RETRACTED ARTICLE: The majority of conversion total hip arthroplasties can be considered a primary replacement: a matched cohort study

A primary total hip arthroplasty (pTHA) is most commonly performed for osteoarthritis (OA), usually has an uneventful post-operative course and is known for its excellent long-term results [1].

Nevertheless, failures do occur, for a variety of reasons, and are most often followed by a revision (r) THA. This is a technically more demanding procedure, revision implants are often necessary, and can range from changing a worn-out polyethylene liner in a not yet unstable hip to a two-stage revision for a difficult to treat infection with substantial bone loss. Results of rTHA’s are less favourable than those seen in pTHA’s due to the fact that complications are more common, survival of implants is shorter, and patients report lower on outcome measures (PROMs) [2‐4].

A third group of hip replacements is made up by the conversion (c) THA’s. These are usually performed when an intervention for a proximal femur fracture has failed (Fig. 1) and is salvaged by THA [5‐9]. Again, this a very diverse group as it can include patients undergoing placement of an additional cup in a hemi-arthroplasty (HA) that is causing painful erosion of the native acetabulum or patients with infected cephalomedullary nails with non-union, significant bone loss and an escaped abductor apparatus. Besides these technical difficulties, there frequently are concomitant medial issues as the typical patient requiring cTHA is of old age, has multiple health issues, and usually has been barely mobile in the period awaiting salvage surgery.

Attempts have been made to determine the success of cTHA among pTHA and rTHA, as this has implications for patient consenting and institutional reimbursement [10‐17]. It has been suggested that a cTHA should be considered an rTHA, but also that it is a distinct entity with outcomes in between pTHA and rTHA [13, 14, 16]. Interpreting these studies is difficult, as matched cohort analyses are rare, follow-up differs between groups, but most importantly because of the fact that very diverse groups of cTHA’s are compared to very diverse groups of rTHA’s [10‐17]. This raises the question whether it is useful to predict outcomes based on this distinction in the first place [15, 16]. There is a subgroup of patients who undergo cTHA using primary implants, who will never develop any complications and whose satisfaction probably resemblances those of patient with pTHA’s [17].

We, therefore, performed a matched cohort study and formulated the following three hypotheses:

This study matched and compared a cohort of patients who underwent cTHA to patients who underwent pTHA and rTHA. Several conclusions can be made.

First, the distinction pTHA/cTHA/rTHA is not able to explain differences in outcomes. No significant differences in major complications, mortality or PROMs were found. We, therefore, propose to stop using this distinction when trying to predict complications, implant survival and costs. The type of primary implant, whether this is a nail, a plate, a HA or a THA, is not correlated to the outcome of redo surgery as this will yield very diverse groups and does not take into account more important predicting factors. In the present study, we found that the use of revision implants and the development of major complications could explain almost all differences seen in PROMs. The development and validation of a prediction model based on these and other parameters, e.g. patient frailty, the presence of pre-existent infection/instability, and significant bone loss, would be highly useful in daily clinical practice and for calculation of long-term costs for the society.

Second, we were able to perform most cTHAs using primary implants and most of them encountered no major complications during follow-up. We know that for this group of patients, costs are low and patient satisfaction is high, comparable to pTHA performed for OA. Other studies have reported similar mid-term results. Archibeck et al. reviewed 102 THA patients after failed internal fixation of a prior hip fractures [7]. Despite needing slightly more revision type femoral implants (32 vs 23% in the present study), they still had excellent outcomes with a mean HHS of 81.8 at last follow-up. Gjertsen JE et al. found that survival of the implants in the Norwegian Arthroplasty Registry 5 years after cTHA for failed internal fixation of femoral neck fractures was 96% [18]. Most recently, Morsi et al. reported on the clinical and radiological outcomes of converting aseptic failures of intertrochanteric fracture fixation using a dynamic hip screw (DHS) to a total hip arthroplasty (THA) in a single stage procedure. Standard straight, polished, collarless, cemented stems were used in all 107 cases. At an average follow-up of 7.4 years, they report 99% implant survivorship, a Harris Hip Score of 89.3 (range 71–95) and only a very small number of surgical complications [19].

We do realize that all our cTHA were performed within a high-volume arthroplasty unit with specialist hip surgeons and fellows. Contrary to proximal femur fractures that are ideally treated within 24 h and, therefore, often by the on-call team, it is our opinion that cTHAs should be performed by a dedicated hip surgeon, even if this means postponing the procedure.

This study has several limitations. Due to its retrospective nature confounding factors such as patient expectations were not investigated. McLawhorn et al. and Qun et al. found that patients who underwent cTHA required more transfusions, had longer operative times and length of hospital stays, and more often had non-home bound discharge [13, 15]. Due to the absence of these data, no cost analysis could be made. Although a period of 13 years was searched, still a relatively small cohort of cTHA patients was found, yet larger than reported in most studies [10‐17]. Major complications could have been missed and not all patients were reached for questionnaire assessment.

In conclusion, predicting outcome and patient satisfaction based on the fact that the surgical procedure to be performed is a conversion rather than a revision is not useful. Nevertheless, most cTHAs can be performed using primary implants, and most patients report no major complications and high satisfaction.