Introduction
For the treatment of talar osteochondral defects (OCDs), a wide variety of treatment strategies have been reported in the literature. These strategies can be divided into a number of treatment groups: conservative treatment, bone marrow stimulation (BMS), retrograde drilling, osteo(chondral) transplantation, cartilage implantation and chondrogenesis-inducing therapies (CIT). In general, the different surgical treatments of talar osteochondral defects have good results, but although the great majority of defects improve after surgical treatment, a minority of lesions will fail first-line surgical treatment and therefore remain symptomatic [
30,
40,
63]. This was exemplified by studies conducted by Yoon et al. [
62] and Choi et al. [
11], in which 11% of 399 patients and 6.7% out of 120 ankles, respectively, required revision surgery. These numbers indicate that secondary and tertiary surgical treatment for talar OCDs is not uncommon [
54].
Although these patients generally represent a therapeutic challenge to the orthopaedic surgeon, most research in the past decades has focused on the treatment of primary talar OCDs. To a lesser extent, researchers in the orthopaedic field have attempted to identify promising surgical treatment options for non-primary lesions [
62]. Systematic reviews aspiring to determine the most effective treatment option for talar OCDs so far include patient populations of both primary and non-primary lesions [
30,
40,
63]. To our knowledge, no previously published systematic review has exclusively investigated the clinical effectiveness of different surgical treatment options for talar OCDs that have failed primary surgery. Hence, the aim of the present systematic review is to identify the most effective surgical treatment for talar OCDs after failed primary surgery.
Discussion
To the best of our knowledge, this is the first systematic review investigating the effectiveness of treatment options for talar osteochondral defects after failed primary surgical treatment. This is in contrast to previous reviews that focused either solely on primary or both primary and non-primary talar OCDs [
30,
40,
63]. The differences in treatment approach for non-primary-treated OCDs often differ and are mainly based on expert opinion since evidence is limited. By means of the present review, it was the goal to give an evidence-based insight into the most effective surgical treatment option.
One of the major differences compared to studies focused solely on primary talar OCDs is that the most described treatment option is different. As for the healing of articular cartilage injuries, O’Driscoll postulated that the treatment options of these defects can be grouped according to four principles. It can be restored, replaced, relieved or resected [
41]. It is generally expected that the first-line surgical treatment should at least incorporate restoration of the cartilage, which is normally accomplished by enhancing the intrinsic capacity of this cartilage and subchondral bone to heal itself. In a previous review on primary OCDs, BMS (including retrograde drilling) was the most described treatment method. Not unexpectedly, the most frequently described treatment method for secondary talar OCDs was not BMS but a type of replacement strategy.
In the literature, numerous treatment recommendations are given considering failed primary surgery, for example that patients with failures of previous arthroscopic treatment should be treated with osteochondral transplantation [
17]. The recommendations are, however, not based on any concrete data. In this review, the success rates of BMS as a revision surgery were found to be 69 and 75%, which seems acceptable and lies within the success rate ranges found in primary OCD surgery. It, however, lies below the confidence interval after pooling of eleven retrospective studies describing primary surgery in 317 ankles which yielded an overall BMS success rate of 82% [CI 78–86%]. In the present review, only 25 ankles treated with BMS were evaluated. The calculated success rate is, however, still promising, and since BMS is a relatively non-invasive and inexpensive treatment, it should still be considered for certain patients with small secondary defects or at least be included in the shared decision process with the patient when discussing further treatment options after a previously failed primary operation [
46]. It should also be noted that a study by Yoon et al. [
62]—which was not included in the present review—described a clinically inferior outcome which corresponded to a calculated success rate of 32%. In this study, the authors compared repeat arthroscopy to an osteochondral autograft procedure with the latter obtaining a success rate of 82%; however, in this patient populations were also ankles included with concomitant tibial lesions (5% in the osteochondral transplantation group and 14% in the repeat arthroscopy group). Since an associated tibial lesion was part of the exclusion criteria and despite multiple requests, it was not possible to obtain the separate data, and therefore, this article had to be excluded. Another remark that has to be made in the light of the study by Yoon et al. [
62] is that the authors included talar OCDs with subchondral cysts (up to an incidence of 64% in the repeat arthroscopy group), while in the study by Savva et al. [
51] subchondral cysts were deliberately excluded. As stated above, an underlying cyst is associated with inferior outcomes, and this could therefore be a plausible reason for the difference observed in the success rates. Thus, when considering performing a BMS procedure after failed previous surgical treatment, the presence of a cyst should be taken into account when choosing the optimal treatment strategy.
Most of the studies described a more invasive osteochondral or cartilage transplantation method as a subsequent procedure for a previously unsuccessfully treated OCD. In the pooled group, the OATS procedure with an autograft showed the highest success rate. Interesting enough, the pooled success rate of this OATS group which combined 73 treated OCDs resulted in a 90% success rate, which was significantly higher than the 77% success rate in our review about primary-treated OCDs (p = 0.0296). The observed difference was a little unexpected and might be explained by differences in size of the treated lesions and concomitant damage to the cartilage of the rest of the ankle joint which were not stated in most studies. Differences in outcome expectancy from the patients can also play a role since the used outcome scores (AOFAS) have a subjective component. Finally, it must be noted that the pooled success rates in the review about primary surgery were all retrospective case series, which were compared to three prospective case series in this review. It is therefore not possible to say whether the difference is due to a clinical or methodological difference.
A difference was found in the autograft versus the allograft procedure with success rates of 90 and 55%, respectively. Differences in these procedures have been previously highlighted in the literature [
4,
34,
35,
44]. Since an allograft procedure is typically used for larger defects, it is to be expected that a difference in success percentage was likely to be found. The substantial difference underlines the recommendation that, if possible, an autograft procedure deserves preference over an allograft procedure. The same is the case for the mosaicplasty procedure, in most cases autogenous in nature but also used for larger defects. When comparing the allograft procedure with mosaicplasty, no significant difference was found, and therefore, it is not possible to indicate whether one has superiority in treating larger defects.
One of the major strengths of our systematic review is the contacting with the authors of included studies with the goal of acquiring separate data. This, however, also resulted in a limitation: almost half of the extracted data concerning outcome and success percentages was acquired through the direct approach of the authors which made it virtually impossible to collect all the variables initially being desired to collect in the constructed data set, such as complications reported, lesion size, or classification systems used.
As for pooling of the data, it was not possible to perform a formal meta-regression, that is, utilizing mixed-effects logistic regression in order to compare treatment groups. This is because the number of patients included in the studies was substantially lower than required to obtain stable parameters estimates for this type of analysis [
37]. Instead, the authors decided to pool data through a simplified manner where different patients from the same treatment group were added and a new success percentage was calculated. This means that the results presented in the review need to be interpreted with caution. When comparing two different treatment groups, one cannot with certainty state that the difference observed was based on clinical differences or on methodological differences. For example, since the allograft technique is mainly used for the larger defects, it will consequently give a worse outcome.
As for the outcome measurements, the AOFAS score was the most frequently used scoring system. This score as with all the other scores used for success percentage calculation is not officially validated for the clinical evaluation of the treatment of talar OCDs as such. Subsequently, the calculated success percentages have to be interpreted with care. This is clearly exemplified by the outcome reported by the study of Johnson et al. [
26]. The adjusted Mazur score was unsatisfactory in the majority of patients, which resulted in a rather low success percentage. However, they found a high average subjective patient-based satisfaction score. This again brings up the question to what extent we should rely on these questionnaires.
The majority of the included studies were of low methodological quality. As long as no randomized comparative clinical trials are conducted (such as mosaicplasty versus allograft transplantation or OATS versus AMIC), data will remain insufficient to draw any firm conclusions. These results should therefore not be used in making decisions about technique but rather for prediction of outcome. In clinical practice, this review can be used to illustrate the different treatment techniques and to give patients an indication about the expected success percentages of the different treatment methods for talar OCDs after failed primary surgery.
Acknowledgements
The authors would like to thank F. S. van Etten-Jamaludin, clinical librarian, for her help with the search and Dr. R. Holman, statistician, for her help with the statistical analysis. The authors also thank Mr. H. K. Marchbank for proofreading the manuscript.