Tibial Tuberosity Anteromedialization Osteotomy
William R. Beach
INTRODUCTION
John Fulkerson, MD, described the anteromedialization (AMZ) of the tibial tuberosity in 1983.1 His landmark work blended two well-known procedures that had been previously described for the treatment of patellofemoral disorders: Elmslie-Trillat2 and Maquet3,4 osteotomies.
The AMZ is indicated when the primary problem is an abnormality of the alignment vector.
The procedure is, therefore, valuable in the treatment of selected patients with patellar instability when there is an associated increased tibial tuberosity-trochlear groove (TT-TG) distance.5 A newer measurement to estimate the tibial tuberosity position has been the tibial tuberosity-posterior cruciate ligament (TT-PCL) distance.6
The AMZ procedure is also useful in selected patients with patellofemoral arthrosis or chondral defects preferably of the distal/lateral patella.1
Surgical considerations, complications, and outcomes of tibial tuberosity osteotomy are discussed in Chapter 14. The following chapter would discuss the surgical technique of tibial tuberosity AMZ osteotomy.
Table 15.1 lists the indications and contraindications for tibial tuberosity osteotomy.7
EVALUATION
Patient History
Patients present with a history of recurrent lateral patellar dislocation or a single patellar dislocation with subsequent episodes of lateral subluxation and feelings of instability.
Patients may have pain related to isolated distal, lateral patellar chondrosis with lateral subluxation, and/or tilt.
Physical Examination and Findings
Physical examination prior to surgery should demonstrate patellar apprehension with lateral patellar translation near full knee extension.
The patient would have an increased quadriceps angle (Q-angle), although Q-angle is not a very reliable indicator for lateralized tibial tuberosity.
The tightness of the lateral retinaculum should be assessed by evaluation of medial patellar translation and the degree to which the patella can be everted.
Standing alignment and rotational profile should be evaluated to rule out significant valgus, femoral anteversion, or tibial torsion, which may manifest as a lateralized tibial tuberosity.
Imaging
Plain radiographs should be obtained in all patients and include a true lateral view of the knee in 20° to 30° of flexion to assess trochlear dysplasia and patellar height via the calculation of the Caton-Deschamps index or Insall-Salvati ratio.
An axial view near full knee extension can provide insight into patella tilt or subluxation. Axial views in high degrees of knee flexion are useful to assess for the presence of patellofemoral osteoarthritis.
Anteroposterior and notch view of the knee can help in assessment of tibiofemoral joint narrowing.
Full-length lower extremity films are useful for assessment of overall alignment and should be obtained in those patients in whom significant varus or valgus is suspected on the basis of the physical examination.
Cross-sectional imaging (computed tomography or magnetic resonance imaging [MRI]) is useful to further assess trochlear anatomy (sulcus angle and the presence and location of a supratrochlear bump or spur) and allow for measurement of the TT-TG and/or TT-PCL distance.
TABLE 15.1 Indications and Contraindications for Tibial Tuberosity Osteotomy | ||||
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MRI also allows for evaluation of the articular cartilage surfaces.
DIFFERENTIAL DIAGNOSIS
In patients with increased TT-TG/TT-PCL distance, coronal plane and rotational plane assessment should be performed to identify other related causes for its increase. Though tibial tuberosity osteotomy can compensate for lesser degrees of lower limb malalignment, it would not suffice in the presence of significant malalignment.
SURGICAL MANAGEMENT
Preoperative Planning
The amount of medialization and/or anteriorization required during surgical correction would be based on medial/lateral position of the tuberosity (TT-TG/TT-PCL distance), proximal/distal position of the patella (patellar height measurements), and patellofemoral chondral lesions.
Normal TT-TG distance is around 15 mm, and TT-TG distance more than 20 mm is considered pathologic.5 Typical correction done during AMZ is around 10 mm.
Normal TT-PCL distance is around 18 mm, and more than 24 mm is considered pathologic.6
In the presence of patella alta, simultaneous distalization of tibial tuberosity should be considered (Chapter 16).
The slope of AMZ osteotomy allows for varied degrees of medialization and anteriorization. A slope of 45° would provide similar amount of medialization and anteriorization. For example, 10 mm of medialization and 45° slope would lead to 10 mm of anteriorization.
When AMZ is performed for patellar instability, MPFL reconstruction should be performed concomitantly.
When AMZ is performed for lateral/distal patellar chondral lesions, lateral retinacular release or lengthening should be strongly considered.
Patients should be counseled against nicotine/smoking before surgery.
SURGICAL TECHNIQUE (Video 15.1 
)
)Incision and Approach
The patient is placed supine on an operating table. Tourniquet is applied over the proximal aspect of thigh. The knee should be positioned such that lateral fluoroscopy of the knee could be performed.
The tibial tuberosity is identified, and a longitudinal incision measuring approximately 5 cm is made over the central portion of the tuberosity (Figure 15.1). Because the tuberosity will be transferred medially, the incision will no longer be over the bony prominence.
The patellar tendon can be exposed by splitting the paratenon (Figure 15.2). There is likely significant benefit by not interrupting the paratenon in the center, and the tendon can be exposed and mobilized by splitting the paratenon on each side of the tendon. This may avoid any scarring that might potentially occur.
The tibial tuberosity is exposed for 4 to 5 cm, but the skin is relatively mobile, so a smaller incision is possible.
Because the osteotomy must include the tibia above the tuberosity, the paratenon is slit longitudinally on either side of patellar tendon. The tendon insertion onto the tibial tuberosity is visualized (Figure 15.3).
The exposure is carried distally from the lateral edge of the patellar tendon, down onto the tibia (Figure 15.4). The anterolateral calf musculature is elevated from the lateral wall of the tibia, beginning distal to Gerdy’s tuberosity for 5 to 6 cm.
The release is extended proximally along the flare of the tibia. This would allow for exposure of the entire anterolateral tibia for the safe placement of the drill bits and creation of the osteotomy.
 Figure 15.1 The tibial tuberosity is identified, and an incision is made over the central portion of the tuberosity. The right knee is demonstrated. |
 Figure 15.2 The patellar tendon can be exposed by splitting the paratenon. |
 Figure 15.3 An incision on each side of the patellar tendon would maintain the paratenon over the tendon and avoid any scarring that might potentially occur. The insertion of patellar tendon onto the tibial tuberosity is identified. |
Osteotomy
The next step is really the key to the correction of the pathology.
The angle of the impending osteotomy is determined by several factors including the preoperative assessment of patellar tracking, the TT-TG distance, the condition of the patellar and trochlear articular cartilage, and the patellar height (alta vs baja).
The advantage of the tibial tubercle osteotomy is that the osteotomy can be tailored to each individual patient. For laterally based articular cartilage disorders, a steeper inclination of the osteotomy is selected, and for patellar instability with a large TT-TG distance, a flatter osteotomy is performed. The angle of the drill bit is very flat for patellar instability with an increased TT-TG distance (Figure 15.5A).Related posts:
Surgical Considerations During Patellar Stabilization
Quadricepsplasty Techniques for Patellar Stabilization
Lateral Retinacular Release and Lengthening
Chondral Lesions and Patellar Instability
Proximal Femur Rotational Osteotomy
Failed Medial Patellofemoral Ligament Reconstruction: Causes and Treatment
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