John P. Fulkerson
DEFINITION
Tibial tubercle transfer is a versatile surgical alternative in the treatment of difficult and resistant patellofemoral disorders ranging from patellofemoral instability to patellofemoral arthritis.
Patients with combined instability and arthritis often benefit from tibial tubercle transfer.
Tibial tubercle transfer may be best regarded as “compensatory.” In other words, if a multiplicity of structure and alignment factors leads to patellar instability or arthritis, carefully planned repositioning of the tibial tubercle can compensate for other deficiencies, providing permanent relief of pain and instability.
ANATOMY
The patella articulates within the femoral trochlea in such a way that the distal aspect of the patella enters the trochlea from a slightly lateralized position upon initiation of knee flexion. Normally the patella enters the trochlea promptly within the first 10 degrees of flexion, first making contact with the distal aspect of the patella.
As the knee flexes further, load is transferred more proximally on the patella such that in full flexion, contact is on the proximal aspect of the patella. The intervening flexion transfers load more gradually along the patella, moving proximally with each degree of flexion load.11
As the patella enters the trochlea with further knee flexion, the trochlea becomes deeper, so that containment of the patella is improved. Therefore, in most people, the point of greatest instability is early flexion of the knee, when the trochlea is at its shallowest and containment of the patella is most limited.
The position of the tibial tuberosity relative to the femoral trochlea further complicates the process of patella entry into the trochlea.4
This relationship has been referred to as the tibial tuberosity to trochlea groove (TT-TG) index, measured in millimeters using superimposed tomographic images of the position of the central trochlea and the tibial tubercle (FIG 1).
The patella is contained within a soft tissue investing layer of tendon and retinacular structure.
The lateral retinaculum extends to the iliotibial band but also proximally to the lateral femur and to the tibia (the patellofemoral and patellotibial components, respectively, of the lateral retinaculum).
On the medial side is the medial patellofemoral ligament (MPFL), which extends from the proximal half of the patella to the adductor tubercle region.1
The patellar tendon is located distally, with the quadriceps tendon proximally connecting the patella to the quadriceps muscle. The quadriceps tendon is a massive tendon, including a major vastus lateralis tendon component on the proximal lateral aspect of the patella.
The superolateral corner of the patella is supported dynamically by the vastus lateralis obliquus, which inderdigitates with the lateral intermuscular septum.14
PATHOGENESIS
The pathogenesis of problems around the patellofemoral joint relates to dysplasia of anterior knee anatomy, malalignment, and trauma.
Most patients with significant dysplasia have a congenital underlying imbalance of the extensor mechanism, which leads to improper morphologic development.
FIG 1 • The relation of the tibial tubercle (TT) to the central trochlear groove (TG)—the TT-TG relationship— pertains to patella instability. A. Normal TT-TG relationship, in which the tibial tubercle and trochlear groove are lined up. B. Lateralized tibial tubercle.
FIG 2 • A. Normal trochlear groove. B. With prolonged lateral patella tracking, the lateral trochlea becomes flattened, further aggravating lateral patella instability and stretching the medial patella support structure (including the medial patellofemoral ligament). *, center of trochlea; spTG, sagittal plane of trochlear groove; spTT, sagittal plane of tibial tubercle; TT, tibial tubercle.
A chronically lateralized extensor mechanism is likely to cause abnormally high lateral pressure on the femoral trochlea, thereby leading to developmental flattening of the lateral trochlea and also flattening of the patella (FIG 2). Although it is not always the case, this pattern of development most likely explains the poor development of the lateral trochlea and persistent instability in patients with abnormal extensor mechanism alignment. Such patients stretch the medial patella support structure over time, leading to subluxation and tilt of the patella in many cases.
This stretching can lead to chronic instability, chronic overload of the lateral patellofemoral joint, dislocation (which often causes medial patella articular damage), breakdown of the lateral patellofemoral joint, and pain related to overload of the joint and peripatellar retinacula.13
Some patients have anterior knee pain as the result of blunt trauma, usually with the knee flexed.
An impact to the flexed knee and resulting trauma to the patellofemoral joint usually leads to proximal patella injury. This is important, because anteriorization of the tibial tubercle shifts contact on the patella proximally and can, therefore, exacerbate a lesion on the proximal patella related to blunt injury.
Because movement of the tibial tubercle was not involved in the injury in many patients who have had blunt trauma, the problem usually is not one of abnormal extensor mechanism alignment requiring correction.
NATURAL HISTORY
The natural history of patellofemoral pain, instability, or arthrosis often relates to the imbalance noted earlier. With chronic lateral tracking of the patella in the trochlea, overload occurs with increased point loading on the patella and trochlea, particularly the patella.
Eventually this can lead to breakdown of articular cartilage and what Ficat7 has called excessive lateral pressure syndrome (FIG 3).
Schutzer21 demonstrated a high incidence of patellofemoral tilt and subluxation in patients with patellofemoral pain, compared with controls.
With dislocation of the patella, the medial patellofemoral ligament is torn and, even after healing, elongated. This further exacerbates any tendency toward lateral displacement of the patella out of the trochlea.
With blunt trauma, pain is related to impact and subchondral bone injury, generally on the proximal patella. This pain, then, originates from injured subchondral bone, because there are no nerves in cartilage.
PATIENT HISTORY AND PHYSICAL FINDINGS
With the patient who may be a candidate for tibial tubercle transfer, it is important to establish that this definitive surgery truly is indicated because of a structural alignment imbalance or articular overload condition leading to instability or pain.
The physical examination should emphasize a very critical look at patella tracking within the femoral trochlea, the condition of the medial patellofemoral ligament, evidence of articular breakdown of the patellofemoral joint, evidence of retinacular or soft tissue pain, and a search for other possible causes of pain such as medial or lateral compartment disease or referred pain from the hip or back.
Careful palpation of the retinacular structure around the patella will indicate whether there is soft tissue or retinacular overload contributing to pain.18
In some cases, simple release of the painful retinacular structure may be all that is needed.
When examining the medial patellofemoral ligament, holding the patella laterally in extension is recommended, then slowly
FIG 3 • Excessive lateral pressure leads to lateral patella chondropathy and breakdown. (Courtesy of David Dejour.)
FIG 4 • Test for medial patella subluxation. The patella is held medial and knee is flexed abruptly. If patella relocation reproduces the patient's symptom, pathologic medial subluxation probably is present. flexing the knee to see whether the medial patellofemoral ligament delivers the patella into the central trochlea by 20 to 30 degrees of knee flexion. A distinct pressure, pushing the examining finger back as the patella enters the trochlea, should be encountered using this technique.
If the patella remains lateralized with the examining finger holding it lateral as the knee is flexed to 20 to 30 degrees of flexion, the medial patellofemoral ligament is incompetent.10
Similarly, in a patient who has had previous extensor mechanism surgery, the examiner should hold the patella medially in extension and flex the knee abruptly to 30 to 40 degrees of flexion (FIG 4).
If the patella enters the trochlea very suddenly and reproduces the patient's symptom, he or she actually may have a medial instability problem (ie, medial subluxation) that requires repair or reconstruction of the lateral support structure or even lateralization of the tibial tubercle if it previously was over-medialized.
The patella is held in the central trochlea, and the knee is flexed with compression of the patella to see if this elicits crepitus or pain. The degree of flexion at which this crepitus or pain occurs is important in localizing the location of the lesion, bearing in mind that the articulation surface of the patella moves proximally as the knee is flexed. This compression of the patella in the trochlea should be repeated as the patient extends the knee actively against resistance of the other examining hand from full flexion up to full extension, taking note of where pain or crepitus occurs with active extension against resistance.
Every patient should be examined prone so that the hip can be rotated internally and externally to see if there is a source of pain within the hip. With the patient prone, the pelvis is flat, and, therefore, flexion of the knee may be completed to compare with the contralateral side to establish whether the quadriceps and extensor mechanism are overly tight. The patient should be taught at this time how to stretch the extensor mechanism.
Nonoperative treatment should be exhausted before considering surgical intervention.
IMAGING AND OTHER DIAGNOSTIC STUDIES
In diagnosis of the anterior knee, a standardized office radiograph with the knee flexed 45 degrees and standardized axial radiograph of the patellofemoral joint with the knee flexed exactly to 30 degrees is very important.15
By 45 degrees of knee flexion, the patella normally is centralized in the femoral trochlea. This is a good screening test in the office to determine whether there is significant imbalance of the extensor mechanism.
Radiographs taken in more than 45 degrees knee flexion are not particularly useful in most patients.
Our practice has not found 30-60-90–degree radiographs useful.
Many patients present for evaluation with axial radiographs taken only at 90 degrees of flexion. This probably is easier for radiology technicians, because they can simply hang the patient's legs over the side of an examining table and take the axial radiograph in this fashion. It is very important to standardize flexion to 45 degrees, using a support frame as needed.
The other important office radiograph is the true lateral view16 (FIG 5), which is taken with the knee at 30 degrees of flexion and standing. The posterior femoral condyle should be overlapped.
This view is technically demanding, but most radiology technicians with reasonable experience can palpate the posterior condyles, and with one or sometimes two tries, obtain a good lateral view with overlap (or near-complete overlap) of the posterior condyles.
This study shows the femoral trochlea completely, so that the central sulcus can be identified as well as both medial and lateral aspects of the trochlea from proximal to distal.
Other imaging studies include CT, MRI, and radionuclide scan. Relatively few patients require these studies.
If CT is done, it is best performed at 0, 15, 30, and 45 degrees of knee flexion, obtaining mid-patella transverse images to see how the patella enters the trochlea. This should be done with reproduction of normal standing alignment on the tomographic table.
MRI is less useful in many patients but can be helpful in evaluating articular cartilage and soft tissue structure, as well as gaining insight into subchondral bone reaction.
FIG 5 • The true lateral radiograph defines the osseous structure of the trochlea most accurately.
Radionuclide scanning is not often used but can be extremely helpful in determining subchondral bone reaction to overload.5 It may be most applicable in patients with trauma to the anterior knee, unexplained anterior knee pain, or chronic patella overload, and in cases involving workers' compensation litigation where objective findings beyond the normal studies needed to determine appropriate treatment are particularly important.
In some cases, a single photon emission computed tomographic (SPECT) scan also can be helpful in accurately locating a source of subchondral bone overload. SPECT may play a role, selectively, in patients who require a patella unloading or resurfacing procedure.
NONOPERATIVE MANAGEMENT
Before tibial tubercle transfer is considered, all patients must exhaust nonoperative management, including complete lower extremity core stability therapy, patellofemoral taping and bracing (I prefer the Tru-Pull brace that I helped design, DJ ORTHO, Vista, CA), and modification of activity.
Viscosupplementation may be helpful in some patients with patellofemoral arthritis but has not been very helpful in most cases?
SURGICAL MANAGEMENT
In patients with more severe extensor mechanism malalignment, instability, pain, and eventual articular cartilage breakdown are fairly common. When specific factors such as disruption of the MPFL cause instability, reconstruction of the deficient structure should be considered first.
In many patients with patella instability, restoration of medial support, either by imbrication (open or arthroscopic) or reconstruction of the medial patellofemoral ligament and release of tight lateral retinaculum, may be the procedure of choice. In general, this is the first line of surgical treatment after failed nonoperative measures in a patient with patella instability related to deficiency of medial support structure.
In patients with more severe dysplasia, a high TT-TG index (see Fig 1B), and degenerative change in the patella or trochlea, tibial tubercle transfer offers an opportunity to improve balance permanently and provide long-term relief of instability.
Tibial tubercle transfer in the treatment of patella instability is best used when the TT-TG index is high (>20 in most cases), the Q angle is high (usually >20 degrees) or the lateral trochlea is dysplastic, such that soft tissue reconstruction alone will either be less likely to succeed or require excessive tension resulting in overload of the medial patellofemoral joint.20
Anteriorization alone is best reserved for patients with patella arthritis alone without malalignment.
The primary concern with MPFL reconstruction in the face of more serious malalignment and patella instability is the need to “pull” the patella in a posteromedial direction to gain stability, thereby adding load to the patella that eventually might lead to patellofemoral joint degeneration. For this reason, the wise surgeon will recognize the inherent benefit of tibial tubercle transfer in selected patients with more severe patella instability to compensate for the malalignment problems leading to the instability in a way that limits or avoids point articular loading on the patella.6
Tibial tubercle transfer also provides immediate fixation and stability, making early ROM possible, further reducing the risk of stiffness, tightness, and chronic pain in the anterior knee following reconstructive surgery for instability.
In the treatment of patellofemoral arthritis, tibial tubercle transfer plays an important role in joint preservation.
Many patients have patellofemoral arthritis as a result of excessive lateral pressure, as originally described by Ficat.7 This excessive lateral pressure eventually causes erosion of the lateral patellofemoral joint, sometimes to bone, because of the constant lateralization of the patella related to lateral subluxation and high lateral pressure on the lateral patella facet. Lateral release has been used to reduce some of this pressure and is helpful in the early stages when patella tilt is prominent.
Tibial tubercle transfer is a powerful procedure for unloading and rebalancing the extensor mechanism, however, placing the patella into the center trochlea and maintaining it there through a range of motion.
By adding some anteriorization to a medial tibial tubercle transfer (ie, anteromedial tibial tubercle transfer) the distal articular surface of the patella also may be unloaded.19 This is important, because many patients with patellofemoral chondrosis or arthrosis have distal patella articular breakdown or pain. Anteriorization of the tibial tubercle unloads the distal articular surface of the patella permanently, and the medialization component of this procedure rebalances the patella in the central trochlea, unloading the lateral facet.
Most patients with chronic lateralization of the extensor mechanism develop lateral facet breakdown and distal patella degeneration over time because of the abnormal shear stress and lateral overload. Anteromedial tibial tubercle transfer compensates for this and is, therefore, the procedure of choice for treating articular degeneration and pain emanating from the distal or lateral patella articular surface.
Anterolateral tibial tubercle transfer9 may be best regarded as a salvage procedure in patients who have had previous overmedialization of the tibial tubercle. It has been helpful in relieving pain related to chronic medial patellofemoral arthritis resulting from a previous Hauser procedure in which the tibial tubercle was moved posteriorly, medially, and distally to stabilize the extensor mechanism at an earlier time.
TECHNIQUES
MEDIAL TIBIAL TUBERCLE TRANSFER
Incision and Dissection
Medial tibial tubercle transfer is best approached through a midline incision from the mid patella to a region approximately 5 to 7 cm distal to the tibial tubercle.3
The medial and lateral borders of the patella tendon are identified, the anterior tibialis muscle is reflected posteriorly and retracted, the skin edges are retracted, and a cut is made deep to the tibial tubercle.
Osteotomy
A flat incision is made posterior to the tibial tubercle, tapered anteriorly at its distal extent such that only about 1 mm of bone is left at the distal tip of the osteotomy and the proximal cut is made about 2 mm above the patellar tendon insertion.
This cut should be made perpendicular to the anterior surface of the tibia such that a flat ledge is left to add additional stability to the transferred tibial tubercle. This proximal cut must be made in such a way that the tibial tubercle may be freely moved medially, ie, so that the medial side of the proximal cut is more proximal than the lateral side of the proximal cut, open medially.
The thickness of the cut deep to the tibial tubercle will vary depending on the individual patient's need for medialization.
In patients with a severe dysplasia requiring more than 1 cm of medialization, a deeper cut will be required.
In patients requiring 1 cm of medialization, a proximal tibial tubercle thickness of 1 to 1.5 cm is ample in most cases.
Care must be taken to taper this osteotomy anteriorly at the distal extent of the cut to allow for easy greenstick fracturing of the tip of the osteotomy to move the tubercle medially.
Completion of the Transfer
After the osteotomy has been completed with an oscillating saw, the proximal cut usually is made with a ½-inch osteotome.
The osteotomized fragment is elevated and then displaced medially. If there is an overhang of bone medially, it can be removed with the saw or a rongeur.
The fragment is then stabilized securely with two cortical lag screws (TECH FIG 1), carefully measuring the depth of the drill hole, overdrilling the proximal fragment, and lagging the fragment down using the posterior cortex to hold the cortical screw.
Care must be taken not to allow the cortical screw tip to protrude any more than necessary beyond the posterior cortex.
TECH FIG 1 • Correction of abnormal TT-TG relationship by medialization of tibial tubercle.
The surgeon releases the lateral retinaculum either arthroscopically or by open surgery to achieve the needed balance of the extensor mechanism upon tibial tubercle transfer.
Some thickening and even mild infrapatellar contracture may be observed in patients who have had longstanding and more severe imbalance of the extensor mechanism. This also should be released at the time of surgery.
Tracking of the patella within the central trochlea should be confirmed arthroscopically or openly after the tibial tubercle transfer.
ANTEROMEDIAL TIBIAL TUBERCLE TRANSFER
Incision and Dissection
To unload both the distal and lateral aspects of the patella, an oblique osteotomy must be created deep to the tibial tubercle, and the tibial tubercle transferred in both anterior and medial directions.8,12
To perform anteromedial tibial tubercle transfer, a longitudinal incision close to midline, extending from a region about halfway between the patella and the tibial tubercle to about 7 cm distal to the tibial tubercle usually is sufficient.
After isolating the patellar tendon, the anterior tibialis muscle is released and reflected posteriorly.
Because an oblique osteotomy will be made from medial to lateral, a large retractor must be placed to retract the anterior tibialis muscle laterally to view the saw making the osteotomy cut as it exits on the posterolateral aspect of the tibia. The entire lateral side of the tibia must be under direct view11 (TECH FIG 2).
Osteotomy
At this point, it usually is best to use a guide, such as the Tracker guide (Mitek, Norwood, MA), to ensure an accurate osteotomy cut. With experience, some surgeons can make this cut without a guide, but only a surgeon who is doing this type of surgery on a regular basis will feel comfortable without guide control.
TECH FIG 2 • Retraction of the tibialis anterior gives a full view of the entire lateral proximal tibia.
TECH FIG 3 • A. Displacement of the tibial tubercle transfer showing planes for cuts. B. For anteromedial tibial tubercle transfer, the cut proceeds obliquely from medial to lateral, tapering toward the anterior crest distally. After transferring the tibial tubercle along the osteotomy (C), both anteriorization and medialization of the tibial tubercle are achieved (D).
An external fixator block also may be used to create an appropriate orientation for the osteotomy (TECH FIG 3A). A drill bit is left at the top and bottom of the osteotomy.
The osteotomy usually extends from the level of the tibial tubercle to a level of about 7 to 9 cm distally on the tibia and again must exit at the level of the anterior cortex of the tibia to avoid a large fragment distally.
Making a deep cut distally increases the risk of tibia fracture; this should be avoided.
After the guide is placed at the desired angle to create an oblique osteotomy from medial to lateral, a cut is made from the region immediately adjacent to the patella tendon insertion medially and angled posterolaterally so that the saw blade will exit on the lateral cortex (TECH FIG 3B).
This strategy avoids injury to the anterior tibial artery and deep peroneal nerve, which are around the posterolateral corner of the tibia posteriorly.
The cut should start distally first where it is most visible, and as the oblique cut proceeds proximally, it will become more posterior.
Once the proximal extent of the cut has reached the level of the mid to posterior portion of the lateral tibia cortex, it should be stopped at the lateral side. An osteotome or saw then is used to make a back cut from the corner of the proximal lateral corner of the osteotomy up to a point proximal to the patellar tendon laterally.
This allows for release of the lateral cortex when the osteotomy has been completed, and the osteotomized fragment will be displaced anteromedially.
The third cut for anteromedial tibial tubercle transfer is directly proximal to the patellar tendon insertion on the tibia, about 2 mm above the patellar tendon insertion.
This cut usually is made with a ¼- or ½-inch osteotome under direct vision using an Army-Navy retractor to hold the patellar tendon anteriorly.
It is best made from medial to lateral and connects the proximal extent of the medial osteotomy cut to the oblique back cut on the lateral side so that the osteotomy is now free to displace anteromedially.
It is moved anteromedially by greenstick fracturing the anterior cortex distally, which should be no more than 1 to 2 mm thick at its distal extent.
The osteotomized fragment is moved about 1 cm but may be moved slightly more, as needed, to achieve more anteriorization or medialization.
The obliquity of this osteotomy will be determined by how much anteriorization and how much medialization the surgeon wants (TECH FIG 3C,D).
When there is a greater need for realignment of the extensor mechanism, the cut should be made flatter, so that more medialization can be achieved.
When it is more urgent to unload a damaged or painful distal patella, the cut should be made more oblique (steeper), allowing more anteriorization.
Thus, this osteotomy is customized for each patient, depending on the specific need.
Completion of the Transfer
The osteotomized fragment is fixed securely with two cortical lag screws.
These screws must be carefully positioned to ensure that they remain within the cortex and that they have good cortical bone purchase on both sides.
If the most proximal cut has been made carefully, there will be a ledge of bone on which the osteotomized fragment will rest, which will add stability to the osteotomy beyond what the screws offer.
Lateral release is accomplished as needed to free the patella. In patients with any retropatellar tendon contracture, this tendon also is released to free up the extensor mechanism.
After tibial tubercle transfer, hemostasis must be meticulous, and then the subcutaneous tissue and skin are closed. We prefer skin sutures or skin clips rather than subcuticular sutures.
ANTEROLATERAL TIBIAL TUBERCLE TRANSFER
In the very small number of patients who have had previous overmedialization of the tibial tubercle, an osteotomy cut deep to the previously transferred tibial tubercle may be made in a slightly oblique lateral-to medial direction, and the tibial tubercle transferred anterolaterally.
Fixation and rehabilitation are similar to anteromedial tibial tubercle transfer.
POSTOPERATIVE CARE
Following tibial tubercle transfer, immediate ROM is important.
If stability is secure, patients are started immediately on ROM exercises.
These may start with a single cycle of flexion a day if proximal reconstruction has been done and there is concern about stretching out a proximal repair.
In such cases, a short period of immobilization in extension may be appropriate for soft tissue healing, but a single cycle of knee flexion daily after the first 10 to 12 days is important to ensure full ROM later and maximal ROM ultimately.
Patients are kept on crutches for 6 to 8 weeks and resume weight bearing as tolerated after 6 weeks.
During the initial 6 weeks, we recommend toe-touch or light weight bearing on the affected side.
We recommend anticoagulation with aspirin for at least 4 to 6 weeks for most patients.
Most of our patients go home from same-day surgery and are seen in 1 to 3 days as needed and then for suture removal and radiographs at 10 to 12 days.
Steri-strips are applied and kept in place for 4 to 6 weeks to minimize wound spread.
COMPLICATIONS
The primary concerns following tibial tubercle transfer are fracture of the tibia,22 stiffness, thrombophlebitis, nonunion, infection, and hematoma.
These complications usually can be avoided with proper care.
Gross obesity increases the risk of complications.
OUTCOMES
Buuck2 reviewed the results of anteromedial tibial tubercle transfer in patients 4 to 12 years following the procedure and demonstrated that good results are maintained over time.
Our follow-up studies have consistently revealed a satisfactory outcome in 85% to 90% of patients. Pidoriano et al17 demonstrated that results are closely related to the location of articular lesions. Patients with lateral and distal patellar lesions are more likely to experience relief than patients with proximal (dashboard) or medial (s/p dislocation) lesions.
REFERENCES
1. Amis AA, Firer P, Mountney J, et al. Anatomy and biomechanics of the medial patellofemoral ligament. Knee 2003;10:215–220.
2. Buuck DA, Fulkerson JP. Anteromedialization of the tibial tubercle: a 4to 12year follow-up. Oper Tech Sports Med 2000;8:131–137.
3. Cox JS. Evaluation of the Roux-Elmslie-Trillat procedure for knee extensor realignment. Am J Sports Med 1982;10:303–310.
4. Dejour H, Walch G, Nove-Josserand L, et al. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc 1994;2:19–26.
5. Dye SF, Chew MH. The use of scintigraphy to detect increased osseous metabolic activity about the knee. J Bone Joint Surg Am 1993; 75A:1388–1406.
6. Farr J. Anteromedialization of the tibial tubercle for treatment of patellofemoral malpositioning and concomitant isolated patellofemoral arthrosis. Tech Orthop 1997;12:151–164.
7. Ficat P. The syndrome of lateral hyperpressure of the patella (translated from French). Acta Orthopaedica Belgica 1978;44(1):65–76.
8. Fulkerson JP. Anteromedialization of the tibial tuberosity for patellofemoral malalignment. Clin Orthop Rel Res 1983;177: 176–181.
9. Fulkerson JP. Anterolateralization of the tibial tubercle. Tech Orthop 1997;12:165–169.
10. Fulkerson JP. A clinical test for medial patella tracking. Tech Orthop 1997;12:144.
11. Fulkerson JP. Disorders of the Patellofemoral Joint. Philadelphia: Lippincott Williams & Wilkins, 2005.
12. Fulkerson JP, Becker GJ, Meaney JA, et al. Anteromedial tibial tubercle transfer without bone graft. Am J Sports Med 1990;18:490–497.
13. Fulkerson JP, Tennant R, Jaivin JS, et al. Histologic evidence of retinacular nerve injury associated with patellofemoral malalignment. Clin Orthop Rel Res 1985;197:196–205.
14. Hallisey MJ, Doherty N, Bennett WF, et al. Anatomy of the junction of the vastus lateralis tendon and the patella. J Bone Joint Surg Am 1987;69A:545–549.
15. Merchant AC, Mercer RL, Jacobsen RH, et al. Radiographic analysis of patellofemoral congruence. J Bone Joint Surg Am 1974;56A: 1391–1396.
16. Murray TF, Dupont J-Y, Fulkerson JP. Axial and lateral radiographs in evaluating patellofemoral malalignment. Am J Sports Med 1999; 27:580–584.
17. Pidoriano AJ, Weinstein RN, Buuck DA, et al. Correlation of patellar articular lesions and results from anteromedial tibial tubercle transfer. Am J Sports Med 1997;25:533–537.
18. Post WR. Clinical evaluation of patients with patellofemoral disorders [current concepts]. Arthroscopy 1999;15:841–851.
19. Saleh KJ, Arendt EA, Eldridge J, et al. Operative treatment of patellofemoral arthritis. J Bone Joint Surg Am 2005;87A:659–671.
20. Schepsis AA, DeSimone AA, Leach RE. Anterior tibial tubercle transposition for patellofemoral arthrosis: a long-term study. Am J Knee Surg 1994;7:13–20.
21. Schutzer SF, Ramsby GR, Fulkerson JP. Computed tomographic classification of patellofemoral pain patients. Orthop Clin North Am 1986;17:235–248.
22. Stetson WB, Friedman MJ, Fulkerson JP, et al. Fracture of the proximal tibia with immediate weightbearing after a Fulkerson osteotomy. Am J Sports Med 1997;25:570–574.