The present study demonstrated that PSI guided chevron-cut close-wedge DFO, followed by immediate weight bearing as tolerated achieved targeted correction in 92% of patient, and consolidation of the osteotomy at 11.3 weeks. There was a short mean operative time of 58.8 minutes, 6.2 intraoperative radiographs, and no blood transfusion was required.
DFO is a widely accepted treatment option for lateral uni-compartmental arthritis associated with valgus deformity. It improves pain and function of the affected knee [6, 12, 13], as well as patellar tracking and patellofemoral arthritis . Satisfactory results and a high rate of survivorship with total knee arthroplasty as the endpoint was found across studies at 10 years, ranging from 78% to 89 %. The rate generally declined to 45-71% at 15 years, and 24% at 20 years [12, 14-16].
We planned the target with a WBL ratio instead of HKA, since the WBL ratio is more subtle in minor corrections . In the current study, a linear regression study evaluating the association between the WBL ratio and HKA found a correlation coefficient of 3.2.
The medial close-wedge and lateral open-wedge provide similar union, survival, and complication rates [3, 4, 11]. However, after lateral open-wedge DFO, a 4-12 weeks period of non-weight bearing is typically required, while immediate partial weight bearing was allowed after medial close-wedge DFO in most series. Besides, bone grafting is often required, and the plate seating under the iliotibial band commonly irritates and leads to a 40-86% rate of removal [4, 5, 13, 18, 19]. We therefore prefer to perform medial close-wedge DFO.
Although close-wedge osteotomy theoretically offers the advantage of native bone-to-bone healing and inherent stability, the conventional technique is not without associated complications. A 3%-25% rate of delayed union or non-union, a 5% rate of loss of correction, and malrotated correction have been mentioned in several studies [5, 6] [7, 8]. Union of the osteotomy ranged from 2-9 months . The rate of delayed union or non-union hovered around 4%-5%, even with the advent of locking plates [8, 9].
To improve the inherent stability of osteotomy, biplanar osteotomy had been proposed . Further saw-bone studies found the femoral contact surface of biplanar osteotomy increase more than two-fold in comparison to the uniplanar technique . However, a subsequent biomechanical study found that biplanar osteotomy, counter-intuitively, is less stable under torsion force than the single-plane technique . This may be explained by the observation in a clinical study by Nha et al., which found that the anterior wedge of osteotomy is prone to fracture in patients with a small size of the femur . Without a solid anterior wedge, the contact area is not different from single plane osteotomy.
To address the shortcoming of the weak anterior wedge, chevron-shape osteotomy seems to be a reasonable design. It has been shown to be one of the biomechanically superior constructs, and is utilized in various sites of the body [23-25]. In comparison to the biplanar technique, the chevron-cut technique avoids the posterior condyle in addition to the femoral trochlea. Therefore, it bears the potential to place the osteotomy site more distally, into the area of cancellous bone in the femur, a region with better healing potential (Figure 5).
In our study, the mean time to union was 11.3 weeks. The rate of non-union or loss of fixation (both 4%) were non-inferior in comparison with the literature. Notably, the patients were allowed immediate weight bearing as tolerated, in contrast with a typical 6-8 weeks of partial weight bearing in most series of close-wedge DFO . Furthermore, the age of the current studied population averaged 65 years, which was older than that in most studies. In addition, two factors that likely contributed to the non-union were the smoking habit of the patient, and simultaneous bilateral surgery. Further mechanical studies and a control group may be required to demonstrate whether chevron-cut osteotomy leads to better mechanical property or clinical outcomes.
Chevron-cut close-wedge osteotomy requires four accurate bone cuts converging to the hinge point, while the bone cuts are not perpendicular to the AP view of intraoperative radiographs. It is therefore hardly practical with a conventional freehand technique, as the closing-wedge technique is already known to be difficult, and highly reliant on preoperative planning and accurate bone cutting [3, 4, 26].
Several techniques have been proposed to increase the accuracy of DFO, such as computer-assisted navigation surgery . But the technique is currently limited by the longer learning curve, prolonged operative time, as well as the rather expensive cost .
The use of PSI is another promising technique. It has been compared in three studies with conventional DFO techniques. Arnal-Burró et al. and Jacquet et al. studied the application in the uniplanar open-wedge technique (a single bone cut). The PSI groups in both studies achieved less alignment deviation in comparison with the conventional groups (0.28° v.s. 1.8° and 0.52° v.s. 3.1°) [29, 30]. Shi et al. performed the uniplanar close-wedge technique (two bone cuts) with cutting guides with a bolt to ensure an accurate reduction. They reported less deviation from the surgical plan in comparison with the conventional group (4.9% v.s. 7.6%) . The current study attempted the use of PSI in a chevron-cut close-wedge technique (four bone cuts). The deviation from the plan was 1.3% in terms of the WBL ratio, and 0.5° in terms of HKA. The results were non-inferior to the PSI groups of previous studies.
In the current study, a mean operative time of 58.8 minutes, and an average of 6.2 intraoperative radiographs were required. The results were also similar to the previous studies, finding the PSI groups take 39.5-77.7 minutes (7.7-32 minutes less time than the freehand groups), and 5-6 intraoperative images (7-59 less than the freehand groups) [29-31].