## 1 Introduction  
Knee osteoarthritis (OA) is a musculoskeletal disorder that has been reported to affect 303 million people globally, with a cumulative incidence rate of up to 8.5% among middle aged and older people in China [1, 2]. Proximal fibuelectomy was recently shown to be as an effective way to relieve pain and to improve knee functionality in patients with medial knee OA [3]. Good short-term clinical outcomes of this surgery demonstrated improved knee alignment and the restoration of joint spacing [3, 4, 5]. However, some complications were also reported, including neuroproxia of the superficial and deep branches of the peroneal nerve, wound hematoma, and post-surgery infection [6]. In addition, previous studies only considered the short-term outcome of proximal fibuelectomy. The long-term performance of this surgery is unclear. Thus, it is essential to study the association between proximal fibula morphology and knee OA to better understand how changing the structure of the joint affects knee performance.  
The proximal tibiofibrular joint (PTF) is a synovial joint composed of the tibial condyle and the fibular head and acts to dissipate torsional stresses applied to the ankle, to dissipate lateral tibial bending moments, and to alleviate tensile weight-bearing [7]. Several recent publications investigated the relationship between PTF) morphological parameters and knee OA severity. [PERSON] et al. [8] demonstrated that PTFJ might be associated with the occurrence and development of OA, especially with the height of fibula (HF) and the types of PTFJ. [PERSON] et al. [9] reported that irregular PTFJ joint shapes were associated with osteoarthritis changes in the lateral knee compartment in older adults. [PERSON] et al. [10] showed how morphological changes in the PTFJ could be used to predict the risks of receiving total knee replacements (TKR). [PERSON] et al. [11] found that changes in PTFJ surface area were associated with the presence of incident radiographic osteoarthritis, especially in the medial tibofemoral compartment. [PERSON] et al. [12] reported that PTFJ morphology in healthy people was significantly different from that in OA patients and that it was associated with the presence of knee OA. However, the factors considered in these studies were mostly related to cartilage structure and incidence of knee OA while the relationship between PTFJ morphology and knee alignment has not been investigated in detail. Neutral knee alignment is vital for balanced knee load-bearing. Malignment causes the load-bearing axis to be biased to one side, resulting in a longer moment arm and greater load in one knee compartment. Such unbalanced loading presents a significant risk for the progression of OA [13].  
The aim of this study was to evaluate the association between the morphology of PTFJ and knee alignment in OA patients. The morphology of PTFJ was measured in constructed bone models from CT scans. Knee alignment was measured by the femorotibial angle (FTA) on weight-bearing X rays. We hypothesized that the PTFJ morphology would be associated with knee alignment and that there would be a significant difference in PTFJ morphology between varus knees and valgus knees.