Tibial Tuberosity Anteromedialization Osteotomy
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Tibial Tuberosity Anteromedialization Osteotomy
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.
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
Recurrent lateral patellar dislocations (medial patellofemoral ligament reconstruction indicated in all surgical candidates with recurrent patellar dislocations)
Tibial tuberosity-trochlear groove distance >20 mm
Advanced patellofemoral osteoarthritis
Knee pain or instability that does not have a rational biomechanical or articular cartilage basis
Localized or systemic inflammatory disease
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.
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)
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