Sulcus Deepening Trochleoplasty

Sulcus Deepening Trochleoplasty

Paulo R.F. Saggin, Paolo Ferrua and David Dejour

Chapter Synopsis

• Deepening trochleoplasty is a procedure designed to correct high-grade trochlear dysplasia, which is one of the most important factors involved in the genesis of patellar instability. Trochlear correction improves patellar tracking, reduces the patellofemoral joint reaction force, and decreases the tibial tubercle–trochlear groove (TT-TG) value. It must be considered in patients undergoing surgery for patellar instability.

Important Points

• Indications

– Severe trochlear dysplasia (types B and D) with patellar dislocations

• Contraindications

– Mild trochlear dysplasia

– Open growth plates

– Early arthritis

• Trochlear dysplasia classification

– Type A: Presence of crossing sign. The trochlea is still symmetric and concave.

– Type B: Crossing sign and trochlear spur. The trochlea is flat or convex.

– Type C: Crossing sign in addition to the double-contour sign. There is no spur; the lateral facet is convex and the medial facet is hypoplastic.

– Type D: Combines all the mentioned signs: crossing sign, supratrochlear spur, and double-contour sign. Cliff pattern.

– Types B and D have prominence of the trochlea and increased patellofemoral reaction forces.

Clinical and Surgical Pearls

• Positioning must allow full range of motion during procedure.

• Midline incision with adapted midvastus approach.

• Adequate exposure and access to the undersurface of the trochlea.

• Intraoperative new trochlea planning.

• Adequate bone removal and achievement of a malleable osteochondral flap.

• Correction of associated abnormalities.

• Early rehabilitation.

Clinical and Surgical Pitfalls

• Avoid cartilage damage during the osteochondral flap confection—keep a safe distance from the cartilage.

• Achieve a well-molded bone bed; otherwise the new trochlea will not be adequately refashioned.

• Avoid prolonged immobilization (sometimes required for the associated procedures).

• Be alert for the indication; pain is not an indication.

Trochlear dysplasia is one of the major factors causing patellar dislocations (together with patella alta, excessive tibial tubercle–trochlear groove distance, and excessive patellar tilt). This anatomic abnormality is present in 96% of patients with patellar dislocations.¹ Trochlear osteotomy or trochleoplasty is the procedure designed to correct the abnormal shape of the trochlea, improving patellar tracking and preventing instability. It is a logical procedure from the biomechanical point of view. Despite being technically demanding, it yields good results, and therefore it should be known to surgeons dealing with the patellar dislocation population. Trochleoplasty should be combined with other procedures to treat the other major causes of instability and is rarely performed alone.

Preoperative Considerations

Trochleoplasty is indicated in patients with high grade trochlear dysplasia and patellar instability, and particularly when abnormal tracking of the patella is observed during active and passive motion of the knee. As with any surgery performed in this group of patients, it is indicated after the second or third documented dislocation. The dislocation is usually confirmed if the patient has had the patella reduced by a physician, if radiographs obtained on the occasion of the trauma evidence a medial patellar bone avulsion, or if magnetic resonance imaging (MRI) confirms the medial soft tissue rupture and the associated medial patellar and lateral femoral condyle bruises. At times the history is not so clear, but the patient usually recalls the sensation of instability followed by pain, edema, and ecchymosis.

Imaging is essential to understand trochlear dysplasia and to allow its classification. Whereas normal trochleae have sulci of adequate depth, dysplastic trochleae are shallow, flat, or even convex. On lateral x-ray projections, this is represented by the crossing sign—the groove line reaches (or crosses) the line representing the superior edge of the facets. Two other features are typical of dysplastic trochleae on lateral views: the supratrochlear spur and the double contour sign. The supratrochlear spur is the same sometimes visualized in the surgical exposure, located in the superolateral aspect of the trochlea. It corresponds to an attempt to contain the lateral displacement of the patella. The double contour represents the medial hypoplastic facet, seen posterior to the lateral one in the lateral view. Based on these signs, and sometimes aided by computed tomography (CT) axial views, trochlear dysplasia may be classified into four types ²:

• Type A: Presence of crossing sign in the lateral true view. The trochlea is shallower than normal ones, but still symmetric and concave.

• Type B: Crossing sign and trochlear spur. The trochlea is flat or convex in axial images.

• Type C: Presence of crossing sign, and in addition the double-contour sign can be found on the lateral view, representing the medial hypoplastic facet. There is no spur. In axial views, the lateral facet is convex and the medial hypoplastic.

• Type D: Combines all the mentioned signs: crossing sign, supratrochlear spur, and double-contour sign. In the axial view, there is clear asymmetry of the facets’ height, also referred to as a cliff pattern (Fig. 89-1).

Figure 89-1 Trochlear dysplasia classification according to Dejour.

Trochleoplasty is indicated in dysplasia types B and D, when there is prominence of the trochlea. Type A is low-grade trochlear dysplasia and should not be responsible for instability, if present. Type C represents a subtype of trochlear dysplasia not suited for sulcus-deepening trochleoplasty because the trochlea is already hypoplastic and should not benefit from bone removal.

Open growth plates are a contraindication to trochleoplasty. Pain is not specifically addressed by this procedure and should not be the only element taken into account when the procedure is indicated. It should be remembered that this procedure is indicated for instability. Early (or established) arthritis is another contraindication because trochleoplasty can worsen the cartilage status.

To achieve successful outcomes, associated abnormalities should be addressed in the same procedure. The TT-TG value is addressed when trochleoplasty is carried out, because the proximal part of it (the trochlear groove) is moved laterally from its native location. The other major factors involved in patellar instability should also be evaluated and treated, so plain radiographs (anteroposterior view, true lateral view, and axial view at 30 degrees of knee flexion) and CT scan with the Lyon protocol must be routine in the preoperative evaluation ¹ (Table 89-1).

TABLE 89-1

Computed Tomography (CT) with Lyon Protocol

SD, standard deviation; TT-TG, tibial tubercle–trochlear groove distance.

Surgical Technique

Anesthesia and Positioning

After regional anesthesia and sedation, the patient is positioned lying supine. A lateral pad is applied to the proximal thigh, and a distal support under the foot allows the knee to be kept flexed by approximately 80 degrees. Full range of motion is possible during the procedure. A tourniquet is applied to the proximal thigh.

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