Introduction

Valgization high tibial osteotomy (HTO) was first described in 1960s [7] It has been considered a successful procedure for varus osteoarthritis in young and active adults shifting the weight-bearing axis into the nonaffected lateral knee compartment [7, 13, 17]. The two most common approaches to valgus-producing HTOs are the lateral closing wedge and the medial opening wedge. Although known to be successful, however, osteoarthritis often progresses necessitating total knee arthroplasty (TKA). Insall et al. [13] reported that 23 % of patients previously underwent HTO needed TKA.

Given the change in mechanical axis of limb alignment and proximal tibia geometry after HTO, performance of TKA following HTO has been studied previously. Most of the studies reported outcomes after closing wedge HTO converted to TKA [1, 2, 10, 14, 20, 24]. In comparison with primary TKAs, most studies reported similar outcomes of TKAs converted from HTO [23, 25].

Traditionally, lateral closing wedge HTOs were more common; however, in the late 1990s and early 2000s, medial opening wedge HTOs became increasingly popular as an alternative to lateral closing wedge HTO. Its potential advantages include easier correction of varus deformities, preservation of proximal tibia bone stock and no disruption of the proximal tibiofibular joint, avoidance of peroneal nerve injury, and less incidence of compartment syndrome [12]. Because of preservation of proximal tibia bone stock after medial opening wedge HTO, it has been reported to have lesser technical issues during TKA procedure than the lateral closing wedge HTO [3].

The present systematic review was conducted to provide an objective analysis of TKA outcomes following previous knee osteotomy (medial opening wedge vs. lateral closing wedge). To the authors’ knowledge, this is the first review written in English directly comparing the TKA results after medial opening wedge and lateral closing wedge HTO. The hypothesis was that medial opening wedge HTO enables easier conversion to TKA than does lateral closing wedge HTO and thus superior performance of TKA.

Materials and methods

Eligibility criteria

Published studies meeting the selection criteria listed in Table 1 were included in the systematic review.

Table 1 Inclusion and exclusion criteria
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Search strategy

A literature search of online databases (MEDLINE, EMBASE, Cochrane database) was performed. For each databases, search protocol was employed. Citations in the included studies were screened, and relevant experts in the field were contacted in order to identify additional studies. Two review authors independently selected from citations based on the corresponding titles and abstracts. The eligibilities of the relevant full papers were then assessed. In cases where consensus could not be reached, a third review author was consulted.

Data extraction

Each of the selected studies was evaluated by the two independent review authors for methodological quality. Data were extracted according to the following standardized protocol: study type, level of evidence, demographic information, prostheses used, surgical details, outcome measures, clinical and radiographic findings, complications, and survival rates. The extracted data were then cross-checked for accuracy. Any disagreements, again, were settled by the third review author.

Quality assessment

The methodological quality of each of the studies was assessed on the Newcastle–Ottawa Scale (NOS) [27]. The assessment proceeded within three domains: study group selection, intergroup comparability, and ascertainment of exposure and outcome of interest. Within the “selection” (four numbered items) and “outcome” (three numbered items) domains, each assessed study could be awarded a maximum of one star for each numbered item. Within the “comparability” (one numbered item) domain, a maximum of two stars could be awarded. On the NOS, the higher the score, the higher the study quality. All of the scores were determined by the two review authors, first independently and then by consensus. An assessment tool suggested by the Effective Practice and Organization of Care (EPOC) review for case series was utilized. Seven standard criteria are used for interrupted time series.

Results

Included studies

After the full-text review, ten studies were subjected to the final systematic review. The search strategy is outlined in Fig. 1, and an overview of the study characteristics is presented in Tables 2 and 3. All of the included studies had a minimum follow-up of at least 1 year. The rationale for conversion of HTO to TKA was progression of osteoarthritis.

Fig. 1
figure 1

PRISMA flow diagram

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Table 2 Characteristics of included studies
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Table 3 Demographics of included studies
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Quality assessment

Details on the NOS- and EPOC-based methodological quality assessment of the included studies are presented in Table 4. The nonrandomized comparative studies [1, 3, 6, 22] had cohort and control groups (within studies) that were well matched in terms of demographics, prognostic variables, and surgical technique.

Table 4 Newcastle–Ottawa Scale and EPOC review
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Surgical intervention

The intraoperative results are shown in Table 5. Seven studies reported on knee prosthesis design. Regarding the operation time, Bastos et al. [3] found no significant differences in operation time between TKA after medial opening and lateral closing wedge HTO. For the soft tissue release during TKA procedure, Bastos et al. [3] reported that significantly more medial releases were required in the medial opening wedge HTO group and that there was no significant difference in the need for lateral release between the two groups. Regarding the exposure, there were more incidences of procedures such as a quadriceps snip or tibial tubercle osteotomy for the lateral closing wedge HTO group.

Table 5 Surgical details of TKA procedure
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Clinical outcomes

The clinical outcomes are provided in Table 6. Eight studies reported clinical scores: a Hospital for Special Surgery (HSS) score in one study, a Knee Society Clinical Rating System score (KSS) in five studies, a Western Ontario and McMaster University Osteoarthritis Index (WOMAC) in one study, an Oxford knee score in one study, a SF-12 in one study, and an International Knee Society score (IKS) in one study. All of the case series [1, 2, 8, 10, 24] showed improvement in clinical scores. Between the use of CR- or PS-type prosthesis after lateral closing wedge HTO, Akasaki et al. [1] reported statistically significant inferior clinical outcome in CR-TKA group. However, Chen et al. [6] did not show difference between the use of CR- and PS-type prostheses. Comparative studies between TKA following medial opening and lateral closing wedge HTO did not demonstrate statistical significant clinical differences [3, 22].

Table 6 Clinical outcome
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Radiologic outcomes

The radiologic outcomes are shown in Table 7. Eight studies reported radiologic outcome [1–3, 8, 10, 14, 20, 24]. All studies demonstrated towards neutral alignment after performing TKA. Regarding the patella height, no significant differences were demonstrated between pre- and postoperation TKA in case series for lateral closing wedge HTO studies [2, 10, 20]. There was also no difference in patella height in medial opening wedge HTO case series [8].

Table 7 Radiologic outcome
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Revision and complications

Two studies reported survival rates [10, 22]. Overall, there were no significant differences between groups. Detailed information regarding the reasons for revisional surgeries and complications is demonstrated in Table 8.

Table 8 Revisional surgeries and complications
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Discussion

The important finding of this systematic review is that although the TKA conversion from medial opening wedge HTO was technically easier than the lateral closing wedge HTO, the clinical and radiologic outcome including revision rates (survival rate) did not statistically differ between two groups. The initial hypothesis failed to demonstrate superior performance of TKA following medial opening wedge HTO than the lateral closing wedge HTO group.

Total knee arthroplasty (TKA) after failed HTO is known to be a technically demanding procedure [4, 5, 9, 21]. A number of studies have emphasized issues including soft tissue problems, difficulty with patella eversion, management of retained hardware, handling of coronal and sagittal plane deformities of the proximal tibia, and difficulties with ligament balancing. When performing TKA after either medial opening or lateral closing HTO, surgeons should consider the following factors: higher rates of preoperative limb malalignment, instability, stiffness, patellar maltracking, patella infera, surgical approaches, and previous hardware. Careful preoperative planning is required, and intraoperative difficulties should be anticipated [3, 9].

Specific knee prosthesis choice may be one of the important factors relevant to knee implant longevity [16]. Walther et al. [26] reported that posterior cruciate ligament (PCL) substituting implants seem to produce more predictable results, with less pain, and provide more stability in the anteroposterior direction, especially in cases with severe bone loss and a tenuous PCL. They suggested that inadequate PCL function would be observed more often in post-HTO arthroplasty than in patients without previous surgery. Akasaki et al. [1] performed comparative study between PS- and CR-type prostheses following failed HTO. They concluded that the midterm clinical results following CR-TKA were inferior to those after PS-TKA. They suggested that postoperative knee instability might be due in part to postoperative PCL insufficiency and that PCL-substituting TKA would be more suitable after HTO. However, Chen et al. [6] recently reported that although PS prostheses offer better range of motion in TKA after previous HTO, knee stability, clinical scores, and revision rates were similar in PS and CR prostheses. According to the included studies (Table 5) for this systematic review, there was no preference in using CR or PS for TKA after HTO.

There were surgical issues in performing TKA on patients who underwent HTO. In the aspect of surgical exposure, quadriceps snip and tibial tuberosity osteotomy were performed more frequently in the lateral closing wedge HTO group. Gupta et al. [10] reported 12.1 % of quadriceps snip in their lateral closing wedge HTO case series. Erak et al. [8] reported 2.9 % of quadriceps snip in their medial opening wedge HTO case series. In the comparative study performed by Bastos et al. [3], they needed more additional procedures for the lateral closing wedge HTO group in comparison with medial opening wedge HTO group in the aspect of quadriceps snip (2.6 vs. 0 %) and tibial tuberosity osteotomy (22.2 vs. 8.3 %). The difficulty of patella eversion in TKA after lateral closing wedge HTO has also been noted in other studies. Haddad et al. [11] reported that rectus snip was necessary in 16 % of patients, and Nizard et al. [19] found that tibial tubercle osteotomy was needed in 11 % of cases. Windsor et al. [28] previously reviewed 45 patients who had been treated with TKA after tibial osteotomy. They reported technical difficulties, not only with exposure particularly, but also in relation to the loss of bone stock and to impingement of the stem of the tibial component on the lateral tibial cortex. Impingement can be avoided by implanting undersized tibial trays and leaving the lateral tibial plateau partially uncovered or by positioning the tibial tray more medially, with the risk of overhang and medial collateral ligament impingement [10, 15]. The proximal tibia is shortened and therefore must be cut as thin as possible to expose cancellous bone for cementation of the tibial component and avoidance of flexion and extension gap imbalance [18]. This is more frequent situation during TKA surgery in patients who previously had lateral closing wedge HTO. One of the theoretical advantages of TKA after opening wedge HTO is preservation of proximal tibial anatomy; therefore, technical difficulties such as the tibia stem impingement on the lateral cortex do not occur.

In the present systemic review, similar TKA clinical improvements were demonstrated in both medial opening and lateral closing wedge HTO. There was no clear clinical and/or radiologic difference between groups. However, some studies reported less satisfactory TKA outcomes, which may be due to post-HTO patients. Gupta et al. [10] reported poor results in four knees due to the presence of patella baja. They hypothesized that patella baja was due to patellar tendon shortening from 6 to 8 weeks of post-HTO cast immobilization. Among results, patella baja was more common in TKA after lateral closing wedge HTO group than that after medial opening wedge HTO group (Table 7) [3].

An increased tibial slope causes anterior tibial translation and possible instability in flexion. Likewise, a decrease in the slope leads to posterior tibial translation, posterior capsule contraction, and decrease in flexion. Maintenance of tibial slope is mandatory for satisfactory outcome after HTO. One study mentioned the issue of the posterior tibial slope. Erak et al. [8] noted that 21 % of their medial opening wedge HTO had a tibial slope of over 15° after operation. Tibial slope tends to be increased after medial opening HTO, which can lead to large anterior tibial resections and/or defects in the posterior tibia, and can also affect flexion/extension balancing.

Ligament balancing is another important outcome factor after TKA. A tibial osteotomy produces an extra-articular deformity that influences soft tissue tension. At the time of prosthesis implantation, a tibial bone cut perpendicular to the mechanical axis leads to asymmetric tibial resection. This asymmetric tibial resection produces the so-called resection laxity, which may increase the pre-existing imbalance. Erak et al. [8] found that extra medial dissection for removal of hardware on patients with previous medial opening wedge HTO can lead to medial laxity requiring lateral ligament release to balance the knee. Bastos et al. [3] suggested that higher rates of lateral release following lateral closing wedge HTO are most likely due to postosteotomy scarring that occurs on the lateral side of the knee.

Limitations of this systematic review should be noted. First, no randomized controlled trial was included. Second, there were only two studies directly reporting TKA outcomes between medial opening and lateral closing wedge HTO. Although single-arm case series were included to support the comparative studies, there are possible consequences that the pooled analyses are biased. Third, since medial opening wedge HTO procedure has recently increased in contrast to lateral closing wedge HTO which has been a much older procedure, lateral closing wedge HTO had more time to fail requiring conversion to TKA. Well-designed longer follow-up studies are further required for definitive conclusions.

Conclusion

The present systematic review suggests that TKA after medial opening and lateral closing wedge HTO showed similar performance. Clinical and radiologic outcome including revision rates did not statistically differ from included studies. However, there are more surgical technical concerns in TKA conversion from lateral closing wedge HTO than from the medial opening wedge HTO group.