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Sulcus-deepening trochleoplasty improves patellar tracking
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A combination of bony and dynamic and static soft tissue stabilizers provides for stability of the patellofemoral joint. Therefore, the etiology of patellar instability is multifactorial and often includes trochlear dysplasia, patella alta, coronal malalignment, torsional abnormalities and incompetent medial soft tissue constraints. Recent studies have indicated that trochlear dysplasia is the key anatomic risk factor leading to persistent patellar instability. Though trochlear dysplasia is frequently present in patients with patellar instability, correction of this dysplasia through deepening trochleoplasty is only indicated in a subset of patients. This article describes the sulcus-deepening trochleoplasty, including indications and technical pearls.
Indications
A thorough understanding of the underlying etiology of a patient’s instability is critical, as correct patient selection is paramount. The most widely used classification system for trochlear dysplasia was developed by Henri Dejour, MD, and further refined by David H. Dejour, MD. A large supratrochlear spur is present in type B and type D trochlear dysplasia. It is this supratrochlear spur that is the “high-value target” when performing trochleoplasty. As the knee moves from extension to flexion, this spur can act as a “ski ramp” and produce a lateral moment that leads to patellar subluxation or dislocation in early knee flexion, the effect of which is magnified in patients with patella alta and genu valgum.
Our current indications for sulcus-deepening trochleoplasty include patients with persistent instability with Dejour B or D dysplasia and a spur height greater than 5 mm to 7 mm, especially in the revision setting (Figure 1). The presence of a J-sign is also important as it demonstrates the effect of the spur on patella tracking. As the knee is brought from flexion to extension, the patella suddenly laterally translates as it exits the trochlear groove. This J-sign is especially appreciable in patients with a large spur and patella alta. It must be emphasized that a shallow groove (type A dysplasia) is not an indication for trochleoplasty, as there is no spur to remove.
Technique with diagnostic arthroscopy
We perform a diagnostic arthroscopy to document and address any intra-articular pathology. This also allows for direct visualization of the patellar maltracking. A longitudinal, medial parapatellar incision allows for arthrotomy, as well as hamstring harvest and placement of the tunnels for medial patellofemoral ligament (MPFL) reconstruction. In patients with chronic patellar instability, the medial retinacular structures, including the MPFL, are torn or incompetent. Therefore, we universally perform a concomitant MPFL reconstruction.
After arthrotomy, the height of the supratrochlear spur can be measured directly (Figure 2). The native sulcus and new desired position of the sulcus aligned with the femoral shaft are marked. The new sulcus can be lateralized by 4 mm to 5 mm, which effectively decreases the tibial tubercle-to trochlear groove (TT-TG) distance. This is important, as a tubercle osteotomy may be avoided in patients with a slightly elevated TT-TG of 15 mm to 22 mm. The anticipated osteochondral flaps are then marked. Medial and lateral lines are drawn starting at the “inflection point” of curvature where the condyles are tallest, which is just proximal to the sulcus terminalis. The convergence of all three of these lines is at the level of the anterior femoral cortex extended distally when viewed from the side. This allows removal of the entire spur anterior to the cortex, with the new trochlear groove positioned flush at the front of the femur.
Figure 2. Following arthrotomy, the height of the supratrochlear spur can be directly measured with an osteotome or other instrument. In this case, the height of the supratrochlear spur is 12 mm.
Figure 3. A proximal osteotomy is first performed. An initial cut is made just off of the articular surface (a). The second cut is along the femoral shaft at the base of the spur (b). These two cuts produce a wedge of bone that is removed (c) and should be saved for use later in this case.
Figure 4. The drill and guide with 5-mm offset is used to precisely remove subchondral bone and contour the flap (a). The 5-mm offset helps prevent chondral perforation. This guide works best when rotated like a windshield wiper around a pivot point distally. It is critical to not go beyond the marked flap’s most distal border. In this case, the central dashed line represents the original trochlear groove. The more lateral solid line represents the new lateralized groove (b).
Source: David R. Diduch, MD
We perform deepening trochleoplasty by the “thick shell” osteotomy method popularized by David Dejour, MD. We begin the osteotomy with an osteotome proximally. An initial cut is made slightly onto the articular margin with a second cut along the femoral shaft at the base of the supratrochlear spur. This produces a wedge of removed bone around the articular margin of the trochlea (Figure 3). It is important to save and mince these cortical wedges for later use as bone graft. We start removing bone with a rongeur followed by using the drill and guide with 5-mm offset from the RetroConstruction Drill Guide System Instrument Set (Arthrex) to create a cavity beneath an osteochondral shell (Figure 4). As the commercially available guide and drill go slowly through denser bone, we sometimes start with a 3-mm egg-shaped high-speed burr. The aforementioned guide is helpful for precisely removing and contouring the subchondral bone and avoiding chondral perforation and it works best when rotated like a windshield wiper around a pivot point. To minimize the risk of perforating the articular cartilage, it is critical to not go beyond the marked flap’s most distal border. Creating a trough below the new sulcus will help the “leaflets” compress deeper into the center upon fixation. Of note, the alternative “thin flap” trochleoplasty method further thins the osteochondral shell to a 3-mm malleable flap using a 3-mm offset guide.
Following completion of the resection, the osteochondral shell should be ballotable like a trampoline. If not, there are likely still areas of inadequate resection. A #20 scalpel blade is then positioned along the new sulcus and a bone tamp and mallet are used to split the shell longitudinally. The “leaflets” can then be deformed and depressed into their new positions. A separate cut may be needed on the lateral edge of the lateral “leaflet” if it is not able to be depressed. This additional cut should not extend more than halfway along its marked course in order to prevent a free “shingle” of bone and cartilage. The medial facet is almost always malleable enough that it does not require an osteotomy cut.
Bony pieces removed at the beginning of the osteotomy are placed into the cavity at the most distal extent of the osteochondral flaps to prevent collapse of the shell at the transition from the cavity to intact bone. Pieces can also be placed along the medial and lateral edges of the facet to contour and deepen the sulcus (Figure 5).
We secure the osteochondral flaps with three biocomposite suture anchors that can be loaded with absorbable sutures. The distal anchor is loaded with two #2 absorbable sutures and placed 5 mm to 10 mm distal to the most distal extent of the sulcus cut line. One of the pairs of sutures is then draped over each osteochondral flap at an angle of pull that maintains flap reduction. It is important that the sutures not slide into the central osteochondral cut line. Each suture pair is then placed and secured into an anchor, which is inserted proximal to the osteotomy (Figure 6). This completes the trochleoplasty (Figure 7). The MPFL reconstruction and lateral retinacular Z-lengthening, if needed, are completed and the wound is closed.
Patients are restricted to 50% weight-bearing and placed in a hinged knee brace for 6 weeks. As arthrofibrosis and stiffness are potential complications of the procedure, it is critical that physical therapy begins immediately. The brace is set at 0° to 70° for the first 2 weeks, at 0° to 90° for weeks 2 through 4, and then unrestricted thereafter. The physical therapist can assist with flexion 15° beyond each brace setting and instruct the patient to do the same with heel slides when the brace is removed at home. Return to jogging is allowed after week 12 assuming there is adequate muscle control. Return to sport is usually allowed at 5 to 6 months postoperatively.
Figure 6. A biocomposite anchor loaded with two #2 absorbable sutures is placed distal to the sulcus cut line (a). A pair of sutures is draped across each shell and placed into an additional biocomposite anchor proximally (b), which secures the flap. It is important that these sutures do not “slide” into the center sulcus cut.
Figure 7. The large spur has effectively been removed. The image on the left demonstrates the preoperative spur height and the image on the right demonstrates the height following trochleoplasty.
Discussion
Outcomes have been generally positive following trochleoplasty although there are currently no level-1 randomized clinical trials. At our institution, we prospectively studied 64 patients (71 knees) with severe trochlear dysplasia (type B or D). MPFL reconstructions were performed in all patients along with lateral release or lengthening (50.7%), tibial tubercle osteotomy (TTO) (32.8 %) and some type of cartilage procedure (41.8%). The mean age of patients was 19.6 years and 81.6% were women. The mean follow-up was 27.7 months. No patients had recurrent dislocation. One patient had persistent patellar apprehension and a recurrent J-sign at terminal extension and underwent a distal femoral osteotomy for genu valgum. All patients reported clinically significant improvements in patient-reported outcome scores. Eighty-eight percent of patients were able to return to sport. Ten knees (20.4%) developed stiffness that required manipulation under anesthesia. Eight knees underwent arthroscopic lysis of adhesions, as well. It should be noted these were prior to the institution of our current, more aggressive range of motion protocol.
While certainly not indicated in all patients with patellar instability and trochlear dysplasia, trochleoplasty is a powerful tool for patients with a large supratrochlear spur that affects patella tracking. It should be strongly considered in patients who have failed a previous soft tissue procedure. Eliminating the supratrochlear spur and lateralizing and deepening the trochlear sulcus places the patella in a more advantageous position and is effective in the treatment of patellar instability.
- References:
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- For more information:
- David R. Diduch, MD, can be reached at department of orthopaedic surgery, University of Virginia Health System, P.O. Box 800159 HSC, Charlottesville, VA 22908; email: drd5c@virginia.edu.
- Jeremy K. Rush, MD, a former sports medicine fellow at the University of Virginia, can be reached at department of orthopedics and sports medicine, Nemours Children’s Specialty Care, 807 Children’s Way, Jacksonville, FL 32207; email: jeremy.rush@nemours.org.
Disclosures: Diduch and Rush report no relevant financial disclosures.