The most important finding of this study was that both flake refixation and ACI following patella dislocation with (osteo-)chondral flake fractures provided excellent clinical and radiological outcomes at mid-term follow-up. In addition, there were no significant group differences in the clinical and radiological outcome scores between the groups. Regardless of the technique, the majority of the patients were able to return-to-sport and participate in activities of daily life without significant pain.
(Osteo-)chondral flake fractures present a common pathology in knee surgery. However, there is no general agreement on how to best treat this entity and the scientific evidence regarding the refixation of flake fragments in the current literature is very limited . This emphasizes the need for further investigation comparing different therapeutical concepts to improve decision-making algorithms.
In the present study, refixation of the flake fragments led to good results in the VAS and the Kujala score, which indicates that most of the patients did not suffer relevant pain at follow-up. In addition, patients were able to return-to-sports and even participate in pivoting sports as shown by the results of the Tegner score and the KOOS. In addition, the majority of the patients were able to participate in activities of daily life after refixation and were not impaired by the symptoms as shown in the IKDC and KOOS. This is in accordance with recent literature that shows that the refixation, if possible, shows good clinical results [6, 10, 15]. In a recent study, Gesslein et al. showed that the clinical outcome after refixation is significantly better in comparison with the removal of the flake and debridement of the defect area. However, they did not compare the results with an alternative cartilage repair technique .
Besides, given the limited eligibility for refixation of (osteo-)chondral lesions, there is a need for alternative treatment methods in clinical practice. Today, commonly used techniques for cartilage regeneration in the knee are cell-based techniques like ACI. Several previous studies demonstrated that ACI provides good results for the treatment of cartilage lesions in the knee joint [2, 10, 21, 29]. However, there is also evidence that the results for patellofemoral lesions show a bigger variability and are less predictable in comparison with lesions in the femorotibial compartment [20, 22]. Interestingly, the present study showed that patients treated with ACI for flake fractures after patella dislocation show excellent results. The clinical outcome and return-to-sport rates were better than most of the results after patellofemoral ACI published so far [2, 10, 21, 29, 31]. In a current systematic review, Hinckel et al. showed that patellofemoral cartilage restoration leads to good clinical results, but with a higher complication rate in comparison to the present study . The primary reason for this might be the patient selection, including only traumatic aetiology, fresh injuries, clear causality for the lesion, and young patient age.
Although there are data about the clinical results after flake refixation in the literature, there is a scarcity of data evaluating the radiological results using magnetic resonance imaging. The radiological outcome after refixation in mid-term follow-up was favourable and mostly showed good healing, as reflected by the results of the MOCART score and its subscores. The group comparison of the MR imaging results showed a trend towards worse results after ACI with higher interindividual differences, but the difference was not statistically significant. To further investigate this, a radiological study with a large patient collective should be conducted. Nevertheless, the MR imaging results after ACI were in line with existing literature on the knee joint, given the scarcity of data regarding the specific investigation of ACI on the patellofemoral joint [14, 19, 28, 29]. Siebold et al. showed a radiological success rate of 80% in a cohort of patients with MPFL reconstruction and ACI, but their collective consisted of patients with chronic instability of the patella without flake fractures .
Of interest, the results of the present study are of distinct clinical importance as they allow to discuss the potential treatment options with the patients to enable an informed decision-making process. An important benefit of the refixation is that it can be performed as a one-step procedure in contrast to the 2-step procedure of ACI. In addition, the refixation of the fragment allows preserving the original hyaline cartilage while ACI can form hyaline-like cartilage only . Nevertheless, ACI is an excellent fallback option with similar good clinical and radiological outcome and should always be discussed with the patient before the surgery. For the surgeon, it provides a good alternative if flake refixation is not possible.
The present study has several limitations. First, the study design is retrospective and does not include preoperative data to establish a baseline regarding the joint function. However, as only patients with a primary patella dislocation were included, it can be assumed that the patient collective mostly did not have any major problems with their knee joints prior to the injury. Second, the sample size of each subgroup and the total sample size are limited and a larger study cohort may have had a stronger statistical power to detect group differences. In the present study, strict inclusion and exclusion criteria were applied to create a homogeneous study cohort with primary patella dislocations and no concomitant injuries. This strict selection process led to a limited size of the study cohort but also to a reduction of possible confounders. However, the limited group size might have affected the statistical significance of the results, with a larger group size, the statistical power would be stronger. Third, the results offer mid-term results and a conclusion regarding the development of long-term complications like arthrosis is not possible. Fourth, all patients that were eligible for refixation were treated with a refixation and were not considered for ACI, all others received an ACI. This might have had an effect on the groups. We have tested all relevant factors to ensure group comparability, nevertheless, there might have been an effect on the results of this study. To reduce this effect a randomized study with prospective design should be conducted. The time to return-to-sport was not reported. The distribution of males/females between the groups was different, the difference was not significant, nevertheless, it might have had an influence on the results . Potential differences between retropatellar and trochlear pathologies were not investigated in this study. The follow-up of 81% of eligible patients is adequate, but the drop-out rate might have affected the results.
Despite these limitations, the present data demonstrated no significant difference in clinical and radiological outcomes between flake refixation and ACI, indicating that both techniques are good and reliable surgical options after retropatellar (osteo-)chondral flake fractures following primary patella dislocation. The hypothesis was discarded, as refixation of flake fractures showed no significantly better results than ACI.