For FD combined with hip joint OA patients, especially who have severe proximal femur deformity, corrective osteotomy and THA are both needed. Corrective osteotomy can solve local deformity and re-establish mechanical alignment of the lower extremity . THA can relieve pain and improve the limb function . Some previous publications have demonstrated the value of application of computer-assisted technology, robotics-assisted technology and rapid prototype model in complex hip surgery. One review has summarized computer-assisted technology, robotics-assisted technology can help surgeons perform accurately to achieve the clinical objectives in complicated THA . In 2013, Won et al. reported that the pelvic rapid prototype model was used in 21 complex hips to simulate the implantation of the acetabular prosthesis preoperatively, the implantation of acetabular component was successful and 80.9% of the used acetabular component was within 2 mm of the predicted size . In 2016, Inaba used 3D preoperative planning and intraoperative navigation for rotational acetabular osteotomy in acetabular dysplasia patients, the rotational acetabular osteotomy could be performed more accurate and safer . But the 3D preoperative design is still rare applied in THA with severe proximal femoral deformity. In order to improve the perioperative accuracy rate of corrective osteotomy and THA, 3D preoperative design was firstly used in FD combined with hip joint OA patients. This study demonstrated the details of 3D preoperative design and perioperative management, and the short-term outcomes of THA with long uncemented stem for this kind of patients.
With the progression of proximal femur FD, coxa vara deformity is inevitable. For this deformity, valgus osteotomy can improve the limb function and prevent fractures via re-establishing neck-shaft angle and reconstructing the lower limb strength line . The ways of valgus osteotomy are based on the deformity classification. Ippolito proposed a classification method including six types in 2014 . However, Ippolito’s classification has a major limitation, which is the surgeons cannot determine osteotomy site or internal fixation method according to this classification. In 2015, our institution reported a novel method of radiographic classification including five types according to three parameters: neck-shaft angle, varus deformity of the proximal femoral shaft, and reduction in proximal femoral strength . In our series, according to our institution’s classification, there were two type 2 patients, three type 3 patients, three type 4 patients, and four type 5 patients. Femoral valgus osteotomy was done in the three type 4 and four type 5 patients, who had varus deformity in the proximal femur shaft. Nevertheless, the current classifications, including ours, only evaluate the femoral deformity but not the injury degree of the ipsilateral hip joint [10, 17]. Moreover, valgus osteotomy can lengthen the lower extremity to some extent. Previous researches demonstrated that corrective osteotomy can lengthen extremity by 2.3–3.4 cm on average [16, 18]. In our study, the lower limb has been lengthened by an average of 2.8 (range, 1.5–4) cm.
Current classifications of proximal femur FD are only based on the images of X-ray and CT, but not a multi-dimensional evaluation [10, 17]. To our best knowledge, there is no report using 3D designing femoral reconstruction to guide the operation. Additionally, the proximal femur medullary cavity is varied in diameter and the bone condition is poor for FD patients, the implantation of prosthesis stem is challenging. But it is still very rare to pay attention to the bone condition of the affected proximal femur, especially the surface of medullary cavity. The 3D reconstructive images can fully and precisely evaluate the patients’ femoral deformity sites, affected bone length, abnormal mechanical alignment, bone condition, and multi-level diameter of the medullary cavity. Our results revealed that 3D designing osteotomy did not reduce the hip joint function when comparing the patients only receiving THA and the patients receiving osteotomy and THA. The preoperative 3D design can not only make better plan of the osteotomy but also simulate the feasibility of implanting long prosthesis stem more accurately. During this procedure, we can confirm the length and diameter of the prosthesis stem before surgery, so that the surgical difficulties can be sharply decreased, and the mean operating time and the average amount of intraoperative bleeding can be controlled well.
Primary stability and long-term survival are the most important factors to consider when choose the prosthesis stem, especially for these patients with bone deformity and poor bone condition. Firstly, uncemented stem was chosen in our series. The reasons has been discussed that the affected bone characterized with the wide and irregular medullary cavity and thin cortex, is not strong enough to support the cement-bone interface [19, 20]. Additionally, due to the relatively massive intramedullary bleeding, uncontrollable bleeding will undoubtedly influence the cement-bone interface during cemented stem implantation . What’s more, for patients who require femoral osteotomy, the cement fixation may affect osteotomy healing. Secondly, long stem should be applied. Sierra reported that proximal femur FD patients who received short uncemented stem fixation showed a high rate (60%) of early aseptic loosening, and long stem prosthesis was highly recommended for proximal femur FD patients combined with hip joint OA. Besides, they suggested that the stems length should exceed the lesion length by at least 2 femoral canal diameters to decrease the risk of postoperative fractures . Some data demonstrated that besides long stem, increasing bone mass by cortical bone or compressive bone grafting and custom-made megaprosthesis can also improve the integral strength of the proximal femur . The same theory has been accepted during femoral revision surgery after ordinary THA [22, 23]. What’s more, in some rarely extreme cases, if the usual size of the femoral stem (solution revision femoral prosthesis) was not appropriate for the patient, the customized femoral stem could be produced assisted by 3D design preoperatively.
The surgical skill of the stem implantation is another crucial point worthy of notice. First, precision osteotomy assisted by 3D designing customized osteotomy guides should be performed and micropendulum saw was required to be used to reduce bone loss and cortical injury. Second, The lesion required to be removed thoroughly before reaming, which would prevent poor osteointegration after uncemented fixation . Third, the femoral cavity needed to be reamed before the implantation of long stem. 3D designing preoperative plan and intraoperative X-ray fluoroscopy played a very important role in the precise reaming of the bone cavity and preventing cortical bone damage. Fourth, in order to increase initial stability, the diameter of reaming needed to be slight (0.5 mm) smaller than the diameter of the stem because of the flexibility of the cortical bone with FD. Fifth, during stem implantation, the anteversion angle of the stem should be pay attention to, because the anteversion angle of the host proximal femur is always less than normal. Sixth, the procedure of wire binding was usually used to re-establish abductor muscle and prevent intraoperative periprosthetic fractures . During osteotomy and prosthesis implantation, periosteal should be protected to promote bone healing. Finally, massive impaction of cancellous allograft should be used before the implantation of acetabular cup and prosthesis stem. Massive impaction allograft is the critical procedure to improve the potential of osteointegration and to prevent uncemented implant loosening [16, 25, 26].
It should be noted that this is a retrospective and short-term follow-up study related to 3D designing THA with long uncemented stem for FD patients combined with hip joint OA. Additionally, this study included a limited number of patients. Nevertheless, this study still demonstrates the clinical value and potential of 3D designing osteotomy and implantation of long uncemented stem for FD patients combined with hip joint OA.