Biomechanics have demonstrated that trochlear dysplasia significantly affects the kinematics of the patellofemoral (PF) joint and negatively influences the stabilizing forces of the patella.1,2
For patients with high-grade trochlear dysplasia and patellar instability, trochleoplasty is a well-established procedure aiming to restore normal trochlear anatomy.
Though more than 20 trochleoplasty series have been reported, no randomized studies have demonstrated superiority of trochleoplasty when compared to other patellar stabilizing procedures. Meta-analysis has been faced with many confounding factors such as selection bias, heterogeneity of the groups, sample size, short follow-up, and use of different outcome scores.
Arthroscopic trochleoplasty (AT)3,4,5 is one of the several described trochleoplasty techniques. It is based on the principle of Bereiter technique, characterized by a thin osteochondral flap.6,7,8
The evolution of AT can be compared to anterior cruciate ligament (ACL) reconstructions, which were historically done by an open approach. Because arthroscopically aided ACL reconstructions have been widely accepted, the same could be applicable to AT.
TABLE 22.1 Indications and Contraindications for Arthroscopic Trochleoplasty
Two or more patellar dislocations with a persistent apprehension sign from 0° to 60° of flexion
High-grade (B-D) trochlear dysplasia as evaluated by axial magnetic resonance imaging scans
Generalized patellofemoral arthritis
Large cartilage defect in the trochlea International Cartilage Repair Society grade 3 or 4 (relative contraindication)
Open growth plates (relative contraindication). If the growing potential is nearing its end, that is, patients are close to the height of the parents and if the girls have had menstruation for more than a year, arthroscopic trochleoplasty can be done.
Open trochleoplasty procedures have been associated with the risk of arthrofibrosis, infection, prolonged pain, and scar formation.9 These complications have yet not been reported using the AT technique.
The first series of AT in combination with medial patellofemoral ligament (MPFL) reconstruction demonstrated results comparable to other trochleoplasty procedures with MPFL reconstruction.10
The AT procedure is considered highly demanding and is not used widely.
The AT technique is typically combined with MPFL reconstruction and lateral release or lateral lengthening. This chapter focuses on the trochleoplasty technique.
The goal of the AT procedure is similar to other deepening trochleoplasty procedures, in that to unload the compressive forces in the PF joint and to provide osseous stability to the patella by reshaping the trochlea. Ideally, the trochlea should be made approximately 4.5 mm deep. The new trochlear groove should be lateralized to achieve trochlear facet ratio of 1:2 (medial to lateral facet).11 By lateralizing the groove, the tibial tuberosity-trochlear groove (TT-TG) distance can be reduced by several millimeters.12
Table 22.1 lists indications and contraindications for AT with MPFL reconstruction.
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.
Physical examination prior to surgery should demonstrate patellar apprehension with lateral patellar translation near full knee extension. Apprehension generally resolves as the knee is flexed and the patella enters the trochlear groove, which provides osseous stability. Apprehension that persists beyond 30° and especially 60° of knee flexion indicates the presence of significant trochlear dysplasia or patella alta or both and should be evaluated for possible trochleoplasty.
The author’s preferred parameter for evaluation of the degree of trochlear dysplasia has been the lateral trochlear inclination (LTI) angle and the trochlear facet asymmetry.13 LTI lower than 8° and trochlear facet asymmetry less than 0.40 (<2:5, medial to lateral facet) indicate trochlear dysplasia and need for trochleoplasty.
Part of the trochlear dysplasia is the medialized groove, so it is important to approximate the required lateralization of the groove in order to normalize the increased TT-TG distance as measured preoperatively.
It is recommended to have a unique tailored preoperative plan based on the pathomorphologic findings on the magnetic resonance imaging (MRI) for each individual. A trochlear depth of 4.5 mm is sought, taking into account the size of the involved knee.
The patient is placed in a supine position on the operating table.
A tourniquet around the thigh can help in visualization if there is bleeding but is not needed routinely. Instead, arthroscopic fluid pressure is increased to optimize visualization.
One dose of intravenous antibiotics is given pre- and postoperatively.
Antithrombotic prophylactic treatment is considered in patients above the age of 40 years or in cases with a history of thrombotic complications.
A standard knee arthroscopy is done through anteromedial and anterolateral portals, and the menisci and the cruciate ligaments are assessed. The trochlear configuration and cartilage is evaluated to confirm the MRI findings.
A superior medial portal used as a viewing portal is first established. A spinal needle is inserted just medial to the quadriceps tendon toward the suprapatellar pouch. This is followed by a switching stick and then an arthroscope. A superior position gives an optimal view of both the trochlea and the patella (Figure 22.1).
A 45° arthroscope is preferred, but a 30° scope can be used as well.
The superior lateral working portal is next established.
With the scope in the superior medial portal, the position for the lateral suprapatellar (superior lateral) portal is localized by the needle technique. Correct placement of this portal is vital. The correct location is parallel to the proximal extent of the flat part of the trochlear groove in both the frontal and transverse planes. This would allow an appropriate working angle for the instruments. A portal that is too distal or too posterior can be detrimental. Similarly, a portal that is too proximal would be detrimental because the distance will be too long for instruments to reach, especially toward the end of the procedure when the chondral flap is raised. A 6-mm PassPort Button Cannula (Arthrex Inc, Naples, Florida) is useful in the working portal.
Using a 90° radiofrequency device through the superior lateral portal, the synovium/periosteum is released from the area proximal to the trochlear cartilage.
The release is continued as proximal as necessary (about 10 mm) to expose cortical bone for the placement of the proximal anchors at the end of the procedure.
Once the bone is cleared, a 3- or 4-mm round burr is used to shave the bone proximal and posterior to the trochlear cartilage (Figure 22.2).
Care should be taken at the beginning, until the cleavage between the bone and the cartilage is identified. The release of the cartilage flap is continued by moving the burr in a medial to lateral direction and vice versa. Slowly, the progression of the burr continues further distally beneath the cartilage.
Figure 22.2 Left knee viewing from the superior medial portal. The burr is from the superior lateral portal. A thin chondral flap is raised from proximal to distal.
As a supplement to the burr, a straight and curved lambotte osteotome (6 mm × 27 cm) should be used, similar to open surgery. By adding the osteotome, the bone resection at the most lateral part of the trochlea is minimized, helping to achieve a normal lateral trochlear wall and thereby achieving a more anatomic LTI angle.
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