Outcomes and indications of the single approach to double-channel core decompression and bone grafting with structural bone support for osteonecrosis of the femoral head

Background To report the outcomes of the single approach to double-channel core decompression and bone grafting with structural bone support (SDBS) for osteonecrosis of the femoral head (ONFH) and dene the indications. failure


Abstract Background
To report the outcomes of the single approach to double-channel core decompression and bone grafting with structural bone support (SDBS) for osteonecrosis of the femoral head (ONFH) and de ne the indications.

Methods
One-hundred-and-thirty-nine hips in 96 patients (79 males, 17 females; mean age 37.53±10.31 years, range 14-58 years; mean body mass index 25.15±3.63 kg/m 2 ) were retrospectively analysed. The Harris hip score (HHS) was used to assess hip function, and radiographs were used to assess the depth of femoral head collapse. Treatment failure was de ned as the performance of total hip arthroplasty (THA).
The variables assessed as potential risk factors for surgical failure were: aetiology, Japanese Osteonecrosis Investigation Committee (JIC) type, age, and Association Research Circulation Osseous (ARCO) stage. Complications were recorded.
THA was performed in 18 hips. Thus, the overall femoral head survival rate was 87.05% (121/139). The success rate was adversely affected by JIC type, but not by aetiology, age, or ARCO stage. The only complication was a subtrochanteric fracture in one patient.

Conclusion
The SDBS effectively delays or even terminates the progression of ONFH, especially type B and C1. The SDBS is a good option for early-stage ONFH.

Background
Osteonecrosis of the femoral head (ONFH) is a local abnormal bone metabolism disease caused by interruption of or damage to the blood supply of the femoral head, resulting in the death of bone cells and marrow components [1][2]. Without effective diagnosis and treatment, ONFH has a high rate of clinical progression, eventually leading to femoral head collapse and secondary hip osteoarthritis [3]. When the femoral head is severely collapsed, total hip arthroplasty (THA) is required [4]. However, THA is associated with problems such as wear and loosening of the prosthesis over time, potentially requiring several revision surgeries, which causes a great burden on the patient and their family [5]. Therefore, there is a need for a reliable method of joint preservation in patients with early-stage ONFH.
The main purposes of femoral head-preserving surgery for ONFH are to delay the collapse of the femoral head, maintain and restore the normal function of the hip joint, relieve pain, and delay or even avoid total joint replacement. In 1949, Phemister developed a technique in which a core decompression channel is used to place a graft into the necrotic area. A recent modi ed version of this Phemister technique, called the single approach to double-channel core decompression and bone grafting with structural bone support (SDBS), has shown satisfactory short-term e cacy in treating ONFH [6].
This retrospective cohort analysis of patients who had undergone the SDBS aimed to analyse the outcome and investigate the optimal indications of this technique.

Materials And Methods
This study was approved by the Ethics Committee of our hospital (No: HK2019-01-04) and the written informed consent was obtained from all subjects and/or their legal guardian. A total of 103 patients (149 hips) underwent the SDBS for ONFH in a single centre between October 2016 and October 2020. Seven patients (10 hips) were excluded because they were lost to follow-up. The nal study cohort comprised 139 hips in 96 patients (79 males and 17 females; mean age 37.53±10.31 years, range 14-58 years; mean body mass index 25.15±3.63 kg/m 2 ). The ONFH was bilateral in 43 patients and unilateral in 53 patients (29 left hips, 24 right hips). The ONFH was caused by prolonged excessive alcohol intake in 32 patients (44 hips), glucocorticoid administration in 42 patients (66 hips), trauma in nine patients (nine hips), and had no clear aetiology in 13 patients (20 hips). All patients were diagnosed in accordance with Chinese guidelines for the diagnosis and treatment of ONFH [7]. Osteonecrosis was classi ed as Association Research Circulation Osseous (ARCO) stage II in 63 hips, and ARCO stage III in 76 hips. Based on the Japanese Osteonecrosis Investigation Committee (JIC) classi cation system, the ONFH was classi ed as type B in 21 hips, type C1 in 54 hips, and type C2 in 64 hips. Characteristics of the patients and hips are listed in Table 1. All patients received epidural anaesthesia and were xed on the traction bed. The operation area was routinely disinfected and sterilely draped. After selecting the position of the entrance point, a 2-cm skin incision was made. The rst guidewire was drilled into the region below and inside the area of femoral head necrosis ( Fig.1.A). A 10-mm bit was then reamed along the guidewire to 3 mm below the cartilage( Fig.1.B). Fresh-frozen allograft particles (7.5 mg) (Shanxi AoRui Biological Material Co., Ltd., Taiyuan, China) were transplanted into the channel from the necrotic area to the normal area ( Fig.1.C). A second guidewire was then introduced through the same entrance point into the outer, top necrotic area ( Fig.1.D), and the 10-mm bit was again reamed along the guidewire to 3 mm below the cartilage ( Fig.1.E).
Postoperative care and follow-up Postoperatively, cefazolin sodium pentahydrate for injection (1 g) was administered once to prevent infection. Flurbiprofen axetil injection (100 mg twice daily) was routinely given as analgesia for 3 days.
All patients participated in a rehabilitation and training program after surgery. After recovery from anaesthesia, the patients began ankle dorsi exion exercises to prevent deep vein thrombosis without the need for medication. Patients began walking with two crutches from postoperative day 1 and were restricted to partial weight bearing for 6 months. From 6 months postoperatively, patients were permitted to exercise and walk intermittently without crutches. By 1 year postoperatively, patients were fully weight bearing. Postoperative follow-up was carried out at 3, 6, and 12 months postoperatively, and annually thereafter.

E cacy assessment
The Harris hip score (HHS) was used to assess the hip function as excellent (

Results
The average length of hospital stay was 5.74±0.78 days (range 5-8 days). The average incision length was 3.27±0.22 cm (range 2.0-3.5 cm) and the average intraoperative blood loss volume was 62.02±8.04 ml (range 50-75 ml). The only complication was a subtrochanteric fracture in one patient (Fig. 2); no other complications such as blood vessel or nerve injury, deep vein thrombosis, wound infection, or rejection were observed.
The mean follow-up time was 29.26±10.02 months. In the overall cohort, the mean HHS increased from 79.00±13.61 preoperatively to 82.01±17.29 at nal follow-up (P=0.041); the average improvement in the HHS was 3.00±21.86. The details of the HHS changes from preoperatively to nal follow-up in subgroups of patients are listed in Table 2. An analysis of patients grouped in accordance with the aetiology of ONFH found that the mean postoperative HHS tended to be improved compared with the mean preoperative HHS in all groups; however, these differences were not signi cant.  Fig. 3. According to the radiographic evaluation, 103 (74.10%) hips remained stable (Fig.4), while 36 (25.90%) hips developed collapse of the femoral head or aggravation of ONFH. During the follow-up period, 18 of the 36 hips with radiographically worsened ONFH underwent THA (Fig. 5); the remaining 18 hips did not undergo THA because the hip function was still good. The details of radiographic changes in subgroups of patients are listed in Table 3. There were signi cant differences in the imaging progression rate of ONFH in accordance with JIC type (P=0.001). Radiographic worsening of ONFH was seen in two of 21 hips (8.33%) with JIC type B, eight of 54 hips (14.81%) with JIC type C1, and 26 of 64 hips (40.63%) with JIC type C2; the progression rate of the type C2 group was signi cantly higher than that of the type C1 and type B groups, while there was no signi cant difference between the type C1 and type B groups. There were no signi cant differences in the radiographic changes between patients grouped in accordance with aetiology, age, or ARCO stage (p>0.05). At nal follow-up, 18 hips had undergone THA. Thus, the overall femoral head survival rate was 87.05% (121/139). The single factor analysis of the factors affecting treatment failure are summarized in Table   4. The incidence of THA did not signi cantly differ between hips grouped in accordance with aetiology (P>0.005); of the hips that underwent THA, the aetiology of ONFH was steroid administration in 10 (15.15%) hips, excessive alcohol intake in six (13.64%), trauma in one (11.11%), and idiopathic in one (5%). The incidence of THA signi cantly differed among groups based on JIC type (P<0.05); THA was performed in 15 (23.44%) type C2 hips, three (5.56%) type C1 hips, and no type B hips. The incidence of THA in type C2 hips was signi cantly higher than that in type C1 and type B hips, while the incidence of THA did not signi cantly differ between type C1 and type B hips. There were no signi cant differences in the failure rate among patients grouped in accordance with age and ARCO stage (P>0.05). THA was performed in 10 (9.80%) hips in patients younger than 44 years and six (21.62%) hips in patients aged 44 years or older. THA was performed in eight (12.70%) hips classi ed as ARCO stage II and 10 (13.16%) hips classi ed as ARCO stage III. Univariate analysis showed that the femoral head survival rate was signi cantly affected by the JIC type (χ 2 =14.26, P=0.001) (Fig.6.A), but not the aetiology (Fig. 6.B), age (Fig.6.C), or ARCO stage (Fig.6.D) (P>0.05).

Discussion
The SDBS is an improvement on the Phemister technique [6]. The Phemister technique uses a hole to decompress the necrotic area of the femoral head, and then lls the hole with bone graft material to facilitate the repair of the necrotic area [8][9][10]. The SDBS establishes two channels in the necrotic area for decompression, support, and allograft placement: an outer and upper channel, and an anterior and medial channel. Compared with the Phemister technique, the SDBS is thought to increase the support strength and provide su cient allogeneic cancellous bone in the necrotic areas.
In the present study, a n-HA/PA66 support rod composed of nanometer HA crystal particles evenly dispersed in PA66 was used. Although HA has been successfully used in the treatment of bone injuries, it is brittle and has poor compressive resistance, and cannot be applied in a load-bearing environment [11].
The compressive strength of n-HA/PA66 made by the fusion of HA and PA66 is as high as 13.2 MPa, which is close to the compressive strength of human cancellous bone. This is because when HA and PA66 are under pressure, the relatively hard HA prevents the relatively soft PA from bending and compression, and the toughness of PA makes up for the brittleness of HA [11][12]. The n-HA/PA66 has a porosity of about 70% and pore size of 200-500 µm, and the porosity is interconnected to create a good three-dimensional space for the introduction of blood vessels [13]. Previous studies have shown that n-HA/PA66 implanted into the skull defect of rats resulted in healing of the skull defect within 8 weeks [14], and that n-HA/PA66 implanted into a massive mandibular defect in rabbits resulted in the presence of active osteoblasts and callus formation in the pores of the scaffold at 4 weeks and complete healing of the bone defect at 24 weeks [15]. These previous ndings suggest that n-HA/PA66 has good bone conductivity and promotes bone regeneration.
The JIC classi cation system for ONFH is based on the acetabulum site corresponding to the femoral head lesions [16]. Small lesions located medially or centrally, such as types A and B, are much less likely to progress to collapse than lesions that occupy most of the weightbearing area, such as types C1 and C2 [17]. In type C2, the osteonecrosis extends to the lateral wall of the femoral head, resulting in the loss of structural integrity. In our study, the postoperative imaging progression rate of patients with type C2 ONFH was as high as 40.62% and was signi cantly higher than that of patients with types C1 and B. The rate of surgical failure was also signi cantly higher in patients with type C2 than in those with type C1 and B. There have been no reports that sex, age, BMI, or associated factors are related to the progression of ONFH [17]. However, the progressive necrosis and collapse of the femoral head is reportedly worse in patients with type C2 ONFH compared with other JIC types [18]. Furthermore, after ONFH treatment with non-vascularized bone grafts, patients with type C2 have worse hip function than those with type C1 [19]. By analysing the factors that in uenced the surgical success rate, we found that the JIC classi cation was helpful in predicting the outcome. The success rate of the SDBS for type C2 ONFH was relatively low.
The present study has some limitations. First, many factors may affect the success rate of the SDBS. As we only analysed four factors in this study, other possible in uencing factors need to be studied. Second, the follow-up time was relatively short, and long-term follow-up results are needed.

Conclusion
The SDBS is an effective method to delay or even terminate the natural progression of ONFH, especially for patients with JIC types B and C1. This operation is minimally invasive, causes little bleeding, enables a quick postoperative recovery, and has no donor site complications. The SDBS represents a good method for treating early-stage ONFH.

List Of Abbreviations
Osteonecrosis of the femoral head (ONFH) Consent for publication: All authors agree to publish "Outcomes and indications of the single approach to double-channel core decompression and bone grafting with structural bone support for osteonecrosis of the femoral head" in BMC Musculoskeletal Disorders.
Data and materials availability statement: All data and materials used to support the ndings of this study are included within the article.
Competing interests: We declare that we do not have any commercial or associative interest that represents a con ict of interest in connection with the work submitted. Surgical steps of SDBS.

Figure 2
Images of a 28-year-old man with subtrochanteric fracture. A: Traumatic rotation resulted in subtrochanteric fracture of the femur at 2 weeks after the surgery. B: Open reduction and internal xation was performed 3 days after the fracture occurred. C: At 1 year after fracture xation, the fracture had healed well and the internal xation was removed.

Figure 3
Comparison of the number of hip joints in different stages of hip function. * indicates that composition ratio is statistically signi cant difference (P < 0.05) between the two groups.   Kaplan-Meier survival curve (The endpoint is revision to THA): A-strati ed according to JIC type; Bstrati ed according to aetiology; C-strati ed according to age; D-strati ed according to ARCO stage