The optimal goal of the treatment of tibial plateau fracture is the satisfactory recovery of function and prevention of malalignment and osteoarthritic progression.1,2,3) Successful treatment depends on the anatomical reduction of the articular surface, restoration of the mechanical axis, and treatment of concomitant injuries.1,2) Arthroscopic reduction and internal fixation (ARIF) has recently been suggested especially for lateral joint depression tibial plateau fractures such as Arbeitsgemeinschaft für Osteosynthesefragen/Orthopedic Trauma Association (AO/OTA) 41.B2 or B3 fractures.4,5) Under direct visualization of intra-articular fractures and concomitant injuries via arthroscopy, surgeons could achieve accurate reductions of the articular depressions of fracture fragments and proper management of combined injuries such as lateral meniscus (LM) tears.4,5) Owing to these advantages, a recent study showed that ARIF led to better radiologic results than open reduction and internal fixation (ORIF).6) Therefore, ARIF has been deemed a reliable, effective, and safe treatment for lateral joint depression tibial plateau fractures.7)

Meanwhile, preoperative articular depression distance (ADD) and lateral meniscectomized status are known factors for valgus deformity and subsequent osteoarthritis in lateral joint depression tibial plateau fracture after ORIF.8,9,10) Thus, much attention has recently been directed toward the restoration of the joint depression to minimize intra-articular step-off and meniscal repair of LM tears during ARIF.4,11,12) Despite these efforts, valgus deformity and subsequent osteoarthritis progression may occasionally develop in lateral joint depression tibial plateau fracture after ARIF.4,7) However, there is a lack of evidence regarding valgus deformity and investigating factors affecting valgus deformity after ARIF. Moreover, limited studies have evaluated both preoperative and postoperative findings of computed tomography (CT), which may be a more accurate and reliable radiological method.

Thus, the current study retrospectively assessed lateral joint depression tibial plateau fractures to determine the factors affecting valgus deformity after ARIF using preoperative and postoperative CT evaluations. The proposed hypothesis was that the restoration of lateral plateau widening as well as articular surface and preservation of the LM would be necessary to prevent valgus deformity after ARIF in lateral joint-depression tibial plateau fractures as both joint depression and widening could lead to joint incongruity resulting in the disruption of joint mechanics.13,14)

LM tears were the most common combined injuries (n=23, 59.0%) (Table 1). Among LM tears, meniscal repair, partial meniscectomy, and subtotal meniscectomy were performed in 18, four, and one patient, respectively. The amounts of ADD and LPWD seen observed on CT was significantly decreased, shifting from 10.2±5.1 mm (ADD) and 6.0±3.9 mm (LPWD) preoperatively to 1.4±1.9 mm (ADD, p<0.001) and 4.1±2.6 mm (LPWD, p<0.001) postoperatively (Table 2). The reduction rates were 85.5%±19.5% for ADD and 35.5%±30.5% for LPWD. Overall, osteoarthritis progression was noted in five patients (12.8%) based on the Ahlbäck scale. Clinically, the Tegner activity scale did not differ between the preoperative and postoperative values. All patients had bone union within 6 months postoperatively, but one patient (2.6%) underwent realignment surgery 5 years postoperatively due to valgus deformity with lateral compartment osteoarthritis.

Table 1
Demographic Characteristics

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Table 2
Radiological and Clinical Results

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The mean mechanical and Δmechanical axes axis of the operated knees was –0.2°±3.6° and the mean was 2.5°±3.4°. Valgus malalignment was observed in 10 patients (25.6%), and valgus deviation was observed in five patients (12.8%) (Table 2). The degree of osteoarthritis was significantly more severe in the valgus deformity groups based on the Rasmussen radiologic score (p<0.001). Furthermore, osteoarthritis progression according to the Ahlbäck scale was significantly higher in the valgus deformity groups (valgus malalignment group: 50.0% vs 6.9%, p=0.007; valgus deviation group: 60.0% vs 11.8%, p=0.032) compared to that in the non-valgus deformity group (Table 3).

Table 3
Comparison of Clinical Outcomes Based on Valgus Deformity

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According to multivariate regression analysis, preoperative ADD (β=0.473; p<0.001) and postoperative LPWD (β=0.524; p<0.001) were significantly associated with postoperative mechanical axis (Table 4). In addition, preoperative ADD (β=0.500; p=0.001), postoperative LPWD (β=0.320; p=0.025), and lateral meniscectomized status (β=0.350; p=0.019) were significantly associated with the postoperative Δmechanical axis (Fig. 3).

Fig. 3
Right knee of a 27-year-old male patient with a lateral tibial plateau fracture showing joint depression and lateral plateau widening on a preoperative anteroposterior radiograph (A) and computed tomography (CT) (C). After arthroscopic reduction with allogenic cancellous bone graft and internal fixation with a locked plate, postoperative anteroposterior radiographs (B) and CT (D) show an acceptable reduction of joint depression, but some lateral plateau widening remains. (E) A full-leg standing anteroposterior radiograph shows a valgus of nine degrees on the right knee and a varus of one degree on the left knee at postoperative three years, as evaluated by mechanical axis using hip-knee-ankle angle.

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Table 4
Factors for the Progression of Valgus Deformity after ARIF in AO/OTA 41.B2 or 41.B3 Fractures

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Meanwhile, the inter- and intra-observer reliabilities for the radiological variables showed substantial to almost perfect agreement, with κ values ranging from 0.81 to 0.94 (Appendix).

The results of the current study demonstrated that preoperative ADD, postoperative LPWD, and LM meniscectomized status were significantly associated with valgus deformity after ARIF in lateral joint depression tibial plateau fractures. Although comparable clinical outcomes were observed in patients regardless of valgus deformity, osteoarthritis progression was significantly more prevalent in patients with valgus deformity than in those without valgus deformity, with a mean follow-up of 44.6 months.

Although most previous studies reported that postoperative valgus deformity did not significantly affect postoperative clinical outcomes, relevant literature contains conflicting data regarding the influence of valgus deformity on osteoarthritis progression in patients with lateral joint depression tibial plateau fractures after ORIF.9,10,29) Meanwhile, no studies have assessed this topic after ARIF; thus, the current study was performed to focus on valgus deformity after ARIF. The results of the current study showed comparable postoperative clinical outcomes in patients with and without valgus deformity, whereas the osteoarthritis progression was significantly higher in the valgus deformity group (valgus malalignment group, 50.0%; valgus deviation group, 60.0%) than in the non-valgus deformity group after ARIF (non-valgus malalignment group: 6.9%; non-valgus deviation group: 11.8%). Although the incidence of osteoarthritic progression ranged from 3.2% to 63.0% in a recent systematic review,7) it was highly prevalent in the valgus deformity group based on subgroup analyses in the present study. Valgus deformity theoretically leads to osteoarthritic progression because it changes the load distribution of the joint and increases the maximal contact pressure of the lateral compartment.8,30) Despite this, several previous studies have maintained that postoperative valgus deformity in tibial plateau fractures would not affect osteoarthritic progression because there is a high prevalence of underlying advanced osteoarthritis with varus malalignment in elderly patients, of which the medial compartment would be unloaded by postoperative valgus progression, similar to high tibial osteotomy.10,31) To avoid this confounding factor, the current study excluded patients with underlying osteoarthritis with K-L grades 3 or 4. The results of the current study suggest that surgeons should take care to avoid valgus deformity in lateral joint-depression tibial plateau fracture after ARIF and should recognize preoperative and postoperative factors affecting the valgus deformity to prevent subsequent osteoarthritic aggravation.

In the current study, preoperative ADD and postoperative LPWD were significantly associated with valgus deformity in lateral joint depression tibial plateau fractures after ARIF. In the multivariate regression analysis, preoperative ADD was a significant factor for valgus deformity, which seems plausible as the amount of ADD may reflect the amount of energy absorbed at the time of injury resulting from valgus force.11,17,31) Unexpectedly, postoperative ADD was not a significant factor for valgus deformity after ARIF, although restoration of intra-articular step-off has been well emphasized for the surgical treatment of lateral joint depression tibial plateau fractures to prevent the valgus deformity, osteoarthritic aggravation, and functional impairment.7,8,9,29) Because the primary goal of ARIF is to minimize intra-articular step-off under direct visualization, it would be difficult to show a statistical difference in postoperative ADD values after ARIF in the multivariate regression analysis of valgus deformity. In the present study, the mean postoperative ADD was 1.4±1.9 mm and the mean reduction rate of ADD was 85.5%±19.5%, which were deemed acceptable and successful. Meanwhile, postoperative LPWD was a significant factor for valgus deformity after ARIF. Although several studies reported that LPWD was associated with LM tear,7,11) there is little evidence reporting that postoperative LPWD was significantly associated with valgus deformity in tibial plateau fractures after surgical treatment. It may be cautiously postulated that surgeons tend to concentrate on restoring intra-articular step-off by elevating the depressed fragment and filling the bone graft at the defect area during ARIF. They may tend to overlook the restoration of LPWD by compressing both tibial condyles with a reduction clamp. In particular, it would be more difficult to reduce LPWD if the bone graft was performed before compressing both tibial condyles. In our series, the mean postoperative LPWD was 4.1±2.6 mm and the mean reduction rate was 35.5%±30.5%, which seemed a somewhat insufficient reduction despite the sensitive evaluation of postoperative CT. Accordingly, widening of the lateral tibial plateau may lead to joint incongruency and provide more space for the lateral femoral condyle to glide on the coronal plane, resulting in valgus deformity as medial laxity progresses. Moreover, the hidden injury of medial collateral ligament might lead to progressive medial laxity resulting in valgus deformity in addition to the postoperative widening of lateral tibial plateau. The results of the current study indicate the need for the restoration of LPWD and ADD for the treatment of lateral joint depression tibial plateau fractures, especially after ARIF. A recent study supported the result of current study that postoperative ADD more than 4 mm and postoperative LPWD more than 5 mm were significant risk factors for conversion to total knee arthroplasty because of joint incongruency leading to progressive postoperative arthritis.32)

Previous studies reported that LM tears were the most common concomitant injury in lateral joint depression tibial plateau fractures.4,7,11,12) As the injury mechanism of valgus and axial compressive force and fracture patterns, the LM is occasionally entrapped between lateral femoral and tibial condyles. Furthermore, when the load propagates, the entrapped LM might be pulled medially and inferiorly, leading to longitudinal tears.7,11) In the current study, LM tear was observed in 59.0% of the study cohort, most commonly longitudinal tears. As neglected LM tear and LM meniscectomized status lead to the progression of valgus deformity and subsequent osteoarthritis, great efforts have recently been made to detect LM tears preoperatively and to preserve LM as much as possible.4,11,12,17,18) Consistent with previous studies,8,30) the current study found that LM meniscectomy was significantly associated with valgus deformity, especially valgus deviation (Δmechanical axis). Thus, LM tears should be thoroughly assessed in lateral joint depression tibial plateau fractures and it is important to preserve LM as much as possible during ARIF (Fig. 4).

Fig. 4
(A) Right knee of a 49-year-old male patient with lateral joint depression tibial plateau fracture showing concomitant lateral meniscus (LM) longitudinal tear (asterisk) at the menisco-capsular junction from the anterior horn to mid-body. (B) After the reduction of the articular surface of the joint depression, the LM was repaired with proper tension using a modified outside-in technique. (C) Second-look arthroscopic finding at the time of plate removal showing the well-healed LM repair at one year postoperatively. LFC: lateral femoral condyle

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The current study had several limitations. First, it was a retrospective case series with a relatively small sample size. Moreover, the small sample size of meniscectomized compared with meniscal repair and progression of osteoarthritis might be a potential selection bias for the result. However, it seemed inevitable to perform a retrospective study to identify the factors for valgus deformity after ARIF. Furthermore, the posthoc power calculation for the primary aim of the current study was >80%, which seemed acceptable power for the sample size. Second, the mean follow-up period of 44.6 months was relatively short, and the range of follow-up period was wide. Although a recent study demonstrated that a minimum of 2 years was sufficient to detect osteoarthritic progression,9) longer and homogeneous follow-up with a larger sample size is required to confirm our findings. Third, two surgeons performed ARIF for tibial plateau fractures with AO/OTA 41.B2 or B3 which might be potential bias although two surgeons performed ARIF with a homogeneous philosophy and technique. Fourth, the patients in the study cohort were limited to tibial plateau fractures with AO/OTA 41.B2 or B3 after ARIF; thus, the results cannot be generally applied to tibial plateau fractures overall. Nevertheless, the results of the current study provide useful information on why valgus progression is occasionally observed in AO/OTA 41.B2 or B3 fractures even after accurate reduction of intra-articular step-off and LM repair during ARIF. Lastly, a precise evaluation of medial laxity of the knee is needed to address factors affecting postoperative valgus deformity in such fractures, although the current study evaluated patients with occasional preoperative magnetic resonance imaging and immediate postoperative physical examination for medial collateral ligament injury. Despite several limitations, the current study had strength to provide valuable information to surgeon during ARIF for tibial plateau fractures with AO/OTA 41.B2 or B3 to preserve joint congruence including both articular depression and plateau widening as well as LM, which might prevent valgus malalignment and lateral compartment osteoarthritis.

Osteoarthritis progression was highly prevalent in patients with postoperative valgus deformity. Thus, the restoration of lateral plateau widening as well as articular depression and preservation of the meniscus are necessary to prevent valgus deformity after ARIF in lateral joint-depression tibial plateau fractures.