Trochleoplasty for patients with recurrent patellar instability has been debated the past few years. The procedure is becoming more common in Europe, while orthopedic surgeons in the United States have a more cautious approach, although a few surgeons are doing the procedure. One can ask if there is a need for trochleoplasties when there are other well-established procedures.
Many surgeons are excited about medial patellofemoral ligament (MPFL) reconstructions. Some studies with long-term follow-up seem to have good results; however, it is not a solution for all patients with patellar instabilities. We have to be aware of the underlying pathomorphology. In a recent meta analysis, Shah and colleagues found a complication rate of 26% after MPFL reconstruction. A major complication was postoperative instability with recurrent apprehension, which was 32% of all complications. Howells and colleagues found that 15 of 25 patients with persistent recurrent symptoms after reconstruction of the MPFL had moderate trochlear dysplasia. Patients with severe trochlear dysplasia already had been excluded.
Wagner and colleagues found a negative relationship between the degree of trochlear dysplasia and outcome after MPFL reconstruction. The situation seems to be that when the native MPFL ruptures, without any major trauma, it is likely an injury caused by continuously stress on the ligament. By making the ligament stronger, we can introduce abnormal joint forces leading to either pain at the insertion side, osteoarthritis (OA) or patella stress fractures.
Alternatively or in combination with an MPFL reconstruction, we can transfer the tibial tubercle either medially to reduce the tibial tubercle–trochlear groove distance (TT-TG) distance and/or distally to correct a patella alta. However, it is difficult to ignore the studies from Carney and colleagues and Nakagawa and colleagues, who observed that good to excellent results after transfer of the tibial tubercle declined after 10 years to 15 years, with some patients having increasing pain. Nakagawe and colleagues found radiological osteoarthritic changes grade 2 or worse in 42% of patients after Elmslie-Trillat procedures (no anteriorization at time of medial tibial tubercle transfer).
This brings us back to the question: is there any indication for the trochleoplasty procedure? The procedure is based on the principle of restoring abnormal anatomy in cases with trochlear dysplasia. We know trochlear dysplasia is a main factor for patellar instability and apparently it seems logical to do the trochleoplasty procedure. Trochlear dysplasia is characterized by overstuffing too much bone in the trochlea, resulting in a flat of shallow configuration in the most proximal part of the trochlea. This configuration has impact on many factors. Mostly, the trochlear groove is medialized and this causes an increase of the TT-TG distance.
It is important to notice that in these cases, the abnormal TT-TG is not caused by an external placed tibial tubercle, but an asymmetric trochlea because of a medialized trochlear groove. Furthermore, the patella tilt is caused by overstuffing of the trochlea, forcing the patella to articulate on it lateral facet simply because the patella has no groove to be contained. When a patient has trochlea dysplasia, you will find the trochlea inclination angle is reduced, meaning there is a deficiency of the lateral part of the trochlea which is supposed to give osseous support to the patella. These factors can all be normalized by doing a trochleoplasty and the procedure also has a positive impact on the sulcus angle and eventual patella alta. Depending on the operative trochleoplasty technique, the TT-TG distance can be reduced by 5 mm to 10 mm.
Most surgeons have a reasonably skeptical approach on the trochleoplasty procedure based on several sound arguments. First, the procedure is technically demanding and should only be done by a selected and dedicated group of surgeons who have special knowledge about the biomechanics of patellar instability and have a routine for more standard patellar stabilizing procedures, such as MPFL reconstructions and osteotomies of the tibial tubercle.
Second, this is a procedure that involves the osteochondral interface. Radin and Rose showed this is a delicate structure and impacts on this can potentially lead to arthritis. Schöttle and colleagues studied the cartilage viability after the Bereiter trochleoplasty and found tissue in the trochlear groove remained viable, with retention of distinctive hyaline architecture and composition. However, some pathological changes were found, as lacunae were seen progressing from the subchondral bone through the calcified layer and, in some cases, even into the basal layer of the cartilage. This can be a sign of cartilage degeneration giving profound impact of subchondral bone disruption in mostly young patients. It was hypothesized that the cartilage flake probably undergoes microfractures while being pressed down into the new groove, resulting in these lacunae and cluster formation. Pathologic changes were found in the area just beneath the subchondral bone, therefore, showing processes characteristic of epiphyseal fracture healing.
It was concluded that even though a few minor changes in the calcified layers were identified, the results of the microscopic findings in conjunction with the clinical and radiological results seen at 2-year and 5-year follow-up after trochleoplasty could be expected to persist long term. However, further histological studies with a longer follow-up are recommended. If subchondral bone and cartilage stiffness occur in the trochleoplasty area, it is likely that this might eventually lead to OA.
Third, postoperative detachment of the osteochondral flap or chondrolysis may have serious consequences. Fortunately there have not been any reported cases yet. Today, about 20 case series have now demonstrated good short- to mid-term results of the trochleoplasty procedure. In the past three studies, the trochleoplasty has been combined with an MPFL reconstruction. The obtained results seems to be encouraging in patients with trochlear dysplasia (Dejour grade B-D), resulting in consistent statistically significant improvement in all applied knee function scoring systems. Ntagiopaulos and colleagues found no radiologically signs of OA (follow-up: 7 years; range: 3 years to 9 years). This is contrary to Knoch and colleagues, who reported radiologic osteoarthritic changes grade 2 or worse in 30 % (follow-up: 8 years; range: 4 years to 14 years). In this study, patellofemoral pain became worse in 33% of patients and improved in 49% of patients, but the median Kujala score was 94.
Anterior knee pain
Many factors are involved in anterior knee pain. We should pay attention to the study from Keser and colleagues, who found a significant correlation between trochlear dysplasia and anterior knee pain. Also it is interesting that Goutallier and colleagues successfully used the recession trochleoplasty procedure in cases with trochlea dysplasia, where the patella already had been stabilized successfully but the patient continued to have pain.
We know trochlear dysplasia predisposes patients to OA and this is whether or not the patella is unstable. Albee elevation trochleoplasty increases the forces in the patellofemoral joint and causes secondary OA. Therefore, it is likely to hypothesize that when the forces in an overstuffed dysplastic trochlea are reduced, by doing a deepening or depression trochleoplasty, the risk of OA might be reduced.
In addition to the above mentioned factors, there are other factors involved. For example, the procedure is technically demanding. There is a risk of arthrofibrosis and there is spare data on the long-term follow-up. The differences observed in postoperative stiffness and pain may be attributed to different surgical techniques, rehabilitation protocols and indications. The persistence of instability and the need for reoperation after trochleoplasty procedures are rarely recorded.
In my opinion, we are only at the dawn and hopefully new patient-related outcomes scores, such as the Norwich Patella Instability score and Banff patellar instrument, will be useful instruments to help obtain more precise and comparative data in the future. However, it is difficult to neglect the good clinical results obtained until now. Obviously, trochleoplasty is indicated in some cases, however, is still difficult to say if it is a salvage procedure or if it is also a procedure for primary cases with perhaps less pronounced degrees of trochlear dysplasia. We need to sort out the differences between the types of trochleoplasty techniques including more data on arthroscopic techniques.
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Lars Blønd, MD, is a consultant surgeon, Koege University Hospital and chief surgeon, Teres Medical Group, Copenhagen, and President of the Danish Society of Sports Medicine. He can be reached at Ortopaedkirurgisk afdeling, Koege Universitets Sygehus, Lykkebaekvej 1, DK-4600, Denmark; email: Larsfirstname.lastname@example.org or www.larsblond.com.
Disclosure: Blønd has not relevant financial disclosures.