Unicondylar knee arthroplasty in the UK National Health Service: An analysis of candidacy, outcome and cost efficacy
Introduction
The use of unicondylar knee arthroplasty (UKA) as a treatment option for degenerative arthritis of the knee has been a contentious issue since its introduction in the early 1970s. Initial prostheses yielded variable results, and this unpredictability resulted in broadly low levels of usage. Instead total knee arthroplasty (TKA) emerged as the treatment of choice in this patient group; and currently both TKA and UKA are used in the management of unicompartmental disease [1].
Over the last two decades advances in UKA implant design and surgical technique have generated promising survivorship statistics (94–100% at 10 years and 95% at 15 years) [2], [3], [4], [5], reduced duration of hospital stays and rehabilitation, and good post-operative function. A classic study of individuals with UKA in one knee and TKA in the other for example, found that although most patients were not able to detect a difference between their UKA and TKA knees, 31% preferred their UKA knee; more than twice the number that felt their TKA knee was the better knee [6]. The physical basis for this preference, although open to interpretation, may relate to an improved range of motion (ROM) [6], [7] and general preservation of joint kinematics in these knees. In contrast with TKA, the cruciate ligaments are conserved in UKA; with normal cruciate function maintained up to 10 years post-surgery [8], [9]. These biomechanical advantages of UKA are reflected in comparatively high rates of return to activity (67–95% for UKA [10], [11], [12], [13] versus 34–88% for TKA [14], [15], [16]); with direct comparisons indicating that UKA provides a significantly greater return to sporting activity, although over a broadly equivalent time-scale [13], [17].
As a consequence of these and other similar statistics UKA is steadily increasing in application; at a rate of increase of around 30% year on year in the USA for example [18]. Despite this general trend, total usage of UKA remains low relative to TKA, which has historically been perceived as the more reliable procedure. A recent survey of UKA and TKA implant usage in the USA indicated that UKA accounts for less than 8% of all knee arthroplasty procedures [18], and similar statistics have been obtained in several other countries including the UK (8%) [19], as well as Canada (8%) [20], Australia (12.2%) [21] and Sweden (6.9%) [22].
Commonly quoted reasons for advocating TKA over UKA for the management of unicompartmental osteoarthritis include (a) the unabated advancement of degenerative disease in other joint compartments and (b) observations that UKA is a technically more demanding procedure. Survivorship data now suggest that the longitudinal durability of UKA is good, and that at least when appropriately monitored, revision of UKA to TKA can be successful, ultimately yielding similar levels of functioning to primary TKA [23], [24]. Although a learning curve has been reported in the acquisition of the UKA technique, this curve appears to be short, and results achieved during this period are comparable with TKA [25]. Since surgical inexperience will persist as long as UKA remains an infrequent procedure, the limitations associated with this obstacle can be considered highly circular.
Accepting that a proportion of UKA cases will require revision to TKA we assert that for UKA to attain acceptance as a viable, if not preferable management option for unicompartmental osteoarthritis, candidacy for UKA must be prevalent (allowing the accruement of surgical experience), UKA must offer significant advantages in terms of functional outcome (in order to justify its use as a temporising procedure in some patients), and UKA must be available at a relative cost saving to the hospital (allowing ultimate conversion to TKA where necessary). In this study we set out to quantify the proportion of knee arthroplasty cases that are suitable for UKA, and to compare both post-operative function and costs associated with UKA and TKA procedures in the same hospital.
Section snippets
Applicability of UKA
An orthopaedic surgeon reviewed pre-operative radiographs from a consecutive series of 200 knees booked for any knee arthroplasty surgery at our institution (Charing Cross Hospital). Patients undergoing revision surgery or arthroplasty for rheumatoid arthritis were excluded. All evaluations were blinded as to the type of surgery that was planned or performed (i.e. UKA or TKA), and to any operative findings. Each knee was assessed using antero-posterior weight bearing (AP), lateral in 45° of
Applicability of UKA
Of the 200 knees reviewed, nine cases undergoing surgery for revision or rheumatoid arthritis were excluded. The remaining 191 radiographs were categorised as shown in Fig. 2. Ninety-one knees (47.6%) fell into the three patterns that were deemed potential candidates for UKA. A further 60 knees (31.4%) were classified as M, MMP, MLP or ALP; knees in this group would be debatable candidates for UKA. Twenty knees (10.5%) were patterns MP and LP with isolated patello-femoral disease, which could
Discussion
Currently UKA accounts for only around 8% of all knee arthroplasty procedures, and TKA remains the predominant surgical treatment offered for unicompartmental knee osteoarthritis in the UK today [19], [21]. Here we have shown that candidacy for UKA is much wider; accounting for 47.6% of knee arthroplasties in a series of 200 consecutive knees. Indications and contra-indications remain a matter of some debate. Our figure of 47.6% is high, but represents the first attempt to objectively quantify
Conflict of interests
None.
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