Open Proximal Trochleoplasty (Grooveplasty)

Betina B. Hinckel

Andreas H. Gomoll

Elizabeth A. Arendt

INTRODUCTION

Pathogenesis

Lateral patellar dislocation is an important cause of knee injuries with associated hemarthrosis, especially in young patients.¹
Trochlea dysplasia is present in 68.3% to 99.3%²,³,⁴,⁵ of patients with patellar instability and is the most significant risk factor for both primary and recurrent patellar instabilities.
Different procedures have been described to address the anatomic abnormalities of dysplasia, such as the flat or convexity of the proximal/mid aspects of the trochlear groove.
Trochleoplasty, a surgical procedure that reshapes the femoral groove, has gained popularity, with the deepening trochleoplasty being the most common. Several studies have demonstrated its effectiveness in restoring patellar instability.⁶,⁷,⁸ Concerns remain, however, especially regarding its invasiveness, steep learning curve, and potential for the development of osteoarthritis in the long term.
An alternative technique for reshaping the proximal trochlear groove has been described in 1988 by Peterson et al⁹ with the potential to address some of the concerns with deepening trochleoplasty.
Peterson et al later termed this a “proximal trochleoplasty” (grooveplasty), the purpose of which was to reconstruct a “close to normal trochlear groove and to subsequently stabilize the patella during the first 30° of knee flexion … [with an aim] to avoid and/or minimize interfering with the patella-trochlea congruity.”¹⁰
This procedure removes the proximal trochlear convexity in patients with severe trochlear dysplasia without modifying the distal aspects of the groove.

Classification

The most widely used classification of trochlear dysplasia is the four-part modified Dejour classification¹¹ (Figure 23.1).
Intra- and interobserver reliability for the four-grade analysis is fair; however, when evaluating reliability of distinguishing two grades (low-grade trochlear dysplasia [type A] from high-grade trochlear dysplasia [types B, C, and D]), the reliability is good.¹²
For decision making, the most important factor is the recognition of the bump (also known as supratrochlear spur, spur, or trochlear prominence).
The bump is an anterior prominence of the proximal trochlea, which can be convex or flat rather than concave. It is best observed on the lateral radiographs, with additional information provided by axial and sagittal slice imaging (computed tomography or magnetic resonance imaging [MRI]).
On lateral radiographs, it is a bony prominence characterized by a trochlear floor that is anterior to the anterior femoral cortex line. In control patients without trochlear dysplasia, the trochlear floor is in line with or posterior to the anterior femoral cortical line⁴ (Figure 23.2).
On the MRI, the sagittal slice with the deepest point of the trochlea is used. Simultaneous views of the axial and sagittal planes can be helpful to identify that slice. The cartilaginous bump is measured as the distance between a line parallel to the anterior femoral cortical line and the most anterior cartilaginous point of the trochlea (Figure 23.3). The range in control patients without trochlear dysplasia is between 0 and 10.5 mm, and greater than 8 mm is considered abnormal.¹³
The “cliff” pattern can be seen in the axial slice on type D of modified Dejour classification (Figure 23.4).
Table 23.1 shows indications and contraindications for open proximal trochleoplasty.

Figure 23.1 Dejour classification. Type A: Crossing sign (1), trochlear morphology preserved (shallow trochlea > 145°). Type B: Crossing sign, bump (2), flat or convex trochlea. Type C: Crossing sign, double contour (3, projection on the lateral view of the hypoplastic medial trochlear facet). Type D: Crossing sign, bump (2), double contour (3), cliff sign (4), vertical noncartilaginous link between cartilage of the medial and lateral trochlear facets). Copyright © Regents of the University of Minnesota. All rights reserved.

Figure 23.2 A, Lateral radiograph of the right knee showing the trochlear floor (arrows) and anterior femoral cortical line in a patient without trochlear dysplasia. B, Lateral radiograph of the right knee showing the trochlea floor (arrows) and anterior femoral cortical line in a patient with severe trochlear dysplasia and a bump. Courtesy of Betina B. Hinckel, MD.

Figure 23.3 A, Magnetic resonance imaging (MRI) sagittal slice image in the center of the trochlea (note the cruciates) showing the bony trochlear floor in line with the anterior femoral cortical line and the cartilage trochlear floor just anterior to this line, in a patient without trochlear dysplasia. B, MRI sagittal slice image with the deepest point of the trochlea (per axial view, not shown) demonstrating the bone and cartilage trochlear floor significantly anterior to the anterior femoral cortex, in a patient with severe trochlear dysplasia and a bump. Courtesy of Betina B. Hinckel, MD.

Figure 23.4 Axial magnetic resonance imaging in which there is cartilage coverage up to the cliff sign, with lateral widening because of the elevation of the central groove, and hypoplastic medial trochlear facet. Courtesy of Betina B. Hinckel, MD.

TABLE 23.1 Indications and Contraindications for Open Proximal Trochleoplasty

Indications

Contraindications

Recurrent patella instability associated with:

Abnormal patellar tracking (with a pronounced J-sign/clunk) associated with a bump and/or a related osteophyte in this same region
Dysplasia restricted to proximal trochlea, where the groove deepens in early flexion (below the crossing sign) so less need for deepening trochleoplasty.
Proximal trochlea with focal grade 4 arthritis, negating the ability to do a standard deepening trochleoplasty (Figure 23.5).

Skeletally immature patients (open physis at the distal femur)
Isolated patellofemoral pain with no true episodes of patellar dislocation
Dejour types A and C, because there is no “bump” to be resected
Most of trochlear prominence is not in its proximal aspect but extends too distal into the true cartilaginous groove, when resection can lead to a short trochlea and poor patellofemoral engagement.

EVALUATION

Physical Examination and Findings

A key finding in the physical examination indicating the presence of severe trochlea dysplasia with a bump is a J-sign, which is best recognized with active open chain knee extension to flexion.
The patella is situated lateral to the proximal trochlea (which is often convex) and relocates into the groove in early flexion because of increasing soft-tissue tension. There is a “clunk” or abrupt change in tracking from extension to early flexion, and vice versa (Videos 23.1 and 23.2 ).
Patella alta with or without increased lateral quadriceps vector can lead to more subtle changes in patella tracking (Video 23.3 ) without a high-grade dysplastic trochlea.