate the hip/pelvic flexion as this changes the moment arm of the body mass (e.g., skiing in extension increases the moment arm and flexion of the hip to exit a chair decreases the moment arm). The passive and active soft-tissue stabilizers which influence patellar position and tracking also contribute to the PFJR but for simplicity can be ignored (but not forgotten—that is, procedures that capture or over constrain the patellar, such as excessive medial reefing, may increase PF contact forces)12. The vastus medialis and vastus lateralis muscles (and the obliquus portion of each) of the quadriceps group have insertions to the patella independent from the rectus femoris and vastus intermedius. As a consequence, they each contribute separately to the balance of the patella – vastus medialis medially and the vastus lateralis laterally12,18. Additionally, the vastus lateralis obliquus (VLO), provides a direct lateral pull of the patella and the vastus medialis obliquus with variable patellar attachments and muscle volume exerts variable medial force12,34

In addition to the posteriorly directed resultant force vector on the patella, the patellar and quadriceps tendon impact the patellar balance medially and laterally. The patellar tendon extends from the patella to the tibial tubercle, which is lateral to the trochlear groove (expressed as a tibial tubercle- trochlear groove distance or TT-TG distance7,13. The quadriceps also provides additional lateral force in the coronal plane due to the alignment of the quadriceps as they attach to the femur (and rectus at pelvis), which is typically in anatomic valgus13. Thus, the coronal plane resultant force vector of the patellar tendon during quadriceps contraction is lateral and is functionally effected during range of motion by rotation of the femur and tibia (eg. The tibia in gait follows the foot and internally rotates with pronation). One historic tool for assessing the alignment contributing to this lateral force is the Q (quadriceps) angle, yet intraobserver variation the “Q” angle and variants of the “Q” angle, suggest the objective TT-TG distance is a more reproducible quantification of the extent of lateral tubercle position32

The contact area between the patella and femur is the denominator of stress (force per unit area). With the “normal” knee joint, the articular cartilage of the patella and trochlea have increased contact area during flexion of the knee (obviously, changes as the patella enters the intercondylar notch), and it is further increased under load as demonstrated by Heino and Powers with a dynamic PF MRI19. With flexion of the knee, the patellofemoral contact area shifts proximally on the patella6,17,20. In higher degrees of flexion, the patella changes from contact with the trochlea to contact with the medial and lateral walls of the intercondylar notch; in these flexion angles the patellofemoral contact is supplemented with tendofemoral contact between the quadriceps tendon and trochlea6,17,20

Anteromedialization, as described elsewhere in this article, allows anteriorization and medialization of the tibial tubercle: these components (anteriorization and medialization) may be first considered separately. The procedure of anterior displacement (Maquet) of the tibial tubercle, using 2 dimensional biomechanical analysis, was thought to decrease the absolute contact forces between the patella and femur and was performed as an alternative to patellectomy with the known negative effects of patellectomy9,24,37. This initial mathematical work by Maquet was confirmed by the in vitro work of Ferrandez

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who reported that the greatest reduction of pressure was seen in the first centimeter of anterior displacement of the tibial tubercle10. An investigation by Ferguson later broadened this range to include the first 1.25 centimeters of displacement (93% reduction in stresses)9. Radin in his description of the Maquet procedure suggested a displacement of 2-2.5 cm33. In a later study, the 1.0 cm distance marked the beginning of a statistically significant decrease in contact forces14. Mathematical models have concluded a 40% reduction in stress with a 1 centimeter anteriorization24,26,38

The isolated procedure of medialization was used historically in treatment of both recurrent lateral patellar dislocations and static lateral patellofemoral malalignment when defined as chronic static patellar subluxation. Medialization, by definition, decreases the TT-TG distance and thus decreases the lateral resultant vector acting on the patella. With distal realignment, Huberti and Hayes found an increase in contact area and with a concomitant decrease in the Q angle and an inconsistent shift in contact area to the medial patellofemoral surface10. This study used knees with normal Q angles and investigated pathologically small and large Q angles. The increase in pressure found by Huberti and Hayes was confirmed later with realignment of the tibial tubercle again, in normal knees20,23. The historical use of isolated medialization prevent lateral dislocation has now been supplant largely with attention to the medial patellofemoral ligament (MPFL). However, in the context of cartilage restoration procedures and chondral disease, the effects of isolated medialization (medialization and “over-medilaization” are often not defined) alone have the potential of being detrimental to the PF compartment and Andrish has shown in vitro that it also increases medial tibiofemoral forces1,14,23,26

Several clinical studies indicated that patients with patellofemoral pain improved after the following AMZ2,5,8,11,14,22,27,36. Fulkerson et. al. included a mechanical evaluation of five cadaveric knees that underwent AMZ to compliment a minimum two-year follow-up of patients following AMZ14 . The results of this evaluation were an unloading of the lateral facet in the early degrees of flexion and loading of the medial facet at 90° of flexion. Independently, Molina investigated the biomechanical difference between three procedures: anterior displacement, medial displacement and the combined AMZ of the tubercle26. They concluded that the combined anterior and medial displacement is required to reduce stress over the patellar contact area. Moreover, through statistical analysis, anteriorization of 0.5 to 1.0 cm combined with 1.0 cm medialization provided the optimal results (i.e. it minimized patellofemoral stress). [Author’s editorial comment: medializationof 10mm may not produce the same effect in knees with various TT-TG distances]. While many studies have focused on changes in patellar biomechanics following straight anteriorization or AMZ, Beck evaluated the effect on the trochlea following AMZ1 . Specifically, pressures decreased laterally, only slightly centrally, and increased medially following AMZ1. Finally, in comparing two different methods for medialization, Cosgarea found the Fulkerson oblique osteotomy procedure to have a higher mean load to failure than the Elmslie-Trillat, flat osteotomy6. The method of failure in the oblique realignment was through fixation failure or tibial fracture. Failure in the Elmslie-Trillat method occurred through a tubercle “shingle” fracture6. In summary, AMZ has a solid biomechanical rationale for improving patellofemoral stress. These biomechanical predictions have been verified by clinical results. 

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Operative Technique 

As noted above, the technique classically was used as an isolated procedure. In that case, after arthroscopic evaluation and treatment, an assessment is made to determine the need for lateral release and the extent of release necessary. The historical “turn up” sign (to demonstrate an adequate release) has been replaced by a titrated limited lateral release in recognition of the variability of patients. In those patients with marked clinical and CT proven tilt, a lateral release will be more appropriate and more extensile than in those with predominant subluxation and more medial/lateral translation possible with or reversible tilt. In either case, the goal is to allow neutralization of tilt and unrestricted central positioning of the patella, but without allowing medial patellar subluxation. Once again, the extent of a lateral release is patient specific and, in some patients, a lateral release will not be necessary. The lateral release may be performed in an open or arthroscopic manner. Hemostasis is imperative and should be confirmed with the tourniquet deflated (if used). AMZ does not require use of a tourniquet, yet can decrease initial bleeding during the approach and osteotomy. 

In patients undergoing cartilage restoration, it is easier for the patient to undergo AMZ and cartilage restoration at the same setting rather than perform an AMZ and then return for cartilage restoration. When cartilage restoration is performed concomitantly, then in some cases for exposure, the lateral arthrotomy can be extended more proximally than usual, but the same guidelines apply: at closure, the lateral arthrotomy is closed proximal to distal until the patella is balanced in the trochlea. Too extensive of a lateral release is as detrimental as too little. ([Figure 1] shows the skin incision for an isolated AMZ and [Figure 2] shows the skin incision when performed in conjunction with cartilage restoration). 

As the tubercle will be elevated anteriorly, the capsule is incised on each margin of the patellar tendon [Figure 3]. These releases will remain open at closure. Fat pad hemostatis is critical. The incision along the lateral border of the patellar tendon is continued along the lateral crest of the tibial tubercle; this allows initial sharp elevation of the anterior compartment musculature from the lateral face of the tibia beginning just distal to Gerdy’s tubercle. After an initial 1 cm of sharp dissection, the muscle is elevated with a blunt subperiosteal elevator with care not to plunge posteriorly. After reaching the posterior margin of the lateral tibia, a custom retractor (Tracker AMZ, DePuy/ Mitek, Norwood, Massachusetts) is placed immediately adjacent to the posterior tibia. This retractor will assist in protecting the anterior tibial artery and the deep peroneal nerve, but caution still should be exercised to prevent nerve vascular harm [Figure 4]. 

The desired length of the final tubercle “pedicle” influences the length of the tubercle and lateral wall exposure. Note that a shorter pedicle will result in more patellar tendon rotation (during rotation of the tibial tubercle pedicle there will be some degree of distalization) and in the extreme, can result in some measurable degree of distalization of the patella . 

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The next stage is planning the sloped cut. This involves not only consideration of the slope of the cut, but also the angulation of the cut in the coronal plane. The tubercle anterior cut begins adjacent to the medal border of the tubercle attachment of the patellar tendon proximally. The cut then courses laterally as it progresses distally. This is necessary to end the cut near or through the lateral wall of the tibia, noting the desired pedicle length is 7-10 cm. (Obviously, a cut straight distally would not end and could propagate past the desired tubercle pedicle length.). Tapering the distal end of the cut towards the anterior cortex also yields an osteotomy with a less abrupt stress riser, and therefore, hopefully aids in reducing risk of fracture. 

The slope selector arm of the Tracker set is attached to the cutting jig .It is possible to 1.) plan the orientation of the anterior cut in the coronal plan (where saw starts) and at the same time 2.) plan the slope of the AMZ in the axial plane, as well as 3.) directly visualize the planned lateral wall exit of the tibial cut just anterior to the junction of the lateral wall and posterior wall [Figure 5]. It is important not to cut through the posterior cortex, but rather exit on the lateral face of the tibial just anterior to the posterior border of the tibia. The steepest slope with this technique is approximately 60 degrees and can be decreased to achieve more medialization.. With a 60-degree slope, every one millimeter of medialization results in two millimeters of elevation. Optimal anteriorization probably is in the range 1.0 to 1.5 cm. Thus, with this anteriorization a constant goal, the slope is changed appropriately to effect the desired medialization (an offset graft maybe added when medialization is not desired). 

After the desired slope axial plane and coronal plane anterior cut angulations are finalized, the cutting jig is then anchored with two pins through drill holes. The cut is made with an oscillating saw cooled with saline. [Figure 6]. The cutting jig is then removed. The cut just completed in the tibia is next used as a “saw capture” guide much the same way a saw capture jig is used in arthroplasty. The initial cut in the tibia guides the saw to finish the distal cut near or through the distal extent of the tibial tubercle pedicle and proximally the cut is continued 2-3 mm proximal to the level of the patellar tendon attachment to the tubercle. [Figure 7]. 

The remaining cuts are proximal to free the tubercle. These cuts are made with an osteotome cutting at two slightly different angles to release the bone just proximal to the patellar tendon attachment to the tibial tubercle. [Figure 8]. 

The tubercle pedicle is then free to rotate around the distal pedicle allowing both anteriorization and medialization. The tibial tubercle pedicle can be temporarily held in position with a k-wire placed through the open cancellous bone proximally and then permanently fixed with two cortical lag screws using interfragmentary fixation [Figure 9,10a,10b, 10c]. Fulkerson emphasizes meticulous technique drilling the pedicle with a 4.5 bit, using a sleeve and carefully advancing a 3.2 drill bit through the posteriomedical tibial cortex to avoid neurovascular compromise. A depth gauge measures for a self tapping cortical screw or if a tap is used the depth of desired penetration (from the depth 

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gauge) is marked on the tap with a marking pen to assure the tap does not penetrate too deeply and potentially harm posterior soft tissues. 

At closure, the anterior compartment musculature remains open and with this technique Fulkerson has never experience a compartment syndrome in over 500 cases. If a tourniquet has been used, it is released and thorough hemostasis is achieved prior to closure. 

For patients without need for medialization, a local cancellous graft can be harvested and place along the cut tibial slope before fixation. This lateral offset of the tubercle will effectively neutralize the medialization, allowing a straight anterization alternative to Maquet . The AMZ may also be performed concomitantly with reconstruction of the medial patellofemoral ligament (MPFL). In that setting, the tubercle position is selected and secured before the MPFL reconstruction is performed as the AMZ alters the length/tension of the medial structures. Which are reconstructed anatomometrically allowing full range of motion [Figure 11a,11b,11c] 

Postoperatively, the patient is treated with a standard compression dressing and cryotherapy. The patient is encouraged to begin early patellofemoral safe quadriceps, core stabilizing and lower extremity strengthening. Range of motion is progressed as comfort permits; noting that for cartilage restoration the site of restoration may modify the recommended safe range of motion. The extremity is protected with a long leg splint until there is excellent extremity control and there is no risk of falling. Patients use crutches with protected weight bearing for a full 6 weeks in light of fractures reported with earlier weight bearing5

Application of AMZ in Cartilage Restoration 

Anteromedialization is also frequently performed with cartilage repair or restoration procedures. Currently, these procedures include autologous chondrocyte implantation, osteochondral plug transfers, (either autograft or fresh “cultured” allograft), marrow stimulation (e.g., microfracture) and patellofemoral ostechondral shell transplantation. These techniques may be applied to the patella, trochlea, or both. Frequently, these defects are associated with preexisting malalignment and/or instability. It is critical to correct these associated mechanical problems, which commonly included tubercle anteromedialization for chronic lateral patellar subluxation, and repair, tightening or reconstruction of the medial patellofemoral ligament for lateral patellar instability (these may be isolated or coexist). Likewise it is important to optimized the load (stress = force / contact area) on these cartilage repair/restoration areas during the correction of malalignment. 

From the results of Fulkerson’s outcome studies, comparing results to location of chondrosis, it is questionable however, whether or not an isolated AMZ should be performed when the articular cartilage problem prominent (grade3a,3b,3c International Cartilage Repair Society Grading and greater thatn 1-2cm2 area) and is either in the 

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1.) proximal portion of the patella, 2.) localized solely to the medial half of the patella, 3.) diffusely involves the patella, or 4.) involves the trochlea31. Additionally, the anteromedialization transfers loads to the proximal medial portion of the patella as well as the medial trochlea1 . Nevertheless, the clinician is not infrequently faced with a significant traumatic loss of articular cartilage from the medial facet of the patella after a patellar instability episode as reported by Normura or diffuse midwaist chondrosis with longstanding chronic patellar subluxation29. In the young individual who remains symptomatic with cartilage lesions in these problematic areas (medical, proximal diffuse or bipolar), as an isolated AMZ fairs poorly, then cartilage restoration with potential tubercle surgery may be considered as an option. During the concomitant anteriorization or AMZ and cartilage restoration, the realignment must be carefully plan and coordinated. Specific PF contact areas are noted in during range of motion. As the patella loads distally to proximally through range of motion, it may also be possible to limited loading of the cartilage repair/restoration area(s) by limiting the post operative arc of motion until the neocartilage tissues have developed sufficiently to accept loading. When there is no malalignment and the cartilage repair has been performed in either the distal half of the patella or the medial patella or trochlea, a steep osteotomy with maximum slope, with or without an offset bone graft to reverse all medialization may be performed. Although there are no randomized studies comparing isolated AMZ to AMZ with cartilage restoration, the improved patient scores of PF chondrosis treated with AMZ and cartilage restoration reported by Minas to those reported outcomes of isolated AMZ suggest promise25. Certainly, the converse has been demonstrated: failure to address malalignment and abnormal PF loading leads to poor outcomes for cartilage restoration(s). 

Also relevant to cartilage restoration are procedures that harvest tissues from the margins of the trochlea and sulcus terminals. For example, Garretson investigated the patellofemoral joint pressures of normal knees in regards to sites for osteochondral autograft donor plugs16. From their investigation, they concluded the lowest contact pressures existed along the medial trochlea and pressures of the lateral trochlea decreased as they shift distally along the trochlea16. As predicted in the original description by Fulkerson, the combined anteriorization and medialization of the tibial tubercle clinically appears to lower stress at the patellofemoral joint and improves the mechanical alignment. AMZ application during cartilage restoration procedures must be considered on a case-by-case basis15 [Figure 12a, 12b,12c,12d]. 

Conclusion: 

It appears that with judicious patient and patellofemoral lesion selection AMZ, can be effective in the management of specific patellofemoral pathologies. Combined with cartilage restoration (and vice versa) there is potential, in some cases, to improve the expected outcome to a level better than either procedure performed alone. Close monitoring of future clinical patellofemoral cartilage restoration studies will hopefully allow a more precise algorithm to apply demand matching to optimal use of these surgical alternatives. 

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References 

1. Beck PR, Thomas AL, Farr J, Lewis PB, Cole BJ: Patellofemoral contact pressures following anteromedialization of the tibial tubercle. Am J Sports Med. 

2. Bellman’s J, Cauwenberghs F, Witvrouw E, et al: Anteromedial tibial tubercle transfer in patients with chronic anterior knee pain and a subluxation-type patellar malalignment. Am J Sports Med. 1997;25:375-81. 

3. Brittberg M, Lindahl A, Nilsson A, et al: Treatment of deep cartilage defects in the knee with autologous chondrocyte transplantation. N Engl J Med. 1994;331:889-95. 

4. Buuck, D and Fulkerson,J:.Anteromedialization of the tibial tubercle: a 4-12 year follow up. Op Tech Sports Med 8:131-137, 2000. 

5. Cameron HU, Huffer B, Cameron GM: Anteromedial displacement of the tibial tubercle for patellofemoral arthralgia. Can J Surg. 1986;29:456-8. 

6. Cosgarea AJ, Schatzke MD, Seth A, Litsky AS: Biomechanical analysis of flat and oblique tibial tubercle osteotomy for recurrent patellar instability. Am J Sports Med. 1999 Jul-Aug;27(4):507-12. 

7. Dejour H, Walch G, et al : Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatology. Arthroscopy.1994;2:19-26. 

8. Farr J: Anteromedialization of the tibial tubercle for treatment of patellofemoral malpositioning and concomitant isolated patellofemoral arthrosis. Tech Orthop. 1997;12:151-64. 

9. Ferguson AB, Brown TD, Fu FH, Rutkowski R: Relief of patellofemoral contact stress by anterior displacement of the tibial tubercle. J Bone J Surg Am. 1979 March;61-A(2):159-166. 

10. Ferrandez L, Usabiaga J, Yubero J, Sagarra J, de No L: An experimental study of the redistribution of patellofemoral pressures by the anterior displacement of the anterior tuberosity of the tibia. Clin Orthop 1989; 238:183-189. 

11. Fulkerson JP: Anteromedialization of the tibial tuberosity for patellofemoral malalignment. Clin Orthop Rel Res July 1983;177:176-181. 

12. Fulkerson JP: Disorders of the patellofemoral joint in Chapter 1: normal anatomy. Ed 4. Baltimore, Williams and Wilkins 1997. 

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13. Fulkerson JP: Disorders of the Patellofemoral Joint in Chapter 2: Biomechanics. Ed 4. Baltimore, Williams and Wilkins 1997. 

14. Fulkerson JP, Becker GJ, Meaney JA, Miranda M, Folcik MA: Anteromedial tibial tubercle transfer without bone graft. Am J Sports Med. 1990;18(5):490-497. 

15. Fulkerson, J.P.: Anteromedialization of the tibial tuberosity for patellofemoral malalignment. Clin. Orthop. 177:176-181, 1983. 

16. Garretson RB, Katolik LI, Verma N, Beck P, Bach BR, Cole BJ: Contact pressure at osteochondral donor sites in the patellofemoral joints. Am J Sports Med. 2004;32(4): 967-74. 

17. Goodfellow JW, Hungerford DS, Zindel M: Patellofemoral mechanics and pathology: I. functional anatomy of the patello-femoral joint. J Bone Joint Surg 1976;58B:287. 

18. Heegaard J, Leyvraz F, Van Kampen A, et al: Influence of soft structures on patellar three-dimensional tracking. Clin Orthop Rel Res Feb 1994;299:235-43. 

19. Heino BJ, Powers CM, Teri et al: Quantification of patellofemoral joint contact area using magnetic resonance imaging.Magn Reson Imaging. 2003 Nov;21(9):955-9. 

20. Huberti HH, Hayes WC: Patellofemoral Contact Pressures: The influence of q-angle and tendofemoral contact. J Bone Joint Surg 1984; 66A:715-24. 

21. Hungerford DS, Barry M: Biomechanics of the patellofemoral joint. Clin Orthop Rel Res. Oct 1979; 144:9-15. 

22. Kohn D, Steimer O, Seil R.:Anterior medial correction the tibial tuberosity. Orthopade. 2004;33:218-23. German. 

23. Kuroda R, Kambic H, Valdevit A, Andrish JT: Articular cartilage contact pressure after tibial tuberosity transfer. Am J Sports Med. 2001;29(4):403-409. 

24. Maquet P: Biomecanique de l’articulation patellofemoral. Acta Orthop Belg 44:41-54, 1978. 

25. Minas T, Bryant T: The role of autologous chondrocyte implantation in the patellofemoral joint. Clin Orthop Rel Res. 2005;436:30-39. 

26. Molina A, Ballester J, Martin C, Munoz L, Vazquez J, Torres J: Biomechanical effects of different surgical procedures on the extensor mechanism of the patellofemoral joint. Clin Orthop Rel Res. Nov 1995;320:168-175. 

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27. Morshuis WJ, Pavlov PW, de Rooy KP: Anteromedialization of the tibial tuberosity in the treatment of patellofemoral pain and malalignment. Clin Orthop. 1990;242-50. 

28. Naranja, R. J., Reilly, P.J., et al: “Long-term evaluation of the Elsmlie-Trillat Maquet procedure for patellofemoral dysfunction,” Am J of Sports Med. Vol. 24, 1996: 779-784. 

29. Normura E, Inoue M, Osada N: Chondral and osteochondral injuries associated with acute patellar dislocation. Arthroscopy 2003 Sep;19(7):717-21. 

30. Peterson L, Minas T, Brittberg M, et al.: Two- to 9-year outcome after autologous chondrocyte transplantation of the knee. Clin Orthop 2000;212-34. 

31. Pidoriano AJ, Weinstein RN, Buuck DA, et al: Correlation of patellar articular lesions with results from anteromedial tibial tubercle transfer. Am J Sports Med. 1997;25:533-7. 

32. Post WR: Clinical evaluation of patients with patellofemoral disorders. Arthroscopy 15:841-51. 

33. Radin EL: The Maquet Procedure – Anterior displacement of the tibial tubercle: indications, contraindications, and precautions. Clin Orthop Rel Res 1986;213:241-248. 

34. Reider B, Marshall L, Koslin B, Girgis FG: The anterior aspect of the knee joint. J Bone Joint Surg 1981;63A(3):351-6. 

35. Reilly DT, Martens M: Experimental analysis of the quadriceps muscle force and patellofemoral joint reaction force for various activities. Acta Orthop Scand 172;43:126-37. 

36. Sakai N, Koshino T, Okamoto R: Pain reduction after anteromedial displacement of the tibial tuberosity: 5-year follow-up in 21 knees with patellofemoral arthrosis. Acta Orthop Scand. 1996;67:13-15. 

37. Sutton FS, Thompson CH, Lipke J, Kettelkamp DB: The effect of patellectomy on knee function. J Bone Joint Surg Am. 1976 Jun;58-A(4):537-40. 

38. Waisbrod H, Treiman N: Anterior displacement of tibial tuberosity for patellofemoral disorders: A preliminary report. Clin Orthop Rel Res 1980;153:180-2. 

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Figures 

Figure 1. Incision for an isolated AMZ (Right Knee) 

Figure 2. Exposure for AMZ when performed in conjunction with 

cartilage restoration. (Left Knee) 

Figure 3. As the tubercle will be elevated anteriorly, the capsule is incised on each 

margin of the patella 

Figure 4. Retractor exposing lateral wall of tibia and aiding in protecting 

posterior structures. (Left Knee) 

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Figure 5. Planning the coronally angulated axially sloped cut. The tubercle anterior 

cut begins adjacent to the medial border of the tubercle attachment of the patellar tendon proximally and angles laterally as it courses distally. The tip of the slope selector arm showing the lateral wall exit site of the sloped cut. Pins secure the cutting block. (Left Knee) 

Figure 6. Saw exiting on lateral wall anterior to the posterior tibial face. 

Note: the retractor position aids in protecting posterior structures. 

(Left Knee) 

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Figure 7. The cutting jig is removed and the cut just completed in the tibial is 

next used as a “saw capture” guide much the same way a saw capture jig is used in arthroplasty. The initial cut in the tibia guides the saw to finish the distal cut near or through the distal extent of the tibial tubercle pedicle and proximally the cut is continued 2-3 mm proximal to the level of the patellar tendon attachment to the tubercle. 

Figure 8. The patella attachment to the tibial tubercle is exposed and protected with 

an Army/Navy retractor. The Tracker retractor aids to maintain exposure of the proximal extent of the picture represents two cuts. The larger osteotome connects the proximal posterior slope cut to the lateral attachment site of the patellar tendon to the tubercle. The smaller (more proximal) osteotome cuts across ( at a slight angle) just proximal to the patellar tendon attachment, connecting the medial and lateral cuts and thus, freeing the tubercle. 

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Figure 9. The pedicle can be temporarily held in position with a k-wire through the 

open cancellous bone proximally to allow assessment of the effect of tubercle repositioning on the patella position. (Right Knee) 

Figure 10a . Fixation with two 4.5 AO screws using interfragmentary fixation. 

Figure 10b. Measuring medialization. 

Figure 10c. Measuring anteriorization. 

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Figure 11a. Demonstrates anatomometric length checking in full flexion. 

(Right Knee) 

Figure 11b. In full flexion (Right Knee) 

Figure 11c. Post-operative incision appearances after AMZ and two incision 

tunnel MPFL Reconstruction. 

Figure 12a. Merchant radiograph demonstrates chronic static patellar 

subluxation with mild PF lateral joint space narrowing. 

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Figure 12b. Outline of diffuse midwaist centerolateral grade 3a,3b,3c 

chondrosis uncontained distal laterally. (Left Knee) 

Figure 12c. Debrided lesion with marked region of non-containment. (Left Knee) 

Figure 12d. AMZ slope shown with completed autologous cultured chondrocyte 

implantation (slope will unload lateral lesion). (Left Knee) 

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