The most important finding of this study was that femoral trochlear OCD lesions occurred in virtually identical sites. To the best of our knowledge, this is the first study to conduct an investigation in detail on the sites where femoral trochlear OCD lesions are most commonly found.
The etiology of OCD is unknown, and numerous hypotheses have been proposed, including ischemia, repetitive microtraumas, genetic factors, inflammation, and ossification disorders [14, 15]. A previous study reported that malalignment of PF structures with associated elevated TT-TG distance or occurrence of repetitive microtrauma along with tightness of the lateral retinaculum might be associated with onset of femoral trochlear OCD [16, 17]. In another study, the disease was thought to be caused by repeated shear force transmitted by the patella to the convex surface during extension of the weightbearing knee from a flexed position, which was different from that causing chondral fracture due to sudden trauma [18]. Considering PF biomechanics, as the knee gets close to full extension, the site of femoral trochlea in contact with the patella, moves in a more laterally and superiorly direction [19]. Therefore, the lateral trochlea may be more easily impinged upon by the patella than by the medial trochlea, which makes OCD lesions more likely to occur on the lateral trochlea.
In our study, we did not find any anatomical abnormalities of the PF structure in the femoral trochlear OCD group as compared to that in the control group, and all applicable measurements in the control group were within the normal ranges reported in the literature [8–12]. Furthermore, none of the patients had experienced a traumatic event. Almost all femoral trochlear OCD lesions were located in the notch and in the lateral region in the frontal view and in the superior two-thirds of the anterior region in the lateral view. These regions included areas contacting the patella at slight knee flexion (25°-30°).
Interestingly, in this study, most patients practiced soccer, followed by basketball. Price et al. evaluated the clinical characteristics between femoral trochlear OCD and participation in sporting activities that load the PF joint [20]. They conducted a retrospective study of 34 knees (30 patients) with femoral trochlear OCD and compared these to an age- and sex-matched control group with 102 femoral condyle lesions. According to the study, the odds of patients with femoral trochlear OCD lesions playing either basketball or soccer were 2.84 times higher than in those with femoral trochlear OCD lesions (p = 0.017). These two sports involve rapid deceleration before a change in direction or when landing from jumps, which are activities that increase loading of the patellofemoral joint and expose the trochlea to risk of injury.
In another study, Mc Elroy et al. examined relative characteristics of OCD knee lesions in baseball catchers as compared to those in basketball players who played in other positions [21]. They investigated 33 (29 patients) and 65 (49 patients) knees of catchers and non-catchers, respectively. They discovered that lesions in catchers were more posterior in location on the medial and lateral femoral condyles than those in non-catchers in the sagittal view (p = 0.004). This difference may occur because of repetitive and persistent hyperflexion of the knee in catchers as compared with the upright loading affecting knees of players in other positions. These two studies also revealed that repetitive and persistent loading of the knees may be risk factors for developing lesions in uncommon locations especially for young and active patients.
Management of juvenile OCD of the knee remains a controversial topic. The American Academy of Orthopaedic Surgeons clinical practice guidelines for OCD treatment do not address treatment of lesions in the trochlea [22]. The juvenile knee with a growth plate that is still open has a high potential for recovery, and therefore, conservative treatment should always be the first choice in stable OCD, as about 50% of lesions respond positively in a period of 10–18 months [4, 23]. Nonetheless, it is difficult to determine the time required to return to sports, and if the conservative treatment is ineffective, the treatment period becomes prolonged. Thus, even with early stage OCD, surgical treatment might be preferable to shorten the treatment period and allow return to sports especially in high activity athletes.
Various surgical methods have been proposed to treat OCD lesions and treatment decisions are influenced by clinical symptoms and characteristics of the lesion (location, size, and stability). The goals of treatment are to promote healing of the subchondral bone and to prevent subsequent osteochondral defects, cartilage collapse, and early degenerative changes. Drilling the subchondral bone with an aim to stimulate vascular ingrowth and subchondral bone healing is selected for stable lesions with intact articular cartilage. If the lesion is unstable, internal fixation is indicated. If fixation is impossible, there are some salvage techniques such as OATS, fresh osteochondral allograft, and autologous chondrocyte implantation (ACI) [24–26]. In addition to these common treatments for femoral trochlear OCD patients, some authors recommend releasing the lateral retinaculum in an attempt to centralize the patella in the trochlea to decrease the patellar contact pressures and enhance patellar tracking [17, 27, 28].
The Research in Osteochondritis of the Knee study group reported that two thirds (8/12) of operated femoral trochlear OCD patients show radiographic signs of healing and return to full activity without pain [29]. We achieved better postoperative outcomes than in that study regardless of the stage or the surgical method, and reoperation was not indicated in any patient. Since lateral patellar maltracking due to a tight lateral retinaculum was not observed intraoperatively, lateral release was not performed for any patient.
Our study has certain limitations. Firstly, the small sample size and retrospective nature of the study are important constraints. Secondly, we only focused on operatively treated OCD lesions and thus potentially missed a large proportion of trochlear lesions in our practice. The study does not include data on the percentage of the total trochlear OCD lesions representing operatively treated lesions. Thirdly, the femoral trochlear OCD lesion being in contact with the patella in slight knee flexion was considered in published literature but was not an intraoperative finding in our study. Finally, the contact pressure of the patellofemoral joint also depends on the quadriceps strength, which was not evaluated in this study. It is necessary to include a larger sample size and evaluate soft tissues. However, we have found that femoral trochlear OCD lesions occur in nearly similar locations in affected patients. The lesions are mostly detected on MRI but may easily be missed on radiographic imaging. Knowing the commonly involved location of the OCD lesions can prevent missed diagnoses of this uncommon condition.