Recurrent patellofemoral instability has defined pathoanatomic risk factors: patella alta, trochlear dysplasia and a lateral tracking vector (increased Q-angle, tibial tuberosity-trochlear groove [TT-TG] and TT-PCL). Orthopedic surgeons in the United States have learned a lot from our European colleagues regarding defining and addressing these specific underlying factors.
Ten years ago, during my orthopedic surgery residency training, many of my sports medicine mentors used a specific procedure (tibial tubercle transfer, medial imbrication) for each case of patellofemoral instability without examining or appreciating these risk factors on preoperative imaging or physical examination. We now train our residents and fellows to look for the crossing sign on the lateral radiograph, measure the TT-TG or TT-PCL on advanced imaging, and specifically define each risk factor. We tailor our surgical approach to addressing the anatomic abnormalities (for example: Medial patellofemoral ligament reconstruction for patients with no trochlear dysplasia recurrent patellofemoral instability, no malalignment and deficient proximal medial restraints, but adding or distalization for severe patella alta, C-D ratio greater than 1.4 and TT for excessive lateral tracking vector, TT-TG>20). MPFL reconstruction has proven to be a reliable operative treatment for recurrent patellofemoral instability, but has higher failure rates in case of severe trochlear dysplasia. Indications for trochleoplasty have included severe trochlea dysplasia (Dejour B and D), convex trochlea recurrent patellofemoral instability after a failed, well-done medial patellofemoral ligament (MPFL) reconstruction, and sometimes in patients with apprehension/instability in flexion. Trochleoplasty has been more popular in Europe than the United States with clearly defined techniques and good outcomes for controlling instability, but with the known long-term consequences of osteoarthritis. Orthopedic surgeons in the United States have been skeptical because of concerns of iatrogenic cartilage damage, arthritis risk and an increased risk of complications. In addition, it has been argued and established that patella stability can be achieved with MPFL reconstruction or tubercle osteotomy even in cases of moderate to severe trochlear dysplasia.
Our case series review of trochleoplasty at the University of Iowa a few years ago had similar results to the European studies — improved stability but high risk of postoperative knee pain. In our study, all patients reported better patellofemoral stability after trochleoplasty, but 66% had postoperative anterior knee pain. One reason for this could be that many surgeons in the United States perform trochleoplasty as a salvage procedure after other patellofemoral stability procedures have failed and have less exposure to learning this procedure while in training. However, with high rates of postoperative pain and risk of cartilage damage, I believe trochleoplasty should be reserved for cases of severe trochlear dysplasia when patellar stability cannot be achieved by other means (MPFL reconstruction).
I had a recent case of severe trochlear dysplasia and recurrent patellofemoral instability treated with trochleoplasty and MPFL reconstruction. The surgery went great, but the patient struggled with knee stiffness and quad weakness postoperatively. She required a subsequent knee manipulation and struggled to achieve a good outcome. I have often wondered if she would have done better with a simpler approach of isolated MPFL reconstruction (many of our patients have excellent outcomes with MPFL reconstruction and moderate trochlear dysplasia).
Similar to many orthopedic issues, it is hard to define the critical threshold when a bigger surgery with more risk of complication and morbidity is needed. At this point, I would support the view that trochleoplasty should be reserved for cases of severe trochlear dysplasia (convex trochlea) when patellofemoral stability is not able to be indirectly achieved by other means.
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Matthew Bollier, MD, is the Congdon professor in orthopedic surgery, Sports Medicine fellowship director at the University of Iowa.
Disclosure: Bollier reports no relevant financial disclosures.