Osteonecrosis of the femoral head (ONFH) is mainly caused by a decrease in the vascular supply to the subchondral bone of the femoral head, leading to the death of bone cells, degeneration and necrosis of the subchondral bone, and eventually collapse of the femoral head.[1] Early and accurate diagnosis is the key to successful hip-preserving therapy, and the size/location of necrosis is the main determinant for ONFH treatment. Previous studies have shown that many hip-preserving therapies achieved satisfactory results in ONFH patients with Association Research Circulation Osseous (ARCO) I–II. When ONFH progresses to ARCO IV with clinical manifestations of osteoarthrosis, total hip arthroplasty (THA) may be the only option. However, the optimal therapy for osteonecrosis of the collapsed femoral head (ARCO III) remains unknown.[2] For these patients with osteonecrosis and collapse of the femoral head, especially middle-aged patients, the majority of scholars believe that surgical intervention should be performed as soon as possible to restore structural stability of the femoral head, relieve pain, and stop or delay progression.

At present, although THA is effective and widely used, postoperative secondary revision surgery is becoming increasingly possible in middle-aged patients with a relatively long life expectancy and high activity levels.[3] Recently, we developed a micro femoral head prosthesis and supporting instruments for collapsed ONFH in the weight-bearing dome (ARCO III). The specially designed prosthesis head is consistent with the anatomical curvature of the femoral head and provides stable mechanical support [Figure 1]. In this report, we retrospectively reviewed the clinical data of four middle-aged patients with collapsed ONFH in the weight-bearing dome who underwent this novel surgical technique and evaluated short-term outcomes.

Figure 1:

Introduction and application of the microfemoral head prosthesis and supporting instruments. (A) Schematic diagram of the microfemoral head prosthesis (diameter 18–22 mm): ① metal outer cup (cobalt–chrome–molybdenum alloy), ② main rod (titanium alloy), ③ end cap (titanium alloy). (B) Microfemoral head prosthesis. (C) Schematic diagram of supporting application instruments: ④ sleeve, ⑤ guide frame. (D) Anteroposterior radiograph after implantation.

We retrospectively reviewed four ARCO III ONFH patients who underwent micro femoral head prosthesis arthroplasty between October 2022 and December 2022. The series consisted of three males and one female, aged between 47 years and 52 years (mean 49.8 years). Each patient underwent preoperative planar imaging, including computed tomography (CT) or magnetic resonance imaging (MRI). This study was approved by the Institutional Review Board of Hebei Medical University Third Hospital Ethics Committee (No. 2022-131-1). All patients signed an informed consent form. All patients met the following inclusion criteria: (1) 45–65 years of age; (2) diagnosed with ARCO III ONFH; (3) collapsed area in the weight-bearing dome; (4) consented to hip-preserving surgery. Exclusion criteria included (1) large collapsed area or signs of arthritis; (2) follow-up time was less than 6 months; (3) previous hip-preserving surgery; and (4) incomplete follow-up imaging data.

Surgical procedures were performed under general anesthesia, with patients lying supine and receiving prophylactic antibiotics. Under C-arm fluoroscopy, a 3-mm K-wire was inserted along the axis of the femoral neck toward the center of the necrotic area and its route confirmed by anteroposterior and lateral radiographs. A 3-cm longitudinal incision was made at the center of the entry point of the K-wire and a circular hollow drill was used to advance toward the femoral head along the direction of the guide needle. After the bone column was completely removed, there was obvious degeneration and collapse of the articular cartilage. A large amount of physiological saline was used to clean the bone tunnel and the joint cavity. Autogenous cancellous bone was placed in the space of the prosthesis main rod and auxiliary guiding instruments were assembled. The prosthesis (diameter 20 mm) was inserted along the direction of the bone tunnel so that the external outer metal cup of the prosthesis was well matched with the shape of the femoral head. Two transverse locking screws were used to secure the prosthesis. After installing the end cap, intraoperative fluoroscopy was repeated and the incision was closed when the position was satisfactory [Supplementary Figure 1, https://links.lww.com/CM9/B892].

Routine antibiotic therapy was administered within 24 hours after surgery to prevent infection, and a subcutaneous injection of low-molecular-weight heparin calcium was administered to prevent deep venous thrombosis in the lower limbs. Continuous passive motion was started on the first postoperative day. Weight-bearing activity was restricted for the first 4 weeks. Follow-up radiographs were performed at 1 month, 3 months, and 6 months and then every 6 months. Based on clinical and radiological evidence of bone healing, the patient gradually progressed from partial weight bearing to full weight bearing 3 months after surgery. All surgeries were performed by the senior surgeon, and radiographs were reviewed by an orthopedic surgeon and a neuromuscular radiologist. Visual analog scale (VAS) scores and harris hip score (HHS) were used to evaluate the preliminary results in detail and to confirm the safety and efficacy of the procedure.

All four patients with collapsed ONFH in the weight-bearing dome (ARCO III) underwent this novel surgical technique and achieved excellent short-term results. The etiologies of the four patients were hormonal, alcoholic, traumatic, and idiopathic. Compared with preoperative hip pain, postoperative hip pain was significantly reduced in all patients and hip function continued to improve. The VAS scores and Hospital for Special Surgery (HSS) scores of the four patients at each follow-up time point before and after surgery are shown in Supplementary Table 1, https://links.lww.com/CM9/B892. At follow-up, the prosthetic outer cup fitted well into the bone around the femoral head. None of the patients experienced serious complications after surgery, including deep wound infection, intolerable pain, secondary fracture, loss of the prosthesis, or persistent necrosis. During the six-month follow-up period, none of them required conversion to THA or secondary revision surgery [Supplementary Figures 2–4, https://links.lww.com/CM9/B892].

From the above-mentioned case series, we noticed a satisfactory prognosis for patients with collapsed ONFH in the weight-bearing dome (ARCO III) after micro femoral head prosthesis arthroplasty. As an early treatment strategy for patients with ONFH (ARCO III), this novel surgical technique has the advantages of being a short operation, causing less trauma, with a low incidence of surgical and postoperative complications, and good functional recovery as it may be the last opportunity for good hip preservation.

Many surgical strategies have been used to preserve the hip joint in the early stages, such as core decompression, nonvascularized or vascularized bone grafting, and rotational osteotomy. Although the outcomes of these procedures appear to be somewhat satisfactory, their use in practice has been severely limited by inconsistent efficacy, technical difficulties, donor site morbidity, prolonged rehabilitation, and an increased risk of proximal femoral fracture.[4] In addition, it has been shown that these techniques are still unable to restore the spherical shape of the femoral head in patients with ARCO III ONFH. THA is more appropriate for patients with ARCO IV ONFH. However, the risk of secondary revision should be considered when middle-aged patients undergo THA.[5]

In recent years, our team has designed this micro femoral head prosthesis arthroplasty to treat or delay the development of ARCO III ONFH as a stepwise treatment strategy to preserve the hip joint. The features of micro femoral head prosthesis arthroplasty include removing the necrotic bone tissue through the trochanteric and femoral neck drilling to reduce the pressure on the joint capsule; using a special micro prosthesis to support the femoral head and the metal titanium alloy prosthesis to restore the dome structure; and avoiding cutting off or opening the joint capsule to ensure that the blood supply around the femoral head is not damaged to effectively prevent progression of necrosis and further collapse of the femoral head.[6] We used a specially designed hollow ring drill (18–23 mm diameter range) to effectively remove sclerotic bone and collapsed articular cartilage in necrotic areas without opening the hip joint. In addition, this method preserves most of the bone reserve without compromising subsequent THA due to ONFH progression, implant failure, or major complications.

In addition to the theoretical benefits mentioned above, the short-term effects of using micro femoral head prosthesis arthroplasty in ARCO III ONFH patients are also impressive. In this case series, none of the patients experienced serious complications after surgery, including deep wound infection, intolerable pain, secondary fracture, loss of prosthesis, or persistent necrosis. During the six-month follow-up period, none of the patients required conversion to THA or secondary revision surgery. All patients had relief of postoperative pain and good improvement in hip joint function. We will continue to closely monitor the growth of the residual cavity bone, as well as continued necrosis and collapse.

The present study has several weaknesses. Firstly, it is an retrospective study and may have shortcomings such as selection bias and confounding factors. Secondly, this is a preliminary short-term follow-up study and the selection of surgical indications for patients is relatively broad. Further long-term follow-up and more specific indications need to be developed to achieve the best treatment effect for patients. Finally, postoperative X-ray and CT scans were insufficient due to issues with the patient’s residence and compliance, and the issue of metal artefacts in MRI scans remains unresolved. In future research, we will develop strict follow-up plans and improve follow-up examinations.

To conclude, this case series study suggests that micro femoral head prosthesis arthroplasty appears to be a safe and effective technique for ONFH patients with ARCO III to improve hip motion function and relieve pain. This novel micro femoral head prosthesis arthroplasty would provide surgeons with another option for the treatment of ONFH (ARCO III).

Availability of data and materials

The datasets used and analyzed are available from the corresponding author on reasonable request.

Funding

This work was supported by the grants from the Centre Guiding Local Science and Technology Development Fund Project (Science and Technology Innovation Base Project)-Grand (No. 236Z7754G) and Clinical Innovation Research Team of Hebei Medical University (No. 2022LCTD-B35).

Conflicts of interest

None.

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